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Relationship Between Rock Type, Metamorphic Grade

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Relationship Between Rock Type, Metamorphic Grade Canadian Mineralogist Vol. 25, pp. 485-498(1987) RELATIONSHIPBETWEEN ROCK TYPE, METAMORPHIC GRADE, AND FLUID- PHASECOMPOSITION IN THE GRENVILLESUPERGROUP, LIMERICKTOWNSHIP, ONTARIO P. JAMES LgANDERSON Depaftmentof Geologyand GeologicalEngineering, Colorado School of Mines, Goldm, Colorado8M01, U.S.A. JAMES L. MUNOZ Depafimentof GeologicalSciences, University of Colorado,Boulder, Colorado80309-0250, U.S.A, ABSTRACT entre535 et 550'C dansles marbres et 402et 543"Cou plus dans les lithologies pauvres en carbonate. La valerir de The srudy area in Limerick Township in the southern X(CO) seraitentre 0,45 et 0.55 dansles marbreset moins Grenville Province consistsof a sequenceof late Proterozoic de 0. l0 dansles milieux pauvresen carbonate.La relatlon metabasalts,noncalcareous and calcareousquartzofeld- entre degr€de m6tamorphismeet lithologie refldte la dimi spatlfc granofels,and marblesintruded by two gabbro com- nution du X(CO) du marbre vers les unit€s moins riches plexes.During the Grenville Orogeny,metamorphism of en calcaire.Cette relation pourrait 6tre attribude l) d un marble producedassemblages that are below the titanite, tamponnageinterne de la phasefluide par lesr6actions iso- actinolite - calcite,and hornblende- K-feldsparisograds, gradiquesi des valeurs 6levdesde X(CO) dans les mar- but above the hornblende - K-feldspar isograd in the bres et des valeurs inf6rieures dans les unit6s pauvres en quartzofeldspathicunits and amphibolitss. Calcite-dolomite carbonate, ou 2) d un tamponnagedes fluides i desvaleurs and two-feldspargeothennometry, and calculationof the faibles de X(CO) par les r€actionsisogradiques suite i displacementof intersectingequilibria due to solid-solution, l'infiltration de fluides aqueux au travers des unit€s pau- bracket equilibrium temperaturesbetween 535 and 550'C vres ou sanscarbonate. in the marbles and between402 and 543'C or higher in rocks with low carbonatecontents. X(CO) is estimated Mots-cles:isogrades, marbre, granofels,intersection d'6qui- between0.45 and 0.55 in the marblesand lessthan 0.10 libres, degr6 de m€tamorphisme,composition de la in the carbonate-poorunits. The relationshipbetween meta- phaseaqueuse interstitielle, Grenville, canton de Lime- morphic grade and rock type is due to a decreasein rick, Ontario. X(CO) from the marble to the lesscalcareous units. This relationship may be due to: 1) internal buffering of the fluid INTRODUCTION by the isogradic reactionsto high X(CO, valuesin the marbles and low X(CO) values in the carbonate-poor Experimental investigations (e.g., Skippen 1971, units, or 2) buffering of the fluids at low X(CO, by rhe 1974, Slaughter et al,1975) and theoretical studies isogradic reactions during infiltration of H2O-rich fluids (ag., Greenwood 1962, 1967,1975) of mixed-volatile through the carbonate-deficient and carbonate-absent equilibria have made possible the interpretation of rocks. metamorphosed, interlayered calcareous, pelitic and quartzofeldspathic sedimentary rocks. The tempe- Keywords: isograds, marble, granofels, intersecting not equilibria, metamorphic grade, pore-fluid composition, rature of mixed-volatile equilibria is dependent Grenville, Limerick Township, Ontario. only on pressure but on fluid composition, especially the ratio of H2O to COr, or X(CO). "High-grade" Souvarnr areas defined by mixed-volatile isograds, therefore, do not necessarily indicate regions of high tempera- Dans le canton de Limerick (Ontario), dansla partie sud ture, unlike dehydration reactions in nongraphitic de la province du Grenville, une s6quenced'dge Protdro- pelitic rocks. Mixed-volatile isograds may, and often zoique tardif de mdtabasaltes, granofels quartzo- do, reflect variations in X(CO). feldspathiquesavec calcaires ou non, et marbres est recou- Carmichael (1970) found that isograds based on pde par deux complexesgabbroi'ques. Pendant I'orogendse mixed-volatile reactions intersect one another in Lake grenvillienne,le m6tamorphismedes marbres a donn6 des Township in the southern Grenville Province, Onta- qui assemblages setrouvent au dessousdes isogrades tita- rio. This was interpreted to be the resuh of migra- nite, actinote- calcite,et hornblende- feldspathpotassi tion of H2O from the Whetstone granite into the que, mais au dessusde ce dernierisograde dans les unitds Kerrick (1976) described a simi- quartzofeldspathiqueset lesamphibolites. La gdothermo- wallrocks. Moore & m6trie, utilisant les dquilibres impliquant calcite et dolo- lar situation in the Alta aureole in Utah. mite et les deux feldspaths, ainsi que le calcul des ddplace- Locally, in southeastern Maine, interbedded ments des intersectionsdes r6actions dus aux solutions pelites, micaceous quartzites and calcareous rocks solidesprdsentes, indiquent des temp6raturesd'6quilibre strike parallel to the direction of the thermal gra- 485 Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/25/3/485/3420309/485.pdf by guest on 27 September 2021 486 THE CANADIAN MINERALOGIST 45C)52' I Mil-es N GRENVILLEPROVTNCE 0 20 ffn PALEOZOTC J_ 0km30 WTF'ELO AREA METAMQRPHIC- BOUNDARIES FIc. l. The field area is located in Limerick Township, southern Ontario, 100 km northeastof Toronto (after Lumbers 1964).The field area of Allen (1976)is located in Tudor Township, immediatelysouth of Limerick Township, and that of Car- michael(1970) in Lake Township, immediatelysouthwest of Limerick Township. dient. Calc-silicateisograds are extremelyirregular eousquafizofeldspathic granofels, and marble @ig. and form local, high-gradeareas related to centres 2). The Brinklow Lake and Ormsby Junction of intrusion, and exhibit local cross-cuttingrelations- amphibolite belts consistpredominantly of massive hips. Ferry (1976, 1980)interpreted thesepatterns amphibolites of assumedvolcanic origin. Volumetri- asthe result of a high flux of heat relatedto the plu- cally minor, calcareous,locally schistoseamphibo- tons, introduction of HrO from the intrusive lite may haveformed through the reworking of vol- bodies, dehydration of the pelitic rocks, and inter- canic rocks and introduction of clastic material. The nal control of the fugacities of H2O and CO2by the calcareoushorizons are in greatestabundance in the mineral assemblages. Ormsby Junction amphibolite belt. An ageof 1310 In Grenvillemarble and calcareousmetasedimen- Ma was obtained by Silver & Lumbers (1966) on tary rocks in Tudor Township, southern Ontario zircon from the mafic Tudor metavolcanicrocks (Fig. l), Allen (1976)observed an increasein meta- south of the study area.The similarity of the Tudor morphic grade toward a seriesof metamorphosed volcanicrocks and associatedrock units to thosein tonalite, trondhjemite, granodiorite, and gabbro Limerick Township gives an approximate age of the intrusive bodies. This was attributed to a decrease rocks in the study area. in X(CO) of the intergranular gas-phasetoward the Rusty schistssurround the amphibolite belts and igneous contact, i.e., the relic of a pre-Grenville, occur as discontinuouslenses in them and in the other contact-metamorphicaureole. units. Small, exhalativemassive-sulfide deposits con- taining pyrite, pyrrhotite, sphaleriteand chalcopyrite GENERALGsot-ocv occur in the rusty schistsadjacent to the amphibo- lites. Their composition, clastic host-rocks, and A sequenceof Grenville amphibolitesand quartzo- associationwith mafic volcanic rocks suggestthat feldspathic and calcareousrocks surrounds the Tha- they are Besshi-typedeposits (Franklin et al. l98l). net anil Jocko Lake gabbro complexes(Lumbers Furthermore, it is likely that the volcanic rocks were 1967,1969, LeAnderson 198a, b) approximately22 the heat sourcefor the deposits.This indicatesthat km south of Bancroft, Ontario, in Limerick Town- the amphibolites are the oldest unit in the field area. ship (Figs. l, 2). The areasstudied by Carmichael The quartzofeldspathic granofels is generally (1970) and Allen (1976) lie to the southwestand arkosic in compositionand is assumedto represent south, respectively(Fig. 1). clastic sediments. Calcereous quaftzofeldspathic The most commonly observedsequence of rock granofels contains similar assemblagesin addition to units is amphibolite, rusty (sulfidic) quartzofeld- up to 10Vocalcite and dolomite. Lensesand layers spathicschist, quartzofeldspathic granofels, calcar- of each rock type are found in the others. Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/25/3/485/3420309/485.pdf by guest on 27 September 2021 ROCK TYPE, METAMORPHIC GRADE AND FLUID-PHASE COMPOSITION IN THE GRENVILLE >":i,"ic:)i ="'7?!3-;{ j; .1',,',.j;ct6i1- tt" '',,-.i z"- Loke, ^"- \oor- Compler w "-\ ( "' -. iiii:l-.:"",- .:T'F{ t,l G.:-.)..it])'T::i " )-i=rt: o.o 05 r.o a-"1; r-;r."";,=.'\i :-.', =, gYi [,,j3.:"-i "i lm Ftc.2. Generalizedgeological map of the study area (after LeAnderson 1978a).Symbols: rs rusty schists,qf quartzo- feldspathicgranofels, cqf calcareousquartzofeldspathic granofels, m marble, cs calcsilicate. Marble makesup the youngestof the sedimentary enite and hornblendemetagabbro (Lumbers 1967); units and is presentin four areas(Fig. 2). The miner- its ageis unknown but assumedto be approximately alogy, color and texture are a function of meta- that of the Thanetcomplex. A premetamorphicdate morphic grade.Below the actinolite-calciteisograd for the Thanet complex (Berger& York 1981)and the marble is grey and commonly containschlorite, methmorphictextures in both indicatethat the com- biotite, calcite, dolomite, quartz, plagioclase, plexeswere emplacedprior to the Grenville meta- titanite,
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