petrography and geochemistry of the lapaz icefield...
TRANSCRIPT
Meteoritics amp Planetary Science 40 Nr 7 1073ndash1101 (2005)Abstract available online at httpmeteoriticsorg
1073 copy The Meteoritical Society 2005 Printed in USA
Petrography and geochemistry of the LaPaz Icefield basaltic lunar meteoriteand source crater pairing with Northwest Africa 032
Ryan A ZEIGLER Randy L KOROTEV Bradley L JOLLIFF and Larry A HASKIN
Washington University Department of Earth and Planetary Science One Brookings Drive Saint Louis Missouri 63130 USACorresponding author E-mail zeiglerleveewustledu
(Received 30 May 2005 revision accepted 22 June 2005)
AbstractndashWe report on the bulk composition and petrography of four new basaltic meteorites foundin AntarcticamdashLAP (LaPaz Icefield) 02205 LAP 02224 LAP 02226 and LAP 02436mdashand comparethe LAP meteorites to other lunar mare basalts The LAP meteorites are coarse-grained (up to15 mm) subophitic low-Ti basalts composed predominantly of pyroxene and plagioclase with minoramounts of olivine ilmenite and a groundmass dominated by fayalite and cristobalite All of ourobservations and results support the hypothesis that the LAP stones are mutually paired with eachother In detail the geochemistry of LAP is unlike those of any previously studied lunar basalt exceptlunar meteorite NWA (Northwest Africa) 032 The similarities between LAP and NWA 032 are sostrong that the two meteorites are almost certainly source crater paired and could be two differentsamples of a single basalt flow Petrogenetic modeling suggests that the parent melt of LAP (andNWA 032) is generally similar to Apollo 15 low-Ti yellow picritic glass beads and that the sourceregion for LAP comes from a similar region of the lunar mantle as previously analyzed lunar basalts
INTRODUCTION
To date approximately 32 lunar meteorites have beendiscovered Although the locations of source craters orregions of the Moon from which any one of them originates isspeculative (eg Ryder and Ostertag 1983 Fagan et al 2002Gnos et al 2004) there is strong evidence that certain lunarmeteorites derive from the same crater as lunar meteorites thatfell elsewhere on Earth that is that some lunar meteorites arelaunch paired or source crater paired with others (Warren1994 Arai and Warren 1999 Korotev et al 2003a b) Duringthe 2002 Antarctic Search for Meteorites (ANSMET) thefield team collected four basaltic meteorites on the LaPaz icefield (LAP) LAP 02205 (123 kg) LAP 02224 (025 kg)LAP 02226 (024 kg) and LAP 02436 (006 kg) During thefollowing season a fifth basaltic meteorite LAP 03632(009 kg) was found On the basis of the oxygen isotopecomposition (McBride et al 2003) and a preliminarypetrographic examination during classification McBrideet al (2003 2004a 2004b) concluded that the five stones areof lunar origin and are almost certainly paired with each otherOther investigators have studied the LAP meteorites andreached a similar conclusion (Collins et al 2005 Day et al2005 Anand et al 2004 Joy et al 2005)On the basis of thework we present here for the LAP 02xxx stones we find noreasons to dispute the hypothesis and many reasons to support
it In this paper we use the designation LAP to refercollectively to the stones of the LaPaz Icefield basaltic lunarmeteorite
Here we present the mineralogy mineral chemistrytextures and major- and trace-element composition of LAPWe infer from its composition that the parent melt for LAPhad a composition similar to the low-Ti yellow picritic glassof Apollo 15 We also show on the basis of composition andpetrology that LAP is sufficiently similar to the lunarmeteorite NWA 032 (Northwest Africa Fagan et al 2002)that the two meteorites are almost certainly source craterpaired ie that they were ejected from the Moon by a singleimpact
SAMPLES STUDIED
We were allocated multiple chips of the five differentLAP stones from different areas of the meteorite LAP0220520 (258 mg) LAP 0220524 (268 mg) LAP 022249(122 mg) LAP 0222419 (183 mg) LAP 0222420 (181 mg)LAP 022266 (220 mg) LAP 0222610 (111 mg) LAP0222612 (126 mg) LAP 024367 (120 mg) LAP 024369(112 mg) LAP 0243612 (135 mg) LAP 036327 (246 mg)and LAP 0363213 (226 mg) We were also allocated polishedthin sections LAP 0220533 (surface area of sim15 cm2) LAP0222424 (sim06 cm2) LAP 0222616 (sim11 cm2) LAP
1074 R Zeigler et al
0243614 (sim06 cm2) and LAP 0363218 (sim10 cm2) Forcomparison we present here compositional data for ninesubsamples of basaltic lunar meteorite NWA 032 Wecollected the NWA 032 data under almost identical analyticalconditions to those described below for LAP (see Fagan et al2002 for details) Previously the chemical composition ofNWA 032 has only been reported as mass-weighted averages(Fagan et al 2002)
ANALYTICAL METHODS
We used a variety of analytical techniques tocharacterize the LAP samples We obtained trace-elementcompositions by instrumental neutron activation analysis(INAA) and major-element compositions by a combination ofINAA and electron microprobe analysis (EMPA) on fusedbeads We characterized the textures and mineral assemblageswith a combination of transmitted light and reflected lightoptical microscopy as well as with backscattered electronimaging (BSE) using the electron microprobe A combinationof backscattered electron images and elemental X-ray mapswere used to determine a mode for the thin sections Finallywe characterized the mineral chemistry using EMPA
For INAA we subdivided each of the LAP 02205 chipsinto three sim40 mg subsamples each of the LAP 02224 LAP02226 and LAP 02436 chips into a single sim30 mg subsampleand each of the LAP 03632 chips into two sim35 mgsubsamples We sealed the samples in ultrapure silica tubingfor neutron irradiation The samples and multielementstandards were irradiated in the research reactor of theUniversity of MissourimdashColumbia with a thermal neutronflux of 515 times 1013 cmminus2sminus1 for 24 hr Radioassays were doneusing gamma ray spectrometry at 6 7ndash9 10ndash13 and 28ndash32days following neutron irradiation Several well-characterized rock and synthetic glasses were used asstandards Gamma-ray spectral data were reduced using theTEABAGS program (Lindstrom and Korotev 1982 Korotev1991) INAA-derived compositional data are tabulated inTable 1
We obtained data for mineral and glass compositions byEMPA using a JEOL 733 Superprobe with AdvancedMicrobeam Inc automation Mineral and glass analyses wereconducted using wavelength dispersive spectrometersoperating at 15 kV accelerating voltage and using a 20 nAbeam current for feldspar and glass analyses a 30 nA beamcurrent for pyroxene and olivine analyses and a 40 nA beamcurrent for metal oxide and phosphate analyses A set ofoxide mineral and glass standards were used for calibrationin WDS (wavelength dispersive spectroscopy) analyses Aspot size ranging from 1 to 10 microm was used for all mineralanalyses Count times varied depending on the target phasebut were typically about 10ndash30 sec on peak for majorelements and 30ndash60 sec on peak for minor elements Theconcentrations of Th and the rare earth elements (REEs) inphosphates were calibrated using ThO2 and synthetic REE-
orthophosphate standards (Jarosewich and Boatner 1991Donavan et al 2003) respectively with count times of 90ndash120 sec The detection limits for major and minor elementsare sim002 wt and the detection limits for Th and the REEsranged from 004 to 012 wt Data for mineral and glasscompositions are reported in Tables 2ndash8
For bulk major-element analysis we ground each LAP02xxx INAA subsample in an agate mortar and pestle afterradioassay and fused the resulting powder with amolybdenum strip resistance heater under an argonatmosphere (Jolliff et al 1991) The LAP 03632 INAAsubsamples were still too radioactive to handle so they werenot analyzed at this time We analyzed the resulting fusedbeads (FB) for major elements by EMPA using the previouslydescribed conditions except that the spot size was increasedto 40ndash50 microm and basaltic glass standards were used inaddition to the mineral and oxide standards Molybdenumconcentrations averaged 008 wt in the fused bead analysesand were almost always lt03 wt Concentrations of Na2Odetermined by EMPA were typically 5ndash10 lower(relatively) than INAA-derived concentrations We attributethis discrepancy to systematic volatilization of Na2O duringthe fusing process Concentrations of FeO (ie total Feas FeO) determined by EMPA on fused beads were typically1ndash5 lower (relatively) than FeO concentrations determinedby INAA This is due to the incorporation of a small amountof Fe into the Mo metal during the fusing process The whole-rock major-element concentrations tabulated in Table 1 arereported on a Mo-free basis For FeO Na2O and Cr2O3 theINAA-derived concentrations are reported because they aremore accurate (Na Fe) or precise (Cr) For the other majorelements values are normalized to yield the original EMPAoxides sum
We determined modal mineral proportions by imageanalysis (4ndash9 million pixels per thin section) using acombination of BSE images and elemental X-ray maps forMg Al Si P S K Ca Ti Cr and Fe that covered themajority of each of the LAP 02xxx thin sections The imageswere taken with a JEOL JSM840 scanning electronmicroscope Results of modal analyses are tabulated inTable 9
RESULTS
Petrography
The texture mineral compositions and mineralassemblages observed in the thin sections of the four LAP02xxx stones are strongly alike (Fig 1andashd) The petrographicdescription that follows is that of thin section LAP 0220533and is representative of all four sections To demonstratethe similarity among the different LAP stones we presentmineral composition data for each of the 4 LAP 02xxx stonesWhere one of the thin sections contains features that differfrom those seen in LAP 0220533 this is noted
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1075Ta
ble
1 M
ajor
- and
trac
e-el
emen
t con
cent
ratio
ns o
f LA
P 02
205
and
NW
A 0
32 s
ubsa
mpl
es a
nd w
eigh
ted
aver
ages
Sa
mpl
eLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
P02
205
0220
502
205
0220
502
205
0220
502
224
0222
402
224
0222
602
226
0222
602
436
0243
602
436
0363
2Sp
lit2
0-1
20-
22
0-3
24-
12
4-2
24-
39
-11
9-1
20-
16
-11
0-1
12-
17
-19
-11
2-1
7-1
Maj
or-e
lem
ent c
once
ntra
tions
SiO
245
045
345
245
344
745
245
345
045
745
845
645
745
845
444
9minus
TiO
23
343
333
342
993
283
132
983
332
653
233
193
222
812
742
77minus
Al 2O
39
8410
18
104
89
638
9810
20
104
09
359
769
509
789
1610
67
9
379
37minus
Cr 2
O3
(IN
AA
)0
260
220
260
330
320
330
290
300
360
310
300
310
330
380
420
23Fe
O (I
NA
A)
229
228
219
217
233
216
227
231
215
218
217
219
209
218
228
218
MnO
028
030
029
028
034
032
026
028
028
028
028
029
025
028
027
minusM
gO5
875
465
697
177
116
685
766
567
496
726
457
106
307
937
74minus
CaO
111
112
114
111
105
113
112
109
111
111
114
111
114
110
105
minusN
a 2O
(IN
AA
)0
390
420
410
380
360
390
360
360
370
370
370
370
370
350
350
39K
2O0
080
090
070
060
070
060
100
080
060
060
070
060
080
050
06minus
P 2O
50
110
110
100
090
080
080
120
130
090
090
120
110
130
090
11minus
Tota
ls99
199
499
299
099
099
399
599
399
499
399
399
399
099
499
3minus
Mgprime
3130
3237
3536
3134
3835
3537
3539
38minus
Trac
e-el
emen
t con
cent
ratio
nsSc
590
580
578
595
589
604
602
581
588
600
608
584
617
608
568
592
Cr
1751
1511
1767
2290
2180
2230
1982
2070
2470
2150
2040
2100
2240
2580
2840
1590
Co
346
339
340
378
404
370
385
371
385
355
350
378
343
415
427
315
Sr15
016
019
013
013
011
014
014
013
014
014
010
013
013
013
010
0Zr
200
260
250
210
150
140
130
190
190
180
150
220
190
100
170
200
Ba
166
154
150
124
134
152
153
163
144
144
157
142
139
8612
615
7La
147
153
142
116
153
146
125
145
114
118
127
124
110
106
118
136
Ce
383
396
366
322
370
360
336
388
308
329
345
344
319
273
316
369
Nd
2528
2320
2720
2225
1618
2624
1820
1922
Sm8
608
898
357
048
518
197
488
616
847
247
627
426
806
327
058
13Eu
136
141
136
120
126
129
121
130
112
119
125
122
120
102
114
128
Tb1
892
021
911
631
951
861
732
031
661
681
771
731
671
511
651
85Y
b7
37
47
06
17
06
76
57
36
06
26
66
45
95
36
17
0Lu
099
103
096
083
095
094
091
100
082
087
091
090
084
073
086
100
Hf
627
642
606
510
571
550
567
633
504
525
565
549
501
418
519
597
Ta0
800
800
790
690
670
690
740
800
610
700
730
750
630
570
630
76Th
224
234
220
179
201
193
213
239
180
187
211
204
191
142
200
234
U0
610
520
670
550
530
420
480
640
440
510
540
430
440
370
560
57M
ass (
mg)
353
402
402
345
413
489
279
273
288
283
277
305
273
269
333
324
1076 R Zeigler et al Ta
ble
1 C
ontin
ued
Maj
or- a
nd tr
ace-
elem
ent c
once
ntra
tions
of L
AP
0220
5 an
d N
WA
032
sub
sam
ples
and
wei
ghte
d av
erag
es
Sam
ple
LAP
LAP
LAP
NW
AN
WA
NW
AN
WA
NW
AN
WA
NW
AN
WA
NW
ALA
PN
WA
LAP
NW
A03
632
0363
203
632
032
032
032
032
032
032
032
032
032
032
032
032
Split
7-2
13-
11
3-2
A2
A3
A4
B1
B3
B4
C1
C2
D2
ave
ave
rsde
vrs
dev
Maj
or-e
lem
ent c
once
ntra
tions
SiO
2minus
minusminus
451
442
454
456
434
445
447
445
452
453
447
000
80
015
TiO
2minus
minusminus
285
296
301
333
263
308
302
282
315
311
300
007
90
068
Al 2O
3minus
minusminus
942
902
942
990
867
999
937
858
973
979
932
005
20
054
Cr 2
O3 (
INA
A)
033
031
028
040
037
037
036
042
039
056
036
038
031
040
015
60
154
FeO
(IN
AA
)22
622
322
821
722
622
121
523
721
822
622
021
822
222
20
029
003
1M
nOminus
minusminus
027
028
029
027
030
026
026
029
030
029
028
008
00
060
MgO
minusminus
minus7
978
507
366
3010
26
686
764
985
692
663
797
011
50
170
CaO
minusminus
minus10
710
410
911
59
511
310
49
810
911
09
106
002
50
062
Na 2
O (I
NA
A)
037
038
037
036
034
035
038
033
037
032
034
035
038
035
005
00
052
K2O
minusminus
minus0
080
090
090
110
080
100
100
110
090
070
090
202
012
2P 2
O5
minusminus
minus0
080
080
060
100
070
080
110
110
100
100
090
158
020
8To
tals
minusminus
minus99
098
999
399
399
398
899
198
898
999
28
990
minusminus
Mgprime
minusminus
minus40
4037
3444
3638
4436
347
390
081
008
8
Trac
e-el
emen
t con
cent
ratio
nsSc
585
604
591
608
537
580
579
496
551
507
544
584
592
552
002
10
067
Cr
2280
2100
1930
2760
2500
2500
2430
2870
2660
3800
2490
2600
2096
2760
015
60
154
Co
387
377
370
408
438
396
368
503
399
469
414
385
370
421
007
60
102
Sr14
010
013
012
614
013
016
014
012
619
016
014
013
314
90
162
014
0Zr
140
160
210
160
170
180
180
160
160
160
170
180
183
170
022
40
055
Ba
163
128
163
191
250
229
170
130
166
335
469
266
145
266
013
30
392
La12
711
713
210
511
111
912
110
311
710
511
711
913
111
30
114
006
2C
e33
832
136
228
528
932
332
328
231
627
730
930
534
729
90
090
006
0N
d21
2623
1918
2222
1620
1921
2122
200
151
009
8Sm
758
715
791
637
648
710
705
610
692
618
664
698
774
663
009
40
058
Eu1
201
201
271
061
071
151
201
001
151
021
131
171
241
100
073
006
4Tb
176
165
183
152
152
165
167
144
160
146
159
165
179
157
007
90
054
Yb
65
63
68
57
57
61
62
53
60
54
58
61
659
58
008
40
053
Lu0
910
890
950
810
780
850
850
740
830
750
810
830
920
800
081
005
2H
f5
595
185
854
764
965
295
314
555
134
635
105
325
585
020
099
005
9Ta
076
067
069
056
064
071
068
060
061
060
061
065
071
063
009
70
073
Th1
961
962
171
74 1
91
199
204
167
196
172
187
203
204
189
011
40
074
U0
420
550
590
350
440
440
450
390
400
510
570
490
520
460
158
014
4M
ass (
mg)
341
373
388
90
210
81
107
96
77
182
156
242
641
124
minusminus
Maj
or-e
lem
ent c
once
ntra
tions
in w
t a
nd tr
ace-
elem
ent c
once
ntra
tions
in p
pm M
ajor
ele
men
ts n
ot o
ther
wis
e la
bele
d w
ere
obta
ined
by
EMPA
on
fuse
d be
ads m
ade
from
the
sam
e IN
AA
split
Ave
rage
s(a
ve)
are
wei
ghte
d av
erag
es r
sdev
= re
lativ
e st
anda
rd d
evia
tion
The
rela
tive
unce
rtain
ties
in th
e IN
AA
dat
a ar
e 1
ndash2
for N
a 2O
Sc
Cr
Co
FeO
La
Ce
Sm
Yb
Lu
and
Hf
3ndash4
for E
u T
b a
ndTh
7ndash1
0 fo
r Ta
and
Ba
17
for U
and
25ndash
30
for S
r and
Zr
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1077Ta
ble
2 A
vera
ge a
nd re
pres
enta
tive
oliv
ine
com
posi
tions
in th
e LA
P ba
salti
c m
eteo
rites
LA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
P02
205
0222
602
224
0243
602
205
0222
602
224
0243
602
205
0222
402
436
0220
5co
reco
reco
reco
ret-r
imt-r
imt-r
imt-r
imx-
rimx-
rimx-
rimfa
y s
ymp
N40
2463
2942
1710
54
12
2
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
359
236
01
359
036
28
345
434
24
340
934
21
314
030
43
311
529
72
TiO
20
040
040
040
040
060
060
040
080
110
520
100
34A
l 2O3
003
009
002
003
lt00
2lt0
02
005
lt00
2lt0
02
lt00
2lt0
02
lt00
2C
r 2O
30
240
210
230
220
170
160
110
060
070
060
03lt0
02
FeO
344
432
92
328
233
14
420
640
15
417
545
70
586
362
85
587
966
50
MnO
033
036
035
036
047
041
042
050
063
071
058
065
MgO
282
629
24
301
229
63
224
623
50
225
519
30
881
461
844
177
NiO
lt00
5n
an
an
alt0
05
na
na
na
na
na
na
na
CaO
035
034
036
033
033
036
035
036
045
053
054
055
Na 2
Olt0
02
lt00
2lt0
02
lt00
2lt0
02
lt00
2lt0
02
lt00
20
02lt0
02
lt00
2lt0
02
Tota
l99
65
992
299
85
100
0310
016
989
099
37
100
2210
012
997
199
65
995
5
Cat
ion
ratio
sFa
406
387
380
386
514
490
511
571
787
884
796
950
Fo59
461
362
061
448
751
048
942
921
111
620
44
5
Stoi
chio
met
ry b
ased
on
4 ox
ygen
ato
ms
Si IV
099
90
998
098
90
997
099
50
992
099
01
003
099
50
995
099
40
996
Al V
I0
001
000
30
001
000
10
000
000
00
002
000
00
000
000
00
000
000
0Ti
VI
000
10
001
000
10
001
000
10
001
000
10
002
000
30
013
000
20
009
Cr
000
50
005
000
50
005
000
40
004
000
30
001
000
20
002
000
10
000
Fe+2
080
10
764
075
60
762
101
60
973
101
61
122
155
41
719
156
91
864
Mn+2
000
80
009
000
80
008
001
20
010
001
00
012
001
70
020
001
60
018
Mg
117
11
208
123
61
214
096
21
014
097
40
842
041
60
225
040
10
089
Ca
001
10
010
001
10
010
001
00
011
001
10
011
001
50
018
001
90
020
Na
000
00
000
000
00
000
000
00
000
000
10
000
000
10
000
000
00
000
Tet s
ite0
999
099
80
989
099
70
995
099
20
990
100
30
995
099
50
994
099
6O
ct si
te1
998
199
92
019
200
12
006
201
42
017
199
12
007
199
62
009
199
9N
= n
umbe
r of a
naly
ses i
n th
e av
erag
e t-
rim =
typi
cal r
im x
-rim
= e
xtre
me
rim f
ay s
ymp
= fa
yalit
e sy
mpl
ectit
e n
a =
not
ana
lyze
d
1078 R Zeigler et al Ta
ble
3 A
vera
ge a
nd re
pres
enta
tive
pyro
xene
com
posi
tions
in th
e LA
P ba
salti
c m
eteo
rites
LA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
P02
205
0222
602
224
0243
602
205
0222
602
224
0243
602
205
0243
602
205
pig
cor
epi
g c
ore
pig
cor
epi
g c
ore
aug
cor
eau
g c
ore
aug
cor
eau
g c
ore
hd
hd
pyxf
er
N23
1417
168
2014
111
11
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
516
751
94
520
751
83
495
149
27
494
649
51
456
045
91
439
7Ti
O2
056
051
053
056
135
135
130
134
139
185
112
Al 2O
31
331
201
321
363
173
333
243
281
842
051
73C
r 2O
30
590
540
580
540
971
010
940
98lt0
02
lt00
2lt0
02
FeO
198
419
47
191
619
83
138
613
21
133
213
77
312
130
66
471
8M
nO0
360
350
360
350
250
250
260
270
320
330
59M
gO18
81
192
019
63
185
213
47
138
114
05
138
00
480
330
04C
aO6
396
496
386
8216
81
169
616
74
165
817
88
183
73
53N
a 2O
lt00
20
030
030
020
050
050
060
05lt0
02
lt00
20
02To
tal
995
799
73
100
199
82
994
499
23
993
599
57
987
399
51
981
7
Cat
ion
ratio
sM
gprime62
863
764
662
563
465
165
364
12
61
90
1Fs
317
310
304
316
249
237
237
246
582
580
871
En53
614
614
215
743
132
131
731
340
240
90
1W
o14
754
455
452
632
044
244
644
01
61
112
8
Stoi
chio
met
ry b
ased
on
6 o
xyge
n at
oms
Si IV
194
91
953
194
81
952
188
31
874
187
81
879
191
61
908
193
3A
l IV
005
10
047
005
20
048
011
70
126
012
20
121
008
40
092
006
6Ti
IV0
000
000
00
000
000
00
000
000
00
000
000
00
000
000
00
000
Al V
I0
009
000
60
006
001
20
026
002
30
023
002
60
007
000
80
009
Ti V
I0
016
001
40
015
001
60
038
003
90
037
003
80
044
005
80
054
Cr
001
80
016
001
70
016
002
90
030
002
80
029
000
00
000
000
0Fe
+20
626
061
20
599
062
40
441
042
00
423
043
71
097
106
61
734
Mn+2
001
10
011
001
10
011
000
80
008
000
80
009
001
10
012
002
2M
g1
058
107
61
094
103
90
764
078
30
795
078
10
030
002
10
002
Ca
025
80
261
025
60
275
068
50
691
068
10
674
080
50
818
016
6N
a0
001
000
20
002
000
10
003
000
40
004
000
40
001
000
10
002
Tet s
ite2
000
200
02
000
200
02
000
200
02
000
200
02
000
200
01
999
Oct
site
199
71
999
200
11
995
199
51
999
200
11
997
199
51
983
198
9A
ugite
(aug
) co
res h
ave
an M
gprime gt
60 a
nd W
o gt3
0 w
hile
pig
eoni
te (p
ig)
core
s hav
e M
gprime gt
60 a
nd W
o lt1
8 H
d =
hed
enbe
rgite
pyx
fer
= py
roxf
erro
ite
Mgprime
= M
g(M
g +
Fe)
100
N =
num
ber o
f ana
lyse
s
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1079
All of the LAP stones have relatively coarse-grained (upto approximately 15 mm) subophitic texture They consistpredominantly of pyroxene and plagioclase with minoramounts of olivine ilmenite and a groundmass dominated byfayalite and cristobalite They contain trace amounts ofchromite chromian ulvˆspinel ulvˆspinel troilite Fe-metalbarian K-feldspar fluor-apatite RE-merrillite tranquillityite(Fe8(YZr)2Ti3Si3O24) and baddeleyite (ZrO2) The modalmineral proportions differ slightly from section to section(Table 9) A few veins and pockets of basaltic glass ofpseudo-whole rock composition (likely shock melted) alsooccur in thin sections LAP 0220533 and LAP 0222424 Theorder in which minerals are inferred to have crystallized ischromite olivine pyroxene plagioclase and groundmass
Olivine grains vary in size from 003 to sim1 mm with01 to 03 mm being typical The modal abundance of olivineranges from 23 to 36 The grains are usually anhedral(rarely subhedral Fig 2a) typically with round or irregularmorphology and uneven contact with the surroundingpyroxene (Fig 2b) Some olivine grains have inclusions ofchromite or Cr-ulvˆspinel grains or both and a few haveldquomeltrdquo inclusions that have two phases in them mafic glasswith a pyroxene-like composition (sim10 wt Al2O3 Table 6)and K-rich high-silica glass similar to the glass seen in thefayalite symplectite grains in the groundmass (sim3 wt K2O68 wt SiO2) Most of the larger olivine grains are zonedwith cores of Fo55ndash65 and rims typically in the Fo38ndash45 range(Fig 3a Table 2) though in a few instances zoning to rims ofFosim20 is observed (Fig 3b) Most of the smaller olivine grainsare not zoned (or not strongly zoned) and they typically havecompositions in the Fo52ndash57 range with the smallest grainshaving the most magnesian compositions The apparentreaction texture between olivine and pyroxene and therelatively magnesian rims on compositions of the smallestolivine grains (likely the remnant cores of grains that havebeen almost completely resorbed) are strong indications thatolivine was being resorbed when the rock solidified
Chromite and Cr-ulvˆspinel grains almost always occuras inclusions within or closely associated with olivine grainsThey also have relatively restricted compositional ranges(Fig 4 Table 4) and they occur individually and as compositegrains with cores of chromite (Chr62ndash68Usp13ndash18Spn16ndash25) andrims of Cr ulvˆspinel (Chr6ndash19Usp71ndash91Spn3ndash11) (Figs 5aand 5b) We found few spinel compositions intermediate tothese end members The total modal abundance of spinel(including ulvˆspinel in the groundmass) is small rangingfrom 03 to 04 Where these two phases are intergrown theboundary between them is sharp with differences in Cr2O3concentration exceeding 20 wt within a few micrometers ofthe boundary A few of the chromite grains have inclusionsof pyroxene with a range of compositions (Mgprime of 47ndash59Wo16ndash31 and TiO2 concentrations from 11ndash24 wt)
Pyroxene grains in LAP are anhedral display undulatoryto mosaic extinction and range in size up to sim1 mm (Fig 2c)
In many cases pyroxene grains partially enclose plagioclasegrains in a subophitic texture The modal abundance ofpyroxene ranges from 47 to 52 The pyroxene grains havemagnesian cores of pigeonite and subcalcic augite (Mgprime fromsim50 to 68) with a wide range of CaO concentrations (Wo11 toWo36 Table 3 Fig 6) although there appears to be a bimodaldistribution of Wo contents with a minimum near Wo20(Fig 6 insets) In some cases pyroxene core compositionsgrade continuously to nearly end member hedenbergite(Fs58Wo40) and pyroxferroite (Fs86Wo13) In a few rare casescontacts between magnesian and ferroan pyroxenes are sharpand linear Compositions of pyroxene grains in contact withpartially resorbed olivine grains vary considerably incomposition The most common composition issubcalcic augite (Wo gt 20) with FeO concentrations in therange Fs24ndash49
The TiAl and TiCr ratios in the LAP pyroxenes arestrongly correlated with Mgprime as expected according toelement compatibility (eg Bence and Papike 1972) Theatomic TiCr ratio increases with decreasing Mgprime in LAPpyroxenes (Fig 7a) This reflects the compatible behavior ofCr and the incompatible behavior of Ti in early crystallizingphases of low-Ti lunar basaltic magmas The most magnesianpyroxenes have atomic TiAl ratios very close to 14indicating that aluminum was introduced through boththe Tschermak (AlAlMgminus1Siminus1) and coupled titanium(TiAl2Mgminus1Siminus2) exchange reactions in approximately equalproportions (Thompson 1982) As pyroxene becomesprogressively more ferroan the TiAl cation ratio approaches12 suggesting a gradual increase in the proportion of Alincorporated due to coupled Ti substitution (Fig 7b) Theleast magnesian pyroxenes (Mgprime lt40) have TiAl ratiosapproaching 34 An increase in TiAl ratios in pyroxene from14 to 12 with decreasing Mgprime in lunar basalts has previouslybeen interpreted as a result of pyroxene crystallization bothprior to the onset of plagioclase crystallization (ratiosaround 14) and during plagioclase crystallization (14ndash12Bence and Papike 1972) Bence and Papike (1972) attributedthe high relative concentrations of Ti in the late-stage Fe-richlunar pyroxenes to Ti3+
Plagioclase forms elongated subhedral to anhedralgrains up to 175 mm long The modal abundance ofplagioclase ranges from 32 to 35 Pyroxene inclusions ofa variety of sizes with compositions spanning nearly theentire compositional spectrum observed occur withinplagioclase Most plagioclase grains are highly fracturedalthough some or portions of some are smooth in polishedsections as seen in the BSE images (Fig 2d) These smoothareas consist partially or entirely of maskelynite as indicatedby their isotropic (or nearly isotropic) character in cross-polarized light Plagioclase grains are complexly zoned Theirtypical core composition is An886Ab11Or04 with sim1 wtFeO + MgO and an Mgprime of 34 (Fig 8 Table 5) Their rims areas wide as sim40 microm and gradually increase in K (up to simOr5)
1080 R Zeigler et al
and FeO (up to sim3 wt) while decreasing in MgO(to lt002 wt Fig 9) The Na2O concentrations firstincrease up to simAb14 then decrease sharply to less thanAb10 (which is lower than in the cores) The extreme rimcomposition of the large plagioclase grains is similar to that ofthe plagioclase found as inclusions in groundmass fayaliteand cristobalite grains (next paragraph Table 5) There is noapparent overall compositional difference between the coresof the maskelynite and the plagioclase grains
Fayalite cristobalite and ilmenite are the dominantminerals in the groundmass typically occurring togetheralthough each can be found independently All of the phaseshave relatively minor modal abundances fayalite (29ndash48)cristobalite (18ndash21) and ilmenite (35ndash40) Silicadisplaying the ldquocracklerdquo pattern distinctive to cristobaliteoccurs as anhedral grains up to 05 mm in size Thecristobalite grains contain minor Al2O3 TiO2 FeO and CaO(Σ sim13 wt Table 6) Inclusions of late-crystallizing phasessuch as K-rich plagioclase K-rich glass K-feldspar fayaliteFe-rich pyroxene phosphate and mafic glass withhigh concentrations of incompatible elements are common(Fig 5c) Fayalite grains (Fo45 sim05 wt CaO) range in size
up to 075 mm and usually form a symplectite texture withinclusions of K-rich glass silica K-rich plagioclase andilmenite (Fig 5d) Fayalite with no (or few) inclusions occursonly rarely Ilmenite is the dominant oxide in the groundmassforming elongate laths up to 1 mm in length Typically theilmenite is poor in Mg (sim02 wt average) although a singlegrain of more magnesian ilmenite associated with a largeolivine grain was observed (Fig 2b) Less common aresmaller subhedral ulvˆspinel grains (lt005 mm) thathave compositions approaching end member ulvˆspinel(Chr0ndash4Usp93ndash98Sp2ndash3) A few composite grains of ilmeniteand ulvˆspinel were observed
Also found in the groundmass are a variety of traceminerals including both fluorapatite and RE-merrillite(Table 7) Phosphate grains most commonly occur betweenplagioclase and ferropyroxene sometimes with associatedcristobalite troilite or both Barian K-feldspar (sim5 wt BaO)also occurs in the groundmass usually in the same areas asthe phosphate minerals (Table 5) Only a few K-feldspargrains (the largest) have stoichiometry that unambiguouslyidentifies them as K-feldspar while many K-rich grainshave excess Si suggesting that they may be intergrowths of
Table 4 Average oxide compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02205 02226 02224 02436 02205 02226 02224 02436 02205 02226 02224Al Al Al Al Cr-rich Cr-rich Cr-rich Cr-rich CrAl CrAl CrAlchr chr chr chr usp usp usp usp usp usp usp
N 23 11 13 5 22 1600 7 13 9 22 10
Major elements in wt by EMPAFeO 3444 3503 3532 3433 5705 5832 5846 5868 6191 6198 6180TiO2 546 532 540 517 2833 2871 2892 2909 3254 3151 3161Cr2O3 4384 4357 4331 4391 928 840 851 776 234 310 338Al2O3 1142 1178 1140 1217 287 261 261 276 191 204 203MgO 283 242 218 292 093 061 069 065 021 028 031MnO 027 024 025 027 035 032 034 033 036 032 034V2O3 073 074 076 075 036 031 033 033 022 025 026SiO2 007 009 008 009 lt002 007 008 018 lt002 008 007CaO 004 004 003 lt002 010 005 006 011 008 007 005ZnO 003 na na na 004 na na na 003 na naTotals 991 992 987 996 993 994 1000 999 996 996 999
Stoichiometry based on 4 (spinel) and 3 (ilmenite) oxygen atomsSi IV 0003 0003 0003 0003 0000 0003 0003 0006 0000 0003 0003Al VI 0469 0484 0472 0496 0125 0114 0113 0119 0083 0089 0088Ti 0143 0139 0143 0134 0784 0798 0798 0803 0907 0880 0880V 0020 0021 0021 0021 0011 0009 0010 0010 0007 0007 0008Cr 1208 1201 1204 1199 0270 0245 0247 0225 0068 0091 0099Fe2+ 1004 1021 1039 0992 1756 1802 1794 1801 1920 1925 1913Mn2+ 0008 0007 0007 0008 0011 0010 0011 0010 0011 0010 0011Mg 0147 0126 0114 0151 0051 0034 0038 0035 0012 0016 0017Zn 0001 minus minus minus 0001 minus minus minus 0001 minus minusCa 0002 0002 0001 0000 0004 0002 0002 0004 0003 0003 0002Sum 2+ 1162 1156 1161 1151 1823 1847 1844 1851 1947 1953 1942Sum 3 4+ 1844 1849 1844 1854 1190 1168 1170 1163 1066 1071 1078Total 3003 3001 3002 3001 3012 3013 3012 3007 3013 3020 3017
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1081
K-feldspar and silica (granophyric texture) at a scale smallenough to be beyond the resolution of the electron microprobe(less than sim01 microm)
Two glass types of distinct composition presumably late-stage residual liquids occur in the groundmass The first is aKSi-rich glass (78 wt SiO2 sim56 wt K2O) that makes upa considerable percentage of the inclusions in the cristobaliteand particularly the fayalite grains The second type ofevolved glass occurs as very small (lt5 microm) roundedinclusions in cristobalite grains This glass has a silica-poorFe-rich bulk composition (sim36 wt SiO2 sim39 wt FeOTable 6) but it is also considerably enriched in manyincompatible elements 23 wt P2O5 12 wt SO3 02 wtY2O3) Commonly we observed minute grains of fayalitetroilite or phosphate associated with this glass These twolate-stage glasses could represent conjugate liquids producedby late-stage immiscibility of an evolved residual meltSimilar glasses were observed in some plutonic rocks fromthe Apollo 14 site (Jolliff et al 1991)
Troilite blebs (with nearly ideal stoichiometry Table 8)are scattered throughout the groundmass along with trace Fe-metal grains which are usually intergrown with troilite orovergrown on chromite grains These grains typicallycontained 66 wt Ni and 14 wt Co though one grain had338 wt Ni and 60 wt Co (Table 8) A few grains ofbaddelyite (ZrO2) and tranquillityite (Zr-Fe-Ti silicate) wereidentified by energy-dispersive spectroscopy (EDS) in thegroundmass
A variety of shock effects occur in the minerals of thesethin sections (eg plagioclase converted to maskelynitemosaicism in the pyroxene) The level of shock was such thatlocalized partial melting occurred in some areas of themeteorite The areas of shock melt have severalmorphologies small melt pockets (LAP 02205 Fig 10a)veins of melt (LAP 0222424 Fig 10b) and in some casesareas that were only partially melted (LAP 0222424Fig 10c) with discernable mineral grains still present(typically maskelynite) Although veins of shock melt are rare
Table 4 Continued Average oxide compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02436 02205 02226 02224 02436 02205 02226 02224 02436 02205CrAl end end end end Mgusp usp usp usp usp ilm ilm ilm ilm ilm
N 11 11 2 3 3 24 16 20 18 2
Major elements in wt by EMPAFeO 6202 6375 6445 6355 6465 4657 4647 4634 4624 4463TiO2 3353 3267 3226 3396 3231 5198 5226 5233 5264 5296Cr2O3 209 026 023 011 037 010 012 015 016 038Al2O3 202 179 206 216 227 008 011 013 010 006MgO 022 005 008 007 003 014 010 016 019 150MnO 034 031 027 029 027 038 033 037 027 035V2O3 023 018 015 019 016 031 029 029 028 035SiO2 015 lt002 011 010 007 003 003 024 004 lt002CaO 007 010 007 008 010 013 006 010 009 008ZnO na 008 na na na 003 na na na lt002Totals 1007 992 997 1005 1002 997 998 1001 1000 1003
Stoichiometry based on 4 (spinel) and 3 (ilmenite) oxygen atomsSi IV 0005 0001 0004 0004 0003 0001 0001 0006 0001 0000Al VI 0087 0079 0091 0093 0099 0002 0003 0004 0003 0002Ti 0920 0921 0906 0937 0901 0990 0993 0989 0996 0991V 0007 0005 0004 0006 0005 0006 0006 0006 0006 0007Cr 0060 0008 0007 0003 0011 0002 0002 0003 0003 0007Fe2+ 1893 1999 2012 1950 2005 0986 0982 0974 0973 0928Mn2+ 0010 0010 0009 0009 0009 0008 0007 0008 0006 0007Mg 0012 0003 0004 0004 0002 0005 0004 0006 0007 0056Zn minus 0002 minus minus minus 0001 minus minus minus 0000Ca 0003 0004 0003 0003 0004 0004 0002 0003 0002 0002Sum 2+ 1918 2018 2028 1966 2019 1004 0995 0991 0988 0994Sum 3 4+ 1080 1014 1012 1043 1019 1001 1005 1008 1009 1007Total 2992 3032 3035 3005 3036 2004 2000 1992 1996 2001The spinel catagories where chosen based primarily on Cr2O3 content with Al chromite (chr) having gt40 wt Cr2O3 Cr-rich ulvˆspinel (usp) having 15ndash
5 wt Cr2O3 CrAl ulvˆspinel having 5ndash05 wt Cr2O3 and endmember ulvospinel having lt05 wt Cr2O3 Also seen were TiAl chromite (30ndash40 wtCr2O3) and high-Cr ulvˆspinel (30ndash15 wt Cr2O3) which are likely the result of an anlyses overlapping simultaneously on both an Al chromite and Cr-rich ulvˆspinel grain Similarly compositions intermediate to ilmenite and end ulvˆspinel were seen These compositions are not listed in this table but areshown in Fig 4 N = number of analyses in the average na = not analyzed
1082 R Zeigler et al
in our thin sections such veins were reported as pervasive inthe original macroscopic description of all five LAP stones(McBride et al 2003 2004a 2004b)
The various shock-induced effects observed in LAP canbe used to quantify and constrain the level of shock that LAPexperienced The presence of both plagioclase andmaskelynite in these samples suggests that the lower end ofthe range listed for conversion of plagioclase to maskelynite(30ndash45 GPa Stˆffler and Hornemann 1972 Ostertag 1983)is appropriate The mosaicism seen in the pyroxene istypically associated with shock values in the 30ndash75 GParange (Kieffer et al 1976 Schaal et al 1979) The presenceof shock-melt veins that have melted both pyroxene andplagioclase (based on the melt composition Table 6)indicates LAP should have been subjected to shock levels ofgt75ndash80 GPa (Kieffer et al 1976 Schaal et al 1979) Thedifferent shock effects observed reflect a range fromlt30 GPa (areas were plagioclase is preserved) to gt75 GPa(areas where shock melting occurred) over distances of onlya few millimeters
Bulk Composition and Comparison to Other LunarBasalts
LAP is a moderately aluminous (sim10 wt Al2O3) low-Ti(31 wt TiO2) mare basalt that falls near the Fe-rich(222 wt FeO) end of the range of FeO concentrationsobserved among lunar basalts It is more ferroan (Mgprime = 347)than any basalt in the Apollo or Luna collection (Fig 11a)Among lunar basalts only meteorites Asuka-881757 andYamato-793169 have comparably low Mgprime values (Koeberlet al 1993 Warren and Kallemeyn 1993 Thalmann et al1996 Korotev et al 2003a) LAP is enriched in Na2O(038 wt) relative to other ferroan (eg Asuka-881757 andYamato-793169) and Fe-rich basalts except for NWA 032(Fig 11b)
Regarding trace elements LAP is enriched in Cocompared to most lunar mare basalts with comparable Scconcentrations (Table 1 Fig 12a) Among Apollo and Lunabasalts only the Apollo 12 ilmenite basalts (Rhodes et al1977 Neal et al 1994) are comparable Incompatible trace-
Table 5 Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02205 02226 02224 02436 02205 02226 02224 02436 02205 02226plag plag plag plag mask mask mask mask plag plagcore core core core core core core core Na rim Na rim
N 123 86 48 88 29 49 33 32 12 3
Major elements in wt by EMPASiO2 4715 4657 4689 4639 4753 4741 4663 4673 4949 4960TiO2 010 007 007 006 013 008 006 006 027 019Al2O3 3337 3367 3296 3363 3367 3291 3376 3415 3170 3103Cr2O3 003 lt002 lt002 002 007 002 lt002 002 004 003FeO 068 067 073 058 060 111 066 060 134 136MgO 023 022 017 024 027 029 028 029 008 012CaO 1730 1746 1709 1763 1747 1726 1730 1740 1628 1597BaO na na na na na na na na na naNa2O 120 123 136 121 119 123 131 128 148 153K2O 006 007 010 006 005 009 006 005 020 019Total 1000 1000 994 998 1008 1004 1001 1006 1006 1000
Cation ratiosAn 885 883 869 887 888 881 877 880 848 842Or 04 04 06 04 03 05 03 03 12 12Ab 111 112 125 110 109 113 120 117 140 146Cn 00 00 00 00 00 00 00 00 00 00
Stoichiometry based on 8 oxygen atomsSi IV 2168 2147 2173 2143 2168 2179 2147 2140 2259 2279Al IV 1809 1830 1801 1831 1810 1782 1832 1843 1705 1681Fe+2 0026 0026 0028 0023 0023 0043 0025 0023 0051 0052Mg 0016 0015 0011 0017 0019 0020 0019 0020 0005 0008Ca 0853 0863 0849 0872 0854 0850 0853 0854 0796 0786Ba minus minus minus minus minus minus minus minus minus minusNa 0107 0110 0122 0108 0105 0109 0117 0114 0131 0136K 0004 0004 0006 0004 0003 0005 0003 0003 0011 0011Tet site 3977 3977 3974 3974 3978 3961 3979 3984 3964 3960Oct site 1005 1018 1022 1023 1003 1027 1022 1013 0995 0994
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1083
element concentrations are considerably greater in LAP thanin most of other low-Ti basalts (Fig 12bndashc) including theApollo 12 ilmenite basalts (Haskin et al 1971 Neal et al1994) The exceptions are NWA 032 the high-Al basalts ofLuna 16 (Philpotts et al 1972 Helmke and Haskin 1972 Maet al 1979) and some Apollo 14 high-Al basalts (Dickinsonet al 1985 Shervais et al 1985 Neal et al 1989a 1989b)
Relative concentrations of REEs in the LAP basalt arealso dissimilar to those of most other lunar basalts (Fig 13) inthat LAP is enriched in light REEs The exceptions are NWA032 which has a pattern nearly parallel to LAP and Apollo 14group 3 basalts (Dickinson et al 1985) which have a patternthat is similar although somewhat less steep in the heavyREEs Ratios of Th to REE in LAP are higher than those of allother lunar basalts except NWA 032 (Fig 14) and thedisparity in ThREE ratio between LAP and other lunarbasalts (except NWA 032) increases from the light to heavyREEs The Apollo 14 high-K basalts have similar ThREEratios for the middle REE Sm-Tb however (Neal et al 1989a
1989b) Overall in terms of its trace-element concentrationsLAP 02205 is most similar to NWA 032 The maindifferences are that NWA 032 is richer in elements associatedwith olivine (Mg Cr Co) and has concentrations ofincompatible elements that are 78ndash91 as great as those inLAP 02205
DISCUSSION
Evidence Supporting the Lunar Origin and Pairing of theLAP Stones
As stated in the introduction the meteorites LAP 0220502224 02226 02436 and 03632 were identified as lunarbasalts that were almost certainly paired (McBride et al 20032004a 2004b) A brief summary follows of the attributesfound in our more detailed petrographic examination thatsupport this initial classification and pairing interpretation
Results of oxygen isotope analyses (δ18O = +56 and
Table 5 Continued Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02224 02436 02205 02205 02226 02224 02436 02205 02205 02205plag plag plag plag plag plag plag barian KBa KBaNa rim Na rim matrix K rim K rim K rim K rim K-spar glass glass
N 24 5 13 10 1 5 1 10 10 23
Major elements in wt by EMPASiO2 4901 4879 5122 5152 4888 4935 5017 6026 5935 6356TiO2 008 008 016 017 lt002 008 014 na na naAl2O3 3163 3120 2960 2993 3213 3004 3002 2019 2063 2043Cr2O3 002 002 006 005 lt002 003 lt002 na na naFeO 117 130 267 192 147 195 173 065 074 116MgO 006 009 003 002 lt002 lt002 002 lt002 lt002 010CaO 1620 1622 1520 1549 1618 1602 1560 063 066 207BaO na na na na na na na 501 407 372Na2O 157 155 105 105 132 126 150 031 029 033K2O 023 021 090 067 067 056 086 1354 1162 586Total 1000 995 1007 1006 1007 993 1000 1008 1006 1007
Cation ratiosAn 839 842 846 852 835 845 807 33 minus minusOr 14 13 61 44 41 35 53 842 minus minusAb 147 145 105 104 124 120 140 30 minus minusCn 00 00 00 00 00 00 00 96 minus minus
Stoichiometry based on 8 oxygen atomsSi IV 2253 2257 2342 2344 2237 2293 2312 2863 2864 2951Al IV 1714 1701 1596 1609 1732 1645 1631 1131 1173 1124Fe+2 0045 0050 0102 0073 0056 0076 0067 0026 0030 0045Mg 0004 0006 0002 0001 0000 0001 0001 0001 0001 0007Ca 0798 0804 0745 0757 0793 0798 0770 0032 0034 0100Ba minus minus minus minus minus minus minus 0093 0077 0070Na 0140 0139 0093 0093 0117 0113 0134 0029 0027 0029K 0013 0013 0052 0039 0039 0033 0050 0820 0715 0353Tet site 3967 3957 3938 3954 3969 3938 3943 3994 4037 4075Oct site 0013 1011 0995 0963 1007 1020 1022 1002 0884 0604Plag = plagioclase mask = maskelynite N = number of analyses in the average na = not analyzed
1084 R Zeigler et al Ta
ble
6 A
vera
ge a
nd re
pres
enta
tive
cris
toba
lite
and
glas
s co
mpo
sitio
n in
the
LAP
basa
ltic
met
eorit
es
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
0220
502
226
0222
402
436
0220
502
205
0220
502
205
0220
502
224
0222
4cr
isto
balit
ecr
isto
balit
ecr
isto
balit
ecr
isto
balit
eSi
-ric
hpy
x-lik
eK
gla
ssIT
E-ric
hsh
ock
shoc
ksh
ock
MI g
lass
MI g
lass
in s
ympl
m
afic
gla
ssgl
ass
area
glas
s ar
eagl
ass
vein
N6
25
44
12
51
6515
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
979
598
17
984
798
45
672
542
76
783
236
67
463
486
441
TiO
20
270
270
230
230
664
810
374
032
341
623
13A
l 2O3
073
060
064
078
187
99
4210
13
544
139
86
123
Cr 2
O3
002
lt00
2lt0
02
002
lt00
20
13lt0
02
lt00
20
080
380
28Fe
O0
210
400
190
171
8615
91
183
392
719
618
520
5M
nOn
an
an
an
an
a0
22n
a0
420
220
290
25M
gO0
02lt0
02
lt00
2lt0
02
033
817
lt00
20
213
459
857
17C
aO0
190
200
200
236
8919
16
098
976
127
118
114
BaO
na
na
na
na
117
na
na
na
na
na
na
Na 2
O0
130
100
090
120
620
110
190
060
510
360
49K
2O0
030
050
07lt0
02
167
na
566
030
005
na
na
P 2O
5n
an
an
an
an
an
an
a2
32n
an
an
aF
na
na
na
na
na
na
na
008
na
na
na
Y2O
3n
an
an
an
an
an
an
a0
19n
an
an
aC
e 2O
3n
an
an
an
an
an
an
a0
12n
an
an
aSO
3n
an
an
an
an
an
an
a1
23n
an
an
aTo
tal
995
599
80
999
010
00
992
410
070
974
910
02
991
100
099
6Sy
mpl
= sy
mpl
ectit
e M
I = m
elt i
nclu
sion
N =
num
ber o
f ana
lyse
s in
the
aver
age
na
= n
ot a
naly
zed
The
shoc
ked
glas
s in
LAP
0222
4 is
the
parti
ally
mel
ted
area
(see
Fig
14)
and
onl
y th
e an
ayls
es o
fth
e gl
ass i
tsel
f wer
e in
clud
ed in
the
aver
age
not t
he m
iner
als t
hat w
ere
anal
yzed
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1085
Table 7 Representative phosphate compositions in LAP 0220533LAP LAP LAP LAP LAP LAP LAP LAP02205 02205 02205 02205 02205 02205 02205 02205RE- RE- RE- RE- RE- fluorapatite fluorapatite fluorapatitemerrillite merrillite merrillite merrillite merrillite
Major elements in wt by EMPASiO2 050 044 062 037 321 228 449 137Al2O3 022 lt005 009 lt005 lt005 007 014 lt005FeO 637 774 568 576 250 169 439 202MgO 020 037 025 028 lt005 lt005 lt005 lt005CaO 4326 4035 4233 4245 4983 5241 5003 5351Na2O 000 001 010 014 000 000 001 000P2O5 3885 4171 4382 4360 3540 3949 3771 4077Cl lt005 lt005 lt005 lt005 lt005 006 027 031F 047 044 050 048 168 245 130 186Y2O3 298 293 226 221 172 103 078 053La2O3 093 107 065 064 092 024 014 012Ce2O3 253 259 189 185 253 072 069 053Nd2O3 161 177 108 118 166 057 059 031Sm2O3 043 043 029 028 048 022 015 009Gd2O3 087 090 058 058 079 023 018 008Yb2O3 016 032 009 lt005 010 005 lt005 lt005ThO2 007 009 008 lt005 021 lt005 lt005 lt005minusO = (FCl) 021 020 022 021 072 105 061 085Sums 9930 1010 1001 9968 1004 1005 1003 1006
Table 8 Average sulfide and metal compositions in LAP 0220533Ave Fe metal High-Ni metal Troilite
N 5 1 8
Elemental percentage by EMPAFe 9209 5880 6280Ni 664 3377 lt002Co 141 595 lt002Ti 023 009 006Cr 043 017 lt002Mn lt002 004 lt002S lt002 lt002 3620Totals 1008 988 994Ideal troilite = 365 wt S 635 wt Fe N = number of analyses
Table 9 Modal mineralogy of the different LAP stonesLAP 0220533 LAP 0222616 LAP 0222424 LAP 0243614
Pyroxene 515 505 469 466Plagioclase 319 321 323 346Ilmenite 348 391 386 399Fay sympl 309 290 358 483Olivine 233 271 363 320Cristobalite 214 209 178 200Spinel (all) 034 045 040 039Troilite 025 024 024 022Fractures 49 49 53 421Shock glass 01 02 22 00N 633 times 106 905 times 106 470 times 106 396 times 106
All modal values are listed as percentages N = number of pixels
1086 R Zeigler et al
Fig 1 Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) and fayalite(more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phases arepyroxene and olivine a) LAP 0222616 b) LAP 0243614 c) LAP 0222424 d) LAP 0220533
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1087
δ17O = +27) performed by Mayeda and Clayton (reported inMcBride et al 2003) constrain the origin of LAP 02205 tothe Earth the Moon or an enstatite meteorite parent bodyLAP is clearly a meteorite all four of the stones have fusioncrusts (ruling out a terrestrial origin) The extremely ferroannature of LAP rules out the enstatite parent body as theprovenance FeOMnO ratios of mafic silicates arediagnostic of origins from different planetary bodies in thesolar system (Dymek et al 1976 Papike 1998) Ratios ofFeOMnO in LAP pyroxenes (average sim60) and olivines(average sim95) are consistent only with lunar origin (Fig 15)Furthermore the presence of Fe(Ni) metal and troilite thecompletely anhydrous nature of the sample the apparentlack of Fe3+ in all phases the calcic nature of theplagioclase and the deep negative Eu anomaly are allcommon in lunar basalts
With regard to texture mineral assemblage and mineralchemistry the four LAP 02xxx stones appear to beindistinguishable from each other Although we did not studythe mineral chemistry of the LAP 03632 in depth the textureand mineral assemblage are identical to the LAP 02xxxstones Furthermore the collection locations of the five stonesform a linear array sim3 km in length that is perpendicular to theflow of the ice sheet (John Schutt personal communication)Thus in the absence of cosmic-ray exposure data to thecontrary we conclude that the four LAP 02xxx stones studiedare paired
Compositional Variability among Small Subsamples ofLAP 02205 and NWA 032
Samples of lunar meteorites available for study at most afew hundred milligrams are very small by the standards ofterrestrial geology and geochemistry Nevertheless we havetaken our samples and subdivided them into numerous evensmaller (10ndash50 mg) subsamples for bulk compositionalanalysis (Korotev et al 1983 1996 2003a 2003b Jolliffet al 1991 1998 Fagan et al 2002) This procedure providesan estimate of the whole-rock composition through a mass-weighted mean that is equivalent to a single analysis of theentire mass of the allocated sample The variation amongsmall subsamples however provides additional informationabout compositional variations associated with mineralassemblage and proportions about petrogenesis and aboutpossible relationships to other meteorites (eg Korotev et al2003a 2003b) and how well the ldquowhole-rockrdquo compositionis likely to represent that of the source region of the meteorite(Korotev et al 2000a) In the following discussion weevaluate the causes of differences in composition amongsmall subsamples of LAP and NWA 032
The range of concentrations among the 19 subsamples ofLAP (27ndash40 mg) is relatively small for the most preciselydetermined major elements (SiO2 TiO2 Al2O3 FeO CaONa2O) and most precisely determined trace elements that arecompatible with the major mineral phases (Co Sc Eu) The
Fig 1 Continued Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) andfayalite (more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phasesare pyroxene and olivine d) LAP 0220533
1088 R Zeigler et al
relative sample standard deviations (s ) range from 08 to76 (with only Co and Eu gt 5 Table 1) The exceptionsare MgO and Cr2O3 for which the relative standarddeviations are distinctly greater 12 and 16 respectivelyFor incompatible elements that we determined precisely(lt9 analytical uncertainty La Ce Sm Tb Yb Lu Hf Taand Th) relative standard deviations range from 7 to 11These variations are caused by a combination ofunrepresentative sampling of the major mineral phasesowing to the coarse grain size (up to sim1 mm3) relative to theINAA subsample size (about 12 mm3 assuming that thedensity of LAP is sim35 gmm3) and to the heterogeneousdistribution of some relatively minor phases with high
concentrations of a given element This problem is not new asmany investigators have previously wrestled with theproblem of studying relatively coarse-grained lunar basaltswith small allocated subsample sizes characteristic of rareextraterrestrial samples (Korotev and Haskin 1975 Haskinet al 1977 Lindstrom and Haskin 1978 Ryder and Schuraytz2001) Ryder and Schuraytz (2001) showed that sim5 g ofmaterial are needed to achieve a representative sample ofApollo 15 olivine-normative basalts which have grain sizeson the order of a millimeter or greater
Among the LAP subsamples Cr2O3 and MgOconcentrations correlate positively (R2 = 081) as a result ofthe association of chromite and Cr-ulvˆspinel with olivine
Fig 2 BSE images from LAP 0220533 a) a large round olivine (oli) grain and a smaller subhedral olivine grain (left center of the image)both surrounded by zoned pyroxene (pyx) and plagioclase (plag) with melt inclusions (MI) and inclusions of chromite (chr) A smallulvˆspinel (Usp) grain occurs in the upper left b) A large irregular olivine grain and a smaller mostly resorbed olivine grain The larger graincontains both melt inclusions (MI) and chromite grains The associated ilmenite (Ilm) grain is the most magnesian ilmenite grain observed Acomposite grain of metal and troilite (MetSulf) is also present c) A BSE image showing the zoning in multiple large pyroxene grainsintergrown with plagioclase and maskelynite (mask) grains One small cristobalite (crist) grain is also present d) A BSE image showingseveral large plagioclase grains some of which contain both fractured areas (plagioclase) and smooth areas (maskelynite) Also present areseveral areas of groundmass including a fayalite symplectite and a cristobalite grain cut by an ilmenite lath
x
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1089
The large variations seen in MgO Cr2O3 and to a lesserextent Co concentrations occur because of the large relativevariation in the fraction of modal olivine among thesubsamples Normatively the compositional rangecorresponds to minus03ndash25 olivine (one subsample has 03normative quartz) and 032ndash049 chromite The relativelysmall variations seen among concentrations of the other majorelements as well as Sc and Eu are controlled byunrepresentative sampling of the major mineral phasespyroxene (Sc Ca Fe Si) and plagioclase (Al Na Ca Si Eu)and the minor but widely distributed mineral ilmenite (Ti Fe)Trace amounts of a few minerals that are found only ingroundmass have high concentrations of incompatible traceelements relative to the concentration of those elements inthe bulk meteorite These minerals include K-feldspar (Ba)
Fig 3 a) CaO versus Mgprime (molar Mg[Mg + Fe]100) in the olivinesof the different LAP stones The compositions range from cores ofFo55ndash67 trending towards rims typically in the Fo40 range withextreme zonation to rims of Fo15ndash20 in a few cases Where analyzedthe composition of groundmass fayalite are also shown b) Anelectron microprobe traverse across a small strongly zoned olivinegrain in LAP 0220533 The grain shows zoning from a core of simFo58to a rim composition of simFo18 over sim100 microm The break in the zoning(black arrow) is centered on a fracture in the olivine grain
Fig 4 Compositions of LAP oxides plotted on the (FeMgMn)O-(CrAl)2O3-TiO2 ternary (after El Goresy et al 1971) Compositionsof endmember ilmenite (FeTiO3) ulvˆspinel (Fe2TiO4) andchromite (FeCr2O4) are labeled For a description of theclassification scheme see the footnote of Table 3 a) LAP 0220533b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1090 R Zeigler et al
RE-merrillite (P REEs Th) and baddeleyite (Zr Hf U Th)Therefore the variation in the amount of the groundmassldquophaserdquo in the different subsamples controls the ITEconcentrations in the various subsamples
For most of the major elements subsamples of NWA 032have relative standard deviations (RSD) that areinsignificantly different from those of LAP (Table 1) eventhough the average subsample size for NWA 032 (sim14 mgFagan et al 2002) was smaller than for LAP (sim34 mg) TheRSDs of MgO and Cr2O3 for NWA 032 are again highbecause it has a porphyritic texture with large phenocrysts(millimeter scale) of olivine (with chromite inclusions) andmagnesian pyroxene but a fine-grained groundmass of
plagioclase Fe-rich pyroxene ilmenite and glass keeps theRSDs of other major and incompatible trace elements low
Source Crater Pairing of LAP and NWA 032
We find the similarities in chemistry and petrographybetween LAP and NWA 032 when compared to the largeranges observed among Apollo and Luna samples to be sogreat that it is highly unlikely that two meteorites so similarcould derive from different locations Below we summarizethe similarities and differences
The textures of NWA 032 and LAP are markedlydifferent from each other NWA 032 has a porphyritic texture
Fig 5 BSE images from LAP 0220533 a) oxide grains set in and around a large olivine grain individual grains of ilmenite (Ilm) Cr-ulvˆspinel (Chr-Usp) and chromite (Chr) composite chromian ulvˆspinel-chromite (ChrUsp) grains with accompanying pyroxene andplagioclase (grey and black areas) b) A close-up of a zoned spinel grain with a chromite core and a Cr-ulvˆspinel rim c) A large cristobalite(Crist) grain with many inclusions of fayalite pyroxene (Pyx) plagioclase (Plag) troilite (Sulf) phosphate K-rich glass and the ITE-richglass Also present are several areas of fayalite symplectite (Fay Symp) with inclusions of plagioclase silica ilmenite troilite and K-richglass d) A BSE image of a different area of groundmass showing a large grain of fayalite symplectite containing inclusions of plagioclasesilica ilmenite troilite K-rich glass and Fe-rich pyroxene A large ilmenite (Ilm) grain cuts through the symplectite and several large troilitegrains are also present
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
1074 R Zeigler et al
0243614 (sim06 cm2) and LAP 0363218 (sim10 cm2) Forcomparison we present here compositional data for ninesubsamples of basaltic lunar meteorite NWA 032 Wecollected the NWA 032 data under almost identical analyticalconditions to those described below for LAP (see Fagan et al2002 for details) Previously the chemical composition ofNWA 032 has only been reported as mass-weighted averages(Fagan et al 2002)
ANALYTICAL METHODS
We used a variety of analytical techniques tocharacterize the LAP samples We obtained trace-elementcompositions by instrumental neutron activation analysis(INAA) and major-element compositions by a combination ofINAA and electron microprobe analysis (EMPA) on fusedbeads We characterized the textures and mineral assemblageswith a combination of transmitted light and reflected lightoptical microscopy as well as with backscattered electronimaging (BSE) using the electron microprobe A combinationof backscattered electron images and elemental X-ray mapswere used to determine a mode for the thin sections Finallywe characterized the mineral chemistry using EMPA
For INAA we subdivided each of the LAP 02205 chipsinto three sim40 mg subsamples each of the LAP 02224 LAP02226 and LAP 02436 chips into a single sim30 mg subsampleand each of the LAP 03632 chips into two sim35 mgsubsamples We sealed the samples in ultrapure silica tubingfor neutron irradiation The samples and multielementstandards were irradiated in the research reactor of theUniversity of MissourimdashColumbia with a thermal neutronflux of 515 times 1013 cmminus2sminus1 for 24 hr Radioassays were doneusing gamma ray spectrometry at 6 7ndash9 10ndash13 and 28ndash32days following neutron irradiation Several well-characterized rock and synthetic glasses were used asstandards Gamma-ray spectral data were reduced using theTEABAGS program (Lindstrom and Korotev 1982 Korotev1991) INAA-derived compositional data are tabulated inTable 1
We obtained data for mineral and glass compositions byEMPA using a JEOL 733 Superprobe with AdvancedMicrobeam Inc automation Mineral and glass analyses wereconducted using wavelength dispersive spectrometersoperating at 15 kV accelerating voltage and using a 20 nAbeam current for feldspar and glass analyses a 30 nA beamcurrent for pyroxene and olivine analyses and a 40 nA beamcurrent for metal oxide and phosphate analyses A set ofoxide mineral and glass standards were used for calibrationin WDS (wavelength dispersive spectroscopy) analyses Aspot size ranging from 1 to 10 microm was used for all mineralanalyses Count times varied depending on the target phasebut were typically about 10ndash30 sec on peak for majorelements and 30ndash60 sec on peak for minor elements Theconcentrations of Th and the rare earth elements (REEs) inphosphates were calibrated using ThO2 and synthetic REE-
orthophosphate standards (Jarosewich and Boatner 1991Donavan et al 2003) respectively with count times of 90ndash120 sec The detection limits for major and minor elementsare sim002 wt and the detection limits for Th and the REEsranged from 004 to 012 wt Data for mineral and glasscompositions are reported in Tables 2ndash8
For bulk major-element analysis we ground each LAP02xxx INAA subsample in an agate mortar and pestle afterradioassay and fused the resulting powder with amolybdenum strip resistance heater under an argonatmosphere (Jolliff et al 1991) The LAP 03632 INAAsubsamples were still too radioactive to handle so they werenot analyzed at this time We analyzed the resulting fusedbeads (FB) for major elements by EMPA using the previouslydescribed conditions except that the spot size was increasedto 40ndash50 microm and basaltic glass standards were used inaddition to the mineral and oxide standards Molybdenumconcentrations averaged 008 wt in the fused bead analysesand were almost always lt03 wt Concentrations of Na2Odetermined by EMPA were typically 5ndash10 lower(relatively) than INAA-derived concentrations We attributethis discrepancy to systematic volatilization of Na2O duringthe fusing process Concentrations of FeO (ie total Feas FeO) determined by EMPA on fused beads were typically1ndash5 lower (relatively) than FeO concentrations determinedby INAA This is due to the incorporation of a small amountof Fe into the Mo metal during the fusing process The whole-rock major-element concentrations tabulated in Table 1 arereported on a Mo-free basis For FeO Na2O and Cr2O3 theINAA-derived concentrations are reported because they aremore accurate (Na Fe) or precise (Cr) For the other majorelements values are normalized to yield the original EMPAoxides sum
We determined modal mineral proportions by imageanalysis (4ndash9 million pixels per thin section) using acombination of BSE images and elemental X-ray maps forMg Al Si P S K Ca Ti Cr and Fe that covered themajority of each of the LAP 02xxx thin sections The imageswere taken with a JEOL JSM840 scanning electronmicroscope Results of modal analyses are tabulated inTable 9
RESULTS
Petrography
The texture mineral compositions and mineralassemblages observed in the thin sections of the four LAP02xxx stones are strongly alike (Fig 1andashd) The petrographicdescription that follows is that of thin section LAP 0220533and is representative of all four sections To demonstratethe similarity among the different LAP stones we presentmineral composition data for each of the 4 LAP 02xxx stonesWhere one of the thin sections contains features that differfrom those seen in LAP 0220533 this is noted
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1075Ta
ble
1 M
ajor
- and
trac
e-el
emen
t con
cent
ratio
ns o
f LA
P 02
205
and
NW
A 0
32 s
ubsa
mpl
es a
nd w
eigh
ted
aver
ages
Sa
mpl
eLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
P02
205
0220
502
205
0220
502
205
0220
502
224
0222
402
224
0222
602
226
0222
602
436
0243
602
436
0363
2Sp
lit2
0-1
20-
22
0-3
24-
12
4-2
24-
39
-11
9-1
20-
16
-11
0-1
12-
17
-19
-11
2-1
7-1
Maj
or-e
lem
ent c
once
ntra
tions
SiO
245
045
345
245
344
745
245
345
045
745
845
645
745
845
444
9minus
TiO
23
343
333
342
993
283
132
983
332
653
233
193
222
812
742
77minus
Al 2O
39
8410
18
104
89
638
9810
20
104
09
359
769
509
789
1610
67
9
379
37minus
Cr 2
O3
(IN
AA
)0
260
220
260
330
320
330
290
300
360
310
300
310
330
380
420
23Fe
O (I
NA
A)
229
228
219
217
233
216
227
231
215
218
217
219
209
218
228
218
MnO
028
030
029
028
034
032
026
028
028
028
028
029
025
028
027
minusM
gO5
875
465
697
177
116
685
766
567
496
726
457
106
307
937
74minus
CaO
111
112
114
111
105
113
112
109
111
111
114
111
114
110
105
minusN
a 2O
(IN
AA
)0
390
420
410
380
360
390
360
360
370
370
370
370
370
350
350
39K
2O0
080
090
070
060
070
060
100
080
060
060
070
060
080
050
06minus
P 2O
50
110
110
100
090
080
080
120
130
090
090
120
110
130
090
11minus
Tota
ls99
199
499
299
099
099
399
599
399
499
399
399
399
099
499
3minus
Mgprime
3130
3237
3536
3134
3835
3537
3539
38minus
Trac
e-el
emen
t con
cent
ratio
nsSc
590
580
578
595
589
604
602
581
588
600
608
584
617
608
568
592
Cr
1751
1511
1767
2290
2180
2230
1982
2070
2470
2150
2040
2100
2240
2580
2840
1590
Co
346
339
340
378
404
370
385
371
385
355
350
378
343
415
427
315
Sr15
016
019
013
013
011
014
014
013
014
014
010
013
013
013
010
0Zr
200
260
250
210
150
140
130
190
190
180
150
220
190
100
170
200
Ba
166
154
150
124
134
152
153
163
144
144
157
142
139
8612
615
7La
147
153
142
116
153
146
125
145
114
118
127
124
110
106
118
136
Ce
383
396
366
322
370
360
336
388
308
329
345
344
319
273
316
369
Nd
2528
2320
2720
2225
1618
2624
1820
1922
Sm8
608
898
357
048
518
197
488
616
847
247
627
426
806
327
058
13Eu
136
141
136
120
126
129
121
130
112
119
125
122
120
102
114
128
Tb1
892
021
911
631
951
861
732
031
661
681
771
731
671
511
651
85Y
b7
37
47
06
17
06
76
57
36
06
26
66
45
95
36
17
0Lu
099
103
096
083
095
094
091
100
082
087
091
090
084
073
086
100
Hf
627
642
606
510
571
550
567
633
504
525
565
549
501
418
519
597
Ta0
800
800
790
690
670
690
740
800
610
700
730
750
630
570
630
76Th
224
234
220
179
201
193
213
239
180
187
211
204
191
142
200
234
U0
610
520
670
550
530
420
480
640
440
510
540
430
440
370
560
57M
ass (
mg)
353
402
402
345
413
489
279
273
288
283
277
305
273
269
333
324
1076 R Zeigler et al Ta
ble
1 C
ontin
ued
Maj
or- a
nd tr
ace-
elem
ent c
once
ntra
tions
of L
AP
0220
5 an
d N
WA
032
sub
sam
ples
and
wei
ghte
d av
erag
es
Sam
ple
LAP
LAP
LAP
NW
AN
WA
NW
AN
WA
NW
AN
WA
NW
AN
WA
NW
ALA
PN
WA
LAP
NW
A03
632
0363
203
632
032
032
032
032
032
032
032
032
032
032
032
032
Split
7-2
13-
11
3-2
A2
A3
A4
B1
B3
B4
C1
C2
D2
ave
ave
rsde
vrs
dev
Maj
or-e
lem
ent c
once
ntra
tions
SiO
2minus
minusminus
451
442
454
456
434
445
447
445
452
453
447
000
80
015
TiO
2minus
minusminus
285
296
301
333
263
308
302
282
315
311
300
007
90
068
Al 2O
3minus
minusminus
942
902
942
990
867
999
937
858
973
979
932
005
20
054
Cr 2
O3 (
INA
A)
033
031
028
040
037
037
036
042
039
056
036
038
031
040
015
60
154
FeO
(IN
AA
)22
622
322
821
722
622
121
523
721
822
622
021
822
222
20
029
003
1M
nOminus
minusminus
027
028
029
027
030
026
026
029
030
029
028
008
00
060
MgO
minusminus
minus7
978
507
366
3010
26
686
764
985
692
663
797
011
50
170
CaO
minusminus
minus10
710
410
911
59
511
310
49
810
911
09
106
002
50
062
Na 2
O (I
NA
A)
037
038
037
036
034
035
038
033
037
032
034
035
038
035
005
00
052
K2O
minusminus
minus0
080
090
090
110
080
100
100
110
090
070
090
202
012
2P 2
O5
minusminus
minus0
080
080
060
100
070
080
110
110
100
100
090
158
020
8To
tals
minusminus
minus99
098
999
399
399
398
899
198
898
999
28
990
minusminus
Mgprime
minusminus
minus40
4037
3444
3638
4436
347
390
081
008
8
Trac
e-el
emen
t con
cent
ratio
nsSc
585
604
591
608
537
580
579
496
551
507
544
584
592
552
002
10
067
Cr
2280
2100
1930
2760
2500
2500
2430
2870
2660
3800
2490
2600
2096
2760
015
60
154
Co
387
377
370
408
438
396
368
503
399
469
414
385
370
421
007
60
102
Sr14
010
013
012
614
013
016
014
012
619
016
014
013
314
90
162
014
0Zr
140
160
210
160
170
180
180
160
160
160
170
180
183
170
022
40
055
Ba
163
128
163
191
250
229
170
130
166
335
469
266
145
266
013
30
392
La12
711
713
210
511
111
912
110
311
710
511
711
913
111
30
114
006
2C
e33
832
136
228
528
932
332
328
231
627
730
930
534
729
90
090
006
0N
d21
2623
1918
2222
1620
1921
2122
200
151
009
8Sm
758
715
791
637
648
710
705
610
692
618
664
698
774
663
009
40
058
Eu1
201
201
271
061
071
151
201
001
151
021
131
171
241
100
073
006
4Tb
176
165
183
152
152
165
167
144
160
146
159
165
179
157
007
90
054
Yb
65
63
68
57
57
61
62
53
60
54
58
61
659
58
008
40
053
Lu0
910
890
950
810
780
850
850
740
830
750
810
830
920
800
081
005
2H
f5
595
185
854
764
965
295
314
555
134
635
105
325
585
020
099
005
9Ta
076
067
069
056
064
071
068
060
061
060
061
065
071
063
009
70
073
Th1
961
962
171
74 1
91
199
204
167
196
172
187
203
204
189
011
40
074
U0
420
550
590
350
440
440
450
390
400
510
570
490
520
460
158
014
4M
ass (
mg)
341
373
388
90
210
81
107
96
77
182
156
242
641
124
minusminus
Maj
or-e
lem
ent c
once
ntra
tions
in w
t a
nd tr
ace-
elem
ent c
once
ntra
tions
in p
pm M
ajor
ele
men
ts n
ot o
ther
wis
e la
bele
d w
ere
obta
ined
by
EMPA
on
fuse
d be
ads m
ade
from
the
sam
e IN
AA
split
Ave
rage
s(a
ve)
are
wei
ghte
d av
erag
es r
sdev
= re
lativ
e st
anda
rd d
evia
tion
The
rela
tive
unce
rtain
ties
in th
e IN
AA
dat
a ar
e 1
ndash2
for N
a 2O
Sc
Cr
Co
FeO
La
Ce
Sm
Yb
Lu
and
Hf
3ndash4
for E
u T
b a
ndTh
7ndash1
0 fo
r Ta
and
Ba
17
for U
and
25ndash
30
for S
r and
Zr
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1077Ta
ble
2 A
vera
ge a
nd re
pres
enta
tive
oliv
ine
com
posi
tions
in th
e LA
P ba
salti
c m
eteo
rites
LA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
P02
205
0222
602
224
0243
602
205
0222
602
224
0243
602
205
0222
402
436
0220
5co
reco
reco
reco
ret-r
imt-r
imt-r
imt-r
imx-
rimx-
rimx-
rimfa
y s
ymp
N40
2463
2942
1710
54
12
2
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
359
236
01
359
036
28
345
434
24
340
934
21
314
030
43
311
529
72
TiO
20
040
040
040
040
060
060
040
080
110
520
100
34A
l 2O3
003
009
002
003
lt00
2lt0
02
005
lt00
2lt0
02
lt00
2lt0
02
lt00
2C
r 2O
30
240
210
230
220
170
160
110
060
070
060
03lt0
02
FeO
344
432
92
328
233
14
420
640
15
417
545
70
586
362
85
587
966
50
MnO
033
036
035
036
047
041
042
050
063
071
058
065
MgO
282
629
24
301
229
63
224
623
50
225
519
30
881
461
844
177
NiO
lt00
5n
an
an
alt0
05
na
na
na
na
na
na
na
CaO
035
034
036
033
033
036
035
036
045
053
054
055
Na 2
Olt0
02
lt00
2lt0
02
lt00
2lt0
02
lt00
2lt0
02
lt00
20
02lt0
02
lt00
2lt0
02
Tota
l99
65
992
299
85
100
0310
016
989
099
37
100
2210
012
997
199
65
995
5
Cat
ion
ratio
sFa
406
387
380
386
514
490
511
571
787
884
796
950
Fo59
461
362
061
448
751
048
942
921
111
620
44
5
Stoi
chio
met
ry b
ased
on
4 ox
ygen
ato
ms
Si IV
099
90
998
098
90
997
099
50
992
099
01
003
099
50
995
099
40
996
Al V
I0
001
000
30
001
000
10
000
000
00
002
000
00
000
000
00
000
000
0Ti
VI
000
10
001
000
10
001
000
10
001
000
10
002
000
30
013
000
20
009
Cr
000
50
005
000
50
005
000
40
004
000
30
001
000
20
002
000
10
000
Fe+2
080
10
764
075
60
762
101
60
973
101
61
122
155
41
719
156
91
864
Mn+2
000
80
009
000
80
008
001
20
010
001
00
012
001
70
020
001
60
018
Mg
117
11
208
123
61
214
096
21
014
097
40
842
041
60
225
040
10
089
Ca
001
10
010
001
10
010
001
00
011
001
10
011
001
50
018
001
90
020
Na
000
00
000
000
00
000
000
00
000
000
10
000
000
10
000
000
00
000
Tet s
ite0
999
099
80
989
099
70
995
099
20
990
100
30
995
099
50
994
099
6O
ct si
te1
998
199
92
019
200
12
006
201
42
017
199
12
007
199
62
009
199
9N
= n
umbe
r of a
naly
ses i
n th
e av
erag
e t-
rim =
typi
cal r
im x
-rim
= e
xtre
me
rim f
ay s
ymp
= fa
yalit
e sy
mpl
ectit
e n
a =
not
ana
lyze
d
1078 R Zeigler et al Ta
ble
3 A
vera
ge a
nd re
pres
enta
tive
pyro
xene
com
posi
tions
in th
e LA
P ba
salti
c m
eteo
rites
LA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
P02
205
0222
602
224
0243
602
205
0222
602
224
0243
602
205
0243
602
205
pig
cor
epi
g c
ore
pig
cor
epi
g c
ore
aug
cor
eau
g c
ore
aug
cor
eau
g c
ore
hd
hd
pyxf
er
N23
1417
168
2014
111
11
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
516
751
94
520
751
83
495
149
27
494
649
51
456
045
91
439
7Ti
O2
056
051
053
056
135
135
130
134
139
185
112
Al 2O
31
331
201
321
363
173
333
243
281
842
051
73C
r 2O
30
590
540
580
540
971
010
940
98lt0
02
lt00
2lt0
02
FeO
198
419
47
191
619
83
138
613
21
133
213
77
312
130
66
471
8M
nO0
360
350
360
350
250
250
260
270
320
330
59M
gO18
81
192
019
63
185
213
47
138
114
05
138
00
480
330
04C
aO6
396
496
386
8216
81
169
616
74
165
817
88
183
73
53N
a 2O
lt00
20
030
030
020
050
050
060
05lt0
02
lt00
20
02To
tal
995
799
73
100
199
82
994
499
23
993
599
57
987
399
51
981
7
Cat
ion
ratio
sM
gprime62
863
764
662
563
465
165
364
12
61
90
1Fs
317
310
304
316
249
237
237
246
582
580
871
En53
614
614
215
743
132
131
731
340
240
90
1W
o14
754
455
452
632
044
244
644
01
61
112
8
Stoi
chio
met
ry b
ased
on
6 o
xyge
n at
oms
Si IV
194
91
953
194
81
952
188
31
874
187
81
879
191
61
908
193
3A
l IV
005
10
047
005
20
048
011
70
126
012
20
121
008
40
092
006
6Ti
IV0
000
000
00
000
000
00
000
000
00
000
000
00
000
000
00
000
Al V
I0
009
000
60
006
001
20
026
002
30
023
002
60
007
000
80
009
Ti V
I0
016
001
40
015
001
60
038
003
90
037
003
80
044
005
80
054
Cr
001
80
016
001
70
016
002
90
030
002
80
029
000
00
000
000
0Fe
+20
626
061
20
599
062
40
441
042
00
423
043
71
097
106
61
734
Mn+2
001
10
011
001
10
011
000
80
008
000
80
009
001
10
012
002
2M
g1
058
107
61
094
103
90
764
078
30
795
078
10
030
002
10
002
Ca
025
80
261
025
60
275
068
50
691
068
10
674
080
50
818
016
6N
a0
001
000
20
002
000
10
003
000
40
004
000
40
001
000
10
002
Tet s
ite2
000
200
02
000
200
02
000
200
02
000
200
02
000
200
01
999
Oct
site
199
71
999
200
11
995
199
51
999
200
11
997
199
51
983
198
9A
ugite
(aug
) co
res h
ave
an M
gprime gt
60 a
nd W
o gt3
0 w
hile
pig
eoni
te (p
ig)
core
s hav
e M
gprime gt
60 a
nd W
o lt1
8 H
d =
hed
enbe
rgite
pyx
fer
= py
roxf
erro
ite
Mgprime
= M
g(M
g +
Fe)
100
N =
num
ber o
f ana
lyse
s
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1079
All of the LAP stones have relatively coarse-grained (upto approximately 15 mm) subophitic texture They consistpredominantly of pyroxene and plagioclase with minoramounts of olivine ilmenite and a groundmass dominated byfayalite and cristobalite They contain trace amounts ofchromite chromian ulvˆspinel ulvˆspinel troilite Fe-metalbarian K-feldspar fluor-apatite RE-merrillite tranquillityite(Fe8(YZr)2Ti3Si3O24) and baddeleyite (ZrO2) The modalmineral proportions differ slightly from section to section(Table 9) A few veins and pockets of basaltic glass ofpseudo-whole rock composition (likely shock melted) alsooccur in thin sections LAP 0220533 and LAP 0222424 Theorder in which minerals are inferred to have crystallized ischromite olivine pyroxene plagioclase and groundmass
Olivine grains vary in size from 003 to sim1 mm with01 to 03 mm being typical The modal abundance of olivineranges from 23 to 36 The grains are usually anhedral(rarely subhedral Fig 2a) typically with round or irregularmorphology and uneven contact with the surroundingpyroxene (Fig 2b) Some olivine grains have inclusions ofchromite or Cr-ulvˆspinel grains or both and a few haveldquomeltrdquo inclusions that have two phases in them mafic glasswith a pyroxene-like composition (sim10 wt Al2O3 Table 6)and K-rich high-silica glass similar to the glass seen in thefayalite symplectite grains in the groundmass (sim3 wt K2O68 wt SiO2) Most of the larger olivine grains are zonedwith cores of Fo55ndash65 and rims typically in the Fo38ndash45 range(Fig 3a Table 2) though in a few instances zoning to rims ofFosim20 is observed (Fig 3b) Most of the smaller olivine grainsare not zoned (or not strongly zoned) and they typically havecompositions in the Fo52ndash57 range with the smallest grainshaving the most magnesian compositions The apparentreaction texture between olivine and pyroxene and therelatively magnesian rims on compositions of the smallestolivine grains (likely the remnant cores of grains that havebeen almost completely resorbed) are strong indications thatolivine was being resorbed when the rock solidified
Chromite and Cr-ulvˆspinel grains almost always occuras inclusions within or closely associated with olivine grainsThey also have relatively restricted compositional ranges(Fig 4 Table 4) and they occur individually and as compositegrains with cores of chromite (Chr62ndash68Usp13ndash18Spn16ndash25) andrims of Cr ulvˆspinel (Chr6ndash19Usp71ndash91Spn3ndash11) (Figs 5aand 5b) We found few spinel compositions intermediate tothese end members The total modal abundance of spinel(including ulvˆspinel in the groundmass) is small rangingfrom 03 to 04 Where these two phases are intergrown theboundary between them is sharp with differences in Cr2O3concentration exceeding 20 wt within a few micrometers ofthe boundary A few of the chromite grains have inclusionsof pyroxene with a range of compositions (Mgprime of 47ndash59Wo16ndash31 and TiO2 concentrations from 11ndash24 wt)
Pyroxene grains in LAP are anhedral display undulatoryto mosaic extinction and range in size up to sim1 mm (Fig 2c)
In many cases pyroxene grains partially enclose plagioclasegrains in a subophitic texture The modal abundance ofpyroxene ranges from 47 to 52 The pyroxene grains havemagnesian cores of pigeonite and subcalcic augite (Mgprime fromsim50 to 68) with a wide range of CaO concentrations (Wo11 toWo36 Table 3 Fig 6) although there appears to be a bimodaldistribution of Wo contents with a minimum near Wo20(Fig 6 insets) In some cases pyroxene core compositionsgrade continuously to nearly end member hedenbergite(Fs58Wo40) and pyroxferroite (Fs86Wo13) In a few rare casescontacts between magnesian and ferroan pyroxenes are sharpand linear Compositions of pyroxene grains in contact withpartially resorbed olivine grains vary considerably incomposition The most common composition issubcalcic augite (Wo gt 20) with FeO concentrations in therange Fs24ndash49
The TiAl and TiCr ratios in the LAP pyroxenes arestrongly correlated with Mgprime as expected according toelement compatibility (eg Bence and Papike 1972) Theatomic TiCr ratio increases with decreasing Mgprime in LAPpyroxenes (Fig 7a) This reflects the compatible behavior ofCr and the incompatible behavior of Ti in early crystallizingphases of low-Ti lunar basaltic magmas The most magnesianpyroxenes have atomic TiAl ratios very close to 14indicating that aluminum was introduced through boththe Tschermak (AlAlMgminus1Siminus1) and coupled titanium(TiAl2Mgminus1Siminus2) exchange reactions in approximately equalproportions (Thompson 1982) As pyroxene becomesprogressively more ferroan the TiAl cation ratio approaches12 suggesting a gradual increase in the proportion of Alincorporated due to coupled Ti substitution (Fig 7b) Theleast magnesian pyroxenes (Mgprime lt40) have TiAl ratiosapproaching 34 An increase in TiAl ratios in pyroxene from14 to 12 with decreasing Mgprime in lunar basalts has previouslybeen interpreted as a result of pyroxene crystallization bothprior to the onset of plagioclase crystallization (ratiosaround 14) and during plagioclase crystallization (14ndash12Bence and Papike 1972) Bence and Papike (1972) attributedthe high relative concentrations of Ti in the late-stage Fe-richlunar pyroxenes to Ti3+
Plagioclase forms elongated subhedral to anhedralgrains up to 175 mm long The modal abundance ofplagioclase ranges from 32 to 35 Pyroxene inclusions ofa variety of sizes with compositions spanning nearly theentire compositional spectrum observed occur withinplagioclase Most plagioclase grains are highly fracturedalthough some or portions of some are smooth in polishedsections as seen in the BSE images (Fig 2d) These smoothareas consist partially or entirely of maskelynite as indicatedby their isotropic (or nearly isotropic) character in cross-polarized light Plagioclase grains are complexly zoned Theirtypical core composition is An886Ab11Or04 with sim1 wtFeO + MgO and an Mgprime of 34 (Fig 8 Table 5) Their rims areas wide as sim40 microm and gradually increase in K (up to simOr5)
1080 R Zeigler et al
and FeO (up to sim3 wt) while decreasing in MgO(to lt002 wt Fig 9) The Na2O concentrations firstincrease up to simAb14 then decrease sharply to less thanAb10 (which is lower than in the cores) The extreme rimcomposition of the large plagioclase grains is similar to that ofthe plagioclase found as inclusions in groundmass fayaliteand cristobalite grains (next paragraph Table 5) There is noapparent overall compositional difference between the coresof the maskelynite and the plagioclase grains
Fayalite cristobalite and ilmenite are the dominantminerals in the groundmass typically occurring togetheralthough each can be found independently All of the phaseshave relatively minor modal abundances fayalite (29ndash48)cristobalite (18ndash21) and ilmenite (35ndash40) Silicadisplaying the ldquocracklerdquo pattern distinctive to cristobaliteoccurs as anhedral grains up to 05 mm in size Thecristobalite grains contain minor Al2O3 TiO2 FeO and CaO(Σ sim13 wt Table 6) Inclusions of late-crystallizing phasessuch as K-rich plagioclase K-rich glass K-feldspar fayaliteFe-rich pyroxene phosphate and mafic glass withhigh concentrations of incompatible elements are common(Fig 5c) Fayalite grains (Fo45 sim05 wt CaO) range in size
up to 075 mm and usually form a symplectite texture withinclusions of K-rich glass silica K-rich plagioclase andilmenite (Fig 5d) Fayalite with no (or few) inclusions occursonly rarely Ilmenite is the dominant oxide in the groundmassforming elongate laths up to 1 mm in length Typically theilmenite is poor in Mg (sim02 wt average) although a singlegrain of more magnesian ilmenite associated with a largeolivine grain was observed (Fig 2b) Less common aresmaller subhedral ulvˆspinel grains (lt005 mm) thathave compositions approaching end member ulvˆspinel(Chr0ndash4Usp93ndash98Sp2ndash3) A few composite grains of ilmeniteand ulvˆspinel were observed
Also found in the groundmass are a variety of traceminerals including both fluorapatite and RE-merrillite(Table 7) Phosphate grains most commonly occur betweenplagioclase and ferropyroxene sometimes with associatedcristobalite troilite or both Barian K-feldspar (sim5 wt BaO)also occurs in the groundmass usually in the same areas asthe phosphate minerals (Table 5) Only a few K-feldspargrains (the largest) have stoichiometry that unambiguouslyidentifies them as K-feldspar while many K-rich grainshave excess Si suggesting that they may be intergrowths of
Table 4 Average oxide compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02205 02226 02224 02436 02205 02226 02224 02436 02205 02226 02224Al Al Al Al Cr-rich Cr-rich Cr-rich Cr-rich CrAl CrAl CrAlchr chr chr chr usp usp usp usp usp usp usp
N 23 11 13 5 22 1600 7 13 9 22 10
Major elements in wt by EMPAFeO 3444 3503 3532 3433 5705 5832 5846 5868 6191 6198 6180TiO2 546 532 540 517 2833 2871 2892 2909 3254 3151 3161Cr2O3 4384 4357 4331 4391 928 840 851 776 234 310 338Al2O3 1142 1178 1140 1217 287 261 261 276 191 204 203MgO 283 242 218 292 093 061 069 065 021 028 031MnO 027 024 025 027 035 032 034 033 036 032 034V2O3 073 074 076 075 036 031 033 033 022 025 026SiO2 007 009 008 009 lt002 007 008 018 lt002 008 007CaO 004 004 003 lt002 010 005 006 011 008 007 005ZnO 003 na na na 004 na na na 003 na naTotals 991 992 987 996 993 994 1000 999 996 996 999
Stoichiometry based on 4 (spinel) and 3 (ilmenite) oxygen atomsSi IV 0003 0003 0003 0003 0000 0003 0003 0006 0000 0003 0003Al VI 0469 0484 0472 0496 0125 0114 0113 0119 0083 0089 0088Ti 0143 0139 0143 0134 0784 0798 0798 0803 0907 0880 0880V 0020 0021 0021 0021 0011 0009 0010 0010 0007 0007 0008Cr 1208 1201 1204 1199 0270 0245 0247 0225 0068 0091 0099Fe2+ 1004 1021 1039 0992 1756 1802 1794 1801 1920 1925 1913Mn2+ 0008 0007 0007 0008 0011 0010 0011 0010 0011 0010 0011Mg 0147 0126 0114 0151 0051 0034 0038 0035 0012 0016 0017Zn 0001 minus minus minus 0001 minus minus minus 0001 minus minusCa 0002 0002 0001 0000 0004 0002 0002 0004 0003 0003 0002Sum 2+ 1162 1156 1161 1151 1823 1847 1844 1851 1947 1953 1942Sum 3 4+ 1844 1849 1844 1854 1190 1168 1170 1163 1066 1071 1078Total 3003 3001 3002 3001 3012 3013 3012 3007 3013 3020 3017
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1081
K-feldspar and silica (granophyric texture) at a scale smallenough to be beyond the resolution of the electron microprobe(less than sim01 microm)
Two glass types of distinct composition presumably late-stage residual liquids occur in the groundmass The first is aKSi-rich glass (78 wt SiO2 sim56 wt K2O) that makes upa considerable percentage of the inclusions in the cristobaliteand particularly the fayalite grains The second type ofevolved glass occurs as very small (lt5 microm) roundedinclusions in cristobalite grains This glass has a silica-poorFe-rich bulk composition (sim36 wt SiO2 sim39 wt FeOTable 6) but it is also considerably enriched in manyincompatible elements 23 wt P2O5 12 wt SO3 02 wtY2O3) Commonly we observed minute grains of fayalitetroilite or phosphate associated with this glass These twolate-stage glasses could represent conjugate liquids producedby late-stage immiscibility of an evolved residual meltSimilar glasses were observed in some plutonic rocks fromthe Apollo 14 site (Jolliff et al 1991)
Troilite blebs (with nearly ideal stoichiometry Table 8)are scattered throughout the groundmass along with trace Fe-metal grains which are usually intergrown with troilite orovergrown on chromite grains These grains typicallycontained 66 wt Ni and 14 wt Co though one grain had338 wt Ni and 60 wt Co (Table 8) A few grains ofbaddelyite (ZrO2) and tranquillityite (Zr-Fe-Ti silicate) wereidentified by energy-dispersive spectroscopy (EDS) in thegroundmass
A variety of shock effects occur in the minerals of thesethin sections (eg plagioclase converted to maskelynitemosaicism in the pyroxene) The level of shock was such thatlocalized partial melting occurred in some areas of themeteorite The areas of shock melt have severalmorphologies small melt pockets (LAP 02205 Fig 10a)veins of melt (LAP 0222424 Fig 10b) and in some casesareas that were only partially melted (LAP 0222424Fig 10c) with discernable mineral grains still present(typically maskelynite) Although veins of shock melt are rare
Table 4 Continued Average oxide compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02436 02205 02226 02224 02436 02205 02226 02224 02436 02205CrAl end end end end Mgusp usp usp usp usp ilm ilm ilm ilm ilm
N 11 11 2 3 3 24 16 20 18 2
Major elements in wt by EMPAFeO 6202 6375 6445 6355 6465 4657 4647 4634 4624 4463TiO2 3353 3267 3226 3396 3231 5198 5226 5233 5264 5296Cr2O3 209 026 023 011 037 010 012 015 016 038Al2O3 202 179 206 216 227 008 011 013 010 006MgO 022 005 008 007 003 014 010 016 019 150MnO 034 031 027 029 027 038 033 037 027 035V2O3 023 018 015 019 016 031 029 029 028 035SiO2 015 lt002 011 010 007 003 003 024 004 lt002CaO 007 010 007 008 010 013 006 010 009 008ZnO na 008 na na na 003 na na na lt002Totals 1007 992 997 1005 1002 997 998 1001 1000 1003
Stoichiometry based on 4 (spinel) and 3 (ilmenite) oxygen atomsSi IV 0005 0001 0004 0004 0003 0001 0001 0006 0001 0000Al VI 0087 0079 0091 0093 0099 0002 0003 0004 0003 0002Ti 0920 0921 0906 0937 0901 0990 0993 0989 0996 0991V 0007 0005 0004 0006 0005 0006 0006 0006 0006 0007Cr 0060 0008 0007 0003 0011 0002 0002 0003 0003 0007Fe2+ 1893 1999 2012 1950 2005 0986 0982 0974 0973 0928Mn2+ 0010 0010 0009 0009 0009 0008 0007 0008 0006 0007Mg 0012 0003 0004 0004 0002 0005 0004 0006 0007 0056Zn minus 0002 minus minus minus 0001 minus minus minus 0000Ca 0003 0004 0003 0003 0004 0004 0002 0003 0002 0002Sum 2+ 1918 2018 2028 1966 2019 1004 0995 0991 0988 0994Sum 3 4+ 1080 1014 1012 1043 1019 1001 1005 1008 1009 1007Total 2992 3032 3035 3005 3036 2004 2000 1992 1996 2001The spinel catagories where chosen based primarily on Cr2O3 content with Al chromite (chr) having gt40 wt Cr2O3 Cr-rich ulvˆspinel (usp) having 15ndash
5 wt Cr2O3 CrAl ulvˆspinel having 5ndash05 wt Cr2O3 and endmember ulvospinel having lt05 wt Cr2O3 Also seen were TiAl chromite (30ndash40 wtCr2O3) and high-Cr ulvˆspinel (30ndash15 wt Cr2O3) which are likely the result of an anlyses overlapping simultaneously on both an Al chromite and Cr-rich ulvˆspinel grain Similarly compositions intermediate to ilmenite and end ulvˆspinel were seen These compositions are not listed in this table but areshown in Fig 4 N = number of analyses in the average na = not analyzed
1082 R Zeigler et al
in our thin sections such veins were reported as pervasive inthe original macroscopic description of all five LAP stones(McBride et al 2003 2004a 2004b)
The various shock-induced effects observed in LAP canbe used to quantify and constrain the level of shock that LAPexperienced The presence of both plagioclase andmaskelynite in these samples suggests that the lower end ofthe range listed for conversion of plagioclase to maskelynite(30ndash45 GPa Stˆffler and Hornemann 1972 Ostertag 1983)is appropriate The mosaicism seen in the pyroxene istypically associated with shock values in the 30ndash75 GParange (Kieffer et al 1976 Schaal et al 1979) The presenceof shock-melt veins that have melted both pyroxene andplagioclase (based on the melt composition Table 6)indicates LAP should have been subjected to shock levels ofgt75ndash80 GPa (Kieffer et al 1976 Schaal et al 1979) Thedifferent shock effects observed reflect a range fromlt30 GPa (areas were plagioclase is preserved) to gt75 GPa(areas where shock melting occurred) over distances of onlya few millimeters
Bulk Composition and Comparison to Other LunarBasalts
LAP is a moderately aluminous (sim10 wt Al2O3) low-Ti(31 wt TiO2) mare basalt that falls near the Fe-rich(222 wt FeO) end of the range of FeO concentrationsobserved among lunar basalts It is more ferroan (Mgprime = 347)than any basalt in the Apollo or Luna collection (Fig 11a)Among lunar basalts only meteorites Asuka-881757 andYamato-793169 have comparably low Mgprime values (Koeberlet al 1993 Warren and Kallemeyn 1993 Thalmann et al1996 Korotev et al 2003a) LAP is enriched in Na2O(038 wt) relative to other ferroan (eg Asuka-881757 andYamato-793169) and Fe-rich basalts except for NWA 032(Fig 11b)
Regarding trace elements LAP is enriched in Cocompared to most lunar mare basalts with comparable Scconcentrations (Table 1 Fig 12a) Among Apollo and Lunabasalts only the Apollo 12 ilmenite basalts (Rhodes et al1977 Neal et al 1994) are comparable Incompatible trace-
Table 5 Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02205 02226 02224 02436 02205 02226 02224 02436 02205 02226plag plag plag plag mask mask mask mask plag plagcore core core core core core core core Na rim Na rim
N 123 86 48 88 29 49 33 32 12 3
Major elements in wt by EMPASiO2 4715 4657 4689 4639 4753 4741 4663 4673 4949 4960TiO2 010 007 007 006 013 008 006 006 027 019Al2O3 3337 3367 3296 3363 3367 3291 3376 3415 3170 3103Cr2O3 003 lt002 lt002 002 007 002 lt002 002 004 003FeO 068 067 073 058 060 111 066 060 134 136MgO 023 022 017 024 027 029 028 029 008 012CaO 1730 1746 1709 1763 1747 1726 1730 1740 1628 1597BaO na na na na na na na na na naNa2O 120 123 136 121 119 123 131 128 148 153K2O 006 007 010 006 005 009 006 005 020 019Total 1000 1000 994 998 1008 1004 1001 1006 1006 1000
Cation ratiosAn 885 883 869 887 888 881 877 880 848 842Or 04 04 06 04 03 05 03 03 12 12Ab 111 112 125 110 109 113 120 117 140 146Cn 00 00 00 00 00 00 00 00 00 00
Stoichiometry based on 8 oxygen atomsSi IV 2168 2147 2173 2143 2168 2179 2147 2140 2259 2279Al IV 1809 1830 1801 1831 1810 1782 1832 1843 1705 1681Fe+2 0026 0026 0028 0023 0023 0043 0025 0023 0051 0052Mg 0016 0015 0011 0017 0019 0020 0019 0020 0005 0008Ca 0853 0863 0849 0872 0854 0850 0853 0854 0796 0786Ba minus minus minus minus minus minus minus minus minus minusNa 0107 0110 0122 0108 0105 0109 0117 0114 0131 0136K 0004 0004 0006 0004 0003 0005 0003 0003 0011 0011Tet site 3977 3977 3974 3974 3978 3961 3979 3984 3964 3960Oct site 1005 1018 1022 1023 1003 1027 1022 1013 0995 0994
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1083
element concentrations are considerably greater in LAP thanin most of other low-Ti basalts (Fig 12bndashc) including theApollo 12 ilmenite basalts (Haskin et al 1971 Neal et al1994) The exceptions are NWA 032 the high-Al basalts ofLuna 16 (Philpotts et al 1972 Helmke and Haskin 1972 Maet al 1979) and some Apollo 14 high-Al basalts (Dickinsonet al 1985 Shervais et al 1985 Neal et al 1989a 1989b)
Relative concentrations of REEs in the LAP basalt arealso dissimilar to those of most other lunar basalts (Fig 13) inthat LAP is enriched in light REEs The exceptions are NWA032 which has a pattern nearly parallel to LAP and Apollo 14group 3 basalts (Dickinson et al 1985) which have a patternthat is similar although somewhat less steep in the heavyREEs Ratios of Th to REE in LAP are higher than those of allother lunar basalts except NWA 032 (Fig 14) and thedisparity in ThREE ratio between LAP and other lunarbasalts (except NWA 032) increases from the light to heavyREEs The Apollo 14 high-K basalts have similar ThREEratios for the middle REE Sm-Tb however (Neal et al 1989a
1989b) Overall in terms of its trace-element concentrationsLAP 02205 is most similar to NWA 032 The maindifferences are that NWA 032 is richer in elements associatedwith olivine (Mg Cr Co) and has concentrations ofincompatible elements that are 78ndash91 as great as those inLAP 02205
DISCUSSION
Evidence Supporting the Lunar Origin and Pairing of theLAP Stones
As stated in the introduction the meteorites LAP 0220502224 02226 02436 and 03632 were identified as lunarbasalts that were almost certainly paired (McBride et al 20032004a 2004b) A brief summary follows of the attributesfound in our more detailed petrographic examination thatsupport this initial classification and pairing interpretation
Results of oxygen isotope analyses (δ18O = +56 and
Table 5 Continued Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02224 02436 02205 02205 02226 02224 02436 02205 02205 02205plag plag plag plag plag plag plag barian KBa KBaNa rim Na rim matrix K rim K rim K rim K rim K-spar glass glass
N 24 5 13 10 1 5 1 10 10 23
Major elements in wt by EMPASiO2 4901 4879 5122 5152 4888 4935 5017 6026 5935 6356TiO2 008 008 016 017 lt002 008 014 na na naAl2O3 3163 3120 2960 2993 3213 3004 3002 2019 2063 2043Cr2O3 002 002 006 005 lt002 003 lt002 na na naFeO 117 130 267 192 147 195 173 065 074 116MgO 006 009 003 002 lt002 lt002 002 lt002 lt002 010CaO 1620 1622 1520 1549 1618 1602 1560 063 066 207BaO na na na na na na na 501 407 372Na2O 157 155 105 105 132 126 150 031 029 033K2O 023 021 090 067 067 056 086 1354 1162 586Total 1000 995 1007 1006 1007 993 1000 1008 1006 1007
Cation ratiosAn 839 842 846 852 835 845 807 33 minus minusOr 14 13 61 44 41 35 53 842 minus minusAb 147 145 105 104 124 120 140 30 minus minusCn 00 00 00 00 00 00 00 96 minus minus
Stoichiometry based on 8 oxygen atomsSi IV 2253 2257 2342 2344 2237 2293 2312 2863 2864 2951Al IV 1714 1701 1596 1609 1732 1645 1631 1131 1173 1124Fe+2 0045 0050 0102 0073 0056 0076 0067 0026 0030 0045Mg 0004 0006 0002 0001 0000 0001 0001 0001 0001 0007Ca 0798 0804 0745 0757 0793 0798 0770 0032 0034 0100Ba minus minus minus minus minus minus minus 0093 0077 0070Na 0140 0139 0093 0093 0117 0113 0134 0029 0027 0029K 0013 0013 0052 0039 0039 0033 0050 0820 0715 0353Tet site 3967 3957 3938 3954 3969 3938 3943 3994 4037 4075Oct site 0013 1011 0995 0963 1007 1020 1022 1002 0884 0604Plag = plagioclase mask = maskelynite N = number of analyses in the average na = not analyzed
1084 R Zeigler et al Ta
ble
6 A
vera
ge a
nd re
pres
enta
tive
cris
toba
lite
and
glas
s co
mpo
sitio
n in
the
LAP
basa
ltic
met
eorit
es
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
0220
502
226
0222
402
436
0220
502
205
0220
502
205
0220
502
224
0222
4cr
isto
balit
ecr
isto
balit
ecr
isto
balit
ecr
isto
balit
eSi
-ric
hpy
x-lik
eK
gla
ssIT
E-ric
hsh
ock
shoc
ksh
ock
MI g
lass
MI g
lass
in s
ympl
m
afic
gla
ssgl
ass
area
glas
s ar
eagl
ass
vein
N6
25
44
12
51
6515
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
979
598
17
984
798
45
672
542
76
783
236
67
463
486
441
TiO
20
270
270
230
230
664
810
374
032
341
623
13A
l 2O3
073
060
064
078
187
99
4210
13
544
139
86
123
Cr 2
O3
002
lt00
2lt0
02
002
lt00
20
13lt0
02
lt00
20
080
380
28Fe
O0
210
400
190
171
8615
91
183
392
719
618
520
5M
nOn
an
an
an
an
a0
22n
a0
420
220
290
25M
gO0
02lt0
02
lt00
2lt0
02
033
817
lt00
20
213
459
857
17C
aO0
190
200
200
236
8919
16
098
976
127
118
114
BaO
na
na
na
na
117
na
na
na
na
na
na
Na 2
O0
130
100
090
120
620
110
190
060
510
360
49K
2O0
030
050
07lt0
02
167
na
566
030
005
na
na
P 2O
5n
an
an
an
an
an
an
a2
32n
an
an
aF
na
na
na
na
na
na
na
008
na
na
na
Y2O
3n
an
an
an
an
an
an
a0
19n
an
an
aC
e 2O
3n
an
an
an
an
an
an
a0
12n
an
an
aSO
3n
an
an
an
an
an
an
a1
23n
an
an
aTo
tal
995
599
80
999
010
00
992
410
070
974
910
02
991
100
099
6Sy
mpl
= sy
mpl
ectit
e M
I = m
elt i
nclu
sion
N =
num
ber o
f ana
lyse
s in
the
aver
age
na
= n
ot a
naly
zed
The
shoc
ked
glas
s in
LAP
0222
4 is
the
parti
ally
mel
ted
area
(see
Fig
14)
and
onl
y th
e an
ayls
es o
fth
e gl
ass i
tsel
f wer
e in
clud
ed in
the
aver
age
not t
he m
iner
als t
hat w
ere
anal
yzed
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1085
Table 7 Representative phosphate compositions in LAP 0220533LAP LAP LAP LAP LAP LAP LAP LAP02205 02205 02205 02205 02205 02205 02205 02205RE- RE- RE- RE- RE- fluorapatite fluorapatite fluorapatitemerrillite merrillite merrillite merrillite merrillite
Major elements in wt by EMPASiO2 050 044 062 037 321 228 449 137Al2O3 022 lt005 009 lt005 lt005 007 014 lt005FeO 637 774 568 576 250 169 439 202MgO 020 037 025 028 lt005 lt005 lt005 lt005CaO 4326 4035 4233 4245 4983 5241 5003 5351Na2O 000 001 010 014 000 000 001 000P2O5 3885 4171 4382 4360 3540 3949 3771 4077Cl lt005 lt005 lt005 lt005 lt005 006 027 031F 047 044 050 048 168 245 130 186Y2O3 298 293 226 221 172 103 078 053La2O3 093 107 065 064 092 024 014 012Ce2O3 253 259 189 185 253 072 069 053Nd2O3 161 177 108 118 166 057 059 031Sm2O3 043 043 029 028 048 022 015 009Gd2O3 087 090 058 058 079 023 018 008Yb2O3 016 032 009 lt005 010 005 lt005 lt005ThO2 007 009 008 lt005 021 lt005 lt005 lt005minusO = (FCl) 021 020 022 021 072 105 061 085Sums 9930 1010 1001 9968 1004 1005 1003 1006
Table 8 Average sulfide and metal compositions in LAP 0220533Ave Fe metal High-Ni metal Troilite
N 5 1 8
Elemental percentage by EMPAFe 9209 5880 6280Ni 664 3377 lt002Co 141 595 lt002Ti 023 009 006Cr 043 017 lt002Mn lt002 004 lt002S lt002 lt002 3620Totals 1008 988 994Ideal troilite = 365 wt S 635 wt Fe N = number of analyses
Table 9 Modal mineralogy of the different LAP stonesLAP 0220533 LAP 0222616 LAP 0222424 LAP 0243614
Pyroxene 515 505 469 466Plagioclase 319 321 323 346Ilmenite 348 391 386 399Fay sympl 309 290 358 483Olivine 233 271 363 320Cristobalite 214 209 178 200Spinel (all) 034 045 040 039Troilite 025 024 024 022Fractures 49 49 53 421Shock glass 01 02 22 00N 633 times 106 905 times 106 470 times 106 396 times 106
All modal values are listed as percentages N = number of pixels
1086 R Zeigler et al
Fig 1 Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) and fayalite(more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phases arepyroxene and olivine a) LAP 0222616 b) LAP 0243614 c) LAP 0222424 d) LAP 0220533
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1087
δ17O = +27) performed by Mayeda and Clayton (reported inMcBride et al 2003) constrain the origin of LAP 02205 tothe Earth the Moon or an enstatite meteorite parent bodyLAP is clearly a meteorite all four of the stones have fusioncrusts (ruling out a terrestrial origin) The extremely ferroannature of LAP rules out the enstatite parent body as theprovenance FeOMnO ratios of mafic silicates arediagnostic of origins from different planetary bodies in thesolar system (Dymek et al 1976 Papike 1998) Ratios ofFeOMnO in LAP pyroxenes (average sim60) and olivines(average sim95) are consistent only with lunar origin (Fig 15)Furthermore the presence of Fe(Ni) metal and troilite thecompletely anhydrous nature of the sample the apparentlack of Fe3+ in all phases the calcic nature of theplagioclase and the deep negative Eu anomaly are allcommon in lunar basalts
With regard to texture mineral assemblage and mineralchemistry the four LAP 02xxx stones appear to beindistinguishable from each other Although we did not studythe mineral chemistry of the LAP 03632 in depth the textureand mineral assemblage are identical to the LAP 02xxxstones Furthermore the collection locations of the five stonesform a linear array sim3 km in length that is perpendicular to theflow of the ice sheet (John Schutt personal communication)Thus in the absence of cosmic-ray exposure data to thecontrary we conclude that the four LAP 02xxx stones studiedare paired
Compositional Variability among Small Subsamples ofLAP 02205 and NWA 032
Samples of lunar meteorites available for study at most afew hundred milligrams are very small by the standards ofterrestrial geology and geochemistry Nevertheless we havetaken our samples and subdivided them into numerous evensmaller (10ndash50 mg) subsamples for bulk compositionalanalysis (Korotev et al 1983 1996 2003a 2003b Jolliffet al 1991 1998 Fagan et al 2002) This procedure providesan estimate of the whole-rock composition through a mass-weighted mean that is equivalent to a single analysis of theentire mass of the allocated sample The variation amongsmall subsamples however provides additional informationabout compositional variations associated with mineralassemblage and proportions about petrogenesis and aboutpossible relationships to other meteorites (eg Korotev et al2003a 2003b) and how well the ldquowhole-rockrdquo compositionis likely to represent that of the source region of the meteorite(Korotev et al 2000a) In the following discussion weevaluate the causes of differences in composition amongsmall subsamples of LAP and NWA 032
The range of concentrations among the 19 subsamples ofLAP (27ndash40 mg) is relatively small for the most preciselydetermined major elements (SiO2 TiO2 Al2O3 FeO CaONa2O) and most precisely determined trace elements that arecompatible with the major mineral phases (Co Sc Eu) The
Fig 1 Continued Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) andfayalite (more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phasesare pyroxene and olivine d) LAP 0220533
1088 R Zeigler et al
relative sample standard deviations (s ) range from 08 to76 (with only Co and Eu gt 5 Table 1) The exceptionsare MgO and Cr2O3 for which the relative standarddeviations are distinctly greater 12 and 16 respectivelyFor incompatible elements that we determined precisely(lt9 analytical uncertainty La Ce Sm Tb Yb Lu Hf Taand Th) relative standard deviations range from 7 to 11These variations are caused by a combination ofunrepresentative sampling of the major mineral phasesowing to the coarse grain size (up to sim1 mm3) relative to theINAA subsample size (about 12 mm3 assuming that thedensity of LAP is sim35 gmm3) and to the heterogeneousdistribution of some relatively minor phases with high
concentrations of a given element This problem is not new asmany investigators have previously wrestled with theproblem of studying relatively coarse-grained lunar basaltswith small allocated subsample sizes characteristic of rareextraterrestrial samples (Korotev and Haskin 1975 Haskinet al 1977 Lindstrom and Haskin 1978 Ryder and Schuraytz2001) Ryder and Schuraytz (2001) showed that sim5 g ofmaterial are needed to achieve a representative sample ofApollo 15 olivine-normative basalts which have grain sizeson the order of a millimeter or greater
Among the LAP subsamples Cr2O3 and MgOconcentrations correlate positively (R2 = 081) as a result ofthe association of chromite and Cr-ulvˆspinel with olivine
Fig 2 BSE images from LAP 0220533 a) a large round olivine (oli) grain and a smaller subhedral olivine grain (left center of the image)both surrounded by zoned pyroxene (pyx) and plagioclase (plag) with melt inclusions (MI) and inclusions of chromite (chr) A smallulvˆspinel (Usp) grain occurs in the upper left b) A large irregular olivine grain and a smaller mostly resorbed olivine grain The larger graincontains both melt inclusions (MI) and chromite grains The associated ilmenite (Ilm) grain is the most magnesian ilmenite grain observed Acomposite grain of metal and troilite (MetSulf) is also present c) A BSE image showing the zoning in multiple large pyroxene grainsintergrown with plagioclase and maskelynite (mask) grains One small cristobalite (crist) grain is also present d) A BSE image showingseveral large plagioclase grains some of which contain both fractured areas (plagioclase) and smooth areas (maskelynite) Also present areseveral areas of groundmass including a fayalite symplectite and a cristobalite grain cut by an ilmenite lath
x
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1089
The large variations seen in MgO Cr2O3 and to a lesserextent Co concentrations occur because of the large relativevariation in the fraction of modal olivine among thesubsamples Normatively the compositional rangecorresponds to minus03ndash25 olivine (one subsample has 03normative quartz) and 032ndash049 chromite The relativelysmall variations seen among concentrations of the other majorelements as well as Sc and Eu are controlled byunrepresentative sampling of the major mineral phasespyroxene (Sc Ca Fe Si) and plagioclase (Al Na Ca Si Eu)and the minor but widely distributed mineral ilmenite (Ti Fe)Trace amounts of a few minerals that are found only ingroundmass have high concentrations of incompatible traceelements relative to the concentration of those elements inthe bulk meteorite These minerals include K-feldspar (Ba)
Fig 3 a) CaO versus Mgprime (molar Mg[Mg + Fe]100) in the olivinesof the different LAP stones The compositions range from cores ofFo55ndash67 trending towards rims typically in the Fo40 range withextreme zonation to rims of Fo15ndash20 in a few cases Where analyzedthe composition of groundmass fayalite are also shown b) Anelectron microprobe traverse across a small strongly zoned olivinegrain in LAP 0220533 The grain shows zoning from a core of simFo58to a rim composition of simFo18 over sim100 microm The break in the zoning(black arrow) is centered on a fracture in the olivine grain
Fig 4 Compositions of LAP oxides plotted on the (FeMgMn)O-(CrAl)2O3-TiO2 ternary (after El Goresy et al 1971) Compositionsof endmember ilmenite (FeTiO3) ulvˆspinel (Fe2TiO4) andchromite (FeCr2O4) are labeled For a description of theclassification scheme see the footnote of Table 3 a) LAP 0220533b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1090 R Zeigler et al
RE-merrillite (P REEs Th) and baddeleyite (Zr Hf U Th)Therefore the variation in the amount of the groundmassldquophaserdquo in the different subsamples controls the ITEconcentrations in the various subsamples
For most of the major elements subsamples of NWA 032have relative standard deviations (RSD) that areinsignificantly different from those of LAP (Table 1) eventhough the average subsample size for NWA 032 (sim14 mgFagan et al 2002) was smaller than for LAP (sim34 mg) TheRSDs of MgO and Cr2O3 for NWA 032 are again highbecause it has a porphyritic texture with large phenocrysts(millimeter scale) of olivine (with chromite inclusions) andmagnesian pyroxene but a fine-grained groundmass of
plagioclase Fe-rich pyroxene ilmenite and glass keeps theRSDs of other major and incompatible trace elements low
Source Crater Pairing of LAP and NWA 032
We find the similarities in chemistry and petrographybetween LAP and NWA 032 when compared to the largeranges observed among Apollo and Luna samples to be sogreat that it is highly unlikely that two meteorites so similarcould derive from different locations Below we summarizethe similarities and differences
The textures of NWA 032 and LAP are markedlydifferent from each other NWA 032 has a porphyritic texture
Fig 5 BSE images from LAP 0220533 a) oxide grains set in and around a large olivine grain individual grains of ilmenite (Ilm) Cr-ulvˆspinel (Chr-Usp) and chromite (Chr) composite chromian ulvˆspinel-chromite (ChrUsp) grains with accompanying pyroxene andplagioclase (grey and black areas) b) A close-up of a zoned spinel grain with a chromite core and a Cr-ulvˆspinel rim c) A large cristobalite(Crist) grain with many inclusions of fayalite pyroxene (Pyx) plagioclase (Plag) troilite (Sulf) phosphate K-rich glass and the ITE-richglass Also present are several areas of fayalite symplectite (Fay Symp) with inclusions of plagioclase silica ilmenite troilite and K-richglass d) A BSE image of a different area of groundmass showing a large grain of fayalite symplectite containing inclusions of plagioclasesilica ilmenite troilite K-rich glass and Fe-rich pyroxene A large ilmenite (Ilm) grain cuts through the symplectite and several large troilitegrains are also present
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1075Ta
ble
1 M
ajor
- and
trac
e-el
emen
t con
cent
ratio
ns o
f LA
P 02
205
and
NW
A 0
32 s
ubsa
mpl
es a
nd w
eigh
ted
aver
ages
Sa
mpl
eLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
P02
205
0220
502
205
0220
502
205
0220
502
224
0222
402
224
0222
602
226
0222
602
436
0243
602
436
0363
2Sp
lit2
0-1
20-
22
0-3
24-
12
4-2
24-
39
-11
9-1
20-
16
-11
0-1
12-
17
-19
-11
2-1
7-1
Maj
or-e
lem
ent c
once
ntra
tions
SiO
245
045
345
245
344
745
245
345
045
745
845
645
745
845
444
9minus
TiO
23
343
333
342
993
283
132
983
332
653
233
193
222
812
742
77minus
Al 2O
39
8410
18
104
89
638
9810
20
104
09
359
769
509
789
1610
67
9
379
37minus
Cr 2
O3
(IN
AA
)0
260
220
260
330
320
330
290
300
360
310
300
310
330
380
420
23Fe
O (I
NA
A)
229
228
219
217
233
216
227
231
215
218
217
219
209
218
228
218
MnO
028
030
029
028
034
032
026
028
028
028
028
029
025
028
027
minusM
gO5
875
465
697
177
116
685
766
567
496
726
457
106
307
937
74minus
CaO
111
112
114
111
105
113
112
109
111
111
114
111
114
110
105
minusN
a 2O
(IN
AA
)0
390
420
410
380
360
390
360
360
370
370
370
370
370
350
350
39K
2O0
080
090
070
060
070
060
100
080
060
060
070
060
080
050
06minus
P 2O
50
110
110
100
090
080
080
120
130
090
090
120
110
130
090
11minus
Tota
ls99
199
499
299
099
099
399
599
399
499
399
399
399
099
499
3minus
Mgprime
3130
3237
3536
3134
3835
3537
3539
38minus
Trac
e-el
emen
t con
cent
ratio
nsSc
590
580
578
595
589
604
602
581
588
600
608
584
617
608
568
592
Cr
1751
1511
1767
2290
2180
2230
1982
2070
2470
2150
2040
2100
2240
2580
2840
1590
Co
346
339
340
378
404
370
385
371
385
355
350
378
343
415
427
315
Sr15
016
019
013
013
011
014
014
013
014
014
010
013
013
013
010
0Zr
200
260
250
210
150
140
130
190
190
180
150
220
190
100
170
200
Ba
166
154
150
124
134
152
153
163
144
144
157
142
139
8612
615
7La
147
153
142
116
153
146
125
145
114
118
127
124
110
106
118
136
Ce
383
396
366
322
370
360
336
388
308
329
345
344
319
273
316
369
Nd
2528
2320
2720
2225
1618
2624
1820
1922
Sm8
608
898
357
048
518
197
488
616
847
247
627
426
806
327
058
13Eu
136
141
136
120
126
129
121
130
112
119
125
122
120
102
114
128
Tb1
892
021
911
631
951
861
732
031
661
681
771
731
671
511
651
85Y
b7
37
47
06
17
06
76
57
36
06
26
66
45
95
36
17
0Lu
099
103
096
083
095
094
091
100
082
087
091
090
084
073
086
100
Hf
627
642
606
510
571
550
567
633
504
525
565
549
501
418
519
597
Ta0
800
800
790
690
670
690
740
800
610
700
730
750
630
570
630
76Th
224
234
220
179
201
193
213
239
180
187
211
204
191
142
200
234
U0
610
520
670
550
530
420
480
640
440
510
540
430
440
370
560
57M
ass (
mg)
353
402
402
345
413
489
279
273
288
283
277
305
273
269
333
324
1076 R Zeigler et al Ta
ble
1 C
ontin
ued
Maj
or- a
nd tr
ace-
elem
ent c
once
ntra
tions
of L
AP
0220
5 an
d N
WA
032
sub
sam
ples
and
wei
ghte
d av
erag
es
Sam
ple
LAP
LAP
LAP
NW
AN
WA
NW
AN
WA
NW
AN
WA
NW
AN
WA
NW
ALA
PN
WA
LAP
NW
A03
632
0363
203
632
032
032
032
032
032
032
032
032
032
032
032
032
Split
7-2
13-
11
3-2
A2
A3
A4
B1
B3
B4
C1
C2
D2
ave
ave
rsde
vrs
dev
Maj
or-e
lem
ent c
once
ntra
tions
SiO
2minus
minusminus
451
442
454
456
434
445
447
445
452
453
447
000
80
015
TiO
2minus
minusminus
285
296
301
333
263
308
302
282
315
311
300
007
90
068
Al 2O
3minus
minusminus
942
902
942
990
867
999
937
858
973
979
932
005
20
054
Cr 2
O3 (
INA
A)
033
031
028
040
037
037
036
042
039
056
036
038
031
040
015
60
154
FeO
(IN
AA
)22
622
322
821
722
622
121
523
721
822
622
021
822
222
20
029
003
1M
nOminus
minusminus
027
028
029
027
030
026
026
029
030
029
028
008
00
060
MgO
minusminus
minus7
978
507
366
3010
26
686
764
985
692
663
797
011
50
170
CaO
minusminus
minus10
710
410
911
59
511
310
49
810
911
09
106
002
50
062
Na 2
O (I
NA
A)
037
038
037
036
034
035
038
033
037
032
034
035
038
035
005
00
052
K2O
minusminus
minus0
080
090
090
110
080
100
100
110
090
070
090
202
012
2P 2
O5
minusminus
minus0
080
080
060
100
070
080
110
110
100
100
090
158
020
8To
tals
minusminus
minus99
098
999
399
399
398
899
198
898
999
28
990
minusminus
Mgprime
minusminus
minus40
4037
3444
3638
4436
347
390
081
008
8
Trac
e-el
emen
t con
cent
ratio
nsSc
585
604
591
608
537
580
579
496
551
507
544
584
592
552
002
10
067
Cr
2280
2100
1930
2760
2500
2500
2430
2870
2660
3800
2490
2600
2096
2760
015
60
154
Co
387
377
370
408
438
396
368
503
399
469
414
385
370
421
007
60
102
Sr14
010
013
012
614
013
016
014
012
619
016
014
013
314
90
162
014
0Zr
140
160
210
160
170
180
180
160
160
160
170
180
183
170
022
40
055
Ba
163
128
163
191
250
229
170
130
166
335
469
266
145
266
013
30
392
La12
711
713
210
511
111
912
110
311
710
511
711
913
111
30
114
006
2C
e33
832
136
228
528
932
332
328
231
627
730
930
534
729
90
090
006
0N
d21
2623
1918
2222
1620
1921
2122
200
151
009
8Sm
758
715
791
637
648
710
705
610
692
618
664
698
774
663
009
40
058
Eu1
201
201
271
061
071
151
201
001
151
021
131
171
241
100
073
006
4Tb
176
165
183
152
152
165
167
144
160
146
159
165
179
157
007
90
054
Yb
65
63
68
57
57
61
62
53
60
54
58
61
659
58
008
40
053
Lu0
910
890
950
810
780
850
850
740
830
750
810
830
920
800
081
005
2H
f5
595
185
854
764
965
295
314
555
134
635
105
325
585
020
099
005
9Ta
076
067
069
056
064
071
068
060
061
060
061
065
071
063
009
70
073
Th1
961
962
171
74 1
91
199
204
167
196
172
187
203
204
189
011
40
074
U0
420
550
590
350
440
440
450
390
400
510
570
490
520
460
158
014
4M
ass (
mg)
341
373
388
90
210
81
107
96
77
182
156
242
641
124
minusminus
Maj
or-e
lem
ent c
once
ntra
tions
in w
t a
nd tr
ace-
elem
ent c
once
ntra
tions
in p
pm M
ajor
ele
men
ts n
ot o
ther
wis
e la
bele
d w
ere
obta
ined
by
EMPA
on
fuse
d be
ads m
ade
from
the
sam
e IN
AA
split
Ave
rage
s(a
ve)
are
wei
ghte
d av
erag
es r
sdev
= re
lativ
e st
anda
rd d
evia
tion
The
rela
tive
unce
rtain
ties
in th
e IN
AA
dat
a ar
e 1
ndash2
for N
a 2O
Sc
Cr
Co
FeO
La
Ce
Sm
Yb
Lu
and
Hf
3ndash4
for E
u T
b a
ndTh
7ndash1
0 fo
r Ta
and
Ba
17
for U
and
25ndash
30
for S
r and
Zr
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1077Ta
ble
2 A
vera
ge a
nd re
pres
enta
tive
oliv
ine
com
posi
tions
in th
e LA
P ba
salti
c m
eteo
rites
LA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
P02
205
0222
602
224
0243
602
205
0222
602
224
0243
602
205
0222
402
436
0220
5co
reco
reco
reco
ret-r
imt-r
imt-r
imt-r
imx-
rimx-
rimx-
rimfa
y s
ymp
N40
2463
2942
1710
54
12
2
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
359
236
01
359
036
28
345
434
24
340
934
21
314
030
43
311
529
72
TiO
20
040
040
040
040
060
060
040
080
110
520
100
34A
l 2O3
003
009
002
003
lt00
2lt0
02
005
lt00
2lt0
02
lt00
2lt0
02
lt00
2C
r 2O
30
240
210
230
220
170
160
110
060
070
060
03lt0
02
FeO
344
432
92
328
233
14
420
640
15
417
545
70
586
362
85
587
966
50
MnO
033
036
035
036
047
041
042
050
063
071
058
065
MgO
282
629
24
301
229
63
224
623
50
225
519
30
881
461
844
177
NiO
lt00
5n
an
an
alt0
05
na
na
na
na
na
na
na
CaO
035
034
036
033
033
036
035
036
045
053
054
055
Na 2
Olt0
02
lt00
2lt0
02
lt00
2lt0
02
lt00
2lt0
02
lt00
20
02lt0
02
lt00
2lt0
02
Tota
l99
65
992
299
85
100
0310
016
989
099
37
100
2210
012
997
199
65
995
5
Cat
ion
ratio
sFa
406
387
380
386
514
490
511
571
787
884
796
950
Fo59
461
362
061
448
751
048
942
921
111
620
44
5
Stoi
chio
met
ry b
ased
on
4 ox
ygen
ato
ms
Si IV
099
90
998
098
90
997
099
50
992
099
01
003
099
50
995
099
40
996
Al V
I0
001
000
30
001
000
10
000
000
00
002
000
00
000
000
00
000
000
0Ti
VI
000
10
001
000
10
001
000
10
001
000
10
002
000
30
013
000
20
009
Cr
000
50
005
000
50
005
000
40
004
000
30
001
000
20
002
000
10
000
Fe+2
080
10
764
075
60
762
101
60
973
101
61
122
155
41
719
156
91
864
Mn+2
000
80
009
000
80
008
001
20
010
001
00
012
001
70
020
001
60
018
Mg
117
11
208
123
61
214
096
21
014
097
40
842
041
60
225
040
10
089
Ca
001
10
010
001
10
010
001
00
011
001
10
011
001
50
018
001
90
020
Na
000
00
000
000
00
000
000
00
000
000
10
000
000
10
000
000
00
000
Tet s
ite0
999
099
80
989
099
70
995
099
20
990
100
30
995
099
50
994
099
6O
ct si
te1
998
199
92
019
200
12
006
201
42
017
199
12
007
199
62
009
199
9N
= n
umbe
r of a
naly
ses i
n th
e av
erag
e t-
rim =
typi
cal r
im x
-rim
= e
xtre
me
rim f
ay s
ymp
= fa
yalit
e sy
mpl
ectit
e n
a =
not
ana
lyze
d
1078 R Zeigler et al Ta
ble
3 A
vera
ge a
nd re
pres
enta
tive
pyro
xene
com
posi
tions
in th
e LA
P ba
salti
c m
eteo
rites
LA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
P02
205
0222
602
224
0243
602
205
0222
602
224
0243
602
205
0243
602
205
pig
cor
epi
g c
ore
pig
cor
epi
g c
ore
aug
cor
eau
g c
ore
aug
cor
eau
g c
ore
hd
hd
pyxf
er
N23
1417
168
2014
111
11
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
516
751
94
520
751
83
495
149
27
494
649
51
456
045
91
439
7Ti
O2
056
051
053
056
135
135
130
134
139
185
112
Al 2O
31
331
201
321
363
173
333
243
281
842
051
73C
r 2O
30
590
540
580
540
971
010
940
98lt0
02
lt00
2lt0
02
FeO
198
419
47
191
619
83
138
613
21
133
213
77
312
130
66
471
8M
nO0
360
350
360
350
250
250
260
270
320
330
59M
gO18
81
192
019
63
185
213
47
138
114
05
138
00
480
330
04C
aO6
396
496
386
8216
81
169
616
74
165
817
88
183
73
53N
a 2O
lt00
20
030
030
020
050
050
060
05lt0
02
lt00
20
02To
tal
995
799
73
100
199
82
994
499
23
993
599
57
987
399
51
981
7
Cat
ion
ratio
sM
gprime62
863
764
662
563
465
165
364
12
61
90
1Fs
317
310
304
316
249
237
237
246
582
580
871
En53
614
614
215
743
132
131
731
340
240
90
1W
o14
754
455
452
632
044
244
644
01
61
112
8
Stoi
chio
met
ry b
ased
on
6 o
xyge
n at
oms
Si IV
194
91
953
194
81
952
188
31
874
187
81
879
191
61
908
193
3A
l IV
005
10
047
005
20
048
011
70
126
012
20
121
008
40
092
006
6Ti
IV0
000
000
00
000
000
00
000
000
00
000
000
00
000
000
00
000
Al V
I0
009
000
60
006
001
20
026
002
30
023
002
60
007
000
80
009
Ti V
I0
016
001
40
015
001
60
038
003
90
037
003
80
044
005
80
054
Cr
001
80
016
001
70
016
002
90
030
002
80
029
000
00
000
000
0Fe
+20
626
061
20
599
062
40
441
042
00
423
043
71
097
106
61
734
Mn+2
001
10
011
001
10
011
000
80
008
000
80
009
001
10
012
002
2M
g1
058
107
61
094
103
90
764
078
30
795
078
10
030
002
10
002
Ca
025
80
261
025
60
275
068
50
691
068
10
674
080
50
818
016
6N
a0
001
000
20
002
000
10
003
000
40
004
000
40
001
000
10
002
Tet s
ite2
000
200
02
000
200
02
000
200
02
000
200
02
000
200
01
999
Oct
site
199
71
999
200
11
995
199
51
999
200
11
997
199
51
983
198
9A
ugite
(aug
) co
res h
ave
an M
gprime gt
60 a
nd W
o gt3
0 w
hile
pig
eoni
te (p
ig)
core
s hav
e M
gprime gt
60 a
nd W
o lt1
8 H
d =
hed
enbe
rgite
pyx
fer
= py
roxf
erro
ite
Mgprime
= M
g(M
g +
Fe)
100
N =
num
ber o
f ana
lyse
s
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1079
All of the LAP stones have relatively coarse-grained (upto approximately 15 mm) subophitic texture They consistpredominantly of pyroxene and plagioclase with minoramounts of olivine ilmenite and a groundmass dominated byfayalite and cristobalite They contain trace amounts ofchromite chromian ulvˆspinel ulvˆspinel troilite Fe-metalbarian K-feldspar fluor-apatite RE-merrillite tranquillityite(Fe8(YZr)2Ti3Si3O24) and baddeleyite (ZrO2) The modalmineral proportions differ slightly from section to section(Table 9) A few veins and pockets of basaltic glass ofpseudo-whole rock composition (likely shock melted) alsooccur in thin sections LAP 0220533 and LAP 0222424 Theorder in which minerals are inferred to have crystallized ischromite olivine pyroxene plagioclase and groundmass
Olivine grains vary in size from 003 to sim1 mm with01 to 03 mm being typical The modal abundance of olivineranges from 23 to 36 The grains are usually anhedral(rarely subhedral Fig 2a) typically with round or irregularmorphology and uneven contact with the surroundingpyroxene (Fig 2b) Some olivine grains have inclusions ofchromite or Cr-ulvˆspinel grains or both and a few haveldquomeltrdquo inclusions that have two phases in them mafic glasswith a pyroxene-like composition (sim10 wt Al2O3 Table 6)and K-rich high-silica glass similar to the glass seen in thefayalite symplectite grains in the groundmass (sim3 wt K2O68 wt SiO2) Most of the larger olivine grains are zonedwith cores of Fo55ndash65 and rims typically in the Fo38ndash45 range(Fig 3a Table 2) though in a few instances zoning to rims ofFosim20 is observed (Fig 3b) Most of the smaller olivine grainsare not zoned (or not strongly zoned) and they typically havecompositions in the Fo52ndash57 range with the smallest grainshaving the most magnesian compositions The apparentreaction texture between olivine and pyroxene and therelatively magnesian rims on compositions of the smallestolivine grains (likely the remnant cores of grains that havebeen almost completely resorbed) are strong indications thatolivine was being resorbed when the rock solidified
Chromite and Cr-ulvˆspinel grains almost always occuras inclusions within or closely associated with olivine grainsThey also have relatively restricted compositional ranges(Fig 4 Table 4) and they occur individually and as compositegrains with cores of chromite (Chr62ndash68Usp13ndash18Spn16ndash25) andrims of Cr ulvˆspinel (Chr6ndash19Usp71ndash91Spn3ndash11) (Figs 5aand 5b) We found few spinel compositions intermediate tothese end members The total modal abundance of spinel(including ulvˆspinel in the groundmass) is small rangingfrom 03 to 04 Where these two phases are intergrown theboundary between them is sharp with differences in Cr2O3concentration exceeding 20 wt within a few micrometers ofthe boundary A few of the chromite grains have inclusionsof pyroxene with a range of compositions (Mgprime of 47ndash59Wo16ndash31 and TiO2 concentrations from 11ndash24 wt)
Pyroxene grains in LAP are anhedral display undulatoryto mosaic extinction and range in size up to sim1 mm (Fig 2c)
In many cases pyroxene grains partially enclose plagioclasegrains in a subophitic texture The modal abundance ofpyroxene ranges from 47 to 52 The pyroxene grains havemagnesian cores of pigeonite and subcalcic augite (Mgprime fromsim50 to 68) with a wide range of CaO concentrations (Wo11 toWo36 Table 3 Fig 6) although there appears to be a bimodaldistribution of Wo contents with a minimum near Wo20(Fig 6 insets) In some cases pyroxene core compositionsgrade continuously to nearly end member hedenbergite(Fs58Wo40) and pyroxferroite (Fs86Wo13) In a few rare casescontacts between magnesian and ferroan pyroxenes are sharpand linear Compositions of pyroxene grains in contact withpartially resorbed olivine grains vary considerably incomposition The most common composition issubcalcic augite (Wo gt 20) with FeO concentrations in therange Fs24ndash49
The TiAl and TiCr ratios in the LAP pyroxenes arestrongly correlated with Mgprime as expected according toelement compatibility (eg Bence and Papike 1972) Theatomic TiCr ratio increases with decreasing Mgprime in LAPpyroxenes (Fig 7a) This reflects the compatible behavior ofCr and the incompatible behavior of Ti in early crystallizingphases of low-Ti lunar basaltic magmas The most magnesianpyroxenes have atomic TiAl ratios very close to 14indicating that aluminum was introduced through boththe Tschermak (AlAlMgminus1Siminus1) and coupled titanium(TiAl2Mgminus1Siminus2) exchange reactions in approximately equalproportions (Thompson 1982) As pyroxene becomesprogressively more ferroan the TiAl cation ratio approaches12 suggesting a gradual increase in the proportion of Alincorporated due to coupled Ti substitution (Fig 7b) Theleast magnesian pyroxenes (Mgprime lt40) have TiAl ratiosapproaching 34 An increase in TiAl ratios in pyroxene from14 to 12 with decreasing Mgprime in lunar basalts has previouslybeen interpreted as a result of pyroxene crystallization bothprior to the onset of plagioclase crystallization (ratiosaround 14) and during plagioclase crystallization (14ndash12Bence and Papike 1972) Bence and Papike (1972) attributedthe high relative concentrations of Ti in the late-stage Fe-richlunar pyroxenes to Ti3+
Plagioclase forms elongated subhedral to anhedralgrains up to 175 mm long The modal abundance ofplagioclase ranges from 32 to 35 Pyroxene inclusions ofa variety of sizes with compositions spanning nearly theentire compositional spectrum observed occur withinplagioclase Most plagioclase grains are highly fracturedalthough some or portions of some are smooth in polishedsections as seen in the BSE images (Fig 2d) These smoothareas consist partially or entirely of maskelynite as indicatedby their isotropic (or nearly isotropic) character in cross-polarized light Plagioclase grains are complexly zoned Theirtypical core composition is An886Ab11Or04 with sim1 wtFeO + MgO and an Mgprime of 34 (Fig 8 Table 5) Their rims areas wide as sim40 microm and gradually increase in K (up to simOr5)
1080 R Zeigler et al
and FeO (up to sim3 wt) while decreasing in MgO(to lt002 wt Fig 9) The Na2O concentrations firstincrease up to simAb14 then decrease sharply to less thanAb10 (which is lower than in the cores) The extreme rimcomposition of the large plagioclase grains is similar to that ofthe plagioclase found as inclusions in groundmass fayaliteand cristobalite grains (next paragraph Table 5) There is noapparent overall compositional difference between the coresof the maskelynite and the plagioclase grains
Fayalite cristobalite and ilmenite are the dominantminerals in the groundmass typically occurring togetheralthough each can be found independently All of the phaseshave relatively minor modal abundances fayalite (29ndash48)cristobalite (18ndash21) and ilmenite (35ndash40) Silicadisplaying the ldquocracklerdquo pattern distinctive to cristobaliteoccurs as anhedral grains up to 05 mm in size Thecristobalite grains contain minor Al2O3 TiO2 FeO and CaO(Σ sim13 wt Table 6) Inclusions of late-crystallizing phasessuch as K-rich plagioclase K-rich glass K-feldspar fayaliteFe-rich pyroxene phosphate and mafic glass withhigh concentrations of incompatible elements are common(Fig 5c) Fayalite grains (Fo45 sim05 wt CaO) range in size
up to 075 mm and usually form a symplectite texture withinclusions of K-rich glass silica K-rich plagioclase andilmenite (Fig 5d) Fayalite with no (or few) inclusions occursonly rarely Ilmenite is the dominant oxide in the groundmassforming elongate laths up to 1 mm in length Typically theilmenite is poor in Mg (sim02 wt average) although a singlegrain of more magnesian ilmenite associated with a largeolivine grain was observed (Fig 2b) Less common aresmaller subhedral ulvˆspinel grains (lt005 mm) thathave compositions approaching end member ulvˆspinel(Chr0ndash4Usp93ndash98Sp2ndash3) A few composite grains of ilmeniteand ulvˆspinel were observed
Also found in the groundmass are a variety of traceminerals including both fluorapatite and RE-merrillite(Table 7) Phosphate grains most commonly occur betweenplagioclase and ferropyroxene sometimes with associatedcristobalite troilite or both Barian K-feldspar (sim5 wt BaO)also occurs in the groundmass usually in the same areas asthe phosphate minerals (Table 5) Only a few K-feldspargrains (the largest) have stoichiometry that unambiguouslyidentifies them as K-feldspar while many K-rich grainshave excess Si suggesting that they may be intergrowths of
Table 4 Average oxide compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02205 02226 02224 02436 02205 02226 02224 02436 02205 02226 02224Al Al Al Al Cr-rich Cr-rich Cr-rich Cr-rich CrAl CrAl CrAlchr chr chr chr usp usp usp usp usp usp usp
N 23 11 13 5 22 1600 7 13 9 22 10
Major elements in wt by EMPAFeO 3444 3503 3532 3433 5705 5832 5846 5868 6191 6198 6180TiO2 546 532 540 517 2833 2871 2892 2909 3254 3151 3161Cr2O3 4384 4357 4331 4391 928 840 851 776 234 310 338Al2O3 1142 1178 1140 1217 287 261 261 276 191 204 203MgO 283 242 218 292 093 061 069 065 021 028 031MnO 027 024 025 027 035 032 034 033 036 032 034V2O3 073 074 076 075 036 031 033 033 022 025 026SiO2 007 009 008 009 lt002 007 008 018 lt002 008 007CaO 004 004 003 lt002 010 005 006 011 008 007 005ZnO 003 na na na 004 na na na 003 na naTotals 991 992 987 996 993 994 1000 999 996 996 999
Stoichiometry based on 4 (spinel) and 3 (ilmenite) oxygen atomsSi IV 0003 0003 0003 0003 0000 0003 0003 0006 0000 0003 0003Al VI 0469 0484 0472 0496 0125 0114 0113 0119 0083 0089 0088Ti 0143 0139 0143 0134 0784 0798 0798 0803 0907 0880 0880V 0020 0021 0021 0021 0011 0009 0010 0010 0007 0007 0008Cr 1208 1201 1204 1199 0270 0245 0247 0225 0068 0091 0099Fe2+ 1004 1021 1039 0992 1756 1802 1794 1801 1920 1925 1913Mn2+ 0008 0007 0007 0008 0011 0010 0011 0010 0011 0010 0011Mg 0147 0126 0114 0151 0051 0034 0038 0035 0012 0016 0017Zn 0001 minus minus minus 0001 minus minus minus 0001 minus minusCa 0002 0002 0001 0000 0004 0002 0002 0004 0003 0003 0002Sum 2+ 1162 1156 1161 1151 1823 1847 1844 1851 1947 1953 1942Sum 3 4+ 1844 1849 1844 1854 1190 1168 1170 1163 1066 1071 1078Total 3003 3001 3002 3001 3012 3013 3012 3007 3013 3020 3017
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1081
K-feldspar and silica (granophyric texture) at a scale smallenough to be beyond the resolution of the electron microprobe(less than sim01 microm)
Two glass types of distinct composition presumably late-stage residual liquids occur in the groundmass The first is aKSi-rich glass (78 wt SiO2 sim56 wt K2O) that makes upa considerable percentage of the inclusions in the cristobaliteand particularly the fayalite grains The second type ofevolved glass occurs as very small (lt5 microm) roundedinclusions in cristobalite grains This glass has a silica-poorFe-rich bulk composition (sim36 wt SiO2 sim39 wt FeOTable 6) but it is also considerably enriched in manyincompatible elements 23 wt P2O5 12 wt SO3 02 wtY2O3) Commonly we observed minute grains of fayalitetroilite or phosphate associated with this glass These twolate-stage glasses could represent conjugate liquids producedby late-stage immiscibility of an evolved residual meltSimilar glasses were observed in some plutonic rocks fromthe Apollo 14 site (Jolliff et al 1991)
Troilite blebs (with nearly ideal stoichiometry Table 8)are scattered throughout the groundmass along with trace Fe-metal grains which are usually intergrown with troilite orovergrown on chromite grains These grains typicallycontained 66 wt Ni and 14 wt Co though one grain had338 wt Ni and 60 wt Co (Table 8) A few grains ofbaddelyite (ZrO2) and tranquillityite (Zr-Fe-Ti silicate) wereidentified by energy-dispersive spectroscopy (EDS) in thegroundmass
A variety of shock effects occur in the minerals of thesethin sections (eg plagioclase converted to maskelynitemosaicism in the pyroxene) The level of shock was such thatlocalized partial melting occurred in some areas of themeteorite The areas of shock melt have severalmorphologies small melt pockets (LAP 02205 Fig 10a)veins of melt (LAP 0222424 Fig 10b) and in some casesareas that were only partially melted (LAP 0222424Fig 10c) with discernable mineral grains still present(typically maskelynite) Although veins of shock melt are rare
Table 4 Continued Average oxide compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02436 02205 02226 02224 02436 02205 02226 02224 02436 02205CrAl end end end end Mgusp usp usp usp usp ilm ilm ilm ilm ilm
N 11 11 2 3 3 24 16 20 18 2
Major elements in wt by EMPAFeO 6202 6375 6445 6355 6465 4657 4647 4634 4624 4463TiO2 3353 3267 3226 3396 3231 5198 5226 5233 5264 5296Cr2O3 209 026 023 011 037 010 012 015 016 038Al2O3 202 179 206 216 227 008 011 013 010 006MgO 022 005 008 007 003 014 010 016 019 150MnO 034 031 027 029 027 038 033 037 027 035V2O3 023 018 015 019 016 031 029 029 028 035SiO2 015 lt002 011 010 007 003 003 024 004 lt002CaO 007 010 007 008 010 013 006 010 009 008ZnO na 008 na na na 003 na na na lt002Totals 1007 992 997 1005 1002 997 998 1001 1000 1003
Stoichiometry based on 4 (spinel) and 3 (ilmenite) oxygen atomsSi IV 0005 0001 0004 0004 0003 0001 0001 0006 0001 0000Al VI 0087 0079 0091 0093 0099 0002 0003 0004 0003 0002Ti 0920 0921 0906 0937 0901 0990 0993 0989 0996 0991V 0007 0005 0004 0006 0005 0006 0006 0006 0006 0007Cr 0060 0008 0007 0003 0011 0002 0002 0003 0003 0007Fe2+ 1893 1999 2012 1950 2005 0986 0982 0974 0973 0928Mn2+ 0010 0010 0009 0009 0009 0008 0007 0008 0006 0007Mg 0012 0003 0004 0004 0002 0005 0004 0006 0007 0056Zn minus 0002 minus minus minus 0001 minus minus minus 0000Ca 0003 0004 0003 0003 0004 0004 0002 0003 0002 0002Sum 2+ 1918 2018 2028 1966 2019 1004 0995 0991 0988 0994Sum 3 4+ 1080 1014 1012 1043 1019 1001 1005 1008 1009 1007Total 2992 3032 3035 3005 3036 2004 2000 1992 1996 2001The spinel catagories where chosen based primarily on Cr2O3 content with Al chromite (chr) having gt40 wt Cr2O3 Cr-rich ulvˆspinel (usp) having 15ndash
5 wt Cr2O3 CrAl ulvˆspinel having 5ndash05 wt Cr2O3 and endmember ulvospinel having lt05 wt Cr2O3 Also seen were TiAl chromite (30ndash40 wtCr2O3) and high-Cr ulvˆspinel (30ndash15 wt Cr2O3) which are likely the result of an anlyses overlapping simultaneously on both an Al chromite and Cr-rich ulvˆspinel grain Similarly compositions intermediate to ilmenite and end ulvˆspinel were seen These compositions are not listed in this table but areshown in Fig 4 N = number of analyses in the average na = not analyzed
1082 R Zeigler et al
in our thin sections such veins were reported as pervasive inthe original macroscopic description of all five LAP stones(McBride et al 2003 2004a 2004b)
The various shock-induced effects observed in LAP canbe used to quantify and constrain the level of shock that LAPexperienced The presence of both plagioclase andmaskelynite in these samples suggests that the lower end ofthe range listed for conversion of plagioclase to maskelynite(30ndash45 GPa Stˆffler and Hornemann 1972 Ostertag 1983)is appropriate The mosaicism seen in the pyroxene istypically associated with shock values in the 30ndash75 GParange (Kieffer et al 1976 Schaal et al 1979) The presenceof shock-melt veins that have melted both pyroxene andplagioclase (based on the melt composition Table 6)indicates LAP should have been subjected to shock levels ofgt75ndash80 GPa (Kieffer et al 1976 Schaal et al 1979) Thedifferent shock effects observed reflect a range fromlt30 GPa (areas were plagioclase is preserved) to gt75 GPa(areas where shock melting occurred) over distances of onlya few millimeters
Bulk Composition and Comparison to Other LunarBasalts
LAP is a moderately aluminous (sim10 wt Al2O3) low-Ti(31 wt TiO2) mare basalt that falls near the Fe-rich(222 wt FeO) end of the range of FeO concentrationsobserved among lunar basalts It is more ferroan (Mgprime = 347)than any basalt in the Apollo or Luna collection (Fig 11a)Among lunar basalts only meteorites Asuka-881757 andYamato-793169 have comparably low Mgprime values (Koeberlet al 1993 Warren and Kallemeyn 1993 Thalmann et al1996 Korotev et al 2003a) LAP is enriched in Na2O(038 wt) relative to other ferroan (eg Asuka-881757 andYamato-793169) and Fe-rich basalts except for NWA 032(Fig 11b)
Regarding trace elements LAP is enriched in Cocompared to most lunar mare basalts with comparable Scconcentrations (Table 1 Fig 12a) Among Apollo and Lunabasalts only the Apollo 12 ilmenite basalts (Rhodes et al1977 Neal et al 1994) are comparable Incompatible trace-
Table 5 Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02205 02226 02224 02436 02205 02226 02224 02436 02205 02226plag plag plag plag mask mask mask mask plag plagcore core core core core core core core Na rim Na rim
N 123 86 48 88 29 49 33 32 12 3
Major elements in wt by EMPASiO2 4715 4657 4689 4639 4753 4741 4663 4673 4949 4960TiO2 010 007 007 006 013 008 006 006 027 019Al2O3 3337 3367 3296 3363 3367 3291 3376 3415 3170 3103Cr2O3 003 lt002 lt002 002 007 002 lt002 002 004 003FeO 068 067 073 058 060 111 066 060 134 136MgO 023 022 017 024 027 029 028 029 008 012CaO 1730 1746 1709 1763 1747 1726 1730 1740 1628 1597BaO na na na na na na na na na naNa2O 120 123 136 121 119 123 131 128 148 153K2O 006 007 010 006 005 009 006 005 020 019Total 1000 1000 994 998 1008 1004 1001 1006 1006 1000
Cation ratiosAn 885 883 869 887 888 881 877 880 848 842Or 04 04 06 04 03 05 03 03 12 12Ab 111 112 125 110 109 113 120 117 140 146Cn 00 00 00 00 00 00 00 00 00 00
Stoichiometry based on 8 oxygen atomsSi IV 2168 2147 2173 2143 2168 2179 2147 2140 2259 2279Al IV 1809 1830 1801 1831 1810 1782 1832 1843 1705 1681Fe+2 0026 0026 0028 0023 0023 0043 0025 0023 0051 0052Mg 0016 0015 0011 0017 0019 0020 0019 0020 0005 0008Ca 0853 0863 0849 0872 0854 0850 0853 0854 0796 0786Ba minus minus minus minus minus minus minus minus minus minusNa 0107 0110 0122 0108 0105 0109 0117 0114 0131 0136K 0004 0004 0006 0004 0003 0005 0003 0003 0011 0011Tet site 3977 3977 3974 3974 3978 3961 3979 3984 3964 3960Oct site 1005 1018 1022 1023 1003 1027 1022 1013 0995 0994
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1083
element concentrations are considerably greater in LAP thanin most of other low-Ti basalts (Fig 12bndashc) including theApollo 12 ilmenite basalts (Haskin et al 1971 Neal et al1994) The exceptions are NWA 032 the high-Al basalts ofLuna 16 (Philpotts et al 1972 Helmke and Haskin 1972 Maet al 1979) and some Apollo 14 high-Al basalts (Dickinsonet al 1985 Shervais et al 1985 Neal et al 1989a 1989b)
Relative concentrations of REEs in the LAP basalt arealso dissimilar to those of most other lunar basalts (Fig 13) inthat LAP is enriched in light REEs The exceptions are NWA032 which has a pattern nearly parallel to LAP and Apollo 14group 3 basalts (Dickinson et al 1985) which have a patternthat is similar although somewhat less steep in the heavyREEs Ratios of Th to REE in LAP are higher than those of allother lunar basalts except NWA 032 (Fig 14) and thedisparity in ThREE ratio between LAP and other lunarbasalts (except NWA 032) increases from the light to heavyREEs The Apollo 14 high-K basalts have similar ThREEratios for the middle REE Sm-Tb however (Neal et al 1989a
1989b) Overall in terms of its trace-element concentrationsLAP 02205 is most similar to NWA 032 The maindifferences are that NWA 032 is richer in elements associatedwith olivine (Mg Cr Co) and has concentrations ofincompatible elements that are 78ndash91 as great as those inLAP 02205
DISCUSSION
Evidence Supporting the Lunar Origin and Pairing of theLAP Stones
As stated in the introduction the meteorites LAP 0220502224 02226 02436 and 03632 were identified as lunarbasalts that were almost certainly paired (McBride et al 20032004a 2004b) A brief summary follows of the attributesfound in our more detailed petrographic examination thatsupport this initial classification and pairing interpretation
Results of oxygen isotope analyses (δ18O = +56 and
Table 5 Continued Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02224 02436 02205 02205 02226 02224 02436 02205 02205 02205plag plag plag plag plag plag plag barian KBa KBaNa rim Na rim matrix K rim K rim K rim K rim K-spar glass glass
N 24 5 13 10 1 5 1 10 10 23
Major elements in wt by EMPASiO2 4901 4879 5122 5152 4888 4935 5017 6026 5935 6356TiO2 008 008 016 017 lt002 008 014 na na naAl2O3 3163 3120 2960 2993 3213 3004 3002 2019 2063 2043Cr2O3 002 002 006 005 lt002 003 lt002 na na naFeO 117 130 267 192 147 195 173 065 074 116MgO 006 009 003 002 lt002 lt002 002 lt002 lt002 010CaO 1620 1622 1520 1549 1618 1602 1560 063 066 207BaO na na na na na na na 501 407 372Na2O 157 155 105 105 132 126 150 031 029 033K2O 023 021 090 067 067 056 086 1354 1162 586Total 1000 995 1007 1006 1007 993 1000 1008 1006 1007
Cation ratiosAn 839 842 846 852 835 845 807 33 minus minusOr 14 13 61 44 41 35 53 842 minus minusAb 147 145 105 104 124 120 140 30 minus minusCn 00 00 00 00 00 00 00 96 minus minus
Stoichiometry based on 8 oxygen atomsSi IV 2253 2257 2342 2344 2237 2293 2312 2863 2864 2951Al IV 1714 1701 1596 1609 1732 1645 1631 1131 1173 1124Fe+2 0045 0050 0102 0073 0056 0076 0067 0026 0030 0045Mg 0004 0006 0002 0001 0000 0001 0001 0001 0001 0007Ca 0798 0804 0745 0757 0793 0798 0770 0032 0034 0100Ba minus minus minus minus minus minus minus 0093 0077 0070Na 0140 0139 0093 0093 0117 0113 0134 0029 0027 0029K 0013 0013 0052 0039 0039 0033 0050 0820 0715 0353Tet site 3967 3957 3938 3954 3969 3938 3943 3994 4037 4075Oct site 0013 1011 0995 0963 1007 1020 1022 1002 0884 0604Plag = plagioclase mask = maskelynite N = number of analyses in the average na = not analyzed
1084 R Zeigler et al Ta
ble
6 A
vera
ge a
nd re
pres
enta
tive
cris
toba
lite
and
glas
s co
mpo
sitio
n in
the
LAP
basa
ltic
met
eorit
es
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
0220
502
226
0222
402
436
0220
502
205
0220
502
205
0220
502
224
0222
4cr
isto
balit
ecr
isto
balit
ecr
isto
balit
ecr
isto
balit
eSi
-ric
hpy
x-lik
eK
gla
ssIT
E-ric
hsh
ock
shoc
ksh
ock
MI g
lass
MI g
lass
in s
ympl
m
afic
gla
ssgl
ass
area
glas
s ar
eagl
ass
vein
N6
25
44
12
51
6515
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
979
598
17
984
798
45
672
542
76
783
236
67
463
486
441
TiO
20
270
270
230
230
664
810
374
032
341
623
13A
l 2O3
073
060
064
078
187
99
4210
13
544
139
86
123
Cr 2
O3
002
lt00
2lt0
02
002
lt00
20
13lt0
02
lt00
20
080
380
28Fe
O0
210
400
190
171
8615
91
183
392
719
618
520
5M
nOn
an
an
an
an
a0
22n
a0
420
220
290
25M
gO0
02lt0
02
lt00
2lt0
02
033
817
lt00
20
213
459
857
17C
aO0
190
200
200
236
8919
16
098
976
127
118
114
BaO
na
na
na
na
117
na
na
na
na
na
na
Na 2
O0
130
100
090
120
620
110
190
060
510
360
49K
2O0
030
050
07lt0
02
167
na
566
030
005
na
na
P 2O
5n
an
an
an
an
an
an
a2
32n
an
an
aF
na
na
na
na
na
na
na
008
na
na
na
Y2O
3n
an
an
an
an
an
an
a0
19n
an
an
aC
e 2O
3n
an
an
an
an
an
an
a0
12n
an
an
aSO
3n
an
an
an
an
an
an
a1
23n
an
an
aTo
tal
995
599
80
999
010
00
992
410
070
974
910
02
991
100
099
6Sy
mpl
= sy
mpl
ectit
e M
I = m
elt i
nclu
sion
N =
num
ber o
f ana
lyse
s in
the
aver
age
na
= n
ot a
naly
zed
The
shoc
ked
glas
s in
LAP
0222
4 is
the
parti
ally
mel
ted
area
(see
Fig
14)
and
onl
y th
e an
ayls
es o
fth
e gl
ass i
tsel
f wer
e in
clud
ed in
the
aver
age
not t
he m
iner
als t
hat w
ere
anal
yzed
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1085
Table 7 Representative phosphate compositions in LAP 0220533LAP LAP LAP LAP LAP LAP LAP LAP02205 02205 02205 02205 02205 02205 02205 02205RE- RE- RE- RE- RE- fluorapatite fluorapatite fluorapatitemerrillite merrillite merrillite merrillite merrillite
Major elements in wt by EMPASiO2 050 044 062 037 321 228 449 137Al2O3 022 lt005 009 lt005 lt005 007 014 lt005FeO 637 774 568 576 250 169 439 202MgO 020 037 025 028 lt005 lt005 lt005 lt005CaO 4326 4035 4233 4245 4983 5241 5003 5351Na2O 000 001 010 014 000 000 001 000P2O5 3885 4171 4382 4360 3540 3949 3771 4077Cl lt005 lt005 lt005 lt005 lt005 006 027 031F 047 044 050 048 168 245 130 186Y2O3 298 293 226 221 172 103 078 053La2O3 093 107 065 064 092 024 014 012Ce2O3 253 259 189 185 253 072 069 053Nd2O3 161 177 108 118 166 057 059 031Sm2O3 043 043 029 028 048 022 015 009Gd2O3 087 090 058 058 079 023 018 008Yb2O3 016 032 009 lt005 010 005 lt005 lt005ThO2 007 009 008 lt005 021 lt005 lt005 lt005minusO = (FCl) 021 020 022 021 072 105 061 085Sums 9930 1010 1001 9968 1004 1005 1003 1006
Table 8 Average sulfide and metal compositions in LAP 0220533Ave Fe metal High-Ni metal Troilite
N 5 1 8
Elemental percentage by EMPAFe 9209 5880 6280Ni 664 3377 lt002Co 141 595 lt002Ti 023 009 006Cr 043 017 lt002Mn lt002 004 lt002S lt002 lt002 3620Totals 1008 988 994Ideal troilite = 365 wt S 635 wt Fe N = number of analyses
Table 9 Modal mineralogy of the different LAP stonesLAP 0220533 LAP 0222616 LAP 0222424 LAP 0243614
Pyroxene 515 505 469 466Plagioclase 319 321 323 346Ilmenite 348 391 386 399Fay sympl 309 290 358 483Olivine 233 271 363 320Cristobalite 214 209 178 200Spinel (all) 034 045 040 039Troilite 025 024 024 022Fractures 49 49 53 421Shock glass 01 02 22 00N 633 times 106 905 times 106 470 times 106 396 times 106
All modal values are listed as percentages N = number of pixels
1086 R Zeigler et al
Fig 1 Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) and fayalite(more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phases arepyroxene and olivine a) LAP 0222616 b) LAP 0243614 c) LAP 0222424 d) LAP 0220533
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1087
δ17O = +27) performed by Mayeda and Clayton (reported inMcBride et al 2003) constrain the origin of LAP 02205 tothe Earth the Moon or an enstatite meteorite parent bodyLAP is clearly a meteorite all four of the stones have fusioncrusts (ruling out a terrestrial origin) The extremely ferroannature of LAP rules out the enstatite parent body as theprovenance FeOMnO ratios of mafic silicates arediagnostic of origins from different planetary bodies in thesolar system (Dymek et al 1976 Papike 1998) Ratios ofFeOMnO in LAP pyroxenes (average sim60) and olivines(average sim95) are consistent only with lunar origin (Fig 15)Furthermore the presence of Fe(Ni) metal and troilite thecompletely anhydrous nature of the sample the apparentlack of Fe3+ in all phases the calcic nature of theplagioclase and the deep negative Eu anomaly are allcommon in lunar basalts
With regard to texture mineral assemblage and mineralchemistry the four LAP 02xxx stones appear to beindistinguishable from each other Although we did not studythe mineral chemistry of the LAP 03632 in depth the textureand mineral assemblage are identical to the LAP 02xxxstones Furthermore the collection locations of the five stonesform a linear array sim3 km in length that is perpendicular to theflow of the ice sheet (John Schutt personal communication)Thus in the absence of cosmic-ray exposure data to thecontrary we conclude that the four LAP 02xxx stones studiedare paired
Compositional Variability among Small Subsamples ofLAP 02205 and NWA 032
Samples of lunar meteorites available for study at most afew hundred milligrams are very small by the standards ofterrestrial geology and geochemistry Nevertheless we havetaken our samples and subdivided them into numerous evensmaller (10ndash50 mg) subsamples for bulk compositionalanalysis (Korotev et al 1983 1996 2003a 2003b Jolliffet al 1991 1998 Fagan et al 2002) This procedure providesan estimate of the whole-rock composition through a mass-weighted mean that is equivalent to a single analysis of theentire mass of the allocated sample The variation amongsmall subsamples however provides additional informationabout compositional variations associated with mineralassemblage and proportions about petrogenesis and aboutpossible relationships to other meteorites (eg Korotev et al2003a 2003b) and how well the ldquowhole-rockrdquo compositionis likely to represent that of the source region of the meteorite(Korotev et al 2000a) In the following discussion weevaluate the causes of differences in composition amongsmall subsamples of LAP and NWA 032
The range of concentrations among the 19 subsamples ofLAP (27ndash40 mg) is relatively small for the most preciselydetermined major elements (SiO2 TiO2 Al2O3 FeO CaONa2O) and most precisely determined trace elements that arecompatible with the major mineral phases (Co Sc Eu) The
Fig 1 Continued Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) andfayalite (more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phasesare pyroxene and olivine d) LAP 0220533
1088 R Zeigler et al
relative sample standard deviations (s ) range from 08 to76 (with only Co and Eu gt 5 Table 1) The exceptionsare MgO and Cr2O3 for which the relative standarddeviations are distinctly greater 12 and 16 respectivelyFor incompatible elements that we determined precisely(lt9 analytical uncertainty La Ce Sm Tb Yb Lu Hf Taand Th) relative standard deviations range from 7 to 11These variations are caused by a combination ofunrepresentative sampling of the major mineral phasesowing to the coarse grain size (up to sim1 mm3) relative to theINAA subsample size (about 12 mm3 assuming that thedensity of LAP is sim35 gmm3) and to the heterogeneousdistribution of some relatively minor phases with high
concentrations of a given element This problem is not new asmany investigators have previously wrestled with theproblem of studying relatively coarse-grained lunar basaltswith small allocated subsample sizes characteristic of rareextraterrestrial samples (Korotev and Haskin 1975 Haskinet al 1977 Lindstrom and Haskin 1978 Ryder and Schuraytz2001) Ryder and Schuraytz (2001) showed that sim5 g ofmaterial are needed to achieve a representative sample ofApollo 15 olivine-normative basalts which have grain sizeson the order of a millimeter or greater
Among the LAP subsamples Cr2O3 and MgOconcentrations correlate positively (R2 = 081) as a result ofthe association of chromite and Cr-ulvˆspinel with olivine
Fig 2 BSE images from LAP 0220533 a) a large round olivine (oli) grain and a smaller subhedral olivine grain (left center of the image)both surrounded by zoned pyroxene (pyx) and plagioclase (plag) with melt inclusions (MI) and inclusions of chromite (chr) A smallulvˆspinel (Usp) grain occurs in the upper left b) A large irregular olivine grain and a smaller mostly resorbed olivine grain The larger graincontains both melt inclusions (MI) and chromite grains The associated ilmenite (Ilm) grain is the most magnesian ilmenite grain observed Acomposite grain of metal and troilite (MetSulf) is also present c) A BSE image showing the zoning in multiple large pyroxene grainsintergrown with plagioclase and maskelynite (mask) grains One small cristobalite (crist) grain is also present d) A BSE image showingseveral large plagioclase grains some of which contain both fractured areas (plagioclase) and smooth areas (maskelynite) Also present areseveral areas of groundmass including a fayalite symplectite and a cristobalite grain cut by an ilmenite lath
x
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1089
The large variations seen in MgO Cr2O3 and to a lesserextent Co concentrations occur because of the large relativevariation in the fraction of modal olivine among thesubsamples Normatively the compositional rangecorresponds to minus03ndash25 olivine (one subsample has 03normative quartz) and 032ndash049 chromite The relativelysmall variations seen among concentrations of the other majorelements as well as Sc and Eu are controlled byunrepresentative sampling of the major mineral phasespyroxene (Sc Ca Fe Si) and plagioclase (Al Na Ca Si Eu)and the minor but widely distributed mineral ilmenite (Ti Fe)Trace amounts of a few minerals that are found only ingroundmass have high concentrations of incompatible traceelements relative to the concentration of those elements inthe bulk meteorite These minerals include K-feldspar (Ba)
Fig 3 a) CaO versus Mgprime (molar Mg[Mg + Fe]100) in the olivinesof the different LAP stones The compositions range from cores ofFo55ndash67 trending towards rims typically in the Fo40 range withextreme zonation to rims of Fo15ndash20 in a few cases Where analyzedthe composition of groundmass fayalite are also shown b) Anelectron microprobe traverse across a small strongly zoned olivinegrain in LAP 0220533 The grain shows zoning from a core of simFo58to a rim composition of simFo18 over sim100 microm The break in the zoning(black arrow) is centered on a fracture in the olivine grain
Fig 4 Compositions of LAP oxides plotted on the (FeMgMn)O-(CrAl)2O3-TiO2 ternary (after El Goresy et al 1971) Compositionsof endmember ilmenite (FeTiO3) ulvˆspinel (Fe2TiO4) andchromite (FeCr2O4) are labeled For a description of theclassification scheme see the footnote of Table 3 a) LAP 0220533b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1090 R Zeigler et al
RE-merrillite (P REEs Th) and baddeleyite (Zr Hf U Th)Therefore the variation in the amount of the groundmassldquophaserdquo in the different subsamples controls the ITEconcentrations in the various subsamples
For most of the major elements subsamples of NWA 032have relative standard deviations (RSD) that areinsignificantly different from those of LAP (Table 1) eventhough the average subsample size for NWA 032 (sim14 mgFagan et al 2002) was smaller than for LAP (sim34 mg) TheRSDs of MgO and Cr2O3 for NWA 032 are again highbecause it has a porphyritic texture with large phenocrysts(millimeter scale) of olivine (with chromite inclusions) andmagnesian pyroxene but a fine-grained groundmass of
plagioclase Fe-rich pyroxene ilmenite and glass keeps theRSDs of other major and incompatible trace elements low
Source Crater Pairing of LAP and NWA 032
We find the similarities in chemistry and petrographybetween LAP and NWA 032 when compared to the largeranges observed among Apollo and Luna samples to be sogreat that it is highly unlikely that two meteorites so similarcould derive from different locations Below we summarizethe similarities and differences
The textures of NWA 032 and LAP are markedlydifferent from each other NWA 032 has a porphyritic texture
Fig 5 BSE images from LAP 0220533 a) oxide grains set in and around a large olivine grain individual grains of ilmenite (Ilm) Cr-ulvˆspinel (Chr-Usp) and chromite (Chr) composite chromian ulvˆspinel-chromite (ChrUsp) grains with accompanying pyroxene andplagioclase (grey and black areas) b) A close-up of a zoned spinel grain with a chromite core and a Cr-ulvˆspinel rim c) A large cristobalite(Crist) grain with many inclusions of fayalite pyroxene (Pyx) plagioclase (Plag) troilite (Sulf) phosphate K-rich glass and the ITE-richglass Also present are several areas of fayalite symplectite (Fay Symp) with inclusions of plagioclase silica ilmenite troilite and K-richglass d) A BSE image of a different area of groundmass showing a large grain of fayalite symplectite containing inclusions of plagioclasesilica ilmenite troilite K-rich glass and Fe-rich pyroxene A large ilmenite (Ilm) grain cuts through the symplectite and several large troilitegrains are also present
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
1076 R Zeigler et al Ta
ble
1 C
ontin
ued
Maj
or- a
nd tr
ace-
elem
ent c
once
ntra
tions
of L
AP
0220
5 an
d N
WA
032
sub
sam
ples
and
wei
ghte
d av
erag
es
Sam
ple
LAP
LAP
LAP
NW
AN
WA
NW
AN
WA
NW
AN
WA
NW
AN
WA
NW
ALA
PN
WA
LAP
NW
A03
632
0363
203
632
032
032
032
032
032
032
032
032
032
032
032
032
Split
7-2
13-
11
3-2
A2
A3
A4
B1
B3
B4
C1
C2
D2
ave
ave
rsde
vrs
dev
Maj
or-e
lem
ent c
once
ntra
tions
SiO
2minus
minusminus
451
442
454
456
434
445
447
445
452
453
447
000
80
015
TiO
2minus
minusminus
285
296
301
333
263
308
302
282
315
311
300
007
90
068
Al 2O
3minus
minusminus
942
902
942
990
867
999
937
858
973
979
932
005
20
054
Cr 2
O3 (
INA
A)
033
031
028
040
037
037
036
042
039
056
036
038
031
040
015
60
154
FeO
(IN
AA
)22
622
322
821
722
622
121
523
721
822
622
021
822
222
20
029
003
1M
nOminus
minusminus
027
028
029
027
030
026
026
029
030
029
028
008
00
060
MgO
minusminus
minus7
978
507
366
3010
26
686
764
985
692
663
797
011
50
170
CaO
minusminus
minus10
710
410
911
59
511
310
49
810
911
09
106
002
50
062
Na 2
O (I
NA
A)
037
038
037
036
034
035
038
033
037
032
034
035
038
035
005
00
052
K2O
minusminus
minus0
080
090
090
110
080
100
100
110
090
070
090
202
012
2P 2
O5
minusminus
minus0
080
080
060
100
070
080
110
110
100
100
090
158
020
8To
tals
minusminus
minus99
098
999
399
399
398
899
198
898
999
28
990
minusminus
Mgprime
minusminus
minus40
4037
3444
3638
4436
347
390
081
008
8
Trac
e-el
emen
t con
cent
ratio
nsSc
585
604
591
608
537
580
579
496
551
507
544
584
592
552
002
10
067
Cr
2280
2100
1930
2760
2500
2500
2430
2870
2660
3800
2490
2600
2096
2760
015
60
154
Co
387
377
370
408
438
396
368
503
399
469
414
385
370
421
007
60
102
Sr14
010
013
012
614
013
016
014
012
619
016
014
013
314
90
162
014
0Zr
140
160
210
160
170
180
180
160
160
160
170
180
183
170
022
40
055
Ba
163
128
163
191
250
229
170
130
166
335
469
266
145
266
013
30
392
La12
711
713
210
511
111
912
110
311
710
511
711
913
111
30
114
006
2C
e33
832
136
228
528
932
332
328
231
627
730
930
534
729
90
090
006
0N
d21
2623
1918
2222
1620
1921
2122
200
151
009
8Sm
758
715
791
637
648
710
705
610
692
618
664
698
774
663
009
40
058
Eu1
201
201
271
061
071
151
201
001
151
021
131
171
241
100
073
006
4Tb
176
165
183
152
152
165
167
144
160
146
159
165
179
157
007
90
054
Yb
65
63
68
57
57
61
62
53
60
54
58
61
659
58
008
40
053
Lu0
910
890
950
810
780
850
850
740
830
750
810
830
920
800
081
005
2H
f5
595
185
854
764
965
295
314
555
134
635
105
325
585
020
099
005
9Ta
076
067
069
056
064
071
068
060
061
060
061
065
071
063
009
70
073
Th1
961
962
171
74 1
91
199
204
167
196
172
187
203
204
189
011
40
074
U0
420
550
590
350
440
440
450
390
400
510
570
490
520
460
158
014
4M
ass (
mg)
341
373
388
90
210
81
107
96
77
182
156
242
641
124
minusminus
Maj
or-e
lem
ent c
once
ntra
tions
in w
t a
nd tr
ace-
elem
ent c
once
ntra
tions
in p
pm M
ajor
ele
men
ts n
ot o
ther
wis
e la
bele
d w
ere
obta
ined
by
EMPA
on
fuse
d be
ads m
ade
from
the
sam
e IN
AA
split
Ave
rage
s(a
ve)
are
wei
ghte
d av
erag
es r
sdev
= re
lativ
e st
anda
rd d
evia
tion
The
rela
tive
unce
rtain
ties
in th
e IN
AA
dat
a ar
e 1
ndash2
for N
a 2O
Sc
Cr
Co
FeO
La
Ce
Sm
Yb
Lu
and
Hf
3ndash4
for E
u T
b a
ndTh
7ndash1
0 fo
r Ta
and
Ba
17
for U
and
25ndash
30
for S
r and
Zr
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1077Ta
ble
2 A
vera
ge a
nd re
pres
enta
tive
oliv
ine
com
posi
tions
in th
e LA
P ba
salti
c m
eteo
rites
LA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
P02
205
0222
602
224
0243
602
205
0222
602
224
0243
602
205
0222
402
436
0220
5co
reco
reco
reco
ret-r
imt-r
imt-r
imt-r
imx-
rimx-
rimx-
rimfa
y s
ymp
N40
2463
2942
1710
54
12
2
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
359
236
01
359
036
28
345
434
24
340
934
21
314
030
43
311
529
72
TiO
20
040
040
040
040
060
060
040
080
110
520
100
34A
l 2O3
003
009
002
003
lt00
2lt0
02
005
lt00
2lt0
02
lt00
2lt0
02
lt00
2C
r 2O
30
240
210
230
220
170
160
110
060
070
060
03lt0
02
FeO
344
432
92
328
233
14
420
640
15
417
545
70
586
362
85
587
966
50
MnO
033
036
035
036
047
041
042
050
063
071
058
065
MgO
282
629
24
301
229
63
224
623
50
225
519
30
881
461
844
177
NiO
lt00
5n
an
an
alt0
05
na
na
na
na
na
na
na
CaO
035
034
036
033
033
036
035
036
045
053
054
055
Na 2
Olt0
02
lt00
2lt0
02
lt00
2lt0
02
lt00
2lt0
02
lt00
20
02lt0
02
lt00
2lt0
02
Tota
l99
65
992
299
85
100
0310
016
989
099
37
100
2210
012
997
199
65
995
5
Cat
ion
ratio
sFa
406
387
380
386
514
490
511
571
787
884
796
950
Fo59
461
362
061
448
751
048
942
921
111
620
44
5
Stoi
chio
met
ry b
ased
on
4 ox
ygen
ato
ms
Si IV
099
90
998
098
90
997
099
50
992
099
01
003
099
50
995
099
40
996
Al V
I0
001
000
30
001
000
10
000
000
00
002
000
00
000
000
00
000
000
0Ti
VI
000
10
001
000
10
001
000
10
001
000
10
002
000
30
013
000
20
009
Cr
000
50
005
000
50
005
000
40
004
000
30
001
000
20
002
000
10
000
Fe+2
080
10
764
075
60
762
101
60
973
101
61
122
155
41
719
156
91
864
Mn+2
000
80
009
000
80
008
001
20
010
001
00
012
001
70
020
001
60
018
Mg
117
11
208
123
61
214
096
21
014
097
40
842
041
60
225
040
10
089
Ca
001
10
010
001
10
010
001
00
011
001
10
011
001
50
018
001
90
020
Na
000
00
000
000
00
000
000
00
000
000
10
000
000
10
000
000
00
000
Tet s
ite0
999
099
80
989
099
70
995
099
20
990
100
30
995
099
50
994
099
6O
ct si
te1
998
199
92
019
200
12
006
201
42
017
199
12
007
199
62
009
199
9N
= n
umbe
r of a
naly
ses i
n th
e av
erag
e t-
rim =
typi
cal r
im x
-rim
= e
xtre
me
rim f
ay s
ymp
= fa
yalit
e sy
mpl
ectit
e n
a =
not
ana
lyze
d
1078 R Zeigler et al Ta
ble
3 A
vera
ge a
nd re
pres
enta
tive
pyro
xene
com
posi
tions
in th
e LA
P ba
salti
c m
eteo
rites
LA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
P02
205
0222
602
224
0243
602
205
0222
602
224
0243
602
205
0243
602
205
pig
cor
epi
g c
ore
pig
cor
epi
g c
ore
aug
cor
eau
g c
ore
aug
cor
eau
g c
ore
hd
hd
pyxf
er
N23
1417
168
2014
111
11
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
516
751
94
520
751
83
495
149
27
494
649
51
456
045
91
439
7Ti
O2
056
051
053
056
135
135
130
134
139
185
112
Al 2O
31
331
201
321
363
173
333
243
281
842
051
73C
r 2O
30
590
540
580
540
971
010
940
98lt0
02
lt00
2lt0
02
FeO
198
419
47
191
619
83
138
613
21
133
213
77
312
130
66
471
8M
nO0
360
350
360
350
250
250
260
270
320
330
59M
gO18
81
192
019
63
185
213
47
138
114
05
138
00
480
330
04C
aO6
396
496
386
8216
81
169
616
74
165
817
88
183
73
53N
a 2O
lt00
20
030
030
020
050
050
060
05lt0
02
lt00
20
02To
tal
995
799
73
100
199
82
994
499
23
993
599
57
987
399
51
981
7
Cat
ion
ratio
sM
gprime62
863
764
662
563
465
165
364
12
61
90
1Fs
317
310
304
316
249
237
237
246
582
580
871
En53
614
614
215
743
132
131
731
340
240
90
1W
o14
754
455
452
632
044
244
644
01
61
112
8
Stoi
chio
met
ry b
ased
on
6 o
xyge
n at
oms
Si IV
194
91
953
194
81
952
188
31
874
187
81
879
191
61
908
193
3A
l IV
005
10
047
005
20
048
011
70
126
012
20
121
008
40
092
006
6Ti
IV0
000
000
00
000
000
00
000
000
00
000
000
00
000
000
00
000
Al V
I0
009
000
60
006
001
20
026
002
30
023
002
60
007
000
80
009
Ti V
I0
016
001
40
015
001
60
038
003
90
037
003
80
044
005
80
054
Cr
001
80
016
001
70
016
002
90
030
002
80
029
000
00
000
000
0Fe
+20
626
061
20
599
062
40
441
042
00
423
043
71
097
106
61
734
Mn+2
001
10
011
001
10
011
000
80
008
000
80
009
001
10
012
002
2M
g1
058
107
61
094
103
90
764
078
30
795
078
10
030
002
10
002
Ca
025
80
261
025
60
275
068
50
691
068
10
674
080
50
818
016
6N
a0
001
000
20
002
000
10
003
000
40
004
000
40
001
000
10
002
Tet s
ite2
000
200
02
000
200
02
000
200
02
000
200
02
000
200
01
999
Oct
site
199
71
999
200
11
995
199
51
999
200
11
997
199
51
983
198
9A
ugite
(aug
) co
res h
ave
an M
gprime gt
60 a
nd W
o gt3
0 w
hile
pig
eoni
te (p
ig)
core
s hav
e M
gprime gt
60 a
nd W
o lt1
8 H
d =
hed
enbe
rgite
pyx
fer
= py
roxf
erro
ite
Mgprime
= M
g(M
g +
Fe)
100
N =
num
ber o
f ana
lyse
s
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1079
All of the LAP stones have relatively coarse-grained (upto approximately 15 mm) subophitic texture They consistpredominantly of pyroxene and plagioclase with minoramounts of olivine ilmenite and a groundmass dominated byfayalite and cristobalite They contain trace amounts ofchromite chromian ulvˆspinel ulvˆspinel troilite Fe-metalbarian K-feldspar fluor-apatite RE-merrillite tranquillityite(Fe8(YZr)2Ti3Si3O24) and baddeleyite (ZrO2) The modalmineral proportions differ slightly from section to section(Table 9) A few veins and pockets of basaltic glass ofpseudo-whole rock composition (likely shock melted) alsooccur in thin sections LAP 0220533 and LAP 0222424 Theorder in which minerals are inferred to have crystallized ischromite olivine pyroxene plagioclase and groundmass
Olivine grains vary in size from 003 to sim1 mm with01 to 03 mm being typical The modal abundance of olivineranges from 23 to 36 The grains are usually anhedral(rarely subhedral Fig 2a) typically with round or irregularmorphology and uneven contact with the surroundingpyroxene (Fig 2b) Some olivine grains have inclusions ofchromite or Cr-ulvˆspinel grains or both and a few haveldquomeltrdquo inclusions that have two phases in them mafic glasswith a pyroxene-like composition (sim10 wt Al2O3 Table 6)and K-rich high-silica glass similar to the glass seen in thefayalite symplectite grains in the groundmass (sim3 wt K2O68 wt SiO2) Most of the larger olivine grains are zonedwith cores of Fo55ndash65 and rims typically in the Fo38ndash45 range(Fig 3a Table 2) though in a few instances zoning to rims ofFosim20 is observed (Fig 3b) Most of the smaller olivine grainsare not zoned (or not strongly zoned) and they typically havecompositions in the Fo52ndash57 range with the smallest grainshaving the most magnesian compositions The apparentreaction texture between olivine and pyroxene and therelatively magnesian rims on compositions of the smallestolivine grains (likely the remnant cores of grains that havebeen almost completely resorbed) are strong indications thatolivine was being resorbed when the rock solidified
Chromite and Cr-ulvˆspinel grains almost always occuras inclusions within or closely associated with olivine grainsThey also have relatively restricted compositional ranges(Fig 4 Table 4) and they occur individually and as compositegrains with cores of chromite (Chr62ndash68Usp13ndash18Spn16ndash25) andrims of Cr ulvˆspinel (Chr6ndash19Usp71ndash91Spn3ndash11) (Figs 5aand 5b) We found few spinel compositions intermediate tothese end members The total modal abundance of spinel(including ulvˆspinel in the groundmass) is small rangingfrom 03 to 04 Where these two phases are intergrown theboundary between them is sharp with differences in Cr2O3concentration exceeding 20 wt within a few micrometers ofthe boundary A few of the chromite grains have inclusionsof pyroxene with a range of compositions (Mgprime of 47ndash59Wo16ndash31 and TiO2 concentrations from 11ndash24 wt)
Pyroxene grains in LAP are anhedral display undulatoryto mosaic extinction and range in size up to sim1 mm (Fig 2c)
In many cases pyroxene grains partially enclose plagioclasegrains in a subophitic texture The modal abundance ofpyroxene ranges from 47 to 52 The pyroxene grains havemagnesian cores of pigeonite and subcalcic augite (Mgprime fromsim50 to 68) with a wide range of CaO concentrations (Wo11 toWo36 Table 3 Fig 6) although there appears to be a bimodaldistribution of Wo contents with a minimum near Wo20(Fig 6 insets) In some cases pyroxene core compositionsgrade continuously to nearly end member hedenbergite(Fs58Wo40) and pyroxferroite (Fs86Wo13) In a few rare casescontacts between magnesian and ferroan pyroxenes are sharpand linear Compositions of pyroxene grains in contact withpartially resorbed olivine grains vary considerably incomposition The most common composition issubcalcic augite (Wo gt 20) with FeO concentrations in therange Fs24ndash49
The TiAl and TiCr ratios in the LAP pyroxenes arestrongly correlated with Mgprime as expected according toelement compatibility (eg Bence and Papike 1972) Theatomic TiCr ratio increases with decreasing Mgprime in LAPpyroxenes (Fig 7a) This reflects the compatible behavior ofCr and the incompatible behavior of Ti in early crystallizingphases of low-Ti lunar basaltic magmas The most magnesianpyroxenes have atomic TiAl ratios very close to 14indicating that aluminum was introduced through boththe Tschermak (AlAlMgminus1Siminus1) and coupled titanium(TiAl2Mgminus1Siminus2) exchange reactions in approximately equalproportions (Thompson 1982) As pyroxene becomesprogressively more ferroan the TiAl cation ratio approaches12 suggesting a gradual increase in the proportion of Alincorporated due to coupled Ti substitution (Fig 7b) Theleast magnesian pyroxenes (Mgprime lt40) have TiAl ratiosapproaching 34 An increase in TiAl ratios in pyroxene from14 to 12 with decreasing Mgprime in lunar basalts has previouslybeen interpreted as a result of pyroxene crystallization bothprior to the onset of plagioclase crystallization (ratiosaround 14) and during plagioclase crystallization (14ndash12Bence and Papike 1972) Bence and Papike (1972) attributedthe high relative concentrations of Ti in the late-stage Fe-richlunar pyroxenes to Ti3+
Plagioclase forms elongated subhedral to anhedralgrains up to 175 mm long The modal abundance ofplagioclase ranges from 32 to 35 Pyroxene inclusions ofa variety of sizes with compositions spanning nearly theentire compositional spectrum observed occur withinplagioclase Most plagioclase grains are highly fracturedalthough some or portions of some are smooth in polishedsections as seen in the BSE images (Fig 2d) These smoothareas consist partially or entirely of maskelynite as indicatedby their isotropic (or nearly isotropic) character in cross-polarized light Plagioclase grains are complexly zoned Theirtypical core composition is An886Ab11Or04 with sim1 wtFeO + MgO and an Mgprime of 34 (Fig 8 Table 5) Their rims areas wide as sim40 microm and gradually increase in K (up to simOr5)
1080 R Zeigler et al
and FeO (up to sim3 wt) while decreasing in MgO(to lt002 wt Fig 9) The Na2O concentrations firstincrease up to simAb14 then decrease sharply to less thanAb10 (which is lower than in the cores) The extreme rimcomposition of the large plagioclase grains is similar to that ofthe plagioclase found as inclusions in groundmass fayaliteand cristobalite grains (next paragraph Table 5) There is noapparent overall compositional difference between the coresof the maskelynite and the plagioclase grains
Fayalite cristobalite and ilmenite are the dominantminerals in the groundmass typically occurring togetheralthough each can be found independently All of the phaseshave relatively minor modal abundances fayalite (29ndash48)cristobalite (18ndash21) and ilmenite (35ndash40) Silicadisplaying the ldquocracklerdquo pattern distinctive to cristobaliteoccurs as anhedral grains up to 05 mm in size Thecristobalite grains contain minor Al2O3 TiO2 FeO and CaO(Σ sim13 wt Table 6) Inclusions of late-crystallizing phasessuch as K-rich plagioclase K-rich glass K-feldspar fayaliteFe-rich pyroxene phosphate and mafic glass withhigh concentrations of incompatible elements are common(Fig 5c) Fayalite grains (Fo45 sim05 wt CaO) range in size
up to 075 mm and usually form a symplectite texture withinclusions of K-rich glass silica K-rich plagioclase andilmenite (Fig 5d) Fayalite with no (or few) inclusions occursonly rarely Ilmenite is the dominant oxide in the groundmassforming elongate laths up to 1 mm in length Typically theilmenite is poor in Mg (sim02 wt average) although a singlegrain of more magnesian ilmenite associated with a largeolivine grain was observed (Fig 2b) Less common aresmaller subhedral ulvˆspinel grains (lt005 mm) thathave compositions approaching end member ulvˆspinel(Chr0ndash4Usp93ndash98Sp2ndash3) A few composite grains of ilmeniteand ulvˆspinel were observed
Also found in the groundmass are a variety of traceminerals including both fluorapatite and RE-merrillite(Table 7) Phosphate grains most commonly occur betweenplagioclase and ferropyroxene sometimes with associatedcristobalite troilite or both Barian K-feldspar (sim5 wt BaO)also occurs in the groundmass usually in the same areas asthe phosphate minerals (Table 5) Only a few K-feldspargrains (the largest) have stoichiometry that unambiguouslyidentifies them as K-feldspar while many K-rich grainshave excess Si suggesting that they may be intergrowths of
Table 4 Average oxide compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02205 02226 02224 02436 02205 02226 02224 02436 02205 02226 02224Al Al Al Al Cr-rich Cr-rich Cr-rich Cr-rich CrAl CrAl CrAlchr chr chr chr usp usp usp usp usp usp usp
N 23 11 13 5 22 1600 7 13 9 22 10
Major elements in wt by EMPAFeO 3444 3503 3532 3433 5705 5832 5846 5868 6191 6198 6180TiO2 546 532 540 517 2833 2871 2892 2909 3254 3151 3161Cr2O3 4384 4357 4331 4391 928 840 851 776 234 310 338Al2O3 1142 1178 1140 1217 287 261 261 276 191 204 203MgO 283 242 218 292 093 061 069 065 021 028 031MnO 027 024 025 027 035 032 034 033 036 032 034V2O3 073 074 076 075 036 031 033 033 022 025 026SiO2 007 009 008 009 lt002 007 008 018 lt002 008 007CaO 004 004 003 lt002 010 005 006 011 008 007 005ZnO 003 na na na 004 na na na 003 na naTotals 991 992 987 996 993 994 1000 999 996 996 999
Stoichiometry based on 4 (spinel) and 3 (ilmenite) oxygen atomsSi IV 0003 0003 0003 0003 0000 0003 0003 0006 0000 0003 0003Al VI 0469 0484 0472 0496 0125 0114 0113 0119 0083 0089 0088Ti 0143 0139 0143 0134 0784 0798 0798 0803 0907 0880 0880V 0020 0021 0021 0021 0011 0009 0010 0010 0007 0007 0008Cr 1208 1201 1204 1199 0270 0245 0247 0225 0068 0091 0099Fe2+ 1004 1021 1039 0992 1756 1802 1794 1801 1920 1925 1913Mn2+ 0008 0007 0007 0008 0011 0010 0011 0010 0011 0010 0011Mg 0147 0126 0114 0151 0051 0034 0038 0035 0012 0016 0017Zn 0001 minus minus minus 0001 minus minus minus 0001 minus minusCa 0002 0002 0001 0000 0004 0002 0002 0004 0003 0003 0002Sum 2+ 1162 1156 1161 1151 1823 1847 1844 1851 1947 1953 1942Sum 3 4+ 1844 1849 1844 1854 1190 1168 1170 1163 1066 1071 1078Total 3003 3001 3002 3001 3012 3013 3012 3007 3013 3020 3017
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1081
K-feldspar and silica (granophyric texture) at a scale smallenough to be beyond the resolution of the electron microprobe(less than sim01 microm)
Two glass types of distinct composition presumably late-stage residual liquids occur in the groundmass The first is aKSi-rich glass (78 wt SiO2 sim56 wt K2O) that makes upa considerable percentage of the inclusions in the cristobaliteand particularly the fayalite grains The second type ofevolved glass occurs as very small (lt5 microm) roundedinclusions in cristobalite grains This glass has a silica-poorFe-rich bulk composition (sim36 wt SiO2 sim39 wt FeOTable 6) but it is also considerably enriched in manyincompatible elements 23 wt P2O5 12 wt SO3 02 wtY2O3) Commonly we observed minute grains of fayalitetroilite or phosphate associated with this glass These twolate-stage glasses could represent conjugate liquids producedby late-stage immiscibility of an evolved residual meltSimilar glasses were observed in some plutonic rocks fromthe Apollo 14 site (Jolliff et al 1991)
Troilite blebs (with nearly ideal stoichiometry Table 8)are scattered throughout the groundmass along with trace Fe-metal grains which are usually intergrown with troilite orovergrown on chromite grains These grains typicallycontained 66 wt Ni and 14 wt Co though one grain had338 wt Ni and 60 wt Co (Table 8) A few grains ofbaddelyite (ZrO2) and tranquillityite (Zr-Fe-Ti silicate) wereidentified by energy-dispersive spectroscopy (EDS) in thegroundmass
A variety of shock effects occur in the minerals of thesethin sections (eg plagioclase converted to maskelynitemosaicism in the pyroxene) The level of shock was such thatlocalized partial melting occurred in some areas of themeteorite The areas of shock melt have severalmorphologies small melt pockets (LAP 02205 Fig 10a)veins of melt (LAP 0222424 Fig 10b) and in some casesareas that were only partially melted (LAP 0222424Fig 10c) with discernable mineral grains still present(typically maskelynite) Although veins of shock melt are rare
Table 4 Continued Average oxide compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02436 02205 02226 02224 02436 02205 02226 02224 02436 02205CrAl end end end end Mgusp usp usp usp usp ilm ilm ilm ilm ilm
N 11 11 2 3 3 24 16 20 18 2
Major elements in wt by EMPAFeO 6202 6375 6445 6355 6465 4657 4647 4634 4624 4463TiO2 3353 3267 3226 3396 3231 5198 5226 5233 5264 5296Cr2O3 209 026 023 011 037 010 012 015 016 038Al2O3 202 179 206 216 227 008 011 013 010 006MgO 022 005 008 007 003 014 010 016 019 150MnO 034 031 027 029 027 038 033 037 027 035V2O3 023 018 015 019 016 031 029 029 028 035SiO2 015 lt002 011 010 007 003 003 024 004 lt002CaO 007 010 007 008 010 013 006 010 009 008ZnO na 008 na na na 003 na na na lt002Totals 1007 992 997 1005 1002 997 998 1001 1000 1003
Stoichiometry based on 4 (spinel) and 3 (ilmenite) oxygen atomsSi IV 0005 0001 0004 0004 0003 0001 0001 0006 0001 0000Al VI 0087 0079 0091 0093 0099 0002 0003 0004 0003 0002Ti 0920 0921 0906 0937 0901 0990 0993 0989 0996 0991V 0007 0005 0004 0006 0005 0006 0006 0006 0006 0007Cr 0060 0008 0007 0003 0011 0002 0002 0003 0003 0007Fe2+ 1893 1999 2012 1950 2005 0986 0982 0974 0973 0928Mn2+ 0010 0010 0009 0009 0009 0008 0007 0008 0006 0007Mg 0012 0003 0004 0004 0002 0005 0004 0006 0007 0056Zn minus 0002 minus minus minus 0001 minus minus minus 0000Ca 0003 0004 0003 0003 0004 0004 0002 0003 0002 0002Sum 2+ 1918 2018 2028 1966 2019 1004 0995 0991 0988 0994Sum 3 4+ 1080 1014 1012 1043 1019 1001 1005 1008 1009 1007Total 2992 3032 3035 3005 3036 2004 2000 1992 1996 2001The spinel catagories where chosen based primarily on Cr2O3 content with Al chromite (chr) having gt40 wt Cr2O3 Cr-rich ulvˆspinel (usp) having 15ndash
5 wt Cr2O3 CrAl ulvˆspinel having 5ndash05 wt Cr2O3 and endmember ulvospinel having lt05 wt Cr2O3 Also seen were TiAl chromite (30ndash40 wtCr2O3) and high-Cr ulvˆspinel (30ndash15 wt Cr2O3) which are likely the result of an anlyses overlapping simultaneously on both an Al chromite and Cr-rich ulvˆspinel grain Similarly compositions intermediate to ilmenite and end ulvˆspinel were seen These compositions are not listed in this table but areshown in Fig 4 N = number of analyses in the average na = not analyzed
1082 R Zeigler et al
in our thin sections such veins were reported as pervasive inthe original macroscopic description of all five LAP stones(McBride et al 2003 2004a 2004b)
The various shock-induced effects observed in LAP canbe used to quantify and constrain the level of shock that LAPexperienced The presence of both plagioclase andmaskelynite in these samples suggests that the lower end ofthe range listed for conversion of plagioclase to maskelynite(30ndash45 GPa Stˆffler and Hornemann 1972 Ostertag 1983)is appropriate The mosaicism seen in the pyroxene istypically associated with shock values in the 30ndash75 GParange (Kieffer et al 1976 Schaal et al 1979) The presenceof shock-melt veins that have melted both pyroxene andplagioclase (based on the melt composition Table 6)indicates LAP should have been subjected to shock levels ofgt75ndash80 GPa (Kieffer et al 1976 Schaal et al 1979) Thedifferent shock effects observed reflect a range fromlt30 GPa (areas were plagioclase is preserved) to gt75 GPa(areas where shock melting occurred) over distances of onlya few millimeters
Bulk Composition and Comparison to Other LunarBasalts
LAP is a moderately aluminous (sim10 wt Al2O3) low-Ti(31 wt TiO2) mare basalt that falls near the Fe-rich(222 wt FeO) end of the range of FeO concentrationsobserved among lunar basalts It is more ferroan (Mgprime = 347)than any basalt in the Apollo or Luna collection (Fig 11a)Among lunar basalts only meteorites Asuka-881757 andYamato-793169 have comparably low Mgprime values (Koeberlet al 1993 Warren and Kallemeyn 1993 Thalmann et al1996 Korotev et al 2003a) LAP is enriched in Na2O(038 wt) relative to other ferroan (eg Asuka-881757 andYamato-793169) and Fe-rich basalts except for NWA 032(Fig 11b)
Regarding trace elements LAP is enriched in Cocompared to most lunar mare basalts with comparable Scconcentrations (Table 1 Fig 12a) Among Apollo and Lunabasalts only the Apollo 12 ilmenite basalts (Rhodes et al1977 Neal et al 1994) are comparable Incompatible trace-
Table 5 Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02205 02226 02224 02436 02205 02226 02224 02436 02205 02226plag plag plag plag mask mask mask mask plag plagcore core core core core core core core Na rim Na rim
N 123 86 48 88 29 49 33 32 12 3
Major elements in wt by EMPASiO2 4715 4657 4689 4639 4753 4741 4663 4673 4949 4960TiO2 010 007 007 006 013 008 006 006 027 019Al2O3 3337 3367 3296 3363 3367 3291 3376 3415 3170 3103Cr2O3 003 lt002 lt002 002 007 002 lt002 002 004 003FeO 068 067 073 058 060 111 066 060 134 136MgO 023 022 017 024 027 029 028 029 008 012CaO 1730 1746 1709 1763 1747 1726 1730 1740 1628 1597BaO na na na na na na na na na naNa2O 120 123 136 121 119 123 131 128 148 153K2O 006 007 010 006 005 009 006 005 020 019Total 1000 1000 994 998 1008 1004 1001 1006 1006 1000
Cation ratiosAn 885 883 869 887 888 881 877 880 848 842Or 04 04 06 04 03 05 03 03 12 12Ab 111 112 125 110 109 113 120 117 140 146Cn 00 00 00 00 00 00 00 00 00 00
Stoichiometry based on 8 oxygen atomsSi IV 2168 2147 2173 2143 2168 2179 2147 2140 2259 2279Al IV 1809 1830 1801 1831 1810 1782 1832 1843 1705 1681Fe+2 0026 0026 0028 0023 0023 0043 0025 0023 0051 0052Mg 0016 0015 0011 0017 0019 0020 0019 0020 0005 0008Ca 0853 0863 0849 0872 0854 0850 0853 0854 0796 0786Ba minus minus minus minus minus minus minus minus minus minusNa 0107 0110 0122 0108 0105 0109 0117 0114 0131 0136K 0004 0004 0006 0004 0003 0005 0003 0003 0011 0011Tet site 3977 3977 3974 3974 3978 3961 3979 3984 3964 3960Oct site 1005 1018 1022 1023 1003 1027 1022 1013 0995 0994
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1083
element concentrations are considerably greater in LAP thanin most of other low-Ti basalts (Fig 12bndashc) including theApollo 12 ilmenite basalts (Haskin et al 1971 Neal et al1994) The exceptions are NWA 032 the high-Al basalts ofLuna 16 (Philpotts et al 1972 Helmke and Haskin 1972 Maet al 1979) and some Apollo 14 high-Al basalts (Dickinsonet al 1985 Shervais et al 1985 Neal et al 1989a 1989b)
Relative concentrations of REEs in the LAP basalt arealso dissimilar to those of most other lunar basalts (Fig 13) inthat LAP is enriched in light REEs The exceptions are NWA032 which has a pattern nearly parallel to LAP and Apollo 14group 3 basalts (Dickinson et al 1985) which have a patternthat is similar although somewhat less steep in the heavyREEs Ratios of Th to REE in LAP are higher than those of allother lunar basalts except NWA 032 (Fig 14) and thedisparity in ThREE ratio between LAP and other lunarbasalts (except NWA 032) increases from the light to heavyREEs The Apollo 14 high-K basalts have similar ThREEratios for the middle REE Sm-Tb however (Neal et al 1989a
1989b) Overall in terms of its trace-element concentrationsLAP 02205 is most similar to NWA 032 The maindifferences are that NWA 032 is richer in elements associatedwith olivine (Mg Cr Co) and has concentrations ofincompatible elements that are 78ndash91 as great as those inLAP 02205
DISCUSSION
Evidence Supporting the Lunar Origin and Pairing of theLAP Stones
As stated in the introduction the meteorites LAP 0220502224 02226 02436 and 03632 were identified as lunarbasalts that were almost certainly paired (McBride et al 20032004a 2004b) A brief summary follows of the attributesfound in our more detailed petrographic examination thatsupport this initial classification and pairing interpretation
Results of oxygen isotope analyses (δ18O = +56 and
Table 5 Continued Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02224 02436 02205 02205 02226 02224 02436 02205 02205 02205plag plag plag plag plag plag plag barian KBa KBaNa rim Na rim matrix K rim K rim K rim K rim K-spar glass glass
N 24 5 13 10 1 5 1 10 10 23
Major elements in wt by EMPASiO2 4901 4879 5122 5152 4888 4935 5017 6026 5935 6356TiO2 008 008 016 017 lt002 008 014 na na naAl2O3 3163 3120 2960 2993 3213 3004 3002 2019 2063 2043Cr2O3 002 002 006 005 lt002 003 lt002 na na naFeO 117 130 267 192 147 195 173 065 074 116MgO 006 009 003 002 lt002 lt002 002 lt002 lt002 010CaO 1620 1622 1520 1549 1618 1602 1560 063 066 207BaO na na na na na na na 501 407 372Na2O 157 155 105 105 132 126 150 031 029 033K2O 023 021 090 067 067 056 086 1354 1162 586Total 1000 995 1007 1006 1007 993 1000 1008 1006 1007
Cation ratiosAn 839 842 846 852 835 845 807 33 minus minusOr 14 13 61 44 41 35 53 842 minus minusAb 147 145 105 104 124 120 140 30 minus minusCn 00 00 00 00 00 00 00 96 minus minus
Stoichiometry based on 8 oxygen atomsSi IV 2253 2257 2342 2344 2237 2293 2312 2863 2864 2951Al IV 1714 1701 1596 1609 1732 1645 1631 1131 1173 1124Fe+2 0045 0050 0102 0073 0056 0076 0067 0026 0030 0045Mg 0004 0006 0002 0001 0000 0001 0001 0001 0001 0007Ca 0798 0804 0745 0757 0793 0798 0770 0032 0034 0100Ba minus minus minus minus minus minus minus 0093 0077 0070Na 0140 0139 0093 0093 0117 0113 0134 0029 0027 0029K 0013 0013 0052 0039 0039 0033 0050 0820 0715 0353Tet site 3967 3957 3938 3954 3969 3938 3943 3994 4037 4075Oct site 0013 1011 0995 0963 1007 1020 1022 1002 0884 0604Plag = plagioclase mask = maskelynite N = number of analyses in the average na = not analyzed
1084 R Zeigler et al Ta
ble
6 A
vera
ge a
nd re
pres
enta
tive
cris
toba
lite
and
glas
s co
mpo
sitio
n in
the
LAP
basa
ltic
met
eorit
es
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
0220
502
226
0222
402
436
0220
502
205
0220
502
205
0220
502
224
0222
4cr
isto
balit
ecr
isto
balit
ecr
isto
balit
ecr
isto
balit
eSi
-ric
hpy
x-lik
eK
gla
ssIT
E-ric
hsh
ock
shoc
ksh
ock
MI g
lass
MI g
lass
in s
ympl
m
afic
gla
ssgl
ass
area
glas
s ar
eagl
ass
vein
N6
25
44
12
51
6515
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
979
598
17
984
798
45
672
542
76
783
236
67
463
486
441
TiO
20
270
270
230
230
664
810
374
032
341
623
13A
l 2O3
073
060
064
078
187
99
4210
13
544
139
86
123
Cr 2
O3
002
lt00
2lt0
02
002
lt00
20
13lt0
02
lt00
20
080
380
28Fe
O0
210
400
190
171
8615
91
183
392
719
618
520
5M
nOn
an
an
an
an
a0
22n
a0
420
220
290
25M
gO0
02lt0
02
lt00
2lt0
02
033
817
lt00
20
213
459
857
17C
aO0
190
200
200
236
8919
16
098
976
127
118
114
BaO
na
na
na
na
117
na
na
na
na
na
na
Na 2
O0
130
100
090
120
620
110
190
060
510
360
49K
2O0
030
050
07lt0
02
167
na
566
030
005
na
na
P 2O
5n
an
an
an
an
an
an
a2
32n
an
an
aF
na
na
na
na
na
na
na
008
na
na
na
Y2O
3n
an
an
an
an
an
an
a0
19n
an
an
aC
e 2O
3n
an
an
an
an
an
an
a0
12n
an
an
aSO
3n
an
an
an
an
an
an
a1
23n
an
an
aTo
tal
995
599
80
999
010
00
992
410
070
974
910
02
991
100
099
6Sy
mpl
= sy
mpl
ectit
e M
I = m
elt i
nclu
sion
N =
num
ber o
f ana
lyse
s in
the
aver
age
na
= n
ot a
naly
zed
The
shoc
ked
glas
s in
LAP
0222
4 is
the
parti
ally
mel
ted
area
(see
Fig
14)
and
onl
y th
e an
ayls
es o
fth
e gl
ass i
tsel
f wer
e in
clud
ed in
the
aver
age
not t
he m
iner
als t
hat w
ere
anal
yzed
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1085
Table 7 Representative phosphate compositions in LAP 0220533LAP LAP LAP LAP LAP LAP LAP LAP02205 02205 02205 02205 02205 02205 02205 02205RE- RE- RE- RE- RE- fluorapatite fluorapatite fluorapatitemerrillite merrillite merrillite merrillite merrillite
Major elements in wt by EMPASiO2 050 044 062 037 321 228 449 137Al2O3 022 lt005 009 lt005 lt005 007 014 lt005FeO 637 774 568 576 250 169 439 202MgO 020 037 025 028 lt005 lt005 lt005 lt005CaO 4326 4035 4233 4245 4983 5241 5003 5351Na2O 000 001 010 014 000 000 001 000P2O5 3885 4171 4382 4360 3540 3949 3771 4077Cl lt005 lt005 lt005 lt005 lt005 006 027 031F 047 044 050 048 168 245 130 186Y2O3 298 293 226 221 172 103 078 053La2O3 093 107 065 064 092 024 014 012Ce2O3 253 259 189 185 253 072 069 053Nd2O3 161 177 108 118 166 057 059 031Sm2O3 043 043 029 028 048 022 015 009Gd2O3 087 090 058 058 079 023 018 008Yb2O3 016 032 009 lt005 010 005 lt005 lt005ThO2 007 009 008 lt005 021 lt005 lt005 lt005minusO = (FCl) 021 020 022 021 072 105 061 085Sums 9930 1010 1001 9968 1004 1005 1003 1006
Table 8 Average sulfide and metal compositions in LAP 0220533Ave Fe metal High-Ni metal Troilite
N 5 1 8
Elemental percentage by EMPAFe 9209 5880 6280Ni 664 3377 lt002Co 141 595 lt002Ti 023 009 006Cr 043 017 lt002Mn lt002 004 lt002S lt002 lt002 3620Totals 1008 988 994Ideal troilite = 365 wt S 635 wt Fe N = number of analyses
Table 9 Modal mineralogy of the different LAP stonesLAP 0220533 LAP 0222616 LAP 0222424 LAP 0243614
Pyroxene 515 505 469 466Plagioclase 319 321 323 346Ilmenite 348 391 386 399Fay sympl 309 290 358 483Olivine 233 271 363 320Cristobalite 214 209 178 200Spinel (all) 034 045 040 039Troilite 025 024 024 022Fractures 49 49 53 421Shock glass 01 02 22 00N 633 times 106 905 times 106 470 times 106 396 times 106
All modal values are listed as percentages N = number of pixels
1086 R Zeigler et al
Fig 1 Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) and fayalite(more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phases arepyroxene and olivine a) LAP 0222616 b) LAP 0243614 c) LAP 0222424 d) LAP 0220533
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1087
δ17O = +27) performed by Mayeda and Clayton (reported inMcBride et al 2003) constrain the origin of LAP 02205 tothe Earth the Moon or an enstatite meteorite parent bodyLAP is clearly a meteorite all four of the stones have fusioncrusts (ruling out a terrestrial origin) The extremely ferroannature of LAP rules out the enstatite parent body as theprovenance FeOMnO ratios of mafic silicates arediagnostic of origins from different planetary bodies in thesolar system (Dymek et al 1976 Papike 1998) Ratios ofFeOMnO in LAP pyroxenes (average sim60) and olivines(average sim95) are consistent only with lunar origin (Fig 15)Furthermore the presence of Fe(Ni) metal and troilite thecompletely anhydrous nature of the sample the apparentlack of Fe3+ in all phases the calcic nature of theplagioclase and the deep negative Eu anomaly are allcommon in lunar basalts
With regard to texture mineral assemblage and mineralchemistry the four LAP 02xxx stones appear to beindistinguishable from each other Although we did not studythe mineral chemistry of the LAP 03632 in depth the textureand mineral assemblage are identical to the LAP 02xxxstones Furthermore the collection locations of the five stonesform a linear array sim3 km in length that is perpendicular to theflow of the ice sheet (John Schutt personal communication)Thus in the absence of cosmic-ray exposure data to thecontrary we conclude that the four LAP 02xxx stones studiedare paired
Compositional Variability among Small Subsamples ofLAP 02205 and NWA 032
Samples of lunar meteorites available for study at most afew hundred milligrams are very small by the standards ofterrestrial geology and geochemistry Nevertheless we havetaken our samples and subdivided them into numerous evensmaller (10ndash50 mg) subsamples for bulk compositionalanalysis (Korotev et al 1983 1996 2003a 2003b Jolliffet al 1991 1998 Fagan et al 2002) This procedure providesan estimate of the whole-rock composition through a mass-weighted mean that is equivalent to a single analysis of theentire mass of the allocated sample The variation amongsmall subsamples however provides additional informationabout compositional variations associated with mineralassemblage and proportions about petrogenesis and aboutpossible relationships to other meteorites (eg Korotev et al2003a 2003b) and how well the ldquowhole-rockrdquo compositionis likely to represent that of the source region of the meteorite(Korotev et al 2000a) In the following discussion weevaluate the causes of differences in composition amongsmall subsamples of LAP and NWA 032
The range of concentrations among the 19 subsamples ofLAP (27ndash40 mg) is relatively small for the most preciselydetermined major elements (SiO2 TiO2 Al2O3 FeO CaONa2O) and most precisely determined trace elements that arecompatible with the major mineral phases (Co Sc Eu) The
Fig 1 Continued Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) andfayalite (more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phasesare pyroxene and olivine d) LAP 0220533
1088 R Zeigler et al
relative sample standard deviations (s ) range from 08 to76 (with only Co and Eu gt 5 Table 1) The exceptionsare MgO and Cr2O3 for which the relative standarddeviations are distinctly greater 12 and 16 respectivelyFor incompatible elements that we determined precisely(lt9 analytical uncertainty La Ce Sm Tb Yb Lu Hf Taand Th) relative standard deviations range from 7 to 11These variations are caused by a combination ofunrepresentative sampling of the major mineral phasesowing to the coarse grain size (up to sim1 mm3) relative to theINAA subsample size (about 12 mm3 assuming that thedensity of LAP is sim35 gmm3) and to the heterogeneousdistribution of some relatively minor phases with high
concentrations of a given element This problem is not new asmany investigators have previously wrestled with theproblem of studying relatively coarse-grained lunar basaltswith small allocated subsample sizes characteristic of rareextraterrestrial samples (Korotev and Haskin 1975 Haskinet al 1977 Lindstrom and Haskin 1978 Ryder and Schuraytz2001) Ryder and Schuraytz (2001) showed that sim5 g ofmaterial are needed to achieve a representative sample ofApollo 15 olivine-normative basalts which have grain sizeson the order of a millimeter or greater
Among the LAP subsamples Cr2O3 and MgOconcentrations correlate positively (R2 = 081) as a result ofthe association of chromite and Cr-ulvˆspinel with olivine
Fig 2 BSE images from LAP 0220533 a) a large round olivine (oli) grain and a smaller subhedral olivine grain (left center of the image)both surrounded by zoned pyroxene (pyx) and plagioclase (plag) with melt inclusions (MI) and inclusions of chromite (chr) A smallulvˆspinel (Usp) grain occurs in the upper left b) A large irregular olivine grain and a smaller mostly resorbed olivine grain The larger graincontains both melt inclusions (MI) and chromite grains The associated ilmenite (Ilm) grain is the most magnesian ilmenite grain observed Acomposite grain of metal and troilite (MetSulf) is also present c) A BSE image showing the zoning in multiple large pyroxene grainsintergrown with plagioclase and maskelynite (mask) grains One small cristobalite (crist) grain is also present d) A BSE image showingseveral large plagioclase grains some of which contain both fractured areas (plagioclase) and smooth areas (maskelynite) Also present areseveral areas of groundmass including a fayalite symplectite and a cristobalite grain cut by an ilmenite lath
x
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1089
The large variations seen in MgO Cr2O3 and to a lesserextent Co concentrations occur because of the large relativevariation in the fraction of modal olivine among thesubsamples Normatively the compositional rangecorresponds to minus03ndash25 olivine (one subsample has 03normative quartz) and 032ndash049 chromite The relativelysmall variations seen among concentrations of the other majorelements as well as Sc and Eu are controlled byunrepresentative sampling of the major mineral phasespyroxene (Sc Ca Fe Si) and plagioclase (Al Na Ca Si Eu)and the minor but widely distributed mineral ilmenite (Ti Fe)Trace amounts of a few minerals that are found only ingroundmass have high concentrations of incompatible traceelements relative to the concentration of those elements inthe bulk meteorite These minerals include K-feldspar (Ba)
Fig 3 a) CaO versus Mgprime (molar Mg[Mg + Fe]100) in the olivinesof the different LAP stones The compositions range from cores ofFo55ndash67 trending towards rims typically in the Fo40 range withextreme zonation to rims of Fo15ndash20 in a few cases Where analyzedthe composition of groundmass fayalite are also shown b) Anelectron microprobe traverse across a small strongly zoned olivinegrain in LAP 0220533 The grain shows zoning from a core of simFo58to a rim composition of simFo18 over sim100 microm The break in the zoning(black arrow) is centered on a fracture in the olivine grain
Fig 4 Compositions of LAP oxides plotted on the (FeMgMn)O-(CrAl)2O3-TiO2 ternary (after El Goresy et al 1971) Compositionsof endmember ilmenite (FeTiO3) ulvˆspinel (Fe2TiO4) andchromite (FeCr2O4) are labeled For a description of theclassification scheme see the footnote of Table 3 a) LAP 0220533b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1090 R Zeigler et al
RE-merrillite (P REEs Th) and baddeleyite (Zr Hf U Th)Therefore the variation in the amount of the groundmassldquophaserdquo in the different subsamples controls the ITEconcentrations in the various subsamples
For most of the major elements subsamples of NWA 032have relative standard deviations (RSD) that areinsignificantly different from those of LAP (Table 1) eventhough the average subsample size for NWA 032 (sim14 mgFagan et al 2002) was smaller than for LAP (sim34 mg) TheRSDs of MgO and Cr2O3 for NWA 032 are again highbecause it has a porphyritic texture with large phenocrysts(millimeter scale) of olivine (with chromite inclusions) andmagnesian pyroxene but a fine-grained groundmass of
plagioclase Fe-rich pyroxene ilmenite and glass keeps theRSDs of other major and incompatible trace elements low
Source Crater Pairing of LAP and NWA 032
We find the similarities in chemistry and petrographybetween LAP and NWA 032 when compared to the largeranges observed among Apollo and Luna samples to be sogreat that it is highly unlikely that two meteorites so similarcould derive from different locations Below we summarizethe similarities and differences
The textures of NWA 032 and LAP are markedlydifferent from each other NWA 032 has a porphyritic texture
Fig 5 BSE images from LAP 0220533 a) oxide grains set in and around a large olivine grain individual grains of ilmenite (Ilm) Cr-ulvˆspinel (Chr-Usp) and chromite (Chr) composite chromian ulvˆspinel-chromite (ChrUsp) grains with accompanying pyroxene andplagioclase (grey and black areas) b) A close-up of a zoned spinel grain with a chromite core and a Cr-ulvˆspinel rim c) A large cristobalite(Crist) grain with many inclusions of fayalite pyroxene (Pyx) plagioclase (Plag) troilite (Sulf) phosphate K-rich glass and the ITE-richglass Also present are several areas of fayalite symplectite (Fay Symp) with inclusions of plagioclase silica ilmenite troilite and K-richglass d) A BSE image of a different area of groundmass showing a large grain of fayalite symplectite containing inclusions of plagioclasesilica ilmenite troilite K-rich glass and Fe-rich pyroxene A large ilmenite (Ilm) grain cuts through the symplectite and several large troilitegrains are also present
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1077Ta
ble
2 A
vera
ge a
nd re
pres
enta
tive
oliv
ine
com
posi
tions
in th
e LA
P ba
salti
c m
eteo
rites
LA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
P02
205
0222
602
224
0243
602
205
0222
602
224
0243
602
205
0222
402
436
0220
5co
reco
reco
reco
ret-r
imt-r
imt-r
imt-r
imx-
rimx-
rimx-
rimfa
y s
ymp
N40
2463
2942
1710
54
12
2
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
359
236
01
359
036
28
345
434
24
340
934
21
314
030
43
311
529
72
TiO
20
040
040
040
040
060
060
040
080
110
520
100
34A
l 2O3
003
009
002
003
lt00
2lt0
02
005
lt00
2lt0
02
lt00
2lt0
02
lt00
2C
r 2O
30
240
210
230
220
170
160
110
060
070
060
03lt0
02
FeO
344
432
92
328
233
14
420
640
15
417
545
70
586
362
85
587
966
50
MnO
033
036
035
036
047
041
042
050
063
071
058
065
MgO
282
629
24
301
229
63
224
623
50
225
519
30
881
461
844
177
NiO
lt00
5n
an
an
alt0
05
na
na
na
na
na
na
na
CaO
035
034
036
033
033
036
035
036
045
053
054
055
Na 2
Olt0
02
lt00
2lt0
02
lt00
2lt0
02
lt00
2lt0
02
lt00
20
02lt0
02
lt00
2lt0
02
Tota
l99
65
992
299
85
100
0310
016
989
099
37
100
2210
012
997
199
65
995
5
Cat
ion
ratio
sFa
406
387
380
386
514
490
511
571
787
884
796
950
Fo59
461
362
061
448
751
048
942
921
111
620
44
5
Stoi
chio
met
ry b
ased
on
4 ox
ygen
ato
ms
Si IV
099
90
998
098
90
997
099
50
992
099
01
003
099
50
995
099
40
996
Al V
I0
001
000
30
001
000
10
000
000
00
002
000
00
000
000
00
000
000
0Ti
VI
000
10
001
000
10
001
000
10
001
000
10
002
000
30
013
000
20
009
Cr
000
50
005
000
50
005
000
40
004
000
30
001
000
20
002
000
10
000
Fe+2
080
10
764
075
60
762
101
60
973
101
61
122
155
41
719
156
91
864
Mn+2
000
80
009
000
80
008
001
20
010
001
00
012
001
70
020
001
60
018
Mg
117
11
208
123
61
214
096
21
014
097
40
842
041
60
225
040
10
089
Ca
001
10
010
001
10
010
001
00
011
001
10
011
001
50
018
001
90
020
Na
000
00
000
000
00
000
000
00
000
000
10
000
000
10
000
000
00
000
Tet s
ite0
999
099
80
989
099
70
995
099
20
990
100
30
995
099
50
994
099
6O
ct si
te1
998
199
92
019
200
12
006
201
42
017
199
12
007
199
62
009
199
9N
= n
umbe
r of a
naly
ses i
n th
e av
erag
e t-
rim =
typi
cal r
im x
-rim
= e
xtre
me
rim f
ay s
ymp
= fa
yalit
e sy
mpl
ectit
e n
a =
not
ana
lyze
d
1078 R Zeigler et al Ta
ble
3 A
vera
ge a
nd re
pres
enta
tive
pyro
xene
com
posi
tions
in th
e LA
P ba
salti
c m
eteo
rites
LA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
P02
205
0222
602
224
0243
602
205
0222
602
224
0243
602
205
0243
602
205
pig
cor
epi
g c
ore
pig
cor
epi
g c
ore
aug
cor
eau
g c
ore
aug
cor
eau
g c
ore
hd
hd
pyxf
er
N23
1417
168
2014
111
11
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
516
751
94
520
751
83
495
149
27
494
649
51
456
045
91
439
7Ti
O2
056
051
053
056
135
135
130
134
139
185
112
Al 2O
31
331
201
321
363
173
333
243
281
842
051
73C
r 2O
30
590
540
580
540
971
010
940
98lt0
02
lt00
2lt0
02
FeO
198
419
47
191
619
83
138
613
21
133
213
77
312
130
66
471
8M
nO0
360
350
360
350
250
250
260
270
320
330
59M
gO18
81
192
019
63
185
213
47
138
114
05
138
00
480
330
04C
aO6
396
496
386
8216
81
169
616
74
165
817
88
183
73
53N
a 2O
lt00
20
030
030
020
050
050
060
05lt0
02
lt00
20
02To
tal
995
799
73
100
199
82
994
499
23
993
599
57
987
399
51
981
7
Cat
ion
ratio
sM
gprime62
863
764
662
563
465
165
364
12
61
90
1Fs
317
310
304
316
249
237
237
246
582
580
871
En53
614
614
215
743
132
131
731
340
240
90
1W
o14
754
455
452
632
044
244
644
01
61
112
8
Stoi
chio
met
ry b
ased
on
6 o
xyge
n at
oms
Si IV
194
91
953
194
81
952
188
31
874
187
81
879
191
61
908
193
3A
l IV
005
10
047
005
20
048
011
70
126
012
20
121
008
40
092
006
6Ti
IV0
000
000
00
000
000
00
000
000
00
000
000
00
000
000
00
000
Al V
I0
009
000
60
006
001
20
026
002
30
023
002
60
007
000
80
009
Ti V
I0
016
001
40
015
001
60
038
003
90
037
003
80
044
005
80
054
Cr
001
80
016
001
70
016
002
90
030
002
80
029
000
00
000
000
0Fe
+20
626
061
20
599
062
40
441
042
00
423
043
71
097
106
61
734
Mn+2
001
10
011
001
10
011
000
80
008
000
80
009
001
10
012
002
2M
g1
058
107
61
094
103
90
764
078
30
795
078
10
030
002
10
002
Ca
025
80
261
025
60
275
068
50
691
068
10
674
080
50
818
016
6N
a0
001
000
20
002
000
10
003
000
40
004
000
40
001
000
10
002
Tet s
ite2
000
200
02
000
200
02
000
200
02
000
200
02
000
200
01
999
Oct
site
199
71
999
200
11
995
199
51
999
200
11
997
199
51
983
198
9A
ugite
(aug
) co
res h
ave
an M
gprime gt
60 a
nd W
o gt3
0 w
hile
pig
eoni
te (p
ig)
core
s hav
e M
gprime gt
60 a
nd W
o lt1
8 H
d =
hed
enbe
rgite
pyx
fer
= py
roxf
erro
ite
Mgprime
= M
g(M
g +
Fe)
100
N =
num
ber o
f ana
lyse
s
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1079
All of the LAP stones have relatively coarse-grained (upto approximately 15 mm) subophitic texture They consistpredominantly of pyroxene and plagioclase with minoramounts of olivine ilmenite and a groundmass dominated byfayalite and cristobalite They contain trace amounts ofchromite chromian ulvˆspinel ulvˆspinel troilite Fe-metalbarian K-feldspar fluor-apatite RE-merrillite tranquillityite(Fe8(YZr)2Ti3Si3O24) and baddeleyite (ZrO2) The modalmineral proportions differ slightly from section to section(Table 9) A few veins and pockets of basaltic glass ofpseudo-whole rock composition (likely shock melted) alsooccur in thin sections LAP 0220533 and LAP 0222424 Theorder in which minerals are inferred to have crystallized ischromite olivine pyroxene plagioclase and groundmass
Olivine grains vary in size from 003 to sim1 mm with01 to 03 mm being typical The modal abundance of olivineranges from 23 to 36 The grains are usually anhedral(rarely subhedral Fig 2a) typically with round or irregularmorphology and uneven contact with the surroundingpyroxene (Fig 2b) Some olivine grains have inclusions ofchromite or Cr-ulvˆspinel grains or both and a few haveldquomeltrdquo inclusions that have two phases in them mafic glasswith a pyroxene-like composition (sim10 wt Al2O3 Table 6)and K-rich high-silica glass similar to the glass seen in thefayalite symplectite grains in the groundmass (sim3 wt K2O68 wt SiO2) Most of the larger olivine grains are zonedwith cores of Fo55ndash65 and rims typically in the Fo38ndash45 range(Fig 3a Table 2) though in a few instances zoning to rims ofFosim20 is observed (Fig 3b) Most of the smaller olivine grainsare not zoned (or not strongly zoned) and they typically havecompositions in the Fo52ndash57 range with the smallest grainshaving the most magnesian compositions The apparentreaction texture between olivine and pyroxene and therelatively magnesian rims on compositions of the smallestolivine grains (likely the remnant cores of grains that havebeen almost completely resorbed) are strong indications thatolivine was being resorbed when the rock solidified
Chromite and Cr-ulvˆspinel grains almost always occuras inclusions within or closely associated with olivine grainsThey also have relatively restricted compositional ranges(Fig 4 Table 4) and they occur individually and as compositegrains with cores of chromite (Chr62ndash68Usp13ndash18Spn16ndash25) andrims of Cr ulvˆspinel (Chr6ndash19Usp71ndash91Spn3ndash11) (Figs 5aand 5b) We found few spinel compositions intermediate tothese end members The total modal abundance of spinel(including ulvˆspinel in the groundmass) is small rangingfrom 03 to 04 Where these two phases are intergrown theboundary between them is sharp with differences in Cr2O3concentration exceeding 20 wt within a few micrometers ofthe boundary A few of the chromite grains have inclusionsof pyroxene with a range of compositions (Mgprime of 47ndash59Wo16ndash31 and TiO2 concentrations from 11ndash24 wt)
Pyroxene grains in LAP are anhedral display undulatoryto mosaic extinction and range in size up to sim1 mm (Fig 2c)
In many cases pyroxene grains partially enclose plagioclasegrains in a subophitic texture The modal abundance ofpyroxene ranges from 47 to 52 The pyroxene grains havemagnesian cores of pigeonite and subcalcic augite (Mgprime fromsim50 to 68) with a wide range of CaO concentrations (Wo11 toWo36 Table 3 Fig 6) although there appears to be a bimodaldistribution of Wo contents with a minimum near Wo20(Fig 6 insets) In some cases pyroxene core compositionsgrade continuously to nearly end member hedenbergite(Fs58Wo40) and pyroxferroite (Fs86Wo13) In a few rare casescontacts between magnesian and ferroan pyroxenes are sharpand linear Compositions of pyroxene grains in contact withpartially resorbed olivine grains vary considerably incomposition The most common composition issubcalcic augite (Wo gt 20) with FeO concentrations in therange Fs24ndash49
The TiAl and TiCr ratios in the LAP pyroxenes arestrongly correlated with Mgprime as expected according toelement compatibility (eg Bence and Papike 1972) Theatomic TiCr ratio increases with decreasing Mgprime in LAPpyroxenes (Fig 7a) This reflects the compatible behavior ofCr and the incompatible behavior of Ti in early crystallizingphases of low-Ti lunar basaltic magmas The most magnesianpyroxenes have atomic TiAl ratios very close to 14indicating that aluminum was introduced through boththe Tschermak (AlAlMgminus1Siminus1) and coupled titanium(TiAl2Mgminus1Siminus2) exchange reactions in approximately equalproportions (Thompson 1982) As pyroxene becomesprogressively more ferroan the TiAl cation ratio approaches12 suggesting a gradual increase in the proportion of Alincorporated due to coupled Ti substitution (Fig 7b) Theleast magnesian pyroxenes (Mgprime lt40) have TiAl ratiosapproaching 34 An increase in TiAl ratios in pyroxene from14 to 12 with decreasing Mgprime in lunar basalts has previouslybeen interpreted as a result of pyroxene crystallization bothprior to the onset of plagioclase crystallization (ratiosaround 14) and during plagioclase crystallization (14ndash12Bence and Papike 1972) Bence and Papike (1972) attributedthe high relative concentrations of Ti in the late-stage Fe-richlunar pyroxenes to Ti3+
Plagioclase forms elongated subhedral to anhedralgrains up to 175 mm long The modal abundance ofplagioclase ranges from 32 to 35 Pyroxene inclusions ofa variety of sizes with compositions spanning nearly theentire compositional spectrum observed occur withinplagioclase Most plagioclase grains are highly fracturedalthough some or portions of some are smooth in polishedsections as seen in the BSE images (Fig 2d) These smoothareas consist partially or entirely of maskelynite as indicatedby their isotropic (or nearly isotropic) character in cross-polarized light Plagioclase grains are complexly zoned Theirtypical core composition is An886Ab11Or04 with sim1 wtFeO + MgO and an Mgprime of 34 (Fig 8 Table 5) Their rims areas wide as sim40 microm and gradually increase in K (up to simOr5)
1080 R Zeigler et al
and FeO (up to sim3 wt) while decreasing in MgO(to lt002 wt Fig 9) The Na2O concentrations firstincrease up to simAb14 then decrease sharply to less thanAb10 (which is lower than in the cores) The extreme rimcomposition of the large plagioclase grains is similar to that ofthe plagioclase found as inclusions in groundmass fayaliteand cristobalite grains (next paragraph Table 5) There is noapparent overall compositional difference between the coresof the maskelynite and the plagioclase grains
Fayalite cristobalite and ilmenite are the dominantminerals in the groundmass typically occurring togetheralthough each can be found independently All of the phaseshave relatively minor modal abundances fayalite (29ndash48)cristobalite (18ndash21) and ilmenite (35ndash40) Silicadisplaying the ldquocracklerdquo pattern distinctive to cristobaliteoccurs as anhedral grains up to 05 mm in size Thecristobalite grains contain minor Al2O3 TiO2 FeO and CaO(Σ sim13 wt Table 6) Inclusions of late-crystallizing phasessuch as K-rich plagioclase K-rich glass K-feldspar fayaliteFe-rich pyroxene phosphate and mafic glass withhigh concentrations of incompatible elements are common(Fig 5c) Fayalite grains (Fo45 sim05 wt CaO) range in size
up to 075 mm and usually form a symplectite texture withinclusions of K-rich glass silica K-rich plagioclase andilmenite (Fig 5d) Fayalite with no (or few) inclusions occursonly rarely Ilmenite is the dominant oxide in the groundmassforming elongate laths up to 1 mm in length Typically theilmenite is poor in Mg (sim02 wt average) although a singlegrain of more magnesian ilmenite associated with a largeolivine grain was observed (Fig 2b) Less common aresmaller subhedral ulvˆspinel grains (lt005 mm) thathave compositions approaching end member ulvˆspinel(Chr0ndash4Usp93ndash98Sp2ndash3) A few composite grains of ilmeniteand ulvˆspinel were observed
Also found in the groundmass are a variety of traceminerals including both fluorapatite and RE-merrillite(Table 7) Phosphate grains most commonly occur betweenplagioclase and ferropyroxene sometimes with associatedcristobalite troilite or both Barian K-feldspar (sim5 wt BaO)also occurs in the groundmass usually in the same areas asthe phosphate minerals (Table 5) Only a few K-feldspargrains (the largest) have stoichiometry that unambiguouslyidentifies them as K-feldspar while many K-rich grainshave excess Si suggesting that they may be intergrowths of
Table 4 Average oxide compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02205 02226 02224 02436 02205 02226 02224 02436 02205 02226 02224Al Al Al Al Cr-rich Cr-rich Cr-rich Cr-rich CrAl CrAl CrAlchr chr chr chr usp usp usp usp usp usp usp
N 23 11 13 5 22 1600 7 13 9 22 10
Major elements in wt by EMPAFeO 3444 3503 3532 3433 5705 5832 5846 5868 6191 6198 6180TiO2 546 532 540 517 2833 2871 2892 2909 3254 3151 3161Cr2O3 4384 4357 4331 4391 928 840 851 776 234 310 338Al2O3 1142 1178 1140 1217 287 261 261 276 191 204 203MgO 283 242 218 292 093 061 069 065 021 028 031MnO 027 024 025 027 035 032 034 033 036 032 034V2O3 073 074 076 075 036 031 033 033 022 025 026SiO2 007 009 008 009 lt002 007 008 018 lt002 008 007CaO 004 004 003 lt002 010 005 006 011 008 007 005ZnO 003 na na na 004 na na na 003 na naTotals 991 992 987 996 993 994 1000 999 996 996 999
Stoichiometry based on 4 (spinel) and 3 (ilmenite) oxygen atomsSi IV 0003 0003 0003 0003 0000 0003 0003 0006 0000 0003 0003Al VI 0469 0484 0472 0496 0125 0114 0113 0119 0083 0089 0088Ti 0143 0139 0143 0134 0784 0798 0798 0803 0907 0880 0880V 0020 0021 0021 0021 0011 0009 0010 0010 0007 0007 0008Cr 1208 1201 1204 1199 0270 0245 0247 0225 0068 0091 0099Fe2+ 1004 1021 1039 0992 1756 1802 1794 1801 1920 1925 1913Mn2+ 0008 0007 0007 0008 0011 0010 0011 0010 0011 0010 0011Mg 0147 0126 0114 0151 0051 0034 0038 0035 0012 0016 0017Zn 0001 minus minus minus 0001 minus minus minus 0001 minus minusCa 0002 0002 0001 0000 0004 0002 0002 0004 0003 0003 0002Sum 2+ 1162 1156 1161 1151 1823 1847 1844 1851 1947 1953 1942Sum 3 4+ 1844 1849 1844 1854 1190 1168 1170 1163 1066 1071 1078Total 3003 3001 3002 3001 3012 3013 3012 3007 3013 3020 3017
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1081
K-feldspar and silica (granophyric texture) at a scale smallenough to be beyond the resolution of the electron microprobe(less than sim01 microm)
Two glass types of distinct composition presumably late-stage residual liquids occur in the groundmass The first is aKSi-rich glass (78 wt SiO2 sim56 wt K2O) that makes upa considerable percentage of the inclusions in the cristobaliteand particularly the fayalite grains The second type ofevolved glass occurs as very small (lt5 microm) roundedinclusions in cristobalite grains This glass has a silica-poorFe-rich bulk composition (sim36 wt SiO2 sim39 wt FeOTable 6) but it is also considerably enriched in manyincompatible elements 23 wt P2O5 12 wt SO3 02 wtY2O3) Commonly we observed minute grains of fayalitetroilite or phosphate associated with this glass These twolate-stage glasses could represent conjugate liquids producedby late-stage immiscibility of an evolved residual meltSimilar glasses were observed in some plutonic rocks fromthe Apollo 14 site (Jolliff et al 1991)
Troilite blebs (with nearly ideal stoichiometry Table 8)are scattered throughout the groundmass along with trace Fe-metal grains which are usually intergrown with troilite orovergrown on chromite grains These grains typicallycontained 66 wt Ni and 14 wt Co though one grain had338 wt Ni and 60 wt Co (Table 8) A few grains ofbaddelyite (ZrO2) and tranquillityite (Zr-Fe-Ti silicate) wereidentified by energy-dispersive spectroscopy (EDS) in thegroundmass
A variety of shock effects occur in the minerals of thesethin sections (eg plagioclase converted to maskelynitemosaicism in the pyroxene) The level of shock was such thatlocalized partial melting occurred in some areas of themeteorite The areas of shock melt have severalmorphologies small melt pockets (LAP 02205 Fig 10a)veins of melt (LAP 0222424 Fig 10b) and in some casesareas that were only partially melted (LAP 0222424Fig 10c) with discernable mineral grains still present(typically maskelynite) Although veins of shock melt are rare
Table 4 Continued Average oxide compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02436 02205 02226 02224 02436 02205 02226 02224 02436 02205CrAl end end end end Mgusp usp usp usp usp ilm ilm ilm ilm ilm
N 11 11 2 3 3 24 16 20 18 2
Major elements in wt by EMPAFeO 6202 6375 6445 6355 6465 4657 4647 4634 4624 4463TiO2 3353 3267 3226 3396 3231 5198 5226 5233 5264 5296Cr2O3 209 026 023 011 037 010 012 015 016 038Al2O3 202 179 206 216 227 008 011 013 010 006MgO 022 005 008 007 003 014 010 016 019 150MnO 034 031 027 029 027 038 033 037 027 035V2O3 023 018 015 019 016 031 029 029 028 035SiO2 015 lt002 011 010 007 003 003 024 004 lt002CaO 007 010 007 008 010 013 006 010 009 008ZnO na 008 na na na 003 na na na lt002Totals 1007 992 997 1005 1002 997 998 1001 1000 1003
Stoichiometry based on 4 (spinel) and 3 (ilmenite) oxygen atomsSi IV 0005 0001 0004 0004 0003 0001 0001 0006 0001 0000Al VI 0087 0079 0091 0093 0099 0002 0003 0004 0003 0002Ti 0920 0921 0906 0937 0901 0990 0993 0989 0996 0991V 0007 0005 0004 0006 0005 0006 0006 0006 0006 0007Cr 0060 0008 0007 0003 0011 0002 0002 0003 0003 0007Fe2+ 1893 1999 2012 1950 2005 0986 0982 0974 0973 0928Mn2+ 0010 0010 0009 0009 0009 0008 0007 0008 0006 0007Mg 0012 0003 0004 0004 0002 0005 0004 0006 0007 0056Zn minus 0002 minus minus minus 0001 minus minus minus 0000Ca 0003 0004 0003 0003 0004 0004 0002 0003 0002 0002Sum 2+ 1918 2018 2028 1966 2019 1004 0995 0991 0988 0994Sum 3 4+ 1080 1014 1012 1043 1019 1001 1005 1008 1009 1007Total 2992 3032 3035 3005 3036 2004 2000 1992 1996 2001The spinel catagories where chosen based primarily on Cr2O3 content with Al chromite (chr) having gt40 wt Cr2O3 Cr-rich ulvˆspinel (usp) having 15ndash
5 wt Cr2O3 CrAl ulvˆspinel having 5ndash05 wt Cr2O3 and endmember ulvospinel having lt05 wt Cr2O3 Also seen were TiAl chromite (30ndash40 wtCr2O3) and high-Cr ulvˆspinel (30ndash15 wt Cr2O3) which are likely the result of an anlyses overlapping simultaneously on both an Al chromite and Cr-rich ulvˆspinel grain Similarly compositions intermediate to ilmenite and end ulvˆspinel were seen These compositions are not listed in this table but areshown in Fig 4 N = number of analyses in the average na = not analyzed
1082 R Zeigler et al
in our thin sections such veins were reported as pervasive inthe original macroscopic description of all five LAP stones(McBride et al 2003 2004a 2004b)
The various shock-induced effects observed in LAP canbe used to quantify and constrain the level of shock that LAPexperienced The presence of both plagioclase andmaskelynite in these samples suggests that the lower end ofthe range listed for conversion of plagioclase to maskelynite(30ndash45 GPa Stˆffler and Hornemann 1972 Ostertag 1983)is appropriate The mosaicism seen in the pyroxene istypically associated with shock values in the 30ndash75 GParange (Kieffer et al 1976 Schaal et al 1979) The presenceof shock-melt veins that have melted both pyroxene andplagioclase (based on the melt composition Table 6)indicates LAP should have been subjected to shock levels ofgt75ndash80 GPa (Kieffer et al 1976 Schaal et al 1979) Thedifferent shock effects observed reflect a range fromlt30 GPa (areas were plagioclase is preserved) to gt75 GPa(areas where shock melting occurred) over distances of onlya few millimeters
Bulk Composition and Comparison to Other LunarBasalts
LAP is a moderately aluminous (sim10 wt Al2O3) low-Ti(31 wt TiO2) mare basalt that falls near the Fe-rich(222 wt FeO) end of the range of FeO concentrationsobserved among lunar basalts It is more ferroan (Mgprime = 347)than any basalt in the Apollo or Luna collection (Fig 11a)Among lunar basalts only meteorites Asuka-881757 andYamato-793169 have comparably low Mgprime values (Koeberlet al 1993 Warren and Kallemeyn 1993 Thalmann et al1996 Korotev et al 2003a) LAP is enriched in Na2O(038 wt) relative to other ferroan (eg Asuka-881757 andYamato-793169) and Fe-rich basalts except for NWA 032(Fig 11b)
Regarding trace elements LAP is enriched in Cocompared to most lunar mare basalts with comparable Scconcentrations (Table 1 Fig 12a) Among Apollo and Lunabasalts only the Apollo 12 ilmenite basalts (Rhodes et al1977 Neal et al 1994) are comparable Incompatible trace-
Table 5 Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02205 02226 02224 02436 02205 02226 02224 02436 02205 02226plag plag plag plag mask mask mask mask plag plagcore core core core core core core core Na rim Na rim
N 123 86 48 88 29 49 33 32 12 3
Major elements in wt by EMPASiO2 4715 4657 4689 4639 4753 4741 4663 4673 4949 4960TiO2 010 007 007 006 013 008 006 006 027 019Al2O3 3337 3367 3296 3363 3367 3291 3376 3415 3170 3103Cr2O3 003 lt002 lt002 002 007 002 lt002 002 004 003FeO 068 067 073 058 060 111 066 060 134 136MgO 023 022 017 024 027 029 028 029 008 012CaO 1730 1746 1709 1763 1747 1726 1730 1740 1628 1597BaO na na na na na na na na na naNa2O 120 123 136 121 119 123 131 128 148 153K2O 006 007 010 006 005 009 006 005 020 019Total 1000 1000 994 998 1008 1004 1001 1006 1006 1000
Cation ratiosAn 885 883 869 887 888 881 877 880 848 842Or 04 04 06 04 03 05 03 03 12 12Ab 111 112 125 110 109 113 120 117 140 146Cn 00 00 00 00 00 00 00 00 00 00
Stoichiometry based on 8 oxygen atomsSi IV 2168 2147 2173 2143 2168 2179 2147 2140 2259 2279Al IV 1809 1830 1801 1831 1810 1782 1832 1843 1705 1681Fe+2 0026 0026 0028 0023 0023 0043 0025 0023 0051 0052Mg 0016 0015 0011 0017 0019 0020 0019 0020 0005 0008Ca 0853 0863 0849 0872 0854 0850 0853 0854 0796 0786Ba minus minus minus minus minus minus minus minus minus minusNa 0107 0110 0122 0108 0105 0109 0117 0114 0131 0136K 0004 0004 0006 0004 0003 0005 0003 0003 0011 0011Tet site 3977 3977 3974 3974 3978 3961 3979 3984 3964 3960Oct site 1005 1018 1022 1023 1003 1027 1022 1013 0995 0994
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1083
element concentrations are considerably greater in LAP thanin most of other low-Ti basalts (Fig 12bndashc) including theApollo 12 ilmenite basalts (Haskin et al 1971 Neal et al1994) The exceptions are NWA 032 the high-Al basalts ofLuna 16 (Philpotts et al 1972 Helmke and Haskin 1972 Maet al 1979) and some Apollo 14 high-Al basalts (Dickinsonet al 1985 Shervais et al 1985 Neal et al 1989a 1989b)
Relative concentrations of REEs in the LAP basalt arealso dissimilar to those of most other lunar basalts (Fig 13) inthat LAP is enriched in light REEs The exceptions are NWA032 which has a pattern nearly parallel to LAP and Apollo 14group 3 basalts (Dickinson et al 1985) which have a patternthat is similar although somewhat less steep in the heavyREEs Ratios of Th to REE in LAP are higher than those of allother lunar basalts except NWA 032 (Fig 14) and thedisparity in ThREE ratio between LAP and other lunarbasalts (except NWA 032) increases from the light to heavyREEs The Apollo 14 high-K basalts have similar ThREEratios for the middle REE Sm-Tb however (Neal et al 1989a
1989b) Overall in terms of its trace-element concentrationsLAP 02205 is most similar to NWA 032 The maindifferences are that NWA 032 is richer in elements associatedwith olivine (Mg Cr Co) and has concentrations ofincompatible elements that are 78ndash91 as great as those inLAP 02205
DISCUSSION
Evidence Supporting the Lunar Origin and Pairing of theLAP Stones
As stated in the introduction the meteorites LAP 0220502224 02226 02436 and 03632 were identified as lunarbasalts that were almost certainly paired (McBride et al 20032004a 2004b) A brief summary follows of the attributesfound in our more detailed petrographic examination thatsupport this initial classification and pairing interpretation
Results of oxygen isotope analyses (δ18O = +56 and
Table 5 Continued Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02224 02436 02205 02205 02226 02224 02436 02205 02205 02205plag plag plag plag plag plag plag barian KBa KBaNa rim Na rim matrix K rim K rim K rim K rim K-spar glass glass
N 24 5 13 10 1 5 1 10 10 23
Major elements in wt by EMPASiO2 4901 4879 5122 5152 4888 4935 5017 6026 5935 6356TiO2 008 008 016 017 lt002 008 014 na na naAl2O3 3163 3120 2960 2993 3213 3004 3002 2019 2063 2043Cr2O3 002 002 006 005 lt002 003 lt002 na na naFeO 117 130 267 192 147 195 173 065 074 116MgO 006 009 003 002 lt002 lt002 002 lt002 lt002 010CaO 1620 1622 1520 1549 1618 1602 1560 063 066 207BaO na na na na na na na 501 407 372Na2O 157 155 105 105 132 126 150 031 029 033K2O 023 021 090 067 067 056 086 1354 1162 586Total 1000 995 1007 1006 1007 993 1000 1008 1006 1007
Cation ratiosAn 839 842 846 852 835 845 807 33 minus minusOr 14 13 61 44 41 35 53 842 minus minusAb 147 145 105 104 124 120 140 30 minus minusCn 00 00 00 00 00 00 00 96 minus minus
Stoichiometry based on 8 oxygen atomsSi IV 2253 2257 2342 2344 2237 2293 2312 2863 2864 2951Al IV 1714 1701 1596 1609 1732 1645 1631 1131 1173 1124Fe+2 0045 0050 0102 0073 0056 0076 0067 0026 0030 0045Mg 0004 0006 0002 0001 0000 0001 0001 0001 0001 0007Ca 0798 0804 0745 0757 0793 0798 0770 0032 0034 0100Ba minus minus minus minus minus minus minus 0093 0077 0070Na 0140 0139 0093 0093 0117 0113 0134 0029 0027 0029K 0013 0013 0052 0039 0039 0033 0050 0820 0715 0353Tet site 3967 3957 3938 3954 3969 3938 3943 3994 4037 4075Oct site 0013 1011 0995 0963 1007 1020 1022 1002 0884 0604Plag = plagioclase mask = maskelynite N = number of analyses in the average na = not analyzed
1084 R Zeigler et al Ta
ble
6 A
vera
ge a
nd re
pres
enta
tive
cris
toba
lite
and
glas
s co
mpo
sitio
n in
the
LAP
basa
ltic
met
eorit
es
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
0220
502
226
0222
402
436
0220
502
205
0220
502
205
0220
502
224
0222
4cr
isto
balit
ecr
isto
balit
ecr
isto
balit
ecr
isto
balit
eSi
-ric
hpy
x-lik
eK
gla
ssIT
E-ric
hsh
ock
shoc
ksh
ock
MI g
lass
MI g
lass
in s
ympl
m
afic
gla
ssgl
ass
area
glas
s ar
eagl
ass
vein
N6
25
44
12
51
6515
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
979
598
17
984
798
45
672
542
76
783
236
67
463
486
441
TiO
20
270
270
230
230
664
810
374
032
341
623
13A
l 2O3
073
060
064
078
187
99
4210
13
544
139
86
123
Cr 2
O3
002
lt00
2lt0
02
002
lt00
20
13lt0
02
lt00
20
080
380
28Fe
O0
210
400
190
171
8615
91
183
392
719
618
520
5M
nOn
an
an
an
an
a0
22n
a0
420
220
290
25M
gO0
02lt0
02
lt00
2lt0
02
033
817
lt00
20
213
459
857
17C
aO0
190
200
200
236
8919
16
098
976
127
118
114
BaO
na
na
na
na
117
na
na
na
na
na
na
Na 2
O0
130
100
090
120
620
110
190
060
510
360
49K
2O0
030
050
07lt0
02
167
na
566
030
005
na
na
P 2O
5n
an
an
an
an
an
an
a2
32n
an
an
aF
na
na
na
na
na
na
na
008
na
na
na
Y2O
3n
an
an
an
an
an
an
a0
19n
an
an
aC
e 2O
3n
an
an
an
an
an
an
a0
12n
an
an
aSO
3n
an
an
an
an
an
an
a1
23n
an
an
aTo
tal
995
599
80
999
010
00
992
410
070
974
910
02
991
100
099
6Sy
mpl
= sy
mpl
ectit
e M
I = m
elt i
nclu
sion
N =
num
ber o
f ana
lyse
s in
the
aver
age
na
= n
ot a
naly
zed
The
shoc
ked
glas
s in
LAP
0222
4 is
the
parti
ally
mel
ted
area
(see
Fig
14)
and
onl
y th
e an
ayls
es o
fth
e gl
ass i
tsel
f wer
e in
clud
ed in
the
aver
age
not t
he m
iner
als t
hat w
ere
anal
yzed
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1085
Table 7 Representative phosphate compositions in LAP 0220533LAP LAP LAP LAP LAP LAP LAP LAP02205 02205 02205 02205 02205 02205 02205 02205RE- RE- RE- RE- RE- fluorapatite fluorapatite fluorapatitemerrillite merrillite merrillite merrillite merrillite
Major elements in wt by EMPASiO2 050 044 062 037 321 228 449 137Al2O3 022 lt005 009 lt005 lt005 007 014 lt005FeO 637 774 568 576 250 169 439 202MgO 020 037 025 028 lt005 lt005 lt005 lt005CaO 4326 4035 4233 4245 4983 5241 5003 5351Na2O 000 001 010 014 000 000 001 000P2O5 3885 4171 4382 4360 3540 3949 3771 4077Cl lt005 lt005 lt005 lt005 lt005 006 027 031F 047 044 050 048 168 245 130 186Y2O3 298 293 226 221 172 103 078 053La2O3 093 107 065 064 092 024 014 012Ce2O3 253 259 189 185 253 072 069 053Nd2O3 161 177 108 118 166 057 059 031Sm2O3 043 043 029 028 048 022 015 009Gd2O3 087 090 058 058 079 023 018 008Yb2O3 016 032 009 lt005 010 005 lt005 lt005ThO2 007 009 008 lt005 021 lt005 lt005 lt005minusO = (FCl) 021 020 022 021 072 105 061 085Sums 9930 1010 1001 9968 1004 1005 1003 1006
Table 8 Average sulfide and metal compositions in LAP 0220533Ave Fe metal High-Ni metal Troilite
N 5 1 8
Elemental percentage by EMPAFe 9209 5880 6280Ni 664 3377 lt002Co 141 595 lt002Ti 023 009 006Cr 043 017 lt002Mn lt002 004 lt002S lt002 lt002 3620Totals 1008 988 994Ideal troilite = 365 wt S 635 wt Fe N = number of analyses
Table 9 Modal mineralogy of the different LAP stonesLAP 0220533 LAP 0222616 LAP 0222424 LAP 0243614
Pyroxene 515 505 469 466Plagioclase 319 321 323 346Ilmenite 348 391 386 399Fay sympl 309 290 358 483Olivine 233 271 363 320Cristobalite 214 209 178 200Spinel (all) 034 045 040 039Troilite 025 024 024 022Fractures 49 49 53 421Shock glass 01 02 22 00N 633 times 106 905 times 106 470 times 106 396 times 106
All modal values are listed as percentages N = number of pixels
1086 R Zeigler et al
Fig 1 Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) and fayalite(more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phases arepyroxene and olivine a) LAP 0222616 b) LAP 0243614 c) LAP 0222424 d) LAP 0220533
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1087
δ17O = +27) performed by Mayeda and Clayton (reported inMcBride et al 2003) constrain the origin of LAP 02205 tothe Earth the Moon or an enstatite meteorite parent bodyLAP is clearly a meteorite all four of the stones have fusioncrusts (ruling out a terrestrial origin) The extremely ferroannature of LAP rules out the enstatite parent body as theprovenance FeOMnO ratios of mafic silicates arediagnostic of origins from different planetary bodies in thesolar system (Dymek et al 1976 Papike 1998) Ratios ofFeOMnO in LAP pyroxenes (average sim60) and olivines(average sim95) are consistent only with lunar origin (Fig 15)Furthermore the presence of Fe(Ni) metal and troilite thecompletely anhydrous nature of the sample the apparentlack of Fe3+ in all phases the calcic nature of theplagioclase and the deep negative Eu anomaly are allcommon in lunar basalts
With regard to texture mineral assemblage and mineralchemistry the four LAP 02xxx stones appear to beindistinguishable from each other Although we did not studythe mineral chemistry of the LAP 03632 in depth the textureand mineral assemblage are identical to the LAP 02xxxstones Furthermore the collection locations of the five stonesform a linear array sim3 km in length that is perpendicular to theflow of the ice sheet (John Schutt personal communication)Thus in the absence of cosmic-ray exposure data to thecontrary we conclude that the four LAP 02xxx stones studiedare paired
Compositional Variability among Small Subsamples ofLAP 02205 and NWA 032
Samples of lunar meteorites available for study at most afew hundred milligrams are very small by the standards ofterrestrial geology and geochemistry Nevertheless we havetaken our samples and subdivided them into numerous evensmaller (10ndash50 mg) subsamples for bulk compositionalanalysis (Korotev et al 1983 1996 2003a 2003b Jolliffet al 1991 1998 Fagan et al 2002) This procedure providesan estimate of the whole-rock composition through a mass-weighted mean that is equivalent to a single analysis of theentire mass of the allocated sample The variation amongsmall subsamples however provides additional informationabout compositional variations associated with mineralassemblage and proportions about petrogenesis and aboutpossible relationships to other meteorites (eg Korotev et al2003a 2003b) and how well the ldquowhole-rockrdquo compositionis likely to represent that of the source region of the meteorite(Korotev et al 2000a) In the following discussion weevaluate the causes of differences in composition amongsmall subsamples of LAP and NWA 032
The range of concentrations among the 19 subsamples ofLAP (27ndash40 mg) is relatively small for the most preciselydetermined major elements (SiO2 TiO2 Al2O3 FeO CaONa2O) and most precisely determined trace elements that arecompatible with the major mineral phases (Co Sc Eu) The
Fig 1 Continued Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) andfayalite (more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phasesare pyroxene and olivine d) LAP 0220533
1088 R Zeigler et al
relative sample standard deviations (s ) range from 08 to76 (with only Co and Eu gt 5 Table 1) The exceptionsare MgO and Cr2O3 for which the relative standarddeviations are distinctly greater 12 and 16 respectivelyFor incompatible elements that we determined precisely(lt9 analytical uncertainty La Ce Sm Tb Yb Lu Hf Taand Th) relative standard deviations range from 7 to 11These variations are caused by a combination ofunrepresentative sampling of the major mineral phasesowing to the coarse grain size (up to sim1 mm3) relative to theINAA subsample size (about 12 mm3 assuming that thedensity of LAP is sim35 gmm3) and to the heterogeneousdistribution of some relatively minor phases with high
concentrations of a given element This problem is not new asmany investigators have previously wrestled with theproblem of studying relatively coarse-grained lunar basaltswith small allocated subsample sizes characteristic of rareextraterrestrial samples (Korotev and Haskin 1975 Haskinet al 1977 Lindstrom and Haskin 1978 Ryder and Schuraytz2001) Ryder and Schuraytz (2001) showed that sim5 g ofmaterial are needed to achieve a representative sample ofApollo 15 olivine-normative basalts which have grain sizeson the order of a millimeter or greater
Among the LAP subsamples Cr2O3 and MgOconcentrations correlate positively (R2 = 081) as a result ofthe association of chromite and Cr-ulvˆspinel with olivine
Fig 2 BSE images from LAP 0220533 a) a large round olivine (oli) grain and a smaller subhedral olivine grain (left center of the image)both surrounded by zoned pyroxene (pyx) and plagioclase (plag) with melt inclusions (MI) and inclusions of chromite (chr) A smallulvˆspinel (Usp) grain occurs in the upper left b) A large irregular olivine grain and a smaller mostly resorbed olivine grain The larger graincontains both melt inclusions (MI) and chromite grains The associated ilmenite (Ilm) grain is the most magnesian ilmenite grain observed Acomposite grain of metal and troilite (MetSulf) is also present c) A BSE image showing the zoning in multiple large pyroxene grainsintergrown with plagioclase and maskelynite (mask) grains One small cristobalite (crist) grain is also present d) A BSE image showingseveral large plagioclase grains some of which contain both fractured areas (plagioclase) and smooth areas (maskelynite) Also present areseveral areas of groundmass including a fayalite symplectite and a cristobalite grain cut by an ilmenite lath
x
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1089
The large variations seen in MgO Cr2O3 and to a lesserextent Co concentrations occur because of the large relativevariation in the fraction of modal olivine among thesubsamples Normatively the compositional rangecorresponds to minus03ndash25 olivine (one subsample has 03normative quartz) and 032ndash049 chromite The relativelysmall variations seen among concentrations of the other majorelements as well as Sc and Eu are controlled byunrepresentative sampling of the major mineral phasespyroxene (Sc Ca Fe Si) and plagioclase (Al Na Ca Si Eu)and the minor but widely distributed mineral ilmenite (Ti Fe)Trace amounts of a few minerals that are found only ingroundmass have high concentrations of incompatible traceelements relative to the concentration of those elements inthe bulk meteorite These minerals include K-feldspar (Ba)
Fig 3 a) CaO versus Mgprime (molar Mg[Mg + Fe]100) in the olivinesof the different LAP stones The compositions range from cores ofFo55ndash67 trending towards rims typically in the Fo40 range withextreme zonation to rims of Fo15ndash20 in a few cases Where analyzedthe composition of groundmass fayalite are also shown b) Anelectron microprobe traverse across a small strongly zoned olivinegrain in LAP 0220533 The grain shows zoning from a core of simFo58to a rim composition of simFo18 over sim100 microm The break in the zoning(black arrow) is centered on a fracture in the olivine grain
Fig 4 Compositions of LAP oxides plotted on the (FeMgMn)O-(CrAl)2O3-TiO2 ternary (after El Goresy et al 1971) Compositionsof endmember ilmenite (FeTiO3) ulvˆspinel (Fe2TiO4) andchromite (FeCr2O4) are labeled For a description of theclassification scheme see the footnote of Table 3 a) LAP 0220533b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1090 R Zeigler et al
RE-merrillite (P REEs Th) and baddeleyite (Zr Hf U Th)Therefore the variation in the amount of the groundmassldquophaserdquo in the different subsamples controls the ITEconcentrations in the various subsamples
For most of the major elements subsamples of NWA 032have relative standard deviations (RSD) that areinsignificantly different from those of LAP (Table 1) eventhough the average subsample size for NWA 032 (sim14 mgFagan et al 2002) was smaller than for LAP (sim34 mg) TheRSDs of MgO and Cr2O3 for NWA 032 are again highbecause it has a porphyritic texture with large phenocrysts(millimeter scale) of olivine (with chromite inclusions) andmagnesian pyroxene but a fine-grained groundmass of
plagioclase Fe-rich pyroxene ilmenite and glass keeps theRSDs of other major and incompatible trace elements low
Source Crater Pairing of LAP and NWA 032
We find the similarities in chemistry and petrographybetween LAP and NWA 032 when compared to the largeranges observed among Apollo and Luna samples to be sogreat that it is highly unlikely that two meteorites so similarcould derive from different locations Below we summarizethe similarities and differences
The textures of NWA 032 and LAP are markedlydifferent from each other NWA 032 has a porphyritic texture
Fig 5 BSE images from LAP 0220533 a) oxide grains set in and around a large olivine grain individual grains of ilmenite (Ilm) Cr-ulvˆspinel (Chr-Usp) and chromite (Chr) composite chromian ulvˆspinel-chromite (ChrUsp) grains with accompanying pyroxene andplagioclase (grey and black areas) b) A close-up of a zoned spinel grain with a chromite core and a Cr-ulvˆspinel rim c) A large cristobalite(Crist) grain with many inclusions of fayalite pyroxene (Pyx) plagioclase (Plag) troilite (Sulf) phosphate K-rich glass and the ITE-richglass Also present are several areas of fayalite symplectite (Fay Symp) with inclusions of plagioclase silica ilmenite troilite and K-richglass d) A BSE image of a different area of groundmass showing a large grain of fayalite symplectite containing inclusions of plagioclasesilica ilmenite troilite K-rich glass and Fe-rich pyroxene A large ilmenite (Ilm) grain cuts through the symplectite and several large troilitegrains are also present
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
1078 R Zeigler et al Ta
ble
3 A
vera
ge a
nd re
pres
enta
tive
pyro
xene
com
posi
tions
in th
e LA
P ba
salti
c m
eteo
rites
LA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
PLA
P02
205
0222
602
224
0243
602
205
0222
602
224
0243
602
205
0243
602
205
pig
cor
epi
g c
ore
pig
cor
epi
g c
ore
aug
cor
eau
g c
ore
aug
cor
eau
g c
ore
hd
hd
pyxf
er
N23
1417
168
2014
111
11
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
516
751
94
520
751
83
495
149
27
494
649
51
456
045
91
439
7Ti
O2
056
051
053
056
135
135
130
134
139
185
112
Al 2O
31
331
201
321
363
173
333
243
281
842
051
73C
r 2O
30
590
540
580
540
971
010
940
98lt0
02
lt00
2lt0
02
FeO
198
419
47
191
619
83
138
613
21
133
213
77
312
130
66
471
8M
nO0
360
350
360
350
250
250
260
270
320
330
59M
gO18
81
192
019
63
185
213
47
138
114
05
138
00
480
330
04C
aO6
396
496
386
8216
81
169
616
74
165
817
88
183
73
53N
a 2O
lt00
20
030
030
020
050
050
060
05lt0
02
lt00
20
02To
tal
995
799
73
100
199
82
994
499
23
993
599
57
987
399
51
981
7
Cat
ion
ratio
sM
gprime62
863
764
662
563
465
165
364
12
61
90
1Fs
317
310
304
316
249
237
237
246
582
580
871
En53
614
614
215
743
132
131
731
340
240
90
1W
o14
754
455
452
632
044
244
644
01
61
112
8
Stoi
chio
met
ry b
ased
on
6 o
xyge
n at
oms
Si IV
194
91
953
194
81
952
188
31
874
187
81
879
191
61
908
193
3A
l IV
005
10
047
005
20
048
011
70
126
012
20
121
008
40
092
006
6Ti
IV0
000
000
00
000
000
00
000
000
00
000
000
00
000
000
00
000
Al V
I0
009
000
60
006
001
20
026
002
30
023
002
60
007
000
80
009
Ti V
I0
016
001
40
015
001
60
038
003
90
037
003
80
044
005
80
054
Cr
001
80
016
001
70
016
002
90
030
002
80
029
000
00
000
000
0Fe
+20
626
061
20
599
062
40
441
042
00
423
043
71
097
106
61
734
Mn+2
001
10
011
001
10
011
000
80
008
000
80
009
001
10
012
002
2M
g1
058
107
61
094
103
90
764
078
30
795
078
10
030
002
10
002
Ca
025
80
261
025
60
275
068
50
691
068
10
674
080
50
818
016
6N
a0
001
000
20
002
000
10
003
000
40
004
000
40
001
000
10
002
Tet s
ite2
000
200
02
000
200
02
000
200
02
000
200
02
000
200
01
999
Oct
site
199
71
999
200
11
995
199
51
999
200
11
997
199
51
983
198
9A
ugite
(aug
) co
res h
ave
an M
gprime gt
60 a
nd W
o gt3
0 w
hile
pig
eoni
te (p
ig)
core
s hav
e M
gprime gt
60 a
nd W
o lt1
8 H
d =
hed
enbe
rgite
pyx
fer
= py
roxf
erro
ite
Mgprime
= M
g(M
g +
Fe)
100
N =
num
ber o
f ana
lyse
s
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1079
All of the LAP stones have relatively coarse-grained (upto approximately 15 mm) subophitic texture They consistpredominantly of pyroxene and plagioclase with minoramounts of olivine ilmenite and a groundmass dominated byfayalite and cristobalite They contain trace amounts ofchromite chromian ulvˆspinel ulvˆspinel troilite Fe-metalbarian K-feldspar fluor-apatite RE-merrillite tranquillityite(Fe8(YZr)2Ti3Si3O24) and baddeleyite (ZrO2) The modalmineral proportions differ slightly from section to section(Table 9) A few veins and pockets of basaltic glass ofpseudo-whole rock composition (likely shock melted) alsooccur in thin sections LAP 0220533 and LAP 0222424 Theorder in which minerals are inferred to have crystallized ischromite olivine pyroxene plagioclase and groundmass
Olivine grains vary in size from 003 to sim1 mm with01 to 03 mm being typical The modal abundance of olivineranges from 23 to 36 The grains are usually anhedral(rarely subhedral Fig 2a) typically with round or irregularmorphology and uneven contact with the surroundingpyroxene (Fig 2b) Some olivine grains have inclusions ofchromite or Cr-ulvˆspinel grains or both and a few haveldquomeltrdquo inclusions that have two phases in them mafic glasswith a pyroxene-like composition (sim10 wt Al2O3 Table 6)and K-rich high-silica glass similar to the glass seen in thefayalite symplectite grains in the groundmass (sim3 wt K2O68 wt SiO2) Most of the larger olivine grains are zonedwith cores of Fo55ndash65 and rims typically in the Fo38ndash45 range(Fig 3a Table 2) though in a few instances zoning to rims ofFosim20 is observed (Fig 3b) Most of the smaller olivine grainsare not zoned (or not strongly zoned) and they typically havecompositions in the Fo52ndash57 range with the smallest grainshaving the most magnesian compositions The apparentreaction texture between olivine and pyroxene and therelatively magnesian rims on compositions of the smallestolivine grains (likely the remnant cores of grains that havebeen almost completely resorbed) are strong indications thatolivine was being resorbed when the rock solidified
Chromite and Cr-ulvˆspinel grains almost always occuras inclusions within or closely associated with olivine grainsThey also have relatively restricted compositional ranges(Fig 4 Table 4) and they occur individually and as compositegrains with cores of chromite (Chr62ndash68Usp13ndash18Spn16ndash25) andrims of Cr ulvˆspinel (Chr6ndash19Usp71ndash91Spn3ndash11) (Figs 5aand 5b) We found few spinel compositions intermediate tothese end members The total modal abundance of spinel(including ulvˆspinel in the groundmass) is small rangingfrom 03 to 04 Where these two phases are intergrown theboundary between them is sharp with differences in Cr2O3concentration exceeding 20 wt within a few micrometers ofthe boundary A few of the chromite grains have inclusionsof pyroxene with a range of compositions (Mgprime of 47ndash59Wo16ndash31 and TiO2 concentrations from 11ndash24 wt)
Pyroxene grains in LAP are anhedral display undulatoryto mosaic extinction and range in size up to sim1 mm (Fig 2c)
In many cases pyroxene grains partially enclose plagioclasegrains in a subophitic texture The modal abundance ofpyroxene ranges from 47 to 52 The pyroxene grains havemagnesian cores of pigeonite and subcalcic augite (Mgprime fromsim50 to 68) with a wide range of CaO concentrations (Wo11 toWo36 Table 3 Fig 6) although there appears to be a bimodaldistribution of Wo contents with a minimum near Wo20(Fig 6 insets) In some cases pyroxene core compositionsgrade continuously to nearly end member hedenbergite(Fs58Wo40) and pyroxferroite (Fs86Wo13) In a few rare casescontacts between magnesian and ferroan pyroxenes are sharpand linear Compositions of pyroxene grains in contact withpartially resorbed olivine grains vary considerably incomposition The most common composition issubcalcic augite (Wo gt 20) with FeO concentrations in therange Fs24ndash49
The TiAl and TiCr ratios in the LAP pyroxenes arestrongly correlated with Mgprime as expected according toelement compatibility (eg Bence and Papike 1972) Theatomic TiCr ratio increases with decreasing Mgprime in LAPpyroxenes (Fig 7a) This reflects the compatible behavior ofCr and the incompatible behavior of Ti in early crystallizingphases of low-Ti lunar basaltic magmas The most magnesianpyroxenes have atomic TiAl ratios very close to 14indicating that aluminum was introduced through boththe Tschermak (AlAlMgminus1Siminus1) and coupled titanium(TiAl2Mgminus1Siminus2) exchange reactions in approximately equalproportions (Thompson 1982) As pyroxene becomesprogressively more ferroan the TiAl cation ratio approaches12 suggesting a gradual increase in the proportion of Alincorporated due to coupled Ti substitution (Fig 7b) Theleast magnesian pyroxenes (Mgprime lt40) have TiAl ratiosapproaching 34 An increase in TiAl ratios in pyroxene from14 to 12 with decreasing Mgprime in lunar basalts has previouslybeen interpreted as a result of pyroxene crystallization bothprior to the onset of plagioclase crystallization (ratiosaround 14) and during plagioclase crystallization (14ndash12Bence and Papike 1972) Bence and Papike (1972) attributedthe high relative concentrations of Ti in the late-stage Fe-richlunar pyroxenes to Ti3+
Plagioclase forms elongated subhedral to anhedralgrains up to 175 mm long The modal abundance ofplagioclase ranges from 32 to 35 Pyroxene inclusions ofa variety of sizes with compositions spanning nearly theentire compositional spectrum observed occur withinplagioclase Most plagioclase grains are highly fracturedalthough some or portions of some are smooth in polishedsections as seen in the BSE images (Fig 2d) These smoothareas consist partially or entirely of maskelynite as indicatedby their isotropic (or nearly isotropic) character in cross-polarized light Plagioclase grains are complexly zoned Theirtypical core composition is An886Ab11Or04 with sim1 wtFeO + MgO and an Mgprime of 34 (Fig 8 Table 5) Their rims areas wide as sim40 microm and gradually increase in K (up to simOr5)
1080 R Zeigler et al
and FeO (up to sim3 wt) while decreasing in MgO(to lt002 wt Fig 9) The Na2O concentrations firstincrease up to simAb14 then decrease sharply to less thanAb10 (which is lower than in the cores) The extreme rimcomposition of the large plagioclase grains is similar to that ofthe plagioclase found as inclusions in groundmass fayaliteand cristobalite grains (next paragraph Table 5) There is noapparent overall compositional difference between the coresof the maskelynite and the plagioclase grains
Fayalite cristobalite and ilmenite are the dominantminerals in the groundmass typically occurring togetheralthough each can be found independently All of the phaseshave relatively minor modal abundances fayalite (29ndash48)cristobalite (18ndash21) and ilmenite (35ndash40) Silicadisplaying the ldquocracklerdquo pattern distinctive to cristobaliteoccurs as anhedral grains up to 05 mm in size Thecristobalite grains contain minor Al2O3 TiO2 FeO and CaO(Σ sim13 wt Table 6) Inclusions of late-crystallizing phasessuch as K-rich plagioclase K-rich glass K-feldspar fayaliteFe-rich pyroxene phosphate and mafic glass withhigh concentrations of incompatible elements are common(Fig 5c) Fayalite grains (Fo45 sim05 wt CaO) range in size
up to 075 mm and usually form a symplectite texture withinclusions of K-rich glass silica K-rich plagioclase andilmenite (Fig 5d) Fayalite with no (or few) inclusions occursonly rarely Ilmenite is the dominant oxide in the groundmassforming elongate laths up to 1 mm in length Typically theilmenite is poor in Mg (sim02 wt average) although a singlegrain of more magnesian ilmenite associated with a largeolivine grain was observed (Fig 2b) Less common aresmaller subhedral ulvˆspinel grains (lt005 mm) thathave compositions approaching end member ulvˆspinel(Chr0ndash4Usp93ndash98Sp2ndash3) A few composite grains of ilmeniteand ulvˆspinel were observed
Also found in the groundmass are a variety of traceminerals including both fluorapatite and RE-merrillite(Table 7) Phosphate grains most commonly occur betweenplagioclase and ferropyroxene sometimes with associatedcristobalite troilite or both Barian K-feldspar (sim5 wt BaO)also occurs in the groundmass usually in the same areas asthe phosphate minerals (Table 5) Only a few K-feldspargrains (the largest) have stoichiometry that unambiguouslyidentifies them as K-feldspar while many K-rich grainshave excess Si suggesting that they may be intergrowths of
Table 4 Average oxide compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02205 02226 02224 02436 02205 02226 02224 02436 02205 02226 02224Al Al Al Al Cr-rich Cr-rich Cr-rich Cr-rich CrAl CrAl CrAlchr chr chr chr usp usp usp usp usp usp usp
N 23 11 13 5 22 1600 7 13 9 22 10
Major elements in wt by EMPAFeO 3444 3503 3532 3433 5705 5832 5846 5868 6191 6198 6180TiO2 546 532 540 517 2833 2871 2892 2909 3254 3151 3161Cr2O3 4384 4357 4331 4391 928 840 851 776 234 310 338Al2O3 1142 1178 1140 1217 287 261 261 276 191 204 203MgO 283 242 218 292 093 061 069 065 021 028 031MnO 027 024 025 027 035 032 034 033 036 032 034V2O3 073 074 076 075 036 031 033 033 022 025 026SiO2 007 009 008 009 lt002 007 008 018 lt002 008 007CaO 004 004 003 lt002 010 005 006 011 008 007 005ZnO 003 na na na 004 na na na 003 na naTotals 991 992 987 996 993 994 1000 999 996 996 999
Stoichiometry based on 4 (spinel) and 3 (ilmenite) oxygen atomsSi IV 0003 0003 0003 0003 0000 0003 0003 0006 0000 0003 0003Al VI 0469 0484 0472 0496 0125 0114 0113 0119 0083 0089 0088Ti 0143 0139 0143 0134 0784 0798 0798 0803 0907 0880 0880V 0020 0021 0021 0021 0011 0009 0010 0010 0007 0007 0008Cr 1208 1201 1204 1199 0270 0245 0247 0225 0068 0091 0099Fe2+ 1004 1021 1039 0992 1756 1802 1794 1801 1920 1925 1913Mn2+ 0008 0007 0007 0008 0011 0010 0011 0010 0011 0010 0011Mg 0147 0126 0114 0151 0051 0034 0038 0035 0012 0016 0017Zn 0001 minus minus minus 0001 minus minus minus 0001 minus minusCa 0002 0002 0001 0000 0004 0002 0002 0004 0003 0003 0002Sum 2+ 1162 1156 1161 1151 1823 1847 1844 1851 1947 1953 1942Sum 3 4+ 1844 1849 1844 1854 1190 1168 1170 1163 1066 1071 1078Total 3003 3001 3002 3001 3012 3013 3012 3007 3013 3020 3017
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1081
K-feldspar and silica (granophyric texture) at a scale smallenough to be beyond the resolution of the electron microprobe(less than sim01 microm)
Two glass types of distinct composition presumably late-stage residual liquids occur in the groundmass The first is aKSi-rich glass (78 wt SiO2 sim56 wt K2O) that makes upa considerable percentage of the inclusions in the cristobaliteand particularly the fayalite grains The second type ofevolved glass occurs as very small (lt5 microm) roundedinclusions in cristobalite grains This glass has a silica-poorFe-rich bulk composition (sim36 wt SiO2 sim39 wt FeOTable 6) but it is also considerably enriched in manyincompatible elements 23 wt P2O5 12 wt SO3 02 wtY2O3) Commonly we observed minute grains of fayalitetroilite or phosphate associated with this glass These twolate-stage glasses could represent conjugate liquids producedby late-stage immiscibility of an evolved residual meltSimilar glasses were observed in some plutonic rocks fromthe Apollo 14 site (Jolliff et al 1991)
Troilite blebs (with nearly ideal stoichiometry Table 8)are scattered throughout the groundmass along with trace Fe-metal grains which are usually intergrown with troilite orovergrown on chromite grains These grains typicallycontained 66 wt Ni and 14 wt Co though one grain had338 wt Ni and 60 wt Co (Table 8) A few grains ofbaddelyite (ZrO2) and tranquillityite (Zr-Fe-Ti silicate) wereidentified by energy-dispersive spectroscopy (EDS) in thegroundmass
A variety of shock effects occur in the minerals of thesethin sections (eg plagioclase converted to maskelynitemosaicism in the pyroxene) The level of shock was such thatlocalized partial melting occurred in some areas of themeteorite The areas of shock melt have severalmorphologies small melt pockets (LAP 02205 Fig 10a)veins of melt (LAP 0222424 Fig 10b) and in some casesareas that were only partially melted (LAP 0222424Fig 10c) with discernable mineral grains still present(typically maskelynite) Although veins of shock melt are rare
Table 4 Continued Average oxide compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02436 02205 02226 02224 02436 02205 02226 02224 02436 02205CrAl end end end end Mgusp usp usp usp usp ilm ilm ilm ilm ilm
N 11 11 2 3 3 24 16 20 18 2
Major elements in wt by EMPAFeO 6202 6375 6445 6355 6465 4657 4647 4634 4624 4463TiO2 3353 3267 3226 3396 3231 5198 5226 5233 5264 5296Cr2O3 209 026 023 011 037 010 012 015 016 038Al2O3 202 179 206 216 227 008 011 013 010 006MgO 022 005 008 007 003 014 010 016 019 150MnO 034 031 027 029 027 038 033 037 027 035V2O3 023 018 015 019 016 031 029 029 028 035SiO2 015 lt002 011 010 007 003 003 024 004 lt002CaO 007 010 007 008 010 013 006 010 009 008ZnO na 008 na na na 003 na na na lt002Totals 1007 992 997 1005 1002 997 998 1001 1000 1003
Stoichiometry based on 4 (spinel) and 3 (ilmenite) oxygen atomsSi IV 0005 0001 0004 0004 0003 0001 0001 0006 0001 0000Al VI 0087 0079 0091 0093 0099 0002 0003 0004 0003 0002Ti 0920 0921 0906 0937 0901 0990 0993 0989 0996 0991V 0007 0005 0004 0006 0005 0006 0006 0006 0006 0007Cr 0060 0008 0007 0003 0011 0002 0002 0003 0003 0007Fe2+ 1893 1999 2012 1950 2005 0986 0982 0974 0973 0928Mn2+ 0010 0010 0009 0009 0009 0008 0007 0008 0006 0007Mg 0012 0003 0004 0004 0002 0005 0004 0006 0007 0056Zn minus 0002 minus minus minus 0001 minus minus minus 0000Ca 0003 0004 0003 0003 0004 0004 0002 0003 0002 0002Sum 2+ 1918 2018 2028 1966 2019 1004 0995 0991 0988 0994Sum 3 4+ 1080 1014 1012 1043 1019 1001 1005 1008 1009 1007Total 2992 3032 3035 3005 3036 2004 2000 1992 1996 2001The spinel catagories where chosen based primarily on Cr2O3 content with Al chromite (chr) having gt40 wt Cr2O3 Cr-rich ulvˆspinel (usp) having 15ndash
5 wt Cr2O3 CrAl ulvˆspinel having 5ndash05 wt Cr2O3 and endmember ulvospinel having lt05 wt Cr2O3 Also seen were TiAl chromite (30ndash40 wtCr2O3) and high-Cr ulvˆspinel (30ndash15 wt Cr2O3) which are likely the result of an anlyses overlapping simultaneously on both an Al chromite and Cr-rich ulvˆspinel grain Similarly compositions intermediate to ilmenite and end ulvˆspinel were seen These compositions are not listed in this table but areshown in Fig 4 N = number of analyses in the average na = not analyzed
1082 R Zeigler et al
in our thin sections such veins were reported as pervasive inthe original macroscopic description of all five LAP stones(McBride et al 2003 2004a 2004b)
The various shock-induced effects observed in LAP canbe used to quantify and constrain the level of shock that LAPexperienced The presence of both plagioclase andmaskelynite in these samples suggests that the lower end ofthe range listed for conversion of plagioclase to maskelynite(30ndash45 GPa Stˆffler and Hornemann 1972 Ostertag 1983)is appropriate The mosaicism seen in the pyroxene istypically associated with shock values in the 30ndash75 GParange (Kieffer et al 1976 Schaal et al 1979) The presenceof shock-melt veins that have melted both pyroxene andplagioclase (based on the melt composition Table 6)indicates LAP should have been subjected to shock levels ofgt75ndash80 GPa (Kieffer et al 1976 Schaal et al 1979) Thedifferent shock effects observed reflect a range fromlt30 GPa (areas were plagioclase is preserved) to gt75 GPa(areas where shock melting occurred) over distances of onlya few millimeters
Bulk Composition and Comparison to Other LunarBasalts
LAP is a moderately aluminous (sim10 wt Al2O3) low-Ti(31 wt TiO2) mare basalt that falls near the Fe-rich(222 wt FeO) end of the range of FeO concentrationsobserved among lunar basalts It is more ferroan (Mgprime = 347)than any basalt in the Apollo or Luna collection (Fig 11a)Among lunar basalts only meteorites Asuka-881757 andYamato-793169 have comparably low Mgprime values (Koeberlet al 1993 Warren and Kallemeyn 1993 Thalmann et al1996 Korotev et al 2003a) LAP is enriched in Na2O(038 wt) relative to other ferroan (eg Asuka-881757 andYamato-793169) and Fe-rich basalts except for NWA 032(Fig 11b)
Regarding trace elements LAP is enriched in Cocompared to most lunar mare basalts with comparable Scconcentrations (Table 1 Fig 12a) Among Apollo and Lunabasalts only the Apollo 12 ilmenite basalts (Rhodes et al1977 Neal et al 1994) are comparable Incompatible trace-
Table 5 Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02205 02226 02224 02436 02205 02226 02224 02436 02205 02226plag plag plag plag mask mask mask mask plag plagcore core core core core core core core Na rim Na rim
N 123 86 48 88 29 49 33 32 12 3
Major elements in wt by EMPASiO2 4715 4657 4689 4639 4753 4741 4663 4673 4949 4960TiO2 010 007 007 006 013 008 006 006 027 019Al2O3 3337 3367 3296 3363 3367 3291 3376 3415 3170 3103Cr2O3 003 lt002 lt002 002 007 002 lt002 002 004 003FeO 068 067 073 058 060 111 066 060 134 136MgO 023 022 017 024 027 029 028 029 008 012CaO 1730 1746 1709 1763 1747 1726 1730 1740 1628 1597BaO na na na na na na na na na naNa2O 120 123 136 121 119 123 131 128 148 153K2O 006 007 010 006 005 009 006 005 020 019Total 1000 1000 994 998 1008 1004 1001 1006 1006 1000
Cation ratiosAn 885 883 869 887 888 881 877 880 848 842Or 04 04 06 04 03 05 03 03 12 12Ab 111 112 125 110 109 113 120 117 140 146Cn 00 00 00 00 00 00 00 00 00 00
Stoichiometry based on 8 oxygen atomsSi IV 2168 2147 2173 2143 2168 2179 2147 2140 2259 2279Al IV 1809 1830 1801 1831 1810 1782 1832 1843 1705 1681Fe+2 0026 0026 0028 0023 0023 0043 0025 0023 0051 0052Mg 0016 0015 0011 0017 0019 0020 0019 0020 0005 0008Ca 0853 0863 0849 0872 0854 0850 0853 0854 0796 0786Ba minus minus minus minus minus minus minus minus minus minusNa 0107 0110 0122 0108 0105 0109 0117 0114 0131 0136K 0004 0004 0006 0004 0003 0005 0003 0003 0011 0011Tet site 3977 3977 3974 3974 3978 3961 3979 3984 3964 3960Oct site 1005 1018 1022 1023 1003 1027 1022 1013 0995 0994
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1083
element concentrations are considerably greater in LAP thanin most of other low-Ti basalts (Fig 12bndashc) including theApollo 12 ilmenite basalts (Haskin et al 1971 Neal et al1994) The exceptions are NWA 032 the high-Al basalts ofLuna 16 (Philpotts et al 1972 Helmke and Haskin 1972 Maet al 1979) and some Apollo 14 high-Al basalts (Dickinsonet al 1985 Shervais et al 1985 Neal et al 1989a 1989b)
Relative concentrations of REEs in the LAP basalt arealso dissimilar to those of most other lunar basalts (Fig 13) inthat LAP is enriched in light REEs The exceptions are NWA032 which has a pattern nearly parallel to LAP and Apollo 14group 3 basalts (Dickinson et al 1985) which have a patternthat is similar although somewhat less steep in the heavyREEs Ratios of Th to REE in LAP are higher than those of allother lunar basalts except NWA 032 (Fig 14) and thedisparity in ThREE ratio between LAP and other lunarbasalts (except NWA 032) increases from the light to heavyREEs The Apollo 14 high-K basalts have similar ThREEratios for the middle REE Sm-Tb however (Neal et al 1989a
1989b) Overall in terms of its trace-element concentrationsLAP 02205 is most similar to NWA 032 The maindifferences are that NWA 032 is richer in elements associatedwith olivine (Mg Cr Co) and has concentrations ofincompatible elements that are 78ndash91 as great as those inLAP 02205
DISCUSSION
Evidence Supporting the Lunar Origin and Pairing of theLAP Stones
As stated in the introduction the meteorites LAP 0220502224 02226 02436 and 03632 were identified as lunarbasalts that were almost certainly paired (McBride et al 20032004a 2004b) A brief summary follows of the attributesfound in our more detailed petrographic examination thatsupport this initial classification and pairing interpretation
Results of oxygen isotope analyses (δ18O = +56 and
Table 5 Continued Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02224 02436 02205 02205 02226 02224 02436 02205 02205 02205plag plag plag plag plag plag plag barian KBa KBaNa rim Na rim matrix K rim K rim K rim K rim K-spar glass glass
N 24 5 13 10 1 5 1 10 10 23
Major elements in wt by EMPASiO2 4901 4879 5122 5152 4888 4935 5017 6026 5935 6356TiO2 008 008 016 017 lt002 008 014 na na naAl2O3 3163 3120 2960 2993 3213 3004 3002 2019 2063 2043Cr2O3 002 002 006 005 lt002 003 lt002 na na naFeO 117 130 267 192 147 195 173 065 074 116MgO 006 009 003 002 lt002 lt002 002 lt002 lt002 010CaO 1620 1622 1520 1549 1618 1602 1560 063 066 207BaO na na na na na na na 501 407 372Na2O 157 155 105 105 132 126 150 031 029 033K2O 023 021 090 067 067 056 086 1354 1162 586Total 1000 995 1007 1006 1007 993 1000 1008 1006 1007
Cation ratiosAn 839 842 846 852 835 845 807 33 minus minusOr 14 13 61 44 41 35 53 842 minus minusAb 147 145 105 104 124 120 140 30 minus minusCn 00 00 00 00 00 00 00 96 minus minus
Stoichiometry based on 8 oxygen atomsSi IV 2253 2257 2342 2344 2237 2293 2312 2863 2864 2951Al IV 1714 1701 1596 1609 1732 1645 1631 1131 1173 1124Fe+2 0045 0050 0102 0073 0056 0076 0067 0026 0030 0045Mg 0004 0006 0002 0001 0000 0001 0001 0001 0001 0007Ca 0798 0804 0745 0757 0793 0798 0770 0032 0034 0100Ba minus minus minus minus minus minus minus 0093 0077 0070Na 0140 0139 0093 0093 0117 0113 0134 0029 0027 0029K 0013 0013 0052 0039 0039 0033 0050 0820 0715 0353Tet site 3967 3957 3938 3954 3969 3938 3943 3994 4037 4075Oct site 0013 1011 0995 0963 1007 1020 1022 1002 0884 0604Plag = plagioclase mask = maskelynite N = number of analyses in the average na = not analyzed
1084 R Zeigler et al Ta
ble
6 A
vera
ge a
nd re
pres
enta
tive
cris
toba
lite
and
glas
s co
mpo
sitio
n in
the
LAP
basa
ltic
met
eorit
es
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
0220
502
226
0222
402
436
0220
502
205
0220
502
205
0220
502
224
0222
4cr
isto
balit
ecr
isto
balit
ecr
isto
balit
ecr
isto
balit
eSi
-ric
hpy
x-lik
eK
gla
ssIT
E-ric
hsh
ock
shoc
ksh
ock
MI g
lass
MI g
lass
in s
ympl
m
afic
gla
ssgl
ass
area
glas
s ar
eagl
ass
vein
N6
25
44
12
51
6515
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
979
598
17
984
798
45
672
542
76
783
236
67
463
486
441
TiO
20
270
270
230
230
664
810
374
032
341
623
13A
l 2O3
073
060
064
078
187
99
4210
13
544
139
86
123
Cr 2
O3
002
lt00
2lt0
02
002
lt00
20
13lt0
02
lt00
20
080
380
28Fe
O0
210
400
190
171
8615
91
183
392
719
618
520
5M
nOn
an
an
an
an
a0
22n
a0
420
220
290
25M
gO0
02lt0
02
lt00
2lt0
02
033
817
lt00
20
213
459
857
17C
aO0
190
200
200
236
8919
16
098
976
127
118
114
BaO
na
na
na
na
117
na
na
na
na
na
na
Na 2
O0
130
100
090
120
620
110
190
060
510
360
49K
2O0
030
050
07lt0
02
167
na
566
030
005
na
na
P 2O
5n
an
an
an
an
an
an
a2
32n
an
an
aF
na
na
na
na
na
na
na
008
na
na
na
Y2O
3n
an
an
an
an
an
an
a0
19n
an
an
aC
e 2O
3n
an
an
an
an
an
an
a0
12n
an
an
aSO
3n
an
an
an
an
an
an
a1
23n
an
an
aTo
tal
995
599
80
999
010
00
992
410
070
974
910
02
991
100
099
6Sy
mpl
= sy
mpl
ectit
e M
I = m
elt i
nclu
sion
N =
num
ber o
f ana
lyse
s in
the
aver
age
na
= n
ot a
naly
zed
The
shoc
ked
glas
s in
LAP
0222
4 is
the
parti
ally
mel
ted
area
(see
Fig
14)
and
onl
y th
e an
ayls
es o
fth
e gl
ass i
tsel
f wer
e in
clud
ed in
the
aver
age
not t
he m
iner
als t
hat w
ere
anal
yzed
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1085
Table 7 Representative phosphate compositions in LAP 0220533LAP LAP LAP LAP LAP LAP LAP LAP02205 02205 02205 02205 02205 02205 02205 02205RE- RE- RE- RE- RE- fluorapatite fluorapatite fluorapatitemerrillite merrillite merrillite merrillite merrillite
Major elements in wt by EMPASiO2 050 044 062 037 321 228 449 137Al2O3 022 lt005 009 lt005 lt005 007 014 lt005FeO 637 774 568 576 250 169 439 202MgO 020 037 025 028 lt005 lt005 lt005 lt005CaO 4326 4035 4233 4245 4983 5241 5003 5351Na2O 000 001 010 014 000 000 001 000P2O5 3885 4171 4382 4360 3540 3949 3771 4077Cl lt005 lt005 lt005 lt005 lt005 006 027 031F 047 044 050 048 168 245 130 186Y2O3 298 293 226 221 172 103 078 053La2O3 093 107 065 064 092 024 014 012Ce2O3 253 259 189 185 253 072 069 053Nd2O3 161 177 108 118 166 057 059 031Sm2O3 043 043 029 028 048 022 015 009Gd2O3 087 090 058 058 079 023 018 008Yb2O3 016 032 009 lt005 010 005 lt005 lt005ThO2 007 009 008 lt005 021 lt005 lt005 lt005minusO = (FCl) 021 020 022 021 072 105 061 085Sums 9930 1010 1001 9968 1004 1005 1003 1006
Table 8 Average sulfide and metal compositions in LAP 0220533Ave Fe metal High-Ni metal Troilite
N 5 1 8
Elemental percentage by EMPAFe 9209 5880 6280Ni 664 3377 lt002Co 141 595 lt002Ti 023 009 006Cr 043 017 lt002Mn lt002 004 lt002S lt002 lt002 3620Totals 1008 988 994Ideal troilite = 365 wt S 635 wt Fe N = number of analyses
Table 9 Modal mineralogy of the different LAP stonesLAP 0220533 LAP 0222616 LAP 0222424 LAP 0243614
Pyroxene 515 505 469 466Plagioclase 319 321 323 346Ilmenite 348 391 386 399Fay sympl 309 290 358 483Olivine 233 271 363 320Cristobalite 214 209 178 200Spinel (all) 034 045 040 039Troilite 025 024 024 022Fractures 49 49 53 421Shock glass 01 02 22 00N 633 times 106 905 times 106 470 times 106 396 times 106
All modal values are listed as percentages N = number of pixels
1086 R Zeigler et al
Fig 1 Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) and fayalite(more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phases arepyroxene and olivine a) LAP 0222616 b) LAP 0243614 c) LAP 0222424 d) LAP 0220533
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1087
δ17O = +27) performed by Mayeda and Clayton (reported inMcBride et al 2003) constrain the origin of LAP 02205 tothe Earth the Moon or an enstatite meteorite parent bodyLAP is clearly a meteorite all four of the stones have fusioncrusts (ruling out a terrestrial origin) The extremely ferroannature of LAP rules out the enstatite parent body as theprovenance FeOMnO ratios of mafic silicates arediagnostic of origins from different planetary bodies in thesolar system (Dymek et al 1976 Papike 1998) Ratios ofFeOMnO in LAP pyroxenes (average sim60) and olivines(average sim95) are consistent only with lunar origin (Fig 15)Furthermore the presence of Fe(Ni) metal and troilite thecompletely anhydrous nature of the sample the apparentlack of Fe3+ in all phases the calcic nature of theplagioclase and the deep negative Eu anomaly are allcommon in lunar basalts
With regard to texture mineral assemblage and mineralchemistry the four LAP 02xxx stones appear to beindistinguishable from each other Although we did not studythe mineral chemistry of the LAP 03632 in depth the textureand mineral assemblage are identical to the LAP 02xxxstones Furthermore the collection locations of the five stonesform a linear array sim3 km in length that is perpendicular to theflow of the ice sheet (John Schutt personal communication)Thus in the absence of cosmic-ray exposure data to thecontrary we conclude that the four LAP 02xxx stones studiedare paired
Compositional Variability among Small Subsamples ofLAP 02205 and NWA 032
Samples of lunar meteorites available for study at most afew hundred milligrams are very small by the standards ofterrestrial geology and geochemistry Nevertheless we havetaken our samples and subdivided them into numerous evensmaller (10ndash50 mg) subsamples for bulk compositionalanalysis (Korotev et al 1983 1996 2003a 2003b Jolliffet al 1991 1998 Fagan et al 2002) This procedure providesan estimate of the whole-rock composition through a mass-weighted mean that is equivalent to a single analysis of theentire mass of the allocated sample The variation amongsmall subsamples however provides additional informationabout compositional variations associated with mineralassemblage and proportions about petrogenesis and aboutpossible relationships to other meteorites (eg Korotev et al2003a 2003b) and how well the ldquowhole-rockrdquo compositionis likely to represent that of the source region of the meteorite(Korotev et al 2000a) In the following discussion weevaluate the causes of differences in composition amongsmall subsamples of LAP and NWA 032
The range of concentrations among the 19 subsamples ofLAP (27ndash40 mg) is relatively small for the most preciselydetermined major elements (SiO2 TiO2 Al2O3 FeO CaONa2O) and most precisely determined trace elements that arecompatible with the major mineral phases (Co Sc Eu) The
Fig 1 Continued Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) andfayalite (more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phasesare pyroxene and olivine d) LAP 0220533
1088 R Zeigler et al
relative sample standard deviations (s ) range from 08 to76 (with only Co and Eu gt 5 Table 1) The exceptionsare MgO and Cr2O3 for which the relative standarddeviations are distinctly greater 12 and 16 respectivelyFor incompatible elements that we determined precisely(lt9 analytical uncertainty La Ce Sm Tb Yb Lu Hf Taand Th) relative standard deviations range from 7 to 11These variations are caused by a combination ofunrepresentative sampling of the major mineral phasesowing to the coarse grain size (up to sim1 mm3) relative to theINAA subsample size (about 12 mm3 assuming that thedensity of LAP is sim35 gmm3) and to the heterogeneousdistribution of some relatively minor phases with high
concentrations of a given element This problem is not new asmany investigators have previously wrestled with theproblem of studying relatively coarse-grained lunar basaltswith small allocated subsample sizes characteristic of rareextraterrestrial samples (Korotev and Haskin 1975 Haskinet al 1977 Lindstrom and Haskin 1978 Ryder and Schuraytz2001) Ryder and Schuraytz (2001) showed that sim5 g ofmaterial are needed to achieve a representative sample ofApollo 15 olivine-normative basalts which have grain sizeson the order of a millimeter or greater
Among the LAP subsamples Cr2O3 and MgOconcentrations correlate positively (R2 = 081) as a result ofthe association of chromite and Cr-ulvˆspinel with olivine
Fig 2 BSE images from LAP 0220533 a) a large round olivine (oli) grain and a smaller subhedral olivine grain (left center of the image)both surrounded by zoned pyroxene (pyx) and plagioclase (plag) with melt inclusions (MI) and inclusions of chromite (chr) A smallulvˆspinel (Usp) grain occurs in the upper left b) A large irregular olivine grain and a smaller mostly resorbed olivine grain The larger graincontains both melt inclusions (MI) and chromite grains The associated ilmenite (Ilm) grain is the most magnesian ilmenite grain observed Acomposite grain of metal and troilite (MetSulf) is also present c) A BSE image showing the zoning in multiple large pyroxene grainsintergrown with plagioclase and maskelynite (mask) grains One small cristobalite (crist) grain is also present d) A BSE image showingseveral large plagioclase grains some of which contain both fractured areas (plagioclase) and smooth areas (maskelynite) Also present areseveral areas of groundmass including a fayalite symplectite and a cristobalite grain cut by an ilmenite lath
x
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1089
The large variations seen in MgO Cr2O3 and to a lesserextent Co concentrations occur because of the large relativevariation in the fraction of modal olivine among thesubsamples Normatively the compositional rangecorresponds to minus03ndash25 olivine (one subsample has 03normative quartz) and 032ndash049 chromite The relativelysmall variations seen among concentrations of the other majorelements as well as Sc and Eu are controlled byunrepresentative sampling of the major mineral phasespyroxene (Sc Ca Fe Si) and plagioclase (Al Na Ca Si Eu)and the minor but widely distributed mineral ilmenite (Ti Fe)Trace amounts of a few minerals that are found only ingroundmass have high concentrations of incompatible traceelements relative to the concentration of those elements inthe bulk meteorite These minerals include K-feldspar (Ba)
Fig 3 a) CaO versus Mgprime (molar Mg[Mg + Fe]100) in the olivinesof the different LAP stones The compositions range from cores ofFo55ndash67 trending towards rims typically in the Fo40 range withextreme zonation to rims of Fo15ndash20 in a few cases Where analyzedthe composition of groundmass fayalite are also shown b) Anelectron microprobe traverse across a small strongly zoned olivinegrain in LAP 0220533 The grain shows zoning from a core of simFo58to a rim composition of simFo18 over sim100 microm The break in the zoning(black arrow) is centered on a fracture in the olivine grain
Fig 4 Compositions of LAP oxides plotted on the (FeMgMn)O-(CrAl)2O3-TiO2 ternary (after El Goresy et al 1971) Compositionsof endmember ilmenite (FeTiO3) ulvˆspinel (Fe2TiO4) andchromite (FeCr2O4) are labeled For a description of theclassification scheme see the footnote of Table 3 a) LAP 0220533b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1090 R Zeigler et al
RE-merrillite (P REEs Th) and baddeleyite (Zr Hf U Th)Therefore the variation in the amount of the groundmassldquophaserdquo in the different subsamples controls the ITEconcentrations in the various subsamples
For most of the major elements subsamples of NWA 032have relative standard deviations (RSD) that areinsignificantly different from those of LAP (Table 1) eventhough the average subsample size for NWA 032 (sim14 mgFagan et al 2002) was smaller than for LAP (sim34 mg) TheRSDs of MgO and Cr2O3 for NWA 032 are again highbecause it has a porphyritic texture with large phenocrysts(millimeter scale) of olivine (with chromite inclusions) andmagnesian pyroxene but a fine-grained groundmass of
plagioclase Fe-rich pyroxene ilmenite and glass keeps theRSDs of other major and incompatible trace elements low
Source Crater Pairing of LAP and NWA 032
We find the similarities in chemistry and petrographybetween LAP and NWA 032 when compared to the largeranges observed among Apollo and Luna samples to be sogreat that it is highly unlikely that two meteorites so similarcould derive from different locations Below we summarizethe similarities and differences
The textures of NWA 032 and LAP are markedlydifferent from each other NWA 032 has a porphyritic texture
Fig 5 BSE images from LAP 0220533 a) oxide grains set in and around a large olivine grain individual grains of ilmenite (Ilm) Cr-ulvˆspinel (Chr-Usp) and chromite (Chr) composite chromian ulvˆspinel-chromite (ChrUsp) grains with accompanying pyroxene andplagioclase (grey and black areas) b) A close-up of a zoned spinel grain with a chromite core and a Cr-ulvˆspinel rim c) A large cristobalite(Crist) grain with many inclusions of fayalite pyroxene (Pyx) plagioclase (Plag) troilite (Sulf) phosphate K-rich glass and the ITE-richglass Also present are several areas of fayalite symplectite (Fay Symp) with inclusions of plagioclase silica ilmenite troilite and K-richglass d) A BSE image of a different area of groundmass showing a large grain of fayalite symplectite containing inclusions of plagioclasesilica ilmenite troilite K-rich glass and Fe-rich pyroxene A large ilmenite (Ilm) grain cuts through the symplectite and several large troilitegrains are also present
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1079
All of the LAP stones have relatively coarse-grained (upto approximately 15 mm) subophitic texture They consistpredominantly of pyroxene and plagioclase with minoramounts of olivine ilmenite and a groundmass dominated byfayalite and cristobalite They contain trace amounts ofchromite chromian ulvˆspinel ulvˆspinel troilite Fe-metalbarian K-feldspar fluor-apatite RE-merrillite tranquillityite(Fe8(YZr)2Ti3Si3O24) and baddeleyite (ZrO2) The modalmineral proportions differ slightly from section to section(Table 9) A few veins and pockets of basaltic glass ofpseudo-whole rock composition (likely shock melted) alsooccur in thin sections LAP 0220533 and LAP 0222424 Theorder in which minerals are inferred to have crystallized ischromite olivine pyroxene plagioclase and groundmass
Olivine grains vary in size from 003 to sim1 mm with01 to 03 mm being typical The modal abundance of olivineranges from 23 to 36 The grains are usually anhedral(rarely subhedral Fig 2a) typically with round or irregularmorphology and uneven contact with the surroundingpyroxene (Fig 2b) Some olivine grains have inclusions ofchromite or Cr-ulvˆspinel grains or both and a few haveldquomeltrdquo inclusions that have two phases in them mafic glasswith a pyroxene-like composition (sim10 wt Al2O3 Table 6)and K-rich high-silica glass similar to the glass seen in thefayalite symplectite grains in the groundmass (sim3 wt K2O68 wt SiO2) Most of the larger olivine grains are zonedwith cores of Fo55ndash65 and rims typically in the Fo38ndash45 range(Fig 3a Table 2) though in a few instances zoning to rims ofFosim20 is observed (Fig 3b) Most of the smaller olivine grainsare not zoned (or not strongly zoned) and they typically havecompositions in the Fo52ndash57 range with the smallest grainshaving the most magnesian compositions The apparentreaction texture between olivine and pyroxene and therelatively magnesian rims on compositions of the smallestolivine grains (likely the remnant cores of grains that havebeen almost completely resorbed) are strong indications thatolivine was being resorbed when the rock solidified
Chromite and Cr-ulvˆspinel grains almost always occuras inclusions within or closely associated with olivine grainsThey also have relatively restricted compositional ranges(Fig 4 Table 4) and they occur individually and as compositegrains with cores of chromite (Chr62ndash68Usp13ndash18Spn16ndash25) andrims of Cr ulvˆspinel (Chr6ndash19Usp71ndash91Spn3ndash11) (Figs 5aand 5b) We found few spinel compositions intermediate tothese end members The total modal abundance of spinel(including ulvˆspinel in the groundmass) is small rangingfrom 03 to 04 Where these two phases are intergrown theboundary between them is sharp with differences in Cr2O3concentration exceeding 20 wt within a few micrometers ofthe boundary A few of the chromite grains have inclusionsof pyroxene with a range of compositions (Mgprime of 47ndash59Wo16ndash31 and TiO2 concentrations from 11ndash24 wt)
Pyroxene grains in LAP are anhedral display undulatoryto mosaic extinction and range in size up to sim1 mm (Fig 2c)
In many cases pyroxene grains partially enclose plagioclasegrains in a subophitic texture The modal abundance ofpyroxene ranges from 47 to 52 The pyroxene grains havemagnesian cores of pigeonite and subcalcic augite (Mgprime fromsim50 to 68) with a wide range of CaO concentrations (Wo11 toWo36 Table 3 Fig 6) although there appears to be a bimodaldistribution of Wo contents with a minimum near Wo20(Fig 6 insets) In some cases pyroxene core compositionsgrade continuously to nearly end member hedenbergite(Fs58Wo40) and pyroxferroite (Fs86Wo13) In a few rare casescontacts between magnesian and ferroan pyroxenes are sharpand linear Compositions of pyroxene grains in contact withpartially resorbed olivine grains vary considerably incomposition The most common composition issubcalcic augite (Wo gt 20) with FeO concentrations in therange Fs24ndash49
The TiAl and TiCr ratios in the LAP pyroxenes arestrongly correlated with Mgprime as expected according toelement compatibility (eg Bence and Papike 1972) Theatomic TiCr ratio increases with decreasing Mgprime in LAPpyroxenes (Fig 7a) This reflects the compatible behavior ofCr and the incompatible behavior of Ti in early crystallizingphases of low-Ti lunar basaltic magmas The most magnesianpyroxenes have atomic TiAl ratios very close to 14indicating that aluminum was introduced through boththe Tschermak (AlAlMgminus1Siminus1) and coupled titanium(TiAl2Mgminus1Siminus2) exchange reactions in approximately equalproportions (Thompson 1982) As pyroxene becomesprogressively more ferroan the TiAl cation ratio approaches12 suggesting a gradual increase in the proportion of Alincorporated due to coupled Ti substitution (Fig 7b) Theleast magnesian pyroxenes (Mgprime lt40) have TiAl ratiosapproaching 34 An increase in TiAl ratios in pyroxene from14 to 12 with decreasing Mgprime in lunar basalts has previouslybeen interpreted as a result of pyroxene crystallization bothprior to the onset of plagioclase crystallization (ratiosaround 14) and during plagioclase crystallization (14ndash12Bence and Papike 1972) Bence and Papike (1972) attributedthe high relative concentrations of Ti in the late-stage Fe-richlunar pyroxenes to Ti3+
Plagioclase forms elongated subhedral to anhedralgrains up to 175 mm long The modal abundance ofplagioclase ranges from 32 to 35 Pyroxene inclusions ofa variety of sizes with compositions spanning nearly theentire compositional spectrum observed occur withinplagioclase Most plagioclase grains are highly fracturedalthough some or portions of some are smooth in polishedsections as seen in the BSE images (Fig 2d) These smoothareas consist partially or entirely of maskelynite as indicatedby their isotropic (or nearly isotropic) character in cross-polarized light Plagioclase grains are complexly zoned Theirtypical core composition is An886Ab11Or04 with sim1 wtFeO + MgO and an Mgprime of 34 (Fig 8 Table 5) Their rims areas wide as sim40 microm and gradually increase in K (up to simOr5)
1080 R Zeigler et al
and FeO (up to sim3 wt) while decreasing in MgO(to lt002 wt Fig 9) The Na2O concentrations firstincrease up to simAb14 then decrease sharply to less thanAb10 (which is lower than in the cores) The extreme rimcomposition of the large plagioclase grains is similar to that ofthe plagioclase found as inclusions in groundmass fayaliteand cristobalite grains (next paragraph Table 5) There is noapparent overall compositional difference between the coresof the maskelynite and the plagioclase grains
Fayalite cristobalite and ilmenite are the dominantminerals in the groundmass typically occurring togetheralthough each can be found independently All of the phaseshave relatively minor modal abundances fayalite (29ndash48)cristobalite (18ndash21) and ilmenite (35ndash40) Silicadisplaying the ldquocracklerdquo pattern distinctive to cristobaliteoccurs as anhedral grains up to 05 mm in size Thecristobalite grains contain minor Al2O3 TiO2 FeO and CaO(Σ sim13 wt Table 6) Inclusions of late-crystallizing phasessuch as K-rich plagioclase K-rich glass K-feldspar fayaliteFe-rich pyroxene phosphate and mafic glass withhigh concentrations of incompatible elements are common(Fig 5c) Fayalite grains (Fo45 sim05 wt CaO) range in size
up to 075 mm and usually form a symplectite texture withinclusions of K-rich glass silica K-rich plagioclase andilmenite (Fig 5d) Fayalite with no (or few) inclusions occursonly rarely Ilmenite is the dominant oxide in the groundmassforming elongate laths up to 1 mm in length Typically theilmenite is poor in Mg (sim02 wt average) although a singlegrain of more magnesian ilmenite associated with a largeolivine grain was observed (Fig 2b) Less common aresmaller subhedral ulvˆspinel grains (lt005 mm) thathave compositions approaching end member ulvˆspinel(Chr0ndash4Usp93ndash98Sp2ndash3) A few composite grains of ilmeniteand ulvˆspinel were observed
Also found in the groundmass are a variety of traceminerals including both fluorapatite and RE-merrillite(Table 7) Phosphate grains most commonly occur betweenplagioclase and ferropyroxene sometimes with associatedcristobalite troilite or both Barian K-feldspar (sim5 wt BaO)also occurs in the groundmass usually in the same areas asthe phosphate minerals (Table 5) Only a few K-feldspargrains (the largest) have stoichiometry that unambiguouslyidentifies them as K-feldspar while many K-rich grainshave excess Si suggesting that they may be intergrowths of
Table 4 Average oxide compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02205 02226 02224 02436 02205 02226 02224 02436 02205 02226 02224Al Al Al Al Cr-rich Cr-rich Cr-rich Cr-rich CrAl CrAl CrAlchr chr chr chr usp usp usp usp usp usp usp
N 23 11 13 5 22 1600 7 13 9 22 10
Major elements in wt by EMPAFeO 3444 3503 3532 3433 5705 5832 5846 5868 6191 6198 6180TiO2 546 532 540 517 2833 2871 2892 2909 3254 3151 3161Cr2O3 4384 4357 4331 4391 928 840 851 776 234 310 338Al2O3 1142 1178 1140 1217 287 261 261 276 191 204 203MgO 283 242 218 292 093 061 069 065 021 028 031MnO 027 024 025 027 035 032 034 033 036 032 034V2O3 073 074 076 075 036 031 033 033 022 025 026SiO2 007 009 008 009 lt002 007 008 018 lt002 008 007CaO 004 004 003 lt002 010 005 006 011 008 007 005ZnO 003 na na na 004 na na na 003 na naTotals 991 992 987 996 993 994 1000 999 996 996 999
Stoichiometry based on 4 (spinel) and 3 (ilmenite) oxygen atomsSi IV 0003 0003 0003 0003 0000 0003 0003 0006 0000 0003 0003Al VI 0469 0484 0472 0496 0125 0114 0113 0119 0083 0089 0088Ti 0143 0139 0143 0134 0784 0798 0798 0803 0907 0880 0880V 0020 0021 0021 0021 0011 0009 0010 0010 0007 0007 0008Cr 1208 1201 1204 1199 0270 0245 0247 0225 0068 0091 0099Fe2+ 1004 1021 1039 0992 1756 1802 1794 1801 1920 1925 1913Mn2+ 0008 0007 0007 0008 0011 0010 0011 0010 0011 0010 0011Mg 0147 0126 0114 0151 0051 0034 0038 0035 0012 0016 0017Zn 0001 minus minus minus 0001 minus minus minus 0001 minus minusCa 0002 0002 0001 0000 0004 0002 0002 0004 0003 0003 0002Sum 2+ 1162 1156 1161 1151 1823 1847 1844 1851 1947 1953 1942Sum 3 4+ 1844 1849 1844 1854 1190 1168 1170 1163 1066 1071 1078Total 3003 3001 3002 3001 3012 3013 3012 3007 3013 3020 3017
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1081
K-feldspar and silica (granophyric texture) at a scale smallenough to be beyond the resolution of the electron microprobe(less than sim01 microm)
Two glass types of distinct composition presumably late-stage residual liquids occur in the groundmass The first is aKSi-rich glass (78 wt SiO2 sim56 wt K2O) that makes upa considerable percentage of the inclusions in the cristobaliteand particularly the fayalite grains The second type ofevolved glass occurs as very small (lt5 microm) roundedinclusions in cristobalite grains This glass has a silica-poorFe-rich bulk composition (sim36 wt SiO2 sim39 wt FeOTable 6) but it is also considerably enriched in manyincompatible elements 23 wt P2O5 12 wt SO3 02 wtY2O3) Commonly we observed minute grains of fayalitetroilite or phosphate associated with this glass These twolate-stage glasses could represent conjugate liquids producedby late-stage immiscibility of an evolved residual meltSimilar glasses were observed in some plutonic rocks fromthe Apollo 14 site (Jolliff et al 1991)
Troilite blebs (with nearly ideal stoichiometry Table 8)are scattered throughout the groundmass along with trace Fe-metal grains which are usually intergrown with troilite orovergrown on chromite grains These grains typicallycontained 66 wt Ni and 14 wt Co though one grain had338 wt Ni and 60 wt Co (Table 8) A few grains ofbaddelyite (ZrO2) and tranquillityite (Zr-Fe-Ti silicate) wereidentified by energy-dispersive spectroscopy (EDS) in thegroundmass
A variety of shock effects occur in the minerals of thesethin sections (eg plagioclase converted to maskelynitemosaicism in the pyroxene) The level of shock was such thatlocalized partial melting occurred in some areas of themeteorite The areas of shock melt have severalmorphologies small melt pockets (LAP 02205 Fig 10a)veins of melt (LAP 0222424 Fig 10b) and in some casesareas that were only partially melted (LAP 0222424Fig 10c) with discernable mineral grains still present(typically maskelynite) Although veins of shock melt are rare
Table 4 Continued Average oxide compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02436 02205 02226 02224 02436 02205 02226 02224 02436 02205CrAl end end end end Mgusp usp usp usp usp ilm ilm ilm ilm ilm
N 11 11 2 3 3 24 16 20 18 2
Major elements in wt by EMPAFeO 6202 6375 6445 6355 6465 4657 4647 4634 4624 4463TiO2 3353 3267 3226 3396 3231 5198 5226 5233 5264 5296Cr2O3 209 026 023 011 037 010 012 015 016 038Al2O3 202 179 206 216 227 008 011 013 010 006MgO 022 005 008 007 003 014 010 016 019 150MnO 034 031 027 029 027 038 033 037 027 035V2O3 023 018 015 019 016 031 029 029 028 035SiO2 015 lt002 011 010 007 003 003 024 004 lt002CaO 007 010 007 008 010 013 006 010 009 008ZnO na 008 na na na 003 na na na lt002Totals 1007 992 997 1005 1002 997 998 1001 1000 1003
Stoichiometry based on 4 (spinel) and 3 (ilmenite) oxygen atomsSi IV 0005 0001 0004 0004 0003 0001 0001 0006 0001 0000Al VI 0087 0079 0091 0093 0099 0002 0003 0004 0003 0002Ti 0920 0921 0906 0937 0901 0990 0993 0989 0996 0991V 0007 0005 0004 0006 0005 0006 0006 0006 0006 0007Cr 0060 0008 0007 0003 0011 0002 0002 0003 0003 0007Fe2+ 1893 1999 2012 1950 2005 0986 0982 0974 0973 0928Mn2+ 0010 0010 0009 0009 0009 0008 0007 0008 0006 0007Mg 0012 0003 0004 0004 0002 0005 0004 0006 0007 0056Zn minus 0002 minus minus minus 0001 minus minus minus 0000Ca 0003 0004 0003 0003 0004 0004 0002 0003 0002 0002Sum 2+ 1918 2018 2028 1966 2019 1004 0995 0991 0988 0994Sum 3 4+ 1080 1014 1012 1043 1019 1001 1005 1008 1009 1007Total 2992 3032 3035 3005 3036 2004 2000 1992 1996 2001The spinel catagories where chosen based primarily on Cr2O3 content with Al chromite (chr) having gt40 wt Cr2O3 Cr-rich ulvˆspinel (usp) having 15ndash
5 wt Cr2O3 CrAl ulvˆspinel having 5ndash05 wt Cr2O3 and endmember ulvospinel having lt05 wt Cr2O3 Also seen were TiAl chromite (30ndash40 wtCr2O3) and high-Cr ulvˆspinel (30ndash15 wt Cr2O3) which are likely the result of an anlyses overlapping simultaneously on both an Al chromite and Cr-rich ulvˆspinel grain Similarly compositions intermediate to ilmenite and end ulvˆspinel were seen These compositions are not listed in this table but areshown in Fig 4 N = number of analyses in the average na = not analyzed
1082 R Zeigler et al
in our thin sections such veins were reported as pervasive inthe original macroscopic description of all five LAP stones(McBride et al 2003 2004a 2004b)
The various shock-induced effects observed in LAP canbe used to quantify and constrain the level of shock that LAPexperienced The presence of both plagioclase andmaskelynite in these samples suggests that the lower end ofthe range listed for conversion of plagioclase to maskelynite(30ndash45 GPa Stˆffler and Hornemann 1972 Ostertag 1983)is appropriate The mosaicism seen in the pyroxene istypically associated with shock values in the 30ndash75 GParange (Kieffer et al 1976 Schaal et al 1979) The presenceof shock-melt veins that have melted both pyroxene andplagioclase (based on the melt composition Table 6)indicates LAP should have been subjected to shock levels ofgt75ndash80 GPa (Kieffer et al 1976 Schaal et al 1979) Thedifferent shock effects observed reflect a range fromlt30 GPa (areas were plagioclase is preserved) to gt75 GPa(areas where shock melting occurred) over distances of onlya few millimeters
Bulk Composition and Comparison to Other LunarBasalts
LAP is a moderately aluminous (sim10 wt Al2O3) low-Ti(31 wt TiO2) mare basalt that falls near the Fe-rich(222 wt FeO) end of the range of FeO concentrationsobserved among lunar basalts It is more ferroan (Mgprime = 347)than any basalt in the Apollo or Luna collection (Fig 11a)Among lunar basalts only meteorites Asuka-881757 andYamato-793169 have comparably low Mgprime values (Koeberlet al 1993 Warren and Kallemeyn 1993 Thalmann et al1996 Korotev et al 2003a) LAP is enriched in Na2O(038 wt) relative to other ferroan (eg Asuka-881757 andYamato-793169) and Fe-rich basalts except for NWA 032(Fig 11b)
Regarding trace elements LAP is enriched in Cocompared to most lunar mare basalts with comparable Scconcentrations (Table 1 Fig 12a) Among Apollo and Lunabasalts only the Apollo 12 ilmenite basalts (Rhodes et al1977 Neal et al 1994) are comparable Incompatible trace-
Table 5 Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02205 02226 02224 02436 02205 02226 02224 02436 02205 02226plag plag plag plag mask mask mask mask plag plagcore core core core core core core core Na rim Na rim
N 123 86 48 88 29 49 33 32 12 3
Major elements in wt by EMPASiO2 4715 4657 4689 4639 4753 4741 4663 4673 4949 4960TiO2 010 007 007 006 013 008 006 006 027 019Al2O3 3337 3367 3296 3363 3367 3291 3376 3415 3170 3103Cr2O3 003 lt002 lt002 002 007 002 lt002 002 004 003FeO 068 067 073 058 060 111 066 060 134 136MgO 023 022 017 024 027 029 028 029 008 012CaO 1730 1746 1709 1763 1747 1726 1730 1740 1628 1597BaO na na na na na na na na na naNa2O 120 123 136 121 119 123 131 128 148 153K2O 006 007 010 006 005 009 006 005 020 019Total 1000 1000 994 998 1008 1004 1001 1006 1006 1000
Cation ratiosAn 885 883 869 887 888 881 877 880 848 842Or 04 04 06 04 03 05 03 03 12 12Ab 111 112 125 110 109 113 120 117 140 146Cn 00 00 00 00 00 00 00 00 00 00
Stoichiometry based on 8 oxygen atomsSi IV 2168 2147 2173 2143 2168 2179 2147 2140 2259 2279Al IV 1809 1830 1801 1831 1810 1782 1832 1843 1705 1681Fe+2 0026 0026 0028 0023 0023 0043 0025 0023 0051 0052Mg 0016 0015 0011 0017 0019 0020 0019 0020 0005 0008Ca 0853 0863 0849 0872 0854 0850 0853 0854 0796 0786Ba minus minus minus minus minus minus minus minus minus minusNa 0107 0110 0122 0108 0105 0109 0117 0114 0131 0136K 0004 0004 0006 0004 0003 0005 0003 0003 0011 0011Tet site 3977 3977 3974 3974 3978 3961 3979 3984 3964 3960Oct site 1005 1018 1022 1023 1003 1027 1022 1013 0995 0994
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1083
element concentrations are considerably greater in LAP thanin most of other low-Ti basalts (Fig 12bndashc) including theApollo 12 ilmenite basalts (Haskin et al 1971 Neal et al1994) The exceptions are NWA 032 the high-Al basalts ofLuna 16 (Philpotts et al 1972 Helmke and Haskin 1972 Maet al 1979) and some Apollo 14 high-Al basalts (Dickinsonet al 1985 Shervais et al 1985 Neal et al 1989a 1989b)
Relative concentrations of REEs in the LAP basalt arealso dissimilar to those of most other lunar basalts (Fig 13) inthat LAP is enriched in light REEs The exceptions are NWA032 which has a pattern nearly parallel to LAP and Apollo 14group 3 basalts (Dickinson et al 1985) which have a patternthat is similar although somewhat less steep in the heavyREEs Ratios of Th to REE in LAP are higher than those of allother lunar basalts except NWA 032 (Fig 14) and thedisparity in ThREE ratio between LAP and other lunarbasalts (except NWA 032) increases from the light to heavyREEs The Apollo 14 high-K basalts have similar ThREEratios for the middle REE Sm-Tb however (Neal et al 1989a
1989b) Overall in terms of its trace-element concentrationsLAP 02205 is most similar to NWA 032 The maindifferences are that NWA 032 is richer in elements associatedwith olivine (Mg Cr Co) and has concentrations ofincompatible elements that are 78ndash91 as great as those inLAP 02205
DISCUSSION
Evidence Supporting the Lunar Origin and Pairing of theLAP Stones
As stated in the introduction the meteorites LAP 0220502224 02226 02436 and 03632 were identified as lunarbasalts that were almost certainly paired (McBride et al 20032004a 2004b) A brief summary follows of the attributesfound in our more detailed petrographic examination thatsupport this initial classification and pairing interpretation
Results of oxygen isotope analyses (δ18O = +56 and
Table 5 Continued Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02224 02436 02205 02205 02226 02224 02436 02205 02205 02205plag plag plag plag plag plag plag barian KBa KBaNa rim Na rim matrix K rim K rim K rim K rim K-spar glass glass
N 24 5 13 10 1 5 1 10 10 23
Major elements in wt by EMPASiO2 4901 4879 5122 5152 4888 4935 5017 6026 5935 6356TiO2 008 008 016 017 lt002 008 014 na na naAl2O3 3163 3120 2960 2993 3213 3004 3002 2019 2063 2043Cr2O3 002 002 006 005 lt002 003 lt002 na na naFeO 117 130 267 192 147 195 173 065 074 116MgO 006 009 003 002 lt002 lt002 002 lt002 lt002 010CaO 1620 1622 1520 1549 1618 1602 1560 063 066 207BaO na na na na na na na 501 407 372Na2O 157 155 105 105 132 126 150 031 029 033K2O 023 021 090 067 067 056 086 1354 1162 586Total 1000 995 1007 1006 1007 993 1000 1008 1006 1007
Cation ratiosAn 839 842 846 852 835 845 807 33 minus minusOr 14 13 61 44 41 35 53 842 minus minusAb 147 145 105 104 124 120 140 30 minus minusCn 00 00 00 00 00 00 00 96 minus minus
Stoichiometry based on 8 oxygen atomsSi IV 2253 2257 2342 2344 2237 2293 2312 2863 2864 2951Al IV 1714 1701 1596 1609 1732 1645 1631 1131 1173 1124Fe+2 0045 0050 0102 0073 0056 0076 0067 0026 0030 0045Mg 0004 0006 0002 0001 0000 0001 0001 0001 0001 0007Ca 0798 0804 0745 0757 0793 0798 0770 0032 0034 0100Ba minus minus minus minus minus minus minus 0093 0077 0070Na 0140 0139 0093 0093 0117 0113 0134 0029 0027 0029K 0013 0013 0052 0039 0039 0033 0050 0820 0715 0353Tet site 3967 3957 3938 3954 3969 3938 3943 3994 4037 4075Oct site 0013 1011 0995 0963 1007 1020 1022 1002 0884 0604Plag = plagioclase mask = maskelynite N = number of analyses in the average na = not analyzed
1084 R Zeigler et al Ta
ble
6 A
vera
ge a
nd re
pres
enta
tive
cris
toba
lite
and
glas
s co
mpo
sitio
n in
the
LAP
basa
ltic
met
eorit
es
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
0220
502
226
0222
402
436
0220
502
205
0220
502
205
0220
502
224
0222
4cr
isto
balit
ecr
isto
balit
ecr
isto
balit
ecr
isto
balit
eSi
-ric
hpy
x-lik
eK
gla
ssIT
E-ric
hsh
ock
shoc
ksh
ock
MI g
lass
MI g
lass
in s
ympl
m
afic
gla
ssgl
ass
area
glas
s ar
eagl
ass
vein
N6
25
44
12
51
6515
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
979
598
17
984
798
45
672
542
76
783
236
67
463
486
441
TiO
20
270
270
230
230
664
810
374
032
341
623
13A
l 2O3
073
060
064
078
187
99
4210
13
544
139
86
123
Cr 2
O3
002
lt00
2lt0
02
002
lt00
20
13lt0
02
lt00
20
080
380
28Fe
O0
210
400
190
171
8615
91
183
392
719
618
520
5M
nOn
an
an
an
an
a0
22n
a0
420
220
290
25M
gO0
02lt0
02
lt00
2lt0
02
033
817
lt00
20
213
459
857
17C
aO0
190
200
200
236
8919
16
098
976
127
118
114
BaO
na
na
na
na
117
na
na
na
na
na
na
Na 2
O0
130
100
090
120
620
110
190
060
510
360
49K
2O0
030
050
07lt0
02
167
na
566
030
005
na
na
P 2O
5n
an
an
an
an
an
an
a2
32n
an
an
aF
na
na
na
na
na
na
na
008
na
na
na
Y2O
3n
an
an
an
an
an
an
a0
19n
an
an
aC
e 2O
3n
an
an
an
an
an
an
a0
12n
an
an
aSO
3n
an
an
an
an
an
an
a1
23n
an
an
aTo
tal
995
599
80
999
010
00
992
410
070
974
910
02
991
100
099
6Sy
mpl
= sy
mpl
ectit
e M
I = m
elt i
nclu
sion
N =
num
ber o
f ana
lyse
s in
the
aver
age
na
= n
ot a
naly
zed
The
shoc
ked
glas
s in
LAP
0222
4 is
the
parti
ally
mel
ted
area
(see
Fig
14)
and
onl
y th
e an
ayls
es o
fth
e gl
ass i
tsel
f wer
e in
clud
ed in
the
aver
age
not t
he m
iner
als t
hat w
ere
anal
yzed
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1085
Table 7 Representative phosphate compositions in LAP 0220533LAP LAP LAP LAP LAP LAP LAP LAP02205 02205 02205 02205 02205 02205 02205 02205RE- RE- RE- RE- RE- fluorapatite fluorapatite fluorapatitemerrillite merrillite merrillite merrillite merrillite
Major elements in wt by EMPASiO2 050 044 062 037 321 228 449 137Al2O3 022 lt005 009 lt005 lt005 007 014 lt005FeO 637 774 568 576 250 169 439 202MgO 020 037 025 028 lt005 lt005 lt005 lt005CaO 4326 4035 4233 4245 4983 5241 5003 5351Na2O 000 001 010 014 000 000 001 000P2O5 3885 4171 4382 4360 3540 3949 3771 4077Cl lt005 lt005 lt005 lt005 lt005 006 027 031F 047 044 050 048 168 245 130 186Y2O3 298 293 226 221 172 103 078 053La2O3 093 107 065 064 092 024 014 012Ce2O3 253 259 189 185 253 072 069 053Nd2O3 161 177 108 118 166 057 059 031Sm2O3 043 043 029 028 048 022 015 009Gd2O3 087 090 058 058 079 023 018 008Yb2O3 016 032 009 lt005 010 005 lt005 lt005ThO2 007 009 008 lt005 021 lt005 lt005 lt005minusO = (FCl) 021 020 022 021 072 105 061 085Sums 9930 1010 1001 9968 1004 1005 1003 1006
Table 8 Average sulfide and metal compositions in LAP 0220533Ave Fe metal High-Ni metal Troilite
N 5 1 8
Elemental percentage by EMPAFe 9209 5880 6280Ni 664 3377 lt002Co 141 595 lt002Ti 023 009 006Cr 043 017 lt002Mn lt002 004 lt002S lt002 lt002 3620Totals 1008 988 994Ideal troilite = 365 wt S 635 wt Fe N = number of analyses
Table 9 Modal mineralogy of the different LAP stonesLAP 0220533 LAP 0222616 LAP 0222424 LAP 0243614
Pyroxene 515 505 469 466Plagioclase 319 321 323 346Ilmenite 348 391 386 399Fay sympl 309 290 358 483Olivine 233 271 363 320Cristobalite 214 209 178 200Spinel (all) 034 045 040 039Troilite 025 024 024 022Fractures 49 49 53 421Shock glass 01 02 22 00N 633 times 106 905 times 106 470 times 106 396 times 106
All modal values are listed as percentages N = number of pixels
1086 R Zeigler et al
Fig 1 Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) and fayalite(more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phases arepyroxene and olivine a) LAP 0222616 b) LAP 0243614 c) LAP 0222424 d) LAP 0220533
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1087
δ17O = +27) performed by Mayeda and Clayton (reported inMcBride et al 2003) constrain the origin of LAP 02205 tothe Earth the Moon or an enstatite meteorite parent bodyLAP is clearly a meteorite all four of the stones have fusioncrusts (ruling out a terrestrial origin) The extremely ferroannature of LAP rules out the enstatite parent body as theprovenance FeOMnO ratios of mafic silicates arediagnostic of origins from different planetary bodies in thesolar system (Dymek et al 1976 Papike 1998) Ratios ofFeOMnO in LAP pyroxenes (average sim60) and olivines(average sim95) are consistent only with lunar origin (Fig 15)Furthermore the presence of Fe(Ni) metal and troilite thecompletely anhydrous nature of the sample the apparentlack of Fe3+ in all phases the calcic nature of theplagioclase and the deep negative Eu anomaly are allcommon in lunar basalts
With regard to texture mineral assemblage and mineralchemistry the four LAP 02xxx stones appear to beindistinguishable from each other Although we did not studythe mineral chemistry of the LAP 03632 in depth the textureand mineral assemblage are identical to the LAP 02xxxstones Furthermore the collection locations of the five stonesform a linear array sim3 km in length that is perpendicular to theflow of the ice sheet (John Schutt personal communication)Thus in the absence of cosmic-ray exposure data to thecontrary we conclude that the four LAP 02xxx stones studiedare paired
Compositional Variability among Small Subsamples ofLAP 02205 and NWA 032
Samples of lunar meteorites available for study at most afew hundred milligrams are very small by the standards ofterrestrial geology and geochemistry Nevertheless we havetaken our samples and subdivided them into numerous evensmaller (10ndash50 mg) subsamples for bulk compositionalanalysis (Korotev et al 1983 1996 2003a 2003b Jolliffet al 1991 1998 Fagan et al 2002) This procedure providesan estimate of the whole-rock composition through a mass-weighted mean that is equivalent to a single analysis of theentire mass of the allocated sample The variation amongsmall subsamples however provides additional informationabout compositional variations associated with mineralassemblage and proportions about petrogenesis and aboutpossible relationships to other meteorites (eg Korotev et al2003a 2003b) and how well the ldquowhole-rockrdquo compositionis likely to represent that of the source region of the meteorite(Korotev et al 2000a) In the following discussion weevaluate the causes of differences in composition amongsmall subsamples of LAP and NWA 032
The range of concentrations among the 19 subsamples ofLAP (27ndash40 mg) is relatively small for the most preciselydetermined major elements (SiO2 TiO2 Al2O3 FeO CaONa2O) and most precisely determined trace elements that arecompatible with the major mineral phases (Co Sc Eu) The
Fig 1 Continued Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) andfayalite (more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phasesare pyroxene and olivine d) LAP 0220533
1088 R Zeigler et al
relative sample standard deviations (s ) range from 08 to76 (with only Co and Eu gt 5 Table 1) The exceptionsare MgO and Cr2O3 for which the relative standarddeviations are distinctly greater 12 and 16 respectivelyFor incompatible elements that we determined precisely(lt9 analytical uncertainty La Ce Sm Tb Yb Lu Hf Taand Th) relative standard deviations range from 7 to 11These variations are caused by a combination ofunrepresentative sampling of the major mineral phasesowing to the coarse grain size (up to sim1 mm3) relative to theINAA subsample size (about 12 mm3 assuming that thedensity of LAP is sim35 gmm3) and to the heterogeneousdistribution of some relatively minor phases with high
concentrations of a given element This problem is not new asmany investigators have previously wrestled with theproblem of studying relatively coarse-grained lunar basaltswith small allocated subsample sizes characteristic of rareextraterrestrial samples (Korotev and Haskin 1975 Haskinet al 1977 Lindstrom and Haskin 1978 Ryder and Schuraytz2001) Ryder and Schuraytz (2001) showed that sim5 g ofmaterial are needed to achieve a representative sample ofApollo 15 olivine-normative basalts which have grain sizeson the order of a millimeter or greater
Among the LAP subsamples Cr2O3 and MgOconcentrations correlate positively (R2 = 081) as a result ofthe association of chromite and Cr-ulvˆspinel with olivine
Fig 2 BSE images from LAP 0220533 a) a large round olivine (oli) grain and a smaller subhedral olivine grain (left center of the image)both surrounded by zoned pyroxene (pyx) and plagioclase (plag) with melt inclusions (MI) and inclusions of chromite (chr) A smallulvˆspinel (Usp) grain occurs in the upper left b) A large irregular olivine grain and a smaller mostly resorbed olivine grain The larger graincontains both melt inclusions (MI) and chromite grains The associated ilmenite (Ilm) grain is the most magnesian ilmenite grain observed Acomposite grain of metal and troilite (MetSulf) is also present c) A BSE image showing the zoning in multiple large pyroxene grainsintergrown with plagioclase and maskelynite (mask) grains One small cristobalite (crist) grain is also present d) A BSE image showingseveral large plagioclase grains some of which contain both fractured areas (plagioclase) and smooth areas (maskelynite) Also present areseveral areas of groundmass including a fayalite symplectite and a cristobalite grain cut by an ilmenite lath
x
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1089
The large variations seen in MgO Cr2O3 and to a lesserextent Co concentrations occur because of the large relativevariation in the fraction of modal olivine among thesubsamples Normatively the compositional rangecorresponds to minus03ndash25 olivine (one subsample has 03normative quartz) and 032ndash049 chromite The relativelysmall variations seen among concentrations of the other majorelements as well as Sc and Eu are controlled byunrepresentative sampling of the major mineral phasespyroxene (Sc Ca Fe Si) and plagioclase (Al Na Ca Si Eu)and the minor but widely distributed mineral ilmenite (Ti Fe)Trace amounts of a few minerals that are found only ingroundmass have high concentrations of incompatible traceelements relative to the concentration of those elements inthe bulk meteorite These minerals include K-feldspar (Ba)
Fig 3 a) CaO versus Mgprime (molar Mg[Mg + Fe]100) in the olivinesof the different LAP stones The compositions range from cores ofFo55ndash67 trending towards rims typically in the Fo40 range withextreme zonation to rims of Fo15ndash20 in a few cases Where analyzedthe composition of groundmass fayalite are also shown b) Anelectron microprobe traverse across a small strongly zoned olivinegrain in LAP 0220533 The grain shows zoning from a core of simFo58to a rim composition of simFo18 over sim100 microm The break in the zoning(black arrow) is centered on a fracture in the olivine grain
Fig 4 Compositions of LAP oxides plotted on the (FeMgMn)O-(CrAl)2O3-TiO2 ternary (after El Goresy et al 1971) Compositionsof endmember ilmenite (FeTiO3) ulvˆspinel (Fe2TiO4) andchromite (FeCr2O4) are labeled For a description of theclassification scheme see the footnote of Table 3 a) LAP 0220533b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1090 R Zeigler et al
RE-merrillite (P REEs Th) and baddeleyite (Zr Hf U Th)Therefore the variation in the amount of the groundmassldquophaserdquo in the different subsamples controls the ITEconcentrations in the various subsamples
For most of the major elements subsamples of NWA 032have relative standard deviations (RSD) that areinsignificantly different from those of LAP (Table 1) eventhough the average subsample size for NWA 032 (sim14 mgFagan et al 2002) was smaller than for LAP (sim34 mg) TheRSDs of MgO and Cr2O3 for NWA 032 are again highbecause it has a porphyritic texture with large phenocrysts(millimeter scale) of olivine (with chromite inclusions) andmagnesian pyroxene but a fine-grained groundmass of
plagioclase Fe-rich pyroxene ilmenite and glass keeps theRSDs of other major and incompatible trace elements low
Source Crater Pairing of LAP and NWA 032
We find the similarities in chemistry and petrographybetween LAP and NWA 032 when compared to the largeranges observed among Apollo and Luna samples to be sogreat that it is highly unlikely that two meteorites so similarcould derive from different locations Below we summarizethe similarities and differences
The textures of NWA 032 and LAP are markedlydifferent from each other NWA 032 has a porphyritic texture
Fig 5 BSE images from LAP 0220533 a) oxide grains set in and around a large olivine grain individual grains of ilmenite (Ilm) Cr-ulvˆspinel (Chr-Usp) and chromite (Chr) composite chromian ulvˆspinel-chromite (ChrUsp) grains with accompanying pyroxene andplagioclase (grey and black areas) b) A close-up of a zoned spinel grain with a chromite core and a Cr-ulvˆspinel rim c) A large cristobalite(Crist) grain with many inclusions of fayalite pyroxene (Pyx) plagioclase (Plag) troilite (Sulf) phosphate K-rich glass and the ITE-richglass Also present are several areas of fayalite symplectite (Fay Symp) with inclusions of plagioclase silica ilmenite troilite and K-richglass d) A BSE image of a different area of groundmass showing a large grain of fayalite symplectite containing inclusions of plagioclasesilica ilmenite troilite K-rich glass and Fe-rich pyroxene A large ilmenite (Ilm) grain cuts through the symplectite and several large troilitegrains are also present
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
1080 R Zeigler et al
and FeO (up to sim3 wt) while decreasing in MgO(to lt002 wt Fig 9) The Na2O concentrations firstincrease up to simAb14 then decrease sharply to less thanAb10 (which is lower than in the cores) The extreme rimcomposition of the large plagioclase grains is similar to that ofthe plagioclase found as inclusions in groundmass fayaliteand cristobalite grains (next paragraph Table 5) There is noapparent overall compositional difference between the coresof the maskelynite and the plagioclase grains
Fayalite cristobalite and ilmenite are the dominantminerals in the groundmass typically occurring togetheralthough each can be found independently All of the phaseshave relatively minor modal abundances fayalite (29ndash48)cristobalite (18ndash21) and ilmenite (35ndash40) Silicadisplaying the ldquocracklerdquo pattern distinctive to cristobaliteoccurs as anhedral grains up to 05 mm in size Thecristobalite grains contain minor Al2O3 TiO2 FeO and CaO(Σ sim13 wt Table 6) Inclusions of late-crystallizing phasessuch as K-rich plagioclase K-rich glass K-feldspar fayaliteFe-rich pyroxene phosphate and mafic glass withhigh concentrations of incompatible elements are common(Fig 5c) Fayalite grains (Fo45 sim05 wt CaO) range in size
up to 075 mm and usually form a symplectite texture withinclusions of K-rich glass silica K-rich plagioclase andilmenite (Fig 5d) Fayalite with no (or few) inclusions occursonly rarely Ilmenite is the dominant oxide in the groundmassforming elongate laths up to 1 mm in length Typically theilmenite is poor in Mg (sim02 wt average) although a singlegrain of more magnesian ilmenite associated with a largeolivine grain was observed (Fig 2b) Less common aresmaller subhedral ulvˆspinel grains (lt005 mm) thathave compositions approaching end member ulvˆspinel(Chr0ndash4Usp93ndash98Sp2ndash3) A few composite grains of ilmeniteand ulvˆspinel were observed
Also found in the groundmass are a variety of traceminerals including both fluorapatite and RE-merrillite(Table 7) Phosphate grains most commonly occur betweenplagioclase and ferropyroxene sometimes with associatedcristobalite troilite or both Barian K-feldspar (sim5 wt BaO)also occurs in the groundmass usually in the same areas asthe phosphate minerals (Table 5) Only a few K-feldspargrains (the largest) have stoichiometry that unambiguouslyidentifies them as K-feldspar while many K-rich grainshave excess Si suggesting that they may be intergrowths of
Table 4 Average oxide compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02205 02226 02224 02436 02205 02226 02224 02436 02205 02226 02224Al Al Al Al Cr-rich Cr-rich Cr-rich Cr-rich CrAl CrAl CrAlchr chr chr chr usp usp usp usp usp usp usp
N 23 11 13 5 22 1600 7 13 9 22 10
Major elements in wt by EMPAFeO 3444 3503 3532 3433 5705 5832 5846 5868 6191 6198 6180TiO2 546 532 540 517 2833 2871 2892 2909 3254 3151 3161Cr2O3 4384 4357 4331 4391 928 840 851 776 234 310 338Al2O3 1142 1178 1140 1217 287 261 261 276 191 204 203MgO 283 242 218 292 093 061 069 065 021 028 031MnO 027 024 025 027 035 032 034 033 036 032 034V2O3 073 074 076 075 036 031 033 033 022 025 026SiO2 007 009 008 009 lt002 007 008 018 lt002 008 007CaO 004 004 003 lt002 010 005 006 011 008 007 005ZnO 003 na na na 004 na na na 003 na naTotals 991 992 987 996 993 994 1000 999 996 996 999
Stoichiometry based on 4 (spinel) and 3 (ilmenite) oxygen atomsSi IV 0003 0003 0003 0003 0000 0003 0003 0006 0000 0003 0003Al VI 0469 0484 0472 0496 0125 0114 0113 0119 0083 0089 0088Ti 0143 0139 0143 0134 0784 0798 0798 0803 0907 0880 0880V 0020 0021 0021 0021 0011 0009 0010 0010 0007 0007 0008Cr 1208 1201 1204 1199 0270 0245 0247 0225 0068 0091 0099Fe2+ 1004 1021 1039 0992 1756 1802 1794 1801 1920 1925 1913Mn2+ 0008 0007 0007 0008 0011 0010 0011 0010 0011 0010 0011Mg 0147 0126 0114 0151 0051 0034 0038 0035 0012 0016 0017Zn 0001 minus minus minus 0001 minus minus minus 0001 minus minusCa 0002 0002 0001 0000 0004 0002 0002 0004 0003 0003 0002Sum 2+ 1162 1156 1161 1151 1823 1847 1844 1851 1947 1953 1942Sum 3 4+ 1844 1849 1844 1854 1190 1168 1170 1163 1066 1071 1078Total 3003 3001 3002 3001 3012 3013 3012 3007 3013 3020 3017
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1081
K-feldspar and silica (granophyric texture) at a scale smallenough to be beyond the resolution of the electron microprobe(less than sim01 microm)
Two glass types of distinct composition presumably late-stage residual liquids occur in the groundmass The first is aKSi-rich glass (78 wt SiO2 sim56 wt K2O) that makes upa considerable percentage of the inclusions in the cristobaliteand particularly the fayalite grains The second type ofevolved glass occurs as very small (lt5 microm) roundedinclusions in cristobalite grains This glass has a silica-poorFe-rich bulk composition (sim36 wt SiO2 sim39 wt FeOTable 6) but it is also considerably enriched in manyincompatible elements 23 wt P2O5 12 wt SO3 02 wtY2O3) Commonly we observed minute grains of fayalitetroilite or phosphate associated with this glass These twolate-stage glasses could represent conjugate liquids producedby late-stage immiscibility of an evolved residual meltSimilar glasses were observed in some plutonic rocks fromthe Apollo 14 site (Jolliff et al 1991)
Troilite blebs (with nearly ideal stoichiometry Table 8)are scattered throughout the groundmass along with trace Fe-metal grains which are usually intergrown with troilite orovergrown on chromite grains These grains typicallycontained 66 wt Ni and 14 wt Co though one grain had338 wt Ni and 60 wt Co (Table 8) A few grains ofbaddelyite (ZrO2) and tranquillityite (Zr-Fe-Ti silicate) wereidentified by energy-dispersive spectroscopy (EDS) in thegroundmass
A variety of shock effects occur in the minerals of thesethin sections (eg plagioclase converted to maskelynitemosaicism in the pyroxene) The level of shock was such thatlocalized partial melting occurred in some areas of themeteorite The areas of shock melt have severalmorphologies small melt pockets (LAP 02205 Fig 10a)veins of melt (LAP 0222424 Fig 10b) and in some casesareas that were only partially melted (LAP 0222424Fig 10c) with discernable mineral grains still present(typically maskelynite) Although veins of shock melt are rare
Table 4 Continued Average oxide compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02436 02205 02226 02224 02436 02205 02226 02224 02436 02205CrAl end end end end Mgusp usp usp usp usp ilm ilm ilm ilm ilm
N 11 11 2 3 3 24 16 20 18 2
Major elements in wt by EMPAFeO 6202 6375 6445 6355 6465 4657 4647 4634 4624 4463TiO2 3353 3267 3226 3396 3231 5198 5226 5233 5264 5296Cr2O3 209 026 023 011 037 010 012 015 016 038Al2O3 202 179 206 216 227 008 011 013 010 006MgO 022 005 008 007 003 014 010 016 019 150MnO 034 031 027 029 027 038 033 037 027 035V2O3 023 018 015 019 016 031 029 029 028 035SiO2 015 lt002 011 010 007 003 003 024 004 lt002CaO 007 010 007 008 010 013 006 010 009 008ZnO na 008 na na na 003 na na na lt002Totals 1007 992 997 1005 1002 997 998 1001 1000 1003
Stoichiometry based on 4 (spinel) and 3 (ilmenite) oxygen atomsSi IV 0005 0001 0004 0004 0003 0001 0001 0006 0001 0000Al VI 0087 0079 0091 0093 0099 0002 0003 0004 0003 0002Ti 0920 0921 0906 0937 0901 0990 0993 0989 0996 0991V 0007 0005 0004 0006 0005 0006 0006 0006 0006 0007Cr 0060 0008 0007 0003 0011 0002 0002 0003 0003 0007Fe2+ 1893 1999 2012 1950 2005 0986 0982 0974 0973 0928Mn2+ 0010 0010 0009 0009 0009 0008 0007 0008 0006 0007Mg 0012 0003 0004 0004 0002 0005 0004 0006 0007 0056Zn minus 0002 minus minus minus 0001 minus minus minus 0000Ca 0003 0004 0003 0003 0004 0004 0002 0003 0002 0002Sum 2+ 1918 2018 2028 1966 2019 1004 0995 0991 0988 0994Sum 3 4+ 1080 1014 1012 1043 1019 1001 1005 1008 1009 1007Total 2992 3032 3035 3005 3036 2004 2000 1992 1996 2001The spinel catagories where chosen based primarily on Cr2O3 content with Al chromite (chr) having gt40 wt Cr2O3 Cr-rich ulvˆspinel (usp) having 15ndash
5 wt Cr2O3 CrAl ulvˆspinel having 5ndash05 wt Cr2O3 and endmember ulvospinel having lt05 wt Cr2O3 Also seen were TiAl chromite (30ndash40 wtCr2O3) and high-Cr ulvˆspinel (30ndash15 wt Cr2O3) which are likely the result of an anlyses overlapping simultaneously on both an Al chromite and Cr-rich ulvˆspinel grain Similarly compositions intermediate to ilmenite and end ulvˆspinel were seen These compositions are not listed in this table but areshown in Fig 4 N = number of analyses in the average na = not analyzed
1082 R Zeigler et al
in our thin sections such veins were reported as pervasive inthe original macroscopic description of all five LAP stones(McBride et al 2003 2004a 2004b)
The various shock-induced effects observed in LAP canbe used to quantify and constrain the level of shock that LAPexperienced The presence of both plagioclase andmaskelynite in these samples suggests that the lower end ofthe range listed for conversion of plagioclase to maskelynite(30ndash45 GPa Stˆffler and Hornemann 1972 Ostertag 1983)is appropriate The mosaicism seen in the pyroxene istypically associated with shock values in the 30ndash75 GParange (Kieffer et al 1976 Schaal et al 1979) The presenceof shock-melt veins that have melted both pyroxene andplagioclase (based on the melt composition Table 6)indicates LAP should have been subjected to shock levels ofgt75ndash80 GPa (Kieffer et al 1976 Schaal et al 1979) Thedifferent shock effects observed reflect a range fromlt30 GPa (areas were plagioclase is preserved) to gt75 GPa(areas where shock melting occurred) over distances of onlya few millimeters
Bulk Composition and Comparison to Other LunarBasalts
LAP is a moderately aluminous (sim10 wt Al2O3) low-Ti(31 wt TiO2) mare basalt that falls near the Fe-rich(222 wt FeO) end of the range of FeO concentrationsobserved among lunar basalts It is more ferroan (Mgprime = 347)than any basalt in the Apollo or Luna collection (Fig 11a)Among lunar basalts only meteorites Asuka-881757 andYamato-793169 have comparably low Mgprime values (Koeberlet al 1993 Warren and Kallemeyn 1993 Thalmann et al1996 Korotev et al 2003a) LAP is enriched in Na2O(038 wt) relative to other ferroan (eg Asuka-881757 andYamato-793169) and Fe-rich basalts except for NWA 032(Fig 11b)
Regarding trace elements LAP is enriched in Cocompared to most lunar mare basalts with comparable Scconcentrations (Table 1 Fig 12a) Among Apollo and Lunabasalts only the Apollo 12 ilmenite basalts (Rhodes et al1977 Neal et al 1994) are comparable Incompatible trace-
Table 5 Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02205 02226 02224 02436 02205 02226 02224 02436 02205 02226plag plag plag plag mask mask mask mask plag plagcore core core core core core core core Na rim Na rim
N 123 86 48 88 29 49 33 32 12 3
Major elements in wt by EMPASiO2 4715 4657 4689 4639 4753 4741 4663 4673 4949 4960TiO2 010 007 007 006 013 008 006 006 027 019Al2O3 3337 3367 3296 3363 3367 3291 3376 3415 3170 3103Cr2O3 003 lt002 lt002 002 007 002 lt002 002 004 003FeO 068 067 073 058 060 111 066 060 134 136MgO 023 022 017 024 027 029 028 029 008 012CaO 1730 1746 1709 1763 1747 1726 1730 1740 1628 1597BaO na na na na na na na na na naNa2O 120 123 136 121 119 123 131 128 148 153K2O 006 007 010 006 005 009 006 005 020 019Total 1000 1000 994 998 1008 1004 1001 1006 1006 1000
Cation ratiosAn 885 883 869 887 888 881 877 880 848 842Or 04 04 06 04 03 05 03 03 12 12Ab 111 112 125 110 109 113 120 117 140 146Cn 00 00 00 00 00 00 00 00 00 00
Stoichiometry based on 8 oxygen atomsSi IV 2168 2147 2173 2143 2168 2179 2147 2140 2259 2279Al IV 1809 1830 1801 1831 1810 1782 1832 1843 1705 1681Fe+2 0026 0026 0028 0023 0023 0043 0025 0023 0051 0052Mg 0016 0015 0011 0017 0019 0020 0019 0020 0005 0008Ca 0853 0863 0849 0872 0854 0850 0853 0854 0796 0786Ba minus minus minus minus minus minus minus minus minus minusNa 0107 0110 0122 0108 0105 0109 0117 0114 0131 0136K 0004 0004 0006 0004 0003 0005 0003 0003 0011 0011Tet site 3977 3977 3974 3974 3978 3961 3979 3984 3964 3960Oct site 1005 1018 1022 1023 1003 1027 1022 1013 0995 0994
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1083
element concentrations are considerably greater in LAP thanin most of other low-Ti basalts (Fig 12bndashc) including theApollo 12 ilmenite basalts (Haskin et al 1971 Neal et al1994) The exceptions are NWA 032 the high-Al basalts ofLuna 16 (Philpotts et al 1972 Helmke and Haskin 1972 Maet al 1979) and some Apollo 14 high-Al basalts (Dickinsonet al 1985 Shervais et al 1985 Neal et al 1989a 1989b)
Relative concentrations of REEs in the LAP basalt arealso dissimilar to those of most other lunar basalts (Fig 13) inthat LAP is enriched in light REEs The exceptions are NWA032 which has a pattern nearly parallel to LAP and Apollo 14group 3 basalts (Dickinson et al 1985) which have a patternthat is similar although somewhat less steep in the heavyREEs Ratios of Th to REE in LAP are higher than those of allother lunar basalts except NWA 032 (Fig 14) and thedisparity in ThREE ratio between LAP and other lunarbasalts (except NWA 032) increases from the light to heavyREEs The Apollo 14 high-K basalts have similar ThREEratios for the middle REE Sm-Tb however (Neal et al 1989a
1989b) Overall in terms of its trace-element concentrationsLAP 02205 is most similar to NWA 032 The maindifferences are that NWA 032 is richer in elements associatedwith olivine (Mg Cr Co) and has concentrations ofincompatible elements that are 78ndash91 as great as those inLAP 02205
DISCUSSION
Evidence Supporting the Lunar Origin and Pairing of theLAP Stones
As stated in the introduction the meteorites LAP 0220502224 02226 02436 and 03632 were identified as lunarbasalts that were almost certainly paired (McBride et al 20032004a 2004b) A brief summary follows of the attributesfound in our more detailed petrographic examination thatsupport this initial classification and pairing interpretation
Results of oxygen isotope analyses (δ18O = +56 and
Table 5 Continued Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02224 02436 02205 02205 02226 02224 02436 02205 02205 02205plag plag plag plag plag plag plag barian KBa KBaNa rim Na rim matrix K rim K rim K rim K rim K-spar glass glass
N 24 5 13 10 1 5 1 10 10 23
Major elements in wt by EMPASiO2 4901 4879 5122 5152 4888 4935 5017 6026 5935 6356TiO2 008 008 016 017 lt002 008 014 na na naAl2O3 3163 3120 2960 2993 3213 3004 3002 2019 2063 2043Cr2O3 002 002 006 005 lt002 003 lt002 na na naFeO 117 130 267 192 147 195 173 065 074 116MgO 006 009 003 002 lt002 lt002 002 lt002 lt002 010CaO 1620 1622 1520 1549 1618 1602 1560 063 066 207BaO na na na na na na na 501 407 372Na2O 157 155 105 105 132 126 150 031 029 033K2O 023 021 090 067 067 056 086 1354 1162 586Total 1000 995 1007 1006 1007 993 1000 1008 1006 1007
Cation ratiosAn 839 842 846 852 835 845 807 33 minus minusOr 14 13 61 44 41 35 53 842 minus minusAb 147 145 105 104 124 120 140 30 minus minusCn 00 00 00 00 00 00 00 96 minus minus
Stoichiometry based on 8 oxygen atomsSi IV 2253 2257 2342 2344 2237 2293 2312 2863 2864 2951Al IV 1714 1701 1596 1609 1732 1645 1631 1131 1173 1124Fe+2 0045 0050 0102 0073 0056 0076 0067 0026 0030 0045Mg 0004 0006 0002 0001 0000 0001 0001 0001 0001 0007Ca 0798 0804 0745 0757 0793 0798 0770 0032 0034 0100Ba minus minus minus minus minus minus minus 0093 0077 0070Na 0140 0139 0093 0093 0117 0113 0134 0029 0027 0029K 0013 0013 0052 0039 0039 0033 0050 0820 0715 0353Tet site 3967 3957 3938 3954 3969 3938 3943 3994 4037 4075Oct site 0013 1011 0995 0963 1007 1020 1022 1002 0884 0604Plag = plagioclase mask = maskelynite N = number of analyses in the average na = not analyzed
1084 R Zeigler et al Ta
ble
6 A
vera
ge a
nd re
pres
enta
tive
cris
toba
lite
and
glas
s co
mpo
sitio
n in
the
LAP
basa
ltic
met
eorit
es
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
0220
502
226
0222
402
436
0220
502
205
0220
502
205
0220
502
224
0222
4cr
isto
balit
ecr
isto
balit
ecr
isto
balit
ecr
isto
balit
eSi
-ric
hpy
x-lik
eK
gla
ssIT
E-ric
hsh
ock
shoc
ksh
ock
MI g
lass
MI g
lass
in s
ympl
m
afic
gla
ssgl
ass
area
glas
s ar
eagl
ass
vein
N6
25
44
12
51
6515
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
979
598
17
984
798
45
672
542
76
783
236
67
463
486
441
TiO
20
270
270
230
230
664
810
374
032
341
623
13A
l 2O3
073
060
064
078
187
99
4210
13
544
139
86
123
Cr 2
O3
002
lt00
2lt0
02
002
lt00
20
13lt0
02
lt00
20
080
380
28Fe
O0
210
400
190
171
8615
91
183
392
719
618
520
5M
nOn
an
an
an
an
a0
22n
a0
420
220
290
25M
gO0
02lt0
02
lt00
2lt0
02
033
817
lt00
20
213
459
857
17C
aO0
190
200
200
236
8919
16
098
976
127
118
114
BaO
na
na
na
na
117
na
na
na
na
na
na
Na 2
O0
130
100
090
120
620
110
190
060
510
360
49K
2O0
030
050
07lt0
02
167
na
566
030
005
na
na
P 2O
5n
an
an
an
an
an
an
a2
32n
an
an
aF
na
na
na
na
na
na
na
008
na
na
na
Y2O
3n
an
an
an
an
an
an
a0
19n
an
an
aC
e 2O
3n
an
an
an
an
an
an
a0
12n
an
an
aSO
3n
an
an
an
an
an
an
a1
23n
an
an
aTo
tal
995
599
80
999
010
00
992
410
070
974
910
02
991
100
099
6Sy
mpl
= sy
mpl
ectit
e M
I = m
elt i
nclu
sion
N =
num
ber o
f ana
lyse
s in
the
aver
age
na
= n
ot a
naly
zed
The
shoc
ked
glas
s in
LAP
0222
4 is
the
parti
ally
mel
ted
area
(see
Fig
14)
and
onl
y th
e an
ayls
es o
fth
e gl
ass i
tsel
f wer
e in
clud
ed in
the
aver
age
not t
he m
iner
als t
hat w
ere
anal
yzed
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1085
Table 7 Representative phosphate compositions in LAP 0220533LAP LAP LAP LAP LAP LAP LAP LAP02205 02205 02205 02205 02205 02205 02205 02205RE- RE- RE- RE- RE- fluorapatite fluorapatite fluorapatitemerrillite merrillite merrillite merrillite merrillite
Major elements in wt by EMPASiO2 050 044 062 037 321 228 449 137Al2O3 022 lt005 009 lt005 lt005 007 014 lt005FeO 637 774 568 576 250 169 439 202MgO 020 037 025 028 lt005 lt005 lt005 lt005CaO 4326 4035 4233 4245 4983 5241 5003 5351Na2O 000 001 010 014 000 000 001 000P2O5 3885 4171 4382 4360 3540 3949 3771 4077Cl lt005 lt005 lt005 lt005 lt005 006 027 031F 047 044 050 048 168 245 130 186Y2O3 298 293 226 221 172 103 078 053La2O3 093 107 065 064 092 024 014 012Ce2O3 253 259 189 185 253 072 069 053Nd2O3 161 177 108 118 166 057 059 031Sm2O3 043 043 029 028 048 022 015 009Gd2O3 087 090 058 058 079 023 018 008Yb2O3 016 032 009 lt005 010 005 lt005 lt005ThO2 007 009 008 lt005 021 lt005 lt005 lt005minusO = (FCl) 021 020 022 021 072 105 061 085Sums 9930 1010 1001 9968 1004 1005 1003 1006
Table 8 Average sulfide and metal compositions in LAP 0220533Ave Fe metal High-Ni metal Troilite
N 5 1 8
Elemental percentage by EMPAFe 9209 5880 6280Ni 664 3377 lt002Co 141 595 lt002Ti 023 009 006Cr 043 017 lt002Mn lt002 004 lt002S lt002 lt002 3620Totals 1008 988 994Ideal troilite = 365 wt S 635 wt Fe N = number of analyses
Table 9 Modal mineralogy of the different LAP stonesLAP 0220533 LAP 0222616 LAP 0222424 LAP 0243614
Pyroxene 515 505 469 466Plagioclase 319 321 323 346Ilmenite 348 391 386 399Fay sympl 309 290 358 483Olivine 233 271 363 320Cristobalite 214 209 178 200Spinel (all) 034 045 040 039Troilite 025 024 024 022Fractures 49 49 53 421Shock glass 01 02 22 00N 633 times 106 905 times 106 470 times 106 396 times 106
All modal values are listed as percentages N = number of pixels
1086 R Zeigler et al
Fig 1 Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) and fayalite(more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phases arepyroxene and olivine a) LAP 0222616 b) LAP 0243614 c) LAP 0222424 d) LAP 0220533
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1087
δ17O = +27) performed by Mayeda and Clayton (reported inMcBride et al 2003) constrain the origin of LAP 02205 tothe Earth the Moon or an enstatite meteorite parent bodyLAP is clearly a meteorite all four of the stones have fusioncrusts (ruling out a terrestrial origin) The extremely ferroannature of LAP rules out the enstatite parent body as theprovenance FeOMnO ratios of mafic silicates arediagnostic of origins from different planetary bodies in thesolar system (Dymek et al 1976 Papike 1998) Ratios ofFeOMnO in LAP pyroxenes (average sim60) and olivines(average sim95) are consistent only with lunar origin (Fig 15)Furthermore the presence of Fe(Ni) metal and troilite thecompletely anhydrous nature of the sample the apparentlack of Fe3+ in all phases the calcic nature of theplagioclase and the deep negative Eu anomaly are allcommon in lunar basalts
With regard to texture mineral assemblage and mineralchemistry the four LAP 02xxx stones appear to beindistinguishable from each other Although we did not studythe mineral chemistry of the LAP 03632 in depth the textureand mineral assemblage are identical to the LAP 02xxxstones Furthermore the collection locations of the five stonesform a linear array sim3 km in length that is perpendicular to theflow of the ice sheet (John Schutt personal communication)Thus in the absence of cosmic-ray exposure data to thecontrary we conclude that the four LAP 02xxx stones studiedare paired
Compositional Variability among Small Subsamples ofLAP 02205 and NWA 032
Samples of lunar meteorites available for study at most afew hundred milligrams are very small by the standards ofterrestrial geology and geochemistry Nevertheless we havetaken our samples and subdivided them into numerous evensmaller (10ndash50 mg) subsamples for bulk compositionalanalysis (Korotev et al 1983 1996 2003a 2003b Jolliffet al 1991 1998 Fagan et al 2002) This procedure providesan estimate of the whole-rock composition through a mass-weighted mean that is equivalent to a single analysis of theentire mass of the allocated sample The variation amongsmall subsamples however provides additional informationabout compositional variations associated with mineralassemblage and proportions about petrogenesis and aboutpossible relationships to other meteorites (eg Korotev et al2003a 2003b) and how well the ldquowhole-rockrdquo compositionis likely to represent that of the source region of the meteorite(Korotev et al 2000a) In the following discussion weevaluate the causes of differences in composition amongsmall subsamples of LAP and NWA 032
The range of concentrations among the 19 subsamples ofLAP (27ndash40 mg) is relatively small for the most preciselydetermined major elements (SiO2 TiO2 Al2O3 FeO CaONa2O) and most precisely determined trace elements that arecompatible with the major mineral phases (Co Sc Eu) The
Fig 1 Continued Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) andfayalite (more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phasesare pyroxene and olivine d) LAP 0220533
1088 R Zeigler et al
relative sample standard deviations (s ) range from 08 to76 (with only Co and Eu gt 5 Table 1) The exceptionsare MgO and Cr2O3 for which the relative standarddeviations are distinctly greater 12 and 16 respectivelyFor incompatible elements that we determined precisely(lt9 analytical uncertainty La Ce Sm Tb Yb Lu Hf Taand Th) relative standard deviations range from 7 to 11These variations are caused by a combination ofunrepresentative sampling of the major mineral phasesowing to the coarse grain size (up to sim1 mm3) relative to theINAA subsample size (about 12 mm3 assuming that thedensity of LAP is sim35 gmm3) and to the heterogeneousdistribution of some relatively minor phases with high
concentrations of a given element This problem is not new asmany investigators have previously wrestled with theproblem of studying relatively coarse-grained lunar basaltswith small allocated subsample sizes characteristic of rareextraterrestrial samples (Korotev and Haskin 1975 Haskinet al 1977 Lindstrom and Haskin 1978 Ryder and Schuraytz2001) Ryder and Schuraytz (2001) showed that sim5 g ofmaterial are needed to achieve a representative sample ofApollo 15 olivine-normative basalts which have grain sizeson the order of a millimeter or greater
Among the LAP subsamples Cr2O3 and MgOconcentrations correlate positively (R2 = 081) as a result ofthe association of chromite and Cr-ulvˆspinel with olivine
Fig 2 BSE images from LAP 0220533 a) a large round olivine (oli) grain and a smaller subhedral olivine grain (left center of the image)both surrounded by zoned pyroxene (pyx) and plagioclase (plag) with melt inclusions (MI) and inclusions of chromite (chr) A smallulvˆspinel (Usp) grain occurs in the upper left b) A large irregular olivine grain and a smaller mostly resorbed olivine grain The larger graincontains both melt inclusions (MI) and chromite grains The associated ilmenite (Ilm) grain is the most magnesian ilmenite grain observed Acomposite grain of metal and troilite (MetSulf) is also present c) A BSE image showing the zoning in multiple large pyroxene grainsintergrown with plagioclase and maskelynite (mask) grains One small cristobalite (crist) grain is also present d) A BSE image showingseveral large plagioclase grains some of which contain both fractured areas (plagioclase) and smooth areas (maskelynite) Also present areseveral areas of groundmass including a fayalite symplectite and a cristobalite grain cut by an ilmenite lath
x
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1089
The large variations seen in MgO Cr2O3 and to a lesserextent Co concentrations occur because of the large relativevariation in the fraction of modal olivine among thesubsamples Normatively the compositional rangecorresponds to minus03ndash25 olivine (one subsample has 03normative quartz) and 032ndash049 chromite The relativelysmall variations seen among concentrations of the other majorelements as well as Sc and Eu are controlled byunrepresentative sampling of the major mineral phasespyroxene (Sc Ca Fe Si) and plagioclase (Al Na Ca Si Eu)and the minor but widely distributed mineral ilmenite (Ti Fe)Trace amounts of a few minerals that are found only ingroundmass have high concentrations of incompatible traceelements relative to the concentration of those elements inthe bulk meteorite These minerals include K-feldspar (Ba)
Fig 3 a) CaO versus Mgprime (molar Mg[Mg + Fe]100) in the olivinesof the different LAP stones The compositions range from cores ofFo55ndash67 trending towards rims typically in the Fo40 range withextreme zonation to rims of Fo15ndash20 in a few cases Where analyzedthe composition of groundmass fayalite are also shown b) Anelectron microprobe traverse across a small strongly zoned olivinegrain in LAP 0220533 The grain shows zoning from a core of simFo58to a rim composition of simFo18 over sim100 microm The break in the zoning(black arrow) is centered on a fracture in the olivine grain
Fig 4 Compositions of LAP oxides plotted on the (FeMgMn)O-(CrAl)2O3-TiO2 ternary (after El Goresy et al 1971) Compositionsof endmember ilmenite (FeTiO3) ulvˆspinel (Fe2TiO4) andchromite (FeCr2O4) are labeled For a description of theclassification scheme see the footnote of Table 3 a) LAP 0220533b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1090 R Zeigler et al
RE-merrillite (P REEs Th) and baddeleyite (Zr Hf U Th)Therefore the variation in the amount of the groundmassldquophaserdquo in the different subsamples controls the ITEconcentrations in the various subsamples
For most of the major elements subsamples of NWA 032have relative standard deviations (RSD) that areinsignificantly different from those of LAP (Table 1) eventhough the average subsample size for NWA 032 (sim14 mgFagan et al 2002) was smaller than for LAP (sim34 mg) TheRSDs of MgO and Cr2O3 for NWA 032 are again highbecause it has a porphyritic texture with large phenocrysts(millimeter scale) of olivine (with chromite inclusions) andmagnesian pyroxene but a fine-grained groundmass of
plagioclase Fe-rich pyroxene ilmenite and glass keeps theRSDs of other major and incompatible trace elements low
Source Crater Pairing of LAP and NWA 032
We find the similarities in chemistry and petrographybetween LAP and NWA 032 when compared to the largeranges observed among Apollo and Luna samples to be sogreat that it is highly unlikely that two meteorites so similarcould derive from different locations Below we summarizethe similarities and differences
The textures of NWA 032 and LAP are markedlydifferent from each other NWA 032 has a porphyritic texture
Fig 5 BSE images from LAP 0220533 a) oxide grains set in and around a large olivine grain individual grains of ilmenite (Ilm) Cr-ulvˆspinel (Chr-Usp) and chromite (Chr) composite chromian ulvˆspinel-chromite (ChrUsp) grains with accompanying pyroxene andplagioclase (grey and black areas) b) A close-up of a zoned spinel grain with a chromite core and a Cr-ulvˆspinel rim c) A large cristobalite(Crist) grain with many inclusions of fayalite pyroxene (Pyx) plagioclase (Plag) troilite (Sulf) phosphate K-rich glass and the ITE-richglass Also present are several areas of fayalite symplectite (Fay Symp) with inclusions of plagioclase silica ilmenite troilite and K-richglass d) A BSE image of a different area of groundmass showing a large grain of fayalite symplectite containing inclusions of plagioclasesilica ilmenite troilite K-rich glass and Fe-rich pyroxene A large ilmenite (Ilm) grain cuts through the symplectite and several large troilitegrains are also present
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1081
K-feldspar and silica (granophyric texture) at a scale smallenough to be beyond the resolution of the electron microprobe(less than sim01 microm)
Two glass types of distinct composition presumably late-stage residual liquids occur in the groundmass The first is aKSi-rich glass (78 wt SiO2 sim56 wt K2O) that makes upa considerable percentage of the inclusions in the cristobaliteand particularly the fayalite grains The second type ofevolved glass occurs as very small (lt5 microm) roundedinclusions in cristobalite grains This glass has a silica-poorFe-rich bulk composition (sim36 wt SiO2 sim39 wt FeOTable 6) but it is also considerably enriched in manyincompatible elements 23 wt P2O5 12 wt SO3 02 wtY2O3) Commonly we observed minute grains of fayalitetroilite or phosphate associated with this glass These twolate-stage glasses could represent conjugate liquids producedby late-stage immiscibility of an evolved residual meltSimilar glasses were observed in some plutonic rocks fromthe Apollo 14 site (Jolliff et al 1991)
Troilite blebs (with nearly ideal stoichiometry Table 8)are scattered throughout the groundmass along with trace Fe-metal grains which are usually intergrown with troilite orovergrown on chromite grains These grains typicallycontained 66 wt Ni and 14 wt Co though one grain had338 wt Ni and 60 wt Co (Table 8) A few grains ofbaddelyite (ZrO2) and tranquillityite (Zr-Fe-Ti silicate) wereidentified by energy-dispersive spectroscopy (EDS) in thegroundmass
A variety of shock effects occur in the minerals of thesethin sections (eg plagioclase converted to maskelynitemosaicism in the pyroxene) The level of shock was such thatlocalized partial melting occurred in some areas of themeteorite The areas of shock melt have severalmorphologies small melt pockets (LAP 02205 Fig 10a)veins of melt (LAP 0222424 Fig 10b) and in some casesareas that were only partially melted (LAP 0222424Fig 10c) with discernable mineral grains still present(typically maskelynite) Although veins of shock melt are rare
Table 4 Continued Average oxide compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02436 02205 02226 02224 02436 02205 02226 02224 02436 02205CrAl end end end end Mgusp usp usp usp usp ilm ilm ilm ilm ilm
N 11 11 2 3 3 24 16 20 18 2
Major elements in wt by EMPAFeO 6202 6375 6445 6355 6465 4657 4647 4634 4624 4463TiO2 3353 3267 3226 3396 3231 5198 5226 5233 5264 5296Cr2O3 209 026 023 011 037 010 012 015 016 038Al2O3 202 179 206 216 227 008 011 013 010 006MgO 022 005 008 007 003 014 010 016 019 150MnO 034 031 027 029 027 038 033 037 027 035V2O3 023 018 015 019 016 031 029 029 028 035SiO2 015 lt002 011 010 007 003 003 024 004 lt002CaO 007 010 007 008 010 013 006 010 009 008ZnO na 008 na na na 003 na na na lt002Totals 1007 992 997 1005 1002 997 998 1001 1000 1003
Stoichiometry based on 4 (spinel) and 3 (ilmenite) oxygen atomsSi IV 0005 0001 0004 0004 0003 0001 0001 0006 0001 0000Al VI 0087 0079 0091 0093 0099 0002 0003 0004 0003 0002Ti 0920 0921 0906 0937 0901 0990 0993 0989 0996 0991V 0007 0005 0004 0006 0005 0006 0006 0006 0006 0007Cr 0060 0008 0007 0003 0011 0002 0002 0003 0003 0007Fe2+ 1893 1999 2012 1950 2005 0986 0982 0974 0973 0928Mn2+ 0010 0010 0009 0009 0009 0008 0007 0008 0006 0007Mg 0012 0003 0004 0004 0002 0005 0004 0006 0007 0056Zn minus 0002 minus minus minus 0001 minus minus minus 0000Ca 0003 0004 0003 0003 0004 0004 0002 0003 0002 0002Sum 2+ 1918 2018 2028 1966 2019 1004 0995 0991 0988 0994Sum 3 4+ 1080 1014 1012 1043 1019 1001 1005 1008 1009 1007Total 2992 3032 3035 3005 3036 2004 2000 1992 1996 2001The spinel catagories where chosen based primarily on Cr2O3 content with Al chromite (chr) having gt40 wt Cr2O3 Cr-rich ulvˆspinel (usp) having 15ndash
5 wt Cr2O3 CrAl ulvˆspinel having 5ndash05 wt Cr2O3 and endmember ulvospinel having lt05 wt Cr2O3 Also seen were TiAl chromite (30ndash40 wtCr2O3) and high-Cr ulvˆspinel (30ndash15 wt Cr2O3) which are likely the result of an anlyses overlapping simultaneously on both an Al chromite and Cr-rich ulvˆspinel grain Similarly compositions intermediate to ilmenite and end ulvˆspinel were seen These compositions are not listed in this table but areshown in Fig 4 N = number of analyses in the average na = not analyzed
1082 R Zeigler et al
in our thin sections such veins were reported as pervasive inthe original macroscopic description of all five LAP stones(McBride et al 2003 2004a 2004b)
The various shock-induced effects observed in LAP canbe used to quantify and constrain the level of shock that LAPexperienced The presence of both plagioclase andmaskelynite in these samples suggests that the lower end ofthe range listed for conversion of plagioclase to maskelynite(30ndash45 GPa Stˆffler and Hornemann 1972 Ostertag 1983)is appropriate The mosaicism seen in the pyroxene istypically associated with shock values in the 30ndash75 GParange (Kieffer et al 1976 Schaal et al 1979) The presenceof shock-melt veins that have melted both pyroxene andplagioclase (based on the melt composition Table 6)indicates LAP should have been subjected to shock levels ofgt75ndash80 GPa (Kieffer et al 1976 Schaal et al 1979) Thedifferent shock effects observed reflect a range fromlt30 GPa (areas were plagioclase is preserved) to gt75 GPa(areas where shock melting occurred) over distances of onlya few millimeters
Bulk Composition and Comparison to Other LunarBasalts
LAP is a moderately aluminous (sim10 wt Al2O3) low-Ti(31 wt TiO2) mare basalt that falls near the Fe-rich(222 wt FeO) end of the range of FeO concentrationsobserved among lunar basalts It is more ferroan (Mgprime = 347)than any basalt in the Apollo or Luna collection (Fig 11a)Among lunar basalts only meteorites Asuka-881757 andYamato-793169 have comparably low Mgprime values (Koeberlet al 1993 Warren and Kallemeyn 1993 Thalmann et al1996 Korotev et al 2003a) LAP is enriched in Na2O(038 wt) relative to other ferroan (eg Asuka-881757 andYamato-793169) and Fe-rich basalts except for NWA 032(Fig 11b)
Regarding trace elements LAP is enriched in Cocompared to most lunar mare basalts with comparable Scconcentrations (Table 1 Fig 12a) Among Apollo and Lunabasalts only the Apollo 12 ilmenite basalts (Rhodes et al1977 Neal et al 1994) are comparable Incompatible trace-
Table 5 Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02205 02226 02224 02436 02205 02226 02224 02436 02205 02226plag plag plag plag mask mask mask mask plag plagcore core core core core core core core Na rim Na rim
N 123 86 48 88 29 49 33 32 12 3
Major elements in wt by EMPASiO2 4715 4657 4689 4639 4753 4741 4663 4673 4949 4960TiO2 010 007 007 006 013 008 006 006 027 019Al2O3 3337 3367 3296 3363 3367 3291 3376 3415 3170 3103Cr2O3 003 lt002 lt002 002 007 002 lt002 002 004 003FeO 068 067 073 058 060 111 066 060 134 136MgO 023 022 017 024 027 029 028 029 008 012CaO 1730 1746 1709 1763 1747 1726 1730 1740 1628 1597BaO na na na na na na na na na naNa2O 120 123 136 121 119 123 131 128 148 153K2O 006 007 010 006 005 009 006 005 020 019Total 1000 1000 994 998 1008 1004 1001 1006 1006 1000
Cation ratiosAn 885 883 869 887 888 881 877 880 848 842Or 04 04 06 04 03 05 03 03 12 12Ab 111 112 125 110 109 113 120 117 140 146Cn 00 00 00 00 00 00 00 00 00 00
Stoichiometry based on 8 oxygen atomsSi IV 2168 2147 2173 2143 2168 2179 2147 2140 2259 2279Al IV 1809 1830 1801 1831 1810 1782 1832 1843 1705 1681Fe+2 0026 0026 0028 0023 0023 0043 0025 0023 0051 0052Mg 0016 0015 0011 0017 0019 0020 0019 0020 0005 0008Ca 0853 0863 0849 0872 0854 0850 0853 0854 0796 0786Ba minus minus minus minus minus minus minus minus minus minusNa 0107 0110 0122 0108 0105 0109 0117 0114 0131 0136K 0004 0004 0006 0004 0003 0005 0003 0003 0011 0011Tet site 3977 3977 3974 3974 3978 3961 3979 3984 3964 3960Oct site 1005 1018 1022 1023 1003 1027 1022 1013 0995 0994
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1083
element concentrations are considerably greater in LAP thanin most of other low-Ti basalts (Fig 12bndashc) including theApollo 12 ilmenite basalts (Haskin et al 1971 Neal et al1994) The exceptions are NWA 032 the high-Al basalts ofLuna 16 (Philpotts et al 1972 Helmke and Haskin 1972 Maet al 1979) and some Apollo 14 high-Al basalts (Dickinsonet al 1985 Shervais et al 1985 Neal et al 1989a 1989b)
Relative concentrations of REEs in the LAP basalt arealso dissimilar to those of most other lunar basalts (Fig 13) inthat LAP is enriched in light REEs The exceptions are NWA032 which has a pattern nearly parallel to LAP and Apollo 14group 3 basalts (Dickinson et al 1985) which have a patternthat is similar although somewhat less steep in the heavyREEs Ratios of Th to REE in LAP are higher than those of allother lunar basalts except NWA 032 (Fig 14) and thedisparity in ThREE ratio between LAP and other lunarbasalts (except NWA 032) increases from the light to heavyREEs The Apollo 14 high-K basalts have similar ThREEratios for the middle REE Sm-Tb however (Neal et al 1989a
1989b) Overall in terms of its trace-element concentrationsLAP 02205 is most similar to NWA 032 The maindifferences are that NWA 032 is richer in elements associatedwith olivine (Mg Cr Co) and has concentrations ofincompatible elements that are 78ndash91 as great as those inLAP 02205
DISCUSSION
Evidence Supporting the Lunar Origin and Pairing of theLAP Stones
As stated in the introduction the meteorites LAP 0220502224 02226 02436 and 03632 were identified as lunarbasalts that were almost certainly paired (McBride et al 20032004a 2004b) A brief summary follows of the attributesfound in our more detailed petrographic examination thatsupport this initial classification and pairing interpretation
Results of oxygen isotope analyses (δ18O = +56 and
Table 5 Continued Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02224 02436 02205 02205 02226 02224 02436 02205 02205 02205plag plag plag plag plag plag plag barian KBa KBaNa rim Na rim matrix K rim K rim K rim K rim K-spar glass glass
N 24 5 13 10 1 5 1 10 10 23
Major elements in wt by EMPASiO2 4901 4879 5122 5152 4888 4935 5017 6026 5935 6356TiO2 008 008 016 017 lt002 008 014 na na naAl2O3 3163 3120 2960 2993 3213 3004 3002 2019 2063 2043Cr2O3 002 002 006 005 lt002 003 lt002 na na naFeO 117 130 267 192 147 195 173 065 074 116MgO 006 009 003 002 lt002 lt002 002 lt002 lt002 010CaO 1620 1622 1520 1549 1618 1602 1560 063 066 207BaO na na na na na na na 501 407 372Na2O 157 155 105 105 132 126 150 031 029 033K2O 023 021 090 067 067 056 086 1354 1162 586Total 1000 995 1007 1006 1007 993 1000 1008 1006 1007
Cation ratiosAn 839 842 846 852 835 845 807 33 minus minusOr 14 13 61 44 41 35 53 842 minus minusAb 147 145 105 104 124 120 140 30 minus minusCn 00 00 00 00 00 00 00 96 minus minus
Stoichiometry based on 8 oxygen atomsSi IV 2253 2257 2342 2344 2237 2293 2312 2863 2864 2951Al IV 1714 1701 1596 1609 1732 1645 1631 1131 1173 1124Fe+2 0045 0050 0102 0073 0056 0076 0067 0026 0030 0045Mg 0004 0006 0002 0001 0000 0001 0001 0001 0001 0007Ca 0798 0804 0745 0757 0793 0798 0770 0032 0034 0100Ba minus minus minus minus minus minus minus 0093 0077 0070Na 0140 0139 0093 0093 0117 0113 0134 0029 0027 0029K 0013 0013 0052 0039 0039 0033 0050 0820 0715 0353Tet site 3967 3957 3938 3954 3969 3938 3943 3994 4037 4075Oct site 0013 1011 0995 0963 1007 1020 1022 1002 0884 0604Plag = plagioclase mask = maskelynite N = number of analyses in the average na = not analyzed
1084 R Zeigler et al Ta
ble
6 A
vera
ge a
nd re
pres
enta
tive
cris
toba
lite
and
glas
s co
mpo
sitio
n in
the
LAP
basa
ltic
met
eorit
es
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
0220
502
226
0222
402
436
0220
502
205
0220
502
205
0220
502
224
0222
4cr
isto
balit
ecr
isto
balit
ecr
isto
balit
ecr
isto
balit
eSi
-ric
hpy
x-lik
eK
gla
ssIT
E-ric
hsh
ock
shoc
ksh
ock
MI g
lass
MI g
lass
in s
ympl
m
afic
gla
ssgl
ass
area
glas
s ar
eagl
ass
vein
N6
25
44
12
51
6515
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
979
598
17
984
798
45
672
542
76
783
236
67
463
486
441
TiO
20
270
270
230
230
664
810
374
032
341
623
13A
l 2O3
073
060
064
078
187
99
4210
13
544
139
86
123
Cr 2
O3
002
lt00
2lt0
02
002
lt00
20
13lt0
02
lt00
20
080
380
28Fe
O0
210
400
190
171
8615
91
183
392
719
618
520
5M
nOn
an
an
an
an
a0
22n
a0
420
220
290
25M
gO0
02lt0
02
lt00
2lt0
02
033
817
lt00
20
213
459
857
17C
aO0
190
200
200
236
8919
16
098
976
127
118
114
BaO
na
na
na
na
117
na
na
na
na
na
na
Na 2
O0
130
100
090
120
620
110
190
060
510
360
49K
2O0
030
050
07lt0
02
167
na
566
030
005
na
na
P 2O
5n
an
an
an
an
an
an
a2
32n
an
an
aF
na
na
na
na
na
na
na
008
na
na
na
Y2O
3n
an
an
an
an
an
an
a0
19n
an
an
aC
e 2O
3n
an
an
an
an
an
an
a0
12n
an
an
aSO
3n
an
an
an
an
an
an
a1
23n
an
an
aTo
tal
995
599
80
999
010
00
992
410
070
974
910
02
991
100
099
6Sy
mpl
= sy
mpl
ectit
e M
I = m
elt i
nclu
sion
N =
num
ber o
f ana
lyse
s in
the
aver
age
na
= n
ot a
naly
zed
The
shoc
ked
glas
s in
LAP
0222
4 is
the
parti
ally
mel
ted
area
(see
Fig
14)
and
onl
y th
e an
ayls
es o
fth
e gl
ass i
tsel
f wer
e in
clud
ed in
the
aver
age
not t
he m
iner
als t
hat w
ere
anal
yzed
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1085
Table 7 Representative phosphate compositions in LAP 0220533LAP LAP LAP LAP LAP LAP LAP LAP02205 02205 02205 02205 02205 02205 02205 02205RE- RE- RE- RE- RE- fluorapatite fluorapatite fluorapatitemerrillite merrillite merrillite merrillite merrillite
Major elements in wt by EMPASiO2 050 044 062 037 321 228 449 137Al2O3 022 lt005 009 lt005 lt005 007 014 lt005FeO 637 774 568 576 250 169 439 202MgO 020 037 025 028 lt005 lt005 lt005 lt005CaO 4326 4035 4233 4245 4983 5241 5003 5351Na2O 000 001 010 014 000 000 001 000P2O5 3885 4171 4382 4360 3540 3949 3771 4077Cl lt005 lt005 lt005 lt005 lt005 006 027 031F 047 044 050 048 168 245 130 186Y2O3 298 293 226 221 172 103 078 053La2O3 093 107 065 064 092 024 014 012Ce2O3 253 259 189 185 253 072 069 053Nd2O3 161 177 108 118 166 057 059 031Sm2O3 043 043 029 028 048 022 015 009Gd2O3 087 090 058 058 079 023 018 008Yb2O3 016 032 009 lt005 010 005 lt005 lt005ThO2 007 009 008 lt005 021 lt005 lt005 lt005minusO = (FCl) 021 020 022 021 072 105 061 085Sums 9930 1010 1001 9968 1004 1005 1003 1006
Table 8 Average sulfide and metal compositions in LAP 0220533Ave Fe metal High-Ni metal Troilite
N 5 1 8
Elemental percentage by EMPAFe 9209 5880 6280Ni 664 3377 lt002Co 141 595 lt002Ti 023 009 006Cr 043 017 lt002Mn lt002 004 lt002S lt002 lt002 3620Totals 1008 988 994Ideal troilite = 365 wt S 635 wt Fe N = number of analyses
Table 9 Modal mineralogy of the different LAP stonesLAP 0220533 LAP 0222616 LAP 0222424 LAP 0243614
Pyroxene 515 505 469 466Plagioclase 319 321 323 346Ilmenite 348 391 386 399Fay sympl 309 290 358 483Olivine 233 271 363 320Cristobalite 214 209 178 200Spinel (all) 034 045 040 039Troilite 025 024 024 022Fractures 49 49 53 421Shock glass 01 02 22 00N 633 times 106 905 times 106 470 times 106 396 times 106
All modal values are listed as percentages N = number of pixels
1086 R Zeigler et al
Fig 1 Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) and fayalite(more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phases arepyroxene and olivine a) LAP 0222616 b) LAP 0243614 c) LAP 0222424 d) LAP 0220533
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1087
δ17O = +27) performed by Mayeda and Clayton (reported inMcBride et al 2003) constrain the origin of LAP 02205 tothe Earth the Moon or an enstatite meteorite parent bodyLAP is clearly a meteorite all four of the stones have fusioncrusts (ruling out a terrestrial origin) The extremely ferroannature of LAP rules out the enstatite parent body as theprovenance FeOMnO ratios of mafic silicates arediagnostic of origins from different planetary bodies in thesolar system (Dymek et al 1976 Papike 1998) Ratios ofFeOMnO in LAP pyroxenes (average sim60) and olivines(average sim95) are consistent only with lunar origin (Fig 15)Furthermore the presence of Fe(Ni) metal and troilite thecompletely anhydrous nature of the sample the apparentlack of Fe3+ in all phases the calcic nature of theplagioclase and the deep negative Eu anomaly are allcommon in lunar basalts
With regard to texture mineral assemblage and mineralchemistry the four LAP 02xxx stones appear to beindistinguishable from each other Although we did not studythe mineral chemistry of the LAP 03632 in depth the textureand mineral assemblage are identical to the LAP 02xxxstones Furthermore the collection locations of the five stonesform a linear array sim3 km in length that is perpendicular to theflow of the ice sheet (John Schutt personal communication)Thus in the absence of cosmic-ray exposure data to thecontrary we conclude that the four LAP 02xxx stones studiedare paired
Compositional Variability among Small Subsamples ofLAP 02205 and NWA 032
Samples of lunar meteorites available for study at most afew hundred milligrams are very small by the standards ofterrestrial geology and geochemistry Nevertheless we havetaken our samples and subdivided them into numerous evensmaller (10ndash50 mg) subsamples for bulk compositionalanalysis (Korotev et al 1983 1996 2003a 2003b Jolliffet al 1991 1998 Fagan et al 2002) This procedure providesan estimate of the whole-rock composition through a mass-weighted mean that is equivalent to a single analysis of theentire mass of the allocated sample The variation amongsmall subsamples however provides additional informationabout compositional variations associated with mineralassemblage and proportions about petrogenesis and aboutpossible relationships to other meteorites (eg Korotev et al2003a 2003b) and how well the ldquowhole-rockrdquo compositionis likely to represent that of the source region of the meteorite(Korotev et al 2000a) In the following discussion weevaluate the causes of differences in composition amongsmall subsamples of LAP and NWA 032
The range of concentrations among the 19 subsamples ofLAP (27ndash40 mg) is relatively small for the most preciselydetermined major elements (SiO2 TiO2 Al2O3 FeO CaONa2O) and most precisely determined trace elements that arecompatible with the major mineral phases (Co Sc Eu) The
Fig 1 Continued Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) andfayalite (more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phasesare pyroxene and olivine d) LAP 0220533
1088 R Zeigler et al
relative sample standard deviations (s ) range from 08 to76 (with only Co and Eu gt 5 Table 1) The exceptionsare MgO and Cr2O3 for which the relative standarddeviations are distinctly greater 12 and 16 respectivelyFor incompatible elements that we determined precisely(lt9 analytical uncertainty La Ce Sm Tb Yb Lu Hf Taand Th) relative standard deviations range from 7 to 11These variations are caused by a combination ofunrepresentative sampling of the major mineral phasesowing to the coarse grain size (up to sim1 mm3) relative to theINAA subsample size (about 12 mm3 assuming that thedensity of LAP is sim35 gmm3) and to the heterogeneousdistribution of some relatively minor phases with high
concentrations of a given element This problem is not new asmany investigators have previously wrestled with theproblem of studying relatively coarse-grained lunar basaltswith small allocated subsample sizes characteristic of rareextraterrestrial samples (Korotev and Haskin 1975 Haskinet al 1977 Lindstrom and Haskin 1978 Ryder and Schuraytz2001) Ryder and Schuraytz (2001) showed that sim5 g ofmaterial are needed to achieve a representative sample ofApollo 15 olivine-normative basalts which have grain sizeson the order of a millimeter or greater
Among the LAP subsamples Cr2O3 and MgOconcentrations correlate positively (R2 = 081) as a result ofthe association of chromite and Cr-ulvˆspinel with olivine
Fig 2 BSE images from LAP 0220533 a) a large round olivine (oli) grain and a smaller subhedral olivine grain (left center of the image)both surrounded by zoned pyroxene (pyx) and plagioclase (plag) with melt inclusions (MI) and inclusions of chromite (chr) A smallulvˆspinel (Usp) grain occurs in the upper left b) A large irregular olivine grain and a smaller mostly resorbed olivine grain The larger graincontains both melt inclusions (MI) and chromite grains The associated ilmenite (Ilm) grain is the most magnesian ilmenite grain observed Acomposite grain of metal and troilite (MetSulf) is also present c) A BSE image showing the zoning in multiple large pyroxene grainsintergrown with plagioclase and maskelynite (mask) grains One small cristobalite (crist) grain is also present d) A BSE image showingseveral large plagioclase grains some of which contain both fractured areas (plagioclase) and smooth areas (maskelynite) Also present areseveral areas of groundmass including a fayalite symplectite and a cristobalite grain cut by an ilmenite lath
x
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1089
The large variations seen in MgO Cr2O3 and to a lesserextent Co concentrations occur because of the large relativevariation in the fraction of modal olivine among thesubsamples Normatively the compositional rangecorresponds to minus03ndash25 olivine (one subsample has 03normative quartz) and 032ndash049 chromite The relativelysmall variations seen among concentrations of the other majorelements as well as Sc and Eu are controlled byunrepresentative sampling of the major mineral phasespyroxene (Sc Ca Fe Si) and plagioclase (Al Na Ca Si Eu)and the minor but widely distributed mineral ilmenite (Ti Fe)Trace amounts of a few minerals that are found only ingroundmass have high concentrations of incompatible traceelements relative to the concentration of those elements inthe bulk meteorite These minerals include K-feldspar (Ba)
Fig 3 a) CaO versus Mgprime (molar Mg[Mg + Fe]100) in the olivinesof the different LAP stones The compositions range from cores ofFo55ndash67 trending towards rims typically in the Fo40 range withextreme zonation to rims of Fo15ndash20 in a few cases Where analyzedthe composition of groundmass fayalite are also shown b) Anelectron microprobe traverse across a small strongly zoned olivinegrain in LAP 0220533 The grain shows zoning from a core of simFo58to a rim composition of simFo18 over sim100 microm The break in the zoning(black arrow) is centered on a fracture in the olivine grain
Fig 4 Compositions of LAP oxides plotted on the (FeMgMn)O-(CrAl)2O3-TiO2 ternary (after El Goresy et al 1971) Compositionsof endmember ilmenite (FeTiO3) ulvˆspinel (Fe2TiO4) andchromite (FeCr2O4) are labeled For a description of theclassification scheme see the footnote of Table 3 a) LAP 0220533b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1090 R Zeigler et al
RE-merrillite (P REEs Th) and baddeleyite (Zr Hf U Th)Therefore the variation in the amount of the groundmassldquophaserdquo in the different subsamples controls the ITEconcentrations in the various subsamples
For most of the major elements subsamples of NWA 032have relative standard deviations (RSD) that areinsignificantly different from those of LAP (Table 1) eventhough the average subsample size for NWA 032 (sim14 mgFagan et al 2002) was smaller than for LAP (sim34 mg) TheRSDs of MgO and Cr2O3 for NWA 032 are again highbecause it has a porphyritic texture with large phenocrysts(millimeter scale) of olivine (with chromite inclusions) andmagnesian pyroxene but a fine-grained groundmass of
plagioclase Fe-rich pyroxene ilmenite and glass keeps theRSDs of other major and incompatible trace elements low
Source Crater Pairing of LAP and NWA 032
We find the similarities in chemistry and petrographybetween LAP and NWA 032 when compared to the largeranges observed among Apollo and Luna samples to be sogreat that it is highly unlikely that two meteorites so similarcould derive from different locations Below we summarizethe similarities and differences
The textures of NWA 032 and LAP are markedlydifferent from each other NWA 032 has a porphyritic texture
Fig 5 BSE images from LAP 0220533 a) oxide grains set in and around a large olivine grain individual grains of ilmenite (Ilm) Cr-ulvˆspinel (Chr-Usp) and chromite (Chr) composite chromian ulvˆspinel-chromite (ChrUsp) grains with accompanying pyroxene andplagioclase (grey and black areas) b) A close-up of a zoned spinel grain with a chromite core and a Cr-ulvˆspinel rim c) A large cristobalite(Crist) grain with many inclusions of fayalite pyroxene (Pyx) plagioclase (Plag) troilite (Sulf) phosphate K-rich glass and the ITE-richglass Also present are several areas of fayalite symplectite (Fay Symp) with inclusions of plagioclase silica ilmenite troilite and K-richglass d) A BSE image of a different area of groundmass showing a large grain of fayalite symplectite containing inclusions of plagioclasesilica ilmenite troilite K-rich glass and Fe-rich pyroxene A large ilmenite (Ilm) grain cuts through the symplectite and several large troilitegrains are also present
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
1082 R Zeigler et al
in our thin sections such veins were reported as pervasive inthe original macroscopic description of all five LAP stones(McBride et al 2003 2004a 2004b)
The various shock-induced effects observed in LAP canbe used to quantify and constrain the level of shock that LAPexperienced The presence of both plagioclase andmaskelynite in these samples suggests that the lower end ofthe range listed for conversion of plagioclase to maskelynite(30ndash45 GPa Stˆffler and Hornemann 1972 Ostertag 1983)is appropriate The mosaicism seen in the pyroxene istypically associated with shock values in the 30ndash75 GParange (Kieffer et al 1976 Schaal et al 1979) The presenceof shock-melt veins that have melted both pyroxene andplagioclase (based on the melt composition Table 6)indicates LAP should have been subjected to shock levels ofgt75ndash80 GPa (Kieffer et al 1976 Schaal et al 1979) Thedifferent shock effects observed reflect a range fromlt30 GPa (areas were plagioclase is preserved) to gt75 GPa(areas where shock melting occurred) over distances of onlya few millimeters
Bulk Composition and Comparison to Other LunarBasalts
LAP is a moderately aluminous (sim10 wt Al2O3) low-Ti(31 wt TiO2) mare basalt that falls near the Fe-rich(222 wt FeO) end of the range of FeO concentrationsobserved among lunar basalts It is more ferroan (Mgprime = 347)than any basalt in the Apollo or Luna collection (Fig 11a)Among lunar basalts only meteorites Asuka-881757 andYamato-793169 have comparably low Mgprime values (Koeberlet al 1993 Warren and Kallemeyn 1993 Thalmann et al1996 Korotev et al 2003a) LAP is enriched in Na2O(038 wt) relative to other ferroan (eg Asuka-881757 andYamato-793169) and Fe-rich basalts except for NWA 032(Fig 11b)
Regarding trace elements LAP is enriched in Cocompared to most lunar mare basalts with comparable Scconcentrations (Table 1 Fig 12a) Among Apollo and Lunabasalts only the Apollo 12 ilmenite basalts (Rhodes et al1977 Neal et al 1994) are comparable Incompatible trace-
Table 5 Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02205 02226 02224 02436 02205 02226 02224 02436 02205 02226plag plag plag plag mask mask mask mask plag plagcore core core core core core core core Na rim Na rim
N 123 86 48 88 29 49 33 32 12 3
Major elements in wt by EMPASiO2 4715 4657 4689 4639 4753 4741 4663 4673 4949 4960TiO2 010 007 007 006 013 008 006 006 027 019Al2O3 3337 3367 3296 3363 3367 3291 3376 3415 3170 3103Cr2O3 003 lt002 lt002 002 007 002 lt002 002 004 003FeO 068 067 073 058 060 111 066 060 134 136MgO 023 022 017 024 027 029 028 029 008 012CaO 1730 1746 1709 1763 1747 1726 1730 1740 1628 1597BaO na na na na na na na na na naNa2O 120 123 136 121 119 123 131 128 148 153K2O 006 007 010 006 005 009 006 005 020 019Total 1000 1000 994 998 1008 1004 1001 1006 1006 1000
Cation ratiosAn 885 883 869 887 888 881 877 880 848 842Or 04 04 06 04 03 05 03 03 12 12Ab 111 112 125 110 109 113 120 117 140 146Cn 00 00 00 00 00 00 00 00 00 00
Stoichiometry based on 8 oxygen atomsSi IV 2168 2147 2173 2143 2168 2179 2147 2140 2259 2279Al IV 1809 1830 1801 1831 1810 1782 1832 1843 1705 1681Fe+2 0026 0026 0028 0023 0023 0043 0025 0023 0051 0052Mg 0016 0015 0011 0017 0019 0020 0019 0020 0005 0008Ca 0853 0863 0849 0872 0854 0850 0853 0854 0796 0786Ba minus minus minus minus minus minus minus minus minus minusNa 0107 0110 0122 0108 0105 0109 0117 0114 0131 0136K 0004 0004 0006 0004 0003 0005 0003 0003 0011 0011Tet site 3977 3977 3974 3974 3978 3961 3979 3984 3964 3960Oct site 1005 1018 1022 1023 1003 1027 1022 1013 0995 0994
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1083
element concentrations are considerably greater in LAP thanin most of other low-Ti basalts (Fig 12bndashc) including theApollo 12 ilmenite basalts (Haskin et al 1971 Neal et al1994) The exceptions are NWA 032 the high-Al basalts ofLuna 16 (Philpotts et al 1972 Helmke and Haskin 1972 Maet al 1979) and some Apollo 14 high-Al basalts (Dickinsonet al 1985 Shervais et al 1985 Neal et al 1989a 1989b)
Relative concentrations of REEs in the LAP basalt arealso dissimilar to those of most other lunar basalts (Fig 13) inthat LAP is enriched in light REEs The exceptions are NWA032 which has a pattern nearly parallel to LAP and Apollo 14group 3 basalts (Dickinson et al 1985) which have a patternthat is similar although somewhat less steep in the heavyREEs Ratios of Th to REE in LAP are higher than those of allother lunar basalts except NWA 032 (Fig 14) and thedisparity in ThREE ratio between LAP and other lunarbasalts (except NWA 032) increases from the light to heavyREEs The Apollo 14 high-K basalts have similar ThREEratios for the middle REE Sm-Tb however (Neal et al 1989a
1989b) Overall in terms of its trace-element concentrationsLAP 02205 is most similar to NWA 032 The maindifferences are that NWA 032 is richer in elements associatedwith olivine (Mg Cr Co) and has concentrations ofincompatible elements that are 78ndash91 as great as those inLAP 02205
DISCUSSION
Evidence Supporting the Lunar Origin and Pairing of theLAP Stones
As stated in the introduction the meteorites LAP 0220502224 02226 02436 and 03632 were identified as lunarbasalts that were almost certainly paired (McBride et al 20032004a 2004b) A brief summary follows of the attributesfound in our more detailed petrographic examination thatsupport this initial classification and pairing interpretation
Results of oxygen isotope analyses (δ18O = +56 and
Table 5 Continued Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02224 02436 02205 02205 02226 02224 02436 02205 02205 02205plag plag plag plag plag plag plag barian KBa KBaNa rim Na rim matrix K rim K rim K rim K rim K-spar glass glass
N 24 5 13 10 1 5 1 10 10 23
Major elements in wt by EMPASiO2 4901 4879 5122 5152 4888 4935 5017 6026 5935 6356TiO2 008 008 016 017 lt002 008 014 na na naAl2O3 3163 3120 2960 2993 3213 3004 3002 2019 2063 2043Cr2O3 002 002 006 005 lt002 003 lt002 na na naFeO 117 130 267 192 147 195 173 065 074 116MgO 006 009 003 002 lt002 lt002 002 lt002 lt002 010CaO 1620 1622 1520 1549 1618 1602 1560 063 066 207BaO na na na na na na na 501 407 372Na2O 157 155 105 105 132 126 150 031 029 033K2O 023 021 090 067 067 056 086 1354 1162 586Total 1000 995 1007 1006 1007 993 1000 1008 1006 1007
Cation ratiosAn 839 842 846 852 835 845 807 33 minus minusOr 14 13 61 44 41 35 53 842 minus minusAb 147 145 105 104 124 120 140 30 minus minusCn 00 00 00 00 00 00 00 96 minus minus
Stoichiometry based on 8 oxygen atomsSi IV 2253 2257 2342 2344 2237 2293 2312 2863 2864 2951Al IV 1714 1701 1596 1609 1732 1645 1631 1131 1173 1124Fe+2 0045 0050 0102 0073 0056 0076 0067 0026 0030 0045Mg 0004 0006 0002 0001 0000 0001 0001 0001 0001 0007Ca 0798 0804 0745 0757 0793 0798 0770 0032 0034 0100Ba minus minus minus minus minus minus minus 0093 0077 0070Na 0140 0139 0093 0093 0117 0113 0134 0029 0027 0029K 0013 0013 0052 0039 0039 0033 0050 0820 0715 0353Tet site 3967 3957 3938 3954 3969 3938 3943 3994 4037 4075Oct site 0013 1011 0995 0963 1007 1020 1022 1002 0884 0604Plag = plagioclase mask = maskelynite N = number of analyses in the average na = not analyzed
1084 R Zeigler et al Ta
ble
6 A
vera
ge a
nd re
pres
enta
tive
cris
toba
lite
and
glas
s co
mpo
sitio
n in
the
LAP
basa
ltic
met
eorit
es
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
0220
502
226
0222
402
436
0220
502
205
0220
502
205
0220
502
224
0222
4cr
isto
balit
ecr
isto
balit
ecr
isto
balit
ecr
isto
balit
eSi
-ric
hpy
x-lik
eK
gla
ssIT
E-ric
hsh
ock
shoc
ksh
ock
MI g
lass
MI g
lass
in s
ympl
m
afic
gla
ssgl
ass
area
glas
s ar
eagl
ass
vein
N6
25
44
12
51
6515
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
979
598
17
984
798
45
672
542
76
783
236
67
463
486
441
TiO
20
270
270
230
230
664
810
374
032
341
623
13A
l 2O3
073
060
064
078
187
99
4210
13
544
139
86
123
Cr 2
O3
002
lt00
2lt0
02
002
lt00
20
13lt0
02
lt00
20
080
380
28Fe
O0
210
400
190
171
8615
91
183
392
719
618
520
5M
nOn
an
an
an
an
a0
22n
a0
420
220
290
25M
gO0
02lt0
02
lt00
2lt0
02
033
817
lt00
20
213
459
857
17C
aO0
190
200
200
236
8919
16
098
976
127
118
114
BaO
na
na
na
na
117
na
na
na
na
na
na
Na 2
O0
130
100
090
120
620
110
190
060
510
360
49K
2O0
030
050
07lt0
02
167
na
566
030
005
na
na
P 2O
5n
an
an
an
an
an
an
a2
32n
an
an
aF
na
na
na
na
na
na
na
008
na
na
na
Y2O
3n
an
an
an
an
an
an
a0
19n
an
an
aC
e 2O
3n
an
an
an
an
an
an
a0
12n
an
an
aSO
3n
an
an
an
an
an
an
a1
23n
an
an
aTo
tal
995
599
80
999
010
00
992
410
070
974
910
02
991
100
099
6Sy
mpl
= sy
mpl
ectit
e M
I = m
elt i
nclu
sion
N =
num
ber o
f ana
lyse
s in
the
aver
age
na
= n
ot a
naly
zed
The
shoc
ked
glas
s in
LAP
0222
4 is
the
parti
ally
mel
ted
area
(see
Fig
14)
and
onl
y th
e an
ayls
es o
fth
e gl
ass i
tsel
f wer
e in
clud
ed in
the
aver
age
not t
he m
iner
als t
hat w
ere
anal
yzed
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1085
Table 7 Representative phosphate compositions in LAP 0220533LAP LAP LAP LAP LAP LAP LAP LAP02205 02205 02205 02205 02205 02205 02205 02205RE- RE- RE- RE- RE- fluorapatite fluorapatite fluorapatitemerrillite merrillite merrillite merrillite merrillite
Major elements in wt by EMPASiO2 050 044 062 037 321 228 449 137Al2O3 022 lt005 009 lt005 lt005 007 014 lt005FeO 637 774 568 576 250 169 439 202MgO 020 037 025 028 lt005 lt005 lt005 lt005CaO 4326 4035 4233 4245 4983 5241 5003 5351Na2O 000 001 010 014 000 000 001 000P2O5 3885 4171 4382 4360 3540 3949 3771 4077Cl lt005 lt005 lt005 lt005 lt005 006 027 031F 047 044 050 048 168 245 130 186Y2O3 298 293 226 221 172 103 078 053La2O3 093 107 065 064 092 024 014 012Ce2O3 253 259 189 185 253 072 069 053Nd2O3 161 177 108 118 166 057 059 031Sm2O3 043 043 029 028 048 022 015 009Gd2O3 087 090 058 058 079 023 018 008Yb2O3 016 032 009 lt005 010 005 lt005 lt005ThO2 007 009 008 lt005 021 lt005 lt005 lt005minusO = (FCl) 021 020 022 021 072 105 061 085Sums 9930 1010 1001 9968 1004 1005 1003 1006
Table 8 Average sulfide and metal compositions in LAP 0220533Ave Fe metal High-Ni metal Troilite
N 5 1 8
Elemental percentage by EMPAFe 9209 5880 6280Ni 664 3377 lt002Co 141 595 lt002Ti 023 009 006Cr 043 017 lt002Mn lt002 004 lt002S lt002 lt002 3620Totals 1008 988 994Ideal troilite = 365 wt S 635 wt Fe N = number of analyses
Table 9 Modal mineralogy of the different LAP stonesLAP 0220533 LAP 0222616 LAP 0222424 LAP 0243614
Pyroxene 515 505 469 466Plagioclase 319 321 323 346Ilmenite 348 391 386 399Fay sympl 309 290 358 483Olivine 233 271 363 320Cristobalite 214 209 178 200Spinel (all) 034 045 040 039Troilite 025 024 024 022Fractures 49 49 53 421Shock glass 01 02 22 00N 633 times 106 905 times 106 470 times 106 396 times 106
All modal values are listed as percentages N = number of pixels
1086 R Zeigler et al
Fig 1 Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) and fayalite(more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phases arepyroxene and olivine a) LAP 0222616 b) LAP 0243614 c) LAP 0222424 d) LAP 0220533
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1087
δ17O = +27) performed by Mayeda and Clayton (reported inMcBride et al 2003) constrain the origin of LAP 02205 tothe Earth the Moon or an enstatite meteorite parent bodyLAP is clearly a meteorite all four of the stones have fusioncrusts (ruling out a terrestrial origin) The extremely ferroannature of LAP rules out the enstatite parent body as theprovenance FeOMnO ratios of mafic silicates arediagnostic of origins from different planetary bodies in thesolar system (Dymek et al 1976 Papike 1998) Ratios ofFeOMnO in LAP pyroxenes (average sim60) and olivines(average sim95) are consistent only with lunar origin (Fig 15)Furthermore the presence of Fe(Ni) metal and troilite thecompletely anhydrous nature of the sample the apparentlack of Fe3+ in all phases the calcic nature of theplagioclase and the deep negative Eu anomaly are allcommon in lunar basalts
With regard to texture mineral assemblage and mineralchemistry the four LAP 02xxx stones appear to beindistinguishable from each other Although we did not studythe mineral chemistry of the LAP 03632 in depth the textureand mineral assemblage are identical to the LAP 02xxxstones Furthermore the collection locations of the five stonesform a linear array sim3 km in length that is perpendicular to theflow of the ice sheet (John Schutt personal communication)Thus in the absence of cosmic-ray exposure data to thecontrary we conclude that the four LAP 02xxx stones studiedare paired
Compositional Variability among Small Subsamples ofLAP 02205 and NWA 032
Samples of lunar meteorites available for study at most afew hundred milligrams are very small by the standards ofterrestrial geology and geochemistry Nevertheless we havetaken our samples and subdivided them into numerous evensmaller (10ndash50 mg) subsamples for bulk compositionalanalysis (Korotev et al 1983 1996 2003a 2003b Jolliffet al 1991 1998 Fagan et al 2002) This procedure providesan estimate of the whole-rock composition through a mass-weighted mean that is equivalent to a single analysis of theentire mass of the allocated sample The variation amongsmall subsamples however provides additional informationabout compositional variations associated with mineralassemblage and proportions about petrogenesis and aboutpossible relationships to other meteorites (eg Korotev et al2003a 2003b) and how well the ldquowhole-rockrdquo compositionis likely to represent that of the source region of the meteorite(Korotev et al 2000a) In the following discussion weevaluate the causes of differences in composition amongsmall subsamples of LAP and NWA 032
The range of concentrations among the 19 subsamples ofLAP (27ndash40 mg) is relatively small for the most preciselydetermined major elements (SiO2 TiO2 Al2O3 FeO CaONa2O) and most precisely determined trace elements that arecompatible with the major mineral phases (Co Sc Eu) The
Fig 1 Continued Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) andfayalite (more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phasesare pyroxene and olivine d) LAP 0220533
1088 R Zeigler et al
relative sample standard deviations (s ) range from 08 to76 (with only Co and Eu gt 5 Table 1) The exceptionsare MgO and Cr2O3 for which the relative standarddeviations are distinctly greater 12 and 16 respectivelyFor incompatible elements that we determined precisely(lt9 analytical uncertainty La Ce Sm Tb Yb Lu Hf Taand Th) relative standard deviations range from 7 to 11These variations are caused by a combination ofunrepresentative sampling of the major mineral phasesowing to the coarse grain size (up to sim1 mm3) relative to theINAA subsample size (about 12 mm3 assuming that thedensity of LAP is sim35 gmm3) and to the heterogeneousdistribution of some relatively minor phases with high
concentrations of a given element This problem is not new asmany investigators have previously wrestled with theproblem of studying relatively coarse-grained lunar basaltswith small allocated subsample sizes characteristic of rareextraterrestrial samples (Korotev and Haskin 1975 Haskinet al 1977 Lindstrom and Haskin 1978 Ryder and Schuraytz2001) Ryder and Schuraytz (2001) showed that sim5 g ofmaterial are needed to achieve a representative sample ofApollo 15 olivine-normative basalts which have grain sizeson the order of a millimeter or greater
Among the LAP subsamples Cr2O3 and MgOconcentrations correlate positively (R2 = 081) as a result ofthe association of chromite and Cr-ulvˆspinel with olivine
Fig 2 BSE images from LAP 0220533 a) a large round olivine (oli) grain and a smaller subhedral olivine grain (left center of the image)both surrounded by zoned pyroxene (pyx) and plagioclase (plag) with melt inclusions (MI) and inclusions of chromite (chr) A smallulvˆspinel (Usp) grain occurs in the upper left b) A large irregular olivine grain and a smaller mostly resorbed olivine grain The larger graincontains both melt inclusions (MI) and chromite grains The associated ilmenite (Ilm) grain is the most magnesian ilmenite grain observed Acomposite grain of metal and troilite (MetSulf) is also present c) A BSE image showing the zoning in multiple large pyroxene grainsintergrown with plagioclase and maskelynite (mask) grains One small cristobalite (crist) grain is also present d) A BSE image showingseveral large plagioclase grains some of which contain both fractured areas (plagioclase) and smooth areas (maskelynite) Also present areseveral areas of groundmass including a fayalite symplectite and a cristobalite grain cut by an ilmenite lath
x
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1089
The large variations seen in MgO Cr2O3 and to a lesserextent Co concentrations occur because of the large relativevariation in the fraction of modal olivine among thesubsamples Normatively the compositional rangecorresponds to minus03ndash25 olivine (one subsample has 03normative quartz) and 032ndash049 chromite The relativelysmall variations seen among concentrations of the other majorelements as well as Sc and Eu are controlled byunrepresentative sampling of the major mineral phasespyroxene (Sc Ca Fe Si) and plagioclase (Al Na Ca Si Eu)and the minor but widely distributed mineral ilmenite (Ti Fe)Trace amounts of a few minerals that are found only ingroundmass have high concentrations of incompatible traceelements relative to the concentration of those elements inthe bulk meteorite These minerals include K-feldspar (Ba)
Fig 3 a) CaO versus Mgprime (molar Mg[Mg + Fe]100) in the olivinesof the different LAP stones The compositions range from cores ofFo55ndash67 trending towards rims typically in the Fo40 range withextreme zonation to rims of Fo15ndash20 in a few cases Where analyzedthe composition of groundmass fayalite are also shown b) Anelectron microprobe traverse across a small strongly zoned olivinegrain in LAP 0220533 The grain shows zoning from a core of simFo58to a rim composition of simFo18 over sim100 microm The break in the zoning(black arrow) is centered on a fracture in the olivine grain
Fig 4 Compositions of LAP oxides plotted on the (FeMgMn)O-(CrAl)2O3-TiO2 ternary (after El Goresy et al 1971) Compositionsof endmember ilmenite (FeTiO3) ulvˆspinel (Fe2TiO4) andchromite (FeCr2O4) are labeled For a description of theclassification scheme see the footnote of Table 3 a) LAP 0220533b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1090 R Zeigler et al
RE-merrillite (P REEs Th) and baddeleyite (Zr Hf U Th)Therefore the variation in the amount of the groundmassldquophaserdquo in the different subsamples controls the ITEconcentrations in the various subsamples
For most of the major elements subsamples of NWA 032have relative standard deviations (RSD) that areinsignificantly different from those of LAP (Table 1) eventhough the average subsample size for NWA 032 (sim14 mgFagan et al 2002) was smaller than for LAP (sim34 mg) TheRSDs of MgO and Cr2O3 for NWA 032 are again highbecause it has a porphyritic texture with large phenocrysts(millimeter scale) of olivine (with chromite inclusions) andmagnesian pyroxene but a fine-grained groundmass of
plagioclase Fe-rich pyroxene ilmenite and glass keeps theRSDs of other major and incompatible trace elements low
Source Crater Pairing of LAP and NWA 032
We find the similarities in chemistry and petrographybetween LAP and NWA 032 when compared to the largeranges observed among Apollo and Luna samples to be sogreat that it is highly unlikely that two meteorites so similarcould derive from different locations Below we summarizethe similarities and differences
The textures of NWA 032 and LAP are markedlydifferent from each other NWA 032 has a porphyritic texture
Fig 5 BSE images from LAP 0220533 a) oxide grains set in and around a large olivine grain individual grains of ilmenite (Ilm) Cr-ulvˆspinel (Chr-Usp) and chromite (Chr) composite chromian ulvˆspinel-chromite (ChrUsp) grains with accompanying pyroxene andplagioclase (grey and black areas) b) A close-up of a zoned spinel grain with a chromite core and a Cr-ulvˆspinel rim c) A large cristobalite(Crist) grain with many inclusions of fayalite pyroxene (Pyx) plagioclase (Plag) troilite (Sulf) phosphate K-rich glass and the ITE-richglass Also present are several areas of fayalite symplectite (Fay Symp) with inclusions of plagioclase silica ilmenite troilite and K-richglass d) A BSE image of a different area of groundmass showing a large grain of fayalite symplectite containing inclusions of plagioclasesilica ilmenite troilite K-rich glass and Fe-rich pyroxene A large ilmenite (Ilm) grain cuts through the symplectite and several large troilitegrains are also present
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1083
element concentrations are considerably greater in LAP thanin most of other low-Ti basalts (Fig 12bndashc) including theApollo 12 ilmenite basalts (Haskin et al 1971 Neal et al1994) The exceptions are NWA 032 the high-Al basalts ofLuna 16 (Philpotts et al 1972 Helmke and Haskin 1972 Maet al 1979) and some Apollo 14 high-Al basalts (Dickinsonet al 1985 Shervais et al 1985 Neal et al 1989a 1989b)
Relative concentrations of REEs in the LAP basalt arealso dissimilar to those of most other lunar basalts (Fig 13) inthat LAP is enriched in light REEs The exceptions are NWA032 which has a pattern nearly parallel to LAP and Apollo 14group 3 basalts (Dickinson et al 1985) which have a patternthat is similar although somewhat less steep in the heavyREEs Ratios of Th to REE in LAP are higher than those of allother lunar basalts except NWA 032 (Fig 14) and thedisparity in ThREE ratio between LAP and other lunarbasalts (except NWA 032) increases from the light to heavyREEs The Apollo 14 high-K basalts have similar ThREEratios for the middle REE Sm-Tb however (Neal et al 1989a
1989b) Overall in terms of its trace-element concentrationsLAP 02205 is most similar to NWA 032 The maindifferences are that NWA 032 is richer in elements associatedwith olivine (Mg Cr Co) and has concentrations ofincompatible elements that are 78ndash91 as great as those inLAP 02205
DISCUSSION
Evidence Supporting the Lunar Origin and Pairing of theLAP Stones
As stated in the introduction the meteorites LAP 0220502224 02226 02436 and 03632 were identified as lunarbasalts that were almost certainly paired (McBride et al 20032004a 2004b) A brief summary follows of the attributesfound in our more detailed petrographic examination thatsupport this initial classification and pairing interpretation
Results of oxygen isotope analyses (δ18O = +56 and
Table 5 Continued Average and representative feldspar compositions in the LAP basaltic meteoritesLAP LAP LAP LAP LAP LAP LAP LAP LAP LAP02224 02436 02205 02205 02226 02224 02436 02205 02205 02205plag plag plag plag plag plag plag barian KBa KBaNa rim Na rim matrix K rim K rim K rim K rim K-spar glass glass
N 24 5 13 10 1 5 1 10 10 23
Major elements in wt by EMPASiO2 4901 4879 5122 5152 4888 4935 5017 6026 5935 6356TiO2 008 008 016 017 lt002 008 014 na na naAl2O3 3163 3120 2960 2993 3213 3004 3002 2019 2063 2043Cr2O3 002 002 006 005 lt002 003 lt002 na na naFeO 117 130 267 192 147 195 173 065 074 116MgO 006 009 003 002 lt002 lt002 002 lt002 lt002 010CaO 1620 1622 1520 1549 1618 1602 1560 063 066 207BaO na na na na na na na 501 407 372Na2O 157 155 105 105 132 126 150 031 029 033K2O 023 021 090 067 067 056 086 1354 1162 586Total 1000 995 1007 1006 1007 993 1000 1008 1006 1007
Cation ratiosAn 839 842 846 852 835 845 807 33 minus minusOr 14 13 61 44 41 35 53 842 minus minusAb 147 145 105 104 124 120 140 30 minus minusCn 00 00 00 00 00 00 00 96 minus minus
Stoichiometry based on 8 oxygen atomsSi IV 2253 2257 2342 2344 2237 2293 2312 2863 2864 2951Al IV 1714 1701 1596 1609 1732 1645 1631 1131 1173 1124Fe+2 0045 0050 0102 0073 0056 0076 0067 0026 0030 0045Mg 0004 0006 0002 0001 0000 0001 0001 0001 0001 0007Ca 0798 0804 0745 0757 0793 0798 0770 0032 0034 0100Ba minus minus minus minus minus minus minus 0093 0077 0070Na 0140 0139 0093 0093 0117 0113 0134 0029 0027 0029K 0013 0013 0052 0039 0039 0033 0050 0820 0715 0353Tet site 3967 3957 3938 3954 3969 3938 3943 3994 4037 4075Oct site 0013 1011 0995 0963 1007 1020 1022 1002 0884 0604Plag = plagioclase mask = maskelynite N = number of analyses in the average na = not analyzed
1084 R Zeigler et al Ta
ble
6 A
vera
ge a
nd re
pres
enta
tive
cris
toba
lite
and
glas
s co
mpo
sitio
n in
the
LAP
basa
ltic
met
eorit
es
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
0220
502
226
0222
402
436
0220
502
205
0220
502
205
0220
502
224
0222
4cr
isto
balit
ecr
isto
balit
ecr
isto
balit
ecr
isto
balit
eSi
-ric
hpy
x-lik
eK
gla
ssIT
E-ric
hsh
ock
shoc
ksh
ock
MI g
lass
MI g
lass
in s
ympl
m
afic
gla
ssgl
ass
area
glas
s ar
eagl
ass
vein
N6
25
44
12
51
6515
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
979
598
17
984
798
45
672
542
76
783
236
67
463
486
441
TiO
20
270
270
230
230
664
810
374
032
341
623
13A
l 2O3
073
060
064
078
187
99
4210
13
544
139
86
123
Cr 2
O3
002
lt00
2lt0
02
002
lt00
20
13lt0
02
lt00
20
080
380
28Fe
O0
210
400
190
171
8615
91
183
392
719
618
520
5M
nOn
an
an
an
an
a0
22n
a0
420
220
290
25M
gO0
02lt0
02
lt00
2lt0
02
033
817
lt00
20
213
459
857
17C
aO0
190
200
200
236
8919
16
098
976
127
118
114
BaO
na
na
na
na
117
na
na
na
na
na
na
Na 2
O0
130
100
090
120
620
110
190
060
510
360
49K
2O0
030
050
07lt0
02
167
na
566
030
005
na
na
P 2O
5n
an
an
an
an
an
an
a2
32n
an
an
aF
na
na
na
na
na
na
na
008
na
na
na
Y2O
3n
an
an
an
an
an
an
a0
19n
an
an
aC
e 2O
3n
an
an
an
an
an
an
a0
12n
an
an
aSO
3n
an
an
an
an
an
an
a1
23n
an
an
aTo
tal
995
599
80
999
010
00
992
410
070
974
910
02
991
100
099
6Sy
mpl
= sy
mpl
ectit
e M
I = m
elt i
nclu
sion
N =
num
ber o
f ana
lyse
s in
the
aver
age
na
= n
ot a
naly
zed
The
shoc
ked
glas
s in
LAP
0222
4 is
the
parti
ally
mel
ted
area
(see
Fig
14)
and
onl
y th
e an
ayls
es o
fth
e gl
ass i
tsel
f wer
e in
clud
ed in
the
aver
age
not t
he m
iner
als t
hat w
ere
anal
yzed
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1085
Table 7 Representative phosphate compositions in LAP 0220533LAP LAP LAP LAP LAP LAP LAP LAP02205 02205 02205 02205 02205 02205 02205 02205RE- RE- RE- RE- RE- fluorapatite fluorapatite fluorapatitemerrillite merrillite merrillite merrillite merrillite
Major elements in wt by EMPASiO2 050 044 062 037 321 228 449 137Al2O3 022 lt005 009 lt005 lt005 007 014 lt005FeO 637 774 568 576 250 169 439 202MgO 020 037 025 028 lt005 lt005 lt005 lt005CaO 4326 4035 4233 4245 4983 5241 5003 5351Na2O 000 001 010 014 000 000 001 000P2O5 3885 4171 4382 4360 3540 3949 3771 4077Cl lt005 lt005 lt005 lt005 lt005 006 027 031F 047 044 050 048 168 245 130 186Y2O3 298 293 226 221 172 103 078 053La2O3 093 107 065 064 092 024 014 012Ce2O3 253 259 189 185 253 072 069 053Nd2O3 161 177 108 118 166 057 059 031Sm2O3 043 043 029 028 048 022 015 009Gd2O3 087 090 058 058 079 023 018 008Yb2O3 016 032 009 lt005 010 005 lt005 lt005ThO2 007 009 008 lt005 021 lt005 lt005 lt005minusO = (FCl) 021 020 022 021 072 105 061 085Sums 9930 1010 1001 9968 1004 1005 1003 1006
Table 8 Average sulfide and metal compositions in LAP 0220533Ave Fe metal High-Ni metal Troilite
N 5 1 8
Elemental percentage by EMPAFe 9209 5880 6280Ni 664 3377 lt002Co 141 595 lt002Ti 023 009 006Cr 043 017 lt002Mn lt002 004 lt002S lt002 lt002 3620Totals 1008 988 994Ideal troilite = 365 wt S 635 wt Fe N = number of analyses
Table 9 Modal mineralogy of the different LAP stonesLAP 0220533 LAP 0222616 LAP 0222424 LAP 0243614
Pyroxene 515 505 469 466Plagioclase 319 321 323 346Ilmenite 348 391 386 399Fay sympl 309 290 358 483Olivine 233 271 363 320Cristobalite 214 209 178 200Spinel (all) 034 045 040 039Troilite 025 024 024 022Fractures 49 49 53 421Shock glass 01 02 22 00N 633 times 106 905 times 106 470 times 106 396 times 106
All modal values are listed as percentages N = number of pixels
1086 R Zeigler et al
Fig 1 Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) and fayalite(more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phases arepyroxene and olivine a) LAP 0222616 b) LAP 0243614 c) LAP 0222424 d) LAP 0220533
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1087
δ17O = +27) performed by Mayeda and Clayton (reported inMcBride et al 2003) constrain the origin of LAP 02205 tothe Earth the Moon or an enstatite meteorite parent bodyLAP is clearly a meteorite all four of the stones have fusioncrusts (ruling out a terrestrial origin) The extremely ferroannature of LAP rules out the enstatite parent body as theprovenance FeOMnO ratios of mafic silicates arediagnostic of origins from different planetary bodies in thesolar system (Dymek et al 1976 Papike 1998) Ratios ofFeOMnO in LAP pyroxenes (average sim60) and olivines(average sim95) are consistent only with lunar origin (Fig 15)Furthermore the presence of Fe(Ni) metal and troilite thecompletely anhydrous nature of the sample the apparentlack of Fe3+ in all phases the calcic nature of theplagioclase and the deep negative Eu anomaly are allcommon in lunar basalts
With regard to texture mineral assemblage and mineralchemistry the four LAP 02xxx stones appear to beindistinguishable from each other Although we did not studythe mineral chemistry of the LAP 03632 in depth the textureand mineral assemblage are identical to the LAP 02xxxstones Furthermore the collection locations of the five stonesform a linear array sim3 km in length that is perpendicular to theflow of the ice sheet (John Schutt personal communication)Thus in the absence of cosmic-ray exposure data to thecontrary we conclude that the four LAP 02xxx stones studiedare paired
Compositional Variability among Small Subsamples ofLAP 02205 and NWA 032
Samples of lunar meteorites available for study at most afew hundred milligrams are very small by the standards ofterrestrial geology and geochemistry Nevertheless we havetaken our samples and subdivided them into numerous evensmaller (10ndash50 mg) subsamples for bulk compositionalanalysis (Korotev et al 1983 1996 2003a 2003b Jolliffet al 1991 1998 Fagan et al 2002) This procedure providesan estimate of the whole-rock composition through a mass-weighted mean that is equivalent to a single analysis of theentire mass of the allocated sample The variation amongsmall subsamples however provides additional informationabout compositional variations associated with mineralassemblage and proportions about petrogenesis and aboutpossible relationships to other meteorites (eg Korotev et al2003a 2003b) and how well the ldquowhole-rockrdquo compositionis likely to represent that of the source region of the meteorite(Korotev et al 2000a) In the following discussion weevaluate the causes of differences in composition amongsmall subsamples of LAP and NWA 032
The range of concentrations among the 19 subsamples ofLAP (27ndash40 mg) is relatively small for the most preciselydetermined major elements (SiO2 TiO2 Al2O3 FeO CaONa2O) and most precisely determined trace elements that arecompatible with the major mineral phases (Co Sc Eu) The
Fig 1 Continued Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) andfayalite (more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phasesare pyroxene and olivine d) LAP 0220533
1088 R Zeigler et al
relative sample standard deviations (s ) range from 08 to76 (with only Co and Eu gt 5 Table 1) The exceptionsare MgO and Cr2O3 for which the relative standarddeviations are distinctly greater 12 and 16 respectivelyFor incompatible elements that we determined precisely(lt9 analytical uncertainty La Ce Sm Tb Yb Lu Hf Taand Th) relative standard deviations range from 7 to 11These variations are caused by a combination ofunrepresentative sampling of the major mineral phasesowing to the coarse grain size (up to sim1 mm3) relative to theINAA subsample size (about 12 mm3 assuming that thedensity of LAP is sim35 gmm3) and to the heterogeneousdistribution of some relatively minor phases with high
concentrations of a given element This problem is not new asmany investigators have previously wrestled with theproblem of studying relatively coarse-grained lunar basaltswith small allocated subsample sizes characteristic of rareextraterrestrial samples (Korotev and Haskin 1975 Haskinet al 1977 Lindstrom and Haskin 1978 Ryder and Schuraytz2001) Ryder and Schuraytz (2001) showed that sim5 g ofmaterial are needed to achieve a representative sample ofApollo 15 olivine-normative basalts which have grain sizeson the order of a millimeter or greater
Among the LAP subsamples Cr2O3 and MgOconcentrations correlate positively (R2 = 081) as a result ofthe association of chromite and Cr-ulvˆspinel with olivine
Fig 2 BSE images from LAP 0220533 a) a large round olivine (oli) grain and a smaller subhedral olivine grain (left center of the image)both surrounded by zoned pyroxene (pyx) and plagioclase (plag) with melt inclusions (MI) and inclusions of chromite (chr) A smallulvˆspinel (Usp) grain occurs in the upper left b) A large irregular olivine grain and a smaller mostly resorbed olivine grain The larger graincontains both melt inclusions (MI) and chromite grains The associated ilmenite (Ilm) grain is the most magnesian ilmenite grain observed Acomposite grain of metal and troilite (MetSulf) is also present c) A BSE image showing the zoning in multiple large pyroxene grainsintergrown with plagioclase and maskelynite (mask) grains One small cristobalite (crist) grain is also present d) A BSE image showingseveral large plagioclase grains some of which contain both fractured areas (plagioclase) and smooth areas (maskelynite) Also present areseveral areas of groundmass including a fayalite symplectite and a cristobalite grain cut by an ilmenite lath
x
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1089
The large variations seen in MgO Cr2O3 and to a lesserextent Co concentrations occur because of the large relativevariation in the fraction of modal olivine among thesubsamples Normatively the compositional rangecorresponds to minus03ndash25 olivine (one subsample has 03normative quartz) and 032ndash049 chromite The relativelysmall variations seen among concentrations of the other majorelements as well as Sc and Eu are controlled byunrepresentative sampling of the major mineral phasespyroxene (Sc Ca Fe Si) and plagioclase (Al Na Ca Si Eu)and the minor but widely distributed mineral ilmenite (Ti Fe)Trace amounts of a few minerals that are found only ingroundmass have high concentrations of incompatible traceelements relative to the concentration of those elements inthe bulk meteorite These minerals include K-feldspar (Ba)
Fig 3 a) CaO versus Mgprime (molar Mg[Mg + Fe]100) in the olivinesof the different LAP stones The compositions range from cores ofFo55ndash67 trending towards rims typically in the Fo40 range withextreme zonation to rims of Fo15ndash20 in a few cases Where analyzedthe composition of groundmass fayalite are also shown b) Anelectron microprobe traverse across a small strongly zoned olivinegrain in LAP 0220533 The grain shows zoning from a core of simFo58to a rim composition of simFo18 over sim100 microm The break in the zoning(black arrow) is centered on a fracture in the olivine grain
Fig 4 Compositions of LAP oxides plotted on the (FeMgMn)O-(CrAl)2O3-TiO2 ternary (after El Goresy et al 1971) Compositionsof endmember ilmenite (FeTiO3) ulvˆspinel (Fe2TiO4) andchromite (FeCr2O4) are labeled For a description of theclassification scheme see the footnote of Table 3 a) LAP 0220533b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1090 R Zeigler et al
RE-merrillite (P REEs Th) and baddeleyite (Zr Hf U Th)Therefore the variation in the amount of the groundmassldquophaserdquo in the different subsamples controls the ITEconcentrations in the various subsamples
For most of the major elements subsamples of NWA 032have relative standard deviations (RSD) that areinsignificantly different from those of LAP (Table 1) eventhough the average subsample size for NWA 032 (sim14 mgFagan et al 2002) was smaller than for LAP (sim34 mg) TheRSDs of MgO and Cr2O3 for NWA 032 are again highbecause it has a porphyritic texture with large phenocrysts(millimeter scale) of olivine (with chromite inclusions) andmagnesian pyroxene but a fine-grained groundmass of
plagioclase Fe-rich pyroxene ilmenite and glass keeps theRSDs of other major and incompatible trace elements low
Source Crater Pairing of LAP and NWA 032
We find the similarities in chemistry and petrographybetween LAP and NWA 032 when compared to the largeranges observed among Apollo and Luna samples to be sogreat that it is highly unlikely that two meteorites so similarcould derive from different locations Below we summarizethe similarities and differences
The textures of NWA 032 and LAP are markedlydifferent from each other NWA 032 has a porphyritic texture
Fig 5 BSE images from LAP 0220533 a) oxide grains set in and around a large olivine grain individual grains of ilmenite (Ilm) Cr-ulvˆspinel (Chr-Usp) and chromite (Chr) composite chromian ulvˆspinel-chromite (ChrUsp) grains with accompanying pyroxene andplagioclase (grey and black areas) b) A close-up of a zoned spinel grain with a chromite core and a Cr-ulvˆspinel rim c) A large cristobalite(Crist) grain with many inclusions of fayalite pyroxene (Pyx) plagioclase (Plag) troilite (Sulf) phosphate K-rich glass and the ITE-richglass Also present are several areas of fayalite symplectite (Fay Symp) with inclusions of plagioclase silica ilmenite troilite and K-richglass d) A BSE image of a different area of groundmass showing a large grain of fayalite symplectite containing inclusions of plagioclasesilica ilmenite troilite K-rich glass and Fe-rich pyroxene A large ilmenite (Ilm) grain cuts through the symplectite and several large troilitegrains are also present
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
1084 R Zeigler et al Ta
ble
6 A
vera
ge a
nd re
pres
enta
tive
cris
toba
lite
and
glas
s co
mpo
sitio
n in
the
LAP
basa
ltic
met
eorit
es
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
LAP
0220
502
226
0222
402
436
0220
502
205
0220
502
205
0220
502
224
0222
4cr
isto
balit
ecr
isto
balit
ecr
isto
balit
ecr
isto
balit
eSi
-ric
hpy
x-lik
eK
gla
ssIT
E-ric
hsh
ock
shoc
ksh
ock
MI g
lass
MI g
lass
in s
ympl
m
afic
gla
ssgl
ass
area
glas
s ar
eagl
ass
vein
N6
25
44
12
51
6515
Maj
or e
lem
ents
in w
t b
y EM
PASi
O2
979
598
17
984
798
45
672
542
76
783
236
67
463
486
441
TiO
20
270
270
230
230
664
810
374
032
341
623
13A
l 2O3
073
060
064
078
187
99
4210
13
544
139
86
123
Cr 2
O3
002
lt00
2lt0
02
002
lt00
20
13lt0
02
lt00
20
080
380
28Fe
O0
210
400
190
171
8615
91
183
392
719
618
520
5M
nOn
an
an
an
an
a0
22n
a0
420
220
290
25M
gO0
02lt0
02
lt00
2lt0
02
033
817
lt00
20
213
459
857
17C
aO0
190
200
200
236
8919
16
098
976
127
118
114
BaO
na
na
na
na
117
na
na
na
na
na
na
Na 2
O0
130
100
090
120
620
110
190
060
510
360
49K
2O0
030
050
07lt0
02
167
na
566
030
005
na
na
P 2O
5n
an
an
an
an
an
an
a2
32n
an
an
aF
na
na
na
na
na
na
na
008
na
na
na
Y2O
3n
an
an
an
an
an
an
a0
19n
an
an
aC
e 2O
3n
an
an
an
an
an
an
a0
12n
an
an
aSO
3n
an
an
an
an
an
an
a1
23n
an
an
aTo
tal
995
599
80
999
010
00
992
410
070
974
910
02
991
100
099
6Sy
mpl
= sy
mpl
ectit
e M
I = m
elt i
nclu
sion
N =
num
ber o
f ana
lyse
s in
the
aver
age
na
= n
ot a
naly
zed
The
shoc
ked
glas
s in
LAP
0222
4 is
the
parti
ally
mel
ted
area
(see
Fig
14)
and
onl
y th
e an
ayls
es o
fth
e gl
ass i
tsel
f wer
e in
clud
ed in
the
aver
age
not t
he m
iner
als t
hat w
ere
anal
yzed
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1085
Table 7 Representative phosphate compositions in LAP 0220533LAP LAP LAP LAP LAP LAP LAP LAP02205 02205 02205 02205 02205 02205 02205 02205RE- RE- RE- RE- RE- fluorapatite fluorapatite fluorapatitemerrillite merrillite merrillite merrillite merrillite
Major elements in wt by EMPASiO2 050 044 062 037 321 228 449 137Al2O3 022 lt005 009 lt005 lt005 007 014 lt005FeO 637 774 568 576 250 169 439 202MgO 020 037 025 028 lt005 lt005 lt005 lt005CaO 4326 4035 4233 4245 4983 5241 5003 5351Na2O 000 001 010 014 000 000 001 000P2O5 3885 4171 4382 4360 3540 3949 3771 4077Cl lt005 lt005 lt005 lt005 lt005 006 027 031F 047 044 050 048 168 245 130 186Y2O3 298 293 226 221 172 103 078 053La2O3 093 107 065 064 092 024 014 012Ce2O3 253 259 189 185 253 072 069 053Nd2O3 161 177 108 118 166 057 059 031Sm2O3 043 043 029 028 048 022 015 009Gd2O3 087 090 058 058 079 023 018 008Yb2O3 016 032 009 lt005 010 005 lt005 lt005ThO2 007 009 008 lt005 021 lt005 lt005 lt005minusO = (FCl) 021 020 022 021 072 105 061 085Sums 9930 1010 1001 9968 1004 1005 1003 1006
Table 8 Average sulfide and metal compositions in LAP 0220533Ave Fe metal High-Ni metal Troilite
N 5 1 8
Elemental percentage by EMPAFe 9209 5880 6280Ni 664 3377 lt002Co 141 595 lt002Ti 023 009 006Cr 043 017 lt002Mn lt002 004 lt002S lt002 lt002 3620Totals 1008 988 994Ideal troilite = 365 wt S 635 wt Fe N = number of analyses
Table 9 Modal mineralogy of the different LAP stonesLAP 0220533 LAP 0222616 LAP 0222424 LAP 0243614
Pyroxene 515 505 469 466Plagioclase 319 321 323 346Ilmenite 348 391 386 399Fay sympl 309 290 358 483Olivine 233 271 363 320Cristobalite 214 209 178 200Spinel (all) 034 045 040 039Troilite 025 024 024 022Fractures 49 49 53 421Shock glass 01 02 22 00N 633 times 106 905 times 106 470 times 106 396 times 106
All modal values are listed as percentages N = number of pixels
1086 R Zeigler et al
Fig 1 Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) and fayalite(more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phases arepyroxene and olivine a) LAP 0222616 b) LAP 0243614 c) LAP 0222424 d) LAP 0220533
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1087
δ17O = +27) performed by Mayeda and Clayton (reported inMcBride et al 2003) constrain the origin of LAP 02205 tothe Earth the Moon or an enstatite meteorite parent bodyLAP is clearly a meteorite all four of the stones have fusioncrusts (ruling out a terrestrial origin) The extremely ferroannature of LAP rules out the enstatite parent body as theprovenance FeOMnO ratios of mafic silicates arediagnostic of origins from different planetary bodies in thesolar system (Dymek et al 1976 Papike 1998) Ratios ofFeOMnO in LAP pyroxenes (average sim60) and olivines(average sim95) are consistent only with lunar origin (Fig 15)Furthermore the presence of Fe(Ni) metal and troilite thecompletely anhydrous nature of the sample the apparentlack of Fe3+ in all phases the calcic nature of theplagioclase and the deep negative Eu anomaly are allcommon in lunar basalts
With regard to texture mineral assemblage and mineralchemistry the four LAP 02xxx stones appear to beindistinguishable from each other Although we did not studythe mineral chemistry of the LAP 03632 in depth the textureand mineral assemblage are identical to the LAP 02xxxstones Furthermore the collection locations of the five stonesform a linear array sim3 km in length that is perpendicular to theflow of the ice sheet (John Schutt personal communication)Thus in the absence of cosmic-ray exposure data to thecontrary we conclude that the four LAP 02xxx stones studiedare paired
Compositional Variability among Small Subsamples ofLAP 02205 and NWA 032
Samples of lunar meteorites available for study at most afew hundred milligrams are very small by the standards ofterrestrial geology and geochemistry Nevertheless we havetaken our samples and subdivided them into numerous evensmaller (10ndash50 mg) subsamples for bulk compositionalanalysis (Korotev et al 1983 1996 2003a 2003b Jolliffet al 1991 1998 Fagan et al 2002) This procedure providesan estimate of the whole-rock composition through a mass-weighted mean that is equivalent to a single analysis of theentire mass of the allocated sample The variation amongsmall subsamples however provides additional informationabout compositional variations associated with mineralassemblage and proportions about petrogenesis and aboutpossible relationships to other meteorites (eg Korotev et al2003a 2003b) and how well the ldquowhole-rockrdquo compositionis likely to represent that of the source region of the meteorite(Korotev et al 2000a) In the following discussion weevaluate the causes of differences in composition amongsmall subsamples of LAP and NWA 032
The range of concentrations among the 19 subsamples ofLAP (27ndash40 mg) is relatively small for the most preciselydetermined major elements (SiO2 TiO2 Al2O3 FeO CaONa2O) and most precisely determined trace elements that arecompatible with the major mineral phases (Co Sc Eu) The
Fig 1 Continued Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) andfayalite (more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phasesare pyroxene and olivine d) LAP 0220533
1088 R Zeigler et al
relative sample standard deviations (s ) range from 08 to76 (with only Co and Eu gt 5 Table 1) The exceptionsare MgO and Cr2O3 for which the relative standarddeviations are distinctly greater 12 and 16 respectivelyFor incompatible elements that we determined precisely(lt9 analytical uncertainty La Ce Sm Tb Yb Lu Hf Taand Th) relative standard deviations range from 7 to 11These variations are caused by a combination ofunrepresentative sampling of the major mineral phasesowing to the coarse grain size (up to sim1 mm3) relative to theINAA subsample size (about 12 mm3 assuming that thedensity of LAP is sim35 gmm3) and to the heterogeneousdistribution of some relatively minor phases with high
concentrations of a given element This problem is not new asmany investigators have previously wrestled with theproblem of studying relatively coarse-grained lunar basaltswith small allocated subsample sizes characteristic of rareextraterrestrial samples (Korotev and Haskin 1975 Haskinet al 1977 Lindstrom and Haskin 1978 Ryder and Schuraytz2001) Ryder and Schuraytz (2001) showed that sim5 g ofmaterial are needed to achieve a representative sample ofApollo 15 olivine-normative basalts which have grain sizeson the order of a millimeter or greater
Among the LAP subsamples Cr2O3 and MgOconcentrations correlate positively (R2 = 081) as a result ofthe association of chromite and Cr-ulvˆspinel with olivine
Fig 2 BSE images from LAP 0220533 a) a large round olivine (oli) grain and a smaller subhedral olivine grain (left center of the image)both surrounded by zoned pyroxene (pyx) and plagioclase (plag) with melt inclusions (MI) and inclusions of chromite (chr) A smallulvˆspinel (Usp) grain occurs in the upper left b) A large irregular olivine grain and a smaller mostly resorbed olivine grain The larger graincontains both melt inclusions (MI) and chromite grains The associated ilmenite (Ilm) grain is the most magnesian ilmenite grain observed Acomposite grain of metal and troilite (MetSulf) is also present c) A BSE image showing the zoning in multiple large pyroxene grainsintergrown with plagioclase and maskelynite (mask) grains One small cristobalite (crist) grain is also present d) A BSE image showingseveral large plagioclase grains some of which contain both fractured areas (plagioclase) and smooth areas (maskelynite) Also present areseveral areas of groundmass including a fayalite symplectite and a cristobalite grain cut by an ilmenite lath
x
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1089
The large variations seen in MgO Cr2O3 and to a lesserextent Co concentrations occur because of the large relativevariation in the fraction of modal olivine among thesubsamples Normatively the compositional rangecorresponds to minus03ndash25 olivine (one subsample has 03normative quartz) and 032ndash049 chromite The relativelysmall variations seen among concentrations of the other majorelements as well as Sc and Eu are controlled byunrepresentative sampling of the major mineral phasespyroxene (Sc Ca Fe Si) and plagioclase (Al Na Ca Si Eu)and the minor but widely distributed mineral ilmenite (Ti Fe)Trace amounts of a few minerals that are found only ingroundmass have high concentrations of incompatible traceelements relative to the concentration of those elements inthe bulk meteorite These minerals include K-feldspar (Ba)
Fig 3 a) CaO versus Mgprime (molar Mg[Mg + Fe]100) in the olivinesof the different LAP stones The compositions range from cores ofFo55ndash67 trending towards rims typically in the Fo40 range withextreme zonation to rims of Fo15ndash20 in a few cases Where analyzedthe composition of groundmass fayalite are also shown b) Anelectron microprobe traverse across a small strongly zoned olivinegrain in LAP 0220533 The grain shows zoning from a core of simFo58to a rim composition of simFo18 over sim100 microm The break in the zoning(black arrow) is centered on a fracture in the olivine grain
Fig 4 Compositions of LAP oxides plotted on the (FeMgMn)O-(CrAl)2O3-TiO2 ternary (after El Goresy et al 1971) Compositionsof endmember ilmenite (FeTiO3) ulvˆspinel (Fe2TiO4) andchromite (FeCr2O4) are labeled For a description of theclassification scheme see the footnote of Table 3 a) LAP 0220533b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1090 R Zeigler et al
RE-merrillite (P REEs Th) and baddeleyite (Zr Hf U Th)Therefore the variation in the amount of the groundmassldquophaserdquo in the different subsamples controls the ITEconcentrations in the various subsamples
For most of the major elements subsamples of NWA 032have relative standard deviations (RSD) that areinsignificantly different from those of LAP (Table 1) eventhough the average subsample size for NWA 032 (sim14 mgFagan et al 2002) was smaller than for LAP (sim34 mg) TheRSDs of MgO and Cr2O3 for NWA 032 are again highbecause it has a porphyritic texture with large phenocrysts(millimeter scale) of olivine (with chromite inclusions) andmagnesian pyroxene but a fine-grained groundmass of
plagioclase Fe-rich pyroxene ilmenite and glass keeps theRSDs of other major and incompatible trace elements low
Source Crater Pairing of LAP and NWA 032
We find the similarities in chemistry and petrographybetween LAP and NWA 032 when compared to the largeranges observed among Apollo and Luna samples to be sogreat that it is highly unlikely that two meteorites so similarcould derive from different locations Below we summarizethe similarities and differences
The textures of NWA 032 and LAP are markedlydifferent from each other NWA 032 has a porphyritic texture
Fig 5 BSE images from LAP 0220533 a) oxide grains set in and around a large olivine grain individual grains of ilmenite (Ilm) Cr-ulvˆspinel (Chr-Usp) and chromite (Chr) composite chromian ulvˆspinel-chromite (ChrUsp) grains with accompanying pyroxene andplagioclase (grey and black areas) b) A close-up of a zoned spinel grain with a chromite core and a Cr-ulvˆspinel rim c) A large cristobalite(Crist) grain with many inclusions of fayalite pyroxene (Pyx) plagioclase (Plag) troilite (Sulf) phosphate K-rich glass and the ITE-richglass Also present are several areas of fayalite symplectite (Fay Symp) with inclusions of plagioclase silica ilmenite troilite and K-richglass d) A BSE image of a different area of groundmass showing a large grain of fayalite symplectite containing inclusions of plagioclasesilica ilmenite troilite K-rich glass and Fe-rich pyroxene A large ilmenite (Ilm) grain cuts through the symplectite and several large troilitegrains are also present
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1085
Table 7 Representative phosphate compositions in LAP 0220533LAP LAP LAP LAP LAP LAP LAP LAP02205 02205 02205 02205 02205 02205 02205 02205RE- RE- RE- RE- RE- fluorapatite fluorapatite fluorapatitemerrillite merrillite merrillite merrillite merrillite
Major elements in wt by EMPASiO2 050 044 062 037 321 228 449 137Al2O3 022 lt005 009 lt005 lt005 007 014 lt005FeO 637 774 568 576 250 169 439 202MgO 020 037 025 028 lt005 lt005 lt005 lt005CaO 4326 4035 4233 4245 4983 5241 5003 5351Na2O 000 001 010 014 000 000 001 000P2O5 3885 4171 4382 4360 3540 3949 3771 4077Cl lt005 lt005 lt005 lt005 lt005 006 027 031F 047 044 050 048 168 245 130 186Y2O3 298 293 226 221 172 103 078 053La2O3 093 107 065 064 092 024 014 012Ce2O3 253 259 189 185 253 072 069 053Nd2O3 161 177 108 118 166 057 059 031Sm2O3 043 043 029 028 048 022 015 009Gd2O3 087 090 058 058 079 023 018 008Yb2O3 016 032 009 lt005 010 005 lt005 lt005ThO2 007 009 008 lt005 021 lt005 lt005 lt005minusO = (FCl) 021 020 022 021 072 105 061 085Sums 9930 1010 1001 9968 1004 1005 1003 1006
Table 8 Average sulfide and metal compositions in LAP 0220533Ave Fe metal High-Ni metal Troilite
N 5 1 8
Elemental percentage by EMPAFe 9209 5880 6280Ni 664 3377 lt002Co 141 595 lt002Ti 023 009 006Cr 043 017 lt002Mn lt002 004 lt002S lt002 lt002 3620Totals 1008 988 994Ideal troilite = 365 wt S 635 wt Fe N = number of analyses
Table 9 Modal mineralogy of the different LAP stonesLAP 0220533 LAP 0222616 LAP 0222424 LAP 0243614
Pyroxene 515 505 469 466Plagioclase 319 321 323 346Ilmenite 348 391 386 399Fay sympl 309 290 358 483Olivine 233 271 363 320Cristobalite 214 209 178 200Spinel (all) 034 045 040 039Troilite 025 024 024 022Fractures 49 49 53 421Shock glass 01 02 22 00N 633 times 106 905 times 106 470 times 106 396 times 106
All modal values are listed as percentages N = number of pixels
1086 R Zeigler et al
Fig 1 Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) and fayalite(more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phases arepyroxene and olivine a) LAP 0222616 b) LAP 0243614 c) LAP 0222424 d) LAP 0220533
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1087
δ17O = +27) performed by Mayeda and Clayton (reported inMcBride et al 2003) constrain the origin of LAP 02205 tothe Earth the Moon or an enstatite meteorite parent bodyLAP is clearly a meteorite all four of the stones have fusioncrusts (ruling out a terrestrial origin) The extremely ferroannature of LAP rules out the enstatite parent body as theprovenance FeOMnO ratios of mafic silicates arediagnostic of origins from different planetary bodies in thesolar system (Dymek et al 1976 Papike 1998) Ratios ofFeOMnO in LAP pyroxenes (average sim60) and olivines(average sim95) are consistent only with lunar origin (Fig 15)Furthermore the presence of Fe(Ni) metal and troilite thecompletely anhydrous nature of the sample the apparentlack of Fe3+ in all phases the calcic nature of theplagioclase and the deep negative Eu anomaly are allcommon in lunar basalts
With regard to texture mineral assemblage and mineralchemistry the four LAP 02xxx stones appear to beindistinguishable from each other Although we did not studythe mineral chemistry of the LAP 03632 in depth the textureand mineral assemblage are identical to the LAP 02xxxstones Furthermore the collection locations of the five stonesform a linear array sim3 km in length that is perpendicular to theflow of the ice sheet (John Schutt personal communication)Thus in the absence of cosmic-ray exposure data to thecontrary we conclude that the four LAP 02xxx stones studiedare paired
Compositional Variability among Small Subsamples ofLAP 02205 and NWA 032
Samples of lunar meteorites available for study at most afew hundred milligrams are very small by the standards ofterrestrial geology and geochemistry Nevertheless we havetaken our samples and subdivided them into numerous evensmaller (10ndash50 mg) subsamples for bulk compositionalanalysis (Korotev et al 1983 1996 2003a 2003b Jolliffet al 1991 1998 Fagan et al 2002) This procedure providesan estimate of the whole-rock composition through a mass-weighted mean that is equivalent to a single analysis of theentire mass of the allocated sample The variation amongsmall subsamples however provides additional informationabout compositional variations associated with mineralassemblage and proportions about petrogenesis and aboutpossible relationships to other meteorites (eg Korotev et al2003a 2003b) and how well the ldquowhole-rockrdquo compositionis likely to represent that of the source region of the meteorite(Korotev et al 2000a) In the following discussion weevaluate the causes of differences in composition amongsmall subsamples of LAP and NWA 032
The range of concentrations among the 19 subsamples ofLAP (27ndash40 mg) is relatively small for the most preciselydetermined major elements (SiO2 TiO2 Al2O3 FeO CaONa2O) and most precisely determined trace elements that arecompatible with the major mineral phases (Co Sc Eu) The
Fig 1 Continued Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) andfayalite (more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phasesare pyroxene and olivine d) LAP 0220533
1088 R Zeigler et al
relative sample standard deviations (s ) range from 08 to76 (with only Co and Eu gt 5 Table 1) The exceptionsare MgO and Cr2O3 for which the relative standarddeviations are distinctly greater 12 and 16 respectivelyFor incompatible elements that we determined precisely(lt9 analytical uncertainty La Ce Sm Tb Yb Lu Hf Taand Th) relative standard deviations range from 7 to 11These variations are caused by a combination ofunrepresentative sampling of the major mineral phasesowing to the coarse grain size (up to sim1 mm3) relative to theINAA subsample size (about 12 mm3 assuming that thedensity of LAP is sim35 gmm3) and to the heterogeneousdistribution of some relatively minor phases with high
concentrations of a given element This problem is not new asmany investigators have previously wrestled with theproblem of studying relatively coarse-grained lunar basaltswith small allocated subsample sizes characteristic of rareextraterrestrial samples (Korotev and Haskin 1975 Haskinet al 1977 Lindstrom and Haskin 1978 Ryder and Schuraytz2001) Ryder and Schuraytz (2001) showed that sim5 g ofmaterial are needed to achieve a representative sample ofApollo 15 olivine-normative basalts which have grain sizeson the order of a millimeter or greater
Among the LAP subsamples Cr2O3 and MgOconcentrations correlate positively (R2 = 081) as a result ofthe association of chromite and Cr-ulvˆspinel with olivine
Fig 2 BSE images from LAP 0220533 a) a large round olivine (oli) grain and a smaller subhedral olivine grain (left center of the image)both surrounded by zoned pyroxene (pyx) and plagioclase (plag) with melt inclusions (MI) and inclusions of chromite (chr) A smallulvˆspinel (Usp) grain occurs in the upper left b) A large irregular olivine grain and a smaller mostly resorbed olivine grain The larger graincontains both melt inclusions (MI) and chromite grains The associated ilmenite (Ilm) grain is the most magnesian ilmenite grain observed Acomposite grain of metal and troilite (MetSulf) is also present c) A BSE image showing the zoning in multiple large pyroxene grainsintergrown with plagioclase and maskelynite (mask) grains One small cristobalite (crist) grain is also present d) A BSE image showingseveral large plagioclase grains some of which contain both fractured areas (plagioclase) and smooth areas (maskelynite) Also present areseveral areas of groundmass including a fayalite symplectite and a cristobalite grain cut by an ilmenite lath
x
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1089
The large variations seen in MgO Cr2O3 and to a lesserextent Co concentrations occur because of the large relativevariation in the fraction of modal olivine among thesubsamples Normatively the compositional rangecorresponds to minus03ndash25 olivine (one subsample has 03normative quartz) and 032ndash049 chromite The relativelysmall variations seen among concentrations of the other majorelements as well as Sc and Eu are controlled byunrepresentative sampling of the major mineral phasespyroxene (Sc Ca Fe Si) and plagioclase (Al Na Ca Si Eu)and the minor but widely distributed mineral ilmenite (Ti Fe)Trace amounts of a few minerals that are found only ingroundmass have high concentrations of incompatible traceelements relative to the concentration of those elements inthe bulk meteorite These minerals include K-feldspar (Ba)
Fig 3 a) CaO versus Mgprime (molar Mg[Mg + Fe]100) in the olivinesof the different LAP stones The compositions range from cores ofFo55ndash67 trending towards rims typically in the Fo40 range withextreme zonation to rims of Fo15ndash20 in a few cases Where analyzedthe composition of groundmass fayalite are also shown b) Anelectron microprobe traverse across a small strongly zoned olivinegrain in LAP 0220533 The grain shows zoning from a core of simFo58to a rim composition of simFo18 over sim100 microm The break in the zoning(black arrow) is centered on a fracture in the olivine grain
Fig 4 Compositions of LAP oxides plotted on the (FeMgMn)O-(CrAl)2O3-TiO2 ternary (after El Goresy et al 1971) Compositionsof endmember ilmenite (FeTiO3) ulvˆspinel (Fe2TiO4) andchromite (FeCr2O4) are labeled For a description of theclassification scheme see the footnote of Table 3 a) LAP 0220533b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1090 R Zeigler et al
RE-merrillite (P REEs Th) and baddeleyite (Zr Hf U Th)Therefore the variation in the amount of the groundmassldquophaserdquo in the different subsamples controls the ITEconcentrations in the various subsamples
For most of the major elements subsamples of NWA 032have relative standard deviations (RSD) that areinsignificantly different from those of LAP (Table 1) eventhough the average subsample size for NWA 032 (sim14 mgFagan et al 2002) was smaller than for LAP (sim34 mg) TheRSDs of MgO and Cr2O3 for NWA 032 are again highbecause it has a porphyritic texture with large phenocrysts(millimeter scale) of olivine (with chromite inclusions) andmagnesian pyroxene but a fine-grained groundmass of
plagioclase Fe-rich pyroxene ilmenite and glass keeps theRSDs of other major and incompatible trace elements low
Source Crater Pairing of LAP and NWA 032
We find the similarities in chemistry and petrographybetween LAP and NWA 032 when compared to the largeranges observed among Apollo and Luna samples to be sogreat that it is highly unlikely that two meteorites so similarcould derive from different locations Below we summarizethe similarities and differences
The textures of NWA 032 and LAP are markedlydifferent from each other NWA 032 has a porphyritic texture
Fig 5 BSE images from LAP 0220533 a) oxide grains set in and around a large olivine grain individual grains of ilmenite (Ilm) Cr-ulvˆspinel (Chr-Usp) and chromite (Chr) composite chromian ulvˆspinel-chromite (ChrUsp) grains with accompanying pyroxene andplagioclase (grey and black areas) b) A close-up of a zoned spinel grain with a chromite core and a Cr-ulvˆspinel rim c) A large cristobalite(Crist) grain with many inclusions of fayalite pyroxene (Pyx) plagioclase (Plag) troilite (Sulf) phosphate K-rich glass and the ITE-richglass Also present are several areas of fayalite symplectite (Fay Symp) with inclusions of plagioclase silica ilmenite troilite and K-richglass d) A BSE image of a different area of groundmass showing a large grain of fayalite symplectite containing inclusions of plagioclasesilica ilmenite troilite K-rich glass and Fe-rich pyroxene A large ilmenite (Ilm) grain cuts through the symplectite and several large troilitegrains are also present
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
1086 R Zeigler et al
Fig 1 Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) and fayalite(more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phases arepyroxene and olivine a) LAP 0222616 b) LAP 0243614 c) LAP 0222424 d) LAP 0220533
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1087
δ17O = +27) performed by Mayeda and Clayton (reported inMcBride et al 2003) constrain the origin of LAP 02205 tothe Earth the Moon or an enstatite meteorite parent bodyLAP is clearly a meteorite all four of the stones have fusioncrusts (ruling out a terrestrial origin) The extremely ferroannature of LAP rules out the enstatite parent body as theprovenance FeOMnO ratios of mafic silicates arediagnostic of origins from different planetary bodies in thesolar system (Dymek et al 1976 Papike 1998) Ratios ofFeOMnO in LAP pyroxenes (average sim60) and olivines(average sim95) are consistent only with lunar origin (Fig 15)Furthermore the presence of Fe(Ni) metal and troilite thecompletely anhydrous nature of the sample the apparentlack of Fe3+ in all phases the calcic nature of theplagioclase and the deep negative Eu anomaly are allcommon in lunar basalts
With regard to texture mineral assemblage and mineralchemistry the four LAP 02xxx stones appear to beindistinguishable from each other Although we did not studythe mineral chemistry of the LAP 03632 in depth the textureand mineral assemblage are identical to the LAP 02xxxstones Furthermore the collection locations of the five stonesform a linear array sim3 km in length that is perpendicular to theflow of the ice sheet (John Schutt personal communication)Thus in the absence of cosmic-ray exposure data to thecontrary we conclude that the four LAP 02xxx stones studiedare paired
Compositional Variability among Small Subsamples ofLAP 02205 and NWA 032
Samples of lunar meteorites available for study at most afew hundred milligrams are very small by the standards ofterrestrial geology and geochemistry Nevertheless we havetaken our samples and subdivided them into numerous evensmaller (10ndash50 mg) subsamples for bulk compositionalanalysis (Korotev et al 1983 1996 2003a 2003b Jolliffet al 1991 1998 Fagan et al 2002) This procedure providesan estimate of the whole-rock composition through a mass-weighted mean that is equivalent to a single analysis of theentire mass of the allocated sample The variation amongsmall subsamples however provides additional informationabout compositional variations associated with mineralassemblage and proportions about petrogenesis and aboutpossible relationships to other meteorites (eg Korotev et al2003a 2003b) and how well the ldquowhole-rockrdquo compositionis likely to represent that of the source region of the meteorite(Korotev et al 2000a) In the following discussion weevaluate the causes of differences in composition amongsmall subsamples of LAP and NWA 032
The range of concentrations among the 19 subsamples ofLAP (27ndash40 mg) is relatively small for the most preciselydetermined major elements (SiO2 TiO2 Al2O3 FeO CaONa2O) and most precisely determined trace elements that arecompatible with the major mineral phases (Co Sc Eu) The
Fig 1 Continued Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) andfayalite (more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phasesare pyroxene and olivine d) LAP 0220533
1088 R Zeigler et al
relative sample standard deviations (s ) range from 08 to76 (with only Co and Eu gt 5 Table 1) The exceptionsare MgO and Cr2O3 for which the relative standarddeviations are distinctly greater 12 and 16 respectivelyFor incompatible elements that we determined precisely(lt9 analytical uncertainty La Ce Sm Tb Yb Lu Hf Taand Th) relative standard deviations range from 7 to 11These variations are caused by a combination ofunrepresentative sampling of the major mineral phasesowing to the coarse grain size (up to sim1 mm3) relative to theINAA subsample size (about 12 mm3 assuming that thedensity of LAP is sim35 gmm3) and to the heterogeneousdistribution of some relatively minor phases with high
concentrations of a given element This problem is not new asmany investigators have previously wrestled with theproblem of studying relatively coarse-grained lunar basaltswith small allocated subsample sizes characteristic of rareextraterrestrial samples (Korotev and Haskin 1975 Haskinet al 1977 Lindstrom and Haskin 1978 Ryder and Schuraytz2001) Ryder and Schuraytz (2001) showed that sim5 g ofmaterial are needed to achieve a representative sample ofApollo 15 olivine-normative basalts which have grain sizeson the order of a millimeter or greater
Among the LAP subsamples Cr2O3 and MgOconcentrations correlate positively (R2 = 081) as a result ofthe association of chromite and Cr-ulvˆspinel with olivine
Fig 2 BSE images from LAP 0220533 a) a large round olivine (oli) grain and a smaller subhedral olivine grain (left center of the image)both surrounded by zoned pyroxene (pyx) and plagioclase (plag) with melt inclusions (MI) and inclusions of chromite (chr) A smallulvˆspinel (Usp) grain occurs in the upper left b) A large irregular olivine grain and a smaller mostly resorbed olivine grain The larger graincontains both melt inclusions (MI) and chromite grains The associated ilmenite (Ilm) grain is the most magnesian ilmenite grain observed Acomposite grain of metal and troilite (MetSulf) is also present c) A BSE image showing the zoning in multiple large pyroxene grainsintergrown with plagioclase and maskelynite (mask) grains One small cristobalite (crist) grain is also present d) A BSE image showingseveral large plagioclase grains some of which contain both fractured areas (plagioclase) and smooth areas (maskelynite) Also present areseveral areas of groundmass including a fayalite symplectite and a cristobalite grain cut by an ilmenite lath
x
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1089
The large variations seen in MgO Cr2O3 and to a lesserextent Co concentrations occur because of the large relativevariation in the fraction of modal olivine among thesubsamples Normatively the compositional rangecorresponds to minus03ndash25 olivine (one subsample has 03normative quartz) and 032ndash049 chromite The relativelysmall variations seen among concentrations of the other majorelements as well as Sc and Eu are controlled byunrepresentative sampling of the major mineral phasespyroxene (Sc Ca Fe Si) and plagioclase (Al Na Ca Si Eu)and the minor but widely distributed mineral ilmenite (Ti Fe)Trace amounts of a few minerals that are found only ingroundmass have high concentrations of incompatible traceelements relative to the concentration of those elements inthe bulk meteorite These minerals include K-feldspar (Ba)
Fig 3 a) CaO versus Mgprime (molar Mg[Mg + Fe]100) in the olivinesof the different LAP stones The compositions range from cores ofFo55ndash67 trending towards rims typically in the Fo40 range withextreme zonation to rims of Fo15ndash20 in a few cases Where analyzedthe composition of groundmass fayalite are also shown b) Anelectron microprobe traverse across a small strongly zoned olivinegrain in LAP 0220533 The grain shows zoning from a core of simFo58to a rim composition of simFo18 over sim100 microm The break in the zoning(black arrow) is centered on a fracture in the olivine grain
Fig 4 Compositions of LAP oxides plotted on the (FeMgMn)O-(CrAl)2O3-TiO2 ternary (after El Goresy et al 1971) Compositionsof endmember ilmenite (FeTiO3) ulvˆspinel (Fe2TiO4) andchromite (FeCr2O4) are labeled For a description of theclassification scheme see the footnote of Table 3 a) LAP 0220533b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1090 R Zeigler et al
RE-merrillite (P REEs Th) and baddeleyite (Zr Hf U Th)Therefore the variation in the amount of the groundmassldquophaserdquo in the different subsamples controls the ITEconcentrations in the various subsamples
For most of the major elements subsamples of NWA 032have relative standard deviations (RSD) that areinsignificantly different from those of LAP (Table 1) eventhough the average subsample size for NWA 032 (sim14 mgFagan et al 2002) was smaller than for LAP (sim34 mg) TheRSDs of MgO and Cr2O3 for NWA 032 are again highbecause it has a porphyritic texture with large phenocrysts(millimeter scale) of olivine (with chromite inclusions) andmagnesian pyroxene but a fine-grained groundmass of
plagioclase Fe-rich pyroxene ilmenite and glass keeps theRSDs of other major and incompatible trace elements low
Source Crater Pairing of LAP and NWA 032
We find the similarities in chemistry and petrographybetween LAP and NWA 032 when compared to the largeranges observed among Apollo and Luna samples to be sogreat that it is highly unlikely that two meteorites so similarcould derive from different locations Below we summarizethe similarities and differences
The textures of NWA 032 and LAP are markedlydifferent from each other NWA 032 has a porphyritic texture
Fig 5 BSE images from LAP 0220533 a) oxide grains set in and around a large olivine grain individual grains of ilmenite (Ilm) Cr-ulvˆspinel (Chr-Usp) and chromite (Chr) composite chromian ulvˆspinel-chromite (ChrUsp) grains with accompanying pyroxene andplagioclase (grey and black areas) b) A close-up of a zoned spinel grain with a chromite core and a Cr-ulvˆspinel rim c) A large cristobalite(Crist) grain with many inclusions of fayalite pyroxene (Pyx) plagioclase (Plag) troilite (Sulf) phosphate K-rich glass and the ITE-richglass Also present are several areas of fayalite symplectite (Fay Symp) with inclusions of plagioclase silica ilmenite troilite and K-richglass d) A BSE image of a different area of groundmass showing a large grain of fayalite symplectite containing inclusions of plagioclasesilica ilmenite troilite K-rich glass and Fe-rich pyroxene A large ilmenite (Ilm) grain cuts through the symplectite and several large troilitegrains are also present
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1087
δ17O = +27) performed by Mayeda and Clayton (reported inMcBride et al 2003) constrain the origin of LAP 02205 tothe Earth the Moon or an enstatite meteorite parent bodyLAP is clearly a meteorite all four of the stones have fusioncrusts (ruling out a terrestrial origin) The extremely ferroannature of LAP rules out the enstatite parent body as theprovenance FeOMnO ratios of mafic silicates arediagnostic of origins from different planetary bodies in thesolar system (Dymek et al 1976 Papike 1998) Ratios ofFeOMnO in LAP pyroxenes (average sim60) and olivines(average sim95) are consistent only with lunar origin (Fig 15)Furthermore the presence of Fe(Ni) metal and troilite thecompletely anhydrous nature of the sample the apparentlack of Fe3+ in all phases the calcic nature of theplagioclase and the deep negative Eu anomaly are allcommon in lunar basalts
With regard to texture mineral assemblage and mineralchemistry the four LAP 02xxx stones appear to beindistinguishable from each other Although we did not studythe mineral chemistry of the LAP 03632 in depth the textureand mineral assemblage are identical to the LAP 02xxxstones Furthermore the collection locations of the five stonesform a linear array sim3 km in length that is perpendicular to theflow of the ice sheet (John Schutt personal communication)Thus in the absence of cosmic-ray exposure data to thecontrary we conclude that the four LAP 02xxx stones studiedare paired
Compositional Variability among Small Subsamples ofLAP 02205 and NWA 032
Samples of lunar meteorites available for study at most afew hundred milligrams are very small by the standards ofterrestrial geology and geochemistry Nevertheless we havetaken our samples and subdivided them into numerous evensmaller (10ndash50 mg) subsamples for bulk compositionalanalysis (Korotev et al 1983 1996 2003a 2003b Jolliffet al 1991 1998 Fagan et al 2002) This procedure providesan estimate of the whole-rock composition through a mass-weighted mean that is equivalent to a single analysis of theentire mass of the allocated sample The variation amongsmall subsamples however provides additional informationabout compositional variations associated with mineralassemblage and proportions about petrogenesis and aboutpossible relationships to other meteorites (eg Korotev et al2003a 2003b) and how well the ldquowhole-rockrdquo compositionis likely to represent that of the source region of the meteorite(Korotev et al 2000a) In the following discussion weevaluate the causes of differences in composition amongsmall subsamples of LAP and NWA 032
The range of concentrations among the 19 subsamples ofLAP (27ndash40 mg) is relatively small for the most preciselydetermined major elements (SiO2 TiO2 Al2O3 FeO CaONa2O) and most precisely determined trace elements that arecompatible with the major mineral phases (Co Sc Eu) The
Fig 1 Continued Backscattered electron (BSE) images of the different thin sections of LAP The brightest phases are ilmenite (elongate) andfayalite (more equant) the darkest grey phase is cristobalite the dark grey typically elongate phase is plagioclase and the medium grey phasesare pyroxene and olivine d) LAP 0220533
1088 R Zeigler et al
relative sample standard deviations (s ) range from 08 to76 (with only Co and Eu gt 5 Table 1) The exceptionsare MgO and Cr2O3 for which the relative standarddeviations are distinctly greater 12 and 16 respectivelyFor incompatible elements that we determined precisely(lt9 analytical uncertainty La Ce Sm Tb Yb Lu Hf Taand Th) relative standard deviations range from 7 to 11These variations are caused by a combination ofunrepresentative sampling of the major mineral phasesowing to the coarse grain size (up to sim1 mm3) relative to theINAA subsample size (about 12 mm3 assuming that thedensity of LAP is sim35 gmm3) and to the heterogeneousdistribution of some relatively minor phases with high
concentrations of a given element This problem is not new asmany investigators have previously wrestled with theproblem of studying relatively coarse-grained lunar basaltswith small allocated subsample sizes characteristic of rareextraterrestrial samples (Korotev and Haskin 1975 Haskinet al 1977 Lindstrom and Haskin 1978 Ryder and Schuraytz2001) Ryder and Schuraytz (2001) showed that sim5 g ofmaterial are needed to achieve a representative sample ofApollo 15 olivine-normative basalts which have grain sizeson the order of a millimeter or greater
Among the LAP subsamples Cr2O3 and MgOconcentrations correlate positively (R2 = 081) as a result ofthe association of chromite and Cr-ulvˆspinel with olivine
Fig 2 BSE images from LAP 0220533 a) a large round olivine (oli) grain and a smaller subhedral olivine grain (left center of the image)both surrounded by zoned pyroxene (pyx) and plagioclase (plag) with melt inclusions (MI) and inclusions of chromite (chr) A smallulvˆspinel (Usp) grain occurs in the upper left b) A large irregular olivine grain and a smaller mostly resorbed olivine grain The larger graincontains both melt inclusions (MI) and chromite grains The associated ilmenite (Ilm) grain is the most magnesian ilmenite grain observed Acomposite grain of metal and troilite (MetSulf) is also present c) A BSE image showing the zoning in multiple large pyroxene grainsintergrown with plagioclase and maskelynite (mask) grains One small cristobalite (crist) grain is also present d) A BSE image showingseveral large plagioclase grains some of which contain both fractured areas (plagioclase) and smooth areas (maskelynite) Also present areseveral areas of groundmass including a fayalite symplectite and a cristobalite grain cut by an ilmenite lath
x
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1089
The large variations seen in MgO Cr2O3 and to a lesserextent Co concentrations occur because of the large relativevariation in the fraction of modal olivine among thesubsamples Normatively the compositional rangecorresponds to minus03ndash25 olivine (one subsample has 03normative quartz) and 032ndash049 chromite The relativelysmall variations seen among concentrations of the other majorelements as well as Sc and Eu are controlled byunrepresentative sampling of the major mineral phasespyroxene (Sc Ca Fe Si) and plagioclase (Al Na Ca Si Eu)and the minor but widely distributed mineral ilmenite (Ti Fe)Trace amounts of a few minerals that are found only ingroundmass have high concentrations of incompatible traceelements relative to the concentration of those elements inthe bulk meteorite These minerals include K-feldspar (Ba)
Fig 3 a) CaO versus Mgprime (molar Mg[Mg + Fe]100) in the olivinesof the different LAP stones The compositions range from cores ofFo55ndash67 trending towards rims typically in the Fo40 range withextreme zonation to rims of Fo15ndash20 in a few cases Where analyzedthe composition of groundmass fayalite are also shown b) Anelectron microprobe traverse across a small strongly zoned olivinegrain in LAP 0220533 The grain shows zoning from a core of simFo58to a rim composition of simFo18 over sim100 microm The break in the zoning(black arrow) is centered on a fracture in the olivine grain
Fig 4 Compositions of LAP oxides plotted on the (FeMgMn)O-(CrAl)2O3-TiO2 ternary (after El Goresy et al 1971) Compositionsof endmember ilmenite (FeTiO3) ulvˆspinel (Fe2TiO4) andchromite (FeCr2O4) are labeled For a description of theclassification scheme see the footnote of Table 3 a) LAP 0220533b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1090 R Zeigler et al
RE-merrillite (P REEs Th) and baddeleyite (Zr Hf U Th)Therefore the variation in the amount of the groundmassldquophaserdquo in the different subsamples controls the ITEconcentrations in the various subsamples
For most of the major elements subsamples of NWA 032have relative standard deviations (RSD) that areinsignificantly different from those of LAP (Table 1) eventhough the average subsample size for NWA 032 (sim14 mgFagan et al 2002) was smaller than for LAP (sim34 mg) TheRSDs of MgO and Cr2O3 for NWA 032 are again highbecause it has a porphyritic texture with large phenocrysts(millimeter scale) of olivine (with chromite inclusions) andmagnesian pyroxene but a fine-grained groundmass of
plagioclase Fe-rich pyroxene ilmenite and glass keeps theRSDs of other major and incompatible trace elements low
Source Crater Pairing of LAP and NWA 032
We find the similarities in chemistry and petrographybetween LAP and NWA 032 when compared to the largeranges observed among Apollo and Luna samples to be sogreat that it is highly unlikely that two meteorites so similarcould derive from different locations Below we summarizethe similarities and differences
The textures of NWA 032 and LAP are markedlydifferent from each other NWA 032 has a porphyritic texture
Fig 5 BSE images from LAP 0220533 a) oxide grains set in and around a large olivine grain individual grains of ilmenite (Ilm) Cr-ulvˆspinel (Chr-Usp) and chromite (Chr) composite chromian ulvˆspinel-chromite (ChrUsp) grains with accompanying pyroxene andplagioclase (grey and black areas) b) A close-up of a zoned spinel grain with a chromite core and a Cr-ulvˆspinel rim c) A large cristobalite(Crist) grain with many inclusions of fayalite pyroxene (Pyx) plagioclase (Plag) troilite (Sulf) phosphate K-rich glass and the ITE-richglass Also present are several areas of fayalite symplectite (Fay Symp) with inclusions of plagioclase silica ilmenite troilite and K-richglass d) A BSE image of a different area of groundmass showing a large grain of fayalite symplectite containing inclusions of plagioclasesilica ilmenite troilite K-rich glass and Fe-rich pyroxene A large ilmenite (Ilm) grain cuts through the symplectite and several large troilitegrains are also present
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
1088 R Zeigler et al
relative sample standard deviations (s ) range from 08 to76 (with only Co and Eu gt 5 Table 1) The exceptionsare MgO and Cr2O3 for which the relative standarddeviations are distinctly greater 12 and 16 respectivelyFor incompatible elements that we determined precisely(lt9 analytical uncertainty La Ce Sm Tb Yb Lu Hf Taand Th) relative standard deviations range from 7 to 11These variations are caused by a combination ofunrepresentative sampling of the major mineral phasesowing to the coarse grain size (up to sim1 mm3) relative to theINAA subsample size (about 12 mm3 assuming that thedensity of LAP is sim35 gmm3) and to the heterogeneousdistribution of some relatively minor phases with high
concentrations of a given element This problem is not new asmany investigators have previously wrestled with theproblem of studying relatively coarse-grained lunar basaltswith small allocated subsample sizes characteristic of rareextraterrestrial samples (Korotev and Haskin 1975 Haskinet al 1977 Lindstrom and Haskin 1978 Ryder and Schuraytz2001) Ryder and Schuraytz (2001) showed that sim5 g ofmaterial are needed to achieve a representative sample ofApollo 15 olivine-normative basalts which have grain sizeson the order of a millimeter or greater
Among the LAP subsamples Cr2O3 and MgOconcentrations correlate positively (R2 = 081) as a result ofthe association of chromite and Cr-ulvˆspinel with olivine
Fig 2 BSE images from LAP 0220533 a) a large round olivine (oli) grain and a smaller subhedral olivine grain (left center of the image)both surrounded by zoned pyroxene (pyx) and plagioclase (plag) with melt inclusions (MI) and inclusions of chromite (chr) A smallulvˆspinel (Usp) grain occurs in the upper left b) A large irregular olivine grain and a smaller mostly resorbed olivine grain The larger graincontains both melt inclusions (MI) and chromite grains The associated ilmenite (Ilm) grain is the most magnesian ilmenite grain observed Acomposite grain of metal and troilite (MetSulf) is also present c) A BSE image showing the zoning in multiple large pyroxene grainsintergrown with plagioclase and maskelynite (mask) grains One small cristobalite (crist) grain is also present d) A BSE image showingseveral large plagioclase grains some of which contain both fractured areas (plagioclase) and smooth areas (maskelynite) Also present areseveral areas of groundmass including a fayalite symplectite and a cristobalite grain cut by an ilmenite lath
x
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1089
The large variations seen in MgO Cr2O3 and to a lesserextent Co concentrations occur because of the large relativevariation in the fraction of modal olivine among thesubsamples Normatively the compositional rangecorresponds to minus03ndash25 olivine (one subsample has 03normative quartz) and 032ndash049 chromite The relativelysmall variations seen among concentrations of the other majorelements as well as Sc and Eu are controlled byunrepresentative sampling of the major mineral phasespyroxene (Sc Ca Fe Si) and plagioclase (Al Na Ca Si Eu)and the minor but widely distributed mineral ilmenite (Ti Fe)Trace amounts of a few minerals that are found only ingroundmass have high concentrations of incompatible traceelements relative to the concentration of those elements inthe bulk meteorite These minerals include K-feldspar (Ba)
Fig 3 a) CaO versus Mgprime (molar Mg[Mg + Fe]100) in the olivinesof the different LAP stones The compositions range from cores ofFo55ndash67 trending towards rims typically in the Fo40 range withextreme zonation to rims of Fo15ndash20 in a few cases Where analyzedthe composition of groundmass fayalite are also shown b) Anelectron microprobe traverse across a small strongly zoned olivinegrain in LAP 0220533 The grain shows zoning from a core of simFo58to a rim composition of simFo18 over sim100 microm The break in the zoning(black arrow) is centered on a fracture in the olivine grain
Fig 4 Compositions of LAP oxides plotted on the (FeMgMn)O-(CrAl)2O3-TiO2 ternary (after El Goresy et al 1971) Compositionsof endmember ilmenite (FeTiO3) ulvˆspinel (Fe2TiO4) andchromite (FeCr2O4) are labeled For a description of theclassification scheme see the footnote of Table 3 a) LAP 0220533b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1090 R Zeigler et al
RE-merrillite (P REEs Th) and baddeleyite (Zr Hf U Th)Therefore the variation in the amount of the groundmassldquophaserdquo in the different subsamples controls the ITEconcentrations in the various subsamples
For most of the major elements subsamples of NWA 032have relative standard deviations (RSD) that areinsignificantly different from those of LAP (Table 1) eventhough the average subsample size for NWA 032 (sim14 mgFagan et al 2002) was smaller than for LAP (sim34 mg) TheRSDs of MgO and Cr2O3 for NWA 032 are again highbecause it has a porphyritic texture with large phenocrysts(millimeter scale) of olivine (with chromite inclusions) andmagnesian pyroxene but a fine-grained groundmass of
plagioclase Fe-rich pyroxene ilmenite and glass keeps theRSDs of other major and incompatible trace elements low
Source Crater Pairing of LAP and NWA 032
We find the similarities in chemistry and petrographybetween LAP and NWA 032 when compared to the largeranges observed among Apollo and Luna samples to be sogreat that it is highly unlikely that two meteorites so similarcould derive from different locations Below we summarizethe similarities and differences
The textures of NWA 032 and LAP are markedlydifferent from each other NWA 032 has a porphyritic texture
Fig 5 BSE images from LAP 0220533 a) oxide grains set in and around a large olivine grain individual grains of ilmenite (Ilm) Cr-ulvˆspinel (Chr-Usp) and chromite (Chr) composite chromian ulvˆspinel-chromite (ChrUsp) grains with accompanying pyroxene andplagioclase (grey and black areas) b) A close-up of a zoned spinel grain with a chromite core and a Cr-ulvˆspinel rim c) A large cristobalite(Crist) grain with many inclusions of fayalite pyroxene (Pyx) plagioclase (Plag) troilite (Sulf) phosphate K-rich glass and the ITE-richglass Also present are several areas of fayalite symplectite (Fay Symp) with inclusions of plagioclase silica ilmenite troilite and K-richglass d) A BSE image of a different area of groundmass showing a large grain of fayalite symplectite containing inclusions of plagioclasesilica ilmenite troilite K-rich glass and Fe-rich pyroxene A large ilmenite (Ilm) grain cuts through the symplectite and several large troilitegrains are also present
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1089
The large variations seen in MgO Cr2O3 and to a lesserextent Co concentrations occur because of the large relativevariation in the fraction of modal olivine among thesubsamples Normatively the compositional rangecorresponds to minus03ndash25 olivine (one subsample has 03normative quartz) and 032ndash049 chromite The relativelysmall variations seen among concentrations of the other majorelements as well as Sc and Eu are controlled byunrepresentative sampling of the major mineral phasespyroxene (Sc Ca Fe Si) and plagioclase (Al Na Ca Si Eu)and the minor but widely distributed mineral ilmenite (Ti Fe)Trace amounts of a few minerals that are found only ingroundmass have high concentrations of incompatible traceelements relative to the concentration of those elements inthe bulk meteorite These minerals include K-feldspar (Ba)
Fig 3 a) CaO versus Mgprime (molar Mg[Mg + Fe]100) in the olivinesof the different LAP stones The compositions range from cores ofFo55ndash67 trending towards rims typically in the Fo40 range withextreme zonation to rims of Fo15ndash20 in a few cases Where analyzedthe composition of groundmass fayalite are also shown b) Anelectron microprobe traverse across a small strongly zoned olivinegrain in LAP 0220533 The grain shows zoning from a core of simFo58to a rim composition of simFo18 over sim100 microm The break in the zoning(black arrow) is centered on a fracture in the olivine grain
Fig 4 Compositions of LAP oxides plotted on the (FeMgMn)O-(CrAl)2O3-TiO2 ternary (after El Goresy et al 1971) Compositionsof endmember ilmenite (FeTiO3) ulvˆspinel (Fe2TiO4) andchromite (FeCr2O4) are labeled For a description of theclassification scheme see the footnote of Table 3 a) LAP 0220533b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1090 R Zeigler et al
RE-merrillite (P REEs Th) and baddeleyite (Zr Hf U Th)Therefore the variation in the amount of the groundmassldquophaserdquo in the different subsamples controls the ITEconcentrations in the various subsamples
For most of the major elements subsamples of NWA 032have relative standard deviations (RSD) that areinsignificantly different from those of LAP (Table 1) eventhough the average subsample size for NWA 032 (sim14 mgFagan et al 2002) was smaller than for LAP (sim34 mg) TheRSDs of MgO and Cr2O3 for NWA 032 are again highbecause it has a porphyritic texture with large phenocrysts(millimeter scale) of olivine (with chromite inclusions) andmagnesian pyroxene but a fine-grained groundmass of
plagioclase Fe-rich pyroxene ilmenite and glass keeps theRSDs of other major and incompatible trace elements low
Source Crater Pairing of LAP and NWA 032
We find the similarities in chemistry and petrographybetween LAP and NWA 032 when compared to the largeranges observed among Apollo and Luna samples to be sogreat that it is highly unlikely that two meteorites so similarcould derive from different locations Below we summarizethe similarities and differences
The textures of NWA 032 and LAP are markedlydifferent from each other NWA 032 has a porphyritic texture
Fig 5 BSE images from LAP 0220533 a) oxide grains set in and around a large olivine grain individual grains of ilmenite (Ilm) Cr-ulvˆspinel (Chr-Usp) and chromite (Chr) composite chromian ulvˆspinel-chromite (ChrUsp) grains with accompanying pyroxene andplagioclase (grey and black areas) b) A close-up of a zoned spinel grain with a chromite core and a Cr-ulvˆspinel rim c) A large cristobalite(Crist) grain with many inclusions of fayalite pyroxene (Pyx) plagioclase (Plag) troilite (Sulf) phosphate K-rich glass and the ITE-richglass Also present are several areas of fayalite symplectite (Fay Symp) with inclusions of plagioclase silica ilmenite troilite and K-richglass d) A BSE image of a different area of groundmass showing a large grain of fayalite symplectite containing inclusions of plagioclasesilica ilmenite troilite K-rich glass and Fe-rich pyroxene A large ilmenite (Ilm) grain cuts through the symplectite and several large troilitegrains are also present
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
1090 R Zeigler et al
RE-merrillite (P REEs Th) and baddeleyite (Zr Hf U Th)Therefore the variation in the amount of the groundmassldquophaserdquo in the different subsamples controls the ITEconcentrations in the various subsamples
For most of the major elements subsamples of NWA 032have relative standard deviations (RSD) that areinsignificantly different from those of LAP (Table 1) eventhough the average subsample size for NWA 032 (sim14 mgFagan et al 2002) was smaller than for LAP (sim34 mg) TheRSDs of MgO and Cr2O3 for NWA 032 are again highbecause it has a porphyritic texture with large phenocrysts(millimeter scale) of olivine (with chromite inclusions) andmagnesian pyroxene but a fine-grained groundmass of
plagioclase Fe-rich pyroxene ilmenite and glass keeps theRSDs of other major and incompatible trace elements low
Source Crater Pairing of LAP and NWA 032
We find the similarities in chemistry and petrographybetween LAP and NWA 032 when compared to the largeranges observed among Apollo and Luna samples to be sogreat that it is highly unlikely that two meteorites so similarcould derive from different locations Below we summarizethe similarities and differences
The textures of NWA 032 and LAP are markedlydifferent from each other NWA 032 has a porphyritic texture
Fig 5 BSE images from LAP 0220533 a) oxide grains set in and around a large olivine grain individual grains of ilmenite (Ilm) Cr-ulvˆspinel (Chr-Usp) and chromite (Chr) composite chromian ulvˆspinel-chromite (ChrUsp) grains with accompanying pyroxene andplagioclase (grey and black areas) b) A close-up of a zoned spinel grain with a chromite core and a Cr-ulvˆspinel rim c) A large cristobalite(Crist) grain with many inclusions of fayalite pyroxene (Pyx) plagioclase (Plag) troilite (Sulf) phosphate K-rich glass and the ITE-richglass Also present are several areas of fayalite symplectite (Fay Symp) with inclusions of plagioclase silica ilmenite troilite and K-richglass d) A BSE image of a different area of groundmass showing a large grain of fayalite symplectite containing inclusions of plagioclasesilica ilmenite troilite K-rich glass and Fe-rich pyroxene A large ilmenite (Ilm) grain cuts through the symplectite and several large troilitegrains are also present
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1091
Fig 6 Pyroxene quadrilaterals showing the composition of the zoned pyroxenes in the LAP meteorites The patterns are very similar in all fourstones The cores of the zoned pyroxenes are magnesian (Mg55ndash68) and are zoned continuously towards rim compositions that approachhedenbergite and pyroxferroite The insets in each quadrilateral show the histogram of Wo contents in pyroxene analyses with an Mgprime between50 and 70 A gap or at least the hint of a gap is seen at simWo20 in all four stones a) LAP 0220533 b) LAP 0222616 c) LAP 0222424d) LAP 0243614
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
1092 R Zeigler et al
(with a crystalline groundmass) indicating a relatively shortperiod of slow cooling followed by rapid cooling (but notquenching) LAP has a subophitic texture with minerals thatzone to extreme end member compositions indicative ofslow steady cooling over an extended period of time Texturaldifferences such as these by themselves do not preclude apetrogenetic relationship between LAP and NWA 032because such differences can occur within a single basaltflow For example the Elephant Mountain basalt flow in theColumbia River basalt province varies from sim15 crystallineat the top of the flow to gt80 crystalline near the centerof the flow and this is only a 10 m thick basalt flow(Schmincke 1967)
The mineral assemblages and mineral compositions ofNWA 032 and LAP are very similar to each other Theolivine in both meteorites has compositions ranging fromsimFo20 to simFo65 The olivine grains in both meteorites containmelt inclusions with identical morphologies (although nocompositional data is yet published on the olivine melt
inclusions for NWA 032) Pyroxenes in NWA 032 and LAPcover a similar compositional range In both meteorites theyhave magnesian cores (Mgprime 50ndash70) of pigeonite and subcalcicaugite although NWA 032 pyroxene cores are slightly morecalcic and less magnesian Ferroan pyroxene approachingpyroxferroite is found in both meteorites as well withhedenbergite seen in LAP but not reported by Fagan et al(2002) in NWA 032 (Fig 16) The ranges in plagioclasecomposition in NWA 032 (An80ndash90) and LAP (An79ndash91) aresimilar The oxide mineral assemblages in both samples aresimilar with early chromite associated with the olivinegrains followed by later Mg-poor ilmenite and nearly endmember ulvˆspinel The match is not exact however as LAPalso has Cr-ulvˆspinel The FeTi-oxides in NWA 032 alsohave higher concentrations of Al2O3 MgO CaO and SiO2than LAP likely as a consequence of more rapidcrystallization in NWA 032
On nearly any two-element variation diagram forlithophile elements subsamples of NWA 032 and LAP plot
Fig 7 a) Molar TiCr ratio versus Mgacute in LAP pyroxenes All four stones show a similar trend The TiCr ratio increases with decreasing Mgprimelikely as a result of early chromite crystallization depleting the residual magma in Cr b) TiAl ratio versus Mgprime in LAP 0220533 pyroxenesThe pattern is essentially identical for all four stones The TiAl ratio increases from sim025 to sim05 with decreasing Mgprime likely as a result ofplagioclase crystallization The high TiAl ratios seen in the most ferroan pyroxenes suggest the presence of Ti3+ which alters the substitutionpatterns (see text for more detail)
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1093
along a common linear trend with ranges for the twometeorites that overlap (eg Fig 12) For nearly all elementsthat we measured the most magnesian LAP subsamples(ie those with the most normative and presumably modalolivine) are compositionally indistinguishable from the leastmagnesian NWA 032 subsamples (those with the leastolivine) The only elements that we determined that do notfall along a common trend for the two meteorites are Ba andK In NWA 032 the concentrations of both of theseelements are elevated as a result of terrestrial alteration in ahot desert meteorite (Fig 13b Fagan et al 2002 Korotevet al 2003b)
The difference between the average composition of LAPand NWA 032 is consistent with a loss of the earliestcrystallized phases in NWA 032 relative to LAP For majorelements removal of 48 olivine (average LAP corecomposition) 27 magnesian pyroxene (average LAP corecomposition both high- and low-Ca) and 022 chromite(average LAP composition) from the average composition ofNWA 032 yields a residual composition that is very similar to
the average LAP composition (Table 10) For incompatibleelements the loss of sim8 of the earliest crystallized phasesfrom NWA 032 increases the concentrations of incompatibleelements in the residuum by about sim8 (assuming thatolivine pyroxene and chromite are perfectly incompatiblefor all incompatible trace elements) thus accounting for abouttwo thirds of the difference in concentrations of incompatibleelements between NWA 032 and LAP (mean NWALAP =88) Sampling error can account for the remaining sim4difference in mean ITE concentration between LAP and theNWA 032 residuum
The important observation however is that thecompositional range observed among different ldquolargerdquosamples of lunar basalts likely derived from a single floweg samples of the Apollo 12 olivine or Apollo 12 ilmenitebasalts is equivalent to that observed among the LAP andNWA 032 subsamples in this study (Fig 17) Furthermore astudy of 25 large samples (sim10 g) taken from a verticaltraverse of a single Icelandic tholeiite flow foundconsiderable compositional variability that was not correlated
Fig 8 Portion of feldspar ternaries showing the range of plagioclase compositions in the LAP meteorites All show a similar range (An90ndash80)and distribution though LAP 0220533 shows a somewhat higher proportion of evolved (high Or) compositions This difference is anexperimental artifact that resulted from taking multiple traverses on the edges of grains in that sample to elucidate zoning trends (Ab Orenrichment see Fig 9) a) LAP 0220533 b) LAP 0222616 c) LAP 0222424 d) LAP 0243614
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
1094 R Zeigler et al
with the stratigraphic location of the sample within the flow(Lindstrom and Haskin 1981) Lindstrom and Haskin (1981)attribute the compositional variability to the randomdistribution of the phenocrysts groundmass minerals andresidual liquid within the flow The range in compositionsobserved within the tholeiite flow (1022ndash1179 wt FeO84ndash124 pp La) was not as quite as wide as the rangein compositions among LAP and NWA 032 subsamples(215ndash237 wt FeO 103ndash153 pp La) but it was similarand the average size of the tholeiite samples was more than250 times greater than the average size of the LAP and NWAsubsamples
In summary the geochemical and petrologicalsimilarities observed in NWA 032 and LAP indicate that thesetwo meteorites are almost certainly source crater pairedFurthermore given the similarities in mineral chemistry andbulk composition it appears possible that LAP and NWA 032are from the same basalt flow on the Moon The differences intexture are as expected if NWA 032 is from near the margin ofthe flow that cooled quickly after eruption while LAP camefrom a more central location in the flow where it experienceda slower cooling rate The difference in bulk chemicalcomposition is consistent with intraflow fractionation effectsand nonuniform distribution of mineral phases with respect tothe small size of the analyzed samples If cosmic ray exposuredata should show that the two meteorites cannot have been
Fig 9 Variations in Ab and Or values (a) and FeO and MgOconcentrations (b) across a small zoned plagioclase grain show thatMgO steadily decreases and Or and FeO steadily increase from coreto rim but Ab first increases sharply then gradually decreases to avalue less than in the core
Fig 10 a) A BSE image of a small pocket of shock-melted glass inLAP 0220533 This glass is surrounded by maskelynite andpyroxene Notice the schlieren (brightdark bands) in the glass aconsequence of incomplete homogenization of the phases melted b)A vein of shock-melted glass near the edge of LAP 0222424 cutsacross all other minerals present c) Shock-melted glass in LAP0222424 Melting was incomplete so remnants of some minerals arestill discernable particularly maskelynite
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1095
launched from the Moon at the same time then thesimilarities discussed here are a remarkable coincidence
Petrogenesis
Below we briefly discuss possible parent magmas andby inference probable source regions for LAP Regardless ofwhether LAP and NWA 032 are from the same flow theirbulk chemical compositions are sufficiently similar that theyshould have similar parent melts and source regions At issueis whether the parent melt and source region for LAP aresimilar to other lunar basalts or whether the geochemicaldifferences that make LAP (and NWA 032) stand apart fromthe rest of the lunar basalt suite require a unique parent meltand source region Also of interest is whether or not LAP andNWA 032 can be related as fractionation products of the sameparent melt To address these issues we used the
crystallization modelling programs Magpox and Magfox byJohn Longhi (Longhi 1987 1991 Longhi and Pan 1988)
o
Fig 11 FeO versus Mgprime (a) and Na2O (b) comparing LAP (greytriangle) and NWA 032 (grey square) to the average compositions ofthe other basaltic lunar meteorites and Apollo and Luna basalts Thedata used in these averages comes from too many references to listhere (most are listed in Table 1 of Korotev 1998) the entire data setis available upon request The LAP and NWA 032 basalts are moreferroan than all lunar basalts except lunar meteorites Asuka-881757(A88) and Yamato-793169 (Y79) They are more alkali-rich than anyof the other high-Fe lunar basalts including A88 and Y79 In this andsubsequent Figs each circle (Lit averages) represents the averagecomposition of a type of Apollo or Luna basalt
Fig 12 Comparison of concentrations of trace elements in subsplitsof LAP 02005xxx (grey triangles) and NWA 032 (grey squares) withaverage mare basalt compositions from the Apollo and Lunamissions (dark grey circles) The data used in these averages comefrom too many references to list here (most are listed in Table 1 ofKorotev 1998) the entire data set is available upon request a) Thesubsamples of LAP 02005xxx and NWA 032 form a linear trendbecause of variation in modal olivine (high Co low Sc) abundanceand nearly constant clinopyroxene (low Co high Sc) abundanceBoth meteorites are enriched in Co with respect to Sc compared toother lunar basalts with comparable Sc concentrations Theexception to this is the Apollo 12 ilmenite (A12 Ilm) basalt suite b)NWA 032 is enriched in Ba (and K) as a result of terrestrial alteration(Fagan et al 2002) c) LAP 02005xxx and NWA 032 are enriched inincompatible elements eg Sm compared to other lunar basalts withcomparable Sc concentrations As in the case of Ba the only otherbasalts that are comparable or more enriched are from Apollo 14
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
1096 R Zeigler et al
These programs are based on parameterizations of liquidusboundaries and crystal-liquid partition coefficients in themodel basaltic system olivine-plagioclase-pyroxene-silica
We considered as possible parent melts the suite of lunarpicritic glasses (Shearer and Papike 1993) which are thoughtto represent the most primitive (undifferentiated) magmassampled on the Moon Picritic glasses have been consideredas likely parent melts of mare basalts though no direct parent-daughter pair of picritic glass and mare basalt has so far beenidentified (Shearer and Papike 1993) As crystallization of alow-Ti basaltic melt tends to increase the FeMg and the
concentrations of TiO2 and ITE we infer that any plausibleparent melt would have a higher MgFe and lowerconcentrations of TiO2 and ITEs than the bulk LAPcomposition This constraint rules out the high-Ti picriticglasses
Among the VLT and low-Ti picritic glasses the Apollo15 low-Ti yellow picritic glass (Table 11) is the mostplausible parent melt for LAP Starting with a melt that has thebulk composition of Apollo 15 yellow glass the melt thatremains after sim20 olivine crystallization at low pressure(01 kb) under equilibrium conditions is similar to the bulk
Fig 13 Comparison of REE concentrations in LAP 02205 to those of other lunar basalts Only the pattern for NWA 032 and the Apollo 14group 3 high-Al basalts (A14 gr3) are similar that of LAP although the Apollo 14 basalts have a different slope in the heavy REEs Only thoseREEs listed on the axis were used in making the plot the other values were interpolated The high-Ti (HT) basalt pattern is an average of allApollo 11 and Apollo 17 high-Ti basalts The olivine basalt pattern (Ave Olv) is an average of all Apollo 12 and Apollo 15 olivine basaltsIlm = ilmenite Pig = pigeonite Data used in these averages available upon request
Fig 14 NWA 032 (squares) and LAP (triangles) have greater ThSm ratio than any other lunar basalt (circles) except the Apollo 14 high-Kbasalts (HK) Data used in these averages available upon request
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1097
composition of LAP (Table 11) By making a few minormodifications to the bulk composition of the Apollo 15yellow glass (change the Mgprime from 50 to 47 and the CaOAl2O3 ratio from 103 to 114 both of which are within therange observed in picritic glasses) the composition of themelt that remains after sim20 olivine has crystallized is evencloser to that of LAP with only minor differences (principallyin MgO concentration)
The crystallization sequence predicted at low pressure forthe contemporary melt after sim20 olivine has crystallizedfrom the modified Apollo 15 yellow glass composition doesnot quite match the observed crystallization sequence of LAPwhich is olivine followed closely by spinel pigeonite andaugite with plagioclase and ilmenite appearing later If theresidual melt crystallized at a moderate pressure (3 kb) thecrystallization sequence for the resulting melt would beolivine followed shortly by pigeonite spinel and augite withplagioclase and ilmenite crystallizing later
The similarities between the Apollo 15 yellow glass andLAP extend to their ITEs as well Although the ITEconcentrations in Apollo 15 yellow glasses show aconsiderable range (Shearer and Papike 1993) theconcentrations of ITEs in LAP fall near the middle of thisrange and the REE patterns of both yellow glass and LAPshow a similar light-REE enrichment Recent work on picriticglass beads by Hagerty et al (2004) suggests that the ThSmratio in the source areas for lunar basalts varies considerably(from 006 to 027) This means that the unusual ThREE
Fig 15 FeO versus MnO concentrations in LAP olivines (top) andpyroxenes (bottom) The ratio of FeOMnO in mafic silicates isdiagnostic of the parent body on which they were formed (Dymeket al 1976) The FeO to MnO ratio in both the LAP pyroxene andolivine is consistent with a lunar origin The lines on both graphs areafter Papike (1998)
Fig 17 The overall variability seen among all of the LAP 02005 andNWA 032 subsamples (grey triangles) is less than that observedamong large samples within the Apollo 12 ilmenite basalt suite (greycircles) and only slightly greater than that among samples within theApollo 12 olivine basalt suite (grey squares) Data used in this plot isavailable upon request
Fig 16 Comparison of the pyroxene compositions of the four LAPstones (dark grey triangles) with the pyroxene compositions of theNWA 032 meteorite (white squares) The differences are likely aconsequence of somewhat different cooling histories LAP havingcooled more slowly
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
1098 R Zeigler et al
ratios seen in LAP and NWA could be inherited from theirsource region and need not be a result of some type ofunusual differentiation of the ascending magma (Fig 14)
We are not advocating that Apollo 15 yellow glass is theparent melt for LAP but rather that something similar toApollo 15 yellow glass is a plausible parent melt compositionAccording to current models of the lunar mantle (eg Nealand Taylor 1992 Shearer and Papike 1993) the source regionfor a parent melt such as this would be relatively deep(gt400 km) in the mantle It would consist of both earlycrystallized magnesian mafic cumulates which settled earlyfrom a lunar magma ocean and later-crystallized Fe-Ti-ITE-rich mafic cumulates that sank into the underlying moremagnesian cumulates due to density contrast aided by partialmelting due to radiogenic heating This LAP parent meltwould fractionate sim20 olivine while ascending pond some-where near the base of the crust (where the pressure is sim3 kb)and undergo moderate amounts of crystallization there beforeeruption to the surface
NWA 032 and LAP do not appear to be sequentialcrystallization products of the same parent melt that hasundergone varying amounts of fractionation Only olivine ispredicted to be a liquidus phase in the interval thatcorresponds to the difference in the bulk compositions ofNWA 032 and LAP Results shown in Table 10 have shownthat simple olivine fractionation cannot account for thedifferences in bulk composition between NWA 032 and LAPThis supports the idea that if LAP and NWA 032 are portionsof the same flow and their compositional differences resultfrom the random distribution of small amounts of olivinechromite and pyroxene in a basalt flow that eventuallysolidified to become LAP
SUMMARY AND CONCLUSIONS
The four LaPaz Icefield basaltic meteorites studied hereLAP 02205 LAP 02224 LAP 02226 and LAP 02436 arelow-Ti (31 wt) basalts On the basis of the oxygen isotopic
Table 10 Comparing Bulk LAP and NWA 032 compositionsNWA Core oli Core pyx Chromite NWA LAP diffave comp ave comp ave comp ave comp calc ave comp
Major element concentrationsSiO2 4473 3619 5057 008 4517 453 minus02TiO2 300 003 094 542 321 311 +32Al2O3 932 002 226 1144 1001 979 +22Cr2O3 040 025 080 4387 031 031 minus00FeO 2221 3326 1721 3452 2178 222 minus20MnO 028 034 032 027 028 029 minus42MgO 797 2932 1632 277 665 663 +02CaO 1057 036 1094 004 1112 1109 +03Na2O 035 000 003 000 037 038 minus08P2O5 009 000 000 000 010 010 minus15Totals 9900 9979 9940 9841 9900 9921 minus removed minus 48 27 022 minus minus minus
Trace element concentrationsZr 170 minus minus minus 184 183 +09La 113 minus minus minus 122 131 minus65Ce 299 minus minus minus 324 347 minus67Nd 20 minus minus minus 21 22 minus48Sm 663 minus minus minus 719 774 minus71Eu 110 minus minus minus 120 124 minus38Tb 157 minus minus minus 170 179 minus52Yb 58 minus minus minus 628 659 minus47Lu 080 minus minus minus 087 092 minus49Hf 502 minus minus minus 544 558 minus27Ta 063 minus minus minus 068 071 minus41Th 189 minus minus minus 205 204 +03U 046 minus minus minus 050 052 minus33The average major element compostions of LAP 02205 and NWA 032 can be related through the loss of the phases Starting with the average NWA bulk
composition and removing the equivalent of 48 LAP core olivine 27 earliest crystallized LAP core pyroxene and 02 LAP chromite the resultingcomposition is very close to the bulk LAP composition By assuming that the olivine pyroxene and chromite are perfectly incompatible for the listedincompatible trace elements (not true but they should be very low for most of the listed elements) we can see that the loss of ~8 of the earliest crystallizedphases would account for about half of the incompatible trace element discrepancy between NWA and LAP (the average difference is reduced from~12 to ~4) Some other factor such as melt evolution would have to be invoked in order to account for the rest of this discrepancy
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1099
signature (LAP 02205 McBride et al 2003) FeOMnO ratiosin the mafic silicates and a variety of other petrologicindicators the four stones can only be of lunar origin On thebasis of overwhelming similarities in mineral assemblagesand mineral compositions we conclude that the four stones arepaired Despite textural differences mineral assemblagesmineral compositions and bulk major- and trace-elementconcentrations of LAP are similar to those of NWA(Northwest Africa) 032 (Fagan et al 2002) Among smallsubsamples of the two meteorites the most magnesiansubsamples of LAP 02005 are all but indistinguishable fromthe most ferroan subsamples of NWA 032 The texturaldifferences between the meteorites can be attributed todifferent cooling histories and the minor difference in averagebulk composition can largely be explained by a 77 loss inthe earliest crystallizing phases (48 olivine + 27pyroxene + 022 chromite) in LAP with respect to NWA032 Given the similarities we conclude that LAP and NWA032 are almost certainly source crater paired and that there isa possibility that they are genetically related perhapsrepresenting samples from different portions of a singlebasaltic flow LAP is likely derived from a parent melt similarto the Apollo 15 low-Ti yellow picritic glass that hasundergone moderate amounts of olivine fractionation
AcknowledgmentsndashWe would like to thank Tim Fagan forproviding the NWA 032 pyroxene probe data GretchenBenedix for help with the electron microprobe analyses andChristine Floss for providing the X-ray imaging used in themodal analyses Discussions and comments by Dr Robert FDymek and Dr Robert D Tucker were very helpful in
preparing the manuscript Thorough and thoughtful reviewsby Dr Barbara A Cohen Dr Clive R Neal and Dr KevinRighter as well as expert editorial handling by Dr Cyrena AGoodrich greatly improved the finished manuscript Wewould also like to thank John Schutt for the informationregarding where the LAP meteorites were found in the fieldThis work was funded by NASA grant NAG5-10485(L Haskin)
Editorial HandlingmdashDr Cyrena Goodrich
REFERENCES
Anand M Taylor L A Neal C Patchen A and Kramer G (2004)Petrology and geochemistry of LAP 02 205 A new low-Ti mare-basalt meteorite (abstract 1626) 35th Lunar and PlanetaryScience Conference CD-ROM
Arai T and Warren P H 1999 Lunar meteorite Queen AlexandraRange 94281 Glass compositions and other evidence for launchpairing with Yamato-793274 Meteoritics amp Planetary Science34209ndash243
Bence A E and Papike J J 1972 Pyroxenes as recorders of liquidbasalt petrogenesis Chemical trends due to crystal-liquidinteraction Proceedings 3rd Lunar Science Conference pp431ndash469
Collins S J Righter K and Brandon A D 2005 Mineralogypetrology and oxygen fugacity of the LaPaz icefield lunarbasaltic meteorites and the origin of evolved lunar basalts(abstract 1141) 36th Lunar and Planetary Science ConferenceCD-ROM
Day J M D Taylor L A Patchen A D Schnare D W and PearsonD G 2005 Comparative petrology and geochemistry of theLaPaz mare basalt meteorites (abstract 1419) 36th Lunar andPlanetary Science Conference CD-ROM
Table 11 Composition of modeled petrogenic results compared to bulk LAP compositionApollo 15 Modeled diff Yel glass Modeled diff LAPyel glass melt variant melt aveA B C D E F G
SiO2 438 453 00 438 457 08 453TiO2 270 339 91 255 316 16 311Al2O3 834 1050 72 800 99 12 979Cr2O3 055 055 796 030 030 minus22 031FeO 218 207 minus67 233 218 minus18 222MnO 030 029 03 030 029 05 029MgO 1263 777 171 1143 698 52 663CaO 86 108 minus30 91 112 07 111Na2O 054 068 801 054 067 77 038Totals 992 1000 minus 992 1000 minus 992Mg 51 40 153 47 36 46 35CaOAl2O3 103 102 minus96 114 113 minus04 113 olv fract minus 197 minus minus 191 minus minusColumn A Major-element composition of Apollo 15 low-Ti yellow (yel) picritic glass as reported in Table 2 column 2b of Shearer and Papike (1993)
Column D major-element composition of a new parent melt based on the Apollo 15 yellow glass composition but altered slightly to more closely matchthe requirements of LAP Columns B and E the modeled composition of the remaining melt after the parent melts in columns A and D (respectively)underwent equillibrium crystallization at low pressure using the Magpox program (Longhi 1987 1991) until ~19 olivine had crystallized ( olv fract)Columns C and F a measure of how similar the modeled melt compositions in columns B and D are when compared to the average LAP bulk composition(column G) diff = (ModeledLAP)LAP100
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
1100 R Zeigler et al
Dickinson T Taylor G J Keil K Schmitt R A Hughes S S andSmith M R 1985 Apollo 14 aluminous mare basalts and theirpossible relationship to KREEP Proceedings 15th Lunar andPlanetary Science Conference pp 365ndash374
Donavan J J Hanchar J M Picolli P M Schrier M D BoatnerL A Jarosewich E 2003 A re-examination of the rare-earth-element orthophosphate standards in use for electron microprobeanalysis The Canadian Mineralogist 41221ndash232
Dymek R F Albee A L Chodos A A and Wasserburg G J 1976Petrography of isotopically-dated clasts in the Kapoetahowardite and petrologic constraints on the evolution of itsparent body Geochimica Cosmochimica Acta 401115ndash1130
El Goresy A Ramdohr P and Taylor L A 1971 The opaqueminerals in the lunar rocks from Oceanus ProcellarumProceedings 2nd Lunar Science Conference pp 219ndash235
Fagan T J Taylor G J Keil K Bunch T E Wittke J H KorotevR L Jolliff B L Gillis J J Haskin L A Jarosewich EClayton R N Mayeda T K Fernandes V A Burgess RTurner G Eugster O and Lorenzetti S 2002 Northwest Africa032 Product of lunar volcanism Meteoritics amp PlanetaryScience 37371ndash394
Gnos E Hofmann B A Al-Kathiri A Lorenzetti S Eugster OWhitehouse M J Villa I M Jull A J T Eikenberg J SpettelB Kraehenbuehl U Franchi I A Greenwood R C 2004Pinpointing the source of a lunar meteorite Implications for theevolution of the Moon Science 305657ndash660
Hagerty J J Shearer C K and Vaniman D T Thorium andsamarium in lunar pyroclastic glasses Insights into thecomposition of the lunar mantle and basaltic magmatism on theMoon (abstract 1817) 35th Lunar and Planetary ScienceConference CD-ROM
Haskin L A Helmke P A Allen R O Anderson M R KorotevR L and Zweifel K A 1971 Rare-earth elements in Apollo 12lunar materials Proceedings 2nd Lunar Science Conference pp1307ndash1317
Haskin L A Jacobs J W Brannon J C and Haskin M A 1977Compositional dispersions in lunar and terrestrial basaltsProceedings 8th Lunar Science Conference pp 1731ndash1750
Helmke P A and Haskin L A 1972 Rare earths and other traceelements in Luna 16 soil Earth and Planetary Science Letters13441ndash443
Jarosewich E and Boatner L A 1991 Rare-earth element referencesamples for electron microprobe analysis GeostandardsNewsletter 15397ndash399
Jolliff B L Korotev R L and Haskin L A 1991 Geochemistry ofthe 2ndash4 mm particles from the Apollo 14 soil (14161) andimplications regarding igneous components and soil formingprocesses Proceedings 21st Lunar and Planetary ScienceConference pp 193ndash219
Jolliff B L Rockow K M and Korotev R L 1998 Geochemistryand petrology of lunar meteorite Queen Alexandra Range 94281a mixed mare and highland regolith breccia with specialemphasis on very-low-Ti mafic components Meteoritics ampPlanetary Science 33581ndash601
Joy K H Crawford I A Russell S S and Kearsley A 2004Mineral chemistry of LaPaz Ice Field 02205ndashA new lunar basalt(abstract 1545) 35th Lunar and Planetary Science ConferenceCD-ROM
Kieffer S W Schaal R B Gibbons R V Hˆrz F Milton D J andDube A 1976 Shocked basalt from the Lonar impact craterIndia and experimental analogs Proceedings 2nd Lunar ScienceConference pp 1391ndash1412
Koeberl C Kurat G and Brandstpermiltter F 1993 Gabbroic lunar maremeteorites Asuka-881757 (Asuka-31) and Yamato-793169Geochemical and mineralogical study Proceedings of the NIPRSymposium on Antarctic Meteorites 614ndash34
Korotev R L 1991 Geochemical stratigraphy of two regolith coresfrom the central highlands of the Moon Proceedings 21st Lunarand Planetary Science Conference pp 229ndash289
Korotev R L 1998 Concentrations of radioactive elements in lunarmaterials Journal of Geophysical Research 1031691ndash1701
Korotev R L Lindstrom M M Lindstrom D J and Haskin L A1983 Antarctic meteorite ALH A81005mdashNot just another lunaranorthositic norite Geophysical Research Letters 10829ndash832
Korotev R L Jolliff B L and Rockow K M 1996 Lunar meteoriteQueen Alexandra Range 93069 and the iron concentration of thelunar highlands surface Meteoritics amp Planetary Science 31909ndash924
Korotev R L and Haskin L A 1975 Inhomogeneity of traceelement distributions from studies of the rare earths and otherelements in size fractions of crushed lunar basalt 70135Conference on Origins of Mare Basalts and Their Implicationsfor Lunar Evolution LPI Contribution 234 Houston TexasLunar and Planetary Science Institute pp 86ndash90
Korotev R L Jolliff B L Zeigler R A and Haskin L A 2003aCompositional constraints on the launch pairing of threebrecciated lunar meteorites of basaltic composition AntarcticMeteorite Research 16152ndash175
Korotev R L Jolliff B L Zeigler R A Gillis J J and HaskinL A 2003b Feldspathic lunar meteorites and their implicationsfor compositional remote sensing of the lunar surface and thecomposition of the lunar crust Geochimica Cosmochimica Acta674895ndash4923
Lindstrom M M and Haskin L A 1978 Causes of compositionalvariations within mare basalt suites Proceedings 10th Lunar andPlanetary Science Conference pp 465ndash486
Lindstrom M M and Haskin L A 1981 Compositionalinhomogeneities in a single Icelandic tholeiite flow Geochimicaet Cosmochimica Acta 4515ndash31
Lindstrom D J and Korotev R L 1982 TEABAGS Computerprograms for instrumental neutron activation analysis Journal ofRadioanalytical Chemistry 70439ndash458
Longhi J 1987 On the connection between mare basalts and picriticglasses Proceedings 17th Lunar and Planetary ScienceConference pp 349ndash360
Longhi J 1991 Comparative liquidus equilibria of hypersthene-normative basalts at low pressure American Mineralogist 76785ndash800
Longhi J and Pan V 1988 A reconnaissance study of phaseboundaries in low-alkali basaltic liquids Journal of Petrology29115ndash147
Ma M-S Schmitt R A Nielsen R L Taylor G J Warner R Dand Keil K 1979 Petrogenesis of Luna 16 aluminous marebasalts Geophysical Research Letters 6909ndash912
McBride K McCoy T and Welzenbach L 2003 LAP 02205Antarctic Meteorite Newsletter 27(1)
McBride K McCoy T and Welzenbach L 2004a LAP 0222402226 and 02436 Antarctic Meteorite Newsletter 26(2)
McBride K McCoy T and Welzenbach L 2004b LAP 03632Antarctic Meteorite Newsletter 27(3)
Neal C R and Taylor L A 1992 Petrogenesis of mare basalts Arecord of lunar volcanism Geochimica Cosmochimica Acta 562177ndash2211
Neal C R Taylor L A and Patchen A D 1989a High alumina(HA) and very high potassium (VHK) basalt clasts from Apollo14 breccias Part 1mdashMineralogy and petrology Evidence ofcrystallization from evolving magmas Proceedings 19th Lunarand Planetary Science Conference pp 137ndash145
Neal C R Taylor L A Schmitt R A Hughes S S and LindstromM M 1989b High alumina (HA) and very high potassium(VHK) basalt clasts from Apollo 14 breccias Part 1mdashWholerock geochemistry Further evidence for combined assimilation
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57
Petrography and geochemistry of the LaPaz Icefield lunar meteorite 1101
and fractional crystallization within the lunar crust Proceedings19th Lunar and Planetary Science Conference pp 147ndash161
Neal C R Hacker M D Snyder G A Taylor L A Liu Y-G andSchmitt R A 1994 Basalt generation at the Apollo 12 site PartI New data classification and re-evaluation Meteoritics 29334ndash348
Ostertag R 1983 Shock experiments on feldspar crystalsProceedings 14th Lunar and Planetary Science Conference pp364ndash376
Papike J J 1998 Comparative planetary mineralogy Chemistry ofmelt-derived pyroxene feldspar and olivine In Planetarymaterials edited by Papike J J Washington DC MineralogicalSociety of America pp 7-1ndash7-11
Philpotts J A Schnetzler C C Bottino M L Schuhmann S andThomas H H 1972 Luna 16 Some Li K Rb Sr Ba rare-earthZr and Hf concentrations Earth and Planetary Science Letters13429ndash435
Rhodes J M Blanchard D P Dungan M A Brannon J C andRodgers K V 1977 Chemistry of Apollo 12 mare basaltsMagma types and fractionation processes Proceedings 8thLunar Science Conference pp 1305ndash1338
Ryder G and Ostertag R 1983 ALHA 81005 Moon Marspetrography and Giordano Bruno Geophysical Research Letters10791ndash794
Ryder G and Schuraytz B C 2001 Chemical variation of the largeApollo 15 olivine-normative mare basalt rock samples Journalof Geophysical Research 1061435ndash1451
Schaal R B Hˆrz F Thompson T D and Bauer J F 1979 Shockmetamorphism of granulated lunar basalt Proceedings 10thLunar and Planetary Science Conference pp 2547ndash2571
Schmincke H-U 1967 Stratigraphy and petrography of four upperYakima basalt flows in south-central Washington GeologicalSociety of America Bulletin 781385ndash1422
Shearer C K and Papike J J 1993 Basaltic magmatism on theMoon A perspective from volcanic picritic glass beadsGeochimica Cosmochimica Acta 574785ndash4812
Shervais J W Taylor L A and Lindstrom M M 1985 Apollo 14mare basalts Petrology and geochemistry of clasts fromconsortium breccia 14321 Proceedings 15th Lunar andPlanetary Science Conference pp 375ndash395
Stˆffler D and Hornemann U 1972 Quartz and Feldspar glassesproduced by natural and experimental shock Meteoritics 7371ndash394
Thalmann C Eugster O Herzog G F Klein J Krpermilhenbcedilhl UVogt S and Xue S 1996 History of lunar meteorites QueenAlexandra Range 93069 Asuka-881757 and Yamato-793169based on noble gas isotopic abundances radionuclideconcentrations and chemical composition Meteoritics ampPlanetary Science 31857ndash868
Thompson J B Jr 1982 Compositional space An algebraic andgeometric approach In Characterization of metamorphismthrough mineral equilibria edited by Ferry J M WashingtonDC Mineralogical Society of America pp 1ndash31
Warren P H 1994 Lunar and Martian meteorite delivery systemsIcarus 111338ndash363
Warren P H and Kallemeyn G W 1993 Geochemical investigationsof two lunar mare meteorites Yamato-793169 and Asuka-881757 Proceedings of the NIPR Symposium on AntarcticMeteorites 635ndash57