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Geology, geochemistry, and geochronology of the Westcoast Crystalline Complex and related rocks, Vancouver… Isachsen, Clark 1984

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GEOLOGY, GEOCHEMISTRY, AND GEOCHRONOLOGY OF THE WESTCOAST CRYSTALLINE COMPLEX AND RELATED  ROCKS,  VANCOUVER  ISLAND,  BRITISH COLUMBIA by CLARK {ISACHSEN B.Sc.  State  U n i v e r s i t y o f New York a t A l b a n y  1980  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  in  THE FACULTY OF GRADUATE Department  We'accept  of G e o l o g i c a l  this  STUDIES Sciences  t h e s i s as conforming  to the required  standard  THE UNIVERSITY OF BRITISH COLUMBIA September Clark  1984  Isachsen,  1984  In p r e s e n t i n g  this thesis  r e q u i r e m e n t s f o r an of  British  it  freely available  agree t h a t for  in partial  advanced degree a t  Columbia, I agree that for reference  permission by  understood that for  h i s or  be  her  shall  not  University  Library  s h a l l make  and  study.  I  g r a n t e d by  the  of  this  G?(5DL£>C<*itfH _  The U n i v e r s i t y o f B r i t i s h 1956 Main Mall V a n c o u v e r , Canada V6T  1Y3  Date  this  *S  Columbia  C*%JJC(Zr%>  thesis my  It is thesis  a l l o w e d w i t h o u t my  permission.  Department o f  further  head o f  representatives. be  the  the  copying or p u b l i c a t i o n  f i n a n c i a l gain  the  f o r extensive copying of  s c h o l a r l y p u r p o s e s may  department or  f u l f i l m e n t of  written  ii  FRONTISPIECE View  of Meares  Island  from Radar  Hill  v  i i i  Abstract  The  Westcoast  complexly  mixed  Vancouver  Crystalline plutonic  Island. It i s  amphibolitic of  (Westcoast  Diorite),  components  in  lines  Westcoast  arc.  consistently appreciable Sr" r a t i o s between mantle  of e v i d e n c e  Crystalline  magmatic  evidence  source  f o r an  and  are  relatively  of  be  instead,  and  and  the  chemistry  two  were crust  of  the  189  and  chemistry, as  the  Ma  these  a are no  Initial  Complex  are  with a depleted  curves  derived for  iri s i t u  that these  crustal  rocks  were  rock. Westcoast  Crystalline  the deeper c r u s t a l  Island  show  component.  compatible  country  in  separates  Crystalline  indicate  cool  together,  rocks  zircon  c o n s i s t e n t with  interpreted  Taken  176  of  older crustal  t h e more d i f f e r e n t i a t e d  Volcanics.  these  petrogenesis  concave c o o l i n g  not  intruded  can  of  intruded  with  dates  0.70360,  r e g i o n . The  age  composition  that these  and  f o r the Westcoast  but,  Based on  Amphibolite),  shows a s u b a l k a l i n e t h o l e i i t i c  between  magmagenesis into  of  heterogeneous  mixtures  t r a c e element  isotopic  concordant  Westcoast D i o r i t e s  Complex  setting  Complex  U-Pb  0.70329  of  gabbroic  suggest  trend compatible  obtained  of  Migmatite).  t i m e . M a j o r and  to c a l c - a l k a l i n e  to  belt  west c o a s t  (Westcoast  variable  i n a magmatic a r c  Jurassic  as a  the  mainly  rock  and  occurs  along  composed  trondhjemitic  (Westcoast  Various generated  rocks  country  granitoids  Complex  Intrusions  equivalent  and  Bonanza  rocks provide a d i s r u p t e d  iiii  and  perhaps  magmatic  incomplete  arc  of  Vancouver  Reconnaisance Vancouver  of  I s l a n d  i n d i s t i n g u i s h a b l e Westcoast  c r o s s - s e c t i o n  the  Wark/Colquitz i t  petrography,  C r y s t a l l i n e  the  J u r a s s i c  I s l a n d .  shows in  of  Complex,  Complex  to  be  c h e m i s t r y and  of  a  southern  e s s e n t i a l l y  and  age  s i m i l a r  from  h i s t o r y  the i s  i n f e r r e d . A a l s o i s i t s  c a l c - a l k a l i n e  determined  a g a i n  for  c o m p a t i b l e  p r o x i m i t y  to  the  c h e m i s t r y a  C a t f a c e  w i t h  and  low  I n t r u s i o n  m a n t l e - d e r i v e d  c o e v a l  t r e n c h  i s  i n i t i a l dated arc  Sr at  r a t i o Ma.  This  magmatism,  but  e n i g m a t i c .  41  were  V  TABLE OF CONTENTS  ABSTRACT L I S T OF FIGURES L I S T OF TABLES ACKNOWLEDGEMENTS . . .  '  INTRODUCTION CHAPTER I  1  : DESCRIPTION OF MAP UNITS WESTCOAST CRYSTALLINE COMPLEX WESTCOAST AMPHI BOLI TE WESTCOAST MIGMATITE WESTCOAST DIORITE GABBRO-PERIDOTI TE WESTCOAST METASEDIMENTS DIABASE AND A P L I T E F E L S I C VOLCANICS P A C I F I C RIM COMPLEX TERTIARY INTRUSIONS  CHAPTER I I : GEOCHEMISTRY OF THE WESTCOAST CRYSTALLINE COMPLEX AND RELATED ROCKS CHEMICAL ANALYSIS ; CLASSIFICATION TECTONIC SETTING DISCRIMINANTS CONCLUSIONS CHAPTER  III:  STRUCTURE HETEROGENEOUS STRAIN ORIENTATION OF STRUCTURAL FABRICS DUCTILE-BRITTLE TRANSITION BRITTLE FAULTS CONCLUSIONS  CHAPTER I V : METAMORPHISM AMPHI BOLI TES CALCSILICATES QUARTZO-FELDSPATHIC METASEDIMENTS CHAPTER V  Page i i i v i i viiil Jx  : GEOCHRONOLGY OF THE WESTCOAST CRYSTALLINE COMPLEX AND RELATED ROCKS WESTCOAST CRYSTALLINE COMPLEX WARK COMPLEX CATFACE INTRUSION  7 7 7 10 10 20 22 25 27 27 28 30 30 30 36 42 45 45 49 .55 57 59 61 61 62 66 69 69 87 91  CHAPTER VI : COOLING HISTORY WESTCOAST CRYSTALLINE COMPLEX WARK COMPLEX CATFACE INTRUSION  97 97 102 102  CHAPTER V I I :  104  CONCLUSIONS  vi  CHAPTER. VI11 :TECTONIC HISTORY OF VANCOUVER PALEOZOIC TRIASSIC JURASSIC CRETACEOUS TERTIARY REFERENCES APPENDIX APPENDIX APPENDIX  ISLAND  107 107 108 109 113 114 119  1 : SAMPLE DESCRIPTIONS AND LOCATIONS 128 2 : MAJOR AND TRACE ELEMENT CHEMISTRY: WESTCOAST CRYSTALLINE COMPLEX, WARK COMPLEX AND TERTIARY INTRUSIONS 130 3 : GEOCHRONOLOGY: ANALYTICAL METHODS AND RESULTS..137  GEOLOGICAL MAPS  4^R—pos-k^e-t  vii  L I S T OF  FIGURES  Figure Pag^e Frontispiece i i 1 : G e n e r a l i z e d g e o l o g i c map of V a n c o u v e r I s l a n d 2 2 : G e o l o g i c a l map of Meares I s l a n d and a d j a c e n t jz^ £p ,c* JU-tSTi shorelines.... .in pocke^3 : L i n e a t i o n i n Westcoast Amphibolite 8 4 : P o s s i b l e cumulate t e x t u r e i n M e g a c r y s t i c Westcoast Amphibol i t e 8 5 : L i t - p a r - l i t i n j e c t i o n of banded g n e i s s , W e s t c o a s t Complex 11 6 : A g m a t i t e , W e s t c o a s t Complex 11 7 : Complex m i x t u r e of W e s t c o a s t r o c k t y p e s 12 8 : P o s t - t e c t o n i c i n t r u s i o n , W e s t c o a s t Complex 14 9 : S c r e e n s of banded g n e i s s , W e s t c o a s t Complex 15 10 : P l u t o n - p e g m a t i t e c o n t a c t , W e s t c o a s t Complex 17 11 : F o l i a t e d and l i n e a t e d m a r g i n of t h e I n d i a n I s l a n d intrusion 18 12 : S c h e m a t i c r e p r e s e n t a t i o n o f major W e s t c o a s t r o c k types 21 13 : T i g h t l y f o l d e d and d i s r u p t e d a m p h i b o l i t e and metapsammite, W e s t c o a s t M e t a s e d i m e n t s 24 14 : T i g h t l y f o l d e d i n t e r c a l a t i o n s of metapsammite i n a m p h i b o l i t e , Westcoast Metasediments 24 15 : Ambiguous c r o s s c u t t i n g r e l a t i o n s h i p between a p l i t e and d i a b a s e d i k e s i n e p i d i o r i t e , W e s t c o a s t C o m p l e x . . 2 6 16 : H y p a b y s s a l d i k e and d i k e l e t of a n d e s i t e p o r p h r y i n t r u d i n g C a t f a c e I n t r u s i o n on Meares I s l a n d ..29 17 : M a j o r e l e m e n t v a r i a t i o n d i a g r a m s , W e s t c o a s t Complex and r e l a t e d r o c k s 31 18 : T r a c e e l e m e n t v a r i a t i o n d i a g r a m s , W e s t c o a s t Complex and r e l a t e d r o c k s . . . 32 19 : P l o t o f a l k a l i s v e r s u s s i l i c a (wt. p e r c e n t ) 34 2 0 : AFM d i a g r a m 34 21 : P l o t o f n o r m a t i v e c o l o r i n d e x v e r s u s n o r m a t i v e plagioclase composition 35 22 : Z r / T i 0 - Si0 diagram. 37 2 3 : Nb/Y - Z r / T i O d i a g r a m 38 24 : T e c t o n i c s e t t i n g d i s c r i m i n a t i o n diagrams 40 2 5 : N o r m a l i z e d abundance p a t t e r n s of i n c o m p a t i b l e t r a c e e l e m e n t s , W e s t c o a s t Complex and Wark d i o r i t e 41 2 6 : N o r m a l i z e d abundance p a t t e r n s o f i n c o m p a t i b l e t r a c e e l e m e n t s , u l t r a b a s i c r o c k s and T e r t i a r y i n t r u s i o n s . . 4 3 2 7 : G e n e r a l i z e d g e o l o g i c map showing s t r u c t u r a l d a t a , ^ ^s. f . Z / ^ ^ j M e a r e s I s l a n d and a d j a c e n t s h o r e l i n e s tfi—pee-ke-t 2 8 : S k e t c h showing d e v e l o p m e n t o f banded g n e i s s from inclusion-rich granitoid 47 2 9 : D e f l e c t i o n of f o l i a t i o n i n d i o r i t e i n t o m y l o n i t i c s h e a r zone 48 3 0 : S t r u c t u r a l o r i e n t a t i o n s , Meares I s l a n d map a r e a 50 31 : S i m i l a r - s t y l e f o l d s i n banded g n e i s s , W e s t c o a s t Complex 51 2  2  ?  viii  32 : B o u d i n a g e o f a m p h i b o l i t i c l a y e r s i n banded g n e i s s , W e s t c o a s t Complex 51 33 : S c h e m a t i c d i a g r a m showing o r i e n t a t i o n o f p r i n c i p l e s t r a i n axes 53 34 : F o l d i n g and b o u d i n a g e o f t r a n s p o s e d l a y e r i n g i n c a l c s i l i c a t e , Westcoast Metasediments. .54 35 : P h o t o m i c r o g r a p h showing b r i t t l e f r a c t u r e o f d u c t i l e s t r a i n f a b r i c along conjugate planes, Westcoast Amphibolite 56 36 : P h o t o m i c r o g r a p h showing c a t a c l a s i s o f d u c t i l y d e f o r m e d c a l c i t e r i b b o n s , W e s t c o a s t M e t a s e d i m e n t s . . . 56 37 : S k e t c h showing b r i t t l e d e f o r m a t i o n o f a d u c t i l e s h e a r zone, W e s t c o a s t Complex ....58 38 : H 0 - r i c h i s o b a r i c T-X d i a g r a m showing s t a b i l i t y f i e l d s f o r observed c a l c s i l i c a t e assemblages 64 39 : P -T d i a g r a m showing t h e a b - a b s e n t and a n - a b s e n t i n v a r i a n t p o i n t s i n t h e s y s t e m CKNASH 68 40 : Sample l o c a t i o n map f o r i s o t o p i c a n a l y s e s . . . . . 70 41 : P h o t o m i c r o g r a p h o f r e p r e s e n t a t i v e z i r c o n g r a i n s from t h e I n d i a n I s l a n d i n t r u s i o n , W e s t c o a s t Complex.72 42 : C o n c o r d i a d i a g r a m , I n d i a n I s l a n d i n t r u s i o n 73 43 : C o n c o r d i a d i a g r a m , T o f i n o I n l e t p l u t o n 74 44 : P h o t o m i c r o g r a p h o f r e p r e s e n t a t i v e z i r c o n g r a i n s from t h e T o f i n o I n l e t p l u t o n , W e s t c o a s t Complex 75 45 : C o n c o r d i a d i a g r a m , q u a r t z d i o r i t e g n e i s s , W e s t c o a s t Complex 76 46 : P h o t o m i c r o g r a p h o f r e p r e s e n t a t i v e z i r c o n g r a i n s from q u a r t z d i o r i t e g n e i s s , W e s t c o a s t Complex 77 47 : P h o t o m i c r o g r a p h o f r e p r e s e n t a t i v e z i r c o n g r a i n s from t h e q u a r t z d i o r i t e o f B l a c k R i v e r , W e s t c o a s t Complex 79 48 : C o n c o r d i a d i a g r a m , q u a r t z d i o r i t e o f B l a c k R i v e r . . . . 8 0 49 : a) Sr e v o l u t i o n d i a g r a m , I n d i a n I s l a n d i n t r u s i o n b) S r e v o l u t i o n d i a g r a m , q u a r t z d i o r i t e o f B l a c k River 83 50 : S r e v o l u t i o n d i a g r a m , whole r o c k a n a l y s e s , W e s t c o a s t Complex 84 51 : Sr e v o l u t i o n d i a g r a m c o m p a r i n g d a t a f o r t h e W e s t c o a s t Complex w i t h I s l a n d I n t r u s i o n d a t a 86 52 : P h o t o m i c r o g r a p h o f s p o n t a n e o u s f i s s i o n t r a c k s i n a p a t i t e from t h e I n d i a n I s l a n d i n t r u s i o n 88 53 Photomicrograph of r e p r e s e n t a t i v e z i r c o n g r a i n s from t h e Wark Complex 89 54 : C o n c o r d i a d i a g r a m , Wark d i o r i t e 90 55 : C o n c o r d i a d i a g r a m , C a t f a c e I n t r u s i o n , R i t c h i e Bay...92 56 : P h o t o m i c r o g r a p h o f r e p r e s e n t a t i v e z i r c o n g r a i n s from t h e C a t f a c e I n t r u s i o n , R i t c h i e Bay .94 57 : S r e v o l u t i o n d i a g r a m , C a t f a c e I n t r u s i o n , R i t c h i e Bay 95 58 : P h o t o m i c r o g r a p h o f s p o n t a n e o u s f i s s i o n t r a c k s i n a p a t i t e from t h e C a t f a c e I n t r u s i o n , R i t c h i e Bay 96 59 : C o o l i n g c u r v e s 99 60 : N o n c o n f o r m i t y between g e n t l y d i p p i n g s t r a t a o f t h e . Carmanah F o r m a t i o n a n d t h e W e s t c o a s t Complex 118 2  viiii  L I S T OF  TABLES page  Table Table Table  1 : C a l c s i l i c a t e p a r a g e n e s e s and p e r t i n e n t r e a c t i o n s . . 6 3 2 : Summary of age d e t e r m i n a t i o n s l i s t e d i n o r d e r of decreasing b l o c k i n g temperature 98 3 : C o m p a r a t i v e c a l c u l a t i o n s of u p l i f t r a t e f o r t h e Indian Island i n t r u s i o n 101  X  Ac knowledgements  R.  L.  project  Armstrong,  and  throughout  provided  the  S.  laboratory. analyses  by  due  Ar K.  and  the  advice  analyses  K.  Scott,  assistance  and  were p r o v i d e d  by  P.  van  guidance  der  in  J . H a r a k a l and  the K  Scott.  Montgomery and  Parrish,  suggested  supervision  Parrish,  for able  from members of  Geology, U n i v e r s i t y  This  support,  t o R.  Horsky  Assistance of  supervisor,  research.  Thanks are Heyden and  thesis  B.  study J . V.  of  British  Cranston,  benefited R o s s , H.  the  staff  the  Department  C o l u m b i a , most n o t a b l y  also merits  greatly  at  E.  recognition.  from d i s c u s s i o n s  J . Greenwood, J . E.  Muller  with and  M.  R. T.  Brandon. Finally, for  the  assistance  Chessman  summer  L.  and  for patience  National t o R.  the  writer  would  moral  support  and  a  fellowship provided  to  in  thank S. the  field  Casanova and  K.  encouragement.  Research Council  A r m s t r o n g and  like  of  Canada g r a n t  University funding  of  for this  number A-8841  British project.  Columbia  1  INTRODUCTION The is  Westcoast C r y s t a l l i n e  exposed  extending  intermittently  Complex o f  in  a  from t h e San Juan F a u l t  northwest  to  the  Brooks  and  northwestward  Survey Mountain The  first  west c o a s t during  Professor they  geologic  summer  Ernest  surveyed  (Muller,  Renfrew  from  o f Canada  of  1902  by  Mr.  Arthur  most o f t h e major p r o t e c t e d  metamorphic  and  acknowledging  frequent  them  1903; W e b s t e r ,  granodiorite the  Coast  Range  these  along the  sediments,  intrusive  they  series,  i n d i s t i n g u i s h i n g between  investigated Sounds  described  (1965)  rocks  boat,  1903)  and  Batholith  a t t r i b u t e d them t o  Eastwood  sealing  and  the  geology  identified  between  d i o r i t e and  o f Upper J u r a s s i c age b e l i e v e d t o be r e l a t e d t o  (1950,1954a,b) and  difficulty  Dolmage Barkely  an  Webster  inlets  a  and  of  f o r the G e o l o g i c a l Survey  described  Quatsino  city  Island's  H a y c o c k . By means o f a s m a l l  1921,  the  the  1977; F i g . 1 ) .  In a d d i t i o n t o y o u n g e r u n a l t e r e d  In  rocks,  km  45 km t o t h e San Juan  west c o a s t .  (Haycock,  280  i n v e s t i g a t i o n of Vancouver  was c o n d u c t e d  the  extend  Island  t o 15 km wide,  Similar  approximately  faults  10  near P o r t  Peninsula.  W a r k / C o l q u i t z P l u t o n i c Complex, Victoria  zone  Vancouver  a  (Dolmage,  the  to avoid  Jeletzky  Coast  Intrusions  batholithic  major  introduced  1921).  Middle  Jurassic  orogeny.  t h e name I s l a n d I n t r u s i o n s f o r  confusion  with  plutonic  rocks  of  the  mainland. Muller  (Muller  and  Carson,  1969)  noted  a  marked  2  Fig. 1 Generalized geologic map of Vancouver Island. Metamorphic complex e a s t of 124° l o n g , i s W a r k / C o l q u i t z ; t o the west i s t h e W e s t c o a s t C r y s t a l l i n e Complex. M o d i f i e d from M u l l e r (1977).  3  difference  between t y p i c a l  B e d w e l l and coast the  Nanaimo B a t h o l i t h s  and  applied  latter.  the  cross-cutting  Grice  Bay  belief  the  volcanic  rocks  Jurassic,  and  The was  was  the  by  discordant This  and  Tofino,  B.C.,  and  the  west  295  Rb-Sr, and (XRF),  collected  from t h a t  as  the  Crystalline  W a r k / C o l q u i t z complex  on  Group,  the  south  and  Upper  shore  Clapp  384  northwest  the  complex. Island and  Crystalline  1969). One  zircon  Complex Ma  has  (Muller, mapping  the  fishing  age  yielded  1977). of  Meares  village  isotopic dating  t r a c k ) , major and  Complex  in  Westcoast  r e s u l t s of  In  of  Paleozoic  (1909,1912c,1913)  detailed near  for  Muller's  migmatized  'basement'  to  quartz-  date  southern Vancouver  petrographic  area.  for a  192±9 K-Ar  from  Carson,  on  fission  and  264±7 Ma  dike  the  shorelines  well  C r y s t a l l i n e Complex  Colquitz  i s based  analysis  Westcoast  the  derived  with  (Muller  adjacent as  g r a n i t o i d s along  et al.,1974) supports  named by  d a t e s between  Island  K-Ar,  and  for  report  the  with a  Sicker  correlated Muller  as  is a crystalline  described  determination  Tectonic  along  (Muller  complex of  such  d a t e of  amphibolitized  thus  tentatively  Pb,  and  W a r k / C o l q u i t z Complex of  first  Complex  U-Pb  gneiss  near T o f i n o  that  Intrusions  name W e s t c o a s t  A concordant  plagioclase-biotite a  Island  of (U-  trace  element  i n v e s t i g a t i o n s of  samples  addition, near  samples  from  Pachena P o i n t  of V i c t o r i a  were  and  the the  studied.  Setting  Vancouver  Island,  and  the  Queen  Charlotte  Islands  to  4  the  north  large  make  displaced  (Jones  et  tholeiitic  by  by  resumed, related  the  volcanic  Wrangellia tectonic  belt  heterogeneous Mesozoic  includes  assemblage,  Jones  Coast  an arc  the  terrane  suggested  age  Upper  capped Triassic  to  late  was  Paleozoic  magmatic  and  activity  granitoid batholiths Island  the  of  Insular  the  and  Intrusions  Precambrian,  as  another  Upper  and  of  Alexander  (Berg  et  to North America  (Monger e t that  a  Paleozoic,  continental  superjacent to  and  Gravina-  late  interbedded  Lower  flysch  Alaska,  and  indicates  Terrane with Wrangellia  al,  Complex  composite  Terrane,  displaced  Jurassic  deposit  belt, a  Alexander  southeastern  Plutonic  C r e t a c e o u s time  of  a l . ( 1 9 7 2 ) . The  in  time  has  et  basinal  Late J u r a s s i c  Tertiary  of  interpreted  of  subaerial  subordinate carbonate,  the  which  Nutzotin  composite  termed  part  amalgamation  to  is  stratigraphy  Jurassic  i s now  rocks  package  respectively.  by  volcanic  and  emplacement  fragment  Cretaceous  clastic  Triassic  Early  assemblage  rocks,  and  a  Cordillera  t o Upper T r i a s s i c  Group, a m i d d l e  rocks,  Bonanza V o l c a n i c s ,  Canadian  subaqueous  Middle  the  of W r a n g e l l i a ,  tectonostratigraphic  volcanic,  In  with  of  Sicker  of  rocks.  western  distinctive  the  composed  clastic  the  calcareous  This on  of  voluminous  basalts  sediments.  s i g n i f i c a n t portion  1977). T h i s  disconformably  arc  a  terrane  al,  characterized  deposited  up  1972). by  the  Welding  accretion  of  this  mid-Cretaceous  indicates accretion  a l . , 1982). Van  of  by  der  by  Heyden  the  to  mid(1982)  composite  5  Wrangellia/Alexander to in  upper J u r a s s i c the  central  The  Pacific the  Vancouver  Island  1982)  flysch  and  by  sedimentary  paleomagnetic  indicate America  a  large  since on  Recent  determinations  Volcanics  indicate 1983)  translation  rocks  al.,  1982;  similarly North  a  and  has  occured by  Van  der  translation documented  America  These  Cretaceous  Franciscan  Complex  includes  accreted  also  Belt  studies.  Island  or  for  the  S  terranes  Data  from  and  Early  relative  the  that  Early  Alaska  Jurassic.  et  since  (Hillhouse,  data 1977;  a l . , 1 9 8 0 ) . As Lower  for S t i k i n i a  i n about M i d d l e J u r a s s i c  time  the late  1980). Bonanza or  S;  northward This  for  view Insular  Stone  much as  Cretaceous  subsequent  a  (21°N major  to  of  Irving,  Jurassic  paleolatitude  is  several  have y i e l d e d  (Yole  suggest  since  Voo  Complex  Alaska. Lower  s i m i l a r paleomagnetic  in southern  Baranof  of  rocks.  18°N  would  and  Schist  T r i a s s i c . T r i a s s i c basalts  similar  which  strengthened  Belt  of  deformation  Leech River  Insular  Vancouver  paleolatitude  middle  Wrangellia  northward displacement  the  Triassic  northward  of  Upper J u r a s s i c  Belt  as  time.  southeastern  Pacific  and  Karmutsen F o r m a t i o n  is  and  a l l o c t h o n o u s n a t u r e of  Irving,  that  outboard  Complex and  for  Chugach T e r r a n e and  of  The  early  responsible  melange, c o r r e l a t i v e w i t h t h e  indicated  North  as  Complex a t  lies  the  mainly  volcanic  The  workers  Belt  and  California.  Cenozoic  Plutonic  in southern  consist  to S t i k i n i a  have been  P a c i f i c Rim  units  of  may  Coast  includes  (Cowan,  terrane  has  et  13°  of  been  to a c c r e t i o n  to  ( I r v i n g et a l . ,  6  1980; Monger e t  al.,  1982).  7  CHAPTER I DESCRIPTION OF  MAP  UNITS  Westcoast C r y s t a l l i n e Most  of  underlain  the  by  the  heterogeneous rocks,  gneisses,  textural  and  area  shown  Westcoast  assemblage  metamorphosed  during  field  of  compositional  intermediate rocks,  felsic  Amphibolite  and  lithodemic  unit,  variability  ( i n pocket) i s Complex,  to basic  Despite an  a  plutonic and  pronounced  attempt  was  made  between d o m i n a n t l y m a f i c  components, h e r e a f t e r Westcoast Migmatite, the  2  amphibolites,  sediments.  mapping t o d i f f e r e n t i a t e  dominantly  in Figure  Crystalline  migmatitic  calcareous  Complex  Westcoast  termed the  Westcoast  respectively. A  Diorites,  and  third  includes  small  stocks  of  slightly  g n e i s s i c to massive d i o r i t e  and  diorite  as  well  the  pluton.  as  metasedimentary u n i t are  Westcoast  Amphibolite unit  to  granoblastic lineated  is  predominantly  to  3 cm  amphibolitized texture  has  gneiss  a distinctive  i n diameter  amphibolite  grained  a  A  gabbro-  to  (Fig.  which  epidiorite,  diorite  (see F i g . 15),  amphibolite  amphibolite  Inlet  also distinguished.  from m a s s i v e , medium t o c o a r s e applied  Tofino  ( W e s t c o a s t M e t a s e d i m e n t s ) and  peridotite  This  larger  quartz  and fine  3).  spotted  texture  hornblende megacrysts  a  term  gabbro  with  grained In  in a  ranges  and  places, of  well the  rounded 1  finer  grained  8  Fig. 4 Possible Amphibolite.  cumulate  texture  in  Megacrystic  Westcoast  9  matrix  of  plagioclase  megacrysts  and  are a l i g n e d  even more s t r i k i n g  hornblende.  "like  Occasionally,  beads on a s t r i n g "  t e x t u r e r e m i n i s c e n t of a  the  to y i e l d  cumulate  an  (Fig.  4). Also diorite  included gneiss  hornblende-  in  with  and  with  f o l d s a r e common "soupy" o r The  the  Its  textures,  from  schlieren unit.  by  0.1  to 2  cm  and  is  texture Tight  grey  marked  to  isoclinal  g n e i s s e s which o f t e n  i s blue-green displays  completely twins  sieve  abundance  the hornblende  texture ranges  appear  which c o n s t i t u t e s  appears  cloudy  saussuritized are  from A n  4 0  is  gabbroic  and  from  An  a  rare  7 0  about  40  with  relict of  parentage.  5 t o 50  in  indicate  percent  of  and  partially  thin  section.  common but a r e o f t e n they  ragged  a replacement  i n hand s p e c i m e n  when o b s e r v e d  fairly  to  from  pleochroic  i n t h e more m a f i c  is clearly  a probable  a l t e r a t i o n . Where p r e s e r v e d ,  Biotite  to yellow-green  g n e i s s e s t o 90 p e r c e n t  indicating  rocks,  ranging  layering  g n e i s s e s . In some of t h e e p i d i o r i t e s  Plagioclase,  Albite  well-foliated  laminae  migmatite  modal  i n the grey  hypersthene  to  a  i n the d i o r i t e  which o f t e n  amphibolite  these  metamorphic  exhibits  amphibole  terminations.  igneous  is  "swirly".  hornblende  percent  unit  plagioclase-rich  wide. I t f r e q u e n t l y gradational  this  a  obscured  by  composition  . constituent  largely  r e p l a c e d by c h l o r i t e .  except  i n v e i n s and  vugs.  Quartz  of t h e s e is  r o c k s and  generally  Epidote i s usually  present  is  absent (up t o  1 0  5 p e r c e n t ) , and sphene,  apatite,  accessories.  prehnite  percent)  Secondary  and o c c u r s  A relatively see  appendix  opaques  is fairly  i n v e i n s and c l o t t e d  high  2)  and  nickel  is  common  common  (up t o 12  masses.  concentration  suggestive  are  (56 t o 211  of o r i g i n  as mafic  ppm,  igneous  rocks.  Westcoast The  Migmatite Westcoast  migmatitic. generally with  a  migmatite  consists  of  Complex  is  of  leucosome.  between banded g n e i s s ,  stockwork, and a g m a t i t e  is  This  the  is  plagioclase chlorite. to  and  these  gneiss,  i n roughly  extreme of  abundant equal  minerals amounts.  saussuritization  biotite  to  i s s c a r c e and K - f e l d s p a r  Epidote  schollen  i s a common v e i n  prehnite  of and  never exceeds 3  filling.  Diorite  Massive stocks  in  conversion  Amphibole  4 percent.  Westcoast  evident  includes a l l  ( s e e F i g s . 5, 6, a n d 7 ) .  leucosome and a r e p r e s e n t  Alteration  places  intermingled  unit  schlieren  many  c h a r a c t e r but  melasome  Q u a r t z and p l a g i o c l a s e a r e t h e most of  in  variable  amphibolitic  trondhjemitic  gradations gneiss,  The  Crystalline  and  to  faintly  plutons  foliated  dioritic  a r e common. The c o m p o s i t i o n a l  intrusions includes hornblendite,  hornblende trondhjemite  diorite and  and  to rare  quartz  diorite  granodiorite.  tonalitic range of  hornblende  gabbro,  and l e u c o t o n a l i t e o r Diorite  and  quartz  11  Fig.  6 Agmatite,  Westcoast  Crystalline  Complex.  12  F i g . 7 Complex m i x t u r e of Westcoast rock types including megacrystic amphibolite, porphyritic diorite, pegmatite, trondhjemitic a p l i t e , and diabase; Westcoast Crystalline Complex.  13  diorite  are  by  f a r the  Variation great  and  t o the  in  ranges  nearly  size  from  Syntectonic  angular  to  small  style  and  contacts  obscure  are  Large  rafts  and  enveloped (Fig. in  by  9 ) . In  and  both  the  hornblende-rich  (1966)  to  the  types, the  contain  and  have  infolded  enveloping  a  source  Islands  and  meters  correlated  (Fig. diorite  are  were  often  by  apparently c o n s i s t s of  proportions. association.  likely  derived  equilibration  migmatite  with  1977). S u t h e r l a n d  "syntectonic  the  is  i n t r u s i o n and  Chappell,  and  of  wide  in d i f f e r e n t  rocks  similar  of a m p h i b o l i t e  tabular bodies  residuum-melt  and  voluminous,  discordant  x e n o l i t h mineralogy  as  aureoles  less  younger n o n - f o l i a t e d i n t r u s i v e s  same p h a s e s  (White  described  sharply  10  inclusions  pyroxene-bearing melt  up  of  interpreted  hydrous  Inlet  and  foliated  generally  near v e r t i c a l  some  e q u i l i b r i u m with  best  bodies  Tofino  xenoliths  complexly  i n t r u s i o n s are  migmatite  essentially is  the  variably foliated,  more l e u c o c r a t i c , u n f o l i a t e d and  gneiss  intrusions is  sub-map-scale  of  amphibolitic with  these  borders.  Post-tectonic  8).  of  proportions  plutons  nebulitic  gradational  voluminous.  and  batholithic  pluton.  migmatitic  most  batholiths"  i n the  amphibolites  This The from the Brown with  Queen  Charlotte  with  Karmutsen  the  Westcoast  basalts. The  microscopic  textures  Diorites  are  generally  granular.  O c c a s i o n a l l y observed  exhibited  hypidiomorphic contacts  by  to a l l o t r i o m o r p h i c with  late  stage  14  Fig. 8 Post-tectonic intrusion showing s h a r p d i s c o r d a n c e w i t h d e f o r m e d g n e i s s e s , W e s t c o a s t C r y s t a l l i n e Complex.  15  F i g . 9 S c r e e n s of banded gneiss enveloped i n t r u s i v e , W e s t c o a s t C r y s t a l l i n e Complex.  by  late-stage  16  pegmatites (Fig.  of  m i n e r a l o g i c a l composition  suite  of  rocks.  p l a g i o c l a s e (An„  rocks  and  often exhibit  from  90  to  percent  seen  zoning  i s by  percent  as  a  with  f a r the  abundance  replacement  becomes t h e  suite  more  to  sharp  finer  to  45  grained  apatite,  Inlet  ranges  i n most of  It  dominant  the  rocks. ranging  to about  10  occasionally  forming  mafic  of  subhedral  phase  is  this  alteration.  these  dominant m a f i c  diorites.  than  from  a  phase  It  is  often  and  less  than  10  percent  in trondhjemite.  interstitial  include epidote,  uralite as  the  partially  two  and  most n o t a b l e  northeast  corner  intrusions  exhibit  concordant  with  Offshoots  of  p r e h n i t e , and  Tofino  studied are  ( M u l l e r and area  Indian  foliated  the  veins  or  as  accessory  opaques.  o f t h e map  adjacent  the  It i s generally  usually in  intrusions  termed h e r e a f t e r the  in  to p l a g i o c l a s e .  i n p l a g i o c l a s e , secondary  p l u t o n , named by M u l l e r  Island  to  i n the h o r n b l e n d i t e s  cent  sphene, z i r c o n ,  The  percent  v a r y i n g d e g r e e s of  leucocratic.  per  Minor phases alteration  10 t o 50  in  chlorite.  Modal q u a r t z diorite  i s ubiquitous  of c l i n o p y r o x e n e  gabbro. B i o t i t e  altered  )  u s u a l l y anhedral  lacking  i n the q u a r t z  becomes  7 0  c o n s t i t u t e s from  i s s c a r c e or  Hornblende  30  to A n  0  P l a g i o c l a s e grains are  Orthoclase  the  are  10). Cloudy  and  similar  and  Carson,  and  gneisses Inlet  margins  in  Indian  intrusion.  and  pluton  Tofino  1969),  a body on  Island lineated  the  ( F i g l  Both 11)  amphibolites. are  intimately  17  F i g . 10 S h a r p c o n t a c t late-stage pegmatite C r y s t a l l i n e Complex.  between altered plutonic with similar mineralogy,  rock and Westcoast  18  19  intermingled  with  interpreted  as  bodies  the r e s u l t  are quartz  biotite.  Quartz  subhedral similar Black  enveloping  i s mostly  lithology  the q u a r t z Two  but  special  The  would  indicate  be  predominant,  and  to  stockwork,  of in  in  which  undeformed agmatite  containing  rock  gneiss  1)  variable  amphibolite  leucocratic  mafic is  first  which  up t o 40 p e r c e n t  schlieren  association  variables:  the  containing  to  near  and 2) t h e d e g r e e o f  of the outcrop,  variable  of  d e s c r i b e d c a n be  dominant  up t o 60 p e r c e n t  second  replacement  oxide  constitute  The  Pervasive  is a characteristic  thus  injection,  The r a n g e  agmatite,  complex  o f sample V9.  of l e u c o c r a t i c  a  t h e Wark  total  spinel-Fe  i n t e r m s o f two  from  near t h e  t o h e r e i n as  character.  lithodemic units  deformation.  very  more e x t e n s i v e a l t e r a t i o n  A  8 percent  classified  A  to  V8. and V9) a r e l i k e w i s e v e r y  plagioclase  t h r e e major  synplutonic  from  i t i s doubtful that t h i s  about  fraction  plagioclase.  be r e f e r r e d  collected  significance.  constitutes  and i n t e r s t i t i a l  the Westcoast T r a i l  petrographic of  and a l t e r e d  River.  (samples  by c h l o r i t e  Victoria,  the  Both  along  of Black  in  saussuritization  roughly  o f s y n t e c t o n i c emplacement. c o n t a i n i n g hornblende  samples of d i o r i t e  similar  of  are  (sample WCT-3) and w i l l  Victoria  gneisses  recrystallized  occurs  diorite  of  biotite  and  zoned g r a i n s of s a u s s u r i t i z e d  River  north  dioritic  migmatitic  is  veins  to plutonic  rock  inclusions.  shown by t h e t r a n s i t i o n angular  blocks  of  from  country  i n w h i c h t h e i n c l u s i o n s have  been  20  flattened mafic  or e l o n g a t e d  layers.  this  to  banded  12  i s a g r a p h i c a l r e p r e s e n t a t i o n of  Figure  two-dimensional  third  variable  felsic  contrast.  is  gneiss  classification the  degree  with  scheme.  continuous  A  potential  of homogenization  or m a f i c -  Gabbro-Peridotite Several gabbroic  isolated  rock  dike-like  outcrop  near  the  masses  of  central  p a r t o f Lemmens  Inlet.  The t e x t u r e i s a l l o t r i o m o r p h i c  coarse  g r a i n e d , and u n f o l i a t e d .  Augite, percent  inclusions  rocks. I t i s  and  often  crystallographic surrounds percent  poikilitic  contains  planes.  rods  with of  Blue-green  rock.  Enstatite  and  medium  plagioclase  ilmenite  fibrous  olivine  o f t h e r o c k . The  percent  saussuritized  hornblende,  remainder  consists  plagioclase  2 t o 5 percent  chromite  (An  8 0  along uralite  from  5 t o 15  are  largely  by s e r p e n t i n e w h i c h t o g e t h e r make up from  percent  to  composes a b o u t 50  much o f t h e p y r o x e n e a n d c o n s t i t u t e s  of the  replaced  granular,  f r e q u e n t l y showing d i a l l a g e ,  of these  uralitized  of ),  25 t o 35 about  3  and m a g n e t i t e ,  10  percent  a n d minor  chlorite. Similar of  extremely  northwest greenschist  c h e m i c a l l y t o t h e g a b b r o - p e r i d o t i t e a r e a group sheared  corner  mafic  of  facies  chlorite-plagioclase.  rocks  Lemmens  which  Inlet.  assemblage The s i m i l a r  of  crop These  out  i n the  comprise  the  actinolite-epidote-  chemistry  a n d low g r a d e o f  2 1  Synplutonic Deformation  F i g . 12 S c h e m a t i c diagram depicting relationship between f r a c t i o n _ of l e u c o c r a t i c i n j e c t i o n a n d d e g r e e o f s y n p l u t o n i c d e f o r m a t i o n i n t h e W e s t c o a s t C r y s t a l l i n e Complex.  22  metamorphism  of  they  comagmatic  may  be  amphibolites rocks  and  to u l t r a m a f i c rocks  and  younger  Jurassic  than  the  suggests Westcoast  (1941) d e s c r i b e d  Bedwell  Batholith  similar  near  the  River.  An  isolated  observed  been d e r i v e d  Westcoast  of c h l o r i t e - a c t i n o l i t e  t h e mouth of Windy Bay  from  similar  and  may  schist  well  have  rocks.  Metasediments  encountered include  occurrence  near  Pendants  which  mafic  g n e i s s e s . Sargent  i n t r u d i n g the  Bedwell  was  these  and  xenoliths  w i t h i n the  Westcoast  metapsammitic  shed  some l i g h t  of  and  metasedimentary Crystalline  calcsilicate  rocks  Complex  assemblages,  both  are and of  on m e t a m o r p h i c c o n d i t i o n s .  Metapsammite Rocks eastern  of  side  southern  and  are  the is  of  with  were  Island,  xenoliths  the  as  Tofino  calcareous  conformable  sediments  to the  are  n o r t h and  quartz,  biotite,  remaining partially  20  percent  5 percent  3 percent retrograded  garnet,  pyrite,  found  Inlet  south  near  the  and  and  Bay.  On  mylonitized  with brecciated  are  2 percent  to p r e h n i t e .  the  in Ritchie  approximately  plagioclase  epidote  on  pluton,  strongly  v o l c a n i c s . M i n e r a l o g i c a l l y they  percent  percent  Indian  composition  I s l a n d , the metasediments  siliceous 50  of  contact  intercalated Indian  psammitic  (An . 9  1 5  ),  muscovite apatite.  20 and  Biotite  23  Psammitic similar,  consisting  quartz, biotite  xenoliths  20  to  percent  pyrite  apatite,  epidote,  Clastic the but  north  of  30  (altering  to  and  2 percent  garnet  fine  Layering  to 5  pluton 55  to  percent  are  percent  15  percent  muscovite,  Minor phases  3  include  chlorite. within Bay  banded  appear  assemblage  1 2  up  ),  less  p r e h n i t e . The  of c o m p l e t e  calcsilicate  t o be  with 6  and  45  spinel.  p o r p h y r o b l a s t s , and  account  grained  2  plagioclase (An .  chlorite  on  feldspar.  and  intercalations  percent  muscovite, grained  percent  zircon  Inlet  plagioclase,  prehnite),  one  Tofino  approximately  s i d e of R i t c h i e  20  the  percent  contain a similar  quartz,  in  more to  on  quartzitic 75  percent  3 percent  biotite,  than  percent  i s rather  fine  p o l y g o n i z a t i o n of q u a r t z  and  i s often accentuated  rock  one  by  concentrations  of  biotite.  Calcsilicate Isoclinally crops  out  near  contact  with  folded.  The  with  and  14),  northern  here  material, tightly w h i c h may  of R i t c h i e  represent  appears  Bay.  The  southern  be  complexly  c o n t a i n s abundant  s t r e a k s of  f o l d e d and  to  and q u a r t z i t e  disrupted  intercalations  of  (Figs.  sediments  eruptives.  and  wollastonite,  end  calcsilicate  a m p h i b o l i t i c rock  calcsilicate  composition  banded  amphibolite  basaltic The  the  an  metapsammitic 13  folded  consist  layers  are  quite  variable  of v a r y i n g p r o p o r t i o n s of  diopside,  scapolite,  quartz,  in  carbonate, plagioclase  24  Fig. 14 Tightly folded intercalations a m p h i b o l i t e , Westcoast Metasediments.  of metapsammite i n  25  ( A n  5  and z o i s i t e .  - 6 o ) /  0  two  r e p r e s e n t a t i v e samples  section  (52-7B-1,-2) a r e d i s c u s s e d  rocks a r e a l s o exposed  Lemmens I n l e t .  cliff  assemblages  of  fine  Here t h e y  occur  i n the  the  near  cliff  the contact  a s t r o n g l y d i s r u p t e d zone o f  calcsilicate.  These  those  in  exposed  wollastonite  the  with  rocks  Ritchie  are  Westcoast  part  10 meter  g r a i n e d w h i t e m a r b l e and t i g h t l y  l a y e r s of b l u i s h - g r e y d i o p s i d i t e .  Stable  i n the  northern  as a massive  boudinaged  is  from  on metamorphism.  Carbonate of  The s t a b l e m i n e r a l  f o l d e d and  A t t h e base  crystalline  mylonitic  high  and  of  rocks  cataclastic  mineralogically similar to  Bay,  with  the  exception  that  i s r a r e , p e r h a p s due t o a r e t r o g r a d e r e a c t i o n .  assemblages  from t h i s  s e c t i o n on metamorphism  outcrop (samples  are also  discussed  in  50-4,a-j).  D i a b a s e and A p l i t e D i a b a s e and a p l i t e Westcoast  Crystalline diabase,  d i k e s a n d d i k e l e t s a r e common Complex.  crosscut  the  ambiguous  ( F i g . 15). Both appear  Spilitization is  generally  and  variolitic.  percent 20  per cent  diopside,  their  fine  dikes generally  relationship  t o post-date  of the d i a b a s e  very  albitic  but  The a p l i t e  grained,  hyalopilitic composed  p l a g i o c l a s e , 2 t o 30 p e r c e n t a n d 0 t o 10  is  often  deformation.  i s u b i q u i t o u s . The t e x t u r e  They a r e g e n e r a l l y  chlorite  i n the  percent  to trachytic, of  40  to  calcite,  quartz,  90  2 to  epidote,  and i l m e n i t e .  Aplitic  dikes  i n the Westcoast  Crystalline  Complex a r e  26  F i g . 15 Ambiguous c r o s s c u t t i n g r e l a t i o n s h i p between aplite and diabase dikelets i n e p i d i o r i t e , Westcoast C r y s t a l l i n e Complex.  27  trondhjemitic amounts  of  totalling  Felsic  quartz about  chlorite,  highly  southwest  to  of  subequal  percent  with  the  (An  5 0  .  6 0  )  remainder  e p i d o t e and a p a t i t e .  portion  It  maroon  tuffaceous  consists  andesite  with  the  unclear.  I t s proximity  it  be a s l i v e r  may  the P a c i f i c  Bonanza  felsic  volcanic  o f t h e map  generally  relationship  area of  near  white  and  c r o p s out i n  the  breccia.  Crystalline  to the Westcoast  Fault  material  Rim Complex. M u l l e r  Westcoast  to bluish-grey  dacite  Westcoast  of e x o t i c  unit  Its  Complex  suggests  possibly  to  is that  correlative  (1973) mapped t h e s e  as  Volcanics.  The quartz,  rock albite,  fractured filled  95  fractured  Fault.  with  composed  and s a u s s u r i t i z e d p l a g i o c l a s e  90  biotite,  and a r e  Volcanics  A the  i n composition  consists  mostly  sericite,  and e p i d o t e  quartz  and  of  saussurite.  a fine with  Fractures  grained  hash of  phenocrysts  of  are  frequently  not  studied  w i t h q u a r t z and c a l c i t e .  P a c i f i c Rim Complex The  Pacific  petrographically is  Rim in  Complex  the present  composed o f a complex m i x t u r e  ribbon fine  to  sorted  chert, medium clastic  study. of  and minor v o l c a n i c s . grained, material  massive including  was  In t h e map a r e a , i t  greywacke, The greywacke unit  bits  argillite, i s a dark,  containing of c h e r t ,  poorly  argillite,  28  and  v o l c a n i c d e b r i s . The  and  is generally highly fractured  a crude are  fracture  argillite  cleavage.  o c c a s i o n a l 2 t o 4 cm  large  body  of  thick  1969),  i n t r u d e s the Westcoast  granular  in  of  Catface  Ritchie  texture  and  plagioclase  showing  alteration,  30  percent  orthoclase,  14  percent  altering  comprising  sericite,  Hypabyssal chilled both  Intrusions plagioclase Alteration epidote.  (Fig. ( A n  3  products  quartz  Bay.  The  rock  consists  of  zoning  is  (An  3 0  Carson, on  40  . o)  and  5  quartz,  study  5  little percent  8 percent  biotite  and  percent  one and  area  Complex  zircon.  and  and  intrude Catface zoned  phases  include  quartz,  hornblende  and  chlorite,  with  the  Phenocryst  include u r a l i t e ,  the  percent  a n d e s i t e to d a c i t e porphyry i n the  by  hypidiomorphic  about  magnetite  Crystalline  . 5 o ) i  mapped  Complex  brown h o r n b l e n d e ,  of  argillites  diorite,  e p i d o t e , sphene, a p a t i t e  16). 2  the  Crystalline  2 percent  dikes  Westcoast  develops  with  interstitial  m a r g i n s a r e common  the  in places,  I n t r u s i o n s ( M u l l e r and  obvious  to c h l o r i t e ,  in color  ribbon cherts.  massive  as p a r t of t h e  side  to black  Intrusions  Muller  southern  which,  Interbedded  Tertiary A  i s grey  biotite.  sericite  and  29  F i g . 16 H y p a b y s s a l d i k e and dikelet i n t r u d i n g C a t f a c e I n t r u s i o n on M e a r e s  of andesite Island.  porphry  30  CHAPTER II GEOCHEMISTRY OF  Chemical  WESTCOAST CRYSTALLINE COMPLEX  AND  RELATED ROCKS  Analysis  Thirteen as  THE  well  as  intrusions  samples three  were  composition  from the  X-ray  pressed-powder-pellet and  others  using and  (van  der  a Phillips  data  (1979).  analyses  for  r o u t i n e s have been  Analysis  for  H 0  was  2  also described are  graphically  presented  in Figures  of T e r t i a r y  by  a  element whole-rock  van  der  1982). A l l s a m p l e s were  spectrometer.  by in  Operating  Berman. Appendix  17 and  by  2  analyzed  by  l o s s on  Results and  Heyden  conditions  described  done  Complex  trace  using  procedure developed  1410  two  and  fluorescence,  Heyden,  PW  major  reduction  techniques  Crystalline  from t h e Wark Complex and analyzed  by  Westcoast  Berman ignition  from are  these  displayed  18.  Classification Various developed  chemical  for  classification  v o l c a n i c rocks  using  schemes  m a j o r and  have trace  a b u n d a n c e s . S i m i l a r schemes f o r p l u t o n i c r o c k s , using  t r a c e element c o n c e n t r a t i o n s ,  partially  due  to  compared  to  extrusive  classification represent  true  fewer  analytical rocks,  schemes, and liquid  the  the  are  element  particularly  l a c k i n g . T h i s may  data  for  granitoid  traditional  view t h a t  compositions.  been  In  not  use  of  be as  modal  a l l granitoids the  following  31  O- - 0 .  o o  m  0  a  .Q._o O  -O  Co  CaO u X  UJ  OL  to  Z  0°  UJ  z  o  o UJ Q  ^  >< O  o  o -  -  --  • -o  o  0  o>.  MgO TiO/o  0  •• 40  SO  SO  SiO,  TQ  80  WT. PERCENT  Fig. 17 Major e l e m e n t v a r i a t i o n d i a g r a m s f o r t h e W e s t c o a s t Crystalline Complex and r e l a t e d rocks; O = Westcoast Crystalline Complex, • = u l t r a b a s i t e s , A = Wark Complex, • » Tertiary intrusions; dashed lines connect mafite/felsite pair from a Westcoast Migmatite; dash-dot l i n e s connect m a f i t e / f e l s i t e p a i r from a Wark a g m a t i t e .  32  Nd oo  •»  Ba  0  O  'o  «r*^"  .  or*  •  4  Ce  a  a. z"  z"  o  o <  I  CC  ,  ,nnj z  UI  UI  u z o  •  CJ  u z o  0  CJ  z  o-  UI  a  Ni  UI  -I  ui  o  ui  -  a  A——  UI  o  o  Y 0  ••  o- -  Q  O °0  2_  Zr o  SP  oo  SiO, WT. PERCENT  F i g . 18 T r a c e e l e m e n t v a r i a t i o n d i a g r a m s f o r the Westcoast Crystalline Complex and related rocks; symbols and c o n n e c t i n g l i n e s as i n F i g . 17.  o  33  discussion, similarity  A Irvine  assumption  exists  r o c k s and chemical  the  that  is  made  between comagmatic  t h e y may  be  that  a petrochemical  intrusive  expected  to  and  share  extrusive  distinctive  characteristics. standard  and  schemes  major  Baragar  of  considered  (1971)  Floyd  interpretation  of  more  element  classification  as  well  and  Winchester  the  analyses.  reliable  for  as  scheme  immobile  of  element  (1978) were employed The  latter  altered  and  in  scheme  is  metamorphosed  rocks. The by  Irvine  t h e use  and  Baragar  classifications  o f FORTRAN p r o g r a m s w r i t t e n  were  by G.  T.  v a l u e s were n o t m e a s u r e d but were a p p r o x i m a t e d total  Fe  proposed  (reported by  determined  Brooks for  as F e 0 ) 2  the  compositions, intrusive  t h e s e samples  element  the  samples  basalt  rhyolite  (Figures  by  circles  solid  well  on  20,  significance. normative  They  2  C0  FeO  measured  FeO/Fe 0  ratios  3  was  2  presumably  analyses may  and  in Figures  these  was  not  negligible  be  approximate  tentatively  19 and  (samples  diagrams do  plagioclase  not  two  12-2  in  composition  and  samples p o r t r a y e d  and  15-12).  bear  little  Figure is  as  from  dacite  20 a r e u l t r a b a s i c  therefore  plot  ranging  andesite,  2 1 ) . The  magmatic  classified  suite  calc-alkaline  r e p r e s e n t cumulates  positions  from  rocks.  of a s u b a l k a l i n e  to 19,  and  Nixon.  not p r e s e n t .  major  equivalents  tholeiitic  average  (1976) f o r b a s a l t i c  as modal c a r b o n a t e was If  using  3  facilitated  An  1 0 0  21 .  and  may  Their genetic  as  their  Two  other  34  7  ALKALINE  FIELD  6^  o  O  5  CM  I'* fW  m Z 3H  SUBALKALINE  2^  40  F i g . 19 P l o t of a l k a l i s as i n F i g . 17. D i v i d i n g  50  SiO,  60  FIELD  70  80  v e r s u s s i l i c a (wt. p e r c e n t ) . line i s from Irvine and  Symbols Baragar  F i g . 20 AFM d i a g r a m (A = N a 0 + K 0 , F = FeO + 0.S998 F e 0 , M = MgO, wt. p e r c e n t ) . Symbols a s i n F i g . 17. D i v i d i n g l i n e i s from I r v i n e and B a r a g a r ( 1 9 7 1 ) . 2  2  2  3  35  80«  NORMATIVE PLAGIOCLASE COMPOSITION  F i g . 21 P l o t of normative color index versus normative plagioclase composition i n percent cation equivalents. Symbols a s i n F i g . 17. U l t r a b a s i c samples n o t shown ( s e e t e x t ) . F i e l d b o u n d a r i e s a r e from I r v i n e and B a r a g a r ( 1 9 7 1 ) ,  36  analyses  plotting  Westcoast  Amphibolite  (sample V 9 ) ,  On Si0  solutions  sodium t o the  alkaline  ranging samples  a F l o y d and  2  overall slightly  from fall  still  to  within  the  higher  rich  a  alkaline  rocks  Y/Nb  these could  rocks,  thereby  a Wark  diorite  indicates  conceivably driving  a  cumulates.  rocks  to  Various  (1978) p l o t  clearly  have  them  towards  alkaline  data  are  (Sun,  which  the  and  plot  slightly  1980).  versus  2  than  as  ultrabasic  may  be  of  Nb/Y  cumulates versus  be  i s found and  the  classify  trend  more e q u i v o c a l  Pearce  1.00  would  Zr/Ti0  d i s c r e p e n c i e s may  the  to a  in average  Cann  upper  all  due  but  (1973)  limit  for  data  as  e l e m e n t s have  been  subalkaline.  Discriminants  diagrams employing determine  eruptives.  Three  (1973) f o r  basic  the  immobile  tectonic  setting  such diagrams d e v e l o p e d volcanic  "within-plate"  basalts,  tholeiites,  calc-alkaline  and  a  of Nb  of  Again,  field  magma. On  the  of  define a subalkaline  rhyolite.  ratio  Setting  to  and  include  represent  which  concentration  rocks  proposed  devised  also in  s u b a l k a l i n e . The  calc-alkaline  Tectonic  data  basalt  ( F i g . 23),  transitional  may  Winchester  the  from a more s i l i c a Zr/Ti0  35-19)  field  field.  ( F i g . 22),  2  alkaline  (sample  plagioclase  hydrothermal introduced  the  b o t h of w h i c h  Saussuritized  the  within  rocks  to  ocean-floor  by  of  basaltic  P e a r c e and  distinguish b a s a l t s , low  b a s a l t s are  shown  Cann  between potassium  in  Figure  Fig. 22 Zr/TiOj Si0 diagram, Westcoast Crystalline Complex and r e l a t e d r o c k s ; Symbols as i n F i g . 17. Field b o u n d a r i e s a r e from F l o y d and W i n c h e s t e r ( 1 9 7 8 ) . 2  28  1.0 4  P H O N O U T I  0.1  o N B A S A N I T E 0.0 1  N E P M E L I N I T E A L K A L I  S U B - A L K A L I N E  0.001  B A S A L T  B A S A L T  y 0.01  0.10  1.00  10.0  Nb/Y Fig. 23 Nb/Y 2r/Ti0 diagram, Westcoast Crystalline Complex and r e l a t e d r o c k s ; Symbols as i n F i g . 17. Field b o u n d a r i e s a r e from F l o y d and W i n c h e s t e r ( 1 9 7 8 ) . 2  39  24.  As  differentiation  only  samples of b a s a l t i c  plotted.  The  alkaline  effect  (samples  from p l u t o n i c and of  alteration  the  overall  again, found  metamorphic  i n a magmatic  of  depleted basalts  i n T i , Z r , Nb,  and  the  by  the  Westcoast  Wark d i o r i t e enrichment patterns  suggests that Again,  island  are  increase  differentiation  is  of  the  analyses  these  lines  Complex  plotted  bulk  are  degrees chemistry,  diagrams  setting  Th, Ta  i n magmatic U,  Ba,  relative  Rb,  to  of  as  is,  would  comes  arc Cs,  be  from  same  and  25).  patterns  of  more c a l c - a l k a l i n e in  calc-alkaline  ridge  of  average  pattern  (inset, than  and  patterns  the  Comparison Sun  Pb  categories  w e l l as general  Sun  settings  mid-ocean  three  Complex, as  (Fig.  of  of  these  Fig.  25)  tholeiitic.  character  with  evident.  E x t r e m e d e p l e t i o n of T i expression  Wark  to c a l c - a l k a l i n e ,  this  "typical"  they  the  show  depletion  the  dashed  b a s a l t s , r e s p e c t i v e l y . The  Crystalline  clearly  with  by  average compositions  and  calc-  t r a c e e l e m e n t abundance p a t t e r n s .  K,  displayed  increased  showing v a r y i n g  portrayed  b a s a l t s erupted  in  ocean  been  the  have a f f e c t e d t h e  Sr,  and  the  ratio,  2  have  the  f o r a magmatic a r c  normalized  enriched  Zr/Ti0  arc.  evidence  (1980) showed t h a t were  may  by  from  rocks  subalkaline t h o l e i i t i c  plot  pair  V 8 - f ) . Although  which  i s an  is illustrated  identification  Further a  and  and  the  to a n d e s i t i c composition  a mafite/felsite  V8-m  increase  of d i f f e r e n t i a t i o n  character  which connect  tends to  absence  i n the of  average  magnetite  felsite  is  an  i n these  rocks.  40  Ti/ 100  Ti/100  Zr  Y*3  10000  E a a  200  Fig. 24 Tectonic setting d i s c r i m i n a t i o n d i a g r a m s showing delimiting fieids f o r "within-plate basalts" (WPB), oceanfloor basalts (OFB), low-potassium t h o l e i i t e s ( L K T ) , and c a l c - a l k a l i n e b a s a l t s (CAB). D a t a p l o t t e d a r e from samples of basaltic t o a n d e s i t i c c o m p o s i t i o n . Dashed l i n e s c o n n e c t m a f i t e / f e l s i t e p a i r from Wark a g m a t i t e . Symbols as in F i g . 17. F i e l d b o u n d a r i e s a r e from P e a r c e and Cann ( 1 9 7 3 ) .  41  '000,  100041 A  O H M M U X ••MN  100 4  3  eo N  E 10  average amphibolite average diorite  > WCCx  average felalte average diorite: Wark i  l  Rb  Ba  f  Nb  f  f  K  f  Ce  f  Sr  f  Nd  l  Zr  i  11 >  Ti  Y  Fig. 25 N o r m a l i z e d abundance p a t t e r n s of i n c o m p a t i b l e t r a c e e l e m e n t s , W e s t c o a s t C r y s t a l l i n e Complex and Wark diorite. Inset shows t y p i c a l p a t t e r n s f o r ocean i s l a n d , i s l a n d a r c , and o c e a n r i d g e b a s a l t s . N o r m a l i z i n g values are from Sun (1980).  42  Depletion  of V with  similarly  explained.  differentiation in  differentiation Inversion  c a n be a t t r i b u t e d  p l a g i o c l a s e due t o d e c r e a s i n g The n o r m a l i z e d  Tertiary enrichment  o f Rb, Ba a n d  characteristic tectonic  (samples  of these  i n that  they  Eocene c a l c - a l k a l i n e to Alaska.  inversion of  more  particularly observation  lends  with  content. f o r two  14-5) a l s o d i s p l a y  depletion  of  Nb  and T i  arc association ( F i g .26).  signatures ( F i g . 26)  however,  is  The  somewhat of c o e v a l  from Wyoming  are discussed  later.  of  ultrabasic  the  two  and, i n p a r t , depletions  calc-alkaline  f o r Rb, Ba, Nb, K,  cumulates,  peak  be  receptivity  a r c v o l c a n i c s which extend  itself  Crystalline  and  intrusions,  evolved  notable  or  Westcoast  RBP  o f t h e e n r i c h m e n t s and  the  restite  unique  can  abundance p a t t e r n s  The i m p l i c a t i o n s o f t h i s  are  Sr  a r e s i t u a t e d w e l l outboard  The t r a c e e l e m e n t samples  the  anorthite  and  of a magmatic  setting  enigmatic  K  of  to decreasing  t r a c e element  intrusions  ( s e e F i g . 18)  tend  characteristic rocks.  Nd,  t o show  and  This Sr.  is This  to interpretation  of these  rocks as  which  injected  into the  were  later  Complex.  Conclusions Petrographic Crystalline Catface magmatic  and  Complex,  chemical the  data  Wark/Colquitz  I n t r u s i o n s are c o n s i s t e n t with arc  calc-alkaline  setting.  f o r the  Enrichment  Westcoast  Complex,  magma  genesis  and the in  a  o f K, Rb, Ba, a n d S r i n  magmas h a s been e x p l a i n e d  by t h e  mobility  of  43  10004  Tertiary  Intrusions  C a t f a c e qz diorite  1  +j  t  ?  t  t  f  t  f  Rb  Ba  Nb  K  Ce  Sr  Nd  Zr  f  Ti  t  Y  Fig. 26 N o r m a l i z e d abundance p a t t e r n s of i n c o m p a t i b l e t r a c e elements, ultrabasic rocks and Tertiary intrusions. N o r m a l i z i n g v a l u e s a r e f r o m Sun ( i 9 6 0 ) .  44  these  elements  in  aqueous  fluids  which  introduced  t o the mantle  source  region  subducted  ocean  (Best,  1975;  crust  1979). D e p l e t i o n and  Y  in  increased would  of t h e i n c o m p a t i b l e  calc-alkaline 0  fugacity  2  together  (Pearce,1982).  result A higher  magmas  from 0  2  o x i d e s such as r u t i l e ,  retain  elements  compatible  degree of p a r t i a l  incompatible conceivable the  magmas  elements that  need  melting, d i d enter  the r e l a t i v e l y  solidus  of  the  by which  mantle  tend t o s t a b i l i z e  and z i r c o n  such  and  minerals  s o l i d u s would  It  depleted  trace  elements  does  from t h e s u b d u c t e d  ina  whatever  melt.  of remelting  thus  i n the  result  thereby d i l u t i n g  (Green,1973), but t h i s  for a contribution  facilitated  the  were t h e c o n s e q u e n c e  d e p l e t e d mantle  be  would  sphene  residuum, w h i l e a d e p r e s s e d mantle  of  e l e m e n t s Nb, Ce, Nd, Zr  hydration  with  been  Saunders and T a r n e y ,  may  fugacity  have  dehydration  and a d e c r e a s e d m a n t l e  residual  higher  by  may  is  also of  of p r e v i o u s l y  not slab.  escape  the  45  CHAPTER I I I STRUCTURE  Large  scale structural  complicated discrete  by  the  marker  e x p o s u r e s , and Observations to  in  l a c k of a  true  horizons,  on  an  studied  and  sporadic  of  the  shoreline  intrusions.  s c a l e , however, were  style  is  containing  post-deformational  outcrop  structural  area  stratigraphy  limited  d i s r u p t i o n by  i n d i c a t e the  27,  a n a l y s i s i n the  sufficient  r e g i o n mapped  (Fig.  pocket).  Heterogeneous S t r a i n The studied both  most  striking  structural  i s a pronounced v a r i a t i o n  the  amphibolitized  L o c a l l y superimposed  history  of  tectonic  intrusion, fabric.  developed, which  frequently  their  In  the  bodies,  rocks  the  area  exemplified  and  the  showing  granitoids,  faint  evident  granitoid  rock  in  by  intrusive a  complex  i s a heterogeneous, v a r i a b l y developed  from a v e r y only  developed plutonic  on  i s generally defined  ranges  in s t r a i n ,  country  suites.  feature  on  gneiss.  this  by  the  where  a gneissic foliation  alignment weathered In  fabric,  the  deformation  of m a f i c  0  minerals,  surfaces, larger,  (S )  to  well  syntectonic  is largely  confined  to  margins. In  the  a m p h i b o l i t i c country  between u n s t r a i n e d granoblastic  rock,  a l l transitions  a m p h i b o l i t i z e d metagabbro w i t h  textures  to  strongly  foliated  and  exist  isotropic lineated  46  amphibolite Mafic as  very  steep  excellent strain  photograph angular  strain  shear  strain  inclusions  gradients. Figure  28  direction  the  plane  i n c r e a s i n g shear is  of  simple  this  xenoliths  are  shear  advanced no  continuous the  Figure  where l o c a l  diorite  is clearly  dextral  shear.  The response  question to  explanation Graham  very  arises  as  perhaps  constituents.  of  Another to these  Graham,  by  Simpson, the  form more  the  gneiss.  i s a l s o demonstrated strain  zone  the  rocks  put  has  resulted  i n the and  in in  adjacent indicates  show a v a r i a b l e  stress. forth  by  regions  of  A possible Ramsay  and  incipient  of c h e m i c a l m o d i f i c a t i o n  introduction  possibility rocks  and  within  this  a result  mafic  development,  foliation  strain  1970;  such  r e g i o n a l shear  material  and  of  with  shear  t o why  result  towards p a r a l l e l i s m  s o f t e n i n g " at  as  The  flattened  into  bands  deflected into  originally  i n which the  foliation  z o n e . The  (1970) i s " s t r a i n  specifically  high  for heterogeneous  weakening  of  from a  rotated  ellipsoid  a presumably  deformation, and  strain.  r e c o g n i z a b l e as  strain  a narrow m y l o n i t i c s h e a r  which  elongated,  compositional  of  i s a sketch  banded g n e i s s  stage  indicate  increasingly  (Ramsay and  longer  Rotation 29  a  intrusives  places,  in  i n c l u s i o n s are  of maximum e l o n g a t i o n  1983). At  less  transition  have been a t t e n u a t e d ,  the  or  in  to subangular with  dioritic  m a r k e r s and,  showing a r a p i d  elongated  high  schist.  x e n o l i t h s i n c o r p o r a t e d i n the  serve  and  g n e i s s and  which  i s suggested  may  here;  of  mobile  apply the  more  injection  47  Fig. 28 Sketch from a p h o t o g r a p h showing development of banded gneiss from inclusion-rich granitoid by abrupt i n c r e a s e i n s h e a r s t r a i n , W e s t c o a s t C r y s t a l l i n e Complex.  48  Fig. shear  29 Deflection zone, W e s t c o a s t  of f o l i a t i o n i n d i o r i t e C r y s t a l l i n e Complex.  into  mylonitic  49  of  granitoid  melts  cooler  country  local  temperature  a s s m a l l d i k e s and  rock  gradients  resulting  Also, heterogeneity  to  i n v a r i a b l e response  For  whatever  behaved  The rather  reason,  S  to given  foliation,  0  this  strike  a maxima S  small  localized  Despite  although  deformational  likely  event.  v a r i a b l y developed,  an  and a p r e d o m i n a n t l y  steep  of a b o u t  i s frequently  plunging,  are  involved  a  to S ( F i g . 0  a  general  northeasterly  in  tight  ( F i g . 31) showing o n l y  of an S, a x i a l  irregular  folds  shows  317 69NE.  scale folding  often  of p o l e s indicates  development  to the minor southeast  is  that the rocks  distribution  foliation  0  isoclinal  ductility  boundary c o n d i t i o n s .  i s q u i t e apparent  during  density  northwesterly  The  rock  create  of S t r u c t u r a l F a b r i c s  The  dip with  somewhat  in local  i n the country  c o n s i s t e n t o r i e n t a t i o n on a p l o t  30a).  and  it  inhomogeneously  Orientation  into  (see Chapt. VI) c o u l d c o n c i e v a b l y  contrast. result  veins  appearance  crudely  planar  v a r i a b l y developed,  with  minor  foliation.  i n outcrop,  coaxial  to  the axes  a  general  stretching lineation  ( F i g . 30b). Steeply material Westcoast the  plunging  w i t h i n the S gneisses  0  boudins foliation  of  that  competent  are f a i r l y  ( F i g . 3 2 ) . These  interpretation  less  the primary  common  mafic in  f e a t u r e s lend support lineation  the to  i s the r e s u l t  of s t r e t c h i n g . All  of these  structural  elements can  be  explained  in  50  F i g . 30 S t r u c t u r a l o r i e n t a t i o n s , Meares Island map areaequal area p r o j e c t i o n s , a) Plot of p o l e s to S ; contour i n t e r v a l s a r e 5%, 4%, 3%, 1.5%, 0%; 138 p o i n t s . b) P l o t of lineations and minor f o l d a x e s ; c o n t o u r i n t e r v a l s a r e 9% 8%, 5%, 3%, 0%; 78 p o i n t s . 0  F i g . 32 B o u d i n a g e of a m p h i b o l i t i c W e s t c o a s t C r y s t a l l i n e Complex.  layers  in  banded  gneiss,  52  terms of s i m i l a r l y is If  an a t t e m p t these  oriented principal  t o show t h e s e  features truly  strain  relationships  represent  diagrammatically.  a coaxial  with  the  lengths  of  axes,  they  are best  i n t e r p r e t e d as a r e s u l t  two  principal  of  strain  directions  should  structure,  boudins  although  field  flattening  strain  strain  perpendicular  (X< > X  produce  a x e s . F i g u r e 33  the  t o minor  classic  evidence  fold  of e x t e n s i o n  > 1). I d e a l l y ,  2  history,  this  chocolate  f o r these  in  state tablet  structures i s  lacking. This response  to  inherent  the  axes  but  ENE.  here  an  this is  lineations  the  rocks  in northern  (S,) , w h i c h  (S ,  is  this  Figure  unit  Catface  transposed  reason  from  S, f o l i a t i o n 2)  of  this  more  isoclinal  below  pencil),  open  style  left),  3) b o u d i n a g e o f more q u a r t z i t i c  due t o  o r 3) emplacement  anomaly  of p a r t of t h i s (note  for  gneisses  1) r o t a t i o n  I n t r u s i o n . The l i m i t e d  makes r e s o l u t i o n  34 i s a c l o s e - u p  transposed  result  Ritchie  has a g e n e r a l  and d i p s 50 t o 60° SE. The  b u t may  fold  plunge to the  bedding?),  0  2) p r e - J u r a s s i c d e f o r m a t i o n ,  nearby T e r t i a r y  a  and t h e  and m i n o r  have a g e n e r a l l y s t e e p e r  foliation  p o o r l y understood  as  impose.  between  i n these  strike  plutons  d e v i a t i o n from o r i e n t a t i o n s i n t h e c r y s t a l l i n e  faulting,  of  they  earlier  northeasterly  of g r a n i t o i d  i n banded c a l c s i l i c a t e  The f o l i a t i o n  from  they  parallelism  i s observed  Bay,  emplacement  volume p r o b l e m  A similar  c a n p o s s i b l y be e x p l a i n e d  unit fold  minor  exposure difficult.  showing  1) t h e  closure  folds  of  (F,)  ( F , upper  l a y e r s (middle  2  left),  53  Fig. 33 S c h e m a t i c d i a g r a m showing o r i e n t a t i o n of p r i n c i p l e s t r a i n a x e s f o r b o u d i n s , l i n e a t i o n s , and minor f o l d s .  54  F i g . 34 C a l c s i l i c a t e showing t r a n s p o s e d l a y e r i n g (S,) has been f o l d e d and b o u d i n a g e d ; see t e x t f o r d e t a i l s .  which  55  and,  less  fold  c o n s p i c u o u s l y , 4) a  (directly  fold  axis  and  to  left  bisecting  photo) p l u n g i n g  33  small  well-developed  of p e n c i l )  stretching  t o 065  with a doubly  lineation  implying a  sheath plunging  (not v i s i b l e i n  similar  direction  of  shear.  Ductile-Brittle The with  Transition  discussion  structural  up  elements  t o t h i s p o i n t has of  a  ductile  dealt  exclusively  nature.  There  is,  however, ample e v i d e n c e  on m i c r o s c o p i c and  mesoscopic  for  ductile  s t r a i n . Figure  is  a  transition  a photomicrograph  mainly fabric  is  and  disrupted  plagioclase.  along  two  i n response  to a s i n g l e  direction  The by  direction  strain,  the  passes  parallelism  from  a  stress  ductile  the S  0  brittle  deformation  to  compressive  shortening i s gradually so t h a t  with at  increasing right  angles  Graham,  1970),  of s h e a r . As  to a b r i t t l e  fractures  appear  regime,  the  s h e a r s . Note  evidenced  by  the  rock  strain is the  sense  the d e f l e c t i o n  of  foliation.  Another In  the  p l a n e s of  (Ramsay and  brittle  composed strain  of maximum  w i t h the p l a n e  accomodated a l o n g c o n j u g a t e movement on  shear  35  ductile  f o l i a t i o n , which develops  t h e maximum c o m p r e s s i v e  approaches  The  brittle  of p r i n c i p a l  p r o g r e s s i v e simple  amphibolite  conjugate  and  shear  36.  lineated  the d u c t i l e  rotated  of  to b r i t t l e  Both  stress.  to  of a w e l l  of h o r n b l e n d e  fracture. be  from  scales  this  example of t h i s photomicrograph  transition  i s shown  in  of a c a l c i t e m a r b l e  Figure from  the  56  F i g . 35 P h o t o m i c r o g r a p h showing b r i t t l e f r a c t u r e of d u c t i l e s t r a i n f a b r i c a l o n g conjugate p l a n e s , Westcoast A m p h i b o l i t e .  F i g .  36  deformed  Photomicrograph c a l c i t e  r i b b o n s ,  showing Westcoast  c a t a c l a s i s  of  M e t a s e d i m e n t s .  d u c t i l e l y  57  Westcoast Metasediments, calcite are  is  obvious.  strongly  the  The  attenuated  grains  twins  Groshong  (1972) i n d i c a t e s a h i g h  brittle  ( J . V.  regime  cataclastic  The  Here,  a  and  best 5 cm  Westcoast  features  deformation  and  wide m y l o n i t i c  shear  rocks  by  well  a  by high a  developed  transition  from  i n the  i s shown i n i s deformed  brittle  study  Figure into a  37.  Z-fold  fracture.  and by  its  trend,  abrupt  most of  its strike  differential  near  the  fault  the  feature  i n the  erosion  Muller, Vancouver  it  the is  the  juxtaposes Pacific  fairly  i n l i t h o l o g y and  Rim well  topography.  however, r e a d i l y a p p a r e n t  area of  the  b o u n d a r y between  with  therefore,  i s not,  named  along  study area,  Complex  change  fault,  e t a l . , 1974;  marks t h e  B e l t s . In  Crystalline  an  (Muller  m a r g i n and  Pacific  crustal  mappable  s t r u c t u r a l expression  to  by  Muller  regionally  Westcoast  constrained  due  fairly  a l s o present  example  western  Complex,  along  are  northwest-trending  is a  Insular  Its  the  t r a n s i t i o n to  the  indicating  illustrative  Fault  Island's  the  of  described  rate at  by  and  Faults  A major  1977),  Analysis  comm.). The  evidenced  subsequently disrupted  Brittle  strain  the  fabric.  to b r i t t l e  area.  ribbons.  of  twinning  s i m i l a r to that  Ross, p e r s .  is clearly  Mesoscopic ductile  a method  deformation  show m u l t i p l e  i n t o long  calcite  temperatures  using  ductile  mapped. T h i s  the  more h i g h l y  r e s u l t i n g i n p o o r e x p o s u r e of  is  likely  fractured the  fault  58  Fig. 37 S k e t c h from a p h o t o g r a p h showing d u c t i l e d e f o r m e d i n t o a Z - f o l d and s u b s e q u e n t l y d i s r u p t e d f r a c t u r e , W e s t c o a s t C r y s t a l l i n e Complex.  s h e a r zone by b r i t t l e  59  zone.  Its  general  structural  a p p e a r s t o be o f a b r i t t l e Numerous  synthetic  approximately interpreted movement likewise  20  to  as R i e d e l  along  faults to  shears  horizontal  on  evident,  NNW  and  Westcoast  oriented  Fault  related to transcurrent Exposure of these appear  one o f t h e s e  dextral  trending the  fault.  poor, but they a l s o  Slickensides  where  nature.  25°  this  expression,  to  fault  be  dextral  features i s  brittle  surfaces  are  shears.  indicated  near  motion.  Conclusions In  summary,  displayed  suggests that  exemplified  with by  strain there  possibly  perhaps  cooling  brittle  can  elongated  regional  two  is a  evidence  components  to  this  1) a s h e a r  component,  rotated  xenoliths,  stresses  associated  and  tectonic  of f l a t t e n i n g , e v i d e n c e d  stretching  and u p l i f t ,  regime,  lineations,  the d u c t i l e deformation  resulting in cataclasized development  of  major  a t l e a s t at the s t r u c t u r a l l e v e l  be i n t e r p r e t e d  feature  as  a  emplacement.  f r a c t u r e s . The  faults,  structural  C r y s t a l l i n e Complex  unison;  and 2) a component  to granitoid  way t o a b r i t t l e  going  to  in  f o l d s , b o u d i n s , and  With  and  may have been  by v a r i a b l y  subduction,  response  notable  i n a d u c t i l e regime. L i m i t e d  acting  related  minor  most  by r o c k s o f t h e W e s t c o a s t  heterogeneous  strain,  the  a s an e x t e n s i o n  now  or c o n t i n u a t i o n  gave  mylonites throughexposed, of  this  60  brittle  regime.  61  CHAPTER IV METAMORPHISM  The obvious  determination goal  a  rock  i n the area  Metasediments revealing  type  conditions terrains.  u s e f u l f o r such  studied.  to  p r e v i o u s l y d e s c r i b e d appear  by w i d e s p r e a d  superposition  conditions  (intra-  of  Aluminous  the  Westcoast  t o have been  clastic  and  E s t i m a t i o n of c o n d i t i o n s f o r these  made d i f f i c u l t  i s an  determinations, i s  Precursors  quartzo-feldspathic  sediments.  likely  metamorphic  i n s t u d i e s of metamorphic  metapelite, lacking  of  less  calcareous  parageneses i s  r e t r o g r a d e metamorphism and t h e  regional  and c o n t a c t  metamorphic  and p o s t - J u r a s s i c ) .  Amphibolites Metamorphism o f m a f i c Crystalline  Complex  igneous  has r e s u l t e d  f a c i e s assemblage of i n t e r m e d i a t e green  hornblende.  metamorphic amphibolite Engel  absence  clinopyroxene facies  and E n g e l  anatectic  The  is  rocks  in  i n t h e common to calcic of  suggestive  of  i n Westcoast  rocks  The  suggests  or  middle  melting.  Whether  the r e s u l t  of l o c a l  discernable  from  this  of  to  initiate  i s a r e g i o n a l phenomena o r  superposed the  presence  that, at least  partial  not  and  c o n d i t i o n s b a s e d on o b s e r v a t i o n s made by  metamorphic c o n d i t i o n s were s u f f i c i e n t  is  amphibolite  hornblende  locally,  merely  Westcoast  plagioclase  brown  (1962) i n t h e A d i r o n d a c k s .  melts  the  scope  contact  metamorphism  of  study.  this  A  62  temperature  o f T > 600°C b u t < 1000°C  dehydration  temperature;  Wyllie,  1968;  the Westcoast  Millhollen  rocks  some c a s e s with  e t a l . , 1974) f o r metamorphism o f i s inferred.  metamorphic  (determined  by X - r a y  from  assemblages  thin  diffraction)  to  be  of  phase  i s assumed  reaction  with  HC1  carbonates  and  to  are l i s t e d  the  i n the presence  assemblages localities,  i n Table  Ritchie  Bay  Tertiary  Catface  limited  two  Lemmens  (52-7B).  The  by  p a r a g e n e s i s . The main based  on  rapid  stability  of  other  These  representative  separate  Inlet  proximity  i along  assemblages a l l  calcite  of q u a r t z .  characterize northern  be  exhibited  s e c t i o n s and v e r i f i e d i n  a silica-saturated  carbonate  the  1962; Lambert and  p e r t i n e n t r e a c t i o n s . The c a l c s i l i c a t e  appear  amphibole  ^  Characteristic these  Yoder and T i l l e y ,  Amphibolites  Calcsilicates  (approximate  calcsilicate  (50-4)  and  northern  of the l a t t e r  to the  I n t r u s i o n makes i t of q u e s t i o n a b l e v a l u e i n  determination  of  boundary  conditions  for  Jurassic  metamorphism. Stability on  an  compiled al.  fields  isobaric from  T-X  f o r these  C 0 2  diagram  calculations  two l o c a l i t i e s ( F i g . 38) drawn  of R i c e  (1983)  and  are indicated f o r 5 kb and Slaughter  et  (1975).  • f The  Lemmens  Inlet  d i a g r a m by t h e p r e s e n c e wollastonite  paragenesis of g r o s s u l a r i t e  i n rocks c o n t a i n i n g both  is  limited  on  this  and u s u a l a b s e n c e o f calcite  and  quartz,  63  TABLE 1. C a l c s i l i c a t e Sample  no.  parageneses and p e r t i n e n t  Parageneses  reactions  Reactions  Lemmens Irt l e t 50-4a,b,c  cc  - qtz  - di  50-4f  cc  - qtz  50-4h  cc - qtz - d i c c - q t z - wo q t z - d i - g r - sc  cc + q t z  di + v a p o r  tr cc  +  cc  + q t r == wo + CO  qtz •= wo +  2  c c + ojtz = wo + co t r + cc q t z = d i + vapor zo + c c + q t z gr + vapor + wo t2 r + = an a ?  +  <3  50-4 j  qtz  - d i - gr - cc  zo cc + q t z = 25 + v a p o r c c + q t z = WO t r + cc + q t z d i + vapor = an q t z wo gr  R i t c h i e B< 52-7B-1  wo - sc - gr  52-7B-2  t r - an qtz - d i wo - q t z - d i  - di  t r + cc + q t z d i + vapor zo + cc + q t z vaDor 25 + cc q t z = WO + cc tr cc  + ta + q t z tr + cc + q t z = a i + q t z = WO +  an an  +  + vapor + vapor  =  c6  <  3  WO  zo  r=  -  2  qtz cjtz  Notes: S t a b l e p o r t i o n s of the r e a c t i o n s a r e underlined. an=anorthite, cc=calcite, di=diopside, gr=grossularite, qtz=quartz, ta=talc, tr=tremolite, wo=wollastonite, zo=zoisite. Sample locations a r e l i s t e d i n Appendix 1 and shown i n F i g u r e 2 ( i n p o c k e t ) .  64  F i g . 38 H 0 - r i c h p o r t i o n of 5 kb T-X o diagram showing stability fields of observed calcsilicate assemblages; h o r i z o n t a l l i n e s : Lemmens I n l e t exposure, vertical lines: R i t c h i e Bay e x p o s u r e ; d o t t e d l i n e shows t h e 2 kb p o s i t i o n o f the reaction gr+qtz=an+wo; solid and d o t t e d reaction b o u n d a r i e s a r e from R i c e ( 1 9 8 3 ) , d a s h e d a r e from S l a u g h t e r 2  et  al.  (1975).  C  2  65  corresponding  to the  equilibria  vapor  and  cc  on  the  high  temperature  +  quartz  section  ( 710°C  to  the c a l c i t e  cc  imply  and  The  Ritchie  wollastonite  is  + C0  primarily  the  total  Bay  to r e t r o g r a d e  field.  controlled  by  the pore  pressure.  by  a low  However,  i t i s much more common  contact  metamorphism. I t s v a r i a t i o n  study  area  easily  evident a  Ritchie  Bay  most  fine  fluid,  in  this Bay.  by  Contact  immediately  and  gr + q t z  + wo.  back  boundary  of  well into  the  wollastonite of C 0  which  2  composition  and  at high pressures facies  is  rocks  i n the  C 0 / H 0 vapor  phase.  2  2  product  of  shallow  within  c o n d i t i o n and  is  p r o x i m i t y t o the metamorphic  most  effects  amphibolites  are which  t e x t u r e . Assuming t h a t  in equilibrium  with  the p a r a g e n e s i s  on  the  The  at  temperature  the  the  Catface  assemblage of gr-qtz-an-wo  places  = an  t o be  in s t a b i l i t y  adjacent  grained hornfelsic  the c o l l e c t i v e  a  latter  case  p a r a g e n e s e s were  limiting  boundary  in  in Ritchie  exhibit  pore  to f a v o r the  explained  Intrusion also  tends  as  a  reaction  fluid  in granulite  is facilitated  thin  retrograde. This  pressure  Its stability  i t s occurence  i n one  indicates  stability  the p a r t i a l  and  grossularite  metamorphism.  appears  The  +  It is limited  of  exposure are  paragenesis  gr  i t i s doubtful that a l l  on  by  Adirondacks  wollastonite  in this  prior  2  qtz  5 kb). T e x t u r a l evidence  dependent  vapor  evidenced  the presence  r o c k s were c l o s e t o t h e  stability  strongly  by  +  respectively.  2  end  + an/zo  + q u a r t z , but  quartz  t h a t the  + C0 ,  minor  calcite  + q t z = wo  is  at  containing  reaction  may  + q t z = wo  cc  the same  i s the  reaction  which  this  66  reaction  takes  indicated 1983). the  by  the  The  is  fairly  Strain  an upper  suggests  of on  the observed c a l c s i l i c a t e  assemblages  facies.  (>  2  The  they  react  evidence  do .  exposure  during  deformation  from  assemblages  f a c i e s as w e l l  tends kb)  to to of  about form  to  as  600°C +  below  but  situ  indicate  with  a s t h e medium  grade  melting  the Westcoast that  quartz  higher  breaks 2 kb  +  down  in  the  (Helgeson et a l . ,  +  plagioclase  liquid. observed  Migmatites,  minimum m e l t  in  pressure  i n t h e p r e s e n c e of w a t e r , +  The  i s consistent  the  quartz  sillimanite  Metasediments, anatexis,  favor  muscovite  650°C  partial  equivocal.  o c c u r e n c e of m u s c o v i t e  o f q u a r t z above  up  they  Inlet  i s also  of q t z - p l - g t r b i - m s  1978). Above 2 kb, m u s c o v i t e stable  conditions  metasediments  hornfels  paragenesis  presence  but  o f a p p r o x i m a t e l y 700°C  from t h e Lemmens  of metamorphic  hornblende  alternative  limit  reheating,  Metasediments  u b i q u i t o u s assemblage  this  lower  Jurassic  i n e x c e s s o f 600°C  quartzo-feldspathic  amphibolite  will  p e r s . comm.).  Estimation  the  Rice,  during  of c a l c i t e  Quartzo-feldspathic  in  solution  temperature  temperature  temperatures  ( J . V. R o s s ,  line;  as  slightly.  based  analysis  (dotted  solid  c o m p l i c a t e d by p o s s i b l e T e r t i a r y  provide  pressure-sensitive  a t 2 kb  of p l a g i o c l a s e  estimation  metamorphism  is  i t s position  effect  temperature An  place  There in  are where  was  no  Westcoast  i f formed  by i n  temperatures  were  67  attained,  at  composition  with  melting  is  granite  only  water,  slightly  39. The e f f e c t of  the  (1978) i s a l s o observed  of  shown. The  1977).  more p r o f o u n d  point  effect  of  this  amphibolite of  that for  This  may  as  invariant  that  on  the  determined  by T r a c y  composition  i n the  p  H 2  appears  (1972)  point  muscovite  p o i n t shown i n  on i t s p o s i t i o n ,  Kerrick  initial  imply  composition  5  displacement  t o have  particularly  has  t o about  indicated  7 . 5 kb w i t h  0• 5.  =  2  It  should  conditions  grade.  be  noted  that  equating  the  metamorphic  f o r t h e m e t a s e d i m e n t s and f o r t h e m i g m a t i t e s  erroneous.  faulting  is  than  i s An,., . Varying X  pressure.  be  of  temperature  plagioclase  to  HO  rocks  plagioclase  respect  X  the  higher  invariant  assemblages  even  with  excess  For  c o n d i t i o n s were above t h e i n v a r i a n t  position  an  locally.  (=*625-700°C; W y l l i e ,  pressure Figure  least  I t i s q u i t e conceivable that  could  juxtapose  rocks  An e s t i m a t i o n of p r e s s u r e  of  post-metamorphic  different  as being  may  metamorphic  g r e a t e r than  4  kb  t h e r e f o r e made w i t h c a u t i o n .  Conclusions In  summary,  t h e c o n d i t i o n s d u r i n g metamorphism of t h e  Westcoast C r y s t a l l i n e the  middle  amphibolite  is  not u n e q u i v o c a l  T  =  from  Complex a p p e a r  600-700°C, the data.  facies,  t o be  although  f o r the reasons  consistent this  discussed.  P > 4 kb, and f a i r l y  low X  c 0 2  with  determination Nevertheless, are inferred  68  Fig. 39 P o ~ d i a g r a m showing t h e A b - a b s e n t and A n - a b s e n t i n v a r i a n t p o i n t s i n the system CKNASH; possible stability f i e l d f o r q u a r t z o - f e l d s p a t h i c metasediments of the Westcoast Crystalline Complex i s indicated by t h e v e r t i c a l l y l i n e d a r e a ; m o d i f i e d from T r a c y ( 1 9 7 8 ) . T  H ?  69  CHAPTER V GEOCHRONOLOGY OF THE WESTCOAST CRYSTALLINE  COMPLEX  AND RELATED ROCKS  One the  o b j e c t i v e of t h e p r e s e n t  Westcoast  Wark/Colquitz represent and  Crystalline Complex  the  Complex  and  products  study  to  as  is  coeval  determine  of J u r a s s i c  Vancouver Group r o c k s  was t o d e t e r m i n e  if  with  they  migmatization  proposed  by  if the truly  of S i c k e r  Muller  et a l .  (1974). For  this  study,  various  lithodemic  Complex  and  other mineral for  the  and t h r e e  techniques  fission  f o r z i r c o n and zircon  dates  e i g h t K-Ar m i n e r a l  dates,  Rb-Sr  U-Pb  whole  rock  Appendix  isochron  were d e t e r m i n e d .  1  with  analyses  a n d 40  brief and  Sample and  sample  analytical  3.  Complex  Crystalline  fractions,  yielded plot  from  Crystalline  i n F i g u r e s 2 ( i n pocket)  separates  analyses  one  i n Appendix  Westcoast  ten  of t e n  R e s u l t s of i s o t o p i c  Crystalline  Westcoast  and p r o c e s s e d  track dates  in  are listed  Zircon  the  samples,  dates,  listed  descriptions.  Westcoast  rock  are indicated  also  of  Wark Complex  six different  locations are  units  samples were c o l l e c t e d  separates. A t o t a l  t h r e e Rb-Sr b i o t i t e date,  several  from  four  Complex,  a total very  localities  split  into  within various  the size  o f t e n U-Pb a n a l y s e s . N i n e o f t h e close  to  c o n c o r d i a and i n d i c a t e  1 2 3 4 5 6 7 8  C a t f a c e I n t r u s i o n (RHP) Westcoast quartz d i o r i t e giu'iss W e s t c o a s t A m p h i b o l i t e (27-22) T o f i n p I n l e t p l u t o n (27-5) I n d i a n I s l a n d i n t r u s i o n (26-2) q u a r t z d i o r i t e o f B l a c k R i v e r (WCT-3) Wark d i o r i t e (V8) Wark d i o r i t e (V9)  F i g . 40 S a m p l e l o c a t i o n map f o r i s o t o p i c a n a l y s e s . D e t a i l e d l o c a t i o n s a r e l i s t e d i n A p p e n d i x 1. Map l e g e n d a s i n F i g . 1.  71  crystallization  ages  for rocks  Complex  ranging  data  d i f f e r e n c e s are  no  age  from  176  c o n s i s t e n t evidence The  Indian  fractions zircons.  of  (Fig.  are  42),  concordant contain  shown the  not  a t about  coarser Ma.  41.  older  Pb  was  fraction  i s the  The dates  196  two  pluton yielded  results,  189  ± 8 Ma,  are  the  age  shown size  in Figure splits  closely  averaging  183  fraction  are  grouped  i 3 Ma shown  implies that  size cloudy  concordia  diagram  seen  t o be  appears  to  t o be  laboratory.  i t w o u l d be  nearly  the  If  the  expected  whereas the  to  finest  contamination.  two  nearly  ( F i g . 43).  concordant  The  i s r e p o r t e d here from  average as  the  the  of  best  45-75y  44.  of  zircon  from Meares and  (Fig.  is  fraction  o f emplacement. G r a i n s  gneiss collected  yielded  i 3 Ma  slightly  i s suspected  s u s c e p t i b l e to  182  fraction  zircons  most  three  fraction  fractions,  and  of  Three  coarser  there  size  are  the  authentic  i 3 Ma  estimate  diorite  one  Tofino Inlet  of  these  was  geologically  a  this  in  to  the middle On  this  component.  yielded  finest  and  sample c o n t a m i n a t i o n  i n the  r e s o l v e d and  fractions The  o l d e r Pb  ± 8 Ma.  clear  g r a i n s from  of  more e v i d e n t  Within  189  intrusion  result  be  to  to subhedral,  176  a t r a c e of  Crystalline  older zircon  in Figure  two  the Westcoast  clearly  of any  Representative  (75-150tt)  ± 2 Ma  Island  euhedral  of  Grains  46.  the  development  contemporaneous with  emplacement  sample  Island  essentially  45).  in Figure  from a  The of  of  quartz  (sample  11-6)  concordant from  the  concordance  dates 45-75M  of  these  gneissic  layering  i n the Middle  Jurassic,  F i g . 41 P h o t o m i c r o g r a p h o f r e p r e s e n t a t i v e z i r c o n g r a i n s (75150M) from the Indian Island intrusion, Westcoast C r y s t a l l i n e Complex.  73  Oil . Z ^ diagram, Indian W e s t c o a s t C r y s t a l l i n e Complex. 4 2  (  oncor  a  Island  intrusion  uaxun  (26-2) v^o ^;  74  F i g . 43 Concordia diagram, Tofino W e s t c o a s t C r y s t a l l i n e Complex.  Inlet  pluton  (27-5)  75  F i g . 44 P h o t o m i c r o g r a p h 75M) from the Tofino C r y s t a l l i n e Complex.  of r e p r e s e n t a t i v e z i r c o n g r a i n s (45Inlet pluton (27-5), Westcoast  76  F i g . 45 C o n c o r d i a d i a g r a m , quartz Westcoast C r y s t a l l i n e Complex.  diorite  gneiss  (11-6) m o ;  77  F i g . 46 P h o t o m i c r o g r a p h o f r e p r e s e n t a t i v e z i r c o n g r a i n s (4575M) from quartz diorite gneiss (11-6), Westcoast C r y s t a l l i n e Complex.  78  or  that  the z i r c o n s  and  deformation A sample  along 40)  2 0 6  two  pictured  2 3 8  U  date  ± 3 Ma. O n l y without  a  this  and  therefore  date  2 3 5  with  from  and  Ma  d i s c o r d a n t with U  Ma  date  can  through split  biotite  o f 171  be. g i v e n i s that  alteration d i d n o t , and  from  Westcoast  the rocks c o o l e d past the  younger  (see  Chapt.  VI),  t h a n U-Pb a g e s ,  which  of c r y s t a l l i z a t i o n .  inclusions  usually shows  contribute  4  or a c c e p t .  slightly  rocks  f o r t h e same  yielded  The 45-75M  a t 187 ±  shows much  little  Hornblende  of p l a g i o c l a s e . some less.  Both  t o t h e K or Ar  the Indian Island  Biotite  alteration  intrusion  o f 172 ± 6 Ma. T h i s i s i n good agreement  Biotite River  Pb/  f o r these minerals  and h o r n b l e n d e will  2 0 7  the f i n e r  a t which  the time  poikilitic  Hornblende date  while  the time  Westcoast  impurities  is slightly  collected (see F i g .  zircon.  o f 178 ± 12  to explain  approximate  chlorite,  of  e x p e r i e n c e d Pb l o s s  temperatures  is mostly from  date  d a t e s on h o r n b l e n d e  are  closely  fraction  event,  indicate  blocking  heating  a n a l y s e s . The g e o l o g i c i m p l i c a t i o n  is difficult  rocks  fractions  i n F i g u r e 47 i s c o n c o r d a n t  an a v e r a g e  reheating  K-Ar  s o u t h o f Pachena P o i n t  size  the c o a r s e r f r a c t i o n or  of B l a c k R i v e r  of 166 i 2 Ma and a  further  by J u r a s s i c  rocks.  Trail  4 8 ) . The 75-150M  Pb/  reset  of the q u a r t z d i o r i t e  furnished  (Fig. a  of o l d e r  the Westcoast  fraction  were t o t a l l y  of  to  these  observed. gave a K-Ar  w i t h t h e U-Pb  sample.  and h o r n b l e n d e K-Ar d a t e s  from  the quartz d i o r i t e  o f 162 ± 6  Ma  and  144  of B l a c k ±  5  Ma,  79  F i g . 47 P h o t o m i c r o g r a p h o f r e p r e s e n t a t i v e z i r c o n g r a i n s (4575M) from the quartz d i o r i t e of Black River (WCT-3), W e s t c o a s t C r y s t a l l i n e Complex.  Fig. 48 C o n c o r d i a diagram, (WCT-3), Westcoast C r y s t a l l i n e  quartz d i o r i t e Complex.  of  Black  River  81  respectively. blocking that  is  normally  hornblende date  (sample  near  exhibited  by  the  impeded  and  by  Rb  intrusion Sr  should,  biotite  Westcoast  date  K-Ar  leaves  the  of  the  Amphibolite  on M e a r e s I s l a n d 151  ±  cooled a  K-Ar  5  basaltic  resetting  fabric  reflects the  the  400-550°C  metamorphic to  As  genetically  date  through  precursor  Ma.  structural  i s b e l i e v e d t o be  represents  the absence  age.  the  Age  Westcoast  and/or g a b b r o i c ,  (i.e.  Ar-loss  of z i r c o n s i n t h e s e  is  from  rocks,  and  contents. mineral  Diorites  plagioclase,  and  K-Ar  Jurassic  2)  regression). A  heavily  a  w h i c h were l i k e l y  Rb-Sr  Westcoast  8 6  from  emplacement. The  truly  1)  low  Two  The  than  low.  amphibolites  of  hornblende), their  biotite  ( s e e below) w h i c h  which the a m p h i b o l i t e  Amphibolites,  Sr/  a younger date. Rb-Sr  gives  to g r a n i t o i d  at  and  t h e mouth of M o s q u i t o H a r b o r  determination  8 7  by  conventional  (^180-260°C) i s lower  m e n t i o n e d , t h e metamorphism and  isotherms  3)  yield  separate  27-22)  previously  i n t h a t the  (=*400-550°C) ,  puzzlingly  Hornblende  time  for b i o t i t e  confirmed  collected  anomolous  hornblende  therefore,  related  is  temperature  for  date  This  isochrons  (see Appendix  (whole r o c k ,  b i o t i t e ) determined of  15  Ma  ratio  ( F i g . 49a).  The  weighted  consequently,  0.70356  by  biotite  the date  ±  f o r the  i n d i c a t e s a date of  151  obtained  3 for a n a l y t i c a l  four-point isochron and  were  b e c a u s e of represents  data  and  hornblende, Indian  Island  an  initial  isochron  slope i s  and  i t s h i g h Rb/Sr the  from  time  since  ratio, biotite  82  became  closed  temperature thus  about  passed  zircon for  with 300  thru  ± 2 5 ° C ) . The  this  point,  By  an  Indian  temperature  r e f e r e n c e i s o c h r o n of  comparison.  rock  r e s p e c t t o r a d i o g e n i c Sr  176  drawing  initial  Ma  this Sr/  8 7  at  8 6  loss  Island  151  ±  intrusion  15 Ma  i s shown  in  ratio  ago.  The  Figure  isochron through Sr  (closure  of  the  49a whole  0.70354  is  indicated. The of  Black  yields of  four-point mineral River  is similarly  a date  0.70341  of  169  Rb-Sr Westcoast fairly  best-fit 143  Ma,  The  lower  analyses Crystalline  wide s c a t t e r isochron and  dominated  t 3 Ma  ( F i g . 49b).  indicates a slightly  i s o c h r o n f o r the q u a r t z  on  w i t h an  178  a Sr  error  of  zircon  dates)  w i t h an  initial  Indian  Island  of  8 6  Sr  of  and ratio  isochron  0.70329.  lithologies Appendix  3)  from  the  exhibit  ( F i g . 50).  Ma.  is  reflected  An. i s o c h r o n of 8 7  Sr/  and  8 6  Sr  Black  in  177  Ma  ratio River  the  of  rather  (average of  a The  I r e g r e s s i o n ) i n d i c a t e s a date  t h e wide s c a t t e r 27  Sr/  e v o l u t i o n diagram  large  (average  (see  8 7  biotite  reference  ratio  varied  Complex  the  initial  zircon  initial  for  (York  Ma  by  diorite  of  0.70342  intercepts) is  shown f o r r e f e r e n c e . The analyses varying  d e g r e e of  scatter  exceeds experimental degrees  of a l t e r a t i o n ,  assimilation  of  the p r o t o l i t h  isotopic  more  exhibited  than  marine  one  error,  by  and  possibly  the may  with  whole  result  compositions cogenetic  of S r ,  suite  2)  from  seawater,  s e d i m e n t s w h i c h c o u l d have  rock 1) or  modified  inclusion  of  ( i . e . amphibolites  83 0.706  a)  Indian island intrusion  0.705<  86  Sr  • Whole Rock • 0.704  Hornblende  0 Plagioclase •  0  Biotite  0.5 87  1.0  Rb/ Sr 86  0.7 14  b)  Black River quartz diorite 0.7 12* \* #  ^  0.7 10-  0.708"  3L  r  6  Sr  0.704-  0.7033  0.703  0  0.1  0.2  0.3  0.4  2  3  8 7 —  ,  / 86^  'Rb/" r S  Fig.  49  a) S r e v o l u t i o n d i a g r a m , I n d i a n (26-2). b) Sr e v o l u t i o n d i a g r a m , q u a r t z R i v e r (WCT-3).  Island diorite  intrusion of Black  84  Rb/"sr  F i g . 50 S r e v o l u t i o n d i a g r a m , C r y s t a l l i n e Complex.  whole  rock  analyses,  Westcoast  85  vs.  granitoids)  different behavior or  so  ages so  that  and  the  points  initial  represent  ratios,  t h a t r o c k s have v a r i a b l y  or  rocks  3)  gained  of  open-system  or l o s t  Rb,  Sr  radiogenic Sr. Comparison  Intrusions at (Armstrong,  of  prep.)  data  granodiorite intrusions  is  includes  and  and,  hence,  throughout shown  best-fit  indicates  a date  T h i s date  i s in excellent  of  181  Crystalline  variability  a  isochron i 7 Ma  with  Vancouver  of  more  the  The  in addition  greater for an  Island Island  fractionated to  range  the  dioritic of  Rb/Sr  combined  intercept  agreement w i t h U-Pb  Complex, and  and  f o r the I s l a n d  i n F i g u r e 51.  analyses  shows  The  ratio  with data  quartz monzonite,  ratios.  Westcoast  analyses  scattered sites in  Intrusion  these  of  0.70360.  dates  for  t h e m a g n i t u d e of  initial  ratios  data  are  the  initial likewise  similar. The  similarity  demonstrated  between  granitoids  is  relationship. nature  of  in Island  completely  The  intrusive  plutons  from  suggests  t h a t t h e y may  of  Island  the  The  Westcoast  Crystalline in  G.S.C. d a t e  age  264  initial  Intrusions  and  compatible  with  style  less  and  ratio  and,  determinations  a  Complex a r e  ± 7  cogenetic  fractionated  with  the  the  obtained  internally  Bonanza for  the  c o n s i s t e n t and  previously  (Muller et al.,1974).  Complex  equivalents  indirectly, thus  thus  Westcoast  represent deeper c r u s t a l  conflict of  and  the Westcoast C r y s t a l l i n e  Intrusions  Volcanics.  clearly  age  published  R e s o l u t i o n of  86  0.712  Fig. 51 Westcoast Intrusion  Sr evolution diagram comparing data for the Crystalline Complex (this study) with Island data (Armstrong, i n p r e p . ) .  87  this  d i s c r e p e n c y by  location be  further  i s paramount  investigation  f o r an  of t h e same  unequivocal  sample  interpretation  to  made. Zircon  and  apatite  were d a t e d u s i n g Sample  1a  low  150-200°C;  et  were  track  al.,  Indian Island method  counting  (Naeser,  Harrison  (1977).  The  errors  using  the  standard large  ( s e e F i g . 5 2 ) . The  (for a blocking  interval  of  quoted error  because  zircon  temperature  et al.,1979),and a p a t i t e  temperature  1976).  t e c h n i q u e s a t U.B.C. a r e  e t a l . ( 1 9 7 9 ) . They a r e  densities  intrusion  yielded  interval  gave  31  75-120°C;  of  ±  19  of Ma  Harrison  1979).  The  range  isotopic This  track  approximated  ± 20 Ma  a blocking  the  by H a r r i s o n  of J o h n s o n  a d a t e of 80  (for  and  in d e t a i l and  equation fairly  fission  preparation  described are  the  from  of  systems  will  blocking  temperatures  allows a cooling  be d i s c u s s e d  history  f o r the  t o be  various  determined.  i n the next c h a p t e r .  Wark Complex For dated  purposes from  Fig.  40  for  U-Pb  nearly a  2 0 7  ±  1.5  analysis.  furnished  The  45-75M  concordant with a 2 3 5  U  also Ma  d a t e of nearly and  two  samples  of d i o r i t e  were  Sample V8  (see  Wark Complex n e a r V i c t o r i a .  for location)  Pb/  split,  the  of c o m p a r i s o n ,  a  168  2 0 6  2  size  split,  Pb/  ±  two  2 3 8  Ma  U  shown  (Fig.  Pb/  2 3 5  U  d a t e of  2 0 6  171  of  in Figure  d a t e of  c o n c o r d a n t , gave a 2 0 7  fractions  165  54).  Pb/  2 3 8  ±  1.5  The U  ± 2 Ma.  zircon 53, Ma  and  75-150M  date of The  was  168  average  88  Fig. 52 Photomicrograph of a p a t i t e from t h e I n d i a n I s l a n d  spontaneous f i s s i o n i n t r u s i o n (26-2).  tracks  in  89  Fig. 75M)  5 3 P h o t o m i c r o g r a p h of r e p r e s e n t a t i v e from t h e Wark Complex ( V 8 ) .  zircon  grains  (45-  90  Fig.  54 C o n c o r d i a  d i a g r a m , Wark d i o r i t e  (V8).  91  date  of  168  ± 3  designation  of  reported  Ma  is  age  by M u l l e r  therefore  for  preferred  as  the  t h e Wark Complex. The  (1977) was  not  observed  and  best  discordance  is  therefore  suspect. Hornblende of  133  ±  collected Ar  separated  5 Ma. about  hornblende  from  Another 12  k i l o m e t e r s to the  date  of  granitoids  associated  of  177  ± 7  southeast  Colquitz  few  Complex with  Crystalline  a K-Ar  i n number,  were  the  Complex  date  (sample  V9)  produced  a  K-  Ma.  t h e Wark Complex and  contemporaneously Westcoast  yielded  sample o f Wark d i o r i t e  These d a t e s , a l t h o u g h that  sample V8  strongly perhaps the  emplaced  Island  suggest  more  or  Intrusions  in Middle  Jurassic  closely less  and  the  time.  Catface Intrusions Several  epizonal plutons  of  recognized  along  t h e west c o a s t  and  1968)  and  Carson,  Tofino  pluton,  Intrusions. have  Kennedy  P r e v i o u s K-Ar  indicated  a  Sydney  Lake  i n a g e s of  have  pluton,  p l u t o n s and  32  for  been  Island (Muller  Inlet  determinations  range  age  of V a n c o u v e r  i n c l u d e the  the  Tertiary  the  these  t o 59 Ma  the  Catface plutons  (Wanless et  al.,1974). Figure size  55  shows t h e  fractions  collected  from  Both  l a r g e and  42  Ma,  the  of  zircon  Ritchie  respectively,  results  Bay  of  from  on M e a r e s  small f r a c t i o n s indicating  U-Pb the  analysis Catface  Island  on  Intrusion  (sample  are concordant  a crystallization  two  RBP).  at  40  and  age  of  41  92  0.01S  80  Catface Intrusion : Ritchie Bay  0.01  206  Pb  238  U  60  40  •75 u 75-ISOjt  0.0084  41i1  20  o.os 207  (RBP).  5 5  C  0  n  c  °  r  d  i  a  diagram,  Pb/  238  u  Catface Intrusion,  R i t c h i e Bay  93  ±  1  Ma.  Z i r c o n s from  t h e 45-75/u s p l i t  a r e shown  in Figure  56. K-Ar locality  analyses  on h o r n b l e n d e  yielded  dates  respectively,  observed biotite Ma  ratio  reference  13  of  i s probably  8 7  The is  date  Rb/Sr  initial  Sr/  ±  1  48  Sr  ±  analysis  ratio  Ma  the  in  large  error  to  57  from  older,  but  difference  error  i n the The  41  i n d i c a t e s an  curve  are presented  for  this  i n the next  this  intrusion  a g a i n due t o low t r a c k in  t o o low f o r a m e a n i n g f u l  cooling  ± 1 Ma,  fluorescence.  for apatite  proved  implications  somewhat  Figure  same  data.  of a n a l y t i c a l  ( F i g . 5 8 ) . The t r a c k d e n s i t y  The  34  ( F i g . 5 7 ) . The  density  made.  and  the  o f 0.70372.  12  be  from  t h e U-Pb  by X - r a y  shown  t r a c k date  Ma,  7  a reflection  isochron  8 6  Ma  isochron gives a  fission ±  37  i n good agreement w i t h  A Rb-Sr m i n e r a l inaccurate  of  and b i o t i t e  associated  zircon  determination  t o be  intrusion chapter.  and  its  94  F i g . 56 P h o t o m i c r o g r a p h of r e p r e s e n t a t i v e z i r c o n g r a i n s 75M) from t h e C a t f a c e I n t r u s i o n , R i t c h i e Bay ( R B P ) .  (45-  95  nliwi (RBP);  5 7  . * o l u t i o n diagram, C a t f a c e symbols as i n P i g . 4 7 . S r  e  Intrusion,  Ritchie  Bay y  96  97  CHAPTER VI COOLING HISTORY  The chapter in  geochronometric a r e summarized  order  al.,  i n Table  of d e c r e a s i n g  apparent  present  curves,  from  versus  the  possibilities  in  last  to right  (Harrison time,  implications  regarding  the  left  temperature  of temperature  cooling  various  presented  2, l i s t e d  blocking  1979). On a p l o t  define  results  et  the dates of  which  emplacement  and  uplift.  Westcoast The widest best  Crystalline data  f o r the Indian  constrained cooling Three  graphically consists of  cooling  general  possible  59.  into  of  this  Model  indicated  by  slow and r a p i d  the  1.  from  An  case,  the  by t h e  alternate  cooling  curve  thermal  implies  t r a c k s and c o m p l e t e  cooling  shown  indicated  I n t r u s i o n s and  data.  are  interpretation  the subsequent  (Models 2 and 3 ) . In t h i s  Crystalline  intrusion  present  the  provides the  data  simplest  of the  the  account  fission  covers  and t h u s  i s u n r e s o l v a b l e from  the Catface  of z i r c o n  of  The  to  curve  which  takes with  the a p a t i t e not  Figure  crystallizaton  associated  is  intrusion  f o r t h e Westcoast  interpretations  in  interpretation  annealing  curve  of p r o g r e s s i v e c o o l i n g  apparent  in  Island  range o f b l o c k i n g t e m p e r a t u r e s  Complex.  time  Complex  data pulse  partial  r e s e t t i n g of  the c o o l i n g  rate  M o d e l s 2 and 3 r e p r e s e n t  rates,  respectively.  Table 2  Summary o f age d e t e r m i n a t i o n s l i s t e d U-Pb z•7i irY c -orn nn  Sample  (voire)  K-Ar hornblende ( 4 00-5 50° C)  In order o f d e c r e a s i n g b l o c k i n g temperature (L to R) Rb-Sr biotite CV300°C)  Westcoast Indian I s . intrusion  176 ± 2  172  ±6  quartz d i o r i t e o f B l a c k R. (WCT-3)  178 ± 12  144  ± 5  Tofino Inlet p l u t o n (27-5)  189 ± 8  quartz d i o r i t e g n e i s s (11-6)  183 ± 3 151  ± 5  (26-2)  Westcoast Amphibolite  (27-22)  Crvstalline  K-Ar biotite (180-260°C) IkjjjnDiex  151 ± 15 1  169 ± 3  F i s s i o n Track zircon apatite (150-200 C) (75-120 C)  80 ± 20 162  31 ± 19  ± 6  Wark Complex d i o r i t e (V8) diorite  168 ± 3  (V9)  133  i 5  177  i 7 Catface I n t r u s i o n s  quartz d i o r i t e (RBP)  41 ± 1  37 ± I  48 ± 7  34 ± 1  Notes: B l o c k i n g temperatures a r e from H a r r i s o n et a l . , 1979. deviation. 'Anomalously low, not used f o r c o o l i n g curve  13 ± 12  E r r o r s r e p o r t e d a r e f o r one s t a n d a r d  99  Fig. 59 C o o l i n g c u r v e s ; C a t f a c e I n t r u s i o n ( 4 ) , (±) , I n d i a n I s l a n d i n t r u s i o n •(•) , and quartz B l a c k R i v e r (•).  Wark Complex diorite of  100  All initial easily  of t h e s e p o s s i b l e  cooling  cooling  176  between  e x p l a i n e d as t h e  cooler  country  geothermal  rock  magmagenesis t o o k  approximate  has  been  probably includes cooling  Estimation fact  that  setting  gradient depth  300-500°C  a  low  probably varied  on  of  the u p l i f t nature  depths  on  of  Nonetheless,  within  and a  lower  an  limits  realistic  calculations  for  the  by  but  thermal  was  history  position  of  from a h i g h h e a t forearc Thus, as w e l l  the  the  between geothermal  as d e p t h .  The  place  determined.  Crystalline km,  4)  would  i s not p r e c i s e l y  15 t o 20  flow arc  setting  which  the Westcoast  Complex  consistent  with  kb. can  varying  three  temperature  the  rate,  range.  curves  g r a d i e n t i s c o m p l i c a t e d by  intrusion,  attempt  1) The  three  3)  w i t h time  the p r e s s u r e e s t i m a t e of P > 4  that  f o r the  to p i n p o i n t  o n l y be  time.  the order of  a  inferred.  flow  this  to  along  conclusion  ambient  exact can  loss  uplift  reasons:  I f the  the  to mid-Cretaceous  catazonal  upper  2)  T h i s i s most  heat  rates  the  changed  heat  Ma.  rapid  levels.  difficult  range.  Island  of emplacement  implies  is  reheating  Vancouver  constraints The  This  after  of paleogeothermal  mid-Jurassic  the  uplift  i s u n r e s o l v a b l e and  to  rapid  following  true u p l i f t  Tertiary curve  average  172  involve  lateral  supports  f o r the  reached. i n the  of than  This  of  is difficult  only  result  and  place at subcrustal  -Determination models  Ma  rather  gradient.  histories  be  made t o  approximate  the  unknown  parameters  3  shows t h e  Table models  assuming  results an  of  ambient  Table  3. C o m p a r a t i v e c a l c u l a t i o n s o f u p l i f t for the Indian I s l a n d i n t r u s i o n No Reheat i n g  MODEL 1 Cooling °C/Ma  rate  rate  Geothermal Gradient °C/km  400 / 1 67 Ma = 2.4  10  20  30  40  50  0.24  0.12  0.08  0.06  0.05  Uplift km  40  20  MODEL 2  T e r t i a r y Reheating, slow c o o l i n g a f t e r emplacement  U p l i f t rate km/Ma  Cooling °C/Ma  rate  Geothermal Gradient °C/km U p l i f t rate km/Ma Uplift km  1 0  30  40  50  0.35  0.18  0.12  0.09  0.07  40  20  13  10  rate  U p l i f t rate km/Ma Uplift km  8  20  fast  Geothermal Gradient °C/km  10  400 / 1 1 4 Ma = 3.5  MODEL 3 Cooling °C/Ma  1 3  8  T e r t i a r y Reheating, c o o l i n g a f t e r emplacement 400 / 75 Ma *= 3.5  10  20  30  40  50  0.53  0.27  0.18  0.14  0.11  40  20  3  10  1  8  1 02  temperature  of  400°C and g e o t h e r m a l g r a d i e n t s  l0-50°/km c a l c u l a t e d rates  used  lines  i n these c a l c u l a t i o n s  i n Figure The  models  identical  amounts o f u p l i f t  respectively. rates  The (Fig.  are represented  indicated  but i n d i c a t e s  that  i n M o d e l s 2 and 3 was a c c o m p l i s h e d  uplift  similar  cooling  young  curve  not  rapid  reheating  The  models  on t h e o r d e r  59) i s  average  cooling by d o t t e d  59.  i s not f o r t u i t o u s  uplift ago,  a t 10° i n t e r v a l s . The  i n t h e range  initial  of the I n d i a n  hornblende  Island  K-Ar  of Ma  modest  t o 0.5 km/Ma.  below  cooling  100  relatively  f o r the quartz d i o r i t e  constrained  three  the majority  by 50 and  indicate  o f 0.1  by t h e  200°C  and l e n d s  of Black but  support  intrusion.  The  River  indicates  to Tertiary anomalously  d a t e o f 144 ± 5 Ma was o m i t t e d  from  consideration.  Wark  Complex The  59),  apparent  only  constrained  s t e e p between 1) 3)  partial  e v e n t . Eocene  Catface The  curve  f o r t h e Wark  by two p o i n t s ,  700°C and 5 0 0 ° C . T h i s  slower u p l i f t ,  evidence  cooling  2) i n t r u s i o n  resetting  Complex ( F i g .  i s considerably  may be a c c o u n t e d  into hotter  country  intrusions  in  the  Leech  River  f o r by:  rock,  of h o r n b l e n d e by a s u b s e q u e n t  less  or  thermal  Complex  may  s u c h an e v e n t .  Intrusion rapid  cooling  demonstrated  by  the data  f o r the  1 03  Catface  Intrusion  character Indian  of t h e s e p l u t o n s .  Island  Crystalline  ( F i g . 59) i s i n a c c o r d  intrusion  indicate  Complex a t t h e l e v e l  maximum t e m p e r a t u r e Ritchie  The f i s s i o n  Bay was  the  track  dates  that  presently  the  epizonal f o r the  Westcoast  e x p o s e d was a t a  o f 120°C when t h e C a t f a c e  emplaced.  0  with  Intrusion  in  1 04  CHAPTER V I I CONCLUSIONS  Previous  interpretations  Wark/Colquitz Jurassic  metamorphism  basement Muller  Crystalline  rocks et  of  and  migmatization  ( M u l l e r and C a r s o n ,  a l . , 1974). A r e v i s e d  The  chemistry  of the Westcoast  trace  Amphibolites tholeiitic  of is  Paleozoic 1973,  seems  1977;  i n l i g h t of  necessary.  Crystalline  Complex  w i t h p e t r o g e n e s i s i n a magmatic a r c s e t t i n g .  and  generated  study  of  interpretation  in this  and  them t o E a r l y  1969; M u l l e r ,  presented  major  Westcoast  Complexes a t t r i b u t e d  the d a t a  compatible  the  element  and g r a n i t o i d s to  signatures clearly  calc-alkaline  of  the  define  a  Both  Westcoast  subalkaline  trend c h a r a c t e r i s t i c  i n a magmatic a r c . The  is  characteristic  o f magmas enrichment  K, Rb, Ba, a n d S r a n d d e p l e t i o n o f Nb, Ce, Nd, Z r , and Y entirely  compatible  mantle  source  presence  o f what a p p e a r  the  present  region  level  chemical  Paleozoic rocks, have  (Pearce,  settling  evidence  protolith;  similar  1982).  in  a  hydrated  Furthermore,  the  implies  that  was o p e r a t i v e .  alone  Jurassic  calc-alkaline  t h e same c h e m i c a l however,  genesis  t o be c u m u l a t e g a b b r o s  w h i c h have a wide r a n g e  produce not,  magma  o f e r o s i o n h a s e x p o s e d p o r t i o n s o f magma  chambers where c r y s t a l The  with  does  rule  out a  anatexis of S i c k e r v o l c a n i c in silica  chemistry,  features. This  supported  not  by  the  content could  and  likely  conceivably  interpretation isotopic  data.  is The  1 05  consistency to  189 Ma  a n d g e n e r a l c o n c o r d a n c e o f U~Pb d a t e s range  Complex  in  derivation  study  argues  Paleozoic  isotopic source.  is  than  higher  data The  rocks  also  i s about  By  provide  initial  those  0.70360).  8 7  line  history  cooling that  rocks  against  and  casts  o f 264 Ma  obtained  w o u l d be  environment  (Armstrong,  Sicker  i n prep.) which  f o r Westcoast time,  for  rocks  (0.70329  the Sicker v o l c a n i c rocks  the i n i t i a l  ratios  observed  f o r s u b c r u s t a l r a t h e r than  although  presented  was  less  ratio  of evidence  adjacent  emplacement,  Sr  Complex.  evidenced  the  8 6  for a subcrustal  Crystalline  magmagenesis,  cooling  Crystalline  strongly  evidence  Sr/  0.7040  Jurassic  the Westcoast Another  situ  fairly  crustal  would be t o o r a d i o g e n i c t o y i e l d for  Westcoast  on t h e p r e v i o u s l y p u b l i s h e d U-Pb d a t e  volcanic  to  f o r the  e t a l . , 1974).  Sr magma  this  from  uncertainty (Muller  obtained  i n t h e 176  by  more  i n Chapter  the  crust,  Indian at  considerably  easily  tenuous, VI.  The  at  c o o l e r than  explained  comes from t h e fairly  Island intrusion  least  in  terms  in  the  rapid implies  level  of  t h e magma. T h i s of  a  crustal  where a n a t e x i s was underway, and t h e c r u s t  would  p r e s u m a b l y be q u i t e h o t . A preferred interpretation, the  Westcoast  crustal  part  predominantly including  Crystalline of  the  Complex  Jurassic  mantle-derived  Paleozoic  given  and  represents  magmatic  magmas.  Mesozoic  o u r new d a t a ,  arc  Various  supracrustal  i s that  the  deep  invaded  by  protoliths, and  early  1 06  solidified  magmas  were  converted  m i g m a t i t e s and metamorphic  rocks.  in  this  An o l d e r  environment t o  c r u s t a l component  seems i m p r o b a b l e a s t h e p r i m a r y magma s o u r c e ; made rocks  an u n d e t e c t a b l e  coeval  interpreted Westcoast  Island  as higher  acidic  Intrusions level  Island  differential  consequence  of  uplift  this  that  crustal  through  cross  section  uplift and  Volcanics  t o the west.  A  i s t h e p r e s e n t day  possibly  incomplete  t h e J u r a s s i c magmatic a r c o f  Island.  Reconnaisance Vancouver  of t h e W a r k / C o l q u i t z Complex  Island  indistinguishable Westcoast  inferred.  p o s i t i o n of  and Bonanza  was g r e a t e r  differential  are  d i f f e r e n t i a t e s of the  Intrusions  disrupted  Vancouver  a n d Bonanza V o l c a n i c s  comagmatic  e x p o s u r e o f a somewhat  fault  to the plutonic  D i o r i t e s . The more e a s t e r l y g e o g r a p h i c  more  implies  the  have  studied. The  the  but minor c o n t r i b u t i o n  i t may  shows  i t  i n age, petrography,  to and  of  be  southern  essentially  chemistry  from  C r y s t a l l i n e Complex, and a s i m i l a r h i s t o r y i s  The a p p a r e n t  zone  is  displacement  along  offset  consistent that  fault  across with  the  San  Cenozoic  p r o p o s e d by M u l l e r  Juan-Orcas left-lateral (1977).  1 07  CHAPTER  VIII  TECTONIC HISTORY OF  The  tectonic  characterized nature with  VANCOUVER  evolution  by  multiple  of  large-scale  rifting,  and  crustal  transcurrent units  how  this  evolution  i s presented  with  other  Cordilleran The  to T e r t i a r y time including  a  varied  associated subduction,  they here.  relate In  to  of  (1977,  the  addition,  unit  1980b) and  the  aspects  of  correlation  tectonostratigraphic  majority  from M u l l e r  of  is  f a u l t i n g . A b r i e f summary of  lithologic  borrowed  and  Island  episodes  movements  major  considered.  Vancouver  magmatic  spanning Middle Paleozoic  ISLAND  units  is  descriptions  are  Muller  et a l .  (1974,  1 981 )  Paleozoic Rocks Paleozoic  of  history  subdivided volcanic  the  this  unit  Sicker  f o r Vancouver group  limestone  of  a Middle  evidence arc  may  sequence  have  older  arc  crystalline  been e n s i a l i c .  in  i n the  Possible  a  has basal by  a  capped  Group i s e v i d e n c e terrane;  lack  suggests that  correlative  C o r d i l l e r a occur  California  U n i t ) and  arc  basement  of  (1980b)  overlain  (Sediment-Sill  volcanic  record  rhyodacitic  Myra F o r m a t i o n s )  t o Upper P a l e o z o i c  f o r an  only  Muller  ( B u t t l e Lake F o r m a t i o n ) . T h i s  exposed elsewhere Sierran  Island.  the  i n t o a b a s a l t i c to  ( N i t i n a t and  greywacke-argillite by  Group p r o v i d e  in  (Schweickert,  the 1976;  of the  terranes KlamathMuller,  108  1977,1980b), t h e Islands  Roche  (Muller,  1980b)  Wrangell Mountains Sicker  Group  Islands  but  volcanics  of  and  i n the  rocks  are  Harbor  are  of  exposed  to  be  the  the  Alaska  not  Karmutsen  in  portions  Yukon and  presumed  the  terrane  San  St. E l i a s  (Muller,  i n the  present  Juan and  1980b).  Queen  Charlotte  beneath  Triassic  Formation.  Tr i a s s i c Triassic  volcanic  exposed e x t e n s i v e l y of  basaltic  f l o w s of  up  the age  to  pillow  tholeiitic  Vancouver by  Island 1000  the  Vancouver lavas,  r a n g e s up  Karnian,  basin  Rocks c o r r e l a t i v e  linking  suggests  from Oregon  element  paleomagnetic that  with  of  study they  contiguous  terrane  Panuska and  Stone,  the of  i s well 5 to  elastics  constrained  south-central  Wrangellia  et  of The  late  et a l . ,  basalts  and  inter-arc  1977).  to  Hillhouse  as  (Muller  Karmutsen  1977;  on  overlain  respectively.  the  displaced  mainly  thickness  Karmutsen  rocks  are  subaerial  they are  10 Ma  (Muller,  (Hillhouse, 1981;  and  been a t t r i b u t e d t o  these  represent  consist  c a r b o n a t e s and  of  has  development  and  Formations,  outpouring  rifting  identified  and  total  t o 6000 m,  a span of  sedimentation  the  Island  pillow breccias,  P a r s o n s Bay  subsequent  been  Karmutsen F o r m a t i o n  composition. Their  Voluminous  and  the  Karmutsen v o l c a n i c s  Ladinian-early 1981).  of  m of Upper T r i a s s i c  Q u a t s i n o and of  on  rocks  Formation Alaska  terrane. by  various  f r a g m e n t s of Y o l e and  and  have are  Extensive workers a  once  Irving,  1980;  a l . , 1982).  109  Longitudinal provided region for  by  southerly  Cordillera  terrane  (e.g.  source  Some  Muller,  Pangean  1977,1978; D a n n e r ,  is  the  Tipper  have  1977,  and  argued of  Stone et  the  Richards,  1980b) w h i l e (e.g.  not  source  western margin  birthplace 1976;  leaves  workers  the  a l . , 1972;  1976;  or  displacements  which  along  Jones et  propose a Tethyan  data  enigmatic.  Schweickert,  Avraham,  on  paleomagnetic  for Wrangellia  a  1976;  control  Nur  others  and  Ben-  a l . , 1982).  Jurassic A  transition  r e g i m e t o one latest  of  Triassic  Island alkaline  by  from  and  be  magmatic A  Island  edge of  Toarcian  correlative  i n the  The ranging  Triassic  (Muller  on  the  in composition  sediments.  A  of  tuffs,  but  are  range up  Queen C h a r l o t t e  up  along  and to  the  continued  to  youngest  to C a l l o v i a n  in  Islands.  characterized  breccias, of  Crystalline  Piiensbachian  by  from b a s a l t i c a n d e s i t e  thickness  e t a l . , 1974).  and  calcBonanza  M i d d l e J u r a s s i c . The  1970)  are  the  Jurassic  plateau  the  Vancouver  c h a n g e d , now  Westcoast  Early  basalt  the  between  arc,  w i t h Bonanza V o l c a n i c s  Bonanza V o l c a n i c s  with a s s o c i a t e d  and  late  tectonic  i s s u g g e s t e d on  volcanic/plutonic  (Jeletzky, rocks  extensional  subduction  activity  Intrusions,  the  associated  and  Jurassic  a c t i v e t h r o u g h most of  fossils to  Early  renewed  Complex, d e v e l o p e d western  dominantly  compression  character.  Volcanics,  a  lava to  rhyodacite  intercalated  2500 m has  been  flows  clastic suggested  1 10  The  Island  I n t r u s i o n s and  form  successively  are  g e n e r a l l y g r a d a t i o n a l w i t h one  petrology. plutonic early  deeper  Westcoast  Data  as  p o r t i o n s of t h e  presented  emplacement  in  and  migmatization  country  rocks.  Local  general  parallelism  to  northeast  the  and  of  of  strike  indicate  subduction,  and  the c r u s t  began  of  a  crustal  although  this  as  with  the  foliation  the a r c a x i s  and that  Pliensbachian  of  with  arc  indicate  deformation  development  may  northeast-directed  levels  Complex  in chemistry  study  possibly  contemporaneous  Jurassic  another  this  i n deeper  Toarcian  Crystalline  local  showing  and  dipping  response  to  i s admittedly  speculative. Arc  activity  Jurassic  time.  accretion al.  This  van  Lower C r e t a c e o u s Plutonic  region  explanation  result of  the  of with  of  is  collision  zone,  time,  this  collision  landward  Jura-Cretaceous (Chugach, B a r a n o f ,  occured  flysch Pacific  contemporaneous  with  The  et  Upper J u r a s s i c the  but  Heyden,  it  may  Coast  1982).  have  An  been  is a  s h o r t e n i n g , change of d i p  t r e n c h jump, o r  e a s t of sequences and  to  of- a r c magmatism i n  der  m a j o r i t y of  Rim,  by Vance  m i g r a t i o n of a r c a c t i v i t y  tectonic  p a r t of W r a n g e l l i a . The  Late  Lake G r o u p s of  van  eastward  and  to  initiation  1977;  the  in Middle  as p r o p o s e d  (1982).  Fire  the  to give at t h i s  subduction  America  and  mark  (Muller, for  roughly  d e r Heyden  Gambier  Complex  difficult  t o have a b a t e d  to S t i k i n i a / N o r t h  (1980) and  that  appears  subduction  tectonism associated  Vancouver of Leech  the  Island. Pacific  River  The Belt  Complexes)  111  probably this  represent  notion  1981;  has  Island  are  Karmutsen If  and  Cowan,  Jurassic  paleomagnetic  s t u d i e s of  roughly  further  is  south.  paleomagnetism  1982;  the  although  (Cowan and  Brandon,  Brandon,  1984).  to  (Irving, of  1983;  it  view  for these  those  from  Vancouver  obtained  I r v i n g and  on  Yole,  the W r a n g e l l i a / A l e x a n d e r  accepted, This  determined  Bonanza V o l c a n i c s on  equivalent  Formation  Stikinia  complexes,  paleolatitudes  J u r a s s i c amalgamation  with  subduction  r e c e n t l y been q u e s t i o n e d  Fairchild Early  coeval  appears  is  two  to  consistent  terranes discussed  1984). Terrane  have with  the  occured  Cretaceous  i n the  next  sect ion. A  period  Jurassic Island,  and  recognized  uplift  continued  w h i c h was  Early  (1984)  of  to  now  have  into  Border  and  Cenozoic  section  i n the  Ranges of uplift  ultramafics,  on V a n c o u v e r  exposed entire  "an arc",  to the  their  Late  Vancouver  Burns  almost  has and  been Pessel  long  discontinuous  and  andesites There,  Mesozoic  complete  complete  with  in  crosscumulate  plutons,  J u r a s s i c Westcoast  and rocks  striking.  In t h e Queen C h a r l o t t e I s l a n d s , have  km  intermediate  resemblance  Island i s  1000  on  activity  p l u t o n i c rocks  migmatites, The  arc  i n the  region.  south-central Alaska.  has  the  forearc  Insular Belt.  recently described a  through  andesites.  the  Cretaceous  Jurassic  zone of J u r a s s i c a r c - t y p e the  e r o s i o n commenced the  p a r t of  Middle  elsewhere  and  equivalents  in  the  the  Bonanza  Yakoun F o r m a t i o n .  Volcanics Jurassic  11 2  plutons  exposed  along  Sutherland-Brown represent  the  Crystalline In  quartz have  San  been  Middle  Late  suites  age  similar  accomplished  by  finalized  pelagic  a  small to  facies  Middle  that  the  and  British  Columbia,  t h a t time  argue  (Davis et  and  end  to  Late  these  rocks, in  region  Tertiary  al.  represent  Jurassic  oceanic  et a l .  is  of  (1978),  accepted,  Wrangellia  reversed  the J u r a s s i c .  southern  Middle  Coast  and  Wrangellia faulting, and  obscure  and  Jurassic between  Mountains  only to  it was  briefly  e x i s t e n c e o f an  1978)  complicate  by  e l e m e n t s of V a n c o u v e r I s l a n d  f o r the al.,  the  i n some a r e a s  by D a v i s  Jurassic  i n the  of  metamorphism g r e a t l y  ophiolitic  emplacement  interpretation  of  diorite,  B r i d g e R i v e r Group, w h i c h l i e s  Wrangellia  suturing  for  in this  accretion  the M i d d l e by  gabbro,  central  metamorphism. Vance e t  proposed  initial  and  associated amphibolite  indicate  the W r a n g e l l i a n  Stikinia  Cretaceous  Westcoast  predominantly  t h a t the o p h i o l i t e s  c h e r t s i n the  Jurassic  the  followed closely  e a s t e r n Oregon. I f t h i s that  including  determinations  Jurassic  of a  which s e p a r a t e d  then  of  by  syntectonic,  northwestern  and  within  amphibolite  suggest  the opening  at  I s l a n d s and  by Vance e t a l . ( l 9 8 0 ) ,  implies  described  predominantly  trondhjemite,  Various  Jurassic  basin,  coast,  continuation  intrusive  recognized  to  (1980)  and  Juan  diorite,  compiled  as  northerly  local  terrane.  Late  (1966)  west  Complex.  the  Cascades,  the  ocean post  of  basin Middle  Stikinia.  Major  intrusion,  and  this  picture..  11 3  Cretaceous From quietly  in a  mostly was  Cretaceous forearc  onward, V a n c o u v e r  setting.  During  southwestern 1977).  to  the easternmost  edge of t h e  Clastic  sediments  volcanic/plutonic northern  include Middle  edifice  tip  the  Coast  of  Lower  into  this  side  shed  of  of t h e  Plutonic  Vancouver  Cretaceous  from  Longarm  of Vancouver  s h a l l o w b a s i n from  was  intrusion  island  at  the  (Muller,  the  Island.  a forearc  it  Complex  Jurassic sequence  These  on  sediments  Formation  Queen C h a r l o t t e  In t h e L a t e C r e t a c e o u s , east  episode  part  remained  time,  a r e e v i d e n t as a s h e l f  t o Upper C r e t a c e o u s  the  Island  this  e m e r g e n t . A minor m i d - C r e t a c e o u s  confined  the  time  and  the  developed  on  Group.  basin  Island. Clastic  sediments  adjacent highlands  shed  formed  the  Nanaimo G r o u p . Paleomagnetic magnetic  overprint  Vancouver its  present  (Irving 13  Island  and  at that  in  active  until  the  1976),  and  Early  from  to  the E a r l y  a  mid-Cretaceous  Late  Cretaceous  fault  ( D a v i s e t a l . , 1978),  these  faults  offset but  the  south  North was  the  (Tipper  as much  (Irving  implied  known  are fault,  Richards, Creek  displacement  movements.  as  et a l . ,  Yalakom and  of  America  a l o n g the S t r a i g h t  the  that  paleolatitudes on  Cretaceous  Tertiary  than  Stikinia  movement  indicates  20 d e g r e e s  central  different  dextral  i s less  still  Similarly,  apparently  with  time  relative  1984).  south  These  consistent  was  Yole,  obtained  i n t h e Karmutsen F o r m a t i o n  position  degrees  1980).  data  on  11 4  Paleomagnetic central from  Alaska  the  of  for  t h e Chugach T e r r a n e  i n d i c a t e s that  equator  1982). T h i s west  data  in  implies  i t was o n l y  the l a t e s t  equivalent  Vancouver  Cretaceous  or g r e a t e r  Island.  that  in  Middle  i t s present  latitude  average  latitudinal  v e l o c i t y of 3 cm/yr  m i d - C r e t a c e o u s and m i d - T e r t i a r y 6  cm/yr  central seems  was p r o p o s e d  Alaskan more  data.  This  Insular  terranes  appropriate  Gromme latitudinal  and  require  only  Vancouver  Island  Tertiary,  i s indicated  an  between  time. A l a t i t u d i n a l  although a value for  their  o f Cowan  (1981)  f o r 41  based  about  faults  velocity  closer to 8  post-Cretaceous  cm/yr Chugach  west  of  the  o f a t l e a s t 3 t o 5 cm/yr.  displacement  reconstructions  on  by S t o n e e t a l . (1982) f o r s o u t h -  Hillhouse  Terrane  degrees  (Stone e t a l . ,  i n d i c a t e s d e x t r a l m o t i o n on f a u l t s  Belt at a rate  Chugach  the  10  offset  Assuming  reached  of  about  i n south-  on  have  Ma  called  plutons  intruding  paleomagnetic  (1982) f o r  10° b a s e d p u r e l y  the  f o r 25° o f  same  on g e o l o g i c  data, time  the while  period  grounds.  Tert iary Tertiary, the  rocks  Metchosin  intrusions,  the  on V a n c o u v e r  volcanics,. Alert  Island are represented  several  isolated  to  Middle  Eocene  Volcanics  a r e s i t u a t e d south of the Leech River  southern  t i p of Vancouver  lavas,  tuff,  Tertiary  Bay v o l c a n i c s , and s e d i m e n t s o f t h e  Carmanah F o r m a t i o n . The Lower  pillow  by  Island  and c o n s i s t  b r e c c i a , and s u b a e r i a l  Metchosin  fault of  flows,  on t h e  tholeiitic underlain  1 15  by  gabbroic  chemistry  r o c k s of of  Crescent  the  the  volcanics  Formation  exposed  most  c o n s i s t e n t with  ridge  setting The  to  America  accretion north of  Formation The  of which  and  of  strata  overlying  Cowan,  1982).  is  Several  Cowan,  Late  across and  and  low  compatible  the  1982;  the  the  and  is  fault  Oligocene fault  V o l c a n i c s along by Upper  sills  mostly  Eocene  ratio  1977). Leech  Oligocene  (Fairchild  and  Island.  determined  and  plutons  The  the  Carmanah  the  stocks  of  to  predated  (Muller,  boundary  and  and  age  are  calc-alkaline in this  study  w i t h m a n t l e d e r i v e d a r c magmatism. However, bodies  G r o u p , but  i n c e p t i o n of  Juan  constrained  Sr  Ma)  Emplacement  dioritic  initial  these  49°  San  the  accreted  (-40  1982).  Eocene-Early  occured  after  latitude a  i n the  represented  by  forearc  region  of  v o l c a n i c r o c k s of  the  t h e c u l m i n a t i o n of a r c  (1981) d e m o n s t r a t e d a waning of  of  R i v e r Complex  Cowan,  Vancouver  t h e E o c e n e magmatic a r c  north  the Leech  structural  quartz  scattered  Ewing  that  t e r r a n e was  metamorphism  the M e t c h o s i n  that  dikes  Kamloops  of  similarly  associated  of  to  in places overlies  fault  intrusion  Ma)  the  River  are  to  Icelandic-type island-  oceanic  R i v e r Complex a l o n g  emplacement  chemistry  i n an  Crescent  subsequent  (Fairchild  deposition  similar  i n the Olympic Mountains  formation  and  (post-40  the Leech  is  t r a c e element  ( M u l l e r , 1980a).  Metchosin  North  Sooke I n t r u s i o n s . The  at about  transform  magmatism.  i n magmatic a r c 42 Ma  regime  activity  and  attributed  at  the  i t to  continental  1 16  margin. and  This  is close  a c a u s e and  effect  to  the  d e t a i l e d and  required  to  produce  resultant  chemistry  recognized Moore,  are  in southern  (Marshak and  and  Marshak and trench-trench and  the  heat  and  Ewing's  (1981)  configurations invoke  a  been  prism  (1979), reported, a  the  Intrusions.  magma t h a n  likely  that  this  magmagenesis  is  low  in a  yield  1969;  subduction an  over-  a  ridge-  Aleutian  trench  migration  within  the  for  for  melting  ratio of  It  the have  fails  observed  in  to the  accretionary  and  Rb-enriched  Hudson Sr  seem t o a p p l y  here.  which  explain  s e t t i n g . The  also  involving  the  initial  would  plate  g e o m e t r i e s may  h y p o t h e s i s of the  prism.  Island  junction  plate  Sr  increased  Eocene  of V a n c o u v e r  triple  with  of  accretionary  a more r a d i o g e n i c  doesn't  forearc  been  within  responsible  initial  Partial  required  ridge  interpretation.  o b s e r v e d . The  similarly  has  Moore,  i n v o l v i n g the  west c o a s t  although consistent  mechanism  that  r i d g e . Hence, t h e  however,  would  1965;  anatexis  was  melting  with  the  (Hudson e t a l . , 1979).  ridge-trench-trench  explain,  magmatism  reconstructions  consistent  Catface  and  and  stage.  (Burk,  postulated  o f f the  Pacific-Farallon  this  flow  been a t t r i b u t e d t o  ridge  partial  heat  near-trench  junction  Kula-Farallon  flow  necessary  prism  triple  Intrusions  mechanism  Alaska  Karig  Catface  undoubtedly complicated  1977)  deepened a c c r e t i o n a r y  the  operative  e l u s i v e at  has  Karig,  of  have been  the  Tertiary  1973)  age  r e l a t i o n s h i p may  although  Similar  the  answer may  et  al.  ratios  they  Apparently, subcrustal come  from  11 7  a  more t h o r o u g h u n d e r s t a n d i n g of l i t h o s p h e r i c  heat  flow r e l a t e d  to the  evolution  of  r e s p o n s e s and  transcurrent  plate  boundaries. The  L a t e Eocene  as a f r i n g e Vancouver  t o O l i g o c e n e Carmanah F o r m a t i o n o c c u r s  of c l a s t i c Island.  sediments along  It  lies  including  the Leech R i v e r  Westcoast  Crystalline  and  has been  1975).  Subsequent  disrupted  this  The  Volcanics  by  with  a  fault  Port  McNeill  interactions Riddihough  coast  on M e s o z o i c  Bonanza V o l c a n i c s ,  n e a r Pachena  as a b a t h y a l  Point  and  uplift  have  magmatic  e p i s o d e on V a n c o u v e r  of  rocks  and  the  (Fig.  60)  f a n complex  faulting  the L a t e Miocene  exposed  Port M c N e i l l .  Complex  west  (Cameron,  tilted  and  unit.  youngest  represented  unconformably  schist,  interpreted  the  The  f o r t h e most p a r t volcanic  zone and along  (1977).  to E a r l y  which are  centers extends  likely the  Alert  between A l i c e  appear  to  be  from B r o o k s  related  Pacific  Pliocene  Island i s  to  margin  Bay  Lake  colinear  Peninsula  recent  and  to  plate  described  by  118  F i g . 60 N o n c o n f o r m i t y between g e n t l y d i p p i n g s t r a t a of the Carmanah F o r m a t i o n and d i o r i t e of t h e W e s t c o a s t C r y s t a l l i n e Complex n e a r Pachena P o i n t . Rock s t i c k i n g up i n foreground is a stack of W e s t c o a s t D i o r i t e s u r r o u n d e d by t h e y o u n g e r s e d i m e n t s i n b a c k g r o u n d and u n d e r f o o t .  119  REFERENCES B e r g , H. C , J o n e s , D. L., and R i c h t e r , D. 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Sun,  Journal  S., 1980 L e a d i s o t o p i c s t u d y of young v o l c a n i c r o c k s from ocean ridges, ocean islands and i s l a n d a r c s : T r a n s . Roy. Soc. L o n d . , v297, pp. 409-445.  midPhil.  S u t h e r l a n d Brown, A., 1966 Tectonic history of the insular belt of British Columbia: i n T e c t o n i c h i s t o r y and m i n e r a l d e p o s i t s of the Western Cordillera, Can. Inst. Mining Met., S p e c i a l Volume 8, pp.83-100. Tipper,  H.W. and R i c h a r d s , T.A., 1976 Jurassic s t r a t i g r a p h y and history of n o r t h - c e n t r a l British Columbia: Geological Survey of Canada, B u l l e t i n 270, 73 p.  Tracy,  R.J., 1978 High grade m e t a m o r p h i c r e a c t i o n s and in pelitic schist, west-central A m e r i c a n J o u r n a l of S c i e n c e , v278, pp.  p a r t i a l melting Massachusetts: 150-178.  van  der  Heyden, P., 1982 T e c t o n i c and s t r a t i g r a p h i c r e l a t i o n s between t h e C o a s t Plutonic Complex and I n t e r m o n t a n e B e l t , w e s t - c e n t r a l W h i t e s a i l Lake map a r e a , B r i t i s h C o l u m b i a : u n p u b l . MSc t h e s i s , U n i v e r s i t y of B r i t i s h C o l u m b i a , 170 p.  Van  der  Voo, R., J o n e s , M., Gromme, C.S., e t a l . , 1980 P a l e o z o i c p a l e o m a g n e t i s m and n o r t h w a r d drift of the Alexander terrane, southeastern Alaska: J o u r n a l of G e o p h y s i c a l R e s e a r c h , v85, pp. 5281-5296.  V a n c e , J.A., Dungan, A., B l a n c h a r d , D. and Rhodes, J . , 1970 Tectonic setting and trace e l e m e n t g e o c h e m i s t r y of Mesozoic ophiolitic rocks in western Washington: A m e r i c a n J o u r n a l of S c i e n c e , v280-A, pp. 359-388.  1 27  Wanless, R.K., S t e v e n s , R.D., L a c h a n c e , G.R. e t a l . , 1974 Age d e t e r m i n a t i o n s and g e o l o g i c a l studies, K-Ar i s o t o p i c a g e s , R e p o r t 12, G e o l o g i c a l S u r v e y o f Canada, Paper 74-2. W e b s t e r , A., 1903 Geology o f t h e west coast of Vancouver Island: G e o l o g i c a l S u r v e y o f Canada, Summary R e p o r t 1902, pp. 53-74. Wyllie,  Yoder,  P . J . , 1977 Crustal anatexis: An experimental T e c t o n o p h y s i c s , v43, pp. 41-71.  review:  H.S. and T i l l e y , C.E., 1962 O r i g i n of b a s a l t magmas: an e x p e r i m e n t a l study natural and synthetic rock systems: Journal P e t r o l o g y , v 3 , pp. 342-532.  of of  Yole,  R.W. a n d I r v i n g , E . , 1980 Displacement of Vancouver Island, paleomagnetic evidence from t h e Karmutsen Formation: Canadian J o u r n a l o f E a r t h S c i e n c e s v17, pp. 1210-1228.  York,  D., 1967 The best isochron: Earth L e t t e r s , v2, p p . 479-482.  and  Planetary  Science  APPENDIX J_ SAMPLE DESCRIPTIONS AND  LOCATIONS  129 Sample Descriptions and  Locations  Latitude C r y s t a l l i n e Complex  Westcoast  49°  ir  46"  125° 47' 45"  49°  n » 08"  125° 53» 23"  49° 08' 29"  125° 48' 00"  trondhjemite  49° 11' 56"  125° 51' 23"  14-5  trondhjemite  49° 12' 25"  125° 53' 15"  35-17  diorite  49° 11» 15"  125° 53' 26"  26-2 ( l i s )  quartz  diorite  49° 06' 44"  125° 45' 50"  27-5  quartz  diorite  49° 13' 22"  125° 47' 25"  WCT-3  quartz  diorite  48° 43' 55"  125° 06' 18"  11-6  quartz d i o r i t e  49° 12' 02"  125° 52' 56"  12-2  gabbro-peridotite  49° 11' 16"  125° 52' 46"  15-12  sheared  49° 12' 51"  125° 53' 21"  50-4a-j  massive c a l c s i l i c a t e  49° 12' 42"  125° 51' 37"  52-7B-1.2  banded  49° 14' 10"  125° 53' 30"  48° 33' 54"  123° 33' 54"  48° 28' 00"  123° 29' 24"  27-22  megacrystic  35-19  amphibolite  34-3b,d  amphibolite,  30-1  (TIP)  amphibolite  trondhjemite  gneiss  ultrabasite  calcsilicate Wark Complex  V8(m,f)  amphibolite,  d i o r i t e agmatite  V9  d i o r i t e - h o r n b l e n d e gabbro Tertiary  RBP  quartz  diorite  37-14  d a c i t e porphyry d i k e  Intrusions 49° 13' 30"  125° 55' 24"  49° 08' 04"  125° 50' 14"  APPENDIX 2 MAJOR AND TRACE ELEMENT CHEMISTRY WESTCOAST  CRYSTALLINE  COMPLEX  WARK COMPLEX AND TERTIARY INTRUSIONS  131  MAJOR ELEMENT COMPOSITION WESTCOAST CRYSTALLINE COMPLEX Westcoc i s t Sample-*  Amph: b o l i t e  Westcoc i s t  Cx-fe> l s i t e  27-22  35-19  34-3b  34-3d  30-1  44.60  42.25  50.85  74.06  76.50  77.60  15.42  15.19  1 2.62  12.92  12.85  12.50  1 1 .89  1 4.54  9.59  MgO  1 1 .87  10.80  1 1 .65  CaO  12.49  1 1 .84  Si0  2  A1 0 2  Fe 0 2  3  3  1 4-5  2.79  1 .27  1 .86  1 .27  0.30  0.39  9.36  2.09  1 .08  1.81  Na 0  1 .59  1 .76  3.05  4.34  4.37  3.97  K 0  0.34  0.21  0.87  1 .36  2.93  1 .22  0.76  0.89  0.70  0.23  0.06  0.03  0.15  0.14  0.17  0.13  0.11  0.09  0.05  0.06  0.21  0.06  0.02  0.03  H 0"  0.06  0.15  0.06  0.11  0.06  0. 10  H 0  0.77  2.16  0.88  0.64  0.45  0.39  2  2  Ti0  2  MnO P 0 2  5  2  +  2  NOTES:  1) V a l u e s a r e i n w e i g h t p e r c e n t , n o r m a l i z e d t o 100% 2) T o t a l Fe r e p o r t e d a s F e 0 3) C 0 was n o t d e t e r m i n e d 2  2  3  132  MAJOR ELEMENT COMPOSITION WESTCOAST CRYSTALLINE COMPLEX VJ e s t c o a s t . D i o r i t e;s Sample-* Si0  2  Diorite Gnei ss  Westc:oast Ultratjasites  35-17  lis  TIP  WCT-3  1 1-6  45.66  57.50  70.40  55.05  62.02  37.38  38.81  1 2-2  15-12  A1 0  3  1 6.66  1 5.75  14.55  1 5.55  14.24  1 1 .99  1 4.84  Fe 0  3  6.11  8.32  3.19  9. 44  7.81  12.68  13.05  MgO  9.82  4.09  1.27  5.29  3.65  23.56  19.27  CaO  17.41  6.31  3.53  6.62  4.25  8.37  9.07  Na 0 2  2.08  3.69  4.44  2.99  5.02  0.56  1 . 06  K 0  0.15  1 .41  1 .05  1 .60  0.81  0.11  0.20  0.23  0.89  0.28  0.91  0.79  0.17  0.20  0.17  0.18  0. 18  0.18  0.18  0.14  0.16  0.05  0.26  0.10  0.22  0.22  0.03  0.04  H 0~  0. 12  0.10  0.16  0.24  0.11  0.32  0.24  H 0  1 .55  1 .50  0.85  1 .92  0.91  4.70  3.05  2  2  2  Ti0  2  MnO P 0 2  5  2  2  +  NOTES: 1) V a l u e s a r e i n w e i g h t p e r c e n t , n o r m a l i z e d t o 100% 2) T o t a l Fe r e p o r t e d a s F e 0 3) C 0 was n o t d e t e r m i n e d 2  2  3  MAJOR ELEMENT COMPOSITION WARK COMPLEX AND TERTIARY INTRUSIONS Wcirk Comp!.ex Sample-* Si0  2  Tert . i a r y I n t r iisions  V8-m  V8-f  V9  RBP  37-14  50.57  65. 35  45. 17  61 .84  64.90  15.63  14.46  A1 0  3  15.29  13.89  16.91  Fe 0  3  12.51  7.71  1 3.02  5.68  5.71  MgO  6.95  2.64  7.84  3.28  2.37  CaO  7.90  4.54  9.75  5.87  3.49  Na 0 2  3.14  3.58  2.88  4.20  4.49  K 0  1.16  0.92  0.52  0.98  1 .56  0.86  0.44  0.96  0.65  0.40  0.09  0.18  0.17  0.18  0.18  0.25  0.18  0.22  0.16  0.10  H 0'  0.07  0.09  0. 19  0.07  0.17  H 0  1 .20  0.49  2.37  1 .47  2.18  2  2  2  Ti0  2  MnO P O 2  5  2  +  2  NOTES:  1) V a l u e s a r e i n w e i g h t p e r c e n t , n o r m a l i z e d t o 100% 2) T o t a l Fe r e p o r t e d a s F e 0 3) C 0 was n o t d e t e r m i n e d 2  2  3  134  TRACE ELEMENT COMPOSITION WESTCOAST CRYSTALLINE COMPLEX Westcoc i s t Sample-*-  27-22  Amph: b o l i t e  35-19  Westcoa i s t  34-3b  34-3d  C x - f e> l s i t e 30-1  1 4-5  Ba  86  72  294  976  1 486  669  Ce  8  7  17  58  1 7  23  Nb  2  3  8  6  7  9  Nd  6  3  9  27  6  1 1  Ni  56  21 1  101  6  5  1 1  Rb  5  6  35  47  46  Sr  353  200  372  451  249  V  324  307  272  25  1 2  12  Y  13  22  1 5  6  1 2  10  Zr  31  38  72  66  65  NOTE: A l l v a l u e s  i n ppm  213  25 1 94  135  TRACE ELEMENT COMPOSITION WESTCOAST CRYSTALLINE COMPLEX VJ e s t c o a s t .  Sample-* Ba  35-17  TIP  lis  75  563  Diorite Gneiss  Diorite WCT-3  615  547  36  26  1 1-6 444  Westc o a s t U l t r a !) a s i t e s 1 2-2 1 3 3  6  8  3  4  4  2  5  34  Nb  2  7  8  8  Nd  6  1 7  1 6  1 5  21  9  3  1 7  29  40  18  341  372  236  1 23  1 43  Rb  26 5  39  1 6 396  281 5 46  Sr  665  429  V  1 30  1 74  34  Y  3  25  10  24  52  5  1 05  1 20  11 2  1 79  22  Zr  22  NOTE: A l l v a l u e s  i n ppm  57  44  Ce  Ni  15-12  196 6 217 1 10 5 29  TRACE ELEMENT COMPOSITION WARK COMPLEX AND TERTIARY INTRUSIONS Wcirk Comp].ex  Sample-*  V8-m  V8-f  Tert. i a r y I n t r iisions RBP  V9  Ba  534  433  253  Ce  18  30  9  37-1 4  319  838  30  39 8  Nb  4  4  .3  8  Nd  1 1  1 3  3  1 5  18  Ni  54  33  26  18  1 5  Rb  38  34  1 2  25  41  Sr  41 1  277  V  267  Y  25  1 1  Zr  66  1 18  NOTE: A l l v a l u e s  502  485  393  87  383  1 04  i n ppm  1 1 29  1 3 1 25  56 1 6 143  APPENDIX 3  GEOCHRONOLOGY ANALYTICAL METHODS AND  RESULTS  U-Pb  data  I s o t o p i c abundance,' Pb 206 = 100  Zircon Pb (ppm) (ppm)  (M)  (mg)  45-75 75-150 >150  19.. 3 28..7 20.,2  255s 1 244.5 216.2  7. 72 6. 94 6. 22  45-75  2 2 . .0  131.8  3. 8 5  75-150  16. ,0  114.9  3. 65  7. .4  694.9  20. 29  45-75  3 2 , .4  473.4  13. 78  75-150  16..0  524.4  15. 10  45-75 75-150  2 6 . .4  321.3  10.  20,. 5 .  287.7  45-75  18..8  733.4  20. 56  75-150  12,.4  481.0  13. 53  45-75  21 .0  286.9  2. 04  75-150  22,.0  24 7 . 7  1. 6 2  <45  isotopic  07  7. 61  208  207  204  R a t i o s and ages Measured ^Pb/^Pb  A  D  i  a  n  K  ™  2 0 6  Pb/  2 3 8  U  Sample 26-2, I n d i a n I s l a n d i n t r u s i o n 6.236 0.0356 716 4.0 0.02968(189) 5.429 0.0287 1331 2.2 0.02778(177) 5.547 0.0475 1088 1.7 0.02800(178) Sample 2 7 - 5 , T o f i n o I n l e t p l u t o n 10..61 6.299 0.0856 104 10.5 0.02852(181) 1 1 .. 0 2 6.590 0.1054 106 3. 1 0.03075(195) Sample 11-6, Westcoast d i o r i t e g n e i s s 1 2 . .07 0.02848(181) 5.887 0.0541 575 5.1 5.976 0.0645 814 2.3 0.02843(181) 1 1 .. 5 9 10..04 5.371 0.0214 829 2.9 0.02888(184) Sample WCT-3, q u a r t z d i o r i t e of Black R i v e r 13.. 1 0 6.948 0.1344 494 3.5 0.02958(188) 12..34 5.391 0.0197 354 6.0 0.02601(166) Sample V 8 , Wark d i o r i t e 18..85 5.577 0.0354 1220 2.2 0.02587(165) 17.. 8 2 5.404 0.0239 402 5.4 0.02639(168) Sample RBP, C a t f a c e I n t r u s i o n 17..64 6.577 0.1231 230 4.5 0.00649(41.7) 14.. 7 1 5.033 0.0272 423 5.4 0.00633(40.7)  11.. 5 7 12..65 12..85  2 0 7  Pb/  2 3 5  2.3  (Ma)  U  207  p b /  206  p b  0 .2339(213) 0 .1917(178) 0 .1871(174)  i 0.05718(498) 0.05007(198) 0.04848(121)  0 .1980(183) 0 .2137(197)  0.05036(212) 0.05041(214)  0 .2000(185) 0 .1971(183) 0 .2013(186)  0.05094(238) 0.05029(208) 0.05058(222)  0 .2027(187) 0 .1829(171)  0.04973(182) 0.05104(239)  0 .1803(168) 0 .1839(171)  0.05057(221) 0.05053(219)  0 .0426(42.4) 0 .0404(40.3)  0.0476(79.2) 0.0463(13.9)  Notes: A l l s p l i t s were nonmagnetic; z i r c o n s were g e n e r a l l y p a l e p i n k and c l e a r a l t h o u g h some were c l o u d y . 'Corrected f o r blank with composition ^ P b / ^ P b : 37.00; P b / P b : 15.57; ^ P b / ^ P b : 17.75. I s o t o p i c c o m p o s i t i o n o f common Pb i s based upon 180 Ma Pb d e r i v e d from the growth c u r v e o f Stacey and Kramers (1975) except f o r Sample RBP which i s based upon 40 Ma Pb. A = 0.155125 x 10"7yr.; X = 0.98485 x 10'7yr.; U / U = 137.88. 207  204  2  3  238  2 3 e  235  235  A n a l y t i c a l techniques; Z i r c o n s e p a r a t e was prepared u s i n g standard g r i n d i n g and heavy m i n e r a l s e p a r a t i o n procedures. D i s s o l u t i o n and i s o l a t i o n o f U and Pb were done u s i n g the procedure o f Krogh (1973). Samples were analyzed u s i n g s i n g l e Re f i l a m e n t and s i l i c a g e l techniques on a V.G. IS0MASS 54R mass s p e c t r o m e t e r . Data a q u i s i t i o n and r e d u c t i o n were accomplished on a HEWLETT PACKARD HP 85 computer.  CO  139  K-Ar a n a l y t i c a l  Sample  Description  data  Ar (*10 cc/gm)  %K  Sample 26-2, I n d i a n I s l a n d IIs-Hb  hornblende  1.10  %ZAr  Date and la.error (Ma)  intrusion  7.714  94.1  172 ± 6  Sample WCT-3, q u a r t z d i o r i t e of B l a c k R i v e r WCT-Hb  hornblende  0.869  5.076  82.3  144 ± 5  WCT-Bi  biotite  2.30  15.194  84.6  162 ± 6  Sample 27-22, Westcoast 27-22-Hb  hornblende  0.284  Amphibolite  1.742  83.2  151 ± 5  90.3  133 i 5  48.5  177 ± 7  Sample V8, Wark d i o r i t e V8-Hb  hornblende  0.721  3.857  Sample V9, Wark d i o r i t e V9-Hb  hornblende  0.138  0.998  Sample RBP, C a t f a c e I n t r u s i o n RBP-Hb  hornblende  0.321  0.467  48.7  37.1 ± 1.3  RBP-Bi  biotite  4.77  6.380  55.8  34.1 ± 1.3  A n a l y t i c a l techniques: K i s determined i n d u p l i c a t e by atomic a b s o r p t i o n u s i n g a Techtron AA4 spectrophotometer and Ar by i s o t o p e d i l u t i o n u s i n g an AEI MS - 10 mass spectrometer and h i g h p u r i t y Ar s p i k e . E r r o r s r e p o r t e d a r e f o r one s t a n d a r d d e v i a t i o n . The c o n s t a n t s used a r e : \  K  k 0  t  X K k0  - 0.581 x 1 0 -  1 0  y  _ 1  ,  - 4.962 x I 0 - 1 0 - l  o  y  p K/K  k0  = 0.01167 atom percent,  K a n a l y s e s were done by K.L. S c o t t , Ar a n a l y s e s were done by J . E . Harakal  Rb-Sr a n a l y t i c a l  Sample  IIs-WR IIs-Pl IIs-Hb IIs-Bi WCT-WR WCT-P1 WCT-Hb WCT-Bi 30-1-WR TIP-WR IIs-WR WCT-WR 35-17-WR 11-6-WR 27-22-WR RBP-WR RBP-P1 RBP-Hb RBP-Bi  Description  Sr (ppm)  Rb (ppm)  87  Rb/ Sr 86  data  87  Sr/ Sr 86  Date (Ma)  Sample 26-2, Indian I s l a n d i n t r u s i o n 0.70416 ± 6 452 38.5 0.2465 608 0.70374 ± 4 28.7 0.1362 • 151 0.70418 ± 8 66.6 6.1 0.2661 42.8 0.70570 ± 17 123 1.0065 Sample WCT-3, quartz d i o r i t e o f B l a c k R i v e r 0.70408 + 4 351 37.7 0.3113 h b - b i quartz d i o r i t e 0.1886 539 35.1 0.70395 ± 5 plagioclase • 169 86.7 0.70427 ± 8 10.8 0.3590 hornblende 58.6 4.2505 0.71362 ± 6 biotite 86.0 Whole r o c k a n a l y s e s , Westcoast C r y s t a l l i n e Com 43.4 0.5008 0.70463 ± 5 trondhj emite 251 404 13.6 0.0975 0.70383 ± 7 quartz d i o r i t e 0.70416 ± 6 452 38.5 0.2465 quartz d i o r i t e 0.70408 ± 4 • 143 351 37.7 0.3113 quartz d i o r i t e 698 2.4 0.0098 diorite 0.70365 ± 11 378 d i o r i t e gneiss 0.1166 0.70406 ± 3 15.2 0.0344 0.70344 ± 6 361 amphibolite 4.3 , C a t f a c e Sample RBP Intrusion 414 quartz d i o r i t e 0.70382 ± 5 23.5 0.1637 0.70368 ± 4 plagioclase 488 13.7 0.0810 K8.4 0.70387 79.8 0.2158 hornblende 5.9 ± 9 144 0.71181 ± 30 biotite 35.3 11.823  h b - b i quartz plagioclase hornblende biotite  Initial ^Sr/^Sr  Zr' Initial ^Sr/^Sr  diorite  ± 15  0.70356 ± 8  0.70354  ±3  0.70341 ± 5  0.70329  ± 27  0.70360 ± 9  ±7  0.70368 ± 3  0.70372  Notes: A l l e r r o r s a r e r e p o r t e d a t the 1 a confidence i n t e r v a l . The s l o p e s and i n t e r c e p t s were c a l c u l a t e d u s i n g a York I r e g r e s s i o n (York, 1967). Rb A = 1.42 x I 0 " / y r . Z r i n i t i a l ^ S r / ^ S r was determined by drawing the U-Pb z i r c o n r e f e r e n c e i s o c h r o n through t h e whole r o c k p o i n t . 11  8 7  1  141  Analytical  Techniques:  Rb and  Sr c o n c e n t r a t i o n s were determined  by r e p l i c a t e a n a l y s i s  p r e s s e d powder p e l l e t s u s i n g X-ray f l u o r e s c e n c e .  U. S.  G e o l o g i c a l Survey  r o c k standards were used f o r c a l i b r a t i o n ; mass a b s o r p t i o n were o b t a i n e d from Mo have a p r e c i s i o n  of 2%  Ka  Compton s c a t t e r i n g  (1 a ) and  Sr i s o t o p i c c o m p o s i t i o n was standard 54R,  i o n exchange t e c h n i q u e s .  of 5%  (1 a ) .  samples prepared  The mass spectrometer,  a V.G.  using ISOMASS  has data a q u i s i t i o n d i g i t i z e d and automated u s i n g a HEWLETT PACKARD HP Experimental  of  a d j u s t e d so t h a t the NBS  0.1194 and  Sr/  Rb/Sr r a t i o s  concentrations a precision  85 computer.  8 7  coefficients  measurements.  measured on unspiked  of  8 6  Sr  0.70800±2.  data have been n o r m a l i z e d  r a t i o of 0.71020±2 and The p r e c i s i o n  standard S r C 0  3  8 6  Sr/  8 8  Sr  ratio  (SRM987) g i v e s a  the Eimer and Amend Sr a r a t i o of  of a s i n g l e  8 7  Sr/  8 6  Sr  ratio is  Rb-Sr dates a r e based on a Rb decay c o n s t a n t of 1.42 regressions are c a l c u l a t e d  to a  x 10  0.00010 (1 a ) . _ 1 1  y  a c c o r d i n g to the technique of York  - 1  .  The  (1967).  F i s s i o n Track A n a l y t i c a l Data P  Sample  Mineral  (  1  0  6  t  P  S /  c  m  2  )  Tracks,s  ( 1 0  6  i 2)  t / c m  * lVc«2) 1  Tracks,!  (  1  0  2  3 n  »< '*> f l  Indian I s l a n d i n t r u s i o n lis  zircon  8.58  1623  1.33  251  2.08  80  20  15/15  lis  apatite  0.64  475  0.26  190  2.08  31 ± 19  45/45  2.08  13 ± 12  30/30  +  C a t f a c e I n t r u s i o n , R i t c h i e Bay RBP  ' V  0.20  apatite  148  0.19  141  t r a c k d e n s i t y ; 4>=thermal neutron dose  spontaneous t r a c k d e n s i t y ; Pj=induced  S = standard e r r o r number of g r a i n s or f i e l d s counted:  s, spontaneous; i , induced  decay c o n s t a n t s : X  2 3 8  (fission)=7.00 x 10" /yr;  other c o n s t a n t s : U  238  /U  17  235  =137.88; X  235  A  238  (alpha)=l.55125 x 10~ /yr;  = 5 8 0 x 10~ Vm 2  10  2  143  Fission  Track Dating  Analytical  Techniques and  were a d a p t e d  Lovering  population  (1975).  at  480°-520°C  naturally  for at least  and  with  tracks.  Apatite  22°-24°C  f o r about  Zircons procedure eutectic were  zircon  exposed  Dates age  and e t c h e d  a c i d at  and  etched  a t 800x.  according  to  e t a l . (1976) u s i n g FEP t e f l o n  the  induced  for  12  a t 2000x  calculated  until  natural  the  and a tracks  48 h o u r s ) . M u s c o v i t e d e t e c t o r s track  minutes in o i l .  density  and  at 22°-24°C. A  geometry  were  Tracks i n factor  of  d e t e c t o r method.  a c c o r d i n g to the f i s s i o n  track  equation, date=ln[1 + ( p s / p i ) * ( X alpha/X 2 38  x  retained  was  c o n d i t i o n s were 7% n i t r i c  f o r the e x t e r n a l  were  split  natural  (about  HF  were c o u n t e d  0.5 was assumed  spontaneous,  the  mounted  Gleadow  48%  annealed  30 s e c o n d s . T r a c k s were c o u n t e d  to record  in  being  mounted, p o l i s h e d ,  KOH-NaOH e t c h a t 200°-210°C  were used  respectively.  annealed  which  Gleadow  were d a t e d by t h e  t o remove  This  split  etching  were  fully  etched  two h o u r s  tracks.  the other  of  and z i r c o n  were made, one  subsequently  together  (1976) a n d  d e t e c t o r methods,  two s p l i t s  occuring  irradiated  from N a e s e r  Apatite  and e x t e r n a l  For a p a t i t e ,  Techniques  (1/X  where X  2 3 8  2 3 8  238  fission)(U  2 35  /U  2 38  )X  23 s  ]  alpha) alpha  and X  a l p h a and f i s s i o n ,  2 3 8  fission  respectively,  are U * is  2 3 8  decay  the  constants for  thermal  neutron  144  dose, u X  2 3 S  U  2 3 S  2 3 5  /U  is  2 3  "  the  i s the atomic cross-section  ratio  of uranium  f o r neutron  fission  and  reaction  of  . Thermal  Colorado  neutron  at  the  irradiation  USGS  TRIGA  was  performed  research  supervision  of C.W.Naeser and D . R u s l i n g .  determined  by  density the  isotopes,  ratio,  tuff  (Steven  of  ps/pi, Fish  e t a l . , 1967;  Reported formulae  back-calculation  given  errors  using  f o r a p a t i t e and Canyon new  assuming  Denver,  reactor  under  the  Neutron  dose  was  the  zircon their  counted  track  standards age  from  as 27.9  Ma  constants).  for dates are c a l c u l a t e d  by J o h n s o n  in  et a l . (1979).  according  to  

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