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UBC Theses and Dissertations

Geology and metamorphism of the Yale Creek area, B.C. Bartholomew, Paul Richard 1979

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GEOLOGY AND METAMORPHISM o f .feh-.e YALE CREEK "AREA, B.C. PAUL RICHARD•BARTHOLOMEW B . S c , U n i v e r s i t y of*: Minnesota, 1976 A THESIS SUBMITTED IMPARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE .••in-THE FACULTY OF'GRADUATE STUDIES1 DEPARTMENT OF GEOLOGICAL SCIENCES We accept this, thesis as conforming to the required standard THE UNIVERSITY-•OF BRITISH COLUMBIA MARCH, 1979 (c) Paul Rieh'ard -Baa-tholomew I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r a n a d v a n c e d d e g r e e a t t h e 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 , I a g r e e t h a t t h e 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 r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my D e p a r t m e n t o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t Of G e o l o g i c a l S c i e n c e s T h e 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 2075 W e s b r o o k P l a c e V a n c o u v e r , C a n a d a V6T 1W5 D a t e March 1 6 , 1979 E-6 BP 75-51 1 E ABSTRACT , The Y a l e Creek a r e a i s u n d e r l a i n by t h e p e l i t i c S e t t l e r S c h i s t , Spuzzum h o r n b l e n d e q u a r t z d i o r i t e s , and m i n o r g n e i s s and g r a n o d i o r i t e . M i n e r a l t e x t u r e s i n the s c h i s t s d e f i n e t h r e e phases o f f o l d i n g . The s t r u c t u r a l g e o l o g y i s dominated by t h e second phase, f^, c h a r a c t e r i z e d by n o r t h w e s t p l u n g i n g i s o c l i n a l f o l d s . R e g i o n a l metamorphism r e a c h e d i t s c u l m i n a t i o n j u s t a f t e r f^- The s t r u c t u r a l l y c o n c o r d a n t and b r o a d l y s y n - t e c t o n i c Spuzzum i n t r u s i o n s were emplaced o v e r a p e r i o d o f t i m e en-compassing t h e p e r i o d . o f f o l d i n g and r e g i o n a l metamorphism and s e r v e d as a h e a t s o u r c e f o r t h e r e g i o n a l metamorphism and e a r l y c o n t a c t metamor-phism. L a t e f a u l t i n g has j u x t a p o s e d S e t t l e r S c h i s t and C u s t e r G n e i s s a c r o s s t h e Hope F a u l t , and S e t t l e r S c h i s t s o f c o n t r a s t i n g metamorphic g r a d e s . a c r o s s t h e Cogburn Creek F a u l t . A T r i a s s i c Rb-Sr d a t e o b t a i n e d f o r the S e t t l e r S c h i s t i s i n t e r p r e t e d as the d a t e o f deposition:'; o f ^ o r i g i n a l - - e u g e p s y h c l i h a l E s e d i m e n t s . 0>Ho.rn-b l e n d e K-Ar ages o f 75.5±2.6 and 92.1±3.2 Ma o b t a i n e d f o r Spuzzum q u a r t z d i o r i t e s c o n f o r m to a r e g i o n a l e a s t - y o u n g i n g t r e n d i n Spuzzum K-Ar ages w h i c h r e f l e c t s t h e c o o l i n g h i s t o r y o f t h e a r e a r a t h e r t h a n age o f i n t r u s i v e emplacement. The d a t e o f emplacement o f t h e s t r u c t u r a l l y d i s c o r d a n t and p o s t - t e c t o n i c body o f g r a n o d i o r i t e was d e f i n e d as 32±2Ma by c o n c o r d a n t Rb-Sr and K-Ar d a t e s . The d i s t r i b u t i o n o f a l u m i n o s i l i c a t e assemblages i n t h e S e t t l e r S c h i s t d e f i n e s t h r e e r e g i o n a l metamorphic zones i n c r e a s i n g i n grade t o the n o r t h . The k y a n i t e zone and two s i l l i m a n i t e zones a r e s e p a r a t e d by two i s o g r a d s w h i c h mark e q u i l i b r i u m and o v e r s t e p p e d 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 s . The metamorphic c o n d i t i o n s n e a r t h e f i r s t s i l l i m a n i t e i s o -grad are estimated to be 705±45°C and 7.6±0.5kb from the mutual i n t e r -s e c t i o n of e q u i l i b r i a c a l c u l a t e d from thermodynamic data and microprobe analyses. Anatectic r e l a t i o n s established to date f o r p e l i t i c systems appear to be inconsistent with, t h i s thermodynamic P-T estimate. Min-e r a l assemblages i n scattered u l t r a m a f i c pods are consistent with the metamorphic P-T estimates f o r the p e l i t i c assemblages. i v TABLE OF CONTENTS A b s t r a c t i i L i s t o f t a b l e s v i L i s t o f f i g u r e s , and. i l l i s t a t i o n s v i i Acknowledgement i x I n t r o d u c t i o n 1 P r e v i o u s Work 1 R e g i o n a l Geology 3 Rock U n i t s 8 U n i t 1: S e t t l e r S c h i s t ..8 U n i t 2: C u s t e r G n e i s s • 10 U n i t 3: Spuzzum I n t r u s i o n s 11 U n i t 4: Cogburn G r a n o d i o r i t e 13 U n i t 5: U l t r a m a f i t e s — 13 Metamorphic M i n e r a l Development 15 S t r u c t u r e 19 Age R e l a t i o n s 27 Metamorphism. . 33 Metamorphic C o n d i t i o n s 37 M i c r o p r o b e A n a l y s e s 37 E q u i l i b r i u m C a l c u l a t i o n s 46 D i s c u s s i o n 63 Upper L i m i t s on R e g i o n a l Metamorphism 65 C o n t a c t Metamorphism.. 68 U l t r a m a f i t e s 70 R e g i o n a l S y n t h e s i s 76 R e f e r e n c e s 79 A p p e n d i x I 91 A p p e n d i x I I 96 A p p e n d i x I I I 102 Maps i n .po-Gket 9 ^ ' ^ Cp\il<h*^ v i L I S T OF TABLES T a b l e 1. R e g i o n a l t a b l e o f f o r m a t i o n s 7 T a b l e 2. C o m p i l a t i o n o f age e s t i m a t e s 28 T a b l e 3. M i c r o p r o b e s t a n d a r d s 39 T a b l e 4. B i o t i t e a n a l y s e s 40 T a b l e 5. M u s c o v i t e a n a l y s e s 41 T a b l e 6. S t a u r o l i t e a n a l y s e s 42 T a b l e 7. Garnet a n a l y s e s 43 T a b l e 8. P l a g i o c l a s e a n a l y s e s 44 T a b l e 9. I l m e n i t e a n a l y s e s 45 T a b l e 10. M i n e r a l end-members and a c t i v i t y e x p r e s s i o n s 47 T a b l e 11. End-member a c t i v i t i e s 48 T a b l e 12. E q u i l i b r i u m c o n s t a n t s 48 T a b l e 13. Thermodynamic d a t a 50 T a b l e 14. E n t r o p y and e n t h a l p y o f a l m a n d i n e 61 T a b l e 1-1. S e t t l e r S c h i s t : p e l i t i c s c h i s t and q u a r t z i t e . 92 T a b l e 1-2. S e t t l e r S c h i s t : a m p h i b o l i t e and m e t a c h e r t . C u s t e r G n e i s s 93 T a b l e 1-3. I n t r u s i v e r o c k s 94 T a b l e 1-4. U l t r a m a f i c r o c k s 95 T a b l e I I - l . K-Ar d a t a 98 T a b l e I I - 2 . Rb-Sr d a t a 99 T a b l e I I I - l . A c t i v i t y c o e f f i c i e n t s 105 v i i L I S T OF FIGURES AND ILLUSTRATIONS F i g u r e 1. T h e s i s a r e a l o c a t i o n 2 F i g u r e 2. R e g i o n a l g e o l o g y 6 F i g u r e 3. T i m i n g o f metamorphic m i n e r a l development. 16 F i g u r e 4. E q u a l a r e a p l o t o f m i n o r f o l d d a t a f o r th e S e t t l e r S c h i s t 20 F i g u r e 5. P o i n t d e n s i t y p l o t o f p o l e s t o f o l i a t i o n i n t h e S e t t l e r S c h i s t 21 F i g u r e 6. E q u a l a r e a p l o t o f f a b r i c d a t a f o r t h e Spuzzum I n t r u s i o n s . . . . 22 F i g u r e 7. S c h e m a t i c r e p r e s e n t a t i o n o f t h e r e l a t i v e t i m i n g o f d e f o r m a t i o n , r e g i o n a l metamorphism and Spuzzum i n t r u s i v e a c t i v i t y 25 F i g u r e 8. L o c a t i o n s o f Spuzzum K-Ar d a t e s 30 F i g u r e 9. Graph o f K-Ar age v e r s u s p e r p e n d i c u l a r d i s t a n c e from l i n e A-A' 31 F i g u r e 10. E q u i l i b r i a I t h r o u g h IV c a l c u l a t e d f o r P2 a t a j j ^ o = u • 81 > p l u s t h e r e m a i n d e r o f th e a l u m i n o s i l i c a t e e q u i l i b r i a 51 F i g u r e 11. C a l c u l a t e d c u r v e s f o r e q u i l i b r i a I and I I 52 F i g u r e 12. C a l c u l a t e d c u r v e s f o r e q u i l i b r i u m I I I a t ag Q=0.81 w i t h e q u i l i b r i u m I i n c l u d e d f o r r e f e r e n c e . 54 F i g u r e 13. C a l c u l a t e d c u r v e s f o r e q u i l i b r i u m IV a t n=1.0 and 0.81 56 F i g u r e 14. Composite o f f i g u r e s 11, 12, and 13 i n c l u d i n g o n l y t h e c u r v e s d e f i n i n g t h e extremes f o r each e q u i l i b r i u m 57 F i g u r e 15. Mole f r a c t i o n o f H^O as a f u n c t i o n o f f_ a t 700°C and P - t o t a l = 7.6kb 58 U 2 V X 1 1 F i g u r e 16. P-T bands f o r e q u i l i b r i a I t h r o u g h IV a t a u = 0.86 59 H 20 F i g u r e 17. C a l c u l a t e d e q u i l i b r i u m V c u r v e s f o r P2 62 F i g u r e 18. A p p r o x i m a t e a n a t e c t i c r e l a t i o n s f o r . " p e l i t i c r o c k s 66 F i g u r e 19. Some T-X„^ r e l a t i o n s i n t h e s y s t e m C U 2 MgO-Si0 2-H 20-C0 2 a t 2kb t o t a l p r e s s u r e . . 71 F i g u r e 20. Some c a l c u l a t e d e q u i l i b r i a i n t h e s y s t e m MgO-Si0 2-H 20 73 F i g u r e 21. C a l c u l a t e d a n t h o p h y l l i t e e q u i l i b r i a a d j u s t e d f o r s o l i d s o l u t i o n u s i n g m i c r o p r o b e a n a l y s e s from Reamsbottom(1974) 74 F i g u r e 22. S c h e m a t i c e a s t - w e s t c r o s s s e c t i o n s i l l u s t r a t i n g t h e g e o l o g i c h i s t o r y 78 F i g u r e I I - 1 . Rb-Sr i s o c h r o n p l o t f o r the S e t t l e r S c h i s t 100 F i g u r e I I - 2 . Rb-Sr i s o c h r o n p l o t f o r the Cogburn G r a n o d i o r i t e 101 P l a t e l a . O r i e n t e d q u a r t z (?) i n c l u s i o n s i n s t a u r o l i t e c o n -t a i n e d w i t h i n a pseudomorph a f t e r a n d a l u s i t e 86 b. Q u a r t z p r e s s u r e shadows aro u n d a g a r n e t i n c l u d e d w i t h i n a l a r g e s t a u r o l i t e g r a i n 86 P l a t e 2a. A " b o w t i e " shaped c l u s t e r o f k y a n i t e w i t h i n a pseudomorph a f t e r a n d a l u s i t e 88 b. F o l d e d and r e c r y s t a l l i z e d b u n d l e o f s i l l i m a n i t e 88 P l a t e 3a. O u t c r o p o f t h e b r e c c i a " d i k e " i n t h e Y a l e Creek bed 90 b. Embayed g a r n e t w i t h a h a l o o f q u a r t z and p l a g i o c l a s e i n a specimen from t h e second s i l l i m a n i t e zone 90 ACKNOWLEDGEMENT I w o u l d l i k e to thank Dr. H.J. Greenwood f o r a i d and a d v i c e g e n e r -o u s l y g i v e n t h r o u g h o u t t h e development o f t h i s t h e s i s . Dr. L.C. P i g a g e p r o v i d e d much a i d , f r u i t f u l d i s c u s s i o n s and computer programs. A com-p u t e r program by E.H. P e r k i n s was a l s o i n v a l u a b l e . Dr. R.L. A r m s t r o n g , K r i s t a S c o t t and J o e H a r a k a l p r o v i d e d p a t i e n t i n s t r u c t i o n and h e l p i n g hands f o r the a g e - d a t i n g work. I a l s o a p p r e c i a t e B r y o n C r a n s t o n ' s f i n e t h i n - s e c t i o n s and Ed Montgomery's h e l p w i t h , t h e p h o t o g r a p h y . I n a d d i t i o n , J a n Homenuk t y p e d the t e x t and Gord Hodge d r a f t e d some key f i g u r e s . R e s e a r c h c o s t s were d e f r a y e d by Dr Greenwood's NSERC g r a n t //A-4222. I n a d d i t i o n , I was s u p p o r t e d by a N a t i o n a l S c i e n c e F o u n d a t i o n G r a d u a t e F e l l o w s h i p . 1 INTRODUCTION The Y a l e Creek v a l l e y i s on t h e e a s t s i d e o f t h e L i l l o o e t Range o f t h e Coast M o u n t a i n s , B r i t i s h C o l u m b i a ( f i g u r e 1 ) . Y a l e Creek e m p t i e s i n t o t h e F r a s e r R i v e r a t t h e town o f Y a l e . The a r e a i s u n d e r l a i n by p e l i t i c s c h i s t s w h i c h a r e bounded on t h r e e s i d e s by i n t r u s i v e s and f a u l t s . L o w e s ( 1 9 7 2 ) , mapping on a s c a l e o f 1:50000, f o u n d t h e s e s t a u r o l i t e -k y a n i t e zone s c h i s t s t o be upgraded t o s i l l i m a n i t e zone n e a r i n t r u s i v e s . The metamorphism o f s c h i s t s and g n e i s s e s t o t h e n o r t h w e s t were a l s o f ound t o i n c r e a s e i n grade t o s i l l i m a n i t e zone towards a major i n t r u s i v e (Reamsbottom, 1971, 1 9 7 4 ) . However, Read(1960) and P i g a g e ( 1 9 7 3 ) , map-p i n g s c h i s t s c o n t i n u o u s s o u t h o f t h e Y a l e Creek a r e a , f o u n d t h e r e g i o n a l metamorphic g r a d i e n t t o be u n r e l a t e d t o i n t r u s i v e c o n t a c t s . P i g a g e (1973) f o u n d , n e a r t h e s o u t h e r n boundary o f t h e Y a l e Creek a r e a , up-g r a d i n g t o s i l l i m a n i t e zone t h a t was n o t a p p a r e n t l y r e l a t e d t o an i n -t r u s i v e body. D e t a i l e d mapping and s a m p l i n g i n t h e Y a l e Creek a r e a f o r t h e p r e s e n t s t u d y was c o n d u c t e d i n 1977 w i t h t h e i n t e n t i o n o f c l a r i f y i n g t h e n a t u r e o f t h e s i l l i m a n i t e zone metamorphism and i t s r e l a t i o n t o i n -t r u s i v e a c t i v i t y . I n a d d i t i o n , t h e metamorphism and s t r u c t u r e was t o be r e l a t e d t o t h e work o f P i g a g e ( 1 9 7 3 , 1976) i n t h e a d j a c e n t a r e a t o t h e s o u t h . Subsequent a n a l y t i c a l work i n c l u d e d p e t r o g r a p h y , r a d i o m e t r i c age d a t i n g , m i c r o p r o b e a n a l y s e s , and thermodynamic c a l c u l a t i o n o f t h e c o n d i t i o n s o f metamorphism. PREVIOUS WORK G e o l o g i c s t u d i e s o f t h e a r e a s u r r o u n d i n g Hope, B.C., up t o 1969 have been c o m p i l e d by Monger(1970). M i s c h ( 1 9 6 6 ) has r e v i e w e d t h e F i g u r e 1. T h e s i s a r e a l o c a t i o n . g e o l o g y o f t h e N o r t h e r n Cascade M o u n t a i n s . McTaggart(1970) p r e s e n t e d a t e c t o n i c h i s t o r y o f t h e N o r t h e r n Cascade M o u n t a i n s and i t s r e l a t i o n t o t h e g e o l o g y o f 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 . More r e c e n t l y , R i c h a r d s (1971) s t u d i e d t h e p l u t o n i c r o c k s s o u t h o f Hope, Lowes(1972) s t u d i e d t h e g e o l o g y between H a r r i s o n Lake and t h e F r a s e r R i v e r , P i g a g e ( 1 9 7 3 ) s t u d i e d an a r e a s o u t h w e s t o f Y a l e , Bremner(1973) s t u d i e d a s e c t i o n o f t h e F r a s e r R i v e r v a l l e y n o r t h o f Y a l e , Reamsbottom(1971, 1974) s t u d i e d t h e Mt. B r e a k e n r i d g e a r e a , n o r t h w e s t o f Y a l e , V i n i n g ( 1 9 7 7 ) s t u d i e d t h e Spuzzum I n t r u s i o n s s o u t h w e s t o f Y a l e , and D i t s o n ( 1 9 7 8 ) c o m p i l e d t h e economic g e o l o g y o f t h e Vancouver-Hope a r e a . REGIONAL GEOLOGY The map-area i s s e t w i t h i n t h e C oast C r y s t a l l i n e B e l t o f B.C. w h i c h c o n s i s t s l a r g e l y o f c o n c o r d a n t d i o r i t i c and g r a n o d i o r i t i c i n t r u s i v e s and metamorphic s c h i s t s and g n e i s s e s . T h i s b e l t i s i n t e r p r e t e d as b e i n g t h e d e e p l y eroded a x i a l zone o f a C r e t a c e o u s o r o g e n . A s l i c e o f g n e i s s , bounded by f a u l t s o f t h e F r a s e r R i v e r F a u l t Zone, i s i n t e r p r e t e d as r e -p r e s e n t i n g t h e c o r e o f t h i s o r o g e n (McTaggart, 1 9 7 0 ) . To t h e s o u t h , i n -t o W ashington S t a t e , t h e c r y s t a l l i n e b e l t d i p s under t h e c o v e r o f meta-morphosed and deformed s e d i m e n t s and v o l c a n i c s t y p i c a l o f t h e N o r t h e r n Cascade M o u n t a i n s , w h i c h a r e i n t e r p r e t e d as a s h a l l o w e r e r o s i o n a l l e v e l o f t h e same oro g e n (McTaggart, 1970). West o f t h e map-area, a b e l t o f u l t r a m a f i c r o c k s and a t h r u s t f a u l t a r e c o n s i d e r e d n o r t h e r n e q u i v a l e n t s o f t h e Shuksan and Church M o u n t a i n T h r u s t s o f Washington S t a t e (Lowes, 1972) . S t r a t i f i e d r o c k s f l a n k i n g t h e C oast C r y s t a l l i n e B e l t range i n age from D e v o n i a n t o T e r t i a r y and r e c o r d a h i s t o r y o f e u g e o s y n c l i n a l de-p o s i t i o n and v o l c a n i s m . Movement a l o n g t h e F r a s e r R i v e r f a u l t zone may have begun i n t h e M e s o z o i c . Deformed Eocene c o n g l o m e r a t e s i n t h e F r a s e r R i v e r Graben (McTaggart and Thompson, 1967) i n d i c a t e t h a t movement c o n t i n u e d i n t o t h e T e r t i a r y . T e r t i a r y i n t r u s i v e a c t i v i t y i s c h a r a c t e r i z e d by d i s c o r d a n t g r a n o -d i o r i t e p l u t o n s . 5 F i g u r e 2. R e g i o n a l g e o l o g y : Legend. Q u a t e r n a r y 8 D r i f t and A l l u v i u m •jj G r a n i t i c Rocks T e r t i a r y | 7 | Eocene Conglomerate Y Y a l e I n t r u s i o n s 6 J a c k a s s M o u t a i n Group C r e t a c e o u s E3Sp uzzum I n t r u s i o n s J u r a s s i c | 5 j L a d n e r Group T r i a s s i c 4 j Hozameen Group I 3 j S e t t l e r S c h i s t L a t e I 2 j C h i l l i w a c k Group P a l e o z o i c . | I 1 ] C u s t e r G n e i s s Age Unknown U l t r a m a f i c Rocks 121°3l''W t i t T t t t t f . t . t . t t t T t t f t t t t i CHILLIWACK 4 BATHOLITH '»» 1 \ \ v. 1 v..', \ V \.Y...J F i g u r e 2. R e g i o n a l g e o l o g y : from Monger(197), P i g a g e ( 1 9 7 3 ) and t h i s s t u d y . T a b l e 1. R e g i o n a l t a b l e o f f o r m a t i o n s . WESTERN BELT P l i o c e n e . H M Miocene H O l i g o c e n e K ! Eocene P a l e o c e n e CRETACEOUS JURASSIC TRIASSIC M O N O H n g r a n i t i c r o c k s g r a n i t i c r o c k s u l t r a m a f i c r o c k s C u l t u s F o r m a t i o n C h i l l i w a c k Group cr fD o e P a. pi i-i AXIAL BELT CO sr H e C h i l l i w a c k B a t h o l i t h Cogburn G r a n o d i o r i t e Eocene Conglomerate Y a l e I n t r u s i o n s Spuzzum I n t r u s i o n s S e t t l e r S c h i s t C a i r h ' Needle "Fm. ? C u s t e r G n e i s s ? ' B r e a k e n r i d g e Fm.' a4 (0 o c 3 & •EASTERN BELT PJ C N e e d l e Peak P l u t o n P a s a y t e n Group J a c k a s s M o u n t a i n Group Dewdney Creek Group Ladner Group Hozameen Group i u l t r a m a f i c r o c k s Adapted from P i g a g e ( 1 9 7 3 , T a b l e 1 ) ; based on Monger(1970) and t h i s s t u d y . ROCK UNITS U n i t 1: S e t t l e r S c h i s t The S e t t l e r S c h i s t i s dominated by m e t a s e d i m e n t a r y p e l i t i c s c h i s t s M i n o r amounts o f a m p h i b o l i t e and q u a r t z i t e a r e i n t e r l a y e r e d w i t h t h e s c h i s t s . There a r e two t y p e s o f p e l i t i c s c h i s t , termed q u a r t z o f e l d -s p a t h i c and g r a p h i t i c , w h i c h have been mapped as s e p a r a t e u n i t s e l s e -where ( P i g a g e , 1 9 7 3 ) . The g r a p h i t i c s c h i s t s a r e r e s t r i c t e d t o t h e sout h w e s t p o r t i o n o f t h e a r e a mapped i n t h i s s t u d y . The p e l i t i c s c h i s t s c o n s i s t m a i n l y o f q u a r t z , p l a g i o c l a s e , b i o t i t e and a l m a n d i n e - r i c h g a r n e t . I n a d d i t i o n s t a u r o l i t e and c o m b i n a t i o n s o f th e a l u m i n o - s i l i c a t e s k y a n i t e , f i b r o l i t e , and s i l l i m a n i t e a r e commonly p r e s e n t . P r e s e n t i n mi n o r amounts a r e m u s c o v i t e , c h l o r i t e , i l m e n i t e , r u t i l e , a p a t i t e , t o u r m a l i n e , p y r r h o t i t e , and z i r c o n . P l a g i o c l a s e com-p o s i t i o n s range from An^Q t o An^,.. There .are o n l y minor m i n e r a l o g i c a l d i f f e r e n c e s between t h e q u a r t z o f e l d s p a t h i c and g r a p h i t i c s c h i s t s . I n o u t c r o p , t h e q u a r t z o f e l d s p a t h i c s c h i s t s a r e l i g h t g r e y and t h e g r a p h i t i c s c h i s t s a r e a d a r k s t e e l - g r e y . T h i s d i f f e r e n c e i n c o l o r a p p e a r s t o r e f l e c t o n l y t h e d i f f e r i n g amounts o f d u s t - f i n e d i s s e m i n a t e d g r a p h i t e . E s t i m a t e d m i n e r a l modes show t h a t t h e g r a p h i t i c s c h i s t s do n o t c o n t a i n s i g n i f i c a n t l y more b i o t i t e ( s e e A p p e n d i x I . f o r m i n e r a l o g y and modes f o r a l l r o c k t y p e s ) . There i s a d i f f e r e n c e i n t h e mode o f s t a u r o l i t e o c c u r r e n c e . I n c o n t r a s t t o t h e q u a r t z o f e l d s p a t h i c s c h i s t s , s t a u r o l i t e s i n g r a p h i t i c s c h i s t s a r e more common, l a r g e r , and more commonly i d i o m o r p h i c . There i s a g e n e r a l i n c r e a s e i n metamorphic grade t o t h e n o r t h a c -r o s s t h e mapped a r e a . Accompanying t h i s i n c r e a s e i n grade i s a p r o -g r e s s i o n o f a l u m i n o - s i l i c a t e assemblages from k y a n i t e t o f i b r o l i t e + k y a n i t e t o s i l l i m a n i t e + f i b r o l i t e . I n a d d i t i o n , t h e i n c r e a s e i n g r a d i s c h a r a c t e r i z e d by a g e n e r a l i n c r e a s e i n g r a i n s i z e s and t h e a p p e a r -ance o f g n e i s s i c b a n d i n g and t h i n l e u c r o c r a t i c v e i n l e t s . E a r l y c o n t a c t metamorphism i s i n d i c a t e d by t h e o c c u r r e n c e o f pseudomorphs a f t e r a n d a l u s i t e i n p e l i t i c s c h i s t s . S q u a r e - p r i s m shaped m i n e r a l a g g r e g a t e s up t o 1.5cm l o n g a r e i n t e r p r e t e d as pseudomorphs a f t e r c h i a s t o l i t e p o r p h y r o b l a s t s . O c c u r r e n c e s o f t h e s e pseudomorphs a r e a l l c l o s e l y a s s o c i a t e d w i t h i n t r u s i v e c o n t a c t s . The pseudomorphs now c o n s i s t o f q u a r t z , s t a u r o l i t e , m u s c o v i t e , k y a n i t e and mi n o r p l a g i o c l a s e . S t a u r o l i t e and m u s c o v i t e , i n pseudomorph-bearing s p e c i m e n s , a r e commonly r e s t r i c t e d i n t h e i r d i s t r i b u t i o n t o w i t h i n t h e pseudo-morphs. S t a u r o l i t e s w i t h i n t h e pseudomorphs c o n t a i n u n u s u a l g r a p h i c -i n c l u s i o n s o f q u a r t z ( ? ) ( p l a t e l a ) and a r e f r e e o f g r a p h i t e . These s t a u r o l i t e s c l o s e l y match t h e d e s c r i p t i o n o f s t a u r o l i t e s h a v i n g s i m i -l a r p a r a g e n e s e s i n t h e Kwoiek a r e a some 50km t o t h e n o r t h ( H o l l i s t e r , 1 9 6 9 ) . R e c o g n i z e a b l e s e d i m e n t a r y s t r u c t u r e s a r e r a r e i n t h e s e h i g h - g r a d e s c h i s t s . However, graded b e d d i n g has been r e c o g n i z e d i n s c h i s t s a d -j a c e n t t o t h e s o u t h ( P i g a g e , 1 9 7 3 ) . The graded b e d d i n g and t h e a l u m i -nous m i n e r a l o g y i n d i c a t e t h a t t h e p e l i t i c s c h i s t s were o r i g i n a l l y g r e y wackes. A m p h i b o l i t e s i n t e r l a y e r e d w i t h t h e s c h i s t s have been s e p a r a t e d i n t o two t y p e s : banded and m a f i c . The banded a m p h i b o l i t e s a r e c h a r a c t e r i z e d by . t h i n a l t e r n a t i n g l i g h t and d a r k l a y e r s c o n t a i n i n g c o n c e n -t r a t i o n s o f p l a g i o c l a s e ( A n n Q ) and h o r n b l e n d e r e s p e c t i v e l y . O ther M a j o r m i n e r a l s i n c l u d e q u a r t z , g a r n e t and o c c a s i o n a l l y d i o p s i d e and c l i n o z o i s i t e . I l m e n i t e and sphene a r e common a c c e s s o r i e s . O n l y two o u t c r o p s o f m a f i c a m p h i b o l i t e were e n c o u n t e r e d . They c o n s i s t o f 85 t o 95% h o r n b l e n d e w i t h p l a g i o c l a s e (An.,) making up t h e r e m a i n d e r . I l m e n -9o i t e and q u a r t z a r e p r e s e n t i n mi n o r amounts. Based upon a p p r o x i m a t e b u l k c o m p o s i t i o n s , t h e banded a m p h i b o l i t e s a r e i n t e r p r e t e d t o be meta-morphosed, m a r l s o r c a l c a r e o u s a r g i l l i t e s and t h e m a f i c a m p h i b o l i t e s a r e i n t e r p r e t e d as metamorphosed m a f i c i g n e o u s r o c k s . There a l s o a r e two t y p e s o f q u a r t z i t e i n t e r l a y e r e d w i t h t h e s c h i s t s . L a y e r s up t o 50cm t h i c k a r e dominated by q u a r t z and p l a g i o -c l a s e w i t h m i n o r amounts o f g a r n e t , b i o t i t e , m u s c o v i t e and s t a u r o l i t e . These l a y e r s may have been sandy, c l a y - p o o r l a y e r s i n t h e sequence o f greywackes. The o t h e r q u a r t z i t e s a r e s i g n i f i c a n t l y f i n e r g r a i n e d t h a n t h e s u r r o u n d i n g s c h i s t s and have t h i n (2mm), i r r e g u l a r , c l o s e l y s paced d a r k bands c o n t a i n i n g h o r n b l e n d e . The b a n d i n g i s n o t as r e g u l a r as th e metamorphic f o l i a t i o n o f t h e s u r r o u n d i n g s c h i s t s and i s c o n s i d e r e d t o be s e d i m e n t a r y l a y e r i n g . These q u a r t z i t e s may have o r i g i n a t e d as impure c h e r t s . The r o c k s now known as t h e S e t t l e r S c h i s t c o n s i s t e d o r i g i n a l l y m a i n l y o f greywackes w i t h m i n o r i n t e r b e d d e d m a r l s , impure s a n d s t o n e s and c h e r t s and p o s s i b l y some m a f i c f l o w s . T h i s s u g g e s t s d e p o s i t i o n i n a e u g e o s y n c l i n a l e n v i r o n m e n t , and, a n a l y s i s o f t h e g e o l o g y o f t h e s u r -r o u n d i n g r e g i o n i n d i c a t e s t h a t a e u g e o s y n c l i n a l t r o u g h e x i s t e d t h r o u g h much o f t h e P a l e o z o i c and i n t o e a r l y M e s o z o i c (Monger, 1970). U n i t 2: C u s t e r G n e i s s One o u t c r o p o f C u s t e r G n e i s s was sampled j u s t e a s t o f t h e Hope F a u l t . I t c o n s i s t s o f l a r g e ( t o 1cm) g r a i n s o f p l a g i o c l a s e i n a q u a r t z m a t r i x . L a r g e q u a r t z g r a i n s a r e s t r a i n e d , f r a c t u r e d and b r o k e n i n t o s m a l l e r g r a i n s w h i c h have d e n t a t e g r a i n b o u n d a r i e s . The t w i n l a m e l l a e o f t h e p l a g i o c l a s e g r a i n s a r e commonly t a p e r i n g and b e n t . T h i s s p e c i -men a p p a r e n t l y c o r r e s p o n d s t o t h e p e g m a t i t i c phase o f t h e C u s t e r G n e i s s (Bremner, 1973). U n i t 3: Spuzzum I n t r u s i o n s The Spuzzum I n t r u s i o n s a r e c o a r s e g r a i n e d h o r n b l e n d e q u a r t z d i o -r i t e s w h i c h f o r m major p l u t o n s e x t e n d i n g n o r t h and s o u t h o f t h e mapped a r e a . I n t h e specimens s t u d i e d p l a g i o c l a s e c o m p o s i t i o n s range from An^^ t o A n ^ * The p r o p o r t i o n s o f h o r n b l e n d e range f r o m 10 t o 60% and q u a r t z f r o m 5 t o 20%. B i o t i t e i s a l s o a major m i n e r a l i n many s p e c i -mens. A p a t i t e , i l m e n i t e , r u t i l e and z i r c o n a r e common a c c e s s o r i e s . B o t h h o r n b l e n d e and b i o t i t e have been p a r t i a l l y a l t e r e d t o c h l o r i t e . Most specimens show m i c r o s c o p i c s i g n s o f s t r a i n s u c h as d e n t a t e g r a i n b o u n d a r i e s , u n d u l a t o r y e x t i n c t i o n i n q u a r t z and b e n t b i o t i t e f l a k e s . W i t h i n t h e mapped a r e a t h e s e i n t r u s i v e s have been s e p a r a t e d i n t o f i v e d i s t i n c t b o d i e s on t h e b a s i s o f m i n e r a l o g y , t e x t u r e s , l o c a t i o n , and s t y l e of i n t r u s i o n . The o r d e r i n w h i c h t h e y a r e p r e s e n t e d h e r e and on Map.,l:.'.isjnbt i n t e n d e d t o be ^ c h r o n o l o g i c a l . U n i t 3a: South Body L o c a t e d a l o n g t h e s o u t h w e s t edge o f t h e mapped a r e a , t h i s body c o n t a i n s s m a l l s k e l e t a l g a r n e t s i n m i n o r amounts. The body i s w e l l f o l i a t e d i n i t s westernmost p o r t i o n where a l l h o r n b l e n d e has been a l -t e r e d t o b i o t i t e . U n l i k e some o f t h e Spuzzum I n t r u s i o n s , t h e p l a g i o -c l a s e i n t h i s body i s n o t zoned. P e l i t i c s c h i s t s n e a r t h i s body com-monly c o n t a i n pseudomorphs a f t e r a n d a l u s i t e . U n i t 3b: N o r t h Body T h i s i n t r u s i v e , d o m i n a t i n g t h e r i d g e n o r t h o f Y a l e Creek, i s w e l l f o l i a t e d and r e m a r k a b l y u n i f o r m i n m i n e r a l o g y and t e x t u r e . H o r n b l e n d e and b i o t i t e a r e p r e s e n t i n a p p r o x i m a t e l y e q u a l amounts and e p i d o t e i s an a d d i t i o n a l a c c e s s o r y phase. P l a g i o c l a s e i n t h i s body i s a l s o un-zoned. U n i t 3c: Southwest Body L o c a t e d s o u t h o f t h e w e s t e r n tongue o f u n i t 3a, t h i s p o o r l y f o l i a t e d body c o n t a i n s b l o c k y h o r n b l e n d e g r a i n s and thick(2mm) books o f b i o t i t e i n e q u a l p r o p o r t i o n s . P l a g i o c l a s e c o n s i s t s o f c o m p o s i t e g r a i n s zoned a p p r o x i m a t e l y f r o m An a t t h e edges t o A n ^ i n c o r e s . C l i n o -z o i s i t e and sphene a r e p r e s e n t i n m i n o r amounts. U n i t 3d: West Body L o c a t e d a t t h e w e s t e r n edge o f t h e mapped a r e a , t h i s body i s n o t f o l i a t e d and shows no m i c r o s c o p i c i n d i c a t i o n s o f s t r a i n . L i k e u n i t 3c, p l a g i o c l a s e c o n s i s t s o f z o n e d ( A n ^ Q - A n ^ ) , c o m p o s i t e g r a i n s . Pseudo-morphs a f t e r a n d a l u s i t e have a l s o been i d e n t i f i e d n e a r t h i s body. U n i t 3e: F a g e r v i k Body Mount F a g e r v i k , t h e h i g h e s t p o i n t i n t h e a r e a , i s c e n t r a l t o t h i s body. I t i s a complex o f d i o r i t i c phases r a n g i n g f r o m a g a r n e t - b e a r i n g l e u c o c r a t i c phase t o an a m p h i b o l i t i c phase c o n t a i n i n g 60% h o r n b l e n d e . These phases a r e i n j e c t e d a l o n g t h e f o l i a t i o n o f t h e s u r r o u n d i n g s c h i s t s , f o r m i n g s i l l s 3 t o 10 m e t e r s t h i c k . The c o n t a c t w i t h t h e main i n t r u s i v e body i s a wide t r a n s i t i o n a l zone o v e r w h i c h t h e s i l l d e n s i t y i n c r e a s e s u n t i l t h e s c h i s t s a r e p r e s e n t o n l y as minor i n c l u s i o n s . The 13 main body i s a m i g m a t i t i c m i x t u r e o f t h e v a r i o u s p h a s e s . F o l i a t i o n i n t h e s e phases r a n g e s from w e l l - d e v e l o p e d t o a b s e n t . U n i t 4: Cogburn G r a n o d i o r i t e D o m i n a t i n g t h e s l o p e s on t h e e a s t s i d e o f Cogburn Creek, t h i s i n -t r u s i v e i s a medium g r a i n e d , l e u c o c r a t i c g r a n o d i o r i t e c o n t a i n i n g up t o 15% a l k a l i - f e l d s p a r . T h i s u n i t has p r e v i o u s l y been grouped w i t h t h e Spuzzum I n t r u s i o n s ( L o w e s , 1 9 7 2 ) . I t i s c o n s i d e r e d a s e p a r a t e u n i t h e r e on t h e b a s i s o f m i n e r a l o g y , t e x t u r e s and c r o s s c u t t i n g r e l a t i o n s . B i o t i t e , a l t e r i n g t o c h l o r i t e i s t h e dominant m a f i c m i n e r a l , w h i l e h o r n b l e n d e i s p r e s e n t o n l y as a m i n o r component. P l a g i o c l a s e g r a i n s a r e i n t e r g r o w n and commonly zoned a p p r o x i m a t e l y from A n . c t o An,,.. The 35 oU r o c k shows no a p p a r e n t p r e f e r e d o r i e n t a t i o n o f m i n e r a l s . O c c a s i o n a l c o a r s e - g r a i n e d h o r n b l e n d e - r i c h i n c l u s i o n s a r e p r o b a b l y d e r i v e d f r o m Spuzzum I n t r u s i o n s . The b o u n d a r i e s o f t h e i n t r u s i v e c r o s s c u t b o t h S e t t l e r S c h i s t f o l i a t i o n and s i l l s a s s o c i a t e d w i t h Spuzzum u n i t 3e. U n i t 5: U l t r a m a f i t e s A few pods o f u l t r a m a f i c r o c k a r e s c a t t e r e d t h r o u g h t h e S e t t l e r S c h i s t . A body o f b r o w n i s h q u a r t z - c a r b o n a t e r o c k a l o n g t h e Hope F a u l t i s i n t e r p r e t e d as an a l t e r e d u l t r a m a f i t e . The q u a r t z i s f i n e g r a i n e d t o a p h a n i t i c w i t h s m a l l rounded pods c o n t a i n i n g s l i g h t l y more c o a r s e g r a i n s . Coarse m a g n e s i t e o c c u r s i n t h i n v e i n s and rounded' l e n s e s . 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An i s o l a t e d o u t c r o p o f u n f o l i a t e d l i g h t - g r e y r o c k on t h e h i l l s i d e s o u t h o f Y a l e Creek c o n -t a i n s c o a r s e a n t h o p h y l l i t e and f o r s t e r i t e and m i n o r amounts o f t a l c and m a g n e s i t e . A l e n s e o f t a l c s c h i s t o c c u r s w i t h i n g r a p h i t i c s c h i s t s west o f Cogburn Creek. The w e l l - d e v e l o p e d t a l c f o l i a t i o n i s c o n c o r d a n t w i t h t h e f o l i a t i o n o f t h e s u r r o u n d i n g s c h i s t s . P a r t s o f t h i s body c o n t a i n t h e assemblages t a l c - m a g n e s i t e - c h l o r i t e , t a l c - t r e m o l i t e - c h l o r i t e , and q u a r t z - t r e m o l i t e - c h l o r i t e . M a g n e s i t e o c c u r s i n rounded a g g r e g a t e s o f u n s t r a i n e d g r a i n s t h a t a r e i n t e r p r e t e d as b e i n g pseudomorphous a f t e r f o r s t e r i t e . 15 METAMORPHIC MINERAL DEVELOPMENT M i n e r a l t e x t u r e s i n t h e S e t t l e r S c h i s t r e c o r d t h r e e phases o f f o l d i n g w h i c h have been d e s i g n a t e d f ^ , f ^ , and f ^ i n o r d e r o f d e c r e a s i n g age. The w e l l - d e v e l o p e d m i c a f o l i a t i o n i n t h e s c h i s t s was formed d u r i n g f^. The o n l y r e c o r d o f an e a r l i e r phase o f f o l d i n g , f ^ , i s p r o -v i d e d by t r a i l s o f i n c l u s i o n s w i t h i n p o r p h y r o b l a s t s . These i n c l u s i o n , t r a i l s c o n s i s t o f f l a k e s o f g r a p h i t e and e l o n g a t e g r a i n s o f q u a r t z , b o t h o r i e n t e d p a r a l l e l t o t h e t r a i l s . T h i s i n d i c a t e s t h a t t h e t r a i l s a r e r e l i c s o f a f o l i a t i o n r a t h e r t h a n o r i g i n a l c o m p o s i t i o n a l l a y e r i n g . The l a t e s t f o l d i n g e v e n t , f ^ 5 f o l d e d t h e f o l i a t i o n , b u t d i d n o t d e v e l o p an a x i a l p l a n a r f o l i a t i o n o f i t s own. These t h r e e d e f o r m a t i o n a l e v e n t s have been used as t i m e r e f e r e n c e s a g a i n s t w h i c h a s e r i e s o f metamorphic e v e n t s can be measured. F i g u r e 3 shows t h e i n f e r r e d t i m i n g o f m i n e r a l g r o w t h . The d e t a i l s f o l l o w below. The p a r a g e n e t i c sequence shows t h a t c o n t a c t metamorphism p r e c e e d e d f^* and t h e r e g i o n a l metamorphism peaked between f ^ and f ^ . G a r n e t s appear t o have been t h e e a r l i e s t p o r p h y r o b l a s t s t o form, f o r m i n g b e f o r e b o t h f ^ and f ^ . The f ^ m i c a f o l i a t i o n d e f l e c t s around e u h e d r a l g a r n e t s l e a v i n g " p r e s s u r e shadows". G a r n e t s ; i n c l u d e d w i t h i n o t h e r p o r p h y r o b l a s t s can be seen t o s i m i l a r l y d e f l e c t t h e f ^ f o l i a t i o n d e f i n e d by i n c l u s i o n t r a i l s ( p l a t e l b ) . A n d a l u s i t e formed p r i o r t o and was pseudomorphed a f t e r f.^. As w i t h t h e g a r n e t s , t h e m i c a f o l i a t i o n d e f l e c t s around t h e pseudomorphs. I n a d d i t i o n , t h e e l o n g a t e pseudomorphs a r e l i n e a t e d w i t h i n t h e p l a n e o f f o l i a t i o n . W i t h i n t h e pseudomorphs, randomly o r i e n t e d m u s c o v i t e s and " b o w - t i e " shaped s p r a y s o f s t a u r o l i t e and k y a n i t e ( p l a t e 2a).;.::/: '/.";•' i n -d i c a t e t h a t r e p l a c e m e n t o f a n d a l u s i t e t o o k p l a c e under n o n - s t r e s s e d F i g u r e 3. T i m i n g o f metamorphic m i n e r a l development. ; f l . : f 2 . g a r n e t -i • ; a n d a l u s i t e ; : ; I b i o t i t e 1 •-m u s c o v i t e k y a n i t e s t a u r o l i t e f i b r o l i t e s i l l i m a n i t e c o n d i t i o n s . L a t h s o f m u s c o v i t e e x t e n d i n g o u t o f t h e pseudomorphs c r o s s -c u t f o l i a t e d b i o t i t e s , i n d i c a t i n g t h a t t h e r e p l a c e m e n t o c c u r r e d a f t e r V B i o t i t e s formed d u r i n g f ^ and c o n t i n u e d r e c r y s t a l l i z a t i o n e x t e n d e d p a s t b o t h f ^ and f ^ . P a r a l l e l o r i e n t a t i o n o f b i o t i t e f l a k e s d e f i n e s t h e w e l l - d e v e l o p e d f o l i a t i o n . I n t h e h i g h e r grade s c h i s t s , r e o r i e n -t a t i o n o f b i o t i t e s t h a t accompanyed p o s t - f ^ r e c r y s t a l l i z a t i o n has r e n -d e r e d t h i s f o l i a t i o n l e s s pronounced. B i o t i t e s o u t l i n i n g f ^ minor f o l d s f o r m p o l y g o n a l a r c s , showing t h a t r e c r y s t a l l i z a t i o n c o n t i n u e d p a s t f ^ . P o r p h y r o b l a s t s o f k y a n i t e and s t a u r o l i t e p r o b a b l y formed o v e r a p e r i o d between f ^ and f^, c o n t i n u i n g somewhat i n t o f ^ . P r i s m a t i c p o r -p h y r o b l a s t s o f t h e s e m i n e r a l s a r e commonly o r i e n t e d w i t h i n t h e m i c a f o l i a t i o n w h i c h , i n . t u r n , d e f l e c t s a r o u n d them. Many s t a u r o l i t e s and some k y a n i t e s c o n t a i n i n c l u s i o n t r a i l s w h i c h d e f i n e an i n t e r n a l f a b r i c . I n many c a s e s t h i s i n t e r n a l f a b r i c i s d i s c o r d a n t t o t h e m i c a f o l i a -t i o n . I n one specimen t h e i n t e r n a l f a b r i c o f i n c l u s i o n s w i t h i n s t a u r o -l i t e s i s o b v i o u s l y f o l d e d , s w i n g i n g i n t o c o n c o r d a n c e w i t h t h e e x t e r n a l f s b r i c a t t h e edge o f t h e p o r p h y r o b l a s t s . These s t a u r o l i t e s g r a i n s appear t o have begun f o r m i n g when f ^ was d e f o r m i n g t h e f ^ f o l i a t i o n b u t had n o t y e t o b l i t e r a t e d i t . C r y s t a l l i z a t i o n t h e n c o n t i n u e d u n t i l development o f t h e f o l i a t i o n was n e a r l y c o m p l e t e . S t a u r o l i t e c r y s -t a l l i z a t i o n must have c o n t i n u e d l o n g e r t h a n k y a n i t e c r y s t a l l i z a t i o n s i n c e some k y a n i t e g r a i n s can be found p a r t i a l l y t o c o m p l e t e l y e n c l o s e d i n s t a u r o l i t e . I n r a r e c a s e s i n w h i c h b o t h t h e s t a u r o l i t e and e n c l o s e d k y a n i t e have i n t e r n a l f a b r i c s , t h e y a r e c o n c o r d a n t w i t h each o t h e r . B o t h t e x t u r a l v a r i e t i e s o f s i l l i m a n i t e formed between f ^ and f ^ . F i b r o l i t e n o r m a l l y o c c u r s as randomly o r i e n t e d f i b e r s i n t e r g r o w n w i t h b i o t i t e , i n l e n s o i d a g g r e g a t e s and i n e l o n g a t e b u n d l e s . These b u n d l e s and l e n s e s a r e commonly o r i e n t e d p a r a l l e l t o t h e f o l i a t i o n even though i n d i v i d u a l f i b e r s show no such p r e f e r r e d o r i e n t a t i o n . The o r i e n t a t i o n o f t h e s e f i b r o l i t e c l o t s must have been c o n t r o l l e d by a p r e -e x i s t i n g f a b r i c . I n r o c k s c o n t a i n i n g s m a l l - s c a l e f ^ f o l d s , e l o n g a t e b u n d l e s o f f i b r o l i t e a r e deformed and r e c r y s t a l l i z e d i n t o p o l y g o n a l a r c s a r o u n d t h e s e f o l d s ( p l a t e 2 b ) . The p r i s m a t i c p o r p h y r o b l a s t s o f s i l l i -m a n i t e a r e a l s o n o r m a l l y randomly o r i e n t e d . However, i n specimens c o n -t a i n i n g f ^ m i n o r f o l d s , t h e s i l l i m a n i t e p r i s m s a r e a l i g n e d p a r a l l e l t o t h e axes o f t h e s e f o l d s . M u s c o v i t e formed i n two g e n e r a t i o n s . The f i r s t g e n e r a t i o n was s y n - t e c t o n i c t o f^. I t i s c h a r a c t e r i z e d by s m a l l b l a d e s i n t e r g r o w n •;•/ w i t h and p a r a l l e l t o f o l i a t e d b i o t i t e s . The second g e n e r a t i o n i s p o s t -f ^ . I t i s c h a r a c t e r i z e d by l a r g e r p o r p h y r o b l a s t i c b l a d e s w h i c h have no p r e f e r r e d o r i e n t a t i o n and o f t e n c r o s s c u t f o l i a t e d b i o t i t e s . The m i n o r amount., o f c h l o r i t e p r e s e n t i n t h e s c h i s t s has a s i m i l a r h a b i t . 19 STRUCTURE M a c r o s c o p i c s t r u c t u r e s r e f l e c t o n l y f ^ and f ^ , t h e l a t e r two o f t h e f o l d i n g e v e n t s i n f e r r e d f r o m m i c r o s c o p i c t e x t u r e s . C o n t a c t r e -l a t i o n s i n d i c a t e t h a t t h e ages o f t h e Spuzzum I n t r u s i o n s r a n g e from p r e - t o p o s t - t e c t o n i c t o t h e s e two f o l d i n g e v e n t s . L a t e f a u l t i n g has a t t r i b u t e d t o a b r i t t l e phase o f d e f o r m a t i o n . I n t h e S e t t l e r S c h i s t , t h e w e l l - d e v e l o p e d m i c a f o l i a t i o n a s -s o c i a t e d w i t h f ^ i s a x i a l - p l a n a r t o recumbent i s o c l i n a l f o l d s . Axes o f t h e s e f o l d s g e n e r a l l y p l u n g e t o t h e n o r t h (see f i g u r e 4 ) . Away fr o m f o l d h i n g e s , f o l i a t i o n and c o m p o s i t i o n a l l a y e r i n g a r e p a r a l l e l . P o s t - f o l i a t i o n f o l d i n g i s t h e r e s u l t o f b o t h a r e g i o n a l f o l d i n g e v e n t , f^> and i n t r u s i v e a c t i v i t y . Over much o f t h e a r e a f ^ f o l d i n g i s c h a r a c t e r i z e d by g e n t l e w a r p i n g o f t h e m i c a f o l i a t i o n w i t h few r e l a t e d s m a l l - s c a l e f o l d s . T h i s p r o d u c e s o n l y m i n o r s c a t t e r i n g o f p o l e s t o f o l i a t i o n on an e q u a l a r e a p r o j e c t i o n (see f i g u r e 5 ) . S o u t h o f t h e mapped a r e a l a r g e s c a l e f ^ f o l d s t i g h t e n i n t o w e l l d e f i n e d s y n f o r m -a n t i f o r m s t r u c t u r e s c o a x i a l w i t h f o l d i n g ( P i g a g e , 1973)L I n t h e map-ped a r e a p o s t - f o l i a t i o n f o l d i n g i s more i n t e n s e n e a r t h e Spuzzum I n -t r u s i o n s , p a r t i c u l a r l y t h e F a g e r v i k Body. I n t h e s c h i s t s s u r r o u n d i n g th e F a g e r v i k Body l a r g e - s c a l e f o l d i n g i s more pronounced (see Map 2) and s m a l l - s c a l e f o l d s a r e common. The a x i a l p l a n e s o f t h e s e f o l d s a r e t y p i c a l l y a t l o w a n g l e s t o t h e f o l i a t i o n , b u t t h e o r i e n t a t i o n s of t h e f o l d axes a r e s c a t t e r e d (see f i g u r e 4 ) . D u c t i l i t y c o n t r a s t s un-d o u b t e d l y p l a y e d a p a r t i n t h e s e l o c a l v a r i a t i o n s i n f o l d i n t e n s i t y . However, i t cannot e x p l a i n t h e c o n c e n t r a t i o n o f s u c h e f f e c t s n e a r one Spuzzum i n t r u s i v e r e l a t i v e t o t h e o t h e r s . F o r c e f u l i n t r u s i o n , and i n -c r e a s e d d u c t i l i t y due t o h e a t o f i n t r u s i o n may have been i m p o r t a n t N F i g u r e 4. E q u a l a r e a p l o t o f m i n o r f o l d d a t a f o r the S e t t l e r S c h i s t . • - f o l d . a x e s ; 9 p o i n t s O f-j f o l d a x e s ; 23 p o i n t s 0 p o l e s t o a x i a l p l a n e s ; 11 p o i n t s O p o l e s to f ^ a x i a l p l a n e s ; 18 p o i n t s 21 N \ V : • : • • '• • '• :£"^§§§§8§^ F i g u r e 5. • P o i n t d e n s i t y p l o t o f p o l e s t o f o l i a t i o n i n the S e t t l e r S c h i s t (178 p o i n t s ) . The c o n t o u r s . a r e 2, 4, 6, 8, and 10% p e r 1% a r e a . N / ° / < / ° o °o \ 6 \ o \ Y + \ + • ++ + / + / + / • v + + / + + • F i g u r e 6. E q u a l a r e a p l o t o f f a b r i c d a t a f o r the Spuzzum I n t r u s i o n s . O l i n e a t i o n s ; 9 p o i n t s + p o l e s to f o l i a t i o n ; 33 p o i n t s f a c t o r s i f i n t r u s i o n o f t h e F a g e r v i k Body was p o s t - f 2 and l a t e r t h a n t h e o t h e r Spuzzum b o d i e s . S t r u c t u r e s and c o n t a c t r e l a t i o n s i n d i c a t e t h a t t h e Spuzzum q u a r t z d i o r i t e s i n t r u d e d t h e S e t t l e r S c h i s t o v e r a p e r i o d encompasing and p o s s i b l y e x t e n d i n g beyond f ^ . I n g e n e r a l , where t h e Spuzzum b o d i e s have a m i n e r a l f a b r i c , t h i s f a b r i c i s c o n c o r d a n t w i t h s t r u c t u r e s (compare f i g u r e s 4, 5, and 6 ) . The South Body i n t r u d e d p r i o r t o f^-I t s c o n t a c t p a r a l l e l s t h e f o l i a t i o n o f t h e s c h i s t and c o n t a c t meta-morphism a s s o c i a t e d w i t h t h i s body has been i n f e r r e d t o be p r e - f ^ . I n t r u s i o n o f t h e N o r t h Body was s y n t e c t o n i c Exposed c o n t a c t s w i t h s c h i s t show some i n j e c t i o n a l o n g t h e m i c a f o l i a t i o n . I n a d d i t i o n , t h e i n t r u s i v e has a w e l l - d e v e l o p e d f o l i a t i o n o f i t s own. As a l r e a d y n o t e d , i n j e c t i o n o f t h e d i o r i t i c phases o f t h e F a g e r v i k Body a l o n g t h e s c h i s t f o l i a t i o n was e x t e n s i v e . However o n l y some o f t h e s e phases a r e . f o l i a t e d . I n t r u s i o n o f t h e F a g e r v i k Body p r o b a b l y began b e f o r e t h e end o f f.^ d e f o r m a t i o n and c o n t i n u e d p o s t - f ^ . As a l r e a d y n o t e d , t h e n a t u r e o f p o s t - f o l i a t i o n f o l d i n g around t h e F a g e r v i k Body may a l s o i n -d i c a t e p o s t - f 2 i n t r u s i o n . U n i t s 3c and 3d a r e p r o b a b l y t h e y o u n g e s t o f t h e Spuzzum I n t r u s i o n s and may have i n t r u d e d p o s t - f ^ . F o l i a t i o n i n t h e s e b o d i e s i s poor t o a b s e n t . P l a g i o c l a s e g r a i n s i n t h e s e b o d i e s a r e zoned and i n t e r g r o w n . The absence o f t h e s e t e x t u r e s i n t h e p l a g i o -c l a s e s o f t h e o t h e r Spuzzum b o d i e s i s assumed t o be t h e r e s u l t o f r e -c r y s t a l l i z a t i o n a t h i g h grade metamorphic t e m p e r a t u r e s . As a l r e a d y n o t e d , p o s t - f ^ metamorphic t e m p e r a t u r e s were s t i l l s u f f i c i e n t f o r r e -c r y s t a l l i z a t i o n o f b i o t i t e and f i b r o l i t e . T h e r e f o r e , Spuzzum u n i t s 3c and 3 d . i n t r u d e d a f t e r t h e peak o f r e g i o n a l metamorphism and p o s -s i b l y p o s t - f ^ . The p r e s e n c e o f pseudomorphs a f t e r p r e - f 0 a n d a l u s i t e 24 n e a r u n i t 3d i s n o t c o n s i s t e n t w i t h t h i s c o n c l u s i o n . However o n l y one o u t c r o p o f u n i t 3d was e n c o u n t e r e d a t t h e w e s t e r n edge o f t h e mapped a r e a . I t i s c o n s i d e r e d p o s s i b l e t h a t t h e l a r g e Spuzzum body e x t e n d i n g west o f t h e mapped a r e a (Lowes, 1972) i s pre-f^ and t h a t t h e o u t c r o p sampled f o r t h i s s t u d y i s a l a t e phase i n t r u d e d a l o n g t h e c o n t a c t be-tween t h e o l d e r body and s c h i s t . F i g u r e 7 s c h e m a t i c a l l y i l l u s t r a t e s t h e i n f e r r e d i n t e n s i t y and r e -l a t i v e t i m i n g o f d e f o r m a t i o n , r e g i o n a l metamorphism and Spuzzum i n t r u -s i v e a c t i v i t y i n t h e Y a l e Creek a r e a . F a u l t i n g and a b r e c c i a " d i k e " have been a t t r i b u t e d t o l a t e b r i t t l e d e f o r m a t i o n . These s t r u c t u r e s c u t b o t h t h e S e t t l e r S c h i s t and Spuzzum I n t r u s i o n s . A v e r t i c a l b r e c c i a zone 30m w i d e can be t r a c e d down t h e l o w e r Y a l e C r e e k s t r e a m bed f o r 1.5km b e f o r e i t t u r n s up towards t h e r i d g e t o t h e n o r t h (see Map 1 ) . A n g u l a r , a l t e r e d and deformed c l a s t s o f S e t t l e r S c h i s t and Spuzzum d i o r i t e up t o 40cm a c r o s s ( p l a t e 3a) a r e s e t i n a f i n e m a t r i x o f q u a r t z , c h l o r i t e , and m a g n e t i t e . F a u l t s i n the. a r e a s t r i k e N t o NW. O f f s e t s and l o c a l i z e d d e f o r -m a t i o n of t h e s c h i s t s i n d i c a t e t h a t movement o f a l l o f t h e s e f a u l t s has a r i g h t - l a t e r a l s t r i k e - s l i p component. Two major f a u l t s i n c l u d e t h e Hope F a u l t and a p r e v i o u s l y u n r e c o g n i z e d f a u l t i n t h e Cogburn Creek v a l l e y w h i c h w i l l be r e f e r r e d t o as t h e Cogburn c r e e k F a u l t . The Hope F a u l t j u x t a p o s e s C u s t e r G n e i s s a g a i n s t S e t t l e r S c h i s t and Spuzzum I n t r u s i o n s . Movement on t h i s f a u l t i s c o n s i d e r e d t o have b o t h s t r i k e s l i p ( r i g h t - l a t e r a l ) and d i p - s l i p ( e a s t s i d e down) com-ponents (McTaggart, 1970). The l a s t movement on t h e f a u l t has been c o n s t r a i n e d t o have o c c u r r e d between Eocene and M i o c e n e (McTaggart, 1970; P i g a g e , 1 9 7 3 ) . A l t h o u g h t h e Cogburn Creek F a u l t i s h i d d e n by r e c e n t a l l u v i a l s e d i m e n t s , e v i d e n c e f o r i t s e x i s t e n c e i n c l u d e s t r u n c a t e d g e o l o g i c c o n -t a c t s (see map 1) and c o n t r a s t s i n r o c k t y p e s and s t r u c t u r e a c r o s s the Cogburn Creek v a l l e y . S c h i s t s on t h e west s i d e of t h e v a l l e y a r e d o m i n a n t l y g r a p h i t i c s c h i s t s d e v o i d o f a l u m i n o s i l i c a t e s w h i l e on t h e e a s t s i d e o f t h e v a l l e y t h e s c h i s t s a r e l a r g e l y n o n - g r a p h i t i c and c o n -t a i n e i t h e r k y a n i t e o r s i l l i m a n i t e . I n a d d i t i o n , s c h i s t s west o f Cogburn Creek have a p r o m i n e n t w e s t - p l u n g i n g l i n e a t i o h c r e a t e d by a c r e n u l a t i o n t h a t has n o t been seen e a s t o f Cogburn Creek. AGE RELATIONS Rb-Sr and K-Ar r a d i o m e t r i c age d a t i n g methods, were used i n t h i s s t u d y t o h e l p e s t a b l i s h t h e age r e l a t i o n s . The r e s u l t s o f t h e s e i s o -t o p i c a n a l y s e s a l o n g w i t h age e s t i m a t e s by o t h e r a u t h o r s a r e l i s t e d i n t a b l e 2. The a n a l y t i c a l d a t a and methods used i n t h i s s t u d y a r e de-t a i l e d i n A p p e n d i x I I . U n i t 1: S e t t l e r S c h i s t . The S e t t l e r S c h i s t has been e s t i m a t e d t o be E a r l y - t o M i d - P a l e o z o i c by P i g a g e ( 1 9 7 3 ) and a M e s o z o i c age has been s u g g e s t e d f o r s i m i l a r s c h i s t s i n t h e Mt. B r e a k e n r i d g e a r e a 10 t o 20km t o t h e n o r t h w e s t (Reamsbottom, 1971). A T r i a s s i c Rb-Sr whole r o c k age was o b t a i n e d i n t h i s s t u d y . T h i s Rb-Sr age i s i n t e r p r e t e d as t h e age o f d e p o s i t i o n o f o r i g i n a l pre-metamorphic s e d i m e n t s based on t h e f o l l o w i n g c o n s i d e r a t i o n s . F a u r e and P o w e l l ( 1 9 7 2 ) have shown t h a t metamorphism need n o t a f f e c t a Rb-Sr whole r o c k i s o c h r o n . The e x i s t e n c e o f a Rb-Sr i s o c h r o n i n s e d i -mentary r o c k s r e q u i r e s . a n i s o t o p i c a l l y u n i f o r m s e d i m e n t a r y : s o u r c e (Dasch, 1 9 6 9 ) . As a l r e a d y m e n t i o n e d , t h e s e d i m e n t s t h a t were meta-morphosed t o form t h e S e t t l e r S c h i s t were p r o b a b l y d e p o s i t e d i n a e u g e o s y n c l i n a l t r o u g h . The s o u r c e a r e a i s assumed t o have been an a c -t i v e v o l c a n i c b e l t c h a r a c t e r i z e d by comagmatic v o l c a n i c s o f s i m i l a r Rb-Sr i s o t o p i c c o n s t i t u t i o n . The h i g h m e c h a n i c a l e r o s i o n r a t e s i n s u c h an e n v i r o n m e n t would produce s e d i m e n t s w i t h a d e p o s i t i o n a l age i n -s i g n i f i c a n t l y younger ( r e l a t i v e t o a 32Ma a n a l y t i c a l e r r o r - b a r ) t h a n t h e age o f t h e i r s o u r c e and h a v i n g a Rb-Sr i s o t o p i c c o m p o s i t i o n i d e n -87 86 t i c a l t o t h a t o f t h e s o u r c e . The c a l c u l a t e d o r i g i n a l S r - S r r a t i o o f 0.704+.0003 i s c o n s i s t e n t w i t h o r i g i n a l r a t i o s o f v o l c a n i c a r c an-28 T a b l e 2. ' R e f e r e n c e P i g a g e (1973) T h i s s t u d y McTaggart and Thompson(1967) Bremner (1973) C o m p i l a t i o n o f age e s t i m a t e s . Age U n i t 1 Method E a r l y - M i d P a l e o z o i c 214±32 Ma U n i t 2  v P r e - J u r a s s i c 1600Ma t o J u r a s s i c C o r r e l a t i o n w i t h t h e Shuksan Metamorphic S u i t e . Whole r o c k Rb-Sr C o r r e l a t i o n w i t h t h e S k a g i t G n e i s s . U n i t 3 McTaggart and Thompson(1967) 76±4 Ma B i o t i t e K-Ar 76±4 H o r n b l e n d e K-Ar R i c h a r d s (1971) 79±4 B i o t i t e K-Ar 81±4 H o r n b l e n d e K-Ar 83±4 B i o t i t e K-Ar 103+5 B i o t i t e K-Ar McLeod (19 75) 79.4±3 B i o t i t e K-Ar 85.1±3 Ho r n b l e n d e K-Ar 89.5±2.8 H o r n b l e n d e K-Ar 89.6±2.8 Whole r o c k K-Ar T h i s s t u d y 75.5±2.6 (3b) H o r n b l e n d e K-Ar 92.1±3.2 C3e) H o r n b l e n d e K-Ar U n i t 4 T h i s s t u d y 34.411.4 Whole r o c k Rb-Sr 30.710.6 B i o t i t e Rb-Sr 32.811.1 B i o t i t e K-Ar I d e s i t e s ( F a u r e and P o w e l l , 1 9 7 2 ) . Based on t h i s model o f t h e h i s t o r y o f t h e S e t t l e r S c h i s t , t h e 214+32Ma Rb-Sr age d a t e s t h e d e p o s i t i o n o f t h e pre-metamorphic s e d i m e n t s and t h e i r s o u r c e r o c k . U n i t 2: C u s t e r G n e i s s Age e s t i m a t e s f o r t h e C u s t e r G n e i s s a r e a l l based on c o r r e l a t i o n w i t h t h e S k a g i t G n e i s s o f Washington S t a t e ( M c T a g g a r t and Thompson, 1967 Bremner, 1 9 7 1 ) . M i s c h ( 1 9 6 6 ) r e s t r i c t s t h e S k a g i t Metamorphic S u i t e t o be P r e - J u r a s s i c . R a d i o m e t r i c d a t i n g o f z i r c o n s f r o m t h e S k a g i t G n e i s s has e s t a b l i s h e d a maximum age o f 1600Ma ( M a t t i n s o n , 1 9 7 2 ) . U n i t 3: Spuzzum I n t r u s i o n s The B r o a d l y L a t e - C r e t a c e o u s K-Ar d a t e s d e t e r m i n e d f o r t h e Spuzzum I n t r u s i o n s e x h i b i t a r e g i o n a l e a s t w a r d - y o u n g i n g t r e n d . F i g u r e 8 shows t h e l o c a t i o n o f specimens d a t e d by v a r i o u s w o r k e r s i n c l u d i n g two s p e c i -mens d a t e d i n t h i s s t u d y . F i g u r e 9 i s a g r a p h o f ages a g a i n s t e a s t -west d i s t a n c e f r o m a random N-S l i n e . L a r g e r - s c a l e r e g i o n a l t r e n d s i n K-Ar d a t e s i n B.C. and C a l i f o r n i a have been a t t r i b u t e d t o e a s t - w e s t pro g r e s s i v e u p l i f t and an a s s o c i a t e d r e g i o n a l t r e n d i n c o o l i n g h i s t o r y ( H u t c h i s o n , 1970; A r m s t r o n g and Suppe, 1973; Krummenacher and o t h e r s , 1975). I n New Z e a l a n d a y o u n g i n g t r e n d i n K-Ar ages towards t h e A l p i n e F a u l t has been a t t r i b u t e d t o t h e r m a l r e s e t t i n g r e s u l t i n g f r o m f r i c t i o n a l h e a t c r e a t e d d u r i n g f a u l t movement ( S h e p p a r d , Adams, and B i r d , 1975; S c h o l z , Beavan and Hanks, 1 9 7 8 ) . S i n c e t h e Hope F a u l t i s v e r y n e a r l y a N-S l i n e , t h e t r e n d seen i n f i g u r e 9 would n o t be s i g n i -f i c a n t l y d i f f e r e n t i f t h e d i s t a n c e s were measured f r o m t h e f a u l t t r a c e . However, t h e absence o f d a t e s e a s t o f t h e f a u l t makes i t i m p o s s i b l e t o e s t a b l i s h ' a r e l a t i o n s h i p o f t h e y o u n g i n g t r e n d t o t h e Hope F a u l t . • t ' t ' t ' t ' t ' t ' t ' f t ' t ' t ' t ' t ' t ' t ' t ' - i / N 0 A* O R i c h a r d s ( 1 9 7 1 ) -j k i l o m e t e r s • McTaggart and Thompson(1967) © McLeod(1975) © T h i s s t u d y F i g u r e 8. L o c a t i o n s o f Spuzzum K-Ar d a t e s ( . i n Ma). The u n d e r -l i n e d d a t e s a r e a v e r a g e d h o r n b l e n d e - b i o t i t e p a i r s . L i n e A-A 1 i s a N-S g r i d l i n e f r o m NTS Map 92/H. . 31 g 110 100 + E A S T F i g u r e 9, 10 12 14 D I S T A N C E , km 18 WEST Graph o f K-Ar age v e r s u s p e r p e n d i c u l a r d i s t a n c e from l i n e A-A' ( s e e f i g u r e 8 ) . The boxes i n d i c a t e age and d i s t a n c e e r r o r m a r g i n s . S t i p l e d boxes a r e a v e r a g e d h o r n -b l e n d e - b i o t i t e p a i r s . 32 The a u t h o r ' s p r e f e r r e d i n t e r p r e t a t i o n i s t h a t v e r t i c a l movement on t h e Hope F a u l t has r e s u l t e d i n g r e a t e r u p l i f t , deeper e r o s i o n , and l a t e r c o o l i n g t o an argon' " b l o c k i n g " t e m p e r a t u r e n e a r e s t t h e f a u l t f r o m west t o e a s t . However, a s y s t e m a t i c d a t i n g program i s needed t o c l a r i f y t h e s i t u a t i o n . R e l a t i v e t o a c t u a l d a t e o f emplacement, a l l o f t h e Spuzzum K-Ar ages a r e c o n s i d e r e d minimum ages. U n i t 4: Cogburn G r a n o d i o r i t e . C r o s s c u t t i n g r e l a t i o n s i n d i c a t e t h e Cogburn G r a n o d i o r i t e i s younger t h a n t h e Spuzzum I n t r u s i o n s and metamorphism o f t h e S e t t l e r S c h i s t . Lower O l i g o c e n e K-Ar and Rb-Sr d a t e s o b t a i n e d f o r t h e Cogburn G r a n o d i o r i t e i n t h i s s t u d y a g r e e w i t h t h e f i e l d r e l a t i o n s . The c o n c o r -dance o f t h e K-Ar and Rb-Sr ages i n d i c a t e s t h a t t h e r e has been no s i g -n i f i c a n t t h e r m a l " e v e n t " i n t h e a r e a s i n c e emplacement o f t h e Cogburn G r a n o d i o r i t e . The c o m p o s i t i o n and d i s c o r d a n t i n t r u s i v e c h a r a c t e r o f t h e Cogburn G r a n o d i o r i t e a r e t y p i c a l o f T e r t i a r y i n t r u s i v e s i n t h e Hope map-area(Monger, 1 9 7 0 ) . 33 METAMORPHISM The S e t t l e r S c h i s t has been d i v i d e d i n t o t h r e e r e g i o n a l metamor-p h i c zones (see Map 3) on t h e b a s i s o f a l u m i n o s i l i c a t e m i n e r a l o g y . The zones a r e d e f i n e d as f o l l o w s : k y a n i t e zone = k y a n i t e f i r s t s i l l i m a n i t e zone = f i b r o l i t e + k y a n i t e second s i l l i m a n i t e zone = s i l l i m a n i t e + f i b r o l i t e The f i r s t s i l l i m a n i t e i s o g r a d marks t h e f i r s t a ppearance o f f i b r o l i t e and t h e second s i l l i m a n i t e i s o g r a d marks b o t h t h e appearance o f p o r -p h y r o b l a s t i c s i l l i m a n i t e and t h e d i s a p p e a r a n c e o f o f k y a n i t e . R e g r e s s i o n a n a l y s i s by P i g a g e ( 1 9 7 3 ) o f t h e c o m p o s i t i o n s o f c o - : e x i s t i n g m i n e r a l s i n t h e S e t t l e r S c h i s t s u g g e s t two s i l l i m a n i t e p r o -d u c i n g r e a c t i o n s o f t h e form: s t a u r o l i t e + m u s c o v i t e + q u a r t z + r u t i l e = s i l l i m a n i t e + b i o t i t e + i l m e n i t e + H 20 (1) g a r n e t + m u s c o v i t e + r u t i l e = s i l l i m a n i t e + q u a r t z + b i o t i t e + a n o r t h i t e + i l m e n i t e (2) I f t h e s e r e a c t i o n s o p e r a t e d i n t h e Y a l e Creek a r e a t h e y must have been c o n t i n u o u s r a t h e r t h a n d i s c o n t i n u o u s (Thompson, 1957) s i n c e t h e m i n e r a l s r e p r e s e n t a t l e a s t e i g h t components and t h e r e a r e o n l y e i g h t phases i n each r e a c t i o n . I n f a c t , a l l o f t h e phases i n r e a c t i o n s (1) and (2) can be found c o e x i s t i n g i n t h e f i r s t s i l l i m a n i t e zone and, i f k y a n i t e i s r e p l a c e d as t h e a l u m i n o s i l i c a t e p r o d u c t , a l l phases can be found c o -e x i s t i n g i n t h e k y a n i t e zone a l s o . However, p e t r o g r a p h i c o b s e r v a t i o n s o f specimens f r o m t h e second s i l l i m a n i t e zone s u p p o r t t h e p r o p o s e d o p e r a t i o n o f r e a c t i o n s (1) and ( 2 ) . I n t h e s e specimens s t a u r o l i t e and m u s c o v i t e a r e n e v e r found c o e x i s t i n g , and g a r n e t s o f t e n have r a g g e d edges and q u a r t z - p l a g i o c l a s e h a l o s ( p l a t e 3b) . S i m i l a r c o n t i n u o u s r e a c t i o n s have a l s o been p r o p o s e d f o r s i l l i m a n i t e zone metamorphism i n Maine ( G u i d o t t i , 1 9 7 0 ) . The f i r s t and second s i l l i m a n i t e i s o g r a d s a r e i n t e r p r e t e d as m a r k i n g e q u i l i b r i u m and o v e r s t e p p e d 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 s r e -s p e c t i v e l y . I t i s p r o p o s e d h e r e t h a t , as t h e e q u i l i b r i u m P-T c o n d i -t i o n s o f t h e 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 were r e a c h e d , c o n t i n u o u s r e a c t i o n s w i t h an a l u m i n o s i l i c a t e as a p r o d u c t , s u c h as (1) and ( 2 ) , began p r o d u c i n g s i l l i m a n i t e ( f i b r o l i t e ) r a t h e r t h a n k y a n i t e . However, th e d i r e c t 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 was p r e v e n t e d by t h e k i n -e t i c b a r r i e r s t o t h i s r e c o n s t r u c t i v e p o l y m o r p h i c t r a n s i t i o n . Thus t h e appearance o f f i b r o l i t e marks t h e e q u i l i b r i u m t r a n s i t i o n and b o t h f i b r o l i t e and k y a n i t e c o e x i s t i n t h e f i r s t s i l l i m a n i t e zone. F u r t h e r -more, as t e m p e r a t u r e : . i n c r e a s e d , t h e d i r e c t p o l y m o r p h i c t r a n s i t i o n was o v e r s t e p p e d u n t i l t h e f r e e e nergy d i f f e r e n c e between k y a n i t e and s i l -l i m a n i t e was s u f f i c i e n t t o overcome t h e k i n e t i c b a r r i e r s . Thus t h e d i s a p p e a r a n c e o f p o r p h y r o b l a s t i c k y a n i t e and c o i n c i d e n t appearance o f p o r p h y r o b l a s t i c s i l l i m a n i t e marks an o v e r s t e p p e d p o l y m o r p h i c t r a n -s i t i o n . The r e g i o n a l metamorphic g r a d i e n t i n t h e Y a l e Creek a r e a p o i n t s towards a metamorphic h e a t s o u r c e t o t h e n o r t h . The l a r g e Spuzzum P l u t o n t o t h e n o r t h (McTaggart and Thompson, 1967; R o d d i c k and H u t c h i s o n , 1969). must have been t h i s h e a t s o u r c e s i n c e , on t h e wes-t e r n f l a n k o f t h e Spuzzum P l u t o n , the metamorphic grade a l s o i n c r e a s e s towards t h e p l u t o n ( R e a m s b o t t o m , 1 9 7 1 ) . However, i n t h e Y a l e C r e e k a r e a , t h e r e l a t i o n s h i p o f t h e r e g i o n a l metamorphic g r a d i e n t t o i n d i v i d u a l Spuzzum b o d i e s i s v a r i a b l e and t e n d s t o s u p p o r t t h e c o n c l u s i o n , based on s t r u c t u r a l r e l a t i o n s , t h a t Spuzzum i n t r u s i v e a c t i v i t y o c c u r r e d o v e r a l a r g e , b r o a d l y s y n t e c t o n i c , span o f t i m e . S i n c e t h e r e g i o n a l meta-mo r p h i c grade i n c r e a s e s away from t h e South Body, i t must have c o o l e d t o t h e ambient t e m p e r a t u r e o f t h e c o u n t r y r o c k p r i o r t o t h e r e g i o n a l metamorphism. The N o r t h Body a l s o a p p ears t o have i n t r u d e d p r i o r t o t h e c u l m i n a t i o n o f r e g i o n a l metamorphism s i n c e t h e second s i l l i m a n i t e i s o g r a d i n t e r s e c t s i t s s o u t h e r n c o n t a c t (see Map 1) i m p l y i n g t h a t t h e i n t r u s i v e r o c k was s u b j e c t t o t h e same t e m p e r a t u r e g r a d i e n t s as t h e s c h i s t s . On t h e o t h e r hand, t h e metamorphic i s o g r a d s crowd t o g e t h e r n e a r and d e f l e c t around t h e F a g e r v i k Body w h i c h i s s u r r o u n d e d by t h e h i g h e s t g rade s c h i s t s i n t h e mapped a r e a . T h i s p o i n t s towards t h e F a g e r v i k Body as a metamorphic h e a t s o u r c e , i m p l y i n g t h a t t h i s body i s t h e y o u n g e s t o f t h e t h r e e . D i s t r i b u t i o n o f r e g i o n a l metamorphic grade a l s o t e n d s t o s u p p o r t t h e e x i s t e n c e o f a f a u l t i n t h e Cogburn C r e e k v a l l e y . E a s t o f t h i s v a l l e y a r e k y a n i t e and s i l l i m a n i t e zone s c h i s t s . The s c h i s t s on t h e west s i d e of t h e v a l l e y a r e f i n e r g r a i n e d and c o n t a i n pseudomorphs a f t e r a n d a l u s i t e w h i c h a r e c o m p l e t e l y d e v o i d o f k y a n i t e . I n a d d i t i o n , Lowes(1972) r e p o r t e d an o c c u r r e n c e o f a n d a l u s i t e c o e x i s t i n g w i t h f i b r o l i t e a t a l o c a l i t y on t h e west s i d e o f t h e Cogburn Creek v a l l e y and j u s t n o r t h o f t h e a r e a mapped i n t h e p r e s e n t s t u d y . T h i s i n d i -c a t e s a s i g n i f i c a n t d i f f e r e n c e i n p r e s s u r e o f metamorphism a c r o s s t h e Cogburn Creek v a l l e y . T h i s e s t a b l i s h e s a v e r t i c a l component o f move-ment on t h e Cogburn Creek F a u l t (west s i d e down). The v e r t i c a l move-ment must d e c r e a s e i f . t h i s f a u l t c o n t i n u e s t o t h e n o r t h . S c h i s t s t o t h e n o r t h and west i n t h e Mt. B r e a k e n r i d g e a r e a i n c r e a s e i n grade f r o m k y a n i t e zone t o s i l l i m a n i t e zone w i t h o u t an i n t e r v e n i n g zone o f s t a b l e a n d a l u s i t e ( R e a m s b o t t o m , 1971). METAMORPHIC CONDITIONS The metamorphic c o n d i t i o n s i n t h e v i c i n i t y o f t h e f i r s t s i l l i m a n i t e i s o g r a d a r e e s t i m a t e d t o have been 7.6 + 0.5kb and 705 + 45°C, w i t h an a c t i v i t y o f H O between 0.81 and 0.86 and l o g f between -18.1 and 2 -17.3. These e s t i m a t e s , d e t a i l e d below, have been o b t a i n e d from c a l -c u l a t i o n s o f d i s p l a c e d e q u i l i b r i a , u s i n g t h e c o n s t r a i n t s r e q u i r e d by p e t r o g r a p h y and f i e l d r e l a t i o n s and assuming t h a t a C-H-0 f l u i d was i n e q u i l i b r i u m w i t h t h e g r a p h i t e - b e a r i n g m i n e r a l a s s e m b l a g e s . The e s t i m a t e s o f metamorphic p r e s s u r e and t e m p e r a t u r e were ob-t a i n e d by means o f t h e m u t u a l i n t e r s e c t i o n o f s e v e r a l c a l c u l a t e d m i n e r a l e q u i l i b r i a . A l l e q u i l i b r i a t h a t can be e x p r e s s e d between m i n e r a l s i n an e q u i l i b r i u m assemblage must be s a t i s f i e d , and so t h e i r e q u i l i b r i u m c u r v e s i n P-T space must a l l i n t e r s e c t each o t h e r a t t h e p o i n t c o r -r e s p o n d i n g t o t h e e q u i l i b r i u m P and T. The e q u i l i b r i u m c u r v e s were c a l c u l a t e d f r o m a v a i l a b l e thermodynamic d a t a and i n c l u d e t h e e f f e c t s o f s o l i d s o l u t i o n and impure pore f l u i d s t h r o u g h v a r i a t i o n o f t h e a p p r o -p r i a t e e q u i l i b r i u m c o n s t a n t s w i t h c o m p o s i t i o n . A c t i v i t i e s o f t h e s p e c i e s i n t h e s e e q u i l i b r i u m c o n s t a n t s were d e r i v e d f r o m m i c r o p r o b e a n a l y s e s and s o l i d - s o l u t i o n models. The a c c u r a c y o f t h e r e s u l t i n g P-T e s t i m a t e i s dependent upon t h e a s s u m p t i o n of c h e m i c a l e q u i l i b r i u m , t h e a c c u r a c y and p r e c i s i o n o f t h e m i c r o p r o b e a n a l y s e s , t h e v a l i d i t y o f t h e s o l i d - s o l u t i o n models and t h e q u a l i t y o f t h e thermodynamic d a t a . M i c r o p r o b e A n a l y s e s The e q u i l i b r i u m c a l c u l a t i o n s a r e based on t h e a n a l y s e d m i n e r a l a s -semblages o f f o u r specimens t a k e n f r o m l o c a l i t i e s n e a r t h e f i r s t s i l -l i m a n i t e i s o g r a d (see Map 3 ) . These s p e c i m e n s , numbered 122A, 74, 165, and 80, a r e r e f e r r e d t o as P l , P2, P3, and P4 r e s p e c t i v e l y i n t h e f o l -l o w i n g d i s c u s s i o n s . A l l f o u r specimens c o n t a i n t h e assemblage q u a r t z -p l a g i o c l a s e - b i o t i t e - s t a u r o l i t e - k y a n i t e - g a r n e t - m u s c o v i t e - i l m e n i t e -g r a p h i t e + r u t i l e . Each specimen i s a l s o u n i q u e i n some way. P2 i s a t y p i c a l s c h i s t o f t h e k y a n i t e zone. P l i s fr o m a q u a r t z i t i c l a y e r , c o n t a i n i n g a r e l a t i v e abundance o f q u a r t z and p l a g i o c l a s e . I t t h e r e -f o r e r e p r e s e n t s a s i g n i f i c a n t v a r i a n t o f b u l k c o m p o s i t i o n . The k y a n i t e and s t a u r o l i t e o f P3 a r e r e s t r i c t e d t o p r i s m a t i c r e g i o n s i n t e r p r e t e d t o be pseudomorphs a f t e r a n d a l u s i t e . P4, c o n t a i n i n g f i b r o l i t e i n a d d i t i o n t o k y a n i t e , i s t h e o n l y m i c r o p r o b e specimen f r o m t h e h i g h g rade s i d e o f t h e f i r s t s i l l i m a n i t e i s o g r a d . A l l o f t h e m i n e r a l s l i s t e d above were a n a l y s e d e x c e p t q u a r t z , g r a p h i t e , r u t i l e , and t h e a l u m i n o s i l i c a t e s w h i c h were assumed t o be pure and s t o i c h i o m e t r i c . The m i n e r a l a n a l y s e s were made w i t h t h e ARL SEMQ e l e c t r o n m i c r o p r o b e a t t h e 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 . The a c c e l e r a t i o n p o t e n t i a l and specimen c u r r e n t were m a i n t a i n e d a t 15kV and 0.04uA r e s p e c t i v e l y . A beam d i a m e t e r o f lOum was used f o r a l l m i n e r a l s e x c e p t p l a g i o c l a s e and m i c a s . F o r t h e s e m i n e r a l s a 20ym beam was used t o a v o i d v o l a t i l i z a t i o n o f a l k a l i s . Data r e d u c t i o n was p e r -formed by an o n - l i n e m i n i c o m p u t e r u s i n g t h e Bence-Albee c o r r e c t i o n method (Bence and A l b e e , 1968; A l b e e and Ray, 1 9 7 0 ) . T a b l e 3 l i s t s t h e s t a n d a r d s u s e d . R e p l i c a t e a n a l y s e s were made f o r each m i n e r a l and l a t e r a v e r a g e d . G a r n e t s were found t o have m i n o r r a d i a l z o n i n g . Sub-s e q u e n t l y a l l g a r n e t a n a l y s e s were t a k e n w i t h i n 2 beam d i a m e t e r s o f t h e i r g r a i n b o u n d a r i e s . The r e s u l t s o f t h e a n a l y s e s a r e l i s t e d i n t a b l e s 4 t h r o u g h 9. T a b l e 3. M i c r o p r o b e s t a n d a r d s . The numbers a r e U.B.C. m i c r o p r o b e s t a n d a r d numbers. Na Mg A l S i K Ca Ba T i Mn Fe Zn G a r n e t 84 84 83 83 13 15 104 P l a g i o c l a s e 20 20 28 28 102 35 M i c a s 20 24 49 24 24 21 35 13 15 104 S t a u r o l i t e 81 26 26 21 13 15 104 1 I l m e n i t e 81 26 26 13 15 104 1 1. W i l l e m i t e ( N e w J e r s e y ) 13 R u t i l e ( s y n t h e t i c ) 15 S p e s s a r t i n e ( B r a z i l ) 20 A l b i t e ( O r e g o n ) 21 W o l l a s t o n i t e ( N e w Y o r k ) 24 F l u o r o p h l o g o p i t e ( s y n . ) 26 A n d a d u s i t e ( B r a z i l ) 28 O r t h o c l a s e ( O r - l ) 35 B e n i t o i t e ( C a l i f o r n i a ) 49 M u s c o v i t e ( M l ) 81 E n s t a t i t e ( s y n t h e t i c ) 83 G r o s s u l a r ( N e w Y o r k ) 84 P y r o p e ( s y n t h e t i c ) 102 A n o r t h i t e ( s y n t h e t i c ) 104 F a y a l i t e ( s y n t h e t i c ) 40 j Table 4. B i o t i t e analyses. P l P2 P3 " P4 Na 20 0.20(.05) 0.33(.04) 0.23(.02) 0.27(.03) MgO 11.0 (.5) 11.5 (.4) 11.1 (.4) 9.85(.17) A 1 2 0 3 19.6 (.7) 19.5 (.5) 19.5 (.4) 19.1 (.2) S i 0 2 34.7 (.8) 35.8 (.8) 35.9 (.3) 35.2 (.5) K 20 8.07C.25) 8.68(.12) 8.15(.40) 8.84(.19) CaO Tr Tr 0.04(.02) Tr BaO 1.39(.08) 0.28(.04) 0.28(.05) 0.24(.06) T i 0 2 2.28(.38) 1.87(.14) 1.74(.17) 2.20(.22) MnO 0.06(.03) 0.05(.01) 0.03(.01) 0.02(.02) FeO* 16.3 (.4) 17.9 (.8) 17.0 (.5) 19.6 (.5) H 20 + 3.91 4.01 3.96 3.94 Total 97.51(1.6) 99.92(.8) 97.93(1.1) 99.26(.6) Formula based on 22 oxygens S i 5.32 5.36 5.44 5.37 A 1 I V 2.68 2.65 2.56 2.64 A 1 V I 0.86 0.79 0.92 0.78 T i 0.26 0.21 0.20 0.25 Fe 2.09 2.24 2.15 2.49 Mn 0.008 0.007 0.004 0.003 Mg 2.51 2.57 2.50 2.23 £ VI 5.73 5.82 5.77 5.75 Ba 0.08 0.02 0.02 0.02 Ca Tr Tr 0.006 Tr K 1.58 1.66 1.57 1.72 Na 0.06 0.10 0.07 0.08 I 1.72 1.78 1.67 1.82 OH 4.0 4.0 4.0 4.0 .yses 8 7 5. 9 Total i r o n as FeO Parentheses contain la of averaged analyses t Wt.% H O calculated for 4 OH per formula. Tr=mean i s less than la T a b l e 5 M u s c o v i t e a n a l y s e s . P I P2 P3 P4 Na 20 1.97(.24) 1.65(.10) 1.27( .11) 1.10(.05) MgO 0.73(.05) 0.60(.09) 0.60( .05) 0 . 6 5 C.05) A 1 2 0 3 35.5 (.3) 34.9 (.4) 35.9 ( .4) 34.7 (.7) S i 0 2 4 4 . 1 ( 1 . 1 ) . 44.6(1.1) 45.5 ( • 2) 44.8 (.9) K 2 0 7 . 8 4 C.34) 8.75(.18) 8.86( • 21) 9.67(.31) CaO Tr T r Tr Tr BaO. 2.79(.57) 0.83(.03) 0.92( .04) 0 . 6 K . 0 6 ) T i 0 2 0 . 7 9 ( . l l ) 0.59(.10) 0.56( .15) 0.70(.18) MnO Tr 0.0 Tr Tr FeO* H 2 0 + 0.90(. 10) 0.99(.04) 0.91( .04) 1.67(.65) 4.42 4.39 4.48 4.41 T o t a l 99.04(1.1) 97.30(1.4) 99.00(, .6) 98.31(1.3) For m u l a b a s e d on 22 oxygens S i A 1 I V 5.99 2.01 6.09 1.91 6.09 1.91 6.08 1.92 A 1 V I 3.67 3.72 3.76 3.65 T i 0.08 0.06 0.06 0.07 Fe 0.10 0.11 0.10 0.19 Mn Tr 0.0 Tr Tr Mg 0.15 0.12 0.12 0.13 E V I 4.00 4.01 4.04 4.04 Ba 0.15 0.04 0.05 0.03 Ca Tr T r T r T r K 1.36 1.53 1,51 1.68 Na 0.52 0.44 0.33 0.29 E 2.03 ' 2.01 1.89 2.00 OH 4.0 4.0 4.0 4.0 l y s e s 6 8 4 8 * _ — - — — — — T o t a l i r o n as FeO. P a r e n t h e s e s c o n t a i n l a o f a v e r a g e d a n a l y s e s Wt.% H 20 c a l c u l a t e d f o r 4 OH p e r f o r m u l a . T r = mean i s l e s s t h a n l a T a b l e 6. S t a u r o l i t e a n a l y s e s P l P2 P3 P4 MgQ 1.87(.09) 2.00(.07) 2.03(.08) 1.61(.08) A 1 2 0 3 54.7 (.4) 55.2 (.5) 55.0 (.2) 54.1 (.5) S i 0 2 27.3 (.3) 28.1 (.5) 28.4 (.2) 27.6 (.3) CaO T r T r T r T r T i 0 2 0.78(.19) 0 .7K.07) 0.59(.07) 0.75(.05) MnO 0.25(.02) 0.20(.02) 0.11(.02) O . l i ( . O l ) FeO* 12.9 (.2) 14.1 (.1) 12.6 (.3) 13.5 (.3) ZnO 0.58(.16) 0.18(.02) 0.56(.14) 0 . 9 3 ( . l l ) H 0 + 2.17 2.22 2.20 2.17 T o t a l 100.55(.6) 102.71(.6) 101.49(.4) 100.77(.6) F o r m u l a b a s e d on 46 oxygens S i 7. 54 7. 60 7. 72 7. 62 T i - . 0. 16 0. 15 0. 12 0. 16 A l 17. 79 17. 61 17. 65 17. 61 Fe 2. 97 3. 20 2. 88 3. 13 Zn 0. 12 0. 04 0. 11 0. 19 Mn 0. 06 0. 05 0. 03 0. 03 Mg 0. 77 0. 81 0. 82 0. 66 Ca : T r Tr Tr Tr OH 4. 0 4. 0 4. 0 4. 0 A n a l y s e s 9 9 .11 8 * : ~ —— T o t a l i r o n as FeO. P a r e n t h e s e s c o n t a i n l a o f a v e r a g e d a n a l y s e s . Wt.% H O c a l c u l a t e d f o r 4 OH p e r f o r m u l a . Tr = mean i s l e s s t h a n l a . 43 Table. 7. Garnet a n a l y s e s . P I P 2 . P 3 . P 4 MgO 4.3K.10) • 3.66C.08) 3.59(.18) 3.45(.06) A 1 2 0 3 21.5 (.2) 21.4 (.3) 21.7 (.1) 21.3 (.2) S i 0 2 37.4 (.5) 36.9 (.5) 37.0 (.3) 37.2 (.2) > CaO 1.74(.17) 1.45(.07) 2.70(.13) 2.21(.12) T i 0 2 Tr Tr Tr Tr MnO 3 . 3 3 C.20) 3.52(.12) 2.01(.08) 2.00(.04) FeO* 33.1 (.2) 33.1 (.3) 33.5 (.4) 33.6 (.3) T o t a l 101.38(.4) 100.03(.6) 100.50(.5) 99.76(.7) F o r m u l a b a s e d on 24 oxygens S i . 5.93 5.93 5.90 5.97 A l 4.01 4.05 4.08 4.04 T i T r Tr Tr Tr Mg .1.02 0.88 0.85 0.83 Ca 0.29 0.25 0.46 0.38 Mn 0.45 0.48 0.27 0.27 Fe 4.38 4.46 4.48 4.52 E 6.14 6.07 6.06 6.00 X 0.166 0.145 0.141 0.138 p y r >;. X 0.048 0.041 0.076 0.064 X 0.073 0.079 0.045 0.045 spes X 1 0.713 0.735 0.738 0.753 ai m A n a l y s e s 9 11 7 10 T o t a l i r o n as FeO. P a r e n t h e s e s c o n t a i n l a o f a v e r a g e d a n a l y s e s . Tr = mean i s l e s s t h a n l a . 44 r T a b l e 8. P l a g i o c l a s e A n a l y s e s . Na 20 A 1 2 0 SiO k o CaO BaO T o t a l S i A l Z Na K Ca Ba Z X V ab X an X o r A n a l y s e s P I P2 P3 P4 1 8 . 8 5 ( . 2 5 ) 9 . 2 1 0 1 1 ) 8 . 1 3 0 1 5 ) . 7.65(.05) >3 24.4 (.3) 23.4 (.3) 25.4 (.2) 25.5 (.1) • 2 61.7(1.0) 63.0 (.6) 60.1 (.4) 59.8 ( . .2) > . 0 . 0 9 0 0 5 ) 0.09(.06) 0 . 1 3 O 0 7 ) 0.12(.04) 5.19 0 3 3 ) 4 . 3 8 0 2 9 ) ; 6 . 7 7 0 32) 7 . 1 8 0 1 7 ) ' 0 . 0 5 O 0 3 ) T r T r Tr 1 0 0 . 2 8 ( . 8 ) 1 0 0 . 0 8 O 7 ) 100.53(.6) 100.25 0 3) F o r m u l a b a s e d on 8 oxygens 2.73 2.78 2.67 2.66 1.27 1.23 1.33 1.34 4.00 4.01 4.00 4.00 0.76 0.79 0.70 0.66 0.005 0.005 0.007 0.007 . 0.25 0.21 0.32 0.34 0.001 Tr Tr Tr 1.016 1.005 1.027 1.007 0.752 0.788 0.680 0.654 0.243 0.207 0.313 0.339 0.005 0.005 0.007 0.007 12 9 11 9 P a r e n t h e s e s c o n t a i n l a o f av e r a g e d a n a l y s e s , Tr = mean i s l e s s t h a n l a . T a b l e 9. I l m e n i t e a n a l y s e s . P I P2 P3 P4 MgO Tr 0.28(.14) 0.15(.02) 0.28(.10) A 1 2 ° 3 Tr 0.02(.01) 0.03C02) Tr s i o 2 0.10(.06) 0.11C.04) Tr 0.05(.04) T i 0 2 52.8(1.1) 53.0(1.0) 52.2 (.7) 52.5 (.4) MnO 1.61(1.1) 0.82(.06) 0.56(.01) 0.47(.04) FeO* 45.3(1.0) - 46.1 (.7) 46.9 (.3) 46.1 (.4) ZnO NA T r NA 0.08(.05) T o t a l 99.81(1.2) 100.33(.7) 99.84(1.0) 99.48(.7) Fo r m u l a b a s e d on 12 oxygens T i 3.99 4.00 3.97 4.00 A l T r 0.002 0.003 Tr S i 0.01 0.01 Tr 0.005 Fe 3.80 3.87 3.97 3.90 Mg T r 0.04 0.02 0.04 Mn 0.14 0.07 0.05 0.04 Zn NA Tr NA 0.006 A n a l y s e s 3 6 3 8 T o t a l i r o n as FeO. P a r e n t h e s e s c o n t a i n l a o f a v e r a g e d a n a l y s e s . Tr = mean i s l e s s t h a n l a . Na = n o t a n a l y s e d . . : E q u i l i b r i u m C a l c u l a t i o n s The a s s u m p t i o n o f e q u i l i b r i u m i s s u p p o r t e d by t h e c l e a n , s h a r p g r a i n b o u n d a r i e s seen i n t h i n s e c t i o n and c o m p o s i t i o n a l u n i f o r m i t y . A l l o f t h e a n a l y s e d m i n e r a l s were f o u n d t o have u n i f o r m c o m p o s i t i o n s ( w i t h i n a n a l y t i c a l p r e c i s i o n ) o v e r t h e a r e a o f a s t a n d a r d t h i n s e c t i o n . C h e m i c a l z o n i n g o f i n d i v i d u a l m i n e r a l g r a i n s was a b s e n t e x c e p t f o r minor Mn z o n i n g i n g a r n e t s . O n l y g a r n e t edge c o m p o s i t i o n s were used i n t h e c a l c u l a t i o n s . A l t h o u g h s i l l i m a n i t e and k y a n i t e i n specimen P4 may n o t be i n e q u i l i b r i u m , t h i s p r o b a b l y does n o t a f f e c t t h e c a l c u l -a t i o n s . I f t h e i n t e r p r e t a t i o n o f t h e f i r s t s i l l i m a n i t e i s o g r a d i s c o r r e c t , t h e d e p a r t u r e o f P4 from e q u i l i b r i u m w o u l d be s m a l l . The m i n e r a l end-members c o n s i d e r e d and t h e e x p r e s s i o n s r e l a t i n g t h e i r a c t i v i t i e s t o t h e c h e m i c a l a n a l y s e s a r e l i s t e d i n t a b l e 10. The method o f K e r r i c k and Darken(1975) was used t o c a l c u l a t e a c t i v i t i e s f o r i d e a l s o l u t i o n s . A c t i v i t y c o e f f i c i e n t s were c a l c u l a t e d f r o m M a r g u l e s p a r a m e t e r s where t h e s e a r e a v a i l a b l e . A d e t a i l e d m i n e r a l -b y - m i n e r a l e x p l a n a t i o n o f t h e a c t i v i t y c a l c u l a t i o n s i s p r e s e n t e d i n A p p e n d i x I I I and t h e c a l c u l a t e d a c t i v i t i e s a r e l i s t e d i n t a b l e 11. S i x i n d e p e n d e n t e q u i l i b r i a can be e x p r e s s e d w i t h t h e m i n e r a l e n d -members i n t a b l e 10. These e q u i l i b r i a and t h e i r e q u i l i b r i u m c o n s t a n t e x p r e s s i o n s (assuming a ^=1) a r e as f o l l o w s : I ky = s i l l K = 1 I I I 3 F e - s t + l l q t z = 4alm + 23ky + 3H'20- K IV p a r + q t z = a l b + ky + H o0 K I I g r + q t z + 2ky = 3an -K a a l m a F e - s t a a l b p a r /a a ann mu a i m V mu + a i m = ann + 2ky + q t z K a V I aim + p h i = p y r + ann K a p y r ann p h i a i m T a b l e 10. M i n e r a l end-members and a c t i v i t y e x p r e s s i o n s . M i n e r a l End-members Formula A c t i v i t y E x p r e s s i o n Comment o r R e f e r e n c e g a r n e t a l m a n d i n e F e 3 A l 2 S i 3 0 1 2 a = X F e Y F e Ganguly and Kennedy(1974) py r o p e M g 3 A l 2 S i 3 0 1 2 X 3 3 n*g YMg M i i g r o s s u l a r C a 3 A l 2 S i 3 0 1 2 Y 3 3 X C a Y C a i i I I p l a g i o c l a s e a l b i t e N a A l S i o 0 o 3 o ^ a ^ a O r v i l l e ( 1 9 7 2 ) a n o r t h i t e C a A l 2 S i 2 O g X C a Y C A t i b i o t i t e a n n i t e K F e 3 A l S i 3 O 1 0 ( O H ) 2 \4e Assumed i d e a l s o l u t i o n p h l o g o p i t e K M g 3 A l S i 3 0 1 Q ( O H ) 2 3 I I I I m u s c o v i t e m u s c o v i t e K A l 2 S i 3 A 1 0 1 G ( O H ) 2 ^ K ( A 1 V I - 1 ) 2 E u g s t e r and o t h e r s ( 1 9 7 2 ) p a r a g o n i t e N a A l 2 S i 3 A 1 0 1 0 . ( O H ) ; 2 X A 1 „ ( A l -1) Na Na ' I I i t s t a u r o l i t e F e - s t a u r o l i t e F e 4 M 1 8 S i 8 P 4 6 ( O H ) 2 ( F e / 4 )4 ( A 1 / 1 8 ) 1 8 ( S i / 8 ) 8 Assumed i d e a l s o l u t i o n j j u a r t z S i 0 2 a = 1 Assumed p u r e phase k y a n i t e A l 2 S i 0 5 a = 1 i i I I s i l l i m a n i t e A l 2 S i 0 5 a = 1 I I I I U n d e r l i n e d l e t t e r s a r e used _ atoms o f i i n s i t e t o a b b r e v i a t e . i t o t a l atoms i n s i t e T a b l e 11. End-member a c t i v i t i e s . End-member P I P2 P3 P4 al m a n d i n e 0.4102 0.4351 0.4354 0.4611 py r o p e 0.1457 0.1157 0.1134 0.1076 3 g r o s s u l a r ( x l O ) 0.1616 0.0920 0.5795 0.3423 a l b i t e 0.752 0.788 0.680 0.654 a n o r t h i t e 0.311 0.265 0.401 0.434 a n n i t e 0.0335 0.0432 0.0362 0.0613 p h l o g o p i t e 0.0578 0.0650 0:0571 0.0442 m u s c o v i t e 0.6415 0.7053 0.7274 0.7044 p a r a g o n i t e 0.8227 0.8289 0.7569 0.6445 F e - s t a u r o l i t e 0.1524 0.1827 0.1411 .0.1714 T a b l e 12. E q u i l i b r i u m c o n s t a n t s . P I P2 P3 P4 K I I 186.8 202.3 111.3 238.8 K I I I 8.001 5.878 12.792 8.979 K IV 0.9149 0.9507 0.8984 1.0147 K V 0.1274 0.1409 0.1143 0.1888 K V I 0.2061 0.1769 0.1650 0.3233 * V 1 ' 0.1938 0.1719 0.1639 0.2037 \ = ( M g / F e ) 8 a r / ( M g / F e ) b : L O , F e r r y and Spear(1978) T a b l e 12 l i s t s t h e e q u i l i b r i u m c o n s t a n t s f o r t h e s e e q u i l i b r i a c a l c u l -a t e d f r o m t h e a c t i v i t i e s i n t a b l e 11. The P-T c u r v e s f o r t h e above e q u i l i b r i a have been c a l c u l a t e d u s i n g t h e computer program EQ-CURVE w r i t t e n by E.H. P e r k i n s . The b a s i c method o f t h e s e c a l c u l a t i o n s i s p r e s e n t e d by S k i p p e n ( 1 9 7 7 ) . The t h e r m o c h e m i c a l d a t a used i n t h e s e c a l c u l a t i o n s i s l i s t e d i n t a b l e 13. EQUILIBRIUM I A l l f o u r a n a l y s e d specimens come f r o m l o c a t i o n s n e a r t h e f i r s t s i l l i m a n i t e i s o g r a d w h i c h i s i n t e r p r e t e d as m a r k i n g t h e k y -s i l l e q u i l i b r i u m . P4, b e i n g t h e o n l y specimen f r o m t h e h i g h - g r a d e s i d e of t h e i s o g r a d , must have e x p e r i e n c e d t h e h i g h e s t t e m p e r a t u r e s . The c o n d i t i o n s o f t h e k y - s i l l e q u i l i b r i u m i s n o t w i t h o u t u n c e r -t a i n t y . The a l u m i n o s i l i c a t e phase r e l a t i o n s i n t h i s s t u d y were c a l -c u l a t e d f r o m t h e t h e r m o c h e m i c a l d a t a o f H e l g e s o n and o t h e r s ( 1 9 7 8 ) (see f i g u r e 1 0 ) . The c a l c u l a t e d k y - s i l l c u r v e a g r e e s c l o s e l y w i t h t h e p r e f e r r e d c u r v e o f Holdaway(1971) based upon e x p e r i m e n t a l work. How-e v e r , t h e r e a r e u n c e r t a i n t i e s i n t h e p o s i t i o n o f t h e k y - s i l l e q u i l i -b r i u m due t o t h e p o s s i b l e a f f e c t s o f minor element s u b s t i t u t i o n ( S t r e n s , 1968; A l t h a u s , 1969) and A l - S i d i s o r d e r i n s i l l i m a n i t e ( G r e e n w o o d , 1972; N a v r o t s k y and O t h e r s , 1973). EQUILIBRIUM I I C a l c u l a t e d c u r v e s f o r t h i s e q u i l i b r i u m a r e s e n s i t i v e t o t h e c h e m i c a l a n a l y s e s and a t b e s t , p r o v i d e o n l y a minimum P and T. F o r t h e p r e s e n t s t u d y t h e P-T c u r v e s were c a l c u l a t e d u s i n g t h e thermo-c h e m i c a l d a t a of H e l g e s o n and o t h e r s ( 1 9 7 8 ) a l o n g w i t h c p d a t a f o r q u a r t z from Brown(1978, p e r . comm.). T h i s d a t a i s c o n s i s t e n t w i t h t h e e x p e r i m e n t a l d a t a o f H a r i y a and K ennedy(1968). The c a l c u l a t e d c u r v e s a r e n e a r l y p a r a l l e l t o t h e k y - s i l l e q u i l i b r i u m ( see f i g u r e 1 1 J . As T a b l e 13. Thermodynamic d a t a . E q u i l i b r i u m AH°(J/mole) AS°(J/mole °C) Aa = Aa + AbT + A b x l O 2 -2 AcT Ac . . . 3 AV^(cm /mole) I 7523 13.095 -5.7277 0.24015 505428 5.81 I I 67837 172.88 12.970 -4.7696 -437963 66.2 I I I 1100444* 1305.0* 13.786 -8.6672 -7423387 -114.7 IV 86283* 158.90* -15.702 -0.80664 1319772 -10.51 V see t e x t -23.463 2.8341 1930854 9.20 V I see t e x t 0 0 0 2.53 A l l d a t a f r o m H e l g e s o n and o t h e r s ( 1 9 7 8 ) e x c e p t where n o t e d and c d a t a f o r a - q u a r t z ( B r o w n p e r s . comm P i g a g e ( 1 9 7 8 ) . 51 F i g ;ure 11. C a l c u l a t e d curves, f o r e q u i l i b r i a I and I I . 53 e x p e c t e d , t h e c u r v e f o r P4 i n d i c a t e s t h e h i g h e s t t e m p e r a t u r e s and c r o s s e s t h e k y - s i l l e q u i l i b r i u m a t about 7kb and 670°C. S i n c e s i l l i -m a n i t e was assumed t o be t h e s t a b l e a l u m i n o s i l i c a t e i n P4, t h i s i n t e r -s e c t i o n p r o v i d e s a minimum P and T f o r t h e a n a l y s e d s p e c i m e n s . - The p o s i t i o n o f t h e c a l c u l a t e d c u r v e i s v e r y s e n s i t i v e t o t h e c h e m i c a l a n a l y s e s because t h e a n a l y s e d g a r n e t s c o n t a i n o n l y 3 t o 7% o f t h e g r o s s u l a r component. The s p r e a d o f t h e c a l c u l a t e d c u r v e s over.50°C-i s u n d o u b t e d l y a r e f l e c t i o n o f t h i s s e n s i t i v i t y . EQUILIBRIUM I I I C a l c u l a t e d c u r v e s o f e q u i l i b r i u m I I I i n t e r s e c t i n g w i t h e q u i l i b r i u m I p r o v i d e a w e l l d e f i n e d e s t i m a t e o f p r e s s u r e and t e m p e r a t u r e . The e n t h a l p y and e n t r o p y o f r e a c t i o n used i n c a l c u l a t i n g t h i s e q u i l i b r i u m were c a l c u l a t e d by P i g a g e ( 1 9 7 8 ) from t h e e x p e r i m e n t a l d a t a o f R i c h a r d s o n ( 1 9 6 8 ) and G a n g u l y ( 1 9 7 2 ) . The t i g h t c l u s t e r i n g o f the c a l c u l a t e d c u r v e s ( s e e f i g u r e 12) r e f l e c t a l a c k o f s e n s i t i v i t y t o s o l i d s o l u t i o n , an e f f e c t t h a t was a l s o n o t e d b y ' P i g a g e ( 1 9 7 6 ) . V a r i a t i o n i n a c t i v i t y a l s o has o n l y a m i n o r e f f e c t on t h e p o s i t i o n o f t h i s e q u i l i b r i u m . T h e r e f o r e t h e i n t e r s e c t i o n o f t h e bank o f e q u i l i -b r i u m I I I c u r v e s w i t h t h e k y - s i l l e q u i l i b r i u m p r o v i d e s w e l l d e f i n e d P-T e s t i m a t e s o f 7.5 t o 7.7kb and 700 t o 710°C. These e s t i m a t e s i n -c l u d e a range o f a d e t e r m i n e d w i t h e q u i l i b r i u m I V. These p r e s s u r e s and t e m p e r a t u r e s a r e a l s o c o n s i s t e n t w i t h e q u i l i b r i u m I I (see f i g u r e 1 4 ) . Due t o t h e t i g h t c l u s t e r i n g o f t h e c a l c u l a t e d c u r v e s , t h e d e p a r t u r e o f the c u r v e f o r P4 from t h e h i g h e s t - t e m p e r a t u r e p o s i t i o n r e q u i r e d by t h e f i e l d r e l a t i o n s i s n o t c o n s i d e r e d s i g n i f i c a n t . EQUILIBRIUM IV T h i s e q u i l i b r i u m cannot be used t o c a l c u l a t e p r e s -s u r e and t e m p e r a t u r e e s t i m a t e s w i t h o u t an i n d e p e n d e n t e s t i m a t e o f t h e 54 600 700 800 T E M P E R A T U R E , °C F i g u r e 12. C a l c u l a t e d c u r v e s f o r e q u i l i b r i u m I I I a t a^. 0=0.81 w i t h e q u i l i b r i u m ' I i n c l u d e d f o r r e f e r e n c e . a c t i v i t y o f H^O. C a l c u l a t i o n s f o r t h i s e q u i l i b r i u m were made u s i n g an e n t h a l p y and e n t r o p y o f r e a c t i o n c a l c u l a t e d f r o m t h e e x p e r i m e n t a l d a t a of C h a t t e r j e e ( 1 9 7 2 ) and t h e n a d j u s t e d f o r l o w - a l b i t e as a p r o d u c t w i t h an i d e a l c o n f i g u r a t i o n a l e n t r o p y term ( P i g a g e , 1 9 7 8 ) . A l t h o u g h h i g h -a l b i t e was p r o duced i n e x p e r i m e n t s w i t h Na end-members, i n t e r m e d i a t e p l a g i o c l a s e s i n metamorphic r o c k s a r e assumed t o have th e l o w - a l b i t e s t r u c t u r e ( S m i t h , 1 9 6 9 ) . The P-T c u r v e s c a l c u l a t e d f o r a u =1 i n t e r -net) s e c t t h e k y - s i l l e q u i l i b r i u m a t p r e s s u r e s and t e m p e r a t u r e s t o o h i g h t o be c o n s i s t e n t w i t h e q u i l i b r i u m I I I . However, c o n s i s t e n c y can be a c h i e v e d by l o w e r i n g t h e a c t i v i t y o f H^Ofsee f i g u r e s 13 and 14).• Water a c t i v i t i e s l e s s t h a n 1.0 a r e n o t o n l y r e a s o n a b l e , b u t r e q u i r e d i f t h e i n t e r s t i t i a l f l u i d i s assumed t o have been a C-H-0 f l u i d i n e q u i l i b r i u m w i t h t h e g r a p h i t e . The mole f r a c t i o n o f ^ 0 i n s u c h a f l u i d i s depen-dent on t h e oxygen f u g a c i t y . The d i s t r i b u t i o n o f gaseous s p e c i e s i n s u c h a f l u i d a t 700°C, 7.6kb and v a r i o u s v a l u e s o f f n was c a l c u l a t e d 2 w i t h a computer program w r i t t e n by L.C. P i g a g e (see a l s o F r e n c h , 1 9 6 6 ) . The mole f r a c t i o n o f w a t e r was f ound t o p a s s t h r o u g h a maximum o f 0.86 a t l o g f _ = -17.64 ( s e e f i g u r e 1 5 ) . Assuming i d e a l m i x i n g o f gaseous 2 s p e c i e s , mole f r a c t i o n and a c t i v i t y a r e i d e n t i c a l . A minimum a o f H 20 0.81 i s r e q u i r e d t o keep e q u i l i b r i u m IV f r o m b e i n g i n c o n s i s t e n t w i t h e q u i l i b r i u m I I I on t h e low P and T s i d e ( s e e f i g u r e 1 4 ) . As s e e n i n f i g u r e 16, t h e e q u i l i b r i a a r e s t i l l c o n s i s t e n t a t a = 0.86. T h e r e -at) f o r e a u n i s r e s t r i c t e d i n t h e range o f 0.81 t o 0.86 w h i c h r e s t r i c t s H 20 l o g f _ t o t h e range -18.1 t o 17.3. Thus, w i t h o u t an i n d e p e n d e n t e s t i -°2 mate o f a , e q u i l i b r i u m IV cannot be used i n e s t i m a t i o n P and T. H2U However, w i t h t h e i n d e p e n d e n t e s t i m a t e o f P and T p r o v i d e d by e q u i l i -b r i a I and I I I , e q u i l i b r i u m IV can be used t o e s t i m a t e a _ i n t h e H 2u 56 600 700 T E M P E R A T U R E , °C F i g u r e 13. C a l c u l a t e d c u r v e s f o r e q u i l i b r i u m IV a t a^ n=1.0 and 57 F i g u r e 14. Composite o f f i g u r e s .11, 12, and 13 i n c l u d i n g o n l y t h e c u r v e s d e f i n i n g t h e extremes f o r each e q u i l i b r i u m . Mole f r a c t i o n o f H O as a f u n c t i o n o f f 2 a t 700°C and P - t o t a l = 7.6kb. The dashed l i n e i s a minimum ^ c o n s t r a i n e d by e q u i l i -l i b r i a I , I I I , and IV. The r e m a i n d e r o f t h e f l u i d c o n s i s t s o f CH^, CO^, B.^, a n d CO i n o r d e r o f d e c r e a s i n g abundance. 59 550 600 650 700 750 TEMPERATURE, °C F i g u r e 16. P-T bands f o r e q u i l i b r i a I t h r o u g h IV a t a^ = 0.86. The c i r c l e d specimen numbers i n d i c a t e T c a l c u l a t e d a t 7.6kb f o r e q u i l i b r i u m V I as c a l i b r a t e d by F e r r y and S p e a r ( 1 9 7 8 ) . metamorphic f l u i d . As w i t h e q u i l i b r i u m I I , t h e h i g h e s t t e m p e r a t u r e P-T c u r v e was c a l -c u l a t e d f o r specimen P 4 . The r e l a t i v e p o s i t i o n s o f c u r v e s c a l c u l a t e d f o r t h e f o u r specimens f o r any one e q u i l i b r i u m i s dependent on t h e e q u i l i b r i u m c o n s t a n t . A r e v i e w o f t h e e q u i l i b r i u m c o n s t a n t s i n t a b l e 1 2 shows t h a t t h e h i g h e s t v a l u e was c a l c u l a t e d : f o r . P 4 i f o r every' e q u i l i -b r i u m e x c e p t I I I . T h i s c o n s i s t e n c y w i t h t h e f i e l d r e l a t i o n s s u p p o r t s th e c o n f i d e n c e i n t h e a c c u r a c y o f t h e c h e m i c a l a n a l y s e s and t h e v a l i d i t y o f t h e c a l c u l a t i o n s . EQUILIBRIUM V T h i s e q u i l i b r i u m was n o t used i n e s t i m a t i n g metamor-p h i c c o n d i t i o n s b ecause o f u n c e r t a i n t i e s i n t h e e n t h a l p y and e n t r o p y o f a l m a n d i n e . A l t h o u g h t h e end-member r e a c t i o n has n o t been d e t e r m i n e d e x p e r i m e n t a l l y , i t can be c a l c u l a t e d f r o m a v a i l a b l e t h e r m o c h e m i c a l d a t a on t h e i n d i v i d u a l p h a s e s . F l e t c h e r and G r e e n w o o d ( 1 9 7 9 ) f o u n d t h a t P-T c u r v e s c a l c u l a t e d i n t h i s manner t o be i n c o n s i s t e n t w i t h e q u i l i b r i a I I and I I I u n l e s s t h e y used H° and S° v a l u e s f o r a l m a n d i n e a t t h e s t a t e d u n c e r t a i n t y l i m i t s o f t h e c a l c u l a t i o n s o f Z e n ( 1 9 7 3 ) . S t a n d a r d e n t h a l -p i e s f o r a l m a n d i n e c o n s i s t e n t w i t h t h e P-T e s t i m a t e s d i s c u s s e d above were c a l c u l a t e d w i t h t h e same e q u a t i o n used i n c a l c u l a t i n g t h e P-T c u r v e s . A l l o f t h e r e q u i r e d thermodynamic p a r a m e t e r s were t a k e n f r o m H e l g e s o n and o t h e r s ( 1 9 7 8 ) e x c e p t S o f a l m a n d i n e . S t a n d a r d e n t h a l p i e s o f a l m a n d i n e c o n s i s t e n t w i t h t h e e s t i m a t e o f P and T were t h e n c a l c u - . l a t e d s e p a r a t e l y f o r t h e S ° ^ m o f H e l g e s o n and o t h e r s ( 1 9 7 8 ) , Z e n ( 1 9 7 3 ) , and F l e t c h e r .and G r e e n w o o d ( 1 9 7 9 ) . The r e s u l t s a r e l i s t e d i n t a b l e 1 4 . E q u i l i b r i u m c u r v e s c a l c u l a t e d f r o m t h i s d a t a (see a l s o t a b l e 1 3 ) a r e i l l u s t r a t e d i n f i g u r e 1 7 . The c u r v e c a l c u l a t e d f r o m t h e t h e r m o c h e m i c a l 61 T a b l e 14. E n t r o p y and e n t h a l p y o f a l m a n d i n e . S°(J/mole °C) H°(J/mole) Data S o u r c e A 285.8 CD -5328360 (1) CD Zen(1973) B 273.2 (2) -5303260 (2) (2) F l e t c h e r and r Greenwood(1979) C . 285.8 (1) -5297570 (4) (3) H e l g e s o n and o t h e r s ( 1 9 7 8 ) D 316.3 (3) -5267440 (4) (4) T h i s s t u d y E 273.2 (2) -5309700 (4) 2Q0 400 600 800 1000 1200 TEMPERATURE, °C F i g u r e 17. C a l c u l a t e d e q u i l i b r i u m V c u r v e s f o r P2. The l e t t e r s r e f e r to d a t a s e t s f rom t a b l e 14. The r u l e d box d e f i n e s t h e e r r o r l i m i t s f o r t h e P-T e s t i m a t e d e r -i v e d from from e q u i l i b r i a I - I V . d a t a c o n s i s t e n t w i t h t h i s s t u d y may be more a c c u r a t e . EQUILIBRIUM VI T h i s e q u i l i b r i u m has been c a l i b r a t e d e x p e r i m e n t a l l y as a geothermometer by F e r r y and Spear (1978).. Temperatures c a l c u l a t e d from t h e i r e q u a t i o n (7) a t 7.6kb, r a n g i n g f r o m 564 t o 636°C, a r e shown g r a p h i c a l l y on f i g u r e 16. The 75°C t e m p e r a t u r e range i n d i c a t e s a s e n -s i t i v i t y o f t h i s e q u i l i b r i u m t o c h e m i c a l a n a l y s e s t h a t i s even g r e a t e r t h a n t h a t o f e q u i l i b r i u m I I . The i n c o n s i s t e n c y w i t h t h e P-T c a l c u l a -t i o n s f o r e q u i l i b r i a I t h r o u g h IV may be t h e r e s u l t o f d i f f e r e n c e s be-tween t h e s y n t h e t i c m i n e r a l s s t u d i e d by F e r r y and Spear and t h e n a t u r a l m i n e r a l s s t u d i e d h e r e . Ca, Mn, T i , and Na were n o t p r e s e n t i n t h e s y n -t h e t i c m i n e r a l s , and t h e e x p e r i m e n t s cannot a c c o u n t f o r t h e i r e f f e c t s . The s y n t h e t i c g a r n e t s were 80,;:and 90% a l m a n d i n e and t h e Fe-Mg g a r n e t s o l u t i o n was c o n c l u d e d by F e r r y and Spear t o be i d e a l o v e r t h i s r a n g e . The c a l c u l a t i o n s o f Ganguly and Kennedy(1974) show t h e Fe-Mg g a r n e t s o l u t i o n t o be n o n - i d e a l . I n a d d i t i o n , t h e g a r n e t s a n a l y s e d f o r t h i s s t u d y a r e a l l l e s s t h a n 80% a l m a n d i n e . D i s c u s s i o n U n c e r t a i n t i e s i n t h e P-T e s t i m a t e s d e r i v e d f r o m e q u i l i b r i a I , I I I , and IV have been e s t i m a t e d t o +400 b a r s and +40°C ( P i g a g e , 1978). Thes e r r o r e s t i m a t e s t a k e i n t o a c c o u n t u n c e r t a i n t i e s i n t h e a l u m i n o s i l i c a t e phase r e l a t i o n s , t h e r m o c h e m i c a l d a t a d e r i v e d f r o m e x p e r i m e n t a l P-T b r a c k e t s , and t h e s t r u c t u r a l s t a t e o f metamorphic p l a g i o c l a s e . U n c e r -t a i n t i e s i n s o l i d s o l u t i o n models were found t o have a r e l a t i v e l y m i n o r e f f e c t on t h e P-T e s t i m a t e s ( P i g a g e , 1 9 7 8 ) . A n o t h e r s o u r c e o f e r r o r t h a t may need t o be c o n s i d e r e d i s p o s s i b l e e r r o r s i n t h e e x p e r i m e n t a l d a t a used i n c a l c u l a t i n g e q u i l i b r i u m I I I . An a p p a r e n t i n c o n s i s t e n c y 64 between f i e l d studies and experimental determination of the s t a b i l i t y of s t a u r o l i t e has been noted by.Carmichael(1978). The inconsistency of c a l c u l a t i o n s for e q u i l i b r i a V and VI also reduce confidence i n the P-T estimate. However, the method of mutually i n t e r s e c t i n g calculated e q u i l i b r i a promises to become an accurate method of estimating e q u i l i -brium metamorphic conditions with the completion of a d d i t i o n a l experi-mental work and refinement of thermodynamic data. UPPER LIMITS ON REGIONAL METAMORPHISM The upper l i m i t s on c o n d i t i o n s e x p e r i e n c e d by t h e p e l i t i c r o c k s o f h i g h e s t metamorphic grade (second s i l l i m a n i t e zone) a r e u n c e r t a i n . A l o w e r l i m i t i s , o f c o u r s e , t h e c o n d i t i o n s a l r e a d y c a l c u l a t e d f o r r o c k s n e a r t h e f i r s t s i l l i m a n i t e i s o g r a d . M u s c o v i t e i s p r e s e n t , a l t h o u g h .. m i n o r , and K - f e l d s p a r i s a b s e n t t h r o u g h o u t t h e second s i l l i m a n i t e zone. Q u a r t z o f e l d s p a t h i c v e i n s a r e i n c r e a s i n g l y common i n t h e h i g h e s t grade s c h i s t s . However, t h e s e v e i n s a r e t i g h t l y f o l d e d , i n d i c a t i n g t h a t t h e y appeared e a r l y i n t h e phase o f f o l d i n g and a r e p r o b a b l y r e l a t e d t o th e Spuzzum I n t r u s i o n s r a t h e r t h a n t o p a r t i a l m e l t i n g . T h e r e f o r e , n e i t h e r m u s c o v i t e d e h y d r a t i o n n o r a n a t e x i s has o c c u r e d and so t h e s e r e a c t i o n s may be c o n s i d e r e d upper l i m i t s on t h e r e g i o n a l metamorphism. S t u d i e s o f t h e a n a t e x i s o f p e l i t i c rocks(Thompson and A l g o r , 1977; T r a c y , 1978) i n d i c a t e t h a t a n a t e x i s , r a t h e r t h a n m u s c o v i t e d e h y d r a t i o n , would be t h e l i m i t i n g metamorphic r e a c t i o n a t t h e p r e s s u r e s assumed h e r e (7 t o 8 k b ) . F i g u r e 18 shows t h e a p p r o x i m a t e P-T c o n d i t i o n s o f a n a t e c t i c r e a c t i o n s i n t h e s i m p l i f i e d p e l i t i c system: Ca0-Na20-K20-Al20 '.^ •SIO^ -H-O ( T r a c y , 1 9 7 8 ) . R e a c t i o n s a r e i d e n t i f i e d w i t h t h e phase a b s e n t f r o m t h e r e a c t i o n . The two i n v a r i a n t p o i n t s a r e f o r t h e S i 0 2 s a t u r a t e d Ca and Na end-member s y s t e m s . The i n v a r i a n t p o i n t f o r an i n t e r m e d i a t e s y s t e m would be somewhere a l o n g t h e c o n n e c t i n g p l a g i o -c l a s e - a b s e n t r e a c t i o n . A t a c t i v i t i e s o f ^ 0 l e s s t h a n 1.0 t h e i n -v a r i a n t p o i n t s would be d i s p l a c e d t o h i g h e r P and T a l o n g t h e v a p o r -a b s e n t r e a c t i o n s (Thompson and A l g o r , 1977) a l l shown by t h e arrows i n f i g u r e 18. I n t h e absence o f K - f e l d s p a r t h e f i r s t , and t h e r e f o r e l i m i t i n g a n a t e c t i c r e a c t i o n would be t h e K - f e l d s p a r - a b s e n t r e a c t i o n : mus + p l a g + q t z + v a p o r = Al-SiO,. + l i q u i d . 66 600 700 800 TEMPERATURE, °C F i g u r e 18. A p p r o x i m a t e a n a t e c t i c r e l a t i o n s f o r p e l i t i c r o c k s . ( a d a p t e d from T r a c y , 19 78, f i g u r e 11) Arrows i n d i -c a t e d i s p l a c e m e n t o f i n v a r i a n t p o i n t s w i t h r e d u c t i o n o f a^. Q. The box o u t l i n e s t h e P-T e s t i m a t e f o r t h e f i r s t s i l l i m a n i t e i s o g r a d . 67 The P-T p o s i t i o n o f t h i s r e a c t i o n f o r t h e S e t t l e r S c h i s t r o c k s (An^^-An^^) wo u l d be c l o s e t o t h e Na end-member. The p o s i t i o n o f t h i s l i m i t i n g r e a c t i o n i n d i c a t e d by t h e P-T r e l a t i o n s o f f i g u r e 18 i s not : c o n s i s t e n t w i t h b o t h t h e f i e l d r e l a t i o n s and t h e P-T e s t i m a t e f o r t h e f i r s t s i l l i m a n i t e i s o g r a d . R e d u c t i o n o f a n can make t h e l i m i t i n g r e a c t i o n c o n s i s t e n t o n l y w i t h t h e low t e m p e r a t u r e end o f t h e e r r o r e s t i m a t e f o r t h e P-T c a l c u l a t i o n s . M a j o r components n o t c o n s i d e r e d i n t h e P - T , r e l a t i o n s o f f i g u r e 18, p a r t i c u l a r l y FeO and MgO, may a c c o u n t f o r t h e s e a p p a r e n t i n c o n s i s t e n c i e s . A l t e r n a t i v e l y , i f t h e p o s i t i o n of e q u i l i b r i u m I I I g i v i n g s t a u r o l i t e breakdown i s g i v e n l e s s w e i g h t and assumed t o l i e a t l o w e r t e m p e r a t u r e s ( C a r m i c h a e l , 1978) t h e l a c k o f a n a t e x i s would t h e n be c o n s i s t e n t w i t h t h e P-T e s t i m a t e . As i t i s , a f i r m upper l i m i t on t h e r e g i o n a l metamorphism cannot be a s s i g n e d w i t h - . out r e f i n e m e n t o f d a t a on a n a t e c t i c r e l a t i o n s and s t a u r o l i t e breakdown r e a c t i o n s . 68 CONTACT METAMORPHISM C o n t a c t metamorphism a s s o c i a t e d w i t h Spuzzum i n t r u s i v e c o n t a c t s i s r e c o r d e d by pseudomorphs a f t e r a n d a l u s i t e . Pseudomorphic r e p l a c e m e n t t o o k p l a c e d u r i n g t he l a t e r r e g i o n a l metamorphism. The o r i g i n a l a n-d a l u s i t e i s assumed t o have c r y s t a l l i z e d s t a b l y a t a p r e s s u r e below th 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 . I f t h e a n d a l u s i t e formed a t h i g h e r p r e s s u r e s i t would n e c e s s a r i l y have c r y s t a l l i z e d m e t a s t a b l y . T h i s i n -t e r p r e t a t i o n has been s u g g e s t e d ( H o l l i s t e r , 1969) f o r pseudomorphs a f t e r a n d a l u s i t e i n s i m i l a r s c h i s t s o f t h e Kwoiek a r e a 50 km t o t h e n o r t h . P r e s s u r e s o f r e g i o n a l metamorphism e s t i m a t e d i n t h i s s t u d y a r e about 4kb 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 . S t a b l e f o r m a t i o n o f a n d a l u s i t e w o u l d thus r e q u i r e t h a t c o n t a c t and r e g i o n a l metamorphism were s e p a r a t e d by t h e t i m e span r e q u i r e d f o r an i n c r e a s e i n d e p t h o f b u r i a l o f a t l e a s t 14km. M i n e r a l t e x t u r e s i n d i c a t e t h a t a n d a l u s i t e formed b e f o r e t h e most i n t e n s e p e r i o d o f f o l d i n g , w h i c h i n t u r n p r e -ceeded t h e c u l m i n i a t i o n o f r e g i o n a l metamorphism. C o n s e q u e n t l y , t h e p r e s s u r e d i f f e r e n c e and a s s o c i a t e d t i m e span i m p l i e d by s t a b l e f o r -m a t i o n o f a n d a l u s i t e i s c o n s i d e r e d n o t o n l y p o s s i b l e , b u t p r o b a b l e . The m i n e r a l o g y o f t h e a n d a l u s i t e pseudomorphs i n d i c a t e s t h a t r e p -l a cement o f a n d a l u s i t e p r o c e e d e d t h r o u g h two r e a c t i o n s . Some r e p l a c e -ment t o o k p l a c e v i a t h e d i r e c t p o l y m o r p h i c t r a n s i t i o n t o k y a n i t e . How-ev e r k y a n i t e i s n o t c o n s i s t e n t l y a c o n s t i t u e n t o f t h e pseudomorphs. The pseudomorphs c o n s i s t e n t l y c o n t a i n s t a u r o l i t e , q u a r t z and m u s c o v i t e , i m p l y i n g a r e p l a c e m e n t r e a c t i o n o f t h e t y p e ; a n d a l u s i t e + b i o t i t e + ^ 0 = s t a u r o l i t e + m u s c o v i t e + q u a r t z U n u s u a l . g r a p h i c • i n t e r growths:: of. quar t z ( ? ) : . . l n ^ s t a u r o l i t e s c c o n t a i n e d ~ . w i t h i n pseudomorphs i n the Y a l e C r e e k a r e a ( p l a t e l a ) a r e a l s o c l e a r l y d e s c r i b e d 69 by H o l l i s t e r ( 1 9 6 9 ) f o r s t a u r o l i t e s o f i d e n t i c a l p a r a g e n e s i s i n t h e Kwoiek a r e a . The s t a u r o l i t e s r e s t r i c t e d t o w i t h i n pseudomorphs i n t h e s t u d y a r e a and i n t h e Kwoiek a r e a p r e s u m a b l y formed by s i m i l a r c h e m i c a l p r o c e s s e s . 70 ULTRAMAFITES U l t r a m a f i c m i n e r a l assemblages i n d i c a t e t h a t t h e s c a t t e r e d u l t r a -m a f i c pods were emplaced p r i o r t o t h e r e g i o n a l metamorphism, e x c e p t f o r th o s e pods found n e a r the Hope F a u l t . U l t r a m a f i c s n e a r t h e f a u l t e x h i b i t low t e m p e r a t u r e a l t e r a t i o n a s s e m b l a g e s , u n d o u b t e d l y t h e r e s u l t o f h y d r o t h e r m a l a c t i v i t y a l o n g t h e f a u l t . Away from t h e f a u l t , u l t r a -m a f i c assemblages a r e c o n s i s t e n t w i t h t h e metamorphic c o n d i t i o n s assumed f o r t h e e n c l o s i n g s c h i s t s . U l t r a m a f i c r o c k s n e a r t h e Hope F a u l t a r e e i t h e r s e r p e n t i n i z e d o r a l t e r e d t o q u a r t z + m a g n e s i t e . E x p e r i m e n t a l work i n the s y s t e m MgO-SK^-^O-CX^ (Johannes, 1969) r e s t r i c t s t h e s e assemblages t o low te m p e r a t u r e s w i t h l o c a l v a r i a t i o n s i n f l u i d c o m p o s i t i o n . A t 2kb s e r -p e n t i n e i s r e s t r i c t e d to t e m p e r a t u r e s below about 500°C and low X (see f i g u r e 19) w h i l e q u a r t z + m a g n e s i t e i s r e s t r i c t e d t o t e m p e r a t u r e s below about 450°C f o r X r n l e s s t h a n 0.8. The e x i s t e n c e o f b o t h assem-L.U 2 b l a g e s c l e a r l y r e q u i r e s v a r i a t i o n s i n f l u i d c o m p o s i t i o n . A t e l e v a t e d p r e s s u r e s s e r p e n t i n e s t a b i l i t y i s e x t e n d e d to s l i g h t l y h i g h e r tempera-t u r e s and the l i m i t o f q u a r t z + m a g n e s i t e s t a b i l i t y i n c r e a s e s t o 530°C (X <0.8) a t 7kb (Joh a n n e s , 1969). The a c t u a l p r e s s u r e c o n d i t i o n s t»u 2 c a n n o t be c o n s t r a i n e d by t h e m i n e r a l a s s e m b l a g e s , b u t a r e assumed n o t to be g r e a t e r t h a n the 7 to 8kb e s t i m a t e s f o r t h e r e g i o n a l metamorphism and more l i k e l y s u b s t a n t i a l l y l e s s . S i m i l a r u l t r a m a f i c a l t e r a t i o n assemblages a l o n g the Hope F a u l t t o t h e s o u t h c o n s t r a i n h y d r o t h e r m a l c o n d i t i o n s between 300 and 500°C ( P i g a g e , 1973). Only two s m a l l u l t r a m a f i c pods were found away f r o m t h e v i c i n i t y o f t he Hope F a u l t . One pod l i e s w i t h i n s c h i s t s i n t h e f i r s t s i l l i m a n -i t e zone. The u l t r a m a f i c assemblage o f a n t h o p h y l l i t e p l u s f o r s t e r i t e appears c o n s i s t e n t w i t h t h i s grade o f metamorphism. M i n o r f i n e - g r a i n e d 71 0 0.2 0.4 0.6 0.8 1.0 [2° X C 0 2 C 02 F i g u r e 19. Some T - X C Q r e l a t i o n s i n t h e s y s t e m MgO-Si0 2-H 20-C 0 2 a t 2kb t o t a l p r e s s u r e . The shaded a r e a i s t h e s t a b i l i t y f i e l d o f s e r p e n t i n e . Adapted f r o m J o h a n n e s ( 1 9 6 9 ) . t a l c and m a g n e s l t e a r e i n t e r p r e t e d t o be r e t r o g r a d e a l t e r a t i o n . I n metamorphosed u l t r a m a f i c s o f t h e Mt. B r e a k e n r i d g e a r e a , a n t h o p h y l l i t e i s n o t o n l y p r e s e n t w i t h i n t h e s i l l i m a n i t e zone, b u t i s c o m p l e t e l y r e -s t r i c t e d t o t h i s zone (Reamsbottom, 1974) . F i g u r e 20 shows some e q u i l i b r i a r e s t r i c t i n g a n t h o p h y l l i t e a t a b i l i t y i n t h e s y s t e m MgO-SiQ 2 -H^O. These e q u i l i b r i a were c a l c u l a t e d u s i n g t h e d a t a o f H e l g e s o n and o t h e r s ( 1 9 7 8 ) , and a r e c o n s i s t e n t w i t h t h e e x p e r i m e n t a l d a t a o f Greenwood ( 1 9 6 3 ) . The upper p r e s s u r e - l i m i t o f a n t h o p h y l l i t e i s d e f i n e d by r e a c t i o n (3) and a n t h o p h y l l i t e + f o r s t e r i t e , i n t h e p r e s e n c e o f p u r e H 20, i s r e s t r i c t e d between r e a c t i o n s (1) and ( 2 ) . A n t h o p h y l l i t e w o u l d n o t be s t a b l e , i n t h e p u r e Mg s y s t e m , a t t h e P-T c o n d i t i o n s c a l -c u l a t e d f o r t h e f i r s t s i l l i m a n i t e i s o g r a d . S o l i d s o l u t i o n e f f e c t s were a p p r o x i m a t e d by c a l c u l a t i n g i d e a l a c t i v i t i e s f r o m t h e m i c r o p r o b e ana-l y s e s o f Reamsbottom(1974)l o f a t a l c - f o r s t e r i t e - e n s t a t i t e - a n t h o p h y l l i t e -t r e m o l i t e - c h l o r i t e a s s e m b l a g e ( s p e c i m e n D ) . The r e s u l t s a r e i l l u s t r a t e d i n f i g u r e 21. F i g u r e 19 shows t h a t r e d u c i n g ^ as l o w as 0.6 would have o n l y m i n o r a f f e c t on r e a c t i o n s (1) and ( 2 ) . The r e s u l t s o f t h e . c a l c u l a t i o n o f d i s p l a c e d e q u i l i b r i a ( f i g u r e 21) c a n o n l y be c o n s i d e r e d a p p r o x i m a t e s i n c e t e x t u r e s i n d i c a t e t h a t t h e m i n e r a l s of specimen D a r e no t a l l i n e q u i l i b r i u m (Reamsbottom, 1 9 7 4 ). I n a d d i t i o n , e f f e c t s o f s o l i d s o l u t i o n w i l l depend on t h e amount o f i m p u r i t i e s , p r i n c i p a l l y F e, i n t h e system. However,: i t i s c o n s i d e r e d q u i t e p o s s i b l e f o r s o l i d s o l u t i o n t o expand t h e s t a b i l i t y o f an a n t h o p h y l l i t e + f o r s t e r i t e a s -semblage t o i n c l u d e s i l l i m a n i t e zone c o n d i t i o n s . The second o f t h e s e i s o l a t e d u l t r a m a f i c pods i s l o c a t e d on t h e west s i d e o f Cogburn C reek. The u l t r a m a f i c assemblage i s c o n s i s t e n t w i t h a c o n t r a s t i n metamorphic grade a c r o s s t h e Cogburn Creek F a u l t . 73 10 0 200 600 1000 TEMPERATURE, °C F i g u r e 20. Some c a l c u l a t e d e q u i l i b r i a i n the s y s t e m M g 0 - S i 0 2 -R^O. The box i s t h e P-T e s t i m a t e f o r t h e f i r s t s i l l i m a n i t e i s o g r a d . F i g u r e 21. C a l c u l a t e d a n t h o p h y l l i t e e q u i l i b r i a a d j u s t e d f o r s o l i d s o l u t i o n u s i n g m i c r o p r o b e a n a l y s e s from Reamsbottom(19 74 ) . A c o n c o r d a n t t a l c f o l i a t i o n i n d i c a t e s t h a t t h e u l t r a m a f i c pod was i n p l a c e p r i o r t o f ^ and t h e r e f o r e p r i o r t o peak r e g i o n a l metamorphism. The u l t r a m a f i c assemblage i s t a l c + m a g n e s i t e + c h l o r i t e , b u t rounded a g g r e g a t e s o f u n s t r a i n e d m a g n e s i t e s e t i n w e l l - f o l i a t e d t a l c a r e i n -t e r p r e t e d t o be pseudomorphs a f t e r f o r s t e r i t e . Thus t a l c + f o r s t e r i t e i s c o n s i d e r e d t o be t h e p r o g r a d e assemblage. T h i s assemblage i s r e -s t r i c t e d t o t h e low t e m p e r a t u r e s i d e o f r e a c t i o n (1) ( s e e ( f i g u r e 2 1 ) . A l t h o u g h t h e c a l c u l a t e d e q u i l i b r i a o f f i g u r e 21 a r e o n l y a p p r o x i m a t e , a peak metamorphic grade s i g n i f i c a n t l y b e l o w s i l l i m a n i t e zone i s c l e a r l y i n d i c a t e d . The mode o f emplacement o f t h e u l t r a m a f i c pods i s u n c e r t a i n . Con-t a c t r e l a t i o n s w h i c h m i g h t show t h e s e b o d i e s t o be c o n c o r d a n t , d i s c o r -d a n t , o r f a u l t bounded a r e e i t h e r c o n c e a l e d o r o b l i t e r a t e d by d e f o r -m a t i o n and metamorphism. One q u a r t z - m a g n e s i t e body i n c o n t a c t w i t h t h e Hope F a u l t i s c o n s i d e r e d t o have been f a u l t - e m p l a c e d . The t a l c s c h i s t pod west o f Cogburn Creek i s c l o s e t o t h e b e l t o f u l t r a m a f i c s d e f i n i n g t h e Shuksan T h r u s t r o o t zone (Lowes, 1972) and may be r e l a t e d t o i t . 76 REGIONAL SYNTHESIS I n L a t e P a l e o z o i c t o E a r l y M e s o z o l c t i m e g r e y w a c k e s , m a r l s , c h e r t s and m a f i c v o l c a n i c s o f t h e C a i r n N e e d l e F o r m a t i o n (Reamsbottom, 1971), C h i l l i w a c k Group (Lowes, 1972) and S e t t l e r S c h i s t were d e p o s i t e d i n a e u g e o s y n c l i n a l t r o u g h a d j a c e n t . t o an a c t i v e v o l c a n i c b e l t . As t h e s e r o c k s became d e e p l y b u r i e d t h e y were i n v o l v e d , d u r i n g C r e t a c e o u s t i m e , i n o r o g e n i c a c t i v i t y h a v i n g a n o r t h w e s t - t r e n d i n g a x i s . An e a r l y event i n t h i s orogeny a p p e a r s t o have been e a s t - o v e r - w e s t t h r u s t i n g a l o n g t h e Shuksan and C h u r c h i l l M o u n t a i n t h r u s t f a u l t s (Lowes, 1972). The b r o a d l y s y n t e c t o n i c Spuzzum I n t r u s i o n s i n t r u d e t h e Shuksan f a u l t - z o n e w i t h o u t b e i n g f a u l t e d t h e m s e l v e s . I n a d d i t i o n , an u l t r a m a f i c pod found n e a r t h e Shuksan r o o t - z o n e i n t h i s s t u d y c l e a r l y had t o have been em-p l a c e d p r i o r t o t h e most i n t e n s e d e f o r m a t i o n and metamorphism o f t h e orogeny. Movement on t h e Shuksan T h r u s t may d e c r e a s e n o r t h w a r d s s i n c e , i n t h e Mt. B r e a k e n r i d g e a r e a , t h e C a i r n N e e d l e F o r m a t i o n a p p e a r s t o pass c o n f o r m a b l y i n t o r o c k s e q u i v a l e n t t o t h o s e o f t h e C h i l l i w a c k Group (Reamsbottom, 1974). The e a r l i e s t o f t h e Spuzzum q u a r t z d i o r i t e s i n -t r u d e d t h e s e r o c k s when^the d e p t h o f t h e b u r i a l was s t i l l l e s s t h a n about 14km ( d e p t h t o an 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 p r e s s u r e n e a r 4kb, assuming an a v e r a g e d e n s i t y o f t h e o v e r b u r d e n o f 2.8g/cm ) . C o n t a c t metamorphism around t h e s e e a r l y i n t r u s i v e s p r o duced c h i a s t o l i t e h o r n -f e l s e s . The e a r l i e s t phase o f d u c t i l e d e f o r m a t i o n ( f ^ , o f Reams-bottom, 1974 and S^ o f Lowes, 1972) i s r e c o r d e d t o d a y o n l y i n m i n e r a l t e x t u r e s (Lowes, 1972, and t h i s s t u d y ) and r o o t l e s s i s o c l i n e s (Reams-bot t o m , 1974). W i t h t i m e , d e p t h o f b u r i a l i n c r e a s e d and d i o r i t i c i n -t r u s i v e a c t i v i t y i n c r e a s e d becoming a heat s o u r c e f o r r e g i o n a l meta-morphism. As t e m p e r a t u r e s i n c r e a s e d , d u c t i l e d e f o r m a t i o n i n c r e a s e d , r e a c h i n g a maximum j u s t b e f o r e t h e metamorphic t e m p e r a t u r e s r e a c h e d a maximum. T h i s c u l m i n a t i o n o f d u c t i l e d e f o r m a t i o n (f„, F o f Reamsbottom, / B . 1974, f ^ o f P i g a g e , 1973, and o f Lowes, 1972) r e s u l t e d i n recumbent i s o c l i n a l f o l d i n g o f t h e me t a s e d i m e n t s . I t s i n f l u e n c e on c o n c u r r e n t metamorphic c r y s t a l l i z a t i o n r e s u l t e d i n a w e l l - d e v e l o p e d a x i a l p l a n a r f o l i a t i o n w h i c h o v e r p r i n t e d most o f any p r e - e x i s t i n g d e f o r m a t i o n a l t e x -t u r e s . Near t h e l a r g e , c o m p o s i t e Spuzzum P l u t o n and some i n d i v i d u a l Spuzzum i n t r u s i o n s , metamorphism r e a c h e d s i l l i m a n i t e zone a t tempera-t u r e s as h i g h a t 700+50°C and d e p t h o f b u r i a l up t o 27+2km ( a p p r o x i -m a t e l y c o r r e s p o n d i n g t o p r e s s u r e s o f 7.6+0.5kb). The c o n t a c t meta-m o r p h i c e f f e c t s o f t h e e a r l i e r i n t r u s i v e s were o v e r p r i n t e d by t h i s r e g i o n a l - s c a l e metamorphism. v A l a t e and r e l a t i v e l y m i l d phase o f duc-t i l e d e f o r m a t i o n ( f 3 , F c o f Reamsbottom, 1974, o f P i g a g e , 1973, S^ of Lowes, 1972)) o c c u r r e d w h i l e t e m p e r a t u r e s were s t i l l h i g h enough to a l l o w s t r a i n - r e l e a s i n g r e c r y s t a l l i z a t i o n . U p l i f t began i n M i d d l e C r e t a c e o u s (about 100 mybp) and was accompanied by h i g h - a n g l e n o r m a l f a u l t i n g . The e a s t - y o u n g i n g t r e n d i n K-Ar d a t e s on t h e Spuzzum I n t r u -s i o n s , i n d i c a t e s t h a t movement a l o n g t h e F r a s e r V a l l e y F a u l t Zone p r o -duced t i l t i n g o f the r e g i o n west o f t h e f a u l t zone w i t h t h e maximum up-l i f t and e r o s i o n n e a r e s t t h e f a u l t zone. Thus, t h e p r e s e n t day e r o -s i o n a l e x p o s u r e west o f t h e f a u l t zone r e p r e s e n t s a c r o s s s e c t i o n o f maximum P-T c o n d i t i o n s , d e c r e a s i n g t o t h e w e s t . An o c c u r r e n c e o f anda-l u s i t e west o f k y a n i t e and s i l l i m a n i t e zone metamorphism i n t h e Mt. B r e a k e n r i d g e a r e a (Reamsbottom, 1974) s u p p o r t s a westward d e c r e a s i n g p r e s s u r e g r a d i e n t . 78 F i g u r e 22. S c h e m a t i c e a s t - w e s t c r o s s s e c t i o n s i l l u s t r a t i n g t h e g e o l o g i c h i s t o r y . REFERENCES A l b e e , A.L. and Ray, L., 1970. C o r r e c t i o n f a c t o r s f o r e l e c t r o n probe . m i c r o a n a l y s i s o f s i l i c a t e s , o x i d e s , c a r b o n a t e s , p h o s p h a t e s and s u l f a t e s . Anal.Chem., 42^ pp. 1408-1414. A l t h a u s , E., 1969. E x p e r i m e n t a l e v i d e n c e t h a t t h e r e a c t i o n o f k y a n i t e to f o r m s i l l i m a n i t e i s a t l e a s t b i v a r i a n t . Am. J . S c i . , 267, pp. 273-277. A r m s t r o n g , R.L. and Suppe, J . , 1973. P o t a s s i u m - a r g o n geochronometry o f M e s o z o i c i g n e o u s r o c k s i n Nevada, 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 u l l . , J 3 4 , pp. 1375-1392. Bence, A.E. and A l b e e , A.L., 1968. E m p i r i c a l c o r r e c t i o n f a c t o r s f o r th e e l e c t r o n m i c r o a n a l y s i s o f s i l i c a t e s and o x i d e s . J . G e o l . , 76, pp. 382-403. Bremner, T . J . , 1973. Metamorphism i n t h e F r a s e r Canyon, B r i t i s h Colum-b i a . Unpub. M.Sc. t h e s i s , U. o f B r i t i s h C o l u m b i a , 92pp. C a r m i c h a e l , D.M., 1978. Metamorphic b a t h o z o n e s and b a t h o g r a d s : a measure o f t h e d e p t h o f post-metamorphic u p l i f t and e r o s i o n on th e r e g i o n a l s c a l e . Am. J . S c i . , 278, pp. 769-797. C h a t t e r j e e , N.D., 1972. The upper s t a b i l i t y l i m i t o f t h e assemblage p a r a g o n i t e + q u a r t z a n d . i t s n a t u r a l o c c u r e n c e s . C o n t r i b . M i n e r a l P e t r o l . , 34, pp. 288-303. Dasch, E . J . , 1969. S t r o n t i u m i s o t o p e s i n w e a t h e r i n g p r o f i l e s , deep se a s e d i m e n t s , and s e d i m e n t a r y r o c k s . Geochim. Cosmochim. A c t a , 83, pp. 1521-1552. D i t s o n , G.M., 1978. M e t a l l o g e n y o f t h e Vancouver-Hope A r e a , B r i t i s h C o l u m b i a . Unpub. M.Sc. t h e s i s , U. o f B r i t i s h C o l u m b i a , 187pp. E u g s t e r , H.P., A l b e e , A.L., Bence, A.E., Thompson, J . B . J r . and Waldbaum, D.R., 1972. The two-phase r e g i o n and e x c e s s m i x i n g p r o p e r t i e s o f p a r a g o n i t e - m u s c o v i t e c r y s t a l l i n e s o l u t i o n s . J . P e t r o l . , 13, pp. 147-179. F a u r e , G. and P o w e l l , J . L . , 1972. S t r o n t i u m I s o t o p e G e o l o g y . S p r i n g e r -V e r l a g , New Y o r k , 188pp. F e r r y , J.M. and S p e a r , F.S., 1978. E x p e r i m e n t a l c a l i b r a t i o n o f t h e p a r -t i t i o n i n g o f Fe and Mg between b i o t i t e and g a r n e t . C o n t r i b . M i n e r a l . P e t r o l . , 66, pp. 113-117. F l e t c h e r , C.J.N, and Greenwood, H.J., 1979. 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IV IV Greenwood, H.J., 1972. A l - S i d i s o r d e r i n s i l l i m a n i t e and i t s e f f e c t o n phase r e l a t i o n s o f t h e aluminum s i l i c a t e m i n e r a l s . G e o l . Soc. Am. Memoir 132. G r i f f e n , D.T..,and R i b b e , P.H., 1973. The c r y s t a l c h e m i s t r y o f s t a u r o -l i t e . Am. J . S c i . , 273-A, pp. 479-495. G u i d o t t i , C.V., 1970. The m i n e r a l o g y and p e t r o l o g y o f t h e t r a n s i t i o n f r om l o w e r t o upper s i l l i m a n i t e zone i n t h e Oquossoc a r e a , Maine. J . P e t r o l . , YL, pp. 277-336. H a r i y a , Y. and Kennedy, G.C., 1968. E q u i l i b r i u m s t u d y o f a n o r t h i t e under h i g h p r e s s u r e and hi g h , t e m p e r a t u r e . Am. J . S c i . , 266, pp.193-203. H e l g e s o n , H.C., D e l a n y , J.M., N e s b i t , H.W. and B i r d , D.K., 1978. 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S t a t i s t i c a l thermodynamic models f o r i d e a l o x i d e and s i l i c a t e s o l i d s o l u t i o n s , w i t h a p p l i c a t i o n t o p l a g i o c l a s e . Geochim. Cosmochim. A c t a , J39_, pp. 1431-1442. Krummenacher, D., G a s t i l , R.G., Bushee, J . and Doupont, J . , 1975. K-Ar a p p a r e n t ages, P e n n i n s u l a r Ranges B a t h o l i t h , S o u t h e r n C a l i f o r n i a and B a j a C a l i f o r n i a . G e o l . Soc. Am. B u l l . , J36, pp. 760-768. Lowes, B.E., 1972. Metamorphic P e t r o l o g y and S t r u c t u r a l Geology 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 r i t i s h C o l u m b i a . Unpub. Ph.D. t h e s i s U. o f W a s h i n g t o n , S e a t t l e , 161pp. M a t t i n s o n , J.M., 1972. Ages o f z i r c o n s from t h e N o r t h e r n Cascade Moun-t a i n s , W a s h i n g t o n . G e o l . Soc. Am. B u l l . , 83, pp. 3769-3784. McLeod, H.A., 1975. The G i a n t Mascot U l t r a m a f i t e and i t s R e l a t e d O r e s . Unpub. M.Sc. t h e s i s , U. o f B r i t i s h C o l u m b i a . McTaggart, K.C., 1970. T e c t o n i c h i s t o r y o f t h e N o r t h e r n Cascade Moun-t a i n s . jLn S t r u c t u r e f o the S o u t h e r n C a n a d i a n C o r d i l l e r a . ( J . 0 . W h e e l e r , Ed.) G e o l . A s s o c . Can. S p e c i a l P a p e r 6, pp. 137-148. 82 McTaggart, K..C. and Thompson, R.M. , 1967. Geology o f p a r t o f t h e N o r t h -ern: Cascades 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 . Can. J . E a r t h S c i . , 4., pp. 1199-1228. 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 Cascades o f Wash-i n g t o n S t a t e . Can. I n s t . M i n i n g Met., S p e c i a l v o l . 8, pp.101-148. Monger, J.W.H., 1970. Hope map a r e a , west 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, 75pp.. .. '.. 7 • \-< N a v r o t s k y , A., Newton, R.C. and K l e p p a , O.J., 1973. S i l l i m a n i t e - d i s o r -d e r i n g e n t h a l p y by c a l o r i m e t r y . Geochim. Cosmochim. A c t a , 37, pp. 2497-2508. O r v i l l e , P.M., 1972. P l a g i o c l a s e c a t i o n exchange e q u i l i b r i a w i t h aqueous c h l o r i d e s o l u t i o n : R e s u l t s a t 700°C and 2000bars i n t h e p r e s e n c e o f q u a r t z . Am. J . S c i . , 272, pp. 234-272. P i g a g e ^ L.C., 1973. Metamorphism Southwest o f Y a l e , B r i t i s h C o l u m b i a . Unpubl M.Sc. t h e s i s , U. o f B r i t i s h C o l u m b i a . 95pp. P i g a g e , L.C., 1976. Metamorphism o f t h e S e t t l e r S c h i s t , 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 . Can. J . E a r t h S c i , _13, pp. 405-421. P i g a g e , L.C., 1978. Metamorphism and D e f o r m a t i o n on t h e N o r t h e a s t M a r g i n o f the Shuswap Metamorphic Complex, A z u r e L a k e , B r i t i s h C o l u m b i a . Unpub. Ph.D. t h e s i s , U. o f B r i t i s h C o l u m b i a , 289pp. Read, P.B., 1960. Geology o f t h e F r a s e r V a l l e y from Hope t o Emory Creek, B.C. Unpub. M.Sc. t h e s i s , U. o f B r i t i s h C o l u m b i a , 145pp. Reamsbottom, S.B., 1971. The Geology 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.C. Unpub. M.Sc. t h e s i s , U. o f B r i t i s h C o l u m b i a , 161pp. Reamsbottom, S.B., 1974. Geology and Metamorphism o f t h e Mt. 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.C. Unpub. Ph.D. t h e s i s , U. o f B r i t i s h C o l u m b i a , 155pp. 83 R i c h a r d s , T., 1971. P l u t o n i c Rocks Between Hope, B.C., and t h e 4 9 t h P a r a l l e l . Unpub. Ph.D. t h e s i s , U. o f B r i t i s h C o l u m b i a , 178pp. R i c h a r d s o n , S.W., 1968. S t a u r o l i t e s t a b i l i t y i n a p a r t o f t h e s y s t e m F e - A l - S i - O - H . J . P e t r o l . , 9^, pp. 467-488. R o d d i c k , J.A. and H u t c h i s o n , W.W., 1969. N o r t h w e s t p a r t o f t h e Hope 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 69-1, pp.29a-38a. S c h o l z , C.H., Beavan, R . J . and Hanks, T.C., 1978. Metamorphism, a r g o n d e p l e t i o n , h e a t f l o w and s t r e s s on t h e A l p i n e F a u l t . ( a b s t r a c t ) T r a n s . Am. Geophys. U n i o n , _59, p. 1206. Sheppard, D.S., Adams, C.J. and B i r d , G.W., 1975. Age o f metamorphism and u p l i f t i n the A l p i n e S c h i s t B e l t , New Z e a l a n d . G e o l . Soc. Am. B u l l . , 86, pp. 1147-1153. S k i p p e n , G.B., 1977. D e h y d r a t i o n and d e c a r b o n a t i o n e q u i l i b r i a . I n S h o r t Course i n A p p l i c a t i o n o f Thermodymanics t o P e t r o l o g y and Ore D e p o s i t s , ( H . J . Greenwood, E d . ) . M i n e r a l . A s s o c . Canada, 231pp. S m i t h , J.V., 1968. The c r y s t a l s t r u c t u r e o f s t a u r o l i t e . Am. M i n e r a l . , 53, PP. 1139-1155. S m i t h , J.V., 1969. A t o m i c movements i n p l a g i o c l a s e f e l d s p a r s : a k i n e t i c i n t e r p r e t a t i o n . ' C o n t r i b . M i n e r a l . P e t r o l . , 21^, pp. 157-202. S t r e n s , R.G.J., 1968. S t a b i l i t y o f A ^ S i O , . s o l i d s o l u t i o n s . M i n e r a l . Mag., 36, pp. 839-849. Thompson, A.B. and A l g o r , J.R., 1977. Model systems f o r the a n a t e x i s o f p e l i t i c r o c k s : I . Theory o f m e l t i n g r e a c t i o n s i n the s y s t e m K A 1 0 2 - N a A 1 0 2 - A l 2 0 3 - S i 0 2 - H 2 0 . C o n t r i b . M i n e r a l . P e t r o l . , 63, pp. 247-269. Thompson, J . B . J r . , 1957. The g r a p h i c a l a n a l y s i s o f m i n e r a l assemblages i n p e l i t i c s c h i s t s . Am. / M i n e r a l . , 42^, pp. 842-858. 84 T r a c y , R . J . , 1978. H i g h grade metamorphic r e a c t i o n s and p a r t i a l m e l t i n g i n p e l i t i c s c h i s t , w e s t - c e n t r a l M a s s a c h u s e t t s . Am. J . S c i . , 278, pp. 150-178. V i n i n g , H R . , 1977. The Spuzzum P l u t o n N o r t h w e s t o f Hope, B.C. Unpub. M.Sc. t h e s i s , U. o f B r i t i s h . Columbia. Wood, B. , 1977. E x p e r i m e n t a l d e t e r m i n a t i o n o f t h e m i x i n g p r o p e r t i e s o f s o l i d s o l u t i o n s w i t h p a r t i c u l a r r e f e r e n c e t o g a r n e t and c l i n o -p y r o x e n e s o l u t i o n s . I n Thermodynamics i n Geology (D.G. F r a s e r , E d . ) . D. R e i d e l , B o s t o n , 410pp. Zen, E-An, 1973. Thermochemical p a r a m e t e r s o f m i n e r a l s f r o m oxygen-b u f f e r e d h y d r o t h e r m a l e q u i l i b r i u m d a t a ; Method, a p p l i c a t i o n t o a n n i t e and a l m a n d i n e . C o n t r i b . M i n e r a l . P e t r o l . , _39_, pp. 65-80. \ PLATE 1 O r i e n t e d q u a r t z ( ? ) i n c l u s i o n s i n s t a u r o l i t e c o n t a i n e d w i t h -i n a pseudomorph a f t e r a n d a l u s i t e . Specimen 161. b. Q u a r t z p r e s s u r e shadows around a g a r n e t i n c l u d e d w i t h i n a l a r g e s t a u r o l i t e g r a i n . The p h o t o g r a p h c o n t a i n s about 20% o f the a r e a o f the s t a u r o l i t e g r a i n i n the t h i n s e c t i o n . Specimen 244. 87 PLATE 2 a. A "bow t i e " shaped c l u s t e r o f k y a n i t e w i t h i n a pseudo-morph a f t e r a n d a l u s i t e . Specimen 161. b. F o l d e d and r e c r y s t a l l i z e d b u n d l e o f s i l l i m a n i t e ( c r o s s e d p o l a r i z e r s ) . Specimen 131a. 88 PLATE 3 O u t c r o p o f t h e b r e c c i a " d i k e " i n the Y a l e Creek bed. Embayed g a r n e t w i t h a h a l o o f q u a r t z and p l a g i o c l a s e i n a specimen f r o m t h e second s i l l i m a n i t e zone. Specimen 221. 90 b. I 1mm APPENDIX I V i s u a l l y E s t i m a t e d Modes f o r R e p r e s e n t a t i v e Specimens Fo r o r i g i n a l l o c a t i o n s o f t h e s e s p e c i m e n s , see Map. 3. T a b l e 1-1. S e t t l e r S c h i s t : p e l i t i c s c h i s t and q u a r t z i t e . P2 74 P4 80. 89b 98 131a P I 122a P3 165 173 179a 201 207 221 244 267 283 199 a q u a r t z 50 63 75 58 35 24 58 70 52 53 30 55 65 51 47 65 p l a g i o c l a s e 20 5 4 6 55 70 20 5 5 6 20 .8 25 25 5-b i o t i t e 20 20 3 25 7 2 15 20 20 20 40 20 • ;8 18 15 20 m u s c o v i t e 2 2 5 1 X X X 12 X 12 X 3 g a r n e t 2 3 2 X X 2 2 2 5 3 2 11 3 X 5 4 k y a n i t e 2 3 3 X X 1 2 s i l l i m a n i t e 1 :. 10 2 2 15 3 1 5 s t a u r o l i t e 3 1 4 1 1 X 3 4 2 5 2 c h l o r i t e X X X X 1 X X 3 X i l m e n i t e X X X X X X 1 1 1 1 1 1 2 2 2 X r u t i l e X X X X X X a p a t i t e X X X X X X X t o u r m a l i n e X X X X X X X X g r a p h i t e X X X 2 1 3 2 X z i r c o n X X X X X X X = p r e s e n t , b u t l e s s t h a n 1%. T a b l e 1-2. S e t t l e r S c h i s t : a m p h i b o l i t e and m e t a c h e r t . C u s t e r G n e i s s . 28 49 186 280 51 q u a r t z 63 30 85 40 p l a g i o c l a s e 20 20 9 3 60 h o r n b l e n d e 16 45 90 "6 b i o t i t e .6 g a r n e t X X X d i o p s i d e 12 c l i n o z o i s i t e X sphene 2 i l m e n i t e X 1 X r u t i l e X a p a t i t e c a r b o n a t e X X X = p r e s e n t , b u t l e s s t h a n 1%. T a b l e 1-3. I n t r u s i v e r o c k s . U n i t 3b 3a 3e 3e 3a 4 3 c 3d 14 96 185h 190b 199b 209 239 254 ' p l a g i o c l a s e 65 57 36 70 65 50 50 40 h o r n b l e n d e 10 16 60 X 12 45 q u a r t z 8 15 2 7 25 18 25 13 b i o t i t e 10 10 15 7 8 10 1 K - f e l d s p a r X 13 c h l o r i t e ;X7 X 1 5 1 8 e p i d o t e 5 c l i n o z o i s i t e 2 sphene X X i l m e n i t e 1 1 X 1 X 1 r u t i l e X X X a p a t i t e X X 1 X X g a r n e t X X 1 z i r c o n X s e r i c i t e X X X X X = p r e s e n t , b u t l e s s t h a n 1%. T a b l e 1-4. U l t r a m a f i c r o c k s . ' 12 17 52 81 241b 241c o l i v i n e 10 55 o r t h o p y r o x e n e 33 a n t h o p h y l l i t e 45 t a l c X 68 25 s e r p e n t i n e 55 97 m a g n e s i t e 23 X 30 t r e m o l i t e 60 q u a r t z 75 m a g n e t i t e X X I X l i m o n i t e 2 X = p r e s e n t b u t l e s s t h a n 1%. 96 APPENDIX I I I s o t o p i c Age D a t i n g Data and. A n a l y t i c a l Methods K-Ar and Rb-Sr r a d i o m e t r i c age d a t i n g a n a l y s e s were c o n d u c t e d a t t h e 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 w i t h t h e a i d and a d v i c e o f Dr. R.L. A r m s t r o n g , K r i s t a S c o t t , and J o e H a r a k a l . The f o l l o w i n g s y n o p s i s o f t h e a n a l y t i c a l t e c h n i q u e s was p r o v i d e d by Dr. A r m s t r o n g . Rb and S r c o n c e n t r a t i o n s were d e t e r m i n e d by r e p l i c a t e a n a l y s i s o f p r e s s e d powder p e l l e t s u s i n g X - r a y f l u o r e s c e n c e . U.S. G e o l o g i c a l S u r v e y r o c k s t a n d a r d s were used f o r c a l i b r a t i o n ; mass a b s o r p t i o n c o e f f i c i e n t s were o b t a i n e d f r o m Mo Ka Compton s c a t t e r i n g measure-ments. Rb/Sr r a t i o s have a p r e c i s i o n o f 2 % ( l a ) and c o n c e n t r a t i o n s a p r e c i s i o n o f 5 % ( l a ) . S r i s o t o p i c c o m p o s i t i o n was measured on u n s p i k e d samples p r e p a r e d u s i n g s t a n d a r d i o n exchange t e c h n i q u e s . The mass s p e c t r o m e t e r (60° s e c t o r , 30cm r a d i u s , s o l i d s o u r c e ) i s o f U.S. N a t i o n a l B u r e a u o f S t a n d a r d s d e s i g n , m o d i f i e d by H F a u l . D a t a a q u i s i t i o n i s d i g i t i z e d and automated u s i n g a NOVA computer. 86 88 E x p e r i m e n t a l d a t a have been n o r m a l i z e d t o a S r / S r r a t i o o f 0.1194 and a d j u s t e d so :that t h e NBS s t a n d a r d SrCO (SRM987) g i v e s Q"7 Of. ^ a S r / S r r a t i o o f 0.7102212 and the Eimer and Amend S r a r a t i o 87 86 o f 0.7080012. The p r e c i s i o n o f a s i n g l e S r / S r r a t i o i s 0.00013(.la) . Rb-Sr d a t e s a r e b a s e d on. a Rb decay c o n s t a n t o f 1.42xl0'''^y ^. The r e g r e s s i o n s a r e c a l c u l a t e d a c c o r d i n g t o t h e t e c h n i q u e o f Y o r k ( 1 9 6 7 ) . K i s d e t e r m i n e d i n d u p l i c a t e by a t o m i c a b s o r p t i o n u s i n g a T e c h t r o n AA4 s p e c t r o p h o t o m e t e r and Ar by i s o t o p e d i l u t i o n u s i n g 38 an A E I MS-10 mass s p e c t r o m e t e r and h i g h p u r i t y A r s p i k e . E r r o r s r e p o r t e d a r e f o r one s t a n d a r d d e v i a t i o n . The c o n s t a n t s used a r e : KA = 0 . 5 8 5 x l 0 " 1 0 y _ 1 , KA = 4 . 7 2 x l 0 ~ 1 0 y _ 1 , 4 0 K / K = 0.0119 atom %. 6 p T a b l e s I I - 1 and I I - 2 l i s t t h e a n a l y t i c a l d a t a . Specimen l o c a t i o n s a r e a l l on Map 3 e x c e p t specimen 14. S t a t i o n 14 i s t h e t y p e l o c a l i t y o f Spuzzum u n i t 3b. However, t h e o v e r s i z e specimen needed f o r K-Ar d a t i n g was a c t u a l l y t a k e n f r o m an o u t c r o p w h i c h c o u l d be r e a c h e d by l o g g i n g r o a d s j u s t n o r t h o f t h e mapped a r e a . T a b l e . I I - 1 . K-Ar data. ! sample it 209 14 185 r o c k t y p e g r a n o d i o r i t e h o r n b l e n d e q u a r t z d i o r i t e h o r n b l e n d e q u a r t z d i o r i t e m a t e r i a l a n a l y s e d b i o t i t e h o r n b l e n d e h o r n b l e n d e w e i g h t % K 6.98+0.04 0.27210.004 0.22510.001 r a d i o g e n i c A r / t o t a l . A r 0.687 0.525 0.481 r a d i o g e n i c ^ ^ A r ( 1 0 ^mL/g) 9.204 0.8355 0.8473 a- • 4 0 A ,40,, r a d i o g e n i c A r / K 1 . 9 3 4 x l 0 ~ 3 4 . 5 0 4 x l 0 ~ 3 5 . 5 2 2 x l 0 ~ 3 a p p a r e n t age (Ma) 32.811.1 75.512.6 92.113.2 K c h e m i c a l a n a l y s e s by P.R. Bartholomew. A r mass s p e c t r o m e t r y and age c a l c u l a t i o n s by Joe H a r a k a l . T a b l e I I - 2 . Rb-Sr d a t a . imple # d e s c r i p t i o n ppm Sr ppm Rb 8 7 R b / 8 6 S r 8 7 S r / 8 6 S r 122b s c h i s t 640 5.28 0.0239 0.7038 72 s c h i s t 421 43.8 0.3012 0.7055 172 s c h i s t 276 46.6 0.4886 0.7054 117 s c h i s t 317 73.5 0.6716 0.7065 173 s c h i s t 144 41.2 0.8303 0.7064 80 s c h i s t 213 80.2 1.089 0.7066 90 s c h i s t 204 80.7 1.145 0.7079 209 g g r a n o d i o r i t e 399 63,3 0.4591 0.7043 20 9 a p l a p l i t e 26. 4 133. 14.59 0.7112 209bio b i o t i t e s e p. 35. 8 428. 34.67 0.7192 See a l s o f i g u r e s I I - 1 , and I I - 2 . 0 0.2 0.4 0.6 0.8 1.0 1. S r / S r F i g u r e I I - 1 . . Rb-Sr i s o c h r o n p l o t f o r the S e t t l e r S c h i s t . 101 Figure I I - 2 . Rb-Sr isochron p l o t for the Cogburn Granodiorite. 102 APPENDIX I I I A c t i v i t i e s i n S o l i d S o l u t i o n s G arnet Thermodynamic a c t i v i t i e s o f g a r n e t s p e c i e s were c a l c u l a t e d i n terms o f f o u r end-members h a v i n g the f o r m u l a (Y^) ^ A ^ S i ^ O ^ where +2 +2 = Fe (alma n d i n e ) Y^ = Mg (pyrope) +2 +2 = Ca ( g r o s s u l a r ) Y^ = Mn ( s p e s s a r t i n e ) The a c t i v i t i e s o f t h e s e end-members i n an. i d e a l s o l i d s o l u t i o n a r e g i v e n 3 by a^ = (X^) ( K e r r i c k and Darken, 1975) where X^ . = atoms o f i / t o t a l atoms i n t h e s i t e , o r , i n t h i s c a s e , X. = Y. / Y, + Y„ + Y„ + Y. . i x l 2 3 4 Ganguly and Kennedy(1974) show t h i s s o l u t i o n t o be n o n - i d e a l . F o r a 3 i n o n - i d e a l s o l u t i o n the a c t i v i t y e x p r e s s i o n becomes a^ = (^/y^) • The a c t i v i t y c o e f f i c i e n t s a r e g i v e n by e x p r e s s i o n s o f t h e form: , R T l n Y l = W 1 2X 2 + W^X 2 + W^X 2 + ( W ^ - + W ^ X ^ + ( w 1 3 - w 3 4 + w 1 4 ) x 3 x 4 + ( w 1 2 - w 2 4 + w 1 4 ) x 2 x 4 (Ganguly and Kennedy, 1974). T h e M a r g u l e s p a r a m e t e r s used i n t h i s s t u d y a r e ( i n J / m o l e ) : W 1 2 = 12470 V = 0 W., -.0 W 0 0 = 15980 14 23 W 0 / = 13390 W. = 0 24 34 These were t a k e n f r o m Ganguly and Kennedy(1974) e x c e p t W^3 w h i c h was e s t i m a t e d f r o m d a t a p r e s e n t e d by Wood(1977) and assuming g a r n e t composi-t i o n s t o be n e a r t h e alman d i n e end-member. A c t i v i t y c o e f f i c i e n t s were c a l c u l a t e d f o r an i n i t i a l t e m p e r a t u r e e s t i m a t e o f 650°C. The e f f e c t s o f l a t e r r e c a l c u l a t i o n f o r a more a c c u r a t e t e m p e r a t u r e e s t i m a t e ( see 103 t e x t ) were n o t c o n s i d e r e d s i g n i f i c a n t . The a c t i v i t y c o e f f i c i e n t s a r e l i s t e d i n t a b l e I I I - l . P l a g i o c l a s e The a c t i v i t i e s o f a l b i t e and a n o r t h i t e i n i d e a l p l a g i o c l a s e s o l u t i o n a r e a , = X , and a = X , c o n s i d e r e i n g t h e f a c t t h a t A l - S i s u b s t i t u -ab ab an an t i o n i s c o u p l e d t o t h e Na-Ca s u b s t i t u t i o n , and i g n o r i n g t h e p o s s i b l e e f f e c t s o f aluminum a v o i d a n c e ( K e r r i c k and Darken, 1975). O r v i l l e ( 1 9 7 2 ) shows t h a t t h e p l a g i o c l a s e s o l i d s o l u t i o n i s n o n - i d e a l and c a l c u l a t e d t h e a c t i v i t y c o e f f i c i e n t s t o be Y_. ->.1.28 and Y „ = 1-0 f o r p l a g i o -J Ca Na c l a s e c o m p o s i t i o n s l e s s t h a n 50% a n o r t h i t e . S t a u r o l i t e S t u d i e s o f c r y s t a l c h e m i s t r y and s i t e p o p u l a t i o n o f s t a u r o l i t e ( S m i t h , 1968; G r i f f e n and R i b b e , 1973) i n d i c a t e t h a t t h e c h e m i c a l sub-s t i t u t i o n s on t h e v a r i o u s c r y s t a l l o g r a p h i c s i t e s a r e complex. F o r example, Fe-Mg s o l i d . s o l u t i o n . c a n n o t be c o n s i d e r e d as s u b s t i t u t i o n on a s i n g l e s i t e , b u t a l s o i n v o l v e s Al-Mg and A l - F e s u b s t i t u t i o n s . T h e r e-f o r e , t h e method o f K e r r i c k and Darken(1975) ca n n o t be used d i r e c t l y t o d e r i v e an a c t i v i t y e x p r e s s i o n . I n s t e a d , an e x p r e s s i o n was used w h i c h compares t h e c o m p o s i t i o n w i t h an i d e a l F e - s t a u r o l i t e end-member h a v i n g t h e f o r m u l a F e . A l 1 r ( S i o 0 . , (OH) „. T h i s e x p r e s s i o n i s a ^ = 4 18 8 46 2 F e - s t : ( F e / 4 ) 4 ( A l / . 1 8 ) ( S i / 8 ) 8 . V a r i a t i o n s i n OH c o n t e n t a r e c o n s i d e r e d c o u p l e d to the o t h e r s u b s t i t u t i o n s ( s e e a l s o P i g a g e , 1978). B i o t i t e Two end-member a c t i v i t i e s were c a l c u l a t e d f o r b i o t i t e s : a n n i t e ( K F e 3 A l S i 3 0 1 ( ) ( O H ) 2 ) and p h l o g o p i t e ( K M g 3 A l S i 3 0 ( O H ) ^ ) . The a c t i v i t i e s o f t h e s e end-members i n an i d e a l s o l i d s o l u t i o n a r e g i v e n by a = ann 3 3 X^Xp^ and a ^ = ^ j ^ j g w n e r e the X's a r e i n t e r l a y e r and o c t a h e d r a l s i t e f r a c t i o n s . . V a r i a t i o n s i n t e t r a h e d r a l S i and A l a r e c o u p l e d t o o c t a -h e d r a l A l s u b s t i t u t i o n w h i c h i s a c c o u n t e d f o r i n t h e o c t a h e d r a l s i t e term.' M u s c o v i t e M u s c o v i t e s o l i d s o l u t i o n i s c o n s i d e r e d h e r e t o c o n s i s t o f two i n d e -pendent s o l u t i o n s w i t h f o u r p o s s i b l e end-members: m u s c o v i t e ( K A l 2 S i 3 A 1 0 1 0 ( O H ) 2 ) , p a r a g o n i t e ( N a A J ^ S i ^ A l O ^ Q ( O H ) 2 ) , and t h e Na and K end-member c e l a d o n i t e s ( ;(Na,K) (Fe,Mg)AlSi^0^Q(0H) 2 ) . The m u s c o v i t e and p a r a g o n i t e a c t i v i t i e s , assuming i d e a l s o l u t i o n s a r e g i v e n by a = X K ( A 1 V I - 1 ) 2 and a p a r = X ^ A l ^ - 1 ) 2 . The A l V I - l t e r m i s u s e d , r a t h e r t h a n an o c t a h e d r a l s i t e f r a c t i o n , s i n c e i t w i l l have a v a l u e o f 1 f o r an Na-K m u s c o v i t e and z e r o f o r an Na-K c e l a d o n i t e . S u b s t i t u t i o n o f S i f o r t e t r a h e d r a l A l i s c o u p l e d t o t h e (FejMg)-Al^"'" s u b s t i t u t i o n . The Na-K s o l i d s o l u t i o n i s known t o be n o n - i d e a l and a c t i v i t y c o e f f i c i e n t s were c a l c u l a t e d f r o m t h e e x p r e s s i o n s : l n y K = ^ N 2 A ( W 1 + 2CW2 - W^N-), N R = K/K + Na l n Y N a = lTT NK ( W2 + 2 ( W 1 " W 2 ) N N a ) ' N N a = N a / K + N a where W 1(J/mole) = 17421 + 0 . 5 6 7 4 P ( b a r s ) + 1.6543T(°K) and W 2 = 12895 + 0.3439P + 0.7014T ( E u g s t e r and o t h e r s , 1972) T a b l e I I I - l . A c t i v i t y c o e f f i c i e n t s . m i n e r a l Y P I P2 P3 P4 g a r n e t Ca 1.123 1.102 1.097 1.093 Fe 1.048 1.031 1.027 1.026 Mg 3.168 3.360 3.433 3.466 p l a g i o c l a s e Ca 1.28 1.28 1.28 1.28 Na 1.0 1.0 1.0 1.0 m u s c o v i t e K 1.138 1.083 1.050 1.032 Na 3.822 4.440 5.012 5.463 

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