Download 4. The Kapuskasing Uplift: Archean greenstones and granulites

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Institute on Lake Lake Superior Superior Geology Geol Thirty-Third Annual Meeting THE ICAPUSKASING UPLIFT: ARCHEAN GREENSTONES AND GRANULITES

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a Wawa, Wawa, Ontario. Ontario Vol. Vol. 33, Part Part 55

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THE THE KAPUSKASING KAPUSKASING UPLIFT: ARC-lEAN ARCHEAN GREENSTONES GREENSTONES AND GRANULITES GRANULITES

3.A. 3.A. Percival Percival Geological Geological Survey of Canada, Canada, 588 Booth Street Street Ottawa KIA OE4 0E4 Ottawa KIA

Annual Institute Institute on Lake Superior Superior Geology 33rd Annual Geology Wawa, Ontario Ontario Wawa,

Vol. 33, Part 55 Vol. 33,

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TABLE OF CONTENTS

TABLE OF CONTENTS

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h U ZI:?GEOLOGICAL ~GE~L-FRAMEWORKOFTHEKAPU~KA~INGUPLIFT PART FRAMEWORK OF THE KAPUSKASING UPLIFT

Introduction Introduction RegionalSetting Setting Regional Geophysical characteristics of south-central Superior Province Geophysical characteristics of south-central Superior Province General Geology ofthe theWawa Wawa- Abitibi Abitibi Region General Geology of

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Greenstone- Granite GraniteTerranes Terranes Greenstone

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WawaGneiss GneissTerrane Terrane Wawa

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Kapuskas'ingStructural StructuralZone Zone Kapuskasing Relationshipof ofKapuskasing Kapuskasingstructural structural zone to adjacent subprovinces Relationship zone to adjacent subprovinces Structure of the Kap~crustal crass-section Structure of the Kapuskasing crustal cross-section ATcheanevolution evolutionofofthe tileKapuskasing ingcrustal crustatstructure structure Archean Uptiftofofthe theKapuskasing Kapustasingstructure structure Uplift 3)3 )

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PART II: ROAD LOG Summary Summary DayI:1: Stops Stops1-1 1-ltoto1-10; 1-18;Geology Geologyof ofthe the Wawa subprovince, Day Wawa subprovince, Wawa to C h a p k u Wawa to Chapleau Day 2: Stops2-1 2-1toto2-9; 2-9sGeology Geologyofofthe theKapuskasing Kapuskasing structural Day 2: Stops structural zone in the Chapteau-Poleyet area zone in the Chapleau-Foleyet area

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ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS

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REFERENCES REFERENCES

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PARTI PART t Figure1 1 Figure F i r e22 Figure Figure3 3 Figure Figure44 Figure Figure5 5 Figure Figure66 Figure figure7 7 Figure Eggre88 Figure

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LETOF OFILLUSTRATIONS BAUSTKATIONS LIST Geoiogyof of central centralSuperior SuperiorProvince Province Geology Geologyof ofthe theWawa-Chapleau-Foleyet Wawa-Chapteau-Foleyetarea area Geology Crustedthickness thicknessininthe theLake LakeSuperior Superiorarea area Crustal Bouguergravity gravitymap m p Bouguer Pressurebased basedon enhornblende hornblendeAl A1content content Pressure Geology of of the theKapuskasing Kapuskasing structural structuralzone zoneand andvicinity vicinity Geology Geologyof of the theShawmere Shawmereanorthosite anorthositecomplex complex Geology Metamorphicmineral mineralassemblages assemblagesin inthe theChapleau-Foleyet Chageau-Fokyet area Metamorphic

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Metamorphic reactions and P-I conditions for Kapuskasing granulites Paleo-pressure map for the Chapleau_Foleyet area

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Concorcfia diagram for zircon samples Gravity profile and crosssection for Kapuskasing zone in the Chapleau area Seismic reflection profile

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Restored vertical section 40Ar/39Ar age spectra

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PART II

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Location of outcrops at Stop 2-5

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PART ft PART b GEOLOGICAL GEOLOGICALFRAMEWORK FRAMEWORK OF OF THE THE KAPUSKASING KAPUSKASING UPLIFT

INTRODUCTION

The purpose purposeofofthe the trip trip is is to to examine examine the the characteristics characteristics and The and interrelationships interrelationships of of Archean high-grade gneiss gneiss terranes terranes of of the Superior Province. A Archean greenstone-granite greenstone-granite and high-grade Superior Province. A 300-km long west transect westtot oeast east transect between Wawa Wawa and Timmins, Ontario will be be used ttoo illustrate illustrateregional-scale regional-scale relationships. Figure Figure 11 shows the the major major geological features features of the theSuperior Superior Province Province and and Figure 22 traces trip route. The traces the the trip The first first day day will will be spent spent examining features features of of the the Michipicoten belt, a dominantly dominantly metavolcanic metavolcanic portion of the theWawa Wawa subprovince, subprovince, and and contact of the contact relationships between the the Michipicoten Michipicoten supracrustal supracrustal rocks and intrusions of Wawa domal gneiss gneiss tterrane. Wawa domal Onday daytwo, two,the theWawa-Kapuskasing Wawa-Kapuskasing boundary boundary will willbe be e r r a e . On examined, features of examined, as well as features of the theKapuskasing Kapuskasing structural structuralzone, zone, including including the the Shawmere anorthosite complex, high-grade gneisses, and the Ivanhoe Lake cataclastic cataclastic high-grade gneisses, zone separating zone from from those of of the Abitibi separating rocks of the the Kapuskasing Kapuskasing zone Abitibi Belt.

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REGIONAL REGIONAL SETTING SETTING

The Superior Province Province is is an an Archean Archean tterrane composed of of east-west east-west trending belts e r r a composed of alternate alternatevolcanic-rich volcanic-rich and and sediment-rich sediment-rich character, character,termed termedsubprovinces subprovinces(Fig. (Fig. 1). I). The continuity continuity of of the the east-west east-west belts belts is is interrupted interrupted by by aa northeast-trending northeast-trending zone zone of of highhighgrade metamorphic rocks, rocks, the Kapuskasing structural zone zone (Thurston (Thurstonet et al., al., 1977). Kapuskasing structural 1977). At its its southern end, the Kapuskasing structure is fault-bounded fault-bounded on on the the southeast southeast but but the Kapuskasing structure western contact contactisiscomplex complexand and gradational gradationalover over120 120 km to low-grade low-grade rocks of the the Michipicoten belt near near Lake Lake Superior Superior (Percival (Percivaland and Card, Card,1983; 1983;1985) 1985) (Figs. (Figs. I1and and 2). 2). The Kapuskasing Kapuskasing"high", "high",aaprominent prominentnortheasterly northeasterly gravity and aeromagnetic aeromagnetic anomaly, was interpreted indicate pronounced interpretedby byWilson Wilson and and Brisbin Brisbin (1965) (1965) tto o indicate pronounced upwarp of the the Conrad Conrad discontinuity. Bennett Bennettetetal. al.(1967) (1967)concluded concluded that that the theKapuskasing Kapuskasing structure structure is aa complex complex horst uplifted during during the Proterozoic. Proterozoic. The Theassociation associationofof1,100-1,000 1,100-1,000 Ma Ma alkalic that the alkalic rock-carbonatite rock-carbonatitecomplexes complexesled ledBurke Burkeand and Dewey Dewey (1973) (1973) tto o suggest that the Kapuskasing structure is a failed arm of the the Keweenawan Keweenawan rift structure. structure. Watson Watson(1980) (1980) Kapuskasing structure postulated postulated that thatthe theKapuskasing Kapuskasingzone zone was was uplifted uplifted during during late late Archean Archean or or early early Proterozoic sinistral transcurrent movement. transition aatt the movement. The The low-to-high-grade low-to-high-grade transition the southern of the the structure southern end of structurehas has been been interpreted interpreted as asan an oblique oblique cross-section of the crust uplifted along an east-verging east-verging thrust (Percival and Card, Card, 1983). 1983). Recent earthquakes in the region region indicate that that the thestructure structureisisstill stillactive active(Forsyth (Forsythand Morel, 1982; Forsyth et et a!., al.,1983). 1983).

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Figure1.1. Geology Geologyof of the thecentral centralSuperior SuperiorProvince. Province. Inset: Inset:positive positive gravity anomalies Figure gravity anomalies dark stipple b-25 mGal); limes (-25 mGal t o -35 mGal); blank ( 0 o

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Initial 1986). Ellis, and Boland 1986; West, and Northey 1985; al., et (Northey interpretation of stages preliminary in still are zone, Kapuskasing the beneath structure crustal examine to 1984 in conducted study, refraction major a of Results velocities. mantle and crustal averaging of necessity the to due partly and areas some in coverage insufficient of because partly preliminary, as thickness crustal apparent of map contour the viewed Halls east. the to km —35 to abruptly drop zone Kapuskasing the beneath range km 39 the in Values zone. Kapuskasing the of boundary eastern the with associated Moho to depth in decrease step—like a be to appears there addition, In Timmins. near km 35 to Wawa near km 45 about of values from easterly decreases Province Superior the of crust the of thickness apparent the

advised. was map using in caution extreme and Halls by listed are data of Sources 1982). Halls, (after area Superior Lake the in crust the of thickness Apparent

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Bouguer gravity map superimposed on simplified geology. (Gravity values in mGal), with 5 mGal Contour interval are from Earth Physics Branch maps 44078, 44084, 48078 and 48084). Checks - greenstone belts; dots -Kapuskasing unpatterned_undjyided granitoid rocks. gneiss;

interpretation indicates that the crust is at least 48 km thick beneath the Kapuskasing zone and thins abruptly to about 40 km to the southeast; high seismic velocities characterize the high-grade rocks of the Kapuskasing zone (0. Northey, oral communication, 1985; Cook, 1985; Fountain and Salisbury, 1986). The Bouguer gravity anomaly map for the Wawa-Timmins region is shown in Figure 4. In general, areas underlain by metavolcanic rocks have associated positive gravity anomalies and granitoid..gneissic rocks have negative anomalies. The Kapuskasing structural zone has an assoçiate linear positive gravity anomaly extending

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from from James JamesBay b y in in the the north north to t o some some 50 50 km km southwest southwest of of Chapleau. Chapleau. In In the the WawaWawaChapleau.-Foleyet Chapleau-Foleyet area, the the gradient gradient isisgradual gradual on on the the west west and and abrupt abrupt on the east, east, suggesting contact between betweenthe theKapuskasing Kapuskasing zone and Abitibi Abitibi suggesting a west-dipping contact subprovince. In this thisregion, region,the thegravity gravityprofile profile(Fig. (Fig.12) 12)shows shows aa paired pairedhigh—low high-low subprovince. In

anomaly. anomaly. The The trough trough of of the the low low is coincident with the fault fault at a tthe theeastern easternboundary boundaryof of the the Kapuskasing Kapuskasing zone. zone. To the north, as itit coalesces coalesces with with the the north, the thepositive positiveKapuskasing Kapuskasinganomaly anomaly broadens broadens as east-west east-west gravity gravity high high associated with with the the Quetico-Opatica Quetico-Opatica metasedimentary metasedimentary subprovince.

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1 GENERAL GENERAL GEOLOGY GEOLOGY OF OFIL-fE THE WAWA WAWA -- ABITIBI ABITIBI REGION REGION Three Three distinct distinct types types of of terrane terraneare arerecognized recognized in inthis thispart partof ofthe theSuperior Superior Province: Province: 1) greenstone-granite greenstone-granite belts, belts, 2) 2) regions regionsdominated dominated by by orthogneiss orthogneiss in in the the amphibolite fades, facies, and 3) 3)heterogeneous heterogeneousgneisses gneisses in in the the granulite granulite to t oupper upper amphibolite amphibolite fades. facies. Differences between terranes terranes in in metamorphic metamorphic grade grade and and pressure pressure suggest suggest that that the the terrane terranetypes typesrepresent representcrustal-scale crustal-scaleniegalayers megalayers(Percival (Peruvaland andCard, Card,1985), 1985),the the components components of the the upper upper and and middle middle continental crust. crust. The TheWawa Wawaand and Abitibi Abitibi belts belts are are greenstone-granite terranes; of terrane type terranes; the theWawa Wawa gneiss terrane is an example of type 22 and zone represents type and the the Kapuskasing Kapuskasing zone type 33 terrane terrane(Fig. (Fig. 2). 2). ~

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Greenstone-Granite Greenstone-Granite Terranes Terranes

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The partofofthe thevolcanic-rich volcanic-richWawa Wawasubprovince, subprovince,Isiscomposed composed The Michipicoten Michipicoten belt, part

mainly IC and mafic andfetsic felsiccomposition composition(Goodwin, (Goodwin, mainly of metavolcanic metavolcanicrocks rocksofofultrarnafic, ultramafic,maf 1962), with intercalated intercalated greywacke, 1962), with greywacke, conglomerate, chert chertand andiron iron formation, formation,mainly mainly siderite. as well as downward-facing downward-facing strata strata siderite. Dome Dome and basin structures structures(Goodwin, (Goodwin, 1962) 1962) as and and overturned overturned structures structures(Attoh, (Attoh, 1980) 1980)have have been recognized. recognized. Metamorphic Metamorphic grade grade ranges amphibolite facies facies (Fraser (Fraser et al., ranges from sub-greenschist sub-greenschist to amphibolite al., [978). 1978). Several Severalsuites suitesof of intrusive ranging from from peridotite peridotite to intrusive rocks rocks include include synvolcanic synvolcanic bodies ranging t o granodiorite, granodiorite, younger younger granodiorite granodiorite batholiths, batholiths, and and still stillyounger younger granite graniteand andsyenite syeniteplutons plutons (Card, (Card, 1982). 1982). The of the southern part of The supracrustal rocks ro of the the belt belt were weredivided divided into three three major (1962). A lower lower cycle, cycle, consisting of of roafic major cycles cycles by by Goodwin Goodwin (1962). rnafic and felsic felsic volcanics, volcanics, isis capped iron formation, formation, mainly mainly siderite, siderite, but with lesser pyrite-, capped by by Michipicoten-type Michipicoten-type iron

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chert- and and graphite-rich graphite-rich rocks. rocks. The Theassociated associatedJubilee JubileeStock, Stock,aa high-level high-level subvolcanic SU~VO~C~N intrusion, was was emplaced emplaced within aa caldera caldera structure structure(Sage, (Sage, 1980). 1980). The middle cycle cyc Icvolcanics volcanicsoverlain overlain by byclastic clastic metasediments metasediments and and comprises maf comprises mafic and felsic tuffs an breccias. The breccias. The clastic clasticsediments, sediments, including including the the Doré Dor6 conglomerate, conglomerate, wacke, wacke, siltstone, siltstone, and an

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crossbeddedarkose, arkose,a are thef facies equivalentsofof the the felsic felsic pyroclastics and crossbedded r e the a d e s equivalents and are formed mainly of detritus detritus eroded eroded from the t h e felsic felsic centres. centres. The Theupper upper cycle cycle comprises comprises intermediate to felsic -dacite) tuffs tuffs and quartz-feldspar porphyry. porphyry. Recent felsic (andesite (andesite -&cite) and quartz-feldspar Recent (pers.comm., comm., 1986) 1986)indicates indicatesonly onlytwo twocycles cycleswithin within tthe work by Sage Sage (pers. h e main volcanic pile. The Abitibi Abitibi subprovince The subprovince is is dominated dominated by a thick thick sequence sequence of volcanic volcanic and and

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of the sedimentary rocks of t h e Abitibi Abitibigreenstone greenstonebelt belt(Jensen, (Jensen, 1981; 1981; 1985). 1985). The supracrustal successiontypically typically comprises comprisessequences sequencesofofultramafic, ultramafic, mafic, mafic, and and felsic felsic volcanics. succession volcanics. high proportion of volcanic volcanic detritus. detritus. Intercalated turbiditic turbiditicsedimentary sedimentary rocks rocks contain contain aa high In the Abitibi Abitibibelt, belt,the t h euppermost uppermostgroup, group, the t h eTimiskaming, Timiskaming,isisan anunconformity-bounded unconformity-bounded sequenceofof alkal~c alkalic volcanics and fluviatile fluviatile sediments sediments(Hyde, (Hyde,1980) 1980) localized localized along along major major sequence east-west fault east-west faultzones. zones. Large areas areas of of the Abitibi Abitibi greenstone Large greenstone belt belt are aremetamorphosed metamorphosed to t o greenschist greenschist prehnite-pumpellyite Ifacies acies rocks rocks are common common in in tthe Timminsh e Timminsffacies; a d e s ; subgreenschist, subgreenschist, prehnite-pumpellyite Rouyn area areaand andnarrow narrowaureoles aureolesofofamphibolite amphibolite ffacies rocks occur occur adjacent adjacent tto Rouyn a d e s rocks o plutonic plutonic bodies (Jolly, (Jolly, 1978). 1978). The supracrustal supracrustal rocks rocks of of the Abitibi The Abitibisubprovince subprovince display display evidence evidence of polyphase polyphase orientations. deformation in the t h e form form of of major majorand and minor minor structures structuresof ofseveral severalages ages and orientations. In the Abitibi Abitibigreenstone greenstone belt, older northerly-trending folds folds are are overprinted overprinted by by easteaststructures west trending major and minor folds, forming formingmajor major dome dome and and basin basin structures (Pyke, 1982). The Themajor majorisoclinal isoclinal folds folds with with east-west east-west striking striking subvertical (Pyke, 1982). subvertical axial axialplanes, planes, steeply-plunging minor folds, folds, subvertical axial plane foliation, foliation, and steeply-plunging minor and steeply steeply plunging plunging stretching stretching lineation lineation were were probably probably formed formed under under subhorizontal, subhorizontal, generally generally north-south north-south major compression. compression. Toward Towardtthe southernmargin marginofofAbitibi Abitibi belt the major h e southern t h e major folds are overturned northward, and and in the the adjacent adjacent Pontiac Pontiac subprovince, subprovince; folds folds are a r e recumbent. recumbent. The Cadillac-Larder Lake fault fault zone, between tthe Abitibi The Cadillac-Larder zone, which constitutes the the boundary boundary between h e Abitibi and probably has hasboth both transcurrent transcurrent and and thrust components and Pontiac subprovinces, subwovinces. orobablv comDonents of movement.

Several suites of intrusive rocks in the Abitibi subprovince can be distinguished on

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of composition, composition, structural structural relationships, the basis basis of relationships, setting, setting,and andage a g e(Card, (Card, 1982). 1982). The The sills, dykes and and plutons plutons ranging rangingin in composition composition from from oldest suite includes synvolcanic sills, peridotite typically quartz diorite peridotite to t o granodiorite; granodiorite; the more more felsic intrusions aare r e typically diorite and and

trondhjemite. Gneissic Gneissic plutonic plutonic rocks rocks of of tonalite tonaliteand and granodiorite granodiorite composition, composition,

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commonly containing amphibolitic amphiboliticenclaves, enclaves, occur occur in in the the northeastern and commonly containing and southwestern southwestern Abitibi subprovince. Massive felsic plutonic plutonic rocks rocks intrude intrude both both the the greenstones and the Abitibi subprovince. Massive felsic gneissic rocks in in the form of simple and and composite composite plutons plutons and and batholiths. batholiths. They They form several suites, suites, including including early early granodiorites, granodiorites, younger younger granite granite batholiths, batholiths, and andstill stillyounger younger syenite-diorite plutons. plutons. Contacts Contactsbetween between the theplutons plutons and and the the country country rocks rocks are are commonly concordant and and steeply steeply dipping; dipping;dominant dominanteast-west east-weststructural structural trends are commonly concordant are locally deflected about about the theintrusions. intrusions. A time framework for events events in in the theMichipicoten Michipicoten and and Abitibi Abitibi belts belts can can be be constructed U-Pb zircon dates. In the western Abitibi Abitibi belt, volcanic volcanic rocks rocks range in in constructed from from U-Pb age from Nunes and and Jensen, Jensen, 1980), with late late to 2,703 2,703 Ma Ma (Nunes and Pyke, 1980; 1980; Nunes 19801, with from 2,725 2,725 to alkaline Group) aatt 2685 Ma, Ma, and and in in the the Michipicoten Michipicoten belt, from from alkaline volcanics volcanics (Timiskaming (Timiskaming Group) 2,749 a t 2737, 2737, 2744 2744 (Turek (Turek et etal., al., 1982) 1982)and and2745 2745 2,749 tto o 2,696 Ma, with synvolcanic plutons at Ma (Sullivanetetal., al., 1985). 1985). A number numberofoflatelate- ttoo post-tectonic plutons M a (Sullivan plutons from from the the Abitibi Abitibi and Michipicoten Michipicoten belts have zircon dates dateswithin within aafew fewmillion million years yearsof of2,680 2,680(Icrogh (Krogh et et al., al., 1982; 1982;Frarey Frareyand and Krogh, Krogh, 1986). 1986). Thus Thus the themain main Abitibi Abitibi and and Michipicoten Michipicoten supracrustal supracrustal sequences sequences and and early earlyintrusions intrusionsdeveloped developed between between 2,750 2,750 and and 2,700 2,700 Ma Ma ago. The dates on volcanics and late late plutons bracket the volcanics and the age age of of deformation deformation and and regional regional metamorphism Ma ago. Major a ago. Major volcanic, plutonic, and metamorphism aatt between between 2,700 2,700 and 2,680 2,680 M tectonic tectonic events events of of relatively relatively brief brief duration durationwere wereessentially essentiallysynchronous synchronous throughout throughout the Abitibi and Wawa subprovinces, a region some 1,200 km wide. wide. The Wawa subprovinces, 1,200 km long and 200 km The lithologic and age similarities similaritiesbetween between the theAbitibi Abitibiand andWawa Wawa subprovinces subprovinces strongly strongly suggest original continuity, now structural zone. now interrupted by the Kapuskasing Kapuskasing structural Diabase dyke dyke swarms swarms of of late late Archean Archean and and Proterozoic age are present present throughout throughout the region. The Theoldest oldestdykes, dykes, the thenorth-trending north-trending Matachewan Matachewan swarm swarm of of the the Abitibi subprovince, Rb-Sr age age of of 2633 2633 Ma Ma (Gates and Hurley, Hurley, 1973). 1973). NorthwestNorthwestsubprovince, have a Rb-Sr striking subprovince are are petrographically petrographically similar to t o and and have have been been striking diabase diabase dykes dykes in in Wawa Wawa subprovince paleomagnetically correlated correlatedwith withthe theMatachewan Matachewanswarm swarm(Ernst, (Ernst,1981; 1981;Ernst Ernstand and paleomagnetically Halls, subprovincesare are thus thus inferred inferred ttoo have been tectonically Halls, 1984). 1984). Abitibi Abitibi and Wawa Wawa subprovinces tectonically time. Northeast-striking Northeast-striking tholelltic tholeiiticdykes dykesare areabout about2105 2105Ma Ma old old stable cratons cratons by by this time. stable (Gates 1973);northwest northwest olivine diabase diabase dykes (Gates and and 1-lurley, Hurley, 1973); dykes (Sudbury (Sudbury swarm) swarm) are a r e about about 1250 Ma Ma old old (Van (VanSchmus, Schmus,1975); 1975);and andeast-northeast east-northeast olivine diabase diabase dykes dykes (Abitibi (Abitibi swarm) swarm) are M aold old(Lowden (Lowdenand andWanless, Wanless,1963). 1963). are approximately approximately1100 1100Ma

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The belt is intruded intruded ttoo the The Michipicoten Michipicoten belt the southeast southeast by by tonalitic tonalitic gneiss and plutons plutons of gneiss terrane terrane (Fig. 2). The consist of of aatt least of the theWawa Wawa domal domal gneiss (Fig. 2). The rocks in this region consist least four four lithologic lithologic components: components; (1) (1)hornblende-plagioclase hornblende-plagioclase ±+ clinopyroxene clinopyroxene mafic and rare rare paragneiss paragneiss xenoliths, xenoliths, ranging ranging from centimetres centimetresto totens tensofofmetres metresininmaximum maximumdimension, dimension, making most makingup up55to to 50% 50% of of individual individual outcrops, and enclosed in (2) the volumetrically most abundant abundant phase, phase, hornblende-biotite hornblende-biotite tonalitic tonaliticgneiss gneisswhich which is iscut cutby by (3) (3) concordant concordant to to discordant discordant layers layers of of foliated foliatedto t ogneissic gneissicbiotite-hornblende biotite-hornblende granodiorite, granodiorite,which whichin in turn turn are arecut cutby by (4) (4)late late discordant discordant quartz quartz monzonite monzonite pegmatite. Xenolith-rich Xenolith-rich tonalitic tonaliticgneiss gneiss units units alternate alternateon on aa 55 to to 10 10 km krn scale with xenolith-poor xenolith-poor units and can be be traced traced for for distances distances of of at a tleast least50 50km. km. Layering Layeringininmafic maficxenoliths xenolithsisislocally locallydiscordant discordant to tolayering layering in in enclosing enclosing gneiss. gneiss. Small Small folds folds of of layering layering in in tonalitic tonaliticgneiss gneiss are arecommonly commonly truncated truncated by by layers layers of of foliated foliatedgranodiorite. granodiorite. Tonalite Tonalitegneiss gneisshas hasa aminimum minimumU-Pb U-Pb zircon zirconage ageof of2707 2707 Ma, M a(Percival (Percivaland andKrogh, Krogh, Ma, partly partly reset resetby bythe theintrusion intrusionofofgranodiorite granodioritesheets sheetsata 2677 t 2677Ma 1983) 1983)(Fig. (Fig. 5). 5). The The layers layers of of granodiorite granodiorite on on the cm cm to to km km scale scale in the the gneiss gneiss terrane terrane can can be be correlated correlatedby byzircon zircongeochronology geochronologywith with discordant discordantplutons plutonsof of 2680 2680Ma Ma age age in in the the greenstone greenstone belts, belts, suggesting suggesting that that the the plutons plutons have have deep roots in the gneissic gneissic terrane. In In the the area areabetween betweenthe theMichipicoten Michipicotenbelt beltand andKapuskasing Kapuskasingzone zone (Fig. (Fig. 2) 2) the the orientation orientationof of foliation, foliation,gneissosity gneissosityand and axial axial surfaces surfacesof of small smallfolds foldspermit permitdefinition definitionof of several severalstructural structuraldomains domainscharacterized characterizedby bydomal domalgeometry geometry(Fig. (Fig. 6). 6). The Thespacing spacing of of major major domal domal or or antiformal antiformalculminations culminations is is on on the the order order of of 20 20 to t o25 25 km, km, although althoughmany many smaller smaller culminations culminations are arealso alsopresent. present.The TheHighbrush HighbrushLake Lakeand andRacine RacineLake Lakedomes domeshave have cores coresof of tonalite-granodiorite tonalite-granodioritegneiss gneisswhereas whereasthe theChaplin C h a p lLake i Lakedome domeand andMissinaibi MissinaibiLake Lake arch planar fabric fabricin in the the archhave have granitic graniticcores coresflanked flanked by by foliated foliated to to gneissic gneissic rocks. AAplanar homogeneous homogeneous granitic rocks, defined by by lenticular quartz quartz and and biotite biotitealignment, alignment,isis generally generally concordant concordant to t ogneissosity gneissosity in in mantling mantling gneiss. gneiss. The Thestructural structuraldomes domesmay maybe be related relatedtotothe theemplacement emplacementofofplutons, plutons,possibly possiblyby bydiapiric diapiricrise. rise.The TheRobson RobsonLake Lakedome, dome, adjacent adjacentto t othe theKapuskasing Kapuskasiig structural structuralzone, zone, has has aa core coreof of interlayered interlayeredmafic maficgneiss, gneiss, paragneiss paragneiss and and tonalitic tonaliticgneiss. gneiss. InIngeneral, general,asymmetric asymmetricsmall smallfolds foldsofofgneissic gneissiclayering layeringdo donot nothave have aa consistent consistent sense senseof of asymmetry asymmetrywith with respect respectto todomal domalculminations culminations and and are are therefore thereforenot notcongruent congruent with withthe thedomes. domes. Near Nearsome somedomal domal crests, crests,the theorientation orientationofofgneissic gneissiclayering, layering,small small folds are widely variable to chaotic and definee aa pattern foldsand and lineations 1 patternof ofcoalescing coalescing domes. domes.

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Wawa Wawa Gneiss Terrane Terrane

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geobarometer for calc-alkaline igneous rocks is based on the Al content of hornblende (l-lammarstrorn and Zen, 1986): A

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5.03

Allotal

Application of the barometer to a suite of tonalites from the Wawa gneiss terrane suggests suggests that thatthe thepressure pressureofofigneous igneouscrystallization crystallizationincreases increasesfrom fromabout about55kbar kbarininthe the central over Kapuskasing 6 kbarnear nearthe the Kapuskasingzone zone(Fig. (Fig. 5). 5). These These centralpart partofofthe theterrane terranetoto over6 kbar results areintermediate intermediatebetween betweenindependent independentpressure pressureestimates estimatesfor forthe theMichipicoten Michipicoten resultsare belt basedon onsphalerite-pyrrhotite sphalerite-pyrrhotitegeobarometry geobarometry(Studemeister, (Studemeister,1983) 1983)and and beltof of2-3 2-3kbar, kbar, based for 6-8kbar kbarbased basedon ongarnet-pyroxene-plagioclase_quartz garnet-pyroxene-plagioclase-quartz forthe theKapuskasing Kapuskasingzone zoneof of6-8 barometry barometry(Percival, (Percival,1983). 1983).AAvalue valueofof8 8kbar kbarnear nearWawa Wawaisisderived derivedfrom fromaabiotite biotite tonalite tonalhewhich whichcontains containshornblende hornblende only on adjacent to contacts with amphibolite; the hornblende hornblendeisisprobably probablyxenocrystic. xenoaystic. Metasedimentary Metasedimentaryrocks rocksoccur occurini two locations in the eastern Wawa subprovince. AAdiscontinuous, discontinuous, antiformal antiformalto t odomal domalbelt beltofofparagneiss paragneisswest westofofthe theRacine RacineLake Lakedome dome may 6). maybe becontinuous continuous to t othe theeast eastwith withparagneiss paragneissofofthe theKapuskasing Kapuskasingzone zone(Figs. (Figs.22and and6). Stretched-pebble Stretched-pebble metaconglomerate metaconglomerateoccurs occursininassociation associationwith withquartz quartzwacke wackeand and amphibolite Thepolymictic polymictic(tonalite, (tonalite,granodiorite, granodiorite,metame amphibolitein inthe thevicinity vicinityof of Borden Borden Lake. Lake. The andesite, andesite,metasediments, metasediments,amphibolite, amphibolite,vein veinquartz), quartz),clast-supported clast-supported rock rockcontains contains cobbles cm)with withaaprominent prominentshallow shallow cobblesranging rangingfrom fromequant equanttotoconstricted constricted(1.5 (1.5mmx x7 7x x7 7cm) northeast plunge. In cross-section the clasts vary from equidimensional to northwestdipping ellipses. The Floranna Lake complex is a strongly lineated and foliated complex crescentic pluton plutonof ofintermediate intermediatecomposition compositionthat thatoccurs occursbetween betweenthe theRobson RobsonLake Lakeand andRacine Racine Lake medium-grained Lakedomes. domes. The Themargins marginsofofthe thecomplex complexare arefinefine-toto medium-grainedhypersthene.hypersthenebiotite contains medium-grained biotitegranite, granite,whereas whereasthe thecore core contains medium-grainedrnonzonite rnonzoniteand anddiorite dioritewith with rare raregabbro gabbroand andcoarse coarsebiotite-clinopyroxene biotite-clinopyroxene melagabbro melagabbrolayers. layers. The Theleast-deformed least-deformed interior igneous(?) interiorportions portionscontain containrelict relict igneous(?)clinopyroxene clinopyroxeneand andfeldspar feldsparaugen augenphenocrysts. pheno Migmatitic Migmatiticquartz quartzmonzonite monzonitelayers layersconstitute constituteupuptot o10% 10%ofofsome someoutcrops. outcrops.The The complex complexhas hassimilar similarstructural structuraland andlithological lithologicalcharacteristics characteristicstotocrescentic crescenticplutons plutonsofof the theWabigoon Wabigoonsubprovince subprovinceof of northwestern northwesternOntario Ontario(Schwerdtner (Schwerdtneretetal., al., 1979,1983; 1983 1979, Sutcliffe 1979). Sutcliffeand andFawcett, Fawcett, 1979). The donial region a semi-continuous Theeastern easternlimit limitofofthe the domal regionis is a semi-contin"ous zone zoneofofnorth, north, northeast easterly-dipping and northeastand andnorthwest northweststriking, striking,gently gently easterly-dippinggneissosity gneissosity andeasterlyeasterlyplunging 6)6may plunginglineation. lineation. This Thiscurvilinear curvilinearfeature feature(Fig. (Fig. ) mayrepresent revresentthe theeastern easternextremity extremity

I I

I I I I I

— 11

2.6 0 0

a) Ia -0

interior

intermediate

edge

8

S S.-

I.

U (3)

¼

I I

a

S

a2E

6-

(I,

0

4

(4

Lu

— 0

0

•

.40

••

5

A

150

Wowa I

&ne/ss

Terr one

100

I

I

I

I

I

-

—

. 50

L8r() N

Structural Zone I

I

I

I

ao

>' 0

Kop uskasing

S

0

A.4

I

p

p

2

I_

'4' ----------

0

9-1.6

C

Distance Distance from from Ivanhoe Ivanhoe Lake Lake cataciastic cataclastic zone, km km

Al/n A/ in

Horn b/en de Barometer Hornblende Barometer ............ ...,......... ..

b'}

. .. . . .,

Wa wa/ / 4•97

I

I

0

I

I 1

•1 24

0 0

I

I

0---

r

0

-S.

1*

I I I

—

to 11.0

&ne/ss

V

/ A bit/b -

V

,

,.

/

Belt

5.1

Terrane

50

0 km

Figure Figure 5.5. a)a) Plot Plotof ofhornblende hornblende composition composition vs vs spatial spatial distribution. distribution. Vertical Vertical array arrayof of points represents representswithin-sample within-sample compositional variation. Hornblende at a t far far left leftisis points variation. Hornblende probably xenocrystic, xenocrystic, from from adjacent adjacent amphibolites amphibolites of of Michipicoten Michipicoten belt. Dashed-line Dashed-line box box probably representsindependent independentpressure pressure estimates estimatesfrom fromgranulites granulitesofofthe theKapuskasing Kapuskasing zone. zone. represents b)b) Map Map showing average pressure in kbar, kbar, based based on on hornblende hornblende geobarometry geobarometry in in the theWawa-Chapleau Wawa-Chapleau area. area.

63'Oo'

LEGEND Proterozoic Alkalic rock—carbonatite complex: I: Lackner Lake complex; n: Nemegosenda Lake Lake complex; comple%s: a: Shenango Shenango complex Complex

1100 t i 0 0 Ma Ma intrusions intrusions

Archean

I

m +

massive granite, granodiorite, grenodiorite, with minor minor tonalite tonalite diorite—monzonite intrusive complex; minor hornblendite, granite diorite-monzonite intrusive 2707-2668 Ma Me sequence sequence 2707—2668

foliated foliated to to flaser flaser tonalite tonalite

I@ tg;4

tonalite—granodiorite tonelite-granodiorite gneiss; gneis

metavolcanic metavolcanic rocks, rocks, mainly mainly metabasalt metabasait .

::

----------

~....'

-

Shawmere Shawmere anorthosite anorthositecomplex: complex: metamorphosed metamorphosed gabbroic gabbroic anorthosite, anorthosite, anorthosite, anorthosite, gabbro, gabbro, minor minor tonalite tonalite pre—2765 pre-2765 Ma sequence sequence

Amq gneiss: highhigh Ca,AI basaltic composition, with gneiss: Ca,AI basaltic composition, withtonalitic tonaliticleucosome ieucosome "fl-i,maficmafic

lAp 0

'

/

^

2749-2696 Ma sequence sequence 2749—2696

flaser ic tonalite flaser diorite dioritetotomat mafic tonalite— includes inciudesminor minorgabbro, gabbro

.._.:j .-.--hornbiendite, granodiorite granodiorite hornblendite,

"'Bsojl

I

metasedimentary metasedimentery rocks rocks (includes (includes metaconglomerate metaconglomerste with with tonalite tonalite cobbles zircon date date of of 2664±12 cobbles with with aa U—Pb U-Pb zircon 2664±1Ma) Ma)

paragneiss- quartz-rich paragneiss— quartz—richcomposition, composition,wi with up to 15% tonalitic leucosome

—

fault; fault; Ivanhoe ivanhoe Lake Lake cataclastic cstaclasticzone zone

Figure Figure 6. 6. Geology Geologyof ofthe theiCapuskasing Kapuskasing structural s t r u c t u r a l zone zone and and vicinity. vicinity.

I I

I I

I I I -

I

-13of of aa first-order first-order dome domeof of 75-100 75-100 km km diameter, diameter, of of which which the t h e individual individual structural structural domains domains are a r e higher-order higher-order domes domes of of similar similarscale scaleand andspacing spacingtot othose thoseofofthe theWabigoon Wabigoonsubprovince subprovince (Schwerdtner (Schwerdtner and and Lumbers, Lumbers, 1980). 1980). Dome development development can can be be temporally temporally related related to t o the the formation formation of of minor minor structures structuresin in gneiss. gneiss. The Thediscordant discordant foliations foliationsin in mafic mafic gneiss gneiss predate predate the thegneissic gneissic layering layering in the tonalite-granodiorite tonalite-granodiorite host. host. Small Smallfolds foldsof of this thisgneissic gneissiclayering layering in in turn turn predate layers. Crosscutting predate intrusion intrusion of granodiorite layers. Crosscutting pegmatite pegmatite dykes dykes and and sills are still still younger younger and are a r e probably probably the t h e same same age age as asthe thehomogeneous homogeneous plutonic plutonic rocks rocks which which locally locally have by lenticular quartz grains, have a planar planar fabric defined by grains, biotite alignment, alignment, fracture fracture cleavage, of granulation. granulation. The cleavage, or minor minor planar zones of The absence absence of aa consistent consistent sense sense of asymmetry asymmetry of small small folds with respect to t o domal domal culminations culminations and the t h e random random orientation orientation of of re-orientation of small small folds folds near dome crests argue in favour of re-orientation of of pre-existing pre-existing small small folds layering during duringthe the latest latest doming. doming. The folds and gneissic gneissic layering The quartz-lenticle foliation foliation and and fracture plutonic rocks rocks cannot cannot be be readily readily attributed attributed to fracturecleavage cleavagein inhomogeneous homogeneous plutonic to magmatic magmatic flow flow and therefore suggest suggest that that the the plutons plutons were were emplaced emplaced at their their present present structural structurallevel levelat a tsub-solidus sub-solidus temperature, possibly possibly relating to t o late l a t e diapiric diapiric rise. rise.

3)

Kapuskasing Structural Zone

The The Kapuskasing Kapuskasing structural zone zone comprises comprises northeast-striking, northwest-dipping northwestdipping belts tonalite, and belts of of paragneiss, paragneiss, mafic mafic gneiss, gneiss, gneissic gneissic and xenolithic tonalite, and rocks rocks of of the the Shawmere Shawmere anorthosite anorthosite complex complex (Bennett (Bennett et et al., al., 1967; 1967; Thurston Thurston et et al., al., 1977) 1977) (Figs. (Figs. 22 and and 6). 6).

Migmatitic layered with with garnet, biotite, Migmatitic paragneiss paragneiss is compositionally layered biotite, quartz-rich quartz-rich and and rare rare graphitic graphitic varieties. varieties. Concordant Concordanttonalitic tonaliticleucosome leucosome constitutes constitutes up up to to 20 Ic gneiss 20 per per cent cent of of many many outcrops. outcrops. Enclaves Enclavesand andlayers layersofofmaf mafic gneiss in in paragneiss paragneiss occur occur on on the the10 10cm cm to t o 11km km scale. scale. Migmatitic Migmatiticmafic maficgneiss gneiss isis characterized characterizedby by garnetgarnetclinopyroxene-hornblende-plagioclase-quartz-ilmenite+orthopyroxenemineral mineral clinopyroxene-hornblende-plagioclase-quartz-ilmenite÷orthopyroxene assemblages assemblages and and generally contains concordant tonalitic tonalitic leucosome. leucosome. Layering, Layering, on on the the i1to t o10 10cm c m scale, scale,isisproduced produced by by variable variable proportions proportions of minerals. minerals. Table Table11presents presentstwo two sets setsof of whole-rock whole-rock analyses analyses from from adjacent adjacentanhydrous anhydrous (garnet-clinopyroxene-plagioclase(garnet-clinopyroxene-plagioclasequartz)and and hornblende-bearing hornblende-bearing layers from mafic gneiss in two different locations. locations. quartz) From From the t h e analyses analyses iti tisisunclear unclear whether whether the t h elayering layeringisisaapreserved preservedcompositional compositional heterogeneity heterogeneity or or aa product product of of metamorphic metamorphic differentiation. differentiation.The Thebulk bulkcomposition composition corresponds correspondsto t ohigh highcalcium calcium(10-15 (10-15wt% wt%CaO), CaO),high high alumina alumina(13.4-17.2 (13.4-17.2 wt% wt%A1203) AIn03) basalt basalt

-

I I I

- 14 Table Table 1: 1:

e

Si02 Si02 Ti02 1102 A1203

Whole rock chemical analyses of Whole of mafic gneiss from the the Kapuskasing Kapuskasing zone, with CIPW norms. Analyst: I: granulite layer, Analyst: R. R. Charbonneau, Charbonneau, GSC GSC Lab. 1: layer, P79-475 P79-475 CIPW norms. (Gt-Cpx-Pl-Qz, 5% 2: amphibolite amphibolite layer, P-475 (Gt-Cpx-PI-Qz, 5% Nb); Hb); 2: P-475 (Gt-Cpx-Pl-Qz, (Gt-Cpx-PI-Qz, 25% 25% Nb); Hb); 3: granulite (Gt-Cpx—Pl,trtrQz); Qz);4:4:amphibolite amphibolitelayer, layer, P79-371 granulitelayer, layer,P79—371 P79-371 (Gt-Cpx-PI, (Nb 40%, 40%, Gt Gt 15%, 15%, Cpx Cpx 15%, 15%,PI Fl20%); 20%);5:5:average averageofofthree three mafic gneisses from (Hb the the KSZ KSZ (79-84A, (79-84A, 123, 123, 299); 6: 6: high-alumina basalt basalt (Ringwood, (Ringwood,1975). 1975). 1

2

3

4

5

6

47.8

46.6

52.5

43.1

47.8

49.9

1.0

1.3

0.81

0.81

1.81

1.59

15.5

15.6

17.2

13.4

16.2

17.0

Fe203

1.3

2.2

2.2

5.7

3.4

1.5

FeO FeO

9.1

9.4

8.5

12.8

8.5

7.6

MnO MnO

0.27

0.19

0.32

0.3

0.32

0.2

MgO MgO

4.53

5.29

3.64

9.25

5.41

8.2

13.50

11.4

CaO CaO

Na20 Na20 K20 K2Â

fl20 Co2 C02 Ni Ni Cr

Total Total

QZ OR AB

AN DI HE EN PS

P0 PA MT IL

AP

CC

15.4

14.2

11.2

10.0

2.0

2.4

2.8

1.6

2.3

2.8

0.25

0.41

0.12

0.58

0.33

0.2

0.5

1.1

0.3

1.6

0.8

2.3

2.0

0.4

0.1

0.6

0.014

0.014

0.0095

0.0098

0.024

0.019

0.018

0.018

0.014

0.015

100.0

1.5 1.49 17.02

32.77 11.42 12.80 6.05 7.83 1.9 1.55

0.12 5.26

100.4

2.44 20.46 30.81 11.52 10.90 3.64 3.95 3.01 3.60 3.21 1.55 0.14 4.58

100.6 100.6

100.4

CIPW CIPW Norm Norm 6.6 6.6 0.71 3.47 0.71 23.63 13.72 13.72 33.92 28.03 28.03 6.99 10.20 8.28 6.41 8.28 5.80 5.39 7.89 3.89 9.26 7.36 3.18 8.37 2.24 3.06 3.06 0.26 0.24 0.26 0.24 0.91 0.46 0.91 0.46

100.2

100.1 100.1

1.95 1.95 19.8 32.97 13.77 13'77 10.58 4.96 4.43 4.43 1.54

1.0 1.0 23.5 33.4 33.4

1-54 4.95 4.95 1.90 0.19 0.19 1.44 1.44 1.21 1.21

18.9

9.4 9.3 2.2 2.2 2.5 2.5

t I I I I

R

mafic gneiss in the 95-220 and 1212(Table 1). Nickel and chromium abundances abundance5 ofof mafic gneiss aare r e in 95-220 and 190ppm ppmranges rangesrespectively respectivelyand andare arenot notdefinitive definitive in distinguishing between 190 between basaltic igneousand andmarly martysedimentary sedimentaryparentage parentagefor for the the rock rock type. type. igneous In the the area area of of Figure Figure 6, 6,four four linear, linear, northeast-striking northeast-striking bodies bodiesofof flaser-textured flaser-textured tto In o foliated diorite foliated dioriteand and mafic mafictonalite tonaliteoccur occurdominantly dominantlywithin withinparagneiss paragneiss terranes. terranes. These These

ff' SHAWMERE ANORrHOSITE COMPLEX

Megacrystic qabbrac anorthosile

//

Banded zone cpabbrO/anar I hosite/qarneti let

I'

I

Anorthosite zone

I

5 / hornbleedet

/

'a

Tonahtic racks

Liiiilii Paraqnetss

——

$

—

——

km

——

I I I

Ia

p -

I

I

_—_—_—

1

/

____iii___

±61r'-

/

/

----

—

/

/

-

/ —:——7

a

C'

/

/-';Y/ /

—

:Y /

//

// / -

// / /// -:

Renee

/ _/ /

/

/

,:-:i /

Catty

/

*34B

\/

a-

1

ii / /r //c/:-/// /

/-/

_—_/

-/

—

/1—-

/—

a

/

J-& -- -

--

I I

/ /-:j // 7 // I',) / /-;: I / z __ / _// / / / /

—

Mat a yneiss. amohibolute

FseIt

___I —

;;/ /ft\/// // S

Luneament

/

". E::E J

?-

couNrAt ROCKS

$

/

'1-

/

ronalilic rocks

___

//

C

Border zone-am phibolite. mat'c gnetss

4à2

—

-

-

-yI

/

IMd::y 3 4A

/

// 13.:c::_J --

—-——

/

' -:

-

—:—:—-- — -

8300----f ':':nFigure 7.

-

t' a

/ 8230

Geologyof of the the Shawmere Shawmereanorthosite anorthositecomplex complex (after (after Riccio, 1981 and Geology 1981 and Percival, 1981).

48

- 16 -

medium- to coarse-grained, coarse-grained, locally locally migmatitic migmatitic rocks mediumrocks consist consist of of hornblende, hornblende, biotite biotite and and per cent cent quartz plagioclase, with up to 10 plagioclase, 10 per quartz as as well well as as orthopyroxene, orthopyroxene, clinopyroxene clinopyroxene and and hornblendite and rare pyroxenite pyroxenite occur cm to garnet. Gabbro, as layers layers 10 10 cm to rare garnet. Gabbro, hornblendite and rare occur locally locally as cii thick, generally within 2 km km of of paragneiss contacts. 2 2m present south south of of the t h e main main Discrete belts of of xenolithic xenolithic and and gneissic gneissic tortalite tonalite are present and small small bodies are present present to to the north. anorthosite complex and body of the the Shawmere Shawmere anorthosite The southern southern belt belt is made up of of coarse coarse garnet-hornblende-biotite-plagioclase-quartz garnet-hornblende-biotite-plagioclase-quartz made up and garnettonalite containing enclaves of of mafic gneiss, paragneiss, hornblendite and orthopyroxene-hornblende-biotite rocks. orthopyroxene-hornblende-biotite rocks. Southwest Southwest along along this belt, garnet decreases decreases in

composition is is granodioritic. granodioritic. Inclusions abundance and the composition Inclusions in this area area are are amphibolite, amphibolite, and cummingtonite-hornblende-biotite cummingtonite-hornb!ende-biotite rocks. hornblendite, and rocks. The Shawmere Shawmere anorthosite anorthosite complex (Thurston et et al., al., 1977) 1977) consists of a main main northern body, measuring 55 xx 15 km. km. The 50 km and a smaller mass, mass, measuring The bodies bodies taper to to body, 15 15 x 50 the northeast and and thus thus have haveconcordant concordantcontacts. contacts. Gneissic and southwest and Gneissic textures textures prevail in in the the outer outerportions portionsof ofthe themain mainbody, body,whereas whereas primary primaryigneous igneous minerals minerals and and textures are preserved preserved in the interior interior(Simmons (Simmons et et al., al.,1980). 1980). The Themain mainbody body comprises comprises four distinct (1)aaborder border zone zone of of distinctlithological-textural lithological-texturalunits units(Riccio, (Riccio,1981; 1981;Fig. Fig.7): 7):(1) rnigmatitic, foliated migmatitic, foliatedtot ogneissic gneissicgarnetiferous garnetiferousamphibolite, amphibolite,(2)(2)a abanded banded zone zone consisting consisting of 11 ttoo 30 30 cm-thick layers layers of anorthosite, anorthosite, gabbro, gabbro, garnet-rich, and and ultramafic ultramafic rock, rock, (3) (3)an an anorthosite zone gabbro and (14) megacrystic gabbroic gabbroic anorthosite (4)aamegacrystic anorthosite zone containing containing minor gabbro zone with plagioclase phenocrysts cm and and minor minor anorthosite, anorthositic phenocrysts to t o 50 cm anorthositicgabbro, gabbro, gabbro and andmelagabbro. melagabbro. AA 1 km km wide wide body bodyofoffoliated foliated garnetiferous tonalite tonalite is gabbro is present present within the the outcrop outcrop area of the anorthosite. anorthosite. Its Itsgenetic geneticrelationship relationshipto t othe theanorthosite anorthosite complex is not clear although although ititappears appears to tobe be temporally temporallyrelated related(Simmons (Simmonsetetal., al.,1980). 1980). southern body body consists consistsdominantly dominantly of of coarse coarse gabbroic anorthosite. The southern The orientation orientation of gneissosity and lithological lithological contacts the prominent prominent The gneissosity and contacts make make up up the east-northeast structural structural grain of the structural zone. zone. Gneissosity in all east-northeast the Kapuskasing Kapuskasing structural Gneissosity in rock types is folded or warped gently-plunging (0-25°) northeast-trending axes. warped about gently-plunging (0-25O) northeast-trending axes. The folds vary from from isoclinal "Z"sense senseasymmetry asymmetrywhen when viewed viewed toward toward isoclinalwith withconsistent consistent"Z" the east to northwest-facing northwest-facing monoclinal flexures. flexures. Axial Axialsurfaces surfacesare arerarely rarelyaccompanied accompanied by a foliation foliation defined defined by by flattened flattened quartz quartzgrains. grains. The Thetrend trendofoflineations lineationsand andfold foldaxes axesisis northeast-southwest throughout throughout this part of but plunge plunge direction direction northeast-southwest of the theKapuskasing Kapuskasing zone, zone, but varies on on aa regional regional scale scale from from dominantly dominantly southeasterly southeasterly in in the the south south tto northeasterly in o northeasterly the north. Between lineations are are within within 10° Between these these areas, areas, lineations 1O0 of horizontal horizontal and and abrupt changes plungedirection direction occur occur on on the the 100 m m scale. scale. Both Both regional regional and and local local plunge plunge changes inin plunge reversals can be be related related to aa gently gently southeast-plunging southeast-plunging warp axis. reversals can

r

LI

I

- 17 -

I

A A

I I

I I

'A

-4-

-s

A

'c

-e A

Sc

"INDEX

MINERAL'

ISOGRADS

(teeth point

p

up—grade)

0

A

/ Clinopyroxene

/

-f

n

A

A

Garnet — cIinopyroxene

Orthopyroxene

A A

I

'Lfl

A A

4,

/

1'

A

A4

A

n

I I I I

I I

I I I I I

.

.

LEGEND LEGEND

1

SYMBOLS SYMBOLS Alkalic rock-carbonotite complex

Granitic Graniticrocks rocks '

Anorthositic Anorthositic rocks rocks

.

Retrograde Retrograde greenscllst greemctist fades facies

laI

Unsubdivided — Unsubdivldedgreenschist ÇMnSchist amphibolite amphibolite facies facie* supra— supracrustal crustal rocks rocks

Cataclastic

ASSEMBLAGES ASSEMBLAGES MAFIC(BASALTIC) (BASALTIC)GNEISS GNEISS MAFIC C HbHb-P1PI —Hb—PI CE Gt Gt-Hb-PI nfl Cpx—Hb—PI Cpx-Hb -PI ttton ton Q Gt Gt—Cpx-Hb-PI -Cpx-Hb-PI -Qz -02 GI~t—Cpx —Qz ton -CPX-Hb—PI -~b-PI -02—-ton Gt -ton Gt—Opx-Cpx-Hb—PI -0px-Cpx-Hb-PI—Qz -02-ton

DIOR ITIC ROCKS ROCKS DIORITIC

A Hb—Bt-PI Hb-Bt-PI -Qz -02

r

A Hb—Bt Hb-Bt—P1 -PI—Qz -02—ton -ton AA Cpx-Hb—Bt Cpx-Hb-Bt—P1 -PI -02 -ton -Qz -ton AA Opx-Cpx-Hb—Bt Opx-Cpx-Hb-Bt—P1 -PI -Qz -02-ton -ton

PARAGNEIS PARAGNEISSS 00 BtBt—P1 -PI —Qz±Hb -0ztHb(+sfauroliteØ) (*stniirnl~te 0) 020 1 1.3,COW

17-6.5 —

48°00 -

2 1—6.7

0

Chapeat

10

0

40

I

I I

6-7.3

2 3—5.4

06.7 grossular 06.7 Anorthite+diopside=2/a ~northite+diopside=~/s grossu ÷+ 1/3 pyrope+quartz V3 pyrope+quartz

I

I

3 1-6.00

km km

Figure Figure10. 10. Paleopressure Paleopressure map Symbols represent rock map of of the Chapleau-Foleyet Chapleau-Foleyet area. area. Symbols type paragneiss; squares squares - mafic mafic gneiss; gneiss; triangles triangles - orthogneiss). orthogneiss). type (circles (circles- paragneiss; Numbers Numbers to to the the right rightofofthe thedash dashare arepressure pressure estimaters estimators(kbar) (kbar)keyed keyed to tothe the equilibrium equilibriumused used to t o derive derive the t h e value. value. The The6.3 6.3 kbar kbar reference referenceline lineisisbased based on on garnet-dinopyroxene-plagioclase-quartz equilibrium. (afterPercival, Percival,1983) 1983) garnet-clinopyroxene-plagioclase-quartz equilibrium. (after

-

-

-

RELATIONSHIP OF OFKAPUSKASING KAPUSKASING STRUCTURAL STRUCTURAL ZONE ZONE TO TOAD3ACENT ADJACENTSUSPROVINCES SUBPROVINCES RELATIONSHIP The The contact contactbetween between the theKapuskasing Kapuskasing structure structureand and Abitibi Abitibisubprovince subprovinceisis aa zone zone

of faulting faultingand andcataclasis, cataclasis,the theIvanhoe Ivanhoe Lake Lake cataclastic cataclasticzone, zone, that thatseparates separates the the two two of terranes of of contrasting contrasting lithological, lithological, structural, structural,and and metamorphic metamorphic characteristics. characteristics. The The terranes

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Paragneiss Paragneiss leucosorne leucosome (

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Mafia Mafic gneiss gneiss (2) (2)

013 Shawmere Shawmere tonalite tonalite (3) (3)

(vanttoe Ivanhoe Lake Lake ptuton pluton (4) (4) 0a Gneissic Gneissic tonalite tonalite (5) (5)

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OneissicGneissic- foliated granodiorite granodiorite (6) (6)

7

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Figure Figure 11. 11. Concordia Concordia diagram diagram with with isotopic isotopic ratios ratiosof of zircon zircon samples. samples. Ab: Ab:abraded abraded (Krogh, N: non-magnetic (Frantz); MI: magnetic at : non-magnetic MI: magnetic atj0l oside side tilt tilt (Krogh, 1982); 1982); N (Frantz); (Frantzk pr: pr: prismatic; prismatic; an: an: anhedral. anhedral. Solid Solidlines lines are areempirical empiricallead-loss lead-loss trajectories; Ma trajectories;dashed dashedline: line: hypothetical hypothetical lead-loss lead-loss trajectory trajectory(projects (projectstoto0 0Ma lower lower intercept); intercept); dash-dot line: empirical mixing xing line. line. (after (afterPercival Percivaland and Krogh, Krogh, 1983) 1983)

zone zone is is defined defined in part by by positive, positive, linear north-northeast-trending north-northeast-trending aeromagnetic aeromagnetic anomalies pairedhigh high(Kapuskasing) (Kapuskasing) --low low (Abitibi) (Ab'itibi) anomalies and and coincides coincideswith withthe thetrough troughofofa apaired gravity and12). 12). gravityanomaly anomaly(Figs. (Figs.44and The Ivanhoe Ivanhoe Lake cataclastic zone is is characterized characterizedby bynarrow narrowveinlets veinletsof offinely finely The cataclastic zone comminuted rock rock which which form form discontinuous, discontinuous, randomly-oriented randomly-oriented pods pods and networks. networks. Two Two comrninuted foliatedtotomassive, massive,semi-opaque semi-opaque typesof of fault faultrocks rockscan canbe bedistinguished. distinguished. The Thefirst firstisisfoliated types mylonite, cataclasite cataclasiteand andblastomylonite, blastomylonite, partly partly or or totally totallyrecrystallized recrystallizedtot ofine finegrained grained mylonite, epidote, chlorite, chlorite, carbonate, carbonate, and and actinolite. actinolite. The Thesecond secondtype typegrades gradesfrom from cataclasite cataclasitetoto epidote, pseudotachylite with with aphanitic, aphanitic,almost almostopaque opaquematrix matrixand androunded, rounded,embayed embayed pseudotachylite monomineralic rnonomineralicporphyroclasts. porphyroclasts.

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Shawmere Shawmere anorthosite anorthosite complex complex

PROTEROZOIC

1100 Ma alkalic-rock complex ARCHEAN

Massive granite. granodiorite (G2.70)

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Ivanhoe Ivanhoe Lake cataclastic cataclastic zone zone

1

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Tonalitic gneiss (G.270)

H

Metavolcanic rocks (Gz2.90)

Anorthositic rocks (G~2.82) (G2.82) Anorthositic rocks Kapuskasing gneisses (G2.52) Kapuskasing zone zone gneisses (G=2.82)

Figure Figure12. 12. Generalized Generalized west-east west-east cross-section cross-section from fromthe theWawa Wawa domal domal gneiss gneiss terrane, terrane, through structural zone zone into into tthe Abitibi subprovince, through the t h e Kapuskasing Kapuskasing structural h e Abitibi subprovince, showing showing gross gross crustal structure. The The gravity gravity model modelbased based on on the t h e average average rock rock densities: densities: tonalitic tonaliticgneiss gneissand andgranite: granite:2.70; 2.70; metavolcanics: metavolcanics: 2.90; 2.90; Kapuskasing structural zone Kapuskasing structural zoneand and lower lower crust: crust:2.82 2.82 g/cm g/cm 3.3.

The cataclastic zone The dip of the the Ivanhoe Ivanhoe Lake cataclastic zoneisisnot notwell wellconstrained constrainedgeologically. geologically. Although fault-rock veinlets are Although some fault-rock are parallel parallel to t ogneissosity gneissosity and and therefore thereforedip dipgently gently northwest, northwest, many many others others have have random random orientation. The Thejuxtaposition juxtapositionofofhigh-grade high-grade against displacement across across the the cataclastic cataclastic zone. against low-grade low-grade rocks indicates reverse displacement zone. The The associated associated paired paired gravity gravity anomaly anomaly is i s characteristic characteristic of of many many well-documented well-documented overthrust terranes terranes(Smithson (Smithsonetetal., al.,1978; 1978;Fountain Fountainand andSalisbury, Salisbury,1981) 1981) and suggests that that the the Ivanhoe cataclastic zone Ivanhoe Lake cataclastic zone is is the t h esurface surfaceexpression expression of of aanorthwest-dipping northwest-dipping thrust thrust fault fault(Fig. (Fig. 12). 12). AAshort short(10 (10km) km) seismic reflection survey survey over the zone indicates aa reflector reflectorininthe t h eappropriate appropriateposition positionwith withaatrue truenorthwesterly northwesterlydip dipofof38-40° 38-40-(Cook, (Cook,1985; 1985; Fig. Fig. 13). 13). The boundaryvaries variesinincharacter character over over its its length. length. North The Wawa-Kapuskasing Wawa-Kapuskasing boundary North of of Bonar Bonar Lake, Lake, it i t is is aafault, fault,with withdistinct distinctaeromagnetic aeromagneticexpression, expression,which whichdiverges diverges westward westward into into Wawa Wawa tonalites tonalites toward toward the thesouthwest. southwest. South SouthofofBonar BonarLake, Lake,the t h eboundary boundaryhas has

T

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Figure 13. a )

Figure 13. a)

Seismic reflection profile over the eastern Kapuskasing zone. The data

Seismic reflection profile on left the Kapuskasing continuity of zone. reflections is are plotted with east overbecause the eastern The data are plotted with east on left Reflection because theAcontinuity better in this orientation. is likely from the Ivanhoeis Lake of reflections better in this zone; orientation. cataclastic reflections B a r e from t h e Abitibi Reflection A is within likely from the subprovince. Lake cataclastjc zone; reflections B are from within the Abitibi Ivanhoe subprovince. b) Line drawing interpretation of a ) (after Cook, 1985). b) Line drawing interpretation of a) (after Cook, 1985).

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gradational lithogical, structural and lithogical, structural and metamorphic metamorphic characteristics. Mafic Maficgneiss gneiss with with

minor paragneiss paragneiss is typical of the minor the Kapuskasing Kapuskasing zone but also occurs in in the the Robson Robson Lake Lake dome with characteristic structural style subprovince. GarnetGarnetdome style of the the Wawa Wawa subprovince. clinopyroxene-hornblende-plagioclase assemblages are common commonhere, here, suggesting suggestingthat that the clinopyroxene-hornblende-plagioclase assemblages are metamorphic similar to that in the structural zone. zone. The metamorphic grade grade is similar the Kapuskasing Kapuskasing structural The discontinuous paragneiss paragneiss belt belt that extends 30km kminto intothe theWawa Wawasubprovince subprovince extends for for up upto t o30 discontinuous may also be be a part of lithological sequence. sequence. Tonalitic of the the Kapuskasing Kapuskasing lithological Tonalitic gneiss gneiss can be be

traced eastward eastward from from the the Borden Borden Lake area, where it i t has has the the complex complex structures structures characteristic of characteristic of the theWawa Wawa subprovince, subprovince, into strongly foliated and lineated gneiss typical of the the Kapuskasing Kapuskasing zone. zone. The change in in structural structural style The change style from from domal domal in in the the eastern easternWawa Wawa subprovince subprovince to ENEbelts belts in inthe the Kapuskasing Kapuskasingstructural structural zone zonecan can be be used usedto to define define aa transitional transitional linear ENE boundary zone zone between betweenterranes terranes with with contrasting structural boundary structural styles, styles,but butno nosharp sharpline linecan can drawn on on this this bask. basis. South be drawn South of Chapleau, the orientation orientation of of gneissic gneissic layering layering changes changes eastward from horizontal horizontal near near the theHighbrush Highbrush Lake Lake dome, through a zone with a superimposed upright uprighteasterly easterly foliation, foliation, ttoo strong northeast-striking, superimposed northeast-striking, northwest-dipping northwest-dipping north-south-trending structural structural culmination coincides with with the eastern gneissosity. A north-south-trending eastern domes of of the Wawa subprovi.nce.East Eastofof the the culmination, culmination, lineations plunge plunge easterly easterly domes Wawa subprovince. toward a structural structuraldepression depression into into which which southwest-trending southwest-trending lineations of the southern southern Kapuskasingzone zonealso alsoplunge. plunge. To To the the north, lineations plunging northeasterly off the Kapuskasing plunging northeasterly the Lake arch arch appear ttoo be continuous with with northeastnortheastnortheastern flank flank of the the Missinaibi Missinaibi Lake plunging, reclined reclined folds in in tthe structural zone plunging, h e northern Kapuskasing Kapuskasing structural zone (Percival, (Percival, 1981 1981a,b). a,b). Cataclastic veinlets veinlets characterize the the faulted faulted contact contactbetween between mafic maficgneiss gneiss and and tonalitic tonalitic gneiss southwest southwest of of Kapuskasing KapuskasingLake. Lake. To To the the south, south, the the gradational nature of gneiss lithological contacts as well as the structural lithological structural and and metamorphic metamorphic continuity continuity between between high-grade gneisses gneissessuggests suggeststhat that the the contacts contacts were etablished prior tonalites and high-grade prior ttoo metamorphism and doming, doming, and and that that rock units of of the theKapuskasing Kapuskasing zone zone locally occur the Wawa Wawatonalite-granodiorite tonalite-granodiorite gneiss. gneiss. Based structurally below below the Based on on the the change change in in average rock density density across across this thisdiffuse diffusesubhorizontal subhorizontalboundary, boundary, Percival Percival(1986) (1986) suggested that it could represent an exposed mid-crustal mid-crustal (Conrad) (Conrad)discontinuity. discontinuit

STRUCTURE OF THE THE KAPUSKASING KAPUSKASING CRUSTAL CROSS-SECTION

I $

The The transition from from the the Michipicoten Michipicoten belt to t o the the eastern eastern boundary boundary of the the

- 26 -

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\Ivanhoe Ivanhoe Lake Lake cataciastic cataclasticzone zone

Figure Figure 14. 14. Restored Restoredvertical verticalsection sectionthrough throughthe theMichipicoten Michipicotenbelt, belt,domal domalgneiss gneiss

terraneand andKapuskasing Kapuskasing zone. zone. Numbers Numbersare a r ezircon zircondates dates(÷4 (54Ma) Ma)on onigneous igneous terrane and meta-igneous rocks (after Percival and Card, 1983).

Kapuskasing Kapuskasing zone can be interpreted interpreted as asan anoblique oblique crustal crustal cross-section cross-section based basedon onthe the following: following: 1)1)metamorphic metamorphic grade gradeincreases increaseseastward eastwardfrom fromlow lowgreenschist greenschistfacies faciesininthe the Michipicoten Michipicoten belt belt(Studemeister, (Studemeister,1983) 1983)through through amphibolite amphibolite facies faciesin inthe theWawa Wawadomal domal gneiss gneissterrane terranetotoupper upperamphibolite amphiboliteand andgranulite granulitefades faciesininthe theKapuskasing Kapuskasing zone; zone;2)2)the the proportion proportion of of plutonic plutonicto t osupracrustal supracrustalrocks rocksincreases increaseseastward eastwardininthe theWawa Wawasubprovince; subprovince; 3)3)the theoldest oldestrocks rocks(>2,765 b2.765 Ma) Ma)are a r eininthe theKapuskasing Kapuskasing zone zone at atthe theinferred inferredbase baseofofthe the section; section;4)4)the thegravity gravityanomaly anomalycan canbebebest bestmodelled modelledbybyusing usingaawest-dipping west-dipping crustal crustalslab slab (Fig. (Fig.12); 12);and and5)5 ) rocks rockswith withseismic seismicvelocities velocities typical typicalof of the theupper uppercrust crustare a r enot notpresent present

r

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-27the Kapuskasing zone. The three major terrane types recognized in the Abitibi-Wawa region can be be related region can related to t o depth depth zones zones in in the the crust crustbased based on on metamorphic metamorphic evidence evidence and and consistent seismicvelocity velocitycharacteristics characteristics of of the the crust consistent with with known known seismic crust of of the t h e Superior Superior Province. crust is of supracrustal supracrustal rocks rocks of of the the greenstone Province. Thus Thus the the uppermost uppermost crust is made made up up of greenstone belts and and discordant discordant plutonic plutonic rocks. rocks. Beneath megalayer made made up up of of variably variably belts Beneath is is aa megalayer deformed felsic felsic ttoo intermediate deformed intermediate plutonic plutonic rocks, rocks, with with large-scale large-scale domal domal geometry. geometry. With With increasing depth within within this this layer, layer, the the attitude attitude of from sub-vertical, sub-vertical, increasing depth of gneissosity gneissosity changes changes from near zone. The near greenstone greenstone contacts, contacts, to t o sub-horizontal, sub-horizontal, near near the the Kapuskasing Kapuskasing zone. The lowermost lowermost exposed megalayer is represented represented by exposed megalayer by the t h e Kapuskasing Kapuskasing zone, made made up of aa heterogeneous heterogeneous lithological assemblage assemblage aatt high metamorphic grade. grade. Moderate high metamorphic Moderate dips dips of of lithological lithological layering lower crustal crustal attitude attitude rotated layering aare r e interpreted as as the t h e dominant dominant sub-horizontal sub-horizontal lower rotated passively uplift. passively during uplift. Construction of of a generalized generalized crustal crustal cross-section cross-section (Fig. (Fig. 14) 14) requires requires several several Construction assumptions: 1)the the dip dip of of the the crustal slab is constant; 2) assumptions: 1) 2) pressure is a function of depth de so that estimates of the estimates of of metamorphic metamorphic pressure pressure can be used used to derive tthe h e thickness of section; 3) the metamorphic assemblages assemblages aare r e the product product of of aa single single metamorphic metamorphic event; event; post-metamorphic vertical displacement on faults within 4) post-metamorphic and 4) within the the section section is isnegligible. negligible. The highest-grade highest-grade assemblage from tthe area is garnet-andalusite in h e Wawa Wawa area in indicating aa maximum maximum pressure pressure of of 3.3 3.3 kb kb and and aa depth of of metagreywacke (Ayres, (Ayres, 1969), 1969), indicating about 11 km (Carmichael, (Carmichael, 1978). 11 km 1978). Similar pressures, in the t h e 2-3 2-3 kb kb range, are arebased based on on sphalerite-pyrrhotite geobarometry on rocks rocks from Gutcher Lake, 30 km km northwest of o Wawa (Studemeister, 1983). 1983). The The range range of of pressures pressures estimated estimated from Wawa (Studemeister, from the t h eKapuskasing Kapuskasing garnet-clinopyroxene-plagioclase-quartz zone, based on Newton Newton and Perkins' Perkins' (1982) (1982) garnet-clinopyroxene-plagioclase-quartz barometer, is is 5.4 5.4 to to 8.4 8.4 kb kb (average (average of of 6.3 6.3 kb, kb, Percival, Percival, 1983) 1983) but the t h e lower lower values values may may result from re-equilibration re-equilibration during during cooling. cooling. These These values values correspond ttoo depths of 18 18 ttoo km (average (average 21 21km). km). The The minimum minimumerosion-level erosion-leveldifference difference isis therefore therefore 7 km, but the 28 km the closer ttoo 15 km. The maximumdip dipestimates estimates over over aa difference is is probably probably closer 15 km. The minimum minimum and maximum 100. constantly-dipping slab 120 km long long aare constantly-dipping 120 km r e approximately 5° 5O and lo0. The dips of of post-metamorphic post-metamorphic dykes dykes in in the the Kapuskasing Kapuskasing zone zone and and eastern easternWawa Wawa providean anindependent independentestimate estimateofoft the tilt of of tthe subprovince may may provide h e tilt h e slab in this area. dykes dip dip NE NE at at 75' 75° ttoo 85° and ENE ENE Kapuskasing Kapuskasing dykes dykes dip dip SE SEaatt 70Â 70° ttoo 85° 85' and 85"'. Matachewan dykes ' on measurements measurements of of dykes dykeswith withvertical vertical exposure exposureininroadcuts. roadcuts. Post-metamorphic based on Post-metamorphic maf Icdykes dykesinint the Shieldgenerally generallyhave havenear-vertical near-vertical orientations, rnafic h e Shield orientations, as asdo do Matachewan Matachewan dykes in the Abitibi subprovince (Thurston et a!., 1977; Mime, 1972). The consistent nonin

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vertical dip may thus have resulted from large-scale crustal rotation. To restore the dykes of both both swarms swarmsto to vertical, vertical, a dykes of a 14° 14O counter-clockwise counter-clockwise rotation rotation about about an an axis axis trending 038° is necessary. necessary. Thus 14°northwesterly northwesterly dip dip is is indicated indicated in in this trending 038'' is Thus aa 14" this eastern eastern area. area. The difference difference in The in dip dip estimate estimateprovided provided by by these these two twomethods methods may may be be due due to to uncertainties in the the calculations, calculations, faulty or real uncertainties in in the the data data used used in faultyassumptions, assumptions, or real differences differences in in dip dip from from east east to t o west. west. The The overall overall dip dipmust must flatten flattentot othe thenorthwest northwestand andisisreversed reversed northwest northwest of of the t h e Michipicoten h4ichipicoten belt beltwhere whereErnst ErnstU981, (1981, p. p. 87; 87; 1983) 1983) reported reported consistent consis 85° SW dipsofof Matachewan Matachewandykes. dykes. Therefore, Therefore, an an intermediate intermediate dip 85O SW dips dip value value of of 10° 10'

If dips flatten perpendicular tto the fault fault was for construction construction of perpendicular o the was chosen chosen for of Figure Figure 14. 14. If dips flatten toward the the northwest, northwest, this this will will result of the toward result in in over-estimation over-estimation of of the the true true thickness thickness of the section.

The generalized section section is is a a valid valid representation representation provided provided that that(1) (I)aa single si The generalized regional event affected affected all (2) late late vertical vertical regional metamorphic metamorphic event all of of these these rocks, rocks, and and (2) displacement along faults isisnegligible Wawa negligiblebetween betweenthe theIcapuskasing Kapuskasingzone zone and and eastern e displacement along faults

subprovince. In subprovince. In view of of the thecomplex complex relationships relationships described described and and uncertainties uncertainties involved, involved, these simplifications simplifications may information which be these may be be unwarranted; unwarranted; however, however, the information which can can be derived from an exposed exposedcross-section cross-sectionthrough throughpart partofofthe thecrust crust is is potentially potentially valuable derived enough permit some enough tto o permit some speculation. The generalized crustal cross-section, cross-section, constructed constructedusing using aa dip dipof of10° 10' (Fig. (Fig.14), 14),has has

at its upperamphibolite amphibolite tto its base base a sequence sequence ofof upper o granulite granulite facies faciesgneiss gneiss and anorthosite, unknown,and andof ofwhich whichsome some55tot o10 10km km isisexposed exposed in i the the full fullthickness thicknessofofwhich whichisisunknown, Kapuskasing zone. Structurally Kapuskasing zone. Structurallyabove aboveand and separated separated by by an an analogue analogue of the the Conrad Conra

an estimated estimated 10 tto km thickness thicknessof of tabular tabular ba batholiths discontinuity (Percival, (Percival, 1986) 1986) is an o 15 km of gneissic and xenolithic tonalite. sheetsand anddeepdeepgneissic and tonalite. Massive Massivegranitic graniticrocks rocksoccur occurasassheets rooted plugs at this this structural structural level. upper 5-10 km, both both granitic granitic rocks level. In the upper 5-10 km, rocks and and plugs at gneissic migmatitic migmatitic haloes surroundthe thelow-grade low-gradeMichipicoten Michipicotenbelt. belt. The interfaces gneissic haloes surround between the the adjacent, adjacent, generally horizontal megalayers undulating surfaces surfaces with with between megalayers are undulating several kilometres kilometres of of relief, domesatatintermediate intermediate structural structural levels as gneiss gneiss domes several relief, manifest manifest as and as as intrusive intrusive bodies bodies aatt higher levels. and In the western Superior Superior Province, two seismic seismic discontinuities discontinuitiesat at16-19 16-19and and 21-22 21-22 km, define upper, km, upper, middle and and lower crust (Hall (Hall and and Brisbin, Brisbin, 1982). 1982). Using Usingthe theKapuskasing Kapuskasing model, boundary between betweenaastructurally structurally higher model, the upper upper discontinuity corresponds corresponds tto o the boundary granitoid gneissic subjacent heterogeneous heterogeneous high-grade high-grade gneiss gneiss complex, granitoid gneissic layer layerand and aasubjacent whereas the lower discontinuity, corresponding to the middle-lower crustal boundary, is

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-29probably aa metamorphic metamorphic isograd (orthopyroxene (orthopyroxene isograd?) within withinthe theheterogeneous heterogeneous gneiss.

Woods (1985)studied studiedelectrical electrical conductivity conductivity in Woods (1985) in the theKapuskasing Kapuskasing region with with aa large-scale array. Although large-scale magnetometer magnetometer array. Although the t h elower lowercrust crustisisanomalously anomalously conductive conductive in in

the area (Duncan et al., al., 1980), there is is no no conductivity conductivity anomaly associated associated with with the 1980), there (Duncan et Kapuskasing zoneofofmidmid-t otolower lowercrustal crustalorigin. origin. This was wasinterpreted interpreted tto indicate that that Kapuskasing zone o indicate

the conductivity the result of in conductivity anomaly anomaly at depth depth is the & situ fluids fluids which which were were lost during uplift uplift ofofthe theKapuskasing Kapuskasing structure. Similar gravity Similar models models of mega-layered mega-layered continental continental crust crustare arebased based on on seismic seismic and and gravity data (Smithson and Brown, Brown, 1977; 1977;Berry Berryand andMair, Mair,1980). 1980). Other Other inferred inferred cross-sections (Smithson and cross-sections through the the crust crust (Ivrea (Ivrea zone, zone, Pikwitonei Pikwitoneiregion, region,Musgrave, Musgrave, Fraser Fraser ranges; ranges; Fountain Fountain and and Salisbury, haveinincommon commonaadownward downwardincreasing increasingmetamorphic metamorphic grade grade and and aa thick, thick, Salisbury, 1981)have

intermediate-depth intermediate-depth amphibolite-facies amphibolite-fades section section of of quartzofeldspathic quartzofeldspathicgneiss, gneiss, corresponding gneissterrane terrane of of the Wawa Wawasubprovince. subprovince. In In the the central corresponding tto o the domal gneiss Superior Province section, intrude and and assimilate assimilate both the section, these these gneisses gneisses intrude the overlying overlying supracrustal succession successionand andparts partsofofthe theunderlying underlyingcomplex. complex. The entire section down The entire down tto o

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20 addedt to the crust crust in the interval 20 km was was added o the intervalbetween between 2750 2750and and 2680 2680 Ma. Ma. The The prepreexisting as thick thick as present present continental continental crust crust existing crust crust may may have, have, but but need need not have have been been as

prior to to the the major major thickening thickeningevent. event. The Thehigh highmetamorphic metamorphic grade grade in in this this older older crust crust can can be accounted accountedfor for by by burial, burial, first first by later by by intrusion intrusion of of by aa volcanic volcanic pile pile and and somewhat somewhat later tonalite tonalitesheets. sheets.

ARCHEAN ARCHEANEVOLUTION EVOLUTION OF OF THE THE KAPUSKASING KAPUSKASING CRUSTAL CRUSTAL STRUCTURE STRUCTURE

I

The and mafic gneiss of the The oldest rocks so far far recognized, recognized, paragneiss paragneiss and gneiss of the Kapuskasing zone, aare considered part part of a sedimentary-volcanic Kapuskasing zone, r e considered sedimentary-volcanic succession succession deposited deposited

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probably also prior to and probably probably as asaastratiform stratiform body t o 2765 2765 Ma M a ago and body at a t depths depths of less less than than 20 20 km, as inferred from from the the presence presence of relict relictolivine olivine(Thurston (Thurstonetetal., al., 1977; 1977; Kushiro Kushiro

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prior prior to t o2765 2765 Ma Ma ago. ago. The TheShawmere Shawmere anorthosite anorthositewas was emplaced emplaced into intothis thissuccession, succession,

and by Simmons et al. (1980), the intrusion intrusion may represent the As suggested suggested by Simmons et (1980), the the and Yoder, 1966). 1966). As

differentiation basalt differentiationproduct productofoftholeiitic tholeiitic basaltmagmas magmaswhich whichalso also erupted erupted at a t surface. surface. Major Major eruption eruption of ofvolcanic volcanicrocks rocksand anddeposition deposition of ofsediments sedimentsoccurred occurredbetween between al.,1982) 1982)and andbetween between 2725 2725 and and 2749 and 2696 2696 Ma Ma ago in the Michipicoten Michipicotenbelt belt(Turek (Tureketetal., 2749and 2703 M Ma ago in in the western Abitibi a ago Abitibibelt belt(Nunes (Nunesand and PyRe, Pyke, 1980). 1980). The lowermost volcanics are dated by the U-Pb are generally generally mafic maficand and so so have have not been been dated U-Pb zircon method. method.

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including ultramafic, ultramafic, mafic, and trondhjemitic to Synvolcanic intrusions, including Synvolcanic to granodioritic granodioritic bodies, were intruded into into the theMichipicoten Michipicoten and and Abitibi Abitibi piles piles 2750 2750 ttoo 2700 MMa ago. Large Large volumes volumesofoftonalite tonalite intruded intruded beneath beneath and andadjacent adjacent tto the greenstone 2700 a ago. o the at this thistime. time.The Theminimum minimumage ageofof2707 2707Ma Mafor forWawa Wawa tonalite tonalh? (Fig. (Fig. 11) 11)isisgiven given by by aa belts at concordant point point and and is is therefore therefore probably close tto the age of of crystallization. nearly concordant probably close o the The tonalites tonalites could could be be the the subsurface expression expression of of magmas magmas that that produced produced &cites dacites in the The upper parts of the upper the volcanic volcanic piles. piles. Tonalite Tonaliteintrusions, intrusions,now now gneissic, gneissic, engulfed engulfed and and represented as detached fragments of the the lower lower parts parts of of the thegreenstone greenstone succession succession (now (now represented rnafic mafic xenolith trains), possible possible older, older, tonalite tonalitebasement basementenclaves enclaves(e.g. (e.g. 1-lillary Hillmy and and Ayres, 1980), 1980),and andthe thewestern western parts parts of of the Kapuskasing which extend extend into the Ayres, Kapuskasing zone which tonalite gneiss gneiss terrane. The Thetonalitic tonaliticrnagmas magmasmay mayrepresent representjuvenile juvenilemaginas magmas derived derived

from the mantle, or may products of partial partial melting melting of of aa heterogeneous heterogeneous lower lower from may be the products crust similar to zone. The t o that that exposed exposed in in the the Kapuskasing Kapuskasing zone. The tonalitic tonalitic intrusions intrusions have have imposed amphibolite-facies amphibolite-facies aureoles on metavolcanic metavolcanic host host rocks; rocks; considering considering the thevolume volume imposed sufficient ttoo account for most of of tonalite, the the heat heat from fromthese thesemagmas magmas was was probably probably sufficient the metamorphism of the volcanics. metamorphism of volcanics. Tonalitic Tonaliticmagmatism magmatismthus thusmay mayhave havecoincided coincided with with regional metamorphism metamorphismand andacted actedas asthe the main mainagent agentofofheat heat transfer transfer into the upper regional upper crust (cf Wells, Wells, 1979). 1979). Isoclinally Isoclinallyfolded foldedgneissosity gneissosityininthe thetonalite tonalite demonstrates demonstrates that major (cf major deformation post-dates post-dates these these intrusions. intrusions. The age of of major deformation Abitibi and and Wawa Wawa subprovinces is closely deformation in in the the Abitibi Ma, the the approximate approximate age age of of the youngest volcanics of of the main youngest volcanics main bracketed between 2696 Ma, pile, and 2680 Ma,the the approximate approximateage ageofoflatelate- to post-tectonic plutons plutons (Frarey (Frarey and 2680 Ma, In supracrustal supracrustal rocks rocks at at high high crustal levels, this this deformation deformation produced produced Krogh 1986). 1986). In upright to vertically-plunging structural features upright vertically-plunging structural features as as well well as as thrusts thrusts and and nappe-like nappe-like structures etal., al.,1981; 1981; Gorman German et et al., al., 1978; 1978; Thurston and Breaks, Breaks, 1978). 1978). At structures(Poulsen (Poulsen et deeper structural structural levels, levels, the thedeformation deformationresulted resultediningneissosity gneissosity and and subsequent subsequent folds folds in in plutonic rock rock and and paragneiss, paragneiss, followed followedby bylater later doming. doming. Forceful emplacement of plutonic massive plutons plutons also also deflected deflected structural structural trends massive trends in in country country rock rock into into concordance concordance with with of these bodies. at 2680 2680Ma, Ma, the margins of bodies. Following Following intrusion of the the massive massive plutons at subprovinces. There there was was relative relative tectonic tectonicquiesence quiesencein inAbitibi Abitibi and and Wawa Wawa subprovinces. There is is evidence, however, of continued activity activity in in the theKapuskasing Kapuskasing zone. zone. High-grade metamorphic rocks of of the Kapuskasing yield concordant U-Pb High-grade Kapuskasing zone yield U-Pb zircon dates of 2696 Ma. U-Pb U-Pb zircon dates dates are a r e generally generally considered considered to t o record record 2696 ttoo 2616 2616 Ma. case are a r eof of metamorphic metamorphic origin. origin. the age of crystallization of of the the zircons, zircons, which which in in this this case interpretation would This interpretation would imply imply tthat h a t metamorphism metamorphism in in the t h e Kapuskasing Kapuskasing zone occurred

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2696 Ma ago,up upt to 60M Ma aftertectonic tectonic stabilization of of much much of of the the rest of 2696 ttoo 2616 2616 M a ago, o 60 a after of

Superior province. A discrete burial and metamorphism metamorphismevent, event,restricted restricted tto burial and o the Superior province. Kapuskasing zone, could explain the deformed, metamorphosed metamorphosed conglomerate conglomerate cobbles cobbles from Borden Lake which which have have aa zircon zircon date date of 2664 2664 Ma Ma (Percival et al., al., 1981). 1981). However, However, Borden Lake an anomalously young zircon zircon date date of of 2552 M Ma on aa trondhjemitic trondhjemitic cobble from the anomalously young a on the weakly weakly metamorphosed Ma Doré conglomerate conglomerate near Wawa, reported by Turek et et metamorphosed >2696 >2696 M a Dore Wawa, reported by Turek al. (1984), suggests that that the date (1984), suggests date on on the theBorden Borden Lake Lake conglomerate conglomerate cobble cobble may may not represent the age of crystallization of the source source pluton. pluton. In In addition, addition, tectonic mechanisms which which could could lead lead tto of the 500 krn wide wide o deep burial of 500 km long xx 50 50 km Kapuskasing "sliver"are are unknown unknownand andseem seemt otobe beunlikely unlikelyafter after termination termination of of the major Kapuskasing "sliver" tectonism theAbitibi Abitibiand andWawa Wawasubprovinces. subprovinces. It is more likely that aa single single tectonism ininthe protracted protracted metamorphic metamorphic event eventwas wasresponsible responsible for forproducing producing the the observed observed characteristics. One must must therefore examine the assumption that zircons zircons are a r e closed closed to t o lead lead loss loss immediately following crystallization, regardless of the following crystallization, the cooling cooling history. Slowly Slowly decreasing temperatures from decreasing metamorphic temperatures from peak levels of 800°C 800° could could result result in in lead lead diffusion years after after crystallization, provided that there diffusion out out of of zircon zircon for several million million years provided that is temperature" for zircon. 50°C was was estimated is some finite "blocking "blocking temperature" zircon. AAvalue value of of 700 700 ± -+ 50° for this hypothesis ttoo explain for zircon blocking blocking by Mattinson (1978). (1978). Invoking Invoking this explain the theyoung young "metamorphic" "metamorphic" dates dateswould would allow allow aa simpler simpler geological geological history historyinvolving involving only only the the metamorphism with later fluid metamorphism at at 2700 2700 to t o 2680 2680 Ma M a with fluid circulation and and possible possible ductile shear at at depth. depth. The east-northeast structural The prominent prominent east-northeast structuraltrends trendsininthe theKapuskasing Kapuskasing zone zone are are the the result of of relatively relatively late late tectonism. tectonism. The Thestructural structuralgrain grainisisdefined defined by by the orientation orientation of inigmatitic axes. This nigmatiticand and gneissic gneissiclayering layering folded folded about aboutshallow-plunging shallow-plunging ENE ENE axes. This folding folding event event therefore therefore post-dates post-dates crystallization crystallization of of tonalitic tonaliticmelts, melts,thought thought to t ocoincide coincide with with the netamorphic peak. units that can be the inetamorphic peak. Similarly, Similarly, structurally structurally complex complex tonalitic gneiss units traced into the Kapuskasing have a strong, strong, superimposed superimposed traced from from Wawa Wawa subprovince into Kapuskasing zone have ENE ENE foliation foliation and lineation in in the theKapuskasing Kapuskasing zone zone(Percival (Peruvaland andCoe, Coe,1981). 1981). If the the correlation correlation is isvalid valid between between massive massive granodiorite dated at a t 2680 2680 ± Ma and granodiorite granodiorite -+ 3 Ma gneiss then the the ductile gneiss adjacent to to the theKapuskasing Kapuskasing zone in the Abitibi subprovince, subprovince, then strain strain occurred occurred after after2680 2680 Ma Ma but pre-dated pre-dated post-metamorphic post-metamorphic cooling. cooling. This This timing timing is consistent that sinistral sinistral transcurrent transcurrent movement consistent with with the thesuggestion suggestion of of Watson Watson (1980) 0980) that movement occurred occurredalong alongthe theKapuskasing Kapuskasing zone zone during during emplacement emplacement of of the theMatachewan Matachewandyke dyke swarm swarm at at 2633 2633 Ma Ma (Gates and Hurley, Hurley, 1973). 1973). Late Late Archean Archean deformation deformation could could have have promoted promoted resetting resettingofof2700-2680 2700-2680 Ma Ma zircons zircons to toages agesdown downto t o2616 2616Ma. Ma.

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— 32 32 —

UPLIFT UPLIFT OF OF THE THE KAPUSKASING KAPUSKASING STRUCTURE STRUCTURE

The age of of uplift of the Kapuskasing constrained. Evidence Kapuskasing zone is not well constrained. Evidence of of late lateArchean Archean transcurrent transcurrentmovement movementwas wascited citedby byWatson Watson(1980) (1980) and Percival Percival and and Coe Coe (1980), however its its magnitude was probably probably small, small, judging judging by bythe the minor minor apparent apparent offset (1980), however offset of occurred aatt that of the the Abitibi-Opatica Abitibi-Opatica contact contact (Fig. (Fig. 1). I). Major Major thrusting thrusting could could also also have occurred that time, time, setting settingU-Pb U-Pb and andK-Ar K-Ar isotopic isotopicsystems systemsininthe thehigh-grade high-graderocks rocksata t2,650-2,250 2,650-2,250 Ma. Ma. Geochronological evidence indicates indicates activity activity at Ma. Three Three alkalic alkalic Geochronological evidence at 1,655-1,850 1,655-1,850 Ma. rock-carbonatite rock-carbonatite complexes complexesnear nearKapuskasing Kapuskasiighave haveK-Ar K-Ar dates datesofof1,655-1,720 1,655-1,720 Ma Ma (Gittins (Gittins et et a!., al., 1967). 1967). AAbiotite-whole-rock biotite-whole-rock Rb-Sr Rb-Sr isochron isochron from tonalite of of the the Shawmere arid others, others, 1980). 1,850Ma Ma (Simmons (Simmons and 1980). A A whole-rock whole-rock Shawmere anorthosite anorthositecomplex complexisis1,850 40Ar/39Ar analysis of blastomylonite from from the Ivanhoe Lake Lake cataclastic cataclastic zone gave aa '+o~r/^~ r of date dateof of 1,720 1,720Ma Ma (Percival, (Percival,1981; 1981;Fig. Fig. 15). 15).

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Fraction Fraction 39Ar " ~ rre'eased released

Figure Figure15. 15. 40Ar/39Ar 40Ar/39Ar age agespectra spectrafor forhornblende, hornblende,plagioclase plagioclaseand andwhole-rock whole-rock separates separatesfrom fromnear near the theIvanhoe IvanhoeLake Lake cataclastic cataclasticzone. zone. Increasingly Increasinglyhigh high release releasetemperature temperature from from left lefttotoright. right.Width Widthofofbars barsare are2o-uncertainty 2uuncertainty estimates. estimates.

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-33rock-carbonatite complexes in the southern Three alkalic rock-carbonatite southern Kapuskasing Kapuskasing zone have of 1,050-1,100 Ma (Gittins (Gittins et at., K-Ar K-Ar dates of 1,050-1,100 Ma al., 1967). 1967). Plagioclase Plagioclase from from amphibolite4n amphibolite-in tthe he of tthe Ivanhoe Lake Lake cataclastic cataclastic zone footwall of h e Ivanhoe zone yields a 40Arf39Ar ^O~r/39Arplateau at at 1107 1107 Ma Ma (Fig. 15), suggestingmild mildresetting, resetting, possibly possiblydue duet otofaulting. faulting. Lower concordia intercepts intercepts (Fig. 15), suggesting Lower concordia of zircon discordia in tthe Ma (Percival (Percival and and Krogh, Krogh, 1983) 1983)may mayrelate relatetto of h e range 827-1,108 827-1,108 Ma o ago. uplift 1,100-1,000 1,100-1,000 Ma ago. events along along tthe structure with major The coincidence of Proterozoic events h e Kapuskasing Kapuskasing structure orogenic activity activity elsewhere Shield suggests suggeststhat thatt hthe structure is is an anintracratonic intracratonic orogenic elsewhere in tthe h e Shield e structure basementuplift uplift related to possibly an anearly early Proterozoic Proterozoic basement t o aa distant distant compressional compressional event, possibly collision in the Churchill Province to t o the t h e northwest northwest (Percival (Percivaland andMcGrath, McGrath, 1986). 1986).

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PART lb ROAD LOG

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KAPIJSKASING UPLIFT: UPLIFT: ARCHEAN THE KAPUSKASING ARCHEAN GREENSTONES GREENSTONES AND AND GRANULITES GRANULITES

SUMMARY Variousstructural structural levels within tthe Various h e central centralSuperior Superior Province Province will will be be examined examined to to

demonstrate their characteristics characteristics and and interrelationships. interrelationships. Starting Startingwith with the thelowest-grade lowest-grade area, we we will will progress up-grade up-grade through an rocks in the Michipicoten Michipicoten belt of the t h e Wawa Wawa area, unbrokenoblique obliqueccrustal cross-section into tonalitic gneisses and granulites of the unbroken r Kapuskasing zone. DAYI Geology of the Geology of the Wawa Wawa Subprovince, Wawa ttoo Chapleau Chapleau in well-preserved well-preserved supracrustal rocks of of tthe h e Michipicoten Michipicoten belt The first day begins in and ends ends in in the the lowest lowest structural structural levels gneiss terrane (Fig. and levels of the the Wawa Wawa gneiss (Fig. 2). 2). Exposures Exposures near Wawa willdemonstrate demonstrate lithological, lithological,structural structural and and metamorphic metamorphic characteristics characteristics of Wawa will of the low-grade terrane. To rocks ocks and and internal low-grade terrane. To the theeast, east,the thetransition transitiontot ogneissic gneissicplutonic pi characteristics gneiss terrane will be examined. W characteristicsof of the t h eWawa

STOP 1-1: 1-1: Doré STOP Dore Conglomerate Conglomerate(E. (E.and andW. W. sides sidesof of Hwy Hwy 17) 17) The Dore Doré isis aa thick, thick, coarse polymictic polyrnictic conglomerate unit tthat h a t isis overlain overlain by by The

metavolcanic rocks at2696 2696 Ma Ma (Turek (Turek et et al., al., 1982) 1982)and and underlain underlain by by rocks of cycle cycle HI, 111, dated dated at older inetavolcanic metavolcanic rocks. rocks. Eastward f a d e s transition transitionfrom from Doré Dore conglomerate conglomerate older Eastward there there is is aa facies of wacke, siltstone, cross-bedded cross-bedded arkose and conglomerate called the the into a sequence of "Eleanor Slate". Slate". At this locality, coarse felsic tuff-breccias to "Eleanor t o the t h enorth north are aresucceeded succeeded southward by by aa sequence sequence of of wacke wacke (reworked (reworked tuff?) tuff?) and and Dore Doré conglomerate. conglomerate. Bedding southward Bedding and foliation dip approximately 45° 45" eastward eastward and and may may face facedownward downward (west). (west). The Dore Dare consists of of pebbles pebbles and and boulders boulders of of mafic mafic and and felsic volcanics, The volcanics, quartz quartz porphyry, iron iron formation formation and andtrondhjemite trondhjemiteininaa schistose, schistose, chloritic chloritic matrix. matrix. The The pebbles pebbles porphyry, aare r e flattened flattenedininthe thefoLiation foliation plane plane and and elongated elongated in in the the east-plunging east-plunging rodding rodding lineation. lineation. Variations in pebble pebblepacking packingand andsize sizedefine definecrude crudestratification stratification units. units. A Variations in A single trondhjemitic boulder apparent age age of of 2552 2552 Ma Ma boulder yielded discordant zircons with an apparent (Turek et et al., at., 1984), approximately 150 150M Ma youngerthan thant hthe stratigraphicage age of of the the unit unit 1984), approximately a younger e stratigraphic (Turek likely that that the source of of the based on zircon zircon dates of bracketing volcanic volcanic rocks. rocks. It is likely based trondhjemitic boulders syn—volcanic M a age. trondhjernitic bouldersand andcobbles cobblesis is syn-volcanic plutons plutonsofof2744—2735 2744-2735 Ma

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1-2: Helen Iron Range Section at McLeod Mine, Algoma Ore Properties Ltd. The McLeod Mineextracts extracts siderite siderite and and pyrite pyrite from from the base of the McLeod Mine the Helen Helen iron iron range. This 1800 m m thick unit of intermediate to t o felsic felsic Thisiron iron range range lies lies at a t the thetop topof of aa1800 metavolcanics metavolcanics consisting of oligomictic and polymictic breccia, thin thin bedded bedded to t o massive massive tufts, flows, and andcrystal crystal tuffs. tuffs. These tuffs, lapilli lapilli tuffs, tuffs, spherulitic spheruliticflows, flows, flow flow banded banded flows, These intermediate to felsic felsic metavolcanics metavolcanics are areintruded intruded by by gabbro gabbro ttoo quartz quartz diorite diorite dykes dykes and intermediate to sills sills that that reach reach290 290m m thickness. thickness. The intermediate intermediate to dominantly massive massive and and t o felsic felsicmetavolcanics metavolcanicsoverlie overlieaadominantly pillowed of intermediate to ed sequence of t o mafic mafic metavolcanics. metavolcanics. The The mafic to t o felsic felsic metavolcanics metavolcanics are arebimodal bimodal in in composition composition and represent the the oldest cycle cycleof ofvolcanism volcanism(Fig. (Fig. 14). 14). The The iron formation caps the first firstvolcanic volcanic cycle cyclein in the theMichipicoten Michipicoten greenstone greenstone belt belt and and from from the the stratigraphic stratigraphicbottom bottom to totop t o pconsists consistsof of five fivelithologic lithologic rock rock types types that that are are gradational gradational into into each other. Upper Upper and and lower lower contracts are sharp. sharp. From From stratigraphic stratigraphic bottom bottom to t o top top the t h eiron iron formation formation consists consists of of siderite, siderite, pyrite, pyrite, banded banded chert, chert, thin chert-wacke-magnetite, and graphite-pyrite. thin bedded bedded chert-wacke-magnetite, graphite-pyrite. AAU-Pb U-Pb isotopic isotopic age age of of approximately has been been obtained obtained from from the the crystal M a has crystal tuffs tuffslying lyingimmediately immediately below below approximately 2749 2749 Ma the the iron iron formation formation (Turek (Turek et et al., al., 1982). 1982). Overlying intermediate to Overlying tthe h e iron formation are massive massive pillowed pillowed intermediate t o mafic mafic inetavolcanics inetavolcanics of of cycle cycle two. two. The The area area of of the themine minedisplays displays numerous numerous major and minor faults, and and contains contains several a1Proterozoic Proterozoic diabase diabase dykes that strike strike northeast northeast and and northwest. northwest. Beneath areaofofapproximately approximately1800 1800mmby by 750 750 m m has has been been Beneath the theiron iron formation formationan anarea outlined outlined that that contains containschloritoid. chloritoid. These Thesecrystals crystalsare aregenerally generallyup upto t o22mm mrn in in diameter diameter and and are a r erandomly randomly oriented with with respect ttoo the schistosity. schistosity. Chloritoid Chloritoid alteration alterationoccurs occurs above above the the iron iron formation formation as aswell, well, in in less less abundant abundant quantities. quantities. The The volcanics volcanics above above and and below below the the iron iron range range are arepervasively pervasivelysoaked soakedwith with carbonate. carbonate. Carbonate Carbonatealteration alterationisisofofregional regionalextent extentand andoccurs occursin inall allrock rock types, types, volcanic, volcanic. sedimentary, sedimentary, and and intrusive. intrusive. STOP

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Spherulitic rhyolite rhyolite(100-200 (100-200 m m south south of of gate gateon onMcLeod McLeod Mine Mine road) road) Stop 1-3 1-3 Spherulitic Stop This This stop stop contains containsthe thebest bestexposure exposureofofaaspherulitic spherulitic(hollow) (hollow)flow flowbanded banded felsic felsic & . flow Mine area. area. The flow within within the the McLeod McLeod Mine The spherulitic spherulitic unit unit isis overlain overlain by by aa flow flow breccia breccia containing well well developed developed fiamme fiamme and and this this unit unit isisin in turn turnoverlain overlainby by aa massive massivetuff tuffwith with containing scattered scattered lapilli-size lapilli-size clasts. clasts. This Thisexposure exposure lies lies in in the the lower lower part of of the the felsic felsic part part of of the the

— 36 -

oldest oldest cycle cycle of of volcanism. volcanism. Stratigraphic Stratigraphic tops tops are are north north and and the t h esection sectionisisoverturned, overturned, dipping along Wawa atWawa Wawa dipping south. south. Interpreted Interpretedfaulting faulting along WawaLake Lakeand andbeach beachdeposits depositsat prevent any estimate as to how far above the contact with the intermediate prevent any estimate as t o how far above t h e contact with t h e intermediate to t o mafic mafic pillowed metavolcanics this this felsic felsic section pillowed and and massive massive metavolcanics section occurs. occurs. Return Return to t o Hwy Hwy 101 101

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00.0 km - Junction Me, Wawa. Junction of of Highway Highway IOIE 101Eand and Broadway Broadway Ave, Wawa. Proceed Proceed east east on on 00.0 km Highway Highway 101. 101.

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20.9 20.9 km -- Stop Stop 1-4: 1-k Mafic Maficgneiss gneiss - tonalite tonalitecontact contactzone zone(N. (N.and andS.S.sides sides of of Hwy Hwy101) 101) , A Ic gneiss A large large enclave enclave of of maf mafic gneiss is enclosed in and and intruded by tonalitic tonaliticgneiss gneissininaa migmatitic migmatiticzone zone marginal marginal to t o the the Michipicoten Michipicoten greenstone greenstone belt. The Thehornblendehornblendeplagioclase considered tto represent deformed, metamorphosed plagioclase gneiss is considered o represent metamorphosed Michipicoten volcanics and and metagabbro. metagabbro. In In this this exposure exposurei titisiscut cut by byearly earlytonalitic tonalitic intrusions, intrusions, llate ate

aplitic apliticand and pegmatitic pegmatiticdykes, dykes, and and still stilllater latermafic maficand andlamprophyric lamprophyricdykes. dykes. The Thegneiss gneiss displays subvertical foliation, foliation, mineral displays subvertical mineral lineation, lineation,and and tight tightsteeply-plunging steeply-plunging isoclinal isoclinal minor folds.

45.1 45.1 km km

Jct. Jct. Hwy. Hwy. 651. 651. Continue Continueeast. east.

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68.5 gneiss Budd and 68.5 km Stop Stop1-5: 1-5: Xenolithic Xenolithictonalite tonalite gneissatat BuddLake Lake(N. (N. andS.S.sides sidesofofHwy Hwy101) 101) This This complex complex outcrop outcropconsists consists of of several severalphases: phases: 1) 1) xenoliths of mafic maficgneiss, gneiss, interpreted interpreted as asrafts raftsofofthe t h eMichipicoten Michipicotenmetavolcanic metavolcanicsequence, sequence, 2) 2)gneissic gneissic tonalite tonalite

with small, wispy mafic xenoliths, cut by 3) foliated to gneissic hornblende-epidote-

biotite-sphene tonalite, all cut by 4) pink-white granitic pigmatite. Hornblende from foliated wt% ,41203, A1203, indicating indicating crystallization crystallization at foliated tonalite tonalite(3) (3) contains contains 10.4 10.4 wt% approximately approximately5.6 5.6 kbar kbar(Hammarstrom (Hammarstromand andZen, Zen, 1985). 1985). Continue east on 101

94.4 km Stop 1-6; Tonalite gneiss and maf Ic dykes (N. and S. of Hsy 101)

Tonalite northeast-trending mafic Tonalite gneiss gneiss iiss cut by northwest- and and northeast-trending mafic dykes dykes with wit chilled dykes (Ernst and chilledmargins. margins. The Theolder oldernorthwest-striking northwest-strikingHearst Hearst dykes (Ernst andHalls, Halls,1980, 1980,1984) 1984) occur have aa similar similar trend and occur west west of of the t h eKapuskasing Kapuskasing zone. zone. The The dykes dykes have and similar similar

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including plagioclase plagioclase phenocrysts phenocrystsand andtholeiitic tholeiitic composition, composition, tto characteristics, including o Matachewan dykes dykes east east of of the Kapuskasing zone. The Kapuskasing zone. The Matachewan Matachewan dykes dykes have an Rb-Sr Rb-Sr Matachewan whole-rock age of 2633 ± 75 M Ma (Gates and andHurley, Hurley, 1973). 1973). Ernst and Halls (1980, a (Gates (1980, 1984) 1984) whole-rock 2633 + also reported reported similar paleomagnetic poles poles for for the two zone 50 50 km km wide wide also two swarms. swarms. InInaa zone " zone, the the Hearst dykes average average 44 m m in in width and west of the the Kapuskasing Kapuskasing zone, and have have a consistent easterly easterly dip dip of of 80Â 80° (Ernst, (Ernst, 1983; Percival, 1981). 1981). The Thetonalitic tonalitic gneiss is thinly thinly consistent 1983; Percival, gneiss is layered and and has hassparse sparsemafic maficxenoliths. xenoliths. Gneissosity appearstto havechaotic chaotic orientation orientation Gneissosity appears o have but is subhorizontal onaverage. average. There Thereisisevidence evidencefor forat at least least two two sets setsofof structure: structure: an an but subhorizontal on older gneissosity gneissosity is is reoriented reoriented by by younger younger subhorizontal subhorizontalfoliation foliation to t o give give complex complex patterns. sigmoidal patterns. Continue east 122.2km km Stop 1-7: 122.2 1-7: Highbrush Highbrush Lake Lake Dome Dome (N. (N.side of Hwy Hwy 101) 101) Small domes domesexposed exposedininroadcuts roadcutshere hereare aretypical typicalofof the the local local and and possibly possibly of of the the Small regional-scalestructural structural pattern. pattern. The rock type is fine-grained, fine-grained, thinly-layered thinly-layered regional-scale The main main rock biotite and biotite and hornblende-biotite hornblende-biotite gneiss gneiss with with local localaugen augen of potash potash feldspar. The outcrop outcrop consists consists of of several several domes domesor orcanoe-shaped canoe-shapedfolds foldswith withaarolling rolling easteastThe west mineral mineral and andstretching stretchinglineation. lineation. Small parts west Small intrafolial intrafolialfolds foldsare arepresent present in in some some parts

as are areamphibolitic amphibolitic xenoliths, xenoliths,locally locally with with clinopyroxene. clinopyroxene. Pink Pink granitic granitic of the outcrop, outcrop, as and sills sills cut cut gneissic gneissic layering layering in in some some areas. areas. Late sub-horizontal highpegmatite dykes dykes and are common commonininthe the vicinity vicinity of strain zones zones are of the thetransition transitionzone zonebetween betweenWawa Wawa and and Kapuskasing gneisses. gneisses.

Continue east

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131.6km km - Junction Junction of of Highway andHighway Highway129. 129. Follow Follow 101E, lOlE, 129N toward Highway 101 101 and 129N toward 131.6

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Chapleau

Stop 1-8: 1-8: Xenolithic tonalite (w. side side of of Hwy Hwy Stop tonalite with withhorizontal horizontalshear shear zones zones (W. 101—129) 101-129)

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Xenolith alignment and gneissosityhave havesub-vertical sub-verticalorientations orientations in in the the central central and gneissosity thin part of this this road-cut. road-cut. Layering Layeringbecomes becomes horizontal horizontal and and mafic mafic xenoliths xenoliths become become thin and bottom bottom of of the mafic layers in 1/2 112 m-thick horizontal horizontalshear shear zones zones near near the top and outcrop.

139.5

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km . Junction )unction of of Highways and 129N: 129N: Proceed north km Highways 1OIE 101E and north on on Highways Highways 101-129 101-129 through Chapleau. Chapleau. Follow Follow the t h eMissinaibi Missinaibi Provincial Park Park signs north of town on gravel road. road. Proceed Proceednorth northand andeast easton onpark parkroad roadand andlogging logging roads roads leading ttoo the the Chapleau Chapleau River. River.

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178.3 FlorannaLake LakeComplex Complex Stop 1-9: 1-9: Floranna 178.3 km - Stop The Floranna Floranna Lake Lake Complex Complexisisaacomplex complexcrescentic crescentic pluton plutonofof intermediate intermediate composition. composition. The The western western margin margin consists of lineated, h e a t e d , fine fine grained grained granite granite with with orthopyroxene and and biotite. biotite. inside Inside the the marginal marginal unit is is lineated diorite diorite to t o monzonite rnonzonite

containing hornblende-rimmed augenclinopyroxene clinopyroxenephenocrysts. phenocrysts. The Thecentral central part of the hornblende-rimmed augen the complex is foliated hornblende-clinopyroxene-biotitediorite, diorite, gabbro gabbroand and foliated and and lineated lineated hornblende-clinopyroxene-biotite melagabbi-o. well-exposed eastern eastern contact contact of melagabbro. The well-exposed of the thecomplex complexshows shows extremely extremely attenuated attenuatedand and contorted contortedlayering layering in in granite granite of of the thecomplex complex adjacent adjacent to t o rocks rocks of of the the Robson Lake dome dome tto the east. Robson Lake o the Clinopyroxene augen diorite-monzonite diorite-monzonite C l i p y r o x e n e augen These coarse-grained monzonite. medium- to coarse-grained monzonite. RodRodThese rocks are strongly lineated, mediumshaped shaped clinopyroxene clinopyroxene phenocrysts, rimmed rimmed by by hornblende, hornblende, make make up up some some 20% 20% of the the rock. rock. Original Originaloutlines outlines of of feldspar feldspar grains grains are arevisible visible but but these theseare arenow now polycrystalline polycrystalline aggregates. aggregates. j-y,

-

179.3 -

Foliated and lineated h e a t e d diorite dioritewith with gabbro gabbro and and melagabbro melagabbro layers layers

Igneous clinopyroxene with with hornblende hornblende overgrowths overgrowths and and granitic leucosome leucosome layers layers are are present. present.

-

183.2 Granulitegneiss, gneiss,Robson Robson Lake Lake dome dome 183.2 km - Stop Stop 1-10: 1-10: Granulite The of tthe complexisisaa foliated foliated to to augen-textured, augen-textured, The easternmost exposure of h e igneous complex

xenolithic porphyritic granite granite with with leucogranite leucogranite veinlets veinlets parallel ttoo foliation xenolithic hornblende hornblende porphyritic on on the the 11 mm-2 mm-2 cm scale. scale. The Thelayering layeringisisfolded foldedabout aboutnorthwesterly-plunging northwesterly-plunging axes. axes. Parts Partsof of the theoutcrop outcropare a r efine-grained fine-grained and andmylonitic myloniticwith with highly highly attenuated attenuatedlayering. layering. To of interlayered mafic To tthe h e west, the t h e Robson Robson Lake dome consists of mafic and and tonalitic tonalitic gneiss. gneiss. Near Near the thecontact contactwith withthe theFloranna FlorannaLake LakeComplex, Complex, the t h e layering layering in in rocks in the dome concordant tto west, however, however, the the attitude attitude is dome is concordant o the contact and and dips steeply west, is horizontal Ic rocks eastin in the thecore coreof of the thedome. dome. AtAtthis thisoutcrop outcropthe themaf mafic rocks consist consist horizontal farther farther east of garnet-clinopyroxene-hornblende-plagioclase-quartzassemblages, assemblages, with with layering layering of garnet-clinopyroxene-hornblende-plagioclase-quartz defined and hornblende-rich defined by by different different proportions proportions of of minerals, minerals,including including garnet-rich garnet-rich'and hornblende-rich varieties. varieties. Concordant Concordanttonalitic tonaliticlayers layerslocally locallyhave havelarge largeclinopyroxene clinopyroxenecrystals crystalsrimmed rimmed by by hornblende, hornblende, in clots up ttoo 4 cm. The Thelayering layering isisfolded folded about about upright upright isoclinal isoclinal folds folds locally. locally.

r

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-39inclusions of of mafic gneiss gneiss in in granite granite of granite in mafic gneiss and inclusions Small dykes of granite in indicate an indicate an intrusive intrusivecontact contactbetween betweenthe theFloranna FlorannaLake LakeComplex Complexand and Robson Robson Lake

dome.

The interpretation interpretation of the Lake dome, dome,which whichhas hasthe thestructural structural attributes attributes The the Robson Robson Lake of the domal gneiss gneissterrane terraneand andthe thelithological lithological characteristics characteristics of t h e Wawa Wawa domal of Kapuskasing Kapuskasing zone, is is that rocks zone underlie underlie the Wawa domal zone, rocks like likethose those exposed exposed in the the Kapuskasing Kapuskasing zone Wawa domal terrane been exposed exposedhere hereininaastructural structural culmination. culmination. terrane and and have have been

Return to t o Chapleau Chapleau DAY 2 Geologyof of the Kapuskasing KapuskasingStructural Structural Zone Zone in in the the Chapleau-Foleyet Chapleau-Foleyet Area Geology In this this section we will will examine In examine the t h e rocks rocks and and structures of of the t h e Wawa Wawa domal doma' gneiss -- Kapuskasing Kapuskasingzone zoneboundary boundaryand andofofthe theKapuskasing Kapuskasingzone zoneitself itself along along gneiss

Highway 101. 101.

-

0.0 km km 0.0

I I

I I I I I * ii.

and Highway Highway 129 south south of of Chapleau. Chapleau. Proceed Junction of Highway Highway 101E 101E and Proceed east

on Highway 101. 101.

2-1: Borden 13.0 km km Stop 101) Lake conglomerate conglomerate (S. (S. side of Hwy 101) 13.0 Stop 2-1: Borden Lake This outcrop outcrop consists consists of of stretched-pebble stretched-pebble metaconglornerate metaconglomerate with with aa strong rodding rodding This

weak, gently gently north-dipping north-dipping foliation. foliation. The lineation and and weak, The rock rockisisaaclast-supported clast-supported conglomerate containing 10% 10%matrix matrix of of garnet-hornblende-biotite-quartz. garnet-hornblende-biotite-.quartz. The The cobbles, cobbles, conglomerate which range range up uptto m in in length, length, aare felsic metavolcanics, metasediments,granodioritegranodioriter e felsic metavolcanics, metasediments, which o 1m amphibolite, with rare hornblendite tonalite, plagioclase-porphyritic plagioclase-porphyritic meta-andesite meta-andesite and and amphibolite, and vein vein quartz. quartz. The and The metaconglomerate metaconglomerate is spatially spatially associated associated with amphibolite and and paragneissto tothe the south southon onBorden BordenLake, Lake,and andisiscut cutby bygranite, granite, however, however,tthe stratigraphic h e stratigraphic paragneiss relations of relations of the thesupracrustal supracrustal rocks rocks are areunknown. unknown. An aggegate aggegateofoftonalitic tonalitic cobbles extracted from the An cobbles extracted the metaconglomerate metaconglomerate yielded yielded

Ma (Percival et et al., 1981). 1981). The The zircons zircons have have aa corroded corroded zircons dated at at 2664 2664 ±+ 12 12 M a (Percival appearanceand andproduced produceddiscordant discordantdata datapoints pointsand andhence hencet hthe interpretation of of the the data appearance e interpretation open. Rather than recording recording the the original original crystallization crystallization age of the source pluton for for is open. Rather than age of source pluton the cobbles the zircons zircons probably probablydate dateaalater later deformation-metamorphic deformation-metamorphic event. event. The cobbles the The source pluton plutonfor for the the cobbles cobblesmay maybe besimilar similart otothat that which which provided providedmaterial material for for the source Doré conglomerate. Dor6

— 40

-

Continue east on 101 Continue . .. -

..

2-2: Mafic 25.9 km Stop 2-2: 25.9 Mafic gneiss gneiss xenoliths xenoliths with with amphibolitic amphibolitic margins margins (N. (N. side of Hwy Hwy 101) 101) This exposure exposuredemonstrates demonstrates an an important important aspect aspect of between the This of the boundary boundary between

Kapuskasingzone zoneand andWawa Wawagneiss gneiss terrane. Aside Asidefrom fromthe thelarge-scale large-scale structural structural Kapuskasing terrane. terrane and contrast between between the the domal domal Wawa Wawa terrane and the t h e linear linear belts beltsin inthe theKapuskasing Kapuskasing zone,

intrusive relations relations are also instructive. The intrusive Theoutcrop outcropconsists consists of of two two main main components: components: (1)coarse-grained coarse-grainedhornblende-biotite hornblende-biotitetonalite, tonalite, the the dominant dominant rock rocktype type tto the west, west, and and (1) o the (2) medium mediumgrained grained mafic mafic gneiss gneiss consisting consisting of of garnet-clinopyroxene-hornblendegarnet-clinopyroxene-hornblende(2) plagioclase-quartz assemblages. assemblages. Small xenoliths of of mafic mafic gneiss gneiss in intonalite tonalite have have plagioclase-quartz Small xenoliths margins, up up tto cm thick, thick, consisting consisting of of hornblende-plagioclase. hornblende-plagioclase. Dykes Dykesofoftonalite tonalite margins, o several cm cutting mafic gneiss gneiss are are bordered bordered by mafic rock with hornblende-plagioclase hornblende-plagioclase

assemblages. The assemblages. The interpretation of of age age relationships relationships is that that the thehigh-grade high-grade metamorphism that that produced the garnet-clinopyroxene assemblages in mafic gneiss metamorphism gneiss preceded the the intrusion intrusion of of tonalite. tonalite. Water preceded Water in in the the tonalite tonalitemagma magma was was presumably presumably ,. crystallization and and hydrated hydrated the the adjacent less-hydrous mafic rock. rock. released upon upon crystallization less-hydrous mafic Althoughthe the tonalite tonalite at this outcrop has not been dated, iti t probably either to Although probably belongs belongs either Ma tonalite gneiss gneiss suite suite or ttoo the 2680 group of of plutons. plutons. The high-grade the >2707 >2707 M a tonalite 2680 Ma M a group high-grade metamorphismisistherefore therefore older olderthan than 2680 2680Ma. Ma. This Thisisisininconflict conflictwith withthe thedirect direct dates dates metamorphism of metamorphic zircons from the as 2616 2616 Ma. Ma. of the Kapuskasing Kapuskasing zone that yield yield ages ages of of as aslow low as The conflict conflict has led ttoo the that the The the suggestion suggestion (Percival (Percival and and Krogh, Krogh, 1983) 1983) that the Kapuskasing Kapuskasing gneisses, although although metamorphosed metamorphosed prior prior tto 2680 M Ma ago,remained remainedat at high high temperatures temperatures gneisses, o 2680 a ago,

where radiogenic lead diffused readily out of zircon until at least 2616 Ma ago. Continue east 37.0 km 37.0

2-3: Thinly-layered Stop 2-3: Thinly-layered tonalitic gneiss gneiss and diatreme diatreme breccia breccia (N. (N. side side of of Hwy Iiwy

101) 101) Fine grained grained tonalitic tonalitic gneiss Fine gneiss aatt this exposure is strongly foliated and layered on a 1-5mm mmscale scalewith withgarnet, garnet,hornblende hornblendeand andbiotite-rich biotite-richlayers. layers. Extremely Extremelyattenuated attenuated 1-5 intrafolial folds folds are are present present locally. locally. Units foliation intrafolial Units characterized characterized by by extremely planar foliation such as as this this aare relatively rare in tthe zone. Although the orientation orientation of of such r e relatively h e Kapuskasing Kapuskasing zone. Although the

foliation in this exposure exposure is typical typical for for the theKapuskasing Kapuskasing zone, zone, most most Kapuskasing Kapuskasing gneisses gneisses

coarse-grained and andlayered layeredwith withdistinctive distinctiveleucocratic leucocratic portions. portions. In are mediummedium- tto o coarse-grained addition, the the layering layering in in the the typical gneisses gneisses is is warped warped about about gently gently northeast northeast or or addition, southwest-plungingaxes. axes. The fine grain size and thin thin planar layering in this outcrop southwest-plunging suggest aa relatively relatively late, high-strain suggest high-strain flattening flattening or shearing shearing event.

r —41 -

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A A thin thin diatreme diatremedyke dykeoccurs occursininthis thissame sameexposure. exposure. ItIt has has not not been been dated dated but but presumably presumably is part of of aa set set of of lamprophyre lamprophyre dykes dykes of 1100 . ~ l l 0Ma 0M aage age(Stevens (Stevens et et a!, al, 1982) 1982) that are particularly particularly common thatoccur occurininthe t h eKapuskasing Kapuskasing zone zone and and are common in the the area area between between the

I I I

Lackner Lakecomplexes. complexes. Both Both the the matrix matrix and fragments in the Lackner and and Nemegosenda Nemegosenda Lake the dyke dyke are be identified. identified. These are altered, altered, but but some some fragments can be These include include tonalitic tonaliticgneiss, gneiss, spinel spinel

n

Continue Continue east east on on Hwy Hwy101 101

lherzolite not occur occur in the Iherzoliteand and massive massive pink granite. As Asmassive massive granite granite does does not Kapuskasing zone,the thegranite granite fragments fragments are arerelatively relatively exotic. Their Kapuskasing zone, Theirsource sourcewas was probably below Kapuskasingzone, zone,possibly possiblyiningranite graniteofofthe the Abitibi Abitibi belt, below the Kapuskasing belt, which which according according to t o the the gravity gravitymodel, model, lies liesvertically verticallybelow belowatata adepth depthofof—15 -15 km. km. '

52.1 52.1 km km

Stop KapuskasingGneiss Gneiss (S. (S. side side of of Hwy Hwy101) 101) Stop 2-4: 2-4: Kapuskasing

Layered ruafic in situ tonalitic tonaliticleucosome, leucosome,and and crosscrossmafic gneiss gneiss with concordant & cutting cuttingtonalitic tonaliticand andpegmatitic pegmatiticdykes. dykes. Layering Layeringononthe the5 5tot o1010cm c mscale scaleisisgiven givenby by

I

alternating of similar alternatinghornblende-rich hornblende-rich and and garnet-pyroxene-rich garnet-pyroxene-rich layers layers(see (see analyses analyses of layers layers in Table 1). 1). Metre-scale Metre-scale blocks blocks of mafic mafic gneiss gneiss in breccia give parts of the outcrop moutcrop aa chaotic chaoticappearance. appearance. These These structurally structurallycomplex complexpanels panelsare areseparated separated by. bym-

scale high-strain high-strain zones with gently rolling, north-dipping, foliation. zones with north-dipping, pronounced pronounced foliation. Continue Continue east east on on Hwy Hwy101 101

59.8 59.8 km Stop Stop2-5: 2-5: Kapuskasing Kapuskasinggneisses gneisses (N. (N. and and S. S. sides sides of Hwy Hwy 101) 101) There are several several features features of of interest interest at this this outcrop outcrop (Fig. (Fig. 23): 23);

Mafic Maficgneiss gneiss is present on the northwest side side of the the road. road. ItIt isis aa coarse coarse grained grained rock rock consisting consisting of of three threetypes types of of layers layerson on the the5-100 5-100 mm mm scale: scale: i)i)relatively relativelyanhydrous anhydrous A.

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rnafic and quartz, quartz, with some mafic rock rock made made up of garnet, clinopyroxene, clinopyroxene, plagioclase and some hornblende to analyses analyses I1 && 3, 3, Table Table 1); ii) more hornblende (analogous (analogous to 1); ii) more hydrous hydrous layers layers containing containingless less garnet garnet and and clinopyroxene clinopyroxeneand and more morehornblende hornblende (analogous (analogous to t o analyses analyses 22 &&4, 4, Table Table1); I); and and

iii) iii)tonalitic tonaliticleucosome leucosomelayers, layers, both both concordant concordant to t o layering layering and and transverse transverse in the amphibole-rich amphibole-rich mafic rocks. rocks. Note Note that that the thetonalite tonalitehas has no no retrogressive retrogressive effect effect on on adjacent anhydrous mafic gneiss. gneiss. The tonalitic tonalitic leucosome anhydrous mafic leucosome veinlets are are considered considered ttoo be in situ anatectic anatecticmelt meltsegregations segregationsdeveloped developed during prograde prograde metamorphic reactions of the outcrop, submicroscopic (see reaction 2). 2). In the western end of submicroscopic symplectites of orthopyroxene-plagioclase identified by form barely-visible coronas orthopyroxene-plagioclase identified by microprobe microprobe analyses, analyses, form coronas around garnet, clinopyroxene clinopyroxene and andhornblende. hornblende. Analyses Analysesofof the the symplectite symplectite minerals, at around garnet, at

-- 42 42 lower size size limit limit of of microprobe microprobe resolution, resolution, aare reported along along with with those those of of tthe tthe h e lower r e reported h e other minerals in in the the rock, rock, in in Table Table 2.2. The minerals The rock contains three three plagioclase plagioclase compositions. compositions. An39 Ana9 is present in in coronas coronas whereas worm-like worm-like intergrowths intergrowths of of An35 An35 and and An50 Anro make up tthe he matrix plagioclase. plagioclase.

The mineral mineral compositions compositions yield yieldestimates estimates of of 735°C usingtthe and Green Green The 735'C using h e Ellis and (1979)garnet-clinopyroxene garnet-clinopyroxenethermometer thermometer and and 6.2 6.2 kbar kbar using usingtthe garnet-clinopyroxene(1979) h e garnet-clinopyroxene-

plagioclase-.quartzbarometer barometer (Newton (Newtonand andPerkins, Perkins,1982). 1982).At Atthe thesame sametemperature temperature tthe plagioclase-quartz he and matrix matrix garnet yield 9.1 coronal minerals and 9.1 kbar kbar with tthe h e garnet-orthopyroxenegarnet-orthopyroxeneplagioclase-quartzz Newton and Perkins Perkins barometer. barometer. plagioclase-quart Newton and

Kapuskasing dike Kapuskasing dike

1

B,

. .

A A

orthopyroxeneorthopyroxeneplagioclase coronas

22Dm 0m

0 I

I

I

orthopyroxene bearma bearing orthopyroxene metasedimentary imentary rock

'7

ic and tonalitic gneiss

Figure 23. 23. Location Location of of outcrops outcrops at at Stop Stop 2-5. 2-5.

-

A Kapuskasing Kapuskasingmafic maficdyke dykecuts cutsthe theeastern easternend endofofthe theoutcrop. outcrop. The overal overall BB.. A attitude SE although although tthe h e margin is offset by by numerous small attitudeof of the t h edyke dykeisis070/75 070175 SE sinistral faults. The Theouter outer22cm c mof of the themargin margin isischilled. chilled. Sparse Sparseplagioclase plagioclase phenocrysts phenocrysts are present in olivine-bearing gabbro. gabbro. Several in the t h e dominantly dominantly medium medium grained ophitic olivine-bearing Several dykes of of this swarm been dated by tthe dykes swarm have been h e whole-rock whole-rock K-Ar K-Ar method method and and yield yield "ages" "ages" and 3649 3649 Ma, Ma,indicating indicatingt the presence of of excess argon between 2367 2367 and h e presence (Stevens et et al., 1982). al, (1986) (1986)estimated estimated an age of 2040 2200 Ma Ma based based on (Stevens 1982). 1-lanes Hanes etet al, 2040 -- 2200 dyke and and its its baked baked country country rock. rock. ^40Ar/39Ar ~ r / ^ ~ ranalyses of a Kapuskasing Kapuskasing dyke Homogeneousmetasedimentary metasedimentary rock C. Homogeneous

South of the road is a flat outcrop of medium grained rock with the h e assemblage

.

.

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Table 2. 2. Microprobe Microprobeanalyses analyses of minerals minerals in coronitic coronitic mafic mafic gneiss, gneiss. Stop Stop 2-5 2-5

1

2

4

3

Si02 Si02

38.01

51.57

49.06

42.29

hO2 Ti02

0.00

0.34

0.03

2.03

A1203

20.99

2.92

4.75

12.98

Cr203

0.22

0.21

0.34

0.08

28.06

11.81

31.20

18.43

0.70

0.81 13.35 1.39

0.17 9.28

8.32

0.00 11.34 22.65

11.41

0 27

0.74

0.52

1.95

Cr203 10* FeO* MnO MnO MgO MgO CaO CaO Na 0 Na20 2 K20 K2Â

4.11

0.00

0.08

0.00

0.69

Total Total

100.67

101.79

101.45

99.31

Si Si

2.973

1.908

1.885

6.252

Aliv Aliv

0.00

0.092

0.115

1.748

Alvi Alvi

1.935

0.035

0.100

0.513

Ti

Ti

0.00

0.009

0.001

0.226

Cr c r

0.014

0.008

0.010

0.009

0.0

0.087

0.042

0.288

1.835

Mg

Me

0.040 0.479

0.278 0.003 0.625

0.960 0.026 0.764

Ca Ca

0.697

0.898

0.057

1.990 0.021 2.044 1.807

Na Na

0.041

0.053

0.039

0.559

K K

0.00

0.004

0.00

0.130

3+ pe3 Fe 2÷ 2+ Fe Fe Mn Mn

(0) (0)

*

*

(12)

(6)

(6)

(23)

1: 1: garnet; garnet; 2: 2: clinopyroxene; clinopyroxene; 3: 3: orthopyroxene; orthopyroxene;4: 4: hornblende hornblende Total Fe3 by Total iron as FeO; Fe3+ bystoichiometry stojcHiornetry

Specimen Specimen also also contains contains quartz quartzand andplagioclase plagioclase(An33 Art88 in syrnplectite) symplectite) Ann8 in

I 1.:jyt-

mntrir. in matrix,

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z. Plagioclase garnet-orthopyroxene-biotite-plagioclase-quart garnet-orthopyroxene-biotite-plagioclase-quartz. Plagioclase occurs occursas asporphyroblasts porphyroblasts to is up uptto mm. The t o 22 cm cm and and orthopyroxene orthopyroxene is o5 5 mm. The rock rock has has the the same same mineral mineral assemblage assemblage as as high-grade in tthe zone but but lacks lacks tthe high-grade paragneiss paragneiss in h e Kapuskasing Kapuskashg zone h e migmatitic migmatitic layering layering typical typical of of paragneiss. paragneiss. Application Application of of the the garnet-orthopyroxene-plagioclase-quartz garnet-orthopyroxene-plagioclase-quartz geobarometer geobarometer yields values values in in excess excess of and Perkins yields of 11 11 kbar kbar by by both both Newton Newton and and Perkins Perkins (1982) (1982) and Perkins and and Chipera (1985) calibrations. calibrations. Chipera Interlayered mafic mafic and tonalitic gneiss D. Interlayered and tonalitic gneiss D. complex relations relations between Ic and and tonalitic tonalitic gneiss. outcrop demonstrates This This outcrop demonstrates complex between maf mafic gneiss. Isoclinal folds of of layering layering are are truncated truncated by Isoclinal folds by tonalite tonalitepods pods and and dykes, dykes, suggesting suggesting multiple multiple generations of of tonalite. tonalite. Thin generations Thinmylonite mylonite seams seams are are sub-parallel sub-parallel to t o gneissic gneissic layers. layers. Continue east

67.0 km km Stop 67.0 Stop 2-6: 2-6: Xenolithic Xenolithictonalitic tonaliticgneiss gneiss(S. (5.side sideof ofHwy Hwy101) 101) This outcrop outcrop consists consists of of mediummedium-t to coarse-grained tonalite tonalite made up of of garnet, garnet, This o coarse-grained hornblende, biotite, biotite, plagioclase plagioclase and and quartz. quartz. AA variety hornblende, variety of of xenoliths xenoliths includes includes mafic gneiss gneiss (garnet-.clinopyroxene-plagioclase-quart z),amphibolite, amphibolite,biotite-rich biotite-rich schists and spinel (garnet-clinopyroxene-plagioclase-quartz), pyroxenite. Amphibole-rich rims characterize characterize the pyroxenite. Amphibole-rich rims t h e high-grade high-grade inclusions. inclusions. Continue east

69.2 km Stop 2-7: Ivanhoe Lake cataclastic cataclastic zone 69.2 km Stop 2-7: Ivanhoe Lake zone(S. (S. side sideof ofHwy Hwy 101) 101) The outcrop outcrop is is on ont the western, high-grade high-grade side sideofoft the cataclastic zone and consists h e western, h e cataclastic The of migmatitic garnet-clinopyroxene-hornblende-plagioclase-quaitz of migmatitic mafic mafic gneiss gneiss with with garnet-clinopyroxene-hornblende-plagioclase-quartz assemblages. ItIt is assemblages. is transected transactedby by numerous numerous small fault offsets offsetsand and by by one one major major cataclasite thin section, section, this black black aphanitic material is cataclasite vein. vein. In In thin is seen seen to t o consist consist mainly mainly of (recrystallized) (recrystallized) fine fine actinolitic actinoliticamphibole amphibole and and of porphyroclasts porphyroclasts of hornblende. hornblende. AA 39 40Ar/39Ar whole-rock analysis of material from art age age plateau plateau at analysis of from this this vein vein yielded yielded an A r / Ar whole-rock 1720MMa (Fig.15). 15). On Ont hthe west side sideofoftthe outcrop aare rusty-weathering 1720 a (Fig. e west h e outcrop r e thin (3 cm) rusty-weathering lamprophyre dykes. dykes. Tonalitic by cataclasite cataclasite are of the lamprophyre Tonalitic rocks rocks cut cut by a r eexposed exposed 150 150 m north of highway on an overgrown road.

Continue east

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metavolcanics, Abitibi 2-8: Mafic km Stop 70.5 km 70.5 Stop 2-8: Mafic metavolcanics, Abitibi subprovince subprovince (N. (N. side sideof of Hwy Hwy 101) 101) on the eastern, low-grade the IL,CZ and is is the the westernmost This outcrop is on low-grade side of the ILCZ and belt. It is aa fine hornblendegrained, layered hornblendeof rnetavolcanics metavolcanics of of the Abitibi belt. fine grained, exposure of clinopyroxene rock rock with with local local rusty-weathering rusty-weathering patches. plagioclase + patches. ± clinopyroxene The structural characteristics characteristics of the east-west strike of of The structural t h e outcrop, outcrop, including including east-west isoclinal small small folds, folds,aare typical of of the the Abitibi layering, vertical dip dip and steeply-plunging steeply-plunging isoclinal r e typical Abitibi

belt. Chlorite belt. Chloriteand and epidote epidote are are common common tto o tthe h e east along strike, where where the belt is wider, wider, suggesting an an easterly easterly decrease in metamorphic grade. grade. suggesting 40Ar/39Ar of hornblende hornblende and and plagioclase plagioclase from from this this outcrop outcrop by by tthe Analyses of he A ~ I A ~ method (Fig. (Fig. 15) show showaa plateau plateau for for hornblende hornblende at at 2567 M Ma and aa saddle-shaped saddle-shaped spectrum spectrum method a and plagioclase with with aa plateau plateau at 1107 Ma. The for plagioclase 1107 Ma. The plagioclase plagioclase plateau may may be due to t o argon argon

loss resulting resulting from from aa mild mild thermal thermal event, event, possibly possiblyrelated related tto faulting. loss o faulting. 72.3 km km Turn main road. road. 72.3 Turn north on on logging logging road follow main side of 87.2 km km Stop 2-9: 2-9: Shawmere of road) 87.2 Shawmere gabbroic anorthosite (w. (W. side mainly coarse-grained coarse-grained gabbroic anorthosite anorthosite with The outcrop is mainly with hornblende hornblende and

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I

minerals. Ultramafic Ultramaficlayers layersconsisting consistingof of orthoortho- and andclinopyroxene clinopyroxene rare garnet as mafic minerals.

with hornblende hornblende rims rims and and sparse sparse plagioclase plagioclase to 3 cm, occurs occurs in in layers layers and and pods pods up to to 44 m m with Mafic and and ultramafic ultramafic layers are structures thick. Mafic thick. are locally locally folded folded into into shallow shallow NE-plunging NE-plunging structures

with aa prominent prominent lineation. lineation. One part of the with the outcrop outcrop is is a spectacular spectacular coronitic coronitic gabbroic gabbroic anorthosite with football-sized football-sized plagioclase megacysts. megacysts. Coronas Coronas have have orthopyroxene orthopyroxene or clinopyroxene cores; cores; orthopyroxene orthopyroxene has has successive successive hornblende hornblende and and pale pale garnet garnet rims; clinopyroxene clinopyroxene has has hornblende hornblenderims rims and andrare rare orthopyroxene orthopyroxene cores. cores. clinopyroxene Return to Hwy 101.

km END 134.1 km END OF OF DAY DAY 2. 2. Return to t o Wawa. Wawa.

- 46 ACKNOWLEDGEMENTS

Weberimproved improvedthe themanuscript. manuscript. C.W. by P.C. W. Weber Reviews by P.C. Thurston and W. C.W. Jefferson is thanked for editorial editorial revisions. revisions. . .

.

REFERENCES REFERENCE

in the the Attoh, K., K., 1980. Stratigraphic relations of the the volcanic-sedimentary volcanic-sedimentary successions in Wawa greenstonebelt, belt, Ontario. Ontario. In Current Research, part 5 Current,Research, part A. A. Geological GeologicalSurvey Survey of of Wawa greenstone Canada, Paper Paper 80-lA, 80-1A, pp. pp. 101-106. 101-106. . >.w :~:: . .