Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Structure, metamorphism, and geochronology of the Northern Wolverine complex near Chase Mountain, Aiken… Parrish, Randall Richardson 1976

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1977_A6_7 P37.pdf [ 9.1MB ]
Metadata
JSON: 831-1.0052839.json
JSON-LD: 831-1.0052839-ld.json
RDF/XML (Pretty): 831-1.0052839-rdf.xml
RDF/JSON: 831-1.0052839-rdf.json
Turtle: 831-1.0052839-turtle.txt
N-Triples: 831-1.0052839-rdf-ntriples.txt
Original Record: 831-1.0052839-source.json
Full Text
831-1.0052839-fulltext.txt
Citation
831-1.0052839.ris

Full Text

STRUCTURE, METAMORPHISM, AND GEOCHRONOLOGY  OF  THE NORTHERN WOLVERINE COMPLEX NEAR CHASE MOUNTAIN, AIKEN LAKE MAP-AREA, BRLTISH COLUMBIA  by  RANDALL RICHARDSON PARRISH B.A., Middlebury  C o l l e g e , 1974  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  xn THE FACULTY OF GRADUATE STUDIES (Department o f G e o l o g i c a l S c i e n c e s )  We accept  t h i s t h e s i s as conforming  to the r e q u i r e d  standard  THE UNIVERSITY OF BRITISH COLUMBIA September, 1976  ©  R a n d a l l R i c h a r d s o n . P a r r i s h , 1976  In  presenting  this  thesis  an a d v a n c e d d e g r e e a t the I  Library  further  for  agree  scholarly  by h i s of  shall  this  written  the U n i v e r s i t y  make  it  freely  that permission  thesis  for  It  for  financial  gain  of  2075 W e s b r o o k  V a n c o u v e r , V6T 1W5  of  British  Columbia  P l a c e  Canada  3qyhua/i^  I  /y 7 ? /  f  of  of  Columbia,  British  ?  for  extensive by  shall  the  requirements  reference copying of  I agree and this  that  not  copying or  for that  study. thesis  t h e Head o f my D e p a r t m e n t  is understood  permission.  The U n i v e r s i t y  fulfilment  available  p u r p o s e s may be g r a n t e d  representatives.  Department  Date  in p a r t i a l  or  publication  be a l l o w e d w i t h o u t my  ia  ABSTRACT  The Wolverine to the northwest  Complex (Armstrong,  are of Precambrian  1949;  age,  Roots,  1954)  and s i m i l a r  rocks  c o r r e l a t e w i t h Wlnderemere-type  s t r a t i g r a p h y , and are poly-metamorphic and p o l y - d e f o r m a t i o n a l .  Wolverine  rocks near Chase Mountain have e x p e r i e n c e d two  to  folding  ( F l , F2) o v e r p r i n t e d by one  l a r g e - s c a l e open f o l d i n g  p e r i o d s of t i g h t  o r more p e r i o d s of  isoclinal  northwest-trending  ( F 3 ) , s m a l l - s c a l e c r e n u l a t i o n f o l d i n g of v a r i o u s  o r i e n t a t i o n s , and minor f a u l t i n g .  The  two  e a r l i e r p e r i o d s of f o l d i n g were  accompanied by metamorphism c u l m i n a t i n g i n a m p h i b o l i t e f a c i e s a t the c l o s e of F2.  These e a r l y f o l d s are recumbent to g e n t l y i n c l i n e d , and  of F2 i s c o n s i s t e n t w i t h north-eastward fashion.  the geometry  t r a n s p o r t of r o c k s i n n a p p e - l i k e  An F3 l a r g e - s c a l e f o l d deformed e a r l i e r f o l i a t i o n s i n t o an u p r i g h t  to s t e e p l y eastward  i n c l i n e d a n t i f o r m which c o r r e l a t e s w i t h s t r u c t u r e s mapped  to the n o r t h by Mansy (1972, 1974). Geochronometric  d a t a s t r o n g l y suggest  t h a t metamorphic c u l m i n a t i o n  occured i n mid-Cretaceous o r e a r l i e r time, and t h a t many r o c k s i n widespread areas south of 56^°N have e x p e r i e n c e d r e s e t t i n g of K-Ar dates d u r i n g the Eocene.  and  A s t o c k of b i o t i t e q u a r t z monzonite, termed the  B l a c k p i n e Lake g r a n i t i c s t o c k , has a Rb-Sr whole r o c k i s o c h r o n age 62+7 m.y. m.y.,  @ 0.7052+.0002 Sr 87/86  of  and a m i n e r a l i s o c h r o n age of 44.7+2  i  and i t i n t r u d e s the Wolverine  g n e i s s e s , pegmatites,  Rb-Sr  Complex.  and m u s c o v i t e - b e a r i n g  In s u r r o u n d i n g  schists,  g r a n i t i c r o c k s r e l a t e d to the  metamorphism, Rb-Sr m i n e r a l dates  (muscovite, p l a g i o c l a s e , K - f e l d s p a r ,  whole rock) range from 52-84 m.y.  and r e f l e c t p a r t i a l  whereas K-Ar  dates are e n t i r e l y r e s e t t o 43-47 m.y..  to complete  resetting,  Rb-Sr m i n e r a l dates  on  b i o t i t e from metamorphic r o c k s a r e anomalously problem which i s not  r o c k s and sediments i n d i c a t i v e of r a p i d  o c c u r w i t h i n or f l a n k i n g  the Omineca C r y s t a l l i n e B e l t ,  d i s t r i b u t i o n b e a r s no r e l a t i o n s h i p Rb-Sr d a t e s .  up-  their spatial  to the areas of r e s e t t i n g of K-Ar  Though an e n t i r e l y s a t i s f a c t o r y e x p l a n a t i o n remains  the r e s e t t i n g of dates must i n p a r t be due trusions  dates, a  understood.  Though Eocene v o l c a n i c lift  younger than K-Ar  and  elusive,  t o the thermal e f f e c t of i n -  of g r a n i t i c rock s i m i l a r to the B l a c k p i n e Lake g r a n i t i c s t o c k  which i s shown to have d i s t u r b e d dates i n s u r r o u n d i n g metamorphic r o c k s .  ic  T A B L E  PART I  OF  C O N T E N T S  S t r u c t u r e and Metamorphism  Page  Introduction  1  Previous  Work  4  Geologic  Setting  5  Stratigraphy  7  S t r u c t u r a l Geology  13  Chase Mountain A r e a  13  Phase 1 Phase 2 Phase 3 Other Minor S t r u c t u r e s Stereographic Analysis Domains 1 , 2 Domains 3, 4, 5 Domain 6 Summary Blackpine  13 16 22 25 25 29 32 34 34  Lake A r e a  35  Phases 1, 2 S t r u c t u r a l Relations of the Blackpine  Lake Stock  R e l a t i o n s between C r y s t a l Growth and Deformation Metamorphic P e t r o l o g y  38 43  Introduction Chase Mountain Area B l a c k p i n e Lake a r e a Summary o f P - T - f l u i d c o n d i t i o n s G r a n i t i c Rocks PART I I  35 38  43 43 51 58 58  Geochronology and the Eocene R e s e t t i n g Event  Introduction  61  Geologic  63  S e t t i n g o f t h e W o l v e r i n e Complex  Geochronology o f t h e W o l v e r i n e Complex  and R e l a t e d  Review of P r e v i o u s Work Rb-Sr and K-Ar Data of t h i s Study Discussion  and Problems o f I n t e r p r e t a t i o n  Early T e r t i a r y Tectonic Summary Bibliography  Setting  Rocks  69 69 69 77 81 85 86  LIST OF FIGURES  1.  G e o l o g i c Map of W o l v e r i n e Complex and a d j a c e n t areas o f n o r t h c e n t r a l B r i t i s h Columbia. 2. a,b S t r u c t u r a l map o f t h e s i s area showing o r i e n t a t i o n s o f compos i t i o n a l layering. 3. C o r r e l a t i o n c h a r t o f uppermost Precumbrian and lowermost Cambrian r o c k s i n n o r t h - and e a s t - c e n t r a l B r i t i s h Columbia. 4. S t r u c t u r a l map o f t h e s i s a r e a showing phase 1 d a t a . 5. Photographs o f phase 1 f o l d s and r e l a t e d s t r u c t u r a l f e a t u r e s . 6. S t r u c t u r a l map of t h e s i s area showing phase 2 d a t a . 7. Photograph o f phase 2 f o l d s showing c r e n u l a t e d s c h i s t o s i t y . 8. Photograph o f phase 2 f o l d r e f o l d i n g phase 1 f o l d . 9. Photograph of phase 2 f o l d s d e p i c t i n g g e n e r a l form. 10. Sketches o f e a s t - v e r g i n g phase 2 f o l d s . 11a. Sketch o f s t r u c t u r a l c r o s s - s e c t i o n e a s t o f Chase Mountain, lib. Photograph of d i s l o c a t i o n zone. 12. Schematic and somewhat c o n j e c t u r a l t e c t o n i c p r o f i l e near Chase Mountain. 13. Sketch of "phase 3b f o l d s . 14. C r o s s - s e c t i o n s of Mansy a c r o s s Wrede and R u s s e l l Ranges. 15a. Sketches o f l a t e r , b r i t t l e minor s t r u c t u r e s . 15b. E q u a l - a r e a s t e r e o n e t diagram o f l a t e minor s t r u c t u r e s . 16. Map of the Chase Mountain a r e a showing domain b o u n d a r i e s . 17a. E q u a l - a r e a s t e r e o n e t s o f s t r u c t u r a l f e a t u r e s , Domain 1-5. 17b. E q u a l - a r e a s t e r e o n e t o f s t r u c t u r e s , Domain 6. 18. S t r u c t u r a l Map'of SQ, S p and S2 o r i e n t a t i o n s a c r o s s f a u l t e a s t of Chase Mountain. 19. Photograph o f r e f o l d e d l i n e a t i o n s . 20. Photograph of phase 1 f o l d s , B l a c k p i n e Lake a r e a . 21. Photograph and s k e t c h o f f o l d s and r e l a t e d p e g m a t i t e s , B l a c k p i n e Lake a r e a . 22. E q u a l - a r e a s t e r o n e t of s t r u c t u r a l d a t a , B l a c k p i n e Lake a r e a . 23. Photomicrographs of d e f o r m a t i o n a l t e x t u r e s w i t h i n and s u r r o u n d i n g the B l a c k p i n e Lake G r a n i t i c Stock. 24. Photomicrographs o f metamorphic t e x t u r e s i n s c h i s t s . 25. Photograph and photomicrograph of muscovite pseudbmorphs o f kyanite. 26. Diagram d e p i c t i n g i n t e r r e l a t i o n s o f d e f o r m a t i o n , metamorphism, and i n t r u s i o n . 27. Map o f t h e s i s area showing d i s t r i b u t i o n o f samples r e f e r r e d t o in text. 28. Photomicrograph of muscovite pseudormorphs a f t e r k y a n i t e . 29. PH2O-T diagram of g e n e r a l metamorphic c o n d i t i o n s . 30. T-X diagrams o f P =6 kbars f o r the system S1O2 - CaO - MgO K 0 - AI2O3 - CO2 - H 0 31. T-X diagram o f Pf=6 kbars f o r samples 17, 18, and 271-2. 32. T-X diagram o f Pf=6 kbars f o r sample 87-2. 33a. T-X-..diagram o f Pf=6 kbars f o r Fe - f r e e , Na - f r e e system 33b. T-X diagram o f Pf=6 kbars f o r system c o n t a i n i n g b i o t i t e , p l a g i o d a s e , and actinojjjtic amphibole. 34. T-X diagram of Pf=6 kbars f o r B l a c k p i n e Lake a r e a . 35. Photomicrographs of Rock 304B showing r e l a t i o n s of g a r n e t , s t a u r o l i t e , s i l l i m a n i t e , and m u s c o v i t e . 36. PH2O - T diagram o f c o n d i t i o n s o f Sample 304b near B l a c k p i n e Lake. 37. Map o f W o l v e r i n e Complex and r e l a t e d metamorphic r o c k s showing a l l available geocronologicdata. f  2  2  ii  TABLE OF FIGURES cont.  38. 39. 40. 41. 42.  Rb-Sr e v o l u t i o n diagram f o r S c h i s t of sample 134. Rb-Sr e v o l u t i o n diagram f o r " W o l v e r i n e " G r a n i t i c r o c k s . Rb-Sr e v o l u t i o n diagram f o r B l a c k p i n e Lake G r a n i t i c Stock. Rb-Sr diagram showing a l l whole r o c k d e t e r m i n a t i o n s . Sketch map showing the t e c t o n i c s e t t i n g d u r i n g Eocene time N o r t h - c e n t r a l B r i t i s h Columbia.  XV  LIST OF TABLES Page I.  R e p r e s e n t a t i v e assemblages  from the Chase Mountain Area  46  Ila.  K-Ar d a t a from the G e o l o g i c a l Survey of Canada.  70  lib.  K-Ar  71  III.  a n a l y t i c a l d a t a from t h i s study.  Rb-Sr a n a l y t i c a l d a t a from t h i s study.  74  V  ACKNOWLEDGEMENTS  F i e l d and a n a l y t i c a l expenses were d e f r a y e d by NRC grant.678841 awarded t o R.L. Armstrong B r i t i s h Columbia  and by the Department of Labor, P r o v i n c e o f  under the C a r e e r s  '75 program.  L o g i s t i c a l support  the G e o l o g i c a l Survey of Canada i s a l s o g r a t e f u l l y  acknowledged.  from  During  the tenure o f t h i s study the author was supported on a Graduate F e l l o w s h i p a t the U n i v e r s i t y of B r i t i s h Columbia. g r e a t l y improved Armstrong,  The manuscript has been  by the comments and s u g g e s t i o n s o f H. G a b r i e l s e , R.L.  and Ian Duncan.  Competent and c h e e r f u l f i e l d  a s s i s t a n c e was  p r o v i d e d by C. P a r r i s h , and t h e h e l p o f K. S c o t t and J . H a r a k a l d u r i n g the c o l l e c t i o n of a n a l y t i c a l d a t a i s a l s o g r a t e f u l l y  acknowledged.  1  PART I .  STRUCTURE, STRATIGRAPHY, AND METAMORPHISM OF THE CHASE MOUNTAINBLACKPINE LAKE AREA INTRODUCTION  The  t h e s i s area i s s i t u a t e d a t t h e northwestern  Complex as d e f i n e d by Armstrong 1.  end o f the Wolverine  (1949) and Roots (1954), as shown i n f i g u r e  Rocks i n c l u d e metamorphosed c l a s t i c sediments,  now mica s c h i s t , micaceous  and f e l d s p a t h i c q u a r t z i t e , b i o t i t e - m u s c o v i t e g n e i s s , and r a r e , d i s c o n t i n u ous l a y e r s o f c a l c - s i l i c a t e marble, a m p h i b o l i t e , t o u r m a l i n e s c h i s t , and q u a r t z - p e b b l e conglomerate. some areas lower  Metamorphic grade i s a m p h i b o l i t e f a c i e s , i n  s i l l i m a n i t e grade.  phase d e f o r m a t i o n .  Broad  The r o c k s have been i n v o l v e d i n p o l y -  open f o l d i n g and l a t e r f a u l t i n g a r e superimposed  on e a r l i e r syn-metamorphic n e a r - i s o c l i n a l f o l d i n g and f l a t t e n i n g .  The  g e o c h r o n o l o g i c e v o l u t i o n i s complex and i n d i c a t e s a l o n g and c o m p l i c a t e d thermal  history.  T h i s study was undertaken  because i t was f e l t  t h a t the s t r u c t u r a l ,  metamorphic, and g e o c h r o n o l o g i c e v o l u t i o n o f t h e Wolverine p o o r l y known and warranted  d e t a i l e d study.  Complex was  The s p e c i f i c a r e a near  Mountain was chosen because i t i s l o c a t e d a t the northwestern Complex where t h e dominant s t r u c t u r a l a n t i c l i n o r i u m plunges beneath lower grade and s t r u c t u r a l l y h i g h e r r o c k s .  Chase  end o f t h e  northwesterly  I t was hoped t h a t  metamorphic i s o g r a d s and a change i n s t r u c t u r a l s t y l e might be documented. The B l a c k p i n e Lake g r a n i t i c s t o c k was examined f o r d e f o r m a t i o n a l and g e o c h r o n o l o g i c h i s t o r y i n hopes t h a t t h e a b s o l u t e ages o f s t r u c t u r a l events might be determined.  The a r e a was a l s o s e l e c t e d because o f the  p r o x i m i t y o f Eocene K-Ar d a t e s , so t y p i c a l o f the Wolverine Complexes, and nearby E a r l y Cretaceous  dates on s i m i l a r  and Shuswap  'Wolverine'  rock  2  types  (Wanless e t a l , 1971).  I t was f e l t  t h a t a combined K-Ar and Rb-Sr  approach t o the 'Eocene r e s e t t i n g ' problem on b o t h metamorphic  and igneous  rocks might shed some i n s i g h t i n t o t h e thermal h i s t o r y . The s i g n i f i c a n c e o f the W o l v e r i n e Complex t o t h e e v o l u t i o n o f t h i s p a r t o f the! B r i t i s h Columbia c o r d i l l e r a i s p o o r l y known, and i t s r e l a t i o n to p l a t e t e c t o n i c s even more o b s c u r e ; a r e g i o n a l s y n t h e s i s to p r o v i d e a u s e f u l r e f e r e n c e pertinent  t o these problems.  i s presented  frame i n which t o view the accumulated d a t a  3  STRATIGR APHIC  ROCKS  QUATERNARY I^V]  Drift  0 » « AlloriMt  MID-LATE TERTIARY "'•'titO-MocOr-O'  [»3  XUll  Oteooeooo-Miooooo' noMly k e i o t l  EOCENE | ; ; | O g t n Loko Volcomct'  LATE [  tfacito,  rhyoiito  CRETACEOUS-EOCENE  : | Soohrl-SiHeo Awo*b>oeO' conflorooroto, SQotfotOAO  LATE  JURASSIC-EARLY  | ' ' | BoMOr AtMffiblogO  EARLY  CRETACEOUS  ClCSbC l t d i A * l l l  1  JURASSIC  || | | H O » l t M Group' bOMrr, OfttfoUtO, >«4tRHHlT*  LATE |  TRIASSIC | Toklo Groap' botolt, broccio, s o d M n o n t f  PENNSYLVANIAN AND PERMIAN A i i t k o Group |Pe>—M  b o w l t , cbort.  Cocli* Crook Grout  >  Lo> R a n g o - N i M Crook * » * - y  SILURIAN  linootooo, orgiaito  AND DEVONIAN do*om*»», quortzito, obolo  |»-Dw| Umostono,  LATEST  PRECAMBRIAN  | pC | Ptlyllito, limefttono, quortzito, ocMst, g o o i » »  INTRUSIVE  ROCKS  GRANITIC ROCKS [N/ —[ Jurostic -  and Crotacoooo (I,K)=  oorly (o), n a o l o ( » > } . l o t . (I)  GABBROIC  IIHlJ [igg  AND ULTRAMAFIC  Zoned U l t r a n v r i c Alpioo-typo  CONTACT \  \ FAULT  Caoplox  UltroMfic  THRUST  INFERRED  \  ROCKS  Crotocoou* Axriooid Goborotc Complox  \  Rocks  FAULT  ANT1F0RMAL T R A C E SYNFORMAL T R A C E ,  GARNET  ISOGRAD  t i c k ! on kigk graoo * *  S0_ kilometers  F i g u r e 1. G e o l o g i c map of W o l v e r i n e Complex and a d j a c e n t areas of n o r t h c e n t r a l B r i t i s h Columbia.  too  4 PREVIOUS WORK  Armstrong (1949) d e f i n e d the Wolverine Complex as the metamorphic and igneous r o c k s c o n s t i t u t i n g the Wolverine Range o f the F o r t S t . James area.  map-  He a l s o mapped p o r t i o n s of the A i k e n Lake map-area w i t h Roots (Arm-  s t r o n g and Roots, 1948) e x t e n d i n g t h e ' n o r t h w e s t e r n end of the Complex. Roots (1954) d e f i n e d and examined the uppermost P r o t e r o z o i c and lowest Camb r i a n T e n a k i h i and Ingenika groups i n the n o r t h e a s t e r n h a l f of the A i k e n Lake map-area i n g r e a t e r d e t a i l , b r i e f l y  s u b d i v i d i n g the s t r a t i g r a p h y and  c r u d e l y documenting metamorphic z o n a t i o n s and major s t r u c t u r e s .  Roots a l s o  mapped the remainder o f the A i k e n Lake sheet on a s c a l e o f 1" = 4 m i l e s , i n which mainly P a l e o z o i c and Mesozoic r o c k s are found. More r e c e n t work i n the A i k e n Lake map-area has been done by the Geol o g i c a l Survey of Canada.  Mansy (1971, 1972, 1974, 1976) has mapped the  n o r t h e r n h a l f i n g r e a t e r detail,-, and has d e l i n e a t e d d e t a i l e d and  structure.  the  west have been r e c e n t l y s t u d i e d by I r v i n e  P a l e o z o i c and Mesozoic sedimentary and igneous r o c k s t o  1976), Woodsworth Lord  (1948).  stratigraphy  (1976), G a r n e t t  (1975, 1976), Monger (1974,  (1974), R i c h a r d s  (1976), and e a r l i e r by  Wanless e t a l (1967, 1971, 1973, 1974) i n a s s o c i a t i o n w i t h  workers from the G e o l o g i c a l Survey of Canada have been the p r i n c i p l e of K-Ar  creators  and W o l v e r i n e Metamorphic Complex d a t a on p l u t o n i c r o c k s o f the Hogem composite b a t h o l i t h . E i s v  bacher (1974a) has s t u d i e d the Sustut and S i f t o n B a s i n s , o u t l i e r s of which occur i n the A i k e n Lake map-area. prepared by G a b r i e l s e  A r e g i o n a l t e c t o n i c s y n t h e s i s has been  (1967) f o r the n o r t h e r n Canadian C o r d i l l e r a .  GEOLOGIC SETTING  The a r e a s t u d i e d  (figure  5  1) l i e s w i t h i n t h e e x t e n s i v e uppermost P r e -  cambrian metamorphosed c l a s t i c sequence b r o a d l y c o r r e l a t i v e w i t h the KazaMiette  (Winderemere)  assemblage o f r o c k s f a r t h e r south i n the McBride map-  area (Campbell e t a l , 1973; G a b r i e l s e ,  1972) and w i t h the M i s s i n c h i n k a  Group t o the n o r t h e a s t a c r o s s t h e Rocky Mountain Trench ( I r i s h , T h i s group  1970) .  of rocks forms t h e backbone of the Omineca C r y s t a l l i n e  Belt  and comprises a deformed, metamorphosed, u p l i f t e d b l o c k n e a r l y 60 km. wide t h a t i s fault-bounded on the e a s t a d j a c e n t t o the Rocky Mountain Trench and Rocky Mountains and  on  the west a g a i n s t t h e n o r t h e r n e x t e n s i o n  of the Quesnel Trough. The Quesnel Trough can be d i v i d e d continuous M i s s i s s i p p i a n - Permian  i n t o an e a s t e r n  (±Upper T r i a s s i c  group of f a i r l y  ?) c l a s t i c sediments rocks  w i t h conglomerate and a western group o f Upper T r i a s s i c volcanicY, the T a k l a Group. sills  The e a s t e r n upper P a l e o z o i c rocks a r e i n t r u d e d by gabbro  and a l p i n e and zoned u l t r a m a f i c r o c k s , and a r e a s s o c i a t e d w i t h  dant b a s a l t s .  abun-  The western T a k l a rocks a r e i n t r u d e d by v a r i o u s phases o f  the Hogem composite b a t h o l i t h o f E a r l y Jurassic  (175 my.) and E a r l y C r e -  taceous (120 my.) ages ( E a d i e , 1976; G a r n e t t , 1974; Woodsworth, 1976). The c o n t a c t between  these two t e r r a n e s i s g e n e r a l l y f a u l t e d , a l t h o u g h  d e p o s i t i o n a l c o n t a c t s have been shown i n some p l a c e s . The Hogem b a t h o l i t h i s composite and c o n s i s t s of e a r l y m a f i c phases f o l l o w e d by more c a l c - a l k a l i n e and s y e n i t i c p l u t o n i c r o c k s .  Much o f the  o l d e r Hogem t e r r a n e i s deformed, e s p e c i a l l y near i t s western margin w i t h the P i n c h i f a u l t  system, which s e p a r a t e s i t from an assemblage of upper  P a l e o z o i c and Upper T r i a s s i c e u g e o c l i n a l sedimentary, m a f i c and u l t r a m a f i c p l u t o n i c , and m a f i c v o l c a n i c rocks f a r t h e r west i n c l u d i n g both the S t u a r t Lake b e l t of Monger and P a t t e r s o n Lord  (1948) and R i c h a r d s  (1976).  (1974) and the A s i t k a Group of  The H a z l e t o n Group, c o n s i s t i n g of v o l -  6 c a n i c s and  sediments of E a r l y J u r a s s i c age,  o z o i c and Upper T r i a s s i c r o c k s , and d u r i n g l a t e r Mesozoic and Cenozoic  r e s t s upon these upper P a l e -  they i n t u r n are f a u l t e d and f o l d e d deformation  ( R i c h a r d s , 1976).  The boundary between the Precambrian rocks and rocks to the west i s a f a u l t .  the upper P a l e o z o i c  Roots (1954) concluded  t h a t i t was  a steep  normal f a u l t , whereas Mansy (1974) and G a b r i e l s e e t a l (1976) p r o v i d e evidence fault.  t h a t the c o n t a c t i s i n p l a c e s e i t h e r a steep t h r u s t o r a r e v e r s e S e v e r a l p e r i o d s of movement are  probable.  To the e a s t , normal f a u l t s s e p a r a t e the Rocky Mountain Trench from the h i g h l a n d s on e i t h e r s i d e .  A c r o s s the Trench  floor  t o the e a s t , e a s t -  v e r g i n g f o r e l a n d t h r u s t - f o l d b e l t geometry i n g e n e r a l p r e v a i l s i n l a t e Precambrian - Mesozoic  m i o g e o c l i n a l rocks  the north,, the s t y l e of f o l d i n g  becomes  (Irish,  1970), a l t h o u g h  . more r e m i n i s c e n t of the Mac-  k e n z i e Mountains where o l d e r P r o t e r o z o i c s t r a t a are p r e s e n t . P r o t e r o z o i c rocks neath  These o l d e r  ( P u r c e l l - B e l t e q u i v a l e n t s t r a t a ) are not exposed  be-  the Ingenika - T e n a k i h i Group rocks i n the A i k e n Lake map-area, and  they may  be absent  altogether.  W i t h i n the Rocky Mountain Trench sediments of Upper Cretaceous relief K-Ar  to  sedimentary  region (Sifton Basin), d e t r i t a l  to Eocene age  and metamorphic source  dates from d e t r i t a l mica and  are p r e s e n t and r e c o r d h i g h -  t e r r a n e ( E i s b a c h e r , 1974a).  g r a n i t i c boulders indicate u p l i f t  c o o l i n g of metamorphic core zone r o c k s by mid-Cretaceous time,  and  although  the e r o s i o n a l h i s t o r y i s no doubt more complex. The  geology  Mesozoic and  of t h i s g e n e r a l area i s dominated by  Cenozoic  p l u t o n i c and  p o s s i b l e P a l e o z o i c a c t i v i t y , and  the e f f e c t s of  deformational events,  thereby  obscuring  the g e o l o g i c a l e v o l u t i o n i s i n many ways  analogous to t h a t of the Shuswap complex of southern B r i t i s h where T r i a s s i c and P a l e o z o i c r o c k s are j u x t a p o s e d metamorphic rocks of complex h i s t o r y .  Columbia  a g a i n s t h i g h e r grade  7 STRATIGRAPHY S t r a t i g r a p h i c r e l a t i o n s w i t h i n the study a r e a a r e c o n s i d e r a b l y d i s r u p t e d because of obvious  l o c a l r e p e t i t i o n and  structural  complexity.  Rock types t h a t are most abundant c o n s i s t of t h i n - l a y e r e d c o a r s e q u a r t z mica s c h i s t s and micaceous, f e l d s p a t h i c , and s c h i s t o s e q u a r t z i t e s w i t h comp l e t e g r a d a t i o n between these l i t h o l o g i e s .  Many rocks show p o r p h y r o b l a s -  t i c garnet and p l a g i o c l a s e , and m i n e r a l s e g r e g a t i o n s are w e l l developed places.  Q u a r t z o - f e l d s p a t h i c mica g n e i s s e s which appear to be  e q u i v a l e n t s of the s c h i s t s and q u a r t z i t e s are a l s o abundant. marbles,  a m p h i b o l i t e s , t o u r m a l i n e s c h i s t s , and q u a r t z  are a l s o p r e s e n t but are q u i t e r a r e and f i c u l t to map were found meters.  f o r any  great d i s t a n c e .  in  feldspar-rich Calc-silicate  pebble-conglomerates  t h i n ; consequently,  they were d i f -  N e a r l y a l l conspicuous marker l a y e r s  to p i n c h out i n t o the s u r r o u n d i n g s c h i s t s w i t h i n s e v e r a l hundred  With the e x c e p t i o n of a few t h i c k q u a r t z i t e s , the abundant s c h i s t o s e  l i t h o l o g y proved  to be d i s c o u r a g i n g d u r i n g mapping because of i t s d i s c o n t i n u -  ous and g r a d a t i o n a l n a t u r e caused by boudinage, r e p e a t e d f o l d i n g , and discontinuous inherited depositional  possibly  characteristics.  Because of these s t r a t i g r a p h i c c o m p l e x i t i e s , i n t e r p r e t a t i o n of the s t r u c t u r a l e v o l u t i o n r e l i e s upon minor s t r u c t u r e s ; the l a r g e s c a l e of e a r l y syn-metamorphic d e f o r m a t i o n  i s l a r g e l y unknown.  The monotonous n a t u r e of the l i t h o l o g y was pegmatite  sills  and b o d i e s , b o t h concordant  and  o c c a s i o n a l l y i n t e r r u p t e d by discordant.  These  rocks are minor c o n s t i t u e n t s i n the a r e a near Chase Mountain and Ravenal  igneous  south o f  Creek ( f i g u r e 2 a ) , but become v e r y numerous i n the h i g h grade r o c k s  near B l a c k p i n e Lake ( f i g u r e 2b). section.  effect  These r o c k s w i l l be d e a l t w i t h i n a l a t e r  R e c r y s t a l l i z e d m y l o n i t i c r o c k s are p r e s e n t south and  e a s t of  Ravenal Creek; they o c c u r i n a s m a l l a r e a as a 10 meter t h i c k l a y e r , d i p p i n g 20°-30° to the southwest.  T h i s m y l o n i t i c zone s e p e r a t e s r o c k s of s i m i l a r  8  F i g u r e 2a. S t r u c t u r a l and g e o l o g i c map of t h e s i s a r e a showing a t t i t u d e o f c o m p o s i t i o n a l l a y e r i n g .  near Chase Mountain  kilometers  F o l d a x i s or l i n e a t i o n A t t i t u d e of layering  compositional  F l a x i a l plane  attitude  F2 a x i a l p l a n e  attitude  F l ( ? ) o r F2(?) a x i a l plane a t t i t u d e Trend of c o m p o s i t i o n a l layering  F i g u r e 2b.  G e o l o g i c and s t r u c t u r a l map  of t h e s i s area near B l a c k p i n e  Lake.  10 s c h i s t o s e l i t h o l o g y and i t s r e l a t i o n to t h e s t r u c t u r a l sequence i s u n c l e a r . The  g r a i n s i z e o f the mica s c h i s t s i n c r e a s e s i n a v e r y g e n e r a l way t o  the southeast and c o r r e l a t e s w i t h an i n c r e a s e i n q u a n t i t y o f pegmatites. There i s p r o b a b l y a c o r r e s p o n d i n g i n c r e a s e i n t h e metamorphic grade a l t h o u g h this i s d i f f i c u l t  to prove due t o s c a r c i t y o f aluminous s c h i s t s o r o t h e r  grade i n d i c a t o r s . O r i g i n a l bedding of t h e e a r l i e s t and  i n most cases has been t r a n s p o s e d i n t o the a x i a l  f o l d s ; however, r e c o g n i z a b l e l o a d s t r u c t u r e s , graded  s l i g h t l y deformed c r o s s - b e d d i n g were observed  i n a few p l a c e s .  i n a l sediments may have been d i s t a l p a r t s of t u r b i d i t e sequences. c r e a s i n g d e f o r m a t i o n and f l a t t e n i n g ,  plane  bedding, The o r i g -  With i n -  these s t r u c t u r e s become u n r e c o g n i z a b l e .  D e s p i t e the r a r e d e v i a t i o n s from the dominant l i t h o l o g y , the l a s t i n g  impres-  s i o n o f these rocks i s one o f a u n i f o r m , monotonous sequence o f metamorphosed d i r t y sandstones,  s i l t s t o n e s , and q u a r t z - r i c h s e m i - p e l i t i c sediments.  No  e s t i m a t e ' o f s t r a t i g r a p h i c t h i c k n e s s can be made because o f s t r u c t u r a l c a t i o n s t h a t r e n d e r t h e s t r a t i g r a p h i c s e c t i o n s o f Roots Group r o c k s o f dubious The resembles  compli-  (1954) f o r T e n a k i h i  value.  l i t h o l o g y o f the T e n a k i h i Group mapped i n t h i s study i n many ways a more h i g h l y metamorphosed s t r a t i g r a p h i c c o r r e l a t i v e o f the  M i d d l e M i e t t e and Kaza Groups as d e s c r i b e d i n the McBride map-area by Campbell and o t h e r s (1973) and S u t h e r l a n d Brown (1963). M i e t t e c o n s i s t s o f c o a r s e sandstone, stone and a r g i l l i t e , and  pebbly sandstone  There,  the Middle  ' g r i t ' , quartz  the c o a r s e r u n i t s b e i n g v e r y immature b o t h  c h e m i c a l l y , i n p l a c e s c o n t a i n i n g up t o 25% f e l d s p a r g r a i n s .  silt-  texturally Overlying the  M i d d l e M i e t t e , the Upper M i e t t e group c o n s i s t s of mudstones, s i l t y  argillites,  a zone o f c o a r s e c l a s t i c r o c k s , and a t h i c k l i m e s t o n e c o r r e l a t i v e w i t h the Cunningham Formation which r e s t s on t h e Kaza Group west o f t h e Rocky Mountain Trench.  The M i d d l e M i e t t e i s c o r r e l a t i v e w i t h the Kaza Group west o f the  Trench w h i c h ; l i e s below a t h i c k , r e c e s s i v e a r g i l l a c e o u s u n i t known as the Isaac Formation, which i n t u r n forms the base of the Cariboo Group. These same r o c k s ( T e n a k i h i - K a z a - M i d d l e M i e t t e ) are p r o b a b l y a l s o b r o a d l y c o r r e l a t i v e w i t h the lower p a r t of the M i s s i n c h i n k a Group desc r i b e d by I r i s h (1970) i n Halfway  R i v e r map-area, and correspond i n g e n e r a l  to the lower p o r t i o n o f the Windermere S e r i e s exposed  through  the e n t i r e  l e n g t h of the B r i t i s h Columbia  1972).  Figure 3  Cordillera  shows the r e l a t i o n s h i p s between these rock  (Gabrielse, groups.  S i m i l a r l i t h o l o g i c c o r r e l a t i v e s to the Upper M i e t t e group  are p r e s e n t  i n the A i k e n Lake a r e a ; these r o c k s have been r e c e n t l y d e s c r i b e d and c o r r e l a t e d by Mansy (1972).'  B r i e f l y , from o l d e s t to youngest,  they are as  follows: 1) g r i t t y c l a s t i c u n i t : s h a l e , s i l t s t o n e , q u a r t z o - f e l d s p a t h i c sandstone and conglomerate ( T e n a k i h i and lower I n g e n i k a g r o u p s ) . 2) thin-bedded c a l c a r e o u s p h y l l i t e , e q u i v a l e n t t o the Isaac Formation. 3) r e s i s t a n t , well-bedded mation.  l i m e s t o n e , e q u i v a l e n t t o Cunningham F o r -  4)' d i v e r s e u n i t of l i m e s t o n e , p h y l l i t e , impure q u a r t z i t e , sandy l i m e s t o n e , dark green s h a l e s , and impure sandstone, e q u i v a l e n t to the Yankee B e l l e Formation. 5) pure white q u a r t z i t e , e q u i v a l e n t to the Yanks Peak Formation. 6) impure q u a r t z i t e i n t e r b e d d e d w i t h s h a l e , e q u i v a l e n t to the Midas Formation. 7) b l u e - g r a y l i m e s t o n e w i t h s i l t s t o n e i n i t s middle p a r t , e q u i v a l e n t to the M u r a l F o r m a t i o n o f lowest Cambrian age. The above u n i t s 3 and 4 c o r r e l a t e w i t h the Good Hope Group and u n i t s 5 to 7 are e q u i v a l e n t to the Atan Group i n the C a s s i a r Mountains  (Mansy,  1972) . In g e n e r a l , the d i s t i n c t i o n made by Roots  (1954) between the T e n a k i h i  Group and the lower Ingenika Group has been found d i f f i c u l t  to apply, both  i n the study a r e a where the s t r a t a at B l a c k p i n e Lake and near Chase Mount a i n are i d e n t i c a l  (but b e l o n g to Ingenika and T e n a k i h i Groups, r e s p e c -  12  age  Cassiar  Omineca  Cariboo  Mountains  Mountains  Mountains  Gabrielse,  1963  Mansy,  i.e Atari  Group  a. 3 O  Group base  not exposed  Mural  Fm.  6  Midas  Fm.  Y a n k s Peak Fm.  O  4  Yankee Belle F m .  eni  Hope  7  1973'.  5  Ihg  Good  Campbelletal,  w  CD  pe  1972  Rocky McBride Mural  Cunningham  2  bas e  (Gog  Fm.  Group) Misinchinka Miette  Fm.  Group  Isaac  Fm.  Kaza  Fm.  b a s e not exposed  not  exposed  Middle Miette F m . Lower Miette base  not  Fm.  exposed  C o r r e l a t i o n c h a r t of uppermost Precambrian and lowermost Cambrian r o c k s i n n o r t h and e a s t - c e n t r a l B r i t i s h Columbia.  t i v e l y ) and elsewhere as noted by Mansy (1976). lithologic  1970  Fm.  1  F i g u r e 3.  Irish,  McNaughton Fm.  Upper  3  Mountains  I n many p l a c e s ,  the apparent  c o n t r a s t may be a f u n c t i o n o f metamorphic grade and s t r u c t u r a l  s t y l e rather  than r o c k type.  The r o c k s i n the study a r e a near Chase Moun-  t a i n a r e l o c a t e d near the 'apparent' base of the exposed s e c t i o n , and they lie  s e v e r a l thousands o f f e e t s t r u c t u r a l l y below the t h i c k e r q u a r t z i t e s and  l i m e s t o n e s i n the F i n l a y and Swannell Ranges near P e l l y Lake where the s t r u c t u r a l h i s t o r y appears much s i m p l e r  (Mansey, 1972, 1974).  14  F i g u r e 4.  S t r u c t u r a l map  of t h e s i s a r e a showing phase 1 data.  STRUCTURAL GEOLOGY  There a r e a t l e a s t f o u r phases of d e f o r m a t i o n r e c o g n i z e d w i t h i n the Chase Mountain a r e a ( P a r r i s h , related  1976).  Phases 1 and 2 ( F l , F2) appear t o be  t o d u c t i l e rock c o n d i t i o n s a s s o c i a t e d  characterized  w i t h metamorphism; they a r e  by N to NW-trending, t i g h t to i s o c l i n a l ,  gently i n c l i n e d to  recumbent f o l d s w i t h abundant m i n e r a l r e c r y s t a l l i z a t i o n and development o f a x i a l plane f o l i a t i o n . are  L a t e r phases 3a and 3b t r e n d NW and N  open u p r i g h t f o l d s , and appear t o be post-metamorphic.  respectively,  These l a t e r  phases have produced an e l o n g a t e a n t i f o r m a l  dome or c u l m i n a t i o n i n the  e a r l i e r f o l i a t i o n s and a r e p r o b a b l y r e l a t e d  t o the l a r g e  scale  structures  i n the Ingenika Group r o c k s t o the n o r t h i n Wrede Range and near P e l l y Lake i n the R u s s e l l The  Range.  study area has been d i v i d e d  into  six  domains p o s s e s s i n g moderately  homogeneous geometry f o r s t e r e o g r a p h i c s t r u c t u r a l  Phase 1 ( F i g u r e Fl  analysis.  4)  f o l d s a r e a p p r o x i m a t e l y s i m i l a r i s o c l i n a l f o l d s t r e n d i n g from N-S  to NW-SE, and a r e c h a r a c t e r i z e d  by a g e n t l y d i p p i n g a x i a l p l a n e s c h i s t o s i t y .  Amplitudes v a r y from a meter o r so t o s e v e r a l are most commonly r o o t l e s s has  resulted  the  two a r e s u b p a r a l l e l .  been r e f o l d e d  tens of meters, and t h e f o l d s  and extremely f l a t t e n e d  i n transposition  (figure 5).  of the bedding i n t o the a x i a l p l a n e , so that  The p l a n a r and l i n e a r elements o f t h i s event have  both by F2 and F3 f o l d s ; F l o r i e n t a t i o n s  the major a n t i f o r m i n a s y s t e m a t i c way ( f i g u r e 4 ) . of F l h i n g e s i s no doubt due t o renewed c l o s u r e  d u r i n g F2 f o l d i n g so t h a t  o r i g i n a l form o f F l f o l d s p r i o r t o F2 i s n o t known.  the  field  t a c u l a r boudins  F e a t u r e s seen i n  w i t h F l a r e i s o l a t e d f o l d h i n g e s ( f i g u r e 5a),  ( f i g u r e 5b),  extremely f l a t t e n e d ,  therefore vary across  The extreme f l a t t e n i n g  the  associated  F l folding  flaggy  d i s c o n t i n u o u s and t r a n s p o s e d l a y e r i n g , appearance o f c o m p o s i t i o n a l l a y e r i n g .  specand an When  15  F i g u r e 5a. F.. f o l d hinges w i t h i n a quartzo-feldspathic layer, l o o k i n g northwest.  F i g u r e 5c. Photograph of hinge of F^ f o l d , l o o k i n g NW, showing the development of a x i a l p l a n e s c h i s t sity.  F i g u r e 5b. I s o c l i n a l F^fold with a x i a l plane s c h i s t o s i t y i n q u a r t z - m i c a s c h i s t , l o o k i n g NW.  F i g u r e 5d. Photograph of l a r g e boudin of q u a r t z i t e i n f l a g g y s c h i s t , l o o k i n g NW.  q u a r t z pebble  conglomerate i s seen,  a marked f l a t t e n i n g and an  '  e l o n g a t i o n p a r a l l e l to f o l d axes i s p a r t i c u l a r l y e v i d e n t w i t h aspect of the pebbles t y p i c a l l y  1:4:15.  ratios  I t i s not known whether t h i s s t r a i n i s  r e g i o n a l l y r e p r e s e n t a t i v e or not.  Phase 2 ( F i g u r e 6) F2 f o l d s are d i s t i n g u i s h e d from F l f o l d s by the presence and  c r e n u l a t e d s c h i s t o s i t y i n the cores of F2 f o l d s  of F l h i n g e s  ( f i g u r e 8), l o c a l d i v e r g e n c e  gure 8), and by t h e i r t i g h t hinges  (figure 9).  (fi-  (as opposed to s u b - i s o c l i n a l ) f o r m w i t h rounded  A near h o r i z o n t a l to moderately  as p e n e t r a t i v e l y as F l s c h i s t o s i t y , and  e a r l i e r f a b r i c are g e n e r a l l y p r e s e n t . rish,  ( f i g u r e 7), r e f o l d i n g  of a x i a l plane o r i e n t a t i o n  dipping axial  f o l i a t i o n i s o f t e n a s s o c i a t e d w i t h these f o l d s , but developed  of a f o l d e d  1976") i l l u s t r a t e these f o l d s  i t i s only  plane  rarely  r e l i c t s of a f o l d e d  Many exposures ( f i g u r e  10 and  Par-  ' c a s c a d i n g ' or v e r g i n g to the e a s t -  n o r t h e a s t , and these vergences have been shown i n the s t e r e o g r a p h i c diagrams. No  s i g n i f i c a n t r e v e r s a l of vergence was  it  i s not known whether t h e r e i s a c o r r e s p o n d i n g  s t r u c t u r e i n which vergences would be  r e c o g n i z e d throughout lower  the a r e a ,  and  limb of a v e r y l a r g e  reversed.  S e v e r a l l a r g e exposures were observed  where t h e r e i s a p r o g r e s s i v e  t r a n s p o s i t i o n of the c o m p o s i t i o n a l l a y e r i n g i n t o the F2 a x i a l plane ( f i gure 11a).  T h i s t r a n s p o s i t i o n i s accomplished  by  increased f l a t t e n i n g  t i g h t e n i n g of h i n g e s , accompanied by h i g h s t r a i n and/or s l i p along zones of s t r u c t u r a l d i s l o c a t i o n r e s u l t i n g i n the s h e a r i n g o f f and one  limb of a f o l d .  tural style  (figure  M y l o n i t i c r o c k s are sometimes a s s o c i a t e d . 11a)  i s r e c o g n i z a b l e on both  s m a l l and  and  discreet l o s s of  This  struc-  l a r g e (over  100  meters) s c a l e s . Many d i s l o c a t i o n or f a u l t (figure  l i b ) , and  zones are p r e s e n t throughout  the study  these are l i k e l y F2 s t r u c t u r e s ; t h e i r displacements  area are  18  F i g u r e 7. Photograph of f o l d e d s c h i s t o s i t y f o l d , l o o k i n g S.  i n h i n g e r e g i o n of F  F i g u r e 8. Photograph of r e f o l d e d F^ hinge on the limb of l a t e r F^ f o l d , l o o k i n g S. The F r i n g e was t i g h t e n e d d u r i n g F_ d e f o r m a t i o n .  17  N  1 56°35' Chase \5£  Mountain  125°10*  Quartzite Flattened  conglomerate  Recrystalized Dislocation  mylonite  zone  2r  -M w  ••'  ; i-B..^! Geologic contact A n t i f o r m a l t r a c e & plunge  10  A x i a l p l a n e , a x i s o f F2 Limit  of outcrop  fold  8(Jf*^  F i g u r e 6. S t r u c t u r a l map o f Chase Mountain a r e a phase 2 f o l d o r i e n t a t i o n .  showing  •  19  F i g u r e 10. Sketches of e a s t - v e r g i n g phase 2 f o l d s . A l l of the l o c a t i o n s e x h i b i t v e r y s t r o n g development of r o d d i n g or l i n e a t i o n p a r a l l e l to the f o l d axes.  21  F i g u r e l i b . Photograph of d i s l o c a t i o n  zone i n mica s c h i s t s , l o o k i n g  W.  22  Ch-«e  Kr\. Q0fl«TZlT6 ^fif  Figure  0  J  Z  I  I  I  COI^OlLOMERATE  12.  Schematic tectonic p r o f i l e near Chase Mountain.  not known but are not thought to be great as no exotic rocks were found. In spite of the lack of mappable stratigraphic u n i t s , an attempt  was  made to construct a tectonic p r o f i l e across the area showing gross geometry (figure 12).  The section indicates that e x i s t i n g data are consistent with  eastward transport of rocks i n nappe-like fashion where the lower limbs of large recumbent folds are either sheared o f f or not exposed.  Lack of  stratigraphic control renders the section somewhat conjectural.  Phase 3 Two  additional d i s t i n c t sets of folds are present within the area,  but their r e l a t i v e ages are indeterminate.  Phase 3a i s the major northwest  trending antiformal f o l d which culminates i n the thesis area and deforms e a r l i e r F l and F2 f a b r i c s (figures 4, 6). an antiform at least 15 km. dips being 30°-40°, and  i n width.  This i s a very large feature, being  It i s an open upright f o l d , the limb  i t does not appear to be associated with minor  structures which r e f l e c t i t s geometry and orientation.  This  structure  causes the variable orientation of F l and F2 planar and l i n e a r structures as well as the regional changes i n attitude of the compositional layering. The antiform plunges both NW  and SE away from the Chase Mountain area, and  the a x i a l t r a c e i s not o f f s e t by l a t e r f a u l t i n g or f o l d i n g w i t h i n the study area.  In a d d i t i o n , a minor c u l m i n a t i o n - d e p r e s s i o n p a i r i s p r e s e n t 3  km.  southeast of the Summit of Chase Mountain and near Ravenal Creek, r e s p e c tive tively  (figure 2).  Metamorphism does not appear t o a c c o m p a n i e d  this  v  folding.  Phase 3b i s an a r e a l l y r e s t r i c t e d s e t of f o l d s of v a r i a b l e but cons i d e r a b l e s i z e and wavelength t h a t i s p r e s e n t i n a northwest t r e n d i n g near the c r e s t of the F3a a n t i f o r m s o u t h e a s t of Ravenal Creek. themselves a r e n o r t h - t r e n d i n g , u p r i g h t to s t e e p l y i n c l i n e d and have v a r i a b l e form.  They possess f l e x u r a l s l i p  The  zone-  folds  t o the e a s t ,  t o f l e x u r a l f l o w geo-  metry, and t h e i r form v a r i e s from open at h i g h e r s t r u c t u r a l l e v e l s t o t i g h t at depth  (figure  13).  These s t r u c t u r e s deform b o t h F l and F2 f o l d s and are  en e c h e l o n near the F3a a n t i f o r m a l c r e s t . (but not c o p l a n a r )  These f o l d s  are.:colinear  w i t h F l and F2 f o l d s found i n the immediate  and i t appears lifcely t h a t the o l d e r s t r u c t u r a l f a b r i c has been upon compression i n the c o r e of the F3a a n t i f o r m .  vicinity,  reactivated  This explanation  t h a t they r e s u l t from a 'room' problem i n the c o r e of the l a r g e r  implies  structure.  T h i s i n t e r p r e t a t i o n i s supported by the i n c r e a s i n g c l o s u r e of the f o l d limbs at depth as w e l l as t h e i r en e c h e l o n and s p a t i a l l y r e s t r i c t e d n a t u r e . The l a r g e a n t i f o r m i s most p r o b a b l y r e l a t e d to the l a r g e f o l d s and a s s o c i a t e d t h r u s t s mapped by Roots  (1954) and Mansy (1972,  19 74) i n the  c e n t r a l Swannell Ranges u n d e r l a i n by the I n g e n i k a Group r o c k s ,  especially  near the Wrede Range, the major s t r u c t u r e of which i s shown i n f i g u r e The geometry  14.  of the l a r g e a n t i f o r m s a r e r e a s o n a b l y c o m p a t i b l e , a l t h o u g h  i n the ranges t h a t are at l o w metamorphic  grade  ( c h l o r i t e ) , t h e r e appears  to be a l a c k of the e a r l i e r d e f o r m a t i o n s p r e s e n t near Chase More work i s o b v i o u s l y needed  to s u b s t a n t i a t e or r e j e c t  Mountain.  t h i s view.  Recent  work by Mansy (1976) i n g r e e n s c h i s t and lower a m p h i b o l i t e f a c i e s r o c k s i n c e n t r a l Swannell Ranges i n d i c a t e the presence of e a r l i e r i s o c l i n a l  folds  and a more complex h i s t o r y than p r e v i o u s l y r e c o g n i z e d , i n accord w i t h the  24  10 nn.  5  m. c)  F i g u r e 13. Sketches o f F „ f o l d s , l o o k i n g S. These f o l d s deform F^ f o l d s , as shown i n c ) , as w e l l as structures.  F i g u r e 14. Mansy  Structure  s e c t i o n s a c r o s s Wrede and R u s s e l l Ranges from J . L.  B  WR60£WW**  GARNET  BI0TIT6  INGENIKA Riven  B R.M.TRJWCH  RAKS NUUWTOW . RAVENAL PEAK POLY CREEK \ \ * L  SIUTY <AA&lUACeooS Mtt«TOI\lE, CALCAREOUS SHAU: ^  MTNS.  sr.  fc V i ' j q DARK WEATHEAlNS SHALE, QOARTnTE LOWER CAMBRIAN Q0AATHT6 , SHALE  157'  SHAte, QUAATZITE, UMe»ToN6 LIMESTONE, D0L0ST0NE ( F0W£5  CALCAREOUS PHfLUTK  MTN.  126°  9O O /Z5°  GiKIT, SILTST01M6, SHALE ( t o t e not e«f»«d)  25 data presented Ingenika 1972,  i n t h i s paper.  However, the s t r u c t u r e i n the v e r y low  Group i n R u s s e l l Range near P e l l y Lake i s f a i r l y  1974); an e a r l i e r ,  i s o c l i n a l f o l d i n g i s missing  that d i f f e r e n c e s i n pressure  and  rocks behave under s t r e s s , and  grade.  the n o r t h  and  the way  In-  and  (1970) i n the Cariboo  at  different  Mountains.  s t r u c t u r e s i n the study a r e a and'those c o r r e l a t i v e s t r u c t u r e s to occurred during i n the Wrede Range  author  V  b e l i e v e s t h a t these  e i t h e r non-  or o n l y low-grade metamorphism, and  s t r u c t u r e s f o l d metamorphic i s o g r a d s . f o l d i n g near Chase Mountain  d u r i n g analagous f o l d i n g i n Wrede Range were p r o b a b l y d i f f e r e n t , and Other Minor  not  the s t r u c t u r a l c o r r e l a t i o n i s r e a s o n a b l y  If and  significantly  justified.  Structures  L a t e r f o l d s of more b r i t t l e d e f o r m a t i o n a l throughout the a r e a .  s t y l e are l o c a l l y  These i n c l u d e s m a l l k i n k and  present  crenulation structures  a s s o c i a t e d l i n e a t i o n s , f l e x u r a l s l i p f o l d s of s m a l l amplitude  15a),  that  temperature c o n d i t i o n s  that a r e ' s t r u c t u r a l l y higher  so, the metamorphic c o n d i t i o n s d u r i n g F3a  and  It i s clear  d i f f e r e n t metamorphic grade.  T h i s has been shown by Campbell  F3a  the  i n rocks  (Mansy,  c a u t i o n must be used when c o r r e l a t i n g s t r u c -  deed, s t r u c t u r e s developed at h i g h e r p r e s s u r e not be p r e s e n t  there.  temperature c o n d i t i o n s a f f e c t  t u r e s i n rocks of v a r i a b l e l i t h o l o g y and  may  simple  grade  f a u l t s , and  found i n these  joints.  No  (figure  c o n v i n c i n g l y c o n s i s t e n t o r i e n t a t i o n s were  late structures, (figure  15b)  and  t h e i r s i g n i f i c a n c e i s not  known.  Stereographic The  Analysis  o r i e n t a t i o n of F l , F2, F3a,  stereographic  and  f a s h i o n i n f i g u r e s 16 and  northwest p l u n g i n g mains 3, 4, and  r e g i o n of the F3a  F3b 17.  s t r u c t u r e s i s summarized i n Domains 1 and  2 define  the  a n t i f o r m near Chase mountain, and  5 d e f i n e the southeast  p l u n g i n g hinge southeast  do-  of Ravenal  26  (NW)  F i g u r e 15a. Sketches of l a t e s t r u c t u r e s , viewed towards d i r e c t i o n i n parentheses.  F i g u r e 15b. E q u a l - a r e a s t e r e o n e t p l o t of o r i e n t a t i o n s of l a t e s t r u c t u r e s ; s o l i d c i r c l e represents l i n e a t i o n or f o l d a x i s , open c i r c l e denotes a x i a l p l a n e or cleavage of l a t e s t r u c t u r e , t r i a n g l e denotes a t t i t u d e of d i k e .  0 _ | _ a x i a l p l a n e of  late  fold  4_,dike •  f o l d a x i s of  late  structure  28  Figure  16.  S t r u c t u r a l map  of Chase Mountain a r e a showing domain  boundaries.  Creek. metry  Domain 6 i s overwhelmed by F3b f o l d s and n e a t l y d e p i c t s F3b geo( f i g u r e 17b).  Domain 1, 2 ( f i g u r e  17a-l,2)  On a s t a t i s t i c a l b a s i s , F l and F2 f o l d axes ( L I , L2) near Chase Mountain a r e c o a x i a l , t r e n d i n g 3 2 4 - 1 0 ° and p l u n g i n g a x i a l planes  l e s s than 20°.  (SI) i n domain 1 c l u s t e r about 105°/24°NNE a t the h i n g e b u t  are v e r y s c a t t e r e d along a p a r t i a l great c i r c l e g i r d l e roughly c u l a r t o the c o n c e n t r a t i o n o f L I . poles to compositional Fl  Fl  perpendi-  The c o n c e n t r a t i o n o f SI c o i n c i d e s w i t h  l a y e r i n g , confirming  the n e a r - i s o c l i n a l n a t u r e o f  folds. When SI and t h e c o m p o s i t i o n a l  and  layering, S  q  a r e compared f o r domains 1  2, i t i s c l e a r t h a t SI forms a s c a t t e r e d a r r a y of p o i n t s t h a t l i e along  a p a r t i a l s m a l l c i r c l e g i r d l e approximately vertical  fold axis.  20 -30  about a n o n - c y l i n d r o i d a l  T h i s i n d i c a t e s the presence of a dome-shaped  a t i o n d e f i n e d by t h e p l a n a r elements So and S I . I n domain 2, f o l d F l and F2 v a r y plunging  from 145*/0  <>  p a r t of t h i s dome.  t o 1 8 2 / 3 5 ° , most p o i n t s b e i n g e  In g e n e r a l  SI and S  Q  culminaxes o f  from the southwardd i p g e n t l y t o the  south and southwest i n domain 2, and t o t h e n o r t h i n domain 1. Phase 2 s t r u c t u r e s a r e v e r y common i n domain 1, b u t l e s s so i n domain 2. Despite and  t h e f a c t t h a t g r e a t care was taken t o a p p r o p r i a t e l y i d e n t i f y F l  F2 f o l d s , i t i s p o s s i b l e t h a t some f o l d s were m i s t a k e n l y  the f i e l d teria.  due t o t h e i r s i m i l a r appearance and l a c k o f other d i a g n o s t i c  cri-  I n domain 1, f o l d axes L2 t r e n d from 291°/10° to 340°/10° w i t h most  data c l u s t e r i n g near 325°±10°/13°±11°; they  a r e c h a r a c t e r i z e d by a s t r o n g  sense o f assymetry or vergence toward t h e n o r t h e a s t 17a.  identified i n  as i n d i c a t e d i n f i g u r e  S2 data a r e s c a t t e r e d a l o n g a g r e a t c i r c l e g i r d l e w i t h  a calculated  f o l d a x i s o f 322°/19*, which d e f i n e s the F3a f o l d and v e r i f i e s t h a t F3a de-  30  F i g u r e 17a. E q u a l - a r e a s t e r e o n e t s of s t r u c t u r a l f e a t u r e s , domains 1-5. compositional  layering  °  F l a x i a l planes  •  F2  0  Fl fold  axis  9  F2  axis  A  unspecified f o l d axis lineation  (~*  axial  fold  planes  sense of vergence  or  F i g u r e 17b. E q u a l - a r e a s t e r e o n e t o f o r i e n t a t i o n s of s t r u c t u r e s i n domain 6 which i s dominated by phase 3b f o l d s .  • j. c o m p o s i t i o n a l •1F2  axial  planes  AJ. F3b a x i a l x mineral  layering  planes  lineation  © F2 f o l d axes F3b f o l d axes  32  forms and  i s a l s o i . c o l i n e a r w i t h F l and F2 on a s t a t i s t i c a l b a s i s .  t h a t S2 p l a n e s do not f a l l  on a s m a l l c i r c l e l o c u s i s due  d i s t r i b u t i o n of d a t a and o u t c r o p . form, i s a post-F2 In  event  F o l d F3a,  t h a t deforms e a r l i e r  domain 1 below an important  The  to non-random  the r e g i o n a l l a r g e s c a l e  anti-  structures.  zone of d i s l o c a t i o n o r f a u l t i n g ,  F2  s t r u c t u r a l d a t a are markedly d i s t i n c t from F2 o r i e n t a t i o n s above t h i s as shown i n f i g u r e southwest.  18.  The r o c k s below are c h a r a c t e r i z e d by extreme f l a t t e n i n g  t o be analogous  p r o b a b l y of l a t e F2  Domains 3,4,  fault,  Below the f a u l t , S2 s t r i k e s SSE and d i p s 20°-40°  s t r o n g t r a n s p o s i t i o n of f o l i a t i o n i n t o the F2 a x i a l p l a n e . thought  fact  o r continuous  and  This fault i s  t o t h a t shown i n figurer.,6 and i t i s  age.  and 5 ( f i g u r e 17a - 3,4,5)  Domains 3, 4, and 5 r e s p e c t i v e l y occupy the SE-plunging hinge r e g i o n and  a d j a c e n t limbs of the major F3a a n t i f o r m ( f i g u r e 16).  dominant f o l i a t i o n s t r i k e s northwest from  and  In domain 5,  the  the d i p s steepen n o r t h e a s t e r l y  18°, 500 meters east of the c r e s t , to about 50°, at a d i s t a n c e of 3  from the c r e s t . plunge  Axes of F2 f o l d s plunge  southwest f a r t h e r away.  to the n o r t h near  the c r e s t  km.  but  Phase 1 f o l d s where seen are i s o c l i n a l  and  t r e n d NW-SE. Domains 3 and 4 were s t u d i e d i n g r e a t e r d e t a i l and of  F2 s t r u c t u r e s t h a t overwhelm F l f o l d s .  c o l i n e a r and plunge  10°-25° to 176°+ 5 ° .  r e v e a l the dominance  G e n e r a l l y , L I and L2 are r o u g h l y Because most d a t a l i e on the r:  south to s o u t h w e s t e r l y d i p p i n g limb of the F3a a n t i f o r m , p o l e s t o S I , and  S2 do not f a l l  on a w e l l - d e f i n e d g i r d l e .  SO,  However, combined w i t h  p o l e s to d a t a from domain 5, t h e i r d i s t r i b u t i o n can_.be c o n s i d e r e d c o n s i s t e n t w i t h a n e a r - g r e a t c i r c l e d i s t r i b u t i o n about the F3a f o l d Due  to c o n s i d e r a b l e s t r u c t u r a l c o m p l e x i t y ,  axis,  the s c a t t e r i s g r e a t .  33  Figure S , n  18. S i m p l i f i e d s t r u c t u r a l map of change i n o r i e n t a t i o n s of S.. , and S„ s u r f a c e s a c r o s s major f a u l t , domain 1.  F i g u r e 19. Photograph of r e f o l d e d l i n e a t i o n s . The deformed l i n e a r s t r u c t u r e i s p r o b a b l y r e l a t e d t o F , which i s i n t u r n r e f o l d e d by a l a t e r F,, (?) f o l d . 2  34 Where seen, F2  f o l d s r e t a i n the  s t r o n g e a s t - n o r t h e a s t vergence r e c o r d e d  f a r t h e r to the northwest i n domains 1 and  Domain 6 ( f i g u r e  17b)  Domain 6 c o n t a i n s F3b e a r l i e r F l and SI are  f o l d axis allel F2  F2  scattered i s due  are  P o l e s to SO,,  the  overwhelm  compositional layering,  g r e a t c i r c l e whose c a l c u l a t e d  n o r t h and  (±5*).  horizontal  f o l d s seen i n the  regional  f i e l d as w e l l  lineation.  F3b  v e r t i c a l limb and  pole  to  these f o l d s are  lineations  c l u s t e r about  As  interpeted  core r e g i o n  as  of the  dip-  stated  t i g h t e s t a t lowest s t r u c t u r a l l e v e l s and  are  more  f o l d s developed en e c h e l o n l a r g e F3a  or  older  a moderately eastward  previously,  'room' problem i n the  refolded  westward.  and  i s subpar-  as s u b p a r a l l e l  a x i a l p l a n e s , S3b,  I n c l i n a t i o n of these f o l d s i s t h e r e f o r e  open a t h i g h e r l e v e l s and  orientation  R e f o l d e d f o l d s and  ( f i g u r e 19).  bisect a nearly  This  p i n g limb.  a  that  about a w e l l d e f i n e d  l o c a l l y p r e s e n t here  176°/60°E and  f o l d s that are numberous and  structures.  to minor F3b  f o l d axes and  2.  as  antiform.  Summary The  following  o b s e r v a t i o n s are  pertinent:  1)  S t r u c t u r a l o v e r p r i n t i n g has caused c o n s i d e r a b l e s c a t t e r i n the data. The d i s t r i b u t i o n of p o l e s to SO, SI, and i n most cases S2 c l e a r l y d e f i n e s the geometry of F3a and F3b f o l d s which p o s t - d a t e these e a r l i e r events.  2)  I t i s c l e a r that p r e v i o u s l y developed s t r u c t u r a l f a b r i c and anisot r o p y p r o v i d e continued i n f l u e n c e on the o r i e n t a t i o n of l a t e r s t r u c t u r a l features. The c o l i n e a r i t y of f o l d s i n any r e g i o n or domain a t t e s t s to t h i s .  3)  The major F3a a n t i f o r m i s d i v i s i b l e i n t o two s u b - c u l m i n a t i o n s , cent e r e d 3 km. and 8 km. r e s p e c t i v e l y southeast of the c r e s t of Chase Mountain, as d e f i n e d by the o r i e n t a t i o n s of SO, SI, and S2 p l a n a r and L l and L2 l i n e a r s t r u c t u r e s .  4)  In at l e a s t one a r e a e a s t of Chase Mountain, a g e n t l y d i p p i n g zone of s t r u c t u r a l d i s l o c a t i o n s e p a r a t e s r o c k s h a v i n g markedly d i f f e r e n t f a b r i c o r i e n t a t i o n s and s t y l e s , but the r e g i o n a l importance of t h i s type of f e a t u r e i s not c l e a r .  35 5)  F2 d e f o r m a t i o n has c o n s i s t e n t northeastward vergence, and no r e v e r s a l of t h i s vergence was r e c o g n i z e d . I t i s p o s s i b l e that the e n t i r e s e quence observed l i e s on the upper limb o f a l a r g e recumbent e a s t f a c i n g a n t i f o r m that may have s u f f e r e d detachment a l o n g i t s lower s y n c l i n a l hinge, i n a nappe-like structure. This i n t e r p r e t a t i o n , a l t h o u g h c o n s i s t e n t w i t h mesoscopic geometry, i s e n t i r e l y c o n j e c t u r a l and cannot be proved without knowledge of s t r u c t u r e s a t depth.  B l a c k p i n e Lake Area ( F i g u r e s 20-22)  Phases 1, 2 The  s t r u c t u r a l evolution  e a r l i e r stages to that  o f the B l a c k p i n e Lake a r e a i s s i m i l a r i n i t s  o f t h e Chase Mountain a r e a .  F l f o l d s are present  which a r e s u b - i s o c l i n a l and possess a x i a l p l a n e s c h i s t o s i t y F2  f o l d s a r e p r e s e n t that  foliation.  f o l d t h i s s c h i s t o s i t y and r e l a t e d  ( f i g u r e 20); transposition  Both g e n e r a t i o n s o f f o l d s a r e t i g h t t o s u b - i s o c l i n a l , and both  seem t o be syn-metamorphic and formed i n a d u c t i l e r o c k regime. b o d i e s and s i l l s  a r e i n t r u d e d b e f o r e , d u r i n g , and a f t e r f o l d i n g  corresponding deformational f a b r i c  a r e i n t r u d e d p a r a l l e l t o the a x i a l p l a n e s o f F2 f o l d s .  folds  c l u s t e r about northwest t r e n d i n g orientations,  50°)  t o t h e n o r t h and northwest  possible the  granitic  These  (323°±5°), g e n t l y p l u n g i n g  early  (10°-20°)  and F l and F2 a x i a l p l a n e s d i p a t moderate a n g l e s (30°-  to c l a s s i f y a l l early  structural history  ( f i g u r e 22).  I n many c a s e s , i t was not  f o l d s as e i t h e r F l o r F2, and c o n s e q u e n t l y ,  i s l e s s c l e a r . The grade of metamorphism i s h i g h e r  here and may account f o r i n c r e a s e d development of F2 a x i a l p l a n e s i t y , making i t more d i f f i c u l t SO, however, a r e s c a t t e r e d calculated  and bear  ( f i g u r e 2 1 ) ; many s y n k i n e m a t i c  sills  axis  Pegmatitic  f o l d axis  to d i s t i n g u i s h  about a f a i r l y w e l l  these f o l d s e t s .  schistoPoles to  d e f i n e d g r e a t c i r c l e whose  i s 340°/0°-30°, and t h i s may r e f l e c t l a t e r open f o l d i n g  c o r r e l a t i v e w i t h Phase 3 near Chase Mountain.  F i g u r e 21. Photograph of f o l d e d and deformed g r a n i t i c s i l l s i n the B l a c k p i n e Lake a r e a , l o o k i n g S. B l a c k l i n e s o u t l i n e f o l d s .  37  N  S  Figure 22. Equal-area stereonet plot of orientations of s t r u c t u r a l data i n the Blackpine Lake area.  • 1compositional layering o 1F1 a x i a l planes • J.F2 a x i a l planes o 1 f o l i a t i o n i n Blackpine Lake stock x l i n e a t i o n or f o l d axis of unknown generation 0 F l f o l d axis ® F2 f o l d axis  38 S t r u c t u r a l R e l a t i o n s o f the B l a c k p i n e Lake G r a n i t i c  Stock  The B l a c k p i n e Lake g r a n i t i c s t o c k i s f o l i a t e d , and i n t h i n s e c t i o n appears s t r o n g l y deformed, p o s s e s s i n g mortar  fabric  ( f i g u r e 23a).  The surround-  i n g c o u n t r y r o c k s possess a s i m i l a r t e x t u r e t h a t can be i n t e r p r e t e d t o have been caused by f l a t t e n i n g a p p r o x i m a t e l y normal t o t h e f o l i a t i o n c,d).  ( f i g u r e 23b,  Roots (1954) s t a t e d t h a t f o l i a t i o n i n the g r a n i t i c s t o c k was c r u d e l y  p a r a l l e l w i t h the margin of the i n t r u s i o n , and he a t t r i b u t e d t h i s to igneous flow processes.  He a l s o c o n s i d e r e d t h i s body t o be p a r t o f the W o l v e r i n e  Complex and r e l a t e d to the g r a n i t i z i n g ' a c t i v i t y . 1  However, u n d u l a t o r y  e x t i n c t i o n and s t r o n g r e c r y s t a l l i z a t i o n i n q u a r t z i n d i c a t e s i g n i f i c a n t p o s t c r y s t a l l i z a t i o n d e f o r m a t i o n , a t l e a s t near the margins. and domal f o l i a t i o n  The o u t c r o p p a t t e r n  (Roots, 1954) a r e i n t e r p r e t e d i n t h i s study t o be due  to f o r c e f u l , p o s s i b l y d i a p i r i c emplacement w i t h c o r r e s p o n d i n g of s u r r o u n d i n g c o u n t r y r o c k .  deformation  These p r o c e s s e s c l e a r l y p o s t - d a t e e a r l y  folding  as w e l l as the peak o f r e g i o n a l metamorphism. Mortar f a b r i c s a r e b e s t developed  i n the q u a r t z - r i c h c o u n t r y r o c k s u r -  rounding the s t o c k ; however, undulose e x t i n c t i o n and s u t u r e d q u a r t z g r a i n boundaries  a r e p r e s e n t i n many rocks throughout  the Chase  p i n e Lake a r e a and i n d i c a t e t h a t d e f o r m a t i o n has c o n t i n u e d  Mountain-Black( o r resumed)  a f t e r most r e c r y s t a l l i z a t i o n has ceased.  R e l a t i o n s between C r y s t a l Growth and Deformation In g e n e r a l , the metasediments have a c q u i r e d t h e i r m i n e r a l o g y t u r e by s y n k i n e m a t i c r e c r y s t a l l i z a t i o n .  and t e x -  The s c h i s t o s i t y d e f i n e d by the p r e -  f e r r e d o r i e n t a t i o n o f b i o t i t e and muscovite was o r i g i n a l l y formed d u r i n g F l folding.  F2 f o l d i n g  a new g e n e r a t i o n  deformed  o f micas has  this  foliation  and  grown p a r a l l e l t o S2  i n many  rocks,  ( f i g u r e 24 a ) .  39  F i g u r e 23a. Photomicrograph of Blackp i n e g r a n i t i c s t o c k showing mortar f a b r i c and r e c r y s t a l l i z e d q u a r t z grains. X - n i c h o l s , 25X.  F i g u r e 23b. Photomicrograph of pegmatite of c o u n t r y r o c k showing k i n k bands i n mica and r e c r y s t a l l i z e d q u a r t z . X - n i c h o l s , 25X.  F i g u r e 23c. Photomicrograph of pegm a t i t e showing k i n k e d micas and m y l o n i t i c t e x t u r e of r i b b o n q u a r t z . X - n i c h o l s , 25X.  F i g u r e 23d. Photomicrograph of pegmatite showing broken f e l d spar g r a i n w i t h q u a r t z f r a c t u r e f i l l i n g and m y l o n i t i c f a b r i c . X - n i c h o l s , 25X.  40  Figure 24a. Photomicrograph of r e l i c t F_ fold with some growth of new micas. Plane-polarized l i g h t , 25X.  Figure 24b. Photomicrograph of r e l i c t f o l d with well-developed polygonization of micas i n d i cating that r e c r y s t a l l i z a t i o n outlasted deformation. Planepolarized l i g h t , 25 X.  F i g u r e 24c. Photomicrograph of s e r i c i t e + c h l o r i t e pseudomorph a f t e r synkinematic garnet. X-nichols, 25X.  Figure 24d. Photomicrograph of c h l o r i t e + muscovite + quartz pseudomorph after synkinematic garnet. Plane l i g h t , 25X.  41  During t h i s F2 f o l d i n g , micas were s t r o n g l y k i n k e d , b e n t , and c r e n u l a t e d i n the cores of F2 f o l d s  ( f i g u r e 24b), i n d i c a t i n g  p r o d u c i n g the s c h i s t o s i t y . it  i s clear  Where u n c h l o r i t i z e d  a pre-F2 metamorphism  garnets r e t a i n  t h e i r form,  t h a t the f o l i a t i o n wraps around p o r p h y r o b l a s t s of g a r n e t  w e l l as p l a g i o c l a s e r a r e to absent  (figure  24c, d ) ; ' s p i r a l ' or 'snowball' g a r n e t s  as are  and t h i s o b s e r v a t i o n supports a f l a t t e n i n g as opposed to shear  o r i g i n f o r the f o l i a t i o n .  F o l l o w i n g F2 d e f o r m a t i o n , p o s t - k i n e m a t i c p o l y -  g o n i z a t i o n of micas and r e c r y s t a l l i z a t i o n of q u a r t z have g i v e n r i s e to present f a b r i c s . deformation  The metamorphism accompanying F2 p r o b a b l y o u t l a s t e d  i n most a r e a s .  L a t e b r i t t l e f o l d s , k i n k s , and f r a c t u r e s  have deformed the rocks are p r o b a b l y r e l a t e d lose  extinction  the a r e a .  The  and somewhat s u t u r e d g r a i n late  t o the development of undu-  boundaries  i n quartz  throughout  (post F2) development of c a t a c l a s t i c and mortar  s u r r o u n d i n g the B l a c k p i n e s t o c k may Retrograde  alteration  widespread  (figure  that  be an e n t i r e l y s e p a r a t e and  fabric  l o c a l event.  of garnet to c h l o r i t e and k y a n i t e t o s e r i c i t e i s  25), and  p h i c event which developed  t h i s i s most l i k e l y a post-F2  low grade metamor-  l a t e r than the p o l y g o n i z a t i o n of micas.  t i o n s h i p s are i l l u s t r a t e d i n f i g u r e  26.  Rela-  F i g u r e 25a,b.  Photomicrographs of s e r i c i t e replacement o f k y a n i t e . 25X.  ••u£te!t  +  - -  k-Ar « Rb-Sr Systems  -Eocene W i n e , o  i  ^ s e  I  pre-rnid-Cretaceoos-  mid-la+e Crelaceoos  55mu  I  4-5  F i g u r e 26. Schematic diagram showing r e l a t i o n s between d e f o r m a t i o n , metamorphism, g r a n i t i c i n t r u s i o n , g e o c h r o n o l o g i c d i s t u r b a n c e , and time.  43 METAMORPHIC PETROLOGY  Introduction The  Chase Mountain and B l a c k p i n e Lake areas have been s u b j e c t e d t o  both a m p h i b o l i t e f a c i e s metamorphism (medium grade of W i n k l e r , later retrogression.  T h i s statement  1974) and  i s supported by t h e f o l l o w i n g d a t a :  1) presence o f s t a u r o l i t e , k y a n i t e , and/or s i l l i m a n i t e i n aluminous schists; 2) absence o f the e q u i l i b r i u m assemblage c h l o r i t e + muscovite q u a r t z throughout the study a r e a ; 3) s t a b i l i t y o f muscovite field;  + q u a r t z i n t o the s i l l i m a n i t e - f i b r o l i t e  4) l a c k o f i n s i t u m e l t i n g o f p e l i t i c  compositions;  5) a l t e r a t i o n of k y a n i t e , s t a u r o l i t e , and garnet to muscovite chlorite. Because o f the low alumina  +  content of the metasediments, d i a g n o s t i c  m i n e r a l assemblages a r e o n l y r a r e l y developed c a t e marbles,  +  i n p e l i t i c rocks.  Calc-sili-  however, h o s t a v a r i e t y o f m i n e r a l a s s o c i a t i o n s , some o f  which p r o v i d e d a t a on temperature  and composition o f t h e f l u i d  Rocks t h a t do p r o v i d e c r i t i c a l P-T-X  phase.  i n f o r m a t i o n a r e s c a t t e r e d , and  s p e c i f i c i s o g r a d s c o u l d not be mapped ( f i g u r e 2 7 ) .  Chase Mountain Area Because d e t a i l e d c o m p o s i t i o n a l d a t a on c o e x i s t i n g m i n e r a l phases was not o b t a i n e d , and because aluminous s c h i s t s were so r a r e , the p r e s s u r e o f metamorphism i s n o t w e l l determined. were found a t s e v e r a l l o c a l i t i e s  Muscovite  pseudomorphs a f t e r k y a n i t e  ( f i g u r e 28), and the assumption  w i l l be  made t h a t k y a n i t e r e p r e s e n t e d the s t a b l e a l u m i n o s i l i c a t e polymorph d u r i n g the p r i n c i p l e metamorphic e p i s o d e . of  R i c h a r d s o n , G i l b e r t , and  pressure  of  Bell  U s i n g the a l u m i n o s i l i c a t e t r i p l e p o i n t (1969) o f 5.5 kbars a t 622° C, the  metamorphism w i l l be assumed to have  been  about  6 kbars.  44  INGENIKA RANGE  / <  +  TlTLflr'  j  / + CHAS6 MTN. /  <?<> s\  1?,ISO  *  \  LAKE  /R/We^Au tMCK  /A  0 1 7 3  ^ CARINA LAKE  S\  Z f|ILE6  1  F i g u r e 27.  Map  3  N  KYANITE. (?) SlLWIMANITE  of area showing d i s t r i b u t i o n of samples r e f e r r e d  to i n t e x t .  Near B l a c k p i n e Lake, s t a u r o l i t e breakdown o c c u r s i n the s i l l i m a n i t e which p l a c e s an upper l i m i t of p r e s s u r e at about 7-8  field,  kbars.  In the Chase Mountain a r e a , no s t a u r o l i t e or f i b r o l i t e were found, but the  absence of the e q u i l i b r i u m  dicates  stability  assemblage  c h l o r i t e + muscovite + q u a r t z i n -  i n the a m p h i b o l i t e f a c i e s or medium grade of W i n k l e r (1974).  Retrograde metamorphismhas produced c h l o r i t e ± q u a r t z ± s e r i c i t e pseudomorphs a f t e r garnet  ( f i g u r e 24c) and muscovite pseudomorphs a f t e r k y a n i t e  P e l i t e s and c a r b o n a t e s a r e c h a r a c t e r i z e d in table  1  ( f i g u r e 28).  by the r e l e v a n t assemblages  listed  I.  * The a u t h o r i s aware of the e x p e r i m e n t a l and thermodynamic problems w i t h the d e t e r m i n a t i o n of . k y a h i t e - s i l l i m a n i t e - a n d a l u s i t e equilibria, .but the d a t a of R i c h a r d s o n , G i l b e r t , and B e l l i s thermodynamically cons i s t e n t and seems as good as d a t a from o t h e r workers.  F i g u r e 29«  G e n e r a l pressure-temperature c o n d i t i o n s of metamorphism.  TABLE I.  Representative  P e l i t e s and qtz qtz qtz qtz qtz qtz  + + + + + +  assemblages from the Chase Mountain  area.  semi-pelites:*  mus + b i o t + ox ± p l a g ( o l i g o c l a s e ) ± gnt ± cc mus + b i o t + p l a g + cc + czo ± sph ± apa ± ox mus + ky (pseudomorphs) + b i o t ± gnt ± p l a g ± ox p l a g + k f + b i o t + mus + ox b i o t + gnt + Mg-chl t o u r + ep + mus  Amphibole-bearing  rock:  q t z + h b l ± gnt + p l a g ± czo ± sph ± b i o t h b l + gnt + p l a g + b i o t + qtz + cc + k f h b l + gnt + p l a g + mus + b i o t + czo + sph  Calc-silicates: czo + a c t + b i o t + qtz + p l a g + k f ± mus ± Mg-chl ± cc + trem + q t z + p l a g + k f + b i o t + sph cc + czo + q t z + diop + Mg-chl + k f + trem qtz + cc + mus ± b i o t ± czo ± sph ± c h l  sph  * Retrograde c h l o r i t e and muscovite are p r e s e n t i n many of these but have not been i n c l u d e d i n e q u i l i b r i u m assemblages.  Mineral  rocks,  abbreviations  q t z - q u a r t z , mus - muscovite, b i o t - b i o t i t e , p l a g - p l a g i o c l a s e , gnt - garnet, c h l - c h l o r i t e , ky - k y a n i t e , k f - K - f e l d s p a r , ox o x i d e s , ep - e p i d o t e , czo - c l i n o z o i s i t e , cc - c a l c i t e , h b l - h o r n blende, trem - t r e m o l i t e , a c t - a c t i n o l i t e , diop - d i o p s i d e , sph sphene, apa - a p a t i t e , t o u r - t o u r m a l i n e , c t d - c h l o r o t o i d , aim almandine.  ; 47 A l l p e l i t e s appear t o have e q u i l i b r a t e d above the s t a b i l i t y muscovite  + F e - c h l o r i t e and w i t h i n the s t a b i l i t y  + p l a g i o c l a s e due t o the l a c k of primary and  field  chlorite  of quartz +  (except M g - r i c h  muscovite variety)  the l a c k of A^SiO,. + K - f e l d s p a r and i n s i t u m i g m a t i t i c r o c k s t h a t have  e x p e r i e n c e d m e l t i n g a c c o r d i n g t o the r e a c t i o n , muscovite I^O = melt + A^SiO,. ( W i n k l e r , 1974). restrict P  of quartz +  Assuming P = 6 k b a r s , these  limits  the P-T environment t o the shaded r e g i o n of f i g u r e 29 assuming  = P  total  + quartz + a l b i t e +  H 0" 2  The  c o m p o s i t i o n o f the f l u i d  because o f the u b i q u i t o u s presence silicates  and most a m p h i b o l i t e s .  c a l c - s i l i c a t e s and c l i n o z o i s i t e  phase i n a l l r o c k types of c l i n o z o i s i t e  was  H^O-rich  (or z o i s i t e ) i n c a l c -  G r o s s u l a r garnet i s not p r e s e n t i n any ( z o i s i t e ) + q u a r t z remains a s t a b l e assem-  blage.  At 6 k b a r s , t h i s demands t h a t X  Hewitt,  1975).  be l e s s than 0.1 ( S t o r r e , 1973;  T h i s i s c o n s i s t e n t w i t h o b s e r v a t i o n s by Ghent and D e v r i e s  (1972) i n s i m i l a r types o f r o c k s .  The s t a b i l i t y  of z o i s i t e + quartz i s  l i m i t e d by the r e a c t i o n , z o i s i t e + q u a r t z = g r o s s u l a r 4- a n o r t h i t e + ^ 0 , and  the s t a b i l i t y o f z o i s i t e alone by the r e a c t i o n , z o i s i t e + CO^ = c a l c i t e + a n o r t h i t e + ^ 0 ,  as shown i n f i g u r e 30a. D i l u t i o n of t h e a n o r t h i t e content o f p l a g i c l a s e s h i f t s the i s o b a r i c , univariant  curve toward lower  temperatures  and more H^O-rich  s i t i o n s as d e p i c t e d s c h e m a t i c a l l y i n f i g u r e 30b. lated  t h i s displacement  Hewitt  fluid  compo-  (1973) has c a l c u -  f o r the r e a c t i o n s .  z o i s i t e + CC>2 = c a l c i t e + a n o r t h i t e + ^ 0 , and muscovite at 6 kbars  + c a l c i t e + q u a r t z = a n o r t h i t e + K - f e l d s p a r + vapor  f l u i d p r e s s u r e , as shown i n f i g u r e 30a.  P l a g i o c l a s e compositions i n  r o c k s o f t h i s study are l e s s than A n ^ , g e n e r a l l y about ,-Q> which An  X  L.U2  to l e s s than  .05 o r so, v a r y i n g s l i g h t l y w i t h  temperature.  limit  J  J  .1  .2.  I  L_ A  .3  Xco  z  F i g u r e 30a,b. T-X diagrams f o r S i 0 - C a O - A l 0 - K „ 0 - M g O - H 0 - C 0 ; a) c a l i b r a t e d diagram b) schematic diagram snowing d i s p l a c e m e n t . 2  2  3  2  2  Rocks 17,  18, and 271-2  c o n t a i n the assemblage,  q u a r t z + muscovite + c a l c i t e + ' c l i n o z o i s i t e + p l a g i o c l a s e , which r e s t r i c t s them to the r e g i o n below the s t a b i l i t y of An^Q and on the r e a c t i o n of z o i s i t e breakdown ( f i g u r e 31). curves of Hewitt  + K-feldspar  Using the d i s p l a c e d  (1973), c o n d i t i o n s f o r these r o c k s w i t h o l i g o c l a s e - a n d e s i n e o  p l a g i o c l a s e are approximately T i The  fluid  510  ,  = .04,  and P f - ^ ^  =  6 kbars.  c o m p o s i t i o n of the r o c k s t h a t c o n t a i n z o i s i t e + c a l c i t e +  plagi-  o c l a s e i s b e i n g b u f f e r e d by the r e a c t i o n , and the rock i s c o n s t r a i n e d to remain  on t h i s r e a c t i o n u n t i l one of the components i s used  Sample 87-2  up.  c o n t a i n s the assemblage,  k f + trem + diop + cc + czo + Mg-chl + q t z , which l i e s on the r e a c t i o n trem + cc + q t z = d i o p + vapor, on the ^ O - r i c h s i d e o f z o i s i t e + CC^ = cc + a n o r t h i t e + H^O, g r o s s u l a r + vapor,  below z o i s i t e + cc + qtz =  and above b i o t + cc + qtz = amphibole + k f + H^O  (figure  32). The f l u i d c o m p o s i t i o n i s l e s s than .08 and p r o b a b l y l e s s than .05 X , and without any f u r t h e r c o n s t r a i n t s , the temperature a t 6 kbars may LU  2  vary g r e a t l y  ( l e s s than 550°) w h i l e r e t a i n i n g the same m i n e r a l o g y .  s t a b i l i t y of p h l o g o p i t e + cc + q u a r t z i s enhanced w i t h i n c r e a s i n g t u t i o n of FeO,  T i 0 , and F i n t o p h l o g o p i t e and w i t h a r e a l i s t i c 2  t h i s curve p r o b a b l y would r e s t r i c t Unless X  were l e s s than .02,  the temperature  the temperature  The substi-  composition,  to g r e a t e r than 500  must be g r e a t e r than  or so.  about  2 510 . Q  Sample 273  c o n t a i n s the assemblage,  k f + b i o t + a c t i n o l i t e + cc + czo + A n ^ T h i s assemblage and  2  + qtz.  i t s s t a b i l i t y has been d i s c u s s e d by Hewitt  (1975); i t i s  u s u a l l y found i n a m p h i b o l i t e grade r o c k s i n r e g i o n a l metamorphic t e r r a n e . T h i s assemblage must l i e on the curves z o i s i t e + CO,, = cc + a n o r t h i t e (An^ ) + 2  *Curve f o r trem + cc + q t z = diop + vapor i s e x t r a p o l a t e d from 5kb S l a u g h t e r , K e r r i c k and W a l l (1975).  curve of  F i g u r e 32. T-X diagram showing c o n d i t i o n s of metamorphism f o r sample 87-2 f o r the same p r e s s u r e c o n d i t i o n s .  51 CO^  and b l o t + c c + q t z = k f + amphibole  c r o s s e d the r e a c t i o n mus  + vapor.  I t must have a l r e a d y  + cc + q t z = a n o r t h i t e + k f + vapor t o produce  a  b u l k c o m p o s i t i o n s u i t a b l e to p l a c e i t on the b i o t + cc + q t z r e a c t i o n .  This  c o n d i t i o n p r e s e n t s problems  i f phases  33a.  However, as noted by Hewitt  (1975), FeO,  are pure as i l l u s t r a t e d i n f i g u r e  T i C ^ , and F s u b s t i t u t i o n i n p h l o -  g o p i t e enhances the thermal s t a b i l i t y of t h i s r e a c t i o n . the s t a b i l i t y o f the mus  + cc + q t z r e a c t i o n due  Na, however, reduces  to s u b s t i t u t i o n i n p l a g -  i o c l a s e ; these two e f f e c t s must b r i n g these curves t o g e t h e r so a r e a s o n a b l e topology i s produced ( f i g u r e 33b).  to account  f o r the n a t u r a l occurence of t h i s  There i s i n s u f f i c i e n t d a t a to determine  assemblage  the q u a n t i t a t i v e e f -  f e c t of such s o l i d s o l u t i o n upon s t a b i l i t y r e l a t i o n s , so t h a t the p h l o g o p i t e + cc + q t z r e a c t i o n i s o f l i t t l e v a l u e . and the absence and T = 510  These  However, the presence of  of d i o p s i d e i n d i c a t e c o n d i t i o n s a p p r o x i m a t i n g X  a t 6 kbars P  .,, as shown i n f i g u r e fluid r i  ^  c a l c - s i l i c a t e s are d i s t r i b u t e d over a l a r g e a r e a near Chase Mounfluid o  condio  t i o n s and t e m p e r a t u r e S j a t 6 k b a r s f l u i d p r e s s u r e ^ o f about 510 -530 amphibolite f a c i e s .  G i v e n the l i m i t e d  a c r o s s the f i e l d  , or lower  c o m p o s i t i o n a l range of r o c k s s t u d i e d ,  i s not p o s s i b l e t o argue t h a t metamorphic c o n d i t i o n s v a r y i n any  matic way  .04  33b.  t a i n and t h e i r m i n e r a l o g i e s are a l l compatible w i t h ^ O - r i c h  it  An^  syste-  area.  B l a c k p i n e Lake Area The B l a c k p i n e Lake a r e a appears to have been metamorphosed to h i g h e r temperatures  than the Chase Mountain  a r e a ; t h i s i s concluded by the f o l l o w i n g  data: 1) both f i b r o l i t e and coarse s i l l i m a n i t e have been observed i n add i t i o n to muscovite pseudomorphs a f t e r k y a n i t e ; 2) the r e a c t i o n trem + cc + q t z = diop + vapor has o c c u r r e d i n c a l c s i l i c a t e marbles;  T  Figure  33a.  T-X diagram of  :  (  1  T  Fe and N a - f r e e system at 6 kb.  F i g u r e 33b. Schematic T-X diagram showing a p o s s i b l e t o p o l o g y i n a system w i t h Na and Fe t h a t c o u l d e x p l a i n the m i n e r a l o g y of sample 273.-  53  3)  s t a u r o l i t e bearing p e l i t e s also biotite;  c o n t a i n s i l l i m a n i t e + garnet +  4) muscovite + garnet b e a r i n g g r a n i t i c r o c k s and pegmatites a r e v e r y common; 5) muscovite + q u a r t z remains In p e l i t e s , the f o l l o w i n g  stable.  assemblages have been observed:  qtz + mus + b i o t + f i b + p l a g  ( A n ^ ) + op  qtz + mus + b i o t + gnt + s t a u r + r i b + p l a g + op + c h l ( r e t r o g r a d e ) qtz + mus + b i o t + gnt + p l a g + op + ky (pseudomorph). And,  of s p e c i a l  clusions  sill  + gnt + b i o t  and s t a u r + gnt form i n -  i n a mus + b i o t + q t z + p l a g + f i b + s t a u r + and s c h i s t .  silicates, is  significance,  the assemblage c c + d i o p + trem + c z o + p l a g  (An^)  In c a l c -  + sph + apa  common. C a l c - s i l i c a t e s p r o b a b l y remain on the curve zo + CC^ = p l a g + cc + H^O  and  above t h e s t a b i l i t y of trem + cc + q t z .  again, X  Assuming ^ £ - ^ ^ u  = .05 and T = 530 , b u t l e s s than 640  =  6 kbars once  because zo + c c + q t z  2 remains s t a b l e  ( f i g u r e 34).  j a c e n t rocks i n d i c a t e s triple  Presence o f f i b r o l i t e and s i l l i m a n i t e i n ad-  T £• 622  based on the R i c h a r d s o n , G i l b e r t , and B e l l  point.  Pelites contain f i b r o l i t e  (300, 304, 305) t h a t  i s usually  w i t h muscovite o r l e s s commonly b i o t i t e , b u t the r e a c t i o n ( s ) f o r m a t i o n i s not c l e a r .  associated  leading to i t s  P r o b a b l y Na-muscovite + q t z = f i b + a l b i t e + K-  r i c h e r muse + HgO i s o c c u r r i n g , forming s l i g h t l y more s o d i c rims on p l a g i o clase,  analogous t o : t h a t  present, i t i s usually  observed by G u i d o t t i  (figure  be t e x t u r a l l y a s c e r t a i n e d . and s t a u r o l i t e  b i o t + mus ( f i g u r e  When s t a u r o l i t e i s  surrounded by a sheath o f c o a r s e and  muscovite w i t h o u t f i b r o l i t e can  (1970).  35a),  fine-grained  and no obvious r e a c t i o n  relations  However, i n 304b, t h e presence o f both s i l l  +  3 5 c ) i n c l u s i o n s i n garnet seems s i g n i f i c a n t and p o i n t s v  towards e i t h e r more than one p e r i o d of metamorphic e q u i l i b r a t i o n , d i s e q u i l i brium, or toward a b u f f e r e d r e a c t i o n .  I n t h e m a t r i x of t h i s r o c k  staurolite  F i g u r e 34. T-X diagram of c o n d i t i o n s of metamorphism f o r c a l c - s i l i c a t e marbles near B l a c k p i n e Lake. Hatched l i n e i n d i c a t e s p o s s i b l e c o n d i t i o n s . Because s i l l i m a n i t e i s found i n p e l i t e s , temp e r a t u r e a r e n e a r e r the h i g h temperature l i m i t .  55  F i g u r e 35a. Photomicrograph of s t a u r o - F i g u r e 35b. Photomicrograph of l i t e w i t h h a l o of s e r i c i t e near l a r g e r s i l l i m a n i t e + b i o t i t e + musgarnet. S t a u r o l i t e + q u a r t z are not c o v i t e i n c l u s i o n i n garnet, i n c o n t a c t . P l a n e l i g h t , 25X. X - n i c h o l s , 160X.  F i g u r e 35c. Photomicrograph of staurolite + sericite (alterat i o n ) i n c l u s i o n i n garnet. Note absence of q u a r t z w i t h s t a u r o l i t e . X - n i c h o l s , 40X.  F i g u r e 35d. Photomicrograph of a n d a l u s i t e + muscovite + b i o tite + fibrolitic sillimanite i n m a t r i x of r o c k . X - n i c h o l s , 32X.  i s surrounded by pseudomorphous coarse-and f i n e - g r a i n e d muscovite and a n d a l u s i t e + mus + b i o t  ( f i g u r e 35d) and may be i n v o l v e d i n r e a c t i o n r e l a t i o n s .  F i b r o l i t e grows i n and appears t o be r e p l a c i n g muscovite and a n d a l u s i t e o f the m a t r i x ,  and a n d a l u s i t e p o r p h y r o b l a s t s  b i o t i t e , quartz, is  i t s e l f being  been l a t e  oxides,  are p o i k i l i t i c  about muscovite,  and p l a g i o c l a s e , but not s t a u r o l i t e .  Andalusite  r e p l a c e d by f i b r o l i t e , muscovite, and c h l o r i t e , and may have  synkinematic.  Reaction  r e l a t i o n s o f s t a u r o l i t e and e s p e c i a l l y muscovite pseudomorphs  a f t e r s t a u r o l i t e have been d e a l t w i t h by Albee  (1972) and G u i d o t t i  (1970).  Where pseudomorphs a r e o f coarse muscovite without obvious r e t r o g r e s s i v e t e x t u r e s and where chemical  e q u i l i b r i u m between phases can be shown, the  pseudomorphs a r e l i k e l y prograde ( G u i d o t t i , 1970).  Staurolite crystalsi n  t h i s study a r e n o t l a r g e and a r e surrounded by coarse c o v i t e g e n e r a l l y without f i b r o l i t e . garnets  and k y a n i t e ,  and f i n e - g r a i n e d mus-  There i s e v i d e n c e f o r r e t r o g r e s s i o n o f  f o r i n s t a n c e , and most l i k e l y t h e r e  i s prograde and  r e t r o g r a d e muscovite growth . a f t e r s t a u r o l i t e , and perhaps more than one generation  of s t a u r o l i t e .  The f o l l o w i n g r e a c t i o n s a r e p r o b a b l y  involved:  Na-mus + q t z = f i b + a l b i t e + K - r i c h e r mus + R^O s t a u r + Na-mus + q t z = f i b + b i o t + K - r i c h e r mus + a l b i t e + H^O ± gnt low Z n - s t a u r + mus + q t z = f i b + b i o t + Z n - r i c h e r s t a u r +  ± gnt.  Rock 304b i s i n t e r p r e t e d t o have formed s t a u r o l i t e and upon f u r t h e r heating,  t o have c r o s s e d  i n t o s i l l i m a n i t e f i e l d and p r o b a b l y  c r o s s e d the  r e a c t i o n s t a u r + mus + q t z = gnt + s i l l + b i o t + 1^0 ( f i g u r e 36). c i t y of water was p r o b a b l y  b u f f e r e d by t h i s r e a c t i o n w h i l e  s o l u t i o n s u b s t i t u t i o n i n t h e manner d e s c r i b e d lowering  of pressure,  g r a n i t i c stock,  probably  performing  solid  i n t h e above r e a c t i o n s .  Upon  r e l a t e d t o c o n t a c t metamorphism  andalusite porphyroblasts  The fuga-  c r y s t a l l i z e d and were  by- the partially  r e p l a c e d by f i b r o l i t e and l a t e r r e t r o g r a d e muscovite and c h l o r i t e .  Ambi-  F i g u r e 36. G e n e r a l i z e d pressure-temperature diagram of path of sample 304b i n the B l a c k p i n e Lake r e g i o n , assuming an H„0 p r e s sure of 6000 b a r s p r i o r t o the f o r m a t i o n of post-kinematic andalusite.  58  g u i t i e s r e s u l t i n g from a l t e r a t i o n and l a c k of c o m p o s i t i o n a l d a t a f o r c o e x i s t i n g phases p r e c l u d e s making more d e f i n i t e statements  concerning  equilibrium conditions.  Summary Though c h e m i c a l a n a l y s e s of m i n e r a l phases were not done, r e a s o n a b l e e s t i m a t e s can be o b t a i n e d f o r the c o n d i t i o n s of metamorphism. phase has been shown to be IL^O-rich w i t h no more than no CH^as g r a p h i t e i s absent. c o n s t a n t throughout from 5 1 0 - 5 3 0 Lake a r e a .  Fluid  the a r e a .  compositions  P  10% CO^  = P  up  and  probably  have been r e l a t i v e l y  i n the Chase Mountain a r e a to n e a r l y 650  If P  fluid  Given these c o n d i t i o n s , temperatures  varied  i n the B l a c k p i n e  .. , then m e l t i n g would have begun to occur i n  p l a c e a t s l i g h t l y h i g h e r temperatures. temperatures  may  The  to 680° and  t h i s may  Staurolite relations  i n d i c a t e that  ^  w  a  indicate g r e a t e r than  s  , or t h a t o t h e r elements (Zn?) enhance the s t a b i l i t y of  staurolite.  L a t e r lower p r e s s u r e c o n t a c t (?) metamorphism i n the a r e a near p i n e Lake g r a n i t i c s t o c k i s p r o b a b l y r e s p o n s i b l e f o r the of a n d a l u s i t e i n some r o c k s .  Retrograde  the B l a c k -  crystallization  metamorphism(s) has  variably  a f f e c t e d most rocks s t u d i e d .  G r a n i t i c Rocks As noted p r e v i o u s l y , pegmatites are p r e s e n t throughout  and  small g r a n i t i c s i l l s  and  bodies  the Chase Mountain - B l a c k p i n e Lake a r e a , and  the  q u a n t i t y of g r a n i t i c m a t e r i a l bears a d i r e c t r e l a t i o n to the grade of r e g i o n a l metamorphism.  In the Chase Mountain a r e a , pegmatites  than 1% of the r o c k volume and level.  i n c r e a s e i n q u a n t i t y w i t h lower  In the B l a c k p i n e Lake a r e a where s i l l i m a n i t e o c c u r s ,  form  less  structural  granitic  r o c k s are v e r y common and c o n s t i t u t e g r e a t e r than 10% of the r o c k volume  59 and i n p l a c e s much more. rocks were n o t melted elsewhere.  F i e l d e v i d e n c e suggests t h a t t h e s e  granitic  i n p l a c e , but represent m a t e r i a l i n j e c t e d  The mineralogy  from  of these rocks i s s i m p l e w i t h the f o l l o w i n g  assemblages: q t z + p l a g + mus + op + k f + gnt + b i o t + z i r c o n . Most t a b u l a r g r a n i t i c r o c k s a r e f o l d e d o r f l a t t e n e d and n e a r l y a l l ... have a d e f o r m a t i o n a l f o l i a t i o n d e f i n e d by the p r e f e r r e d o r i e n t a t i o n o f mica and t h e mortar,  o r r i b b o n s t r u c t u r e o f q u a r t z which o c c u r s as e l o n g a t e  f l a t t e n e d and r e c r y s t a l l i z e d g r a i n s ( f i g u r e 23b).  Some, however, a r e  c r o s s - c u t t i n g and undeformed, showing o n l y u n d u l a t o r y e x t i n c t i o n i n q u a r t z grains.  Most g r a n i t i c rocks were emplaced s y n k i n e m a t i c a l l y w i t h  Fl folds  ( f i g u r e 21).  probably  These rocks p r o b a b l y c r y s t a l l i z e d a t p r e s s u r e s  g r e a t e r than about 3 kbars due to the c o e x i s t e n c e o f muscovite  + quartz.  The B l a c k p i n e Lake g r a n i t i c s t o c k , as shown i n f i g u r e 2, i s a b i o t i t e q u a r t z monzonite i n t r u s i o n t h a t c o n t a i n s no muscovite p r o b a b l y p o s t - k i n e m a t i c w i t h r e s p e c t t o F2. shaped (Roots,  1954), s l i g h t l y  I t i s s e m i - d i s c o r d a n t and dome-  f o l i a t e , and ranges  g r a n o d i o r i t e t o q u a r t z monzonite.  o r garnet and i s  i n composition  from  I t i s , however, deformed and c o n t a i n s  abundant evidence o f r e c r y s t a l l i z a t i o n of q u a r t z g r a i n s .  Elongate  quartz  g r a i n s u s u a l l y have mortar s t r u c t u r e and a r e s e p a r a t e d from s m a l l e r , p o l y g o n a l , s t r a i n - f r e e r e c r y s t a l l i z e d g r a i n s by s u t u r e d g r a i n  boundaries.  B i o t i t e c r y s t a l s a r e v a r i a b l y bent and r o t a t e d i n t o the f o l i a t i o n  plane  of the i n t r u s i o n . Roots (1954) c o n s i d e r e d both the pegmatites g r a n i t i c s t o c k as p a r t o f the Wolverine  and the B l a c k p i n e Lake  Metamorphic Complex and consequently  r e l a t e d to the metamorphic and ' g r a n i t i z i n g ' a c t i v i t y .  He a l s o c o n s i d e r e d  60 the s t o c k of m u s c o v i t e - b i o t i t e g r a n o d i o r i t e 5 .km. p i n e Lake ( f i g u r e 2) to be s i m i l a r the c o n c l u s i o n s of t h i s study. P a r t I I suggests  to the B l a c k p i n e s t o c k , c o n t r a r y to evidence  presented  here and i n  t h a t the f o l i a t e d muscovite + g a r n e t - b e a r i n g  rocks and pegmatites and  The  n o r t h e a s t of B l a c k -  a r e d i s t i n c t i n age,  mineralogy,  granitic  intrusive  relations,  o r i g i n from the c o a r s e - g r a i n e d B l a c k p i n e Lake g r a n i t i c s t o c k .  more, i t i s suspected  t h a t the pegmatites  are p a r t i a l l y a product relationship  and m u s c o v i t e - b e a r i n g  of a n a t e x i s a t g r e a t e r depths and bear  to the r e g i o n a l metamorphism of the country  rocks.  Further-  rocks a genetic  61  PART I I .  Geochronology and the Eocene R e s e t t i n g Event  INTRODUCTION Throughout e x t e n s i v e r e g i o n s o f s o u t h e r n B r i t i s h Columbia, a d j a cent n o r t h e a s t e r n Washington, and n o r t h e r n and c e n t r a l Idaho, K-Ar dates on pre-Eocene igneous and metamorphic r o c k s have been r e s e t t o 45-55 m.y.  Many o f the metamorphic r o c k s a r e p a r t o f o r c o r r e l a t i v e  w i t h the Shuswap Metamorphic Complex of s o u t h e r n B r i t i s h Columbia.  Most  workers a t t r i b u t e t h i s to an Eocene thermal event accompanied by i n t e n s e v o l c a n i s m , p l u t o n i s m , and h y d r o t h e r m a l a l t e r a t i o n 1974a; M i l l e r and E n g e l s , 1975; Medford, 1975).  (Ross, 1974; Armstrong, I n many p l a c e s Eocene  v o l c a n i c r o c k s l i e upon an e r o s i o n s u r f a c e above g r a n i t i c and g n e i s s i c r o c k s t h a t i n t u r n g i v e Eocene apparent ages.  Mathews (1976) has shown  t h a t apparent ages of g n e i s s e s d e c r e a s e w i t h i n c r e a s i n g depth below u n c o n f o r m i t y , l e v e l i n g o f f a t about 45 m.y.  this  An a d d i t i o n a l e x p l a n a t i o n of  Eocene r e s e t t i n g i s r a p i d u p l i f t and u n r o o f i n g , and t h i s has been invoked to e x p l a i n Eocene dates i n some a r e a s of Idaho (Ferguson, 1975). In n o r t h - c e n t r a l B r i t i s h Columbia, e x t e n s i v e Eocene r e s e t t i n g of K-Ar d a t e s o c c u r s i n medium t o h i g h grade metamorphic r o c k s o f the W o l v e r i n e Complex between l a t i t u d e s 54°N and about 56%°N.  The W o l v e r i n e Complex  Armstrong, 1949), s i m i l a r to the Shuswap Complex  i n many ways, i s a b e l t  of l a t e s t Precambrian (Winderemere) sediments t h a t were r e g i o n a l l y  meta-  morphosed by m i d d l e Cretaceous time and perhaps e a r l i e r i n the M e s o z o i c or P a l e o z o i c .  The e x p l a n a t i o n f o r the r e s e t t i n g o f dates i n these r o c k s  i s l e s s obvious because v o l c a n i c rocks of Eocene age, where p r e s e n t , do not o v e r l i e the metamorphic  complex.  The Eocene r e s e t t i n g o f K-Ar dates i n the Omineca C r y s t a l l i n e  Belt  of the B r i t i s h Columbia  c o r d i l l e r a i s one m a n i f e s t a t i o n o f a profound  d i s t u r b a n c e d u r i n g the e a r l y T e r t i a r y , and i t c o i n c i d e s w i t h the abrupt t e c t o n i c t r a n s i t i o n from c o m p r e s s i o n a l c o n t i n e n t a l a r c t e c t o n i c s t o r e l a t i v e q u i e s c e n c e i n the O l i g o c e n e and Miocene (Coney, 1972; 1972;  Souther,  1976):  T h i s paper p r e s e n t s new  Wheeler e t a l  Rb-Sr and K-Ar  d a t a and  d i s c u s s e s b o t h the Wolverine Complex and the Eocene 'event' i n r e l a t i o n to the e a r l y T e r t i a r y t e c t o n i c  setting.  63 GEOLOGIC SETTING OF THE The Wolverine (Figure  Complex and  WOLVERINE COMPLEX  r e l a t e d lower  1) c o n s i s t of l a t e s t Precambrian  (Mansy, 1972;  G a b r i e l s e , 1972)  e a r l i e r time.  Higher  grade r o c k s of the Wolverine  Parrish,  i n polyphase  deformation  northwest-trending  1976  northwest-trending  clude b r i t t l e  i n c l u d i n g two  (Armstrong,  1949;  g e n e r a t i o n s of e a r l y  synmetamorphic  the development of n e a r l y f l a t  These s t r u c t u r e s a r e o v e r p r i n t e d by open to  1972,  1974;  thrusting, principally  Parrish,  1976..).  lying  tight  southwest-  Later structures i n -  f o l d s , j o i n t s , or f a u l t s , some of which a r e p r o b a b l y  to Eocene(?) f a u l t i n g and d e f o r m a t i o n (Eisbacher,  schists,  c a l c - s i l i c a t e marbles i n t r u d e d by  l a r g e s c a l e f o l d i n g and 1971,  or  These medium to h i g h grade r o c k s are i n v o l v e d  i s o c l i n a l f o l d s and  metamorphic f o l i a t i o n .  (Mansy,  ).  Cretaceous  Complex are  dykes, s m a l l s t o c k s , and p e g m a t i t i e s  Roots, 1954;  directed  Winderemere-equivalentstrata  metamorphosed i n middle  q u a r t z i t e s , g n e i s s e s , a m p h i b o l i t e s , and granitic s i l l s ,  grade r o c k s to the n o r t h  related  i n the Rocky Mountain Trench  region  1972).  Medium to h i g h grade metamorphism accompained the e a r l y phase(s) of t i g h t to i s o c l i n a l f o l d i n g which l e d to the development of the metamorphic foliation  (Parrish,  r o c k s are now  1976  ).  exposed m a i n l y  metamorphic f o l i a t i o n and probably  f o l d e d by  K y a n i t e , s t a u r o l i t e , and in anticlinoria,  sillimanite  indicating that this  earlier  r e l a t e d g e n t l y d i p p i n g i s o g r a d i c s u r f a c e s are  the l a t e r l a r g e s c a l e n o r t h w e s t - t r e n d i n g  which are southwest v e r g e n t .  f o l d s , many of  A l a t e r p o s t - k i n e m a t i c prograde metamorphism  has been noted by Mansy (1976) i n some a r e a s , and metamorphism i s p r e s e n t  bearing  throughout  a still  later  retrograde  e x t e n s i v e r e g i o n s , e s p e c i a l l y near Chase  Mountain. The well  age  of the h i g h grade metamorphism and  determined  •  intense deformation  Because medium grade rocks near and  to the n o r t h  i s not and  64  northwest  o f Chase Mountain  yield  K-Ar  ages of 87-128 my.,  (figure  t h i s metamorphic p e r i o d must be middle Cretaceous or e a r l i e r . felt  t h a t t h i s p e r i o d of metamorphism was  b r i a n , p r e - M i s s i s s i p p i a n time because  accomplished  37),  Roots  (1954)  i n post-Lower  Cam-  1) Lower Cambrian r o c k s are i n v o l v e d  and 2) sedimentary and v o l c a n i c r o c k s of the Lay Range o f M i s s i s s i p p i a n to Permian ( p o s s i b l y i n c l u d i n g T r i a s s i c ) age do not appear (though no unconformity. > was  observed).  the presence of g r a n i t e , q u a r t z i t e , and  to be  pre-Mesozoic metamorphism Further j u s t i f i c a t i o n f o r v is s c h i s t - b e a r i n g micaceous  i n the Lay Range assemblage 20 m i l e s west of Chase Mountain A K-Ar  affected  conglomerate  (Roots,  1954).  d e t e r m i n a t i o n on d e t r i t a l white mica by the G e o l o g i c a l Survey of  Canada y i e l d s an age o f 246 my. s c a l e of Armstrong,  1974b).  or P e r m o - T r i a s s i c (based on the r e v i s e d  T h i s conglomerate  i s a r e a l l y very  time  restricted  and a p p a r e n t l y u n f o s s i l i f e r o u s , but t o date i n t h i s r e g i o n i s the o n l y  sub-  s t a n t i a l e v i d e n c e f o r pre-Mesozoic metamorphic and p l u t o n i c a c t i v i t y .  Pene-  t r a t i v e d e f o r m a t i o n of r o c k s of the Omineca C r y s t a l l i n e B e l t occured i n pre-middle Cretaceous time because  g r a n i t i c r o c k s of the E a r l y  Cretaceous  C a s s i a r b a t h o l i t h c u t p e n e t r a t i v e s t r u c t u r e s and metamorphic i s o g r a d s ( G a b r i e l s e and Reesor,  1974).  In summary, i t i s known t h a t many o f the r o c k s of the Omineca C r y s t a l l i n e B e l t are polymetamorphic activity  and most are p o l y d e f o r m a t i o n a l .  Thus P a l e o z o i c  i n t h i s a r e a i s p o s s i b l e but not proved; much of the d e f o r m a t i o n  however, i s p r o b a b l y J u r a s s i c or Cretaceous i n age based r a d i o m e t r i c , and s t r u c t u r a l arguments.  on  stratigraphic,  No u n c o n f o r m i t i e s s e p a r a t i n g lower  Mesozoic or l a t e P a l e o z o i c r o c k s from metamorphic "basement" have been d i s covered, and where metamorphic and nonmetamorphic r o c k s are j u x t a p o s e d , s e v e r a l a l t e r n a t i v e e x p l a n a t i o n s are p o s s i b l e and type of metamorphic t e r r a n e (see Campbell,  1970;  i n f a c t documented i n t h i s Coney, 1974;  Davis,  1975).  + + -4+•  0  4 7 ' K-Ar date  0  7 6 R ' R b - S r date  b> biotite TO' muscovite h'  hornblende  \t'  whole r o c k  +  +  + •f-  sample number (this study only) S e e figure I for geologic  legend.  F i g u r e 37. Map o f W o l v e r i n e Complex and r e l a t e d metamorphic r o c k s showing the g e o c h r o n o l o g i c d a t a , i n c l u d i n g dates of t h i s study.  66  The Wolverine  Complex i s f l a n k e d to the n o r t h e a s t by the n o r t h e r n  Rocky Mountain Trench which c o n t a i n s Upper Cretaceous sedimentary  rocks  g l a c i a l deposits  to Eocene  ( S i f t o n B a s i n ) o v e r l a i n by Quaternary ( E i s b a c h e r , 1974a).  clastic  g l a c i a l and p o s t -  The o r i g i n o f the Rocky Mountain  Trench and i t s sediments has been d i s c u s s e d by Leech (1966) and E i s b a c h e r (1972),  and i t i s f a i r l y  c l e a r t h a t fanglomerates  d e r i v e d from the e a s t and  r e l a t e d sediments o f the S i f t o n f o r m a t i o n a r e the r e s u l t o f normal f a u l t i n g v e r y near the p r e s e n t Trench  and the D a l l Lake lineament  s o n a l communication, 1976).  These rocks o f L a t e Cretaceous  t i a r y age have been a f f e c t e d by a l a t e stage  (H. G a b r i e l s e , p e r and e a r l y  (probably Eocene)  i n v o l v i n g k i n k f o l d i n g , f a u l t i n g , and p o s s i b l y r i g h t l a t e r a l faulting  Ter-  deformation  strike-slip  ( E i s b a c h e r , 1972).  V o l c a n i c r o c k s o f p r o b a b l y Eocene age a r e p r e s e n t i n t h e Rocky Mount a i n Trench n o r t h o f 5 6 ° , i n p a r t o f the D a l l Lake lineament, merous  f e l s i c : d i k e s i n the P e l l y lineament  munication,  1976).  and as nu-  (H. G a b r i e l s e , p e r s o n a l com-  Because t h e i r e x t e n t does n o t c o i n c i d e w i t h t h e a r e a  of  Eocene d a t e s , the s i g n i f i c a n c e o f these v o l c a n i c rocks f o r r e s o l u t i o n  of  the r e s e t t i n g problem i s n o t c l e a r . The  and  Rocky Mountains l i e t o the n o r t h e a s t o f the Rocky Mountain  t h e i r s t r a t i g r a p h y and s t r u c t u r e have been d e s c r i b e d by many workers  ( B a l l y , Gordy, and Stewart, The  Trench,  1966; I r i s h ,  1970; P r i c e and Mountjoy, 1970).  p r i n c i p l e d e f o r m a t i o n a l p e r i o d i n t h e Rockies  Cretaceous ceous.  i s thought  t o be L a t e  and e a r l y T e r t i a r y , b u t may extend back i n t o the E a r l y C r e t a -  L a t e Precambrian r o c k s c o r r e l a t i v e w i t h those west o f t h e Trench a r e  p r e s e n t i n the western ranges o f the Rocky Mountains where metamorphic . grade i s v e r y low.  In a d d i t i o n , a s m a l l wedge o f g r a n i t i c g n e i s s w i t h a  k y a n i t e - b e a r i n g a u r e o l e i s p r e s e n t on t h e e a s t s i d e o f t h e T r e n c h near F o r t Grahame ( G a b r i e l s e , 1971).  67 To the west of the Wolverine Complex and r e l a t e d Precambrian l i e s a complex sequence o f low grade upper P a l e o z o i c and lower  rocks  Mesozoic  v o l c a n i c and sedimentary r o c k s o f both " o c e a n i c " and " v o l c a n i c a r c " a f finity of  (Monger, 1975; R i c h a r d s , 1976) t h a t have been i n t r u d e d by a v a r i e t y  igneous r o c k s r a n g i n g from u l t r a m a f i c , b o t h zoned A l a s k a n type  1975,  (Irvine,  1976) and a l p i n e type (Monger and P a t t e r s o n , 1974; Monger, 1975) t o  gabbroic Reesor,  (Irvine,  1975, 1976) t o g r a n i t i c  1974; Woodsworth, 1976).  ( G a r n e t t , 1974; G a b r i e l s e and  The b u l k of the g r a n i t i c rock i s E a r l y  J u r a s s i c and l a t e - E a r l y Cretaceous i n age.  The Wolverine Complex i s f a u l t e d  a g a i n s t and i n e x t e n s i v e areas t h r u s t westward over these younger r o c k s (Mansy, 1974). morphic  The l a r g e s c a l e southwest-vergent  s t r u c t u r e s i n the meta-  t e r r a n e a r e p r o b a b l y a s s o c i a t e d w i t h t h i s f a u l t i n g , b u t i t s age i s  not w e l l known though p r o b a b l y J u r a s s i c or C r e t a c e o u s .  Recurrent movement  d u r i n g l a t e r times i s a l s o p r o b a b l e . To the west o f t h i s l a t e P a l e o z o i c and e a r l y Mesozoic  terrane l i e  c l a s t i c d e p o s i t s of the M i d d l e J u r a s s i c t o E a r l y Cretaceous Bowser and L a t e Cretaceous t o e a r l y T e r t i a r y Sustut B a s i n s .  Both sequences  have been f o l d e d  and f a u l t e d and much of the d e f o r m a t i o n i n the Sustut B a s i n i n v o l v i n g comp r e s s i o n a l f o l d i n g and t h r u s t i n g i s dated as e a r l y T e r t i a r y The Wolverine Complex and r e l a t e d l a t e s t Precambrian (Ingenika group) thus form the westernmost exposures  ( E i s b a c h e r , 1974a).  r o c k s t o the n o r t h  o f Precambrian  rocks  believed  to have been d e p o s i t e d a l o n g the c r a t o n i c c o n t i n e n t a l margin (Ga-  brielse,  1972).  These r o c k s a r e j u x t a p o s e d a g a i n s t younger upper P a l e o z o i c  and lower Mesozoic r o c k s to the west t h a t r e c o r d an e n t i r e l y d i f f e r e n t s e t of  s t r u c t u r a l and metamorphic c o n d i t i o n s .  The Wolverine Complex i s p a r t of  the C o r d i l l e r a n metamorphic core zone t r a c e a b l e southward  i n t o the Shuswap  Complex, n o r t h e a s t Washington, p a r t s of c e n t r a l and s o u t h e a s t Idaho, and n o r t h e a s t and e a s t e r n Nevada (Armstrong  and Hansen, 1966; Snoke, 1975;  68  Coney, belts  1974).  Though t h e i r h i s t o r i e s a r e not i d e n t i c a l , t h e s e metamorphic  form a fundamental s t r u c t u r a l  ficance  i n plate  tectonic  element o f the C o r d i l l e r a whose s i g n i -  terms i s n e i t h e r f u l l y u n d e r s t o o d nor a p p r e c i a t e d .  69 Geochronology  of the Wolverine Complex and R e l a t e d Rocks  The G e o l o g i c a l Survey o f Canada has been the p r i n c i p l e c o l l e c t o r o f K-Ar  d a t a i n t h i s r e g i o n (Wanless  et a l , 1971,  are compiled i n f i g u r e 37 and t a b l e I l a .  1973,  1974), and  These c o m p i l a t i o n s c l e a r l y show  the occurence of Eocene dates c l u s t e r i n g about  45-50 my.  56^°N, i n c l u d i n g some dates e a s t of the Rocky Mountain are incomplete, the evidence suggests t h a t Mountain  r e g i o n , the apparent K-Ar  87-128 my.  these d a t a  from 55 N to about  Trench.  northwest  Though d a t a  from the Chase  ages a b r u p t l y i n c r e a s e from 45-55 my.  to  Where m i n e r a l p a i r s have been a n a l y s e d , the d e t e r m i n a t i o n s are  concordant w i t h o n l y a few e x c e p t i o n s d i f f e r i n g by 10% o r so.  Eocene dates  i n the Wolverine Complex, however, are a l s o r e l a t i v e l y concordant but much younger.  The c o i n c i d e n c e of h i g h e r grade  'Wolverine' r o c k s w i t h Eocene  ages a t f i r s t would seem to suggest t h a t the l a s t morphism was  K-Ar  important h i g h grade meta-  d u r i n g the Eocene; however, p r e s e n t e v i d e n c e i n d i c a t e s t h a t  i s not the case.  The key to the Eocene r e s e t t i n g problem may  t r a n s i t i o n zone from young to o l d e r dates and  this  l i e i n the  i n areas s u r r o u n d i n g Eocene  plutons.  Rb-Sr and K-Ar Data of t h i s Near Chase Mountain a concordant K-Ar in table l i b .  study  a sample (no. 134) o f m u s c o v i t e - b i o t i t e s c h i s t  p a i r of 89 my.  Less than 1 km.  ( b i o t i t e ) and  92 my.  (muscovite) as shown  away a s t r u c t u r a l l y d i s c o r d a n t hornblende  porphyry d i k e y i e l d s a hornblende K-Ar  date of 42.6  my.  i s i d e n t i c a l t o s i m i l a r dated d i k e s i n the Rocky Mountain ( t a b l e I l a , samples GSC clase, b i o t i t e ,  yields  73-55, 73-56).  T h i s 42.6  my.  date  Trench r e g i o n  Rb-Sr a n a l y s e s of muscovite,  plagio-  and whole rock from sample 134 y i e l d comparable r e s u l t s  gure 38) and i n d i c a t e t h a t excess Ar r e t e n t i o n i s not a problem.  (fi-  Individual  m i n e r a l i s o c h r o n dates are d i s c o r d a n t , and the b i o t i t e - p l a g i o c l a s e and  biotite-  70  Table H a .  analysis #  G e o l o g i c a l Survey of Canada K-Ar data on rocks r e l a t e d t o the Wolverine Complex rock type  mineral  age(m.y.)  l a t i t u d e ( N ) longitude(w'  70-1 2 70-13  schist schist  muscovite biotite  128+6 124+6  5 6 ° 3 1 . 5' 5 6 ° 3 1 . 5'  125°36' 125°36'  70-14 70-15  granite granite  muscovite biotite  47+3 43+3  56°23' 56°23'  125°21.5' 125°21 .5'  70-37  schist  muscovite  45+3  55°23' 30"  123°39'50"  70-38  pegmatitic granite  muscovite  50+6  55°23' 30"  1 23°39'50"  70-39  gneiss  muscovite  47+3  55°19'  123°30'  70-40 70-41  gneiss gneiss  biotite muscovite  44+4 46+3  55°07*35" 55 07 35"  123°29'15"  70-42  gneiss  biotite  43+4  55°32' 10"  123°52'40"  70-43  granite greisen  muscovite  40+2  55°07' 35"  123°29'15"  70-44  amphibolite  biotite  45+2  55°32- 1 0"  123°52'40"  72-27  micaceous sandstone  detrital muscovite  117+5  56°02'  124°U'  72-28  pegmatite  muscovite  49+4  56°29"  124°44'  72-29  pegmatite  muscovite  45+4  56°03' 30"  124°29'  73-46  garnet amphibolite  hornblende  64.8+2  56°22'  124°39'  73-47 73-48  amphibolite amphibolite  hornblende biotite " .  53.8+3 40.5+2  56°22' 56°22'  124°39' 124°39'  73-49 73-50  amphibolite amphibolite  hornblende biotite  73-51 73-52  granodiorite granodiorite  1  45.4+2, 47.9+2 56°52'30" 40.8+2 5 6 5 2 ' '30" u  123°29'15"  124°48* 124°48'  biotite muscovite  86.8+3 88.4+4  58°00' 58°00'  126°48* 1 26°48'  muscovite  94.9+4  57°27'i  125°47'  muscovite  104+4  57°27'i  125°47'  73-54  qtz. monzonite boulder qtz. monzonite boulder  73-55  lamprophyre  biotite  49+2  5 7 ° 2 5 'i  125°47'  73-56  lamprophyre  biotite  37+2  57°27'i  125°52'  73-53  71  Table  n ( c o n t i n u e d ) .  Unpublished Geological  a  analysis  rock  #  dates  l a t i t u d e ( N ) 1o n g i t u d e ( w )  42  56°47'  124°46'  schist schist  muscovite b i o t i t e  47 4-1-  56°32' 56°32'  124°42' 124°42'  micaceous conglomerate  muscovite  246  56°32'  125°48*  gneiss/schist gneiss/schist  b i o t i t e muscovite  106 120  57°03' 57°03'  126°14'  granite granite  muscovite b i o t i t e  99.7 94.2  57°18' 57°18'  126°28' 1 26°28'  granite granite  muscovite b i o t i t e  99.5 90.9  57°22' 57°22'  126°29' 126°29  T a b l e lib. K - A r d a t a f r o m #  o f Canada  b i o t i t e  gneiss/schist  rock  age(m.y.)  mineral  type  Survey  rock  this  !  study A r ( r a d ) / A r ( t o t a l ) * * Ar  mineral  type  126°14'  4 0 (rad)/K 4 0  134  schist  muscovite  8.01  0.915  5.528 x1 0 ~  5  134  schist  b i o t i t e  7.55  0.954  5.324 x 1 0 ~  3  144  hornblende porphyry  hornblende  0.77  0.632  2.52  rock #  apparent  a g e (m.y.)  latitude(N)  longitude(w)  134 m u s c o v i t e  92.2+3-3  56°32'  125°18'  134 b i o t i t e  8 8 . 9 + 3 . 2  56°32'  125°18"  144 hornblende  4 2 . 6 + 2  56°32'  125°19'  *K  analyses performed  b y K. Scott  o f University  x1 0 ~  o f British  Columbia  **Ar mass spectrometry performed b y J . Harakal o f University o f British Columbia; K4 0 t o A r 4 0 = 0 . 5 8 5 x 1 0 ~ y r , = 4.72. * JO" ^"* , 10  A  4 O  K/K  = 1.181 *  \0'\  10  3  .800  H  .790  -\  134  SCHIST  MUSCOVITE ^ TO.  Sr87 Sr86  " ,780  1  ^  ^  ^  ^  ^ ^ ^ ^ ^ ^134  WHOLE ROCK  ^  ""PLAGIOCLASE  .770  i  4  6  8  Rb 87 /  12  10  Sr 86  F i g u r e 38.  Rb-Sr e v o l u t i o n diagram f o r s c h i s t o f sample  134.  F i g u r e 39.  Rb-Sr e v o l u t i o n diagram f o r " W o l v e r i n e " g r a n i t i c  rocks.  .725  "WOLVERINE"  GRANITIC  ROCKS TO  .720  Sr87 Sr86  X-" '  79 + 10  1  SC0V]I!  1  PLAGIOCLASE 308  PEGMATITE  WHOLE  .715  ROCK  i 0RTH0CLASE_7\-M^ 52  .710  7 0 5  M.Y  1 PLAGIOCLASE  31  308  M.Y-  WHOLE ROCK  1  1  2  Rb 87 / Sr 86  1-  3  4  73 whole r o c k dates are anomalously  younger  (77 m.y.)  than the K-Ar  date  (89  * m.y.), and  thus g e o l o g i c a l l y unreasonable.-  whole r o c k date i s 106 + 6 m.y. age  The m u s c o v i t e - p l a g i o c l a s e -  and c o n f i r m s a L a t e Cretaceous  or  earlier  f o r the metamorphism.  m The  r o c k s near s a m p l e ^ l i e a t the n o r t h w e s t e r n  Complex, and  end of the  they a r e metamorphosed to lower a m p h i b o l i t e f a c i e s but have  s u f f e r e d e x t e n s i v e r e t r o g r e s s i o n of k y a n i t e and  garnet.  F a r t h e r s o u t h near B l a c k p i n e Lake ( f i g u r e 37), K-Ar mica g r a n i t i c r o c k s are 47 and 43 m.y. pair  Wolverine  two-  respectively for a muscovite-biotite  ( t a b l e I l a ; Wanless and o t h e r s , 1971).  t h a t these muscovite  dates from  Field investigation  indicates  + g a r n e t - b e a r i n g g r a n i t i c rocks are c l o s e l y r e l a t e d to  the r e g i o n a l metamorphism which i n t h i s s p e c i f i c a r e a i s s i l l i m a n i t e  grade.  Here, where the t y p i c a l o c c u r r e n c e of W o l v e r i n e - t y p e  inter-  g r a n i t o i d rocks  s p e r s e d w i t h s c h i s t s and g n e i s s e s i s w e l l - d e v e l o p e d , Rb-Sr a n a l y s i s these m u s c o v i t e - b e a r i n g of 79 +  10 m.y.  g r a n i t i c r o c k s y i e l d s a composite  mineral isochron  and p l a g i o c l a s e - m i n e r a l i s o c h r o n s of 52-84 m.y.  t a b l e I I I ) and are thus somewhat o l d e r than the K-Ar The a r e a 10-15 s m a l l (8 sq. km.)  km.  from  (figure  39,  dates.  south of Chase Mountain has been i n t r u d e d by a  s t o c k of c o a r s e - g r a i n e d b i o t i t e q u a r t z monzonite  (figure  2 ) , termed the B l a c k p i n e Lake g r a n i t i c s t o c k . T h i s s t o c k was o r i g i n a l l y mapped by Roots (1954) as p a r t of the Wolverine Complex and y i e l d s a Rb-Sr 87 whole r o c k i s o c h r o n age of 62 + 7 m.y. a l i s o c h r o n age of 44.7  + 2 m.y.  a t S r ^ - ^ of  @ .7058 ( f i g u r e 40,  .7052 +  .0002 and a miner-  table I I I ) .  This stock  i s deformed by p a s t - c r y s t a l l i z a t i o n d e f o r m a t i o n r e l a t e d to i t s d i a p i r l c placement, but i t i s p o s t - t e c t o n i c w i t h r e s p e c t to the e a r l i e r  (?)  em-  synmetamorphic  In a l l 'Wolverine' Complex b i o t i t e s a n a l y z e d i n t h i s study, t h i s anomaly was encountered, and n e i t h e r i t s cause nor i t s s i g n i f i c a n c e i s understood. S i m i l a r r e s u l t s , however, have been encountered elsewhere i n t e r r a n e of o l d metamorphic r o c k r e s e t a t a l a t e r date ( S a t i r , 1974; R. L. Armstrong, p e r s o n a l communication, 1976).  Table  'III.Rb-Sr  sample  a n a l y t i c a l data ppm  rock/mineral  #  Rb  S r  Rb Sr  87 86  Sr Sr  87* error 86 -  134  schist  209  84  7.20  .7864  .0001  134  b i o t i t e  491  10.5  135.5  .9247  .0003  134  muscovite  252  85  8.58  .7897  .0002  134  plagioclase  34  233  0.42  .7767  .0001  300  schist  196  1 62  3.50  .7604  .0001  308  qtz.  140  254  1 .60  .7113  .0001  308  muscovite  333  32  30.1  .7408  .0001  308  b i o t i t e  605  71  24.7  .7211  .0001  308  orthoclase  242  380  1 .84  .7115  .0001  308  plagioclase  26  193  0.39  .71 0 5  .0001  monzonite  308  peg  pegmatite  88  227  1 .12  .7183  .0001  308  peg  muscovite  363  41  25.6  .7475  .0001  308  peg  plagioclase  37  358  0.30  .7176  .0001  318  granodiorite  123  446  0.80  .7098  .0001  324  aplite  254  63  11 .7  .7367  .0001  204  307  1 .92  .7069  .0001  B l a c k p i n e :L a k e  g r a n i t i c  stock  323  qtz.  323  b i o t i t e  571  89  18.6  .7180  .0001  323  orthoclase  552  402  3.97  .7082  .0001  323  plagioclase  37  371  0.29  .7060  .0001  qtz.  234  272.  2.49  .7073  .0001  148  317  1 .35  .7063  .0001  standard  SrCO.  323  2  monzonite  monzonite  granodiorite  325  *Sr 87/86 r a t i o s have been adjusted (987) a c t u a l value of .71022. **1<r R b ARb  ppm  87  x 10~  1 1  yr  ;  t o t h e NBS  t o w i t h i n 2$>, or 1 ppm. , a s * , determined by XRF. Rb 87/Sr 86 = 2.894 x Rb/Sr  and S r concentrations = 1.42  to conform  are accurate  .709  BLACKPINE .708  LAKE  GRANITIC STOCK  i  ORTHOCLASE (323)  Sr 8 7 S r 8 6  *\  323?  WHOLE  ROCK  .707 ^ > ^ - ^  I  .706  325  3  2  WHOLE  WHOLE  3  ROCK  ROCK  H  feT- ^-  ~ | T  .705  INITIAL=  -I  .7052' ± .0002 1  r  1  2  Rb 8 7  3  / Sr 8 6  F i g u r e 40.  Rb-Sr e v o l u t i o n diagram f o r B l a c k p i n e Lake g r a n i t i c  F i g u r e 41.  Rb-Sr diagram showing a l l whole rock  determinations.  .800  50  * 134  r n ^  SCHIST  .780-  300  .760-1  SCHIST  Sr87 Sr86 .740 3 2 4APLITE  . 7 2 0  308 318 325  .700  PEGMATITE .308  }  TWO-MICA  323 323z  }  GRANITIC  BLACKPINE  LAKE  ROCKS GRANITIC  —r~  —r—  -r-  2  4  8  Rb 8  7 / Sr 8 6  ROCKS  i— 10  —r— 12  stock.  76 s t r u c t u r e s i n the country rock ( P a r r i s h ,  1976).  primary igneous f e a t u r e as thought by Roots  I t s f o l i a t i o n i s not a  (1954) , and i s b e s t developed  near c o n t a c t s . 87 The whole r o c k Rb-Sr and Sr^-r v a l u e s o f the s y n d e f o r m a t i o n a l , s y n oo metamorphic m u s c o v i t e - b e a r i n g g r a n i t i c r o c k s do n o t d e f i n e an i s o c h r o n ( f i g u r e 41), and i t i s n o t p o s s i b l e to date these igneous r o c k s w i t h r e s pect to the e a r l y t i g h t t o i s o c l i n a l f o l d s t h a t they a r e i n v o l v e d i n ; hence, the age o f e a r l y s t r u c t u r e s i s n o t known. The Sr i s o t o p i c compositions o f the c o u n t r y rock s c h i s t s and g n e i s s e s were n o t s y s t e m a t i c a l l y determined, b u t two d e t e r m i n a t i o n s i n d i c a t e  that  t h e i r r a t i o s are much h i g h e r than t h e igneous r o c k s t h a t i n t r u d e them ( f i g u r e 41).  T h i s i m p l i e s t h a t t h e o r i g i n o f t h e 'Wolverine'  r o c k s i s both  granitic  a n a t e c t i c as w e l l as magmatic and p r o b a b l y i n v o l v e s  con-  t a m i n a t i o n o f a l e s s r a d i o g e n i c source magma by h i g h l y r a d i o g e n i c country rock. 87 The  initial  Sr  r a t i o o f t h e B l a c k p i n e Lake s t o c k i s .7052 + .0002  and i s much lower than b o t h c o u n t r y r o c k s c h i s t s  (>.740) and m u s c o v i t e -  bearing  A different,  'Wolverine' g r a n i t i c r o c k s (.710-.737).  less  g e n i c magma i s thus c l e a r l y d i s t i n g u i s h a b l e b o t h i n age, s t r u c t u r a l  radiorela-  t i o n s , and Sr i s o t o p i c c o m p o s i t i o n from the synmetamorphic type. I n i t i a l Sr i s o t o p i c compositions from the Hogem composite to the west  (figure  batholith  1) a r e v e r y low, g e n e r a l l y l e s s than .704 ( E a d i e , 1976),  and i t i s p o s t u l a t e d t h a t a n c i e n t Precambrian basement r o c k may extend beneath b u t e s s e n t i a l l y no f a r t h e r west than the W o l v e r i n e Complex and r e l a t e d Precambrian  metasediments.  to extend t h i s boundary.  O b v i o u s l y more i n f o r m a t i o n i s needed  77 D i s c u s s i o n and Problems of  Wolverine-type and pegmatites  Interpretation  r o c k s are metasediments w i t h g r a n i t i c s i l l s ,  p r e s e n t i n abundance and w i t h the metamorphic grade r o u g h l y  c o r r e s p o n d i n g to the s i l l i m a n i t e zone (see P a r t I ) . i s now  dikes,  exposed i n s e v e r a l a n t i c l i n o r i a throughout  This rock  association  the e n t i r e l e n g t h of the  metamorphic b e l t from 54°N to 58°N where s t r u c t u r a l u p l i f t  i s great.  Though  d e t a i l e d s t r u c t u r a l and metamorphic d a t a are l a c k i n g i n most a r e a s , r e g i o n a l studies  (Mansy, 1976;  throughout  G a b r i e l s e , 1976)  i n d i c a t e t h a t the h i g h grade r o c k s  the b e l t have e x p e r i e n c e d a r e a s o n a b l y s i m i l a r s t r u c t u r a l e v o l u -  t i o n t o t h a t near Chase Mountain, whereas i n low grade areas 20 km.  t o the  n o r t h of Chase Mounatin, the s t r u c t u r a l h i s t o r y appears  s i m p l e r and  apparently  does not i n v o l v e e a r l y synmetamorphic i s o c l i n a l f o l d i n g  (Mansy, 1972,  1974).  These s t r u c t u r a l and metamorphic c o n s i d e r a t i o n s demonstrate t h a t s i m i l a r r o c k s both n o r t h and p h i c and  south of about 56%°N have e x p e r i e n c e d s i m i l a r metamor-  s t r u c t u r a l c o n d i t i o n s , but they have v e r y d i f f e r e n t  histories.  The Eocene r e s e t t i n g event observed  geochronologic  south of 56^° cannot be r e -  s p o n s i b l e f o r the dominant metamorphic f a b r i c of the h i g h e r grade rocks s i n c e r o c k s w i t h the same f a b r i c possess E a r l y Cretaceous region.  dates n o r t h of the r e s e t  The main p e r i o d of metamorphism of these r o c k s must be l a t e  Cretaceous  or o l d e r .  T h i s i s supported by the presence of d e t r i t a l mica  and g r a n i t e b o u l d e r s y i e l d i n g K-Ar  dates of 95-117 m.y.  i n coarse  sediments found w i t h the S i f t o n f o r m a t i o n of L a t e Cretaceous t i a r y age  i n the Rocky Mountain Trench  ( E i s b a c h e r , 1974a).  i n t h i s s t r u c t u r a l - t e m p o r a l c o n t e x t , the Wolverine 1949)  i s not unique  Early  Complex  clastic  to e a r l y T e r When viewed (Armstrong,  because i d e n t i c a l r o c k s are found i n many a n t i c l i n o r i a  where the s t r u c t u r a l u p l i f t  i s s u f f i c i e n t l y great  ( f i g u r e 1).  • 78 The p r o b l e m o f r e s e t K - A r d a t e s i s n o t planations Columbia  for reset  (see  instance,  ages i n the  Introduction)  Shuswap C o m p l e x o f s o u t h e r n  have s e r i o u s  o n l y a few s c a t t e r e d  easily explained.  shortcomings  Gabrielse,  personal  north.  abundant  lineament  no s p a t i a l c o r r e l a t i o n w i t h K - A r r e s e t d a t e s .  These v o l c a n i c s  o n c e b e e n much m o r e e x t e n s i v e ,  supported  Rapid b l o c k u p l i f t dates because the present bear  cannot  sedimentary  i n fanglomerates  but  this  yet  s a t i s f a c t o r i l y e x p l a i n the  e v i d e n c e o f Eocene u p l i f t  needed  to  fully  evaluate  this  the  reset area.  to  the  to r e l a t e  retrograde  retrograde  effects  Cretaceous  dates,  such heat  metamorphic But a g a i n , appreciable in  the  except  does  not  H o w e v e r , more d a t a  are  to;  indeed,  (Eisbacher,  a l l dated  as  throughout  extensive  of feldspar  areas.  However,  preserving  presently  the  porphyry  sporadically present  'older'  various  in  (table  Ila)  s l i g h t l y y o u n g e r and p e r h a p s u n r e l a t e d  fall  the  lineament.  t e r r a n e and i n d i c a t e  d i k e s on the K - A r ages o f metamorphic on d i k e s  further  (Roots,  Rocky M o u n t a i n T r e n c h and P e l l y the  A  i n j e c t i o n of  and h o r n b l e n d e  1972) t h a t a r e  addition, nearly a l l determinations  and 43 m . y . w h i c h i s  might  interactions)  r o c k s and r o c k s  i n t r o d u c e d upon the  dikes are w i t h i n  of the  one  perhaps oxygen i s o t o p e v a r i a t i o n s .  heat f l u x  t e r r a n e as w e l l  affect  faulting  and s u c h h i g h h e a t f l o w w o u l d h a v e no o t h e r  d i k e s and s i l l s  1954) and m i n e t t e  and  data.  observed  (with possible hydrothermal  are present w i t h i n both reset  c a n be made t o  post-tectonic  flow  metamorphism o b s e r v e d  recognized manifestation appeal  by present  statement.  U n u s u a l l y h i g h h e a t f l o w may a l s o b e a p p e a l e d be tempted  bear may h a v e  i n Rocky M o u n t a i n T r e n c h and e l s e w h e r e  a spatial relationship with  in  (H.  c o m m u n i c a t i o n , 1 9 7 6 ) , a r e n o t w i d e s p r e a d and  i s not  For  into Wolverine-  type r o c k s a r e known, and Eocene v o l c a n i c s , though l o c a l l y and P e l l y  ex-  British  farther  small Teriary intrusions  Rocky M o u n t a i n T r e n c h , D a l l Lake l i n e a m e n t ,  The  rocks;  no and,  between  to Eocene  37  resetting.  79 S e v e r a l of these d i k e s were observed  to occupy f a u l t s or j o i n t s which  be r e l a t e d to p o s s i b l e Eocene f a u l t i n g i n the Rocky Mountain Trench;  may simi-  l a r r e l a t i o n s have been observed by E i s b a c h e r (1972) near Ware, B r i t i s h Columbia. A workable e x p l a n a t i o n of the r e s e t t i n g phenomena i n t h i s r e g i o n must take i n t o account  the  following:  1) P e r v a s i v e r e s e t t i n g of K-Ar d u r i n g the Eocene;  dates between 55°N and r o u g h l y 56Jg°N  2) Occurrence of young K-Ar dates i n some metamorphic r o c k s e a s t of the Rocky Mountain Trench as w e l l ; 3) Occurrence 45-50 m.y.  of o l d e r Rb-Sr m i n e r a l dates (52-84 m.y.) K-Ar a r e a near B l a c k p i n e Lake;  directly  w i t h i n the  4) Absence of s p a t i a l r e l a t i o n s h i p between Eocene v o l c a n i c r o c k s r e s e t metamorphic r o c k s ;  and  5) Presence of sedimentary r e c o r d of i n t e n s e Eocene (?) u p l i f t , but l a c k of s p a t i a l c o r r e l a t i o n w i t h the r e s e t a r e a , g i v e n p r e s e n t d a t a ; 6) Occurrence of E a r l y Cretaceous K-Ar dates i n d e t r i t a l r o c k s of the S i f t o n f o r m a t i o n d i r e c t l y e a s t of as w e l l as f a r t h e r n o r t h of the reset terrane; 7) Emplacement of d i k e s throughout the r e g i o n i n the Eocene, perhaps accompanied by f a u l t i n g i n the Rocky Mountain Trench; 8) Presence of a few s m a l l but important Eocene g r a n i t i c s t o c k s gene r a l l y w i t h i n the r e s e t area ( s e v e r a l more no doubt remain u n d i s c o v ered) . I n t r u s i o n of s m a l l Eocene g r a n i t i c p l u t o n s such as the B l a c k p i n e Lake s t o c k accompanied by h i g h heat flow, hydrothermal  c i r c u l a t i o n , and  oxygen i s o t o p e r e e q u i l i b r a t i o n i s p r o b a b l y important r e s e t dates. K-Ar  perhaps  i n e x p l a i n i n g the  The B l a c k p i n e Lake s t o c k i s l i k e l y r e s p o n s i b l e f o r the young  dates s u r r o u n g i n g i t and  f o r the p a r t i a l r e s e t t i n g of Rb-Sr d a t e s .  F a u l t i n g , doming, and r a p i d u p l i f t may  a l s o be important  f a c t o r s , but  the  s i g n i f i c a n c e of these p r o c e s s e s i n e x p l a i n i n g r e s e t t i n g of dates remains u n c l e a r and e l u s i v e .  Based upon s p a t i a l arguments, b l o c k f a u l t i n g ,  related  (?) d i k e emplacement, and Eocene (?) v o l c a n i s m are p r o b a b l y not r e l a t e d the r e s e t t i n g  event.  to  Rather, a l l of these e v e n t s - d e f o r m a t i o n , and  uplift,  erosion, volcanism,  i n t r u s i o n may have been o c c u r i n g s i m u l t a n e o u s l y as p a r t of an i n t e n s e  p u l s e of e a r l y T e r t i a r y t e c t o n i s m .  The o n l y c l e a r c o r r e l a t i o n  w i t h the r e -  s e t t i n g of K-Ar and Rb-Sr m i n e r a l dates i s the e f f e c t of s m a l l Eocene granitic  i n t r u s i v e r o c k s which have caused g e o c h r o n o l o g i c d i s t u r b a n c e i n p r e -  v i o u s l y metamorphosed  country  rock.  Early Tertiary Tectonic Setting  In o r d e r t o e v a l u a t e the s i g n i f i c a n c e o f the Eocene K-Ar r e s e t t i n g event, i t i s n e c e s s a r y to view the event  i n terms of the e a r l y  Tertiary  t e c t o n i c s e t t i n g i n which v o l c a n i s m , p l u t o n i s m , d e f o r m a t i o n , and sediment a t i o n a r e interwoven. D u r i n g the Eocene, v o l c a n i s m was e x p e c i a l l y widespread i n B r i t i s h Columbia  as shown i n f i g u r e 42.  c e n t r a l B r i t i s h Columbia,  and i n t e n s e  I n the Intermontane zone o f  the Odtsa Lake v o l c a n i c s occupy l a r g e r e g i o n s  from t h e Skeena Arch southward and a r e c o r r e l a t i v e w i t h the P r i n c e t o n and Marron v o l c a n i c s o f southern B r i t i s h Columbia Washington and Idaho.  and r e l a t e d v o l c a n i c s i n  These Eocene v o l c a n i c s a r e r e l a t e d t o s m a l l i n t r u -  s i v e b o d i e s o f Eocene age i n the Intermontane zone, the K a t z b e r g sions  ( R i c h a r d s , 1974), which extend without  i n t o the e a s t e r n Bowser B a s i n and elsewhere metamorphic t e r r a n e .  intru-  their volcanic equivalent i n c l u d i n g a few b o d i e s i n the  Eocene v o l c a n i c rocks a r e l a c k i n g i n t h e Bowser  B a s i n , b u t the Sloko v o l c a n i c s l i e f a r t h e r to the n o r t h (Souther, 1972, 1976). Much l a r g e r b o d i e s o f i n t r u s i v e r o c k a r e a s s o c i a t e d . i w i t h the Sloko Group near the e a s t e r n margin o f the Coast P l u t o n i c Complex where many l a r g e d i s c o r d a n t p l u t o n s y i e l d Eocene r a d i o m e t r i c d a t e s .  Though l a r g e r e g i o n s  of the c e n t r a l and e a s t e r n Coast Mountains have a l s o been r e s e t to young Eocene ages (Hutchinson,  1970), many of the ages on e a s t e r n b o r d e r p l u t o n s  are p r o b a b l y emplacement ages (Smith, 1975).  D u r i n g the i n t e n s e v o l c a n i s m  and p l u t o n i s m i n the Intermontane zone and e a s t e r n Coast P l u t o n i c Complex, metamorphic r o c k s o f the Wolverine Complex were b e i n g  reset.  Sedimentation d u r i n g t h i s igneous e p i s o d e was c o n f i n e d mainly t o the Sustut and S i f t o n b a s i n s where c o a r s e c l a s t i c sediments relief  were shed  from h i g h  source t e r r a n e composed o f g r a n i t i c , metamorphic, sedimentary and  82  "jv\ Vv  W =  tywNmc  INTRUSION  /  SILICIC VOLCANISM  teotmmm^ /\ft£A  THRUSTING  DISTDWWCE  OF 5ePIHEWTflT|0rJ  TOLDIM*  NCWIAL F A U L T S 0  50  ico  l  5  0  200  K f t ]  Figure.'42. ... Sketch map i l l u s t r a t i n g tectohi'c-event's during' the Eocene.  v o l c a n i c rocks.  The  p r e s e n t form of these b a s i n s i s a r e s u l t of both  i g i n a l b a s i n e x t e n t as w e l l as l a t e r e r o s i o n a l m o d i f i c a t i o n , and d o u b t f u l t h a t the Sustut and 1974a).  S i f t o n b a s i n s were ever connected  or-  i t is  (Eisebacher,  I t i s l i k e l y t h a t the Bowser and western p a r t of the Sustut  basins  were source areas d u r i n g the Eocene i n a d d i t i o n to p a r t s of the Omineca C r y s t a l l i n e B e l t and Deformation  the Rocky Mountains.  d u r i n g the Eocene was  the C o r d i l l e r a .  The  c o n s i d e r a b l e and  1966;  p r e s s i o n a l deformation  and  and  P r i c e and Mountjoy, 1970).  Upper Cretaceous,  Eocene time Probable  o c c u r r e d i n the S i f t o n and  ( B a l l y , Gordy, and  contemporaneous  Sustut B a s i n s  ( E i s b a c h e r , 1972,  1974a).  F o l d s and  western p a r t of the<upper P a l e o z o i c and  folding  f a u l t i n g i n the  t h r u s t s p r e s e n t on  and  T e r t i a r y sediments and  b a b l y of more than one Deformation taceous  and  of the Bowser and  to post-45 my.  tion patterns  over  (Richards^ 1976)  are  Sustut B a s i n s c o n t i n u e d  from post-Lower C r e -  Early Tertiary u p l i f t  sedimenta-  of the Coast P l u -  s t r u c t u r a l l y impinged on the western Bowser B a s i n  and v o l c a n i s m are widespread i n  the Mesozoic and e a r l y T e r t i a r y h i s t o r y of the C o r d i l l e r a but a r e  e p i s o d i c , but  causing  t h r u s t i n g ( E i s b a c h e r , 1974b).  metamorphism, p l u t o n i s m ,  i n t e n s e i n the Eocene.  pro-  be e a r l y T e r t i a r y s t r u c t u r e s .  time c o n t r o l l i n g p a l e o c u r r e n t t r e n d s and  s t y l e f o l d i n g and  Deformation,  o l d e r rocks  l o c a l l y may  ( E i s b a c h e r , 1974a).  t o n i c Complex has decollement  age,  the  lower Mesozoic t e r r a n e t h a t d i s -  p l a c e Permian, Upper T r i a s s i c , and Lower J u r a s s i c r o c k s westward Cretaceous  com-  deforming  P a l e o c e n e ( ? ) , and Eocene s t r a t a by e a s t - v e r g e n t  t h r u s t i n g i n the Sustut B a s i n and by k i n k f o l d i n g and  S i f t o n Basin  across  f i n a l s t a g e s of c r u s t a l s h o r t e n i n g i n the Rocky Moun-  t a i n s f o o t h i l l s took p l a c e i n Paleocene Stewart,  extended  T h i s Eocene e p i s o d e was  c o n s i s t e n t l y compressional  especially  the c o n c l u d i n g stage of  regime e x t e n d i n g  from e a r l i e r  an in  84 the Mesozoic.  T h i s s i t u a t i o n was  f o l l o w e d by an abrupt  q u i e s c e n t t e n s i o n a l r e g i i m e f o r much of the remaining  t r a n s i t i o n to a  Cenozoic  e t a l , 1972), c h a r a c t e r i z e d by absence o f a c i d i c v o l c a n i s m , and  folding,  of b a s a l t i c  and by  (Wheeler  plutonism,  the p r e s e n c e of r e s t r i c t e d b l o c k f a u l t i n g , e x t r u s i o n  p l a t e a u l a v a s , and  t i o n u n t i l the P l i o c e n e  i n t e r m i t t e n t sedimentation  rejeuvenation.  and  peneplana-  Summary  In t h i s study Rb-Sr whole rock i s o c h r o n d a t a show; t h a t .a s m a l l Eocene p l u t o n i c body i n t r u d e s r o c k s grouped i n the Wolverine  Complex.  Sr m i n e r a l i s o c h r o n s on medium to h i g h grade metamorphic and g r a n i t o i d r o c k s w i t h i n the Eocene K-Ar  r e s e t t e r r a n e near  Lake stock are p a r t i a l l y r e s e t to 52-84 my. or o l d e r o r i g i n a l dates.  have K-Ar  synmetamorphic  the B l a c k p i n e  from p r o b a b l e middle  Cretaceous  Metamorphic r o c k s to the n o r t h t h a t a r e  continuous w i t h the Wolverine  Rb-  structurally  Complex and w i t h the Eocene r e s e t p r o v i n c e  and Rb-Sr m i n e r a l ages of 89-1P6 my.  i n d i c a t i n g t h a t the medium  to h i g h grade metamorphism and i t s accompanying s t r u c t u r a l d i s t u r b a n c e are middle  Cretaceous  or o l d e r i n age.  Although much work needs to be done to f u l l y e x p l a i n the phenomena, the Eocene r e s e t t i n g event  i s l i k e l y the r e s u l t of both the i n t r u s i o n of  s m a l l b o d i e s of g r a n i t i c rock and the accompanying h i g h heat f l o w . i n g and u p l i f t may  be r e s p o n s i b l e f o r some of the p a t t e r n i n K-Ar  d i s t r i b u t i o n , but t h e i r importance  is difficult  Faultdate  to e v a l u a t e because of l a c k  of d e t a i l e d data i n s u r r o u n d i n g r e g i o n s . The Eocene event was deformation  accompanied by i n t e n s e v o l c a n i s m , p l u t o n i s m ,  i n o t h e r areas of n o r t h e r n and c e n t r a l B r i t i s h Columbia.  c o i n c i d e s w i t h the c e s s a t i o n of compressional and  and It  t e c t o n i c s i n the C o r d i l l e r a  i s a b r u p t l y f o l l o w e d by a t e c t o n i c a l l y q u i e s c e n t regime u n t i l the  ocene r e j e u v e n a t i o n which has r e s u l t e d i n much of the p r e s e n t  Pli-  physiography.  86  BIBLIOGRAPHY  A l b e e , A., 1972, Metamorphism of p e l i t i c s c h i s t s : Reaction r e l a t i o n s of c h l o r o t o i d and s t a u r o l i t e : G e o l . Soc. Amer. B u l l . 83, 3249-3268. Armstrong, J.E., 1949, F o r t S t . James map-area, C a s s i a r and Coast d i s t r i c t s , B r i t i s h Columbia: G e o l . Surv. Can. Mem. 252, 210 p. and Roots, E.F., 1948, A i k e n Lake map-area, B r i t i s h G e o l . Surv. Can. Paper 48-5.  Columbia:  Armstrong, R.L., 1974a, Geochronometry of the Eocene v o l c a n i c - p l u t o n i c e p i s o d e i n Idaho: Northwest Geology, v.3, p. 1-15. , and McDowall, W.G., 1974b, Proposed r e f i n e m e n t of the P h a n e r o z o i c time s c a l e ( a b s . ) : I n t ' l . Meeting f o r Geochron., P a r i s , Abs. V o l . and Hansen, E., 1966, C o r d i l l e r a n i n f r a s t r u c t u r e i n the e a s t e r n Great B a s i n : Am. J o u r . S c i . 264, 112-127. B a l l y , A.W., Gordy, P.L., Stewart, G.A., 1966, S t r u c t u r e , s e i s m i c d a t a , and o r o g e n i c e v o l u t i o n of s o u t h e r n Canadian Rocky Mountains: Bull. Can. P e t . G e o l . , 14, 337-381. Campbell, R.B., 1970, S t r u c t u r a l and metamorphic t r a n s i t i o n s from i n f r a s t r u c t u r e t o s u p r a s t r u c t u r e , C a r i b o o Mountains, B r i t i s h Columbia: G e o l . Assn. Can. Sp. Paper 6, 67-72. , Mountjoy, E.W., and Young, F.G., 1973, Geology of McBride a r e a , B r i t i s h Columbia: G e o l . Surv. Can. Paper 72-35.  map-  Coney, P.J., 1972, C o r d i l l e r a n t e c t o n i c s and North America p l a t e motion: Am. J o u r . S c i . 272, 603-628. , 1974, S t r u c t u r a l a n a l y s i s of the Snake Range " d e c o l l e m e n t " , e a s t - c e n t r a l Nevada: G e o l . Soc. Amer. B u l l . 85, 973-978. D a v i s , G., 1975, G r a v i t y - i n d u c e d f o l d i n g o f f a g n e i s s dome complex, Rincon Mountains, A r i z o n a : G e o l . Soc. Amer. B u l l . 86, 979-990. E a d i e , E.T., 1976, K-Ar and Rb-Sr geochronology of the n o r t h e r n Hogem b a t h o l i t h , B r i t i s h Columbia: unpub. B.Sc. t h e s i s , Univ. of B r i t i s h Columbia. E i s b a c h e r , G.H., 1972, T e c t o n i c o v e r p r i n t i n g near Ware, n o r t h e r n Rocky Mountain T r e n c h : Can. J o u r . E a r t h S c i . 9, 903-913. , 1974a, Sedimentary h i s t o r y and t e c t o n i c e v o l u t i o n of the S u s t u t and S i f t o n b a s i n s , n o r t h - c e n t r a l B r i t i s h Columbia: G e o l . Surv. Can. Paper 73-31. , 1974b, E v o l u t i o n o f s u c c e s s o r b a s i n s i n t h e Canadian Soc. Econ. P a l . and Miner. Sp. Pub. 19, 274-291.  Cordillera:  87 Ferguson, J.A., 1975, T e c t o n i c i m p l i c a t i o n s of some geochronometric d a t a from the n o r t h e a s t e r n b o r d e r zone of the Idaho b a t h o l i t h : Northwest Geology 4, 53-58. G a b r i e l s e , H., 1967, T e c t o n i c framework of the n o r t h e r n Canadian Cordillera: Can. J o u r . E a r t h . S c i . 4, 271-298. , 1971, O p e r a t i o n F i n l a y : Can. Paper 71-1A.  i n Rept. of A c t . , p a r t A, G e o l . Surv.  , 1972, Younger Precambrian of t h e Canadian C o r d i l l e r a : S c i . 272, 521-536.  Am.  Jour.  , Dodds, C.J., and Mansy, J . L . , 1976, O p e r a t i o n F i n l a y : i n Rept. of A c t . , p a r t A, G e o l . Surv. Can. Paper 76-1A, 87-90. and Reesor, J.E., 1974, The n a t u r e and s e t t i n g of g r a n i t i c p l u t o n s i n t h e c e n t r a l and e a s t e r n p a r t s of the Canadian C o r d i l l e r a : P a c i f i c Geology 8, 109-138. G a r n e t t , J.A., 1974, Geology and copper-molybdenum m i n e r a l i z a t i o n i n the s o u t h e r n Hogem b a t h o l i t h , n o r t h - c e n t r a l B r i t i s h Columbia: Can. I n s t . Min. and M e t a l . B u l l . 749,101-106. Ghent, E. and D e v r i e s , .C.D.S., 1972, P l a g i o c l a s e - g a r n e t - h o r n b l e n d e e q u i l i b r i a i n h o r n b l e n d e - b e a r i n g r o c k s from the Esplanade Range, B r i t i s h Columbia: Can. J o u r . E a r t h . S c i . 9, 618-6 G u i d o t t i , C.V., 1970, The m i n e r a l o g y and p e t r o l o g y of the t r a n s i t i o n from lower t o upper s i l l i m a n i t e zone i n the Oquossoc a r e a , Maine: J o u r . P e t r o l o g y 11, 277-336. H e w i t t , D.A., 1973, S t a b i l i t y of the assemblage q u a r t z : Amer. M i n e r a l . 58, 785-791. , 1975, S t a b i l i t y of the assemblage  muscovite-calcite-  phlogopite-calcite-quartz:  Amer. M i n e r a l . 60, 391-397. H u t c h i s o n , W.W., 1970, Metamorphic framework and p l u t o n i c s t y l e s i n the P r i n c e Rupert r e g i o n of the c e n t r a l Coast Mountains, B r i t i s h Columbia: Can. J o u r . E a r t h S c i . 7, 376-405. I r i s h , E.J.W., 1970, Halfway R i v e r map-area, B r i t i s h G e o l . Surv. Can. Paper 69-11.  Columbia:  I r v i n e , T.N., 1975, A x e l g o l d l a y e r e d gabbro i n t r u s i o n , McConnell Creek map-area, B r i t i s h Columbia: i n Rept. of A c t . p a r t B, G e o l . Surv. Can. Paper 75-1B, 81-88. , 1976, S t u d i e s of C o r d i l l e r a n g a b b r o i c and u l t r a m a f i c i n t r u s i o n s , B r i t i s h Columbia,•part 1 and p a r t 2: i n Rept. of A c t . p a r t A, G e o l . Surv. Can. Paper 76-IA, 75-81.  88  Leech, G.B., 1966, The Rocky Mountain T r e n c h : i n I r v i n e , T.N., ed., The w o r l d r i f t system, G e o l . Surv. Can. Paper 66-14, 307-330. L o r d , C.S., 1948, McConnell Creek map-area, B r i t i s h Surv. Can. Memoir 251.  Columbia:  Mansy, J . L . , 1971, The I n g e n i k a Group: i n Rept. of A c t . p a r t G e o l . Surv. Can. Paper 71-1A, 26-28.  Geol.  A,  , 1972, S t r a t i g r a p h y and s t r u c t u r e of the I n g e n i k a Group i n F i n l a y and Swannell Ranges, B r i t i s h Columbia: i b i d . , Paper 72-1A, 29-32. , 1974, O p e r a t i o n F i n l a y :  i b i d . , Paper 74-1A, 17-18.  , and Dodds, C.J., 1976, S t r a t i g r a p h y , s t r u c t u r e , and metamorphism i n n o r t h e r n and c e n t r a l Swannell Ranges, B r i t i s h Columbia: ibid., Paper 76-1A, 91-92. Mathews, W.H., 1976, Anomalous K-Ar d a t e s from g n e i s s e s of t h e T r i n i t y H i l l s , B r i t i s h Columbia: G e o l . Ass. Can. Prog, w i t h Abs. 1, p.47. Medford, G., 1975, K-Ar and f i s s i o n t r a c k geochronometry of an Eocene t h e r m a l event i n the K e t t l e R i v e r (west/2) map-area, s o u t h e r n B r i t i s h Columbia: Can.Jour. E a r t h S c i . , 12, 836-843. M i l l e r , F.K., and E n g e l s , J.C., 1975, D i s t r i b u t i o n and t r e n d s of d i s c o r d a n t ages o f t h e p l u t o n i c r o c k s o f n o r t h e a s t e r n Washington and n o r t h e r n Idaho: Geol. Soc. Amer. B u l l . , 86, 517-528. Monger, J.W.H., 1975, C o r r e l a t i o n o f e u g e o s y n c l i n a l t e c t a n o - s t r a t i g r a p h i c b e l t s i n the North American C o r d i l l e r a : G e o s c i e n c e s Canada 2, , 1976, Lower Mesozoic r o c k s i n M c C o n n e l l Creek map-area: i n Rept. of A c t . p a r t A, G e o l . Surv. Can. Paper 76-1A, 51-55. and P a t t e r s o n , I.A., 1974, Upper P a l e o z o i c and lower Mesozoic r o c k s of the Omineca Mountains: i b i d . , Paper 74-IA, 19-20. P a r r i s h , R.R., 1976, S t r u c t u r e and metamorphism i n s o u t h e r n Swannell Ranges, B r i t i s h Columbia: i b i d . , Paper 76-1A, 83-86. P r i c e , R.A., and Mountjoy, E.W., 1970, G e o l o g i c s t r u c t u r e of the Canadian Rocky Mountains between Bow and Athabasca R i v e r s - a p r o g r e s s report: G e o l . Assn. Can. Sp. Paper 6, 7-26. R i c h a r d s , T.A., 1974, H a z l e t o n e a s t h a l f : G e o l . Surv. Can. Paper 74-1A, 35-38.  i n Rept. of A c t . p a r t  , 1976, McConnell Creek map-area (94 D e a s t / 2 ) : 76-1A, 43-50.  ibid.,  A,  Paper  4-9.  89 R i c h a r d s o n , S.W., G i l b e r t , M.C., and B e l l , P.M., 1969, 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 of k y a n i t e - a n d a l u s i t e and a n d a l u s i t e - s i l l i m a n i t e e q u i l i b r i a , the aluminum s i l i c a t e t r i p l e p o i n t : Amer. Jour. S c i . 267, 259-272. Roots, E.F., 1954, Geology and m i n e r a l d e p o s i t s of A i k e n Lake map-area, B r i t i s h Columbia: Geol. Surv. Can. Memoir 274. Ross, J.V., 1974, A T e r t i a r y thermal event i n s o u t h - c e n t r a l B r i t i s h Columbia: Can. J o u r . E a r t h S c i . 11,1116-1122. S a t i r , M., 1975, Die e n t w i c k l u n g s g e s c h i c h t e der w e s t l i c h e n Hohen Tauern und der s u e d l i c h e n Oetztalmasse auf grund r a d i o m e t r i s c h e r a l t e r s b e s timmungen: I n a u g u r a l d i s s e r t a t i o n der U n i v e r s i t a t Bern. S l a u g h t e r , J . , K e r r i c k , D.M., and W a l l , V . J . , 1975, E x p e r i m e n t a l and thermodynamic study of e q u i l i b r i a i n the system CaO-MgO-SiC^-t^O-CC^: Amer. Jour. S c i . 275, 143-162. Smith, J.G., 1975, K-Ar evidence f o r t i m i n g of metamorphism and p l u t o n i s m i n the Coast Mountains near K e t c h i k a n , A l a s k a : G e o l . Assn. Can. C o r d i l l e r a n S e c t . , Prog, w i t h Abs., p. 21. Snoke, A.W., 1975, A s t r u c t u r a l and g e o c h r o n o l o g i c p u z z l e : Secret Creek Gorge a r e a , n o r t h e r n Ruby Mountains, Nevada: G e o l . Soc. Amer. Abs. w i t h Prog. 7, no. 7, p. 78. Souther, J.G., G e o l . Surv.  1972, T e l e g r a p h Creek map-area, B r i t i s h Can. Paper 71-44.  Columbia:  , 1976, V o l c a n i s m and t e c t o n i c environments i n the Canadian C o r d i l l e r a - a second l o o k : ms. i n prep. S t o r r e , B. and N i t s c h , K., 1972, Die r e a k t r o n 2 z o i s i t + 1 C 0 a n o r t h i t + 1 c a l c i t + H^O: Cont. M i n e r a l . P e t r . 35, 1-10.  2  S u t h e r l a n d Brown, A., 1963, Geology of the C a r i b o o R i v e r a r e a , Columbia: B.C. Dept. of Mines and P e t . Res. B u l l e t i n 47.  = 3  British  Wanless, R.K., Stevens, R.D., Lachance, G.R., and D e l a b i o , R.N., 1967, 1971, 1973, 1974, Age d e t e r m i n a t i o n s and g e o l o g i c s t u d i e s : Geol. Surv. Can. Papers 67-2, 71-2, 73-2, 74-2. Wheeler, J.O., A i t k e n , J.D., B e r r y , M.J., G a b r i e l s e , H., H u t c h i s o n , W.W., Jacoby, W.R., Monger, J.W.H., N i b l e t t , E.R., N o r r i s , D.K., Price, R.A., and Stacey, R.A., The C o r d i l l e r a n s t r u c t u r a l p r o v i n c e : Geol. Assn. Can. Sp. Paper 11, 1-82. W i n k l e r , H.G.F., 1974, P e t r o g e n e s i s of Metamorphic Rocks, 3rd S p r i n g e r - V e r l a g , New York.  ed.,  Woodsworth, G.J., 1976, P l u t o n i c rocks of M c C o n n e l l Creek and Lake map-areas: i n Rept. of A c t . p a r t A, Geol. Surv. Can. 76-1A, 69-73.  Aiken Paper  

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0052839/manifest

Comment

Related Items