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Geology of the Pinchi Lake area, central British Columbia Paterson, Ian Arthur 1973

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THE GEOLOGY OF THE PINCHI LAKE AREA, CENTRAL BRITISH COLUMBIA  by IAN ARTHUR PATERSON B.Sc. (Hons.) , Aberdeen U n i v e r s i t y , 1967  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE  REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department of G e o l o g i c a l Sciences  We accept t h i s t h e s i s as conforming required  THE  to the  standard  UNIVERSITY OF BRITISH COLUMBIA June 1973  In presenting  this thesis i n p a r t i a l fulfilment of the requirements for  an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t freely available for reference  and study.  I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may by his representatives.  be granted by the Head of my Department or  It i s understood that copying or publication  of this thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission.  Department of  GEOLOGICAL SCIENCES  The University of B r i t i s h Columbia Vancouver 8, Canada  ABSTRACT THE  The  GEOLOGY OF THE PINCHI LAKE AREA  area mapped, 75 square m i l e s , l i e s a s t r i d e the  P i n c h i F a u l t near F o r t S t . James i n c e n t r a l Columbia.  British  Northeast o f the f a u l t system i s the lower  Mesozoic T a k l a Group composed of greywackes, conglomerates and minor l i m e s t o n e s .  Southwest of the f a u l t system i s  the Pennsylvanian-Permian  Cache Creek Group, made up of  l i m e s t o n e s , c h e r t s , a r g i l l i t e s and greenstones. these r e g i o n s , a complex n o r t h w e s t e r l y - t r e n d i n g  Between fault  system i n v o l v e s a s e r i e s of elongate fault-bounded  blocks  o f c o n t r a s t i n g l i t h o l o g y and/or metamorphic grade.  Rock  types making up i n d i v i d u a l b l o c k s i n c l u d e : Ca)  lawsonite-glaucophane  metasediments and meta-  volcanics, Cb) p u m p e l l y i t e - a r a g o n i t e  greenstones,  Cc) s e r p e n t i n i z e d h a r z b u r g i t e s and d u n i t e s and (d) a sequence o f a m p h i b o l i t i z e d  gabbro-diabase  basalt. Boulders o f lawsonite-glaucophane  .^eclogite are a l s o found  i n the a r e a . W i t h i n the g l a u c o p h a n i t i c rocks a metamorphic CS^)  p a r a l l e l s the bedding  and c o n t a i n s a m i n e r a l ii  foliation  lineation  (L^).  T h i s f o l i a t i o n i s deformed by F^ f o l d s and m u l l i o n s  which are accompanied by a prominent These s t r u c t u r e s are deformed by  crenulate lineation. kink  folds.  S i g n i f i c a n t m i n e r a l assemblages w i t h i n the g l a u c o p h a n i t i c rocks i n c l u d e : (i) q u a r t z + lawsonite + sphene + phengite + glaucophane ± carbonaceous m a t e r i a l ( i i ) a r a g o n i t e + dolomite (iii)  (metacherts)  (limestones)  j a d e i t i c pyroxene + lawsonite + q u a r t z + white mica + c h l o r i t e  (metagreywacke)  (iv) q u a r t z + white mica + lawsonite ± glaucophane + p y r i t e + carbonaceous m a t e r i a l (carbonaceous schists) (v) a c m i t i c pyroxene + lawsonite + sphene + c h l o r i t e (metavolcanics) (vi) glaucophane + lawsonite + sphene + c h l o r i t e (metavolcanics). Comparison of these assemblages w i t h e x p e r i m e n t a l l y determined phase e q u i l i b r i a favours the hypothesis t h a t the g l a u c o p h a n i t i c rocks formed a t high l i t h o s t a t i c p r e s s u r e s and r e l a t i v e l y low temperatures.  Because there i s no evidence f o r a metamorphic  zonation w i t h r e s p e c t to the P i n c h i F a u l t , and because metagreywackes and metavolcanics are commonly unsheared, t e c t o n i c overpressures are not c o n s i d e r e d t o have c o n t r i b u t e d  a p p r e c i a b l y to the t o t a l p r e s s u r e .  In the l a t e stages of  metamorphism the f l u i d phase i n carbonaceous s c h i s t s became p r o g r e s s i v e l y more r e d u c i n g and may a p p r e c i a b l e methane. metavolcanics tvi). 3+ Fe  have c o n t a i n e d  This f l u i d reacted with acmitic  (v) to g i v e glaucophane b e a r i n g assemblages  Thus h i g h p r e s s u r e m i n e r a l assemblages w i t h high 2+  /Fe  (.i.e. v) e x i s t e d w i t h i n the metavolcanics  to r e a c t i o n w i t h the reducing  prior  fluid.  A three stage t e c t o n i c model i s proposed.  Firstly,  d u r i n g the Late Permian, a narrow wedge of Upper P a l e o z o i c sediment was  metamorphosed i n the b l u e s c h i s t f a c i e s along  an e a s t e r l y d i p p i n g subduction s i t e of the P i n c h i F a u l t .  zone approximately  on  the  T h i s event i s c o n s i d e r e d to be  contemporaneous w i t h the formation of  structures.  At  a higher c r u s t a l l e v e l , an o p h i o l i t e sequence of which u n i t (d) i s a remnant was  obducted over the Cache Creek Group  sediments which had accumulated above the subduction During  the second stage, a change i n the s t r e s s system  converted the subduction  zone i n t o a r i g h t - l a t e r a l  s l i p or o b l i q u e - s l i p f a u l t . of the  zone.  deformation.  T h i s event marked the  strikebeginning  S t r i k e - s l i p movement r e s u l t e d i n  formation of zones of low p r e s s u r e where t h e r e were d e f l e c t i o n s o r o f f s e t s i n the o r i g i n a l f a u l t . such zones were a t once f i l l e d  At Pinchi,  from below by d i a p i r s of  low average d e n s i t y c o n s i s t i n g of subducted b l u e s c h i s t , s e r p e n t i n i z e d u l t r a m a f i t e s and minor iv  e c l o g i t e which rose  i n the c r u s t t o a l e v e l governed by i s o s t a s y .  I t i s con-  s i d e r e d t h a t the Middle or Upper T r i a s s i c K-Ar  dates o b t a i n e d  from p h e n g i t i c micas  (211, 214,  216 and 218 ± 7 m yrs)  r e c o r d e i t h e r the time of c o o l i n g of the u p l i f t e d or  the end of the F  the Upper T r i a s s i c , exposed  2  deformation.  blueschists  The t h i r d stage, d u r i n g  i n v o l v e d e r o s i o n of the o p h i o l i t e s  on a topographic high to the west o f the P i n c h i  F a u l t and f l y s c h d e p o s i t i o n i n the a d j a c e n t trough t o the east. The atization  deformation was  contemporaneous w i t h carbon-  of f a u l t zones and p o s s i b l y o c c u r r e d d u r i n g the  Eocene.  v  TABLE OF CONTENTS Page ABSTRACT  i i  LIST OF TABLES  xiv  LIST OF FIGURES  xvi  LIST OF PLATES  xviv  LIST OF MAPS  xx  ACKNOWLEDGEMENTS I.  II.  xxi  INTRODUCTION  1  General I n t r o d u c t i o n  1  Location  1  and A c c e s s i b i l i t y  Physiography and G l a c i a t i o n  3  P r e v i o u s Work  4  Work Done i n t h i s Study  6  GENERAL GEOLOGY  7  Regional Setting  7  Cache Creek Group  11  Introduction  11  Greenstones o f P i n c h i Mountain  13  L i t h o l o g y and p e t r o l o g y  14  I n t e r n a l s t r u c t u r e and c o n t a c t s  14  Age  15  Origin  16  vi  Page Glaucophane-lawsonite b e a r i n g rocks around P i n c h i Lake Distribution  16 . . . i  16  Rock types and p r o p o r t i o n s  17  Petrology  18  Internal structure  21  External contacts  22  Age  22  Origin  23  B a s i c rocks south of P i n c h i Lake  . . . . . .  24  D i s t r i b u t i o n and p e t r o l o g y  24  I n t e r n a l s t r u c t u r e and c o n t a c t s  25  Age and o r i g i n  26  Massive limestones  and c h e r t s of the Mount  Pope b e l t  27  Distribution  27  L i t h o l o g y and p e t r o l o g y  27  Fauna and age  29  I n t e r n a l s t r u c t u r e and c o n t a c t s  29  Origin  30  T a k l a Group  32  Introduction  32  Lithology  34  Conglomerate  36  I n t e r n a l s t r u c t u r e and c o n t a c t s vii  39  Page Fauna  40  Origin  41  Diorite  43  Cretaceous III.  (?) Conglomerate  ULTRAMAFITES AND SILICA-CARBONATE ROCKS  44 . . . .  Ultramafites  46  Introduction  46  Rock types  46  Internal structure  . . .  48  Contact r e l a t i o n s h i p s Petrology  51 . . . . .  51  D i s c u s s i o n on the o r i g i n o f ultramafites  53  O r i g i n of P i n c h i ultramafites  57  S i l i c a - c a r b o n a t e Rocks Distribution Rock types,  IV.  46  62 62  i n t e r n a l and e x t e r n a l  structure  62  Petrology  64  Age and o r i g i n  65  METAMORPHISM  68  PART I - METAMORPHISM IN GREENSTONE AND BLUESCHIST FAULT BLOCKS  68  Introduction  68  P a r a g e n e t i c Sequence o f M i n e r a l s viii  71  Page M i n e r a l Assemblages  74  Metamorphic R e a c t i o n s  78  Metabasic r o c k s  78  Metasediments  8  3  Relevant Phase E q u i l i b r i a  84  Aragonite s t a b i l i t y  84  J a d e i t e and a c m i t e - j a d e i t e s t a b i l i t y  87  Phengite s t a b i l i t y  90  S t a b i l i t y o f s o d i c amphiboles  91  Lawsonite s t a b i l i t y  91  P u m p e l l y i t e and p r e h n i t e s t a b i l i t y  92  Eclogite stability  93  Oxygen i s o t o p e s  94  Pressure-temperature C o n d i t i o n s o f Metamorphism  96  F l u i d Phase Composition  96  F l u i d Phase Composition a t 10 kb and 327°C  . . .  104  E v o l u t i o n of F l u i d Phase  108  Pressure-Temperature T r a j e c t o r i e s o f P i n c h i Rocks PART I I - METAMORPHISM IN THE REMAINING  11°  FAULT BLOCKS  112  Metabasic Rocks South o f P i n c h i Lake  112  Mount Pope B e l t  114  T a k l a Group  114 ix  Page  V.  Ultramafites  116  STRUCTURAL GEOLOGY  118  Introduction  118  . .'  S t r u c t u r a l Elements i n the LawsoniteGlaucophane  B e a r i n g Rocks  123  F^ Deformation  125  ^2 Deformation  127  F^ Deformation  12 8  Microscopic Analyses  130  Timing of Metamorphism and Deformation  134  S t r u c t u r a l Geology o f Remaining  Fault  Blocks . .  139  Greenstones o f P i n c h i Mountain  139  Mount Pope b e l t  139  Ultramafites  140  B a s i c r o c k s south of P i n c h i Lake  141  T a k l a Group  142  Important F a u l t s i n the P i n c h i Area Pinchi Fault  . . . . . .  (No.l)  142 143  F a u l t system no. 2  145  F a u l t system no. 3  147  F a u l t system no. 4  148  FF aa uu ll tt s system i n the no. v i c i5n i t y of P i n c h i Mine . . . .  148 149  x  Page VI.  TECTONIC IMPLICATIONS  150  Introduction Constraints ( F a c t u a l and  15 0 to T e c t o n i c  Model  Inferred)  15 2  C o n c l u s i o n s of t h i s study  152  Inferred c r u s t a l structure i n central B r i t i s h Columbia  153  The  157  P i n c h i F a u l t as a "Suture Zone"  Evidence f o r s t r i k e - s l i p movement on the P i n c h i F a u l t P o s s i b i l i t y t h a t the P i n c h i G e a n t i c l i n e was o v e r l a i n by oceanic c r u s t Absence of metamorphic zonation w i t h i n the Cache Creek Group .  161 161  T e c t o n i c Models  162  Subduction model  162  Subduction/obduction model Mesozoic and  160  . . . .  168  T e r t i a r y events  172  REFERENCES CITED  174  APPENDIX I - FOSSIL LOCALITIES IN THE  PINCHI  AREA  188  APPENDIX I I - MINERALOGY  191  A n a l y t i c a l Methods  191  Minerals  . . . . . .  193  Sodic amphiboles  193  Brown and  198  green amphiboles  Pyroxenes . . . . .  200 xi  Page Chlorite  207  Aragonite  209  White mica  212  Celadonite  215  A l b i t i c plagioclase  215  Pumpellyite  216  Stilpnomelane  216  Lawsonite  216  Prehnite Garnet  .  .  217 217  Deerite  217  Opaques  218  Carbonaceous m a t e r i a l  220  APPENDIX I I I - BULK CHEMICAL ANALYSES  221  Metabasic rocks  2 21  Metagreywackes  .  APPENDIX IV - PETROLOGY Greenstones  228 231  o f P i n c h i Mountain . . . . . . . .  Lawsonite-Glaucophane Bearing Rocks  231 2 37  Metabasic r o c k s  237  D o l o m i t i c carbonates  2 41  Metagreywackes  245  Metacherts  247  Quartz-carbonate rocks and s c h i s t s  249  xii  Page APPENDIX V - ECLOGITE BOULDERS  250  APPENDIX VI - POTASSIUM-ARGON RADIOMETRIC DATES  . . .  253  APPENDIX V I I - CALCULATION OF EQUILIBRIUM CONSTANT FOR REACTION: PLAGIOCLASE = JADEITIC PYROXENE + QUARTZ  256  APPENDIX V I I I - SPECIMEN..NUMBERING  258  PLATES  SYSTEM ( f o l l o w i n g page 261)  MAPS  (at end of t h e s i s ) \»\ e v w e l o | > e , -C; ie I  xiii  6a s i d e .  LIST OF TABLES Table  Page  1.  TABLE OF FORMATIONS IN PINCHI AREA  2.  MODAL ANALYSES OF GREYWACKES FROM THE TAKLA GROUP  33  PEBBLE CONTENT OF CONGLOMERATES WITHIN TAKLA GROUP  38  3. 4.  9  GENERALIZED PARAGENETIC SEQUENCE OF METABASALTS  7  5  5a.  POSSIBLE REACTIONS IN METABASIC ROCKS  . . . .  76  5b.  MINERAL COMPOSITIONS USED IN REACTIONS . . . .  77  6.  OPTICAL PROPERTIES OF PYROXENES AMPHIBOLES  7. 8. 9. 10. 11. 12. 13.  AND 194  CELL DIMENSIONS FOR GLAUCOPHANE AND JADEITIC PYROXENE  195  ELECTRON MICROPROBE ANALYSES OF GLAUCOPHANES  196  ELECTRON MICROPROBE ANALYSES OF RELICT AUG ITE  199  ELECTRON MICROPROBE ANALYSES OF METAMORPHIC PYROXENES  201-202  ELECTRON MICROPROBE ANALYSES OF CHLORITES  208  CARBONATE MINERALOGY AND DISTRIBUTION  211  SAMPLE  PARTIAL ELECTRON MICROPROBE ANALYSES OF PHENGITES AND CELADONITE  213  STANDARD DEVIATIONS FOR SELECTED MINERAL ANALYSES  214  15.  ACCURACY OF BULK CHEMICAL ANALYSES  222  16a.  CHEMICAL ANALYSES OF METABASALTS FROM THE PINCHI AREA  223  14.  xiv  Table 16b. 17.  Page ADJUSTED CHEMICAL ANALYSES OF METABASALTS  .  224  C.I.P.W. NORMS FOR ANALYZED METABASALTIC ROCKS  224  SUMMARY OF SIGNIFICANT CHEMICAL CHARACTERISTICS OF METABASALTS  227  19.  CHEMICAL ANALYSES OF METAGREYWACKES  22 9  20.  EQUILIBRIUM MINERAL ASSEMBLAGES IN THE GREENSTONES OF PINCHI MOUNTAIN  2 32  21.  TEXTURAL DOMAINS WITHIN THE PINCHI MOUNTAIN GREENSTONES . .  233  EQUILIBRIUM MINERAL ASSEMBLAGES IN THE LAWSONITE-GLAUCOPHANE BEARING METAVOLCANICS . . . . . . . . . . . . . . . .  238  23.  TEXTURAL DOMAINS IN LAWSONITE-GLAUCOPHANE BEARING METABASIC ROCKS . .  239  24.  EQUILIBRIUM MINERAL ASSEMBLAGES IN METAGREYWACKES  244  25.  EQUILIBRIUM MINERAL ASSEMBLAGES IN. CHERTS AND CHERTY GRAPHITE SCHISTS  244  SAMPLE LOCATIONS AND ANALYTICAL DATA FOR POTASSIUM-ARGON ANALYSES  254  . 18.  22.  26.  xv  LIST OF FIGURES Figure  Page  1.  L o c a t i o n and r e g i o n a l geology map  2  2.  Major t e c t o n i c elements of B r i t i s h Columbia  8  3.  G e o l o g i c a l s u b d i v i s i o n s a t P i n c h i Lake  4.  T a k l a Group: s e c t i o n s , f o s s i l and specimen localities  12  5.  S t r u c t u r a l features i n  . . . .  47  6.  P a r a g e n e t i c sequence o f metamorphic m i n e r a l s i n metabasalts and e c l o g i t e s  . . . .  72  7. 8. 9.  10. 11. 12.  Harzburgites  . . .  P a r a g e n e t i c sequence of metamorphic m i n e r a l s i n metasediments Phase e q u i l i b r i a r e l e v a n t t o f o r m a t i o n of m i n e r a l assemblages Pressure-temperature c o n d i t i o n s o f metamorphism of greenstones, b l u e s c h i s t s and e c l o g i t e s Phase e q u i l i b r i a phase chemistry  12  73 85-86  95  r e l e v a n t to f l u i d 97-99  Schematic i l l u s t r a t i o n of f l u i d phase chemistry T-f.Q diagram i l l u s t r a t i n g e v o l u t i o n o f f l u i d phase composition  105-106 106  13.  Pressure-temperature t r a j e c t o r i e s f o r greenstone, b l u e s c h i s t and e c l o g i t e  I l l  14.  Phase e q u i l i b r i a Si02-H 0  I l l  i n the system  MgO-  2  15.  Stereographic projections i l l u s t r a t i n g lr 2 ^ ^3 o r i e n t a t i o n s  s  L  a n c  xv i  Figure  Page  16.  S t r u c t u r a l elements i n s c h i s t s  120  17.  F  121  18.  Recumbent i s o c l i n a l F2 f o l d s and F f o l d e d by F (22c)  2  folds  2  19.  C22a,  22b) 122  3  R e l a t i o n of metamorphic r e c r y s t a l l i z a t i o n to deformation  .  131  20.  Depth-time t r a j e c t o r y f o r P i n c h i r o c k s  21.  C r u s t a l model f o r c e n t r a l B r i t i s h Columbia G e n e r a l i z e d diagram i l l u s t r a t i n g l o c a t i o n of major g e o l o g i c u n i t s i n c e n t r a l B r i t i s h Columbia i n r e l a t i o n to the p r o b l e m a t i c a l b e l t of P a l e o z o i c rocks between the T a k l a Group and the Omineca G e a n t i c l i n e  22.  . . .  135 154  158  23.  Subduction model  24.  Subduction  25.  P o s s i b l e mechanism f o r i n t r u s i o n of b l u e s c h i s t s and s e r p e n t i n i z e d u l t r a m a f i t e s along s t r i k e - s l i p f a u l t s  169  26.  Element v a r i a t i o n in. zoned glaucophane . . .  197  27.  C o m p o s i t i o n a l v a r i a t i o n of pyroxenes P i n c h i and C a l i f o r n i a  28.  163  - obduction model  166-167  from 203-205  Map of a r a g o n i t e occurrences i n P i n c h i area  210  29.  Map of p r e h n i t e , p u m p e l l y i t e and s e l e c t e d glaucophane-lawsonite occurrences  210  30.  Textures i n opaque m i n e r a l s  219  31.  A-F-M diagram i l l u s t r a t i n g compositions  32.  basalt  A l k a l i - s i l i c a v a r i a t i o n diagram f o r metabasalts . . . . . . xv i i  225 225  Figure  Page  33.  Textures i n P i n c h i Mountain greenstones.  34.  Textures i n lawsonite-glaucophane b e a r i n g metabasic rocks  240  35.  T e x t u r e s i n carbonates  242  36.  Textures i n metasediments  246  37.  E c l o g i t e l o c a l i t i e s and source areas as i n f e r r e d from g l a c i a l t r a n s p o r t directions  251  xviii  .  236  Plate  LIST OF PLATES ( f o l l o w i n g p. 2 61)  1.  View o f the P i n c h i Lake area l o o k i n g northwest from the summit of Mount Pope  2.  Laminated s i l t s t o n e s and the T a k l a Group  3.  Northwesterly p l u n g i n g m u l l i o n s i n q u a r t z mica carbonate s c h i s t s  4.  Angular limestone cobble conglomerates i n T a k l a Group  5.  Northerly dipping compositional i n s i l i c a - c a r b o n a t e rocks  6.  Primary (?) two phase f l u i d i n c l u s i o n i n metacherts  7.  L a t e p y r o x e n i t e l a y e r s p a r a l l e l to d u n i t e r i c h layers i n harzburgite  8.  Late discordant pyroxenite layer c r o s s c u t t i n g i r r e g u l a r dunite  9.  Smooth weathering d u n i t e l a y e r p a r a l l e l to f o l i a t i o n i n h a r z b u r g i t e o u t l i n e d by v a r y i n g o l i v i n e : pyroxene r a t i o  sandstones i n  10.  Folded e a r l y pyroxenite layers  11.  Folded dunite layers i n f o l i a t e d harzburgite  xviv  layering  LIST OF MAPS (Following  p.263 a t end of t h e s i s )  Map  I. II. III. IV. V. VI. VII.  Geology o f P i n c h i Lake area Cross s e c t i o n s of P i n c h i Lake area Aeromagnetic map  of P i n c h i area  Geology i n the v i c i n i t y o f P i n c h i Mine Geology of an area on the northwest shore of P i n c h i Lake Important f a u l t s i n the P i n c h i area Specimen l o c a t i o n map  xx  ACKNOWLEDGEMENTS  Cominco L t d . permitted l i e w i t h i n the area mapped. advice  access t o t h e i r c l a i m s  which  The kindness, c o o p e r a t i o n and  of employees i n the course of t h i s study i s g r a t e -  f u l l y acknowledged, e s p e c i a l l y G. Warning, g e o l o g i s t a t P i n c h i Lake Mercury Mine. The  author i s deeply indebted  to Drs. H.J. Greenwood  and K.C. McTaggart o f the U n i v e r s i t y o f B r i t i s h Columbia who i n t r o d u c e d  the w r i t e r to the p r o j e c t , p r o v i d e d  early  s u p e r v i s i o n and made c o n s t r u c t i v e c r i t i c i s m s o f the manuscript.  H e l p f u l suggestions f o r improvements to v a r i o u s  p a r t s o f the manuscript were a l s o made by Drs. W.C. Barnes, W.R. Danner and P.B. Read"' C a l l a t U . B . C ) . 1  c a t i o n s were made by Drs. W.R. Danner Cameron and H. F r e b o l d were obtained  (G.S.C.).  Fossil  CU.B.C), B.E.B.  K-Ar r a d i o m e t r i c  a t the U n i v e r s i t y o f B r i t i s h Columbia.  and Geophysics  A s s i s t a n c e and  i n the use of the e l e c t r o n microprobe a t the  U n i v e r s i t y of Washington were provided Leitz.  dates  by J.E. H a r a k a l .and V. Bobik i n the l a b o r a t o r -  i e s o f the departments of G e o l o g i c a l Sciences  training  identifi-  by Dr. B.W.. Evans and L.  The author a l s o wishes t o thank members o f the  Vancouver branch of the G e o l o g i c a l Survey o f Canada who gave generously o f t h e i r time i n h e l p f u l d i s c u s s i o n s and were xxi  i n s t r u m e n t a l i n o b t a i n i n g f i f t e e n chemical a n a l y s e s from the G.S.C. l a b o r a t o r y i n Ottawa. C o s t s of f i e l d work were defrayed by a grant from the G e o l o g i c a l Survey of Canada and l o g i s t i c a l support was p r o v i d e d by Cominco L t d .  From 1968-71, the author  was  supported by a s c h o l a r s h i p from the N a t i o n a l Research C o u n c i l of  Canada. F i n a l l y , the author's s i n c e r e thanks are extended t o  the f a c u l t y , t e c h n i c a l s t a f f and graduate U n i v e r s i t y of B r i t i s h Columbia  students a t /the  f o r t h e i r i n t e r e s t and  c o n s t r u c t i v e suggestions i n the course of t h i s  study.  S p e c i a l thanks are due t o my w i f e Barbara f o r a s s i s t a n c e i n the f i e l d  and i n e d i t i n g the manuscript.  xxii  ADDENDA  p. 65, Line 23.  Recent (1972) radiometric dates from the Sustut Group show i t to be of Upper Cretaceous to Eocene age (G.H. Eisbacher, oral commun.)  p. 180  The following reference was omitted: Fyfe, W.S., Turner, F.J., and Verhoogen, J., 1958, Metamorphic reactions and metamorphic f a c i e s , Geol. Soc. Am., Mem 73.  xxiii  I INTRODUCTION  General I n t r o d u c t i o n The purpose of t h i s t h e s i s i s to d e s c r i b e the g e n e r a l geology  i n the v i c i n i t y of P i n c h i Lake, c e n t r a l  Columbia.  T h i s area i s 325  square km  British  i n extent and  lies  a s t r i d e the P i n c h i F a u l t zone, one of the major t e c t o n i c lineaments i n the Canadian C o r d i l l e r a .  Particular  i s p a i d t o the s t r u c t u r e , metamorphism and of r o c k s of the lawsonite-glaucophane  L o c a t i o n and  attention  petrogenesis  facies.  Accessibility  The map  area i s s i t u a t e d i n c e n t r a l B r i t i s h Columbia,  600 km n o r t h of Vancouver, and can be reached v i a P r i n c e George and F o r t St. James ( F i g . 1 ) .  A road 49 km  long  connects F o r t S t . James w i t h P i n c h i Lake Mercury Mine on the n o r t h e r n shores of P i n c h i Lake. P i n c h i and  The r e g i o n between  S t u a r t Lakes i s served by the B r i t i s h Columbia  Railway and a g r a v e l road l e a d i n g to T a c h i e Indian Reserve  (Map I ) .  LOCATION  a  GENERAL  GEOLOGY  LEGEND C r e t a c e o u s ft T e r t i a r y Mesozoic Lower  rocks  intrusives  Mesozoic  Ultramafites Carboniferous Proterozoic  (Takla ft H a z e i t o n  (Trembleur ft 6  Groups)  Intrusives) 40  Permian Cambrian Com piled  miles  6 4 5 km  b y W. H W f t i t * ( 1 9  66)  3  Physiography and  Glaciation  There i s a c l o s e r e l a t i o n s h i p between the and  geology  the topography w i t h i n the P i n c h i Lake a r e a .  Pope (1472  m)  i s the h i g h e s t p o i n t on a l o n g  Mount  limestone  r i d g e between P i n c h i and  S t u a r t Lakes, forming a prominent  f e a t u r e i n the landscape  (Plate 1 ) .  Other landmarks to  the n o r t h e a s t of t h i s r i d g e are P i n c h i Mountain Murray Ridge mafic r o c k s .  (14 00 m)  (127 0 m)  both of which are composed of  Between these landmarks and  the  and  ultra-  limestone  r i d g e the area i s of subdued r e l i e f , broken o n l y o c c a s i o n a l l y by b l u f f s of limestone or c a r b o n a t i z e d s e r p e n t i n i t e . The area i s f o r e s t e d w i t h spruce, lodgepole pine. 1000  A l p i n e f i r and  silver birch  j u n i p e r are found  and  above  m. Armstrong  (1949) and  Tipper  (1971) g i v e accounts  the P l e i s t o c e n e g l a c i a l h i s t o r y of the a r e a . the f o l l o w i n g events  In b r i e f ,  took p l a c e which s t r o n g l y i n f l u e n c e d  the development of the  landforms:  (a) the development of the C o r d i l l e r a n i c e c a p l e d to  the d e p o s i t i o n of an e x t e n s i v e cover  glacial  of  till;  (b) a f t e r the i c e r e t r e a t e d , i t advanced again formed a d r u m l i n i s e d t i l l of  of  i c e flow was  plain.  towards the  The  and  direction  east-northeast;  4 (c) d u r i n g r e c e s s i o n o f the i c e , drainage  channels  were blocked and g l a c i a l l a k e s formed. One such l a k e , o f which P i n c h i Lake i s a remnant, covered much o f the ground below 840 m.  Silt,  sand and c l a y  d e p o s i t e d i n the lake and the e a r l i e r d r i f t d e p o s i t s cover most o f the area and a r e r e s p o n s i b l e f o r the s c a r c i t y o f outcrops.  P r e v i o u s Work On the grounds o f l i t h o l o g i c s i m i l a r i t y , A.R.C. Selwyn (1877) c o r r e l a t e d r o c k s i n the F o r t S t . James area  with  those i n the Lower Cache Creek Group which he had p r e v i o u s l y defined had  (1872) i n the Cache Creek a r e a .  found brachiopods  In t h i s area he  i n d i c a t i v e of a Late P a l e o z o i c age.  In the course o f a journey a c r o s s c e n t r a l B r i t i s h Columbia i n 187 6, G.M. Dawson c o l l e c t e d f u s u l i n i d b e a r i n g  limestones  from the Mount Pope area and v e r i f i e d Selwyn's c o r r e l a t i o n . J.G. Gray  (1938) mapped the area f o r the G e o l o g i c a l Survey  of Canada and worked o u t the g e n e r a l s t r a t i g r a p h y i n the area.  He a l s o d i s c o v e r e d cinnabar i n 1937 on a limestone  b l u f f on the n o r t h shore of P i n c h i Lake. During the Second World War, a mercury  shortage  s t i m u l a t e d p r o s p e c t i n g and a development i n the r e g i o n . P i n c h i Mine, on the s i t e  of Gray's d i s c o v e r y , came i n t o  5 p r o d u c t i o n i n 1940.  Stevenson  (1940) p u b l i s h e d a r e p o r t  which i n c l u d e d a s e c t i o n on the geology vicinity.  of the mine and  He r e c o g n i z e d t h a t the Cache Creek Group  sediments had been d y n a m i c a l l y metamorphosed and the presence of glaucophane.  The  recorded  cinnabar m i n e r a l i z a t i o n  took p l a c e a f t e r the g l a u c o p h a n i t i c metamorphism and  was  a s s o c i a t e d w i t h c o n s i d e r a b l e metasomatic replacement  and  complex f a u l t i n g . In 1942, the geology  A.C.  Freeze completed a Ph.D.  of the P i n c h i Lake a r e a .  He d i v i d e d the  s t r a t i f i e d r o c k s i n t o l i t h o l o g i c a l l y and  structurally  d i s t i n c t s e r i e s separated by u n c o n f o r m i t i e s : Triassic series series series. was  due  t h e s i s on  a pre-Upper  (the Cache Creek Group), an Upper T r i a s s i c  (the Takla Group) and a C r e t a c e o u s - T e r t i a r y He a l s o suggested  (?)  t h a t the f o r m a t i o n of glaucophane  to soda metasomatism a t r e l a t i v e l y shallow depths  and moderate  temperatures.  J.E. Armstrong of the G e o l o g i c a l Survey of Canada p u b l i s h e d a number of r e p o r t s on the P i n c h i Lake mercury belt  (1942, 1944)  James map-area  and produced a memoir on the F o r t S t .  (1949).  A major c o n t r i b u t i o n was  r e c o g n i t i o n of the P i n c h i F a u l t which juxtaposed  the late  P a l e o z o i c Cache Creek Group r o c k s to the west w i t h Mesozoic Takla Group r o c k s to the e a s t . a l s o made by Freeze T r i a s s i c pelecypod  (1942) was Monotis  sub  An important  observation,  t h a t the d i a g n o s t i c Upper circular  is  occurred i n c l o s e  6 association Armstrong  w i t h a conglomerate  a l s o noted  containing detrital  the association  chromite.  between the f a u l t  and  mercury d e p o s i t s . A review of  glaucophane  of the l i t e r a t u r e schists will  Work Done i n T h i s  pertaining  be g i v e n  F a u l t was  carried  months) , and 1971  out during  (.3 w e e k s ) .  G r o u p w e r e mapped i n d e t a i l stratigraphic fault  zone.  and s t r u c t u r a l Drilled  Reconnaissance S t u a r t Lake, to  Two  by  8 km  1968  TV.  i n an attempt relations  area  to  at Pinchi  and  sampled.  arm o f  Lake and t h e V i t a l M o u n t a i n s  i n order  elsewhere  with  Lake.  L a b o r a t o r y work has i n v o l v e d t h e examination thin  s e c t i o n s and s u p p l e m e n t a l  diffraction of  examinations  t r a c e s where necessary.  15 r o c k s w e r e  carried  of  Details  belonging  of analytical  o f 23 0  X-ray  Bulk chemical  analyses  o u t by t h e G e o l o g i c a l Survey  Canada and m i n e r a l a n a l y s e s were o b t a i n e d w i t h an microprobe  Creek  to the  logged  exposed  (3  interpret  t r i p s w e r e made t o t h e n o r t h - w e s t Tsayta  the  i n the Cache  adjacent  c r o s s s e c t i o n s were  astride  (1 m o n t h ) , 1969  localities  compare Cache Creek Group r o c k s  those  i n Chapter  genesis  Study  G e o l o g i c a l m a p p i n g o f a 4 0 km Pinchi  to the  to the University techniques  of  are given  of  A.R.L.  Washington. i n the  appendices.  II GENERAL GEOLOGY  Regional Setting In c e n t r a l B r i t i s h Columbia, the 450  km-long P i n c h i  F a u l t demarcates the P i n c h i G e a n t i c l i n e , l a r g e l y c o n s i s t i n g of the Late P a l e o z o i c  Cache Creek Group, from the  Quesnel  Trough", . composed of the Lower Mesozoic Takla Group.  To  the e a s t o f the Quesnel Trough i s the Omineca G e a n t i c l i n e , a mountainous r e g i o n carved from r o c k s of and  Cambrian age The  Proterozoic  ( F i g s . 1 & 2).  Late P a l e o z o i c  Cache Creek Group to the west of  the P i n c h i F a u l t c o n s i s t s of i n t e r b e d d e d c h e r t ,  cherty  p h y l l i t e , a r g i l l i t e , greenstone, minor greywacke  and  massive limestone, the l a s t mentioned forming a conspicuous u n i t s t r i k i n g p a r a l l e l to the P i n c h i F a u l t . Triassic  times, these r o c k s were:  n o r t h e r l y or n o r t h e a s t e r l y by a l p i n e type p e r i & d o t i t e s lower g r e e n s c h i s t conditions.  (a) deformed about  trending and  f o l d axes;  (b)  intruded  (c) metamorphosed under  or l o c a l l y lawsonite-glaucophane f a c i e s  These r o c k s were then i n t r u d e d  g r a n o d i o r i t e s and  During Permo-  granites during  by  the J u r a s s i c  diorites, Period.  8  FIG.  2  9 TABLE 1  ERA MESOZOIC  FORMATIONS  PERIOD OR EPOCH CRETACEOUS (?)  PRESENT IN THE PINCHI AREA  LIXHOLOGi  GROUP OR FORMATION USI.IKA FORMATION  chert conglomerate  UNCONFORMITY MESOZOIC  JURASSIC  OMINECA INTRUSIONS  hornblende diorite  UPPER TRIASSIC  plagloclase arkose, slltstones limestones, conglomerates and minor tuff.  TAKLA GROUP  •  FAULT CONTACT PALEOZOIC OR  PRE-UPPER TRIASSIC  KESCZCIC  POST-LOWER PERMIAN  TREMBLEUR INTRUSIONS  serpentlnlte, harzburglte, dunlte and pyroxenlte.  FAULT CONTACT PALEOZOIC  LOWER PERMIAN PENN SYLVANIAH  MISSISSIPPI A;; (?) ro PERMIAN  CACHE CREEK CROUP MOUNT POPE BELT  limestone, chert, minor volcanic breccia  CACHE CREEK CROUP (?) GREENSTONES OF PINCHI MOUNTAIN  BASIC ROCKS SOUTH  pumpellylte bearing basalts, minor aragonltlc limestone and graphite schist basalt, diabase, gabbro  .OF PINCHI LAKE GLAUCGPHANITIC ROCKS OF PINCHI LAKE  metabasalts, metacherts, schists, greywacke, dolomitic limestone.  \  10 The  Takla Group l i e s to the e a s t of the f a u l t  and  everywhere appears to be i n f a u l t c o n t a c t w i t h the Cache Creek Group.  A dominantly sedimentary Upper T r i a s s i c  sequence of greywackes, s i l t s t o n e s , limestones and  occasional  conglomerates i s o v e r l a i n by J u r a s s i c a n d e s i t e s , b r e c c i a s , t u f f s and  i n t e r c a l a t e d sediments.  In c o n t r a s t to the  Cache Creek Group, Takla Group rocks are u n f o l i a t e d and have undergone a low grade b u r i a l r a t h e r than dynamic metamorphism.  A l s o , f a u l t i n g r a t h e r than f o l d i n g i s the  c h a r a c t e r i s t i c type of deformation  i n these younger r o c k s .  E x t e n s i v e emplacement of d i o r i t e s and g r a n o d i o r i t e s o c c u r r e d d u r i n g the Mesozoic. Cretaceous  or Paleocene c o n t i n e n t a l sediments were  d e p o s i t e d unconformably on Takla Group r o c k s , and are preserved a t v a r i o u s l o c a l i t i e s zone.  outliers  along the P i n c h i F a u l t  Such r o c k s , d e s c r i b e d by Roots  (1954) i n the  Aiken  Lake area to the n o r t h , have been i n v o l v e d i n p o s t Paleocene f a u l t movements. These d i s t u r b a n c e s were f o l l o w e d by e r u p t i o n of Oligocene and Miocene f l o o d b a s a l t s , remnants o f which are preserved mainly  i n the southern p a r t of the F o r t S t .  James a r e a . The  f o r e g o i n g sequence of events  the t a b l e of formations The area mapped  i s summarized i n  (Table 1 ) . (Map  mentioned r o c k u n i t s and  I) i n c l u d e s most of the above  l i e s a s t r i d e the P i n c h i F a u l t  11  system.  For d e s c r i p t i v e purposes, r o c k u n i t s are c o n s i d e r e d  under f i v e headings:  Cache Creek Group, U l t r a m a f i t e s ,  Takla Group, D i o r i t e and Cretaceous  (?)  conglomerate.  Cache Creek Group Introduction In 187 5, A.R.C. Selwyn noted the l i t h o l o g i c a l  similar-  i t y of l i m e s t o n e s i n the v i c i n i t y of Mount Pope w i t h those of L a t e P a l e o z o i c age which he had found p r e v i o u s l y on banks of the Thompson R i v e r i n the Cache Creek a r e a . f o l l o w i n g year, G.M.  the The  Dawson (18 76) v i s i t e d Mount Pope and  c o l l e c t e d f u s u l i n i d s which confirmed the c o r r e l a t i o n . Armstrong  (1949) concluded  that  The Cache Creek Group may.be d e f i n e d as a very t h i c k assemblage 20,000 f t or more of interbedded sedimentary and v o l c a n i c r o c k s , mainly of Permian age, but a l s o probably i n p a r t of Pennsylvanian age. The whole of the Permian may be r e p r e s e n t e d . F o r a m i n i f e r a l limestones and r i b b o n c h e r t s are c h a r a c t e r i s t i c of the group. He r e c o g n i z e d f o u r main l i t h o l o g i c a l d i v i s i o n s i n the Cache Creek Group, namely s l a t e , r i b b o n c h e r t , limestone and greenstone d i v i s i o n s .  On account of s t r u c t u r a l complexity,  s t r a t i g r a p h i c r e l a t i o n s are i n doubt but he suggested the greenstone d i v i s i o n predominates the  group.  that  i n the upper p a r t of  12  Fig.  3  GEOLOGICAL  Em  m «3J  Fig. 4  SUBDIVISIONS  AT  PINCHI  LAKE.  2 miles  Ultraraafite  Greenstones of F l n c h l Mountain  3-2 km  Lawsonite-glaucophane r o c k s o f P i n c h i Lake  l\ , \ I  T a k l a Group  Basic rocks south of P i n c h i Lake  mm  Diorite  Fault  L i m e s t o n e s and c h e r t s o f K o u n t Pope b e l t  |o>g ;»i L ^  Cretaceous (?) conglomerate  Unconformity  TAKLA  GROUP  :  6  =  STRATIGRAPHIC SECTIONS,  FOSSIL  a  SPECIMEN  (approx. o r assumed) (?)  LOCALITIES.  13 W i t h i n the a r e a covered by t h i s t h e s i s , divisions  f o u r sub-  ( F i g . 3) have been made i n r o c k s thought t o belong  to the Cache Creek Group, namely: (a) greenstones of P i n c h i (b) glaucophane  Mountain,  b e a r i n g r o c k s around P i n c h i  Lake,  (c) b a s i c r o c k s south o f P i n c h i Lake and (d) massive  limestones and c h e r t s o f the Mount  Pope b e l t . Each o f these u n i t s i s bounded by f a u l t s which juxtapose b l o c k s o f c o n t r a s t i n g metamorphic grade.  In t h i s chapter  o n l y the l i t h o l o g i c a l and m i c r o s c o p i c f e a t u r e s r e l a t e d to the primary r o c k type w i l l be d i s c u s s e d .  Description  o f metamorphism and s t r u c t u r e i s r e s e r v e d f o r Chapters IV and V r e s p e c t i v e l y .  Greenstones o f P i n c h i  Mountain  The main occurrence of greenstone i s on the southern s l o p e s o f P i n c h i Mountain  between the lawsonite-glaucophane  b e a r i n g r o c k s and the P i n c h i Mountain north.  Exposure  u l t r a m a f i t e to the  i s poor and much i n f o r m a t i o n has been  o b t a i n e d from trenches and d r i l l h o l e s .  Rocks c o r r e l a t e d  w i t h these a r e found a t the west end o f Murray Ridge and 11 km n o r t h e a s t o f F o r t S t . James (Map I ) .  14 1. L i t h o l o g y and p e t r o l o g y T h i s u n i t c o n s i s t s dominantly o f brown weathering, h i g h l y f r a c t u r e d b a s a l t s o r , l o c a l l y , f i n e grained intrusives.  Some members a r e p o r p h y r i t i c ,  euhedral p l a g i o c l a s e l a t h s  diabasic  containing  C l cm) or a u g i t e  phenocrysts  (8 mm) s e t i n a green a p h a n i t i c m a t r i x ; elongate 4 mm c h l o r i t e b l e b s a r e a l s o common. Within t h i s dominantly v o l c a n i c u n i t ,  occasional  outcrops and d r i l l hole data show the presence of two sedimentary u n i t s separated by 28 m of greenstone.  The  upper u n i t c o n s i s t s of 15 m o f g r a p h i t i c c h e r t i n 1 cm beds, grading i n t o a grey limestone c o n t a i n i n g The  lower u n i t c o n t a i n s  and  graphitic schist.  green laminated t u f f ,  styolites. limestone  In t h i n s e c t i o n , the greenstones c o n s i s t o f r e l i c t a u g i t e o r a l b i t i s e d p l a g i o c l a s e phenocrysts s e t i n a f i n e grained  m a t r i x o f metamorphic m i n e r a l s  (see Appendix IV).  C h l o r i t e - f i l l e d b l e b s a r e common and may o r i g i n a l l y have been amygdules, or o l i v i n e or hornblende p h e n o c r y s t s . R e l i c t ilmenite i s o c c a s i o n a l l y present i n diabasic  rocks.  2. I n t e r n a l s t r u c t u r e and c o n t a c t s The metabasalts on the n o r t h e r n slopes of P i n c h i Mountain s t r i k e a t 100° and d i p to the n o r t h a t 45°,  approxi-  mately p a r a l l e l to the f a u l t which separates, the u n i t from  15 s i l i c a - c a r b o n a t e rocks and u l t r a m a f i t e s to the n o r t h . the south,  the u n i t i s juxtaposed  a g a i n s t rocks of  lawsonite-glaucophane f a c i e s by a n e a r l y v e r t i c a l which i s l o c a l l y c a r b o n a t i z e d .  To  the fault  A similar situation exists  on the Darbar c l a i m group, where a n o r t h e a s t e r l y d i p p i n g f a u l t separates p o r p h y r i t i c a u g i t e b a s a l t s from glaucophane b e a r i n g r o c k s . all  The e x i s t e n c e and  lawsonite-  a t t i t u d e of  the f a u l t s mentioned above have been confirmed  diamond d r i l l  holes.  Thicknesses pervasive  are i n doubt owing to poor exposure and  shearing.  l e s s than 450  by  I t i s suggested t h a t the u n i t i s not  m t h i c k , of which approximately  30 m i s  composed of i n t e r c a l a t e d sediments.  3.  Age Freeze  (1942) and Armstrong  rocks i n the Takla Group. be excluded  but evidence  (1949) i n c l u d e d  these  T h i s p o s s i b i l i t y cannot t h a t the u n i t may  belong  definitely to  the  Cache Creek Group i n c l u d e s the f o l l o w i n g : (a) the presence of a r a g o n i t e , a c m i t i c pyroxene and p o s s i b l e lawsonite t h a t metamorphism was Triassic  (Chapter  IV)  suggests  contemporaneous w i t h  g l a u c o p h a n i t i c metamorphism of  Cache Creek Group, and i s of p r e - T a k l a Group  the  the  t h e r e f o r e t h a t the u n i t age;  16  (b) g r a p h i t i c c h e r t s interbedded w i t h the b a s a l t s suggest an a f f i n i t y w i t h the Cache Creek Group. I t i s concluded t h a t t h i s u n i t may  be r e p r e s e n t a t i v e of the  "upper greenstone  d i v i s i o n " of the Cache Creek Group  (Armstrong,  and presumably of l a t e Permian  4.  1949)  age.  Origin These r o c k s have been c a l l e d b a s a l t s or diabases  because of t h e i r b a s i c composition and r e l i c t Chemical  evidence  (Appendix  mineralogy.  I I I ) i n d i c a t e s t h a t the b a s a l t s  are of the a l k a l i - o l i v i n e type.  The presence of  c a l a t e d l i m e s t o n e s , g r a p h i t i c c h e r t s and suggests t h a t the b a s a l t s may  inter-  laminated  tuffs  have been extruded i n a  submarine environment.  Glaucophane-lawsonite 1.  b e a r i n g r o c k s around P i n c h i Lake  Distribution Glaucophane-lawsonite-bearing  fault-bounded b e l t , 2.5 the map  area.  r o c k s form a narrow  km wide, extending the l e n g t h of  The b e s t exposures  are i n the immediate  v i c i n i t y of P i n c h i Lake Mercury Mine and along the n o r t h west shore of P i n c h i Lake; b o t h of these areas were mapped in detail  (Maps IV and V ) .  G l a u c o p h a n i t i c r o c k s are a l s o  found on the Darbar c l a i m group,  (Map  I ) , 11 km  northeast  17  of  Fort  S t . James, a n d i t i s p r e s u m e d t h a t  u n d e r l i e much o f t h e l o w u n e x p o s e d R i d g e a n d Mount Pope. of  i t s proximity  ground  such r o c k s between  Murray  An e x p o s u r e , o f i m p o r t a n c e  t o the southwest margin  block,  lies  3.6  island  near  the southwest  because  of the f a u l t  km s o u t h o f P i n c h i M i n e on a  small  shore of P i n c h i Lake.  The most  n o r t h w e s t e r l y o u t c r o p s a r e 1.6 km s o u t h o f t h e w e s t e n d of  Tezzeron Lake.  geology because  2.  metabasic  o f poor exposure  rocks, dolomitic  greywackes  fairly  certain  by g r a p h i t i c Because and  consists of  limestones, cherts, Estimates of  graphitic lithological  because o f poor exposure, b u t i t  t h a t much o f t h e low g r o u n d  c h e r t s which grade  of resistance  cherts  into  to erosion,  i s underlain  greywacke  and s c h i s t s .  limestones, basic  tend t o form r i d g e s w i t h o u t c r o p s g i v i n g abundance.  estimated as f o l l o w s :  rocks,  and d i f f i c u l t a c c e s s .  and s c h i s t s .  impression of their are  i s known a b o u t t h e  glaucophane-lawsonite bearing b e l t  proportions are d i f f i c u l t is  little  Rock t y p e s a n d p r o p o r t i o n s The  cherts,  Beyond t h i s ,  5%; m e t a g r e y w a c k e s ,  c h e r t s and s c h i s t s , 45%.  Lithological  rocks a  false  proportions  l i m e s t o n e , 10%; m e t a b a s i c 15%; m e t a c h e r t s , 25%; g r a p h i t i c  18 3.  Petrology (a) Metabasic  Metabasic  rocks  r o c k s a r e a s s o c i a t e d w i t h the limestone  l e n s e s along the n o r t h e r n shores o f P i n c h i Lake.  Metabasic  r o c k s were a l s o i n t e r s e c t e d i n diamond d r i l l h o l e s 2.4 km northwest  o f P i n c h i Mine.  F o r d e s c r i p t i v e purposes,  these  r o c k s a r e s u b d i v i d e d i n t o f o l i a t e d and massive r o c k s but rock types w i t h i n t e r m e d i a t e c h a r a c t e r i s t i c s a r e v e r y common. F o l i a t e d r o c k s a r e b l u e , f i n e t o medium g r a i n e d and have a w e l l d e f i n e d f o l i a t i o n o u t l i n e d by p a r a l l e l c r y s t a l s o f glaucophane.  acicular  They may a l s o show a c o m p o s i t i o n a l  l a y e r i n g c o n s i s t i n g o f 1 cm a l t e r n a t i n g blue and green p a r a l l e l t o the f o l i a t i o n .  layers  Commonly c r e n u l a t i o n s can be  seen on f o l i a t e d s u r f a c e s which c r o s s - c u t the glaucophane mineral  lineation. Massive  by brownish  metabasic  weathering,  measurable s t r u c t u r e s .  r o c k s a r e r e c o g n i z e d i n outcrop complex f r a c t u r i n g and l a c k o f F r a c t u r e s a r e commonly f i l l e d  with  q u a r t z , carbonate or glaucophane, the l a t t e r growing p e r p e n d i c u l a r to the w a l l s .  F r e s h r o c k between v e i n s i s  green, f i n e g r a i n e d , and o c c a s i o n a l l y m i c r o p o r p h y r i t i c or amygdaloidal.  One d i s t i n c t i v e l a y e r c o n t a i n s 1 cm  b l a s t o p o r p h y r i t i c a u g i t e s s e t i n a l i g h t green a p h a n i t i c matrix.  19  In t h i n s e c t i o n , f o l i a t e d r o c k s are metamorphically  reconstituted.  thoroughly  Massive r o c k s , however,  d i s p l a y a v a r i e t y of r e l i c t t e x t u r e s s i m i l a r to those observed  i n the metabasic  r o c k s on P i n c h i Mountain.  amygdules c o n t a i n a r a g o n i t e or c h l o r i t e and r e l i c t  Relict plagio-  c l a s e l a t h s c o n t a i n l a w s o n i t e , c h l o r i t e and white mica. B l a s t o p o r p h y r i t i c a u g i t e s are common and t r a c h y t i c or p y r o c l a s t i c t e x t u r e s occur Two mineralogy  l a r g e metabasic  occasionally. boulders, containing a d i f f e r e n t  from anything p r e v i o u s l y mentioned were found  i n the a r e a .  A g l a u c o p h a n e - e c l o g i t e boulder i s l o c a t e d  9 km e a s t of P i n c h i Mercury Mine on the Tezzeron l o g g i n g road  ( l o c a l i t y E on Map  I).  I t measures 12 by 4  by 3 m,  i s rounded and  appears  to have been t r a n s p o r t e d eastwards from  i s embedded i n g l a c i a l t i l l .  v i c i n i t y of P i n c h i Mine d u r i n g g l a c i a t i o n . c o n t a i n s f o l i a t e d and diameter  Lake  The  It  the boulder  l i n e a t e d b l o c k s up to 30 cm i n  c o n s i s t i n g of green pyroxene, and garnet a l t e r i n g  to s t i l p n o m e l a n e .  Glaucophane and  l a w s o n i t e occupy the  i n t e r s t i c e s between the b l o c k s and a l s o permeate them. Late c r o s s - c u t t i n g f r a c t u r e s are f i l l e d w i t h c h l o r i t e a brown amphibole. west of the mine  A second boulder i s l o c a t e d 3.2  ( l o c a t i o n Br on Map  b e l t of low ground between two  I).  transported f l o a t .  km n o r t h -  It lies in a  silica-carbonate  a s t r i d e a major f a u l t zone and i s thought  and  to be  bluffs little  T h i s boulder c o n t a i n s green b r e c c i a t e d  20  fragments up t o 2 cm  i n diameter  s e t i n a dark b l u e g l a u -  cophanitic matrix.  (b) Metasedimentary r o c k s D o l o m i t i c limestones g r a d i n g i n t o c a l c i t i c form a d i s c o n t i n u o u s s e r i e s of steep b l u f f s along the shore of P i n c h i Lake northwest are grey weathering  dolomites  (180 m  high)  of the mine.  massive r e c r y s t a l l i z e d r o c k s  They  consisting  of v a r y i n g p r o p o r t i o n s of d o l o m i t e , metamorphic a r a g o n i t e , c a l c i t e and carbonaceous m a t e r i a l . v a r i e s from 20%  The dolomite  to 90% and o c c u r s as evenly d i s t r i b u t e d  rhombs or mottled anastamosing patches. stones possess  a  content  w e l l developed  L o c a l l y the l i m e -  f o l i a t i o n , characterized  by a l t e r n a t i n g s t r e a k y l a m i n a t i o n s of grey a r a g o n i t e , carbonaceous m a t e r i a l and white a r a g o n i t e w i t h o c c a s i o n a l d o l o m i t i c laminae  ( F i g . 35).  P e t r o g r a p h i c data on  limestones i s g i v e n i n Appendix  the  IV.  Massive metagreywackes are of l i m i t e d e x t e n t and form a u n i t 30 m i n t h i c k n e s s Mine.  1.6  km northwest  of P i n c h i  F r e s h s u r f a c e s are grey or. b l u i s h green and  white c l a s t s or 2 mm be seen in.hand  carbonaceous fragments can  specimen.  1  mm  usually  T h i n s e c t i o n s show t h a t metagrey-  wackes possess.a r e c r y s t a l l i z e d f a b r i c , but r e l i c t  angular  p o o r l y sorted, quartz, g r a i n s , and. pseudomorphs a f t e r  plagioclase  can s t i l l be d e t e c t e d .  A steep d i p p i n g f r a c t u r e  cleavage  i s s p o r a d i c a l l y developed and l a t e q u a r t z or carbonate veins  ( l e s s than 1 mm  i n width) are common.  Metacherts are f a i r l y r e s i s t a n t to e r o s i o n and are b e s t exposed immediately n o r t h of the l a r g e limestone b l u f f west o f the mine.  They weather grey and the f r e s h  s u r f a c e has a p a l e b l u i s h sheen due t o the presence of a c i c u l a r n e m a t o b l a s t i c glaucophane.  Thin s c h i s t o s e laminae  c o n t a i n i n g white mica and glaucophane occur between c h e r t y layers  (2 to 5 cm t h i c k ) and show a w e l l developed l i n e a t i o n  d e f i n e d by c r e n u l a t i o n s . P o o r l y exposed p y r i t i c carbonaceous s c h i s t s and q u a r t z + white mica + l a w s o n i t e ± glaucophane s c h i s t s a r e interbedded w i t h the c h e r t s and l i m e s t o n e s .  Being incompe-  t e n t r o c k s , they tend to be c o n t o r t e d and on exposure to weathering decompose to a micaceous or b l a c k carbonaceous mud.  A t y p i c a l specimen of carbonaceous s c h i s t c o n t a i n s  white beds o f c h e r t y q u a r t z i t e g e n e r a l l y l e s s than 3 cm i n t h i c k n e s s w i t h i n t e r l a y e r s of micaceous carbonaceous s c h i s t . Quartz + mica + lawsonite ± glaucophane s c h i s t s a r e green w i t h white 2 mm  l a w s o n i t e and 6 mm  blue a c i c u l a r  glaucophane  porphyroblasts.  4.  Internal  structure  Limestones form i s o l a t e d l e n s e s , s t r i k i n g  north-  w e s t e r l y and d i p p i n g a t a p p r o x i m a t e l y 6 0° n o r t h e a s t . G e n e r a l l y the l e n s e s show no t r a c e of bedding, but a  22  f o l i a t i o n may be p r e s e n t l o c a l l y .  The r a p i d v a r i a t i o n i n  t h i c k n e s s and the l e n s i n g o u t o f t h e limestone may e i t h e r be the r e s u l t of f o l d i n g phenomenon.  (Chapter V) o r a primary  depositional  Some c o n t a c t s may be f a u l t e d b u t a t P i n c h i  Mine massive limestone grades  i n t o w e l l bedded  (15 cm max)  c h e r t y q u a r t z i t e , mica s c h i s t and limestone w i t h no suggestion of a f a u l t contact. M e t a v o l c a n i c r o c k s have sharp c o n t a c t s and appear i n many cases to have an i n t e r - t o n g u i n g r e l a t i o n s h i p w i t h limestones. to  T h i s r e l a t i o n s h i p c o u l d a l s o be a t t r i b u t e d  folding. D r i l l h o l e s 1.6 km northwest  o f P i n c h i Mine i n d i c a t e  t h a t carbonaceous c h e r t s and s c h i s t s have g r a d a t i o n a l c o n t a c t s w i t h greywackes.  5.  External contacts A l l glaucophane-lawsonite  against adjacent rocks.  bearing rocks are f a u l t e d  In some p l a c e s c o n t a c t s have been  d r i l l e d , g i v i n g i n t e r s e c t i o n s of f a u l t b r e c c i a s and carbonatized rocks.  6.  Age The a s s o c i a t i o n o f rock types i s s i m i l a r to t h a t  found i n the Cache Creek Group.  However, no f o s s i l s have  been found i n t h i s s u b d i v i s i o n and the p o s s i b i l i t y remains  t h a t these r o c k s are o l d e r than the Cache Creek Group.  Pennsylvanian-Permian  Since i t i s to be i n f e r r e d  (Chapter IV)  t h a t these r o c k s have been b u r i e d t o f a r g r e a t e r depths than the Cache Creek r o c k s to the southwest, of M i s s i s s i p p i a n age or o l d e r .  they may  L i t h o l o g i c a l l y , these r o c k s  are a l s o s i m i l a r to those of the M i s s i s s i p p i a n Mountain  7.  Group  (Sutherland-Brown  be  Slide  1963) .  Origin P r i o r t o metamorphism and deformation, the  c o n s i s t e d of b l a c k s h a l e , c h e r t , carbonaceous  sediments  dolomitic  limestone and greywacke i n order o f d e c r e a s i n g abundance. P o r p h y r i t i c b a s a l t flows and t u f f s were c l o s e l y a s s o c i a t e d w i t h the d o l o m i t i c l i m e s t o n e s . On account of the complexity of the s t r u c t u r e , the l a r g e l y unknown s t r a t i g r a p h i c r e l a t i o n s and  conflicting  o p i n i o n s on the o r i g i n of d o l o m i t i c carbonates, c h e r t s and p y r i t i c b l a c k s h a l e s , the nature of the d e p o s i t i o n a l environment  i s highly speculative.  (1957, p. 421)  A c c o r d i n g to P e t t i J o h n  e a r l y f o r m a t i o n of d o l o m i t e suggests a near  shore f a c i e s , a s i t u a t i o n which r e c e i v e s some c o n f i r m a t i o n w i t h the presence of greywackes a t P i n c h i .  Bedded c h e r t s  have been a s s i g n e d a deep water o r i g i n by R i c h (1951), and Trumpy  (1960).  However, Danner  (1967) suggests a shallow  water o r i g i n f o r a t l e a s t some c h e r t s and t h e i r  depth  significance i s therefore s t i l l uncertain.  presence  The  24 of p y r i t i c b l a c k s h a l e s suggests accumulation reducing  under  stagnant  c o n d i t i o n s but i t i s a l s o p o s s i b l e t h a t the reduc-  i n g environment formed i n the sediment d u r i n g  diagenesis.  I t appears, t h e r e f o r e , t h a t a l l t h a t can be s a i d about the d e p o s i t i o n a l environment i s t h a t i t may  have been  adjacent  to a land mass.  B a s i c r o c k s south of P i n c h i Lake 1.  D i s t r i b u t i o n and  petrology  A b e l t of b a s i c rocks l i e s to the southwest of P i n c h i Lake, between a s l i v e r of Takla Group sediments and elongate  s e r p e n t i n i t e body  long and  1500  (Map  I).  an  I t i s a t l e a s t 16  km  m i n maximum w i d t h .  The b a s i c rocks are c r u d e l y l a y e r e d p a r a l l e l to the e l o n g a t i o n of the body.  The  southern  h a l f of the  c o n s i s t s of brown weathering massive gabbro, w i t h granular  belt equi-  t e x t u r e , c o n t a i n i n g 60% mafic c o n s t i t u e n t s and  40% f e l d s p a r . f r a c t u r e s occur  Quartz v e i n s and locally.  e p i d o t i z a t i o n along  Towards the n o r t h e a s t ,  finer  g r a i n e d rocks w i t h d i a b a s i c t e x t u r e predominate and  contain  sporadic anastamosing patches of medium g r a i n e d gabbro. These r o c k s a r e h i g h l y sheared fractures. are b a s a l t s  Finally,  and c h l o r i t i z e d  along  the most n o r t h e r l y r o c k s i n the  (?) c o n t a i n i n g 2 mm  c a l c i t e blebs.  belt  25  The  gabbro c o n s i s t s p r i m a r i l y o f e q u i g r a n u l a r  hedral p l a g i o c l a s e  (2 mm average) and i n t e r s t i t i a l  subaugite;  ilmenomagnetite and orthopyroxene a r e a l s o p r e s e n t . P l a g i o c l a s e i s a l b i t i c and i s mottled with s e r i c i t e o r granular  e p i d o t e making i d e n t i f i c a t i o n d i f f i c u l t .  s t i t i a l pyroxenes commonly a r e r e p l a c e d amphibole  by a green  Interpleochroic  (Z"c = 22° max) and a l l t h a t remains o f a n h e d r a l  ilmenomagnetite g r a i n s i s a r e t i c u l a t e sphene Diabasic  skeleton.  rocks are a l t e r e d i n a s i m i l a r fashion,  the assemblage commonly c o n s i s t i n g o f s a u s s u r i t i z e d p l a g i o c l a s e + a c t i n o l i t e + c h l o r i t e + sphene. g r a i n s i z e i s approximately 0.4  mm.  Basalts are inequigranular, c r y s t s and a l b i t i c sub-ophitic and  Average  containing  s e r i c i t i s e d plagioclase  augite  pheno-  (1 mm max) i n a  f i n e - g r a i n e d m a t r i x of a u g i t e , a l b i t e ,  chlorite,  sphene.  2.  I n t e r n a l s t r u c t u r e and  contacts  Takla Group sediments appear to be conformable w i t h the n o r t h e r n c o n t a c t o f the b a s i c r o c k s . northwards and a r e o v e r t u r n e d .  They a l s o young  As pebbley limestones near  the base o f the sequence c o n t a i n . s k e l e t a l ilmenomagnetite and  c h l o r i t i s e d amphibolitic  to the b a s i c r o c k s contact  (Table  pebbles l i t h o l o g i c a l l y s i m i l a r  3) , i t may be t h a t the n o r t h e r n  i s an unconformity which has been o v e r t u r n e d and  d i p s to t h e southwest a t 6 0°.  3.  Age and o r i g i n The age and o r i g i n o f these b a s i c r o c k s i s p r o b l e m a t i c -  al.  A summary o f f a c t s and reasonable i n f e r e n c e s i s as  follows: Ca) gabbro o c c u r s lowest i n the sequence f o l l o w e d by d i a b a s e and b a s i c v o l c a n i c s (?) a t the t o p . R e l a t i o n s h i p s between the rock types a r e a p p a r e n t l y gradational; (b) the gabbro and diabase belong to the lower schist  green-  facies;  (c) a s e r p e n t i n i t e b e l t bounds the gabbro t o the south; (d) there may be an unconformity  between Upper  T r i a s s i c sediments and the u n d e r l y i n g b a s i c sequence, as the l a t t e r appears to the T a k l a Group Ce) i f an unconformity  to provide d e t r i t u s  (Table 3 ) ; and i s p r e s e n t , the sequence has  been overturned. The b a s i c rocks a p p a r e n t l y l i e below Upper T r i a s s i c (?) sediments.and a r e presumably of Cache Creek Group or T r i a s s i c age.  I t i s suggested  t h a t the g r e e n s c h i s t f a c i e s metamor-  phism was contemporaneous w i t h the lower g r e e n s c h i s t f a c i e s metamorphism i n the Cache Creek Group The apparent  (see Chapter  IV, P a r t 2 ) .  succession serpentinite-gabbro-diabase-  b a s a l t i s of great i n t e r e s t .  Such b a s i c or o p h i o l i t i c  complexes are being oceanic  crust  i n c r e a s i n g l y recognized  CBailey et al.,  1970  and Page, 1972).  p o s s i b i l i t y w i l l be f u r t h e r d i s c u s s e d  Massive limestones 1.  This  i n Chapter V I .  and c h e r t s of the Mount Pope b e l t  Distribution Between P i n c h i and  controlled  S t u a r t Lakes the topography i s  by a continuous r i d g e of limestone  the l e n g t h of the map-area.  i n t e r c a l a t i o n s of v o l c a n i c b r e c c i a . to the n o r t h e a s t  and  L i t h o l o g y and limestone  w i t h two  minor  Flanking this  limestone  southwest are b e l t s of c h e r t ,  c o n t a i n i n g i n t e r b e d s o f t u f f and  The  which s t r e t c h e s  T h i s r i d g e i s almost e n t i r e l y  composed of massive c r y s t a l l i n e limestone  2.  elsewhere as  locally  siltstone.  petrology  ranges from l i g h t grey to dark grey i n  c o l o u r and weathers l i g h t grey.  In c o n t r a s t to the  lime-  stones n o r t h of P i n c h i Lake, i t i s o n l y l o c a l l y carbonaceous, and  dolomite i s a minor c o n s t i t u t e n t which occurs  veins.  B r e c c i a ted i r o n stained zones occur  in late  adjacent  to  fractures. C r i n o i d a l d i s c s and columnals are the most abundant f a u n a l elements, o c c u r r i n g as fragments up to 1 cm F u s u l i n i d s , c o r a l s and  i n length.  a l g a l s t r u c t u r e s are a l s o o c c a s i o n a l l y  28  seen i n hand specimen.  The  p r o p o r t i o n of b i o c l a s t i c  allo-  chemical c o n s t i t u e n t s ranges between 40%  and  7 0% i n the  four specimens s t u d i e d i n t h i n s e c t i o n .  The  framework  g r a i n s are p o o r l y s o r t e d and  set i n a m i c r i t i c  matrix.  Most l i m e s t o n e s c o u l d be c l a s s i f i e d as f i n e , medium or coarse b i o m i c r i t i c c a l c a r e n i t e s grading  (FolK, 1968)  locally  i n t o f i n e or medium c a l c i r u d i t e s . Flanking  the limestone b e l t are grey to  black  bedded c h e r t s w i t h t h i n a r g i l l a c e o u s p a r t i n g s . beds are g e n e r a l l y from 2 to 5 cm may  r e a c h 12 cm.  t h i c k but  In t h i n s e c t i o n , c h e r t s are  c r y s t a l l i n e w i t h m i c r o c r y s t a l l i n e quartz The  occasionally  S i l i c e o u s s i l t s t o n e s are commonly i n t e r -  bedded w i t h c h e r t s .  tests.  Individual  crypto-  replacing radiolaria  grey to b l a c k c o l o u r i s caused by d i f f u s e opaque  s t r i n g e r s which have a b l a c k amorphous appearance i n r e f l e c t e d l i g h t and  are probably carbonaceous.  Cross  c u t t i n g d i l a t a t i o n a l quartz v e i n s o c c a s i o n a l l y g i v e  the  c h e r t a b r e c c i a t e d appearance. V o l c a n i c b r e c c i a s occur a t two southwestern f l a n k s of the limestone. green and  purple  flow rocks and  s p a r r y c a l c i t e cement.  l o c a l i t i e s on  the  Fragments i n c l u d e  minor s i l t s t o n e s e t i n a  In t h i n s e c t i o n , p l a g i o c l a s e  l a t h s i n v o l c a n i c fragments are h i g h l y s e r i c i t i s e d and i n a green or dark brown c h l o r i t i c  set  matrix.  A s c h i s t o s e t u f f , i n t e r c a l a t e d w i t h c h e r t on the s i d e of the limestone, and  quartz  contains  in a chloritic  b l a s t o p o r p h y r i t i c augite  matrix.  north  29  3.  Fauna and  age  Faunas from the Mount Pope b e l t have been c o l l e c t e d by s e v e r a l workers.  A l l previous l o c a l i t i e s ,  together  w i t h s e v e r a l found i n the course of t h i s work, are t a b u l a t e d i n Appendix I .  G.M.  Dawson c o l l e c t e d f u s u l i n i d s from the  Mount Pope a r e a , which were l a t e r dated as E a r l y Permian (Freeze, 1942) .  Thompson  (1953) c o l l e c t e d from a number  s  of St.  l o c a l i t i e s and concluded t h a t i n the v i c i n i t y  of Fort  James the limestone b e l t ranged i n age from Pennsylvanian  to E a r l y Permian.  F o r t y m i l e s n o r t h , between  and Kloch Lakes, Armstrong  Trembleur  (1949) c o l l e c t e d f u s u l i n i d s o f  Leonardian and Guadalupian age.  No such f u s u l i n i d s were  found i n the Mount Pope a r e a . A l g a l s t r u c t u r e s , bryozoa, echinoderm  fragments,  c r i n o i d a l d e b r i s and o c c a s i o n a l c o r a l s have a l s o been found i n the area but few are d i a g n o s t i c of age.  Radiolaria  t e s t s were found by the author i n c h e r t s n o r t h of Mount Pope. 4.  I n t e r n a l structure, and c o n t a c t s Most bedded c h e r t s f l a n k i n g the limestone b e l t d i p  southwest.  The o l d e s t f u s u l i n i d s of Desmoinesian  (Thompson, 1965) localities:  age  are found a d j a c e n t to c h e r t s a t two  on the northwest  shore of P i n c h i Lake and  30 two m i l e s n o r t h w e s t Pope  (Map I ) .  o f F o r t S t . James a t t h e b a s e o f M o u n t  Thompson  also states that fusulinids  become  p r o g r e s s i v e l y y o u n g e r s t r a t i g r a p h i c a l l y t o w a r d s t h e summit o f M o u n t Pope and n o r t h w e s t w a r d s Lake.  a l o n g t h e shore  of Stuart  F r o m t h e s e o b s e r v a t i o n s t h e f o l l o w i n g c o u l d be  inferred:  (a) l i m e s t o n e s o v e r l i e t h e c h e r t s ;  (b) t h e p a r t  o f t h e l i m e s t o n e b e l t s o u t h o f M o u n t Pope h a s b e e n o v e r t u r n e d and  locally  (c) t h e l i m e s t o n e b e l t c o n t a i n s a s y n c l i n e  w i t h a x i a l plane d i p p i n g southwest.  Undoubtedly,  s t r u c t u r e i s n o t as simple as t h i s , but f u r t h e r  the unravelling  must a w a i t d e t a i l e d f a u n a l s t u d i e s . The n o r t h e r n b o u n d a r y o f t h e b e l t a p p e a r s t o b e t h e s i t e o f a major f a u l t c l o s e l y a s s o c i a t e d w i t h  slivers  o f u l t r a m a f i c r o c k f o r much o f i t s l e n g t h .  5.  Origin The l i m e s t o n e b e l t i s r e m a r k a b l y  c e n t r a l B r i t i s h Columbia,  s u b - p a r a l l e l to the P i n c h i F a u l t . ( A i k e n , 1959  the Cache Creek a r e a  In  l i m e s t o n e s o f s i m i l a r age and  l i t h o l o g y f o r m a p e r s i s t e n t b e l t , 200  on t h e A t l i n H o r s t  continuous.  (Selwyn,  km i n l e n g t h , s t r i k i n g  Similar  limestones  occur  a n d M o n g e r , 19 69) a n d i n  1872  The c o n t i n u i t y o f t h e b e l t s u g g e s t s  a n d D a n n e r , 1964,  p.  109).  t h a t i t may h a v e f o r m e d  a barrier reef during the Late Paleozoic. a d j a c e n t t o a l a n d m a s s i s n o t known..  Whether i t formed  31  The o r i g i n and d e p o s i t i o n a l environment of bedded c h e r t s are c o n t r o v e r s i a l .  In the p a s t , many g e o l o g i s t s  f e l t t h a t they o r i g i n a t e d from i n o r g a n i c p r e c i p i t a t e s  result-  ing  sea  from submarine v o l c a n i s m and  silica  s a t u r a t i o n of  Ce.g. B a i l e y , Irwin and Jones, 1964).  water  However, t h i s  i s not c o n s i d e r e d a v a l i d argument where there i s no evidence  for volcanic a c t i v i t y  I t i s now  commonly accepted  as a r e s u l t o f accumulation (Bramlette, 1946) D i e t z , 1966)  (Krauskopf,  of s i l i c e o u s o r g a n i c  or i n shallow water  169).  skeletons  (Trumpy, 1960  (Danner, 1967).  and  In the  the c l o s e a s s o c i a t i o n of  o r g a n i c a l l y d e r i v e d bedded c h e r t s and limestones  p.  t h a t most bedded c h e r t s formed  e i t h e r at g r e a t depths  l a t t e r case, Danner noted  1967,  f u s u l i n i d or  i n the Cache Creek a r e a , and was  a shallow water o r i g i n f o r the c h e r t s .  The  algal  l e d to p o s t u l a t e c h e r t s occur  p r e f e r e n t i a l l y i n the lower p a r t of the Cache Creek s u c c e s s i o n and  grade upwards i n t o limestones  (Danner, 1964,  p.  109).  With r e s p e c t to the o r i g i n of c h e r t s i n the Mount Pope b e l t three f a c t o r s are o f  significance:  (a) the c h e r t s c o n t a i n r a d i o l a r i a and are not a s s o c i ated w i t h s i g n i f i c a n t amounts of v o l c a n i c m a t e r i a l ; (b) they appear to u n d e r l i e shallow water  limestones;  (c) the c h e r t - l i m e s t o n e c o n t a c t i s sharp. There are three p o s s i b l e e x p l a n a t i o n s f o r these ships.  Firstly,  relation-  the c h e r t s c o u l d have been d e p o s i t e d i n  32  deep water and  subsequently r a i s e d to a near s u r f a c e  environment where limestones were d e p o s i t e d . c h e r t s and  limestones may  Secondly,  have o r i g i n a t e d i n a shallow  b a s i n w i t h r a t e of subsidence roughly equal t o r a t e of deposition.  L a s t l y , shallow water limestones may  have been  t h r u s t over deep water c h e r t s .  Takla Group Introduction The term Takla Group was  f i r s t used by Armstrong  (1949) t o d e s c r i b e r o c k s of sedimentary  and v o l c a n i c o r i g i n  d e p o s i t e d d u r i n g the Upper T r i a s s i c and J u r a s s i c .  Armstrong  r e c o g n i z e d two s u b d i v i s i o n s : (a) Upper T r i a s s i c Monotis  • •—bearing  sedimentary  rocks, (b) Undivided Takla Group c o n s i s t i n g of b a s i c v o l c a n i c s , p y r o c l a s t i c s and  interbedded  sediments. The r o c k s exposed a t P i n c h i belong to the f i r s t  subdivision  and occur mainly on the n o r t h e a s t s i d e of the P i n c h i F a u l t zone.  A b e l t of sediments a l l o c a t e d to the T a k l a Group i s  a l s o found on the southwest s i d e of the f a u l t ,  striking  s u b p a r a l l e l to the southern shore of P i n c h i Lake  ( F i g . 3).  33  TABLE 2 MODAL ANALYSES OF GREYWACKES FROM THE TAKLA GROUP  Specimen Number  4  Feldspar  43.0*  26.7  44.9  Matrix  40.6  50.5  30.1  Hornblende Clinopyroxene Rock fragments Quartz  7  -  1  -  12.2  -  3.9  10.0  14.4  10.1  6.4  3.6  2.6  Notes: 1.  1000 p o i n t counts made on each t h i n  2.  Rock fragments i n c l u d e hornblende p l a g i o c l a s e porphyry, and t r a c h y t i c b a s i c  section.  volcanics.  3.  Sample l o c a t i o n s are g i v e n i n F i g . 4.  4.  Minor K-Feldspar.  *  34 Lithology The decreasing  rock types p r e s e n t w i t h i n  the area a r e ,  in  o r d e r of abundance, a r k o s i c greywacke, laminated  s i l t s t o n e , l i m e s t o n e , conglomerate, b a s i c i n t r u s i v e s and basic  volcanics. Arkosic  greywackes are dark grey weathering  g e n e r a l l y t h i c k to massive bedded  (1-3 m)  shale or laminated s i l t s t o n e i n t e r b e d s surfaces,  and  (8-30  they are dark grey or green, and  f e l d s p a r , b i o t i t e and  hornblende can be  into s i l t  s i z e a t the top.  s i l t s t o n e occur s p o r a d i c a l l y .  possessing cm).  On  seen.  Most beds a t the  Black l i t h i c  Thin s e c t i o n s  (Table  i s plagioclase,  a u g i t e , brown hornblende, v o l c a n i c  lithic  amounts.  constitutents include quartz,K-feldspar, G r a i n s are p o o r l y  s o r t e d , angular and  base  c l a s t s of  show t h a t the dominant c o n s t i t u e n t  c a l c i t e can a t t a i n a p p r e c i a b l e  fresh  c l a s t s of  are graded, w i t h p a r t i c l e s i z e averaging 1 mm grading  rocks,  2) but  fragments,  and  Accessory p y r i t e and  hematite.  embedded i n an  i n c i p i e n t l y metamorphosed m i c r o c r y s t a l l i n e m a t r i x c o n s i s t i n g of c h l o r i t i c or l i m o n i t i c m a t e r i a l , p l a g i o c l a s e and  calcite.  P o r p h y r i t i c v o l c a n i c fragments, w i t h p h e n o c r y s t s of p l a g i o c l a s e and/or hornblende i n a m i c r o g r a n u l a r t r a c h y t i c or f e l t e d m a t r i x , r a r e l y c o n s t i t u t e more than 2% of rock.  Micaceous q u a r t z i t e c l a s t s and  aggregates were a l s o i d e n t i f i e d .  the  tremolite-epidote  Interbedded s i l t s t o n e s  35 possess s i m i l a r mineralogy and t e x t u r e s . S i l t s t o n e s , c a l c a r e o u s s i l t s t o n e s and are dark grey weathering, o c c a s i o n a l b u f f weathering interbeds  (Plate 2 ) .  and graded bedding,  thin-bedded  shales  (2-10 cm) rocks w i t h  f i n e grained  Beds may  silty  sandstone  show f i n e s i l t y i n t r a l a m i n a e  f i n e crossbedding, c o n v o l u t i o n s or  intraformational siltstone clasts.  P l a g i o c l a s e i s again  the dominant c o n s t i t u e n t , w i t h q u a r t z a l s o abundant i n a few samples. to  Clinopyroxene and hornblende  have decomposed  c h l o r i t e which c o n s t i t u t e s the m a t r i x along w i t h  carbonate. Limestones of  l i e i n the b e l t of sediments  southwest  P i n c h i Lake, between Murray Ridge and P i n c h i Lake and  i n t e r m i t t e n t l y along the n o r t h shore of the l a k e .  A t the  first  dark  l o c a l i t y the limestones are grey weathering,  grey t o b l a c k r o c k s which emit a bituminous odour on fracturing.  Well bedded b i o m i c r i t i c c a l c a r e n i t e s  i n t o , or are interbedded w i t h , dark grey  calcilutites,  c a l c a r e o u s s i l t s t o n e s and pebbley c a l c a r e n i t e s . at  the second  grade  Limestones  l o c a l i t y are massive, bituminous and c o n t a i n  c o l o n i a l c o r a l s and c r i n o i d a l d e b r i s .  A t the  third  l o c a l i t y , on the n o r t h shore of P i n c h i Lake, the limestones are i n d i s t i n c t l y bedded, weather grey and are b u f f c o l o u r e d on a f r e s h s u r f a c e .  They are dominantly  poorly sorted  b i o m i c r i t i c c a l c a r e n i t e s c o n t a i n i n g abundant c r i n o i d a l  discs,  36  c o r a l and s h e l l fragments.  Pebbles  (1 cm max)  found i n t h i n l a y e r s or are d i s t r i b u t e d through the l i m e s t o n e s .  are commonly  sporadically  Limestones a s s o c i a t e d w i t h con-  glomerates a t t h i s l o c a l i t y are d i s c u s s e d l a t e r . B a s i c r o c k s were found a t o n l y two (Map I ) .  A basaltic l a p i l l i  localities  t u f f i s found 2 00 m e a s t of  the conglomerate on the n o r t h shore o f P i n c h i Lake and an unusual b i o t i t e - q u a r t z gabbro shore of P i n c h i Lake 1.6  i s l o c a t e d on the south  km west o f the e a s t end o f the  lake.  Conglomerate Conglomerate  has been t r e a t e d s e p a r a t e l y because of  i t s importance r e g a r d i n g the d e p o s i t i o n a l environment provenance  and  of the Takla Group sediments.  The most i n t e r e s t i n g l o c a l i t y on a promontary  ( F i g . 4, No.  2)  on the n o r t h shore o f the lake 6.4  from the e a s t end.  lies  km  The limestone beds a s s o c i a t e d w i t h the  conglomerate a r e near v e r t i c a l and the way-up c o u l d not be determined.  A s t r a t i g r a p h i c s e c t i o n i s as f o l l o w s .  37  limestone 0  w  O  polymict  O  o  150  ft.  o  47 m .  cobble pebble  well-bedded  o  0  0  conglomerate cm)  (30  Monotis  M  conglomerate  limestone  suboivoulavis  O o  M  Fine  grained,  grade  into  well  poorly  cobbles  also  diameter.  The  pebbles and  was  (4  first  bed o f  embedded the  cobble  in  a  to  presence noted  by  of  pebble  is  a  is  given  very  conglomerate.  sub-rounded,  in  Table  cobbles  3  (10  poorly matrix.  (loc.  chromite  (1942).  In  the  at  this  course  locality of  2).  cm max)  layer.  detrital  Freeze  18 cm i n  to  black,  of The  biomicritic calcarenite  pebbles  this  4).  conglomerate  intraformational limestone in  consisting (Plate  up  polymict  grey  Monotis  containing  cobbles  and a r e  this  cm m a x ) a r e  present  The  to  5 m thick  composition of  also  limestone  Monotis  contain  are  Sub-angular are  sorted  Adjacent  interesting  sorted  limestones  intraformational conglomerates  angular  The  bedded  this  38  TABLE 3  PEBBLE CONTENT OF CONGLOMERATES WITHIN TAKLA GROUP  LOCATION (See Fig. k ) N. shore of Pinchi Lake. Loc. 2.  PETROLOGY OF FEBBLES  Typp  A  ABUNDANCE (% of total i-ebbles ln specimen)  K0CK  anphlbolltlsed gabbro.  i  medium grained; ab-actln -sph-ep-qtz-rellct opx. Type B i fine grained; ab-actlnchl i relict diabasic texture. Type C i ab laths ln microgranular matrix; trachytic texture Type D i cryptocrystalllne chert Type E i chromite grains East of Pinchi Type A i Mine, Loc. 5 cryptocrystalllne chert Type B i trachytic basalt. coarse grained plagioclase and quartz grains are also present. S.- shore of Pinchi Type A i Lake. Loc. 6 ab-sph-chl ; porphyrltlc or equlgranular texture. Type B i cryptocrystalllne chert Type C i assorted grains i skeletal llmenomas-netlte, cllnopyroxene, serpentine.  SOUiiCE  50*  metadiabase, metabasalt.  2%  basalt.  5%  bedded chert.  156  harzburgite, dunite. bedded chert..  75% 5%  basalt. intrusives ?  20%  50%  metabasalt.  »5%  bedded chert.  5%  gabbro, eerpentlnlte ? .  ab=albltei actlr.=actlnoll te i sph=sphenei qtz=quartzs opx=orthopyroxenei chl=chlorlte.  39 study the i d e n t i f i c a t i o n of chromite was v e r i f i e d by e l e c t r o n probe a n a l y s e s and r e f l e c t i n g microscopy. types o f chromite were noted, opaque chromite and brown t r a n s l u c e n t p i c o t i t e . i n nearby u l t r a m a f i t e s .  partial Two  dark  Both v a r i e t i e s were observed  The chromite g r a i n s are monominer-  a l i c and a r e embedded i n the limestone m a t r i x .  W i t h i n the  b a s i c a m p h i b o l i t i c pebbles, the opaque g r a i n s were found to c o n s i s t o f s k e l e t a l ilmenomagnetite a l t e r e d to sphene and hematite, s u g g e s t i n g t h a t these b a s i c pebbles could not have been the source f o r the chromite. Conglomerates Group  (Table 3 ) .  Two  are a l s o found elsewhere i n the T a k l a beds of medium pebble  conglomerate  (8-18 m t h i c k ) a r e i n t e r b e d d e d w i t h s i l t s t o n e s a t the e a s t end of P i n c h i Lake.  They c o n t a i n rounded, moderately  grey and b l a c k c h e r t pebbles matrix.  Pebbley  of P i n c h i Mine  (5 mm)  (1-2 cm max)  sorted  in a siliceous  sandstones were found 4.8  km e a s t  ( F i g . 4, l o c . 5) and i n the b e l t o f T a k l a  Group sediments south o f P i n c h i Lake  ( l o c . 6).  I n t e r n a l s t r u c t u r e and c o n t a c t s The l a c k o f d i s t i n c t i v e marker h o r i z o n s , poor and p a u c i t y o f f o s s i l s have obscured s t r a t i g r a p h i c of the T a k l a Group w i t h i n the a r e a .  The  exposure  relations  stratigraphy  observed i n a r e a s o f f a v o u r a b l e exposure i s g i v e n i n F i g . 4 together w i t h approximate  t h i c k n e s s e s . C o r r e l a t i o n between  s e c t i o n s i s p r o b l e m a t i c a l but i t appears t h a t t h e r e i s a t  40 l e a s t 900 m of Takla Group sediments i n the Northeast  area.  of the P i n c h i F a u l t zone, the r o c k s of  the  Takla Group seem to be h i g h l y f a u l t e d r a t h e r than f o l d e d . A marked change i n s t r i k e i n the n o r t h e a s t e r n map  p a r t of  the  area suggests t h a t a major f a u l t passes from Murray  Ridge to Tezzeron Lake.  South of P i n c h i Lake, the  northern  margin of the T a k l a Group i s f a u l t e d a g a i n s t glaucophane b e a r i n g metacherts.  Because sediments a t the base of  b e l t c o n t a i n gabbro and b a s a l t d e t r i t u s , i t may the southern  that  c o n t a c t i s an unconformity r a t h e r than a  ( s e e a l s o p. 2 5  fault  be  this  ).  Fauna Armstrong  (1949) made f o s s i l c o l l e c t i o n s a t two  t i e s i n the Takla Group. localities study. 1.  locali-  In a d d i t i o n to these, three  ( F i g . 4) were d i s c o v e r e d i n the course  of  new this  D e s c r i p t i o n s of the fauna are as f o l l o w s : Limestones on the n o r t h shore of P i n c h i Lake 6.5  km  oivoulavis  from the e a s t end  c o n t a i n Monotis  of Upper T r i a s s i c age  sub-  (Armstrong,  1949) . 2.  Sandstones 6.4  km e a s t of P i n c h i Mine, 60 m  o f the road c o n t a i n Eevinea, i n d i c a t i n g a J u r a s s i c age  Astarte  and  south Tvigonia  (Armstrong, 1949).  3.  A bioclastic  l i m e s t o n e i n Takla Group sediments  south o f P i n c h i Lake c o n t a i n s c r i n o i d columnals, b i v a l v e fragments, o o l i t e s o r p s e u d o o l i t e s , e c h i n o i d s p i n e s and e c h i n o i d s h e l l s G.S.C, w r i t t e n commun.)..  (Cameron,  Cameron a l s o suggested  t h a t t h e limestone formed i n a h i g h energy environment and was o f l a t e P a l e o z o i c o r e a r l y Mesozoic age. 4.  An ammonite fragment was found i n a shale bed at  the west end of the i s l a n d a t the e a s t end  of  P i n c h i Lake.  be J u r a s s i c 5.  H. F r e b o l d c o n s i d e r e d i t t o  ( o r a l commun.).  An o u t c r o p of limestone 30 m n o r t h o f a carbonat i z e d u l t r a m a f i t e between Murray Ridge and P i n c h i Lake c o n t a i n s c o l o n i a l c o r a l s thought t o be of Upper T r i a s s i c age (Danner, o r a l commun.)  6.  Carbonaceous at  wood fragments were found i n sandstone  two l o c a l i t i e s .  Origin The o l d e s t r o c k s appear t o be Monotis  bearing lime-  stones and a s s o c i a t e d conglomerates, s i l t s t o n e s and greywackes.  The s h e l l y fauna, the presence of i n t r a f o r m a t i o n a l  limestone b r e c c i a s and pebble conglomerates suggest shallow water deposition..  A c c o r d i n g to Souther and Armstrong  (1966) ,  conglomerates occur a t i n t e r v a l s a l o n g the e a s t e r n margin  42 of the P i n c h i F a u l t zone and mark the time of emergence of the P i n c h i G e a n t i c l i n e a t the b e g i n n i n g o f the Upper Triassic. The  s t r a t i g r a p h i c r e l a t i o n s h i p of the t h i c k a r k o s i c  greywacke sequence to the above mentioned limestones i s unknown/ but i t i s suggested t h a t the former was  deposited  on  lying  the l a t t e r d u r i n g  northeast  r a p i d subsidence of a b a s i n  o f the f a u l t zone.  Graded bedding and the p o o r l y  s o r t e d angular nature o f the c l a s t s imply d e p o s i t i o n by turbidity  currents.  The  composition o f the a r k o s i c greywacke and o f the  pebbles i n the conglomerates  (Table  3) i n d i c a t e t h a t the  source f o r the Takla Group sediments i n c l u d e d  the f o l l o w i n g  rocks: (a) amphibolitis^ed and  gabbro, d i a b a s e ,  amphibolite,  chlorite schist;  (b) p o r p h y r i t i c b a s i c v o l c a n i c s w i t h phenocrysts of p l a g i o c l a s e , hornblende and o c c a s i o n a l l y c l i n o p y r o x e n e or b i o t i t e ; (c)  chert;  (d)  limestone;  (e) K - f e l d s p a r b e a r i n g (f) chromite b e a r i n g  i n t r u s i v e s or v o l c a n i c s ; ultramafites.  P o r p h y r i t i c b a s i c v o l c a n i c s and h o r n b l e n d i z e d b a s i c i n t r u s i v e s seem t o have provided  the b u l k of the d e t r i t u s .  Because  43 b a s i c i n t r u s i v e pebbles c o n t a i n a l b i t e , amphibole epidote  and  (a lower g r e e n s c h i s t f a c i e s mineralogy) i t  seems t h a t metamorphic r o c k s must have been exposed a t the s u r f a c e p r i o r to d e p o s i t i o n o f the Upper T r i a s s i c .  The  presence o f u l t r a m a f i t e s a t the s u r f a c e i s i m p l i e d by the presence o f d e t r i t a l chromite w i t h i n T a k l a Group sediments. I t c o u l d be argued t h a t the chromite o r i g i n a t e d i n a layered basic intrusion.  However, chromite b e a r i n g g a b b r o i c  r o c k s have not y e t been found i n the Cache Creek Group. The most r e a s o n a b l e h y p o t h e s i s f o r the provenance the T a k l a Group sediments i s t h a t the d e t r i t u s  of  originated  from the l i m e s t o n e s , c h e r t s , gabbros and greenstones belongi n g to the Cache Creek Group, southwest o f the f a u l t  zone.  I t i s s i g n i f i c a n t t h a t many of the b a s i c pebbles are v e r y s i m i l a r to the gabbros and b a s a l t s exposed  south o f P i n c h i  Lake. The presence of carbonaceous  fragments suggests t h a t  the area being eroded was nearby and covered w i t h v e g e t a t i o n .  Diorite A body of hornblende d i o r i t e a p p a r e n t l y i n t r u d e s Takla Group greywackes e a s t o f P i n c h i Lake Mercury Mine, j u s t n o r t h o f the r o a d .  I t i s grey-green or brownish  weathering and i s w e l l f o l i a t e d ; l o c a l l y i t i s p o r p h y r i t i c or c o n t a i n s greenstone x e n o l i t h s .  Hand specimens  show  44 a l i g n e d phenocrysts of p l a g i o c l a s e hornblende  (5 mm)  (5 mm)  and  acicular  s e t i n a grey a p h a n i t i c m a t r i x .  In t h i n s e c t i o n , 75% of the r o c k c o n s i s t s of euhedral p l a g i o c l a s e l a t h s , w e l l zoned w i t h cores i n the An  80-70  a n <  ^  carbonate.  e  x  t  r  e  m  e  l y  range  a l t e r e d to s e r i c i t e , e p i d o t e  Patchy low r e l i e f  suggests p a r t i a l  Subhedral brown p l e o c h r o i c hornblende,  (?) and  albitization.  and minor  clino-  pyroxene and b i o t i t e phenocrysts a r e a l s o p r e s e n t , the f i r s t being h i g h l y a l t e r e d to c a l c i t e , c h l o r i t e and  sphene.  The m a t r i x c o n s i s t s of a m i c r o g r a n u l a r mixture of p l a g i o c l a s e , q u a r t z , c h l o r i t e and  sphene.  Contacts, where observed, are f a u l t e d and  argillites  showing no s i g n s of thermal metamorphism can be seen w i t h i n a few metres of the d i o r i t e .  The n o r t h e a s t c o n t a c t has  not been examined. The age of the i n t r u s i v e i s u n c e r t a i n .  The  incipient  metamorphism or a l t e r a t i o n suggests an E a r l y Mesozoic  Cretaceous  (?) Conglomerate  Cretaceous  (?) conglomerate  i s exposed o n l y a t the  western end of Murray Ridge where i t forms two k n o l l s 1.6  age.  km  southwest  elongate  of the e a s t end of P i n c h i Lake.  The pebbles and cobbles are p o o r l y s o r t e d , sub-rounded and up to 12 cm i n diameter.  They c o n s i s t of green c h e r t  (.85%) , b l a c k c h e r t (.2%), r e d c h e r t (2%) and grey limestone  45 (3%) i n a r e d weathering sandstone m a t r i x ( 8 % ) . The u n i t d i p s to the south a t 50° and appears to be f a u l t e d a g a i n s t greenstones to the n o r t h . The age i s u n c e r t a i n , but because o f i t s p o o r l y i n d u r a t e d nature and l i t h o l o g i c a l resemblance ates d e s c r i b e d by Armstrong  to conglomer-  (.194 9) , i t i s thought to be o f  Cretaceous or Paleocene age. A r e d d i s h l i m o n i t i c matrix suggests s u b a e r i a l d e p o s i t i o n i n a c o n t i n e n t a l environment.  Presumably  the c h e r t  and l i m e s t o n e pebbles were d e r i v e d from the Cache Creek Group.  Ill ULTRAMAFITES AND SILICA-CARBONATE ROCKS  Ultramafites Introduction Three u l t r a m a f i c bodies, on Murray Ridge, P i n c h i Mountain and the n o r t h e r n slopes uous northwest s t r i k i n g r i d g e s ultramafites  of Mount Pope, form (Map I). .  conspic-  Each of these  i s l e n t i c u l a r i n o u t l i n e and appears t o be  bounded by f a u l t s . Swampy a r e a s , which a r e b e l t s of magnetic  highs,  l i e along t h e s i d e s o f the u l t r a m a f i t e s and a l s o along some f a u l t zones.  Diamond d r i l l i n g o f a magnetic high  east  of P i n c h i Mercury Mine and near the P i n c h i F a u l t zone intersected serpentinite.  This suggests t h a t such anomalies  elsewhere i n the map area a r e a l s o the l o c a t i o n of b u r i e d serpentinites. in extrapolating  Aeromagnetic data  (Map III) has been used  serpentinite contacts  beneath d r i f t  cover.  Rock Types The  dominant rock type, c o n s t i t u t i n g 95% of the  exposures, i s h a r z b u r g i t e .  In outcrop, i t i s generally  47  Fig. 5  STRUCTURAL  L a t e fractures altered  FEATURES  with red  IN  H ARZBURG JTES  xE-arly c o n c o r d a n t  __.  ^^7_A--—)---^' S.  8  s  •'\)(  • ( a ) ' Concordant dunite of M u r r a y R i d g o .  and  c  ^"N>  p y r o x e n i t e layers in h a r z b u r g i t e  Harzburgite  (b)> Dunite - p y r o x e n i t e  Folded  v e i n in h a r b u r g i t e  pyroxenite  layer  Murray  r  n  wide  Ridge  cut by l a t e p y r o x e n i t e .  dunite  stringers.  ot western  Dunite  (c)r  pyroxenite  margins  edge  48 massive or blocky,  weathers r e d d i s h brown to b u f f  possesses a rough mottled s u r f a c e .  L o c a l l y i t may  s e l y s e r p e n t i n i z e d or f r a c t u r e d and  d i f f i c u l t to  and be  recognize.  However, the p l a t e y b a s t i t e s e r p e n t i n e which r e p l a c e s orthopyroxene g r a i n s g e n e r a l l y p e r s i s t s .  inten-  Dunites,  1  cm  comprising  over 4% of the u l t r a m a f i t e s , have a c h a r a c t e r i s t i c b u f f weathered s u r f a c e which i s smooth i n comparison to t h a t of the h a r z b u r g i t e ,  and  are h i g h l y f r a c t u r e d .  Pyroxenite  l a y e r s are minor but are conspicuous by t h e i r  differential  weathering c h a r a c t e r i s t i c s ( P l a t e s 7 & 8 ) .  Internal  structure  Much of the h a r z b u r g i t e foliation.  i s massive w i t h no  obvious  However, i n the v i c i n i t y of d u n i t e or  pyroxenite  l a y e r s , a f o l i a t i o n o u t l i n e d by d i f f e r i n g  olivine-orthopyro-  xene r a t i o s can o c c a s i o n a l l y be d i s c e r n e d  (Plate 9 ) .  of the d u n i t e and  pyroxenite  are g r a d a t i o n a l over 1  l a y e r s w i t h the  bodies up to 100  to 1.5  harzburgite  cm.  Dunite bodies are of two l i k e d u n i t e s up  Contacts  varieties:  m i n t h i c k n e s s , and  m i n diameter.  The  s i l l or v e i n i r r e g u l a r dunite  former are commonly  concordant w i t h the l a y e r i n g i n the h a r z b u r g i t e  and  generally  c o n t a i n chromite s t r i n g e r s ( F i g . 5a, P l a t e 9 ) .  Occasionally,  r o o t l e s s f o l d s with.limbs of v a r i a b l e t h i c k n e s s are o u t l i n e d by the s i l l - l i k e d u n i t e s  (Plate 11).  Dunite v e i n s , up  to  49 5 cms i n width, were o c c a s i o n a l l y observed g i v i n g way t o pyroxenite layers  ( F i g . 5b).  The t r a n s i t i o n from d u n i t e  to p y r o x e n i t e i s sharp and occurs where the d u n i t e v e i n narrows down to 2 cm i n t h i c k n e s s .  I r r e g u l a r d u n i t e bodies  are r e l a t i v e l y r a r e , the o n l y w e l l d e f i n e d on  the southern slopes  harzburgite  example being  of P i n c h i Mountain.  a r e sharp and very  Contacts w i t h  irregular.  Two d i s t i n c t types o f p y r o x e n i t e l a y e r were observed: e a r l y concordant l a y e r s and l a t e d i s c o r d a n t many l a y e r s c o u l d n o t be  layers.  However,  categorized.  E a r l y concordant p y r o x e n i t e l a y e r s occur i n swarms p a r a l l e l to the h a r z b u r g i t e  foliation  (Plate 1 0 ) .  l a y e r s range from 2 to 6 cm i n thickness.' great  Individual  They do not have  l a t e r a l c o n t i n u i t y , and commonly wedge out, disappear  i n t o shear zones o r a r e c u t o f f by shears. the p y r o x e n i t e l a y e r s a r e f o l d e d  Occasionally,  (Plate 10) and i n one case  ( F i g . 5c) a c r o s s - c u t t i n g p y r o x e n i t e l a y e r has an a x i a l planar o r i e n t a t i o n with respect  to e a r l i e r l a y e r s .  o r i e n t a t i o n of these l a y e r s i s f a i r l y r e g u l a r r e g i o n s and e r r a t i c i n o t h e r s .  i n some  Strikes are generally  w e s t e r l y to n o r t h w e s t e r l y w i t h steep n o r t h e r l y Late discordant to 10 cm i n width. occur i n groups but  The  dips.  p y r o x e n i t e l a y e r s are commonly up  Within harzburgite,  they  occasionally  (Plate 7) p a r a l l e l to d u n i t e r i c h  layers,  u s u a l l y they occur as s i n g l e p y r o x e n i t e l a y e r s which  cross-cut e a r l i e r (Plate 8 ) .  l a y e r s and i r r e g u l a r d u n i t e  bodies  A d i s t i n c t i v e f e a t u r e a t a few l o c a l i t i e s i s  a black-weathering,  s e r p e n t i n e - r i c h zone, 5 cm wide, i n  the h a r z b u r g i t e o r d u n i t e a d j a c e n t to the c o n t a c t s o f the pyroxenite layers.  Folding of l a t e pyroxenite layers  i s r e l a t e d to movement along l a t e J o i n t s a r e w e l l developed i n frequency and o r i e n t a t i o n .  fractures. and a r e h i g h l y v a r i a b l e  One s u b - h o r i z o n t a l and two  v e r t i c a l j o i n t s e t s can be d e t e c t e d i n most o u t c r o p s . Commonly one p a r t i c u l a r j o i n t s e t becomes dominant and c l o s e l y spaced  (1 cm), i n which case the term  cleavage  might be more a p p r o p r i a t e , e s p e c i a l l y where t h e r e a r e i n d i c a t i o n s of movement along the planes of d i s c o n t i n u i t y . I t appears t h a t the spacing of the j o i n t or cleavage depends on the l i t h o l o g y and the amount o f l o c a l  planes  deformation.  G e n e r a l l y , d u n i t e s a r e f r i a b l e because of the presence of a p e r v a s i v e f r a c t u r e system which s u b d i v i d e s the rock a s e r i e s o f rhombs. conspicuous  into  Weathered p y r o x e n i t e s possess a  columnar s t r u c t u r e ( P l a t e s 7 and 8) caused by  d i f f e r e n t i a l weathering  along the s e r p e n t i h i z e d cleavage  planes which t r a n s e c t the p y r o x e n i t e l a y e r s and o f f s e t the c o n t a c t s . In summary, f i e l d o b s e r v a t i o n s i n d i c a t e the f o l l o w i n g sequence o f events:  51 (a) f o r m a t i o n o f e a r l y p y r o x e n i t e l a y e r s and d u n i t e bodies, (b) f o l d i n g , Cc)  formation of l a t e pyroxenite  layers,  Cd) p e r v a s i v e s e r p e n t i n i z a t i o n , and Ce)  f o r m a t i o n of j o i n t s and cleavages and minor serpentinization.  Contact  relationships  As i s the case w i t h most a l p i n e u l t r a m a f i t e s , c o n t a c t s are p o o r l y exposed. or i n d r i l l  Where c o n t a c t s a r e v i s i b l e , i n outcrop  h o l e s , h i g h l y sheared  s e r p e n t i n i t e i s juxtaposed  a g a i n s t s i l i c e o u s sediments o r v o l c a n i c s showing no s i g n s of thermal metamorphism.  In g e n e r a l , c o n t a c t s a r e thought  to be the s i t e s o f major f a u l t zones (Chapter V) which have been l o c a l l y  carbonatized.  Petrology H a r z b u r g i t e s have an average o l i v i n e :  pyroxene r a t i o  of 7:3 and o c c a s i o n a l l y c o n t a i n up to 3% c l i n o p y r o x e n e . P i c o t i t e c o n s t i t u t e s 2% o f the r o c k , and s e r p e n t i n e a minimum of 20%. O l i v i n e g r a i n s  (4 mm)  a r e anhedral and v e i n e d  by s e r p e n t i n e , g i v i n g r i s e t o a mesh t e x t u r e i n h i g h l y serpentinized rocks.  Disseminated  grains or s t r i n g e r s of  magnetite a r e commonly a s s o c i a t e d w i t h the s e r p e n t i n e .  Kink  52 bands o r deformation present  (Loney et a l . ,  1971) a r e  i n o l i v i n e i n most t h i n s e c t i o n s . Enstatite  bastite  lamellae  ( E n ^ - E n ^ ) p a r t l y r e p l a c e d by p l a t e y  ( l i z a r d i t e according  to Page, 1967) forms 1 cm  g r a i n s which o c c a s i o n a l l y appear t o have an i n t e r g r a n u l a r r e l a t i o n s h i p t o o l i v i n e or to have o l i v i n e i n c l u s i o n s . Such t e x t u r e s suggest magmatic c r y s t a l l i z a t i o n o f o l i v i n e f o l l o w e d by orthopyroxene.  Most e n s t a t i t e g r a i n s c o n t a i n  f a i n t e x s o l u t i o n l a m e l l a e p a r a l l e l to (010) and b l e b s o f a u g i t e a l i g n e d along cleavage are deformed by f r a c t u r e s .  planes.  L o c a l l y , the l a m e l l a e  There i s a marked tendency  f o r both a u g i t e b l e b s and e x s o l u t i o n l a m e l l a e t o s u r v i v e replacement by b a s t i t e . Raleigh  Contrary  to the o b s e r v a t i o n s of  (1963), there i s no i n d i c a t i o n of o f f s e t t i n g o f  e x s o l u t i o n l a m e l l a e because o f expansion d u r i n g replacement by b a s t i t e .  Clinopyroxene  has an i n t e r g r a n u l a r r e l a t i o n s h i p  to both orthopyroxene and o l i v i n e .  P i c o t i t e grains are  u s u a l l y i n t e r g r a n u l a r and equant b u t may be i r r e g u l a r . Commonly they a r e c r o s s - c u t by s t r i n g e r s o f s e r p e n t i n e . Dunites  c o n t a i n , on average, 7 0% s e r p e n t i n e and b r u c i t e ,  30% o l i v i n e and 1% p i c o t i t e or chromite.  Textural features  of o l i v i n e and s p i n e l a r e s i m i l a r to those Three types of s e r p e n t i n e were noted: serpentine, and  i n the h a r z b u r g i t e s .  (a) grey banded mesh  (b) c r o s s - c u t t i n g c o l o u r l e s s r i b b o n  (c) brownish s e r p e n t i n e grading  serpentine  into iddingsite.  The  brownish s e r p e n t i n e appears t o be r e l a t e d to the p e r v a s i v e  f r a c t u r e cleavage and  the r i b b o n s e r p e n t i n e i s o f t e n found  near f r a c t u r e s a s s o c i a t e d w i t h chromite presence  grains.  of b r u c i t e i n three d u n i t e samples was  The confirmed  by X-ray d i f f r a c t i o n . The e a r l y p y r o x e n i t e l a y e r s c o n t a i n on average e n s t a t i t e , 10% o l i v i n e and the c h a r a c t e r i s t i c  (010)  2% p i c o t i t e .  Enstatite contains  exsolution lamellae, o c c a s i o n a l l y  c o n t a i n s o l i v i n e i n c l u s i o n s and may  possess kink bands.  Coarse b l e b s of c l i n o p y r o x e n e are a l i g n e d along cleavage p l a n e s .  88%  the  O l i v i n e occurs as i r r e g u l a r i n t e r g r a n u l a r  g r a i n s which have rounded boundaries  w i t h the  enstatite.  P i c o t i t e i s i n t e r g r a n u l a r and a s s o c i a t e d w i t h o l i v i n e . The m i n e r a l s i n the p y r o x e n i t e l a y e r s are remarkably  un-  a l t e r e d , w i t h s e r p e n t i n e l i m i t e d to the margins of the l a y e r s and  to c a t a c l a s t i c Only one  zones formed by c r o s s - c u t t i n g c l e a v a g e s .  specimen was  cordant p y r o x e n i t e l a y e r s .  o b t a i n e d from the l a t e I t c o n s i s t s o f 90%  pyroxene, 8% c l i n o p y r o x e n e and  2%  dis-  ortho-  picotite.  D i s c u s s i o n on the o r i g i n of u l t r a m a f i t e s The problem of the o r i g i n of a l p i n e u l t r a m a f i t e s , t h a t i s h a r z b u r g i t e - d u n i t e bodies p o s s e s s i n g no  apparent  a s s o c i a t i o n w i t h s t r a t i f o r m cumulate type u l t r a m a f i t e s , i s l o n g s t a n d i n g and no attempt w i l l be made to review v a r i o u s hypotheses.  the  T h i s has been adequately done by  54 Turner and Verhooge.n (1960, p. 307) . Recent sampling o f u l t r a m a f i t e s i n oceanic  areas  ( B o n a t t i , 1971; Aumento, 1971) and a renewed i n t e r e s t i n t e r r e s t r i a l u l t r a m a f i t e s has shed much l i g h t on t h e i r o r i g i n and on c r u s t a l s t r u c t u r e i n oceanic i s t s working i n Cyprus California  (Moores and V i n e ,  ( B a i l e y et a l . ,  areas.  Geolog-  1971) and  197 0) t h i n k t h a t u l t r a m a f i t e s  are d e r i v e d from the upper mantle and t h a t r e l a t i v e l y undisturbed  s e c t i o n s of oceanic  continents. and  The suggestion  c r u s t can be found on the  has been made (Monger, Souther  G a b r i e l s e , 1972; Danner, o r a l communication) t h a t much  of c e n t r a l B r i t i s h Columbia i s u n d e r l a i n by oceanic  crust.  T h i s i s because the Cache Creek Group possesses no apparent c o n t i n e n t a l basement and c o n t a i n s o f r o c k types.  an o p h i o l i t i c a s s o c i a t i o n  Ten y e a r s ago, s i m i l a r ideas were t e n t a t i v e l y  suggested f o r the F r a n c i s c a n  Group, and now many g e o l o g i s t s  (Ernst, 1965; Page, 1972) a c c e p t the view t h a t the Franciscan deposited  Group and p a r t of the Great V a l l e y sequence were on oceanic  crust.  T h i s h y p o t h e s i s must be t e s t e d  s e r i o u s l y f o r B r i t i s h Columbia. Concerning the o r i g i n o f the u l t r a m a f i t e s i n the area,  two t h e o r i e s w i l l be d i s c u s s e d  c u r r e n t hypotheses.  McTaggart  as r e p r e s e n t a t i v e o f  (1971) suggested  that  " U l t r a m a f i c bodies o r i g i n a t e d as cumulates i n b a s i c magma chambers high, i n t h e c r u s t . . . .  These were subsequently  f o l d e d , or dismembered by f a u l t i n g , and because of t h e i r  h i g h d e n s i t y , subsided  during  enclosed  The main advantage of t h i s h y p o t h e s i s  intrusions."  i s t h a t i t e x p l a i n s why  tectonism,  to form c o l d  bodies of h i g h d e n s i t y should  fault  be  found a t h i g h l e v e l s i n the e a r t h ' s c r u s t amidst sediments of r e l a t i v e l y low d e n s i t y . deficiencies. and  mineral  I t does, however, possess  F i r s t , i n the cases where data on  serious  fabric  compositions are a v a i l a b l e , (Loney et al.,  i t has been demonstrated t h a t the a l p i n e u l t r a m a f i t e s metamorphic t e c t o n i t e s which have r e c r y s t a l l i z e d  1971) are  at  approximately 1200°C a f t e r primary magmatic c r y s t a l l i z a t i o n . High temperature r e c r y s t a l l i z a t i o n c o u l d not have taken place during  tectonism  the low g r e e n s c h i s t  of an u l t r a m a f i t e s i t u a t e d w i t h i n  f a c i e s Cache Creek Group r o c k s .  Secondly,  McTaggart suggests t h a t u l t r a m a f i t e s of B r i t i s h Columbia are complementary to Late P a l e o z o i c or T r i a s s i c v o l c a n i c s . However, a c c o r d i n g  to Stueber and Murthy  (1966), t y p i c a l 87/86  a l p i n e u l t r a m a f i t e s possess unique Rb/Sr and  Sr  which are not r e l a t e d g e n e t i c a l l y to s p a t i a l l y gabbros and v o l c a n i c s .  values associated  Because data on f a b r i c and  Rb/Sr  v a l u e s are not a v a i l a b l e f o r u l t r a m a f i t e s i n B r i t i s h Columbia, McTaggart's h y p o t h e s i s cannot y e t be A second, more a t t r a c t i v e theory by the C a l i f o r n i a n s c h o o l Coleman, 1971)..  (Coleman and  disproved.  i s t h a t proposed Keith.,  1971;  T h e i r model. i n v o l v e s c r y s t a l l i z a t i o n o f  a primary u l t r a m a f i c magma f o l l o w e d by p l a s t i c deformation and  r e c r y s t a l l i z a t i o n d u r i n g which a m i n e r a l o g i c a l  foliation,  56 o l i v i n e microfabric were formed.  and c h a r a c t e r i s t i c i n t e r l o c k i n g  Fracturing  textures  and s e r p e n t i n i z a t i o n o f the cooled  p e r i d o t i t e o c c u r r e d on t e c t o n i c emplacement i n the Franciscan  melange.  T h i s model i s , o f course,  by c u r r e n t  ideas on p l a t e t e c t o n i c s .  influenced  I t i s envisaged  the primary p e r i d o t i t e forms a t an a c t i v e oceanic acquires  that  ridge,  a t e c t o n i c f a b r i c i n the upper mantle and undergoes  c o o l i n g , f r a c t u r i n g , emplacement and s e r p e n t i n i z a t i o n a t a subduction o r o b d u c t i o n zone a t the p l a t e margin.  The main  weakness o f t h i s theory i s the problem, e f f e c t i v e l y d e a l t w i t h by McTaggart, o f emplacement of dense p e r i d o t i t e s ' high; i n the c r u s t . lowering d u r i n g  Presumably t h i s i s overcome by d e n s i t y  p a r t i a l serpentinization, tectonic  ment and/or " r a f t i n g up" o f u l t r a m a f i t e s l i g h t sediments on i s o s t a t i c u p l i f t  emplace-  by r e l a t i v e l y  (Burch, 1968).  Recent i n t e n s i v e work on the Burro Mountain p e r i d o t i t e i n C a l i f o r n i a (Burch, 1968; Page, 1967; Loney et al. Coleman and K e i t h ,  1971) has c o n t r i b u t e d  o f the above mentioned model.  }  1971;  t o the f o r m a t i o n  This ultramafite  closely  resembles those i n the P i n c h i a r e a , both p e t r o l o g i c a l l y and  structurally.  information but  F a b r i c data and d e t a i l e d s t r u c t u r a l  a r e not a v a i l a b l e f o r the P i n c h i  ultramafites,  i t i s f e l t t h a t the s i m i l a r i t y to Burro Mountain i s  s u f f i c i e n t l y great conclusions.  to warrant some e x t r a p o l a t i o n of  57 Origin of Pinchi The  ultramafites  o r i g i n o f the primary mineralogy and t e x t u r e s  in ultramafites i s conjectural. suggest t h a t h a r z b u r g i t e  Loney et al. (1971)  and d u n i t e c r y s t a l l i z e d penecontem-  poraneously from g e n e t i c a l l y r e l a t e d u l t r a m a f i c magmas r a t h e r than having d i f f e r e n t i a t e d from a b a s i c magma or having formed as a . r e s i d u a l product o f p a r t i a l m e l t i n g p r i m i t i v e mantle.  They s u b s t a n t i a t e  of the  t h i s by p o i n t i n g o u t  the l a c k of c r y p t i c or rhythmic l a y e r i n g i n a l p i n e u l t r a m a f i t e s and the d e a r t h o f cumulate t e x t u r e s  compared w i t h  s t r a t i f o r m l a y e r e d complexes such as the Bushveld and S t i l l water.  As p o s i t i v e evidence f o r a magmatic o r i g i n , they  s t a t e t h a t the d i f f e r e n c e s i n the c h e m i s t r y of o l i v i n e and chromite i n d i f f e r e n t d u n i t e harzburgite composition.  has been i n t r u d e d Ringwood  bodies suggest t h a t the by d u n i t e magmas o f c o n t r a s t i n g  (1962) suggested t h a t a l p i n e  ultra-  m a f i t e s a r e the r e s i d u a l products o f p a r t i a l m e l t i n g o f the p r i m i t i v e mantle.  T h i s p o s s i b i l i t y i s given  by the Rb/Sr work o f Stueber and Murthy  some support  (1966) who suggested  t h a t a l p i n e u l t r a m a f i t e s a r e r e s i d u a l and were p r o b a b l y depleted  o f l i t h o p h i l e elements a t some e a r l y stage i n t h e i r  history. On  the b a s i s o f the work done a t P i n c h i so f a r , the  above mentioned hypotheses cannot be s u b s t a n t i a t e d or refuted.  However, t e x t u r e s which a r e s u g g e s t i v e of magmatic  58  crystallization  (p. 52 ) do e x i s t and may be a r e l i c t  f e a t u r e o f a primary magmatic o r i g i n . The pyroxenite  o r i g i n o f the concordant  harzburgite-dunite-  layering i s also problematical.  Four hypotheses  have been suggested: (a) c r y s t a l s e t t l i n g from a magma (Raleigh, 1965), (b) magmatic i n t r u s i o n o f d u n i t e and p y r o x e n i t e dykes and s i l l s  (Loney et al., 1971),  (c) metasomatic replacement along f r a c t u r e s (Bowen, 1949)  and  (d) metamorphic d i f f e r e n t i a t i o n caused by s h e a r i n g s t r e s s and d i f f e r i n g p h y s i c a l p r o p e r t i e s o f o l i v i n e and pyroxene The  f i r s t hypothesis  Raleigh  (Burch,  r e c e i v e s support  1968). from a study by  (1965) c a r r i e d o u t on the Cypress I s l a n d p e r i d o t i t e ,  considered  t o be a t y p i c a l a l p i n e type u l t r a m a f i t e .  contains a dunite-chromitite-harzburgite  l a y e r i n g and  accumulative t e x t u r e s which R a l e i g h considered by c r y s t a l s e t t l i n g from a magma.  Later  It  to have formed  recrystallization  and p e n e t r a t i v e deformation produced a p r e f e r r e d o r i e n t a t i o n of o l i v i n e .  However, Burch  (1968) decided  o r i g i n f o r the p y r o x e n i t e - d u n i t e - h a r z b u r g i t e  a g a i n s t such an layering i n  the Burro Mountain p e r i d o t i t e because of the sharpness o f c o n t a c t s between l a y e r s and absence of c r y p t i c l a y e r i n g , rhythmic l a y e r i n g , graded bedding and w e l l d e f i n e d cumulate  59 textures.  T h i s a l s o appears t o be the case a t P i n c h i b u t ,  because l i t t l e and  i s known about the primary magmatic c o n d i t i o n s  the extent o f m o d i f i c a t i o n by r e c r y s t a l l i z a t i o n and  deformation,  c r y s t a l s e t t l i n g must be c o n s i d e r e d a p o s s i b l e  mechanism f o r l a y e r  formation.  Magmatic i n t r u s i o n  (b) i s a p l a u s i b l e h y p o t h e s i s f o r  the o r i g i n o f the i r r e g u l a r d u n i t e s .  However, i t does n o t  e x p l a i n the common p a r a l l e l i s m o f d u n i t e and p y r o x e n i t e ' l a y e r s , the s i m i l a r i t y i n t h i c k n e s s o f p y r o x e n i t e l a y e r s and the absence of c r o s s - c u t t i n g r e l a t i o n s h i p s between d u n i t e l a y e r s and e a r l y p y r o x e n i t e s .  Bowen (1949) suggested  that  S i C ^ - d e f i c i e n t f l u i d s moving along f r a c t u r e s (c) c o u l d r e s u l t i n replacement dunite layers.  o f orthopyroxene  forming  Presumably, i t would a l s o be p o s s i b l e f o r  S i C ^ - r i c h f l u i d s to cause replacement orthopyroxene.  by o l i v i n e ,  of o l i v i n e by  T h i s hypothesis possesses  to t h a t o f magmatic i n t r u s i o n .  similar  deficiencies  In a d d i t i o n , i t i s d i f f i c u l t  to e x p l a i n why metasomatic f l u i d s should be of d i f f e r e n t compositions Burch  i n adjacent  layers.  (1968) suggested  t h a t p y r o x e n i t e and d u n i t e  l a y e r s a r e formed by metamorphic d i f f e r e n t i a t i o n  along  shears because of the d i f f e r i n g p h y s i c a l p r o p e r t i e s o f o l i v i n e and orthopyroxene.  He argued t h a t d u n i t e would  tend to c o n c e n t r a t e i n areas o f shear, as o l i v i n e y i e l d s r e a d i l y by p l a s t i c flow, and pyroxene would c o n c e n t r a t e i n areas o f l e a s t s t r e s s o r p o t e n t i a l t e n s i o n f r a c t u r e s .  60 As d u n i t e and p y r o x e n i t e l a y e r s are concordant, s e g r e g a t i o n i n a shear plane may  have l e f t a pyroxene-  r i c h r e s i d u e , thus g i v i n g r i s e to the observed of d u n i t e and p y r o x e n i t e l a y e r s .  olivine  parallelism  T h i s hypothesis i s a l s o  c o n s i d e r e d a c c e p t a b l e because i t e x p l a i n s the absence of early pyroxenite layers i n dunites. The p y r o x e n i t e and d u n i t e l a y e r s w i t h i n the P i n c h i u l t r a m a f i t e s have been f o l d e d .  S i m i l a r s t r u c t u r e s have  been observed  (Loney et al.  a t Burro Mountain  o l i v i n e f a b r i c data i n d i c a t e :  the presence  3  1971)  where  of a p e r v a s i v e  p l a n a r f a b r i c which c r o s s - c u t s h a r z b u r g i t e - d u n i t e c o n t a c t s and  i s a x i a l p l a n a r to minor, f o l d s .  Analyses o f co-  e x i s t i n g o l i v i n e and chrome s p i n e l suggest  that t h i s  fabric  r e c r y s t a l l i z e d a t an approximate temperature of 12 00°C. T h i s c o n c l u s i o n i s supported  by experimental work on  olivine  deformation a t 1200°C which produced a f a b r i c s i m i l a r to t h a t p r e s e n t i n d u n i t e s from Burro Mountain and C a r t e r , 1969).  (Ave  L'Allement  On the b a s i s of s i m i l a r i t i e s i n i n t e r n a l  s t r u c t u r e between the Burro Mountain and P i n c h i u l t r a m a f i t e s i t i s suggested  t h a t the l a t t e r has a l s o undergone a deep-  seated p l a s t i c deformation  a t 1200°C.  The o r i g i n of the l a t e d i s c o r d a n t p y r o x e n i t e l a y e r s can p o s s i b l y be e x p l a i n e d by f o l d i n g of p r e - e x i s t i n g l a y e r s and f o r m a t i o n of a new  g e n e r a t i o n of shear  c r o s s - c u t t i n g the e a r l y l a y e r s .  However, t h i s  planes  hypothesis  cannot e x p l a i n the occurrence of l a t e p y r o x e n i t e v e i n s  61 cutting i r r e g u l a r dunite bodies.  I t i s t h e r e f o r e concluded  t h a t the o r i g i n of the l a t e d i s c o r d a n t p y r o x e n i t e s has be accounted  f o r by magmatic i n t r u s i o n of an  to  "orthopyroxenite  magma," o r , more l i k e l y , by metasomatic a c t i v i t y . The  f o r m a t i o n of k i n k bands i n o l i v i n e i s r e l a t e d  to the g l i d e system {Okl} (Ave L'Allemant,  [10 0 ] .  Experimental  evidence  1968)  i n d i c a t e s t h a t t h i s g l i d e system  operates predominantly  i n the temperature range 90 0° to  1200°C and  suggests  t h a t kink band formation took p l a c e  a f t e r r e c r y s t a l l i z a t i o n a t 1200°C and p r i o r to s e r p e n t i n i zation . The main p e r i o d of s e r p e n t i n i z a t i o n i s b e l i e v e d to have been contemporaneous w i t h f r a c t u r i n g and d u r i n g the F ^ and F^  deformations  emplacement  (Chapter V) .  The  pressure-  temperature c o n d i t i o n s of s e r p e n t i n i z a t i o n are d i s c u s s e d i n Chapter  IV Two  (p. 116  ) .  hypotheses are c o n s i d e r e d f o r the emplacement of  ultramafites.  The  f i r s t i n v o l v e s o v e r t h r u s t i n g of oceanic  c r u s t d u r i n g P e r m o - T r i a s s i c tectonism, i n which case, P i n c h i u l t r a m a f i t e s may  be downfaulted  remnants of an  o p h i o l i t i c cover to the Cache Creek Group. h y p o t h e s i s suggests  s o l i d emplacement of a  b l o c k of low average d e n s i t y l i m e s t o n e s , s c h i s t and  the  The  second  fault-bounded  (2.7-2.8 gms/cc)containing  s e r p e n t i n i z e d p e r i d o t i t e , along  of low p r e s s u r e i n the P i n c h i F a u l t system. are f u r t h e r d i s c u s s e d i n Chapter  VI.  cherts zones  These hypotheses  62 The  l a t e s t d e f o r m a t i o n a l event w i t h i n  m a f i t e s was  during  ultra-  the f o r m a t i o n of a complex f r a c t u r e cleavage  a s s o c i a t e d w i t h minor s e r p e n t i n i z a t i o n . occurred  the  during  the F^  T h i s may  the l a t t e r stages of the F^  deformation  have  deformation o r  (Chapter V ) .  S i l i c a - c a r b o n a t e Rocks Distribution Because of t h e i r r e s i s t a n c e to e r o s i o n , s e r p e n t i n i t e s are conspicuous i n the f i e l d .  carbonatized  Generally  they  form a c o l i n e a r s e r i e s of r u s t y weathering south f a c i n g b l u f f s up  to 120  m wide o c c u r r i n g  s p o r a d i c a l l y along  zones a t the margins of u l t r a m a f i t e s . are on  The  best  examples  the southern slopes of P i n c h i Mountain and  southeast end  of P i n c h i Lake.  Carbonatized  fault  at  the  ultramafites  are a l s o found i n the v i c i n i t y of P i n c h i Mercury Mine the Darbar c l a i m group, 7 m i l e s n o r t h e a s t  of F o r t  and  St.  James.  Rock types,  i n t e r n a l and  external  structure  F e r r o a n magnesite, the predominant c o n s t i t u e n t the s i l i c a - c a r b o n a t e r o c k s ,  i s orange-brown and  has  in  a rough  weathered s u r f a c e because of the presence of anastamosing quartz v e i n l e t s . mariposite  R e l i c t chromite g r a i n s or p a l e  green  ( f u c h s i t e ) are commonly seen i n hand specimen.  63  Layers of sugary white magnesite, up to 1 m i n t h i c k n e s s are o c c a s i o n a l l y found.  These l a y e r s c o n t a i n i n c l u s i o n s of  f e r r o a n magnesite. Compositional  l a y e r i n g w i t h i n the f e r r o a n magnesite  zones i s p a r a l l e l to the c o n t a c t s and  i s d e f i n e d by  s i l i c i f i e d b r e c c i a zones and white magnesite l a y e r s (Plate 5 ) . The  c o n t a c t s of r e l i c t l e n s e s of s e r p e n t i n i z e d h a r z b u r g i t e  are concordant  w i t h the l a y e r i n g and are h i g h l y  and v e i n e d by magnesite. at  approximately  60°.  of  P i n c h i Mountain l i e s  sheared  Dips are to the n o r t h or  northeast  A magnesite zone on the south s i d e s t r u c t u r a l l y beneath u l t r a m a f i c  and g l a u c o p h a n i t i c r o c k s and o v e r l i e s the P i n c h i Mountain greenstones.  However, on the assumed path o f the P i n c h i  F a u l t , a t the southeast end  of P i n c h i Lake, s i l i c a - c a r b o n a t e  rocks appear to pass under Upper T r i a s s i c r o c k s .  On  the  Darbar c l a i m group the f o l i a t i o n i n c a r b o n a t i z e d s e r p e n t i n i t e s p a r a l l e l s a f a u l t zone which d i p s under greenstones a t  60°  to  the  the n o r t h e a s t .  hypothesis  A l l the evidence  i s compatible  with  t h a t the l a y e r i n g o r i g i n a t e d d u r i n g contemporan-  eous c a r b o n a t i z a t i o n and movement along major  faults.  Late b r e c c i a t i o n a f f e c t e d a l l the above mentioned rocks.  D i l a t a t i o n a l f r a c t u r e s or v o i d s were f i l l e d  by d o l o m i t e , c h a l c e d o n i c quartz or agate and quartz.  i n turn  crystalline  Dolomite v e i n s c u t by quartz v e i n s are common,  the former p o s s e s s i n g s t r i a t e d c r y s t a l s w i t h long axes  64 p e r p e n d i c u l a r t o the s i d e s o f f r a c t u r e s .  These l a t e v e i n s  are c r o s s - c u t by a near v e r t i c a l s e t of n o r t h - s o u t h s tr iking frac tures.  Petrology The s i l i c a - c a r b o n a t e r o c k s c o n s i s t o f f e r r o a n magnesite ± quartz ± serpentine.  Magnesite  and q u a r t z a r e u s u a l l y  m i c r o c r y s t a l l i n e but may be l o c a l l y coarse g r a i n e d .  Relict  subhedral chromite p o s s e s s i n g r e d d i s h t r a n s l u c e n t margins i s common i n a l l specimens.  Annabergite  ("nickel bloom")  i s found on f r a c t u r e s u r f a c e s near P i n c h i Mine. The presence o f r e l i c t chromite and l e n s e s of serpent i n i z e d h a r z b u r g i t e w i t h i n the s i l i c a - c a r b o n a t e r o c k s demons t r a t e s t h a t they were u l t r a m a f i t e s p r i o r t o a l t e r a t i o n by along f a u l t zones.  The most common e q u i l i b r i u m m i n e r a l  assemblage i s magnesite + q u a r t z , but a n t i g o r i t e + magnesite i s a l s o p r e s e n t i n one specimen.  Talc i s not present.  s i d e r i n g these assemblages, the r e a c t i o n : s e r p e n t i n e + CC^ = magnesite + q u a r t z + H^O is applicable.  T h i s has been s t u d i e d e x p e r i m e n t a l l y and  t h e o r e t i c a l l y by Greenwood T h e i r data  (1967) and Johannes  (1969).  indicate:  (a) the assemblage a n t i g o r i t e + magnesite must have formed a t low p a r t i a l p r e s s u r e of CC^ ( than 0.03 a t 1 kb);  x C  o less  Con-  (b) the predominant assemblage magnesite + quartz i s stable at X _  g r e a t e r than  0.03  a t 1 kb  and  300°C and (c) the temperature of the r e a c t i o n was 350°C a t 4 kb and  (Wenner, 1971;  occurrence suggest  Coleman, 1971).  of a n t i g o r i t e and  serpentine  Therefore,  Age  rocks was  and  the  the quartz-magnesite assemblage  t h a t the temperature of formation of the  carbonate  than  l e s s than 310°C a t 1 kb.  A n t i g o r i t e i s c o n s i d e r e d a "high temperature" mineral  less  silica-  i n the 2 00° to 300°C range.  origin  C a r b o n a t i z a t i o n i s r e s t r i c t e d to the major f a u l t s i n the a r e a .  Because of the presence of s i l i c i f i e d  breccias i t i s considered  l i k e l y t h a t the l a y e r i n g w i t h i n  the s i l i c a - c a r b o n a t e rocks was f a u l t s during a l t e r a t i o n .  magnesite  c o n t r o l l e d by movement along  T h e r e f o r e , the problem o f  the  t i m i n g of the a l t e r a t i o n i s a s s o c i a t e d w i t h the t i m i n g of active  faulting. A number o f authors c o n s i d e r t h a t a c t i v e f a u l t i n g  a s s o c i a t e d w i t h the Laramide orogeny took p l a c e b e f o r e Late Eocene.  In the McConnell Creek map  area and on  the  the  S p a t s i z i P l a t e a u , Sustut Group rocks of Upper Cretaceous  to  Paleocene age have been a c t i v e l y i n v o l v e d i n n o r t h e a s t e r l y directed thrust faulting  (Lord, 1949;  Eisbacher,  North of F o r t S t . James, conglomerate beds of  1969).  Cretaceous  66  or Paleocene F a u l t zone  age are found i n t e r m i t t e n t l y along the P i n c h i (Armstrong,  1949) and such a conglomerate i s  found a t the west end o f Murray Ridge a p p a r e n t l y i n f a u l t contact with older rocks.  Roots  (1953) staterd t h a t r o c k s  o f the T a k l a Group a r e c a r b o n a t i z e d a d j a c e n t t o a mercury m i n e r a l i z e d f a u l t zone the c o n t i n u a t i o n o f which i s b e l i e v e d to d i s p l a c e r o c k s o f Cretaceous A i k e n Lake map a r e a .  or Paleocene  age i n the  For these reasons, evidence  favours  a period of a c t i v e f a u l t i n g associated with c a r b o n a t i z a t i o n i n the F o r t S t . James area d u r i n g the Eocene. The f o r m a t i o n o f s i l i c a - c a r b o n a t e r o c k s i s commonly c o n s i d e r e d as an e a r l y stage o f the hydrothermal which l a t e r r e s u l t s i n the d e p o s i t i o n of cinnabar 1963; Henderson, 1 9 6 8 ) .  activity (Bailey,  Cinnabar m i n e r a l i z a t i o n i s g e n e r a l l y  c o n s i d e r e d e p i t h e r m a l , and cinnabar i s a t p r e s e n t being d e p o s i t e d by hot s p r i n g s a t v a r i o u s l o c a t i o n s i n the western United States  (White, 1968, p. 1 6 7 5 ) .  Henderson  (1968)  s t a t e s t h a t cinnabar d e p o s i t s i n the s i l i c a - c a r b o n a t e r o c k s of C a l i f o r n i a occur a t depths o f l e s s than 8 00 m and commonly the sequence of events i s : (a) s i l i c a - c a r b o n a t e a l t e r a t i o n o f s e r p e n t i n i t e , (b) f r a c t u r i n g o f s i l i c a - c a r b o n a t e rock, and Cc) cinnabar v e i n m i n e r a l i z a t i o n o f the f r a c t u r e s . In the P i n c h i a r e a , cinnabar m i n e r a l i z a t i o n occurs as f r a c t u r e f i l l i n g s i n s i l i c a - c a r b o n a t e r o c k s a t two l o c a l i t i e s  and  i t i s suggested t h a t the h i s t o r y of m i n e r a l i z a t i o n i s  s i m i l a r t o t h a t o f the C a l i f o r n i a n o c c u r r e n c e s and t h a t the m i n e r a l i z a t i o n took p l a c e  i n a near s u r f a c e  environment  a f t e r the formation o f the s i l i c a - c a r b o n a t e r o c k s . Armstrong consider  (1966) and H.W.  Tipper  J.E.  ( o r a l communication) a l s o  the mercury m i n e r a l i z a t i o n  i n B r i t i s h Columbia  to be o f T e r t i a r y age. In summary, evidence f a v o u r s the f o l l o w i n g of  sequence  events: (a) The s i l i c a - c a r b o n a t e r o c k s were formed d u r i n g a r e a c t i v a t i o n of the P i n c h i F a u l t i n the Eocene. Carbon d i o x i d e — r i c h f l u i d s , p o s s i b l y a c t i n g as l u b r i c a n t s i n the f a u l t p l a n e , r e a c t e d  with  a d j a c e n t u l t r a m a f i t e s g i v i n g r i s e t o the magnesite + q u a r t z assemblage.  The type o f f a u l t i n g and  sense o f movement i s unknown, but n o r t h e a s t e r l y d i r e c t e d t h r u s t i n g was widespread 240 km to the north during  the Eocene  (Eisbacher,  197 0).  common occurrence o f n o r t h e a s t e r l y d i p p i n g planes suggests t h a t s i m i l a r l y o r i e n t e d may have given r i s e to u n d e r t h r u s t i n g  The fault  stresses  i n the  P i n c h i area, b u t t h i s i s s p e c u l a t i v e . (b) F r a c t u r i n g o f the s i l i c a - c a r b o n a t e rocks during  occurred  the Eocene, Oligocene or Miocene contem-  poraneous w i t h hot s p r i n g a c t i v i t y and mercury mineralization.  IV METAMORPHISM  I.  METAMORPHISM IN GREENSTONE AND BLUESCHIST FAULT BLOCKS  Introduction Four p o s s i b l e hypotheses  c u r r e n t l y e x i s t which  attempt  to e x p l a i n the occurrence of the "high p r e s s u r e " b l u e s c h i s t f a c i e s mineralogy.  The hypotheses  a r e l i s t e d below together  w i t h t h e i r p r i n c i p a l exponents. (a) The necessary p r e s s u r e s a r e a t t a i n e d by t e c t o n i c overpressures i n a d d i t i o n t o l i t h o s t a t i c  pressures  (Blake, Irwin and Coleman, 1967, 1969). (b) High p r e s s u r e s a r e a t t a i n e d by an " i n t e r n a l l y c r e a t e d gas o v e r p r e s s u r e " (c)  (Brothers, 1970).  B l u e s c h i s t f a c i e s m i n e r a l s a r e formed at  metastably  lower p r e s s u r e s than those i n d i c a t e d i n e x p e r i -  mental s t u d i e s because of r e d u c i n g c o n d i t i o n s i n the pore f l u i d accompanying metamorphism  (Gresens,  1969) . (d) B l u e s c h i s t f a c i e s m i n e r a l assemblages a r e formed a t h i g h l i t h o s t a t i c p r e s s u r e s and r e l a t i v e l y low temperatures 1958,  (Fyfe, Turner and Verhoogen,  p. 226; E r n s t , 1965, 1971b).  69  A b r i e f summary of each of these hypotheses  follows with  emphasis on a s p e c t s of the metamorphism a t P i n c h i which bear d i r e c t l y on the problem of d i s c r i m i n a t i n g between the suggested  hypotheses.  The h y p o t h e s i s of Blake, I r w i n and Coleman 1969}  (1967,  t h a t t e c t o n i c o v e r p r e s s u r e s i n a f a u l t zone can  e x p l a i n b l u e s c h i s t mineralogy by Brace et al.,  (1970) who  has been shown to be  unlikely  showed e x p e r i m e n t a l l y t h a t  F r a n c i s c a n greywacke cannot support even one k i l o b a r of t e c t o n i c o v e r p r e s s u r e and by E r n s t (1971b) who  concludes  t h a t none of the g e o l o g i c , s t r u c t u r a l , p e t r o g r a p h i c or experimental work i s c o n s i s t e n t w i t h the e x i s t e n c e of s u f f i c i e n t tectonic overpressure. A t P i n c h i , the h y p o t h e s i s of t e c t o n i c  overpressures  f i n d s no support i n s t r u c t u r e or t e c t o n i c f a b r i c .  No  g r a d a t i o n e x i s t s i n metamorphic r e c o n s t i t u t i o n towards the P i n c h i F a u l t and metabasalts  and j a d e i t i z e d metagreywackes  commonly c o n t a i n r e l i c t igneous or c l a s t i c t e x t u r e s (Appendix  IV).  T h e i r unsheared  nature excludes the p o s s i b i l i t y  of a s i g n i f i c a n t c o n t r i b u t i o n from t e c t o n i c There may  overpressure.  w e l l be a t e c t o n i c - g e n e t i c r e l a t i o n s h i p between  the g l a u c o p h a n i t i c r o c k s and the P i n c h i F a u l t but there i s no evidence t h a t movement on the f a u l t produced  tectonic  o v e r p r e s s u r e i n the a d j a c e n t r o c k s . Brothers  (197 0) proposed  an h y p o t h e s i s  involving  the c r y s t a l l i z a t i o n of l a w s o n i t e - a r a g o n i t e rocks i n an  70  environment w i t h an  " i n t e r n a l l y c r e a t e d gas o v e r p r e s s u r e . "  T h i s o v e r p r e s s u r e was  thought  to be c o n t a i n e d by an  impermeable t e c t o n i c s e a l i n the form of an  overlying  ultramafite.  Under such c o n d i t i o n s , P^, . , = P fluid solids CG reenwood, 1961) but l o c a l l y , ^ f ] _ j ^ ^solid s > , , 4 . 4. • • T h i s h y p o t h e s i s i s unsupported by the 1 1 t n o s ta t i c —  u  P i n c h i rocks because i t seems u n l i k e l y t h a t f]_ j_£ c o u l d P  u  exceed  P, ... +..•-• throughout litnostaric  a r e g i o n a l l y metamorphosed  t e r r a i n and because there i s no evidence f o r an t e c t o n i c s e a l " which c o u l d have encapsulated  "impermeable  the  blueschists. Gresens  (1968) emphasized the g l o b a l a s s o c i a t i o n of  u l t r a m a f i t e s w i t h b l u e s c h i s t s and presence  suggested  of u l t r a m a f i t e s undergoing  t h a t the  serpentinization  and  o x i d a t i o n of i r o n r e s u l t e d i n the f o r m a t i o n of a r e d u c i n g pore f l u i d  i n the a d j a c e n t sediments.  induced the metastable  T h i s pore  fluid  growth of the c h a r a c t e r i s t i c  b l u e s c h i s t f a c i e s m i n e r a l s a t lower p r e s s u r e s than i n d i c a t e d by e x p e r i m e n t a l l y produced  P/T  those  stability  diagrams. In a d d i t i o n to the arguments advanced by E r n s t (1971b) a g a i n s t t h i s h y p o t h e s i s , f i e l d evidence a t P i n c h i demonstrates t h a t u l t r a m a f i t e s are commonly a s s o c i a t e d w i t h greenstones  b e l o n g i n g to the p r e h n i t e - p u m p e l l y i t e  f a c i e s r a t h e r than the lawsonite-glaucophane Gresens  1  bearing rocks.  h y p o t h e s i s i s t h e r e f o r e not d i r e c t l y a p p l i c a b l e  71 to  the P i n c h i b l u e s c h i s t s .  However, there i s evidence  at  P i n c h i t h a t i n d i c a t e s some of the b l u e s c h i s t f a c i e s m i n e r a l s c r y s t a l l i z e d under r e d u c i n g c o n d i t i o n s and  certain  a s p e c t s of the hypothesis are t h e r e f o r e worthy of c o n s i d e r a tion.  These are d i s c u s s e d l a t e r The  (p. 96 )•  f o u r t h hypothesis f o r b l u e s c h i s t formation  i n v o l v e s h i g h l i t h o s t a t i c p r e s s u r e s and r e l a t i v e l y temperatures 1965,  1970,  (Fyfe, Turner and Verhoogan, 1958; etc.).  low  Ernst,  The h y p o t h e s i s i s based l a r g e l y on  f a v o u r a b l e comparison of the observed w i t h e x p e r i m e n t a l l y determined In the succeeding  mineral  the  paragenesis  phase e q u i l i b r i a .  s e c t i o n s , i t i s demonstrated  (a) t h a t the P i n c h i b l u e s c h i s t s formed a t h i g h pressures,  and  (b) t h a t methane may  have been an important  constitu-  ent of the f l u i d phase i n metamorphic assemblages which c o n t a i n carbonaceous m a t e r i a l .  P a r a g e n e t i c Sequence of M i n e r a l s P o s s i b l e m i n e r a l p a r a g e n e t i c sequences f o r r o c k s and metacherts based on t e x t u r a l and a r e g i v e n i n F i g s . 6 & 7.  field  metabasic evidence  As e x t e n s i v e work has been done  r e c e n t l y on p r o g r e s s i v e metamorphism of F r a n c i s c a n grey-' wackes, a p a r a g e n e t i c sequence i s taken from E r n s t and  (1971)  the stage of e v o l u t i o n of the P i n c h i greywackes i s  i n d i c a t e d f o r comparison.  72 FIG. 6  KINEF1AL PARAGEMESES  METABASALTS  Minerals  Greenstones  Lato  Blueschists  minerals  alblte Bodlo pyroxene acmlte-JadeIte chlorite quartz calcite aragonite pumpellylte white mica celadonlte Ephene glaucophane lawsonite stllpnomelane prehnite brown amphlbole deerite  ?  pyrite  ?  magnetite hematite Increase l n P ECLOGITE  Early  minerals  :  ^  Decrease l n P  Late minerals  omphaclte garnet  ?  rutlle glaucophane lawsonite sphene brown amphlbole + chlorite  Decrease l n P (?) — —  ; major constituent : minor constituent : accessory c o n s t i t u e n t :  >  ^  73  FIG. 7 KETACHERTS Minerals glaucophane lawsonlte quartz white mica pyrite hematite alblte carbonaceous material sphene acmltlc pyroxene METAGREYWACKES Minerale  MINERAL PARACENBSES Early minerals Blueschist facies Late minerals  ?  Diablo Range (Ernst, 1971) Increasing grade  clastic biotite pumpellylte lawsonite alblte Jadeltic pyroxene glaucophane white mica chlorite stilpnomelane calcite aragonlte quartz rock fragments sphene : major constituent s minor constituent : accessory constituent  Finchl area  74 M i n e r a l Assemblages D e t a i l s o f t h e petrography,  m i n e r a l assemblages and  specimen l o c a t i o n s o f the f a u l t bounded b l o c k s c o n t a i n i n g the greenstones o f P i n c h i Mountain and the g l a u c o p h a n i t i c rocks a r e g i v e n i n Appendix IV. E q u i l i b r i u m phase assemblages can be summarized as follows: (a) Greenstones o f P i n c h i Mountain (i) ab + NaPx + c h l + sph ± wh m ± arag ± pump ± c e l a d Cii) q t z + NaPx + c h l + sph ± wh m ± arag ( i i i ) arag + d o l (only i n i n t e r c a l a t e d  limestones)  (iv) ab + c h l + pump + sph ± prehn ± cc ± c e l a d ± wh m (only found a t west end of Murray Ridge) (b) Glaucophane-lawsonite b e a r i n g assemblages Metabasic  rocks  (v) acm-jd + lws + sph + c h l ± wh m ± arag ± g l p h (vi) g l p h + lws + sph ± c h l ± wh m  (massive) (foliated)  Limestone ( v i i ) arag + carbonaceous m a t e r i a l ± d o l ± q t z Metasediments ( v i i i ) arag + q t z ± wh m (ix) q t z + lws + glph + wh m + c h l (xl q t z + wh m ± lws + g l p h ± carb mat ± sph ± py •^•Abbreviations g l p h = glaucophane; NaPx = s o d i c pyroxene; acm-jd = acmitej a d e i t e ; lws = lawsonite; q t z = q u a r t z ; ab = a l b i t e ; c h l = c h l o r i t e ; sph = sphene; wh m = white mica (phengite); arag= a r a g o n i t e ; pump = p u m p e l l y i t e ; celad.= c e l a d o n i t e ; prehn = p r e h n i t e ; c c = c a l c i t e ; d o l = dolomite; s t i l p = s t i l p n o m e l a n e ; py = p y r i t e ; c a r b mat = carbonaceous m a t e r i a l .  75  TABLE 4 GENERALIZED PARAGENETIC SEQUENCE OF METABASALTS  -> GREENSTONE  BASALT  chlorite albite sphene zeolites prehnite calcite  augite plagioclase ilmenite olivine  -> PINCHI MT.  GREENSTONE  chlorite albite sphene s o d i c pyroxene pumpellyite aragonite prehnite celadonite white mica quartz  ECLOGITE / /  retrograde reaction I \  omphacite garnet rutile  \  FOLIATED GLAUCOPHANITIC METABASALTS glaucophane lawsonite sphene chlorite stilpnomelane  ACMITE-JADEITE METABASALT acmite-j adeite lawsonite chlorite sphene aragonite phengite glaucophane stilpnomelane deerite  TABLE 5a  POSSIBLE REACTIONS IN METABASIC ROCKS  (A) Metastnble r e a c t i o n s (1) p l a g i o c l a s e - x a l b l t e + (1-x) a n o r t h l t e (2) 2 l l m e n l t e + | 0 (3)  2  » hematite + 2 r u t l l e  a n o r t h l t e • r u t l l e •» sphene + A l j S l O ^ ( A l - S l component l n phenglte o r c h l o r i t e )  (4) 7 a n o r t h l t e + 5 d i o p s i d e + 10H 0 = 6 p r e h n l t e + c h l l n o c h l o r e + 3 quartz 2  (5) 6 C a ( K g , F e ) S l 0 2  + 4H 0 + 6 C 0  6  2  = (Mg.Fe) S1^0 (OH)g + 6 C a C 0  2  6  augite  10  chlorite  (B) S i g n i f i c a n t prograde  3  + 8S10  2  calcite — — laKSonlte-glaucophane  r e a c t i o n s (I.e. greenstones  metabasltes)  * (6) c a l c i t e = aragonite **(?) laumontlte + prehnlte + c h l o r i t e = pumpellylte + quartz + H 0 2  (8) a m e s i t e ( c h l o r l t e ) + 8 prehnlte + 2H 0 = 4 pumpellylte + 2 quartz 2  *  (9)  laumontlte = lawsonite + 2 quartz + 2H 0 2  * (10) heulandlte = lawsonite + 5 quartz + 4H 0 2  ••(11) C a ( M g , F e ) S i 0 2  + Na • (Al.Fe) * = Na(Al,Fe)Si 0 +  6  3  2  augite  EOln.  (12) NaAlSljOg + 0.33?ejO alblte  + Ca  Jadelte-acmlte comp. l n p y r o x e n e  + 0.1702 = N a F e S l 0 2  k  6  hematite  acmlte  6  +  (Kg,Fe)  2+  soln.  + 0.5 A 1 0 2  comp.  2 +  3  + S10  2  A l - S l component l n p h e n g l t e o r  ln pyroxene (13) NaAlSljOg + ( K e . F e ) S l 0 6  4  1 0  2  ehlorlte-1  alblte  chlorite  + 0.120 = N a A l ^ ^ F e ^ +  (Kg,Fe)  ecmlte-Jadelte  $>5  A 1 _^51  ^O^fOHjg  chlorlte-2 + 1.12 S i 0  2  * (14) a l b l t e = Jadelte + quartz **(15) 2 a l b l t e + C a  2 +  + 2H 0 = lawsonite + 2 Na* + 4 S 1 0 2  H  (16a)  *  2 acmlte + 3 hematite + 4 quartz +  •  (16bj  2  2  *°2  CH^ = r l e b e c k l t e + m a g n e t i t e + H 2  2  °  °  H  .250  2  2 acmlte + 1 . 5 hematite + 4 quartz + CH^ + . 250  2  2  = rlebecklte + C + H 0  2  2  .750  Ho 2  fluid (17) 2 a l b l t e + 0.5 c h l o r i t e ( s e r p e n t i n e )  C + H 0  2  fluid  = glaucophane + water  (C) P o s s i b l e r e a c t i o n s r e l a t i n g P i n c h i assemblages, with higher temperature ( i . e . g r e e n s c h i s t f a c i e s ) assemblages. *  (18) lawsonite = a n o r t h l t e + 2H 0  *  (19)  2  4 lawsonite = 2 z o l s l t e + kyanlte  + quartz + 7H 0 2  Ellllmanlte *  (20) 12 p r e h n l t e + 6 c l l n o c h l o r e + 2 quartz = 12 c l l n o z o l s i t e + 5 serpentine + 10H 0 2  * (21) 20 pumpellylte = 16 c l l n o z o l s i t e + 5 ameslte + 16 g r o s s u l a r + 14 quartz + 2H 0 2  (22) 2 4 C a A l S l 0 ( 0 H ) . H 0 + SMg^Sl^O „ ) ( O H ) 2  2  ?  2  2  lawsonite , *  chlorite •  8  = 12Ce Al S I ( O H ) + 2  cllnozolsite + 14S10  2  6l1 ^Al Sl 0 (OK) E  2  3  1 0  chlorite  + 38H 0 (Turner, 1968. p. 155)  (23) f e r r o g l e u c o p h n n e • i 0 = 2 e l b l t e + 2 q u a r t z • m a g n e t i t e • H 0 * e x p e r i m e n t a l d e t e r m i n a t i o n - s e e ? l j . ; . C f o r p o s i t i o n c f e q u i l i b r i u m c u r v e ond a u t h o r ** u n b a l a n c e d o r i o n i c r e a c t i o n m l n c r n l c o n - . p o n l t l o n R o r o g i v e n l n 'pil.lc 5b ?  2  0  77 TABLE 5b MINERAL  pumpellyite: prehnite:  C a M g A l 0 COHl C S i 0 ) ( S i 0 ) • 2H 0; 4  5  3  2  7  2  4  2  2  C a ^ l ^ i - j O . ^ (OHl ; 2  grossular :  i  C a ^ A ^ (SL^O^l  clinozoisite: amesite:  COMPOSITIONS  Ca^-L^Si-jO.^  '>  Mg^Al^Si-jO^g (OH) g;  clinochlore: serpentine: laumonite: heulandite: glaucophane:  Mg Al Si O 5  2  3  1 0  COH) ; g  Mg^-SiO.^ (OH) g; CaAl Si 0 2  4  1 2  *  CaAl Si 0 » 2  7  1 8  4H 0; 2  6H 0; 2  Na Mg Al Sig0 2  3  2  2 2  (OH) ; 2  +2 +3 r i e b e c k i t e : Na Fe^ F e S i g 0 (OH) ; +2 ferroglaucophane: NaFe^ A l S i g 0 (OH) j 2  2  2 2  2  2  2 2  2  78 (c)  Eclogite (xi) garnet + omphacite (xii)  glph + lws + sph + s t i l p ( r e t r o g r a d e ) .  Metamorphic R e a c t i o n s M i n e r a l chemistry i s g i v e n i n Appendix I I and  bulk  rock chemistry i n Appendix I I I .  Metabasic Prior r o c k s was  rocks  t o metamorphism, the mineralogy  of the  metabasic  augite + plagioclase + ilmenite ± o l i v i n e .  These  m i n e r a l s are metastable under low grade metamorphic c o n d i t i o n s i n the presence a catalytic  of water.  effect  I n t r o d u c t i o n of H^O  on t h e i r breakdown.  may  Reactions  have had illustrat-  ing breakdown o f primary m i n e r a l s are i l l u s t r a t e d i n Table Chlorite,  a l b i t e , c a l c i t e and  sphene were probably the most  important breakdown p r o d u c t s , w i t h p r e h n i t e and h e u l a n d i t e and  the  zeolites  laumontite as p o s s i b l e a d d i t i o n a l phases.  P r o g r e s s i v e depth  zonation i n v o l v i n g such m i n e r a l s has been  demonstrated by Coombs (1961) and J o l l y and Smith i s suggested  t h a t the P i n c h i greenstones may  (1972).  The greenstones  of P i n c h i Mountain are c h a r a c t e r i z e d  by the absence of c a l c i t e , z e o l i t e s  and p r e h n i t e and  the  of a r a g o n i t e , p u m p e l l y i t e and s o d i c pyroxene.  Glaucophane and  It  a l s o have passed  through t h i s stage d u r i n g b u r i a l .  presence  5.  lawsonite are p r e s e n t as minor c o n s t i t u e n t s  i n two samples. c a l c i t e present stones.  Aragonite  presumably r e c r y s t a l l i z e d  i n amygdules, v e i n s o r interbedded  Pumpellyite  formation  i s problematical.  from  limeCoombs  (1961) c o n s i d e r s t h a t r e a c t i o n 7 (Table 5) i s a p p l i c a b l e and  H i n r i c h s e n and Schurmann  (1972) e x p e r i m e n t a l l y  gated breakdown o f p u m p e l l y i t e  i n r e a c t i o n 8.  investi-  The absence  o f - t h e z e o l i t e s laiimontite and h e u l a n d i t e can be e x p l a i n e d by r e a c t i o n s 9 and 10. Sodic pyroxene may have formed as the r e s u l t o f two processes.  Firstly,  r e l i c t a u g i t e may have taken p a r t  i n a c a t i o n exchange r e a c t i o n w i t h the f l u i d ( r e a c t i o n 11). analyses  phase  E p i t a x i a l s o d i c pyroxenes a r e common and  (p. 2 06)  show them t o be poorer  i n Ca and Mg and  r i c h e r i n Na, A l and Fe w i t h r e s p e c t t o r e l i c t a u g i t e s . Secondly, K e r r i c k  (1971) proposed r e a c t i o n 12 as being o f  importance i n the formation  o f the a c m i t i c component  i n j a d e i t i c pyroxene i n metagreywackes.  In the P i n c h i  r o c k s , i r o n oxides would have been a v a i l a b l e on the breakdown o f i l m e n i t e a t low temperatures.  On d e p l e t i o n of i r o n  o x i d e s , a l b i t e may c o e x i s t w i t h s o d i c pyroxene, a compatab i l i t y o f t e n observed. together likely  Hematite and a l b i t e were n o t found  i n any specimen.  take  -  pumpellyite.,  The r e s i d u a l A ^ O ^ and Si02 most  p a r t i n r e a c t i o n s forming  c h l o r i t e or  The assemblage s o d i c pyroxene + c h l o r i t e +  sphene + q u a r t z ± a r a g o n i t e , p r e s e n t  i n a few r o c k s ,  80 presumably r e f l e c t s r e a c t i o n 12 having gone to  completion  because of s u i t a b l e c o m p o s i t i o n a l  /_ 2  requirements,  or  u  kinetics.  There i s no evidence  to suggest t h a t the absence  of alb'ite i s because of higher p r e s s u r e c o n d i t i o n s . The  lawsonite-glaucophane b e a r i n g r o c k s  probably  developed by r e c o n s t i t u t i o n of the assemblages p r e s e n t i n the P i n c h i Mountain Greenstones.  These b l u e s c h i s t s are  d i s t i n g u i s h e d by the absence of p u m p e l l y i t e , a l b i t e and  c e l a d o n i t e and  glaucophane, lawsonite phengite  glaucophane and Appendix I I .  the presence of widespread  and  and d e e r i t e may  jadeite-acmite.  a l s o be p r e s e n t .  c h l o r i t e compositions  Two  prehnite,  Stilpnomelane, Pyroxene,  are given i n  main assemblages are commonly  w i t h i n the matabasic rocks and  recognized  are c h a r a c t e r i z e d by  presence of a c m i t e - j a d e i t e or glaucophane.  the  Textural  r e l a t i o n s h i p s i n d i c a t e t h a t the g l a u c o p h a n i t i c assemblages formed l a t e r .  Therefore,  i t appears t h a t greenstones  r e a c t e d to form a c m i t e - j a d e i t e assemblages which i n t u r n r e a c t e d to g i v e g l a u c o p h a n i t i c assemblages  (Table 4 ) .  The main m i n e r a l s w i t h i n a c m i t e - j a d e i t e metabasalts are l a w s o n i t e , c h l o r i t e , a c m i t e - j a d e i t e and Lawsonite formation  (Table 5, r e a c t i o n 15)  w i t h i n a l b i t e pseudomorphs. down of a l b i t e , Ca entered nucleated.  sphene. commonly  occurs  I t appears t h a t on the breakthe pseudomorphs and  lawsonite  The c a l c i u m o r i g i n a t e d from the breakdown of  r e l i c t augite  (Reaction 11), p u m p e l l y i t e  or p r e h n i t e .  81  The presence of white mica and c h l o r i t e i n pseudomorphs associated with lawsonite, potassium, magnesium and  suggests inward d i f f u s i o n of  i r o n i n a d d i t i o n to c a l c i u m .  The  j a d e i t e - a c m i t e component i n the pyroxene p r o g r e s s i v e l y i n c r e a s e d as a r e s u l t of r e a c t i o n s 11 and previously).  Reaction  13 may  there i s l i t t l e evidence c h l o r i t e analyses.  12  (described  have been of importance but  to support  i t from the a v a i l a b l e  The absence of c e l a d o n i t e as a  separate  phase can be accounted f o r by i n c r e a s e i n extent o f s o l u t i o n i n phengite  (see p.  solid  90 ).  G l a u c o p h a n i t i c rocks appear to have formed from a c m i t e - j a d e i t e assemblages. the common occurrence  Evidence f o r t h i s i s seen i n  of glaucophane v e i n s which c r o s s -  c u t a c m i t e - j a d e i t e bearing assemblages.  Many rocks show  t r a n s i t i o n a l c h a r a c t e r i s t i c s and c o n t a i n glaucophane acmite-jadeite.  In such r o c k s , glaucophane commonly rims  or c r o s s - c u t s a c m i t e - j a d e i t e p o r p h y r o b l a s t s . of bulk compositions  (Table 16a)  Inspection  r e v e a l s o n l y minor  d i f f e r e n c e s between a c m i t e - j a d e i t e and glaucophane and  and  rocks  i t i s suggested t h a t g l a u c o p h a n i t i c assemblages were  formed from a c m i t e - j a d e i t e assemblages as a r e s u l t o f a r e a c t i o n s i m i l a r to no.  16  (Table 5 ) .  Glaucophane  a l s o have been produced by r e a c t i o n of a l b i t e and T h i s r e a c t i o n (17) can be combined w i t h no. crossite.  may chlorite.  16 to g i v e  82  I t i s g e n e r a l l y c o n s i d e r e d t h a t the p r e h n i t e p u m p e l l y i t e and b l u e s c h i s t f a c i e s pass i n t o the s c h i s t f a c i e s w i t h i n c r e a s e i n temperature.  green-  Associated  w i t h t h i s t r a n s i t i o n i s the breakdown of such m i n e r a l s as p r e h n i t e , p u m p e l l y i t e and l a w s o n i t e and the growth of e p i d o t e and  (Table 5 ) .  tremolite-actinolite  The absence of  l a s t mentioned m i n e r a l s a t P i n c h i puts a somewhat d e f i n e d upper l i m i t on the temperature  these  ill-  of metamorphic  recrystallization. The occurrence of e c l o g i t e boulders i n the P i n c h i area might suggest, as i l l u s t r a t e d i n Table 4 ,  t h a t they  are the product of the next stage i n the metamorphism of the metabasic  rocks.  Presumably, the c r i t i c a l  reaction  must be of the type: lws + acm-jd + g l p h + sph + c h l = omphacite + garnet + rutile +  H0 2  Being a d e h y d r a t i o n r e a c t i o n , i t would be favoured by i n c r e a s e i n temperature  as u n i v a r i a n t curves f o r such r e a c t i o n s have  steep s l o p e s on the p e t r o g e n e t i c g r i d . to Morgan  (197 0) e c l o g i t e s may  b a s a l t s without the involvement  However, a c c o r d i n g  form d i r e c t l y from d r y of ^ 0 .  W i t h i n the  eclogite,  garnet and omphacite are r e p l a c e d by glaucophane, l a w s o n i t e , sphene and  stilpnomelane.  I t i s suggested  that t h i s  o c c u r r e d d u r i n g r e t r o g r e s s i v e metamorphism a s s o c i a t e d w i t h decrease i n temperature  and p r e s s u r e , r e v e r s a l o f the above  83 r e a c t i o n and r e - e n t r y i n t o the glaucophane-lawsonite  facies.  Metasediments Assemblages i n metasedimentary r o c k s a r e g i v e n i n Tables 24 and 25.  L i t t l e can be s a i d about  metamorphic r e a c t i o n s as the mineralogy  prograde  o f lower grade r o c k s  i s n o t known w i t h c e r t a i n t y . W i t h i n metacherts, with F e - r i c h cores Al  glaucophane c r y s t a l s may be zoned  ( c r o s s i t e ) and margins  show an a n t i p a t h e t i c v a r i a t i o n .  ( F i g . 26). Mg and  In the sample s t u d i e d  (No. 151) glaucophane c o - e x i s t s w i t h q u a r t z , l a w s o n i t e , p h e n g i t e , carbonaceous m a t e r i a l and magnetite. microprobe  a n a l y s e s o f phengites  Partial  (Table 13) i n d i c a t e t h a t  they are c o m p o s i t i o n a l l y homogeneous and presumably have e q u i l i b r a t e d w i t h the F e - r i c h rims of glaucophane c r y s t a l s . T h i s zoning c o u l d be a r e s u l t o f the changing of  composition  the f l u i d phase d u r i n g metamorphism but the presence o f  carbonaceous m a t e r i a l , lawsonite and magnetite narrow range of f l u i d composition  (see  defines a  p. 104)•  A  second  a l t e r n a t i v e i s t h a t the zoning i n the glaucophane r e f l e c t s the changing  composition o f the c o - e x i s t i n g phengite  i n c r e a s e and decrease i n p r e s s u r e .  with  A c c o r d i n g t o Velde  (1965) there i s evidence t h a t i n c r e a s e i n p r e s s u r e f a v o u r s s o l i d s o l u t i o n between muscovite c e l a d o n i t e end-members.  and v a r i o u s  The e f f e c t of p r e s s u r e on the  84  extent of phengite  solid  s o l u t i o n w i t h Mg-Al c e l a d o n i t e  ( F i g . 8c) i s p a r t i c u l a r l y n o t a b l e b u t i s a l s o a p p r e c i a b l e +3 w i t h Mg-Fe  celadonites.  I t i s suggested  t h a t an F e - r i c h  p h e n g i t e may c o e x i s t w i t h g l a u c o p h a n e a t h i g h  pressures.  Decrease i n pressure would r e s u l t i n i n s t a b i l i t y of the Fe-phengite + crossite.  and r e a c t i o n w i t h glaucophane t o g i v e This suggests  phengite  that the c r o s s i t e cores,  t o glaucophane, c r y s t a l l i z e d d u r i n g an e p i s o d e  zoned  of i n c r e a s i n g  p r e s s u r e and t h a t t h e narrow c r o s s i t e r i m s formed d u r i n g a r e t r o g r e s s i v e phase o f metamorphism a s s o c i a t e d w i t h decrease  i n pressure.  An a l t e r n a t i v e e x p l a n a t i o n o f t h e  z o n i n g c o u l d be s o u g h t i n R a l e i g h f r a c t i o n a t i o n growth a t c o n s t a n t P and T ( H o l l i s t e r , does n o t e x p l a i n t h e F e - r i c h r i m s  1966).  during However,  this  i n the glaucophane  crystals. Relevant  Phase  Aragonite  Equilibria stability  For the c a l c i t e - a r a g o n i t e t r a n s i t i o n ,  the experimental  r e s u l t s o f B o e t t c h e r a n d W y l l i e (1968) a n d C r a w f o r d Fyfe  (1964) a r e shown i n F i g u r e 8a.  by C r a w f o r d by B o e t t c h e r The  and  R e v e r s a l s were o b t a i n e d  a n d F y f e b e t w e e n 4.2 a n d 4.5 k b a t 100°C a n d a n d W y l l i e b e t w e e n 7.8 a n d 8.6 k b a t 400°C.  common o c c u r r e n c e  i n nature of aragonite  co-existing  T° C F i g s . 8 a to 8 f ! Experimentally determined phene e q u i l i b r i a r e l e v a n t to the formation of minerals In P i n c h i rocke. Where H-0 Is Involved l n the r e a c t i o n P f i u i d « P t o t a l *  86  F I G. 8 ( c o n t . )  1 - 8  -6  -4  -2  0  Fig. 8g P-X diagram illustrating effect of solid solution ln lowering the pressure of formation of jadeltio pyroxene from albite. The experimental results of Newton and Smith ln the system NaAlSioOg-KaFeSi at 600°C are Indicated by a solid line. Calculated equilibrium curves for different temperatures and values of K = are Indicated by dashed lines (see also Appendix VII). Values of for each of the analysed pyroxenes (Fig. 27b) are also shown.  87 with d e f i n i t i v e high pressure minerals  such as  pyroxene s u b s t a n t i a t e s the experimental However, a number o f a u t h o r s or  i m p l i e d the  at pressures  "metastable"  significantly  transitions.  Newton et  al. ,  have g i v e n e v i d e n c e  than  of  from s t r a i n e d  t h a t g i v e n by  below the  field  calcite  and  Fyfe  several kilobars  g i v e n by p r e v i o u s  authors.  (1968) showed t h a t a h i g h Mg  i n aqueous s o l u t i o n s i n h i b i t e d within  the  calcite  i n metastable  stability  the o c c u r r e n c e metabasic pressure 1.3  kb  field.  not  of a r a g o n i t e  r o c k s and  than  temperatures  of  inhibited.  i f the Vance  formation (1968)  suggested  on  exceed  3 kb.  aragonite occurs  Firstly,  and  in several different  i t i s t h e common CaCO^ p o l y m o r p h  jadeitic  aragonite co-exists with  the greenstone  s o d i c p y r o x e n e + sphene + c h l o r i t e s o d i c p y r o x e n e and  differentiates  at  100°C.  metagreywackes.  of  the  This i s  t r a n s i t i o n pressure  metabasic  presence  noted  g e o l o g i c grounds t h a t  lawsonite-glaucophane  +  nuclei  result  within dolomitic limestones, rocks  ratio  i n prehnite-pumpellyite.bearing  the accepted  At Pinchi, associations.  /H  This could  d u r i n g metamorphism d i d n o t  less  +  the growth o f c a l c i t e  p r e c i p i t a t i o n of aragonite  o f a r a g o n i t e n u c l e i i was  accepted  the  2+ Bischoff  for,  aragonite  (1969) d e m o n s t r a t e d  growth o f a r a g o n i t e stability  results.  crystallization lower  jadeitic  bearing  Secondly,  assemblage  albite  ± pumpellyite.  the absence of  The  prehnite  the P i n c h i assemblages from those  described  88  by Vance  (1968) i n the San Juan I s l a n d s .  occurrence  of a r a g o n i t e was  (?) limestones location).  of u n i t s 1 and  noted w i t h i n Upper  south of P i n c h i Lake  T h i s was  T h i r d l y , an  (see  Triassic  F i g . 28 f o r  the only occurrence  discovered  outside  2 ( F i g . 3) .  Greenstones a t the west end of Murray Ridge c o n t a i n c a l c i t e c o e x i s t i n g w i t h p r e h n i t e and p u m p e l l y i t e .  There  are no i n d i c a t i o n s t h a t the c a l c i t e has formed by i n v e r s i o n from a r a g o n i t e and  i t i s i n f e r r e d t h a t c a l c i t e was  s t a b l e polymorph d u r i n g metamorphism.  the  I t i s perhaps s i g -  n i f i c a n t t h a t t h i s i s the o n l y r e g i o n where p r e h n i t e  occurs  i n greenstones. Despite it  i s concluded  the p o s s i b i l i t y of metastable c r y s t a l l i z a t i o n , from t h i s evidence  a t P i n c h i Lake t h a t the  a r a g o n i t e - c a l c i t e t r a n s i t i o n i s a v a l i d geobarometer. means t h a t the d o l o m i t i c limestones, metagreywackes, glaucophane metavolcanics  This lawsonite-  and most of the greenstones  c r y s t a l l i z e d a t p r e s s u r e s above the t r a n s i t i o n .  The  prehnite-  c a l c i t e b e a r i n g greenstones formed a t lower p r e s s u r e s . presence of a r a g o n i t e i n the Upper T r i a s s i c is problematical. and  There i s no evidence  (?)  The  limestones  f o r deep b u r i a l  the p r e s e r v a t i o n of d e t r i t a l a r a g o n i t e seems u n l i k e l y .  89  J a d e i t e and a c m i t e - j a d e i t e s t a b i l i t y The e q u i l i b r i u m curve f o r the r e a c t i o n a l b i t e = j a d e i t e + q u a r t z a c c o r d i n g to Newton and g i v e n i n F i g . 8b.  T h i s curve was  of B i r c h and LeComte  Smith  (1967) i s  used r a t h e r than t h a t  (1960) as i t takes i n t o account  entropy change of d i s o r d e r i n g of a l b i t e .  the  A l s o shown on  F i g . 8b are v a l u e s of the e q u i l i b r i u m c o n s t a n t f o r the r e a c t i o n p l a g i o c l a s e = j a d e i t i c pyroxene + q u a r t z . t h i s case, K = X ? ^ / x j ^ ^  In  assuming u n i t a c t i v i t i e s f o r  pure phases and mole f r a c t i o n  (X)  = activity.  I f the  p l a g i o c l a s e i s pure a l b i t e , the v a l u e s of K correspond t o mole f r a c t i o n of j a d e i t e i n c l i n o p y r o x e n e . c a l c u l a t i o n see Appendix V I I .  For d e t a i l s of  Newton and Smith  also  i n v e s t i g a t e d the e f f e c t of Fe i n the system u s i n g s y n t h e t i c g l a s s e s w i t h or without m i n e r a l seeds.  They concluded  t h a t the presence of 10 mole per c e n t acmite has a t the most a few hundred bars e f f e c t on the s t a b i l i t y o f j a d e i t e w i t h quartz  ( F i g . 8g).  Using 40 mole per c e n t acmite, the  p r e s s u r e of the a l b i t e breakdown curve i s lowered by kb a t 600°C.  The c a l c u l a t e d p r e s s u r e s f o r the  1.6  transition  f o r d i f f e r e n t v a l u e s of Xtj^ are compatible w i t h Newton and Smith's experimental r e s u l t s a t 6 00°C. Microprobe a n a l y s e s of pyroxenes area are g i v e n i n Table 10 and Two  groups of pyroxenes  from the P i n c h i  i l l u s t r a t e d i n F i g . 27.  were noted; a c m i t e - j a d e i t e s from  90  m e t a v o l c a n i c s and j a d e i t i c pyroxenes from metagreywackes. Both a r e c o n s i d e r e d t o have formed under s i m i l a r P-T c o n d i t i o n s and the c o m p o s i t i o n a l d i f f e r e n c e i s a s s i g n e d to the c o n t r a s t i n b u l k composition. of c r y s t a l l i z a t i o n  The minimum p r e s s u r e  o f the j a d e i t i c pyroxene  (coexisting  w i t h quartz) can be o b t a i n e d from the c a l c u l a t e d  stability  curves f o r d i f f e r e n t v a l u e s o f the e q u i l i b r i u m c o n s t a n t ( F i g . 8g) .  F o r the pyroxene  J (  ^78  A c  ii ^ii D  ( - ^) , No  7  K = 0.78 and the minimum p r e s s u r e of c r y s t a l l i z a t i o n i s 9.5 kb a t 300°C and 7.6 kb a t 200°C. approximately  8 00 and 60 0 bars below the s t a b i l i t y o f pure  jadeite with quartz. of  These v a l u e s l i e  The minimum p r e s s u r e s f o r f o r m a t i o n  the a c m i t e - j a d e i t e pyroxenes are below those f o r  j a d e i t i c pyroxenes and can be o b t a i n e d from F i g . 8 g -  Phengite Velde  stability (1965) c a r r i e d o u t a study o f the s t a b i l i t y o f  p h e n g i t i c micas.  H i s r e s u l t s show t h a t the e x t e n t o f s o l i d  s o l u t i o n i s dependent on p r e s s u r e , temperature of  the c e l a d o n i t e end-member..  and composition  Increase i n s o l i d  solution  i s favoured by h i g h p r e s s u r e s , low temperatures  and i n v o l v e -  ment o f the Mg-Al c e l a d o n i t e end-member.  end-members  Other  show a l e s s pronounced i n c r e a s e i n s o l i d s o l u t i o n w i t h h i g h pressures. for  F i g u r e 8c i n d i c a t e s the e q u i l i b r i u m boundary  the reaction M u s c C e l ^ 7 n  n  going t o muscovite,  biotite,  91  K - f e l d s p a r , q u a r t z and f l u i d as g i v e n by V e l d e . rium r e f e r s to the The approximate  KAlMgSi^O^Q(OH)^ c e l a d o n i t e end-member.  o b t a i n e d from g r a p h i c a l e x t r a p o l a t i o n of  results.  Stability  of s o d i c  amphiboles  Experimental work on the s t a b i l i t y of and r i e b e c k i t e  (Ernst, 1961,  s o d i c amphiboles  1962)  crystallization  and  (197 2)  glaucophane  demonstrates  have broad s t a b i l i t y f i e l d s and  do not impose r e s t r i c t i o n s on the P-T  Hoffman  equilib-  p o s i t i o n of the Musc^gCel^g boundary shown  on the f i g u r e was Velde's  The  s y n t h e t i c ferroglaucophane  t h a t they  c o n d i t i o n s of  of b l u e s c h i s t f a c i e s m i n e r a l s . has determined  t h a t these  More r e c e n t l y ,  the s t a b i l i t y of n a t u r a l ( F i g . 8d).  The breakdown  curve has a steep s l o p e and i s l i t t l e a f f e c t e d by change of oxygen b u f f e r .  Thus ferroglaucophane, when  c o u l d r e s t r i c t metamorphic temperatures 360°C.  The T-log f  Q  identified,  t o l e s s than  s t a b i l i t y f i e l d s of s o d i c  amphiboles  w i l l be d i s c u s s e d i n the s e c t i o n on f l u i d phase c h e m i s t r y .  Lawsonite  stability  The breakdown c u r v e f o r l a w s o n i t e was by Newton and Kennedy  (1963) and i s shown i n F i g . 8e.  g i v e s a maximum temperature at a given pressure.  investigated This  f o r the s t a b i l i t y of l a w s o n i t e  In nature, coupled r e a c t i o n s w i t h  92 m i n e r a l s such as c h l o r i t e w i l l d o u b t l e s s s h i f t to  lower  temperatures.  2  (1968).  curve  Phase r e l a t i o n s f o r the r e a c t i o n :  laumontite = l a w s o n i t e + q u a r t z + H 0 s e p a r a t e l y by L i o u  the  (.1971) , Thompson  have been  determined  (1970) and N i t s c h  The u n i v a r i a n t curves f o r the r e a c t i o n are f a i r l y  compatable and suggest t h a t l a w s o n i t e i s u n s t a b l e a t p r e s s u r e s l e s s than 2.5 the presence for  kb a t 200°C and  of q u a r t z and water.  3 kb a t 300°C i n  The e q u i l i b r i u m curve  the r e a c t i o n : h e u l a n d i t e = lawsonite + quartz + f l u i d  a c c o r d i n g to N i t s c h (1968) i s a l s o g i v e n on F i g . 8e.  P u m p e l l y i t e and p r e h n i t e H i n r i c h s e n and for  stability  Schurmann  (1972) d e f i n e d the  curve  the breakdown of F e - f r e e p u m p e l l y i t e shown i n F i g u r e 8 f .  During t h e i r experiments,  they n o t i c e d t h a t , w i t h the  i n c l u s i o n of i r o n i n the system, r e a c t i o n r a t e s were i n c r e a s e d and e q u i l i b r i u m curves s h i f t e d towards temperatures. of  The p l e o c h r o i s m  scheme and e x t i n c t i o n  P i n c h i p u m p e l l y i t e s shows them to be i r o n  t h e r e f o r e a t 5 kb  temperatures  have been l e s s than 315°C.  lower  bearing,and  i n the greenstones  Reaction 20  the breakdown of p r e h n i t e i n the presence  angle  must  ( F i g . 8f) d e f i n e s of c h l i n o c h l o r e  and q u a r t z to g i v e c l i n o z o i s i t e , s e r p e n t i n e and water. T h i s experimental d e t e r m i n a t i o n was t h a t t h e r e was  not w e l l d e f i n e d i n  some doubt about the compositions  of  the  93 c h l o r i t e s i n v o l v e d , b u t i t does y i e l d a maximum temperature of 285°C a t 5 kb f o r the metamorphism o f the p r e h n i t e b e a r i n g greenstones a t the west end o f Murray  Eclogite  Ridge.  stability  E x t r a p o l a t i o n s o f the garnet g r a n u l i t e - e c l o g i t e t r a n s i t i o n to temperatures below 800°C have been made by Green and Ringwood  (1967) and I t o and Kennedy  are shown on F i g . 9b.  (1971) and  N e i t h e r o f these e x t r a p o l a t i o n s  have a sound t h e o r e t i c a l b a s i s and t h e l a r g e d i f f e r e n c e i n pressure between the two may be e n t i r e l y caused by d i f f e r i n g b u l k compositions. assemblages  Green and Ringwood s t u d i e d m i n e r a l  i n b a s a l t s a t p r e s s u r e s from 1 t o 30 kb and a t  temperatures above 1000°C.  The l i n e a r e x t r a p o l a t i o n o f  t h e i r experimental data on the disappearance o f p l a g i o c l a s e i n t e r s e c t s the 5 00°C i s o t h e r m a t p r e s s u r e s of 5 t o 8 kb and the temperature a x i s a t around pressure.  200°C a t atmospheric  T h i s i m p l i e s the s t a b i l i t y o f e c l o g i t e i n a  wide range o f g e o l o g i c a l c o n d i t i o n s .  The r e c r y s t a l l i z a t i o n  of a t h o l e i i t i c b a s a l t t o g a r n e t g r a n u l i t e and to e c l o g i t e was  e x p e r i m e n t a l l y i n v e s t i g a t e d by I t o and Kennedy  a t temperatures between 8 00° and 12 00°C.  (1971)  The e x t r a p o l a t i o n  of t h e i r e c l o g i t e / p l a g i o c l a s e e c l o g i t e t r a n s i t i o n curve to lower temperatures l i e s 400 bars below the a l b i t e / j a d e i t e + q u a r t z boundary  as determined by Newton and Smith  94 (1966) .  A t 500°C, t h i s y i e l d s a p r e s s u r e of 14 kb f o r  disappearance of p l a g i o c l a s e , 6 to 9 kb h i g h e r than equivalent  r e a c t i o n i n Green and  the  Ringwood's experiments.  There i s some evidence t h a t the e x t r a p o l a t i o n Green and  the  Ringwood l i e s a t too low  a pressure.  An  of  analysed  TOX  omphacitic pyroxene from a P i n c h i e c l o g i t e has On F i g . 8b, 9.1  0.26.  t h i s g i v e s a minimum p r e s s u r e of formation of  kb a t 5 00°C which i s 1.1  Green and  Xtj^ =  Ringwood.  kb above the e x t r a p o l a t i o n  Because of t h i s f a c t and  of  compatability  w i t h the commonly accepted high pressure o r i g i n of e c l o g i t e s the data o f I t o and Oxygen  and  Coleman  formation of g l a u c o p h a n i t i c  0  (1968) o b t a i n e d temperatures of r o c k s from Cazadero  using  16 /0  f r a c t i o n a t i o n between c o e x i s t i n g m i n e r a l s .  conclude t h a t in s i t u and  preferred.  isotopes  Taylor  18  Kennedy are  Lee,  1963)  Type I I and  III blueschists  Mineral  (Coleman  form a t temperatures of 200° to 325°C, where-  as higher grade b l u e s c h i s t s from New tectonic blocks  They  C a l e d o n i a and  Type IV  from C a l i f o r n i a form a t 400° t o 550°C.  assemblages a t P i n c h i are s i m i l a r to those of  Cazadero Type I I and  I I I b l u e s c h i s t s and  formed a t s i m i l a r temperatures.  The  therefore  glaucophane  possibly bearing  e c l o g i t e b o u l d e r s a t P i n c h i c o n t a i n a s i m i l a r mineralogy to Type IV b l u e s c h i s t s and and  500°C.  p o s s i b l y formed between 400°  95 ,  ,  ,  FIG. 9 a  ,  1  1  1  (  1  !  1  1  1  P-T CONDITIONS OF METAMORPHISM  1  1  1  1  TEMPERATURE, °C  r-  FIG. 9b  T  1  1  «  •  1  i  1  1  P-T CONDITIONS OF METAMORPHISM OF BLUESCHIST AND  T°C  1  OF GREENSTONES .  96 Pressure-temperature  G o n d i t i o n s of Metamorphism  C o n s t r a i n t s on the P-T  c o n d i t i o n s of metamorphism  are given by phase e q u i l i b r i u m s t u d i e s and oxygen i s o t o p e geothermometry.  These are c o n s i s t e n t w i t h a minimum  geothermal g r a d i e n t of 6°C/km.  I n f e r r e d metamorphic  c o n d i t i o n s f o r the v a r i o u s fault-bounded illustrated (Fig. and  i n F i g s . 9a and  9b.  blocks  are  For the P i n c h i Greenstones  9a), the h i g h temperature l i m i t i s somewhat a r b i t r a r y  i s based on the s t a b i l i t y of F e - f r e e p u m p e l l y i t e  by H i n r i c h s e n and  Schurmann  (1972).  Fe-pumpellyite  given would  l i m i t the f i e l d even more but the s h i f t i n the e q u i l i b r i u m boundary towards lower temperatures i s not known. Estimated  P-T  c o n d i t i o n s are as f o l l o w s :  Murray Ridge greenstones P i n c h i Mountain Greenstones Blueschists Eclogite  > 12-15  >  Phase  kb  100-225°C  4.5-9  kb  100-250°C  8-12  > 9 kb  Fluid  3-6  kb  kb..  (Ito & Kennedy,  225-325°C 1971)  (from X?* a t 5 00°C)  3-6  kb  (Green & Ringwood,  1967)  Composition  The presence of l a w s o n i t e , quartz and assemblage s e v e r e l y l i m i t s fluid.  400-550°C  Experimental  the C 0  2  sphene i n an  content of the c o e x i s t i n g  s t u d i e s by N i t s c h  (1972) demonstrate  97 F i g . 10a P +  E  CO 2  P-T diagram i l l u s t r a t i n g p r e s s u r e of C 0  (.i.e.  2  ) i n e q u i l i b r i u m w i t h the r e a c t i o n : c a l c i t e + q u a r t z  r u t i l e + sphene + C 0  2  ( a f t e r E r n s t , 1971).  Estimated  P-T c o n d i t i o n s f o r f o r m a t i o n of P i n c h i b l u e s c h i s t s a r e a l s o shown. F i g . 10b  T-X^Q  diagram i l l u s t r a t i n g phase e q u i l i b r i a a t  4 kb and 7 kb i n the system C a 0 - A l 0 - S i 0 - H 0 - C 0 2  3  2  2  (after  2  N i t s c h , 1972) . py = p y r o p h y l l i t e ; zo = z o i s i t e ; lws = l a w s o n i t e ; cc = c a l c i te; qtz = quartz. F i g . 10c  diagram i l l u s t r a t i n g v a r i a t i o n i n p a r t i a l p r e s s u r e  of gaseous s p e c i e s a t 3 27°C and P g in f^ .  a s  = 10 kb w i t h change  The estimated oxygen f u g a c i t y w i t h i n l a w s o n i t e -  quartz-magnetite-carbonaceous  c h e r t s i s i n d i c a t e d by the  shaded a r e a . S e l e c t e d v a l u e s o f n c o 2 ^ C 0 H20^ -"shown. Assuming i d e a l behaviour of gaseous phases, l a w s o n i t e n  +  n  a  r  e  a  so  2  + q u a r t z i s s t a b l e a t v a l u e s of n_-- / (n^^ +n„ ,_) l e s s *-02 "-2, .05 ( F i g . 10b) i n the s t a b i l i t y f i e l d o f f a y a l i t e .  than  Dis-  placement o f s t a b i l i t y f i e l d o f l a w s o n i t e + q u a r t z to v a l u e s of £Q  above the q u a r t z - f a y a l i t e - m a g n e t i t e b u f f e r i s  a t t r i b u t e d to n o n - i d e a l behaviour lOd T - l o g f g  of gaseous s p e c i e s . F i g .  diagram i l l u s t r a t i n g experimental and c a l c u -  l a t e d phase e q u i l i b r i a i n v o l v i n g r i e b e c k i t e and f e r r o g l a u cophane  ( a f t e r E r n s t , 1962; Hoffman, 1972).  hem = hematite; q t z = q u a r t z ; mt = magnetite;  acm = acmite;  fay = f a y a l i t e ; f e g l = ferroglaucophane; a l b = a l b i t e ; arfved = arfvedsonite s o l i d  solution.  (b) System  CoO-AlgOj-SiC^-Hp-COg  400r  Lws + Qtz TC  300r  experimentally determined  \ y' 200\  schematic metastable extension  after Nitsch (1972) •01  •02 X C0„  •03  •04  99  100 t h a t l a w s o n i t e and q u a r t z can c o e x i s t w i t h a f l u i d o n l y i f n ^ <-/(n„ <+ n„ -») does n o t exceed cc^*' '"2 ( F i g . 10b).  C a l c u l a t i o n s by Thompson  conclusion.  S c h u i l i n g and Vink  e q u i l i b r i u m f o r the r e a c t i o n : sphene + CC^.  0.03 ± 0.02 a t 4 kb (1971) support  this  (1967) determined the c a l c i t e + quartz + r u t i l e =  The u n i v a r i a n t curve demonstrated t h a t  sphene f o r m a t i o n can o n l y take p l a c e a t extremely low P  (e.g. l e s s than 35 bars a t 300°C w i t h P  C Q  =  t o t a l  )  p c  o  2  2  otherwise, the assemblage c a l c i t e + quartz + r u t i l e would occur.  Using t h i s curve and a d d i t i o n a l  thermochemical  d a t a , E r n s t (1972) made a s e m i q u a n t i t a t i v e estimate of the maximum p a r t i a l p r e s s u r e of C 0 i n . c o n d i t i o n s where P X  C 0  2  i n e q u i l i b r i u m w i t h sphene  < fT_ j_£ P  C Q  u;  ( F i g . 10a) .  Values f o r  were c a l c u l a t e d independently and suggested  that high  grade F r a n c i s c a n r o c k s e q u i l i b r a t e d w i t h a f l u i d phase i n which X Q C  was l e s s than 0.01.  T h i s compares f a v o u r a b l y  2  w i t h N i t s c h ' s experimental r e s u l t s f o r the s t a b i l i t y o f lawsonite + quartz.  From these data, i t i s concluded  that  f o r the P i n c h i r o c k s a t 7 kb, the assemblage l a w s o n i t e + quartz formed a t n  '/(n__ ^~^2  L.U2  + n„ „) < 0.02 ± 0.02. 2 —  b e a r i n g assemblages c r y s t a l l i z e d w i t h n 0.01  or with  P C 0  2  a  t  a  m  a  x  i  m  u  m  C Q  ^/(  n C  Q^  +  n  Sphene  H 0^ —  v a l u e of 1500 b a r s .  P h e n g i t i c mica c o e x i s t s w i t h l a w s o n i t e i n the P i n c h i metacherts.  Velde  (1965) and E r n s t (1963) suggest t h a t the  presence of phengite i s i n d i c a t i v e of metamorphism under s i g n i f i c a n t water p r e s s u r e s a l t h o u g h P j ^ o load*  P  n e e c  ^  n o  *-  e <  3  u a  l  101 Carbonaceous m a t e r i a l i s abundant i n s c h i s t s , metac h e r t s and massive limestones.  X-ray d i f f r a c t i o n  (Appendix  II) i n d i c a t e d the presence of n e a r l y amorphous g r a p h i t i c m a t e r i a l i n one  sample  c l a s s i f i c a t i o n , 1971)  (graphite-d^, according and  C a l c u l a t i o n s by French  to  Landis'  amorphous m a t e r i a l i n 4 o t h e r s .  (1966) i n the system C-H-0  are  s t r i c t l y a p p l i c a b l e o n l y to c r y s t a l l i n e g r a p h i t e and to amorphous carbonaceous m a t e r i a l .  They a l s o depend  the assumption of i d e a l behavior of the gaseous involved.  I t i s considered,  e q u i l i b r a t i o n has m a t e r i a l and  C-H-0  species  however, t h a t p a r t i a l  the f l u i d phase and  1) and  on  taken p l a c e between the carbonaceous  some a p p l i c a b i l i t y . Fig.  not  i s adapted from French  (1966,  g i v e s the f l u i d phase composition i n the  system  a t 327°C and  F i g . 10c  t h a t the c a l c u l a t i o n s have  10 kb, c o n d i t i o n s approximating those  of b l u e s c h i s t f a c i e s metamorphism. carbonaceous m a t e r i a l , lawsonite work of N i t s c h r e q u i r e s t h a t QQ^/ n  have exceeded 0.04 From t h i s and  a t 7 kb and  In rocks  and  quartz,  ^ H20 n  +  n  containing the  C02^  c  experimental o  u  l  c  ^  n  o  t  p o s s i b l y even l e s s a t 10  the r a t i o s of the p a r t i a l p r e s s u r e s  and  i l l u s t r a t e d i n F i g . 10c  the f  must have been l e s s than 10  kb.  of CO2  i t can be i n f e r r e d t h a t -33  n u  bars.  2 presence of magnetite + quartz i m p l i e s an f  Q  greater  However, the  i n g r a p h i t i c metacherts -33 than 10 bars. I t i s suggested  t h a t the e x c e s s i v e l y low values of f  i n f e r r e d from  n u  2  the  102 s t a b i l i t y o f l a w s o n i t e and g r a p h i t e i s brought about the assumption  by  of i d e a l i t y and t h a t a r e a s o n a b l e estimate  f o r the f _ i s between 10 °2  -33  and 10  -32  bars.  If this i s  the case, methane must have been a dominant c o n s t i t u e n t i n the f l u i d phase i n carbonaceous Ernst  rocks.  (1962) c o n s t r u c t e d a l o g  -T diagram  showing  the s t a b i l i t y f i e l d s of r i e b e c k i t e and acmite a t 2 kb (Fig. lOd).  The curve which d e f i n e s the r e a c t i o n acmite +  hematite + q u a r t z + f l u i d = r i e b e c k i t e + oxygen approximately p a r a l l e l s the a b s c i s s a a t temperatures  of 500°C.  p o s i t i o n of t h i s r e a c t i o n curve a t 10 kb can be determined  The approximately  by r e c a l c u l a t i n g the p o s i t i o n of the b u f f e r  curves and by g r a p h i c a l e x t r a p o l a t i o n of the e x p e r i m e n t a l data on a c m i t e / r i e b e c k i t e s t a b i l i t y to h i g h p r e s s u r e s .  At  500°C, the i n c r e a s e i n p r e s s u r e from 2 to 10 kb r a i s e s the -17 -15 equilibrium f from 10 to 10 b a r s . The e x t r a p o l a t i o n 2 Q  of the r e a c t i o n curve to lower temperatures,  applicable  to b l u e s c h i s t f a c i e s metamorphism, i s c r i t i c a l but n e i t h e r e x p e r i m e n t a l nor thermochemical suggested  data are a v a i l a b l e .  It is  t h a t the curve takes on a p o s i t i v e s l o p e w i t h  decrease i n temperature.  T h i s i s compatible w i t h the  steepening of the s o l i d phase oxygen b u f f e r curves w i t h decrease i n  temperature.  At 300°C and f  Q  of l e s s than 1 0 ~  3 kb, ferroglaucophane i s s t a b l e a t an 3 2  bars  (Hoffman, 1972).  An  extra-  103  p o l a t i o n s i m i l a r to t h a t c a r r i e d out i n the case of r i e b e c k i t e enables an approximation 10 kb  (Fig. lOd).  o f the s t a b i l i t y f i e l d  at  Presumably, s o d i c amphiboles of  inter-  mediate composition have breakdown curves on a l o g  -T 2  diagram between those of ferroglaucophane and Oxidation r a t i o s bulk analyses  riebeckite.  (Chinner, 1960), o b t a i n e d  (Table 16a)  should g i v e a crude measure of  the oxygen p r e s s u r e a t the p r e v a i l i n g p r e s s u r e temperature  from  and  (Miyashiro, 1964). W i t h i n the u n f o l i a t e d  m e t a v o l c a n i c s , o x i d a t i o n r a t i o s are commonly i n the range 40 to 5 5 .  Rocks w i t h a h i g h modal per c e n t of a c m i t e - j a d e i t e  y i e l d the h i g h e s t r a t i o s and presumably e q u i l i b r a t e d w i t h an o x i d i s i n g f l u i d phase.  F o l i a t e d g l a u c o p h a n i t i c meta-  v o l c a n i c s w i t h s i m i l a r b u l k composition have lower o x i d a t i o n (e.g. no. 5 5 ,  ratios  Table 16a)  and p r o b a b l y formed a t  lower  oxygen p r e s s u r e s . Opaque o x i d e s can g i v e c l u e s as to composition.  W i t h i n carbonaceous c h e r t s , magnetite c o e x i s t s  w i t h glaucophane,  T h i s l i m i t s the /_ u  -27 10  f l u i d phase  bars, a t 10 kb and  325°C.  to v a l u e s l e s s 2  I f the c o e x i s t i n g  carbon-  aceous m a t e r i a l behaved as g r a p h i t e , the -31  would be  reduced  325°C.  t o l e s s than 10  than  bars a t 10 kb and  Hematite i s a l s o found i n c h e r t s but i s b e l i e v e d to have formed d u r i n g r e t r o g r a d e metamorphism as i t commonly rims magnetite.  Opaque o x i d e s are r a r e i n metabasic  and where observed  are composite,  rocks  c o n s i s t i n g of p y r i t e  104  rimmed by magnetite and hematite i n t u r n  ( F i g . 30).  It is  u n c e r t a i n whether p y r i t e , magnetite or hematite was  stable  d u r i n g b l u e s c h i s t metamorphism. Two  phase f l u i d  i n c l u s i o n s a r e p r e s e n t i n metachert  samples and p r o v i d e evidence for. the presence of a phase d u r i n g metamorphism.  fluid  In g e n e r a l , they can be d i v i d e d  i n t o two groups; 20y i n c l u s i o n s c o n t a i n i n g 3y gas  bubbles  (Plate 6) and aggregates of s m a l l l y i n c l u s i o n s along p a r t l y healed f r a c t u r e s .  Roedder  (1968) c o n s i d e r s t h a t l a r g e  i n c l u s i o n s showing no r e l a t i o n s h i p to r e l i c t f r a c t u r e are  more l i k e l y  t h a t the f i r s t  to be primary.  zones  Therefore i t i s p o s s i b l e  type represent" primary syn-metamorphic  i n c l u s i o n s and the second type r e p r e s e n t secondary  inclusions.  F l u i d Phase Composition a t 10 kb and 327°C The f l u i d composition a t 327°C and c o n t r a s t i n g rock types, i s i l l u s t r a t e d  10 kb, w i t h i n  i n F i g . 11.  Water,  methane and carbon d i o x i d e are c o n s i d e r e d t o be the major components w i t h P„ _ + P_,„ + p__. = P.... . , = p, ,. * CH4 C0 fluid load  The  2  c a l c u l a t i o n s of French of  minor importance  (1966) suggest t h a t CO and H  a t the temperature  are  2  and p r e s s u r e of  b l u e s c h i s t formation. W i t h i n a c m i t e - j a d e i t e m e t a v o l c a n i c s , the presence of  l a w s o n i t e , q u a r t z and sphene r e q u i r e s t h a t the  (n„ A + ti2>-' of  ) be l e s s than 0.04  a t 10 kb.  The  n ^/ C Q  stability  a c m i t e - j a d e i t e suggests t h a t the c o e x i s t i n g f l u i d  was  105 Fig.  11  diagram i l l u s t r a t i n g  in Pinchi blueschists AC  Con t h e  graphite  compositions lawsonite,  at  f l u i d phase  10 kb and 3 2 7 ° C .  buffer),  matic  i n e q u i l i b r i u m w i t h carbonaceous  quartz  bars  and m a g n e t i t e b e t w e e n f  CC) as  obtained  from F i g .  phase e q u i l i b r i u m boundaries  C-O-H.  The i n f e r r e d  indicated  by  Fig.  T - l o g f.  12  (a)„ The  represents possible  -33 and 10  composition  stability  of  i n the  2  line  fluid  material, -32  =10  10c.  9 * CA)  Cb) D i a g r a m -  system  Ca-Al-Si-  lawsonite + quartz  is  shading.  in Pinchi rocks.  2  diagram i l l u s t r a t i n g  Explanation is  given  in  fluid text.  compositions  106 FIG. II  FLUID  PHASE  COMPOSITION  AT  10 KB a  327°C  HX> f > I O b a r s ( ? ) l o  0  massive metabasalt acm-jd + lws«sph+chl g l a u c o p h a n e veins transition foliated  metabasalt  glph+lws+sph*chl  c a r b o n a c e o u s cherts, schists  Fig. 12  Temp, range of blueschist metamorphism < •>  metamorphic conditions in metacherts 8 carbonaceous schists. -40 200  400 T C  600  107 r e l a t i v e l y oxidizing, possibly with  g r e a t e r than °2  10  -25  bars.  Methane i s i n c o m p a t i b l e w i t h j\_ g r e a t e r than °2  -30 10  bars and t h e r e f o r e i t appears  t h a t H^O  was  the main  the  fluid  component i n the f l u i d phase. In  the t e r n a r y system B^O  - CC>2 - CH^  composition i n e q u i l i b r i u m w i t h g r a p h i t e a t v a r y i n g /_ 2 u  l i e s on the g r a p h i t e b u f f e r curve AD.  I t was  inferred  e a r l i e r , that rocks containing c o e x i s t i n g lawsonite, quartz, carbonaceous i n the u  m a t e r i a l and magnetite may have c r y s t a l l i z e d —33 -32 range 10 to 10 bars ( i . e . j u s t above the  2  quartz-fayalite-magnetite buffer curve). case, f l u i d compositions J*  = 10~  0  3 2  bars  I f t h i s i s the  l i e on the curve AC.  ( i . e . point C), P  C Q  For  = 500 b a r s , P  R  Q  =  2 2 2 3200 bars and P-,„ = 6300 b a r s . Decrease i n v a l u e of n_,_ / (n + n_,_ ) (and f_ ) r e s u l t s i n i n c r e a s e of methane  CO2  CO2  TT n  water r a t i o towards A.  O2  ( F i g . 10c) and the f l u i d composition On  the e x t e n s i o n of t h i s curve  migrates  (CD),lawsonite  i s c o n s i d e r e d to be u n s t a b l e i n the presence of g r a p h i t e and q u a r t z .  Diagrammatic phase e q u i l i b r i u m boundaries i n  the system Ca-Al-Si-C-O-H and of  the i n f e r r e d s t a b i l i t y  limit  the assemblage lawsonite + quartz are a l s o shown i n  Fig.  11. The carbonaceous  metasediments are f a r more abundant  than the metavolcanics. and i t i s t o be expected t h a t w i t h p r o g r e s s i v e metamorphism and deformation a methane-water mixture w i t h a r b i t r a r y composition B permeated a c t i v e  108 shear zones i n the m a t a v o l c a n i c s .  The o x i d i z e d acmite-  j a d e i t e assemblage r e a c t e d w i t h the f l u i d to g i v e a  reduced  g l a u c o p h a n i t i c assemblage which c o e x i s t s w i t h methane-water. A r e a c t i o n i n v o l v i n g the acmite end-member  (Table 5,  16a)  precipitates  consumes methane, l i b e r a t e s water and  graphite.  As g r a p h i t e was  No.  not i d e n t i f i e d i n glaucophane  v e i n s or f o l i a t e d m e t a v o l c a n i c s , i t appears  t h a t methane  and water f u g a c i t i e s were e x t e r n a l l y c o n t r o l l e d and  the  f l u i d phase composition i n the metasediments migrated from B towards C.  E v o l u t i o n o f F l u i d Phase The changing  composition of the f l u i d phase w i t h  p r o g r e s s i v e metamorphism can a l s o be i l l u s t r a t e d w i t h ence t o a T - / Q  diagram  ( F i g . 12) .  r e s p e c t i v e l y the hematite-magnetite, magnetite  Curves 1, 2 and  refer-  3 are  the q u a r t z - f a y a l i t e -  and the m a g n e t i t e - i r o n oxygen b u f f e r curves  c a l c u l a t e d a t 10 kb. water a t 1 bar and a f t e r Miyashiro  The  i n e q u i l i b r i u m w i t h pure  10 kb  (1964).  b u f f e r i n the system C-0  (curves 4 and 5) were c a l c u l a t e d Curve 6 r e p r e s e n t s the g a s - g r a p h i t e c a l c u l a t e d a t 10 kb employing  equation g i v e n by French and Eugster  (1965).  an  T h i s curve  i s very c l o s e to the g r a p h i t e b u f f e r as c a l c u l a t e d i n the system C-H-0 1966).  employing  an H/O  r a t i o o f 2/1  (French,  Curve 7 r e p r e s e n t s the h y p o t h e t i c a l e x t r a p o l a t i o n  109 at  10 kb o f the r e a c t i o n acmite + quartz + hematite +  fluid  = r i e b e c k i t e + oxygen d e s c r i b e d i n the p r e v i o u s s e c t i o n . During d i a g e n e s i s of the carbonaceous sediments, the It  interstitial  l i q u i d was p r o b a b l y a s a l i n e  i s supposed t h a t the  i n the l i q u i d was  brine. initially  s i m i l a r to t h a t o f pure water, i t can be i n f e r r e d from -30 curves 4 and 5 t h a t /_ was approximately 10 °2 p o i n t B).  bars ( i . e .  With d i a g e n e s i s and metamorphism, oxygen  r e a c t e d w i t h carbonaceous m a t e r i a l to g i v e CC^ and the changed along the a r b i t r a r y t r a j e c t o r y BX. temperatures i n the 200° to 300°C range  Presumably, a t  (shaded area) the  carbonaceous m a t e r i a l behaved as g r a p h i t e w i t h the r e s u l t t h a t the f u g a c i t i e s of the v a r i o u s components can be s p e c i f i e d u n i q u e l y i n terms o f / ' a t f i x e d temperature and 2 U  t o t a l pressure  (French, 1966) .  B a s a l t s w i t h i n the sedimentary rocks may  have under-  gone h y d r a t i o n i n the z e o l i t e or p r e h n i t e - p u m p e l l y i t e f a c i e s d u r i n g p r o g r e s s i v e b u r i a l and/or d e f o r m a t i o n . sumably, the water o r i g i n a t e d i n the adjacent p r i o r to lowering of /  Pre-  metasediments  and e q u i l i b r a t i o n w i t h g r a p h i t e .  °2 A f t e r h y d r a t i o n , i t appears t h a t massive b a s a l t u n i t s behaved e s s e n t i a l l y as c l o s e d systems and the f changed 2 n  u  along the curve BY.  The p o s i t i o n o f t h i s curve i s d i r e c t l y  dependent on the e x t r a p o l a t i o n o f the a c m i t e / r i e b e c k i t e reaction  ( F i g . 12, No. 7 ) .  must have lowered the f  i n the hydrous pore f l u i d to  n U  O x i d a t i o n of i r o n t o form acmite  2  110  v a l u e s below t h a t o f pure water  (curves 4 and 5) but the  presence of a c m i t e - j a d e i t e b e a r i n g rocks which do not c o n t a i n glaucophane or c r o s s i t e suggests t h a t the f_ i n the f l u i d °2 remained w i t h i n the acmite s t a b i l i t y f i e l d and d i d n o t e q u i l i b r a t e w i t h g r a p h i t e as temperature i n c r e a s e d .  A t Y,  a c m i t i c r o c k s were i n d i s e q u i l i b r i u m w i t h the r e s e r v o i r of methane r i c h f l u i d and glaucophane forming r e a c t i o n s probably took p l a c e along shears and f r a c t u r e s . Pressure-Temperature T r a j e c t o r i e s o f P i n c h i Rocks Three assumptions have been made i n drawing the pressure-temperature t r a j e c t o r i e s shown i n F i g . 13. are:  They  (a) an average c r u s t a l d e n s i t y of 3.1 grams/cc,  (b) a minimum geothermal g r a d i e n t of 6°C/km and maximum geothermal g r a d i e n t o f 12°C/km. i s based on a t e c t o n i c model  (c) a  The f i r s t  assumption  (Chapter V) i n v o l v i n g a major  p r o p o r t i o n o f b a s i c or u l t r a m a f i c r o c k s .  The second i s  h y p o t h e t i c a l , but geothermal g r a d i e n t s as low as 8.56°C/km have been measured  (Clark, 1957). .  The l a s t assumption i s  based on a study o f a r a g o n i t e / c a l c i t e k i n e t i c s by Brown et at.,  (1962), who i n f e r r e d from t h i s t h a t f o r s u r v i v a l  of metamorphic a r a g o n i t e the geothermal g r a d i e n t c o u l d not have g r e a t l y exceeded dependent by C l a r k  10°C/km.  T h i s e s t i m a t e was  on the c a l c i t e / a r a g o n i t e t r a n s i t i o n as determined (1957) and Jamieson  (1953).  L a t e r work by  Ill ,  P-T  , -  ,  1  - T -  -i-  r  Irojectories for eclogite, blueschist and greenstone.  400  600 T C 0  r—  1  Fig. 13  800  112 Boettcher  and W y l l i e  (1967) lowered the t r a n s i t i o n  pressure,  and geothermal g r a d i e n t s o f 12°C/km can be accommodated. i s t h e r e f o r e concluded  t h a t the a r a g o n i t e b e a r i n g  It  rocks  a t P i n c h i c r o s s e d the a r a g o n i t e / c a l c i t e t r a n s i t i o n a t temperat u r e s l e s s than 300°C on t h e i r r e t u r n to the s u r f a c e . U p l i f t was accompanied by r e t r o g r a d e metamorphism. E c l o g i t e s were v e i n e d and p a r t l y r e p l a c e d by glaucophane, lawsonite and stilpnomelane blueschist facies.  i n t h e i r passage through the  Late a l b i t e v e i n s i n the b l u e s c h i s t s  must have formed below the a l b i t e / j a d e i t e + q u a r t z a t pressure-temperature  transition  c o n d i t i o n s s i m i l a r to the metamorphism  of the greenstones.  II  METAMORPHISM IN THE REMAINING FAULT BLOCKS  Metabasic The  Rocks South o f P i n c h i Lake  (Map,I, U n i t 4)  f o l l o w i n g metamorphic m i n e r a l assemblages were  noted d u r i n g examination  of s i x thin sections.  Minerals  are thought to be i n e q u i l i b r i u m w i t h one another  except  f o r white mica which o n l y occurs w i t h i n p l a g i o c l a s e . (al metabasalts:  a l b i t e + sphene + c e l a d o n i t e i white mica  (calcite + chlorite  veins) (bX metagabbro:  a l b i t e + a c t i n o l i t e + sphene ± white mica ± s e r p e n t i n e ± e p i d o t e (?)  113  R e l i c t m i n e r a l s , namely orthopyroxene, c l i n o p y r o x e n e , ilmenomagnetite and c a l c i c p l a g i o c l a s e are abundant i n the gabbros and may  c o n s t i t u t e up t o 9 0% o f the r o c k .  Metadiabase and metabasalt tend t o be more h i g h l y ted w i t h few r e l i c t s .  reconstitu-  S i g n i f i c a n t l y , a c t i n o l i t e i s absent  from the metavolcanic u n i t which a l s o i s a p p a r e n t l y the h i g h e s t i n the sequence  isee  p. 24  ) .  The presence o f a p a l e green amphibole  and p o s s i b l e  e p i d o t e suggests t h a t the lower gabbro u n i t was metamorphosed i n the g r e e n s c h i s t f a c i e s .  No meaningful p r e s s u r e estimates  can be made, but the temperature may  have been i n the 200°  to 400°C range based on the f a c i e s diagrams p. 366}  and L i o u  of Turner  (1968,  (1971) .  The a l b i t e / c e l a d o n i t e - c a l c i t e a s s o c i a t i o n i n the o v e r l y i n g b a s a l t s suggests t h a t they were metamorphosed i n c o n d i t i o n s e q u i v a l e n t to the p r e h n i t e - p u m p e l l y i t e f a c i e s . I t was  suggested  (p. 27 ) t h a t the b a s i c rocks  r e p r e s e n t p a r t of an o p h i o l i t e sequence.  may  I t i s therefore  s i g n i f i c a n t t h a t the metamorphic m i n e r a l assemblages  in  these rocks a r e s i m i l a r to those r e c e n t l y i n v e s t i g a t e d o c e a n i c environments  (Aumento et al.  3  1970).  from  Such r o c k s ,  c h a r a c t e r i z e d by a g r e e n s c h i s t f a c i e s mineralogy, and g e n e r a l absence of a t e c t o n i t e f a b r i c are t y p i c a l of ocean metamorphism  (Miyashiro, 1972). '  floor  114 Mount Pope B e l t  (Map  I, Units  7, 8 and  9)  S e n s i t i v e i n d i c a t o r s of metamorphic grade are w i t h i n the Mount Pope b e l t , as limestone and the dominant l i t h o l o g i e s . on the n o r t h e r n assemblage:  chert  are  A s c h i s t interlayered with  margin of the limestone c o n t a i n s  a l b i t e + c h l o r i t e + c a l c i t e + quartz  mica + u n i d e n t i f i e d opaques and s i d e of the map  rare  the + white  amorphous m a t e r i a l .  area on the northwest arm  cherts  Out-  of S t u a r t Lake,  the author noted a r e g i o n a l l y metamorphosed b a s i c assemblage containing a c t i n o l i t e + c h l o r i t e + c l i n o z o i s i t e + a l b i t e + sphene.  S i m i l a r assemblages w i t h i n the Cache Creek Group  have been r e p o r t e d  by Armstrong  t h a t the Mount Pope b e l t was  facies conditions.  T a k l a Group  (Map.  I, U n i t s 10,  greywackes and  I t i s concluded  metamorphosed under lower  greenschist  The  (1949).  11 and  12)  s i l t s t o n e s of the T a k l a Group are  o n l y i n c i p i e n t l y metamorphosed.  D e t r i t a l p l a g i o c l a s e , the  main c o n s t i t u e n t of the sediments, commonly d i s p l a y s a t u r b i d a l t e r a t i o n and may clasts  be l o c a l l y a l b i t i s e d .  (e.g. hornblende) are g e n e r a l l y a l t e r e d to c h l o r i t e +  sphene + c a l c i t e .  M a t r i x minerals  c h l o r i t e , s e r i c i t e and A t one  R e l i c t mafic  include  microgranular  the o c c a s i o n a l grain: of  celadonite.  l o c a l i t y , a dark grey, hard s i l t s t o n e c o n t a i n s  dodecahedra c o e x i s t i n g w i t h c h l o r i t e , quartz albitised plagioclase.  and  analcite  partly  However, t h i s l o c a l i t y i s near  the  115 P i n c h i F a u l t and  the a n a l c i t e may  r e s u l t of hydrothermal Only one  have been formed as a  activity.  small outcrop of b a s a l t was  encountered  w i t h i n the area and c o n t a i n e d the f o l l o w i n g domain assemblages : matrix:  a l b i t e + c h l o r i t e + sphene + c a l c i t e  amygdules:  Prehnite + quartz  veins:  Epidote + c a l c i t e  A p u z z l i n g f e a t u r e i s the occurrence of minor a r a g o n i t e (.Table 12, No.  23 0)  in a bioclastic  limestone thought  of Upper T r i a s s i c age south of P i n c h i Lake.  to be  Aragonite  was  not found i n a d j a c e n t limestone beds or i n Upper T r i a s s i c limestones to the n o r t h e a s t of the f a u l t .  Aragonite at  t h i s l o c a l i t y r e p l a c e s r e c t a n g u l a r c l a s t s , which were p o s s i b l y originally crinoid The presence  columnals. of p r e h n i t e and e p i d o t e i n b a s a l t i c  suggests t h a t the T a k l a Group was  rocks  metamorphosed i n t r a n s i t i o n a l  c o n d i t i o n s between the p r e h n i t e - p u m p e l l y i t e and g r e e n s c h i s t facies. C7 km)  Lord  (,1949) estimated a t h i c k n e s s of 23,000 f t  f o r T a k l a Group sediments and v o l c a n i c s i n the  McConnell  Creek area so t h a t l i t h o s t a t i c p r e s s u r e s i n the  P i n c h i area may  w e l l have approached 3 kb.  of a r a g o n i t e i n T a k l a Group may  The  occurrence  (?) rocks southwest of the f a u l t  i n d i c a t e t h a t higher p r e s s u r e s were a t t a i n e d l o c a l l y  ( i . e . 5.5  kb a t 200°C).  116 Ultramafites  (Map  I, U n i t s 14a and  14b)  H a r z b u r g i t e s and d u n i t e s a t P i n c h i have been serpentinized.  D.B.  thoroughly  Wenner (.Written communication! examined  three h a r z b u r g i t e s from the P i n c h i area and s e r p e n t i n e mineralogy  by X-ray d i f f r a c t i o n .  identified The  the  r e s u l t s were:  Spec. 85  (from P i n c h i Mt.)  : lizardite + chrysotile  Spec. 88  (from P i n c h i Mt.)  : chrysotile  Spec. 236 B r u c i t e was samples  (from Murray Ridge) : l i z a r d i t e + c h r y s o t i l e  i d e n t i f i e d by X-ray d i f f r a c t i o n i n t h r e e d u n i t e  (Nos. 87,  88,  240)  and one  harzburgite  S t a b i l i t y of s e r p e n t i n e - b e a r i n g m i n e r a l i s i l l u s t r a t e d on F i g . 14.  A t 10 kb and  breaks down to f o r s t e r i t e , t a l c and water 1966).  (No.  assemblages  585°C s e r p e n t i n e (Kitahara et  B r u c i t e c o e x i s t i n g w i t h s e r p e n t i n e lowers  stability limit.to occurrence  460°C a t 10 kb  239).  al.  3  the  (Johannes, 196.8).  The  of s e r p e n t i n e and b r u c i t e a t P i n c h i t h e r e f o r e  i n d i c a t e s t h a t s e r p e n t i n i z a t i o n took p l a c e below 460°C at 10 kb and  390°C a t 3 kb.  Oxygen i s o t o p e work (Wenner and T a y l o r , 1969) out on s e r p e n t i n i t e s from B r i t i s h Columbia and  western  North America i n d i c a t e s t h a t s e r p e n t i n e m i n e r a l s w i t h meteoric  water a t low temperature.  equilibrated  F r a c t i o n a t i o n of  oxygen i s o t o p e s between c o e x i s t i n g s e r p e n t i n e and suggest  carried  magnetite  that continental l i z a r d i t e - c h r y s o t i l e serpentinites  117 e q u i l i b r a t e d a t 85° t o 115°C and oceanic s e r p e n t i n i t e s a t 130° t o 185°C  lizardite-chrysotile  (.Wenner and T a y l o r , 1971).  A n t i g o r i t e e q u i l i b r a t e s a t temperatures above 200°C.  From  t h i s i t may be i n f e r r e d t h a t a major episode of s e r p e n t i n i z a t i o n occurred  i n the P i n c h i u l t r a m a f i t e s a t temperatures  l e s s than 185°C to g i v e the c h r y s o t i l e - l i z a r d i t e a s s o c i a t i o n . For blocks  the s u r v i v a l o f metamorphic a r a g o n i t e ,  c o n t a i n i n g greenstones' and b l u e s c h i s t s must have been  rapidly uplifted The  the f a u l t  (p. 110 ) along  the P-T t r a j e c t o r y i n F i g . 13.  p o s s i b i l i t y e x i s t s t h a t u l t r a m a f i c bodies, which are  c l o s e l y a s s o c i a t e d w i t h these r o c k s , underwent a s i m i l a r r a p i d u p l i f t and a p o s s i b l e P-T t r a j e c t o r y i n the system M g O - S i 0 H 0 i s i l l u s t r a t e d i n F i g . 14. -  2  2  From the oxygen  i s o t o p e geothermometry i t appears t h a t a n t i g o r i t e i s the stable serpentine The  mineral  a t b l u e s c h i s t f a c i e s temperatures.  absence o f a n t i g o r i t e suggests t h a t e i t h e r a n t i g o r i t e  never formed o r t h a t i t was completely r e p l a c e d by the lower temperature l i z a r d i t e - c h r y s o t i l e m i n e r a l o g y . d u r i n g and  cooling.  a t i o n occurred  I n the w r i t e r s o p i n i o n much of t h i s s e r p e n t i n i z during  a period of s t r i k e - s l i p  a s s o c i a t e d w i t h u p l i f t and the F^ deformation and V I ) .  uplift  faulting (Chapters V  V STRUCTURAL GEOLOGY  Introduction The structure  emphasis i n t h i s chapter i s p l a c e d on the of the f a u l t b l o c k c o n t a i n i n g  glaucophane b e a r i n g rocks  ( F i g . 3, U n i t  the  internal  lawsonite-  2).  I t was  hoped  t h a t a s t r u c t u r a l study of these r o c k s , which l i e a d j a c e n t to the P i n c h i F a u l t , would help to e l u c i d a t e movements on was  the f a u l t .  c a r r i e d out  To  the h i s t o r y  t h i s purpose, s t r u c t u r a l mapping  i n the v i c i n i t y of the mine (Map  along the northwest shore of P i n c h i Lake  (Map  IV)  V).  and  Structural  data c o l l e c t e d i n the v i c i n i t y of the mine were p l o t t e d stereographic projections  ( F i g . 15).  I t should be  on  emphasized  that s t r u c t u r a l i n t e r p r e t a t i o n i s seriously constrained (a) the poor exposure,  of  by  (b) the undoubtedly complex  d e f o r m a t i o n a l h i s t o r y and  (c) the  l a c k of a  stratigraphic  sequence. S t r u c t u r a l geology of the remaining f a u l t b l o c k s been adequately d e a l t w i t h i n Chapters I I and o n l y be  summarized i n t h i s  section.  I I I and  has  will  119  FIG. 15  EQUAL ABE A STEREOGRAPH IC PROJECTIONS OF STRUCTURAL DATA OBTAINED IN THE VICINITY OF PINCHI KINE ( HAP IV )  Poles to foliation (S±)  Llneatlons (L ) and fold axes (Fj). 2  Fold exes (F-) a i 1 1 6 points contoured using Kalsbeck counting net (Kalsbeck, I 9 6 3 ) . Contour Intervals at 1,4,and 6% of points per 1% area of net. b 1 1 5 3 points contoured using Kalsbeck counting net (Kalsbeck, I 9 6 3 ) . Contour intervals at 2 , 4 , 6 and 8% of points per 1% area of net. c t 5 9 points contoured using the Mellis method (Turner * Weiss, I 9 6 3 , p. 6 2 ) contour Intervals at 1 , 2 end k% of points per 1% area of net.  120  S. F O L I A T I O N  Fig.  16a  Fig.  16b  S t r u c t u r a l elements i n f o l i a t e d glaucophane m e t a v o l c a n i c (drawn from hand specimen!.  f _ f o l d i n metachert.  F,  KINK  FOLDS  JOINTS  Fig.  16c  F~ k i n k f o l d s i n metachert.  rich  121  Fig.  17a  Fig.  17b  F f o l d i n quartz-carbonate-mica s c h i s t . i n g out of micaceous l a y e r s . 2  Note l e n s -  ^2 f o l d s i n metachert. Note v a r i a t i o n i n plunge and c u r v i n g a x i a l plane of F f o l d s . F o l d s are c r o s s - c u t by q u a r t z - f i l l e d j o i n t . 2  122  2 cms  F i g s . 18a and b: Recumbent I s o c l i n a l F f o l d s i * i metachert. These F f o l d s appear t o have been r e f o l d e d by l a t e t ? l F folds. 2  2  2  F i g . 18c  F  2  f o l d i n metachert f o l d e d by F 3 .  123 S t r u c t u r a l Elements i n the Lawsonite-Glaucophane Bearing Rocks (al F o l i a t i o n s  tS-surfaces) :  The most obvious  s t r u c t u r a l f e a t u r e of the metasediments and the f o l i a t e d m e t a v o l c a n i c s i s the f o l i a t i o n  tSj)  concordant w i t h the l i t h o l o g i c  l a y e r i n g or bedding  which appears  In l i t h o l o g i e s r i c h i n white mica and glaucophane, f o l i a t i o n might be termed a s c h i s t o s i t y .  to be (S^). this  Within limestones,  i s c h a r a c t e r i z e d by a l t e r n a t i n g l a y e r s of dolomite and s t r e a k y carbonaceous  a r a g o n i t e ( F i g . 35). No t r a c e o f  i s seen i n greywackes, massive metavolcanics and much o f the l i m e s t o n e . The  S-^ f o l i a t i o n i s c r o s s - c u t by an  cleavage b e s t developed glaucophane-mica  strain-slip  i n f o l i a t e d m e t a v o l c a n i c s and  schists.  g e n e r a l l y cannot be r e c o g n i z e d  i n metacherts, metagreywackes and massive  metavolcanics.  Growth o f mimetic m i n e r a l s i s not a s s o c i a t e d w i t h S^Metacherts possess a f r a c t u r e cleavage  (S^) with  s i m i l a r o r i e n t a t i o n to the j o i n t s d e s c r i b e d below. w e l l developed,  the cleavage i s w i d e l y spaced  a x i a l planar to kink f o l d s .  Where  (1 cm) and i s  On account o f d i f f i c u l t y of  r e c o g n i t i o n and c o n f u s i o n w i t h complex f r a c t u r e s r e l a t e d to f a u l t s , o n l y a few measurements o f field.  were made i n the  124 (b) L i n e a t i o n s :  The e a r l i e s t s t r u c t u r e (L-^) i s a  m i n e r a l l i n e a t i o n , best d e f i n e d i n f o l i a t e d  metavolcanics  and metacherts by n e m a t o b l a s t i c glaucophane  (Figs.  16b) . " Very  few measurements were made of  16a,  i n the  field  because of the s c a r c i t y of rocks i n which the glaucophane was  s u f f i c i e n t l y coarse g r a i n e d to d i s c e r n the W i t h i n the f o l i a t e d m e t a v o l c a n i c s ,  an i 2 c r e n u l a t e l i n e a t i o n  ( F i g . 16b).  by spindle-shaped micas.  The  aggregates  i s deformed by  In the  occurs as a prominent c r e n u l a t i o n on  lineation.  metacherts,  surfaces, defined  of quartz and c r e n u l a t e d white  l i n e a t i o n commonly p a r a l l e l s the  mineral  l i n e a t i o n w i t h i n the metacherts but i n samples p o s s e s s i n g t i g h t recumbent F^ f o l d s the o r i e n t a t i o n i s v a r i a b l e ( F i g . 18b) .  Coaxial  and 'L^ may  glaucophane g r a i n s d u r i n g the F^  r e s u l t from r o t a t i o n of deformation.  A t some l o c a l i t i e s , metacherts and s c h i s t s form i r r e g u l a r m u l l i o n s  (Wilson, 1953)  boudins w i t h a t t i t u d e s s i m i l a r to  (c) J o i n t s :  quartz-carbonate or  elongate  (Plate 3).  Most exposures of metachert and  metavolcanic  rock e x h i b i t a prominent s e r i e s of j o i n t s o r i e n t e d a p p r o x i mately p e r p e n d i c u l a r to  ( F i g . 16b) .  Frequently,  are f i l l e d by vuggy, undeformed q u a r t z v e i n s .  they  125 (d) F o l d s :  Three d i s t i n c t p e r i o d s o f f o l d i n g have  been r e c o g n i z e d and are termed F^, F^ and F^, to youngest  from o l d e s t  respectively.  C o n v i n c i n g f o l d c l o s u r e s a s s o c i a t e d w i t h F^ a r e seldom seen.  The presence o f mesoscopic  w i t h a x i a l p l a n e s p a r a l l e l to  macroscopic  isoclines  i s i n f e r r e d from the  l e n s i n g out o f c o m p o s i t i o n a l l a y e r i n g r e p e t i t i o n of l i t h o l o g i c  tight  layering  ( F i g . 17) and  (on mesoscopic  apparent  and  scales).  Within metacherts, mesoscopic F^ f o l d s  ( F i g s . 17 and  18) are v e r y conspicuous and, inasmuch as they do not show a p p r e c i a b l e t h i c k e n i n g o f the hinge zones, are of c o n c e n t r i c type.  S l i g h t t h i c k e n i n g of f o l d hinges does occur i n  incompetent and s c h i s t s .  l i t h o l o g i e s such as interbedded l i m e s t o n e s F^ f o l d axes are p a r a l l e l to  and i n areas  where F^ i s of m i l d i n t e n s i t y they trend a t 300° and a t 55°  (Fig. 1 5 b ) .  plunge  F^ f o l d s g e n e r a l l y have a complex  geometry w i t h c u r v i n g a x i a l planes and may  grade i n t o  fold  mullions. Kink f o l d s  ( F i g . 16c) are c h a r a c t e r i s t i c of F^  deform F^ f o l d s and a s s o c i a t e d l i n e a r  F^  and  structures.  Deformation Both mesoscopic and macroscopic f o l d c l o s u r e s a s s o c i -  ated w i t h F^ are v e r y d i f f i c u l t  to demonstrate.  The o n l y  p o s s i b l e example o f a mesoscopic c l o s u r e i s l o c a t e d on a  12 6  small  i s l a n d 4 km  bedded c h e r t s  south of P i n c h i Mine.  form a t i g h t southwesterly p l u n g i n g  synform c o n t a i n i n g  a s c h i s t o s e greywacke w i t h  plane cleavage deformed by The  Southerly  dipping, isoclinal  axial  crenulations.  possible existence  of  t h a t t r a n s p o s i t i o n o f bedding may  i s o c l i n a l f o l d s suggests have caused the  apparent  p a r a l l e l i s m o f the primary l i t h o l o g i c l a y e r i n g w i t h Bedding t r a n s p o s i t i o n can  5^.  be i n f e r r e d i n incompetent u n i t s  such as g r a p h i t i c c h e r t s , where q u a r t z i t i c l a y e r s are sheared and  wedge out a f t e r a few  inches.  However, c e r t a i n  l i t h o l o g i e s such as massive metavolcanics and generally  show no s i g n s  layering has  (Sg).  thus e x p l a i n i n g  which  p a r a l l e l s the  I t i s considered l i k e l y that  occurred only  metagreywackes  of the p e r v a s i v e shearing  must accompany t r a n s p o s i t i o n , and  highly  lithologic  transposition  i n the hinge zones of competent u n i t s  the r a r i t y of c o n v i n c i n g  F^  fold  closures.  In summary, i t appears t h a t the F^ deformation i n v o l v e d i s o c l i n a l f o l d i n g , t r a n s p o s i t i o n of the p a r a l l e l to S^ and  bedding  synkinematic r e c r y s t a l l i z a t i o n of a  b l u e s c h i s t f a c i e s mineralogy on a t t a i n i n g the depth of b u r i a l ( F i g . 19). p a r a l l e l s F, f o l d axes.  The  necessary  lineation possibly  127 F^ Deformation Mesoscopic F^ s t r u c t u r e s a r e widespread w i t h i n the area.  and m u l l i o n s p a r a l l e l the axes.of minor f o l d s  which deform  and have an average t r e n d and plunge of  300° and 5.5° ( F i g . 15b) .  Minor f o l d s a r e g e n e r a l l y o f the  symmetric c o n c e n t r i c type; both t i g h t and open f o l d s a r e common.  A x i a l planes o f minor f o l d s a r e d i f f i c u l t t o  measure because o f the prevalence and  of disharmonic  folding  mullioning. Because of widespread d i s r u p t i o n by f a u l t i n g and  f l e x u r e s a s s o c i a t e d w i t h F^, macroscopic F^ f o l d s a r e difficult  to recognize.  In the mine area w i t h i n domains  of low F^ i n t e n s i t y , the average s t r i k e and d i p of the enveloping and Map I V ) .  s u r f a c e i s 120° and 57° n o r t h e a s t  V a r i a t i o n i n s t r i k e i s common i n the v i c i n i t y  o f l a r g e limestone attitudes. dip  ( F i g . 15a  lenses which impose a l o c a l c o n t r o l on  However, on the northwest shore of P i n c h i Lake,  to the southwest along the lakeshore  the n o r t h e a s t  f a r t h e r i n l a n d (Map V ) .  but d i p t o  Southerly  dipping  occur on the s m a l l i s l a n d . 4 km south of P i n c h i Mine. These a t t i t u d e s suggest the e x i s t e n c e . o f a macroscopic antiformal structure with a x i a l trace  approximately  c e n t r e d on the long dimension of the g l a u c o p h a n i t i c b l o c k and t r e n d i n g a t 100°. the p l o t of p o l e s t o 5  1  fault  There i s no obvious g i r d l e i n  ( F i g . 15a) which would demonstrate  128  the e x i s t e n c e o f t h i s s t r u c t u r e .  T h i s i s because the s t r u c -  t u r a l data were o b t a i n e d from the northern limb of the postulated antiform.  A second p o s s i b l e a n t i f o r m was i d e n t i f i e d  130 m n o r t h of the limestone  l e n s 1.5 km west o f P i n c h i  Mine. There i s a marked d i f f e r e n c e i n plunge o f the northwest P i n c h i area  (Map V) and the mine area  between (Map I V ) ;  i n the former the average plunge i s 10°W and i n the l a t t e r it  i s 55°W.  found  I t i s c o n s i d e r e d t h a t the steeper plunges a r e  immediately  adjacent to the main P i n c h i F a u l t where  the i n t e n s i t y o f the F^ deformation  was s t r o n g e r .  In summary, the F^ deformation  i s c h a r a c t e r i z e d by a  prominent l i n e a t i o n and c o n c e n t r i c , t i g h t t o open f o l d s . M u l l i o n s a r e common and there i s some suggestion t h a t the i n t e n s i t y o f deformation the P i n c h i F a u l t .  t r e n d i n g a n t i f o r m i s c e n t e r e d on P i n c h i  B l u e s c h i s t f a c i e s m i n e r a l s have been deformed by F^  and metamorphic r e c r y s t a l l i z a t i o n quartz and hematite  F^  t o the p r o x i m i t y of  Major s t r u c t u r e s a r e i n t e r p r e t a t i v e but  a probable east-west Lake.  i s related  i s limited to a l b i t e ,  (see p. 133)•  Deformation S t r u c t u r e s r e l a t e d to F^ a r e c l o s e l y a s s o c i a t e d w i t h  f a u l t s and a r e b e s t demonstrated i n the P i n c h i Mine area (Map  IV) where a s e r i e s of macroscopic  earlier  structures.  F^ c r o s s f o l d s deform  Mesoscopic kink f o l d s appear to be  129 a s s o c i a t e d w i t h these c r o s s - f o l d s and  t r e n d 100° to  and plunge  a x i a l plane  10° to 60° southeast.  The  125°  (S^) i s  g e n e r a l l y c o p l a n a r w i t h the j o i n t s p e r p e n d i c u l a r t o F^ s t r i k i n g from 60° to 90° and d i p p i n g southeast a t 45°. v a r i a t i o n i n t r e n d of F^ f o l d axes depends on the o r i e n t a t i o n of  w i t h r e s p e c t to F^>  o r i e n t a t i o n s of  axes i n a g r e a t c i r c l e w h i c h i d e f i n e s S^.  F^ f o l d s deform F^ f o l d s and t r a t e d i n F i g . 18c. of  The  the l o c a l  2  fold  spread of  out. lineations.as  illus-  Theoretically, for concentric folding  ^2 s i t u a t e d on a plane of known o r i e n t a t i o n  the l o c u s of L  initial  Therefore, varying  t h e o r e t i c a l l y , should d i s p o s e F^  F^ f o l d axes i n F i g . 15c bears t h i s  The  (e.g.  should l i e on a p a r t i a l s m a l l c i r c l e  "b" kinematic a x i s (Turner and Weiss, p.  L i t t l e can be s a i d as to whether the spread i n  S^), on  498). in Fig.  15b d e f i n e s a g r e a t c i r c l e or a s m a l l c i r c l e . On the n o r t h e r n s l o p e s of P i n c h i Mine s t r i k e s east-west southerly.  and, r a t h e r unexpectedly,  hill, d i p s are  T h i s g i v e s the impression t h a t on the mine  the c o n t r o l l i n g s t r u c t u r e i s an e a s t e r l y t r e n d i n g F^ which plunges a t 30°  (Map  IV).  synform  synform  The occurrence of s i m i l a r  l i t h o l o g i c sequences on both n o r t h and this interpretation.  hill,  south limbs r e i n f o r c e s  However, the a x i a l zone of t h i s  i s h i g h l y f a u l t e d and c a r b o n a t i z e d and  between the limbs a r e obscure.  relations  Similar easterly trending  130 f o l d s were mapped a t v a r i o u s l o c a t i o n s south of the  fault  s e p a r a t i n g the g l a u c o p h a n i t i c rocks from the greenstones. I t appears t h a t the o n l y way  to make sense out of  the  s t r u c t u r e i n the mine area i s t o d i v i d e the area i n t o domains which d i s p l a y some degree of homogeneity and draw f a u l t s along the domain boundaries. some degree but i t presents  T h i s i s s u b j e c t i v e to  a complex p a t t e r n of warping,  f a u l t i n g , b l o c k r o t a t i o n and  c a r b o n a t i z a t i o n along  zones which i s p o s s i b l y c l o s e to the t r u t h . of the trend and plunge of warping i n the limestone  f o l d s and  along f a u l t number 2 (Map VI)  The minerals  of the sense of  during  have taken p l a c e F^.  Analyses r e l a t i o n s h i p between growth of metamorphic  and deformation  Within  i s i l l u s t r a t e d i n F i g . 19.  the metacherts, t h i n l a y e r s of  white mica, a c i c u l a r glaucophane and define  Consideration  beds suggest t h a t r i g h t - l a t e r a l  movement w i t h a d i p - s l i p component may  Microscopic  fault  and  L^.  tabular  In f o l i a t e d metavolcanics  o r i e n t a t i o n of glaucophane d e f i n e s  and  lepidoblastic lawsonite the p r e f e r r e d  L^.  l i t h o l o g i e s such as metagreywackes and massive  Some metavolcanics  do not have a p r e f e r r e d o r i e n t a t i o n of t h e i r metamorphic mineralogy and are u n f o l i a t e d .  Both l i t h o l o g i e s  however, grade i n t o s c h i s t o s e types.  do,  I t i s assumed t h a t  131  Fig.  19  R e l a t i o n s h i p of metamorpic r e c r y s t a l l i z a t i o n to deformation  TYPE Mineral acmitic  OF  RECRYSTALLIZATION Transitional  stage  S y n k i n e m a t i c (F,)  1  Synkinematic  1  (F ) z  1  pyroxene  1  I  jadeitic pyroxene  1 1  lawsonite  l I  phengite  1 I  sphene  I i  chlorite  i  glaucophane I  aragonite  i  calcite  i  —  " 1 1  stilpnomelane  1  1  brown amphibole  I  +  albite  1  ?--  magnetite hematite  I  1  v. Increase in P and T  Decrease  in P a n d T  possibly  accompanied by strike slip faulting Uncertainty  132 u n f o l i a t e d r o c k s possessed  s u f f i c i e n t s t r e n g t h to withstand  the F ^ p e n e t r a t i v e deformation which gave r i s e t o the foliated  zones.  Some f e a t u r e s o f f e r f a i r l y d i s t i n c t i v e evidence t h a t a t l e a s t some m i n e r a l s c h a r a c t e r i s t i c o f the b l u e s c h i s t f a c i e s continued to r e c r y s t a l l i z e a f t e r t h e F^ deformation. For i n s t a n c e , a r a g o n i t e v e i n s c r o s s - c u t  i n limestones  t F i g . 35) and the m i n e r a l commonly i s found c l o s e l y a s s o c i a t e d w i t h undeformed r a d i a t i n g c l u s t e r s o f a brown amphibole growing along f r a c t u r e s .  A network o f glaucophane or  glaucophane + q u a r t z v e i n s t y p i f i e s massive v o l c a n i c s . Glaucophane i s a l i g n e d e i t h e r p a r a l l e l or p e r p e n d i c u l a r to the w a l l s .  The problem a r i s e s as to whether these v e i n s  formed d u r i n g o r a f t e r the F^ deformation.  I n hand specimen,  some o f them appear t o be shears f i l l e d w i t h glaucophane growing along s m a l l t h r u s t f a u l t s which o f f s e t glaucophane v e i n s . t e n s i o n gashes,  Other v e i n s a r e s i g m o i d a l , resembling  and i n one specimen a glaucophane v e i n was  seen c r o s s - c u t t i n g a weak f o l i a t i o n suggested  earlier  i n Chapter  a c t e d as channels  (S^) .  I t was p r e v i o u s l y  IV (p. 110) t h a t minute f r a c t u r e s  f o r f l u i d s which r e a c t e d w i t h  acmite i n the metavolcanics t o form glaucophane.  jadeiteA  reasonable e x p l a n a t i o n f o r the o r i g i n of the f r a c t u r e s i s t h a t some a r e shears r e l a t e d t o F ^ and t h a t o t h e r s may be p o s t - F ^ t e n s i o n f r a c t u r e s which formed d u r i n g and/or the e a r l y stages o f the F„ deformation.  uplift Presumably,  133 t h i s r e c r y s t a l l i z a t i o n came to a h a l t w i t h decrease i n pressure  and  temperature.  B l u e s c h i s t f a c i e s m i n e r a l s are deformed by crenulations.  F^  Glaucophane and l a w s o n i t e are commonly  f r a c t u r e d , and white mica forms c o n t o r t e d swathes i n metacherts  ( F i g . 36d). .  undulose  Quartz  shows sutured boundaries  and  e x t i n c t i o n i n some samples, but i n o t h e r s , s t r a i n -  f r e e p o l y g o n a l aggregates accompanied  suggest t h a t r e c r y s t a l l i z a t i o n  F^.  R e s t r i c t e d r e c r y s t a l l i z a t i o n of r e t r o g r a d e m i n e r a l s o c c u r r e d d u r i n g F^.  A l b i t e v e i n s form i n metacherts  and  metavolcanics and a l s o h e a l f r a c t u r e s i n glaucophane crystals  ( F i g . 36c).  Magnetite  g r a i n s , b e l i e v e d to have  formed d u r i n g the g l a u c o p h a n i t i c metamorphism, are commonly rimmed by r e t r o g r a d e hematite.  B r e c c i a t i o n of the  limestones  r e s u l t e d i n p a r t i a l i n v e r s i o n of aragonite to c a l c i t e  and  v e i n i n g by s p a r r y c a l c i t e . F^ deformation was along a c t i v e f a u l t zones. fill  j o i n t s i n metacherts  accompanied by c a r b o n a t i z a t i o n Vuggy q u a r t z v e i n s which commonly may  be a s s o c i a t e d w i t h the  latter  stages of F ^ . In summary, three stages of metamorphic r e c r y s t a l l i z a t i o n are proposed  ( F i g . 19).  The  first is a  synkinematic  stage a s s o c i a t e d w i t h b l u e s c h i s t f a c i e s metamorphism and the f o r m a t i o n of second  and  the m i n e r a l l i n e a t i o n L^.  The  i s an i l l - d e f i n e d t r a n s i t i o n a l stage between F , and  134 ^2 accompanied by r e c r y s t a l l i z a t i o n of minor glaucophane, a r a g o n i t e , s t i l p n o m e l a n e and brown amphibole.  A  third  stage i n v o l v e d deformation of b l u e s c h i s t f a c i e s m i n e r a l s and r e c r y s t a l l i z a t i o n o f q u a r t z , and minor a l b i t e , white mica and hematite.  T h i s stage must have o c c u r r e d a t much lower  pressure-temperature  c o n d i t i o n s than the f i r s t  Timing of Metamorphism and  stage.  Deformation  Because of the absence of f o s s i l s , the age of d e p o s i t i o n of sediments i n the b l u e s c h i s t b e a r i n g b l o c k i s not known w i t h c e r t a i n t y , but the  fault  lithologies  p r e s e n t are s i m i l a r t o those i n the Cache Creek or S l i d e Mountain Groups, suggesting a M i s s i s s i p p i a n t o Permian age.  Armstrong  (1949) gave evidence f o r a P e r m o - T r i a s s i c  deformation of the Cache Creek Group. t h i s deformation was  I t i s inferred that  contemporaneous w i t h the F^  deformation  i n the b l u e s c h i s t s , but the former o c c u r r e d a t a higher s t r u e tura1 1eve1. A number of authors  (e.g. E r n s t , 1965)  have  argued  t h a t b l u e s c h i s t f a c i e s metamorphism takes p l a c e d u r i n g r a p i d b u r i a l of sediments, temperature  c r e a t i n g c o n d i t i o n s of  and h i g h p r e s s u r e w i t h i n the c r u s t .  p r e s e r v a t i o n of the c h a r a c t e r i s t i c mineralogy,  low For  i t is  e s s e n t i a l t h a t the metasediments have undergone a r a p i d uplift  (Brown et al.,  1962).  Metamorphic ages i n a  r a p i d l y u p l i f t e d t e r r a i n should c l o s e l y approximate the  135 FIG. 20  DEPTH-TIME  TRAJECTORY  FOR  _ _  PERMIAN i Upper  GLAUCOPHANITIC 1  j  ' !  TRIASSIC  [Lower 8 Middle J  « i Upper  ROCKS  ? J  >' !  JUR.  Lower  Note : a) The T r i a s s i c - J u r a s s i c boundary i s a r b i t r a r i l y p l a c e d a t 200 m.yrs. w i t h the u n c e r t a i n t y i n d i c a t e d . Data are from Tozer, 196k (190-200 m.yrs.); Bochkarev & Pogorelov, 196? (204 m.yrs.); Armstrong, 1970 (210 m.yrs.). b) The Middle-Upper T r i a s s i c (230 m. y r s . ) i s taken from B o r s i and F e r r a r a ( 1 9 6 7 ) . . c) The P e r m o - T r i a s s i c boundary (255-260 m.yrs.) i s obtained from Bochkarev & Pogorelov ( 1 9 6 7 ) .  136 a c t u a l age of metamorphism  (Suppe,. 1972) .  In the case of  the P i n c h i r o c k s , i t has been argued t h a t r e c r y s t a l l i z a t i o n of b l u e s c h i s t f a c i e s m i n e r a l s was but there i s a l s o evidence  largely  synkinematic  f o r a phase of post E ' ^ r e c r y s t -  a l l i z a t i o n which c o u l d only have o c c u r r e d d u r i n g  the  uplift. Three K-Ar  dates were o b t a i n e d from p h e n g i t i c micas  present i n schistose layers i n cherts.  D e t a i l s of specimen  l o c a t i o n and a n a l y t i c a l techniques are g i v e n i n Appendix V.  The dates o b t a i n e d were 211,  f o u r t h date of 218 m y r s was  214  and  216  * 7 m yrs.  A  o b t a i n e d from a micaceous  eclogite. These a b s o l u t e ages correspond  to Middle or Upper  T r i a s s i c g e o l o g i c ages depending on which time s c a l e i s used.  I f the T r i a s s i c - J u r a s s i c boundary i s taken a t  2 00 m y r s  (Tozer, 1964)  c o u l d be Middle T r i a s s i c .  i t i s c o n c e i v a b l e t h a t the Armstrong  and B o r s i and  (1967) e s t a b l i s h e d a date of 230 m y r s  Middle-Upper T r i a s s i c boundary.  dates  (1971) proposed a  boundary between the p e r i o d s a t 210 m y r s Ferrara  190-  f o r the  T h i s being the case,  the ages obtained a t P i n c h i are Upper T r i a s s i c . I f i t i s assumed t h a t the micas d i d not excess argon,  two  absorb  f a c t o r s would have been r e s p o n s i b l e f o r  these T r i a s s i c dates.  They c o u l d r e f l e c t  (a) the age  u p l i f t and c o o l i n g to a temperature below the  critical  isotherm f o r argon r e t e n t i o n and  of the  (b) the age  of  137  crenulation  (L^)  w i t h the F^  deformation.  which deforms the micas and T y p i c a l F^  i s associated  s t r u c t u r e s such as  minor f o l d s , c r e n u l a t i o n s and m u l l i o n s are not p r e s e n t i n the Upper T r i a s s i c T a k l a Group even a d j a c e n t t o the zone.  T h i s f a c t , together w i t h the age dates,  t h a t the F^  deformation was  of the Upper  suggests  i n progress d u r i n g d e p o s i t i o n  T r i a s s i c but a f f e c t i n g r o c k s a t a  structural level.  fault  lower  U p l i f t and c o o l i n g of the f a u l t b l o c k  to below 2 00°C must have o c c u r r e d e i t h e r b e f o r e or d u r i n g the F^  deformation. The f o r e g o i n g f a c t s and i n f e r e n c e s suggest t h a t  F  1  deformation, metamorphism, u p l i f t and F^ deformation a l l took p l a c e between the b e g i n n i n g of the l a t e Permian and the end of the T r i a s s i c  ( i . e . between 245  and 200 m y r s  ago) . P o s s i b l e depth time t r a j e c t o r i e s f o r the b l u e s c h i s t s are i l l u s t r a t e d i n F i g . 20. invoked  I f a subduction model i s  (see Chapter V I ) , the r a t e of b u r i a l of  sediments  i s approximately dependent on the r a t e of u n d e r t h r u s t i n g and the d i p of the subduction zone.  For a subduction zone  d i p p i n g a t 45°, the times taken t o descend  30 km a t under-  t h r u s t i n g r a t e s of 10 cm per year  1 cm per year  (BCl are 0.35  m y r s and  (AC) and  3.5 m y r s r e s p e c t i v e l y .  The  p r e s e n t day u n d e r t h r u s t i n g r a t e s o f 10 cm per year i n the Japan Trench  (Oxburgh, 1971)  suggest t h a t the former  appears  138 t h e more r e a l i s t i c  time.  A t C,  during blueschist facies  m e t a m o r p h i s m , i t i s assumed t h a t t h e r e was  a  relaxation  o r change i n o r i e n t a t i o n o f the s t r e s s w h i c h caused e x t r e m e d e p t h o f b u r i a l , and t h e b l o c k was isostatically re-equilibrate.  allowed  the to  Maximum u p l i f t r a t e s o f t h e  o r d e r o f 1 cm p e r y e a r h a v e b e e n u s e d t o r e c o n s t r u c t t h e CD  p a r t of the t r a j e c t o r y .  was  accompanied  Presumably,  this uplift  by m i n o r b l u e s c h i s t f a c i e s  recrystallization  u n t i l c o o l i n g r e s u l t e d i n a " f r e e z i n g " of the mineralogy.  A t D,  assuming  stage  metamorphic  a geothermal g r a d i e n t of  12°C/km, t h e g l a u c o p h a n i t i c r o c k s p a s s e d t h r o u g h t h e 200°C isotherm which represents the approximate temperature f o r argon r e t e n t i o n i n muscovites this  (Suppe,  1972).  Theoretically  s h o u l d r e p r e s e n t t h e maximum age d a t e o b t a i n a b l e f r o m  the b l u e s c h i s t s .  From D t o E t h e b l o c k c o n t i n u e d  a t a d e c r e a s i n g r a t e because equilibrium.  of approach t o  The F ^ d e f o r m a t i o n  to  isostatic  must have o c c u r r e d  during  t h i s p a r t of the t r a j e c t o r y , p o s s i b l y causing argon i n t h e m i c a s and r e s e t t i n g t h e age d a t e s . somewhat a r b i t r a r i l y c h o s e n a t 4.6  loss  Point E i s  km f r o m t h e s u r f a c e .  T h i s d e p t h r e p r e s e n t s t h e amount o f r o c k e r o d e d i n m i l l i o n y e a r s , assuming  rise  230  an;. -_\ e r o s i o n r a t e o f 1 m p e r 4  50,000 y e a r s . F^ d e f o r m a t i o n along f a u l t  zones.  was  I t was  accompanied  by c a r b o n a t i z a t i o n  previously inferred  t h a t the c a r b o n a t i z a t i o n occurred during the  ( p . 67  Eocene.  )  139  S t r u c t u r a l Geology of Remaining F a u l t Blocks The  i n t e r n a l s t r u c t u r e o f the remaining  fault  blocks  has been adequately d e a l t w i t h i n the a p p r o p r i a t e s e c t i o n s i n Chapter  II.  The  f o l l o w i n g summary f a c i l i t a t e s  comparison  of s t r u c t u r e s i n d i f f e r e n t f a u l t b l o c k s .  Greenstones of P i n c h i Mountain  (Map  These rocks are w e l l f o l i a t e d and s c h i s t s possess an S^.  I , U n i t s 5 and  6)  interbedded g r a p h i t e  D r i l l hole i n t e r s e c t i o n s of an  i n t e r c a l a t e d limestone u n i t i n d i c a t e t h a t these d i p n o r t h or n o r t h e a s t a t 45°.  rocks  T h i s d i p i s conformable w i t h  the l a y e r i n g i n the s i l i c a - c a r b o n a t e rocks which form the n o r t h e a s t e r n boundary of the greenstone  Mount Pope b e l t  (Map  unit.  I , U n i t s 7, 8 and  9)  The Mount Pope b e l t i s of Pennsylvanian Permian age and was  deformed d u r i n g the P e r m o - T r i a s s i c .  The b a s i c rocks belong to the lower A r g i l l i t e s possess c u t s the bedding  to Middle  greenschist facies.  a s l a t y cleavage which commonly c r o s s -  i n the hinge  zones of e a r l y f o l d s .  To  the west of the map-area, a p a r t i a l c r o s s s e c t i o n of the Cache Creek Group i s r e v e a l e d i n the n o r t h arm Lake.  The n o r t h w e s t e r l y s t r i k i n g cleavage  d i p s grade from v e r t i c a l i n the west to 25° towards the e a s t .  Deformation  of S t u a r t  i s fanned  and  southwest  i s of P e r m o - T r i a s s i c  age  140 (Armstrong, 1949)  and  i s c o n s i d e r e d to be the low  high l e v e l e x p r e s s i o n of the F^ deformation  pressure,  i n the b l u e -  schists . P a l e o n t o l o g i c a l evidence  (Appendix I) demonstrates  the presence of a s y n c l i n e which appears to run the of the map  area.  Judging  length  from the southwest d i p of c h e r t  beds on e i t h e r s i d e of the limestone b e l t , i t would appear t h a t the s y n c l i n e i s asymmetric with a southwesterly  dipping  a x i a l plane.  A t i n t e r v a l s along the s t r i k e of the  belt,  the limestone  appears to c u t out; t h i s i s thought to be  due  to l o c a l c u l m i n a t i o n s i n the plunge of the s y n c l i n e .  Ultramafites  (Map  I , U n i t s 14a and  14b)  S t r u c t u r a l r e l a t i o n s h i p s o u t l i n e d i n Chapter I I I suggest  t h a t the f o l l o w i n g sequence of events  p l a c e w i t h i n the u l t r a m a f i t e s .  C o r r e l a t i o n of  has  taken  deformational  phases w i t h those r e c o g n i z e d i n the b l u e s c h i s t s i s tentative. (a) Magmatic c r y s t a l l i z a t i o n of h a r z b u r g i t e  and  i n t r u s i o n of d u n i t e pods, (b) Formation of e a r l y p y r o x e n i t e and d u n i t e  layers,  tc) F o l d i n g and h i g h temperature metamorphic r e c r y s t a l l i z a t i o n w i t h i n the mantle ( ? ) , (d) Formation of l a t e p y r o x e n i t e  layers,  (e) Emplacement, p e r v a s i v e f r a c t u r i n g , i n t r o d u c t i o n of connate  (?) water and  s e r p e n t i n i z a t i o n (This  141 event was  p o s s i b l y contemporaneous w i t h F^  and/or  F^ d e f o r m a t i o n s ) , Cf). Formation of l a t e f r a c t u r e c l e a v a g e , f o l i a t i o n of the s e r p e n t i n i t e along f a u l t zones and minor serpentinization  (.contemporaneous w i t h F^ or F^  deformations).  B a s i c rocks south of P i n c h i Lake  (Map I , U n i t 4)  T h i s b e l t of r o c k s i s bounded to the n o r t h by T a k l a Group sediments of Upper T r i a s i c  (?) age and to the south  by an elongate s e r p e n t i n i t e body thought t o be a s s o c i a t e d w i t h a major f a u l t  (Map VI, No.  3).  I t i s u n c e r t a i n whether  the n o r t h e r n c o n t a c t of u n i t 4 i s a f a u l t or an unconformity. An unconformity i s more probable because a conglomerate  of the presence of  c o n t a i n i n g pebbles of a metabasic rock near  the base of a T a k l a Group  (?) sedimentary sequence ( u n i t 10).  I f t h i s i s an unconformity, the f o l l o w i n g sequence of events must have taken p l a c e : (a) f r a c t u r i n g , i n t r o d u c t i o n of water and a m p h i b o l i z a t i o n of metabasic r o c k s p r i o r to or d u r i n g P e r m o - T r i a s s i c deformation, (h\  d e p o s i t i o n of Upper T r i a s s i c  (?) sediments  of the  T a k l a Group, and (cl o v e r t u r n i n g of the sequence d u r i n g Mesozoic T e r t i a r y deformation.  or  142 Takla Group  (Map  I, U n i t s  10,  11 and  12)  Rocks b e l o n g i n g to t h i s group are u n f o l i a t e d and been s u b j e c t  to low grade b u r i a l metamorphism r a t h e r  the dynamic metamorphism which c h a r a c t e r i z e s Creek Group.  have  than  the Cache  S t r u c t u r a l elements i n c l u d e a f r a c t u r e  cleavage i n s i l t s t o n e s and  sparse k i n k bands.  Folds  r a r e and  appear to be g e n t l e warps i n the v i c i n i t y  faults.  The  are  of  i n t e n s i v e f a u l t i n g i s the r e s u l t of Mesozoic  or T e r t i a r y deformation.  Important F a u l t s i n the P i n c h i Area The  f a u l t p a t t e r n a t P i n c h i i s h i g h l y complex and  d i v i d e d the area i n t o a s e r i e s of elongate t e c t o n i c of c o n t r a s t i n g metamorphic grade. numbered f o r r e f e r e n c e  purposes  slices  A l l f a u l t s have been  (Map  VI)  i n d i c a t e d by an a l p h a b e t i c a l s u b s c r i p t  w i t h splay f a u l t s (e.g. 2a,  2b).  In areas of poor exposure, f a u l t r e c o g n i t i o n i s extremely d i f f i c u l t . are as  Some of the c r i t e r i a used a t P i n c h i  follows:  (a) abrupt change i n metamorphic grade, s t r u c t u r a l complexity or l i t h o l o g y , (b) presence of c a r b o n a t i z e d  zones i n u l t r a m a f i t e s  or metasediments, (c) presence of s e r p e n t i n i t e s and magnetic  highs,  has  associated  linear  143 (d) o c c u r r e n c e o f l i n e a r topographic lows c o n t a i n i n g s p o r a d i c sag ponds, and (e) f a u l t b r e c c i a s encountered i n d r i l l core o r , r a r e l y , i n outcrop. Once a f a u l t has been e s t a b l i s h e d on these c r i t e r i a , i t i s even more d i f f i c u l t i n g and type of movement.  to demonstrate the age of f a u l t This d i f f i c u l t y  i s largely  because of the s c a r c i t y o f r o c k s younger than Lower J u r a s s i c . However, i n f o r m a t i o n on the age and type of f a u l t  activity  can be o b t a i n e d from (a) proven r e l a t i o n s h i p s i n a d j a c e n t  map-areas,  (b) minor s t r u c t u r e s such as drag f o l d s ,  lineations  and s l i c k e n s i d e s , and (c) metamorphic  grade of r o c k s which have been  juxtaposed. An a d d i t i o n a l f a c t o r which must be c o n s i d e r e d , e s p e c i a l l y i n areas of major f a u l t s , i s the p o s s i b i l i t y of r e a c t i v a t i o n of an o l d f a u l t under a d i f f e r e n t s t r e s s system.  Pinchi Fault  (No. 1)  W i t h i n the map  a r e a , the P i n c h i F a u l t juxtaposes  rocks o f the T a k l a and Cache.Creek Groups.  To the southwest  of the f a u l t zone, the Cache Creek Group i s c l o s e l y a s s o c i a t e d w i t h u l t r a m a f i c bodies and has been metamorphosed under lower g r e e n s c h i s t or b l u e s c h i s t f a c i e s  conditions.  144  Evidence and F^,  has been given f o r two  p e r i o d s of deformation,  p r i o r to the d e p o s i t i o n of the Upper  Triassic.  Most i n f o r m a t i o n on the f a u l t zone was  obtained  F^  just  e a s t of P i n c h i Mine where i t appears to be about 2 000 f t wide.  Percussion d r i l l  cores across the f a u l t i n d i c a t e d  the presence of s l i v e r s of s e r p e n t i n i t e , b r e c c i a t e d v o l c a n i c s , c a r b o n a t i z e d u l t r a m a f i t e s and aceous s c h i s t s .  contorted  Ground magnetics i n d i c a t e an e x c e l l e n t  c o r r e l a t i o n between s e r p e n t i n i t e s l i v e r s and highs.  The  linear  magnetic  s l i g h t o f f s e t of the magnetic highs w i t h r e s p e c t  to the d r i l l h o l e i n f o r m a t i o n suggests i t e s d i p s t e e p l y to the  zone i s the occurrence  t h a t the s e r p e n t i n -  northeast.  The o n l y other evidence  on the a t t i t u d e o f the  margin of Murray Ridge.  fault  of a n o r t h e a s t e r l y d i p p i n g f r a c t u r e  cleavage w i t h i n the u l t r a m a f i t e s along the  probably  carbon-  northeast  These p l a n a r s t r u c t u r e s  (^^?)  p a r a l l e l the f a u l t zone i n the P i n c h i a r e a .  30 m i l e s f a r t h e r n o r t h , symmetric aeromagnetic a c r o s s the f a u l t zone suggest  profiles  that i t i s v e r t i c a l ,  i n d i c a t e t h a t the d i p of the f a u l t zone may  However,  and  be v a r i a b l e  along i t s l e n g t h . The P i n c h i F a u l t i s one lineaments  of the major t e c t o n i c  i n c e n t r a l B r i t i s h Columbia.  from near Quesnel 500 km north-northwest  I t has been t r a c e d t o the McConnell  Creek map-area where i t appears to d i s s i p a t e i n a number of  splay f a u l t s .  Lord  (19491 and E i s b a c h e r  (1969)  demonstrated  145 t h a t i n the McConnell Creek area S u s t u t Group r o c k s of l a t e Cretaceous to Eocene age  have been i n v o l v e d  easterly directed thrust f a u l t i n g . communication) b e l i e v e s  Eisbacher  i n north-  (oral  t h a t the presence of the  extension  of the P i n c h i F a u l t a t depth i n a P a l e o z o i c - e a r l y basement may  have c o n t r o l l e d the p o s i t i o n i n g of  f a u l t s i n the cover r o c k s .  This  (p. 67  thrust  l i n e of r e a s o n i n g suggests  a c t i v e movement of the f a u l t d u r i n g the mercury m i n e r a l i z a t i o n  Mesozoic  the Eocene p r i o r to  ).  Along the northern p a r t of the f a u l t zone, r o c k s o f the Cache Greek Group are  faulted against  b a t h o l i t h which, a c c o r d i n g t o Armstrong J u r a s s i c age. was  A K-Ar  radiometric  obtained f o r the Hogem (Koo,  the Hogem  (1949), i s of  date of 170 1968).  m i l l i o n years  Significantly,  metasediments of the Cache Creek Group a d j a c e n t t o f a u l t zone are h i g h l y sheared and thermal metamorphism.  show no s i g n of  These data a l s o i n d i c a t e  a c t i v e f a u l t i n g must have taken p l a c e  a f t e r the  the contact  that emplacement  of the Hogem b a t h o l i t h  ( i . e . p o s t Middle J u r a s s i c ) .  h i s t o r y o f movement on  the P i n c h i F a u l t i s complex  c l o s e l y l i n k e d to the deformations as d i s c u s s e d  The and  i n Chapter  VI. F a u l t system no. The  2  t r a c e of t h i s f a u l t system i s s u b - p a r a l l e l  the P i n c h i F a u l t and  numerous s p l a y s  intersect i t .  to  The  most p e r s i s t e n t f a u l t separates the P i n c h i Mountain green-  146 stones to the n o r t h from the rocks. dips  lawsonite-glaucophane b e a r i n g  D r i l l i n t e r s e c t i o n s of f a u l t 2d i n d i c a t e t h a t i t  to the n o r t h e a s t a t 60° on  the Darbar c l a i m group  immediately e a s t of P i n c h i Mine.  However, 3 km west of  P i n c h i Mine, the f a u l t i s a p p a r e n t l y v e r t i c a l . juxtapose u l t r a m a f i t e s , greenstones and Carbonatization and  ultramafic  along these f a u l t  (p. 63  or n o r t h e a s t a t 60°  to 70°  plane as v e r i f i e d by d r i l l  and  faults  blueschists.  zones i s l o c a l l y  ; Plate 5).  the s i l i c a - c a r b o n a t e outcrop g e n e r a l l y  magnetic  Splay  extensive  s l i v e r s have been p a r t l y c o n v e r t e d to  s i l i c a - c a r b o n a t e rocks  and  The  foliation in  d i p s to the  is parallel  the  to the  north fault  hole i n t e r s e c t i o n s and  ground  profiles.  A s l i v e r of c h e r t pebble conglomerate i s l o c a t e d the f o o t w a l l of f a u l t no.2d on only  the Darbar c l a i m group.  conglomerate w i t h which i t could  i s found a t the west end to be  in  p o s s i b l y be  of Murray Ridge and  of Cretaceous or Paleocene age  (p. 44  The  correlated  i s believed ).  At  the  Darbar l o c a l i t y , f a u l t 2d d i p s to the n o r t h e a s t a t 60°  and  separates greenstones from a c h a o t i c mixture of g l a u c o p h a n i t i c metabasic r o c k s , stones and  carbonatized  serpentinites,  conglomerates c o n s t i t u t i n g the  footwall.  sandThe  involvement of a Cretaceous or Paleocene conglomerate i n the  f a u l t i n g suggests t h a t t h i s f a u l t was  Eocene t e c t o n i c a c t i v i t y .  active  Presumably, southwesterly  d i r e c t e d t h r u s t i n g of the greenstones caused the of a melange zone i n the  during  footwall.  formation  147  A  similar  Mine where  the  northeasterly mainly  so  but  suggests  of  the  the  conglomerate.  It  pebbles  resorbed  Fault  stone its  belt  and  northeast Triassic among  the  clearly  be  the  sites  of  no.  system  southwest  faults from  sliver dip  Mount Pope,  the  serpentinite  the  a t t i t u d e of  has the  Pinchi  along  the  This  "breccia"  fragments  in  magnesitic  rounded  chert  originally however,  angular  lies  and  a  pebbles  have  that  been  the  fragments  between shore  a  rounded  but  of  the  were  with  fault  profile  moderate  bedding  to  the and  Upper  relationship and  may  this  ultramafites or  may  not  system.  profiles  across  the  fault  zone,  varies  along  the  GH  limeAlong  cherts  The  gabbros  Pope  Lake.  rocks  contacts  parallels  the  the a  bearing  aeromagnetic  which  Pinchi  siltstones.  and  Mount  ultramafites,  associated  the  the  of  sediments,  understood  the  found  of  3  mentioned  of  Judging  North  as  is  east  carbonatization.  limestones  not  that  may  zone  the  contact.  rare,  faulted against  is  appear  the  the  last  serpentinite  of  lawsonite-glaucophane  are (?)  chert  is possible,  fault  length,  angular  "breccia"  system  This  greenstone  originated  during  just to  "breccia"  presence  that  chert  called  dipping  consists  matrix,  situation exists  the i t would  strike.  (Map. I I ) . s u g g e s t s  southwest  i n cherts  dip,  adjacent  similar to  the  that to fault  148 zone.  Towards the north-northwest however, c h e r t s near the  f a u l t zone d i p t o the southwest a t 80° and the aeromagnetic anomaly decreases i n i n t e n s i t y , s u g g e s t i n g t h a t the serpent i n i t e s l i v e r i s no longer p r e s e n t .  F a u l t system no. 4 The lineaments 4a and 4c trend e a s t - n o r t h e a s t and may w e l l be major f r a c t u r e zones r a t h e r than f a u l t s as there i s no s i g n o f o f f s e t o f l i t h o l o g i c u n i t s .  They form low  l y i n g swampy a r e a s , and f o l d s w i t h i n the limestone b e l t tend to plunge away from the f r a c t u r e zones.  F a u l t s 4b and 4d  are i n f e r r e d , f i r s t l y because they occupy t o p o g r a p h i c lows and secondly because o f the apparent r i g h t - l a t e r a l  offset  of the l i n e a r magnetic h i g h which f o l l o w s the s e r p e n t i n i t e belt  (Map I I I ) southwest o f P i n c h i Lake.  Whether t h i s  " o f f s e t " i s the r e s u l t o f normal o r s t r i k e - s l i p movement is uncertain.  I t i s i n t e r e s t i n g to note t h a t the P i n c h i  F a u l t appears to have undergone  l e f t - l a t e r a l o f f s e t by  fault l a .  F a u l t system no. 5 The only evidence f o r t h i s f a u l t i s an abrupt change i n s t r i k e o f the T a k l a sediments on e i t h e r s i d e of i t .  The  f a u l t i s p a r a l l e l t o the P i n c h i F a u l t and appears t o i n t e r s e c t i t n o r t h of Murray Ridge.  149  F a u l t s i n the v i c i n i t y of P i n c h i Mine The complex and here.  f a u l t pattern only  I t may  2c and  the w e l l documented f a u l t s w i l l be d i p s to the  w e l l be an e a r l y f a u l t as i t i s  with ultramafic s l i v e r s .  6)  around the mine i s e x c e e d i n g l y  F a u l t 2c trends southeast and  a t 80°.  (Nos.  F a u l t s 6b  listed  northeast associated  (the "south f a u l t " )  and  6a d i p to the southwest a t 50°  to 60° and  are  ation.  (1949) and  the mine g e o l o g i s t s ,  A c c o r d i n g to Armstrong  post-mineraliz-  f a u l t 6a i s a t h r u s t f a u l t w i t h l e f t l a t e r a l o b l i q u e - s l i p displacement. trending  These f a u l t s are c r o s s c u t  by  late northerly  normal f a u l t s w i t h near v e r t i c a l d i p .  VI TECTONIC IMPLICATIONS  Introduction The g e n e r a l c o n c l u s i o n a r r i v e d a t i n r e c e n t s t u d i e s i s t h a t the formation of o r o g e n i c b e l t s c o n t a i n i n g b l u e s c h i s t s i s r e l a t e d to the i n t e r a c t i o n of plates.  E r n s t (JL970) suggested  lithospheric  that blueschist  facies  metamorphism r e s u l t s from, the down-warping of the e a r t h ' s c r u s t i n a subduction zone and deep b u r i a l of Coleman  (.1971). agrees t h a t t h i s may  sediments.  be a v a l i d mechanism  but a l s o suggests t h a t b l u e s c h i s t f o r m a t i o n takes p l a c e as the r e s u l t of t e c t o n i c o v e r p r e s s u r e s developed shallow d i p p i n g zones underneath  obducted  in  oceanic c r u s t .  In c o n t r a s t t o subduction zones, obduction zones are c h a r a c t e r i z e d by a complete l a c k of a s s o c i a t e d v o l c a n i c activity. An  important f e a t u r e of orogenic b e l t s c o n t a i n i n g  b l u e s c h i s t s i s t h e i r a s s o c i a t i o n w i t h o p h i o l i t e s , and presence  i s commonly taken as evidence f o r  of o c e a n i c c r u s t d u r i n g p l a t e i n t e r a c t i o n 1970; New  Coleman, 1971).  their  involvement (Dewey and  Bird,  Commonly c i t e d examples occur i n  Caledonia. ( L i l l i e and B r o t h e r s , 1970)  and  western  151 California litic  CBailey et al.  1970;  s  Page, 1972)  where  ophio-  sequences are b e l i e v e d to have been t h r u s t over  sediments undergoing b l u e s c h i s t f a c i e s metamorphism presuma b l y d u r i n g a c t i v e subduction According  to Ernst  or  obduction.  (1971), former subduction  can be r e c o g n i z e d by a c h a r a c t e r i s t i c metamorphic w i t h r e s p e c t to a major f a u l t . Japan, western C a l i f o r n i a and developed  zonation  He g i v e s examples from the A l p s where the commonly  metamorphic sequence towards the f a u l t i s :  (a) z e o l i t i z e d r o c k s ,  (b) p u m p e l l y i t e b e a r i n g  (c) g r e e n s c h i s t s and/or b l u e s c h i s t s and lites.  zones  rocks,  (d) a l b i t e amphibo-  The p r e s e r v a t i o n of t h i s zonation i s a t t r i b u t e d  to a change i n o r i e n t a t i o n of the s t r e s s f i e l d which caused the formation of the subduction, the b u r i e d sediments.  An  and  i s o s t a t i c u p l i f t of  i n t e r e s t i n g f e a t u r e of the  r e f e r r e d to i s the occurrence movement on the major f a u l t  of p o s t - u p l i f t  areas  strike-slip  zones.  These f a u l t zones separate  regions with c o n t r a s t i n g  sedimentary r e c o r d s , s t r u c t u r a l s t y l e and grade of metamorphism, and are b e l i e v e d to be zones of p l a t e i n t e r a c t i o n . The  term "suture zone" i s used to d e s c r i b e the c o n t a c t  between two  such juxtaposed  regions.  Examples commonly  given are the Median T e c t o n i c L i n e i n Japan, the  Coast  Range T h r u s t i n C a l i f o r n i a and the I n s u b r i c L i n e i n the Swiss and  Italian Alps.  These suture zones are thought  to r e p r e s e n t fundamental zones of weakness i n the  earth's  152 c r u s t which may have been the l o c u s of u n d e r t h r u s t i n g subduction suture lift  g i v i n g r i s e t o B e n i o f f zones.  during  T h e r e a f t e r , the  zone may have been the s i t e of post-subduction  up-  or s t r i k e - s l i p movement.  C o n s t r a i n t s to T e c t o n i c Model Conclusions  of t h i s  ( F a c t u a l and  Inferred)  study  (a) The i n f e r r e d pressure-temperature c o n d i t i o n s f o r metamorphism w i t h i n the v a r i o u s  fault-bounded  b l o c k s are as f o l l o w s : 3-6  Murray Ridge greenstones  kb  100-225°C  kb  100-250°C  8-12 kb  225-325°C  12-15 kb  400-550°C  (b) The b l u e s c h i s t f a c i e s metamorphism was  contemporan-  P i n c h i Mountain greenstones  4.5-9  Blueschists Eclogite  eous w i t h the F^ d e f o r m a t i o n .  T h i s was c l o s e l y  f o l l o w e d by the F^ deformation which seems t o have been a s s o c i a t e d w i t h u p l i f t and c o o l i n g .  The K-Ar  dates o f 211, 214, 216 and 218 ± 7 m y r s a r e cons i d e r e d to r e c o r d c o o l i n g below 200°C and/or the c l o s e of the F^ deformation  (p. 1 3 6 ) .  tc) Greywackes and conglomerates w i t h i n the Upper T r i a s s i c T a k l a Group c o n t a i n d e t r i t u s which o r i g i n a t e d i n a landmass c o n s i s t i n g of b a s a l t , a m p h i b o l i t i z e d gabbro, u l t r a m a f i t e and c h e r t tp. 42  ) .  153 (d) South o f P i n c h i Lake, s e r p e n t i n i t e i s o v e r l a i n by amphibolitized Triassic  gabbro, d i a b a s e , b a s a l t and  C?l conglomerate.  metabasic rocks may sequence Ce) The  Upper  These b a s i c and  represent  an o p h i o l i t i c  Cp- 2 6 ) .  deformation was contemporaneous  w i t h the  c a r b o n a t i z a t i o n o f f a u l t zones and p o s s i b l y occurred  during  the Eocene  (p. 6 7 ).  I n f e r r e d c r u s t a l s t r u c t u r e i n c e n t r a l B r i t i s h Columbia L a r g e l y because there are no i n l i e r s of o l d e r i n the Cache Creek Group and because i t c o n t a i n s sequences, Monger et al.  3  (1972) and Dercourt  i m p l i e d t h a t the Group i s u n d e r l a i n by oceanic analogy w i t h other  regions  1972), such an oceanic of b a s a l t s grading b u r g i t e and  ( B a i l e y et al.  ophiolitic  (1972)  have  crust.  1970;  3  rocks  By  Page,  c r u s t would be expected t o c o n s i s t  downwards i n t o diabase, gabbro,  harz-  dunite.  In c e n t r a l B r i t i s h Columbia s e i s m i c and g r a v i t y data suggest t h a t the M - d i s c o n t i n u i t y below the s u r f a c e t h a t the oceanic  (Berry,  Therefore  et al.  M-discontinuity  burgite t r a n s i t i o n  l i e s between 30 and 35 km 3  1971).  Evidence suggests  represents  a gabbrd/harz-  (Coleman, 1971; Aumento et al.  3  1970).  i t would appear t h a t the Cache Creek Group  within  the P i n c h i G e a n t i c l i n e must be a t l e a s t 25 km t h i c k ,  allow-  i n g f o r 5 km o f b a s a l t and gabbro.  However, Armstrong  FIG. 21  CRUSTAL  MODEL  FOR C E N T R A L BRITISH  PINCHI GEANTICLINE  Toklo Fault  COLUMBIA  OMINECA  QUESNEL TROUGH  Pinchi Fault  Topley Intrusions Cache Creek Group  GEANTICLINE  Hogem  0  MOUNTAIN BELT  Rocky Mf. Trench  Wolverine Fault  Bafholifh Paleozoic Lower Mesozoic volcanics.clastics  ROCKY THRUST  Proterozoic ond Lower Paleozoic  Proterozoic 8 Paleozoic  10 Km 20 30-  — Conrad  /y// highly conductive (hydroted ?)  •—M  lower crust  (Dragert, 1970; Caner, 1970) •• M  approximate  depth to Mohorovicic discontinuity  (Berry et al., 1971; D.A.G. Forsyth, M.Sc. thesis in prep., U.B.C, 1973) For section location, see Fig. I, A-B  Discontinuity  20 km  155  (1949) estimates  the maximum t h i c k n e s s of the Cache Creek  Group as being 6 km. as wherever  T h i s i s c o n s i d e r e d an  overestimate,  d e t a i l e d work has been done, r e p e t i t i o n s of  s t r a t a have been r e c o g n i z e d  (Douglas et al.  3  1970,  p.  I t f o l l o w s t h a t i f the i n t e r p r e t a t i o n s o f s e i s m i c  416).  and  g r a v i t y data are v a l i d , a s u r p r i s i n g amount of t e c t o n i c t h i c k e n i n g of the Cache Creek Group must have taken to g i v e a depth of over  25:'km to o c e a n i c c r u s t .  Geomagnetic depth sounding and s t u d i e s i n c e n t r a l B r i t i s h Columbia the presence of an important  magnetotelluric  (Dragert, 1970)  suggest  d i s c o n t i n u i t y i n the c o n d u c t i v i t y  of the e a r t h ' s c r u s t a t a depth of 10 t o 15 km. t r a n s i t i o n from a p o o r l y conductive conductive  place  The  s u r f a c e l a y e r to a h i g h l y  lower l a y e r i s i n t e r p r e t e d as being due  m e l t i n g or h y d r a t i o n of the lower c r u s t (Caner,  to p a r t i a l  1970).  P a r t i a l m e l t i n g a t depths of 10 to 15 km commences a t approximately  7 00°C i n a "wet"  g r a n i t e and would  imply  steep, u n r e a l i s t i c , geothermal g r a d i e n t s of the order of 40°to 70°C per km.  Moreover, i f p a r t i a l m e l t i n g d i d e x i s t ,  i t would be expected a t the s u r f a c e .  to g i v e r i s e to Quaternary v o l c a n i c i t y  Study of nodules w i t h i n Quaternary b a s a l t s  from B r i t i s h Columbia they had to 70 km,  ( L i t t l e J o h n , 1972), suggests  that  a f a i r l y deep-seated source, p o s s i b l y around  35  and c o u l d not t h e r e f o r e be r e l a t e d to p a r t i a l  m e l t i n g between 10 and  30 km.  T h e r e f o r e , h y d r a t i o n seems  156 to be the b e s t mechanism f o r e x p l a i n i n g  the i n c r e a s e i n  c o n d u c t i v i t y o f the lower c r u s t . The presence of a 10 t o 15 km d i s c o n t i n u i t y beneath the Cache Creek Group t h e r e f o r e u n r e a l i s t i c thickness and  suggests t h a t the somewhat  o f over 25 km i n f e r r e d from  g r a v i t y r e s u l t s may be i n e r r o r .  g e o l o g i c a l and g e o p h y s i c a l proposed  seismic  To compromise the  evidence, a c r u s t a l model i s  ( F i g . 21). i n which the P i n c h i G e a n t i c l i n e ,  s i s t i n g of t e c t o n i c a l l y thickened  con-  Cache Creek Group w i t h  a s s o c i a t e d o p h i o l i t e s , i s 10 t o 15 km t h i c k and the lower c r u s t i s a mixture of s e r p e n t i n i z e d  peridotite,  amphibolite,  s l i v e r s o f Cache Creek Group and p o s s i b l y minor e c l o g i t e . Increasing  temperatures may r e s u l t i n d e h y d r a t i o n  reactions  which g i v e r i s e t o i n t e r s t i t i a l water vapour, thus c r e a t i n g the c o n d u c t i v i t y anomaly.  The d i s c o n t i n u i t y a t 3 0 to 35 km  proposed by g r a v i t y and seismic models may r e p r e s e n t the t r a n s i t i o n to anhydrous p e r i d o t i t e . A p o s s i b l e a l t e r n a t i v e model would show the Cache Creek Group and a s s o c i a t e d lower P a l e o z o i c M-discontinuity.  o p h i o l i t e s as being u n d e r l a i n by  rocks and/or basement g n e i s s e s down t o the Such a basement c o u l d  have been t h r u s t under  the Cache Creek Group d u r i n g Mesozoic t e c t o n i s m . i s thought u n l i k e l y as lower P a l e o z o i c  T h i s model  or g n e i s s i c r o c k s  which c o u l d be i n t e r p r e t e d as basement have n o t been recognized and  i n the intermontane r e g i o n .  Also,  serpentinite  p e r i d o t i t e have a much lower r e s i s t i v i t y than g r a n i t o i d  157 rocks  (Caner, 1970)  and would t h e r e f o r e be more l i k e l y t o  y i e l d the c o n d u c t i v i t y anomaly below 15  km.  The P i n c h i F a u l t as a "Suture Zone" The p o s s i b i l i t y e x i s t s t h a t the P i n c h i F a u l t l i e s w i t h i n a P e r m o - T r i a s s i c "suture zone" which welded together  two  t e c t o n i c b e l t s of c o n t r a s t i n g age and/or primary d e p o s i t i o n a l environment. Creek Group  For much of the l e n g t h of the f a u l t , Cache r o c k s are i n c o n t a c t with lower  greywackes, v o l c a n i c s and i n t r u s i v e s of the Mesozoic  ( F i g . 22).  To the e a s t  i s a b e l t o f rocks f o r m e r l y mapped as  P a l e o z o i c by Armstrong were re-examined  Mesozoic  (1949) and Roots  by Monger  (1954).  late  These rocks  (197 3) and h i s p r e l i m i n a r y  s t r a t i g r a p h i c data are shown i n F i g . 22.  A number of  important o b s e r v a t i o n s emerge from these s t u d i e s .  Firstly,  the b e l t c o n t a i n s r o c k s r a n g i n g i n age from P r o t e r o z o i c t o Middle Pennsylvanian.  Younger r o c k s may  d i a g n o s t i c f o s s i l s have not been found.  be p r e s e n t but Secondly, i n the  Lay Range, Pennsylvanian r o c k s are i n t r u d e d by the P o l a r i s ultramafite.  T h i r d l y , the Pennsylvanian r o c k s , of s i m i l a r  age to the lower p a r t of the Cache Creek Group west of the P i n c h i F a u l t , c o n s i s t of v o l c a n i c sandstone,  agglomerate,  carbonate pods, r e d r a d i o l a r i a n c h e r t and a r g i l l i t e . t h e r e f o r e appears t h a t rocks of s i m i l a r age, and metamorphic grade are found on both s i d e s  It  association of the P i n c h i  F a u l t and t h e r e i s no obvious j u s t i f i c a t i o n f o r c a l l i n g  158  F i g . 22  G e n e r a l i z e d diagram i l l u s t r a t i n g l o c a t i o n of major g e o l o g i c u n i t s i n c e n t r a l B r i t i s h Columbia i n r e l a t i o n to the p r o b l e m a t i c a l b e l t of P a l e o z o i c r o c k s between the T a k l a Group and the Omineca Geanticline Cstippled area). The s t r a t i g r a p h y i n t h i s b e l t was r e p o r t e d on by Monger (1973). Area "A" i n the Lay Range c o n t a i n s a h i g h l y f a u l t e d s e c t i o n c o n s i s t i n g of (a) E a r l y Pennsylvanian (?) v o l c a n i c sandstone and agglomerates, and (b) M i d d l e P e n n s y l v a n i a n carbonate, b r e c c i a and sandstone. Area "B", near Germansen Landing, c o n t a i n s a s e c t i o n extending from l a t e s t P r o t e r o z o i c to p o s s i b l e Mississippian.  15 9  the f a u l t a "suture zone."  However, i n the e a s t e r n  belt  a much longer d e p o s i t i o n a l h i s t o r y i s r e c o r d e d extending from the P r o t e r o z o i c  to the Upper P a l e o z o i c .  d i f f e r e n c e s i n l i t h o l o g i e s between the two important of which are  There are  b e l t s , the most  the p a u c i t y of bedded c h e r t  and  the occurrence of an a p p r e c i a b l e  thickness  sandstone and  the b e l t to the e a s t  the f a u l t .  agglomerate w i t h i n  Whether these two  also  of v o l c a n i c  f a c t o r s present  of  sufficient  j u s t i f i c a t i o n to c a l l the P i n c h i F a u l t a suture zone i s open to s p e c u l a t i o n .  Perhaps the term may  equally well  be  a p p l i e d to the major f a u l t which separates the Omineca G e a n t i c l i n e from the P a l e o z o i c  r o c k s to the e a s t  ( i . e . the  Wolverine F a u l t ) . P a l e o n t o l o g i c a l evidence suggests t h a t the F a u l t separates two  l a t e Paleozoic  and  there  Ross, 1970)  but  faunal belts  i s uncertainty  Pinchi  (Monger  as to whether  the d i f f e r e n t faunas are the r e s u l t of l o c a l v a r i a t i o n i n d e p o s i t i o n a l environment or the i s o l a t e d biogeographic provinces On  " j u x t a p o s i t i o n of  originally  by major c r u s t a l movements."  account of A s i a t i c f a u n a l a f f i n i t i e s , Wilson  (1968)  suggested t h a t the western p a r t of the Canadian C o r d i l l e r a had  d r i f t e d across  from A s i a .  The  c o l l i s i o n zone as  r e p r e s e n t e d by Wilson l i e s to the west of the Omineca G e a n t i c l i n e and fault  zones.  presumably f o l l o w s  the P i n c h i or Wolverine  160 Evidence f o r s t r i k e - s l i p movement on the P i n c h i The  length  (450 km) and s t r a i g h t n e s s  Fault  o f the P i n c h i  F a u l t suggest t h a t a t some time i n i t s h i s t o r y , i t may have been a s t r i k e - s l i p f a u l t . Upper T r i a s s i c continuation significant prior  In the McConnell Creek map-area,  T a k l a Group r o c k s a r e found a s t r i d e the  o f the f a u l t , suggesting t h a t i f there was s t r i k e - s l i p displacement i t must have taken  t o the Late T r i a s s i c .  As the f a u l t c u t s a c r o s s  place  folded  Cache Creek Group l i m e s t o n e s , s t r i k e - s l i p movement probably post-dates P e r m o - T r i a s s i c  (F^) deformation and may have been  contemporaneous w i t h the T r i a s s i c  F^ deformation i n the  blueschists. I t i s i n t e r e s t i n g to s p e c u l a t e whether o b l i q u e - s l i p movement on the f a u l t c o u l d have g i v e n r i s e to the F^ structures  at Pinchi.  These s t r u c t u r e s  by moderately p l u n g i n g f o l d s  (55°) which trend  to the P i n c h i F a u l t and a r e a s s o c i a t e d structures  If dip-slip  the Middle and/or Upper T r i a s s i c ,  t h a t the F  2  structures  formed as the r e s u l t the P i n c h i F a u l t .  sub-parallel  mullion  f a u l t r e s u l t e d i n e l e v a t i o n o f the P i n c h i  during  on  with  i n incompetent r o c k s and a c r e n u l a t e  ( I ^ ) p a r a l l e l to the f o l d axes. the  are c h a r a c t e r i z e d  lineation  movement on Geanticline  i t i s conceivable  i n the b l u e s c h i s t s may w e l l have  of r i g h t - l a t e r a l Steeply  o b l i q u e - s l i p movement  plunging f o l d s adjacent to  major f a u l t zones have a l s o been d e s c r i b e d  i n the South  161 I s l a n d of New Zealand. they formed d u r i n g  Lillie  01964) has suggested  an episode of s t r i k e - s l i p  that  faulting.  P o s s i b i l i t y t h a t the P i n c h i G e a n t i c l i n e was o v e r l a i n by o c e a n i c c r u s t There i s some evidence which suggests t h a t the Cache Creek Group i n c e n t r a l B r i t i s h Columbia may have been o v e r l a i n by o c e a n i c c r u s t . contain  The Upper T r i a s s i c rocks a t P i n c h i  abundant d e t r i t u s which i n d i c a t e s e r o s i o n  landmass c o n s i s t i n g of a m p h i b o l i t i z e d and  cherts.  of a  gabbro, b a s i c  volcanics  The presence o f conglomerate and carbonaceous  wood fragments i n the Upper T r i a s s i c . suggests t h a t the landmass was c l o s e - b y ,  most l i k e l y on the s i t e of what i s  now the P i n c h i G e a n t i c l i n e .  South of P i n c h i Lake, a serpen-  t i n i t e - a m p h i b o l i t i z e d g a b b r o - d i a b a s e - b a s a l t sequence i s o v e r l a i n by Upper T r i a s s i c stones and l i m e s t o n e s . rocks might r e p r e s e n t  (?) pebble conglomerates,  I t i s suggested t h a t these b a s i c a downfaulted remnant of the cover  of the P i n c h i G e a n t i c l i n e d u r i n g t h a t the b a s a l t / p e b b l e  the Upper T r i a s s i c and  conglomerate c o n t a c t  Absence o f metamorphic zonation Creek Group Ernst  silt-  within  (1971) has r e l a t e d p r o g r e s s i v e  isa  disconformity.  the Cache  metamorphic  zonations i n Japan, C a l i f o r n i a and the A l p s t o descent o f l i t h o s p h e r i c p l a t e s down subduction zones.  Reconnaissance  162 work by Armstrong (1949) and the w r i t e r i n d i c a t e s t h a t the bulk of the Cache Creek Group west of the f a u l t zone has been metamorphosed  i n the lower g r e e n s c h i s t f a c i e s ,  and a p a r t from the elongate fault-bounded  wedge of b l u e -  s c h i s t adjacent t o the f a u l t t h e r e i s a p p a r e n t l y no change i n metamorphic grade.  There i s t h e r e f o r e no  evidence  w i t h i n the Cache Creek Group of a metamorphic zonation which c o u l d be a t t r i b u t e d to p l a t e descent.  T e c t o n i c Models Subduction  model  I f hypotheses i n v o l v i n g t e c t o n i c o v e r p r e s s u r e s are discarded  (p.  6 9 ) , the most p l a u s i b l e mechanism  g e n e r a t i o n of b l u e s c h i s t s i s by subduction.  f o r the  T h i s model  i n v o l v e s descent o f an oceanic p l a t e under the c o n t i n e n t a l c r u s t and formation o f an eastward d i p p i n g B e n i o f f zone. Downwarping o f the e a r t h ' s c r u s t i s accompanied by deep b u r i a l , deformation  and metamorphism  of the sediments which  accumulated i n an o f f s h o r e o c e a n i c t r e n c h .  Consumption of  oceanic c r u s t i s b e l i e v e d to be r e l a t e d to c a l c - a l k a l i n e p l u t o n i s m and v o l c a n i s m above a descending 1968).  plate  (Dickenson,  T h e r e f o r e the absence of P e r m o - T r i a s s i c v o l c a n i c s  or p l u t o n i c s t o the e a s t o f the P i n c h i F a u l t c o u l d be looked upon as a major drawback to the subduction model.  However,  163  F i g . 23  Subduction model  164  major s t r i k e - s l i p movements on the f a u l t may and  have taken  place  the igneous rocks a s s o c i a t e d w i t h the subduction have  to be  sought elsewhere.  One  p o s s i b i l i t y i s the A s i t k a  Group which i s s i t u a t e d i n the McConnell Creek map-area 240  km n o r t h of F o r t S t . James.  P e r m o - T r i a s s i c age of r h y o l i t e and  I t i s considered  (Monger, 1973)  minor  and  to be  of  c o n s i s t s of 2000 m  andesite.  I n t r u s i v e s are p r e s e n t i n the Omineca G e a n t i c l i n e and  could represent  the source f o r o v e r l y i n g  volcanics  which have s i n c e been eroded, i n which case the T e r t i a r y K-Ar  dates  (Douglas et a l . , 1970)  u p l i f t or a r e h e a t i n g therefore  represent  event.  would r e f l e c t a r e g i o n a l  The  Omineca G e a n t i c l i n e  may  the high temperature-high pressure zone  i n a P e r m o - T r i a s s i c p a i r e d metamorphic b e l t which formed above an a c t i v e e a s t - d i p p i n g  subduction zone.  On r e l a x a t i o n of the s t r e s s e s which caused s u b d u c t i o n , i s o s t a t i c readjustment of the deeply b u r i e d  sediment p i l e  gave r i s e to a r e g i o n a l u p l i f t r e s u l t i n g i n the of the P i n c h i G e a n t i c l i n e .  The  formation  formation of the Quesnel  Trough i to the e a s t of the P i n c h i G e a n t i c l i n e may  w e l l have  been caused by downwarping of the c r u s t above the exhumed subduction zone. responsible,for  Such a mechanism i s b e l i e v e d the  formation o f the Po Basin and  Great V a l l e y of C a l i f o r n i a may  to  o r i g i n a l l y have been one  (Ernst, 1971).  The  be the  Pinchi Fault  of the major f a u l t s i n the  165 subduction zone. may  During the u p l i f t , the  w e l l have been r e v e r s e d  and  such as the b l u e s c h i s t - b e a r i n g  sense of movement  deeply b u r i e d  sediments  fault-block exploited  f a u l t zone as an easy upward path i n e s t a b l i s h i n g  the  isostatic  equilibrium. There are three main drawbacks to t h i s model.  Firstly,  i t i s d i f f i c u l t to e x p l a i n the occurrence o f o p h i o l i t e s exposed a t the s u r f a c e  of the u p l i f t e d P i n c h i G e a n t i c l i n e .  Presumably, the o p h i o l i t e s were t h r u s t over the Cache Creek Group e i t h e r from the west or the e a s t .  Secondly, i t i s  to be expected t h a t a r e g i o n a l u p l i f t o f the metasedimentary p i l e should g i v e r i s e to a p r o g r e s s i v e with respect  metamorphic  to the P i n c h i F a u l t as seems t o have happened  i n Japan, the A l p s and  California  (Ernst, 1971).  However,  the bulk of the Cache Creek Group i s i n the lower f a c i e s and  the b l u e s c h i s t s form an  wedge a d j a c e n t to the f a u l t .  The  contemporaneous w i t h subduction.  and  was  t h i r d drawback i s the  A possible  t h a t the subduction zone had s i m i l a r to an obduction zone.  t h a t obduction zones are c h a r a c t e r i z e d of v o l c a n i c a c t i v i t y .  greenschist  i s o l a t e d fault-bounded  apparent absence of c a l c - a l k a l i n e p l u t o n i s m and  could be  zonation  volcanism  explanation  a v e r y shallow d i p Coleman  (1971) s t a t e s  by a complete  However, a shallow d i p p i n g  zone would make i t d i f f i c u l t to e x p l a i n the high  lack  obduction lithostatic  p r e s s u r e s necessary t o c r e a t e the P i n c h i b l u e s c h i s t s without r e s o r t i n g to t e c t o n i c o v e r p r e s s u r e s .  166 F i g . 24  Subduction-obduction model i l l u s t r a t i n g of main t e c t o n i c f e a t u r e s Columbia  evolution  in central British  (a) During the P e n n s y l v a n i a n , rocks  of the S l i d e Mountain Group were obducted over the P r o t e r o z o i c  and  Lower Cambrian rocks con-  s t i t u t i n g the Omineca G e a n t i c l i n e et al.  3  1972).  wards d i p p i n g  (b) The  ( a f t e r Monger,  f o r m a t i o n of an  subduction zone gave r i s e to  s c h i s t f a c i e s metamorphism and Cache Creek Group sediments.  a large thickness  d e n s i t y m a t e r i a l , was  not  blue-  deformation of (c) An  impinged on the subduction zone and contained  east-  i s l a n d arc because i t  of buoyant  subducted.  low Obduction of  an o p h i o l i t e s l a b , e i t h e r from the e a s t or west appears to have accompanied t h i s event. c r u s t below the P i n c h i G e a n t i c l i n e may have been thickened after this period of 30 km  by u n d e r t h r u s t i n g  The well  during  or  to g i v e the observed depth  to the M - d i s c o n t i n u i t y .  (d) A change  i n o r i e n t a t i o n of the s t r e s s regime, r e s u l t e d i n r i g h t - l a t e r a l o b l i q u e - s l i p movement along the P i n c h i F a u l t zone and Geanticline.  u p l i f t of the  B l u e s c h i s t and  serpentinized  u l t r a m a f i t e d i a p i r s were emplaced along fault.  Pinchi  the  D e t r i t u s from o p h i o l i t i c rocks exposed  on the P i n c h i G e a n t i c l i n e was Quesnel 'T.r.ough.  shed i n t o  the  167  Cache Creek Group sediments Pinchi  elastics  Pinchi Foult Geanticline  I  limestone  Quesnel Trough v  basalt  c  gabbro  II//}/  peridotite  20 km  (d)  LATE Rocky Mt. Trench  (c)  EARLY TRIASSIC melting (?)  Island  arc trench  obducted  (a)  PENNSYLVANIAN  slab (Slide Mt  168 Subduction/obduction  model  Because of the drawbacks of the subduction model, a second model i s suggested which i n v o l v e s a of subduction and obduction  ( F i g . 24).  combination  A t a number of  l o c a l i t i e s i n the C o r d i l l e r a , l a t e P a l e o z o i c v o l c a n i c s , c h e r t s and minor v o l c a n i c s o v e r l i e o l d e r m i o g e o c l i n a l r o c k s and i t has been suggested  (Monger et a l . ,  1972;  Dercourt,  1972)  t h a t the l a t e P a l e o z o i c rocks are a l l o c h t h o n o u s , having been t h r u s t e a s t e r l y over the m i o g e o c l i n a l e l a s t i c s s t i t u t i n g the Omineca G e a n t i c l i n e d u r i n g the Orogeny.  con-  Caribooan  T h i s s i t u a t i o n i s i l l u s t r a t e d i n the e a s t e r n h a l f  of F i g . 24a.  During the Pennsylvanian, an i s l a n d arc w i t h  a s s o c i a t e d limestones was  s i t u a t e d a t an unknown d i s t a n c e  from the North American c r a t o n  ( F i g . 24a).  c o n t i n u e d t o grow i n t h i c k n e s s d u r i n g the and Permian and may  The  limestones  Pennsylvanian  have formed an e x t e n s i v e b a r r i e r r e e f  type d e p o s i t a d j a c e n t to the i s l a n d a r c .  A t the c l o s e of  the Permian an east-west p r i n c i p a l s t r e s s , p o s s i b l y r e s u l t of ocean f l o o r s p r e a d i n g , caused  the  the f o r m a t i o n of a  subduction zone, and the sea f l o o r between the a r c and c o n t i n e n t was  consumed.  the  There i s no c e r t a i n evidence t h a t  v o l c a n i c i t y accompanied the s u b d u c t i o n .  E v e n t u a l l y the  i s l a n d a r c approached the subduction zone and because i t c o n t a i n e d a l a r g e t h i c k n e s s of buoyant low d e n s i t y r o c k s , d i d not descend  the subduction zone.  The  s c a r c i t y of a r c  169  (a) development of en echelon fractures  (b) s t r i k e - s l i p movement r e s u l t s i n "rhombochasm" formation (Carey, 1958)  (c) d i a p i r i c i n t r u s i o n o f b l u e s c h i s t and serpent i n i z e d u l t r a m a f i t e along zones of low l i t h o s t a t i c pressure  Fig.  25  P o s s i b l e mechanism f o r i n t r u s i o n o f b l u e s c h i s t s and s e r p e n t i n i z e d u l t r a m a f i t e s along s t r i k e - s l i p faults.  170 type v o l c a n i c r o c k s a s s o c i a t e d w i t h the limestones i n the P i n c h i G e a n t i c l i n e i s a major problem. the v o l c a n i c basement  I t i s possible that  C?) o f the i s l a n d a r c was  subducted.  The  c o l l i s i o n of the i s l a n d a r c w i t h the subduction zone  was  p o s s i b l y f o l l o w e d by o v e r t h r u s t i n g or obduction of  o c e a n i c c r u s t over the accumulation sediments above the subduction  of Cache Creek Group  zone.  A change i n o r i e n t a t i o n o f the p r i n c i p a l s t r e s s e s brought  about o b l i q u e - s l i p movement along the main f a u l t i n  the subduction zone  ( i . e . the P i n c h i F a u l t ?) .  I t i s suggested  t h a t a s t r i k e - s l i p component of movement on the f a u l t c r e a t e d zones of low p r e s s u r e s p o r a d i c a l l y along the f a u l t zone , which were a t once f i l l e d  from below by i n t r u s i o n of  low  d e n s i t y f a u l t bounded d i a p i r s attempting t o r e g a i n i s o s t a t i c e q u i l i b r i u m and o r i g i n a t i n g i n the depths of the subduction zone.  former  These low p r e s s u r e zones can p o s s i b l y  compared w i t h Carey's  (1956) rhombochasms  t h i s mechanism, composite  ( F i g . 25).  b l o c k s of low average  Using  density  c o n t a i n i n g b l u e s c h i s t , s e r p e n t i n i z e d u l t r a m a f i t e and could have worked t h e i r way  be  eclogite  up to a higher s t r u c t u r a l  level  and are t h e r e f o r e r e p r e s e n t a t i v e of the lower c r u s t or mantle a t t h a t time.  As the b l u e s c h i s t s rose i n the  they c o o l e d to temperatures retention l?l  of the F~  below those necessary f o r argon  (c. 200°C) and were deformed by F^.  T r i a s s i c K-Ar  crust,  The  Upper  dates are c o n s i d e r e d to mark the c l o s e  deformation.  171  During the Upper T r i a s s i c , u p l i f t and e r o s i o n of the P i n c h i G e a n t i c l i n e brought about d e p o s i t i o n of conglomerates  and f l y s c h i n the a d j a c e n t Quesnel  The composition of the sediments  Trough.  i s compatible w i t h a l a n d -  mass which c o n s i s t e d of b a s i c r o c k s , c h e r t s and  ultra-  mafites . T h i s model i s p r e f e r r e d f o r a number of reasons. F i r s t l y , the presence of an obducted  o p h i o l i t e cover to the  Cache Creek Group i s compatible w i t h the presence of b a s i c d e t r i t u s i n the Upper T r i a s s i c sediments.  I t i s considered  p o s s i b l e t h a t the o p h i o l i t e sequence south of P i n c h i Lake, which appears  to be o v e r l a i n conformably  by Upper T r i a s s i c  w i t h no i n t e r v e n i n g Cache Creek Group sediments, remnant of t h i s cover.  is a  Secondly, the presence of a major  zone of c r u s t a l weakness a s s o c i a t e d w i t h a subduction zone accounts f o r the development and  subsequent  reactivation  of the P i n c h i F a u l t . The absence of a metamorphic z o n a t i o n i n the Cache Creek Group w i t h r e s p e c t to the P i n c h i F a u l t i s p r o b l e m a t i c a l . Perhaps such zonations are c h a r a c t e r i s t i c of r e g i o n s where l a r g e amounts of m a t e r i a l have been subducted and exhumed. I t may  be t h a t a r e l a t i v e l y s m a l l volume of rock was  sub-  ducted and metamorphosed i n the b l u e s c h i s t f a c i e s along the P i n c h i F a u l t and a s i g n i f i c a n t i s o s t a t i c anomaly which c o u l d produce  a r e g i o n a l u p l i f t and exhumation of a  metamorphic zonation was  not formed.  172 Mesozoic and T e r t i a r y events Mesozoic movement on the P i n c h i F a u l t i s p o o r l y recorded.  Movement may  w e l l have o c c u r r e d d u r i n g the  Mesozoic, as the f a u l t forms the western margin of the m i l l i o n year o l d Hogem b a t h o l i t h . may  However, t h i s  late 170  feature  a l s o have formed as the r e s u l t of T e r t i a r y a c t i v i t y . The  occurrence  of Cretaceous or Paleocene conglomerate  i n v o l v e d i n f a u l t i n g i n the P i n c h i area i s c o n v i n c i n g evidence  f o r a p e r i o d of T e r t i a r y F a u l t a c t i v i t y .  inferred  Cp. 67  It  was  ) t h a t s i l i c a - c a r b o n a t e rocks formed d u r i n g  a r e a c t i v a t i o n of the P i n c h i F a u l t d u r i n g the Eocene. Because of the a s s o c i a t i o n of c a r b o n a t i z a t i o n and F^ deformation  intense  i n the mine a r e a , i t i s b e l i e v e d t h a t  formation of s i l i c a - c a r b o n a t e rocks was f a u l t i n g and F^ deformation.  contemporaneous w i t h  C o n s i d e r a t i o n of the  trend  and plunge of F^ f o l d s and of the sense of warping i n the limestone  u n i t s suggests t h a t r i g h t - l a t e r a l movement w i t h  a d i p - s l i p component may (Map  VI)  d u r i n g F^.  widespread 240 1970).  The  f a u l t planes may  km  have taken p l a c e along f a u l t NO.  Northeasterly directed thrusting  to the n o r t h d u r i n g the Eocene  common occurrence  was  (Eisbacher,  of n o r t h e a s t e r l y d i p p i n g  suggests t h a t s i m i l a r l y o r i e n t e d s t r e s s e s  have given r i s e to u n d e r t h r u s t i n g  but t h i s i s s p e c u l a t i v e .  2  i n the P i n c h i a r e a ,  173  Mercury m i n e r a l i z a t i o n o c c u r r e d  a f t e r the  a t i o n , p o s s i b l y a s s o c i a t e d w i t h hot s p r i n g  carbonatiz-  activity.  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M i n e r a l , P e t r o l . , v o l . 33, p. 145. n  2  Thompson, M.L., 1965,Pennsylvanian and E a r l y Permian f u s u l i n i d s from F o r t S t . James a r e a , B r i t i s h Columbia, Canada: J o u r . P a l e o n t o l . v o l . 39, p. 224. T i p p e r , H.W., 1971, G l a c i a l geomorphology and P l e i s t o c e n e h i s t o r y of c e n t r a l B r i t i s h Columbia: G e o l . Surv. Canada, B u l l . 196. Tozer, E.T., 1964, The T r i a s s i c P e r i o d i n The Phanerozoic Time S c a l e : G e o l . Soc. Lond. Quart. J o u r . , v o l . 1205, p. 207. Trumpy, R., 1960, P a l e o t e c t o n i c e v o l u t i o n of the c e n t r a l and western A l p s : G e o l . Soc. Am. B u l l . , v o l . 71, p. 843. Turner, F . J . , 1968, Metamorphic New York.  P e t r o l o g y : McGraw-Hill Co.,  Turner, F . J . , and Verhoogan, J . , 1960, Igneous and P e t r o l o g y : McGraw-Hill, New York.  Metamorphic  Turner, F . 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P e t r o l . , v o l . 32, p. 165.  187 White, D.E., 1967, Mercury and base-metal d e p o s i t s w i t h a s s o c i a t e d thermal and m i n e r a l waters: i n Geochemistry of Hydrothermal Ore D e p o s i t s , H.L. Barnes ed., H o l t , R i n e h a r t and Winston, Inc., New York, p. 575. White, W.H., E r i c k s o n , G.P., Northcote, K.E., Dirom, G.E., and Harakal, J.E., 1967, I s o t o p i c d a t i n g of the Guichon B a t h o l i t h : Canad. J o u r . E a r t h S c i . , v o l . 4 p. 677. Wilson, G., 1953, M u l l i o n and rodding s t r u c t u r e s i n the Moine s e r i e s o f S c o t l a n d : G e o l . Assoc. P r o c , v o l . 64, p. 118. Wilson, J.T., 1968, S t a t i c of mobile e a r t h : the c u r r e n t s c i e n t i f i c r e v o l u t i o n : P r o c . Am. P h i l . Soc., v o l . 112, p. 309. W i n c h e l l , A.N., 1936, A t h i r d study of c h l o r i t e : M i n e r a l . , v o l . 21, p. 642.  Am.  Yoder, H.S. and T i l l e y , C.E., 1962, O r i g i n o f b a s a l t magma an experimental study of n a t u r a l and s y n t h e t i c rock systems: J o u r . P e t r o l . , v o l . 3, p. 342. Zwart, H., 1969, Metamorphic f a c i e s s e r i e s i n the European o r o g e n i c b e l t s and t h e i r b e a r i n g on the causes of orogeny: i n Age R e l a t i o n s i n High Grade Metamorphic T e r r a i n s , G e o l . Assoc. Canada, Spec. Paper no. 5, p. 7.  APPENDIX I FOSSIL LOCALITIES IN THE PINCHI AREA  The p o s i t i o n s of the f o l l o w i n g f o s s i l are shown i n Map  I.  localities  In the l i s t which f o l l o w s ,  assigned by other authors are g i v e n i n b r a c k e t s a f t e r the l o c a l i t y number used i n t h i s A.  p. B.  immediately  study.  C o l l e c t e d by I . Paterson; i d e n t i f i e d by W.R. Fauna from f o s s i l  localities  l o c a l i t i e s F - l to F-6  Danner  are g i v e n on  40 .  C o l l e c t e d by J.E. Armstrong workers F - 7  and  i d e n t i f i e d by v a r i o u s  (.51 : southeast end of a r i d g e l y i n g between P i n c h i v i l l a g e , S t u a r t Lake and Lake; Tvitioites;  Pinchi  age; probably Upper  Pennsylvanian. F-8  (.81 : south s i d e of Mount Pope;  Lonsdaleia-  l i k e c o r a l and c r i n o i d d i s c s and Age; C.  Carboniferous  C o l l e c t e d and i d e n t i f i e d by M.L. F-9 F-10  (BC-12) Eosohubevte ;  (BC-141; Fusulinella  I la ;  ParamiIlereI  (?1.  Thompson.  Millerella;  jamesensis:  Pseudostaffella  sandersoni; la.  stems.  Favamillevella Fusulinella; Millevella;  .  189 F- 11  (BC- 17} : Pseudostaffella  sandevsoni;  jamesensis  C?); P a v a m i l l e r e l l a ;  F- 12  (BC- 11) : Eosehubevtella;  F- 13  CBC- 13) : Fusulina  F- 14  CBC-  Millevella  Fusulinella.  ? ocoasa  15) : Quasifusulina popensis  Fusulinella  ?  popensis  n.  n. sp.;  Sohubertella  sp.  18) : Quasifusulina  ?;  F- 15  CBC-  F- 16  (BC- •52) : Sohubertella  F- 17  tBC- •24) : P r o f u s u l i n e l l a  F- 18  tBC- 23) : Fusulina  ?;  Sohubertella. Fusulinella.  ?;  ? ocoasa  Pseudostaffella; n. sp.;  Pseudostaffella;  Schubevtella. F- 19  CBC- 49) : Fusulina  p i t v a t i n. sp.;  Fusulinella; F- 20  (BC- •48} : Fusulina  Sohubertella.  p i t r a t i n. sp.;  Fusulinella; F- •21  CBC-  Oketaella; CBC-  F- 23  CBC-  amerioana  19). : Fusulina tella;  n. sp.;  Tritioites  n. sp.; Sohubertella Tritioites  •53) : Pseudoschwagerina stuartensis  Fusulina;  Sohubertella.  •21} : Quasifusulina pinohiensis  F- •22  Fusilina;  n.  stuartensis  arta;  n.  sp.?  Tritioites  sp.  pitrati?; Pseudostaf  kingi?  Fusulinella; fella.  Eosohuber-  190  D.  C o l l e c t e d by I.A. P a t e r s o n , i d e n t i f i e d by W.R. F-24:  Fusulinella  jamesensis;  Akiyoshiella  Danner.  sp.?  Middle P e n n s y l v a n i a n . F-25:  Sahwagerina  sp.  E a r l y Permian. F-26:  Tetvataxis  sp.  Pennsylvanian and Permian range. A l g a l s t r u c t u r e s , bryozoa and echinoderm are a l s o p r e s e n t .  clasts  APPENDIX I I MINERALOGY  A n a l y t i c a l Methods Approximately  200 t h i n s e c t i o n s and 10 p o l i s h e d  s e c t i o n s of greenstones, were examined.  g l a u c o p h a n i t i c r o c k s and carbonates  Whole rock or s i n g l e m i n e r a l d i f f r a c t i o n  t r a c e s were used to c o n f i r m o p t i c a l i d e n t i f i c a t i o n o f minerals.  X-ray  standards were prepared by r e p e a t e d l y  c e n t r i f u g i n g the 200-250 mesh f r a c t i o n i n diodomethane o r bromoform.  Measurements of r e f r a c t i v e i n d i c e s were not made  because of u n c e r t a i n t y of c o r r e l a t i o n of r e f r a c t i v e w i t h chemical  index  composition.  C e l l parameters of three glaucophanes and one j a d e i t i c pyroxene are g i v e n along w i t h the d i f f r a c t i o n method i n Table 7. To i l l u s t r a t e t e x t u r e s i n carbonate r o c k s , s l a b s from 7 d o l o m i t i c limestones were etched w i t h HCl and s t a i n e d using a l i z a r i n e r e d s o l u t i o n and F i e g l ' s s o l u t i o n  (Friedman,  19591. Because of f i n e g r a i n s i z e , f a b r i c h e t e r o g e n i e t y and d i f f i c u l t y of r e c o g n i t i o n o f phases, a c c u r a t e modal a n a l y s e s are d i f f i c u l t t o o b t a i n .  However, modal analyses u s i n g a  Z e i s s micrometer eyepiece were obtained f o r f o u r rocks and  192 estimates made f o r many more  (.Tables 20, 22, 24 and 25).  M i n e r a l compositions were determined u s i n g an A.R.L. e l e c t r o n microprobe a t the U n i v e r s i t y o f Washington. i n g c o n d i t i o n s were as f o l l o w s :  15 KV a c c e l e r a t i n g  Operatpotential,  1-2 u. spot s i z e , specimen c u r r e n t of 0.09 y-amps f o r major elements and 0.18 y-amps f o r minor elements.  The time taken  f o r a c o n s t a n t amount o f c u r r e n t t o pass was monitored f o r a l l points.  A check was a l s o made on the specimen  current  p r i o r t o a n a l y s e s o f each m i n e r a l i n order to monitor sample c o n d u c t i v i t y .  W i t h i n each p o l i s h e d t h i n  section,  three to f i v e g r a i n s of each m i n e r a l were a n a l y s e d . i m a t e l y 5 spots were probed on each g r a i n .  Approx-  Compositional  h e t e r o g e n i e t y gave r i s e to a spread o f 1-2 wt.% f o r major elements w i t h i n i n d i v i d u a l g r a i n s and from g r a i n t o g r a i n . Any g r a i n o r spot w i t h an a n a l y s i s d i f f e r i n g  significantly  from the norm was omitted i n the f i n a l a v e r a g i n g .  In order  to o b t a i n a crude e s t i m a t e of the a n a l y t i c a l p r e c i s i o n , a normal d i s t r i b u t i o n of g r a i n composition w i t h i n one s l i d e was assumed and the standard d e v i a t i o n s f o r each element i n a pyroxene calculated  (Px-74) and a glaucophane  (Gl-103) were  (Table 14).  C h l o r i t e compositions were o b t a i n e d from a working curve prepared f o r each element u s i n g c h l o r i t e s t a n d a r d s . Glaucophanes  and pyroxenes were a n a l y z e d u s i n g n a t u r a l and  s y n t h e t i c pyroxene standards f o r Mg, F e , A l , T i , S i , Na and Ca, a g a r n e t standard f o r Mn and a muscovite standard  193  f o r K.  A l l standards  were o b t a i n e d  of Washington c o l l e c t i o n . atomic those  from t h e U n i v e r s i t y  A b s o r p t i o n , f l u o r e s c e n c e and  number c o r r e c t i o n s w e r e c a r r i e d o u t i n a d d i t i o n t o f o r deadtime, d r i f t and background u s i n g  programmes  (UWPROBE, EMX2A) i n t h e p o s s e s s i o n  U n i v e r s i t y o f Washington. t o t a l s was n o t e d  computer  of the  A considerable increase i n •  a f t e r c o r r e c t i o n on a c c o u n t o f h i g h  absorp-  t i o n by Fe o f r a d i a t i o n from elements o f l o w atomic number. 2+  3+  As  no d i s t i n c t i o n c a n b e made b e t w e e n F e  using the microprobe,  and Fe  r e s u l t s a r e r e p o r t e d a s FeO o r F e 2 0 ^  d e p e n d i n g o'n w h i c h o x i d e p r e d o m i n a t e s i n p u b l i s h e d w e t chemical  analyses  of similar minerals.  Therefore,  i s g i v e n a s FeO i n c h l o r i t e a n d g l a u c o p h a n e . o f t h e p y r o x e n e s FeO a n d Fe20.j v a l u e s  iron  I n the case  have been c a l c u l a t e d .  Minerals Sodic  amphiboles  Sodic amphiboles a r e widely d i s t r i b u t e d w i t h i n the lawsonite-glaucophane  b e a r i n g r o c k s , where they o c c u r i n  m e t a b a s i c r o c k s , m e t a c h e r t s and i n t e r l a y e r e d s c h i s t s . s m a l l g r a i n s o f glaucophane were a l s o observed greenstones  o f P i n c h i Mountain approximately  A few  i n the  50 f e e t n o r t h  of a f a u l t e d c o n t a c t w i t h t h e g l a u c o p h a n i t i c b l o c k .  194  TABLE 6  Spec, no. 26 31  Mineral  PleochrolBm  colourless  «  M  1*9*  II  205*  n  103*  H H H  134  a  glaucophane  33  210  OPTICAL PROPERTIES OF PYROXENES AND AMPHIBOLES  •  -  lavendej:  blue  N  •  *  •  .m  •  • •  m  bluegreen  pale brown  dark brown  green amphlbole  pale  36 1 201 J  brown amphlbole  f aim  27  relict euglte  211  relict augite  -  -  acmltic pyroxene  -  •  205*.  •  green  155  -  -  4° 20°  -20°  9°  -38°*4°#  5°  -15°  8°  -50°  20°  0°-8°  »°  +  46°  55°#  -  -  -  -  -  -  fawn  fawn  103*  omphacltlc pyroxene  pale green  pale green  green  •  17°  -  pale green  -  9°  +60°#  acmltic pyroxene  -  -  -  +75°  -  •  -  analysed mineral  # 2V determined using u n i v e r s a l stage All  other 2V measurements were estimated from curvature  and separation of l s o g y r e s .  A  0*. c  10°  -  49*  Jadeltlo pyroxene  -  •  m  A  -  •  •  y c  -  010  II  m  green  2V  Optic plane  e  39° 1*0°  0°-2° 0°  195 TABLE 7 CELL DIMENSIONS FOR GLAUCOPHANE.AND Cell Dimensions  Gl-206  Gl-208.  9.636±6 A  b  'IT". 909+6 A  c  5.30 ±1 A  B  V  (a)  890±2 i  o  17 .860±9 A  880±1 A  8.633±3 A  o  o  5 .316±4 A  103 °33'±6' 3  . 9.484±3 A  o  0  17 .79±3 A 5 .314±5 A  •  0  9 .602±3 A  o  0  Px-209 o  9 .571±9 A  o  103°20'±8  Gl-207  o  0  a  JADEITIC PYROXENE  5.244±2 A  103 ° 2 4 ± 3 '  107 27 ±2  1  3  o  887±1 A  3  ,  ,  409.6±0.2 A  3  D i f f r a c t o m e t e r p a t t e r n s were o b t a i n e d from a P h i l l i p ' s X-ray d i f f r a c t o m e t e r .  F o r the j a d e i t i c pyroxene (Px-209),  a K-Br i n t e r n a l standard was employed and the 8 o r 9 b e s t - peaks i n 3 o s c i l l a t i o n s were measured t o w i t h i n 0.01° 2 6 and averaged.  The c h a r t speed was 5 x 240 mm/hr and the  scan r a t e ,i-°/min.  A s i m i l a r method was used f o r the  glaucophanes except t h a t a s i l i c o n i n t e r n a l standard was employed t o measure  the 6 b e s t peaks.  Peaks were indexed  by comparison w i t h p u b l i s h e d data f o r s i m i l a r m i n e r a l s : j a d e i t i c pyroxene-Coleman and C l a r k , 1968; glaucophaneColeman and Papike, 19 68. (b)  C e l l parameters were c a l c u l a t e d t o three decimal p l a c e s u s i n g a programme which gave a l e a s t squares refinement o f  (c)  the u n i t c e l l  (author: Evans et al. , 1963; s u p p l i e r :  E.P. Meagher,  U.B.C).  Given e r r o r s a r e standard e r r o r s and r e f e r t o the f i n a l decimal p l a c e i n the c e l l dimensions.  (d)  Specimens have not been a n a l y z e d . Map V I I .  Locations are given i n  196 TABLE 8 ELECTRON MICROPROBE ANALYSES OF GLAUCOPHANES  s±o A l  2  2°3  Ti0 FeO  2  t  Gl-103  Gl-49  Gl-205  56.5  56.2  56.7  8.9  7.4  6.3  0.00  0.13  0.09  1  15.1  17.2  21.5  MnO  0.03  0.19  0.03  MgO  9.2  8.4  5.9  CaO  0.9  1.0  0.3  Na 0  6.9  6.8  7.3  K 0  0. 02  0.07  0.04  H 0*  2.1  2.1  2.1  99.7  99.5  100.3  2  2  2  Total  assumed H 0 content on b a s i s o f average analyses o f two glaucophanes r e p o r t e d by R u c k l i d g e et a l . , (1971)'. 2  t  t o t a l Fe c a l c u l a t e d as FeO.  103:  assemblage i s glaucophane + lawsonite + sphene + s t i l p n o m e l a n e ; occurs as a l t e r a t i o n o f garnet + pyroxene i n e c l o g i t e .  49:  assemblage i s glaucophane + lawsonite + sphene + white mica + a c m i t i c pyroxene.  205:  the assemblage glaucophane + white mica + a r a g o n i t e + c h l o r i t e occurs as f r a c t u r e  f i l l i n g s i n an acmite  + sphene + lawsonite + q u a r t z rock.  197  Fig.  26  Element v a r i a t i o n i n zoned g l a u c o p h a n e . Note i r o n e n r i c h m e n t a t c o r e s and m a r g i n s o f g l a u c o p h a n e c r y s t a l s w i t h A I 2 O 3 and MgO s h o w i n g an a n t i p a t h e t i c v a r i a t i o n . Oxide percentages are considered semiquantitative.  198  O p t i c a l p r o p e r t i e s are g i v e n i n Table  6.  C e l l dimensions f o r three glaucophanes are g i v e n i n Table 7.  C e l l volumes are c h a r a c t e r i s t i c of the  "high  p r e s s u r e " polymorph, glaucophane I I ( E r n s t , 1963)  rather  than the lower p r e s s u r e higher temperature glaucophane I which has not been r e c o g n i z e d i n n a t u r e . Microprobe  analyses f o r three s o d i c amphiboles are  g i v e n i n Table 8 together w i t h host rock l i t h o l o g y m i n e r a l assemblage.  and  Atomic p r o p o r t i o n s of elements were  not c a l c u l a t e d on account of the absence of v o l a t i l e  analyses  3+ and the i n a b i l i t y o f the probe to d i s t i n g u i s h Fe A glaucophane from a metachert was  2+ and  Fe  traversed with  the e l e c t r o n - p r o b e g i v i n g the zonation i l l u s t r a t e d i n F i g . 26. Of p a r t i c u l a r i n t e r e s t i s the a n t i p a t h e t i c v a r i a t i o n of MgO  and A ^ O ^  w i t h FeO,  the l a t t e r oxide being  i n the cores and the margins.  concentrated  The weight per cent  oxide  v a l u e s are to be c o n s i d e r e d s e m i q u a n t i t a t i v e as a b s o r p t i o n c o r r e c t i o n s were not made, and an u n s a t i s f a c t o r y standard was  used f o r s i l i c o n .  The  s i g n i f i c a n c e of t h i s  d i s t r i b u t i o n i s d i s c u s s e d on p. Brown and green A t two No.  zonal  83.  amphiboles  l o c a l i t i e s , j u s t west of P i n c h i Mine  36) and on the Darbar c l a i m group  dark r a d i a t i n g sprays of amphibole  (Map V I I , No.  C l cm max  (Map  VII,  201),  length) were  199 TABLE 9 ELECTRON MICROPROBE ANALYSES OF RELICT PYROXENES Px-163  Px-165  51.0  50.0  2.7  2.3  0.96  0.81  -  -  FeO  9.7  8.1  MnO  0.14  0.13  sio  2  A1 0 2  Ti0 F e  3  2  2°3  MgO  15.2  17.5  CaO  19.6  19.4  0.7  0.3  100.0  98.5  Na 0 2  Total  Numbers o f ions on the b a s i s o f 6 oxygens Si A1  I V  Ti  1.90  1.89  • 0.10  0.10  0.03  0.02  A1  V I  0.03  -  Fe  2 +  0.30  0.25  Mg  0.85  0.98  Mn  -  0.01  Na  0.05  0.02  Ca  0.78  0.78  Total  4.04  4.05  200 noted o c c u r r i n g along f r a c t u r e s .  The  w i t h coarse g r a i n e d a r a g o n i t e and  i n p l a c e s forms rims  glaucophane.  amphibole c o e x i s t s  O p t i c a l p r o p e r t i e s (Table 6) suggest  i s either kataphorite  (Na CaFe^ ( F e A l ) S i A l 0 +  3 +  2  2  2 2  on  that i t  (OH ,F) ) 2  or an a r f v e d s o n i t i c amphibole. Green amphibole was  observed  a t o n l y one  as a minor c o n s t i t u e n t i n a l a r g e boulder of  P i n c h i Mine  lawsonite and  (Map  V I I , No.  155).  locality,  one m i l e  I t coexists with  i s l o c a l l y rimmed w i t h glaucophane.  p r o p e r t i e s are g i v e n i n Table  northeast  Optical  6.  Pyroxenes F i v e types of pyroxene a r e p r e s e n t i n the  area:  r e l i c t augites, sodic-augites, acmite-jadeites, j a d e i t i c pyroxenes and omphacitic  pyroxenes.  Pyroxene nomenclature  i s i l l u s t r a t e d on an acmite-jadeite-Ca(Mg,Fe)Si Og  triangular  2  diagram i n F i g . 27  ( a f t e r Essene et al.  igneous a u g i t e s are found  3  Metamor-  only i n the P i n c h i Mountain  greenstones and a c m i t e - j a d e i t e s are found  i n lawsonite  J a d e i t i c pyroxene i s p r e s e n t i n  lawsonite b e a r i n g metagreywackes, and omphacitic i s observed  Relict  i n most metabasic r o c k s .  p h i c s o d i c - a u g i t e s are found  b e a r i n g metabasic r o c k s .  1967).  only i n e c l o g i t e  pyroxene  boulders.  O p t i c a l p r o p e r t i e s o f pyroxenes are g i v e n i n Table 6 and c e l l parameters of a j a d e i t i c pyroxene i n Table  7.  201 TABLE 10 ELECTRON MICROPROBE ANALYSES OF METAMORPHIC PYROXENES  sio A 1  2  2°3  Ti0  Px-49  Px-205  Px-48  Px-74  Px-103  53.9  57.3  56.1  58.1  53.2  8.4  13.3  7.5  18 .5  6.7  0.10  0.34  0.41  0.20  0.08  16.2*  14.0*  19.6*  4.2*  4.8*  FeO  2.2  0.4  0.9  0.8  6.6  MnO  0.20  0.03  0.04  0.03  0.07  MgO  2.0  0.5  1.5  1.7  8.0  CaO  4.5  1.1  2.7  3.0  16.3  12.1  14.3  12.8  13.4  6.2  F e  2  2°3  Na 0 2  K 0 2  Total  0.01 99.6  0.00 101.3  0.00 101.5  0.00 99.9  0. 01 102.0  Numbers of ions on the b a s i s of 6 oxygens Si A1  I V  Ti  1.99  2.01  0.01  -  2.02  2. 01  1.94  -  -  0.06  -  0. 01  0.01  0.01  -  A1  V I  0.35  0.55  0 .32  0.75  0.23  Fe  3 +  0.45  0.37  0.53  0.11  0.13  Fe  2 +  0.07  0.01  0.03  0.02  0.20  Mg  0.11  0.03  0.08  0.09  0.43  Mn  0.01  -  -  -  Na  0.87  0.97  0.89  0.90  0.44  Ca  0.18  0.04  0.11  0.11  0.64  Total  4.04  3.99  3.99  4.00  4.07  -  TABLE 10  (continued)  (a) Approximate v a l u e s o f Fe20.j and FeO were o b t a i n e d from t o t a l Fe a f t e r assuming charge balance, n e g l i g i b l e Mn and no A l ^ . 1  _ 2+ 2+ Ca = Mg M  In t h i s case  .• _ 2+ + Fe  (b) Standard d e v i a t i o n s f o r Px-74 are g i v e n i n T a b l e 14.  Specimen Data Px-4 9:  assemblage: glaucophane + lawsonite + a c m i t i c pyroxene + sphene + white mica  Px-2 05:  assemblage: a c m i t i c pyroxene + sphene + lawsonite + quartz  Px-4 8:  assemblage: lawsonite + a c m i t i c pyroxene + sphene + c h l o r i t e ; glaucophane i s p r e s e n t but may  not be i n e q u i l i b r i u m w i t h the  assemblage. Px-74:  metagreywacke; assemblage: j a d e i t i c pyroxene + q u a r t z + white mica + lawsonite + sphene + glaucophane + p y r i t e + carbonaceous m a t e r i a l .  Px-103:  glaucophane-lawsonite e c l o g i t e ;  assemblage:  omphacitic pyroxene + g a r n e t . Specimen l o c a t i o n s are g i v e n i n Map V I I .  203  F i g . 27a:  diagram i l l u s t r a t i n g nomenclature (Essene and F y f e , 19671 and compositions of F r a n c i s c a n and Sanbagawa c l i n o p y r o x e n e s (Ernst et al. , 19701.  Franciscan  terrain  •  :  j a d e i t i c pyroxene from metagreywackes (Bloxam, 1956, 1959; Coleman, 1965; E r n s t et al. 19701. t  •  :  omphacitic pyroxene from "greenstones" and e c l o g i t e s (Switzer, 1945; Bloxam, 1959; Coleman et al. 1965; Essene and F y f e , 19671. 3  Mt.B.  :  c o m p o s i t i o n a l range of j a d e i t e - a c m i t e from Mount Boardman (Essene and F y f e , 1967)  Sanbagawa •  :  c l i n o p y r o x e n e s from e c l o g i t e s c h l i e r e n i n u l t r a m a f i c r o c k s (Miyashiro and S e k i , 1958; Shido, 1959; E r n s t et al. 1970). 3  •  :  F i g . 27b: 74 : 103 : 48 49 {: 205 P.M.G. : Note  (a)  c l i n o p y r o x e n e s from s i l i c e o u s metasedimentary s c h i s t s (Banno, 1959, 1964; Iwasaki, 1963). diagram i l l u s t r a t i n g c o m p o s i t i o n a l range of c l i n o p y r o x e n e s from P i n c h i Lake. j a d e i t i c pyroxene from metagreywacke omphacitic pyroxene from e c l o g i t e j a d e i t e - a c m i t e s from l a w s o n i t e b e a r i n g metabasic r o c k s c o m p o s i t i o n a l range of s o d i c a u g i t e s from P i n c h i Mountain greenstones End member p r o p o r t i o n s were c a l c u l a t e d employing procedure o u t l i n e d by Banno (1959). (Na+K)  Jd =  (Na+K+Ca)  100A1 •  rv=  7-^— ;  (Al +Fe ) V I  Ca ( j M g , F e l S i 0 2  6  (Na+K)  VI  + 3  = 100  '  -  Ac =  (Jd +  (Na+K+Ca) Ac)  100Fe (Al  V I  +3  +Fe  + 3  204 PLOT OF PYROXENE COMPOSITIONS  205  F i g . 27b (continued! :  Spec. No.  J a d e i t e (Jd).  Acmite CAc)  Ca (Mg,Fe) S i O 2  ("Augite"!  Px-74  77.9  11.3  10.8  Px-103  26.0  14.8  59.2  Px-49  36.7  46.4  16.9  Px-48  33.5  55.9  10.6  Px-205  57.5  38.5  4.0  Note  (b)  g  98% o f c a t i o n s are r e p r e s e n t e d on the diagram. The remaining 2% i s comprised of A 1 , Mn and T i . I V  206 R e l i c t igneous a u g i t e s w i t h i n the P i n c h i Mountain greenstones have been metamorphosed to b l o t c h y s o d i c a u g i t e s which c o e x i s t w i t h a l b i t e and have s m a l l Microprobe a n a l y s e s of two Table  r e l i c t a u g i t e s are given i n  9 together with atomic p r o p o r t i o n s .  analyses  a^c.  Reproduceable  of s o d i c - a u g i t e s were not o b t a i n e d but they show 3+  an i n c r e a s e i n Na,  Fe  (Fe  ?) and A l and an a n t i p a t h e t i c  decrease i n Ca and Mg w i t h r e s p e c t to the r e l i c t which they commonly r e p l a c e . Na 0 2  (2-3 wt.%), CaO  obtained  The  (13-17 wt.%)  approximate v a l u e s f o r and A l 0 2  from p a r t i a l probe analyses  2  Analyses omphacitic  and  4.07.  (2.5-4  wt.%)  i n the system  ( F i g . 27b).  of three a c m i t e - j a d e i t e s , a j a d e i t i c and  pyroxene are given i n Table 10.  between 99.6  3  i n d i c a t e t h a t Px-163  and Px-165 p l o t i n the s o d i c - a u g i t e f i e l d a c m i t e - j a d e i t e - C a (Mg ,Fe) S i O g  pyroxenes  and  102 wt.%  and  The  t o t a l s range  c a t i o n t o t a l s between  Approximate v a l u e s of F e 0 2  3  and FeO  from t o t a l Fe a f t e r making the reasonable  an  3.99  were obtained  assumptions of  charge balance, n e g l i g i b l e Mn and A l . In t h i s case, 2+ 2+ 2+ Ca = Mg + Fe T h i s enabled c a l c u l a t i o n of atomic I V  p r o p o r t i o n s of elements and of end-member p r o p o r t i o n s a f t e r Banno (1959). The  compositional  Franciscan  Compositions are i l l u s t r a t e d i n F i g .  range of c l i n o p y r o x e n e s  (Ernst et al.  3  w i t h the P i n c h i a n a l y s e s .  from the  197 0) i s i n d i c a t e d f o r comparison The  j a d e i t i c pyroxene  (Px-74)  27b.  207  and the omphacitic pyroxene  (Px-103), o b t a i n e d r e s p e c t i v e l y  from a metagreywacke and an e c l o g i t e a t P i n c h i , are s i m i l a r to j a d e i t i c and o m p h a c i t i c pyroxenes from the F r a n c i s c a n . The a c m i t e - j a d e i t e s  (Px-48,49,205) are c o m p o s i t i o n a l l y  s i m i l a r to F r a n c i s c a n pyroxenes from the Mount Boardman area a n a l y z e d by Essene et al.,  (1967).  They may  be  similar  to the "omphacitic" pyroxenes from m e t a v o l c a n i c r o c k s i n the Pacheco Pass a r e a (Ernst et al.  3  1970) but c h e m i c a l  a n a l y s e s were not performed because of f i n e g r a i n  size.  A t Pacheco Pass these m e t a v o l c a n i c s are c o n s i d e r e d to have formed under P-T  c o n d i t i o n s s i m i l a r to the j a d e i t i c  b e a r i n g metagreywackes w i t h which they are c l o s e l y T h i s i s a l s o the case a t P i n c h i .  pyroxene associated.  The c o n t r a s t i n compositions  i s accounted f o r by Fe-Mg enrichment i n m e t a v o l c a n i c s .  Chlorite C h l o r i t e i s widespread i n the greenstones o f P i n c h i Mountain and the g l a u c o p h a n i t i c r o c k s . p l e o c h r o i c i n greens, but may it  i s pseudoisotropic.  l e n g t h slow  I t i s generally  be c o l o u r l e s s , i n which case  Almost a l l  samples  s t u d i e d are  ( i . e . o p t i c a l l y n e g a t i v e ) but a few  specimens  were found c o n t a i n i n g both l e n g t h slow and l e n g t h chlorite.  fast  I n t e r f e r e n c e c o l o u r s are low f i r s t order and  produce anomalous b l u e or brown t i n t s i n some samples.  208 TABLE 11 ELECTRON MICROPROBE ANALYSES OF CHLORITES Specimen Number sio  Chi-38  Chl-48  Chl-165  31.6  30.0  29.3  Al 03  15.9  15.3  15.9  FeO*  19.1  26.5  27.4  2  2  MnO  0.27  0.33  0.25  MgO  22.4  17.4  15.8  H 0**  11.0  11.0  11.0  Total  100.3  100.5  99.7  2  * **  T o t a l Fe c a l c u l a t e d as FeO based on approximate water c o n t e n t o f c h l o r i t e s a c c o r d i n g to Deer, Howie and Zussman (1963), H„0 c o n t e n t f o r most c h l o r i t e s ranges between 10.3 and 12  Numbers of ions on b a s i s of 2 8 oxygens Specimen Number  38  48  165  Si  6.30  6.11  6.11  Al!V  1.70  1.89  1.89  AlVI  2.04  1.78  2.00  Fe  3.20  4.56  4.78  6.62  5.33  4.89  19.86  19.67  19.67  2 +  Mg Total Specimen Data Chl-38:  c h l o r i t e b l e b s i n lws + acm + sph + c h l ± wh m + glph ± s t i l p matrix  Chl-48:  assemblage: lws + acm + c h l + sph ± l a t e ( ? )  Chl-165: assemblage: c h l + acm + ab + sph; P i n c h i Mt. Greenstones  glph  209 Chemical formulae  analyses are g i v e n i n Table 11.  Chlorite  were c a l c u l a t e d on the b a s i s of 28 oxygen equiv-  a l e n t s and a l l i r o n was  assumed to be f e r r o u s , as E r n s t ,  (.197 0, p. 163). s t a t e s t h a t three F r a n c i s c a n c h l o r i t e s , analyzed by wet 1.57  wt.%  chemical methods, c o n t a i n an average of  Fe2G-2«  The a n a l y s e s p l o t w i t h i n the p y c n o c h l o r i t e  or d i a b a n t i t e f i e l d s (1936) and Hey negative  (Hay,  19541.  A c c o r d i n g to W i n c h e l l  (1954). , A l poor c h l o r i t e s are  optically  (length slow) and A l r i c h are o p t i c a l l y  (length f a s t ) .  positive  I t f o l l o w s t h a t the predominance of  o p t i c a l l y n e g a t i v e c h l o r i t e s a t P i n c h i suggests  t h a t they  are c o m p o s i t i o n a l l y s i m i l a r to those of the C a l i f o r n i a n Coast Ranges.  In a comparison of C a l i f o r n i a n and  blueschists, Ernst  Japanese  (.1970) notes a tendency f o r the A l  content of c h l o r i t e s to i n c r e a s e w i t h r i s e i n metamorphic temperatures.  Aragonite A r a g o n i t e , the h i g h p r e s s u r e polymorph o f i s commonly found  i n the metasediments and metabasic  of the P i n c h i Mountain greenstones rocks.  calcite,  and  rocks  the g l a u c o p h a n i t i c  L o c a l i t i e s are shown i n F i g . 28.  I t occurs  as  v e i n s or b l e b s i n mafic rocks and i s an important c o n s t i t u e n t of the limestones n o r t h of P i n c h i Lake. p a r t i a l i n v e r s i o n to c a l c i t e may or along  cleavages.  Almost  invariably,  be. noted on g r a i n margins  210  2 miles 3 2 km  Fig.  28  Aragonite  occurrences  • • \  aragonite ± inverted c a l c i t e only fault  i  i  3-2 km.  Fig.  29  P r e h n i t e , p u m p e l l y i t e and s e l e c t e d glaucophanel a w s o n i t e occurrences • • ± 1^  pumpellyite prehnite lawsonite + glaucophane boundary of lawsonite + glaucophane ..bearing f a u l t b l a c k  calcite  211 TABLE 12 CARBONATE MINERALOGY AND SAMPLE DISTRIBUTION Mineralogy Ca) arag + d o l + c c ± q t z C t r ) : spec. nos. 77, 78, 79, 82, 215,  217, 221, 224, 227.  Cb) arag + d o l : spec. no. 213. Cc) arag + c c ± q t z ( t r ) : spec. nos. 80, 222, 223, 225, 230. Cd) d o l + c c ± q t z : spec. nos. 216, 226, 234. Ce) cc + q t z + b a r i t e : spec. no. 81. C f ) c c ± q t z ± p l a g : spec. nos. 219, 220, 228, 229, 231, 232,  233, 235.  Sample d i s t r i b u t i o n Ci) samples from carbonates a s s o c i a t e d w i t h l a w s o n i t e glaucophane r o c k s : 77, 78, 79, 80, 81, 82, 215, 216, 217,218 221,  222, 223, 224, 225, 226, 227, 234.  Cii) samples from carbonates  interbedded w i t h P i n c h i Mt Green-  stones: 82, 218. C i i i ) samples from Mt. Pope b e l t : 228, 235, 229, 232. Civ) samples from T a k l a Group l i m e s t o n e s : 219, 220, 230, 231, 233. Note:  Ca) Specimen l o c a t i o n s a r e g i v e n on F i g . 28. Cb) cc = c a l c i t e ; d o l = d o l o m i t e ; arag = a r a g o n i t e ; qtz = guartz; plag = p l a g i o c l a s e ; t r = t r a c e .  212  A r g o n i t e can be e a s i l y i d e n t i f i e d i n t h i n  section  by i t s c h a r a c t e r i s t i c n e g a t i v e 2V o f 18°, s t r a i g h t e x t i n c t i o n on i t s p r i s m a t i c c l e a v a g e , low r e l i e f w i t h a p a r a l l e l to the p o l a r i s e r and {110} twinning on b a s a l sections.  T h i r t y X-ray d i f f r a c t o m e t e r t r a c e s of limestones  from the area were a l s o made.  Carbonate mineralogy and  sample d i s t r i b u t i o n a r e g i v e n i n Table 12.  White mica White mica i s most abundant w i t h i n g l a u c o p h a n i t i c metacherts metabasic  and s c h i s t s .  Greenstones  and g l a u c o p h a n i t i c  rocks commonly c o n t a i n disseminated  sericite  (<5y) w i t h c o a r s e r g r a i n e d v a r i e t i e s near f r a c t u r e s or as c l u s t e r s i n amygdules. The white mica appears  g r e e n i s h t o the unaided eye  and shows f a i n t p l e o c h r o i s m i n t h i n s e c t i o n w i t h a - c o l o u r l e s s and  3 = y -very p a l e green.  Micas  examined i n two specimens  (151, 212) a r e u n i a x i a l negative but some show a n e g a t i v e 2V o f up to 1 0 ° .  Deer, Howie & Zussman  ( V o l . 3, p. 22) s t a t e  t h a t s m a l l 2Vs are o c c a s i o n a l l y seen i n white micas. reason i s u n c e r t a i n , but i t may be caused  The  by anomalous o p t i c a l  e f f e c t s r e s u l t i n g from s u p e r i m p o s i t i o n of mica f l a k e s . X-ray examination  of three micas i n d i c a t e d t h a t they were  the normal 2M^ p o l y t y p e . P a r t i a l microprobe  analyses o f micas from a g l a u c o -  213 TABLE 13 PARTIAL ELECTRON MICROPROBE ANALYSES OF. PHENGITES AND  s±o 2  Ti0  Ph-151  Ph-205  Cel-196  A  B  -  -  -  50.50  46.50  6.1  20.57  29.82  tr  0.76  0.18  -  6.95  1.50  0.00  1.86  2  A1 0  3  26  2  21  0.1  2  Fe 0  CELADONITE  3  0.1  -  FeO  3.3*  MnO  tr  tr  0. 05  0.82  0.02  MgO  4.4  4.7  6.1  5.68  3.97  CaO  0.00  0.04  0.09  0.26  0.23  Na 0  tr  tr  0.00  tr  0.37  -  10.95  9.15  2.74  4.77  2  K 0 2  H0 2  —  5.3*  -  16.4*  -  * T o t a l Fe c a l c u l a t e d as FeO = not determined tr = trace Specimen data Ph-151: metachert, P i n c h i Lake; assemblage: glaucophane + lawsonite + q u a r t z + p h e n g i t e . Ph-205: metabasic rock; assemblage: glaucophane + p h e n g i t e + a r a g o n i t e + c h l o r i t e (occurs as f r a c t u r e f i l l i n g s i n acmite + sphene + lawsonite + quartz r o c k ) . Cel-196: assemblage: a l b i t e + c h l o r i t e + p u m p e l l y i t e + sphene + celadonite. P r e h n i t e , c a l c i t e and white mica are a l s o p r e sent s p o r a d i c a l l y i n b l e b s ( P i n c h i Mt. Greenstone). A: f e r r i p h e n g i t e from q u a r t z + a l k a l i f e l d s p a r + green b i o t i t e + c a l c i t e + e p i d o t e g n e i s s (Plas, 1959) . B: phengite from glaucophane + c h l o r i t e + a r a g o n i t e + j a d e i t i c pyroxene s c h i s t (Ernst, 1963, Table 1, No. 10).  214 TABLE 14 STANDARD DEVIATIONS FOR SELECTED MINERAL ANALYSES Px-74  s±o  A l  2°3  Ti0  F e  2  2  2°3  FeO  a  Gl-49  a  58 .1 ± 1.0  56.2 ± 0.4  18 .5 ± 0.6  7.4 ± 0.8  0. 20 ± 0.20  0.1 3 ± 0. 06  5. 1* ± 0.81  • -  -  -  -  17. 2** + 0.2  -  0. 19 ± 0 .07  MnO  0. 03  MgO  1. 7 ± 0.2  8. 4 ± 0. 4  CaO  3. 0 ± 0.4  1. 0 ± 0. 4  13. 4 ± 0.3  6. 8 ± 0. 1  Na 0 2  K 0 2  0. 00  -  0. 07 +  t o t a l Fe c a l c u l a t e d as F e 0 2  **  t o t a l Fe c a l c u l a t e d as FeO  -  215  phanitic rock  metachert  (Ph-2051  uncorrected considered  (Ph-151) a n d f r o m v e i n s  are given  i n Table  f o r absorption  and t h e FeO v a l u e s  micas  are phengites  T h e MgO  C3.3,  5.3  metabasic  These r e s u l t s  and f l u o r e s c e n c e  semiquantitative.  wt.%)  13.  i n a  and should  values  wt.%)  are  show  C4.4,  be  4.7  that the  or ferriphengites.  Celadonite  Celadonite Mountain  greenstones,  aggregates.  Cot-fawn,  character.  A  partial  occurs  replacements  phenocrysts,  metabasic  was  green  and i t s l e n g t h confirmed  semiquantitative  within  of primary  rare,  by  slow  X-ray  analysis i s given  rocks  inclusions relief  the P i n c h i Mountain  ( N o . 49,  In the glaucophanitic  58)  determinations  as  late  and g r a p h i t i c  albites  Csericite,  greenstones  p l a g i o c l a s e m i c r o l i t e s and  occurring only  Blastoporphyritic  and  i t s bright  Y -blue-green),  and as v e i n s .  exceedingly  with  by  i n radiating  plagioclase  Albite  is  recognized  the Pinchi  13.  Albitic  as  B =  within  occurring  Optical identification  diffraction. Table  typically  I t i s easily  pleochroism  in  i s sporadically present  veins i n cherts  are generally  pumpellyite, are d i f f i c u l t .  rocks i t  118).  charged  chlorite Where  CNo.  and unknowns) determined  216 the r e l i e f  i s low w i t h the Michel-Levy  sitions  AnQ_j-.  has  of  positive  Vein albite  sign,  and 3  method g i v i n g  compo-  i n the glaucophanitic rocks  o r y" = 1.536.  1  Pumpellylte Pumpellylte P i n c h i Mountain matted  i s found  only within  ( f o rl o c a l i t i e s  acicular  aggregates  s e e F i g . 29).  i n veins,  pseudomorphs and b l a s t o p o r p h y r i t i c ties  size.  These a r e :  anomalous b l u i s h  albites.  identification  a = y-fawn,  or brownish  was c o n f i r m e d  of  I t occurs  as  ferromagnesian  are obtained only with d i f f i c u l t y  grain  the greenstones  Optical  because of  3-green;  interference by X-ray  8 c A  proper-  fine =  tints.  5°;  Optical  diffraction.  S t i l p n omelane Stilpnomelane glaucophanitic garnet  r o c k s and a l s o  i n an e c l o g i t e  ferrostilpnomelane, with  typically  boulder.  occurs  as l a t e  veins i n  as an a l t e r a t i o n The g r e e n  (a-colourless,  product  of  pleochroic variety,  $ = y-pale  green)  occurs  t h e m o r e common b r o w n s t i l p n o m e l a n e .  Lawsonite  Metabasic all  r o c k s , metasediments and e c l o g i t e  contain lawsonite.  identified  i n one t h i n  The m i n e r a l was a l s o section  from  boulders  tentatively  the greenstones  of  217 P i n c h i Mountain.  W i t h i n the e c l o g i t e boulder and some  s c h i s t s i t commonly occurs as p o l y s y n t h e t i c a l l y  twinned  p o r p h y r o b l a s t s , but otherwise i t i s r e c o g n i z e d by i t s t a b u l a r h a b i t , s t r a i g h t e x t i n c t i o n and n e g a t i v e e l o n g a t i o n .  Prehnite C o l o u r l e s s s h e a f - l i k e aggregates noted i n the P i n c h i Mountain greenstones  o f p r e h n i t e were a t the west end o f  Murray Ridge i n a s s o c i a t i o n w i t h p u m p e l l y i t e , c e l a d o n i t e , c h l o r i t e , a l b i t e and c a l c i t e  ( F i g . 29). The m i n e r a l a l s o  occurs w i t h q u a r t z i n amygdules i n b a s i c v o l c a n i c s o f presumed Upper T r i a s s i c age.  Garnet An e c l o g i t e boulder c o n t a i n s subhedral garnets max diameter)  p a r t l y r e p l a c e d by s t i l p n o m e l a n e .  Cl mm  Reconnaissance  probe work i n d i c a t e s t h a t they a r e c h e m i c a l l y s i m i l a r t o those found elsewhere schists  i n e c l o g i t e s associated with blue-  (Coleman,.at.., 1965) .  They a r e s l i g h t l y  w i t h the cores having the composition almandine grossular  (.30%) and s p e s s a r t i n e + pyrope  zoned  (60%),  (10%) .  Deerite A specimen of d r i l l c o r e taken from the P i n c h i Mine area c o n t a i n s dark brown r a d i a t i n g sprays up t o 1 cm i n  218  diameter  of d e e r i t e ( A g r e l l et al.  1965).  3  The  mineral  appears l a t e i n the p a r a g e n e t i c sequence and c r o s s - c u t s glaucophane, lawsonite and  s o d i c pyroxene.  It is slightly  p l e o c h r o i c on t h i n edges (dark brown to b l a c k ) , has  straight  e x t i n c t i o n and an a m p h i b o l e - l i k e c r o s s s e c t i o n ( F i g . 3 4). X-ray examination a KBr  of a d e e r i t e c o n c e n t r a t e u s i n g  i n t e r n a l standard and P h i l l i p ' s d i f f r a c t o m e t e r r e v e a l e d  a fairly  good correspondence  w i t h the c a l c u l a t e d cl^kl  o b t a i n e d from the c e l l parameters p u b l i s h e d by A g r e l l . well defined of  9.42  (020)  and  ± 0 . 0 2 A and  (110)  9.04  The  r e f l e c t i o n s y i e l d e d d-spacings  ± 0.02  A.  The  d i f f e r e n c e from the  o  calculated values  (9.42  and  9.18  A r e s p e c t i v e l y ) can  a t t r i b u t e d to s h i f t of peak p o s i t i o n s due  to s o l i d  D e e r i t e peaks a t higher 26 v a l u e s were d i f f i c u l t because of contamination and  be  solution.  to index  by r i e b e c k i t e , s o d i c pyroxene  lawsonite. Opaques  relict  W i t h i n metabasic  r o c k s , opaque m i n e r a l s other  ilmenomagnetites  are very f i n e g r a i n e d  (0.3 mm  G r a i n s s t u d i e d w i t h the r e f l e c t i n g microscope are w i t h creamy y e l l o w p y r i t e forming by magnetite hematite schists.  Cor maghemite).  ( F i g . 30).  the nucleus,  than max).  composite,  surrounded  T h i s i n t u r n i s rimmed by  P y r i t e i s widespread w i t h i n g r a p h i t e  219  Fig.  30  Textures  i n opaque  minerals  220 Carbonaceous  material  Carbonaceous m a t e r i a l from s c h i s t s and c h e r t s separated  was  employing the method of French (1964) by  d i g e s t i o n w i t h HF and HCl and X-rayed u s i n g a P h i l l i p ' s diffractometer  tCuK^ r a d i a t i o n ; scan-rate  speed - 5 x 240 mm/hr).  chart  A f t e r d i g e s t i o n , p y r i t e and  r a l s t o n i t e were the only phases p r e s e n t carbonaceous m a t e r i a l .  - 2°/min;  One  i n a d d i t i o n to  sample out of the f i v e  gave a broad d i f f u s e peak a t 26°, suggesting of n e a r l y amorphous g r a p h i t i c m a t e r i a l to the c l a s s i f i c a t i o n of L a n d i s ,  1971).  studied  the presence  (graphite-d^  according  Four samples y i e l d e d  f e a t u r e l e s s d i f f r a c t o m e t e r c h a r t s i n d i c a t i v e of amorphous material.  APPENDIX I I I BULK CHEMICAL ANALYSES  Representative  homogeneous samples of t h i r t e e n  metabasic rocks and two metagreywackes were analysed by the G e o l o g i c a l Survey o f Canada l a b o r a t o r y i n Ottawa. Analyses  f o r MnO,  T i 0 , CaO, K 0 , S i 0 2  2  2  and A l 0 2  were  3  obtained by X-ray f l u o r e s c e n c e methods; Fe ( t o t a l ) , FeO, Na 0, P ° 5 ' 2  2  C 0  2  a  n  d  H  2° (  t o t a l  )' Y b  " r a p i d chemical  a n a l y t i c a l techniques" and MgO by atomic a b s o r p t i o n .  Esti-  mated e r r o r s quoted by the G e o l o g i c a l Survey are given i n Table 15.  The a n a l y s t a l s o noted  values f o r T i 0 used.  2  were o u t s i d e the normal range of the method  P r e c i s i o n may be estimated  d u p l i c a t e specimens 97.8%  t h a t some of the h i g h  by i n s p e c t i o n of the  (36a and 36b).  T o t a l s range from  to 101.2% by weight.  Metabasic  rocks  P r i o r t o norm c a l c u l a t i o n f o r metabasic r o c k s , two adjustments were made to the a n a l y t i c a l data as by I r v i n e and Baragar  (1971).  suggested  This involved recalculation  of the f e r r i c - f e r r o u s r a t i o to c o r r e c t f o r o x i d a t i o n d u r i n g metamorphism, and r e c a l c u l a t i o n o f the analyses o m i t t i n g H„0 and CO».  t o 100%  O r i g i n a l analyses and o x i d a t i o n  222 TABLE 15 ACCURACY OF BULK CHEMICAL ANALYSES Range i n V a l u e  one a  30-75%  ± 1.2  0-20%  ± 0.7  0-15%  ± 0.5  CaO  0-40%  ± 0.3  MgO  0-40%  ± 1.0  K 0  0-5%  ± 0.1  0-2%  ± 0.05  MnO  0-1%  ± 0.02  FeO  0-15%  ± 0.2  Na 0  0-10%  ± 0.15  0-1%  ± 0.04  Oxide  sio  2  A1 0 2  F e  tot  2  Ti0  2  2  P  3  2°5  co  C F e  2°3>  2  ± 0.1  H 0  ± 0.1  2  Note: e r r o r s a r e those r e p o r t e d by the a n a l y s t o f the G e o l o g i c a l Survey of Canada.  TABLE 16a  CHEMICAL ANALYSES OF METABASALTS FROM THE PINCHI LAKE AREA  GREENSTONES OF  LAWSONITE-GLAUCOPHANE BEARING METABASALTS  PINCHI MT.  Si0  2  Ti0  2  A1 0 2  1?0  163  43.8  44.6  4.35 3  ?e Oj  14.7  2.72 13.1  MASSIVE ROCKS 162 44.2 3.36  45 45.6 3.22  36a  36b  33.I 32.3 1.75  1.63  FOLIATED  48  61  42.9  47.9  5.51  202  1.49  40.2 2.45  18.1  13.7  9.1  9.2  10.5  14.4  12.2  5.6  5.2  5.0  4.2  4.1  7.5  23  1.20 4.00 13.8 16.4  3.9  5.0 ' 3.1  FeO  9.6  6.7  6.8  6.3  4.3  4.3  8.1  7.8  5.7  KnO  O.13  0.16  0.18  0.17  0.20  0.21  0.11  0.14  0.14  MgO  4.5  7.2  3.0  5.4  6.2  6.0  7.3  5.6  7.0  2  11.1  37  42.7 44.8  31 46.7  47.5  1.49 14.1  A  55  3.64 14.6  B  C  D  49.20 44.10 45.40 49.16 3.40 12.87  2.70  3.60  2.29  12.10 14.70 13.33  5.2  5.1  3.6  4.94  3.20  4.10  1.31  5.5  5.2  7.0  7.6  12.04  9.60  9.20  9.71  0.10  0.06  0.14  0.13  0.27  0.20  0.20  0.16  4.4  7.5  4.9  4.94 13.00  4.4  7.80 10.41  CaO  6.5  9.5  8.6  9.8  20.0  21.0  11.1  7.9  8.8  13.8  8.8  9.2  3.9  8.54 11.50 10.50 10.93  Na 0  4.8  2.0  5.1  2.6  3.2  3.1  2.9  2.9  2.7  1.1  2.7  1.9  3.3  3.09  .1.90  K 0  0.1  2.6  0.3  0.8  1.3  1.4  0.1  0.2  0.1  0.2  1,7  0.1  0.8  0.31  2  2  p o 2  co  5  2  H20  t  O.56  0.28  0.36  0.37  1.29  0.08  0.13  0.27  0.11  0.17  0.11  0.46  0.8  0.6  0.7  0.3  9.2  10.4  0.8  1.2  0.2  4.0  0.1  1.3  0.1  4.7  4.3  4.6  4.5  3.9  3.8  4.8  5.1  6.4  6.0  5.7  6.6  5.0  98.4  98.4  98.7 100.5 98.2  98.9  97.8  99.9  99.1 [101.2 100.5  29  44  51  32  54  41  47  Total  98.4  98.8  Oxidn.  26  40  2.14  52  32  39  30  0.36  27  3.00  2.15  0.70  1.00  0.51  0.30  0.40  0.16  23  ratio A 1 F r a n c i s c a n greenstonei Coleman & Lee, (1963, Table 2, no. 60-804). B 1 Average Hawaiian ankaramitei Macdonald (1968, Table 8 ) . C • Average Hawaiian a l k a l i - o l i v i n e b a s a l t i  Macdonald (1968, Table 8)  D 1 O l i v i n e t h o l e i i t e , K i l a u e a volcano, Hawaii) Yoder & T i l l e y , ( 1 9 6 2 , Table 2, no,14). Note  1 f o r mineral assemblages, see Table 22.  29  11  224 TABLE 17  C. I . P. W. NORMS FOR ANALYSED METABASALTIC  GREENSTONES OF  LAWSONITE-GLAUCOPHANE BEARING METABASALTS  orthoclase  FOLIATED  MASSIVE ROCKS  PINCHI KT. 1?0  163  162  -  -  -  quartz  0.65 16.37  ROCKS  45  36  -  2.43  1.77  43  5-32  61  202  3.U  -  1.18  0.59  37  31  55  0.94  2.85  1.85  1.18 10.75  0.65  4.96  23  -  0.59  albite  41.85 17.00 33.07 23.69  -  26.49 26.57 20.08 10.15 24.45 17.26 29.28  anorthite  19.68 20.33 27.56 24.77  -  16.60 27.83 22.88 35.93 29.54 31.83 23.74  -  0.98  diopside  9.05 22.37 12.82 19.68  -  hypersthene  7.20  -  nepheline  0.51  -  11.43 10.57  olivine  -  9.38  4.96  -  -  6.09  6.52  4.83  7.32  ilmenite  8.89  5.51  6.86  6.53  apatite  1.39  0.70  0.90  0.93  -  -  2.88  -  -.  -  32.94 11.24 18.66 31.99 12.47 13.37 15.65 1.97 21.99  -  magnetite  -  -  3.39  -  12.34  22.83  1.11  5.95 26.07 10.70  -  -  -  6.73  4.68  6.23  4.35  5.74  4.65  5.47  11.30  3.06  5.13  2.54  8.13  3.04  7.24  0.21  0.32  0.70  0.28  0.42  0.28  1.11  Note 1 a) norms i n wt.?S  TABLE 16b  "ADJUSTED"  GREENSTONES' OF  CHEMICAL ANALYSES OF METABASALTS  LAUSONITE-GLAUCOFHANE BEARING METABASALTS  PINCHI MT.  sio  2  T10  A1 0 2  Fe 0 2  I63  162  47.1  47.6  47.5  4.68  2  3  3  FeO  2.90  3.61  45  36a  36b  48.8  38.7  37.5  3.44  2.04  1.89  FOLIATED  48  61  202  23  37  31  55  46.3  51.8  44.3  47.5  48.0  50.1  49.8  5.95  1.61  2.70  1.34  4.28  1.60  3.81  15.8  14.0  19.4  14.7  10.7  10.7  11.3  15.6  13.4  15.4  17.6  15.1  15.3  4.2  4.5  3.3  5.1  3.8  3.6  4.6  3.2  4.3  3.0  5.6  3.2  3.8  10.3  7.9  7.3  7.6  7.1  7.0  8.8  9.5  9.8  7.9  .5.6  9.6  8.0  0.1?  0.19  0.18  0.23  0.24  0.12  0.15  0.15  0.11  0.06  0.15  0.14  0.14  MnO  MASSIVE ROCKS  170  KgO  4.8  7.7  3.2  5.8  7.3  7.0  7.9  6.1  12.2  7.8  4.7  8.1  5.1  CaO  7.0  10.1  9.2  10.5  23.4  24.4  11.9  8.6  9.7  15.4  9.4  9.9  9.3  Na,0  5.2  2.1  5.5  2.8  3.8  3.6  3.1  3.1  3.0  1.2  2.9  2.0  3-5  K0 po  0.1  2.8  0.3  0.9  1.5  1.6  0.1  0.2  0.1  0.2  1.8  0.1  0.8  0.60  0.30  0.39  0.18  0.12  0.48  2  2  5  0.40  1.51  2.49  0.09  0.14  0.30  0.12  The analyses were a) r e c a l c u l a t e d to 100# omitting H 0 and CO, and b) c o r r e c t e d f o r o x i d a t i o n during metamorphism by a d j u s t i n g the f e r r i c - f e r r o u s ratlo(assuming % F e 0 = % T10 + 1.5) - a f t e r I r v i n e and Baragar (1971). 2  2  3  2  FIG. 31  225 A-F-M DIAGRAM ILLUSTRATING BASALT COMPOSITIONS  F  FIG. 32 t  ALKALI-SILICA VARIATION DIAGRAM FOR BASALTS  Si0 (wt%) 2  226 r a t i o s a r e g i v e n i n Table 16a and a d j u s t e d a n a l y s e s i n T a b l e 16b.  C.I.P.W. norms are presented i n T a b l e 17.  R e l i c t mineralogy and t e x t u r e s show t h a t the m a j o r i t y of the b a s i c rocks were o r i g i n a l l y v o l c a n i c s p r i o r t o the f o r m a t i o n of the metamorphic m i n e r a l s rocks  (Appendix  IV).  Two  (Nos. 23 and 48) a r e c o n s i d e r e d to have been b a s i c  intrusives.  The b a s a l t i c composition of the a n a l y s e d  rocks i s i l l u s t r a t e d  i n an A.F.M. diagram  ( F i g . 31) w i t h  the area encompassing F r a n c i s c a n b a s a l t s shown f o r comparison  (Ernst et a l . ,  1970).  R e l e v a n t i n f o r m a t i o n r e l a t i n g t o the c l a s s i f i c a t i o n of the primary b a s a l t type i s p r e s e n t e d i n Table 18 and i n the a l k a l i - s i l i c a v a r i a t i o n diagram Mountain greenstones  ( F i g . 32).  (Specs. 162, 163 and 170) possess the  c h e m i c a l c h a r a c t e r i s t i c s of a l k a l i b a s a l t s . hypersthene  Normative  i s absent and on the a l k a l i - s i l i c a  diagram, the b a s a l t s p l o t i n the a l k a l i f i e l d MacDonald  (1968).  The P i n c h i  The h i g h T i 0  2  values  variation as g i v e n by  (>2.9) are thought  to be r e p r e s e n t a t i v e o f the primary b a s a l t , as t i t a n i u m i s g e n e r a l l y c o n s i d e r e d immobile d u r i n g metamorphism. et al*  3  C1965) p r e s e n t the f o l l o w i n g average  for basalts;  (a) o c e a n i c t h o l e i i t e s  (b) a l k a l i b a s a l t s (2.87 wt.% T i 0 ) . 2  Ti0  (.1.49 wt.%  2  Engels  values  Ti0 ); 2  The range of T i 0  v a l u e s i n the P i n c h i Mountain greenstones  (.4.7, 2.9, 3.6  wt.%) suggests an a f f i n i t y w i t h the a l k a l i b a s a l t W i t h i n the glaucophane-lawsonite  2  bearing  type.  metabasic  r o c k s , both types o f b a s a l t appear to be r e p r e s e n t e d .  Three  227  TABLE  Spec, no.  170* 163* 162* 45  36  18  SUMMARY OF SIGNIFICANT CHEMICAL CHARACTERISTICS OF METABASALTS  Normative hyp. qtz.  9.4  T10  5.2 + 0.1  4.7  a l k a l i , basalt  2.1 + 2.8  2.9  a l k a l i basalt  5-5 + 0.3  3.6  a l k a l i basalt  2.8 + 0.9  3.4  2  2  2  Basalt type  ?  h i g h l y carbonated sample  48  2.0  61  22.0  202  2.4  Na 0 + K 0  3.1  -  3.1 + 0.1  6.0  a l k a l i basalt  3.1 + 0.2  1.6  tholelltic  basalt  3.0 + 0.1  2.7  a l k a l i basalt  1.2 + 0.2  1.3  tholelltic  23  12.3  37  6.0  0.9  2.9 + 1.8  4.3  ?  31  26.1  2.9  2.0 + 0.1  1.6  tholelltic  55  10.7  1.9  3.5 + 0.8  3.8  ?  * P i n c h i Mountain greenstones Oxide values obtained from Table 16b  basalt  basalt  228 out of e i g h t analyzed r o c k s have normative hypersthene and  quartz,  have low T i C ^ v a l u e s  (1.3  - 1.6  wt.%)  and  p l o t i n the t h o l e i i t i c f i e l d on an a l k a l i - s i l i c a v a r i a t i o n diagram.  One  basalt  Hawaiian ankaramite  (No.  202)  (Table  has  16a)  an a n a l y s i s s i m i l a r to a  and  possesses  c h a r a c t e r i s t i c s of an a l k a l i b a s a l t . b a s a l t s are a l k a l i n e i n t h a t the T i 0  The 2  the  four remaining  c o n t e n t i s high  and  they p l o t i n the a l k a l i b a s a l t f i e l d i n the v a r i a t i o n diagram. and  However, they a l s o c o n t a i n normative hypersthene  q u a r t z which, a c c o r d i n g  to Yoder and  c h a r a c t e r i s t i c of t h o l e i i t i c b a s a l t s .  Tilley is  The  conflicting  evidence as to the b a s a l t type suggests e i t h e r and  titanium  a l k a l i enrichment of a t h o l e i i t i c b a s a l t or s i l i c a  enrichment o f an a l k a l i b a s a l t d u r i n g metamorphism. s i d e r i n g the probable i m m o b i l i t y metamorphism, the therefore  of t i t a n i u m  during  l a t t e r suggestion i s p r e f e r r e d .  concluded t h a t both t h o l e i i t i c and  Con-  It is  alkali  basalts  were p r e s e n t i n the rock sequence p r i o r to metamorphism.  Metagreywackes Analyses f o r two 19.  Also included  f o r purposes of comparison are  average of 21 F r a n c i s c a n Table 2, No.  1).  metagreywackes are shown i n Table  The  greywackes  ( B a i l e y et al.,  the 1964,  P i n c h i metagreywackes have lower  229 TABLE 19 CHEMICAL ANALYSES OF METAGREYWACKES  Specimen Number  sio  2  Ti0  2  71  70  A  B  50.5  57.0  67.5  65.0  0.82  0.68  0.5  0.69  19.8  17.6  13.5  14.14  3.4  2.7  1.2  0.58  FeO  4.4  4.0  3.0  5.44  MnO  0.16  0.12  0.1  0.08  MgO  3.2  3.1  2.2  3.44  CaO  5.7  3.3  2.4  2.28  Na 0 2  3.7  5.4  3.6  2.29  K 0  1.9  1.4  1.7  2.24  0.28  0.23  0.1  0.14  0.1  0.1  0.8  0.01  5.4  2.1  2.9  4.02  Total  99.4  97 .7  99.5  100.35  71: metagreywacke,  P i n c h i Lake  (analysed by G.S.C.)  70: metagreywacke, P i n c h i Lake  (analysed by G.S.C.)  A 1  2°3  Fe 0 2  3  2  P  2°5  co H  2  2°t  A:  average of 21 F r a n c i s c a n metagreywackes et al.  B:  }  (Bailey  1964, Table 2, No. 1 ) .  j a d e i t i c pyroxene b e a r i n g metagreywacke 1965, Table 12, No. 190).  (Ernst,  230 S i C ^ and higher Al^O^ and CaO v a l u e s .  Presumably  this  r e f l e c t s e i t h e r l e s s quartz or a higher a n o r t h i t e c o n t e n t i n the i n i t i a l  sediment.  APPENDIX IV PETROLOGY  Greenstones  of P i n c h i Mountain  Metamorphic and r e l i c t m i n e r a l s p r e s e n t i n the stones of P i n c h i Mountain are g i v e n i n Table 20.  green-  Chlorite,  a l b i t e , s o d i c pyroxene and sphene are the main m i n e r a l s with celadonite, quartz, pumpellyite, prehnite, f e r r o s t i l p n o m e l a n e , a r a g o n i t e and white mica s p o r a d i c a l l y tributed.  A few  s m a l l g r a i n s of l a w s o n i t e and  were a l s o observed.  dis-  glaucophane  O p t i c a l p r o p e r t i e s and m i n e r a l composi- .  t i o n s are covered i n Appendix I I . The r e l i c t mineralogy  and bulk chemistry  (Appendix  III)  suggest t h a t the primary rocks were a l k a l i b a s a l t s c o n s i s t i n g of a u g i t e , p l a g i o c l a s e , i l m e n i t e and o l i v i n e  (?) e x h i b i t i n g  p o r p h y r i t i c , t r a c h y t i c and amygdaloidal t e x t u r e s . Domains w i t h i n i n d i v i d u a l t h i n s e c t i o n s are of f i v e t e x t u r a l types: and v e i n s .  m a t r i x , r e l i c t s , b l e b s , pseudomorphs  Metamorphic m i n e r a l assemblages  of each domain are given i n Table 21 and are i n F i g . 33.  characteristic illustrated  The d i s t i n c t i o n between b l e b s and pseudomorphs  i s somewhat a r b i t r a r y and dependant on the l a t t e r p o s s e s s i n g a euhedral or subhedral o u t l i n e .  Blebs may  have o r i g i n a t e d  232  TABLE 20  S p e c No.  MINERAL ASSEMBLAGES IN THE GREENSTONES OF PINCHI MOUNTAIN  160  albite  161 162  163  X  60  20  164  165  166  169 170 171  172  173 193 195 196 197 203  204  X  55  -  -  40  X  X  X  X  X  X  X  X  X  10  X  X  35  X  X  X  X  X  X  X  X  X  X  X  -  X  X  11  chlorite  X  X  20  3  X  quartz  X  -  -  7  - -  sodic pyx.  X  X  8  12  X  pumpellyite  -  X  3  -  white mica  X  -  -  2  7  -  sphene  X  X  8  2  X  aragonite  X  -  tr  - - - - - - - - - - - - - -  X  X  X  X  X  X  X  X  X  X  X  X  prehnite  X  X  -  -  calcite  X  X  - -  X  X  X  X  -  -  -  - -  - -  celadonite  X  3  5  -  - - X  X  X  -  5  X  X  X  5  X  X  4  X  X  X  X  X X  X  X  X  7  augite ( r )  X  X  ilraenite ( r i  -  -  -  35  -  5  -  27  -  * = t r a c e o f lawsonite + = t r a c e o f glaucophane r = relict  mineral  Modes are approximate.  -  X  X  X  -  -  - -  x = mineral  present  -  -  233 TABLE 21 TEXTURAL DOMAINS WITHIN THE PINCHI MOUNTAIN GREENSTONES  S i z e range:  relicts  0.5 -.1.5 mm  matrix  albite microlites  CO.2 mm),  c h l o r i t e , sphene (.0.01 mm average). , a c m i t i c pyroxene average) blebs  0.5 - 5 mm  pseudomorphs  2 - 8 mm  veins  0.1 - 3 mm  R e l i c t minerals: Matrix  augite,  (0.05 mm  ilmenite  assemblages: ab + Na px + c h l + sph ± wh m ± c e l a d ± arag ± lws q t z + c h l + Na px + sph ± wh m ± arag ab + c h l + pump + sph ± prehn ± cc ± c e l a d ± wh m  R e l i c t m i c r o g r a n u l a r a u g i t e may a l s o be p r e s e n t i n the m a t r i x Blebs:  c h l ( r a d i a t i n g aggregates) pump ± c h l ± c e l a d ± prehn ± wh m arag ± c e l a d ± pump celad  Pseudomorphs: plagioclase — olivine  ab ± s e r ± c h l ± pump  (?) — c h l — cc — c h l ± pump ± c e l a d ± prehn c l i n o p y r o x e n e — b l o t c h y s o d i c pyroxene  234 TABLE 21  Veins:  (continued).  pump + q t z ± wh m  early  q t z + Na px + arag arag + q t z ± ab  l a f c e  ab  A b b r e v i a t i o n s given on p,  74.  235  F i g u r e 33  Textures  i n P i n c h i Mountain Greenstones  (a)  E a r l y q u a r t z - p u m p e l l y i t e v e i n i s c r o s s - c u t by an a r a g o n i t e - q u a r t z v e i n rimmed w i t h a l b i t e . Microg r a n u l a r matrix c o n s i s t s of a l b i t e + s o d i c pyroxene + sphene (Spec. 204).  (b)  C h l o r i t e blebs and r e l i c t a u g i t e s occur i n matrix c o n s i s t i n g of a l b i t e m i c r o l i t e s , s o d i c pyroxene, sphene and c h l o r i t e (Spec. 165).  Cc)  P l a g i o c l a s e phenocrysts are pseudomorphed by a l b i t e , p u m p e l l y i t e and s e r i c i t e . M a t r i x c o n t a i n s a l b i t e l a t h s , c h l o r i t e and sphene C S p e c . 162).  (d).  R e l i c t a u g i t e s are p a r t l y r e p l a c e d by a brownish s o d i c pyroxene w i t h s t r a i g h t e x t i n c t i o n . Note c e l a d o n i t e b l e b s , i l m e n i t e p a r t l y r e p l a c e d by sphene and white mica + q u a r t z + l a w s o n i t e matrix  CSpec.  163).  Ce)  Large b l e b c o n t a i n s a r a g o n i t e p a r t l y i n v e r t e d to c a l c i t e and rimmed by f e r r o s t i l p n o m e l a n e and c h l o r i t e . M a t r i x c o n s i s t s of a l b i t e + s o d i c pyroxene + sphene + white mica (Spec. 170) .  Cf)  C h l o r i t e and p u m p e l l y i t e r e p l a c e ferromagnesian phenocrysts ( o l i v i n e ? ) . A l b i t e and a u g i t e c r y s t a l s l i e i n a m i c r o g r a n u l a r m a t r i x (Spec. 196) .  236  FIG. 3 3  TEXTURES  IN  PINCHI  MT. G R E E N S T O N E S  237 either  as phenocrysts o r amygdules which were l a t e r s u b j e c t  to deformation and r e c r y s t a l l i z a t i o n . by f a r the most common type. most l i k e l y  Chlorite  blebs are  Hornblende or o l i v i n e a r e the  p r e c u r s o r s of some b l e b s , but the l a t t e r i s  p r e f e r r e d on account of the b a s i c composition o f the rocks and absence of a c i c u l a r  pseudomorphs.  P r e h n i t e occurs o n l y i n the greenstones  a t the west  end o f Murray Ridge, c o e x i s t i n g w i t h a l b i t e , c h l o r i t e , pumpellyite,  c e l a d o n i t e and c a l c i t e .  Lawsonite-Glaucophane Bearing Rocks Metabasic  rocks  Metamorphic m i n e r a l assemblages and r e l i c t observed  i n 39 t h i n s e c t i o n s a r e g i v e n i n Table 22.  analyses were performed  f o r a l l other modes.  Rough e s t i m a t i o n s were made  Sample l o c a t i o n s a r e g i v e n i n  The metabasic  two groups:  Modal  f o r four r e p r e s e n t a t i v e rocks using  a Z e i s s micrometer e y e p i e c e .  Map V I I .  minerals  r o c k s have been s u b d i v i d e d  into  f o l i a t e d g l a u c o p h a n i t i c rocks and massive  rocks c o n t a i n i n g j a d e i t e - a c m i t e pyroxene.  Gradations  between each o f these rock types a r e , however, common. Foliated  metabasic  r o c k s a r e c h a r a c t e r i z e d by a h i g h  glaucophane content, a d e a r t h o f r e l i c t m i n e r a l s and fairly  uniform f a b r i c .  Typically  they c o n t a i n : glaucophane  238 TABLE 22  24  MINERAL ASSEMBLAGES IN LAWSONITE-GLAUCOPHANE BEARING METAVOLCANICS  2?  28  29  31  32  33  34  36  37  38  39  40  42  8  -  5  10  -  -  44  45  -  -  46  49  10  chlorite  -  tr  -  x  6  x  x  lo  1  x  15  10  20  x  5  -  tr  tr  10  10  glaucophane  5  30  15  x  27  x  x  l l  1  x  5  5  20  x  16  15  -  65  5  45  52  35  41  x  48  x  x  22  10  x  35  20  32  x  50  46  50  22  39  27  -  12  12  x  6  x  x  11  3  x  10  8  13  x  17  23  -  10  1  5  -  tr  -  -  1  tr  tr  tr  -  -  15  -  -  -  5  x  x  37 70  x  5  27  5  -  12  16  30  tr  25  7  x  x  9  t  r  -  4  -  -  -  -  - t r -  -  -  -  sphene quartz acmitic px. white mica  8 - 2  x  t  r  -  x  -  -  -  -  10  -  -  -  -  48  aragonite  lawsonite  -  47 -  t  2  r  pyrite stilpnomelane^  -  2  0  x  7  x  15  x  -  -  -  tr  -  -  -  tr  -  -  -  -  brown hbl. ^ magnetite  #  hematite  #  deerite  #  dolomite  #  calcite  #  3 10  augite (r)  -  3  -  -  -  -  -  -  t r - t r - - t r  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  5  x  -  x  x  9  7  x  53  54  55  56  57  58  59  60  61  X  x  15  -  -  -  tr  20  -  -  -  10  10  10  x  -  -  20  62  63  64  65  X  X  X  3  15  opaques (r) 50  51  52  chlorite  x  x  5  glaucophane  X  lawsonite  x  sphene  x  x  quartz  -  x  -  acmitic px.  x  -  1  white mica  x  66 201 202 205  aragonite  t r x 8 x  68 l  0  x  65  -  l  x 5  5  x  x  -  4  31 l  l  -  -  x 5  2  -  11  tr  x  x  57  x  x -  x  x x  x  l  -  -  5  x x  x  40  x  x  x  x  l  0  l  8  x  x  l  x  x  8  -  -  X  x  -  -  2  0  -  x  x x  x x  x X  X  X  X  x  x x  X  -  15  X  -  X  -  X  x  30  x  x x  l  0  x  -  X  -  -  X  X  x  15  X  x  X x  pyrite stilpnomelane^ brown hbl,  #  magnetite  #  hematite  ^  deerite  ^  dolomite calcite  augite (r)  x  tr  & ^  15  30  opaques (r) :ote a) e p p r o x l m c . t e melon £ l v e n l n Korae c a E e s , b ) * rnodsl a n a l y s i s o b t n i n e d u s i n g a Z e i s s a l c r o m e t c r e y e p i e c e o:.d c o u n t i n g o v e r 500 p o l n t f l , c ) " M " ratw.p t r a c e o f m i n e r a l l r . p r e s e n t , J) ( r ) = r e l i c t m l n e r n l , c:) // = r e t r o g r e s K l ve o r n l t';r'« t l o n s i l r s n r n l tmd c ) 7. = m i n e r a l p r e s e n t .  1  239 TABLE 23 TEXTURAL DOMAINS IN LAWSONITE-GLAUCOPHANE BEARING METABASIC ROCKS Matrix:  jd-acm + lws + sph + c h l ± g l p h ± wh m ± s t i l p ± q t z ± py  R e l i c t minerals:  ilmenite,  augite  Coften a l t e r e d t o j a d e i t e -  acmite pyroxene or glaucophane) Blebs and pseudomorphs: lws + wh m + c h l ( p l a g i o c l a s e  pseudomorphs)  lws + c h l + arag + g l p h + s t i l p arag + c h l + wh m ± s t i l p  (plag. pseudomorphs)  (plag. pseudomorphs)  lws chl ± s t i l p  ( o l i v i n e pseudomorphs ?)  jd-acm + lws ± wh m ± g l p h arag ± sph (rims)  (amygdules)  V e i n assemblages and p a r a g e n e s i s : Time jd-acm lws + c h l ± wh m arag + c h l ± wh m glph + qtz ± s t i l p  -?  stilp ab + magn  -?  arag + brown h b l  - ?  '  calcite R e l i c t textures: porphyritic,  trachytic,  glomeroporphyritic. Note:  A b b r e v i a t i o n s g i v e n on p. 74 .  amygdaloidal,  240 PIG. .34  TEXTURES IN LAWSONITE-GLAUCOPHANE BEARING METABASIC ROCKS  acm-jd 025  rims 0-5mm  a) P l a g i o c l a s e phenocrysts pseudomorphed by t a b u l a r l a w s o n i t e and c h l o r i t e i n sphene 4- J a d e i t e - a c m i t e m a t r i x ; c r o s s c u t t i n g a l b l t e v e i n (Spec. 6l)« b) R e l i c t a u g i t e zoned to jadeIte-acmlte and s p o r a d i c a l l y rimmed by r i e b e c k i t e l n l a w s o n i t e + c h l o r i t e m a t r i x ; l a t e d e e r i t e sprays (Spec. 2 3 ) . c) A r a g o n i t e / c a l c i t e b l e b s rimmed w i t h sphene i n l a w s o n i t e + sphene + c h l o r i t e + glaucophane T j a d e i t e - a c m i t e matrix; r e l i c t a u g i t e w i t h a c m i t e - j a d e i t e on rims and along f r a c t u r e s ; b l e b c o n t a i n s c h l o r i t e + stilpnomelane (Spec.38) d) glaucophane + q u a r t z + l a w s o n i t e £ c h l o r i t e v e i n s c r o s s c u t t i n g jadeite-aomite v e i n l n lawsonite + Jadeite-acmite + sphene matrix (Spec. 57) •  241 + l a w s o n i t e + sphene ± c h l o r i t e ± s t i l p n o m e l a n e .  Sporadic  g r a i n s c o n t a i n i n g hematite rimming p y r i t e and/or  magnetite  may  a l s o be p r e s e n t .  I d i o b l a s t i c l a w s o n i t e s are s e t i n a  f i n e l y woven m a t r i x of l i n e a t e d glaucophane w i t h sphene o c c u r r i n g i n s t r i n g e r s p a r a l l e l to the Massive  foliation.  rocks d i s p l a y an abundance of r e l i c t  t e x t u r e s s i m i l a r to the greenstones  igneous  of P i n c h i Mountain.  M i n e r a l assemblages c h a r a c t e r i s t i c of t h i n s e c t i o n domains are g i v e n i n Table 23: The  t e x t u r e s are i l l u s t r a t e d i n F i g . 34.  t y p i c a l assemblage c o n t a i n s j a d e i t e - a c m i t e , l a w s o n i t e ,  sphene and c h l o r i t e w i t h glaucophane, a r a g o n i t e and mica as p o s s i b l e a d d i t i o n a l phases. found f i l l i n g ( F i g . 34}.  white  Glaucophane i s commonly  f r a c t u r e s or immediately  a d j a c e n t to f r a c t u r e s  In r o c k s c o n t a i n i n g both a c m i t e - j a d e i t e and  glaucophane, t e x t u r e s i n d i c a t e t h a t the pyroxene formed p r i o r to the glaucophane. and hematite  ( F i g . 30)  P y r i t e , rimmed by  c o n s t i t u t e s about 0.1%  magnetite of a l l t h i n  sections.  Dolomitic  carbonates  The main m i n e r a l s p r e s e n t w i t h i n the d o l o m i t i c l i m e stones are a r a g o n i t e , c a l c i t e and dolomite Disseminated  (Table 12).  carbonaceous m a t e r i a l i s a minor a c c e s s o r y  i n most limestones and b a r i t e and quartz are found Limestones  locally.  have been s u b d i v i d e d i n t o two c a t e g o r i e s :  242 PIG.  35  TEXTURES IN CARBONATES  rial  Spec. 7 7 , ( |:| scale)  S p e c . 213  (scale  I-l  )  Note : samples were s t a i n e d f o r CaCO^ u s i n g red s o l u t i o n and f o r a r a g o n i t e u s i n g s o l u t i o n (Friedman, 1959)  alizarine Fiegl's  j i d e n t i f i c a t i o n of carbonate mineralogy was confirmed by o p t i c s and X-ray d i f f r a c t i o n .  243 m a s s i v e l i m e s t o n e s w h i c h c o n s t i t u t e most e x p o s u r e s and foliated  limestones  o c c u r r i n g e i t h e r as t h i n l a y e r s i n  v o l c a n i c s o r as f o l i a t e d A typical  zones i n m a s s i v e  limestones.  specimen o f massive limestone  contains 50% euhedral  dolomite  rhombs  CO.2 mm)  (Fig. 35a) closely  a s s o c i a t e d w i t h g r a n u l a r , opaque c a r b o n a c e o u s m a t e r i a l i n an a r a g o n i t e - c a l c i t e m a t r i x .  In thin section, aragonite  shows no s i g n s o f d i s e q u i l i b r i u m w i t h d o l o m i t e p r e f e r e n t i a l l y replaced along grained  C80y)  calcite.  v e i n i n g by white  Late i r r e g u l a r  sparry c a l c i t e  rock a b r e c c i a t e d appearance. aceous granules late calcite  cleavages  i s commonly  and i s  a n d m a r g i n s by  fine  f r a c t u r i n g and  CO.4 mm)  tends t o g i v e the  A concentration of  seen a t the margins o f  carbonthese  veins.  A foliated  limestone  i s illustrated  i n F i g . 35b.  It  contains concordant s t r i n g e r s of carbonaceous a r a g o n i t e , white  a r a g o n i t e and d o l o m i t e w h i c h a r e c r o s s - c u t by an  aragonite vein. calcite,  T h e r e i s no i n v e r s i o n o f a r a g o n i t e t o  the l a t t e r mineral being  found only i n l a t e  fractures. I n summary, i t a p p e a r s t h a t a c a r b o n a c e o u s w i t h v a r i a b l e dolomite  c o n t e n t was m e t a m o r p h o s e d i n t h e  blueschist facies to aragonite + dolomite. aragonite  laminae w i t h i n f o l i a t e d carbonates  t h a t t h e m e t a m o r p h i s m was s y n k i n e m a t i c deformation.  limestone  The  dolomite-  may i n d i c a t e  d u r i n g t h e F^  T h i s was f o l l o w e d b y a r a g o n i t e v e i n i n g w h i c h  244  MINERAL ASSEMBLAGES IN METAGREYWACKES  TABLE 24  s p e c no.  69  70  76  75  74  71  j a d e i t i c px.  X  X  X  X  X  glaucophane  X  X  X  X  -  X  3  X  lawsonite  X  X  X  X  X  38  X  quartz  X  X  X  X  X  7  X  white mica  X  X  X  X  X  10  X  chlorite  X  X  -  -  -  5  X  sphene  -  aragonite  X  pyrite  -  -  opaques  X  -  TABLE 25  X  X  -  -  2  X  -  X  X  X  X  - -  X  -  X  X  X  -  -  ~  -  X  X  —  -  MINERAL ASSEMBLAGES IN CHERTS AND CHERTY GRAPHITE SCHISTS  116 122 12? 143 13tt 151 H 8 123 148 150  spec. no. quartz  98  90  65  2  5  tr  4  5  2  glaucophane lawsonite white mica carb.granules pyrite  tr  acmitlo  x t  x r  x x  x  x x  x  x  -  -  -  -  10  x  tr  3  -  x  -  -  x  x  x  -  -  -  -  -  -  x  x  x  x  tr  stilpnomelane §  magn.Aem. #  x  x  x  px. #?  sphene  x  x  aragonite  albite  X  X  stilpnomelane  clasts carbonaceous  72  x x tr  tr  X  note i a) modes are approximate b) " t r " means t r a c e . c) # ! retrograde mineral d) x : mineral  present  x  x  x  245 c r o s s - c u t s the f o l i a t i o n and presumably took p l a c e i n a d i f f e r e n t s t r e s s regime from t h a t e x i s t i n g d u r i n g the F^ deformation. ite  Sparry c a l c i t e v e i n s and i n v e r s i o n o f aragon-  t o c a l c i t e o c c u r r e d d u r i n g a l a t e r deformation (F^7)  presumably a t a h i g h e r s t r u c t u r a l  level.  Metagreywackes The metagreywackes r e t a i n many sedimentary  features  d e s p i t e having a thoroughly r e c r y s t a l l i z e d f a b r i c . o r i g i n a l sediment appears c o n s i s t e d predominantly  The  to have been p o o r l y s o r t e d and  o f p l a g i o c l a s e w i t h minor q u a r t z ,  i l m e n i t e and carbonaceous c l a s t s ; c l a y m i n e r a l s and carbonates probably c o n s t i t u t e d much of the m a t r i x .  Drill  core shows f i n e - g r a i n e d carbonaceous i n t e r b e d s and a c l o s e a s s o c i a t i o n with g r a p h i t i c c h e r t s . Metamorphic r e c o n s t i t u t i o n of the greywacke  produced  the m i n e r a l assemblage: j a d e i t i c pyroxene + lawsonite + white mica + q u a r t z + glaucophane + c h l o r i t e + s t i l p n o m e l a n e + a r a g o n i t e + sphene.  Apparent  e q u i l i b r i u m assemblages  w i t h modes a r e given i n Table 24. F a b r i c elements can be c o n s i d e r e d under f o u r m a t r i x , pseudomorphs, r e l i c t m i n e r a l s and v e i n s .  headings:  The matrix  c o n s i s t s o f m i c r o g r a n u l a r q u a r t z , white mica, c h l o r i t e , j a d e i t i c pyroxene, sphene, and l a w s o n i t e . present.  Rectangular  c l a s t s , thought  A r a g o n i t e may be  t o have been p l a g i o -  PIG.  36  246 TEXTURES IN METASEDIMENTS  a) Dolomite rhombs i n a r a g o n i t e / i n v e r t e d c a l c i t e m a t r i x ( d o l o m i t i c l i m e s t o n e - s p e c . 82). b) Pseudomorphed d e t r i t a l g r a i n s i n metagreywacke; p l a g i o c l a s e i s r e p l a c e d by l a w s o n i t e aggregates and J a d e i t e 4- q u a r t z g r a i n s appear to r e p l a c e d e t r i t a l pyroxene, amphibole o r p l a g i o c l a s e . Note d e t r i t a l q u a r t z and u n f o l i a t e d f a b r i c (Spec. 7 1 ) . c) F r a c t u r e d glaucophane i n metachert (assemblage : glaucophane + q u a r t z + l a w s o n i t e + phengite + magnetite + carbonaceous g r a n u l e s ) ; a l b l t e g r a i n s appear to have c r y s t a l l i z e d a f t e r the deformation which f r a c t u r e d the glaucophanes ( i . e . F ) ( S p e c . 1 5 3 ) . 2  d) Contorted phengite i n metachert  (Spec.153).  247 c l a s e p r i o r to metamorphism, c o n t a i n lawsonite ( F i g . 36b)..  aggregates  These g e n e r a l l y show a p r e f e r r e d o r i e n t a t i o n ,  presumably c o n t r o l l e d by the atomic s t r u c t u r e of the existing albite  (?\.  pre-  J a d e i t i c pyroxene and quartz a l s o  appear to r e p l a c e r e l i c t d e t r i t a l g r a i n s which by  their  morphology c o u l d have been pyroxene, amphibole or p l a g i o clase.  However, as lawsonite  commonly r e p l a c e s p l a g i o c l a s e ,  pyroxene or amphibole are c o n s i d e r e d precursors.  Other r e l i c t c l a s t i c g r a i n s i n c l u d e  p y r i t i c carbonaceous m a t e r i a l and pseudomorphed by sphene. a few  the most l i k e l y  thin sections.  quartz,  skeletal ilmenite  Aragonite  v e i n s were observed i n  Glaucophane c r y s t a l s are  idioblastic  and g e n e r a l l y comprise only a s m a l l p r o p o r t i o n o f  the  rock. Retrograde metamorphism or a l t e r a t i o n gave r i s e s t r i n g e r s of leucoxene, y e l l o w or white i n r e f l e c t e d and v e i n i n g a l l metamorphic m i n e r a l s . commonly a s s o c i a t e d w i t h hematite  The  to  light  s t r i n g e r s are  granules.  Metacherts T y p i c a l metacherts c o n s i s t o f 1 mm beds separated + lawsonite  to 2 cm  quartzitic  by t h i n laminae of glaucophane + white mica  ± carbonaceous m a t e r i a l ± sphene ± p y r i t e .  Metacherts grade i n t o g r a p h i t e s c h i s t s . assemblages are given i n Table 25. between 20 and  200]i.  p o l y g o n a l but may  Individual mineral  Quartz g r a i n s i z e v a r i e s  G r a i n boundaries are g e n e r a l l y  be sutured  i n specimens where undulose  248 e x t i n c t i o n i s observed.  I d i o b l a s t i c , f r a c t u r e d glaucophanes,  averaging 1 mm in. l e n g t h  ( F i g . 36c) show a strong  preferred  o r i e n t a t i o n g e n e r a l l y w i t h the c axes s u b - p a r a l l e l to the (L^l  crenulate  lineation.  A microprobe t r a v e r s e of a  glaucophane i n specimen 151 showed the c r y s t a l s t o be zoned w i t h Fe r i c h cores and margins generally  contorted  CFig. 2 6 ) . P h e n g i t i c mica i s  ( F i g . 36d) and wraps around l a w s o n i t e  CO.5 mm) and glaucophane p o r p h y r o b l a s t s .  Carbonaceous  g r a n u l e s commonly occur as i n c l u s i o n s i n the mica. Retrogressive  m i n e r a l s appear to have formed  a post-metamorphic p e r i o d of deformation  {F^ ? ) •  during  Glauco-  phanes a r e broken, w i t h the f r a c t u r e s f i l l e d w i t h q u a r t z or o c c a s i o n a l l y a l b i t e  ( F i g . 36c).  p o s t - t e c t o n i c p y r i t i c quartz v e i n s  Within g r a p h i t i c cherts are common and c o n t a i n  a l b i t e a t i n t e r s e c t i o n s w i t h micaceous l a y e r s . and  Magnetite  hematite r e p l a c e p y r i t e and form as i n c l u s i o n s i n  glaucophane.  Lawsonite t a b l e t s c o n t a i n  microgranular  aggregates and possess c r o s s - f r a c t u r e s f i l l e d by q u a r t z veins.  Some samples  to 70y a c m i t i c  (e.g.  134) c o n t a i n  (?) pyroxene.  aggregates o f 50  Whether t h i s pyroxene i s p a r t  of the i n i t i a l e q u i l i b r i u m assemblage or i s r e t r o g r e s s i v e is uncertain.  I t i s concluded t h a t the a l b i t e , hematite,  magnetite, leucoxene, the q u a r t z - p y r i t e v e i n s the a c m i t i c pyroxene formed during  and p o s s i b l y  r e t r o g r e s s i v e metamorphism  which was p o s s i b l y a s s o c i a t e d w i t h the F.  0  deformation.  249 Quartz-carbonate  rocks and  schists  In the v i c i n i t y of the mine, where exposures are p l e n t i f u l , the f o l l o w i n g assemblages were noted interbedded w i t h c h e r t s or Ci) Cii)  limestones:  q u a r t z + a r a g o n i t e + white mica q u a r t z + white mica + glaucophane + +  The  in lithologies  lawsonite  chlorite.  f i r s t assemblage c o n s i s t s of e q u i g r a n u l a r  C3Ou)  quartz  and a r a g o n i t e c o n t a i n i n g o c c a s i o n a l a r a g o n i t e p o r p h y r o b l a s t s CO.7  mm).  W i t h i n the second assemblage lawsonite forms  euhedral p o r p h y r o b l a s t s  Cl mm  max)  exhibiting polysynthetic  twinning and i s commonly f r a c t u r e d and a l t e r e d .  In g e n e r a l ,  p h e n g i t i c mica and glaucophane d i s p l a y t e x t u r a l r e l a t i o n s h i p s s i m i l a r to those i n  metacherts.  Most t h i n s e c t i o n s from the mine v i c i n i t y show s i g n s of a p e r v a s i v e a l t e r a t i o n which preceded i z a t i o n and post-dated  the f o r m a t i o n of metamorphic m i n e r a l s .  C a l c i t e , dolomite, a n k e r i t e , quartz and found as replacements  the mercury m i n e r a l -  l i m o n i t e are commonly  or v e i n s i n most r o c k s ,  o b s c u r i n g the primary metamorphic  mineralogy.  locally  APPENDIX V ECLOGITE BOULDERS  Glaucophane b e a r i n g e c l o g i t e b o u l d e r s were found a t two (Fig.  l o c a l i t i e s i n the course of t h i s study. 37, spec. 103)  The  i s l o c a t e d 9 km e a s t of P i n c h i Lake  Mercury Mine on the Tezzeron Lake l o g g i n g road. measures 12 x 4 x 3 m and till  It  i s a p p a r e n t l y embedded i n g l a c i a l  o v e r l y i n g T a k l a Group r o c k s .  f o l i a t e d and  first  The boulder c o n t a i n s  l i n e a t e d b l o c k s up to 30 cm i n diameter  con-  s i s t i n g of green pyroxene and garnet a l t e r i n g t o s t i l p n o m e l a n e . Glaucophane and  lawsonite occupy i n t e r s t i c e s between b l o c k s  and a l s o permeate them.  Late c r o s s - c u t t i n g f r a c t u r e s are  f i l l e d w i t h c h l o r i t e and a brown amphibole. locality  ( F i g . 37, spec. 214)  The  second  l i e s o u t s i d e the t h e s i s area  24 km e a s t - s o u t h e a s t of F o r t S t . James beside the Beaver Lake l o g g i n g road. 4 x 2 x 2 m and  Two  boulders are p r e s e n t , measuring  7 x 5 x 3 m;  both are embedded i n t i l l  possess g l a c i a l s t r i a e on t h e i r s u r f a c e s .  and  The main l i t h o l o g y  i s dark blue massive g l a u c o p h a n i t i c rock c o n t a i n i n g zones r i c h i n g a r n e t , white mica, pyroxene, lawsonite and Quartz v e i n s are a l s o p r e s e n t . mica appears white mica  undeformed.  A K-Ar  pyrite.  In t h i n s e c t i o n the white r a d i o m e t r i c date on the  (Appendix VI) gave an age of 218  ± 7 m yrs.  251 Tezzeron Lake  ^^y'LS^'  0  Fig.  37  •  eclogite  locality  %  inferred  source area  5 kms.  E c l o g i t e l o c a l i t i e s and source areas from g l a c i a l t r a n s p o r t d i r e c t i o n !  Cas  inferred  252 The  i n f e r r e d source area f o r these boulders i s  illustrated  i n F i g . 37.  ment d u r i n g  t h e l a t e s t g l a c i a t i o n was t o w a r d s t h e e a s t -  northeast  B e c a u s e t h e d i r e c t i o n o f i c e move-  ( A r m s t r o n g , 19491  were d e r i v e d  from the west.  i t i s assumed t h a t t h e b o u l d e r s E c l o g i t e has n o t been found  w i t h i n t h e glaucophane lawsonite considering and  bearing region but  the high pressure o r i g i n of e c l o g i t e s  their association with  they o r i g i n a t e d  from w i t h i n  glaucophane, i ti s b e l i e v e d the Pinchi Fault  zone.  C a l i f o r n i a , e c l o g i t e specimens have been o b t a i n e d isolated tectonic blocks C o l e m a n et al.,  (1965)  (Chapter IV) that  In from  w i t h i n glaucophane s c h i s t t e r r a i n . consider:  That t h e s e e c l o g i t e s a r e n o t i n p l a c e and have been t r a n s p o r t e d t o t h e i r p r e s e n t p o s i t i o n as i n c l u s i o n s i n ' d x a p i r i c s e r p e n t i n e s or i n shear zones o f major f a u l t s . A s i m i l a r o r i g i n i s proposed f o r the P i n c h i  eclogites.  APPENDIX VI POTASSIUM-ARGON RADIOMETRIC DATES  Sample l o c a t i o n s a r e g i v e n i n Map V I I (237, 124, 151) and F i g . 37 (214).  Specimens  237 and 124 (quartz + white  mica + lawsonite + glaucophane s c h i s t ) were c o l l e c t e d from the  open p i t a t P i n c h i Lake Mercury Mine.  There i s con-  s i d e r a b l e c a r b o n a t i z a t i o n i n the area b u t the micas appear to be f r e s h and u n a l t e r e d i n t h i n s e c t i o n a p a r t from the presence of minute a c i c u l a r r u t i l e  (?) n e e d l e s .  lawsonite and white mica a r e deformed by F^.  Glaucophane,  Sample 151  (quartz + glaucophane + p h e n g i t e + magnetite metachert) was c o l l e c t e d 3.5 km northwest o f P i n c h i Mine'.  Phengitic  muscovites a r e deformed by F^ and c o n t a i n minor amounts of carbonaceous m a t e r i a l .  Approximately 10% o f the micas a r e  s l i g h t l y iron stained.  Sample 238 was obtained o u t s i d e the  t h e s i s area 24 km e a s t - s o u t h e a s t o f F o r t S t . James, from an e c l o g i t e b o u l d e r c o n t a i n i n g glaucophane + lawsonite + pyroxene + g a r n e t + p y r i t e and white mica o c c u r r i n g i n sehlieren.  I n t h i n s e c t i o n , the white mica i s undeformed. A f t e r c r u s h i n g and s i e v i n g , e s s e n t i a l l y pure white  mica s e p a r a t e s were o b t a i n e d using a water column and heavy l i q u i d s .  Potassium-argon a n a l y s e s were c a r r i e d out  by J.E. H a r a k a l and V. Bobik i n the l a b o r a t o r i e s o f the  254  TABLE 26  ANALYTICAL DATA FOR POTASSIUM-ARGON  237  Sample n o . Location  : lat. long.  54°  ANALYSES  151  124  3 8 ' 5"  124° 2 6 ' 1 5 "  54°  38' 5 "  124°  26'"l5"  54°  214 54°  3 9 ' 9"  124° 28• 48"  123°  24* 3 0 " 53*  00*  Hock t y p e  mica-schist  mica-schist  metachert  eclogite  Mineral  muscovite  muscovite  muscovite  muscovite  Mesh s i z e K  48-65  28-48 8.63  % ± <r  !* Ar r a d * 40 Ar t o t a l  ± 0.05  8.36  48-65  ± 0.04  7.60  60-80  + 0.04  7.96  + 0.02  0  4<>Ar r a d (10~5cc STP/gm)  K  0.95  O.96  7.810  7.375  1.337  40  xIO  1.303  - 2  216 + 7 m.y.  A p p a r e n t age  0.94  0.93 6.823  x IO  1.326  - 2  211 + 7 m.y.  7.285  x  IO  - 2  214 + 7 m.y.  x  1.352  1  K / K  =  1  >  l  8  1  x  1 Q  -  218 + 7 m.y.  ** P o t a s s i u m a n a l y s e s by J . S . H a r a k a l , and V. B o b l k u s i n g KY and KY-3 f l a m e p h o t o m e t e r s ; Q- = s t a n d a r d d e v i a t i o n . * Argon a n a l y s e s by J . E . H a r a k a l u s i n g MS-10 mass s p e c t r o m e t e r . C o n s t a n t s u s e d l n model age c a l c u l a t i o n s : \ = 0.585 x l O - l O y " , \ - 4.72 10-1V1. S0 _4 .  x  10  e  Specimen l o c a t i o n s a r e g i v e n I n ' F i g . 4 3 ( 2 3 7 , 124, 151) and F i g . 42 (214).  2  255 Geology and Geophysics Departments a t the U n i v e r s i t y o f B r i t i s h Columbia  u s i n g procedures and equipment p r e v i o u s l y  d e s c r i b e d by White et al.  3  (1967).  A n a l y t i c a l data and  apparent ages are g i v e n i n T a b l e 26.  APPENDIX V I I  CALCULATION OF  EQUILIBRIUM:CONSTANT FOR  REACTION:  PLAGIOCLASE = J A D E I T I C PYROXENE + QUARTZ  S i n c e AG •  Jl  8  A  = -RT, I n K  ATT  G  and  =  _ then  A V  31nK  whence l n K  Now,  - A V  =  - In K  2  i n K ^  According  in  ="||  i f standard state and-  ing  ±  in albite  Smith  -  P.^  i s t a k e n a t P^  = =^  then l n  and  and M c K i e  C1960)  most  625°C.  (a) T  =  (b) T  = 473°K, P  p o i n t s on  773°K, P^ o  = 14.3  kb  =  kb  8.2  t h i s curve  are:  disorderTherefore,  been  e x p e r i m e n t a l d a t a , Newton  a breakdown c u r v e f o r low  Two  0 (A)  o f A V , d a t a f o r low a l b i t e has  theoretical  + quartz.  =  (P, - P,)  t a k e s p l a c e between 575° and  (J.966) p r o d u c e d  jadeite  2  to McConnell  the c a l c u l a t i o n  Employing  (P  used.  and  albite =  257 Equation  (A) can be s o l v e d f o r s e v e r a l d i f f e r e n t  values of  3 K a t each temperature u s i n g R = 83.14 bar cm  -1 deg  -1  mol  and AV = 16.98 cm  mol  .  A t T a = 773°K ln K and a t T ln K = ^  (P  c  b  - 14300)  = 473°K, CP  d  - 8200)  R e s u l t s a r e t a b u l a t e d v/below;,. and i l l u s t r a t e d  K  Assuming  P  b  P  on F i g . 8b,  d  .05  2.96  1.26  .1  5.58  2.87  .2  8.21  4 .47  .3  9.74  5.41  .4  10.81  6 .08  .5  11.68  6.59  .6  12.37  7.02  .7  12.95  7.37  .8  13.45  7.68  .9  13.90  7.95  u n i t a c t i v i t y f o r q u a r t z and mole f r a c t i o n  equal to a c t i v i t y ,  K = X?* / X ^ ^  g  .  (X)  258  APPENDIX V I I I SPECIMEN NUMBERING Note:  Thesis Number 1 2 3 4 5 6 7 8 9 10 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38  SYSTEM  l o c a t i o n s o f most specimens a r e g i v e n i n Map V I I u s i n g " t h e s i s number". Hand Specimen Number  Thesis Number  P-17-69 P-66-69 P-218-69 P-234-69 5-71P-5A 8-71P-4 P-70-69 P-19-69 P-60-69 P-68-69 P-116-69 P-117-69 P-200-69 P-210-69 P-214-69 P-225-69 P-232-69 P-242-69 P-243-69 S-6-69 P-122-68 420-1589 420-1579 420-1581 P-2 CH-67 P-8-67 P-9-67 P-6-68 P-18-68 P-23-68 P-23-68 P-29-68 P-30-68 P-44-68 P-45-68 P-78-68 P-80-68  39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75  Hand Specimen Number P-81-68 P-91-68 P-93-68 P-94-68 P-79-68 P-27-69 P-30-69 P-31-69 P-33-69 P-92-69 P-93-69 P-96-69 P-101-69 P-105-69 P-106-69 P-119-69 P-121-69 P-131-69 P-138-69 P-140-69 P-142-69 H-C-5 P-188-69 P-195-69 P-196-69 P-249-69 HM-10-604 HM-8-149 HM-200-417 P-131-135 P-7-68 P-99-68 P-191-69 P-207-69 HM-20-651 HM-11-344 HM-I1-185  259 Thesis Number  Hand Specimen Number  76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 115 116 117 118 119 120 121 122 123 124 125  HM-8-610 P-l-67 P-19-68 P-58-68 P-75-68 P-98-68 P-148-68 P-90-68 P-65-68 P-70-68 P-72-68 P-73-68 . P-152-68 P-153-68 P-154-68 P-165-69 P-2-70 P-28-68 P-38-68 P-40-68 P-56-68 P-62-68 P-104-68 P-105-68 P-110-68 5-71P-9E 5-71P-9E 5-71P-9E 5-71P-9E P-59-69 5-71P-3 11-71P-1 16-71P-3 6-71P-5B 8-71P-3 8-71P-2A 8-71P-2B P-3-67 P-5-68A P-5-68B P-8-68 P-14-68 P-15-68 P-16-68 P-21-68 P-48-68 P-50-68 P-49-68  Thesis Number 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 17 0 171 172 173  Hand Specimen Number P-76-68 P-82-68 P-88-68 P-89-68 P-135-68 P-10-69 P-12-69 P-13-69 P-25-69 P-48-69 P-53-69 P-73-69 P-77-69 P-83-69 P-88-69 P-90-69 P-143-69 P-146-69 P-157-69 P-170-69 421-155 HM-10-79 HM-10-458 HM-10-690 HM-11-613 P-220-69(1) P-220-69 (2) P-220-69(3) P-152-69 P-152-69 P-154-69 r S t u a r t Lake Antimony Mine P-112-68 P-145-68 P-146-68 P-39-69 P-162-69 P-189-69 HM-2-54 HM-4-102 HM-3-94 HM-5-308 P-37-69 P-100-68 P-101-68 P-161-69  260 Thesis Number 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209  Hand Specimen Number HC-1 HC-2 HC-3 HC-4 P-275-69 P-110-69 P-282-70 2020-169. 1-Nat Cu 2-Nat Cu 2022-362 HMP-11-120 HMP-12-140 P-68-68 P-216-69 S-71P-7 10-71P-6 P-147-68 HMP-8-100 3-71P-7A 9-71P-2A 9-71P-2B 6-71P-4A P-2 (.2) -67 10-71P-4B 10-71P-4C P-282 10-71P-SC P-252-69 P-85-68 P-85-68 P-283-69 P-721 P-185-69  Thesis Number 210 211 212 213 214 ' 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 239 240 241 242 243 244  Hand Specimen Number P-87-68 P-6-68 P-224 P-112-69 24-72P-1 P-2-68 P-12-68 P-25-68 P-102-68 P-123-68 P-65-69 P-94-69 P-97-69 P-116-69 P-118-69 P-124-69 P-131-69 P-247-69 S-7-69 1-71P-2 4-71P-1C 4-71P-2 6-71P-3 7-71P-2 13-71P-1 P-201-69 P-4-67 15-71P-4 P-109-68 S-11-69 15-71P-2 15-71P-3 P-87-68 P-278-69  261  LIST OF PLATES 1.  View of the P i n c h i Lake area l o o k i n g northwest from the summit of Mount Pope.  2.  Laminated s i l t s t o n e s and Group.  3.  Northwesterly plunging m u l l i o n s i n quartz-micacarbonate s c h i s t . Note prominent j o i n t s u r f a c e s p e r p e n d i c u l a r to m u l l i o n s .  4.  Angular limestone cobble conglomerate i n T a k l a Group. "M" p o i n t s to Monotis s u b e i r e u l a r i s occurring within cobbles and i n m a t r i x .  5.  Northerly dipping compositional layering i n s i l i c a carbonate r o c k s . Note l a y e r s of rough weathering f e r r o a n magnesite v e i n e d by q u a r t z , e n c l o s i n g l a y e r of pure white magnesite.  6.  Primary  7.  Late p y r o x e n i t e l a y e r s p a r a l l e l to d u n i t e layers i n harzburgite.  8.  Late discordant pyroxenite layer c r o s s - c u t t i n g i r r e g u l a r d u n i t e . To the l e f t , o f f the photograph, t h i s p y r o x e n i t e c r o s s - c u t s the d u n i t e h a r z b u r g i t e c o n t a c t and a l s o an e a r l y p y r o x e n i t e l a y e r . Note s l i g h t o f f s e t of p y r o x e n i t e by f r a c t u r e cleavage.  9.  Smooth weathering d u n i t e l a y e r p a r a l l e l to f o l i a t i o n i n h a r z b u r g i t e o u t l i n e d by v a r i a t i o n i n o l i v i n e / pyroxene r a t i o . Note the chromite s t r i n g e r i n the dunite layer.  sandstones i n the T a k l a  (?) two phase f l u i d  i n c l u s i o n i n metachert. rich  10.  Folded e a r l y p y r o x e n i t e layer..  11.  F o l d e d d u n i t e l a y e r i n h a r z b u r g i t e . Note the weak f o l i a t i o n which p a r a l l e l s j o i n t s on r i g h t s i d e of outcrop.  262  LEGEND  CRETACEOUS OR LOVER TERTIARl USLIKA FORMATION  (?)i  conglomerate  SYMBOLS  UPPER TRIASSIC 4 LOWER JURASSIC  s t r i k e and d i p of bedding  TAKLA GROUP  s t r i k e and d i p o f bedding  10) greywacke, s l l t s t o n e i  11) limestone  12) b a s i c rocks  pyroxenite l a y e r i n g l n u l t r a m a f i t e s  CACHE CREEK CROUP  l i n e a t i o n (J-2)  MOUNT POPE BELT PI  7) l l n e s t o n e s i  axial 8) c h e r t t 9) v o l c a n i c b r e c c i a .  CACHE CREEK CROUP (?)  y ^// 1  TERTIARY (?)  GREENSTONES OF PINCHI MOUNTAIN 5) b a s a l t i 6) limestone  gabbro, diabase,  greenstone  1) metabasic  r o c k s i 2) c h e r t , s c h i s t , greywacke  3) d o l o m i t i c limestone i  j hornblende  diorite  Ei e c l o g i t e  plane  — » . l i m i t of exposure  STUART  LAKE  •P-2 f o s s i l  locality  Note i a) exposure Is poor l n l i g h t l y coloured areas  h a r z b u r c l t e , minor dunite and pyroxenite (14a)  b) e x t r a p o l a t i o n beneath d r i f t cover I s based on topographic and magnetic expression of rock u n i t s and sparse d r i l l hole Information.  s e r p e n t i n i t e (lUb)  o ) geology by I . A . Paterson  TREMBLEUR INTRUSIONS jfrofiVttl  f a u l t s ( d e f i n e d , approximate, assumed)  S^, g e o l o g i c contact ( d e f i n e d , approximate)  GEOLOGY OF THE PINCHI LAKE A R E A  PERMO-TRIASSIC  GLAUCOPHANE BEARING ROCKS OP PINCHI LAKE M W|  carbonatlsed s e r p e n t i n i t e . ( l 6 a ) , sediments (16b)  |^ 13  trace of f o l d s  i n f e r r e d d i p of f a u l t  JURASSIC (?)  BASIC ROCKS SOUTH 0? PINCHI LAKE  a  bedding  f o l i a t i o n (SjJ  PENNSYLVANIAN & PERMIAN  |H  (tops known)  s t r i k e and d i p of overturned  IOOO  2000  3000  4000  m»rr»»  (1968, 1969i 1971)  MAP II  CROSS  SECTIONS  AEROMAGNETIC  OF  PROFILES  TS£  PINCHI  OBTAINED  LAKE  FROM  AREA  M A P HI  MAP /  MAP III  JT  SAM MAP IV  BBBMJ foliation (Sj) lineation  ( L ) and f o l d ?  axea ( P " ) 2  s fold  axes ( P j )  \ ^ I n f e r r e d  '"X "^•^  Inferred limit  P  2  P j antlforras/synforms  o f exposure  approximate '•"»  *  *I  breccia  limit  antlforma/synforma  geological  of alteration  contact  l n nine  area  zone  MESOZOIC UPFEB TRIASSIC & LOWER JURASSIC greywacke ( T a k l a  Croup)  FERKO- TRIASSIC serpentinite  (Trembleur I n t r u a l o n s )  L A T E PALEOZOIC CACHE CREEK GROUP ( ? ) greenstones  of Flnchl  lawsonite-glaucophane massive  dolomitic  metacherts, 200  300  400  500  Metres See  Map  I  for  mop location  minor l i m e s t o n e . -  be'arlng m e t a b a s i c  rocks  limestones  graphite s c h i s t s , quartr-caxbonate  metagreywacke 100  Mountain,  schists  MAP  <-o  MAP V  GEOLOGY  OF  AN  AREA  ON  THE  NORTHWEST  SHORE OF PINCHI  OUTCROP  fj  CLIFF  LAKE  ilk  ^—>  (S,)  TALUS  >%  CLEAVAGE  (Sj)  ROAD-  ""V  MASSIVE FOLIATED i3  /^j? METAVOLCANIC METAVOLCANIC LIMESTONE LIMESTONE  METACHERT  rupj S«t  C O N T A C T (OEF1NEO, A P P R O X - ) FOLIATION  MASSIVE  f  (APPROXIMATE)  *V.  FOLIATED  7 5  FAULT  MARSH  STREAM  «0&  r  F-ty, 3  f o r mop l o c a t i o n  ///  V  ' JOINT LINEATIONS  <L,,L ,L >  MINOR  AXES  I'  2'  FOLD  a  r  3'  APPROXIMATE  AXIAL  TRACE  MAP V I  MAP  PINCHI  LAKE  VII  MAP  PINCHI MOUNTAIN  PINCHI FAULT  MURRAY  CROSS  SECTiONS  AESOMAGNETIC  II  OF  PROFILES  T*tE  PINCHI  L A* E  OSTAiNEO F R O M  AREA  MAP III  r  c  a  L  AND  LEG  MAP  l  RIDGE  PINCHI FAULT  MAP  III  MAP IV f o l i a t i o n (Sj) l i n e a t i o n ( L ) and f o l d axes (F^) 2  f o l d axes (Fj) \  Inferred F j antlforms/sjnfoiiaa  " " \ * \ inferred F j a n t l f o r a i / i / n f o n u l i m i t of expoaura approximate geological contact H a l t of a l t e r a t i o n l n alne area  1,\  ^  f a u l t a (defined, approximate, assumed)  HESOZOIC JffFEB TBIASSIC * 10VEB JliBASSIC greywacke (Takla Group) FERMO-TRIASSIC  .  serpentinite (Treaoleur Intrusions) .. LATE PALEOZOIC CACHE CHEEK GBODP (») rpm  greenstones o f F l n c h l (fountain, nlnor llnestone. laaaonlte-glaucophane bearing metabasic rocks • B B S I I T O dolomitic line8tone•  SCALE:  400 100  800 200  300  1200 400  1 6 0 0 Feat  1  5 0 0 Mitret  [s^lc^lf See  Map f for mop location  I  metachert*, graphite s c h i s t s , quartz-carbonate s c h i s t s netagrejwacke  N  MAP V  MAP  VI  *  MAP  VII  

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