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Petrology of the Shingle Creek porphyry Bostock, Hewitt Hamilton 1956

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PETROLOGY  OF THE mtmtM  CHEEK PORPHTRY  HEWITT IAKILT0W BOSTOCK B8«« Qa*«n*« University, Kingston, Ont., 1954  A THESIS SUBMITflS I I PiMUL  THR  I I Q U I B I I M T S FCSB THE  •UASTBR OF APPLIED  FUSFXLMEHY OF  DRGSfiE  OF  SCIENCE  In the Bepartitent of GBOLO0Y AND «JE0<JRAPIY  We  accept t h i s  thesis  as conforming  to  the  staaiard required of candidates- for the degree o f MASTER Of APPLIED SCIEBCB  Members of th© Bepartsent of GSOLOGY  TH  wiiERsitf  Aim rnmrn^m  OP B i r r i s i i covsmu.  April, 1956  A b r i e f description o f the geology o f the Shingle Creek area s o a t t e w t  e f Pent let©** 1,0,,  together with a  more detailed report ©a the mineralogy and petrology of the Shingle Creek I n t r u s i o n ( g r a n i t e porphyry) ar© given, fhe presence o f flows and t u f f * showing s i m i l a r mlneralogic&l features t o th© S h i n g l e Creek: I n t r u s i o n suggest that t h i s intrusion was shallow r a t h e r than de«p-seat®d. f a a i i i a e phenoorysts  showing o s c i l l a t o r y zoning are  described with a rang® i n composition o f fro® 40 to 70 percent o r t h o c l a s e (based ©a & comparison of o p t i c a l p r o p e r t i e s  with  those  determined  by T a t t l e 1952).  Tho  sonss  often  occur i n p a i r s showing a gradation fro® an a l b i t e - r i c h inner zona t o an erthoel&se-rieh  outer  gone,  I t i s tentatively  suggested here that pressure changes i n the magma, by a l t e r i n g th® llquldus - s o l i d u s r e l a t i o n s , s i g h t provide t h i s reversed- soning, Plagioelase  ph«noerysts from th® i n t r u s i o n show  t r a n s i t i o n a l t o high temperature o p t i c s when cost-pared with the r e s u l t s of Seven and Tattle 1950. Beta quartz phenoorysts showing rounded o u t l i n e s and development o f late kaloe ar© described, i t Is suggested  from evidence given  that these f«&t«r@s are due to r e s o r p t i o n o f  quartz la a magma  chamber  p r i o r to i n t r u s i o n , followed fey  l a t e growth a f t e r i n t r u s i o n and  daring c r y s t a l l i s a t i o n of  the porphyry matrix, Petrographlc study of th© l a r g e s t dyke associated with the p o r p h y r i t i c i n t r u s i o n has  suggested  aay have been intruded i n s e v e r a l stages.  that t h i s dyke  TAJSLB 6? C0UTURT8  £§£f  Chapter 1  INTRODUCTION  LOCATION PREVIOUS  AND A C C E S S I B I L I T Y G E O L O G I C A L WORK  . .  FIELD \ORK  .  ACKmw:s>mmtB . . . , . . . . » . . . . * . . . .  BTBLIOCRAPRY Chapter I I  GENERAL -CHARACTER  7  9  GENERAL STATEMENT . . . . M O U N T A I N SLOWS SILT GRAVEL SHINGLE CREEK FLOOD PLAIN POST GLACIAL HISTORY VEGETATION A N D  AND  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  9  . . .  TERRACFS . . . . .  .  .  . .  . .  JU  GENERAL  SOT§IARY S T A T E M E N T  .  .  .  .  .  10  OTOLOGY .  .  .  .  .  .  .  .  .  .  .  13  OF FORMATIONS  POST T R I A S S I C DIORITE  9  1 0 11 1 2  CLIMATE . . . . . . . . . . . . . .  T A B L E  3  6  THE ATilA  OF  PHYSIOGRAPHY  Chapter  1 3  1 4  INTRUSIONS  . . . . * , . . » - . , » * .  14  . . . . . . . . . . . .  14  APLITB • . « • » . . » . • . » • » » « » » » »  20  SHINGLE CREEK INTRUSION . . . . . . . . . . . . . . . SPFINGBHOOK FORMATION . . . . . . . . . . . . . . GENERAL D E S C R I P T I O N , S O U T H E A S T C O N T A C T JkKF.A . . . MARRON F O R M A T I O N GENERAL D F S C R I ^ I O N . . . . . . . . . . . . .  22 23  ORANODIORITF. . . . . . . . . . . . . . . . . . . 1? GRAN ITS 18  ASSOCIATED  BASIC  DY1C1S  2  2%  .............  26  G E O L O G Y O P YHF iSINGLE CBE8K FOSMTIOi  Cha.pt** VT  INTRODUCTORY PETROLOGY  .  STATEMENT .  .  .  .  .  .  . .  .  .  .  *  .  .  *  #  .  .  *  . .  27  27  HEOfiSCOPIC DESCRIPTION . . . . . . . . . . . . . . 2? M I C R O S C O P I C BTSSCBI^TXOS . . . . . . . . . . . . . . . . 31 Composition . . . . 31 Mineralogy . . . . . . . . . . . . . . . . . 32 ( 1 ) Phenoorysts , , . . » , , . . . . 32 ( a ) 8«Bldlft«*Aito*tht>eXM«  . . . . . 32  TABLE OF  Gomm Pag®  Plagioclase * * » * * * » • * •  42  Quartz  44  (2) K & t s l x . . .  (3)  T<3Xtttr@5  Accessory .  .  .  .  . . . . . . . . . . .  Mmmls •  (1) Phenocrysts  »  •  «  •  . . . •  •  •  •  •  •  »  •  45  47  47  47  (a) Protoclastic S t r u c t u r e . . . . 47 <b) Besorption and Secondary Growth 4 f  (c) -Seconder? alteration  Parageneels H.CTAMCKPHI3M  . . . . .  . . . . .  .  60  STRUCTURAL ?1<ATUBES GF-RIiEAL CONFIGURATION INTERNAL FKATflRES Internal Contacts , Inclusions (1)  (2)  Inclusions of Granite  (b)  63  |3 63 65 . . . . . .  Formation  65  66  66  54a j or Inclusions  60  Cobbl® Inclusions  EXTERNAL F^TURSS Contact Features STRUCTURAL CONCLUSIONS  PlifECGEMFS IS  63  Inclusions o f th© Sprlngbroofc  (a)  55  57  . . . .  CRYSTALLIZATION CF THE PHENOCIttSTS . . . . . . INTRUSION Of THE NORTH DYKE . . . . . . . . . .  68 68 70  73  TABLE OF ILLtJSTHATIGHS (1)  Key map  the Shingle Creek Area {scales one ©lie t o one inch) . , . * . . . » . « . . , •  (2)  The outer aones i n p l a g i o c l a s e c r y s t a l s from the g r a n i t e at S h i n g l e Creek . . . . . . . . .  (3) a  A s t e r e o f r a p h l c p r o j e c t i o n of the o r i e n t a t i o n  ©f  M  of the » X V f » , ana «£" axes, and th©  (010)  pole of a s a o l i i n e Carlsbad twin frost S h i n g l e Creek . , - * » . » « > . . # . . . . . . . (3) b  Asketeh showing th© approximate r e l a t i v e p o s i t i o n s of tha X « , "Y , and "Z" axes, th© o p t i c plan®, and the e r y s t a l o g r a p h l c faces o f a t y p i c a l saaldiine phenoeryst f r o a Shingle Creek . . . . . . . . . . . B  (4)  M  A graph showing the type of Boning th© l a r g e s a a l l l a e phenoerytt* ttm  Creek . . . . .  <5)  observed Shingle  in  ..........  A graph showing th® v a r i a t i o n i n iniex w i t h wave l e n g t h of l i g h t o f two o i l s used, and of th® "Y and "2" i n d i c e s o f a fragment o f s&nlcllfie « • • . • « » . . • • • > « • * • . . H  (6)  A graph showing the variation of the o p t i c a x i a l angle, 2V with composition In p l a g i o c l a s e frm th© S h i n g l e Creek area .  (?)  Contact features i a g r a n i t e i n c l u s i o n s i n the f o r t h Dyke .............  ...  <8)  Contact f e a t u r e the l o r t h Dyke  (9)  A sketch shoving the c o n f i g u r a t i o n and nature e f the contacts o f a l a r g e congloserate i n c l u s i o n i n the S h i n g l e Creek Porphyry . . . .  (10)  Phase  (11)  Figure showiJag some systematic a i n e r a l o g i e a l mad s t r u c t u r a l v a r i a t i o n s i n the l o r t h Dyke . .  g r a n i t e India*ion* i a . . . . . . . . . . . . . . . .  ia  diagram f o r the systee nephelenek a l i o p & l l l i t e - s i l i c a . ( a f t e r jr.F, I c h a i r e r audi i«L.. fowe»)#  TmtM OF lUBSTRAflORS (Cont)  sum  MM  .  tl)  S h i n g l e Creak Plorlte (photomicrograph)  17  (2)  tprlnfaroolc f o r m a t i o n shoving angular fragments' ©f diorlte and granodiorite  24  C3)  A s i m p l e Sanidlae c r y s t a l  29  (4)  A t y p i c a l s a n l d i n e C a r l s b a d Win  29  (5)  An i n t e r g r o w t h o f two. s.aaiditie c r y s t a l ® . . . . .  30  (6) .  A l a r g e . specimen o f t h i a g l t C r e t k Porphyry  (7)  A aenad saaidln© phenocryst (photomicrograph) . .  (8)  A  (9)  A quart* phenoeryst showing s l i g h t develop* jaeat of c r a c k i n g {photoaieroirsfsh) , . • » * .  46  (10)  A quart* p&eneeryst showing »any f i n e c r a c k s (photomicrograph) .»'.*..,  46  gonad  »aaiai»a phenocryst  «...  |0 36  (photomicrograph) . . 36  (11)  P r o t e o l y t i c structure o f quart* (pbotomierograph) 48  (12)  A qumtM phenocryst w i t h growth halo f o l l o w i n g , raaorfead outline* (photomicrograph)  (13) '  F O O T quart* grain* o f non parallel o r i e n t a t i o n •orvouadod hy a h a l o variocg* p a r t s o f which are p a r a l l e l t o the adjacent quart* grain*  (photomicrograph) . » . . , . , , » . . * , . * •  (14) Plate (13) e n l a r g e d , (15)  f2  (photoeiorograen) . . . . . 52  S l i d e (m$4) showing a fine-grained h a l o i n a fine-grained  50  matrix (photomicrograph) . . . . . .  (16)  S l i d e (*?D55) Bhowing a  coarse-grained  (17)  A sanidlae Carlsbad t w i n showing inelnsion* of  halo in a  coarse-grained matrix (photomicrograph).  . . . .  p l a g i o e l s s e and r e s o r p t i o n rists. (photomicrograph) , . , . . * . * * » . . » » . . » *  53  53  56  Ti%p& O F inmmm&m  (18)  A s a a l d i n e c r y s t a l showing mMme®  resorption o n l y a t i t s o u t e r s u r f a c e (photomicrograph)  (If)  (20)  (21)  (22) (23) (24) (255  (26)  ccoat)  of  . . . . . . . . . .  A 0 © a r s « * f r a l a e i nmrn^mj growth halo o f raarts easier h i g h a a g r i l f i o a t l o n (photomicrograph) . . . . •  58  A eoarsa-gralnafl secondary growth h a l o of suarta: under high m a g n i f i c a t i o n A f i n e - g r a i n e d secondary growth h a l o o f quarts i r a i e r low m a g n i f i c a t i o n i a mm p o l a r i s e d l i g h t Cphotomicrograph) « . . .  58 * . .  59  A f i n e g r a i n e d secondary growth b a l e under high s i g n i f i c a t i o n Cthotooleroiraph} . , . . •  59  Xadwated conglo®#raf «i at the contact between a b a s i c dyke ana th© S p r i a g b r c o k f o r m a t i o n . .  62  Ah Internal' contact v i t h l a the S h i n g l e Creek Porphyry # • » » . « « » * » • . »  64  . . . .  S h e a r i n g a t th# c o n t a c t s between S h i n g l e Creek Porphyry and a l a r g e conglomerate inclusion ^ « . » * . . » . .  &t  f h e c o n t a c t between g r a n i t e and S h i a g l e Creek Porphyry . . . . . . . . . . . . . . . .  $9  The centre o f the Shingle Creek i n t r u s i o n I s l o c a t e i n the v a l l e y o f S h i n g l e Crook r o u g h l y t h r e e miles south southwest o f the P e n t l e t o n r a i l w a y s t a t i o n and on the boundary between the Gsoyoos M s t r i e t to tha n o r t h and Siinllkamaen D i s t r i c t t o the south {see key map  th©  F i g u r e 1).  f h e e n t i r e i n t r u s i o n i s w i t h i n the Pemtietoa I n d i a n Reserve* f h e i n t r u s i o n underlies an area about f o u r n l l e s (east*¥est) hy one aad a h a l f a l l s * C n o r t h - s o u t h ) , hut sone d i s c o n t i n u o u s dykes extend some two  a l i a s west o f the main  body. The a r e a i s eonvaniently reached e i t h e r hy  th®  north  branch o f the S h i n g l e f r e a k road froa- Pontic ton or by the south'branch from Skaha ^ & r f (see key map f i g u r e 1). branches are open d a r i n g th® e n t i r e y s a r .  loth  Of the areas mapped  i a d e t a i l {mm® key reap f i g u r e 1) tho l o r t h Byke S e c t i o n »ay be reached by c l i m b i n g up the f i r s t g u l l y v#st o f the abandoned f a n i n the e e a t r a l s t r e t c h o f S h i n g l e C r t e k V a l l e y . South l a s t Contact Area may  The  he reached by the o l d S h i n g l e  Creek road which i a a c c e s s i b l e t o v e h i c l e * a t a p o i n t d i r e c t l y s o u t h o f the abandoned farm mentioned above.  T h i s road i s  passable o n l y f o r v e h i c l e s o f s h o r t wheel bat© and h i g h underc a r r i a g e clearaaea.  Figure (1)  T h e S h i n g l e C r e e k Porphyry Scale  I inch to I m i l e Symbols EE3 500 foot contour  Rock T y p e s Te r t i a r y 1. -J M o r r o n  Formation  I  I Shingle C r e e k  1  I Springbrook  Post T r i a s s i c  H •  Porphyry Formation  Intrusions  Aplite G  interval E3 Creek EZ3 Rood h i Approximate geologic contact I J Dn Ft-covered area  Granodiorite  I 1 Diorite  Reproduced  Crom  Geological  S^«-ye>  Mup  6 2.7 A  The Shingle Greek intrusion and areas to the south and west were sapped H.S.Bostoek of the Geological Survey of Canada i n 1928 (published i n 1936) on a seal© of one a l l s to on©  inch*  fhe geology of an. area  extend-  i n g f r o a the 49th p a r a l l e l n o r t h to the 50th parallel, and • i n c l u d i n g the S h i n g l e Creek a r e a , i s shown oa a map on  a  s c a l e of four m i l e s t o the inch compiled i n 1936 by C.S* C a i r n e s of the G e o l o g i c a l Survey of Canada. accompanied  Both maps a r e  by a brief set o f d e s c r i p t i v e g e o l o g i c a l n o t e s .  B . f . F l i n t , M.l.Sathews, S . J . S c h o f i e l d aad  others  have g i v e n accounts o f the P l e i s t o c e n e aad Beeent d e p o s i t s , aad of the geoaorphlc f e a t u r e s of the  Okanagan,valley.  I n his study of the e t c h r e a c t i o n s of a l p h a and beta quarts Mean used quarts phenoerysts f r o s th© •'Quarts Porphyry* at P e s t i c t o a B.C.  fiUJS the igneous geology of the Shiagle Creek a r e a was suggested  to t h e author as an interestlag subject f o r r e -  search by I,S.Bostock  i a the f a l l o f I f $ 4 .  In the f o l l o w i n g  w i n t e r the author spent s e v e r a l days i a the a r e a d u r i n g which a b r i e f reconnaissance of soma of the v a r i o u s i a trueIves was made aad specimens collected.  During the f o l l o w i n g s p r i n g the reconnaissance of the a r e a was continued w i t h th® aid,4]of a i r photographs  4  from  purchased  and F o r e s t s .  th® . B r i t i s h Columbia  department o f Lands  I t v&s hopad that an I n t r u s i o n o f t h i s s i z e  might show some evidence o f d i f f e r e n t i a t i o n , and some days  were  spent i n c a r e f u l search f o r i t i n th© c e n t r a l and  eastern p a r t s o f th® i n t r u s i o n .  Although some evidence of  compound' i n t r u s i o n was d i s c o v e r e d , the extreme weathering of outcrop surfaces over most o f the area and the lack of outcrop at I t was  c r u c i a l points made progress slow and u n c e r t a i n .  t h e r e f o r e decided to s h i f t th© emphasis In capping  to contact features of the i n t r u s i o n end h o  areas (see  F i g u r e 1) were s e l e c t e d f o r d e t a i l e d mapping where th® rock appeared  t o be l e a s t a l t e r e d and best exposed.  These areas  ares (1)  f h e North Dyke S e c t i o n  (2)  t h e South East Contact Area.  The l o r t h Bytee S e c t i o n was mapped i n the s p r i n g of 1955  at 50 f e e t to the i n c h w i t h a 5 foot contour I n t e r v a l  using plane t a b l e and s t a d i a .rod.  fhe outcrops of th®  s e c t i o n ©eeur p r i n c i p a l l y on the f l o o r and w a l l s of & small  culler transecting  the dyke at r i g h t  angles.  Specimens  were c o l l e c t e d , at average i n t e r v a l s o f one hundred f e e t , along t h i s g u l l e y where the rock surfaces were f r e s h .  Happing of  the South l a s t Contact Area a t 200 f e e t  to th© inch with a 10 foot contour i n t e r v a l was the  last throe  days o f the s p r i n g season and  begun In  eonpletod  during th* following autumn.  The  rock  was found t o bo  too deeply weathered aad f r i a b l e f o r d e t a i l e d sampling and  only  a few specimens of the l e a s t weathered oatcrops were  collected. J, standard e l e v a t i o n f o r each d e t a i l e d map was  taken  f r o a sap 6271  Survey of Canada*  (Okanagan F a l l s )  of  area  th© G e o l o g i c a l  6  the  author wishes to express his  appreciation  for the guidance and encouragement given him iC.C.Ifefagg&rt aad the h e l p f u l suggestions l.M. Thompson. Brack, Mr*  Professor  of Professor  Further acknowledgment i s due to Mr.  S* Chown aad Mr.  author i n the  hy  S. Saunders who  P.  a s s i s t e d the  field.  f h e author Is g r a t e f u l to Mr. B. Freeman f o r the use of h i s camera i n taking photomicrographs and Mr.  to  J . Ooaaan f o r providing h a l f ef the t h i n - s e c t i o n s  used i n t h i s study. fhe author i s indebted C o u n c i l f o r the of t h i s  award  research*  to the Ontario l e s e a r c h  of a s c h o l a r s h i p grant i n support  7  H.S.  Bostock,  (1936) D e s c r i p t i v e Motaas Geol. Surv.  Can.  Map  627A, Okanagan F a l l s .  Boven, ! . L . f t l t t i c , 0.?,  (1950) The System SaAlSliOg - KAlSl^Og SgOs Journ. 0@ol, v o l , 58, no. 5, p p , 489-511.  Carr, J..J4,  (1954) Zoned P l a g i o c l a s e In Layered Qabbros of the Skaergaard I n t r u s i o n , east Greenland* Mia. Mag.., v o l . 30, no. 225, p p , 367-375.  Brugs»», J .  (1938) Unusual twin. Laws l a Orthoclase C r y s t a l s from Ooodsprings, Nevada: Min. Mag,, v o l . 25, no. 160, pp. 1-14.  Flint*  B.F.  f  (1935) White S i l t Deposits i n the Okanagan V a l l e y , B.C.J Roy. Soc. Can. Trans., 3rd, v o l . 38 s e c t , 4, pp. 39-57. t  l e i t h , M.L, tattle, o.F,  (1950) geological S i g n i f i c a n c e . o f T a r l a t l o n s l a the iigh-L©w Inversion of Quarti? -leol. Soc. Aster. B o l l , 1 Abstracts, v o l . 6 1 , no. 12, p t . 2, p. 1476.  Hackansla  (1953) Bffect o f Taaperatera on the Syaetry of «ifh~f«ip®»tttre Ka~rleh F e l d spar I Aser* Journ. 8 e l . , Bowes volume,  V.S.  pp. 319-342,  Mathews, H . I ,  (1944) Glacial takes and Ice Retreat South C e n t r a l B.C.i Boy. See, Can., »•*#, v o l . 38, s e c t . 4, pp. 3 9 - 5 8 .  Meen,  %mttm  ?,B,  Misch, P.  Sehairer,  In 3rd.  (1934) The I t c h i n g of Alpha and Beta University of f o r o n t o Studies, no. 3 6 , C o n t r i b u t i o n s to Canadian H l n e r a l Wf PP. 37-43, (1949) Metasoiaatlc G r a n l t i z & t l c n of B a t h o l l t h l c Dimensions? Amer. Jour, S c i , , v o l . 247, pp. 372-406. J.F. (1950) The A l k a l a i - F e l d s p a r J o i n i n the System SaAlSi04 » KAlSi04«Si02 Journ. Geol.  v o l . 58, no, 5» vt>* 512-517.  8 furrier, F . J .  (1951) Igneous and Meta»orphie P e t r o l o g y 2fettraw»Hill Book Company Inc.?  Verhoogea, J . turner F.J. •  pp. 99-402•  (19*7) Determination of P l a g i o c l a s e w i t h th® Four-axis U n i v e r s a l Stage: Amer.  M i n . , v o l , 32, pp. 389*410. Tattle,  O.F.  futtle,  O.F.  (1951) Alkalai Feldspars*-  (1952)  O.P,  Optical S t u d i e s of the Alkalai Joura, Geol,* lowen Volume,  Feldsparsi 1952,  tattle,  M i n . Mag.,  v o l , 29, no. 215» P P . 757-758.  PP.  553-567.  (195D O r i g i n o f the C o n t r a s t i n g M i n e r a l ogy of I s t t r u s l v e and Plutonic s i a l i c Bocksi Journ. S e a l . , v o l , 60,' no, 2, pp. 107-It4»  (195D O p t i c a l S t u d i o s on n a t u r a l Tan der gaadea 0, l a : ^ i o c l a s e F e l d s p a r s v i t h High end Low Temperature Optics: Doctor's Thesis l a P h y s i c s and Mathematics, s t a t e U n i v e r s i t y r  of Otreeht, Netherlands.  W l a e h e l l , H.  (1951) Elements o f O p t i c a l M i n e r a l o g y , F o u r t h E d i t i o n , Part I I , D e s c r i p t i o n s o f .^in^rals: John w'iley and Boas, Inc., Sew f o r k , pp. 246-3.49, 261-330.  Toder, ft»S.  (1954) S y n t h e t i c Basalt« Annuel Baoort o f the S i r e c t o r o f the CJeophysieal  WlnohelX,  A.I,  Ztttooratory* paper no. 1235, pp. 106-107,  CHAPTER II  iisiSAf, s f Afimif The S h i n g l e Creek Arm. i s located, tt the southeast ead ©f the I n t e r i o r P l a t e a u which System o f B r i t i s h  forms p a r t o f the I n t e r i o r  Coluabia. Tho S h i n g l e Creek i n t r u s i o n i s  contained e n t i r e l y w i t h i n S h i n g l e Creek v a l l e y , one o f ©any t r i b u t a r y v a l l e y s which d i s s e c t s t h e p l a t e a u rather deeply at i t s  southern end.  aojeiKUfe o f 3»4O0 f e e t  S h i n g l e Creek 4,^00  R e l i e f within  the area reaches a  with the r i d g e s n o r t h and sonth  of  attaining an a l t i t u d e of slightly a c r e than  f e e t above sea  level.  Fhyolographloally t h e area aay b<» d i v i d e d into t h r e e d i s t i n c t i v e parts? (1)  t h e Mountain Slopes  (f>  fhe S i l t and Gravel ferraees  (3)  f h e Rceent  Shingle Creek Flood Plain.  frosa t h e r i d g e aoanltt down t o approximately 3,500 f e e t t h e mountain slopes are relatively  gentlef b u t , f r o a  t h i s l e v e l down t o a n olevation o f about 2,000 f e e t , s l o p e s :  are s t e e p e r .  cooaaon.  Mere  talus and g&llles l a g l a c i a l t i l l a r e  tow lagged b l u f f s  coaooaly p r o j e c t above t h e t i l l  and s l i d e d e b r i s . B©l©v tho 2,000 foot contour bedrock I s e x t e n s i v e l y covered by a l l n v i w . , s i l t , and t i l l .  S I L T AID CBAVIL fSBRACFS Th® s i l t  and gravel deposits of Okanagan v a l l e y  have been described by F l i n t (1935) and at Shingle Creek* fresh to  foldsp«tbio  ar®  w e l l exposed  These deposits c o n s i s t p r i n c i p a l l y of rock f l o u r ( F l i n t 1935)  of cream white  pale b u f f -colour, w i t h interbedded c l a y laminae near the  bottom o f the s e c t i o n and some sand and g r a v e l near the top p a r t i c u l a r l y along the course of S h i n g l e C r e e k .  Vertical  s i l t b l u f f s and steep-sided g u l l i e s along Okanagan v a l l e y above and below the creek mouth show many f r e s h l y exposed s e c t i o n s with f i n e l a m i n a t i o n aad  cross bedding.  Another group of g r a v e l and s i l t  benches are found  i a the v a l l e y at the j u n c t i o n of Shatford aad. S h i n g l e fhe upper beaches o f t h i s group approach 1,500 the  Okanagan  Creaks,  f e e t above  V a l l e y bottom and eons-Ist predominantly  of  bedded gravelf however, a d i s t i a e t lower s i l t beach  was  found roughly 100 t?pper Shingle  siiiem  mwm  feet above the present beds of  Shotford  and  Creeks. FLOOD  P M I I  At t h e i r j u n c t i o n Shatford and S h i n g l e Creeks are s l u g g i s h streams meandering across a n e a r l y f l o o d p l a i n two t o three hundred yards wide.  flat,  marshy  Below the  j u n c t i o n th® v a l l e y steepens and the creek flows between  gravel  fans aad, s i l t b l u f f s i n a  yards wide. the- ©reek  At  a  point  Is confined  galley f i f t y to  two miles'west  of  one hundred:  Okanagan v a l l e y  to a rock walled gorge about t h i r t y  11 yards a c r o s s | below t h i s the grade diminishes aad the f l o o d p l a i n g r a d u a l l y widens to I t s f u n c t i o n with the Okanagan v a l l e y * POST QhkClkt  IISTOHY  lit the end of the ^Isistoeen© a l a r g e mass of i c e i s b e l i e v e d t o have o c c u p i e d Okanagan Trench, and masses probably remained  stagnant f o r a while w i t h i n the One such s m a l l e r mass probably  siaaller surrounding v a l l e y s .  occupied the v a l l e y s of S h a t f o r d aad at their junction.  smaller  Upper S h i n g l e Creeks  Draining of melt water south along the  border o f th® ie® against the south east f a c i n g slopes aay account f o r th® upper g r a v e l benches here. While the i c e continued t o block the v a l l e y of Upper S h i n g l e Creek, drainage f r o * the north developed a prominent  o u t l e t f a n at the mouth of  Parlolgh Creek  crossed the present v a i l s y of Shatford Creek aad south toward  fhs &arron E l v e r ,  which  extended  letter the ie® receeded  Upper S h i n g l e Creek, the F a r l e l g h Creek o u t l e t was  froa  aban-  doned and a shallow l a k e (herein r e f e r r e d t o as 6hatford  I«ak0} formed  at the head o f lower S h i n g l e Creek.  was presumably  aaiatained  at  this  high  This lake  olevetion by  the high  l e v e l of ie© i n Okanagan V a l l e y , and probably overflowed along the edge of the i c e t o the e a s t .  Bry v a l l e y s along  the southeast slopes above T.ov;er Shingle Creek fog. th® South l a s t Contact Canyon of th© South fiast Contact Area Map) have acted as drainage channels at t h i s time.  may  With the lowering o f the i c e l e v e l Irs Okanagan V a l l e y a lower o u t l e t may hav« b^en achieved In t h i s d i r e c t i o n , and Shotford Lake  was  drained i n t o a new lake f o r c -  ing between the io© and the south of Lowar S h i n g l e Creek. At the same time Shatford Creek ©at a channel through the fan formed a t the Farleig-h Creek o u t l e t and adopted i t s present eoaroe i n t o Lower S h i n g l e Creek. Development o f th® prominent s i l t b l u f f s above  Pentloton  has been a t t r i b u t e d by F l i n t  (1935) t o the  formation o f a lake between tha i c e and the v a l l e y walls which extended south to a das bel©%? ^aseaux Lake.  -.* ith the J  br@ak.lnf of t h i s ism S h i n g l e Creek was abla to ©rod© i t s present course.  fhe area  surrounding  S h i n g l e Creek i s below timber-  l i n e and the f o r e s t cover i s predominantly coniferous w i t h deciduous t r e s s l a r g e l y r e s t r i c t e d t o the Shingle Creek f l o o d p l a i n and seme o f the l a r g e r  gullies.  slope.® are dry and s p a r s e l y timbered, but the north f a c i n g  slope*  South f a c i n g  sheltered  support some t h i c k stands o f spruce and  pine. fhe c l i m a t e at S h i n g l e Creek i s a r i d but c o n s i d e r able v a r i a t i o n s  aotuttoin  in precipitation  tops and the v a l l e y .  wo** encountered when the v a l l e y  are apparent  S i x inches  by tha author at 3*500  bottom  had  a  between  of f r e s h  feet  in  snow  December  cevsr of l e s s than one i n c h .  III  mmmjmmx C o n s o l i d a t e d rocks i a . the S h i n g l e Creek area range from p o s t - T r i a s s i e -  pre-Tertiary to e a r l y T e r t i a r y  i n age*.' The  o l d e s t reeks oomprise a sequence of  f r i a s s i e i n t r u s i o n s of  d i o r l t e , granodiorite, granite  a p l i t e w h i c h were i n t r u d e d o v e r l a i n by the  post-  I n the order g i v e n .  aad  These are  Springbrook Formation o f Paleocene (?)  age  which c o n s i s t s , w i t h i n the Shingle Creek a r e a , of c o n glomerate aad sandy t u f f .  Contemporaneous w i t h the  Spring-  brook f o r m a t i o n i s a p i n k to grey granite porphyry (the Shingle Creek i n t r u s i o n ) w h i c h has been found c u t t i n g  the  l o v e r beds of the Sprlngbrook Formation.  latter  f o r m a t i o n , however, contains  Most o f ta®  a n g u l a r fragments ef  the  porphyry. f h e S h i n g l e Creek i n t r u s i o n and  tho  Sprlagferook  Formation are intruded' by l a t e r b a s i c dykes probably r e l a t e d t o ths  MaiTon F o r m a t i o n . The a r e a i s o v e r l a i n t o the  west and s o u t h by the  Marron b a s i c v o l c a n i c s .  CBKGSOXC P l e i s t o c e n e and Kecent S h i n g l e Creek a l l u v i u m , g r a v e l and sand g l a c i a l t i l l , g l a c i a l lake s i l t f» r e - l a t e  .Eocene  Marroa Formation  - b a s a l t and  S h i n g l e Creek I n t r u s i o n granite  porphyry  endeslte  Springbrook  Formation  conglomerate and t u f f  HSSOZOIC Pmt~£rlassie !  KlOSIfl  Intrusions  ApUt* Granite Gfranodlorlt* Merita  fhe Shingle Creek d i o r i t e i s a mtsotyp© equl-  granular  medlam-gralned r o c k showing Im degrees o f mate*  morphism.  I t i s s i t u a t e d i n the area surrounding the  j u n c t i o n o f Shotford and S h i n g l e Creeks and extends down the lower  Shingle  Creek  valley  f o r about two .utiles below  this Junction, three specimens from the d i o r i t e I n t r u s i v t o f s l i g h t l y d i f f e r e n t appearance were  examined  under the micro-  scope and t h e i r content i s summariafed i n t a b l e C I ) .  Specimens ¥11 aad '.14 represent t y p i c a l d i o r l t e . f h e development o f c h l o r i t e and epldota i n these specimens i s probably due t o m e t a m o r p h i s m which may be associated with the subsequent Intrusions, f a b l e (1)* ¥11 Potash Feldspar.  ¥14 —  ¥5 4$  Plagioclase  5®$' A»4«j  Quarts  *—  2$  13$  Pyroxene  •*»  -«—  2%  Ataphibale  17%  Biotlte  n  Chlorite  60^ A n ^  - l$$ \% —  69$ An r,. 2  % % — -  spidoto  m  1%  ™  Accessories Hagnetite Alatite Uphea®  2%  2$  2$  Specimea %I15 represents the f r e s h e s t outcrop found which occurs i n a recent road cut along the north vest «dge o f the i n t r u s i o n .  * f o o b t a i n t h e oovoentage g i v e n , the a r e a oocupied by each m i n e r a l was.oattented i a five d i f f e r e n t f i e l d s f o r each t h i a - s e e t i o a , t h e r e s u l t a v e r a g e d , aad tho r e s i d u a l e r r o r d i s t r i b u t e d a c c o r d i n g t o the relative aosndanoo o f each m i n e r a l .  weatheyod  Specimen ¥11 represents somewhat a c r e  diorite  f r o a the edge of the middle bench three quarters of a a l l s northwest of tha of 8hatford and Specimen  Shingle  junction  Creeks.  represents d l o r i t a from the slopes above l o w e r S h i n g l e Creek and a l o n g tha  southern  c o n t a c t of the i n t r u s i o n . Specimen V5  represents a p o r p h y r i t i c .phase of  d i o r i t e i n which l a r g e r  g r a i n s of p l a g i o c l a s e a r e  surround*  ed and replaced by a mass of f i n © g r a i n e d quartz and feldspar,  fhe  o v e r a l l composition  of the  suggests  s l i g h t l y chilled quartz-alkalai r i c h  phase  alkalal  or  material.  ©f andeslae a l t e r e d  potash  specimen Is some*  what d l f f s t e n t f r o a $11 and fe'14, and  c r contamination  the  either a  of the  a l t e r a t i o n o f d i o r i t o by  diorits,  qaavt**  P l a t a (1) page 17, shows a phonooryst  to ollgoolaao  p a r t r e p l a c e d fey Quarts and  at i t s periphery and  potash f e l d s p a r *  In  P l a t e (1) A p l a g i o c l a s e phenocryst replaced by quartz and potash f e l d s p a r Specimen S$  (x50)  GRANODIORITE The S h i n g l e Creek g r a n o d i o r i t e i s a l i g h t grey aadiuE to f i n a - ^ r a i n ' d equigranul&r rock which underlies the upper mountain slopes south east o f the j u n c t i o n of Shatford and Upper Shingle Creeks. The g r a n o d i o r i t e vas not observed  i n contact I i t h  any o f the othor i n t r u s i o n s during a s i n g l e traverse made i n t h i s area and none o f i t s outcrops appear i n c l o s e proximity to t h * Shingle Creek orphyry r,  intrusion.  The composition o f th?. g r a n o d i o r i t e i s suiaiEarizad in Tabl^ (2).  18 fable (2) Granodlorlte W4 Mleroellne  14H  Plagioclase  6lfS  Quarta  -llH  Biotite  13*  Accessories Magnetite Slrcon  If  Apatite  Specimen ¥4 was taken frost the g r a n o d l o r l t e a t the head of-the  first  prominent gully  p a r a l l e l and  east  . c f S h a t f o r d Creek, iftMITS  where t h e  granite- Intrusion was examined  by the  author ( p r i n c i p a l l y on t h e s l o p e s n o r t h o f .L@w«r Shingle Creek) i t c o n s i s t s o f a mfdlum-graiaed e^uif-ranular rock* phase o f t h i s  Bostock (1936) r e f e r s to a p o r p h y r i t i c  Intrusive at  porphyritic textures  lettoeoratie  Shingl© Creek but no marked  wer* observed  in  the  t h e c o m p o s i t i o n o f the analteres  outcrops  granite  summarised in t a b l e ( 3 ) on the f o l l o w i n g page.  is  examla**".  19 f a b l e «3) G r a n i t e VX5  Potash feldspar Plagioclase QU*rt|  Unfit®  m> m Tr.  Uuscovlto  Tf.  Chlorite  Tr.  *eoe*oorie*  «agn«tli® Spheae Epldot* Apatite  If  Froa th* table It Is apparent that ths sp#ei»#as W15t sight b o l t e r oo dosorlfced m a groaodlerltof however, tho mow granlto Is retained here m the apeelaen renreftoiito only one estorop of a lares oody designated grantto on Hap #17% distinctly ooanser grained and ©aataining lass mafic ttlneraia. thaa the graaadlarite to tho »0«tk*  la this sootiea the graaiia is slightly fiorphyrftie with largor e«fe»iral to sahh#4»l crystals of plagioolaso e^rooadod by ^oarta aai potash feldapar* Snail grains of pl«fiooloso are iaeiadsi in potash foldapar sad five the rook a foikllitin appearanae* Zoning in tae plagioelaoo is Speelftoa s l j  was taken frea a fresh aatoroip of granite at the Month of the largest galley «xt#aiiag north fro® iLovor SM»fie Crook*  w e l l developed. and .shows an o s c i l l a t o r y normal son® pattern. trated  Three p r i n c i p a l zones aay be seen as I l l u s -  i a figure  (2).  Increasing A north ite Content  Crystal  b o r d e r  figure  crystal  centre  (2)  The inner zone (1) shows o s c i l l a t o r y normal or reverse development*  f h e two outer somas, Ct) tad ( 3 ) ,  together show pronounced o s c i l l a t o r y normal development. fhe  prm-am®  of the outer two normal zones Is  common to many c r y s t a l s showing zoning i n the s e c t i o n examined, were not  t h i s may suggest that the p l a g i o c l a s e  moving relative  t o one  anetha*  crystals  d a r i n g the form*  a t i o n of these outer sones.  The S h i n g l e  Creek Ajplite ta  a fine-grained pinkish  rock forming dykas and small stock-Ilk© bodies v i t h l a and along the edges o f 'the g r a n o d l o r l t e .  These bodies were  designated " g r a n i t e , granophyre and f e l s l t e  H  by Bostock  (1936). fhe composition o f a s i n g l e specimen o f A p l i t e i s summarised i n ' f a b l e ( 4 ) , fable ( 4 ) Mierocline Plagioclase  V13  19$ A n ^  Quartz  44#  Muscovite  1$  Accessories Magnetite Elreon Apatite  Specimen  3M  IS  was taken f r o ® p i n k s p l i t s where a dykel i k e body o f t h i s r o c k eosea cles«? t o the road s o u t h o f S h a t f o r i Qreek.  22  The S h i n g l e Creek I n t r u s i o n or S h i n g l e Creek Porphyry forms aa elongate stock or d y k e - l i k e body approximately a a i l e and a h a l f wide a t i t s broadest s e c t i o n and four miles long with a s e r i e s of dyk«s extending west o f the main body f o r two a l i a s ,  At the upper end of Lover  S h i n g l e Creek these dykes pass beneath the Marron volcanics.. The general trend o f the i n t r u s i o n i s w e s t e r l y with subs i d i a r y dykes shoving a somewhat r a d i a t i n g p a t t e r n about the s a i n body. The porphyry intrudes the g r a n i t e and d i o r l t e of th© post-Trias®ic i n t r u s i o n s and parts o f the Springbrook formation w i t h which i t i s considered contemporaneous. Specimens o f the porphyry are of g r a n i t i c comp o s i t i o n and the minerals present together with t h e i r r e l a t i v e proportions are l i s t e d i n t a b l e (4)  i n Chapter  IV,  The most s t r i k i n g f e a t u r e of the S h i n g l e Creek i n t r u s i o n i s i t s p o r p h y r i t i c texture*  phenoorrets  up t o four  tneheo  i n length  luhedrai  aanldlno  with .mailer  plagio-  c l a s e quarts and b i o t i t e phenoorysts up t o one h a l f Inch is  length  occur i n a pink grey or greenish  for a  more  ophanltie  matrix.  d e t a i l e d d e s c r i p t i o n of t h i s rock type  the reader i s r e f e r r e d t o chapter I f .  (mm&h DiscBiPtioH Bostock (1936) has mapped the Springbrook Formation a t S h i n g l e Creek and the south and west,  this  I n the s u r r o u n d i n g  formation r e s t s  areas t o  on a p r e * T e r t l a r y  rock s u r f a c e o f steep r e l i e f ; and I s composed o f l i t h l f i e d s o i l s , a l l u v i a a , t a l u s , s t r e s s and  l a k e d e p o s i t s , and  ttiffeeeeus materials t h a t accumulated i n the v a l l e y s extrusion o f the Marron v o l c a n i c r o c k s ,  before  ".-here the S p r i n g -  brook Formation i s t h i c k , the b a s a l b^ds are of conglomerate containing- l a r g e a n g u l a r and unsorted b o u l d e r s ,  t h e s e beds  grade upward i n t o conglomerate* eoaposed o f s m a l l , rounded, and sorted .materials.  Uppermost s t r a t a include beds of  p o l i s h e d pebbles, ttiffaceeos s a n d s t o n e s , and In  slltstones.  the C l a l l a a r e a t o the wast t h e s e beds c o n t a i n p l a n t s of  e a r l y t e r t i a r y , perhaps Paleocene, age. T1S  SPKIH0B100S FOimTIOH  TBS SOOTH EAST  CONTACT AEBA  At S h i n g l e Creek examination of t h i s formation by the author wm  r e s t r i c t e d t o the S o u t h l a s t Contact A r e a .  Here the b a s a l p a r t of the f o r m a t i o n i s made up of  two  parts c o n s i s t i n g of a " b a s a l " coarse conglomeratic member showing c o n s i d e r a b l e range- o f t h i c k n e s s but probably  not  exceeding t h r e e hundred f e e t , aad an upper sandy tuffaeeoos aeaber up t o s e v e r a l hundred f e e t t h i c k .  However, a  few  feet o f the tuffaeeous member can be seen t o moderly the  eoBglotterete  at the n o r t h west end of  the  area  mapped*  24 The coarse conglomeratic member i s buff to dark grey-brown i n colour and c o n s i s t s l a r g e l y of d i o r i t e , granod i o r l t a , and  r a n i t e boulder*? ut» to sev ;ral feet In diaraeter  v i t h some blocks exceeding tventy f a c t i n diameter.  Some  outcrops shov angular fragments a few of uhich are granite porphyry s i m i l a r to the S h i n g l e Creek i n t r u s i o n .  The  a n g u l a r i t y o f some of these fragments i s v e i l i l l u s t r a t e d i n p l a t e (2).  *late  (2)  Angular fragments of d i o r i t e and g r a n o d l o r l t e In the Springbrook Formation  The matrix of the conglomerate consists of poorly sorted f a l d s p a t h i c sandy or s i l t y material showing various degrees of ceaiintation.  Local lenses of sand  i t h i n the  conglomerate provide approximate a t t i t u d e s . fhe  sandy  tuffaceous member i s grey to * grey-green  l a c o l o u r and consist® l a r g e l y of and f e l d s p a r g r a i n s .  Many  wall  cemented quarts  angular fragments of granite  porphyry up to tv.-o inches i n diameter and s i m i l a r i n appearance to the Shingle Creek intrusion, were found.  The  freshness of the b i o t l t e f l a k e s and "resorbed" surfaces  observed  on SOBS quarts grains i n t h i s rock a l s o suggest  that such of the m a t e r i a l e f t h i s formation was. derived  k few patches of v e i l  from the S h i n g l e Creek i n t r u s i o n ,  rounded cobbles i n a f i n e - g r a i n e d grey sandy s a t r l x observed i n the upper parts o f t h i s  wore  aeaber,  A p o o r l y preserved segatenttd p l a n t f o s s i l res eabling a " h o r s e - t a i l * was  found i a t h i s rock but as t h i s type of  1  plant f o s s i l has a wide s t r a t i g r a p h i c range i t s  occurrence  here i s o f l i t t l e s t r a t i g r a p h i c s i g n i f i c a n c e .  f h e v o l c a n i c rocks of the Matron formation were extruded over  hills  p a r t l y f i l l e d by rocks f i n a l l y thousand  of  pre-Tsrtlary  rocks and i n t o v a l l e y s  tho Sprlngbroofc Fomatlon.  aeeisBolated t o a  The  volcanic  thickness of over four  f e e t in. some p l a c e s , aasl are b e l i e v e d t o have  covered most of  the  area*  surrounding  s i s t s mainly ef l a v a f l o w  ten  the  formation con-  t o twenty feet t h i c k , but i n  places there are l a r g e masses of  agglomerate.  At S h i n g l e Creek the Karron v o l c a n l c s c o n s i s t  of  dark greenish-brown flows c o n t a i n i n g W t o 30 percent of plagioclase  phenocry«ts  ranging  o f an i n c h I n length, and  minor  in  up to three quarters  nlze  amounts  mafic phenoorysts, i n a f i n e - g r a i n e d  of  r e l a t i v e l y small  matrix.  The author examined these rocks a t only two  ities;  one south o f the South l a s t Contact area, and  localthe  other vest o f th® j u n c t i o n o f Shatford and Shingle C r e e k s .  ASSOCIATED BASIC OTIS S a v e r a l b a s i c dykes cut the  porphyritic intrusive  and th® S p r i a g b r o o k Formation a t Shingle Creek,  These a r e  f i n e - g r a i n e d rocks o f s e v e r a l colours i n c l u d i n g g r e e n i s h b l a c k , r e d d i s h , or grey-green. T h e i r ^Jointed s t r u c t u r e has made  thoa  particularly  subject to  d i s i n t e g r a t i o n , and  most places t h e i r occurrence Is marked by  In  a long coloured  talus slope. The general s t r i k e c f these dykes i s somewhat east  of north, ritic  obliquely across  intrusive.  the general t r e n d o f the porphy-  'S',« '  CHAPTER TV WQlQQt  OF TljrK S l i l ^ - ;  CKWK  IKTROSICIf  A b r i e f d e s c r i p t i o n of the geologic s e t t i n g of the S h i n g l e Creok porphyry has  chapter.  baan  given In  the  preceding  Ia t h i s chapter are described some of the ®ore  d e t a i l e d f e a t u r e s o f th®  intrusion.  f h e ©atIre i n t r u s i o n , i n p a r t i c u l a r that p o r t i o n of  underlying the sore h e a v i l y wooded slopes southwest  Lower Shingle Creek, has not been examined i n d e t a i l * intrusion  la. v a i l  exposed along  i t s south  and  east  margins,  hut the rock here i s deeply weathered and u n f i t f o r s c o p i c study,  gov ever., on  S h i n g l e Creek the  figure  herein  Micro-  the north slopes above kewer  rock i a f r e s h e r and  the microscopic study  to follow deals c h i e f l y w i t h an elongated lobe of trusion  the i n -  r e f e r r e d to as the l o r t h Dyke (see key  1). A few  specimens taken  southeast are g e n e r a l l y  The  similar  froai  map  the a a l a body to the  though more  deoply  weathered,  ^TRoipcy  MEGASCOPIC D\eCRIPTlO» In hand specimen the  Shlagle  p o r p h y r i t i c w i t h a ground mm® of  Creek I n t r u s i o n i s  aphanitle  appearance con-  t a i n i n g pfeenocrysts of s a a i d i n e , q u a r t s , p l a g i o c l a s e , and  aafle  minerals.  The p r o p o r t i o n  of phenoerysts  ranges from f o r t y to s i x t y percent  to matrix  approximately,  Th®  f  quartz and p l a g i o c l a s e vhenocrysts, and a large p o r t i o n of the sanldins phenoorysts range from one eighth to one  h a l f inch l a length.  Some parts of the i n t r u s i o n , however,  contain l a r g e r than average sanldines which reach rear inches i n l e n g t h . present  m  B i o t i t e , hornblende and magnetite are  phenoorysts o f smaller slxe seldom exceeding  one quarter of as Inch i n length! however, c l o t s of hornblende and b i o t i t e up to one h a l f inch In diameter ware observed i n one or two specimens. The l a r g e euhedral sanidlne phenoorysts are white, pink, or crimson, tha l a s t colour being peculiar to deeply  weathered outcrops. Many of th® sanidlae c r y s t a l s show a suggestion of zoning i n the form of layers of cracks conc e n t r i c about th® c r y s t a l  centres.  In some places, p a r t i c u l a r l y noticeable In the f o r t h Pyks, the large sanldins phenoerysts show a poorly developed preferred orientation giving a trachytle  texture  to the rock as a wholei however, in most outcrops the orientation of phenoorysts I s random. twinning* and  intergrowths  o f two or  more c r y s t a l  i n d i v i d u a l s are common amongst the eaaldlne pheaocrystf. That® features are i l l u s t r a t e i n plates ( 4 ) to <6)» oa the f o l l o w i n g pages.  Plate (3) A simole Sanldini crystal shoving ( 0 0 1 ) , ( 0 1 0 ) , ( 1 1 0 ) , and  (201)  faces  Plate (4) A typical Sanidina Carlsbad twin  Plate  (5)  I n t a r g r o w t h o f two S a n i d i n e I n d i v i d u a l s s i m i l a r t o t h a t shown i n l a t e (3) a  P  late  (6)  A l a r g e b l o c k o f p o r p h y r y f r o a t h e N o r t h Dyke The f a c e exposed has d i m e n s i o n s 14"x6"  31 Plagioclase. •jfcanoerysts ar© wMto to brownish aad generally ar® mora deeply va&thsred thaa the sanidlne. Quart* phenocrysts- occur as subhedral bipyramids s©mevhat rounded hy coresIon, fhe porphyry matrix appears uniformly fine-grained ia  hand apeeJU&en  fro®  bat ramgaa  grey-green, with the  grey*buff through grey to  grey-buff variety occurring predominant-  l y along the north side of the intrusions and th© grey aad grey-green  varieties  occurring i n the central and eastern  parts, MICROSCOPIC B E B C l I P f l O l Composition fable ( 4 ) i s a summary of the ©©imposition of several specimens representing the Shingle Creek Porphyry as a whole. fable C 4 ) Phenoerysts faaidiae  a  mm m  48  47  m  #5  Sl$  Plagioclase Quarts  12$,  m  Biotite* Aeoeaseries Matrix  2*  2^ 46%  m  4%  Aa^  •m  Ano  14$  m  4$  u  3*  1%  54^  5f?S  <quarts aad potash feldspar approximately equally represented) &  inoladas hornblende in amotion 47*  this line  which is present chiefly  Specimens 1052  and >W ©Q represent two phases o f the  Shingle Creek intrusion froa the Worth Dyke section. Specimen 48 was taken from t h a south side of Lower Shingle Creek Valley opposite the Worth Dyke Section. Specimen 47 was taken from a bluff in th© south central part of the intrusion. Speeliaea 3© was taken from the South last Contact Are*. Mineralogy Cl)  Phenocrysts (a) Sanidiae-Anorthoelase Investigation of thin-s-actIons shoved that th®  large potash feldspar crystals have a s m a l l optic angle and this indicates t h a t they are members of the sanidineanorthoclase series rather than microellne ©r orthoclase. At high temperatures a continuous solid solution series i s believed to axist between h i g h alblte and sanidine (Il.lSi^O|) named by Tattle the Samidine-tocrthoclas««Cryptoperthite terl.ee«  High alfelte and anorthoolase  are t r l c l i n l c but s a a i d l B e i s considered to ba m o n o c l i n l e so that a transItion occurs within tha eerie*.  In an  attempt to dtterstlas tha c r y s t a l system of the large phono* eryste from Shingle Creek, a thin-sectloo cf a c r y s t a l twinned according t© the Carlsbad law was -made approximately perpendicular t o the *** crystelegraphic a x i s ,  The *X*  n  l  m  t  33 aad W Z W axas of tho optic indicatrlx f o r each twin unit, together with the pola o f t h e composition face (010) were very carefully d@t«rmin@d and plotted on a stereenot, and the angl® betwean th©ttZ m a x l e and the (010) p o l e determined to b# of tha order of one degree (approximately the order of magnitude o f t h e arror o f  maa*areateAt)«  This  suggests t h a t the c r y s t a l i n v e s t i g a t e d i t s l t h e r v s r y s l i g h t l y triellale o r else is aoaoellnie.  llo evidence o f  unmixing o r m i c r o s c o p i c t w i n n i n g was observed i a t h a section.  The o p t i c p l a n t was shown t o be approximately  jporpoitdleiilar t o t h e m o n o c l l n i e symmetry plane (010). f i g u r e Oa) is a r e p r o d u c t i o n of t h e p l o t o b t a i n e d . S e v e r a l t h l a - s * e t i « n s of aatwinned l a r g e sanidlmo pheneerysts ware c a t perpendloular t o t h e "X" a x i s ( s e e f i g u r e (2b)) f o r the purpose- of measuring t h e o p t i c axial a n g l a , 2f•  These c r y s t a l s were found t o be c o n c e n t r i c a l l y  sons* as I l l u s t r a t e d l a plates  (7) and (S). f h e  n&y&mm  and minima® 2f f o r sach of those c r y s t a l s was measured, and th® range found t o extend from •»  A  specimen @  f3 -  (-12? » 24° t o {•)iW  aiagla thinniaetioa of unusual c o a p o a l t i o a (see  47 table i f ) } showed potash feldspar with (-)ST  59°.  Many of the sones show abrupt i n n e r boundariesf  with a g r a d u a l dooroaso i a  2? outwards toward the next sons  reprosentlng a g r a d u a l iaoreaso i n potash content within the sone. The soning i s o s c i l l a t o r y  and ao taarkad general  treads either towards more sodlo o r a o r t p o t a s s l c oompoai-  3*  Figure (3a) Stereogr&pMs pr©3#-eti#n of tho orientation  of th* **!*% *T% »n4 *S* of tie *x*t and the  (010) pole'of a saniaine Carlsbad* twin f r o * t h i B g l e Creek*  Y  ftgare ( m Sketch  shewing the approximate r e l a t i v e p o s i t i o n s of the " 1 % "Y", and «Z* axes, th® o p t i c plane, and erystalographic faces of a t y p i c a l sanidine phenocryst from Shingle Greek.  36  Plate (7) A zoned sanidine ohenocryst (x 25)  Plate ( 8 ) A zoned sanidine phonocryst (x 25)  tioas  war® observed l a oa© c r y s t a l , ftifforont c r y s t a l s ,  however* appear to vary about s l i g h t l y different average  compositions, f h a s , ©f three c r y s t a l s whoso Boning was studied i a d e t a i l , one approximated an average of  and the ©ther <-}2f * 38°. Figure 14) i s an l l l a s t r a t i o n of the type of v a r i a t i o n la <-)2V - 3 0 ° • one {>»)m « 34®,  ff measured i a th© large, s a n i i l a e psa&eerysts*  F i g u r e C4>  In example of the type of sotting observed  i a the large saaidiss phenoexysts  For t h e p u r p o s e s o f  pendleolar normal  f  *X** a x i s  & fragment  in  2V,  with  a slab  a large  two w a l l  defined  sanidine  pheno-  sones  was r e m o v e d a a d  aa i n d e x o i l c l o s e l y approximating the i n d i c e s The Y  n  a n d Z"  the  fragment.  the  fragment  for  v a r i o u s wave l e n g t h s o f l i g h t ,  M  M  indices  the  the o i l  index o f  u s i n g a a a r c lamp a a d  The wave lengths for which matching was  achieved were noted.  The fragment  was w a s h e d  i n benzene  aad p l a c e d i n o i l o f s l i g h t l y d i f f e r e n t index? the  corn*  o f i n d i c e s was r e p e a t e d , and the w a v e l e n g t h s f o r  which matching was achieved again noted, the  of  f o r each zone of  ware then compared w i t h  soaochrometer.  parison  per-  o f the s l a b showing a minimum o f a l t e r -  and c o n t a i n i n g  placed  indices of r e -  and somewhat t h i c k e r thaa a  t h i n - s e c t i o n was c u t f r o m  cryst, ation  t o ths  conjunction  in  fraction accurately  measuring ths  variation  graphs  representing  i n i n d e x o f the o i l a s e d , w i t h v a r i a t i o n i n  the wave l e n g t h o f l i g h t , were p l o t t e d before and checked after  each  comparison  j u n c t i o n with liass  ia  tho  these  figure  tho 5).  fragment graphs.  a r c l a w and  »oitoohro»ot«r,  tho  matching wave  P r o m the data  extrapolated  (See s o l i d  variation  thus  lengths wars  of  o f tha i n d i c e s of th® axes them-  each uone i n  from these  of the t y p o o f graph  read from  obtained l i n e s ver® d r a w n  w i t h . t h e wave l e n g t h o f l i g h t .  «Y» and *Z* axes  i n con-  Tha I n d i c t s o f t h e t w o a x e s o f each z o n e at  representing the  selves  u s i n g a n Abbe r e f r a e t o a e t e r  linos,  obtained.  The i n d i c e s o f the  sodinw  fi f a r e  y e l l o w l i g h t were  (5)  i s a reproduction  500  X  550  600  650  QJ  T)  The solid lines r e p r e s e n t \ t h e v a r i a t i o n i n index \. \ of t h e t w o o i l s u s e d at 23°C.  \^  C  l—I  > 0 <_— i t_  h.535  r 1.530  rr CO  c  t.525  0 Sodium  Q>  u C  yellow  \ \ .  light  v-—I  1 Increasing of  1^ ^  '  W a v e - (encjt h Li9 ^ +  Figure ( S )  graph showing variation in index with the wave l e n g t h ©f light o f two oils w  A  used, ead of the *T* and « l i a d i e e e of  the fragment o f sanldiae.  The  fragment was then.  placed on the four axis  u n i v e r s a l stage and th® o p t i c angle, 2V measured as a c c u r a t e l y as p o s s i b l y f o r each mm.  Using the 2V and the  values o f the "Y** and "2" i n d i c e s p r e v i o u s l y obtained the M  X  M  index o f each son© was c a l c u l a t e d *  xe&ee s t u d i e d  (5)  and  ( 6 ) are  infor-  estimates o f t h e compositions o f the  mation independent two  Using t h i s  were nade nsing  Tattle's  curves*  Tables  a sumaary o f the data obtained.  The o p t i c a l p r o p e r t i e s o f the l a r g e phenocryste from tho porphyry are i n agreement with the r e s u l t s obtained Sanidlne-Anorthoclase-Cryptoperthite  by T a t t l e f o r the  B«tlm range  and i n d i c a t e that the c r y s t a l s ar® zoned over a  CtagQ, AhAagQt  to f t e ^ t iMn^9  somewhat beyond these values* present throughout ©f  tha  the sase s e r i e s *  w i t h extreme son as  The smaller phenoorysts  pmfihyvy  are  to be members  f h l n - s e c t i o a s aad® o f these c r y s t a l s *  however, were o f normal thickness and t h i n for accurate  considered  determination  of  proved to b® too  2V.  41  Table C5)* Zone (1)  (1) (2)  *x« index  (calculated) *T*  index  «g* i n d e x  (2)  Son©  (3)  (1)  (2)  (3)  U5108  1,5201  1*5*55 1*5*57 1.525©  1,5264  1.5264  1,5264  U5&0  1.5270  1.5274  1.5272  1*53*0  1*5»60 29®  MTf  33° 2®  2°  Table (6)* Zone CI)  Ion*  <2>  Composition derived  froa «T* eoneposltlon derived from »2* Composition derived from 2?  6r 71  Or 61  Or 69  Or 61  Or 71  Or 60  Colomns (1) and (2) o f t a b l e ( 5 ) represent independent readings on the same z o n e , and column ( 3 ) r e p r e s e n t s the average o f columns (1) and ( 2 ) . I n t a b l e (6) the f i g u r e s given represent percentage o f  orthoelase as read from Tuttle*» otzrvss. t h e remaining constituents are assumed to be Alblte (Afe) and A n o r t h i t e (An).  4a Co) Plagioclase  Sttaedral  to *sfehed**X plagioclase phenoerysts up  to em* qmarter t e c h i n length are more or Xe*s uniformly  distributed throughout oy the author,  those  parts of th® intrusion v i s i t o r  The p l e g i o o l a s * ph*ao*rysts  standard t h l a » s « t i o n s  mada  froa apeoimena  wore examined ta  froa  son©  of  the  fresher outcrops at various points i n the i n t r u s i o n , and f r o a a detailed set of specimens collected across the Korth fyke s e c t i o n .  For each c r y s t a l examined  the A n o r t h i t e -  A l b l t e CAn»Ab) content was determined using Van £*r Kwden*s  carves for aarsml plegie*Xass f and the optic axial angle, f t , measured*  Only grains with Alfeite twin lamellae, and with  the *X« axis  nearly a o m a l  measurements.  to the s l i d e were tteed i a these  The * n ~ J * content was checked with Index © l i s *  f a r i a t i o n i n Wf was plotted against-An»Ab composition on th® diagram o f Severn and T a t t l e here reproduced- as figure (4).  Fro® figure (4) i t Is apparent that the p l a g i o c l a s e * Of the intrusion may he divided Into two main groups, one approxiowtimg t h * composition Aa^Q-Ab.^ with a r e l a t i v e l y s m a l l (~)2¥ e l o e e to 7©^8  ead a second group approximating  the composition Ah^-Ab^g with a larger (~)2? ft0*  between f 4 0 and  A suggestion of a third group i s present but this i s  "represented  by one speoimen only I taken close to an Internal  contact i n the west central part of the Intrusion, (see table If))*  This l a t t e r group i s d 1 s t  inert  from the former two l a  43  Figure  30  20  10  0  (6)  Percentage  of  4.0  Anorthite  In Figure (6) points marked : X  represent crystals from the North Dyke Section.  O  represent crystals from other* parts of the porphyritic intrusion  A  represent crystals f r o m the plutonic post Triassic intrusions  (curves  after  B  ow'en  an  d Tuttle, l95o)  44  •touring • w i l l developed oscillatory normal gone pattern, and a r e l a t i v e l y higher An percentage.  In  figure  (4) the l i n e CI (after Bowen and T u t t l e )  represents the variation of 2 ? for "low temperature* pleglo* clasa,  Th®  line  the variation  AB  of 2?  pleglaelaaes.  (also  after Bowen  range of  Bowen  and  tuttle  (-)2Y  and the  towards  third  group  and  from a  **hlgh temperature**  Intrusions  t h e i r plots f a l l  range. Five  wall below the  1  helonglng t o  appear to belong  froa ths  crystals  w  sake  of  the  to the  post-Triaasle  comparison  l o w temperature"  and  lines.  Quarts  Quarts occurs in  specimen  investigated for the  ware  (c)  single  "high temperature *  fhe crystals  Tuttle,  temperstore*  tha «low  group approximating A n ^ - A h ^  shows t r a n s i t i o n a l o p t i c s towards the Bowen  temperatore"  Thus the group of crystals approximating  shows t r a n s i t i o n a l  of  Tuttle) represents  with composition for "high  Aa2»&©^g  range  and  as phenoerysts  up to one half inch  length throughout the intrusion* In  many  places the  rock  i s severely weathered and the quarts phwriocrysts may be broken out unite readily* The forma observed on these crystals are  t y p i c a l l y somewhat corroded  blftyramids.  Quarts phenocrysts fro® the "Quarts Porphyry at Pentletoa mined  were investigated by Mean  as b#ta quartz on the  basis  (1934)  and deter-  of crystal form, fracturing  due to inversion, and twin pattern'developed by etching.  4f  tame doubt hasfceene a s t oa the v a l u e of thota c r i t e r i a f o r distinguishing  between a l p h a  aad beta  quarts  by  Frondel  (1955). 1® states that*  (1) fhe extent of twinning aad crscfciag o f quarts at  crystals  the  reduced ©a slow  (2)  quarts  The beta  inversion  tends to ba  ooollag. h a b i t (equal  rhomhohedrezts w i t h ao •he found  point  i a alpha-  development of  prismatic  quarts  faces)  may  d e p o s i t e d fro®  iron  r i c h solutions*  3-ome of the q u a r t s phenocrysts froa Shingle Creels examined i a thin-section are only slightly fractured (see p l a t e (9)) but others show many fine freetare* (s«s@ p l a t e (16)}* fhe notably Iron poor environment i a which the quart* p'haaoerysts formed a t Shingle Creek weald seem to suggest that these c r y s t a l s a r e b#ta quarts as eoneludad by mm* (2) Matrix l a thln-aeetien porphyry c o n s i s t s o f  feldspar ranging  the matrix of  ellntriemerphie  the ehlngle Creek:  grains  of  i a diameter f r o a 0*000$ i n c h e s  quarts aad  to o,003  Inches in different specimens* Quarts comprises about h a l f ©f t h e m a t r i x and  consists of uncracked grains of relatively h i g h relief. The feldspar eomslats chiefly o f sUetriemerphla potash f e l d s p a r {sanidine ©r o r t h o e l a s e erypteperthito) distinguish* a b l e from quarts fey its low relief and <~)2V of 40° to 5®°*  46  Plato (10)  Quartz phenocryst showing development of many fine cracks (x 50)  io»« p l a g i o c l a s e i s present as  shown by the presence of  multiple  i n one  (3)  twin  lamelae  observed  train*  Accessory Minerals The accessory a l n e r a l s c o n s i s t of b i o t i t e , horn»  blende spheae, a p a t i t e , magnetite and  ubiquitous  c r y s t a l s ar#  pyrlte*  Biotite  the i n t r u s i v e being found In  In  approximately s i m i l a r q u a n t i t i e s (2 t o 3 percent) i n almost a l l t h i n s e c t i o n s examined. Hornblende was s e c t i o n showing the mm$ occurs as  found i n greatest abundance In the c a l c i c p l a g i o c l a s e (An-^) where I t  eufeedral phenoorysts up  t o one quarter o f an i n c h  Tha c r y s t a l s a r e pleoehroie and  i n length, inent zones.  On -one c r y s t a l measured the centre sone showed  <*)2?»74® &hd the outer sone C-)2?»B#* r i x mZ m  natal® an angle of 15*  Spheae  The  obtose  bisect-  *e*.  with  and a p a t i t e ©cent i n t r a c e amounts i n almost  specimens examined» 8phone  a l l the  show two prom-  shows th© t y p i c a l wedge  shaped c r y s t a l s o f h i g h r e l i e f and i s n o t i c e a b l y concentrated  with  hornblende i n specimen (47).  f l u o r e s c e n t v a r i e t y and glows violet  dull  The a p a t i t e i s a  whit© under the u l t r a -  Imp.  Textures CD  F'henocrysts  Ca) Pretoelastie S t r u c t u r e The  pheaoeryst*  of the porphyry are  aadeformed  In  48 most  specimens  cludin,  few  •..•xamined. A  those from a r e l a t i v e l y  spocimens, however,  narrow  In-  dyke at the west  extremity of tha i n t r u s i o n , show a marked p r o t o c l a s t i c structure.  This s t r u c t u r e  i s p a r t i c u l a r l y evident i n  the  quartz phanocrysts which were perhans severely cracked phenoc r y s t s which were -oerhaps s e v e r e l y cracked by i n v e r s i o n consolidation  of the m a t r i x .  mobile magma a f t ^ r i n v e r s i o n out"  of quart?, fragments.  S l i g h t movoenent i n the caused an i n c i p i e n t  before  still  "stringing  This feature i s i l l u s t r a t e d i n  plate (11).  r  Protoclastic structure  late  (11)  of quartz i n a narrow dyke (x  25)  49 (b)  l e s o r p t i o a end Secondary Growth  Quartz, p l a g i o c l a s e and  sanidlne  phenoorysts a l l  show e f f e c t s o f r e s o r p t i o n to so©.© extent. The o u t l i n e s o f quarts c r y s t a l s range  hedral to s e v e r e l y section  rounded and  both subhedral and  8*ep embajvents  embayed,  anhedrai  i n the quart?,  from  sub-  and i n any on®  thin-  quarts nay be found.  pheneerysti appear  to contain  f e l d s p a r and quarts i n proportions s i a i l a r to those i n the matrix., though some fine  embaymente  myraekitio Intergrowths  #  resorption  offsets  contain feldspar with  very  In the f o r t h tyke these  a r e considered t o have been  formed  prior  to emplacement of the dyke because!  (1)  Around many  of  the embayed  crystals resorbed  s i l i c a appears to have bsen r e d i s t r i b u t e d throughout the matrix, highly  (2)  only  resorbed  grains a r e  slightly reeorbed  intermingled  grains I n  with  the sase  thin-section. (3)  th© degree o f r e s o r p t i o n shows no r e l a t i o n  (4)  to  the g r a i n  as  resorbed  else of t h e matrix. quarts  phenoeryst  was found I n -  cluded i n a l a r g e s a a i d i a s phenoeryst•  Quarts phenoorysts ence  from the porphyry a l i o show «vld-  o f growth a f t e r r e s o r p t i o n .  secondary  In the North Dyke s e c t i o n  growth'phenomena have been examined i n d e t a i l and  tho following generalisations nay be made*  50  (1) Secondary growth halos approximate the form of resorbed phenoorysts and not that of quarts mh-'dra (sa  plate 1?).  Plate (12) A quarts \henocryst with .rowth halo following resorbed outlines (x 50) (2) Secondary , ro-th halos consist of an interlockin.,* aesh of quarts grains which show ex« tinction parallel with the central phenocryst. Interstitial oaterial consists of feldspar, (see plates 1? and 14). (3) The grain sire of the halos is directly related to th« t ;ral' also of tho surrounding matrix (co^piira plates 15 and 16).  (4)  t h i c k n e s s of  The  the h a l o appears  to  dependent of t h e g r a i n s i z e o f t h e  (5) where  two  or three quarts c r y s t a l s  p a r a l l e l o r i e n t a t i o n o c c u r in  th©  oriented p a r a l l e l with Its adjacent  a radiating  i n p l a t e s ( 1 3 and  secondary  n o r t h Cyke. a d j a c e n t to  of  non  pattern  group i s quartz  as shown  14).  data i t i s considered that the h a l o s r e -  Froa these present  matrix.  c o n t a c t with  e a c h o t h e r the h a l o s u r r o u n d i n g  crystal giving  be i n -  growth of q u a r t s a f t e r emplacement o f  Quartz  g r a i n s of the m a t r i x  the  crystallising  q u a r t z phenoerysts were o r i e n t e d p a r a l l e l w i t h  tha adjacent q u a r t z c r y s t a l ,  A a i n g l e s e c t i o n (JIB  54)  shows  u n u s u a l l y wide f i n e - g r a i n e d h a l o s surrounding q u a r t z phono*crysts  i n a f i n e grained matrix.  This f e a t u r e aay fen a  deuterle e f f e c t l a the v i c i n i t y o f a n i n t e r n a l contact f i g u r e B)  and  (see  d i s c u s s i o n of t h e i n t r u s i o n of t h e Worth Dyke)  In c o n c l u d i n g the d e s c r i p t i o n o f the r e s o r p t i o n aad  secondary  that K i s c h  growth o f q u a r t z i t Is I n t e r e s t i n g t o note  (1949) d e s c r i b e s seam f e a t u r e s o f v e r y s i m i l a r  appearance to those observed S h i n g l e Greek  9  l a . the q u a r t z phenoorysts  i n quart* "porahyroblaste* from " g r a a l t l s e d  redbeds* near Sh@ka» Korthvest Yunnan* s c r i b e d as w h i c h grade pyramids*  froa  containing  T h e s e r o c k s ar©  de-  l a r g e ©henocryst l i k e quarts g r a i n s  f r o a rounded g r a i n s resembling p e b b l e s t© b i -  Plate  (13)  Slide (ND54) showing four quartz phenocrysts of non parallel orientation vith a single e n c o E p a s s l n  halo. Various parts of the halo can be soen to be the same stage of extinction as the nearest quartz phenocryst. (x 2 5 )  Plate (14) Central portion of plate (13) enlarged, (x 250)  Plate  (15)  S l i d e (NP54) BhevlQg a f i n e - g r a i n e d h a l o i n S f i n e - g r a i n e d m a t r i x , ( x 50)  s>late Slide  (16)  showing a c o a r s e - g r a i n e d i n a c o a r s e c i s t r i x ( x 50)  (ND55)  halo  Mlsch advances "two  general arguments" against  reapertlon of the quartz c r y s t a l s described: CI)  (2)  "It i s hard t o conceive new a r e s i d u a l magma exceedingly r i c h in s i l i c a fro® which the quarts-rich groundnuts* would have to be derived could have res orbed earlier termed quarts phenoerysts,  It i t difficult te understand why magmat 1c c o r r o s i o n should form narrow embaymeata instead o f attacking th® quarts crystals in a sore uniform manner along their surfaces and f i r s t rounding off any c r y s t a l edges which might have been p r e s e n t . " (Misch suggests uneven growth to account f o r this f e a t u r e ) In response to these arguments applied t o the  S h i n g l e Creek Porphyry the reader is f i r s t r e f e r r e d to the section o f this r e p o r t entitled  HSBSSE&Mi f®* a  suggested  explanation for the resorption of quarts in a silica-rich environment* If t  as in the second argument. It Is assumed t h a t  embayments formed In quarts as a result o f irregular growth,  one i s l e d t o wonder why the growth of other "poprhyrohlasts* was not s i m i l a r l y e f f e c t e d .  A- second  problem a r i s e s when  the secondary growth halos a r e considered f o r thest show no tendaney t o develop  preferentially on the most exposed  p o r t i o n s of th® c r y s t a l (thus p e r p e t u a t i n g th®  es&ayaents),  It s h o u l d , perhaps, be added that, on the basis of cross c u t t i n g structure, unlfornlty of composition i n different  host r o c k s , and email but s y s t e m a t i c v a r i a t i o n s i n grain-  s i z e of th© matrix, t h e r e is no question of the I n t r u s i v e  origin o f the S h i n g l e Creek P o r p h y r y .  55  the saaidlae phenoorysts show  Many o f repeated  resorption  ustrates  a  p a r a l l e l t o the  sanidlne carlsbad  p a r a l l e l to the faces o f the visible l a standard s o r p t i o n only  on  but  phsnocryst,  Is  boundaries of most  loss  O t h e r c r y s t a l s show r e -  in t h *  in piste  plagioclase  rounding o f the o u t e r  Alteration  Secondary a l t e r a t i o n c o n s i s t s c h i e f l y o f  isatioa in  teaellaisation of  and  the South 'East Contact  the  west end of  repiaeed by  the feldspars which  Area and  wall exposed:•  Intrusion is  18.  phenocrysts.  of these  <c) Secondary  obvious  in th®  evident  ill-  (the zoning i s not  the outsr surface as shown Is  P l a t e 17  twin, s h o w i n g r e s o r p t i o n Fins  thln*section)«  Heaorption phenoorysts  zonin;.  offsets of  A  elsewhere  is  where  thin-section froa  ssrlcltIntense  th©  the  dyke at  the I n t r u s i o n shows p l a g i o c l a s e completely  f r i a b l e w h i t e kaolin...  One  s e c t i o n , (30), from the South Sast Contact area  shows minute  fractures  f i l l e d with  secondary  amounts o f c a l c i t e t r a n s e c t i n g both  Small amounts o r i g i n , occur  of  quartz  phenoorysts  c a l c i t e , b e l i e v e d of  and small  and matrix.  secondary  at grain boundaries or replace previous minerals  i a the more altered specimens through the intrusion* B i o t i t e c r y s t a l s are  remarkably  f r e s h and  show  no  evidence of alteration to chlorite which is ©emraoa i a the surrounding  P l u t o n i c rocks.  Plate ( 1 7 ) Plate 17 shows a sanidine ohenoeryst twinned according to the Carlsbaa law (upper left) with inclusions of plagioclase. Dark outlines within t h e crystal are b e l i e v e d to be resorption  rims (x 25).  " l a t e (18)  Plata (18) i l l u s t r a t e s a sanidine pphenocryst (left centre) 3 l i ^ S l J u »# » e » » t l a a only on i t s outer surface. M ihowins- evidence of resoprtion on  Jfr2l«-  (x  25)  Parageusia Table (7),is  a suggested  parabasals  f o r the pheao*  e r y s t s aad matrix o f t h e S h i n g l e C r e e k P o r p h y r y baser] oa the p r e s e n c e or a b s e n c e o f i n c l u s i o n s  of various minerals i n each  other. Table  (?) Matrix  Pheaoerysts  Acoes s o r i ea Ilotite  Plagioclase Quarts  Resorption  Saaidlae One its  small i n c l u s i o n : of p l a g i o c l a s e , i d e n t i f i e d  p o i y s y a t h e t i c t w i n n i n g , was, found l a a s m a l l uneracked  quartz phenocryst.  Many o t h e r i n c l u s i o n s in c r a c k e d  have been a l t e r e d beyond r e c o g n i t i o n but clase.  Biotite  several  Include  One l a r g e  small ones  quarts plagio-  were ••  well.  P l a g i o c l a s e and sanidin©*  may  and some s m a l l s a n l d i n e i n c l u s i o n s  found i n q u a r t z as  ia  by  biotite form aamereas  resorbed  quartz  were a l s o f o u n d  in  inclusions  phenoeryst  sanldln®.  and  Plato (19)  This pair of  plates shows the appearance of the secondary growth haloa of quartz under h i g h and low magnification. Dark grey cusps i a the quartz phencc y s t contain feldspar. The specimen r e p r e s e n t s the porphyry w i t h coarse grained  matrix.  Clate (20) (x 250)  59  P l a t e ( 2 1 ) (x 50)  This pair of plates shows the appearance of secondary provth halos of quartz i n section h® 54 unoer high and low magnification. This specimen represents porphyry with finegrained aatrlx and shows tho widest halos observed. Plate (21) was taken in non nolarized l i r h t .  Plate (22)  (x 250)  mm&mm In  a l l natural been  country rook has  outcrops  examined  by the author th©  so deeply weathered near the  that i t d i s i n t e g r a t e s at the stroke o f a  intrusion  hammer«  Secant b l a s t i n g i n conjunction with widening of  Lower  road, at the  Shingle Creek has  contact between g r a n i t e aad  i s w i t h i n a few  exposed some sound rock at the porphyry,  feet of the creek bed  est exposures -within the Intrusion.  and The  t h i s road cut  i s one o f the deepg r a n i t e here' i s  j o i n t e d i n t o l a r g e i r r e g u l a r blocks which show a brown s t a i n s e v e r a l inches deep along j o i n t s . c e n t r a l parts o f the blocks  ar®  reddish  The  unstained  grey, and a narrow yellow-  orange t r a n s i t i o n ion© e x i s t s between the grey centra aad red-stained  rifts.  the  the  ID hand specimen th® b i o t i t e aad horn*  blende of the normal g r a n i t e have been replaced by magnetite aad a green micaceous mineral* l a t h i n - s e c t i o n the  red and  grey sones were found to  be e s s e n t i a l l y s i m i l a r , the red c o l o u r a t i o n being due finely  diseminated  Plagioclase  grains  to those found i n  to  specks of hematite i n th® a l t s r a d f e l d s p a r s . Show s i m i l a r composition and  the normal granite.  sone  relations  Potash feldspar c r y s t a l s  are severely aerieltized and some large quarts grains  are  present. At the contact with the porphyry the the granite i s aad  different  texture  of  f r o a that o f the normal g r a n i t e ,  i s somewhat similar to that observed in specimen W5  of  elese te I t s  altered d i o r i t e  contact  with  granodlorlte*  A  between th®  f i n e ©ash o f sonant quartz grains has developed  l a r g e r c r y s t a l s , and a few o f these smaller quartz grains appear w i t h i n the borders of the  plag-loelase  crystals  the.rock a p o i k i l i t i e appearance (see plat© ( 1 ) ) .  minerals  mafic  i l l the  with t h e exception o f magnetit® have been r e -  placed by c a l c i t e and  a hydrnmiea  of low  I n the Southeast Contact Area glomerate  giving  has been  stained  (-)2f*  the $prlngbrook  reddlsh-brown  dark  con-  f o r a distance  •of t h r e e or four f e e t from i t s contacts with t h e porphyry, The conglomerate i s very f r i a b l e and  the r e d d i s h colour  lends  a baked appearance t o the reck, & thin-S'#cticn was made  from the l a r g e  froa a  r sd s t a i n e d cobble  conglomerate I n c l u s i o n , f h e  cobMe i t s e l f  was  found to be f r i a b l e and had to be Impregnated with Canada bals&ia  of  to permit grinding  the cobble  lshvgreen been were  the  f h e mafic minerals  to a  brown*  very w a l l («)SV, The f e l d s p a r s hate  altered to seticite  with  section,  found t o be e n t i r e l y a l t e r e d  c h l o r i t e of  partly  powdered  were  of  a needle p o i n t ,  and  Sose  kaolin!te, -narrow  and are r e a d i l y  myrekltlc sones  found between quartz and p l a g i o c l a s e and I n c i p i e n t  development of a p o l k i l l t i c - l l k e texture o f quarts i n p l a g i o clase  similar to that  found i a the altered granite was ob-  served, these textures, however are not extensively developed i n the section and may have been part of the original texture of  the  diorite.  62 The conglomerate adjacent to the largest basic dyke (see Southeast Contact Area Man) i s thoroughly i n durated over a width of several feet in striking contrast to the friable condition of the conglomerate contact with the porphyry.  This Bight be the result of a higher temper-  ature of intrusion associated with the basic dykes.  Plate (23) *^late (23) shows a two foot wall of Indurated conglomerate at the contact of a basic dyke in the South East Contact Area. The dyke ( l e f t ) has disintegrated as a result of close joinging.  CtJUnODRAtlOW Th®  i n t r u s i o n i s elongated  i n an east-west d i r -  e c t i o n and narrows t o a group o f discontinuous dykes to the west.  of  I n th® e a s t , however, I t passes beneath the alluvium  the Okanagan  Valley  a t what appears t© be i t s widest  s e c t i o n , and does not reappear on the opposite side o f the valley.  This suggests that the i n t r u s i o n may b® s t r u c t u r a l l y  r e l a t e d t o th® Okanagan Trench,  IMTSBNaX FMTUREi Internal  Contacts Outcrops o f the e e n t r a l and eastern part o f the  I n t r u s i o n were examined In d e t a i l f o r I n t e r n a l v a r i a t i o n s , JLarge outcrops were found t o be e s s e n t i a l l y homogeneous with some v a r i a t i o n i a s i z e o f phenoerysts and colour o f matrix. One i n t e r n a l contact was found In an i s o l a t e d group o f b l u f f s i n the western c e n t r a l part ©f the i n t r u s i o n (see Key sap  approximately  parallel to  the general tread ©f the i n t r u s i o n , and shows a  sinuous but  figure  The contact s t r i k e s  (1)),  f a i r l y r e g u l a r surface along an exposed length of s e v e r a l hundred f e e t , contact (see  J o i n t i n g present shows no r e l a t i o n to th©  plate  (24)} on f o l l o w i n g page.  summary o f the compositions either  side  Table  (6), i s  a  o f two specimens taken one on  o f the i n t e r n a l contact, (see f o l l o w i n g  page).  64  l a t e (24) P l a t e (24) shows an I n t e r n a l contact with large phenocrysts i n the rock t o the l e f t of the hammer head and s r a l l • enocrysts ? +1° ^ V 1 ^ * contact i t s e l f i t not c l e a r l y v i s i b l e i n the p i c t u r e but follows a l i n e p a r a l l e l with the hammer head passing just to the f i g h t of the two large a a n i (upper l e f t ) . J o i n t s show no r e l a t i o n t o t h i s contact T  T  h  e  Table ( 8 ) Specimen (45) S.' .Side  Specimen (47) N.E.Side Description  "r.Size  Description  Sanidine*  (-)2V 53°-59°  max. 2"  (-)2V 43°  Plagioclase  An35-An46  Quartz  Pesorbed  Biotite  tl nor  - - - -  Hornblende  dom. acces.  - - --  "henocrysts  Matrix  0.2"  An8-Anll  " 0.1"  Resorbed  B  0.0005"  Gr. Size  max. 0 . 2 5 " "  0.1"  o.o5"  dom. acces. minor  0.0005"  g Potash f e l d s p a r i n the two s l i d e s may be e i t h e r sanidineanorthoclase-cryptooorthite or a potash r i c h orthoclasec r y p t o p e r t h i t e on the basis of these data.  65  Inclusions (1)  Inclusions  of Granite  numerous g r a n i t e i n c l u s i o n s are f o r t h Dyke and  a im  exposed  i n the  of these hays been sapped In d e t a i l  as part of the l o r t h Byke S e c t i o n ,  these i n c l u s i o n s  are  found in.two zones on e i t h e r s i d e of the dyke leaving a cent r a l zone forming roughly on® clusions.  As ean  h a l f of th©  be seen i n f i g u r e (9)  dyke f r e e of i n -  there i s a d i r e c t  r e l a t i o n between th® presence o f i n c l u s i o n s i n the dyke and the g r a i n s i z e o f the matrix, the l a t t e r being f i n e r grained i n the zones of  i n c l u s i o n s and  towards the margins because of  chilling, fhe i n c l u s i o n s and  show rough  were  irregular  surfaces.  l e t s of porphyry commonly  clusions  are  found  well Jointed,  in  Small  penetrate the and  apophyses and  granite.  many sharp  features  i n figures (?)  (Following  and  (8),  The  embarments  contacts are thought to be the r e s u l t of plucking blocks by the i n t r u s i o n ,  sizes  a v i d e range of  inia  th®  of j o i n t e d  of t h i s type ar® page)  dyke-  illustrated  F i g u r e (7)  Figure  A l t e r a t i o n of the t r u s i o n i s not pronounced,  (8)  granite inclusions by and  obscured  has been  the i n by shearing  and deep weathering along the contact®. (2)  I n c l u s i o n s of tha Spriagbrook (a) A  member  of  Formation  Major I n c l u s i o n s  l a r g e I n c l u s i o n of the Coarse  ths Spriagbrook  formation l i e s i n the  the South East Contact Area (see map). a t r i a n g u l a r s e c t i o n with  Conglomerate  Its entire  porphyry i n  This i n c l u s i o n forms  periphery exposed  to  view on a c l i f f face at the north end of the area mapped. The s i d e s of (25)  aad  th® i n c l u s i o n are sheared  figure  (9).  as  shows, i n p l a t e  67  Plate (25) Plate (25) and figure (9) i l l u s t r a t e the shearing which occurred at the contacts of the large conglomerate inclusion.  figure ( 9 )  68 ta© i n c l u s i o n probably represents the ead o f a tongue o f conglomerate  extending east down th© north s i d e  of the South l a s t Contact Canyon and has probably not been moved t o any great extent by the I n t r u s i o n , that tha conglomerate bouring conglomerate  I t Is l i k e l y  between th® i n c l u s i o n and the neighoutcrops has been eroded l e a v i n g a l a r g e  block appareatly surrounded by p o r p h y r i t i c I n t r u s i o n , <b) Cobble I n c l u s i o n s In two instances outcrops o f porphyry were found to c o n t a i n rounded g r a n o d l o r l t e and d i o r i t e cobbles presumably derived fro® the o v e r l y i n g Springbrook Formation., One such outcrop was found i n the i n t r u s i o n at the top o f the r i d g e forming the north w a l l o f the Southeast Contact Canyon about one hundred yards f r o a the contact.  A similar  occurrence was found at the top o f a h i l l i a the c e n t r a l part of the I n t r u s i o n near the i n t e r n a l contact described above. EXT ESHAL FEATURES Contact Features Some parts o f the contact between the Berth Dyke and the g r a n i t e a r e uniform and s t r a i g h t .  In s e v e r a l g u l l i e s  along the northern slopes above tower Shingle Creek th® porphyry at the content r i s e s as a looking deeply  weathered  well  ten to twenty feet high over-  granite.  Plate  (26)  shows porphyry  to the l e f t , r i s i n g along a f a i r l y even contact with sheared and deeply weathered g r a n i t e .  69  (Plate  26)  A granite-poprhyry contact showing norphyry (upper l e f t ) and sheared g r a n i t e (centre r i g h t ) . Other parts of the contact are i r r e g u l a r  with  sharp l o c a l changes i n s t r i k e as i l l u s t r a t e d by the north of the North Dyke s e c t i o n .  The  end  general trend of the con-  tacts of the North Dyke, however, form a wide arc or crescent concave to the  south.  In the Southeast Contact  area the contact  are somewhat d i f f e r e n t from those already described. general trend of the contact i s i r r e g u l a r , being  features The  interrupted  by at l e a s t three dykes which •strike south to southwest from the main i n t r u s i o n .  ;<iuch of the  a l l - r o c k conglomerate appears  to l i e on top of the i n t r u s i o n and shows a pattern of block f a u l t s of small movement extending  down towards the surface of  70 the I n t r u s i o n .  These f a u l t s are thought to represent  of minor adjustments  in  allowed some blocks of  the r o o f during i n t r u s i o n  conglomerate  loci  which  to r i s e or s e t t l e  s l i g h t l y w i t h respect t o others.  dontheaat of  the i n t r u s i o n , outcrops  ©f white or  greenish rocks containing l a r g e potash f e l d s p a r c r y s t a l s were reported by H.S.Bostock.  conglomerate beds  these  are exposed i n c l i f f s between  and show s t r u c t u r e s t y p i c a l of flew rocks.  llfWCTimiX OOMCtOSMS Ths f o l l o w i n g s e c t i o n w i l l attempt to i n t e r p r e t the structural  environment  at the time of I n t r u s i o n of the  Shingle Creek Porphyry. S e v e r a l features In the c e n t r a l and southeast  part  of th® porphyry I n t r u s i o n suggest that th® i n t r u s i o n reached the contemporaneous (Paleocsne) surface which was  not f a r  above the present l e v e l of bedrock In t h i s area*  These  features are enumerated as followsJ (1)  In s p i t e of the s i z e of the I n t r u s i o n there i s a© appreciable v a r i a t i o n i a g r a i n s i z e fro© th® w a l l s inward suggesting that the present ©f the i n t r u s i o n underwent f a i r l y  surface  uniform  chilling*  (2)  The upper  member of  the  i n the Southeast Contact s e v e r a l hundred f e e t o f  Springbrook formation area c o n s i s t s of  rhyolltio  tuff  similar  i n composition to tho porphyry and d i s t i n c t l y d i f f e r e n t frm <3)  tne succeeding b a s i c flows..  Southeast o f the area white or greenish rocks e o a t a i n i a t l a r g e potash feldspar c r y s t a l s ar© exposed In c l i f f s between conglomerate  b?ds and  are reported to show s t r u c t u r e s t y p i c a l of flow r o c k s . West o f the main body o f the i n t r u s i o n and along th© n o r t h slopes above Lower S h i n g l e Creek the reck surface contemporaneous with the porphyry i n t r u s i o n may have been c o n s i d e r a b l y higher than a t  proa ant.  this  ts suggested  by  the f e e t that a l a r g e p r o p o r t i o n o f the cobbles and boulders of the conglomerate  i n the Southeast Contact Area ire of rock  types represented by the p l u t o n l e i n t r u s i o n s t© the north and west,  f h e s i z e and a n g u l a r i t y <s®e p l a t e (£)) o f  these boulders present t e s t i f y t o the raggedness  some ©f  o f this  topography, South and southeast o f the Southeast Contact Area the l a t e Mesctoi© surface i s o v e r l a i n by s e v e r a l  thousand  f e e t ©f T e r t i a r y sediments and voleanies aad dees not outcrop even i n the creek v a l l e y one a l l s south o f , but a t about the same present e l e v a t i o n as, the Southeast Contact Area.  The  land surface to the southeast a t the time o f Intrusion o f the porphyry may thus have been considerably lower than the s u r face to th® north -and west, and l a t h i s southeasterly d i r e c t ! o a (fro® the i n t r u s i o n ) ar® located th® remnants o f t u f f s aad  flows which .appear to be r e l a t e d t o th©  e«*t 9  intra*ion.  To- th®  Okanagan v a l l e y (Lower Eocene o f S c h o e f i e l d ) was  pro-  bably i n the ©ariy s t a f f s o f formation and a major p o r t i o n o r the v o l c a n i c products o f the i n t r u s i o n may have bean deposited oa low ground i a  this  direction.  • The S h i n g l e Creek Porphyry may thus be i n t e r p r e t e d as marking the s i t e of sa e a r l y Y e r t l a r r voleaao w i t h a vent l o c a t e d west of  intrusion.  Peatieten  i n the e e a t r a l part of the  P o s s i b l y during an e x p l o s i v e phase i n the l i f e  o f t h i s volcano® the  North  Dyke aad other dykes were i n -  truded along f r a c t u r e s showing sons w h a t curved o u t l i n e s s i m u l a t i n g roughly aa  extended r i n g p a t t e r n .  73  mmmmmm In tae f o l l o w i n g paragraphs and th*  th© data discussad  conclusions a r r i v e d at apply s p e c i f i c a l l y to ths  North Dyke S e c t i o n which has been studied i n d e t a i l . the conclusions,, however, may  Many of  apply to other parts of the  i n t r u s i o n as w e l l . CBfSTAIXIl&TIOI OF THE PHSSOORYSfS Without  a c h e a l e a l a n a l y s i s i t i s not p o s s i b l e t o  s t a t e a c c u r a t e l y the composition of the Worth Dyk®, but an approximation can be made.  F r o a the estimates, made e a r l i e r  i n t h i s chapter, of the r e l a t i v e compositions o f two specimens the composition o f the  north  Dyke may  he reduced to three  p r i n c i p a l components) Quarts, a l b l t e , and o r t h o e l a s e . a l b i t e content of the saMdine-anorthoolase alblte and  o f the p l a g i o c l a s e .  aaerthlte come to  The  i s added to the  l a f i e minerals, a c c e s s o r i e s ,  l e s s than, tm  regarded i n t h i s approximation,  percent and may be d i s -  fable (9)  gives the estimated  amounts o f each o f these three components as a c c u r a t e l y as the method o f c a l c u l a t i o n w i l l allows fable  (9)  Quarts . . . . . . . . . . . Alblte . . Orthoelase . . . . . . . . .  40^ 40|  20$  Khen t h i s composition i s p l o t t e d on a ternary diagram representing the a l b i t e - o r t h o c l a s e - n i l i c a system  74 (J,P,  ftehalrar  and  W.CBoven  - see f i g u r e ( 1 0 ) i t i s seen  to  f a l l very n e a r l y on the c o t e c t i c l i n e d i v i d i n g the diagram into  trldymite  and f e l d s p a r f i e l d s ,  This may suggest that  the S h i n g l e Creek Porphyry .magma represents th© product o f an e a r l i e r d i f f e r e n t i a t i o n or o f s e l e c t i v e f u s i o n . Considering f i g u r e <10), a as that represented In  table  molt  o f composition such  (9) (see f i g u r e 1.0, point A ) , on  slow c o o l i n g , slight be expected t o p r e c i p i t a t e potassium poor high a l b i t e f i r s t .  T h i s would b® followed e a r l y by beta  quarts w i t h c o n c e n t r a t i o n o f potassium i n the r e s i d u a l magma, shea the melt reach*! the t e r n a r y euteetie, f , saaidine would begin t o c r y s t a l l i s e .  This sequence (up t o the f i r s t appearance  of s a a i d i n e phenoorysts i a the melt as suggested by small sanldiae I n c l u s i o n s i n beta quartz) i s born out by the paragenesis presented e a r l i e r i n the chapter. At t h i s time, however, beta quartz became unstable i n the magma and began t o be accounted  be resorbed.  T h i s r e s o r p t i o n aay  f o r I f the c o t e c t i c trough, Ct>» Is lowered and  s h i f t e d toward the s i l i c a apex o f the s h i f t i n g o f the  (10)  (anaiogus t©  diepalde-anerthite~eutecti©  water vapor pressure, {Yoder,  With  figure  with increased  19!>4)*  f u r t h e r c o o l i n g under the new conditions ( I n -  creased water vapor pressure t o account f o r r e s o r p t i o n o f quartz),  the  potassium r i c h r e s i d u a l  magma would begin  to  crystallze a potassium r i c h sanidla® which was the l a s t a l n e r a l to for® phenoorysts.  f i g u r e CIO) Phase diagram for th® system a e p h e l i n e - k a l i o p h i l i t e - s l i l e a ( a f t e r JVF* Sehalrer aad S.L.Bowea) Point "A" renrsseats th® eompositioa ©f th© Shingle Croak Porphyry approximately. l e y to F i g u r e 1 g 3 4 5  6  (10)  Cristoballte field frldyinite field Ia»£-Feldspar f i e l d teueite f i e l d Ha»K»ifephellas f i e l d Caraeglelte f i e l d  The aaaldlae paenoerysts  formed at  this  time show  aa i n t r i c a t e o s c i l l a t o r y zone p a t t e r n described e a r l i e r l a the chapter.  Many of the s c a t s  occur i a pairs with abrupt  contacts between p a i r s , i n some casss marked by r e s o r p t i o n (see p l a t e ( 1 7 ) ) , and gradual Increase i n potash content from the innermost  t o th® outermost members of the p a i r s .  This  gradation i s i n the reverse sense to what s i g h t be expected, for  pheaoerysts o f the present composition  under constant pressure.  crystallising  However, th® c o n f i g u r a t i o n o f the  l i q u i d u s aad s o l l d u s carves f o r the a l b l t e - o r t h o c l a s a system (Bowen aad f u t i l e ) v a r i e s with th© vapor pressure of water i n th®  system*  f h e data are incomplete so i t  t e n t a t i v e l y suggested  is  only very  here that pressure changes i n the magma,  by a l t e r i n g the l i f u i d u s -  solidus relations  might provide  9  the reversed s e a i a g observed i n the s a n i d i n e .  A repeated  sequence o f gradual buildups of pressure followed by sudden releases would  be required*  l a some eases th® pressure  r e l e a s e was s u f f i c i e n t t o cause some r e s o r p t i o n of sanidine by s h l f t l a g the e o t s e t i c l i n t , CD, o f the s i l i c a apex,  intermittent  How«ver, beta quartz  figure (10) snows  away from  no evidence o f  r e s o r p t i o n so that t h i s s h i f t was probably never  l a r g e enough t o cause resumed c r y s t a l l i z a t i o n of beta quarts,  Ifffi'fBlOI Of TUB HOOT DfXl I t i s suggested that the crystallisation o f the pheaocrysts described above took place i n a magma chamber at  77  depth  and that t h e I n i t i a l increase In pressure associated  w i t h the beginning ©f r e s o r p t i o n ©f beta quartz was probably a major change as beta quarts remained unstable i n the magma op u n t i l j u s t before f i n a l c o n s o l i d a t i o n ,  T h i s postulated  i n c r e a s e i n pressure may have been r e s p o n s i b l e f o r the beginning of the i n t r u s i v e and v o l c a n i c stages i n the h i s t o r y of the magma.  Th© increased pressure In th© chamber, however,  d i d not remain constant and i s thought to have o s c i l l a t e d i n the manner suggested by the zoning In the sanidlne phenoorysts,  these ©setll&tlcas i n pressure aay have been r e l a t e d  to eruptions o r t o I n t r u s i o n o f th® dykes surrounding the intrusion, Patrogr&phle v a r i a t i o n s i n the rocks o f the North Pyke S e c t i o n suggest that the I n t r u s i o n of the dyke occurred, i n s e v e r a l phases..  In order t o I l l u s t r a t e these v a r i a t i o n s  f i g u r e (11) has been constructed showing the v a r i a t i o n ©f each  feature'described  as o r d i n a t e , and the r e l a t i v e p o s i t i o n  w i t h i n the dyke as a b s c i s s a , f i g u r e (11) i t i s suggested  fro© the data presented i n  that the i n t r u s i o n o f the dyke  . a t some stage i n Its h i s t o r y reached  a auudaesi o f  intrusive  a e t i v i t y during which the w a l l s were a c t i v e l y plucked and i n c l u s i o n s were incorporated i n the dyke. of the p l a g i o c l a s e chamber was then  phenoorysts  AUg-Aboa.  The composition  being s u p p l i e d by the source  approximately, and th© matrix  the i n t r u s i o n was c h i l l e d to a §»©re or l e s s uniform f i n e grain size,  of  78  Figure ( 1 1 ) No I n c l u s i o n s  Inolusicns  Inclusions  Grain-size of Matrix  Sanidine (-)2V (increasing (Ab)  Plagioclase An  %  49  Figure  50  (11) illustrates  54  55  56  petrasrapbi ir. i s  60  61  62  79 Intrusive  a e t i v i t y then waned and movement of  eentrel  magma occupied a l e s s e r  now  contains  no  p o r t i o n o f the dyke which  inclusions. ,hen the I n t r u s i o n  ceased the w a l l rock (formed now r e c e n t l y consolidated w a l l s had mitted  been  greater s i z e ,  a large  extent of  porphyry) was somewhat hotter than the  during the  matrix of the  the  to  phase  of maximum a c t i v i t y and per-  i n t r u s i o n t o reach a somewhat  f h e p l a g i o c l a s e supplied during  stage o f I n t r u s i o n was  with  finally  approximately  tha f i n a l  toj^-Ab^.  normal d i f f e r e n t i a t i o n i n the source chamber  c a l c i c p l a g i o c l a s e would be expected t o form f i r s t with acre  albitie  p l a g i o c l a s e c r y s t a l l i s i n g as c r y s t a l l i s a t i o n t h e later c e n t r a l phase o f the Korth Syke i s  progressed,  thus out o f harmony with a f h e higher  dyke  enortblte  simple  process o f  differentiation,  content o f the c e n t r a l s e c t i o n  cannot be explained  by  assimilation  of  the  o f th© dyke walls  as the p l a g i o c l a s e o f th® e a r l i e r phase o f the dyk« i s p r a c t i c a l l y pare  alblte.  However, progressive  assimilation  o f g r a n i t e (see t a b l a (3)) from the walls o f the source chamber s i g h t account f o r the enrichment o f the magma- i n anorthite.  As  can be seen from f i g u r e (9) the  composition  of p l a g i o c l a s e i n s e c t i o n J8> 49 (taken c l o s e t o th® upper contact of  the  o f the Sorth Dyke) c e n t r a l part of  the  corresponds dyke... fhe  with the  plagioclase  matrix, however,  f i n e - g r a i n e d s i m i l a r t o the adjacent dyke rock,  is  This aay be  explained i f i t i s assumed that the l a t e r phase o f the I n t r u s i o n was not e n t i r e l y confined to the centre of the dyke hut sent dykeiets i n t o the surrounding s t r u c t u r a l l y s u s c e p t i b l e planes.  rocks  along  The contact between the  g r a n i t e walls o f th® dyke and the r e c e n t l y consolidated i n i t i a l phase of tha dyke may have provided such a s t r u c t u r a l plane.  The temperature at the granite w a l l s was  probably  considerably l e s s than the temperature of the inner w a l l s of the f i r s t grained  phase o f th© dyke i n t r u s i o n so that the f i n e -  texture  expected.  o f tho matrix i n s e c t i o n 1049 i s to b©  

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