metamorphism of the ultramafic rocks of …rruff.info/doclib/cm/vol22/cm22_77.pdf · metamorphosed...

Canadian MineralogistYol.22, pp. 77-91 (1984)

METAMORPHISM OF THE ULTRAMAFIC ROCKS OF THE THOMPSON MINE,THOMPSON NICKEL BELT, NORTHERN MANITOBA*

A. DOGAN PAKTUNq

Department of Geology, University of Ottawa, Ottawa, Ontario KIN 6N5

ABSTRACT

Abundant sill-like bodies of serpentinized ultramaficrocks, associated with nickel sulfide deposits, are found onthe western side of the Thompson Nickel Belt (Manitoba),near the Moak-Setting Lakes cataclastic fault-zone. Anunusually fresh ultramafic body, found on the 4000 levelof the Thompson mine, is composed of dunitic, peridotitic,orthopyroxenitic and amphibolitic units. Tremolite is pres-ent as a Ca-bearing silicate in most of these rocks. TheMg,z(Mg+Fe) ratio of olivine ranges from 0.83 to 0.90,whereas that of orthoplroxene ranges from 0.85 to 0.91as a function of the bulk-rock chemistry, Spinel ranges incompostion from Al-chromite to Mg-Al-spinel as the gadeof metamorphism increasq. The ultramafic body was partlyaltered before being progressively metamorphosed underupper-amphibolite-facies conditions. The approximate m,D(-imum temperature attained during metamorphism isestimated to be 7ffi'C. The body was subsequently deform-ed. Recrystallization processes, which resulted in the for-mation of equigranular mosaics of olivine neoblasts, follow-ed the deformational episode. Late-stage shearing andretrognde metamorphism led to secondary chlorite and thinveins of serpentine developed locally parallel to the fabric,along the margins of the ultramafic body.

Keywords: metamorphism, ultramafic rocks, nickel sulfidedeposit, Thompson, Manitoba.

Soruuenn

On trouve d'abondants massifs du tlpe filon-couche deroches ultramafiques serpentinisdes, associ6s d des d6p6tsde nickel sur le cot6 Ouest de la ceinture nick6lifdre deThompson (Manitoba), prbs de la zone de faille cataclasti-que des lacs Moak-Setting. Un massif ultramafique tr0speu altdr6, observ6 au niveau 4000 de la mine Thompson,se compose d'unit6s dunitiques, p6ridotitiques, orthopy-roxdnitiques et amphibolitiques. La tr6molite est prdsentecomme min6ral calcifbre dans la plupart de ces roches. Lerapport Mg/(Mg+Fe) de l'olivine varie de 0.83 i 0.90, alorsque celui de I'orthopyroxbne varie de 0.85 i 0.91 en fonc-tion du chimisme global de la roche, En composition, lespinelle passe de la chromite alumineuse au spinelle-Mg-Al quand augmente I'intensitd du m6tamorphisme. Le mas-sif ultramafique fut partiellement altere avant d'6tre gra-duellement m6tamorphis6 au facies amphibolite sup6rieur.Les roches ont atteint une temp€rature maximum d'envi-ron 700oC au cours du mdtamorphisme. Le massif se

*Publication 25-83, Ottawa-Carleton Centre for GeoscienceStudies.

d6forma par la suite. Les processus de recristallisation res-ponsables de la formation de mosaiques dquigranulaires den6oblastes d'olivine suivirent l'6pisode de d6formation. Lecisaillement tardif et le m6tamorphisme rdtrograde sontmarquds par la chlorite secondaire et les filonnets de ser-pentine que l'on trouve ddveloppds localement parallble-ment e Ia fabrique, en bordure du massif ultramafique.

(Traduit par la R€daction)

Mots-cl4s: m6tamorphisme, roches ultramafiques, gise-ments de sulfures de nickel, Thompson, Manitoba.

INTRoDUcTIoN

The Thompson Nickel Belt lies on the boundarybetween the Churchill and the Superior provinces innorth-central Manitoba (Fig. l). The Moak - Set-ting Lakes cataclastic fault-zone defines the north-western boundary with the Churchill Province. Thesoutheastern boundary, on the other hand, is partlya cataclastic fault-zone and partly a zone ofmetamorphic transition (Cranstone & Turek 1976)that defines the border with the Pikwitonei Province.In addition to the structural importance of this belt,it contains important deposits of nickel sulfide;therefore, the belt has been mapped in detail, andvarious aspects have been studied. A comprehensivegeological outline of the belt is given by Peredery(1982).

Ultramafic rocks occur close to the northwesternside ofthe belt. Individual bodies have been studiedby various workers: the bodies of the Manibridgemine by Coats (1960, those located on the south-western edge ofthe belt, under the Paleozoic coverby Bliss (1973), and the Pipe II and West Manasanultramafic bodies by Saboia (1978). Generally theyare extensively serpentinized and sheared, retainingvery little relict texture.

In this study, ultramafic rocks from the differentlevels of the Thompson mine have been investigated.However, special attention is given to a largeultramafic body found at the 4000 level since it isremarkably fresh compared to the other ultramaficbodies found in the belt.

GENERAL GEOLOGY

The belt is underlain predominantly by migrnatitic

77

78 THE CANADIAN MINERALOGIST

gneisses that mainly contain amphibolite-faciesmineral assemblages. However, granulite-faciesassemblages are also common in the belt and are in-terpreted by Weber & Scoates (198), Peredery (1979)and Russell (1981) as relict Archean granulites thatsurvived the Hudsonian Orogeny.

Near the western margin of the belt, the basementgneisses are overlain by thin (150-1500 m) Aphebiansupracrustal rocks (Peredery 1982) that includemetasedimentary and metavolcanic assemblages.These exhibit a range of metamorphic grades frommiddle amphibolite to granulite. Two metasedimen-tary assemblages, the Pipe and Thompson groups,have been distinguished on the basis of lithology andmetamorphic grade @eredery 1982). The Thompsonmetasediments show a higher metamorphic gradeand include quartzite, skarn, iron formation andschist.

These supracru$tal rocks and the basementgneisses were intruded by abundant ultramafic andmafic sills and dykes. Ultramafic bodies are generallylensoid or tabular in shape and vary in width fromseveral metres to several hundreds of metres. Thecontact between the ultramafic bodies and the enclos-ing rocks is usually conformable, but the contactrocks are so deformed and altered that their truecharacter is uncertain (Peredery 1982). Ultramaficrocks range in composition from peridotite to pyrox-enile and are extensively altered. Peredery (1979) alsoused a field term, 'ultramafic amphibolite', todescribe a variely of ultramafic rocks that ranges incorrrposition from picrite to pyroxenite.

In the Thompson mine, nickel sulfides are foundmainly as massive sulfide bodies together withultramafic rocks in the metasedimentary rocks.Ultramafic rocks are mainlv in the form of inclu-

IHOMPSON NICKEL BELT

I Mctavolcanlc

l*l Mctascdimant

l---l Migmatitic gnciss

PIKWITONEI PROVINCE

[-Z uol.on dikcswarm

f-----l Granutita facias acidic' ' and basic rocks

,i,/l l

,ir--t lault , tQ

-: gcological boundary i'y'(E Ni deposit"

^.'.#, J

! t \

atQ n tll, I

T

I

N.W.T.-i-'-

I r| " tl li I Oni.rio- - { . _

\u's'A' 36iov">

Ftc. l. Regional setting of the Thompson Nickel Belt.

METAMORPHOSED ULTRAMAFIC ROCKS, THOMPSON, MANITOBA 79

sions, which range in size up to several metres across,in massive sulfides. Although larger ultramaficbodies are not uncommon in the Thompson mine,their volume is small relative to the amount ofsulfides.

Nickel sulfide deposits of the Pipe II mine,Mystery and Moak localities mainly occur in theform of disseminated sulfides in the ultramafic rocks.According to Peredery (1982), the distribution ofsulfides is largely the result of remobilization dur-ing the complex tectonic and metamorphic historyof the belt.

The major structure of the Thompson mine is ananticlinical fold striking northeast and plungingsteeply to the south, according to Zurbrigg (1963).However, the fold could be synclinal, judging fromsimilarities in stratigraphic succession between the

Thompson and Pipe sedimentary sequences, accord-ing to Peredery (1982). Cross folding, with an axialtrend close to north-south, accounts for the con-figuration of the Thompson Group of metasedimen-tary rocks (Peredery 1982). The earlier folds aresubhorizontal, and their axial plane strikes north-northeast.

MtNSRAI-ocv aNn PsrnocRAPHY

The ultramafic body at the 4000 level of theThompson mine, as seen along two drill holes (Fie.2), is 130 metres thick, probably lensoid in shape andenclosed in a garnet-sillimanite-biotite schist. Thebody is composed of peridotitic, orthopyroxeniticand amphibolitic rocks. Using the scheme of Evans(1977), the mineral assemblages correspond to

FIc. 2. 3600 N vertical section of the Thompson mine (T-3).


tremolite peridotite and tremolite pyroxenite (Fig.3), which are indicative of the amphibolite facies.The unit named 'amphibole-rich pyroxenite' inFigure 3 is mineralogically similar to the ultramaficamphibolite of Peredery Q979). The main sulfidemineralization is found in the enclosing schist in theform of massive and stringer ore. Minor dissemina-tions of sulfides are present in the ultramafic body,close to its contact with mineralized schist. Asobserved in core from drill hole 64599, tremoliteperidotite and its serpentinized equivalents amountto one half of the body, whereas the tremoliteplroxenite makes up more than one third (Frg. 3).Tremolite-olivine pyroxenite is the main rock typeseen along drill hole 64816.

Tremolite peridotite

Olivine in the peridotitic zones is of two types:megacrystic (2-4 mm) and fine grained (less than Imm). Megacrystic olivine usually is black owing tofine opaque dusty material disseminated or concen-trated along irregular fractures in olivine (Frg. 4).This material, possibly magnetite, may be the prod-uct of high-temperature oxidation of olivine (Hag-gerty & Baker 1967, Champness 1970, Putnis 1979).

ffi rmuor-m eenoorm

llllll rneuom ouvnr oFrHopyRoxENm

lilijilill rnevor-m onnropyRoxENrrE

llllll'Jitillll senrer.nom rnEMoLrrE pEFrDonrE

ffi rumrnor.e-nrcH PYBoXENTTE

El eunrnor-m

I sn.rnrarne eorne sorsr

Frc. 3. Nature of the ultramafic body, as observed in twodi"mond-drill holes.

Alternately, it may be magnetite formed during aprevious episode of serpentinization and included inmetamorphic olivine during progressive metamor-phism (Arai 1975, Vance & Dungan 1977). A similartexture, consisting of black olivine megacrysts withdense tiny ilmenite granules, occurring in the outer-most zone of the Bergell aureole in the Malencoserpentinite, is described by Trommsdorff & Evans(1980). Fluid and fine solid inclusions are common-ly associated with the dusty material @9. 4). Palebrown to brownish yellow, euhedral to subhedralsolid inclusions are probably spinel. Some of theolivine megacrysts display undulatory extinction andkink banding (Fig. 5).

Small light green grains of olivine, on the otherhand, do not contain opaque dusty material and arestrain-free. This variety forms an equigranular sugarymosaic texture that is well developed in zone 5b @ig.6). Among these grains, 120" interfacial angles arecommonly seen @ig. 7). Textural relations indicatethat these fine grains of olivine are formed frommegacrystic olivine by recrystallization proce$ses.Recrystallization starts along grain boundaries anddislocations @igs. 5, 8). This new generation ofolivine is called neoblasl, following the terminologyadvocated by Mercier & Nicolas (1975) for deformedupper-mantle peridotites.

Peridotite in zone 5a consists of loosely packedolivine megacrysts, neoblastic olivine mosaic and alight green-grey orthopyroxene-amphibole matrix,giving the rock a 'spotted' appearance. Dunite inzone 5c, on the other hand, is composed of closelypacked megacrysts of olivine with a minimum of in-terstitial area (occupied by orthopyroxene, am-phibole and aluminian chromite), with a texture verysimilar to the cumulus texture (Fig. 9). Theseequigranular olivine megacrysts very commonlyenclose tiny subhedral inclusions of amphibole andchlorite, forming parallel oriented flakes or bunches

Fro. 4. Fine opaque dusty material concentrated along ir-regular fractures in olivine. Also shown are fluid andfine solid inclusions disseninated and concentratedalong microfractures in olivine. Plane-polarized light.

ili

METAMORPHOSED ULTRAMAFIC ROCKS, THOMPSON, MANITOBA

FIc. 5. Kink-banding (black and dark grey horizontal bands) in olivine megacryst. Parallel oriented flakes are amphiboleand chlorite. Crossed polarizers.

Ftc. 6. Neoblastic olivine occurring with megacrystic olivine from which it was derived. The megacrystic olivine com-pletely recrystallized into neoblasts, forming a fine-grained mosaic texture on the right-hand side of thephotomicrograph. Crossed polarizers.

Ftc. 7. Fine-grained neoblastic olivine occurring together with onhopyroxene megacrysts, Idioblastic flakes are chlorite.Plane-polarized light.

Ftc. 8. Large olivine megacryst containing olivine neoblasts, presumably developed along dislocation planes. Crossedpolarizers.

Ftc. 9. closely packed olivine megacrysts forming cumulus texture. crossed polarizers.

Ftc. 10. Secondary chlorite developing along a preferred crystallographic direction of olivine megacryst, probably asa result of olivine and spinel reaction. Small relics of spinel are enclosed in chlorite. Crossed polarizers.

8 l


(Fig. 5) that are similar to those constituting thematrix. Close to the serpentinized tremolite peridotite(zone 6), there are anhedral chlorite inclusions inmegacrystic olivine. It seems that they develop alongcertain crystallographic directions of the host olivineand usually enclose greenish yellow spinel (Fig. l0).

Tremolite peridotite in zones 2 and 6 is ser-pentinized, the degree of serpentinization varyingthroughout the zones. Thin serpentine veins formplanar systems of veinlets probably parallel to thefabric of the body and the foliation of the enclosingschist. They cut megacrystic and neoblastic olivineand tremolite. Magnetite occurs in stringers follow-ing serpentine veins and along the cleavages ofchlorite. Minor carbonate is also present in thin veinsof serpentine.

Medium-grained orthopyroxene is found intersti-tially to olivine megacrysts, enclosing xenomorphicislands of olivine showing communal extinction @g.

11), and enclosing medium-grained amphibole andchlorite. Amphiboles are mainly colorless tremoliteand cummingtonite. They generally form smallfibrous and prismatic crystals, coexisting with olivineneoblasts.

Two types of spinel are present. One is palebrownish yellow chromian spinel, which is cornmon-ly seen as fine disseminated erains in the olivineorthopyroxenite and orthopyroxenite units. It is ran-domly disseminated throughout the peridotitic zones.In some place$, however, it is preferentially concen-trated along the grain boundaries of olivine mega-crysts. The spinel usually forms fine anhedral zon-ed grains, the core of which is darker than the rim.The other type of spinel is opaque aluminianchromite, which is coarser than the first type. It oc-curs interstitially to the olivine megacrysts in zone5b, in which the olivine grains are closely packed,forming a cumulus texture (Fig. l2).

Frc. 11. Orthopyroxene (at extinction) replacing olivine megacryst. Clossed polarizers.

Frc. 12. Euhddrat and subhedral olivine megacrysts. Al-chromite and minor orthopyroxene are interstitial to olivine.Crossed polarizers.

Frc. 13. Elongate orthopyroxene megacrysts enclosing fine inclusions similar to those constituting matrix. Crossedpolarizers.

Frc. 14. Deformation lamellae in orthopyroxene. Crossed polarizers'

METAMORPHOSED ULTRAMAFIC ROCKS, THOMPSON. MANITOBA 83

Tremo lite ort hopyroxenite

Orthopyroxene forms coarse, slightly elongateequigranular grains. Its grain size ranges from 0.3to I cm, and it is pale brown. Abundant fine-grainedamphibole, phlogopite and brown spinel are dissem-inated in some of the orthopyroxene megacrysts. Theinterstices of the orthopyroxene megacrysts are oc-cupied by fine-grained light green amphibole andphlogopite, which are similar to those enclosed inthe orthopyroxene but coarser in grain size @ig. l3).Thin lamellae parallel to (100) of orthopyroxene;ueobserved in some grains and characterized by a verylow Ca content (Fig. I 1, 14). Strained crystals of or-thopyroxene are cornmon. The orthopyroxenemegacrysts in zone I are elongate, probably alongthe foliation plane of the enclosing schist. Tremoliteis common as medium- to coarse-grained xenoblasts,whereas anthophyllite forms randomly oriented,radiating prismatic bladelike crystals in a finer-grained matrix. Phlogopite occurs as strained platyand fine grains. It is partly replaced by orthopyrox-ene in zone l. In zone 12, on the margin ofthe body,phlogopite is recrystallized and replaced by apseudomorph of green chlorite. Close to zone 3,minor olivine is present as small inclusions in or-thopyroxene. Brown to greenish yellow spinel is very

common as small subhedral to anhedral crystals;these commonly are zoned (brownish core, yellowrim) disseminated grains, preferentially concentratedin the interstices of orthopyroxene megacrysts or inorthopyroxene close to its margins. Sulfides are pres-ent as disseminated anhedral grains.

Tremolite olivine orthopyroxenite

Texture is quite uniform in this unit. The grainsize of olivine is 4 mm and less, and it formsxenomorphic grains that are usually enclosed incoarser (l-1.5 cm) orthopyroxene. Some of theseorthopyroxene grains have triple junclions showing120' interfacial angles.

Amphibolite

The unit in zone 8 is composed of amphibole,phlogopite and minor plagioclase. Amphibole formsa medium-grained (l mm) granular texture with aweak fabric. Two amphiboles are present: magne-sian cummingtonite and anthophyllite. Medium:grained phlogopite forms the groundmass forequigranular amphibole, and shows a foliationparallel to the margin of the body. Plagioclase, onthe other hand, is fine- to medium-grained, occur-

TABLE 'I.

REPRESENTATIVE COMPOSITIONs OF OLIVINE, ORTHOPYROXENE AND SPINEL

r J l t v l n e

2 3 40 r t h o p y r o x e n e

1 ? 3 4 1S p i n e l

2 3

s i 0 z 3 9 . t 9 3 9 . 6 4

T i 0 2 0 . 0 0 . 0

A ' , t 2 0 3 0 . 0 0 . 0

C r r 0 , 0 . 0 0 . 0

z 5

' - 2 " 3

F e o I 4 . 2 3 | 2 . 8 9

M g O 4 5 . 7 0 4 7 . 2 0

C a o 0 . 0 0 . 0

l { n 0 0 . 2 8 0 . 1 8

N i o 0 . 0 8 0 . 1 2

4 0 . 4 8 3 9 . 6 8 5 7 . 5 9 5 6 . 7 5

0 . 0 0 . 0 0 . 0 0 . 0

0 . 0 0 . 0 0 . 5 7 1 . 3 6

0 . 0 0 . 0 0 . 0 0 . 1 0

' I 0 . 8 5 I 0 . 1 9

5 8 . 0 5 5 6 . 3 0 0 . 0

0 . 0 6 0 . 0 9 0 . 0

0 . 6 8 1 . 0 6 5 8 . 7 8

0 . 1 t 0 . 1 8 9 , 1 2

0 . 2 0

7 . 1 1 8 . 6 5 1 0 . 7 6

3 4 , ' 1 7 3 3 . 0 9 1 9 , 7 2

0 . 1 3 0 . 1 9 0 . 7 1

0 . 3 0 0 . 3 5 0 . 1 4

0 . 0 0 . 0 0 . 3 0

0 . 0 0 . 0

0 . ' l l 0 . 0 5

0 . 0 0 . 0 0 . 0 0 . 0

0 . 0 0 . 0 0 . 0 5 0 . ? 7

5 1 , 2 2 4 9 . 3 0 3 7 . 8 4 1 4 . 5 8' I

5 . 3 6 1 9 . 5 4 3 0 . 7 5 5 3 . 2 8

0 . 5 7 0 . 0 0 . 9 8 ' l . t 8

0 . 1 1 0 . 2 0 0 . 3 9 0 . 1 5

2 0 . 3 0 I 4 . 2 0 1 7 . 7 7 2 3 . 3 7' I

2 , 8 0 I 6 . 4 6 1 2 . 6 5 6 . 8 2

6 . 5 9 9 . 4 8

4 7 . 8 6 4 8 . 6 4 3 4 . 8 8 3 2 . 7 I

0 . 0 0 . 0 0 . 1 3 0 . 1 5

0 . 2 1 0 . 2 4 0 . 2 0 0 . 3 0

0 . 2 7 0 . 2 7 0 . 0 7 0 . 0

0 . 0 0 . 0

0 , 0 0 . 0

0 . 2 3 0 . 0 7

0 . 0 0 . 0

0 . 0 0 . 0

0 , 2 3 0 . 5 4

0 . . 0 9 0 . 0

K z o

N a 2 0

T OTAL

t tn

' C r

0 . 0

9 9 . 4 8 1 0 0 . 0 3 9 9 . 6 7 9 9 . 2 0 ' 1 0 0 . 0 3 1 0 0 . 9 2 1 0 0 . 7 2 9 9 . 9 6 1 0 0 . 0 8 1 0 0 . 5 9 g g , s 7 1 0 0 . 7 6 . 1 0 0 . 1 9

0 . 8 5 1 0 . 8 6 7 0 . 8 8 7 0 . 8 9 5 0 . 9 0 4 0 . 8 6 0 0 . 8 9 5 0 . 8 1 2 0 . 7 6 6 0 . 5 2 9 0 . 6 7 4 0 . 5 5 9 0 , 3 4 2

0 . 0 9 4 0 . 1 6 7 0 . 2 1 0 0 . 3 5 1 0 . 7 0 9

F€0 represents total iron for olivine and orthopyroxene. Ferric iron is ca]culated assuming perfect stoichiometrjfor spinel . 0 l iv ine l , 2: neoblasts: 3, 4: megacrysts. Spine' l l : brown, 2: yel lowish brown, 3: red, 4: semiopaque,5: oDaoue.


Fo

E

ttC':CD

ring in the interstices between phlogopite and amphi-bole. This unit is cut by several thin (up to I cm)pegmatite veins.

MINERAL CHEMISTRY

Mineral analysis was performed with a CambridgeMark V electron microprobe at the Depafiment of

r olivinc. Orthopyrorcnar Amphibota

Mg /(Mg+Fel.*1

Frc. 15. Relationship of bulk-rock chemistry to the con-stituting minerals,

Geology, Dalhousie University. The instrument isequipped with an Ortec energy-dispersion spec-trometer automated to produce simultaneousmultielement analyses and reduce data using the pro-gram'EDATA2' of Smith & Gold (1979). Naturaland synthetic minerals were used as standards.Several representative compositions of olivine,pyroxene and spinel from the ultramafic rocksdescribed above are listed in Table l. The completeset of analytical results, together with the precisionof the analyses obtained from replicate determina-tions, are available on request from the Depositoryof Unpublished Data, CISTI, National ResearchCouncil of Canada, Ottawa, Ontario KIA 0S2,

Olivine

The composition of olivine in the dunitic zone 5bis uniform, ranging from Fo6r to Forr. However, itis not uniform in zone 5a, and exhibits a rapid changefrom Fose to Fos5 toward zone 4, In zone 3, it isslightly more magnesian, Fose.5. The olivine fromdrill hole 64816 is more iron-rich, showing a com-positional range from Fo63 to Fo6r. This composi-tional variation is controlled mainly by the bulk-rockcomposition (Fig. l5). The NiO content of olivineranges from the limit of detection to 0.40 wt. q0, in-creasing with the magnesium content (Fig. lO.However, this relationship is not the same as shownby magmatic olivine. The olivine compositions withlow nickel content fall outside the range defined byolivine in cumulates and mantle peridotites. TheMnO content ranges from 0.1 to 0.35 wt. Vo andshows weak negative correlation wilh forsteritecontent.

The compositional difference between megacrysticand neoblastic varieties is small, although neoblasticolivine seems to be enriched in Ni and Mn comparedto the megacrystic olivine from which it formed (Fig.16). The individual grains of olivine megacrysts seemto be compositionally homogeneous.

Orthopyroxene

The Mgl(Mg+Fe) ratio (Xsr) of orthopyroxeneranges from 0.84 to 0.91. It is 0.89 in zone 5b anddecreases to 0.865 in zone 5a, showing a similar pat-tern to the Xr, value of olivine. In zone 4, this ratiois about 0.85 and shows an increase toward zone 3.It reaches a maximum value of 0.905 in zone 3 (closeto zone 4) and decreases toward zone 2. The ortho-pyroxene from zones ll and 12 is more iron-rich,ranging from En65 to E[s7, similar to the coexistingolivine (Forr-Fos). The Xr" of both olivine and or-thopyroxene is probably controlled by the bulk-rockchemistry (Fig. l5).

The distribution coefficient for Mg and Fe betweencoexisting olivine and orthopyroxene [Ko:

0.

0 .

0.

0 .

-<':ez

g,o

a a

' ' d ' ' '- ' /^ . t . . /

45 46 t;7 48 49 5bMgo(wt'"/')

Frc. 16. Plots of MgO versus NiO and MnO (wt. 9o) inolivine. Tie-lines connect neoblastic olivine (triangles)to megacrystic olivine (solid circles) from which it wasderived.

Il .

: i.{.

1a ^

' \ ' ' '


lx.rys/XFJ'x (XFe/XM)oel is 0.985 (Fig. l7). Thisis similar to the value for'regionally metamorphos-ed peridotites from the Alps (0.96: Trommsdorff &Evans 1974) and smaller than those of zone IV ofthe Tari-Misaka contact-metamorphosed ultramaficcomplex (1.03: Arai 1975), Totalp serpentinites (1.05:Peters 1968) and metaperidotites of Paddy-Go-EasyPass (1.10: Frost 195). According to Medaris (1969),Mg and Fe partitioning between olivine and or-thopyroxene is not sensitive to temperature over therange 700oC to 1300.C. However, recent ther-modynamic formulations (Sack 1980) show that itis potentially a useful geothermometer.

Ca concentrations in orthopyroxene are very lowQess than 0,21 wt,Vo CaO), similar to orthopyroxenefrom contact metamorphosed (Arai 1975) andregionally metamorphosed peridotites @vans &Trommsdorff 1974), The Al content of ortho-pyroxene, here less than 1.75 wt.9o Al2O3, has beenshown to be essentially a function of temperature@obretsov 1968, Fujii 1976, Mercier 1976) and ofcoexisting minerals. Its pressure dependence isrestricted to temperatures above 9(X)oC according tothe T-P phase diagram of Gasparik & Lindsley(1980). Low contents of aluminum and calcium arecharacteristics of orthopyroxene in the amphibolitefacies, though there is a gradual increase in thesecomponents as the higher-temperature parts of thefacies are reached @vans 1977). Highly aluminousorthopypyroxene, on the other hand, is well knownin alpine spinel peridotites equilibrated in thegranulite facies @vans 1977).

Amphibole

Calcic amphibole compositions plot betweentremolite and pargasite end-members, forming alinear trend on the tuAl-(Na+ K) diagram Grg. lf)in the field of metamorphic amphiboles defined byJamieson (1981). Al2O, content ranges from 3.3 to8.4 9o (wt.), increasing with an increase in alkali con-tent. The CaO content is relatively constant at about12.5 (wt.)90. The Mgl(Mg+Fe) rario of calcic am-phibole ranges from 0.90 to 0.94 and is higher thanthat of the coexisting olivine and orthopyroiene @ig.17) and of the bulk rock (Fig. l5).

Spinel

In the peridotitic parts ofthe body, spinel rangesin composition from aluminian chromite to chro-mian spinel, whereas in the pyroxenitic parts it rangesfrom chromian spinel to Mg-Al-spinel. Accordingto Evans (1977), these compositional ranges are con-fined close to the transition between the granulite andpyroxene-hornfels facies. Evans also indicated thatthe spinel is chromian magnetite in low-grade serpen-

tinites, ferritchromite in antigorite serpentinites andchromite in talc-olivine rocks.

The ratio Cr,/(Cr+Al+Fe3*), labeled I",, fallsbetween 0.60 to 0.75 in the dunitic part of zone 5band ranges from 0.10 to 0.75 in the rest of zone 5.Some of this wide range is defined by zoned grainsand by grains in the same section. The rim of zonedgrains is enriched in Al and Mg relative to Cr andFd+ (Fig. l9). Similar paths from core to rim are

. Orthopyrdo€^ Amphlboto

4l'ory=o.gg

4L'AMP"o.$l

Fto. 17. Distribution of Mg and Fe between olivine andcoexisting silicates.

h

F

0

Ytoz.

[Jll lieumorpnic omphibote

llfffl Mosmotic omphibole

Edenite '{ru[J-:,1,,".;r

a - ' - a ^ a a . '

176 ^t^/.' Tschermdkite

t.0 rv 2.0 3:0Al..

Fro. 18. Plot of tvAl yer,rzs Na+K (number of atoms per23 oxygen atoms) in calcic amphibole. Location of end-member compositions are after Deer et al. (196O. Fieldsof metamorphic and magmatic amphibole are those ofJamieson (1981).


reported by Evans & Frost (1975). This ratio is ratheruniform in zone 4, ranging from 0.10 to 0.20.

The effect of temperature on Y6, of spinel andthe Mg-Fd* partition between spinel and co-existing silicates was first studied by Irvine (1965)'then by Evans & Frost (1975) and Frost (1975). Ingeneral, spinel becomes more AI- and Mg-richrelative to Cr and Fe2*, similar to the path seen inFigure 19, as the grade of metamorphism increases.

Minor elements such as Ti, V and Mn are enrichedin Cr-rich varieties @ig. 20). No such correlation ex-ists for Ni. TiO2 goes up to 0.30 wt.Vo, whereasVrO3 is less than 1.90 wt.Vo.

GEoISI\4pSRATURE ESTIMATES

Olivine-spinel geothermometry based on the par-tition of Mg and Fd* between coexisting spinel andolivine has been applied to pairs from Thompson.Two different calibrations of this geothermometerhave been used. One of them, that of Roeder et ol.(1979), is basically the geothermometer of Jackson(1969) except that a different value for the free energyof FeCrrOa has been used. The other is that ofFabriis (1979), which is based on the tentativegraphical calibration of Evans & Frost (1975).

Temperatures obtained from these two calibra-tions are different. Those obtained from the equa-tion of Roeder et ol. (1979) vary from 400oC for Cr-rich spinel to ll00'C for Al-rich spinel. Thesetemperatures are ulueasonable for the mineralassemblages. The applicability of the Roeder e/ a/.(1979) geothermometer has been challenged, sincetheir isotherms are inconsistent with recently deter-mined reversed experimental data at low

F]do.F

at .. 3!.

a . 'a a

a aa

*'z

oos

itrotL+

+o

c)

a

a

a

. t t

'

t

aa

a r I t a t

. . t t ! | '

:

^ ^ ^ ^l ^

^ t ^

rb lo 3b ao sb 6bCr2O3(wt.%)

Frc. 20. Plots of Cr2O3 versus TiO2, V2O3 and MnO (wt.Yo) in spinel.

E2oc-

Frc. 19. Plot of X1,4n versus Ys, in spinel.Xvn = Mg/(Mg + r'd+ )' Yc, = Cr/(Cr + AI + Fe3 * ).Cor-e and rim compositions of zoned spinel grains areconnected. Spinel changes from opaque to gxeen as thetemperature increases.

Mg/(Mg*Fd'l


temperatures and with trends from metamorphic and.igneous rocks @ngi & Evans 1980) and since the free-energy values for the end-member spinels are notknown accurately @abrids 1979).

In contrast to the isotherms of Roeder et ol. (lW9)@ig. 2l), those of Fabrids (1979) coincide with theregression line for the olivine-spinel pairs fromThompson. They plot linearly with a correlationcoefficient of 0.996 rn the lnKo-Y.. diagram @ig.2l). The regression line lies between the 600 and800oC isotherms and intersects the 700.C isothermwhere Is, is 0.17. This may indicate that not all thesamples have equilibrated under the same thermalconditions, but some of them, with I", < 0.17,have re-equilibrated during progressive metamor-phism. Thus, the regression line may represent thepath of progressive metamorphism.

The presence of zoned spinel indicates that com-plete equilibrium between olivine and spinel was notachieved at the high grades. In the lnKD-yc,diagram, the core composition of two zoned crystaliof spinel plots near the 660oC isotherm. If we assumethat the olivine is in equilibrium with spinel rims,the assemblage plots very close to the 7@oC isotherm(Fie. 2l).

Other geotemperature data are obtained from theT-P phase diagram of Gasparik & Lindsley (1980).The diagram is a reconstruction of aluminumsolubility in orthopyroxene coexisting with olivineand spinel in the system MgO-AlrOr-SiO, after Fu-jii (1976) and Danckwerrh & Newron (1978), andrepresents an approximation to the model of idealsolution. Extrapolated temperatures using the con-tent of the Mg-Tschermak component (mol. go) inthe orthopyroxene solid-solution are approximately640oC for orthopyroxene coexisting with Mg-Al-spinel. The reason for the low temperature is prob-ably because of the limitation of the geother-mometer. This geothermometer in the systemAI2O,-MgO-SiO, is an approximation to the idealsolid-solution model. According to Danckwerth &Newon (1978), corrections for ideal solution involv-ing FeO and CrrO, in coexisting spinel specieswould raise temperature estimates.

PETROGENESIS

As deduced from the mineral assemblages and tex-tures, the ultramafic body has experienced a seriesof complex hydration and dehydration reactions

ln Ko

v,CrFtc.2l. Plot of /nK2 versus.Yg,.K, = (Xp1r/Xp)o1 x (Xp"/X;4)ro. yc, = Crl(Cr + Al).The composition of two

sprnel cores (stars) and rims (fllled stars)-shown for comparisoi. Dashed Ene (2.97Yc.-laKD+0.755:0) is theregression line of plots with a correlation coefficient of 0.996. Solid lines are the isothermi calculated irom the equa-tion ofFabribs (1979): dash-dot lines are calculated using the equation of Roeder et at. (1979), precision is wiihinr 50'c.

Yr"r", =0.00


before, during and following progressive metamor-phism. The dominant mineral assemblage is olivine+ tremolite + orthopyroxene + aluminous spinel,$uggesting upper-amphibolite-facies conditions. Thepresence of tremolite as the Ca-bearing silicate in-stead of diopside and the absence of talc and cor-dierite constrain the pressure and temperature con-ditions for the ultramafic rocks in the system MgO-CaO-AI2O3-SiO2-H2O (Fie. 22). The sporadic oc-curence of minerals representing lower grades, suchas aluminian chromite, chlorite and Ca-poor am-phibole, together with olivine and orthopyroxene,may be explained by polymetamorphism or locallyvarying fluid-phase composition, according to Evans(1977). The fine opaque material may represent relictmagnetite stringers formed during serpentinizationand enclosed in olivine during deserpentinization, oralternately, it may be a result of high-temperatureoxidation of olivine. Since high-temperature productsof oxidation usually form more regular patterns(Haggerty & Baker 1967), pyroxene and magnetiteusually defining a dendritic intergrowth (Putnis1979), the former possibility is favored for the for-mation of the fine opaque material. In addition to

these stringers of relict magnetite, amphibole andchlorite inclusions forming parallel oriented flakesoptically continuous with grains adjacent to enclos-ing olivine megacrysts indicate metamorphic growthof olivine. Similarly, very irregular grain-boundaryrelations of anhedral olivine with other metamo.rphicminerals strongly suggest the same. Subhedral andeuhedral olivine megacrysts, in part forming acumulus texture, may be interpreted as recrystalliz-ed grains of igneous olivine with minor metamor-phic modification. This is supported by the relativelyregular content of forsterite in the olivine within in-dividual specimens and uniform MgO-NiO andMgO-MnO relationships in subhedral and euhedralolivine.

Low CaO and AlrO3 content of the ortho-pyroxene megacrysts and their poikiloblastic natureindicate that they are metamorphic, and not igneousrelics. Minute inclusions of amphibole, chlorite andphlogopite are similar to the matrix material butsmaller in size. They probably resulted from highgrowth-rate of orthopyroxene relative to the rate ofdiffusion of components of the inclusions throughthe host orthopyroxene. According to the phase rela-

iP""*'*-1

,,.#'

elN

CL

800T('C)

Frc. 22. Phase diagram showing mineral assemblages in ultramafic rocks as a functron of temperature and water pressure.Solid lines are experimentally determined curves; dashed lines are theoretical (calculated) curves, after Evans (1977)and Jenkins (1981). Also shown is the interpreted path of metamorphism for ultramafic rocks at the Thompsonmine. Abbreviations: Amp amphibole, Anth anthophyllite, Antig antigorite, Chl chlorite, Co cordierite, Dio diop-side, En enstatite, Fo forsterite, Gt garnet, Serp serpentine, Sp spinel, Ta talc, Tr tremolite, w water.

METAMORPHOSED ULTRAMAFIC ROCKS, THOMPSON, MANITOBA 89

tions in Figure 22, enstatite forms from forsterite and This fact is further supported by the unrecrystalliz-anthophyllite at temperatures above 700oC, below ed grains of oliving.8 kbar pressure. Recrystallization-accompanied or followed defor-

During progressive metamorphism, spinel chang- mation. It seems to have been an annealing or staticed in compositlon from Al-chromite ttyouglt pi"oiii" type of recrystallization because of the large grain-

and Cr-spinel to Mg-Al-spinel, as suggesbd'bi Su*, size, . equant ,grain-shapes, polygonal grain-

(1977). Equilibration of coexisting Al-chromite and boundaries, and absence of features of intragranularolivine was probably achieved

-at approximatety strain (Green et,al. 1970), as opposed to inequant

660"C. This opaque Al-chromite ctrarftea to a dari erain-shapes and strong preferred orientation, whichbrownish red s-erniopaque variety at its margin, which are characteristics.of syntectonic recrystallization.became more Al- and tvtg-ricn iehtive to b, a"O f" The presence of a bimodal texture seen in zone 5a,during an increase of temperature. pale brownish lgwever,llggoj: ||ut recrystallization is syntectonicyellow and yellowish green spinels, on the othei (Goetze 1975)..If this is the case, some features suchLand, probaLly formedat temperatures of 685 and as, eqg.anl andlarge grain-size may have been form-720"C, respectively. Spinel, together with olivine anJ ed withthe help.of a small amount of water (Greenorthopyroiene, muy be formed from chlorite accor- et al. 1970) during the recovery stage. The drivingding io the dehydiation reaction: clinochlore = forceforthetype-ofrecrystallizationthatdevelopedforiterite + 2 enstatite + spinel + 4Hro. This alonggar.nboundariesanddislocationsoftheolivinereaction in the system MgO-C;O-AI2O3-SiO2-H2O megacrysts is probably strain energy stored in

@vans 1977, Jenkins pdt; tatces pta6e Uet*e6n ft-O megacrysts..On the other hand, the driving force forand 825.C at 4-9 kbar pressure. The upper-pressure th^e recrYstalljzation that resulted in the formationlimit was estimated from the intersection of ihe reac_ of equigranular olivine mosaic is more likely grain-

tion above with the reaction Fo + Tr : En + Dio oounqary ano surlace energy.+ Sp + w (Fig. 22), whereas the lower limit wasestimated from the reaction En + Sp = Fo + Co.Addition of iron into this 5-component system, CoNcrusroushowever, shifts the reaction curves toward lowertemperatures. Furthermore, reaction boundaries in _ The_ultramafic rocks in the Thompson mine werethe system will be shifted to lower temperatures and altered prior to metamorphism, as indicated by 1)pressures if the activity of HrO in the ambient fluid relict.magnetite.stringers in olivine megacrysts, 2)is not close to unity (ienkins l98l). As a result, a Parallel oriented amphibole and chlorite flakes intemperature of appioximately 7?.0"t,obtained from olivine megacrysts, and 3) abundant minute inclu-MgiAl-spinel and olivine pairs, would be realistic sions of amphibole, chlorite and phlogopite in or-for the formation of spinel. Anhedral inclusions of tnopyroxene megacrysts'chlorite (chromium-bearing clinochlore), which Olivine megaqysts may have recrystallized fromdevelopedalong certain cryJtalographic airectioni partly altered olivine during progressive metamor-in the host olivine, are interpreted ai a product of phism. Orthopyroxene may have formed at the ex-the reaction betwein the host olivine and spinel in- pense of olivine and (probably) anthophyllite atclusions @ig. l0).

' temperatures above 700oC.

Serpenrinization seen in zones 2 and 6is a late- .#fi[*tif*"j$?r3:Ufffi}}ff"?:1#;stage eYent, developed following metamorphism anq n-

-il Meri.h ;*gitt relative to the cr- and Fe-deformation. This is indicated by thin veins of ,Lf, .*" li

-rpinei p.oOaUfV took place at higherserpentine cutting olivine neoblasts as well as other gr-"0* i"..e ;r"gessive metamorphism. This couldmetamorphic minerals. On the margin of the body f.;;;il;;;-d'.i, i'p"rti"f re-equiribrarion, in terms(zone l2), recrystallized pllogopite is larer replaced ;i ; M;_F"r;".iifr*g. reaction between olivineby a green chlorite pseudomorph. and spinel at higher temperatures.

Deformation of the body is indicated by the fabric,kink banding and undulatory extinction of olivineand orthopyroxene megacrysts. According to Poirier& Nicolas (1975), spinel in peridotite nodules is pro-gressively scattered with increasing flow since it isless ductile than the silicates. By their interpretation,the scatter seen in Mg-Al-spinel may be due to in-creasing deformation. However, the situation is dif-ferent in zone 5b, where the spinel is Al-chromiteoccupying the interstices of olivine megacrysts. Thiszone is probably the least deformed part of the body.

Temperatures estimates and the mineralassemblage of olivine + tremolite + orthopyrox-ene + Al-spinel correspond to the upper amphibolitefacies of metamorphism. During or followingmetamorphism, the ultramafic body was deformedand subsequently recrystallized.

Locally developed secondary serpentinization isthe latest event observed. This secondary serpen-tinization probably corresponds to the extensiveserpentinization of the peridotitic rocks elsewhere inthe belt.


ACKNOWLEDGEMENTS

This work was done as part of a Ph.D. thesis underthe supervision of Dr. G. Armbrust. The researchwas supported by a grant from the University of Ot-tawa and a scholarship from the Mineral Researchand Exploration Institute of Turkey MTA). IncoMetals Ltd., Manitoba Division, supported fieldwork. The author is greatly indebted to Dr. W.Peredery for suggesting the topic and for hisgenerous help in the field. Drs. R. Kretz, W.Peredery and R. F. Emslie reviewed the earlier ver-sion of the paper and gave constructive suggestions.The final version of the paper was reviewed by Drs.C. Pride and O. R. Eckstrand.

RsrsRENcss

Aner, S. (1975): Contact metamorphosed dunite-harzburgite complex in the Chugoku district, westernJapa* Contr. Mineral. Petrology 52, l-16.

Blrss, N.W. (1973): A Comparative Study of TwoUltramafic Bodies at the Southwest End ol theManitoba Nickel Belt, with Special Reference to theChromite Mineralogy. Ph.D. thesis, McGill Univ.,Montreal, Que.

CnaupNsss, P.E. (1970): Nucleation and growth ofiron oxides in olivines. Mineral. Maq.37,790-800.

Coars, C.J.A. (1966): Serpentinized Uhramafic Rocksof the Manitoba Nickel Belt. Ph.D. thesis, Univ.Manitoba, Winnipeg, Man.

CnaNsroNe, D.A. & Tunx, A.T. (1976): Geologicaland geochronological relationships of the Thomp-son nickel belt, Manitoba. Can. J. Eqrth Sci. 13.1058-1069.

Darcrwrnnr, P.A. & NEwroN, R.C. (1978): Ex-perimental determination of the spinel peridotite togarnet peridotite reaction in the system MgO-AI2O3-SiO2 in the range 900'C-l100'C and Al2O3isopleths of enstatite in the spinel fi,eld. Contr.Mineral. Petrologlt 66, 189-201.

Dren, W.A., HowrB, R.A. & Zussrr4aN, J. (1966): AnIntrcduction to the Rock-Forming Minerals.Longman, London.

DosRErsov, N.L. (1968): Paragenetic types and com-positions of metamorphic pyroxenes. J. Petrology9, 358-3',77.

Eror, M. & EvaNs, B.W. (1980): A re-evaluation of theolivine-spinel geothermometer: discussion. Corzlr.Mineral. Petrologlt 73, 201-203.

EvaNs, B.W. (1977): Metamorphism of alpineperidotite and serpentinite. Ann. Rev. Earth Planet.Sci. 5, 397447.

& Fnosr, B.R. (1975): Chrome-spinel in pro-gressive metamorphism - a preliminary analysis.Geochim. Cosmochim. Acta 39. 959-972,

& Tnovusoonrr, V. (1974): Stability ofenstatite + talc, and CO2-metasomatism ofmetaperidotite, Val d'Efra, Lepontine Nps. Amer.J. Sci. 274,274-296.

FanruEs, J. (1979): Spinel-olivine geothermometry inperidotites from ultramafic complexes. Contr.Mineral. Petrology 69, 329-336,

Fnosr, B.R. (1975): Contacl metamorphism of serpen-tinite, chloritic blackwall and rodingite at Paddy-Go-Easy Pass, Central Cascades, Washington. ,I.Petrology 16,272-313.

Fu;rr, T. (1976): Solubility of Al2O3 in enstatite coex-isting with forsterite and spinel. Carnegie Inst.ll'ash. Yearbook 15, 566-571.

Gespanrr, T. & Lrrosr-rv, D.H. (1980): Phaseequilibria at high pressure of pyroxenes containingmonovalent and trivalent ions. /z Pyroxenes (C. T.Prewitt, ed.). Mineral. Soc. Amer., Rev. Mineral.7.309-339.

Goerzs, C. (1975): Sheared lherzolites: from the pointof view of rock mechanics. Geology 3, 172-173.

GnreN, H.W., Gnrccs, D.T. & Cnrusrrs, J.M. (1970):Synthetic and annealing recrystallization of finegrained quartz aggregales. In Experimental andNatural Rock Deformation (P. Paulitsch, ed.).Springer-Verlag, New York.

Heccnnrv, S.E. & Baxrn, I. (1967): The alteration ofolivine in basaltic and associated lavas. I. Hightemperature alteration. Contr. Mineral. Petro logyt6,233-257.

Invrre, T.N. (1965): Chromian spinel as a petrogeneticindicator. I. Theory. Can. J. Earth Sci.2,648-672,

JacrsoN, E.D. (1969): Chemical variation in coexistingchromite and olivine in the chromite zones of theStillwater Complex. In Magmalic Ore Deposits(H.D.B. Wilson, ed.). Econ. Geol., Mon.4,4l-71.

JnvrrsoN, R.A. (1981): Metamorphism duringophiolite emplacement - the petrology of the St. An-thony Complex, J. Petrology 22,397-M9.

JrNrrNs, D.M. (1981): Experimental phase relations ofhydrous peridotites modelled in the system H2O-CaO-MgO-Al2O3-SiO2. Contr. Mineral. Petrology77,166- t76 ,

Meoenrs, L.G. (1969): Partitioning of Fe+ + andMg+ + 6.t*..n coexisting synthetic olivine and or-thopyroxene. Amer. J. Sci. Xi1,945-968.

METAMORPHOSED ULTRAMAFIC ROCKS, THOMPSON, MANITOBA 9 l

Mrncrsn, J.-C. C. (1976): Single pyroxene geother-mometry and geobarometry. Amer. Mineral. 61,603-615.

& Nrcons, A. (1975): Textures and fabrics ofupper-mantle peridotites as illustrated by xenolithsfrom basalts. J. Petrology 16,454-487.

PBnronny, W.V. (1979): Relationship of ultramaficamphibolites to metavolcanic rocks and serpentinitesin the Thompson belt, Manitoba. Can. Mineral. 17,187-200.

- (1982): Geology and nickel sulphide deposits ofthe Thompson belt, Manitoba. .lz PrecambrianSulphide Deposits (R.W. Hutchinson, C.D. Spence& J.M. Franklin, eds.). Geol. Assoc. Can., Robin-son VoL, 165-209.

PBrBns, T. (1968): Distribution of Mg, Fe, Al, Ca andNa in coexisting olivine, orthopyroxene andclinopyroxene in the Totalp serpentinite (Davos,Switzerland) and in the Alpine metamophosedMalenco serpentinite (N. Italy). Contr. Mineral.Petrology 18, 65-75.

PornrEn, J.P. & Nrcoras, A. (1975): Deformation-induced recrystallization due to progressive misorien-tation of subgrains, with special reference to man-tle peridotites. J. Geol. E3,707-720.

Purus, A. (1979): Electron petrography of high-temperature oxidation in olivine from the Rhumlayered intrusion. Mineral. Mag. 43,293-296.

RonoEn, P.L., Caurnerr, I.H. & JaMresoN, H.E.(1979): A re-evaluation of the olivine-spinel geother.mometer. Contr. Mineral. Petrology 68, 325-334.

Russsr.r-, J.K. (1981): Metamorphism of the Thompsonnickel belt gneisses: Paint Lake, Manitob a. Can. J.Earth Sci.18. l9l-209.

Sesoh, L.A. (1978): The ll/est Manasan and the PipeMine: 2 Ultramalic Bodies of the Thompson NickerBelt. M.Sc. thesis, Univ. Western Ontario, London,Ont.

Secr, R.O. (1980): Some constraints on the ther-modynamic mixing properties of Fe-Mg orthopy-roxenes and olivines. Contr. Mineral. Petrology 71,257-269.

Srrarrn, D.G.W. & Gorp, C.M. (1979): EDATA2: aFortran IV computer program for processingwavelength- and,/or energy-dispersive electronmicroprobe analysis. In Proc. Microbeam Ana-.Soc., l4th Ann. Conf. (San Antonio; D.E.Newbury, ed.), 273-27 8.

Tnovvrsoonrr, V. & Evars, B.W. (1974): Alpinemetamorphism of peridotitic rocks. Schweiz.Mineral. Petrog. Mitt. 54, 333-352.

& - (1980): Titanian hydroxylclinohumite:formation and breakdown in antigorite rocks(Malenco, ltaly). Contr. Mineral. Petrology 72,229-242.

VaNcn, J.A. & DuNcaN, M.A. (1977): Formation ofperidotites by deserpentinization in the Darringtonand Sultan areas, Cascade Mountains, Washington.Geol. Soc. Amer. Bull. 88, 1497-1508.

Wsnsn, W. & Scoarns, R.F.J. (1978): Archean andProterozoic metamorphism in the northwesternSuperior Province and along the Churchill-Superiorboundary, Manitoba. 1r? Metamorphism in theCanadian Shield (J.A. Fraser & W.W. Heywood,eds.). Geol. Surv. Can. Pap.78-10,5-16.

ZunsRrcc, H.F. (1963): Thompson Mine geology. Can.Inst. Mining Metall. Bull. 56,451-460.

Received May 20, 198i, revised manuscript acceptedAugust 1, 1983.

metamorphism of the ultramafic rocks of …rruff.info/doclib/cm/vol22/cm22_77.pdf · metamorphosed...

Documents