"Science, Faculty of"@en . "Earth, Ocean and Atmospheric Sciences, Department of"@en . "DSpace"@en . "UBCV"@en . "Nelson, JoAnne Lee"@en . "2010-02-08T21:03:44Z"@en . "1976"@en . "Master of Science - MSc"@en . "University of British Columbia"@en . "Georgia Depression is a major northwest-trending structural\r\ntrough that lies between the Coast Mountains and Vancouver Island, along the western boundary of the Coast Plutonic Complex. Field work on a part of this boundary on Hardwicke and West Thurlow Islands in Johnstone Strait established it as an intrusive\r\ncontact between an Upper Jurassic quartz diorite and stratified\r\nrocks of the Vancouver Group. The Vancouver Group in the vicinity of the contact is broken by two major west-northwest trending preplutonic faults. Contact metamorphic conditions\r\ndetermined from basic and carbonate assemblages are P ,-3 kb.\r\ntotal\r\nand T . = (650 - 720\u00B0C . Post-plutonic fractures and dikes maximum\r\ntrend northeast. The main result of the field study was to confirm for a particular area that the western margin of the Coast Plutonic Complex is essentially a magmatic front.\r\nGeorgia Depression began to subside in the Upper Cretaceous\r\nas the Coast Plutonic Complex rose. It is proposed that the initial subsidence of Georgia Depression was complementary to the uplift of the Coast Mountains. Georgia Depression is part of the Coastal Trough of western North America, an elongate depression that lies between a series of colinear magmatic arcs (the Coast Plutonic Complex, the Cascades, and the Sierra Nevada) and the western margin of the North American plate. The various sub-basins of the Coastal Trough formed at different times, from the Upper Jurassic to the Late Tertiary, that correspond\r\nto the times of uplift of the adjacent igneous complexes.\r\n\r\nThis coincidence suggests that the subsidence of the whole Coastal Trough, including Georgia Depression, was coupled to the uplift of the magmatic arcs of North America. The Coastal Trough may be analogous to the marginal synclines developed in Ramberg's (1967) diapir experiments."@en . "https://circle.library.ubc.ca/rest/handle/2429/19795?expand=metadata"@en . "THE ORIGIN OF GEORGIA DEPRESSION ; AND THE COAST- PLUTONIC COMPLEX/ INSULAR BELT PROVINCE BOUNDARY ON HARDWICKE AND WEST THURLOW ISLANDS, B.C. by JoAnne Lee Nelson B.Sc., U n i v e r s i t y of Washington 1973 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the 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 J u l y 1976 \u00C2\u00A9 JoAnne Lee Nelson, 1976 In p resent ing t h i s t he s i s in p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree that permiss ion for ex ten s i ve copying o f t h i s t he s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r ep re sen ta t i ve s . It i s understood that copying or p u b l i c a t i o n of t h i s t he s i s f o r f i n a n c i a l gain s h a l l not be al lowed without my w r i t t e n permis s ion. The U n i v e r s i t y of B r i t 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Depa rtment ABSTRACT G e o r g i a D e p r e s s i o n i s a major n o r t h w e s t - t r e n d i n g s t r u c t -u r a l t r o u g h t h a t l i e s between the C o a s t M o u n t a i n s and V a n c o u v e r I s l a n d , a l o n g t h e w e s t e r n b o u n d a r y of t h e C o a s t P l u t o n i c Complex. F i e l d work on a p a r t of t h i s b o u n d a r y on H a r d w i c k e and West T h u r l o w I s l a n d s i n J o h n s t o n e S t r a i t e s t a b l i s h e d i t as an i n t r u -s i v e c o n t a c t between an Upper J u r a s s i c q u a r t z d i o r i t e and s t r a t -i f i e d r o c k s of t h e V a n c o u v e r Group. The V a n c o u v e r Group i n t h e v i c i n i t y of t h e c o n t a c t i s b r o k e n by two major w e s t - n o r t h w e s t t r e n d i n g p r e p l u t o n i c f a u l t s . C o n t a c t metamorphic c o n d i t i o n s d e t e r m i n e d from b a s i c and c a r b o n a t e a s s e m b l a g e s a r e P ,-3 kb. t o t a l and T . = (650 - 720\u00C2\u00B0C . P o s t - p l u t o n i c f r a c t u r e s and d i k e s maximum t r e n d n o r t h e a s t . The main r e s u l t of t h e f i e l d s t u d y was to c o n f i r m f o r a p a r t i c u l a r a r e a t h a t t h e w e s t e r n m a r g i n of t h e C o a s t P l u t o n i c Complex i s e s s e n t i a l l y a magmatic f r o n t . G e o r g i a D e p r e s s i o n began to s u b s i d e i n t h e Upper C r e t a c e -ous as t h e C o a s t P l u t o n i c Complex r o s e . I t i s p r o p o s e d t h a t t h e i n i t i a l s u b s i d e n c e of G e o r g i a D e p r e s s i o n was complementary to t h e u p l i f t of t h e C o a s t M o u n t a i n s . G e o r g i a D e p r e s s i o n i s p a r t of t h e C o a s t a l T r o u g h of w e s t e r n N o r t h A m e r i c a , an e l o n g a t e d e p r e s s i o n t h a t l i e s between a s e r i e s of c o l i n e a r magmatic a r c s ( t h e C o a s t P l u t o n i c Complex, t h e C a s c a d e s , and t h e S i e r r a Nevada) and t h e w e s t e r n m a r g i n of t h e N o r t h A m e r i c a n p l a t e . The v a r i o u s s u b - b a s i n s of t h e C o a s t a l T r o u g h formed a t d i f f e r e n t t i m e s , from the Upper J u r a s s i c to t h e L a t e T e r t i a r y , t h a t c o r r e s -pond to t h e t i m e s of u p l i f t of t h e a d j a c e n t i g n e o u s c o m p l e x e s . i i i . T h i s c o i n c i d e n c e s u g g e s t s t h a t t h e s u b s i d e n c e of t h e w h o l e C o a s t a l T r o u g h , i n c l u d i n g G e o r g i a D e p r e s s i o n , was c o u p l e d t o t h e u p l i f t o f t h e m a g m atic a r c s o f N o r t h A m e r i c a . The C o a s t a l T r o u g h may be a n a l o g o u s t o t h e m a r g i n a l s y n c l i n e s d e v e l o p e d i n Ramberg's (1967) d i a p i r e x p e r i m e n t s . . iv, TABLE OF CONTENTS SECTION I : I n t r o d u c t i o n and R e g i o n a l S y n t h e s i s 1 I n t r o d u c t i o n 1 CHAPTER I : The H i s t o r y o f G e o r g i a D e p r e s s i o n and V i c i n i t y 4 i . T h e I n s u l a r B e l t 4 i i . T h e C o a s t P l u t o n i c Complex 9 i i i . G e o r g i a D e p r e s s i o n 20 iv.Summary and E v a l u a t i o n of R e g i o n a l S y n t h e s i s 24 SECTION I I : F i e l d Study 30 I n t r o d u c t i o n - G e n e r a l G e o l o g y o f t h e Map-Area 30 CHAPTER I I : S t r a t i g r a p h y o f t h e V a n c o u v e r Group 33 i . K a r m u t s e n F o r m a t i o n 33 i i . T h e V a n c o u v e r Group s e d i m e n t s : Q u a t s i n o , P a r s o n Bay and H a r b l e d o w n F o r m a t i o n s 38 i i i . B o n a n z a V o l c a n i c s 40 i v . S t r a t i g r a p h y and M a j o r S t r u c t u r e 41 CHAPTER I I I : P l u t o n i c Rocks 44 i . O l d e r B o d i e s 44 i i . Q u a r t z D i o r i t e and A s s o c i a t e d H o r n b l e n d e Gabbros 48 i i i . R a d i o m e t r i c D a t i n g : Q u a r t z D i o r i t e 66 CHAPTER IV: P r e - and S y n - P l u t o n i c S t r u c t u r e and D i k e s 73 i . P r e - P l u t o n i c D i k e s 73 i i . P h a s e One ( P r e - P l u t o n i c ) : The M a j o r F a u l t s ' 75 i i i . P h a s e T w o : S y n - P l u t o n i c D e f o r m a t i o n 77 iv.Summary 86 CHAPTER V: Metamorphism 89 i . B u r i a l Metamorphism 89 i i . C o n t a c t Metamorphism 90 a) A s s e m b l a g e s i n B a s i c Rocks 91 b) C a r b o n a t e M e t a m o r p h i c A s s e m b l a g e s 107 c) C o n c l u s i o n s 113 V . CHAPTER XI: P o s t - P l u t o n i c S t r u c t u r e and Dikes 119 Summary of F i e l d Results 126 SECTION I I I : The C o a s t a l Trough 130 CHAPTER VII: Geologic S e t t i n g of the C o a s t a l Trough 130 i.Hecate Depression 130 i i . T h e Puget and W i l l i a m e t t e Depressions 134 i i i . T h e Great V a l l e y 145 CHAPTER VIII:Deep S t r u c t u r e of the C o a s t a l Trough 149 i . B r i t i s h Columbia 149 ii.Washington and Oregon 153 i i i . C a l i f o r n i a 156 iv.Summary 159 CHAPTER IX: Synthesis and Conclusions 160 LIST OF TABLES vi, T a b l e 1. C o m p a r i s o n between l a y e r i n g i n h o r n b l e n d e g a b b r o s , c u m u l a t e and s c h l i e r e n l a y e r i n g . T a b l e 2. R a d i o m e t r i c age d a t a from q u a r t z d i o r i t e . T a b l e 3. C a r b o n a t e p a r a g e n e s e s . T a b l e 4. P e t r o g r a p h i c D a t a - P o s t - P l u t o n i c D i k e s . 55 69 108 123 v i i . LIST OF FIGURES F i g u r e 1. The C o a s t a l T r o u g h 2 2. Upper C r e t a c e o u s p a l e o g e o g r a p h y 10 3. P a l e o m a g n e t i c p o l e s and f a u n a l a f f i n i t i e s , s o u t h w e s t e r n B r i t i s h C o l u m b i a 13 4. P a l e o g e o g r a p h i c e v o l u t i o n of s o u t h w e s t e r n B r i t i s h C o l u m b i a 25 5. Index map = F i e l d a r e a on H a r d w i c k e and West T h u r l o w I s l a n d s 31 6. S t r a t i g r a p h y of t h e V a n c o u v e r Group 34 7. S t r a t i g r a p h y of i n t e r v o l c a n i c s e d i m e n t a r y c y c l e , Helmcken I s l a n d 36 8. P o l e s to b e d d i n g , Domain I 42 9. P o l e s to b e d d i n g , Domain I I 44 10. a) Miner's Bay gabbro 4 6 b) W e l l b o r e C h a n n e l g n e i s s i c q u a r t z d i o r i t e 11. Q u a r t z d i o r i t e 49 12. L a r g e - s c a l e i n t r u s i v e b r e c c i a , M i n e r ' s Bay 49 13. P o l e s to f o l i a t i o n i n q u a r t z d i o r i t e 51 1\u00C2\u00AB. T e x t u r a l v a r i a t i o n s i n h o r n b l e n d e g a b b r o s 54. 15. a) \"Hornblende - p l a g i o c l a s e l a y e r i n g 56. b) L a y e r e d h o r n b l e n d e - r i c h gabbro t r u n c a t e d by l i g h t e r u n l a y e r e d phase 16. a) N e a r - v e r t i c a l c r o s s - b e d d i n g 58. b) A g m a t i t i c zone between n o r m a l l a y e r s 17. a) Deformed l a y e r i n g t r u n c a t e d by p l a n a r l a y e r s 59 b) L a y e r e d gabbro i n t r u d e d by gabbro d i k e v i i i F i g u r e 18. a) \" C l a s t i c d i k e \" 60 b) Channel 19. a) Path of melt composition i n a supercooled 62 boundary l a y e r b) E v o l u t i o n of the boundary l a y e r 20. Radiometric d a t i n g of quartz d i o r i t e 67 21. B i o t i t e i s o c h r o n s from quartz d i o r i t e 68 22. S t r i k e o r i e n t a t i o n s of p r e - p l u t o n i c dikes 74 23. R o t a t i o n a l r e l a t i o n s h i p s between homoclinal 76 domains 24. S t r i k e o r i e n t a t i o n s of epidote v e i n s 79 25. O r i e n t a t i o n s of minor f o l d s 80 26. Minor f o l d s i n i n t e r l a v a sediments, upper 81 Karmutsen Formation, West Thurlow I s l a n d 27. a) O r i e n t a t i o n s of c h a o t i c f o l d s , east of 83 Vans i t t a r t Point b) F o l d - a x i s d i s t r i b u t i o n s i n v e r t i c a l shear 28. Poles to f o l i a t i o n i n metavolcanics and 85 marbles 29. S t r u c t u r a l c r o s s - s e c t i o n , Hkusam to 87 Hardwicke I s l a n d 30. Metamorphic assemblages i n the Vancouver 92 Group 31. a) Karmutsen g r e e n s c h i s t with amygdule, 93 Helmcken I s l a n d b) G r e e n s c h i s t - hornblende h o r n f e l s t r a n s i t i o n i n amygdule i n Upper Karmutsen, West Thurlow I s l a n d 32. Schematic diagram of the g r e e n s c h i s t - 97 amphibolite t r a n s i t i o n 33. Epidote breakdown, T - f n space 101 \u00C2\u00B02 ix F i g u r e 34. C o n t a c t b e t w e e n L a t e J u r a s s i c q u a r t z 103 d i o r i t e and K a r m u t s e n h o r n f e l s , H a r d w i c k e I s l a n d 35. a) B o n a n z a t u f f ( ? ) i n h o r n b l e n d e h o r n f e l s zone 105 b) B o n a n z a h o r n f e l s 36. C a r b o n a t e a s s e m b l a g e s p l o t t e d i n t h e s y s t e m 109 CaO - A-120 - S i 0 2 - C 0 2 - H O 37. S c h e m a t i c T-'X _ d i a g r a m = t h e s y s t e m CaO - 112 C U 2 A 1 2 0 3 - F e 2 0 3 - S i 0 2 - H 20 - C 0 2 38. T e m p e r a t u r e v s . d i s t a n c e f r o m t h e c o n t a c t 115 39. P o l e s t o p o s t - p l u t o n i c d i k e s and j o i n t s 120 40. S t r i k e o r i e n t a t i o n s o f p o s t - p l u t o n i c d i k e s 121 41. C r o s s - c u t t i n g p o s t - p l u t o n i c d i k e s 122 42. C o m p a r a t i v e I n s u l a r B e l t s t r a t i g r a p h i e s 131 43. D i s t r i b u t i o n o f t h e Skonum F o r m a t i o n 133 44. The C o a s t a l T r o u g h and g e o t e c t o n i c p r o v i n c e s 135 o f w e s t e r n W a s h i n g t o n and Oregon 45. L i t h o l o g i c c h a r t = w e s t e r n W a s h i n g t o n 137 46. L i t h o l o g i c c h a r t = w e s t e r n O r e g o n 138 47. Upper M i o c e n e p a l e o g e o g r a p h y o f t h e C o l u m b i a n 142 Embayment 48. U p p e r J u r a s s i c - Lower C r e t a c e o u s e v e n t s : 146 w e s t e r n C a l i f o r n i a 49. a) Sh o t p o i n t s , r e c o r d i n g s t a t i o n s and u p p e r , 150 m a n t l e v e l o c i t i e s f o r r e v e r s e d s e i s m i c p r o f i l e s i n w e s t e r n B r i t i s h C o l u m b i a b) C r u s t a l p r o f i l e a c r o s s s o u t h w e s t e r n B r i t i s h Columb i a 50. a) V a r i a t i o n s i n c r u s t a l t h i c k n e s s , B r i t i s h 152 Columb i a b) R e l a t i v e c r u s t a l d e n s i t i e s , B r i t i s h C o l u m b i a X F i g u r e 51. Index map = c r u s t a l s e i s m i c s t u d i e s i n t h e 154 P a c i f i c N o r t h w e s t 52. C r u s t a l t h i c k n e s s e s b e n e a t h w e s t e r n W a s h i n g t o n 155 53. I s o s t a t i c anomaly map, W a s h i n g t o n 157 54. a) S e i s m i c p r o f i l e a c r o s s w e s t e r n C a l i f o r n i a 158 b) Model of t h e c r u s t under C a l i f o r n i a f r o m Bougner a n o m a l i e s 55. R i s i n g d i a p i r w i t h m a r g i n a l s y n c l i n e s 163 LIST OF PLATES Time-space p l o t f o r the Upper P a l e o z o i c - ( i n back Mesozoic of Vancouver I s l a n d and the ' pocket) Coast Mountains, 49\u00C2\u00B0 - 52\u00C2\u00B0N. Geologic Map of Hardwicke and West ( i n back Thurlow I s l a n d s , B.C. pocket) xii ACKNOWLEDGEMENTS H. R. Wynne-Edwards s u g g e s t e d the p r o j e c t to me and p r o v i d e d m o r a l and f i n a n c i a l s u p p o r t t h r o u g h o u t . S t a n Reamsbottom m e n t i o n e d H a r d w i c k e I s l a n d as an i n t e r e s t i n g e x p o s u r e of the p r o v i n c e b o u n d a r y . Jenny S t a r k , Fang B e n d i c k s o n and my p a r e n t s , Anne and George N e l s o n , gave a b l e and u n c o m p l a i n i n g a s s i s t a n c e i n t h e f i e l d . J enny and I owe our c o m f o r t (and p e r h a p s s u r v i v a l ) to B r u c e , E d i e and H a r o l d B e n d i c k s o n and Mac and Hug C a r m i c h a e l of H a r d w i c k e I s l a n d , f a i r y g o d p a r e n t s i n d e e d . Lee P i g a g e , H.R. Wynne-Edwards and R i c h a r d A r m s t r o n g v i s i t e d H a r d w i c k e I s l a n d and p r o v i d e d u s e f u l i n s i g h t s about f i e l d r e l a t i o n s . C o n v e r s a t i o n s w i t h J a n M u l l e r , v G l e n n Woodsworth, W.R. Danner, F r a n k Danes, John G r i f f i t h s , B i l l C o u l b o u r n , I a n Duncan, and Lee P i g a g e c o n t r i b u t e d to t h e e v o l u t i o n of my i d e a s . Joe H a r a k a l , R i c h a r d A r m s t r o n g , P e t e r L e C o u t e u r and Cathy Lamb c a r r i e d o ut and/or c o a c h e d me i n a n a l y t i c a l p r o c e d u r e s f o r r a d i o -m e t r i c d a t i n g . J a n M u l l e r and G l e n Woodsworth i m p r o v e d t h e m a n u s c r i p t w i t h t h e i r s u g g e s t i o n s . J e a n n e t t e W i l l i a m s d i d t h e f i n a l t y p i n g w i t h e f f i c i e n c y and aplomb. I would l i k e to thank the g e o l o g y t e c h n i c i a n s , R.B. Coo p e r , and J o h n Payne f o r k i n d a s s i s t a n c e i n the p u r s u i t of my g o a l s . * N a t i o n a l R e s e a r c h C o u n c i l o p e r a t i n g g r a n t A8302. 1. SECTION 1: INTRODUCTION AND REGIONAL SYNTHESIS I n t r o d u c t i o n G e o r g i a D e p r e s s i o n i s a t o p o g r a p h i c and s t r u c t u r a l low t h a t l i e s between t h e m o u n t a i n o u s r e g i o n s of V a n c o u v e r I s l a n d and t h e C o a s t M o u n t a i n s of B r i t i s h C o l u m b i a . I t i s a p a r t of the C o a s t a l T r o u g h t h a t e x t e n d s from H e c a t e S t r a i t i n t h e n o r t h , t h r o u g h t h e Puget and W i l l i a m e t t e Lowlands to t h e C e n t r a l V a l l e y of C a l i f o r n i a ( F i g u r e 1 ) . The C o a s t a l T r o u g h has been d e s c r i b e d i n g e o m o r p h o l o g i c l i t e r a t u r e (Fenneman 1931; H o l l a n d 1964) but no a t t e m p t has been made so f a r to a c c o u n t f o r i t s o r i g i n . In c o n t r a s t to p r e v i o u s s t u d i e s w h i c h have em p h a s i z e d l o c a l c a u s e s , t h i s i n v e s t i g a t i o n , a l t h o u g h p r i n c i p a l l y c o n c e r n e d w i t h t h e o r i g i n of G e o r g i a D e p r e s s i o n , has f o l l o w e d the h y p o t h e s i s t h a t s i n c e t h e C o a s t a l T r o u g h i s a c o n t i n u o u s f e a t u r e t h e n a common mode of o r i g i n s h o u l d be s o u g h t . C e r t a i n l o c a l f e a t u r e s s e t G e o r g i a D e p r e s s i o n a p a r t from t h e t r o u g h f u r t h e r s o u t h . I t i s deep: ( T i f f i n (1969) e s t i m a t e s t h a t h a l f of t h e f l o o r of G e o r g i a S t r a i t l i e s below c o n t i n e n t a l s h e l f d e p t h , 132 m e t e r s . I t l i e s between t h e C o a s t P l u t o n i c Complex ( w h i c h i n l a r g e p a r t c o i n c i d e s w i t h the p h y s i o g r a p h i c C o a s t M o u n t a i n s ) and t h e I n s u l a r B e l t ( w h i c h i n c l u d e s V a n c o u v e r I s l a n d and t h e Queen C h a r l o t t e I s l a n d s ) . S e v e r a l h y p o t h e s e s f o r the o r i g i n o f G e o r g i a D e p r e s s i o n have been p r o p o s e d . They a r e : 1. Upper C r e t a c e o u s to e a r l y T e r t i a r y downwarping a n d / o r d o w n f a u l t i n g ( J e l e t z k y 1965; S u t h e r l a n d Brown 1966; M u l l e r and J e l e t z k y 1970) . 1 3. 2. E a s t w a r d t i l t i n g o f t h e V a n c o u v e r I s l a n d b l o c k ( M u l l e r 1 9 7 5 ) . 3. F o u n d e r i n g o f a zone o f l i t h o s p h e r i c w e a k n e s s o v e r a s u t u r e j o i n i n g t h e two p r o v i n c e s . Monger e t a l . (1972) s u g g e s t t h a t t h e I n s u l a r B e l t i s a l l o c h t h o n o u s , a l t h o u g h t h e y f a v o r a s u t u r e a l o n g t h e Y a l a k o m f a u l t s y s t e m . 4. N o r t h e a s t - s o u t h w e s t e x t e n s i o n a s s o c i a t e d w i t h a C r e t a c e o u s o r C e n o z o i c r i f t zone o r rhombochasm ( B o s t r o m 1968; Wynne-Edwards p e r s . comm. 1 9 7 3 ) . 5. S u b s i d e n c e c o m p l e m e n t a r y t o and a c c o m p a n y i n g t h e u p l i f t o f t h e C o a s t M o u n t a i n s ( t h i s s t u d y ) . T h e s e h y p o t h e s e s a r e a d d r e s s e d t o t h r e e i s s u e s : t h e t i m i n g , s t y l e , and u l t i m a t e c a u s e s o f t h e D e p r e s s i o n . I n o r d e r t o e v a l -u a t e them t h i s s t u d y u t i l i z e s b o t h p u b l i s h e d l i t e r a t u r e and t h e r e s u l t s o f a f i e l d i n v e s t i g a t i o n o f t h e I n s u l a r B e l t / C o a s t P l u t o n i c Complex b o u n d a r y c a r r i e d o u t i n t h e summer o f 1974. I t b e g i n s w i t h a summary of p r e s e n t k n o w l e d g e o f t h e h i s t o r y o f G e o r g i a D e p r e s s i o n and t h e two t e c t o n i c p r o v i n c e s t h a t i t s p a n s . The f i e l d p r o j e c t p r o v i d e s f u r t h e r d e t a i l on t h e n a t u r e o f t h e p r o v i n c e b o u n d a r y . The p i c t u r e p r e s e n t e d does n o t c o n f o r m e a s i l y t o e i t h e r a s u t u r e o r a r i f t ; t h e p o s i t i o n and t i m i n g o f t h e D e p r e s s i o n s u g g e s t t h a t i t f o r m e d as a complement t o t h e r i s i n g C o a s t - M o u n t a i n s . L i t e r a t u r e s u r v e y s o f t h e r e s t o f t h e t r o u g h show t h a t t h e o t h e r segments l i k e w i s e s u b s i d e d s y n c h r o n o u s l y w i t h t h e u p l i f t o f t h e a d j a c e n t r a n g e . P o s s i b l e m e c h anisms of c o u p l i n g a r e d i s c u s s e d i n t h e f i n a l c h a p t e r . 4. CHAPTER I; THE HISTORY OF GEORGIA DEPRESSION AND VICINITY The most obvious f e a t u r e of the ge o l o g i c s e t t i n g of Georgia Depression i s that i t l i e s across the Coast P l u t o n i c Complex/ I n s u l a r B e l t province boundary. The h i s t o r y of these two pr o v i n c e s , so f a r as they are known, are summarized below. The o r i g i n of t h e i r present boundary i s of p a r t i c u l a r i n t e r e s t . For c l a r i t y , the two provinces w i l l f i r s t be d i s c u s s e d s e p a r a t e l y . (The Time-Space P l o t , P l a t e 1, and the Fraser River 1 : 1,000,000 Map-Sheet (Roddick, Muller and O k u l i t c h 1973) should be co n s u l t e d during the f o l l o w i n g d i s c u s s i o n ) . i . The I n s u l a r B e l t The o l d e s t s t r a t i g r a p h i c u n i t i n Vancouver I s l a n d i s the Sicker Group which contains s t r a t a from e a r l i e s t Devonian or ol d e r (Muller 1976) to Pennsylvanian-Permian i n age. M u l l e r (1975) has d i v i d e d the S i c k e r Group i n t o three u n i t s . The lowest c o n s i s t s of ande s i t e and d a c i t e p y r o c l a s t i c s and subordinate flows. A t u r b i d i t e sequence, r e s t r i c t e d i n occurrence, o v e r l i e s the S i c k e r v o l c a n i c s . The uppermost u n i t i s a limestone c o n t a i n -ing f u s i l i n i d s dated as Pennsylvanian or Permian. The species present are of A u s t r a l i a n , not North American, a f f i n i t y (Danner pers. comm. 1973). I f t h i s a f f i n i t y has paleogeographic r a t h e r than paleoenvironmental s i g n i f i c a n c e the southern I n s u l a r B e l t must be al l o c h t h o n o u s . The uneven d i s t r i b u t i o n of limestone and c l a s t i c sediments i n Si c k e r Group exposures, as w e l l as the abundance of a n d e s i t e , has l e d Monger et a l (1972) and Mul l e r (1974) to suggest that i t i s the remains of a P a l e o z o i c i s l a n d arc . 5. The S i c k e r Group was metamorphosed to g r e e n s c h i s t f a c i e s , and i n p l a c e s d e v e l o p e d p e n e t r a t i v e c l e a v a g e , b e f o r e the M i d d l e T r i a s s i c , as undeformed a r g i l l i t e s of t h a t age o v e r l i e i t uncon-f o r m a b l y . The a r g i l l i t e s a r e s u c c e e d e d by the Karmutsen Form-a t i o n o f Upper K a r n i a n age. The K a r m u t s e n F o r m a t i o n i s m a i n l y a p i l e of b a s a l t r e m a r k a b l e f o r i t s t h i c k n e s s (up to 8000 m.) and s h o r t e r u p t i o n i n t e r v a l ( p a r t of a f a u n a l z o n e ) . I t embodies an emergent s e q u e n c e ( C a r l i s l e and S u z u k i 1974) r a n g i n g upward from p i l l o w b a s a l t to p i l l o w b r e c c i a and b r e c c i a to a m y g d a l o i d a l f l o w s w i t h s p a r s e d i s c o n t i n u o u s s e d i m e n t a r y i n t e r c a l a t i o n s . Geo-c h e m i c a l l y t h e K armutsen b a s a l t s a p p e a r to r e s e m b l e o c e a n i c X h o l e i i t e s or ocean i s l a n d b a s a l t s more c l o s e l y t h a n i s l a n d a r c t h o l e i i t e s ( K u n i y o s h i 1 972). K u n i y o s h i p o s t u l a t e d t h a t t h e y were e x t r u d e d a t a m i d - o c e a n r i d g e . C o n t a c t r e l a t i o n s between the Karmutsen and the u n d e r l y i n g S i c k e r Group a r e c l e a r l y d e p o s i t -i o n a l and n o t r e l a t e d to a t h r u s t p l a n e ( M u l l e r p e r s . comm. 1975), so K u n i y o s h i ' s i n t e r p r e t a t i o n must be m o d i f i e d a c c o r d i n g l y . M u l l e r et a l (1974) s u g g e s t t h a t the b a s a l t s were formed a t a r i d g e i n an i n t e r a r c b a s i n . Symons (1971b) and I r v i n g and Y o l e (1972) have d e t e r m i n e d p a l e o m a g n e t i c p o l e s f r o m t h e K a r m u t s e n b a s a l t s . The p o l e s l i e about 50\u00C2\u00B0 s o u t h of t h e mean Upper T r i a s s i c p o l e f o r N o r t h A m e r i c a . I n o r d e r to r e c o n c i l e t h e p o l e s V a n c o u v e r I s l a n d would have had to l i e i n t h e s o u t h e r n h e m i s p h e r e d u r i n g t h e Upper K a r n i a n . T h i s i s c o m p a t i b l e . 6. with the A u s t r a l i a n a f f i n i t y of Pennsylvanian-Permian f u s i l i n i d s i n the S i c k e r Group. The t h i n l e n s o i d sedimentary i n t e r c a l a t i o n s i n the Karmutsen Formation are probably lagoonal d e p o s i t s . A t y p i c a l lens c o n t a i n s an upward sequence of benthic limestone to p e l a g i c limey shale that C a r l i s l e and Suzuki (1974) i n t e r p r e t as submergent. Gentle subsidence, then, accompanied accumulation of the Karmutsen v o l c a n i c p i l e . The shallow-water r a t h e r than a b y s s a l e n v i r o n -ment l e s s e n s the l i k e l i h o o d that the Karmutsen was formed at an oceanic r i d g e . I t a l s o precludes d i r e c t a n a l o g i e s with modern back-arc b a s i n s , which are deep (a necessary consequence of t h e i r t h i n c r u s t ) . The Karmutsen b a s a l t s are succeeded by upper Karnian to P l i e n s b a c h i a n sediments, which are d i v i d e d i n t o three formations with g r a d a t i o n a l contacts (also i n t e r p r e t e d by C a r l i s l e and Suzuki as a subergent sequence); the upper Karnian Quatsino Formation ( l i m e s t o n e ) ; the Norian Parson Bay Formation, a ser-i e s of thin-bedded c h e r t s , a r g i l l i t e s , and carbonates; and the Lower J u r a s s i c Harbledown Formation, .'.distinguished from the Parson Bay Formation by absence of carbonate and presence of greywacke. V o l c a n i c c l a s t i c sediments i n the Harbledown Formation mark the resurgence of volcanism. The Harbledown sediments are succ-eeded by and are i n part coeval with the Sinemurian to Lower P l i e n s b a c h i a n Bonanza V o l c a n i c s . Dominantly a n d e s i t i c , they are thought to represent a c a l c - a l k a l i n e i s l a n d arc (Monger et a l . 1972; M u l l e r et a l . 1974). Most of the p l u t o n s , and a l l of the l a r g e ones, on V a n c o u v e r I s l a n d a r e of J u r a s s i c age (148 to 181 m.y.: M u l l e r e t a l . 1974). The J u r a s s i c I s l a n d I n t r u s i o n s o c c u p y about t e n p e r c e n t of t h e i s l a n d ' s s u r f a c e a r e a and a r e r o u g h l y c o e v a l w i t h t h e Bonanza V o l c a n i c s . M u t u a l i n t r u s i v e r e l a t i o n s h i p s have been o b s e r v e d : a n d e s i t i c d i k e s i n t h e p l u t o n s and p l u t o n s i n t r u d i n g and m e t a m o r p h o s i n g Bonanza a n d e s i t e s . N o r t h c o t e and M u l l e r (1972) s u g g e s t t h a t t h e y a r e comagmatic. C o n f i r m a t i o n a w a i t s t r a c e - e l e m e n t and i s o t o p i c c o m p a r i s o n s and d a t i n g of p o s s i b l e Bonanza d i k e s i n the p l u t o n s . Symons (1971a) has d e t e r m i n e d a p a l e o m a g n e t i c p o l e f o r t h e I s l a n d I n t r u s i o n s w h i c h , w i t h i n the l i m i t s o f e r r o r , c o i n c i d e s w i t h t h e M i d d l e J u r a s s i c N o r t h A m e r i c a n p o l e . The s o u t h e r n I n s u l a r B e l t must have been i n p l a c e by t h a t t i m e . The d a t e of p o s s i b l e s u t u r i n g i s t h u s c o n s t r a i n e d between upper K a r n i a n ( a p p r o x i m a t e l y 210 m.y.) and 166 m.y., t h e o l d e s t i n t r u s t i o n sampled by Symons. E x c e p t f o r a few Lower C r e t a c e o u s b o d i e s on Texada I s l a n d and t h e n o r t h e a s t s h o u l d e r o f V a n c o u v e r I s l a n d , t h e y o u n g e s t d a t e d I s l a n d I n t r u s t i o n i s 148 m.y. o l d . S i g n i f i c a n t i g n e o u s a c t i v i t y i n t h e s o u t h e r n I n s u l a r B e l t c e a s e d a t t h a t t i m e . I t d i d not resume u n t i l t h e T e r t i a r y , and t h e n i n subdued f o r m . T h i s l a c k o f C r e t a c e o u s i g n e o u s a c t i v i t y i s one -of t h e main d i f f e r e n c e s between t h i s p r o v i n c e and t h e C o a s t P l u t o n i c Complex w h i c h c o n t a i n s an enormous volume of C r e t a c e o u s - E o c e n e i n t r u s i v e m a t e r i a l . D u r i n g and a f t e r emplacement of t h e I s l a n d I n t r u s i o n s t h e a r e a now o c c u p i e d by V a n c o u v e r I s l a n d and G e o r g i a S t r a i t was u p l i f t e d enough to shed a p p r e c i a b l e c l a s t i c d e b r i s , i n c l u d i n g g r a n i t i c m a t e r i a l , westward onto the c o n t i n e n t a l s h e l f ( J e l e t z k y 1965; Muller et a l . 1 9 7 4 ) . A d d i t i o n a l evidence f o r r e g i o n a l u p l i f t above wavebase i n c l u d e s : 1) the absence of P l i e n s b a c h i a n to Santonian s t r a t a on most of Vancouver I s l a n d and 2) the unconformity below the Upper Cretaceous Nanaimo Group which cuts across a l l o l d e r u n i t s and d i s p l a y s over 300 meters of r e l i e f (Ross and Barnes, unpub. ms.). Upper J u r a s s i c and V a l a n g i n i a n to Barremian c l a s t i c marine sediments of the Longarm Formation accumulated on the northern and western edges of the u p l i f t . A nearshore to o f f s h o r e environment i s i n f e r r e d from the Longarm fauna. Conglomerates i n the Longarm Formation c o n t a i n few i f any g r a n i t i c c l a s t s . On northwestern Vancouver I s l a n d the Longarm Formation i s o v e r l a i n by the Aptian to Cenomanian Queen C h a r l o t t e Group. As i n the type area i n the Queen C h a r l o t t e Islands (Sutherland Brown 1968) i t i s p a r t l y non-marine and contains coarse g r a n i t i c d e b r i s , which may r e f l e c t more vigourous u p l i f t of the I n s u l a r B e l t (Muller et a l . 1 9 7 4 ) . The P a c i f i c Rim Complex, p a r t l y coeval with the Longarm Formation, occurs i n fault-bounded blocks along the western margin of Vancouver I s l a n d . It c o n s i s t s mostly of h i g h l y deformed t u r b i d i t e s with subordinate c h e r t , b a s a l t and lime-stone. Page ( 1 9 7 4 ) has d e s c r i b e d o l i s t o s t r o m e s i n the P a c i f i c Rim Complex. Both Page and M u l l e r (1973) term i t a melange. It may be a F r a n c i s c a n e q u i v a l e n t , or at l e a s t an analogue, i n which case the Late J u r a s s i c - E a r l y Cretaceous trench lay somewhat east of the present p l a t e boundary. 9. The S a n t o n i a n to H a e s t r i c h t i a n Nanaimo Group o u t c r o p s i n and a r o u n d G e o r g i a S t r a i t . I t s i n f e r r e d o r i g i n a l d i s t r i b u t i o n ( F i g u r e 2) i m p l i e s a b a s i n c o n f i g u r a t i o n v e r y s i m i l a r to t h e modern G e o r g i a D e p r e s s i o n . The Nanaimo Group i s a complex i n t e r t o n g u i n g s e quence of g r e y w a c k e - s i l t s t o n e r h y t h m i t e s , c o n g -l o m e r a t e l e n s e s , s h a l e , m a s s i v e greywacke, s h a l e and c o a l . I t i s c u r r e n t l y i n t e r p r e t e d as a complex d e l t a / s u b m a r i n e f a n i n a s u b s i d i n g b a s i n (Ross and B a r n e s p e r s . comm. 1973; R i n n e 1973; Simmons 1973; Hudson 1974; S t u r d a v a n t 1974). The s o u r c e of s e d i m e n t f o r t h e Nanaimo Group was the I n s u l a r B e l t u p l i f t : p a l e o c u r r e n t s a r e e a s t e r l y to n o r t h e r l y and c o b b l e s i n c o n g l o -m e r a t e s s u g g e s t a V a n c o u v e r I s l a n d p r o v e n a n c e . The Upper C r e t -a c e ous b a s i n was t h e d i r e c t p r e c u r s o r o f G e o r g i a D e p r e s s i o n , s u p e r i m p o s e d on a p o s t - p l u t o n i c r e g i o n a l u p l i f t of t h e s o u t h e r n I n s u l a r B e l t . I t s p l a c e i n t h e h i s t o r y of t h e C o a s t P l u t o n i c Complex w i l l n e x t be shown. i i . The C o a s t P l u t o n i c Complex The C o a s t M o u n t a i n s a r e d o m i n a t e d by p l u t o n i c and p o l y d e f -ormed metamorphic r o c k s ( s e e F r a s e r R i v e r map-sheet, R o d d i c k , M u l l e r and O k u l i t c h 1973) t h a t have n e a r l y o b l i t e r a t e d t h e s t r a t i g r a p h i c r e c o r d . The e x i s t e n c e of P r e c a m b r i a n basement i n t h e s o u t h e r n C o a s t M o u n t a i n s i s s t i l l u n p r o v e n . The C u s t e r G n e i s s n o r t h of t h e F r a s e r R i v e r ( D a l y 1912) i s c o n s i d e r e d c o r r e l a t i v e w i t h t h e S k a g i t G n e i s s i n the N o r t h C a s c a d e s ( M i s c h 1966) b a s e d on l i t h -o l o g i c s i m i l a r i t y . The S k a g i t G n e i s s has g i v e n z i r c o n ages 1Zt\u00C2\u00B0 lit' 10 \u00E2\u0080\u00A2Vp-pcr Crctactovs \^ /_J\u00C2\u00BBftrrut limit af WVcr ~^ -. J Cretacmcs basin-J (present qcagia,'Dtynssipyu Me \u00E2\u0080\u00A2 fauna th^tlm-rE-rn-nt-trum ^ms .'rticLtyitiffid as lowtx CYllauows,. thus matPHmUmo ttpuvaitM- (jcldxAy fz> .0/. Qrce^i,,\" t^-t)/ 1 1 . greater than 1650 m.y. OMattl.ns.on 1973). Even assuming that the Custer Gneiss i s autochthonous and not tr a n s p o r t e d from the south by f a u l t i n g , the extent of basement i n the Coast Mountains cannot be guessed a t . Upper P a l e o z o i c (Lower Pennsylvanian to Lower Permian) s t r a t a i n the southern Coast Mountains are co n f i n e d to p a r t l y f a u l t -bounded septa near H a r r i s o n Lake. They are c o r r e l a t i v e with the C h i l l i w a c k Group i n the North Cascades (Monger 1970). L i t h o l o g -i c a l l y the C h i l l i w a c k Group resembles the S i c k e r Group, but i t s s t r a t i g r a p h i c order i s d i f f e r e n t . I t i n c l u d e s v o l c a n i c sandstone, p e l i t e , c h e r t , s i l t s t o n e , limestone, metabasalt and/or meta-an d e s i t e , and v o l c a n i c e l a s t i c s . As f u s i l i n i d s i n the C h i l l -iwack limestones are of North American a f f i n i t y (Monger and Ross 1971), the S i c k e r and C h i l l i w a c k Groups may have been deposited thousands of k i l o m e t e r s a p a r t . If so a suture zone l i e s between them. Does i t f o l l o w Georgia Depression? The T r i a s s i c record sheds some l i g h t on t h i s q u e s t i o n . The Karmutsen Formation i s truncated a b r u p t l y on the east by voluminous i n t r u s i o n s . There are no c e r t a i n Karmutsen e q u i v a l e n t s w i t h i n the Coast P l u t o n i c Complex, although a few have been suggested. P i l l o w b a s a l t s i n J e r v i s I n l e t bear a s t r i k i n g resemblance to the Karmutsen (Woodsworth pers. comm. 1974). Tipper (pers. comm.) a l s o r e p o r t s l i k e l y analogues. These may argue a g a i n s t a p o s t - T r i a s s i c suture between the two p r o v i n c e s . T r i a s s i c s t r a t a i n the southern Coast Mountains between Pemberton and L i l l o o e t are in c l u d e d i n the Fergusson 12. and C a d w a l l a d e r G r o u p s , The F e r g u s s o n Group i s d o m i n a t e d by c h e r t , a r g i l l i t e and b a s a l t w i t h m i n o r l i m e s t o n e . P a r t o f i t has b e e n d a t e d as L a d i n i a n (Cameron and Monger 1 9 7 1 ) , c o e v a l w i t h t h e M i d d l e T r i a s s i c a r g i l l i t e s on V a n c o u v e r I s l a n d . Monger e t a l . (1972) i n t e r p r e t i t as an o c e a n i c a s s e m b l a g e . The Hozomeen G r o u p , l y i n g b e t w e e n t h e Y a l e and Hozameen F a u l t s , has y i e l d e d no f o s s i l s , b u t i s c o r r e l a t e d on l i t h o l o g i c g r o u n d s w i t h t h e F e r g u s s o n Group (Cameron and Monger 1 9 7 1 ) . The C a d w a l l -a d e r Group has y i e l d e d f o s s i l s o f N o r i a n age ( R o d d i c k and H u t c h i s o n 1 9 7 3 ) . I t c o n t a i n s g r e e n s t o n e , c l a s t i c s e d i m e n t s i n c l u d i n g v o l c a n i c c o n g l o m e r a t e w i t h q u a r t z m o n z o n i t e b o u l d e r s , a r g i l l i t e , p y r o c l a s t i c s , c h e r t and l i m e s t o n e . U n l i k e t h e K a r m u t s e n F o r m a t i o n a l l T r i a s s i c u n i t s w i t h i n t h e C o a s t M o u n t a i n s a r e h i g h l y d e f o r m e d . F i g u r e 3 shows f u s i l i n e a f f i n i t i e s and p a l e o m a g n e t i c p o l e s i n s o u t h e r n B r i t i s h C o l u m b i a t o d e m o n s t r a t e p o s s i b l e p o s i t i o n s f o r an Upper T r i a s s i c - Lower J u r a s s i c s u t u r e . Of t h e p o s s i b l e l o c a t i o n s , t h e I n s u l a r B e l t / C o a s t P l u t o n i c Complex b o u n d a r y seems much l e s s l i k e l y t h a n t h e S h u l a p s T e r r a n e , w h i c h f i t s w e l l i n t o t h e p r e c o n c e p t i o n o f s u t u r e . I n i t a r e c h e r t s - \" o c e a n b o t t o m s e d i m e n t s \" , g r e y w a c k e s - \" t r e n c h s e d i m e n t s \" , v o l c a n i c s , and u l t r a m a f i t e s , a l l h i g h l y d e f o r m e d and f a u l t e d . The S h u l a p s u l t r a -m a f i c body o v e r l i e s F e r g u s s o n Group r o c k s a l o n g a s h a l l o w l y e a s t -d i p p i n g c o n t a c t , p o s s i b l y a s h e a r zone ( N a g e l p e r s . comm. 1 9 7 5 ) . The u l t r a m a f i c s a r e t h o u g h t t o have b e e n e m p l a c e d i n Upper T r i a s s i c t o Lower J u r a s s i c t i m e , as t h e y a r e f a u l t e d a g a i n s t M i d d l e T r i a -s s i c and N o r i a n r o c k s and d e t r i t a l c h r o m i t e a p p e a r s i n l a t e Lower yolt -positions -from- \u00E2\u0080\u00A2\u00E2\u0080\u00A2 Jjnwns 1371a,, 13/1 b, nju, 1973 Jnryim and JoLc ~19JP~ 14 J u r a s s i c s e d i m e n t s ( L e e c h 1953) . A l t h o u g h s h e a r z o n e s a r e d e s c r i b e d i n t h e e a s t e r n I n s u l a r B e l t ( K u n i y o s h i 1972; M u l l e r p e r s . comm. 1975; C a r l i s l e p e r s . comm. 1975) t h e y a r e n o t o f t h e same s c a l e , n o r a r e u l t r a m a f i t e s p r e s e n t a l o n g them. The most c o m p l e t e J u r a s s i c - C r e t a c e o u s r e c o r d p e r t a i n i n g t o t h e C o a s t P l u t o n i c Complex i s p r e s e r v e d i n a n a r r o w f a u l t - b o u n d e d band ( i n c l u d i n g t h e P a s a y t e n and Methow G r a b e n s ) s o u t h and e a s t o f t h e C o a s t M o u n t a i n s . The s e q u e n c e , r a n g i n g i n age f r o m S i n e m u r i a n t o C e n o m a n i a n , c o n s i s t s o f g r e y w a c k e - s i l t s t o n e r h y t h m i t e s , c o n g l o m e r a t e and p h y l l i t e . A few v o l c a n i c and v o l c a n i c c l a s t i c u n i t s o c c u r e a s t o f Mt. W a d d i n g t o n ( T i p p e r 1 9 6 9 ) . U n t i l r e c e n t l y t h e s e s e d i m e n t s were t h o u g h t t o have been d e p o s i t e d i n a f a i r l y r e s t r i c t e d t r o u g h , t h e T y a u g h t o n T r o u g h . However, s e v e r a l d e t a i l e d f a c i e s and p a l e o c u r r e n t s t u d i e s ( C o l e 1 973; C o a t e s 1974; T e n n y s o n 1974) ha v e shown t h a t t h e \" t r o u g h \" was open t o t h e w e s t u n t i l A p t i a n t i m e . C u r r e n t d i r e c t i o n s were f r o m t h e e a s t o r l o n g i t u d i n a l , as was s e d i m e n t t r a n s p o r t d e d u c e d f r o m f a c i e s c h a n g e s The p a l e o s l o p e was w e s t e r l y : t h e r e i s no i n d i c a t i o n o f a p r o t o -C o a s t M o u n t a i n s e i t h e r as a p o s i t i v e t o p o g r a p h i c f e a t u r e o r as a s e d i m e n t s o u r c e u n t i l A l b i a n t i m e . J u r a s s i c - L o w e r C r e t a c e o u s s t r a t a w i t h i n t h e C o a s t M o u n t a i n s i n c l u d e 1) t h e Gamb i e r Group and c o r r e l a t i v e s t r a t a , 2) t h e F i r e L a k e G r o u p , and 3) t h e H a r r i s o n L a k e G r o u p . The s e q u e n c e a t H a r r i s o n L a k e i s M i d d l e J u r a s s i c t o Lower C r e t a c e o u s , l a r g e l y c o e v a l w i t h t h e P a s a y t e n G r a b e n s e q u e n c e . The s o u r c e f o r t h e m a r i n e c l a s t i c s e d i m e n t s , i n c l u d i n g g r a n i t i c c o b b l e s , a t H a r r i s o n 15. L a k e i s u n d e t e r m i n e d . I n c o n t r a s t t o t h e P a s a y t e n s t r a t a t h e s e c t i o n i s b r o k e n by a n g u l a r u n c o n f o r m i t i e s and c o n t a i n s a b u n d a n t a n d e s i t e and p y r o c l a s t i c s . The F i r e L a k e Group n o r t h o f H a r r i s o n L a k e i n c l u d e s Upper J u r a s s i c / L o w e r C r e t a c e o u s v o l c a n i c s and m a r i n e s e d i m e n t s , I n c l u d i n g g r a n i t i c d e b r i s ( R o d d i c k 1 9 6 5 ) . The G a m b i e r Group and i t s e q u i v a l e n t s . o u t c r o p i n t e r m i t t e n t l y f o r 150 km. a l o n g t h e s o u t h w e s t e r n s i d e o f t h e C o a s t M o u n t a i n s . They r e s t u n c o n f o r m a b l y on p l u t o n i c r o c k s ( R o d d i c k 1965; C a r o n 1974) b u t a r e i n t r u d e d and m e t a m o r p h o s e d by l a t e r p l u t o n s . A l b i a n ammonites h a v e been f o u n d i n t h e G ambier Group ( J e l e t z k y p e r s . comm. t o Mathews 1 9 7 2 ) : t h e s e a r e t h e y o u n g e s t known m a r i n e s e d i m e n t s i n t h e w e s t e r n C o a s t M o u n t a i n s . The s p a r s e J u r a s s i c and Lower C r e t a c e o u s s e d i m e n t s w i t h i n t h e C o a s t M o u n t a i n s , m o s t l y m a r i n e , s u g g e s t t h a t much of t h e C o a s t P l u t o n i c Complex l a y a t o r b e l o w s e a l e v e l d u r i n g t h a t t i m e . S u f f i c i e n t e r o s i o n o c c u r r e d t o u n r o o f p l u t o n s : b u t some o f t h e g r a n i t i c d e b r i s may have b e e n d e r i v e d f r o m I n s u l a r B e l t and I n t e r m o n t a n e . h i g h l a n d s . C e r t a i n l y no e x t e n s i v e p l u t o n i c / m e t a m o r p h i c t e r r a n e was e x p o s e d . The e a r l i e s t w e s t e r l y -d e r i v e d c o n g l o m e r a t e s i n t h e Methow and P a s a y t e n G r a b e n s c o n t a i n m a i n l y c h e r t and v o l c a n i c c o b b l e s ( T e n n y s o n 1 9 7 4 ) . T h e s e a r e A p t i a n - A l b i a n i n age and p r o v i d e a maximum age f o r t h e s o u t h e r n C o a s t M o u n t a i n s as a h i g h - s t a n d i n g r a n g e . The J u r a s s i c p l u t o n i c h i s t o r y o f t h e C o a s t M o u n t a i n s i s u n d e f i n e d . Two J u r a s s i c d a t e s have been o b t a i n e d so f a r i n t h e s o u t h e r n p a r t o f t h e r a n g e (Mathews 1968; M c K i l l o p 1 9 7 3 ) . G r a n i t i c c o b b l e s i n Upper J u r a s s i c - L o w e r C r e t a c e o u s c o n g l o m e r a t e s 1 6 . i n d i c a t e e a r l y p l u t o n i s m b u t n o t h i n g c a n be s a i d y e t a b o u t i t s i n t e n s i t y o r t i m i n g . Was t h e C o a s t P l u t o n i c Complex a l o c u s o f i n t e n s e magmatism t h e n as i n t h e C r e t a c e o u s , o r was i t s J u r a s s i c i n t r u s i v e h i s t o r y s i m i l a r t o t h a t of t h e I n s u l a r B e l t ? T h i s p r o b l e m may be r e s o l v e d by Rb/Sr and U/Pb d a t i n g . I n t h e E a . r l y C r e t a c e o u s t h e C o a s t P l u t o n i c Complex became t h e s i t e o f a n a r r o w zone o f i n t e n s e p l u t o n i s m . I t r e m a i n e d so u n t i l E o c e n e t i m e . P o t a s s i u m - a r g o n d a t e s i n t h e s o u t h e r n C o a s t m o u n t a i n s g e n e r a l l y d e c r e a s e i n age e a s t w a r d f r o m E a r l y C r e t a c -eous a l o n g t h e w e s t e r n m a r g i n t o E o c e n e i n t h e e a s t . The u l t i m a t e o r i g i n o f t h e p l u t o n i c r o c k s i s d e b a t a b l e . Two s o u r c e s h a v e been p r o p o s e d : g e n e r a t i o n w i t h i n a s u b d u c t e d l i t h o s p h e r i c p l a t e , and c r u s t a l a n a t e x i s , p o s s i b l y i n v o l v i n g r e m e l t i n g of B e n i o f f - z o n e - d e r i v e d r o c k s ( G r i f f i t h s p e r s . comm.). C r u s t a l d e r i v a t i o n i s f a v o r e d by G e o l o g i c a l S u r v e y w o r k e r s who have mapped t h e n o r t h e r n C o a s t M o u n t a i n s ( H u t c h i s o n 1970; R o d d i c k and H u t c h i s o n 1 9 7 2 ) . They h a v e o f f e r e d c o n v i n c i n g a r g u m e n t s . t h a t p l u t o n i c b o d i e s i n t h e P r i n c e R u p e r t a r e a c a n be t r a c e d t o o r i g i n s i n t h e C e n t r a l G n e i s s Complex. A g r a d a t i o n a l s e q u e n c e e x t e n d s f r o m m i g m a t i t i c , h i g h l y f o l i a t e d a u t o c h t h o n o u s b o d i e s , c o n c o r d a n t w i t h s u r r o u n d i n g m i g m a t i t e s , t o u n f o l i a t e d , d i s c o r d -a n t p l u t o n s i n t r u d i n g l o w - g r a d e r o c k s . Some, t e r m e d \" p a r a -a u t o c h t h o n o u s p l u t o n s \" , embody t h e e n t i r e s e q u e n c e . R o d d i c k and H u t c h i s o n e n v i s a g e p a r t s o f t h e m i g m a t i t i c t e r r a n e b e c o m i n g m o b i l i z e d and m o v i n g by p l a s t i c f l o w i n t o t h e o v e r l y i n g r o c k s . T h i s m o d e l may o r may n o t a p p l y t o t h e s o u t h e r n C o a s t M o u n t a i n s . 17. An i m p o r t a n t c o n s e q u e n c e o f p l a t e - t e c t o n i c t h e o r y i s t h a t calc,\".?. > a l k a l i n e magmas may be d e r i v e d by p a r t i a l m e l t i n g a l o n g B e n i o f f z o n e s . By a n a l o g y w i t h t h e Andean a r c , H a m i l t o n (1969) r e a s o n s t h a t l o n g a r c u a t e v o l c a n i c / p l u t o n i c / m e t a m o r p h i c t e r r a n e s s u c h as t h e S i e r r a Nevada a r e t h e d e e p l y e r o d e d r e m n a n t s o f v o l c a n i c a r c s . U s e f u l g u i d e l i n e s f o r r e c o g n i z i n g f o s s i l magmat-i c a r c s i n c l u d e : 1. e l o n g a t e a r c u a t e shape a n d / o r p a r a l l e l i s m t o an i n f e r r e d p l a t e b o u n d a r y ( s u c h as a c o n t i n e n t a l m a r g i n ) ; r e a s o n a b l e p r o x i m i t y t o t h e p l a t e b o u n d a r y , say 100 t o 400 km. 2. p r e d o m i n a n c e o f a n d e s i t e s and t h e i r i n t r u s i v e e q u i v a l e n t s , g r a n o d i o r i t e o r q u a r t z d i o r i t e . 3. h i g h T/P m e t a m o r p h i s m 4. a c o e v a l low T/P m e t a m o r p h i c zone t o w a r d s t h e p l a t e b o u n d a r y ( M i y a s h i r o 1 9 6 1 ; E r n s t 1 9 7 1 ) . 5. y o u n g i n g o f i n t r u s i o n s away f r o m t h e p l a t e b o u n d a r y . 6. i n c r e a s e i n K^O l i k e w i s e . 7. l o w S r 87/86 and Pb 206/204 r a t i o s p a r t i c u l a r l y i n v o l c a n i c s , as an i n d e x of s u b c r u s t a l o o r j g i n . The C r e t a c e o u s / E o c e n e C o a s t P l u t o n i c Complex c o n f o r m s t o 1 ) , 2 ) , 3 ) , 5 ) , and 6 ) ; t h e P a c i f i c Rim Complex as a p o s s i b l e F r a n c i s c a n c o r r e l a t i v e s u g g e s t s t h a t i t c o n f o r m s t o 4 ) , a l t h o u g h g l a u c o p h a n e and l a w s o n i t e h ave n o t as y e t b een f o u n d i n i t . S t r o n t i u m i s o t o p i c r a t i o s i n t h e C o a s t P l u t o n i c C o mplex t e n d t o be l o w . However, t h e y a r e n o t e a s i l y i n t e r p r e t e d ( s e e b e l o w ) , 18. The Coast P l u t o n i c Complex as a magmatic arc i s not incom-p a t i b l e with the d e r i v a t i o n of i t s p l u t o n i c bodies by c r u s t a l m e l t i n g . Greenwood (1975) favors a two-stage h i s t o r y f o r i n t r u s i v e rocks: primary o r i g i n at a B e n i o f f zone and r e m e l t i n g w i t h i n the c r u s t . This model i s favoured by P r e s n a l l and Bateman (1973) f o r the S i e r r a Nevada. Strontium i s o t o p e s are not u s e f u l f o r d i s t i n g u i s h i n g between s u b c r u s t a l and c r u s t a l o r i g i n f o r i n t r u s i o n s i n the Coast Mountains. Although as yet inadequately sampled, they tend to be rudidium poor; t h e i r Sr 87/86 r a t i o s i n c r e a s e very slowly through time (Culbert 1972; and t h i s s t u d y ) . Magmas d e r i v e d from them would have essen-t i a l l y the same S r - i s o t o p i c r a t i o s as B e n i o f f zone melts. Pre-Cretaceous metamorphic events have been deduced by v a r i o u s authors (Tipper 1969; Roddick and Hutchison 1972; Reamsbottom 1973). L i k e pre-Cretaceous plutonism, assessments of degree, extent or timing of these events cannot be made. Extensive r e g i o n a l meta-morphism accompanied the Cretaceous-Eocene plutonism. The p a t t e r n of Cretaceous metamorphism i s complex and not w e l l known due to a lack of d e t a i l e d pressure-temperature s t u d i e s . Although presumably accompanying plutonism i t i s i n many cases u n r e l a t e d to s p e c i f i c plutons ( H o l l i s t er 1969; Reamsbottom 1973; Woodsworth 1974). Metamorphic grade seems to i n c r e a s e towards the e a s t e r n Coast Mountains, p o s s i b l y refleeting :a deeper e r o s i o n l e v e l . 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 i s observed i n s e v e r a l places i n the eastern Coast Mountains ( H o l l i s t e r 1969; Lowes 1972; Pigage 1973). This r e a c t i o n r e q u i r e s a minimum of 3.8 kb p r e s s -19. u r e ( H o l d a w a y 1 9 7 1 ) . W oodsworth ( p e r s . comm.) r e p o r t s t h a t t h e r e may be a p a t t e r n o f m e t a m o r p h i c h i g h s and l o w s i n t h e s o u t h e r n p a r t o f t h e r a n g e . D e s p i t e t h e s k e t c h i n e s s and o b v i o u s i n t r i c a c y o f t h e C r e t a c e o u s s t o r y t h r e e f a i r l y s a f e and s i g n i f i c a n t g e n e r a l i z a t ^ -i o n s c a n be made: 1. The g r o s s c h a r a c t e r i s t i c s o f t h e C o a s t P l u t o n i c Complex -i t s p r e p o n d e r a n c e o f p l u t o n i c r o c k , i t s p r e v a l e n t m o d e r a t e t o h i g h g r a d e o f m e t a m o r p h i s m , i t s n a r r o w n e s s and a b r u p t b o u n d a r i e s , and t h e g r e a t d e p t h o f e r o s i o n a t t a i n e d i n p l a c e s w i t h i n i t - were a c q u i r e d o r ( i n t h e c a s e o f e r o s i o n ) i n i t i a t e d d u r i n g t h e C r e t a c e o u s . 2. The p r e s e n t b o u n d a r i e s o f t h e C o a s t P l u t o n i c Complex a r e e i t h e r i n t r u s i v e c o n t a c t s o r f a u l t s ( B a e r 1 973; R o d d i c k and H u t c h i s o n 1 9 7 4 ) . The w e s t e r n c o n t a c t i s a l i n e a l o n g w h i c h I n s u l a r B e l t s t r a t a a r e t r u n c a t e d by i n t r u s i o n s m o s t l y d a t e d as E a r l y C r e t a c e o u s . The w e s t e r n edge o f t h e p r o v i n c e t h u s was e s t a b l i s h e d i n Lower C r e t a c e o u s t i m e . 3. The c r e a t i o n o f t h e .Coast P l u t o n i c Complex was l i n k e d t o subdue t i o n . The amount o f u p l i f t i s v a r i a b l e : some s e p t a a r e - i n l o w e r g r e e n s c h i s t f a c i e s ; some have been m e t a m o r p h o s e d a t p r e s -s u r e s above t h e a l u m i n o s i l i c a t e t r i p l e p o i n t . G e n e r a l l y t h e e r o s i o n l e v e l d e pens e a s t w a r d , b u t t h i s i s c o m p l i c a t e d by w a r p i n g , f a u l t i n g and s m a l l e r - s c a l e m e t a m o r p h i c c u l m i n a t i o n s . E v i d e n c e f o r t i m i n g o f u p l i f t i s s p a r s e . W e s t e r l y - d e r i v e d A p t i a n - A l b i a n s e d i m e n t s i n t h e P a s a y t e n G r a b e n i n d i c a t e t h a t 20. the e a s t e r n C o a s t M o u n t a i n s began to r i s e i n t h e M i d d l e C r e t a c e o u s . Much of t h e u p l i f t was a c c o m p l i s h e d a l o n g t h e F r a s e r R i v e r F a u l t System. Movement on the Hozameen F a u l t , w h i c h j u x t a p o s e s M i d d l e T r i a s s i c Hozameen Group and J u r a - C r e t -aceous s e d i m e n t s , c e a s e d b e f o r e 84 m.y. ago, t h e d a t e of a s m a l l p l u t o n t h a t c u t s a c r o s s i t and i s not d i s p l a c e d ( C o a t e s 1 9 7 4 ) . The Y a l e F a u l t has b r o u g h t the C u s t e r G n e i s s i n c o n t a c t w i t h Hozameen r o c k s . T i l t e d Eocene c o n g l o m e r a t e a l o n g i t a t t e s t s to T e r t i a r y a c t i v i t y . The C h i l l i w a c k B a t h -o l i t h , 26 m.y. o l d , ( F r a s e r R i v e r map-sheet) c u t s a c r o s s i t s s o u t h e r n e x t e n s i o n , the S t r a i g h t C r e e k F a u l t . I t i s s u g g e s t e d t h a t t h e e a s t e r n C o a s t M o u n t a i n s began to r i s e i n M i d d l e C r e t a c e o u s t i m e and were the w e s t e r n s o u r c e t h a t ( C o a t e s ( 1 9 7 4 ) i n f e r s f o r t h e P a s a y t e n / J a c k a s s M o u n t a i n F o r m a t i o n s . The w e s t e r n p a r t of the r a n g e c o u l d n o t have been a h i g h - s t a n d i n g f e a t u r e u n t i l a t l e a s t t h e L a t e C r e t a c e o u s , as t h e r e a r e A l b i a n m a r i n e s e d i m e n t s i n t h e Gambier Group. F u t h e r -more, had the w e s t e r n C o a s t M o u n t a i n s e x i s t e d i n S a n t o n i a n t i m e , t h e y s u r e l y would have c o n t r i b u t e d s e d i m e n t to t h e p r o t o - G e o r g i a D e p r e s s i o n t h e n f o r m i n g i m m e d i a t e l y to the w e s t . T h e r e i s no e v i d e n c e t h a t t h e y d i d . The P a l e o c e n e (?) Chuckanut F o r m a t i o n has a d o m i n a n t l y e a s t e r n s o u r c e : the C a s c a d e and C o a s t Mount-a i n s must have been e l e v a t e d by t h a t t i m e . The L i o n s Gate Member of Campanian age (Rouse e t a l 1 9 7 5 ) , the o l d e s t Nanaimo c o r r e l a t i v e on t h e e a s t s i d e of G e o r g i a S t r a i t , r e s t s u n c o n f o r m a b l y on p l u t o n i c r o c k s i n C a p i l a n o Canyon. I t 21. contains l e s s than 10% g r a n i t i c c l a s t s ( l e s s even than the Gambier Group) and v i r t u a l l y no high-grade metamorphic or f o l i a t e d p l u t o n i c c l a s t s , r e f l e c t i n g a mostly v o l c a n i c source t e r r a n e without l a r g e amounts of exposed p l u t o n i c / c r y s t a l l i n e rocks as are seen i n the southern Coast Mountains today. T h i s shallow e r o s i o n l e v e l as l a t e as Upper Cretaceous i s another i n d i c a t i o n that strong r e g i o n a l u p l i f t had not occurred before that t ime. In summary, the province boundary that u n d e r l i e s Georgia Depression i s a (roughly) EaTly Cretaceous i n t r u s i v e c o n t a c t . The Depression i t s e l f , however, began to form i n the Santonian: i t w e l l postdates the establishment of t h i s boundary. What evidence there i s suggests that i t accompanied another s i g n i f -i c a n t event i n Coast P l u t o n i c Complex h i s t o r y , the Upper C r e t -aceous-Eocene u p l i f t of the range. i i i Georgia Depression The Upper Cretaceous s t r u c t u r a l d e p ression was not a graben sensu s t r i c t o , as both downfaulting and downwarping were i n v o l v e d . The prevalence of f a u l t s on g e o l o g i c maps i s m i s l e a d i n g : there are s e v e r a l generations of f a u l t s i n the Depression, some of which have nothing to do with i t s o r i g i n . The massive v o l c a n i c u n i t s of Vancouver I s l a n d have tended to undergo b r i t t l e f a i l u r e under compression, y i e l d i n g a map p a t t e r n of f a u l t blocks and open f o l d s . Major f a u l t s on the east s i d e of Georgia S t r a i t have been proposed (Hopkins 1966\"; Berry et a l . 1971) but not confirmed. I t i s hoped that f u t u r e s t u d i e s w i l l separate the d i f f e r e n t s t r e s s systems. 22. The p r e s e n t G e o r g i a D e p r e s s i o n i s a m o d i f i e d v e r s i o n of the o r i g i n a l b a s i n . I t s C e n o z o i c h i s t o r y i s d i f f i c u l t to r e -( c o n s t r u c t b e c a u s e , e x c e p t f o r a few o u t c r o p s n e a r V a n c o u v e r , no T e r t i a r y r o c k s a r e exposed above sea l e v e l . The s e d i m e n t o l o g i -c a l r e c o r d of the u p l i f t of the C o a s t M o u n t a i n s i s l i k e w i s e s c a n t y ( E i s a b a c h e r , p e r s . comm. 19 7 5 ) . Nanaimo Group d e p o s i t i o n a p p a r e n t l y c e a s e d i n the M a e s t r i c h t i a n . I t may have c o n t i n u e d i n t o t h e P a l e o c e n e ( M u l l e r and J e l e t z k y . 1970); i t may have e v o l -ved i n t h e s o u t h i n t o c o n t i n e n t a l - d e l t a i c s e d i m e n t a t i o n of t h e Chuckanut F o r m a t i o n (P.Ward, p e r s . comm. 1974). B o t h t h e Chuckanut F o r m a t i o n and the Nanaimo Group were i n v o l v e d i n p r e -M i d d l e Eocene d e f o r m a t i o n . F o l d s and f a u l t s i n t h e C h u c k a n u t F o r m a t i o n a r e o v e r l a i n u n c o n f o r m a b l y by t h e M i d d l e Eocene Hunt-i n g t o n F o r m a t i o n ( M i s c h 1 9 6 6 ) . On S a l t s p r i n g I s l a n d t h e Nanaimo Group i s f o l d e d a b o u t n o r t h w e s t e r l y a x e s . The major f o l d s v e r g e w e s t e r l y . E a s t e r n l i m b s of the - a n t i c l i n e s a r e g e n e r a l l y s t e e p ; some a r e o v e r t u r n e d . F a u l t i n g was more i m p o r t a n t t h a n f o l d i n g on V a n c o u v e r I s l a n d where a t h i n c o v e r of Nanaimo s e d i m e n t s o v e r l i e s v o l c a n i c / p l u t o n i c basement (Ross and Barnes,Ms. u n p u b . ) . B l o c k s bounded by s t e e p f a u l t s d i p g e n t l y e a s t towards G e o r g i a S t r a i t ( M u l l e r 1 9 7 4 ) . I t was p r o b a b l y d u r i n g t h e E a r l y T e r t i a r y e p i s o d e t h a t the Nanaimo Group r o c k s i n Mt. W a s h i n g t o n and t h e F o r b i d d e n P l a t e a u were r a i s e d to t h e i r p r e s e n t e l e v a t i o n a l m o s t 2000 m e t e r s above s e a l e v e l . A t l e a s t p a r t of G e o r g i a D e p r e s s i o n r e m a i n e d a s e d i m e n t a r y b a s i n t h r o u g h o u t T e r t i a r y t i m e . The T e r t i a r y r e c o r d i n Whatcom 23. Basin near Vancouver i s f a i r l y complete. Dating i s mainly based on spores and p o l l e n (Hopkins 1966; Rouse et a l 1975). D e p o s i t i o n i n the::Whatcom . Basin.-was not interrupted', by Ittie.\" \u00E2\u0080\u00A2 Eocene deformation. The Lions Gate Member passes without s i g n i f i c a n t break i n t o Eocene d e l t a i c sediments of the K i t -s i l a n o Formation (Hopkins 1966; Blunden 1971). The K i t s i l a n o Formation i s succeeded by an unnamed u n i t of Miocene age seen only i n d r i l l h o l e s (Hopkins 1966). T o t a l t h i c k n e s s of the T e r t i a r y s e c t i o n exceeds 3000 meters. The T e r t i a r y d e p o s i t i o n a l environment was t e r r e s t r i a l d e l t a i c . T i f f i n (1969),using s e i s m i c r e f l e c t i o n p r o f i l e s , traced T e r t i a r y u n i t s part of the way across Georgia S t r a i t . Major T e r t i a r y f a u l t s under the s t r a i t are p o s s i b l e . T i f f i n suggested that the T e r t i a r y sequence i s truncated by a major f a u l t at the base of the eastern slope of Vancouver I s l a n d . The southern part of Georgia Depression was a f f e c t e d by the same Miocene event that produced west-northwest f o l d s i n the Columbian Embayment. The San Juan Islands are the backbone of a Miocene upwarp (Snavely and Wagner 1963),that cuts o b l i q u e l y across the southern end of Georgia S t r a i t . F o l d o r i e n t a t i o n s i n the Nanaimo Group change from northwest to west-northwest between the Gulf Islands and the San Juans; t h i s may p a r t l y be due to the Miocene t e c t o n i c event. Late T e r t i a r y movements have accentuated Georgia Depression; i t has remained low while the f l a n k i n g ranges rose. The lack of marine sediments except i n the l a t e s t P l e i s t o c e n e , however, i n d i c a t e s that i t probably stood above sea l e v e l , t h r o u g h o u t the 24. T e r t i a r y . L a t e C e n o z o i c u p l i f t o f t h e C o a s t M o u n t a i n s amounted t o a b o u t two t h o u s a n d m e t e r s . ( R o d d i c k 1 9 6 6 ) . R e c o g n i z a b l e M i o c e n e and P l i o c e n e e r o s i o n s u r f a c e s p e n e t r a t e deep i n t o t h e r a n g e . M i o c e n e v o l c a n i c s l i e on d e e p l y b e v e l e d s u r f a c e s ( B a e r 1973 and t h e F r a s e r R i v e r m a p - s h e e t ) . Downward movement of t h e D e p r e s s i o n was p r o b a b l y somewhat l e s s t h a n t h e u p l i f t ( B l u n d e n 1 9 7 1 ) . The p r e s e n t s t r a i t owes much o f i t s d e p t h and n a r r o w n e s s t o g l a c i a l e r o s i o n , f i r s t b e c a u s e g l a c i e r s were c h a n n e l l e d b e t w e e n t h e a d j a c e n t r a n g e s and s e c o n d b e c a u s e o f d i f f e r e n t i a l e r o s i o n o f s o f t Nanaimo Group s e d i m e n t s (Mathews 1 9 6 8 ) . The s o u t h e a -s t e r n p a r t o f t h e D e p r e s s i o n i s c u r r e n t l y s u b s i d i n g . The p a t t e r n seems u n r e l a t e d to t h e g e o m e t r y o f t h e F r a s e r D e l t a (Mathews e t . a l . 1970) and t h u s may be p a r t l y t e c t o n i c , i v . Summary and E v a l u a t i o n of R e g i o n a l S y n t h e s i s F i g u r e 4 s u m m a r i z e s t h e t e c t o n i c and p a l e o g e o g r a p h i c e v o l -u t i o n o f t h e I n s u l a r B e l t and t h e C o a s t P l u t o n i c Complex up t o t h e o r i g i n o f G e o r g i a D e p r e s s i o n . T h i s h i s t o r i c a l v i e w b e a r s on t h e h y p o t h e s e s l i s t e d on Page 1. The t i m i n g o f o r i g i n o f t h e D e p r e s s i o n i s c e r t a i n . The S a n t o n i a n - M a e s t r i c h t i a n Nanaimo Group s e d i m e n t s w e re d e p o s i t e d i n a b a s i n whose c o n f i gur a t its tin m i m i c s t h e p r e s e n t one. T h e r e f o r e t h e D e p r e s s i o n was c r e a t e d i n t h e U pper C r e t a c e o u s : C e n o z o i c r i f t i n g , f a u l t i n g and e r o s i o n c a n o n l y have m o d i f i e d a p rfi~--ex i s t i n g t r o u g h . The s t r u c t u r a l n a t u r e o f t h e D e p r e s s i o n i s p o o r l y known. I t i s r e f e r r e d t o as a comb-i n a t i o n d o w n w a r p - d o w n f a u l t i n r e g i o n a l s t u d i e s , b u t d e f i n i t i v e e v i d e n c e as t o t h e i m p o r t a n c e o f f a u l t c o n t r o l has y e t t o be 26. p r e s e n t e d . H o p e f u l l y some of t h e s t u d i e s now i n p r o g r e s s w i l l f i l l t h i s gap . The u l t i m a t e c a u s e of t h e s u b s i d e n c e of G e o r g i a D e p r e s s i o n has been l i n k e d to a s u t u r e , a r i f t zone, or a complement to the u p l i f t of t h e C o a s t M o u n t a i n s . I t i s w o r t h w h i l e b e f o r e e v a l u a t i n g t h e s e h y p o t h e s e s to enumerate the e v i d e n c e t h a t p e r t a i n s to e a c h . C o u p l e d u p l i f t s and s u b s i d e n c e s o c c u r of c o u r s e s i m u l t a n -e o u s l y , making f i e l d e v i d e n c e as to t i m i n g c l e a r l y v a l u a b l e . On t h e o t h e r hand, as no p a r t i c u l a r s t r u c t u r a l s t y l e i s r e q u i r e d , f i e l d e v i d e n c e p e r t a i n i n g to s t r u c t u r e i s not d i a g n o s t i c . G r e a t f a u l t s s u c h as the T e t o n F a u l t may be i n v o l v e d ; or t h e movement may c o n s i s t of g e n t l e t i l t i n g . The c u r r e n t method of i d e n t i f y i n g s u t u r e s and r i f t zones i s by c o m p a r i s o n w i t h a c c e p t e d e x a m p l e s . Examples of s u t u r e s w h i c h have r e c e i v e d g e n e r a l a c c e p t a n c e a r e t h o s e i n the K l a m a t h M o u n t a i n s ( I r w i n 1973; Cashman 1974 ) ; n o r t h e r n New G u i n e a (Dewey and B i r d 1970); and N ewfoundland ( W i l l i a m s e t . a l . 1 9 7 1). Dewey and B i r d (1970) and Le P i c h o n et a l (1973) t r e a t s u t u r i n g and s u t u r e zones i n g e n e r a l . C h a r a c t e r i s t i c s of s u t u r e zones a r e : 1. j u x t a p o s i t i o n of u n r e l a t e d g e o l o g i c p r o v i n c e s . 2. a l i n e of o p h i o l i t e s or a l p i n e u l t r a m a f i t e s , \"dismembered o p h i o l i t e s \" m a r k i n g th e s u t u r e . 3. b l u e s c h i s t a nd/or melange t e r r a n e between the two p r o v i n c e s , i n d i c a t i n g a f o s s i l s u b d u c t i o n zone. 27. 4. i n t e n s e deformation - i s o c l i n a l f o l d i n g , t h r u s t i n g , obduction. Since there i s no r e c o g n i z a b l e Upper Cretaceous oceanic c r u s t i n Georgia Depression, any r i f t i n g there must have i n v o l v e d a small amount of e x t e n s i o n . There are s e v e r a l w e l l -known modern c o n t i n e n t a l r i f t s of t h i s s o r t , the B a i k a l and Rhine Grabens (Beloussov 1969; Milanovsky 1972), and the East A f r i c a n r i f t system ( G i r d l e r et a l 1969; Baker et a l 1972). Important c h a r a c t e r i s t i c s of c o n t i n e n t a l r i f t zones i n c l u d e : 1. They are narrow l i n e a r complex grabens. F a u l t s e i t h e r dip s t e e p l y inwards or are v e r t i c a l . Dominant f a u l t s p a r a l l e l the s i d e s of the graben; cross f a u l t s are a l s o present. 2. C h a r a c t e r i s t i c t o t a l v e r t i c a l displacement i s 2 to 5 km. 3. High heat flow and vulcanism ( t h o l e i i t i c and a l k a l i c ) accompany r i f t i n g . High temperature metamorphic assemb-lages may provide evidence f o r high heat flow i n deeply eroded f o s s i l r i f t zones. 4. The graben w i l l probably f i l l with sediment, producing a l a r g e negative g r a v i t y anomaly. F a u l t c o n t r o l should be evidenced by coarse, unsorted border f a c i e s . 5. In east A f r i c a a r e g i o n a l negative BoBguer anomaly has been a s c r i b e d to low-density m a t e r i a l i n the upper mantle ( G i r d l e r et a l 1969). The evidence f o r a suture zone between the I n s u l a r B e l t and the Coast P l u t o n i c Complex i s that Vancouver I s l a n d lay i n the southern hemisphere i n the Karnian but was i n place by the Middle J u r a s s i c (166 m.y.). Paleomagnetic data (Symons 1971b; 28. I r v i n g and Yole 1972) r e q u i r e s the suture to l i e between Vancouver I s l a n d and the southern Intermontane B e l t : i t need not c o i n c i d e with the I n s u l a r B e l t / C o a s t P l u t o n i c Complex boundary. Monger et a l . ' s (1972) suggestion that the Upper T r i a s s i c - Lower J u r a s s i c suture l i e s along the Yalakom F a u l t System i s probably the c o r r e c t one, as the T r i a s s i c rocks there are h i g h l y deformed and f a u l t e d and p i e r c e d by Upper T r i a s s i c -Lower J u r a s s i c u l t r a m a f i c bodies. The i m p r o b a b i l i t y of a suture between the I n s u l a r B e l t and the Coast P l u t o n i c Complex i s f u r t h e r demonstrated by the f i e l d study d e s c r i b e d i n the next s e c t i o n . A r i f t zone, i f i t engendered the Depression, must have been a c t i v e i n the Upper Cretaceous. Arguments based on s t r u c t u r a l s t y l e are f u t i l e at t h i s p o i n t . There are no v o l c a n i c s i n the Nanaimo Group. Heat flow at present i n the Georgia S t r a i t area i s low (Hyndman 1976). Past heat flow can only be guessed at from metamorphic assemblages. Metamorphic phases i n the Nanaimo Group i n c l u d e h e u l a n d i t e , laumontite and u n i d e n t i f i e d p h y l l o s i l i c a t e s (Stewart and Page 1974). The absence of high-temperature z e o l i t e s such as w a i r a k i t e might be taken as evidence against high heat flow (and consequently r i f t i n g ) i n the past. At the time of i t s formation Georgia Depression lay between an e v o l v i n g magmatic ar c , the Coast P l u t o n i c Complex, and i t s trench. Because i t lay w i t h i n an a r c - t r e n c h gap, the Cretaceous depression was by d e f i n i t i o n a f o r e a r c b a s i n (Dickinson 1974). It i s important that t h i s term be used without g e n e t i c s i g n i f -i cance. The f o r e a r c basins o f f the coast of C h i l e (Ross and Shor 1965; Coulbourn and Moberly 1975) l i e immediately above t h e t r e n c h - s l o p e b r e a k . They a r e bounded oceanward by a h i g h l y d e formed and t h r u s t e d w e l t o f s e d i m e n t s . G e o r g i a D e p r e s s i o n , by c o n t r a s t , l i e s a hundred k i l o m e t e r s from t h e P a c i f i c / N o r t h A m e r i c a n p l a t e b o u n d a r y and i s basement-c o n t r o l l e d . I t s l o c a t i o n i m m e d i a t e l y west o f t h e w e s t e r n l i m i t o f c r e t a c e o u s p l u t o n i s m and i t s c o i n c i d e n c e w i t h t h e major u p l i f t of t h e C o a s t P l u t o n i c Complex s u g g e s t t h a t i t s s u b s i d e n c e was l i n k e d to the r i s e o f t h e r a n g e , r a t h e r t h a n some s u b d u c t i o n - r e l a t e d p r o c e s s . 30. SECTION I I : FIELD STUDY I n t r o d u c t i o n - G e n e r a l G e o l o g y of the Map A r e a The p o s i t i o n of the C o a s t a l T r o u g h i n B r i t i s h C o l u m b i a o v e r the C o a s t P l u t o n i c C o m p l e x / I n s u l a r B e l t b o u n d a r y ought to have g e n e t i c s i g n i f i c a n c e , w h a t e v e r t h e c a u s e of t h e d e p r e -s s i o n . I u n d e r t o o k a f i e l d s t u d y of a s e c t i o n of t h e b o u n d a r y i n o r d e r to i n v e s t i g a t e i t s n a t u r e and p o s s i b l y i t s r o l e i n e n g e n d e r i n g a s t r u c t u r a l t r o u g h . The map-area c h o s e n f o r t h i s p u r p o s e i n c l u d e s H a r d w i c k e , West T h u r l o w and n e i g h b o r i n g s m a l l e r i s l a n d s , and the c o a s t of V a n c o u v e r I s l a n d n e a r K e l s e y Bay ( F i g u r e 5 ) . The i s l a n d s were p r e v i o u s l y mapped a t 4 m i l e s to the i n c h d u r i n g t h e t e n - y e a r r e c o n n a i s s a n c e of the C o a s t M o u n t a i n s c o n d u c t e d by the G e o l o g i c a l S u r v e y of Canada ( R o d d i c k et a l . 1971 and i n p r e p a r a t i o n ) . K u n i y o s h i (1972) and M u l l e r (1972) mapped the V a n c o u v e r I s l a n d s h o r e a t m i l e and 4 m i l e s to the i n c h r e s p e c t i v e l y . The p r o v i n c e b o u n d a r y has been mapped e l s e w h e r e , a l t h o u g h not w i t h t h e o b j e c t of s t u d y i n g the r e l a t i o n s h i p of t h e two p r o v i n c e s . The work of C a r l i s l e and S u z u k i (1965) on Quadra I s l a n d , A s i h e n e (1970) on Texada I s l a n d , and K u n i y o s h i (1972) on the n o r t h e a s t s h o u l d e r o f V a n c o u v e r I s l a n d , w i l l be d i s c u s s e d i n t h e summary c h a p t e r f o r c o m p a r i s o n . The b o u n d a r y between the I n s u l a r B e l t and t h e C o a s t P l u t o n i c Complex exposed on H a r d w i c k e and West T h u r l o w I s l a n d s i s an i n t r u s i v e c o n t a c t ( G e o l o g i c Map, P l a t e 2 ) . To t h e n o r t h . Oven Hay, QimcLra. JsUncL \u00C2\u00B0 ( Carlisle avid SwLuKi 196(0) H\"wada. Jsla-nd/ (tAsihimt lljo ~) jplutcmvc rocks Index wiGLp : (Field area on JrfardwfdU and \"West Tkurlow Js lands 0 and other detailed majytinfl oJ the Coast 'Plutonic Complex/'JnsuUr 'delt 'proyvnet boundary 32. and east of i t are p l u t o n i c rocks, dominated by a Late J u r a s s i c quartz d i o r i t e . S t r a t i f i e d u n i t s of the Mesozoic Vancouver Group l i e to the south and west. The southwestern ends of Hardwicke and West Thurlow Islands and the northern coast of Vancouver I s l a n d are u n d e r l a i n by b a s a l t s of the Karmutsen Formation. The Quatsino Formation outcrops on the southern coast of West Thurlow I s l a n d . I t passes upwards i n t o the Parson Bay Formation, which a l s o occurs as septa w i t h i n p l u t o n i c rocks near Eden P o i n t . The Harbledown Formation outcrops east of Carmichael Point on Hardwicke I s l a n d . I t i s succeeded i n l a n d by the Bonanza V o l c a n i c s . Two major west-no r t hwe s t - t rend i n g f a u l t s , the J o h n s t o n e S t r a i t and the Telegraph H i l l f a u l t s , have broken the Vancouver Group i n t o homoclinal b l o c k s . P r i o r to i n t r u s i o n the Vancouver Group underwent p r e h n i t e - p u m p e l l y i t e b u r i a l metamorphism. Contact-metamorphic g r e e n s c h i s t assemblages are developed i n Vancouver Group rocks l e s s than 4 k i l o m e t e r s from the quartz d i o r i t e , and hornblende h o r n f e l s assemblages l e s s than 500 meters from i t . S y nplutonic d u c t i l e deformation a f f e c t e d the Vancouver Group w i t h i n the inner aureole. N o r t h e a s t - t r e n d i n g d i k e s , p e r v a s i v e l y a l t e r e d to c h l o r i t e -e p i d o t e - a l b i t e , cut both the quartz d i o r i t e and the o l d e r rocks. They mark the c l o s e of igneous a c t i v i t y and are the l a s t recorded event i n the map area except f o r P l e i s t o c e n e g l a c i a t i o n . 33. CHAPTER I I : STRATIGRAPHY OF THE VANCOUVER GROUP Every formation i n the e a r l y Mesozoic Vancouver Group i s represented i n the map-area (Figure 6, column 3; a l s o see the Geologic Map, P l a t e 2), although no complete s e c t i o n i s seen. Most u n i t s are bounded by f a u l t s , i n t r u s i v e c o n t a c t s , or water. Probable f a u l t r e p e t i t i o n and, near the i n t r u s i o n s , t e c t o n i c t h i n n i n g , render t h i c k n e s s estimates approximate only. A reasonable sequence may n e v e r t h e l e s s be r e c o n s t r u c t e d by t a k i n g account of l i t h o l o g y and s t r u c t u r e . i . Karmutsen Formation The Karmutsen Formation i s r e a d i l y d i v i d e d i n t o three parts based on l i t h o l o g y . Kuniyoshi (1972) assigned f o r m a t i o n a l names to them. However, to avoid ambiguity, Kuniyoshi's names w i l l not be used here. The lower Karmutsen Formation (Kuniyoshi's Kelsey Bay Formation) i s w e l l exposed as shore c l i f f s near Kelsey Bay. I t i s a monotonous p i l e of p i l l o w b a s a l t r e l i e v e d by minor b r e c c i a s and tongues and flows of massive b a s a l t . The i n t e r i o r s of the p i l l o w s are h y a l o p i l i t i c with small phenocrysts and amygdules ( l e s s than 1 mm. a c r o s s ) . T h e i r o r i g i n a l g l a s s y selvages are a l t e r e d to f i n e - g r a i n e d e p i d o t e - p u m p e l l y i t e - c h l o r i t e mixtures. P i l l o w i n t e r s t i c e s are f i l l e d with quartz, c a l c i t e , epidote and c l i n o z o i s i t e . Only approximate bedding a t t i t u d e s can be obtained from the p i l l o w s . These a t t i t u d e s are somewhat e r r a t i c , perhaps r e f l e c t i n g i n i t i a l sea-bottom topography. 35 . The m i d d l e Karmutsen F o r m a t i o n ( K u n i y o s h i ' s Hkusam F o r m a t i o n ) i s c h a r a c t e r i z e d by a p r e d o m i n a n c e of p i l l o w b r e c c i a s w i t h sub-s i d i a r y f l o w s , aquagene t u f f s and t r u e b r e c c i a s . I t i s exposed i n a h o m o c l i n e a l o n g t h e n o r t h e a s t s h o u l d e r of V a n c o u v e r I s l a n d , e a s t o f Camp P o i n t . The b a s a l c o n t a c t i s a f a u l t ( s e e K u n i y o s h i 1972; M u l l e r 1 9 72). The c o n t a c t w i t h t h e upper Karmutsen F o r m a t i o n i s a g r a d a t i o n a l zone i n w h i c h a m y g d a l o i d a l f l o w s r e p l a c e b r e c c i a upwards. S e v e r a l p a r t i a l s e c t i o n s of the upper Karmutsen F o r m a t i o n ( K u n i y o s h i ' s M e n z i e s F o r m a t i o n ) a r e p r e s e n t i n the n o r t h w e s t e r l y d i p p i n g h o m o c l i n e between th e J o h n s t o n e S t r a i t and T e l e g r a p h H i l l F a u l t s ( s e e C h a p t e r IV). A l l of t h e s e c t i o n s a r e p r e d o m i n a n -t l y composed of a m y g d a l o i d a l f l o w b a s a l t w i t h v a r y i n g p r e c e n t -ages of b r e c c i a , p i l l o w b a s a l t , and i n t e r l a v a s e d i m e n t s . On t h e n o r t h e a s t s h o u l d e r o f V a n c o u v e r i s l a n d a p p r o x i m a t e l y 2000 m e t e r s of upper Karmutsen F o r m a t i o n o v e r l i e the m i d d l e K a r m u t s e n . P i l l o w b a s a l t , p i l l o w b r e c c i a and b r e c c i a form about 10% o f t h e s e c t i o n , w h i l e s e d i m e n t s a r e l a c k i n g . T h i s a s s e m b l a g e i s t y p i c a l of the l o w e r p a r t of the u p p e r K a r m u t s e n . On Helmcken I s l a n d , by c o n t r a s t , o n l y one b r e c c i a - p i l l o w b r e c c i a u n i t i s p r e s e n t , and i s a s s o c i a t e d w i t h an i n t e r l a v a s e d i m e n t a r y c y c l e ( F i g u r e 7 ) . The p r e s e n c e of s e d i m e n t s i s t y p i c a l of t h e top 1000 m e t e r s of t h e Karmut-sen F o r m a t i o n ( K u n i y o s h i 1 9 72). On s o u t h w e s t e r n H a r d w i c k e I s l a n d t h e upper Karmutsen F o r m a t i o n c o n s i s t s e n t i r e l y o f f l o w b a s a l t . S t r a t i g r a p h i c a l l y above i t on Y o r k e I s l a n d a r e b r e c c i a s , p i l l o w b a s a l t s and i n t e r l a v a s e d i m e n t s . A l l of t h e s e C7Y* \u00E2\u0080\u00A2 7 Stratx^mykj icLot( surriiuntlid by spUjftclastr: I'ht Clear splajfotlasej m Oit centre art a.fter lp*xrtz. Cmjiare efiiite habits witt O^yvrt Jia.. J \u00E2\u0080\u00A2 \u00C2\u00A3 \u00E2\u0080\u00A2 3 94. e p i d o t e and m i n o r c a l c i t e and p y r i t e . C h l o r i t e , an i m p o r t a n t a m y g d u l a r phase e l s e w h e r e , i s a b s e n t . E p i d o t e - r i c h zones g r a d e i n t o n o r m a l a l b i t e - e p i d o t e - a c t i n o l i t e - c h l o r i t e g r e e n s c h i s t . The c o n c e n t r a t i o n o f e p i d o t e i n f a u l t s , f r a c t u r e s and f l o w t o p s s u g g e s t s a m e t a s o m a t i c p r o c e s s . V e r t i c a l f a u l t s and f r a c t u r e s form l i k e l y passageways f o r m i g r a t i n g f l u i d s d u r i n g d e h y d r a t i o n . The h i g h l y a m y g d a l o i d a l f l o w t o p s must have been r e l a t i v e l y p e r m e a b l e , a c t i n g as c a t c h m e n t zones s e a l e d above by d e n s e , n e a r l y u n v e s i c u l a r f l o w b o t t o m s . J o l l y and S m i t h (1972) have s t u d i e d a s i m i l a r p a t t e r n o f e p i d o t e s e g r a t i o n i n t h e l o w e r P o r t a g e Lake b a s a l t s of n o r t h e r n M i c h i g a n . As i n the p r e s e n t a r e a , t h e y f o u n d a m y g d a l o i d a l f l o w -t o p s and f r a c t u r e s to be so e n r i c h e d i n e p i d o t e as to form \" e l p i d -o t e metadomains\". J o l l y and Smith model f l o w t o p s and f r a c t u r e s as p e r m e a b l e z o n e s . D u r i n g d e h y d r a t i o n w a t e r would e s c a p e from them more r e a d i l y t h a n f r o m m a s s i v e b a s a l t . I n t h e e p i d o t e meta-domains the c o n d i t i o n P T T n < P, , would p r e v a i l , t e n d i n g to H^O l o a d s t a b l i z e t h e r e l a t i v e l y a n h y d r o u s m i n e r a l e p i d o t e . J o l l y and S m i t h ' s a n a l y s e s f o r w a t e r c o n t e n t s t e n d to s u b s t a n t i a t e t h i s m odel. Un-a l t e r e d P o r t a g e Lake b a s a l t s c o n t a i n an a v e r a g e of 3.8 wt.% w a t e r ; a l b i t e b a s a l t 2.7% and e p i d o t e metadomains 1.1%. The p o s s i b i l i t y t h a t f l u i d p r e s s u r e was l e s s t h a n l o a d p r e s s u r e i n p a r t s of t h e K armutsen b a s a l t s d u r i n g g r e e n s c h i s t metamorphism a f f e c t s t h e a p p l i c a t i o n of e x p e r i m e n t a l d a t a to r e a c t i o n s o c c u r r i n g i n them as a means of d e t e r m i n i n g d e p t h o f b u r i a l . A more d e t a i l e d c o m p a r i s o n between c o n d i t i o n s i n t h e 95. Portage Lake S e r i e s and the Karmutsen Group i s t h e r e f o r e a p p r o p r i a t e . Epidote metadomains i n the Portage Lake b a s a l t s . are a s s o c i a t e d with uppermost z e o l i t e assemblages. In the Karmut-sen they occur with the g r e e n s c h i s t assemblage alb i t e-epido t e-a c t i n o l i t e - c h l o r i t e - m a g n e t i t e - s p h e n e - q u a r t z which i s i t s e l f r e l -a t i v e l y anhydrous. L i o u et a l . (1974) obtained a water content of 1.61 wt. % from a g r e e n s c h i s t c o n t a i n i n g 24% c h l o r i t e . Green-s c h i s t s from Helmcken and southern Hardwicke Islands g e n e r a l l y c o n t a i n l e s s than 10% c h l o r i t e ; t h e i r water contents may approach those of the epidote metadomains. I f , as J o l l y and Smith propose, present water contents are r e l i a b l e i n d i c a t o r s of r e l a t i v e PTT \u00E2\u0080\u009E, H 2 O / P, , i t can be argued that d i f f e r e n c e s between f l u i d and load load b pressure i n Karmutsen b a s a l t s were s m a l l . N e v e r t h e l e s s , water-pressure g r a d i e n t s provide an a t t r a c t i v e e x p l a n a t i o n f o r epidote s e g r e g a t i o n . I n t e r p r e t a t i o n of parageneses i s t h e r e f o r e s u b j e c t to a dual u n c e r t a i n t y : the exact value of PTT n/P, , i n a p a r t i c -H 2 O load u l a r rock, and the e f f e c t of t h i s r a t i o on the r e a c t i o n s observed i n i t . Less than 1250 meters from the quartz d i o r i t e , g r e e n s c h i s t assemblages give way to g r e e n s c h i s t - a m p h i b o l i t e t r a n s i t i o n a l assem-blages \u00E2\u0080\u00A2(Figure 30). At the outer l i m i t of the t r a n s i t i o n a n o r t h i t e contents i n p l a g i o c l a s e i n c r e a s e sharply from near zero to g r e a t e r than 20%. Epidote, quartz, and c h l o r i t e are r e p l a c e d by i d i o b l a s t i c amphibole and new p l a g i o c l a s e (Figure 31b). Blue-green hornblende r e p l a c e s or grows s i d e - b y - s i d e with pale green a c t i n o l i t e . Quartz i n amygdules decreases and f i n a l l y d i s a p p e a r s . The inner l i m i t 96. o f t h e t r a n s i t i o n zone, a p p r o x i m a t e l y 500 m e t e r s from th e i n t r u s -i o n , i s marked by t h e d i s a p p e a r a n c e o f e p i d o t e and c h l o r i t e . The s i g n i f i c a n t t r a n s i t i o n a l a s s e m b l a g e s o b s e r v e d i n r o c k s f r o m H a r d w i c k e and West T h u r l o w I s l a n d s a r e the f o l l o w i n g : ( s e e F i g u r e 30 f o r l o c a t i o n s ) T^ : p l a g ( A n ^ g ) - a c t - h b - m t - e p - q z - a p - p y - s p h e n e - c h l ( a n d e s i t e d i k e ) : p l a g ( A n ^ Q ) - a c t i n o 1 i t i c h o r n b l e n d e - c h l - b i ( 5 % ) - m t - p y - q z (Bonanza) T^ : p l a g ( A n 2 0 ) - h b - c h l - e p - q z - m t - p y (Karmutsen) T^ : p l a g ( A n 2 0 ) - h b - a c t - e p - m t (Karmutsen) T^ : p l a g ( A n 3 0 ) - h b - a c t - c h l - e p - m t - i l m ; i n v e i n , e p - q z - g a (Karmutsen). ( p l a g = p l a g i o c l a s e , a c t = a c t i n o 1 i t e , hb=hornb1ende, m t = m a g n e t i t e , e p = e p i d o t e , q z = q u a r t z , a p = a p i t e , p y = p y r i t e , c h l = c h l o r i t e , b i = b i o t i t e , i l m = i l m e n i t e , g a = g a r n e t t ) The t r a n s i t i o n from g r e e n s c h i s t to a m p h i b o l i t e i n Karmutsen b a s a l t s has been i n v e s t i g a t e d e x p e r i m e n t a l l y by L i o u et a l . (1974) a t PJJ2Q, = ^ t o t a l a n ^ oxygen f u g a c i t i e s d e f i n e d by t h e q u a r t z - f a y -a l i t e - m a g n e t i t e b u f f e r . They c o n s i d e r t h e t r a n s i t i o n to be bounded by two r e a c t i o n s : 1) c h l + ep + ab + qz = o l i g + t s c h e r m a k i t e + Fe^O^ + H^O and 2. c h l + sphene + qz = A l - a m p h i b o l e + i l m + H^O ( u p p e r ) . The f i r s t i n v o l v e s a d e c r e a s e i n c h l o r i t e w i t h r i s i n g t e m p e r a t u r e ; th e s e c o n d i t s e l i m i n a t i o n . T h e s e r e a c t i o n s a r e shown s c h e m a t i c a l l y i n F i g u r e 32 a l o n g w i t h t h e r e a c t i o n ep + qz = g r a n d i t e ^ + an + mt ( L i o u 1973) w h i c h may o c c u r i n e p i d o t e - q u a r t z v e i n s . F i e l d 1 i s g r e e n s c h i s t ; F i e l d 2 i s a m p h i b o l i t e . The t r a n s i t i o n a l f i e l d s 3 to 6 a r e of g r e a t e s t i n t e r e s t . F i e l d 3 i s a l b i t e - e p i d o t e amphi-98. b o l i t e . In F i e l d 4 t r a n s i t i o n a l assemblages and e p i d o t e - q u a r t z segregations c o e x i s t ; i n F i e l d 5 amphibolites may c o n t a i n e p i d o t e -quartz v e i n s . F i e l d 6 i n c l u d e s c h l o r i t e - b e a r i n g assemblages i n which epid o t e - q u a r t z i s u n s t a b l e . Because of the d i f f e r i n g slopes of the c h l o r i t e - d e c r e a s i n g and c h l o r i t e - o u t curves g r e e n s c h i s t - a m p h i b o l i t e t r a n s i t i o n a l assemblages can be used as pressure i n d i c a t o r s . On Hardwicke and West Thurlow I s l a n d s a l b i t e amphibolite i s conspicuously absent; p l a g i o c l a s e r e p l a c e s a l b i t e at the outer border of the t r a n s i t i o n zone. Pressure c e r t a i n l y d i d not exceed, that at point A on F i g u r e 32. Epidote + quartz i s a s t a b l e v e i n and v e s i c l e assemblage i n T ^ and T^. They t h e r e f o r e l i e i n F i e l d 4. The r e a c t i o n ep + qz = gr = an + mt + H\u00E2\u0080\u009E0 i s i n f e r r e d i n T,. , as garnet occurs ss 2 5 i n contact with epidote and quartz i n the wider v e i n s . ( I n v e i n l e t s l e s s than 1 mm. across amphibole has r e p l a c e d ep-qz, i n d i c a t i n g exchange with the matrix over short d i s t a n c e s . ) Epidote and c h l o r i t e i n the matrix of t h i s .rock are sparse and t e x t u r a l l y u n s t a b l e . Epidote i n v e s i c l e s i s embayed and engulfed by amph-i b o l e . Small patches of c h l o r i t e are t r a n s e c t e d by i d i o b l a s t i c amphibole c r y s t a l s . and T^ are more d i f f i c u l t to i n t e r p r e t . T^ i s a Bonanza b a s a l t i c andesite c o n t a i n i n g no e p i d o t e . I t might f o r that reason f i t i n F i e l d 6. However the ACF diagram approximating assemblages i n F i e l d 4 shows that epidote may be e l i m i n a t e d e a r l y i n A l - r i c h , Ca-poor rocks. T y p i c a l Bonanza v o l c a n i c s c o n t a i n f a r l e s s calcium 99. t h a n K a r m u t s e n b a s a l t s ; some c o n t a i n a p p r e c i a b l y more a l u m i n u m ( M u l l e r e t a l 1974 T a b l e s 2 and 4 ) . The p o s i t i o n of i s u n -c e r t a i n . I t i s shown i n b o t h F i e l d s 2 and 6. T^ c o n t a i n s e p i d -o t e b u t no c h l o r i t e . T h e s e c h a r a c t e r i s t i c s p l a c e i t i n F i e l d 5. However T^ i s h i g h l y a m y g d a l o i d a l and c o n t a i n s enough e p i d o t e t o be an e p i d o t e m e t a d o m a i n , w h i c h as d e s c r i b e d above c o n t a i n l i t t l e o r no c h l o r i t e e v e n i n g r e e n s c h i s t f a c i e s . The c l o s e s p a t i a l a s s o c i a t i o n o f T^ and T^ s u g g e s t . t h a t T^ b e l o n g s i n F i e l d 4. The a b o v e a s s e m b l a g e s a l l l i e b e l o w p o i n t A. T,. and p o s s i b l y i n d i c a t e p r e s s u r e s b e l o w p o i n t B. P u t t i n g a n u m e r i c a l v a l u e on t h e p r e s s u r e s a t p o i n t s A and B r e q u i r e s a k n o w l e d g e o f t h e o x y g e n f u g a c i t i e s i n t h e r o c k s d u r i n g t h e i r m e t a m o r p h i s m . The p o s i t i o n s o f t h e c u r v e s , w h i c h i n v o l v e o x i d a t i o n - r e d u c t i o n r e a c t -i o n s , and t h u s o f t h e i r i n t e r s e c t i o n s , a r e v e r y s e n s i t i v e t o o x y g e n f u g a c i t y . The d i s p l a c e m e n t v e c t o r s shown on F i g u r e 32 f o r i n c r e a s i n g f g s h i f t t h e i n t e r s e c t i o n p o i n t s t o l o w e r p r e s s -u r e ( L i o u e t a l 1 9 7 4 ) . The v a l u e o f f . i n K a r m u t s e n m e t a b a s a l t s 0 2 i s u n c e r t a i n . L i o u e t a l t a k e t h e u b i q u i t y o f m a g n e t i t e + q u a r t z i n many a u r e o l e s t o s i g n i f y f_ h i g h e r t h a n t h a t d e f i n e d by t h e \u00C2\u00B02 QFM b u f f e r . T h i s a s s o c i a t i o n i s commonly o b s e r v e d h e r e . However, s m a l l amounts o f t i t a n i u m i n m a g n e t i t e t e n d t o s t a b i l i z e i t r e l a t i v e t o f a y a l i t e ( I . D u n c a n , p e r s . comm. 1974) r e n d e r i n g q u a r t z - m a g n e t i t e an u n r e l i a b l e i n d i c a t o r o f o x y g e n f u g a c i t y . The a p p l i c a t i o n o f t h e m a g n e t i t e - i l m e n i t e g e o t h e r m o m e t e r ( B u d d i n g t o n and L i n d s l e y 1964) t o K a r m u t s e n m e t a b a s a l t s w o u l d p r o v e a u s e f u l s t u d y . 100. While f grea t e r than QFM cannot be demonstrated, f,. l e s s (J 2 U 2 than QFM i s u n l i k e l y . In n a t u r a l systems oxygen f u g a c i t y i s c o n t r o l l e d by the phases and r e a c t i o n s present. The breakdown 3+ 2+ of epidote i n v o l v e s r e d u c t i o n of Fe to Fe . I t has a p o s i t i v e slope on a temperature-F diagram (Liou 1973): as temperature u2 inc r e a s e d the r e a c t i o n would move through i n c r e a s i n g oxygen f u g a c i t i e s ( Figure 33). The c h l o r i t e - d e c r e a s i n g r e a c t i o n would behave s i m i l a r l y . I t i s p o s s i b l e , then, that the g r e e n s c h i s t -amphibolite t r a n s i t i o n i t s e l f acted as an oxygen b u f f e r and that f i n c r e a s e d with r i s i n g temperature. With the QFM b u f f e r \u00C2\u00B02 p o i n t B l i e s s l i g h t l y above 3 kb (Liou et a l 1974). This provides a maximum estimate f o r load pressure ( h y d r o s t a t i c ) during contact metamorphism. The inner l i m i t of the t r a n s i t i o n i s about 500 meters from the quartz d i o r i t e . The temperature here, assuming QFM c o n d i t i o n s , was 550\u00C2\u00B0 (L i o u et a l 1974). Basi c assemblages t y p i c a l of the hornblende-hornfels f a c i e s are developed i n Karmutsen and Bonanza v o l c a n i c s l e s s than 500 meters from the i n t r u s i o n . Textures i n the Karmutsen are t y p i c -a l l y granoblas t i c , or s u b l e p i d o b l a s t i c i f dominated by hornblende. This hornblende lac k s the ragged (001) terminations of g r e e n s c h i s t and t r a n s i t i o n zone amphiboles. I t tends to form s t r a i g h t , r a t i o n -a l boundaries, p a r t i c u l a r i l y the prism f a c e s , although polygonal g r a i n s with 120\u00C2\u00B0 i n t e r s e c t i o n s are not uncommon. Hornblende c o l o r s vary from brownish green to brown. Rims and new c r y s t a l s of prograde texture are browner than the amphibole which they super-cede. Within a few centimeters of the quartz dior-ite the horn-blende i n the Karmutsen i s green, as i s that i n the i n t r u s i o n T \u00C2\u00B0C 102 ( F i g u r e 34). C o m p o s i t i o n a l e q u i l i b r i u m between magma and c o u n t r y r o c k p r o b a b l y o b t a i n e d o v e r a s h o r t d i s t a n c e . P o i k i l i t -i c h o r n b l e n d e p r o p h y r o b l a s t s a r e d e v e l o p e d i n t h e i n n e r m o s t a u r e o l e . I n t e r g r o w n m a g n e t i t e and i l m e n i t e o c c u r as s c a t t e r e d round, g r a i n s o r clumps i n s i d e h o r n b l e n d e . P a t t e r n s of opaque m i c r o l i t e s i n h o r n b l e n d e may be r e l i c s o f t h e d e s t r u c t i o n of i g n e o u s c l i n o p y r o x e n e . P o i k i l i t i c m e t amorphic c l i n o p y r o x e n e o c c u r s i n some p a r a g e n e s e s . I t seems to c o n c e n t r a t e i n and a r o u n d amygdules.. I t a p p a r e n t l y r e f l e c t s e x c e p t i o n a l l y c a l c i c c o m p o s i t i o n due to l o c a l abundance of e p i d o t e . B i o t i t e and c u m m i n g t o n i t e p o r p h y r o b l a s t s have d e v e l o p e d i n t h e K armutsen m e t a b a s a l t s o n l y a d j a c e n t to i n t r u s i v e c o n t a c t s ( F i g u r e 34). L i k e g r e e n h o r n b l e n d e t h e y a r e p r o b a b l y the r e s u l t of s m a l l -s c a l e metasomatism. P l a g i o c l a s e c o m p o s i t i o n s i n K armutsen r o c k s o f t h i s zone, d e t e r m i n e d from e x t i n c t i o n a n g l e s , a r e An to A n o n . T h e i r z o n i n 4U o U p a t t e r n s a r e n o r m a l , p a t c h y , o r i r r e g u l a r . E x c e p t r a r e l y i n amyg d u l e s p l a g i o c l a s e does not f o r m p o r p h y r o b l a s t s . On the c o n t r a r y , p h e n o c r y s t s t e n d to r e c r y s t a l l i z e to s m a l l , x e n o b l a s t i c g r a i n s . New c r y s t a l s c r e a t e a p o l y g o n a l g r a n o b l a s t i c f a b r i c w h i c h b e a r s no r e s e m b l a n c e e i t h e r to the mat of p l a g i o c l a s e l a t h s i n the o r i g i n a l r o c k o r to t h e e u h e d r a l to s u b h e d r a l s t r o n g l y n o r m a l -zoned p l a g i o c l a s e s i n t h e p e r i p h e r a l gabbro phase of the main i n t r u s i o n . P o l y g o n a l f a b r i c i s r e t a i n e d even w i t h i n 2 mm. of i n t r u s i v e c o n t a c t s . P l a g i o c l a s e c o m p o s i t i o n s n e x t to the q u a r t z d i o r i t e , r a n g i n g from An^ f i to A n / R i n s t r o n g l y n o r m a l - z o n e d 10 3 . 0*8? Jf X JO Contact between Loctt- Jurassic quartz diorxtt and XarnuLtstn hornfels^ Jfardwicke JslcmcL, (the iarji ylajwclases at the -toy of the yhotojrayh cure ycurt of~~\" \u00E2\u0080\u00A2tht o/mrtz cLiorittr. CNoti thejnen korribliwcLe a.nd the L&rtjt skiUtai biotite- [UbeUecC) jrvwmj nnm.net small yiajiocU^s in tht hcrrytfUs.Hint harnjiLs has d yobjCjtmO'l tstytun dnd a fai-nt pliatfcm nnat -visible-in the yhfftojrayk \u00E2\u0080\u00A2 ^ PLa^iocLaj-t is strcmtjUy normal z-cnecL~ . 104. c r y s t a l s , a r e e q u i v a l e n t t o and p r o b a b l y i n e q u i l i b r i u m w i t h c o m p o s i t i o n s i n t h e i n t r u s i o n . B o n a n z a m e t a v o 1 c a n i c s , u n l i k e 'Karmutsen r o c k s , a r e f o l i a t e d e v e r y w h e r e w i t h i n t h e h o r n b l e n d e - p l a g i o c l a s e z o n e . B o n a n z a h o r n b l e n d e i s g r e e n . I f a c i c u l a r i t l i e s i n t h e f o l i a t i o n ( F i g u r e . 3 5 a ) . I t s most common h a b i t i s x e n o b l a s t i c t o sub i d i o b l a s t i c and e q u a n t . Such g r a i n s , a l t h o u g h l y i n g i n c o m p o s i t i o n a l b a n d s , a r e n o t i n d i v i d u a l l y o r i e n t e d . As i n t h e K a r m u t s e n , l a r g e p l a g i o c l a s e g r a i n s a r e b l a s t o -p o r p h y r i t i c . I n t h i n s e c t i o n t h e y a r e s e e n t o c o n t a i n p a t c h e s o r s y m m e t r i c a l z o n e s o f a m p h i b o l e m i c r o l i t e s , a p r o b a b l e r e l i c o f b u r i a l m e t a m o r p h i s m . The p l a g i o c l a s e s a r e r a n d o m l y o r i e n t e d and commonly b r o k e n and r e e r y s t a l l i z e d . The f o l i a t i o n bends a r o u n d them ( F i g u r e 3 5 a ) . I n t h e o u t e r p a r t o f t h e h o r n b l e n d e - p l a g i o c l a s e zone some a r e s t i l l o s c i 1 l a t o r y - z o n e d . T h i s i s a r e l i c t , n o t a p r o g r a d e f e a t u r e , a b s e n t c l o s e r t o t h e i n t r u s i o n . S t a b l e m e t a -m o r p h i c z o n i n g modes a r e n o r m a l , p a t c h y , o r i r r e g u l a r . A n o r t h i t e c o n t e n t s o f m e t a m o r p h i c p l a g i o c l a s e r a n g e f r o m An 0 t o An . T h i s 2. o / U v a r i a b i l i t y p r o b a b l y r e f l e c t s d i f f e r e n c e s i n b u l k c o m p o s i t i o n ; t h e r e i s no c o r r e l a t i o n w i t h d i s t a n c e f r o m t h e i n t r u s i o n . New p l a g i o c l a s e s a r e s m a l l r o u n d o r p o l y g o n a l g r a i n s , o r sub i d i o b 1 a s t i c l a t h s l y i n g i n t h e f o l i a t i o n . W i t h i n 70 m e t e r s o f p l u t o n i c c o n t a c t s t h e g r o w t h o f l a r g e p o i k i l o b l a s t i c to s k e l e t a l b i o t i t e , h o r n b l e n d e , and c u m m i n g t o n i t e p a r t l y o b s c u r e s t h e f o l i a t i o n ( F i g u r e 3 5 b ) . C u m m i n g t o n i t e i s n o t e w o r t h y i n t h a t i t h a s n o t b e e n p r e v i o u s l y r e p o r t e d f r o m I n s u -l a r B e l t c o n t a c t a u r e o l e s . I t i s c o l o r l e s s t o s l i g h t l y g r e e n 105 d) 3onanzii tuff C V in hornbltndb hornfcLs z. of tte ph.otcjfT.ph, when albrtfLatfrn wuld. hayt free-n iwtstr severe. b) 'Bonanza, hor/nfcLs ( x S'o) Larje bfotfbCj hornblende a,nd tu^mfnyto^ike jr*\u00C2\u00BB across a foUtutity, defined by yiajroclase Laths. Hv. larot ^ Utjioanses kxn embayed borders a-ncL art fx tiu process of /ricrys+a.LLT2.r*a to maJL ycAobtastfc jrafwi. 7-19 \u00E2\u0080\u00A2 r 1 0 6 . w i t h numerous l a m e l l a r t w i n s . Two s e t s of g r e e n p l e o c h r o i c l a m e l l a e , p r e s u m a b l y o f c a l c i c a m p h i b o l e , a r e d i s c e r n i b l e . The c o m b i n a t i o n of l a r g e p o s i t i v e 2V and r e l i e f s i m i l a r to h o r n b l e n d e s e r v e to d i s t i n g u i s h c u m m i n g t o n i t e from c l i n o p y r o x e n e . S h i d o (1958) n o t e s the p r e s e n c e of c u m m i n g t o n i t e i n b a s i c r o c k s f r o m c o n t a c t a u r e o l e s i n t h e Abukuma P l a t e a u . She c o n s i d e r s i t a low p r e s s u r e phase f o r two r e a s o n s . The f i r s t i s i t s a s s o c i a t i o n w i t h o t h e r l o w - p r e s s u r e i n d i c a t o r s , a n d a l u s i t e i n p e l i t i c h o r n f e l s e s and the a c t i n o l i t e - p l a g i o c l a s e t r a n s i t i o n a l a s s e m b l a g e i n m e t a v o l c a n i c r o c k s . S e c o n d l y , a l i k e l y r e a c t i o n f o r i t s f o r m a t i o n i s : 7 t s c h e r + 10 qz = 14 an + 3 cumm + 4 ^ 0 T h e r e i s a c o n s i d e r a b l e volume i n c r e a s e f r o m l e f t to r i g h t (2044 v s . 2221 c c . f o r the s o l i d p h a s e s ) . (Note t h a t abundant f r e e q u a r t z f a v o r s c u m m i n g t o n i t e d e v e l o p m e n t , a c c o u n t i n g f o r i t s p r e s e n c e i n Bonanza but not Karmutsen h o r n f e l s e s . ) The p r e s e n c e of cumming-t o n i t e c o r r o b o r a t e s the l o w - p r e s s u r e c o n d i t i o n i n f e r r e d above from g r e e n s c h i s t - a m p h i b o 1 i t e t r a n s i t i o n a l p a r a g e n e s e s . S e v e r a l t e x t u r a l f e a t u r e s of K armutsen and Bonanza meta-v o l c a n i c s i n the h o r n b l e n d e - p l a g i o c l a s e zone d e s e r v e r e i t e r a t i o n as t h e y b e a r on t h e o r i g i n of t h e p l u t o n i c r o c k s , p a r t i c u l a r i l y the p e r i p h e r a l g a b b r o s . Rocks i n t h i s zone a l l have p o l y g o n a l g r a n o b l a s t i c or l e p i d o b l a s t i c f a b r i c s ( F i g u r e s 34, 3 5 ) . Near t h e p l u t o n i c c o n t a c t s a m p h i b o l e s and b i o t i t e d e v e l o p as l a r g e p o i k i l o b l a s t i c g r a i n s w h i c h a p p e a r to p o s t d a t e t h e f o l i a t i o n . 107. P l a g i o c l a s e e x h i b i t s no such tendency. I t t y p i c a l l y forms as small x e n o b l a s t i c to s u b i d i o b l a s t i c g r a i n s with simple zoning and twinning p a t t e r n s . I t i s d i s t i n g u i s h a b l e from the p l a g i o c l a s e i n the p e r i p h e r a l gabbros, and bears no resemblance to that i n the quartz d i o r i t e . Convincing arguments f o r d i o r i t i z a t i o n based on t r a n s i t i o n a l m e t a v o l c a n i c - p l u t o n i c textures cannot be made . b) Carbonate Metamorphic Assemblages Impure carbonate l a y e r s are common i n the i n t r a v o l c a n i c s e d i -ments .of: the upperKarmutseh Formation and i n the Quatsino and Parson Bay Formations on West Thurlow I s l a n d . Carbonates a l s o occur on Yorke I s l a n d and Hardwicke I s l a n d . Fanny I s l a n d i s an i s o l a t e d marble block surrounded by gabbro. Metamorphic minerals i n the impure carbonates i n c l u d e c a l c i t e , quartz, w o l l a s t o n i t e , c l i n o z o i s i t e , e p i d o t e , garnet, d i o p s i d e , i d o c r a s e , sphene, and p l a g i o c l a s e . A number of carbonate parageneseswere found to be u s e f u l i n determining temperature and P^ ,_ /P .. . They can be CO2 t o t a l approximated by parageneses i n the system CaO - Al^O^ - SiO^ - H^O - CO^ i n v e s t i g a t e d by Gordon and Greenwood (1971) and St o r r e and N i t s c h (1972). They are l i s t e d i n Table 3 and p l o t t e d on a s i m p l i f i e d v e r s i o n of Gordon and Greenwood's phase diagram ( F i g -ure 36). T o t a l pressure i n t h e i r experiments was 2 kb., c l o s e to the estimated t o t a l pressure i n the aureole. I t w i l l be noted that s e v e r a l p l o t t e d assemblages e i t h e r l i e on or bracket r e a c t i o n boundaries. The most s i g n i f i c a n t of these i s the r e a c t i o n g r o s s u l a r + quartz = a n o r t h i t e + w o l l a s t o n i t e . As 108. T a b l e 3 = Carbonate Parageneses Cj_. p l a g - ga - qz p l a g = A n 6 5 ga = g r o s ^ a n d r 5 0 (d\u00C2\u00B1-sphene-ap) ( r e f r a c t i v e , index.) C 2- ga - p l a g (An 28-36) - qz; ga - ep ( l a y e r e d ) C.j. ga - wo - p l a g (sphene - py - d i ) . C 4- p l a g ( A n 6 8 ) - wo - ga (sphene - py - d i ) C^. cc - wo - qz Cg. cc - wo - qz - ga (ga & qz not t o u c h i n g . q z i n wo) C^. cc - q z - wo - ep - ga C g . cc - c z t - p l a g ; cc - wo - ga ( i d o c r a s e - d i ) ( l a y e r e d ) Cg. wo - ga ( i d o c r a s e - d i ) not d i a g n o s t i c C 1 Q . cc - wo - ga ( d i ) A b r e v i a t i o n s p l a g p l a g i o c l a s e ga g a r n e t qz q u a r t z d i d i o p s i d e ap a p a t i t e ep e p i d o t e wo w o l l a s t o n i t e y p y r i t e cc c a l c i t e c z t c l i n o z o i s i t e 109. J00 r ice 500 art a/nr J^zP 0 zorp^ T _ : x c o z 5Vacc -VT- Zkb. 5 Carbonate assemblages plotted in tht system CaO - M z 0 5 - S i O L - C O z - \u00E2\u0080\u00A2 H t O 400 .2, X co. LO i COL Qoriom and Qrtmwod 19 71 an-1- ca <\u00E2\u0080\u00A2 Xt0 jro-m Storrt und. Kitsch 1372. 110. o n l y s o l i d p h a s e s a r e i n v o l v e d t h e p o s i t i o n o f t h e c u r v e does n o t change w i t h f l u d i c o m p o s i t i o n : t h e t e m p e r a t u r e of t h e r e -a c t i o n i s a f u n c t i o n o f t o t a l p r e s s u r e a l o n e . The a s s e m b l a g e s w h i c h b r a c k e t t h i s r e a c t i o n were a l l c o l l e c t e d w i t h 30 m e t e r s o f t h e m a i n i n t r u s i o n ; t h e r e f o r e i t c a n be u s e d t o e s t i m a t e t h e maximum t e m p e r a t u r e i n t h e c o u n t r y r o c k n e x t t o t h e c o n t a c t . On G o r d o n and Greenwood's d i a g r a m f o r 2 kb. t o t a l p r e s s u r e t h e r e a c t i o n t e m p e r a t u r e i s s l i g h t l y l e s s t h a n 600\u00C2\u00B0C. The r e a c t i o n b o u n d a r i e s d e p i c t e d on F i g u r e 36 a r e n o t q u a n t i t a t i v e l y a p p l i c a b l e t o t h e a s s e m b l a g e s a t h a n d . I t i s e v i d e n t f r o m t h e p h a s e s p r e s e n t ( i . e . d i o p s i d e , e p i d o t e , i d o c r a s e , p l a g i o c l a s e i n s t e a d o f a n o r t -h i t e , and g r a n d i t e so 1 i d - s o 1 u t i o n i n s t e a d o f g r o s s u l a r ) t h a t F e , Mg, and Na a r e p r e s e n t i n a d d i t i o n t o t h e f i v e c o m p o n e n t s o f G o r d o n and Greenwood's s y s t e m . To be u s e f u l , t h e p o s i t i o n s o f t h e r e a c t i o n s must be a d j u s t e d t o a c c o u n t f o r m i x i n g i n t h e p a r t -i c i p a t i n g p h a s e s . The d i s p l a c e m e n t s o f t h e l i n e g r o s + gz = an + wo due t o and-r a d i t e i n t h e g a r n e t and a l b i t e i n t h e p l a g i o c l a s e c a n be c a l c u l -a t e d f r o m t h e e q u i l i b r i u m c o n s t a n t i f i d e a l m i x i n g i s assumed (Greenwood l e c t u r e 1 9 7 4 ) . The b a l a n c e d r e a c t i o n i s : g r o s + qz = an + 2 wo. 2 The e q u i l b r i u m c o n s t a n t K = ( a ) ( a ) an wo (a , ( a ) g r o s ) q z 7 The e q u a t i o n f o r t h i s c o n s t a n t , u s i n g t h e d a t a o f Newton ( 1 9 6 6 ) , i s : 111. l o g K = 3492.2 + 4.4464 - .17060 (P - 1)' T T K o r T\u00C2\u00B0 = 3492.2 + .17060 ( P - 1 ) / T, , (P i s i n b a r s ) 4.4464 - l o g 1 Q K I n t h e a s s e m b l a g e C. a = .65 and a = .25 t h e r e f o r e log,\u00E2\u0080\u009EK = 1 an g r o s 6 1 0 .415. The r e a c t i o n p r o c e e d s a t 656.7\u00C2\u00B0C. a t 1.5 k b . ; 677.8 \u00C2\u00B0 a t 2 kb. ; and 720.2\u00C2\u00B0 a t 3 kb. T e m p e r a t u r e s a t t h e c o n t a c t , t h e n , l a y b e t w e e n 650 and 720\u00C2\u00B0C. S i O I f c o n s i d e r a b l e Fe 0 i s added t o t h e s y s t e m CaO - A l 0 2 o 2 3 2 - H 20 - C 0 2 t h e l o w - t e m p e r a t u r e l i m i t o f g a r n e t s t a b i l i t y a t v e r y low i s d e f i n e d by: 2 ep + 2 c c + 3 wo = g r a n d i t e + 2 CO + IH 0 ( C h a t t e r j e e S S I I 1966) r a t h e r t h a n b y : 2 zo + 5 cc + 3 qz = 3 g r o s + 5 C 0 2 + 2 H^O. C h a t t e r j e e ' s n u m e r i c a l d a t a f o r g r a n d i t e b r e a k d o w n a r e n o t a p p l i c a b l e b e c a u s e f . was u n b u f f e r e d i n h i s r u n s and P ., was 0 2 t o t a l h e l d a t 1 k b . The g e o m e t r i e s o f h i s r e a c t i o n s a r e , h o w e v e r , i n t e r -e s t i n g . They a r e r e p r o d u c e d on F i g u r e 37 w h i c h shows s c h e m a t i c a l l y t h e e f f e c t o f f e r r i c i r o n on G o r d o n and Greenwood's s y s t e m . I n t h e i r o n - f r e e s y s t e m z o i s i t e and w o l l a s t o n i t e c a n n o t c o e x i s t ( K e r r i c k e t a l 1 9 7 3 ) . E p i d o t e and w o l l a s t o n i t e c a n , and a r e o b s e r v e d h e r e . The a s s e m b l a g e c c - q z - w o - e p - g a f a l l s on an i n v a r i a n t p o i n t on C h a t t e r j e e ' s d i a g r a m . C a l c i t e and q u a r t z i n i t a r e i n t h e p r o c e s s o f r e a c t i n g t o f o r m w o l l a s t o n i t e , b u f f e r i n g X n t o t h e C 0 2 .112. 1 1 3 i n v a r i a n t p o i n t . t h e r e a c t i o n s cp + c c + wo = Gr + C0\u00E2\u0080\u009E + H\u00E2\u0080\u009E0 s s 2 2 and ep + wo .= 8 r s s + gz + R^O w o u l d t h e n have p r o c e e d e d s i m u l t -a n e o u s l y u n t i l one r e a c t a n t was u s e d up. T h i s p athway i n d i c a t e s an i n i t i a l l y v e r y w a t e r - r i c h f l u i d b e c o m i n g somewhat l e s s so w i t h r i s i n g t e m p e r a t u r e . H i g h X _ i s a l s o e v i d e n t i n t h e o t h e r H 2 U h y d r o u s p h a s e s p r e s e n t i n t h e a u r e o l e - c l i n o z o i s i t e and i d o c r a s e -and i n t h e p r e s e n c e o f g a r n e t w h i c h r e q u i r e s l o w X__. ( F i g u r e 3 6 ) . C 0 2 A h y d r o u s f l u i d p h a s e f a v o u r s t h e f o r m a t i o n o f w o l l a s t o n i t e a t r e l a t i v e l y l o w t e m p e r a t u r e s ; t h e f i r s t a p p e a r a n c e o f w o l l a s t o n -i t e h e r e ( ) i s a p p r o x i m a t e l y 500 m e t e r s f r o m t h e i n t r u s i o n w here t h e t e m p e r a t u r e was n e a r 550\u00C2\u00B0C. The o c c u r r e n c e o f t h e a s s e m b l a g e cc-qz-wo a t s e v e r a l d i s t a n c e s f r o m t h e i n t r u s i o n s u g g -e s t s p o s s i b l e b u f f e r i n g o f X \u00E2\u0080\u009E N by t h i s r e a c t i o n . W i t h a l l t h e s e L. (J 2 i n d i c a t o r s i t i s s a f e t o s a y t h a t X ^ Q i n most c a r b o n a t e s was a t l e a s t 0.8. c. C o n c l u s i o n s T h i s s t u d y o f c o n t a c t m e t a m o r p h i c a s s e m b l a g e s has p r o d u c e d f i v e q u a n t i t a t i v e r e s u l t s . T h e y a r e as f o l l o w s : F . -j ^ 3 kb. t o t a l X _ \u00E2\u0080\u009E i n c a r b o n a t e s \u00C2\u00A30.2 L U 2 T e m p e r a t u r e s d u r i n g c o n t a c t m e t a m o r p h i s m ( m a x i m a ) : b e t w e e n 200\u00C2\u00B0 and 400\u00C2\u00B0, p r o b a b l y c l o s e t o 350\u00C2\u00B0 ( K u n i y o s h i 1972) * 6 km f r o m t h e m a i n i n t r u s i o n 550\u00C2\u00B0 500 m e t e r s f r o m t h e i n t r u s i o n ( u p p e r l i m i t o f g r e e n -s c h i s t - a m p h i b o l i t e t r a n s i t i o n , QFM c o n d i t i o n s ) 650 - 72 0\u00C2\u00B0 a t t h e c o n t a c t ( g r + qz = a n + w o ) 114 . Since these r e s u l t s w i l l be used to make important i n f e r e n c e s a caveat should be o f f e r e d before proceeding. They are sub j e c t to s e v e r a l u n c e r t a i n t i e s : oxygen f u g a c i t y , phase compositions, the assumption of i d e a l mixi'ng, P\u00E2\u0080\u009E _/P, . i n the metavolcanics and load experimental u n c e r t a i n t i e s . The f i r s t two could be e l i m i n a t e d by extensive microprobe work. The three temperatures determined i n the aureole d e f i n e a curve (Figure 38) l i k e those computed by Jaeger (1959). A f u r t h e r r e s t r i c t i o n oh pressure can be drawn from t h i s temperature-d i s t a n c e curve. The g r e e n s c h i s t - a m p h i b o l i t e t r a n s i t i o n commences 1.3 km. from the i n t r u s i o n . The temperature at that p o i n t a c c o r d i n to F i g u r e 38 i s l e s s than or equal to 500\u00C2\u00B0C . For QFM c o n d i t i o n s such a s i t u a t i o n o btains only i f P ., 2.5 kb. (Liou et a l 1974) t o t a l The maximum s t r a t i g r a p h i c load at the top of the Karmutsen Formation on Vancouver I s l a n d i s 1.5 kb. I f the maximum pressure i n the present area d i d not exceed 2.5 kb. i t i s reasonably c e r t -a i n that we are d e a l i n g with the Vancouver I s l a n d s t r a t i g r a p h i c column. Therefore here, at the edge of the Coast P l u t o n i c Complex, n e i t h e r depth of b u r i a l or depth of e r o s i o n have s i g n i f i c a n t l y exceeded c o n d i t i o n s anywhere i n the I n s u l a r B e l t . Jaeger's c a l c u l a t i o n s allow the i n i t i a l temperature of an i n t r u s i o n to be i n f e r r e d from the temperature at i t s c o n t a c t s . It i s assumed that i n t r u s i o n i s instantaneous. I f f u r t h e r i t i s assumed that there i s no l a t e n t heat of c r y s t a l l i z a t i o n then the simple r e l a t i o n ( T - T . . . . . ) = h ( T. contact i n i t i a l i n t r u s i o n -T \u00E2\u0080\u00A2. . . , ) holds, where the i n i t i a l temperature i s that of i n i t i a l 0. 650 (bOO 550 1 ( Z k b ) max. ^emperaturer ys. Distance from the Contact-Jnmr Limitojimnntion (assuming QTM) Outer Ifmltraj grans chist-\u00C2\u00AB transitional asswiblLti. .2 fr0 ( D * Width of intrusion. = Wdtk/of awriolt (?) ^5hnJ 1 1 6 . the country rocks before emplacement of the p l u t o n . T i s ^ contact at most 700\u00C2\u00B0C. The ambient temperature, using Kuniyoshi's estimate (1972), i s 350\u00C2\u00B0. T. ^ . i s then 1050\u00C2\u00B0. I f l a t e n t i n t r u s i o n heat i s allowed f o r i t i s approximately .1000\u00C2\u00B0. d) S t r u c t u r e and Metamorphic Textures Pervasive deformation i n the a l b i t e - e p i d o t e - a c t i n o l i t e zone i s c onfined to close-spaced shear-planes i n the f a u l t zones. Stress-indueed r e e r y s t a l 1 i z a t i o n has not o c c u r r e d . V e s i c l e s are equant; r e l i c t phenocrysts, even i f bent or broken, r e t a i n : t h e i r o r i g i n a l form. A c t i n o l i t e needles form a n o n - d i r e c t i o n a l matte. These t e x t u r e s i n d i c a t e s l u g g i s h r e c r y s t a l l i z a t i o n . Under g r e e n s c h i s t metamorphism the Karmutsen Group behaved as competent; and b r i t t l e b l o c k s . I t s response to t e c t o n i c s t r e s s was l i m i t e d to f a u l t i n g , as d e s c r i b e d i n the l a s t chapter. F o l i a t i o n i s r a r e l y observed i n Karmutsen metabasalts. Bonanza rocks, by c o n t r a s t , a c q u i r e a f o l i a t i o n i n the innermost greenschist-amphibo1ite t r a n s i t i o n zone which c h a r a c t e r i s e s them throughout the inner aureole. This planar f a b r i c can be a t t r i b u to three f e a t u r e s : the f l a t t e n i n g of b r e c c i a c l a s t s , alignment of b i o t i t e and a c i c u l a r hornblende, and the a c c e n t u a t i o n of d e l i c a t e primary m i n e r o l o g i c a l / t e x t u r a l l a y e r i n g i n t u f f a c e o u s u n i t s by r e c r y s t a 1 1 i z a t i o n . Why Bonanza rocks were able to develop f o l i a t i o n i n response to s t r e s s while Karmutsen rocks g e n e r a l l y were not may be explained i n s e v e r a l ways. 1. B i o t i t e , which r e a d i l y assumes a planar o r i e n t a t i o n , i s abundant i n Bonanza metavolcanics. 117. 2. Q u a r t z i s a l s o a b u n d a n t . I t d e f o r m s w i t h e a s e a t much l o w e r t e m p e r a t u r e s t h a n h o r n b l e n d e and p l a g i o -c l a s e , t h e p r i n c i p a l c o n s t i t u e n t s o f K a r m u t s e n h o r n f e l s e s . 3. Some o f t h e \" f o l i a t i o n \" o b s e r v e d i n t h e f i e l d may a c t u a l l y be b e d d i n g f e a t u r e s t r a n s p o s e d p a r a l l e l t o t h e b i o t i t e s c h i s t o s i t y . A c c o r d i n g t o s t r u c t u r a l e v i d e n c e ( C h a p t e r I V ) t h i s f o l i a t i o n r e s u l t e d f r o m f o r c i b l e e m p lacement o f t h e q u a r t z d i o r i t e . T e x t u r a l r e l a t i o n s h i p s show t h a t i t a c c o m p a n i e d c o n t a c t metamor-p h i s m . Q u a r t z - b i o t i t e - p l a g i o c l a s e and h o r n b l e n d e v e i n s a r e f o l d e d w i t h a x i a l p l a n e s p a r a l l e l t o t h e f o l i a t i o n . S m a l l b i o t i t e p l a t e s a r e o r i e n t e d . I n one e x a m p l e o f r e f o l d i n g i n a s i l t s t o n e l e n s a s e c o n d a x i a l - p l a n e a l i g n m e n t s u p e r c e d e s b i o t i t e b e d d i n g -p a r a l l e l a l i g n m e n t . E x c e p t i m m e d i a t e l y a d j a c e n t t o t h e q u a r t z d i o r i t e s t a t i c r e c r y s t a l l i z a t i o n has n o t o v e r p r i n t e d t h e f o l i a t i o n . T h i s s u g g e s t s t h a t d e f o r m a t i o n : a f f e c t e d t h e m e t a v o l c a n i c s a t t h e maximum t e m p e r a t u r e s a c h i e v e d . A c c o r d i n g t o J a e g e r ' s d a t a (1957 F i g u r e 1 ) , t h e t e m p e r a t u r e maximum a t t h e o u t e r l i m i t o f d e v e l o p e d f o l i a t i o n , 500 m e t e r s f r o m t h e i n t r u s i o n , p e r s i s t e d t o a b o u t 320,000 y e a r s a f t e r i t s e m p l a c e m e n t . D u r i n g t h i s t i m e - i n t e r v a l , o f c o u r s e , t h e p l u t o n i t s e l f was c o o l i n g . The d i s t a n c e o f t h e p l a n e o f s o l i d i f i c a t i o n f r o m t h e c o n t a c t 320,000 y e a r s a f t e r i n t r u s i o n i s a b o u t 750 m e t e r s ( f r o m J a e g e r 1957 e q u a t i o n ( 9 ) ) . I t i s t h u s p r o b a b l e t h a t s o l i d u s o r n e a r - s o l i d u s c o n d i t i o n s p r e v a i l e d i n t h e o u t e r p a r t o f t h e i n t r u s i o n w h i l e t h e c o u n t r y r o c k s were s t i l l d e f o r m i n g . T h i s i s s u b s t a n t i a t e d by t h e d e f o r m -118. a t i o n o f i n c l u s i o n s i n t h e q u a r t z d i o r i t e ( C h a p t e r I I I ) , w h i c h p r o b a b l y o c c u r r e d a t a l a t e s t a g e o f c r y s t a l l i z a t i o n . The s i m u l t a n e o u s d e v e l o p m e n t o f f o l i a t i o n i n t h e q u a r t z d i o r i t e and i t s c o u n t r y r o c k s may have r e s u l t e d f r o m c o n t i n u e d u p r i s e o f magma i n t o t h e c e n t e r o f t h e i n t r u s i o n , c a u s i n g i t t o e x p a n d o u t w a r d s . 119. CHAPTER V I : POST-PLUTONIC STRUCTURE AND DIKES F r a c t u r i n g , f a u l t i n g d i k e emplacement, and l o w - t e m p e r a t u r e metamorphism f o l l o w e d c r y s t a l l i z a t i o n o f t h e q u a r t z d i o r i t e . T h e s e p o s t - p l u t o n i c s t r u c t u r e s t r e n d n o r t h e a s t e r l y , n e a r l y p e r p e n d i c u l a r to the e a r l i e r s t r u c t u r a l g r a i n . N o r t h e a s t - t r e n d i n g j o i n t s e t s a r e w i d e s p r e a d b o t h i n t h e p l u t o n and i n t h e V a n c o u v e r Group. P o s t - p l u t o n i c d i k e s t e n d to s t r i k e p a r a l l e l to l o c a l j o i n t s e t s ( F i g u r e 39). A p l o t of d i k e o r i e n t a t i o n s ( F i g u r e 40) has a w e l l -d e f i n e d maximum n e a r N 45 E. The p a t t e r n of s t r a i g h t e a s t - n o r t h -e a s t v a l l e y s on H a r d w i c k e I s l a n d f o l l o w s a s y s t e m of c h l o r i t i z e d f r a c t u r e z o n e s . The b o r d e r o f t h e q u a r t z d i o r i t e i s n o t s i g n i f -i c a n t l y o f f s e t a c r o s s t h e s e l i n e a r s . F a u l t i n g was g e n e r a l l y l e s s i m p o r t a n t t h a n f r a c t u r i n g . The o n l y major n o r t h e a s t t r e n d i n g f a u l t i n t h e a r e a o f f s e t s t h e i n t r u s i v e c o n t a c t 200 m e t e r s i n a r i g h t -l a t e r a l s e n s e and j u x t a p o s e s Q u a t s i n o and upper K a r m u t s e n Form-a t i o n s i n M i n e r ' s Bay; i t s p r o b a b l e e x t e n s i o n s o u t h of J o h n s t o n e S t r a i t j u x t a p o s e s upper and m i d d l e Karmutsen F o r m a t i o n s ( K u n i y -o s h i 1972). P o s t - p l u t o n i c d i k e s a r e d i s r u p t e d i n a number of l o c a l i t i e s , s u g g e s t i n g s m a l l - s c a l e movements. P o s t - p l u t o n i c d i k e s c o n s t i t u t e f i v e p e r c e n t o f o u t c r o p volume a l o n g t h e c o a s t between P a t t e r s o n Bay and the s o u t h e a s t e r n t i p of H a r d w i c k e I s l a n d : t h e i r emplacement i n v o l v e d a f i v e p e r c e n t n o r t h w e s t - s o u t h e a s t c r u s t a l e x t e n s i o n . B e c a u s e of p e r v a s i v e e p i d o t e - c h l o r i t e a l t e r a t i o n the d i k e s a r e t y p i c a l l y g r e e n . They c r o s s c u t each o t h e r a t many l o c a l i t i e s ( F i g u r e 41) but i n no a p p a r e n t p e t r o l o g i c s e q u e n c e . They r a n g e from h o r n -b l e n d e b a s a l t to d a c i t e w i t h a n d e s i t e p r e d o m i n a n t ( T a b l e 4 ) . . 1 . 2 1 . O2?^ \u00C2\u00B10 J Strike orientations aj'yostylutmic dikes CN ^ 7 total points : f f J Cross- cultinj post-plutonic dikes Chilled, mora in visible on Inter cLiktr: T a b l e 4 3 P e t r o g r a p h i c Data = Post P l u t o n i c Dikes Sample Number //1 Primary: c l i n o p y r o x e n e h o r n b l e n d e p l a g i o c l a s e 1 0 10(An54) //2 //3 5 0 40(An60-63) 3 0 10 //5 0 0 0 86 0 40 0 Secondary: a l b i t e ( + s a u s s u r i t e + s e r i c i t e ) e p i d o t e c h l o r i t e p r e h n i t e p u m p e l l y i t e c a l c i t e s p h e n c 55 1 15 0 0 2 1 50 5 30 0 1 0 1 25 2 15 0 0 0 0 60 5 10 2 0 0 1 7 5 2 5 3 0 t r 0 35 10 10 0 0 0 0 E i t h e r : q u a r t z m a g n e t i t e i l m e n i t e 5 10 0 2 1 10 3 10 0 1 5 ( p h e n o c r y s t s ) 2 1 3 0 ; 0 Percentage of secondary mineralai 74 87 42 78 85 Rock name: a n d e s i t e a n d e s i t e a n d e s i t e a n d e s i t e d a c i t e h o r n b l e n d e b a s a l t 124. The l a r g e p r o p o r t i o n s o f s e c o n d a r y p h a s e s shown i n T a b l e 4 a t t e s t t o t h e h i g h d e g r e e o f a l t e r a t i o n . By c o n t r a s t t h e q u a r t z d i o r i t e and m e t a v o l c a n i c s i n t r u d e d by t h e s e d i k e s a r e g e n e r a l l y q u i t e f r e s h . They c o n t a i n o n l y s m a l l q u a n t i t i e s o f l o w - t e m p e r a t u r e p h a s e s , i n c l u d i n g c h l o r i t e i n b i o t i t e and h o r n b l e n d e , p r e h n i t e i n b i o t i t e , s a u s s u r i t e , e p i d o t e , and p u m p e l l y i t e . S i g n i f i c a n t l o w - t e m p e r a t u r e a l t e r a t -i o n i s c o n f i n e d t o j o i n t s u r f a c e s ( m a i n l y e p i d o t e ) and t o t h e e a s t - n o r t h e a s t f r a c t u r e z o n e s ( c h l o / t / i t e - a l b i t e , q u a r t z - a l b i t e -e p i d o t e - c h l o r i t e ) . T h u s , a l t h o u g h t h e e n t i r e a r e a has been s u b j . e c t e d t o l a t e p r e h n i t e - p u m p e l l y i t e m e t a m o r p h i s m , p e r v a s i v e a l t e r a t i o n has o c c u r r e d o n l y i n f r a c t u r e s and i n t h e d i k e s w h i c h f i l l them. T h i s a s s o c i a t i o n o f a b u n d a n t l o w - t e m p e r a t u r e p h a s e s w i t h f r a c t u r e s s u g g e s t s t h a t f l u i d c i r c u l a t i o n i n them e x e r t e d a c o n t r o l l i n g i n f l u e n c e on t h e a l t e r a t i o n p r o c e s s . P r e h n i t e - p u m p e l l y i t e f a c i e s m e t a m o r p h i s m a t l o w p r e s s u r e r e q u i r e s t e m p e r a t u r e s b e t w e e n 200\u00C2\u00B0C ( a n a l c i m e + qz = a l b i t e + H 20 - L i o u 1971) and 400\u00C2\u00B0C ( p r e h n i t e b r e a k d o w n - L i o u 1 9 7 0 ) . I f t h e f r a c t u r e s were f o r m e d and t h e d i k e s e m p l a c e d s h o r t l y a f t e r c r y s t a l l i z a t i o n o f t h e p l u t o n t h e r e m a i n i n g h e a t w o u l d have been s u f f i c i e n t t o metamorphose them. T h i s m o d e l i s somewhat p r e f e r a b l e , t o t h a t o f a p o s t - p l u t o n i c b u r i a l - m e t a m o r p h i c e p i s o d e b e c a u s e o f t h e c o n c o r d a n c e o f t h e r a d i o m e t r i c d a t e s ( s e e C h a p t e r I I I ) . The n o r t h e a s t f r a c t u r i n g and d i k e emplacement a r e t h e l a t e s t t e c t o n i c e v e n t s r e c o r d e d i n t h e map a r e a . As t h e y a r e p r o b a b l y r e f l e c t e d i n t h e r a d i o m e t r i c d a t e s on t h e q u a r t z d i o r i t e , no p o s t -125. J u r a s s i c t e c t o n i c e v e n t s o f any s i g n i f i c a n c e a r e s e e n a t t h i s p a r t o f t h e p r o v i n c e b o u n d a r y . I n p a r t i c u l a r t h e r e a r e no n o r t h w e s t - t r e n d i n g f a u l t s o r d i k e swarms t h a t m i g h t be a s s o c i a t e d w i t h a n o r t h w e s t - t r e n d i n g U p p e r C r e t a c e o u s r i f t z o n e . T h i s o f c o u r s e does n o t e l i m i n a t e t h e p o s s i b i l i t y , i t m e r e l y f a i l s t o s u p p o r t i t . 126. SUMMARY OF FIELD RESULTS The h i s t o r y of the map area began with the d e p o s i t i o n of the Vancouver Group - the Karmutsen b a s a l t s , the Quatsino limestone, the limestones and f i n e s i l t s t o n e s of the Parson Bay and Harbledown Formations,and l a s t the v o l c a n i c b r e c c i a s and s i l t s t o n e s of the Bonanza Formation. E x t e n s i v e d i k i n g accompanied both Karmutsen and Bonanza volcanism. F o l l o w i n g t h e i r d e p o s i t i o n , rocks of the Vancouver Group were subjected to p r e h n i t e - p u m p e l l y i t e b u r i a l metamorphism at pressures l e s s than 3 kb. Two e a r l y p l u t o n i c phases have been i d e n t i f i e d at Miner's Bay and on eastern Hardwicke I s l a n d . The main i n t r u s -i o n , a homogeneous quartz d i o r i t e with a gabbroic rim, dated as Eater J u r a s s i c , was probably emplaced along deep west-northwest f r a c t u r e s p a r a l l e l to the Telegraph H i l l and J o h n s t o n e S t r a i t f a u l t s . The Telegraph H i l l F a u l t i s demonstrably p r e - p l u t o n i c . The e x i s t e n c e of these l a r g e f a u l t s provides an e x p l a n a t i o n f o r the anomalous west-northwest trend of the province boundary along J o h n s t o n e S t r a i t . The quartz d i o r i t e produced a thermal aureole about 4 km. wide; maximum temperatures at the contact reached 650\u00C2\u00B0C. I t a l s o generated a l l the important s t r u c t u r e s i n the area except the monoclines between the major f a u l t s and the 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 system, which i s p o s t - p l u t o n i c P o s t - p l u t o n i c dikes i n d i c a t e 5% northwest-southeast e x t e n s i o n , i . e . p a r a l l e l to the r e g i o n a l t e c t o n i c t r e n d . The dikes have been metamorphosed i n p r e h n i t e - p u m p e l l y i t e f a c i e s . They probably predate the 150 m.y. r a d i o m e t r i c age of the quartz d i o r i t e . 127. No s u p p o r t was f o u n d i n t h e a r e a f o r a Lower J u r a s s i c s u t u r e b e t w e e n t h e two p r o v i n c e s ; i n f a c t a r g u m e n t s c a n be made a g a i n s t i t . No s t r o n g p r e - p l u t o n i c d e f o r m a t i o n c a n be demonst-r a t e d and no \" t r e n c h \" s e d i m e n t s o c c u r i n t h e V a n c o u v e r G r o u p . B o n a n z a b r e c c i a s a r e m o n o l i t h o l o g i c and p u r e l y v o l c a n i c ; t h e f i n e g r e y w a c k e s i n t h e H a r b l e d o w n F o r m a t i o n a r e most l i k e l y a c c u m u l a t i o n s o f l o c a l b a s a l t w e a t h e r i n g d e b r i s ( C a r l i s l e and S u z u k i 1 9 7 4 ) . No e v i d e n c e was f o u n d e i t h e r t o s u p p o r t o r r e f u t e t h e e x i s t e n c e o f a n o r t h w e s t - t r e n d i n g r i f t z o n e . The T e l e g r a p h H i l l F a u l t w i t h a maximum s t r a t i g r a p h i c s e p a r a t i o n o f 5000 m e t e r s , and t h e J o h n s t o n e S t r a i t F a u l t w i t h a maximum o f 7000 m e t e r s , a r e t h e o n l y m a j o r t e c t o n i c f e a t u r e s i n t h e a r e a n o t d i r e c t l y r e l a t e d t o t h e i n t r u s i o n . F a u l t s o f s i m i l a r m a g n i t u d e a r e common on V a n c o u v e r I s l a n d . They c a n n o t be s a i d t o c o n s t i t u t e a m a j o r t e c t o n i c b r e a k b e t w e e n t h e I n s u l a r B e l t and t h e C o a s t P l u t o n i c C omplex. I n f a c t t h e most s i g n i f i c a n t f e a t u r e o f t h e b o u n d a r y h e r e i s an i n t r u s i v e c o n t a c t . The p r o v i n c e b o u n d a r y has a l s o been mapped on Quadra I s l a n d by C a r l i s l e and S u z u k i (1965) and on t h e n o r t h e a s t s h o u l d e r o f V a n c o u v e r I s l a n d by K u n i y o s h i (1972) ( F i g u r e 5 ) , who s i m i l a r i l y d e s c r i b e i t as an i n t r u s i v e c o n t a c t . The p l u t o n i c r o c k s i n v o l v e d a r e g e n e r a l l y E a r l y C r e t a c e o u s . M e t a m o r p h i c c o n d i t i o n s r e s e m b l e t h o s e f o u n d h e r e : p r e h n i t e - p u m p e l l y i t e r e g i o n a l m e t a m o r p h i s m p r e c e d e d c o n t a c t m e t a m o r p h i s m on n o r t h e a s t e r n 128. V a n c o u v e r I s l a n d ( K u n i y o s h i 1972) and j u s t w e s t o f t h e p r o v i n c e b o u n d a r y on T e x a d a I s l a n d ( A s i h e n e 1 9 7 0 ) . K u n i y o s h i d e t e r m i n e d a t o t a l p r e s s u r e o f a p p r o x i m a t e l y 2 kb. ; A s i h e n e , a s s u m i n g 2 kb . , e s t i m a t e d a maximum c o n t a c t m e t a m o r p h i c t e m p e r a t u r e o f 700\u00C2\u00B0C. On Q u a d r a I s l a n d i n t e n s e p r e - p l u t o n i c d e f o r m a t i o n - f o l d i n g o f t h e l i m e s t o n e s and f o l i a t i o n i n t h e m e t a v o l c a n i c s - was i n t e r p r e t e d by C a r l i s l e as due to r e g i o n a l d e f o r m a t i o n i n a s h e a r zone e x t e n d i n g o n t o V a n c o u v e r I s l a n d ( K u n i y o s h i 1 9 7 2 ) . On H a r d w i c k e and West T h u r l o w I s l a n d s t h e f o l i a t i o n and i n t e n s e f o l d i n g a r e i n t e r p r e t e d as due t o f o r c i b l e i n t r u s i o n . No n o r t h -w e s t r e g i o n a l d e f o r m a t i o n i s e v i d e n t p r i o r t o t h e w e s t - n o r t h w e s t s y n p l u t o n i c p h a s e . The c a s e o f H a r d w i c k e and West T h u r l o w I s l a n d s p o i n t s o u t t h e i m p o r t a n c e o f i n t r u s i o n - r e l a t e d d e f o r m a t i o n , w h i c h may be o f s i g n i f i c a n c e e l s e w h e r e a l o n g t h e p r o v i n c e b o u n d a r y . T h i s f i e l d s t u d y has v e r i f i e d on a s m a l l s c a l e what i s a p p a r e n t on l a r g e - s c a l e g e o l o g i c maps, t h a t t h e b o u n d a r y b e t w e e n t h e I n s u l a r B e l t and t h e C o a s t P l u t o n i c Complex i s s i m p l y t h e w e s t e r n l i m i t o f v o l u m i n o u s i n t r u s i o n . W h i l e t h i s l i m i t may i n p a r t be c o n t r o l l e d by f a u l t s , i t i s e s s e n t i a l l y D i c k i n s o n ' s m a g m a t i c f r o n t ( 1 9 7 1 ; 1 9 7 3 ) . I t has shown so f a r t h a t G e o r g i a D e p r e s s i o n l i e s w e s t o f a m a i n l y E a r l y C r e t a c e o u s m a g m a t i c f r o n t , and t h a t t h e d e p r e s s i o n f o r m e d i n t h e . U p p e r C r e t a c e o u s , t e n t a t i v e l y as a complement t o t h e u p l i f t o f t h e C r e t a c e o u s a r c . I t has been p r o p o s e d t h a t t h e w h o l e C o a s t a l T r o u g h has had a common mode o f o r i g i n . I f s o , i t t o o s h o u l d l i e . . i m m e d i a t e l y w e s t o f m a g m a t i c a r c s and 129. f o r m a t t h e same t i m e t h a t t h e y r o s e . I n t h e f o l l o w i n g s e c t i o n s on H e c a t e D e p r e s s i o n , t h e P u g e t and W i l l i a m e t t e L o w l a n d s and t h e G r e a t V a l l e y t h e s e r e l a t i o n s h i p s w i l l be e s t a b l i s h e d . 130. SECTION I I I : THE COASTAL TROUGH CHAPTER V I I : GEOLOGIC SETTING OF THE COASTAL TROUGH i . H e c a t e D e p r e s s i o n H e c a t e D e p r e s s i o n i s t h e n o r t h e r n m o s t s u b - b a s i n o f t h e C o a s t a l T r o u g h . L i k e G e o r g i a D e p r e s s i o n i t l i e s a c r o s s t h e C o a s t P l u t o n i c C o m p l e x / I n s u l a r B e l t b o u n d a r y . The e x a c t p o s i t i o n o f t h e p r o v i n c e b o u n d a r y u n d e r H e c a t e S t r a i t i s u n c e r t a i n . T r i a s s i c and J u r a s s i c v o l c a n i c s , i n c l u d i n g p r o b a b l e K a r m u t s e n e q u i v a l e n t s , o c c u r n e a r P r i n c e R u p e r t ( S k e e n a R i v e r 1 : 1,000,000 map s h e e t H u t c h i s o n e t a l . 1 9 7 3 ) . They may r e p r e s e n t t h e e a s t e r n m a r g i n o f t h e I n s u l a r B e l t , i n w h i c h c a s e i t e x t e n d s c o n s i d e r a b l y e a s t o f t h e a x i s o f t h e d e p r e s s i o n , as i t does u n d e r G e o r g i a S t r a i t . The p a l e o g e o g r a p h i c e v o l u t i o n o f H e c a t e D e p r e s s i o n i s n o t w e l l known. Most o f i t l i e s u n d e r w a t e r and i s o n l y a c c e s s i b l e t o d r i l l i n g and s e i s m i c m e t h o d s . The a d j a c e n t C o a s t M o u n t a i n s have b e e n mapped on a r e g i o n a l s c a l e by t h e G e o l o g i c a l S u r v e y ( H u t c h i s o n 1970; B a e r 1 973; R o d d i c k and H u t c h i s o n 1 9 7 4 ) . However s t r a t i f i e d i n l i e r s a r e t o o s c a r c e t o s u p p o r t a d e t a i l e d h i s t o r y . The Queen C h a r l o t t e I s l a n d s h a v e b e e n mapped on a r e g i o n a l s c a l e by S u t h e r l a n d Brown ( 1 9 6 8 ) . The T r i a s s i c to m i d - C r e t a c e o u s h i s t o r y o f t h e Queen C h a r l o t t e s r e s e m b l e s t h a t o f t h e s o u t h e r n I n s u l a r B e l t ( F i g u r e 4 2 ) . The Lower t o M i d d l e C r e t a c e o u s c l a s t i c s e q u e n c e s - t h e Longarm F o r m a t i o n and Queen C h a r l o t t e Group -a r e c h r o n o l o g i c a l l y and l i t h o l o g i c a l l y e q u i v a l e n t t o t h o s e on 1>lw-?kJs1ouni J Toctnt CrUacams J Turassic Iriassic-Qtrni i an yancouvcr is. (Alert lay) NANAIMO Grip-^UEEN_^CttA1J.L0TTE Grp. Qtmsylyimcin RM T^n. ^BONANZA Tjn. B A U S O N B*Y/QlMT5mo middle Triassic nrq. QH.OVV .1.31 'MASS-ET Tn, basalt/Thy oUtc Q U E E N C H A R L O T T E Q-rp. JjOHQAHhA olc-std-Sutherland Iraym i%% \u00E2\u0080\u00A2Shouldiu 13J1 I D yUulUrttal 1974 Comparative Jnsular mt Stratigraphies 132. V a n c o u v e r I s l a n d , b u t w h i l e t h e Queen C h a r l o t t e Group on V a n c o u v e r I s l a n d seems t o be d e r i v e d f r o m an e a r l y I n s u l a r B e l t u p l i f t ( M u l l e r a t a l - 1 9 7 4 ) , s e d i m e n t p a t t e r n s i n t h e Queen C h a r l o t t e s a r e more c o m p l e x and i n s u f f i c i e n t l y s t u d i e d ( S u t h e r l a n d Brown 1 9 6 8 ) . The p r e s e n c e o f M i d d l e C r e t a c e o u s l a n d i n t h e p l a c e o f H e c a t e D e p r e s s -i o n has y e t t o be e s t a b l i s h e d . H e c a t e D e p r e s s i o n p r o b a b l y d i d n o t d e v e l o p a t t h e same t i m e as G e o r g i a D e p r e s s i o n . T h e r e i s n o t known e q u i v a l e n t o f t h e Nanaimo Group e i t h e r on t h e Queen C h a r l o t t e s o r b e l o w H e c a t e S t r a i t , so f a r as c a n be a s c e r t a i n e d f r o m w e l l and s e i s m i c r e f l -e c t i o n d a t a ( S h o u l d i c e 1 9 7 1 ) , a l t h o u g h t h e S k i d e g a t e F o r m a t i o n ( u p p e r Queen C h a r l o t t e Group) may e x t e n d i n t o t h e U p p e r C r e t a c e o u s ( M u l l e r p e r s comm. 1 9 7 6 ) . A p r e - T e r t i a r y u n c o n f o r m i t y s e p a r a t e s t h e P a l e o c e n e - E o c e n e M a s s e t V o l c a n i c s f r o m a l l o t h e r f o r m a t i o n s . The M a s s e t V o l c a n i c s t h e m s e l v e s a r e p r e d o m i n a n t l y c o n t i n e n t a l . On t h e e a s t e r n Queen C h a r l o t t e s and u n d e r H e c a t e S t r a i t t h e y a r e o v e r l a i n , a g a i n u n c o n f o r m a b l y , by Upper M i o c e n e and P l i o c e n e m a r i n e and n o n - m a r i n e s e d i m e n t s o f t h e Skonun F o r m a t i o n , t h e f i r s t c l e a r i n d i c a t i o n o f a c o a s t a l t r o u g h i n n o r t h e r n B r i t i s h C o l u m b i a ( F i g u r e 4 3 ) . The M a s s e t v o l c a n i c s and t h e e r o s i o n s u r f -a c e s on t o p o f them d i p . g e n t l y i n t o H e c a t e D e p r e s s i o n . The o v e r -l y i n g Skonun F o r m a t i o n t h i c k e n s b a s i n w a r d s ; i t c h a n g e s f r o m d o m i n a n t l y c o n t i n e n t a l t o d o m i n a n t l y m a r i n e i n a s e r i e s o f w e l l s f r o m n o r t h e r n Graham I s l a n d s o u t h e a s t i n t o H e c a t e S t r a i t ( S h o u l d i c e 1 9 7 1 ) . S u t h e r l a n d Brown (1968) d e s c r i b e s t h e M i o - P l i o c e n e b a s i n as \" . . . m o d e r a t e l y r a p i d l y s i n k i n g . . . p o s s i b l y f a u l t c o n t r o l l e d a t i t s e a s t e r n and n o r t h e r n m a r g i n s . . . f i l l e d t o c a p a c i t y w i t h d e t r i t -us f r o m t h e p r o t o - Q u e e n C h a r l o t t e I s l a n d s and p r o b a b l y t h e M a i n l a n d . \" 133, distribution oj thtr^ 5konunc7m . \u00E2\u0080\u00A2o \u00E2\u0080\u00A2 wtM Locutions after ShouUfct 0 ' \u00C2\u00B0 O' .o 134. Two e v e n t s i n t h e h i s t o r y o f t h e C o a s t P l u t o n i c C o mplex nee d t o be e m p h a s i z e d h e r e - t h e d a t e s o f i n t r u s i o n and t h e t i m i n g o f u p l i f t . P o t a s s i u m - a r g o n d a t e s f o l l o w an e a s t w a r d y o u n g i n g t r e n d f r o m E a r l y C r e t a c e o u s t o E o c e n e (Woodsworth p e r s . comm.), l i k e t h o s e i n t h e s o u t h e r n C o a s t M o u n t a i n s . E i s b a c h e r (1974) a t t r i b u t e s p r e - C e n o m a n i a n d e f o r m a t i o n o f t h e Bowser Group and t h e a d v e n t o f w e s t e r l y - d e r i v e d e l a s t i c s i n t o t h e S u s t u t B a s i n 54 m.y. ago t o p u l s e s o f u p l i f t i n t h e n o r t h e r n C o a s t P l u t o n i c C o mplex. The l a t e s t p h a s e has i n v o l v e d as much as 1000 m e t e r s of u p l i f t o f M i o c e n e e r o s i o n s u r f a c e s ( B a e r 1 9 7 3 ) ; i t i s r o u g h l y c o e v a l w i t h t h e d e p o s i t i o n o f t h e Skonun F o r m a t i o n . H e c a t e and G e o r g i a D e p r e s s i o n s , w h i l e o c c u p y i n g s i m i l a r p o s i t i o n s w i t h r e s p e c t t o t h e t e c t o n i c b e l t s , a r e n o t t i m e -e q u i v a l e n t . G e o r g i a D e p r e s s i o n f o r m e d i n t h e Upp e r C r e t a c e o u s w h i l e t h e C o a s t P l u t o n i c Complex was an a c t i v e m a g m a t i c a r c . H e c a t e D e p r e s s i o n f o r m e d i n t h e Upper M i o c e n e , l o n g a f t e r p l u t -o n i s m had c e a s e d . Y e t b o t h a c c o m p a n i e d s i g n i f i c a n t p u l s e s o f u p l i f t o f t h e C o a s t P l u t o n i c Complex'. i i . The P u g e t and W i l l i a m e t t e D e p r e s s i o n s The f i r s t e v i d e n c e f o r a c o a s t a l t r o u g h i n w e s t e r n W a s h i n g t o n and O r e g o n i s i n t h e Upper M i o c e n e , c o n t e m p o r a r y w i t h t h e b e g i n n i n g of u p l i f t o f t h e C a s c a d e s . The p r e s e n t t r o u g h c o m p r i s e s two e l o n g a t e d e p r e s s i o n s , t h e P u g e t and W i l l i a m e t t e L o w l a n d s ( F i g u r e 4 4 ) . They a r e bounded on t h e e a s t by t h e C a s c a d e Range and on t h e w e s t by t h e C o a s t Ranges and O l y m p i c M o u n t a i n s . T h e s e f l a n k -i n g r a n g e s b e l o n g t o two d i s t i n c t g e o t e c t o n i c p r o v i n c e s ( F i g u r e s 135. 1 3 6 . 45 and 4 6 ) . The C o a s t Range P r o v i n c e i n c l u d e s b o t h t h e C o a s t Ranges and most o f t h e C o a s t a l T r o u g h . The C a s c a d e P r o v i n c e c o i n c i d e s w i t h the C a s c a d e Range, an u p l i f t e d C e n o z o i c magmatic a r c . The backbone of t h e C o a s t Ranges i s a n o r t h - s o u t h t r e n d i n g c h a i n of Eocene v o l c a n i c c e n t e r s w h i c h p r o d u c e d the v o l u m i n o u s t h o l e i i t i c and a l k a l i c b a s a l t s of the S i l e t z R i v e r , C r e s c e n t , M e t c h o s i n and Umpqua F o r m a t i o n s . C h e m i c a l l y t h e y r e s e m b l e m i d - o c e a n r i d g e and o c e a n i s l a n d b a s a l t s ( S n a v e l y and Wagner 1968). The Eocene b a s a l t s i n t e r t o n g u e w i t h and a r e o v e r l a i n by m i d d l e Eocene to P l e i s t o c e n e c l a s t i c s e d i m e n t s . The s e d i m e n t s a r e d e r i v e d b o t h from w i t h i n t h e C o l u m b i a n Embayment and from i t s p r e - C e n o z o i c m a r g i n s , t h e K l a m a t h M o u n t a i n s and t h e I n s u l a r B e l t . T u f f s and t u f f a c e o u s s e d i m e n t s from t h e C a s c a d e P r o v i n c e form an i m p o r t a n t p a r t of t h e s e c t i o n , p a r t i c u l a r i l y t h e O l i g o -cene ( S n a v e l y and Wagner 1963). A f t e r t h e E o c e n e , f l o w s and i n t r u s i o n s w i t h i n t h e C o a s t Range P r o v i n c e become r a r e . The C a s c a d e P r o v i n c e i s a n o r t h - s o u t h t r e n d i n g l i n e a r v o l c -a n i c b e l t a p p r o x i m a t e l y 150 km. wide l y i n g a bout 200 to 250 km. from t h e w e s t e r n edge of the N o r t h A m e r i c a n p l a t e . I t may be s u p e r i m p o s e d on Eocene C o a s t Range P r o v i n c e r o c k s ( S n a v e l y and Wagner 1963; B a l d w i n 1964). I t s n o r t h e r n end l a p s onto t h e p r e -T e r t i a r y N o r t h C a s c a d e s , i t s s o u t h e r n end onto t h e K l a m a t h s . W h i l e C a s c a d e v u l c a n i s m spans the e n t i r e C e n o z o i c e r a s i n c e t h e m i d d l e E o c e n e , i t has been d i s t i n c t l y e p i s o d i c . ( S u t t e r and Mc-B i r n e y 1974; M c B i r n e y et a l 1 9 7 4 ) . A n d e s i t e i s most abundant w i t h l e s s e r amounts of b a s a l t , d a c i t e and r h y o d a c i t e . C h u r c h and C O A S T H A N O I P R O V I N C E C T t c j 4 f ?|iOC(H( leant ~ ~ 12. \u00E2\u0080\u00A2\u00E2\u0080\u00A2iVCWiii T i l TWm Hivir T m . v y y v y v y v ' \u00C2\u00AB Cv\u00C2\u00AB t\u00C2\u00AB\u00C2\u00AB lTFin. w v \" * ' \u00E2\u0080\u00A2 y \" . \u00C2\u00A3incoin Cruh. O'm. y y y y ^ v * C w\u00C2\u00ABnf? \u00C2\u00BB i .v * \u00C2\u00BB v y v y y V V V V V \u00E2\u0080\u009E r v y \u00E2\u0080\u009E \u00E2\u0080\u009E ;Vr~v:.-=\u00C2\u00BB.*.-;'*;-=f-: \u00E2\u0080\u00A2 t \u00E2\u0080\u0094 V 4 V V \u00C2\u00AB\u00C2\u00BB \u00C2\u00BB 4 <) XtllKttvi AnAlllit \" v , <\u00E2\u0080\u00A2\u00E2\u0080\u00A2 Scrtts o \u00E2\u0080\u00A2 \" o * * a \u00E2\u0080\u00A2\u00C2\u00AB \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 ' 1 5 ' ' ic y v. v* - ' ^ \u00C2\u00BB t y t \u00E2\u0080\u00A2 >' '\u00E2\u0080\u00A2'.'\u00E2\u0080\u00A2(Juye 'Pin.'\". * / \":V SouRCf J : Tabor CH7i) 1Uu CU67) \u00C2\u00BB y < \u00E2\u0080\u00A2t 1 + \u00E2\u0080\u00A2 (\u00E2\u0080\u00A2 o.a-M r | 1 ^ I + OT\u00C2\u00AB\u00C2\u00BB\u00C2\u00BB\u00C2\u00AB\u00C2\u00ABi\u00C2\u00AB'ir7\u00C2\u00BB>'. w .. ' y y y s/ lithologic chart = western \"Wash.. l* jyrvilistits 4*. \u00E2\u0080\u00A2 SlOilout ^= Anil/ Jinutc I -C0AS1 HANOI - syiiuiAMmi ^njyiNcE \u00E2\u0080\u0094 on. Central coai\id tmx Southern CMitOtna: y/illkmiHi ixlUy CiiUdt 'TUyai QltiillttM * \u00E2\u0080\u00A2..:#.*.\u00E2\u0080\u00A2 T-l . \u00C2\u00BB 1 y v < v ^ v \u00E2\u0080\u00A2 v y'8grm(|\"\"Uwvv'yvv v-'E-nipire T=w-^:;\" ^. / \u00E2\u0080\u00A2\u00E2\u0080\u00A2\u00E2\u0080\u00A2\u00E2\u0080\u00A2 ;/Tr(>uti*U.7rtu. ; . * \u00C2\u00AB \u00E2\u0080\u00A2/Caftan ~r \u00E2\u0080\u00A2 v y ' ^ v v y v V V -ns 37 5S \u00E2\u0080\u009E Sihlf.'Kpk- V , V/V Vf v v v, * v\u00E2\u0080\u0094*\u00E2\u0080\u0094* \u00E2\u0080\u00A2 v v\"v V v \"V V V V X i t h o l o g i c c h a r t = w e s t e r n Oregon \u00C2\u00AB\u00E2\u0080\u00A2 V Vv, u p. d o t s \u00E2\u0084\u00A2fc 140, T i l t o n (1972) have used lead i s o t o p i c r a t i o s and low, r e l a t i v e l y constant Sr87/Sr86 (.7037 ave.) i n P l e i s t o c e n e Cascade v o l c a n i c s to support a s u b c r u s t a l o r i g i n . In a d d i t i o n to v o l c a n i c s , Miocene i n t r u s i o n s ( g r a n o d i o r i t e with subordinate d i o r i t e , quartz monzonite, g r a n i t e , etc.) are exposed i n the Washington Cascades. The boundary between the Cascade and Coast Range Provinces ( i . e . the western l i m i t of Cascade volcanism) l i e s w i t h i n the C o a s t a l Trough. I t s exact p o s i t i o n i s l a r g e l y obscured by d r i f t and a l l u v i u m . In places i t i s expressed as a vol c a n i c / s e d i m e n -tar y f a c i e s change near the eastern s i d e of the trough. In King County, Washington, T e r t i a r y v o l c a n i c rocks, mostly andesite b r e c c i a s and flows, extend westward to the Cascade f o o t h i l l s ( L i v i n g s t o n 1971). T e r t i a r y sediments, arkose, v o l c a n i c sand, t u f f , c l a y and c o a l , predominate i n the Puget Lowland. The t r a n s i t i o n ( f o r example the zone of i n t e r f i n g e r i n g between Eocene and Puget Group sediments and the Keechelus V o l c a n i c S e r i e s ) occurs near the eastern margin^of the lowland and i n the Cascade f o o t h i l l s . The p o s i t i o n of the v o l c a n i c f r o n t i n the Miocene i s not as w e l l bracketed as the Eocene. Cascade s t r a t -igraphy i s not yet p r e c i s e enough to d e f i n e the western l i m i t of Miocene v o l c a n i c s ; however i t must have l a i n between the westernmost exposure of Miocene Snoqualmie G r a n o d i o r i t e f i v e k i l o m e t e r s east of North Bend and sediments of the Miocene Hammer B l u f f Formation (Glover 1936) along the Green River south of Black Diamond. 1 4 1 -The O l i g o c e n e v o l c a n i c f r o n t i n O r egon i s e x p o s e d on t h e e a s t e r n s i d e o f t h e W i l l i a m e t t e L o w l a n d . The Eugene F o r m a t i o n ( M i d d l e O l i g o c e n e ) and t h e B u t t e C r e e k beds ( U p p e r O l i g o c e n e ) , o u t c r o p p i n g w i t h i n t h e L o w l a n d , a r e p r e d o m i n a n t l y m a r i n e v o l c a n i c s a n d s t o n e and w a t e r l a i n t u f f . They i n t e r f i n g e r a l o n g i t s e a s t e r n s i d e w i t h t h e Mehama V o l c a n i c s , a s e r i e s o f a n d e s i t i c and d a c i t i c t u f f s , b r e c c i a s , and f l o w s ( B a l d w i n 1964; B e a u l i e u 1 9 7 1 ) . T h e s e e x a m p l e s s h o u l d n o t be t a k e n t o i m p l y t h a t t h e w e s t e r n l i m i t o f C a s c a d e v o l c a n i s m r e m a i n e d f i x e d a t t h e e a s t e r n edge o f t h e p r e s e n t C o a s t a l T r o u g h . I t i s e v i d e n t f r o m p a l e o g e o -g r a p h i c r e c o n s t r u c t i o n s ( S n a v e l y and Wagner 1963) t h a t t h e p o s i t i o n o f t h e v o l c a n i c f r o n t v a r i e d w i t h t i m e . However o n l y i n f r e q u e n t l y and o n l y i n p l a c e s d i d i t a d v a n c e w e s t o f t h e f r o n t o f t h e C a s c a d e Range, w h i c h a c c o r d i n g l y c o r r e s p o n d s t o a s i g n i f i c a n t d e c r e a s e i n v o l c a n i c v o l u m e . The l o c a t i o n o f t h e C o a s t a l T r o u g h , t h e n , i s l i n k e d t o t h e d i s t r i b u t i o n o f C a s c a d e v o l c a n i c s . B u t w h i l e C a s c a d e v o l c a n i s m b egan i n t h e M i d d l e E o c e n e , t h e f i r s t e v i d e n c e f o r a n o r t h - s o u t h t r e n d i n g d e p r e s s i o n on t h e s i t e o f t h e p r e s e n t t r o u g h i s shown by t h e d i s t r i b u t i o n o f t h e C o l u m b i a B a s a l t w e s t o f t h e C a s c a d e s and t h e f l u v i a l - l a c u s t r i n e W i l k e s F o r m a t i o n ( F i g -u r e 4 7 ) . The C o l u m b i a B a s a l t s a r e d a t e d as 13-16 m.y. ( M c B i r n e y e t a l . 1 9 7 4 ) ; t h e W i l k e s F o r m a t i o n i s ftpper M i o c e n e and p o s s i b l y P l i o c e n e ( R o b e r t s 1958) . S i n k i n g o f t h e t r o u g h a c c o m p a n i e d u p l i f t o f t h e C a s c a d e s . As t h e C a s c a d e s r o s e t h e y became a b a r r i e r t o m o i s t u r e f r o m t h e P a c i f i c Ocean. The p r o g r e s s i v e l o w e r i n g o f r a i n f a l l e a s t o f tr CMiocenc -paleoaeoaraj tht Columbian Ir/ibavmcvui: -Jj'nav&iy and, Wayncr 1J)63 143. the Cascades caused an e v o l u t i o n of the f l o r a from moist-to-dry c l i m a t e assemblages. The f i r s t m a n i f e s t a t i o n of t h i s trend i s i n the Upper Miocene M a s c a l l f l o r a , which shows a decrease i n abundance of Metasequoia from e a r l i e r f l o r a s (Chaney 1925). The x e r i c trend culminated i n the middle P l i o c e n e ( D e t l i n g 1968). D i s t r i b u t i o n of the P l i o c e n e T r o u t d a l e Formation provides and estimate of . the amount of d i f f e r e n t i a l movement between the Oregon Cascades and the W i l l i a m e t t e Lowland i n the l a t e P l i o c e n e -P l e i s t o c e n e . F l u v i a l i n o r i g i n , i t i s i n t e r p r e t e d as the remains of a P l i o c e n e Columbia River a l l u v i a l p l a i n which extended from the P o r t l a n d Basin eastward to The D a l l e s (Baldwin 1964). Near P o r t l a n d the Tr o u t d a l e Formation outcrops a few hundred f e e t above sea l e v e l ; at Nesmith Point above the Columbia Gorge i t has been el e v a t e d to 700 meters ( A l l e n 1958). The Oregon Coast Ranges have a l s o r i s e n markedly i n the l a t e Cenozoic. P l e i s t o c e n e beach t e r r a c e s l i e as much as 300 meters above sea l e v e l (Baldwin 1964) . P 1 i o - P l e i s t o c e n e u p l i f t of the Cascades i n c e n t r a l Washington exceeds 1500 meters (McKee 1972). The great t h i c k n e s s of Quat-ernary sediments near S e a t t l e , more than 500 meters (Rogers 1970), a t t e s t s to c o n s i d e r a b l e s i n k i n g of the Puget Lowland. The ques t i o n of warping versus f a u l t i n g i s not e a s i l y r e s o l v e d : examples of both can be found. The Columbia B a s a l t s along the Columbia River Gorge form a simple upwarp of 1000 meters amplitude, somewhat modified by open f o l d s and minor f a u l t s . The g e o l o g i c p r o f i l e across northwestern Oregon by Wells and Peck (1961) shows the Coast Range-Williamette Lowland-Cascade Range as upwarp-down-144. w a r p - u p w a r p ; however t h e d i s c o n t i n u i t y o f u n i t s a c r o s s t h e L o w l a n d may o b s c u r e s i g n i f i c a n t f a u l t s . B r o m e r y and S n a v e l y ( 1 9 6 4 ) i n f e r t h e p r e s e n c e o f a m a j o r n o r m a l f a u l t f r o m s t e e p g r a v i t y g r a d i e n t s on t h e w e s t e r n s i d e o f t h e W i l l i a m e t t e L o w l a n d . B e a u -l i e u ( 1971) p o i n t s o u t t h a t l a r g e f a u l t s a r e p o s s i b l e a l o n g t h e e a s t e r n m a r g i n o f t h e L o w l a n d . N e a r S e a t t l e t h e c a s e i s c l e a r e r f o r f a u l t c o n t r o l . The w e s t f a c e of Mount S i i s a f a u l t s c a r p o f c o n s i d e r a b l e m a g n i t u d e ( R o g e r s 1 9 7 0 ) ; t h e Mount S i f a u l t c a n be t r a c e d n o r t h t o t h e San J u a n s . E a r t h q u a k e s a l o n g i t demon-s t r a t e c o n t i n u e d m o t i o n ( D a n n e r p e r s . comm. 1 9 7 5 ) . A c c o r d i n g t o Danes e t a l . ( 1 9 6 5 ) , t h e Hood C a n a l L i n e a m e n t i s a m a j o r f a u l t b e t w e e n t h e P u g e t L o w l a n d and t h e O l y m p i c M o u n t a i n s . R o g e r s (1970) i n t e r p r e t s t h e B o u g u e r g r a v i t y f i e l d i n t h e P u g e t L o w l a n d as t h e e x p r e s s i o n o f l a r g e f a u l t b l o c k s c o n c e a l e d by a l l u v i u m and d r i f t . He c o u l d n o t d e t e r m i n e wwhether t h e s e d i m e n t s w e re i n v o l v e d i n f a u l t i n g o r m e r e l y d r a p e d o v e r basement b l o c k s . S i n c e h i s work s e v e r a l P l e i s t o c e n e - R e c e n t f a u l t s c a r p s have b e e n i d e n t i f i e d n e a r t h e Hood C a n a l L i n e a m e n t and n e a r S e a t t l e ( L i v i n g s t o n , Gower 1 9 7 5 ) . The P u g e t and W i l l i a m e t t e L o w l a n d s f i t t h e m o del f o r t h e C o a s t a l T r o u g h s u g g e s t e d by G e o r g i a and H e c a t e D e p r e s s i o n s . They l i e i m m e d i a t e l y w e s t o f t h e C a s c a d e v o l c a n i c f r o n t . They have f o r m e d s i m u l t a n e o u s l y w i t h t h e u p l i f t o f t h e C a s c a d e Range. The C o a s t Range a l s o r o s e a t t h e same t i m e , m a k i n g t h e t r o u g h an a r e a o f s u b s i d e n c e b e t w e e n two a c t i v e u p l i f t s . I t i s s i g n i f i c a n t t o n o t e t h a t b o t h f a u l t i n g and w a r p i n g were i n v o l v e d . v 1 4 5 . i i i . The G r e a t V a l l e y The G r e a t V a l l e y of C a l i f o r n i a i s a g e n t l e s y c l i n o r i u m o f U pper M e s o z o i c and C e n o z o i c s e d i m e n t s . On t h e e a s t t h e y o n l a p o n t o t h e S i e r r a N e v a d a , an u p l i f t e d J u r a - C r e t a c e o u s c o m p o s i t e m a g m atic a r c . On t h e w e s t t h e y a r e i n p r o b a b l e f a u l t c o n t a c t w i t h t h e F r a n c i s c a n t e r r a n e , an 1 a r c h t y p i c a l t r e n c h c o m p l e x (Hsu 1971; E r n s t 1 9 7 1 ) . The C r e t a c e o u s G r e a t V a l l e y i s one o f t h e e x a m p l e s o f a r c - t r e n c h gaps c i t e d by D i c k i n s o n ( 1 9 7 1 ) , a zone of t e c t o n i c q u i e t b e t w e e n t h e a r c and t h e t r e n c h . The b a s a l u n i t of t h e G r e a t V a l l e y S e q u e n c e i s t h e T i t h o n i a n K n o x v i l l e F o r m a t i o n , w h i c h marks t h e b e g i n n i n g o f s u b s i d e n c e . A t t h e same t i m e t h e G r e a t V a l l e y a l s o became an a r c - t r e n c h gap ( F i g u r e 4 8 ) . T h e r e i s e v i d e n c e f o r a d i f f e r e n t a r c - t r e n c h c o n f i g u r a t i o n p r i o r t o t h a t t i m e . V o l c a n i c f l o w s , p y r o c l a s t i c d e b r i s and m a r i n e v o l -c a n i c s e d i m e n t s r a n g i n g i n age f r o m M i d d l e T r i a s s i c t o K i m m e r i d -g i a n a r e e x p o s e d i n t h e K l a m a t h M o u n t a i n s and t h e S i e r r a N e v a d a . They were s e v e r e l y d e f o r m e d and m e t a m o r p h o s e d i n K i m m e r i d g i a n -T i t h o n i a n t i m e . A peak i n p l u t o n i c d a t e s , 158-132 m.y. ( L a n p h e r e and Reed 1 9 7 3 ) , c o i n c i d e s w i t h t h i s l a t e J u r a s s i c t e c t o n i c e p i s o d e . M o o r e s (1972) i n t e r p r e t s t h e e v e n t as t h e r e s u l t o f an a r c - a r c c o l l i s i o n . S c h w e i c k e r t and Cowan(1974) e n v i s a g e a T r i a s s i c - J u r a s s i c t r e n c h i m m e d i a t e l y w e s t o f t h e S i e r r a n f o o t h i l l s w h i c h became c h o k e d and s t e p p e d o u t w a r d t o t h e F r a n c i s a n a b o u t 150 m i l l i o n y e a r s ago. The b e g i n n i n g of s u b s i d e n c e of t h e G r e a t V a l l e y a l s o c o i n c i d e d w i t h t h e i n i t i a l u p l i f t o f t h e S i e r r a n a r c above w a v e b a s e : t h e y o u n g e s t m a r i n e s e d i m e n t s i n t h e S i e r r a < T i j 4 8 Upper Jurassic. ~ Lower Cretaceous events * western California COAST R A N G E S S I E R R A S G R E A T VALLEY loo my. no no 130 HO y -Aptkn fdarrtm\an Jfautcrivian 'Valanqinian 73trriKSian Titiwnian cKimmmdflian, 150-oidat flimxptwn*-Oxjordianr l 6 0 Cailovicuv ijo \u00E2\u0080\u0094subsidtvet btflivs 1N = \u00C2\u00AB-oy C7ij\u00E2\u0080\u00A2 52-km bltow S-t-10 4 *5H % ; upper wtmUt *>* * 7-96 jo-Crustal thicknesses beneath western 'M/ash. (projected, onto tht 2A5\u00C2\u00B0 refraction Live of 'Johnson nvd Couch 13JO) 1 5 6 . t h i c k e n i n g , t o l i g h t e n i n g o f t h e l i t h o s p h e r e , o r b o t h . The f r e e a i r a n o m a l i e s show an a p p a r e n t mass e x c e s s a s s o c i a t e d w i t h t h e C o a s t Ranges w h i c h T h i r u v a t h u k a l e t a l . (1970) a t t r i b u t e e i t h e r t o d e n s e n e a r - s u r f a c e r o c k s o r s h a l l o w m a n t l e o r b o t h . The W i l l i a m e t t e D e p r e s s i o n and t h e C a s c a d e s l i e i n a zone o f n e g a t i v e f r e e - a i r a n o m a l i e s w h i c h may i n d i c a t e l i g h t c r u s t , l i g h t m a n t l e , o r a mass d e f i c i e n c y i n t h e t o t a l c o l u m n . The P u g e t L o w l a n d i s r e m a r k a b l e i n s e v e r a l r e s p e c t s . I t l i e s e a s t o f t h e O l y m p i c s , t h e h i g h e s t and most d e f o r m e d s e c t i o n o f t h e C o a s t R a n g e s ; i t i s u n d e r l a i n by as much as 10 km. o f s e d i m e n t s , and i t i s c h a r a c t e r i z e d by l a r g e d e l a y s i n s e i s m i c a r r i v a l s and one o f t h e l a r g e s t B o u g u e r / f r e e - a i r l o w s i n t h e w o r l d ( W o o l l a r d 1 9 6 9 ) . F i g u r e 5 3, a f t e r Danes ( 1 9 6 9 ) , shows t h i s l o w f l a n k e d by f r e e - a i r h i g h s o v e r t h e C o a s t Ranges and t h e C a s c a d e s . Danes b e l i e v e s t h a t t h e a n o m a l i e s a r e m a i n t a i n e d by h y d r o d y n a m i c s t r e s s e s w h i c h c o u n t e r t h e t e n d e n c y of P u g e t L o w l a n d t o r i s e and t h e a d j a c e n t r a n g e s t o s i n k . i i i . C a l i f o r n i a The c r u s t a l s t r u c t u r e o f w e s t e r n C a l i f o r n i a i s s t i l l s u b j e c t t o m a j o r u n c e r t a i n t i e s . ' E a t o n ( 1 9 6 6 ) , b a s e d on p r o f i l e s a l o n g and a c r o s s s t r i k e , has d e t e r m i n e d a 50 km. r o o t u n d e r t h e S i e r r a N evada. C a r d e r ( 1 9 7 0 , 1973) i n t e r p r e t e d e a r l y a r r i v a l t i m e s a c r o s s t h e S i e r r a s f r o m t h e Nevada T e s t S i t e as e v i d e n c e a g a i n s t a deep r o o t . P a k i s e r . (1974) has r e i n t e r p r e t e d C a r d e r ' s d a t a t o be c o m p a t i b l e w i t h t h i c k e n e d c r u s t u n d e r t h e S i e r r a s . 157 . ria.55 Jsostatlc anomaly map \"^Vashifwtoru \u00E2\u0080\u00A2~L)an\u00C2\u00A3S Wi Tia 2. . i n f B \u00C2\u00BB \u00C2\u00BB C I S C O I H O t P O U T Chjjl 158 F \u00C2\u00BB u o a I H O T r o i m iHoil moi mini a.. Seismic profile across western California. b.ZModd of tht crust under '\" California, from 73oujuer momaliis - Chapman 1%G \w-R\u00C2\u00A3GIONAL GRAVITY ANOMALY TOTAL GRAVITY ANOMALY -rpr-in 0 S1CRAUENT0 S H E L F , C C * i S T | V A L L E Y i S I E R P A | B A S I N A N O R A N G E | R A N \u00C2\u00AB \u00C2\u00A3 S ] I N E V A 0 4 * . ! ! ! / * /\"2-zr j ~r -400, -loo o too 0 I S T A . 1 C C i * K M 159. F i g u r e 54a f r o m E a t o n ( 1 966) shows two a l t e r n a t e i n t e r p r e t a t i o n s o f e a r l y P^ a r r i v a l s a c r o s s t h e G r e a t V a l l e y . One i n v o l v e s t h i n n i n g o f t h e w h o l e c r u s t ; t h e o t h e r a t a p e r i n g o u t o f t h e , : g r a n i t i c \" l a y e r t o w a r d s t h e w e s t e r n s i d e o f t h e v a l l e y . B o u g u e r d a t a ( F i g u r e 54b) i n d i c a t e c r u s t a l t h i c k n e s s e s u n d e r t h e G r e a t V a l l e y t h a t a r e c o m p a t i b l e w i t h t h e s e i s m i c d a t a . The l o w o v e r t h e w e s t e r n s i d e o f t h e v a l l e y and t h e h i g h o v e r t h e e a s t a r e p r o b a b l y t h e r e s u l t o f v a r i a t i o n s i n t h e u p p e r c r u s t . The B o u g u e r f i e l d does n o t p o i n t t o m a j o r d e p a r t u r e s f r o m i s o s t a s y s u c h as t h o s e o b s e r v e d o v e r t h e P u g e t L o w l a n d . i v . Summary The w e s t e r n s e a b o a r d of t h e U n i t e d S t a t e s and Canada i s g e n e r a l l y \"anomalous i n l i t h o s p h e r i c s t r u c t u r e . Upper m a n t l e v e l o c i t i e s t e n d t o be l o w - 7.7 t o 7.9. The c r u s t i n many a r e a s i s much t h i n n e r t h a n a v e r a g e ( W o o l l a r d ' s s t a n d a r d s e a - l e v e l c r u s t i s 33 km. t h i c k ) . T h e r e a r e no r o o t s u n d e r t h e C a s c a d e s o r C o a s t M o u n t a i n s . The C o a s t a l T r o u g h g e n e r a l l y seems compen-s a t e d i n B r i t i s h C o l u m b i a and C a l i f o r n i a : c r u s t a l t h i n n i n g may be r e s p o n s i b l e . N e g a t i v e f r e e - a i r a n o m a l i e s o v e r t h e t r o u g h i n W a s h i n g t o n and O r e g o n may i n d i c a t e t h a t i t i s u n d e r c o m p e n s a t e d , i . e . t h a t a mass d e f i c i e n c y u n d e r l i e s i t . The p o s s i b l e i m p l i c -a t i o n s o f t h e s e d a t a a r e d i s c u s s e d i n t h e f i n a l c h a p t e r . 160. CHAPTER I X : SYNTHESIS AND CONCLUSIONS T h r e e a s p e c t s o f t h e o r i g i n o f G e o r g i a D e p r e s s i o n - t i m i n g , s t r u c t u r a l s t y l e , and c a u s e - have been c o n s i d e r e d i n t h i s s t u d y . Of t h e t h r e e , o n l y t i m i n g i s w e l l - k n o w n . G e o r g i a D e p r e s s i o n b egan t o s u b s i d e i n t h e Upper C r e t a c e o u s , as i s shown by t h e d i s t r i b u t -i o n o f t h e Nanaimo G r o u p . The s t r u c t u r e s t h a t g o v e r n e d t h e Upper C r e t a c e o u s s u b s i d e n c e have so f a r been i m p o s s i b l e t o s e p a r a t e f r o m p o s t - N a n a i m o Group s t r u c t u r e s .(\u00C2\u00A3.!\u00E2\u0080\u00A2 M u l l e r and J e l e t z k y 1972 ; Rimme 1973; Simmons 1973; Hudson 1974; S t u r d a v a n t 1 9 7 5 ) ; t h e r e f o r e t h e s t r u c t u r a l s t y l e o f t h e o r i g i n a l d e p r e s s i o n r e m a i n s o b s c u r e . T h i s s t u d y has f o c u s s e d on t h e c a u s e o f t h e U p p e r C r e t a c e o u s d e p r e s s i o n and i t s r e l a t i o n t o t h e t e c t o n i c h i s t o r y o f s o u t h w e s t e r n B r i t i s h C o l u m b i a . H y p o t h e s e s f o r i t s o r i g i n i n c l u d e r i f t i n g , l i t h o s p h e r i c c o l l a p s e o v e r a p a l e o s u t u r e , and s u b s i d e n c e c o u p l e d t o t h e u p l i f t o f t h e C o a s t P l u t o n i c C omplex. T h e r e i s no e v i d -ence f o r a r i f t zone b e l o w G e o r g i a D e p r e s s i o n . H e a t f l o w i n t h e G e o r g i a S t r a i t a r e a i s s u b n o r m a l t o n o r m a l a t p r e s e n t (Hyndman 1 9 7 6 ) ; m e t a m o r p h i c a s s e m b l a g e s i n Upper C r e t a c e o u s - T e r t i a r y r o c k s a r e n o t i n d i c a t i v e o f h i g h g e o t h e r m a l g r a d i e n t s . V o l c a n i c s f o r m an i n s i g n i f i c a n t p a r t o f t h e Upper C r e t a c e o u s - T e r t i a r y s e c -t i o n i n G e o r g i a D e p r e s s i o n . The m a j o r argument f o r a s u t u r e n e a r t h e I n s u l a r B e l t / C o a s t P l u t o n i c Complex p r o v i n c e b o u n d a r y i s t h a t t h e P a l e o z o i c and T r i a s s i c o f V a n c o u v e r I s l a n d seem t o be a l l o c h t h o n o u s w i t h r e s p e c t t o N o r t h A m e r i c a . H owever, s u c h a s u t u r e more p r o b a b l y 1 6 1 . l i e s i n t h e S h u l a p s T e r r a n e , w h i c h i s c h a r a c t e r i z e d by s t r o n g d e f o r m a t i o n , j u x t a p o s i t i o n o f \" o c e a n i c \" and t e r r i g e n o u s s e d i m -e n t s , and Upper T r i a s s i c / L o w e r J u r a s s i c u l t r a m a f i t e e m p l a c e m e n t , r a t h e r t h a n i n t h e e a s t e r n I n s u l a r B e l t . The b o u n d a r y b e t w e e n t h e I n s u l a r B e l t and t h e C o a s t P l u t o n i c Complex on H a r d w i c k e and West T h u r l o w I s l a n d s shows no Upper T r i a s s i c - L o w e r J u r a s s i c t e r r i g e n o u s s e d i m e n t s o r s t r o n g d e f o r m a t i o n a s c r i b a b l e t o a p r e - p l u t o n i c s u t u r i n g e v e n t . I n s t e a d , i t i s a s t r a i g h t f o r w a r d \" and r e l a t i v e l y u n d i s t u r b e d i n t r u s i v e c o n t a c t . I n g e n e r a l t h e b o u n d a r y b e t w e e n t h e two p r o v i n c e s i s t h e m a g m a t i c f r o n t o f t h e C o a s t P l u t o n i c C omplex. G e o r g i a D e p r e s s i o n l i e s i m m e d i a t e l y w e s t o f t h e w e s t e r n l i m i t o f d o m i n a n t l y p l u t o n i c t e r r a n e . I t b e g a n t o s u b s i d e i n t h e Upper C r e t a c e o u s , a p p r o x i m a t e l y a t t h e same t i m e t h a t t h e s o u t h e r n C o a s t P l u t o n i c Complex b e g a n t o r i s e , as shown by l a c k o f p o s t - A l b i a n m a r i n e s e d i m e n t s w i t h i n i t and w e s t e r l y -d e r i v e d A l b i a n e l a s t i c s i n t h e T y a u g h t o n T r o u g h . P r i o r t o t h e Upper C r e t a c e o u s t h e s i t e o f G e o r g i a D e p r e s s i o n was a g e n e r a l l y p o s i t i v e a r e a u n d e r g o i n g e r o s i o n . The c o i n c i d e n c e o f o p p o s i t e v e r t i c a l movements i n G e o r g i a D e p r e s s i o n and t h e C o a s t P l u t o n i c Complex i s s t r o n g e v i d e n c e t h a t t h e y w e re c o u p l e d . T h i s c o n c l u s i o n a l s o f i t s t h e o t h e r s e g ments o f t h e C o a s t a l T r o u g h - H e c a t e D e p r e s s i o n , t h e P u g e t - W i l l i a m e t t e L o w l a n d s , and t h e G r e a t V a l l e y . The C o a s t a l T r o u g h l i e s b e t w e e n a s e r i e s o f c o l i n e a r m a g m a t i c a r c s - t h e C o a s t P l u t o n i c C o m p l e x , t h e C a s c a d e P r o v i n c e , and t h e S i e r r a Nevada - and t h e w e s t e r n edge 162. o f t h e N o r t h A m e r i c a n P l a t e . I t s v a r i o u s s e g m e n t s do n o t ha v e a common s t r u c t u r a l s t y l e - t h e P u g e t L o w l a n d i s l a r g e l y f a u l t c o n t r o l l e d , w h i l e o n l y g e n t l e t i l t i n g a f f e c t e d t h e e a s t e r n G r e a t V a l l e y . N e i t h e r f a u l t i n g o r w a r p i n g emerges as t h e d o m i n a n t m e c h a n i s m o f s u b s i d e n c e . The s u b - b a s i n s o f t h e C o a s t a l T r o u g h o r i g i n a t e d a t d i f f e r e n t t i m e s , t h e G r e a t V a l l e y i n t h e Upper J u r a s s i c - Lower C r e t a c e o u s , G e o r g i a D e p r e s s i o n i n t h e Upper C r e t a c e o u s , and H e c a t e D e p r e s s i o n and t h e P u g e t - W i l l i a m e t t e L o w l a n d s i n t h e L a t e C e n o z o i c . Y e t i n e a c h c a s e t h e b e g i n n i n g o f s u b s i d e n c e r o u g h l y c o i n c i d e d w i t h t h e u p l i f t o f t h e a r c i m m e d i a t e l y t o t h e e a s t . T h i s c o i n c i d e n c e i s b e s t e x p l a i n e d by c o n p l e d v e r t i c a l movements o f a r c and t r o u g h . The C e n t r a l G r a b e n o f C h i l e , l y i n g w e s t o f t h e An d e a n - a r c on P r e c a m b r i a n - P a l e o z o i c b a s e m e n t , may have a s i m i l a r o r i g i n . The most o b v i o u s mechanism o f v e r t i c a l movement c o u p l i n g i s h o r s t - a n d g r a b e n t e c t o n i c s , as e x e m p l i f i e d by t h e T e t o n s and J a c k s o n H o l e . The C o a s t a l T r o u g h i s n o t a c o n v i n c i n g g r a b e n , h o w e v e r . A l t h o u g h m a j o r f a u l t s a r e p o s s i b l e , d o w n w a r p i n g has p l a y e d an i m p o r t a n t r o l e i n i t s f o r m a t i o n , a t l e a s t i n O r e g o n and C a l i f o r n i a . Thus a more c o m p l i c a t e d m echanism o f i n t e r a c t i o n i s l i k e l y . One p o s s i b i l i t y i s s u g g e s t e d by t h e e x p e r i m e n t s o f Ramberg ( 1 9 6 7 ) . I n h i s c e n t r i f u g e d m o d e l s , domes f o r m i n g f r o m a f l a t s o u r c e r e g i o n a r e a c c o m p a n i e d by m a r g i n a l s y n c l i n e s ( F i g u r e 5 5 ) . The r i s e o f m a t e r i a l i n t o t h e dome c r e a t e s a p r e s s u r e d e f i c i e n c y i n i t s v i c i n i t y i n t o w h i c h t h e o v e r l y i n g l a y e r c o l l a p s e s . A r i s i n g m o u n t a i n s y s t e m c o u l d c r e a t e a s i m i l a r 164. p r e s s u r e d e f i c i e n c y a r o u n d i t s e l f . I t i s p r o p o s e d h e r e t h a t t h e s u b s i d e n c e o f t h e C o a s t a l T r o u g h was i n i t i a t e d by l i t h o s p h -e r i c c o l l a p s e i n t o t h e \" h o l e \" g e n e r a t e d d u r i n g t h e u p l i f t o f t h e a d j a c e n t a r c . Such a d e p r e s s i o n , s i n c e i t i s d r i v e n by a p r e s s u r e / mass d e f i c i e n c y , i s n o t i s o s t a t i c . N e g a t i v e f r e e - a i r and i s o s t a t i c a n o m a l i e s s h o u l d be a s s o c i a t e d w i t h i t . I t w i l l be r e c a l l e d t h a t n e g a t i v e f r e e - a i r / i s o s t a t i c a n o m a l i e s a r e o b s e r v e d o v e r t h e P u g e t and W i l l i a m e t t e L o w l a n d s , t h e y o u n g e s t s e c t i o n s o f t h e t r o u g h . T h i s a n i s o s t a t i c c o n d i t i o n s h o u l d be e l i m i n a t e d i n t i m e by c o n t i n u e d m a n t l e f l o w . Y e t t h e G r e a t V a l l e y and G e o r g i a D e p r e s s i o n have been i n e x i s t e n c e s i n c e t h e C r e t a c e o u s . M o r e o v e r H e c a t e D e p r e s s i o n and p o s s i b l y t h e G r e a t V a l l e y a r e a p p r o x i m a t e l y i n i s o s t a t i c e q u i l i b r i u m : some me c h a n i s m o f c o m p e n s a t i o n must p e r -p e t u a t e t h e t r o u g h once i t i s c r e a t e d . B e s i d e s s e d i m e n t l o a d i n g , two s u c h m echanisms a r e p o s s i b l e : c r u s t a l t h i n n i n g e i t h e r by e r o s i o n a t t h e b a s e o r by e x t e n s i o n ( A r t e m j e v and A r t y u s h k o v 1 9 7 1 ) , and p h a s e c h a n g e s , f o r ex a m p l e t h e g a b b r o - e c l o g i t e t r a n s f o r m a t i o n ( G r e e n and R i n g w o o d 1967; C o l l e t t e 1 9 6 8 ) . The s e i s m i c e v i d e n c e so f a r a v a i l a b l e f r o m B r i t i s h C o l u m b i a i s c o m p a t i b l e w i t h e i t h e r o f b o t h o f t h e s e c o m p e n s a t i o n m o d e l s . E l o n g a t e b a s i n s a r e a c h a r a c t e r i s t i c f e a t u r e o f a r c - t r e n c h g a p s . So f a r , v e r t i c a l movements, u p l i f t s , and d e p r e s s i o n s i n a r c - t r e n c h gaps have been e x p l a i n e d i n r e l a t i o n t o t h e p r o c e s s o f s u b d u c t i o n ( 6 . 1 . L o m n i t z 1969; F y f e and M c B i r n e y 1 9 7 5 ) . T h i s s t u d y o f t h e C o a s t a l T r o u g h has shown t h a t some f o r e a r c b a s i n s a r e g e n e r a t e d , n o t by s u b d u c t i o n , b u t by e v e n t s w i t h i n t h e o v e r -165 . r i d i n g p l a t e i t s e l f . A b e t t e r u n d e r s t a n d i n g o f t h e r e l a t i o n s h i p b e t w e e n a r c magmatism and u p l i f t and o f t h e mechanisms o f a r c u p l i f t w i l l d o u b t l e s s s h e d more l i g h t on t h e g e n e s i s o f t h e C o a s t a l T r o u g h . 166 . BIBLIOGRAPHY A l l e n , J . E . , 1958. C o l u m b i a R i v e r Gorge - P o r t l a n d t o t h e D a l l e s , G u i d e b o o k f o r F i e l d T r i p s . G e o l . S o c . Am. C o r d i l l e r a n S e c t i o n , E u g ene, O r e g o n , p.4. A r m s t r o n g , R.L., J . Suppe, 1973. P o t a s s i u m - a r g o n g e o c h r o n o m e t r y of M e s o z o i c i g n e o u s r o c k s i n N e v a d a , U t a h and s o u t h e r n C a l i f o r -n i a . G e o l . Soc. Am. B i i i l l . 8 4 , p . 1 3 7 5 . A r t e m j e v , M.E., E.V. Artyushkov-j.. 1 9 7 1 . S t r u c t u r e and i s o s t a s y o f t h e B a i k a l R i f t and t h e m echanism o f r i f t i n g . J o u r . Geophys. Res. 76, p.1197. A s i h e n e , K.A.B., 1970. The T e x a d a F o r m a t i o n o f B.C. and i t s a s s o c i a t e d m a g n e t i t e c o n c e n t r a t i o n s . unpub. PhD - UCLA. B a e r , A . J . , 1973. B e l l a C o o l a - L a r e d o Sound m a p - a r e a s , B.C. G e o l . S u r v . Can. Memoir 372. B a i l e y , E.H., W.P. I r w i n , D.L. J o n e s , 1964. F r a n c i s c a n and r e l a t e d r o c k s , and t h e i r s i g n i f i c a n c e i n t h e g e o l o g y o f w e s t e r n C a l i f o r n i a . C a l i f . D i v . M i n e s G e o l . B u l l . 183. B a k e r , B.H., P.A. Mohr, L . A . J . W i l l i a m s , 1972. G e o l o g y of t h e e a s t e r n r i f t s y s t e m of A f r i c a . G e o l . Soc. Am. S p e c i a l P a p e r 136, p.67. B a l d w i n , E w a r t , 1964. G e o l o g y o f O r e g o n . 2nd e d i t i o n . J.W. E d w a r d s , pub. B a r b a t , W.F., 1 9 7 1 . M e g a t e c t o n i c s o f t h e C o a s t R a n g e s , C a l i f . G e o l . Soc. Am. B u l l . 82, p. 1541. B e a u l i e u , J.D., 1 9 7 1 . G e o l o g i c f o r m a t i o n s o f w e s t e r n O r e g o n . O r e . D e p t . G e o l . M i n . Res. B u l l . 70. B e l o u s s o v , V.V., 1969. C o n t i n e n t a l r i f t s i n P . J . H a r t , e d . , The E a r t h ' s C r u s t and U p p e r M a n t l e . Amer. Geophys. Un. monograph 13. p. 539. B e r g , J.W., L y n n T r e m b l y , D.A. E m i l i a , J.R. H u l t , J.M. K i n g , L.T. L o n g , W.R. M c K n i g h t , S.K. Sarmah, R. S o n d e r s , J.V. T h i r u v a t -h u k a l , D.A. V a s s l e r , 1966. C r u s t a l r e f r a c t i o n p r o f i l e , O r e g o n C o a s t Range. S e i s . S o c . Am. B u l l . 56, p.1357. B e r r y , F.A., 1973. H i g h f l u i d p o t e n t i a l s i n t h e C a l i f . C o a s t Ranges a n d . t h e i r t e c t o n i c s i g n i f i c a n c e . A.A.P.G. B u l l . 5 7 , p .1219. B e r r y , M.J., W.R. J a c o b y , E.R. N i b l e t t , R.A. S t a c e y , 1 9 7 1 . A r e v i e w o f g e o p h y s i c a l s t u d i e s i n t h e C a n a d i a n C o r d i l l e r a . Can. J o u r . E a r t h S c i . 8,p.788. 167 . B e r r y , M.J., D.A. F o r s y t h , 1975. S t r u c t u r e o f t h e C a n a d i a n C o r d i l l e r a f r o m s e i s m i c r e f r a c t i o n and o t h e r d a t a . Can. J o u r . E a r t h S c i . 1 2 , p.2. B l u n d e n , R.H. V a n c o u v e r ' s Downtown ( G o a l ) P e n i n s u l a . Unpub. B.Sc. UBC 1971 B o s t r o m , R.C., 1968. The o c e a n r i d g e s y s t e m i n t h e n o r t h e a s t P a c i f i c Ocean. P a c . G e o l . 1, p . 2 1 . B r a n e r y , R.W., P.D. S n a v e l y , 1964. G e o l o g i c i n t e r p r e t a t i o n o f r e c o n a i s s a n c e g r a v i t y and a e r o m a g n e t i c s u r v e y s i n n o r t h w e s t e r n O r e g on USGS B u l l . 1181 - N. Brown, R.D. and E . I . R i c h , 1967. I m p l i c a t i o n s o f two C r e t a c e o u s mass t r a n s p o r t d e p o s i t s , S a c r a m e n t o V a l l e y , C a l i f o r n i a . J o u r . . S e d . P e t . p . 3 7 . B u d d i n g t o n , A.F., D.H. L i n d s l e y , 1964. I r o n t i t a n i u m o x i d e m i n e r a l s and s y n t h e t i c e q u i v a l e n t s . J o u r . P e t r o l . 5, p.310. Cameron, B.E.B. and J.W.H. M o n g e r , 1 9 7 1 . M i d d l e T r i a s s i c c o n o d o n t s f r o m t h e F e r g u s s o n G r o u p , N.E. P e m b e r t o n m a p - a r e a , B.C. G e o l . S u r v . Can. p a p e r 7 1 . I B , p.94. Cameron, B.E.B., 1975. G e o l o g y o f t h e T e r t i a r y r o c k s n o r t h o f l a t i t u d e 49 , West C o a s t o f V a n c o u v e r I s l a n d . G e o l . S u r v . Can. p a p e r 7 5 . I A , p.17. C a r d e r , D.S.,1970. T r a n s - C a l i f o r n i a s e i s m i c p r o f i l e ; Owens V a l l e y t o M o n t e r e y . G e o l . S o c . Am. A b s . V2, p.2. C a r d e r , D.S.,1973. T r a n s - C a l i f o r n i a s e i s m i c p r o f i l e , D e a t h V a l l e y t o M o n t e r e y Bay. S e i s . S oc. Am. B u l l . 63, p . 5 7 1 . C a r l i s l e , D., T. S u z u k i , 1 965 . S t r u e t u r e , s t r a t i g r a p h y and p a l e o n -t o l o g y o f an u p p e r T r i a s s i c s e c t i o n on t h e West C o a s t o f B.C. Can. J o u r . E a r t h S c i . 2, p. 445. C a r l i s l e , D., T. S u z u k i , 1974. Emergent b a s a l t and s u b m e r g e n t c a r b o n a t e - c l a s t i c s e q u e n c e s i n c l u d i n g t h e Upper T r i a s s i c D i l l e r i and W e l l e r i z o n e s on V a n c o u v e r I s l a n d . Can. J o u r . E a r t h S c i . 1 1 , p. 254. C a r o n , 'Mike, 1974. G e o l o g y and g e o c h r o n o l o g y o f t h e S t r a c h a n C r e e k a r e a , Howe Sound, S.W. B r i t i s h C o l u m b i a . Unpub. B.Sc. , UBC. Cashman, P.H., 1974. M e l a n g e t e r r a n e i n t h e w e s t e r n:: E a1e o z d i c and T r i a s s i c s u b p r o v i n c e , K a l a m a t h M o u n t a i n s , C a l i f o r n i a . G e o l . S u r v . Am. a b s . 6, p.153. Chaney, R.W., 1925. The M a s c a l l F l o r a - i t s d i s t r i b u t i o n and c l i m a t i c r e l a t i o n . C a r n e g i e I n s t . Pub. 349, p . 2 3 . 168 . Chapman, R.H., 1966. The g r a v i t y f i e l d i n n o r t h e r n C a l i f o r n i a . I n : G e o l o g y o f N o r t h e r n C a l i f o r n i a , B u l l . 1 90, C a l i f . D i v . M i n e s , G e o l . p.395. C h a t t e r j e e , N.D., 1967. E x p e r i m e n t s on t h e p h a s e t r a n s i t i o n c c + wo + ep = g r o s - and + C0\u00E2\u0080\u009E + H 0. C o n t r i b . M i n e r a l . P e t r . 2 C h u r c h , S.E., G.R. T i l t o n , 1973. L e a d and s t r o n t i u m i s o t o p i c s t u d i e s i n t h e C a s c a d e M o u n t a i n s , b e a r i n g on a n d e s i t e g e n e s i s . G e o l . S oc. Am. B u l l . 84, p . 4 3 1 . C l a r k , E.D., 1964. S t r a t i g r a p h y and s t r u c t u r e o f p a r t o f t h e w e s t e r n S i e r r a Nevada m e t a m o r p h i c b e l t , C a l i f o r n i a . U.S.G.S. P r o f . P a p e r 410. C o a t e s , J.A., 1974. G e o l o g y o f t h e M a n n i n g P a r k a r e a , B r i t i s h C o l u m b i a . G e o l . S u r v . Can., B u l l . 238. C o l e , M., 1973. P e t r o l o g y and d i s p e r s a l p a t t e r n s o f J u r a s s i c and C r e t a c e o u s s e d i m e n t a r y r o c k s i n t h e Methow R i v e r a r e a , N o r t h C a s c a d e s , W a s h i n g t o n . Unpub. Ph.D., U. o f W a s h i n g t o n . C o l l e t t e , B . J . , 1968. On t h e s u b s i d e n c e o f t h e N o r t h Sea a r e a . G e o l o g y o f S h e l f Seas ( P r o c . 1 4 t h I n t e r - U n i v e r s i t y G e o l . C o n g . ) , D.T. Donovan, ed. ^ O l i v e r and B o y d , E d i n b u r g h . C o u l b o u r n , W.J., R. Mob e r l y , 1975. S t r u c t u r e o f a b a s i n o f t h e u p p e r c o n t i n e n t a l m a r g i n o f s o u t h e r n P e r u and n o r t h e r n C h i l e . 1 3 t h P a c . S c i . C o n g r e s s p r o c . p. 395. C u l b e r t , R.R., 1972. A b n o r m a l i t i e s i n t h e d i s t r i b u t i o n o f K, Rb and S r i n t h e C o a s t M o u n t a i n s b a t h o l i t h , B r i t i s h C o l u m b i a . G e o c h i m , Cosmochim. A c t a 36, p.1 0 9 1 . D a l y , R.A., 1912. G e o l o g y o f t h e N o r t h A m e r i c a n C o r d i l l e r a a t t h e 4 9 t h p a r a l l e l . G e o l . S u r v . Can. Memoir 38, p.840. D a n e s , L . F . , 1969. G r a v i t y r e s u l t s i n w e s t e r n W a s h i n g t o n . E.O.S. 50, p.548. D a n e s , L . F . , M. Bonno, E. B r a u , W.D. G i l m a n , T.F. H o f f m a , D. J o h a n s e n , M.H. J o n e s , B. M a l f a i t , J . M a s t e n , G. Hagne, 1965. G e o p h y s i c a l i n v e s t i g a t i o n o f t h e s o u t h e r n P u g e t Sound a r e a , W a s h i n g t o n . J o u r . Geophys. Res. 70, p.5573. D e h l i n g e r , P., E.F. C h i b u r t s , M.M. C o l l v e r , L o c a l t r a v e l - t i m e c u r v e s and t h e i r g e o l o g i c i m p l i c a t i o n s f o r t h e P a c i f i c N.W. s t a t e s . S e i s . Soc. Am., B u l l . 5 5 , p.587. D e t l i n g , L . E., 1968. H i s t o r i c a l b a c k g r o u n d o f t h e f l o r a o f t h e P a c i f i c N o r t h w e s t . B u l l . 1 3 , Museum o f N a t u r a l H i s t o r y , U n i v e r s i t y o f O r e g o n . 169 . Dewey, J . F . and J.M. B i r d , 1970. M o u n t a i n b e l t s and t h e new g l o b a l t e c t o n i c s . J o u r . G e o p hys. R e s . 75, p.2 6 2 5 . D i c k i n s o n , W.R., 1971. C l a s t i c s e d i m e n t a r y s e q u e n c e s d e p o s i t e d i n s h e l f , s l o p e and t r o u g h s e t t i n g s b e t w e e n m agmatic a r c s and a s s o c i a t e d t r e n c h e s . P a c . G e o l . 3, p.15. D i c k i n s o n , W.R., 1973. R e c o n s t r u c t i o n o f p a s t a r c - t r e n c h s y s t e m s f r o m p e t r o t e c t o n i c a s s e m b l a g e s i n t h e i s l a n d a r c s o f t h e w e s t e r n P a c i f i c . I n The W e s t e r n P a c i f i c , P . J . C o l e m a n , e d . , p.569. D i c k i n s o n , W.R., 1974. P l a t e t e c t o n i c s and s e d i m e n t a t i o n , i n T e c t o n i c s and S e d i m e n t a t i o n , W.R. D i c k i n s o n , e d. Soc. E c o n . P a l e o n t o l . M i n e r a l . S p e c . Pub. 22, p . l . E a t o n , J . P . , 1966. C r u s t a l s t r u c t u r e i n n o r t h e r n and c e n t r a l C a l i f o r n i a f r o m s e i s m i c e v i d e n c e . ' . C a l i f . D i v . M i n e s . G e o l . B u l l . 1 90, p.419. E r n s t , W.G., 1971. M e t a m o r p h i c z o n a t i o n s on p r e s u m a b l y s u b -d u c t e d l i t h o s p h e r i c p l a t e s f r o m J a p a n , C a l i f o r n i a and t h e A l p s . C o n t r i b . M i n e r a l P e t r . 34, p. 43. Fenneman, N.M., 1931. P h y s i o g r a p h y o f t h e W e s t e r n U n i t e d S t a t e s ( M c G r a w - H i l l ) . F i s k e , R.S., C.A. Hopson, A.C. W a t e r s , 1 963. G e o l o g y o f Mt. R a i n i e r N a t i o n a l P a r k , W a s h i n g t o n . U.S.G.S. p r o f , p a p e r 444. F o r s y t h , D.A.F., M.J. B e r r y , R.M. E l l i s , 1974. A r e f r a c t i o n s u r v e y a c r o s s t h e C a n a d i a n C o r d i l l e r a a t 54 N. Can. J o u r . E a r t h S c i . 1 1 , p.533. F y f e , W.S., A.R. M c B i r n e y , 1975. S u b d u c t i o n and t h e s t r u c t u r e o f a n d e s i t i e v o l c a n i c b e l t s . Am. J o u r . S c i . 275-A, p.285. G i r d l e r , R.W., J.D. F a i r h e a d , R.C. S e a r l t , W.T.C. S o w e r b u t t s , 1969. E v o l u t i o n o f r i f t i n g i n A f r i c a . N a t u r e 224 - D e c . 2 0 , p. 1178. G l o v e r , S.L., 1936. Hammer B l u f f F o r m a t i o n o f w e s t e r n W a s h i n g t o n . A b s . Pan - Amer. G e o l . 6 5 - 1 , p.77. G o r d o n , T.M., H.J. Greenwood, 1 9 71. The s t a b i l i t y o f g r o s s u l a r i t e i n H O - CO^ m i x t u r e s . Amer. M i n e r a l . 56, p.1674. G r e e n , D.H., A.E. R i n g w o o d , 1967. An e x p e r i m e n t a l i n v e s t i g a t i o n o f t h e g a b b r o t o e c l o g i t e t r a n s f o r m a t i o n and i t s p e t r o l o g i c a l i m p l i c a t i o n s . Geochim. Cosmochim. A c t a 3 1 , p.767. 170. G reenwood, H . J . , 1975. G e n e s i s o f magmas i n i n t r u s i v e r o c k s and r e l a t e d m i n e r a l i z a t i o n o f t h e C a n a d i a n C o r d i l l e r a , a b s . G e o l . S u r v . Can. C o r d i l l e r a n S e c t i o n Symposium, p.13. H a c k e l , 0., 1966. Summary o f t h e g e o l o g y o f t h e G r e a t V a l l e y . C a l i f o r n i a D i v . M i n e s . G e o l . B u l l . 1 90, p.217. H a m i l t o n , W a r r e n , 1974. S u b d u c t i o n - m e l a n g e wedges o f modern C i r c u m . P a c i f i c a r c s and o f C r e t a c e o u s C a l i f o r n i a . G e o l . S o c . Am. a b s . 6, p.187. H a m i l t o n , W. The V o l c a n i c C e n t r a l Andes - a modern model f o r t h e C r e t a c e o u s b a t h o l i t h s and t e c t o n i c s o f W. N o r t h A m e r i c a - i n P r o c . A n d e s i t e C o n f . O r e g o n D e p t . M i n e s B u l l . 65, p.175. A. R. M c B i r n e y , e d . 1969. Hammond, P., 1961. S t r u c t u r e and s t r a t i g r a p h y o f t h e Keechelus V o l c a n i c g r o u p and a s s o c i a t e d T e r t i a r y v o l c a n i c r o c k s i n t h e w e s t - c e n t r a l C a s c a d e Range, W a s h i n g t o n . Unpub. PhD, U . W a s h i n g t o n . H a r t , S.R., 1964. The p e t r o l o g y and i s o t o p i c - m i n e r a l age r e l a t i o n s o f a c o n t a c t zone i n t h e F r o n t Range, C o l o r a d o . J o u r . G e o l . 72, p.493. H o l d a w a y , M.J., 1 9 7 1 . S t a b i l i t y o f a n d a l u s i t e and t h e a l u m i n u m s i l i c a t e p h a s e d i a g r a m . Am. J o u r . S c i . 2 7 1 , p.97. H o l l a n d , S.S., 1964. L a n d f o r m s o f B.C. - a p h y s i o g r a p h i c o u t l i n e . B. C. D e p t . M i n e s . B u l l . 48. H o l l i s t e r , L . S . , 1969. M e t a s t a b l e p a r a g e n e t i c s e q u e n c e o f a n d a l u s i t e , k y a n i t e and s i l l i m a n i t e , K w o i c k a r e a , B r i t i s h C o l u m b i a . Am. J o u r . S c i . , p. 267. H o p k i n s , V.S. J r . 1966. P a l y n o l o g y o f T e r t i a r y r o c k s o f Whatcom B a s i n , s o u t h w e s t e r n B r i t i s h C o l u m b i a and n o r t h w e s t e r n W a s h i n g t o n . Unpub. PhD, UBC. Hsu , K . J . , 1 9 7 1 . F r a n c i s c a n m e l a n g e s as a model f o r e u g e o s y n c l i n a l s e d i m e n t a t i o n and u n d e r t h r u s t i n g t e c t o n i c s . J o u r . Geophys. Res. 76, p. 1162. Hu d s o n , J o n P a r k , 1974. S t r a t i g r a p h y and p a l e o e n v i r o n m e n t s of t h e C r e t a c e o u s r o c k s , N o r t h and S o u t h P e n d e r I s l a n d s , B r i t i s h Columb-i a . Unpub. M.Sc. O r e g o n S t a t e U n i v e r s i t y . H u t c h i s o n , W.W., 1970. M e t a m o r p h i c f r a m e w o r k and p l u t o n i c s t y l e s i n t h e P r i n c e R u p e r t r e g i o n o f t h e C e n t r a l C o a s t M o u n t a i n s , B r i t i s h C o l u m b i a . Can. J o u r . E a r t h S c i . 7, p.376. H u t c h i s o n , W.W., A.V. O k u l i t c h , H.C. B e r g , 1973. S k e e n a R i v e r 1:1,000,000 map s h e e t , G e o l . S u r v . Can. open f i l e map. Hyndman, R.D., 1976. Heat f l o w m e a s u r e m e n t s i n t h e i n l e t s o f s o u t h w e s t e r n B.C. J o u r . G e o p hys. Res. 8 1 , p.337. 171. I r v i n g , E. and R.W. Y o l e , 1972. P a l e o m a g n e t i s m and t h e k i n e m a t i c h i s t o r y o f m a f i c and u l t r a m a f i c r o c k s i n f o l d m o u n t a i n b e l t s . I n : The A n c i e n t O c e a n i c L i t h o s p h e r e , Pub. E a r t h P h y s . B r a n c h . E n e r g y , M i n e s , R e s o u r c e s V 42 - n 3, p.87. I r w i n , W.P., 1973. S e q u e n t i a l minimum ages o f o c e a n i c c r u s t i n a c c r e t e d t e c t o n i c p l a t e s o f n o r t h e r n C a l i f o r n i a and s o u t h e r n O r e g o n . G e o l . S o c . Am. a b s . 5, p.62. J a e g e r , J . C . , 1957. The t e m p e r a t u r e i n t h e n e i g h b o r h o o d o f a c o o l i n g i n t r u s i v e s h e e t . Am. J o u r . S c i . 255, p.306. J a e g e r , J . C . , 1959. T e m p e r a t u r e s o u t s i d e a c o o l i n g i n t r u s i v e s h e e t . Am. J . S c i . 257, p.44. J e l e t z k y , J.A., 1965. Age and t e c t o n i c n a t u r e o f t h e G e o r g i a S t r a i t seaway. G e o l . S u r v . Can. p a p e r 65 - 2, p.72. J o h n s o n , S.H., R.W. C o u c h , 1970. C r u s t a l s t r u c t u r e i n t h e N o r t h C a s c a d e s o f W a s h i n g t o n and B r i t i s h C o l u m b i a f r o m s e i s m i c r e f r a c t i o n m e a s u r e m e n t s . S e i s . S o c . Am. B u l l . 60, p. 1259. J o h n s o n , S.H., R.W. C o u c h , M. G e m p e r l e , E.R. B a n k s , 1972. S e i s m i c r e f r a c t i o n m e a s u r e m e n t s i n S.E. A l a s k a and w e s t e r n B r i t i s h C o l u m b i a . Can. J o u r . E a r t h S c i 0, p. 1756. J o l l y , W.J., R.E. S m i t h , 1972. D e g r a d a t i o n and m e t a m o r p h i c d i f f e r e n t i a t i o n o f t h e Keweehawan t h o l e i t i c l a v a s o f n o r t h e r n M i c h i g a n , U.S.A. J o u r . P e t 13, p.273. K e r r i c k , D.M., 1970. C o n t a c t m e t a m o r p h i s m i n some a r e a s of t h e S i e r r a N e v a d a , C a l i f . G e o l . S o c . Am. B u l l . 8 1 , p . 2913. K e r r i c k , D.M., K.E. C r a w f o r d , A.F. R a n d a z z o , 1973. M e t a m o r p h i s m o f c a l c a r e o u s r o c k s i n t h r e e r o o f p e n d a n t s i n t h e S i e r r a N e v a d a , C a l i f o r n i a . J o u r . P e t r . 14, p .303. K u n i y o s h i , S., 1 9 7 2 a . P e t r o l o g y of t h e K a r m u t s e n ( v o l c a n i c ) G r o u p , n o r t h e a s t e r n V a n c o u v e r I s l a n d , B r i t i s h C o l u m b i a . Unpub. PhD, UCLA. L a n p h e r e , M.A., B.L. R e e d , 1973. T i m i n g of M e s o z o i c and C e n o z o i c \"..plutonic ' e v e n t s : . i n : . C i r c u m - P a c i f i d j N o r t h A m e r i c a . G e o l . ' S u r v : Am. abs . 5 , p . 70. L e c o u t e u r , P.C. and D.J. Templem a p r o f i l e o f i n i t i a l S r 87/ S r 8 t h e Y u k o n C r y s t a l l i n e T e r r a n e . p. 319. L e e c h , G. B., 1953. Range, B.C. D e p t . n - K l u i t , 1976. R b / S r ages and r a t i o s f o r p l u t o n i c r o c k s a c r o s s Can. J o u r . E a r t h S c i . 1 3 - 2 , G e o l o g y and m i n e r a l d e p o s i t s of t h e S h u l a p s of M i n e s , B u l l . 32. L e P i c h o n , X., J . F r a n c h e t e a u , J . B o n n i n , 1973. P l a t e T e c t o n i c s . E l s e v i e r , A msterdam. 172 . L i o u , J.G., 1970. S t a b i l i t y r e l a t i o n s o f z e o l i t e s and r e l a t e d m i n e r a l s . Unpub. PhD, UCLA L i o u , J.G., 1973. S y n t h e s i s and s t a b i l i t y r e l a t i o n s o f e p i d o t e , C a 2 A l Fe S i 3 0 1 2 (OH). J o u r . P e t . 14, p . 3 8 1 . L i o u , J.G., S. K u n i y o s h i , K. I t o , 197'4. E x p e r i m e n t a l s t u d i e s o f t h e p h a s e r e l a t i o n s b e t w e e n g r e e n s c h i s t and a m p h i b o l i t e i n a b a s a l t i c s y s t e m . Am. J o u r . S . c i . 274, p. 613. L i v i n g s t o n , V . E . , 1 9 7 1 . G e o l o g y and m i n e r a l R e s o u r c e s o f K i n g C o u n t y , W a s h i n g t o n . Wash. D i v . M i n e s G e o l . B u l l . 63. L i v i n g s t o n , V.E., H. Gower, 1975. q u o t e d i n The S e a t t l e T i mes .Feb. 23, 1975 , p.B . 1 . L o f g r e n , G.E., C.H. D o n a l d s e n , 1975. C u r v e d b r a n c h i n g c r y s t a l s and d i f f e r e n t i a t i o n i n comb l a y e r e d r o c k s . C o n t r i b . M i n e r a l . P e t r . 4 9 , p . 3 0 9 . L o m n i t z , C., 1969. S e a f l o o r s p r e a d i n g as a f a c t o r o f t e c t o n i c e v o l u t i o n i n s o u t h e r n C h i l e . N a t u r e p. 222. L o wes, B.E., 1972. M e t a m o r p h i c p e t r o l o g y and s t r u c t u r a l g e o l o g y o f t h e a r e a e a s t o f H a r r i s o n L a k e , B.C. Unpub. PhD, U. W a s h i n g -t o n . Mathews, W., 1972. G e o l o g y o f t h e V a n c o u v e r a r e a o f B r i t i s h C o l u m b i a . I.G.C. F i e l d E x c u r s i o n A05-C05, I.G.C. 2 4 t h S e s s i o n Mont r e a l . M athews, W. H., J.G. F y l e s , H.W. N a s m i t h , 1970. P o s t - g l a c i a l . c r u s t a l movements i n s o u t h w e s t e r n B r i t i s h C o l u m b i a and a d j a c e n t W a s h i n g t o n S t a t e . Can. J o u r . E a r t h S c i . 7, p.690. M a t t i n s o n , J.M., 1973. Ages o f z i r c o n s f r o m t h e N o r t h C a s c a d e M o u n t a i n s , W a s h i n g t o n . G e o l . S u r v . Can. B-83, p.2769. M c B i r n e y , A.R., J . F . S u t t e r , H.R. N a s l u n d , 1974. E p i s o d i c v o l c a n i s m i n t h e C e n t r a l O r e gon C a s c a d e Range. G e o l o g y V.fio.,12, p.585. McKee, B a t e s , 1972. C a s c a d i a : The G e o l o g i c E v o l u t i o n o f t h e P a c i f i c N o r t h w e s t . M c G r a w - H i l l , New Y o r k . M c K i l l o p , G.R., 1973. G e o l o g y o f s o u t h w e s t e r n G a m b i e r I s l a n d , Howe Sound, B r i t i s h C o l u m b i a . Unpub. B.Sc. , U.B.C. M i l a n o v s k y , E.E., 1972. C o n t i n e n t a l r i f t z o n e s - t h e i r a r r a n g e -ment and d e v e l o p m e n t . T e c t o n o p h y s . 15, p. 6;5 . M i s c h , P. 1966. T e c t o n i c e v o l u t i o n o f t h e N o r t h e r n C a s c a d e s o f W a s h i n g t o n S t a t e . Can. I n s t . M i n . M e t . , s p e c . v o l . 8, p. 101. 173. M i y a s h i r o , A., 1961. E v o l u t i o n o f m e t a m o r p h i c b e l t s . J o u r . P e t r o l . 2, p.277. M o n g e r , J.W.H., 1970. Hope m a p - a r e a , w e s t h a l f , B r i t i s h C o l u m b i a . G e o l . S u r v . Can. p a p e r 69-47, p.75. Monger, J.W.H., C.A. R o s s , 1 9 7 1 . D i s t r i b u t i o n o f f u s i l i n a c e a n s i n t h e W e s t e r n C a n a d i a n C o r d i l l e r a . Can. J o u r n . E a r t h S c i . 8, p . 2 . Monger, J.W.H., J.G. S o u t h e r , H. G a b r i e l s e , 1972. E v o l u t i o n o f t h e C a n a d i a n C o r d i l l e r a - a p l a t e - t e c t o n i c m o d e l . Am. J o u r n . S c i . 272, p.577. Moore, J.G., J . P . L o c k w o o d , 1973. O r i g i n o f comb l a y e r i n g and o r b i c u l a r s t r u c t u r e , S i e r r a N evada B a t h o l i t h , C a l i f o r n i a . G e o l . S o c . Am B u l l . 84, p . l . M o o r e s , E.M., 1972. M o d e l f o r J u r a s s i c i s l a n d a r c - c o n t i n e n t a l m a r g i n c o l l i s i o n i n C a l i f o r n i a . G e o l . S o c . Am. abs 4, p.202. M u l l e r , J . E . , 1972. G e o l o g i c a l R e c o n . Map o f V a n c o u v e r I s l a n d and G u l f I s l a n d s , G e o l . S u r v . Can. open f i l e map 61. M u l l e r , J . E . , 1973. Lower C r e t a c e o u s f l y s c h s e q u e n c e on t h e w e s t c o a s t o f V a n c o u v e r I s l a n d . G e o l . S o c . Am. a b s . 5, p.84. M u l l e r , J . E . 1974. V i c t o r i a m a p - a r e a , P a c i f i c Rim N a t i o n a l P a r k , V a n c o u v e r I s l a n d , B r i t i s h C o l u m b i a i n G e o l . S u r v . Can, p a p e r 7 4 - 1 , p . 21 . M u l l e r , J . E . , 1976. Cape F l a t t e r y map a r e a , B r i t i s h C o l u m b i a . G e o l . S u r v . Can. p a p e r 76-1A, p. 107. M u l l e r , J . E . , J.A. J e l e t s k y , 1970. G e o l o g y o f t h e Upper C r e t a c e o u s Nanaimo Group , V a n c o u v e r I s l a n d and G u l f I s l a n d s , B r i t i s h C o l u m b i a . G e o l . S u r v . C a n . p a p e r 69, p.25. M u l l i n e u x , D.R., L.M. G a r d , D.R. C r a n d e l l , 1959. C o n t i n e n t a l s e d i m e n t s o f M i o c e n e age i n P u g e t Sound l o w l a n d s , W a s h i n g t o n . A.A.P.G. B u l l . 4 3 , p.688. Newton, R . C , 1966. Some c a l c - s i i i c a t e e q u i l i b r i u m r e a c t i o n s . Am. J o u r . S c i . 264, p.204. N o r t h c o t e , K.E., J . E . M u l l e r , 1972. V o l c a n i s m , p l u t o n i s m and m i n e r a l i z a t i o n - V a n c o u v e r I s l a n d . Can. M i n i n g Met. B u l l . O c t o b e r 1972 p.1. O j a k a n g a s , R.W., 1968. C r e t a c e o u s s e d i m e n t a t i o n , S a c r a m e n t o V a l l e y , C a l i f . G e o l . S o c. Am. B u l l . 79, p.973. P a g e , R . J . , 1974. A t e c t o n i c m e l a n g e on t h e w e s t c o a s t o f V a n c o u v e r I s l a n d , B r i t i s h C o l u m b i a . G e o l . S o c . Am. a b s . 6, p.233. 174. P a k i s e r , L.C., 1974. Root o f t h e S i e r r a N e v a d a . G e o l . S o c . Am., C o r d i l l e r a n S e c t i o n , a b s . 6-3, p.234. P e c k , D.L., A.B. G r i g g s , H.G. S c h l i c k e r , F.G. W e l l s , H.M. D o l o , 1964. G e o l o g y o f t h e c e n t r a l and n o r t h e r n p a r t s o f t h e w e s t e r n C a s c a d e Range i n O r e g o n . USGS p r o f , p a p e r 449. P i g a g e , L.C., 1973. M e t a m o r p h i s m s o u t h w e s t o f Y a l e , B r i t i s h C o l u m b i a . Unpub. M.Sc., U n i v e r s i t y o f B r i t i s h C o l u m b i a . P r e s n a l l , D.C., P.C. Bateman, 1973. F u s i o n r e l a t i o n s i n t h e s y s t e m NaAl\" S i 3 0 - C a A l ^ S i g O - K A L S i 0^ . - S i G ? -.HO, and t h e g e n e r a t i o n o f g r a n i t i e magmas i n t h e S i e r r a Nevada b a t h o l i t h . G e o l . Soc. Am. B u l l . 84, p . 3 1 8 1 . Ragan, D.M., 1968. S t r u c t u r a l G e o l o g y - An I n t r o d u c t i o n t o G e o m e t r i c a l T e c h n i q u e s , W i l e y and S o n s , New Y o r k . Ramberg, H., 1967. G r a v i t y , D e f o r m a t i o n and t h e E a r t h ' s C r u s t . A c a d e m i c P r e s s , N.Y. Raney, J.A., 1973. G r e a t V a l l e y - C o a s t Range c o n t a c t - An a l t e r n -a t e h y p o t h e s i s . G e o l . S o c . Am. a b s t r . w i t h p r o g . 1973 , p.93. Rau, W.W., 1967. G e o l o g y o f t h e Wynoochee V a l l e y q u a d r a n g l e , G r a y s H a r b o r Co., W a s h i n g t o n . W a s h i n g t o n D e p t . N a t . R e s . B u l l . 5 6 . R e a msbottom, S., 1974. G e o l o g y and m e t a m o r p h i s m o f t h e Mount B r e a k e n r i d g e a r e a , H a r r i s o n L a k e , B r i t i s h C o l u m b i a . Unpub. Ph.D. U n i v e r s i t y o f B r i t i s h C o l u m b i a . R e p e n n i n g , C.A., 1960. G e o l o g i c summary o f t h e G r e a t V a l l e y o f C a l i f o r n i a w i t h r e f e r e n c e t o d i s p o s a l o f 1 i q u i d . r a d i o a c t i v e w a s t e . U.S.G.S., T . E . I . R e p t . 769. R i n n e , R.W., 1973. G e o l o g y o f t h e Duke P o i n t - K u l l e e t Bay A r e a , V a n c o u v e r I s l a n d , B r i t i s h C o l u m b i a . Unpub. L-IM.Sc. O r e g o n S t a t e . R o b e r t s , A.E., 1958. G e o l o g y and c o a l r e s o u r c e s o f t h e T o l e d o - C a s t l e Rock d i s t r i c t , C o w l i t z and L e w i s C o u n t i e s , W a s h i n g t o n . U.S.G.S. B u l l . 1062. R o d d i c k , J.A., 1965. V a n c o u v e r N o r t h , C o q u i t l a m and P i t t L a k e map a r e a s , w i t h s p e c i a l e m p h a s i s on t h e e v o l u t i o n o f p l u t o n i c r o c k s . Geo 1 . S u r v . C a n . Memoir 335. R o d d i c k , J.A., 1966. The c o a s t c r y s t a l l i n e b e l t o f B.C. T e c t o n i c H i s t o r y and M i n e r a l D e p o s i t s o f t h e W e s t e r n C o r d i l l e r a . C a n . I n s t . M i n . M e t . s p e c , v o l . 8 , p.73. R o d d i c k , J.A., W.W. H u t c h i s o n , 1972. P l u t o n i c and a s s o c i a t e d r o c k s o f t h e C o a s t M o u n t a i n s o f B r i t i s h C o l u m b i a . 1 5 t h G e o l . Cong. 2 4 t h Can. G u i d e b o o k f o r F i e l d E x c u r s i o n s A.C.O. 4. 175 . R o d d i c k , J.A., W.W. H u t c h i s o n , 1 973. E x a m i n a t i o n o f t h e s h o r e -l i n e b e t w e e n K n i g h t I n l e t and Howe Sound. G e o l . S u r v . Can. p a p e r 73-1A p.42. R o d d i c k , J.A., W.W. H u t c h i s o n , 1973. P e m b e r t o n ( E a s t - h a l f ) map a r e a , B.C. (92 J . E . h)\u00E2\u0080\u00A2 G e o l . S u r v . Can. p a p e r 73. p. 17. R o d d i c k , J.A., W.W. H u t c h i s o n , 1974. S e t t i n g o f t h e C o a s t P l u t o n i c C o m p l e x , B.C. P a c i f i c G e o l . 8, p. 91. R o d d i c k , J.A., J . E . M u l l e r , A.V. O k u l i t c h , 1973. F r a s e r R i v e r 1:1,000,000 map s h e e t . G e o l . S u r v . Can. open f i l e map. R o g e r s , W.P., 1970. A g e o l o g i c a l and g e o p h y s i c a l s t u d y o f t h e c e n t r a l P u g e t L o w l a n d . unpub. Ph.D. U. W a s h i n g t o n . R o s s , D.A., G.G. S h o r , J r . , 1965. R e f l e c t i o n p r o f i l e s a c r o s s t h e M i d d l e A m e r i c a T r e n c h . J o u r . Geophys. Res. 70, p . 5 5 5 1 . R o u s e , G.E., W.H. Mathews, R.H. B l u n d e n , 1975. The L i o n s G a t e member: a new L a t e C r e t a c e o u s s e d i m e n t a r y s u b d i v i s i o n i n t h e V a n c o u v e r a r e a o f B.C. Can. J o u r . E a r t h S c i . 1 2 , p.3. Rya n , B., 1973. G e o l o g y and Rb/Sr g e o c h r o n o l o g y o f t h e A n a r c h i s t M o u n t a i n a r e a , s o u t h c e n t r a l B r i t i s h C o l u m b i a . Unpub. PhD., U.B.C. S c h w e i c k e r t , R.A., D.S. Cowan, 1974. P r e - T i t h o n i a n m a g m atic a r c s and s u b d u c t i o n z o n e s , S i e r r a N e v a d a , C a l i f o r n i a . G e o l . S oc. Am. abs . 6-3 , p.2 5 1 . S h i d o , F., 1958. P l u t o n i c and m e t a m o r p h i c r o c k s o f t h e Nakoso and I r i t o n o d i s t r i c t s i n t h e c e n t r a l Abukuma P l a t e a u . J o u r . F a c . S c i . Tokyo U n i v e r s i t y X I , p t . 2, p . 1 3 1 . S h o u l d i c e , D.H. , \u00E2\u0080\u00A2 19 7 1 v G e o l o g y o f .the W e s t e r n C a n a d i a n C o n t i n e n t a l S h e l f . . ;Can .-. P e t r o l e u m G e o l . B u l l . .19.2, p . 405 . S i b l e y , D.F., T.A. V o g e l , B.M. W a l k e r , G. B y e r l y , 1976. The o r i g i n o f o s c i l l a t o r y z o n i n g i n p l a g i o c l a s e : a d i f f u s i o n and g r o w t h c o n t r o l l e d m o d e l . Am. J o u r . S c i . 2 7 6 - 3 , p . 2 7 3 . Simmons, M i c h a e l L e e , 1 9 7 3 . The s t r a t i g r a p h y and p a l e o e n v i r o n m e n t of T h e t i s , K u p e r and a d j a c e n t i s l a n d s , B r i t i s h C o l u m b i a , unpub. M.Sc., O r e g o n S t a t e . S n a v e l y , P.D., H.C. Wagner, 1963. T e r t i a r y g e o l o g i c h i s t o r y o f w e s t e r n O r e g o n and W a s h i n g t o n . W a s h i n g t o n D i v . M i n e s . G e o l . Rep t . I n v . 2 2 . 176 . S n a v e l y , P.D., N.S. M a c L e o d , H.C. Wagner, 1968. T h o l e i i t i c and a l k a l l c b a s a l t s o f t h e Eo c e n e S i l e t z R i v e r V o l c a n i c s , O regon C o a s t Range. A m . J o u r . S c i . p.266. S t a c e y , R.A., 1973. G r a v i t y a n o m a l i e s , c r u s t a l s t r u c t u r e , and p l a t e t e c t o n i c s i n t h e C a n a d i a n C o r d i l l e r a . C a n . J o u r . E a r t h S c i . 10, p.615. S t a c e y , R.A., L.E. S t e v e n s , 1969. An i n t e r p r e t a t i o n o f g r a v i t y m e a s u r e m e n t s on t h e w e s t c o a s t o f Canada. C a n . J o u r . E a r t h S c i . 6, p. 463. S t e w a r t , R . J . , R . J . P a g e , 1974. Z e o l i t e f a c i e s m e t a m o r p h i s m o f t h e L a t e C r e t a c e o u s Nanaimo G r o u p , V a n c o u v e r I s l a n d and G u l f I s l a n d s , B r i t i s h C o l u m b i a . C a n . J o u r . E a r t h S c i . 1 1 , p.280. S t o r r e , B., K. N i t s c h , 1972. D i e r e a k t i o n 2zo + 1 CO ^ = 3 a n + 1 c c + 1 H 2 0 . C o n t r i b . M i n e r a l P e t r o l . 35, p . l . S t u r d a v a n t , C.D., 1975. S e d i m e n t a r y e n v i r o n m e n t s and s t r u c t u r e o f t h e C r e t a c e o u s r o c k s o f S a t u r n a and Tumbo I s l a n d s , B r i t i s h C o l u m b i a . Unpub. M.Sc. Or e g o n S t a t e . Surdam, R.C., 1973. Lo w - g r a d e m e t a m o r p h i s m o f t u f f a c e o u s r o c k s i n t h e K a r m u t s e n g r o u p , V a n c o u v e r I s l a n d , B r i t i s h C o l u m b i a , B u l l . 84, p.1911. S u t h e r l a n d Brown, A., 1966. T e c t o n i c H i s t o r y o f t h e I n s u l a r B e l t of B r i t i s h C o l u m b i a . C a n . I n s t . M i n . M e t . S p e c . V o l . 8, p . 83. S u t h e r l a n d Brown, A., 1968. G e o l o g y o f t h e Queen C h a r l o t t e I s l a n d s . B.C. D e p t . M i n e s , B u l l . 54. S u t t e r , J . F . , A.R. M c B i r n e y , 1974. P e r i o d s o f C e n o z o i c v o l c a n i s m i n t h e C a s c a d e P r o v i n c e o f O r e g o n . G e o l . S o c . Am. a b s . 6-3, p. 264. Symons, D.T.A., 1971. P a l e o m a g n e t i s m o f t h e J u r a s s i c I s l a n d I n t r u s i o n s o f V a n c o u v e r I s l a n d , B r i t i s h C o l u m b i a . G e o l . S u r . Can. p a p e r 70-63, p . l . Symons, D.T.A., 1971. P a l e o m a g n e t i c n o t e s on t h e K a r m u t s e n b a s a l t s , V a n c o u v e r I s l a n d , B r i t i s h C o l u m b i a . G e o l . S u r v . Can. p a p e r 71-24, p.9. Symons, D.T.A. , 1972 . B a t h o l i t h and r o t a t C a n . J o u r . E a r t h S c i . P a l e o m a g n e t i s m o f i o n i n t h e I n t e r i o r 8, p.1388 . t h e T r i a s s i c G u i c h o n P l a t e a u , B r i t i s h C o l u m b i a . 177 . Symons, D.T.A., 1973, U n i t c o r r e l a t i o n s and t e c t o n i c r o t a t i o n f r o m p a l e o m a g n e t i s m o f t h e T r a i s s i c C o p p e r M o u n t a i n I n t r u s i o n s , B r i t i s h C o l u m b i a . G e o l . S u r v . Can. p a p e r 73-19, p . 1 1 . T a b o r , R.W., 1972. Age o f t h e O l y m p i c m e t a m o r p h i s m , W a s h i n g t o n : K-Ar d a t i n g o f l o w - g r a d e m e t a m o r p h i c r o c k s , G e o l . S o c . Am. B u l l . 83, p.1805. T a t e l , H.E., M.A. T u v e , 1955. S e i s m i c e x p l o r a t i o n o f a c o n t i n e n t a l c r u s t . i n : C r u s t o f t h e E a r t h , A, P o l d e r v a a r t , e d . G e o l . S o c . Am. s p e c , p a p e r 62, p.35. T e n n y s o n , M. L., 1974. S t r a t i g r a p h y , s t r u c t u r e and t e c t o n i c s e t t i n g o f J u r a s s i c and C r e t a c e o u s s e d i m e n t a r y r o c k s i n t h e w e s t -c e n t r a l M e t h o w - P a s a y t e n a r e a , N.E. C a s c a d e Range, W a s h i n g t o n and B r i t i s h C o l u m b i a . unpub. PhD, U . W a s h i n g t o n . T h i r u v a t h u k a l , J.V., 1968. R e g i o n a l g r a v i t y o f O r e g o n . unpub. PhD, O r e g o n S t a t e . T h i r u v a t h u k a l , J.V., J.W. B e r g , D.F. H e i n r i c h s , 1970. R e g i o n a l g r a v i t y o f O r e g o n . B u l l . G e o l . S o c . Am. p. 725. T i f f i n , D. L. 1969. C o n t i n u o u s s e i s m i c r e f l e c t i o n p r o f i l i n g i n t h e S t r a i t o f G e o r g i a , B r i t i s h C o l u m b i a . unpub. PhD, UBC T i p p e r , H.W., 1969. M e s o z o i c and C e n o z o i c g e o l o g y o f t h e N.E. p a r t o f Mount W a d d i n g t o n m a p - a r e a , C o a s t - D i s t r i c t , B r i t i s h C o l u m b i a . G e o l . S u r v . Can. p a p e r 68, p.33. T s e n g , K. 1968. A new m o d e l f o r t h e c r u s t i n t h e v i c i n i t y o f V a n c o u v e r I s l a n d . unpub. MSc., U.B.C. V e r h o o g e n , J o h n , F . J . T u r n e r , L.E. W e i s s , C. W a h r h a f t i g , 1970. The E a r t h . H o l t , R i n e h a r t and W i n s t o n , New Y o r k . Wager, L.R., and B r o w n , G.M., 1968. L a y e r e d I g n e o u s R o c k s . O l i v e r and B o y d . E d i n b u r g h . W a l c o t t , R.L., 1972. G r a v i t y , f l e x u r e and t h e g r o w t h o f s e d i m e n t -a r y b a s i n s a t a c o n t i n e n t a l edge. G e o l . S a c . Am. 83, p .1845. . W e l l s , F.G., D.L. P e c k , 1961. G e o l o g i c map of O r e g o n w e s t of t h e 121 s t . m e r i d i a n ^ 3 t a t e o f O r e g o n D e p t . G e o l . M i n e r a l R e s . M i s c . G e o l . I n v e s t i g a t i o n s Map 1-325. W h i t e , W.R.H., J.C. S a v a g e , 1965. A s e i s m i c r e f r a c t i o n and g r a v i t y s t u d y of t h e e a r t h ' s c r u s t i n B.C. S e i s . Soc. Am. B u l l . 55, p . 4 6 3 . 178 . W i l l i a m s , H a r o l d , M.J. K e n n e d y , E.R.W. N e a l e , 1972. The A p p a l a c h -i a n S t r u c t u r a l P r o v i n c e , i n : V a r i a t i o n s i n T e c t o n i c S t y l e s i n Canada . G e o l . A s s . Can. S p e c . P a p e r 11, p. 118. W i l s h i r e , H.G., 1969. M i n e r a l l a y e r i n g i n t h e T w i n L a k e s Q r a n o d i o r i t e , C o l o r a d o . G e o l . S o c . Am. Memoir 115, p . 2 3 5 . Woodsworth, G., 1974. G e o l o g y o f t h e Mount R a l e i g h a r e a , B r i t i s h C o l u m b i a . unpub. PhD, P r i n c e t o n U n i v e r s i t y . W o o l l a r d , G. P. 1969. R e g i o n a l v a r i a t i o n s i n g r a v i t y . A.G.U. memo. 13, p. 3 2 0. Y o r k e , D. and F a r g u h a r , R.M., 1972. The E a r t h ' s Age and G e o c h r o n o -l o g y . Pergamon P r e s s , O x f o r d . CPldtfr WAtstriChttav: QamQa \" - a > 5ar\.cn\a.^ 1 suro-nm M riy\C-Y>\Q.r j i Allot cun (Jtxrrtmx > Qtor^CL Strtutr' cc Coast /Mown\a.ins Oia\u00C2\u00BBam!i? G r p mc / cc o f t p t i tNN5YL\A NJAN mc 4-Qimbiir 'Viayil bos tasic yoteamc rottis ^rredoyniYiarihr ts [fmtttfit Ch chtrt later x 50*22' 126* 00' V\"\u00C2\u00AB8a F A N N Y I S L A N D C O A S T M O U N T A I N S Striitiaraphic units HtNANZA TM volcanic breccia, twn btuatu. to massivt Jim Hack, grvywacki uHTB AR.8LEDOWN TM thi>< ntOJed btaclt durt amyinc firiyv/ackl TARSON 3A V TM black, la \u00C2\u00BBn nutt a, siliceous limstctu, bead chert, any SfmisitM QI/ATSINO TM massivi iiglit'arty limestone with sparse siliceous iincfbtds uTIKu u%Km ' ftow'5 Sparse sediment breccia ftnses 5 UPPER- basalt pillow basalt \u00C2\u00A3 MiDDIE - broken-yilltw breccia, | aqua/jent t*ff, breccia. * tcvvEft jtfllm basalt Jntrusivc units JURASSIC o j M a r i UIOIUTZ weak. Jjliuti?n defined (nclteisnSj *najtc ybases Jfomblivde qabbros Ynainly peripheral to younqist quartz aimtt : 'tviaU textural/ ctnupositi/nai variability 'vVtUbfri Channel autistic quartz, dioritf 'Miners 'Bay aabbro Larai cquant jHaqtoelasi, interstitial Hnaf[c phases rToj>ojra,phic Ltyitawnt rg) hm'itmtal bedding _JV- ctrtunud bidding . \u00E2\u0080\u0094 J J U L V C U (rninorjold.) axial plant, (minorplA) joliation Vancouver Orp ^> h^iation yluttmic rocks ZMctcrs 1000 SO' 22 I26\"00' I25\"42' G E O L O G Y of J-CARDWICKZ and WEST THURLOW ISLANDS, B.C. J.ZNchon 19 74 "@en . "Thesis/Dissertation"@en . "10.14288/1.0052440"@en . "eng"@en . "Geological Sciences"@en . "Vancouver : University of British Columbia Library"@en . "University of British Columbia"@en . "For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use."@en . "Graduate"@en . "The origin of Georgia depression and the Coast Plutonic Complex/Insular Belt province boundary on Hardwicke and West Thurlow Islands, B. C."@en . "Text"@en . "http://hdl.handle.net/2429/19795"@en .