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Geology of the Three Ladies Mountain/Mount Stevenson area, Quesnel Highland, British Columbia Getsinger, Jennifer Suzanne 1985

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GEOLOGY OF THE THREE LADIES MOUNTAIN/MOUNT STEVENSON QUESNEL HIGHLAND, BRITISH COLUMBIA  by  JENNIFER SUZANNE GETSINGER A.B., HARVARD UNIVERSITY, 1974 M.S.,  UNIVERSITY OF WASHINGTON, 1978  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF GEOLOGICAL SCIENCES  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 APRIL 1985 ©  JENNIFER SUZANNE GETSINGER,  1985  AREA  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of  requirements f o r an advanced degree a t the  the  University  o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make it  f r e e l y a v a i l a b l e f o r reference  and  study.  I  further  agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may department o r by h i s or her  be granted by the head o f representatives.  my  It i s  understood t h a t copying or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l gain  s h a l l not be  allowed without my  permission.  Department o f  G&ot-o &i cfrk  "Sd^jces  The U n i v e r s i t y of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date  written  ABSTRACT In l a t e P r o t e r o z o i c to e a r l y P a l e o z o i c continent-derived c l a s t i c  sediment and minor carbonate  the Snowshoe Group were d e p o s i t e d s h e l f environment, and carbonates  time, of  in a c o n t i n e n t a l slope to  shallow marine e l a s t i c s  and  of the Cariboo Group were d e p o s i t e d nearer  shore of North America.  The  Snowshoe Group i s d i v i d e d i n t o  a lower sequence of micaceous q u a r t z i t e , p e l i t e , and amphibolite,  to the  a l l i n t e r l a y e r e d with quartz d i o r i t e  minor  sheets;  and an upper sequence of micaceous q u a r t z i t e , p e l i t e , carbonate Early  and  with minor c a l c - s i l i c a t e and a m p h i b o l i t i c r o c k s . isoclinal  (F1A)  and NE-verging t i g h t  formed together with a metamorphic f o l i a t i o n .  folds  (F1B)  T i g h t to  normal, c y l i n d r o i d a l second phase (F2) f o l d s , c h a r a c t e r i z e d by SW-vergence and NW  plunge, formed during the  mid-Jurassic  Columbian orogeny at about the same time as a c c r e t i o n of suspect  t e r r a n e s southwest of the map  metamorphism i n the B a r r o v i a n was  synkinematic  area.  Prograde  s e r i e s of amphibolite  to postkinematic  to F2 f o l d i n g ,  facies  with  maximum metamorphic r e c r y s t a l l i z a t i o n o u t l a s t i n g deformation.  G a r n e t - b i o t i t e geothermometry i n d i c a t e s  temperatures of 525  ± 20°C f o r p e l i t e s near the kyanite to  s i l l i m a n i t e zone i s o g r a d .  Garnet-aluminosilicate-ilmenite  geobarometry l i m i t s P to l e s s than  7 kb.  G r o s s u l a r - a n o r t h i t e - a l u m i n o s i 1 i c a t e geobarometry g i v e s P = 5.5  ± 0.7  kb.  ii  Retrograde metamorphism and F3 k i n k - f o l d i n g occurred during u p l i f t , The  followed by broad  warping  low-angle, postmetamorphic L i t t l e  (F4) with NE trend.  River F a u l t emplaced  c h l o r i t e to b i o t i t e zone p h y l l i t e and carbonate  of the  Cariboo Group, i n the hanging w a l l , a g a i n s t s t a u r o l i t e - k y a n i t e to s i l l i m a n i t e s c h i s t s and g n e i s s e s of the Snowshoe Group, i n the f o o t w a l l , with l a t e s t movement of the hanging w a l l i n an ESE d i r e c t i o n . A Rb-Sr model d e p o s i t i o n a l age of approximately assuming an i n i t i a l for  Sr/  8 6  Sr  r a t i o of 0.708, was obtained  Snowshoe Group metasedimentary rocks.  plutonism of  8 7  Paleozoic  i s i n d i c a t e d by a Rb-Sr whole-rock i s o c h r o n  530 ± 94 Ma with  initial  U-Pb dates on z i r c o n ,  8 7  Sr/  8 6  Sr  date  r a t i o of 0.706, and  i n d i c a t i n g a minimum age of 335 Ma and  maximum age of about 450 Ma, f o r quartz d i o r i t i c intrusive  750 Ma,  gneiss  i n t o the Snowshoe Group e a r l y i n i t s deformational  h i s t o r y , pre-F1B f o l d i n g .  Late- to post-metamorphic  pegmatite cooled through 400-500°C at 86 ± 3 Ma. the L i t t l e River F a u l t i s bracketed  The age of  between i n t r u s i o n of  pegmatite and a Miocene(?) e r o s i o n s u r f a c e .  Table of Contents ABSTRACT  i i  LIST OF TABLES  vii  LIST OF FIGURES  ..viii  LIST OF PLATES  xiii  ACKNOWLEDGEMENT  xiv  1.  2.  INTRODUCTION  1  1.1 LOCATION AND OBJECTIVES  1  1 . 2 PREVIOUS WORK  4  1.3 REGIONAL GEOLOGIC SETTING  6  LITHOSTRATIGRAPHY  8  2.1 LITHOSTRATIGRAPHY OF SNOWSHOE GROUP  8  2.2 LITHOSTRATIGRAPHY ABOVE THE LITTLE RIVER FAULT ..18 3.  STRUCTURE  25  3.1 DEFORMATION:  FOLD PHASES  "  25  3.1.1 FOLD NOTATION  25  3.1.2 OUTLINE OF FOLD PHASES  28  3.1.2.1 F 1 A  28  3.1.2.2 F1B  28  3.1.2.3 F 1A and F1B  31  3.1.2.4 F2  34  3.1.2.5 F3  36  3.1.2.6 F4  40  3.1.3 FOLDS ABOVE LITTLE RIVER FAULT  41  3.2 STEREOGRAPHIC PROJECTIONS OF STRUCTURAL ELEMENTS  43  3.2.1 DOMAINS 3.2.2 DEFINITION OF TERMS  43 45  iv  3.2.3 SUMMARY OF STEREOGRAPHIC  PROJECTIONS  46  3.2.4 SUMMARY OF FOLDING  70  3.3 DEFORMATION: FAULTING  4.  71  3.3.1 LITTLE RIVER FAULT  71  3.3.2 DISCUSSION OF LITTLE RIVER FAULT  81  3.3.3 OTHER FAULTS  89  METAMORPHISM  91  4.1 INTRODUCTION  •  4.2 METAMORPHIC ZONES IN PELITES 4.2.1  91 95  INTRODUCTION  95  4.2.2 METAMORPHIC ZONES  97  4.3 GARNET ZONING  122  4.3.1 DESCRIPTION OF ZONING PROFILES  122  4.3.2 DISCUSSION OF GARNET ZONING  134  4.4 STAUROLITE BREAKDOWN  137  4.5 GARNET-BIOTITE GEOTHERMOMETRY  144  4.6 GEOBAROMETRY: GRAIL  150  4.7 GEOBAROMETRY: GROSSULAR ANORTHITE-ALUMINOSI -  5.  6.  LICATE-QUARTZ  155  4.8 CONCLUSION  1 62  IGNEOUS ACTIVITY  170  5.1 QUARTZ DIORITIC GNEISS  170  5.2 GRANODIORITlC GNEISS  172  5.3 PEGMATITE  1 73  5.4 QUARTZ VEINS  175  5.5 ECONOMIC GEOLOGY  176  5.6 VOLCANIC ROCKS GEOCHRONOLOGY  177 179 v  6.1 GEOCHRONOLOGY ABSTRACT  179  6.2 INTRODUCTION  180  6.3 GEOLOGIC SETTING OF DATED SAMPLES  183  6.4 R e s u l t s and i n t e r p r e t a t i o n  185  6.5 Conclusions  196  7.  SUMMARY  197  8.  CONCLUSION  201  REFERENCES  208  APPENDIX I: METAMORPHIC MINERALS  215  APPENDIX I I : MICROPROBE ANALYSES  227  APPENDIX IIIA: ANALYTICAL METHODS FOR GEOCHRONOLOGY  236  APPENDIX IIIB: GEOCHRONOLOGY SAMPLE DESCRIPTIONS  237  vi $0 DR=621  $5.47,  $5.57T  LIST OF TABLES  TABLE I . TABLE I I . TABLE I I I .  TABLE IV. TABLE V.  MINERAL DATA GARNET-BIOTITE TEMPERATURES  141 147  GROSSULAR-ANORTHITE-ALUMINOSILICATE GEOBAROMETRY 160 RUBIDIUM-STRONTIUM ANALYTICAL DATA  U-PB ZIRCON DATA FROM QUARTZ DIORITIC GNEISS INTRUSIVE INTO SNOWSHOE FORMATION  187  188  LIST OF FIGURES  Figure  1 .  L o c a t i o n map  2  F i g u r e 2.  L i t h o s t r a t i g r a p h y of Snowshoe Group  10  F i g u r e 3.  L i t h o s t r a t i g r a p h y above L i t t l e River F a u l t .  F i g u r e 4.  Diagrammatic summary of f o l d phases  . 19 26  F i g u r e 5. A. Refolded i s o c l i n e (F1A, F1B) i n q u a r t z i t e . B. Q u a r t z i t e l a y e r s (Q) preserve F1 f o l d s 29 F i g u r e 6 A and B. isoclines F i g u r e 7.  Quartzitic  l a y e r s (Q) preserve F1 30  T e c t o n i c p r o f i l e through Three Ladies Mountain. 33  F i g u r e 8. A. SW-verging F2 f o l d i n q u a r t z i t e (Q) f l a n k e d by p e l i t e ( P ) . B. I s o c l i n a l l y f o l d e d quartz segregation (Q) and q u a r t z o - f e l d s p a t h i c l a y e r (QF) i n kyanite-grade g n e i s s . 35 F i g u r e 9. A, B, C. G e n e r a l i z e d c r o s s s e c t i o n s through S e r v i c e Mountain ("6287'") showing geology and r e l a t i o n s h i p s among F2, F3, and F4 f o l d s F i g u r e 10. Sketch of sample showing F3 c r e n u l a t i o n c r o s s c u t t i n g an F1 f o l d  37  cleavage 39  F i g u r e 11. A. Weak f o l i a t i o n i n micaceous q u a r t z i t e (Q) p a r a l l e l to NE-dipping a x i a l plane of SW-verging f o l d (F2) . B. Thin l a y e r s in grey marble at "6287'" are s u b p a r a l l e l to r e g i o n a l NE-dipping F2 a x i a l plane, but l o c a l l y kinked by F3 f o l d s with SE-dipping a x i a l planes. 42  viii  i  Figure  12.  S t r u c t u r a l domain map of the Three  Ladies  Mountain area  44  Figure  13.  Equal  area p r o j e c t i o n s f o r Domain II  50  Figure  14.  Equal  area p r o j e c t i o n s f o r Domain III  52  Figure  15.  Equal area p r o j e c t i o n s f o r Domain IV  54  F i g u r e 16. Equal area p r o j e c t i o n s f o r Domain VIII and Domain X. . Figure 17. Equal area p r o j e c t i o n s f o r Domains I, V, and VII, f o l i a t i o n s and l i n e a t i o n s Figure 18. Equal area p r o j e c t i o n s f o r combinations of s t r u c t u r a l elements from s e v e r a l domains  56 58  60  F i g u r e 19. Equal area p r o j e c t i o n s of pre-F2 f o l d elements for combinations of domains; a n d F 2 f o l d elements i n Domain IX, Mount Stevenson area 62 Figure 20. Equal area p r o j e c t i o n s f o r Domains VI and IX. Mount Stevenson area 64 Figure 21. Equal area p r o j e c t i o n s of f a u l t s l i c k e n s i d e s , and j o i n t s  surfaces, 66  Figure 22. Equal area p r o j e c t i o n s of s t r u c t u r a l elements i n hanging w a l l of L i t t l e River F a u l t , Domain XI 68 Figure 23. A. View of Three Ladies Mountain from S e r v i c e Mountain. B. Sketch of view i n A showing t r a c e of L i t t l e River F a u l t and exhumed t e c t o n i c denudation s u r f a c e (stippled) 72 Figure 24. S t r u c t u r e s below but r e l a t e d to L i t t l e F a u l t ; f o r l o c a t i o n see F i g u r e 23 B  ix  River 77  F i g u r e 25. Pressure/temperature diagram i l l u s t r a t i n g AFM assemblages f o r metamorphic zones i n the Three Ladies Mountain/Mount Stevenson area in r e l a t i o n to bathozones as d e f i n e d by Carmichael (1978), and m o d i f i e d by A r c h i b a l d et a l . (1983) 96 F i g u r e 26. Garnet zone (2), sample 82-376. Main metamorphic f o l i a t i o n ( S ) of b i o t i t e and muscovite, wrapping around garnet, was subsequently f o l d e d by F3 folds 99 f  F i g u r e 27. S t a u r o l i t e zone ( 3 ) , sample 81-344. Large s t a u r o l i t e porphyroblast i n c l u d e s i d i o b l a s t i c garnet and t r a i l s of r u t i l e and q u a r t z (S -) p a r a l l e l to S ( S ) 102 t  e  2  F i g u r e 28. S t a u r o l i t e - k y a n i t e zone (4), sample 79-13. Staurolite-kyanite-garnet-muscovite schist contains c h l o r i t o i d (CD) i n c l u s i o n s i n 'snowball' ( r o t a t i o n a l ) garnet synkinematic with F2 f o l d i n g 106 F i g u r e 29. S t a u r o l i t e - k y a n i t e zone (4), sample 81-234. Garnet rims, s t a u r o l i t e , and kyanite are a l l h e l i c i t i c , i n c l u d i n g folded t r a i l s of g r a p h i t e . Sj-is p a r a l l e l to S 107 e  F i g u r e 30. S t a u r o l i t e - k y a n i t e - s i l l i m a n i t e zone (5), sample 81-279. A t o l l , or ring-shaped, garnet 110 F i g u r e 31. S t a u r o l i t e - s i l l i m a n i t e zone (6), sample 80-30. F i b r o l i t i c s i l l i m a n i t e forming at the expense of staurol ite 115 F i g u r e 32. S i l l i m a n i t e zone ( 7 ) , sample 80-31. Tiny g a r n e t s o u t l i n e a former garnet p o r p h y r o b l a s t F i g u r e 33. Garnet zoning p r o f i l e 82-389, s t a u r o l i t e zone  118  f o r Garnet 2 from sample 125  Figure 34. Garnet zoning p r o f i l e f o r Garnet 3 from sample 81-279, s t a u r o l i t e - k y a n i t e zone 126 F i g u r e 35. Garnet zoning p r o f i l e f o r Garnet 4 from sample 81-278, s t a u r o l i t e - k y a n i t e - s i l l i m a n i t e zone 127 x  F i g u r e 36. Garnet zoning p r o f i l e f o r Garnet 1 from sample 80-33, s t a u r o l i t e - k y a n i t e - s i l l i m a n i t e zone 128 F i g u r e 37. Garnet zoning p r o f i l e f o r Garnet 1 from sample 80-119, s t a u r o l i t e - k y a n i t e - s i l l i m a n i t e zone 129 F i g u r e 38. Garnet zoning p r o f i l e f o r Garnet 2 from sample 80-19, s t a u r o l i t e - s i l l i m a n i t e zone 130 Fi.gure 39. Garnet zoning p r o f i l e 80-31, s i l l i m a n i t e zone  f o r Garnet 3 from sample 131  F i g u r e 40. Garnet zoning p r o f i l e s f o r Garnets 3.1 and 2 from sample 81-325, kyanite zone 132 F i g u r e 41. Garnet zoning p r o f i l e s f o r Garnets 4 and 1 from sample 81-325, kyanite zone 133 F i g u r e 42. C a l c u l a t e d s t a u r o l i t e breakdown r e a c t i o n s using thermodynamic data from Lang and Rice (1985) 142 F i g u r e 43. Pressure/temperature diagram of "GRAIL" geobarometer (modified from Bohlen et a l . 1983).  .. 151  F i g u r e 44. Sketch of photomicrograph (sample 81-344) i l l u s t r a t i n g how r u t i l e i s s t a b l e as i n c l u s i o n s i n s t a u r o l i t e , but unstable r e l a t i v e to i l m e n i t e where i n c o n t a c t with quartz 153 F i g u r e 45. Schematic c r o s s s e c t i o n s of Three L a d i e s Mountain (3LM) area showing r e l a t i o n s h i p between metamorphic isograds (symbols as on P l a t e I I I ) , f o l i a t i o n (dashed l i n e s ) , and L i t t l e R i v e r F a u l t (LRF). 166 F i g u r e 46. Summary diagram showing v a r i a t i o n of temperature, pressure (or depth), and " i n t e n s i t y of deformation" through time, p l o t t e d on l o g a r i t h m i c s c a l e . 168 F i g u r e 47.  Sample l o c a l i t y map f o r dated samples  xi  186  F i g u r e 48. Rb-Sr isochrons f o r metasedimentary rocks, quartz d i o r i t i c g n e i s s , g r a n o d i o r i t i c g n e i s s , and pegmatite  189  Figure 49. gneiss  190  U-Pb  zircon concordia  for quartz  dioritic  F i g u r e 50. Schematic t e c t o n i c h i s t o r y of the Omineca B e l t in the v i c i n i t y of the Three Ladies Mountain/Mount Stevenson area 202  L I S T OF  ALL PLATES ARE SEPARATE MAP  PLATES  SHEETS.  PLATE I . BEDROCK GEOLOGY OF THREE LADIES MOUNTAIN/MOUNT STEVENSON AREA, QUESNEL HIGHLAND, BRITISH COLUMBIA PLATE I I . GEOLOGIC CROSS SECTIONS, THREE LADIES MOUNTAIN/MOUNT STEVENSON AREA  / [  PLATE I I I . METAMORPHIC ZONES AND SAMPLE LOCALITIES, THREE i LADIES MOUNTAIN AREA / PLATE IV. PLATE V. PLATE V I .  FOLIATION AND BEDDING F l AND  I  F2 FOLDS  F3 AND F4 FOLDS; JOINTS, FAULTS, AND  SLICKENSIDES  ACKNOWLEDGEMENT  I am s i n c e r e l y indebted  t o my s u p e r v i s o r , Dr.  Greenwood, for a l l h i s encouragement and support the d u r a t i o n  of t h i s p r o j e c t .  Armstrong, and Dr.  K.C.  J.V. Ross, Dr.  McTaggart — for t h e i r  e f f o r t s toward h e l p f u l and e d u c a t i o n a l d i s c u s s i o n , and a d v i c e .  throughout  I am g r a t e f u l to the other  members of my a d v i s o r y committee — Dr. R.L.  Hugh •  criticism,  T h i s work c o u l d not have been done  without the p a t i e n t h e l p of those who a s s i s t e d me i n the field and  and i n the l a b , and the help of numerous  f r i e n d s who kept me  going.  The'work was supported by grant  EMR-65-1677 from the  G e o l o g i c a l Survey of Canada and NSERC grant H.J. was  Greenwood, research  colleagues  supervisor.  67-4222 t o  The 1981 f i e l d  season  p a r t l y supported by the G e o l o g i c a l S o c i e t y of America,  grant  2831-81.  E l e c t r o n microprobe work was done under the  s u p e r v i s i o n of John Knight;  and Rb-Sr a n a l y t i c a l work was  done under the s u p e r v i s i o n of K. S c o t t , i n R.L. Armstrong's l a b o r a t o r y a t the U n i v e r s i t y of B r i t i s h  Columbia.  P. van der Heyden d i d the U-Pb d a t i n g of the z i r c o n separate. possible  R.L. Armstrong suggested d a t i n g methods and i n t e r p r e t a t i o n s of the data.  xiv  1.  1.1  LOCATION AND The  INTRODUCTION  OBJECTIVES  Three Ladies Mountain/Mount Stevenson area i s  l o c a t e d along the west s i d e of the north arm Lake, w i t h i n the Quesnel Highland Mountains.  of Quesnel  part of the  Cariboo  It i s e n t i r e l y w i t h i n the Omineca B e l t ,  although  the suture with the Intermontane B e l t l i e s only about 10 south of Mount Stevenson The of  present  study  km  (see F i g u r e 1).  i n v o l v e d d e t a i l e d mapping at a s c a l e  1:25,000 i n the Three Ladies Mountain/Mount Stevenson  area d u r i n g the approximately  1979-1982 f i e l d seasons,  200  km  T h i s rugged t e r r a i n Lake (725 m) Mountain over  PLATE I ) .  i s covered with r a i n f o r e s t at Quesnel  to a l p i n e meadows on Three Ladies  (2187  1500  (see Geologic Map,  2  c o v e r i n g an area of  m)  and Mount Stevenson  (2243 m),  a relief  of  m.  O b j e c t i v e s of t h i s study were to sort out the stratigraphic  sequence, and  internal  s t r u c t u r a l and metamorphic  h i s t o r y of the Snowshoe Group, which was  p r e v i o u s l y poorly  defined in t h i s area. The  Snowshoe Group l i e s w i t h i n an area of  metasedimentary rocks between sediments d e r i v e d from North America which l i e to the east and v o l c a n i c and rocks belonging to suspect  t e r r a n e s to the west.  has r e c e n t l y been r e f e r r e d to as the "suspect" terrane  i  (Struik  1984,  sedimentary  Monger and Berg 1  1984).  T h i s area  Barkerville The  d e t a i l s of  2  F i g u r e 1. L o c a t i o n map showing r e l a t i o n s h i p of study area ( s t i p p l e d p a t t e r n ) to t e r r a n e s of the Canadian C o r d i l l e r a . Cretaceous and/or T e r t i a r y g r a n i t o i c bodies are in f l e c k e d p a t t e r n ; P a l e o z o i c o r t h o g n e i s s e s are in s q u i g g l e p a t t e r n . A b b r e v i a t i o n s : IB = Intermontane B e l t , OB = Omineca B e l t , RMFTB = Rocky Mountain F o l d and Thrust B e l t , NAm = North America, CC = Cache Creek Terrane, QN = Q u e s n e l l i a , SM = S l i d e Mountain Terrane, BV = B a r k e r v i l l e Terrane, KO = Kootenay Terrane, CB = Cariboo Terrane, SH = Shuswap Complex, MO = Monashee Complex, MG = Malton Gneiss; FR = Fraser R i v e r , QL = Quesnel Lake, TR = Thompson R i v e r , RMT = Rocky Mountain Trench, CR = Columbia R i v e r . References: Monger and Berg (1984); Tipper e t . a l (1981).  3  the  s t r u c t u r a l and metamorphic h i s t o r y of t h i s area are  t h e r e f o r e important hypotheses and  in r e s t r a i n i n g large-scale  speculations.  tectonic  4 1.2  PREVIOUS WORK Reconnaissance  Quesnel B.C.  Lake was  Department  g e o l o g i c work done  of M i n e s  1957,  1963)  and  1961,  1963), p a r t l y  around Wells described t o the Brown  work has  Campbell Cariboo of  named t h e  (Struik  1963)  with  1978;  and  1979, the  1981a,  late  Proterozoic juxtaposed  with  faults  the  (Struik  Many d e t a i l e d  Group  1983,  1984b).  geologic  problems such  structural and  the  history,  nature  as  on  recent Cariboo  1973;  but  not  the east  age  r o c k s of  students  late terrane")  terrane")  and  various aspects  stratigraphic  apparently  the  Fault  ( i n "Cariboo  graduate  s u p e r v i s o r s have c o n c e n t r a t e d  More  (in "Barkerville  Cariboo  s t u d i e s by  Sutherland  1981b); or as p a r t of  g r o u p of  a n d / o r P a l e o z o i c age  first  assigned i t  below  Paleozoic in  1982); or as a s e p a r a t e  (Campbell  et a l .  Pleasant Valley  partly  and  1963).  (Campbell  the  Brown  (1954)  Group, as d i d  Snowshoe G r o u p e i t h e r  Struik  by  of  i n g o l d mines  Holland  (1961,  t h e Kaza G r o u p  possibly  of Canada  Snowshoe F o r m a t i o n  Campbell  60's  Sutherland  interest  B.C.  northwest  early  1954;  to  the C a r i b o o  G r o u p west of  i t , and  along  Barkerville,  p l a c e d the  Group a l o n g  (Holland  in response  upper p a r t of (1957,  1950's and  the G e o l o g i c a l S u r v e y  and  and  i n the  i n the area  their  of r e g i o n a l  correlations,  s t e e p metamorphic g r a d i e n t s ,  of t h e b o u n d a r i e s  of  t h e Shuswap M e t a m o r p h i c  5  Complex  (K.V. Campbell  1971; F l e t c h e r  1978; F l e t c h e r and Greenwood Klepacki Pell  1972; Pigage 1977,  1979; Poulton and Simony 1980;  1980, 1981; Rees 1981; P e l l and Simony 1981, 1982;  1982; Murphy and Journeay  1982; G e t s i n g e r 1982, 1983a,  1983b; Murphy and Rees 1983; Raeside and Simony 1983; Rees and F e r r i  1983; Dechesne et a l . 1984; Murphy  1984).  6  1.3  REGIONAL GEOLOGIC SETTING The  Three L a d i e s Mountain/Mount Stevenson area  completely  w i t h i n t h e Omineca C r y s t a l l i n e  e a s t e r n o f two  rocks  i n the Canadian C o r d i l l e r a .  of p r i m a r i l y m e t a m o r p h i c r o c k s l i e s m e t a m o r p h o s e d and  Intermontane B e l t  B e l t took  or T e r r a n e ,  less of  t o t h e e a s t and  the  (Monger e t a l . 1 9 8 2 ) .  intense deformation  i n the  p l a c e i n m i d - J u r a s s i c time  t h e end  Omineca  during  composite  of the T r i a s s i c  terrane  ( E a s t e r n Assemblage  Q u e s n e l l i a , Cache C r e e k T e r r a n e ,  Stikine Block) subsequently  (Monger e t a l . 1 9 8 2 ) .  underthrust  t e r r a n e t o t h e n o r t h and contributing  t e r r a n e s , and  may  to North  and  Stikinia  Stikine of t h e  composite thus  (Monger e t a l . 1 9 8 2 ) .  which i n c l u d e s mainly  rocks  of  e a s t of a l l known a c c r e t e d  be c o n s i d e r e d t o be p a r a u t o c h t h o n o u s i n America.  the Three L a d i e s Mountain/Mount Stevenson a r e a ,  Snowshoe G r o u p c o n s i s t s of a t h i c k shelf  or  Block  east d u r i n g the m i d - J u r a s s i c ,  to increased deformation  t h e Snowshoe G r o u p , l i e s  The  p a r t of t h e r e s t  B a r k e r v i l l e Terrane,  s l o p e and  belt  f o u r v a r i o u s l y d i s p l a c e d t e r r a n e s w h i c h were  a m a l g a m a t e d by  In  Belt  of N o r t h America w i t h a w e s t e r n  composed o f  relation  Thrust  t o t h e west  R e g i o n a l m e t a m o r p h i s m and  The  between the  This  unmetamorphosed s u p r a s t r u c t u r a l r o c k s  t h e R o c k y M o u n t a i n F o l d and  collision  B e l t , which i s the  m a j o r e x p o s u r e s o f m e t a m o r p h i c and p l u t o n i c  infrastructural  Crystalline  lies  e l a s t i c s and  l a t e P r o t e r o z o i c age  the  s e c t i o n of c o n t i n e n t a l  minor c a r b o n a t e s  of  probable  w h i c h have been m e t a m o r p h o s e d u n d e r  7  amphibolite  facies conditions.  I t i s o v e r l a i n by more  shallow marine rocks of the l a t e P r o t e r o z o i c to P a l e o z o i c Cariboo Group, which are metamorphosed to g r e e n s c h i s t facies.  Both groups of rocks were f o l d e d and metamorphosed  d u r i n g the m i d - J u r a s s i c Columbian orogeny. contact between the study area  The  present  the Snowshoe Group and the Cariboo Group i n i s a low-angle postmetamorphic  the L i t t l e River  Fault.  fault  known as  2.  2.1  LITHOSTRATIGRAPHY  LITHOSTRATIGRAPHY OF SNOWSHOE GROUP The rocks i n the map area have not been p o s i t i v e l y  c o r r e l a t e d with those i n any other area of the C o r d i l l e r a . The high grade metamorphic rocks west of the North Arm of Quesnel Lake, c o n s i s t i n g of f o l d e d metasediments  and v a r i o u s  i n t r u s i v e phases, have been c a l l e d Snowshoe Group and assigned a l a t e P r o t e r o z o i c t o P a l e o z o i c age by Campbell (1978) and other workers.  Fletcher  (1972) d i v i d e d the same  rocks i n t o Isaac and Kaza Formations on the b a s i s of a s i m i l a r i t y t o h i s own f i e l d area at P e n f o l d Creek, east of the North Arm of Quesnel Lake.  Snowshoe Group rocks a t  Three L a d i e s Mountain may share some s i m i l a r i t i e s with the Snowshoe Group near Wells as mapped by S t r u i k  (1981), and  resemble p a r t s of the H o r s e t h i e f Creek Group as mapped by Pell  ( P e l l and Simony, 1981) near Blue R i v e r .  sedimentary s t r u c t u r e s showing have not been found.  d e f i n i t e facing  F o s s i l s and directions  O r i g i n a l bedding i s o b l i t e r a t e d by  cleavage and metamorphism, but l i t h o l o g i c  u n i t s that can be  d i s t i n g u i s h e d a r e shown on the map ( P l a t e I ) . The Snowshoe Group i n the Three L a d i e s Mountain map area may  be d i v i d e d  i n t o a lower s t r u c t u r a l sequence,  up to 6 km  t h i c k , u n d e r l y i n g most of the area from Mount Stevenson t o the North Arm of Quesnel Lake, and an upper sequence  structural  best d e f i n e d i n the Three L a d i e s Mountain a r e a ,  where i t i s approximately 3 km t h i c k . 8  Much of the t h i c k n e s s  9  may  be due  to s t r u c t u r a l  repetition.  been d i f f e r e n t before deformation The  lower  Thicknesses may  have  (see F i g u r e 2).  sequence c o n s i s t s of i n t e r l a y e r e d ,  grey micaceous q u a r t z i t e , brownish-weathering b i o t i t e - m u s c o v i t e s c h i s t , and minor impure c a l c - s i l i c a t e , and a m p h i b o l i t i c g n e i s s .  foliated  quartz-rich  carbonate,  G r a i n s i z e of the  psammitic l a y e r s i s r e l a t i v e l y constant and does not granule s i z e ; the coarse granule g r i t  and  conglomerate  c h a r a c t e r i s t i c of the Kaza Group elsewhere lacking.  Pelitic  are c o n s p i c u o u s l y  Sedimentary s t r u c t u r e s other than  l a y e r i n g and p o s s i b l e graded  bedding  rare i n the lower  sequence.  lithologic  were not  schist containing aluminosilicate  exceed  observed.  index minerals i s  Much of the s c h i s t i s  s e m i - p e l i t i c , containing quartz, b i o t i t e ,  muscovite,  p l a g i o c l a s e , and garnet, with no i n d i c a t o r f o r d i s t i n g u i s h i n g kyanite zone from s i l l i m a n i t e Amphibolite  and carbonate  zone.  occur as small l e n s e s and are not  a s s o c i a t e d with each other; amphibolite pods tend to occur near quartz d i o r i t i c may  sills,  whereas small carbonate  be found d i s p e r s e d w i t h i n the s c h i s t .  units  Greenish-grey,  h o r n b l e n d e - b i o t i t e g n e i s s i n t e r c a l a t e d with the paragneiss is  i n t e r p r e t e d as quartz d i o r i t i c  up to 25% of the f o l i a t e d  rocks.  sills, A l l are  and may  constitute  irregularly  intruded by q u a r t z - p l a g i o c l a s e - m u s c o v i t e pegmatite,  which  l o c a l l y c o n s t i t u t e 50% of the t o t a l rock mass. Mixed metasedimentary gneisses and quartz d i o r i t i c crop out from the western  shore of the North Arm  of  sills  Quesnel  10  UNIT Rock Type BRALCO MARBLE Coarse white calcite marble SNOWSHOE FORMATION UPPER SEQUENCE Grey, micaceous quartzite with interlayered pelite  Pelite Carbonate/Amphibolite Pelite with impure carbonate Thinly-layered micaceous quartzite and pelite LOWER SEQUENCE Amphibolite lenses Quartz dioritic gneiss Thinly-layered micaceous quartzite and pelite (Covered) Micaceous quartzite, pelite, rare carbonate, and migmatitic gneiss  Figure Ladies  2. L i t h o s t r a t i g r a p h y o f Snowshoe Mountain/Mount Stevenson area.  Group  i n the  Three  11 Lake south of G r a i n Creek to Mount Stevenson, and are practically  indivisible  s t r a t i g r a p h i c a l l y at the map  scale,  although some s i l l s have been mapped over s e v e r a l kilometres. resembling  A l t e r n a t i n g l i g h t e r and darker gneisses "lit-par-lit"  migmatite, in which d i s t i n c t i o n  between o r t h o g n e i s s e s and p a r a g n e i s s e s i s u n c e r t a i n , are c h a r a c t e r i s t i c of the lower p a r t of the s e c t i o n , near Quesnel Lake.  The uppermost  especially  part of the lower sequence  c o n s i s t s mostly of t h i n l y - l a y e r e d , b i o t i t e - r i c h  micaceous  q u a r t z i t e and s e m i - p e l i t e ; l a y e r s are 5 to 10 cm t h i c k and flaggy where exposed. pelite  T h i s f l a g g y micaceous q u a r t z i t e and  i s t r a n s i t i o n a l to the upper sequence.  The upper  boundary of the lower sequence i s a r b i t r a r i l y chosen at the top  of the f i r s t  c o n t i n u o u s l y mappable hornblende-bearing  quartz d i o r i t i c  sill,  metasedimentary  rocks.  which i s s u b p a r a l l e l to the i n t r u d e d  The upper sequence, i n c o n t r a s t , c o n t a i n s major carbonate and c a l c - s i l i c a t e , a m p h i b o l i t e , and common p e l i t i c schist.  I t l a c k s quartz d i o r i t i c  extensively  s i l l s , and i s not as  i n t r u d e d by pegmatite.  Internal stratigraphy i s  v a r i a b l e due to d i s c o n t i n u o u s l a y e r i n g and p o s s i b l e r e p e t i t i o n caused by complex  folding.  The  lowermost  s u b d i v i s i o n of the upper sequence c o n s i s t s of rusty-weathering p e l i t i c  s c h i s t , micaceous q u a r t z i t e ,  marble, and some m a g n e t i t e - b e a r i n g s c h i s t .  minor  Between Welcome  Mountain and Three L a d i e s Mountain the p e l i t i c  schist  c o n t a i n s l a r g e p o r p h y r o b l a s t s of garnet, s t a u r o l i t e , and  12 kyanite. about  Whitish quartzite  1 m thick  i n d i s t i n c t i v e , massive  i s i n t e r l a y e r e d with p e l i t e .  micaceous q u a r t z i t e occurs i n the lowermost section, transitional sequence.  layers  Some f l a g g y , part of t h i s  to s i m i l a r rocks i n the lower  T h i s mainly p e l i t i c  unit averages about 500 m  t h i c k , but i s thickened b y ~ l e u c o c r a t i c g r a n o d i o r i t i c sills  gneiss  north of Welcome Mountain.  O v e r l y i n g the lower p e l i t e s u b d i v i s i o n of the upper  i s the most  distinctive  sequence, c o n t a i n i n g a v a r i e t y of  rock types i n c l u d i n g hornblende amphibolite, carbonate, and c l a s t i c metasedimentary  rocks.  Most of the u n i t ,  which  v a r i e s i n t h i c k n e s s from 10 to over 150 m, weathers r e c e s s i v e l y to reddish-brown s o i l , d i s t i n c t i v e both on a e r i a l photographs and i n the f i e l d .  T h i c k , massive  amphibolite l a y e r s are more r e s i s t a n t , as on the north  face  of  Three L a d i e s Mountain, where a sheer 60 degree d i p - s l o p e  of  a m p h i b o l i t e drops 500 m from the summit to the v a l l e y .  The a m p h i b o l i t e u n i t  itself  a m p h i b o l i t i c metasedimentary between p e l i t i c  appears to be a combination of rocks formed  in reaction  and carbonate u n i t s during  metamorphism, and metamorphosed d i o r i t i c  regional  sills.  Reaction  a m p h i b o l i t e i n c l u d e s n e a r l y monomineralic l a y e r s of metamorphic hornblende g r a i n s up to s e v e r a l c e n t i m e t r e s long, as w e l l as more common c a l c - s i 1 i c a t e gneiss which may c o n t a i n hornblende, d i o p s i d e , garnet, e p i d o t e , p l a g i o c l a s e , and c a l c i t e .  Hornblende  i n l a y e r e d a m p h i b o l i t e and  calc-silicate  rocks tends to be a l i g n e d along metamorphic  13 lineations  ( u s u a l l y F2 f o l d a x i a l t r e n d s ) , or e l s e i n  r a d i a t i n g habit on f o l i a t i o n planes be e i t h e r Other  ( g a r b e n s c h i e f e r ) ; i t may  synkinematic or postkinematic to F2 s t r u c t u r e s . amphibolite, o c c u r r i n g i n d i s c o n t i n u o u s pods, i s  u n f o l i a t e d , with c o a r s e - g r a i n e d , blocky hornblende and plagioclase, Examination  resembling d i o r i t e  of t h i n s e c t i o n s shows that the amphibole i s  pseudomorphic a f t e r  former  blockier-shaped  although no r e l i c t pyroxene was Other  i n hand specimen.  pyroxene,  identified.  rock types w i t h i n the carbonate-amphibolite  unit  i n c l u d e impure c a l c i t e marble up to 20 m t h i c k , minor c a l c - s i l i c a t e zones between p e l i t e and carbonate f l a k y q u a r t z - b i o t i t e s c h i s t , black s i l t i t e , pyritic quartzite black s i l t i t e  layers,  and green,  (with up to 20 % p y r i t e l o c a l l y ) .  i s a d i s t i n c t i v e rock type, o c c u r r i n g as  d i s c o n t i n u o u s l a y e r s up to 5 m t h i c k of f i n e - g r a i n e d , black, g r a p h i t i c quartz s i l t i t e sheen,  The'  and l o c a l  with a s l i g h t  phyllitic  " p e n c i l cleavage", i n t e r f o l d e d  porphyroblastic p e l i t i c  schist  limy s c h i s t , and a m p h i b o l i t e .  hard,  with  ( s t a u r o l i t e - k y a n i t e grade), The black s i l t i t e  i s not a  g r a p h i t e s c h i s t , as i t i s not s c h i s t o s e . The carbonate-amphibolite u n i t  i s more h i g h l y  fractured  than the surrounding p e l i t e and q u a r t z i t e , and has a p p a r e n t l y s u f f e r e d more hydrothermal  alteration.  C r o s s c u t t i n g rusty zones with sparse s u l f i d e  mineralization  are a s s o c i a t e d with minor, l a t e , n e a r - v e r t i c a l the nearby  pelitic  schist  f a u l t s , and  i s more s e v e r e l y r e t r o g r a d e d to  14 c h l o r i t e than that The  farther  from the  carbonate-amphibolite unit  carbonate-amphibolite. is generally  overlain  by  another s t a u r o l i t e - k y a n i t e s c h i s t with minor magnetite-bearing l a y e r s , and of grey, micaceous q u a r t z i t e garnetiferous a coarsely The  1978;  The  i n t e r l a y e r e d with quartzose,  the  base of  Snowshoe Group near Maeford  mapped as Cunningham Formation  Klepacki  assigned to the marble by  km)  c r y s t a l l i n e white marble.  previously  (Campbell  (up to 2  mica s c h i s t , which continues up to the  marble o v e r l y i n g  Lake was  a thick section  1981), and  has  recently  Snowshoe Group as the B r a l c o  Struik  (?)  been  Succession  (1983).  marble i s up to 500  m t h i c k near Maeford Lake, forms  l i g h t - g r e y to b u f f - w e a t h e r i n g c l i f f s ,  and  several  It i s a  k i l o m e t r e s to the  northwest.  can  be  traced  for  coarsely  c r y s t a l l i n e , massive, r e l a t i v e l y pure white c a l c i t e marble, with l o c a l  s i l i c e o u s dolomite c o n t a i n i n g  of white t r e m o l i t e . places, rootless  and  Layering  i s marked by  criss-crossing  of bedding.  The  f o l d i n g and Typical  f o l i a t i o n s which may  cleavages from v a r i o u s cataclastic  f a b r i c , or as merely  and  rare  possible  specimens d i s p l a y be  f o l d phases or,  interpreted  as  in some p l a c e s ,  some t h i n , garnet and  as a  fractures.  base of the marble i s apparently conformable  Snowshoe Formation p e l i t e and  i  i s d i s c o n t i n u o u s , l e n s o i d a l in  f a i n t grey streaks  i s o c l i n e s implying  transposition  r a d i a t i n g needles  quartzite.  hornblende-bearing  on  Although there calc-silicate  are  15 l a y e r s in the s c h i s t below the c o n t a c t , the Snowshoe Group i s not g r a d a t i o n a l across the contact with the marble. There are no marble u n i t s w i t h i n the Snowshoe near contact.  The  the  g e n t l e r d i p of the marble, in c o n t r a s t to a  steeper d i p in the u n d e r l y i n g p e l i t e , may  be a r e s u l t  measuring d i f f e r e n t  u n i t s , or  foliations  in the two  for a d u c t i l i t y c o n t r a s t or t e c t o n i c c o n t a c t .  The  i s f o l d e d along with the rocks on both s i d e s , but no c o n v i n c i n g evidence The  that i t i s a f a u l t  of evidence  contact there i s  contact.  environment of d e p o s i t i o n of the Snowshoe Group  was  o f f s h o r e from the margin of a c o n t i n e n t which c o n t r i b u t e d fine p e l i t i c  and  c o a r s e r q u a r t z - r i c h c l a s t i c d e t r i t u s to a  r e l a t i v e l y s t a b l e but  s u b s i d i n g slope or b a s i n .  s e c t i o n of q u a r t z i t i c and  pelitic  in the Mount Stevenson area  The  thick  rocks exposed p a r t i c u l a r l y  (Snowshoe Group "lower  sequence") c o u l d have been d e p o s i t e d  o f f the c o n t i n e n t a l  slope in a r i s e environment, whereas the carbonate and p e l i t e higher  i n the s e c t i o n must have been d e p o s i t e d  water shallower  than about 200  m.  The  limy in  Snowshoe Group i s  t y p i c a l of sediments i n c l u d e d in the l a t e P r o t e r o z o i c package of the C o r d i l l e r a n miogeosyncline; c h a r a c t e r i z e d by voluminous g r i t s and  shale d e p o s i t e d  t h i c k c l a s t i c wedge, with some bank and and minor mafic The  v o l c a n i c s (Poulton and  i t is  offbank  in a  carbonate,  Simony 1980).  s t r a t i g r a p h i c p o s i t i o n of the Snowshoe Group has  long been u n c l e a r ; no Snowshoe Group was  f o s s i l s have been r e p o r t e d .  The  b e l i e v e d by e a r l y workers to o v e r l i e  the  16 Cariboo Group, and maps by R.B.  i s shown as  Campbell  "Lower Cambrian or l a t e r "  (1961, 1963).  Later work by  Campbell  et a l . (1973) suggested that the Snowshoe Group was western f a c i e s of the Kaza Group" (p. 32), P r o t e r o z o i c Windermere age.  Getsinger  Creek Group, rather  thus of  late  than the Kaza Group.  i s s i m i l a r to that d e s c r i b e d  Simony (1980) for the H o r s e t h i e f Proterozoic  age.  Creek Group of  S t r u i k proposed that one  in age,  based on u n c e r t a i n  The  Ladies  by Poulton  of the  uppermost B.C.), i s  lithologic  c o r r e l a t i o n with a nearby u n i t c o n s i s t i n g of marble, and  crinoidal  However, i t would be  involved  (even along  as  unit in  further uncertainty  i n making l i t h o l o g i c c o r r e l a t i o n across s t r i k e ) of u n f o s s i l i f e r o u s rocks  themselves cannot be t r a c e d with complete directly  pure  to t r y to c o r r e l a t e t h i s u n i t with any  the Three Ladies Mountain area, be  slate,  limestone which y i e l d e d M i s s i s s i p p i a n  conodonts ( S t r u i k 1982). speculation  and  late  u n i t s of the Snowshoe Group (northwest of Wells, late Paleozoic  late  Proterozoic  sedimentology of the Snowshoe Group in the Three Mountain area  "a  (1982) suggested that  the Snowshoe Group resembles p a r t s of the Horsethief  and  on  would  100  km  which  confidence  i n t o the Three Ladies Mountain—Mount  Stevenson  area. T h i s study suggests that the age Snowshoe Group in t h i s area  of at l e a s t most of  i s late Proterozoic,  comparison with d e s c r i p t i o n s from other according  to a p r e l i m i n a r y  areas,  by  as w e l l  Rb-Sr whole rock date of  as  the  17 approximately s e c t i o n on  750 Ma  f o r the time of sedimentation  geochronology).  (see  18 2.2 LITHOSTRATIGRAPHY ABOVE THE LITTLE RIVER FAULT The s t r a t i g r a p h y of the low-grade marble and p h y l l i t e above the L i t t l e  River F a u l t  i s not yet uniquely  defined.  However, the rocks i n t h i s area have been a s s i g n e d to some part of the l a t e P r o t e r o z o i c to lower Cambrian (Campbell  1978; Klepacki  The lowermost  1981; S t r u i k  Cariboo Group  1983) (see F i g u r e 3).  u n i t s i n the upper p l a t e of the L i t t l e  River F a u l t are exposed at Limestone P o i n t , j u s t east of where the f a u l t d i s a p p e a r s i n t o Quesnel Lake. bluff  Below the  i s a sequence of i n t e r l a y e r e d grey p h y l l i t e and  t h i n l y - b e d d e d q u a r t z i t e , most of which  i s pinkish-colored  from i r o n - s t a i n i n g , and which i s kinked with chevron Bedding i s s t i l l places.  folds.  d i s t i n g u i s h a b l e from cleavage i n some  B i o t i t e p o r p h y r o b l a s t s are common i n  m u s c o v i t e - c h l o r i t e p h y l l i t e below occur north of S e r v i c e Creek.  the limestone, but do not  T h i s u n i t resembles a  d e s c r i p t i o n of the uppermost  part of the Isaac Formation,  "grey p h y l l i t e with s p a r s e l y  interbedded s i l t s t o n e and  limonitic et  f i n e - g r a i n e d sandstone" i n Campbell  a l . (1973, p. 34). Limestone Point  i s named f o r the massive, white  c r y s t a l l i n e marble which forms a prominent c l i f f high v i s i b l e Quesnel Lake. but  from the whole length of the North Arm of I t resembles the B r a l c o marble  occupies a d i f f e r e n t  position.  about 50 m  s t r u c t u r a l and s t r a t i g r a p h i c  Bedding i s d i f f i c u l t  i n d i c a t e d by small, t h i n ,  i n appearance,  to d i s t i n g u i s h , but may be  sandy l a y e r s i n the midst of more  19  Rock Type Grey marble (Service Ridge)  50 m  Greenish phyMite and minor quartzite Intercalated grey marble and calcareous phy Mite  (Covered)  Green and grey phyllite (Covered) White marble (Limestone Point) Pink and grey quartzite and phyllite, with biotite  Figure  3.  Lithostratigraphy  above  L i t t l e River  Fault.  20 massive l a y e r s .  Most of the marble  i s pure c a l c i t e , but  some dolomite and more s i l i c e o u s l a y e r s are a l s o present. Carbonate b r e c c i a with brownish-weathering lenses  (2-10 cm)  in a whiter matrix i s f o l i a t e d p a r a l l e l to the base of the marble u n i t .  I t i s unclear whether  the contact between the  marble and the u n d e r l y i n g p e l i t e and q u a r t z i t e i s sedimentary or t e c t o n i c . thick g l a c i a l d r i f t ;  The marble  i s d i r e c t l y o v e r l a i n by  i t s upper c o n t a c t  i s not exposed.  The  marble at Limestone Point may be c o r r e l a t e d with the Cunningham Formation, as shown on Quesnel Lake map sheet (Campbell  1978).  The next s e c t i o n of metasedimentary  rocks to the north,  and s t r u c t u r a l l y higher than the marble of Limestone P o i n t , i s a sequence of i n t e r l a y e r e d marbles and limy,  siliceous  p h y l l i t e , which i s exposed up to the top of the ridge above S e r v i c e Creek. least  From Quesnel Lake north of S e r v i c e Creek, at  100 m of grey-green, s i l v e r y p h y l l i t e  i s o v e r l a i n by  a l t e r n a t i n g c l i f f s of grey, c r y s t a l l i n e c a l c i t e marble and poorly-exposed, r e c e s s i v e l y - w e a t h e r e d l a y e r s of limy phyllite.  There are at l e a s t s i x l a y e r s of marble of n e a r l y  uniform t h i c k n e s s  (10-15 m) and s i m i l a r l i t h o l o g y ,  slightly  from grey to p i n k i s h with black  in color  varying streaks.  S i m i l a r a l t e r n a t i n g marble and p h y l l i t e near the saddle where the L i t t l e River F a u l t c r o s s e s the ridge are probably c o r r e l a t i v e with those on the slope above Quesnel Lake. Poor exposure prevents c e r t a i n d e t e r m i n a t i o n of whether the apparent r e p e t i t i o n of rock types i s s t r a t i g r a p h i c or  i  21 s t r u c t u r a l , or both.  T h i s sequence (which i s at l e a s t  500 m  t h i c k ) has been mapped by K l e p a c k i (1981) as Yankee B e l l e Formation, and by S t r u i k resembles  (1983) as Cunningham Formation.  the d e s c r i p t i o n of the  It  "rhythmic  l i m e s t o n e - s i l t s t o n e - s h a l e f a c i e s " of the Yankee B e l l e Formation  in Campbell  Exposure  et a l . (1973).  i s b e t t e r near the top of the r i d g e , where  another greenish-grey p h y l l i t e with t h i n  intercalated  q u a r t z i t e l a y e r s u n d e r l i e s a t h i c k , grey marble, the peak l a b e l l e d  "6287'" (geodetic survey p o i n t ) ,  i n f o r m a l l y r e f e r r e d to as S e r v i c e Mountain It  which forms  or S e r v i c e Ridge.  i s p o s s i b l e to c o r r e l a t e t h i s p h y l l i t e u n i t with the  Midas Formation, which i s a l s o r e c e s s i v e and  incompetent  where f o l d e d , and u n d e r l i e s a r e s i s t a n t  marble  (Campbell et a l . 1973).  grey  The Cariboo Group s u c c e s s i o n may  have been t h i n n e r i n t h i s area than i n the type  sections.  No u n i t resembling Yanks Peak Formation q u a r t z i t e  was  ident i f ied. The grey marble at "6287'" i s about  50 m t h i c k and d i p s  g e n t l y to the northeast except where t h i c k e n e d and by major f o l d s , as at the top of the r i d g e . i s the most r e s i s t a n t u n i t ridges; i t may  The grey  marble  i n the area and forms the tops of  i t s upper contact was be t h i c k e r than 50 m.  stylolitic,  distorted  not observed  i n t h i s a r e a , so  It i s a fine-grained,  s i l i c e o u s , grey c a l c i t e marble  with white  and  grey s t r e a k y l a y e r i n g , and l o c a l p y r i t e , and i s inhomogeneous i n t e x t u r e .  It i s less coarsely  crystalline  22 than the B r a l c o marble,  and c o u l d be c a l l e d a limestone,  although i t has been r e c r y s t a l l i z e d conditions.  in g r e e n s c h i s t f a c i e s  C l o t s of more r e s i s t a n t white carbonate  and o v a l r i n g s about  1 cm a c r o s s in one  sample  suggest  r e c r y s t a l l i z e d o r g a n i c a l l y - p r o d u c e d t e x t u r e s , but r e c o g n i z a b l e f o s s i l s were found. grey marble about  no  T h i n , slabby l a y e r s of  5 cm t h i c k , which look l i k e bedding  outcrop s c a l e , d i p 30-50° to the n o r t h e a s t . intersect  blebs  These l a y e r s  the more s h a l l o w l y e a s t - d i p p i n g bedding  c o n t a c t s of the mappable u n i t at a high a n g l e . are i n t e r p r e t e d as bedding  on  and  These l a y e r s  transposed i n t o F2 a x i a l  plane  or i e n t a t i o n . L o c a l l y near S e r v i c e Mountain the grey marble i s c r o s s c u t by n e a r l y v e r t i c a l  zones of buff to pink  c a l c i t e / d o l o m i t e b r e c c i a t r e n d i n g north to n o r t h e a s t . C a l c i t e c r y s t a l s up to 5 cm and pink c a l c i t e marble angular c l a s t s weathering.  form  i n a b r e c c i a with boxwork-1ike, p i t t e d  These areas are i n t e r p r e t e d as hydrothermally  a l t e r e d zones along f a u l t s or f r a c t u r e s w i t h i n the grey marble,  r a t h e r than as separate u n i t s .  Struik  (1983) d i v i d e d the grey marble i n t o an upper u n i t  on S e r v i c e Mountain, which he c o r r e l a t e d with the Mural Formation,  and  the r e s t , which he c o r r e l a t e d with the  Cunningham Formation.  T h i s study i n t e r p r e t s the grey marble  as a s i n g l e , continuous, but complexly  f o l d e d marble u n i t  probably c o r r e l a t i v e with the Lower Cambrian Format i o n .  Mural  23 The e n t i r e s e c t i o n of rocks above the L i t t l e  River F a u l t  i s assigned here, with some u n c e r t a i n t y , to undivided Cariboo Group. The environment mainly nearshore, Campbell  of d e p o s i t i o n of the Cariboo Group shallow-water  According to  et a l . (1973), the c o n d i t i o n s v a r i e d  d e l t a i c environment  to l i t t o r a l ,  r e s t r i c t e d marine environments all  marine.  l e s s than 200 m.  was  from a  fluvial  shallow s h e l f , or  to deeper  marine depths,  but  These c o n d i t i o n s are reasonable f o r  the types of sediments  observed, although there i s l i t t l e  evidence to support an a l l u v i a l  environment  i n t h i s area  because of lack of coarse e l a s t i c s or r e c o g n i z a b l e sedimentary The  structures.  l a t e P r o t e r o z o i c to Cambrian Cariboo Group  deposited closer  to shore and  Snowshoe Group.  E i t h e r the Cariboo Group was  approximately  was  i n shallower water than the laterally  t i m e - e q u i v a l e n t to the Snowshoe Group, and  t h e i r present j u x t a p o s i t i o n  i s due  to t e l e s c o p i n g of the  c o n t i n e n t a l margin d u r i n g deformation; or the Cariboo Group was  d e p o s i t e d conformably  upon and o v e r l y i n g the Snowshoe  Group, and t h e i r present j u x t a p o s i t i o n uplift  of the deeper  the L i t t l e  i s due  to g r e a t e r  rocks with a normal displacement  River F a u l t .  A combination  along  of these  interpretations i s preferred. If hanging  the c o r r e l a t i o n of t h i s s e c t i o n of rocks i n the w a l l of the L i t t l e R i v e r F a u l t with a p p a r e n t l y  u n i n t e r r u p t e d Cariboo Group i s c o r r e c t , then the Pleasant  24 V a l l e y Thrust, as mapped by S t r u i k of the L i t t l e River boundary.  (1983) i n the upper  F a u l t , cannot be a major  Other s t r u c t u r a l i m p l i c a t i o n s  are discussed  in the f o l l o w i n g  s e c t i o n on  plate  terrane  of t h i s c o r r e l a t i o n structure.  3.  3.1 DEFORMATION:  STRUCTURE  FOLD PHASES  3.1.1 FOLD NOTATION Four d i s t i n c t phases of f o r d i n g distinguished  on the b a s i s  surfaces,  associated  relations  of r e f o l d e d  have been  of o r i e n t a t i o n  metamorphic  of a x i a l  f a b r i c s , and f i e l d  f o l d s and i n t r u s i v e rocks.  These  f o l d phases are designated as F1, F2, F3, and F4 (see Figure 4 ) .  Metamorphic r e c r y s t a l l i z a t i o n was  synkinematic to postkinematic to F2 f o l d i n g , c r y s t a l l i z a t i o n outlasting relationships.in  metamorphic  folds,  crosscutting  i n t r u s i v e c o n t a c t s , and o v e r p r i n t i n g  fabrics.  folds; Figures  Time  the f i e l d a r e determined by  o b s e r v a t i o n s of r e f o l d e d relationships,  deformation.  with  of  F i g u r e s 5 to 11 are sketches of  12 to 22 show domains and s t e r e o g r a p h i c  project ions. Pre-F2 f o l d s have been d i v i d e d (F1A  i n t o two subphases  and F1B) of i s o c l i n a l and t i g h t f o l d s which may be  r e l a t e d and are commonly i n d i s t i n g u i s h a b l e except their  i n a few p l a c e s . separation.  refolded  Two l i n e s of evidence l e d to  Some i n t r a f o l i a l  p r i o r to F2 f o l d i n g  isoclinal  i s o c l i n e s were  (see F i g u r e S4 A ) .  Mt. Stevenson, quartz d i o r i t i c crosscut  i n the f i e l d  Near  gneiss s i l l s l o c a l l y  f o l d limbs and are i s o c l i n a l l y and 25  26  F1 A NE  SVV^.  F1 B F2 ^  ^  ^  ^  ^  ^  F3 F4 F i g u r e 4.  Diagrammatic  ISOCLINAL AXIAL PLANES PARALLEL TO FOLIATION  NORTH- & EAST-VERGING AXIAL PLANES 084/48N or VARIABLE AXES WNW WEST-VERGING AXIAL PLANES 118/60NE AXES NW 315-340/30-45 VARIABLE AXIAL PLANES S W - or E-DIPPING AXES NW or SE UPRIGHT WARPS AXIAL PLANES 040/90 AXES NE 020-050/10-20  summary of f o l d phases.  27  tightly  folded  overprinted  i  by  themselves; F2  fabrics.  these  structures  are  28 3.1.2  OUTLINE OF FOLD PHASES  3.1.2.1 F1 A True  isoclines, particularly  intrafolial  isoclines  and those r e f o l d e d by l a t e r  f o l d phases, are designated  F1A  Limbs are attenuated  (see F i g u r e s 5 and  6).  that some have r o o t l e s s hinges. approximate that of s i m i l a r 1967).  except  F o l d geometry tends to  folds  (S,), p a r a l l e l  locally  variable.  I I , Ramsay  to the dominant  to c o m p o s i t i o n a l l a y e r i n g ( S ) , 0  i n the carbonate  l a y e r s , where they are  F o l d axes were not easy to measure i n most  intrafolial  i s o c l i n e s ; they show no p a r t i c u l a r p a t t e r n  but tend to l i e i n the northwest plunge  (Type  A x i a l planes are a l l p a r a l l e l  foliation  such  northeast.  The  quadrant;  some a l s o  i n c o n s i s t e n t trends are  i n t e r p r e t e d as c o n s i s t e n t with an e a r l i e r  fold  episode.  3.1.2.2 F1B T i g h t to i s o c l i n a l , asymmetrical foliation  f o l d s which  fold  (S,) and are a l s o o v e r p r i n t e d by c r o s s c u t t i n g  F2 a x i a l plane c r e n u l a t i o n cleavage phase F1B.  They tend to verge  ( S ) are assigned to 2  to the north and east,  with SW-NW d i p p i n g a x i a l p l a n e s , u n l i k e the more obvious F2 f o l d s which verge west with NE-dipping Phase F1B  f o l d s are r a r e l y preserved, most commonly i n  competent q u a r t z i t e l a y e r s i n the lower  sequence, as  near Welcome Mountain and Mount Stevenson; dioritic  a x i a l planes.  the quartz  s i l l s a l s o show t h i s s t y l e of f o l d i n g .  These  29  Figure 5. A. Refolded i s o c l i n e (F1A, F1B) in q u a r t z i t e ; hammer i s p a r a l l e l to dominant r e g i o n a l f o l i a t i o n . 2 km east of Three Ladies Mountain. • B. Q u a r t z i t e l a y e r s (Q) preserve F1 i s o c l i n a l and NE-verging (FIB) f o l d s whereas p e l i t i c l a y e r s (P) are r e f o l d e d i n t o SW-verging F2 f o l d s . 3 km east of Mount Stevenson.  30  F i g u r e 6 A and B. Q u a r t z i t i c l a y e r s (Q) preserve F1 i s o c l i n e s whereas surrounding p e l i t e (P) i s c r e n u l a t e d and i n c i p i e n t l y transposed along NE-dipping F2 a x i a l p l a n e s . 3 km south of Mount Stevenson.  31 more competent l a y e r s folded by b u c k l i n g , whereas the l e s s competent p e l i t i c zones, later  l a y e r s show t h i c k e n i n g i n hinge  as w e l l as a tendency folding.  F1B  to become transposed  by  f o l d s were recognized l o c a l l y  by  c l e a r c r o s s c u t t i n g r e l a t i o n s h i p s i n which the Z-folds had  r e t a i n e d t h e i r geometry in the more  competent l a y e r s whereas the p e l i t i c developed  F1B  layers  had  c r e n u l a t i o n cleavage a x i a l planar to  superimposed F2 S - f o l d s on the same outcrop  (see F i g u r e  5 B) . On most outcrops, F1B with F2 f o l d axes. lineation  f o l d axes are n e a r l y c o a x i a l  On outcrops where a quartz rod  l i e s at an angle to the dominant  the quartz rod l i n e a t i o n  is parallel  whereas the dominant l i n e a t i o n  lineation,  to F1B  fold  (a combination  of  i n t e r s e c t i o n and mineral o r i e n t a t i o n l i n e a t i o n s ) parallel  to F2 f o l d  were formed during e a r l y and  observed  folding.  F1B  Both F1A and F1B  appear to f o l d previous  and c o m p o s i t i o n a l l a y e r i n g . seen  lies  axes.  T h i s i m p l i e s that most quartz rod l i n e a t i o n s  3.1.2.3 F1A  axes,  foliations  The dominant f o l i a t i o n  (S,)  i n outcrop i n the Three L a d i e s Mountain/ Mount  Stevenson  area i s a x i a l planar to F1A and F1B  variation  i n limb a t t i t u d e s l i e s w i t h i n the spread of  values f o r each limb and they are e s s e n t i a l l y  folds;  the a x i a l planes, showing that  parallel.  32 No pre-F2 f o l d s l a r g e r than o u t c r o p s c a l e have been positively  identified  i n the f i e l d  that they may be there compositional  i n the form of r e p e t i t i o n of  layering.  Ladies Mountain  but i t i s suspected  A possible closure  near Three  (between middle and south peaks) d e f i n e d  by narrowing and p i n c h i n g with p o r p h y r o b l a s t i c ,  out of an amphibolite u n i t ,  aluminous p e l i t e on e i t h e r s i d e ,  i s f o l d e d around an F2 synform (about 3 km a c r o s s ) , ending i n the hinge zone of the c o r r e s p o n d i n g It but  i s p o s s i b l e that t h i s s t r u c t u r e the regular  succession  i s not an F1 c l o s u r e  truncated  n e a r - p a r a l l e l to the F2 a x i a l plane Plate I ) . the  antiform.  by a t e c t o n i c (see F i g u r e  7 and  The more monotonous q u a r t z i t e s and p e l i t e s of  lower sequence east  Lake may c o n t a i n  of Mount Stevenson to Quesnel  s e v e r a l r e p e t i t i o n s of o r i g i n a l  s t r a t i g r a p h y , but even more e x t e n s i v e  fieldwork  not  are no c l e a r  be expected t o show t h i s as there  marker u n i t s and the sequence i s t h i c k e n e d granitoid  slide  intrusions.  would  by v a r i o u s  If pre-F2 f o l d s do e x i s t on a  r e g i o n a l s c a l e , they could  be very l a r g e and e s s e n t i a l l y  i s o c l i n a l , with limbs p o s s i b l y exceeding  10 km i n  length. The  reasons f o r s e p a r a t i n g  F1 f o l d s i n t o F1A and F1B  are that  (1) i n some p l a c e s , m i d - P a l e o z o i c quartz  dioritic  gneiss,  which appears to c r o s s c u t  i s o c l i n e s and f o l i a t i o n , are o v e r p r i n t e d  earlier  i s f o l d e d by t i g h t f o l d s which  by F2 a x i a l planar  f a b r i c , and (2) some  33  F i g u r e 7. T e c t o n i c p r o f i l e through Three L a d i e s Mountain p r o j e c t e d t o a s u r f a c e with o r i e n t a t i o n 060/45 SE, approximately p e r p e n d i c u l a r to F2 f o l d a x i s (330/45), with datum (X-X') a t 1970 m (6000').  34 i s o c l i n e s are r e f o l d e d by n e a r l y  isoclinal  are  Such r e l a t i o n s h i p s are  i n turn  f o l d e d by F2 f o l d s .  f o l d s which  not c o n c l u s i v e , but rather suggestive  evidence h i n t i n g  at a p o s s i b l e P a l e o z o i c  deformation.  Because the  evidence f o r s e p a r a t i n g  F1A from F1B i s sparse, and  because i t i s p o s s i b l e to e x p l a i n these s t r u c t u r e s i n more than one way, they are designated one  as subphases to  episode of F1 or "pre-F2" f o l d i n g .  3.1.2.4 F2 Folds assigned penetrative  to phase F2 are the most prominent  s t r u c t u r e s seen i n the Three  Mountain/Mount Stevenson area  (see F i g u r e s  9 A, 11, 13-15, and 19). They vary microscopic  to macroscopic.  Ladies 5 B, 6, 8,  i n s c a l e from  A l a r g e F 2 - f o l d with  wavelength about 5 km has been mapped on Three Mountain lie  (see map P l a t e I and F i g u r e  in large cirques,  limb  7).  Ladies  Hinge zones  i n which steep north  faces are  f o l d s are t i g h t to normal, i n c l i n e d  plunging,  dipslopes. F2  asymmetrical S - f o l d s (S,).  that f o l d the dominant  Some t h i c k e n i n g  especially  foliation  of l a y e r s i n f o l d hinges  i n the more p e l i t i c  layers.  occurs,  They are mainly  f l a t t e n e d f l e x u r a l s l i p f o l d s (Type IC and I I , Ramsay 1967). folding,  Peak metamorphic c o n d i t i o n s accompanied F2 implying  format i o n .  a warm, d u c t i l e environment of  35  F i g u r e 8. A. S W - v e r g i n g F2 f o l d i n q u a r t z i t e (Cj) i s f l a n k e d by p e l i t e (P) s h o w i n g N E - t r e n d i n g F4 c r e n u l a t i o n s ( l e f t ) and i n t e r f e r e n c e p a t t e r n s ( r i g h t ) . 2 km e a s t of T h r e e Ladies Mountain. B. I s o c l i n a l l y f o l d e d q u a r t z s e g r e g a t i o n (Q) and q u a r t z o - f e l d s p a t h i c l a y e r (QF) i n k y a n i t e - g r a d e g n e i s s a r e r e f o l d e d by S W - v e r g i n g F2 f o l d . Large f e l d s p a r p o r p h y r o b l a s t s form p e g m a t i t i c s e g r e g a t i o n ( p a t t e r n ) a l o n g F2 a x i a l p l a n e , s u g g e s t i n g p a r t i a l m e l t o r i g i n f o r p e g m a t i t e d i k e s . 3 km s o u t h e a s t of T h r e e L a d i e s M o u n t a i n .  36  Probably over 75% of f o l d s d e f i n i t e l y F2 f o l d s verge southwest. NE-dipping  as  They have c o n s i s t e n t l y  a x i a l planes with average  F o l d axes plunge  identified  20 to 60 degrees  attitude  to the NNW  118/60 NE. and  NW,  v a r y i n g from more steep at Three Ladies Mountain to l e s s steep at Mount Stevenson  (see s t e r e o g r a p h i c  projections). Well-defined mineral l i n e a t i o n s s u b p a r a l l e l to F2 f o l d axes.  ( L ) are p a r a l l e l or 2  F o l d axes and  lineations  are p e r p e n d i c u l a r to the plane c o n t a i n i n g p o l e s to f o l d e d f o l i a t i o n , demonstrating  the g e n e r a l l y  c y l i n d r i c a l nature of the f o l d i n g . obvious  F2 f o l d s are most  i n c o n t r a s t i n g and competent c o m p o s i t i o n a l  l a y e r s such as q u a r t z i t e s and carbonates. cleavage  (S ) 2  i s developed  in p e l i t e s , and  Grenulation  p a r a l l e l to F2 a x i a l  i s completely transposed p a r a l l e l to the  F2 a x i a l plane i n some p l a c e s , p a r t i c u l a r l y hinge  planes  in l a r g e  zones.  Parasitic  f o l d s on the l a r g e S-shaped f o l d at Three  L a d i e s Mountain are a l s o dominantly  west-verging,  although some r e v e r s a l s i n vergence  were noted.  both S-shaped and  Z-shaped f o l d s are seen  Where  i n the same  outcrop, the Z - f o l d s are o v e r p r i n t e d by c r e n u l a t i o n cleavage a x i a l planar to the S - f o l d s (see F i g u r e 5 B). 3.1.2.5 F3 L o c a l k i n k i n g and c r e n u l a t i o n  f o l d s which are  c l e a r l y post-F2 have been a s s i g n e d to F3  (see F i g u r e  9).  37  F4  NW F3  <  SE  1 6 2 8 7 ' "* ^  F3  rn^^^  ^_  _  —  500 m  F i g u r e 9. A, B, C. G e n e r a l i z e d c r o s s s e c t i o n s through S e r v i c e Mountain ("6287'") showing geology and r e l a t i o n s h i p s among F2, F3, and F4 f o l d s , m = marble; p = p h y l l i t e and micaceous q u a r t z i t e . The small "B" i n A l o c a t e s the outcrop shown i n B.  38  Many F3 f o l d s are c o a x i a l or nearly so with F1 and F2 f o l d s plunging NW, southwest-dipping  and some are e a s t - v e r g i n g with a x i a l planes.  A x i a l planes of F3  f o l d s tend to be r e l a t i v e l y upright except group,  which appears  to be p a r a l l e l  f o r one  to j o i n t  planes  p e r p e n d i c u l a r to F2 f o l d axes (see F i g u r e 18 C ) . lower angle f e a t u r e s may be due to s l i g h t l y f a u l t - r e l a t e d deformation. effect  These  later  F3 deformation had the  of t i g h t e n i n g and steepening F2 s t r u c t u r e s i n the  Three L a d i e s Mountain area, and may have s l i d i n g along steepened chevron  F2 a x i a l p l a n e s .  initiated Kinks and  f o l d s are p a r t i c u l a r l y well-developed i n  phyllites  i n the hanging  but l e s s v i s i b l e  w a l l of the L i t t l e R i v e r F a u l t ,  i n the more h i g h l y metamorphosed  Snowshoe Group s c h i s t , where F3 f o l d s are observed mainly  in p e l i t i c  were observed.  units.  Rare sets of conjugate  kinks  V a r i a b l e f o l d a t t i t u d e s and sparse  occurrence account  f o r the i r r e g u l a r and spread-out  p a t t e r n on the s t e r e o g r a p h i c p r o j e c t i o n s  (see F i g u r e  18 C and D). In one case, e a s t - v e r g i n g , NW-plunging F3 crenulation  f o l d s f o l d i n g F2 a x i a l plane cleavage i n  p e l i t e are c l e a r l y  superimposed  on an e a s t - v e r g i n g  WNW-plunging F1B f o l d preserved i n a f e l s i c Figure  l a y e r (see  10). In t h i s sample, q u a r t z - r o d l i n e a t i o n s are  parallel  to the F1B f o l d a x i s and mica c r e n u l a t i o n s are  parallel  to the F3 f o l d a x i s , they d i v e r g e by about 25°.  Quartz-Biotite-Muscovite Schist Sample 81-286 F1 Axis  F i g u r e 10. Sketch of sample 81-286, a q u a r t z - b i o t i t e muscovite s c h i s t from S t a t i o n 104, showing F3 c r e n u l a t i o n cleavage i n p e l i t e c r o s s c u t t i n g an F1 f o l d in a f e l s i c layer.  40  S p e c i f i c examples of c r o s s c u t t i n g and s u p e r p o s i t i o n of f o l d s t y l e s such as these have allowed f o r d i s t i n c t i o n of f o l d elements  that p l o t as' o v e r l a p p i n g d i s t r i b u t i o n s  because of the v a r i a b i l i t y  i n each data s e t .  Pegmatite  intruded along F2 a x i a l planes shows p o o r l y - d e f i n e d foliation parallel  to F3 trends i n some outcrops.  t h i n s e c t i o n , green c h l o r i t e planes, and appears  In  i s a l i g n e d along F3 a x i a l  to be r e t r o g r a d e .  Retrograde  metamorphism i s b e l i e v e d to be contemporaneous with or l a t e r than F3 deformation. 3.1.2.6 F4 Large to s m a l l , u p r i g h t open f o l d s with v e r t i c a l a x i a l planes and shallow NNE to NE plunge, by minor c r e n u l a t i o n s i n p e l i t i c  accompanied  l a y e r s , are assigned t o  f o l d episode F4 (see F i g u r e 8 A, 9 C ) .  Large F4 f o l d s  are c o n c e n t r i c buckle f o l d s of moderate amplitude wavelength  on the order of a few k i l o m e t e r s .  f o l d s may account  f o r the wide v a r i a t i o n  axes and l i n e a t i o n s ,  parallel  These  i n plunge of F2  i n c l u d i n g the southeast d i p i n  p a r t s of the map a r e a . Stevenson  with  Quartz v e i n s near Mount  are commonly n e a r l y v e r t i c a l with NE s t r i k e , to F4 a x i a l plane f r a c t u r e s .  Some of the  c u r v a t u r e i n the L i t t l e R i v e r F a u l t s u r f a c e may be due to warping  by F4 deformation, or perhaps  both  faulting  and F4 f o l d i n g o c c u r r e d d u r i n g the same e x t e n s i o n a l event.  i  41 3.1.3  FOLDS ABOVE LITTLE RIVER FAULT  Fold history River F a u l t  i n Cariboo Group rocks above the  is similar  to that  i n the Snowshoe Group  below i t , but only one p o s s i b l e f o l d was  observed.  Little  first-phase,  In the hanging  isoclinal  w a l l of the L i t t l e  River F a u l t , the grey marble has n e a r - h o r i z o n t a l to g e n t l y e a s t - d i p p i n g bedding slabs  (average 5 cm  0  i s broken  into  t h i c k ) p a r a l l e l to F2 a x i a l  ( S ) except where r e f o l d e d 2  folds  ( S ) , but  (see F i g u r e 11 B).  i n t o F3 kinks and The  planes  chevron  p e l i t e , which i s a  c h l o r i t e grade p h y l l i t e , e x h i b i t s e i t h e r F2 a x i a l  plane  cleavage  ( S ) or i s transposed l o c a l l y to F3 a x i a l  cleavage  ( S ) ; both cleavages may  be developed  3  same outcrop.  Quartzite layers  tend to r e t a i n pre-F2 l a y e r i n g  100  11 A).  0  and plunge  or up to 15° to the e a s t , depending F4 warp.  units  ( S ? ) , although micas i n  F3 kinks and chevron  (approximately E-W)  i n the  in the p e l i t i c  f o l d hinges are r e o r i e n t e d on F2 a x i a l planes Figure  plane  2  (S )  (see  2  f o l d s plunge  080  to  up to 30° to the west on the limb of the  A x i a l planes of kink f o l d s t r e n d around  010/30E l o c a l l y , p a r a l l e l  to minor f a u l t s u r f a c e s  r e l a t e d to the L i t t l e R i v e r F a u l t .  T h i s suggests  movement r e l a t e d to the L i t t l e River F a u l t  that  took  advantage of F3 a x i a l plane s u r f a c e s , or that there i s some g e n e t i c r e l a t i o n s h i p between f a u l t i n g and folding.  kink  Figure 11. A. Weak f o l i a t i o n in micaceous q u a r t z i t e (Q) i s p a r a l l e l to NE-dipping a x i a l plane of SW-verging f o l d (F2), whereas cleavage of i n t e r l a y e r e d p h y l l i t e (P) d i p s southeast (F3 a x i a l p l a n e ) , p a r a l l e l to the face of the outcrop. Near S e r v i c e Mountain ("6287'"). B. Thin l a y e r s i n grey marble at "6287'" are s u b p a r a l l e l to r e g i o n a l NE-dipping F2 a x i a l plane, but l o c a l l y kinked by F3 f o l d s with SE-dipping a x i a l planes.  43 3.2 STEREOGRAPHIC PROJECTIONS  OF STRUCTURAL ELEMENTS  Domains are shown on F i g u r e  12 and s t e r e o g r a p h i c  p r o j e c t i o n s f o r v a r i o u s s t r u c t u r a l elements i n eleven domains are shown i n F i g u r e s  13 to 22.  3.2.1 DOMAINS Domains f o r p l o t t i n g  s t r u c t u r a l elements were chosen  on the b a s i s of large s t r u c t u r e s and l i t h o s t r a t i g r a p h i c boundaries i n the f i e l d .  Domains I through VII are i n  Snowshoe Group "upper sequence"; Domains V I I I , IX, and X are i n Snowshoe Group "lower sequence"; and Domain XI i s in Cariboo Group rocks above the L i t t l e River  Fault.  Domains I, V, V I I , and IX i n c l u d e areas of g e n e r a l l y homoclinally dipping f o l i a t i o n  (on a l a r g e  scale);  Domains I I , I I I , IV, and X i n c l u d e known hinge zones of l a r g e F2 f o l d s ; Domain VI c o n t a i n s a f a u l t which tilts  f o l i a t i o n ; and Domain VIII spans an area  to be a f f e c t e d by movement on the L i t t l e River  locally  believed Fault.  C o l l e c t e d data are more numerous i n some domains than i n others, and f o r some s t r u c t u r a l elements as f o l i a t i o n ) .  (such  Where data are sparse, or where  stereograms p l o t t e d s e p a r a t e l y were e s s e n t i a l l y the same, data from two or more domains have been combined in one stereogram. Centers of c o n c e n t r a t i o n s of p o i n t s were c a l c u l a t e d by computer p l o t t i n g program or by eye; where both methods were used there was good agreement between them.  44  F i g u r e 12. S t r u c t u r a l domain map of the Three Ladies Mountain area showing domains r e f e r r e d to on s t e r e o g r a p h i c projections. Refer to P l a t e I f o r geology and to P l a t e s IV-VI f o r s t r u c t u r a l d e t a i l .  45 3.2.2  DEFINITION OF TERMS S t r u c t u r a l elements p l o t t e d on  p r o j e c t i o n s i n c l u d e those IV, V, and VI. 7r-diagrams  Planar  stereographic  shown on P l a t e I, and  Plates  f e a t u r e s a r e p l o t t e d on  as poles to s u r f a c e s .  Bedding i s p l o t t e d only where i t can  be  d i s t i n g u i s h e d from metamorphic l a y e r i n g , as in the low-grade rocks above the L i t t l e River F a u l t . high-grade s c h i s t and g n e i s s , c o m p o s i t i o n a l  For  l a y e r i n g and  f o l i a t i o n are combined as " f o l i a t i o n " , as they generally p a r a l l e l  in the f i e l d  entirely.  r e f e r s to the dominant metamorphic  in an outcrop, compositional  which i s g e n e r a l l y p a r a l l e l l a y e r i n g , and may  include  r e l a t e d to e i t h e r F1 or F2 s t r u c t u r e s . c o u l d be  are  and when p l o t t e d  separately t h e i r d i s t r i b u t i o n s overlap "Foliation"  the  foliation  to  foliation Where f o l i a t i o n  i d e n t i f i e d as a x i a l planar to a p a r t i c u l a r  phase, i t i s p l o t t e d in the category  of " a x i a l  fold  planes".  " A x i a l planes" are e i t h e r measured a x i a l s u r f a c e s , a x i a l planar  f o l i a t i o n s , or c r e n u l a t i o n cleavage,  approximations  to a x i a l planes of f o l d s with no  measurable a x i a l hinge  or  surfaces.  easily  " F o l d axes" are measured  l i n e s of f o l d s , or approximated by measuring  l i n e a t i o n s a p p a r e n t l y p a r a l l e l to hinge  lines.  Where  f o l d phases c o u l d be d i s t i n g u i s h e d , a x i a l planes f o l d axes are separated westerly-overturned  i n t o groups of F1, F2  f o l d s ) , F3, F4, and  and  (mainly  "pre-F2" f o l d s  46 (including easterly-overturned i s o c l i n a l and  r o o t l e s s F1A  measured i n the  field  folds).  include  ( u s u a l l y a combination of F1 crenulations,  and  intersection and  F2  structures), l i n e a t i o n s such as  alignment of elongate hornblende.  be d i s t i n g u i s h e d  are F3  are p a r a l l e l  to F1  coaxial  to F1  Quartz  or F4 or F2  in most a r e a s .  structures.  Kinks Most  "Fault  surfaces"  are  nearly surfaces  as are  on  indicated not  these are meaningless d i s t i n c t i o n s here  slickensides  observed appear to c o n s i s t  smoothed-over, f i b r o u s - l o o k i n g generally  smooth and  l i n e s that  shiny s u r f a c e .  commonly those p e r p e n d i c u l a r to F2  SUMMARY OF  of  form a  "Joints"  mainly to prominent f r a c t u r e planes i n the  3.2.3  and  i n t o s i i c k e n f i b r e s , s i i c k e n l i n e s , or  slickensurfaces; as the  "Slickensides"  can  lineations  which movement appears to have taken p l a c e ,  divided  rod  f o l d axes, which are  by o f f s e t or s l i c k e n s i d e s .  of micas,  f o l d axes where they  from other l i n e a t i o n s .  crenulations  lineations  dimensional o r i e n t a t i o n  l i n e a t i o n s are p a r a l l e l  as  "Lineations"  mineral o r i e n t a t i o n  quartz rods, p r e f e r r e d and  F 1 B f o l d s as w e l l  refer  rocks, most  f o l d axes.  STEREOGRAPHIC PROJECTIONS  In the Three L a d i e s Mountain area, or Domains foliation  is generally  parallel  to  compositional  l a y e r i n g and  probably r e l a t e d to to F1  F2  be d i v i d e d  f o l d s can  I-V,  folds.  Limbs of  i n t o a dominant limb at 075/44N  47 and a short limb of  135/70N.  (Combination  stereograms  were c o n s t r u c t e d from averages for c o n c e n t r a t i o n s from each domain and given here.) p o s s i b l e F1 moderately  used to determine the average  Other c o n c e n t r a t i o n s i n Domain IV limbs, one  west, and  the other of which trends  at 334/42, approximately  southeast  p e r p e n d i c u l a r to the great indicating  c y l i n d r o i d a l and has not been  d i s t u r b e d by any major d e f o r m a t i o n a l event. spread  dips  Average F2 f o l d a x i s l i e s  c i r c l e which c o n t a i n s poles to f o l i a t i o n , f o l d i n g was  indicate  of which trends north and  and d i p s s t e e p l y southwest.  that F2  trends  The  wide  i n p o i n t s on the stereograms can be accounted  by F3 and F4 f o l d i n g .  F3 f o l d i n g  from s t r u c t u r a l data, and may changes i n d i p from one  is d i f f i c u l t  only be apparent  area to another,  for  to d e f i n e as  such as the  steeper d i p of f o l i a t i o n s at Three Ladies Mountain, shallower  to the north and  south.  F4 f o l d s , which are  broad warps with a NE t r e n d , have the most e f f e c t on plunge of F2 axes to NW In Domains VI-X,  or  the  SE.  i n c l u d i n g the Mount Stevenson  and  Quesnel Lake area, the f o l i a t i o n s are l e s s steep than at Three L a d i e s Mountain, but not much, with dominant a t t i t u d e of 073/36N.  There i s no evidence  the L i g h t n i n g Creek A n t i c l i n o r i u m (Campbell Fletcher mainly  1972)  through  f o r extending et a l . 1973,  t h i s area, as f o l i a t i o n  north everywhere from the L i t t l e R i v e r  boundary of map  area) to G r a i n Creek (southwest  dips (north of Mount  48  Stevenson). Axes of pre-F2 f o l d s and F1 l i n e a t i o n s are d i f f i c u l t to d i s t i n g u i s h  from F2 s t r u c t u r e s , but i t appears that  in the Three L a d i e s Mountain area the most n o r t h e r l y axes and l i n e a t i o n s belong to F1, whereas near Mount Stevenson there i s a d i s t i n c t WNW F1 s t r u c t u r e s . i s o c l i n a l ) F1B  grouping belonging to  Easterly-overturned, tight  (not t r u l y  f o l d s occur mainly in the Mount Stevenson  and Welcome Mountain a r e a s .  F1A  intrafolial  isoclines  occur i n every domain (except XI*). F2 a x i a l planes from the e n t i r e area average at 118/58N, and are remarkably c o n s i s t e n t c o n s i d e r i n g the l a t e r phases of f o l d i n g .  F2 f o l d axes from the "upper  sequence" rocks, or Domains I-IV and V I I , average at 332/42, whereas F2 f o l d axes from the "lower  sequence"  rocks, or Domains V, VI, and VIII-X, average a more westerly and shallower at 315/24.  little  Foliations,  l i n e a t i o n s , and f o l d axes i n Domain I I , which c o n t a i n s the north face of Three L a d i e s Mountain, are unusually steep.  T h i s may  be due to l a t e r  l a r g e , asymmetrical F2 S - f o l d  f o l d i n g or f a u l t i n g .  i s well exposed  A  i n the  Three L a d i e s Mountain area; the middle limb extends from the middle peak of Three L a d i e s Mountain down Marten Creek, and has v e r t i c a l  f o l i a t i o n as w e l l as  d i p p i n g to both s i d e s of v e r t i c a l , F1  fold.  foliation  suggesting a refolded  49 S t r u c t u r a l elements assigned  t o F3 f o l d i n g are  i n c o n s i s t e n t w i t h i n and between domains, a t t e s t i n g to the r e l a t i v e subordinate  nature  compared with F2 f o l d s .  As kinks and c r e n u l a t i o n s do  not occur on every  outcrop,  of these s t r u c t u r e s ,  there are fewer data p o i n t s  for F3 elements, and no c o n s i s t e n t p a t t e r n s emerged from the  stereonets. L i n e a t i o n s are dominantly F2, p a r a l l e l  axes.  to F2 f o l d  For Domains II-IV, l i n e a t i o n s group at 340/45;  for Domains IV-X, at 315/30; and f o r Domains I and X, at 336/28 (these are i n t e r p r e t e d as having  been r o t a t e d to  lower angles by f a u l t s r e l a t e d to the L i t t l e Fault).  River  Quartz rod l i n e a t i o n s are a s s o c i a t e d with F1  f o l d s , p a r t i c u l a r l y e a s t e r l y - o v e r t u r n e d F1B f o l d s i n the Mount Stevenson area, where quartz  rod l i n e a t i o n s  average 288/20. See c a p t i o n s of s t e r e o g r a p h i c p r o j e c t i o n s f o r more details.  50  F i g u r e 13. Equal a r e a p r o j e c t i o n s L a d i e s M o u n t a i n , n o r t h e a s t r i d g e . w e s t e r l y - o v e r t u r n e d F2 synform.  for Domain II. I n c l u d e s hinge  Three zone of  a  a . F o l i a t i o n s are f o l d e d about a c a l c u l a t e d a x i s of 335/48; the dominant f o l d l i m b i s 070/48N, w i t h the s h o r t e r l i m b at 124/66N, s u b p a r a l l e l to the a x i a l p l a n e (compare ( e . ) ) .  b . , d . , and f. L i n e a 332/56, a n d F2 f o l d a c a l c u l a t e d f o l d a x i s f o l d i n g was c y l i n d r o i F1 s t r u c t u r e s .  t i o n s p l o t at 335/44, f o l d axes at xes at 332/56, a l l comparable w i t h shown i n ( a . ) . This i m p l i e s that F2 d a l and that most of the f o l i a t i o n s are  c . P o l e s to a x i a l p l a n e s of f o l d s of u n c e r t a i n show a g r o u p i n g around 095/64N i n t e r p r e t e d a s F1 p l a n e s .  e. P o l e s t o F2 125/66N; s p r e a d t r e n d (F4).  a f f i n i t y a x i a l  a x i a l p l a n e s are spread b r o a d l y around may be d u e to l a t e r broad warping w i t h  NE  51  52  F i g u r e 14. Equal area p r o j e c t i o n s for Domain III. Three L a d i e s Mountain north peak and e a s t c i r q u e . I n c l u d e s F2 a n t i f o r m a n d p o s s i b l e F1 c l o s u r e s .  a . F o l i a t i o n s are f o l d e d about a dominant l i m b i s at 078/45N, w i t h 137/68N.  c a l c u l a t e d a x i s of 352/53? s u b o r d i n a t e l i m b at  b . , d . , and f. L i n e a t i o n s p l o t at 340/50, f o l d 340/50, a n d F2 f o l d axes at 338/45. Domain III axes and l i n e a t i o n s i n e n t i r e a r e a .  axes has  c . Non-F2 a x i a l p l a n e s p l o t i n 3 groups: 088/38N, i n t e r p r e t e d as F l ; 150/34N, i n t e r p r e t e d as p o s s i b l e and 035/85N, i n t e r p r e t e d as F4.  e. F2 a x i a l p l a n e s show a r e a s ; s p r e a d may be d u e N E - t r e n d (F4).  g r e a t e r spread to l a t e r broad  than i n warping  some w i t h  at steepest  F 3 ( ? ) ;  other  53  54  F i g u r e 15. E q u a l a r e a p r o j e c t i o n s f o r Domain I V . L a d i e s M o u n t a i n m i d d l e and s o u t h p e a k s . Includes synform i n c a r b o n a t e - a m p h i b o l i t e u n i t .  Three large  a. P o l e s t o f o l i a t i o n show 4 c o n c e n t r a t i o n s . L i m b s a t 083/44N and 124/67N a r e i n t e r p r e t e d a s F2 and g i v e a c a l c u l a t e d f o l d a x i s o f 3 2 3 / 4 0 , p a r a l l e l t o l i n e a t i o n s and f o l d a x e s , i n d i c a t i n g t h a t F2 f o l d i n g was dominantly cylindroidal. L i m b s a t 018/46W and 142/76S ( o v e r t u r n e d e q u i v a l e n t of 124/67N l i m b ) s u g g e s t c o n t r o l f r o m p r e v i o u s F1 ant i form. b. L i n e a t i o n s c e n t e r around 325/40, p a r a l l e l t o f o l d axes ( d . , f . ) and t o c a l c u l a t e d a x i s i n ( a . ) . Wide s p r e a d of l i n e a t i o n s s u g g e s t s two g r o u p s o f F1 l i n e a t i o n s now a t 350/54 and 2 8 7 / 2 6 . c. Non-F2 a x i a l p l a n e s f a l l i n t o g r e a t c i r c l e o f p o l e s t o f o l i a t i o n f o l d e d by F2 f o l d s ; i n t e r p r e t e d as m a i n l y F1 a x i a l planes. d., f . F o l d a x e s and F2 f o l d a x e s b o t h p l o t a t p a r a l l e l t o the dominant l i n e a t i o n . e.  F2 a x i a l  planes  have o r i e n t a t i o n  of  109/52N.  324/38,  55  56  F i g u r e 16. E q u a l a r e a p r o j e c t i o n s f o r Domain V I I I , M a r t e n C r e e k t o L i t t l e R i v e r F a u l t ; and Domain X, Q u e s n e l Lake from Devoe C r e e k t o L i t t l e R i v e r F a u l t . B o t h c o n t a i n F2 a n t i f o r m in Marten Creek.  a. Domain V I I I . F o l i a t i o n shows up i n 3 g r o u p s . Limbs of a n t i f o r m : 072/42N and 125/42S. F o l i a t i o n r o t a t e d by d r a g on f a u l t s r e l a t e d t o L i t t l e R i v e r F a u l t : 170/20E. b. Domain V I I I . L i n e a t i o n s and f o l d a x e s show concentration a t 310/33 but a few n e a r Q u e s n e l L a k e p l u n g e SE i n d i c a t i n g e f f e c t o f F4 f o l d i n g a n d / o r d r a g on L i t t l e River Fault. c. Domain X. F o l i a t i o n s f a l l i n t o 4 groups. Limbs o f M a r t e n C r e e k F2 a n t i f o r m : 081/27N and 124/42S. Foliations a t 120/58N a r e a p p r o x i m a t e l y p a r a l l e l t o F2 a x i a l p l a n e s . A f o u r t h g r o u p l o o s e l y c e n t e r e d a t 000/12E i s i n t e r p r e t e d a s f o l i a t i o n s r o t a t e d by L i t t l e R i v e r F a u l t movement. d. Domain X. L i n e a t i o n s and f o l d a x e s show a b r o a d s p r e a d w i t h a dominant c o n c e n t r a t i o n a t 314/22. S p r e a d t o NNW and WNW i s a t t r i b u t e d t o f o l d e d F1 l i n e a t i o n s . S o u t h e a s t - p l u n g i n g l i n e a t i o n s and a x e s n e a r Q u e s n e l L a k e a r e f o l d e d by F4 f o l d s a n d / o r r o t a t e d by L i t t l e R i v e r F a u l t . e. Domain X. A x i a l p l a n e s a r e e i t h e r F 1 , w h i c h f a l l i n two g r o u p s s u b p a r a l l e l t o l i m b s o f F2 f o l d s a t 077/37N and 136/46S; o r F2, a t 134/66N. f. Domain X. F a u l t s u r f a c e s c o u l d be d i v i d e d i n t o two g r o u p s , one a t 171/21E, i n t e r p r e t e d a s r e l a t e d t o L i t t l e R i v e r F a u l t ; and one a t 099/23N, w h i c h i s p a r a l l e l t o some f a u l t s a t L i m e s t o n e P o i n t , w h i c h may o r may n o t be r e l a t e d to L i t t l e R i v e r F a u l t .  57  58  F i g u r e 17. E q u a l a r e a p r o j e c t i o n s f o r Domains I , V, and V I I , f o l i a t i o n s and l i n e a t i o n s . A l l c o n t a i n a r e a s of relatively homoclinally dipping foliations. a. Domain I . F o l i a t i o n s c e n t e r a t 072/32N, t h a n i n Domains I I a n d I I I .  much l e s s  b. Domain I . L i n e a t i o n s c e n t e r a t 333/28, a l s o s t e e p a s i n Domains I I and I I I .  steep  not as  c. Domain V I I . F o l i a t i o n s p l o t a t 070/46N. These rocks a p p e a r v e r y s i m i l a r t o t h o s e i n Domain I and may be c o n t i n u o u s w i t h them; t h i s would i m p l y a l a r g e S - f o l d w i t h a m i d d l e l i m b o f a b o u t 124/67N ( a n a l o g o u s t o Domain IV) between I s h k l o o C r e e k and T h r e e L a d i e s M o u n t a i n , an a r e a which i s not w e l l exposed.  d. Domain V I I . L i n e a t i o n s and f o l d a x e s p l o t s i m i l a r t o F2 s t r u c t u r e s i n Domain IV.  a t 320/40,  e. Domain V. F o l i a t i o n s c o n c e n t r a t e a t 082/42N, t h e dominant l i m b o f t h e f o l d shown i n Domain I V .  forming  f. Domain V. L i n e a t i o n s p l o t a t 317/34, w i t h a few more n o r t h e r l y and w e s t e r l y l i n e a t i o n s i n t e r p r e t e d i n t h e f i e l d as F1 l i n e a t i o n s .  59  60  F i g u r e 18. Equal area p r o j e c t i o n s f o r combinations s t r u c t u r a l elements from s e v e r a l domains. a. Domain V. F2 a x i a l p l a n e s p l o t a t p a r a l l e l t o t h o s e i n Domain I V .  110/47,  of  approximately  b. D o m a i n s I-V, I X . P o l e s t o c o n t a c t s of p e g m a t i t e d i k e s p l o t a r o u n d 121/62N, s u b p a r a l l e l t o F2 a x i a l p l a n e s . c. D o m a i n s I-V, I X , and X. F3 a x i a l p l a n e s . Three groups emerge: one a t 048/56S, a p p r o x i m a t e l y p e r p e n d i c u l a r t o F2 f o l d a x e s and p a r a l l e l t o t h e d o m i n a n t j o i n t s e t ; one a t 158/61S; and one a t 166/61E. T h e s e m i g h t be i n t e r p r e t e d as c o n j u g a t e k i n k s , b u t a c t u a l f i e l d r e l a t i o n s of t h e s e two s e t s a r e unknown. d. Domains I I - V I , V I I I , and I X . Crenulation lineations p l o t a l l o v e r t h e NE q u a d r a n t of t h e s t e r e o n e t c e n t e r i n g a t 0 5 4 / 3 6 . They c o u l d be i n t e r p r e t e d a s r e l a t e d t o e i t h e r F3 o r F4 f o l d s . e. Domains I-V, V I , and I X . P o l e s t o c o n t a c t s of p l a n a r q u a r t z v e i n s f a l l i n t o two g r o u p s ; one approximately p a r a l l e l t o m e t a m o r p h i c f o l i a t i o n , and one a t 0 5 0 / 9 0 , s u b p a r a l l e l t o F4 a x i a l p l a n e s . f. Domains I-V, V I , I X , and F4 a x i a l p l a n e s were t o o few 040/90.  X. F4 f o l d a x e s p l u n g e 035/16. t o p l o t but a v e r a g e a r o u n d  62  F i g u r e 19. E q u a l a r e a p r o j e c t i o n s o f p r e - F 2 f o l d f o r c o m b i n a t i o n s o f d o m a i n s ; and F2 f o l d e l e m e n t s IX, Mount S t e v e n s o n a r e a .  elements i n Domain  a. Domains I I - I V , V I , and X. A x i a l p l a n e s of pre-F2 f o l d s p l o t i n two g r o u p s . E a s t - v e r g i n g F1B f o l d s p l o t a r o u n d 177/29W, whereas o t h e r F1 f o l d s i n c l u d i n g F1A i s o c l i n e s a r e p a r a l l e l t o f o l i a t i o n a t 084/48N.  b. WNW  Domains I I , I I I , a n d V. t o NNW a n d NE.  c. Domain I X . A x i a l i n t o two g r o u p s w h i c h (see F i g u r e 20 ( c . ) ) , and one a t 143/43S.  F1  fold  axes  show a s p r e a d from  p l a n e s o f p r e - F 2 f o l d s c a n be d i v i d e d are roughly concordant with f o l i a t i o n one a t 041/24N ( e a s t e r l y o v e r t u r n e d )  d. Domains VI a n d I X . F1 f o l d a x e s a r e c o n c e n t r a t e d a t 295/16, more w e s t e r l y and s h a l l o w e r t h a n F2 a x e s . e. Domain I X . F2 a x i a l p l a n e s p l o t those near Three L a d i e s Mountain.  a t 116/54N,  similar to  f. Domain I X . F2 f o l d a x e s p l o t a t 314/25. F2 s t r u c t u r e s n e a r Mount S t e v e n s o n a r e c o n s i s t e n t w i t h but l e s s s t e e p l y d i p p i n g than those near Three L a d i e s Mountain.  64  F i g u r e 20. E q u a l a r e a p r o j e c t i o n s f o r Domains VI and IX. Mount S t e v e n s o n a r e a . a. Domain V I . F o l i a t i o n s a r e c o n c e n t r a t e d m a i n l y a t 076/36N e x c e p t near f a u l t i n upper Long C r e e k . b. Domain V I . L i n e a t i o n s and f o l d a x e s p l o t a r o u n d 3 1 5 / 1 6 e x c e p t t h o s e p l u n g i n g SE where f o l d e d a d j a c e n t t o f a u l t i n u p p e r Long C r e e k . c. Domain SW-dipping  IX. F o l i a t i o n s f o l i a t i o n s from  p l o t m a i n l y a t 073/29N w i t h s o u t h of Mount Stevenson.  some  d. Domain IX. L i n e a t i o n s p l o t i n 3 g r o u p s . F1 l i n e a t i o n s p l o t a t 251/16; F2 l i n e a t i o n s a t 314/22; and F4 l i n e a t i o n s a t 028/05. T h e s e a r e a l l more g e n t l y p l u n g i n g than a t T h r e e Ladies Mountain. e. Domain I X . F o l i a t i o n i n q u a r t z d i o r i t i c g n e i s s i s g e n e r a l l y p a r a l l e l to f o l i a t i o n i n other r o c k s ; the spread of p o l e s i n d i c a t e s a c a l c u l a t e d a x i s of 314/25, i n d i c a t i n g t h a t t h e q u a r t z d i o r i t i c g n e i s s i s f o l d e d c y l i n d r o i d a l l y by F2 f o l d s . f.  Domain  IX.  F o l d axes  ( n o t F2) p l o t  a t 311/27.  65  6  o m n i a 9 rxiflnot IN OMIT o i w m c  ocisa  aw IN 3 r X Q OT3  66  F i g u r e 21. E q u a l a r e a p r o j e c t i o n s s l i c k e n s i d e s , and j o i n t s .  of f a u l t  surfaces,  a. Domains I-V. Three Ladies Mountain. Fault surfaces d i p s h a l l o w l y e a s t , and a r e i n t e r p r e t e d a s r e l a t e d t o t h e L i t t l e River Fault.  b. Domains I-V. Three Ladies Mountain. Slickensides point m o s t l y t o w a r d 118 w i t h low plunge*- f i e l d e v i d e n c e s u c h a s d i s p l a c e m e n t and d r a g i n d i c a t e s movement o f t o p down t o SE. c. Domains VI a n d IX, Mount S t e v e n s o n . shallowly i n every d i r e c t i o n . d. SW.  Domains VI and I X .  Slickensides  Fault  point  surfaces d i p  t o NE, SE, and  e. Domains I-V, V I I I - X I . Fault surfaces are generally s h a l l o w l y - d i p p i n g , and i f r e l a t e d , c e n t e r a r o u n d 178/16E, which i s p a r a l l e l t o p a r t of the L i t t l e R i v e r F a u l t near Quesnel Lake. Because the L i t t l e R i v e r F a u l t i s c u r v e d , a l l o f t h e s e f a u l t s u r f a c e s may be r e l a t e d t o i t . f. Domains I-V, V I I I , and IX. P o l e s t o j o i n t s u r f a c e s a r e concentrated i n t h e n o r t h w e s t q u a d r a n t , i n d i c a t i n g t h a t most j o i n t s m e a s u r e d a r e p e r p e n d i c u l a r t o F2 f o l d a x e s ( p e r p e n d i c u l a r t o 324/45) a t 054/45S. Some o v e r l a p w i t h f a u l t s u r f a c e s i s e x p e c t e d a s some o f t h e s e j o i n t p l a n e s show d i s p l a c m e n t a n d d r a g i n d i c a t i n g movement o f t o p down t o southeast.  68  F i g u r e 22. Equal area p r o j e c t i o n s of s t r u c t u r a l h a n g i n g w a l l o f L i t t l e R i v e r F a u l t , Domain X I .  a. Bedding 097/21N.  and c o m p o s i t i o n a l l a y e r i n g  elements  in  i n marble p l o t a t  b. B e d d i n g and c o m p o s i t i o n a l l a y e r i n g i n p h y l l i t e and q u a r t z i t e p l o t a t 108/24N, n o t t o o d i f f e r e n t from b e d d i n g i n marble.  c. Foliation in phyllite/quartzite f o l d i n g a t 139/60N.  is axial  p l a n a r t o "F2"  d. F o l d a x e s and l i n e a t i o n s p l o t m a i n l y a t 342/12, more s h a l l o w t h a n i n t h e u n d e r l y i n g Snowshoe G r o u p s c h i s t . These a r e m a i n l y "F2" s t r u c t u r e s . S p r e a d t o SE i n d i c a t e s c h a n g e of p l u n g e due t o N E - t r e n d i n g F4 w a r p i n g .  e. Axial planes whereas F2 a x i a l  o f F3 k i n k s i n p h y l l i t e p l o t a t 174/60N, p l a n e s i n m a r b l e p l o t a t 118/69N.  A d d i t i o n a l measurements t a k e n i n 1982 were n o t p l o t t e d on t h e s e s t e r e o n e t s b u t c o n f i r m F2 a x i a l p l a n e s c o n s i s t e n t w i t h t h o s e i n t h e Snowshoe G r o u p ; and t h e p r e s e n c e o f a b r o a d F4 a n t i c l i n e t r e n d i n g NE on S e r v i c e R i d g e , w h i c h i n t e r s e c t s w i t h an F2 a n t i f o r m a t "6287'", f o r m i n g a domal i n t e r f e r e n c e pattern.  70  3.2.4 SUMMARY OF FOLDING Metamorphic rocks i n the Three L a d i e s Mountain were f o l d e d  first  area  by f o l d s which are now t i g h t to  i s o c l i n a l and s u b p a r a l l e l developed d u r i n g e a r l y  with F2 f o l d s ; quartz rods  folding.  F2 f o l d i n g was  accomplished mainly by a combination of b u c k l i n g i n more competent l a y e r s layers,  and shear f o l d i n g  producing f l a t t e n e d  between t r u e s i m i l a r  flexure  i n l e s s competent folds  transitional  f o l d s and pure f l e x u r a l s l i p  folds  Dominant s o u t h w e s t e r l y - o v e r t u r n e d F2 f o l d geometry across the e n t i r e compressive  study area suggests maximum  s t r a i n i n a northeast-southwest  and a sense of shear implying northeast over translation.  Alignment  direction, southwest  of m i n e r a l s p a r a l l e l to f o l d  axes i m p l i e s e l o n g a t i o n i n a northwest-southeast di r e c t i o n . The n e a r l y c o a x i a l and p o s s i b l y orientation stress  F3 f o l d s ,  orientation  of F1 and F2 f o l d s ,  i m p l i e s f a i r l y constant  of s t r a i n d i r e c t i o n s  and maximum  compressive  d u r i n g p r o g r e s s i v e deformation over a time p e r i o d  which spanned an e n t i r e metamorphic episode.  F4 f o l d s ,  which a r e p e r p e n d i c u l a r to dominant e a r l i e r trends, may have formed  late during u p l i f t .  71 3.3 DEFORMATION: FAULTING  3.3.1  LITTLE RIVER FAULT  One major  fault  numerous minor  zone  faults  ( L i t t l e River F a u l t ) and '  were i d e n t i f i e d  Ladies Mountain/Mount Stevenson  i n the Three  area.  The L i t t l e River F a u l t , which separates schist  and gneiss  metasedimentary Klepacki  in the f o o t w a l l from lower grade  rocks  map  of the f a u l t  in the hanging w a l l , was mapped by  area.  was  In t h i s  study,  the c o n t i n u a t i o n  t r a c e d from the saddle west of S e r v i c e  south down S e r v i c e Creek, and thence west of  Limestone Point  i n t o Quesnel Lake.  Klepacki  (1981)  found that i n the Maeford Lake area the L i t t l e fault  grade  (1981) near Maeford Lake, immediately north of  the present  Mountain  higher  River  d i p s s h a l l o w l y to the east, whereas toward Quesnel  Lake the d i p i s more v a r i a b l e , although east-dipping.  generally  Where i t i n t e r s e c t s Quesnel Lake, the  o r i e n t a t i o n of the f a u l t  i s about  surface appears to be convexly planar.  still  T h i s curvature  170/20 E.  curved  The  fault  rather than  i s seen i n the shape of the  rounded r i d g e east of Three L a d i e s Mountain, b e l i e v e d to have formed as the f a u l t  s u r f a c e was  exhumed by e r o s i o n  (see F i g u r e 23). The f a u l t  trace i t s e l f  i s p o o r l y exposed.  crops out at Quesnel Lake, i t i s marked by a  Where i t brittle  zone s e v e r a l tens of meters wide f e a t u r i n g f r a c t u r e d ,  B. S k e t c h of v i e w i n A s h o w i n g t r a c e of L i t t l e R i v e r F a u l t and exhumed t e c t o n i c d e n u d a t i o n s u r f a c e ( s t i p p l e d ) . A and B r e f e r t o F i g u r e 24 A and B, r e s p e c t i v e l y .  73  non-cohesive, p h a c o i d a l ,  g r a p h i t i c rocks  recognizable  s c h i s t , q u a r t z i t e , or  pegmatite.  as o r i g i n a l Microscopic  barely  s t r a i n markers were not  investigated. The  f o o t w a l l rocks  marble ( S t r u i k 1983)  include coarse-grained  and  Bralco  u n d e r l y i n g metamorphic rocks  Snowshoe Formation  ( l a t e P r o t e r o z o i c to P a l e o z o i c )  probable P a l e o z o i c  g r a n i t o i d gneisses.  rocks,  The  some of which were mapped by K l e p a c k i  of  and  hanging wall (1981) as  Yankee B e l l e Formation, c o n s i s t of a s e r i e s of marble l a y e r s i n t e r c a l a t e d with quartzite.  fine-grained  These are mapped as l a t e P r o t e r o z o i c  Cambrian Cariboo the two  p h y l l i t e and  sets Of  Formation and  Group, u n d i v i d e d . rocks may  Cariboo  to  Although the ages of  be s i m i l a r , the Snowshoe  Group cannot be c o r r e l a t e d ( S t r u i k  1982) . The  L i t t l e River F a u l t c r o s s c u t s complex  s t r u c t u r e s on both s i d e s of the Group rocks and  in the  fault.  The  fold Snowshoe  f o o t w a l l were f o l d e d at l e a s t once  intruded by at l e a s t  two  types of g r a n i t o i d s i l l s  p r i o r to F2  f o l d i n g , whereas the hanging w a l l rocks show  very  evidence for pre-F2 s t r u c t u r e s .  little  isoclinal  f o l d s were observed in the marble on  Mountain p a r a l l e l to l a y e r i n g , and identifiable later and  Only a  (F2 and  metamorphic h i s t o r y i n the  Service  bedding i s s t i l l  in some of the p h y l l i t i c F3) c l e a v a g e s .  few  units, crosscut  by  Although the s t r u c t u r a l f o o t w a l l rocks appears to  have begun e a r l i e r and i s more complex hanging wall rocks, the s i m i l a r i t i e s  than in the  i n F2 and  later  f o l d episodes are notable c o n s i d e r i n g the d i f f e r e n c e i n metamorphic  grade and proposed s t r a t i g r a p h i c  packages  across the f a u l t . The d e s i g n a t i o n  "F2" i s used for f o l d s which are  c h a r a c t e r i z e d on both s i d e s of the f a u l t  by  northeast-dipping a x i a l planes, consistent  southwest  vergence, and an a s s o c i a t i o n with maximum  metamorphic  recrystallization.  Usage of F2 i n t h i s sense equals F1  f o l d s as mapped by K l e p a c k i  (1981).  Plunge of F2 axes  in the f o o t w a l l rocks i s steep to the northwest except near Quesnel Lake, where i t i s near h o r i z o n t a l or to the southeast; plunge of F2 axes i n the hanging w a l l i s g e n e r a l l y shallower, to the northwest west of the r i d g e , and to the southeast or v a r i a b l e near Quesnel Lake (see F i g u r e 9, and P l a t e s I and I V ) .  These r e v e r s a l s i n  plunge are due to a combination of drag on the L i t t l e River F a u l t and superimposed F4  folding.  In the f o o t w a l l , prograde metamorphism a s s o c i a t e d with F2 f o l d i n g reached a m p h i b o l i t e f a c i e s , with s t a u r o l i t e - k y a n i t e zone on the r i d g e , and zone at Quesnel Lake.  F3 k i n k - f o l d i n g was  sillimanite accompanied  or followed by r e t r o g r a d e metamorphism i n d i c a t e d by growth, perhaps mimetic, of c h l o r i t e along F3 a x i a l planes.  Prograde metamorphism a s s o c i a t e d with  F2 f o l d i n g reached g r e e n s c h i s t  f a c i e s i n the hanging  75  wall  with  the development  chlorite-sericite  phyllite  chlorite-sericite-biotite Recrystallization the  same g r a d e ,  outlined  of r e c r y s t a l l i z e d on t h e r i d g e , and phyllite  by c h l o r i t e  i n some p h y l l i t e s .  i n both  growth of c h l o r i t e , rock  regime a r o u n d  t h e time  least  some r e l a t i v e  grade  rocks c l o s e r  therefore likely,  that both  of c o m p l e t i o n  t o the higher  occurred either  w i t h F3 f o l d i n g .  trend  around  fault  s u r f a c e s b e l i e v e d t o be r e l a t e d  River  Fault.  Group  (below  River  Fault  movement to  as VI)  i n the hanging  parallel  Minor  slickensides  folds  t o minor  to the L i t t l e  indicators  i n t h e Snowshoe  of the t r a c e of the L i t t l e indicates  w a l l was e a s t - s o u t h e a s t  that  relative  s t r u c t u r e s b e l i e v e d t o be  t o movement a l o n g  and drag  o f some F3  toward Three L a d i e s Mountain)  the f o o t w a l l .  related  t o o r , more On t h e e a s t e r n  planes  010/30 E, a p p r o x i m a t e l y  the p r o j e c t i o n  At  r o c k s had  postkinematic  kinematic  P/T  o f F3 f o l d i n g .  grade  of S e r v i c e Mountain, a x i a l  from  p a c k a g e s of  b r i n g i n g t h e lower  flank  Evidence  w a l l r o c k s by  t h e same m e t a m o r p h i c  displacement  synkinematic  was  f o o t w a l l and h a n g i n g  were i n a p p r o x i m a t e l y  cleavages "Retrograde"  F3 f o l d i n g  suggesting  Lake.  was a t a p p r o x i m a t e l y  i n two d i f f e r e n t  metamorphism a s s o c i a t e d w i t h characterized  at Quesnel  d u r i n g F3 f o l d i n g  resulting  m a r b l e and  the L i t t l e  River Fault,  such  ( s e e s t e r e o g r a p h i c p r o j e c t i o n s and P l a t e  features a s s o c i a t e d with  repeated  fault  76  s u r f a c e s , show c o n s i s t e n t o r i e n t a t i o n toward the southeast.  Many minor f a u l t  n e a r - p a r a l l e l to the unusual  zones are found rounded meadow slope east  of Three. Ladies Mountain to Quesnel Lake, which c o u l d be an exhumed f a u l t Fault  s u r f a c e r e l a t e d to the L i t t l e  (see f i g u r e S10) .  observed  River  Minor numerous f a u l t s are  with v a r i o u s o r i e n t a t i o n s ranging  from p a r a l l e l  to j o i n t planes which are p e r p e n d i c u l a r to F2 f o l d axes, to northeast d i p p i n g to eastward d i p p i n g . though any a v a i l a b l e s u r f a c e - - j o i n t planes,  I t looks as foliation  planes, and a x i a l planes--took  up part of the movement.  S l i c k e n s i d e s on j o i n t - p a r a l l e l  f a u l t s show movement to  have been down toward 118 (ESE), confirmed F2 f o l d axes and l i n e a t i o n s the j o i n t  i n the same d i r e c t i o n ,  s u r f a c e s showing the displacement  displacements  by drag of near  Small  are common, no more than ten meters.  However, on s u r f a c e s spaced  l e s s than one meter to ten  meters apart f o r at l e a s t  500 m below what may have been  the o r i g i n a l , major f a u l t  s u r f a c e (now j u s t above Three  Ladies Mountain), very l a r g e . evident  the combined displacement  The j o i n t - p a r a l l e l  c o u l d be  f a u l t s are p a r t i c u l a r l y  i n the carbonate-amphibolite  u n i t that makes up  the north slope of Three L a d i e s Mountain.  In some  p l a c e s , marble has been r e m o b i l i z e d and smeared  into  f r a c t u r e s p e r p e n d i c u l a r to F2 f o l d axes and l i n e a t i o n s (see F i g u r e 24). The marble c o n s i s t s of f i n e - g r a i n e d , f i n e l y - l a m i n a t e d c a l c i t e , with t h i n g r a p h i t i c  horizons  77  F i g u r e 24. S t r u c t u r e s below but r e l a t e d t o L i t t l e F a u l t ; f o r l o c a t i o n see F i g u r e 23 B.  River  A. M u l t i p l e j o i n t s p e r p e n d i c u l a r t o F2 f o l d axes i n f o l d e d q u a r t z i t e and p e l i t e showing d r a g f e a t u r e s of t o p down t o southeast. C l i f f h e i g h t i s about 20 m. B. 150 m below A. M a r b l e (m) (1-2 m t h i c k ) i s smeared f r a c t u r e p e r p e n d i c u l a r t o dominant f o l d s t r u c t u r e s i n amphibolite unit (a).  along  C. Schematic b l o c k d i a g r a m showing how marble (m; s t i p p l e d ) i n t e r c a l a t e d w i t h a m p h i b o l i t e (a) c o u l d have been smeared a l o n g f a u l t s u r f a c e as upper b l o c k was d i s p l a c e d t o southeast.  78  which are folded such that the a x i a l planes are p e r p e n d i c u l a r to F2 f o l d axes and p a r a l l e l  to the shear  zone. C l o s e r to Quesnel  Lake, these minor f a u l t s u r f a c e s  show v a r i a b l e a t t i t u d e s , but r e t a i n ESE s l i c k e n s i d e s and drag f e a t u r e s .  The average  whole area i s about  a t t i t u d e of f a u l t s  i n the  170/20 E, p a r a l l e l to some f a u l t  s u r f a c e s measured i n the f a u l t zone, and c o n s i s t e n t the a t t i t u d e of the f a u l t Displacement  t r a c e near Limestone  on the L i t t l e  River F a u l t  Point.  i s unknown.  The most recent movement was hanging w a l l down  toward  the east and southeast r e l a t i v e to the f o o t w a l l . c o u l d have been merely displacement  with  This  the l a t e s t episode of  due to d i f f e r e n t i a l  uplift.  The metamorphic d i f f e r e n c e across the t r a c e of the Little  River F a u l t c o u l d be as much as 200°C and 2 kb,  i n d i c a t i n g a p o s s i b l e throw of as much as about T h i s i s based on an assumption  6 km.  of a t y p i c a l Barrovian  P-T path, with the k y a n i t e / s i l l i m a n i t e zone rocks at approximately  5 to 7 kb and 500° to 600°C, and the  adjacent c h l o r i t e and b i o t i t e zone rocks a t approximately  3 to 4 kb and 300° to 400°C (see s e c t i o n  on metamorphic p e t r o l o g y ) . Little  River Fault  The c o n t i n u a t i o n of the  from where i t disappears i n t o  Quesnel  Lake i s unknown, although the shape of i t s s u r f a c e suggests Quesnel  i t continues south along the North Arm of Lake, at l e a s t as f a r south as Marten  Creek.  79  The d i f f e r e n c e of  i n metamorphic  grade a c r o s s the North Arm  Quesnel Lake has been a s c r i b e d to a l a t e normal  (Campbell and Campbell  fault  1969), but i t i s probably due to  e a r l i e r movement on the L i t t l e  River F a u l t .  evidence, such as the c o n t r a s t  in e l e v a t i o n between  Three Ladies Mountain and Mount Watt, there i s a l a t e normal f a u l t  Topographic  suggests that i f  i n the North Arm  of Quesnel  Lake, i t has downdropped the west side by a few hundred meters, not u p l i f t e d Campbell  i t , as implied by Campbell and  (1969).  No d e f i n i t e premetamorphic the  Three L a d i e s Mountain/Mount  Premetamorphic  to e s t a b l i s h .  a r e c r y s t a l l i z e d mylonitic  River F a u l t .  Stevenson a r e a .  movement on the L i t t l e  would be d i f f i c u l t for  f a u l t s were i d e n t i f i e d i n  Two  River Fault  itself  There i s no evidence  zone near the L i t t l e  p o s s i b l e t e c t o n i c s l i d e s , p a r a l l e l to  f o l i a t i o n , have been mapped along a t t e n u a t e d limbs of F2 f o l d s where marker  units  (carbonate-amphibolite) are  t r u n c a t e d by a p p a r e n t l y continuous l a y e r s of f o l i a t e d micaceous q u a r t z i t e and p e l i t i c I).  in the p e l i t i c  the  Plate  way  i s f o l d e d s y n f o r m a l l y , and then l o s t  plus q u a r t z i t i c  u n i t that continues a l l  up to the base of the B r a l c o marble.  L a d i e s Mountain middle peak, of  (see map  Northeast of Three Ladies Mountain, the amphibolite  p l u s carbonate u n i t  the  schist  Near Three  i t looks as though a band  p e l i t e has been transposed i n t o the a x i a l plane of l a r g e F2 f o l d , and c r o s s c u t the adjacent l a y e r of  i  80 amphibolite p l u s carbonate.  An a l t e r n a t i v e e x p l a n a t i o n  for these s t r u c t u r e s i s that they represent hinge of F1  folds,  r e f o l d e d by the F2  folds.  zones  81 3.3.2 DISCUSSION OF LITTLE RIVER FAULT Struik called  (1982) proposed a premetamorphic  fault,  the Pleasant V a l l e y Thrust, s e p a r a t i n g known  Cariboo Group s t r a t i g r a p h y on the northeast (hanging  side  wall) from Snowshoe Group u n i t s on the  southwest side ( f o o t w a l l ) .  The Pleasant V a l l e y Thrust  i s s a i d to d e l i n e a t e the eastern margin of Snowshoe Group rocks from north and east of Wells and B a r k e r v i l l e to  east of the North Arm of Quesnel Lake.  mainly  on the b a s i s of c o n t r a s t between major  lithostratigraphic identify  packages, and i s d i f f i c u l t to  i n the f i e l d ,  major t e r r a n e boundary. northern  although  i t i s supposed to be a  S t r u i k (1983) proposes that the  contact of the B r a l c o marble at Maeford Lake i s  a high-angle  f a u l t which may be p a r t of the Pleasant  V a l l e y Thrust.  The rocks t o the north of t h i s  have been mapped by K l e p a c k i of  It i s defined  fault  (1981) as s c h i s t and marble  Cariboo Group, a l s o i n the f o o t w a l l of the L i t t l e  River F a u l t .  Mapping i n t h i s study  interpreted this  f a u l t as a l a t e normal f a u l t with l i t t l e  displacement,  which has r e s u l t e d i n a small topographic  scarp  (on the  order of tens of meters) at Maeford Lake; rocks on the north  (down) s i d e are obsured by cover, or o u t s i d e the  l i m i t s mapped here.  Although  t h i s f a u l t appears to  i n t e r s e c t the L i t t l e  River F a u l t on the r i d g e west of  S e r v i c e Mountain, i t i s not c l e a r whether e i t h e r f a u l t  from f i e l d  o f f s e t s the other.  relations  However,  82 present  topography suggests that the L i t t l e  River F a u l t  s u r f a c e was r a i s e d s l i g h t l y t o the southwest, and has been eroded away.  I t i s p o s s i b l e that t h i s  displacement i s a r e a c t i v a t i o n of an o l d e r Struik  (1983) shows the c o n t i n u a t i o n  V a l l e y Thrust  small normal fault.  of the Pleasant  i n t o the hanging w a l l of the L i t t l e  F a u l t north of Limestone P o i n t . V a l l e y Thrust  River  Here the Pleasant  t r a c e i s mapped (by S t r u i k ) along the  lower part of S e r v i c e Creek between the marble and clastic  rocks of Limestone Point  phyllites  ( f o o t w a l l ) and the  and marbles above (hanging w a l l ) .  the same area  revealed mainly sparse  n o n d i s t i n c t i v e calcareous  Mapping i n  outcrops of  p h y l l i t e , a difference in  metamorphic grade from b i o t i t e zone to c h l o r i t e and  minor f a u l t  foliation  zone,  s u r f a c e s n e a r - p a r a l l e l to bedding and  i n b r e c c i a i n the marble at Limestone Point  (110/25 N).  Such evidence might support  slight  syn- or  postmetamorphic movement on a s u r f a c e p a r a l l e l to layering  somewhere i n the v i c i n i t y of Limestone P o i n t ,  but does not n e c e s s a r i l y c o n f i r m  or deny the e x i s t e n c e  of the Pleasant  V a l l e y Thrust  as mapped by  Struik  Geometrically  i t would be d i f f i c u l t to  (1983).  j u s t i f y c o n t i n u i n g a high-angle f a u l t i n t o n e a r l y adjacent  from the f o o t w a l l  hanging w a l l rocks, c o n s i d e r i n g the  d i r e c t i o n and p o s s i b l e l a r g e magnitude of movement on the L i t t l e River F a u l t which i s supposed t o postdate the higher-angle  fault.  83 The c h l o r i t e - b i o t i t e zone rocks of the Cariboo Group (?) were presumably at higher l e v e l s i n the c r u s t at  the time of metamorphism  than were the s t a u r o l i t e to  s i l l i m a n i t e zone rocks of the Snowshoe Group, unless the isotherms were s t e e p l y i n c l i n e d to the e a r t h ' s s u r f a c e . S t r u c t u r a l evidence in the hanging or  i n d i c a t e s that the low-grade rocks  wall of the L i t t l e River F a u l t  down r e l a t i v e to the higher-grade  footwall,  implying t h a t the hanging  slid  over  rocks i n the w a l l was  s t r u c t u r a l l y higher than the f o o t w a l l p r i o r to the l a t e s t movement on the L i t t l e evidence  River F a u l t .  This  r e q u i r e s t h a t n e a r l y unmetamorphosed  late  P r o t e r o z o i c to Cambrian sediments must have been emplaced above p r e f o l d e d l a t e P r o t e r o z o i c to P a l e o z o i c sediments which had been i n t r u d e d by quartz d i o r i t i c g r a n o d i o r i t i c bodies the Cariboo Group may  i n the e a r l y P a l e o z o i c .  and  Although  i n f a c t be younger than the  Snowshoe Group, i t i s o l d e r than the o r t h o g n e i s s e s i n t r u d e d i n t o the Snowshoe Group.  The Cariboo Group (?)  was not i n t r u d e d by these bodies, so was probably not immediately  adjacent to the Snowshoe Group i n the e a r l y  Paleozoic.  Rocks of the Cariboo Group (?) c o u l d have  been t h r u s t over rocks of the Snowshoe Group from east to west  (or Snowshoe Group underthrust  some time p r i o r to peak metamorphism, synkinematic Struik  from west) at probably  with F2 f o l d i n g , as suggested  (1982).  by  84 T h i s type of east-over-west  movement could have  occurred p a r t l y on the proposed surface of the  Pleasant  V a l l e y Thrust, along which the Cariboo Group and Snowshoe Group are now  juxtaposed  ( S t r u i k 1982).  In the  Three L a d i e s Mountain area, the dominant southwest vergence of F2  f o l d s t r u c t u r e s , lack of vergence  r e v e r s a l s over a l a r g e area, and s l i d e s along a t t e n u a t e d  layer-parallel tectonic  limbs of F2  folds attest  strong component of p r o g r e s s i v e simple northeast  over  metamorphism.  strain  in a  southwest d i r e c t i o n during prograde These o b s e r v a t i o n s are c o n s i s t e n t with  the o b s e r v a t i o n s and and  shear  to a  i n t e r p r e t a t i o n s of Murphy (1984)  Brown (1978), who  propose that  northeastward  u n d e r t h r u s t i n g d u r i n g a c c r e t i o n of t e r r a n e s in the e a r l y m i d - J u r a s s i c caused c o n s i s t e n t l y structures  southwest-verging  (F2 f o l d s ) i n the c o n t i n e n t a l margin sequence  being underthrust  from the southwest.  Large  l i t h o s t r a t i g r a p h i c packages, i n c l u d i n g c o n t i n e n t a l margin sediments of Kaza Group, Cariboo Group, and Snowshoe Group, formed l a r g e nappes separated and/or d u c t i l e shear broad  shear  faults  zones, which together d e f i n e "a  zone accommodating shear  with northeastward  by  underthrusting"  Pleasant V a l l e y Thrust  ( S t r u i k 1982)  strains associated  (Murphy 1984). may  The  have been of  t h i s type, a c t i v e d u r i n g F2 f o l d i n g and metamorphism; the "premetamorphic mylonite P e n f o l d Creek and  zone" ( F l e t c h e r 1972)  other p o r t i o n s of  "Campbell's  at  85 Enigmatic L i n e " may a l s o have been a c t i v e during the u n d e r t h r u s t i n g proposed by Murphy  (1984).  The L i t t l e River F a u l t , however, i s not a t h r u s t f a u l t , at l e a s t  in i t s latest  low-angle normal rocks s l i d  stage, but rather a  f a u l t along which the hanging wall  down r e l a t i v e to the f o o t w a l l , as suggested  by the minor  s t r u c t u r e s a l r e a d y mentioned.  Movement  d i s p l a c i n g the Cariboo Group rocks down r e l a t i v e to the Snowshoe Group rocks probably began around the time of F3 f o l d i n g and a s s o c i a t e d r e t r o g r a d e metamorphism. Movement continued through u p l i f t , most l i k e l y  i n the  T e r t i a r y , as i t postdated c o o l i n g of l a t e Cretaceous (86 Ma) pegmatite  (see s e c t i o n on  geochronology' (Chapter I I I ) ) . Columbia Mountains  Most of the u p l i f t  (which i n c l u d e the Cariboo Mountains  and Quesnel Highland) was completed by Miocene (Wheeler and G a b r i e l s e the  Intermontane  low r e l i e f  in. the  1972).  time  In the area which  i s now  B e l t , a widespread e r o s i o n surface with  (about 500 m) was covered by Miocene  lavas.  A s i m i l a r e r o s i o n surface covered much of the Quesnel Highland at higher e l e v a t i o n s , and i s now b l o c k - f a u l t e d to  various l e v e l s .  Although t h i s surface has been  deeply d i s s e c t e d by g l a c i a l e r o s i o n ,  i t is still  r e c o g n i z a b l e as an upper e l e v a t i o n l i m i t  i n each b l o c k .  The Three L a d i e s Mountain/Mount Stevenson area i s a s i n g l e block r a i s e d above the l e v e l of the surrounding h i l l s west of the North Arm of Quesnel Lake.  As  86 evidence,  a l l three peaks of Three Ladies Mountain and  Mount Stevenson reach a height c l o s e to 2200 m, in the Goose Range, a c r o s s  whereas  Ishkloo Creek to the west and  Grain Creek to the southwest, a l l of the "B" peaks (Barker,  Borland,  15 m of 2045 m.  Browntop,  Badger, and Brew) are w i t h i n  The peaks to the southeast  Arm of Quesnel Lake are much higher, Watt at  (2529 m).  of the North  such as Mount  North of the L i t t l e River  i s a plateau  about 1800 m which r i s e s g e n t l y to the east, u n t i l i t  i s a b r u p t l y terminated high Cariboo  by the Mathew River F a u l t and the  Mountains beyond  (2600 m).  The topography near the top of Three Ladies Mountain, which appears to approximate the l e v e l of the old  e r o s i o n s u r f a c e , has been s t r o n g l y i n f l u e n c e d by the  L i t t l e River F a u l t s u r f a c e and minor s t r u c t u r e s a s s o c i a t e d with interpretation  i t i n the u n d e r l y i n g  rocks.  i s c o r r e c t , then most of the movement on  the L i t t l e River F a u l t was pre-Miocene, and Cretaceous. formation  If t h i s  post-Late  The timing of events i n v o l v e d in the  of metamorphic  core complexes elsewhere i n the  C o r d i l l e r a was a l s o l a t e Cretaceous (post-Laramide orogeny) to middle T e r t i a r y Metamorphic et  (Coney  1980).  core complexes, according  to C r i t t e n d e n  a l . (1980), are c h a r a c t e r i z e d by cores of o l d e r  metamorphic  and p l u t o n i c basement  o v e r p r i n t e d by  g e n t l y - d i p p i n g g n e i s s i c f a b r i c , and o v e r l a i n by less-metamorphosed, younger, commonly attenuated  i  rocks.  87 These a r e separated "decollement"  from the basement rocks by  zones c h a r a c t e r i z e d by a p p a r e n t l y  steep  metamorphic g r a d i e n t s , b r e c c i a t i o n , and s t r u c t u r e s i n d i c a t i v e of detachment i n v o l v i n g low-angle l i s t r i c ) normal f a u l t i n g  (Coney 1980).  zones formed during u p l i f t events  Laramide orogenies  These detachment  f o l l o w i n g major  such as the Cretaceous  (commonly  compressional  to T e r t i a r y S e v i e r and  i n the U n i t e d States and the J u r a s s i c  Columbian orogeny i n Canada, but p r i o r to e x t e n s i o n a l events rifting  such as Basin and Range s t y l e f a u l t i n g and i n the mid to l a t e  In a d e s c r i p t i v e sense,  Tertiary. the L i t t l e  River F a u l t i n  the Three Ladies Mountain area d i s p l a y s c h a r a c t e r i s t i c s that are s i m i l a r to detachment s u r f a c e s of t y p i c a l metamorphic core complexes.  These f e a t u r e s , as w e l l as  the t i m i n g of the movement on the L i t t l e R i v e r F a u l t , between l a t e Cretaceous suggest led  pegmatite  and Miocene e r o s i o n ,  a r e l a t i o n s h i p to the t e c t o n i c processes  which  to formation of other metamorphic core complexes. However, many d i f f e r e n c e s between the Three Ladies  Mountain area and the t y p i c a l core complexes of the southwestern Little  United S t a t e s c a u t i o n a g a i n s t lumping the  R i v e r F a u l t with other detachment zones.  For  i n s t a n c e , the rocks i n the hanging w a l l a r e not as young as T e r t i a r y , and may be approximately the f o o t w a l l rocks  the same age as  ( l a t e P r o t e r o z o i c to P a l e o z o i c ) , nor  are they undeformed nor completely  unmetamorphosed.  88 There are a l s o no m y l o n i t i c s c h i s t s and gneisses  f a b r i c s i n the f o o t w a l l  that can be proven to be r e l a t e d to  T e r t i a r y movement on- the L i t t l e  River F a u l t .  Mylonitic  f a b r i c s have been observed i n the f o o t w a l l carbonate by Klepacki  (1981).  D u c t i l e s t r a i n occurred  during  compressional t e c t o n i c events i n the m i d - J u r a s s i c , whereas b r i t t l e  features  r e l a t e d to the L i t t l e  F a u l t are c l e a r l y younger than m i d - J u r a s s i c  River  f o l d s , and  are a l s o postmetamorphic. S l i d i n g of hanging w a l l rocks River F a u l t occurred underlying  during  f o o t w a l l rocks,  r o t a t i o n , as c r o s s c u t  down along  uplift  the L i t t l e  and t i l t i n g of the  but d i d not i n v o l v e much  F2 s t r u c t u r e s r e t a i n s i m i l a r  o r i e n t a t i o n s on e i t h e r s i d e of the f a u l t .  Variations in  o r i e n t a t i o n of p r e - f a u l t and f a u l t - r e l a t e d s t r u c t u r e s are due to l a t e r n o r t h e a s t - t r e n d i n g normal f a u l t s .  The l a t e s t  f o l d s (F4) and  f o l d phase (F4) was  accompanied by l o c a l l y - o c c u r r i n g , a x i a l - p l a n e mica c r e n u l a t i o n s with n e a r - v e r t i c a l a x i a l planes and g e n t l e northeast  plunge.  F4 f o l d s may imply minor compression  in a northwest-southeast d i r e c t i o n , but l a t e r northeast-trending  normal f a u l t s , which appear to  d i s p l a c e a Miocene e r o s i o n  surface,  imply extension i n  the same northwest-southeast d i r e c t i o n .  89 3.3.3  OTHER FAULTS  Other  than low-angle  faults  to the L i t t l e River f a u l t faults  occur throughout  high-angle f a u l t s  b e l i e v e d to be  system,  v a r i o u s higher-angle  the a r e a .  Most of the  in the Three Ladies Mountain area are  d i s c o n t i n u o u s and show r e l a t i v e l y  small displacements;  they probably formed d u r i n g u p l i f t . striking,  related  Late,  steeply north-dipping f a u l t s  east-west  were observed i n  the Three Ladies Mountain area, none of which showed any more than a few meters of i d e n t i f i a b l e  displacement;  however, as they are n e a r l y p a r a l l e l to f o l i a t i o n , and lithologies  are s i m i l a r over hundreds of meters of  t h i c k n e s s , a c t u a l displacement c o u l d be much g r e a t e r . Some n o r t h e a s t - t r e n d i n g f a u l t s , p a r a l l e l planes, near Mount Stevenson,  to F4 a x i a l  are a s s o c i a t e d with quartz  v e i n s ; sparse occurrences of molybdenite, c h a l c o p y r i t e occur in small r u s t y  pyrite,  zones.  N o r t h - n o r t h e a s t - t r e n d i n g f r a c t u r e s and parallel  and  faults,  to F4 a x i a l planes, are common and  influence  topographic f e a t u r e s i n c l u d i n g U-shaped g l a c i a l  valleys  such as Cariboo Lake, Ishkloo Creek V a l l e y , and  the  North Arm  of Quesnel  Lake.  Displacement  on these  faults  i s mostly down to the west, probably on the order of a few hundred meters,  deduced from the assumption  f a u l t e d pre-Miocene  erosion surface.  The  of a  large  metamorphic displacement a c r o s s the North Arm  of  Quesnel  Lake i s due mainly to e a r l i e r movement down to the  90  southeast along the L i t t l e  River F a u l t .  north and n o r t h e a s t - t r e n d i n g f a u l t s late Tertiary,  is inferred  to be  and p r e - P l e i s t o c e n e .  Northwest-trending, displacement  The age of the  high-angle f a u l t s with  of unknown d i r e c t i o n  than a few hundred meters a l s o lineaments; they may  but magnitude  less  appear as topographic  f o l l o w F2 a x i a l plane f o l i a t i o n .  If there i s any northwest-trending, high-angle f a u l t i n Long Creek, i t i s of t h i s type. lithologic  units,  C o n t i n u i t y of  f o l i a t e d g n e i s s bodies, and  structural  trends a c r o s s the lower Long Creek v a l l e y a b s o l u t e l y rules  out the p o s s i b i l i t y of major s t r i k e - s l i p f a u l t i n g  in t h i s l o c a t i o n . was  No evidence  for s t r i k e s l i p  observed anywhere in the study area.  faulting  4.  4.1  METAMORPHISM  INTRODUCTION Most of the high-grade metamorphic rocks i n the southern  Omineca B e l t are included  i n the Shuswap Metamorphic  Complex, which i s l o o s e l y d e f i n e d as a metamorphic and p l u t o n i c complex bounded by the s i l l i m a n i t e Shuswap Complex  has been d i v i d e d by O k u l i t c h  three major p a r t s :  isograd.  The  (1984) i n t o  (1) the Monashee Complex, which c o n t a i n s  gneisses o l d e r than 2 Ga, surrounded by the Monashee Decollement;  (2) the northwestern Shuswap Complex, which i s  an area of s i l l i m a n i t e grade paragneiss of l a t e  Proterozoic  to e a r l y P a l e o z o i c d e p o s i t i o n a l age., and p o s s i b l e minor mid-Paleozoic g r a n i t o i d g n e i s s ; and (3) the Okanagan  P l u t o n i c and Metamorphic  Complex.  Although not f o r m a l l y part of the Shuswap Metamorphic Complex, and separated from i t by about 20 km, the area of high-grade metamorphic rocks of the Snowshoe Group west of the North Arm of Quesnel Lake can be viewed as a window i n t o the "northwestern Shuswap Complex" as d e f i n e d by Okulitch  (1984).  Struik  (1984) includes the Snowshoe Group  in the "suspect" B a r k e r v i l l e Terrane, which l i e s  between  d e f i n i t e North American s t r a t a such as the Kaza Group and Cariboo Group to the n o r t h e a s t , and the suture zone between the Omineca B e l t and Q u e s n e l l i a .  The suture c r o s s e s Quesnel  Lake about 10 km south of Mount Stevenson ( O k u l i t c h 1984). The r e l a t i o n s h i p between B a r k e r v i l l e Terrane and the Shuswap 91  92 Metamorphic  Complex has not yet been c l a r i f i e d .  sillimanite  i s o g r a d in the Three L a d i e s Mountain area as  w e l l as the s i l l i m a n i t e  The  i s o g r a d d e f i n i n g the western  boundary of the Shuswap Complex do not c o i n c i d e with major lithologic  or t e c t o n i c c o n t a c t s , but are p a r t of a normal  metamorphic  p r o g r e s s i o n from low grade to high grade  w i t h i n an a p p a r e n t l y continuous succession. Terrane  lithostratigraphic  T h i s i m p l i e s that rocks  are t r a n s i t i o n a l  i n the B a r k e r v i l l e  i n t o the Shuswap Metamorphic  Complex at l e a s t on i t s west s i d e . northeastern  T h i s i s not true of the  boundary of the northwestern  where steep metamorphic c o i n c i d e with  1984).  Shuswap Complex,  g r a d i e n t s have been shown to  f a u l t s or shear  Pigage 1978; Engi  zones ( F l e t c h e r 1972;  The n o r t h e a s t e r n  boundary of the  s i l l i m a n i t e zone in the Three L a d i e s Mountain area fault  zone.  metamorphic  rocks  Here, the L i t t l e  i s also a  River Fault crosscuts  isograds at a high angle  rather than  parallels  them, and p l a c e s c h l o r i t e and b i o t i t e zone rocks d i r e c t l y on s t a u r o l i t e - k y a n i t e and s i l l i m a n i t e zone rocks. River F a u l t i s not continuous northeastern  along  whereas the Matthew F a u l t , which l i e s about i s . The L i t t l e  Little  s t r i k e with the  boundary of the Shuswap Metamorphic  n o r t h e a s t , probably  The  Complex,  10 km to the  River F a u l t i s d i s c u s s e d  in a separate s e c t i o n . The r e g i o n a l metamorphic Mountain/Mount  Stevenson area  progression  i n the Three Ladies  follows a t y p i c a l  sequence from g r e e n s c h i s t f a c i e s to amphibolite  Barrovian facies,  with  93 maximum metamorphic r e c r y s t a l l i z a t i o n postkinematic  synkinematic  to second-phase deformation  m i d - J u r a s s i c Columbian Orogeny.  Timing  and  during the  of formation of the  o l d e s t metamorphic f o l i a t i o n  i s unclear.  P o s s i b l e evidence  for p r e - J u r a s s i c deformation  and/or metamorphism r e s t s  e n t i r e l y on a few o b s e r v a t i o n s that quartz d i o r i t i c f o l d e d by f i r s t - p h a s e foliation  sills  f o l d s apparently truncate metamorphic  i n the adjacent metasedimentary rock.  Prograde  metamorphism i n v o l v i n g growth of index minerals such garnet,  staurolite,  k y a n i t e , and  sillimanite  (and  as  rarely  preserved c h l o r i t o i d ) took p l a c e p r i m a r i l y during and second-phase f o l d i n g  i n one  metamorphic-deformational  relatively  cycle.  continuous  R e c r y s t a l l i z a t i o n of  muscovite accompanied l a t e r . f o l d i n g , f o l l o w e d by growth of  after  retrograde  chlorite.  Metamorphic isograds mapped i n the Three Ladies Mountain/Mount Stevenson area f o l l o w the general p a t t e r n shown by F l e t c h e r (1972) and Campbell differences resulting and  (1978) with a  few  from s u b d i v i s i o n of metamorphic zones  r e c o g n i t i o n of the L i t t l e River F a u l t (see P l a t e I I I ) .  Pelitic  rocks of the Snowshoe Group i n t h i s area are  mainly  in the s t a u r o l i t e - k y a n i t e zone of the B a r r o v i a n s e r i e s i n amphibolite  f a c i e s , with s l i g h t l y  lower  grade rocks to the  west near I s h k l o o Creek and  first  s i l l i m a n i t e zone rocks to  the east near the North Arm  of Quesnel Lake.  To  the  northwest, metamorphic grade i n the Snowshoe Group to garnet and  then b i o t i t e zone a few  decreases  k i l o m e t e r s west of  94 Ishkloo Creek. northeast,  Metamorphic grade a l s o decreases  southeast,  and  southwest; the  original  d i s t r i b u t i o n of isograds i s d i s r u p t e d by f a u l t s northeast and  southeast,  metamorphism and cover The  and  i s obscured  to the  by  in the  retrograde  in the southwest toward Grain Creek.  r e l a t i o n s h i p of metamorphism to the suture zone between  the Snowshoe Group rocks and Q u e s n e l l i a has been s t u d i e d by Rees (1981).  95 4.2 METAMORPHIC ZONES IN PELITES  4.2.1  INTRODUCTION  Ten metamorphic defined  s u b d i v i s i o n s or zones have been  in the Three L a d i e s Mountain/Mount  area on the b a s i s of metamorphic assemblages i n p e l i t e s . metamorphic through  Stevenson  t e x t u r e s and  P l a t e III i s a map  zones and sample  localities.  mineral  showing  Zones  (1)  (8) are i n p e l i t e s of the Snowshoe Group, and  represent  d i v i s i o n s of the B a r r o v i a n  amphibolite  facies.  Zones  (9) and  series in  (10) are i n p h y l l i t e s  of the hanging w a l l of the L i t t l e River F a u l t , and are d i v i s i o n s of g r e e n s c h i s t d i s t i n c t i v e mineral supporting  facies.  For each zone,  t e x t u r e s are summarized  as  evidence f o r a suggested metamorphic  history.  I l l u s t r a t i o n s showing r e p r e s e n t a t i v e t e x t u r e s accompany the t e x t ( F i g u r e s 26 to 32).  Schematic AFM diagrams f o r  zones (3) through (8) are shown on a P-T grid  in F i g u r e  petrogenetic  25.  The minerals  that c h a r a c t e r i z e the zones are  r e f e r r e d to by t h e i r a b b r e v i a t i o n s , which are given in Appendix I.  i  96  BATHOZONES  8-  Zone ( 8 )  +  QUARTZ  +  MUSCOVITE  KY  + PLAGIOCLASE  1-  + H20  400  T  500  -r  600  700  F i g u r e 2 5 . P r e s s u r e / t e m p e r a t u r e d i a g r a m i l l u s t r a t i n g AFM assemblages f o r metamorphic zones i n t h e Three L a d i e s Mountain/Mount Stevenson' a r e a i n r e l a t i o n t o bathozones as d e f i n e d by C a r m i c h a e l ( 1 9 7 8 ) , a n d m o d i f i e d by A r c h i b a l d et a l . (1983) .  97 4.2.2 METAMORPHIC ZONES ZONE (1).  RETROGRADE GARNET ZONE  QZ-BI-MS-PL-GT (GT r e p l a c e d by CH) ± CH, OP, AP, RU, ZR, CA,  EP, SP  Garnets are completely other  retrograded to c h l o r i t e .  index minerals are present.  s t r a i g h t S. p a r a l l e l Foliation  2  was overgrown by garnet.  deformation  formed S , d e f i n e d by b i o t i t e . 2  cracked garnets and kinked b i o t i t e ,  than b i o t i t e . garnet a l t e r i n g  Retrograde  biotite  which appears  Renewed also  to be l a t e r  r e a c t i o n s i n v o l v e b i o t i t e and  to c h l o r i t e  titanium-rich biotite  and s e r i c i t e .  Red-brown,  i s r e p l a c e d by pale-green,  (sagenitic) c h l o r i t e  haloes from  and perhaps  Further metamorphic  kinked and smeared muscovite,  rutilated  c o n t a i n vague  to S, but not to S .  (S,) d e f i n e d by muscovite  crystallization  Garnets  No  with prominent p l e o c h r o i c  zircon.  Highest metamorphic grade achieved was at l e a s t g a r n e t - b i o t i t e zone, and c o u l d have been much h i g h e r .  98 ZONE ( 2 ) .  GARNET-BIOTITE ZONE  QZ-BI-MS-PL-GT ± CH,  Garnets  range from  p o s s i b l e zoning and severely  OP,  ZR,  RU,  SP,  2 to 6 mm  KS,  i n diameter,  some r o t a t i o n a l  Most are  retrograded to c h l o r i t e on the rims, and  Cores show s t r a i g h t  core  I n c l u s i o n s are q u a r t z , opaques, and i n t e r p r e t e d as r e l i c t  clastic  ( S T ) , was  foliation  and  biotite.  rims.  Some retrograded  rims, with undeformed  Garnet  grew on l a y e r i n g or  then  r o t a t e d while growing  s y n k i n e m a t i c a l l y with formation of S 2 , by muscovite  (see F i g u r e  K - f e l d s p a r , which i s  grains.  garnets have deformed c h l o r i t e inner r e t r o g r a d e zones.  Large,  which i s d e f i n e d  postkinematic  p o r p h y r o b l a s t s of red-brown b i o t i t e are kinked c r o s s c u t by muscovite, and  to  i n c l u s i o n p a t t e r n , with some  r o t a t i o n a l t e x t u r e ( S - p a t t e r n ) toward the  first  with  texture.  c h l o r i t e plus s e r i c i t e between rim and 26).  CA  which grows along kink  and direction  i s e i t h e r a l s o kinked or mimetic on p o l y g o n a l a r c s .  Some r e t r o g r a d e c h l o r i t e muscovite,  and  w i t h i n garnet  later  i s a l s o kinked, and  retrograde c h l o r i t e  outlines.  c r o s s c u t by  i s undeformed  99  Figure 26. Garnet zone (2), sample 82-376. Main metamorphic f o l i a t i o n (S ) of b i o t i t e and muscovite, wrapping around garnet, was subsequently f o l d e d by F3 f o l d s ( S with minor a d d i t i o n a l muscovite r e c r y s t a l l i z a t i o n ; retrograde c h l o r i t e and s e r i c i t e a f t e r garnet are postkinemat i c . g  3  1 00 ZONE (2a).  "GARNET" ZONE  Subset of Zone (3) or Zone  QZ-BI-MS-PL-GT-TO ± CH,  (4)  OP,  ZR,  AP,  SP,  RU  T h i s zone i s d i s t i n g u i s h e d on the b a s i s of t e x t u r e s and mineral recognizable  a s s o c i a t i o n , and  as a separate  garnet  i s not  zone in the  field.  The  samples were c o l l e c t e d from w i t h i n the s t a u r o l i t e s t a u r o l i t e - k y a n i t e zones. 14 mm,  with S^  trails  of quartz  r o t a t i o n and other  parallel and  2  the  to S^  ( S ) , d e f i n e d by s t r a i g h t 2  These samples escaped  further porphyroblast  p e l i t e s in the same a r e a s .  (less A l 0 , higher  Garnets range from 2 to  opaques.  they were l e s s p e l i t i c 3  H 0)  grades.  2  the  growth so common in I t i s p o s s i b l e that  i n i t i a l l y and  so fewer  reactants  were a v a i l a b l e to r e c r y s t a l l i z e at  the  Most of these samples are a s s o c i a t e d in  f i e l d with the uppermost Snowshoe Formation  q u a r t z i t e and  and  p e l i t e , and  c l o s e to outcrops  s t a u r o l i t e and/or k y a n i t e . compositionally c o n t r o l l e d .  T h i s t e x t u r e may  with be  101 ZONE ( 3 ) .  STAUROLITE ZONE  QZ-BI-MS-PL-GT-ST-TO ± CH, OP, ZR, RU, AP  F i v e subgroups are based  on t e x t u r e s i n garnets:  (a) Garnets are about 5 mm and have t e x t u r a l Straight  S- i n core i s d e f i n e d by quartz and opaques, ;  surrounded trails,  zoning.  by a r o t a t i o n a l zone with S-shaped  and a c l e a r  (b) Garnets  rim free  have s t r a i g h t  from  inclusion  inclusions.  S^ i n core, but no obvious  r o t a t i o n a l zone; however, they have been r o t a t e d a f t e r c e s s a t i o n of growth. (c) Garnets c o n t a i n folded helicitic,  or c r e n u l a t e d S- , so are  but not r o t a t i o n a l .  (d) Garnets are broken and r e t r o g r a d e d , as i s staurolite. (e) S t a u r o l i t e c o n t a i n s t i n y , i d i o b l a s t i c garnets, with no garnets  All  i n matrix  (see F i g u r e 27).  the garnets i n t h i s zone are t e x t u r a l l y zoned,  i n d i c a t i n g at l e a s t two p e r i o d s of growth, or changing c o n d i t i o n s during growth. straight  S- of dominantly f  renewed shear and r o t a t i o n  Most cores c o n t a i n only quartz.  Rapid growth during  l e d t o syndeformational,  "snowball" t e x t u r e s i n the intermediate zone of the garnet. without  F i n a l l y , some garnets continued to c r y s t a l l i z e inclusions,  resulting  in clear  rims.  Some  102  Figure 27. S t a u r o l i t e zone (3), sample 81-344. Large s t a u r o l i t e p o r p h y r o b l a s t i n c l u d e s i d i o b l a s t i c garnet and t r a i l s of r u t i l e and quartz (S,- ) p a r a l l e l to S ( S ) . e  2  103 s t a u r o l i t e s , as w e l l as garnets, show S-shaped patterns, indicating growth.  synkinematic  S- may be p a r a l l e l ;  to S  g  rotation  inclusion  during  , e i t h e r at edges of  g r a i n s showing r o t a t i o n a l t e x t u r e s or a l l through postkinematic of garnet  grains.  S t a u r o l i t e growth o u t l a s t e d that  i n some r o c k s .  (helicitic)  I t c o n t a i n s garnets and f o l d e d  i n t e r n a l t r a i l s of opaques.  appear to be contemporaneous with crystallization foliation  foliation  Garnet  rims  biotite  ( S ) i n some p l a c e s . 2  Later  ( S ) i s d e f i n e d by muscovite and i s at a 3  s l i g h t angle to S ; i t may represent f l a t t e n e d and 2  kinked S  2  that has been only p a r t l y  recrystallized.  Both s t a u r o l i t e and p l a g i o c l a s e p o r p h y r o b l a s t s c o n t a i n inclusion t r a i l s and most garnet Presence  r e l a t e d to S . 2  Finally,  some b i o t i t e  rims have r e t r o g r a d e d to c h l o r i t e .  of s t a u r o l i t e may be p a r t l y c o n t r o l l e d by  composition  of the host p e l i t e .  One l o c a l l y mappable  u n i t c o n t a i n s the l a r g e s t percentage porphyroblasts  of s t a u r o l i t e  (>10%), as w e l l as l a r g e p l a g i o c l a s e  p o r p h y r o b l a s t s , uncommon i n other p e l i t e s samples 80-69, 80-135, 82-344).  ( f o r example,  1 04 ZONE ( 4 ) .  STAUROLITE-KYANITE ZONE  QZ-BI-MS-PL-GT-ST-KY-TO ± CH, OP, GR, ZR, AP, RU, SP, EP  Pelitic  s c h i s t s i n t h i s zone show the g r e a t e s t  v a r i e t y of t e x t u r e s which record the c r y s t a l l i z a t i o n h i s t o r y of the r o c k s .  Garnet, s t a u r o l i t e , and kyanite  reach t h e i r maximum s i z e and modal abundance i n t h i s zone, and the recorded complex than  deformational  f o r the other zones.  history  i s more  T h i s may be a  consequence of i n c r e a s e d r e a c t i o n r a t e s and shearing due to  i n c r e a s i n g temperatures during p r o g r e s s i v e  deformation,  l e a d i n g to r a p i d c r y s t a l l i z a t i o n and l a r g e  s i z e of p o r p h y r o b l a s t s , which tend to preserve the textural  history.  Garnets range i n s i z e from 1 to 15 mm, 2 to 5 mm,  and make up 5-25% (average  of  schist.  pelitic  subidioblastic, and  rounded, or s k e l e t a l , or a t o l l - s h a p e d ,  are q u a r t z ,  Minerals  included i n  i l m e n i t e and other opaques, g r a p h i t e ,  and minor c h l o r i t o i d , tourmaline.  10%) of a sample  They are i d i o b l a s t i c to  c o n t a i n up t o 40% i n c l u s i o n s .  garnet  averaging  s t a u r o l i t e , c h l o r i t e , and  I t i s p o s s i b l e that some c h l o r i t e and/or  staurolite  i n c l u d e d i n garnet  chloritoid  inclusions.  have r e p l a c e d former  105  A l l garnets show some degree of r o t a t i o n , with S^ not p a r a l l e l  to S  . Most garnet  e  t e x t u r e s in the  s t a u r o l i t e - k y a n i t e zone are s i m i l a r to those s t a u r o l i t e zone.  P a t t e r n s of i n c l u s i o n  i n the  t r a i l s and  t e x t u r e s w i t h i n garnet may be c a t e g o r i z e d as f o l l o w s (number of examples f o r each shown i n p a r e n t h e s e s ) : - Straight S  /  (3)  - S t r a i g h t S- only i n core (8) ;  - Helicitic - Snowball  ( f o l d e d or c r e n u l a t e d S^) (2) or r o t a t i o n a l  (S-shaped  p a t t e r n ) (9)  - T e x t u r a l l y zoned (9) - Atoll  (3), mostly near ST-KY-SIL t r a n s i t i o n zone (5)  (see F i g u r e s 28, 29, and 30) • C h l o r i t o i d occurs only as i n c l u s i o n s i n a l a r g e garnet ( F i g u r e 28), between the inner core and the outer zone, w i t h i n the r o t a t i o n a l zone of the garnet,  implying that  f o l d i n g was t a k i n g place during c h l o r i t o i d growth.  This  rock, which i s now i n the s t a u r o l i t e - k y a n i t e zone, must have c r y s t a l l i z e d along a prograde formation of c h l o r i t o i d ,  P-T path that i n c l u d e d  such as a t y p i c a l medium to  h i g h - p r e s s u r e Barrovian sequence.  The c h l o r i t o i d  in t h i s sample are l a r g e enough to determine  inclusions  complete  o p t i c a l p r o p e r t i e s , and to d i s t i n g u i s h them from  chlorite  i n c l u s i o n s i n the same garnet  Many  chlorite  (see Appendix I ) .  i n c l u s i o n s i n garnet may be replacements  c h l o r i t o i d grains.  In one rock  i n c l u s i o n s of s t a u r o l i t e  (81-315),  of e a r l i e r  abundant small  i n a garnet may have r e p l a c e d  106  F i g u r e 28. S t a u r o l i t e - k y a n i t e zone ( 4 ) , sample 7 9 - 1 3 . Staurolite-kyanite-garnet-muscovite schist contains c h l o r i t o i d (CD) i n c l u s i o n s in 'snowball' ( r o t a t i o n a l ) garnet synkinematic with F2 f o l d i n g , i n d i c a t i n g prograde metamorphic growth of garnet. Green c h l o r i t e (CH) i s included i n garnet c o r e . S t a u r o l i t e and kyanite are postkinematic to S but prekinematic to S , and some kyanite i s r e p l a c e d by retrograde s e r i c i t e . 2  3  107  Figure 29. S t a u r o l i t e - k y a n i t e zone (4), sample 81-234. Garnet rims, s t a u r o l i t e , and kyanite are a l l h e l i c i t i c , i n c l u d i n g f o l d e d t r a i l s of g r a p h i t e . S - i s p a r a l l e l to S  1 08 former c h l o r i t o i d , as t h i s t e x t u r e  i s unusual f o r  s t a u r o l i t e , which i s u s u a l l y p o r p h y r o b l a s t i c . S t a u r o l i t e continues where i t i s as important Staurolite  a porphyroblast  forms i d i o b l a s t i c  porphyroblasts < 1 cm.  i n t o the s t a u r o l i t e - k y a n i t e zone,  to s u b i d i o b l a s t i c  up to 3 cm long by 1 cm wide, but i s commonly  I t i n c l u d e s g r a i n s of quartz, g r a p h i t e , i l m e n i t e ,  rutile, biotite,  kyanite, garnet,  I n c l u s i o n t r a i l s may be p a r a l l e l folded  as k y a n i t e .  (helicitic),  tourmaline,  and z i r c o n .  to the o u t s i d e  or r o t a t i o n a l  (S-shaped).  foliation, Some  s t a u r o l i t e s are t e x t u r a l l y zoned, showing two growth p e r i o d s , that are d i s t i n c t  i n terms of deformation.  cores c o n t a i n many i n c l u s i o n s that d e f i n e a vague and  the rims are c l e a r , and apparently  The foliation,  post-kinematic.  S t a u r o l i t e may i n c l u d e k y a n i t e , or kyanite may i n c l u d e staurolite,  i n some cases  i n the same t h i n s e c t i o n , so  s t a u r o l i t e and kyanite are i n t e r p r e t e d as contemporaneous. Poikiloblastic  s t a u r o l i t e may i n c l u d e smaller  staurolite  g r a i n s as w e l l as k y a n i t e , a t t e s t i n g to a long growth p e r i o d , or wide s t a b i l i t y Kyanite  field  commonly occurs  for staurolite.  i n two d i f f e r e n t  s e t t i n g s i n the  s t a u r o l i t e - k y a n i t e zone: (1) I t i s common as p o r p h y r o b l a s t s up to 2 cm long i n p e l i t i c garnet.  Kyanite  s c h i s t along with s t a u r o l i t e and  i s somewhat a l i g n e d on f o l i a t i o n and  l i n e a t i o n , but i s n e i t h e r s t r o n g l y o r i e n t e d nor completely random.  I t tends to be synkinematic  f o l d i n g , but some i s bent, kinked,  i  with respect to F2  and has undulose  1 09 e x t i n c t i o n , probably as a r e s u l t of F3 or l a t e r Some g r a i n s c o n t a i n S-shaped i n c l u s i o n t r a i l s , S^ i s p a r a l l e l to S  e  deformation. and g e n e r a l l y  . I n c l u s i o n s are q u a r t z , g r a p h i t e ,  i l m e n i t e , r u t i l e , muscovite,  b i o t i t e , and tourmaline.  the kyanite to s i l l i m a n i t e zone t r a n s i t i o n ,  Near  kyanite g r a i n s  are rounded and embayed by q u a r t z ; i n some cases the core has been r e p l a c e d by quartz and b i o t i t e , rim.  (2) Kyanite  tabular c r y s t a l s  i s more s p a r s e l y d i s t r i b u t e d as l a r g e , (up to 2 cm wide by 10 cm long) w i t h i n  u n f o l i a t e d quartz-muscovite pelitic  l e a v i n g part of the  segregations occurring in  s c h i s t or micaceous q u a r t z i t e , throughout the  s t a u r o l i t e - k y a n i t e and kyanite In the same area, near  zones.  the k y a n i t e to s i l l i m a n i t e  boundary, l a r g e garnets a r e a l s o beginning to break down to " a t o l l garnets" (Figure 30). The rim of the garnet  remains  as a ring-shaped g r a i n , whereas the intermediate zone, which probably contained S-shaped i n c l u s i o n t r a i l s , r e p l a c e d by quartz and b i o t i t e .  has been  In some cases the core has  been the l a s t part of the i n t e r i o r of the garnet to break down. The outermost  zone of the garnet would s t i l l  be i n  e q u i l i b r i u m with the p e l i t e matrix, whereas the i n t e r i o r would be unstable i f exposed t o the matrix, and able to r e a c t with i t or with the i n c l u s i o n s  ( i n some of these  garnets, the mid-zone c o n t a i n s up to 40% i n c l u s i o n s ) .  The  components of the i n t e r i o r p a r t of the garnet would then be available  f o r f u r t h e r r e a c t i o n s , i n c l u d i n g those  producing  110  Figure 30. S t a u r o l i t e - k y a n i t e - s i l l i m a n i t e zone (5), sample 81-279. A t o l l , or ring-shaped, garnet near k y a n i t e - s i l l i m a n i t e i s o g r a d ; i n t e r i o r of garnet has been replaced by muscovite, b i o t i t e , and q u a r t z .  111 new  garnets.  Such a r e a c t i o n might be that of the breakdown  of s t a u r o l i t e and  QZ + MS  formation of  + ST = BI + GT  sillimanite:  + SI + H 0  (1.1a)  2  There must a l s o be a garnet breakdown r e a c t i o n , such  MS  as  + GT = SI + BI + QZ.  (1.2)  These r e a c t i o n s c o u l d occur simultaneously as long as d i f f e r e n t garnet compositions of the r e l i c t  were i n v o l v e d .  If the cores  garnets were the l a s t part to break down, Mn  would be r e l e a s e d a f t e r  the new  garnets had  s t a r t e d to grow.  Then the rims of the newly regenerated garnets would be. higher i n Mn the case  than expected  f o r s i l l i m a n i t e zone.  i n some of the a n a l y s e d garnets  This i s  (see s e c t i o n  on  garnet z o n i n g ) . Most of the l a r g e r opaque i n c l u s i o n s  in p o r p h y r o b l a s t s  in the s t a u r o l i t e - k y a n i t e zone are lath-shaped i l m e n i t e (confirmed with probe d a t a ) .  Other  T i - r i c h m i n e r a l s are  r a r e , such as sphene, which only occurs i n s l i g h t l y calcareous s c h i s t s . s t a u r o l i t e and kyanite zone).  R u t i l e occurs as i n c l u s i o n s w i t h i n  k y a n i t e , but not  i n garnet  (except  i n the  Where r u t i l e comes in c o n t a c t with q u a r t z ,  whether i n s i d e a g r a i n of s t a u r o l i t e or k y a n i t e , or at the rim next to the matrix,  i t i s r e p l a c e d by i l m e n i t e .  a common t e x t u r e throughout  This i s  both the s t a u r o l i t e zone and  11 2 s t a u r o l i t e - k y a n i t e zone. an elongate  Some s t r i k i n g examples occur where  g r a i n s t r a d d l e s the contact between the  porphyroblast  and the s c h i s t matrix,  and the part included  w i t h i n the s t a u r o l i t e or kyanite i s c l e a r l y part p r o j e c t i n g i n t o the matrix  i s opaque  r u t i l e , and the  i l m e n i t e , with the  t r a n s i t i o n c o i n c i d i n g e x a c t l y with the rim of the porphyroblast.  See the s e c t i o n on the GRAIL geobarometer  for an i l l u s t r a t i o n and i n t e r p r e t a t i o n of t h i s t e x t u r e . The i l m e n i t e - r u t i l e t e x t u r e s suggest  that the s t a u r o l i t e  zone and kyanite zone were formed in P-T c o n d i t i o n s below those  f o r the p r e s s u r e - s e n s i t i v e r e a c t i o n  ALM + RUT = ILM + KY/SI + QZ,  known as the GRAIL geobarometer  (1.3)  (Bohlen  et a l . 1983).  Tourmaline i s commonly zoned i n p e l i t e s from to o l i v e green.  In t h i n s e c t i o n s of p e l i t e s cut  p e r p e n d i c u l a r to the dominant F 2 f o l d a x i s , end-sections  (0001) are more abundant than  the c - a x i s , i n d i c a t i n g some synkinematic tourmaline,  blue-green  tourmaline those p a r a l l e l to  o r i e n t a t i o n of  implying e i t h e r r o t a t i o n or growth d u r i n g peak  metamorphism.  Grain s i z e  most hand specimens.  i s too small to see tourmaline i n  11 3 ZONE (5).  STAUROLITE-KYANITE~SILLIMANITE ZONE  A l s o r e f e r r e d to as " T r a n s i t i o n  Zone".  QZ-BI-MS-PL-GT-ST-KY-SI-TO ± CH, OP, RU, ZR, AP  T h i s zone i s d e f i n e d by the " s i l l i m a n i t e - i n first  appearance of f i b r o l i t e  s t a u r o l i t e are s t i l l  i s o g r a d " , or  in thin sections.  Kyanite and  present, but are a p p a r e n t l y  breaking  down to s e r i c i t e , or q u a r t z , b i o t i t e , and g a r n e t . Tourmaline  i n t h i s zone shows complex zoning with more  than three c o n c e n t r i c colour-zones, i n c o n t r a s t to the usual two.  In sample 80-33, c o l o u r - z o n i n g c o n c e n t r i c to the  c - a x i s i s as f o l l o w s , from core to rim: (1) b l u i s h - g r e e n to brown, (2) o l i v e green, green.  C a t i o n zoning  in probe data variation  (3) pale y e l l o w i s h o l i v e ,  (4) o l i v e  i n one g r a i n of t h i s sample i s shown  (see Appendix I I ) .  Probe data  indicate a  from higher Mg than Fe i n the c o r e , to lower Mg  than Fe i n the rim, as w e l l as higher Na i n the core than i n the rim, but lower Ca i n the core than  i n the rim.  There i s  no Mn i n t h i s tourmaline, n e g l i g i b l e K, and c o n s t a n t T i from core to rim. abrupt  T h i s zoning p a t t e r n i s continuous  with no  transitions.  Tourmaline  i n t h i s zone may c o n t a i n i n c l u s i o n s of  q u a r t z , z i r c o n , or opaques, and may a l s o c r o s s c u t b i o t i t e . In another  sample (81-279),  tourmaline  inclusions  inside  kyanite have only one zone, and c o n t a i n i n c l u s i o n s that are p a r a l l e l to inclusion t r a i l s  i n the k y a n i t e , which are  11 4 p a r a l l e l to the o u t s i d e f o l i a t i o n .  Tourmaline  of t h i s rock shows two c o l o u r - z o n e s , of the matrix tourmaline  i n the matrix  implying that the rim  i s contemporaneous with kyanite  growth. Garnet  t e x t u r e s are markedly d i f f e r e n t  s t a u r o l i t e - k y a n i t e zone. 3 mm  remain,  comprise  Although  most garnets are now  l e s s than  contain straight  5% of the rock.  some r e l i c t < 1 mm  gl  i n diameter  Small, new  garnets  rutile  garnets have few  i n the  inclusions,  are a s s o c i a t e d with f i b r o l i t e near embayed s t a u r o l i t e Figure  and  are zoned, and  i n c l u d e k y a n i t e , s t a u r o l i t e , b i o t i t e , and outer p o r t i o n s .  in the  garnets up to  Larger, r e l i c t  S- p e r p e n d i c u l a r to S ;  from those  and  (see  31).  These t e x t u r e s have preserved evidence  for  two  uncompleted r e a c t i o n s :  KY = SIL  QZ  P-T  + MS  (1.4)  + ST = BI + GT + SI + H 0.  c o n d i t i o n s were probably near  reactions.  (1.1a)  2  See  the i n t e r s e c t i o n of these  the s e c t i o n on s t a u r o l i t e breakdown f o r  estimated temperatures  and p r e s s u r e s of t h i s  intersection.  115  Figure 31. S t a u r o l i t e - s i 1 1 i m a n i t e zone (6), sample 80-30. F i b r o l i t i c s i l l i m a n i t e forming at the expense of s t a u r o l i t e . Note small s i z e of garnets (<1 mm).  11 6 ZONE ( 6 ) . STAUROLITE-SILLIMANITE ZONE  QZ-BI-MS-PL-GT-ST-SI ± CH, OP, ZR, RU, AP, KS, EP  Staurolite  is s t i l l  present, but s k e l e t a l  kyanite i s no longer p r e s e n t . staurolite, tiny,  which appears  < 2 mm,  A few r e l i c t That  Fibrolite  and embayed;  surrounds  to be breaking down.  Garnets are  look new, and are a s s o c i a t e d with new b i o t i t e . garnets are broken and embayed.  kyanite has disappeared before s t a u r o l i t e i s  suggestive of a P/T path  i n Bathozone 4 (Carmichael  1978).  1 17 ZONE ( 7 ) . SILLIMANITE ZONE  QZ-BI-MS-PL-GT-SI ± CH, OP, RU, ZR, SP, ST  T h i s corresponds to the c l a s s i c zone".  As muscovite  "first  sillimanite  i s present i n a l l p e l i t e s , c o n d i t i o n s  are below those of the r e a c t i o n MS + Q = SI + KS + H 0. 2  Garnets a r e small (< 1 mm) except comprise  1-5% of the rock.  rounded,  s u b i d i o b l a s t i c , or o v a l .  relicts  (3 to 6 mm), and  They tend to be blocky to Garnets c o n t a i n l e s s  5% i n c l u s i o n s , which are q u a r t z , opaques, and b i o t i t e . Sillimanite  i s i n the form of f i b r o l i t e  knots, which a r e  bundles of t i n y , a c i c u l a r s i l l i m a n i t e g r a i n s , commonly a s s o c i a t e d with b i o t i t e .  than  118  F i g u r e 32. S i l l i m a n i t e zone ( 7 ) , sample 80-31. Tiny garnets o u t l i n e a former garnet porphyroblast r e p l a c e d by q u a r t z , p l a g i o c l a s e , b i o t i t e , and muscovite. S i m i l a r t e x t u r e s , i n v o l v i n g both garnet and k y a n i t e , were observed in the kyanite zone ( 8 ) .  1 19 ZONE ( 8 ) .  KYANITE ZONE  QZ-BI-MS-PL-GT-KY ± CH, OP, RU, ZR, AP, ST, TO, KS  Garnets  2-5 mm are r e l i c t ,  opaques, r u t i l e , Garnets  embayed, and i n c l u d e q u a r t z ,  b i o t i t e , muscovite,  < 2 mm have rare i n c l u s i o n s of q u a r t z , opaques,  b i o t i t e , and r u t i l e .  A l l are very small and i n some p l a c e s  appear to be growing i n an o l d garnet little  and s t a u r o l i t e .  garnets  shape, as a r i n g of  (see F i g u r e 32). In some rocks, t i n y  c o n t a i n no i n c l u s i o n s .  Kyanite i n t h i s zone i s a l s o  garnets tiny,  o c c u r r i n g along l a y e r s with g a r n e t s .  B i g k y a n i t e s are  pseudomorphed by s e r i c i t e ;  i s r e a c t i n g out. T h i s  staurolite  i s the only zone i n which garnets Textures suggest  regenerated  i n c l u d e b i o t i t e or r u t i l e . forms of garnet,  biotite,  and kyanite i n t h i s zone, although a l l were a l s o present i n Zone ( 4 ) .  Such t e x t u r e s are c o n s i s t e n t with an  i n t e r p r e t a t i o n that the d i s c o n t i n u o u s r e a c t i o n  QZ + MS + ST = BI + GT + KY + H 0  (1.1b)  2  has taken p l a c e i n Bathozone 5 (Carmichael  1978).  1 20 ZONE ( 9 ) .  BIOTITE-CHLORITE ZONE  QZ-MS-CH-BI-OP  T h i s zone i s r e s t r i c t e d  to the hanging wall of the  L i t t l e River F a u l t near Limestone p o i n t , i n p h y l l i t i c i n t e r l a y e r e d with with carbonates.  Foliation  d e f i n e d by muscovite and c h l o r i t e .  Biotite  it  occurs  and  retrograded  to c h l o r i t e .  foliation,  i s mainly  i s r a r e ; where  i t i s red-brown and p o r p h y r o b l a s t i c ,  to the main m u s c o v i t e - c h l o r i t e  rocks  postkinematic  but a l s o  kinked  121 ZONE (10).  CHLORITE ZONE  T h i s zone a l s o occurs i n the hanging w a l l of the L i t t l e River F a u l t , but s t r u c t u r a l l y h i g h e r , on S e r v i c e Mountain, in p h y l l i t i c  rocks i n t e r l a y e r e d with carbonates.  The  f o l l o w i n g assemblages are present: Q-MS-CHL ± CA, TO, ZR, OP (IL, HE, MG) Q-MS ± GP, OP Q-MS-CA-GP ± OP, PY The p e l i t i c phyllitic  rocks i n t h i s zone may show two d i s t i n c t  cleavages, a x i a l planar to F2 and F3 f o l d s .  E i t h e r one of these cleavages may be dominant  in a  p a r t i c u l a r outcrop, which makes them d i f f i c u l t to d i s t i n g u i s h with c e r t a i n t y , as both were formed i n c h l o r i t e grade g r e e n s c h i s t f a c i e s c o n d i t i o n s , and are d e f i n e d by muscovite-chlorite c r y s t a l l i z a t i o n  foliation.  The more q u a r t z - r i c h u n i t s tend to preserve the F2 a x i a l planar cleavage, whereas  i n t e r l a y e r e d p h y l l i t e may show F3  a x i a l planar cleavage n e a r l y p e r p e n d i c u l a r to i t Figure 9).  (see  1 22 4.3 GARNET ZONING  4.3.1  DESCRIPTION OF ZONING PROFILES  Garnets from e i g h t samples were analyzed on the e l e c t r o n microprobe (data shown i n Appendix  II).  All  garnets analyzed can be c h a r a c t e r i z e d by the mineral formula (Fe,Mg,Ca,Mn) Al Si 0 , . 3  2  3  2  They are dominantly almandine (28 to 37 Wt.% FeO) with l e s s e r amounts of pyrope (1 to 4 Wt.% MgO), s p e s s a r t i n e (0.1 to 4.5 Wt.% MnO), and g r o s s u l a r  (1 to 8 Wt.% CaO).  Zoning p r o f i l e s of garnets are shown i n F i g u r e s 33 to 41.  The s t a u r o l i t e zone  (Zone 3) i s represented by  sample 82-389; the s t a u r o l i t e - k y a n i t e zone  (Zone 4) by  sample 81-279; the s t a u r b l i t e - k y a n i t e - s i l l i m a n i t e  zone  (Zone 5) by samples 80-33, 80-119, and 81-278; the s t a u r o l i t e - s i l l i m a n i t e zone the s i l l i m a n i t e zone  (Zone 6) by sample 80-19;  (Zone 7) by sample 80-31; and the  kyanite zone (Zone 8) by sample 81-325. Although the number of analyzed samples i s l i m i t e d , c e r t a i n p a t t e r n s have emerged that may have significance.  general  O b s e r v a t i o n s and i n t e r p r e t a t i o n s made  here have been supplemented by t e x t u r a l evidence from additional  samples.  1 23 In the samples analyzed, Fe i s lower  i n the core of  the garnet and i n c r e a s e s toward the rim i n a l l but one sample.  The maximum d i f f e r e n c e between core and rim i s  5 Wt.% (32 to 37) i n 81-279.  The exception i s sample  81-325, i n which the garnets are very small (<0.5 mm); Fe i s r e l a t i v e l y constant with s l i g h t l y higher values i n the core  ( a l l w i t h i n 1 Wt.% (34 to 35 Wt.%).  Some of  the l a r g e r garnets near the kyanite to s i l l i m a n i t e t r a n s i t i o n show a drop i n Fe values near the rim (81-278, 81-279). Mg v a r i e s l e s s s t r o n g l y than does Fe. grade samples i t i s lowest  In the lower  i n the core of the garnet,  and higher near the rim, with a s l i g h t drop r i g h t at the rim (81-278, 81-279, 82-389).  Mg i s highest i n the core  of garnets i n rocks from the high-grade kyanite to s i l l i m a n i t e t r a n s i t i o n  side of the  (80-19, 80-119, 80-33,  and 80-31) and i n the kyanite zone (Zone 8) (81-325). Mg and Fe zoning p a t t e r n s i n garnet are r e l a t e d i n that i n the lower grade rocks Mg and Fe are both  lower  in the core and higher i n the rim, but i n s i l l i m a n i t e zone (Zones 6 and 7) they are opposite, with Mg higher in the core whereas Fe i s s t i l l  lower.  In kyanite zone  (Zone 8) both Fe and Mg show s l i g h t l y higher values i n the core of the garnet, but the v a r i a t i o n  i s small.  Mn zoning p a t t e r n s a l s o vary from the low-grade to the high-grade  rocks.  The l a r g e r garnets from the  s t a u r o l i t e and s t a u r o l i t e - k y a n i t e zones (82-389, 81-279,  1 24 81-278) have higher Mn rim, and pattern  higher Mn is fairly  prograde  in the c o r e , lower Mn  on the rim i t s e l f .  The  h i g h e r Mn  these l a r g e , zoned garnets may  be due  metamorphism of the rim of the  garnet.  T h i s i s probably  of  Mn  i n the rims  the higher-grade  garnets  not the case  from  on the rim of  to retrograde  i n some of the  garnets, however, i n which the Mn  p r o f i l e s show lower higher Mn  T h i s kind of  t y p i c a l of garnets t h a t r e t a i n  t e x t u r a l zoning.  higher-grade  toward the  i n the c o r e s grading out (80-19, 80-119, 81-325).  garnets  samples 80-31  p a t t e r n s with Mn  higher  zoning to Not a l l  f o l l o w t h i s p a t t e r n ; small and  80-33 show normal zoning  i n the c o r e , and Fe lower  i n the  core. Ca zoning p a t t e r n s in garnets s t a u r o l i t e and  i n the rim.  or  reflect  rocks i n the  s t a u r o l i t e - k y a n i t e zone (82-389, 81-279)  show extreme zoning with higher Ca Ca  from  T h i s may  a prograde  i n the core and  lower  be c o m p o s i t i o n a l l y c o n t r o l l e d  metamorphic c a t i o n p r e f e r e n c e .  values i n the higher-grade  rocks are f a i r l y  low  and  constant. Presence  of T i i n garnets  nearby i l m e n i t e i n c l u s i o n s and insigni f icant.  is directly  related  i s c o n s i d e r e d to be  to  Ca  125  Figure 33. Garnet zoning p r o f i l e 82-389, s t a u r o l i t e zone.  f o r Garnet 2 from sample  126  Figure 34. Garnet zoning p r o f i l e 81-279, s t a u r o l i t e - k y a n i t e zone.  for Garnet 3 from sample  127  81-278  GARNET  (Fe,Mg Ca,Mn) AI Si 0 f  3  2  3  Figure 35. Garnet zoning p r o f i l e f o r Garnet 4 from sample 81-278, s t a u r o l i t e - k y a n i t e - s i l l i m a n i t e zone.  128  Figure 36. Garnet zoning p r o f i l e f o r Garnet 80-33, s t a u r o l i t e - k y a n i t e - s i l l i m a n i t e zone.  1 from sample  129  80-119 GARNET 1  F i g u r e 37. Garnet zoning p r o f i l e f o r Garnet 80-119, s t a u r o l i t e - k y a n i t e - s i l l i m a n i t e z o n e .  1. from  sample  130  F i g u r e 38. Garnet z o n i n g p r o f i l e f o r Garnet 2 from 80-19, s t a u r o l i t e - s i l l i m a n i t e z o n e .  sample  131  80-31  GARNET 3  Figure 39. Garnet zoning p r o f i l e for Garnet 3 from sample 80-31, s i l l i m a n i t e zone.  Figure 40. Garnet zoning p r o f i l e s f o r Garnets 3.1 from sample 81-325, kyanite zone.  and 2  133  81-325 GARNET 4  GARNET 1  F i gure 41. Garnet zoning p r o f i l e s for Garnets 4 and sample 81-325, kyanite zone.  1 from  1  4.3.2  DISCUSSION OF GARNET ZONING As mentioned i n the s e c t i o n  staurolite-kyanite near  34  on  the  zone, t e x t u r e s i n garnets from  the kyanite to s i l l i m a n i t e t r a n s i t i o n  breakdown of l a r g e r ,  texturally  rocks  suggest  zoned garnets  and  formation of s m a l l e r , apparently homogeneous garnets. A t o l l garnets a t t e s t  to the breakdown of the  intermediate zone of the garnet area r i c h e s t  in i n c l u s i o n s ,  of the garnet.  Both a t o l l  first,  s t a r t i n g with the  which i s the r o t a t i o n a l  zone  garnets and whole garnets  from sample 81-279 appear to be of the same generation because of s i m i l a r represent d i f f e r e n t  s i z e and  inclusion  p a t t e r n s , but  stages of breakdown.  The  whole  "garnet shown in F i g u r e 34 c o n t a i n s more Ca and Mn core than the rim, and which has  rotational  i n the  i s normally zoned f o r a garnet  r e t a i n e d some of i t s prograde  staurolite-kyanite  they  zone c o n d i t i o n s .  history  into  It exhibits  a  p a t t e r n i n the mid-zone of the garnet, which  i s t y p i c a l f o r garnets i n t h i s metamorphic zone. a t o l l garnet observed  An  i n the same sample shows complete  breakdown of t h i s mid-zone to b i o t i t e , q u a r t z , and muscovite,  and  i n c i p i e n t breakdown of the core, whereas  the rim i s c l e a r of i n c l u s i o n s  and a p p a r e n t l y  Rims of some a t o l l garnets appear to be  stable.  in the process  of breaking up i n t o s m a l l e r , more idiomorphic g r a i n s . similar  t e x t u r e has been observed  i n the kyanite zone  (Zone 8) where t i n y garnets are arranged around a r i n g  i  A  1 35 as i f mimicking  the former  rim of a l a r g e r garnet which  has broken down (see F i g u r e 32). garnets may  The  i n t e r i o r of  be unstable i n the presence  of  larger  inclusions.  A l t e r n a t i v e l y , the breakdown of garnet of a p p r o p r i a t e composition may  be due  to a combination  of r e a c t i o n s ,  including  MS  The  + GT = 2 SIL + BI + QZ.  (2.4)  inner cores are the l a s t part of the garnet to break  down, thus r e l e a s i n g Ca and Mn--the Ca going p l a g i o c l a s e r a t h e r than garnet, and the Mn rims of the new  into  going to the  garnets that have n u c l e a t e d on  relict  g r a i n s of the o l d rim, producing  zoning  i n the small g a r n e t s .  the  r e v e r s e Mn  F a r t h e r from  this  t r a n s i t i o n , the higher grade garnets show normal zoning. The  new  garnets may  the breakdown of  QZ + MS  a l s o be a c q u i r i n g components  from  staurolite,  + ST = BI + GT + KY/SIL + H 0  (2.1)  2  which i s c o n s i s t e n t with t e x t u r e s observed  in thin  section. Whatever combination the s t a u r o l i t e - o u t  of r e a c t i o n s i s r e s p o n s i b l e ,  i s o g r a d i s accompanied by a d i s t i n c t  change i n garnet t e x t u r e s , as w e l l as changes i n the stable a l u m i n o s i l i c a t e .  Below the  staurolite-out  1 36 i s o g r a d , garnets are l a r g e , t e x t u r a l l y c o m p o s i t i o n a l l y zoned and prograde metamorphic and staurolite-out  and  r e t a i n evidence  of  structural history.  their Above the  i s o g r a d , s m a l l , c l e a r garnets appear  homogeneous but show reverse Mn  zoning.  At Three L a d i e s  Mountain, kyanite p o r p h y r o b l a s t s become unstable with l a r g e garnets,  f i b r o l i t e appears,  and  along  staurolite  p e r s i s t s f o r a short d i s t a n c e i n t o the s i l l i m a n i t e  zone.  East of Mount Stevenson, on the other hand, l a r g e garnet and  kyanite p o r p h y r o b l a s t s are r e p l a c e d above the  staurolite-out (rather than zoning.  i s o g r a d by much smaller g r a i n s of k y a n i t e  f i b r o l i t e ) and  Such evidence  t i n y garnets with reverse  Mn  i s c o n s i s t e n t with a change from  Bathozone 4 to Bathozone 5 (Carmichael  1978). d e f i n e d by  the i n t e r s e c t i o n between the r e a c t i o n s  KY = SIL  (1.4)  and QZ  + MS  + ST = BI + GT + KY/SIL + H 0.  This i n t e r s e c t i o n  2  (2.1)  i s d i s c u s s e d i n the s e c t i o n on  s t a u r o l i t e breakdown, and would be l o c a t e d i n the somewhere near lower  field  Long Creek between Three Ladies  Mountain and Mount Stevenson.  1 37 4.4  STAUROLITE BREAKDOWN For d e f i n i n g the bathograd  Carmichael  ST + MS  (2.1)  2  and t e x t u r a l evidence, and  l o c a t e d i t on a  w i t h i n reasonable c o n d i t i o n s f o r the host  P/T  pelites This  i s a reasonable r e p r e s e n t a t i o n of changes i n  assemblages observed across the s t a u r o l i t e - o u t  isograd in  rocks from the Three Ladies Mountain/Mount Stevenson Carmichael reaction  5,  a s t a u r o l i t e breakdown r e a c t i o n  based on other i n d i c a t i o n s of metamorphic grade. reaction  4 and  + QZ = GT + BI + KY/SIL + H 0  from f i e l d diagram  (1978) has chosen  between bathozones  area.  (1978) shows the i n t e r s e c t i o n of  (2.1) with KY = SI at 4.75  kb and 540°C, but  that the experimental data f o r s t a u r o l i t e are  states  inconsistent  with these c o n d i t i o n s of s t a u r o l i t e s t a b i l i t y , and would i n d i c a t e a higher temperature  for the breakdown of  staurolite.  A r c h i b a l d et a l . (1983) p l a c e the  at  kb and  about  5.5  intersection  580°C, having r e v i s e d Carmichael's  curve  using an a n a l y s i s of experimental data on s t a u r o l i t e by Pigage and Greenwood (1982).  Higher temperatures  s t a u r o l i t e breakdown were c a l c u l a t e d by Pigage  for  and  Greenwood (1982) f o r the r e a c t i o n  6ST + 12.5QZ = 4ALM + 23KY/SIL + 6H 0. 2  (2.2)  Experimental data f o r s t a u r o l i t e are i n c o n s i stent with f i e l d  1 38 evidence  f o r the l o c a t i o n of t h i s r e a c t i o n  in P/T  space.  According to Pigage and Greenwood (1982), experimental for s t a u r o l i t e with a composition  of F e A l S i 2  are i n t e r n a l l y c o n s i s t e n t , but s t i l l between t h i s r e a c t i o n 680°C. melt, Rice  (2.2) and KY  As t h i s temperature i t appears  9  put the  3  7 5  2 2  (OH)  kb  and  that of g r a n i t e  high f o r breakdown of s t a u r o l i t e .  (1985) give values f o r AH°f and  S°  2 9 8  2  intersection,  = SIL at 6.5  i s approaching  0  data  Lang and  for s t a u r o l i t e  which are c o n s i s t e n t with the range of best data chosen by Pigage and Greenwood (1982), in c a l c u l a t i o n s Staurolite  in t h i s  so these values have been used  study.  in rocks from the Three Ladies Mountain area  i s a b i n a r y s o l u t i o n of F e  2 +  and Mg  end-members, with XFe =*  6.85. The  ST + MS  reaction  + QZ = GT + BI + KY/SIL + H 0,  (2.1)  2  d e s c r i b e d by Carmichael between bathozones 4 and  (1978) as d e f i n i n g the  5, i n v o l v e s s i x components and  seven phases, and so cannot end-member system.  bathograd  be c a l c u l a t e d  i n the Fe  Data f o r M g - s t a u r o l i t e are p o o r l y known,  and have not yet been found to be c o n s i s t e n t with other sets of d a t a .  Instead of c a l c u l a t i n g  reaction  (2.1), two  other  s t a u r o l i t e breakdown r e a c t i o n s i n v o l v i n g Fe end-member phases were c o n s i d e r e d :  1 39 25QZ + 3ST = 46KY + 8ALM + 12H 0  (2.2)  2  17ALM + 25MS + 3ST = 96KY + 25BI + 12H 0.  (2.3)  2  (Note that s t a u r o l i t e  formula of F e A l S i . 2  3  3  7 5  0  2 2  (OH)  2  has  been m u l t i p l i e d by four in order to have an i n t e g r a l value for S i f o r computing purposes, unusually  so c o e f f i c i e n t s appear  high.)  These r e a c t i o n s were c a l c u l a t e d and then d i s p l a c e d assuming the o v e r s i m p l i f i c a t i o n  that measured values of XFe i n  s t a u r o l i t e , b i o t i t e , and garnet approximate these phases,  and that a l l other phases are pure, and using  the thermodynamic data compiled (Table I ) . .  a c t i v i t i e s of  by Lang and R i c e (1985)  1 40  E x p r e s s i o n s for a c t i v i t y assume i d e a l s i t e mixing, as follows:  Almandine  Biotite  (Fe A1 S i 0 , ) 3  2  3  3  3  2  (Fe Al  AG, = AG °  RT  r  B  +  3 6  f2  2)  0  8 8  _  \  =  ( y C '  8  =  a  8  3  3  = (xj?' ) g  st  =  (X)%)  \  2«  o -(X)%)" =  (2.2a)  —  (Xf )'» e  R e s u l t s are presented g r a p h i c a l l y  —  (2.3a)  i n F i g u r e 42.  Both  r e a c t i o n s are d i s p l a c e d to lower temperatures as expected. Reaction  (2.2) i s only d i s p l a c e d by about 20°C,  reaction  (2.3), i n v o l v i n g muscovite and b i o t i t e , as w e l l as  whereas  breakdown of garnet, i s d i s p l a c e d by over 250°C, so the e f f e c t of Mg  in b i o t i t e  is significant.  Temperatures and  p r e s s u r e s of i n t e r s e c t i o n of these r e a c t i o n s with KY = SIL (P = 7-7.3  8  (2.4)  (a6f)as  . =  (OH) )  <X^)  di5pl  (a^) K.  1 5  =  in K  where (  Si  f l / m  afc|-  ( K F e S i A10, o (OH) )  Staurolite  K  a  2  kb, T =670-690°C) s t i l l  appear too high, but are  beginning to approach reasonable v a l u e s .  Water a c t i v i t y  would d i s p l a c e these r e a c t i o n s to lower temperatures. However, r e d u c t i o n of XH 0 to 0.88, assuming 2  equilibrium  <1  141  MINERAL  T A B L E I.  DATA  MINERAL  FORMULA AH" f (vl/mol )  ABBREVIATION  b  S' 298K (d/m-K)  c (J/m-K)  Vs (J/bar)  .034309  -1129700.  23.2400  .14075  -7837000.  115.28  (O/m-K)  (J/m-K' )  A-QTZ 46.94000  ••MINERALS** A-OUARTZ SI(1)0(2) -910648.00 41.33800  ALMANDINE FE(3)AL(2)SI(3)0(12) -527720O.00 298.700 408.15  ALM  FE-BIOTITE -5155504.  K(1)FE(3)AL(1)SI(3)0(12)H(2) 398 . 3 1246 445.30  MUSCOVITE -5972275.  K( 1 ) A L ( 3 ) S I ( 3 ) 0 ( 1 2 ) H ( 2 ) 287.9 408.19  KYANITE -2581097.  AL(2)SI( 1 )0(5) 83.68  SILLIMANITE AL(2)SI(1 )0(5) -2573574. 96.776  KY 173. 189 SIL 167.46  FE -BIO 154.32 -8079000.  MS 1 1037  140.71 - 10644000.  .02852  44 .09 -5389900.  .030922  49 .90 FE-ST -4884400. -93880000.  FE-STAUROLITE -47497890.  FE(8)AL(36)SI(15)0(96)H(8) .6704 1770.0 3467 .6  ANORTHITE  CA( 1 ) A L ( 2 ) S I ( 2 ) 0 ( 8 ) 205.4 264.83  AN .061898  -6460100.  100.79  CA(3)AL(2)SI(3)0(12) 254.7 435.207  GROS .071182  -11429900.  125 . 3  H(2)0( 1 ) 188.72  .01029  GROSSULAR  **GASES** STEAM -241818.  Data  from  H20 30.54  Lang and R1ce (1985)  A c t i v i t i e s used f o r d i s p l a c e d XFe ST = ( 0 . 8 5 ) • = -0.56465 XFe BI = ( 0 . 5 4 ) = -0.8028 XFe ALM = ( 0 . 7 9 ) = -0.30712 1  1  reactions  a r e as  follows.  897.6  142  F i g u r e 42. C a l c u l a t e d s t a u r o l i t e breakdown r e a c t i o n s using thermodynamic data from Lang and Rice (1985) and measured s t a u r o l i t e XFe = 0.85, garnet XFe = 0.79, and b i o t i t e XFe = 0.54. Dashed curves i n d i c a t e Fe end-member r e a c t i o n s . I n t e r s e c t i o n of r e a c t i o n (A) with KY = SIL i s d i s p l a c e d from 7224 bars and 683°C to 6985 bars and 670°C; i n t e r s e c t i o n of r e a c t i o n (B) with KY = SIL i s d i s p l a c e d from 11825 bars and 945°C t o 7333 bars and 689°C. Reduction of XH 0 to 0.88 d i s p l a c e s both curves by only 10°C. 2  1 43 with g r a p h i t e , only d i s p l a c e s these r e a c t i o n s by about Use  10°C.  of a more comprehensive and c o n s i s t e n t database  ( i n c l u d i n g data f o r M g - s t a u r o l i t e ) and a c t i v i t y models f o r s o l i d more r e a l i s t i c  less  simplified  s o l u t i o n phases may  petrogenetic g r i d  involving  result  in a  staurolite  react i o n s . A n a l y s i s of rocks from the Three Ladies Mountain area i n d i c a t e s that s t a u r o l i t e breakdown i s accompanied by t e x t u r a l and c o m p o s i t i o n a l changes i n garnet discontinuous reaction muscovite reaction  and b i o t i t e . (2.2) nor  (suggesting  i n v o l v i n g garnet) and a l s o i n v o l v e s Therefore, neither  (2.3) alone  i s completely adequate for  d e s c r i b i n g s t a u r o l i t e breakdown i n these rocks, However, according to the displacement F i g u r e 42,  of the r e a c t i o n s shown i n  they would occur n e a r l y simultaneously near  kyanite to s i l l i m a n i t e t r a n s i t i o n . suggested  by Carmichael  Reaction  (1978), cannot  (2.1),  be balanced e x a c t l y  with the m i n e r a l s of t h i s study, as the XFe  (St) i s almost  equal to the XFe  (Gt).  However, simultaneous  among muscovite,  q u a r t z , garnet, s t a u r o l i t e , b i o t i t e ,  kyanite must a l s o s a t i s f y e q u i l i b r i a  the  (2.2) and  equilibrium  (2.3).  and  1 44 4.5 GARNET-BIOTITE GEOTHERMOMETRY Ferry  and Spear  (1978) f i r s t  introduced a c a l i b r a t e d  geothermometer based on the Fe-Mg c a t i o n exchange between garnet and b i o t i t e . have o f f e r e d c o r r e c t i o n s e f f e c t s on c a l c u l a t e d garnet  reaction  Subsequently, s e v e r a l authors  f o r taking  i n t o c o n s i d e r a t i o n the  temperature of Ca and Mn components i n  (Newton and Haselton (1981); Pigage and Greenwood  (1982); Ganguly and Saxena (1984)).  Calculated  temperatures  can vary by over 100°C depending on which s o l u t i o n models are  used, e s p e c i a l l y those i n v o l v i n g manganese.  and Lang and Rice (1985) favor Haselton  Engi (1984)  the c o r r e c t i o n by Newton and  (1981) as g i v i n g the most r e a l i s t i c  and c o n s i s t e n t  temperatures. Eight  samples were chosen  r e t r o g r a d e metamorphism. calculated several  from those l e a s t a f f e c t e d , by  One g a r n e t - b i o t i t e  temperature was  f o r each sample using averaged a n a l y s e s of  points  on garnet rims and b i o t i t e g r a i n s .  microprobe analyses are presented i n Appendix standard d e v i a t i o n s  Averaged  I I ; note that  among d i f f e r e n t b i o t i t e g r a i n s  i n the  same s e c t i o n are approximately the same as those from one grain  (biotite  from sample 80-19 i s given as an example).  Garnet-biotite  temperatures were c a l c u l a t e d  f o r garnet  rims and a l s o f o r c o r e s p a i r e d with matrix b i o t i t e samples; biotite  temperatures were a l s o c a l c u l a t e d i n c l u s i o n s from sample 80-119.  were those of F e r r y Haselton  and Spear  i n some  f o r garnet with  The methods used  (1978; T1), Newton and  (1981; T2), and Ganguly  and Saxena (1984; T 3 ) .  145 The f o l l o w i n g garnet-biotite  formulas were used f o r c a l c u l a t i n g temperatures (Lang and Rice  1985):  2089 + 0.00956*P (bar)  T1  (K) =  0.7820 - In K  F e r r y and Spear (1661  (1978)  ( K ) ) x £ * + 2089 + 0.00956*P (bar) — 0.7820 - l n K  - 0.755*T1  T2 (K) =  Newton and Haselton (1981)  „  (  K  )  . »W%  - M X  S  -  °- / 8)  R  0.7820 - l n K 1510*(X^ + Y^n)  + 2089 + 0.00956*P (bar)  0.7820 - l n K  Ganguly and Saxena  where ^  F  e  M  g  = 11.34 kJ and R = 8.314  JK- mol" 1  1  (1984)  1 46 Table II (A and B) shows the temperatures given by these three methods at 5000 and 6000 b a r s . (80-119,  Four of the  80-33, 81-278, 81-279) were chosen  samples  from as c l o s e to  the k y a n i t e - s i l l i m a n i t e t r a n s i t i o n as p o s s i b l e . Average  rim temperatures f o r samples  from the area as a  whole as w e l l as from the k y a n i t e - s i l l i m a n i t e shown.  Garnet  i s o g r a d are  rim temperatures using the method of Newton  and Haselton (1981) average around 525 ± 18°C at 5 kb and 528 ± 18°C at 6 kb f o r the whole area and 521  ± 25°C at 5 kb  and 525 ± 25°C at 6 kb for the k y a n i t e to s i l l i m a n i t e transition  zone.  temperatures about and Saxena  Uncorrected F e r r y and Spear  (1978) gives  35°C lower, whereas the method of Ganguly  (1984) g i v e s temperatures about  that v a r i a t i o n of temperature among samples  35° h i g h e r .  Note  from a s i n g l e  mapped i s o g r a d exceeds v a r i a t i o n a c r o s s the whole area from s t a u r o l i t e zone to s i l l i m a n i t e zone.  If the s i 11imanite-in  isograd corresponds to the r e a c t i o n KY = SI, then the best fit  temperature and pressure are those given by Ganguly  and  Saxena (1984) at 557°C and 5 kb. Note that t h e r e i s not much d i f f e r e n c e temperature between samples  i n rim  from the s t a u r o l i t e  zone,  kyanite zone, and s i l l i m a n i t e zone, but that core "temperatures"  (using matrix b i o t i t e ) are lower than rim  temperatures i n the s t a u r o l i t e zone sample,  and higher than  rim temperatures i n the s i l l i m a n i t e zone, kyanite zone, and kyanite to s i l l i m a n i t e  transition  zone.  TABLE IIA. GARNET-BIOTITE TEMPERATURES SAMPLE  82-389 RIM  82-389 CORE  81-279 RIM  81-278 RIM  80-33 RIM  80-33 CORE  80-119 RIM  80-119 INC1  80-119 INC2  MET. ZONE  ST  ST  ST-KY  ST-KY-SI  ST-KY-SI  ST-KY-SI  ST-KY-SI  ST-KY-SI  ST-KY-SI  XMgGt XFeGt XCaGt XMnGt SUM  O.100 0.690 0.175 0.035 3.030  0.081 0.657 0.188 0.O73 3.063  0.087 0.806 0.075 0.032 3.028  0.089 0.770 0.078 0.064 3.030  0.085 0.801 0.061 0.053 2.966  0.095 .0.779 0.047 O.080 2.958  0.090 0.811 0.063 0.036 3.006  0.123 0.778 0.067 0.033 2.992  0.119 0.799 0.050 0.033 3.012  Mg/Fe Gt Mg/Fe Bi K  0.145 1.253 0.116  0.124 1.253 0.097  0.108 0.760 0.142  0.115 0.978 0.118  0.106 0.785 0.135  0.121 0.785 0.155  0.112 0.761 0.147  0.157 1.213 0.130  0.149 1.143 0.130  416 486 544  508 537 567  459 488 532  494 517 555  533 552 605  517 542 573  44 1 466 49 1  484 504 528  419 489 547  51 1 541 570  462 491 535  497 521 559  537 555 609  521 546 576  444 469 495  488 507 532  1  CO  T  T1 (FS') T2 (NH') T3 (GS«)  at  P  5 kb  454 521 562  T (*C) at P = 6 kb T1 (FS') T2 (NH ) T3 (GS ) 1  4  458 524 565  K = (Mg/Fe Gt)/(Mg/Fe BI) 'FS = F e r r y and Spear (1978) NH = Newton and H a s e l t o n (1981) 'GS = Ganguly and Saxena (1984) 1  1  4 ^ .  TABLE IIB. GARNET-BIOTITE TEMPERATURES SAMPLE  80-19 RIM  80-19 CORE  80-31 RIM  80-31 CORE  81-325 RIM  81-325 CORE  AVERAGE RIMS  AVERAGE RIMS  MET. ZONE  ST-SI  ST-SI  ST-SI  ST-SI  KY  KY  ST-KY-SI*  ALL ZONES  XMgGt XFeGt XCaGt XMnGt SUM  0 089 0.784 0.07G 0.051 3.005  O. 131 0. 753 0. 091 0. 026 3.025  0.094 0.806 0.058 0.041 3.025  0. 106 0.772 0.047 0.076 3.030  O.108 0.758 0.085 0.049 3.040  O.122 0.758 0.082 0.038 3.055  Mg/Fe Gt Mg/Fe BI K  0.114 0.856 0. 133  0. 173 0. 893 O. 194  0.117 0.823 0. 142  0. 138 0.823 0. 167  0.142 1.003 O.142  0.160 1.003 O.160  609 647 682  509 532 564  558 577 630  508 542 582  544 577 613  494 (+26) 52 1 (+25) 557 (+18)  492 (+24) 525 (+18) 562 (+15)  613 651 686  513 536 568  562 581 634  512 545 586  548 580 617  498 525 560  496 528 565  1  C C)  T  T1 (FS<) T2 (NH ) T3 (GS') 1  C C)  T  T1 (FS') T2 (NH ) T3 (GS*) 3  at P = 5 kb 489 5 19 558 at P = 6 kb 493 522 561  K = (Mg/Fe Gt)/(Mg/Fe BI) 'FS = F e r r y and Spear (1978) 'NH = Newton and Haselton (1981) 'GS = Ganguly and Saxena (1984) 'Average of 4 samples at KY=SI Isograd: 80-33, 80-119, 1  -278,  81-279  (+26) (+25) (+18)  (+24) (+18) (+15)  149 O v e r a l l , g a r n e t - b i o t i t e geothermometry  estimates  temperatures between about 490° and 570°C at pressures between 5 and 6 kb.  Presence of s i l l i m a n i t e  in the rocks  i n d i c a t e s that e i t h e r the pressure was somewhat lower (4 kb?) at the same T, or that the temperatures given by a l l  of these methods, except perhaps Ganguly and  Saxena  (1984) are too low at the k y a n i t e - s i l l i m a n i t e  by approximately 50°C.  isograd  No temperature gradient from  s t a u r o l i t e zone to s i l l i m a n i t e zone was demonstrated using g a r n e t - b i o t i t e geothermometry.  Assuming that changes in  metamorphic assemblages i n p e l i t e s are due to changes i n pressure and temperature c o n d i t i o n s during metamorphism, e i t h e r the g a r n e t - b i o t i t e geothermometer does not adequately estimate metamorphic temperatures, or the temperature gradient r e q u i r e d between s t a u r o l i t e zone and  sillimanite  zone i s smaller than the r e s o l u t i o n p o s s i b l e with method so f a r , or l e s s than about 50°C.  this  1 50 4.6  GEOBAROMETRY: GRAIL A new geobarometer r e f e r r e d t o as "GRAIL" has been  c a l i b r a t e d by Bohlen  et a l . (1983) f o r the r e a c t i o n  3 IL + SI/KY + 2 QZ = AM + 3 RU.  The  (3.1)  almandine p l u s r u t i l e assemblage i s on the high-pressure  s i d e of the r e a c t i o n (see F i g u r e 43). only be a p p l i e d i n d i r e c t l y  T h i s geobarometer can  to the metamorphic rocks of the  Three L a d i e s Mountain area as the u n i v a r i a n t assemblage i l m e n i t e + a l u m i n o s i l i c a t e + quartz + almandine + r u t i l e i s nowhere observed  to be s t a b l e .  However, t e x t u r e s i n v o l v i n g  subsets of t h i s assemblage have been u s e f u l i n l i m i t i n g the pressure c o n d i t i o n s over most of the area to those  pressures  below the GRAIL r e a c t i o n . Of t h i r t e e n p e l i t e samples c o n t a i n i n g both rutile,  i l m e n i t e and  seven are i n s t a u r o l i t e - k y a n i t e zone (Zone 4).  these seven samples, r u t i l e  In  i s only present as small  i n c l u s i o n s w i t h i n p o r p h y r o b l a s t s of s t a u r o l i t e and/or kyanite,,whereas i l m e n i t e i s present p o r p h y r o b l a s t s such as garnet,  both as i n c l u s i o n s i n  s t a u r o l i t e , and k y a n i t e , and  as i n d i v i d u a l l a t h s i n the matrix p e l i t e . were noted and  The same t e x t u r e s  i n one sample from the s t a u r o l i t e zone (Zone 3)  two samples from the s t a u r o l i t e - k y a n i t e - s i l l i m a n i t e zone  (Zone 5).  Where r u t i l e comes i n contact with q u a r t z ,  whether w i t h i n a p o r p h y r o b l a s t or near the rim, i t i s r e p l a c e d by i l m e n i t e .  This texture i s i l l u s t r a t e d in  151  "GRAIL"  400  500  GEOBAROMETER  J°Q  600  700  F i g u r e 43. P r e s s u r e / t e m p e r a t u r e d i a g r a m o f "GRAIL" g e o b a r o m e t e r ( m o d i f i e d f r o m B o h l e n e t a l . 1 9 8 3 ) . Shaded a r e a shows a p p r o x i m a t e P/T c o n d i t i o n s i n d i c a t e d by assemblages observed i n r o c k s from Three L a d i e s M o u n t a i n / Mount S t e v e n s o n a r e a .  1 52  F i g u r e 44, where a t r a i l  of r u t i l e  i s continuous with a t r a i l  inclusions in s t a u r o l i t e  of i l m e n i t e g r a i n s i n the matrix.  Elongate g r a i n s s t r a d d l i n g the rim of the p o r p h y r o b l a s t are r u t i l e w i t h i n the s t a u r o l i t e and  i l m e n i t e where p r o j e c t i n g  (or in other p l a c e s kyanite) i n t o the matrix.  assemblage ST + RU + QZ appears ST + RU without QZ.  The  to b e — l e s s s t a b l e  than  I l m e n i t e i s s t a b l e with garnet, q u a r t z ,  kyanite, s t a u r o l i t e , and  the other minerals of the  pelite  matrix. The  remaining  three samples c o n t a i n i n g both  i l m e n i t e and  r u t i l e are from the a p p a r e n t l y h i g h e r - p r e s s u r e kyanite zone (Zone 8 ) .  They are the only samples i n which  occurs both as i n c l u s i o n s in the matrix without that r u t i l e  rutile  i n garnet and as i n d i v i d u a l g r a i n s  i l m e n i t e rims, but i t must be  noted  i s a very minor c o n s t i t u e n t of these rocks.  R u t i l e i n c l u s i o n s in k y a n i t e s t i l l  show replacement  i l m e n i t e where in c o n t a c t with q u a r t z . approximating  by  Perhaps p r e s s u r e s  those f o r the "GRAIL" r e a c t i o n have been  approached. In  s t a u r o l i t e to s t a u r o l i t e - k y a n i t e zone rocks near  Three Ladies Mountain, l a c k of r u t i l e  i n c l u s i o n s i n garnet  suggests a pressure below that of the "GRAIL" r e a c t i o n .  In  the same rocks, t e x t u r e s i n v o l v i n g r u t i l e , q u a r t z , and s t a u r o l i t e suggest  ST + RU + QZ  temperatures  = KY + IL +  H 0, 2  compatible  with the  reaction  (3.2)  153  SAMPLE 81-344  st g q r -  STAUROLITE ZONE  -  staurolite garnet quartz rutile ilmenite biotite muscovite  S2  5 mm  Figure 4 4 . Sketch of photomicrograph (sample 8 1 - 3 4 4 ) i l l u s t r a t i n g how r u t i l e i s s t a b l e as i n c l u s i o n s in s t a u r o l i t e , but unstable r e l a t i v e to i l m e n i t e where i n contact with quartz, as i n p e l i t e matrix. Note that garnet, which predates s t a u r o l i t e , contains only i l m e n i t e i n c l u s i o n s , and no r u t i l e . T h i s sample i s from the s t a u r o l i t e zone near the k y a n i t e - i n i s o g r a d , and may be evidence f o r the r e a c t i o n ST + RU + Q = KY + IL + H 2 0 as shown i n F i g u r e 4 3 .  1 54 which  i s s t a b l e at temperatures between about 550° and  650°C, and below pressures for the "GRAIL" r e a c t i o n  (3.1)  (see F i g u r e 43). A r e p r e s e n t a t i v e value of 0.78 microprobe data) f o r XFe  was chosen  (using  i n garnet in order to estimate  displacement of the "GRAIL" curve to lower pressure (about 7 kb) than that  f o r the same r e a c t i o n  (about  Non-garnet  pure  10 kb).  (a = 1).  i n v o l v i n g pure phases  phases are assumed to be  Displacement i s e s t i m a t e d using curves from  Bohlen et a l . (1983).  Because of assumptions and  g e n e r a l i z a t i o n s made here, and because a c c u r a t e P/T c o n d i t i o n s f o r those r e a c t i o n s i n v o l v i n g s t a u r o l i t e are incompletely known, the "GRAIL" curve and a s s o c i a t e d i n v a r i a n t p o i n t cannot be e x a c t l y l o c a t e d i n P/T  space.  P/T  conditions  i n the Three L a d i e s Mountain area can be  indirectly  estimated from the "GRAIL" geobarometer  associated  r e a c t i o n s as below about 7 kb and between about  550° and 650°C.  and  These c o n d i t i o n s are reasonably c o n s i s t e n t  with those estimated from other r e a c t i o n s  (see F i g u r e  for s t a u r o l i t e - k y a n i t e zone rocks near Three L a d i e s Mountain, c o n s i d e r i n g the u n c e r t a i n t y a s s o c i a t e d with staurolite.  25)  1 55 4.7 GEOBAROMETRY: GROSSULAR-ANORTHITE-ALUMINOSILICATE-QUARTZ Estimates of pressure can be made using a geobarometer suggested  by Ghent  (1976) based  3 AN = GR + 2 KY/SI  Other  authors  on the r e a c t i o n  + QZ  (4.1)  i n c l u d i n g Newton and Haselton  and Rice (1985) have r e f i n e d the method. Haselton  (1981) and Lang  Newton and  (1981) present a c t i v i t y models f o r g r o s s u l a r and  p l a g i o c l a s e , methods of c a l c u l a t i o n , and d i s c u s s i o n of the thermodynamics of the geobarometer. Haselton  (1981),  as C a A l / S i O , 2  3  a  equation  F o l l o w i n g Newton and  (4.1) i s r e w r i t t e n with g r o s s u l a r  such that  3 AN = 3 GR + 2 KY + QZ  (4.1a)  3 AN = 3 GR + 2 SI + QZ  (4.1b)  T h e i r f o r m u l a t i o n i s given as f o l l o w s :  &G°  + RT  ln(a  /a  f l f l  )  (Newton and Haselton  3  + PAV,  ^ 0  1981, p. 132).  (4.2)  156  AG°  (at 1 bar) can be approximated  by -P°AV°,  where P°  i s the pressure of the end-member e q u i l i b r i u m at T and AV° i s the end-member volume change.  The end-member r e a c t i o n  can be represented i n P/T space by the l i n e  P = -7111.9 + 22.77 T ( f o r kyanite)  (4.3)  (Lang and Rice 1985). To modify  equation  method was used.  (4.3) f o r s i l l i m a n i t e ,  A similar  the f o l l o w i n g  l i n e a r approximation  r e a c t i o n SI = KY was obtained  f o r the  (from Rice, p e r s . comm.,  m o d i f i e d from Ghent 1976):  P = -6367.2 + 20.23 T°C or P = -11893 + 20.23 T (K)  (4.4)  1 57  Pressure terms from r e a c t i o n s (4.3) and by AV°  to g i v e energy  terms, AG°  j / b a r f o r (4.1a), -5.40 for  SI = KY.  J/bar  . AV of r e a c t i o n  f o r (4.1b), and  P i s i n bars, and AG  S u b t r a c t i n g 2*AG° f o r SI = KY  (4.4) are m u l t i p l i e d  0  is  -6.57  -0.581 J/bar  i s in j o u l e s .  from AG°  (4.1a) g i v e s AG°  (4.1b).  3 AN = 3 GR - (2 SI = 2  3 AN = GR  AG°  + 2 KY + QZ  (4.1a)  KY)  + 2 SI + QZ  for reaction  (4.1b)  (4.1b) i s then d i v i d e d by AV  for reaction  (4.1b) to g i v e the e x p r e s s i o n shown i n (4.5).  Thus, f o r  sillimanite,  P = -6093.6 + 23.35 T ( f o r s i l l i m a n i t e )  (4.5)  P i s i n bars; T in K e l v i n s . AV  i s the p a r t i a l molar volume change at 1 bar.  molar volume of garnet depending on composition directly p.  138).  can be read  from the graph given in Newton and Haselton Differential  Volume of a n o r t h i t e was plagioclase.  Partial  (1981,  c o m p r e s s i b i l i t i e s are n e g l e c t e d . used  f o r V of a n o r t h i t e component i n  1 58  Activity anorthite  models used  for grossular  i n garnet and  i n p l a g i o c l a s e are those given by Lang and Rice  (1985), which are m o d i f i e d from Newton and Haselton  a  gr  a  gr g r  =  X  = x g ^ e x p ( L  where ^  a  an  (where Gr =  Ca'1gr  W  c  ^  [  (  X  ^  )  = —  +  X  % ' ^  CaAl / SiO ) 2  3  a  .  ] }  ( 4  a  M  g  = 13807 - 6.3 T (J,K)  *  e x  P[  (  1  0  P u t t i n g t h i s a l l together and i s o l a t i n g  3  2  +  4  7  2  6  X  a «  )  ]  (  4  '  7  )  P on one s i d e of the  equation, pressure may be c a l c u l a t e d using -the f o l l o w i n g formula:  6 )  RT  Q  C  2  (1981).  159 Seven of the eight microprobe samples from the Three Ladies Mountain area c o n t a i n the r e q u i r e d  assemblage  garnet-plagioclase-aluminosilicate-quartz. composition  ranges from A n  2 2  P l a g i o c l a s e rim  to A n , and i s c o n s i s t e n t 3 8  w i t h i n each sample, but does not show any c o n s i s t e n t  pattern  of d i s t r i b u t i o n across the area; but systematic changes with P and T would only be expected in maximum-phase assemblages. The a l u m i n o s i 1 i c a t e i s kyanite only i n two samples and 81-325), and s i l l i m a n i t e only i n two samples 80- 31).  The remaining three samples  (81-279  (80-19 and  (80-33, 80-119, and  81- 278) c o n t a i n both kyanite and s i l l i m a n i t e , as they are taken from the s t a u r o l i t e - k y a n i t e - s i l l i m a n i t e zone, r e p r e s e n t i n g the KY = SI i s o g r a d . Pressure estimates f o r these samples have been c a l c u l a t e d using the geobarometer o u t l i n e d above and the temperatures at 6 kb given by g a r n e t - b i o t i t e using the method of Newton and Haselton on g a r n e t - b i o t i t e geothermometry,  geothermometry  (1981) (see s e c t i o n  Table I I ) .  Pressure  estimates using the g r o s s u l a r - a n o r t h i t e geobarometer from 4.6 kb to 6.6  kb (Table I I I ) , but do not vary  s y s t e m a t i c a l l y across metamorphic matter how  range  isograds i n the area.  No  the group of samples i s subdivided on reasonable  g e o l o g i c grounds, the pressure estimates cannot be narrowed down any f u r t h e r or f o r c e d to show any s i g n i f i c a n t The two c l o s e s t  samples i n the f i e l d ,  gradient.  81-278 and 81-279,  found w i t h i n a few hundred meters of one another, give a pressure estimate d i f f e r e n c e of n e a r l y 2 kb between them.  TABLE I I I . GROSSULAR-ANORTHITE-ALUMINOSILICATE GEOBAROMETRY Sample  81-325  80-19  81-279  81-278  80-33  80-119  80-31  MET. ZONE  KY  ST-SI  KY-ST  ST-KY-SI  ST-KY-SI  ST-KY-SI  SI  XAn XFeGt XMgGt XCaGt XMnGt  0.374 0.758 0.108 0.085 0.049  0.381 0.784 0.089 0.076 0.051  0.228 0.806 0.087 0.075 0.032  0.307 0.770 0.089 0.079 0.064  0.263 0.801 0.085 O.061 0.031  0.277 0.811 0.090 0.063 0.036  0.217 0.806 0.094 0.058 0.041  V.gr ' AV KY AV SI AV r KY AV r SI  12.67 -6.43 -6.57 -  12.61 -5.32 -5.40  12.60 -6.50 -6.57 -  12.63 -6.47 -5.30 -6.57 -5.40  12.51 -6.59 -5.42 -6.57 -5.40  12.52 -6.58 -5.41 -6.57 -5.40  12.50  T CO  !  at 6kb  P (bar) KY SI  545  522  541  5559  6610 4687  'V i n J/bar. 'T2, method of Newton and H a s e l t o n (1981).  491 4695 4946  520 4906 507 1  546 5391 5552  -5.43 -5.40 536  6144  161 Using only one sample per metamorphic sufficient  to produce s i g n i f i c a n t  s i m p l i f i e d a c t i v i t y models may mineral  zone may  not be  r e s u l t s , and the  make the r e s u l t s s e n s i t i v e to  composition.  In c o n c l u s i o n , g a r n e t - p l a g i o c l a s e p r e s s u r e s for a l l samples c o n s i d e r e d average 5.5 ± 0.7  kb.  Temperatures  c a l c u l a t e d f o r these rocks u s i n g the method of Newton and Haselton  (1981) f o r P = 6 kb average around 530°C.  P/T c o n d i t i o n s are approximately  These  c o n s i s t e n t with the KY = SI  i s o g r a d , but not with the P/T c o n d i t i o n s c a l c u l a t e d from s t a u r o l i t e breakdown r e a c t i o n s .  1 62 4.8  CONCLUSION Pelitic  rocks of l a t e P r o t e r o z o i c Snowshoe Group were  metamorphosed to g r e e n s c h i s t to amphibolite  facies  c o n d i t i o n s d u r i n g the m i d - J u r a s s i c Columbian Orogeny, and can be d i v i d e d of  i n t o zones corresponding to c l a s s i c  the B a r r o v i a n s e r i e s .  The d i s t r i b u t i o n of metamorphic  zones as d e f i n e d by mineral assemblages and amphibolite  facies p e l i t i c  Mountain/Mount Stevenson  schist  area  i m p l i e s an i n c r e a s e i n  are due  static  southeast.  overgrowths of p o r p h y r o b l a s t s  to metamorphic c r y s t a l l i z a t i o n  deformation  from garnet zone  to s i l l i m a n i t e zone in the  T e x t u r a l zoning and  textures in  i n the Three Ladies  metamorphic grade over a d i s t a n c e of 10 km in the northwest  divisions  (high temperatures  outlasting  outlasting active strain)  to d i s c o n t i n u o u s r e a c t i o n s i n v o l v i n g s o l i d - s o l u t i o n as expected  of  prograde  to support more than one  There episode  metamorphism i n v o l v i n g r e c r y s t a l l i z a t i o n of  garnet, s t a u r o l i t e , or k y a n i t e . i n v o l v i n g garnet and  Discontinuous r e a c t i o n s  s t a u r o l i t e breakdown i n t e r p r e t e d  m i c r o s c o p i c t e x t u r e s , along with garnet zoning t r e n d s , suggest a metamorphic temperature to  minerals  d u r i n g c o n d i t i o n s of i n c r e a s i n g T and P.  i s no unequivocal evidence  from  profile  i n c r e a s e from west  e a s t , with a pressure i n c r e a s e from north to south.  i n t e r s e c t i o n of the s t a u r o l i t e breakdown r e a c t i o n KY = SI d e f i n i n g the bathograd (Carmichael  and  1978)  the s t a u r o l i t e - o u t  with  between bathozones 4 and  should correspond  The  5  to the i n t e r s e c t i o n of  i s o g r a d with the s i l l i m a n i t e - i n i s o g r a d  1 63 in the f i e l d ,  thus e s t a b l i s h i n g a pressure-temperature  somewhere near Long Creek south of Welcome Mountain  (see  Plate I I I ) .  U n f o r t u n a t e l y , estimates of t h i s p o i n t of  intersection  in P/T  space vary from Carmichael  p l a c e s i t e m p i r i c a l l y at about 4.75 A r c h i b a l d et a l .  (1983), who  kb and  point  (1978),  who  540°C; to  p l a c e i t at about 5.5  kb and  580°C; to c a l c u l a t i o n s i n t h i s study which only approximate the a p p r o p r i a t e r e a c t i o n and p l a c e the i n t e r s e c t i o n at about 7-7.3 be  kb and  670-690°C.  The  latter  is clearly  too high to  reasonable. Maximum pressure estimated using the GRAIL geobarometer  (Bohlen et a l . 1983)  i s about 7 kb; c o m p a t i b i l i t y of  kyanite, i l m e n i t e , s t a u r o l i t e , and quartz a l s o temperatures  between 550° and  g a r n e t - b i o t i t e temperatures  650°C.  suggests  These are higher  but lower  than  than  temperatures  estimated from other s t a u r o l i t e breakdown r e a c t i o n s . Estimates of metamorphic c o n d i t i o n s based  on r e a c t i o n s  i n v o l v i n g s t a u r o l i t e tend to g i v e higher temperatures other methods. on s t a u r o l i t e  than  F u r t h e r experimental and thermodynamic work i s r e q u i r e d f o r r e s o l u t i o n of t h i s problem.  Geothermometry and geobarometry r e s u l t s show no significant  temperature  or pressure g r a d i e n t a c r o s s the  area corresponding to the v a r i a t i o n i n d i c a t e d by mapped i s o g r a d s .  i n metamorphic grade as  U n f o r t u n a t e l y , no  samples  from the garnet zone were s u i t a b l e f o r g a r n e t - b i o t i t e geothermometry. correction-method  map  G a r n e t - b i o t i t e geothermometry using the of Newton and Haselton  (1981) g i v e s  1 64 average peak metamorphic temperatures at 5 kb and  528  ± 18°C at 6 kb f o r the whole area,  the k y a n i t e - s i l l i m a n i t e t r a n s i t i o n temperatures,  of around 525  zone.  Using  ±  18°C  including  these  pressures c a l c u l a t e d a c c o r d i n g to the  g r o s s u l a r - a n o r t h i t e - a l u m i n o s i 1 i c a t e - q u a r t z geobarometer average 5.5  ± 0.7  kb with no systematic v a r i a t i o n i n  d i s t r i b u t i o n across the study pressures are reasonable  area.  These temperatures  and  f o r the s t a u r o l i t e - k y a n i t e zone  rocks which cover most of the Three Ladies Mountain/Mount Stevenson area.  However, the l a c k of P or T g r a d i e n t s  demonstrated by these geothermometric and methods does not r e f l e c t  geobarometric  the g r a d i e n t s in c o n d i t i o n s which  are represented by p r o g r e s s i v e changes in mineral assemblages, even though these changes correspond  w e l l with  the t y p i c a l Barrovian s e r i e s of metamorphic zones i n pelites. The  r e s o l u t i o n of these methods as used here  no b e t t e r than about  1-2  seems to be  50°C f o r g a r n e t - b i o t i t e temperatures  kb for g a r n e t - p l a g i o c l a s e p r e s s u r e s .  and  Temperature  and pressure g r a d i e n t s r e q u i r e d f o r metamorphic changes from s t a u r o l i t e zone to f i r s t than these v a l u e s .  s i l l i m a n i t e zone may  Although  s t a u r o l i t e may composition  smaller  the mapped changes i n  metamorphic assemblages are r e a l , l a r g e changes i n P and T.  be  For  they may  not  i n s t a n c e , presence  be more s t r o n g l y c o n t r o l l e d by  of the host p e l i t e  indicate of  bulk  than by measurable g r a d i e n t s  in temperature and pressure w i t h i n the l a r g e s t a b i l i t y  field  1 65 for s t a u r o l i t e , although  i f the i s o g r a d r e a c t i o n s were t r u l y  u n i v a r i a n t , t h i s e f f e c t would be e l i m i n a t e d . The  l a r g e area covered by a comprehensive  s t a u r o l i t e - k y a n i t e zone (8 km wide between garnet zone and s i l l i m a n i t e zone, and at l e a s t  25 km long in a northeast  d i r e c t i o n ) i n d i c a t e s that the d i p of s i g n i f i c a n t isograds such as KY = SI must be r e l a t i v e l y northwest,  metamorphic  shallow to the  c r o s s c u t t i n g the s l i g h t l y more steep and  n o r t h e r l y r e g i o n a l d i p of the metamorphosed s t r a t a Figure  45).  There area  (see  i s no u n u s u a l l y steep metamorphic g r a d i e n t in t h i s  (nor any  i n v e r t e d i s o g r a d s ) , although there i s  s i g n i f i c a n t post-metamorphic displacement along the River  Fault.  Given peak metamorphic c o n d i t i o n s of about 500-600°C, metamorphism o c c u r r e d at a depth of 15-20  Little  km with a geothermal  i s a normal geothermal  g r a d i e n t of about  g r a d i e n t so no s p e c i a l  5-6  kb and  about  30°C/km.  This  temperature  and p r e s s u r e c o n d i t i o n s need to be invoked to e x p l a i n  the  r e g i o n a l metamorphism.  However, metamorphism c o u l d not have  been simply by b u r i a l .  If the apparent  bathograd  shown i n  F i g u r e 45 i s r o t a t e d to h o r i z o n t a l , the isotherms appear to o u t l i n e a thermal dome under Three Ladies Mountain. S t r u c t u r a l c o n d i t i o n s necessary f o r r e g i o n a l metamorphism are (1) subsidence to 20 km with the r e q u i r e d t h i c k n e s s of o v e r l y i n g rock, (2) accompanying deformation, and  (3) subsequent  uplift  compressive  to present  position.  166  F i g u r e 45. Schematic c r o s s s e c t i o n s of Three Ladies Mountain (3LM) area showing r e l a t i o n s h i p between metamorphic isograds (symbols as on P l a t e I I I ) , f o l i a t i o n (dashed l i n e s ) , and L i t t l e River F a u l t (LRF).  1 67 If the Snowshoe Group rocks, which are p r e s e n t l y at  least  6 km t h i c k , are l a t e P r o t e r o z o i c Windermere-equivalent strata,  then  they were d e p o s i t e d  in one  of the t h i c k e s t  s e c t i o n s of the C o r d i l l e r a n miogeosyncline, during n e a r l y continuous  subsidence  c o n t i n e n t a l margin from about  of the North American  1500  entire Paleozoic miogeosynclinal  which formed  Ma  to about 200 Ma.  The  s e c t i o n c o u l d have been  d e p o s i t e d above the Snowshoe Group p r i o r to metamorphism, amounting i n the t h i c k e r s e c t i o n s to w e l l over o v e r l y i n g sediment.  10 km of  A d d i t i o n a l t h i c k n e s s c o u l d have been  caused by p i l e - u p of a c c r e t e d t e r r a n e s during c o l l i s i o n North America in the m i d - J u r a s s i c This event  was  (Monger et a l . 1982).  a l s o r e s p o n s i b l e f o r the intense  which accompanied r e g i o n a l metamorphism. t h r u s t i n g d u r i n g the Cretaceous  with  deformation  Uplift  removed much of  and the  o v e r l y i n g rock e i t h e r t e c t o n i c a l l y or by e r o s i o n (see F i g u r e 46) . Plagioclase-quartz-muscovite anatectically  in deep-seated metamorphic rocks  r e g i o n a l metamorphism and zone rocks area. age  pegmatite formed  i n t r u d e d kyanite and  during sillimanite  i n the Three Ladies Mountain/Mount Stevenson  Renewed heating  in the Cretaceous  r e s e t the muscovite  i n the pegmatite, g i v i n g a c o o l i n g date of 86 Ma  (see  s e c t i o n on geochronology).  T h i r d phase f o l d i n g , which  a f f e c t e d the pegmatite, was  accompanied in p e l i t e s  muscovite r e c r y s t a l l i z a t i o n . considered  T h i s "thermal  to be a separate episode  i  event"  by i s not  of prograde r e g i o n a l  time, Ma F i g u r e 46. Summary diagram showing v a r i a t i o n of temperature, p r e s s u r e (or d e p t h ) , and " i n t e n s i t y of d e f o r m a t i o n " through time, p l o t t e d on l o g a r i t h m i c s c a l e .  169 metamorphism in t h i s area, but r a t h e r an thermal high during a general u p l i f t  intermediate  and c o o l i n g trend which  was c h a r a c t e r i z e d metamorphically p r i m a r i l y b y chlorite.  retrograde  5.  IGNEOUS ACTIVITY  Igneous a c t i v i t y occurred at s e v e r a l i n t e r v a l s  i n the  h i s t o r y of the Snowshoe Group i n the Three Ladies Mountain/Mount Stevenson area. geochronology  See the s e c t i o n on  f o r a d i s c u s s i o n of timing of  igneous  episodes.  5.1 QUARTZ DIORITIC GNEISS Quartz and  dioritic  sills,  containing b i o t i t e ,  e p i d o t e , are common i n the lower micaceous q u a r t z i t e and  p e l i t e of the Snowshoe Group. of  hornblende,  the lower  They c o n s t i t u t e about a 20%  sequence, thus accounting  t h i c k n e s s of t h i s u n i t .  The s i l l s vary  f o r some of the great i n width; one that  has been mapped f o r s e v e r a l kilometers averages.about 50 m thick.  Amphibolite  l e n s e s tend to be concentrated at or  near the c o n t a c t s with the adjacent q u a r t z i t e and p e l i t e . They are s m a l l , i r r e g u l a r , and c o n t a i n minor s u l f i d e s , and are d i f f e r e n t  from the amphibolites near Three Ladies  Mountain, i n that they are not a s s o c i a t e d with The quartz d i o r i t i c foliation  carbonates.  g n e i s s e s d i s p l a y well-developed  s u b p a r a l l e l to that i n the adjacent  metasedimentary rocks; they appear to be f o l d e d by e a s t - v e r g i n g phase F1B f o l d s , so t h e i r  f o l i a t i o n may have  been formed p a r a l l e l to a x i a l planes of F1A i s o c l i n e s .  In a  few p l a c e s the gneisses c r o s s c u t limbs of e a r l i e r , n e a r l y isoclinal, The  intrafolial  foliation  f o l d s i n the metasedimentary r o c k s .  i n the g n e i s s i s p a r a l l e l 170  to the a x i a l  plane  171  of the i n t r a f o l i a l  f o l d s and a l s o to the general  in the micaceous q u a r t z i t e . f e a t u r e i s caused by l a t e r foliation  foliation  I t c o u l d be that t h i s kind of shearing along the a x i a l  of f o l d s i n v o l v i n g both q u a r t z d i o r i t i c  and the rocks they i n t r u d e , and that small-scale tectonic relationship.  plane  gneisses  i t represents  s l i d e s r a t h e r than a t r u l y  crosscutting  The d i s t i n c t i o n between f o l d phases F1A  F1B i s d i f f i c u l t  and  i t may  i n some cases be  and  meaningless.  Mineral l i n e a t i o n s  in the quartz d i o r i t i c  generally p a r a l l e l  to those i n the surrounding rocks; some  t r e n d i n g WSW  gneiss are  and W are p a r a l l e l to f o l d axes of phase F 1 B ,  but most t r e n d w i t h i n the spread of values f o r F 2 axes. quartz d i o r i t i c  layers s u p e r f i c i a l l y  greywackes, and  i n p l a c e s are d i f f i c u l t  i n t e r c a l a t e d micaceous q u a r t z i t e s .  resemble  The  metamorphosed  to d i s t i n g u i s h  from  However, c r o s s c u t t i n g  r e l a t i o n s h i p s and r e l a t i v e l y homogeneous composition that i s more mafic than that of the common psammite i n the area, as w e l l as idiomorphic hornblende  and  igneous a c c e s s o r y  m i n e r a l s such as z i r c o n and a l l a n i t e , are c o n v i n c i n g evidence  f o r an igneous o r i g i n .  Because these s i l l s  are  i n v o l v e d i n pre-F2 f o l d i n g and appear to be r e s t r i c t e d t o the lower  sequence of the Snowshoe Group, they are i n c l u d e d  in the l i t h o l o g i c column (see F i g u r e 2 ) . igneous z i r c o n s from the quartz d i o r i t i c  I s o t o p i e dates on gneiss g i v e a  p o s s i b l e minimum age  f o r d e p o s i t i o n of the Snowshoe Group of  approximately  (see s e c t i o n on  335 Ma  geochronology).  1 72 5.2 GRANODIORITlC GNEISS Granodioritic leucocratic in  and quartz monzonitic  than the quartz d i o r i t i c  the Snowshoe Group.  The l a r g e s t  sills,  more  group, are a l s o  found  bodies occur on the  slope toward Quesnel Lake, as i n d i c a t e d  by abundance of  angular g r a n i t i c f l o a t boulders, but cannot be mapped i n d e t a i l due to heavy v e g e t a t i o n . were mapped by Campbell  These g r a n i t i c  gneisses  (1963, 1978) as "Kg", or Cretaceous  granite. Between Three Ladies Mountain and Welcome Mountain, granodioritic layering  gneiss l a y e r s  are p a r a l l e l to c o m p o s i t i o n a l  and general f o l i a t i o n , and folded  F o l i a t i o n and mineral  lineations  are p a r a l l e l to F2 t r e n d s .  i n the g r a n o d i o r i t i c  Apophyses of these  c r o s s c u t the s c h i s t as d i k e s connecting r i d g e north of Welcome Mountain. gneiss seems to be r e l a t e d bodies of pegmatite, the g r a n o d i o r i t i c  by F2 f o l d s .  the g r a n o d i o r i t i c  to nearby dikes and i r r e g u l a r  gneiss must be an e a r l i e r  igneous  that  phase.  g n e i s s s i l l s must have been  intruded p r i o r to the end of F2 deformation, post-kinematic.  baked or contact-metamorphosed. gneiss c o n t a i n s large  on the  s t r u c t u r a l r e l a t i o n s demonstrate  Whereas the g r a n o d i o r i t i c  d i k e s are mainly  bodies  two s i l l s  Although  sills  Intruded Locally,  the pegmatite  sediments are not the g r a n o d i o r i t i c  g r a i n s of magnetite up to 1 cm a c r o s s .  1 73 5.3  PEGMATITE Large areas of pegmatite are exposed on the west s i d e of  the North Arm  of Quesnel Lake, southeast of Mount Stevenson,  and near Welcome Mountain.  The l a r g e r bodies, l o c a t e d  mainly i n the lower sequence  of the Snowshoe Group, are  i r r e g u l a r masses of c o a r s e - g r a i n e d , l e u c o c r a t i c  pegmatite  c o n s i s t i n g of q u a r t z , p l a g i o c l a s e , and muscovite with minor garnet, but no K - f e l d s p a r . 5 cm.  L o c a l l y , mesoscopic  G r a i n s i z e v a r i e s from 0.5 g r a p h i c texture may  to  be observed.  The pegmatites are c o m p o s i t i o n a l l y homogeneous, with no unusual m i n e r a l s , not even t o u r m a l i n e .  These are regarded  as forming from m e l t i n g of metamorphic rocks at depth. Higher  in the s e c t i o n where the pegmatite bodies are smaller  they tend to occur i n the form.of dikes p a r a l l e l to the F2 a x i a l plane.  T h i s i s shown by the c l o s e correspondence on a  s t e r e o g r a p h i c p r o j e c t i o n of the p o l e s of F2 a x i a l planes and the p o l e s of pegmatite dike c o n t a c t s (Figure  18 B).  Some  pegmatites have intruded along other s u r f a c e s as w e l l . l a r g e s t pegmatite dike in the study area i s about  The  150 m  t h i c k and extends from the northwest flank of Mount Stevenson  f o r at l e a s t  10 km to the ESE where i t j o i n s a  l a r g e r pegmatite body and i t s c o n t a c t s become obscured i n the f o r e s t .  The l a r g e r bodies of pegmatite c o n t a i n up to  30 % x e n o l i t h s of s c h i s t and q u a r t z i t e , most of which  retain  s t r u c t u r a l a t t i t u d e s c o n s i s t e n t with those of the surrounding metasedimentary  rocks.  There i s some r o t a t i o n  of s c h i s t o s i t y e s p e c i a l l y near the c o n t a c t s with the l a r g e r  1 74 dikes.  Crude f o l i a t i o n  i n the l a r g e r bodies  and f o l d s i n  the pegmatite d i k e s are b e l i e v e d to be r e l a t e d to F3 deformat i o n . Pegmatites l i k e these may have formed from p a r t i a l m e l t i n g of paragneisses  during metamorphism at upper  s i l l i m a n i t e zone c o n d i t i o n s .  I t i s a l s o p o s s i b l e that  they  are l a t e - s t a g e d i f f e r e n t i a t e s of the same magma that produced the g r a n o d i o r i t i c g n e i s s e s , be expected.  but more K-spar would  The pegmatites c o n t a i n l i t t l e  or no  K-feldspar. A Rb-Sr date of 86 Ma on a muscovite separate obtained 500°C.  and i s thought to represent  c o o l i n g through 400° to  T h i s i s i n t e r p r e t e d as i n d i c a t i n g  mid-Jurassic Cretaceous.  has been  slow c o o l i n g from  metamorphism or r e h e a t i n g d u r i n g the l a t e  1 75 5.4 QUARTZ VEINS Quartz veins a v e r a g i n g about one meter t h i c k are present but not common.  Those observed  crosscut e a r l i e r  structures.  s u r f a c e s probably are p a r a l l e l  are roughly planar and  Whereas some occur along  r e l a t e d to the L i t t l e River F a u l t ,  joint  others  or a t a low angle to c o m p o s i t i o n a l or  metamorphic l a y e r i n g .  Some quartz v e i n s p a r a l l e l to  f o l i a t i o n are the r e s u l t  of e a r l y segregation of quartz i n  the rocks during formation of f o l i a t i o n ; these are common f e a t u r e s i n metamorphic rocks of t h i s  grade.  Many quartz v e i n s i n the Mount Stevenson area are n e a r l y vertical  and n o r t h e a s t - t r e n d i n g , p a r a l l e l  planes.  T h i s i s an example of how quartz v e i n s i n areas of  simple  t o F4 a x i a l  f o l d systems with s t e e p l y d i p p i n g a x i a l  to occur p a r a l l e l  to the a x i a l  zones along t h e i r  b o r d e r s , some a s s o c i a t e d with  faults,  planes.  c o n t a i n sparse molybdenite,  chalcopyrite.  Rusty  s u r f a c e s tend alteration  p y r i t e , and  local  176  5.5  ECONOMIC GEOLOGY The  Snowshoe G r o u p i n t h e T h r e e L a d i e s  Stevenson area deposits. prospect  i s mostly  barren  Teck C o r p o r a t i o n  a r e a s , but  no  prospects.  of e c o n o m i c  mineral  examined a s m a l l  a t Mount S t e v e n s o n , but  sulfide-bearing amphibolites  Mountain/Mount  has  molybdenite  abandoned i t .  have been s t a k e d  in small  work a p p e a r s t o have been done on  Several  gold values  f o r g o l d at the U n i v e r s t i y  i n t h e W e l l s and  northwest,  q u a r t z v e i n s t r e n d i n g n o r t h and  rich  a r e m i n o r and  Columbia;  Sinclair,  Where t h e Snowshoe G r o u p i s i n g r e e n s c h i s t  f a c i e s , as  yielded  similar  Mountain  of B r i t i s h  were b e l o w l i m i t s o f d e t e c t i o n ( A . J .  p e r s . comm.).  these  s a m p l e s of p y r i t i c q u a r t z i t e and  r o c k s c o l l e c t e d d u r i n g mapping near Three L a d i e s were a s s a y e d  Many  B a r k e r v i l l e area  g o l d mines i n the p a s t . can  be  to  the  northeast  Other m i n e r a l  f o u n d on maps s h o w i n g m i n i n g  have showings  districts.  177 5.6  VOLCANIC ROCKS Olivine basalt  flows of l i m i t e d extent were d i s c o v e r e d  on the f l o o r of a c i r q u e at 1800 Mt.  Stevenson.  They are small flows no more than 3 m t h i c k ,  n e a r l y h o r i z o n t a l , and  lying  with g l a c i a l d e p o s i t s .  The  jointing,  m e l e v a t i o n , 3 km east of  i n two  adjacent c i r q u e s along  b a s a l t e x h i b i t s crude  i s v e s i c u l a r and d i k t y t a x i t i c , and  i s uniform  in c o l o u r , with pale green o l i v i n e phenocrysts a p h a n i t i c groundmass.  columnar  (2 mm)  in an  At c o n t a c t s with g l a c i a l c l a y ,  pillow  s t r u c t u r e s with c o o l e d , g l a s s y margins have developed, baked c l a y embedded i n the c r a c k s . glacially The  grey  with  B a s a l t boulders are  striated.  evidence  suggests that the l a v a was  erupted i n t o  wet  g l a c i a l c l a y , or i n t o a t a r n , or beneath an a l p i n e g l a c i e r occupying  the c i r q u e at the time of e r u p t i o n .  The c i r q u e s  where the lava flows were found are e a s t - f a c i n g and part of the headwaters of Devoe Creek, which l i e s U-shaped v a l l e y . volcaniclastic  More o l i v i n e b a s a l t  flows and  form  i n a deep  basaltic  rocks l o c a t e d at the mouth of Devoe Creek l i e  in a . h o r i z o n t a l p i l e about 250 m t h i c k above lake l e v e l , r e s t r i c t e d to a small a r e a .  The  top of t h i s s e c t i o n of  v o l c a n i c rocks i s l e v e l with g l a c i a l next to i t and elsewhere  t e r r a c e s i n outwash  along the lake shore.  probably had a l o c a l source vent near  lower Devoe Creek, and  pooled up a g a i n s t a l a r g e g l a c i e r occupying Quesnel  Lake at that time.  These lavas  the North Arm  The p r e v i o u s l y unmapped l a v a s  higher up i n the c i r q u e s probably had t h e i r own  source  of  vents.  S i m i l a r lavas are l o c a t e d on the west s i d e of the  j u n c t i o n of the North Arm and main arm of Quesnel Lake, and along Grain Creek. small c o n i c a l h i l l  South of Grain Creek near Tasse Lake, a with a c e n t r a l d e p r e s s i o n looks l i k e a  small volcano covered with t r e e s .  I t has been mapped as a  Recent or I n t e r g l a c i a l c i n d e r cone  (Campbell  1978).  These  o l i v i n e b a s a l t s are probably r e l a t e d to the Anahim v o l c a n i c b e l t that extends a l l the way Park  (Hickson and Souther  1977).  a c r o s s B.C.  1984,  i n t o Wells Gray  F i e s i n g e r and N i c h o l l s  6.  GEOCHRONOLOGY  6.1 GEOCHRONOLOGY ABSTRACT In  the Three Ladies Mountain area, Quesnel  B r i t i s h Columbia,  the Snowshoe Group c o n s i s t s of s i l i c e o u s  p e l i t e , micaceous q u a r t z i t e , amphibolitic  impure carbonate, and minor  rocks, which have been metamorphosed to upper  a m p h i b o l i t e f a c i e s and m u l t i p l y deformed. d e p o s i t i o n a l age of approximately initial  8 7  Sr/  Highland,  8 6  A Rb-Sr model  750 Ma, assuming an  S r r a t i o of 0.708 f o r the Snowshoe Group  c l a s t i c metasedimentary rocks, supports c o r r e l a t i o n s with late Proterozoic strata. is 530  i n d i c a t e d by a Rb-Sr whole-rock ± 94 Ma with i n i t i a l  dioritic its  E a r l y t o mid-Paleozoic plutonism  gneiss intrusive  deformational history  8 7  Sr/  8 6  isochron date of  S r r a t i o of 0.706 f o r q u a r t z  i n t o the Snowshoe Group e a r l y i n (pre- or synkinematic  f o l d i n g ) , and by U-Pb dates on z i r c o n dioritic  to F1  from the same q u a r t z  g n e i s s , which i n d i c a t e a minimum age of 335 Ma and  a maximum age of about determined  450 Ma.  No Rb-Sr i s o c h r o n c o u l d be  f o r younger, syndeformational  S r - r i c h granodioritic gneiss. (post-F2 f o l d i n g ) pegmatite  (pre-F2  Late to post-metamorphic  c o o l e d through 400-500°C at  86 ± 3 Ma, c o n s i s t e n t with J u r a s s i c metamorphism from r e g i o n a l  folding),  geology.  1 79  inferred  180 6.2 INTRODUCTION T h i s i s o t o p i e d a t i n g study i s part of a PhD t h e s i s on the s t r u c t u r a l and metamorphic h i s t o r y of the Snowshoe Group in the Three L a d i e s Mountain/Mount Stevenson area. Snowshoe Group (Campbell et a l .  The  1973) comprises q u a r t z - r i c h  p e l i t i c metasedimentary rocks, impure marbles, minor a m p h i b o l i t e s , and a s s o c i a t e d o r t h o g n e i s s e s of i n f e r r e d P r o t e r o z o i c to P a l e o z o i c age.  late  I t occurs in a fault-bounded  western part of the Omineca B e l t . e u g e o s y n c l i n a l Intermontane B e l t  To the west i s the ( Q u e s n e l l i a ) and to the  east are North American sediments such as the Kaza Group. The study area i s i n c l u d e d i n the B a r k e r v i l l e (Struik  1984).  Monger and Berg (1984) suggest  of the B a r k e r v i l l e and Kootenay t e r r a n e s .  terrane  equivalence  Polyphase  deformation i n the B a r k e r v i l l e t e r r a n e was accompanied by r e g i o n a l metamorphism  of the B a r r o v i a n type.  Rocks of the  Snowshoe Group range i n metamorphic grade from lower greenschist  f a c i e s northwest of W e l l s , B.C.,  to s i l l i m a n i t e  zone of amphibolite f a c i e s in Quesnel Highland and Wells Gray Park, where they are a northwest part of the Shuswap metamorphic complex. The s t r a t i g r a p h i c p o s i t i o n of the Snowshoe Group has long been u n c l e a r ; no f o s s i l s have been r e p o r t e d .  The  Snowshoe Group was b e l i e v e d by e a r l y workers to o v e r l i e the Cariboo Group, and i s shown as "Lower Cambrian or l a t e r " on maps by R.B. Campbell (1961, 1963). et a l .  L a t e r work by Campbell  (1973) suggested that the Snowshoe Group was "a  i  181 western f a c i e s of the Kaza Group" P r o t e r o z o i c Windermere age.  (p. 32), and thus of l a t e  G e t s i n g e r (1982) suggested that  the Snowshoe Group resembles p a r t s of the l a t e H o r s e t h i e f Creek Group,  Proterozoic  rather than the Kaza Group.  proposed that one of the uppermost Group (northwest of Wells, B.C.),  Struik  u n i t s of the Snowshoe i s late Paleozoic  in age,  based on an u n c e r t a i n l i t h o l o g i c c o r r e l a t i o n with a nearby u n i t c o n s i s t i n g of marble, s l a t e , and c r i n o i d a l limestone which y i e l d e d M i s s i s s i p p i a n conodonts  (Struik  1982).  Further u n c e r t a i n t y would be i n v o l v e d in making a l i t h o l o g i c c o r r e l a t i o n across 100 km  (even along s t r i k e ) of  u n f o s s i 1 i f e r o u s rocks which themselves cannot be t r a c e d with complete confidence d i r e c t l y  i n t o the Three L a d i e s  Mountain—Mount Stevenson a r e a : P r e v i o u s d a t i n g i n the Quesnel Highland has been  limited  to s t u d i e s of the Quesnel Lake G n e i s s , a heterogeneous of g r a n i t i c  suite  i n t r u s i o n s and augen gneiss a s s o c i a t e d with the  Snowshoe Group near Quesnel Lake. south of G r a i n Creek, and was study a r e a .  I t i s exposed about 5 km  not included i n the mapped  Blenkinsop (1972) r e p o r t e d a whole-rock Rb-Sr  date of 752 ±76 Ma on Quesnel Lake Gneiss c o l l e c t e d by C.J.N. F l e t c h e r from the East Arm  of Quesnel Lake.  K-Ar  dates on the East Arm g n e i s s , c o l l e c t e d by O k u l i t c h , are 153 ± 8 Ma on hornblende (metamorphic biotite  108 ± 4 Ma on  (reset by Cretaceous plutonism) (Stevens  et a l . 1982). U-Pb  age) and  O k u l i t c h et a l . ( i n p r e p a r a t i o n ) report a  date of 350 Ma on z i r c o n s from the East Arm  gneiss,  182 with i n h e r i t e d Precambrian l e a d . communication,  Okulitch  (written  1981) a l s o suggested a p r e l i m i n a r y  U-Pb date  of about 350 Ma on z i r c o n s from Quesnel Lake G n e i s s which I c o l l e c t e d i n 1981 at the j u n c t i o n of the North Arm of Quesnel Lake JSG-81-166).  (see Appendix  11 IB, samples JSG-80-QLGNW and  K-Ar and Rb-Sr dates on post-metamorphic  plutons i n Wells Gray Park a r e 143 ± 14 Ma and 163 ± 7 Ma, respectively  (Wanless et a l . 1965; Pigage  1977).  183 6.3  GEOLOGIC SETTING OF DATED SAMPLES In the study area, west of the North Arm  Lake, the Snowshoe Group i s p r i m a r i l y zone and  s i l l i m a n i t e zone.  The  of Quesnel  in s t a u r o l i t e - k y a n i t e  clastic  metasedimentary  rocks i n c l u d e grey micaceous q u a r t z i t e s and q u a r t z - r i c h , garnet-bearing  two-mica s c h i s t s with s t a u r o l i t e ,  and/or s i l l i m a n i t e .  Impure carbonates  have  recrystallized  as c a l c - s i l i c a t e marbles and minor a m p h i b o l i t e . experienced  at l e a s t two  kyanite,  phases of p e n e t r a t i v e  These rocks deformation  (F1 and F2) during prograde metamorphism, with n e a r l y c o a x i a l f o l d s plunging northwest. reached  a maximum a f t e r F2  folding.  accompanied b r i t t l e deformation  Metamorphic Retrograde  temperatures metamorphism  (F3) c h a r a c t e r i z e d by  kink  f o l d s and c r e n u l a t i o n s with v a r i a b l e a x i a l planar a t t i t u d e s and northwest or southeast low-angle normal f a u l t i n g  plunging axes.  Post-metamorphic,  ( L i t t l e River F a u l t ) was  followed  by g e n t l e warping (F4), with f o l d axes plunging s h a l l o w l y to the n o r t h e a s t . Mapping i n the Three Ladies Mountain—Mount area i n d i c a t e s s e v e r a l episodes of igneous  Stevenson  intrusion during  the s t r u c t u r a l and metamorphic h i s t o r y of the Snowshoe Group.  Four groups of rock types have been s e l e c t e d f o r  d a t i n g from samples c o l l e c t e d during 1979-1982 f i e l d seasons.  R e l a t i v e ages, from o l d e s t to youngest, a r e :  metasediments, quartz d i o r i t i c and pegmatite. observations.  This order Quartz  gneiss, g r a n o d i o r i t i c gneiss,  i s based on the f o l l o w i n g f i e l d  dioritic  gneiss sheets i n t r u s i v e  into  184 l a y e r e d paragneisses  are i n v o l v e d i n e a s t - v e r g i n g F1 f o l d s .  In a few p l a c e s , the o r t h o g n e i s s appears to c r o s s c u t an earlier  foliation  syndeformational  i n the paragneiss, to F1 f o l d i n g .  implying  intrusion  Younger, g r a n o d i o r i t i c  d i k e s and s i l l s are f o l d e d only by F2 s t r u c t u r e s , and are f o l i a t e d and l i n e a t e d along F2 trends only.  The  g r a n o d i o r i t i c gneisses and F2 s t r u c t u r e s are c r o s s c u t by pegmatite d i k e s , many of which have been i n t r u d e d p a r a l l e l to a x i a l planes of F2 f o l d s .  Rocks metamorphosed during and  a f t e r F2 f o l d i n g c o n t a i n pegmatitic  segregations  i n some  p l a c e s , and are c l e a r l y c r o s s c u t by pegmatite d i k e s elsewhere, implying a l a t e to post-metamorphic r e l a t i v e age for the pegmatitic  intrusions.  185 6.4  RESULTS AND  INTERPRETATION  A n a l y t i c a l methods in use at UBC Appendix IIIA.  Sample l o c a t i o n s are shown in F i g u r e 47,  rock d e s c r i p t i o n s in Appendix I I I B . presented  are summarized in  in Table  IV  (Rb-Sr) and  Analytical  in F i g u r e  49.  c a l c u l a t e d r e g r e s s i o n f o r the Snowshoe Group  metasediment isochron and an  r e s u l t s are  Table V (U-Pb), Rb-Sr  isochrons rn F i g u r e 48, and c o n c o r d i a p l o t The  and  initial  1967).  The  8 7  Sr/  8 6  ( F i g . 2) g i v e s a date of 418 Sr  Ma  r a t i o of 0.726 (method of York  s c a t t e r of p o i n t s exceeds that of  e r r o r alone, and  ± 54  experimental  t h e r e f o r e the i n t e r p r e t a t i o n of the date i s  h e a v i l y dependent on the model used to c a l c u l a t e i t (Cameron et  a l . 1981).  Rb-Sr whole rock analyses of  clastic  metasedimentary rocks give i s o c h r o n s that may  range from  of  et a l .  p r o t o l i t h to age  Chaudhuri  1976).  of metamorphism (Spanglet  In g e n e r a l ,  1978;  isochrons from unmetamorphosed  p e l i t e s approximate time of d e p o s i t i o n or d i a g e n e s i s , those  from psammites approach the age  while  of provenance.  Metamorphism causes r o t a t i o n of i n i t i a l metamorphic age,  age  isochrons toward the  in some cases n e a r l y completely,  as a  r e s u l t of r e d i s t r i b u t i o n of r a d i o g e n i c strontium,  especially  during deformation.  Sr  for  The  calculated i n i t i a l  8 7  Sr/  such metasedimentary rocks i s u s u a l l y high,  r o t a t i o n of the isochron d u r i n g metamorphism. date may  1969).  be meaningless ( F i e l d and  However, an estimate  of the age  ratio  suggesting The  not n e c e s s a r i l y be assumed to represent  metamorphism, and may  8 6  resulting  the age  of  Raheim  of d e p o s i t i o n can  be  186  THREE  LADIES  MOUNTAIN  AREA  (mineca Crystalline Belt ^ —  121°10'W  in British Columbia  j EXPLANATION p g  Pegmatite  Geological  Granodioritic  qd  Quartz  €c  Cariboo  contact  dioritic gneiss Group(?), undivided  m  Marble  s  Snowshoe  Figure 47.  gneiss Fault  •  245  Sample and  locality  number  Formation, undivided  Sample l o c a l i t y map f o r dated  samples.  187  T a b l e IV.  Sample  Rubidium-strontium  a n a l y t i c a l data  Description  Sr (ppm)  Rb (ppm)  Rb 87 Sr 86  122  134  3 .19  0.7356  85  228  7 .81  0.7728  133  1..63  0.7393  1 .36  0.7349  Sr 87 Sr 86  Metasedimentary Rocks 80-42  Gar-bio-ms  schist  79-15  Gar-bio  80-67  Gar-staur  schist  237  80-80  Micaceous  quartzite  193  80-96  Gar-bio-ms  schist  83  161  5 .68  0.7580  82-375  Ms-bio-gar  schist  114  137  3 .50  0.7471  81-245  Amphibolite  408  74  0 .53  0.7075  80-21  Biotite  240  115  1 .39  0.7350  80-22  Muscovite  282  9 .66  0.7470  81-171  Biotite  118  1 .21  0.7224  81-281  Gar-bio-chl  74  134  5 .28  0.7562  81-328  Kyanite  96  172  5 .25  0.7687  0 .30  0.7093  schist  gneiss schist  85  gneiss  283  schist  schist  90  Orthogneiss 81-X1  Quartz  dioritic  gneiss  495  52  81-X2  Quartz  dioritic  gneiss  355  138  1 .13  0.7139  81-X3  Quartz  dioritic  gneiss  1082  67  0 .18  0.7070  81-X4  Quartz  dioritic  gneiss  1037  80  0 .22  0.7066  81-X5  Quartz  dioritic  gneiss  508  118  0 .67  0.7108  81-X6  Quartz  dioritic  gneiss  612  94  0 .45  0.7099  80-99  Granodioritic  gneiss  1879  60  0 .09  0.7081  80-136A  Granodioritic  gneiss  1463  11  0 .02  0.7084  81-205  Granodioritic  gneiss  862  52  0 .18  0.7051  81-327  Granodioritic  gneiss  137  3 .88  0.7484  0 .13  0.7150  7 .50  0.7239  0 .03  0.7146  183  Pe;?matite rock  752  35  pegmatite  L15  298  80-36-WR  Pegmatite - whole  80-36-MUS  Muscovite  80-36-PL  P l a g i o c l a s e from  from  pegmatite  7 68  8.0  Table's?.  U-Pb z i r c o n data from q u a r t z d i o r i t i c g n e i s s i n t r u s i v e i n t o Snowshoe  JSG-81-X (A)  JSG-81-X (B)  74-149  44-74  Weight (mg)  9.8  6.3  U (ppm)  357.8  581.2  Pb (ppm)  21.6  34.7  100  100  5.596  5.462  16.30  17.41  0.0067  0.0007  3823  12989  Mole % Blank Pb  0.5  0.4  Radiogenic Pb/(Radiogenic + „ Common Pb)  0.996  0.999  Sample Number Size Fraction  (fxm),  handpicked  Abundances:^  Pb Pb 208^ Pb 204,,, Pb  Observed  Atomic  204^ 206 Pb Pb/  ratios:  2 0 6  Pb/238u  0.05760  0.05646  2 0 7  Pb/235u  0.4366  0.4244  0.05498  0.05452  2 0 7  3 Dates (Ma): (+ 2 c r )  pb/  2 0 6  p  b  2 0 6  Pb/238u  361.0 + 3 .1  3 5 4 . 1 + 3 .1  2 0 7  Pb/  3 6 7 . 9 + 3 .3  359.2 + 3 .2  411.3  392.4 + 2 .6  2 3 5  u  207^.206^ Pb/ Pb * C o r r e c t e d f o r blank Pb.  + 3 .2  Formation  T o t a l b l a n k = 0 . 5 ng.  I s o t o p i e c o m p o s i t i o n o f common l e a d i s t h a t o f 345 Ma o l d Pb on t h e growth c u r v e o f Stacey and Kramers (1975). 3 238 -9 -1 235 -9 -1 238 235 Decay c o n s t a n t s : U, 0.155125 x 10 a ; U, 0.98485 x 10 a ; U/ U = 137.88.  0.7001 0  i  i  i  i  i 5  i  «  1  1  F i g u r e 48. Rb-Sr i s o c h r o n s f o r metasedimentary rocks ( t r i a n g l e s ) , q u a r t z d i o r i t i c g n e i s s (hexagons), g r a n o d i o r i t i c g n e i s s ( s o l i d c i r c l e s ) , and pegmatite ( s q u a r e s ) .  L_ 10  191 made using an an assumed i n i t i a l  8 7  Sr/  8 6  Sr  r a t i o and  the  c e n t r e of g r a v i t y of the sample d i s t r i b u t i o n , around which the isochron i s presumed to have r o t a t e d by metamorphism (Peterman 1966; A reasonable  Spanglet  initial  8 7  et a l . 1978;  Sr/  8 6  Sr  Cameron et a l . 1981).  r a t i o f o r sediments d e p o s i t e d  in e a r l y P a l e o z o i c or l a t e P r o t e r o z o i c seawater i s 0.708 (Faure and Powell  1972,  c e n t r e of g r a v i t y based p o i n t s , a date of 753 Ma cannot  be c a l c u l a t e d ) .  p. 78).  Using t h i s r a t i o , and a  on an a r i t h m e t i c average was  calculated  of the data  (a meaningful  T h i s l a t e P r o t e r o z o i c date  error  supports  p r e v i o u s c o r r e l a t i o n s of Snowshoe Group with p a r t of the Windermere Supergroup. Six one  whole-rock samples of quartz d i o r i t i c  gneiss  from  c o l l e c t i n g were s i t e were analysed f o r Rb-Sr and  combined to produce a z i r c o n c o n c e n t r a t e f o r U-Pb Rb-Sr whole rock  dating.  isochrons i n meta-igneous rocks tend to  preserve age of c r y s t a l l i z a t i o n  (Faure and Powell  1972).  The quartz d i o r i t i c  g n e i s s i s o c h r o n g i v e s a date of  530  initial  ± 94 Ma  with an  8 7  Sr/  i m p l i e s a Cambrian or o l d e r age  8 6  Sr  r a t i o of 0.706.  This  f o r the Snowshoe Group i n t o  which the g n e i s s i n t r u d e s , but the u n c e r t a i n t y i s l a r g e . Zircons from the quartz d i o r i t i c  g n e i s s are  typically  c o l o u r l e s s to pale pink, subhedral prisms with rounded edges and  terminations.  uncracked,  whole c r y s t a l s of two  (100-200 mesh) and vs.  2 0 7  Pb/  Handpicked z i r c o n s c o n s i s t of c l e a r ,  2 3 5  44-74 Mm  s i z e f r a c t i o n s : 74-140 um  (200-325 mesh).  U c o n c o r d i a graph,  On a  2 0 6  Pb/  2 3 8  these p o i n t s l i e j u s t below  U  192 the concordia curve The  near 360  Ma  (Figure 49; Table  V).  a n a l y t i c a l e r r o r s are small enough that the p o i n t s are  c l e a r l y discordant.  Two  p o s s i b l e i n t e r p r e t a t i o n s are  suggested: a) If a s t r a i g h t chord points,  i t i n t e r s e c t s the concordia  T h i s "reverse discordance" has  i s p l o t t e d through the  a minimum age  curve  amount of o l d e r lead from the country  Ma.  gneiss  i n h e r i t e d a small  rocks.  Mesozoic  lead l o s s c o u l d b r i n g the lower  i n t e r c e p t below the true value of the  around 335  c o u l d i n d i c a t e that the  of M i s s i s s i p p i a n , and  metamorphism causing  two  for i n i t i a l  crystallization  gneiss.  b) These p o i n t s c o u l d be part of a d i s c o r d a n t p o i n t s from a gneiss which was around 450  Ma)  (around 175  and  (perhaps O r d o v i c i a n ,  lead during Mesozoic metamorphism  Ma).  With only two  nearly overlapping points, either  interpretation mid-Paleozoic  is possible. minimum age  Early Paleozoic recognized  lost  older  s e r i e s of  In e i t h e r case, an e a r l y to  of i n t r u s i o n i s i n d i c a t e d .  i n t r u s i o n s have only r e c e n t l y been  in l o c a l i t i e s s c a t t e r e d through the  and are probably  more common than g e n e r a l l y  Cambrian-Ordovician plutonism reported by K.V.  Evans (1981).  Cordillera,  realized.  in e a s t - c e n t r a l Idaho Mortensen  was  (1983) d e f i n e d  four p l u t o n i c s u i t e s i n t r u s i v e i n t o a sequence of metasedimentary rocks lithologically  in the Yukon-Tanana terrane that  s i m i l a r to metasedimentary rocks of  the  are  193 Snowshoe Group in Quesnel are 359 ± 6 Ma, maximum age  Highland.  349 ±5 Ma,  of 400 Ma.  and  342  The Quesnel  Dates on the ± 12 Ma,  with a  O k u l i t c h at about 350 Ma  and O k u l i t c h 1976;  suggested  Lake Gneiss and  o r t h o g n e i s s e s i n the Omineca B e l t have been dated A.V.  intrusions  similar  by  ( O k u l i t c h et a l . 1975;  Wanless  O k u l i t c h , w r i t t e n communication,  1981;  O k u l i t c h et a l . , i n p r e p a r a t i o n ) . It  i s unclear as yet whether the Quesnel  belongs  to the same i n t r u s i v e s u i t e as the quartz  gneiss dated here.  Although  gneiss occurs along Quesnel  some of the quartz Lake near  Gneiss, no contact i s exposed.  These two  2-4  Lake Gneiss  i s a l a r g e body  concordant  structurally.  The  (over 30 km long and  f e l d s p a r megacrysts.  with l a y e r i n g  Lake  gneisses are  km wide) of c o a r s e - g r a i n e d , l e u c o c r a t i c ,  g r a n i t e with potassium  dioritic  dioritic  the Quesnel  d i s t i n c t l y d i f f e r e n t p e t r o l o g i c a l l y and Quesnel  Lake Gneiss  gneissose It i s generally  i n the Snowshoe Formation  as p a r a l l e l to the border of the Intermontane B e l t ;  as w e l l i t is  unclear whether the c o n t a c t with the Snowshoe Group i s i n t r u s i v e or t e c t o n i c  (Blenkinsop 1972;  c o n t r a s t , the quartz d i o r i t i c mafic  g n e i s s dated here  (30%), f i n e r - g r a i n e d , and  l a c k s potassium  e i t h e r as megacrysts or i n groundmass. i n t e r l a y e r e d with and  intrusive  the Snowshoe Group and was  Rees 1981).  i s more feldspar,  It i s intimately  i n t o metamorphic rocks of  clearly  f o l d e d and metamorphosed  along with the metasedimentary r o c k s . gneiss occurs i n s i l l s no wider  In  This quartz  dioritic  than a few hundred meters  1 94 w i t h i n the Snowshoe Group from Mount Stevenson Lake.  Although  the Quesnel suggested  the quartz d i o r i t i c  Lake Gneiss may  that they belong  to  Quesnel  gneiss dated here  be s i m i l a r  in age,  to two d i f f e r e n t  and  i t is  intrusive  sui t e s . . Four whole-rock samples of g r a n o d i o r i t i c analysed f o r Rb-Sr. closely  related  Two  of them (80-99, 80-136A) are  s i l l s connected  s t r u c t u r e s i n the surrounding f o l i a t e d , and  lineated  These syndeformational of F2 deformation extremely  gneiss were  by d i k e s which c r o s s c u t F1  s c h i s t , but which are f o l d e d ,  by F2 f o l d i n g and metamorphism. intrusions  should approximate the  and metamorphism.  high c o n c e n t r a t i o n s of strontium (over 1000  ppm;  r a t i o s of about 0.708,  r e g a r d l e s s of t h e i r exact age.  In order to e s t a b l i s h  for t h i s g r a n o d i o r i t i c  g n e i s s , samples with a wider  Rb/Sr r a t i o or z i r c o n s f o r U-Pb  an o l d age or synmetamorphic  with the metasedimentary rocks. i s o l a t e d with a r a t h e r low sample was  collected  8 7  Sr/  from an  range of Sample  this  Sample 81-205 stands 8 6  Sr  r a t i o of 0.705.  This  i s o l a t e d outcrop i n an area relations  no c o n c l u s i o n s can be drawn. t y p i c a l specimen of pegmatite  mineral f r a c t i o n s .  was  separated  A plagioclase-muscovite-whole  isochron g i v e s a date of 86.4  age  equilibration  l a r g e l y covered with v e g e t a t i o n ; because f i e l d  One  an  d a t i n g are r e q u i r e d .  81-327 p l o t s w i t h i n the Snowshoe paragneiss f i e l d ; suggests e i t h e r  age  Both samples c o n t a i n  see Table IV) and have i n i t i a l  obscure,  from  ± 3.3  Ma  into  rock  approximating  are  1 95 post-metamorphic al.  c o o l i n g through about 400-500°C  1967; H a r r i s o n et a l . 1978).  (Jager et  The c o o l i n g date i s  c o n s i s t e n t with dates from s i m i l a r  post-metamorphic  pegmatites elsewhere i n the Omineca B e l t  (Parrish  1979).  Time of metamorphism has been dated by other workers as mid-Jurassic 1977).  (Wanless et a l . 1965; Wheeler  1970; Pigage  Mid-Cretaceous c o o l i n g ages imply e i t h e r a very  gradual c o o l i n g from a middle J u r a s s i c metamorphism (about 100-200°C  i n 70 Ma,  or about 2°C/million  heating d u r i n g the mid-Cretaceous.  y e a r s ) , or  renewed  1 96 6.5  CONCLUSIONS The  time of d e p o s i t i o n of the Snowshoe Group i s  approximately 8 7  Sr/  early  8 6  Sr  750 Ma  ( l a t e P r o t e r o z o i c ) assuming an  r a t i o of 0.708.  Quartz  dioritic  initial  gneiss i n t r u d e d  i n the d e f o r m a t i o n a l h i s t o r y of the Snowshoe Group  gives a Rb-Sr date of 530 r a t i o of 0.706. suggests  U-Pb  ± 94 Ma  with an  initial  around 450 Ma.  widespread e a r l y to mid-Paleozoic  orogeny.  almost  deformation  completely  metamorphism, was  through  400-500°C.  initial  i n t r u d e d a f t e r F2  and  8 7  gneiss  Sr/  8 6  Sr  Coarse folding  dated by Rb-Sr as 86 ±3 Ma,  with J u r a s s i c metamorphism and  indicate  granodioritic  not s u c c e s s f u l l y dated.  from pegmatite  Ma  o v e r p r i n t e d by J u r a s s i c  with high s t r o n t i u m c o n c e n t r a t i o n s and  muscovite,  Sr  Such g n e i s s e s i n the  Younger, syndeformational  r a t i o of 0.708 was  8 6  of 335  Snowshoe Group and other p a r t s of the C o r d i l l e r a  metamorphism, now  Sr/  d a t i n g of z i r c o n s from the same gneiss  P a l e o z o i c i n t r u s i o n with a minimum age  and a maximum age  8 7  and  consistent  subsequent gradual c o o l i n g  7. The  SUMMARY  g e o l o g i c h i s t o r y of the Three Ladies Mountain/Mount  Stevenson earliest  area i s summarized b r i e f l y , events that can  s t a r t i n g with the  reasonably be i n t e r p r e t e d from  rocks, c o n t i n u i n g up to the present  the  time.  LATE PROTEROZOIC TO EARLY PALEOZOIC D e p o s i t i o n of sediments on c o n t i n e n t a l margin of North America  (Kaza, Snowshoe, Cariboo Groups)  Lithification  of sandstone,  marl;  western  mudstone, s h a l e , limestone,  bedding  Subsidence,  heating, diagenesis  Beginning of prograde  metamorphism, quartz  and mica r e c r y s t a l l i z a t i o n P o s s i b l e deformation,  (chlorite,  formation of  segregations  muscovite)  foliation  EARLY TO MID-PALEOZOIC I n t r u s i o n of q u a r t z d i o r i t i c protolith  i n t o lower  dioritic  lineations  amphibolite  sequence ( p o s s i b l y a x i a l planar to  i s o c l i n e s although a l s o Quartz  s i l l s and  folded)  gneisses d i s p l a y WSW  and W to  NW  (L1)  Asymmetrical  tight  to i s o c l i n a l  folding  (F1B),  e a s t - v e r g i n g ; f o l d s f o l i a t i o n and quartz d i o r i t e , WNW NW  plunge  to  (L1); some a x i a l planes SW-dipping, some  p a r a l l e l to f o l i a t i o n ; preserved mainly  i n competent  q u a r t z i t e l a y e r s ; F2 a x i a l plane cleavage superimposed a c r o s s many F1  (S2) i s  folds in p e l i t i c  1 97  hinge  zones  198 Dominant f o l i a t i o n  (S1B) i s formed p a r a l l e l to a x i a l  planes of F1B f o l d s PALEOZOIC TO MESOZOIC Prograde  metamorphism c o n t i n u e s i n t o a m p h i b o l i t e  facies;  e a r l y garnet growth Granitic  s i l l s and d i k e s i n t r u d e d l o c a l l y  quartz monzonite);  they look l i k e  p r e c u r s o r s of pegmatite  (granodiorite,  finer-grained  i n t r u s i o n s which come l a t e r and  with which they are a s s o c i a t e d i n the f i e l d ;  they show  F2 s t r u c t u r e s (S2, L2) MID-JURASSIC F2 f o l d i n g : west-verging,  asymmetrical,  t i g h t to normal,  i n c l i n e d plunging f o l d s , with NW plunge a x i a l planes  (very c o n s i s t e n t ) ; a x i a l plane  with complete t r a n s p o s i t i o n especially  in pelitic  cleavage  l a y e r s i s common  i n l a r g e f o l d hinges; r e f o l d s F1A and F1B  folds; lineations F1 l i n e a t i o n s developed  and NE-dipping  (L2) n e a r l y c o a x i a l  with  (L1); F2 a x i a l planar f o l i a t i o n  most s t r o n g l y i n p e l i t i c  schist  (S2)  is  i n F2 hinge  zones Peak of prograde synkinematic staurolite;  metamorphism; growth of p o r p h y r o b l a s t s ;  garnets, postkinematic  kyanite and  sillimanite  JURASSIC TO CRETACEOUS I n t r u s i o n of pegmatite LATE CRETACEOUS U p l i f t and c o o l i n g  d i k e s i n F2 a x i a l  planes  199 LATE CRETACEOUS TO EARLY TERTIARY F3 k i n k - f o l d i n g and c r e n u l a t i o n f o l d i n g , with v a r y i n g a t t i t u d e s i n c l u d i n g NW-trending, SW-dipping a x i a l planes  (S3); best developed  in pelite;  seen  superimposed  on S2 and on F1B f o l d s ; some development of crude foliation  i n pegmatite;  Major f a u l t i n g ,  c h l o r i t e growth on a x i a l  formation of L i t t l e River F a u l t  s l i c k e n s i d e s and drag  planes system;  i n d i c a t e upper p l a t e moved down  toward ESE Fault  s u r f a c e s vary from F2 A-C j o i n t s to 170/20E  Metamorphic displacement  at Quesnel  Lake i s s i l l i m a n i t e  zone adjacent to c h l o r i t e - b i o t i t e zone Retrograde  metamorphism:  Late muscovite  r e p l a c e s kinked and f o l d e d  biotite;  c h l o r i t i z a t i o n of micas e s p e c i a l l y on F3 a x i a l  planes;  c h l o r i t i z a t i o n of b i o t i t e and garnet and s t a u r o l i t e ; local  s e r i c i t i z a t i o n of kyanite and s t a u r o l i t e  F4 f o l d i n g : broad, open warps or f l e x u r e s with gentle NE plunge;  some c r e n u l a t i o n i n p e l i t e ; quartz v e i n s are  a x i a l p l a n a r ; reverses plunges  of F2 f o l d s  Late quartz v e i n s i n j e c t e d along j o i n t s ,  f a u l t s , and  F4 a x i a l planes, and p a r a l l e l to f o l i a t i o n Minor m i n e r a l i z a t i o n ,  i n c l u d i n g molybdenite,  p y r i t e , and  chalcopyrite MIOCENE (?) U p l i f t and e r o s i o n ; formation of widespread surface  erosion  200  Minor high-angle f a u l t i n g , N, NE trends, EW  trends,  displacement on N and NE trends down to west PLEISTOCENE (?) Glaciation; Extrusion  e r o s i o n by a l p i n e and v a l l e y  glaciers  of o l i v i n e b a s a l t and v o l c a n i c l a s t i c s above  Devoe Creek, at Quesnel Lake, and Tasse Lake c i n d e r cone (subglacial  and s y n g l a c i a l )  G l a c i e r s melt; d e p o s i t i o n of t i l l , RECENT Erosion  outwash and moraines  8.  CONCLUSION  S t r u c t u r a l and metamorphic h i s t o r y of the Three L a d i e s Mountain/Mount Stevenson t e c t o n i c events.  area may  be r e l a t e d to l a r g e r  Refer to F i g u r e 50 f o r schematic  showing r e c o n s t r u c t i o n s of p o s s i b l e t e c t o n i c through  time.  F i g u r e 50A  C o r d i l l e r a n miogeocline Group sedimentary  cartoons  settings  d e p i c t s the development of the  up to the e a r l y Mesozoic.  Snowshoe  rocks were d e p o s i t e d i n a c o n t i n e n t a l  slope to s h e l f environment, perhaps on t r a n s i t i o n a l outboard  of c r a t o n i c basement, probably  in the  crust  late  P r o t e r o z o i c to P a l e o z o i c , some time between about 753 Ma 418 Ma,  a c c o r d i n g to Rb-Sr dates given i n t h i s study  F i g u r e 47).  (see  Late P r o t e r o z o i c to Cambrian Cariboo Group  shallow marine e l a s t i c s and carbonates are shown c l o s e r the shore of North America,  o v e r l y i n g the Snowshoe Group may km by the e a r l y Mesozoic,  r e c r y s t a l l i z a t i o n may Mafic s i l l s amphibolitic  (now  so some metamorphic  have begun during the P a l e o z o i c . quartz d i o r i t i c  gneisses and minor  bodies) were i n t r u d e d i n t o the Snowshoe Group  These quartz d i o r i t i c  Rb-Sr date of 530  ± 94 Ma  and  z i r c o n dates of around 335 Ma 48).  Sediments  have been as t h i c k as  in the mid-Paleozoic; minor deformation intrusion.  to  but p a r t l y t i m e - e q u i v a l e n t and  p a r t l y o v e r l a p p i n g the Snowshoe Group rocks.  10-15  and  A west-dipping  have accompanied  gneisses y i e l d a t e n t a t i v e  somewhat d i s c o r d a n t to 450 Ma  subduction zone may  the edge of the c o n t i n e n t .  may  U-Pb  (see F i g u r e s 47  have e x i s t e d o f f  I s l a n d arc rocks, p a r t s of 201  and  202  EARLY JURASSIC  MID-JURASSIC  TERTIARY to QUATERNARY  Figure 50. Schematic t e c t o n i c h i s t o r y of the Omineca B e l t in the v i c i n i t y of the Three Ladies Mountain/Mount Stevenson area. Not to s c a l e . SG = Snowshoe Group, CG = Cariboo Group, SM = S l i d e Mountain Terrane, QN = Q u e s n e l l i a , PVT = Pleasant V a l l e y Thrust, LRF = L i t t l e River F a u l t , 3LM = Three Ladies Mountain, MT = Matthew R i v e r F a u l t .  203 Q u e s n e l l i a and S l i d e Mountain t e r r a n e s , accumulated  in arc  and ocean environments to the west. By the e a r l y J u r a s s i c , p l a t e convergence b r i n g i n g i n i s l a n d a r c s from the west had begun to a f f e c t the m i o g e o c l i n e , which had been r e l a t i v e l y s t a b l e f o r over a billion  years (1 Ga).  Figure 50B shows c o n t i n u e d  west-dipping subduction as rocks of the S l i d e  Mountain  terrane and Q u e s n e l l i a were obducted to the east over c o n t i n e n t a l margin sediments of the B a r k e r v i l l e and Cariboo terranes.  F o l d i n g was mainly e a s t e r l y - d i r e c t e d ;  large  nappes may have developed i n some areas at t h i s time. N o r t h e a s t e r l y - o v e r t u r n e d F1B f o l d s , some of which quartz d i o r i t i c  sills  involve  i n the Three L a d i e s Mountain/Mount  Stevenson area, may be r e l a t e d to t h i s event. As S l i d e Mountain t e r r a n e and Q u e s n e l l i a p i l e d up, the c r u s t was t e c t o n i c a l l y  thickened, causing f u r t h e r subsidence  of  the m i o g e o c l i n a l rocks to depths of 20-25 km.  of  the c r u s t may have been accompanied  subduction  Thickening  by a r e v e r s a l of  i n the m i d - J u r a s s i c , as i t was around t h i s time  that i s l a n d a r c and oceanic rocks from the west, and perhaps some of the deeper p a r t s of the m i o g e o c l i n e , began u n d e r t h r u s t i n g the c o n t i n e n t a l margin from southwest to northeast  (see F i g u r e 50C). T h i s may have been the cause of  the  second, and s t r o n g e s t , phase of deformation recorded i n  the  rocks of the Three L a d i e s Mountain/Mount Stevenson a r e a .  A marked asymmetry, i n d i c a t i n g shearing i n a northeast over southwest d i r e c t i o n , c h a r a c t e r i z e s second phase  structures  204 throughout  the Omineca B e l t .  F2 f o l d s i n the Three Ladies  Mountain/Mount Stevenson area are dominantly southwesterly-verging.  T h e i r s i m i l a r to f l a t t e n e d  s l i p s t y l e and m i c r o s c o p i c  fabrics  indicate  flexural  formation i n  warm, d u c t i l e c o n d i t i o n s , accompanied by maximum metamorphic recrystallization. postkinematic  Metamorphic assemblages synkinematic to  to F2 f o l d i n g  i n d i c a t e c o n d i t i o n s of pressure  at 5.5 ± 0.7 kb and temperature around 525 ± 20°C, corresponding  to a depth of around 18-20 km with a normal  geothermal g r a d i e n t of about 30°/km (see F i g u r e 46). Parts of the Cariboo Group may have been t h r u s t over the Snowshoe Group to the west a l o n g the e a s t - d i p p i n g Pleasant V a l l e y T h r u s t , which i s a p r e - to synmetamorphic f a u l t , a c c o r d i n g to S t r u i k (1982).  reverse  Although some  t e l e s c o p i n g of these u n i t s has c l e a r l y o c c u r r e d d u r i n g deformation,  the Pleasant V a l l e y Thrust may not be a major  terrane boundary.  The B a r k e r v i l l e terrane i s c o n s i d e r e d  here to be parautochthonous r a t h e r than There i s no evidence  suspect.  i n the Three Ladies Mountain/Mount  Stevenson area f o r the e x i s t e n c e or n e c e s s i t y of having i s o l a t e d b l o c k s of c o n t i n e n t a l c r u s t move i n from west of the m i o g e o c l i n a l basin i n order t o e x p l a i n c r u s t a l t h i c k e n i n g and s o u t h w e s t e r l y - d i r e c t e d f o l d i n g , although may have been the case  this  f o r the Monashee Complex, which i s  cored by much o l d e r rocks  (Read and Brown 1983).  Northeastward u n d e r t h r u s t i n g d u r i n g p r o g r e s s i v e convergence of oceanic  t e r r a n e s with North America has a l s o been  205 proposed by Murphy ( i n p r e p a r a t i o n ) to e x p l a i n w e s t e r l y - v e r g i n g F2 s t r u c t u r e s in the Premier North American rocks of the Kaza Group. i s c o n s i s t e n t with s t r u c t u r e s observed  Range, in  T h i s general view in the Three Ladies  Mountain/Mount Stevenson area, but a more s p e c i f i c  kinematic  model such as that proposed by Murphy ( i n p r e p a r a t i o n ) i s beyond the scope of t h i s Tectonically  study.  loaded c o n t i n e n t a l c r u s t c o n s i s t i n g of  deformed and metamorphosed g e o s y n c l i n a l rocks to the west of the North American c r a t o n would have been anomalously f o l l o w i n g the m i d - J u r a s s i c , r e s u l t i n g uplift.  P a r t i a l m e l t i n g of lower  pegmatites  in r e l a t i v e l y  thick  rapid  c r u s t a l rocks formed  and other p l u t o n i c bodies which intruded deformed  rocks higher  i n the c r u s t .  Continued,  convergence from the west during u p l i f t  but l e s s  severe,  caused t i g h t e n i n g  and/or o v e r t u r n i n g of F2 f o l d s by F3 s t r u c t u r e s . phase deformation  o c c u r r e d i n a more b r i t t l e  Third  regime in the  Three Ladies Mountain/Mount Stevenson area than d i d F2 f o l d s , as i n d i c a t e d by s p a r s e l y - d i s t r i b u t e d F3 k i n k - f o l d i n g and minor r e c r y s t a l l i z a t i o n of retrograde m i n e r a l s , such c h l o r i t e , which i n d i c a t e lower metamorphic Postmetamorphic pegmatite s u r f a c e s i n kyanite and  was  c o o l i n g through  temperatures.  i n t r u d e d along F2 a x i a l planar  s i l l i m a n i t e zone rocks of the  Snowshoe Group p r i o r to F3 deformation. separate date was  as  One  Rb-Sr mineral  obtained for such a pegmatite,  400°C at 86±3 Ma.  as r e p r e s e n t i n g a l a t e Cretaceous  indicating  T h i s has been i n t e r p r e t e d heating event  rather than  206 merely extremely metamorphism.  slow c o o l i n g a f t e r  High heat  mid-Jurassic  flow i n the Cretaceous and  thickened c r u s t c o n t r i b u t e d to u p l i f t and e r o s i o n of deep-seated Tertiary  metamorphic rocks i n the Omineca B e l t  in early  time.  T e c t o n i c denudation,  represented by low-angle normal  f a u l t s such as the L i t t l e River F a u l t i n the Three Ladies Mountain area, c o n t r i b u t e d to more u p l i f t F i g u r e 50D).  and e r o s i o n (see  The L i t t l e River F a u l t i s approximately  contemporaneous with many decollement  zones a s s o c i a t e d with  metamorphic core complexes, having moved at some time between the l a t e Cretaceous  and m i d - T e r t i a r y .  the Snowshoe Group s c h i s t s and gneisses suggest  Structures in that i t i s a  l o w T a n g l e , e x t e n s i o n a l f a u l t a s s o c i a t e d with u p l i f t high grade rocks forming  of the  the core of the Three Ladies  Mountain/Mount Stevenson block, and that the low-grade  rocks  of the hanging w a l l (Cariboo Group) s l i d down toward the e a s t - s o u t h e a s t , at l e a s t near the present  t r a c e of the  L i t t l e River F a u l t east of Three Ladies Mountain. Later broad warping (F4 f o l d i n g ) along a northeast trend, and high-angle and  b l o c k - f a u l t i n g along north, n o r t h e a s t ,  northwest t r e n d s , occurred with minor d i s r u p t i o n of  earlier structures. There i s no evidence  i n the Three L a d i e s Mountain/Mount  Stevenson area f o r s t r i k e - s l i p  faulting.  Minor b a s a l t i c v o l c a n i c rocks are a s s o c i a t e d with P l e i s t o c e n e g l a c i a l d e p o s i t s and geomorphologic f e a t u r e s  i  207  suggesting approximately b a s a l t s may of  synglacial  eruption.  These  olivine  have a mantle source, but there i s no evidence  the s t r u c t u r a l  control  of t h e i r present  distribution.  REFERENCES A r c h i b a l d , D.A., G l o v e r , J.K., P r i c e , R.A., F a r r a r , E., and Carmichael,D.M. 1983. 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E a r t h and P l a n e t a r y  APPENDIX I: METAMORPHIC MINERALS  ABBREVIATIONS AND MINERAL NAMES AB AM AN AP BI CA CH CD Dl DO EP GT GP GR HE HB IL KS KY LI MG MC MS OL OP OR PL PY PR QZ RU SC SI SS SP ST TO TR ZR ZO  = ALBITE = =  = = = = =  = = = = =  = = = = =  = = = = =  = = = = =  = =  = = = = = =  ALMANDINE ANORTHITE APATITE BIOTITE CALCITE CHLORITE CHLORITOID DIOPSIDE DOLOMITE EPIDOTE GARNET GRAPHITE GROSSULAR HEMATITE HORNBLENDE ILMENITE K-FELDSPAR KYANITE LIMONITE MAGNETITE MICROCLINE MUSCOVITE OLIVINE OPAQUES (MG, IL, GP, PY) ORTHOCLASE PLAGIOCLASE PYRITE PYROPE QUARTZ RUTILE SCAPOLITE SILLIMANITE SPESSARTINE SPHENE STAUROLITE TOURMALINE TREMOLITE ZIRCON ZOISITE  215  216 DESCRIPTIONS OF MINERALS SECTION I .  PELITES  Note: Sj- and S r e f e r to i n t e r n a l and e x t e r n a l S-surfaces r e l a t i v e to p o r p h y r o b l a s t s i n t h i n s e c t i o n , r e s p e c t i v e l y . g  QUARTZ Quartz i s u b i q u i t o u s i n p e l i t e s (5-50%). U(+). Grain s i z e v a r i e s even w i t h i n same rock. X e n o b l a s t i c . Boundaries may be g r a n o b l a s t i c to g r a n o b l a s t i c p o l y g o n a l ; mosaic; sutured; dentate. Combinations common i n many rocks. Commonly occurs i n quartz segregation l a y e r s s u b p a r a l l e l to f o l i a t i o n and i n t e r s t i t i a l to other m i n e r a l s , and as i n c l u s i o n s i n other m i n e r a l s . Undulatory e x t i n c t i o n i s common, as w e l l as ribbon q u a r t z , and some mortar t e x t u r e . F i n e - g r a i n e d quartz d e f i n e s i n t e r n a l S-surfaces i n garnets, p a r t i c u l a r l y i n the cores where S^ i s s t r a i g h t . PLAGIOCLASE (+) R e l i e f ; cleavage (010) and (100); 2V high (-) to h i g h (+). Occurs i n small amounts i n most p e l i t e s . Twins: a l b i t e , p e r i c l i n e Zoning may be normal, patchy, reverse Composition mostly An25 to An35, may be as high as An55, low as An22; commonly c a l c i c o l i g o c l a s e to sodic andesine. An content i s s l i g h t l y higher i n s i l l i m a n i t e zone. Deformation twins i n some rocks; rusty along cracks and g r a i n boundaries. U s u a l l y a s s o c i a t e d with quartz i n matrix of p e l i t e , but i n some p l a c e s p l a g i o c l a s e forms p o r p h y r o b l a s t s or g l o m e r o b l a s t s . R o t a t i o n a l t r a i l s of i n c l u s i o n s i n d i c a t e p o r p h y r o b l a s t growth at same time as s t a u r o l i t e (80-69a, 80-135). Commonly a l t e r e d to s e r i c i t e or other f i n e - g r a i n e d m i n e r a l s ( s a u s s u r i t i z a t i o n does not appear t o be common i n pelites). Not much newly r e c r y s t a l l i z e d f e l d s p a r ; much looks overgrown by mica f o l i a t i o n .  217 K-FELDSPAR Occurs i n only a few p e l i t e s , <5% in those. (-) R e l i e f ; untwinned to hazy twins; p o s s i b l y p e r t h i t i c in p l a c e s . P o i k i l o b l a s t i c both i n s i d e and o u t s i d e garnet (82-380). Occurs a l s o i n 81-322, 325 ( k y a n i t e zone) and 80-19 ( S i l . zone). K-spar occurs i n o r t h o g n e i s s e s of g r a n o d i o r i t i c to quartz monzonitic composition, but i s rare i n pegmatite ( p l a g i o c l a s e i s dominant). CHLORITE Pale green to dark green p s e u d o - u n i a x i a l ( - ) or (+)? M i c a - l i k e h a b i t and form. Anomalous blue to brown b i r e f r i n g e n c e . Occurs as f o l i a t i o n - f o r m i n g mineral with muscovite i n low-grade zones, c h l o r i t e zone and b i o t i t e zone; may occur s t a b l y in some higher-grade rocks, but i t i s d i f f i c u l t to t e l l . Most commonly c h l o r i t e i s a retrograde mineral over most of the area, i n some l o c a l i t i e s more than others. I t r e p l a c e s garnet rims and may r e p l a c e the garnet completely; forms from breakdown of b i o t i t e ; forms in a x i a l planes of F3 kinks and c r e n u l a t i o n s a f t e r muscovite; may be kinked by F3 or F4 f o l d s as w e l l ; may a l s o r e p l a c e staurolite.  218  MUSCOVITE  N e a r l y u b i q u i t o u s i n p e l i t e s from c h l o r i t e zone t o s i l l i m a n i t e zone; formed a t v a r i o u s s t a g e s t h r o u g h o u t r o c k history. C o l o r l e s s , though may a p p e a r g r e e n i s h i n hand specimen. (-)2V 40-45; 6 = 0.038 (2° b l u e ) . M i c a h a b i t and appearance. Formed d u r i n g t h e f o l l o w i n g s t a g e s o f crystallization history:  1. O r i g i n a l f o l i a t i o n , i n c h l o r i t e zone and h i g h e r z o n e s . 2. Associated with b i o t i t e i n c r y s t a l l i z a t i o n f o l i a t i o n ( S 1 , S 2 ) . o r c h l o r i t e i n lower z o n e s . 3. P o s t k i n e m a t i c and p o s t - b i o t i t e p o r p h y r o b l a s t growth i n zone 2, and l o c a l l y e l s e w h e r e ; a s l a r g e , c r o s s c u t t i n g g r a i n s e i t h e r i n v o l v e d i n l a t e k i n k s o r m i m e t i c on p o l y g o n a l a r c s of l a t e c r e n u l a t i o n c l e a v a g e ( n o n - p e n e t r a t i v e ) . Replaces b i o t i t e i n some r o c k s . 4. As r e p l a c e m e n t o f u n s t a b l e a l u m i n o s i l i c a t e m i n e r a l s and s t a u r o l i t e as pseudomorphs o f k y a n i t e , s t a u r o l i t e , and g a r n e t ; m u s c o v i t e h e r e i s f i n e - g r a i n e d , s e r i c i t i c ; may a l s o r e p l a c e f e l d s p a r i n form o f s e r i c i t e . M u s c o v i t e i s s t a b l e over e n t i r e f i e l d area t o Quesnel Lake. Second s i l l i m a n i t e zone i s n e v e r r e a c h e d ; k - s p a r i s r a r e . Some m u s c o v i t e p o s t d a t e s r e t r o g r a d e c h l o r i t e . SERICITE F i n e - g r a i n e d , random w h i t e m i c a r e p l a c i n g u n s t a b l e m i n e r a l s s u c h a s k y a n i t e , s t a u r o l i t e , r a r e l y g a r n e t , and p l a g i o c l a s e .  219 BIOTITE O l i v e to green, a = brownish yellow; mica form and h a b i t . Defines dominant f o l i a t i o n i n magnetite-bearing schists. B i r e f r i n g e n c e i s too high f o r c h l o r i t e . Some i s bent, some might be mimetic. Reaction: GT to BI to CH (79-1, 79-27) Brown and reddish-brown; mica form and h a b i t ; pseudo-uniaxial(-). Commonly i n v o l v e d i n c r y s t a l l i z a t i o n f o l i a t i o n , but may be mimetic around polygonal a r c s and a l s o occurs as l a t e , postkinematic p o r p h y r o b l a s t s . Can be bent or kinked, or undeformed; found i n pressure shadows; c r o s s c u t t i n g e a r l i e r f o l i a t i o n . Replaces garnet i n some rocks; i s i n e q u i l i b r i u m with new garnets i n kyanite and s i l l i m a n i t e zones; may be i n t e r s t i t i a l to k y a n i t e . Biotite i s commonly r e t r o g r a d e d to c h l o r i t e , and i n some p l a c e s has gone to form r u t i l a t e d c h l o r i t e (79-22). B i o t i t e contains z i r c o n i n c l u s i o n s o u t l i n e d by p l e o c h r o i c h a l o e s ; they are more obvious i n the l i g h t e r c o l o r e d c h l o r i t e . Postkinematic b i o t i t e p o r p h y r o b l a s t s i n zone (2) are kinked and c r o s s c u t by even l a t e r muscovite. B i o t i t e i s seen only as i n c l u s i o n s in garnet i n kyanite zone or s i l l i m a n i t e zone, not in s t a u r o l i t e - k y a n i t e or s t a u r o l i t e zone.  i  j  220 GARNET I d i o b l a s t i c to s u b i d i o b l a s t i c , some s k e l e t a l , some a t o l l garnets. I s o t r o p i c , p a l e pink (not c o l o r - z o n e d ) , high relief. Composition: 2/3 almandine, the r e s t subequal p a r t s of pyrope, s p e s s a r t i n e , and g r o s s u l a r (see probe d a t a ) . Zoning p a t t e r n s in composition are seen i n probe data. T e x t u r a l zone p a t t e r n s r e v e a l much about the h i s t o r y . Size of garnets ranges from 0.1 mm to 15 mm; bimodal i n that most garnets below s i l l i m a n i t e grade are 2-15 mm; s i l l i m a n i t e and kyanite zone garnets are <2 mm. The l a r g e s t garnets (10-15 mm) are i n the ST-KY zone. Garnets are commonly p o i k i l o b l a s t i c except in the highest grades. T y p i c a l l y they c o n t a i n i n t e r n a l S s u r f a c e s d e f i n e d by t r a i l s of q u a r t z , and/or opaques; other i n c l u s i o n s tend not to be a l i g n e d on d e f i n i t e l a y e r s as not abundant enough. I n t e r n a l S may be s t r a i g h t or curved, in a few p l a c e s f o l d e d , many cases r o t a t i o n a l (snowball). P a t t e r n s of i n c l u s i o n s show t e x t u r a l zoning. In g e n e r a l , toward higher grades garnets get bigger and more complexly zoned, then appear to be breaking down, become embayed and a t o l l , and f i n a l l y they become small r e l i c t s which then provide n u c l e a t i o n s i t e s f o r new garnets coming i n with the the a l u m i n o s i l i c a t e a f t e r breakdown of staurolite. Garnets are s t a b l e across the e n t i r e f i e l d area, but i n d i f f e r e n t forms. The area has been d i v i d e d i n t o 10 metamorphic zones based on mineral assemblages combined with d i s t i n c t i v e t e x t u r e s of p o r p h y r o b l a s t s , p a r t i c u l a r l y garnet, s t a u r o l i t e , and k y a n i t e .  CHLORITOID P l e o c h r o i c formula: a = p a l e green, /3 = p a l e s l a t e blue, 7 = c o l o r l e s s ; a = j3 > 7; 5 = grey; ( + )2V med.-high; r>v. Occurs as a few g r a i n s i n c l u d e d i n a l a r g e garnet (79-13 o n l y ) , between inner core and outer zone, w i t h i n r o t a t i o n a l zone of garnet, implying that f o l d i n g was t a k i n g p l a c e d u r i n g c h l o r i t o i d growth. Rock i s now i n ST-KY zone. C h l o r i t o i d i n t h i s rock i s d i s t i n c t l y d i f f e r e n t from c h l o r i t e i n c l u s i o n s i n same garnet; c h l o r i t e i s p a l e green to dark green, and has much lower 2V. Some c h l o r i t e i n c l u s i o n s i n garnet (and i n 81-315 perhaps a l s o s t a u r o l i t e ) may be replacements of e a r l i e r c h l o r i t o i d g r a i n s .  221 STAUROLITE Low 6; r>>v; (+)2V 70-80; p a r a l l e l e x t i n c t i o n . P l e o c h r o i c formula: a - pale yellow, /3 = yellow, 7 = golden yellow; 7>j3>a. I d i o b l a s t i c to s u b i d i o b l a s t ic p o r p h y r o b l a s t s up to 3 cm long by 1 cm wide. Rarely twinned. Mode i s 2-5% of rock except i n one unit where i t i s 10-25% (80-69, 80-135). I n c l u s i o n s a r e : i l m e n i t e , r u t i l e , q u a r t z , tourmaline, g r a p h i t e , garnet, k y a n i t e , b i o t i t e , z i r c o n . Some S- = S , some s t r a i g h t , some curved ( h e l i c i t i c ) or r o t a t i o n a l S^ . Retrograde r e a c t i o n s : ST to CH + MS + QZ. Ilm i n c l u s i o n s l e f t over. Some s t a u r o l i t e s are completely pseudomorphed by f i n e - g r a i n e d c h l o r i t e and s e r i c i t e . Rocks with abundant s t a u r o l i t e a l s o have p l a g i o c l a s e p o r p h y r o b l a s t s . Staurolite may be i n c l u d e d in b i g garnets as small x e n o b l a s t i c g r a i n s (perhaps a f t e r c h l o r i t o i d ( i n 81-315)) or near the rim of a garnet. S t a u r o l i t e may i n c l u d e i d i o b l a s t i c garnets as i n 80- 69 and 80-135. S t a u r o l i t e i n c l u d e s some k y a n i t e , but kyanite surrounds end of s t a u r o l i t e , so must be about same age. P o i k i l o b l a s t i c s t a u r o l i t e may c o n t a i n smaller s t a u r o l i t e and kyanite, a l s o r u t i l e (79-28). Rutile i n c l u s i o n s i n s t a u r o l i t e become i l m e n i t e at rim of s t a u r o l i t e where r u t i l e i s i n contact with quartz (best example i s 81-344). Synkinematic, r o t a t i o n a l s t a u r o l i t e i s seen i n 80-45; l a t e r embayed. Some s t a u r o l i t e s show two d i s t i n c t growth p e r i o d s : 1. Abundant i n c l u s i o n s , vaguely f o l i a t e d ; 2. Post-kinematic, c l e a r (80-95). S t a u r o l i t e i n c l u d i n g f o l d e d S i , or h e l i c i t i c (80-69, 81- 234). S t a u r o l i t e s i n s i l l i m a n i t e zone are embayed, breaking down. S t a u r o l i t e i s c l e a r l y being r e p l a c e d by f i b r o l i t e in t r a n s i t i o n zone ( ST-KY-SIL zone).  222 KYANITE Low 6, c o l o r l e s s , high r e l i e f , l e n g t h slow; p a r a l l e l e x t i n c t i o n and good cleavage seen l o o k i n g at (010), (001). E x t i n c t i o n angle = 30° on (100); (-)2V = 82. Cleavage {100}, poor {001} v i s i b l e on (010). Up to 2 cm long in s c h i s t ; in i s o l a t e d ky-qz-ms s e g r e g a t i o n s k y a n i t e i s up to 2 cm by 10 cm. Commonly t a b u l a r , pale blue to grey i n hand specimen. Kyanite may form up to 10% of rock. I n c l u s i o n s : I l m e n i t e , muscovite, r u t i l e , q u a r t z , t o u r m a l i n e , b i o t i t e . A l t e r s to : s e r i c i t e (± c h l o r i t e ) ; c h l o r i t e , b i o t i t e may be i n t e r s t i t i a l to cracked k y a n i t e . Kyanite i s somewhat a l i g n e d on f o l i a t i o n and l i n e a t i o n , but not e n t i r e l y oriented. Kyanite tends to be syn- to postkinematic with respect to F2 f o l d i n g ; but some i s bent, kinked, and has undulose e x t i n c t i o n . Some c o n t a i n s r o t a t i o n a l i n c l u s i o n s , i s synkinematic (79-22). G e n e r a l l y S. i s p a r a l l e l to S . Kyanite gets more embayed c l o s e r to t r a n s i t i o n to s i l l i m a n i t e zone. In K y a n i t e - o n l y zone near Mt. Stevenson, kyanites are very t i n y and a l i g n e d on f o l i a t i o n , and may be confused with s i l l i m a n i t e , although they do not occur in the same rock, and kyanite p r o p e r t i e s are d i s t i n c t i v e in t h i n section. These small k y a n i t e s appear to come i n with the r e a c t i o n ST + MS + QZ = KY + BI + GT, along with small garnets and new b i o t i t e . Older, l a r g e r k y a n i t e s are gone, except as l a r g e s e g r e g a t i o n s ; o l d e r , l a r g e r garnets are gone, except as embayed r e l i c t s . R u t i l e i n c l u s i o n s trapped in kyanite are OK as long as they do not come i n contact with q u a r t z . I f they do, they go to i l m e n i t e ; o u t s i d e the k y a n i t e , or where r u t i l e comes i n c o n t a c t with q u a r t z , r u t i l e goes to i l m e n i t e ; t h i s i s the same r e l a t i o n s h i p as seen i n s t a u r o l i t e with r u t i l e i n c l u s i o n s . Kyanite i s contemporaneous with s t a u r o l i t e f o r the most p a r t , although in some rocks c r y s t a l l i z a t i o n of s t a u r o l i t e both pre- and postdates kyanite growth. ;  g  SILLIMANITE Length-slow, a c i c u l a r prisms i n f i b r o u s masses ( f i b r o l i t e ) . B i r e f . i s f i r s t order; no c r y s t a l s are b i g enough to determine r e g u l a r o p t i c a l p r o p e r t i e s . S i l l i m a n i t e i s a s s o c i a t e d with b i o t i t e ; r e p l a c e s s t a u r o l i t e ; a l s o a s s o c i a t e d with small g a r n e t s . Clumps of s i l l i m a n i t e may be in cores of f o l d s (80-30). Knots of s i l l i m a n i t e are v i s i b l e on outcrop on Quesnel Lake(80-31). S i l l i m a n i t e does not r e p l a c e kyanite d i r e c t l y . Kyanite i n the t r a n s i t i o n zone i s embayed and r e p l a c e d by s e r i c i t e , q u a r t z , and b i o t i t e . S i l l i m a n i t e appears to be r e p l a c i n g s t a u r o l i t e : ST + MS + QZ = BI + GT + SIL + H 0 . 2  223 OPAQUES Opaque dust--commonly i n t e r p r e t e d as GRAPHITE. May be i d e n t i f i e d in hand specimen i n some rocks (81-234). Defines t r a i l s of i n c l u s i o n s i n p o r p h y r o b l a s t s , but i s not common in matrix, except in some s c h i s t s , e s p e c i a l l y those w i t h i n 1 km of contact with B r a l c o Limestone. F a u l t rocks have a very high percentage of g r a p h i t e . Blocky, probably c u b i c : may be MAGNETITE, PYRITE. MAGNETITE may be determined with magnet i n some specimens; some s c h i s t s are magnetic enough to swerve the Brunton 90° or so, but have no e f f e c t o u t s i d e of about a meter from the rock s u r f a c e . Magnetite-bearing s c h i s t s are most common near the amphibolite u n i t , and c o n t a i n green r a t h e r than red-brown b i o t i t e ; they are i n t e r l a y e r e d with other s c h i s t s so do not appear to be at a d i f f e r e n t metamorphic grade. Some elongate opaques are a l s o i r o n oxides as shown by probe, but may be retrograded i l m e n i t e s . PYRITE may be recognized i n hand specimen, and i s i n d i s t i n g u i s h a b l e from magnetite, e t c . i n t r a n s m i t t e d l i g h t . It occurs i n some s c h i s t s and many micaceous q u a r t z i t e s , p a r t i c u l a r l y those i n t e r l a y e r e d with amphibolite u n i t , and carbonates. ILMENITE Opaque, elongate, p l a t y , forms a l o n g s c h i s t o s i t y or random. Nearly s t o i c h i o m e t r i c composition confirmed by probe data, although some opaques turned out to be pure i r o n oxide. Lath-shaped to s k e l e t a l ; d e f i n e s Si in some p o r p h y r o b l a s t s such as garnet, s t a u r o l i t e , k y a n i t e ; i n some rocks i t i s c h a r a c t e r i s t i c a l l y i n c l u d e d i n mainly c e r t a i n zones of the p o r p h y r o b l a s t , or p r e f e r e n t i a l l y so. Some garnets have more quartz i n c l u s i o n s i n the core, then more i l m e n i t e i n the r o t a t i o n a l and outer zones as w e l l . In p l a c e s i l m e n i t e i s surrounded by sphene or r u t i l e . In ST-KY zone, i l m e n i t e i s s t a b l e as i n c l u s i o n s i n garnet and i n matrix, or in ST or KY. R u t i l e i n c l u s i o n s i n the same KY or ST react to form i l m e n i t e where i n c o n t a c t with q u a r t z . Ilmenite i s common i n a l l p e l i t e s , 1-2%.  224 RUTILE Very high r e l i e f and high a b s o r p t i o n , r e d d i s h brown, more orange than sphene, and l e s s euhedral, and l e s s red than hematite. Occurs as l i t t l e ovoid blobs r a r e l y i n matrix of p e l i t e , more commonly trapped i n s i d e kyanite or s t a u r o l i t e where not i n contact with q u a r t z . In ST-KY zone, r u t i l e i n c l u s i o n s with an abrupt change from one end of the mineral g r a i n to the other, or e l s e the r u t i l e i s surrounded by ilmenite. R u t i l e i s not commonly a s s o c i a t e d with garnet, except in the kyanite or s i l l i m a n i t e zones (81-283, 81-298, 81-310, 80-119). Most of the study area i s below the react i on ALM + RUT = ILM + ALS + QZ. TOURMALINE T r i g o n a l shape; U ( - ) ; i d i o b l a s t i c , s m a l l . a » e ; u> = blue-green to o l i v e ; e = c o l o r l e s s to pale green. Zoned, c o n c e n t r i c to c - a x i s , not lengthwise, most commonly blue-green to brown-green, but a l s o more complex zoning, as in 80-33: (1) b l u i s h - g r e e n to brown, (2) o l i v e green, (3) pale y e l l o w i s h o l i v e , (4) o l i v e green. In many p e l i t e s , end-sections of tourmaline are very common i n t h i n s e c t i o n s cut p e r p e n d i c u l a r to l i n e a t i o n (= f o l d a x i s ) implying that tourmaline growth i s synkinematic. I n c l u s i o n s seen in tourmaline: QZ, ZR (80-33), opaques (80-148), May c r o s s c u t biotite. In 81-279, tourmaline i n c l u s i o n s i n s i d e kyanite show one zone, with i n c l u s i o n s S^. (to) = S. (ky) = S ; tourmaline o u t s i d e kyanite has two zones. P o s s i b l y outer zone of tourmaline grew at same time as k y a n i t e . Tourmaline occurs i n lowest grade p h y l l i t e s a l s o , and i s zoned t h e r e . Tourmaline with the most zones i s i n ST-KY-SI zone. No tourmaline noted in Kyanite zone or S i l l i m a n i t e zone. Large tourmalines (up to 1 cm) occur i n massive v e i n s with c h l o r i t e near contact of amphibolite u n i t and p e l i t e on east s i d e of middlepeak of Three L a d i e s Mountain, where the rocks look as though they have undergone p a r t i a l m e l t i n g or hydrothermal a l t e r a t i o n . Most tourmalines i n p e l i t e s are too small to see in hand specimen, <0.1 mm. ;  g  225 ACCESSORY MINERALS APATITE U(+), grey 5, small prisms, length f a s t , med.-high Minor c o n s t i t u e n t of most p e l i t e s .  relief.  HEMATITE B r i g h t red a b s o r p t i o n . Late v e i n - f i l l e r ; i n t i n y f r a c t u r e s and g r a i n s , esp. i n retrograde s c h i s t s (ex. 80-123). Probably from o x i d a t i o n of magnetite or i l m e n i t e . SPHENE High r e l i e f , sphene shape, brownish 5 and a b s o r p t i o n . Rare in p e l i t e s (81-340, 82-382, 81-295, 80-123, 81-333, 79-36, 79-38, 81-204), and a very minor c o n s t i t u e n t of these. ZIRCON Tetragonal shape; U(+); very high r e l i e f and 6. Common as i n c l u s i o n s i n b i o t i t e , surrounded by p l e o c h r o i c haloes. A l s o i n c l u d e d i n c h l o r i t e which has r e p l a c e d b i o t i t e ; haloes very obvious i n p a l e r c h l o r i t e . May be up to 1% of rock but commonly much l e s s i n p e l i t e s .  226 SECTION I I .  CALC-SILICATES  C a l c - s i l i c a t e rocks vary i n composition from n e a r l y pure marbles to amphibolites. Assemblages were not as u s e f u l as those i n p e l i t e s f o r d i s t i n g u i s h i n g metamorphic zones. A l l green amphiboles are hornblende rather than a c t i n o l i t e as determined by very dark green c o l o r , a s s o c i a t i o n , and o p t i c a l p r o p e r t i e s . The metamorphic grade i s at l e a s t a m p h i b o l i t e f a c i e s . There i s no a l b i t e . Minerals s u g g e s t i v e of higher metamorphic grades i n c a l c s i l i c a t e rocks are d i o p s i d e , z o i s i t e , s c a p o l i t e , and k - f e l d s p a r , but are not r e s t r i c t e d to one metamorphic zone, except f o r zoisite. C a l c - s i l i c a t e s from Quesnel Lake i n the s i l l i m a n i t e zone are d i s t i n c t i v e , c o n t a i n i n g c a l c i t e , p l a g i o c l a s e , quartz, k - f e l d s p a r , d i o p s i d e , epidote (zoned p i s t a c i t e , high (-)2V, y e l l o w ) , z o i s i t e (/3-zoisite, near p s e u d o - u n i a x i a l ( + ) ) , opaques, ± garnet, sphene, a p a t i t e , or scapolite. Sphene and s c a p o l i t e do not occur in the same rock. Textures i n d i c a t e many r e a c t i o n r e l a t i o n s h i p s i n v o l v i n g d i o p s i d e and garnet, p l a g i o c l a s e and e p i d o t e , two phases of K - f e l d s p a r , and f e l d s p a r - z o i s i t e intergrowths. The only occurrence of s c a p o l i t e that i s not i n the s i l l i m a n i t e zone i s i n a v e i n i n c a l c a r e o u s s c h i s t near sample 79-28, i n d e f i n i t e s t a u r o l i t e - k y a n i t e zone. Diopside and K - f e l d s p a r - b e a r i n g c a l c - s i l i c a t e s a l s o occur i n the S t a u r o l i t e - K y a n i t e zone, but not below i t ; many samples i n t h i s zone c o n t a i n i n g K - f e l d s p a r were c o l l e c t e d adjacent to g r a n o d i o r i t i c g n e i s s e s . As most of the c a l c - s i l i c a t e and a m p h i b o l i t i c u n i t s occur w i t h i n the s t a u r o l i t e - k y a n i t e zone, most of the samples are of the same metamorphic grade, although t h e i r compositions vary widely.  i  APPENDIX I I : MICROPROBE ANALYSES The e l e c t r o n microprobe at the Department of G e o l o g i c a l Sciences, U n i v e r s i t y of B r i t i s h Columbia, was used f o r mineral analyses. Accelerating  p o t e n t i a l = 15 KV  Specimen c u r r e n t  on A l = 40 namps  Aperture s i z e = 200 u Count time = 10 s or 20 s. Analyses of minerals are shown on the f o l l o w i n g t a b l e s . There are three t a b l e s with garnet analyses, two t a b l e s with b i o t i t e analyses, one t a b l e with p l a g i o c l a s e analyses, and one t a b l e with s t a u r o l i t e a n a l y s e s .  227  228 Standards used f o r e l e c t r o n microprobe analyses are from the r e f e r e n c e standards c o l l e c t i o n (number i n parentheses) at the Department of G e o l o g i c a l Sciences, U n i v e r s i t y of B r i t i s h Columbia. A l l minerals were analyzed using the same standards, except as noted.  Element  Standard  Number  Or i g i n  F  F-Phlogopite  (24)  (synthet i c )  Na  Albite  (20)  (Oregon)  Mg  Forsterite  (22)  (synthet i c )  Al  Andalus i te  (26)  (Brazil)  Si  Wollastonite  (21 )  (New York)  K  Orthoclase  (96)  (New York)  Ca  Wollastonite  (21 )  (New York)  Ba  Benitoite  (35)  (California)  Ti  Rutile  (13)  (synthet i c )  Mn  Pyroxmang i te  (245)  (Japan)  Fe  F a y a l i te  (250)  (synthet i c )  Some garnets were a l s o analyzed u s i n g : Mg  Pyrope garnet  (235)  (New Zealand)  Al  Pyrope garnet  (235)  (New Zealand)  Si  Pyrope garnet  (235)  (New Zealand)  GARNET  ANALYSES  Sample  8 0 - 1 9 RIM  8 0 - 1 9 CORE  80-31  Analyses  9  7  10  WEIGHT % MgO A l ,03 S10. CaO TiOi MnO FeO  .22 . 15 .2 1 .64 .02 .27 .04  100 . 5 5 FORMULA  80-31  CORE  7  80-33  RIM  80-33  1  20  CORE  1  (o) 2 21 37 2 0 2 35  Total  RIM  (0 . 17) ( 0 .. 6 2 ) (0 30) (0. 20) (0. 01) ( 0 . 12) (0 28) (0. 54)  3 21 37 3 0 1 34  . 33 . 16 .61 04 . 12 36 21  (0 .30) (0 .45) (0 60) ( 0 18) (0. 32) (0. 31) (0. 31)  2 . 36 2 0 . 74 36 97 2 .03 0 .01 1 ..8 2 35 .93  (0. (0. (0. (0. (0. (0. (0.  100. 83  (0. 64)  99  (0. 84)  86  12) 37) 41) 12) 02) 25) 73)  2.66 20.76 36.89 1 .62 0.00 3 . 34 34.45  (0.04) (0.36) (0.54) (0.03) (0.00) ( 0 . 4 1) (1.20)  2.10 21.65 36.98 2.11 0.05 2.31 35.32  99.72  ( 1 .44 )  100.52  ( 0 . 15) (0. 26) (O. 4 7 ) ( 0 . 14) ( 0 . 13) ( 0 . 13) (0. 50) (0. 95)  2 . 3 4 ( 0 . 2 1) 21.89 (0.44 ) 37.02 (0.59) 1 .60 ( 0 . 1 5 ) 0.01 (0.01) 3.48 (0.43) 34 3 5 ( O . 4 2 ) 100.69  (1.01)  („)  MgO Al i 0 , S10. CaO T10* MnO FeO  0 267 2 .003 2 ,. 9 9 2 0 .. 2 2 7 0 .001 0 .. 155 2 356  Total  8 .001  (0.018) (0.048) (0.031) (0.017) (0.001) (0.008) (0.027)  0 .395 1 .985 2 .993 0 .276 0 .007 0 .077 2 277 8 .010  (0.035) (0.037) (0.035) (0.047) (0.019) (0.030) (0.027)  0. 1 2 0. 0. 0. 2.  286 983 999 176 001 125 438  8.007  .015) .033) .029) .011) .001 ) .016) .045)  0.322 1.986 2.994 0.141 O.OOO 0.229 2.338  (0.006) (0.034) (0.036) (0.003) (0.000) (0.029) (0.058)  0.251 2.052 2.974 0.182 0.003 0 . 158 2.376  (0.016) (0.028) (0.017) (0.012) (0.008) (0.009) (0.025)  0.280 2.069 2.969 0 . 138 0.001 0.237 2.304  (0.023) (0.026) (0.015) (0.014) (O.OOD (0.029) (0.042)  (0.019)  8.009  (0.027)  7.996  (0.013)  7.996  (0.016)  (0 (0 (0 (O (0 (0 (O  ro  •n 3 -I o t/l > s (0 3 — OJ - —(Q  "n S -) O c/i > s (0 3 — 0) — — IQ  o o o o .o O - o  oooa~ o ~oa  o 30 s c  o o  MOOOMUO •U — O — (0 O fo u o O a a ^ >i  o  o oooooo  u  -j -j ro ut O CD O  8  U  o  ~J  UI  ~  8  a> m ro co cn -* ro  b 10  O  O  CJ ID CJ)  O O O O O O CJ  CJ  CJ  ro -~  x*  O ro  en co  01 k 01 CO  O u Ol CJ  O cn  O O O O O OO IO -» O -» 01 CJ - » co cj & ro -j ui  8 b  CJ  CJ  o to o tn cn CJ cn cn co — o ui a> CD o oooooo  bbbbbbb MOO-'-'-O O - * - » CJ O - J  MOOOwuO cj Q ro co O ro cj to o CJ oo o cn ro & ro cn CJ o to O  O O O O O OO  UI  t  b b b b ob b b  t u - ro x» ro co o cn CJ  MOOOro-O x» O O ro to to ro x>. to O ro to to cn ro ~i CJ cn o O cj  O OO OOOp  o obb u oO U 00 to CJ ui  to —. ro  O O O O O O O ui ro o x» £>•-•• -* cn co o cn - J - J  O ui O O  io o O O ro ro O  O O  CJ  CJ  t> O  00 00  -J  bcj ObbO b-* rob b rob — to  O ro  — ui O O -» ro ui co A u) CJ cn cn  b b>•>0 bO<QuOuOuOuO  ro O O O ro ro o O - <D O U ro Q o (D Co ro cn  u <n  b bo U M ->  ro ui CD  ro  ui -» o  CJ  —  to  cn -* ro  cn ^ o - J - J co cn x* — & cn CJ CB  co  O oO O O OO ui o o - t - o b. ro -•. cj A -J CJ  O  CJ  o  cj  ro  cj  M  X* ro O ro cn — ro  ui oo o - J to O ro cj & CJ ro cn ro CJ  oo  O O O O O OO ui ro o ui -•• oi -» ro cn o x* —  O O  cj cn  CJ  CJ  ro  o ro cn o ro — x» o cn to oo —  O ro ui — oo oo oo  -  ui oi  ooooooo  ui — o x* cn x* — co — x>. co ro x»  GARNET ANALYSES Sample  81-325 RIM  81-325 CORE  82-389 RIM  82-389 CORE  Ana 1yses  25  13  13  4  WEIGHT 54 U ) MgO Al 1 O 1 S10> CaO TIO, MnO FeO  2 . 72 (0 18) 20 .85 (0. 45) 36 .85 (0 47) 2 .98 (0. 14) 0 01 (0. 02) 2 16 (0. 26) 34 .02 (0. 38)  3 .09 (0 .08) 20 .87 (O 38) 37 OO (O 40) 2 .90 (0. 10) 0 .04 (0. 09) 1.70 (0. 10) 34 . 37 (0. 39)  Total  99. 59 (0. 88)  2 .55 21 .24 37 36 6 .21 0..06 1 55 31 .32  (0 50) (0. 59) (O 56) (0 86) (0 05) (0. 48) (0. 68)  2 . 10(0. 42) 20 . 74 (0. 37) 37 .. 77 (0. 55) 6 78 (0. 64) 0 09 (0. 04) 3 .. 32 (O. 39) 30. 28 (0. 39)  99 97 (0 62)  100. 29 (O.87)  101 .08 (0. 45)  FORMULA (<j) MgO Al I O I S10; CaO T10, MnO FeO  0 .328 1 990 . 2.985 0. 259 0..001 0. 148 2 .305  (0.021) (0.033) (0.020) (0.012) (0.001) (0.017) (0.032)  0 .372 (0 .010) 1 .983 . (0 .028) 2 982 (0 .014) 0 . 250 (0 .009) 0 .002 (0 .005) 0 , 1 16(0 .006) 2.,317 (0 .035)  0 . 304 (0.059) 1.998 (0.055) 2 982 (0.033) 0.,531 (0.074) 0..004 (0.003) 0 . 105 (0.033) 2 .090 (0.038)  0.. 249 (0 .048) 1 ,944 , (0 .046) 3 003 (0 .029) 0 577 (0 .054) 0 006 (0 .003) O,. 224 (0, 028) 2.014 (0 .027)  Total  8 .017 (0.011)  8 .022 (0. 013)  8.013 (0.013)  8 .016 (0,.012)  BIOTITE  ANALYSES  Sample  80-19  80-19 B  80-31  80-33  81-278  8 1-279  Analyses  9 (d1f.gr.)  16 (same g r . )  6  14  10  8  0.39 ( O . 1 3 ) 0.31 ( 0 . 0 6 ) 9.00 ( 0 . 3 8 ) 19.09 ( 0 . 8 2 ) 35.42 ( 0 . 8 3 ) 8.74 ( 0 . 3 0 ) 0.00 ( 0 . 0 1 ) 0.11 ( 0 . 0 5 ) 2.22 ( 0 . 3 4 ) 0.04 ( O . O I ) 20.42 ( 1 . 1 6 )  0.35 (O.13) 0.29 ( 0 . 0 7 ) 10.11 ( 0 . 3 5 ) 19.30 ( 0 . 5 3 ) 35.42 ( 0 . 6 7 ) 8.42 ( 0 . 0 1 ) 0.01 ( 0 . 0 1 ) 0.07 ( 0 . 0 4 ) 1.70 ( 0 . 1 9 ) 0.04 ( 0 . 0 2 ) 18.45 ( 0 . 5 6 )  0 31 0 23 8 .81 19. 59 35. 54 8 .06 . 0 03 0 . 16 1 .70 0 .04 20 .62  ( 0 . 16) (0. 03) ( 0 85) ( 0 . 47) ( 0 . 71 ) ( 0 . 33) (0. 07) ( 0 . 04 ) (0 . 33) (0. 05) (1 4 0 )  94.16  95 .09  (O 53)  WEIGHT %  (a)  F Na>0 MgO A l 703 S10» K,0 CaO BaO T10r MnO FeO  0 . 37 0 .21 9 .35 18 .31 35 .61 8 .93 0 .00 0 .36 1 98 O 03 19..48  ( 0 . 15) (0 03) ( 0 47) (0 61) ( 0 81) (0 . 36) (0. 01) (0. 08) ( 0 . 31) (O 0 3 ) (1 .04)  0 29 0 22 9 65 18 .25 36 .08 8 .49 0 01 0. 32 1 .76 0 03 19. 23  (0.14) (0.04) (0.19) (0.60) (0.75) (115) (0.01) (0.07) (0.09) (0.02) (0.60)  0. 24 0. 38 8 66 19 26 35 56 8 24 0. 01 0. 20 2 81 0. 03 18..77  (0 (0 (0 (0 (0 (0 (0 (0 (0 (0 (0  08) 05) 25) . 18) 87) 07) 01) 07) .23) 02) 31)  Total  94 63  ( 1 . 12)  94. 43  ( 1 42)  94 . 16 ( 0 . 6 9 )  95.74  (0.98)  (1.07)  FORMULA  22  22.000  22.000  22.000  22.000  22.000  5.484 2.516 8.000  5.535 2.465 8.000  5.442 2.558 8.000  5.397 2.603 8.000  5.409 2.591 8 .OOO  5 .424 2 . 576 8.000  A l VI TI Fe * Mn Mg Sum  0.807 0 230 2.508 0.004 2.147 5.696  0.835 0.203 2.466 0.004 2.203 5.711  0.915 0.324 2.403 0.004 1.977 5.623  0.825 O. 254 2 .604 0.006 2 .044 5.733  0.894 0. 199 2 . 365 0.005 2.313 5.776  0.947 O. 196 2 .634 0006 2 .003 5 . 786  Ca Na K Ba  OOOO 0.063 1.754 0.021 1.838  0.002 0.092 1.659 0.018 1.771  0.001 0.113 1.609 0.012 1.735  0.001 0.091 1 .699 0.006 1 . 797  0.002 0.088 1 .646 0.005 1 .741  0.005 0.069 1 .570 0.010 1 .654  3.937 0.063  3.908 0.092  3.883 0.117  3.810 0. 190  3.835 0. 165  3.850 O. 150  Oxygens S1 Al  IV Sum IV  !  Sum OH F  OOO  BIOTITE ANALYSES Sample  80-119  80-119 INC1  80-119 INC2  81-325  82-389  Analyses  17  3  3  15  7  WEIGHT % (a ) (0. 17) (0. 10) (0 52) (0 . 18) (0 .23) (0 .40) (0..01) (0 04 ) (0. 08) (0 .02 ) (0 42)  F Na>0 MgO Al , 0 i S10, K,0 CaO BaO T107 MnO FeO  0 . 28 (0 10) 0 . 30 (0 05) 8 .72 (0 47) 19 .27 (0 .90) 35 . 20 (0 43) 8 .44 (0 19) O .03 (0..04) 0 . 12 (0. 04) 2 .38 (0 42) 0 .04 (0 02) 20 .42 (0..95)  0 .47 (0 15) 0 .44 (0. 03) 1 1.24 (0 13) 18 . 17 (0 28) 36 .24 (0 94) 8 . 33 (0. 05) 0 OO (0. 01) 0 .09 (0. 03) 2 .23 (0. 03) 0 .03 (0. 02) 16 .52 (0. 18)  0.30 0.37 11 .05 19.75 35.59 7.86 0.00 0.09 1 .86 0.02 17.24  (OH) (O 03) (0.23) (O.15) (O.10) (0.43) (0.01) (0.04) (0.13) (0.02) (0.56)  0.. 37 (O. 14) 0 40 (0. 04) 10 09 (0. 15) 18.. 68 (0. 36) 36 . 15 (O. 32 ) 8 . 45 (0. 20) 0. 02 (0. 04 ) 0 . 13 (0. 05) 2..06 (0. 19) 0. 06 (0..06) 17 . 93 (0. 50)  0..50 0 25 1 1 77 . 18 .05 36 58 8 84 0 01 0. 07 1 41 0. 03 16 .75 .  Total  95 .20 (0. 57)  93 .76 (0. 46)  94.13  (1.05)  94 34 (0. 55)  94 26 (0 .24)  22.000  22.000  22.000  22.OOO  22.000  S1 Al IV Sum IV  5.382 2.618 8.000  5.523 2.477 8.000  5.392 2 .608 8 .000  5 . 509 2.491 8 OOO  5.563 2 .437 8 .000  Al VI T1 Fe'* Mn Mg Sum  0.854 0.273 2.612 0.005 1.988 5.732  0.788 0.256 2.106 0.003 2.555 5.708  0.919 0.212 2 . 184 0.002 2 .496 5.813  0 864 0. 236 2 . 286 0.OO7 2 . 291 5.684  0.797 0.161 2. 130 0.004 2 .669 5.761  Ca Na K Ba  O.O04 0.089 1.646 0.007 1.746  0.001 0.130 1.619 O.005 1.755  0.001 0. 109 1 .519 0.005 1 .634  0.003 0. 1 19 1 .643 0.008 1 . 773  0.002 0.073 1 .741 0.005 1 .821  3.864 0.136  3.771 0.229  3.857 O. 143  3 . 822 0. 178  4.000  FORMULA Oxygens  OH F  Sum  r-o  y  n l - i i i n x w M Z - n (D 3 — 0) 0> » — —IQ g> o o o a o o o ~ a - o o  X  > 3  -nX-tOOOXc/j&SZ-n IB 3 — o> n> •« — — iQ 0) o o o o o o o - o ~ o o  > 3 0)  a X3  ID I  < CO CD Ul  l/l  Dl 3 T3  >  > O O O O O O M - O O O CO 09  CD CO CO  8  OOOC0Ocnc0O9>O O O C J ^ O M B O O O roooocn.uKj — o-Jcn  o b  O O O O  ui  0 0 0 0 0 0 1 0  b  o• o•  cn  o b  —0 0 0  o ~J M O - J O - O ^ M O B O ro  Ul  ro cn CJ  b  CO ro O  O O O O O O O O O O O  88888822828 O O O O O O r o  — O O O  Q O O O M O - l M O - J O O O O Q - J O r o c n o c n o a s O o O — 01 — cn — j * c n O O O O O O O O O O O  019)  O O O O O O O O O O O O O O O r o O ——Oro — u i O O O — ro — co — O r o  Ul  O O O O O O M - O O O  o  Ul CO  8— O0Q 0OO0Q Orc oo—oo ccOnnOcc-doIOoOu^CiiDooO  0  Ul  O O O O O O i o - O O O  CO 0  b  O  ro Ul O  OOQOcoocncoocno O O Q Q — ocncoocoo uioooo&uicnocnoo O O O O O O O O O O O  .008) .057) .OOO) .014) .005) OOI ) .017) .000) OOO) OOO 003)  038) 0  Ul  O O O O O O r o  ro ro  b  ro CO  Q O O O W O - J M O - J O O g o o u o u m o ^ o c o o o o — A-oocn — -0 co  O  O O O O O O O O O O O  00  019) CO  CO  O O O ' co o cn co o cn 0 O Q O 1 cn o *• cn o co o *• O O 1 co *• O — ro  O O O O O O r o CO  — O O O  01 01  ro  KZ  O O O O O O O O O O O O O < O O O —— O r o o ui O 1 O ^ i — c o c n c o r o c o  882  —  CO  oo O  i  8S2  01  — O O O i n O - J c n O ' o O ' O O U t > u - ' - > 0 - > ^  co co  cn ro OOOO<t*OrouO<0O  O O O O O O O O O O O O O O O — OCO.UO—O — O — U1CO — 0 0 O — CJ.U  O O  O O O O m o  O Ul .O  00  O  u o - ' U > i o u a s o u i u  *> CO  cn ro —& 0 0 0 0  U O O Q J 1 - - - 0 - 1 O  — 0-.OCOOco-.ro*.*.  ao O u co  O O O O O O O O O O O — O O 0 * - O u i u i O — O CO — — O O CO ro — — coco  o o  cn ro o o o o c n o c o u i o o o o  03  O Q O Q r o O O o  co co  ao O  — OC0U1O03O — -J — u i o r o o  ui ro • o o o o c n o c o u i o - i O — O 0 0 * - O t o r o o c o o co — — — c o - 4 r o u o c o c n  —  O O O O O O O O O O O O O O O M O - I U O - J O C O M — rocorouicn — o t n  O — to ui  01  ro O O O O * - O r o i i O C 0 O O O O O C O O U i m O - O ~i — — — c o o o * . c o O c n r o  ro CO  O O O O O O O O O O O O O O O U O M U O U O •u — - . r o c o — o o ^ o - ^ c n  co CO  co O  Ul M O O O O - J O c o c n o c n o - O O O ^ O O - i O H O U - 0 0 < H ^ 0 U M U I & O O O O O O O O O O O  cn ^1  — O O O— OCOfOOroO ro — — — oo ro co cn ui O cn  >  z > r-  -< in  O O O O U - > M U O O O  O  O O O O O O O O O O O  o  cn ro O O O O - o O - i c n O c n o O oo co Ul CS CO &  ooooooooooo  — O O O  O O O O O O O O O O O O O O O —O —— O c o o — — 0 0 ~ J — roco — — cn  o  CO  ro  0 0 0 - ( D - . m t n o O - J 0  00  o o o o o o o  g b g b o g bO bO gi b b cn — £• co O ao o  8  CO  o o > cn  co 10  cn  STAUROLITE  ANALYSES  Sample  82-389  81-279  81-278  80-33  Ana 1 y s e s  8  1  1  1  0 .00 0 .00 1 . 58 55 . 42 27 . 73 0 .00 0 .00 0 .00 0 . 29 0 .07 14 . 10  0 .05 O .03 1 . 36 52 . 35 27 . 34 0 .02 0 .00 0 .00 0 . 58 0 . 16 14 . 34  0.00 0.03 1 . 39 53.84 27 . 4 3 0.01 0.00 0.02 0.50 0.11 14 . 59  WEIGHT %, ( « ) F Na*0 MgO A l 70, S10* K*0 CaO BaO T10J MnO FeO  0 .04 0 .01 1 . 76 51 . 8 5 27 . 5 3 0 .01 0 .01 0 .02 0 .64 0 . 13 13 . 27  Total  95 . 25 ( 0 . 42)  99 .21  96 . 23  97 . 92  23 . 0 0  23 .00  23 .00  23 . 00  S1  3 .92  3. 79  3 87  3 . 82  Al T1 Sum  8 . 70 0 .03 8 . 73  8 . 94 O..03 8 . 97  8 . 74 0 . 06 8. 80  8.83 0.05 8 . 88  Fe * Mg Mn Sum  1 . 58 0 38 0 .02 1 .98  1 .61 0 . 32 0 . 01 1 .94  1 .70 0 . 29 0 . 02 2 . 01  1 . 70 0 . 29 0.01 2 .00  14 .64  14 . 70  14 . 68  14 . 70  OH F  2 .00 0 00  2 . OO 0 . 00  1 .98 0 . 02  2 .00 O.OO  XFe  0.80  0.83  0.85  0.85  (0..07) (0..01) ( 0 . 21) (0. 48) ( 0 . 38) (0. 01) (0 . 0 1 ) (0. 03) (0. 04) (0. 02) ( 0 . 20)  FORMULA Oxygens  !  Total  Staurolite  Formula:  (Fe,Mg)(2)  Al(9)  S1(3.75)  0(22)  0H(2)  APPENDIX IIIA: ANALYTICAL METHODS FOR GEOCHRONOLOGY Analytical  Techniques.  Rb and Sr c o n c e n t r a t i o n s were determined by r e p l i c a t e a n a l y s i s of pressed powder p e l l e t s using X-ray f l u o r e s c e n c e . U.S. G e o l o g i c a l Survey rock standards were used f o r c a l i b r a t i o n ; mass a b s o r p t i o n c o e f f i c i e n t s were obtained from Mo K-a Compton s c a t t e r i n g measurements. Rb/Sr r a t i o s have a p r e c i s i o n of 2% (1a) and c o n c e n t r a t i o n s a p r e c i s i o n of 5% (1O). Sr i s o t o p i e composition was measured on unspiked samples prepared using standard ion exchange techniques. The mass spectrometer, V.G. Isomass 54R, has data a c q u i s i t i o n d i g i t i z e d and automated using a H.P. 85 computer. Experimental data have been normalized to a S r / S r r a t i o of 0.1194 and a d j u s t e d so that the NBS standard S r C 0 (SRM987) g i v e s a S r / S r r a t i o of 0.71020 ± 2 and the Eimer and Amend Sr a r a t i o of 0.70800 ± 2. The p r e c i s i o n of a s i n g l e S r / S r ratio is <0.00010 ( l o ) . Rb-Sr dates are based on a Rb decay constant of 1.42 x I 0 " a . The r e g r e s s i o n s are c a l c u l a t e d a c c o r d i n g t o the technique of York (1967). Z i r c o n separate was prepared u s i n g standard g r i n d i n g and mineral s e p a r a t i o n procedures f o r heavy m i n e r a l s . D i s s o l u t i o n of z i r c o n s and i s o l a t i o n of U and Pb were done using a procedure based on that of Krogh'(1973). The sample was analysed using s i n g l e Re f i l a m e n t and s i l i c a g e l techniques on an Isomass 54R mass spectrometer i n the Department of G e o l o g i c a l Sciences, U n i v e r s i t y of B r i t i s h Columbia, by P. van der Heyden. 8 6  8 8  8 7  8 6  3  8 7  1 1  8 6  _ 1  Krogh, T.E. 1973. A low contamination method f o r hydrothermal decomposition of z i r c o n and e x t r a c t i o n of U and Pb f o r i s o t o p i e age d e t e r m i n a t i o n s . Geochimica et Cosmochimica Acta, 37, pp. 485-494.  236  APPENDIX 11 IB: GEOCHRONOLOGY SAMPLE DESCRIPTIONS Sample d e s c r i p t i o n s . JSG-81-X1 to X6. 52°40.5' N. L a t . , 121°05.7' W. Long. F o l i a t e d quartz d i o r i t i c gneiss with p l a g i o c l a s e ( A n „ . ) (35%), quartz (15%), hornblende (10%), and reddish-brown b i o t i t e (20%) and epidote (15%) from metamorphism of hornblende, and sphene, minor a p a t i t e , a l l a n i t e , and z i r c o n . C r y s t a l l i z a t i o n f o l i a t i o n i s d e f i n e d by oriented- b i o t i t e and hornblende, and i n c i p i e n t segregation of mafic from f e l s i c layers. S t a u r o l i t e - k y a n i t e zone. 2  30  JSG-81-X1 to X6 were combined f o r z i r c o n a n a l y s e s . Z i r c o n s are c o l o r l e s s t o l i g h t pink, t y p i c a l l y subhedral p r i s m a t i c with rounded edges and t e r m i n a t i o n s . Length to width r a t i o v a r i e s from 2 to 6. About 50% of the c o a r s e r (100-200 mesh) g r a i n s a r e broken and i n t e r n a l l y cracked. Bulk sample c o n t a i n s 1-2% non-zircon m a t e r i a l . Handpicked f r a c t i o n s c o n s i s t only of c l e a r , c r a c k - f r e e , unbroken c r y s t a l s . Quesnel Lake Gneiss  ( f o r comparison with  JSG-81-X):  JSG-80-QLGNW. 52°33.0' N. L a t . , 121°04.4' W. Long. From j u n c t i o n of north and west arms of Quesnel Lake. L e u c o c r a t i c , medium-grained, f o l i a t e d g r a n i t e with m i c r o c l i n e (40%), quartz (35%), p l a g i o c l a s e (15%), and c h l o r i t e p l u s muscovite (10%), minor opaques(<2%). F o l i a t i o n i s d e f i n e d by mortar t e x t u r e : f i n e - g r a i n e d mica, q u a r t z , and f e l d s p a r between broken g r a i n s of f e l d s p a r and quartz with sutured boundaries and undulose e x t i n c t i o n . JSG-81-166. 52°33.5' N. L a t . , 121°01.1' W. Long. From j u n c t i o n of north and east arms of Quesnel Lake. Weakly f o l i a t e d , c o a r s e - g r a i n e d , pink and green K - f e l d s p a r g r a n i t e with p e r t h i t i c m i c r o c l i n e megacrysts (20%). Groundmass i s m i c r o c l i n e (30%), quartz (30%), epidote and green b i o t i t e (10%), and s a u s s u r i t i z e d f e l d s p a r , c h l o r i t e , sphene, and muscovite (10% t o g e t h e r ) , and minor a l l a n i t e . F o l i a t i o n i s c a t a c l a s t i c rather than metamorphic.  237  238  JSG-80-36. 52°41.75' N. L a t . , 120°55.8' W. Long. Pegmatite with quartz (40%), p l a g i o c l a s e (50%), and muscovite (10%); average g r a i n s i z e i s >1 cm. Intruded as l a t e to post-metamorphic d i k e s . JSG-80-99. 52°43.3' N. L a t . , 120°58.8' W. Long. F o l i a t e d g r a n o d i o r i t i c gneiss with l a r g e (up to 1 cm) magnetite g r a i n s l o c a l l y . S t a u r o l i t e - k y a n i t e zone. JSG-80-136A. 52°43.3' N. L a t . , 120°59.8' W. Long. F o l i a t e d g r a n o d i o r i t i c gneiss with p l a g i o c l a s e (50%), quartz (30 % ) , p e r t h i t i c potassium f e l d s p a r (10%), b i o t i t e (10%), and minor opaque o x i d e s . S t a u r o l i t e - k y a n i t e zone. JSG-81-205. 52°40.6' N. L a t . , 120°59.2' W. Long. Weakly f o l i a t e d g r a n o d i o r i t i c g n e i s s . S i l l i m a n i t e zone. JSG-81-327. 52°37.85' N. L a t . , 121°03.85' W. Long. F o l i a t e d g r a n o d i o r i t i c augen g n e i s s , with f o l i a t i o n s u b p a r a l l e l to l a y e r i n g i n adjacent p a r a g n e i s s . Augen up to 1 cm are f e l d s p a r (45%); other minerals are quartz (30%), b i o t i t e (20-25%), and minor o x i d e s . Kyanite zone. JSG-80-42. 52°47..2' N. L a t . , 120°59.55' W. Long. Graphitic garnet-kyanite(?)-bearing biotite-muscovite schist. Garnets up to 1 cm; quartz s e g r e g a t i o n l a y e r s parallel schistosity. S t a u r o l i t e - k y a n i t e zone. JSG-79-15. 52°46.15' N. L a t . , 120°58.0' W. Long. Q u a r t z - r i c h s c h i s t with garnet, b i o t i t e , muscovite, and plagioclase. S t a u r o l i t e - k y a n i t e zone. JSG-80-67. 52°43.5' N. L a t . , 120°59.3' W. Long. W e l l - f o l i a t e d b i o t i t e - m u s c o v i t e s c h i s t with p o r p h y r o b l a s t s of s t a u r o l i t e , garnet, and p l a g i o c l a s e . S t a u r o l i t e zone. JSG-80-80. 52°44.2' N. L a t . , 120°57.9' W. Long. W e l l - 1 i n e a t e d micaceous q u a r t z i t e with q u a r t z , b i o t i t e , and p l a g i o c l a s e . Kyanite to s i l l i m a n i t e zone. JSG-80-96. 52°43.4' N. L a t . , 120°58.1' W. Long. Folded, l i n e a t e d q u a r t z - b i o t i t e - m u s c o v i t e s c h i s t with porphyroblasts. S t a u r o l i t e - k y a n i t e zone.  garnet  JSG-82-375. 52°45.7' N. L a t . , 121°04.6' W. Long. Crenulated quartz muscovite s c h i s t with b i o t i t e and garnet porphyroblasts. Metamorphosed to at l e a s t garnet zone. JSG-81-245. 52°45.5' N. L a t . , 121°00.05* W. Long. Coarse-grained, h o r n b l e n d e - p l a g i o c l a s e amphibolite with some quartz and i r o n oxides. S t a u r o l i t e - k y a n i t e zone.  239  JSG-80-21. 52°42.0' N. L a t . , 120°55.4' W. Long. F o l i a t e d gneiss with b i o t i t e , q u a r t z , p l a g i o c l a s e , some muscovite. S i l l i m a n i t e zone.  and  JSG-80-22. 52°41.95' N. Lat., 120°55.5' W. Long. Crenulated muscovite s c h i s t with b i o t i t e , q u a r t z , plagioclase. S i l l i m a n i t e zone. JSG-81-171. 52°41.7' N. L a t . , 120°56.0' W. Long. Weakly f o l i a t e d g n e i s s with medium to c o a r s e - g r a i n e d q u a r t z , p l a g i o c l a s e , and b i o t i t e . S i l l i m a n i t e zone. JSG-81-281. 52°40.05' N. Lat., 121°05.2' W. Long. G a r n e t - b i o t i t e s c h i s t with p l a g i o c l a s e and c h l o r i t e . Staurolite-kyanite zone. JSG-81-328. 52°37.85' N. L a t . , 121°03.9' W. Long. Coarse q u a r t z - m u s c o v i t e - b i o t i t e s c h i s t with garnet and kyanite (20%). Kyanite zone.  i  

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