1237

The Canndian M ine ralo gis tYol. 35, pp.1237 -1247 (1997)

A COMPILATION OF THERMOBAROMETRIC DATA FROM THE METASEDIMENTARYBELT OF THE GRENVILLE PROVINCE. ONTARIO AND NEW YORK STATE

MARGARET M. STREEPEYI, ERIC J. ESSENE AND BEN A. VAN DER PLUIJM

Departm.ent of Geological Sciences, 2534 C.C. Ltxle Bailding, University of Michigan, Ann Arbon Michigan 48109, U.S.A.

ABSTRACT

A new compilation of regional metamolphic temperature-pressure data in the Metasedjment ry Belt (MB) of the GrenvilleOrogen, as exposed in Ontario and New York, shows the effect of major zones of ductile shear on metamorphic gradients. Inaddition to other thermometers, available data from gamet-biotite and two-feldspar thermometers were recalculated with asingle calibration to permit comparisons among different fleld areas. Temperatues in the MB range from <500"C near Madoc,Ontario, in the Elzevir domain, and are in excess of 700oC in the western Gneiss Belt (GB) a:rd the eastem Frontenac domain.Offsets in temperatues are observed across the Metasedimentary Belt Boundary Znne (MBBZ), the Sharbot Lake Shear Zone(SLSZ), and perhaps the Carthage{olton Shear Zone (CCSZ). hessures range from <6 kbar (<600 MPa) in the Elzevir domainnear Madoc, Ontario to 8 kbar (800 MPa) il the westernmost part of the Frontenac domain. There is a l-2 kbar (10G-200 MPa)discontinuity in pressure aqoss the Metasedimentary Belt Boundary Znte (|{BBZ) and at the Robertson Lake @LSZ) andSharbot Lake (SISZ) shear zones. However, some shear zones in the MB predate the peak of metamorphism, and do not seemto offset metamorphic gradients in the field (e.g., the Mooroton shear zone). Comparing temperatures and pressures across theseboundaries requires knowledge of the timing of peak metamorphism. Geochronological studies ildicate that some boundariesjuxtapose domains that do not have the same metamorphic histories. In the Grenville Orogen, such integrated data suggest thatzones of ductile shear variably represent tectonically active terrale boundaries and inEa-terrane zones of displacement.

Keywords: Grenville Orogen, Metasedimentary Belt, thermobarometry, shear zones, Ontario, New York.

Sotvnvans

Une nouvelle compilation de donn6es de pression et de temp6rature du mdtamorphisme rdgional dans la ceinturem6tasddimentaire de la province orog6nique du Grenville, telle qu'expos6e en Ontario et dans l'6tat de New York, montre leseffets des zones majeures de cisaillement ductile sur la distribution des gradients m6tamorphiques. En plus des autresthermomdtres, les donn&s disponibles d propos de l'6quilibre grenat - biotite et du g6othermomdtre fond6 sur la coexistencede deux feldspaths ont 6t6 recalcul6es avec un seul calibrage afin de permettre des comparaisons d'une r6gion d I'autre. Lestem$ratues dans la ceinnue m6tas6dimentaire vont de moins de 5@"C, prds de Madoc, en Ontario, dans le domaine d'Elzevir,d au deld de 700oC dans la ceinture gneissique dans le secteur ouest et dans le domaine de Frontenac, d I'est. Des d6placementsdans la temp€rature sont dvidents en traversant la zone limitrophe de la ceinture m€tas6dimentaire, la zone de cisaillement dulac Sharbot, et possiblement la zone de cisaillement de Carthage - Colton. Les valeurs de pression varient entre moins de 6 kbar(<600 MPa) dans le domaine d'Elzevir, prds de Madoc, jusqu'd 8 kbar (800 MPa) d,ns la partie la plus occidentale du domainede Frontenac. Il y a une discontinuit6 de I d,2 kbar (100-200 MPa) en traversant la zone limitrophe de la ceinturemdtas6dimentaire et la zone de cisaillement du lac Sharbot. Toutefois, certaiaes des zones de cisaillement (la zone de Mooroton,par exemple) pr6cddent le paroxysme m6tamorphique, et ne semblent donc pas ddplacer les gradients m6tamolphiques sur leterrain. Une comparaison des temp6ratures et des pressions de part et d'autre de ces discontinuitEs n6cessite une connaissancede l'6ge du mdtamorphisme. Les dtudes g6ochronologiques montrent que le long de certaines zones limitrophes, il y a eujuxtaposition de domaines qui ne partagent pas la mOme 6volution m6tamorphique. Dans la province du Grenville, de tellesdonn6es int6gr6es font penser que les zones de cisaillement ductile repr6sentent soit des bordures de socles tectoniquementactifs, soit des zones de d6placement inter-socle.

(Traduit par la R6daction)

Mots-cl6s: province du Grenville, ceinture m6tasddimentaire, thermobarom6trie, zones de cisaillement, Ontario, New York.

INTRoDUC"iloN

The Grenville Orogen of New York, Ontario,and western Quebec comprises three separatenortheast-trending belts: the Gneiss Belt (GB),

structurally overlain by the Metasedimentary Belt([tIB) and the Granulite Terrane (GT) (Wynne-EdwardsL972, Davidson 1984a, 1986; Fig. 1). These belts aredistinct lithotectonic packages (Wynne-Edwards L97 2)separated by major shear zones (Davidson 1984a,

r E-mail address: mstreepe@umich.edu

t238 TIIE CANADIAN MINERALOGIST

Frc. 1. Regional subdivision of domains and shear zones in the central portion of the Grenville Orogen of southern Ontario andnorthem New York. MB: Metasedimentary Belt, GB: Gneiss Belt GT: Granulite Terrane,lvIBBZ: Metasedimentary BeltBoundary Zone,BSZ: Bancroft Shear Zone, MSZ: Mooroton Shear Zone, RLSZ: Robertson Lake Shear Zone, SLSZ:Sharbot Lake Shear Znte, CCSZ: Carthagetolton Shear Zone. Light gray areas show approximate location of Paleozoiccover. Shear zones zre not continued into the Quebec portion of the Grenville. Inset shorvs generalized subdivision of theGrenville Province, with study area outlined.

1995). The Metasedimentary Belt includes severaldomains, identified on the basis of their individuallithological and geophysical characteristics, whoseboundaries also are the loci of ductile shear zones(Culshaw et aI.1983, Davidson 1984b,1986, L995,Hanmer 1988, Easton L989, 1992a, b; Fig. 1). Inaddition to contractional tectonics, several recentstudies have shown that late extension characterizessome of the major shear zones separating domains ofthe MB. These include the Bancroft shear zone @SZ)between the Bancroft and Elzevir domains, theRobertson Lake shear zone (RLSZ) befween theMazinaw and Sharbot Lake domains, and possibly theCarthage-{olton shear zone (CCSZ), between tleAdirondack t owlands and the Adirondack Highlandsof the GT (Hanmsl 1988, van der Pluijm & Carlson1989, Mezger et al. l99lb, 1992, Davidson 1995,Busch & van der Pluijm 1996).

The Metasedimentary Belt is characterized bymarble, metasedimenta4r, and metavolcanic rocks inwhich metamorphic grade ranges from the uppergreenschist to the granulite facies (e.9., Carmichael et

al. 1978, Davidson 1984b, Anovitz & Essene 1990).Various thermobarometers have been applied to rocksthroughout the region in attempts to constrain thetemperature - pressure conditions of metamorphism.The Grenville Province is ideally suited forthermobarometric studies as a result of tle many typesof metasedimentary and meta-igneous rocks that arepresent. However, metamorphic P-T gtadients havepreviously been drawn across tle region beforeconstraints on the timing of metamorphism weredeveloped (e.9., Bohlen et al. 1985, Anovitz & Essene1990). Since these shear zones co[rmonly separaterocks with different metamorphic and cooling ages(Mezger et aI. l99la, b, van der Pluijm er al. 1994),pressures and temperatures calculated for individualdomains are not necessarily representative of a singlemefamsrphis event and may not correlate across theregion. The purpose ofthis paper is to recompile recentthermobarometric data and generate new metamorphicmaps, taking into account possible offsets across shearzones in the MB. In addition, results of this study pointout discrepancies and weaknesses in quantitative

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;ii' :.::: ii;l:;l::;::;,;i,.,lil:I,:il,ir:r,iii:ri:r:lir:;ii:rjf;i!r\.lii:;li::ilti:ii''

7 e v - r . tAdirondack Gc'.'irl'

pressure and temperature dat " and thus point to possi-bilities for future tlermobarometric work in the MB.

Srnucnrner Ssrm\c

The Grenvillian orogenic cycle (Moore &Thompson 1980) comprises several distinctphases ofdeformation in the area of the Metasedimentary Beltand the Gneiss Belt. RecentU-Pb studies of zircon andtitanite constr'ein the timing of two deformationalevents for the MBBZ in Ontario: one thrusting event atca. ll9o Ma, and a second episode of thrusting asyoung as 1060 Ma (van Breemen & Hanmer 1986,Mezger et al. L99Lb, McEachern & van Breemen1993). The early phase of deformation has been inter-preted as ttre closure of a marginal basin, wherein theElzevir terrane was juxtaposed against the southeasternmargin of Laurentia (the present-day GB; Davidson etaI. L982, Culshaw et al. 1983, Hanmer & McEachern1992,McEachern & van Breemen 1993). The tectonicframework of the younger episode of deformation isless well constrained, but is generally consideredto have been produced by a collision between theGrenville Province (including the AdirondackHighlands) and an unspecified continent to ttresoutheast (Windley 1986, Hanmer & McEachern 1992,McEachern & van Breemen 1993). Direction ofdisplacement along these early tbrusts is predominantlyto the northwest, as defined by shear-sense indicatorsand widespread, gently plunging southeast lineations(e.9., Davidson 1984b, Hanmer 1988).

Structural and geochronological studies havedefined a later extensional component to some of theshear zones in the MB. Rocks in the southeast-dippingBSZ contain shear-sense indicators implying a nonnalsense of movement (Carlson et al. 1990). Althoughages of peak metamorphism on both sides of the BSZare similar,4oAFrAr analyses of hornblende yield agesof lO2I-1026 Ma immediately to the east of the BSZand 959-989 Ma immediately to the west of the shearzone (Cosca et al. 1995), indicating ajuxtaposition ofthe structurally higher Elzevr domain against theBancroft domain (Mezger et aI. I99lb). Structuralstudies in the soutleast-dipping RLSZ yield myloniticFanites with S{ structures and mica fish, as well asbrittle structures, that all indicate a normal (top down tothe east) sense ofdisplacement (Easton 1989, Busch &van der Pluijm 1996).

The U-Pb ages related to peak metamorphism are atleast 100 m.y. older in the Sharbot Lake domain than inthe adjacent Mazinaw domain; +oAileAr cooling agesofhornblende and biotite also reflect this offset (Coscaet al. 1992,1995, Corfu & Easton L995,Busch et aI.1996a). A U-Pb study of rocks along the CCSZ showsthat the Adirondack Lowlands cooled through theclosure temperature of tir2nite (600-650oC: Mezger etal. I99la) between 1156 and 1103 Ma whereas titanirein the adjoining Adirondack Highlands (GT) yields

t239

ages of 1050-982 Ma. This indicates a large differencein the age of peak regional metamorphism on eitherside of the CCSZ Mezeer et al. I99lb, 1992).

Colerarrou or Dera

There have been numerous thermobarometricstudies across the Metasedimentary Belt. Data fromrecent studies at the University of Michigan (Rathmell1993, Busch et al. 1996b, Cureton 1997), comple-mented by data ftom the literature @wert 1977 , Lonker1980, Bohlen et aI. 1980, Edwards & Essene 1988,Anovitz & Essene 1990), were compiled to generate aregional view of temperature-pressure conditionsfor metamorphism in the MB. Figure 2 shows samplelocations, andTable 1 lists the corresponding thermo-metric and barometric results used in this compilation.Mineral analyses used for these calculations are availablefrom the frst author. Ttvo-feldspar temperature datawere checked for consistency arong different studiesusing the computer program SOLVCALC (Wen &Nekvasil 1994), with the activity model of Fubrman& Lindsey (1988). Because several calibrations havebeen used in the literature 16 elrein garnet-biotitetemperafures for the MB, ttrese temperatures wereuniformly recalculated with the calibration ofPatiflo Douce et al. (1993) using an unpublishedtlermobarometry pro$am (M.J. Kohn & F.S. Spear1996, Version 2.0) to maintain intemal consistency in thedatabase. Recalculated temperatures were generallywithin t50'C of the ternperatures reported in theliterature.

Pressures reported from the literature, mostly fromrecent studies at the University of Michigan, weredirectly ssmFiled and averaged without furthercomputation. Barometers used include garnet -amphibole - plagioclase - quattz, ganet-plagioclase- ferrosilite - quartz (GAFS: Bohlen et al. 1983b),garnet - plagioclase - diopside - quartz (GADS:Newton & Perkins 1982, Moecher et al. 1988), garnet- aluminosilicate - quartz - plagioclase (GASP: Koziol& Newton 1988), garnet - rutile - ilmenite -plagioclase - quaxtz (GRIPS: Bohlen & Liotta 1986),and garnet - rutile - ilmenite - aluminosilicate(GRAIL: Bohlen et al. 1983a).

Contours were drawn on the basis of an analysis ofcompiled data, combined with additional informationfrom Anovitz & Essene (1990). Owing to widespreadresetting, the calcite-dolomite thermometer in somecases yielded lemperatures on the order of 300'C lowerthan other ttrermometers from the same area. Theanomalously low calcite-dolomite temperaturesreported by Ewert (1977) and Rathmell (1993) areconsidered to represent retrograde resetting after peakmetamorphism and were generally disregarded whendrawing contours. Tbo-feldspar, calcite-graphite, andgarnet exchange thermometers (garnet-biotite, garnet-

THERMOBAROMETRIC DATA, METASEDIMENTARY BELT. GREI{VILLE PROVINCE

THE CANADIAN MINERALOGIST

Rc. 2. Locations and sources of compiled temperature (a) and pressure (b) data. Thermometers used include gamet - biotite,garnet - homblende, garnet - orthopyroxene, garnet - clinopyroxene, calcite - dolomite, calcite - graphite, and plagioclase- potassium feldspar. Barometers are based on the assemblages gamet - amphibole - plagioclase, garnet - plagioclase -

diopiide-quartz,gamet-plagioclase-fenosilite-quartz,garnet-aluminosilicate-quartz-plagioclase,gamet-rutile- ilmenite - plagioclase - quartz, and garnet - rutile - ilmenite - aluminosilicate.

THERMOBAROMETRIC DATA, MEIASEDIMENIARY BELT. GRENIVILLE PROVINCE

TABLE I. THERMOBAROMETRIC DATA METASEDIMENTARY BELT OF TI]E GRENVILI.E PROVINCEONTARIO AND NEW YORK STATE

r24l

UTM mrdirds Tqrpea!re ("C) md Prffi (kb{) UTMmrdinas T@pqeB("C)udPruq(kbq)

p@83c28 17T50495 3l t0Fn83c36 17T50460 2'152rq83al3 1T150259 3450m83c15 1T150278 3419m83cl7 ITI5O312 3399reo83c28 1T150329 3018ra83c30 17T504@ 3314rqE3c50 LT|5O34 3150but85a5 l7T50ll4 6600hjtlssl2 lTfSmlE 65s5dm8579a lTtsvn1 6720MrNto l tTt49826 6902ALG83C 3 17T50484 7t20ALG83C6tr 17T50522 70so

AICE3C 13 17T50508 6969ALG83C 14 17T50s08 6969Ar.G83C 15 17T50502 6950Ar,G 83C 20 17T50458 6825ALCra3C26 lTl5O332 6700HAL 83 C 7 17T50298 665rHAL 83 C E tTt50226 6608HAL&3C24 tT ts0 tn .6y2HAL E3 C 25 trt50125 6734HAL83 C38 17T4966 6ty2HALr3 C 75 ITI49E94 6698HAL 84849 t7T50048 6502AITGE5A2' lTl5O522 ?A9oALG85 A6 17T50455 6810HUT 85 A 4 tTt5t235 6535

HUT Es A 5 t7T50l 14 6600mTADPM 17T50l,lO 6il4DMM80 ISEB 17T50926 672DM 85 79A 17T50230 6720DMC854002 17T50450 6780DMC 8551 03 171504t4 6910HALA3C50 \TI4W)2 730s

Atr0itz & Ese (1990)

Bobl@ eral (19E0)

Glt-Cpxr 750 r 20, PI-KB: 590Pl-Kfr: 630Pl-K&:700Pl-Kf8:780Pl-K6:650Pl-Kft: 650Pt K&:7@PI-KB:730PI-KS:720PI-K.B:740ft-Opx: 830 f, 40, Gffpx: t00 + 20Pl-K&:720PI-Kft:670Gt-Opx: 710, C'rt{px: 790,GAFS: <10.2Gt-Opx: 79, Pl-Kft: 650, GAFS: 9.1Grt*Opx: 850, Gft{px: 790, GAFS: 9Gttlpx:720Pl-Kfr:670Grr-Opx: 750, GAFS: 10.2Pl-Kfr: 610GI[-Cpx: 740, Pl K6: 740, GRIPS: 10.5Grt-Opx:75Q Gn{px 790, GAFS:9.7Grt-Opx: 790, Gntpx: 730, GAFS: 9.1GASP: 7 2PI-K&:590Gn Op* 750, GAFS: 10.4ft Opr 850, Crt-Cpxr 710, GAFS:8.EGASP:9, GRIPS: X.3, GRAIL: >2.9fr Opx:680, Grt-CpK 71qGAFS: I0 3PI-KB: 720Grt-Opr 670, GAFS: l0ft Opx t30, Grt-Cpx: 810, GAFS: I Ift-Opx: 830, Grt-Cpr 800, GAFS: t.6G!t-Opx: 7@, Grt-Cpx: 750, GAFS: 9.7Gn-Opx: E30, Grt{px:750, GAFS:9Pl-Kfs:730

ADl6593 t8T49770 3470

MS3E93 18T497t5 33E0

c;n€Lon et al. (1997)

Ewelt (1977)

Gd-Bt: 640, Gft-Hbl:510, GAFS: >5.8,GASP: <9.2, GRJPS: <.2Gn*Bt:,160, GAFS: >4.5, GASP: <.7,GRIPS: <5.5Grr-Bt: 470, GAFS: >2.5, GASP: <4.0,GRIPS: <5 IGfl-Bt:540Grt-Bt: 700, GAFS: >5.7, GASP: <13.9.GRIPS: <9.6Gd-Bt: 540, Gfi-Hbl: 530, GAFS: >4.7,GASP: <9.1. GRIPS: <7.7Gn-Bt: 560, GAFS: >2.3, GASP: <4.0,GRIPS: <5.1Grt-Bti 600, GAFS: >5.5, GASP: €.2GRIPS: <.1ft-Bt: 600, GAFS: >3.5, GASP: <5.1,GRIPS: <5.6Grt-Bt: 690, GAFS: >5, GASP: <5.2,GRIPS: <6.1Grl-Br 580, GAFS: >3.7, GASP: <4.7,GRIPS: <6.1

QB8993 18T49385

92-7 t8T49670cll3393 t8T49730

332.43325

AT8?93 1tT49355 3145

a-7393 18T49640 3270

cl-t493 18T49665 3 5

c.I-5793 1ET49685 3280

sKl593 18T49680 3250

8C3293 18T49605 3300

LB-t 1tT48850 47tOLB-2 18T48815 4620lB4 1ET48820 4630LB-5 18T48825 4655GVR-136 18T49065 4825GVR52 ttT4y245 4955GVR-64 1tT49220 4955

AT3693K47593

PDl4 18T49370 50tscT-t7 18T49310 4920RS-14 IET49Z95 4985RSro 18T4y290 489sR$12 18T4935 4895RSLI3 t8T4E295 4975R$33 tAT49270 4970RS-34 t8T4E270 4975cT-10 r8T492@ 4940RS-73 18T4E225 4845RS-IE 18T492@ 4815GVR-s 18T49050 47t0RS-2 t8T4y2t5 4870GVR-46 lET49l45 47E0GVR-30 l8T49lls 4n5GVR-I2 18T49050 4720ANT-99 I8T4E9E5 4500ANI-88 l8T,rE880 4614rB-145 18T48820 4&5

PI-KB:760, GASP:8Pl-Kts:720, GASP:6.8GASP: >5 7PI-KB: 680GASP:6.7GASP:7.5PI-Kft:760, GASP: <10.4Pl-Kft:740GASP:6.7GASP: >3.9GASP: >5.2GASP:7GASP:6.6GASP:7.2GASP: <9GASP:7GASP:5.4GASP: <5.7Pl-Kft:690

18T49360 3155 Grt-Bt:620, GAIS: >3, GASP: <5.818T49445 329o Crt-Bt: 540, Grt-Ilbl: 590, GAFS: >5.5,

GASP: <10.9. GRIPS: <9.3su17593 18T49340 3?30 Grt{rd: 570, GAIS: X.5, GASP: q.2,

GRIPS: <.1

FdMds&Es@(1988)

Pl Kts:690Pl-Kb:690Pl-K&:690PI-KB:740PI-K6:650PI-KB:630PI-Kfr: 6s0

Bwberzl' (1996b)

23726524068t73170

841 t o

6026Lgt52242J :

26827044l,lot37

18T4757460 372380

18T4932900 35637018T4937950 3390701tT4939t50 34t420lBT4yt7050 34432018T4954610 3546301ET4955620 354610

18T4959455 3572901aT4959r80 3533701rT496147s 35EE9st8T4970E75 3728m1ET500390 37035018T5010675 37239018T5015650 398910IrT4032090 33E550ItT49U770 449pt0ItT4958900 364140lET49r93l0 366E@IrT4989250 36621018T4955575 3447@

Grt-Opx 75O, Grt-Cpx: 780,Gn-Arp-Pl: E.9, GAIS: E.2,GADS:7.8Gfl-Cprc 730, GADS: ECrt{pxr t20, GADS:9.tGrt-Hbl:620Gn-Hbl:630ft-Bt: 830, Grt-Opx: 720, GAFS: 6Grt-Bt: 560, Cm-Hbl: 520,Grt-AEp-Pl:5Grt-Ilbl: 630, Gn-Arp-PI: EGlt-Br 650Gn-Amp--Pl:7.7Grt-Hbl: 560, Grt-AEp-Pt 7. IGn-IIbl: 640Grt-Hbl: 570, Gd-AmpPl: 8.3Grt-IIbl: 750, Grt-ArpPt 8.6Crr[rBt: 620Gn-Hbl:590Grr-Hbl: 5E0ft-Bt:660Cn-IIbl: 5E0, Grt-Aap-Pl: 7. IGrt-AEp-Pl:5.5

92@35 l8T5@30 3945895003 lsTs@35 3900857634 r8T49@ 386s0 616'14 18T49685 N4s02800+3 18T50025 N)n095567 18T49575 409594E62t 18T49615 3945

GN-ll-7GA t8T4y250 414nGN-I&76-C tBT4yz25 4o6sWP-62-7GA 1ET49350 3850wP-88-77-A 18T49305 3905wP-l12-774 18T49345 3955GN-165-77-A 18T4S270 4120

PI-KS:670ft{rd:720, PI-KB:700PI-KS:690Pl-K&:670Grt Crd: 73q fl-K6: 690Gntrd: 680, PI-KB: 680

C€.|-Dol: 470Cal-Dol: 390Cal-Dol:320Cal-Dol:290Cal-Dol: 4{10Cal-Dol: 3 l0C€l-Dol:260

Iplkq (19E0)

1242 THEcANADIANMTNERALocIST

TABLE 1. THERMOBAROMETRIC DATA METASEDIMENTARY BELT OF THE GRENVILLE PROVINCEONTARIO A]rlD NEW YORK STATE (comirued)

UTMffidind€ Teopomm('QmdPrM(kbd) UTM @rdid6 T€dpqer6 ('C) @d Pr6sB (klE)

BB9ll59 t8T7g242rBB9ll49 18T709385BB9l148 18fi09384B89il43 18T765345BB9l45 18T840339BB9l4 l8T&r8335G9134 l8T9t52J5BB9l38 18T91384KA9206 tET:2,63t2K 9126 18T3827sKA9t2t l8Tl94l5KA9113A 18T444t9GDI133 lET64l6T3BB9l42 18TE59407BBrmT ran744olBB9l47 18T767422KI902B 18T983,144KI909 1W294649523BB9I4E IET9IE5I2BB9223A 18T754540BB922A 18T753540BB9ll53 t8T6't0s26BB91r54 ftT669526BB9lls5 18T669528BB9ll56 18T671582cH908A 18T916657crDl53 18T850651ctDl52 l8Tr6E603cl{vzL4 18T818615cll9ll30 18T676655clr9lll6 18T634748cH9l ll3 18fnn69cH9l86 18T67849cII9lE4 1tT6757y7BFglto 171282525GH9ll34 tT|3t?62GtDl123 1T1289637G'JgllU |TRW1ZGIDll26 17T333700GlDlEl 17fi|398:10KA9oIB 1AT25324KA9I4A t$r2l32AKAglz{C l8T: 324KA9IU 18T50305KA9ll7 18T14125KA9l163 t8T163361KA9lt35 LET2IZ362Kasul6 t8T233324KeglllS tct278344KA9ul9 18T254306KA9ll38 18Til539sKA9l136 lET3lE456

Rdbnel (1993)

Gft-Bt:590Csl-Dol:480CaH)ol: >slq Cal-$f, 560Cal-Dol: >25q Csl-Cn4@Call)ol:950CaH)ol: <50C€l-Dol: 4,10, Csl-Sn 380Csl-Dol:,180Grt-Bt 540Cal-Dol: >370, Cs!{]r 520Cal-Dol: 430, Ce!{r: z160Cd-Dol:290Grt-Bt:680Call)ol: €50, CaL4c 590Grt-B't: 440C€l-Dol:,|80Cal-DoL >410, Cal-Sr: 440Col-Dol: 470, Cal-Gr: 5@Csl-Dol:>470, CoKr 480Grt-Bt: 600Csl-Dol:e50Cal-Dol:O50CaH)ol: <250, C€l-Cn 550Grt-Bl:670Cal-Dol: 520, Cal-Gr: 640Cal-Dol: 390, Cal-Cr 4t0C8l-Dol:>5@, C8Kfl 470Cal-Dol:X80, Cs'Kr 410Grt-Br 640Cal-Dol: 530, Cal-G. 560Cd-Dol:550Col-Dol: >5@c€.&l:3,10Cal-Dol: >480, C€l-Cn 630Cal-Dol: >300, Ca!-Gr: 3@Cal-Dol: >390Cal-Dol: <50Cal-Dol: €50Cal-Dol: <250, Cal-Cn 530Cal-Dol: >160Cal-Dol: 450, Cal-Sr 490Cal-Dol:<50Cel-Dol: >370C€l-Dol: e50Cal-Dol: e50GIt-Br 560Cal-Dol: >3,10, Cal-Gr 510Cat-Dol: €50, Cal-Gr 530C€l-Dol: @0Cal-Dol: e50, Cal-Sn 230Cal-Dol: 550, C€Kn 580Csl-Dol: €50

KA91t42 18T315394KA9l1l5 'aT201298Klgnt t8T336249@GII920I 1m45805Gt92l5C lrt2'11736GlDlTE lTrlo7779BA9l89 18T786E70BA903A 18T167915BA904A 18T795887BA9l9l 18TA06912B.A92t2 lETt159l5BA92il l8T8l59l28A9168 18T84939BA9l95 18T908963B.A9202 l8T9l897lBA9l97 18T04964BA919E l8TytE96wF92l9 l8T337tnclr9ll07 18rft3718cH9l64 ftT826n3GD06 18T84179cII905 lET8138slcH9t58 l8Tt7l794cIDl59 18T916784(x{9t 100 l8T896t6lc.nlv2u 18T860735c.tg203 18T25802clDl7o 18T989721tclr9lTl ltrlngsc1r9l66 1rT900717qlv)r1 18T751644BB9l12l lETa26542BF9l8 [rn14441BF9l7 ITWU2BF92l6 lTW8535Kr9t2BB9I5BA9l83

At32-l

Ar32-3Al t+ l

A l2 l - l

A l l l - l

A1tl-2

t8T3654496191Tt932567LTn6['a74

C{t-Bt 640Cal-Dol:4@Cel-Dol: q50Grt-Bt: 800Grt-Bt: 800Csl-Dol:280, C€Kn 190Cal-Dol: 55q C8LSC 410Csl-Dol: >470cal-Dol: 3,10, Cal-Gr: 550Cal-Dol: 330Gfl-Bt: 650Gn-Bt:650C€l-Dol:530C€Kr 630Grt-Bt: 6t0, C€l-Dol: 470Caf.Dol: >600, CsKf 360Cal-Dol:<2,50ft-Bl:7/0Csl-Dol:560, C€Kr 540CaFnol: >520Cal-DoL >2@Cal-Dol: 530, Cal-Cf, 600Cal-Dol:500CsHol:510, Csl-Gc 590Csl-Dol:530, CaKn 5406rt-Bt: 620Grt-Bt:670Cal-Dol: 480, C€l-Cf, 480Cal-Dol: 54o, Csl-Gr: 540Cal-Dol: 540, Cal-Cr 550Grt-B'L 690Csl-Dol: >290, Csl-Gr: 190C€l-Dol: >270Cal-Dol:520Gd-Bt:810Cal-Dol: >460Cal-Dol:,160Cd-Dol:570. C€rcr 190

MlvL Stt€p€ry, upubl. .lats

I tT49300

18T4930018T4905

16T,f8955

18T49210

18T492t0

4n54860

Grt-Bt: 710, Pl-K6: 680, GASP: 7.5,GRIPS:6, GRAIL:6.9Grt-Bt: t50ft-Bt: 880, Pl-K6: 520, GASP: 9,GRJPS:6.3, GRAIL:8Grt-Bu 730, Pl-K&: 520, GASP: 7,GRIPS: 7.5, CRAIL:7.3Grt-Bt: 760, GASP: 8.5, GRJPS: 6,GRAIL:7.6Grt-Bs 700, GASP: 8.5, GRIPS: 6,G,AIL:7.5

47tO

4f45

4a45

Mileral symbols in this compilation follow the convention of Kretz (19E3); in addition, Amp is used to reprcsent amphibole. The table is muged

alphabetically rccording to name of authors cited. Limiting tempmturcs md pressm tre noted by the signs '1" and '{'. Aqonyms: GAFS: gmet-plagioclme-fenosil ite-quartz;GRIPS:gmet-ruti le-itmenite-plagimlue-quartz;GASP:garnet-aluninosil icate-quartz-Plagiocl6e;

GRAIL: gamet - rotile - ilmenite - aluninosiliete; GADS: gmet - plagi@lase - diopside - quartz.

cordierite, garnet-hornblende, garnet-orthopyroxene,and garnet-clinopyroxene), on the other hand, areconsidered more reliableo and temFeratures calculatedusing these thermometers were used preferentially incontouring. Some assemblages required the use oflimiling barometers @dwards & Essene 1988, Anovitz& Essene 1990, Cureton et aL 1997), although absolutepressures were used instead of limiting pressureswherever possible.

RFsuLTs oF THE CoMprr-ATroN

Temperatures

Figure 3a shows ttre contour map resulting from thecompilation of temperature data. In the Gneiss Belt,temperature ranged from greater than 750'C in the westto 650-700'C in the east (Anovitz & Essene 1990).There appears to be a discontinuity in temperatureacross the southern part of the MBBZ; temperatures of700-750'C in the west decrease to 600-650'C in theeast. Temperatures decrease south ftom the BSZ to lessthan 500'C at the Hastings Low near Madoc, Ontario(Anovitz & Essene 1990, Rathmell 1993). In theMazinaw domain, temperafure esrimates between 600and 650"C have been reported near the R[52 @usch eral. 1996b, Cureton et al. 1997). Across the RLSZ,lemperatures remain between 600 and 650oC, increasingto 65G-700oC at the SLSZ. Temperature estimates tothe east of the SLSZ are on the order of 70G-750'C inthe Frontenac domain (Reinhardt 1968, Carmichaelet al.1978, Lonker 1980, Davidson 1986, Anovitz &Essene 1990, Busch et al. 1996b). Lonker (1980)argued that the pyroxene granulites in the Frontenacdomain attained ca. 800oC and were variably resetafter the peak of metamorphism. However, an evalua-tion of uncertainties in maximum temperatures ofgranulite-facies rocks are complex and beyond tlescope of this paper. Temperature appears to havedecreased locally to 650-700"C in the AdirondackLowlands and then increased again a.g1qsr the CCSZ to700-750"C in the Adirondack Highlands (Bohlen &Essene 1977,Brown et al. 1978, Bohlen et al. L980,1985, Powers & Bohlen 1985, Edwards & Essene1988, Cartwright et al. 1993,Lamb 1993, Kitchen &Valley 1995). It is possible that peak temperatures inthe Frontenac domain and the Adirondack Highlandswere somewhat higher than those preserved by thesystems that were applied (perhaps in the range of75O-800'C).

Pressures

Although available data on pressure are sparse incomparison to data on temperafure, pressures aresignificantly less variable, and the data are easier tointerpret than data on temperature. Figure 3b shows acontour map based on compiled data on pressure. In the

t243

GB, pressure estimates exceed 8 kbar (800 MPa) anddecrease across the NI3BZ (Anovitz & Essene 1990).We surmise that pressure decreased in a manner similar'to temperafure in the Elzevir domain, to less than 6kbar (600 MPa) in the vicinity of the MSZ @usch e/al. 1996b, Cureton et al. 1997). Pressure est:matesincrease to the east to 7-8 kbar (700-800 MPa) at theRLSZ, and then drop sharply to 6-7 kbar (600-700MPa) across the RLSZ. In the Sharbot Lake domain,higher values are recorded, up to -8 kbar (800 MPa) atthe SLSZ (Busch et al. 1996b). Pressures decreaseacross the SLSZ to approximately 6 kbar (600 MPa) inthe Frontenac domain (Reinhardt 1968, Lonker 1980),and increase slightly to 7-{ kbar (700-800 MPa) in thevicinity of the CCSZ @dwards & Essene 1988, Buschet aI. 1996b).

DrscusstoN

Anovitz & Essene (1990) noted major changes inpeak pressures and temperatures of metamorphism inthe Grenville Province of Ontario, both on a regionalscale and across known tectonic boundaries. However,age determinations on shear zones in the MB were notavailable at the time, and so contours were drawnacross boundaries thatjoin domains that we now knowto have different metemorphic ages. Geochronologicaldat4 considered in conjunction with pressure-temperaturedata, help to elucidate the influence of major shearzones on thermobarometric gradients in the Meta-sedimentary Belt and the pattern of regionalmetamorphism in the Grenville Orogen (van der Pluijmet al. 1994, Cosca et al. 1995). For instance, there is nosystematic offset in ages across the MSZ, and there areno apparent thermobarometric discontinuities (Curetonet aI. 1997). Thus, the MSZ is interpreted to be a shearzone that predates the most recent peak metamorphicevent. Ages are discontinuous across the RLSZ, andthere are also marked changes in pressure-temperatureconditions across this boundary. Thermobarometricconditions are slightly different across the SLSZ, whichseparates rocks that were mer2morphosed at the sametime but have different cooling histories (Bttsch et aI.1996a). Finally, rocks of the Adirondack Lowlands inthe upper amphibolite to granulite facies have meta-morphic ages that are distinctly older than rocks ofthe granulite-facies Adirondack Highlands across theCCSZ. Therefore, the CCSZ separates rocks withdissimilal mstamorphic histories ${ezger et aI. l99la).

Incorporating ttre results of our pressuro-tempera-ture compilation with what is known about ductileshear zones in the MB shows that distinctthermobarometric discontinuities occur across zonesthat represent late to post-orogenic extension (BSZ,RLSZ, CCSZ). Although it is possible to generatecommon contours for ttre entire MB, it is important torecognize that the pattern does not represent a singlemetamorphic event. Rather, at least two major episodes

THERMOBAROMETRIC DATA, METASEDIMENIARY BEUT, GRENTVILLE PROVINCE

LzM TI{E CANADIAN MINERALOGIST

Ftc. 3. Generalized contour maps of temperatures (a) and pressures (b) in the Metasedimentary Belt. Data points from Figure2 have been removed for clarity. Also shown are the major zones of ductile shear (see Fig. l). Dashed lines representinferences, whereas solid lines are based on thermobarometric measurements. Titanite ages range from 1000 to 1070 Main the Bancroft d6main, from 1040 to 1070 Ma in the Elzevir domain, approximately 1010 Ma in the Mazinaw domain, 1150to 1555 Ma in the Sharbot Lake domain, 1150 to 1170 in the Frontenac and the Adirondack Lowlands, and 1030 to 1050in the Adirondack Highlands (e.9., van der Pluijm et al. 1994).

of deformatio\ at ca. 1150 Ma and, ca. 1040 Ma,characterize the region (van Breemen & Hanmer 1986,Mezger et al. l99lb, t993, McEachem & van Breemen1993, Corfu & Easton 1995). It is crucial, therefore, roincorporate geochronological studies when evaluatingtemperature-pressure gradients in regions that exposecomplex structural and metamorphic histories of rocksof the middle to lower crust.

Future work

The purpose of this paper is not only to elucidatethe significance of shear zones on thermobarometricgradients, but also to examine weaknesses in ttredatabase of temperafures and pressures. For instance,there is a marked lack of data in the Bancroft domain aswell as a paucity of data on presslue of metamorphismin the Elzevir and Frontenac domains. Only tentativetemperature-pressure contours can be drawn acrossthese areas. In addition, the reliability of individualthermometers must be evaluated. Calcite-dolomite datafrom Rathmell (1993) and Ewert (l977)havebeen ignoredwhen drawing contours because of the susceptibility ofresetting of the calcite-dolomite thermometer. This issupported in the Elzevir and Mazinaw domains byadditional data from garnet-biotite and calcite-graphitethermometers; however, few other constraints areavailable for temperatures in the Sharbot Lake domain.The portion of the Sharbot Lake domain near theOttawa River may represent a second low-grade lobe ofGrenville metamorphism in Ontario @wert 1977). Asan alternative, the apparent low-grade character ofthese rocks may be produced by extensive retrogrademetamorphism. Application of the calcite-graphitethermometer may prove useful in determining theextent of resetting of the calcite-dolomite thermometerin this area.

Quantitative thermobarometry can have seriouslimitations in that the rocks of interest may not have thefull mineral assemblages needed, and thermo-barometers can also be affected by retrogrademetamorphism. In these cases, the most powerfuldeterminations of peak conditions of metamorphismcome from field characteristics and mapped isograds.In addition, thermometers cannot distinguish betweentemperatues reached by regional metamorphism andtlose influenced by contact metamorphism. In manyinstances, the influence of intrusions on peak tempera-tures is not sffaightforward, and these complexities arereflected in the data. Correlating patterns generatedfrom quantitative data and field isograds will ultimatetygive the most coherent picture of peak conditions ofmetamorphism in the Metasedimentary Belt.

AcIc.IowLEDGEMENTS

This study was most recently supported by NSFgrants EAR 9345736 and EAR 96-27911. F. Spear is

1245

thanked for help with thermobarometric calculationsand generously sharing new software. M. Easton madeinsighrful comments on early versions of the contourmaps. K. Johnson is thanked for help with thecompilation. P. Tropper and S. Keane provided helpfulcomments and discussion of the manuscript. A.Davidson and an anonymous reviewer providedinsights and comments that improved the manuscript.

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Received January 8, 1997, revised manascript accepted July24, 1997.

THERMOBAROMETRIC DATA" METASEDIMENIARY BEUT. GRENVILI,E PROVINCE