u–pb zircon ages of syenitic and granitic rocks in the ashizuri igneous...

275

Geochemical Journal, Vol. 44, pp. 275 to 283, 2010

*Corresponding author (e-mail: [email protected])

Copyright © 2010 by The Geochemical Society of Japan.

the A-type granite (Loiselle and Wones, 1979). The ra-diometric dating of the Ashizuri complex was carried outby K–Ar and zircon fisson track (FT) methods (e.g.,Murakami et al., 1989). The results range from 10 to 16Ma, which suggest that the igneous activities of theAshizuri complex were generally coeval with those of theOuter Zone Granitic Rocks. Relatively large scatter in thereported age, however, obscures the strict temporal rela-tionship between the magmatism of Ashizuri complex andthose of the Outer Zone Granitic Rocks.

We report U–Pb ages of the zircons separated fromtwo felsic samples of the Ashizuri complex using laserablation ICP mass spectrometry (LA-ICP-MS) to clarifythe timing of this peculiar magmatism. Implications tothe origin of the alkaline magmatism in the forearc re-gion will also be discussed.

GEOLOGY

The Ashizuri complex intrudes into the PaleogeneShimizu Formation with northward convex semi-ringstructure (Fig. 1). Murakami et al. (1983) suggested thatthe Ashizuri complex may form a ring pluton, of whichsouthern half is hidden beneath the sea. Murakami et al.(1983, 1989) proposed that the Ashizuri complex wasformed by five igneous stages based on the field rela-tionships; stage I (alkali gabbro and dolerite), stage II(melanocranic syenite, quartz syenite, and alkali granite),stage III (coarse-grained syenitic rocks and rapakivi gran-

U–Pb zircon ages of syenitic and granitic rocks in the Ashizuri igneous complex,southwestern Shikoku: Constraint for the origin of forearc alkaline magmatism

HIRONAO SHINJOE,1* YUJI ORIHASHI2 and TOMOAKI SUMII3

1Tokyo Keizai University, 1-7-34, Minami-cho, Kokubunji, Tokyo 185-8502, Japan2Earthquake Research Institute, University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan

3Geological Survey of Japan, AIST, Tsukuba, Ibaraki 305-8567, Japan

(Received August 20, 2009; Accepted December 6, 2009)

We report two first U–Pb zircon ages of the felsic rocks in the Ashizuri igneous complex, southwestern Shikoku, usingthe LA-ICP-MS. Samples are a syenite (ASH54) and a biotite granite (ASH5). Weighted means of the 238U–206Pb ages ofconcordant data of ASH54 and ASH5 are 13.12 ± 0.09 Ma (2σ) and 12.95 ± 0.06 Ma (2σ), respectively. It is concluded thatthe felsic member of the Ashizuri complex was formed almost simultaneously at ca. 13 Ma after the major activity of theOuter Zone Granitic Rocks. Presence of alkali dolerite dike cutting the syenite indicates that the alkali basaltic magmaintruded after the subduction of Shikoku Basin of the Philippine Sea plate beneath the southwest Japan arc. Alkali basalticmagma of Ashizuri complex may have been derived from a depth possibly deeper than that of subducted Shikoku Basin ofthe Philippine Sea Plate.

Keywords: U–Pb age, zircon, LA-ICP-MS, Miocene, alkaline magmatism, Southwest Japan, Outer Zone

INTRODUCTION

In the middle Miocene time of the southwest Japan,widespread magmatism occurred forearc region, whichwas almost contemporaneous with the clockwise rotationof southwest Japan arc and the commencement of sub-duction of the young hence hot Shikoku Basin of the Phil-ippine Sea plate beneath it (Tatsumi et al., 2001; Sumiiand Shinjoe, 2003; Kimura et al., 2005). To the south ofMedian Tectonic Line, felsic to intermediate volcano-plutonic complexes (Outer Zone Granitic Rocks; Shibata,1962) were emplaced in the forearc accretionary com-plex. The Outer Zone Granitic Rocks consist of calc-alkaline I-type and S-type granitic rocks; the formerdistributes farther to the trench and the latter closer tothe trench (e.g., Nakada and Takahashi, 1979).

Ashizuri igneous complex in the southwestern Shikoku(Fig. 1) may be included into the Outer Zone GraniticRocks, though it is the only alkaline igneous complexamong the Miocene volcano-plutonic complexes in theOuter Zone of southwest Japan. The Ashizuri complex iscomposed mainly of felsic lithology including syeniticand granitic rocks with subordinate amount of alkalinegabbro and dolerite. Murakami et al. (1983) pointed outthat the felsic member of the Ashizuri complex is akin to

276 H. Shinjoe et al.

ite), stage IV (coarse-grained biotite granite), and stageV (alkali dolerite and syenite porphyry dikes). It shouldbe noted that the mafic lithologies are only present in thestage I and V. Stage I gabbro and dolerite occur as en-claves within syenitic rocks of the stage II and III. StageV alkali dolerite occurs as dikes which cut the stage IIsyenitic rocks (Murakami et al., 1989). Stein et al. (1996)demonstrated that the gabbroic rocks of the stage I showincompatible trace element features of the oceanic islandalkalic basalts. Shinjoe et al. (2003) also reported similartrace element characteristics for the alkali dolerite of thestage V. Syenitic and granitic rocks of the Ashizuri com-plex also fall in the within-plate granite field of trace el-ement discrimination diagrams (Pearce et al., 1984) dueto the enrichment in both large ion lithophile and highfield strength elements (Stein et al., 1996).

Shibata and Nozawa (1968) reported the first K–Arage of 13 ± 2 Ma for the mixture of biotite and horn-blende from the sample at the Cape Ashizuri. Murakami

et al. (1989) reported five FT zircon ages and three K–Arages. Reported FT zircon ages ranges from 10.0 to 16.1Ma, though the zeta calibration (Hurford, 1990) had notbeen applied on the age determination. Biotite K–Ar agefor a biotite granite of the stage VI was 12.9 ± 0.6 Ma,which was in accord with the age reported by Shibataand Nozawa (1968), while whole rock K–Ar ages were12.0 ± 0.6 Ma and 14.0 ± 0.7 Ma. The latter age was foralkali dolerite of the stage V, and the rock type for theformer age was not described. Hence the radiometric agesof the Ashizuri complex reported so far scatter from 10to 16 Ma. Additionally, no clear correlation was observedbetween reported ages and igneous stages.

SAMPLES AND EXPERIMENTS

Zircon grains were separated from two samples. Lo-calities of the samples are shown in Fig. 1. One is a syenite(ASH54) in the southwestern part of the Ashizuri com-

10 2 km

Shimizu Formation

Densely accumulated part of garbbo blocks (Stage I)Melanocranic syenite, quartz syenite, and alkali granite (Stage II)

Coarse-grained syenitic rocks and rapakivi granite (Stage III)

Coarse-grained biotite granite (Stage IV)

SH54S2°43'56"N, 132°58'38"E)

ASH5(32( °44'52"N, 132, °59'52"E)

10 km

33°N

133°E

Ashizuriplex

Uwajima Pluton

Miuchi Pluton

Okinoshima Pluton

Kashiwajima Pluton

33°N

34°N

133°E 134°E

ShikokuA)

B)

Fig. 1. A) Index map of the Miocene felsic igneous rocks in the SW Shikoku (modified from Sumii, 2000). B) Geological map ofthe Ashizuri igneous complex compiled after Murakami and Imaoka (1985) with sample locations. Xenolithic blocks of shale andsandstone within the igneous complex are assumed to be derived from the Shimizu Formation (Murakami et al., 1983).

U–Pb zircon ages of the Ashizuri igneous complex 277

plex from the area of the stage II rock of Murakami et al.(1989). The other is a coarse-grained biotite-granite(ASH5) in the north of the complex, which belongs tothe stage IV rock of Murakami et al. (1989). The sam-pling site of the ASH5 is almost same where a biotitegranite sample of 12.9 Ma K–Ar biotite age reported byMurakami et al. (1989) was sampled. Most of separated

zircon crystals are euhedral or subhedral morphology (Fig.2). Color variation is observed in zircon grains in thesesamples (Fig. 2). Most of zircons (>90%) in ASH5 arecomposed of reddish tint grains with subordinate amountof light brownish and dark brownish grains. They are elon-gated or equant crystals and 100–250 µm in diameter.Zircons in ASH54 are composed of almost same amount

Fig. 2. Photographs of analyzed zircon grains. Color variations of zircon grains are also shown. A circled grain of light brownishcolor in ASH5 gives 238U–206Pb ages ranging from 15.67 to 16.10 Ma.


of reddish and light brownish tint grains with subordi-nate amount of dark brownish grains (<3%). They areequant or elongated crystals and 100–300 µm in diam-eter. For the analysis, zircon grains were pressed into asoft PFA sheet, and their surface was polished using 3-,and 1-µm diamond paste.

The U–Pb age of zircon was determined using an ICP-MS (VG Plasma Quad 3) with a frequency quintupled (λ= 213 nm) Nd-YAG laser ablation system (New WaveResearch UP-213) at the Earthquake Research Institute,University of Tokyo. The detail of the analytical protocolfollowed after Orihashi et al. (2003, 2008). The analyti-cal precision and accuracy of the zircon U–Pb dating werediscussed in Orihashi et al. (2008). Weighted means of

the 238U–206Pb and 235U–207Pb ages for the duplicatedanalyses (n = 19) of 91500 zircon standard during thisstudy are 1053.8 ± 5.6 Ma (2σ) and 1065.4 ± 10.8 Ma(2σ), respectively, showing an agreement with the ID-TIMS data determined by Wiedenbeck et al. (1995).

RESULTS AND DISCUSSION

U–Pb isotopic data of the individual analytical spotsare listed in Appendix. Analyzed points were plotted onthe Terra-Wasserburg concordia diagram (Fig. 3) usingthe computer program Isoplot 3.0 (Ludwig, 2003). Dis-cordant data plotted away from the concordia curvegreater than 2σ errors were excluded. Ranges of 238U–206Pb ages of concordant data for the groups of zircongrains with different tint are summarized in Table 1. Noobvious age discrepancy was found between the groups.238U–206Pb ages of concordant data (n = 23) of ASH5range from 12.39 to 14.00 Ma. It is notable that 238U–206Pb ages of three concordant analytical data of a zircongrain of light brownish color in ASH5 (Fig. 2) range from15.67 to 16.10 Ma, older than the other concordant databeyond 2σ errors (Fig. 3). 238U–206Pb ages of concordantdata (n = 31) of ASH54 range from 12.40 to 13.56 Ma.Weighted mean of 238U–206Pb ages and concordant agesof concordant analytical data are shown in Table 2. 238U–206Pb ages of the two samples suggest that the felsiclithologies (stage II to VI) of the Ashizuri complex wereformed almost simultaneously at ca. 13 Ma. 238U–206Pbage of ASH5 (13.12 ± 0.09 Ma) is also consistent withbiotite K–Ar age (12.9 ± 0.6 Ma), previously reportedfor the sample from the same locality (Murakami et al.,1989).

Timing of the Neogene alkaline magmatism and re-lated geologic events in the Shikoku and Chugoku dis-

0.025

0.035

0.045

0.055

0.065

0.075

360 400 440 480 520 560

0.025

0.035

0.045

0.055

0.065

0.075

360 400 440 480 520 560

ASH5

ASH54

17Ma 16Ma 15Ma 14Ma 13Ma 12Ma

17Ma 16Ma 15Ma 14Ma 13Ma 12Ma

207 P

b/20

6 Pb

207 P

b/20

6 Pb

238U/206Pb

238U/206Pb

Fig. 3. Terra-Wasserburg concordia diagrams showing the re-sult of zircon U–Pb concordant data of Ashizuri igneous com-plex. Diagrams were drawn using the program Isoplot 3.0(Ludwig, 2003). Each of the ellipsoids shows error (2σ) forindividual analytical spots.

Table 1. Comparison of the ranges of 238U–206Pb ages of con-cordant data for the groups of zircon grains with different tint

*Range of four concordant data except for three older data.**Three concordant data of a light brownish zircon grain with 238U–206Pb ages older than other concordant data beyond 2σ errors.

Tint of grains Number of concordant data Range of 238U–206Pb age(Number of total spots) of concordant data (Ma)

ASH5Reddish 16 (31) 12.39–14.00Light brownish 7 (14) 12.58–13.39*

15.67–16.10**Dark brownish 3 (13) 12.41–13.61

ASH54Reddish 17 (22) 12.40–13.37Light brownish 12 (24) 12.46–13.56Dark brownish 2 (8) 13.09–13.29


Fig. 4. Summary of the timing of alkaline igneous activity andrelated geologic events in Shikoku and Chugoku district, south-west Japan. Age data are based on Uto et al., (1987) for Shingulamprophyre dike; Otofuji et al. (1991) and Shimada et al.(2001) for clockwise rotation of SW Japan arc; Sumii andShinjoe (2003) for the Outer Zone Granitic Rocks; Kimura etal. (2005) for alkali basaltic magmatism in the Chugoku dis-trict.

0

5

10

15

20

Clockwise rotation of SW Japan Arc

K–Ar ages of the Outer Zone Granitic Rocks U–Pb ages of the Ashizuri complex

Shingu lamprophyre dike

Range of alkali basaltic magmatism

in the Chugoku district

Age (Ma)Table 2. Summary of weighted mean of U–Pb ages for con-cordant data of zircons of Ashizuri igneous complex

No. of data Wtd. mean ± err. (2σ)

of 238U–206Pb age (Ma)

Wtd. mean ± err. (2σ)

of concordia age (Ma)

ASH5(n = 23) 13.12 ± 0.09 13.11 ± 0.02(n = 3) 15.80 ± 0.17 15.80 ± 0.04

ASH54(n = 31) 12.95 ± 0.06 12.94 ± 0.02

trict are summarized in Fig. 4. The U–Pb age of theAshizuri complex is clearly after the clockwise rotationof southwest Japan (Otofuji et al., 1991; Shimada et al.,2001). It is also placed in the youngest part of the rangeof the radiometric ages of the Outer Zone Granitic Rocks(e.g., Sumii and Shinjoe, 2003). Since most of radiomet-ric ages of the Outer Zone Granitic Rocks reported so farwere determined by biotite K–Ar or zircon FT methods,reported ages represent cooling stage (~300°C) of thegranitic rocks. Closure temperature of U–Pb system inzircon (~900°C) suggests that the ages reported in thisstudy represent zircon crystallization in felsic magma.Thus it is certain that the felsic rocks of the Ashizuri com-plex was formed after the intrusion of most of the OuterZone Granitic Rocks. A grain with 15.80 ± 0.17 Ma (2σ)238U–206Pb age from the sample ASH5 (Table 2) mightsuggest the presence of a concealed granitic rocks formedcoeval with Outer Zone S-type Granitic Rocks beneaththe Ashizuri complex, since this age is close to the U–Pbzircon age for the Kumano Acidic Rocks, one of the OuterZone S-type Granitic Rocks in the Kii peninsula (Orihashiet al., 2007). These results also support that the felsicmagmatism in the Ashizuri complex was not simultane-ous with the Outer Zone S-type Granitic Rocks, but suc-ceeded them.

The occurrence of alkali basaltic rock in the forearcregion of Miocene southwest Japan is sometimes ascribedto the off-ridge magmatism of the Shikoku Basin (e.g.,Kimura et al., 2005). However, the incompatible elementcharacteristics of basaltic rocks in the Ashizuri complexare similar to those of OIB (Stein et al., 1996), that is,much enriched character than those reported for off-ridgealkali basalt sill in the Shikoku Basin (e.g., Hickey-Vargas, 1998). By the result of this study, we can onlyconclude that the magmatism of the stage I alkali gabbroand dolerite occurred no later than ca. 13 Ma. However,existence of alkali dolerite dikes of the stage V clearlycutting the stage II rocks suggests that intrusion of thealkali basalt magma did take place later than ca. 13 Mafelsic magmatism in the Ashizuri complex. Hence the in-trusion of alkali basaltic magma in Ashizuri complex did

occur after the subduction of Shikoku Basin of the Phil-ippine Sea plate beneath the southwest Japan arc. Hence,the alkali basaltic magma of Ashizuri complex may havebeen derived from a depth possibly deeper than that ofsubducted Shikoku Basin of the Philippine Sea Plate.

A lamprophyre dike of 17.7 ± 0.5 Ma (Uto et al., 1987)age was reported from Shingu area in central Shikoku(Fig. 4). Therefore, intrusion of alkaline basalt magmaoccurred in Shikoku before and after the rotation of south-west Japan. Activity of forearc alkaline basalticmagmatism in the Shikoku might range over several mil-lion years and have been related to widespread alkalinemagmatism occurred from 17 Ma to present mainly inChugoku and northern Kyushu areas (Kimura et al., 2005).

Acknowledgments—This study was supported by the TokyoKeizai University Research Grant (2B08-02). LA-ICP-MS


analyses were supported by the Earthquake Research Institutecooperative research program, the University of Tokyo. Criti-cal comments by Drs. Jun-Ichi Kimura, Simon Wallis, andanonymous reviewer were helpful to improve the manuscript.We greatly appreciate Messrs. Hideki Iwano and Toru Danharaof Kyoto Fission-Track Co., Ltd. for zircon separation andpreparation of excellent mount of polished zircon grains. Wealso thank Dr. K. R. Ludwig for generously supplying ISOPLOTprogram.

REFERENCES

Hickey-Vargas, R. (1998) Origin of the Indian Ocean-type iso-topic signature in basalts from Philippine Sea plate spread-ing centers: An assessment of local versus large-scale proc-esses. J. Geophys. Res. 103, 20,963–20,979.

Hurford, A. J. (1990) Standardization of fission track datingcalibration: Recommendation by the Fission Track Work-ing Group of the I .U.G.S. Subcommission ofGeochronology. Chem. Geol. 80, 171–178.

Kimura, J., Stern, R. J. and Yoshida, T. (2005) Reinitiation ofsubduction and magmatic responses in SW Japan duringNeogene time. Geol. Soc. Amer. Bull. 117, 969–986.

Loiselle, M. C. and Wones, D. R. (1979) Characteristics andorigin of anorogenic granites. Geol. Soc. Amer. Abst. 11,468.

Ludwig, K. R. (2003) User’s manual for Isoplot 3.00. A geo-chronological toolkit for Microsoft Excel. Berkley Geo-chronological Center, Berkley, California, U.S.A., SpecialPublication No. 4, 70 pp.

Murakami, N. and Imaoka, T. (1985) Rapakivi granites fromCape of Ashizuri, Kochi Prefecture, Southwest Japan. J.Geol. Soc. Japan 91, 179–194 (in Japanese with Englishabstract).

Murakami, N., Kanisawa, S. and Ishikawa, K. (1983) High fluo-rine content of Tertiary igneous rocks from the Cape ofAshizuri, Kochi Prefecture, Southwest Japan. J. Mineral.Petrol. Econ. Geol. 78, 497–504 (in Japanese with Englishabstract).

Murakami, N., Imaoka, T. and Uozumi, S. (1989) Ring com-plex of the Cape of Ashizuri, and its mode of emplacement,Kochi prefecture, Southwest Japan. Monograph, Assoc.Geol. Collab. Japan 36, 115–142 (in Japanese with Eng-lish abstract).

Nakada, S. and Takahashi, M. (1979) Regional variation inchemistry of the Miocene intermediate to felsic magmas inthe Outer Zone and the Setouchi Province of SouthwestJapan. J. Geol. Soc. Japan 85, 571–582 (in Japanese withEnglish abstract).

Orihashi, Y., Hirata, T., Tani, K. and Yoshida, H. (2003) Rapidand simultaneous determination of multi-element abun-dances and U–Pb age for zircon grain using UV laser abla-tion ICP-MS technique: critical evaluation of the techniquewith 91500 zircon standard. J. Mineral. Petrol. Sci. 98, 109–117.

Orihashi, Y., Iwano, H., Hirata, T., Danhara, T. and Shinjoe, H.(2007) U–Pb age and trace element compositions of red-dish, colorless, and detrital zircons in the Kumano AcidicRocks in the Outer Zone of southwest Japan and origin of

the host magma. J. Geol. Soc. Japan 113, 366–383 (in Japa-nese with English abstract).

Orihashi, Y., Nakai, S. and Hirata, T. (2008) U–Pb agedeterminations for seven standard zircons by ICP-MassSpectrometry coupled with frequency quintupled Nd-YAG(λ = 213 nm) laser ablation system: Comparison with LA-ICP-MS zircon analyses with a NIST glass reference mate-rial. Res. Geol. 58, 101–123.

Otofuji, Y., Itaya, T. and Matsuda, T. (1991) Rapid rotation ofsouthwest Japan—Paleomagnetism and K–Ar ages ofMiocene volcanic rocks of southwest Japan. Geophys. J.Intern. 105, 397–405.

Pearce, J. A., Harris, N. B. W. and Tindle, A. G. (1984) Traceelement discrimination diagrams for the tectonic interpre-tation of granitic rocks. J. Petrol. 25, 956–983.

Shibata, H. (1962) Chemical composition of Japanese graniticrocks in regard to petrographic provinces: Part X, petro-graphic provinces of Japan. Sci. Rep. Tokyo Univ. of Edu-cation 8C, 33–47.

Shibata, K. and Nozawa, T. (1968) K–Ar ages of granitic rocksof Ashizuri-misaki, Takatsukiyama and Omogo, Shikoku,Japan. Bull. Geol. Surv. Japan 19, 223–228.

Shimada, M., Sumii, T. and Torii, M. (2001) Paleomagneticdirections and K–Ar ages of Setouchi-volcanic rocks inTakanawa peninsula—Constraints for the timing of theclockwise rotation of Southwest Japan—. J. Geol. Soc. Ja-pan 107, 773–783 (in Japanese with English abstract).

Shinjoe, H., Sumii T. and Orihashi, Y. (2003) Near trench igne-ous activities in Middle Miocene Southwest Japan Arc: con-nection between magmatism and subduction of hot ShikokuBasin. Chikyu Monthly S43, 31–38 (in Japanese).

Stein, G., Lapierre, H. and Charvet, J. (1996) The MioceneAshizuri Complex (SW Japan); source and magma differ-entiation of an alkaline plutonic assemblage in an island-arc environment. Bull. Soc. Geol. France 167, 125–139.

Sumii, T. (2000) K–Ar ages of the Miocene granites in theTakatsuki-yama and the surrounding areas, southwesternShikoku. Japanese Mag. Mineral. Petrol. Sci. 29, 67–73(in Japanese with English abstract).

Sumii, T. and Shinjoe, H. (2003) K–Ar ages of the OhmineGranitic Rocks, south-west Japan. Island Arc 12, 335–347.

Tatsumi, Y., Ishikawa, N., Anno, K., Ishizaka, K. and Itaya, T.(2001) Tectonic setting of high-Mg andesite magmatism inthe SW Japan Arc: K–Ar chronology of the Setouchi vol-canic belt. Geophys. J. Int. 144, 625–631.

Uto, K., Hirai, H., Goto, K. and Arai, S. (1987) K–Ar ages ofcarbonate- and mantle nodule-bearing lamprophyre dikesfrom Shingu, central Shikoku, Southwest Japan. Geochem.J. 21, 283–290.

Wiedenbeck, M., Alle, P., Corfu, F., Griffin, W. L., Meier, M.,Oberli, F., Von Quadt, A., Roddick, J. C. and Spiegel, W.(1995) Three natural zircon standards for U–Th–Pb, Lu–Hf, trace element and REE analyses. Geostan. Newslett. 19,1–23.

APPENDIX

(see p. 281–283)


App

endi

x.

U–P

b is

otop

ic d

ata

for

zir c

on c

ryst

al d

eter

min

ed b

y L

A-I

CP

-MS

Ana

lyti

cal s

pot

Tin

t of

crys

tal

207 P

b/20

6 Pb

(2σ)

206 P

b/23

8 U (

2σ)

207 P

b/23

5 U (

2σ)

238 U

−206 P

b ag

e (M

a)

(2σ )

235 U

−207 P

b ag

e (M

a)

(2σ )

Con

cord

ia A

ge (

Ma)

(2σ )

MS

WD

AS

H5-

1re

ddis

h0.

0517

±0.

0096

0.00

206

±0.

0001

00.

0147

±0.

0028

13.2

7±

0.63

14.7

9±

2.83

13.2

6±

0.63

1.3

AS

H5-

2re

ddis

h0.

0587

±0.

0064

0.00

200

±0.

0000

80.

0162

±0.

0019

12.8

5±

0.51

16.2

7±

1.90

Dis

cord

ant

AS

H5-

3re

ddis

h0.

3156

±0.

0226

0.00

288

±0.

0001

30.

1255

±0.

0107

18.5

7±

0.85

120.

1±

10.2

Dis

cord

ant

AS

H5-

4re

ddis

h0.

0537

±0.

0088

0.00

210

±0.

0001

00.

0155

±0.

0026

13.5

1±

0.62

15.6

5±

2.66

13.4

9±

0.62

2.8

AS

H5-

5re

ddis

h0.

5032

±0.

0130

0.00

288

±0.

0001

20.

1996

±0.

0099

18.5

2±

0.78

184.

8±

9.1

Dis

cord

ant

AS

H5-

6re

ddis

h0.

0523

±0.

0051

0.00

199

±0.

0000

90.

0144

±0.

0015

12.8

3±

0.56

14.4

8±

1.54

12.8

0±

0.56

5.6

AS

H5-

7re

ddis

h0.

3157

±0.

0169

0.00

325

±0.

0001

50.

1417

±0.

0101

20.9

5±

0.98

134.

5±

9.6

Dis

cord

ant

AS

H5-

8re

ddis

h0.

1341

±0.

0117

0.00

230

±0.

0001

10.

0425

±0.

0042

14.8

2±

0.70

42.3

1±

4.19

Dis

cord

ant

AS

H5-

9re

ddis

h0.

2584

±0.

0143

0.00

250

±0.

0001

20.

0889

±0.

0064

16.0

7±

0.74

86.5

1±

6.24

Dis

cord

ant

AS

H5-

10re

ddis

h0.

2701

±0.

0182

0.00

200

±0.

0001

00.

0746

±0.

0062

12.9

0±

0.63

73.0

3±

6.08

Dis

cord

ant

AS

H5-

11re

ddis

h0.

5424

±0.

0341

0.00

476

±0.

0002

50.

3558

±0.

0293

30.6

0±

1.63

309.

1±

25.5

Dis

cord

ant

AS

H5-

12re

ddis

h0.

0468

±0.

0147

0.00

192

±0.

0001

00.

0124

±0.

0040

12.3

9±

0.66

12.5

2±

3.99

12.3

9±

0.66

0.00

42

AS

H5-

13re

ddis

h0.

0485

±0.

0085

0.00

193

±0.

0000

90.

0129

±0.

0023

12.4

3±

0.59

13.0

2±

2.35

12.4

2±

0.59

0.28

AS

H5-

14re

ddis

h0.

0508

±0.

0078

0.00

197

±0.

0000

80.

0138

±0.

0022

12.6

6±

0.55

13.8

8±

2.21

12.6

5±

0.54

1.3

AS

H5-

15re

ddis

h0.

0428

±0.

0067

0.00

199

±0.

0000

80.

0118

±0.

0019

12.8

4±

0.54

11.8

7±

1.94

12.8

4±

0.54

1.09

AS

H5-

16re

ddis

h0.

0454

±0.

0058

0.00

194

±0.

0000

80.

0122

±0.

0016

12.5

0±

0.51

12.2

7±

1.64

12.5

0±

0.51

0.08

6

AS

H5-

17re

ddis

h0.

0809

±0.

0074

0.00

209

±0.

0000

90.

0233

±0.

0024

13.4

6±

0.56

23.4

0±

2.36

Dis

cord

ant

AS

H5-

18re

ddis

h0.

0904

±0.

0045

0.00

210

±0.

0000

80.

0261

±0.

0017

13.5

1±

0.52

26.2

0±

1.66

Dis

cord

ant

AS

H5-

19re

ddis

h0.

3818

±0.

0365

0.00

308

±0.

0001

70.

1620

±0.

0180

19.8

1±

1.12

152.

4±

16.9

Dis

cord

ant

AS

H5-

20re

ddis

h0.

0482

±0.

0066

0.00

198

±0.

0000

80.

0132

±0.

0019

12.7

6±

0.53

13.2

8±

1.90

12.7

6±

0.53

0.34

AS

H5-

21re

ddis

h0.

0521

±0.

0105

0.00

200

±0.

0000

90.

0143

±0.

0030

12.8

5±

0.59

14.4

5±

2.97

12.8

4±

0.59

1.2

AS

H5-

22re

ddis

h0.

2941

±0.

0247

0.00

286

±0.

0001

40.

1160

±0.

0114

18.4

2±

0.92

111.

4±

10.9

Dis

cord

ant

AS

H5-

23re

ddis

h0.

2489

±0.

0124

0.00

272

±0.

0001

00.

0933

±0.

0058

17.5

0±

0.65

90.5

6±

5.63

Dis

cord

ant

AS

H5-

24re

ddis

h0.

0585

±0.

0058

0.00

211

±0.

0000

80.

0170

±0.

0018

13.5

7±

0.51

17.1

1±

1.81

Dis

cord

ant

AS

H5-

25re

ddis

h0.

0459

±0.

0050

0.00

212

±0.

0000

80.

0134

±0.

0016

13.6

8±

0.51

13.5

5±

1.57

13.6

8±

0.51

0.03

1

AS

H5-

26re

ddis

h0.

0454

±0.

0080

0.00

217

±0.

0001

00.

0136

±0.

0025

14.0

0±

0.61

13.7

4±

2.50

14.0

0±

0.61

0.04

7

AS

H5-

27re

ddis

h0.

0527

±0.

0122

0.00

204

±0.

0001

00.

0148

±0.

0035

13.1

7±

0.67

14.9

6±

3.55

13.1

6±

0.67

1.09

AS

H5-

28re

ddis

h0.

0426

±0.

0043

0.00

209

±0.

0000

80.

0123

±0.

0013

13.4

4±

0.49

12.3

6±

1.32

13.4

2±

0.48

3

AS

H5-

29re

ddis

h0.

0550

±0.

0050

0.00

205

±0.

0000

70.

0156

±0.

0015

13.2

2±

0.48

15.6

9±

1.55

Dis

cord

ant

AS

H5-

30re

ddis

h0.

0510

±0.

0050

0.00

208

±0.

0000

80.

0146

±0.

0015

13.3

7±

0.49

14.7

3±

1.53

13.3

5±

0.49

3.7

AS

H5-

31re

ddis

h0.

0542

±0.

0066

0.00

198

±0.

0000

80.

0148

±0.

0019

12.7

2±

0.51

14.8

9±

1.91

12.7

0±

0.51

5.7

AS

H5-

32da

rk b

row

nish

0.50

01±

0.00

910.

0060

9±

0.00

010

0.41

97±

0.01

0439

.12

±0.

6635

5.8

±8.

8D

isco

rdan

t

AS

H5-

33da

rk b

row

nish

0.05

17±

0.00

740.

0019

3±

0.00

006

0.01

37±

0.00

2012

.41

±0.

4013

.86

±2.

0212

.40

±0.

402.

2

AS

H5-

34da

rk b

row

nish

0.04

47±

0.00

210.

0021

1±

0.00

004

0.01

30±

0.00

0613

.61

±0.

2513

.13

±0.

6513

.60

±0.

252.

5

AS

H5-

35da

rk b

row

nish

0.13

29±

0.01

230.

0022

4±

0.00

008

0.04

11±

0.00

4014

.43

±0.

4940

.85

±4.

02D

isco

rdan

t

AS

H5-

36da

rk b

row

nish

0.41

02±

0.01

110.

0035

9±

0.00

007

0.20

29±

0.00

6823

.09

±0.

4618

7.6

±6.

3D

isco

rdan

t

AS

H5-

37da

rk b

row

nish

0.07

65±

0.00

650.

0019

3±

0.00

005

0.02

04±

0.00

1812

.42

±0.

3320

.46

±1.

83D

isco

rdan

t


App

endi

x.

(con

tinu

ed)

Ana

lyti

cal s

pot

Tin

t of

crys

tal

207 P

b/20

6 Pb

(2σ )

206 P

b/23

8 U (

2σ)

207 P

b/23

5 U (

2 σ)

238 U

−206 P

b ag

e (M

a)

(2σ )

235 U

−207 P

b ag

e (M

a)

(2σ)

Con

cord

ia A

ge (

Ma)

(2σ )

MS

WD

AS

H5-

38da

rk b

row

nish

0.20

05±

0.00

730.

0024

3±

0.00

005

0.06

72±

0.00

2815

.66

±0.

3366

.08

±2.

77D

isco

rdan

t

AS

H5-

39da

rk b

row

nish

0.07

76±

0.00

560.

0020

5±

0.00

005

0.02

19±

0.00

1713

.18

±0.

3221

.99

±1.

67D

isco

rdan

t

AS

H5-

40da

rk b

row

nish

0.04

97±

0.00

220.

0021

1±

0.00

004

0.01

45±

0.00

0713

.61

±0.

2514

.59

±0.

7013

.60

±0.

259.

5

ASH

5-41

light

bro

wni

sh0.

0472

±0.

0020

0.00

250

±0.

0000

50.

0163

±0.

0008

16.1

0±

0.33

16.3

9±

0.78

16.1

0±

0.33

0.7

ASH

5-42

light

bro

wni

sh0.

0487

±0.

0022

0.00

244

±0.

0000

50.

0164

±0.

0008

15.7

0±

0.32

16.4

9±

0.81

15.7

0±

0.32

4.6

ASH

5-43

light

bro

wni

sh0.

0544

±0.

0031

0.00

207

±0.

0000

50.

0155

±0.

0009

13.3

0±

0.29

15.6

1±

0.95

Dis

cord

ant

ASH

5-44

light

bro

wni

sh0.

0496

±0.

0032

0.00

199

±0.

0000

50.

0136

±0.

0009

12.7

9±

0.29

13.6

9±

0.94

12.7

8±

0.29

4.2

ASH

5-45

light

bro

wni

sh0.

4063

±0.

0091

0.00

363

±0.

0000

70.

2035

±0.

0061

23.3

7±

0.46

188.

1±

5.6

Dis

cord

ant

ASH

5-46

light

bro

wni

sh0.

7321

±0.

0147

0.02

416

±0.

0004

72.

4385

±0.

0681

153.

9±

3.0

1254

±35

Dis

cord

ant

ASH

5-47

light

bro

wni

sh0.

0431

±0.

0028

0.00

208

±0.

0000

50.

0123

±0.

0008

13.3

9±

0.30

12.4

6±

0.85

13.3

8±

0.30

5.4

ASH

5-48

light

bro

wni

sh0.

0644

±0.

0031

0.00

220

±0.

0000

50.

0196

±0.

0010

14.1

7±

0.31

19.6

6±

1.04

Dis

cord

ant

ASH

5-49

light

bro

wni

sh0.

0448

±0.

0049

0.00

205

±0.

0000

60.

0127

±0.

0014

13.2

1±

0.37

12.7

8±

1.46

13.2

1±

0.37

0.38

ASH

5-50

light

bro

wni

sh0.

0553

±0.

0056

0.00

195

±0.

0000

50.

0149

±0.

0016

12.5

8±

0.30

15.0

0±

1.57

12.5

6±

0.29

10.1

ASH

5-51

light

bro

wni

sh0.

1079

±0.

0031

0.00

349

±0.

0000

60.

0519

±0.

0017

22.4

5±

0.37

51.3

6±

1.70

Dis

cord

ant

ASH

5-52

light

bro

wni

sh0.

3605

±0.

0098

0.00

340

±0.

0000

60.

1689

±0.

0055

21.8

8±

0.40

158.

5±

5.2

Dis

cord

ant

ASH

5-53

light

bro

wni

sh0.

0975

±0.

0039

0.00

217

±0.

0000

40.

0291

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0013

13.9

4±

0.25

29.1

5±

1.29

Dis

cord

ant

ASH

5-54

light

bro

wni

sh0.

0467

±0.

0020

0.00

243

±0.

0000

40.

0157

±0.

0007

15.6

7±

0.27

15.7

9±

0.72

15.6

7±

0.27

0.15

AS

H5-

55da

rk b

row

nish

0.45

40±

0.00

920.

0037

0±

0.00

006

0.23

15±

0.00

5923

.80

±0.

3721

1.5

±5.

4D

isco

rdan

t

AS

H5-

56da

rk b

row

nish

0.47

54±

0.01

060.

0045

5±

0.00

008

0.29

83±

0.00

8329

.27

±0.

4926

5.1

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4D

isco

rdan

t

AS

H5-

57da

rk b

row

nish

0.36

39±

0.00

880.

0034

0±

0.00

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0.17

04±

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5121

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3715

9.7

±4.

8D

isco

rdan

t

AS

H5-

58da

rk b

row

nish

0.60

26±

0.01

210.

0121

0±

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019

1.00

56±

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5777

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2270

6.6

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.1D

isco

rdan

t

AS

H54

-1re

ddis

h0.

0548

±0.

0070

0.00

193

±0.

0000

80.

0146

±0.

0020

12.4

6±

0.54

14.7

3±

1.99

12.4

2±

0.54

5.9

AS

H54

-2re

ddis

h0.

1067

±0.

0095

0.00

201

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0000

90.

0296

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0029

12.9

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29.5

7±

2.94

Dis

cord

ant

AS

H54

-3re

ddis

h0.

0499

±0.

0060

0.00

201

±0.

0000

90.

0138

±0.

0018

12.9

3±

0.55

13.9

2±

1.77

12.9

2±

0.55

1.4

AS

H54

-4re

ddis

h0.

0502

±0.

0119

0.00

194

±0.

0000

90.

0134

±0.

0033

12.4

9±

0.61

13.5

5±

3.29

12.4

9±

0.61

0.44

AS

H54

-5re

ddis

h0.

0459

±0.

0067

0.00

202

±0.

0000

90.

0128

±0.

0019

12.9

8±

0.57

12.8

7±

1.96

12.9

8±

0.57

0.01

6

AS

H54

-6re

ddis

h0.

0420

±0.

0068

0.00

192

±0.

0000

80.

0111

±0.

0019

12.4

0±

0.54

11.2

5±

1.90

12.3

9±

0.54

1.6

AS

H54

-7re

ddis

h0.

1574

±0.

0094

0.00

248

±0.

0001

10.

0537

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0039

15.9

4±

0.68

53.1

1±

3.90

Dis

cord

ant

AS

H54

-8re

ddis

h0.

0456

±0.

0038

0.00

203

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0000

80.

0128

±0.

0012

13.1

0±

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12.9

0±

1.20

13.1

0±

0.53

0.14

AS

H54

-9re

ddis

h0.

0482

±0.

0029

0.00

197

±0.

0000

80.

0131

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0009

12.6

8±

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13.2

1±

0.94

12.6

7±

0.50

1.8

AS

H54

-10

redd

ish

0.04

66±

0.00

420.

0020

2±

0.00

005

0.01

30±

0.00

1213

.03

±0.

3313

.12

±1.

2313

.03

±0.

330.

023

AS

H54

-11

redd

ish

0.04

51±

0.00

400.

0019

9±

0.00

005

0.01

24±

0.00

1112

.81

±0.

3212

.48

±1.

1512

.81

±0.

320.

34

AS

H54

-12

redd

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0.04

42±

0.00

530.

0019

7±

0.00

005

0.01

20±

0.00

1512

.65

±0.

3512

.10

±1.

4812

.65

±0.

350.

6

AS

H54

-13

redd

ish

0.04

57±

0.00

270.

0020

8±

0.00

005

0.01

31±

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0813

.37

±0.

3013

.19

±0.

8413

.37

±0.

300.

21

AS

H54

-14

redd

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0.05

14±

0.00

490.

0019

8±

0.00

005

0.01

40±

0.00

1412

.75

±0.

3314

.16

±1.

4012

.74

±0.

334.

5

AS

H54

-15

redd

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0.05

21±

0.00

460.

0020

5±

0.00

005

0.01

47±

0.00

1413

.17

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3414

.80

±1.

3613

.16

±0.

346.

3

AS

H54

-16

redd

ish

0.04

82±

0.00

350.

0020

4±

0.00

005

0.01

36±

0.00

1013

.13

±0.

3113

.67

±1.

0613

.12

±0.

311.

18


Ana

lyti

cal s

pot

Tin

t of

crys

tal

207 P

b/20

6 Pb

(2σ )

206 P

b/23

8 U (

2σ)

207 P

b/23

5 U (

2 σ)

238 U

−206 P

b ag

e (M

a)

(2σ)

235 U

−207 P

b ag

e (M

a)

(2σ )

Con

cord

ia A

ge (

Ma)

(2σ )

MS

WD

AS

H54

-17

redd

ish

0.05

35±

0.00

870.

0019

4±

0.00

006

0.01

43±

0.00

2412

.49

±0.

4114

.42

±2.

4012

.48

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412.

7

AS

H54

-18

redd

ish

0.07

76±

0.00

600.

0020

5±

0.00

005

0.02

20±

0.00

1813

.22

±0.

3522

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±1.

81D

isco

rdan

t

AS

H54

-19

redd

ish

0.73

03±

0.03

040.

0133

4±

0.00

039

1.34

36±

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8185

.46

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4786

4.8

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.8D

isco

rdan

t

AS

H54

-20

redd

ish

0.61

20±

0.01

580.

0064

6±

0.00

012

0.54

55±

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7541

.54

±0.

7944

2.0

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isco

rdan

t

AS

H54

-21

redd

ish

0.05

04±

0.00

510.

0019

6±

0.00

005

0.01

36±

0.00

1412

.60

±0.

2913

.72

±1.

4212

.60

±0.

292.

6

AS

H54

-22

redd

ish

0.05

04±

0.00

450.

0020

0±

0.00

004

0.01

39±

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1312

.88

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2814

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±1.

3012

.87

±0.

283.

3

ASH

54-2

3lig

ht b

row

nish

0.05

18±

0.00

240.

0020

7±

0.00

004

0.01

48±

0.00

0713

.34

±0.

2314

.91

±0.

73D

isco

rdan

t

ASH

54-2

4lig

ht b

row

nish

0.04

85±

0.00

220.

0021

0±

0.00

004

0.01

41±

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0713

.56

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2314

.19

±0.

6913

.55

±0.

234

ASH

54-2

5lig

ht b

row

nish

0.04

99±

0.00

250.

0019

8±

0.00

003

0.01

36±

0.00

0712

.75

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2213

.73

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7212

.74

±0.

228.

5

ASH

54-2

6lig

ht b

row

nish

0.04

55±

0.00

340.

0019

6±

0.00

004

0.01

23±

0.00

0912

.62

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2512

.40

±0.

9512

.62

±0.

250.

23

ASH

54-2

7lig

ht b

row

nish

0.05

57±

0.00

450.

0019

8±

0.00

004

0.01

52±

0.00

1312

.74

±0.

2715

.31

±1.

29D

isco

rdan

t

ASH

54-2

8lig

ht b

row

nish

0.04

44±

0.00

220.

0020

6±

0.00

006

0.01

26±

0.00

0713

.27

±0.

4112

.72

±0.

7513

.26

±0.

413

ASH

54-2

9lig

ht b

row

nish

0.41

38±

0.00

980.

0041

0±

0.00

013

0.23

42±

0.00

9126

.41

±0.

8221

3.7

±8.

3D

isco

rdan

t

ASH

54-3

0lig

ht b

row

nish

0.04

42±

0.00

300.

0020

0±

0.00

006

0.01

22±

0.00

0912

.88

±0.

4112

.30

±0.

9212

.88

±0.

412

ASH

54-3

1lig

ht b

row

nish

0.05

09±

0.00

340.

0019

3±

0.00

006

0.01

36±

0.00

1012

.46

±0.

4013

.68

±1.

0112

.43

±0.

407.

3

ASH

54-3

2lig

ht b

row

nish

0.13

16±

0.00

550.

0022

0±

0.00

007

0.04

00±

0.00

2114

.20

±0.

4639

.82

±2.

09D

isco

rdan

t

ASH

54-3

3lig

ht b

row

nish

0.13

39±

0.00

420.

0022

4±

0.00

007

0.04

13±

0.00

1814

.41

±0.

4441

.11

±1.

80D

isco

rdan

t

ASH

54-3

4lig

ht b

row

nish

0.04

82±

0.00

330.

0020

3±

0.00

007

0.01

35±

0.00

1013

.10

±0.

4313

.64

±1.

0413

.09

±0.

431.

3

ASH

54-3

5lig

ht b

row

nish

0.05

75±

0.00

320.

0020

7±

0.00

007

0.01

64±

0.00

1113

.32

±0.

4216

.50

±1.

06D

isco

rdan

t

ASH

54-3

6lig

ht b

row

nish

0.07

02±

0.00

230.

0028

2±

0.00

009

0.02

73±

0.00

1218

.15

±0.

5527

.35

±1.

21D

isco

rdan

t

ASH

54-3

7lig

ht b

row

nish

0.43

03±

0.01

130.

0037

0±

0.00

010

0.21

98±

0.00

8223

.84

±0.

6420

1.7

±7.

5D

isco

rdan

t

ASH

54-3

8lig

ht b

row

nish

0.04

69±

0.00

410.

0020

1±

0.00

006

0.01

30±

0.00

1212

.94

±0.

3813

.10

±1.

2212

.94

±0.

380.

078

ASH

54-3

9lig

ht b

row

nish

0.04

10±

0.00

350.

0019

9±

0.00

006

0.01

12±

0.00

1012

.81

±0.

3711

.35

±1.

0112

.78

±0.

369.

4

ASH

54-4

0lig

ht b

row

nish

0.05

05±

0.00

340.

0020

5±

0.00

006

0.01

43±

0.00

1013

.19

±0.

3714

.37

±1.

0513

.18

±0.

376

ASH

54-4

1lig

ht b

row

nish

0.09

03±

0.00

360.

0021

6±

0.00

006

0.02

69±

0.00

1313

.89

±0.

3726

.92

±1.

28D

isco

rdan

t

ASH

54-4

2lig

ht b

row

nish

0.04

57±

0.00

340.

0020

5±

0.00

006

0.01

29±

0.00

1013

.18

±0.

3713

.01

±1.

0413

.18

±0.

370.

12

ASH

54-4

3lig

ht b

row

nish

0.18

05±

0.00

550.

0024

9±

0.00

007

0.06

19±

0.00

2516

.01

±0.

4260

.99

±2.

47D

isco

rdan

t

ASH

54-4

4lig

ht b

row

nish

0.59

39±

0.01

680.

0065

6±

0.00

018

0.53

71±

0.02

1342

.14

±1.

1843

6.5

±17

.3D

isco

rdan

t

ASH

54-4

5lig

ht b

row

nish

0.05

61±

0.00

230.

0022

3±

0.00

006

0.01

73±

0.00

0814

.39

±0.

3817

.41

±0.

85D

isco

rdan

t

ASH

54-4

6lig

ht b

row

nish

0.04

62±

0.00

240.

0020

9±

0.00

006

0.01

33±

0.00

0813

.46

±0.

3913

.44

±0.

7913

.46

±0.

390.

0037

AS

H54

-47

dark

bro

wni

sh0.

0681

±0.

0050

0.00

210

±0.

0000

70.

0197

±0.

0016

13.5

0±

0.43

19.7

9±

1.57

Dis

cord

ant

AS

H54

-48

dark

bro

wni

sh0.

1628

±0.

0064

0.00

226

±0.

0000

70.

0506

±0.

0025

14.5

2±

0.43

50.1

3±

2.47

Dis

cord

ant

AS

H54

-49

dark

bro

wni

sh0.

0441

±0.

0043

0.00

206

±0.

0000

70.

0125

±0.

0013

13.2

9±

0.43

12.6

6±

1.29

13.2

9±

0.43

1.1

AS

H54

-50

dark

bro

wni

sh0.

0507

±0.

0043

0.00

203

±0.

0000

60.

0142

±0.

0013

13.0

9±

0.42

14.3

3±

1.29

13.0

8±

0.42

4.3

AS

H54

-51

dark

bro

wni

sh0.

0913

±0.

0043

0.00

213

±0.

0000

60.

0268

±0.

0015

13.7

3±

0.41

26.9

0±

1.49

Dis

cord

ant

AS

H54

-52

dark

bro

wni

sh0.

0557

±0.

0029

0.00

201

±0.

0000

60.

0154

±0.

0009

12.9

3±

0.38

15.5

4±

0.94

Dis

cord

ant

u–pb zircon ages of syenitic and granitic rocks in the ashizuri igneous...

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