t22l

The Canadian M ine ralo gist Vol. 35, pp. 122l-1236(1997)

PETROLOGYOF THE FLINTON CREEK METAPERIDOTITES: ENSTATITE. AND ANTHOPHYLLITE- MAGNESITE ASSEMBLAGES FROMTHE GRENVILLE PROVINCE

FREDERICK D. FORD* ANDGEORGE B. SKIPPEN

Ottawa - Carleton Geoscience Center, Deparfinent of Geology, Carleton University, Oftawa, Owarto KIS 586

Ansrnacr

TVvotypes of metaperidotite, enstatite - magnesite rock and anthophyllite - magnesite - rock, are present in ultramafic lenses from the southern Flinton Synclinorium, Central Metasedimentary Belt, Grenville Province, in southeastern Ontario. A mantle of the anthophyllite - carbonate rock always surrounds the primary enstatite - magnesite rock, which is preserved only in the interior of the larger ultramafic lenses. The ensta66 - magnesite rock contains enstatite (Mges), magnesite (Mg*), dolomite (Mg+g), as well as (Mgg?), anthophyllite (Mgr6), forsterite (Mg*), and relict chromian magletite. The assemblage enstatite + maglesite requires the presence of a relatively COlrich fluid phase. The presence of late-stage forsterite veins in the enstatite - magnesite rock may be explained by infiltration of comparatively HrO-rich fluid at near-thermal-peak metamorphic conditions. The anthophyllite - carbonate rock is composed of spherically radiuing anthophyllite intergrown with magresite, dolomite and chromian mametite; the compositioas ef ale similar in the two rock types. The presenceof only one silicate in addition to the carbonates suggests that the anthophyllite - carbonate assemblage fomred as a metasomatic mantle duri-ng the early retrograde history of the ultramafic lenses. Kyanite - biotite assemblages in adjacent pelitic rocks indicate a regional metrmorphic grade in the middle facies. Themrobarometry records metamorphic temperatues of 620o to 680oC at pressuresof 6.5 to 7.5 kbar.

Keywords; metaperidotite, ultramafic, anthophyllite, enstatite, nagnesite, Grenville Province, Flinton Group, Ontario.

SonaMan_E

Nous ddcrivons deux sortes de mdtapdridotite, soit une roche d enstatite + map6site et une autre a anthophyllite + magndsite + dolomite, dans des lentilles ultramafiques affleurant dens le synclinorium de Flinton, de la ceinture m6tas6dimentaire centrale de la Province du Grenville, au sud-est de I'Ontario. Un liser6 d anthophyllite + carbonate entoure dans tous les cas Ia roche primaire e enstatite + magn6site, pr6serv6e seulement d I'iltfriew des plus grosses lentilles ultramafiques. [a roche ] enstatite + magn6site contient enstatite (Mg*), magndsite (Mg*), dolomite (Mg"p), de meme que talc (Mge), anthophyllite (Mg88), fors€rite (Mg*), et magndtite cbromiftsre r6siduelle. Llassemblage ensglilB a magn6site implique la pr6sence d'une phase fluide relativement riche en COr. [a pr6sence de veines tardives I forstdrite dans la roche ] enstatite + magndsite resulterait peut-Otre de I'infiltration d'une phase fluide comparativement plus riche en H2O b des conditions de temp6rature proches de celles du paroxysme m6t,morphique. La roche i anthophyllite + carbonate contient des cristaux d'anthophyllite fibroradi6s en intercroissance avec magn6site, dolonite et magndtite chromifdre. Les compositions des mindraux sont semblables dans les deux sortes de roche. Vu Ia pr6sence d'un seul silicate avec ces carbonates, I'association anthophyllite + carbonate repr6senterait un liserd m6tasomatique form6 lors de la r6trogression pr6coce de ces lentilles. l,es assemblages i kyanite + biotite des roches p6litiques adjacentes indiquent un degr6 de m6tamorphisme r6gional dans le facids amphibolite moyen. La thermobarom6trie indique une temp6rature de mdtamorphisme de 620' d 680oC d une pression entre 6.5 et 7.5 kbar. (Iraduit par la R6daction)

Mots-cVs: mdtaffridotite, ultramafique, anthophyllite, enstatite, magn6site, Province du Grenville, Groupe de Flinton, Ontario.

IxrnopucrroN Grenville StructuralProvince, in southeasternOntario (Fig. l). The ultramafic boudins,herein termedthe Metaperidotiticrocks are exposedin a seriesof Flinton CreekMetaperidotites, are associatedwith a discontinuous boudins along the eastern margin suite of metamolphosedmafic rocks ranging from of the Flinton Synclinorium, locatedin the Central metagabbroto amphibolite.The metaperidotitesare MetasedimentaryBelt (Wynne-Edwards1972) of the interesting in that they contain significant proportions

* Presentaddress: Geoscience Laboratorieso 933 RamseyLake Road, Sudbury,Ontario P3E 685. E-mnil address: [email protected] t222 THE CANADIAN MINERALOGIST

Ftc. l. Geology ofthe southern Flinton Synclinorium and surounding area; asterisk in hset map indicates geographic location. Open dots show the location of samples of ultrama.fic rock mentioned in the text. Diamonds indicate location of samples used for thermobarometry. The main !s'dy qgthe Flinton Creek Complex (black) occurs within the Flinton Group, in the core of the synclinorium, with a long teil extending northward to the contact with the Northbrook Tonalite. Sporadic lenses of ultramafic rocks occur north ofthis point, in the contact zone between the tonalite and the Flinton Group. At least two ulffamafic lenses occur entirely within the Northbrook, several hundred meters away from the contact (semple 11M88). The Flinton Synclinorium is bounded on the east and west sides by shear zones that have not been indicated. The compilation was produced from the observations of Thompson (1972), Chappell (1978), and Bright (1986). PETROLOGY OF THE FLINTON CREEK METAPERIDOTITES 1223 of magnesiteand dolomite, in addition to silicate FrupRlx.arnoNs minerals more commonly associatedwith meta- morphosed ultramafic rocks, such as enstatite, The metaperidotites generally occur as lenses in an anthophyllite, and forsterite (Trommsdorff& elongate belt of deformed mafic rocks. Together, the Evans1974). In this paper,we discussthe petrology of mafic and ultramafic rocks form what is herein termed thesecarbonate-bearing ultramafic rocks and describe the Flinton Creek Complex. Individual ultramafic their petrogenesison the basisof observedassemblages lenses vary in size from 1 m to over 50 m in longest and texturesof the minerals,thermobarometry, and dimension. Larger lenses contain a core of enstatite - calculatedphase-relations. magnesite rock surrounded by an envelope of /|lr ild*'r\\ ,,\r

++++++ \\\ilil

t-+-{ 0m 5m lOm

ffil Enstatite-MagnesiteRock

ffi A"thophyllite-CarbonateRock Flinton Creek Complex W Black Wall Alteration Zone N Gabbroic Rocks N MetasedimentaryGneisses tr NorthbrookTonalite

Flc. 2. Hypothetical cross-section of several ultramafic lenses looking along strike. Foliation in the host rock is subparallel to the long axis of the ultramafic lenses as drawn; however, the direction of maximum elongation is perpendicular to the diagram- Note that the fwo -types form concentric zones, with enstatite - magnesite rock in the core of the larger lenses, surrounded by an envelope of anthophyllite - carbonate rock. Smaller ultramafic lenses consist entirely of the anthophyllite - carbonate assemblage. 1224 TIIB CANADIAN MINERALMIST anthophyllite- carbonaterock. Smaller lensesare TABLE I composedenfuely of anthophyllite- carbonaterock.

Samplelocations are shown on Figure 1.An idealized ThmoEEtry("C) Bmnoty (brr) cross-sectionthrough the Flinton Creek Complex is o) Q) (3) (3) (4) shownas Figure 2. A metasomaticreaction-zone or "blackwall" l0 to 9343b 6t4 616+20 64@+ 1280 20 cm thick is developedwhere the ultramafic lenses ct-HAl 638 714 654+7 6765+ 155 75@ are in contactwith the surroundingmetamorphosed 93-36s 737 685 750+ lE 7425*675 62@ mafic rocks. Similar reaction-zones have been describedfrom otler localities of metamorphosed (l) Ganc-bioeetsnmrtyutogtlselibrdim ofHodgps & Spqr (19t2) br ultramaJic rocks around the world, including a pre of 7 kbo. (2) Aqhibol8 - plagi@le ttmorety uiag the elibrdi@ of Honrd & Bhndy (194) tur a pm of 7 tbr. (3) INTERSX rult8 "iing Paddy-Go-EasyPass (Frost 1975) and the northern TwQ (mim 1.02; B@ l9l). Th€ + nlus rspsdt I o Bcdd d Appalachians (Jahns 1967, Sanford 1982). The iocrercim (4) Aqhlole - gqnd - plagi@le bqome|try.dng ths elibmti@ of KolE & Sps (t90) at T(l). lvfudal @blage: Gn - Bt - Mr - Ky - Pl - following zonesprogress outward from the Qtz (93-43b),Cft - Bt - IIbl - Pl - Qtr (93-IIA3, 93-368). Nfnml @mpositi@ ultramafic lens into the surrounding mafic rocks: u8€dto obt8irlthe P-T milts m srdablo uponr€qued ft@ the 6I$ qtrhtr, ed ftm the Dspositoryof Uryublish€dDe, CISTI, Ncional Rerch Corcil of monomineralic tremolite zone, monomineralic biotite Cmada,Ottawa, Odrio KIA 0S2. zone,chlorite zone. This sequenceof mineralzones is similal to the amphibolite-faciesblackwall zones describedby Sanford(1982) at Blandford, Massachu- setts and Gra.fton,Vermont. The presenceof this Tonalite.Thermobarometric results are summarizedin metasomaticreaction-zone between the ultramafic Table 1. Temperafureestimates range from 620" to lensesand the surounding host-rocksindicates that the 680'C. Estimated pressruesare 6.5 to 7.5 kbar. lws fissimilar rock-typeswere in contactwith each Thermobarometric results for 9343b (staurotte - otherduring regionalmetamorphism, eliminating the kyanite- biotite) areconsistent with publishedgrids for possibility of post-metamorphictectonic emplacement metapelite (e.9., Powell & Holland 1990), which for the metaperidotites. indicatethe stabitity of this assemblageat the estimated temperatureand pressure.The tlermobarometry for Mrtauonprusvr sample 9343b indicates metamorphic conditions approachingthe stabilityfield of sillimaaite;this is in Pelitic schistfrom the Bishop CornersFormation, agreementwith the regional location of the kyanite-to- containingthe assemblagekyanite + biotite + staurolite silfimanite isograd(Carmichael et al. 1978)that lies + muscovite + quartz (Ford & Skippen L994), is betweenoutcrop 93-43 (staurolite- kyanite - biotite) coincidentwith the nortlernmost occurrenceof the 614sillimanite-bearing pettic schists4 km 16the east. ultramafic rocks at locality 93-43 (Fig. 1). An increase in regional metamorphic grade southward from Perr.ocnepnvAND MtrIRAL CHEMISTRy this locality has been demonstratedin calcareous sedimentary rocks of the Lessard Formation Approximately 250 samplesdistributed ttrroughout (Thompson 1973), indicating that the assemblage the Flinton Creek Complex were selectedfor detailed kyanite - biotite gives a minimum estrmate of petrographicexamination. The locationsef 5nmples metamorphicgrade for the Flinton Creek Complex. investigatedby electron-microprobeanalysis (fables 2, Mafic rockswithin the gemFlexcontrin assemblages 3) areshown on Figure 1. compatiblewith this estimate( - plagioclase - epidote- garnet).The increasein metamorphicgrade Whole-rockchemisny southward within the Flinton Synclinorium is supportedby the appearanceof two-mica gfanitic Sixteen 5amples of enstatite - magnesite and pegmatite(with or without garnet)in Flinton Group antlophyllite - carbonaterock were collected for psammitic rocks that are spatially related to the whole-rockgeochemistry throughout the Flinton Creek metaperidotitessouthward from localify 101788on Complex; representativecompositions are given in Figure 1; Thompson(1973) interpreted the bodiesof Table4. Low analyticaltotals, due to the presenceof granitic pegmatiteto be producedby partial melting of carbnates andhydrous mine6ls, precludean extensive theFlinton Grouppsammilsg. discussionof tle chemicalpetrogenesis of theserocks; Samplesfor geothermobarometrywere collected however,it is worth noting that both rock typeshave from several rock-types, including: pelitic , high levels of Cr (2000-7500ppm) andNi (1@0-2300 garnet-bearingamphibolite, and semipettic ppm) contents,which is compatiblewith an ultramafic containing garnet, amphibole, and biotite. The protolith. The proportionsof Si, Fe and Mg remain stratigraphicposition of ttris last-namedrock-type is within the range expected for ultramafic rocks, 'nknowtr, as it is exposedonly intermittently between indicatingthat variationsin bulk compositionare not the Flinton Creek Complex and the Northbrook responsiblefor the different mineral assemblages PETROLOGY OF THE FLINTON CREEK METAPERIDOTITES 1225

TABLE Z AVEMGE COMPOSMONOF ENSTATME , ANTHOP}TYLUTEAND TREMOLITE*

ENtalite OlMre Tremollte Saaple I I l5E7-lc I 10.18&c2101788-lb I I I 5E7-I c I I 0.lss{2 I OI 7E8-lb 060489-2b-T$ffi ]d I ll5t7-lc I l0l88a2 lo3lEE{l lllstT-lc llo.ltt{2 (e) (r4) (41) (4) (46) (26) (4E) (26) (6) (46) (18) (2e) a Rk Tlpe EM EM EM EM EM EM EM EM EM EM AC EM EM

SiO2 sLo/o 57.65 51.46 57.93 nt:on *:' 'j' *:' 59.48 59.12 58.33 57.33 v.74 Tio2 0.07 0.10 0.ll Y 0.0t 0.0E 0.07 0.18 o.lt AI203 0.08 0.@ 0.14 0.14 0.36 0.22 0.67 2.U cao3 0.10 0.10 0.14 0.t0 0.06 o.o1 0.33 0.45 FeO 6.05 7.25 6.19 E.09 9.32 8.67 9.30 E.54 6.E8 6.98 7.8t 1.93 2.64 MnO 0.14 0.24 0.15 0.16 0.16 0.14 0.10 0.20 0.35 0.25 0.16 0.12 0.09 MEO 3,1.99 31.57 35.0E 50.98 8.17 49.36 49.37 s0.07 30.72 30.7t 29.85 23.64 22.62 Nio ':' ':' ,:, t:, t.:, CaO 0.09 0.ll 0.10 0.70 0.36 0.34 13.20 12.E5 K20 0.12 0.t2 0.13 0.09 0.09 Total 99.17 ,,, ,; 101.46 99.30 99.76 [email protected] 100.1I 9E.57 98.I I 96.98 n.49 96.t4 O^f'gm abm 6 66 23 ?3 23 23 si 1.998 t.992 t.996 ':':' ':' ':' o1' 1.917 7.9t7 7.9M 7.A$ 7.92 Ti 0.002 0.003 0.003 0.@8 0.@t 0.u}7 0.01E 0.019 Al 0.003 0.000 0.006 0.021 0.057 0.035 0.109 0.402 Cr 0.003 0.003 0.004 0.011 0.007 0.@8 0.036 0.049 Fe 0.175 0.210 0.179 0.t62 0.192 0.178 0.190 0.r74 0.169 0.7E2 0.E90 o.22t 0.313 Mn 0.00{ 0.008 0.00.1 0.@3 0.@3 0.@3 0.002 0.@f 0.040 0.029 0.018 0.014 0.010 Mg 1.808 1.786 t.791 l.8x t.792 1.802 1.799 l.E2l 6.llE 6.t44 6.058 4.E34 4.76 Ni Ca 0.003 0.@t 0.00,1 ":' ":' ":' ":' 0.100 0.050 0.050 1.9{0 t.923 K- 0.020 0.021 0.022 0.015 0.016 Tota.l 3.96 ..; ,,,, 3.002 2.97 2.99E 3.000 3.@5 15.034 15.015 t5.032 15.050 15.0E0 m# t 0.9r 0.89 0.91 0.91 0.90 0.90 0.90 0.91 0.88 0.E8 0.&7 0.95 0.94

f Mgi(FerMdMglNi) { detemi$d by etestm-mimprohe &alysis. The nuuber of amlys is gim itr bmceeb. Asltsis m Csd€tonUnimity Cmbndge Mim V etecrrolmiqoprobe equipD€dwith m f,erry dispeGireA@ronets. Operafingonditiom w 20KV ald I sp6im @rEtrt of 9 Emp. A@ge @[€ti@ tine ru l@s live tire. Data reductiotrM @mpleEdon a p€mDrl 6mpds Ning the EDDI prcgro of Prhgle (19t9).

presentin the enstatite- magnesiteand anthophyllite- to the Flinton Creek Metaperidotites, whereby carbonaterocks. The analytical data of Table 4 are "equilibrium tends to be maintained locally within a comparedwith standardultramafic compositionson reacting system even though the system as a whole may Figure3. be distinctly out of equilibrium." Enstatite in the enstatite - magnesite rock is coarse- Petrographyof the enstatite- mngnesiterock $ained (10 - 30 mm) and subhedral, and forms a network of mutually interfering crystals. Chlorite, The enstatite- nagnesiterock is composedprimarily opaqueminerals and minor amountsof carbonateoccur of coarse-grained,euhedral enstatite and medium- to as randomly oriented inclusions in enstatite. Several fine-grainedmagnesite (Fig. 4a). Pettersen(1883) electron-microprobe traverses across the larger grains applied the name sagvanditeto similar carbonate- of enstatite revealed no compositional zonation. orthopyroxenitesfrom the Troms region of northern Enstatite crystals from different localities throughout Norway.Carbonate-bearing orthopyroxenites have also the complex have similal compositions (TabIe2). beendescribed from Aaheim,western Norway (Kendel The rock is composed of 20 to 3OVo carbonate 1970) and the Central Alps (Evans & Trommsdorff minerals. Magnesite commonly occurs as fine- to 1970,1974).Additional work on theTroms locality has medium-grained, anhedral crystals in magnesite-rich beenpresented by Schreyerer al. (1972)and Ohnmacht domains found interstitially among, and surrounding, (1974). A review of Norwegian metamorphosedthe coarser-grained crystals of enstatite; however, a ultramafic rocks is provided by Bucher-Nurminen small number 6f samples have large, single crystals (1988). of coarse-grained (1 - 5 cm), euhedral magnesite in Texturesin this rock type arecomplex, with obvious textural equilibrium with the adjacent enstatite (Fig. replacementand overgrowth of earlyminel4ls compli- 4a). Anhedral magnesite is commoDly associatedwith catedby the later developmentof vein-relatedminerals anthophyllite. Enclaves of magnesite - anthophyllite suchas magnesiteand olivine. The driving force for the can be found within large grains of enstatite, or on developmentof theseFxfures is believedto be fluid grain boundaries, where the two minerals seem to be influx. As such,the conceptof "local eqrili!fig6", ag growing into the larger crystal (Fig. ab). The following definedby Thompson(1959), is believedto apply reaction describes the relationship among the three 1226 THE CANADIAN MINBRALOGIST

T TABLE & AVERAGE COMPOSMON OF CARBONATES.TAI,C AND CHLORITE enstatite- magnesiteassemblage. Each veinlet has Magncdb DolonlE Talc chloilE a core of irregular, anhedral olivine that passes S@plo lllsS? ll04E8 101788 lllsaT 110488 l0l78t I03lt8 lll5&7 - -lc 43 -Ib -lc +3 -la 42 -lc transitionally into the enstatite magnesiterock. (10) (ll) (9) (t2) (9) (10) (21) (4\ In this transitionzone, olivine forms pseudomorphs RL.IYF EM EM EM EM EM EM AC BM of the original magnesiteinclusions in enstatite. SiO2 { % 62.6 61.t6 32.a9 '1102 The occurrenceof olivine in veins suggeststhat the 0.14 0.12 0.10 AI203 0.t5 Ll3 16.3r presenceof a fluid phasemay have contributedto Cr203 0 12 0.16 l.3l its formation. The following reaction appliesto the FeO 3.56 4.6 4.29 l.16 1.45 l.16 t2t 3.u MtrO 023 0.23 o.lt 0.8 0.08 0.06 0.06 0.ll coexistenceof enstatite,magnesite and olivine in M!o M.a2 43.6 44.4E 2t.25 20.n 30.45 30.5 35.01 the presenceof a fluid phase: Nio 0.35 0.29 0.41 CaO 0.44 0.39 0.44 2925 29.23 K20 Mg2SirO6+ 2VIgCO 3 = 2Mg2SiO4+ 2CO2 TOEI 49.08 8.94 49.39 51.14 52.t1I 94.$ 93.t9 89.58 enstatite magnesite forsterite (3) O,ry.alm ,_ lt u t4 si 3.943 3.942 3.033 Ti 0.@7 0.66 0.d)7 Tbree amphibole minerals, anthophyllite, tremolite " : 0.0t2 0.0E5 |.ns Cr 0.006 0.@E 0.096 and magnesio-, are found in the enstatite 0.043 0.056 0.0sr 0.030 0.038 0.62 0.065 0.265 - magnesite rock. Anthophyllite replaces enstatite and Mn 0.@3 0.003 0.m2 0.@2 0.@2 0.@4 0.003 0.009 Mg 0.94r 0.935 0.940 0.989 0.95 2.912 2.884 4.8t3 talc @g. 4d), and in some cases overgrows olivine, Ni C! 0.006 o.ffi 0 ffi oqg o.9n ":" ":' K TABLE4. BUIXCOMPOSMON TotrI 0.999 1.000 0.99 2.@0 2.0@t 7.003 7.W 10.026 OF THE FLINTON CREEK METAPERIDOTIIES t mg# i 0.95 0.93 0.94 o.49 0.49 0.n o.cl o.94 Sample ll04E8{2 ll04{5 103188{1 110,188d f Mg/edN,tftMgJM) t - ToEl ircludE 0.44610SrO = 0.@E Sr pe! 6 O,(yE@ RL Type EM EM AC AC . d€@i&dbydffin-Elqwrcbaml'sic Thenmrbqof alabs is gi@ itrbtuks Alrl'del @nditim indi€ad @ Table2, SiO2 wLYo 5t.79 39.12 4t.3E 44.24 Ti02 0.06 0.06 0.01 0.05 A1203 1.68 2.07 o.5'7 1.50 Fe2O3t 10.41 I 1.54 7.t5 9.05 minslalso if one assumesthat chemical equilibrium was MnO 0.15 0.l4 0.1I 0.12 achieved: Mgo 33.50 32.64 2a.45 CaO 0,43 1.64 3.25 4.47 4Mg2Si2O6+ HrO + CO, = Mg.tSisO22(OH)2+ MgCO, Na2O 0.00 o.24 0.16 0.29 K:to 0.01 0.01 0.r0 0.0r enstatite anthophyllite magnesite P205 0.0r 0.01 0.0r 0.0t (1) s 0.t2 0.0s 0.09 0.05

Table 2 shows that both textural varieties of Ba T] 70 61 6s magnesite have the same chemical composition Cr 6255 5t56 209t 3333 (101788-lb is the coarse-grainedtype, and 110488--c2 Za 109 75 94 lot Ni 2302 t949 1877 t541 is the anhedral variety). 56 20 2a Dolomite occurs as fine- to medium-grained, anhedralcrystals in textural eqrilifdum with magnesite; Total 99.1I E9.4t E6.04 92.94 dolomite - magnesite slmplectitic intergrowths were observed in fwo thin sections. Most silicate minerals, f Total ircn ro FezOr including enstatite and anthophyllite, seem to be in I AD.lys Mde at the Univmity of Otam X-my Fluorcne tucility stable coexistence with dolomite; however, in several thin sections, dolomite appears to be a product of the replacement of tremolite, suggesting that the following which alsoreplaces enstatite. It hasnot beenpossible solid-phase reaction proceeded from left to right. to distinguish antlophyllite that developed along the prograde metamorphic path ftom retrograde Ca2Mg5SisO2(OtI),+ 4Mg(COs) = 2CaMg(CO.)2 + anthophyllitethat developedat the sametime as the tremolite magnesite dolomite anthophyllite- carbonatemantles that surroundtle MgrSirO,,(OH), enstatite- magnesiterock. anthophyllite (2) The presenceof embayedgrains of tremofte in Olivine has been found in the enstatite - magnesite contactwith carbonatesuggests that tremolitebecame rock at all but the northernmost occurrence (500 m metastable prior to or during the growth of southeast of 93-43b), which is also the lowest-grade anthophyllite. Most tremolite crystals have been locality. Olivine occurs as texturally late crystals overgrown by later anthophyllite. Tremolite grains in in veinlets that cross-cut and replace enstatite and contactwitl magnesiteare corroded,indicating that magnesite (Fig. 4c). At the microscopic scale, the olivine progrademetamorphism exceeded the conditionsof veinlets are not in sharp contact with the surroundins solid-phasereaction (2) above. PETROLOGY OF THE FLINTON CREEK METAPERIDOTITES t227

O Mineral observed in the Flinton Creek Metaperidotites O Mineral not observed in the Flinton Creek Metaperidotites

Tremolite - f Anthophyllite DiopsideQ pyp 6w Enstafite Chrysotile

Forsterite %" o 9o

FeO+MgO +MnO Dolomite Magnesite

Ftc. 3. Minerals commonly observed in metamorphosed ultramafic rocks projected into the system CaO - SiO2 - (FeO + MgO + MnO). Dark circles indicate minerals observed in the Flinton Creek metaperidotites, unfilled circles designate other minsl4ls 966- monly associated with metamorphosed ulramafic rocks tlat were not observed at Flinton Creek. Diagram assumes that a mixed HrO - CO, fluid phase is present in excess. Diamonds indicate the compositions of Flinton Creek metaperidotites list€d in Table 2 (open: althophyllite - magnesite rock, fiIled: enstatite - magnesite rock). The average compositions of various ultramafic rock-types (Le Maitre 1976) are also shown: Py pyroxenite, W webrlite, L lherzolite, H harzburgite, D dunite.

Talc is found both as a prograde metamorphic Penography of anthnphyllite - carbonate rock mineral, and as a product of late-stage alteration. Prograde talc occurs as medium- to fine-grained, This distinctive rock is composed of fine-grained, subhedral laths within enstatite crystals and along anhedral carbonate (magnesite and dolomite) and enstatite grain-boundaries, indicating the early stability medium-grained, subhedral needles of anthophyllite, of talc and enstatite. The assemblagetalc + enstatite, which grow in spherical, radiating rosettes with an where not armored in large crystals of enstatite, is average radius of approximately 1 cm. Other silicate usually overgrown by anthophyllite (Fig. 4d). The minerals are present in the anthophyllite - carbonate coexistence of talc + enstatite with anthophyllite is rock in minor amounts including: magnesio- governed by solid-phase reaction (4) below. cummingtonite, chlorite, and late-stage, retrograde talc. No compositional differences could be detected MgrSioOto(OII)2 + 2MgrSirOu = MgzSieOzz(OH)z between anthophyllite from the enstatite - magnesite talc enstatite anthophyllite (4) and anthophyllite - carbonate rock types (Table 2). 1228 THE CANADIAN MINERALOGIST

qB {; sg 9# ;g 10 ii 6 6'E. H - =O iJ o *! r -' {oc vo trro >F^FT leFq J < -a .= 6 *d =tr'6 B 6'9g $ F€ 9; :F;4 d Eg tr E Z HS €ga'u d 5"aF -^O' FI-ts g' " p d@ ,-tlJ< Fl egsE HRTg =Fs3 *z x;+ THB! -a b R 30 - e5 {8 h"3 pFFEdP qld o -i-

iJ o hnj -€EFE e.6'F'

X --Io EEB EFE 6 n-C 5 !e F? H ;4.f; tr ot!6 e oos s3:g 6'HF' :E'^^ o< X -v H<-. =o5 rl5Ei Q!tx E:s = =:F {s0s sH tt< - PETROLOGY OF THE FLINTON CREEK METAPERIDOTITES 1229

Magnesite and dolomite are more abundant in the obtained by Miider & Berman (199L). These data are anthophyllite - carbonate rock than in the enstatite - used to examine the equilibrium conditions of the fwo magnesite rock, and make up approximately 30 to sOEa solid-phasereactions present in the CaO - MgO - SiO2 of the total volume. Magnesite is generally more abun- - HrO - CO2 system (reactions 2 and 4 above). dant; however, the ratio of dolomite to magnesite is The locatiqhs of these two equilibria in P - T space dependent on proximity of the contact between the have been plotted for tle various thermochemical ultramafic body and the surrounding host-rock. databases using a Microsoft EXCEL spreadsheet Although the total amount of carbonate present in the program that solves the following equation by iteration: rock remains constant, the proportion of dolomite to magnesite increases outward toward the contact, where T.' dolomite comprisesup to 90Voof the carbonatepresent. =0=Nrh"+ AGpr Jcpar-r[s." + l{cntr) ar) (5) This relationship suggeststhat there is a metasomatic 8.m control on the amount of dolomite present in the +w"'' (p-p,\ + (P-P,) +L\(T-T,)+Av4g-T,)'] [-^v1+Av. anthophyllite - carbonaterock. +(Lv\ I 2 - Av) (P'?*l)+(Au. /3) lP' -D + e*+ KflnK

PHaspEerm-rsnra Iwvolvwc Solros IN Tm Sysrev CaO-MgO-SiO2-H2O-CO2 where AH, S and AV are the enthalpy,entropy and volume of reaction at reference pressure P, and The metamorphism of peridotites in the model temperatureT. (1 bar and298K). Cp is the heat capacity, system CaO - MgO - SiO2 - HrO - CO has been calculatedwith the equation of Berman & Brown described by Greenwood (1967), Johannes (1969), (le8s). Ohnmacht (1974), Trommsdorff & Evans (1972, 1974, The Avr - Av, terms in equation (5) account for the 7977a,b), Evans & Trommsdorff (1970,1974), and change in volume of the sohd phases with increasing Evans (1977). Phase relations presented in this paper temperature and pressure,using the following expres- emphasizeonly those aspectsof the model system that sion from Berman (1988): apply to tle rocks at Flinton Creek. The seven major mineral phases observed in the Flinton Creek v - - - (6) ultramafic rocks are shown on Figure 3 in the "'' = | + r, (T - Tr)+ vr(T Tr)2+ v,( P Pr) + vo(P Prf ternary compositional space CaO - MgO - SiO2.Ttvo vn.r, additional components, ferrous and manganese, are treated as dilutants of the component. Note that in equation (5), Avt=A1vr x DPr'rr/105), Aluminum occurs primarily in magnesian chloriteo Lv r= 67y2 7 DP.'Ty'I o5), Avr=^1v. 21r:n'r'/ 1Os) and which is always present and does not seem to be Avr=l11vo2qoPr'ry'lQ8), where vo is the coefficient from involved in reactions with higher- or lower-grade equation (6), and o is the molar volume of each mineral aluminous minerals. Certain minerals observed in the reaction at reference temperature, Tr, and elsewhere in metamorphosed peridotites do not occur pressure,Pr. The Holland & Powell (1990) database at Flinton Creek; these include quartz, diopside and can be made compatible with this expression by serpentine. 6aking the following substitutions for the coeffrcients Three databasescontain thermochemical data for all of isothermal expansion and compression: vr = o( and the required phases: Helgeson et al. (1978), Berman vg=-0.1B. (1988) and Holland & Powell (1990). The Berman The G6i".6*term was used by Berman (1988) to (1988) databasecan be further subdivided, since it model progressive disorder in dolomite with increasing contains two values for magnesite, the first derived temperature from 298.15 K (completely ordered by Chernosky & Berman (1989), and a later value dolomite) to 1423 K (completely disordered). The G6i"o6",term in equation 5 is calculated by: TABLE 5, ACTTVTTYMODELS USED FOR CALCULATING EQTJILIBRIA LG; = NI;-TLS; Q) Componeft Fomula Activity Model CA*

where the AH* and ASa;.disorder terms are calculated Arnhophyllite Mg?SLO2(OH, okJ' 0.39 Tr@olite CaJvlgrSisOz(OH), (3-ca-KxxJ'?Gd5 0.7t using equations 16 and l7 from Berrnan (1988), with a Ensatite Mg?Si?O6 (x"J, 0.79 slight modification (the newer versions of Berman's Foretqhe MgrSiO4 (xel o.E2 databasesupply da and d5terms, which must be substi- Tale M&SLOrc(OH), Cxd' 0.91 tuted for d, and doin these earlier equations). Dolomite CaMg(COJ CXMJ 0.98 Magn6ite MC(CO3) Cxk) 0.94 Figure 5 shows the results given by Equation 5 using average measured compositions of the minerals from the Flinton Creek metaperidotites. Activities, ' Compositiom used uo ttre avenge ofthre listed in Tabl6 2 atd 3, with the q@ptio of talq which is frm wple l0l7E8-l a only. CA @lolaled actMty a. given in Table 4, were calculatedusing an ideal-solution 1230

10000

9000

8000

7000

6000 It n / t

n 200 300 400 500 600 700 800 900 1000 Temperature( "C)

Ftc. 5. Calculated solid-phase equilibria in a portion of the system CaO - SiOz - MgO - HrO - CO, adjusted for the measured compositions of minerals (Tables 2, 3). Solid lines represent the reaction talc + 2 enstatite = anthophyllite. Dashed lines for tremolite + 4 magnesite = anthophyllite + dolomite; Dd indicates that the variable dolomite-disorder model of Berman (1988) was used to the locate the reaction, whereas nDd indicates that the dolomite-disorder model was not used. Thermo- dynamic datasets used in the calculations are indicated as follows: H78: Helgeson et al. (1978), CB89: Chemosky & Berman (1989), HP90: Holland & Powell (1990), MB9l: M[der & Berman (1991). All datasetspredict anthophyllite stability for the pressure - tempemure mnge of metarnorphism, indicated by black dots with enor bars (150'C, +1000 bars); the Berman (1988) database,rvith modified data for magnesite (Mdder & Bermar 1991) and variable degree of disorder i-n dolomite, predicts the stability of anthophyllite + dolomite wirhin enor of the estimated P - T range.

model. Also shown in this figure are the thermo- TABLE 6. FLIJII>BEARING ASSEMBI-A.GESCOD(STING AT barometryresults (Table l), which are consideredto INVARIANT POINTS IN THE SYSTEM MsO-SiO, representpeak conditions of metamorphismfor the Abs€d.Pbse PhrgPrBd Flinton Creekmetaperidotites. The observedreplace- Dsigndim ment of talc + enstatiteby anthophyllite indicatesthat the solid-phaseequilibrium, reaction (4), limi1i11g15" (Arrr) Mg!, ED, Fo, Tlc MtrT' stability of anthophylliteis expectedto lie just below (E!) Mgs, Atb, Fo, Tlc MAFT* the threeP - T estimates.The petrographicdata also (nc) Mgs AlbFo, En MAFE" predict the stability of anthophyllite+ dolomiterelative Go) Mg$ Arb, En, nc MATE to tremolite + magnesitefor the P - T conditions (Ms8) Ab, En, Fo, Tlc FATE (Fo,M$) T]c, Eq Alh TEA and mineral compositionsat zunton Creek.Figure 5 demonsftatesthat the ttrermodynamicdata of Bennan (1988), as modified by Miider & Berman(1991), i As deigaated by Ere & Tromsdorff(1974). correspond best with the thermobarometry and petrographyof Flinton Creekrocks; this databaseis Trommsdorff(1974). At bothlocalities, rocks containing usedin subsequentcalculations. magnesite,talc, enstatiteand forsterite are overgrown at somelater stageby anthophyllite.Although the two Ulrrvanren-rPuesE-RE-ATroNS occurrences41s mi nelalegically si mi I s1, petrographic analysisreveals substantial differences in the sequence The ultramafic lenses at Flinton Creek are of mineralassemblages that developed. mineralogicallysimilar to the ultramafic boudinsat Four mineral phasesand a fluid phase form a Guglia in the Swiss Alps, as describedby Evans & univariant assemblagein the systemMgO - SiO2- PETROLOGY OF TTIE FLINTON CREEK METAPERIDOTITES t23L

12000

11000 't0000 9000

8000 c g zooo E 6000 aq (I) d sooo 4000

3000 2000 1000

400 450 500 550 600 650 700 750 800 Temperature ('C)

Frc. 6. Pressure- temperaturediagram for univariant pofurtswith pure magnesian minerals.Symbols along curvesand numbersrefer to incrementalvalues of the mole fraction of CO, along the univariantpoints. Calculatedwith databaseof Berman (1988),as modified by Mdder& Berman(1991). MAFE, MAFT, MEFI, TEAindicate univariant curves with M (magnesite),A (anthophyllite), F (forsterite), E (enstatite), T (talc). Solid curvesare stable;dashed curves are metastable.

H2O- CO2.Evans & Trommsdortf(1974) described MAIE andFATE thereforeproject throughthe compo- one such assemblagecharacteristic of the univariant sition dimensiononto the P - T path of TEA. TEA and conditioirMEFT (magnesite- enstatite- forsterite- MEFT do not intersecton Figure 6, indicating that the talc - fluid; Table 6), at the Guglia location. The invariant point MEFTA is metastablefor end-member presenceof forsterite in the Guglia rocks from the magnesianphases using the thermodynamicdata of beginningof their petrologicalevolution is essentialto Berman(1988) and Mader & Berman(L991). therecognition of the univariantassemblage MEFT as Evans& ftemmsdorff (1974)pointed out that the a stableone. This situation contrastswith the rocks at addition of iron to the end-membermagnesian phases Flinton Creek, where forsterite overprints the earlier resultsin a substantialincrease in the field of stability 'magnesite- enstatiteassemblage. The significanceof of anthophyllite relative to talc + enstatite,with a these petrographicobservations can be understood correspondingshift in the locationof TEA to signifi- by locatingthe variousrrnivariant assemblages for the cantly lower temperatures.According to the databaseof systemMgO - SiO2- H2O- CO2in P - T space.Figure 6 Berman(1988), the additionof iron causesTEA and has been calculatedwith the program TWQ (Berman the other univariant assemblagesindicated on Figure 6 1991) using thermodynamicdata for end-member to intersect at a single point (the invariant point magnesian compositions. The figure shows the MEFIA) for an anthophyllitecomposition of Athrr; P-T trajectory of the compositionally degenerate TEA shifts to lower temperatureswith further addition univariantcurve, TEA (talc - enstatite- anthophylite), of irono splitting the point MEFIA into duplicate as well as that of three normal univariant curves, invariant points, as implied on Figure 7 for the MAFE , MEFT and MAFT. TEA containsboth MAIE measuredcompositions o1 1trsminerals at Flinton (magnesite- anthophyllite- talc - enstatite)and FATE Creekoas reported in Tables 3 and 4. For these (forsterite- anthophyllite- talc - enstatite)in P-T compositions,the invariant point MEFTA is stableand space,since both assemblagescontain the solid-phase duplicatedat ll,l00 bars and <500 bars.MAFT and equilibrium, talc + 2 enstatite= anthophyllite.Both MAFE are stable between the duplicate invariant 1232 THE CANADIAN MINERALOGIST

13000 12000 11000 't0000 9000 'ul.i., 2. 8000 li (E It o 7000 (I, tl o 6000 :) o o il o- 5000 4000 3000 2000 1000

400 450 500 550 600 650 700 750 800 Temperature (oC)

Frc. 7. hessure - temperafife diagram for nnivariant assemblages, calculated on the basis of measured compositions of the minglals (fables 2, 3). Number and symbols refer to incremental values of the mole fraction of CO2 along the univariant curves. Mi-neral assemblagesand thennodynamic data as for Figure 6.

points, and MEFT is stable beyond this range at TABLE 7. INVARIANT POINTS IN A PORTION pressures lower or higher tlan either of the MEFIA OF THE SYSTEM CaO - MgO - SiO, invariant points. It therefore appezrs that mineral compositions in the Guglia metaperidotites lead Ab$nt PhN PhffiPred D6tgmtlon to the stability of the MEFT assemblage above the (Ath, En) Dol, Fo, Mgs, Tr, Tlc DTRMFT higher-pressure duplicate of the MEFTA invariant (Ath, Mgs) Dol, En, Fo, Tr, Tlc DTREFT point" at approximately l0 kbars. (Ath, Fo) Dol, En, Mgs, Tr, Tlc IITREMT Tlu IwruuBNce oF FLUrD ColposmoN (Ath, Tlc) Dol, En, Fo, Mes, Tr DTREMF (Mgs, Tlc) Ath, Dol, En, Fo, Tr DTRAFE The influence of fluid composition on the mineral (En, Fo) Ath, Dol, Mgs, Tr, Tlc DTRAMT assemblage of the ultramafic rocks at Flinton Creek can be examined on Figures 8 and 9, which consider tfie (En, MeO Ath, Dol, Fo, Tr, Tlc DTRAFT stability of mineral assemblages,including the calcic (En, Tlc) Ath, Dol, Fo, Mgs, Tr DTRAMF - phasesdolomite and tremolite, on ln fugacity (HrO) (Fo, Meo Arh, Dol, En, Tlc, Tr DTRATE In fugacity (CO) diagramsoconstructed uggslding to (Fo, Tlc) Ath, Dol, En, Mgs, Tr DTRAME the method described by Korzhinskii (1959). The free energy of disordering in dolomite (Berman 1988) has been included in the calculation. Also shown on these figures is the mechanical equilibrinm surface along listed in Table 7. The fugacity diagrams allow the which calculated pressure of fluid is equal to lithostatic petrography of the calcic phases to be used as a further pressure P(COr) + P(HrO) = Protar.This surface was check on the evolution of the fluid phase. calculated using the nonideal fluid-mixing model of Figure 8 is calculated for 680oC, the thermal maxi- Jacobs & Kerrick (1981). The addition of calcium as a mrrm applicable to the southern Flinton Synclinorium, component results in the stability of two additional as indicated by thermobarometry of rock fypes other invariant points labelled DTRAFE and DTRAFT, and than peridotite. This figure demonstratesthat enstatite PETROLOGY OF THE FLINTON CREEK METAPERIDOTTTES r233

12.0

ll.0

N En+ (J 2Fo DTRAFT bI) H"ry"#

- o + s

8.0 9.0 10.0 11.0 log / H,O

Ftc. 8. Ln/(H2O) - Inf(COr) diagram at 7000 bars and 680oC. Chemography as shown on Figure 4. The mechanical equilibrium surface, along which fluid partial pressuressum to total pressure,is shown as a curved lile, with solid circles and numbers indicating incremental values for the mole fraction of CO2.Phase relations are indicated for talc (Tlc), anthophyllite (Ath), enstatite (En), forsterite (Fo), rnagnesite (Mgs), tremolite (Tr), and dolomite (Do). Designations of the invariant points arelistedinTables6aadT.Reactionl:Fo+HrO+9COr=4h+9Mgs.Reaction2:.32Fo+9Tr+4HzO+36COr=l3Ath + 18Dol.

- magnesite assemblagesrequire high X(CO2) values earlier assemblagesin the enstatite - magnesite rock. for stability; this result is in agreement with earlier, Decreasing temperature between Figures 8 and 9 lower-pressure (2000 bars) experiments by Greenwood reduces the separation between the pairs of invariant (1967) and Johannes(1969). points MAFE-DTRAFE and MAFT-DTRAFT such Figure 8 provides a possible explanation for the that each pair is almost coincident on Figure 9. The replacement of enstatite - magnesite by late-stage development ofthe anthophyllite - carbonate assemblage olivine, through the introduction of relatively H2O-rich appears to be related to a metasomatic influx of fluid fluids [X(CO) < 0.45] into the enstatite - magnesite that carries the bulk composition of the peridotite into rock. Both enstatite and forsterite can be seen on the the stability field of anthophyllite - magnesite. Forma- fugacity diagram to be in equilibrium with dolomite tion of a metasomatic rind could not have carried on to aDd magnesite, as required by the petrography ofthe much lower temperatures, as the mechanical equilibrium Flinton Creek rocks; enstatite coexists with the surface would intersect the talc - magDesite stability carbonates and high-CO2 fluids along the mechanical field at approximately 64O"C.Talc - magnesite rinds equilibrium surface, whereas forsterite and two have not been observed surrounding the anthophyllite - carbonatescoexist with a more HrO-rich fluid. carbonate envelope at Flinton Creek. Figure 9 is calculated for a temperature of 650"C, The stability field of anthophyllite - magnesite - corresponding to the development of the anthophyllite dolomite on Figure p is limited along the mechanical - carbonate rock in envelopes that completely replace equilibrium surface by enstatite - magnesite - dolomite L234 THE CANADI,AN MINERALOGIST

I t.5

| ?ooobu'r I 650"C I1.0 | I

/ nn \llc t tt \ t tt I t t, \ IN\ htw N -{U$*rr" Q 10.0 bI)

0.05

log / HrO

Frc. 9. Ln(H2O) - lnf(Cot diagram at 7000 bars and 650'C. The curved line indicates the location of the mech:nical equilibrium surface. Symbols and chemography follow the convention established in Figure 8. assemblagesin CO2-richfluids and by forsterite - carbonate rind lie between approximately 650' and tremolite assemblageswith either dolomite or 680'C, if one assumesthat estimates of metamorphic anthophyllite in H2O-rich fluids. Beneattr the pressure of7 kbart I kbar are correct. mechanical eqrrilifdu6 surface, the assemblage anthophyllite- magnesite- dolomite is restrictedto MsrAMoRPrtrcEvor,moN fluids that approachbinary mixtures of CO2and HrO. For example,the point MAFE occursat fugacitieson The metamorphic evolution of the enstatite - Figure 9 correspondingto a P(CO) of.2028bars and a magnesite and anthophyllite - carbonate rocks can be P(HrO) of 4243 bars,with p(COr) + p(HzO) = 6271 summarized using the pressure - temperature and barsusing the mixing relationshipsfor CO, and HrO log/(HrO) - logf(Co) diagnms in conjunction with from Kerrick & Jacobs(1981); only minor dilution of available petrographic evidence. CO2plus H2Oby saltsor otler gasspecies is therefore On the basis of existing dala, little can be said about possiblewith a total fluid pressureof 7000 bars.The the origin of the Flinton Creek metaperidotites prior to metasomaticevent that led to the developmentof their metamorphism in the presence of COlrich fluids anthophyllite - carbonate envelopes around the and the forrnation of enstatite - maglesite assemblages. progradeassemblages apparently took place in the Mineral assemblages such as enstatite + talc and petrological environmentrepresented by Figure 9. tremolite + magnesite appear to have been stable during The absenceof a talc - magnesitealteration rind, the early stages of metamorphism; however, petro- combinedwith the fact that the mechanicalequilibrium graphic evidence suggests that they later became surface fails to pass through the anthophyllite + metastable relative to anthophyllite and anthophyllite + magnesitestabilify field in Figure 8, indicate that dolomite. We propose that vein-related, forsterite- conditions for the formation of the anthophyllite- bearing assemblages were produced at near-peak 1235 conditionsof metamorphism(approximately 680'C), NSERC.R.M. Eastonreviewed an earlyversion of the by infiltration of a relatively HrO-rich fluid along manuscript and encouragedits submission. Rob discretezones, resulting in the local replacementof Berman,Mike Easton,Robert F. Martin, K. Buchet enstatite- magnesiteby forsterite.The anthophyllite- and an anonymousreviewer provided commentand carbonateis consideredto haveformed during the early criticismthat considerablyimproved the manuscript. stegesof cooling(at approximately650"C) by infiltration of a relatively H2O-richfluid phase,resulting in the RBrsnENcss completereplacement of the enstatite- magnesite assemblagein the smaller ultramafic lenses.Rind BERMAN,R.G. (1988): Internally-consistent thermodynamic formationis believedto haveoccurred at approximately data for nrinerals in the system Na2O - KrO - CaO - MgO 650oCbecause Figure 9 indicatesthat at this tempera- - FeO - FEO, - AlrO, - SiO2 - TiO2 -H2O - CO2. J. ture, the anthophyllite- carbonaterind would form Petrol.29. M5-522. from the widestrange of compositionsof infiltrating (1991): - Thermobarometryusing multi-eqnili$du6 fluid without the formation of an additional talc calculations: a new technique, with petrological applica- carbonaterind. tions. Can. Mineral. 29, 833-855. The temperafureest:mates for the formation of forsteriteveins (680"C) and anthophyllite - carbonate & BnowN, T.H. (1985): Heat capacity of minerals rind (650'C) are consistentwith thosederived from in the system Na2O - KrO - CaO - MgO - FeO - Fe2O3- ttrermobarometryof rocks listed in Table 1. Calculation AlrO. - SiO2 - TiO2 - HrO - CO2: representation, of additionalloe/(HzO) - log/(Co, diagramsat lower estimation, and high temperature extrapolation. Contrib. pressuressuggests that the temperatureestimates for Minzral. Petrol. 89, 168-183. the metamorphismof the ultramaficrocks arerelatively independentof the est:matedpressure derived from BRrcm, E.G. (1986): Geology of the Mellon Lake area. Rep. 5598. resultsin Table 1. Theseconsistent est:mates of tem- Ontario Geol. Surv., Open FiIe peraturesupport the suggestionthat the ultramafic Metamorphism of ultramafic rocksof theFlinton CreekComplex were metamorphosed Buclmn-Nunm.rnN, K.(1988): rocks in the central Scandinavian Caledonides. 1n kogress simultaneouslywith the surroundingrocks. in Studies of the Lithosphere in Nonway (Y. Kristoffenen, We tentativelyconclude that the importantfactors in ed.). Nar GeoI. Unders., Spec. Publ.3, 86-95. accountingfor the differencesin the petrographyof metaperidofitesat Flinton Creek and Guglia were CARMTcHAEL,D.M., Moonr, J.M. & SreprN, G.B. (1978): higherpressures along the P-T-t path at Guglia and the Isograds around the Hastings metamorphic "low". In '78 presenceof a CO2-richfluid at Flinton Creek. Toronto Field Tiips Guidebook (A.L. Cunie & W.O. Mackasey, eds.). GeoI. Assoc. Can. - Mineral. Assoc. ConclusroNs Can.,324-346.

Ultramafic lensesalong 7 kilometersof exposurein CHAIIELL, J.F. (1978): The Clare River Strucrure and its Univ., Ottawa, the Central MetasedimentaryBelt Tectonic Setting.Ph.D. thesis, Carleton of the Grenville Ontario. Province were metamorphosedin the presenceof a - CO2-richfluid to produceenstatite magnesiteassem- CHBRNosKy, J.V. & BrRMAN, R.G. (1989): Experimental blagesas well as accompanyingtalc, anthophylliteand, reversal of the equilibrium: clinoctrlore + 2 magnesite = 3 ultimately, forsterite. Petrographicevidence indicates forsterite + spinel +2CO2+ 4H2O aad revised thermody- the mantle of anthophyllite- magnesite- dolomite namic properties for magnesite.Am. J. Sci.7l,9,249-266. rock aroundcores of the progradeassemblages are the product of a metasomaticprocess that occurredduring Evars, B.W. (1977): Metamorphism of alpi-neperidotite and retrogrademetamorphism in the presenceof a fluid . Aznu. Rev. Earth Planet. Sci. 5,397447. phasewith significantcontent a of both CO2and HrO. & Tnomvtsponrr,V. (1970):Regional metamor- Field relationships,including the developmentof phism of ultramafic rocks in the Central Alps: parageneses blackwall alterationaround the lenses,indicate that in the system CaO - MgO - SiO2 - H2O. Schweiz. meramorphismtook placein situ.Thermobarometryof Mineral. Petrogr. Mitt. 50, 48L492. adjacentalnminous indicates that metamorphic conditionsreached at least680"C and 7000 kilobars. & _(1974): Stability of enstatite + talc and COr-metasomatism of metaperidotite, Val d'Efra, AcrNowtpocswGr.ITs Lepontine Alps. tun. J. Sci. 274,274-296.

Instructionon the use of the electronmicroprobe Fono, F.D. & SrrppnN, G.B. (1994): Shear zone associated, metamorphism on was provided by P. Jones.FDF late-stage deformation ald retrognde acknowledgesthe the western margin of the Flinton Synclinorium. GeaL assistanceof an NSERCpost-graduate scholarship. The Assoc. Can. - Mineral. Assoc. Can., Program Abstn researchwas supportedby a grant to GBS from 19,A^37. r236

Fnosr, B.R. (1975): Contact metamorphism of serpentinite, I\&irnn, U.K. & Bnnual, R.G. (1991): An equation of state chloritic blackwall and rodingite at Paddy-Go-Easy Pass, for to high pressure and temperatue. Am. cenffal Cascades,Washington. J. Penol, 16,U2-313. Mineral. 7 6, 1547-1559.

GREENwooD,H.J. (1967): Mineral equilibria in the system Ornnr,recnr, W. (I974): Petrogenesis of carbonate- MgO - SiO2 - H2O -CO2. In Researchesin Geochemistry orthopyroxenites (sagvandites) and related rocks from 2 (P.H. Abelson, ed.). John Wiley, New York, N.Y. Troms, northern Norway. J. Petrol. 15, 303-323. (s42-567\. PsrrRsEN, K. (1883): Sagvaldit, en ny bergart. Tromsd Mw. Arsh.6,8l. Ilu,cesoN,H.C., Ds-aNsy, J.M., NEsnrrr, H.W. & Bno, D.C. (1978): Summary and critique of the thermodynamic PowELL, R. & Hor-lexp, T. (1990): Calculated mineral propeftiesof rock forming minerals.Am. J. Sci. 278A, eqrilibria in the pelite system, KFMASH (KrO - FeO - r-229. MgO - AI2O3- SiO, - HrO). Am. Mineral.75,367-380.

Hopces, K.V. & SeEAR,F.S. (1982): Geothennometry, PRINGLE, G.J. (1989): EDDI - a FORTRAN computer geobarometryand the Al2SiO5 triple point at Mt. program to produce corrected microprobe analyses of Moosilauke,New Hampshire,Am. Mineral. 67, LIIS- minerals using an energy dispersive X-ray spectrometer. t134. GeoI. Surv. Can., Open FiIe Rep.2l2il.

Hollar.tr, T.J.B.& BLuNDy,J. (1994):Non-ideal interactions SANFoRD,R.F. (1982): Growth of ultranafic reaction zones in in calcic amphibolesand their bearingon amphibole- to amphibolite facies metamorphism. Am. J. plagioclasethermometry. Contrib. Mineral. Petrol. 116, Sci. ?.a2,543-616. 433447. Scnrwn, W., Orfl$4AcHr, W. & MaNNcmN, J. (1972): & PowELL,R. (1990):An enlargedand updated Carbonate-orthopyroxenites (sagvandites) from Troms, intemally consistent thermodynamic dataset with uncer- northern Norway. Lithos 5, 345-364. tainties and correlations: the system K2O - Na2O - CaO - MgO - MnO - FeO - FqO3 -AlrO3 - TiO2 - SiO2 - C - TnovnsoN, J.B., Jn. (1959): tocal equilibrium in metasomatic H, - Or. J. Metamorphic GeoI.8,89-124. processes. In Researches in Geochemistry f G.H. Abelson, ed.). John WileS New York, N.Y. (427-457). JAcoBs, G.K. & Krnrucr D.M. (1981): APL and FORTRAN programs for a new equation of state for HrO, COr, aad THoMpsoN, P.H. (1972): Stratigraphy, Structure and Meta- - their mixtures at supercritical conditions. Computers and morphism of the Flinton Groap in the Bishop Corners Geoscience 7, l3l-L43. Madoc Area, Grenville Province, Eastern Onario.Ph.D. thesis, Carleton Univ., Ouawa, Ontario. Janxs, R.H. (1967): of the Roxbury district, (1973): Mineral zones and isograds in "impure" Vermont. Izr tlltramafic and Related Rocks (P.J. Wyllie, calcareous rocks, an altemative means of evaluating ed.). John Mley, New York" N.Y. (137-160). metamorphic grade. Contrib. Mineral. Petrol. 42,63-80.

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