"Science, Faculty of"@en . "Earth, Ocean and Atmospheric Sciences, Department of"@en . "DSpace"@en . "UBCV"@en . "Von Rosen, G. E.A."@en . "2011-09-19T17:31:50Z"@en . "1966"@en . "Master of Science - MSc"@en . "University of British Columbia"@en . "An 800 foot-square outcrop of a gneiss-breccia body at Pasco creek, 3 miles north along the highway from Horseshoe Bay, B.C. was mapped, and its relationship to the gneiss country rock studied. A survey of the literature of breccias included in the present thesis was used as a basis, together with the field data, for a method of breccia formation proposed as a result of this work.\r\nThe body was found to be pipe-like in shape, following directions of structural weakness in the rock. The size of breccia fragments and varying amounts of matrix, as well as the border phase dioritic rocks were thought to have resulted from several processes active in the formation of the breccia. Among these explosive action of gases ahead of an intrusive body, together\r\nwith fluidization of a mixture of these gases and shattered country rock are thought to be of prime importance in the formation of the breccia."@en . "https://circle.library.ubc.ca/rest/handle/2429/37447?expand=metadata"@en . "PASCO CREEK BRECCIA Horseshoe Bay, B. C. by G. E. A. von Rosen B.So., U n i v e r s i t y of B r i t i s h Columbia, 1962 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF ' THE REQUIREMENTS FOR THE DEGREE OF . Master of Science i n the Department of GEOLOGY -We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1966 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n Department The U n i v e r s i t y o f B r i t i s h C olumbia Vancouver 8, Canada ABSTRACT An 800 f o o t - s q u a r e outcrop of a g n e i s s - b r e c c i a body a t Pasco c r e e k , 3 m i l e s n o r t h a l o n g the highway from Horseshoe Bay, B.C. was mapped, and i t s r e l a t i o n s h i p to the g n e i s s c o u n t r y r o c k s t u d i e d , A survey of the l i t e r a t u r e of b r e c c i a s i n c l u d e d i n the p r e s e n t t h e s i s was used as a b a s i s , t o g e t h e r w i t h the f i e l d d a t a , f o r a method of b r e c c i a f o r m a t i o n proposed as a r e s u l t of t h i s work. The body was found to be p i p e - l i k e i n shape, f o l l o w i n g d i r e c t i o n s of s t r u c t u r a l weakness i n the r o c k . The s i z e of b r e c c i a fragments and v a r y i n g amounts o f m a t r i x , as w e l l as the b o r d e r phase d i o r i t i c r o c k s were thought to have r e s u l t e d from s e v e r a l p r o c e s s e s a c t i v e i n the f o r m a t i o n of the b r e c c i a , Amorig these e x p l o s i v e a c t i o n of gases ahead of an i n t r u s i v e body, t o -g e t h e r w i t h f l u i d i z a t i o n of a m i x t u r e of these gases and s h a t t e r e d c o u n t r y r o c k are thought to be of prime importance i n the f o r m a t i o n of the b r e c c i a . i i . iv. TABLE OF CONTENTS I. INTRODUCTION 1 \u00E2\u0080\u00A2 Location and. Access 2 Physiography and Topography 2 Aknowledgements 3 II. GENERAL GEOLOGY OF THE AREA . III. GNEISS-BRECCIA PIPE 5 Fragments 6 1. Schistose fragments 6 2. Gneissic fragments 7 3. Gneiss blocks 7 4 . Granitic pebbles & Pegm. inter-clast material . 8 Matrix 10 Structures 11 1. Orientation of clasts 11 2. Deformation of clasts 11 3. Shear zones 12 4 . Gouge-filled faults 12 5. Joints 12 6. Foliation in border phases 12 7* Secondary foliation 13 Relation of Pipe to Country Rocks 13 1. Gneiss 13 2. Hornblendite 14 V TABLE OP CONTENTS Rel a t i o n of Pipe to Country Rocks (cont'd) 13 3. Border phases of b r e c c i a 14 a. P o r p h y r i t i c d i o r i t e 15 b. F o l i a t e d granite 16 c. Dikes 19 Summary of C h a r a c t e r i s t i c s of t h i s Breccia , 20 IV. EXISTING THEORIES OF BRECCIA FORMATION \u00E2\u0080\u00A2\u00E2\u0080\u009E ' 23 V. INTERPRETATION OF BRECCIA FORMATION ,28 Pre-breccia Geology 28 O r i g i n of Pasco Gneiss-Breccia Pipe 29 A p p l i c a t i o n of Data to Theory 31 Conclusion ; 35 v i . LIST OF PLATES AND FIGURES Figures 1 Index Map: Vancouver North, British Columbia .opp. p. 2 2a Outcrop Distribution Flap, Pasco Creek, Horseshoe Bay, British Columbia appendix 2b Map of Breccia Body, Pasco Creek, Horseshoe Bay, B.C. appendix 3 Diagrammatic Cross-sections, Pasco Creek appendix Plates l a . Mottled plagioclase in typical groundmass opp. p. 7 b. Contact of amphibolite clast with groundmass . opp. p. 7 c. Pyrite-epidote associations opp. p. 7 Ila. Pegmatitic space-fillings and rimmed clasts opp. p. 8 b. Pegmatitic plagioclase against matrix opp. p. 8 c. Recrystallized intruded matrix opp. p. 8 I l i a . Breccia near contact with diorite opp. p. 10 b. Breccia at contact with diorite opp. p. 10 TVa. Granitic pebbles in breccia opp. p. 11 b. Sub-horizontal orientation of fragments opp. p. 11 Va. Gneiss fragment with ellipsoidal shape opp. p. 12 ' b. Deformed elongate breccia clast; opp. p. 12 v i i . Va. Gneiss country rock .opp. p. 13 b. Augen gneiss i n country rock \u00C2\u00A9PP. P\u00C2\u00AB 13 V i l a . Contact of p o r p h y r i t i c d i o r i t e with b r e c c i a ....... opp. p. 15 b. Contact of d i o r i t e dike with b r e c c i a opp. p. 15 V i l l a . P l a g i o c l a s e phenocryst opp. p. 16 b. A l t e r e d p l a g i o c l a s e phenocryst and groundmass ..... opp. p. 16 IXa. Pink, f o l i a t e d border phase rock opp. p. 17 b. S e r i o i t i z e d , f o l i a t e d border phase rock opp. p. 17 Xa. Zoned p l a g i o c l a s e phenocryst- crossed n i c o l s opp. p. 18 b. Zoned p l a g i o c l a s e phenocryst- p l a i n p o l a r i z e d l i g h t opp. p. 18 XIa. South contact of b r e c c i a on road opp. p. 20 b. Relations near north contact of b r e c c i a pipe opp. p. 20 INTRODUCTION B r e c c i a o c c u r r e n c e s have l o n g r e c e i v e d s p o r a d i c a t t e n t i o n by g e o l o g i s t s . T h i s i n t e r e s t has i n c r e a s e d s i n c e the r e a l i z a -t i o n of the a s s o c i a t i o n between ore d e p o s i t s and b r e c c i a p i p e s . Thus t h e r e have been many attemp t s a t d e t a i l e d d e s c r i p t i o n and c l a s s i f i c a t i o n of a l l types of b r e c c i a . B r e c c i a s , l i k e o t h e r o r e - l o c a l i z i n g s t r u c t u r e s , are not always m i n e r a l i z e d . A c c o r d i n g to Walker (1928) o n l y one p e r c e n t are m i n e r a l i z e d , and even t h e n , o n l y s m a l l p a r t s of these are o r e - b e a r i n g . They g e n e r a l l y have no g e n e t i c r e l a t i o n s h i p w i t h ore d e p o s i t s , but are merely phenomena of t e c t o n i c and v o l c a n i c a c t i v i t y . The term \" B r e c c i a p i p e ' , a c c o r d i n g t o B r y n e r ( l 9 6 l ) , r e f e r s t o * . . . a c r u d e l y c y l i n d r i c a l , h i g h l y i n c l i n e d o r v e r t i c a l struC' t u r a l u n i t composed w h o l l y o r p a r t l y of a n g u l a r , or rounded, ro c k fragments w i t h o r w i t h o u t m a t r i x . \" (p. 490) The purpose of t h i s t h e s i s i s t o d e s c r i b e a b r e c c i a m a s s i n c o u n t r y r o c k of g n e i s s , and to c l a s s i f y a\u00C2\u00BBd a s c r i b e a mode o f f o r m a t i o n f o r the same. A r e v i e w of the l i t e r a t u r e on b r e c c i a s i n form o f a summary s h a l l be i n c l u d e d i n t h i s work v 2 Location and Access The l o c a t i o n o f t h e b r e c c i a i s s h o w n i n F i g u r e 1. I t c r o p s o u t on t h e s t e e p w e s t e r n a s p e c t o f t h e C o a s t M o u n t a i n s , w h i c h h e r e r i s e s r a p i d l y f r o m t h e s h o r e o f Howe S o u n d t o 3,992 f e e t , t h e s u m m i t o f B l a c k M o u n t a i n . Two e x c e l l e n t e x p o s u r e s o f t h e b r e c c i a a r e f o u n d i n t h e c u t s o f t h e V a n c o u v e r - S q u a m i s h h i g h w a y and t h e P a c i f i c G r e a t E a s t e r n R a i l w a y , ( f i g , 2) Much b l a s t e d r o c k c o v e r s t h e s l o p e b e t w e e n t h e h i g h w a y a n d t h e r a i l r o a d , o b s c u r i n g some o f t h e o u t c r o p . T h r e e m i l e s s o u t h a l o n g t h e h i g h w a y i s H o r s e s h o e B a y , . B . C . located some 20 m i l e s n o r t h o f V a n c o u v e r . The a r e a c a n easily be r e a c h e d b y b o a t f r o m H o r s e s h o e B a y , a n e c e s s i t y f o r s h o r e -. l i n e m a p p i n g . A p o w e r l i n e r i g h t - o f - w a y o f t h e B . C . H y d r o P o w e r A u t h o r i t y c u t s a c r o s s t h e map a r e a , u p h i l l o f t h e h i g h w a y , l e a v -i n g a t a n g l e o f b r a m b l e s a n d f e l l e d l o g s . Physiography and Tonography The a r e a i s t y p i c a l o f t h e r u g g e d C o a s t M o u n t a i n s S t e e p s l o p e s r i s i n g f r o m t h e s h o r e s o f f j o r d s , i n many p l a c e s t o 5,000 f e e t a l t i t u d e , make t r a v e l on t h e f o r e s t e d s l o p e s h a z a r d o u s , e s -p e c i a l l y b e c a u s e o f t h e s u d d e n p r e c i p i c e s , 1 0 ' s t o 100 ' s o f f e e t h i g h w e l l h i d d e n b y c o n i f e r o u s f o r e s t s a n d u n d e r g r o w t h . O u t c r o p s a r e s c a r c e , s t e e p a n d u s u a l l y c o v e r e d b y moss a n d l i c h e n s . G l a c i a l a n d f l u v i a l g r a v e l c o v e r s many p a r t s o f t h e a r e a , , a n d b e d s o f h i g h l y c o m p e t e n t ' f r e s h e t ' s t r e a m s i n c i s e s l o p e s and widen i n t o s m a l l g r a v e l beaches, t h a t dot the b l u f f y s hore. Acknowledgements I am i n d e b t e d to Dr, J.V. Ross who made me aware of t h i s t h e s i s t o p i c , and hel p e d o r g a n i z e the m a n u s c r i p t . F u r t h e r g r a t i t u d e i s due to Dr.. R.M, Thompson who hel p e d w i t h th\u00C2\u00A9 X-ray i d e n t i f i c a t i o n of some m i n e r a l s , and to Dr. K.C. McTaggart wh\u00C2\u00A9 a i d e d w i t h h e l p f u l . \" d i s c u s s i o n s GENERAL GEOLOGY OF THE AREA Howe Sound, w i t h i t s s e v e r a l i s l a n d s , and the Vancouver A N o r t h map a r e a were mapped by Armstrong (1954) and l a t e r by Roddick (1965). P l u t o n i c r o c k of the Coast Mountain i n t r u s i v e s u n d e r l i e most of the a r e a . P r e p l u t o n i c and p o s t - p l u t o n i c meta-morphic r o c k s comprise the remainder of the a r e a , t o g e t h e r w i t h some sedimentary r o c k s of low metamorphic grade and v o l c a n i c s . P l u t o n i c r o c k s are m a i n l y d i o r i t i c ; they are thought to be c o r r e l a t a b l e on a h o r n b l e n d e - b i o t i t e p ercentage b a s i s r a t h e r , than a q u a r t z - f e l d s p a r r a t i o . (Armstrong, 1954) T h i s p o i n t of view i s supported by Roddick (1965) who m a i n t a i n s t h a t the p l u t o n i r o c k s of t h i s r e g i o n can b e s t be c l a s s i f i e d a c c o r d i n g t o the ma f i c s r a t h e r than q u a r t z - f e l d s p a r i n the c o n v e n t i o n a l manner. Such a c l a s s i f i c a t i o n i s based upon the o b s e r v a t i o n t h a t t h e r e i s a d e f i n i t e p r e v a i l i n g g e n e t i c o r d e r i n the m i n e r a l s , as f o l l o w s : p l a g i o c l a s e - h o r n b l e n d e - b i o t i t e - q u a r t z - p o t a s h f e l d s p a r . He a l s o c o n c l u d e s t h a t through the a c t i o n of s y n p l u t o n i c f a u l t s r o o f pendants are brought to p r e s e n t l e v e l s , whereby p l u t o n i c rock i s brought to c o n t a c t w i t h p r e - e x i s t i n g metamorphic rock i n which connate water has been r e t a i n e d . The r e s u l t t h a t p l u t o n i c r o c k s are c r e a t e d from metamorphic r o c k s i s i n f e r r e d i n the f o l l o w i n g sequence: hornblende d i o r i t e - b i o t i t e g r a n i t e - a l a s k i t e -p e g m a t i t e , d u r i n g r e t r o g r a d e metamorphism. Roddick (1965'p. 29) f i n d s t h a t the c o u n t r y r o c k s of the Pasco b r e c c i a b e l o n g to a s l i c e of metamorphic rock (Twin I s l a n d s Group) which he c a l l s the Horseshoe Bay Pendant. 5. Armstrong (1954) r e p o r t s t h a t the metamorphic r o c k s are m a i n l y , o r e n t i r e l y Mesozoic i n age. The Bowen I s l a n d group c o n s i s t i n g o f s l i g h t l y metamorphosed, f o l d e d b a s a l t i c and ande-s i t i c l a v a s , w i t h i n t e r b e d d e d t u f f s and sed i m e n t a r y r o c k s , i s T r i a s s i c ? and/or e a r l i e r . The Gambier group, T r i a s s i c ? and/or l a t e r , c o n s i s t s m a i n l y o f p y r o c l a s t i c ^ r o c k s and l a v a s , w i t h minor i n t e r b e d d e d s e d i m e n t a r y m a t e r i a l . On Mt. Brunswick a 6,000 f o o t s e c t i o n c o n t a i n i n g a t l e a s t 2,000 f e e t o f s l a t e , a r g i l l i t e , q u a r t z i t e , and a r k o s e , b e l o n g s to the l a t t e r , P r e - g r a n i t i c r o c k s , to which g n e i s s i c . c o u n t r y r o c k s of the t h e s i s a r e a are thought to b e l o n g , had been t e n t a t i v e l y c o r r e l a t e d w i t h the Bowen I s l a n d group m a i n l y on l i t h o l o g i c grounds. Roddick (1965) a s s e r t s t h a t the r o c k s around the t h e s i s a r e a b e l o n g to the P r e - J u r a s s i c Twin I s l a n d s group p o s s i b l y the same as the Bowen I s l a n d group of s i m i l a r age. He s t a t e s t h a t the Gambier group i s Upper J u r a s s i c i n age. S e v e r a l v a r i e t i e s of young d i k e s o c c u r i n the a r e a , of which he b e l i e v e s many to be s y n p l u t o n i c . L i t t l e can be s a i d about the s t r u c t u r e of the a r e a to s u p p l a n t what was mentioned above. Armstrong (1954) mentions t h a t t h e r e \"... i s the n e a r - v e r t i c a l average d i p of the p l a n e of u n c o n f o r m i t y s e p a r a t i n g the Gambier group from the o l d e r r o c k s , i n d i c a t i n g t h a t the l a t t e r , i n c l u d i n g the o l d e r p l u t o n i c r o c k s , w e r e ; a l l s e v e r e l y deformed.\" (Armstrong, 1954, p. l ) TIT. GNEISS-BRECCIA PIPE -The b r e c c i a p i p e , as i t i s c u t by topography, i s about 800 6. feet^square, plunges steeply, and has cross cutting relations with the gneissic country rock. Fragments in the dark breccia, mainly of amphibolitic composition similar to mafic bands i n the gneiss, are surrounded by scant matrix, mostly of nearly microscopic grain si z e , between closely packed fragments. The breccia face looks uniformly dark from a distance of several feet because of the predominance of- mafic fragments. This uniformity changes to variety on closer inspection when smaller compositional and textural changes, as well as the existence of minor structures, become evident. Fragments - Fragment size varies from microscopic, to 30 feet thick; and 35 feet long; a common size i s about 1 to 2 inches wide and 2 to ? inches long. . Small fragments are usually bounded by planar sides p a r a l l e l to s c h i s t o s i t y , but fragments have been noted where the f o l i a t i o n i s oblique to the length. Only one f o l i a t i o n i s evident i n the fragments. Texture and composition of fragments vary from gran i t i c and schistose, to f e l s i c and mafic, respectively, although mafic schists are moat common. The g r a n i t i c and f e l s i c fragments are rare enough to arouse attention especially for their rounded shapes. The term g r a n i t i c pebbles has been applied to these. 1. Schistose fragments--Most common are amphibolite fragments. They are normally dark, tabular in shape, 1 to 4 inches long, variously textured from spotted porphyroblastio, to fine\u00C2\u00ABg?ained P l a t e I f a c i n g page'; 7 xlO c..Association of p y r i t e with epidote near v e i n of f r e s h q u a r t z . schistose. In thin section s c h i s t o s i t y i s defined by orientation of fresh grains of green hornblende, between s l i g h t l y cloudy plagio-clase (oligoclase-andesine), and quartz in a granoblastic texture, (plate lb) Fragment boundaries are sharp and there i s no v a r i a t i o n i n texture or composition near the margins. Where s l i v e r s have separated from schist-fragments brown b i o t i t e i s found to replace 'green hornblende. Epidote, s e r i c i t e , c h l o r i t e , pyrite and mag-netite occur i n minor amounts. 2. Gneissic fragments\u00E2\u0080\u0094Somewhat larger fragments exhibit gneissose banding comprising amphibollte similar to the ones just described, and f o l i a t e d f e l s i c bands composed of plagioclase, with some quartz i n variable proportions. These larger sizes are not common, and one such fragment (Plate V) i s well rounded. It has several gneissic bands obliquely to the axis of i t s sub-e l l i p s o i d a l form. 3. Gneiss blocks\u00E2\u0080\u0094There are larger inclusions of gneiss in the breccia. Two have been observed. One occurs at the north contact along the ra i l r o a d and the other i s within the section along the highway. The l a t t e r i s about 25 feet wide, has a \"fault contact with the breccia on the south side and a porphyritic septum on the north contact. ( f i g . 3) Its attitude d i f f e r s from the normal country rock trend, i n d i c a t i n g r e l a t i v e rotation of the inclusion within the breccia. Another block i s about the same size as the f i r s t and i s Plate I I f a c i n g page 8 a. Pegmatitic s p a c e - f i l l i n g and rimmed c l a s t s . xlO 8. wedged apart from the \"breccia wallrock by tightly-packed breccia and some porphyry. Rotation relative to the country rock again is indicated by the change in strike, as well as the change in dip. . 4. Granitic pebbles and pegmatitic inter-clast material\u00E2\u0080\u0094 Pebbles of foliated granitic material and white plagioclase inter-clast f i l l i n g s are infrequent but contrast noticeably with the dark, angular fragments of the rest of the breccia, (plates Ila, IVa&b) Granitic pebbles with e l l i p t i c a l cross-sections appear to by cylin-drical in shape. Their sides are parallel to their foliations which generally impart to the rock structural weakness in at least two direc-' . .. tions. Various shapes and sizes, of this rock type occur in several places in the breccia. In thin section i t is seen to contain quartz, plagio-clase, and brown and green biotite, sericite, chlorite, and epidote with pyrite. .Most of the plagioclase is cloudy with sericite and kaolin. Quartz is clear. The fabric is medium-grained, or finer. The texture in part is granophyric, especially in plagioclase crystals, but for the most part i t tends to be granoblastic. Cracks in crystals, as well as inter-granular boundaries are f i l l e d with sodic plagioclase and quartz. Undu-latory extinction is common, and the shadowy and indistinct contacts between many grains are due to joined rims of sodic plagioclase. These textures are interpreted as indications of\u00E2\u0080\u00A2recrystallization of a foliated, but i n i t i a l l y granitic textured rock. The hea led c r a c k s , overgrown boundar ie s , and granophyric. tex ture are thought to he s i gns of e i t h e r magmatic processes.-'or p o s s i b l y replacement of these areas by more sod ic p l a g i o c l a s e , a c t i v e d u r i n g the l a t e r .magmatic stages when c r y s t a l l i z a t i o n had a l ready ensued. On weathered su r f a ce white space f i l l i n g s c o n t r a s t sha rp l y with the norma l ly da rk - g reen b r e c c i a . ( p l a te I i ) From a short d i s t a n c e the o v e r a l l aspect of the white areas i s that they are fragments wi th a v a r i e t y of shapes between rounded and angu la r . In d e t a i l they seem r a t h e r to be space f i l l i n g s and rims around other 'fragments. The con tac t s with ba s i c fragments are g r a d a t i o n a l i n some ca se s , sharp i n o t h e r s . There are s c h i s t o s e fragments f o l i a t e d wi th l a y e r s of . s i a l i c m a t e r i a l i n d i r e c t connect ion, wi th the white s p a c e - f i l l i n g s . In such fragments s c h i s t q s i t y tends to be masked by coa r se r f o l i a t i o n , and p l a i n white areas grade i n t o grey ones c o n t a i n i n g wisps of o r i e n t e d ma f i c s . In t h i n s e c t i o n \u00E2\u0080\u00A2 these white s p a c e - f i l l i n g s are no tab ly j pegmat.i t i c , composed o f . p l a g i o c l a s e (An^g) or q u a r t z , se ldomly i n te rg rown, but always more c o a r s e l y c r y s t a l l i z e d than the remainder of the rock . ( p l a te II b) C rys ta l ' 'marg ins are l i g h t l y , overgrown and shadowed. The white areas i n c l u d e c loudy g rano-b l a s t i c i n te rg rowths of p l a g i o c l a s e which are f i n e - g r a i n e d and d i s p l a y a f i s h - n e t t ex tu re under p l a i n l i g h t . Such.a tex ture i s caused by the c o n t r a s t between c louded g ra in s of a l t e r e d p l a g i o c l a s e and sod ic p l a g i o c l a s e rims around these g r a i n s . An an i n t e r p r e t a t i o n of these tex tu re s i t i s thought that the white areas represent m a t e r i a l i n the process of s o l i d i f y i n g P l a t e I I I f a c i n g page 10 Br e c c i a near contact with d i o r i t e . Note p o r p h y r i t i c matrix and loose packing. (Numbers indicate origin of thinsections) b. B r e c c i a near contact with d i o r i t e . Note p o r p h y r i t i c matrix, f l o a t i n g fragments, and s t a r t of t i g h t e r packing. (Numbers indicate origin of thinsections) 10. f r o m l i q u i d f o r m ; some w h i t e a r e a s a p p e a r to he f r a g m e n t s o f the s o l i d form w h i l e o t h e r s have shapes d e p e n d e n t on the o u t l i n e s o f f r a g m e n t s s u r r o u n d i n g them, thus i n d i c a t i n g a t l e a s t p l a s t i c i t y , i f not l i q u i d i t y of the q u a r t z - f e l d s p a r m e l t . M a t r i x - The m a t r i x of the b r e c c i a a t the c o n t a c t w i t h d i o r i t e d i f f e r s from, the i n t e r c l a s t m a t e r i a l w i t h i n the b r e c c i a . At the c o n t a c t , f r a g m e n t s a r e w i d e l y s p a c e d and s u r r o u n d e d by p o r p h y r i t i c d i o r i t e , whereas w i t h i n the b r e c c i a p i p e they, a r e t i g h t l y packed and cemented t o g e t h e r by t h i n seams o f s i a l i c m a t e r i a l . A t the p e r i p h e r y , a p s e u d o - a g m a t i t'e of p o r p h y r y , s u r r o u n d i n g b r e c c i a f r a g m e n t s , r e s t r i c t e d , to the c o n t a c t . ( p l a t e I I I ) In t h i n s e c t i o n t e x t u r e s of t h e p o r p h y r i t i c d i o r i t e m a t r i x b e l o n g i n g t o t h e b o r d e r p h a s e s of the b r e c c i a , w i l l l a t e r be de-s c r i b e d . The m a t r i x of the t i g h t l y - p a c k e d b r e c c i a w i t h i n the p i p e i s p r e s e n t o n l y as t h i n seams as most o f the .fragments a r e i n d i r e c t contact, w i t h each o t h e r . These a earns c o n s i s t of s m a l l a l t e r e d l i t h i c f r a g m e n t s , t h a t have p a r t l y l o s t t h e i r m a f i c m i n e r a l o r i e n t a t i o n ' , and q u a r t z - f e l d s p a r a r e a s . G e n e r a l l y - p l a g i o -c l a s e . q u a r t z , b i o t i t e , c h l o r i t e , e p i d o t e , p y r i t e , and a p a t i t e a r e P r e s e n t i n v a r i e d p r o p o r t i o n s . P I a g i o c l a s e i s o f t e n r i d d l e d w i t h i n t e r g r c w t h s of e p i d o t e and p y r i t e . Q u a r t z i s c l e a r . Some gra.no-p h y r i c i n t e r g r p w t h i s p r e s e n t . Green c h l o r i t e w i t h anomalous b i r e f r i n g e n c e i s a s s o c i a t e d w i t h brown b i o t i t e . T e x t u r e v a r i e s o v e r s h o r t d i s t a n c e s b e c a u s e the l i t h i c f r a g m e n t s t h e m s e l v e s d i f f e r s l i g h t l y i n f a b r i c . On the whole g r a n o b l a s t i c t e x t u r e w i t h g r a n i t i c t e x t u r e d p a r t s i s common. G r a i n b o u n d a r i e s a r e Plate IV a. G r a n i t i c pebbles i n b r e c c i a with some o r i e n t a t i o n of fragments. b. D e f i n i t e sub-horizontal o r i e n t a t i o n of a l l types of fragments. 11. overgrown. . ' The i n t e r p r e t a t i o n g iven f o r these t e x t u r a l r e l a t i o n s i s .that the matr ix of the t i g h t l y packed b r e c c i a c o n s i s t s mainly of f i n e g ra ined l i t h i c fragments. ' The presence of f r e s h , as we l l as disrnembere d f r a gm e n t s , s u gge's t s so r\u00C2\u00AB e process of c o in m i nu t j. o n . Re cry s t a l 1 i'/.a t i on of both smal l whole ~ and dismembered fragments' i s i n d i c a t e d by t h e i r g r a n o b l a s t i c texture ' , g ranophyr ic i n t e r -growth in some p l a c e s , and overgrowths on g ra in boundar ies in n e a r l y a l l i n s t a n c e s , ' S t ruo tu re s - o t rup tu re s encountered d u r i n g mapping are the f o l l o w i n g : o r i e n t a t i o n of c l a s t s . w i th i n the. b r e c c i a , bending of fragments with shea r i n g ac ros s .'small f o l d s , l a r g e r s t r u c t u r e s such as shear zones, gouge - r i ch f au l to , '. j o i n t s , f o l i a t i o n of g r a n i t i c r ock s , gn e i ss o s i ty - o f ten accompanied by j o i n t i n g , and secondary f o l i a t i o n in the gneiss. 1. O r i e n t a t i o n of c l a s t s . - - D e f i n i t e a l ignment of the l ong axes of a l l types o f fragments i n a. s u b - h o r i zon ta l d i r e c t i o n occurs over a 150 f oo t s t r e t c h of the highway s e c t i o n . ( p l a te IV a, b) \" e a r v e r t i c a l a l ignment of l ong axes w i th i n the' p l a n e . o f s e c t i o n was vaguely v i s i b l e at two l o c a l i z e d p o i n t s , but these may be f o r t u i t o u s l y s i m i l a r o r i e n t a t i o n s , whereas the r .ub-horizon.tal a l ignment in tha t s e c t i o n i s very l i k e l y the exp re s s i on ' o f some' c o n t r o l l i n g f a c t o r in the fo rmat ion of the b r e c c i a . 2.. P l a s t i c d e f o r m a t i o n . \u00E2\u0080\u0094 M o s t fragments in the brecc ia , are p 1 anar, ' 'many are bent, \u00E2\u0080\u00A2 some of them are not. only ben t bu t have sheared as shown i n p l a t e Vb. Bent fragments are u b i q u i t o u s in Plate V facing page 12 t h e b r e c c i a . F l e x u r e i s e s p e c i a l l y n o ' t i c e a h l e n e a r the l i n e o f i m p i n g e m e n t o f two f r a g m e n t s . 3. S h e a r zones.-\u00E2\u0080\u0094One 35 f o o t - w i d e - s h e a r zone o c c u r s a t t h e s o u t h c o n t a c t of the b r e c c i a i n the r o a d s e c t i o n . The r o c k i n the zone i s - d a r k g r e e n , w i t h brown a r e a s , and i s f i n e g r a i n e d . The c e n t r a l p o r . t i o n o f t h e s h e a r zone i s i n c i s e d by. P a s c o c r e e k , w h i c h c u t s t h r o u g h a 1 i g h t g r e e n , f r i a b l e v e i n o f v e r y f i n e -g r a i n e d e p i d o t e s h o t t h r o u g h w i t h a n a s t o m o s i n g v e i n l e t s o f f u s e d q u a r t z . T h i s r a t h e r i m p e r m e a b l e , m y l o n i t i c zone r e p r e s e n t s the b o u n d a r y b e t w e e n b r e c c i a and c o u n t r y r o c k i n the r o a d s e c t i o n , 11 c o u I d not. he f o l i o w o d a l o n g s t r i k e i n e i 1;her d i r e c t i o n . The a t t i t u d e o f t h e f r a c t u r e a t the c e n t r a l p a r t of the z o n e , whi ch would he the l a t e s t l o c u s o f movement, i s 06*0\u00C2\u00B0/85\u00C2\u00B0 SS. 4. Gouge f i l l e d f a u l t s a r e m a i n l y f o u n d i n the b r e c c i a , and t o a l e s s e r e x t e n t :i.n. t h e c o u n t r y r o c k s . S c a r p s a r e v a g u e l y s l i c k e n s i d e d , ' a n d i n - some c a s e s c o n s t i t u t e the f a c e o f t h e s e c t i o n o f trie r a i l r o a d ' c u t , o b s c u r i n g much o f t h e d e t a i l o f t h e r o c k . J u n c t u r e o f f a u l t s o f t e n r e s u l t s i n c r a c k l e and f r a g m e n t e d b r e c c i a . 5. J o i n t s .--A1 though, many j o i n t s . a r e f o u n d i n . ho t h c.oun t r y r o c k and b r e c c i a , o n l y t h o s e p a r a l l e l t o ' g n e i s s o s i t y ( l 3 5\u00C2\u00B0/70\u00C2\u00B0NE) and one s e t w h i c h a- w e a t h e r e d d i k e p a r a l l e l s (l50 o/70\u00C2\u00B0N W; have b e e n m e a s u r e d . f\. F o l i a t i o n i n b o r d e r p h a s e s , - - G r a n i t i c r o c k s a t the s o u t h b o r d e r o f t h e b r e c c i a a r e f o l i a t e d . . Prom t h r e e o u t c r o p s , m e a s u r e -ments o f f o l i a t i o n were t a k e n and a r e shown i n f i g u r e 2b. The p o s s i b i l i t y e x i s t s t h a t i f f u r t h e r o u t c r o p s - were t o he f o u n d , t h e y Plate VI f a c i n g page 13 b. \u00E2\u0080\u00A2Typical band with augen from gneiss. would suggest that the f o l i a t i o n hears some r e l a t i o n s h i p to the p ipe o u t l i n e r a t h e r than the trend of the country rock.. 7. Secondary f Q 1 i a t i o n . - - P l a t e VI shows d e f i n i t e secondary f o l i a t i o n in g n e i s s i c country rock . (175\u00C2\u00B0/?) Th.e f o l i a t i o n d ip could not he measured. Only few hands i n the gne i ss show t h i s s t r u c t u r e and the s c a r c i t y of good outcrop reduces the chance of f i n d i n g more examples of secondary f o l i a t i o n . Relat ion, of P:iye to Country Rocks - Va r i ous types of country rock surround/ ' the b r e c c i a p i p e ; they can be d e s c r i b e d as f o l l o w s 1. G n e i s s . - - T h e gne i s s , i n d e t a i l , i s minute ly f o l i a t e d , and on o l a r g e r s ca l e consp i cuous l y banded, and j o i n t e d p a r a l l e l , to the major f o l i a t i o n . A secondary f o l i a t i o n i n the c o a r s e r maf ic l a y e r s i s ev ident i n some smoothly weathered ou tc rops . '\u00E2\u0080\u00A2\u00E2\u0080\u00A2 , ( p l a t e VI a) Minute f o l i a t i o n s f r e q u e n t l y d i sappear i n medium gra ined migrnatized zones with i n d i s t i n c t boundar ie s . In these zones the maf ic m inera l s occur i n c l o t s and f o l l o w s w i r l s which have no r e l a t i o n to the genera l trend of the rock. I n c i p i e n t m igmat i za t ion of t h i s type crops out i n some a rea . I n f i n i t e v a r i a t i o n s i n t e x t u r a l and compos i t i ona l changes w i t h i n very shor t d i s t a n c e s are seen i n many of the ou tc rops . The r o c k - f o r m i n g minera l s are mainly p l a g i o c l a s e ( o l i o g o c l a s e -andes i ne ) , green hornb lende, q u a r t s , and b i o t i t e , and the present assemblage i n c l u d e s smal l q u a n t i t i e s of a l t e r a t i o n minera l s such as p y r i t e , e p i d o t e , c h l o r i t e , b i o t i t e , a p a t i t e , s e r i c i t e , and c a l c i t e , main ly i n v e i n l e t s . Textures vary from f i n e gra ined s c h i s t o s e , through a range of g ra in s i z e s , to p o r p h y r o b l a s t i c with xen.oblast ic augen of 14. f e l d s p a r between a l i g n e d m a f i c s . These e l o n g a t e mafic m i n e r a l s . are o f t e n bent around the l a r g e r c r y s t a l s . ( p l a t e VI b) S p o t t e d s c h i s t s commonly c o n t a i n p a r a l l e l e l o n g a t e c l o t s of hornblende c r y s t a l s a s s o c i a t e d w i t h p l a g i o c l a s e augen s e t i n a f i n e g r a i n e d s c h i s t o s e m a t r i x . 2. H o r n b l e n d i t e . \u00E2\u0080\u0094 D a r k green h o r n b l e n d i t e crops out on a p o i n t of the s h o r e l i n e near a c a v e - l i k e i n d e n t a t i o n of one of the s m a l l bays. The r o c k has no d i r e c t i v e t e x t u r e o t h e r than a vague p a r a l l e l e l o n g a t i o n of- the p i t s which r e p r e s e n t weathered out c l o t s of m a i n l y brown b i o t i t e surrounded by green h o r n b l e n d e . Ridges around the p i t s are due to more r e s i s t a n t p l a g i o c l a s e and h o r n b l e n d e - r i c h a r e a s . S m a l l areas of s e r i c i t i z e d p l a g i o c l a s e and brown b i o t i t e cut the r o c k . The brown b i o t i t e i s s i m i l a r to t h a t i n c i p i e n t l y r e p l a c i n g some of the h o r n b l e n d e . A s e l v a g e of f r e s h p l a g i o c l a s e , s i m i l a r to t h a t i n the rock., b o r d e r s the v e i n s . C o n t a c t r e l a t i o n s of t h i s h o r n b l e n d i t e w i t h the g n e i s s are not known. The l a c k of b a n d i n g and the o t h e r w i s e homogeneous c c h a r a c t e r of the r o c k , t o g e t h e r w i t h the h i g h c o n t e n t of w e l l -c r y s t a l l i z e d hornblende s u r r o u n d i n g i n t e r g r a n u l a r patches of p l a g i o c l a s e c r y s t a l s , i n d i c a t e an igneous o r i g i n , r a t h e r than metamorphic. 3. B o r d e r phases of the b r e c c i a . \u00E2\u0080\u0094 R o c k s , here c l a s s e d under b o r d e r phases of the b r e c c i a , appear to be i g n e o u s . i n o r i g i n and o c c u r near the p e r i p h e r y of the b r e c c i a , but they d i f f e r i n c o l o u r , t e x t u r e , and c o m p o s i t i o n . C o m p o s i t i o n v a r i e s from v e r y dark green d i o r i t e , through l i g h t e r c o l o u r e d igneous r o c k s to Plate VII facing page 15 15. l e u c o c r a t i c p i n k g r a n i t e s . a. P o r p h y r i t i c d i o r i t e . Both a t the b r e c c i a c o n t a c t s and w i t h i n the b r e c c i a mass are o c c u r r e n c e s of p o r p h y r i t i c d i o r i t e . Those w e l l w i t h i n the b r e c c i a are l e s s p l e n t i f u l and s m a l l e r than those a t the p e r i p h e r y . A l t h o u g h ;the m a f i c m i n e r a l c o n t e n t , as w e l l as the degree of p h e n o c r y s t development and the c o n t a c t r e l a t i o n s d i f f e r from one o c c u r r e n c e of d i o r i t e to the n e x t , t e x t u r a l and c o m p o s i t i o n s i m i l a r i t y s u g g ests common o r i g i n f o r a l l of them. The b e s t exposure of p o r p h y r i t i c d i o r i t e , o c c u r r i n g a t the n o r t h c o n t a c t of the b r e c c i a , d i s p l a y s r e l a t i o n s t y p i c a l of t h i s r o c k t y p e . F i g u r e .3 shows the c o n t a c t s of d i o r i t e w i t h g n e i s s i c c o u n t r y r o c k s to the n o r t h and b r e c c i a to the s o u t h . D i o r i t e s l i g h t l y c r o s s c u t s , the g n e i s s i c f o l i a t i o n , y e t seen from the d i s t a n c e of few tens of f e e t the c o n t a c t i s s e n s i b l y p a r a l l e l to the g n e i s s o s i t y . The d i o r i t e - b r e c c i a c o n t a c t i s sharp when seen from t e n f e e t , but somewhat g r a d a t i o n a l i n d e t a i l . P l a t e V I I d e p i c t s two v a r i a t i o n s i n b r e c c i a d i o r i t e c o n t a c t s , one at the p e r i p h e r y and one a t the d i k e w i t h i n . t h e b r e c c i a i t s e l f . The c o n t a c t a t the d i k e w i t h i n the b r e c c i a i s s h a r p ; the d i k e or apo p h y s i s b e i n g younger than the b r e c c i a . The p e r i p h e r a l c o n t a c t , on the o t h e r hand, grades over a w i d t h of 2 to 3 i n c h e s from t i g h t l y packed b r e c c i a on one s i d e to d i o r i t e d e v o i d of b r e c c i a on the o t h e r . P l a t e I I I shows t h a t the p o r p h y r i t i c m a t r i x of the g r a d a t i o n a l c o n t a c t , d e s c r i b e d above, o c c u r s both as m a t e r i a l w i t h few s c a t t e r e d Plate VIII fac ing page 16 x 10 b. Myrmekite in zoned plagioclase phenocryst. Typcia l groundmass. Note zoned crysta l at arrow, (cf. plate X fac ing p. 17) 16. f r a g m e n t a l i n c l u s i o n s , and as s m a l l pockets between fragments i n more t i g h t l y packed b r e c c i a . F u r t h e r m o r e , changes i n mafic m i n e r a l c o n t e n t and ph e n o c r y s t s i z e w i t h i n s h o r t d i s t a n c e s , are e v i d e n t i n the o u t c r o p and are shown i n the photographs. The f r e q u e n c y of the l a r g e p l a g i o c l a s e p h e n o e r y s t s decreases away from the d i o r i t e -b r e c c i a c o n t a c t . I t sh o u l d be p o i n t e d out t h a t t h e r e are o n l y few o c c u r r e n c e s of d i o r i t e w i t h i n the b r e c c i a body, i n c o n t r a s t to f r e q u e n t o c c u r r e n c e near the p e r i p h e r y . Dark green d i o r i t i c r o c k , found a t the n o r t h b r e c c i a margin i n the highway s e c t i o n ( e s p e c i a l l y on the west s i d e of the r o a d ) , e x h i b i t s c o n t a c t r e l a t i o n s which grade from g r e e n i s h d i o r i t e , through f o l i a t e d d i o r i t e , t o dark g n e i s s i c c o u n t r y r o c k . Because t h i s g r a d a t i o n o c c u r s over a few i n c h e s the c o n t a c t i s s e n s i b l y sharp. Of i n t e r e s t , however, i s the f a c t t h a t green h o r n b l e n d i c d i o r i t e o c c u r s i n c l o s e p r o x i m i t y to p o r p h y r i t i c l i g h t c o l o u r e d d i o r i t e ' , a l o n g the c o n t a c t w i t h the same g n e i s s i c c o u n t r y r o c k . b. F o l i a t e d g r a n i t e . P i n k and o t h e r l i g h t c o l o u r e d g r a n i t i c r o c k s near the south margin of the b r e c c i a are w e l l f o l i a t e d w i t h r e s p e c t to b i o t i t e and f e l d s p a r s . C o n t a c t s are not exposed but by t h e i r p r o x i m i t y to the b r e c c i a margin these f o l i a t e s are here grouped under b o r d e r phase r o c k s . I n t h i n s e c t i o n c o m b i n a t i o n t w i n n i n g (Ross, 1957), grano-p h y r i c t e x t u r e , and s e r r a t e d edges on q u a r t z g r a i n s would i n -d i c a t e igneous o r i g i n f o r t h i s r o c k t y p e . A l t e r a t i o n , z o n i n g , and r e c r y s t a l l i z a t i o n of p l a g i o c l a s e can be seen i n some s e c t i o n s . The p i n k f o l i a t e d g r a n i t i c r o c k s c o n s i s t of medium g r a i n e d i Plate IX facing page 17 17. o r t h o c l a s e , q u a r t z , and s o d i c p l a g i o c l a s e mixed i n v a r i o u s p r o p o r t i o n s w i t h c h l o r i t e , e p i d o t e and p y r i t e . A l t e r a t i o n of the f e l d s p a r s i s s t r o n g , masking t w i n n i n g and i n t e r n a l s t r u c t u r e of the c y r s t a l s . F o l i a t i o n of the f o c k ( p l a t e IX a) i s produced by the s e g r e g a t i o n of f e l d s p a r s i n e l o n g a t e zones s u b - p a r a l l e l w i t h s i m i l a r zones of q u a r t z . These are d i v i d e d by l o n g smears of c h l o r i t e and p y r i t e . C r y s t a l b o u n d a r i e s are i r r e g u l a r , s u t u r e d and shadowy as seen w i t h p o l a r i z e d l i g h t . Shadowy m a t e r i a l a t the c o n t a c t s of p h e n o c r y s t s w i t h the m a t r i x surround s m a l l patches of o p t i c a l l y d i s c o n n e c t e d fragments of m a t e r i a l s i m i l a r to the l a r g e r c r y s t a l s . O r t h o c l a s e r e p l a c e s c l o u d y f e l d s p a r , and q u a r t z o c c u r s a l o n g some a l b i t e c l e a v a g e p l a n e s . Quartz and o r t h o c l a s e have u n d u l a t o r y e x t i n c t i o n . Other f o l i a t e d b o r d e r phase r o c k s are s i m i l a r . I n t e r p r e t a t i o n of the t e x t u r e s , such as c o m b i n a t i o n t w i n n i n g , suggests an igneous o r i g i n f o r the f o l i a t e d g r a n i t e , w i t h con-c o m i t a n t s t r e s s a l i g n m e n t d u r i n g c r y s t a l l i z a t i o n of the m a t e r i a l . R e c r y s t a l l i z a t i o n a t some l a t e r t i m e , i n d i c a t e d by the h e a l e d b r e c c i a t e d c r y s t a l b o u n d a r i e s , may have o c c u r r e d a f t e r q u a r t z and o r t h o c l a s e were fragmented a l o n g t h e i r c r y s t a l b o u n d a r i e s . C h l o r i t e a l t e r a t i o n of b i o t i t e o c c u r r e d d u r i n g r e c r y s t a l l i z a t i o n . P o r p h y r i t i c t e x t u r e and l a c k of f o l i a t i o n d i s t i n g u i s h d i o r i t i c r o c k s near the n o r t h margin of the b r e c c i a . T e x t u r e and c o m p o s i t i o n of t h i s r o c k v a r y e s p e c i a l l y near the b r e c c i a c o n t a c t ( p l a t e I I I ) as d e s c r i b e d b e f o r e on page 14. In t h i n s e c t i o n the ro c k i s seen to c o n s i s t of q u a r t z , o l i g o -fac ing page 18 Andesine grain a l tered from the center. Crossed n i co l s . (note that the very center of the c r y s t a l i s more c a l c i c than the zone surrounding i t , - t h i s point i s seen i n Xb where the center i s of higher r e l i e f than the area surrounding i t ) Andesine grain a l tered from the center. Incl ined p la in polar ized l i g h t . 18. c l a s e , w i t h b i o t i t e , s e r i c i t e , c h l o r i t e , a p a t i t e , e p i d o t e and p y r i t e i n a g r a n o b l a s t i c m a t r i x s u r r o u n d i n g zoned p l a g i o c l a s e p h e n o e r y s t s . Zoning of s o d i c p l a g i o c l a s e i s complex, but i t i s t y p i c a l l y of the normal type w i t h a v a r i a t i o n from more c a l c i c a t the c e n t e r through two or t h r e e c o m p o s i t i o n a l zones, to more s o d i c a t the p e r i p h e r y . The p e r i p h e r a l zone, u s u a l l y v e r y s o d i c , i s i n many cases e n l a r g e d to j o i n w i t h p l a g i o c l a s e g r a i n s i n the: m a t r i x . I n some g r a i n s ( p l a t e X ) , however, c o m p o s i t i o n changes from c a l c i c ( a n d e s i n e ) a t the ve r y c e n t e r through s o d i c ( o l i g o -c l a s e ) around the c e n t e r , to more c a l c i c near the p e r i p h e r y , w i t h a s o d i c r i m w i t h the same c o m p o s i t i o n as the m a t r i x . The s o d i c r i m s n o r m a l l y are f r e e of a l t e r a t i o n , w h i l e the c e n t r a l p a r t i s v e r y c l o u d y . Some phenoerysts are r i d d l e d w i t h b l e b s of q u a r t z , r e s u l t i n g i n a g r a n o p h y r i c t e x t u r e . Some c r y s t a l s or c r y s t a l fragments i n the m a t r i x are j o i n e d to,form l a r g e r ones. Twinned p h e n o c r y s t fragments may have overgrowths of untwinned m a t e r i a l , e n l a r g i n g them to e u h e d r a l p l a g i o c l a s e pheno-e r y s t s . I n g e n e r a l c r y s t a l s i n the m a t r i x are o f t e n enveloped by the o u t e r zones of p h e n o e r y s t s and j o i n e d t o g e t h e r to form l a r g e r ones. P l a t e I I c shows a g r a i n i n the top r i g h t hand c o r n e r which i s a c o m b i n a t i o n of two s m a l l e r g r a i n s ; a r e a c t i o n r i m s urrounds b o t h . P l a t e V I I I a,b d e p i c t s two more p o s s i b l e cases of t h i s phenomenon. I n t e r p r e t a t i o n of the z o n i n g i n these p l a g i o c l a s e c r y s t a l s , depending on whether i t o c c u r r e d d u r i n g o r a f t e r c r y s t a l l i z a t i o n , c o u l d be t w o - f o l d . D u r i n g c r y s t a l l i z a t i o n a change i n environment 19. of the melt would r e s u l t i n c o r r o s i o n and subsequent rimming of c r y s t a l s ; i t i s b e l i e v e d t h a t t h i s manner of z o n i n g accounts f o r a g r e a t p r o p o r t i o n of such t e x t u r e s i n these b o r d e r phase r o c k s . The second manner, t h a t of p o s t - c r y s t a l l i z a t i o n r e p l a c e m e n t ; O f p a r t s of c r y s t a l s by more s o d i c p l a g i o c l a s e , i s p o s s i b l e e s p e c i a l l y i n a case as shown i n p l a t e X a & b. The andesine g r a i n i n q u e s t i o n r e p r e s e n t s a v e r y s m a l l p r o p o r t i o n of the r o c k , t h i s i s e v i d e n t from p l a t e I I I b when i t i s r e a l i z e d t h a t o n l y one such c r y s t a l was o b s e r v e d , out of f i v e s e c t i o n s . The c e n t r a l p a r t of the c r y s t a l i s c a l c i c , whereas the zone next to the c e n t e r i s s o d i c h a v i n g a c o m p o s i t i o n s i m i l a r to the ground mass. No p a t h -ways f o r s o l u t i o n exchange are e v i d e n t i n the s e c t i o n , but such s t r u c t u r e s may pass through o t h e r p a r t s of the c r y s t a l . S o d i c a l t e r a t i o n of t h i s type i s thought to be r e l a t e d to the rimming of p l a g i o c l a s e p h e n o c r y s t s a t t e n d a n t w i t h f o r m a t i o n of the grano-b l a s t i c m a t r i x . Fragments and shadows around h e a l e d fragments of c r y s t a l s are b e l i e v e d to i n d i c a t e a p r o c e s s whereby an i g n e o u s , somewhat m e c h a n i c a l l y g r a n u l a t e d m a t r i x e n c l o s i n g p h e n o c r y s t s was r e c r y s t a l l i z e d r e s u l t i n g i n the p r e s e n t t e x t u r e and o v e r -growth on c r y s t a l s . a. D i k e s . One dark brown, h i g h l y weathered a n d e s i t e d i k e c u t s b r e c c i a i n both the r a i l r o a d and the highway s e c t i o n s and seems to f o l l o w a j o i n t s e t a t 050\u00C2\u00B0/70\u00C2\u00B0N. C a v i t y f i l l i n g s , r e s e m b l i n g amygdules, o c c u r near the n o r t h s i d e of t h i s 4-6 f o o t wide d i k e . I n p o l i s h e d hand specimen i t ' i s seen to have a f e l t y t e x t u r e of t h i n p l a g i o c l a s e l a t h s , except near c l u s t e r s of d i k t y -t a x i t i c c a v i t i e s f i l l e d w i t h w h i t e m a t e r i a l . Areas around these Plate XI f a c i n g page 20 a.. South contact at road of br e c c i a and gneiss. Note the 'pink' dike i n the shear zone, and the f a u l t to the r i g h t of i t . (dotted line approximates boundary of breccia; dashed line outlines pink dike; wavy symbol indicates gouge-rich fault zone and Pasco creek) b.. Contact near north end of road section of p o r p h y r i t i c d i o r i t e over b r e c c i a . Note small d i o r i t e 'dike'. 20. c a v i t i e s are s o l i d l y cemented by a secondary m i n e r a l . I n t h i n s e c t i o n the r o c k i s composed of f r e s h a n d e s i n e , o r t h o p y r o x e n e , c h l o r i t e , and p y r i t e , and the d i k t y t a x i t i c c a v i -t i e s are f i l l e d by q u a r t z , c a l c i t e , c h l o r i t e , c h a b a z i t e , and tho m s o n i t e . A dark green, f i n e - g r a i n e d , f r e s h a n d e s i t e d i k e (not shown on the map) c u t s the b r e c c i a i n both highway and r a i l r o a d s e c t i o n s . The c o n t a c t i s v e r y sharp and the d i k e i s f l i n t - l i k e due to c h i l l -i n g a t the margin. P y r i t e , c h l o r i t e , and e p i d o t e occur i n c r a c k s . A d i o r i t e d i k e c u t s the b r e c c i a near the n o r t h highway con-t a c t . I t i s an ap o p h y s i s of the p o r p h y r i t i c d i o r i t e mass of the , b r e c c i a b o r d e r phases. ( p l a t e X i ) Sma l l w h i t e d i k e s c ut the g n e i s s i c c o u n t r y r o c k s i n s e v e r a l l o c a t i o n s . T h e i r a t t i t u d e s are m a i n l y s u b - p a r a l l e l to the g n e i s s o s i t y . One such d i k e was found to be e x t r e m e l y f i n e g r a i n e d , somewhat p o r p h y r i t i c w i t h medium-grained c r y s t a l s of q u a r t z and f e l d s p a r , and a m a t r i x of p l a g i o c l a s e (about An. c) and q u a r t z c r y s t a l s w i t h l o n g i t u d i n a l o r i e n t a t i o n s e t i n a p l i t i c groundmass. The p h e n o c r y s t s are rimmed by s l i g h t l y c l e a n e r m a t e r i a l which a l s o e n v elops g r a i n s of the c l o u d y groundmass. '; U n d u l a t o r y e x t i n c t i o n i s common. C l o t s of c h l o r i t e and s e r i c i t e c o u l d have been d e r i v e d from the w a l l r o c k s . F r a c t u r e s are f i l l e d w i t h s e r i c i t e and p o s s i b l y l i m o n i t e . ' Summary of C h a r a c t e r i s t i c s of t h i s B r e c c i a - The f o l l o w i n g . p o i n t s c h a r a c t e r i z e the b r e c c i a and must be e x p l a i n e d by a t h e o r y of the mode of f o r m a t i o n of the b r e c c i a a t Pasco c r e e k . 21. 1. P r o x i m i t y of the b r e c c i a to the c o n t a c t of a mass of d i o r i t e i n t r u s i v e i n t o c o u n t r y r o c k . 2. G e n e r a l shape of the b r e c c i a body w i t h n e a r l y square p l a n and s t e e p l y d i p p i n g s i d e s . . 3. S u b p a r a l l e l i s m of the b r e c c i a o u t l i n e on two s i d e s w i t h the g n e i s s o s i t y of the c o u n t r y r o c k . 4. E x i s t e n c e of fragments of c o u n t r y r o c k w i t h o n l y s m a l l q u a n t i t i e s of f o r e i g n m a t t e r . 5. U n i f o r m s i z e , t a b u l a r shape, and e l o n g a t i o n p a r a l l e l to s c h i s t o s i t y , of the fragments. 6. R e l a t i v e r o t a t i o n of l a r g e and s m a l l fragments w i t h r e -s p e c t to c o u n t r y r o c k s . 7. H o r i z o n t a l a l i g n m e n t of t a b u l a r fragments i n some s m a l l a r e a s . 8. Loose p a c k i n g of the b r e c c i a fragments near the c o n t a c t of the b r e c c i a w i t h p o r p h y r i t i c d i o r i t e , i n c o n t r a s t t o the t i g h t l y -packed fragments w i t h i n the b r e c c i a . 9. Presence of s c a n t r e c r y s t a l l i z e d m a t r i x w i t h i n the t i g h t l y -packed p o r t i o n of the b r e c c i a , and p l e n t i f u l p o r p h y r i t i c m a t r i x near the l o o s e l y - p a c k e d b o r d e r of the b r e c c i a . 10. M a t r i x c o n s i s t i n g of f i n e l i t h i c f ragments. 11. S m a l l w h i t e p e g m a t i t i c areas w i t h i n the b r e c c i a . 12. G r a n i t i c pebbles i n the b r e c c i a . 13. B e n d i n g and d e f o r m a t i o n of fragments. 14. Occurrence of p o r p h y r i t i c d i o r i t e as a s k i n between c o u n t r y r o c k and b r e c c i a ^ p a r t l y e n g u l f i n g l o o s e fragments a t the b r e c c i a c o n t a c t . 22. 15. Small bodies of. f o l i a t e d granitic rock at the periphery of the breccia. .16. Presence of d i o r i t e within the breccia. 17. Signs of metamorphism in both fragments and matrix. i . \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 . \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 23. IV. EXISTING THEORIES OF BRECCIA FORMATION Much has been w r i t t e n about b r e c c i a and accounts i n the l i t -e r a t u r e have, up to a few y e a r s ago, Often been based on b r e c c i a -ore body r e l a t i o n s h i p s . However, a l t h o u g h i n d i v i d u a l d e s c r i p t i o n s are c l e a r , the mode of f o r m a t i o n , and the r e l a t i o n s p a r t i c u l a r to the mapped l o c a l i t y u n d e r s t o o d , the .general a s p e c t of the problem of c o r r e l a t i n g and c l a s s i f y i n g b r e c c i a t y p e s of w i d e l y d i f f e r e n t c h a r a c t e r i s t i c s and o c c u r r e n c e s has o n l y been d e a l t w i t h i n the l a s t few y e a r s . An attempt a t \" C l a s s i f i c a t i o n of V o l c a n i c B r e c c i a s \" was made by F i s h e r ( i 9 6 0 ) , wherein he groups v o l c a n i c b r e c c i a s i n t o t h r e e major c a t e g o r i e s baaed ...on the p r o c e s s of f r a g m e n t a t i o n . He a l s o uses the term v o l c a n i c b r e c c i a \"... as a g e n e r a l term a p p l y i n g to a l l c o a r s e - g r a i n e d r o c k s composed of a n g u l a r v o l c a n i c f r a g m e n t s . \" ( i 9 6 0 , p. 973) Wright and Bowes (1963) c o u n t e r the proposed c l a s s i f i c a t i o n , p o i n t i n g out s i x i n a d e q u a c i e s and i n c o n s i s t e n c i e s , and c o n s i d e r i t \" . . . n e i t h e r c o n s i s t e n t nor workable and submit the f o l l o w i n g d i s c u s s i o n of n o n - p y r o c l a s t i c v o l c a n i c b r e c c i a s , t h e i r nomenclature, and c l a s s i f i c a t i o n . (1963, p. 79). They f i n d t h a t f o u r c r i t e r i a have commonly been used i n the c l a s s i f i c a t i o n of v o l c a n i c b r e c c i a s , namely, cause, environment, l o c a t i o n , and r o c k - t y p e . These c r i t e r i a s h o u l d be used i n com-b i n a t i o n . A c c o r d i n g to them, of th e s e f o u r c r i t e r i a , cause of f r a g m e n t a t i o n can o n l y be s t a t e d d e f i n i t e l y i n the case where there-hag been l i t t l e 24. t r a n s p o r t of b r e c c i a t e d m a t e r i a l ; when a mass of b r e c c i a t e d m a t e r i a l has been c a r r i e d somewhere e l s e , i t i s d i f f i c u l t to e x p l a i n the i n i t i a l b r e c c i a t i o n , and thus c l a s s i f i c a t i o n a c c o r d i n g to the type of\"environment i s more s i g n i f i c a n t . L o c a t i o n of the b r e c c i a has been used o n l y i n c e r t a i n i n s t a n c e s , i t s use c o u l d be a v o i d e d . A c l a s s i f i c a t i o n based on rock type i s l e a s t open to c o n t r o -v e r s y f o r i t s g e n e r a l n a t u r e , s i n c e the same type of r o c k can be b r e c c i a t e d i n many d i f f e r e n t ways. B r y n e r ( l 9 6 l ) d i v i d e s . m i n e r a l i z e d r o c k fragment columns i n t o two main groups, p r e - h y d r o t h e r m a l s t r u c t u r e s and c o h y d r o t h e r m a l s t r u c t u r e s ; t h i s s t a n d p o i n t i s . b a s e d on. m i n e r a l o g y and. economic geology. \"From th e s t a n d p o i n t of o r i g i n , the b r o a d e s t c l a s s i f i c a t i o n would d i s t i n - g u i s h b r e c c i a s on the b a s i s of the main t r a n s p o r t of f r a g m e n t s . ..Such movement of fragments a r e . e i t h e r (a) i n t r u s i v e \" , o r (b) c o l l a p s e , and c o u l d be (c) o s c i l l a t o r y , a c o m b i n a t i o n of (a) and ( b ) . He has the f o l l o w i n g e x p l a n a t i o n s . . I n t r u d e d f r a g m e n t s , ^ w r i t e s B r y n e r ( l 9 6 l ) , \" g e n e r a l l y are i m p e l l e d by magma, or ...el se by gaseous or aqueous f l u i d s t h a t a r i s e from the magma or are m o b i l i z e d by magmatic h e a t . \" (p. 505). C o l l a p s e can be e f f e c t e d by numerous means. S l a c k e n i n g of i n t r u s i v e a c t i v i t y , t h r ough w i t h d r a w a l of magma f o r example, would reduce the' s t a b i l i t y of the r o o f r o c k s by l o w e r i n g the p r e s s u r e from below. M e l t i n g of rock by gases compressed by an a d v a n c i n g magma column or s t r e t c h i n g of the c r u s t caused by dom-i n g may cause c o l l a p s e . F u r t h e r causes can be s o l u t i o n of l i m e -stone o r gypsum by water, s h r i n k a g e because of c o r r o s i o n by gase-25. ous or hydrothermal f l u i d s , or shrinkage due to c o o l i n g of int r u d e d rock, or c r y s t a l l i z a t i o n . C r a c k l e b r e c c i a s would, be- the . r e s u l t of e i t h e r i n t r u s i o n , c o l -llapse,, or o s c i l l a t i o n , i f any of these methods were i n c i p i e n t . Johnston and Lowell ( l 9 6 l ) , having s t u d i e d the l i t e r a t u r e on the problem of the o r i g i n and c l a s s i f i c a t i o n of these bodies of f r a c t u r e d rock,, concluded that \"The o r i g i n of most 'of the p i p e -l i k e d e p o s i t s has been explained by the f o l l o w i n g t h e o r i e s or by m o d i f i c a t i o n and/or combination of them...\" (p. 931 )\u00E2\u0080\u00A2\u00C2\u00BB and they l i s t the f o l l o w i n g : ( l ) e x p l o s i o n ; ( 2 ) t e c t o n i c ; ( 3 ) igneous i n t r u s i o n ; (4) f l u i d i n t r u s i o n ; ( 5 ) s o l u t i o n and replacement; ( 6 ) m i n e r a l i z a t i o n s t o p i n g ; and ( 7 ) shrinkage. Reynolds (1954) has int r o d u c e d f l u i d i z a t i o n i n t o the l i s t of g e o l o g i c a l processes. There are s i m i l a r i t i e s between ( l ) ex p l o s i o n mentioned above, (8) f l u i d i z a t i o n , and (4) f l u i d i n t r u -s i o n . (1) e x p l o s i o n due to blow-outs of gas a s s o c i a t e d with v o l c a n i c a c t i v i t y produce diatremes which are openings i n many cases across s t r a t i f i c a t i o n . These holes are subsequently f i l l e d with broken v o l c a n i c m a t e r i a l or country rock. ( 2 ) elongate b r e c c i a t e d bodies of rock may form at the i n t e r -s e c t i o n of f a u l t s and shear zones, or at bends i n f a u l t s , -these are t e c t o n i c b r e c c i a s . ( 3 ) p h y s i c a l f o r c e of i n t r u s i o n r e s u l t s i n formation of b r e c c i a columns or d i k e s . (4) f l u i d i n t r u s i o n of fragments broken off the s i d e s of the conduit somewhere below by magmatic gases would cause them to be 26. \" . . . f o r c e d upward i n t o r o c k s above by a r e l a t i v e l y t h i c k mud.\" (Farmin, 1934, p. 370). (5) c o r r o s i o n of s h a t t e r e d r o c k by a s c e n d i n g s o l u t i o n s f a c i l i -.._ts,tes. .rounding of fragments and i n c r e a s e of open space, which sub-s e q u e n t l y may be r e f i l l e d through :the p r e c i p i t a t i o n of m i n e r a l s . (6) Locke's (1926) m i n e r a l i z a t i o n s t o p i n g t h e o r y i s s i m i l a r to the b l o c k - c a v i n g method of m i n i n g , -whereby \"...removal of roc k a l o n g t r u c k c h a n n e l s by r i s i n g s o l u t i o n s d u r i n g an e a r l y stage of t h e i r a c t i v i t y , c o l l a p s e and b r e c c i a t i o n of the roc k thus l e f t u n s u p p o r t e d , and d e p o s i t i o n of ore: and gangue m i n e r a l s i n the b r e c c i a t e d mass.\" (p. 43l)\u00C2\u00BB was. the p r o c e s s . (7) c o n t r a c t i o n on c r y s t a l l i z a t i o n ^ w i t h an e s t i m a t e d 10 p e r c e n t volume s h r i n k a g e i s r e s p o n s i b l e f o r much f r a c t u r i n g and b r e c c i a t i o n i n c e r t a i n - s t o c k s and c h o n o l i t h s , a c c o r d i n g to H u l i n (1948). VAn : i n c r e a s e i n volume w i t h a t t e n d a n t open spaces would r e s u l t . (8) f l u i d i z a t i o n i s a term t h a t o r i g i n a t e d - i n i n d u s t r y f o r a p r o c e s s by which g r a i n - s i z e d p a r t i c l e s c o u l d be s e t i n t o t u r b u -l e n t motion by gas s t r e a m i n g through a bed of them c a u s i n g them to f l o a t i n and w i t h the gas, thus p e r m i t t i n g t h e i r t r a n s p o r t by the movement of the gas. As a g e o l o g i c p r o c e s s i t i s v i s u a l i z e d as a c t i v a t i n g and moving b r e c c i a f r a g m e n t s , and may w e l l f u r n i s h the c h u r n i n g and c o r r o s i v e a c t i o n i n d i c a t e d by f o r example pebble d i k e s . To i n i t i a t e the p r o c e s s , upward s t r e a m i n g gaseous f l u i d s pass t h r o u g h . p r e - f r a c t u r e d r o c k u n t i l the m i x t u r e of r o c k fragments ;and-, gas: a c h i e v e a s t a t e of f l u i d i t y , the a c t i v a t e d fragments are then m o b i l e . Reynolds (1954) s t a t e s t h a t \"...The a s s o c i a t i o n of t u r b u l e n t f l o w s t r u c t u r e w i t h abraded and w e l l - r o u n d e d rock f r a g -27. ments which have not a p p a r e n t l y - b e e n t r a n s p o r t e d away from t h e i r source r o c k s , t o g e t h e r w i t h l a c k of g r a d i n g of the fragments c o n c e r n e d , and the p o s s i b l e presence of d r u s e s . . . \" (p. 579) are c r i t e r i a f o r gas t r a n s p o r t . F l u i d i z a t i o n of a b r e c c i a u ndoubtedly c o u l d a l s o produce s e l e c t i v e t r a n s p o r t a t i o n , a c c o r d i n g to fragment s i z e , a l l o w i n g l a r g e r fragments t o descend and s m a l l e r ones to r i s e w i t h i n the stream, r e l a t i v e to the o t h e r f ragments. B r y n e r ( l 9 6 l ) a s s e r t s t h a t the l a c k of f u s e d m a t r i x , which i s n o r m a l l y found i n i n t r u s i o n b r e c c i a s , i n pebble d i k e s \" . . . i n -d i c a t e s an aqueous or gaseous medium o f t r a n s p o r t a t i o n f o r the p e b b l e s , and the rounding-.of t h e . p e b b l e s show t h a t a t t r i t i o n and p o s s i b l y c h e m i c a l c o r r o s i o n took p l a c e . \" (p. 499). In c o n n e c t i o n w i t h gases, W i l l i a m s (193&) e x p l a i n s t h a t p r e s s u r e from an ad v a n c i n g magma column, e x p l o s i v e v o l c a n i s m b e i n g the d r i v i n g f o r c e , may form d i a t r e m e s i n the f o l l o w i n g manner, \"... R i s i n g gases ' l u b r i c a t e ' the r o o f r o c k s ; p u l s a t i n g magma b r e c c i a t e s the c o v e r ; r e p e a t e d e x p l o s i o n s comminute the cap. r o c k s so t h a t f r o t h i n g magma i s i n t i m a t e l y mingled w i t h them and, near s u r f a c e , steam e r u p t i o n s caused by h e a t i n g of ground water f a c i l i t a t e the d r i l l i n g p r o c e s s w h i l e s l u m p i n g of s l a b s from the c o n d u i t w a l l s e n l a r g e s the c o n d u i t . \" (p. 316). D e s p i t e the f r e q u e n t r e f e r e n c e i n the l i t e r a t u r e to v o l c a n i c o r i g i n and e x p l o s i v e a c t i v i t y , M c K i h s t r y (1955) f i n d s t h a t \"... the r o l e of v o l c a n i c e x p l o s i o n i n c r e a t i n g o r e b e a r i n g p i p e s seems much l e s s i m p o r t a n t - t h a n an u n c r i t i c a l r e a d i n g of the l i t e r a t u r e 28. might suggest., (p. 214). .r Sedimentary b r e c c i a s must be added to t h i s d i s c u s s i o n f o r the sake of completeness. T h i s rock type can.be d e r i v e d from t a l u s and o t h e r s u b - a r e a l o r sub-aqueous c l a s t i c a c c u m u l a t i o n s . These, on b e i n g covered by more m a t e r i a l , and i n c o r p o r a t e d i n the s e d i m e n t a r y s e c t i o n , which i n t u r n w i l l e v e n t u a l l y be meta-morphosed, d i f f e r , g r e a t l y from b r e c c i a s .derived i n the ways mentioned above.' I f the metamorphism were s t a t i c r a t h e r than d i s l o c a t i o n , such a t a l u s b r e c c i a would remain undeformed, the fragments h a v i n g j t h e i r o r i g i n a l a n g u l a r shapes and a s s o r t e d s i z e s . The m a t r i x \" w o u l d tend to be h o r n f e l s i c and p l e n t i f u l , depending on the n a t u r e of the s e d i m e n t a r y b r e c c i a and i t s - h i s t o r y . V. INTERPRETATION OF BRECCIA FORMATION In a d d i t i o n to., the d a t a summarized on the geology of t h i s b r e c c i a , i t . i s n e c e s s a r y to have an u n d e r s t a n d i n g of the g e n e r a l p r e - b r e c c i a g e o l o g y , a s - d e r i v e d -from g e o l o g i c a l r e p o r t s , i n o r d e r to u n d e r s t a n d any i n t e r p r e t a t i o n of b r e c c i a f o r m a t i o n . P r e - B r e c c i a Geology - S t e e p l y d i p p i n g g n e i s s , p o s s i b l y d e r i v e d from s t r o n g l y f o l d e d , metamorphosed, and g r a n i t i z e d i n t e r b e d d e d t u f f s and sediments (Armstrong, 1954) i s thought to have comprised the g e o l o g i c a l s e t t i n g of the a r e a . Emplacement of the v a r i o u s g r a n i t i c Coast i n t r u s i o n s of the Coast Mountains may have been the cause of f o l d i n g and metamorphism observed i n the r o c k s . Mag-m a t i c a c t i v i t y a t t e n d a n t w i t h the emplacement of d i o r i t e - g r a n o d i o r i t e 2 9 . of the Coast Intrusives i s thought to have supplied heat, gases, and magma that were active in breccia formation. Origin of Pasco Gneiss-Breccia Pipe - The chara c t e r i s t i c s of the breccia summarized previously should be explicable by a theory of breccia emplacement.- Realizing t h i s , one may f i r s t l y propose the mechanism of emplacement and then ascertain how each of the char a c t e r i s t i c s may be related to the theory. The emplacement of\the breccia must be envisaged as having taken place during the lat_p.r.-S_tages of one of the; periods of a c t i v i t y of the Coast intrusions. The schi s t s , steeply dipping due to previous folding, have already been metamorphosed to gneiss-migmatites and jointed.. With these basic assumptions in. mind one must then imagine the action of gases r i s i n g from a heat source at depth ahead of'' advancing magma. Explosive action and pulsating pressures due to the plutonic a c t i v i t y shatters parts of the roof rock especially along pronounced gneissosity and j o i n t i n g . Intersections of major fractures provide channel ways for the advancing gas ahead of the magma. This shattering of the country rock, followed by in-streaming of the gas into the fractures ultimately results in a state of f l u i d i z a t i o n . During f l u i d i z a t i o n the fragments, large and small, grain sized to block sized, are envisaged as being in a state of suspension i n the agitated mixture of frag-ments and gas. If this process continues, abrasion by sand blast-ing of the larger fragments occurs; i n this case the sc h i s t o s i t y and the close j o i n t i n g allow the fragments to break along those 30. l i n e s of weakness, t y p i c a l l y r e s u l t i n g i n r e c t a n g u l a r shapes. I n the case of homophanous r o c k s such as m i g m a t i t e i n which t h e r e i s no s t r u c t u r e l e f t , fragments t h a t o r i g i n a l l y s h a t t e r e d a l o n g j o i n t s and f r a c t u r e s i n l a r g e r p i e c e s would abrade a l o n g g r a i n b o u n d a r i e s i n s m a l l e r ones, r e s u l t i n g e v e n t u a l l y i n rounded shapes. The abraded p a r t i c l e s , m o s t l y g r a i n s i z e d and s m a l l e r , are to the most p a r t f l u s h e d out by the gases i n t o apophyses or d i k e s , a c c o r d -i n g to t h e o r y . S i z e - s o r t i n g by r e l a t i v e s i n k i n g depending on the buoyancy of the fragments c o u l d be e n v i s a g e d . I f the heavy p i e c e s sank f a r enough, they would presumably be i n c o r p o r a t e d i n the m e l t , thus g r a d u a l l y changing i t s c o m p o s i t i o n . I f on the o t h e r hand, f l u i d i z a t i o n had not o c c u r r e d l o n g enough f o r a b r a s i o n to produce f i n e p a r t i c l e s , one must imagine t h a t fragments of the s i z e produced by s h a t t e r i n g would be i n dominant numbers. Extreme p r e s s u r e s d u r i n g or a f t e r the o c c u r r e n c e of f l u i d i z a t i o n would compress the m i x t u r e , r e s u l t i n g on c o o l i n g i n a v e r y compact roc k i n which the fragments would impinge upon one a n o t h e r on a l l s i d e s . On the o u t s i d e of t h i s s h a t t e r e d - f l u i d i z e d zone, fragments would impinge upon the w a l l r o c k s . The i n t e r i o r 'mosaic' t h r e e -d i m e n s i o n a l p a c k i n g i s thought of as b e i n g much more competent than the p h y s i c a l c o n t a c t w i t h the w a l l r o c k . On r e l a x a t i o n of the p r e s s u r e , p o s s i b l y due to the escape of most of the gas a l o n g f r a c t u r e s v e r t i c a l l y and l a t e r a l l y , t h i s t i g h t l y packed t h r e e - d i m e n s i o n a l mosaic, not b e i n g f o r c e d a g a i n s t the r o o f and the S i d e s of the r o o f would slump downward somewhat so t h a t a zone of low p r e s s u r e , i f not even a gap would occur be-31. tween w a l l and r o o f r o c k s . Should magma be p r e s e n t below, i t would be f o r c e d upward around t h i s p l u g , and c r y s t a l l i z e as a i -s k i n around i t . As t h e r e c o n c e i v a b l y was a f i e l d of s t a t i c p r e s s u r e i n t h i s magma s u r r o u n d i n g the p l u g , the g r a i n s on c r y s t a l -l i z a t i o n would a l i g n themselves a c c o r d i n g to the s t r e s s . T h i s s h o u l d i n a l l cases be i n s i m i l a r r e l a t i o n to the o u t l i n e of the p l u g . C o n c e r n i n g n a t u r a l p r o c e s s e s which have o c c u r r e d d u r i n g times p a s t , i t i s c o n c e i v a b l e t h a t t h e r e w i l l be s e v e r a l i n t e r p r e t a t i o n s of f i e l d d a t a , depending t o a g r e a t e x t e n t on the e x p e r i e n c e of the o b s e r v e r . The p r i m a r y o b j e c t i v e of a t h e o r y of a mode of f o r m a t i o n however, i s not to be c o r r e c t t o the e x c l u s i o n of a l l o t h e r proposed t h e o r i e s i but to i n c l u d e and s a t i s f a c t o r i l y e x p l a i n the g e o l o g i c a l c h a r a c t e r i s t i c s Of the f o r m a t i o n i n q u e s t i o n . A p p l i c a t i o n of Data to Theory - I t i s i n defence of the t h e o r y p r o f f e r e d h e r e , t h a t the a v a i l a b l e d a t a l i s t e d e a r l i e r i n t h i s t h e s i s , w i l l be e x p l a i n e d as r e s u l t i n g from p r o c e s s e s a c t i v e d u r i n g the f o r m a t i o n of the b r e c c i a . I n t h i s manner i t w i l l be p o s s i b l e t o r e l a t e f i e l d d a t a to the proposed manner of f o r m a t i o n , thus p r o v i d i n g a t e s t of the t h e o r y . The p r o x i m i t y of the b r e c c i a to a g r a n i t i c body, i n t r u s i v e i n t o c o u n t r y r o c k l e a d s to the b e l i e f t h a t the g r a n i t i c i n t r u s i o n was the so u r c e of the b r e c c i a t i n g f o r c e . Gases and heat d e r i v e d from the i n t r u d i n g body a re f a c t o r s i m p o r t a n t i n t h i s t h e o r y . The shape of both the b r e c c i a p l u g and the fragments can be d i r e c t l y connected to the g n e i s s o s i t y and f a u l t s t r u c t u r e s i n the c o u n t r y r o c k as f o l l o w s . C o n t a c t s i n the exposed p l a c e s to the n o r t h and south are p a r a l l e l to g n e i s s o s i t y , and to the e a s t a very g o u g e - r i c h shear zone forms the c o n t a c t . Here i t i s not known whether the f a u l t f o l l o w e d a l o n g the i n i t i a l l y \u00E2\u0080\u00A2.weak con-^ t a c t of the b r e c c i a or whether the f a u l t i s p r e - b r e c c i a and p r o -v i d e d a l a y e r impermeable f o r gases, thus not p e r m i t t i n g b r e c c i a t i o by e x p l o s i v e f o r c e s of them. G e n e i s s o s i t y g r e a t l y f a c i l i t a t e d f r a c t u r i n g of the ro c k a l o n g t h i s s t r u c t u r e . The e x i s t e n c e of c o u n t r y r o c k fragments to the e x c l u s i o n of n o t i c e a b l e q u a n t i t i e s of o t h e r r o c k types i s noteworthy. T h i s tends to c o n f i r m the p o s s i b i l i t y of a s c a r c i t y of o t h e r r o c k types a t d e p t h , as w e l l as the i m p r o b a b i l i t y of s i g n i f i c a n t t r a n s p o r t of m a t e r i a l . The c l o s e p a c k i n g and l a c k of m a t r i x near the c e n t r a l p a r t of the b r e c c i a body i s b e l i e v e d to r e f l e c t the s m a l l e f f e c t of a t t r i t i o n caused by the c h u r n i n g a c t i o n of f l u i d i z a t i o n . Thus, i t i s thought t h a t fluidization\u00E2\u0080\u009Edid not o c c u r l o n g enough to produce the f i n e r , p a r t i c l e s but merely a good d e a l of m i x i n g . Subsequent p r e s s u r e from above and below and l a c k of the a d v a n c i n g gas, c a u s i n g a decrease, of f l u i d i z a t i o n , would r e s u l t i n a t i g h t l y packed t h r e e - d i m e n s i o n a l mosaic of fr a g m e n t s , w i t h v e r y l i t t l e m a t r i x . Loose p a c k i n g a t the p e r i p h e r y i s a p r o d u c t of i n s u r g e n c e of d i o r i t e l a t e r i n the sequence. At t h i s time l o o s e fragments a t the p e r i p h e r y of the t i g h t b r e c c i a body were e n g u l f e d by the d i o r i t e , thus p r o d u c i n g the d i f f e r e n t type of b r e c c i a , and the g r a d a t i o n a l c o n t a c t . D i o r i t e d i k e s w i t h i n the b r e c c i a are s i m p l y e x p l a i n e d by r e -33. c a l l i n g t h a t d i o r i t e was pushed around the b r e c c i a p l u g as a s k i n . As i t was under p r e s s u r e i t f i l l e d any c r a c k s . H o r i z o n t a l a l i g n m e n t and p l a s t i c f l o w are thought to be r e s u l t s of i n t e r n a l f a c t o r s . The d e f o r m a t i o n of fragments i s due to s t r e s s e s s e t up i n fragments due to impingement a g a i n s t one a n o t h e r . The t h r e e d i m e n s i o n a l framework i s not merely caused by a f i t t i n g of fragments a c c o r d i n g to s i z e and shape but by f o r c i b l e p a c k i n g which i s demonstrated by the bent fragments. The g r a n i t i c 'pebbles' have aroused c u r i o s i t y at t h i s l o c a l i t y because they^whow g r e a t c o l o u r c o n t r a s t w i t h the drab background <> of the o u t c r o p . The fragments are u s u a l l y e l o n g a t e and e l l i p t i c a l i n shape, n e a r l y c y l i n d r i c a l . P a r a l l e l to t h e i r l o n g a x i s i s the g e n e r a l o r i e n t a t i o n of m a f i c s , hence the s c h i s t o s i t y . The rock p a r t s e a s i l y i n t h i s d i r e c t i o n , and because t h i s a l i g nment i s a c t u a l l y a l i n e a t i o n the fragments a c q u i r e rounded c r o s s s e c t i o n s . Yet the shapes i n a r o c k f a c e l o o k rounded l i k e p e b b l e s . They are thought to be d i s l o d g e d p i e c e s from b o r d e r phase d i o r i t e a l o n g the lower p e r i p h e r i e s of the b r e c c i a body, presumably c a r r i e d up from below, a l t h o u g h t h e r e i s no i n d i c a t i o n of the d i r e c t i o n of t r a n s -p o r t . The w h i t e p e g m a t i t i c areas p r o b a b l y are space f i l l i n g s by q u a r t z and f e l d s p a r d u r i n g the l a s t s t a g e s of compaction of the b r e c c i a . V a r i a t i o n of fragment s i z e i s l i m i t e d . Most fragments are of one s i z e , a l t h o u g h t h e r e are some t h a t are b l o c k s i z e d . The s m a l l most p l e n t i f u l s i z e d e r i v e d i t s dominance through, the v e r y c l o s e p a r t i t i o n Of the r o c k through s h a t t e r i n g . T h i n s l i v e r s were broken up as a consequence of j o i n t i n g and the i n s t a b i l i t y of 34. t h i n s l i v e r s i n an a g i t a t e d environment. Thus, i t i s seen how the rock was broken up to such s m a l l s i z e . I n a l l p r o b a b i l i t y i t was shredded i n t o s m a l l s l i v e r s too but they were too f r a g i l e f o r t h i s c h u r n i n g environment and were reduced to g r a i n s i z e d p a r t i c l e now found between the l a r g e r f r a g m e n t s , and l a r g e l y r e c r y s t a l l i z e d I t has thus been i n d i c a t e d t h a t the proposed method of b r e c c i a f o r m a t i o n i s i n agreement w i t h the f a c t s o b s e r v e d ; t h a t i t thus i s a t h e o r y of emplacement of t h i s b r e c c i a . The a f o r e m e n t i o n e d l i s t of modes of f o r m a t i o n of b r e c c i a s i s a l s o a l i s t of types of b r e c c i a o c c u r r e n c e s . I t i s u n d e r s t a n d a b l e then t h a t i n normal cases one would f i n d , r a t h e r than a t y p i c a l r o c k f o r m a t i o n , one t h a t i n c o r p o r a t e s s e v e r a l methods--a m i x t u r e of p r o c e s s e s . T h i s i s the case i n t h i s s i t u a t i o n . T h e o r i e s , m e n t i o n e d . b e f o r e , t h a t can be ex c l u d e d w i t h c e r t a i n t y are se d i m e n t a r y b r e c c i a t i o n and b r e c c i a t i o n due to s h r i n k a g e , whereas the o t h e r t h e o r i e s may a p p l y to some e x t e n t , as f o l l o w s . Gases s t r e a m i n g upward ahead of an i n t r u d i n g magma mass would cause e x p l o s i v e a c t i o n ; f l u i d i z a t i o n would o c c u r as e x p l a i n e d b e f o r e ; t e c t o n i c b r e e c c i a t i o n may have been the cause f o r b e t t e r c o n d u i t s f o r the r i s i n g ' m a t e r i a l s ; igneous i n t r u s i o n may f o r c i b l y f r a c t u r e zones of ro c k above the p a r t i a l l y congealed magma; f l u i d i n t r u s i o n , a p r o c e s s s i m i l a r i n many ways to the e x p l o s i o n t h e o r y , would c o n s i s t of gases o r l i q u i d s r i s i n g from depths b r i n g i n g up fragments of c o n d u i t r o c k which then are f o r c e d upward i n t o the ro c k s by a t h i c k mud, t h i s i s p o s s i b l y how g r a n i t i c 'pebbles' were i n t r o d u c e d ; s o l u t i o n and replacement may have o c c u r r e d on a s m a l l s c a l e ; m i n e r a l i z a t i o n s t o p i n g as such i s not i n d i c a t e d , ' 3 5, a l t h o u g h s i g n s of b l o c k c a v i n g have been noted i n c o n n e c t i o n w i t h the b l o c k s of c o u n t r y rock p a r t i a l l y r o t a t e d w i t h i n the b r e c c i a mass. CONCLUSION The Pasco b r e c c i a has been s t u d i e d and the d a t a found to i n d i c a t e a c o m b i n a t i o n of s e v e r a l p r o c e s s e s a c t i v e i n the f o r -mation of the b r e c c i a . Among these e x p l o s i v e a c t i o n of gases ahead of an i n t r u s i v e body, t o g e t h e r w i t h f l u i d i z a t i o n of a m i x t u r e of these gases and s h a t t e r e d r o c k are thought to be of prime importance i n the f o r m a t i o n of the b r e c c i a . . EXTENDED BIBLIOGRAPHY Armstrong, J.E. , 1954 B r y n e r , L., 1961 B u t l e r , B.S., 1913 Emmons, W.H., 1938 F a i r b a i r n , W.H. and Robson, G.M., 1942 F a r m i n , R o l l i n , 1934 F i s h e r , R.V., I 9 6 0 Gates, 0., 1959 Goodspeed, G.E. P r e l i m i n a r y Map, Vancouver N o r t h , B.C. G e o l o g i c a l Survey of Canada, Paper 53-28. B r e c c i a and pebble columns a s s o c i a t e d w i t h e p i g e n e t i c ore d e p o s i t s : Econ.. Geology, v. 56, p. 488-508. 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Walker, R.T., 1928 M i n e r a l i z e d v o l c a n i c e x p l o s i o n p i p e s : Eng. and M i n i n g J o u r . , v. 126, pp. 895. Waters, A.C. and K r a u s k o p f , K. 1941. P r o t o c l a s t i c b o r d e r of the C o l v i l l e B a t h o l i t h : B u l l , G.S.A.,:' v. 52, np. 1355-1418. W i l l i a m s , Howel, 1936 P l i o c e n e v o l c a n o e s of the Navajo-Hopi C o u n t r y : B u l l . G.S.A:, v. 47, pp. 111-172. W r i g h t , A.E. and Bowes, D.R., 1963 C l a s s i f i c a t i o n of v o l c a n i c b r e c c i a s : a d i s c u s s i o n : B u l l . G.S.A., v. 74, pp. 79-86. OUTCROP DISTRIBUTION M A P Pasco Creek, Horseshoe Bay y B.C. L e g e n d : E 3 mlgmotltlo hornbltnd* gn\u00C2\u00ABl\u00C2\u00BB\u00C2\u00AB, hornbl\u00C2\u00BBndl1\u00C2\u00AB g amphibollt* gntltt brcoel a ft border phata* dike g n \u00C2\u00AB l t t o i l t y inferred breccia contact b e d d i n g . OF B R E C C I A B O D Y Pasco Creek, Horseshoe Bay, RC1 Scale' /\"--250 apf o ao no 'So \u00C2\u00A7M Q g . A . * . R o l \u00C2\u00AB r i ' 6 P HIGHWAY S E C T I O N RAILROAD SECTION Legend 0 20 40 60 mam 80ft S H E A R Z O N E G N E I S S B R E C C I A G N E I S S , AMPMiBOL I TE amzmt H O R N B L E N C E D I O R I T E tt P L A G P O R P H Y R T EE ' ' \"133 of BORDER PHASES Fig.3 D I A G R A M M A T I C C R O S S - S E C T I O N S Pasco C r e e k , Horseshoe Bay, B . C "@en . "Thesis/Dissertation"@en . "10.14288/1.0053013"@en . "eng"@en . "Geological Sciences"@en . "Vancouver : University of British Columbia Library"@en . "University of British Columbia"@en . "For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use."@en . "Graduate"@en . "Pasco Creek breccia, Horseshoe Bay, B.C."@en . "Text"@en . "http://hdl.handle.net/2429/37447"@en .