'_ IGEOLOGICAL, GEOCHEMICAL AND Rb-Sr AND' U-Pb ZIRCON

GEOCHRONOLOGICAL INVESTIGATIONS OF GRANITOIDLROCKS

FROM THE WINNIPEG RIVER BELT,., . ,./NORTHWESTERN ONTARIO AND SOU~EASTERN MANITO~A

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(£) GARY PHI~IP BEAKHOUSE

B.Sc. (University of Manitoba)

M.Sc. (Universaty of Manitoba)

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A Thesis

Submi~ed to the School of Graduate St~dies

~artial Fulfilm~nt of the Requirements

fGlr th.e Degree

Doctor of Philosophy.....

McMaster University

January, 1983

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GEOLOGICAL, GEOCHEMICAL AND'Rb-Sr AND U-Pb ~CON

GEDCHRONOLOGIC~VESTI~ATIONSOF

. FROM THE

GRANITOID ROCKS'

SOUTHEASTERN MANITOBA

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("'.INNIPEG RIVER BELT.

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NORTHWESTERN ONTARIO AND

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Geoc~~~ical and Rb~Sr and U-Pb

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McMASTER UNIVERSITY ('Hamilton. O~o,

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Geological.TITLE:

(GeolC?gy) ,

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).Zircon Geochronological Investigations of

~. Granitoid Rocks from the Winnipeg River

Belt, Northwestern Ontario,and Southeastern

Manitoba

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AUTHOR:

,SUPERVISOR: .

, '.NUMBER OF PAGES:,

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Gary Philip Beakhouse

B.·Sc. (University of Manitoba)

M.Sc. (University;of Manitoba)'""\

Dr. Robert H. McNutt . .

j;.,.xxii, 1-316~

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ABSTRACT,

logical

An ~~~.l;Jrate~.g~Cal. geochemical and ,geoshrono­

study of granitoid roc~s from the winnipeg River belt, .

has revealed a complex geoiogic history spanning at least 500- ,

Ma. Detaired Rb-Sr and U-Pb ~ircon isotqpi~ i~vestigations

have revealed complexit~es that caution-against simplistic,

whole r9ck isochron ages ar~ sUfficiently

geochronological techniqu~ in si~ilarof these'j;

~pplication

impreci~e and/or inaccurate ~hey can not.be used to' 0

.... ~.es~ablish relative and absolute-time scales. Late t9 post-

."

" .tectonic plutons}~aSSiCallYconsidered perfe~t .candidates

q ~r Rb~Sr geochtonolo~ 90mmonly have nOP-ideal'Rb-Sr isotope. -

~yst'emat±cs and suggested ages are Sli9htlY~ig~i~antlY

younge~ than U-Pb zircon ages for the same bnitJ. There is

"..no independent evidence for a-geologic event'that could reset....the Rb-Sr syste~and these younger ages should not be inter­

prete~s representing discrete geologic events. The u-Pb

zircon system is inherently a more ~recise geochronometer pn~'

tliese:ages are interpreted to represent the age of crystal-

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l;zation. • •

o. " ~etailed studi~s of a biotite tonalite gneiss layer

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-\For .certain El1emen~s, including Rb and S ,parts

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~~~he Kenora area reveals a complex redistribution ·of~ ~-

mineralogical, chemical and isotopic species duri meta-

. morphism:!\'

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ct speci-:-

Several different ages of zi con growth1

reliable. cModel initial ratios offer a· more reliable,'\;-:'

though.mo~qualitative, approach to the problem of identi-.~~ ,

fYi~g.'~ncient crust.

.~-cc~rr,ed ~hiS tonalite but i~ is feasible' po- ­fic morphological types of' zircon and to de~rmine

1one ag: from the same rock.

The earliest rocks in the Winnipeg River

of the...[yjr have acted as ,an ~n ~stem suggesting that

~hole rock Rb-Sr isochron ages for ~Ch rocks m~y not be

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"greenstone-ty.pe" supracru'Cial sequence that are now preserved

as highly'met?morPhosed and'deform~d in~lus~ons in younger

plu~oni~ rocks. ' Thes~· supracrustal rocks ar~ not abundant,

but are widespread', anc:l their occurrence as inclusions in 1

and are interpret d to be a product of the partial melting of

.geOchemically sim'lar to other early Precambrian tonalites

. .,

approxi~atelyJcoextensivewith

~o~alite gneiss inte~reted to b~ as ol~ as 3.0 Ga, indicates.....that a greenstone belt s± ificantly older than those in the

, .Wabigoon ~rovinc '-'..,....

,t,he Winnipeg 'Rive...Ma~±ve sF~i~ plutons and complex, banded, predomin-

: , . .antly tonalitic gn~isses are slightly to' considerably older

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. (2.76 to >3.0 Gal f.'han volcanism in the WabigoQP subprovinceA, ..... . --. ..

(2.70-2.75 Gal •• T e t61alite gneiss and sodic pluton.s are

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metamorphosea'tho eiitic' basalt.~. ."

. 'During t. .western .Su~erior

interval 2.7-2.75 Ga, most tetrains in,the""-. . ,

province received voluminous juvenile additions

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from t~e mantle, 'either directly (basalt) or. indirectly

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(felsic plutonic and felsic volcanic and volcaniclastic rocks~

derived from the melting of"the basalts). The consequences .-4of this thermotectonic event (the Kenoran orogeny) in the

, 'viti

.Winnipeg River ,belt was to partially melt and upwardly mobilize

the earlier basa!t-tonal!te association with little addition

•of new material from the mantle.

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Late to post-tectonic mafic pluto~s and voluminous

potassic plutons were emplaced between 2.65 and 2".7 Ga. The

potassic plutons have '~eochemical signatures and elevated sr

isotope init~al ratios that indicate they originated 'from the '\

partial melting of the early tonalites •. The ~Of th~se _

plutons requires that the early tonalites were extensive and

it is probable that much of the pres~t volume of the ~innipeg

River .belt repres~nts relatively ~ld~3.~ Ga) crust reworkedJ.

during the Kenoran orogeny. This implies that the Winnipeg

......analog-

River belt could have acted as a sialic microcontinent-during.. ;',

.the deposition of younger (2.7-2.75 Ga) su~acrustal sequences.

The pattern of pre-existing sialic nuclei and younger,, .

coev~l, interdigit~ing volcanic arcs and sedimentary'basins..• is geometrically, though not necessarily genet~cally,

, .. l'ous to modern plate tectonic regimes.

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ACKNOWLEDGEMENTS" . '.'"

This work could not hqve been completed without the (

assistqnce of the follqwing: \ ...

Dr. R. H. McNutt, who supervised this research, provided funds to

qttend pertinent conferences qnd generously offered his time

to discuss science, golf and his..novel (to a westerner)

political philosophy.

Dr. T. E. Krogh, who supervised the q.- Pb zircon geochronological

invest~gation, contributed constructive criticism~ddeveloped the "state of the art" techniques without which

much of this work could not have been carried out.

Drs. ' J. H. Crocket and T. E., ~ees, who acted as members of my Ph. D.

supervisory committee and actually read. this entire volume.

L. M. Heaman, who shared the frustration of the lab, wrote the, ~ .BASIC computer program;> for Rb - Sr isotopic.,data-acquisition,. .dr~c~ed many of the~oncepts presented he~ and contributedto my physical (at th"gym) and mental (at the Phoenix)

"

well-being.

R. Bowins (McMaster) and B. Podstawskyj (ROM) who maintained the

mass spectrometers an? reassured the author with their calm, •

capable'assistance ddring what I perceived to be catastrophes •

,) ..

vi

legion of comrades at the University of Manitoba, McMaster

Universi ty, Royal Ontari,o "Museum and Ontario Geological

Survey including L. D. Ayro:s, W. C. Brisbin, P., Cerny, G. S.

Clark, C. F. Gower, A. Qr. _ Green, D. H. Hall;\, F. J. Longstaffe"

M. G. Morrice, P. D. Nunes, O. G. Stephenson, A. Raheim, P. C.. .Thurston, A. C. Turnock, P. van de'Kamp and.D. V. Ziehlke,

who contributed invaluable discussion and constructive

critici,*.

..Dr. D~ W., Davis, who demonstrated to the author many of the subtleties

, of zircen picking and unravelleQ the mysteries of how a

straight line intersects a curve.'\A

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more serious side

A. Branicky, who typed preliminary drafts of,.<

G,Hillier, who typed the final manuscript.

•Whorwood, who contributed his photographic

D. Beakhouse and

the thesis. -

Zwikei~ who prepared the thin sections.

Mudroch,~ w!;l~ gave init:ial ins~uction in

spectrometry. "

My son, Brian, who kept me "in touch with the

of life.

The Centre for Precambrian Studies, under whose auspices the

'original' reconnaissance investigation was carried out.

~ntario GeOl~'Cal Survey, who gen~r~USlY allowed t1me for the

final assembly of this volume.

The

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" My wi~e, Norm\,. work couli!

without whose

~ave been

patience and

completed •

encouragement this""

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. TABLE OF CONTE

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1.3 THE SUPERIOR PROVINCE

ABSTRACT \. tACKNOWLEDG~NTS ~

"Pageiii

vi

1

1

2

2.....

2

4

5

5..8

10

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. ..High-Grade Terrains

Greenstone-Tonalite Terra~ns

General

INTRODUCTION

"1.2 ..3

1.3.1 Greensto~~-TonaliteSUbprovinces

1.3.2 Paragneiss Subprovinces

1.3.3 Batholithic-orthogne;~sSUbprovince!

1.3.4 .Relative and Absolute Chronology of the• Superior Province 11

1. 2. 2

1. 2.1-...

THE NATURE OF EARLY PREC~MBRIAN CRUS~

AIMS AND OBJECTIVES

1.2

1.1

CHAPTER 1

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1.4 POSSIBLE NON~UNIFORMITARIAN ASPECT~ OF EARLYEARTH HISTORY 13

1.4.1 'Early Precambrian Geothermal Gradients 15

1.4.2 Crustal Thickness 16·1III!

.'1.5

1.4.3 Extraterrestrial Interaction

MODELS FOR EARLY PRECAMBRIAN CRUSTALEVOLUTION

1.5.1 Uniformitarian and Modif!edUniformitarian Models

1.5.2 Non-uniformitarian Models

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1.5.3 Catastrophic Models•

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< Page,, 1.6 SUMfJ'.ARY 20

~, CHAPTER 2 GEOLOGICAL RELATIONSHIPS IN IrHE ENGLISHI RIVER SUBPROVINCE 22I,

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2.1 INTRODUCTION 22

.~2.2 LITHOLOGIES 27 .\

2.2.1 " RelationshipsRelative Age 27•- .

Supracrus'tal Remnant" Suite

~2.2.2 28

2.~ Orthogneiss, Sui te 31,.7 2.2.4 Paragneiss 42 ,;.. 2.2.5 Internal Greenstone Belts 50

... 2.2.6 Plutonic Rocks ~ 54

2.2:6.1 Sodic ~tPnic Suite 54

2.2.6.2 Potassic Plu~onic Suite 412.2.6.3 Mafic Plu1;.onib <sui,te 67

2.3 . BELT BOUNDARIES l 68

) ,2.3.1 Uchi-Ear Falls-Manigotagan Interface 68

2.3.2 Ear Falls-Manigotagan--Winnipeg RiverInterface '69

.r-2.3.3 Winnipeg River--Wabigoon' Interface 70 -

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2.4 METAMORPHISM 70

2.4.1 Metamorphism in the E:r'FallS~,/ ,

Manigotagan Belt 70

2.4.2 Metamorphism in the Winnipeg River Belt 72•-2.5 STRUC1URE 72

2.5.y Structure in the Ear Falls-ManigotaganBelt 72

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~ (2.5.2 St:ucture

2.6' GEOCHRONOLOGY

2.7 SUMMARY

3.2.2 Chemical'Separat1on of Rb ani Sr, ...

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7.7

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74

Conditions

.~~'0/L

i.n the W,innipeg River Belt··

Operating

"Precision and Accuracy

ISOTOPIC GEOCHEMISTRY . \

General "",)

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3.2.1

3.1. 3

Rb-Sr

ANALYTICAL TECHNIQUESI '

ELEMENTAL GEOCHEMISTRYn3.3.1 'Sample Preparation

3.~. X-RaY Fluorescence

3.2

3.1

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CHAPTER 3

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,3.2.3 Mass Spectr~metry

3.2.4 Statr:Stical Treatment of Data

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3 •. 3 U-Pb ISOTOPIC GEOCHEMISTRY 84

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,3.3.;1.

3.3.2

-. .->..-Zi~p.r'.iO"..Fi'al pIe Selection

3.3.. Introduction,3.3.2.2 Small Sample

3.3.2.3 Air Abrasion,

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3.3.2.4 High Gradient Magne ic Separation 87

3.3.3 ·'·Chemistry. and 'Ma~~ ~ectrome ry 88

CHAPTER 4 GEOCHRONOLOGICAL INVESTIGATION OF 'ORTHOGNEISS

4.1 INTRODUCTI8N

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-4.2 PREVIOUS INVESTIGATIONS

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•_~~~.~.l U-Pb Zircon Investigations

4.2.2 Rb-Sr Investigations

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4.3 PROBLEMS RELATED TO GEOCHRONOLOGICALINVESTIGATION OF ORTHOGNEISS

.<.4.3.1 Problems for U-Pb Zircon Geochronology

4.3.2 Problems for Rb-Sr Investigations

94

94

95 _.i:

4.4 KENORA AREA TONALITE GNEISS

"" /~4.4.1 Petrology of the Tonalite Layer

"4.4.2 Elemental Geochemistry

97

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107

4.4.3 Summary of Mineralogical ~d ChemicalHeterogeneity III

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137

137

124

127

132

135

122

113

117

121

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141

'V'xi

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OF MASSIVE PLUTONIC ~GKS

Redditt Granodiorite5.2.1

5.1.1 Review of Geo~hronol~gical(Investigation

of Winnipeg River Belt Plutonic Rocks

INVESTIGATIO~S OF POTASSIC PLUTONIC ROCKS

4.6.1 Isotopic Results

4.4.4 ~b-Sr Isotop~~ Investigations

4.4.5 U-pb Zircon Inv~tigations

5 INVESTIGATIONS

INTRODUCTI~

4.8:' SUMMARY"

5.2

4 •.5

4.7 MODEL INITIAL RATIOS•

4.4.6 Summary of ISQtopic In~estigations

Rb-Sr IS~TOPIC INVESTIGA~~FMICROCLINEMEGACRYSTS ADJACENT TO THE DALLES GRANODIORITE

4.6 RECONNAISSANCE GEOCHRONOLOGICAL INVESTIGATION• - OF THE CEDAR LAKE AREA

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5.2.3.1 Conclusions

5.2.4 ~he Lount Lake ~atholith

5.2,3. 2 .•b, ee.utionary Note for Rb-SrGeochronology

15'0

154

155

•157

..157

162

164

174

176

177

Page

141Field Relations and Petro19gy

Rb~~~~oc~rOnOlOgicalI~~atiOn

U-Pb Zircon Gebchronology

5.2.2. 3 U-P~ .z~rcon. Geochronology

Geochemistry of Redditt Area GraniticRocks

..5.2.2.2 Rb-Sr Geochronological

Investigation

5.2.1.3

5.2.1.1

5.2.1.2

5.2.2 Birch Lake Granite

5.2.2~1 Field Relatiorls and Petrology\,;

.5.2.4.. 1 I·ni tial Strontiurn IsotopicComposition of the Lount LakeBatholi th ~~ 187

5.2.5' Lac du Bonnet Pluton

5.2.6 Perrault Falls Clotty Granite

5.3 GEOCHRONOLOGICAL INVESTIGATION OF SODICPLUTONIC ROCKS

5.3.1 The Dalles Batholith

191

193

201

201

5.3'.1.1. U-Pb Zircon Results, for theDalles Batholith 202

5.3.2 Further Evidence for the RelativeAntiqpity of Certain Sodic Plutons 204 '

5.4 THE TROUT LAKE PLUTON 205

5.4.1 ,Field Rela~ionships and Petrology 2,05.,

5.4.2 Elemental Geochemistry

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5.4.3 Rb-Sr Geochronology

5.4.4 U-Pb Zircon G~ochronology

5.5 DISTURBED Rb-Sr ISOTOPE SYSTEMS

5.5.1 Discorda~ce of Rb-Sr and U-Pb ages

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224

226

226

5.5~2 Non-;-ideal, Rb-Sr. Isotop~ Systematics 227--5.5.2.1 Multiple ages

5 .5.2.2 'Mul tiple Ri. ""

228

229

231

.5.5.2.3 Open System Behaviour During

Weathering /231

5.5.2.4 Open System Behaviour ShortlyAfter Crystallization

5.6 SUMMARY

5.5.2.5 Summary 233

233

CHAPTER 6...... COMPARATIVE GEOCHEMISTRY OF EARLY'PRECAMBRIAN PLUTONIC ROCKS 237

6.1 INTRODUCTION 237

6.2 TONALITIC ROCKS IN EARLY PRECAMBRI~~ SYSTEMS 237

6. 3 THE AULNEAU BATHOLITH 239

6.3.1 Geochemical Characteristics of theAulneau Batholith 240

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6.3.2 Comparison of the Aulneau Batholithwith Othe~ Early Precambrian Tonalites

6.4 COMPARATIVE GEOCHEMISTRY OF THE LOUNT LAKEAND AULNEAU BATHOLITHS

6.5 A THREE STAGE MODEL FOR MAGMATIC EVOLUTION

6.6 ~Y•l-

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252

262

264

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CHAPTER 7 SUMMARY AND CONCLUSIONS

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266

7.1 INTRODUCTION 266

7.2 APPLICATION OF GEOCHRONOL1mY TO PROBLEMS OFEARLY CRUSTAL ~OLUTION'" / '7.2.1 ~-Pb ~!rcon ~epchrono1ogy

7.2.2 Rb-Sr Geochronology

7.2.3, Strontium Isotope~Initial Ratios

266

267-

267

269

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7.3 STRONTIUM ISOTO~ES AND CRUSTAL'EVOLUTION

7.3.1 The Winnipeg River Belt •7.4 CONTRASTING GEOCHEMICAL CHARACTERISTICS OF

PLUTONIC ROCKS .'

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273

276 ,

7.5 SUMMARY OF GEOLOGICAL RELATIONSHIPS IN THEENGLISH RI~R SUBPROVINCE 277

7.6 IMPLICATIONS FOR CRUSTAL EVOLUTION 280

'- ' REFERENCES

APPENDIX 1

APPENDIX 2

APPENDIX 3

APPENDIX 4

ELEMENTKL GEOCHEMISTRY

Rb-Sr ISOTOPIC GEOCHEMISTRY

U-Pb ISOTOPIC GEOCHEMISTRY

MODAL MINERALOGY

283

304

350

361

367

xiv