UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Geology of the Strachan Creek area, British Columbia Lee, Randolph 1958

You don't seem to have a PDF reader installed, try download the pdf

Item Metadata

Download

Media
[if-you-see-this-DO-NOT-CLICK]
UBC_1958_A6_7 L3 G3.pdf [ 3.77MB ]
[if-you-see-this-DO-NOT-CLICK]
Metadata
JSON: 1.0053024.json
JSON-LD: 1.0053024+ld.json
RDF/XML (Pretty): 1.0053024.xml
RDF/JSON: 1.0053024+rdf.json
Turtle: 1.0053024+rdf-turtle.txt
N-Triples: 1.0053024+rdf-ntriples.txt
Original Record: 1.0053024 +original-record.json
Full Text
1.0053024.txt
Citation
1.0053024.ris

Full Text

GEOLOGY OF THE STRACHAN CREEK AREA, .BRITISH  COLUMBIA  by RANDOLPH LEE 13.A., B „ S c , U n i v e r s i t y of Western Ontario,  1956  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE iii  the Department of GEOLOGY  We accept t h i s -thesis as conforming t o the required standard  THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1958  i  ABSTRACT  The Strachan Creek area i s on the east shore of Howe Sound about three m i l e s north of the town of Horseshoe Bay, B.C. The rocks of the area c o n s i s t of migmatite of the Bowen I s l a n d group, volcanic rocks of the Gambier group, p l u t o n i c rocks of the Coast Intrusions,, and l a t e b a s i c and a c i d i c dykes.  These rocks are described and t h e i r r e l a t i o n s h i p s discussed,  A s t r i k i n g f e a t u r e of the Strachan Creek area i s the banding i n the d i o r i t e , one of the u n i t s of the Coast Intrusions,.  Each complete band  i s a couplet composed of one l i g h t - and one dark-coloured l a y e r , one l a y e r grading i n t o the other.. The l i g h t - c o l o u r e d l a y e r i s composed mostly of p l a g i o c l a s e , whereas the dark-coloured l a y e r i s composed mostly of hornblende and magnetite.  G e n e r a l l y , the r a t i o of hornblende (plus magnetite) t o p l a g i o -  clase decreases downward from a sharp contact, the couplets thus resembling i n v e r t e d "graded-bedding".  The author t e n t a t i v e l y concludes that the  banding i n the d i o r i t e o r i g i n a t e d b y a process o f d i f f e r e n t i a t i o n and c r y s t a l r i s i n g w i t h i n a cooling d i o r i t e magma.  In presenting the  r e q u i r e m e n t s f o r an  of B r i t i s h it  this  freely  agree that for  thesis in partial  advanced degree at the  Columbia, I agree t h a t available  the  f o r r e f e r e n c e and  permission for extensive  s c h o l a r l y p u r p o s e s may  D e p a r t m e n t o r by  fulfilment  be  s h a l l make  study.  I  the  gain  s h a l l not  Department o f  GEOLOGY  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, C a n a d a . Date  April  15,  1958  Columbia,  Head o f  thesis my  I t i s understood  copying or p u b l i c a t i o n of t h i s t h e s i s a l l o w e d w i t h o u t my  further  copying of t h i s  that  be  University  Library  g r a n t e d by  his representative.  of  for  written  financial  permission.  ii  TABLE OF CONTENTS  Page ABSTRACT  i  LIST OF ILLUSTRATIONS  i i  ACMOWLEDGMENTS  iv  CHAPTER I INTRODUCTION  I-  Physiography.  1  CHAPTER I I k  GENERAL GEOLOGY CHAPTER I I I GEOLOGY OF THE STRACHAN CREEK AREA Bowen I s l a n d Group. Gambler Group « . . Diorite Banding i n the D i o r i t e O r i g i n of the Banding Granodiorite. . . . . . . . . Small. I n c l u s i o n s i n Granodiorite Granite Dyke Rocks  8 •  9 16 20 2J> ...» 29 ... 38 ijl 143 k&  LIST OF ILLUSTRATIONS Figure Banded Migmatite G r a n i t i c l e n s i n amphibolite Gneissic amphibolite band containing g r a n i t i c l e n s . . . . G r a n i t i c m a t e r i a l surrounding blocks of amphibolite « • • Thin-section of g n e i s s i c amphibolite. . . . . . . . . . . A t t i t u d e of migmatite i n the road cut near Strachan Creek NO.,  l . e e e . . . .  Road cut j u s t north of Newman Creek  Page  1 2 3 h 5  10 11 11 12 13  6  llj.  7  17  iii  Figure Sections exposed i n the road and r a i l r o a d cut shewing a t t i t u d e of conglomerate bed i n v o l c a n i c s 8 P y r i t e surrounded by epidote . . • . . . . . . . . . . . . 9 Faulted contact between d i o r i t e and g r a n o d i o r i t e . . . . . 10 Pegmatitic lenses i n d i o r i t e . . . . . . . 1 1 Orthoclase-epidote v e i n l e t s i n g r a n o d i o r i t e 12 A p l i t e v e i n i n banded d i o r i t e 13 Epidote v e i n f o l l o w i n g f a u l t plane i n d i o r i t e .11+ Banding i n the d i o r i t e i n the road cut . . . . . . . . . . 1 5 Graphs of the o r i e n t a t i o n of p l a g i o c l a s e . . . . . . . . . . 1 6 Gradation contacts of b a l d i n g i n d i o r i t e . . . . . . . . . 1 7 Banding t h a t G i l b e r t describes from the S i e r r a Nevada p l u t o n , Calif... 18 Thin-section of dark band of the d i o r i t e showing r e l a t i o n ship of hornblende t o p l a g i o c l a s e . . . . . . . . . . 19 Elongated i n c l u s i o n i n g r a n o d i o r i t e . . 20 Oval i n c l u s i o n i n g r a n o d i o r i t e . . . . . . . . . . . . . . 21 Round i n c l u s i o n i n g r a n o d i o r i t e 22 Road cut near Strachan Creek No. 1 showing g r a n i t e dykes in diorite • 23 G r a n i t e - d i o r i t e contact i n road cut. . • 21+ Network of b l a c k v e i n l e t s i n granite . . 2 5 Road cut near Sunset Creek showing the various dykes . . . 26 A p l i t e v e i n containing epidote 27  Page 19 21 22: 23 23 21+ 2JU 27 28 29 30 36 i+l i i l ijl hh 1+1+ 1+5 1+7 1+9  TABLES  Comparison of the mineral composition of the main p l u t o n i c rocks and of the components of the migmatite •  Table  Page  ,. 1.  15  ACKNOVttEDGEMENTS  The w r i t e r acknowledges h i s indebtedness t d the B.C. Department of Highways f o r supplying the base map  (100' t o 1")  on which the geology was  p l o t t e d and t o Marwell Construction L t d . f o r t h e i r co-operation and a s s i s tance i n allowing the author to use the Upper Levels Highway w h i l e s t i l l i n construction.-  Thanks t o Dr.. K.C. McTaggart, R.H.  Dawson, and Min-Min Wei  f o r t h e i r i n v a l u a b l e assistance i n the f i e l d work,. H e l p f u l suggestions during the l a b o r a t o r y work and preparation of the manuscript were given by Dr.- K.C. McTaggart and Dr* J.V.. Ross.. The w r i t e r g r a t e f u l l y acknowledges the assistance of S. Zajac f o r the t r a n s l a t i o n of a German paper.  1  CHAPTER  I  INTRODUCTION  The area mapped i s on the east shore of Howe Sound about f o u r miles north of Horseshoe Bay, B.C.  The area extends from Sunset Creek t o Newman  Creek and from the sea shore i n l a n d about a m i l e .  I t forms a considerable  p a r t of the western slope of Mt. Strachan. The area i s r e a d i l y accessible by c a r , boat or t r a i n .  The  Pacific  Great Eastern Railway runs p a r a l l e l t o the c o a s t l i n e at an e l e v a t i o n of about 100 f e e t above sea l e v e l .  The Upper Levels Highway, a new road, i s being  b u i l t p a r a l l e l t o the r a i l r o a d and about 75 f e e t above i t . F i e l d work was done by the author during the 1957-58 u n i v e r s i t y w i n t e r session.- I t was l m L t e d mostly t o the weekends* Much of the area was d i f f i c u l t t o explore as the slopes are e i t h e r covered w i t h dense growth or are steep rock cliffs» Physiography The map-area i s i n a t y p i c a l l y rugged s e c t i o n of the Coast of B.C.  Mountains  The mountains r i s e a b r u p t l y from Howe Sound t o e l e v a t i o n s of more  than 5000 feet.. F i v e creeks cut through the area.  A l l of them are i n the y o u t h f u l  stage of development as they show V-shaped v a l l e y s and many r a p i d s and waterf a l l s i n places many tens of f e e t high. The l a r g e r creeks are f l o o r e d w i t h huge boulders of g r a n o d i o r i t e s e v e r a l f e e t i n diameter most of which are smooth and f a i r l y w e l l rounded..  The l a r g e s i z e of the boulders a t t e s t t o the  2  great competency of the s p r i n g f l o o d s i n moving m a t e r i a l down stream.. I n the interstream areas, t a l u s i s abundant and i n many places a l i t t l e digging revealed t a l u s below a t h i n s o i l and v e g e t a t i v e cover*  The  t a l u s p i l e s are mostly covered by vegetation and only a t the base of a c t i v e l y eroding rock c l i f f s i s there any exposed talus..  The inter-stream areas are cov-  ered w i t h dense f o r e s t growth whose c o n t i n u i t y , i n many p l a c e s , are broken by steep, high rock c l i f f s .  C l i f f s were encountered mostly at e l e v a t i o n s of  around 700, lUOO, and 3U00 f e e t .  The c l i f f s around lij.00 f e e t coincide w i t h  the approximate p o s i t i o n of a contact between g r a n o d i o r i t e and d i o r i t e .  3  LOCATION Scale: One  Inch t c  MAP 6 Miles  h  CHAPTER I I  GENERAL GEOLOGY  The general geology of the Vancouver North area i s summarized i n the f o l l o w i n g t a b l e which i s based on Armstrong's work (195U)« PLEISTOCENE and RECENT Tertiary Miocene or l a t e r  B a s a l t i c f l o w s , dykes, s i l l s , tuff..  Upper Eocene  K i t s i l a n o formation — sandstone, s h a l e .  Eocene  Burrard f o i m a t i o n — sandstone, s h a l e , conglomerate, minor t u f f and b a s a l t .  CENOZOIC  conglomerate,  Main P l u t o n i c rocks ? T r i a s s i c ? and/or l a t e r Gambier Group MESOZOIC  T u f f , b r e c c i a , agglomerate, slate,, andesite, a r g i l l i t e , arkose, greywacke, q u a r t z i t e , conglomerate.  angular unconformity P l u t o n i c rocks ? T r i a s s i c ? and/or e a r l i e r Bower I s l a n d Group Volcanic and metamorphic rocks,., minor sedimentary r o c k s . The rocks i n the area north of Vancouver c o n s i s t of g r a n i t i c rocks  of the Coast Range b a t h o l i t h , metamorphic and v o l c a n i c rocks of t h e Bowen I s l a n d group,, sedimentary and v o l c a n i c rocks of the Gambier group, and T e r t i a r y sediments and minor i n t r u s i v e s * In a r e a l extent t h e g r a n i t i c rocks of the Coast Range b a t h o l i t h predominate.  Nevertheless, l a r g e areas of Mesozoic rocks (Bowen I s l a n d and  Gambier groups) are found throughout the Vancouver North area, i e . t h e head of Lynn Creek, Mt. Strachan and Mt.. H o l l y b u r n , along the east shore of Howe Sound, Bowen I s l a n d , Gambier I s l a n d , and some of t h e s m a l l e r i s l a n d s i n Howe Sound, (see L o c a t i o n Map, p.3)» The Bowen I s l a n d group has two main d i v i s i o n s , one c o n s i s t i n g of mainly b a s a l t i c and a n d e s i t i c l a v a s and the other of interbedded t u f f s and sedimentary rocks.. A l l the rocks of t h i s group have been r e c r y s t a l l i z e d t o some e x t e n t , but primary s t r u c t u r e s are g e n e r a l l y preserved.  I n some areas,  however, these rocks have been e x t e n s i v e l y metamorphosed and metasomatized such t h a t the o r i g i n a l t e x t u r e s have been o b l i t e r a t e d , i e . the summits of Mounts Strachan and Hollyburn.. I n most places the Gambier group c o n s i s t s of p y r o c l a s t i c rocks and lavas w i t h minor interbedded sedimentary rocks.. On Mount Brunswick, however, the s e c t i o n i s a t l e a s t 6000 f e e t t h i c k of which 2000 f e e t i s composed of s l a t e , a r g i l l i t e , q u a r t z i t e , and arkose. The age r e l a t i o n between the Bowen I s l a n d group and the Gambier group has been w e l l e s t a b l i s h e d by an angular unconformity which separates the two groups.  Armstrong (l°f>i+, P»- 2) s t a t e s t h a t ,  During the i n t e r v a l represented by t h i s unconformity the Bowen I s l a n d group rocks were f o l d e d , metamorphosed, and p a r t l y g r a n i t i z e d j some of the p l u t o n i c rocks were formed; and the l a n d was u p l i f t e d and eroded. Furthermore, at the base of the Gambier group t h e r e i s a b a s a l conglomerate which has rounded and subrounded boulders l i t h o l o g i c a l l y s i m i l a r t o the rock types of the Bowen I s l a n d group and t o the o l d e r p l u t o n i c r o c k s . The b a t h o l i t h i c rocks of the Vancouver North area consist of g r a n i t e , g r a n d i o r i t e , quartz d i o r i t e , d i o r i t e , and minor gabbro.  G r a n d i o r i t e and quartz  d i o r i t e are, by f a r , the most abundant of the p l u t o n i c rocks mentioned above..  6  There i s apparently more than one p e r i o d of i n t r u s i o n of the p l u t o n i c rocks.. G r a n i t i c pebbles i n the v o l c a n i c rocks of the Bowen I s l a n d group i n d i c a t e t h a t some p l u t o n i c rocks were formed p r i o r t o the d e p o s i t i o n of t h i s group, but no bodies of p l u t o n i c rocks were recognized as belonging t o t h i s r e l a t i v e age, Armstrong (1954, P» 5) notes t h a t some p l u t o n i c rocks formed before the deposition of the Gambier group whereas others formed after.. For example, the g r a n o d i o r i t e mass i n the southern part of Gambier I s l a n d i s unconformably o v e r l a i n by the Gambier group rocks,, whereas the hornblende d i o r i t e and quartz d i o r i t e of Mt.. Hanover and Mt. Harvey, about 3 miles north of the Strachan Creek area, appear t o intrude the Gambier group.  Since the contact between  the p l u t o n i c rocks and the Gambier group over most of the Vancouver North area g e n e r a l l y i s not exposed, the age r e l a t i o n s h i p of these rocks can not be d e f i n i t e l y established.  However, by u s i n g the potassium-argon  method,  Folinsbee (1957) has determined an absolute age of 10J? m i l l i o n years f o r the Coast Range b a t h o l i t h at Vancouver. No mention i s made of the type of rock used f o r the age determination, but probably a sample of g r a n o d i o r i t e or quartz d i o r i t e was used since these are the most abundant p l u t o n i c rocks.. This would place the main p e r i o d of p l u t o n i c i n t r u s i o n i n the Middle Cretaceous. T e r t i a r y rocks of the area c o n s i s t of the Burrard f o r m a t i o n , the K i t s i l a n o formation, and minor i n t r u s i o n s and v o l c a n i c rocks of Miocene age or l a t e r . The Burrard formation i s composed of about 2000 f e e t of shale, conglomerate,  sandstone,  and minor t u f f and b a s a l t . I t dips g e n t l y t o the south.  I t i s mostly of c o n t i n e n t a l o r i g i n and f o s s i l , p l a n t s w i t h i n i t are of Eocene age, (Berry, 1926)..  7  The K i t s i l a n o formation consists of about 2000 f e e t of conglomerate, sandstone, and shale mostly of c o n t i n e n t a l o r i g i n r e s t i n g on the eroded surface of the Burrard formation.  I t also dips g e n t l y t o the south and  fossil  p l a n t s w i t h i n i t are of Upper Eocene age, (Berry, 1°26).. The minor i n t r u s i o n s and v o l c a n i c rocks of Miocene age or l a t e r c o n s i s t of b a s a l t i c dykes and s i l l s , and minor t u f f s .  B a s a l t i c dykes are  seen t o cut the K i t s i l a n o and Burrard formations and the p l u t o n i c rocks.  At  S e n t i n a l H i l l and L i t t l e Mountain, l a c c o l i t h - l i k e bodies of b a s a l t crop out.. Tuff i s found on the south side of False Creek,  8  CHAPTER  in  GEOLOGY OF THE STRACHAN CREEK AREA  The geology of the Strachan Creek area i s sham i n the f o l l o w i n g table.  PLEISTOCENE TERTIARY  and  RECE1JT  ' Late dykes P l u t o n i c rocks:  MESOZOIC  Granite, Granodiorite Diorite  Gambier Group Bowen I s l a n d Group-  The oldest rock exposed i n the Strachan Creek area i s migmatite which u n d e r l i e s a small area and i s bordered by g r a n i t e , g r a n o d i o r i t e , and diorite*  This mass of migmatite i s w e l l exposed along the road cut near  Strachan Creek No. 1. and i s c o r r e l a t e d w i t h the Bowen I s l a n d group because of i t s s i m i l a r i t y i n l i t h o l o g y t o the Bowen I s l a n d group rocks of the summits of Mounts Strachan and Hollyburn., This c o r r e l a t i o n i s at best o n l y the most reasonable assumption as there i s the p o s s i b i l i t y that the migmatite belongs t o the Gambier group. The Gambier group w i t h i n the Strachan Creek area i s composed mostly of v o l c a n i c rocks, i . e . t u f f , agglomerate, and p o r p h y r i t i c b a s a l t . -A bed of v o l c a n i c conglomerate w i t h i n the sequence of v o l c a n i c s s t r i k e s Nl4.0°W and dips hO° t o the NE. volcanics.  I t s a t t i t u d e probably represents the general a t t i t u d e of the  The contact between the Gambier group and the Bowen I s l a n d group  i s not exposed i n the Strachan Creek area.  Elsewhere, however, Armstrong  9  recognized an angular unconformity separating the two groups, Bowen Island below and Gambier above.. The plutonic rocks of the area consist of granite, d i o r i t e , and granodiorite.  The age relationships of these rocks are not d e f i n i t e l y  established because outcrops of t h e i r contacts are scarce.  However, ex-  posures of the g r a n i t e - d i o r i t e contact indicate t h a t granite probably formed l a t e r than d i o r i t e .  Granite dykes i n the v i c i n i t y of Strachan Creek  No. 1 contain inclusions of d i o r i t e suggesting that the granite magma stoped off parts of the d i o r i t e during i n t r u s i o n (see Figure 21;, p. hli).  Diorite,  just south of Strachan Creek No. 2, i s cut by what appears to be an apophyse of granodiorite which suggests that the granodiorite i s younger than the d i o r i t e . The age r e l a t i o n s h i p between granodiorite and g r a n i t e , however, i s not determinable because exposures of the contact of these rocks do not reveal conclusive evidence. A l l the plutonic rocks exposed i n the Strachan Creek area appear t o have formed a f t e r the deposition of the Gambier group.  I f the Gambier group  rocks were younger than the plutonic rocks, then the contacts of these rocks would be conformable.  However, i t i s seen that both the d i o r i t e and the grano-  d i o r i t e truncates the general s t r i k e of the Gambier group rocks which i s represented by the attitude of the conglomerate bed. Many l a t e dykes, a c i d i c and b a s i c , are found i n the area. dykes are of d i o r i t i c and b a s a l t i c composition.  The basic  Some are porphyritic and others  are non-porphyritic. The a c i d i c dykes are of granite and aplite..  Bowen Island Group Within the Strachan Creek area, migmatite  of the Bowen Island group  crops out only along and near the road cut i n the v i c i n i t y of Strachan Creek  10  No.. I .  This body of migmatite extends up the slope of the mountain t o an  e l e v a t i o n of approximately 600 f e e t and extends t o the north of Strachan Creek No. 1 f o r about 600 f e e t .  I t s southern contact f o l l o w s the creek  and i s against g r a n i t e , and i t s northern contact i s against g r a n o d i o r i t e . A few miles t o the south, outside of the Strachan Creek area,  :  there i s a l a r g e mass of migmatite which extends from the s h o r e - l i n e t o approximately a h a l f m i l e i n l a n d .  I t appears t o be s i m i l a r t o the migma-  t i t e of the area under i n v e s t i g a t i o n i n both l i t h o l o g y and s t r u c t u r e . Armstrong (l°51+) shows a small mass of migmatite on Strachan Creek No. 2 at an e l e v a t i o n of 1000 i t during a t r a v e r s e up t h i s creek.. than i s i n d i c a t e d on the  f e e t , but the author d i d not  encounter  I t i s probably a much smaller mass  map.  Migmatites are rocks composed of both g r a n i t i c and metamorphic p a r t s and here, the migmatite c o n s i s t s of a metamorphic host rock which i s streaked and veined w i t h g r a n i t i c m a t e r i a l . . The migmatite, i n general, c o n s i s t s of g n e i s s i c amphibolite and g r a n i t i c rock a l t e r n a t i n g i n bands ranging from a few inches t o a f o o t or more i n width. N  Generally, the bands and f o l i a t i o n of the amphibolite s t r i k e  1+0° E and d i p northwest 25° t o 85°» At d i f f e r e n t i n t e r v a l s , the dark  amphibolite bands are i n t e r r u p t e d by l i g h t - c o l o u r e d , quite coarse-grained, g r a n i t i c rock, (see Figure Figure 1. Banded migmatite. Dark amphibolite band i n t e r r u p t e d by g r a n i t i c m a t e r i a l .  1),  11  In some p l a c e s , the g r a n i t i c part c o n s i s t s of i r r e g u l a r patches and streaks of w h i t i s h rock r a t h e r than r e g u l a r bands,, (see Figures 2 and 3).  I n general, however, the streaks seem t o be s t r e t c h e d out p a r a l l e l t o  the f o l i a t i o n w i t h i n the amphibolite.  These g r a n i t i c s t r e a k s , i n many p l a c e s ,  contain areas of coarse, pink orthoclase and small patches of green, r a d i a t i n g c r y s t a l s of epidote..  Figures 2 and 3»- Gneissic amphibolite bands containing g r a n i t i c streaks which are s t r e t c h e d out p a r a l l e l t o the f o l i a t i o n . The g r a n i t i c part i s composed mostly of coarse, anhedral grains of pink orthoclase, white p l a g i o c l a s e , and c l e a r transparent quartz i n approximately equal amounts.  The pink orthoclase commonly occupies the c e n t r a l  part of the g r a n i t i c s t r e a k s . In other places i n the same outcrop, the l i g h t m a t e r i a l i s the matrix which surrounds and cements l a r g e and small angular blocks of amp h i b o l i t e , (see Figure k)» I n some specimens, the banding w i t h i n the amphibolite blocks l i n e up w i t h each other, but i n others, the blocks do not have a common o r i e n t a t i o n .  I n a few p l a c e s , l o c a l areas of o r i e n t e d  and unoriented blocks of amphibolite occur w i t h i n t e n f e e t of each other.  12  F i g u r e k» Amphibolite blocks surrounded b y granitic material.  The a m p h i b o l i t e s a r e d a r k , medium- t o f i n e - g r a i n e d r o c k s composed m o s t l y o f hornblende and p l a g i o c l a s e s e p a r a t e d i n t o d i s t i n c t l a m i n a e t h a t s i m i l a t e bedding*  G e n e r a l l y , t h e d a r k bands a r e t h i c k e r t h a n t h e l i g h t bands.  P y r i t e i s f a i r l y abundant i n t h e m i g r a a t i t e s , b u t t h e r e i s no apparent for  i t s occurence.  control  I t i s f o u n d as l e n s e s o r s m a l l pods b o t h i n and c u t t i n g  a c r o s s t h e d a r k and l i g h t bands.. I n t h i n s e c t i o n s o f t h e dark bands, p l a g i o c l a s e ( A n ^ t o An^g) f>0$, and h o r n b l e n d e h.0% a r e seen t o be t h e dominant m i n e r a l s and c h l o r i t e , o r t h o c l a s e , e p i d o t e , q u a r t z , m a g n e t i t e , p y r i t e , b i o t i t e , and a p a t i t e o c c u r i n s m a l l e r amounts.. The t e x t u r e o f t h e d a r k band i s a U o t r i o m o r p h i c , e q u i g r a n u l a r , :  and medium-grained.  The p r e f e r r e d o r i e n t a t i o n o f t h e h o r n b l e n d e and t h e s e p a r a -  t i o n o f t h e h o r n b l e n d e and p l a g i o c l a s e i n t o d i f f e r e n t l a m i n a e a r e e a s i l y d i s c e r n i b l e i n t h i n - s e c t i o n , ( s e e F i g u r e 5). d i r e c t i o n of f o l i a t i o n . .  C h l o r i t e i s stretched out i n the  The p l a g i o c l a s e g r a i n s o f t h e d a r k bands a r e m o s t l y  untwinned and o c c u r as somewhat s p h e r i c a l g r a i n s p r e d o m i n a n t l y of one s i z e * Quartz i s i n t e r s t i t i a l , f i l l i n g t h e space between h o r n b l e n d e and p l a g i o c l a s e * Hornblende i s g e n e r a l l y f r e e o f i n c l u s i o n s , b u t i n some p l a c e s e n c l o s e s s m a l l , round g r a i n s o f a p a t i t e , p y r i t e , m a g n e t i t e , and p l a g i o c l a s e . ,  Relatively l i t t l e  13  a l t e r a t i o n of the minerals has occurred, although b i o t i t e i s p a r t l y a l t e r e d t o c h l o r i t e , e s p e c i a l l y along the cleavage traces..  In the l i g h t - c o l o u r e d bands, the mineralogy i s e s s e n t i a l l y the same as that of the dark bands except t h a t the r e l a t i v e proportions of the minerals are d i f f e r e n t *  P l a g i o c l a s e and quartz occurs i n approximately equal amounts  and make up approximately 90 per cent of the rock. 8 per cent of the l i g h t bands.  Hornblende makes up about  Quartz occupies l a r g e i n t e r s t i t i a l areas be-  tween p l a g i o c l a s e and hornblende and g e n e r a l l y shows wavy extinction..  A  small q u a n t i t y of b i o t i t e i s present, but i t i s mostly a l t e r e d to c h l o r i t e and z o i s i t e . . Hornblende occurs as s c a t t e r e d g r a i n s , r e g u l a r i n o u t l i n e , and showing s l i g h t p o i k i l i t i c texture having i n c l u s i o n s of p l a g i o c l a s e and i r o n ore*  C a t a c l a s t i c texture i s apparent i n t h i n - s e c t i o n as most quartz grains  show wavy e x t i n c t i o n and f i n e l y crushed grains are found between l a r g e g r a i n s . The general s t r i k e of the banding and f o l i a t i o n of the migmatite i s N 70° E t o N k0° E and the d i p 30° t o 50° t o the northwest, (see Figure 6 ) . The dip may v a r y from 30 t o 50 degrees i n a v e r y short distance., Epidote veins are r a t h e r abundant and cut the rock i n many d i r e c t i o n s . These migmatites could have o r i g i n a t e d i n s e v e r a l ways, (1) by i n j e c t i o n of magma along surfaces of weakness of p r e - e x i s t i n g rocks,, (2) by p a r t i a l replacement of host rock by i o n i c exchange of m a t e r i a l between host  Ik  rock and f l u i d , or (3) by d i f f e r e n t i a l f u s i o n of host rock of v a r i e d composition..  « Figure 6.  200 fect A t t i t u d e of the migmatite i n the road cut near Strachan Creek No. 1.  In some places the g r a n i t i c component appears to have o r i g i n a t e d by i n j e c t i o n of g r a n i t i c magma i n t o amphibolite such t h a t the l i g h t - c o l o u r e d g r a n i t i c m a t e r i a l encloses and surrounds angular blocks of amphibolite and, i n general, acts as the cementing m a t r i x , (see Figure  Here, the g r a n i t i c  m a t e r i a l forms sharp contacts w i t h the amphibolite* In other places the g r a n i t i c m a t e r i a l appears t o have formed by p a r t i a l replacement of the dark m a t e r i a l probably by magmatic emanations, or some a c t i v e f l u i d of unknown o r i g i n .  I o n i c exchange of m a t e r i a l between  the host rock and the f l u i d s which penetrate the host rock along paths of minimum r e s i s t a n c e would r e s u l t i n the formation of migmatite..  I n places  where there are numerous r e g u l a r a l t e r n a t i n g bands of l i g h t and dark m a t e r i a l which show uniform width and sharp contacts f o r s e v e r a l tens of f e e t * (see Figure 1), i t seems l i k e l y t h a t the banding i s due to p a r t i a l replacement  as  i t i s d i f f i c u l t t o v i s u a l i z e such r e g u l a r i n j e c t i o n . There a r i s e s a l s o the p o s s i b i l i t y t h a t the migmatite o r i g i n a t e d by  15  d i f f e r e n t i a l f u s i o n of host rock of uniform composition, y i e l d i n g a l o w melting g r a n i t i c o r pegmatitic l i q u i d (magma) d i s t r i b u t e d through the rock as discontinuous streaks and veins.. To t e s t t h i s p o s s i b i l i t y , a sample of the g r a n i t i c part of the migmatite was taken of an i s o l a t e d lens of the l i g h t m a t e r i a l w i t h i n the dark material.. I f the l i g h t m a t e r i a l were formed by d i f f e r e n t i a l f u s i o n , then i t s components p o s s i b l y could have been derived from the melting (fusion) of parts of the amphibolite.  A comparison of the  mineral composition of the i s o l a t e d lens of g r a n i t i c m a t e r i a l and of the amphibolite i s i l l u s t r a t e d i n Table I * TABLE  I  COMPARISON OF MINERAL COMPOSITION OF THE MAIN PLUTONIC ROCKS AND OF THE COMPONENTS OF THE MIGMATITE Minerals  Amphibolite  I s o l a t e d Granodiorite lens of granitic material.  Plagioclase  Anl^  ^ho  ^1x0  50 %  h$%  60 %  Quartz  3  hS  10-15  K-feldspar  4  l  5-io  Hornblende  ho  8  5  1  1  15  Biotite  Diorite  Granite  kh  An  m  40-60 % 2-15  2 0  1% 30  60 30-40 5-8  I t i s seen that the p l a g i o c l a s e has approximately the same average composition i n both the amphibolite and the i s o l a t e d lens of g r a n i t i c material.. However, i f the g r a n i t i c m a t e r i a l i s the r e s u l t of p a r t i a l f u s i o n of the amphibolite, then the p l a g i o c l a s e of the g r a n i t i c m a t e r i a l would be more  16  sodic i n composition than the p l a g i o c l a s e of the amphibolite,.  The phase  diagram of the a l b i t e - a n o r t h i t e system as determined from a r t i f i c i a l melts by N.L. Bowen shows that i f a c r y s t a l of p l a g i o c l a s e o f a given composition (eg, An)^) i s heated t o i t s melting p o i n t , the f i r s t l i q u i d t o form i s of much more sodic composition,, i e , an a l b i t i c l i q u i d would be formed by p a r t i a l f u s i o n o f more c a l c i c c r y s t a l s . Thus, the i s o l a t e d lens probably i s not the r e u l t of p a r t i a l f u s i o n of amphibolite* A comparison of the estimated mineral composition o f g r a n i t e , g r a n o d i o r i t e , and d i o r i t e w i t h the i s o l a t e d lens of g r a n i t i c material, i s i l l u s t r a t e d i n Table I,. I t i s seen that the mineral composition of n e i t h e r the granite, g r a n o d i o r i t e , nor the d i o r i t e i s s i m i l a r t o the composition o f ;  the i s o l a t e d l e n s *  The g r a n i t e contains much more K-feldspar and much l e s s  p l a g i o c l a s e than the i s o l a t e d l e n s *  The d i o r i t e has much more hornblende and  much l e s s quartz than the i s o l a t e d l e n s *  The g r a n o d i o r i t e has more K-feldspar  and b i o t i t e , and much l e s s quartz and hornblende than the i s o l a t e d l e n s .  Thus,  the evidence i s inconclusive as t o whether the magmatic emanations or a c t i v e f l u i d s came from the g r a n i t e , d i o r i t e , o r g r a n o d i o r i t e magma,. In conclusion i t seems t o the author that the migmatite of the Strachan Creek area formed p o s s i b l y p a r t l y by replacement and p a r t l y b y i n j e c t i o n o f magma. The source of the magma or of the a c t i v e f l u i d s i s not known, but could p o s s i b l y have been derived from the granite,, g r a n o d i o r i t e , or d i o r i t e magma,. The Gambier Group The Gambier group of rocks i s found i n the northern p o r t i o n of the Strachan Creek area.  These rocks occupy an area extending from the shore o f  Howe Sound t o an e l e v a t i o n of about 2000 f e e t .  The eastern contact of the  17  Gambier group i s against g r a n o d i o r i t e , whereas i t s southern contact i s against d i o r i t e . ,  The Gambier group c o n s i s t s of t u f f s , b a s a l t , v o l c a n i c  agglomerate, p o r p h y r i t i c b a s a l t , and v o l c a n i c conglomerate.  The s t r a t i -  graphic sequence of these rocks, however, has not been worked out i n d e t a i l . The best exposures of these rocks are found i n the road and r a i l r o a d cuts j u s t north of Newman Creek.  The sequence of rocks a t t h i s l o c a l i t y i s  i l l u s t r a t e d i n the sketch i n Figure 7.  t  -toff  Y<  /  J  ftoo4  ^  •'  .:  Y  ,  \'.' •••  Road  s  Figure 7.- Section exposed i n the road cut j u s t north of Newman Creek. P o r p h y r i t i c b a s a l t i s found adjacent t o a f a u l t contact w i t h diorite.  The b a s a l t i s a greenish rock containing small white phenocrysts  of p l a g i o c l a s e s c a t t e r e d throughout a dark, a p h a n i t i c groundmass. Phenoc r y s t s make up approximately 15 per cent of the rock. I n t h i n - s e c t i o n s of p o r p h y r i t i c b a s a l t , the e s s e n t i a l minerals are seen t o be c h l o r i t e 35% p l a g i o c l a s e 30%, s e r i c i t e 10$, and epidote 20%. 3  Accessory minerals are p y r i t e , c a l c i t e , and a u g i t e . The p l a g i o c l a s e i n the groundmass i s of l a b r a d o r i t e composition. the contact w i t h d i o r i t e .  S e r i c i t e i s more abundant near  On the other hand, epidote i s evenly d i s t r i b u t e d  and always quite abundant.. The rock has marked t r a c h y t i c texture.. Tuff i s by f a r the predominant rock type of the Gambier group w i t h i n the Strachan Creek area.  I t i s found adjacent t o and north of the  18  porphyritic basalt.  I n general appearance i n hand-specimen, the t u f f r e -  sembles an a l t e r e d greywacke, but the presence, i n t h i n - s e c t i o n , of c h l o r i t e pseudomorphs a f t e r shards suggests that i t i s a t u f f . and f i n e - g r a i n e d .  The t u f f i s green  As seen i n t h i n - s e c t i o n , the main constituents of the  t u f f are l i t h i c fragments 60%, epidote 30$, and c h l o r i t e 10%» The groundmass c o n s i s t s of c h l o r i t e and epidote and a very minor amount of f e l d s p a r . Broken fragments of p l a g i o c l a s e are present as medium-sized grains embedded i n the f i n e - g r a i n e d groundmass. Most of the l i t h i c fragments show textures of v o l c a n i c r o c k s *  A small proportion of quartz i s present as i r r e g u l a r , small  grains or as aggregates of small grains set i n the groundmass* Volcanic agglomerate occurs as a bed w i t h i n the t u f f .  I n outcrop  the agglomerate i s a p u r p l i s h rock w i t h prominent c l a s t i c t e x t u r e .  Most of  the angular fragments of v o l c a n i c rock are l e s s than an i n c h across.  However,  many l a r g e , angular blocks over a f o o t i n diameter are a l s o present*  On a  weathered surface, the angular blocks are conspicuous because they are w h i t i s h , whereas the groundmass i s p u r p l i s h . s c a t t e r e d throughout the rock.  Epidote occurs as small clumps  I t a l s o occurs as t i n y v e i n l e t s ( l / 8 " t o l/k  lt  t h i c k ) c u t t i n g the agglomerate* In t h i n - s e c t i o n s of the v o l c a n i c agglomerate i t i s seen t h a t l i t h i c fragments of varying s i z e s and shapes make up about °5 per cent of the rock* Most of the l i t h i c fragments are angular and so c l o s e l y packed that the groundmass i s d i s t i n g u i s h e d only w i t h d i f f i c u l t y .  A l l the fragments are of  v o l c a n i c rocks and many of them have t r a c h y t i c t e x t u r e .  The groundmass con-  s i s t s of minute grains of f e l d s p a r which, i n some places, appear as d i s t i n c t , separate g r a i n s , but i n other places, appear t o be welded so that i n d i v i d u a l grains are not d i s t i n g u i s h a b l e .  The l a s t feature suggests that the rock has  19  been somewhat re c r y s t a l l i z e d * . A bed of v o l c a n i c conglomerate i s found w i t h i n the t u f f s i n the Strachan Creek area.  This conglomerate bed i s exposed i n the road cut  approximately 2000 f e e t north of Newman Creek.  Here, i t i s about one f o o t  t h i c k , (see Figure 8 ) . The same bed i s exposed i n the r a i l r o a d cut nearby and here the s t r i k e of the conglomerate bed i s N k0° ¥ and the d i p about hO° t o the northeast.  The a t t i t u d e of the conglomerate bed probably r e -  presents the general a t t i t u d e of the v o l c a n i c s of t h i s area.. The conglomerate c o n s i s t s of l a r g e boulders, cobbles,, and pebbles embedded i n a m a t r i x of f i n e - g r a i n e d rock d e t r i t u s .  The boulders are v a r i a b l e  i n s i z e , but average k inches i n diameter. The l a r g e s t ones are about two f e e t i n diameter. The boulders and pebbles are w e l l rounded.  The m a j o r i t y of  the pebbles and boulders are of v o l c a n i c rocks, i e . b a s a l t , andesite, t u f f , p o r p h y r i t i c b a s a l t and andesite*  One pebble of quartz and one of quartz  d i o r i t e occurs i n the conglomerate*  Figure 8.  Sections exposed i n the road and r a i l r o a d cuts north of Newman Creek.  20  The conglomerate probably was l a i d down as e i t h e r a t e r r e s t r i a l (stream) or marine (shore-line) deposit.  The provenance of the conglomerate,  judging by the abundance of v o l c a n i c boulders and pebbles, was a v o l c a n i c t e r r a i n containing small areas of p l u t o n i c r o c k s . Diorite D i o r i t e forms an elongate body having a g e n e r a l N-S t r e n d extending from Newman Creek t o Strachan Creek No. 1, a distance of approximately one and a quarter m i l e s .  I t extends up the slope of the mountain g e n e r a l l y t o an  e l e v a t i o n of 11+00 f e e t , where i t comes i n t o contact w i t h g r a n o d i o r i t e . There are three types of d i o r i t e , i e . banded, non-banded, and p o t a s h - r i c h types. The banded d i o r i t e grades i n t o the non-banded type and the two have e s s e n t i a l l y the same mineral composition.  The potash-rich d i o r i t e , on the other hand,  contains a high proportion of pink K-feldspar and i s due t o a l t e r a t i o n of non-banded d i o r i t e . I n hand specimen, the unhanded d i o r i t e i s t y p i c a l l y greenish and medium-grained, a l l o t r i m o r p h i c , and equigranular i n t e x t u r e .  The mafic  minerals on the average form approximately 30-1+0 per cent of the rock.  The  d i o r i t e i s e s s e n t i a l l y a hornblende-plagioclase rock w i t h appreciable magnetite., P y r i t e i s rather abundant i n c e r t a i n s c a t t e r e d l o c a l i t i e s i n a l l ' types of d i o r i t e . pyrite.  I t occurs as s t r i n g e r s , l e n s e s , or pods of almost s o l i d  S t r i n g e r s are g e n e r a l l y a f r a c t i o n of an i n c h t h i c k , but some  pods may be f a i r l y l a r g e , i e . 15 inches long by 3 inches wide.  Epidote i s  g e n e r a l l y c l o s e l y associated w i t h p y r i t e , (see Figure °)» I n t h i n - s e c t i o n s of the unhanded d i o r i t e , p l a g i o c l a s e (average compos i t i o n An^,) and hornblende are seen t o be the e s s e n t i a l m i n e r a l s * Quartz  21  i s present i n very small amounts (2%), but i n a few samples i s as much as 15" percent of the d i o r i t e *  The accessory minerals are a p a t i t e , z i r c o n ,  i r o n ores ( p y r i t e and magnetite), b i o t i t e , and a u g i t e * A l t e r a t i o n products are epidote, c h l o r i t e , s e r i c i t e , and minor serpentine and t a l c .  Some c a l -  c i t e veins occur i n f i s s u r e s i n the rock.  Figure 9* P y r i t e surrounded by epidote as seen i n an outcrop of d i o r i t e . . The p l a g i o c l a s e shows zoning which i s g e n e r a l l y the normal type ( l a b r a d o r i t e cores, about A n ^ , t o andesine rims, about t h i n - s e c t i o n s o s c i l l a t o r y zoning i s found*  An^cj),  but i n some  The boundary of the zones of  many grains i s corroded i n d i c a t i n g reaction, between the p l a g i o c l a s e and the melt during c r y s t a l l i z a t i o n .  I n some p l a c e s , p l a g i o c l a s e l a t h s are a l t e r e d  to s e r i c i t e and c h l o r i t e and are consequently q u i t e cloudy.  Generally,  p l a g i o c l a s e forms from lj.0-60 per cent of the rock. Hornblende i s dark green i n t h i n - s e c t i o n and i s s t r o n g l y p l e o — c h r o i c (yellow t o l i g h t green t o dark green on r o t a t i o n ) .  It is poikilitic,  containing small roundish i n c l u s i o n s of p l a g i o c l a s e , i r o n ore, and a p a t i t e * In many sections i t i s p a r t l y a l t e r e d t o epidote and c h l o r i t e . , The borders  22  of hornblende are almost i n v a r i a b l y ragged and i r r e g u l a r suggesting c o r r o s i o n by the magma during c r y s t a l l i z a t i o n .  Rarely, i t - i s found as f a i r l y  euhedral c r y s t a l s . Quartz i s i n t e r s t i t i a l , c l e a r , and shows undulatory e x t i n c t i o n . A p a t i t e i s ubiquitous. O r t h o c l a s e - r i c h d i o r i t e i s found j u s t south of Strachan Creek No.. 2 along both the road and r a i l r o a d c u t s .  The southern contact of  o r t h o c l a s e - r i c h d i o r i t e i s against g r a n o d i o r i t e which, near the contact, contains many veins of pink orthoclase, (see Figure 10). I t i s a f a u l t contact.  Pink orthoclase occurs i n both t h e d i o r i t e and g r a n o d i o r i t e ( l )  w i t h epidote as t h i n v e i n l e t s l e s s than a quarter i n c h wide, (2) as d i s seminated g r a i n s , and (3) as pegmatitic lenses (or pods) composed.essent i a l l y of o r t h o c l a s e , quartz, and epidote, (see Figures 11 and 1 2 ) . W i t h i n the g r a n o d i o r i t e , the amount of pink orthoclase decreases away from the f a u l t contact f o r a distance of approximately 100 f e e t , whereas i n the  1 clio>-iie L— vei*.le.(-s l • / p'mK  o r- + U o c  <^  of  ortkocU.se  1  IO f t - .  Figure 10. F a u l t contact between g r a n o d i o r i t e and d i o r i t e i n a road cut near Strachan Creek No. 2. L o c a l i t y has high amount of pink o r t h o c l a s e .  23  d i o r i t e , pink orthoclase i s abundant f o r over 500 f e e t from the contact.  . Figure 11,. Pegraatitic lenses i n d i o r i t e i n the road cut near Strachan Greek No. 2, Pegmatitic lenses; ( u s u a l l y w i t h 60% o r more pink orthoclase) are abundant i n d i o r i t e , and as a r e s u l t gives the rock an o v e r a l l spotted appearance when viewed at a distance, (see Figure 11). These pegmatitic lenses and a l s o the abundant orthoclase are probably the r e s u l t o f l a t e hydro-thermal s o l u t i o n s emanating from the g r a n i t e when i t was c r y s t a l l i z i n g . .  in© rft. o.b i A r t t i o \ " ^ . r *A4.ar \j let*  Figure 12. Orthoclase-epidote v e i n l e t s i n g r a n o d i o r i t e i n road cut near Strachan Creek No. 2.  A thin-  2k  s e c t i o n of o r t h o c l a s e - r i c h d i o r i t e showed t h a t i t i s h i g h l y a l t e r e d and contains much c l i n o z o i s i t e 35$, s e r i c i t e 10$, and c h l o r i t e $%, texture i s apparently due t o f a u l t i n g .  Cataclastic  The hydrothermal. s o l u t i o n s probably  invaded the rock along the f a u l t and permeated the country rock along the crushed zones.  Figure 13. A p l i t e v e i n i n banded d i o r i t e as seen i n road c u t .  Figure lk» Epidote v e i n f o l l o w i n g f a u l t plane i n d i o r i t e .  Epidote i s abundant i n a l l phases of the d i o r i t e .  I t i s frequent-  l y associated w i t h p y r i t e and forms the borders of a p l i t e v e i n s , (see Figure 13).-  I t may a l s o occupy p a r t s of f a u l t planes,, (see Figure lk)  f r a c t u r e s , and may p a r a l l e l the banding..  t  joints,  Epidote occurs as disseminated  grains only i n r a t h e r minor amounts* Armstrong  (195k) t h i n k s t h a t the hornblendic and b i o t i t i c  d i o r i t e s - are border f a c i e s of g r a n o d i o r i t e and may not be of igneous or magmatic o r i g i n .  He s t a t e s ,  Normally, the r a t i o p l u t o n i c rocks increases v o l c a n i c and sedimentary i n f l u e n c e of these o l d e r the p l u t o n i c rocks..  of hornblende t o b i o t i t e i n the near the exposed areas of o l d e r s t r a t a , i n d i c a t i n g the profound formations on the composition of  25  The northern contact of the d i o r i t e of the map-area i s against v o l c a n i c rocks of the G mbier group, whereas i t s southern contact i s w i t h a  granite..  To the east and up the mountain slope d i o r i t e gives way t o grano-  diorite.  The contact between these two rock types i s not exposed, so i t i s  not p o s s i b l e t o s a y whether the contact i s sharp or gradational..  Just  north of Strachan Creek No.. 1 d i o r i t e appears t o be cut by an apophyse of granodiorite suggesting t h a t g r a n o d i o r i t e i s younger than d i o r i t e . Masses of g r a n o d i o r i t e bordered by d i o r i t e have been described from other p a r t s of the w o r l d .  Compton  (1955),  i n h i s study of the B a l d  Rock b a t h o l i t h , found a gradation from leucotrondhjemite t o trondhjemite t o g r a n o d i o r i t e t o t o n a l i t e from the core of the p l u t o n out to the r i m . The width of the t o n a l i t e border was of the order of 1000 f e e t ,  (1956)  Akaad  described the Ardara g r a n i t i c d i a p i r of I r e l a n d i n which he a l s o  found a t o n a l i t e border surrounding a g r a n o d i o r i t e core* The d i o r i t e of the Strachan Creek area p o s s i b l y represent the border f a c i e s of the l a r g e g r a n o d i o r i t e mass. However, exposures of the contact between d i o r i t e and g r a n o d i o r i t e are very poor and much of the d i o r i t e and g r a n o d i o r i t e i s covered such t h a t t h e i r r e l a t i o n s h i p s are obscured. I t seems more l i k e l y that the d i o r i t e and g r a n o d i o r i t e r e present two separate (but perhaps r e l a t e d ) i n t r u s i o n s , whereby the g r a n o d i o r i t e was formed l a t e r and i n places cut through the d i o r i t e as can be seen i n the road cut near Strachan Creek No.  1.  Banding i n the D i o r i t e Banding i s prominent i n the d i o r i t e i n the area j u s t north of  26  the  contact between granite and d i o r i t e , t h a t i s , between Sunset Creek  and Strachan Creek No, 1, and occurs i n both the road cut and the r a i l road c u t *  Each complete band i s a couplet composed of one l i g h t and one  dark-coloured l a y e r : one l a y e r grading i n t o the other* The c h a r a c t e r i s t i c s of the banding are l i s t e d below, (a)  Across the s t r i k e , the banding may be i n t e r r u p t e d by wide zones of massive, unhanded d i o r i t e which range i n width from 2 0 t o 5 0 f e e t . In places the banding i s v e r y f a i n t and d i f f i c u l t t o d i s t i n g u i s h ,  (b)  The banding i s found o n l y near the contacts of the granite and the migmatite,.  (c)  The banding strikes. N 1*0-70° E and dips about 6 0 - 7 0 ° NW.  (d)  The d i f f e r e n c e i n c o l o u r between the l i g h t and dark band i s due t o the  l a r g e d i f f e r e n c e i n the r a t i o of mafic minerals t o f e l d s p a r i n  each.  The white bands have very l i t t l e hornblende and magnetite,  whereas the dark bands have over 1*0 per cent mafic m i n e r a l s . I r o n ore  (magnetite and p y r i t e ) i s g e n e r a l l y c l o s e l y associated with  hornblende, (e)  The l i g h t bands are g e n e r a l l y one h a l f an inch t h i c k , but are an i n c h or more i n a few p l a c e s .  The dark bands are g e n e r a l l y over  one i n c h t h i c k and i n some places are over 6 inches t h i c k . dark bands f i n a l l y grade i n t o unhanded d i o r i t e * g e n e r a l l y much t h i c k e r than the l i g h t ones.  The  The dark bands are  The r a t i o i s approxi-  mately 3 s i but may be ..quite v a r i a b l e , (f)  Over a distance of one f o o t at one l o c a l i t y there are t e n couplets,  (g)  The bands a r e , i n many p l a c e s , wavy and undulating and t h e i r a t t i t u d e v a r i e s considerably over a short distance (a f o o t o r s o ) , but the  27  o v e r a l l t r e n d remains constant, (see Figure  Figure 15. (h.)  15)•  Banding i n the d i o r i t e i n the road cut,.  I n some places the bands merge and look somewhat l i k e i n v e r t e d "cross-bedding", (see Figure 15).  Outside the map-area, near the  Lookout Point on the Upper Levels Highway approximately a mile from the town of Horseshoe Bay, t h i s feature i s w e l l exposed. (i)  Magnetite i s more abundant i n the dark bands and appears t o be most abundant near the sharp contact from where i t g r a d u a l l y decreases i n abundance u n t i l , i n the l i g h t bands, i t becomes a v e r y minor constituent..  (j)  The contact between the l i g h t and dark band i s not everywhere sharp. Both contacts maybe g r a d a t i o n a l , (see Figure  (k)  17).  The p l a g i o c l a s e i n both bands i s zoned (Core An^g t o r i m A n ^ )  and  g e n e r a l l y has a rough l a m i n a t i o n p a r a l l e l t o the banding, (see Figure 16).  The o r i e n t a t i o n of p l a g i o c l a s e l a t h s was measured on the f l a t  -3o  Frequency curve showing the o r i e n t a t i o n of p l a g i o c l a s e i n the l i g h t band of the diorite  y \  -2o  /  No. of grains of p l a g i o c l a s e  - IO  •  J  1  1  Angle of d e v i a t i o n of long a x i s of p l a g i o c l a s e l a t h s from lamination of banding  Frequency curve showing the o r i e n t a t i o n of p l a g i o c l a s e i n the dark band of the diorite  I  too  No. of grains of p l a g i o c l a s e  ,  ,  P  ,  So  6o  4o  2o  1 o  1  1  ,  1  ,  «o  -*o  6o  Bo  too  Angle of d e v i a t i o n of long axis of p l a g i o c l a s e l a t h s from lamination of banding  Figure 16. O r i e n t a t i o n of p l a g i o c l a s e i n the l i g h t and dark bands i n the d i o r i t e . . The measurements were made on the f l a t stage using.oriented t h i n - s e c t i o n s of both the l i g h t and dark bands of the d i o r i t e .  29  stage and i t was found t h a t the p l a g i o c l a s e i n the l i g h t band i s _  b e t t e r o r i e n t e d than those of the dark band.  Hornblende appears t o  be i n t e r s t i t i a l and i s not apparently oriented, (see F i g u r e 19, p, 36).  Figure 17, (1)  Gradational contacts of banding i n d i o r i t e ,  The grains s i z e of the minerals appears t o be s l i g h t l y l a r g e r i n the dark band near the sharp contact. There seems t o be a gradation i n g r a i n s i z e from dark to l i g h t band*  I n other words, i t i s v e r y  s i m i l a r t o i n v e r t e d "graded bedding". O r i g i n of the Banding i n the D i o r i t e The type of banding found i n the d i o r i t e has been described extensively.  Cloos (1936) describes very s i m i l a r banding which he found  i n the g r a n o d i o r i t e of the S i e r r a Nevada p l u t o n i n C a l i f o r n i a * the banding " b l a t t e r s c h l i e r e n " ( b l a t t e r = pages)*  He c a l l s  I t should be noted,  however, that i n the hands of the Sierra.Nevada p l u t o n the r a t i o of mafic minerals t o p l a g i o c l a s e decreases upwards from a sharp contact whereas i n the hands of the Strachan Creek area the r a t i o increases.  G.K.  Gilbert  (1906) describes banding i n g r a n i t e i n the S i e r r a Nevada p l u t o n which i s quite s i m i l a r t o b l a t t e r s c h l i e r e n and t o the banding i n the d i o r i t e of the Strachan, Creek area* However, the banding wMch G i l b e r t describes has one  30  feature t h a t i s not seen i n the  Strachan Creek area. One s e r i e s of bands  i s truncated by another s e r i e s of bands g i v i n g the appearance of an "unconforraity", (see Figure 18)*  Figure 18.  Banding i n g r a n i t e which G i l b e r t describes from the S i e r r a Nevada pluton of C a l i f o r n i a .  The b l a t t e r s c h l i e r e n , G i l b e r t ' s banding, and the banding i n the Strachan Creek area show a sharp c o n t a c t a t the base of the dark band, gradation i n c o l o u r , m i n e r a l s , and grains s i z e from dark t o l i g h t bands, and some alignment of f e l d s p a r s p a r a l l e l to the bands.. Both the b l a t t e r s c h l i e r e n and the banding i n the Strachan Creek area are found near the contacts of older r o c k s , and are cut by a younger g r a n i t e .  The  s i m i l a r i t i e s i n the c h a r a c t e r i s t i c s of the banding i n the three areas described above suggest that t h e i r mode of o r i g i n i s similar.. There are at l e a s t f i v e ways i n which the banding i n the Strachan Creek area might p o s s i b l y have formed.  These are grouped i n t o  non-magmatic and magmatic o r i g i n s and are l i s t e d below. 1.  Non-magmatic O r i g i n s . (a)  Banding represents o r i g i n a l s t r a t i f i c a t i o n of sedimentary rocks which have since been replaced. The banding may have formed as a result of replacement of former  s t e e p l y dipping, overturned, graded beds of sedimentary rocks*  I f the  31  o r i g i n a l rocks were a s e r i e s of a l t e r n a t i n g l a y e r s of sedimentary rocks of d i f f e r e n t composition (eg, arkose and t u f f ) , then t h i s would e x p l a i n the compositional d i f f e r e n c e of the bands,. This hypothesis seems t o f i t most of the features of the bands.  I t accounts f o r the i n v e r t e d "graded-bedding",  the d i f f e r e n c e i n g r a i n s i z e , the sharp c o n t a c t s , the "cross-bedding", and the great number of bands,  A strong argument f o r the g r a n i t i z a t i o n or r e -  placement o r i g i n i s that the a t t i t u d e of the banding i n the d i o r i t e and the a t t i t u d e of the lamination, i n the migmatite roughly c o i n c i d e , Armstrong (19$h) has noted t h a t the lamination i n the Bowen I s l a n d group has the same general trend throughout the North Vancouver area and t h a t i t represents primary s t r u c t u r e s ,  Phemister (l9h5) a l s o observed that the  laminated type of p r e - b a t h o l i t h i c rocks (Bowen I s l a n d group) i n the v i c i n i t y of Vancouver are metasediments.  The l a m i n a t i o n i n these rocks  represent bedding planes and i n the f i e l d show consistent s t r i k e and d i p over considerable areas.  Thus, i t i s l i k e l y that the l a m i n a t i o n i n the  migmatite of the Strachan Creek area i s a primary s t r u c t u r e and represents o r i g i n a l bedding.  Since i t s a t t i t u d e i s congruent w i t h the a t t i t u d e of  the banding i n the d i o r i t e , then i t i s p o s s i b l e t h a t the banding i n the d i o r i t e a l s o represents bedding planes.  Thus, i t i s v i s u a l i z e d t h a t ,  before d i o r i t i z a t i o n , the area now represented by d i o r i t e c o n s i s t e d of a s e r i e s of s t e e p l y dipping sedimentary r o c k s .  Granitization then altered  these rocks t o d i o r i t e and the banding of the d i o r i t e i s the o r i g i n a l bedding of the sedimentary rocks which has been preserved.  The  migmatite  would represent a knot r e s i s t a n t to the wave of g r a n i t i z a t i o n t h a t formed the d i o r i t e . . There are, however, many d i f f i c u l t i e s w i t h t h i s hypothesis.  32  I f , o r i g i n a l l y , the bands were graded beds, then i t seems l i k e l y t h a t graded bedding would be present i n rocks surrounding the Strachan Creek area.  However, graded bedding does not occur i n any of the sedimentary  or metamorphic rocks of the North Vancouver area.  A l s o , the migmatite  of the Strachan Creek area does not show graded bedding.  No metamorphic  textures ( i e . f o l i a t i o n , s c h i s t o s i t y , and c a t a e l a s t i c t e x t u r e ) and no t y p i c a l l y metamorphic minerals are present i n the d i o r i t e .  new  The u n i f o r m i t y  of mineral composition of the d i o r i t e and the u n i v e r s a l occurrence of a p a t i t e , z i r c o n , i r o n ore, and b i o t i t e as accessory minerals i s not e a s i l y explained by an o r i g i n through g r a n i t i z a t i o n . .  I t seems most probably t h a t  the o r i g i n a l sediments would have v a r i a b l e composition and, when g r a n i t i z e d , would not a l l be a l t e r e d t o d i o r i t e of uniform mineral composition* (b)  Banding as a r e s u l t of metamorphism of d i o r i t i c rocks.. The p o s s i b i l i t y a r i s e s t h a t the banding i n the d i o r i t e i s the  r e s u l t of p o s t - c r y s t a l l i z a t i o n metamorphism of p r e - e x i s t i n g d i o r i t i c rocks where metamorphic d i f f e r e n t i a t i o n separated the minerals i n t o l i g h t and dark bands t o produce a g n e i s s i c rock.. There are various processes of metamorphic d i f f e r e n t i t a t i o n by which contrasted mineral assemblages may develop from an o r i g i n a l l y uniform parent rock.  The separation of minerals may be pro-  duced by s o l u t i o n , by s o l i d d i f f u s i o n , and by the f o r c e of c r y s t a l l i z a t i o n . S o l i d d i f f u s i o n i s the migration of ions through continuous c r y s t a l l a t t i c e s , but o n l y through s t r i c t l y l i m i t e d distances ( g e n e r a l l y minute).  The f o r c e  of c r y s t a l l i z a t i o n i s vaguely defined (Turner 191*8, p. 137) as "the d r i v i n g f o r c e causing d i f f u s i o n of appropriate chemical substances through a c r y s t a l l i n e mass towards a c t i v e l y growing porphyroblasts or other crystals".  Most w r i t e r s v i s u a l i z e metamorphic d i f f e r e n t i a t i o n as a  33  phenomenon e s s e n t i a l l y connected w i t h s o l u t i o n and r e d e p o s i t i o n of chemical components of rocks during metamorphism.. There a r e , however, many f a c t s -which can not be r e a d i l y explained, by t h i s hypothesis.  I f the banding of the d i o r i t e was formed by metamor-  phic d i f f e r e n t i a t i o n , then i t i s v e r y l i k e l y that the bands would be symm e t r i c a l , i e . the l i g h t and dark bands would be o f equal w i d t h and a l l . cont a c t s would be g r a d a t i o n a l .  A strong argument against a metamorphic o r i g i n  of the banding i n the d i o r i t e i s t h a t the texture of the d i o r i t e , as seen i n t h i n - s e c t i o n and i n hand-specimen, c e r t a i n l y appear t o be magmatic, i e . the c r y s t a l s intermesh,. there are no r e l i c t minerals, and there are no new, t y p i c a l l y metamorphic minerals. 2,  Magmatic O r i g i n s (a) Banding due t o c o o l i n g e f f e c t s near a c o l d contact. The banding may be the r e s u l t of d i f f e r e n t i a l c o o l i n g i n the  v i c i n i t y of the margins of the d i o r i t e .  During the c o o l i n g stage of the  d i o r i t e , a thermal gradient would be set up at i t s margin.  There would be  a gradual increase i n the temperature of the magma from a c o o l margin i n wards t o a hot c e n t r a l core.  At the margin of the d i o r i t e i n t r u s i o n , the  magma would be against c o o l rocks.  Thus, c r y s t a l l i z a t i o n would begin from  the margin inward. Since p l a g i o c l a s e appears t o be e a r l y , c r y s t a l l i z a t i o n would begin at the margin w i t h p l a g i o c l a s e and would g r a d u a l l y move inward w i t h i n c r e a s i n g formation of hornblende and magnetite u n t i l one complete couplet i s formed*  I n order t o get repeated bands, there must have been  e i t h e r p e r i o d i c h a l t s i n the cooling of the magma o r p e r i o d i c changes i n the thermal, gradient.  The l a t t e r may be brought about by convection  3k  currents which would b r i n g i n new heat supplies and f r e s h magma from below or from the h o t t e r c e n t r a l part of the magma. L o c a l i z a t i o n of c r y s t a l l i z a t i o n along the c o o l i n g w a l l s has f r e quently been invoked t o e x p l a i n gradual v a r i a t i o n i n m i n e r a l constituents near the margin of i n t r u s i v e bodies. There are many examples of c r y s t a l l i z a t i o n from the margin inwards.  I n the Skaergaard i n t r u s i o n (Wager and  Deer, 1933—39) the marginal border group has i n some places elongated f e l d spars perpendicular t o the contact, and everywhere shows a gradation of mineral composition from the margin inwards i n d i c a t i n g that the magma c r y s t a l l i z e d from the margin i n towards the c e n t r e .  Another example i s t h a t  many pegmatite veins have c r y s t a l s perpendicular t o the w a l l s of the v e i n which obviously began t o form at the w a l l s and grew inwards. Also many dykes and s i l l s have c h i l l e d margins and show a gradation i n m i n e r a l comp o s i t i o n and i n the s i z e of the minerals from the contact i n towards the centre suggesting t h a t they c r y s t a l l i z e d  from the w a l l s inward.  Thus, i t  i s seen that c r y s t a l l i z a t i o n from the margin inwards i s not uncommon. I t seems probable that the banding r e s u l t e d from c o o l i n g e f f e c t s near a c o o l contact and c r y s t a l l i z a t i o n from the margin inward, but t h i s e f f e c t i s most probably s u b s i d i a r y t o the greater changes t h a t d i f f e r e n t i a t i o n and c r y s t a l r i s i n g would produce., I t seems very u n l i k e l y that the m u l t i p l e bands could have formed s o l e l y by d i f f e r e n t i a l - c o o l i n g .  Some  other process such as d i f f e r e n t i a t i o n , c r y s t a l s e t t l i n g , or d i f f u s i o n i s necessary t o produce a separation of minerals.. (b)  Banding through d i f f e r e n t i a l movements, (Cloos, 1936). Cloos argues that the b l a t t e r s c h l i e r e n of t h e S i e r r a Nevada  pluton are due t o d i f f e r e n t i a l movements i n the magma. Evidence that  35  movement occurred i n the d i o r i t e magma of Strachan Creek are p o s s i b l y the waviness of some of the bands, the rough alinement of p l a g i o c l a s e p a r a l l e l t o the banding, (see Figure 16, p. 28), and the presence of "cross-bedding". Cloos argues that the b l a t t e r s c h l i e r e n were formed where movements i n the magma were strong, and that areas of unhanded rock were areas of quiesence. Since the b l a t t e r s c h l i e r e n and the banding i n the d i o r i t e are s i m i l a r , there i s a p o s s i b i l i t y that they have s i m i l a r origins.. However, evidence t h a t movements occurred i n the d i o r i t e magma are not common and signs of strong movement are absent.  Thus, i t seems u n l i k e l y , though not  impossible,  that the banding r e s u l t e d from d i f f e r e n t i a l movements i n the d i o r i t e magma, (c)  Banding through d i f f e r e n t i a t i o n and c r y s t a l r i s i n g . I t i s p o s s i b l e t h a t the banding i n the d i o r i t e r e s u l t e d from the  process of d i f f e r e n t i a t i o n and c r y s t a l r i s i n g .  In t h i s process the r e l a t i v e  d e n s i t i e s of p l a g i o c l a s e and hornblende (plus magnetite) and the v i s c o s i t y of the magma would p l a y an important r o l e .  I t i s important to note that  there i s a s i g n i f i c a n t and s u f f i c i e n t d i f f e r e n c e i n the d e n s i t i e s of p l a g i o c l a s e and hornblende t o b r i n g about t h e i r separation through s e t t l i n g or r i s i n g i n an appropriate l i q u i d medium.  P l a g i o c l a s e has a d e n s i t y of  2.60-2,75 whereas common hornblende has a density of 3 , 0 5 - 3 , 1 * 7 (Dana, Textbook of Mineralogy).  From the study of the paragenesis of the minerals  i n the dark bands i t appears that hornblende formed simultaneously s l i g h t l y a f t e r p l a g i o c l a s e , (see Figure 19).  with  and  Hornblende occurs as i n t e r -  s t i t i a l m a t e r i a l f i l l i n g the spaces between l a t h s of p l a g i o c l a s e , and i n places i s intergrown w i t h p l a g i o c l a s e .  There are many i n c l u s i o n s of p l a g i o -  c l a s e i n hornblende, but the reverse i s not t r u e .  The  c r y s t a l s , of p l a g i o -  c l a s e are subhedral, and i n many places are intergrown with one another.  In  36  Figure 19•  Dark band of d i o r i t e as seen i n thin-section tinder crossed n i c o l s . Hornblende i s i n t e r s t i t i a l and contain inclusions of plagioclase and magnet i t e . X 100.  some places they show corroded edges where they are i n contact with hornblende.  Since the hornblende formed after the plagioclase, then i t could  not have settled out to form the dark bands.  I t i s possible, however,  that the plagioclase floated and consequently caused the separation of the l i g h t and dark minerals. The banding may have developed either on the f l o o r or near the roof of the d i o r i t e intrusion.  I t seems improbable, however,  that the banding developed on the f l o o r of the intrusion because the plagioclase, on c r y s t a l l i z a t i o n , would start to r i s e through the denser magma.. The plagioclase would not accumulate into a layer because there would be nothing to arrest their r i s e and consequently the plagioclase crystals would continue to move upwards u n t i l either the magma becomes too viscuous or the plagioclase i s stopped by a barrier.  37  The author v i s u a l i z e s the banding as a r e s u l t of d i f f e r e n t i a t i o n near the roof of the d i o r i t e i n t r u s i v e -whereby the p l a g i o c l a s e separated out from the magma and rose t o the roof where i t accumulated as a layer.. Consider the c r y s t a l l i z a t i o n of the f i r s t couplet a t the roof of the i n trusion.  The composition of the magma forming t h i s couplet would be  uniform before c r y s t a l l i z a t i o n s t a r t e d .  C r y s t a l l i z a t i o n would begin with  p l a g i o c l a s e c r y s t a l s which, being l i g h t e r than the magma, would r i s e and accumulate against the r o o f .  The separation of p l a g i o c l a s e from the melt  forming the couplet would e n r i c h the lower part of the couplet w i t h heavy constituents.  When an appreciable amount of p l a g i o c l a s e c r y s t a l s had  accumulated a t the r o o f , c r y s t a l l i z a t i o n of hornblende began and f i l l e d the  spaces between the p l a g i o c l a s e l a t h s .  the  other minor constituents of the d i o r i t e ) would then continue t o c r y s -  t a l l i z e u n t i l the couplet i s s o l i d i f i e d . c l a s e and hornblende i s produced.  P l a g i o c l a s e and hornblende (and  I n t h i s way a separation of p l a g i o -  A f t e r the f i r s t couplet had s o l i d i f i e d ,  convection currents would bring i n a new supply of magma of uniform compos i t i o n s i m i l a r t o that of the f i r s t couplet.  C r y s t a l l i z a t i o n of p l a g i o -  clase would begin and these c r y s t a l s would r i s e and accumulate against the base of the dark band of the f i r s t couplet.  The process of separation by  d i f f e r e n t i a t i o n and c r y s t a l r i s i n g would be repeated u n t i l the second couplet i s produced.  Many r e p e t i t i o n s of t h i s process would r e s u l t i n  m u l t i p l e bands. The width of the l i g h t band ( p l a g i o c l a s e band) would depend s i g n i f i c a n t l y on the rate of c r y s t a l l i z a t i o n of the p l a g i o c l a s e and the length of time that the p l a g i o c l a s e had t o accumulate at the roof before c r y s t a l l i z a t i o n of hornblende and consequently the whole couplet.. The  38  v a r i a t i o n s i n the width of the couplets may be the r e s u l t of changes i n the temperature gradient as a r e s u l t of convection currents.  The rough  lamination of the p l a g i o c l a s e s i n the l i g h t bands r e f l e c t the tendency .of the p l a g i o c l a s e p l a t e s t o f l o a t t o the roof with t h e i r f l a t faces p a r a l l e l t o the r o o f , or the e f f e c t of currents w i t h i n the magma f l o w i n g p a r a l l e l t o the r o o f .  The v a r i a t i o n s i n the width of a s i n g l e dark band may be the  r e s u l t o f convection currents which c a r r i e d away parts of the heavy c o n s t i tuents or of the s i n k i n g of parts of the heavy constituents of the dark band t o lower parts of the magma as a r e s u l t o f g r a v i t y . A f t e r s o l i d i f i c a t i o n of the d i o r i t e magma, the whole mass o f d i o r i t e was overturned and the banding assumed i t s present attitude.. This i s a necessary inference and a major o b j e c t i o n t o the hypothesis as there i s no evidence t o suggest that the d i o r i t e was overturned a f t e r c o n s o l i d a tion. In conclusion i t i s seen that none o f the hypotheses f i t p e r f e c t l y the features of the banding, but p o s s i b l y the o r i g i n of the landing through d i f f e r e n t i a t i o n and c r y s t a l r i s i n g i s the most reasonable and t h e e a s i e s t t o visualize. Granodiorite A l a r g e part of the Strachan Creek area i s underlain b y granodiorite.  I n general, the g r a n o d i o r i t e covers most of the eastern h a l f of  the Strachan Creek area.  Along the road and r a i l r o a d cut between Strachan  Creek No. 1 and Strachan Creek No. 2, there i s a 500 foot s e c t i o n of granodiorite.  Throughout most of the area, g r a n o d i o r i t e i s bordered by d i o r i t e .  To the northwest, however, g r a n o d i o r i t e i s adjacent t o the v o l c a n i c rocks of the Gambier group, and t o the southwest i t i s i n contact with granite.. The  39  The g r a n o d i o r i t e - g r a n i t e contact i s exposed outside of the Strachan Creek area i n a road cut approximately a h a l f m i l e to the south of Sunset  Creek*  Here, i t i s very sharp, and n e i t h e r the granite nor the g r a n o d i o r i t e shows signs of chilling..-  Instead, both rocks are coarse-grained r i g h t at the  contact and here the c r y s t a l s i n t e r l o c k . . No conclusive evidence of the age r e l a t i o n s h i p of g r a n i t e and g r a n o d i o r i t e i s present i n t h i s exposure* . Granodiorite appears t o have formed l a t e r than the Gambier group..  The s t r i k e of the conglomerate bed of the Gambier group i s t r u n -  cated by g r a n o d i o r i t e .  The granodiorite of the Strachan Creek area i s  connected t o the granodiorite of Mounts Harvey and Hanover three m i l e s t o the north, so as t o form one l a r g e continuous mass r e l a t e d i n age. Armstrong  (1954)  notes that the g r a n o d i o r i t e of Mounts Harvey and Hanover'  o r i g i n a t e d a f t e r the deposition of the Gambier group.  Thus, the granodio-  r i t e of the Strachan Creek area formed at the same time* In hand-specimen, a t y p i c a l sample of g r a n o d i o r i t e i s greyish white and coarse-grained, inequigranular, and a l l o t r i o m o r p h i c i n t e x t u r e . The mafic minerals c o n s t i t u t e from 5 t o 20 per cent of the rock.  The  g r a n o d i o r i t e i s uniform not only i n m i n e r a l o g i c a l composition and t e x t u r e , but a l s o i n the constant presence of round dark inclusions.. These i n c l u sions form approximately one t o two per cent of the rock and are evenly distributed.  The weathering of f e l d s p a r produces a white surface on the  weathered surface of g r a n o d i o r i t e * In t h i n - s e c t i o n s of g r a n o d i o r i t e , i t i s seen t h a t the e s s e n t i a l minerals making up the g r a n o d i o r i t e are p l a g i o c l a s e (average, A n ^ ) b i o t i t e 15$, hornblende 5$, quartz, and orthoclase.  60%,  Quartz forms from  10 t o 15 per cent and orthoclase up t o 10 per cent of the rock. accessory minerals are a p a t i t e , sphene, and i r o n ore.  The  A l t e r a t i o n products  1*0  are epidote, c l i n o z o i s i t e , and s e r i c i t e .  P l a g i o c l a s e shows marked zoning  which i s g e n e r a l l y of the o s c i l l a t o r y type, but normal zoning i s a l s o present.  Phemister (191,5, p* 65) has studied the zoning of p l a g i o c l a s e of  a normal granodiorite of the b a t h o l i t h near Vancouver and  describes  p l a g i o c l a s e c r y s t a l s w i t h up t o ten zones of the o s c i l l a t o r y type* zones range i n composition from An g t o An^ g  of Anjp.  2  These  with an average composition  Phemister also mentions that he observed reverse zoning i n grano-  d i o r i t e , but t h i s i s not found i n any specimens from the Strachan Creek area.  Hornblende i s s t r o n g l y pbochroic i n tones of green and has smooth  grains boundaries, and i n places i s subhedral.- Many c r y s t a l s are twinned. Generally, hornblende contains i n c l u s i o n s of a p a t i t e , f e l d s p a r , and i r o n ore.  B i o t i t e i s present as ragged grains p a r t l y a l t e r e d t o c h l o r i t e ,  e s p e c i a l l y along cleavage t r a c e s *  Generally, i t contains round i n c l u s i o n s  of p l a g i o c l a s e and i r o n ore ( p y r i t e and magnetite).. Quartz i s mainly i n t e r s t i t i a l , but i n places forms l a r g e , i r r e g u l a r l y bounded grains which show wavy e x t i n c t i o n , i n c i p i e n t f r a c t u r i n g , and minute bubbles and inclusions.. Orthoclase occurs as c l e a r , untwinned i n t e r s t i t i a l areas which i n some places surrounds p l a g i o c l a s e l a t h s * A l t e r a t i o n i s not prominent* general, the granodiorite has.no d i r e c t i v e t e x t u r e s , but i n a few  In places  the i n c l u s i o n s are roughly o r i e n t e d * The presence of ( l ) an apophyse of granodiorite c u t t i n g d i o r i t e , (2) the uniform pattern i n the o v e r a l l texture of the g r a n o d i o r i t e , (3) the constant mineral composition of the granodiorite suggests a magmatlc o r i g i n of the g r a n o d i o r i t e .  and  Id  Small I n c l u s i o n s i n Granodiorite Small b a s i c x e n o l i t h s are i n v a r i a b l y found i n the g r a n o d i o r i t e . Generally, they form 1 t o 2 per cent of the rock, but i n some places they make up t o 5 per cent of the rock.,  They appear t o be evenly d i s t r i b u t e d  throughout the granodiorite regardless of contact r e l a t i o n s . .  I n general,  the i n c l u s i o n s are round t o subround i n o u t l i n e , but i n a few places sharp angles are noted.  There are same elongated i n c l u s i o n s (see Figure 20) which  have a r a t i o of length t o width ranging from 2:1 t o  The l a r g e s t  i n c l u s i o n seen i n outcrop i s approximately 7 inches i n i t s longest d i r e c t i o n , but many boulders of g r a n o d i o r i t e i n the creek beds c o n t a i n i n c l u s i o n s over a f o o t or more i n diameter.  The s i z e of the i n c l u s i o n s grade from 7 inches  t o l e s s than a quarter of an i n c h across.  The m a j o r i t y of the i n c l u s i o n s ,  however, are about 1 t o 2 inches i n diameter.  The contact between x e n o l i t h  and g r a n o d i o r i t e i s sharp, but g e n e r a l l y , the c r y s t a l s intermesh across the contact, (see Figures 20, 21, and 22).  I n most places the x e n o l i t h s show  random o r i e n t a t i o n . .  Figure 20.  Figure 21..  Figure 22.  Small i n c l u s i o n s i n the g r a n o d i o r i t e . Figure 20 i s of an e l o n gate i n c l u s i o n w i t h sharp contacts. A l a r g e f e l d s p a r c r y s t a l l i e s across the boundary. Figure 21 i s of an o v a l i n c l u s i o n which has sharp contacts without i n t e r l o c k i n g c r y s t a l s across the contact. Figure 22. i s of a round i n c l u s i o n w i t h phenocrysts or porphyroblasts.  U2  V a r i a t i o n s i n the type of x e n o l i t h s are observed.  Most of them  are of dark, f i n e - g r a i n e d , e s s e n t i a l l y d i o r i t i c rocks, but a few are o f v e r y f i n e - g r a i n e d , dark, b a s a l t i c rocks.  The author found one x e n o l i t h of a meta-  morphic rock w i t h d e f i n i t e f o l i a t i o n and w i t h a composition o f quartz, f e l d s p a r , c h l o r i t e , and epidote.. Some x e n o l i t h s of d i o r i t i c composition have f a i n t banding due t o a p r e f e r r e d o r i e n t a t i o n and segregation o f mafic minerals..- One type of x e n o l i t h i s c h a r a c t e r i s t i c and dominant i n granodiorite.  I t i s a f i n e l y granular rock of d i o r i t i c composition composed  mainly of hornblende and p l a g i o c l a s e .  I h places i t i s p o r p h y r i t i c or por-  p h y r o b l a s t i c , having l a r g e white phenocrysts or porphyroblasts of p l a g i o clase ranging from l / 8 t o l/l+ inches i n diameter i n a f i n e - g r a i n e d , dark groundmass* I n t h i n - s e c t i o n s of the most common ( d i o r i t i c ) type of x e n o l i t h , the minerals are seen t o be p l a g i o c l a s e (zoned, rim A ^ Q t o core An^g) 55$, hornblende 30$, b i o t i t e 5$, quartz, c h l o r i t e , o r t h o c l a s e , z o i s i t e , s e r i c i t e , sphene, and c l i n o z o i s i t e .  Quartz i s i n t e r s t i t i a l , encloses w e l l formed l a t h s  of p l a g i o c l a s e and subhedral c r y s t a l s of hornblende, and has undulatory extinction.  There appears t o be two stages i n the formation of hornblende.  The e a r l y hornblende c r y s t a l s are subhedral t o euhedral and r e l a t i v e l y f r e e of i n c l u s i o n s *  The l a t e r hornblende appear as anhedral grains w i t h ragged  c r y s t a l o u t l i n e s and p o i k i l i t i c t e x t u r e , containing small i n c l u s i o n s of p l a g i o c l a s e , a p a t i t e , and i r o n ore. Phemister (I9k5) proposes that the x e n o l i t h s represent fragments of p r e - b a t h o l i t h i c dykes and other country rocks which were caught up i n t o the i n t r u d i n g magma and made over i n t o b a s i c patches which were i n e q u i l i brium w i t h the surrounding magma*  A strong argument f o r t h i s hypothesis i s  h3  i s that a chemical a n a l y s i s (made by Phemister) of the composition of a common type of x e n o l i t h i n the g r a n o d i o r i t e of the C a u l f i e l d s area near Vancouver i s very s i m i l a r t o t h a t of the p r e - b a t h o l i t h i c dykes.  A l s o , at  C a u l f i e l d s the i n c l u s i o n s show a l l stages of conversion t o g r a n o d i o r i t e . Granite The main mass of pink g r a n i t e occurs i n the southern p a r t of the Strachan Creek area and extends from the southern boundary of t h e area northward t o approximately 1000 f e e t north of Sunset Creek and up the slope of the mountain t o an e l e v a t i o n of more than 3000 f e e t .  Armstrong  (195k)  shows t h i s mass t o continue as an alongate body about h m i l e s long and l / h t o 1/3 m i l e wide, having a general northwesterly t r e n d . Good exposures are found along the seashore, and along the road and r a i l r o a d c u t s .  To the  south, j u s t outside of the Strachan Creek area, granite i s i n contact w i t h granodiorite.  Just t o the north of Sunset Creek the main mass of g r a n i t e  gives way t o d i o r i t e .  The contact here i s not exposed, but w i t h i n a few  f e e t of i t both the g r a n i t e and g r a n o d i o r i t e i s exposed.  About 300 f e e t  above the road cut, the contact i s occupied by a dark, p o r p h y r i t i c , d i o r i t i c dyke* To the north of the main mass of g r a n i t e many smaller dykes of g r a n i t e are found..  They cut the d i o r i t e and range i n width from 20  t o 300 f e e t , (see Figure 23)  The contact of the g r a n i t e dykes w i t h the  d i o r i t e i s g e n e r a l l y quite sharp.  I n a few places the g r a n i t e dykes con-  t a i n s m a l l , angular i n c l u s i o n s of d i o r i t e near the contact, (see Figure 2h)» This suggests t h a t the g r a n i t e magma stoped o f f parts of the w a l l s of the d i o r i t e during i t s i n t r u s i o n .  kh  S+ro.cKqn  Figure 23.  Section exposed i n road cut near Strachan Creek No. 1. D i o r i t e cut by numerous dykes of g r a n i t e *  In hand-specimen, the g r a n i t e i s t y p i c a l l y p a l e pink and coarsegrained, a l l o t r i o m o r p h i c t o hypidiomorphic, and inequigranular i n texture,. Mafic minerals make up l e s s than 5 per cent of the rock and i n general are w e l l d i s t r i b u t e d throughout.  The melanocratic minerals are g e n e r a l l y much  smaller than the l e u c o c r a t i c m i n e r a l s .  The pink colour of the g r a n i t e i s  due t o the abundance of K-feldspar.. The rock i s w e l l j o i n t e d and has many f r a c t u r e s and j o i n t s *  The g r a n i t e i n the v i c i n i t y of Sunset Creek i s cut  Figure 2 l i . G r a n i t e - d i o r i t e contact as seen i n road cut near Strachan Creek No. 1. Note the l a r g e i n c l u s i o n s of d i o r i t e i n g r a n i t e *  16  by numerous t h i n , b l a c k v e h l e t s approximately l / l O t h of an i n c h thick..  These  v e i n l e t s form a s o r t of network or boxwork (see Figure 25) and appear t o be r e l a t e d t o the j o i n t i n g as the two are c l o s e l y a s s o c i a t e d . The v e i n l e t s are composed mainly of b i o t i t e w i t h minor amounts of c h l o r i t e and s e r i c i t e . . These minerals are w e l l o r i e n t e d p a r a l l e l t o the walls of the veinlets..  I n t h i n - s e c t i o n the mineral composition of the g r a n i t e i s seen to be m i c r o p e r t h i t e 60$, quartz 30$, b i o t i t e 5-8$, p l a g i o c l a s e A n ^ , a p a t i t e , magnetite, p y r i t e , s e r i c i t e , c h l o r i t e , z o i s i t e , c l i n o z o i s i t e , and a n d a l u s i t e . M i c r o p e r t h i t e and quartz are predominant and a l l the other minerals are present only i n r a t h e r minor amounts. Mafic minerals form from 1+-8 per cent of the rock.. Andalusite i s present only i n one t h i n - s e c t i o n .  Here, i t  occurs as subhedral, squarish c r y s t a l s surrounded by a v e r y t h i n rim of sericite..  Some andalusite c r y s t a l s are enclosed i n quartz, while others  are embedded i n a f i n e - g r a i n e d , crushed matrix of quartz g r a i n s . The paragenesis of the minerals show t h a t andalusite formed a f t e r the c r y s t a l l i z a -  U6  t i o n of m i c r o p e r t h i t e , p l a g i o c l a s e , and b i o t i t e , but before the of quartz.  formation  This suggests that the andalusite i s of primary origin..  That  i s , the magma had an excess of alumina a f t e r having s a t i s f i e d the r e q u i r e ments of f e l d s p a r and mica, and t h i s excess was used up i n the of a n d a l u s i t e .  formation  I n a l l t h i n - s e c t i o n s the granite shows c a t a c l a s t i c t e x t u r e .  The boundaries of l a r g e microperthite and quartz grains appear to be granulated.  Large areas of the t h i n - s e c t i o n s show f i n e - g r a i n e d , broken up  c r y s t a l s of quartz and K-feldspar.  Many t h i n v e i n l e t s of f i n e - g r a i n e d  granulated m a t e r i a l cut through the rock.  The v e i n l e t s are seen to weave  between the large grains and i n places even cut through the l a r g e g r a i n s * Large microperthite grains are e n c i r c l e d by very f i n e - g r a i n e d granular quartz.  The c a t a c l a s t i c a c t i o n seems t o have occurred a f t e r the c o n s o l i -  dation of the rock because a l l the quartz has wavy e x t i n c t i o n and there i s no i n t e r s t i t i a l quartz between the granulated grains.. The g r a n i t e appears t o be a t y p i c a l high l e v e l g r a n i t e emplaced as magma.. A strong argument f o r t h i s hypothesis  i s t h a t the granite has a.  uniform pattern i n i t s o v e r a l l texture and i t s mineral composition i s everywhere constant..  The presence of granite dykes containing blocks o f  d i o r i t e i n d i c a t e that the magma stoped o f f parts of the d i o r i t e during intrusion.  The general occurrence of c a t a c l a s t i c texture i n the g r a n i t e  suggests t h a t the granite s u f f e r e d p o s t - c r y s t a l l i z a t i o n s t r e s s e s .  Perhaps  i t wedged i t s way f u r t h e r a f t e r s o l i d i f i c a t i o n . Dyke Rocks Several v a r i e t i e s of dykes are found c u t t i n g the p l u t o n i c rocks of the Strachan Creek area.  The dykes can be d i v i d e d on the b a s i s of com-  1*7  p o s i t i o n i n t o two groups, b a s i c dykes and a c i d i c dykes* The b a s i c dykes of the Strachan Creek area consist of gabbro, p o r p h y r i t i c and non-porphyritic d i o r i t e , and b a s a l t i c ( o r trap) dykes.. A l l the b a s i c dykes, except f o r one gabbroic dyke, are found i n the main mass of g r a n i t e .  The best exposures of the basic dykes are found i n the road  and the r a i l r o a d cuts near Sunset  Creek.  Only one dyke of gabbro occurs  i n the map-area and i t i s found j u s t north of Strachan Creek No. 1 a t an e l e v a t i o n of about 1200 f e e t .  I t has v e r y sharp contacts w i t h the adjacent  d i o r i t e and i s f i n e r g r a i n near i t s margin than towards i t s c e n t r e . s e c t i o n the e s s e n t i a l minerals are seen t o be p l a g i o c l a s e ( A n ^ ) %0% 20$, c h l o r i t e 15%, and quartz 5%» a p a t i t e , and c a l c i t e . .  In thinf  augite  Accessory minerals are p y r i t e , magnetite,  The p o r p h y r i t i c d i o r i t e dykes are exposed along the  road cut j u s t north of Sunset Creek, (see Figure 26).  They are medium- t o  f i n e - g r a i n e d , greyish green rocks which are spotted w i t h l a r g e white phenoc r y s t s of p l a g i o c l a s e .  The essential- minerals are p l a g i o c l a s e (average Anj^)  60%, hornblende 30%, and magnetite 5%, and the accessory minerals are quartz, c h l o r i t e , epidote, b i o t i t e , and a p a t i t e . o s c i l l a t o r y zoning.  Phenocrysts of p l a g i o c l a s e show  No d i r e c t i v e textures are apparent i n e i t h e r hand-  specimens or t h i n - s e c t i o n s of the rock.. The non-porphyritic d i o r i t e dykes  Figure 26.  Section exposed i n road cut j u s t north of Sunset Creek. Granite i s cut by numerous dykes*  are a l s o exposed along the road cut j u s t north of Sunset Creek, (see Figure 26). feet.  One of these dykes i s found i n the g r a n i t e at elevations of 12-llt00 The d i o r i t i c dykes are grey and medium-grained, a l l o t r i o r a o r p h i c , and  inequigranular i n t e x t u r e * The mafic minerals occur as evenly d i s t r i b u t e d c l o t s or bunches composed mainly of b i o t i t e , . that p l a g i o c l a s e 60$, essential minerals. orientation.  I n hand-specimen, i t i s seen  b i o t i t e 25%, hornblende Q%, and i r o n ore 3% are the In a few places the mafic minerals show a p r e f e r r e d  The t r a p dykes are very f i n e - g r a i n e d , b l a c k rocks of b a s a l t i c  composition. The b a s i c dykes were i n t r u d e d a f t e r the formation of the plutonic rocks.  Strong evidence f o r t h i s i s that many of the b a s i c dykes  show c h i l l e d borders and are of f i n e r g r a i n near t h e i r margins than i n the central, part of the dyke.  Generally, the contacts of the dykes w i t h the  adjacent rocks are very sharp. dykes i s not c e r t a i n .  The age r e l a t i o n s between the v a r i o u s b a s i c  However, i t i s c l e a r that the t r a p dykes are l a t e r  than the p o r p h y r i t i c and non-porphyritic d i o r i t e dykes as the t r a p dykes cut both of these dykes, (see Figure  26).  The a c i d i c dykes are found i n the d i o r i t e at various i n t e r v a l s from Sunset Creek t o Newman Creek.. A U i r r e g u l a r t o be mapped.  In the Strachan Creek area they are represented  by a p l i t e and pegmatite dykes. Figure 27)..  of them are too small, and too  I n places they f o l l o w f a u l t planes, (see  Where a p l i t e occupies a f a u l t plane, i t i s bounded on one w a l l  by the f a u l t and on the other by country rock, (see Figures 13 and  27).  Both contacts are sharp,. I n some places epidote occurs i n the a p l i t e o n l y along the f a u l t w a l l , but i n other places epidote i s present along both .  Figure 27*  Epidote grading i n abundance from both w a l l s of the a p l i t e v e i n toward the centre,.  contacts, (see Figure 27)*  I n both of these i n s t a n c e s , epidote  i s more abundant near the contact and g r a d u a l l y decreases i n abundance towards the centre of the dyke,. In hand-specimen, the a p l i t e c o n s i s t s e s s e n t i a l l y of orthoclase 50%, p l a g i o c l a s e 25%, and quartz 15% •  The  accessory minerals are epidote, b i o t i t e , c h l o r i t e , magnetite, and hematite. The a p l i t e dykes probably represent the l a t e emanations of a c o n s o l i d a t i n g g r a n i t i c magma,.  50  BIBLIOGRAPHY  Akaad, M.K.. (1956), The Ardara granitic diapir of County Donegal, Ireland; Quarterly Jour.. Geol. Soc, London, v o l . CXII, D e c , p t . 3 , p.  263-290.  Armstrong, J.E.. (1951+), Preliminary map of Vancouver North, B . C . ; Geol.. Surv.. Canada Paper 5 3 - 2 8 . Balk, R.. (1937), Structural behaviour of igneous rocks;; Geol. Soc. Amer. Mem.. 5 , July. Berry, E.W. ( 1 9 2 6 ) , Tertiary floras from British Columbia; Geol.. Surv. Canada, Bulletin No.. i|2, Geol* Series No.. 1+5, p.91-116.. Cheng, Yu-chi (191+1+), The migmatite area around Bettyhill Sutherland, England; Quarterly Jour.. Geol. Soc London, vol., XCIX, pt.. 3 & U, Jan.,  p. .107-151+.  Cloos, E. (1933), Structure of the Sierra Nevada Batholith;; 16th Int. Geol.. Congress, Guidebook 1 6 , p* 1+0-1+5.. (1936), Der Sierra Nevada pluton in California; Neues Jahrbuch fur Min., Geol., und Paleo.. 7 6 , B a i l * Bd., Abt. B . , 3$$rl&0+ Folinsbee, R . E . , Ritchie, W.D., Stansberry, G.F. ( 1 9 5 7 ) , The Crowsnest volcanics and Cretaceous geochronology;, Guidebook, 7 t h Annual Field Conference, Waterton; Alta. Soc of Petroleum Geol., Sept., p.. 20-26..  Gilbert, G.K. (1906), Gravitational assemblage i n granite;; Geol. Soc. Amer. B u l l . , v o l . 17,. p.. 321-328. G i l l u l y , J* (191+8), Origin of granite;;  Geol. Soc. M a r * Mem. 2 8 , April. 1 0 .  Larsen, E.S. Jr* (191+8), Batholith cf Southern C a l i f . : Geol. Soc. Amer.. Mem.. 2 9 * Nockolds, S.R.,'(1932), The contaminated granite of Babette Head, Alderney; Geol.. Mag*. 6 9 , p.- 1*33-1+52. (1933), Some theoretical aspects of contamination of acid  magma; Jour. Geol., vol.. 1+1, p* 5 6 1 - 5 8 9 * Phemister, T . C . , (191+5), The Coast Range batholith near Vancouver, B . C . ; Quarterly Jour. Geol. Soc. London, v o l * C i , pt. 1 & 2 , p* 3 7 - 8 8 .  Turner, F.J.. (1948), M i n e r a l o g i c a l and s t r u c t u r a l evolution of the metamorphic rocks;; Geol. Soc. Amer. Mem.. 30, J u l y 28* Wager, L.R. (1953), l a y e r e d intrusions;,'Meddelelser f r a Dansk Geologisk Forening, Bd* 12, Kobenhavn, August. Wager, L.R. and Deer, W.A. (1933-39), Petrology of Skaergaard I n t r u s i o n Meddelelser om Gronland udgivne af Kommissionen f o r Videnskabelige Undersogelser i Gronland, v o l . 105*  ABSENCE REPORT Please report holidays i n terms of days and s i c k leave i n hours. do not report periods o f l e s s than a h a l f hour. WViSK ENDING SATURDAY  DIVISION NAME  Please  SICK LEAVE  LEAVE V/ITHOUT PAY  . VACATION  APPROVED D i v i s i o n Head.  x  in  to  CM  o  o  0 ro  o  CJ  CM  CM  CM  ro  m  ro  CENOZOIC TERTIARY  z 'A  T R A P  4 9 ° 26  H  D Y K E  BASIC  D Y K E S  -  G A B B R O  ,  DIORIT-E  ESOZOIC GRANODIORITE  GRANITE  -1  v  DIORIT  E  TRIASSIC  AND/OR  LATER V O L C A N I C S  GAMBIER  TRIASSIC B O W E N  ' G R O U P  A N D / O R  I S L A N D  G R O U P  C O N G L O M E R A T E  E ^\ R L. 8 EE! M I G M A T I T  E  49° 2 5 '  H  C O N T O U R S  G E O L O G I C A L  B O U N D A R Y  G E O L O G I C A L  C O N T A C T  A S S U M E D  SO  STRIKE  AND  DIP  OF  SHOWING  DIP  BANDING  R O A D  SHORE  -  LIN.E  I :  S C A L E  1/5  0  INTERVAL  200  A P  GEOLOGICAL  VANCOUVER. BRITISH  4/5  3/5  2/5  1/5  CONTOUR  10,OOO  DISTRICT C OLUMBI A  I  1  MILE  

Cite

Citation Scheme:

    

Usage Statistics

Country Views Downloads
Canada 8 0
United States 6 1
Poland 1 0
United Kingdom 1 0
China 1 2
City Views Downloads
Vancouver 7 0
Unknown 5 3
Ashburn 3 0
Sunnyvale 1 0
Beijing 1 0

{[{ mDataHeader[type] }]} {[{ month[type] }]} {[{ tData[type] }]}
Download Stats

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0053024/manifest

Comment

Related Items