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A petrographic description of a plutonic mass on Gambier Island, Howe Sound, British Columbia Wilson, George Alexander 1951

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A PETROGRAPHIC DESCRIPTION OF A PLUTONIC MASS" ON GAME-IER ISLAND, HOWE SOUND, BRITISH COLUMBIA by GEORGE ALEXANDER WILSON A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF ' MASTER OF- APPLIED . SCIENCEi I n the'Department o f Geology We a c c e p t t h i s . t h e s i s as c o n f o r m i n g t o the s t a n d a r d r e q u i r e d f r o m - c a n d i d a t e s f o r the degree o f MASTER OF APPLIED SCIENCE. Members of the Department o f G e o l o g y THE UNIVERSITY--OF-BRITISH COLUMBIA May, 1951 - ABSTRACT • A g r a n o d i o r i t e p l u t o n n e a r t h e s o u t h w e s t b o u n d a r y o f t h e C o a s t Range o f B r i t i s h C o l u m b i a was examined by f i e l d ' and p e t r o g r a p h i c methods, w i t h t h e o b j e c t o f d e t e r m i n i n g t h e o r i g i n o f t h e p l u t o n . F i e l d and p e t r o g r a p h i c c h a r a c t e r i s t i c s a r e p r e s e n t e d and d e s c r i p t i o n s o f h2 o f 65 t h i n s e c t i o n s s t u d i e d a r e i n c l u d e d . T h e r e a r e no f i e l d s t r u c t u r e s w h i c h c a n be e x p l a i n e d s o l e l y by. magmatic p r o c e s s e s . ' S e v e r a l f i e l d , c h a r a c t e r i s t i c s ' w h i c h s h o u l d be a s s o c i a t e d w i t h magmatic i n t r u s i o n a r e a b s e n t . P e t r o g r a p h i c e x a m i n a t i o n r e v e a l e d no f e a t u r e s w h i c h c a n be e x p l a i n e d o n l y by magmatic p r o c e s s e s . On t h e o t h e r h a n d , t h e r e p l a c e m e n t t e x t u r e s ' . f o u n d by m i c r o s c o p i c exam-i n a t i o n c a n n o t be a t t r i b u t e d t o c r y s t a l l i z a t i o n f r o m a m e l t . The p h y s i c a l c h e m i c a l s y s t e m which, p r o d u c e d t h e p r e s e n t f o r m o f t h e p l u t o n was an open one. P o t a s h was-a d d e d and soda and l i m e were removed i n t h e e a r l y s t a g e s o f r e c o g n i z a b l e r e p l a c e m e n t . L a t e r s i l i c a - w a s a d d e d and p o t a s h , a l u m i n a , soda and l i m e were re m o v e d . The p r o c e s s e s w h i c h d e v e l o p e d t h e g r a n o d i o r i t e p l u t o n a r e most a c c u r a t e l y d e s c r i b e d as g r a n i t i z a t i o n . ACKNOWLEDGEMENTS -- The e n t i r e s t a f f , o f - t h e g e o l o g y d e p a r t m e n t - o f 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 , p a r t i c u l a r l y Madam D b l a r -M a n t u a n i , D r . H.C. Gu n n i n g and .Dr. W.H.- W h i t e , a s s i s t e d w i t h i n s t r u c t i o n and a d v i c e on p e t r o g r a p h i c methods, s i g n i f i c a n c e o f t e x t u r e s , a r r a n g e m e n t - o f m a t e r i a l , and w i t h d i s c u s s i o n s o f r e g i o n a l geology., and c r i t i c i s m o f m a n u s c r i p t . D r . J..E* A r m s t r o n g o f t h e G e o l o g i c a l S u r v e y o f Canada,-s u p e r v i s e d my f i e l d mapping and w i l l i n g l y gave me d e s c r i p t i o n s o f . t h e o t h e r g e o l o g i c a l f o r m a t i o n s i n t h e V a n c o u v e r d i s t r i c t . My w i f e a s s i s t e d c o n s i d e r a b l y i n p r e p a r a t i o n o f p l a t e s and i n t y p i n g . To a l l t h e a b o v e , and t o t h e G e o l o g i c a l S u r v e y o f Canada f o r p e r m i s s i o n t o u s e t h i s t o p i c , and f o r p r e p a r i n g t h i n s e c t i o n s , I am d e e p l y g r a t e f u l . CONTENTS Page INTRODUCTION - v . -1 General Statement ' 1 Previous Work 1 F i e l d I n v e s t i g a t i o n 2 Laboratory I n v e s t i g a t i o n 3 COAST RANGE OF BRITISH COLUMBIA' 4 General Statement ' 4 St r a t i g r a p h y and H i s t o r y 4 Str u c t u r e of the Coast Range 6 GAMBIER ISLAND- AREA 7 Topography 8 Table of Formations 8 General Geology . . . . . . i- 10 Dykes 14 Stru'c ture '. 14 Age and C o r r e l a t i o n -15" INVESTIGATION OF PLUTONIC ROCKS 18 Artaban G r a n o d i o r i t e .. 18 F i e l d R e l a t i o n s ......... 18 Petrography and Laboratory I n v e s t i g a t i o n 19 Matri x of Artaban G r a n o d i o r i t e 19 X e n o l i t h s i n Artaban G r a n o d i o r i t e 23 Gambler Granod i o r i t e 24 F i e l d R e l a t i o n s .' 24 Petrography and Laboratory I n v e s t i g a t i o n 26 M a t r i x of Gambler G r a n o d i o r i t e 26 X e n o l i t h s i n Gambier Granod i o r i t e 39 NOTEWORTHY FEATURES - 52 Artaban G r a n o d i o r i t e 52 Gambier G r a n o d i o r i t e 52 ORIGIN OF XENOLITHS_ . ... 55 ORIGIN OF THE GAMBIER GRANODIORITE 57 CONCLUSIONS 63 BIBLIOGRAPHY 64 APPENDIX Explanation of-Symbols used i n Appendix i PART A (MATRIX OF ARTABAN GRANODIORITE) - i i i Index to Thin Sections - - i i i Part B"(XENOLITHS IN ARTABAN GRANODIORITE) v i i i Index to Thin Sections v i i i PART C (MATRIX OF GAMBIER GRANODIORITE) . - x i Index to Thin Sections " x i PART"D (XENOLITHS IN GAMBIER GRANODIORITE) x x v i Index to Thin Sections x x v i ILLUSTRATIONS PLATE I I n p o c k e t . PLATE I I . F o l l o w s Page 2 PLATE I I I ' F o l l o w s Page h PLATE'IV F o l l o w s Page. 5 PLATES V TO XIX ( i n c l u s i v e ) F o l l o w Page 6 6 1 A: PETROGRAPH-IC DESCRIPTION OF A PLUTONIC MASS ON'GAMBIER ISLAND, HOWE SOUND, BRITISH COLUMBIA INTRODUCTION - • - - G e n e r a l Statement Gambier I s l a n d i s l o c a t e d between l a t i t u d e s 49 degrees 26 m i n u t e s , and 49 degrees 32 m i n u t e s , n o r t h , and between l o n g i t u d e s 123 degrees 18 -minutes, and 123 degrees 2 8 - m i n u t e s , \irest, i n Howe Sound, -a f i o r d - l i k e i n l e t near the s o u t h end of the B r i t i s h Columbia C o a s t Range.- The c i t y o f Vancouver l i e s about 12 m i l e s s o u t h e a s t . The i s l a n d i s a c c e s s a b l e by water t a x i s from Horseshoe Bay and by a i r c r a f t from Sea I s l a n d , the y e a r round and by Union Steamships from Vancouver, i n the summer months. P r e v i o u s Work (V) O.E. Leroy*mapped the s h o r e l i n e and nearby i s l a n d s , from Vancouver t o J e r v i s I n l e t , i n I 9 0 6 ' . H i s map was--p u b l i s h e d - i n 1908 on a s c a l e o f f o u r m i l e s t o one i n c h . I n the summer o f 1913? and a g a i n i n 1914, E.M.J. BurwashCs) mapped p a r t s o f the Coast Range, between Vancouver and the G a r i b a l d i a r e a , n o r t h of Howe Sound. The s c a l e on w h i c h Burwash's map was p u b l i s h e d i s seven m i l e s t o one i n c h . T.C. Phemister A.made a d e t a i l e d f i e l d and p e t r o g r a p h i c . s t u d y o f the Coast Range-near Vancouver. H i s paper i n -c l u d e s d e s c r i p t i o n s o f the s t r u c t u r e - and f o r m a t i o n s o f Bowen I s l a n d , as w e l l as d e s c r i p t i o n s o f the f o r m a t i o n s and I -Fi«o«-e-> • * birtcHe+j t-eFer- -r4> b.i/i 03 t-a joky F<*}e 6-t 2 s t r u c t u r e of the-Coast Range north of Vancouver. H.C.B. L e i t c h A s t u d i e d v a r i o u s l o c a l i t i e s on .Bowen I s l a n d , p a r t i c u l a r l y i n the re g i o n of Wharf and Lodge Coves, i n 19>+7. -- Recently, i n 1948, 1949, and 1950, J.S:. Armstrong of -the G e o l o g i c a l Survey of Canada, mapped much of the Vancouver area, on- a sca l e of -one h a l f m i l e to one i n c h . His r e p o r t has not been published at-the•time of w r i t i n g o f t h i s r e p o r t . F i e l d I n v e s t i g a t i o n During the 1950 f i e l d season, I was employed by,the G e o l o g i c a l Survey of Canada, i n the task of mapping the Howe Sound area between l a t i t u d e s 49 degrees 20 minutes, and 49 degrees 30 minutes, n o r t h , and between l o n g i t u d e s 123 degrees 17 minutes, and 123 degrees 30 minutes, west, at a sc a l e of one mil e to one i n c h . ' We made tr a v e r s e s at approximately quarter mile i n t e r v a l s , except where apparent l a c k of s t r u c t u r e rendered h a l f mile i n t e r v a l s adequate. Dense shrubbery and a covering of d r i f t obscured- s t r u c t u r e to such an extent that i n t e r p r e t a t i o n of d e t a i l was almost impossible between high t i d e l i n e and summits of the h i l l s . A c c o r d i n g l y , except where we found p a r t i c u l a r l y favourable exposures, we determined the l o c a t i o n of the contacts i n l a n d , and the d e t a i l e d r e l a t i o n s h i p s on shore l i n e exposures. The trav e r s e s made are-shown i n P l a t e - I I . -An outcrop map has not-been prepared f o r a number of reasons. The major reason i s that ori a map of t h i s s c a l e To f o l l o w page 2 3 one does not see a b s o l u t e l y a l l r o c k o u t c r o p s and can c o r r e c t l y map o n l y t h o s e he sees. A map w h i c h shows the pre s e n c e of some o u t c r o p s i n f e r s t h a t t h e r e i s d r i f t where o u t c r o p i s n o t shown. However, c e r t a i n a r e a s where outcrop-s h o u l d n o t be e x p e c t e d a r e i n d i c a t e d on P l a t e I . L a b o r a t o r y I n v e s t i g a t i o n L a b o r a t o r y e x a m i n a t i o n c o n s i s t e d e n t i r e l y o f p e t r o -g r a p h i c a n a l y s e s by means o f s t a n d a r d and u n i v e r s a l s t a g e . I had hoped t o make a number o f s i l i c a a n a l y s e s f rom c o n t a c t zones, i n o r d e r to- d e t e r m i n e the i n c r e a s e i n s i l i c a as con -t a c t s were approached f r o m o u t s i d e the p l u t o n . U n f o r t u n a t e l y time has .-not p e r m i t t e d me t o make such a n a l y s e s . D e t e r -m i n a t i o n s by the Fedbrov method p r o v i d e d a c c u r a t e i n f o r m a t i o n on the c o m p o s i t i o n o f f e l d s p a r s . I n s e v e r a l of those few t h i n s e c t i o n s i n . w h i c h amphibole or.dpyroxene were f o u n d , the Fedorov method was a l s o used t o determine o p t i c c h a r a c t e r -i s t i c s . . . I n g e n e r a l , o n l y c e n t e r e d or v e r y n e a r l y c e n t e r e d i n t e r f e r e n c e f i g u r e s were used t o i d e n t i f y f e l d s p a r s . A n o t a t i o n i n the appendix i n d i c a t e s where o f f - c e n t e r f i g u r e s were used. The c o m p o s i t i o n , even where d e t e r m i n e d by u n i v e r s a l s t a g e methods, i s n o t t o be c o n s i d e r e d a b s o l u t e l y r e p r e s e n t a t i v e . A t r u e i m p r e s s i o n o f the range of p l a g i o -c l a s e i n a r o c k can be g a i n e d o n l y by i d e n t i f y i n g many g r a i n s and c o n s i d e r i n g the most c a l c i c and l e a s t c a l c i c p l a g i o c l a s e t o r e p r e s e n t the range i n c o m p o s i t i o n f o r the t h i n s e c t i o n . COAST RANGE OF BRITISH COLUMBIA G e n e r a l Statement The Coast Range of B r i t i s h Columbia i s a t o p o g r a p h i c and g e o l o g i c u n i t w h i c h extends n o r t h w e s t 1,000 m i l e s from the n o r t h e r n p a r t o f Washington t o the Yukon. The w i d t h o f the C o a s t Range averages about - -50-miles,- but l o c a l l y exceeds 125 m i l e s . The peaks v a r y i n h e i g h t from 7,000 t o 11,000 f e e t . • S t r a t i g r a p h y and H i s t o r y A d e t a i l e d d e s c r i p t i o n o f the s t r a t i g r a p h y and h i s t o r y o f the C o a s t Range i s n o t p r o p e r l y p a r t o f t h i s r e p o r t . V a r i o u s G e o l o g i c a l Survey of Canada r e p o r t s l i s t e d i n the b i b l i o g r a p h y c o n t a i n known i n f o r m a t i o n on the C o a s t Range.. T..C. P h e m i s t e r * i n c l u d e d a v e r y complete summary of b o t h s t r a t i g r a p h i c and t e c t o n i c h i s t o r y i n h i s paper on the C o a s t Range b a t h o l i t h near Vancouver, B r i t i s h C o l u m b i a . Only a few b r i e f comments are i n c l u d e d h e r e . P a l e o z o i c s t r a t a o l d e r than C a r b o n i f e r o u s are r a r e > > w i t h i n the C o a s t Range or a d j o i n i n g a r e a s . For t h i s r e a s o n the Coast Range i s g e n e r a l l y assumed t o have been a l a n d mass exposed t o e r o s i o n u n t i l l a t e P a l e o z o i c . From Carbon-i f e r o u s u n t i l L a t e T r i a s s i c , s e d i m e n t a t i o n and v o l c a n i c a c t i v i t y i n the Western C o r d i l l e r a appear to have been c o i n c i d e n t w i t h g r a d u a l s u b s i d e n c e of the g e o s y n c l i n e . No u n c o n f o r m i t y has been mapped between P a l e o z o i c and Mezozoic f o r m a t i o n s , though p a l e o n t o l o g i c e v i d e n c e i n d i c a t e s t h a t a T o f o l l o w page k P L A T E JH PHYSIOGRAPHY OF BRITISH COLUMBIA ADAPTED FROM HS.BOSTOCK 5. h i a t u s e x i s t s . D e v e l o p m e n t o f t h e g e o s y n c l i n e r e a c h e d a maximum i n t h e M e z o z o i c E r a . C o n s i d e r a b l e t h i c k n e s s e s o f b o t h T r i a s s i c and J u r a s s i c s e d i m e n t a r y and v o l c a n i c s t r a t a p r o b a b l y e x t e n d -ed a c r o s s t h e W e s t e r n C o r d i l l e r a , b u t have b e e n e r o d e d away. The g r e a t e s t d e v e l o p m e n t o f t h e g e o s y n c l i n e i s c o i n c i d e n t w i t h e x t e n s i v e i g n e o u s i n t r u s i o n . Toward t h e end o f t h e J u r a s s i c p e r i o d f o r c e s f r o m t h e w e s t f o l d e d p r e - e x i s t i n g r o c k s i n a n o r t h - w e s t d i r e c t i o n . T h i s f o l d i n g - w a s a c c o m p a n i e d by- igneous- i n t r u s i o n and p o s s i b l y by g r a n i t i z a t i o n on a v a s t s c a l e . U p l i f t , a t l e a s t above b a s e l e v e l o f e r o s i o n , must have f o l l o w e d s e d i m e n t a t i o n , f o l d i n g ^ a n d i n t r u s i o n . D e b r i s f r o m J u r a s s i c i n t r u s i v e s o c c u r s I n C r e t a c e o u s c o n g l o m e r a t e s - a t s e v e r a l l o c a l i t i e s . ( Mathextfs,W..H|' Rice,H.M.A; Crickma'y, e t a l . ) . x C r e t a c e o u s v o l c a n i c a c t i v i t y and s e d i m e n t a t i o n d i f f e r f r o m t h e same p r o c e s s e s o f t h e ' T r i a s s i c p e r i o d i n t h a t C r e t a c e o u s sed-i-ments a r e o f c o n t i n e n t a l o r i g i n t o a very c o n s i d e r a b l e e x t e n t . M a r i n e waters' n e v e r a g a i n i n v a d e d t h e r e g i o n o f t h e W e s t e r n C o r d i l l e r a i n l a r g e s c a l e . Renewed f o l d i n g , f a u l t i n g and i g n e o u s i n t r u s i o n f o l l o w e d C r e t a c e o u s v o l c a n i s m and s e d i m e n t a t i o n . Then a g e n t s o f e r o s i o n once a g a i n commenced t o r e d u c e t o p o g r a p h y , b u t d i d n o t e n t i r e l y e l i m i n a t e r e l i e f b e f o r e T e r t i a r y v o l c a n i c and s e d i m e n t a r y r o c k s s t a r t e d t o a c c u m u l a t e i n i n l a n d d e p r e s s i o n s . A l o n g t h e c o a s t , T e r t i a r y s t r a t a a r e r e c o g n i z e d as b e i n g o f b o t h c o n t i n e n t a l and m a r i n e o r i g i n . The e a r l i e s t s t r a t a a r e To follow page 5 P L A T E IV LOCATION MAP OF HOWE SOUND AREA 6 u n c o n f o r m a b l e o v e r p r e - e x i s t i n g r o c k s , b u t are- t h e m s e l v e s g e n t l y f o l d e d . L a t e r T e r t i a r y s t r a t a a r e n e a r l y h o r i z o n t a l . From m i d Upper- C r e t a c e o u s t i m e u n t i l t h e p r e s e n t , e r o s i o n and u p l i f t w i t h m i n o r p e r i o d s o f d e p r e s s i o n combined t o g i v e t h e C o a s t Range i t s p r e s e n t f o r m . S t r u c t u r e o f t h e C o a s t Range As n o t e d i n t h e p r e e e e d i n g ; . s e c t i o n , t h e C o a s t Range i s an u p l i f t e d mass o f p l u t o n i c and metamorphosed r o c k . I m m e d i a t e l y e a s t o f t h e C o a s t Range, t h e s t r a t a a r e c l o s e l y f o l d e d and i n p l a c e s o v e r t u r n e d t o w a r d t h e n o r t h - e a s t . The c o n t a c t i s a b r u p t a t s o m e ' p l a c e s , b u t t r a n s i t i o n a l and i n -d i s t i n c t a t o t h e r s . I n g e n e r a l , t h e C o a s t Range t r e n d s p a r a l l e l w i t h r e g i o n a l f o l d i n g , b u t i n d e t a i l , i n t r u s i v e c o n t a c t s t r a n s e c t s t r u c t u r e a l o n g d i p as w e l l as a l o n g s t r i k e . The known w e s t e r n l i m i t o f t h e C o a s t Range s w i n g s t o w a r d t h e e a s t a few m i l e s n o r t h w e s t o f V a n c o u v e r . T h i s e a s t w a r d t r e n d o f t h e C o a s t Range i n t h e V a n c o u v e r d i s t r i c t , may a c c o u n t f o r t h e e a s t - w e s t t r e n d o f many p r e - b a t h o l i t h i c r o c k s a b o u t Howe Sound. 7' GAMBIER ISLAND AREA T o p o g r a p h y The m o u n t a i n s a r o u n d Howe Sound r i s e a b r u p t l y f r o m s e a l e v e l t o e l e v a t i o n s o f 4 , 5 0 0 t o o v e r 5,SOO f e e t . N e a r l y a l l . o f t h e h i g h e r p e a k s have s h a r p r a g g e d p r o f i l e s . The i s l a n d s w i t h i n Howe Sound a r e much l o w e r . The h i g h e s t e l e v a t i o n s on b o t h Gambier I s l a n d and Bowen I s l a n d t o t h e s o u t h , a r e 2,800 t o 2 , 9 0 0 f e e t . The summits, a r e more r o u n d e d t h a n t h o s e o f t h e m a i n l a n d , and s l o p e s t o o p r e c i p i t o u s t o c l i m b a r e r a r e on Gambier and a b s e n t on t h e i s l a n d s s o u t h of G a m b i e r . The l o w e r h i l l s and r i d g e s a r e somewhat t h e shape o f v e r y l a r g e r o c k d r u m l i n s o r " r o c h e s moutonnees", w i t h t h e s t e e p e s t s l o p e s f a c i n g n o r t h w a r d . T h i s i s p a r t i c u l a r i t y t r u e o f Bowyer I s l a n d and Mt. A r t a b a n on Gambier I s l a n d . The d r u m l i n - s h a p e d r i d g e s , w i t h t h e e x c e p t i o n o f Bowyer I s l a n d , t r e n d i n a d i r e c t i o n o f a b o u t 200 d e g r e e s s u b - p a r a l l e l w i t h g l a c i a l s t r i a e . Bowyer I s l a n d t r e n d s n e a r l y n o r t h - s o u t h . G l a c i a l d e b r i s and g r a v e l s were f o u n d a t a l l e l e v a t i o n s and i t i s assumed, t h e r e f o r e , t h a t t h e g r o u p o f i s l a n d s was e n t i r e l y c o v e r e d by i c e , d u r i n g P l e i s t o c e n e g l a c i a t i o n . Some o f t h e s t r e a m s , f o r example .those n o r t h o f C e n t r e an d West B a y s , on Gambier I s l a n d , f o l l o w s t r u c t u r a l t r e n d s . T h i s i s p a r t i c u l a r i t y n o t i e e a b l e - - i n t h e course- o f a s t r e a m w h i c h f o l l o w s a s u p p o s e d f a u l t ! i n a s o u t h w e s t e r l y d i r e c t i o n i n w e s t Gambier I s l a n d . The e n t i r e a r e a h a s a d r y c l i m a t e i n ~ summer. M o r e o v e r , t h e h e i g h t s on t h e i s l a n d s a r e n o t 8 g r e a t enough t o g a t h e r any l a r g e p r o p o r t i o n of- m o i s t u r e a v a i l a b l e i n w e s t e r l y w i n d s . F o r t h i s r e a s o n many o f t h e s t r e a m s a r e s m a l l i n t h e summer. T a b l e o f F o r m a t i o n s . Q LU U J 8 . A c i d L a v a s . M a s s i v e and f r a g m e n t a l . N o r t h e a s t p a r t o f a r e a mapped, on Gambier I s . P y r o c l a s t i c R o c k s Lower p a r t i s c o n g l o m e r a t e w i t h p e b b l e s f r o m ( 6 a ) ' . - S e p a r a t e d f r o m ( 6 a ) and ( 6 b ) by an u n c o n -f o r m i t y . O c c u r s s o u t h o f (85 and n o r t h o f ( 6 a & b ) . U n c o n f o r m i t y O Lu <0 to < or Zi - 5 6 * . C o a s t I n t r u s i v e s . as Gambier- g r a n o d i o r i t e . . S o u t h p a r t o f Gambier Island;-.-medium g r a i n e d p i n k o r , g r a y : q u a r t z , c h a r a c t e r i s t i c a l l y 2 5 - 3 5 % sub-he d r a l : numerous i n c l u s i o n s , some o f w h i c h a r e t u f f s , younger- t h a n ( 6 b ) , b u t r e l a t i o n s h i p t o ( 6 c ) i s unknown. ( 6 a ) a l s o o c c u r s as p e b b l e s i n . ( 7 ) . I n t r u s i v e c o n t a c t . b . A r t a b a n g r a n o d i o r i t e . . . . . O c c u r s as two s e p a r a t e d masses n o r t h o f Gambier g r a n o d i o r i t e ( 6 a ) , r e d brown w e a t h e r i n g , medium g r a i n e d r o c k , composed o f 6 0 $ - f e l d s p a r and kQ% m a f i c m i n e r a l s . O l d e r t h a n (:'•; ( 6 a ) . Age r e l a t i v e t o ( 6 c ) i s un-known. Not i n c o n t a c t . c . C r y s t a l l i n e r o c k s , o f Bowen and K e a t s I s l a n d s . A l l have t h e f o l l o w i n g c h a r a c t e r i s t i c s ; t r a n s -i t i o n a l c o n t a c t s , f o l i a t i o n and i n -c l u s i o n s p a r a l l e l w i t h c o n t a c t s and r e g i o n a l s t r u c t u r a l t r e n d . Age r e l a t i v e t o ( 6 a ) and ( 6 b ) unknown. 9 I n t r u s i v e c o n t a c t . a j -J O O o to to < 5 CO c O O cC CL. 5. A r g i l l a c e o u s s e d i m e n t a r y f o r m a t i o n . E a s t - w e s t t r e n d ; d i p i s s t e e p . Age r e l a t i v e t o ( l ) unknown. O c c u r s as an i s o l a t e d mass on w e s t - c e n t r a l Gambier I s l a n d . Not i n c o n t a c t . A c i d Lavas, M o s t l y i n c l u s i o n s i n ( 6 a ) and ( 6 b ) . One l a r g e 7 5 f o o t mass s e p a r a t e s ( 6 a ) and ( 6 b ) a t n o r t h end o f West Bay. A s e c o n d mass o u t c r o p s i m m e d i a t e l y n o r t h o f ( 6 b ) on West Bay. Age r e l a t i v e t o ( 3 ) o r ( l ) unknown. Not i n c o n t a c t . L a v a s . M e l a n o c r a t i c a l t e r e d l a v a s n o r t h , ( 3 a ) and s o u t h ( 3 b ) o f Gambier g r a n o d i o r i t e . Not i n c o n t a c t . T u f f s . O n e . i n c h l a m i n a t i o n s o f dense d a r k and l i g h t g r a y or brown m a t e r i a l : s p a r s e i n t e r b e d d e d l a v a s : o a g e o f ( 2 ) r e l a t i v e t o ( 1 ) I s unknown. O c c u r on Bowen and K e a t s I s l a n d as w e s t t r e n d i n g b e l t s one q u a r t e r t o one h a l f m i l e w i d e . 1 . L a v a s . O c c u r on Bowen'and K e a t s I s l a n d s , b a s i c t o medium b a s i c : i n t e r b e d d e d w i t h t u f f s ; age r e l a t i v e t o ( 2 ) , ( 3 ) , and ( 4 ) i s unknown. 1 0 G e n e r a l G e o l o g y Bowen and K e a t s I s l a n d s - a r e u n d e r l a i n by l a v a s ( l ) and t u f f s (-2). (See T a b l e o f F o r m a t i o n s ) . G r a n i t i c r o c k s a r e c o n f o r m a b l y i n t r u d e d - i n t o , or more p r o b a b l y , d e v e l o p e d f r o m t h e s e r o c k s . B e d d i n g i n t h e t u f f s , c o n t a c t z o n e s between l a v a s and g r a n i t i c r o c k s , and i n c l u s i o n s and f o l i a t i o n i n t h e g r a n i t i c r o c k s , a l l t r e n d a t 8 0 d e g r e e s t o 1 1 0 d e g r e e s . Most o f t h e mapped p a r t o f Gambier I s l a n d i s u n d e r l a i n by c r y s t a l l i n e r o c k s , Gambier g r a n o d i o r i t e ( 6 a ) and A r t a b a n g r a n o d i o r i t e ( 6 b ) . The o l d e r o f t h e two p l u t o n i c r o c k s . ( 6 b ) , o c c u r s as two i s o l a t e d m a s s e s . The l a r g e r mass t r e n d s i n an e a s t - w e s t d i r e c t i o n a c r o s s Mt. A r t a b a n . I t i s a r u s t y or-pin k . w e a t h e r i n g , medium g r a i n e d r o c k . The f r e s h s u r f a c e i s m o t t l e d - p i n k and d a r k g r e e r i . M i n e r a l p r o p o r t i o n s - a r e , a p p r o x i m a t e l y , f e l d s p a r 6 0 t o 70 p e r c e n t , and m a f i c m i n e r a l s 3 0 t o k-0 p e r c e n t . The A r t a b a n g r a n o d i o r i t e i s bounded on t h e n o r t h by an u n c o n f o r m i t y and. on t h e s o u t h by a t r a n s -i t i o n a l zone w i t h Gambier g r a n o d i o r i t e . The o t h e r , s m a l l e r mass o f A r t a b a n g r a n o d i o r i t e o c c u r s a t t h e n o r t h w e s t c o r n e r o f West Bay. The n o r t h c o n t a c t w i t h p y r o c l a s t i c s ( 7 ) was n o t f o u n d . On t h e s o u t h 7 5 f e e t o f a c i d v o l c a n i c s s e p a r a t e A r t a b a n g r a n o d i o r i t e f r o m Gambier g r a n o -d i o r i t e . T h e r e i s no A r t a b a n g r a n o d i o r i t e between p y r o -c l a s t i c s ( 7 ) and Gambier g r a n o d i o r i t e on t h e s o u t h s l o p e o f Mt. Gambier. • Gambier g r a n o d i o r i t e , t h e l a r g e s t c r y s t a l l i n e mass 11-mapped, u n d e r l i e s most o f s o u t h Gambier I s l a n d . The n o r t h c o n t a c t e x t e n d s a l o n g a f a u l t e d , spmewhat i r r e g u l a r , l i n e f r o m t h e n o r t h end o f H a l k e t t Bay t o . t h e n o r t h w e s t c o r n e r o f Gambier I s l a n d . An u n c o n f o r m i t y marks t h e n o r t h c o n t a c t o f t h e Gambier g r a n o d i o r i t e , e x c e p t where Gambier g r a n o -d i o r i t e i s i n c o n t a c t w i t h A r t a b a n g r a n o d i o r i t e o r e p r e -b a t h o l i t h v o l c a n i c r o c k s Ob) . The s o u t h c o n t a c t o f t h e Gambier g r a n o d i o r i t e c r o s s e s t h e s o u t h w e s t p o i n t o f Gambier I s l a n d . The t r e n d o f t h e c o n t a c t i s a b o u t 105 d e g r e e s and i s p a r a l l e l w i t h t h e s t r u c t u r e d e f i n e d f o r K e a t s I s l a n d t o t h e s o u t h . A zone o f metamorphosed t u f f s o c c u r s on Bowen I s l a n d s s o u t h w e s t o f Hood P o i n t , on s t r i k e w i t h - t h e c o n t a c t on s o u t h w e s t Gambier I s l a n d . The zone c o n t a i n s q u a r t z p o r p h y r o — b l a s t s t y p i c a l o f some i n c l u s i o n s i n Gambier g r a n o d i o r i t e . Gambier g r a n o d i o r i t e i s a medium g r a i n e d a g g r e g a t e o f q u a r t z up t o 15 m i l l i m e t r e s l o n g , potash- f e l d s p a r up t o 3 m i l l i m e t r e s l o n g , p l a g i o c l a s e up t o 3 m i l l i m e t r e s , and c h l o r i t e and a m p h i b o l e . Q u a r t z c o m p r i s e s 25 -35 p e r c e n t o f t h e r o c k i n t h e f o r m o f s u b h e d r a l g r a i n s . The r e m a i n i n g p a r t i s m i c r o c l i n e - 10 p e r c e n t , p l a g i o c l a s e - 35 -55 p e r c e n t and m a f i c m i n e r a l s - 10-20 p e r c e n t . B o t h (6a)" and (6b) c o n t a i n d a r k x e n o l i t h s . The x e n o l i t h s a r e . z o n e s o f r o c k somewhat f i n e r g r a i n e d and more m a f i c t h a n t h e i r s u r r o u n d i n g s . The x e n o l i t h s i n v a r i a b l y t r e n d p a r a l l e l to one a n o t h e r and t o f o l i a t i o n w h e r e v e r a d i s t i n c t l o n g d i m e n s i o n o r f o l i a t i o n i s r e c o g n i z a b l e . The o n l y p r e - b a t h o l i t h v o l c a n i c and s e d i m e n t a r y r o c k s 12 on Gambler I s l a n d o c c u r a t t h e f o l l o w i n g l o c a l i t i e s : 1. S o u t h w e s t Gambier I s l a n d , -south o f and i n c o n t a c t w i t h Gambier g r a n o d i o r i t e . -2. N o r t h o f Gambier g r a n o d i o r i t e .on t h e west s i d e o f P o r t G r a v e s . 3 . W i t h i n A r t a b a n g r a n o d i o r i t e and Gambier g r a n o d i o r i t e . - M e l a n o c r a t i c l a v a s , d i v i s i o n (3b) o f t h e t a b l e o f f o r m a t i o n s , o u t c r o p a c r o s s t h e s o u t h w e s t end o f Gambier I s l a n d . The o t h e r o u t c r o p o f d a r k c o l o r e d l a v a s (3a) i s : n o r t h o f Gambler g r a n o d i o r i t e on t h e west s i d e o f P o r t G r a v e s . A l t e r a t i o n o f (3a) i s more e x t e n s i v e t h a n a l t e r -a t i o n o f (3b) s o u t h o f Gambier g r a n o d i o r i t e . A c i d l a v a s - l i e n o r t h o f , and w i t h i n A r t a b a n g r a n o d i o r i t e . The o n l y o u t c r o p o f a c i d l a v a s (h) n o r t h o f g r a n o d i o r i t e Is-a t t h e n o r t h - end of- West Bay. - On t h e s o u t h s l o p e o f Mt. Gam-b i e r , c o n g l o m e r a t e (7) and Gambier g r a n o d i o r i t e a r e i n m u t u a l c o n t a c t . C o n g l o m e r a t e a n d A r t a b a n g r a n o d i o r i t e a r e i n c o n -t a c t on t h e s o u t h s l o p e o f Mt. A r t a b a n . A n o t h e r mass o f a c i d v o l c a n i c s e p a r a t e s A r t a b a n g r a n o -d i o r i t e f r o m Gambier g r a n o d i o r i t e (6a) a t t h e n o r t h w e s t c o r n e r o f West Bay. Numerous o t h e r i n c l u s i o n s o f a c i d v o l c a n i c s o c c u r i n b o t h c r y s t a l l i n e r o c k s , b u t a r e c l e a r l y r e c o g n i z a b l e as v o l c a n i c s o n l y i n t h e A r t a b a n g r a n o d i o r i t e . A l a r g e mass o f p r e - b a t h o l i t h a r g i l l a c e o u s s e d i m e n t a r y r o c k s ( 5 ) o c c u r s on w e s t c e n t r a l . G a m b i e r I s l a n d . T h i s s e d i m e n t a r y u n i t i s bounded on t h e n o r t h , e a s t , a n d s o u t h by c r y s t a l l i n e r o c k . On t h e e a s t , i t i s l i m i t e d by a f a u l t : on t h e w e s t by T h o r n b o r o u g h C h a n n e l . S t r i k e o f b e d d i n g i s 13 e a s t - w e s t and d i p i s s t e e p or v e r t i c a l . T h i s r o c k does n o t e x t e n d a c r o s s T h o r n b o r o u g h C h a n n e l t o t h e w e s t s h o r e o f Howe Sound, w i t h i n t h e a r e a mapped. P y r o c l a s t i c r o c k s (7) and l a v a s (8) w i t h an e a s t - w e s t s t r i k e and s t e e p d i p , o c c u r t h r o u g h o u t a l l o f t h e mapped p a r t o f Gambier I s l a n d , n o r t h o f t h e Gambier and A r t a b a n g r a n o d i o r i t e s . The b a s a l u n i t o f p y r o c l a s t i c s (7) i s a c o n g l o m e r a t e composed o f s m a l l g r a n i t i c and v o l c a n i c p e b b l e s i n a m a t r i x o f q u a r t z , f e l d s p a r and o t h e r f r a g m e n t s . The p o s i t i o n o f o t h e u n c o n f o r m i t y was d e f i n i t e l y l o c a t e d a t t h e f o l l o w i n g p o i n t s : t h e 1,400 f o o t l e v e l on t h e s o u t h s l o p e o f Mt. Gambier$ t h e n o r t h e a s t c o r n e r o f West Bay; b o t h s i d e s o f C e n t r e Bay; the e a s t s i d e o f P o r t G r a v e s ; t h e c r e s t o f Mt. A r t a b a n ; t h e s o u t h e a s t s l o p e o f Mt. A r t a b a n ; and t h e n o r t h e a s t c o r n e r o f H a l k e t t Bay. On Mt. Gambier and on West and C e n t r e B a y s t h e c o n g l o m e r a t e i s an i n d e f i n i t e zone w h i c h c o n t a i n s 30 t o 50 p e r c e n t g r a n i t i c d e b r i s . The P o r t G r a v e s and Mt. A r t a b a n e x p o s u r e s c o n s i s t o f r o c k s w h i c h c o n t a i n much more v o l c a n i c t h a n g r a n i t i c d e b r i s . The H a l k e t t Bay o u t c r o p c o n s i s t s o f a s t r a t i g r a p h i c t h i c k n e s s o f 300 f e e t o f r u s t y c o l o r e d c o n g l o m e r a t e w i t h r o u n d e d s i l i c e o u s o r t u f f p e b b l e s , one t o two i n c h e s i n d-iameter. The c o n g l o m e r a t e - o n H a l k e t t Bay i s i n t e r b e d d e d w i t h a c i d l a v a s . T h i s o u t c r o p was v i e w e d a l o n g a narrow- b a n d , a c r o s s s t r i k e , a t w a t e r l e v e l . A c o n -g l o m e r a t e o f t h i s t y p e v/as n o t s e e n e l s e w h e r e . Ik • -. . - - - D ykes P o s t - b a t h o l i t h T e r t i a r y d y k e s o c c u r t h r o u g h o u t t h e a r e a . They a r e n o t u s u a l l y n o t e d e x c e p t n e a r s e a l e v e l , where ex-p o s u r e s are--good. They have a - v a r i e t y o f s t r i k e s , b u t t h e d i r e c t i o n s most f a v o u r e d on Gambier I s l a n d a r e 0 0 0 , 0 1 0 , 0 3 0 , 0 6 5 , and 1 10 d e g r e e s . One brown w e a t h e r i n g d y k e , on a p o i n t s o u t h w e s t o f C e n t r e Bay on Gambier I s l a n d , • f o l l o w s two j o i n t d i r e c t i o n s 0 8 5 and 1 7 5 d e g r e e s . A l l d y k e s d i p s t e e p l y . The w e a t h e r e d s u r f a c e s a r e shades o f brown, g r e e n , g r a y ; some a r e p o r p h y r i t i c and some a r e n o t . A l l o f t h e dykes a r e a p p a r e n t l y unmetamorphosed and h a ve no f o l i a t i o n . T h i s u n i v e r s a l c h a r a c t e r i s t i c , c o u p l e d w i t h t h e f a c t t h a t a l l h a v e s i m i l a r a t t i t u d e s w i t h i n c e r t a i n l i m i t s , s u g g e s t s t h a t t h e d y k e s r e a c h e d t h e i r p r e s e n t p o s i t i o n a f t e r t h e meta-morphism and t i l t i n g o f t h e r o c k s a b o u t Rowe Sound. S t r u c t u r e The t o p o g r a p h i c e f f e c t on the c o n t a c t s a s t h e y c r o s s r i d g e s , shows t h a t c o n t a c t s a r e s t e e p o r v e r t i c a l . The n o r t h c o n t a c t o f t h e A r t a b a n g r a n o d i o r i t e a p p e a r s t o d i p s t e e p l y s o u t h . The e f f e c t o f numerous s m a l l f a u l t s was n o t d e t e r m i n e d , b u t i t i s p r e s u m a b l y s m a l l . The i r r e g u l a r i t y o f the u n c o n f o r m i t y c o u l d be due t o f l a t l y i n g s t r a t a d e p o s i t e d on a v e r y u n e v e n e r o s i o n s u r f a c e , and n o t s u b s e q u e n t l y s t e e p l y t i l t e d , o r s t r a t a d e p o s i t e d on an u n e v e n s u r f a c e and s u b s e q u e n t l y m o d e r a t e l y or s t e e p l y t i l t e d . A l a r g e number o f s t r u c t u r a l a t t i t u d e s were n o t e d 15 on t h e e a s t s h o r e o f Gambier I s l a n d . Most o f them a r e o f s m a l l v a l u e i n d i v i d u a l l y . When c o n s i d e r e d c o l l e c t i v e l y t h e y have some s i g n i f i c a n c e . A l l t h e d o u b t f u l measurements i n d i c a t e w i t h i n a few d e g r e e s , a common we s t w a r d s t r i k e . Some a r e most s u g g e s t i v e o f a s t e e p - d i p . The a c c u r a c y o f t h i s i n f o r m a t i o n i s b o r n e o u t by^.a s i n g l e good s t r i k e d e t e r m i n a t i o n on t h e e a s t s h o r e o f Gambier I s l a n d , a b o u t one h a l f m i l e s o u t h o f t h e map b o u n d a r y . A t t h a t po'int, l a y e r s o f s p h e r u l i t e s i n a r h y o l i t i c v o l c a n i c , s t r i k e a t 125 d e g r e e s and d i p s t e e p l y or v e r t i c a l l y . ( P l a t e V I , B ) . I f t h e v o l c a n i c s n o r t h o f t h e u n c o n f o r m i t y s t r i k e w e s t -ward and d i p s t e e p l y , t h e n t h e u n c o n f o r m i t y i t s e l f , w h i c h o r i g i n a l l y must have b e e n n e a r l y h o r i z o n t a l , h a s a l s o b e e n t i l t e d on edge so t h a t i t d i p s s t e e p l y . I t f o l l o w s , t hen, t h a t t h e e x p o s e d s e c t i o n a c r o s s t h e A r t a b a n and Gambier g r a n o d i o r i t e s , now n e a r l y h o r i z o n t a l , was a t one t i m e n e a r l y v e r t i c a l . ,Age and C o r r e l a t i o n F o s s i l s were n o t f o u n d and so d e f i n i t e i n f o r m a t i o n on r e l a t i v e a g e s o f t h e f o r m a t i o n s i s l a c k i n g . The h i g h l y a l t e r e d zone o f t u f f s n e a r Hood P o i n t may be a zone o f c o n -t a c t w i t h t h e g r a n o d i o r - i - t e . If, t h i s i s s o , l a v a s , and banded t u f f s a r e i n c o n t a c t wiIth,tand,:;older..lthahy.Gambier g r a n o -d i o r i t e . A s t r o n g i n d i c a t i o n t h a t t h e r o c k s o f Bowen and K e a t s I s l a n d s a r e o l d e r , i s t h a t b o t h t h e g r a n o d i o r i t e p l u t o n s o f Gambier I s l a n d i n c l u d e f r a g m e n t s , some o f them o f c o n s i d e r -a b l e s i z e , o f t u f f a c e o u s r o c k . F i n a l l y , t h e l a v a s and t u f f s 1 6 o f Bowen and K e a t s - I s l a n d s a r e i n t r u d e d by p l u t o n i c r o c k s , s o m e w h a t - r e s e m b l i n g t h e Gambier p l u t o n s i n a p p e a r a n c e , b u t d i f f e r i n g - - i n f o l i a t i o n . - The p l u t o n s may be c o n t e m p o r a n e o u s . T h e - o l d e s t v o l c a n i c r o c k s o f Gambier I s l a n d a r e p r o b a b l y s i m i l a r i n age t o t h e v o l c a n i c r o c k s o f Bowen a n d K e a t s I s l a n d s . The r e l a t i v e a g e s of- t h e p l u t o n i c b o d i e s o f Gambier I s l a n d a r e n o t p e r f e c t l y known. The b e s t e v i d e n c e v / i t h r e s p e c t t o r e l a t i v e a g e s was f o u n d , b y t h i n s e c t i o n a n a l y s e s . The A r t a b a n g r a n o d i o r i t e a p p e a r s t o h a v e more q u a r t z n e a r I t s c o n t a c t w i t h g r a n o d i o r i t e . T h i s may be i n t e r p r e t e d as e v i d e n c e t h a t t h e A r t a b a n g r a n o d i o r i t e i s t h e o l d e r r o c k ^ a ^ A The p y r o c l a s t i c r o c k s o f n o r t h Gambier I s l a n d must be y o u n g e r t h a n t h e c r y s t a l l i n e / , , b e c a u s e t h e y c o n t a i n f r a g m e n t s o f c r y s t a l l i n e r o c k s . C o r r e l a t i o n between f o r m a t i o n s of' the- a r e a u n d e r d i s -c u s s i o n s and o t h e r c o a s t a l r e g i o n s , w i t h o u t good s t r a t i g r a p h i c a l o r p a l e o n t o l o g i c a l e v i d e n c e , c a n n o t be d e f i n i t e . However, i t seems f e a s a b l e t o c o r r e l a t e t h e p y r o -c l a s t i c s (7) w i t h s i m i l a r Lower C r e t a c e o u s r o c k s i n t h e P r i n c e t o n , N i c o l a or H a r r i s o n L a k e a r e a s , o r w i t h Upper C r e t a c e o u s f o r m a t i o n s i n t h e G a r i b a l d i a r e a . The g r a n i t i c r o c k s w o u l d t h e n be J u r a s s i c . The v o l c a n i c r o c k s a r e c o n -s i d e r e d t o be T r i a s s i c . W i t h r e g a r d t o c o r r e l a t i o n s and age d e t e r m i n a t i o n s (IS> u s i n g g r a n i t e b e a r i n g c o n g l o m e r a t e , W.H. Mathews (p.75), 17 says: n'~ S i m i l a r g r a n i t i c d e b r i s i s abundant i n known Lower Cretaceous rocks and l o c a l l y i n Upper or Mid J u r a s s i c rocks of the southern doast Mountains and adjacent areas whereas i n s t i l l o l d e r r o c k s i t i s uncommon i f presen t at a l l . " 18 • INVESTIGATION OF PLUTONIC ROCK A r t a b a n G r a n o d i o r i t e F i e l d R e l a t i o n s T h e . A r t a b a n g r a n o d i o r i t e l o c a t e d n o r t h o f t h e Gambier g r a n o d i o r i t e and s o u t h o f v o l c a n i c r o c k s , i s a medium g r a i n e d , r e d brown w e a t h e r i n g r o c k , composed o f a b o u t 6 0 t o 70 p e r c e n t f e l d s p a r and 3 0 t o 40 p e r c e n t m a f i c m i n e r a l s . F r e s h s u r f a c e s o f t h i s r o c k a r e m o t t l e d p i n k and g r a y w i t h m a f i c m i n e r a l s o f v a r i o u s o r i e n t a t i o n s . ( P l a t e V I I I , A ) . L a r g e x e n o l i t h s s o f v o l c a n i c m a t e r i a l o c c u r s p a r s e l y t h r o u g h o u t th e A r t a b a n g r a n o d i o r i t e , b u t a r e more numerous a l o n g t h e n o r t h b o u n d a r y . Many x e n o M t h s s a p p e a r t o have a v o l c a n i c o r i g i n ; some may h a v e been t u f f s . A l m o s t a l l x e n o l i t h s a r e f i n e g r a i n e d , and c l o s e l y j o i n t e d , so t h a t one or two i n c h c u b e s w e a t h e r o u t and l e a v e a r a g g e d s u r f a c e . S t r i k e o f x e n o l i t h s was d e t e r m i n e d w i t h p r e c i s i o n a t o n l y one p o i n t , s o u t h w e s t o f t h e c r e s t o f Mt. A r t a b a n . A t t h a t p o i n t two p a r a l l e l l i g h t c o l o r e d x e n o l i t h s o f v o l c a n i c o r i g i n , (W-2 1 2 ), t r e n d a t 1 0 5 d e g r e e s . B o t h x e n o l i t h s a r e 3 5 f e e t l o n g , and t h r e e t o f i v e f e e t w i d e . The A r t a b a n g r a n o d i o r i t e i s m a s s i v e a p a r t f r o m t h e x e n o l i t h s and t h e r e i s no e v i d e n c e o f f l o w l i n e s or t u r b -u l e n c e a b o u t any o f t h e x e n o l i t h s . A l l numbers, s u c h as W - 2 1 2 , W-64, Z - 7 7 , e t c . r e f e r t o t h i n s e c t i o n s d e s c r i b e d i n t h e a p p e n d i x . 19 P e t r o g r a p h y and L a b o r a t o r y I n v e s t i g a t i o n M a t r i x o f A r t a b a n G r a n o d i o r i t e F o u r s p e c i m e n s were examined p e t r o g r a p h i c a l l y and o n l y one o f them (W-64), th e l e a s t a l t e r e d , was e x amined by means o f t h e F e d o r o v method. Q u a r t z U n s t r a i n e d g r a i n s o f q u a r t z w i t h a p o o r l y d e v e l o p e d p e r i p h e r a l zone o f m i c r o g r a p h i t e a r e p r e s e n t i n amount f r o m 1 0 t o 2 0 p e r c e n t . Some o f t h e q u a r t z o f s p e c i m e n W - 2 0 9 , h a s t h e f o r m o f r o u n d e d v e r m i c u l a r a r e a s . The i n t e r g r o w t h s f o r any g i v e n mass a r e o r i e n t e d s i m i l a r l y so t h a t when t h e s t a g e i s r o t a t e d w i t h p o l a r i z e d l i g h t , one g e t s t h e i m p r e s s i o n t h a t one m i n e r a l i s s u p e r i m p o s e d on top of, t h e o t h e r s , i n s u c h a way t h a t t h e s u p e r i m p o s e d m i n e r a l c o v e r s p a r t s o f s e v e r a l g r a i n s . A n o t h e r f o r m o f q u a r t z i s i r r e g u l a r masses w i t h d i s t i n c t m i c r o g r a p h i c r i m s . The m i c r o g r a p h i c q u a r t z i s s e p -a r a t e d , f r o m c l e a r q u a r t z by a c u s p a t e l i n e w h i c h i s c o n v e x away f r o m t h e c l e a r q u a r t z . The c o r e o f t h i s t y p e o f q u a r t z h a s a t e n d e n c y t o w a r d e u h e d r i s m . ( P l a t e X V I I I , B ) . The t h i r d t y p e o f q u a r t z c o n s i s t s o f s u b h e d r a l masses w i t h o u t m i c r o g r a p h i c b o r d e r s . I f c o a r s e m i c r o g r a p h i c r i m s a r e p r e s e n t t h e y a r e s e p a r a t e d f r o m t h e c l e a r body o f t h e g r a i n by an a r e a w h i c h i s a l m o s t t r a n s i t i o n a l between t h e two p a r t s . The o u t e r p p a r t o f t h e t r a n s i t i o n z o n e , i n p l a c e s , i s m i c r o g r a p h i c g r a n i t e w i t h t r i a n g u l a r or h e x a g o n a l q u a r t z r o d s . The q u a r t z o f t h e c e n t r a l p a r t o f t h e t r a n s i t i o n zone i s c o a r s e r t h a n i n t h e o u t e r p a r t and many o f t h e r o d s a r e 20 sub-hexagonal or rounded, i n s t e a d of t r i a n g u l a r . The inner p a r t of the zone may be f a n c i e d as micrographic quartz i n which the quartz rods enlarged u n t i l i n contact w i t h one another, so that only a t h i n f i l m of extraneous m a t e r i a l now remains between them. The m a t e r i a l between the rods now forms a d e n d r i t i c network across c e r t a i n zones In the quartz. Quartz of the Artaban g r a n o d i o r i t e i s much l e s s s t r a i n -ed than quartz of the Gambier g r a n o d i o r i t e . An attempt to account f o r t h i s w i l l be made l a t e r . M i c r o c l i n e M i c r o c l i n e was p o s i t i v e l y i d e n t i f i e d only i n WS64, Felds p a r , e n t i r e l y s i m i l a r to the m i c r o c l i n e of W-64, has been regarded as m i c r o c l i n e i n a l l other t h i n s e c t i o n s , i n which i t was encountered. I t i s a dusty, i r r e g u l a r mineral which c l e a r l y r e p l a c e s p l a g i o c l a s e as i n P l a t e XII,A. Normally, i t i s f i n e l y twinned i n only one d i r e c t i o n . In appropriate p o s i t i o n s on a u n i v e r s a l stage and w i t h high m a g n i f i c a t i o n , the twin i n d i v i d u a l s appear as sh o r t , very narrow l e n t i c u l a r l a m e l l a e . ^ne 0 f more noteworthy c h a r a c t e r i s t i c s i s a tendency toward euhedrism (See appendix, p. i v . i , w-64, Grain 3 ) . P l a g i o c l a s e Zoned subhedral or anhedral p l a g i o c l a s e i n various stages of a l t e r a t i o n c o n s t i t u t e s up to 60 per cent of the groundmass of the Artaban g r a n o d i o r i t e . A p l a g i o c l a s e g r a i n in.W-64 p a r t l y replaced by m i c r o c l i n e , has a core An46 and a ri m An28. The replaced p a r t of the g r a i n i s about An30 or 2 1 less:: c a l c i c ( p l a g i o c l a s e g r a i n 1 , ¥-64). The p l a g i o c l a s e i n W - 2 0 9 i s a l b i t e , a nd i n ¥ - 2 1 0 i s An55-30. S p e c i m e n W - 2 0 9 was c o l l e c t e d w i t h i n 2 0 f e e t o f known Gambier g r a n o d i o r i t e . The f e l d s p a r s o f a l l t h i n s e c t i o n s a r e much a l t e r e d t o s e c o n d a r y w h i t e m i c a , c h l o r i t e and e p i d o t e . M a f i c M i n e r a l s A u g i t e , t h e o n l y p r i m a r y m a f i c m i n e r a l o f t h e f o u r t h i n s e c t i o n s examined, o c c u r s i n W-64. The o p t i c and p h y s i c a l f e a t u r e s o f t h e a u g i t e a r e g i v e n on page i v o f t h e A p p e n d i x . The a u g i t e i s c o n s i d e r a b l y a l t e r e d t o a p a l e g r e e n a m p h i b o l e , w h i c h i s p r o b a b l y a c t i n o l i t e , and t o e p i d o t e and c h l o r i t e . I n a l l o f t h e o t h e r t h i n s e c t i o n s p r i m a r y m a f i c m i n e r a l s a r e e n t i r e l y a l t e r e d t o e p i d o t e and c h l o r i t e . A c c e s s o r y M i n e r a l s M a g n e t i t e , p r e s e n t i n amounts o f one o r two p e r c e n t a p p e a r s t o f o r m a l a r g e r p r o p o r t i o n o f t h e A r t a b a n g r a n o -d i o r i t e t h a n i t d o e s o f t h e Gambier g r a n o d i o r i t e . The o t h e r a c c e s s o r y m i n e r a l , a p a t i t e , i s p r e s e n t i n s u c h s m a l l q u a n t i t y t h a t i t i s d i f f i c u l t t o make a c o m p a r i s o n b a s e d on a p a t i t e c o n t e n t . P a r a g e n e s i s B o t h p y r o x e n e and p l a g i o c l a s e a r e r o u g h l y s u b h e d r a l . T h e i r r e l a t i v e ages c a n n o t be s u g g e s t e d w i t h any r e a l d e g r e e o f a c c u r a c y . M i c r o c l i n e c l e a r l y r e p l a c e s p l a g i o c l a s e and so 22 must be l a t e r . The p o s i t i o n o f q u a r t z i n t h e s y s t e m c a n be d e t e r m i n e d w i t h n e a r l y as much c e r t a i n t y as t h a t o f m i c r o c l i n e . The p o s s i b l e o r i g i n s f o r m i c r o g r a p h i c b o r d e r s a r e : 1. S i m u l t a n e o u s c r y s t a l l i z a t i o n f r o m a m e l t . 2. E x - s o l u t i o n f r o m a s i n g l e p h a s e , s t a b l e a t h i g h temp-e r a t u r e . 3. R e p l a c e m e n t o f q u a r t z by m i c r o c l i n e o r m i c r o c l i n e by q u a r t z . The f i r s t p o s s i b i l i t y w o u l d r e q u i r e t h a t a number o f s e p a r a t e d q u a r t z c r y s t a l s d e v e l o p a r o u n d a l i q u i d f i l l e d s p a c e w i t h t h e same o r i e n t a t i o n r e g a r d l e s s o f t h e o r i e n t -a t i o n o f t h e i n t e r g r o w n f e l d s p a r g r a i n s . I t w o u l d seem e x t r e m e l y r f o r t u i t o u s and u n l i k e l y t h a t numerous t i n y u n c o n n e c t e d n u c l e i i w o u l d a l l a d o p t t h e same o r i e n t a t i o n . Hence i t seems r e a s o n a b l e t o abandon t h e i d e a t h a t t h e two components o f q u a r t z f e l d s p a r i n t e r g r o w t h s a r e a p r o d u c t o f s i m u l t a n e o u s c r y s t a l l i z s t i o n f f r o m a a m m e l t . S u p p o s e a m e l t w i t h a p p r o p r i a t e c o n s t i t u e n t s t o f o r m f e l d s p a r a n d q u a r t z h a d f i l l e d t h e l a s t s p a c e s r e m a i n i n g i n a s o l i d i f y i n g magma. Suppose a l s o , t h a t i t e o & l e d f f r d m a a . a t e m p e r a t u r e at^w.hichuilt wasbhomogeneous. A m e l t o f s u c h s m a l l s i z e , m e a s u r a b l e o n l y i n m i l l i m e t r e s , w o u l d be homo-geneous a c r o s s t h e s p a c e . I t w o u l d s t i l l c o n t a i n enough o f t h e l a s t p h a s e t o c r y s t a l l i z e , t h a t i t w o u l d n o t r e a c t w i t h t h e o t h e r phases:, i n i t s e n v i r o n m e n t . As i t c o o l e d , t h e f e l d s p a r p h a s e w o u l d s e p a r a t e o u t , e v e n l y d i s t r i b u t e d across:-2 3 t h e s p a c e . T h i s i s n o t t h e c a s e , a s m i c r o g r a p h i c - s t r u c t u r e s e x i s t o n l y i n b o r d e r z o n e s o f g r a i n s . T h e r e f o r e t h e s e c o n d s u g g e s t i o n must be abandoned. The o n l y p o s s i b i l i t y l e f t i s t h a t q u a r t z r e p l a c e d m i c r o c l i n e o r e l s e m i c r o c l i n e r e p l a c e d q u a r t z . E l s e w h e r e i n th e a r e a q u a r t z r e p l a c e s m i c r o c l i n e . The same age r e l a t i o n -s h i p s a r e assumed t o be t h e c a s e h e r e . X e n o l i t h s i n A r t a b a n G r a n o d i o r i t e B o t h x e n o l i t h s e x amined p e t r o g r a p h i c a l l y , a r e t r a c h y t e s . S p e c i m e n W-62 was t a k e n f r o m a c l o s e l y j o i n t e d g r a y t o . b r o w n w e a t h e r i n g x e n o l i t h on t h e s o u t h s l o p e o f Mt. A r t a b a n a t an e l e v a t i o n o f 1 , 0 0 0 f e e t . The p l a g i o c l a s e l a t h s a r e a l b i t e AnO. The o t h e r x e n o l i t h e x a m i n e d p e t r o g r a p h i c a l l y i s W-211. I t i s l o c a t e d 1 , 3 0 0 f e e t above s e a l e v e l , one h a l f m i l e w e s t f r o m t h e x e n o l i t h f r o m w h i c h W-62 was t a k e n . -In W-211, s o d i c o l i g o c l a s e l a t h s Ani 1!-, a r e s u b - p a r a l l e l v / i t h one a n o t h e r and v / i t h i n t e r s t i t i a l q u a r t z . I n b o t h r o c k s no p r i m a r y m a f i c m i n e r a l s r e m a i n . However, e p i d o t e , c h l o r i t e , and i r o n o x i d e s a t t e s t t o t h e i r f o r m e r p r e s e n c e . S p e c i m e n W-282 was c o l l e c t e d f r o m a band o f a c i d v o l c a n i c r o c k , 75 f e e t w i d e , between t h e Gambier g r a n o d i o r i t e and A r t a b a n g r a n o d i o r i t e , a t t h e n o r t h w e s t e n d o f West Bay, Gambier I s l a n d . The c o n t a c t r e l a t i o n s h i p s between t h e v o l c a n i c and t h e p l u t o n i c r o c k s n o r t h and s o u t h o f i - t , a r e not-known. R i g h t f u l l y i t i s n o t - a x e n o l i t h i n e i t h e r t h e A r t a b a n g r a n o d i o r i t e or Gambier g r a n o d i o r i t e , b u t i t c l o s e l y 2 % r e s e m b l e s - o t h e r x e n o l i t h s w i t h i n t h e A r t a b a n g r a n o d i o r i t e . I t i s a l i g h t c o l o r e d , d e n s e v o l c a n i c w i t h v e r y s m a l l s p h e r u l e s , v i s i b l e o n l y i n t h i n s e c t i o n . F e l d s p a r i s s o d i c . Gambier G r a n o d i o r i t e - -- F i e l d R e l a t i o n s The Gambier g r a n o d i o r i t e p l u t o n o c c u p i e s most o f Gambier I s l a n d . The s o u t h c o n t a c t , a c r o s s t h e - s o u t h w e s t p o i n t o f Gambier I s l a n d , i s p a r a l l e l t o t h e r e g i o n a l t r e n d as d e t e r m i n e d on Bowen and K e a t s Island**,. S i m i l a r l y , t h e n o r t h c o n t a c t , i n s p i t e o f b e i n g i n p a r t an e r o d e d s u r f a c e , n e a r l y p a r a l l e l s t h e r e g i o n a l t r e n d , p r o v i d e d t h a t p o s t -b a t h o l i t h f a u l t i n g i s t a k e n i n t o a c c o u n t . F o l i a t i o n w i t h i n t h e Gambier g r a n o d i o r i t e i s q u i t e m a r k e d l y d i f f e r e n t f r o m t h e r e g i o n a l t r e n d , a few d e g r e e s s o u t h o f e a s t . T h r o u g h o u t most o f t h e p l u t o n i c mass, p a r t i c u l a r i t y i n t h e s o u t h e a s t a r e a , n o r t h o f Hope P o i n t , t h e r e i s a s t r o n g f o l i a t i o n a t 050 d e g r e e s l O t d e g r e e s : . T h i s f o l i a t i o n i s r e c o g n i z a b l e i n t h e l i g h t c o l o r e d g r a n o -d i o r i t e m a t r i x by a p a r a l l e l i s m o f q u a r t z g r a i n s and a g g r e g a t e s o r g r a i n s . S m a l l s p e c i m e n s as t h o s e o f P l a t e IX, £ B , do n o t show t h i s f o l i a t i o n c l e a r l y . A d i r e c t i o n a l t r e n d i s a l s o shown i n - t h e - a t t i t u d e o f c e r t a i n i n e q u i d i m e n s i o n a l x e n o l i t h s and by b e d d i n g i n t h o s e x e n o l i t h s where i t i s p r e s e n t . E a s t o f Hope P o i n t -there i s a v e r y c r u d e f o l i a t i o n n e a r 80 degrees-, as w e l l as t h e n o r m a l f o r t h e g r a n o d i o r i t e d i r e c t i o n o f 050 d e g r e e s . A l i g h t g r a y p h a s e on t h e w e s t 25 shore of Gambier I s l a n d at l a t i t u d e 48 degrees 27 minutes, North, has a d i s t i n c t east-west f o l i a t i o n . At the n o r t h end of West Bay, f o l i a t i o n s t r i k e s at 70 degrees. The Gambier g r a n o d i o r i t e i s a medium to coarse grained h o l o c r y s t a l l i n e rock, composed of approximately 25 to 35 per cent quartz; 35 to 50 per cent p l a g i o c l a s e ; 10 per cent m i c r o c l i n e ; and 10 to 20 per cent mafic minerals. There are a few t e x t u r a l v a r i a t i o n s which do not appear to bear any d e f i n i t e - r e l a t i o n s h i p to e i t h e r x e n o l i t h s , extent of x e n o l i t h s , or to the l i m i t s of the p l u t o n . Much of the rock i s p i n k i s h gray on the weathered sur-face and a s l i g h t l y darker c o l o r on the f r e s h s u r f a c e . Quartz occurs mostly as oblong g r a i n s , but i t may con-s i s t of i r r e g u l a r small g r a i n s or s t r e a k s s of g r a i n s . Where the quartz i s i n l a r g e oblong grains i t i s f r e q u e n t l y sub-hexagonal i n o u t l i n e . Close i n s p e c t i o n i n such cases u s u a l l y r e v e a l s that although the quartz appears to be sub-h e d r a l , i n r e a l i t y i t has a number of f e e l e r - l i k e s t r u c t u r e s adjacent extending out between*feldspar g r a i n s . A l l of the quartz appears to be f r a c t u r e d to a sugary mass i n the hand specimen. Many of the f e l d s p a r s , e i t h e r pink or gray i n c o l o r , appear to have i n c l u s i o n s of dark mineral. Only very r a r e l y are mafic minerals recognizable i n hand specimens. O c c a s i o n a l l y mica or amphibole may be i d e n t i f i e d by means of a hand l e n s , but most oft e n the dark mineral i s a shapeless mass of c h i c h l o r i t e or epidote. T h e - l i g h t gray c o l o r e d phases found on the east shore of 26 West Bay and on t h e w e s t s h o r e o f Gambier I s l a n d d i f f e r m a i n l y f r o m t h e p i n k - g r a y p h a s e i n c o l o r and q u a r t z . The q u a r t z o f t h e g r a y p h a s e may be e i t h e r l a r g e g r a i n s o r d i s p e r s e d - s m a l l e r g r a i n s . I t o c c u r s most f r e q u e n t l y as s m a l l g r a i n s . The q u a r t z o f t h e p i n k p h a s e o c c u r s i n b l o c k y s u b h e d r a l g r a i n s . O t h e r w i s e t h e two p h a s e s a r e v e r y s i m i l a r . The p r o p o r t i o n s o f l i g h t and d a r k m i n e r a l s a r e n o t r e c o g n i z a b l y d i f f e r e n t , e x c e p t - o n t h e w e s t s h o r e o f Gambier I s l a n d , where t h e q u a r t z c o m p r i s e s o n l y a b o u t t e n p e r c e n t o f t h e r o c k . P e t r o g r a p h y and L a b o r a t o r y I n v e s t i g a t i o n M a t r i x o f Gambier G r a n o d i o r i t e Q u a r t z The p r o p o r t i o n o f q u a r t z i n t h i n s e c t i o n s v a r i e s f r o m 10 t o 60 p e r c e n t . T h i s g r e a t v a r i a t i o n i s p r o b a b l y more a p p a r e n t t h a n r e a l , b e c a u s e a t h i n s e c t i o n m i g h t j u s t m i s s a l a r g e q u a r t z g r a i n , o r m i g h t i n c l u d e a l a r g e q u a r t z g r a i n or a g g r e g a t e o f g r a i n s , and m i s s an a r e a d e v o i d o f q u a r t z . I t i s c o n s i d e r e d t h a t more a c c u r a t e f i g u r e s c o n c e r n i n g q u a r t z v a r i a t i o n w o u l d g i v e a r a n g e o f 25 t o 35 p e r c e n t . I n p a r a l l e l l i g h t i t i s a l w a y s c l e a r , w i t h r i b b o n s o f d u s t y m a t e r i a l a l o n g f r a c t u r e s . S t r a i n e f f e c t s a r e p r e s e n t i n e v e r y t h i n s e c t i o n . R a r e l y , t h e r e i s o n l y u n d u l a t i n g e x t i n c t i o n . More o f t e n d i s t i n c t l a m e l l a e and m o r t a r s t r u c t u r e d i v i d e g r a i n s t h a t were f o r m e r l y i n t a c t , i n t o an a g g r e g a t e o f s m a l l e r g r a i n s w i t h s u t u r e d b o r d e r s . The 2 7 a g g r e g a t e s a r e u s u a l l y s u r r o u n d e d o r p a r t l y s u r r o u n d e d by m o r t a r s t r u c t u r e . •-F u r t h e r e v i d e n c e o f dynamic metamorphism i s i n d i c a t e d by t h e a l m o s t u n i v e r s a l p r e s e n c e o f two m u t u a l l y sub-p e r p e n d i c u l a r p l a n e s o f f r a c t u r e . These p l a n e s c r o s s q u a r t z and o c c a s i o n a l l y o t h e r m i n e r a l s , as two s e t s o f s t r a i g h t p a r a l l e l l i n e s , h i g h l y r e m i n i s c e n t o f c l e a v a g e i n f e l d s p a r s . Much o f t h e q u a r t z c o n t a i n s f r a g m e n t s o f o t h e r m i n e r a l s . I n f a c t , h a l f o f some q u a r t z c o n s i s t s o f i n c l u d e d p l a g i o -c l a s e . N o r m a l l y , l e s s t h a n t e n p e r c e n t o f a q u a r t z g r a i n i s f o r e i g n m a t e r i a l . T h i s m a t e r i a l may have a number o f f o r m s . I t may be s h a r d or c r e s c e n t s h a p e d w i t h marked r e - e n t r a n t a n g l e s , r e c t a n g u l a r , l o n g and s l e n d e r , o r n e a r l y r o u n d . P o t a s h f e l d s p a r t e n d s t o be s h a r d , c r e s c e n t o r r o d shaped; p l a g i o c l a s e t e n d s t o be r o u n d or r e c t a n g u l a r . Where t h e m a r g i n s o f two q u a r t z g r a i n s a p p r o a c h , a t r i a n g u l a r remnant o f f e l d s p a r w i t h r e - e n t r a n t a n g l e s may r e m a i n , a s e v i d e n c e o f p o s s i b l e r e p l a c e m e n t . The q u a r t z g r a i n s w h i c h c o n t a i n a h i g h p r o p o r t i o n o f i n c l u d e d m a t e r i a l a r e a more b-locky shape t h a n -those w h i c h c o n t a i n - l i t t l e or no f o r e i g n m i n e r a l s . Q u a r t z w h i c h c o n t a i n s v e r y few i s o l a t e d i n c l u s i o n s o f t e n - i s v e r y i r r e g u l a r i n shape and p a r t s o f a g r a i n may p r o j e c t between o t h e r m i n e r a l s f o r some d i s t a n c e . O t h e r m i n e r a l s may e v e n d i v i d e a q u a r t z g r a i n , i n t h e p l a n e o f t h e t h i n s e c t i o n , i n t o a number Of s e p a r a t e p a r t s ( P , a + < 2 A). 28 The b o r d e r s o f q u a r t z g r a i n s a r e i r r e g u l a r e x c e p t -where d e f o r m a t i o n h a s p r o d u c e d m o r t a r s t r u c t u r e . C o n t a c t s a r e b u l b o u s and c u r v e d . T h i s f e a t u r e i s n o t a l w a y s o b v i o u s : u n t i l e x a m i n a t i o n I s done i n d e t a i l . A l a r g e number o f q u a r t z b o u n d a r i e s a r e c h a r a c t e r i z e d by p r o j e c t i o n s o f f e l d s p a r s i n t o q u a r t z , or o f q u a r t z i n t o f e l d s p a r s . S m a l l f e l d s p a r I s l a n d s a r e i s o l a t e d from- o t h e r g r a i n s o f s i m i l a r or i d e n t i c a l o r i e n t a t i o n . T h i s l a t t e r c h a r a c t e r i s t i c i s most n o t i c e a b l e i n t h e c a s e o f q u a r t z - m i c r o c l i n e b o u n d a r i e s . Q u a r t z - p l a g i o c l a s e b o u n d a r i e s t e n d t o be s t r a i g h t e r t h a n q u a r t z - m i c r o c l i n e b o u n d a r i e s . The r e l a t i o n s h i p o f q u a r t z t o o t h e r m i n e r a l s i s o f t e n d i f f i c u l t t o i n t e r p r e t , and i n many o f t h e s p e c i m e n s t h e q u a r t z - f e l d s p a r r e l a t i o n s h i p s c a n n o t be d i r e c t l y d e t e r m i n e d . However, t h e y c a n be i n d i r e c t l y i n f e r r e d v / i t h a r e a s o n a b l e d e g r e e o f c e r t a i n t y . I n s p e c i m e n s w h i c h have b e e n b o t h f r a c t u r e d and a l t e r e d , q u a r t z commonly c o n t a i n s v e i n s o f f i n e q u a r t z , e p i d o t e , s e r i c i t e o r c a r b o n a t e . - I n a t l e a s t one c a s e q u a r t z i n a f r a c t u r e , a d o p t e d an o r i e n t a t i o n i d e n t i c a l v / i t h t h e q u a r t z s u r r o u n d i n g i t . M i c r o c l i n e ' • . • P o t a s h f e l d s p a r i s n o t p r e s e n t i n a l l p h a s e s o f t h e g r a n o d i o r i t e . One s p e c i m e n W-261, c o n t a i n s no r e c o g n i z a b l e p o t a s h f e l d s p a r . I n o t h e r s p e c i m e n s , t h e amount o f p o t a s h f e l d s p a r v a r i e s f r o m two p e r c e n t or l e s s (W-232) t o a b o u t 30 p e r c e n t (W-287)• The g r a i n s a r e h i g h l y v a r i a b l e i n b o t h s i z e - ^ a n d s h a p e . The shape o f m i c r o c l i n e g r a i n s i s n e a r l y 29 e q u i d i r n e n s i o n a l where t h e r e i s l i t t l e p o t a s h f e l d s p a r i n a rock- and e i t h e r e q u i d i r n e n s i o n a l or e x t r e m e l y i r r e g u l a r i n s p e c i m e n s w i t h 15 t o 30 p e r c e n t p o t a s h f e l d s p a r . G r i d t w i n n i n g may or-may n o t o c c u r t h r o u g h o u t a g r a i n o f m i c r o c l i n e . I n f a c t m i c r o c l i n e may a p p e a r w h o l l y u n -t w i n n e d e v e n i n a t h i n s e c t i o n i n - w h i c h o t h e r g r a i n s a r e e n t i r e l y or p a r t l y t w i n n e d . R e - o r i e n t i n g m i c r o c l i n e on t h e u n i v e r s a l s t a g e h a s sometimes shown t h a t g r i d t w i n n i n g i s r e a l l y p r e s e n t b u t i n v i s i b l e i n t h e p l a n e o f t h e t h i n s e c t i o n . Much o f t h e m i c r o c l i n e i s p e r t h i t i c . The p e r t h i t e l a m e l l a e t a k e t h e f o r m o f t i n y b r a n c h i n g o r wavy q u a r t z - l i k e o b j e c t s . They may have a marked "en e c h e l o n " h a b i t l n e W h e r e t h i s h a b i t i s n o t i c e a b l e , t h e l i n e o f "en echelon"'" l a m e l l a e a r e p a r a l l e l w i t h a f r a c t u r e . 0 n e g r o u p o f l a m e l l a e i n t h i n s e c t i o n W-252 i s i n t e r r u p t e d by a t w i n n e d p l a g i o c l a s e g r a i n w h i c h p r o j e c t s i n t o p e r t h i t i c m i c r o c l i n e : a d i s t u r b e d zone e x t e n d s a c r o s s t h e p l a g i o c l a s e c o n t i n u o u s a t b o t h e n d s s w i t h a l i n e o f p e r t h i t e l a m e l l a e . The i n d i c e s o f t h e wavy b o d i e s a r e w e l l , above t h o s e o f t h e p o t a s h f e l d s p a r and t h e i r r e l i e f r e l a t i v e t o f e l d s p a r c o r r e s p o n d s t o t h a t o f q u a r t z . The l a r g e r i r r e g u l a r g r a i n s o f - m i c r o c l i n e c o n t a i n a good d e a l o f i n c l u d e d m a t e r i a l l y - m o s t l y i n t h e f o r m o f r e c t a n g u l a r r o u n d e d or i r r e g u l a r f e l d s p a r ( P l a t e XVI,A & B ) . R a r e l y ^ a m p h i b o l e i s i n c l u d e d a l o n g w i t h f e l d s p a r as i n Z - 7 7 . P l a g i o c l a s e i n c l u d e d i n m i c r o c l i n e may be e i t h e r s i m i l a r l y or d i v e r s e l y o r i e n t e d a c r o s s t h e m i c r o c l i n e . I n g e n e r a l , b o r d e r s o f m i c r o c l i n e a r e o f two d i s t i n c t 30 t y p e s : some a r e s t r a i g h t and some a r e e x t r e m e l y - e r r a t i c -( P l a t e XVI,A & B; P l a t e XVII,A-c&BD. The e r r a t i c t y p e o f b o u n d a r y i s most common where a m i c r o c l i n e g r a i n i s i n c o n t a c t w i t h a number o f p l a g i o c l a s e g r a i n s , w h i c h have a v a r i e t y o f o r i e n t a t i o n s . I n t h e s e , t h e m u t u a l b o u n d a r i e s f o l l o w t h e r e c t a n g u l a r s h a p e s o f p l a g i o c l a s e . The smooth • t y p e o f b o u n d a r y t e n d s t o be more n o r m a l where m i c r o c l i n e i s I n c o n t a c t w i t h a s i n g l e p l a g i o c l a s e g r a i n . T h i s b r o a d g e n e r a l i t y , however, does n o t h o l d when c o n t a c t s a r e examined c a r e f u l l y . Many, a p p a r e n t l y s t r a i g h t , c o n t a c t s t u r n o u t t o be m i n u t e l y s i n u o u s . D e t a i l e d e x a m i n a t i o n w i t h a medium o r h i g h power o b j e c t i v e e x p o s e s v e i n l e t s o f m i c r o c l i n e w h i c h have w o r k e d t h e i r way a l o n g c l e a v a g e s and f r a c t u r e s ( P l a t e X V I , B ) . P l a t e XV, A shows what a p p e a r e d t o be a s u b h e d r a l p l a g i o c l a s e g r a i n s u r r o u n d e d by m i c r o c l i n e . I n r e a l i t y i t i s a p o r t i o n o f a l a r g e r z o n e d p l a g i o c l a s e g r a i n w h i c h h a s b e e n r e p l a c e d by m i c r o c l i n e . The l o b e o f p l a g i o c l a s e i s c o n n e c t e d t o a much l a r g e r g r a i n by a n a r r o w n e c k . R e p l a c e -ment, t h o u g h i t h a s l e f t t h e p l a g i o c l a s e b r o a d l y e u h e d r a l , h a s n o t b e e n c o m p l e t e . Remnants o f p l a g i o c l a s e s t i l l r e m a i n a r o u n d t h e edges o f t h e p a r t l y r e p l a c e d l o b e . Though i s o l a t e d , t h e y a r e o p t i c a l l y c o n t i n u o u s w i t h t h e s u b h e d r a l p l a g i o c l a s e l o b e . M i c r o c l i n e i s a l t e r e d t o k a o l i n - l i k e m a t e r i a l , c h l o r i t e , s e r i c i t e , and e p i d o t e . F r a c t u r e s i n m i c r o c l i n e a r e f r e q u e n t -l y f i l l e d w i t h e p i d o t e . M i c r o c l i n e appears t o h a v e r e s i s t e d a l t e r a t i o n t o a much g r e a t e r d e g r e e t h a n h a s p l a g i o c l a s e . 31 P l a g i o c l a s e - -E s t i m a t e d - p l a g i o c l a s e c o n t e n t i s as low as 2 0 p e r cen-t . i n s p e c i m e n W-253 and as h i g h - a s 50 p e r c e n t i n a number o f o t h e r s p e c i m e n s -(-W-98, 1 6 8 , 1 7 0 , 1 9 1 . ) . Most o f t h e Gambler g r a n o d i o r i t e , however, c o n t a i n s 3 5 t o *+5 p e r c e n t p l a g i o -c l a s e . The s i z e ' and f o r m -of t h e p l a g i o c l a s e i s somewhat v a r i a b l e . The s m a l l e s t g r a i n s u s u a l l y o c c u r as i n c l u s i o n s w i t h i n q u a r t z a n d m i c r o c l i n e . P l a g i o c l a s e n o t i n c l u d e d i n q u a r t z or m i c r o c l i n e , v a r i e s f r o m one h a l f m i l l i m e t r e t o f i v e m i l l i m e t r e s or l a r g e r . S i z e v a r i a t i o n i s s e r i a t e . T h e r e a p p e a r t o be two d i s t i n c t t y p e s o f p l a g i o c l a s e b o u n d a r i e s . . M u t u a l a n h e d r i s m . i s t h e n o r m a l c o n d i t i o n between a d j a c e n t p l a g i o c l a s e g r a i n s , w hereas s u b h e d r i s m o f p l a g i o c l a s e i s n o r m a l i n p l a g i o c l a s e r m m c r o c l i n e o r p l a g i o c l a s e - q u a r t z a s s o c i a t i o n s . The d e t a i l i s o f the. b o u n d a r i e s between p l a g i o c l a s e and m i c r o c l i n e or q u a r t z we're p r e v i o u s l y d i s c u s s e d . The t e n d e n c y t o w a r d - e u h e d r i s m - i s shown by P l a t e XV,A a n d - P l a t e X V I I , B . O c c a s i o n a l l y , r e p l a c e d p l a g i o c l a s e h a s a -six s i d ^ d f o r m , s t r o n g l y r e m i n i s c e n t o f - - c r y s t a l s w h i c h d e v e l o p e d i n a m e l t . Most f r e q u e n t l y t h e f o r m i s r e c t a n g u l a r w i t h t h e l o n g d i m e n s i o n p a r a l l e l w i t h t h e . ( 0 1 0 ) d i r e c t i o n a s i n P l a t e XV,A, P l a t e XVI,A & B, a n d - P l a t e XVII-,B. Two c l e a v a g e s a r e p r o m i n e n t - i n t h e p l a g i o c l a s e l o b e i n P l a t e XV,A. The c l e a v a g e p a r a l l e l t o t h e l o n g d i m e n s i o n i s ( 0 1 0 ) . The o t h e r c l e a v a g e t r a c e , a t an a n g l e t o ( 0 1 0 ) i s ( 1 1 0 ) . I t i s n o t e -3 2 w o r t h y t h a t a t l e a s t two o f t h e p h y s i c a l b o u n d a r i e s o f t h e r e p l a c e d g r a i n a r e r o u g h l y p a r a l l e l t o c l e a v a g e p l a n e s . The c o m p o s i t i o n o f p l a g i o c l a s e r a n g e s f r o m An*+7 t o AnO. The most c a l c i c p l a g i o c l a s e i d e n t i f i e d was i n . a c o m p a r a t i v e l y u n z o n e d g r a i n i n s p e c i m e n W-59* G r a i n 5 o f t h a t t h i n s e c t i o n w i t h c o m p o s i t i o n A n V 7 , i s - i n t e r g r o w n w i t h g r a i n 5b a r i d e s i n e A n 3 4 . N e i t h e r g r a i n i s n o t i c e a b l y z o n e d . I n t h e same t h i n s e c t i o n o t h e r g r a i n s a r e z o n e d or u n z o n e d . G r a i n 3 i s z o n e d t h r o u g h a minimum r a n g e o f An26-14. I f t h e a v e r a g e v a l u e between An26 and 3 5 i s t a k e n f o r t h e c o r e , t h e n t h e z o n i n g i s t h r o u g h a r a n g e o f a t l e a s t • A n 3 0 - l 8 . The l e a s t c a l c i c p l a g i o c l a s e i d e n t i f i e d i s i n t h i n s e c t i o n s W-261 and W-191. G r a i n 1 o f W-261 i s a l b i t e A n 7 , g r a i n s 2 and 3 a r e b o t h a l b i t e , l e s s c a l c i c t h a n An5. Specimen W - 2 8 7 , t h r e e q u a r t e r s o f a m i l e n o r t h - o f W - 2 6 1 , c o n t a i n s o l i g o c - l a s e A n 2 7-24. -S p e c i m e n Z - 7 7 , a s i m i l a r d i s t a n c e ' t o t h e w e s t , i s a p p r o x i m a t e l y An24, as d e t e r m i n e d v / i t h a s t a n d a r d s t a g e . P l a g i o c l a s e i n Z - 7 7 i s o n l y s l i g h t l y z o n e d . Z o n i n g i s g e n e r a l l y o f a n o r m a l t y p e , most c a l c i c a t t h e c o r e and l e a s t c a l c i c a t t h e r i m . B o t h g r a d a t i o n a l and a b r u p t z o n i n g a r e u s u a l l y p r e s e n t . F r e q u e n t l y - as i n s p e c i m e n W - 9 6 , z o n i n g i s o s c i l l a t o r y t h r o u g h S'ery n a r r o w r a n g e s . I n t h a t t h i n s e c t i o n one e l o n g a t e g r a i n , a b o u t t h r e e m i l l i m e t r e s l o n g , h a s a b o u t 38 z o n e s . ( P l a t e X I V , B ) . F o r t u n a t e l y t h i s g r a i n - i s so o r i e n t e d t h a t i t - g i v e s a v e r y n e a r c e n t e r e d b i s e c t r i x • f i g u r e . The c o r e o f the g r a i n - i s Ah28, s e v e r a l i n t e r m e d i a t e z o n e s a r e A n i 5 - 2 0 , t h e r i m i s An23« O s c i l l a t o r y z o n i n g o f t h i s t y p e t h r o u g h a n a r r o w r a n g e 33 i s common though not always as w e l l developed as i n One feature t h i s grain has i n common with a great many zoned grains i s the s l i g h t l y orbicular shape and the unsymmetrical character of the zones. This may be due p a r t l y to s o l u t i o n and p a r t l y to normal tendency to form oblong grains! - However the shape of the zones indicate that the c r y s t a l developed i n a medium where growth was r e s t r i c t e d . Many other grains also show unconformities between c e r t a i n zones, e s p e c i a l l y i n parts where zones are numerous and broad. Three t h i n sections W-191 , W - 2 3 2 , W - 2 8 5 , contain p l a g i o -clase with reversed zoning. One gra in i n t h i n section W-191 was determined by means of the u n i v e r s a l stage and N i k i t i n ' s : diagrams. The core proved to have composition of A n 2 ' and the r im a composition of A n l 3 . There i s a p o s s i b i l i t y that the: reversed zoning merely represents o s c i l l a t o r y zoned grains that were f o r t u i t o u s l y cut by the plane of the t h i n sect ion so that a zone, somewhere away from the core of the o r i g i n a l c r y s t a l , now i s at the leas t c a l c i c phase of the grain measured. Whether the f igures derived t*w representative or not , they do prove that reversa ls i n zoning through a .^od moderately great range are quite p o s s i b l e . Almost a l l p lagioclase i s s l i g h t l y l e s s c lear than m i c r o c l i n e . The usual a l t e r a t i o n products of plagioclase. are secondary white mica, c o l o r l e s s epidote and grass green or pale green pleochroic c h l o r i t e . The most intense a l t e r -a t ion Is i n v a r i a b l y near the core of a g r a i n , whatever i t s i S e e " paye 3h c o m p o s i t i o n may b e . P l a t e XV,A, shows a re m n a n t l o b e o f u n r e p l a c e d p l a g i o c l a s e i n m i c r o c l i n e . The c o r e o f t h i s l o b e i s 20 t o 25 p e r c e n t a l t e r e d to- s e c o n d a r y w h i t e m i c a i n s m a l l p l a t e s p a r a l l e l w i t h c l e a v a g e s , e s p e c i a l l y t h e c l e a v a g e ' a t an a n g l e t o t h e l o n g d i m e n s i o n o f t h e f i g u r e (110). The l e s s c a l c i c r i m o f t h e l o b e i s q u i t e u n a l t e r e d . The m a i n p a r t o f t h e p l a g i o c l a s e g r a i n t o t h e l e f t o f t h e f i g u r e i s s i m i l a r i n t h a t t h e r i m i s r e l a t i v e l y u n a l t e r e d . The p e c u l i a r i t y i s t h a t t h e u n a l t e r e d r i m o f t h e main g r a i n i s more c a l c i c t h a n the a l t e r e d c o r e o f the. l o b e . E p i d o t e a l t e r a t i o n p r o d u c e s a somewhat s i m i l a r e f f e c t t h o u g h much l e s s p r o n o u n c e d . Some g r a i n s have a c o r e o f e p i d o t e s u r r o u n d e d b y a r i m o f p l a g i o c l a s e and' s e c o n d a r y w h i t e m i c a w h i c h i n t u r n i s s u r r o u n d e d by a r i m o f . r e l a t i v e l y u n a l t e r e d p l a g i o c l a s e . E p i d o t e f o r m e d a s an a l t e r a t i o n p r o d u c t v / i t h i n p l a g i o c l a s e i s g e n e r a l l y , b u t n o t a l w a y s , a c o l o r l e s s n o n p l e o c h r o i c , o r a p a l e y e l l o w w e a k l y p l e o c h r o i c v a r i e t y . F r a c t u r e s w h i c h c r o s s p l a g i o c l a s e a r e u s u a l l y f i l l e d v / i t h s e r i c i t e or c h l o r i t e , and l e s s f r e q u e n t l y w i t h e p i d o t e . A few f r a c t u r e s a r e f i l l e d w i t h a c o m b i n a t i o n o f e p i d o t e and s e r i c i t e . M a f i c M i n e r a l s P r i m a r y m a f i c m i n e r a l s , h o r n b l e n d e and, or b i o t i t e , s u f f i c i e n t l y u n a l t e r e d t o be r e c o g n i z a b l e , - o c c u r i n o n l y e l e v e n o u t o f 20 t h i n s e c t i o n s o f Gambier g r a n o d i o r i t e . The ter m p r i m a r y i s u s e d r a t h e r l o o s e l y i n t h i s c a s e , f o r t h e 35 r e l a t i o n s h i p s o f m a f i c m i n e r a l s a r e d i f f i c u l t t o i n t e r p r e t w i t h any r e a l c e r t a i n t y . I n t h e o t h e r n i n e t h i n s e c t i o n s , t h e p r e v i o u s p r e s e n c e o f a m p h i b o l e may be i n d i c a t e d by a g g r e g a t e s o f d i v e r s e l y o r i e n t e d p l e o c h r o i c p a l e y e l l o w i s h g r e e n e p i d o t e - - g r a i n s . S p e c i m e n W-59 c o n t a i n s an a g g r e g a t e o f c a r b o n a t e w i t h p l a t e s o f c h l o r i t e i n t e r s e c t i n g a t a n g l e s a p p r o p r i a t e f o r a m p h i b o l e c l e a v a g e . "I t i s c o n s i d e r e d t o be a pseudomorph a f t e r amphiboOie. ( P l a t e X I X , B ) . The f o r m e r p r e s e n c e o f b i o t i t e may be i n d i c a t e d by l a m i n a r pseudomorphs o f c h l o r i t e a l o n e , or o f c h l o r i t e , y e l l o w i s h g r e e n e p i d o t e , and q u a r t z . Most s p e c i m e n s c o n t a i n b o t h ' t y p e s o f p s e u d o -m o r p h s . One s p e c i m e n (W-285) 5 c o n t a i n s h o r n b l e n d e a l o n e and o t h e r s (W-59,W-?0, W-167) , c o n t a i n b i o t i t e a l o n e . A f o u r t h t h i n s e c t i o n ( W - 2 6 l ) , c o n t a i n s b o t h b i o t i t e s u f f i c i e n t l y u n a l t e r e d t o be r e c o g n i z a b l e , and a g g r e g a t e s o f e p i d o t e p o s s i b l y p s e u d o m o r p h i n g a f t e r h o r n b l e n d e . -O p t i c c h a r a c t e r i s t i c s o f h o r n b l e n d e were d e t e r m i n e d i n most c a s e s on a s t a n d a r d p e t r o g r a p h i c m i c r o s c o p e . O p t i c a n g l e s were e s t i m a t e d by means o f c u r v a t u r e o f t h e i s o g y r e i n o p t i c a x i s f i g u r e s . E x t i n c t i o n a n g l e s were m e a s u r e d on g r a i n s w i t h p a r a l l e l c l e a v a g e t r a c e s a n d h i g h e s t • b i r e f r i n g e n c e f o r any one t h i n s e c t i o n . Such e x t i n c t i o n a n g l e s a r e n o t e d as f o l l o w s : Z ' A C = - 2 0 . G r a i n s so o r i e n t e d t h a t t h e y w o u l d g i v e o p t i c n o r m a l f i g u r e s , and hence a t r u e Z A C v a l u e , were n o t f o u n d . - P l e o c h r o i c f o r m u l a e were d e r i v e d by r e a d i n g the c o l o r o f Y on o p t i c a x i s or b i s e c t r i x f i g u r e s . C o l o r s o f x ' -and z ' w e r e t a k e n f r o m g r a i n s w i t h e i t h e r maximum b i r e f r i n g e n c e 3 6 i n t h e zone p a r a l l e l t o c o r f r o m g r a i n s w h i c h gave b i s e c t r i x f i g u r e s . By t h e above method o p t i c c h a r a c t e r i s t i c s a p p e a r t o be ZAcvL5°- 2Maverage o f 7 - 2 1 ) : -2V-65-75-X y e l l o w l p r b r o w n i s h y e l l o w : Y - g r e e n or b r o w n i s h g r e e n : Z - g r e e n w i t h b l u e g r e e n b o r d e r s - , or b l u e g r e e n . Subsequent d e t e r m i n a t i o n s by t h e F e d o r o v method on a m p h i b o l e o f t h i n s e c t i o n Z - 7 7 , i n d i c a t e d t h a t e s t i m a t e s o f o p t i c a n g l e and p l e o c h r o i s r n , were r e a s o n a b l y a c c u r a t e , b u t t h a t e x t i n c t i o n a n g l e s as r e a d by s t a n d a r d methods may be up t o t e n d e g r e e s t o o l a r g e . O p t i c c h a r a c t e r i s t i c s d e t e r m i n e d on a u n i v e r a l s t a g e a r e : Z A o- 7 - 20 (5 d e t e r m i n a t i o n s ) . - V - r 2 2 ° - 3 2 ' (if d e t e r m i n a t i o n s ) . 110/1110 - 51 - 57' (5 d e t e r m i n a t i o n s ) . I f t h e s e f i g u r e s a r e w e i g h t e d a c c o r d i n g t o the a c c u r a c y f a c t o r s g i v e n f o r t h i n s e c t i o n Z - 7 7 i n t h e a p p e n d i x ( p . * * * ) , and t h e n a v e r a g e d as f o l l o w s : o E x t i n c t i o n A n g l e - 3 x 12"- 36 1 x 7'= 7' 3 x 18*- 5^° 2 x 20 = l+o' 1 x 8"» 8/ 1 0 i 4 5 . o The a v e r a g e ZAc i s V+5 - 15 • 10 3 7 O p t i c A n g l e /2 3 x 3 2 96 1 x 2<?> 25° 2 x 22°- kh-l 2 x 3 5 ' - 70 • 8 - 2 3 ~ Then a v e r a g e V - - 2 3 5 \ - 2 9 ' 8 ' Then • -2V - s. 58 . -I f g r a i n 4 i s d i s r e g a r d e d ; a v e r a g e -V - - 1 9 1 ^ 32 6 Then -2V ^ 6 4 * . X - brown y e l l o w Y = g r e e n Z " b l u e g r e e n The age r e l a t i o n s h i p s between h o r n b l e n d e and o t h e r m i n e r a l s a r e n o t a l w a y s d i s t i n c t . One o f .the c a s e s i n w h i c h t h e r e i s , l i t t l e d o u b t t h a t - h o r n b l e n d e i s o l d e r , i s i n s p e c i m e n Z - 7 7 ( P l a t e X V I , A ) . I n t h a t t h i n s e c t i o n a m p h i b o l e i s d i s t i n c t l y e u h e d r a l t o m i c r o c l i n e . S i m i l a r l y i n some o t h e r s p e c i m e n s , a m p h i b o l e i s e u h e d r a l t o q u a r t z and m i c r o -c l i n e , w h i c h s u r r o u n d e d i t i n p l a c e s . I n t h e same t h i n s e c t i o n and i n o t h e r s , t h e r e i s a t e n d e n c y f o r h o r n b l e n d e t o be i n t e r g r o w n v / i t h p l a g i o c l a s e . T h i s c h a r a c t e r i s t i c i s - w e l l shown i n W-98 i n w h i c h a p l a g i o c l a s e g r a i n i s a l m o s t d i v i d e d by h o r n b l e n d e . I t w o u l d be d i f f i c u l t t o p r o v e w h e t h e r t h e i n t e r g r o w t h i s r e p l a c e m e n t or i n t e r f e r e n c e d u r i n g c r y s t a l g r o w t h . B r o a d l y s p e a k i n g one c a n o n l y n o t e t h a t a m p h i b o l e i s t h e r e and i s i n t e r g r o w n t o some d e g r e e w i t h p l a g i o c l a s e . One c o u l d s c a r c e l y . p o s t u l a t e m i n e r a l s e q u e n c e . B i o t i t e m i c a v/as n o t s t u d i e d v / i t h t h e u n i v e r s a l s t a g e . The c h a r a c t e r i s t i c s a s o b s e r v e d v / i t h a s t a n d a r d s t a g e , a r e a 38 s m a l l n e g a t i v e o p t i c a n g l e and X n e a r l y p a r a l l e l c . P l e o c h r o i c f o r m u l a : X' = s t r a w y e l l o w or honey y e l l o w Y 1 Z - b r o w n i s h • g r e e n or g r e e n A b s o r p t i o n f o r m u l a : X«.Y-- Z o r X ^ K Z ' -• D a r k r e d brown m i c a does n o t o c c u r . B i o t i t e was • p r o b a b l y p r e s e n t i n n e a r l y a l l s p e c i m e n s i n amounts v a r y i n g f r o m 1 0 - 15 p e r c e n t b u t l i t t l e , o t h e r t h a n c h l o r i t e p seudomorphs, now r e m a i n s . Commonly b i o t i t e h a s two f o r m s , e i t h e r g r a i n s one and one h a l f m i l l i m e t r e s by one m i l l i m e t r e , o r a g g r e g a t e s - o f much s m a l l e r g r a i n s . The r e l a t i o n s h i p s between b i o t i t e and o t h e r m i n e r a l s a r e as o b s c u r e a s t h o s e o f h o r n b l e n d e . Some b i o t i t e o c c u r s i n t e r s t i t i a l t o q u a r t z , o t h e r s m a l l b i o t i t e g r a i n s o c c u r i n f r a c t u r e s i n h o r n b l e n d e a s i n W-98. S t i l l o t h e r i n d i v i d u a l h o r n b l e n d e g r a i n s a r e i n t e r g r o w n w i t h mica.-A c c e s s o r y M i n e r a l s -V e r y few a c c e s s o r y m i n e r a l s were f o u n d . A p a t i t e and e i t h e r m a g n e t i t e or p y r i t e or b o t h o c c u r i n a l l - s p e c i m e n s s The q u a n t i t y i s I n v a r i a b l y s m a l l and- does n o t e x c e e d one p e r c e n t . S e c o n d a r y M i n e r a l s S e c o n d a r y w h i t e m i c a , c o l o r l e s s e p i d o t e , p a l e g r e e n c h l o r i t e , d u s t y k a o l i n - l i k e m a t e r i a l , and z o i s i t e a r e t h e most_.common. s e c o n d a r y m i n e r a l s , i n t h e f e l d s p a r s . C l e a r p l e o c h r o i c c h l o r i t e , g r e e n i s h y e l l o w p l e o c h r o i c e p i d o t e , a n d 3 9 sphene are t h e u s u a l s e c o n d a r y m i n e r a l s i n a m p h i b o l e and m i c a . F i n e q u a r t z , a s w e l l as e p i d o t e and c h l o r i t e , o c c u r s m i c a i n some t h i n - s e c t i o n s . F r a c t u r e s i n f e l d s p a r a r e g e n e r a l l y f i l l e d - w i t h a l m o s t c o l o r l e s s e p i d o t e o r c h l o r i t e . F r a c t u r e s i n m a f i c m i n e r a l s a r e g e n e r a l l y f i l l e d w i t h p l e o c h r o i c g r e e n c h l o r i t e o r y e l l o w e p i d o t e . . P a r a g e n e s i s I n summary, r e l a t i v e a g e s o f m a f i c s m t h e a c h o t h e r and w i t h p l a g i o c l a s e , c o u l d n o t be i n t e r p r e t e d . E v i d e n c e on t h e r e l a t i v e a g e s o f m i c r o c l i n e and p l a g i o c l a s e a l m o s t o v e r -w h e l m i n g l y i n d i c a t e s t h a t m i c r o c l i n e r e p l a c e s p l a g i o c l a s e . The p o s i t i o n o f q u a r t z i s l e s s d e f i n i t e . Sfany examples a p p e a r t o show t h a t q u a r t z r e p l a c e s m i c r o c l i n e . I f t h a t i s t r u e , t h e n q u a r t z i s t h e y o u n g e s t m i n e r a l . A l a r g e number o f a s s o c i a t i o n s c a n n o t b e i n t e r p r e t e d , e i t h e r b e c a u s e the b o u n d a r i e s n a t u r a l l y do n o t l e n d t h e m s e l v e s t o s i m p l e i n t e r -p r e t a t i o n , o r b e c a u s e m o r t a r s t r u c t u r e h a s o b s c u r e d d e - t a i l . P l a t e X V I I I , A , i l l u s t r a t e s a q u a r t z g r a i n w h i c h h a s r e p l a c e d b o t h p l a g i o c l a s e a n d m i c r o c l i n e . X e n o l i t h s i n Gambier G r a n o d i o r i t e Fie-14 C ha.ya.cte.r i st I'C S D a r k c o l o r e d f i n e r g r a i n e d p h a s e s o f t h e Gambier g r a n o -d i o r i t e a r e t o be r e f e r r e d t o as x e n o l i t h s . The f i e l d r e l a t i o n s h i p s o f t h e x e n o l i t h s i n Gambier g r a n o d i o r i t e a r e - s i m i l a r t o t h e f i e l d r e l a t i o n s h i p s o f x e n o l i t h s i n A r t a b a n g r a n o d i o r i t e . - F o l i a t i o n i s q u i t e p r o -n o u n c e d i n Gambier g r a n o d i o r i t e a t 050 d e g r e e s *"10 d e g r e e s . ho b u t a b s e n t i n x e n o l i t h s . Long d i m e n s i o n and t r e n d o f x e n o l i t h s were m e a s u r e d a t o n l y one p l a c e . N o r t h o f Hope P o i n t , t r e n d o f x e n o l i t h W-188 i s p a r a l l e l w i t h f o l i a t i o n . T h e r e i s no e v i d e n c e o f t u r b u l e n c e i n f o l i a t i o n o r b e n d i n g o f f o l i a t i o n a r o u n d any x e n o l i t h s . F o l i a t i o n s i m p l y ends a t t h e m a r g i n s o f x e n o l i t h s . T h e r e i s c o n s i d e r a b l e v a r i e t y i n t h e s t r u c t u r e - , c o l o r and t e x t u r e , o f t h e x e n o l i t h s . Some x e n o l i t h s are l a r g e a n d b l o c k y , m e a s u r a b l e - i n t e n s o f f e e t , and maycoompEise up 30 or hO p e r c e n t o f t h e r o c k . O t h e r s a r e s m a l l l e n t i c u l a r , m e a s u r a b l e i n i n c h e s , and amount t o a s l i t t l e as one p e r c e n t o r l e s s , o f t h e w h o l e r o c k . -Some x e n o l i t h s ( t h e r e a r e two or t h r e e n o r t h o f Hope P o i n t ) , have a d i s t i n c t l a m i n a t e d o c h a r a c t e r . R e c o g n i z a b l e b e d d i n g i n x e n o l i t h s ' i s p a r a l l e l w i t h b o t h th e l o n g d i m e n s i o n o f t h e x e n o l i t h and t h e f o l i a t i o n i n t h e m a t r i x . One l a r g e i n c l u s i o n 20 t o 2 5 f e e t w i d e and 50 t o 6 0 f e e t l o n g , h a s a c o m p l e t e l y r e c r y s t a l l i z e d c o r e i n \<rtiich b e d d i n g i s o b l i t e r a t e d , ( S p e c i m e n s W-88 and 9 0 ) , and a very much l e s s r e c r y s t a l l i z e d m a r g i n w i t h o b v i o u s b e d d i n g (W - 8 7 ). ( P l a t e X I I , B ) . Q A t a n o t h e r l o c a l i t y , j u s t n o r t h of-.-Hope P o i n t , two da a d j a c e n t d a r k x e n o l i t h s a r e i d e n t i c a l ' e x c e p t t h a t one o f them ha s a l e n t i c u l a r - c o r e , of- d:enseswhiiiib§--mavterl:aliai8hinches:-"long and s i x i n c h e s w i d e . T h i s c o r e r e s e m b l e s t h e l a m i n a t e d s e d i m e n t a r y x e n o l i t h s so c l o s e l y t h a t i t i s d i f f i c u l t or i m p o s s i b l e t o b e l i e v e t h a t i t c a n be a n y t h i n g b u t a s e d i m e n t a r y r e m n a n t . Y e t t h e r i m o f t h i s x e n o l i t h i s 41 i d e n t i c a l w i t h other dark f i n e grained d i o r i t i c x e n o l i t h s . The contact zone between the l e n t i c u l a r core and the r i m , i s g r a n i t i c and one inch wide. (See appendix p.***^, W-186, 187, and 188.) . -A second type of x e n o l i t h might be r e l a t e d to the Artaban g r a n o d i o r i t e , north of the Gambier g r a n o d i o r i t e . This type occurs near or i n the north contact zone. I t s weathered surface i s reminiscent of the Artaban g r a n o d i o r i t e , but close i n s p e c t i o n of the f r e s h surface r e v e a l s that the x e n o l i t h s n more c l o s e l y resemble others w i t h i n the Gambier granodiorite, and f a r from the Gambier granodiorite-Artaban g r a n o d i o r i t e c o n t a c t , than i t does the f r e s h Artaban g r a n o d i o r i t e . The dark c o l o r e d , f i n e grained x e n o l i t h s show a v a r i e t y of shapes, c o l o r s and t e x t u r e s , even i n adjacent x e n o l i t h s . However, v a r i a t i o n s are through a narrow range and cannot be r e l a t e d to the composition of the o r i g i n a l rock from which the x e n o l i t h was formed. ' I n f a c t , even i n a s i n g l e x e n o l i t h ten f e e t i n diameter, v a r i a t i o n s i n ' t e x t u r e and composition may be as great-as between widely separated x e n o l i t h s . P l a t e VII,B, a photograph of a xenolith- or group of x e n o l i t h s on Hope P o i n t - i l l u s t r a t e s a number of v a r i a t i o n s i n c o l o r and t e x t u r e . The c o l o r i s c o n t r o l l e d i n p a r t by g r a i n s i z e and i n part.by p r o p o r t i o n of dark m a t e r i a l . The darkest blobs have the f i n e s t g r a i n and the l a r g e s t p r o p o r t i o n , about 50 per cent, of dark m i n e r a l . The l i g h t e s t colored x e n o l i t h s have the coarsest g r a i n , s t i l l somewhat f i n e r than the Gambier g r a n o d i o r i t e , and the smallest p r o p o r t i o n , about h2 30 t o kO p e r c e n t , o f d a r k m i n e r a l . T h i s amount i s somewhat g r e a t e r t h a n t h a t o f Gambier g r a n o d i o r i t e m a t r i x . I t c a n be s e e n f r o m t h e p h o t o g r a p h t h a t some o f t h e m a r g i n s a r e s h a r p and some a r e n o t . The m a r g i n s o f d a r k f i n e g r a i n e d x e n o l i t h s : a r e n o t u s u a l l y g r a d a t i o n a l . Normal Gambier g r a n o d i o r i t e e x t e n d s : r i g h t up t o t h e c o n t a c t , w h i c h i s s h a r p b u t j a g g e d i n d e t a i l . B eyond the c o n t a c t , x e n o l i t h s a r e u s u a l l y homogeneous. L o c a l l y , a l t e r a t i o n or g r a n i t i z a t i o n i s n o t i c e -a b l e a l o n g z o n e s w h i c h may h a v e been j o i n t s or f r a c t u r e s . The l i g h t c o l o r e d x e n o l i t h s f r e q u e n t l y a r e m e g a s c o p i c a l l y d i s c e r n a b l e f r o m t h e m a t r i x o n l y by. a r e d u c t i o n i n g r a i n s i z e . T h e r e ivats be l i t t l e change i n m i n e r a l p r o p o r t i o n s o r c o m p o s i t i o n as o b s e r v e d i n ithe.ihand s p e c i m e n . Some v a r i a t i o n s - i n m i n e r a l p r o p o r t i o n s and t e x t u r e s may be s e e n i n P l a t e s V1II,B; X,A & B;;' X I , A & B; X I I , B j a n d X I I I , A & B-. P l a t e X I I I , B , i s a n e a r l y e v e n g r a i n e d a g g r e g a t e o f a m p h i b o l e and f e l d s p a r i n p r o p o r t i o n s o f *+0 p e r c e n t f e l d s p a r and a b o u t 60 p e r c e n t a m p h i b o l e . S p e c i m e n W-78, ( P l a t e XIII',B) h a s a f i n e g r a i n e d g-roundmass o f a b o u t e q u a l l y d i v i d e d p l a g i o -c l a s e and a m p h i b o l e w i t h p o r p h y r o b l a s t s o f q u a r t z and "•la;; p l a g i o c l a s e . The p h o t o g r a p h c l e a r l y shows a b o r d e r zone a b o u t q u a r t z , r i c h i n h o r n b l e n d e , p o s s i b l y e x p e l l e d by t h e g r o w i n g q u a r t z g r a i n . The q u a r t z p o r p h y r o b l a s t s a r e s e r i a t e i n s i z e . The s m a l l e r q u a r t z p o r p h y r o b l a s t s h a v e a much l e s s d i s t i n c t r i m o f h o r n b l e n d e . The b o r d e r s o f many x e n o l i t h s a r e c r o s s e d by q u a r t z o r f e l d s p a r g r a i n s , common t o b o t h x e n o l i t h and m a t r i x . hj Petrographic c h a r a c t e r i s t i c s ; The mineral assemblage of most x e n o l i t h s i n Gambier g r a n o d i o r i t e i s quartz 2-25 per cent, p l a g i o c l a s e 35-50 per cent, hornblende 40-50 per cent, b i o t i t e 0-5 per cent, and minor a p a t i t e , p y r r h o t i t e or magnetite. Specimen ¥-87 con-t a i n s no quartz and specimen W-188 contains no hornblende or b i o t i t e . Specimen ¥-252 resembles the l i g h t c o l o r e d grano-d i o r i t e phase more than i t resembles the x e n o l i t h s - Specimen W-100 i s from an extensive zone of d i o r i t i c rock w i t h l i t t l e quartz and no m i c r o c l i n e , on the east shore of Port Graves.. In g r a i n s i z e , mineral p r o p o r t i o n s and c o l o r , t h i s - r o c k resembles x e n o l i t h s more c l o s e l y than i t resembles Gambier g r a n o d i o r i t e . For t h i s reason i t i s described as a x e n o l i t h . Quartz One x e n o l i t h (¥-87)- contains no q u a r t z . - This x e n o l i t h - i s an a l t e r e d t u f f . ( P l a t e X I I , B ) . Another x e n o l i t h (W£l88) probably derived from a t u f f , contains as- much as 50 per cent quartz. Most of the 15 t h i n sections examined c o n t a i n f i v e to ten per cent" quartz. The form a n d . r e l a t i o n s h i p s of quartz in,the x e n o l i t h s are very s i m i l a r to those of-quartz i n the matrix, but on a smaller s c a l e . In some specimens (¥-84, W-186, ¥-187) quartz c l e a r l y r eplaces plagiocla'se. In/vsection (¥-84)^ quartz appears to-be intergrown w i t h hornblende. Quartz, i n x e n o l i t h s w i t h five:-- per cent quartz or more, i s i r r e g u l a r i n d e t a i l , or el s e c o n s i s t s of i s o l a t e d groups of s i m i l a r l y 44 o r i e n t e d g r a i n s . In such cases the area, bounded by a l i n e which passes through the extremeties of the i r r e g u l a r arms or u n i t s , i s u s u a l l y blocky. These s t r u c t u r e s may be considered intermediate between s i n g l e small grains and of qoq»+"»-i n c l u s i o n f i l l e d masses A . A common type of quartz i n num-erous x e n o l i t h s c o n s i s t s of eye shaped masses which i n the hand specimens appear to approach a euhedral shape. ( P l a t e X I , A). Hornblende may or may not formaa s o r t of r i m p a r t l y embedded i n , and p a r t l y outside quartz. ( P l a t e s XI,A and X I I I , B ) . A - l e s s p e r f e c t l y developed stage occurs i n other x e n o l i t h s as exe m p l i f i e d i n t h i n s e c t i o n ¥-99.. In that t h i n s e c t i o n the conc e n t r a t i o n of small r e c t a n g u l a r hornblende grains- about the periphery of quartz, i s l e s s p e r f e c t l y developed, and the center of the g r a i n contains about ten per cent i n c l u d e d hornblende. Specimen ¥-188 w i t h the highest p r o p o r t i o n of quartz of a l l the x e n o l i t h s examined, i s made up of m i c r o c l i n e and p l a g i o c l a s e i n a f i n e micrographic i n t e r g r o w t h , Quartz, which comprises 50 per cent of the rock, occurs as small t r i a n g u l a r worm or rod shaped s t r u c t u r e s , l e s s than one tenth m i l l i m e t r e across and about one h a l f m i l l i m e t r e l o n g . The x e n o l i t h from which ¥-188 was taken, has been described on page 40. Here i t s u f f i c e s to say tha t the part of the x e n o l i t h sampled,bears a very close Aresemblance to a sedimentary rock. h5 M i c r o c l i n e •- • M i c r o c l i n e i s a c o n s t i t u e n t o f o n l y two x e n o l i t h s . I n W -188, m i c r o c l i n e f o r m s p a r t and p e r h a p s a l l o f t h e h o s t f e l d s p a r i n q u a r t z f e l d s p a r i n t e r g r o w t h s . M i c r o c l i n e w i t h o u t q u a r t z i s f o u n d i n s m a l l q u a n t i t y i n t h e same s p e c i m e n . The o t h e r m i c r o c l i n e o c c u r r e n c e i s i n s p e c i m e n W -252 f r o m a zone w h i c h a p p e a r e d t o he g r a n i t i z e d , i n t h e f i e l d . The amount o f m i c r o c l i n e p r e s e n t i s a b o u t 20 p e r c e n t . I t o c c u r s a s i r r e g u l a r , s t r a g g l i n g m a s s e s w h i c h r e p l a c e a n d i s o l a t e r e c t -a n g u l a r r e m n a n t s o f p l a g i o c l a s e . P l a g i o c l a s e R e c t a n g u l a r g r a i n s o f p l a g i o c l a s e l e s s t h a n one m i l l i m e t r e l o n g c o n s t i t u t e ^0 t o 6 0 p e r c e n t o f a l m o s t e v e r y t h i n s e c t i o n . The f o r m o f p l a g i o c l a s e i s v a r i a b l e . I t may be a f i n e m o s a i c o f u n z o n e d g r a i n s w i t h e p i d o t e or h o r n b l e n d e , a s i n W - 2 5 1 , o r w i t h o u t m a f i c m i n e r a l s a s i n W - 8 7 . More common f o r m s a r e one h a l f m i l l i m e t r e , r e c t a n g u l a r , h i g h l y z o ned a n d e s i n e or c a l c i c o l i g o c l a s e , a c c o m p a n i e d by l a r g e r two t o t h r e e m i l l i m e t r e u n z o n e d g r a i n s o f l e s s c a l c i c p l a g i o c l a s e . The m i x e d v a r i e t y i s f a i r l y w e l l t y p i f i e d by s p e c i m e n W - 7 8 , i n w h i c h b o t h s i z e s o f g r a i n s were d e t e r m i n e d by t h e F e d o r o v method. The f i n e r r e c t a n g u l a r groundmass g r a i n s a r e An60 a t t h e i r c o r e and Ah30 a t t h e r i m . A n o t h e r d e t e r m i n a t i o n i n d i c a t e d a r a n g e o f z o n i n g f r o m An60 t o An7 i n t h e same t h i n s e c t i o n . The l a r g e r two t o t h r e e m i l l i m e t r e p o r p h y r o b l a s t s o f W-78 i+6 a r e u n z o n e d . T h e i r c o m p o s i t i o n i s An35« The l a r g e r p l a g i o -c l a s e g r a i n s i n some x e n o l i t h s , a r e o n l y s l i g h t l y z o n e d and i n s t i l l o t h e r s z o n i n g o f t h e p o r p h y r o b l a s t s may r a n g e f r o m •Anhl t o A h 2 8, as i n t h i n s e c t i o n W-79* I n g e n e r a l , e v e n where p o r p h y r o b l a s t s a r e z o n e d , a v i s u a l e x a m i n a t i o n c o n f i r m s , t h e f a c t t h a t t h e p o r p h y r o b l a s t s a r e l e s s z o ned t h a n t h e g r o u n d mass g r a i n s . An i n t e r e s t i n g t r a n s i t i o n i s shown by t h r e e s p e c i m e n s (W-87,W-89,W-90) f r o m a x e n o l i t h o f s e d i m e n t a r y r o c k . ( P l a t e X I I , B)'. S pecimen W-87 f r o m the edge i s composed o f a m o s a i c o f f e l d s p a r g r a i n s w i t h a s m a l l p r o p o r t i o n o f f e l d s p a r l a t h s . A l l g r a i n s a r e one t e n t h m i l l i m e t r e or l e s s i n d i a m e t e r . The maximum e x t i n c t i o n a n g l e w i t h 1 5 g r a i n s i s f i v e d e g r e e s , and t h e i n d i c e s a r e s l i g h t l y l e s s t h a n b a l s a m . Hence t h e f e l d s p a r i s o l i g o c l a s e . The n e x t s p e c i m e n , W - 8 9 , s e l e c t e d a b o u t f i v e f e e t ' c l o s e r t o t h e c e n t e r o f t h e dyke a t a p o i n t where b e d d i n g ha d become o b s c u r e , c o n t a i n s p l a g i o c l a s e i n two d i s t i n c t f o r m s . S m a l l g r a i n s and r o d s l e s s t h a n one h a l f m i l l i m e t r e ^ f o r m a m a t r i x a b o u t t h e l a r g e s t g r a i n s , w h i c h a r e f o r t h e most p a r t , g r e a t e r t h a n one m i l l i m e t r e . The f i n e g r a i n s a r e z o n e d . Maximum e x t i n c t i o n a n g l e s i n d i c a t e t h a t t h e groundmass i s a n d e s i n e a b o u t Anl+O, tho u g h some g r a i n s h ave an e x t i n c t i o n a n g l e w h i c h v a r i e s f r o m 1 5 d e g r e e s t o z e r o d e g r e e s , f o r d i f f e r e n t p a r t s o f t h e g r a i n . The p o r p h y r o -b l a s t s a r e A n 3 0 as d e t e r m i n e d f r o m a f a i r l y w e l l c e n t e r e d b i s e c t r i x f i g u r e p e r p e n d i c u l a r t o X. I n t h i s c a s e t h e p o r p h y r o b l a s t s a r e n o t v e r y z o n e d and a r e l a t h s h a p e d . 4>7 S p e c i m e n W-90, f r o m t h e c e n t e r o f t h e x e n o l i t h i s s i m i l a r t o W - 8 9 , b u t c o a r s e r . A number o f g r a i n s o f i n t e r -m e d i a t e s i z e a r e s l i g h t l y z o n e d . As f a r as t h e age r e l a t i o n s h i p s o f p l a g i o c l a s e a r e c o n c e r n e d , one c a n do l i t t l e b u t g u e s s . The above b r i e f d e s c r i p t i o n o f t h e p l a g i o c l a s e s i n a x e n o l i t h s u g g e s t s t h a t e u h e d r i s m or s u b h e d r i s m and z o n i n g c a n d e v e l o p i n a s o l i d medium. The g e n e r a l e u h e d r a l a s p e c t o f p l a g i o c l a s e c a n n o t be u s e d t o i n d i c a t e a g e . M a f i c M i n e r a l s The m a f i c m i n e r a l s o f t h e x e n o l i t h s a r e much t h e same as t h o s e o f t h e l i g h t c o l o r e d m a t r i x . The m a i n d i f f e r e n c e s - -l i e i n a f i n e r g r a i n s i z e and h i g h e r p r o p o r t i o n o f m a f i c m a t e r i a l , i n t h e x e n o l i t h s . The p r i n c i p a l m a f i c c o n s t i t u e n t i s a h o r n b l e n d e . The F e d o r o v method was a p p l i e d i n t h i n s e c t i o n s W-78, W-97> W - l 8 7 » i n o r d e r t o d e t e r m i n e o p t i c c h a r a c t e r i s t i c s . The r e s u l t s i n d i c a t e t h a t t h e e x t i n c t i o n a n g l e ZAc i s I n t h e r e g i o n o f 15 t o 20 d e g r e e s , and t h e n e g a t i v e o p t i c a n g l e i s 55-65 d e g r e e s . The p l e o c h r o i c 10 f o r m u l a i s : X - y e l l o w o r y e l l o w i s h brown; Y = g r e e n or b r o w n i s h g r e e n ; and Z ~ b l u e g r e e n o r g r e e n . I t w i l l be n o t e d t h a t i n a l l t h r e e t h i n s e c t i o n s t h e v a l u e o f V on o p p o s i t e s i d e s o f X may show c o n s i d e r a b l e - v a r i a t i o n . T h i s i s n o t c o n s i d e r e d t o r e d u c e t h e g r a d e o f the o p t i c a n g l e d e t e r -m i n a t i o n s i n c e t h e v a l u e o f 2V i s i n d e p e n d e n t o f t h e a c c u r a c y o f t h e X d i r e c t i o n . I n most c a s e s , i f t h e p o s i t i o n o f t h e X 48 d i r e c t i o n . w e r e changed only a few degrees i n the d i r e c t i o n of the l a r g e r angle, the two readings f o r tl.s V would be rendered e q u a l . The d i s c r e p a n c i e s i n the XAc angle cannot be accounted f o r , except through i n a c c u r a c i e s i n determining o p t i c d i r e c t i o n s - as a re-sult of i n d e f i n i t e e x t i n c t i o n or a l t e r a t i o n . I t i s b e l i e v e d however, that the e r r o r i n the weighted average value i s l e s s than f i v e degrees. As i n the l i g h t c o l o r e d Gambier g r a n o d i o r i t e m a t rix, o p t i c a l data determined by means of a standard stage i n d i c a t e a ZAc angle s l i g h t l y higher than the angle found by u n i v e r s a l stage methods. This can probably be accounted f o r i n some cases by poor development of one cleavage so t h a t the angle, read was a c t u a l l y the e x t i n c t i o n between Z and the t r a c e of (110) or ( 1 1 0 ) , and not a true ZAc angl e . Hornblende i s u n i v e r s a l l y f i n e g r a i n e d and n e a r l y equidirnensional. ' In d e t a i l , some aggregates or i n d i v i d u a l g r a i n s are e i t h e r h i g h l y i r r e g u l a r , p r i s m a t i c or a c i c u l a r . R e l a t i o n s h i p s to i t s surroundings are d i f f i c u l t to i n t e r p r e t . The needles and prisms which f r e q u e n t l y occur i n f e l d s p a r g r a i n s can h a r d l y be con s i d e r e d replacement i n view of the h i g h l y i r r e g u l a r c h a r a c t e r o f - t h e b a s a l p o r t i o n s of some i n d i v i d u a l g r a i n s . Hornblende i n c l u s i o n s i n f e l d s p a r are p o s s i b l y i r r e g u l a r p r o j e c t i o n s from a hornblende g r a i n i n t o a contemporaneous p l a g i o c l a s e g r a i n . A l l things c o n s i d e r e d , one cannot p o s i t i v e l y s t a t e that e i t h e r p l a g i o c l a s e r e p l a c e s hornblende or v i c e v e r s a . Regardless of g r a i n s i z e , there appears to have been a simultaneous development of both !+9 h o r n b l e n d e and p l a g i o c l a s e . A l t e r a t i o n p r o d u c t s i n a m p h i b o l e c o n s i s t p r i n c i p a l l y o f y e l l o w i s h e p i d o t e , p l e o c h r o i c deep g r e e n c h l o r i t e , sphene, and c a r b o n a t e . P y r i t e and,--or m a g n e t i t e a p p e a r t o have b e e n i n t r o d u c e d i n t o n e a r l y a l l x e n o l i t h s i . - - G e n e r a l l y , a m p h i b o l e shows a much g l o w e r e r r e s i s t a n c e t o a l t e r a t i o n t h a n f e l d s p a r . The o n l y x e n o l i t h i n w h i c h a l t e r a t i o n has been p a r t i c u l a r l y n o t i c e a b l e i s t h e one r e p r e s e n t e d by W-95. A m p h i b o l e g r a i n s ; o o f t h a t t h i n s e c t i o n a r e l a r g e r t h a n n o r m a l s i z e . They have b o r d e r s , p a r t i c u l a r l y b a s a l s u r f a c e s , so r a g g e d t h a t t h e g r a i n s a p p e a r f e a t h e r y . C o l o r s a r e o f much p a l e r hue t h a n i n t h e compact h o r n b l e n d e o f o t h e r s p e c i m e n s . The e x t i n c t i o n a n g l e i s v e r y l i t t l e s m a l l e r t h a n t h a t o f the d a r k e r c o l o r e d a m p h i b o l e . However, t h e g e n e r a l c h a r a c t e r i s t i c s and t h e o c c u r r e n c e s u g g e s t t h a t i t i s a c t i n o l i t e . B i o t i t e m i c a w i t h s m a l l n e g a t i v e 27 and X n e a r l y e q u a l t o c , o c c u r s i n s p e c i m e n s W-78, W-87, W-97* W-100. I t s p l e o c h r o i c f o r m u l a i s : X - s t r a w y e l l o w ; Y - brown; Z«. brown. - T h e - c o l o r o f Y and Z i s d e f i n i t e l y n o t r e d brovm, b u t i s some-whafcer g r e e n . Many o t h e r x e n o l i t h s p r o b a b l y - c o n t a i n e d b i o t i t e . I t s f o r m e r p r e s e n c e i s i n d i c a t e d by l a m e l l a r pseudomorphs -of c h l o r i t e and e p i d o t e . The p o s i t i o n o f b i o t i t e i n t h e se q u e n c e i s n o t c l e a r e x c e p t i n t h i n s e c t i o n W-100, ( p l a t e XIX, A ) , i n w h i c h i t r e p l a c e s and i s o l a t e s p a r t s o f a p l a g i o c l a s e g r a i n . I n t h e same t h i n s e c t i o n , b i o t i t e i s o l a t e s p a r t s o f an a m p h i b o l e g r a i n . 50 The a l t e r a t i o n . p r o d u c t s o f b i o t i t e a r e e p i d o t e and c h l o r i t e a n d some s p h e n e . Pseudoraorphing o f c h l o r i t e and e p i d o t e a f t e r b i o t i t e , i s i n d i c a t e d by t h e p r e s e n c e o f c h l o r i t e a n d , or e p i d o t e between some b i o t i t e f l a k e s . A s s o c i a t i o n s o f t h a t t y p e a r e c o n s i d e r e d t o be a r r e s t e d s t a g e s i n t h e a l t e r a t i o n o f b i o t i t e .to l a m e l l a r masses o f e p i d o t e and c h l o r i t e . A c c e s s o r y M i n e r a l s A p a t i t e , m a g n e t i t e , p y r i t e o r p o s s i b l y p y r r h o t i t e a r e p r e s e n t as m i n u t e g r a i n s , i n s m a l l amounts, i n a l l x e n o l i t h s . S e c o n d a r y M i n e r a l s The a l t e r a t i o n p r o d u c t s o f x e n o l i t h s , a r e s e c o n d a r y w h i t e m i c a ( p l a g i o c l a s e ) , c o l o r l e s s e p i d o t e ( p l a g i o c l a s e ) , y e l l o w i s h e p i d o t e ( m a f i c m i n e r a l s ) , g r e e n or p a l e g r e e n c h l o r i t e ( p l a g i o c l a s e and m a f i c m i n e r a l s ) , sphene ( m a f i c : m i n e r a l s ) , and o c c a s i o n a l l y t r a c e s o f h y d r a t e d i r o n o x i d e s . I n g e n e r a l , x e n o l i t h s ' a r e much l e s s a l t e r e d t h a n t h e Gambier g r a n o d i o r i t e m a t r i x . P a r a g e n e s i s The p a r a g e n e s i s o f t h e components o f t h e x e n o l i t h s i n Gambier g r a n o d i o r i t e , i s somewhat more i n t e r p r e t a b l e t h a n the'-p a r a g e n e s i s o f t h e Gambier g r a n o d i o r i t e m a t r i x . The f i n e s t g r a i n e d x e n o l i t h , s u c h a s W-253, c o n s i s t s o f a m o s a i c o f c o n -temporaneous f e l d s p a r , e p i d o t e , and some h o r n b l e n d e . The c o a r s e r x e n o l i t h s c o n s i s t o f more o r l e s s i n t e r g r o w n p l a g i o -c l a s e and b l u e g r e e n h o r n b l e n d e . E u h e d r i s m o f p l a g i o c l a s e i n some x e n o l i t h s i s n o t t a k e n t o i n d i c a t e e a r l y f o r m a t i o n , because 51 t h e p l a g i o c l a s e o f W - 9 0 , a r e c r y s t a l l i z e d t u f f a c e o u s r o c k , i s somewhat e u h e d r a l p a r t i c u l a r l y i n t h e more a d v a n c e d s t a g e s o f r e c r y s t a l l i z a t i o n . The l a r g e r s i z e d p o r p h y r o b l a s t i c p l a g i o c l a s e c r y s t a l s , l e s s c a l c i c t h a n t h e f i n e r m a t r i x , a r e h i g h l y s u g g e s t i v e o f d e v e l o p m e n t u n d e r m e t a m o r p h i c , r a t h e r t h a n magmatic c o n d i t i o n s . M i c r o c l i n e r e p l a c e s p l a g i o c l a s e and so- i s y o u n g e r t h a n p l a g i o c l a s e i n W - 2 5 2 , t h e o n l y x e n o l i t h i n w h i c h m i c r o c l i n e o c c u r s . -Quartz- i s t h e l a s t m i n e r a l t o f o r m i n a l l x e n o l i t h s where i t o c c u r s . I t d i s p l a c e s h o r n b l e n d e g r a i n s as i n W-78 and W-99* I t r e p l a c e s m i c r o c l i n e w h i c h r e p l a c e s p l a g i o c l a s e i n W -252 a n d so must be y o u n g e r t h a n p l a g i o c l a s e and m i c r o -c l i n e . 52 NOTEWORTHY FEATURES Artaban Granodiorite 1. ---The megascopic and microscopic f e a t u r e s of the x e n o l i t h s s show that they are remnants of p r e - d i o r i t e v o l c a n i c rocks.-2. The a t t i t u d e of the x e n o l i t h s i n space i s s i m i l a r to that of the r e g i o n a l trend.. 3. There i s no- evidence .of hig h temperature contact metasomatic e f f e c t s of e i t h e r x e n o l i t h s i n Artaban grano-d i o r i t e . , or -contact zones adjacent to Artaban g r a n o d i o r i t e . The only metamorphic e f f e c t on the x e n o l i t h s that -is apparent x e * i o i i ' + i i S K i n the f i e l d , i s cubic j o i n t i n g , so clo s e that weathers i n t o one inch blocks and p i t s . A l b i t i z a t i o n may or may not have taken p l a c e . h. There i s no evidence of turbulence about x e n o l i t h s . 5. There i s microscopic evidence of replacement of p l a g i o c l a s e by m i c r o c l i n e and of m i c r o c l i n e by quartz. 6. The p l a g i o c l a s e of the Artaban g r a n o d i o r i t e i s qu i t e h i g h l y zoned. Gambier Gr a n o d i o r i t e - - 1. F o l i a t i o n i n the Gambier g r a n o d i o r i t e i s q u i t e d i f f e r e n t from the r e g i o n a l trend. 2. The long dimension and bedding of x e n o l i t h s , i f present, i s p a r a l l e l w i t h f o l i a t i o n . 3. There i s no evidence of turbulence i n f o l i a t i o n about x e n o l i t h s , nor i s there any tendency f o r f o l i a t i o n to 53 t o be w r apped a r o u n d t h e x e n o l i t h s . 4. The s o u t h e r n p a r t o f t h e Gambier g r a n o d i o r i t e was o r i g i n a l l y a t a deep l e v e l , p r o b a b l y n e a r t h e b o t t o m o f the p l u t o n . ( E v i d e n c e r e g a r d i n g t h e o r i g i n a l a t t i t u d e , o f t h e p r e s e n t l y e x p o s e d s e c t i o n , r e l a t i v e t o t h e - p l u t o n i s : g i v e n on page 14.)- None t h e l e s s t h e r e h a s b een no a c c u m u l a t i o n o f x e n o l i t h s o r b a s i c - m i n e r a l s n e a r t h e s o u t h • c o n t a c t o f Gambier g r a n o d i o r i t e v / i t h p r e - b a t h o l i t h l a v a s . 5. I n r e g i o n s , n o t a b l y n o r t h o f Hope P o i n t , where q u a r t z z t e n d s t o f o r m s u b h e d r a l g r a i n s i n the m a t r i x , I t has t h e same t e n d e n c y t o f o r m s u b h e d r a l g r a i n s , i n x e n o l i t h s b u t t o a s m a l l e r degree.. 6. A l m o s t a l l x e n o l i t h s i n Gambier g r a n o d i o r i t e h a v e l o s t t h e i r i d e n t i t y . One o f t h o s e w h i c h h a s n o t l o s t i t s i d e n t i t y c o n t a i n s a c o r e 18 i n c h e s ' l o n g and s i x i n c h e s w i d e , o f d ense w h i t e m i c r o c l i n e . - T h i s c o r e i s s u r r o u n d e d by a one i n c h g r a n i t i c zone w h i c h i n t u r n i s s u r r o u n d e d by an o u t e r . zone s e v e r a l f e e t w i d e . The o u t e r zone i s i n d i s t i n g u i s h a b l e f r o m o t h e r x e n o l i t h s . . 7. The f i r s t e f f e c t on one l a m i n a t e d ^lenoljl^fjon, v/as. r e c r y s t a l l i z a t i o n w i t h t h e f o r m a t i o n o f o l i g o c l a s e f e l d s p a r .a. I n a more a d v a n c e d s t a g e , a t t h e c e n t r e o f t h e x e n o l i t h , b e d d i n g i s l e s s d i s t i n c t , z o n i n g o f f e l d s p a r s i s more d i s t i n c t , and p l a g i o c l a s e i s more c a l c i c . A t t h i s s t a g e t h e r o c k c o n t a i n s p o r p h y r o b l a s t s , l e s s c a l c i c t h a n t h e m a t r i x . I n t h e most a d v a n c e d s t a g e , g r a i n s i z e h a s i n c r e a s e d , t h o u g h p o r p h y r o b l a s t i c t e x t u r e r e m a i n s ; z o n i n g i s l e s s e v i d e n t and 9t c a l c i u m c o n t e n t o f f e l d s p a r s i s l e s s t h a n i n t h e i n t e r -m e d i a t e s t a g e . ( W - 8 7 , 8 9 , 9 0 ) . T h i s i s c o n s i d e r e d t o be p r o o f t h a t s u b h e d r a l z o n e d p l a g i o c l a s e i s n o t n e c e s s a r i l y a p r o d u c t o f magmatic c r y s t a l l i z a t i o n . I t i s s u g g e s t i v e i h a & e t f o e v i g i r s t e f f e c t i s r e c r y s t a l l i z a t i o n w i t h o u t d e s t r u c t i o n o f p r i m a r y s t r u c t u r e s s u c h as b e d d i n g . T h i s i s f o l l o w e d by an i n c r e a s e i n g r a i n s s i z e and i n c a l c i u m c o n t e n t o f p l a g i o -c l a s e . F u r t h e r metamorphism i s a t t e n d e d by a d e c r e a s e i n t o t a l c a l c i u m and a d e c r e a s e i n c a l c i u m c o n t e n t o f f e l d s p a r s . 8 * Q u a r t z p o r p h y r o b l a s t s i n many x e n o l i t h s a r e e n v e l o p e d by a zone c h a r a c t e r i z e d by a h i g h p r o p o r t i o n o f h o r n b l e n d e . 9 . The x e n o l i t h s t e n d t o d e v e l o p two v a r i e t i e s o f p l a g i o c l a s e . The more c a l c i c t y p e f o r m s a s u b h e d r a l g r o u n d -mass, w h i c h i s h i g h l y z o n e d . The l e s s c a l c i c t y p e f o r m s much l e s s z o n e d p o r p h y r o b l a s t s . - , 1 0 . O s c i l l a t o r y z o n i n g w i t h a s m a l l n e t change i n a n o r t h i t e c o n t e n t i s common i n p l a g i o c l a s e i n Gambier g r a n o d i o r i t e . 1 1 . - P l a g i o c l a s e and m a f i c m i n e r a l s a r e i n t e r g r o w n i n 3 s u c h a way t h a t age s e q u e n c e c a n n o t be worked o u t i n e i t h e r x e n o l i t h s o r m a t r i x . M o s a i c t e x t u r e between p l a g i o c l a s e and a m p h i b o l e i s common i n x e n o l i t h s . 1 2 . R e p l a c e m e n t o f p l a g i o c l a s e by m i c r o c l i n e , o r m i c r o -c l i n e and p l a g i o c l a s e by q u a r t z , t e n d e d t o p r o d u c e . e u h e d r a l o r s u b h e d r a l r e m n a n t s i n r e p l a c e d m i n e r a l s . 1 3 . Q u a r t z w i t h o u t i n c l u s i o n s t e n d s to be i r r e g u l a r , q u a r t z w i t h i n c l u s i o n s t e n d s t o be b l o c k y . 55 ORIGIN OF XENOLITHS I n t h e f i e l d , - a l l x e n o l i t h s i n A r t a b a n g r a n o d i o r i t e h a v e t h e a p p e a r a n c e o f l a v a s or t u f f s . The x e n o l i t h s - a r e f i n e g r a i n e d a nd some-are l a m i n a t e d . P e t r o g r a p h i c e x a m i n a t i o n o f s p e c i m e n s W -62, 2 1 1 , 2 8 2 , ( a p p e n d i x , - p a r t B ) , d i s c l o s e d t h a t a t l e a s t t h r e e x e n o l i t h s i n s A r t a b a n g r a n o d i o r i t e have a t r a c h y t i c t e x t u r e . One s p e c i m e n W -282, con-tains s m a l l s p h e r u l e s . F e l d s p a r m i c r o l i t e s a r e one h a l f m i l l i m e t r e l o n g i n W-62 and -W-211, and one m i l l i m e t r e l o n g i n W -282. - The few x e n o l i t h s i n Gambier g r a n o d i o r i t e w i t h u n d o u b t e d o r i g i n w i t h r e g a r d to, f i e l d , a p p e a r a n c e , a r e t u f f s . One x e n o l i t h (W -188), w i t h a dense w h i t e t u f f a c e o u s c o r e h a s a • b o r d e r zone i n d i s t i n g u i s h a b l e f r o m a d j a c e n t x e n o l i t h s o f u n -known o r i g i n . X e n o l i t h s w i t h o u t d i s t i n g u i s h i n g f e a t u r e s must 3 be i d e n t i f i e d by i n f e r e n c e . A c c o r d i n g t o F . F . - G r o u t , ( 5 ) an be unknown x e n o l i t h i s l i k e l y t o x s e d i m e n t a r y i f a s s o c i a t e d w i t h s e d i m e n t a r y x e n o l i t h s . G r o u t f ' ( 3 ) s t a t e s a l s o t h a t s e d i m e n t -a r y s t r u c t u r e s may p r o v e s e d i m e n t s b u t t h e i r a b s e n c e p r o v e s n o t h i n g . G r o u t ( 3 ) d i s c u s s e d t h e s i g n i f i c a n c e o f t e x t u r e s a s f o l l o w s : " T r u e i g n e o u s t e x t u r e s " a r e " o f t e n n o t e d as e v i d e n c e o f i g n e o u s o r i g i n ( . . . ) , b u t t h e s e t e x t u r e s a r e n o t e a s i l y d i s t i n g u i s h e d f r o m some r e c r y s t a l l i z e d s e d i m e n t s . T h e r e may be-i n s l a t e , f o r example, a d e v e l o p m e n t l i k e i g n e o u s , p o r p h y r i t i c , p o i k i l i t i c and e v e n g r a n i t o i d t e x t u r e s , so t h a t t h e c r i t e r i o n i s o f -1 i t - t i e • v a l u e . Nor h as t h e zone t r e n d o f t h e p l a g i o c l a s e w i t h d e c r e a s e i n a n o r t h i t e c o n t e n t f r o m c o r e t o r i m any s i g n i f i c a n c e a s a 3 Lac. C/f /=p $ Loc e,r isSJ • 5 6 c r i t e r i o n o f o r i g i n . A c c o r i n g t o G r o u t ( S ) a medium o r A b a s i c f e l d s p a r i n a x e n o l i t h may be zo n e d w i t h ^ h i g h e r p e r -c e n t a g e o f a l b i t e o u t s i d e , r e g a r d l e s s o f t h e o r i g i n o f t h e x e n o l i t h . Thus t h e r e i s good f i e l d and p e t r o g r a p h i c e v i d e n c e t h a t t h e x e n o l i t h s i n A r t a b a n g r a n o d i o r i t e a r e r e m n a n t s o f p r e -g r a n o d i o r i t e c o u n t r y r o c k . . L e s s c o m p l e t e e v i d e n c e i n d i c a t e s t h a t x e n o l i t h s i n Gam-b i e r g r a n o d i o r i t e a r e p r e - g r a n o d i o r i t e c o u n t r y r o c k . T h e r e i s no e v i d e n c e t o s u p p o r t a s u g g e s t i o n t h a t t h e x e n o l i t h s a r e p a r t o f an e a r l y c h i l l e d p h a s e o f a n - i n t r u s i v e magma. 6 F P i r + i 57 ORIGIN OF THE GAMBIER GRANODIORITE S e v e r a l f e a t u r e s o f t h e Gambier g r a n o d i o r i t e s h o u l d be d i s c u s s e d b e f o r e any t h e o r i e s o f o r i g i n c a n be p r e s e n t e d . T hese f e a t u r e s a r e : 1. a b s e n c e o f t u r b u l e n c e i n t h e v i c i n i t y o f x e n o l i t h s . 2. o r i g i n o f f o l i a t i o n and t i m e a t w h i c h f o l i a t i o n was i m p r e s s e d on t h e r o c k . 3. o s c i l l a t o r y z o n i n g of f e l d s p a r s . . h. e x t e n s i v e r e p l a c e m e n t t e x t u r e s . . 5, n o r m a l z o n i n g a n d s u b h e d r i s m o f p l a g i o c l a s e . These f i v e f e a t u r e s w i l l be d i s c u s s e d i n t h e o r d e r named. I f t h e x e n o l i t h s h a d s e t t l e d o r r i s e n t h r o u g h a p a r t l y c r y s t a l l i z e d magma, t h e y s h o u l d h a v e l e f t some e v i d e n c e o f movement. F l o w l i n e s s h o u l d o c c u r on one s i d e o f t h e x e n -o l i t h s . E f f e c t s o f t u r b u l e n c e s h o u l d o c c u r o p p o s i t e t o f l o w l i n e s . The e v i d e n c e o f movement between x e n o l i t h s and magma m i g h t be p a r t l y o b l i t e r a t e d by s u b s e q u e n t metamorphism. None the l e s s , some i n d i c a t i o n t h a t t h e x e n o l i t h s - h a d m o v e d - r e l a t i v e t o magma s h o u l d r e m a i n , u n l e s s - l a t e r metamorphism was p a r t -i c u l a r l y s e v e r e . - T h e r e i s e v i d e n c e o f n e i t h e r movement o f x e n o l i t h s n o r - s u b s e q u e n t s e v e r e metamorphism. I n t h e a b s e n c e o f p r o o f o f movement o f x e n o l i t h s , i t i s r e a s o n a b l e t o assume t h e y h a v e - n o t moved r e l a t i v e t o t h e magma. The f o l i a t i o n i n Gambier g r a n o d i o r i t e c o u l d be e i t h e r p r i m a r y , due t o f l o w a g e o r s e c o n d a r y , due t o dynamic meta-morphism. P r i m a r y f o l i a t i o n - , due t o f l o w o f a p a r t l y s o l i d i f i e d magma, s h o u l d be p a r a l l e l t o the w a l l s o f t h e 58 magma c h a m b e r . F o l i a t i o n i n Gambier g r a n o d i o r i t e i s a t a n a n g l e o f k-0 t o 60 d e g r e e s w i t h t h e m a r g i n s o f the p l u t o n . A n o t h e r f a c t o r w h i c h d e t r a c t s f rom a n h y p o t h e s i s o f p r i m a r y o r i g i n of . t h e f o l i a t i o n , i s t h e c h a r a c t e r of t h e f o l i a t i o n i t s e l f . F o l i a t i o n i s r e c o g n i z a b l e b e c a u s e q u a r t z , one o f t h e most s u s c e p t i b l e m i n e r a l s t o dynamic metamorphism has a t e n d e n c y t o o c c u r as p a r a l l e l s u b h e d r a l - g r a i n s or s t r e a k s o f g r a i n s ( P l a t e I X , A & B ) . No o t h e r m i n e r a l s a r e n o t i c e a b l y p a r a l l e l . F l o w a g e w h i c h c o u l d p r o d u c e f o l i a t i o n i n t h e l a s t m i n e r a l t o f o r m , s h o u l d a l s o h a v e p r o d u c e d f o l i a t i o n i n o t h e r m i n e r a l s . The e x t e n s i v e l y f r a c t u r e d c h a r a c t e r o f q u a r t z i s p l a i n , b o t h m e g a s c o p i c a l l y and m i c r o s c o p i c a l l y . Q u a r t z i n a f l u i d medium c o u l d n o t h a v e been s t r a i n e d t o the e x t e n t one sees i n Gambier g r a n o d i o r i t e . The dynamic f o r c e s w h i c h s t r a i n e d q u a r t z and f o l i a t e d t h e Gambier g r a n o d i o r i t e must have b e e n post- c o n s o l i d a t i o n , or i n any c a s e p o s t q u a r t z . I n f a c t t h e f o l i a t i o n i n Gambier g r a n o d i o r i t e i s p r o b a b l y r e l a t e d t o o r o g e n i c f o r c e s w h i c h t i l t e d t h e r o c k s o f Gambier I s l a n d t o t h e i r p r e s e n t p o s i t i o n . F o l i a t i o n i s a b s e n t i n A r t a b a n g r a n o d i o r i t e b e c a u s e the A r t a b a n g r a n o d i o r i t e d i d n o t c o n t a i n s u f f i c i e n t q u a r t z t o r e c o r d s t r e s s . A p p a r e n t l y s t r e s s was t a k e n up e n t i r e l y by f e l d s p a r w i t h o u t p r o d u c i n g p a r a l l e l i s m o r d i r e c t i o n a l t r e n d . The s a m e - t h e o r y i s p r o b a b l y - a p p l i c a b l e t o the x e n o l i t h s i n Gambier g r a n o d i o r i t e . S t r e s s was s u f f i c i e n t t o s t r a i n q u a r t z b u t i n s u f f i c i e n t t o n o t i c e a b l y r e c r y s t a l l i z e p l a g i o c l a s e o r 59 t o o b l i t e r a t e -textures.-Number t e n o f t h e n o t e w o r t h y f e a t u r e s o f Gambier g r a n o -d i o r i t e r e f e r s t o o s c i l l a t o r y z o n i n g , o f p l a g i o c l a s e , i n w h i c h t h e r e i s a s m a l l n e t change i n a n o r t h i t e c o n t e n t . P l a t e XIV,B i l l u s t r a t e s a z o n e d p l a g i o c l a s e g r a i n f r o m t h i n s e c t i o n W-96. The c o r e o f t h e g r a i n i s An28 and t h e r i m i s An23« A t l e a s t two i n t e r m e d i a t e z o n e s one t h i r d and two t h i r d s o u t f r o m t h e c o r e , a r e Ahl5. I n a d d i t i o n , - t h e r e a r e a number o f u n c o n -f o r m i t i e s due t o s o l u t i o n o f p a r t s o f some z o n e s . E a c h r e v e r s a l i n z o n i n g and e a c h u n c o n f o r m i t y i n d i c a t e s a change i n c h e m i c a l e n v i r o n m e n t . Some w r i t e r s a t t r i b u t e t h e e f f e c t s , i l l u s t r a t e d i n P l a t e X I V , B > t o movement o f a g r o w i n g c r y s t a l r e l a t i v e t o a magma. I f t h e n e t change i n a n o r t h i t e c o n t e n t i s s m a l l , one must assume t h a t c o n d i t i o n s a t t h e p o i n t where t h e c r y s t a l f i n a l l y c e a s e d movement..v/ere s i m i l a r t o c o n d i t i o n s where t h e c r y s t a l s t a r t e d movement. C l o s e e x a m i n a t i o n ' o f P l a t e XIV,B r e v e a l s t h a t g r o w t h p e r p e n d i c u l a r t o t h e l o n g d i m e n s i o n S3 t h e c r y s t a l ( 0 1 0 ) has ; been r e s t r i c t e d more t h a n g r o w th p a r a l l e l t o ( 0 1 0 ) . The z o n e s p a r a l l e l t o ( 0 1 0 ) d i v e r g e a t the l e f t end o f t h e g r a i n . An e x t i n c t zone marks t h e l o c a t i o n o f a s o l u t i o n s u r f a c e w h i c h t r u n c a t e s many z o n e s n e a r th e l e f t end o f t h e c r y s t a l . J h e s o l u t i o n s u r f a c e does n o t e x t e n d s y m m e t r i c a l l y a r o u n d th e c r y s t a l b u t c u r v e s o u t t o t h e r i m o f the c r y s t a l i n t h e same. reg.ix.on where g r o w t h was r e s t i c t e d . O b v i o u s l y t h e a g e n t w h i c h r e s t r i c t e d growth a l s o p r o t e c t e d t h e g r a i n f r o m s o l u t i o n , a t l e a s t d u r i n g t h e l a t t e r p a r t o f t h e p e r i o d o f g r o w t h . The 6 0 c r y s t a l i n P l a t e X I V , B , must have r e t a i n e d i t s p h y s i c a l e n v i r o n m e n t . S i m i l a r l y , many o t h e r p l a g i o c l a s e c r y s t a l s r e t a i n e d t h e i r p h y s i c a l e n v i r o n m e n t t h r o u g h o u t much o f t h e i r g r o wth.. I t i s q u e s t i o n a b l e w h ether g r o u p s o f a t t a c h e d p l a g i o c l a s e c r y s t a l s w o u l d c i r c u l a t e w i t h i n a magma as u n i t s . The p r o b l e m o f o s c i l l a t o r y z o n i n g c a n be s i m p l i f i e d by c o n s i d e r i n g t h a t t h e f e l d s p a r g r a i n s r e m a i n e d i n one p l a c e -w h i l e t h e i n t e r g r a h u l a r s o l u t i o n s c h a nged. E a c h m i n o r change i n c o m p o s i t i o n o f c i r c u l a t i n g s o l u t i o n s w o u l d be r e f l e c t e d i n p r e c i p i t a t i o n of--a new zone or s o l u t i o n o f an o l d one. N e a r l y a l l t h i n s e c t i o n s c o n t a i n e x t e n s i v e r e p l a c e m e n t e f f e c t s . Q u a r t z h a s r e p l a c e d m i c r o c l i n e : q u a r t z and m i c r o -c l i n e have r e p l a c e d p l a g i o c l a s e . L o c a l l y , t h r e e q u a r t e r s o f t h e q u a r t z and a l l o f t h e m i c r o c l i n e have r e p l a c e d o l d e r m i n e r a l s , u s u a l l y p l a g i o c l a s e . T h i s means t h a t t h r o u g h o u t a l a r g e p a r t ' o f t h e Gambier g r a n o d i o r i t e , . t h i r t y , and p e r h a p s f o r t y , p e r c e n t o f t h e r o c k - o r i g i n a t e d by r e p l a c e m e n t p r o -c e s s e s . T h i s i s a c o n s e r v a t i v e e s t i m a t e . R e p l a c e m e n t i n many s p e c i m e n s may have been so c o m p l e t e t h a t no r e c o r d o f t h e p r e - e x i s t i n g m i n e r a l s r e m a i n s . . I t i s d i f f i c u l t t o r e l a t e s u c h e x t e n s i v e r e p l a c e m e n t t o l a t e magmatic a l t e r a t i o n . D e u t e r i c p r o c e s s e s p r o b a b l y c o u l d n o t have p r o d u c e d t e x t u r e s such, as t h e ones. I l l u s t r a t e d i n P l a t e s XV,A ; XVI,A & B; X V I I , A & B ; X V I I I , A <SB. Space now o c c u p i e d by q u a r t z and m i c r o c l i n e , t h e two m i n e r a l s whose r e p l a c e m e n t o r i g i n i s c e r t a i n , was f o r m e r l y o c c u p i e d by a r e p l a c e d m i n e r a l , - - p r o b a b l y p l a g i o c l a s e . The minimum amount o f m i n e r a l , ( q u a r t z and m i c r o c l i n e ) o f 61 r e p l a c e m e n t o r i g i n h as been- c o n s e r v a t i v e l y e s t i m a t e d a t 3 9 p e r c e n t . The a v e r a g e q u a r t z and m i c r o c l i n e c o n t e n t o f Gambier g r a n o d i o r i t e i s 3 5 and 10 p e r c e n t r e s p e c t i v e l y ; a t o t a l o f 4 5 p e r c e n t . T h i s means t h a t n o t more t h a n 1 5 p e r c e n t o f t h e r o c k c o u l d have b e e n s o l u t i o n f i l l e d s p a c e b e f o r e q u a r t z and m i c r o c l i n e s t a r t e d . I f l a t e a l t e r a t i o n h a d o c c u r r e d w i t h i n a magma i n a c l o s e d s y s t e m , s o l u t i o n s c o n t a i n e d i n 1 5 p e r c e n t • o f t h e r o c k c o u l d n o t have p r o v i d e d enough m a t e r i a l t o f o r m 4 5 p e r c e n t o f t h e r o c k . I n f a c t , s o l u t i o n s c o n t a i n e d i n 1 5 p e r c e n t o f t h e r o c k c o u l d s c a r c e l y f i l l t h e s p a c e s w i t h o u t i n t r o d u c t i o n <3f m a t e r i a l f r o m o u t -s i d e t h e s y s t e m . A n o t h e r d i f f i c u l t y i n c o n s i d e r i n g t h e s y s t e m c l o s e d , i s i n a c c o u n t i n g f o r r e p l a c e d m a t e r i a l . Eime r e l e a s e d f r o m r e p l a c e d p l a g i o c l a s e c o u l d have r e a c t e d w i t h p l a g i o c l a s e t o f o r m c l i n o z o i s i t e . S e r i c i t i c a l t e r a t i o n o f p l a g i o c l a s e c o u l d a c c o u n t f o r a s m a l l amount o f t h e p o t a s h t a k e n i n t o s o l u t i o n where q u a r t z r e p l a c e d m i c r o c l i n e . However, t h e r e i s no t r a c e o f A s o d a , most o f t h e p o t a s h , a n d t h e a l u m i n a , w h i c h must have gone i n t o ' s o l u t i o n d u r i n g the r e p l a c e m e n t p r o c e s s e s . M o r e o v e r , amounts o f e p i d o t e and s e r i c i t e i n s p e c i m e n s examined, b e a r n o r r e l a t i o n s h i p t o t h e e x t e n t o f r e p l a c e m e n t o f p l a g i o c l a s e o r m i c r o c l i n e . M a t e r i a l s must have been removed f r o m , a s w e l l as added t o , t h e syst e m . -Tiro c h a r a c t e r i s t i c s o f p l a g i o c l a s e , n o r m a l z o n i n g and e u h e d r i s m , a r e sometimes u s e d a s c r i t e r i a f o r c r y s t a l l i z a t i o n f r o m a magma. The v a l u e o f z o n a l t r e n d f r o m most c a l c i c a t 62" t h e c o r e t o l e a s t c a l c i c a t t h e r i m , h a s b e e n d i s c u s s e d on page 55* E u h e d r i s m and s u b h e d r i s m a r e no more v a l i d t h a n zone t r e n d s as a b a s i s f o r t h e p o s t u l a t l o n o f magmatic c r y s t a l l i z a t i o n . P l a t e s X I I ? A ; XV,A; XVI,A & B;- and X V I I , © , i l l u s t r a t e a s t r o n g t e n d e n c y f o r r e p l a c e m e n t t o p r o d u c e sub-h e d r a l o r r e c t a n g u l a r s h a p e s i n a r e p l a c e d m i n e r a l . M i c r o c l i n e r e p l a c e d p l a g i o c l a s e a l o n g c l e a v a g e s and p r o d u c e d r e c t a n g u l a r s u b h e d r a l g r a i n s . R e p l a c e m e n t o f z o n e d m i n e r a l s p r o b a b l y has a s i m i l a r e f f e c t . Once a zone i s p a r t l y r e p l a c e d a l o n g a c l e a v a g e or f r a c t u r e , r e p l a c e m e n t s h o u l d p r o c e e d most e a s i l y a r o u n d t h e z o n e . I f one zone i s more e a s i l y r e p l a c e d t h a n o t h e r s , r e p l a c e m e n t c o u l d c o n t i n u e w i t h i n t h e e a s i l y r e p l a c e d z o n e , and l e a v e t h o s e z o n e s , w h i c h a r e r e p l a c e d w i t h more d i f f i c u l t y , as r e m n a n t s . Any p r o j e c t i o n b e y o n d t h e g e n e r a l m a r g i n - o f t h e r e p l a c e d m i n e r a l w o u l d p r e s e n t g r e a t e r s u r f a c e p e r u n i t mass, and would-be more e a s i l y r e p l a c e d t h a n a f l a t m a r g i n . I r r e g u l a r i t i e s w o u l d be r e d u c e d so t h a t t h e end r e s u l t w ould be a s u b h e d r a l o r e u h e d r a l g r a i n . 6 3 CONCLUSIONS P a s s i v e s t o p i n g d o e s n o t a c c o u n t f o r t h e x e n o l i t h s i n e i t h e r A r t a b a n g r a n o d i o r i t e or Gambier g r a n o d i o r i t e . I n t r u s i o n and magma f l o w do n o t a c c o u n t f o r f o l i a t i o n i n Gambier g r a n o d i o r i t e : dynamic metamorphism l a t e r t h a n Gambier g r a n o d i o r i t e , does a c c o u n t f o r f o l i a t i o n . T e x t u r e s and s t r u c t u r e s c a n n o t be a t t r i b u t e d t o c r y s t a l l i z a t i o n f r o m a", magma. The p r o c e s s e s w h i c h p r o d u c e d Gambier g r a n o d i o r i t e must have t a k e n p l a c e i n an open s y s t e m . P o t a s h and s i l i c a were added t o t h e s y s t e m , and a t o t h e r t i m e s l i m e , s o d a , p o t a s h and a l u m i n a were removed f r o m t h e s y s t e m . T h i s i s g r a n i t i z a t i o n a c c o r d i n g t o a d e f i n i t i o n 7 by F . F . G r o u t (ft) t h a t g r a n i t i z a t i o n , " i n c l u d e s a g r o u p o f p r o c e s s e s by w h i c h a s o l i d r o c k ( w i t h o u t enough l i q u i d i t y a t any t i m e t o make i t m o b i l e or' r h e o m o r p h i c ) i s made more l i k e a g r a n i t e t h a n i t was b e f o r e , i n m i n e r a l s , o r i n t e x t u r e and s t r u c t u r e or i n b o t h . " " No a t t e m p t t o d e f i n e t h e p f e - g r a n o d i o r i t e r o c k h a s been made. However, i t i s s t r o n g l y s u g g e s t e d t h a t p r e Gambier g r a n o d i o r i t e r o c k c o n s i s t e d o f l a v a s and t u f f s now r e p r e s e n t e d by x e n o l i t h s i n b o t h Gambier and A r t a b a n g r a n o d i o r i t e s . The s o u r c e o f t h e h y d r o t h e r m a l s o l u t i o n s r e s p o n s i b l e f o r g r a n i t i z a t i o n h a s n o t been i d e n t i f i e d , n o r h a s t h e s u b s e q u e n t h i s t o r y o f r e p l a c e d m a t e r i a l b e e n d i s c u s s e d . However, r o c k , such a s A r t a b a n g r a n o d i o r i t e , a d j a c e n t - t o Gambier g r a n o d i o r i t e and x e n o l i t h s w i t h i n G a m b i e r - g r a n o -d i o r i t e may have become more b a s i c a c c o r d i n g t o t h e p r i n c i p a l s l a i d down by D.L. R e y n o l d s (l*0 . 7 ft + <. 64 BTBLIOGRAPHY" T h i s b i b l i o g r a p h y i s n o t i n t e n d e d t o c o m p r e h e n s i v e . Some o f t h e p u b l i c a t i o n s l i s t e d have n o t b e e n r e f e r r e d t o i n t h e c o n t e x t o f t h e t h e s i s , b u t have i n f l u e n c e d my t h o u g h t s . (1) B o s t o c k , H.S.= r. P h y s i o g r a p h y o f t h e C a n a d i a n C o r d i l l e r a w i t h S p e c i a l R e f e r e n c e t o t h e A r e a N o r t h o f t h e F i f t y - f i f t h P a r a l l e l ; G e o l . Stir v . , Canada, Memoir 247, 1948. (2) Bowen, N.L.: " The G r a n i t e P r o b l e m and t h e Method o f M u l t i p l e P r e j u d i c e s ", O r i g i n o f G r a n i t e , G i l l u l y c h a i r m a n ; G e o l . S o c , Am. Memoir 28, 19"48. (3) B u d d i n g t o n , A.F..: A d i r o n d a k I g n e o u s R o c k s and t h e i r Metamorphism; G e o l . S o c , Am. Memoir 7, 193!+» (4) — " " G r a n i t i c R o c k s o f t h e N o r t h w e s t A d i r o n d a k s " O r i g i n o f G r a n i t e , G i l l u l y c h a i r m a n ; G e o l . S o c , Am.-Memoir 28, 1948. (5) Burwash, E . M . J . T h e G e o l o g y o f V a n c o u v e r and V i c i n i t y ; C h i c a g o , U n i v . o f C h i c a g o P r e s s , 1918. (6) E s k o l a , J P . E . : The P r o b l e m o f M a n t l e d G n e i s s Domes; Quar. J o u r . G e o l S o c . Lo n d o n , v o l . CIV,pp 461-476. (7) G e o l o g y and E c o n o m i c M i n e r a l s o f Canada, O f f i c e r s o f t h e G e o l . S u r v . , Canada. 3 e d . 1947. (8) Goodspeed, -G.E.: " O r i g i n o f G r a n i t e s " , ' O r i g i n o f G r a n i t e , G i l l u l y c h a i r m a n ; G e o l . S o c . Am., Memoir 28, 1948. -(9) G r o u t , F . F . : C r i t e r i a o f O r i g i n o f I n c l u s i o n s i n P l u t o n i c R o c k s ; B u l l . . G e o l . Soc.,-Am. v o l . 4 8 , pp 1532 (10) F o r m a t i o n o f Ign e o u s l o o k i n g R o c k s by M e t a -morphism: A C r i t i c a l R e v i e w and S u g g e s t e d R e s e a r c h ; G e o l . S o c . Am. B u l l . v o l . 52, pp 525-576. (11) " O r i g i n o f G r a n i t e " , O r i g i n o f G r a n i t e , G i l l u l y c h a i r m a n ; G e o l . S o c . Am. Mem-. 28, 1949. (12) L e i t c h , H.C.B.: ' C o n t r i b u t i o n s t o t h e G e o l o g y o f Bowen I s l a n d ; U n i v . B r i t . C o l u m b i a , M.A.Sc. t h e s i s , G e o l o g y , 1947. 65' ( 1 3 ) L e r o y , O.B.: P r e l i m i n a r y R e p o r t on a P o r t i o n o f t h e M a i n C o a s t o f B r i t i s h C o l u m b i a and A d j a c e n t I s l a n d s i n c l u d e d i n New W e s t m i n s t e r and Nanaimo D i s t r i c t s ; O t t a wa, Canada. D e p t . M i n e s , G e o l o g i c a l Sixrvey B r a n c h , 1 9 2 8 . (1*+) L o u g h l i n , G.F.: Comments on t h e O r i g i n and M a j o r S t r u c t u r a l C o n t r o l o f Ign e o u s R o c k s and R e l a t e d , M i n e r a l D e p o s i t s : E c o n . G e o l . v o l . x x x v i , 19^+1, p . 6 7 1 . ( 1 5 ) Mathews, W.H..: G e o l o g y o f t h e Mount G a r i b a l d i Map A r e a , S o u t h w e s t e r n B r i t i s h C o l u m b i a , Ph D t h e s i s ; U n i v . C a l i f . 19kS. ( 1 6 ) P h e m i s t e r , T.G.: 'The C o a s t Range B a t h o l i t h n e a r V a n c o u v e r , B.C; Quar. J o u r . G e o l . S o c . Lon d o n , v o l . C I , O c t . - 1 9 ^ 5 . ( 1 7 ) R e a d , H.H.: " G r a n i t e s and G r a n i t e s " , ' O r i g i n o f G r a n i t e , G i l l u l y c h a i r m a n , G e o l S o c . Am. Mem. 2 8 , 19^8 -( 1 8 ) R e y n o l d s , D.L.: The Sequence o f G e o c h e m i c a l Changes L e a d i n g to- G r a n i t i z a t i o n ; Quar. J o u r . G e o l . S o c . - • -London, v o l . C I I . Dec. 19 ! +6. ( 1 9 ) R i c e , H.M.A.: G e o l o g y and M i n e r a l D e p o s i t s o f t h e P r i n c e t o n 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 . Canada, Memoir 2^-3, 19 1 +7. ( 2 0 ) S t o p i n g , "Comments on Magmatic S t o p i n g " , Committee on B a t h o l i t h P r o b l e m s ; D i v i s i o n o f G e o l o g y and Geo-g r a p h y , N a t i o n a l R e s e a r c h C o u n c i l , W a s h i n g t o n , D . C , 1 9 3 5 . ( 2 1 ) C r i c k m a y , C.H.; Horx^ood, H.C.; Snow, W.E.; C a i r n e s , C.E.; . G e o l . S u r v . Canada, Map 737A; . Hope B.C., 1 9 ^ 2 . Numerous a d d i t i o n a l p u b l i c a t i o n s by t h e G e o l o g i c a l S u r v e y o f Canada, p e r t a i n i n g t o c o r d i l l e r a n g e o l o g y , were c o n s u l t e d f o r i n f o r m a t i o n , r e g a r d i n g s t r a t i g r a p h y and s t r u c t u r e o f the c o a s t r e g i o n o f B r i t i s h C o l u m b i a . 66 PLATES: V - XIX. P l a t e V. A. L o o k i n g n o r t h f r o m Bowen I s l a n d . H u t t I s l a n d i n l e f t m i d d l e g r o u n d ; Mt. A r t a b a n i n r i g h t b a c k g r o u n d ; Mt. W r o t t e s l e y and m o u n t a i n s o f w e s t s h o r e o f Howe Sound i n f a r b a c k g r o u n d . B. West s h o r e o f Howe Sound, t o w a r d t h e n o r t h w e s t , f r o m Gambier I s l a n d , a t l a t i t u d e 48*29'N. G. V i e w s o u t h f r o m 1200 f o o t l e v e l s s o u t h s l o p e o f Gambier I s l a n d , n o r t h o f P o r t G r a v e s . Bowen I s l a n d i s i n b a c k g r o u n d ; P o r t G r a v e s i s i n f o r e g r o u n d . P l a t e 71 A. V i e w s o u t h , f r o m 1500 f o o t l e v e l o n w e s t s i d e o f Gambler I s l a n d , a t n o r t h b o u n d a r y o f P l a t e I . S p h e r u l i t e s i n l a v a s on e a s t s h o r e o f Gambier I s l a n d one h a l f m i l e s o u t h o f n o r t h m a r g i n o f P l a t e I . P l a t e V I I . G r a n i t i z a t i o n o f t u f f s , w e s t s h o r e o f Howe Sound, n e a r l a t i t u d e 49° 287V. The v e r t i c a l g r a n i t i z e d a r e a c o n t a i n s l e n t i c u l a r i n c l u s i o n s p a r a l l e l w i t h b e d d i n g , I n c l u s i o n - w i t h t h r e e p h a s e s , i n s o u t h t i p o f Gambier I s l a n d , one q u a r t e r m i l e e a s t o f Hope P o i n t . V a r i a t i o n s i n c o l o r a r e p a r t l y due t o i n c r e a s e i n g r a i n s i z e and p a r t l y due t o r e d u c t i o n i n amount, o f m a f i c c o n s t i t u e n t s . P l a t e V I I I . A. F r e s h s u r f a c e o f W-6k, A r t a b a n g r a n o d i o r i t e , f r o m s o u t h s l o p e o f Mt. A r t a b a n . N a t u r a l - s i z e . [ 3. F r e s h s u r f a c e o f w * - 2 5 l » a h o r n f e l s l i k e i n c l u s i o n f r o m s o u t h w e s t Gambier I s l a n d . N a t u r a l s i z e . Plate IX. A. Weathered surface of W-98, granodiori te located one mile north of Hope P o i n t . The large grains of quartz which i n places appear subhedral, are quite d i s t i n c t . Natural s i z e . Weathered surface of Z-76 g r a n o d i o r i t e , from western Gambier. In t h i s rock,quartz i s i n slender streaks rather than i n s ingle masses. F o l i a t i o n trends from lower l e f t to upper r i g h t . Weathered surface of i n c l u s i o n W-84, from Hope P o i n t N a t u r a l s i z e . P l a t e X I . A. F r e s h s u r f a c e o f i n c l u s i o n W-78, s o u t h Gambier I s l a n d , one h a l f m i l e w e s t o f Hope P o i n t . The d a r k r i m a b o u t t h e q u a r t z p o r p h y r o b l a s t s o f v a r i o u s s i z e s i s b l u e -g r e e n h o r n b l e n d e , p a r t l y embedded i n t h e q u a r t z . The l i g h t p a t c h above t h e l a r g e q u a r t z g r a i n i s a p l a g i o -c l a s e p o r p h y r o b l a s t . N a t u r a l s i z e . (Compare w i t h P l a t e X I I I , B.) B. F r e s h s u r f a c e o f i n c l u s i o n W-97, one m i l e n o r t h o f Hope P o i n t . N a t u r a l s i z e . P l a t e X I I . A. P h o t o m i c r o g r a p h o f W-6If, A r t a b a n g r a n o d i o r i t e . Q u a r t z ( Q ) r e p l a c e s m i c r o c l i n e ( M ) , w h i c h r e p l a c e s p l a g i o c l a s e ( P ) . G r a i n P a t c o r e i s An*+6, i s o l a t e d r emnant a t X i s An28. The d a r k p a t c h e s i n Q a r e rem n a n t s o f m i c r o c l i n e o f same o r i e n t a t i o n a s M. B. B o r d e r zone o f W-87, f r o m an i n c l u s i o n 25" f e e t w i d e , n e a r Hope P o i n t . B e d d i n g p l a n e s a r e d i s t i n c t on b o t h s i d e s o f t h e i n c l u s i o n , b u t have b e e n o b l i t e r a t e d by r e c r y s t a l l i z a t i o n a t c e n t e r o f che i n c l u s i o n . N a t u r a l s i z e . P l a t e X I I I . A. I s o l a t e d p a r t s o f a q u a r t z g r a i n i n i n c l u s i o n W-100. R e p l a c e m e n t e f f e c t s o c c u r e l s e w h e r e i n t h e same t h i n s e c t i o n . G r o s s e d n i c o l s . xto Q u a r t z p o r p h y r o b l a s t i n an i n c l u s i o n e a s t o f Hope P o i n t . The hornblenc<* a r o u n d t h e r i m i s em-b e d d e d i n q u a r t z , one h o r n b l e n d e g r a i n a t t h e r i g h t end i s s u r r o u n d e d by q u a r t z . C r o s s e d n i c o l s . (Compare w i t h P l a t e X I , A.) P l a t e XIV A. Q u a r t z i n W-210, f r o m A r t a b a n g r a n o d i o r i t e . E a c h g r a i n h as a r i m o f m i c r o g r a p h i c q u a r t z , x i o B. H i g h l y z o n e d p l a g i o c l a s e g r a i n i n Gambier g r a n o -d i o r i t e W -96, a b o u t one m i l e n o r t h o f Hope P o i n t . Growth i n a l a t e r a l d i r e c t i o n a p p e a r s t o have b e e n r e s t r i c t e d much more t h a n g r o w t h i n t h e l o n g i t u d -i n a l d i r e c t i o n . xi-S" P l a t e XV. A. S p e c i m e n W-59; a s i n g l e g r a i n o f m i c r o c l i n e ( M i c r o . ) i n r e p l a c i n g a z o n e d g r a i n o f p l a g i o c l a s e ( P l a g . ) h a s l e f t a s u b h e d r a l l o b e o f p l a g i o c l a s e . P l a g i o c l a s e 1 i s g r a i n 3 c o r e , p l a g i o c l a s e 2 i s g r a i n 3 r i m . M i c r o c l i n e i s g r a i n h. D e s c r i p t i o n i s i n Appendix.X5<? S u b h e d r a l m i c r o c l i n e i n W-59. Upper l e f t - m i x e d c h l o r i t e a n d c a r b o n a t e ; l o w e r r i g h t - q u a r t z . K, = ( 0 1 0 ) ; z ( 1 1 0 ) ; K 3 s ( 1 1 1 ) ; - ( 1 1 0 ) ; D, = S = c o m p o s i t i o n p l a n e a n d c l e a v a g e s ( 0 1 0 ) ; D,' S c o m p o s i t i o n p l a n e - ( 0 0 1 ) ; I , p l a n e o f i n c l u s i o n . 1502. "X 6^ P l a t e XVI A . M i c r o c l i n e ( p l a i n ) i n Z -77? r e p l a c i n g p l a g i o c l a s e ( r u l e d ) . I n d i v i d u a l m i c r o c l i n e p l a g i o c l a s e m a r g i n s a r e s t r a i g h t , b u t c o l l e c t i v e m i c r o c l i n e b o u n d a r y i s i r r e g u l a r . S u b h e d r a l b l u e - g r e e n h o r n b l e n d e c r o s s h a t c h e d , e x c e p t one l a r g e s u b - a n g u l a r g r a i n a d j a c e n t t o a m p h i b o l e o f l o w e r l e f t . X V . s r B". P o r t i o n e n c l o s e d i n b r o k e n l i n e o f A a b o v e . The m i c r o c l i n e p l a n e c a n be s e e n r e p l a c i n g p l a g i o c l a s e a l o n g c l e a v a g e d i r e c t i o n . The s m a l l i s o l a t e d p l a g i o c l a s e g r a i n s i n m i d - e e n t r e , a r e s i m i l a r i n o r i e n t a t i o n t o t h e l a r g e g r a i n , and a r e assumed t o be u n r e p l a c e d remnants.xSO P l a t e X V I I . A. M i c r o c l i n e i n W-170 r e p l a c i n g p l a g i o c l a s e a l o n g c l e a v a g e d i r e c t i o n s and m i n e r a l b o u n d a r i e s . M i c r o c l i n e , q u a r t z + , p l a g i o c l a s e c , same o r i e n t a t i o n shown by p a r a l l e l l i n e s . x4-s~ B. M i c r o c l i n e i n W-232 r e p l a c i n g p l a g i o c l a s e i n s u c h a way t h a t a n g u l a r f o r m s r e s u l t . L e g e n d same as i n A . X 3 5 " P l a t e X V I I I S p e c i m e n W -226, Gambier g r a n o d i o r i t e . Q u a r t z r e -p l a c i n g p l a g i o c l a s e and m i c r o c l i n e . The two s e p a r a t e d p l a g i o c l a s e a r e a s marked A, have same o r i e n t a t i o n . S i m i l a r l y , t h e two s e p a r a t e d m i c r o c l i n e m asses have t h e same o r i e n t a t i o n . Q u a r t z + , m i c r o c l i n e 0-0 , p l a g i o c l a s e r=y^. x&o ~>« S p e c i m e n W-107, A r t a b a n g r a n o d i o r i t e . Q u a r t z ( w h i t e ) , i s s u r r o u n d e d by a zone o f m i c r o g r a p h i c q u a r t z o r i e n t e d t h e same as t h e m a i n mass. The d a r k m a t e r i a l I s f e l d s p a r . N o t e t h e f i n e l y r e - e n t r a n t m a r g i n and t e n d e n c y t o w a r d e u h e d r i s m o f t h e m a i n q u a r t z m a s s . x i o P l a t e XIX. A. Specimen W-100, i n c l u s i o n i n A r t a b a n g r a n o d i o r i t e on e a s t s i d e of P o r t Graves. M i c a ( p a r a l l e l l i n e s ) i s i n t e r g r o w n w i t h p l a g i o c l a s e g r a i n ( s o l i d w h i t e ) . Two p a r t s o f the same ho r n b l e n d e g r a i n ( c r o s s hatched) a r e i s o l a t e d by m i c a . P l a g i o c l a s e - l ^ ; h o r n b l e n d e - Hb.X35 Specimen W-59? Gambler g r a n o d i o r i t e , c h l o r i t e -c a r b o n a t e pseudomorph a f t e r amphibole. C h l o r i t e tends t o f o l l o w two d i r e c t i o n s a t about 1 2 5 ° . C h l o r i t e i r * , e p i d o t e - Ep, m a g n e t i t e - Mag, b i o t i t e - B i o . x i S " p APPENDIX' M a f i c M i n e r a l s : -A m p h i b o l e -Z'AC i n d i c a t e s t h a t a c l o s e a p p r o x i m a t i o n o f t h e t r u e Z' c a n g l e i s 20 . Z A c i n d i c a t e s t h a t t h e t r u e a n g l e d e t e r m i n e d on a u n i v e r s a l s t a g e , i s 20 .-2V =• 54 o p t i c a n g l e r e a d on one o p t i c a x i s . 2V - 51+ o p t i c a n g l e r e a d on two o p t i c a x e s . M i c a - - " • -X ^ c i n d i c a t e s t h a t X i s a l m o s t e q u a l t o c . S.W.M. - i s an a b b r e v i a t i o n f o r s e c o n d a r y w h i t e m i c a , p r o b a b l y . s e r i c i t e . G e n e r a l : -M i n e r a l p e r c e n t a g e e s t i m a t e s a r e e n t i r e l y v i s u a l . V e r y h i g h and v e r y low amounts a r e l e s s a c c u r a t e l y e s t i m a t e d t h a n i n t e r m e d i a t e amounts. The e x p r e s s i o n " r e p l a c e m e n t b o u n d a r i e s " i s i n t e n d e d t o s i g n i f y t h a t m i n e r a l c o n t a c t s a r e n o t t h e s t r a i g h t l i n e t y p e n o r m a l l y f o u n d when m i n e r a l s c r y s t a l l i z e f r o m a m e l t i n an o r d e r l y s e q u e n c e . " R e p l a c e m e n t b o u n d a r i e s " h e r e , means t h a t m a r g i n s a r e c u r v e d and c h a r a c t e r i z e d by embayments, b u t t h a t r e l a t i v e ages a r e n o t known'with c e r t a i n t y . Where a g e s a r e d e c i p h e r a b l e , t h e r e p l a c e d m i n e r a l i s n o t e d u n d e r t h e h e a d i n g o f t h e r e p l a c i n g m i n e r a l e.g. M i c r o c l i n e ; r e p l a c e s p l a g i o c l a s e : or v i c e v e r s a P l a g i o c l a s e ... r e p l a c e d 1,,, ... j..-;rocl?>V3. The f o l l o w i n g c r i t e r i a were u s e d i n d i v i d u a l l y and i n c o m b i n a t i o n s a s i n d i c a t o r s o f r e p l a c e m e n t . 1. C u r v e d or r e - e n t r a n t m a r g i n s w h i c h c o u l d n o t be e x p l a i n -ed by o r d e r l y c r y s t a l l i z a t i o n f r o m a m e l t . 2. I s l a n d - l i k e r e m n a n t s o f t h e h o s t m i n e r a l w i t h i n t h e metasome. T h i s c r i t e r i o n was n o t u s e d u n l e s s t h e s t r u c t u r e was a c c o m p a n i e d by s i m i l a r i t y i n o r i e n t a t i o n . 3« Numerous s i m i l a r l y o r i e n t e d i n c l u s i o n s o f t h e h o s t m i n e r a l w i t h i n t h e metasome. The i n c l u s i o n s may o r may n o t be o r i e n t e d t h e same a s a d j a c e n t h o s t m i n e r a l o u t s i d e t h e metasome. T h i s c r i t e r i o n was n o t u s e d where c r y s t a l i r r e g u l a r -i t i e s c o u l d a c c o u n t f o r i n c l u s i o n s o f one m i n e r a l i n a n o t h e r . N o r m a l l y , however, t h e i n c l u s i o n s t h e m s e l v e s have i r r e g u l a r r e p l a c e m e n t t y p e b o u n d a r i e s . h. R e p l a c e m e n t o f h o s t a l o n g c l e a v a g e s . ( E x p l a n a t i o n o f Symbols u s e d i n A p p e n d i x . Q u a r t z ; - - -S t r e s s e f f e c t s on q u a r t z a r e i n d i c a t e d as f o l l o w s : homogeneous e x t i n c t i o n . u n d u l a t i n g e x t i n c t i o n , b u t w i t h l i t t l e o r no f r a c t u r i n g . u n d u l a t i n g e x t i n c t i o n and m i n o r f r a c t u r i n g , u n d u l a t i n g e x t i n c t i o n and c o n s i d e r a b l e f r a c t u r i n g . u n d u l a t i n g e x t i n c t i o n , c o n s i d e r a b l e f r a c t u r i n g and s l i g h t t o m o d e r a t e m o r t a r s t r u c t u r e . u n d u l a t i n g e x t i n c t i o n , e x t e n s i v e f r a c t u r i n g and e x t e n s i v e m o r t a r s t r u c t u r e . I d e n t i f i c a t i o n - o f f e l d s p a r s was made on t h e b a s i s o f c e n t e r e d i n t e r f e r e n c e f i g u r e s , e x c e p t where an o f f c e n t e r f i g u r e i s n o t e d . P r e c i s e s t u d i e s by t h e F e d o r o v method were made on some f e l d s p a r g r a i n s . The d a t a a r e • p r e s e n t e d a s a n g l e s between the p o l e s o f c r y s t a l l o g r a p h i c p l a n e s and t h e Z, Y, and X v i b r a t i o n d i r e c t i o n s . M i c r o c l i n e -Dr: c o m p o s i t i o n p l a n e . I- p l a n e o f r e g u l a r d u s t y i n c l u s i o n s . K=. an o u t l i n e p l a n e . L - t w i n l a m e l l a e . . p e r t h i t e i n d i c a t e s t h a t m i c r o c l i n e p e r t h i t e i s p r e s e n t i n t h e t h i n s e c t i o n , b u t t h a t n o t a l l t h e m i c r o c l i n e i s p e r t h i t i c . P l a g i o c l a s e -. An25-15:- t h e f i r s t number i n d i c a t e s c o m p o s i t i o n o f t h e c o r e ; t h e s e c o n d number i n d i c a t e s t h e compos-i t i o n o f t h e r i m . An25 5 t h e c o m p o s i t i o n o f t h e f e l d s p a r i s known o n l y w i t h i n t h e l i m i t s o f t h e s e c o n d number. G c l e a v a g e . . IT w t w i n l a m e l l a e . S.W.M.- s i g n i f i e s s e c o n d a r y w h i t e m i c a , p r o b a b l y s e r i c i t e . G r ade 0 -Grade 1 -Grade 2 -Grade 3 -G rade h- -G r a d e 5 -F e l d s p a r s : -i i i PART A MATRIX OF ARTABAN GRANODIORITE T h i n S e c t i o n Page W-64 i v W-107 v W-209 v i W-210 v i i v ARTABAN GRANODIORITE (MATRIX). W- 6h - 50 - . - - -Quartz:;- 15$; c l e a r ; 1 mm. g r a i n s ; g r a d e 1; r e p l a c e s p o t a s h f e l d s p a r s . F e l d s p a r s : -M i c r o c l i n e - d u s t y ; 1-1.5 mm. g r a i n s w h i c h s u r r o u n d and r e p l a c e p l a g i o c l a s e . Z". Y. X. E r r o r G r a i n 2. A-(010 )L 17° 78" 78* 7°S.>W..--G r a i n 3. 1(001):S 88 6 20" 70° 15°N.W;.. ( i n d i s t i n c t ) . -L(010 )L 7 88° 85° 20*S.E.. J - F a c e ( l O l ) 88° 30° 60° 10° Sr. ± F a c e ( 0 2 l ) . 39° 52* 83° 3'N-W". O b s e r v e d ^ A n g l e T r u e A n g l e E r r o r (001) A (010)' 8 lT 90° -2T (0Ol))VN(roi) 10° l V J + (OOI)A (021) 533 50° +3 ( O l O ) A ( T O l ) 88° 8 8 ' 0 (010)7\(021) 38° h6° -8 (T01)A(021)' 5h' 62° -8 -2V= 83° P l a g i o c l a s e - kOfo; c l b u d y ; 2 mm; s u b h e d r a l ; h i g h l y a l t e r e d t o e p i d o t e and S.W.M* Z". • Y. X. E r r o r G r a i n 1 C o r e -1(010)1 --26' 6-5' 8k-'• -An^ -6 2% S.W. l ( 1 1 0 ) C -50°- 8CT h?'- An^fO • 15% N.W. a_(010) -- C o m p o s i t i o n p l a n e and q u i t e "sharp i(110) I s i r r e g u l a r and i n d i s t i n c t . I s o l a t e d i s l a n d o f p l a g i o c l a s e , f o r m e r l y the r i m o f G r a i n 1, - -L(010)L " - 9 ' 85-' 83" An28 8% N. l(110)c 63 6h' 39* Ah30 ±5% S.W. ( 1 1 0 ) i s : a p o o r l y d e f i n e d c l e a v a g e and m e a s u r a b l e o n l y i n th e c o r e o f th e g r a i n . M a f i c M i n e r a l s : P y r o x e n e - 15$; s c a t t e r e d l a r g e g r a i n s ; c o n s i d e r a b l y a l t e r e d t o p a l e g r e e n , f e a t h e r y , a m p h i b o l e . V T w i n n e d r p y r o x e n e g r a i n ( u n i v e r s a l s t a g e m e t h o d ) . - C o m p o s i t i o n O p t i c ZAc -f2V l l O A l l O P l a n e P l a n e Sub. 1 W 54" 100 010 Sub. 2 47 i±9_ 92 A v e r a g e 43 j?0 93" ' 100 ' 010 A c c e s s o r y M i n e r a l s : -A p a t i t e M a g n e t i t e - 1-2$ S e c o n d a r y M i n e r a l s : -S-.W.M. and e p i d o t e i n p l a g i o c l a s e ; a b o u t one t h i r d o f p l a g i o c l a s e i s a l t e r e d . A m p h i b o l e - Z A c 12 , p a l e g r e e n t o c o l o r l e s s . F e a t h e r y c l u s t e r s o f g r a i n s a f t e r p y r o x e n e . C h l o r i t e - 10% o f t h i n s e c t i o n . P r e s e n t i n b o t h p y r o x e n e and f e l d s p a r . H y d r a t e d i r o n o x i d e s . W - 1 0 7 7 - 50 . Q u a r t z : - 20$; c l e a r ; 2-3 mm; many q u a r t z g r a i n s a r e s u r r o u n d e d by a zone o f m i c r o g r a p h i c q u a r t z and f e l d s p a r . Some m i c r o g r a p h i c q u a r t z r e t a i n s i t s o r i e n t a t i o n a c r o s s f e l d s p a r b o u n d a r i e s . ( The f e l d s p a r o f t h e m i c r o g r a p h i c s t r u c t u r e s h a s 'a v e r y l ow i n d e x . S i m i l a r f e l d s p a r was i d e n t -i f i e d as m i c r o c l i n e i n W-64.) The main- -body o f q u a r t z i s s e p a r a t e d f r o m m i c r o -g r a p h i c i n t e r g r o w t h s o f q u a r t z a nd f e l d s p a r by a s u r f a c e w h i c h i s composed o f numerous c o n n e c t e d s h o r t a r c s c o n v e x away f r o m q u a r t z . T h i s i s w e l l shown i n s e c t i o n s I n w h i c h t h e m i c r o g r a p h i c -q u a r t z a p p e a r s a s I t r i a n g u l a r b o d i e s i n a zone a r o u n d q u a r t z . Some m i c r o g r a p h i c q u a r t z r o d s c.po ap p e a r t o have e n l a r g e d so t h a t a number n e a r l y c o a l e s c e . The r e s u l t i s an a n g u l a r mass o f q u a r t z t r a n s e c t e d by a f i n e n e t w o r k o f f e l d s p a r . --F e l d s p a r s : - 60%. M i c r o c l i n e a s w e l l as p l a g i o c l a s e , may have b e e n p r e s e n t . A l l f e l d s p a r i s h i g h l y a l t e r -e d t o S.W.M., c h l o r i t e , e p i d o t e , k a o l i n . M a f i c M i n e r a l s : - 20%. E n t i r e l y a l t e r e d t o c h l o r i t e and e p i d o t e , sphene, and o x i d e s ; b o t h a m p h i b o l e or p y r o x e n e and m i c a may have been i n r o c k . v l W - 209 - 5 0 . . Q u a r t z : - 5%\ c l e a r ; l e s s t h a n .5 mm; i n t e r s t i t i a l t o o t h e r m i n e r a l s ; some r o u n d e d m i c r o g r a p h i c - a r e a s a r e up t o 1 o r 2 mm.in d i a m e t e r . " They t r a n s e c t g r a i n "bound-a r i e s , i s o l a t e p a r t s o f g r a i n s and w i t h o u t a p p e a r -i n g t o have e x a c t b o r d e r s t h e y change b i r e f r i n g e n c e o f t h e f e l d s p a r g r a i n s i n w h i c h t h e y o c c u r . F e l d s p a r s : - 60$. F e l d s p a r s i m i l a r t o t h a t i d e n t i f i e d as m i c r o c l i n e i n W-64 i s p r e s e n t . P l a g i o c l a s e - c l o u d y ; 1-2 mm; u n z o n e d ; s l i g h t l y o f f c e n t e r f i g u r e J X ; Z'Acl(OOl) - 13 ; " Z'K l a m e l l a e and c l ( O l O ) = 7 2 , i n d i c e s b e l o w b a l s a m , so c o m p o s i t i o n i s An20. H i g h l y a l t e r e d t o S.W.M., e p i d o t e , and c h l o r i t e . M a f i c M i n e r a l s : - 25%. E n t i r e l y a l t e r e d t o c h l o r i t e a nd e p i d o t e , sphene, h y d r a t e d i r o n o x i d e s . A c c e s s o r y M i n e r a l s : A p a t i t e M a g n e t i t e , t i t a n i f e r o u s - 1%. S e c o n d a r y M i n e r a l s : -S.W.M., e p i d o t e ( c o l o r l e s s , a nd p l e o c h r o i c y e l l o w ) , c h l o r i t e , s p h e ne, h y d r o u s i r o n o x i d e s . Some f e l d s p a r g r a i n s c o n t a i n m i n u t e r o d s o f b l o o d r e d , a l m o s t opaque m a t e r i a l w i t h s q u a r e c r o s s s e c t i o n and e x t r e m e l y h i g h b i r e f r i n g e n c e . T h e s e r o d s a r e t e n t a t i v e l y i d e n t i f i e d a s r u t i l e . W - 210 - 50  Q u a r t z : - 15 - 20%; c l e a r ; 1-2 mm; g r a d e 2; a g g r e g a t e s and s i n g l e g r a i n s , o f f a i r l y r e g u l a r shape. The c e n t r a l p a r t o f e a c h g r a i n i s s o l i d q u a r t z ; be-yo n d t h i s i s a zone o f m i c r o g r a p h i c q u a r t z and f e l d s p a r . The o r i e n t a t i o n o f m i c r o g r a p h i c q u a r t z i s c o n s t a n t , r e g a r d l e s s o f t h e o r i e n t a t i o n o f t h e a s s o c i a t e d f e l d s p a r . F e l d s p a r s: - 50-60$. ' M i c r o c l i n e - 20$(?) ; d u s t y ; 2 mm; - i r r e g u l a r ; r e p l a c e s -p l a g i o c l a s e . T h i s f e l d s p a r v/as n o t p r o v e d t o be m i c r o c l i n e . However, i t s c h a r a c t e r i s t i c s - i n d e x w e l l below b a l s a m ; l o w e r b i r e f r i n g e n c e t h a n t h e p l a g i o c l a s e $ i n d i s t i n c t , v e r y f i n e . , p a r a l l e l , l e n s i f o r m t w i n n i n g , a n d i t s S i m i l a r i t y t o m i c r o -c l i n e o f W-64, s u g g e s t t h a t i t i s m i c r o c l i n e . v i i P l a g i o c l a s e - 3 0-40$; d u s t y t o v e r y c l o u d y ; 2 mm; sub-h e d r a l t o a n h e d r a l ; J L ^ Z ( c o r e ) A 0 1 0 ^ 6 2 ; Z(rim ) 4 0 1 Q = 78 j i n d i c e s v a r y f r o m w e l l above t o j u s t b e l o w b a l s a m , so p l a g i o c l a s e i s An55-30. C o n s i d e r a b l y a l t e r e d t o S.W.M., e p i d o t e , c h l o r i t e . M a f i c M i n e r a l s : - 20$. E n t i r e l y a l t e r e d t o e p i d o t e , c h l o r i t e , sphene, and m i n o r h y d r a t e d o x i d e s . The c h l o r i t e i s m o s t l y a deep g r e e n p l e o c h r o i c v a r i e t y w i t h a b l u e i n t e r f e r e n c e c o l o r . A c c e s s o r y M i n e r a l s : - " A n a t i t e - v e r y s m a l l q u a n t i t y . M a g n e t i t e - 1 - 2 %. v i i i PART B5 XENOLITHS IN ARTABAN GRANODIORITE T h i n S e c t i o n Page W-62 i x -W-211 i x W-282 x XENOEITHS IN ARTABAN GRANODIORITE W - - 62" - -50 . - ' - -Quartz;:- 15$; c l e a r ; .2 mm; g r a d e 0.- - . - ' F e l d s p a r s ; - 60$; d u s t y ; l e s s t h a n ,5 mm. l o n g . . Maximum e x t i n c t i o n a n g l e •==• 12" (10 g r a i n s ) ; i n d i c e s , b e l o w b a l s a m . A l b i t e , A n l O . M a f i c M i n e r a l s : ' E p i d o t e - some e p i d o t e i s i n t e r s t i t i a l t o f e l d s p a r s . K a o l i n i t e - - -S b m e t - f r a c t u r e s a r e f i l l e d w i t h e p i d o t e , o t h e r s w i t h quartz^, and t h e f o r m e r c u t t h e l a t t e r . T e x t u r e : - t r a c h y t i c ; many f e l d s p a r m i c r o l i t e s a r e s e p a r a t e d by q u a r t z g r a i n s . W - 211 - 50 Q u a r t z : - 15$; c l e a r ; 2 mm. g r a i n s ; g r a d e 0 . F l o w t e x t u r e a b o u t q u a r t z i n d i c a t e s t h a t q u a r t z i s p r i m a r y . F e l d s p a r s : - C l e a r ; sub p a r a l l e l , , t w i n n e d m i c r o l i t e s up t o 0.2 mm. l o n g ; maximum e x t i n c t i o n a n g l e =• 10";? i n d i c e s a r e j u s t b e l o w b a l s a m so m i c r o l i t e s a r e Anl !+. A c c e s s o r y M i n e r a l s : -A p a t i t e - t i n y n e e d l e s i n q u a r t z . S e c o n d a r y M i n e r a l s : -" Sphene - 3$; t i n y f l a k e s o f h i g h r e l i e f and h i g h b i r e f r i n g e n c e . E p i d o t e - y e l l o w i s h g r e e n . P y r i t e - s m a l l c u b e s up t o .2 mm. a c r o s s . T e x t u r e : - t r a c h y t i c but. n o t w e l l d e v e l o p e d . x: W - 282 - 50 . . • . Q u a r t z : - .15%', c l e a r ; g r a d e 0; f i n e r a d i a t i n g n e e d l e s w i t h f e l d s p a r i n s p h e r u l i t e s and a s 1 mm. g r a i n s w h i c h may.have r e p l a c e d p l a g i o c l a s e . F e l d s p a r : - 7 5 $ ; ' d u s t y ; a l t e r e d t o S..W.M; o c c u r s a s r e c t a n g u l a r 1 mm. p h e n o c r y s t s and w i t h q u a r t z i n 0.2 mm»-s p h e r u l i t e s . M a f i c M i n e r a l s : • Amphibole - 5%* Z7\ c - 5° o r l e s s . . X"'= c o l o r l e s s ; Z b l u e . V e r y f i n e n e e d l e s b e t w e e n and- p r o j e c t i n g i n t o s p h e r u l i t e s . Opaque Oxides:;- 1%.-S e c o n d a r y M i n e r a l s : -S.W.M. - i n f e l d s p a r s . C h l o r i t e - p a l e g r e e n , i n f e l d s p a r s . T e x t u r e : - s p h e r u l i t i c . xl PART C MATRIX OF GAMBIER GRANODIORITE' T h i n S e c t i o n Page W-59 x i i W-79 x i i i W-85 x i v W-96- X V W-98 x v i W-101 x v i i W-103 x v i i W-166 x v i i i W-167 x v i i i W-169 x i x W-170 x i x -W-191 xx: . W-226 x x W-232 x x i W-239 ..... x x i l W-253 x x i i W-261 x x i i i W -285 x x i v W-287 .......... x x i v Z - 7 7 x x v x i i GAMBIER .GRANODIORITE;- (MATRIX). W- 59 - 50 Quartz;- 3 0 $ ; irregular; grade 2 ; sutured borders; inter-s t i t i a l to feldspar and replaces plagioclase and microcline. Feldspars:-Microcline;- 10$; up to 2 mm. long; irregular in shape dusty patches; replaces plagioclase (Plate XV, A. Grain h Grain 2 D = S I' Ii" S" K:, K , K, Forms Z. 8j° 13° 791 83° 75° 13". 59/ h(y: Y. X. Pole Error -1(001) 5F'W. 2 V . - 2 V =79i 8h° 83\ 8j> 76' 83° 82° 65° 82° 79 13 \ 88t 20° 80° 50°. !+0i K, ("010)AKX (110).-K, ( O I O ) A K , (111) K, (QIO)AK, (110) K4 (llO)AK, (111) K ( 1 1 0 ) A K , (111) D (010)4 Kj (111) -L(010T -L(1502) J - ( O O l ) . ) 1 ( 1 1 0 ) -1(010) -L(I10)" - K i n ) -L(110) Observed 52° 5^ 56 \ 7 6 i 89° 59° 5 .S.E. 5\ W.N..W. 6 , s . w . 3 i N.E. 5*; s . 2 i E. lV. N.E". 5° N.N.W. True 5 9 i 63° 59° 60° 7 i ; 63 K. is rather poorly developed - See Plate XV, B. Plagioclase:- *+5$; dusty; subhedral to anhedral; size is seriate from 1 mm. to 5 mm. Z.ZV Y. X. Grain 3 • Core(x(010)C i H 76° 88" (1(110)C 6 7 ' 69" 31° Rim (1(010)C -2° 89° 89° (1(110)0-62° 75' 33-An35 A n 2 6 <> Anl9i or An23 An-20 :'-'-W5$ N.W. 1$ S.W. 1$ N.W. Those based on "(010) are probably more accurate than those based on . (110) . x i i i Z. ~'Y. X. G r a i n 5 a . ->-(00l)G -70" - 120* 90°o Anh? - ' 2 $ S.E. G r a i n 5b. J-(001)C 80° 12° 8 3 i A n ^ 2% N.E. 5a and 5b a r e i n t e r g r o w n ; - n e i t h e r i s n o t i c e a b l y z o n e d . G r a i n 6. j_(010)C 19° 70° 88° An39 2% S.W. x(001)C 67° 2 3 i ° 8 5 ° An37 2% S.E. G r a i n 7 . - L(010)C -1-5° - 76° 85° An3^ 2% NlE'. G r a i n 7 l ( 0 1 0 ) G 11° ---79 ' ' 87° An31 2% N . S l i g h t l y e l o u d y , n o t n o t i c e a b l y z oned u n t i l r o t a t e d ; f a i n t z o n i n g t h e n shows. G r a i n 6 and G r a i n 7 a r e s u b - i n d i v i d u a l s o f a c a r l s b a d t w i n . M a f i c M i n e r a l s : -CaFe S i l i c a t e s : - 1 5 - 2 0 $ ; a l m o s t e n t i r e l y a l t e r e d t o p a l e y e l l o w p l e o c h r o i c e p i d o t e ( Z ' A c - 2 7 ° ) ; brown or g r e e n p l e o c h r o i c c h l o r i t e ( s m a l l 2 V ) ; q u a r t z , sphene, c a r b o n a t e . P o s s i b l e f o r m e r p r e s e n c e o f m i c a shown by l a m e l l a r bands o f q u a r t z , c h l o r i t e , e p i d o t e . A m p h i b o l e g r a i n s r e p r e s e n t e d by c a r b o n a t e w i t h i n t e r v e n i n g c h l o r i t e p l a t e s , a l o n g f o r m e r c l e a v a g e l i n e s . One s m a l l remnant o f g r e e n b i o t i t e . W - 79 - 50 . Q u a r t z : - 35$? i r r e g u l a r ; g r a d e 3 ; s u t u r e d b o r d e r s ; m i n o r f l a s e r s t r u c t u r e a b o u t e d g e s ; r e p l a c e s f e l d s p a r s ; 5-10$ i n c l u d e d m a t e r i a l , m o s t l y f e l d s p a r . One g r a i n h as a marked t e n d e n c y t o w a r d e u h e d r i s m . F e l d s p a r s : -M i c r o c l i n e - 10$; c l e a r ; s t r a g g l i n g ; p e r t h i t i c i n p l a c e s ; r e p l a c e s p l a g i o c l a s e . P l a g i o c l a s e - 50$; s l i g h t l y d u s t y ; s u b h e d r a l t o a n h e d r a l ; s e r i a t e f r o m 1 mm. t o 5 mm. G r a i n 1:- c o m p a r a t i v e l y u n z o n e d An35« -G r a i n 2:- An35-l8. -2V c o r e - 8 9 ; -2V r i m = 8 8 . some f r a c t u r i n g o f g r a i n s ; o b s t r u c t e d g r o w t h ; much o f z o n i n g i s e l l i p t i c a l . A l t e r a t i o n to S.W.M., e p i d o t e , c h l o r i t e , n o t e x t e n s i v e . x i v Z. Y. X, ,- 2V. G r a i n 1. e ' Sub. 1-±(010)LC -16 7 5 8 9 An35 i $ S.S.W., -87 . 1 ( 0 0 1 ) C 77° 14° 85° An31- 1$ N.W. Sub. 2--L(010)LC 17° 77° 85° An36 5$ N.N.E. - -i(001)C 80" 1 3 ° 8 5 " A n 3 4 2$' N.E.-: An26-2$N:.E. G r a i n 2. • Sub. 1-±(010)L. 17' 7 5 ° 8 3 ' Ah-32 6$.'N.N.E. - 8 7 ' ( G o r e ) ±(001)'C 72° 18' 88* Ah32 1$ S.E.-Sub. I-if010)>L -8' 87' 83° A h l 7 ; 6$ N.N.E'. -86 (Rim)i 1(001);C 8 9 ° 7' 83° A n l 6 1$ N.W. Sub. 2-1(010)'L 14 0 76* 87° An35 1$ N.E. ( C o r e ) n ' . Sub. 2-11.010) L 2 89° 90 1 Anl"9 1$ S.W.-(Rim) orAn23 M a f i c Minerals::.-M i c a - -2V s m a l l . X" =£=c-X" = y e l l o w , n e a r l y c o l o r l e s s Y:* = Z = b r o w n i s h g r e e n . 10$; o c c u r s as 1 . 5 mm. p l a t e s a n d . 5 mm. a g g r e -g a t e s . " A l t e r s t o z o r / s i t e , c h l o r i t e , S.W.M.,. i n p l a t e s . Ac c e s s or y M i n e r a l S-::r-A p a t i t e - T i n y .1 mm. n e e d l e s . P y r r h o t i t e (?) W - 8 5 - 5 0 Q u a r t z : - 2 5 $ ; i r r e g u l a r ; g r a d e 4; many g r a i n s have s u t u r e d b o r d e r s ; r e p l a c e s p l a g i o c l a s e ; 3-5$ i n c l u d e d m a t e r i a l . One f r a c t u r e w h i c h c r o s s e s t h e t h i n s e c t i o n i s f i l l e d w i t h s t r a i n e d q u a r t z . F e l d s p a r s : ; -M i c r o c l i n e - 5 $ ; c l e a r t o c l o u d y ; p e r t h i t e ; g r i d t w i n n i n g i s n o t d i s t i n c t ; r e l a t i o n s h i p t o p l a g i o c l a s e i s n o t d i s t i n c t . P l a g i o c l a s e - 4 5 $ ; d u s t y ; c l o u d y ; 3 - 5 mm; f r a c t u r e d ; m a r g i n s i r r e g u l a r ; e a c h g r a i n i s s h o t w i t h s m a l l e p i d o t e g r a i n s and k a o l i n ; f r a c t u r e s f i l l e d w i t h e p i d o t e ; m i n o r a l t e r a t i o n t o c h l o r i t e . M a f i c M i n e r a l s : - 1 5 $ ; e n t i r e l y a l t e r e d t o c h l o r i t e ( p o s s i b l y p e n i n i t e ) , y e l l o w i s h g r e e n e p i d o t e , t i t a n i t e . A c c e s s o r y M i n e r a l s : - None. Remarks:;- F r a c t u r e s f i l l e d w i t h c o l o r l e s s e p i d o t e where t h e y c r o s s f e l d s p a r ; q u a r t z where t h e y c r o s s q u a r t z . X V W - 96 - 50 . Quartzr- 40$; ir r e g u l a r or blocky; grade 4; 5$ included plagioclase, hornblende, epidote; included plagio-clase grains are c l e a r . Replacement borders with feldspars; replaces amphibole inc l u s i o n . Feldspars-: -Microcline - 5 $ ; c l e a r ; grains 1 . 5 to 2 mm;; p e r t h i t i c ; wavy lamellae; not d i s t i n c t l y twinned. Plagioclase - 3 5 $ ; cloudy and clear; 1-5 mm; obstructed zoning (Plate X I V , B). Some evidence of grain deformation; s l i g h t epidote and kaolin a l t e r a t i o n ; fractures f i l l e d with epidote. Plagioclase Inter-grown with, and may be replacing, mica. Highly zoned grain very near center b i s e c t r i x figure; J .Z X A ( 0 1 0 ) core = 0 An28 X A ( 0 1 0 ) 1/3 & 2/3 out from center - 1 5 Anl5 X A ( O I O ) rim • r 4 An23 Both -indices of rim are d i s t i n c t l y below quartz so zone trend i s assumed to be normal. Extinction angle retains the same sign, so least c a l c i c phase i s Ani 5 . Mafic Minerals:- - t Hornblende - 1 0 $ . - 2 V r 6 5 1 1 0 , maximum Z * c c 2 1 X = yellow green, Y^ green, Z'c bluish green Slender grains up to 1 . 5 mm; replaced by quartz and altered to brownish green c h l o r i t e . B i o t i t e - 10$. - 2 V = 5 X ^ c X ^ pale yellow, Y ~- Z - brownish green. In \ mm. grains and groups of much f i n e r diversely oriented plates; altered to epidote and c h l o r i t e . Accessory Minerals:-Apatite - . 1 mm. and smaller; needles. Magnetite (?) - very small proportion. x v i W - 98 - 50 Q u a r t z ; - 20$; i r r e g u l a r ; g r a i n s h-5 mm; s t r a i n e d ; g r a d e *+; most b o r d e r s a r e c r u s h e d ; age r e l a t i o n s h i p s a r e o b s c u r e . F e l d s p a r s ; M i c r o c l i n e - 5$; s u b - e q u i d i m e n s i o n a l .5mm; g r i d t w i n n i n g ; p e r t h i t e ; some wavy q u a r t z - l i k e i n t e r -g r o w t h s . P l a g i o c l a s e - 50$; c o m p o s i t i o n An30 - 20; c l e a r ; s u b -h e d r a l t o a n h e d r a l ; g r a i n s t o 6 mm; zone d ; p a r t l y r e s t r i c t e d ; some d i s t o r t i o n ; - v e r y s l i g h t a l t e r a t i o n to s m a l l g r a i n s o f e p i d o t e a nd S.W.M. F r a c t u r e d z o n e s c o n t a i n an a g g r e g a t e o f S.W.M; e p i d o t e and q u a r t z . s • , i M a f i c M i n e r a l s ; -H o r n b l e n d e - 15$. Z A c ^2? . -2V- 70 X i ^ y e l l o w , Y'=- g r e e n , Z''-blue g r e e n . S l e n d e r g r a i n s t o 1 . 5 mm; i n t e r g r o w n w i t h a t l e a s t one p l a g i o c l a s e g r a i n ; a l t e r s t o c h l o r i t e . B r o w n i s h g r e e n b i o t i t e o c c u r s i n a f r a c t u r e i n h o r n b l e n d e , a s t i n y d i v e r s e l y o r i e n t e d p l a t e s . B i o t i t e , - 15$. -2V s m a l l ; X'-s y e l l o w , Y — g r e e n i s h brown, Z — b r o w n i s h g r e e n O c c u r s as g r a i n s up t o 1 mm. and a g g r e g a t e s o f s.r.a s m a l l g r a i n s ; some b i o t i t e o c c u r s i n f r a c t u r e s i n h o r n b l e n d e . One m i c a g r a i n i s i n t e r g r o w n w i t h a q u a r t z g r a i n w h i c h i t may be r e p l a c i n g , b u t p r e c i s e i n t e r p r e t a t i o n i s d i f f i c u l t . Much o f b i o t i t e i s de f o r m e d i n t o wavy s h a p e s . I t i s a l t e r e d t o e p i d o t e , c h l o r i t e , q u a r t z . A c c e s s o r y M i n e r a l s : -A p a t i t e Opaque m i n e r a l s - v e r y l i t t l e M a g n e t i t e (?) S e c o n d a r y M i n e r a l s ; -S.W.M. - i n f e l d s p a r . E p i d o t e - i n f e l d s p a r and m i c a . C h l o r i t e - i n a m p h i b o l e and m i c a . Q u a r t z - i n b i o t i t e . x v i i W - 101 - 50 Q u a r t z : - 45 - 50$; i r r e g u l a r ; g r a d e 4 - 5 ; v e r y l i t t l e i n -c l u d e d m a t e r i a l ; r e l a t i o n s h i p s - o b s c u r e d by f l a s e r s t r u c t u r e b u t g e n e r a l s h apes a r e h i g h l y s u g g e s t i v e o f r e p l a c e m e n t . P o o r l y d e v e l o p e d t e n d e n c y t o w a r d e u h e d r i s m . F e l d s p a r s ; -M i c r o c l i n e - 10$; p e r t h i t i c ; 2 mm; c l e a r g r a i n s w i t h i n c l u s i o n s o f h o r n b l e n d e ; wavy l a m e l l a e ; some wavy l a m e l l a e a r e s u b - p a r a l l e l w i t h f r a c t u r e s i n q u a r t z . T h e r e i s a t e n d e n c y t o w a r d s u b - p a r a l l e l i s m o f l a m e l l a e f r o m g r a i n t o g r a i n , and i n a t l e a s t one g r a i n , l a m e l l a e do n o t f o l l o w c l e a v a g e s . P l a g i o c l a s e - 35-40$; An34-29; c l e a r ; 1.5mm; s u b h e d r a l t o i r r e g u l a r ; a l t e r s t o e p i d o t e a nd S.W.M. M a f i c M i n e r a l s : -H o r n b l e n d e - 10$. , Z A c - 2 0 X ^ y e l l o w , Y » y e l l o w i s h g r e e n , Z z b l u e g r e e n . I r r e g u l a r t o s u b h e d r a l g r a i n s t o 1.5 mm; v e r y s l i g h t a l t e r a t i o n t o c h l o r i t e . M i c a - s m a l l -2V; X---yellow,. Y- b r o w n i s h g r e e n , Z ; brown A s e c o n d t y p e X~ y e l l o w , Y - g r e e n Z- g r e e n Type 2 i s c o n s i d e r a b l y a l t e r e d t o c h l o r i t e . B o t h t y p e s a l t e r t o e p i d o t e . A c c e s s o r y M i n e r a l s : -A p a t i t e - r a r e M a g n e t i t e - v e r y l i t t l e . W - 103 - 50 . Q u a r t z ; - 15-20$; i r r e g u l a r ; and i n a g g r e g a t e s o f g r a i n s up t o 1 cm. l o n g ; g r a d e 3; c o n t a i n s 3-5$ i n c l u d e d m a t e r i a l ; . c l e a r l y r e p l a c e s p l a g i o c l a s e . F e l d s p a r s t -M i c r o c l i n e - 10$; i r r e g u l a r ; 1 mm; t w i n n e d and u n t w i n n e d ; c l e a r p e r t h i t e ; r e p l a c e s p l a g i o c l a s e . P l a g i o c l a s e - 40$; An31; d u s t y ; 4-5 mm; b l o c k y ; n o t e x t e n s i v e l y z o n e d ; c o n s i d e r a b l y a l t e r e d t o S.W.M, e p i d o t e . M a f i c M i n e r a l s ; - 20$; e n t i r e l y a l t e r e d t o y e l l o w i s h e p i d o t e , g r e e n p l e o c h r o i c c h l o r i t e , t i t a n i t e , and opaque o x i d e s . B o t h m i c a and h o r n b l e n d e may have b e e n p r e s e n t . x v i i i W - 1 6 6 - 50 Quartz r- 35-)+0%; large blocky grains with s l ightly irregular boundaries; grade 3 ; included material 10-15% (pla;g;i0*~ clase and orthoclase) in the form of small angular and shard shaped masses. One microcline inclusion l i e s along what may be a fracture in quartz. Quartz borders are of a bulbous replacement type. At one point, quartz definitely replaces microcline. Secondary white mica f i l l s some fractures. Feldspars:-Microcline - 2 5 $ ; clear; . 5 - 2 mm; sub-equal dimension's with' perthite; much included plagioclase; replaces plagioclase. Plagioclase - 35$; dusty; two sizes- about 1 mm. and 5-6 mm; not highly zoned. Mafic Minerals:- 15$; entirely altered to yellowish green pleochroic epidote, nearly colorless chlor i te , and hydrated iron oxides. Accessory Minerals:-Apatite Pyrite ('?)'- small grains enclosed in chlori te . W - 1 6 7 - 5 0 Quartz:- 3 0 $ ; irregular grains and aggregates of grains up to 7 mm. long; grade 3-*+; 5$ included material in form of crescent and rounded plagioclase and microcline grains; replaces microcline; less definite inform-ation suggests replacement of plagioclase. Feldspars:-Microcline - 1 0 $ ; clear; 2 mm; includes-' plagioclase; ^perthite; replaces plagioclase. Plagioclase - 30$; AnlS; subhedral; cloudy; 5 mm; zoned; some distort ion; considerably altered to S.W.M; veined by chlori te . Mafic Minerals* 1 5 - 2 0 $ ; almost entirely altered to chlor i te , epidote, hydrated iron oxides, and S.W.M. A few distorted'flakes of greenish brown biotite are only partly altered. Accessory Minerals:-Apatite - Rare. - • ' General subhedrism in plagioclase. None in other minerals. W - 169 - 50. Q u a r t z : - 40$; i r r e g u l a r g r a i n s ; g r a d e 3 ; i n c l u d e d m a t e r i a l 5 - 1 0 $ ; some o f I t i s s m a l l e r g r a i n s o f q u a r t z w i t h a d i f f e r e n t o r i e n t a t i o n ; f r a c t u r e s a r e f i l l e d w i t h s e c o n d a r y w h i t e m i c a , t i t a n i t e and i r o n o x i d e s . These f r a c t u r e s p a r a l l e l one s e t o f f r a c t u r e s i n t h e q u a r t z g r a i n s . R e l a t i o n s h i p s a r e n o t d e f i n i t e , b u t i s l a n d s o f f e l d s p a r , p r o b a b l y m i c r o c l i n e , a r e I s o l a t e d f r o m o t h e r g r a i n s o f i d e n t i c a l o r i e n t a t i o n . •-- R e p l a c e m e n t i s most l i k e l y . F e l d s p a r s : - 5 0 $ . • M i c r o c l i n e and P l a g i o c l a s e - F o r m e r l y p r e s e n t , b u t now a l m o s t e n t i r e l y a l t e r e d t o masses o f v e r y f i n e S.W.M.,'some k a o l i n , b u t a l m o s t no e p i d o t e o r z o i s i t e . M a f i c M i n e r a l s : - E n t i r e l y a l t e r e d t o p a l e c h l o r i t e , sphene, e p i d o t e . W - 170 - 50 : Q u a r t z : - 5 $ ; - i r r e g u l a r ; g r a d e 2 ; 3$ i n c l u d e d m a t e r i a l i n f o r m o f a n g u l a r and c u r v e d f e l d s p a r s . R e p l a c e s . . m i c r o c l i n e a nd p l a g i o c l a s e . F e l d s p a r s : -M i c r o c l i n e - 1 5 $ ; c l e a r ; 2-3 mm;t p e r t h i t e ; r e p l a c e s p l a g i o c l a s e ^ up t o 20$ i n c l u d e d p l a g i o c l a s e . P l a g i o c l a s e - 50$; An36 - 2 5 ; d u s t y ; '3-5 mm; z o n i n g p a r t l y a b r u p t , p a r t l y g r a d a t i o n a l ; t e n d e n c y t o w a r d e u h e d r i s m ; some g r a i n s c o n s i d e r a b l y r e p l a c e d by S.W.M. and e p i d o t e . M a f i c M i n e r a l s : -B i o t i t e - 1 0 - 1 5 $ ; a l m o s t e n t i r e l y a l t e r e d t o g r e e n p l e o c h r o i c c h l o r i t e and e p i d o t e a n d o x i d e s . O r i g i n a l m i c a a p p e a r s t o have b e e n a brown or b r o w n i s h g r e e n b i o t i t e . A c c e s s o r y M i n e r a l s : -A p a t i t e . - 1 $ . V e r y s m a l l h e x a g o n a l n e e d l e s . S e c o n d a r y M i n e r a l s : -. S.W.M. - i n p l a g i o c l a s e . -E p i d o t e - i n p l a g i o c l a s e a nd m i c a . C h l o r i t e , g r e e n p l e o c h r o i c - o c c u r s i n m i c a . H y d r a t e d i r o n o x i d e s - i n m i c a . X X w - 191 - 50. Q u a r t z : - 2 5 $ j i r r e g u l a r ; g r a d e 2; 3 0 - 5 0 $ i n c l u d e d f e l d s p a r s i n i r r e g u l a r s h a p e s ; r e p l a c e s b o t h f e l d s p a r s . F e l d s p a r s : : - • M i c r o c l i n e - 1 5 $ ; c l e a r ; . 5 - 1 m m ; r p e r t h i t e , and some p e r t h i t e l a m e l l a e d e f i n i t e l y q u a r t z - l i k e ; r e p l a c e - ^ ment o f p l a g i o c l a s e a l o n g f r a c t u r e s . P l a g i o c l a s e -'+5 - 5 0 $ ; c l e a r o r c l o u d y ; 2-h mm;- s u b h e d r a l ; z o n i n g p a r t l y g r a d a t i o n a l , p a r t l y a b r u p t ; a l t e r e d t o S.W.M., c h l o r i t e , e p i d o t e ; some g r a i n s much more h i g h l y a l t e r e d t h a n o t h e r s . Z. Y; X. G r a i n 1. ( C o r e ) . - 1 ( 0 1 0)CL- 1 5 ' 76° 8 7 ; o An2' 3 $ N.E. JL( 1 1 0 ) 0 5 5 " 877 3 6 AnO 5 $ E . ( R i m ) . 1 ( 0 1 , 0 ) 0 1 8 8 2 ' ' 8 9 -Anl3 1 $ S". . 1 ( 1 1 0 ) 0 6 0 7 9 335 A n l S 2$ E. ( 0 1 0 ) i s a d i s t i n c t c l e a v a g e and more r e l i a b l e t h a n ( 1 1 0 ) ( 1 1 0 ) i s marked by s t r i n g s of d u s t y i n c l u s i o n s . C o m p o s i t i o n i s An2 - 1 3 . M a f i c M i n e r a l s : - 1 0 $ --H o r n b l e n d e - -2V= 7 0 ^ ZA c - 2 5 X ^ p a l e y e l l o w , YL~ g r e e n , ZM b l u e g r e e n . I n t e r g r o w n w i t h f e l d s p a r s ; a p p e a r s t o be y o u n g e r , b u t r e l a t i o n s h i p s a r e o b s c u r e . B i o t i t e - 5 $ . s m a l l 2V. X i y e l l o w i s h , Y:^ b r o w n i s h g r e e n . - A l t e r e d t o e p i d o t e , c h l o r i t e . A c c e s s o r y M i n e r a l s : : A p a t i t e - l e s s t h a n 1 $ . -M a g n e t i t e - l e s s t h a n 1 $ . W - 2 2 6 - 50 Q u a r t z : - hO - 5 0 $ ; l a r g e i r r e g u l a r g r a i n s and a g g r e g a t e s t o 1 5 mm. l o n g ; g r a d e 2 ; 2 0 $ i n c l u d e d f e l d s p a r s , p l a g i o -c l a s e , and m i c r o c l i n e ; some s m a l l i s o l a t e d i n c l u s i o n s w i t h r e - e n t r a n t b o u n d a r i e s a r e s i m i l a r l y o r i e n t e d . Remnants w i t h r e - e n t r a n t a n g l e s a r e l e f t where d i f f e r e n t q u a r t z g r a i n s meet. Some o f t h e b r o a d e r f r a c t u r e s a r e f i l l e d w i t h S.W.M. and h y d r a t e d i r o n o x i d e s . x x i F e l d s p a r s : — -M i c r o c l i n e - 1 5 $ ; d u s t y ; g r a i n s 1 mm; b l o c k y t o e r r a t i c w i t h i n c l u d e d s u b h e d r a l p l a g i o c l a s e ; r e p l a c e s p l a g i o c l a s e . P l a g i o c l a s e - 3 0-40$; An20; c l o u d y ; 5 mm; s u b h e d r a l a nd a n h e d r a l ; n o t e x t e n s i v e l y z o n e d ; c o n s i d e r a b l y -a l t e r e d t o S.W.M.; much l e s s a l t e r a t i o n t o e p i d o t e and c h l o r i t e ; f r a c t u r e s i n p l a g i o c l a s e ' a r e f i l l e d w i t h c h l o r i t e , S.W.M., and i r o n ox-ides. M a f i c M i n e r a l s : — -15$. E n t i r e l y a l t e r e d t o d i v e r s e l y o r i e n t e d a g g r e g a t e s o f c h l o r i t e and p l e o c h r o i c e p i d o t e o r t o l a m i n a t e d p l a t e s o f g r e e n p l e o c h r o i c c h l o r i t e . The two t y p e s may i n d i c a t e f o r m e r p r e s e n c e o f b o t h h o r n b l e n d e and m i c a . Some sphene and i r o n I d e s f o r m e d . A c c e s s o r y M i n e r a l s : -A p a t i t e • P y r i t e - s m a l l c u b e s i n l a m i n a t e d t y p e o f c h l o r i t e . W - 232 -- 50 Q u a r t z : - 10 - 1 5 $ ; h i g h l y i r r e g u l a r g r a i n s ; g r a d e 1; l i t t l e i n c l u d e d m a t e r i a l ; r e p l a c e s m i c r o c l i n e ; f i l l s l a t e f r a c t u r e s i n p l a g i o c l a s e , b u t e v i d e n c e i s n o t good f o r r e p l a c e m e n t o f p l a g i o c l a s e . F e l d s p a r s : - " --M i c r o c l i n e - 2$; c l e a r t o s l i g h t l y d u s t y ; 1-2 mm; s u b -b l o c k y graains w i t h i n c l u d e d m a t e r i a l ; r e p l a c e s p l a g i o c l a s e . P l a g i o c l a s e - 7 0 $ ; A n 0 - 3 ; d u s t y ; 4 - 5 mm; a l m o s t u n z o n e d ; b r o a d l y e u h e d r a l t o m i c r o c l i n e , e x c e p t i n d e t a i l ; p l a g i o c l a s e c o n t a c t s a n h e d r a l ; some d i s t o r t i o n ; e x t e n s i v e a l t e r a t i o n t o e p i d o t e i n some g r a i n s , l e s s a l t e r a t i o n t o c h l o r i t e and S.W.M. M a f i c M i n e r a l s : - 15$: e n t i r e l y a l t e r e d t o a g g r e g a t e s o f s m a l l g r a i n s o f y e l l o w p l e o c h r o i c e p i d o t e , • s p h ene, and c h l o r i t e . ' The c h l o r i t e i s g r e e n p l e o c h r o i c and l a m i n a t e d . A c c e s s o r y M i n e r a l s : -A p a t i t e - v e r y few t i n y p r i s m s . x x i i W- 239- 50 . Q u a r t z : - 35$j; i r r e g u l a r g r a i n s and a g g r e g a t e s of" g r a i n s i n r a g g e d s t r i n g s up t o 15 ram. l o n g and 3 ram. w i d e ; g r a d e 3 ; v e r y d u s t y ; some s m a l l e r g r a i n s c o n t a i n i n c l u s i o n s of unreplaced ( P l a g i o c l a s e of same o r i e n t a t i o n a s a d j a c e n l ? * g r a i n s . One g r a i n o f q u a r t z i s e n t i r e l y o f r e p l a c e m e n t o r i g i n , p l a g i o -c l a s e b e i n g t h e r e p l a c e d m i n e r a l . Quartz' a l s o r e p l a c e s m i c r o c l i n e p e r t h i t e ; ; . 10 - 3 0 % i n c l u d e d s u b h e d r a l p l a g i o c l a s e g r a i n s . F e l d s p a r s : -M i c r o c l i n e - 1 0 $ ; c l e a r t o s l i g h t l y d u s t y ; sub e q u i -d i r n e n s i o n a l 1 mm; i n c l u d e s and r e p l a c e s p l a g i o c l a s e ; t p e r t h i t e ; f r a c t u r e s f i l l e d w i t h e p i d o t e or q u a r t z . P l a g i o c l a s e - 40$; i n d i c e s j u s t above b a l s a m ; d u s t y ; 4 - 5 mm. b l o c k y g r a i n s ; b r o a d l y s u b h e d r a l t o q u a r t z and m i c r o c l i n e , b u t a n h e d r a l t o o t h e r p l a g i o c l a s e ; m o d e r a t e a l t e r a t i o n t o e p i d o t e and S.W.M.. i n a b o u t e q u a l p a r t s ; c h l o r i t e f i l l s f r a c t u r e s . V e r y l i t t l e z o n i n g . M a f i c M i n e r a l s : - 1 5 $ . . E n t i r e l y a l t e r e d ; now r e p r e s e n t e d by a g g r e g a t e s o f y e l l o w e p i d o t e and c h l o r i t e or l a m i n a t e d c h l o r i t e . A c c e s s o r y M i n e r a l s : -A p a t i t e -W- 253- 50 Q u a r t z : - 3 0 $ ; . i r r e g u l a r 6 mm. a g g r e g a t e s o f s m a l l e r r a g g e d g r a i n s w i t h s u t u r e d b o r d e r s ; g r a d e 4 ; l i t t l e i n -c l u d e d m a t e r i a l ; b u l b o u s m a r g i n s t o w a r d m i c r o c l i n e • I s o l a t e d p a r t s o f m i c r o c l i n e g r a i n s a r e p r o b a b l y r e m n a n t s o f r e p l a c e d m i c r o c l i n e ; - s m a l l p e n i n s i i l a s o f p l a g i o c l a s e p r o t r u d e i i h t o c q - u a r t z . F e l d s p a r s : -M i c r o c l i n e - 20$; c l e a r ; 2 mm. p e r t h i t e and l a m e l l a e a r e sub p a r a l l e l f r a c t u r e s ; i n c l u d e s and r e p l a c e s p l a g i o c l a s e . P e r - t h i t e l a m e l l a e o f one m i c r o c l i n e g r a i n a r e c o n n e c t e d a c r o s s a d i s t u r b e d zone o f <* p a r t l y i n c l u d e d t w i n n e d p l a g i o c l a s e g r a i n . P l a g i o c l a s e - 20$; s l i g h t l y d u s t y ; 2-4 mm; z o n e d g r a d -a t i o n a l l y ; s u b h e d r a l t o q u a r t z and m i c r o c l i n e ; a n h e d r a l t o o t h e r p l a g i o c l a s e ; some f r a c t u r i n g ; r e p l a c e d by q u a r t z and m i c r o c l i n e ; some a l t e r a t i o n t o S.W.M.. x x i i i M a f i c M i n e r a l s : -Amphibole - 20$; p r i s m s up t o l | M . Z>\c=l5 . X'=- b r o w n i s h yellow; green ; Z' = gr e e n . A l t e r e d t o h y d r a t e d i r o n o x i d e s . B i o t i t e - 10$; brown; c o n s i d e r a b l y a l t e r e d " t o l a m i n a t e d g r een p l e o c h r o i c c h l o r i t e and e p i d o t e . A c c e s s o r y M i n e r a l s ; -A p a t i t e -M a g n e t i t e -Secondary M i n e r a l s : -S.W.M, C h l o r i t e , E p i d o t e . W - 261 - 50. Qu a r t z : - ^5$, 6 mm. ag g r e g a t e s o f sutured- g r a i n s ; grade h\ f r a c t u r e s are f i l l e d w i t h c a r b o n a t e s . D e f o r m a t i o n has made i n t e r p r e t a t i o n o f q u a r t z f e l d s p a r N b o u n d a r i e s d i f f i c u l t b u t r e - e n t r a n t b o u n d a r i e s convex toward f e l d s p a r cannot be r e s u l t o f si m u l t a n e o u s c r y s t a l l i z a t i o n . F e l d s p a r s : -M i c r o c l i n e - absent. P l a g i o c l a s e - kOfo) An8 or l e s s ; c l o u d y ; 3 - ^ mm; con-s i d e r a b l y deformed; mosaic type o f b o u n d a r i e s ; a l t e r e d t o e p i d o t e , c h l o r i t e , S.W.M., c a r b o n a t e ; f r a c t u r e s - f i l l e d ' w i t h c h l o r i t e . -Z. Y. X. G r a i n l . l ( 0 l 0 ) L C 88* An6 1% N.W. - \ L ( 0 0 1 ) L C 81° 23* 69° An6 h% N;W. G r a i n 3-1(010)CL 18° 71' 88° AnO 1$ W. K 0 0 l ) C 75" 27* 68' AhO 1$ N.E.. G r a i n h. J-(010)CL" 12° 79* 8 3 ' • A h l 2 10$ N. J - ( 0 0 1)C 80' 28° 6V An2 10$ N.W. M a f i c M i n e r a l s : - 15$; p o s s i b l e gmphibole r e p l a c e d by ag g r e -g a t e s o f y e l l o w i s h - g reen e p i d o t e and green c h l o r i t e , s i m i l a r t o t h a t i n m i c a , S.W.M., sphene, c a r b o n a t e . M i c a r e p l a c e d by c h l o r i t e . -2V l e s s than 5° X=£= c. X=pale y e l l o w , Z ^ b l u i s h g r e e n ; i n t e r f e r e n c e c o l o r ----- - u l t r a b l u e . ( - p e n i n i t e " , r l p i d o l i t e - ^ a p h r o s i d e r i t 4 ) . Other a l t e r a t i o n s - y e l l o w i s h g r e e n e p i d o t e , s p h e n e , q u a r t z . Secondary M i n e r a l s : E p i d o t e , C h l o r i t e , S.W.M., Sphene, q««r + t x x i v W - 28 5 - 50 • Quartz;-. 25-30$: i r r e g u l a r g r a i n s ; grade 5; d u s t y ; r e l a t i o n s o b s c u r e d by f r a c t u r i n g . F e l d s p a r s : -M i c r o c l i n e - 15$; somewhat d u s t y ; 2 mm; m i c r o c l i n e -l i k e , b ut n o t proved t o be m i c r o c l i n e . P l a g i o c l a s e - 30$ A n i 5 - 2 8 ; cloudy.; 1-3 mm-; b l o c k y a n h e d r a l ; d i s t o r t e d ; c o n s i d e r a b l y a l t e r e d t o S.W.M, c h l o r i t e and e p i d o t e ; some f r a c t u r e s f i l l e d w i t h e p i d o t e and S.W.M. M a f i c M i n e r a l s : - , Hornblende- X> y e l l o w c l e a r g r e e n . Z ~ ' A c = 2^ -°. A c i c u l a r forms 1§- mm. l o n g . " About h a l f a l t e r e d t o green c h l o r i t e s i m i l a r to t h a t i n W- 2 6 l , and t o y e l l o w i s h g r een e p i d o t e , sphene, h y d r a t e d i r o n o x i d e s . A c c e s s o r y M i n e r a l s : -A p a t i t e -M a g n e t i t e -Secondary M i n e r a l s : ' -S.W.M.; C h l o r i t e ; E p i d o t e ; H y d r a t e d i r o n o x i d e s . y-_ 287 - 50 Q u a r t z r - 30$: 7 mm..aggregates o f s m a l l e r g r a i n s ; grade 5; b u l b o u s ; p e n e t r a t i o n of both p l a g i o c l a s e and m i c r o c l i n e g r a i n s ; g r e a t e s t i r r e g u l a r i t y toward m i c r o c l i n e . F e l d s p a r s : -M i c r o c l i n e - 20-30$'; c l e a r ; 2-3 mm; sub b l o c k y ; 50$ i n c l u d e d ; rounded t o s u b h e d r a l p l a g i o c l a s e ; r e -p l a c e s p l a g i o c l a s e . P l a g i o c l a s e - 20 -30$; An27-214-; c l e a r t o s l i g h t l y dusty;; 2-3 mm; r e c t a n g u l a r t o b l o c k y ; s u b h e d r a l t o a n h e d r a l ; a l t e r e d t o S.W.M... M a f i c M i n e r a l s : - 10$.- 9 -Hornblende- ZV\ c = 2h X ^ y e l l o w i s h g r e e n ; z'= g r e e n . -2V — 70* - c o n s i d e r a b l y a l t e r e d t o c h l o r i t e , as I n W - 261. - , , B i o t i t e - X'^ p a l e y e l l o w , Y'= Z = brown. A l t e r e d t o c h l o r i t e , e p i d o t e , sphene-.-A c c e s s o r y M i n e r a l s : - A p a t i t e . M a g n e t i t e - bp t h i n s m a l l q u a n t i t i e s . Secondary M i n e r a l s : - S.W.M.,, C h l o r i t e , Sphene. X X V Z - 77 - 50 Qu a r t z : - 25$; i r r e g u l a r g r a i n s ; grade 2; v e r y l i t t l e i n -c l u d e d m a t t e r ; f i l l s i n t e r s t i c e s a g a i n s t f l a t p l a g i o c l a s e f o r m s , but some i s o l a t e d p a r t i c l e s do e x i s t a d j a c e n t t o o t h e r g r a i n s . F e l d s p a r s : - -M i c r o c l i n e - 10-15$; c l e a r ; $.mm, g r a i n s ; h i g h l y i r r e g u l a r shape; 60-80$ i n c l u d e d s u b h e d r a l p l a g i o c l a s e ; r e p l a c e s p l a g i o c l a s e . P l a g i o c l a s e - 40$; An24; c l e a r ; 2-4 mm; zoned through narrow ra n g e ; r e c t a n g u l a r d i s t o r t i o n and f r a c t u r i n g ; moderate a l t e r a t i o n t o S.W.M, M a f i c M i n e r a l s : ^ ' 20$ Hornblende - Almost u n a l t e r e d s u b h e d r a l t o e u h e d r a l shapes; up t o !•§- mm. d i a m e t e r . ZAc A c c u r a c y —2V Ac c u r a c y HOAiDOiQ F a c t o r F a c t o r . ~W. 3 ~ ??T r[Z3. 50° 1 5 6 * - i * * " 44° 2 51° = 70° 2 52° -X=Brown y e l l o w , Y = Green, Z~ B l u e Green. B i o t i t e —-X^: y e l l o w , Y'- Z '-brown. A b s o r p t i o n X ^ Y - Z; P a r t l y a l t e r e d t o green p l e o c h r o i c c h l o r i t e . A c c e s s o r y M i n e r a l s : -A p a t i t e ' M a g n e t i t e Secondary M i n e r a l s : - S.W.M., C h l o r i t e . G r a i n 1. 12° 3 G r a i n 2. r 1 G r a i n 3. 18° 3 G r a i n 4 . 20° 2 G r a i n 5. 8' i x x v i - PART D .•XENOLITHS IN GAMBIER GRANODIORITE T h i n S e c t i o n Page W-60 x x v i i W-78 x x v i i W-S1* x x i x W-87 x x x W-89 x x x i .W-90 ............. x x x i W-95 ' x x x i i W-97 x x x i i i W-99 x x x i v W-100 ............ x x x i v W-186 x x x v i W-187 x x x v i W-188 ............ x x x v i i i W-251 ............ x x x v i i i • W-252 ............. . x x x i x x x v i i XENOLITHS IN GAMBIER GRANODIORITE W —60 - 50- . . - - -Quartz:- 5-10$: small - •§- mm. and l e s s ; grade 0-1; i n t e r s t i t i a l to f e l d s p a r s e t c . ; arcuate margins. Feldspars:-M i c r o c l i n e - None. P l a g i o c l a s e - 45$; An38-42 (J-ZX*C1=8° .12°):- i n d i c e s s i m i l a r to q u a r t z . Zoning i s s l i g h t and grad-a t i o n a l ; c l e a r ; 1 mm.; subhedral; p o s s i b l e a l t e r a t i o n to another f e l d s p a r around edges; a l t e r e d to S .W.M.-, epidote, c h l o r i t e (pale green), k a o l i n . MflfnrV Mi nerflT.gr- 50$' , Amphibole - Maximum Z A c = 22~°, X'^nearly c o l o r l e s s ; Yrz pale brownish green, Z = pale blue green; Occurs as aggregates and ragged growth intermixed w i t h f i b r o u s m a t e r i a l of very low b i r e f r i n g e n c e , (Z"/» c = 12°); f i n e prisms and needles p r o j e c t i n t o p l a g i o c l a s e . , The darker v a r i e t y . i s probably horn-blende, the p a l e r v a r i e t y - a c t i n o l i t e . Acce s s orv M i n e r a l s : -A p a t i t e - l e s s than 1$~. Secondary M i n e r a l s : -~~ Epidote - 10$. 2V near 90° ; le n g t h f a s t ; m i l d l y or non p l e o c h r o i c ; i t i s an a l t e r a t i o n product which occurs ..mostly i n amphibole. Sphene - 10$ - i n femic-minerals. - -Carbonates -•5$ C h l o r i t e - 5$. Paleggreen, i n f e l d s p a r and femic m i n e r a l s . S...W.M. - occurs i n f e l d s p a r . P y r i t e - l e s s than 1$. W - 78 - 50 , Quartzr- 25$: c l e a r ; . 1 - 2 mm. g r a i n s ; grade 1-2; i s o l a t e d s i m i l a r l y o r i e n t e d groups,-or as l a r g e porphyro-b l a s t s w i t h a rim-of hornblende-(Plate X I I I , B ) . The hornblende- of the rim Is s t i l l p a r t l y embedded i n q u a r t z . Some quartz contains zoned rectangular I n c l u s i o n s of p l a g i o c l a s e . The borders of the I n c l u s i o n s , though f a i r l y s t r a i g h t , cross c r y s t a l d i r e c t i o n s at small angles. x x v i i i F e l d s p a r s : -M i c r o c l i n e - None. P l a g i o c l a s e - 35$; c l e a r ; two d i s t i n c t s i z e s ; t h e s m a l l e r - g r a i n s a r e l e s s than 1 mm. i n l e n g t h ; s u b h e d r a l ; h i g h l y zoned and twinned.- C o m p o s i t i o n r anges from An59 t o An31. The l a r g e r g r a i n s a r e about 2 mm. or more i n d i a m e t e r ; c o m p a r a t i v e l y un-zoned and n o t e x t e n s i v e l y t w i n n e d ; c o m p o s i t i o n An 3 5 i 2 . The p o r p h y r o b l a s t s c o n t a i n f i n e p r i s m a t i c g r a i n s of 1 a m p h i b o l e , some of w h i c h a r e o r i e n t e d s i m i l a r l y to one an o t h e r ; t h e s e may have r e p l a c e d f e l d s p a r . A l t e r a t i o n t o S.W.M. i s n o t i c e a b l e i n b o t h types but i s most prominent i n the f i n e , h i g h l y zoned l a t h s , t n some g r a i n s the c o r e i s e n t i r e l y r e p l a c e d by an aggregate o f S*W.M. z-. Y, x. G r a i n l(groundmass) Core JJC010)CE7:. 33'" 59° 76' • ' An59 8$lS'.W... 1.(001)C 57° 51° 56° An62 8$ N.W. Rim JU010)CL" 12° 80° 8 9 ' Ah31 - 1$ N. 1(001)0 81° lh° 81" A n 3 1 7$ N.VT. Remarks:- C010) i s p r o b a b l y more r e l i a b l e than ( 0 0 1 ) . 7iY rim•> . q u a r t z . * 2 r i m q u a r t z . G r a i n 2 ( p o r p h y r o b l a s t ) J_(001 )C 72° 19' 86 An3*+ 1$ N.W". J . ( 1 T 0 )C 69° 55° U V Ah36 1$~N.W.' (001) and (110) a r e e q u a l l y a c c u r a t e , average , v a l u e i s An35» G r a i n 3(groundmass) Gore x("001)C 60° U8 56 An60 5$ Wi Rim K O O l l C 81° 22° 71° Ah7 1$ N.W; M a f i c M i n e r a l s : -Amphibole - 30$; i r r e g u l a r or p r i s m shaped; maximum s i z e i s 1 mm. Age r e l a t i v e t o p l a g i o c l a s e i n d e t e r m i n a t e , appears t o be p r e - q u a r t z . O p t i c p r o p e r t i e s d e t e r m i n e d by Fedorov Method: ZAc -2T 110 110 G r a i n 1 1^" 5 1 + ° = i a e G r a i n 2 16° Ml Average IT" 6*0"°" Then ZAc = 15 -2V = 60 P l e o c h r o l s m : -X'= g r e y i s h green w i t h b l u e t i n t a t b o r d e r s . Y = br o w n i s h green w i t h green b o r d e r s . Z = b l u i s h g r e e n . x x i x -B i o t i t e - 10$; v e r y s m a l l -2V; . , P l e o c h r o i s m X"'~ s t r a w y e l l o w , Y' ^ brown, Z'- brown. A b s o r p t i o n X<-<Y'c Z Occurs as i r r e g u l a r g r a i n s 1 mm. or l e s s ; s l i g h t l y a l t e r e d t o c h l o r i t e and e p i d o t e . P y r i t e - L e s s t h a n 1$. A c c e s s o r y M i n e r a l s : -A p a t i t e - t r a c e . M a g n e t i t e - l e s s t h a n 1$. Secondary M i n e r a l s : -E p i d o t e - i n mica and amphibole; fnpetotea i n mica i s as f o l l o w s : - 2 V * 89° (Fed.) Z* • Y X Cleavage 2 ' " 90° %° S.W.M. - i n f e l d s p a r s . W - 34 - 50 Qu a r t z : - l 5$-20$; c l e a r ; .2 mm; grade 2; i n c l u d e s and r e p l a c e s p l a g i o c l a s e , p a r a l l e l w i t h c l e a v a g e ; i n t e r g r o w n wth h o r n b l e n d e . F e l d s p a r s : - . M i c r o c l i n e - None. P l a g i o c l a s e - 40$; clear;--two s i z e s " - r e c t a n g u l a r and i r r e g u l a r g r a i n s l e s s t h a n 1 mm., and equidirnen-s i o n a l g r a i n s n e a r l y 2 mm. i n d i a m e t e r . The s m a l l e r g r a l n s e a r e s u b h e d r a l i n some ca s e s and show c r y s t a l forms t o q u a r t z ; l a m e l l a r t w i n -n i n g i s pr o m i n e n t . They are a l t e r e d t o S.W.M., p a r t i c u l a r i l y a t c o r e s . The l a r g e g r a i n s a r e not much zoned, and a r e an-h e d r a l . C r o s s t w i n n i n g i s p r e s e n t . Some o f them have a n e a r l y c i r c u l a r r i n g o f S.W.M. near b o r d e r s , B o t h t y p e s c o n t a i n s l i g h t a l t e r a t i o n t o e p i d o t e and c h l o r i t e . M a f i c M i n e r a l s : -Amphibole - 35$; b r o w n i s h green w i t h b l u e green b o r d e r s ; s i z e - 1 mm. o r . l e s s . , Z'A C =18^ X ' - y e l l o w i s h g reen; Y — b r o w n i s h g r e e n ; Z ' c b l u i s h g r e e n ; -2V = 6 5 " j " t h i s amphibole r e -sembles t h a t o f W-78 ve r y c l o s e l y . Some ragged edges o f amphibole p r o j e c t i n t o f e l d -s p a r ; s m a l l p l a g i o c l a s e i n c l u s i o n s i n amphibole; s l i g h t l y a l t e r e d t o green p l e o c h r o i c c h l o r i t e . B i o t i t e - O r i g i n a l c o n t e n t may have been 10$; former p r e s e n c e now sug g e s t e d by c h l o r i t e pseudomorphs. X X X A c c e s s o r y M i n e r a l s : -A p a t i t e -M a g n e t i t e ( ? ) . Secondary M i n e r a l s : -S.W.M. i n p l a g i o c l a s e - moderate. E p i d o t e I n p l a g i o c l a s e - v e r y l i t t l e . C h l o r i t e i n p l a g i o c l a s e - p a l e g r e e n . Q u a n t i t y s m a l l . C h l o r i t e i n amphibole - p l e o c h r o i c g r e e n . Q u a n t i t y s m a l l . Z ' o i s i t e - i n m a f i c m i n e r a l s p o s s i b l y as pseudomorphs a f t e r b i o t i t e ; mixed w i t h c h l o r i t e . C a rbonates - v e r y l i t t l e . N ote:-The n e x t t h r e e specimens ( W -87 , 8 9 , and 9 0 ) were c o l l e c t e d from a x e n o l i t h o f t u f f 2 5 . f e e t i n w i d t h , n o r t h o f Hope P o i n t . The x e n o l i t h i s bounded p a r t l y by f a u l t s . The t r e n d of the x e n o l i t h and bedding i s 0 0 7 • The margins o f the c o n t a c t a re d i s t i n c t l y , s e d i m e n t a r y , P l a t e X I , A. ; Bedding i s obsc u r e f o u r f e e t from the margin and i m p e r c e p t i b l e s i x f e e t from-the m a r g i n . The c e n t r a l p a r t , r e p r e s e n t e d by W - 9 0 , has the same c o l o r and appearance as the o u t e r p a r t , except t h a t g r a i n i s c o a r s e r and bedding, has been o b l i t e r a t e d . W - 8.7 - 50 One f o o t from m a r g i n o f i n c l u s i o n . Q u a r t z : - .5$. C o n t a i n s minute r o d s o f a p a t i t e - l i k e m i n e r a l . F e l d s p a r s f - 7 5 $ ; c l o u d y ; two k i n d s - some w i t h i n d e x below balsam, some w i t h i n d e x n e a r ' b a l s a m . L a t h shaped g r a i n s w i t h maximum e x t i n c t i o n a n g l e - 5°(15 g r a i n s ) , hence l a t h s a re o l i g o c l a s e . Mosij/^c i n t e r l o c k i n g g r a i n s have an i n d e x below balsam, n o t a c c u r a t e l y i d e n t i f i e d . A l t e r a t i o n P r o d u c t s :> P a l e green c h l o r i t e , z o i s i t e ? , c a r b o n a t e . M a f i c M i n e r a l s : -Sphene ) x<& E p i d o t e ) ~ J I Secondary M i n e r a l s : - . . /S.W.M. ) E p i d o t e ) none e x t e n s i v e . C h l o r i t e ) XXXI. W - 89 - 50 S i x - f e e t from margin o f i n c l u s i o n . ' Q u a r t z : - 5$ or l e s s ; c l e a r ; l e s s than 0.2 mm; grade 0; i n t e r s t i t i a l t o f e l d s p a r g r a i n s . F e l d s p a r s : -M i c r o c l i n e - none. P l a g i o c l a s e - 80$; c l o u d y ; two d i s t i n c t s i z e s - l e s s t h a n j? mm. a n d . l mm. or more. The s m a l l e r s i z e o c c u r s as mosaic i n t e r l o c k i n g o r s u b h e d r a l r e c t -a n g u l a r g r a i n s ; t h e y a r e h i g h l y zoned; i n d e x v a r i e s from c o n s i d e r a b l y above t o s l i g h t l y below balsam. The l a r g e r type i s much -less zoned; 71* j u s t l e s s t h a n balsam, ^  j u s t g r e a t e r t h a n balsam. F e l d s p a r s c l o s e l y resemble t h o s e of W-78, b u t w i t h l e s s euhedrism. B o t h t y p e s are' a l t e r e d t o p a l e g r e e n c h l o r i t e , v e r y . l i t t l e S.W.M.,, and c o n s i d e r a b l e C a r b o n a t e . ' " O f f c e n t e r f i g u r e on l a r g e r s i z e g i v e s c o m p o s i t i o n An30 ± 5. Maximum e x t i n c t i o n a n g l e ( 15 g r a i n s ) o f groundmass p l a g i o c l a s e »2 3 °j i n d i c e s j u s t above balsam. There-f o r e groundmass p l a g i o c l a s e i s andfcsine about An40. M a f i c M i n e r a l s : - 2$. M a f i c m i n e r a l s a r e e n t i r e l y a l t e r e d t o sphene, c h l o r i t e . A c c e s s o r y M i n e r a l s : -A p a t i t e . Secondary M i n e r a l s : - T o t a l 20$. Sphene, C h l o r i t e , S.W.M., Carbonate. W - 90 - 50 , Twelve f e e t from m a r g i n of i n c l u s i o n . Q u a r t z : - 2$ or l e s s ; c l e a r ; 0.2 mm; grade 0. F e l d s p a r s : -M i c r o c l i n e - None. P l a g i o c l a s e - 85$. V e r y s i m i l a r t o W-89, but c o a r s e r . S m a l l g r a i n s have a maximum o f mm. and l a r g e g r a i n s have a maximum o f 3 mm. I n t h i s s e c t i o n t h e r e a re a number o f v e r y s l i g h t l y zoned s u b h e d r a l p l a g i o c l a s e g r a i n s o f i n t e r m e d i a t e s i z e . I n d i c e s o f b o t h s i z e s a r e s l i g h t l y l e s s t h a n balsam', and n e i t h e r type i s h i g h l y zoned. A l t e r a t i o n P r o d u c t s : - C a r b o n a t e ^ c o n s i d e r a b l e S.W.M., and p a l e green c h l o r i t e . x x x i l M a f i c M i n e r a l s - : - One a r e a which, may have been a Ca-F'e-Mg s i l i c a t e ^ , i s - e n t i r e l y a l t e r e d t o green c h l o r i t e . E l s e w h e r e , sphene -occurs i n s m a l l groups of g r a i n s . Opaque o x i d e or s u l p h i d e - 1$. Content of m a f i c m a t e r i a l i s s l i g h t l y above t h a t o f t h i n s e c t i o n W-89. Accessory- M i n e r a l s : ; -A p a t i t e . Secondary M i n e r a l s : S.W.M. i n " f e l d s p a r . E p i d o t e i n m a f i c m i n e r a l s . C h l o r i t e i n m a f i c m i n e r a l s and f e l d s p a r . Sphene. Carbonate i n f e l d s p a r . W- 95 - 50 :• Qu a r t z : - 15$; c l e a r ; mm. a n d . s m a l l e r ; grade 0 - 1;^  i n t e r s t i c e s - a n d m i c r o g r a p h i c i n t e r g r o w t h s . F e l d s p a r s : -M i c r o c l i n e - None. P l a g i o c l a s e - presen t , c o n t e n t i s s m a l l ; i n d i c e s v e r y near balsam; unzoned; h i g h l y a l t e r e d t o e p i d o t e . M a f i c ' M i n e r a l s : - , . 0 Amphibole - 15$. Z/Tc = l V (6 g r a i n s ) - 2 Y = - 7 0 ° X —very p a l e y e l l o w ; X'- p a l e green; Z'~ p a l e g r e e n . Forms s l e n d e r f e a t h e r y a g g r e g a t e s . I t appears t o be of secondary o r i g i n , some a c i c u l a r p r i s m s p r o -j e c t i n t o f e l d s p a r and q u a r t z . A c c e s s o r y M i n e r a l s : -A p a t i t e -Secondary Mi n e r a l s : : - •' , • E p i d o t e - 25$. -2V—85°, o p t i c p l a n e c l e a v a g e and p a r a l l e l w i t h p a r t i n g . X'Ac - 3 ° , X A ,001*. 69' 'Z* A ,001- 22' X ' ' - c o l o r l e s s ; Y — p a l e y e l l o w ; Z^-pale y e l l o w . I t o c c u r s t h r o u g h o u t the t h i n s e c t i o n and appears t o r e p l a c e b o t h m a f i c and f e l s i c m i n e r a l s . C h l o r i t e - p a l e g r e e n , not p r o m i n e n t . K a o l i n - du s t y a l t e r a t i o n f e l d s p a r s . x x x i i i W - 97 - 50 Quartz:- 5 - 10$; c l e a r ; 1 mm; grade 2; i n c l u d e s h o r n -b l e n d e and p l a g i o c l a s e , s i n g l e g r a i n s or a g g r e g a t e s o f s m a l l g r a i n s ; i n p l a c e s g r a i n s of s i m i l a r o r i e n t a t i o n a r e i s o l a t e d . F e l d s p a r s : -M i c r o c l i n e - None. P l a g i o c l a s e - 40$; c l e a r ; two s i z e s ; s m a l l s u b h e d r a l \ mm. and l a r g e r 2 mm. g r a i n s ; b o t h k i n d s a r e zoned, some o f th e l a r g e r g r a i n s c o n t a i n c l e a r q u a r t z i n c l u s i o n s w i t h l o w e r i n d e x . Some s e p a r a t e d q u a r t z and h o r n b l e n d e i n c l u s i o n s a r e s i m i l a r l y o r i e n t e d . C o m p o s i t i o n of one l a r g e g r a i n An4l-28", some have i n d i c e s below balsam. A l t e r e d t o e p i d o t e , S.W.M., mic a ( ? ) , z o i s i t e ( ? ) . M a f i c M i n e r a l s : Amphibole - o c c u r s i n a v a r i e t y of shapes up t o 1 mm. l o n g ; r e l a t i o n s h i p s t o o t h e r m i n e r a l s a r e such t h a t age r e l a t i o n s h i p s cannot be d e c i p h e r e d . I t oc c u r s as s i m i l a r l y o r i e n t e d f i n e p r i s m s i n some p l a g i o c l a s e . A l t e r a t i o n v e r y m i n o r . Hornblende - ( F e d o r o v ) . ZAc -2V 110A110 G r a i n 1. 13' 50° 55 ' , r ! r° G r a i n 2. 22" ££L Average - 17 "5% X - y e l l o w ; Y ^  brownish green; E - b l u i s h g r e e n . When Y or Z i s i n t h e p l a n e o f the t h i n s e c t i o n , the g r a i n s appear t o have d i s t i n c t l y b l u e b o r d e r s . B i o t i t e - 10$; s m a l l -2V; f X — c. X'= s t r a w y e l l o w ; Y = brown; Z ^ d a r k brown; A b s o r p t i o n X<-<Y<< Z; Occurs as i r r e g u l a r masses up t o 1 mm. diam e t e r i n t e r g r o w n w i t h o t h e r m i n e r a l s . A c c e s s o r y M i n e r a l s : -A p a t i t e -M a g n e t i t e -Secondary M i n e r a l s : -S.W.M. - 15$; o c c u r s I n p l a g i o c l a s e . E p i d o t e - 5$; o c c u r s i n m i c a and p l a g i o c l a s e . x x x i v W - 99 -50 Qu a r t z ; - 10$; c l e a r ; two s i z e s , v e r y s m a l l 0 . 1 mm. or l e s s , and medium 3- 1* mm.; grade 2; the s m a l l e r g r a i n s a re i n t e r s t i t i a l t o o t h e r m i n e r a l s , the l a r g e r ones o c c u r as eye shaped masses w i t h i n c l u d e d r e c t a n g u l a r h o r n b l e n d e , p a r t i c u l a r l y a t b o r d e r s . F e l d s p a r s t -M i c r o c l i n e - none. P l a g i o c l a s e - 20$; c l e a r ; 2 mm. p o r p h y r o b l a s t s i n m a t r i x o f \ mm. s u b h e d r a l g r a i n s . P o r p h y r o b l a s t - An39, n e a r l y unzoned. The s m a l l e r g r a i n s a re more h i g h l y zoned and a l l i n d i c e s a r e above balsam. S l i g h t a l t e r a t i o n t o S.W.M. and e p i d o t e . Some o f l a r g e r p l a g i o c l a s e g r a i n s c o n t a i n p r i s m s and i r r e g u l a r masses o f h o r n b l e n d e . M a f i c M i n e r a l s : -Amphibole - 50$; -2V = 65°±- i Z*c -19*. X ; p a l e y e l l o w ; Y'=^green; Z'-green. Occurs as v e r y f i n e e q u i d i m e n s i o n a l g r a i n s , m o s t l y l e s s t h a n .1 mm.,of p r i s m a t i c or i r r e g u l a r shape; i n t e r g r o w n w i t h f e l d s p a r s ; some i s o l a t e d p r i s m s i n c l u d e d i n p l a g i o c l a s e . Amphibole i s u n a l t e r e d . M i c a - B i o t i t e may have c o n s t i t u t e d 5-10$ o f the r o c k f o r m e r l y . I f so , i t i s now a l t e r e d t o l a m i n a r masses o f e p i d o t e ( c o l o r l e s s ) and green c h l o r i t e . A c c e s s o r y M i n e r a l s : A p a t i t e and M a g n e t i t e a r e both p r e s e n t b u t v e r y s p a r s e . Secondary M i n e r a l s : S.W.M. - i n f e l d s p a r s . E p i d o t e c h l o r i t e - pseudomorphous a f t e r mice* C h l o r i t e i n f e l d s p a r s . W - 1 0 0 - 50 Q u a r t z : - 20 -30$; i r r e g u l a r g r a i n s , p a r t s o f whi c h may be i s o l a t e d from one a n o t h e r ; grade 2; hO - 50$ i n c l u d e d m a t e r i a l i n the form of e u h e d r a l p l a g i o -c l a s e . R e l a t i o n s d i f f i c u l t t o i n t e r p r e t b u t q u a r t z f i l l s I n t e r s t i c e s between p l a g i o c l a s e g r a i n s and e i t h e r r e p l a c e s or i s r e p l a c e d by brow n i s h b i o t i t e . X X X V / F e l d s p a r s : -M i c r o c l i n e - Absent. -P l a g i o c l a s e - 40$; zoned; An40 - 2 7 , A n 4 9 - 3 4 ; c l e a r ; twinned subhedral g r a i n s ; euhed'rism best a g a i n s t q u a r t z . Most are l e s s than . 5 mm. lon g ; d i v e r s e o r i e n t a t i o n . Moderately a l t e r e d to S.W.M. Mafic M i n e r a l s : -Hornblende' - 3 5 $ . 2V= 7 0 i 5 ' , Z / » c = 1 9 * X ^ y e l l o w , Y''=-brownish green, Z ^ g r e e n to b l u e . I r r e g u l a r 1 mm. g r a i n s and aggregates of g r a i n s 2 -3 mm. ac r o s s , i n t e r l o c k i n g to smooth boundaries w i t h p l a g i o c l a s e ; r e l a t i o n s d i f f i c u l t to deci p h e r . S l i g h t a l t e r a t i o n to c h l o r i t e and e p i d o t e . B i o t i t e - 5 $ . -2V= 5 X ^ c . X-'- y e l l o w , Y^ Z = g r e e n i s h brown. Ragged boundaries; intergrown w i t h p l a g i o c l a s e ; d i v i d e s one g r a i n of hornblende; a l t e r s to c h l o r i t e and epidote ( P l a t e XIX, A'.). Accessory M i n e r a l s : -A p a t i t e Magnetite- 1 - 2 $ . ' • _ Secondary M i n e r a l s : -S.W.M. - i n f e l d s p a r s . C h l o r i t e )•> both occur i n mafic m i n e r a l s i n small Epidote )> q u a n t i t y . Note;-Specimens W-186, W-187, and W-188, were c o l l e c t e d n o r t h - e a s t of Hope P o i n t . W-186 and W-187 are from a x e n o l i t h 10 to 15 f e e t wide. W-186 was c o l l e c t e d near the center o f the x e n o l i t h and W-187, near the border zone. A l t e r a t i o n of the m i n e r a l s of W-186 p r e c l u d e s accurate comparison of composition. However, the border zone does appear to have more q u a r t z and l e s s mafic m a t e r i a l . W-188 was taken from a dense white l e n t i c u l a r mass w i t h i n a x e n o l i t h adjacent to the above x e n o l i t h . This l e n t i c u l a r mass eigh t e e n inches by s i x inches i s separated from the outer p a r t of the i n c l u s i o n by a one i n c h g r a n i t i c zone. Some quartz c r y s t a l s c r o s s the margin between the g r a n i t i c zone and the dense white l e n t i c u l a r c o re. The same i s true of the boundary between the g r a n i t i c zone and the outer p a r t of the x e n o l i t h . x x x v i The outer r e g i o n of the x e n o l i t h i s m e g a s c o p i c a l l y i n d i s t i n g u i s h a b l e from the!-.adjacent x e n o l i t h (W- 1 8 6 , 1 8 7 ) . The s t r i k e of the dense white core i s 0 6 0 ° . W- 1 8 6 - 50 . Quartz:- 15$5 c l e a r ; 1-g- mm; grade 1 - 2 ; i n c l u s i o n s of sub-h e d r a l to r e c t a n g u l a r p l a g i o c l a s e and hornblende; r e p l a c e s p l a g i o c l a s e . Grains are i r r e g u l a r i n d e t a i l . F e l d s p a r s : -M i c r o c l i n e - None. P l a g i o c l a s e - 35$; h i g h l y a l t e r e d and not determined; in d i c e s ? v a r y from s l i g h t l y above quartz to s l i g h t l y above ha q u a r t z . Hence p l a g i o c l a s e i s probably c a l c i c o l i g o c l a s e or sodic andesine. A l t e r e d t o S.W.M., e p i d o t e , c h l o r i t e . M a f i c M i n e r a l s ; - o / . - , Amphibole - k-0% o r i g i n a l l y ; -2V = 6 0 -70 ;• Z AQ - 2 6 . X ^ p a l e y e l l o w ; Y-brown; Z- brownish green. X'=^pale y e l l o w ; Y'—brown; Z= blue - green. Occurs as ragged, h i g h l y a l t e r e d masses 1 - 2 mm. i n . diameter. A l t e r a t i o n products are carbonate, epidote and p l e o c h r o i c green c h l o r i t e . B i o t i t e - may have been one of the o r i g i n a l c o n s t i t u e n t s as i n d i c a t e d by c h l o r i t e , e p i d o t e , pseudomorphs. Accessory M i n e r a l s : -A p a t i t e , and magnetite - combined amount about 2 $ of rock, though a p a t i t e i s i n very s m a l l q u a n t i t y . Secondary M i n e r a l s : -S.W.M. - much of f e l d s p a r s . Carbonate - c o n s i d e r a b l e amount i n mafic m i n e r a l s . C h l o r i t e - green p l e o c h r o i c , deep blue i n t e r f e r e n c e c o l o r ; - occurs i n mafic m i n e r a l s . E p i d o t e - pale y e l l o w . Sphene - a s s o c i a t e d w i t h mafic m i n e r a l s . W - 187 - 50 . Quartz:- 25$: c l e a r ; .5 - 3mm; i r r e g u l a r ; i n c l u d e s and r e p l a c e s p l a g i o c l a s e . F e l d s p a r s : -M i c r o c l i n e - None. x x x v i i P l a g i o c l a s e - 45$; much a l t e r e d to S.W.M. Occurs as zoned grains' g e n e r a l l y l e s s than 1 mm; some g r a i n s are cfcoudy, some are c l e a r . Z, Y.- X. E r r o r Grain "1. groundmass -Core -1.(010) L 13 79 83 An33 6% N.E. 1(001)C 75 15 88 Ah32 1$ N ;W. Rim 1(010)L 7 90 83 An20 • 7$ N. - 1 ( 0 0 1 ) C 86 6 87 An22 2$ S . W . G r a i n 2. groundmass l ( 0 0 l ) L 69 24 87 An38 1(010)L 10 77 87 An32 (010) i s l e s s a c c u r a t e than (001) G r a i n 3« groundmass . . -Gore K O O D c . 69 23 79 An38 2% N . W . Rim 1(001 ) 0 80 11 84 Ah25 1$' N.E. Gr a i n 4. encl o s e d i n quartz - unzoned. 1(010)C- 9 83. 87 Ah28 3$' N.E-1(001)G 76 15 84 Ah28 2% N.E. The most c a l c i c p l a g i o c l a s e i s An38 and the l e a s t c a l c i c i s An20. The unzoned g r a i n i n c l u d e d i n • quar t z i s Ah28. Mafic M i n e r a l s : - 3 0 $ . Amphibole. - g r a i n s and. masses -of g r a i n s up to 2 mm.; ragged to l i n e a r margins; a l t e r e d to epi d o t e , c h l o r i t e . ZAc -2V 1 1 0 A 1 1 0 G r a i n 1 28 Gr a i n 2 18 ... .64 48 * 132 G r a i n 3 12 64 Weighted average Z'Ac^Ol x 28> (2 x 18) -(1 x 12) /4 19 . average •-2V,=-64. Both 2V determinations are c o n s i d e r e d to be of equal v a l u e . X- y e l l o w i s h brown; Y - brownish green; • Z = green w i t h blue green borders. Mica - only'pseudomorphs of c h l o r i t e and epidote r e -main as I n d i c a t o r s of the p o s s i b l e former presence of mica. Accessory M i n e r a l s : A p a t i t e and. Magnetite - t o t a l content very s m a l l . Secondary M i n e r a l s : S.W.M. - i n f e l d s p a r s , some g r a i n s of which are much a l t e r e d . E p i d o t e - s i n g l y and i n masses i n f e l d s p a r s and amphibole. C h l o r i t e Sphene. x x x v i i i W - 188 - 50 . . . Quartz:'- 50$; c l e a r ; 2 mm.; grade 2; o c c u r s p p a r t l y a a s -s o l i t a r y masses but mostly as f i n e worm-like growths i n m i c r o c l i n e , and p l a g i o c l a s e . „ The myrmekitic quartz g r a i n s are sub p a r a l l e l i n one dimension; but are t r i a n g u l a r i n c r o s s s e c t i o n . F e l d s p a r s : - I+5$. Some of the f e l d s p a r s i n the i n t e r g r o w t h are d e f i n i t e l y m i c r o c l i n e . A l l f e l d s p a r has an index l e s s than q u a r t z . A few g r a i n s o f m i c r o c l i n e up to 2 cm. ac r o s s , a r e not m i c r o g r a p h i c . M a f i c M i n e r a l s : -E p M o t e - as i s o l a t e d g r a i n s and-aa masses of p l e o c h r o i c g r a i n s (X'= col o r l e s s . ; Z'— very p a l e - g r e e n . ) . Max-imum s i z e - 2 em. l o n g . T o t a l content about 5$ or l e s s . Remarks:- 75% of t h i s t h i n s e c t i o n i s a f i n e m i c r o g r a p h i c i n t e r g r o w t h of quartz and potash or sodic f e l d s p a r . W - 251 - 50. Quartz:- 10$; c l e a r ; 0.1 mm; grade 0; mosaic in t e r g r o w t h s w i t h f e l d s p a r and ep i d o t e . F e l d s p a r s : -M i c r o c l i n e - not r e c o g n i z e d . P l a g i o c l a s e - h0%. F i n e g r a i n e d mosaic of c a l c i c f e l d -spar 0.05"mm. and l e s s . Maximum e x t i n c t i o n angle of 10 g r a i n s -33" • Index w e l l above balsam so p l a g i o c l a s e i s An57i3» Mafic M i n e r a l s : - . - - , • -Hornblende - 5$; 0 .05 to 0-.1 mm; -X--yellowish; Y - green; Z'= blue green. He CUB'S as f i n e needles which p r o j e c t i n t o f e l d s p a r and as masses of small g r a i n s . E p i d o t e - ^-0$; 0.1 mm. g r a i n s , e q u i d i m e n s i o n a l , mosaic. *2V-- 85° ; Z'A cleavage = kh°. Magnetite - 5$; s m a l l - 0.1 mm. Sphene - 0.1 mm. aggregates o f ve r y f i n e g r a i n s . A p o o r l y developed banded e f f e c t i s produced by a l t e r -n a t i n g epidote r i c h and p l a g i o c l a s e r i c h zones. xxxix~ W - 2 5 2 - 50 -T h i s specimen was taken from a shadowy zone, s l i g h t l y darker than the g r a n o d i o r i t e m a t r i x . I t appeared to be a remnant of a very h i g h l y a l t e r e d or g r a n i t i z e d x e n o l i t h . Quartz:- 3 0 $ ; c l e a r ; up to 1 mm; grade 2 ; wavy, s l i g h t l y b u l g i n g or i r r e g u l a r boundaries; age r e l a t i v e to f e l d s p a r s obscure. F e l d s p a r s : -M i c r o c l i n e - 20$; c l e a r ; 2 mm; i r r e g u l a r ; r e p l a c e s p l a g i o c l a s e and le a v e s r e c t a n g u l a r remnants. P l a g i o c l a s e - 20 - 2 5 $ ; s l i g h t l y dusty; 1 . 5 mm; h i g h l y zoned; subhedral; r e p l a c e d by m i c r o c l i n e . Centered f i g u r e g i v e s composition of one g r a i n as; core Anl9; i n t e r m e d i a t e p a r t An35; r i m Anl9« hy r i m i s l e s s than £ f t q u a r t z . Mafic M i n e r a l s : - -Amphibole - 40$. Z A c ^ 2 5 ; - 2 V = 6 5 X'=: p a l e yellow; Y'—brownish green; Zk green to b l u i s h green; s m a l l equidirnensional g r a i n s . 1 - . 5 mm. i n diameter form mosaic p a t t e r n v/ith f e l d s p a r s and q u a r t z . Minor a l t e r a t i o n to e p i d o t e , p a r t i c u l a r ly.yak ongg f r a c t u r e s . Accessory M i n e r a l s : -A p a t i t e - many g r a i n s are q u i t e small but a t l e a s t one • i s about 1 mm. l o n g . Sphene - g r a i n s up to 1 mm. Secondary M i n e r a l s : -Epidote - occurs as aggregates which show no i n d i c a t i o n t h a t they are a l t e r a t i o n products from other m i n e r a l s , and as a l t e r a t i o n products o f f e l d s p a r s or f r a c t u r e f i l l i n g . E p i dote which f i l l s f r a c t u r e s i n hornblende i s more y e l l o w and more d i s t i n c t l y p l e o c h r o i c than epidote which f i l l s f r a c t u r e s i n f e l d s p a r . o 

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