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Structure of the western margin of the Queen Charlotte Basin, British Columbia Young, Ian Fairley 1981

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STRUCTURE OF THE WESTERN MARGIN OF THE QUEEN CHAROLETTE BASIN BRITISH COLUMBIA by IAN B.Sc,  FAIRLEY YOUNG  M c G i l l U n i v e r s i t y , 1975  A THESIS SUBMITTED IN PARTIAL  FULFILLMENT  OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE  STUDIES  (Department o f Geology, I n s t i t u t e o f Oceanography) We a c c e p t t h i s t h e s i s as c o n f i r m i n g to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA May, 1981  t^cT) Ian F a i r l e y Young, 1981  11 In presenting  this  thesis  in partial  f u l f i l m e n t of the  r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e of B r i t i s h Columbia, I agree that it  freely  the L i b r a r y  a v a i l a b l e f o r r e f e r e n c e and study.  agree that p e r m i s s i o n f o r extensive for  University  s c h o l a r l y p u r p o s e s may  for  financial  shall  Geology  The U n i v e r s i t y o f B r i t i s h 2075 W e s b r o o k P l a c e V a n c o u v e r , Canada V6T 1W5 Date  May 6, 1981  thesis  Columbia  my  It is thesis  n o t be a l l o w e d w i t h o u t my  permission.  Department o f  further  be g r a n t e d by t h e h e a d o f  copying or publication of this  gain  I  make  copying of t h i s  d e p a r t m e n t o r by h i s o r h e r r e p r e s e n t a t i v e s . understood that  shall  written  i ii  ABSTRACT  The ment  o f t h e w e s t e r n margin  British  Columbia.  Fault trend, on  t h e s i s i n v e s t i g a t e s t h e g e o l o g y and s t r u c t u r a l  They  Field  o f t h e Neogene Queen C h a r l o t t e  study  area,  (Queen C h a r l o t t e  Hecate S t r a i t  along  the  magnetic  profiling  presumed  southern  and  marine  s e a bottom  extension  across  I s l a n d s ) and o f f s h o r e  and n o r t h w e s t e r n  i n v e s t i g a t i o n s comprised  measurements  situated  Basin, Sandspit  i n c l u d e s both t h e onshore p o r t i o n o f t h e f o r e a r c  Graham I s l a n d  southwestern  develop-  of  the f a u l t  Queen  high  Charlotte  in vicinity  the Sandspit on  portion i n Sound.  r e s o l u t i o n seismic  sampling  zone  basin  Fault  Queen  and  Charlotte  and  of the gravity Islands.  Samples were c o l l e c t e d f o r geochronometry and a n a l y s i s o f magnetic properties.  Additional  unpublished  s u r v e y maps and s e i s m i c  profiles,  synthesis  information  of a v a i l a b l e  data, have on  including  also  been  aeromagnetic  incorporated.  the geologic  and  tectonic  h i s t o r y o f t h e Queen C h a r l o t t e I s l a n d s and t h e Queen C h a r l o t t e and p l a t e motions i n t h e n o r t h e a s t e r n f o r i n t e r p r e t a t i o n of the f i e l d Newly r e p o r t e d the  ages  Queen  Charlotte  Paleocene, tectonic"  Upper  Eocene  plutons  were  Lower-Middle volcanic  Islands.  Miocene  episodes.  later  The t i m i n g  and p l u t o n i c  volcanic  Lower  emplaced  and  d a t e s have c o n f i r m e d  volcanic  Masset and  Basin  as a b a s i s  data.  radiometric  of Mesozoic-Cenozoic  P a c i f i c Ocean serve  A  episodes  Miocene  i n Upper and  time.  o f wrench  and Rennel-Louscoone systems i s c o n s t r a i n e d  rocks  of the  occured Coeval  Eocene-Lower  appear  or revised  in ? "post-  Oligocene,  to  postdate  Masset  faulting  on t h e  Sandspit  by t h e new age d a t a .  iv  Magnetic Charlotte  susceptibilities  Islands volcanic  and  and  remnant i n t e n s i t i e s  plutonic  i n t e r p r e t a t i o n o f a i r b o r n e and marine zations  and  associated  with  plutons. Masset  corresponding  High  NRM  magnetic  the Q  Masset  ratios  i s stable  field.  high  and  r o c k s were measured  magnetic  amplitude  volcanic  and  peak  magnetic  and  syn-  larger  anomalies  and  are  post-tectonic  fields  indicates  percentage  the  Charlotte  elements,  basin  including  Hecate  Cape S t . James r i d g e s , Neogene s u b c r o p . Louscoone  faults  edge.  Anomaly  and  p a t t e r n s over  Charlotte  reflect  depth  magnetics  of  p r o b a b l e seacrop p a t t e r n s on an i n n e r s h e l f between Queen the  marine  magneti-  outlined  and  of  the  High  to aid  has  Islands  Interpretation  data.  demagnetizing  comprises  of Queen  major  s u b - b a s i n s and  t o s o u r c e and  basin  Moresby  n a t u r e of p r e -  O f f s h o r e e x t e n s i o n s of the S a n d s p i t , R e n n e l , and  associated  wrench s t r u c t u r e s  and  and  are suggested  by  development  in  anomaly t r e n d s . Seismic  profiles  illustrate  structural  s h a l l o w Neogene sediments of the western Queen C h a r l o t t e B a s i n . Skidegate  Inlet,  Pleistocene  the  seismic  faulting.  d a t a shows p o s s i b l e  In Hecate  evidence  sub-basin, continuous  are draped  colinear fault Miocene opment.  with  zone  over Mesozoic  t h e onshore in  the  wrench f o l d s  Sandspit Fault.  sedimentary  wrench f a u l t development  cover  of  i n Neogene  Lack  of  i s i n an i n c i p i e n t  a  throughgoing  that  post-Lower  s t a g e of d e v e l -  In the n o r t h e r n C h a r l o t t e s u b - b a s i n f o l d s are p o o r l y  the s u b b a s i n f a u l t s  that  parallel  to  i n a d e f o r m a t i o n zone  indicates  oped and d e f o r m a t i o n has been l e s s s e v e r e .  late  parallel  en-echelon f o l d s , t h a t e v i d e n t l y e x p e r i e n c e d some growth time,  of  In  devel-  In the s o u t h e r n p o r t i o n  the S a n d s p i t t r e n d  have been  V  mapped.  Marine a r k o s i c sands dredged from seacrop  sub-basin blage.  c o n t a i n an Upper M i o c e n e - e a r l y  The  sands are p r o b a b l y  i n the  Charlotte  P l i o c e n e m i c r o f l o r a l assem-  e q u i v a l e n t t o the upper marine member  of the Skonun Formation on Graham I s l a n d . The associated the  nature  and  timing  volcanism  and  plutonism  western  oceanic  Queen  plate  Charlotte  motions  c o n t i n e n t a l margin.  and  of  Basin  Cenozoic  on  wrench  faulting  Queen C h a r l o t t e I s l a n d s and may  possible  be plate  related edge  to  changes  effects  at  and in in the  vi  TABLE OF CONTENTS  Page  Abstract  i i i  T a b l e o f Contents  vi  L i s t of Tables  *  L i s t of Figures  xi  L i s t of Plates  xvi  Acknowledgments  xvii  CHAPTER  I.  II.  PREFACE  1  SUMMARY OF THE GEOLOGY AND TECTONIC HISTORY OF THE QUEEN CHARLOTTE ISLANDS  5  Introduction Upper P a l e o z o i c ( ? ) and t h e A l l o c h t o n o u s I n s u l a r Terrane Upper T r i a s s i c Lower J u r a s s i c W r a n g e l l i a Succession Lower-Upper J u r a s s i c S u c c e s s i o n Lower-Upper Cretaceous S u c c e s s i o n T e r t i a r y Succession  5 7  HISTORY OF PLATE INTERACTIONS AT QUEEN CHARLOTTE ISLANDS L a t e M e s o z o i c - M i d d l e Eocene M i d d l e Eocene-Present P r e s e n t P l a t e Boundary  III.  RADIOMETRIC AGE DATES OF QUEEN CHARLOTTE ISLANDS VOLCANIC AND PLUTONIC ROCKS Introduction Data A n a l y s i s , P r e c i s i o n , and I n t e r p r e t a t i o n D i s c u s s i o n o f Age Data Karmutsen F o r m a t i o n Syntectonic Intrusions Masset F o r m a t i o n Post-Tectonic Intrusions Timing o f Movement on S a n d s p i t and R e n n e l Louscoone F a u l t s Block R o t a t i o n - T r a n s l a t i o n o f Graham I s l a n d  13 16 23 27 30 31 37 42 46 46 48 53 54 54 55 58 62 63  vii  TABLE OF CONTENTS ( c o n t ' d ) Page III.  RADIOMETRIC AGE DATES OF QUEEN CHARLOTTE ISLANDS VOLCANIC AND PLUTONIC ROCKS ( c o n t ' d ) P o s s i b l e R e l a t i o n s h i p s o f Cenozoic Magmatism t o " P a c i f i c " P l a t e Motions Masset V o l c a n i c s Post-Tectonic Plutons  IV.  GEOLOGY OF THE QUEEN CHARLOTTE BASIN General S e t t i n g Stratigraphy Age and C o r r e l a t i o n o f Skonun F o r m a t i o n Structure  V.  VI.  MAGNETIC PROPERTIES OF QUEEN CHARLOTTE ISLANDS VOLCANIC AND PLUTONIC ROCKS  67 72 75 75 77 85 85 94  Introduction Magnetic S u s c e p t i b i l i t y Measurement S t a t i s t i c a l Analysis Frequency D i s t r i b u t i o n s Remnant M a g n e t i z a t i o n s Remnant I n t e n s i t i e s A l t e r n a t i n g F i e l d Demagnetization Discussion  94 96 96 97 101 104 105 107 109  AEROMAGNETIC MAPS OF THE QUEEN CHARLOTTE ISLANDS  111  Introduction High L e v e l Aeromagnetic Map o f B r i t i s h Columbia N o r t h e r n Moresby I s l a n d S o u t h e a s t e r n Moresby I s l a n d N o r t h e a s t e r n Graham I s l a n d R e l a t i o n s h i p o f Magnetic Anomalies t o Magnetic Rock P r o p e r t i e s VII.  65  MAGNETIC ANOMALIES OF WESTERN HECATE STRAIT AND NORTHWESTERN QUEEN CHARLOTTE SOUND Introduction I n t e r p r e t a t i o n Procedure Depth t o Basement E s t i m a t e s I n t e r p r e t a t i o n o f Marine Magnetic Anomalies Inner S h e l f Queen C h a r l o t t e B a s i n Hecate Sub-Basin Moresby Ridge C h a r l o t t e Sub-Basin  111 114 116 123 125 126 130 130 132 132 134 134 140 141 144 147  vi i i  TABLE OF CONTENTS ( c o n t ' d ) Page VII.  MAGNETIC ANOMALIES OF WESTERN HECATE STRAIT AND NORTHWESTERN QUEEN CHARLOTTE SOUND ( c o n t ' d ) Oceanic Area A d j a c e n t t o Queen C h a r l o t t e Sound T e c t o n i c I m p l i c a t i o n o f Magnetic Anomalies o v e r Western Queen C h a r l o t t e Sound  VIII.  CONTINUOUS SEISMIC REFLECTION PROFILING Introduction P r e v i o u s P u b l i c a t i o n s and Open F i l e R e p o r t s I n s t r u m e n t a t i o n and S e i s m i c Record C h a r a c t e r i s t i c s V e l o c i t y o f Sound i n Seawater, Sediments, and Bedrock Seawater Quaternay Sediments Bedrock A n a l y s i s Procedure o f P r o f i l e Data Acoustic-Stratigraphic Units Bedrock S t r u c t u r e o f t h e Western Margin o f t h e Queen C h a r l o t t e B a s i n Sandspit F a u l t i n Skidegate I n l e t Hecate Sub-Basin C h a r l o t t e Sub-Basin Morphology and S t r u c t u r e o f Northwestern Queen C h a r l o t t e Sound K u n g h i t Channel Moresby Trough Moresby and M i t c h e l l Canyons C o n t i n e n t a l S l o p e O f f N o r t h - C e n t r a l Queen C h a r l o t t e Sound  IX.  BEDROCK SAMPLING AND BOTTOM PHOTOGRAPHY Introduction Neogene (Upper Miocene) Bedrock Samples Sample D e s c r i p t i o n s and M i c r o s c o p y Age o f Dredged Samples Bottom Photography  X.  149 153 161 161 162 163 168 169 171 173 176 178 181 182 185 198 206 207 208 211 213 216 216 217 217 222 225  WRENCH FAULT DEVELOPMENT ON QUEEN CHARLOTTE ISLANDS AND IN WESTERN HECATE STRAIT  229  Introduction Wrench F a u l t S t r u c t u r a l S t y l e D e f i n i t i o n and T e c t o n i c H a b i t a t Wrench S t r u c t u r e s The Rennel-Louscoone Wrench F a u l t System General D e s c r i p t i o n G e o l o g i c E x p r e s s i o n o f F a u l t Zone  229 231 231 232 237 237 237  ix  TABLE OF CONTENTS ( c o n t ' d ) Page X.  WRENCH FAULT DEVELOPMENT ON QUEEN CHARLOTTE ISLANDS AND IN WESTERN HECATE STRAIT ( c o n t ' d ) S t r u c t u r a l Evidence o f Wrench F a u l t O r i g i n Folds Synthetic Faults Antithetic Faults Main Wrench F a u l t Displacement Age o f F a u l t i n g S a n d s p i t Wrench F a u l t System General D e s c r i p t i o n G e o l o g i c E x p r e s s i o n o f F a u l t Zone Displacement Age of F a u l t i n g Wrench S t y l e Development Queen C h a r l o t t e I s l a n d s Western Hecate S t r a i t Cenozoic P l a t e M o t i o n s and Wrench F a u l t Development  XI.  239 240 242 243 244 244 246 248 248 250 254 256 260 260 261 263  SUMMARY AND CONCLUSIONS  269  REFERENCES  277  APPENDIX I .  PROCESSING OF NAVIGATION AND TOTAL MAGNETIC FIELD DATA  297  APPENDIX I I .  FORTRAN PROGRAMS  329  APPENDIX I I I .  LISTING OF SEISMIC AND MAGNETIC PROFILES 377  APPENDIX IV.  DESCRIPTION OF SEABOTTOM SAMPLES  380  X  LIST OF TABLES  TABLE  TITLE  PAGE  I  T a b l e o f F o r m a t i o n s f o r Queen C h a r l o t t e I s l a n d s  6  II  Cenozoic P l a t e I n t e r a c t i o n s a t Queen C h a r l o t t e Islands  39  III  Summary o f K-Ar Age D e t e r m i n a t i o n s : Queen C h a r l o t t e I s l a n d s  50  IV  K-Ar Age D e t e r m i n a t i o n s : S h e l l Canada W e l l s , Queen C h a r l o t t e B a s i n  52  V  C r i t i c a l S t r a t i g r a p h i c R e l a t i o n s f o r Syn- and Post-Tectonic Intrusions  59  VI  Masset and Mean North American D i r e c t i o n s and Poles  65  VII  M a g n e t i c S u s c e p t i b i l i t y of Queen C h a r l o t t e I s l a n d s and Vancouver I s l a n d Rocks  99  VIII  Magnetic Hardness o f Queen C h a r l o t t e I s l a n d s Core Samples  108  IX  Aeromagnetic Survey Data - Queen C h a r l o t t e Islands  113  X  R e l a t i o n s h i p o f Magnetic Anomalies and M a g n e t i c Rock P r o p e r t i e s t o G e o l o g i c U n i t s  128  XI  S e i s m i c Record C h a r a c t e r i s t i c s  166  XII  V e l o c i t y i n T e r t i a r y Masset and Mesozoic Sediments: Queen C h a r l o t t e I s l a n d s and Queen C h a r l o t t e Basin  175  XIII  Comparative M i n e r a l o g y of Upper M a r i n e Member, Skonun F o r m a t i o n , and Dredge Samples  220  XIV  Summary o f Major Cenozoic Events a t t h e Queen Charlotte Islands  265  XV  Sample Output from Program MERGE  307  XVI  S e i s m i c and Magnetic P r o f i l e s  377  XVII  D e s c r i p t i o n of Seabottom Samples  380  xi  LIST OF FIGURES FIGURE  TITLE  PAGE  1  L o c a t i o n o f Study A r e a Showing S h i p ' s T r a c k s  2  2  D i s t r i b u t i o n o f Upper T r i a s s i c W r a n g e l l i a Sequences  9  3  Breakup o f P a c i f i c a , Opening o f P a c i f i c Ocean, and Emplacement o f A l l o c h t h o n o u s Terranes  12  4  Paleogeography o f Canadian C o r d i l l e r a i n Lower-Middle J u r r a s i c  18  5  D i s t r i b u t i o n o f V o l c a n i c and P l u t o n i c Rocks on Queen C h a r l o t t e I s l a n d s  22  6  E v o l u t i o n o f t h e Western P a c i f i c Ocean  32  7  Upper C r e t a c e o u s - T e r t i a r y P l a t e R e c o n s t r u c t i o n of N o r t h e r n P a c i f i c  34  8  L a t e Paleogene-Neogene P l a t e R e c o n s t r u c t i o n of N o r t h e a s t e r n P a c i f i c  40  9  Magnetic L i n e a t i o n s and T e c t o n i c F e a t u r e s o f the G u l f o f A l a s k a  43  10  Sample L o c a t i o n s on Queen C h a r l o t t e I s l a n d s f o r K-Ar D a t i n g  47  11  Histogram o f K-Ar and Rb-Sr Dates o f T e r t i a r y Masset V o l c a n i c s and P o s t - T e c t o n i c P l u t o n s  66  12  Neogene V o l c a n i c Trends o f Southwestern B r i t i s h Columbia and O f f s h o r e P l a t e Boundaries  68  13  Neogene Displacement o f Queen C h a r l o t t e I s l a n d s  70  14  T e r t i a r y P l u t o n i s m and Ridge M i g r a t i o n  73  15  D i s t r i b u t i o n o f L a t e Mesozoic-Cenozoic o f Western North America  Basins  76  16  W e l l L o c a t i o n s on Queen C h a r l o t t e I s l a n d s and i n Queen C h a r l o t t e B a s i n  78  xii  LIST OF FIGURES ( c o n t ' d ) FIGURE  TITLE o f Queen C h a r l o t t e  PAGE  17  Structural Cross-Section Basin  18  Isopach o f Queen C h a r l o t t e B a s i n  82  19  I s o s t a t i c G r a v i t y Anomalies and Models o f Queen C h a r l o t t e B a s i n  87  20  T o t a l I n t e n s i t y Aeromagnetic Map o f Queen C h a r l o t t e Basin  89  21  G r a v i t y Map o f Queen C h a r l o t t e B a s i n R e g i o n  90  22  Earthquake E p i c e n t e r s Charlotte Islands  92  23  Sample L o c a t i o n s on Queen C h a r l o t t e I s l a n d s f o r A n a l y s i s o f Magnetic P r o p e r t i e s  95  24  Histograms o f Magnetic S u s c e p t i b i l i t y o f Queen C h a r l o t t e I s l a n d s and Vancouver I s l a n d Samples  98  25  Comparison o f Remnant and Induced M a g n e t i z a t i o n s of Core Samples from Queen C h a r l o t t e I s l a n d s  106  26  L o c a t i o n o f Queen C h a r l o t t e I s l a n d s Aeromagnetic Surveys  112  27  V e r t i c a l Component Magnetic F i e l d Map o f SouthWestern B r i t i s h Columbia  115  28  Constant A l t i t u d e Aeromagnetic Survey Map of N o r t h e r n Moresby I s l a n d  i n -poek-et  29  Constant T e r r a i n C l e a r a n c e Aeromagnetic Survey Map o f N o r t h e r n Moresby I s l a n d  30  G e o l o g i c C r o s s - S e c t i o n and M a g n e t i c P r o f i l e s of N o r t h e r n Moresby I s l a n d Along A-A'  117  31  G e o l o g i c C r o s s - S e c t i o n and M a g n e t i c P r o f i l e s of N o r t h e r n Moresby I s l a n d Along B-B'  118  i n V i c i n i t y o f Queen  79  in-poeket-  XI  11  LIST OF FIGURES ( c o n t ' d ) TITLE  Aeromagnetic Map  of Southern Moresby I s l a n d  Aeromagnetic Map o f N o r t h e a s t e r n Graham Island Magnetic Anamaly Map of Southwestern Hecate S t r a i t and Northwestern Queen C h a r l o t t e Sound Magnetic Anomalies Along S h i p ' s T r a c k s i n Southwestern Hecate S t r a i t S t u c t u r e of Moresby I s l a n d and Western Strait Magnetic Anomaly Map  Hecate  of Queen C h a r l o t t e Sound  S e i s m i c R e f l e c t i o n and Magnetic Anomaly P r o f i l e Over Cape S t . James Ridge U.B.C. S e i s m i c P r o f i l i n g  System  I n t e r v a l V e l o c i t i e s o f Neogene Sediments f r o m S h e l l Canada W e l l s as F u n c t i o n o f Depth Bathymetry of Southwestern Hecate S t r a i t and Northwestern Queen C h a r l o t t e Sound Geology o f Moresby I s l a n d and W e s t - C e n t r a l Queen C h a r l o t t e B a s i n Bathymetry of S k i d e g a t e I n l e t L i n e Drawings of S e i s m i c P r o f i l e s A c r o s s Sandspit F a u l t , Skidegate Inlet L i n e Drawings of S e i s m i c P r o f i l e s of Southern Hecate Sub-Basin S e i s m i c P r o f i l e 76-16, Hecate Sub-Basin S e i s m i c P r o f i l e 76-19, Hecate Sub-Basin S e i s m i c P r o f i l e 76-25, Hecate Sub-Basin  xiv  LIST OF FIGURES ( c o n t ' d ) FIGURE  TITLE  PAGE 195  49  Composite L i n e Drawing of S e i s m i c ( s - 4 5 2 ) , Hecate Sub-Basin  Profiles  50  M u l t i f o l d Seismic Basin  51  L i n e Drawings of S e i s m i c C h a r l o t t e Sub-Basin  52  Seismic  53  M u l t i f o l d Seismic Sub-Basin  P r o f i l e from C h a r l o t t e  203  54  L i n e Drawings of S e i s m i c P r o f i l e s A c r o s s K u n g h i t Channel, C h a r l o t t e Sub-Basin  205  55  S e i s m i c P r o f i l e s A c r o s s Moresby Trough, Northern Queen C h a r l o t t e Sound  209  56  S e i s m i c P r o f i l e s A c r o s s Moresby and M i t c h e l l Canyons, Northwestern Queen C h a r l o t t e Sound  212  57  L i n e Drawings of S e i s m i c P r o f i l e s A c r o s s C o n t i n e n t a l S l o p e o f f N o r t h e r n Queen C h a r l o t t e Sound  214  58  Examples of Major F a u l t Systems C h a r a c t e r i z e d by P a r a l l e l - C o n v e r g e n t Wrenching  230  59  S t r a i n E l l i p s e and Composite of S t r u c t u r e s f o r R i g h t L a t e r a l Wrench System  233  60  E v o l u t i o n of S t r u c t u r e s A s s o c i a t e d w i t h Wrench F a u l t i ng  234  61  Rennel-Louscoone F a u l t on Queen C h a r l o t t e  238  62  Sandspit  63  Processing  64  D i f f e r e n c e Between IGRF and nomial R e f e r e n c e F i e l d s  P r o f i l e from Hecate  196  Sub-  P r o f i l e s of N o r t h e r n  201  P r o f i l e 76-31, C h a r l o t t e Sub-Basin  F a u l t on Queen C h a r l o t t e  199  Islands  Islands  Sequence of Magnetic Data T h i r d Degree P o l y -  249 302 311  XV  LIST OF FIGURES ( c o n t ' d ) FIGURE  TITLE  PAGE  65  Temporal V a r i a t i o n Curves o f T o t a l magnetic Field  317  66  Histograms o f C r o s s o v e r D i s c r e p a n c i e s  320  67  A l i a s i n g and Smoothing E f f e c t s i n Contour Map R e p r e s e n t a t i o n o f M a g n e t i c Data  326  68  Flow Diagram o f Program MPTAPE  330  69  Flow Diagram o f Program NAVF  335  70  Flow Diagram o f Program MERGE  341  71  Flow Diagram o f Program TRAK  369  xvi  LIST OF PLATES PLATE  TITLE  PAGE  I  P h o t o m i c r o g r a p h s o f Skonun Dredged Samples  219  II  Polynomorphs from Skonun Dredge Sample  223  III  Sea-Bottom Photographs from Western Hecate S t r a i t  226  IV  S a n d s p i t F a u l t on N o r t h e a s t e r n Moresby I s l a n d  251  xvi i  ACKNOWLEDGEMENTS The the  author  i s s i n c e r e l y g r a t e f u l t o Dr. R.L. Chase f o r  s e l e c t i o n of the t h e s i s t o p i c ,  field  expenses, f o r c o n s t a n t  f o r securing  funds  encouragement d u r i n g  t o defray  the length of the  p r o j e c t , and f o r c r i t i c a l r e a d i n g o f t h e m a n u s c r i p t . In  addition t o the o f f i c e r s  ENDEAVOR, t h e author Department Mr.  of  Mrs. J . Carne  students),  and  cruise  Mr. R. Maxwell  U.B.C.  who  (nee G r e t t e )  ably  76-10.  (graduate  -  a s s o c i a t e ) , Mr. D.  Mr. B. Jensen-Schmidt  students),  I.O.U.B.C.  Sciences,  (research  assistant),  graduate  o f t h e C.F.A.V.  extends h i s a p p r e c i a t i o n t o colleagues  Geologic  R.D. Macdonald  and crew  The  student)  (research  and Ms. D. Runkle  (graduate  Mr. G. M y r f i e l d  i n data  author  Dr. R.L. Chase, Reimer  and  assisted  at the  thanks  acquisition  (underduring  Dr. R.L. Chase and  f o r assistance during  t h e two week-  long f i e l d e x c u r s i o n s t o t h e Queen C h a r l o t t e I s l a n d s . Drs. R.M. Clowes and W.C. committee,  a r e thanked  manuscript. Geoscience  f o r their  Mr. R.G. C u r r i e Centre)  provided  Barnes, members o f t h e t h e s i s comments  (Geological  and  Survey  considerable  advice  critique  o f Canada,  on  chapters  in this  thesis  Dr. R.L. Armstrong and Ms. J . Nelson and  Mr. C . J . Zinkan  portions  (Esso  of the t h e s i s .  concerned  data. with  He a l s o  magnetics.  (Department o f Geology, U.B.C.)  Resources Discussions  Pacific  and a s s i s t a n c e i n  computer programming and p r o c e s s i n g o f magnetic f i e l d commented  of the  Canada) with  critically  reviewed  Dr. A. S u t h e r l a n d  Brown  ( B r i t i s h Columbia Department o f Mines) and Mr. D.R. S h o u l d i c e  (Shell  Canada Resources) were o f c o n s i d e r a b l e b e n e f i t t o t h e a u t h o r .  xvi i i  Ms. Dr. G.E. Rouse  S.  and  o f Botony,  of  Zoology,  Canada  Resources  L t d . (courtesy  Mr. D.W.  Smith)  maps  Islands  were  Department  of  Queen  Charlotte  Dr. A. S u t h e r l a n d Brown  (B.C.  Mr. A.T. A v i s o n  Mines  were measured Physics  data  Ltd.).  Magnetic  remnant  (courtesy Hicken  and  intensities.  L t d . a r e thanked  Financial  provided  by  Mines)  and  susceptibilities  E. I r v i n g . Shell  f o r release  Dr. E I r v i n g  Canada  Resources  of data  on  support f o r the project  cores  supplied and  Amoco  radiometric  age  samples.  was  provided  by t h e  o f Energy, Mines and Resources (E.M.R. Research Agreement  1 135-013-4-25/76),  British  Petroleum Resources; S h e l l Council  Aeromagnetic  Dr. R.L. C o l e s ) on o r i e n t e d  d e t e r m i n a t i o n s o f Queen C h a r l o t t e I s l a n d s and w e l l  Department  kindly  f o r t h e a u t h o r by t h e D i v i s i o n o f Geomagnetism, E a r t h  by D r s . A.  on  Canada  (Dennison  Branch, Ottawa  collected  epifauna  Survey o f Canada ( c o u r t e s y Dr. D.L. T i f f e n )  Basin.  the  and  samples r e s p e c -  r e l e a s e d s e i s m i c d a t a from t h e Queen C h a r l o t t e of  U.B.C.)  U.B.C.) i d e n t i f i e d  from bottom photographs and dredge  The G e o l o g i c a l  Shell  (Department  (Department  and polynomorphs tively.  Millen  (grants  Columbia  Department  of  Mines  Canada Resources L t d . , N a t i o n a l  t o Dr. R.L. Chase), and t h e U n i v e r s i t y  and  Research  of B r i t i s h  Columbi a. In a d d i t i o n t o academic and r e s e a r c h a s s i s t a n t s h i p s , t h e author  received  Society (1976-77)  of and  financial  Exploration a University  Summer F e l l o w s h i p ( 1 9 7 7 ) .  assistance  i n t h e form  Geophysicists  Trust  of B r i t i s h  Columbia  of  Fund  a  Canadian  Scholarship  Graduate  Research  xix  Typing Ms. L L e e ,  assistance  Mrs. J . Watmore  R e p r o d u c t i o n Departments  and  was  provided  Ms. D. Gray.  a t Esso Resources  by The  Ms. L Donders, Drafting  and  Canada L t d . are thanked  f o r h e l p i n p r e p a r i n g some o f t h e i l l u s t r a t i o n s  i n the t h e s i s .  1  PREFACE  As was  i n i t i a t e d , the  p r i m a r y purpose  t o i n v e s t i g a t e the g e o l o g y and  of the Queen C h a r l o t t e B a s i n .  of  the t h e s i s  study  s t r u c t u r e of the w e s t e r n margin  S p e c i f i c o b j e c t i v e s were:  1) t o map  a  p o s s i b l e submarine e x t e n s i o n of the S a n d s p i t F a u l t and d e t e r m i n e , i f p o s s i b l e , t i m i n g , magnitude, and sense of d i s p l a c e m e n t and s h i p t o complementary shallow nature Neogene  Queen and  wrench  Charlotte  fault  Basin  distribution  of  systems; 2) t o map  Neogene  bedrock;  subcropping  s t r u c t u r e of  3)  (basement)  relation-  to  ascertain  rocks  beneath  resolution  seismic  strata. Field  investigations  included  high  and magnetic p r o f i l i n g and bottom s a m p l i n g and photography i n s o u t h western  Hecate  (I.O.U.B.C.  Strait  Cruise  and  76-10;  northwestern  data  (exclu-  s i v e of g r a v i t y measurements) t o be a c q u i r e d f o r t h e c e n t r a l  portion  F i g . 1).  non-proprietary geophysical  the Queen C h a r l o t t e B a s i n .  program  1976,  Sound marine  of  18-28,  Charlotte The  s u r v e y c o m p r i s e s the f i r s t  June  Queen  Only r e c e n t l y  (1979)  has  of s y s t e m a t i c r e s o u r c e mapping by t h e Department  the of  Mines, and Resources ( P a c i f i c G e o s c i e n c e Centre) and Canadian  joint  Energy, Hydro-  g r a p h i c S e r v i c e been extended o v e r t h i s p o r t i o n of the b a s i n . Two  week-long  field  I s l a n d s were made d u r i n g May  excursions  to  and O c t o b e r , 1976.  the  Queen  Charlotte  Work c o n s i s t e d  g r a v i t y and magnetic measurements a c r o s s the S a n d s p i t F a u l t , reconnaissance metric  geologic  mapping,  and  sample  age d e t e r m i n a t i o n s and magnetic  Preliminary  results  of both onshore  and  collecting  susceptibility marine  of  limited  for  radio-  measurements.  investigations  were  2  Fig. 1  L o c a t i o n o f s t u d y a r e a showing s h i p ' s t r a c k s . i s i n d i c a t e d by heavy l i n e .  Sandspit Fault  3 given  i n Young and  Chase ( 1977a, 1977b, 1977c) and  Chase and  Young  (1977). The laboratory in  s t u d i e s and  terms  of  recorded  on  Cordillera. the  Queen  the  history  the  Queen  Charlotte  to  are the  discussing  included  the  constrained  plate  Basin.  ages  of  oceanic I  major  1  and  tectonic western  structure  Charlotte Basin (chapter  and  to  serve  as  the  igneous  volcanic the  a  the  basis  for  western margin of unpublished  rocks  and  plate  introduce  plutonic  Sandspit  and  the  radiometric  (chapter  I I I ) have  episodes  and  Rennel-Louscoone  and  stratigraphy  i s summarized i n c h a p t e r V)  and  of  IV.  aeromagnetic p a t t e r n s  the  (chapter  d i s t r i b u t i o n of pre-Neogene basement seacrop and from for  a  magnetics  data,  is  submarine e x t e n s i o n  described  of  the  Neogene  Magnetic rock  used t o a i d i n t e r p r e t a t i o n of marine magnetic d a t a .  Evidence  Canadian  systems. The  primarily  data events  Pacific'-America II)  previously  Islands  i n t e r p r e t the  and  and  development of and  and  s t u d i e s r e l a t e d t o the g e o l o g y of  area  t i m i n g of movement on  wrench-fault  motions  (chapters  New  and  Islands  and  study  Queen C h a r l o t t e  refined  ties  Islands  structural  Queen C h a r l o t t e d a t e s of  of  analyze  Charlotte  regional  the  d e s c r i b e the r e s u l t s of f i e l d  endeavors t o  A summary of p r e v i o u s  interactions reader  f o l l o w i n g chapters  Sandspit  proper-  VI)  have  The  nature  subcrop, in  Queen  been and  identified  chapter Fault  VII.  and  its  p o s s i b l e r o l e i n b a s i n margin e v o l u t i o n i s a l s o d i s c u s s e d .  margin  of  reflection  The  s t r u c t u r e of s h a l l o w  the  Queen  profiles  Charlotte  included  Neogene bedrock  Basin  i n chapter  is  at the  illustrated  VIII.  Major  by  western seismic  physiographic  4 features  of the c o n t i n e n t a l  shelf  and s l o p e of n o r t h w e s t e r n Queen  C h a r l o t t e Sound a r e a l s o i l l u s t r a t e d . the  seafloor  of western  Hecate  Strait  A bedrock sample r a i s e d and bottom  photographs  from are  d e s c r i b e d i n c h a p t e r IX. In Chapter X, a model f o r t h e g e o l o g i c a l development suggested  o f t h e w e s t e r n margin based  and s t r u c t u r a l  o f t h e Queen C h a r l o t t e  on o b s e r v a t i o n s and c o n c l u s i o n s  Basin i s  o f t h e s t u d y and  comparisons w i t h s i m i l a r b a s i n s a l o n g t h e P a c i f i c m a r g i n .  5  CHAPTER 1  SUMMARY OF THE OF THE  GEOLOGY AND  TECTONIC HISTORY  QUEEN CHARLOTTE ISLANDS  INTRODUCTION The Insular  Queen C h a r l o t t e I s l a n d s f o r m t h e n o t h e r n p a r t of  Tectonic  Belt  Paleozoic(?)-Recent  of  the  Canadian  geologic history  of  Cordillera.  the  The  the Late  Islands i s s i m i l a r  to  t h a t of Vancouver I s l a n d , a l t h o u g h d i f f e r e n c e s i n t i m i n g and  facies  become more i m p o r t a n t from t h e b e g i n n i n g of the  Wrench  faulting  and  the  interaction  of  oceanic  Cretaceous.  "Pacific"  plates with  the  western  C o r d i l l e r a have p l a y e d a s i g n i f i c a n t r o l e i n t e c t o n i c d e v e l -  opment  of  the  controlling  Islands  and  likely  were  the  dominant  factors  in  t h e t h r e e major p e r i o d s of v o l c a n i s m , f o u r main p e r i o d s  of s e d i m e n t a t i o n and  two  major p e r i o d s of p l u t o n i s m t h a t have been  recorded. S u t h e r l a n d Brown Islands  on  a  regional  d e s c r i p t i o n of the which an  (1968)  scale  (1:125,000)  rock u n i t s of the  of  types  which  t h e Queen C h a r l o t t e B a s i n . specific  aspects  of  the  provided  The  study area.  Islands (Table  geophysical data rock  and  Queen  Charlotte a  detailed  following  summary,  h i s comprehensive s t u d y , i s i n t e n d e d  i n t r o d u c t i o n t o the r e g i o n a l  tion  the  exposed g e o l o g i c u n i t s .  r e l i e s e x t e n s i v e l y on  interpret  mapped  and may  Knowledge of the major  I) i s i m p o r t a n t  establish  the  i n attempting  approximate  u n d e r l i e Neogene-Recent  Reference  or  to  distribu-  sediments  i s made t o a l l p u b l i c a t i o n s  stratigraphy  as  b i o s t r a t i g r a p h y of  in on the  6  TABLE I :  PERIOD  QUATERNARY  TABLE OF FORMATIONS FOR QUEEN CHARLOTTE ISLANDS  1  .MAXIMUM  EPOCH/ STAGE  GROUP OR FORMATION  RECENT Cape Ball Formation  PLEISTOCENE  LITHOLOGY  [ECTONIC OR HICKNES^ DEPOSITIONAL (METERS) ENVIRONMENT  [Alluvium  Non-mar1ne and near-shore marine  frill,  sand, s i l t ,  klay,  ,  Glacial marine _ani noji-marlne  Conglomerate Pyroclastic breccias volcanic Ss.norphyja, Rhyollte tuffs*flows Kootenay Fades dadte, basalt flows 1200+ Dana Fades  LOWER MIOCENE) OLIGOCENE  Masset Fm.  Basalt Mbr. Basalt flows, pyro- 1500+ clastlcs. andeslte Rhyollte Mbr Rhyollte, ash flows,! 2100 basalt flows 'Basalt breccias & Mixed Mbr. 2000 flows  EOCENE PALEOCENE ?  Skidegate Formation Is 11ts tone, sandstone) 600+  TURONIAN  . a. O  Halda  {j ae Fm.  ALBIAN  U3  BARREMIAN HAUTERIVIAN J^LiNGJAN.  BAJOCIAN TOARCIAN PLEINSBACHIANI SINEMURIAN HETTANGIAN NORIAN </>  KARNIAN  Near-shore marine  C Mbr. B Mbr. A Mbr.  Maude Formation  Slltstone, sandstone) 1200+ conglomerate  Andesltlc agglomerates and tuffs Shale, Ss. tuffs lalcareous ami l a p l l l i tuffs  290 30+ 200  Shale, sandstone  225  Black Argil- Arg1111te.sltstone, Hte Mbr. shale, Ls., Ss. Kunga Fm.  Black Limestone Mbr. Grey Limestone Mbr.  Karmutsen Formation  Carbonaceous limestone, arglllHe  PEfWSYLVAWIAN  Sicker Group ?  Limestone, shale, basalt, diabase  Modified In part from Sutherland Brown (1968).  Syn tec ton 1c BathoHths Marine  Lower Cretaceous (?) Upper Jurassic Collision event  Volcanic arc Marine Marine  580 270  180 Limestone Basalt flows & pillows, tuffs, minor 4.300  U s a t i S K B J s ^ , OR  Shallow marine  [Shale, siltstone 330 Sdstone Mbr. Sandstone, slltstonej 820  Shale Mbr.  Post Tectonic PIutons Middle Miocene Upper Eocene Ridge subductlon ? Divergent wrenching ?  Divergent wrenching  Near-shore marine or non-marine  Longara Formation  Yakoun Fm.  Rifting ?  1200  Honna Formation  CENOMANIAN P  'Conglomerate, sandstone, shale  Mantle plume ?  INTRUSIVE ROCKS  Marine  Ocean crust ? Volcanic arc ? Intenirc_bMlnJ> Shallow marine  (not ex posed ?)' Volcanic arc ?  For other data sources, see text.  7  I s l a n d s t h a t have appeared i n t h e l i t e r a t u r e i s r e f e r r e d t o Sutherland works.  Also  Cordillera  noted  that  Insular B e l t .  s i n c e 1968; t h e reader  Brown (1968) f o r a b i b l i o g r a p h y o f e a r l i e r  are  any  have d e s c r i b e d Regional  recent  tectonic  models  f o r t h e development  major wrench f a u l t i n g , radiometric  volcanic  the  of the  o f t h e p o s s i b l e Upper  t e c t o n i c h i s t o r y o f t h e Queen C h a r l o t t e I s l a n d s .  The s t r u c t u r a l  new  of  g e o l o g i c a l c o r r e l a t i o n s and p a l e o m a g n e t i c s ,  i n p a r t i c u l a r , have advanced o u r u n d e r s t a n d i n g Paleozoic-Mesozoic  syntheses  h i s t o r y o f t h e I s l a n d s , t h a t has i n v o l v e d  i s discussed  age d a t a  that  i n Chapter  has c o n s t r a i n e d  and p l u t o n i c e p i s o d e s and f a u l t i n g  Islands, i s described.  S i m p l i f i e d geologic  X.  In Chapter I I I ,  timing  o f t h e major  on t h e Queen  Charlotte  maps a r e i l l u s t r a t e d i n  F i g s . 61 and 62.  UPPER PALEOZOIC ( ? ) AND THE ALLOCHTHONOUS INSULAR TERRANE  Positive Triassic  on  Sutherland  Charlotte  shale,  Island  Vancouver overlies  rocks  Islands  glomerophorphyritic  a t t h e base o f Upper T r i a s s i c  Moresby  and  Queen  of  ( F i g . 42)  Island, rocks  the  which  Karmutsen  of the Sicker  Group  older  has  Brown (1968, p.50) however, r e p o r t e d  limestones, sills  the  identification  not  than  Upper  been  made.  tuffaceous  pillow  basalt  crinoidal  and  diabase  Karmutsen F o r m a t i o n on  might  be  Upper  unconformably (Sutherland  or  eastern  Paleozoic.  On  disconformably  Brown, 1966; M u l l e r  Carson, 1969; M u l l e r e t al_, 1974; M u l l e r , 1980) t h a t crop o u t i n  the c o r e o f u p l i f t s along  the c e n t r a l part of the i s l a n d .  Paleozoic,  Queen  some  of  the  Charlotte  Islands  rocks  I f Upper might  be  8  correlated  with  the  upper l i m e s t o n e  S i c k e r Group, c o n s i d e r e d  ( B u t t l e Lake Formation) of  on t h e b a s i s of f u s u l i n i d s and  t o be P e n n s y l v a n i a n or Lower Permian (Danner, 1977; On bryozoans t h a t brachiopods boreal  Island  have c l o s e  ties  and  realm  1977).  Vancouver  fusulinids,  and  the  with  Urals  Tethyan  with  t h o s e of  of  Russia  could  have  environments,  Permian  and  s o l e l y from  i t i s more l i k e l y  t i o n of a l l o c h t h o n o u s separated  older  1971;  Scattered lying  the  Upper  discussion)  has  been  should  argil lite  outcrop  Jurassic 2000 km  in  must  be  of  see  the  Danner, contrast  (Danner's  Trafton-  Islands,  northern  local  differences depositional  o r i g i n a t e d by  (Tozer,  juxtaposi-  representing  1970;  ( i n c l u d i n g the Wrangellia  Monger  Jones,  1973;  limestone  as  Sicker  succession a  thick  Muller, shelf  Karmutsen F o r m a t i o n on the Queen C h a r l o t t e  Islands  those  Though f a u n a l  tectonic slivers  interpreted  and  early  Australia;  and  Juan  widely  and  Ross,  Group),  under-  tectonic  inferred  insular terrain  from that  from southern Alaska  history rocks  extends  of  1977)  following  Paleozoic  o v e r l a i n by  sediments.  arc Lower  Further  at the  work  base of  the  Islands. of  the  an  Upper  along  to eastern  (see  Upper  e s t a b l i s h whether a s i m i l a r sequence l i e s  The  and  contain  Monger, 1977).  Triassic  sequence ( R i c h t e r and Permian  San  variations  provinces  Monger e t aj_, 1972;  Timor  faunas  on  1977).  limestones  (for discussion  that they  "oceanic"  biogeographic  Muller,  s i m i l a r to  s o u t h e r n Intermontane B e l t .  resulted  macrofossils  c o o l e r water c o n d i t i o n s  Cache Creek b e l t ) found f u r t h e r e a s t Cascades, and  Lake  however, are  These faunas r e p r e s e n t  markedly  Buttle  the  the  Queen  Charlotte  Paleozoic-Lower  continental  Oregon ( F i g . 2 ) .  margin Unifying  9  Wrangellia  Location of generalized. Triassic columnar sections (Fig. 2) of typical Wrangellia sequence •  Western limit of Triassic rocks related to the North American craton  /  Fig.  2  Map  showing d i s t r i b u t i o n  sequences.  " 4  of  .  Upper T r i a s s i c  Reproduced from Jones  Wrangellia  e t al_ (1977,  Fig.  1)  10  c h a r a c t e r i s t i c s of t h i s t e r r a n e (termed 1977)  include grossly similar  Upper  "Wrangelia"  by  Paleozoic-Lower  u n i t s , f a u n a s , t e c t o n i c s t y l e and g e o l o g i c h i s t o r y . continuity areas  cannot  now  be  ( e a s t e r n Oregon,  B a r a n o f f and Alaska  Chichagof  mountains)  similar  the  t h a t these  constituting  one  demonstrated  Vancouver  between  Island,  disjunct  rocks  areas  continuous  allochthonous  constitutes  an  been c a r r i e d  p o s s i b l y e a s t of i t s o r i g i n a l  allochthonous 1977; the  Danner, 1977; western  a^,  1972;  Monger and  Canadian  1).  Cascades  Cordillera  "suspect"  Stratigraphic  and  terrane.  fomerly  Considerable  (see below) suggests block  of  that  subcontinental  to  the  east,  and  terranes  also  1979;  these  thought  terranes  include  (see  1976;  the  to  suggests  be  Monger, In  predominately  Taku, B r i d g e R i v e r a]_,  Coney e t  control  its  Coney e t aj_, 1980).  T r a c y Arm,  structural  throughout  Templeman-Kluit,  Price,  " o c e a n i c " P a l e o z o i c - L o w e r Mesozoic Northern  as  so  position.  dissimilar  (Monger e t  regarded  a considerable distance north  i s juxtaposed  against  in particular  must be  Wrangellia  length,  Charlotte Islands,  are  Triassic  paleomagnetic  entire  outcrop  Upper  now  Wrangellia  major  direct  eastern  homogeneous,  t h a t has  Although  rock  I s l a n d s , W r a n g e l 1 - S t . E l i a s Mountains,  e v i d e n c e , both g e o l o g i c and  dimensions  Jurassic  the  Queen  Jones e t a]_,  1980,  and Fig.  that Wrangellia  and the A l e x a n d e r t e r r a n e of s o u t h e a s t e r n A l a s k a (Jones e t aj_, 1972; C h u r k i n and Cretaceous American 1977;  Eberlein, before  margin  Coney  convergence  1977)  final  collision  i n Lower  et caused  a2,  were amalgamted and  translation  Concurrent and  Jurassic-Lower  a c c r e t i o n onto  Cretaceous-Early  1980).  i n Upper  Tertiary and  intra-plate  post  the  (Jones  North et  jH,  accretionary  deformation  with  Ill  reactivation  of  Cretaceousof  o l d sutures  Lower  hundreds  Tertiary  of  stages  kilometers  southern  Alaska,  Tertiary systems  of  the  Alaskan and  successive  t o step  on  accretion  Chugach  disrupted  northwestward  Rennel-Louscoone, and o t h e r final  that  Wrangellia.  strike-slip  Tintina,  displacements  Denali,  and Canadian f a u l t s  later  tectonic  against  Wrangellia  southward  i n late  Cretaceous  Yalakom,  may  record  adjustments.  a c c r e t i o n of t h e Upper  terrane  Upper  In  Mesozoic-Early  caused time  subduction  (Coney  eta l ,  1980). Symons  (1971)  and  Irving  and  Yole  (1972)  determined  paleomagnetic  p o l e s f o r " W r a n g e l l i a n " Karmutsen b a s a l t s of Vancouver  Island.  poles  The  magnetization)  (though  l i e 46+15  based  In o r d e r  I s l a n d paleomagnetic  have had t o l i e a p p r o x i m a t e l y  e x t r u s i o n o f Karmutsen l a v a s .  Islands  poles  (Hicken  15°  p o l e s , Vancouver I s l a n d  3,000 km f u r t h e r south  during  (Because o f T e r t i a r y ? r e m a g n e t i z a t i o n  f o r Karmutsen  and I r v i n g ,  west  remnant  Upper T r i a s s i c p o l e f o r t h e s t a b l e North American c r a t o n .  paleomagnetic  about  unstable  t h e mean  would  and  relatively  of  t o r e c o n c i l e Vancouver  south  on  rocks  of  the  Queen  Charlotte  1977, a r e not s i g n i f i c a n t l y  displaced  from mean c r a t o n i c p o l e s . ) Paleomagnetic Cretaceous, western 1979)  from  (Packer  and M i d d l e - L a t e  and  Stone,  Triassic  1974; Stone  Nicolai  Island.  Alaska  30°  The d a t a since  Late  Jurassic,  Upper  Peninsula,  south-  and  Packer,  b a s a l t s from  ( H i l l h o u s e , 1978) are i n g e n e r a l  Vancouver  southern  f o r Middle-Upper  and Eocene sediments from t h e A l a s k a  Alaska  Mountains  poles  suggests Triassic  the  Wrangell  agreement w i t h northward and  1977;  results  t r a n s l a t i o n of  18°  since  Upper  12  Fig. 3  S c h e m a t i c model o f t h e breakup o f " P a c i f i c a " , o p e n i n g o f the P a c i f i c Ocean, and t h e r e s u l t i n g c o l l i s i o n o f a l l o c h thonous t e r r a n e s a t c i r c u m P a c i f i c m a r g i n s . Ages o f r e c o n s t r u c t i o n stages are approximate only. Fine l i n e s mark t h e p r e s e n t - d a y c o n t i n e n t a l o u t l i n e . Heavy l i n e s mark t h e f o r m e r p o s i t i o n o f c o n t i n e n t s d u r i n g g e o l o g i c a l evolution. Reproduced from Nur and Ben-Avraham (1977, F i g . 1 ) .  1'3  Jurassic delayed  (Hillhouse, until  1978).  latest  Much  Cretaceous,  of  this  accompanied  r o t a t i o n ( S t o n e , 1977; Stone and P a c k e r , The other  portions  uncertain. slip  exact of  origin  the  motion  from  southwestern  Charlotte  Wrangellia  North  may  America central  be  a fragment  of e a s t e r n  America  as North America d r i f t e d Atlantic  (Monger  Asia  I s l a n d s and  terrane  remains  by l a r g e s c a l e  that  northwestward  strike-  and C e n t r a l  (Monger, e t aj_, 1972; Jones e t a l _ , 1972; M u l l e r , or  been  by a l a r g e c l o c k w i s e  The t e r r a n e may have been r a f t e d  faulting  have  1979).  o f t h e Queen  allochtonous  may  America  1977; Stone, 1977)  collided  with  North  a f t e r opening- o f t h e  e t _aj_, 1972; Danner,  1977).  Nur  and  Ben-Avraham (1977) e n v i s a g e t h a t W r a n g e l l i a was f o r m e r l y p a r t o f a mid-Permian  continental  mass  ("Pacifica")  and was  carried  to i t s  p r e s e n t p o s i t i o n embedded i n t h e a n c i e n t K u l a and/or F a r a l l o n  plates  (Fig. 3).  UPPER TRIASSIC-LOWER JURASSIC WRANGELLIA SUCCESSION  On succession  Queen  include  Charlotte the  Karmutsen  Karmutsen c o n s i s t s o f t h o l e i i t i c sion of c h l o r i t i z e d lava,  pillow  breccia  4,000 meters  thick,  limestone.  Brown, 1968).  Kunga  the W r a n g e l l i a  Formations.  amygdaloidal b a s a l t , w i t h very minor  The e n t i r e  was d e p o s i t e d m a i n l y  by g e n t l e s u b s i d e n c e  of  l a v a s i n a g e n e r a l upward  and aquagene t u f f  lenticular  rocks  and  g r e e n s t o n e , massive  intercalated  accompanied  Islands,  of the volcanic  pile  succespillow  amounts o f  sequence,  or e n t i r e l y  The  more  than  subaqueously (Sutherland  A l t h o u g h t h e age o f t h e Karmutsen F o r m a t i o n on Queen  14  Charlotte  Islands  Vancouver  Island  where  between  Upper  interval  span of p o s s i b l y  i s poorly the  defined, entire  (Jeletzky,  probably  sequence  Ladinian-Upper  10 Ma  i t is  was  Karnian  1970;  similar  produced  (Upper  to  in  the  Triassic),  M u l l e r e t _al_, 1974;  a  Muller,  1977). Other pillow  basalts  than  on  Bonilla  Mount Waddington map Coast  Plutonic  Vancouver  Island,  Island,  along  outcrops Jervis  Complex  element  percentage  (see  chemistry  of  Hutchison  pillow  to  Muller  was  the s o u t h e r n i n s u l a r criteria of  e_t _al_,  ocean  crust,  Jeletzky, Griffiths, et  suggests  a direct  the  i . e . ridge  1970;  Souther,  that  result Central  i n the  The  the  Nicolai  i n age  contains  and  a  lower  tuffs  (Muller,  1977;  rapid  outpouring  of  rifting  that  America.  separated  unequivocal  f o r determining tectonic  environment  r o c k s have been v a r i o u s l y or  of  No  ocean  K u n i y o s h i , 1972),  1977;  but  aquagene  t e r r a n e from  and  1979).  i s similar  Karmutsen  and  have been e s t a b l i s h e d  the Karmutsen  and  1977).  (1977)  volcanics  the  basalts  S o u t h e r , 1977; Jones e t aj_,  Karmutsen  Inlet,  Karmutsen  a r e a suggest c o n t i n u i t y of W r a n g e l l i a i n t o  greenstone of the W r a n g e l 1 - S t . E l i a s Mountains major  of  1977)  island island  interpreted  ( S u t h e r l a n d Brown, arc  (Monger e t  or m a r g i n a l - i n t e r a r c  as  1968;  a l _ , 1972;  basin  (Muller  a l , 1974). The  ably  overlain  sandstone  of  Karmutsen by  Formation  limestone,  the  Upper  ( S u t h e r l a n d Brown,  1968).  i s conformably  argil l i t e  (siliceous  Triassic-Lower Jurassic The  formation  t h r e e i n f o r m a l members ( o p . c i t . ) :  has  been  or  paraconform-  mudstone) Kunga  and  Formation  subdivided  into  1) a massive g r e y l i m e s t o n e member  15  that overlies aceous  t h e Karmutsen; 2) a m i d d l e t h i n l y - b e d d e d b l a c k c a r b o n -  member;  member.  and  3)  an  upper  thinly  bedded  argillite  The upper two members c o n t a i n admixtures o f l i t h i c s i l t and  sand  w h i l e t h e upper  tuff  ( S u t h e r l a n d Brown, 1968; T i p p e r , 1977).  idual  black  member a l o n e c o n t a i n s t h i n  members a r e g r a d a t i o n a l  beds o f s i l i c e o u s  C o n t a c t between  and i n some c a s e s  indiv-  diachronous.  composite t h i c k n e s s o f t h e f o r m a t i o n ( o f t y p e l o c a l i t y  The  sections) i s  at l e a s t 950 meters. The  lower member  Brown,  1968; Cameron  corals  and p e l e c y p o d s .  ceans to  and T i p p e r ,  K a m i an  1981) c o n t a i n s  age ( S u t h e r l a n d poorly  The m i d d l e member c o n t a i n s common  preserved pectina-  ( H a l o b i a and Monoti s) and r a r e ammonites o f l a t e Upper K a m i an  Upper N o r i a n age.  contains  Sinemurian  lowermost  interval  blage  of probable  The uppermost t w o - t h i r d s o f t h e upper  arietitid  ammonites  lacks megafossils.  of p a n t a n e l l i a n  radiolarians  member  (eg. A r i e t i t e s ) , while the However, an abundant  from  t h e lower  interval  assemi s of  p r o b a b l e H e t t a n g i a n ( p r e - S i n e m u r i a n ) age (Pessagno and Blome, 1980). The Vancouver  Island  Quatsino,  Parson  Bay, and Harbledown  are 1 i t h o l o g i c a l l y ,  Formations o f  stratigraphically,  and p a l e o n -  t o l o g i c a l l y s i m i l a r t o t h e l o w e r , m i d d l e , and upper members r e s p e c tively  of  Jeletzky, similar  the  Kunga  1970; M u l l e r ,  Formation  ( S u t h e r l a n d Brown,  1977; M u l l e r  age and l i t h o l o g y  from  e t a_l_, 1974).  other  outcrop  areas  1966, 1968; Sediments  of  of W r a n g e l l i a  have been noted by M u l l e r ( 1 9 7 7 ) , Jones e t aj_ (1978) and P l a f k e r and Hudson ( 1 9 8 0 ) . The Kunga l i m e s t o n e ( b a s a l member) was d e p o s i t e d i n open ocean  at probable  shallow  depths,  on  submerged  Karmutsen  lavas.  16  With  advancing  a n o x i c , and  time  the  depths may  marine  basin  became  have i n c r e a s e d .  basic  (Karmutsen?) source  rain  and  eventually,  r o c k s was  with  barred,  Fine d e t r i t u s  the  from  introduced, i n i t i a l l y  increased  rate  ( S u t h e r l a n d Brown,  of  basin  uplifted as  a  slow  filling,  currents  H a l o b i a and  Monotis b e a r i n g sediments (middle member) were d e p o s i t e d  shallower waters;  later  was  d e p o s i t e d as an  ashfall.  Jeletzky,  by  turbidity  in  1968;  bottom  t u f f a c e o u s m a t e r i a l , of  1970).  unknown  origin,  LOWER-UPPER JURASSIC SUCCESSION  Conformably Charlotte  Islands  i s the  tion,  a thin  lite,  shale, calcareous  limestone  (up  t o 225  (lense  Although  and  considered  P l e i n s b a c h i a n and and  overlying  Lower-early  earlier  studies  has  (Tipper,  T i p p e r , 1981).  An  1976;  age,  to  expanded  1967;  e a r l y Middle 1981).  A  only  Toarcian  Toarcian  ammonites,  1970;  T i p p e r and  and  include  number of  1968). beds  of  stratigraphic  Maude  Formation  Cameron, 1979;  belemnites,  Cameron  to  and  pelecypods  and M i d d l e  1968;  Toarcian-  (Cameron and  abundant and  and  comprises  S u t h e r l a n d Brown,  belemnites  beds have y i e l d e d an  and  Lower t o e a r l y M i d d l e  F r e b o l d , 1970)  B a j o c i a n ammonites and  argil-  minor t u f f  detailed the  d e s c r i b e d i n e a r l i e r s t u d i e s (McLearn, 1949; Freehold,  u n i t comprising  abundant megafauna w i t h i n the f o r m a t i o n  Pleinsbachian-Lower  Queen  J u r a s s i c Maude Forma-  recent  and  the  ( S u t h e r l a n d Brown,  workers  Tipper  on  s a n d s t o n e , and  interbeds  i n c l u d e a l l of P l e i n s b a c h i a n and B a j o c i a n time  Middle  shale, l i t h i c  Lower T o a r c i a n  biostratigraphic  argillites  meters) sedimentary  nodule) by  Kunga  Tipper,  distinctive  17  microfauna and  i n c l u d i n g f o r a m i n i f e r s , o s t r a c o d s and f i s h  Tipper,  1981)  Brome, 1980). radiolarians  and  pantanel1inae  The o c c u r r e n c e i s restricted  of well  t o black  t e e t h (Cameron  radiolarians preserved  limestone  (Pessagno  and  Lower P l e i n s b a c h i a n  (calcilutite)  nodules  ( op.cit.). The part  Maude F o r m a t i o n  o f t h e Harbledown  (Jeletzky,  Formation  southeastern  1976).  on n o r t h e a s t e r n  Coast  Presumably  succession  in  Mountains  these  an  rocks  extensive  region  were  zone",  Jeletzky,  1970),  F a u l t and t o t h e west on western arc  deposited  northwest  bounded  (Tipper  and  on  areas o f Richards,  the Wrangellia  trending  (1976);  Island  sedimentary  H a r r i s o n Lake, and Manning Park  ("Vancouver B a s i n " , T i p p e r and R i c h a r d s cent  Vancouver  1970; M u l l e r e t al, 1974) and p r e d o m i n a t e l y  r o c k s i n t h e Taseko Lakes, the  has been c o r r e l a t e d w i t h t h e upper  marine  basin  "tectonical l y quies-  t o the east  by t h e Yalakom  Vancouver I s l a n d by c a l c - a l k a l i n e  v o l c a n c i c s o f t h e Lower J u r a s s i c Bonanza Group ( F i g . 4 ) . ( A r c  volcanism sites,  on Queen C h a r l o t t e I s l a n d s , r e p r e s e n t e d  was d e l a y e d  until  Middle  Jurassic).  by Yakoun  Emplacement  and  andeuplift  of t h e Coast P l u t o n i c Complex has o b l i t e r a t e d much o f t h e e v i d e n c e for  a  single  Lower-Middle  e x t e n s i o n o f t h e Yalakom  Jurassic  basin  and  Hazelton  partly  Vancouver B a s i n . and  volcanic  The p r e s e n t  i t s juxtaposition  Trough was a r e s u l t  northwest  (1976) t h e Lower-Middle  Trough o f t h e Intermontane B e l t ,  continental  for a  fault.  A c c o r d i n g t o T i p p e r and R i c h a r d s Jurassic  and  a r c was  a partly  coextensive  marine  with  o b l i q u e t r e n d o f t h e Vancouver  against  dissimilar  rocks  of  the  the Basin  Hazelton  o f northwestward movement on t h e Yalakom F a u l t  18  Fig. 4  Paleogeography of the Lower and Middle J u r a s s i c of the Canadian C o r d i l l e r a showing l o c a t i o n of the Vancouver Basin and Hazel ton Trough. Reproduced from Tipper and Richards (1976, F i g . 14).  19  and  c o u n t e r - c l o c k w i s e r o t a t i o n of the  volcanics of  of western Vancouver I s l a n d , p o s s i b l y the  Queen C h a r l o t t e  Islands,  1 i t h o l o g i c a l l y and  regime of  If t h i s  Vancouver and  from r i f t i n g  and  even  the  Hazelton v o l c a n i c s ,  Bonanza volcanics  a l l similar  would have formed a s i n g l e c o n t i n u o u s  Queen C h a r l o t t e  tectonic  have  changed  i n Upper T r i a s s i c ( M u l l e r ,  1977)  during  of  Islands  the  must  transport  though  The  Yakoun  interpretation i s correct,  volcanism  northward  volcanism  and  chemically,  north-south b e l t .  initial  Vancouver B a s i n .  Wrangellia  transposition  to  and  subduction  amalgamation  and of  arc major  c r u s t a l blocks continued i n Jurassic time. In  Bajocian  time  s h i f t e d t o the  e a s t and  n o r t h w e s t , r e p r e s e n t e d by  ism  on  Queen C h a r l o t t e  breccias Park  at  Harrison  (Ladner  Islands  Lake  Group).  arc  (Yakoun  (Harrison  Andesitic  p r o b a b l e Maude e q u i v a l e n t s e a s t e r n Vancouver I s l a n d  volcanism  (Muller  the  Vancouver andesitic  Formation),  and  Lake F o r m a t i o n ) and  lava  i n the  in  flows  Buttle and  and  Lake and  Carson, 1969)  Basin volcan-  tuffs  and  i n Manning  tuffs,  overlying  Alberni  areas  of  have been  tenta-  (McLearn,  1949;  t i v e l y c o r r e l a t e d w i t h the Yakoun ( J e l e t z k y , 1970). The  Middle  S u t h e r l a n d Brown, 1968) volcanic  unit  and  t u f f s but  shale,  conglomerate  and  by  most A  member c o n s i s t s  shales,  pyroclastic  also  divided  Yakoun  Formation  i s a t h i c k (up t o  comprising  erates  lapalilli  Jurassic  including minor  1800  porphyritic volcanic  coal.  The  The  sandstones  and  agglom-  formation  has  been  sub-  members.  The  cemented  scoriaceous  (30 meter) B member c o m p r i s e s  interbedded  dominately  thin  andesitic  sandstones, s i l t s t o n e ,  S u t h e r l a n d Brown i n t o f i v e i n f o r m a l  tuff.  meters) p r e d o m i n a t e l y  tuffs,  of  overlain  calcite  by  thick  sections  lower-  (greater  20  than  300  meters)  of  andesitic  agglomerate  t u f f a c e o u s sandstone and conglomerate member  i s a predominately  shale,  calcareous  siltstone,  Yakoun  i s locally  conformable  (member  (member D).  sedimentary  unit  pebbly  The  the  Maude,  tuff,  uppermost E  of v o l c a n i c  conglomerate  over  C ) , and  and  sandstone, coal.  though  The  regionally  unconformable on a l l o l d e r u n i t s . The sedimentary tive  ammonite  gastropods, contains Hall  index  and  i n a d d i t i o n t o belemnites,  microflora,  Bajocian  Westermann,  Bathonian  and  microfauna.  Stephanoceras  1980)  while  1980) and  1980) f a u n a s . characteristic i n southern  Iniskinites  The  realm  A l a s k a and mainland  indicating  warmer  member  (McLearn,  water  dominated  (similar  British  by  The the  1949; T i p p e r and and  Cameron,  Columbia) c o n t a i n s  colonial  c o n d i t i o n s not r e c o g n i z e d  Charlotte  a much g r e a t e r d i s t a n c e than  B r i t i s h Columbia  Upper  strata  Islands  northerly  contains  to correlatable  Jurassic  Queen  1949;  genera  T h i s suggests  the  member  ammonite  r e g i o n s ( T i p p e r and Cameron, 1980). time  B  (McLearn,  ( F r e b o l d , 1979; T i p p e r  E member, though  of the Boreal  E  pelecypods,  The  ammonites  the  t o Lower C a l l o v i a n Seymourites  Cameron,  corals,  fossils  corals,  Middle  u n i t s (members B and E) c o n t a i n d i s t i n c -  have  southern  i n other  that s i n c e Middle been  transported  A l a s k a and  mainland  (op.cit.). Yakoun  Lower J u r a s s i c  v o l c a n i c s and  Bonanza) p r o b a b l y  related  arc rocks  represent  evolved  (including products  of  Karmutsen and o l d e r Upper P a l e o z o i c a r c r o c k s and sediments d e r i v e d l a r g e l y from p a r t i a l related  t o subduction  Griffiths,  m e l t i n g above t h e broad  zone o f h i g h heat  ( S u t h e r l a n d Brown, 1968; Monger  1977; M u l l e r ,  1977).  On  the east  coast  flow  e t a]_,  1972;  of the  proto  21  Queen  Charlotte  Islands  a  line  s h a l l o w marine Vancouver B a s i n the  later  Sandspit  processes volcanic below arc  Fault  distributed  sea  level.  volcanism  on  (Sutherland  volcanic  emplacement  and and  and  this  (?)  5).  or  the  1968).  and  Erosive  west  of  the  a l t e r n a t e l y above  Islands  erected  extended  s o u t h e r n p o r t i o n of  and by  southeast  Georgia S t r a i t s .  on  Vancouver and by  Queen  intense  Cessation mark  the i n s u l a r  and  plutons.  t h e i r t e c t o g e n e s i s was  faults.  and On  satellitic rocks,  Charlotte  deformation  Queen  Charlotte  d i k e s and  mostly  sills  hornblende  Islands  uplift  and  According  to  related to  Alexander terranes  West Kano B a t h o l i t h s , S a n d s p i t  plutonic  the  e a r l y Upper J u r a s s i c may  syntectonic-j b a t h o l i t h s  Yalakom  were  of  subparallel to  1966,  east  out  M u l l e r , 1977).  postdated  s i m i l a r plutons, The  i n the  a c c r e t i o n of  Chase (1981),  and  Charlotte  trend  cones  ( J e l e t z k y , 1970)  Queen C h a r l o t t e and  s u t u r i n g of W r a n g e l l i a  Christoval and  of  that  Queen  volcanism  accompanied  Yorath  detritus  the  t e r r a n e ( D i c k i n s o n , 1976; Arc  Brown,  "tectonic land"  of magmatism along  built  a l i n e west and  The  present  the t i m e of f i n a l  vents  along  structures i n depressions  through the  was  of  along  collision the  Islands  and  Rennel  the  Southern  groups,  were i n t r u d e d diorite  to  San  (Fig. quartz  "Syntectonic" and " p o s t - t e c t o n i c " are i n f o r m a l g e n e t i c names used by S u t h e r l a n d Brown (1968, pp. 128-129) t o d e s c r i b e (?) Upper J u r a s s i c - C r e t a c e o u s mesozonal and (?) Cretaceous-Lower T e r t i a r y epizonal plutons r e s p e c t i v e l y . Although syntectonic p l u t o n s were c e r t a i n l y emplaced d u r i n g a p e r i o d of major s t r e s s , not a l l p o s t - t e c t o n i c p l u t o n s , where dated (Chapter 3 ) , are younger than s i g n i f i c a n t deformation. The informal names, however, have been r e t a i n e d i n t h i s t h e s i s because t h e y or o t h e r synonyms (eg. " o l d " and "young") have been e n t r e n c h e d i n the 1iterature.  22  Fig. 5  S i m p l i f i e d g e o l o g i c map o f t h e Queen C h a r l o t t e I s l a n d s shewing d i s t r i b u t i o n o f v o l c a n i c and p l u t o n i c r o c k s . A f t e r S u t h e r l a n d Brown (1968, F i g . 5 ) .  23 d i o r i t e o f Upper J u r a s s i c t o Lower C r e t a c e o u s 1968;  this  study,  pre-existing Associated zation  crust  rocks  partial  melting  Brown,  may  have  and  aY,  1968;  been  by a n a t e x i s o f  Griffiths,  generated  1977).  by r e m o b i l i -  recrystallization  western  and d i k e s  Vancouver  extending  from  Island,  along  major  high  level  where  b a t h o l i t h s apparently  magma chambers and s u b v o l c a n i c f e e d e r s et  generated  Brown,  shears. Unlike  plutons  (Sutherland  migmatitic  or  transverse  C h a p t e r 3) were p r o b a b l y  age ( S u t h e r l a n d  represent  o f Bonanza v o l c a n i c s ( M u l l e r  1974) t h e " s y n t e c t o n i c " p l u t o n s and Yakoun v o l c a n i c s o f Queen  Charlotte  Islands  are not s p a t i a l l y  related  and may n o t be comag-  matic. The Charlotte  Upper  Islands  younging  trend  Plutonic  Complex  stratigraphic Plutonic  which  et  (Jeletzky,  may  aj_,  to  of  i n the  across  that  related terranes  From  zones were  Vancouver  the  and  predominant  the Insular  1970; G r i f f i t h s ,  suggests be  1980).  onwards, s u b d u c t i o n Belt  extends  evidence  Complex  plutons  are the oldest  Wrangellia-Alexander (Coney  Jurassic  Belt  eastward and  S t r u c t u r a l and  origin  of  the  and  further  i n Mesozoic  east  Juarssic  Coast  1977).  to collision  Upper  Queen  or  Coast  accretion of  Lower  time  Cretaceous  l i k e l y s i t u a t e d west o f t h e I n s u l a r  (Monger e t a l , 1972; D i c k i n s o n ,  1976; G r i f f i t h s ,  1977; M u l l e r ,  1977).  LOWER-UPPER CRETACEOUS SUCCESSION  Since  the  Lower  Cretaceous,  sedimentary  basins  and  24  t r o u g h s o f Vancouver and Queen C h a r l o t t e I s l a n d s appear t o have been l o c a l i z e d i n the I n s u l a r B e l t although may be d i s t r i b u t e d a c r o s s of  non-deposition  and  northern  were  some " s u p e r j a c e n t "  amalgamated t e r r a n e s .  i n t h e Late  deposition  Following  J u r a s s i c on Queen  a period  Charlotte  Islands  Vancouver I s l a n d , marine sediments (Longarm F o r m a t i o n )  deposited  in  Valangian-Barremian  (Early-Middle  Lower  C r e t a c e o u s ) t i m e ( S u t h e r l a n d Brown, 1968). On Queen C h a r l o t t e  I s l a n d s t h e Longarm i s a t l e a s t 1200  meters t h i c k and r e s t s d i s c o n f o r m a b l y older units. ized  The f o r m a t i o n  i s predominately sedimentary,  by massive dark c a l c a r e o u s  shell  debris,  but a l s o  t o unconformably on Yakoun and  siltstone  containing  with  lithic  character-  abundant  greywacke,  Inoceramus  fine  pebble  c o n g l o m e r a t e s , v o l c a n i c sandstones and minor p y r o c l a s t i c r o c k s t o t h o s e o f t h e Yakoun F o r m a t i o n ( S u t h e r l a n d s e c t i o n s o f Longarm fault due  l i n k a g e , suggesting to  Facies  fault  of  detritus,  clasts  145 Ma  along  and  the f a u l t  volcanics,  of g r a n i t i c  (Upper  Longarm along  slumping  outside  Yakoun  are found  Thickest  t h e Rennel-Louscoone  i n a d d i t i o n t o marine d e p o s i t i o n , e f f e c t s  movement,  deposited  margins  and  sediments  Brown, 1968).  akin  Jurassic)  turbidity  zone  contain  (or trough), in  addition  and metamorphic obtained  t h e Louscoone F a u l t  redistribution.  from  to  rocks.  granitic  eroded volcanic  Dates o f 142 clasts  i n d i c a t e a probably  the Upper J u r a s s i c (142 Ma) Burnaby I s l a n d p l u t o n  on  of the  source  (Yorath  from  and Chase,  1981). On age 1974;  northern  and l i t h o l o g y o c c u r Jeletzky,  1976).  Vancouver  Island  unnamed  i n t h e Q u a t s i n o Sound A  succession  rocks  area  of a r g i l l i t e s  of  similar  ( M u l l e r jer a U and  greywacke  25  exposed  on t h e c o n t i n e n t a l  have a l s o al,  s l o p e west of n o r t h e r n Vancouver  been t e n t a t i v e l y  1977).  A  marine  correlated  trough  forearc  Longarm  basin  (Muller,  tectonic  lands  (Jeletzky,  because  1976)  Crystalline  western  with  British  Wrangellia  and  the  to  Complex  o f Coast Mountain  co-extensive  and  south  (Muller,  tectonic  Mesozoic  Columbia  by  Island  the  It  that  Tyaughton-Methow  the  in  east)  the as  northern  and  Brooks  1977).  barriers,  (located  terranes to  Vancouver  to  was  I s l a n d d u r i n g the Lower C r e t a c e o u s , bounded t o the e a s t by eastern  Islands  1977)  Vancouver  encompassing  Charlotte  (Yorath et  continuous  Westcoast  Queen  the  probably  Ranges  from  or  with  Island  Penisula  is  unlikely,  this  trough  Trough  suture  of  zone  suggested  Coast  was  southbetween  by  Dickinson  (1976). Unconformably units  is a  thick  overlying  succession  the Longarm F o r m a t i o n  (maximum  3,000 meters)  and  of  older  uppermost  Lower C r e t a c e o u s and Upper C r e t a c e o u s c l a s t i c sediments of the Queen C h a r l o t t e Group. formations  The  Queen C h a r l o t t e Group i s s u b d i v i d e d i n t o t h r e e  ( S u t h e r l a n d Brown,  1968):  the b a s a l  Haida F o r m a t i o n  of  g l a u c o n i t i c sandstones and s h a l e , o v e r l a i n by the Honna F o r m a t i o n o f polymictic  orthoconglomerates, coarse  s h a l e and s i l t s t o n e , o v e r l a i n siltstone, gradational  shale,  and  arkosic  sandstone,  well  sandstone.  Contacts  ( t o i n t e r f i n g e r i n g ) , conformable  dated  and  between  Honna and  ( S u t h e r l a n d Brown, 1968;  Skidegate Formations  contain  few  formations  o r unconformable.  i s of A l b i a n - T u r o n i a n ( l a t e s t  Upper C r e t a c e o u s ) age  minor  i n t u r n by the S k i d e g a t e Formation of  H a i d a F o r m a t i o n , c o n t a i n i n g T r i g o n i a , Inoceramus, is  and  are The  and o t h e r f o s s i l s , Lower t o  McLearn,  fossils  and  earliest  1972). their  The age  26  cannot be d e f i n e d c l o s e r than Upper C r e t a c e o u s . The  " l o w e r " sandstones  and  "upper"  shales  F o r m a t i o n are t i m e e q u i v a l e n t s of the Blumberg shale  unit  (Coal  (Jeletzky, alents.  1976)  Harbour though  Sediments  Group) of  the  Upper  Haida  Formation and  upper  northwestern  o n l y the upper u n i t s  of  of the  are  Cretaceous  Vancouver  Island  lithologic  equiv-  Nanaimo  d o w n f a u l t e d Suquash B a s i n of n o r t h e a s t e r n Vancouver e q u i v a l e n t t o t h e Honna and 1966;  Muller  certainly  e t _al_,  exist.  1974)  though  and  Shell  (Shouldice, evidence  differences  Upper C r e t a c e o u s sandstone, s i l t s t o n e ,  Anglo  1973).  available,  Tyee  N-39  wells  It i s d i f f i c u l t , to  determine  According  Basin) from  were  to  of  considerable  still  emergent  based  a  the  basins  Brown  subsiding  topography.  Yakoun  on  conglomerates  were  volcanic  and  facies  Sockeye  E-66,  Hecate  Strait  limited  faunal  were  (1968),  marine  Detritus  continuous  the  basin  was  structures  deposited e i t h e r  uplands and reworked  Brown,  shale  and  in  the  by f l u v i a l  streams.  Haida  (Skidegate  supplied  mainly  syntectonic northeast.  sinking  b a s i n , l a p p i n g onto i t s margins o r were d e r i v e d e n t i r e l y from exposed  be  and  p l u t o n s ; c u r r e n t d i r e c t i o n s are m a i n l y from the e a s t and Honna  the  Islands.  Sutherland  deposited i n  Anglo  i n western  whether  between Vancouver and Queen C h a r l o t t e  sediments  i n timing  c o r e d i n the S h e l l  of  I s l a n d might  Skidegate Formations (Sutherland  ( S k i d e g a t e e q u i v a l e n t ? ) was B-10,  Group  marine  subaerially  The S k i d e g a t e  F o r m a t i o n appears t o have o r i g i n a t e d i n a s h a l l o w marine b a s i n .  27  TERTIARY SUCCESSION  The  Tertiary  s u c c e s s i o n , which c o m p r i s e s Masset  ics,  and  o v e r l y i n g sediments o f  the  IV),  are  the most e x t e n s i v e  t h i c k e s t u n i t s on  I s l a n d s and  and  Skonun F o r m a t i o n  volcan-  (see  chapter  Queen C h a r l o t t e  i n the Queen C h a r l o t t e B a s i n . The  Masset  v o l c a n i c s comprising  flows  and  pyroclastics  o f d i f f e r i n g a s p e c t have, on the b a s i s o f l i m i t e d mapping and genic  s t u d y , been s e p a r a t e d  into three d i f f e r e n t  facies  petro-  (Sutherland  Brown, 1968): the T a r t u f a c i e s c o v e r i n g most o f Graham I s l a n d , and the  Kootenay  east coasts  and  Dana f a c i e s  occurring  are  associated  as  Exploratory wells d r i l l e d Tartu Hecate  facies  a t depth  Strait  and  on  feeders  Charlotte  Sound  west  The  formation  hypabyssal of  Graham  Brown,  the  the  and  above  facies.  Island penetrated  1968).  Wells  drilled  bottoming  c o r e d b a s a l t i c f l o w s and  a l l older  have been e r u p t e d  u n i t s from The  the  Karmutsen  and  intrusives,  in  Formation  the in  Masset  pyroclastics  Each of the above f a c i e s o v e r l i e s w i t h  Queen C h a r l o t t e Group. to  gabbroic  northern  (Sutherland  Queen  uncertain a f f i n i t y .  and  possible  v o l c a n i c s ( S h o u l d i c e , 1973)  unconformity  on  r e s p e c t i v e l y o f Moreby I s l a n d ( F i g . 5 ) .  a l s o i n c l u d e s f e l d s p a r porphyry which  primarily  of  angular to  the  b u l k of exposed Masset v o l c a n i c s appear  i n Upper O l i g o c e n e  t o Lower Miocene  (chapter  III). The  T a r t u f a c i e s i s a p l a t e a u sequence w i t h an  t h i c k n e s s of about 5.5 Brown,  km.  I t c o n s i s t s of t h r e e members ( S u t h e r l a n d  1968): a b a s a l mixed member of  f l o w s , and  aggregate  basaltic  b r e c c i a s , columnar  r h y o l i t i c ash f l o w t u f f s , an o v e r l y i n g r h y o l i t e member of  28  rhyolite  ash  flow  tuffs  and  topmost b a s a l t member of and  rhyolitic  mostly  of  w h i l e the feldspar  rocks.  welded  Dana f a c i e s  columnar  basalt  columnar b a s a l t f l o w s  pyroclastic  rhyolite  minor  The  tuff  flows,  and  minor  Kootenay f a c i e s  breccias  and  i n c l u d e s mixed c l a s t ,  p o r p h y r i e s w i t h minor a n d e s i t e  and  tuff  dacite.  a  basaltic  i s comprised  aphanitic  fine  and  rhyolites  breccias  and  V a r i a t i o n s of  the g e n e r a l rock t y p e s w i t h i n each f a c i e s are known but are minor. Chemical these  r o c k s t o be  basalt. ous, new  Compared t o Karmutsen b a s a l t s , the Masset  tap  more a l k a l i  slightly  modified  Masset r h y o l i t e s  fractional  ^Sr/^Sr  1977).  ratios  10,  see  of  Table  The facies,  was as  III)  erupted subaqueous  of  lite  flows  ash  vents  of  three  differentiation  basaltic  samples that  of  range  i s more  alumin-  represents  (Sutherland  Brown,  have e v o l v e d  (Sutherland by  the  Tartu  facies  from  .7039  to  by  Brown, initial  (nos.  .7044  formation,  with  subaerially.  the  Dana  pryroclastic  exception  of  6,  (R.L.  the  occurred  are  breccias  probably  or  subaqueous  slumps.  flows  indicated  major  phase  of  Dana  mixed  from which e r u p t i o n of Masset b a s a l t s and  second  a  the o v e r l y i n g  i s supported  by  gabbroic  d i k e s and p l u g s ( S u t h e r l a n d Brown, 1966, A  alkali  by  material  interpretation  alumina,  likely  may  of  data).  Masset  Locations  by  This  Armstrong, u n p u b l i s h e d  porphyry  and  are h i g h i n sodium and  crystallization  Souther,  formed  rich,  of mantle m a t e r i a l s somewhat contaminated  or  1968).  1968;  Masset b a s a l t s have shown most  h i g h l y s i l i c e o u s , moderately high  more o x i d i z e d , and  crust  9,  a n a l y s i s of  plutonism  rhyo-  and  feldspar  Queen  Charlotte  1968). on  29  Island  i s represented  by  some seven  "post-tectonic plutons2"  that  locally  i n t r u d e o r metamorphose Masset v o l c a n i c s ( S u t h e r l a n d Brown,  1968).  The  to  p l u t o n s , which range w i d e l y i n c o m p o s i t i o n  g r a n i t e (average  composition:  from  diorite  g r a n o d i o r i t e ) are c o e v a l w i t h  Masset v o l c a n i c s though emplacement appears t o have p o s t d a t e d volcanic episodes. the high l e v e l  Age  determinations  ( c h a p t e r I I I ) suggest  p l u t o n s were emplaced o r u p l i f t e d  Upper O l i g o c e n e  time.  A number of the  plutons  t r e n d of t h e Rennel-Louscoone wrench f a u l t Possible plutonism  on  the  relationships  major  most of  i n Upper Eocene t o are  localized  along  system.  between  Cenozoic  Queen C h a r l o t t e I s l a n d s , " P a c i f i c "  volcanism  and  p l a t e motions  and major t e c t o n i c e v e n t s are d i s c u s s e d i n c h a p t e r s I I and  2  the  X.  A number of p l u t o n s ( i n c l u d i n g t h o s e of the S a n d s p i t and Southern groups), considered by S u t h e r l a n d Brown " to r e p r e s e n t t h e " p o s t - t e c t o n i c " phase ( S u t h e r l a n d Brown, 1968) are o f Upper J u r a s s i c age ( c h a p t e r I I I ) and are t h e r e f o r e i n c l u d e d w i t h t h e o l d e r " s y n t e c t o n i c " group.  30  CHAPTER I I  HISTORY OF PLATE INTERACTIONS AT QUEEN CHARLOTTE ISLANDS  Because t h e Queen C h a r l o t t e margin o f t h e North closely sea  liked  floor  Islands  America p l a t e , t h e i r  t o the h i s t o r y of p l a t e  of t h e P a c i f i c  Ocean.  l i e on t h e western  tectonic  i n t e r a c t i o n s r e c o r d e d on t h e  Oceanic  magnetic  mount paleomagnetism, Deep Sea D r i l l i n g  Project  ages of seamounts along hot spot t r a c e s  have allowed  of p a s t p l a t e m o t i o n s . eastern the  sequence  Islands. et with  Cenozoic p a l e o p l a t e  P a c i f i c , modelled of  major  Previously,  al_, 1979; Ewing, varying  success  by v a r i o u s tectonic  h i s t o r y must be  anomalies, sea-  (DSDP) r e s u l t s and reconstruction  p o s i t i o n s i n the North-  a u t h o r s , can be compared  events  on  the  Queen  a number o f a u t h o r s ( e g . M u l l e r , 1980; Y o r a t h t o compare  and Chase, onshore  Charlotte  1977; B e v i e r  1981) have  studies  with  of  attempted  the  western  Canadian C o r d i l l e r a t o h i s t o r y o f p l a t e i n t e r a c t i o n s a t t h e c o n t i n e n t a l margin. somewhat needed  Paleoplate  speculative  f o r accurate  p o s i t i o n s p r i o r t o M i d d l e Eocene t i m e are  as much o f t h e e v i d e n c e from t h e ocean reconstructions  has  since  been  floor  destroyed  at  s u b d u c t i o n zones along t h e n o r t h e r n and western margins of t h e North America p l a t e .  In a d d i t i o n , Cenozoic t e c t o n i c o v e r p r i n t i n g may have  obscured c o n t i n e n t a l e x p r e s s i o n s o f p l a t e i n t e r a c t i o n s . A b r i e f h i s t o r y o f t h e major o c e a n i c p l a t e s t h a t must a t one  t i m e have l a i n  based on r e c e n t  a d j a c e n t t o t h e Queen C h a r l o t t e  publications.  Plate reconstructions  b e i n g dependent on t h e t y p e o f d a t a used, m o d e l l i n g  Islands  follows,  are not unique, t e c h n i q u e , and  31  i n f e r e n c e s where o n l y s p a r s e d a t a e x i s t s .  LATE MESOZOIC - MIDDLE EOCENE  H i l d e e t a l (1977) and S h i e l d s the  Pacific  p l a t e , which  now b o r d e r s t h e Queen  originated  at the j u n c t i o n  of the ancient  1970)  Phoenix  and  and  Morgan,  plates  1969) i n E a r l y  (1979) h y p o t h e s i z e d t h a t  time.  Islands,  K u l a (Grow and A t w a t e r ,  the Farallon  Jurassic  Charlotte  plate  The s i t e  (McKenzie  of b i r t h  and  i n the  s o u t h w e s t e r n P a c i f i c i s i n f e r r e d from p a l e o l a t i t u d e s determined from Pacific  seamounts  lineations longitude  ( F r a n c h e t e a u e t _aj_, 1970) and M e s o z o i c  ( L a r s o n and Chase, 1972; L a r s o n and Pitman,  magnetic  1972).  The  i s u n c e r t a i n due t o t h e a m b i g u i t y o f p a l e o m a g n e t i c d a t a . After i t s i n i t i a l  formation, the P a c i f i c plate  increased  i n s i z e w i t h c o n t i n u e d s p r e a d i n g along i t s margins ( F i g . 6 ) . By 135 Ma  B.P.  (Early  established:  Cretaceous)  two major  triple  junctions  had  been  a n o r t h e r n one between t h e K u l a , F a r a l l o n , and P a c i f i c  p l a t e s , and a s o u t h e r n one between t h e F a r a l l o n , P a c i f i c and Phoenix plates  ( H i l d e e_t aY  triple  junctions  length  of the P a c i f i c - F a r a l I o n ridge.  moved  northwestward  t  subducted  along  America-Europe time  (Dietz  1977).  Increased spreading rates  forced  these  t o migrate i n opposite d i r e c t i o n s , increasing the  and  the  the F a r a l l o n  western  was moving  and Holden,  margin  northwestward 1970).  The K u l a and P a c i f i c plate of  North  away  A t 80 Ma  northeastward  from  plates t o be  America. Africa  B.P. ( L a t e  North at  this  Cretaceous)  N o r t h A m e r i c a changed i t s m o t i o n from west t o southwest as a r e s u l t of  s i g n i f i c a n t reorganization  i n p l a t e motion,  which  i n t h e North  32  Fig. 6  S c h e m a t i c model o f t h e e v o l u t i o n a r y h i s t o r y o f t h e w e s t e r n Pacific. R e c o n s t r u c t i o n s a r e shown f o r a) J u r a s s i c C r e t a c e o u s boundary (135 Ma), b) Lower-Upper C r e t a c e o u s boundary (100 Ma), c ) C r e t a c e o u s - T e r t i a r y boundary (65 Ma), d) O l i g o c e n e - M i o c e n e boundary (25 Ma). Solid lines indicate l o c a t i o n s o f r i d g e s , f r a c t u r e zones and s u b d u c t i o n z o n e s . S h o r t dashed l i n e s i n d i c a t e f o r m e r p o s i t i o n s o f r i d g e s and f r a c t u r e z o n e s . Redproduced from Hi 1de e t a l (1977, F i g s . 4-7). —  33  Atlantic  initiated  separation  of Europe  from North A m e r i c a .  t i v e motion of the North America p l a t e s was, t o t h a t of t h e ' P a c i f i c '  Canadian  a s p e c t of the P a c i f i c  Cenozoic was  however, s m a l l compared  plates.  For t h e w e s t e r n cant  Rela-  the p o s i t i o n  plate  Cordillera,  system d u r i n g  the most  Late Mesozoic-Early  of t h e n o r t h e r n t r i p l e  junction  p a r t i c u l a r , the p o s i t i o n of the K u l a - F a r a l l o n ridge w i t h the c o n t i n e n t a l margin ( F i g . 7 ) .  signifi-  and, i n  respect to  The e x i s t e n c e of the K u l a - F a r a l l o n  r i d g e i s p o s t u l a t e d because of g e o m e t r i c c o n s t r a i n t s of the magnetic anomaly  pattern  known  as  the  Alaskan  Magnetic  Bight  (Hayes  and  Pitman, 1968; Grow and A t w a t e r , 1970), a l t h o u g h t h e e n t i r e r i d g e and the anomalies c r e a t e d by i t s s p r e a d i n g were subducted 30-40 Ma (Atwater,  1970;  Cooper  et  a]_,  1976;  Stone,  1977;  Coney,  1976,  1978).  I t s f o r m e r p o s i t i o n w i t h r e s p e c t t o t h e N o r t h America  remains  uncertain.  unknown a f t e r early  The  50 Ma  e x a c t geometry  B.P.  of  ( A t w a t e r , 1970).  spreading at the K u l a - F a r a l l o n  ridge  B.P.  the  triple  The  only  plate  junction  is  indications  of  are n o r t h e a s t t r e n d i n g  J u r a s s i c - E a r l y C r e t a c e o u s magnetic anomalies ( F i g . 7) t r a p p e d i n the Bering  Sea  eastern  70 Ma  Bering  1976).  B.P.  Sea  ago  when s u b d u c t i o n jumped  Basin to  the  Aleutian  Trench  seaward (Cooper  from  the  e_t a l ,  The a s s i g n e d ages f o r t h e anomalies s u p p o r t e a s t w a r d m i g r a -  t i o n of the K u l a - F a r a l l o n r i d g e . Cooper development  of the n o r t h e a s t e r n P a c i f i c  M i d d l e Eocene, magnetic 1973)  and  e t a l (1976) p r e s e n t two models f o r t h e  the f i r s t  anomalies the  L a t e Cretaceous  based on p a l e o m a g n e t i c p o l e p o s i t i o n s  (Larson  second  during  tectonic  and  ( F i g . 7)  Chase, based  1972; on  Atwater  and from  and  Molnar,  absolute plate  motions  34  140  -J  140  160  L  180  1  1S0 180  160  140  120  140  120  a—I  1  160  l  i  140  140 60  i  •  •  160  180  160  160  180  i  160  140 I  - y^yf^  /  is (i> Jt /• 30 r M 1 3 ^  ;  l  140 120  120  1  N - 60 " 45  45  15  K  160  180  160  140  120  F  30  M1  -  15  0  140  7  0  P  15  -  30  • 70 MY 140  160  - 15 30  i 180  160  140  120  Reconstruction of Late Cretaceous-Paleogene p l a t e l o c a t i o n s in the N o r t h e a s t e r n P a c i f i c assuming c o n t i n u o u s p l a t e motion r e l a t i v e to a s t a t i o n a r y h o t - s p o t r e f e r e n c e frame. N = North American p l a t e ; F = Farallon plate; K = Kula p l a t e ; P = Pacific plate; M l - M l 3 = Mesozoic anomaly sequence  35  derived  from  Jarrard, Middle  the  1973).  Hawaiian-Emperor Both  Eocene, the  southeastern  models  northern  Alaska.  Kula-Farallon  perpendicular  possibly  in  1977).  With  the  vicinity  of  constant  eastern  Islands.  Alaska  spot  trace  that  from  Late  70  Ma  Gulf  ago,  Kodiak  the  with  of  p l a t e motion, B.P.  (Clague  and  Cretaceous  to  j u n c t i o n moved n o r t h e a s t  straight  to  s o u t h e a s t and by 50-35 Ma Charlotte  to  (assumed  oriented  the  triple  Sixty  ridge  show  hot  no  Alaska Island  the  extension  toward of  the  transforms)  continental (Marshak  r i d g e would  was  margin,  and  have  Karig, migrated  would have l a i n a d j a c e n t t o the Queen  D i r e c t l y n o r t h of t h e t r i p l e j u n c t i o n i n s o u t h -  obligue  subduction  c h a r a c t e r i z e d the A m e r i c a - K u l a  or  transform  motion  would  have  p l a t e boundary.  The model of Cooper e t _al_, 1976,  (see a l s o Coney, 1977),  i s not u n i q u e ,  being based on r e l o c a t e d p a l e o p l a t e p o s i t i o n s c o n s i s -  t e n t w i t h age  and  B e r i n g Sea  B a s i n and  Hawaiian  hot  (1970),  Atwater  tions off  o r i e n t a t i o n o f magnetic anomalies  based  southern  spot  on  c o n s t a n t motion of the to  and  form  Molnar  relative  the  Emperor  (1973) and  motion,  California  at  80  Pacific  seamount  to  the  p r e v i o u s l y ) but o r i e n t e d w i t h r e p e c t t o the North that  the  K u l a - F a r a l l o n r i d g e migrated  Vancouver I s l a n d 40 Ma B.P. northern 1970;  Queen  Stone,  1977).  never extended the  triple  Charlotte This  The  model  f u r t h e r north  junction.  The  than  Kula  northwards  r i d g e was  Islands  or  chain.  northern  (similar  plate  i n reconstructriple  junction  model  discussed  up  the  coast  f i n a l l y subducted  implies that of and  the  Atwater  America p l a t e ,  southeastern  point  Eastern  p l a t e over  Coney (1976),  show the Ma  i n the  Alaska  the  northward  to  beneath (Atwater,  Farallon  plate  migration  p o s s i b l y other  so  of  unknown  36  p l a t e s l a y west of s o u t h e a s t The  Alaska.  differences  in postulations  the K u l a - F a r a l l o n r i d g e , and, northern  triple  based  fixed  hot  Though  hot  on  plates.  junction,  s i n c e 50 Ma  are  due  to  spots  and  those  spots  i n the  concerning  B.P.,  the  p o s i t i o n of  differences  based  northern  on  between  relative  Pacific  validity  as  an  absolute  frame of  r e c o n s t r u c t i o n p r i o r t o 10 Ma  is still  of  construction  relative  various  motion  time  rely  periods  on  by  vector  addition  to  extending  Farallon  Antarctic, plates.  Australia,  India,  Kula  Africa  plate) and  in  the  Indian  Antarctica  i s probable.  Ocean Both  and  are  motion assume a l l s p r e a d i n g  i s symmetric.  Though  relative  motion  with  and  p o s i t i o n of the K u l a  hence the  respect  rigid  above, d i f f e r  to  while  and  p o s i t i o n of and  the  Queen C h a r l o t t e  Islands  ridge-trench-trench  boundary.  type  at  30-40 Ma  the  A f t e r d i s a p p e a r a n c e of the  spot the  for and  the  Pacific,  North  America  B.P.  are  motion hot  very  within  spot  models  on r e l a t i v e  models,  described  Kula-Farallon  ridge  F a r a l l o n p l a t e s , both models ridge B.P.  s u p p o r t development of a t r i p l e j u n c t i o n of or  and  rate  models based  hot  appear t o suggest t h a t the K u l a - F a r a l l o n of  to  furthermore  assume l i t h o s p h e r i c p l a t e s  Analyses  M o l n a r , 1973),  finally  r e l a t i v e motion  global  circuits  These r e c o n s t r u c t i o n s f o r the p e r i o d 40-80 Ma  difficult  for  spreading  as many as seven p l a t e s ( A t w a t e r and (and/or  ( M i n s t e r e_t aj_,  vector  d i r e c t i o n across from  models  Ocean appear  reference  of  the  of  a m a t t e r of d e b a t e . of  of  motion  have remained s t a t i o n a r y f o r at l e a s t the past 10 Ma 1974), t h e i r  position  a  western  l a y i m m e d i a t e l y west Further,  both  models  ridge-trench-transform Norh  Kula-Farallon  America ridge  plate  a similar  37  triple  junction  between  the F a r a l l o n ,  Pacific,  and North  America  p l a t e s developed.  MIDDLE EOCENE - RECENT  After  mid-Eocene  time  tectonics  of  the northeastern  P a c i f i c were c o n t r o l l e d by i n t e r a c t i o n o f t h e F a r a l l o n , P a c i f i c , and North America to  plates.  A change i n P a c i f i c  p l a t e motion  from  north  n o r t h w e s t , e v i d e n c e d by t h e bend i n t h e Hawaiian-Emperor seamount  c h a i n , d a t e d a t 42 Ma B.P. ( C l a g u e and J a r r a r d , 1977) c o i n c i d e d w i t h a  reduced  plates. sition  convergence  between t h e F a r a l l o n  and North  T h i s d a t e c l o s e l y c o r r e s p o n d s w i t h a major i n western  magmatism the  rate  Rocky  Initial  North  i n t h e Coast Mountain  America, Plutonic  Belt  which  included  Complex  (Ewing,  tectonic  cessation  and f o r e l a n d  1980; Monger  America  and  tranof arc  thrusting i n Price,  subduction of the K u l a - P a c i f i c ridge at the A l e u t i a n  1979). Trench  l i k e l y o c c u r r e d a p p r o x i m a t e l y 30 Ma B.P. (Grow and A t w a t e r , 1970; De e t a2>  Long  (1979)  1978) a l t h o u g h  i n a more r e c e n t  suggests s u b d u c t i o n may  have  been  investigation  as e a r l y  Byrne  as 56 Ma ago.  P r i o r t o 29 Ma B.P. ( A t w a t e r , 1970; Atwater and M o l n a r ,  1973) o r 26  Ma B.P. (Handschumacher, 1976) t h e P a c i f i c - F a r a l I o n r i d g e was i n t a c t and At  migrating east r e l a t i v e  t o the o v e r r i d i n g  29 o r 26 Ma B.P. t h e r i d g e  collided  North  with  America  plate.  the FaralIon-North  America t r e n c h s t o p p i n g s p r e a d i n g a t p o i n t o f c o n t a c t and i n i t i a t i n g transform Farallon plate  motion plate  along  then  t h e San Andreas  broke  into  readjustments occurred.  and r e l a t e d  two s e p a r a t e u n i t s The Juan  de Fuca  faults.  The  and l a r g e  scale  complex  of rotated  38  and  fractured microplates  e t a l , 1975;  (Silver,  Riddihough,  1976)  p l a t e i n the n o r t h e a s t e r n Plate present Stone  by  between  the  analysis changes  i s the  and  support North  (1973),  Atwater's  and  last  f o r the  Molnar  America  (Atwater  B a r r and  Chase, 1974;  vestige  of  the  Chase  Farallon  Pacific.  reconstructions  Atwater  (1977)  1971;  Molnar,  i n d i r e c t i o n and  rate  model  Pacific 1973) of  40  Ma  B.P.  Handschumacher  (1970)  and  period  of  plates.  suggests,  motion  may  to  the  (1976)  and  constant  motion  Relative  motion  however,  that  have o c c u r r e d  some during  t h i s time p e r i o d . The pattern with  reconstructions  differ  respect  somewhat  America  Icelandic and  relative spot  Forsyth,  1972)  to  the  (models of and  that  does  were  a model based on c o n s t a n t  of  due  to  basis  s p o t ) , position of ridge  system  1972  motion  compared  or  and  Phillips  between  North  not  require  the  i n i t i a t e d 15-20  The  the San  Andreas  i s the o n l y  model, ( F i g . 8)  (1970) suggests t h a t between the The  (1977),  F a r a l l o n - P a c i f i c spreading  then r e a p p e a r .  Ma B.P.  Stone  s p o t s combined w i t h the A t l a n t i c model  (1972) because t h i s  Islands  by  motion along  Forsyth  of A t w a t e r  Charlotte  rates  are  Talwani,  and  subducted and that  ridge  Pacific plates.  preferred  Philips  FaralIon-Pacific  mid-Atlantic  Pitman and  inferred  F a u l t , w i t h f i x e d P a c i f i c hot of  gross  These d i f f e r e n c e s  These d i f f e r e n t models who  the  similar in  ( r e l a t i v e motion a n a l y s i s or hot  hot  America and  I I ) though  i n p o s i t i o n of  t o North A m e r i c a .  of r e c o n s t r u c t i o n North  (Table  transform  North America and  combination ridge  to  be  i n agreement w i t h  motion at the Pacific  Queen  plates  was  t r i p l e j u n c t i o n between the Juan de Fuca  39  TABLE TI  CENOZOIC PLATE INERACTI0N5 AT QUEEN CHARLOTTE ISLANDS  ATWATER(1°70) ATWATER & M0LNAR(1973) CONEY(1976/  ATWATER(1970)  COOPER ET.AL.U976)  ST0NE(1977)  HANOSCHUMACHER (1976)  CONSTANT RELATIVE MOTION PITMAN S TALWANI ATLANTIC MOD&  RELATIVE MOTION (0-5 MA)  HOT SPOT. SEAMOUNT PALEOMAGNETICS, RELATIVE (ATWATER & MOLNAR) PHILIPS 4 FORSYTH ATLANTIC MODEL  CONSTANT MOTION PACIFIC HOT SPOT; PHILIPS S FORSYTH ATLANTIC MODEL  RELATIVE MOTION  TRANSFORM-PACIFIC-N. AMERI-  TRANSFORM^. AMERICA-PACIFIC)  TRANSFORM OR OBLIQUE CONVERGENCES. AMERICA-KULA) I  TRANSFORM(N. AMERICA-PACIFIC SUBOUCTION-FARALLON PLATE  TRANSFORM OR OBLIQUE CONVERGENCE-N.AMERICA KULA A  INTERACTION KULA-FARALLON RIDGE-N.AMERICA  SU8DUCTION-FARALL0N PLATE  TRANSFORM(N.AMERICA-PACIFIC)  INTERACTION FARALLON-PACIFIC RIDGE-N.AMERICA  INTERACTION FARALLON-PACIFIC RIDGEN. AMERICA  FARALLON PLATE SUBOUCTION  SUBOUCTION FARALLON PLATE  t  INTERACTION-KULAFARALLON RIDGEN.AMERICA  TRANSFORM OR OBLIQUq CONVERGENCE KULA-N. AMERICA  40  Fig. 8  P r e f e r r e d r e c o n s t r u c t i o n of the northwestern P a c i f i c f o r l a t e Paleogene-Neogene based on P h i l l i p s and F o r s y t h (1972) A t l a n t i c model, c o n s t a n t m o t i o n on t h e San Andreas f a u l t and f i x e d Hawaiian-Emperor hot s p o t . Reproduced from Stone (1977, F i g . 1 4 ) ; a l s o Stone and P a c k e r (1977, F i g . 3 ) .  41  (Farallon),  Pacific,  and North  America  plates  has remained  s t a t i c f o r t h e p a s t 10 Ma a t a p o s i t i o n west o f n o r t h e r n Island and  (Riddihough,  North  place  America  the t r i p l e  Queen C h a r l o t t e  1976). plates  Any c o u p l i n g during  this  Vancouver  between t h e Juan  time  j u n c t i o n f u r t h e r north,  almost  period,  de  however,  would  p r o b a b l y west o f s o u t h e r n  Islands.  Changes i n d i r e c t i o n and v e l o c i t y o f p l a t e motion Late  Cenozoic  plate  may  have  i n t e r a c t i o n s and  Island  and  translation  Fuca  severely hence  the developing of  affected  the geology  Queen  Islands  (Hicken  Vancouver  Island  (Symons,  and  of t h e Queen  Charlotte  microcontinental  Charlotte  "oceanic"-North  blocks  Basin.  including  I r v i n g , 1977; t h i s  during America  Charlotte  Rotation northern  study),  and Queen  southern  1973; H e p t o n s t a l l ,  1977) and t h e Oregon  Coastal  Ranges (Simpson and Cox, 1977) d u r i n g  t h e Cenozoic may have  changed  the c o n f i g u r a t i o n  o f t h e North  changed t h e d i r e c t i o n o f ' P a c i f i c '  America  plate  p l a t e convergence.  boundary and In a d d i t i o n ,  the  i n f l u e n c e of f a c t o r s such as r i d g e jumps, asymmetric  spreading,  and  v a r i a b l e d i p o f t h e subducted p l a t e a r e d i f f i c u l t t o d i s c e r n but  may have a profound e f f e c t on c o n t i n e n t a l margin t e c t o n i c s . and  Menard (1970) noted t h e d i f f i c u l t y  i n dating  magnetic  younger t h a n 35 Ma B.P. west of t h e Queen C h a r l o t t e lineations and  are missing  evolution  or repeated, f a c t u r e  of the present  spreading  Atwater anomalies  Islands:  some  zone o f f s e t s d i s a p p e a r  ridge  system  from  earlier  ones i s not e n t i r e l y c l e a r . The p r e s e n t magnetic Charlotte  anomaly p a t t e r n  west o f t h e Queen  I s l a n d s , mapped by Pitman and Hayes ( 1 9 6 8 ) , Couch  (1969),  S r i v a s t a v a e t a]_ (1971) and Naugler and Wageman (1973) i s shown i n  42  Fig.  9.  The a n o m a l i e s ,  generated  at the F a r a l I o n - P a c i f i c  t r e n d n o r t h w i t h o u t apparent o f f s e t from anomalies west de  Fuca  ridge  system  (Raff  and Mason,  o f t h e Juan  1961) and t e r m i n a t e a t t h e  Queen C h a r l o t t e Trough, west o f t h e Queen C h a r l o t t e I s l a n d s . lation  ridge,  Corre-  and a s s i g n e d ages f o r t h e s e anomalies ( F i g . 9) are t e n a t i v e  because o f s p a r s e magnetic d a t a f o r t h i s  region.  PRESENT PLATE BOUNDARY  The  present  boundary  between  t h e North  America  and  P a c i f i c p l a t e s a t t h e Queen C h a r l o t t e I s l a n d s i s t h e Queen C h a r l o t t e transform f a u l t  zone  (Wilson,  1968; A t w a t e r , 1970). junction located  between  1965; Morgan, 1968; T o b i n and Sykes,  The f a u l t  the North  i n the v i c i n i t y  zone extends n o r t h from t h e t r i p l e  America,  Pacific  o f Delwood  knolls  and E x p l o r e r (Bertrand,  e t al_, 1975; R i d d i h o u g h , 1977; Chase and T i f f i n ,  plates,  1972; Chase  1977 o r Tuzo W i l s o n  k n o l l s ( R i d d i h o u g h e_t aj[, 1980) and c o n n e c t s i n onshore and o f f s h o r e southeastern Alaska with  the Fairweather Fault  system  (Page, 1969;  P l a f k e r e t aj_, 1978, von Huene e t _aj_, 1978). At t h e A l e u t i a n Trench, t h e boundary and  Pacific  plates  changes  between t h e America  t o one o f convergence.  The  a r e a o f s o u t h e a s t e r n A l a s k a and a d j a c e n t areas o f B r i t i s h c o n s e q u e n t l y has a complex  tectonic  framework.  transition Columbia  In t h e n o r t h e a s t e r n  G u l f o f A l a s k a , west o f t h e F a i r w e a t h e r F a u l t , an a r e a o f c o n t i n e n tal  crust  (termed  Yukutut  miniplate  probably coupled t o the P a c i f i c T a y l o r and 0 " N e i l ,  1974).  plate  Because  by P l a f k e r  e t aj_, 1978) i s  ( N a u g l e r and Wageman, 1973;  o f i t s low d e n s i t y t h e m i n i p l a t e  43  es*  Fig. 9  tto  #  as*  go*  M a g n e t i c l i n e a t i o n s and m a j o r t e c t o n i c f e a t u r e s o f t h e G u l f o f A l a s k a . L i n e a t i o n s shown by heavy s o l i d l i n e s , f r a c t u r e zones by d o u b l e l i n e s and A l e u t i a n t r e n c h by hachured l i n e . Reproduced from N a u g l e r and Wageman (1973, F i g . 1 ) .  44  cannot  be  significantly  region  i s therefore  thickening,  consumed  the s i t e  and high  at the A l e u t i a n  of considerable  Published fault  show i n t e n s e Pleistocene movement  zone  e t a2,  Srivastava  seismic (Chase  sediment  may  have  reflection and T i f f i n ,  profiles  on t h e c o n t i n e n t a l occurred  on  slope.  several  Although  parallel  or  Islands  (Hyndman, 1981) i n d i c a t e s f a u l t  t r a c e was l o c a t e d  t h e landward Earlier  Tiffin,  o f two  studies  steep  over  the  suggested  1981).  The a x i s o f a f r e e - a i r  terrace  Linear  continental  that  separates  magnetic  slope,  the  anomalies  but cannot  subparallel  scarps  that  t h e main  slope  gravity  fault  continue  be t r a c e d  activity i s  fault  a t t h e base o f t h e c o n t i n e n t a l  1972).  transform  microearthquake study o f f southern  Brown, 1968) o r a l o n g t h e a x i s o f t h e Queen C h a r l o t t e and  1978)  and development of c o m p r e s s i v e f o l d s i n P l i o -  Queen C h a r l o t t e  slope.  Queen  1973; von Huene e t a]_,  a recent  continental  the  1972; Chase e t aj_, 1975;  faults,  beneath  convergence  over  steeply dipping  currently  crustal  1978; von Huene e t al_, 1978).  1971; S r i v a s t a v a ,  faulting  and t h e  deformation,  s e i s m i c i t y as a r e s u l t of o b l i q u e  ( P l a f k e r e t al_, 1978; M i l n e e t a U  Charlotte  Trench  beneath  fault  (Sutherland Trough  (Chase  low i s c e n t e r e d  scarps to  on t h e  the  (Riddihough, base  i t (Currie  of the et a l ,  1980). First fault  motion  zone ( f o r r e c e n t  studies  of shallow  summary, see M i l n e  pure s t r i k e - s l i p on a near v e r t i c a l thrusting profiles of  however may  be  present  i n d i c a t e a compressional  gravity  (Couch,  plane. along  earthquakes  the  e t aj_, 1978) show almost Some element o f under-  the f a u l t  zone: ' s e i s m i c  component and model  1969; S r i v a s t a v a ,  along  1973) and s e i s m i c  computations refraction  45  data  (Horn e t aj_, 1981) s u g g e s t s  crust  toward  implied  Islands.  Oblique  convergence i s  by t h e M i n s t e r e t a j (1974) a n a l y s i s o f i n s t a n t a n e o u s  motions N26°W  t h e Queen C h a r l o t t e  s h a l l o w d i p (2-6°) o f t h e o c e a n i c  which  where  determined  an  the topographic  N35°W.  Moresby  Channel,  source,  Moresby  Trough  azimuth expression  offset  of  dextral  of the f a u l t  approximately  i n Charlotte  strike  Sound  50  plate  slip  of  i s actually km  from i t s  ( F i g . 41)  i s direct  e v i d e n c e o f d e x t r a l t r a n s f o r m movement (Chase ejb a l , 1975).  46  CHAPTER I I I  RADIOMETRIC DATES OF  QUEEN CHARLOTTE  ISLAND VOLCANIC AND  PLUTONIC ROCKS  INTRODUCTION In t h i s c h a p t e r the M e s o z o i c - C e n o z o i c v o l c a n i c and Islands made  to  changes Tartu  and  Queen  relate in  Charlotte  timing  'Pacific'  of  r e s u l t s of K-Ar  Basin  are  major  constrain  reported  phases  of  (Chapter timing  new  r o t a t i o n of Graham I s l a n d  age d a t a , i s Of  the  Masset v o l c a n i c s  p.  19;  obtained  p.  53  dates  Islands  discussed,  and  1964)  post-tectonic  11-13;  1972,  was  geochronologic  data,  Brown's proposed Three d a t e s of R i c h a r d s e t _al_,  attempt  is  activity  to  Dates f o r  Masset and  A r e v i s e d model f o r  I r v i n g , 1977), based  p.  (Sutherland some r e v i s i o n  ages of a  late 1979  the  K-Ar  dates  one  biotite  and  seven  from  on  mineral  date  of  6-7).  A l l of  Sutherland  major v o l c a n i c  ( f o r d e t a i l s and  In  discussion  see  the  of  new  Sutherland  plutonic  phase, o b t a i n e d  were  Charlotte  light in  1968,  only  Queen  required and  dates  Brown but  1968).  i s now  Masset p l u t o n i c  these  s t u d y of the  Brown,  the  biotite-hornblende  i n t r u s i o n s (Wanless _et _ a j ,  a v a i l a b l e when g e o l o g i c  completed  8  previously:  from samples c o l l e c t e d by A.  Masset d a t e was  Charlotte  major down-to-basin  ( H i c k e n and  (Mathews, 1963;  syn-  1970,  of  described.  s e p a r a t e s have been p u b l i s h e d  d a t e s of the  an  magmatic II).  of  Queen  and  p o s s i b l e wrench movement on the S a n d s p i t F a u l t . block  Rb-Sr d a t i n g  p l u t o n i c r o c k s of the  p l a t e motion  facies volcanics  and  episodes.  recently Champigny  by and  47  F i g . 10  Sample l o c a t i o n s f o r K-Ar  age  determinations.  48  Sinclair,  i n press)  and  two  o f the Longarm Formation  dates  of  ( Y o r a t h and  1  syntectonic' granitic  Chase, 1981)  clasts  none of which  are  t a b u l a t e d here, are d i s c u s s e d elsewhere i n the t h e s i s . Twenty-five Rb-Sr  mineral  dates  Resources L t d . Shell  during  K-Ar  were  whole rock  released  mineral  the  author  These d a t e s were o b t a i n e d r e g i o n a l mappping  1962-63 and  to  and  of  from c u t t i n g s and  wells d r i l l e d  the  dates by  and  three  Shell  Canada  from samples c o l l e c t e d  Queen  sidewal1-core  Charlotte  Islands  samples of  i n the Queen C h a r l o t t e B a s i n i n 1968-69.  by in  exploratory In a d d i t i o n ,  9 K-Ar  whole rock and m i n e r a l d a t e s from samples c o l l e c t e d on Graham  Island  (Steen,  Pan  American  obtained  1967)  were r e l e a s e d  Petroleum  from  Corp.).  by  Three  samples c o l l e c t e d  by  Amoco Canada L t d . K-Ar  the  whole  author  on  rock  (formerly dates  Graham  were  Island in  1976.  DATA ANALYSIS, PRECISION, AND  Samples  dated  analyzed  r e s p e c t i v e l y at  Texas),  Geochron  (Cambridge, British  aY,  isotope  atomic  absorption  dilution  and  Amoco,  Development of  the  (The  laboratory  1965,  stable  Shell  and  Wanless e t al_ a t the Wanless e t  Shell,  Laboratories  Mass.)  Columbia.  for  INTERPRETATION  and  Laboratory,  techniques  used  Canada are  p.  Potassium  content  flame  photometry  (Shell),  (U.B.C.).  conventional  Argon  mass  analyses  spectrometric  (Houston,  were by  Ltd.  Univ.  of  dating  by  described  in  measured  by  in  Survey of  dilution  were  Enterprises  Geological 1-7).  author  Corporation  Krueger  Geochronometry  the  was  (Geochron) stable  techniques  at  and  isotope a l l of  49  the above l a b o r a t o r i e s . Standardized a n a l y t i c a l data are presented and  i n Tables I I I  IV and sample l o c a t i o n s on Queen C h a r l o t t e I s l a n d s a r e shown i n  Fig.  10.  W e l l l o c a t i o n s and a c r o s s - s e c t i o n a r e i n c l u d e d i n Chapter  IV ( F i g s . (16):  16 and 1 7 ) . Reported  errors i n i t i a l l y  e r r o r s are at 1 standard d e v i a t i o n  r e p o r t e d a t 3 6 by S h e l l  (G. Edwards,  Shell  Development Corp., w r i t t e n communication, 1977) and a t 26 by Wanless et  a l have been a d j u s t e d a c c o r d i n g l y . The  accuracy  of  reported  here.  been  of  isotopic  assigned  precision,  o f K-Ar and Rb-Sr  determinations  A reliability t o each  date  sample q u a l i t y ,  minerals  Geochron  precision  and g e o l o g i c  and a t U.B.C.  considered  vary  ranking based  on known  a r e based  on  for  least r e l i a b l e .  I I I and IV) has  o r assumed argon  analytical retentivity made a t  replicate  and a r e  Because  analyses  of generally  argon c o r r e c t i o n s , S h e l l  poor dates  F o r f o u r o f t h e samples a n a l y z e d by  t h e r a d i o g e n i c argon c o n t e n t  was i n s u f f i c i e n t  ( < 10"^ ml/g)  q u a n t i t a t i v e measurement and maximum ages o n l y a r e r e p o r t e d . Dates from w e l l  and  f o r dates  Age d e t e r m i n a t i o n s  reliable.  sample q u a l i t y and l a r g e atmospheric  Shell  (see Tables  accordance.  and g e o l o g i c  considerably  concordance o f d a t e s ,  t o be t h e most  are c o n s i d e r e d  analyses  p o s s i b l e mixed  considered  cuttings,  lithologies  estimates  only.  because o f s m a l l  resulting  Dates  from  obtained  caving  from  sample should  sidewall  size be core  samples s h o u l d be more r e l i a b l e . The volcanic  m a j o r i t y o f dates  and i n t r u s i v e  rocks  reported  that, with  here  are from  Cenozoic  few e x c e p t i o n s , ^have not  been a f f e c t e d by s i g n i f i c a n t post-emplacement d e f o r m a t i o n  o r thermal  50  TABLE H I :  No. Original Sample No.  Ut.N/ Long.W  Rock Type  Summary of K-Ar Age Determinations: Queen Charlotte Islands  K 100.RadJ°Ar Material Analyzed (wt.J) T o t a l * Ar 0  1  S0-546-N63 54°04.73' o l i v i n e 131°47.65' basalt  WR  0.48  2  GS-29-66  54°Q4.4' 131°47.7  WR  0.373, 0.355  3  GS-54-66  54°p4.17' basalt 132°14.25'  WR  4  GS-51-66  54°09.33' 132°39.0'  5  *  Rad^Arj Age or . Period/ Mean Age, Epochj «°K (Mails) ' <.0003  <5  56.0,49.9  .00208  0.492, 0.453  33.7,33.8  WR  1.97, 1.91  basalt SD-256-N63 54 03.53 132°14.33' porphyry  WR  0.95  6  MR 8  basalt  WR  0.809 0.789  7  SD-278-N63 S3°25.07' 131°54.78  olivine basalt porphyry  WR  0.62  3  .0021  8  SD-544-N63 53°31.68' 132°21.2'  rhyollte ash flow tuff  WR  1.44  12  .0012  9  MR 9  53 30.6' 132 20.0'  basalt  WR  0.961 0.966  10  MR 2  53 30.6' 132°20.0'  rhyollte ash flow tuff  WR  11  GS-39-66  53 42.08' 132°59.17'  basalt  WR  12  AK 378  53°24.2' 132°23.r  biotite fleldspar porphyry  Bt  2.56  13  GS-49-66  54 10.17' 132°58.0'  rhyollte ash flox tuff  WR  2.00, 1.53  14  andesite SD-250-N63 53°p6.8' 131°38.23  WR  1.46  15  SO-252-N63 52°41.4' basalt 131°23.27 porphyry  WR  16  SD-253-N63 52°40.4' basalt 131°24.75 porphyry  17  G5-50-66  0  olivine basalt  basalt  ,  53°24.6" 131°55.5'  0  D  o  0  ReliaOata b i l i t y , Source,.  Locality/Feature Formation (Sutherland Brown 1968)  U. Miocene or younger  5  b  35.2*2  L. OUgocene  5  c  .00169  28.7±2  U. OHgocens  2  c  62.1,47.5  .00140  23.8±1.3 L. Miocene  2  c  Shag Rock o f f Klashwun Pt., N.W.shore Graham Is.  7  .0007  11*3  M. Miocene  3  b  Head of Masset Sound, N shore of Graham Is.  L. Miocene  2  g  Between Lawnpolnt i Lawnhill beach expos u r e s shore Graham Is  I. OUgocene  5  b  L. Miocene  2  b  54.8  .001396 23.910.8 L. Miocene  2  9  2.96, 2.93  S5.0  .001404 23.7*0.8 L. Miocene  2  9  0.201 0.180  5.4,12.1  2  c  Masset, Tartu Fades Mixed Member  Solide I s . , Port Louis, W. coast Graham I s .  Masset, Hypabyssa Equivalent  9 km E of Rennel Sound SW Graham I s .  59.6  .001164 19.8t0.7  .00125  36*3  20*2  21.2*4  L. Miocene  Tow H i l l S i l l s  Tow H i l l , N shore Graham I s .  Masset, Tartu Fades Basalt Member  South Westacott Pt., W.snore, mouth of Mas set Sound, Graham Is.  Masset, Tartu Fades Rhyollte Member  Mamin River, 10 km SSM of Juskatla, central Graham I s . East of Marmln R., 11 km S of Juskatla, central Graham I s .  .0037  62*3  L. Paleoceni  2  a  .00264  44.6*3  M. Eocene  2  c  20  .'0010  17*1  L. Miocene  3  b •  Masset (undivided! I s l e t E of Point Grey, N.E. Moresby E of Sandspit Fault  0.75  17  .0012  20*1  L. Miocene  2  b  Masset, Dana Fades (undivided  WR  0.92  16  .0016  27*1  U. Oligoceni  2  b  diorite  Nb  2.94, 2.83  18  SD-257-63 54°Q0.63' auglte 133°00.57 d i o r i t e  WR  0.44  19a  GSC 67-16  53°17' 132°26*  granodiorite  Hb  19b  GSC 67-17 53°13' 132°29'  granadioH te  20  GSC 70-2  0  132°58.83  47  28.1,32.9  F i r s t point E of Bruin Bay, Parry Passage on NW t i p of Graham I s .  Skaga Is. E of Lyell Is. Tar I s . , E of Lyell Is.  Post Tectonic (younger) Plutons  Langara Pluton: Mcpherson Point on NW shore Langara I s .  .00136  23.1*1.4  L. Miocene  4  c  *  <.0003  <5  U. Miocene or younger  5  b  Pivot Mountain Pluto n ^ km SE of Beresford Bay, SW Graham Is.  0.44  6  .0015  26*3  U. OUgocene  1  e  Kano Batholith (East phase); S head of Shield Bay, SW Graham Island  Bt  7.52  69  .0017  29*1  U. OUgocene  1  e  Bt  7.08  54  .0018  30*2  U. OUgocene  2,4  f  21.7,20.6  Kano Batholith (Central phase), head of Dawson Inlet SW Graham Island  51  TABLE I I I ( c o n t ' d ) No.  Original Sample No.  21  SO-262-63  Lat.N/ long.W  Rock Type  Materia Analyse  K (wt »)  100.Rad*°Ar Rad*°Ar Total Ar * k , u  U  Age o r Mean Age, (Mail6) '  Period/ Epochj  ReliaData b i l i t y Source^  5^ 36.35• 131 54.43'  granite  Or  10.33  50  .0013  25i2  U.  OUgocene  5  b  0  0  Formation' ( S u t h e r l a n d Brown 1968)  Locality/Feature  Post Tectonic (Younger) P l u t o n s  P o c k e t B a t h o l i t h (marg i n ) S s h o r e , head o f < P o c k e t I n l e t , M Moresby I s l a n d  22  S0-263-63  52 36.91' 131°52.08'  blotlte granod1or1t<  MR  3.10  46  .0018  30±2  U.  OUgocene  4  b  Pocket B a t h o l i t h ( c o r e ) H s h o r e , head o f Pocket I n l e t , W Moresby I s l a n d  23a  BSC  67-18  52°34' 131°48"  granite  Hb  1.04  33  .0022  3811  U.  Eocene  1  e  Pocket B a t h o l i t h (core) S shore o f Barry I n l e t , W Moresby I s .  23b  SSC  67-19  Bt  7.30  71  .0023  39±1  U.  Eocene  1  e  24  SD-265-63  52°43.67'  quartz  WR  2.04  15  .0014  24±2  U.  OUgocene  3,4  b  25  GSC  66-14  52°22'  granodiorite  Hb  0.41  49  .0086  142H9  U.  Jurassic  4  d  26  GSC  70-3  53°19'  quartz diorlte  Hb  0.33  42  .0095  156*10  U.  Jurassic  4  f  0  131°35.95' m o n z o n i t e  131 ]5' 6  131°S8'  27  GS-33-66  53°32.17' q u a r t z 132°S7.17' d i o r l t e  Hb  0.315, 0.299  57.1, 78.1  .00721  119.416  L.  Cretaceous  3.4  c  28  GSC  S2°54.5'  Hb  0.43  54  .0086  14217  U.  Jurassic  2,4  e  67-20  quartz diorlte  131°40"  GSC  70-1  53°17-5'  gnelsslc granodiorite  Hb  0.40  47  .0087  30  GS  31-66  S3°14.87 132°37.0  blotlte quartz diorlte  WR  1.73, 1.67  57.4, 21.5  .00193  31  SD-261-63  52°40.53 131°59.70  blotlte quartz diorlte  Bt  3.80  40  32  GS  43-6  53 56.93 133°09.58  basalt  WR  65.5, 45.1  29  132°38.5'  •  u  ^Materials analysed: 2  Constants  used: X  £  0.515, 0.539  1 0  yr"',  *  8  -4.72  x 10"'°  ^Bounds o f g e o l o g i c epoch o r p e r i o d f r o m t i m e s c a l e s o f Van H1nte,1976a ( J u r a s s i c ) .  U.  Jurassic  2.4  Syntectonic (older) Plutons  NW p o i n t o f H l p p a I s . , o f f SW c o a s t o f Graham I s . E c o n t a c t o f San C h r i s t o v a l B a t h o l i t h ; E Oarwin Sound, w e s t e r n Moresby I s .  f  Syntectonic part of Kano B a t h o l i t h (west) SE t i p o f Cadman I s , Kano Bay, SW Graham I s  c  Syntectonlc part of Kano B a t h o l i t h ( w e s t ) S s h o r e , mouth o f Van I n l e t , SW Graham I s . Near c o n t a c t w i t h M a s s e t , 4 km SE o f Mt De l a Touche, W c o a s t Moresby I s .  5  .0019  32l2  L. O U g o c e n e  5  b  .0106  173120  4  c  Jurassic  Bumaby I s . P l u t o n ; P o o l e P t , 8urnaby I s . Chfnukundl P l u t o n ; C M n u k u n d l C r e e k , SE Graham I s .  L. O U g o c e n e  M.  .  *  32.712.4  WR » whole r o c k , Bt » blotlte, Hb • h o r n b l e n d e . . 0.585 x I O "  14314  A t H Inlet PIuton, N L y e l l I s . SE s h o r e o f Richardson I n l e t  Karmutsen  E side of Frederick I s . w e s t c o a s t Graham Is.  Or • o r t h o c l a s e  y r " ' . *°K,  Ryan e t a l , 1 9 7 4 (Neogene); B e r g g r e n e t a l . 1 9 7 8  ( P a l e o g e n e ) ; Van  H1nte,1976b ( C r e t a c e o u s )  and  R e l i a b i l i t y r a n k i n g o f age measurement based on sample q u a l i t y (degree o f a l t e r a t i o n ) , c o n c o r d a n c e o f a g e s , a n a l y t i c a l p r e c i s i o n , argon r e t e n t l v l t y o f m i n e r a l s , and g e o l o g i c a c c o r d a n c e : 1) c o n c o r d a n t a g e s , r e l i a b l e ; 2) s i n g l e age, p r o b a b l y reliable; 3) s i n g l e age, r e l i a b i l i t y u n c o n f i r m e d ; 4) minimum age; 5 ) u n r e l i a b l e age. ' s o u r c e s : a) Mathews ( 1 9 6 3 , 1 9 6 4 ) ; b) S h e l l Canada R e s o u r c e s L t d . ( u n p u b l i s h e d d a t a ) , a n a l y s e s by S h e l l Development Corp. ( H o u s t o n , T e x a s ) ; c ) Pana m e r l c a n P e t r o l e u m C o r p . ( u n p u b l i s h e d d a t a n o t e d 1n S t e i n , 1 9 6 7 ) , a n a l y s e s by Geochron L a b o r a t o r i e s o f K r e u g e r E n t e r p r i s e s L t d . ( C a m b r i d g e , Mass.) d) Wanless e t a l ( 1 9 6 8 ) ; e) Wanless e t a l ( 1 9 7 0 ) ; g) Wanless e t a l ( 1 9 7 2 ) ; f ) t h i s s t u d y , a n a l y s t s : K. S c o t t , J H a r a k a l . *Rad. *°Ar n o t d e t e c t e d ( l i m i t 1 0 "  7  ml/g)  of  Table IV:K-Ar Age Determloatlona: Original No.  33a  Sample No.  Well name  lac N/LonglT Depth (metes) lock "type Type of Prom Seaflmr Sample  Shell Anglo S l ^ . l O ' Osprey D-36 129°20.79'  4136D  4136H  33c  41351  34  4143  Shell Anglo 51°55.06' Harlequin M 6 129°58.21'  35  413SJ  Shell Anglo 52"20.27" Auklet G-41 130 36.55' '  36  5003*  37a  413SH  37b  4135F  52 24.69• 0  130°47.63'  52°49.14' 131 00.74" <,  Shell Anglo 52 45.41• Sockeye 130°55.32 E-66 0  38a  413SB2  38b  413SE  well 0.77 porphyry cuttings  1  4124A1  39b  4124A2  39c  4124A3  39d  4124B  39e 39f  4124C  C00013  <10  U Miocene or younger  5  Top of 40(+)m section of basalt, o v e r l a i n by 55 a of sandstone, minor s i l t s t o n e , coal  5717  Paleocene  4  Base o f above section  0.94  12  .0025  42t?  11 Eocene  4  5  .0021  3624  L.OUgocene  4  Near base of 95(*) • aection of mixed volcanic p y r o c l a s t l c s and flows. Overl a i n by L. Miocene sediments Base o f 206(+) • s e c t i o n of basalt and p y r o c l a s t l c s . Overlain b/Mlocene(?) . sediments Near middle of 65(+)m section o f basalt with shale lnterbeds. Overlain by Mlocene(?) sediments Top of 99m section o f basalt and shale sandstone lnterbeds. Overlain by Mloc e n e ( l ) . o r older sediments  sldewall 0.61 basalt porphyry core well 0.32 cuttings  0.7  <D023  <39  U. OUgocene or younger  5  basalt sldewall 0.36 porphyry core (altered well 0.44 4447.6-44S3.7 basalt cuttings well 2573.4-2576.5 basalt 0.66 porphyry cuttings  4 .  11043  7216  U. Cretaceous  3  16  j0050  84110  U. Cretaceous  3  19  0071  11817  L. Cretaceoua  4  4433.9  3381.5  A l l analyses are whole rock. 1  Near middle of 303 m. section of basalt and p y r o c l a s t l c a . Overlain by L.-M. Miocene sediments  .0034  2686.8-2708.1 basalt  4124E  Sample descriptions:  4  15  3402.8  Note:  U. OUgocene  baaalt well 0.62 porphyry cuttings  basalt (Uteres: mlcrogabbro  sldewall 1.20 core well 0.40 cuttings  ,.  well 0.37 cuttings well 1.81 granite? cuttings well 3381.5-3384.5 o l c r o 0.325 gabbro cuttings well 0.33 3393.6-3396.7 mlcrogabbro cuttings  ••  2914  2437.8  ••  ••  £017  0  2612.1  "  3  1.77  2166.2  S h e l l Anglo 53 18.91• tyee N-39 131°20.36'  microgabbro  well 0.44 cuttings  30  J0101  16518  M,Jurassic  3  26  J0271  >14tl0  U. S i l u r i a n  5  20  ,0163  160110  L. Permian  4  18  .0105  ^71*9  11 J u r a s s i c  4  24  .0167  265111  L. Permian  4  15  .0124  201111  11 T r i a s s i c  4  24  J0153  24517  Constants: X - 0.585 x 1 0 ~ y r ~ , AB- 4.72 x 1 0 ~ y r 10  x  e  B.E.P. Scarborough ( S h e l l Canada Ltd.), Age laboratory:  10  .  U. Permian  =  B  Near middle o f 165(+)a section o f basalts, p y r o c l a s t l c s . Overlain by lS2n of U. Cret.-Paleocene sediments ••  Near base of 97(+)m o f predominately Plutonic rock. Overlain by 406a aection of 0. Cret. sediments  4  K/K - 1.19 x 10"* atom r a t i o  S h e l l Development Corp., Houston, Texas  eee footnotes. Table HI,. ell  Comae nt 2  y i  baaalt sldewdl porphyry core  3056.8-3059.9 baaalt well porphyry cuttings  0  39a  lelia,ilit  2411.3  o  Shell Anglo Murrelet L-15 Shell Anglo Sockeye B-10  40  2098.9-2101.9 basalt  "  33b  S h e l l Canada Wella, Queen Charlotte Basin  100Rad.*°Ar Rad. Ar K *g«l Period/ (Mallo) Epoch} (wt.Z) 40K Total*°Ar  l l t h o l o g l e s and tentative ages f o r U. T e r t i a r y sediments from S h e l l Canada Well History Repts.  ••  ••  - t*  53  events.  S i n g l e K-Ar d a t e s a r e minimum d a t e s as t h e y may r e l a t e t o  tectonic  uplift  and c o o l i n g  through  a  critical  isotherm  r e t e n t i o n ( f o r r e c e n t summary, see H a r r i s o n e t to  time  o f emplacement  and  initial  m i n e r a l - p a i r dates-| a r e i n t e r p r e t e d (Lanphere shallow  and Reed, 1973). post  tectonic  Rapid  1978) r a t h e r t h a n  crystallization.  as e v i d e n c e cooling  plutons suggests  f o r Ar  Concordant  o f emplacement age  following  concordant  c l o s e lower l i m i t t o t h e t i m e o f c r y s t a l l i z a t i o n .  emplacement o f dates  provide a  Discordant dates  i n d i c a t e t h a t t h e p l u t o n e i t h e r has been r e h e a t e d o r has undergone a long c o o l i n g  history  and t h a t  i t s age i s o l d e r t h a n e i t h e r m i n e r a l  date.  DISCUSSION OF AGE DATA  Dates  f o r samples from  t h e Queen C h a r l o t t e  Queen C h a r l o t t e B a s i n a r e d e s c r i b e d h e r e . (localities Sills of to  exists  n o t be d i s c u s s e d .  o f K-Ar whole  i n t h e age o f basement Anglo Tyee N-39 w e l l .  rock  intrusive  Tow  Hill  Some u n c e r t a i n t y , due dates  (see Table  r o c k s encountered  A mean age o f 228 Ma (Lower  5 o f t h e 6 samples dated  suggests  e q u i v a l e n t t o t h e Upper P a l e o z o i c - L o w e r  1  basaltic  ( S u t h e r l a n d Brown, 1968, p. 127-128) a r e i n d e t e r m i n a t e because  considerable scatter  from  Two K-Ar whole rock d a t e s  1, 2) f o r t h e P l i o c e n e - P l e i s t o c e n e  t h e i r young age and w i l l  Shell  I s l a n d s and  IV)  i n the  Triassic)  t h e basement r o c k s may be Mesozoic a r c p l u t o n s o f t h e  Concordance o f m i n e r a l p a i r s was determined by u s i n g t h e c r i t i c a l v a l u e F t e s t ( D a l r y m p l e and Lanphere, 1969, p. 120) a t the 95 p e r c e n t c o n f i d e n c e l e v e l .  54  Alexander  terrane  of  southeastern  Alaska  (Churkin  and  Eberlein,  1977). Karmutsen F o r m a t i o n : A Jurassic) Island  single  was  K-Ar  obtained  (west  coast  whole  for  of  a  rock  massive  Graham  date  of  basaltic  Island,  173 lava  locality  on  32),  S u t h e r l a n d Brown (1968) as L a d i n i a n - K a r n i a n Karmutsen number o f p o s s i b l e e f f e c t s might 1)  the  date  reflects  the  age  Ma  cataclastic  Frederick mapped  by  Formation.  e x p l a i n the anomalously of  (Middle  young  deformation  A age:  along  a  s m a l l wrench f a u l t t h a t c u t s F r e d e r i c k I s l a n d ; 2) the d a t e  reflects  low-grade  dikes  (partial  Middle  Jurassic  loss  of  metamorphism  or  h e a t i n g by  radiogenic argon);  3)  the  nearby date  Masset  reflects  Yakoun ( p r e d o m i n a t e l y a n d e s i t i c ) v o l c a n i s m . S y n t e c t o n i c (Old) I n t r u s i o n s : Three syntectonic and  K-Ar  hornblende  intrusions.  The  West Kano B a t h o l i t h s  two  largest  (localities  J u r a s s i c d a t e s of 142 and  143 Ma  in  relations  accordance  time  of  uplift  with f i e l d and  Ma  (Lower  have  been  obtained  b o d i e s , the San  28,  29),  respetively.  unroofing rather  younger d a t e of 119.4  dates  (see T a b l e than  Christoval  have y i e l d e d  Upper  Both t h e s e d a t e s V)  but may  emplacement.  C r e t a c e o u s ) was  for  A  are  indicate somewhat  obtained f o r a small  i n t r u s i v e body on Hippa I s l a n d ( l o c a l i t y 2 7 ) . The Jurassic-Middle p. 133)  three  K-Ar  Cretaceous,  dates  fall  suggested  within by  the  range  Sutherland/Brown  Upper (1968,  from f i e l d r e l a t i o n s as the age of the s y n t e c t o n i c p l u t o n s ,  but i n d i c a t e t h a t t h e major  d e f o r m a t i o n a s s o c i a t e d w i t h emplacement  i s p r o b a b l y of Upper J u r a s s i c age.  The  i n t r u s i o n s may  be comagmatic  55  with  Yakoun v o l c a n i s m  date  volcanism.  The  have y i e l d e d K-Ar d a t e o f 174 Ma Masset  ( i f dates Island  reflect  uplift)  I n t r u s i o n s on  slightly  Vancouver  d a t e s r a n g i n g from 181-142 Ma  ( M u l l e r , 1977)  or  and  post-  I s l a n d , which  a Rb-Sr i s o c h r o n  appear t o be somewhat o l d e r .  Formation: The  underlying Island  L a t e C r e t a c e o u s ? - T e r t i a r y Masset v o l c a n i c s u c c e s s i o n  much of  comprises  Graham  thin  I s l a n d and  flows  of  p o r t i o n s of  northern  Moresby  columnar b a s a l t , b a s a l t i c b r e c c i a s ,  s o d i c r h y o l i t i c ash f l o w t u f f s and welded t u f f b r e c c i a s and b r e c c i a s of mixed b a s a l t and r h y o l i t e c l a s t s (see summary, Chapter t e e n K-Ar  dates  (13 whole r o c k ,  Masset T a r t u and volcanic Lower  pile  Miocene  volcanism K-Ar  Dana f a c i e s  (Table  on  Queen  time.  S u t h e r l a n d Brown  date of 62 Ma  Charlotte  t h a t much of  Islands  (1968,  was  p.  Paleocene-Eocene t i m e  based  tilting,  M i o - P l i o c e n e Skonun sediments",  and  erosion  prior  and o c c u r r e n c e  to  the  erupted  118)  from t h e base of t h e T a r t u f a c i e s ,  faulting,  Four-  s e p a r a t e ) f o r the  I I I ) suggest  exposed  t o have spanned  "extensive  1 b i o t i t e mineral  I).  in  considered on  a  single  evidence  for  deposition  of widespread  of  volcan-  ism i n s o u t h - c e n t r a l B r i t i s h Columbia d u r i n g Eocene t i m e . Ten K-Ar and  r h y o l i t e t u f f s of t h e b a s a l t and  facies. the  whole rock d a t e s have been o b t a i n e d from b a s a l t  Most of the  north  shore  of  samples d a t e d Graham  Masset I n l e t ( F i g . 1 0 ) . q u a l i t y ) K-Ar Ma  dates  r h y o l i t e members of t h e (Table  I s l a n d and  (Lower M i o c e n e ) .  somewhat younger than  I I I ) were c o l l e c t e d  near  Mamin  E x c l u d i n g samples no.  range from 17 t o 28.7, Though d a t e s those  f o r the  Tartu  River,  5 and  south  7 (poor  w i t h a mean age  from  sample of  b a s a l t member s h o u l d  f o r the u n d e r l y i n g r h y o l i t e  of  member,  22.3 be no  56  systematic  age  difference  geochronologic  study  is  will  seen.  be  More  required  detailed  to  mapping  resolve  this  and  apparent  discrepancy. Tartu western  facies  ( b a s a l t and  Graham I s l a n d appear t o be  rhyolite  somewhat o l d e r than  Masset v o l c a n i c s exposed f u r t h e r n o r t h . metamorphosed  by  intrusion  B a t h o l i t h , dated a t 30 Ma Dates phases  on  of  Graham  of  the  to  central  phase  of  and  Island  44.6  Ma  (localities  from 12,  consolidated  intrusive  13)  are  The  Graham  porphyry and  Sample  with  the  Cape  rock d i s t r i b u t i o n  northwestward  Lyell  Kano  vents  or  hypabbyssal minimum  upper  magma  are  chambers  Sample no. 12 body, presum-  with  13  was  obtained  Knox-Parry  from  Passage  Graham I s l a n d .  similar  volcanic  biotitic  As suggested  o f T a r t u members, v o l c a n i s m  time,  a  to  a  feldspar  by t h e s e  may  possible  tuff  have  dates  shifted  progression  of  Post-Tectonic Intrusions. Two  basalt  no.  of n o r t h w e s t e r n  Cenozoic  the  near t h e base o f the T a r t u mixed member on s o u t h c e n t r a l  Island.  associated  of  been  i n t r u s i v e phases  o b t a i n e d from a t a b u l a r b i o t i t i c f e l d s p a r porphyry  ably a s i l l ,  bulk  probable  r e l a t e d t o e a r l y Masset f l o w s ( S u t h e r l a n d Brown 1968). was  the  south-  (Lower O l i g o c e n e ) .  62  represent  of  These v o l c a n i c s have  ages f o r s t a r t o f T a r t u f a c i e s v o l c a n i s m . thought  members)  samples Island  underlain  by  post-tectonic  K-Ar of  dates  the  facies  intrusions,  samples i n d i c a t e l i t t l e  20  and  Dana f a c i e s  (localities Dana  of  no.  15,  rocks the  27  from 16).  has  the  have been o b t a i n e d Tar  Though  been  sample  alteration.  Ma  for  Islands, east much  of  metamorphosed  d e s c r i p t i o n s of  Dyke-like connections  the  of area  by  young  the  dated  to basalt  57  f l o w s on Skaga I s l a n d for  Dana  likely  volcanics  that  the  (locality  (Sutherland  date f o r  this  phase s i n c e  dated  at  o r i g i n a t e d from  within  the  the  flow the  synchroneity  on  p.  117).  Ma)  the  adjoining  f o r Tartu  must  appears  represent Tar  Both  basalts  a vent  It  (20  same s o u r c e .  range of d a t e s o b t a i n e d  t u f f s , suggesting  1968,  locality  extrusive Ma  are thought t o r e p r e s e n t  Brown,  later  27  15)  Island,  dates  and  a  fall  rhyolitic  of t h e s e l a t e phase e r u p t i o n s .  No d a t e s are p r e s e n t l y a v a i l a b l e f o r the Masset Kootenay f a c i e s of western Moresby I s l a n d . Jurassic  San  20  volcanics,  'Masset-like'  Christoval Batholith (locality  b i o t i t e d a t e of 32.7 located  A  km  Ma  and  northwest  the  dyke  30)  dyke i n the Upper  has  a Rb-Sr b i o t i t e d a t e of  of  the  main  exposure  be  related to  i n t r u s i o n may  of  yielded  a  42  Though  Ma.  Kootenay  an  early  K-Ar  facies  Kootenay  phase e r u p t i o n . Five  K-Ar  whole rock  from C h a r l o t t e  subbasin  G-41,  L-15)  Murrelet  (Upper O l i g o c e n e ) . are  recorded  wells  Two  Sockeye  E-66  subbasin. close Canada  Osprey D-36  K-Ar  Dates of  agreement w i t h  volcanics.  Ma  (Lower  well.  D-87,  Paleocene)  late-phase  Volcanism  basalts Auklet  to and  i n the  29 29  Ma Ma)  Charlotte  Tartu  and  Dana e r u p t i o n s  for  the  Sockeye  on  Islands.  wells  Ltd.,  57  Harlequin  d i s t i n c t v o l c a n i c e p i s o d e s (57 Ma  s u b b a s i n must have preceeded  Four  (Osprey D-36,  range from  i n the  Queen C h a r l o t t e  d a t e s o f basement' Masset  whole  rock  record  late  72  84  and an  1968b) f o r  Upper  dates Mesozoic  Ma  on  basalt  Cretaceous  sediments  eruptions  in  the  i n Sockeye B-10  palynological  interbedded  V o l c a n i s m r e c o r d e d at Sockeye B-10  B-10  and may  age  and  Hecate are  in  (Shell  underlying  the  be an e a r l y phase  58 Masset e r u p t i o n . clastics  Dates of  underlying  plutons from  on  spatial  Ma  from f l o w s  sediments  i n the  and  pyro-  Sockeye  E-66  M i d d l e J u r a s s i c Yakoun v o l c a n i s m .  Intrusions  the  Charlotte  Queen to  granite  Islands  (average  two  large  bodies,  the  five  major  groups  of  r e l a t i o n s h i p s and  teristics. young  165  Brown (1968) mapped some t w e l v e  to  recognized  and  Sutherland  diorite  addition  Ma  Upper Cretaceous  w e l l , l i k e l y record Post-Tectonic  118  Local  intrustions  that  range  composition, Kano  and  smaller  cross-cutting ranged  from  K-Ar  dates,  composition  granodiorite).  plutons  on  textural  suggested  Cretaceous  to  In  Batholiths, based  and  relationships  Early  in  Pocket  s i m i l a r minerological  'high-level'  close charac-  that  Upper  he  Eocene  the in  age. Twelve  hornblende p a i r s , and seven of  of  3 Rb-Sr m i n e r a l  of i n d i v i d u a l d a t e s and  each sample l o c a l i t y the  lished.  Kano The  and  Pocket  apparent  phase of the Kano B a t h o l i t h d a t e ( l o c a l i t y 20).  T h i s d a t e i s not  the e a s t e r n phase o f the  grounds. of  the  A hybrid batholith  now  for  i s 30 Ma,  c o n f i d e n c e from c o n c o r d a n t m i n e r a l  T a b l e V the c e n t r a l  is  III).  stratigraphic The  reasonably  based on  for The  relations  apparent  age  well  estab-  the  central  a s i n g l e K-Ar  biotite  emplacement  of  s i g n i f i c a n t l y d i f f e r e n t at  p a i r d a t e s of  26  and  29  Ma  95% from  b a t h o l i t h ( l o c a l i t y 19), though as noted i n  phase i s judged t o be K-Ar  biotite-  available  (Table  i n T a b l e V.  Batholiths age  concordant  plutons  critical  i s included  minimum  two  p a i r d a t e s are  S u t h e r l a n d Brown's p o s t - t e c t o n i c  reliability for  including  age  (locality  of 33 Ma 30)  somewhat o l d e r on  f r o m the  dates  a  older  thermal  geologic  syntectonic event  related  part to  TABLE V .  SAMPLE NO.  DATE(S)  RELIABILITY  CRITICAL STRATI6RAPHIC RELATIOHS FOR 5TH AND POST-TECTONIC INTRUSIONS  CRITICAL STRATIGRAPHIC RELATIOHS. COKNTS  17  23.111.4 (K-Ar, lib)  4  LANGARA PLUTON (LANGARA GROUP). INTRUOES AND METAMORPHOSES TURONIAN HONNA FORMATION.  18  <5 (K-Ar, WR)  S  PIVOT MOUNTAIN PLUTON (LANGARA GROUP). INTRUDES HASSET TARTU FACIES RIIYOLITES.  1  KANO BATHOLITH (EASTERN PHASE). INTRUDES AHD HETAKORPHOSES CENTRAL PHASE OF BATHOLITH) INTRUDES VALANGIANBARREHIAN LONGARM FORMATION; HETAHORPIIOSES MASSET TARTU FACIES MIXED MEMBER BASALTS AND RIIYOLITES.  19  26tj 29T1  K-Ar. lib) K-Ar, Bt)  20  3012  (K-Ar, Bt)  2. 4  KANO BATHOLITH (CENTRAL PHASE). INTRUDES AND HETAHORPIIOSES HASSET TARTU FACIES RIIYOLITES. THIS PHASE JUDGED TO BE SLIGHTLY OLDER THAN EASTERN PHASE BECAUSE OF COARSER 6RAIN SIZE AND MORE ACIDIC CHARACTER (SUTHERLAND BROWN, 1968, p. 139).  30  32.712.4 (K-Ar, WR)  S  SYNTECTONIC PART OF KANO BATHOLITH (WESTERN PHASE) OF UPPER JURASSIC AGE. RESET AGE DATES THERMAL EVENT RELATED TO INTRUSION OF CENTRAL PHASE.  21  25*2 (K-Ar, Or) 49f2 (Rb-Sr. Or)  S  POCKET BATHOLITH (MARGINAL ZONE). INTRUDES AHPIIIB0LI2E0 PRE UPPER KARNIAN KARMUTSEN BASALTS OF ITS METAMORPHIC AUREOLE.  22  30»2 (K-Ar. MR) 39*1 (Rb-Sr. Bt)  4  POCKET BATHOLITH (CORE ZONE). INTRUDES UPPER JURASSIC SAN CIIRISTOVAl BATHOLITH AND AHPIIIBOLIZED KARMUTSEN BASALTS  23  3811 39jl  (K-Ar. Hb) (K-Ar, Bt)  1  POCKET BATHOLITH (CORE ZONE). GEOLOGIC RELATIONS SAME AS HO. 22.  24  2412  (K-Ar, WR)  3. 4  ATLI INLET PLUTON (LOUISE GROUP). INTRUDES HASSET DANA FACIES MIXED CLAST VOLCANIC BRECCIAS (K-Ar 21 AND 27 Ma).  25  142M9 (K-Ar. lib)  4  BURHABV ISLAND PLUTON (SOUTHERN GROUP). INTRUDES VALANOIAN-BARREHIAH LONGARM FORMATION.  26  15615  4  CHINUKUNDL PLUTON (SANDSPIT GROUP). PLUTON CORED IN ROYAL1IE QUEEN CHARLOTTE NO. 1 WELL AFTER ALBIAN HAIDA AND BAJOCIAN-CAUOVIAN YAKOUN FORMATIONS. UNCERTAIN WHETHER CONTACT WITH YAKOUN METAMORPHIC OR UNCONFORMABLE. IN UKHETANORPIIOSEO CONTACT WITH MIO-PLIOCENE SKONUN FORMATION ALONG SANDSPIT FAULT.  (K-Ar, lib)  SYNTECTONI : PLUTONS: 27  119.416 (K-Ar, lib)  3. 4  H1PPA ISLAND INTRUSION. OVERLAIN BY HASSET TARTU FACIES MIXED CLAST VOLCANIC BRECCIAS.  28  14217 (K-Ar. lib)  2, 4  SAN CHRISTOVAl BATHOLITH (EASTERN MARGIN). INTRUDES PRE UPPER KARNIAN KARMUTSEN FORMATION AND LOWER PART (KARNIAN-NORIAN) KUNGA FORMATION.  29  I43M  2. 4  KANO BATHOLITH (WESTERN PHASE). MIXED CLAST VOLCANIC BRECCIAS.  (K-Ar. Kb)  INTRUDES KARNIAN-SIHEMURIAN KUNGA FORMATION, UNDERLIES HASSET TARTU FACIES  60  i n t r u s i o n of the c e n t r a l  phase.  The minimum age f o r emplacement o f t h e c o r e zone o f t h e Pocket  Batholith  (locality to for  i s 39 Ma based  on a concordant  23) and a Rb-Sr b i o t i t e m i n e r a l  discordance  o f K-Ar (25 Ma) and Rb-Sr  t h e western  marginal  date  phase o f t h e b a t h o l i t h  the core.  critical  apparently  somewhat  the  younger  hornblende the  volcanism.  Langara P l u t o n o f t h i s date.  dates  Since orthoclase  i s probably  t o o young.  i s o t h e r m s f o r Ar and S r  Graham and Langara  than  both  B a t h o l i t h s , though l i k e t h e Kano B a t h o l i t h , Masset T a r t u f a c i e s  Due  r e h e a t i n g may e x p l a i n t h e d i s c o r d a n c e .  The Langara p l u t o n group o f n o r t h w e s t e r n is  22).  (49 Ma) o r t h o c l a s e  i s not h i g h l y argon r e t e n t i v e t h e K-Ar date  r e t e n t i o n o r Ar l o s s through  (locality  pair  i t i s u n c e r t a i n whether t h e  zone i s younger o r o l d e r than  A l t e r n a t i v e l y , slow c o o l i n g through  K-Ar m i n e r a l  Kano  and  i t sintrusion  Pocket  postdates  The minimum age f o r emplacement of  group  An apparent  the  Islands  i s 23 Ma based  on a s i n g l e K-Ar  age o f l e s s than 5 Ma was o b t a i n e d f o r  P i v o t Mountain P l u t o n o f t h i s  same group which  intrudes Tartu  rhyolites. The apparent Pocket  batholiths  post-tectonic  ages o f t h e Langara  suggest  a  plutons northward  progression along  plutons  of  t h e west  and Kano and  decreasing coast  age  of  of t h e Queen  Charlotte Islands. With  p o s s i b l e e x c e p t i o n o f t h e L o u i s e Group p l u t o n s and  some o f t h e S a n d s p i t sions  on  the east  Group p l u t o n s , i n d i c a t e d coast  of t h e Queen  considerably  o l d e r than  those  minimum  of  was  age  24  Ma  along obtained  post-tectonic intru-  Charlotte  t h e west f o r the  Islands  coast.  An  Atli  Inlet  may  be  apparent Pluton  61  (locality  24)  volcanics. fault  of  The  the  Louise  l o c a t i o n of  suggests  the  group  the  that  pluton,  possibility  intrudes  along  that  the  the  K-Ar  Dana  facies  Louscoone wrench date  may  reflect  northeastern  Moresby  movement along t h i s t r e n d . The Island  and  Southern  eastern  Longarm  hornblende d a t e of  Pluton  of  this  date,  in  addition  group.  be  142  Ma  was  Though  to old  as  plutons  are more b a s i c , m a f i c  intrusives  intrude and  fall  A  single  Burnaby  than  the  Island  expected  this  suggests  Southern  Group  intrusions.  Southern  Group  coarser  within  (Sutherland  of  rocks.  f o r the  older  relations,  r i c h and  sediments  older  obtained  syntectonic  i n t r u s i o n s and  of  somewhat  field  may  syntectonic  Island  Formation  plutons  post-tectonic  as  plutons  Burnaby  Valangian-Barremian K-Ar  Group  grained  than  compositional  Brown,  1968,  p.  average  limits  of  137).  In  a d d i t i o n , t h e y are d i s t i n c t f r o m most l a t e phase i n t r u s i o n s i n t h a t they  are  plutons or  not  may  aligned  then  represent  an  be  along  a  major  transcurrent  consanguinious with  the  fault.  syntectonic  a d d i t i o n a l i n t r u s i v e phase d i s t i n c t  These  intrusions  from  syn-  and  p o s t - t e c t o n i c phases. Like are K-Ar  distinctly  the more  Southern basic  hornblende d a t e of  sample  quality)  was  Group.  The  Sandspit possibly dating  of  the the  plutons,  than  156  Ma  obtained pluton  Sandspit  Group  post-tectonic  (somewhat q u e s t i o n a b l e the  Chinukundl  plutons  plutons.  Yakoun  i s required  Formation. as  their  A  due  to  poor  Pluton  of  the  i n t r u d e s the A l b i a n Haida F o r m a t i o n  Group  the west s i d e of the S a n d s p i t  average  for  Bajocian-Callovian Sandspit  the  More  and  complete  alignment  along  F a u l t zone s u g g e s t s emplacement may  be  62  e l a t e d t o an e a r l y wrench f a u l t o r s u t u r e zone along t h i s t r e n d .  TIMING OF MOVEMENT ON SANDSPIT AND  RENNEL-LOUSCOONE FAULTS  Dates o f Masset T a r t u f a c i e s b a s a l t s c o n s t r a i n t i m i n g of major  down-to-basin  Fault.  and  Whole rock K-Ar  p o s s i b l e wrench movement on  d a t e s of 19.8  and  samples o f b a s a l t f l o w s from l o c a l i t i e s fault  zone.  basalt the  80km  basalt  zone and  considered  tentative  equivalents source.  and  the  be  14  and  required basalt  correct,  little,  on  Graham  of  the  southern  i n order  to  This  the  may  not  have 116)  contact  of  e x p l a i n the conclusion  in Atlantic  that  Richfield  present be  roughly  the  same  distribution e_t a]_  wells  'member c o n t a c t s ' t o e a s t e r n Graham I s l a n d .  i f any,  wrench movement on  the  of  the  must  o r i g i n a t e d from suggests  Tartu  displacement  however, as ages of the f l o w are o n l y flows  the  I s l a n d , west  D e x t r a l wrench  flows.  v o l c a n i c s encountered  a p r o j e c t i o n of  14) e a s t o f  equivalents  Inlet  S u t h e r l a n d Brown (1968, p.  Tartu  fits  the  probably  Sandspit  Ma were o b t a i n e d from  (nos. 6 and  at 20-28 Ma.  locality  member would of  are  near Masset  dated  offsetting  distribution  of  flows  member exposed  fault  of  These  17.4  the  Sandspit  need  If be  invoked. Major  down-to - basin  movement, must have been i n i t i a t e d ics,  17.4  Ma  ago  Miocene-Pliocene subsidence and  movement,  o f t h i s sediment p i l e .  v o l c a n i c b r e c c i a s of  the  possible  a f t e r e x t r u s i o n of T a r t u  ( l a t e Lower M i o c e n e ) , Skonun sediments.  like  p r i o r t o d e p o s i t i o n of  Later displacements  wrench volcanMiddle  accompanied  U p l i f t of subaqueous p y r o c l a s t i c s  Dana f a c i e s  of  northeastern  Moresby  63  Island  may  have  been  associated  with  movement  on  the  southern  Sandspit F a u l t extension. Dates  of  wrench d i s p l a c e m e n t strand  of  the  (1968, p. 151) facies  may  indicating  Dana f a c i e s  on t h e Louscoone and  Rennel'-Louscoone suggests  combined  fault  constrain timing Beresford f a u l t s system).  have  been  right  faults.  significant  Oligocene  opposed  lateral  Two  K-Ar  displacement  - Lower Miocene.  emplacement of the dated  at  across  movement o f whole rock  s h a l l o w East and  29+1  fault  the  dates  Inlet  Similarly,  hornblende  and  likely  controlled  strand  of  the  Rennel'-Louscoone  activity  Upper  controlled Group), of of  the  the 26+3  Rennell  fault  system may  from b e f o r e t h e L a t e J u r a s s i c o r E a r l y Cretaceous major p o r t i o n of t h i s  in  dates by  27+1  indicate  (Louise  biotite  likely  Rennel -Louscoone  and  emplacement  was  the  20+1  15, 16)  Pluton  lines,  kilometers  deposition  Louscoone f a u l t  24).  (K-Ar  after  20  of  19)  movement on  (southern  fault  about  locality  (northern  Although  The  (locality  Kano body  May,  occurred  Post T e c t o n i c A t l i  24+2 May  late  S u t h e r l a n d Brown  o b t a i n e d from Dana b a s a l t p o r p h r i e s ( l o c a l i t i e s  that  of  t h a t mid p o i n t s of o u t c r o p b e l t s of the Dana  initially  a c r o s s t h e two Ma,  Masset  system).  have  lasted  t o the p r e s e n t ,  appears t o have o c c u r r e d  a  i n Neogene  time. BLOCK ROTATION-TRANSLATION OF GRAHAM ISLAND  Hicken  and  Irving  (1977) r e p o r t  a discordant  n e t i c p o l e f o r Masset T a r t u f a c i e s b a s a l t s and Graham the  Island.  Tartu  facies  Assuming they  an  age  of  show t h a t t h e  Paleocene  paleomag-  r h y o l i t e s of  central  f o r magnetization  Masset p a l e o p o l e  of  i s displaced  64  53+28  i n a c o u n t e r - c l o c k w i s e sense from  American  cratonic  pole,  indicating  the  that  mean Paleocene  Graham  Island  North  must  have  r o t a t e d at l e a s t 25° c l o c k w i s e s i n c e t h i s t i m e . Subsequent d a t i n g of the T a r t u f a c i e s , chapter, Miocene  has in  coherent  shown age.  that It  these  is  magnetization  volcanics  noteworthy  for  are  that  paleomagnetic  reported i n t h i s  as  young  eight  Upper  sites  providing  determinations  were a l l  c l o s e t o Masset I n l e t , west of the S a n d s p i t F a u l t . d a t e s f o r t h r e e samples c o l l e c t e d  as  K-Ar  whole rock  south of Masset I n l e t ranged  from  20-24 Ma. Using volcanics,  M.E.  calculated  the  a revised Beck  age o f 20 Ma  J r . (written  expected  f o r m a g n e t i z a t i o n of T a r t u  communication,  directions  an  VI.  eastward  inclination declination,  deviation in declination 7.6+6°.  one  Because  cannot  state  t h a t t h e Masset p a l e o p o l e cratonic explain would netic  pole. the  be  consistent with  by  discordance  in  rotation  Beck of  could  28  the  the  +30  and  large  95  the  results  right as  paleomagnetic occurred  declination.  from  Cordillera.  (1976)  have  in  lateral a  from be  directions.  to On  the  level  t h e mean  Such  to  rotation paleomag-  microcontinental  strike slip faults  mechanism  between  of  in  invoked  a l a r g e number of Rotation  in  error  confidence  different  show  steepening  standard  percent  is significantly  difference  b l o c k s between en-echelon proposed  at  of  at  Masset d i r e c t i o n s  However, some c l o c k w i s e r o t a t i o n may  'apparent'  studies  of  has  S t a t i s t i c s are summarized  Compared t o t h e s e d i r e c t i o n s ,  of  1978)  (declination-inclination)  Graham I s l a n d f o r t h e mean c r a t o n i c p o l e . i n Table  April,  explain Graham Queen  has  the  been  common  Island, Charlotte  such and  65  Sandspit f a u l t s ,  i n post-Lower  Miocene t i m e .  T a b l e V I . Masset and Mean North American D i r e c t i o n s and P o l e s (T = 20 Ma) Means a°95  D/I o r Lat/Long Masset d i r e c t i o n s Masset p o l e s N.A. d i r e c t i o n s N.A. p o l e s * * from I r v i n g (1977)  026, 72N, 358, 88N,  52 52 10 10  6 11  81 24  -78 97W -70.5 171°W  175  POSSIBLE RELATIONSHIPS OF CENOZOIC MAGMATISM TO ' P A C I F I C PLATE MOTIONS  Although and  more  i s o t o p i c data i s s t i l l  possible  relationships  detailed  mapping,  petrologic,  chemical,  r e q u i r e d , i t i s t e m p t i n g t o s p e c u l a t e on  between  Cenozoic  igneous  activity  on  Queen  C h a r l o t t e I s l a n d s and ' P a c i f i c ' p l a t e m o t i o n s . The Masset  close  volcanics  spatial  and  and Cenozoic  temporal  epizonal  c o e v a l , but as d i s c u s s e d below,  relationship  plutons indicates  may not be c o g e n e t i c .  t i o n s , i n i t i a t e d i n L a t e Cretaceous  t h e y are  Masset  erup-  ( ? ) o r Paleocene t i m e c u l m i n a t e d  i n t h e Lower Miocene ( F i g . 11) w i t h d e p o s i t i o n l a v a sequence o f a l k a l i  between  of a t h i c k  b a s a l t and l e s s e r s o d i c r h y o l i t e .  p l u t o n s on t h e west c o a s t o f Queen C h a r l o t t e  plateau Epizonal  I s l a n d s were emplaced  from Upper Eocene t o Upper O l i g o c e n e ( o r l a t e r ? ) .  Magmatic  activity  appears t o have been e p i s o d i c (though not n e c e s s a r i l y p e r i o d i c ) w i t h possible  peaks  (Fig. 11).  i n Paleocene,  Upper Eocene  and Lower Miocene  times  66  10r  B £3  8h  P  0  S  T  TECTONIC PLUTONS  MASSET VOLCANICS, BASALT RHYOLITE  (0  z o  fca OTHER  < K ill IUl  Q  Ul  O < u.  O <r  ui  m S 3  10  MIOCENE  PL  Fig.  20  11  30  O L I G O C E N E  40  SO  E O C E N E  H i s t o g r a m o f K-Ar and Rb-Sr age d e t e r m i n a t i o n s Masset v o l c a n i c s and p o s t - t e c t o n i c p l u t o n s .  60 Ma  P A L E O C E N E  of Cenozoic  B.P.  67  Masset V o l c a n i c s The transitional  bimodal  basalt  c h a r a c t e r i s t i c of as  defined  t h a n 100  by  km)  of  and  sodic  flows  Masset  an e x t e n s i o n a l or  Martin  and  siliceous  rhyolite  tuffs  volcanism  to  Paleogene was  subalkalineand  flows  are  a n o r o g e n i c t e c t o n i c environment  Piwinskii  (1972).  Close  proximity  of Masset v o l c a n i c c e n t e r s t o Cenozoic  z o n e ( s ) west of the of  suite  (less  paleosubduction  Queen C h a r l o t t e I s l a n d s argues a g a i n s t any  arc  related  largely  processes.  confined  to  the  Arc  activity  eastern  link  during  margin of  the  the Coast  P l u t o n i c Complex (see Ewing, 1980). Several explain  the  t e c t o n i c models have been p o s t u l a t e d  origin  of  the  Masset  i n s u f f i c i e n t e v i d e n c e f o r proof t h a t has gained and  age  the w i d e s t  volcanics  may  propagation  et  the  there  is  the  one  of these models, but  acceptance t o d a t e r e l a t e s the  form  a]_  (1979) suggest  the  eastward  peralkalic  British  present  occurrence  American p l a t e o v e r a  spot. Bevier  rate,  of any  At  of the Masset t o passage o f the North  mantle hot  and  volcanics.  t h a t might  western  end  of  that a  Upper Miocene hot  in  Upper  Miocene-Quaternary  eruptions  along  the  Columbia (estimated  ( F i g . 12). at  The  approximately  predicted direction  and  spot  Masset  trace  produced  whose alkalic  Anahim v o l c a n i c b e l t  in central  east-west  propagation  2.5  trend  and  cm/year) i s c o n s i s t e n t  r a t e o f movement of the  North  with  American  p l a t e r e l a t i v e t o the M i n i s t e r e t a l (1974) g l o b a l hot spot frame of reference. location  I f the  north  of  Masset the  v o l c a n i c s form  westward  extension  part of  of  the  this  trend  their  Anahim b e l t  would  r e q u i r e the Queen C h a r l o t t e I s l a n d s t o have been d i s p l a c e d northward  68  F i g . 12 S k e t c h map o f Neogene v o l c a n i c t r e n d s o f s o u t h w e s t e r n B r i t i s h Columbia ( m o d i f i e d a f t e r B e v i e r ejt a l _ (1979) and p r e s e n t p l a t e b o u n d a r i e s o f B r i t i s h Columbia and Washington c o a s t s ( a f t e r R i d d i h o u g h , 1977) showing Anahim v o l c a n i c b e l t and Masset v o l c a n i c s ( c i r c l e s ) , Pemberton v o l c a n i c b e l t ( s q u a r e s ) , A l e r t Bay v o l c a n i c b e l t ( s t a r s ) , G a r a b a l d i v o l c a n i c b e l t ( t r i a n g l e s ) and K-Ar d a t e s (Ma B.P.). O u t l i n e d d o t t e d a r e a shows e x t e n t o f Miocene p l a t e a u l a v a s ; s t i p p l e d a r e a shows t r a c e o f f o r m e r s u b d u c t e d p l a t e edge. Anahim hot s p o t t r a c e i n d i c a t e d by dashed l i n e s . PP = P a c i f i c p l a t e , EP = E x p l o r e r p l a t e , JdFP - Juan de Fuca p l a t e , NAP = N o r t h A m e r i c a p l a t e , Bp = Brooks P e n i n s u l a , PRfz = Paul Revere f r a c t u r e zone, S f z = Sovance f r a c t u r e zone. D o t t e d l i n e ( N f z = Nootka f a u l t zone) i s EP-JdFP boundary.  69  in  p o s t Lower Miocene t i m e .  the  Sandspit  discussion  and  Such movement may  Rennel-Louscoone x).  i n chapter  faults  Further  have o c c u r r e d  (Chase  analyses  of  al,  et  Masset  r e q u i r e d however t o d e t e r m i n e i f t h e y are s i m i l a r  ally  and  to  the  alkalic  Souther (1977) s u g g e s t s t h a t the  lavas  of  1975,  see  volcanics  still  isotopically  along  the  are  compositionAnahim  belt.  b a s a l t - r h y o l i t e a s s o c i a t i o n may  t h o l e i i t i c rather than a l k a l i n e t o t r a n s i t i o n a l  be  in trend.  A second model r e l a t e s the o r i g i n of the Masset l a v a s t o an  extension  and  rifting  event  i n Queen C h a r l o t t e  t h a t f o l l o w e d passage of the Anahim hot dislocation  of  the  Queen  1981).  A l t h o u g h the  sional  origin,  "crustal and  Chase, 1981)  faults  have  central  British  Graham  Island.  (Stacey, the  occurrence  Islands  for  Columbia, nor  Souther, of  1977)  northeast  normal f a u l t s "  and  rift  along  the  postulated which may  rocks,  suggests  extentrending  basins  (Yorath  S i m i l a r trending Anahim  are t h e y p r e s e r v e d  and  13)  Chase,  an  of  model  Masset  and  development  recognized  Another  (Yorath  Masset a s s o c i a t i o n s u p p o r t s  listric  been  (Fig.  spot but preceeded northward  i s i n s u f f i c i e n t at p r e s e n t .  not  1974,  bimodal  evidence  penetrative  Charlotte  Sound  for be  belt  major  trend  in  i n Masset r o c k s the  Anahim  invoked  volcanic  to  belt  explain  activity  r e l a t e d t o an "edge e f f e c t " of a subducted ocean p l a t e .  The  on  rise  is of  magmas from deep mantle f r a c t u r e s at the edge of the subducted p l a t e might r e s u l t t h r o u g h f l e x u r e of the downgoing lation  slab,  or  of m e l t .  parallel  trend  mantle  perturbations  Evidence against of  Masset  p l a t e margin which may  not  l i t h o s p h e r e , i m b r i c a t i o n of  eruption  causing  t h i s model centers,  anomalous  i s the and  accumu-  apparent  proximity  a l l o w s u f f i c i e n t descent of the  the  to  coast the  subducted  70  F i g . 13  S k e t c h map showing proposed Neogene d i s p l a c e m e n t o f t h e Queen Charlotte Islands. P r e - d r i f t and d r i f t p o s i t i o n o f w e s t e r n Queen C h a r l o t t e I s l a n d s , Anahim hot s p o t t r a c e , r i f t b a s i n s and t h e i r bounding f a u l t s a r e shown. From Y o r a t h & Chase (1981  71  p l a t e t o p e r m i t magma g e n e r a t i o n . A would  fourth  r e l a t e Masset  oceanic  plate  model,  of  considered  motions.  The  Sandspit  and  as deep c r u s t a l  previous  fluids.  Probable  Masset  workers,  changes i n  Rennel-Louscoone  wrench  shears i n pre-Cenozoic  have s e r v e d as c o n d u i t s f o r p a r t i a l  Masset  by  e r u p t i o n s t o major wrench f a u l t s and  f a u l t s , which developed might  not  m e l t i n g and  time  mobilization  eruption centers  are  located  c l o s e t o major f a u l t t r e n d s ( S u t h e r l a n d Brown, 1966).  A  divergent  wrench  fault  X).  Major  component  appears  to  have  development d u r i n g much o f T e r t i a r y changes  in  'Pacific'  plate  motion  Upper O l i g o c e n e ( c a . 26-30 Ha) resulted  be  expected  tensional  to  stress.  at  Given  Chapter  II) that  reduced  occurred  convergence  I n c r e a s e d magmatic  these an  (see  and M i d d l e Eocene ( c a . 40-45 Ma)  p l a t e margin. occur  time  (Chapter  i n p l a t e r e a d j u s t m e n t s and  the North America  characterized  significant  times  as  approximate  a  time  in time  rates  along  activity  might  result  of  increased  l a g of  5 Ma  between  changes i n p l a t e motion and s u r f a c e m a n i f e s t a t i o n on Queen C h a r l o t t e Islands  (Snyder  e t _al_,  c l o s e t i m e correspondence events. the  More  1976)  peaks  of  t o t h e M i d d l e Eocene and  accurate plate  northeastern P a c i f i c  apparent  and  reconstructions additional  magmatism Upper  f o r the  show  a  Oligocene  Paleogene  r a d i o m e t r i c dates  of  f o r the  Masset F o r m a t i o n are r e q u i r e d t o t e s t t h i s model. Each  of  the  e v i d e n c e but r e q u i r e s its  validity.  above  additional  the  fourth  model  suggests  documents  d a t a and  A l t h o u g h t h e n a t u r e and  of the ? e p i s o d i c T e r t i a r y Masset only  models  further  some  analysis  to  test  possible association  of  each  e r u p t i o n s has y e t t o be a  supportive  possible  mechanism  determined, to  support  72 long-lived, models  plate-edge  might  only  volcanic  activity.  used  to  explain  coeval,  the  be  The the  hot  spot  final  or  Lower  rift  Miocene  volcanic episode.  Post-Tectonic  Intrusions Although  contrasts  with  post-tectonic in  melting  the  shallow  plutons  and  and  related  here (see  a l s o Chapter X)  r i d g e may  be r e s p o n s i b l e  Cenozoic  plutons  (anatexis) ridge.  of the  Karig  the  (1977)  volcanics  and  instrusives  plutons.  Borderland)  southward m i g r a t i o n  to  of the  of a  The the  trending  n o r t h e r n edge of the et  a l , 1979).  epizonal  plutons  Farallon-Pacific  The  differences described  Kula-Farallon  plutonism.  related to  with  high  partial  proximity  paleotrench,  Alert  melting  Kula-Farallon  of  Ridge has  and  Bay  Miocene area  been  volcanic  related to partial  ridge  at  the  with  a  of  along the  belt  The on  melting  stationary  continental  the  the  silicic  explained  Snyder, 1979).  Upper M i o c e n e - P l i o c e n e age  along  (California  continorigin  along  position the  the  (Bevier  volcanics  margin d u r i n g  by  northern  subducted Juan de Fuca ( F a r a l l o n ) p l a t e  i s consistent  level  i s o t o p i c ages f o r  FaralIon-Pacific ridge  appears t o be  Tertiary  model,  migrating  arc  Patton  e n t a l margin (Crouch, 1.981; D i c k i n s o n northeast  of  fundamental One  volcanics  ridge-trench-triple junction  A l e u t i a n Trench i s c o n s i s t e n t  Vancouver I s l a n d  magmas  have  Aleutian  of the  trench  the  Masset  s u b d u c t i o n complex by passage of the  near  of  of  processes.  eastern  anomalous  Continental  of  f o r anomalous near t r e n c h  Eastward m i g r a t i o n  the e a s t e r n  origin  s u g g e s t s t h a t the  and  of  crustal  suggests p o s s i b l e  tectonic  Marshak  mantle o r i g i n  of  and the  period  73  (.ANGARA PLUTON  ^  KILOMETRES  Fig.  14  S k e t c h map showing p o s s i b l e r e l a t i o n s h i p between m i d T e r t i a r y ' n e a r t r e n c h ' p l u t o n i s m and northward m i g r a t i o n o f the K u l a - F a r a l l o n r i d g e .  74  5-10  Ma  ago  ( R i d d i h o u g h , 1977). By  analogy w i t h  the  above examples, the  origin  near t r e n c h  Upper 01 igocene-Upper Miocene p o s t - t e c t o n i c  be  to  related  passage  plate  reconstructions  Stone  (1977) t h i s  Islands  age  23 Ma  ago  (Fig.  14),  slightly the  would  was  Alternatively, may  be  ridge  the  may  (see  occurred  discussion,  the  oriented age  roughly  transform in  the  Louscoone f a u l t may  II).  Charlotte  The  The  Islands, a  rate  i n t e r p r e t a t i o n assumes  that  be  north  to  the  at  paleotrench.  partly coincidental along  the  junction  origin  of  and  Kula-Farallon position  smaller  more r e a d i l y be  Chapter X ) , s i m i l a r t o the  p r e v i o u s l y f o r the Masset F o r m a t i o n .  and  Queen  migrated  triple  plutons  (see  (1978),  to  faults  r i d g e proceeded.  wrenching  to  Langara i n t r u s i o n s f r o m 39  may  the  divergent  According  of the Queen C h a r l o t t e  s u b d u c t i o n of along  may  of  perpendicular  shifts  plutons  Coney the  some  trend  This  progression  cause  at  Chapter  ridge  1 cm/year.  ridge.  al_ (1976),  the west c o a s t  than  would  et  have  indicate that  the  Kula-Farallon  Cooper  consequence of  which  the  P o c k e t , Kano and  along  greater  ridge  ago  of the  north  of  event  30-40 Ma  decreasing  of  of  epizonal  explained  model  as  by  described  75  CHAPTER IV  GEOLOGY OF THE  QUEEN CHARLOTTE BASIN  GENERAL SETTING The in  Queen C h a r l o t t e B a s i n  a northwest-southeast  direction  i s a p p r o x i m a t e l y 400  and  100  km  wide,  with  km  long  a  total  2 surface  area  of  eastern  Dixon  Entrance,  Queen  approximately  53,000  km  .  The  basin  n o r t h e a s t e r n Graham I s l a n d ,  C h a r l o t t e Sound  and  possibly  Queen  b a s i n o c c u p i e s the Hecate D e p r e s s i o n  underlies  Hecate  Charlotte S t r a i t .  ( H o l l a n d , 1964),  and an  i t s l e n g t h by  Queen C h a r l o t t e I s l a n d s . extensive  coastal  trough  The  I n s u l a r Mountains  that  extends  southwards  North  America  Neogene Queen C h a r l o t t e B a s i n i s one  (Fig.  15).  from  These  b a s i n s t h a t l i e along the  southwestern basins  "Pacific"  have  interation  of  convergent  t o t r a n s f o r m margin.  Vancouver  through  Alaska developed  p l a t e s and  to  of a s e r i e s  Pacific  the  Gulf  a  result  as  the North America  The  1976).  of  Chapter  Mesozoic-Cenozoic  Coast  Mountain  of  California  of  continued  plate  along  a  Queen C h a r l o t t e B a s i n , though  I) i s a r e s i d u a l  b a s i n ( D i c k i n s o n and S e e l y , 1979)  of  margin  i n a p a r t a s u c c e s s o r f e a t u r e of p r e - e x i s t i n g sedimentary b e l t s previous discussion,  the  W i l l a m e t t e Lowlands o f Washington  and Oregon t o t h e Great V a l l e y of C a l i f o r n i a ( N e l s o n ,  Late Mesozoic-Cenozoic  of  and t o  d e p r e s s i o n i n t u r n forms p a r t of  G e o r g i a D e p r e s s i o n , the Puget and  The  The  a topographic  and s t r u c t u r a l low bounded t o the e a s t by the Coast Mountains the west f o r much of  Strait,  o r composite  forearc  o c c u p y i n g the gap between the volcanic-plutonic  arc  (see  and  late an  76  LATE  MESOZOIC — CENOZOIC WESTERN  Major  sedimentary  Calc - alkaline Geosynclinal  NORTH AMERICA  basins  plutonic  rocks  structural  trends  Tertiary — Quaternary  volcanic  Spreading  ^  center  BASINS  cover  Subduction  zone  / Transform  fault  F i g . 15 G e o l o g i c s k e t c h map o f w e s t e r n N o r t h A m e r i c a showing d i s t r i b u t i o n o f major Late Mesozoic-Cenozoic b a s i n s . Present p l a t e b o u n d a r i e s a r e i n d i c a t e d . M o d i f i e d , i n p a r t , from Orwig (1976) and B l a k e e t a i (1978).  77 ancestral  trench  l o c a t e d < west  of  Vancouver  and  Queen  Islands.  Of t h e b a s i n s shown i n F i g . 15 the G e o r g i a  the  Inlet  Cook  Sacramento  Basin  Charlotte basinal  and  Basin  Bristol  Bay  (California) with  are  respect  c o n f i g u r a t i o n and  basins  to  structural  (Alaska)  most general  (B.C.), Joaquin-  the  and  and  t e c t o n i c framework t o placement of p o s i t i v e source  San to  size  alignment  Basin  and  similar  Charlotte  orientation,  relationship  Queen C h a r l o t t e Sound, c h a r a c t e r i z e d by major banks and  (Fig.  16)  Holocene prep).  i s largely infilling  In  of g l a c i a l  and  (Luternauer,  general  there  glaciomarine o r i g i n  1972;  is little  Luternauer  correlation  of  areas.  The morphology of the c o n t i n e n t a l s h e l f of Hecate and  Queen  and  Strait  channels  w i t h minor Murray,  between  topography and basement s t r u c t u r e mapped on t h e b a s i s of  in  submarine geophysical  data.  STRATIGRAPHY Knowledge of t h e s t r a t i g r a p h y of the M i o - P l i o c e n e of the Queen C h a r l o t t e B a s i n has  been o b t a i n e d  Skonun  succession  l a r g e l y from e x p l o r -  a t o r y w e l l s d r i l l e d on n o r t h e a s t e r n Graham I s l a n d by R i c h f i e l d e t a l and  i n Hecate S t r a i t  Scattered Island.  outcrops The  118-127) and structural  well  three  of  Queen C h a r l o t t e Sound by S h e l l Skonun  data,  Shouldice  rock  described (1973),  occur by  on  S u t h e r l a n d Brown  i s summarized  d e p o s i t i o n a l environments.  additional  wells  I s l a n d i s shown i n F i g . 16.  drilled  Canada L t d .  north-eastern  here  the  pp. as  a  correlations,  L o c a t i o n of t h e s e  outside  Graham  (1968,  ( F i g . 17)  c r o s s - s e c t i o n showing ages of r o c k s , b a s i c  l i t h o f a c i e s and and  and  basin  on  wells Graham  78  F i g . 16  Well l o c a t i o n s on Queen C h a r l o t t e I s l a n d s and i n Queen C h a r l o t t e B a s i n and morphology o f c o n t i n e n t a l s h e l f . Bathym e t r i c contours i n meters.  GRAHAM  ISLAND—*H  HECATE  STRAIT  —QUEEN CHARLOTTE  TOW HILL MAS.  S.L.  GOLD CR C. BALL NADU TLELL COHO  SOCK. SOCK.  TYEE  MUR.  AUK.  HARL.  VVV I  2-  1  VVV  OSP.  ~--m  TT*  m  SOUND  L.P.I  V V V  *  S.L.  hi  VVV  Pi-*  h2 U. Mi AAA  S / L . Mi  AAA  •net 7i  3-  I I65t8' I  228*28 (Ay. of 5) \  4-  / UK -}72±6 84tlO  Km  J  h3  ffW142t2  Mio-Pliocene  Skonun  Km  L  sediments  Non - marine s a n d - sandstone  Marine  +++<•, f+++ Plio.-Pleistocene  Tow Hill Sills*  I H I i I H  basalt, diabase  W W W W  Lower -Middle Tertiary Masset volcanicsi basalt, rhyolite, breccia  sand - sandstone Non*- marine siltstone r- shale  Marine siltstone - shale  I  Coal , lignite  Conglomerate  W W W W  IA A A A JA A A A (A A A A IA A A A i  Upper Cretaceous Queen Charlotte Group* sandstone, siltstone, shale  Microflora, Microfauna  Unconformity  Cretaceous volcanics« basalt, pyroclastics Upper Paleozoic diorite, gabbro  2914  K-Ar  age  intrusivess  (Ma±16)  F i g . 17 S t r u c t u r a l c r o s s s e c t i o n o f Queen C h a r l o t t e B a s i n . Well l o c a t i o n s a r e shown i n Fig.16 Sutherland Brown (1968, F i g . 20) and S h o u l d i c e (1973, F i g s . 8, 9, 1 1 ) .  HO  Modified  from  80  On penetrated  northeastern  a comparatively  Graham  Island  t h i n (up t o  six  1.83  exploratory  km)  succession  M i d d l e M i o c e n e - P l i o c e n e Skonun sandstone, s i l t s t o n e , minor  lignite,  c o a l , marl  and  claystone  Conglomerate i s dominant near the rare  i n a l l other  wells.  and  (Sutherland  base of  the  Tow  of e a r l y  shale,  Brown,  Hill  A l l w e l l s e x c e p t f o r Tow  wells  1968).  well  Hill  with  but  and  is  Tlell  reached base of the Skonun F o r m a t i o n , bottoming i n b a s a l t i c b r e c c i a , r h y o l i t e , or b a s a l t of the Masset Formation ( T a r t u A vicinity  of  portion  of  (Sutherland  basement  volcanic  the  Masset w e l l  the  Queen  ridge  extending  eastward  appears t o s u b d i v i d e  Charlotte  Brown, 1968).  facies).  The  Basin  into  f a c i e s and  the  two  from  Graham  small  the  Island  sub-basins  t e c t o n i c s on  either  side  of the r i d g e d i f f e r though s t r a t i g r a p h i c u n i t s i n the s o u t h e r n w e l l s appear  to  southern toward  thin  and  sub-basin Hecate  (25-30°)  and  fault  regime.  on  of  Sandspit  In  and  The  Graham  the  thicken the  fold  north  eastward,  northern  structures  and  eastern  dipping  indicate  northeastern  In  steeper a  Moresby  the  10-15°  more  Island  NE dips  active  Queen C h a r l o t t e  environment of d e p o s i t i o n of  Graham  Island  Addicott,  1978;  (Martin  and  Champigny  and  Rouse,  Skonun r o c k s 1966;  Sinclair,  between marine ( s h a l l o w w a t e r , near shore) and deltaic, finger  east.  sub-basin  w e s t e r n boundary o f the  Island  and  Basin is  the  Fault. The  1968;  toward  sediments  Strait.  tectonic much  overlap  to  deposition  swamp,  lagoon,  some degree is  as  represented  lacustrine). a by  r e s u l t of the  The  north-  Sutherland  Brown,  i n press) non-marine  facies  pulsating  upper  on  marine  alternated (fluvial-  probably onlap.  member  The  interlast  comprising  81  mollusc-bearing Skonun  calcareous  Point  Addicott, volcanic  (Martin  1978). and  metamorphic  and  Much  was  sandstones, Rouse,  of  derived  and  some  the from  best  1966;  exposed  Sutherland  detritus for the  intrusive  proto clastic  small  offshore  sub-basins  sub-basins separated here  by  18)  but  extending  Charlotte gravity VII).  at  Islands)  and  has  Sedimentary  ridge.  In the  penetrated  least  magnetic  55  been  highs  km  recognized (Shouldice,  northern (up  sequence  (500  m)  non-marine e l a s t i c s ,  divided  of on  the  1973;  differ  Stacey, on  either  succession  bottoming  i n Middle  c o n t i n e n t a l l y derived  additional Charlotte  sediment Islands  sediments was  may  and  well  have  wells  been  Pliocene  succession  of  a  predominately  derived  sands,  Paleogene Masset v o l c a n i c s  silts,  ( F i g . 17,  and  Table  chapter  side  of  the wells  coal, a  Charlotte  The  Group)  volcanics  major s o u r c e  from  though  the  Queen  w i t h i n the  basin.  Lower  shales, IV).  (Queen  1975;  t h r e e out of f o u r marine  The  coincident  Coast Mountains  p o s i t i v e basement f e a t u r e s  penetrated  of  J u r a s s i c Yakoun  In the s o u t h e r n ( o r " C h a r l o t t e " ) s u b - b a s i n atory  basin.  s h a l e s and  (Queen  the  (termed  Upper Miocene-Lower  sands, s i l t s ,  Cretaceous  major  exploratory  or Upper P a l e o z o i c i n t r u s i v e s ( F i g . 17, T a b l e I V ) . for  two  Island  basis  of  Upper  the  Burnaby  to  of  have  a number of  into  of  four  3 km)  is  Islands;  must  contains  ("Hecate") s u b - b a s i n  P l i o c e n e non-marine t o t r a n s i t i o n a l thin  be  east  1968;  Alaska.  central portion  facies generally  a thick  Charlotte  an e a s t - w e s t t r e n d i n g basement r i d g e  "Moresby Ridge") near the  ridge,  can  at  sediments  constituents  Queen C h a r l o t t e B a s i n  (Fig.  outcrop  Brown,  Skonun  Queen  o r i g i n a t e d from the Coast Mountains and S.E. The  as  The  explor-  Miocene-Upper bottoming  in  volcanics  are  82  133°  F i g . 18  132°  131°  130°  129°  J28°  127°  S i m p l i f i e d i s o p a c h map o f Neogene Queen C h a r l o t t e B a s i n showing l o c a t i o n o f m a j o r b a s i n e l e m e n t s . C o n t o u r s i n f e e t . M o d i f i e d from S h o u l d i c e (1973, F i g . 3 2 ) .  83  subaerial  and  indicating  an  are  alteration  transgressions volcanics indicated  interbedded of  (Shouldice,  is  diachronous  with  volcanic  episodes  1973).  The  upper  and  the  (Fig.  neritic,  meters).  17)  at i n d i v i d u a l w e l l s i s t h e r e f o r e  marine sediments were d e p o s i t e d (inner  Paleogene  0-50  There was  marine  with  shallow  surface  to  deep  a minor r e g r e s s i o n  marine of  sedimentary  slightly  (upper  near the  the  history  different.  i n water depths r a n g i n g  meters)  sediments  from  bathyal, end  The  shallow 200-1000  of the  Miocene  i n the a r e a of the M u r r e l e t w e l l where marine Upper Miocene e l a s t i c s are  overlain  shales  by  non-marine  (Shouldice,  sub-basin  wells  climate  in  cooling  into  1973).  Early  the  Miocene  and  Pliocene  1975;  or  1976)  Middle  Pleistocene.  suggests  Miocene,  The  a  followed  E a r l y Miocene  Unconsolidated  to consolidated  the dominant l i t h o l o g i e s  litharkoses Reports,  by  a  general  i s considered Miocene.  i n a l l Queen C h a r l o t t e B a s i n w e l l s and  are  and  sands and  mechanically 1968,  Based on  Shell  immature a r k o s e s Canada  a petrographic  Well  study  a c t i v e development  volcanic-plutonic from  unroofing  arc:sediment  of  the  e x t r u s i v e or s h a l l o w convergence  and  subsequent b u r i a l  arc of  debris  plutons  intrusive  of f o u r  the  adjacent  appears t o  rather  than  Coast  have  from  Rapid  must  been  derived  contemporaneous  sedimentation  predominately terrigenous  of  Mountains  igneous masses a s s o c i a t e d w i t h  development. the  of  and  History  the o f f s h o r e w e l l s G a l l o w a y (1974) s u g g e s t s t h a t b a s i n f i l l i n g have p o s t d a t e d  to  are  Brown,  G a l l o w a y , 1974).  temperate  sandstones  chemically  (Sutherland  and  Charlotte  warm  have been somewhat c o o l e r and more damp than the M i d d l e  characteristically  sands  P a l y n o l o g i c a l s t u d y of the f o u r  (Hopkins,  late  Upper  active  rates  clastic  and  sediment  84  has  resulted i n a systematic, recurrent series of diagenetic  (Galloway,  1974; 1979).  events  Geothermal g r a d i e n t s i n t h e Queen C h a r l o t t e  B a s i n , as h i g h as 3.4°C/100 meters i n t u r n have r e s u l t e d i n c o m p a r i tively  shallow  metamophism  depths o f p o r o s i t y l o s s from c e m e n t a t i o n  (op.cit.).  Some o f t h e d i a g e n e t i c  been a l t e r e d by t e c t o n i c d e f o r m a t i o n extensive basin f i l l  Graham  Island  unconformities and  Quaternary  likely  which f o l l o w e d t h e  been mapped  overlie  Skonun  Queen  on  north-  Charlotte  Basin  1973):  (Pleistocene-Recent)  disconformably  have  i n the offshore  ( S u t h e r l a n d Brown, 1968; S h o u l d i c e , 1)  has  and s u b s i d e n c e .  Three major eastern  and u p l i f t  fabric  and b u r i a l  sediments sediments  unconformably (Late  to  Pliocene-Early  Pleistocene surface); 2)  r e g i o n a l s e i s m i c e v i d e n c e ( S h o u l d i c e , 1973) suggests a h i a t u s o f E a r l y P l i o c e n e age i n t h e Skonun s u c c e s s i o n ;  3)  Skonun  rocks  unconformably  overlie  Masset  volcanics  and  all  o l d e r r o c k s (pre L a t e Miocene s u r f a c e ) . This  latter  surface  geomorphological  may  be r e g i o n a l  evidence  from  widespread  unconformity  of  1978).  On  northeastern  Graham  margin,  resulting  from  post  i n extent  t h e Western  post  Middle Island,  Miocene s u r f a c e s may be r e l a t e d i n p a r t r e g i o n a l changes i n s e a l e v e l dated 1977).  Cordillera Miocene  emergence  depositional  exposed Late Miocene marine s e d i m e n t s .  as g e o l o g i c a l and  uplift  age  indicate  a  (Drummond,  of the basinal and f o l d i n g ,  has  The E a r l y P l i o c e n e and Late t o g l o b a l o r major  inter-  a t 11 and 4 Ma B.P. ( V a i l e t a l ,  85  AGE AND  Attempts rocks  of  the  Comparisons North  themselves 1975;  are  Reports).  Queen  are  Charlotte and  of  Oil  and  disagreement  been  successful.  sequences  these  on  are based  latter  Rouse,  in  on  assemblages  1966;  microflora  (Shell  Canada  or micro-  Well  cited  ( M a r t i n and  o r perhaps e a r l y  Montesano  Island  by S h o u l d i c e  have  been  (Addicott, of  studied  Rouse, 1966), m i c r o f a u n a  Addicott,  Formation  therefore  (op.cit.).  1968,  1978)  suggest  1978)  an  in  some  macrofauna  Upper  Micocene  The m o l l u s c a n f a u n a  w i t h f a u n a o f the  western  marine  (Richfield  p.126) and  P l i o c e n e age f o r t h e s e r o c k s .  have been c o r r e l a t e d  History  1 i t h o l o g i e s or mechanical log  i n S u t h e r l a n d Brown,  Brown, 1968;  suggested  are  Hopkins,  from o u t c r o p of the uppermost  n o r t h e a s t e r n Graham  Microflora  western  sequences  either  on c o r r e l a t i o n s  C o r r e l a t i o n s based on e i t h e r  Corp.,  the  not  Neogene  (Martin  f o r Mio-Pliocene  B i o s t r a t i g r a p h i c z o n a t i o n s i n d i c a t e d i n F i g . 17  (Sutherland  of  ages  have  since  ages based  commonly • i n  Fossil  detail.  with  use  c h a r a c t e r i s t i c s was not p o s s i b l e  member  precise  Basin  fauna  little  Suggested  •are t e n t a t i v e and (1973).  determine  i n a d e q u a t e l y dated  1976).  fauna  to  of f l o r a  America  CORRELATION OF SKONUN FORMATION  Washington  lower  (the  part  Wishkahan  s t a g e of the P a c i f i c Northwest m o l l u s c a n sequence).  STRUCTURE  The asymmetric  Queen  trough  or  Charlotte  Basin  megasyncline  ( F i g . 18) that  is  broadens  an and  elongate, plunges  86  r e g i o n a l l y t o the southeast. ment o f t h e b a s i n has been  Much o f t h e e a r l y related  structural  t o subsidence  initiated  u p l i f t o f t h e Coast Ranges i n l a t e Cretaceous-mid c o n t i n u e d d u r i n g sediment of  uplift,  T e r t i a r y t i m e and  l o a d i n g i n Neogene t i m e .  pulse  occurred  a p p r o x i m a t e l y 10 Ma ago ( H a r r i s o n e t aj_, 1979).  According  to Bell  ( 1 9 6 7 ) , t h e Queen C h a r l o t t e B a s i n p r o b a b l y o r i g i n a t e d  zones  maximum  along  initial  the eastern  t r a n s g r e s s i v e onlap  episodes  of  stratigraphy  and  displacement  margin  eventual  uplift  relief  The f i n a l  Mountains  graben:  the present  during  o f t h e Coast  half  producing  develop-  with  onto  less  severe  t h e western  erosion,  w i t h v a r y i n g degrees  occurred  affecting  along  fault  breakdown  margin.  local  of i n t e n s i t y  as a  and  Several  structure  and  characterized  later  basin h i s t o r y . A  simplified  reflection,  refraction  illustrates  the  Charlotte Basin. previously modelling  gross  isopach and  structural  are shown. isostatic  anomaly  km  of  sediment.  configuration,  basins  northeast-southwest map  shown  p o s i t i o n o r form  of  1973),  the  Queen  i s o p a c h maps p r e p a r e d  data,  reproduced  from  from Stacey  covered  f l a n k e d by s u b b a s i n s t h a t c o n t a i n up varying  ridges  and e a s t - w e s t  i n F i g . 19  seismic  (Shouldice  basement r i d g e s o r u p l i f t s  Though and  on  and Moresby R i d g e , d e s c r i b e d  F o r comparison,  gravity  data  configuration  The major s u b - b a s i n s  w i t h l e s s than 1 km o f sediment 5  ( F i g . 18) based  aeromagnetic  (1975) ( F i g . 1 9 ) , show p o s i t i v e  to  map  are  considerably generally  directions.  ( b ) , though  in  elongate  The d e t a i l e d  not n e c e s s a r i l y  overall in  isopach  showing  true  o f a l l s u b b a s i n s and r i d g e s , p r o b a b l y r e f l e c t s t h e  t r u e c o m p l e x i t y o f basement s t r u c t u r e .  87  ISOSTATIC  SEDIMENTARY BASIN (b)  ANOMALIES  (a)  I  MODEL  50 km i  Fig. 19(a) Airy-Heiskanen isostafic gravity anomalies for the Queen Charlotte Basin region at 10 mgal contour interval and (b) computed and (c) filtered sedimentary basin models' derived from gravity data at 0.5 km contour interval. Model assumes a density contrast between Neogene sediments and 'basement' of -0.31 gmcm . Reproduced from Stacey (1975, Figs. 4 and 5).  88  The g r o s s (Fig.  18; F i g . 19  sediment and  thickness  predominantly  these  ( c ) ) suggest  of  volcanics:  gravity  anomalies  or a single density  contrast  between  v o l c a n i c basement  Mesozoic negative  and  rocks.  Major  Early  reflect sediments  discrepancies i n  (1975) t o v a r i a t i o n s i n  Cenozoic  rocks  underlying  the  r e s i d u a l s i n Queen C h a r l o t t e Sound may be due  pre-Masset g r a n i t i c  while  i s o p a c h maps  that  maps have been a t t r i b u t e d by S t a c e y  density  to  s i m i l a r i t y between t h e s i m p l i f i e d  or sedimentary rocks  positive residuals  i n Hecate  (Queen C h a r l o t t e  Strait  may  be  Group)  due t o dense  v o l c a n i c (Karmutsen) r o c k s . Like g r a v i t y data, t o t a l Queen C h a r l o t t e B a s i n Charlotte  Sound  variations  ( F i g . 20) and magnetic anomaly d a t a f o r Queen  (Tiffin  and C u r r i e  i n thickness  rock.  High-amplitude,  margin  of the basin  i n t e n s i t y aeromagnetics f o r t h e  1976) can y i e l d  o f T e r t i a r y sediments short  reflect  wave-length basement  overlying  anomalies  rocks  information  on  basement  on t h e e a s t e r n  o f t h e Coast  Plutonic  Complex. P u b l i s h e d deep s e i s m i c r e f l e c t i o n p r o f i l e s 53,  (Figs.  50 and  Chapter V I I I ) show g e n t l e f o l d s i n b a s i n a l Skonun sediments and  onlap  onto  relief.  a basement  Though  basement  not shown  topography  Considering  (volcanic?) surface  may  i n t h e above represent  t h e importance o f major  of v a r i a b l e profiles,  faults  topographic  steep  dips  (Shouldice,  structural  on  1973).  d i s l o c a t i o n s i n the  t e c t o n i c h i s t o r y o f t h e western C o r d i l l e r a ( s e e F i g . 22 f o r l o c a t i o n of major f a u l t s )  one would Queen  expect  Charlotte  significant Basin.  deformation  occurred  i n the  Fault-block  producing  h o r s t and graben s t r u c t u r e s i n basement r o c k s  t o have tectonics  and Neogene  89  F i g . 20  S i m p l i f i e d t o t a l i n t e n s i t y a e r o m a g n e t i c map o f t h e Queen Charlotte Basin. I.G.R.F. v a l u e s a r e a p p r o x i m a t e from a r b i t r a r y r e f e r e n c e l e v e l v a l u e s . Redrawn from S h o u l d i c e (1973, F i g . 3 ) .  90  F i g . 21  Combined Bouguer (on l a n d ) and f r e e - a i r ( a t sea) g r a v i t y anomaly map o f t h e Queen C h a r l o t t e B a s i n r e g i o n a t 10 mgal contour i n t e r v a l . From E a r t h P h y s i c s Branch ( 1 9 8 0 ) .  91  cover  i s suggested  gravity  anomaly  data  Northwest-southeast gravity Queen  Charlotte  Strait  1969;  east-west  The  free  Stacey  a i r and  and  lineaments,  anomaly maps  Basin.  anomalies  Sandspit  (Couch,  and  and magnetic  gravity  basin  i n i n t e r p r e t a t i o n s of  Bouguer  Stephens,1969).  apparent  in  both  ( F i g . 20 and 21) s u b d i v i d e  linear  trend  and  steep  ( F i g . 21) marks t h e approximate  F a u l t and a p o s s i b l e s o u t h e a s t e r n  the  gradient  of  p o s i t i o n of the  extension  of the Clarence  F a u l t on t h e w e s t e r n and e a s t e r n margins r e s p e c t i v e l y o f t h e (Stacey  magnetic  and Stephens, 1969).  highs  Elongate c o i n c i d e n t  g r a v i t y and  mark t h e p o s i t i o n o f basement r i d g e s .  One o f t h e s e  r i d g e s e x t e n d s d i s c o n t i n u o u s l y between t h e s o u t h e r n Queen Islands  and n o r t h e r n  Vancouver  Island  (Shouldic,  Charlotte  1973; S t a c e y and  Stephens, 1969). Earthquake  epicenters  in  ( M i l n e e t j H , 1978) a r e c o n c e n t r a t e d Sound r e g i o n to  ( F i g . 22).  likely  or local  due t o secondary  Queen  though  normally  isostatic  e f f e c t s of seismic  Queen C h a r l o t t e F a u l t and t h e r i d g e and t r a n s f o r m of Queen C h a r l o t t e Sound.  p r i o r t o 1965 ( M i l n e et. j i l _ ,  Seismic northern al,  Stephens, crustal  refraction  Graham I s l a n d (Shor,  1974)  and  gravity  Basin  interpreted  readjustments, activity fault  are  on t h e  system west  The s c a t t e r i n s e i s m i c i t y may be due i n  p a r t t o l a r g e ( i n t h e o r d e r o f 100 km) s y s t e m a t i c events recorded  Charlotte  i n t h e western Queen C h a r l o t t e  These e v e n t s ,  be t h e r e s u l t o f f a u l t i n g  more  the  results  1978).  from  Dixon  1962; Johnson e t aU  anomaly  data  1969) i n d i c a t e s a c r u s t a l  location errors i n  (Couch,  thickness  Entrance  and  1972; F o r s y t h e t 1969;  Stacey  o f 25-30 km  v e l o c i t y o f 6.4 km/sec) f o r t h e Queen C h a r l o t t e  and  (average  I s l a n d s and  92  Fig.  22  D i s t r i b u t i o n o f e a r t h q u a k e e p i c e n t e r s o f magnitude 2.0 o r g r e a t e r i n v i c i n i t y o f Queen C h a r l o t t e I s l a n d s . The c i r c l e d i a m e t e r s a r e p r o p o r t i o n a l t o e a r t h q u a k e magnitude. Earthquakes o f magnitude l e s s t h a n 3.0 a r e marked by 'X'. QCF = Queen C h a r l o t t e f a u l t , RLF = Rennel-Louscoone fault, SF - S a n d s p i t f a u l t , CSF = C l a r e n c e S t r a i t f a u l t , MF = M a l i s p i n a f a u l t . Double l i n e s a r e a c t i v e r i d g e s . Redrawn from M i l n e e t a l _ (1978, F i g s . 14 and 1 5 ) .  93  Queen  Charlotte  Basin.  Gravity  C h a r l o t t e B a s i n i s compensated Heat generally area  and  tectonic  low Coast  flow  values  f o r the  the  suggests.„ t h a t  the  Queen  isostatically.  measurements  Plutonic  h i s t o r y of  data  (eg.  Insular  Hyndman,  1981)  B e l t compared t o  Complex.  Because of  region,  resulting in  the  long  the  oceanic  and  complex  imprinting  t h e r m a l e v e n t s , paleogeotherms cannot be d e t e r m i n e d .  indicate  of  major  94 CHAPTER V  MAGNETIC PROPERTIES OF QUEEN CHARLOTTE ISLANDS VOLCANIC AND PLUTONIC ROCKS  INTRODUCTION As magnetic  an  aid  to  anomaly maps of  interpretation the  Queen  of  Charlotte  airborne  and  marine  Islands  and  Hecate  S t r a i t , the magnetic properties of Queen Charlotte Island volcanic and p l u t o n i c rocks  have been i n v e s t i g a t e d .  Aeromagnetic maps  (see  following  i n d i c a t e that volcanic and p l u t o n i c rocks  have  chapter)  associated magnetic  anomalies  of  s i g n i f i c a n t l y d i f f e r e n t amplitude  and pattern which could r e f l e c t changes i n magnetic volume ibility  and remnant magnetization.  A study  by  Coles  suscept-  and  Currie  (1977) of magnetic properties of Vancouver Island and Coast Plutonic Complex rocks demonstrates  the a p p l i c a t i o n and s u i t a b i l i t y of  rock  sample analysis when combined with aeromagnetic i n t e r p r e t a t i o n . Sampled rock types of the major volcanic and p l u t o n i c u n i t s of the Queen Charlotte Islands are as f o l l o w s : 1)  Tow H i l l s i l l s (PIio-Pleistocene)  :  2)  Masset volcanics (01igocene-Miocene):  diabase, o l i v i n e b a s a l t .  basalt and r h y o l i t e members of the Tartu f a c i e s .  3)  Yakoun volcanics (Middle Jurassic)  :  p o r p h y r i t i c andesite.  95  LANG AHA  WM  Q U E E N CHARLOTTE ISLANDS DISTRIBUTION OF VOLCANIC AND PLUTONIC ROCKS AND LOCATIONS OF MAGNETIC ROCK PROPERTY SAMPLING SITES  PALEOCENE-LOWER MIOCENE ] MASSET VOLCANICS MIDOLE JURASSIC YAKOUN VOLCANICS UPPER TRIASSIC E l l KARMUTSEN VOLCANICS  h" ••'•!:)  LOWER-MIDDLE TERTIARY W2M POST TECTONIC PLUTONS UPPER JURASSIC fcftffi SYNTECTONIC PLUTONS X HAND SPECIMEN ® CORE SITE  I  F i g . 23  L o c a t i o n o f v o l c a n i c and p l u t o n i c samples a n a l y z e d f o r magnetic p r o p e r t i e s .  96  4)  Karmutsen v o l c a n i c s (Upper T r i a s s i c ) :  basalt pillow lavas, massive b a s a l t f l o w s greenstone.  5)  P o s t - t e c t o n i c p l u t o n s (Lower-Middle :  q u a r t z monozonite ( L o u i s e and Cumshewa p l u t o n s ) ,  Tertiary)  q u a r t z d i o r i t e ( E a s t Kano and S a n d s p i t ) g r a n o d i o r i t e (Chinukundl).  6)  S y n t e c t o n i c p l u t o n s (Upper J u r a s s i c ) :  quartz d i o r i t e  and  hornblende d i o r i t e (San C h r i s t o v a l Batholith). The  generalized  distribution  of  volcanic  and  plutonic  hand  specimens  r o c k s and sample l o c a l i t i e s are shown i n F i g . 23.  MAGNETIC SUSCEPTIBILITY  Measurement The  volume magnetic s u s c e p t i b i l i t y  collected  by  the  volcanics  and  post-tectonic plutons  eastern  Moresby  author  from  the  I s l a n d s ( F i g . 23)  Tow  Hill,  on  eastern  was  determined  of B r i t i s h Columbia u s i n g a G e o p h y s i c a l S u s c e p t i b i l i t y Bridge ment of crushed  (Model Ms-3).  samples was  +2  of  The  54  Masset  and  Yakoun  Graham  and  north-  at  the U n i v e r s i t y  S p e c i a l t i e s Company Magnetic r e p r o d u c i b i l i t y of measure-  s c a l e d i v i s i o n s which  i s equivalent  97  t o from +50 t o +1 p e r c e n t w i t h  p r e c i s i o n increasing with  increasing  susceptibi1ity. The volume magnetic s u s c e p t i b i l i t y o f 214 o r i e n t e d collected  i n 1971 by D r s . A. Hicken  and E.  Irving  Branch) f r o m 31 s i t e s on t h e Queen C h a r l o t t e for  (Earth  The 1-inch d i a m e t e r c o r e s a n a l y z e d  3 - i n c h minimum l e n g t h bridge;  exceptions  correction June,  required  were  f a c t o r was  1977).  short  applied  Cores were  f o r standard 1 inch  included  Physics  normally  Branch  exceeded t h e  c a l i b r a t i o n o f t h e MS-3  long  specimens  (R.L. C o l e s ,  written  a v a i l a b l e f o r t h e Tow  f o r which  a  communication,  Hill,  Karmutsen v o l c a n i c s and p o s t and s y n t e c t o n i c p l u t o n s Also  Physics  I s l a n d s was determined  t h e a u t h o r by t h e D i v i s i o n o f Geomagnetism, E a r t h  (Ottawa).  cores  Masset, and  ( F i g . 23).  i n t h i s s t u d y are t h e r e s u l t s o f  suscept-  i b i l i t y measurements of Vancouver I s l a n d samples ( C u r r i e and M u l l e r , 1976; C o l e s which  and C u r r i e ,  (excluding  1977; C u r r i e ,  the Metchosin  northern  portion  of  chemical  similarity  the  volcanics)  Island.  Island  previously  (see Chapter  volcanic  and  limited  number  were  age, Queen  plutonic  I ) . The a d d i t i o n  measurements has made s t a t i s t i c a l a  The  of p r e - C r e t a c e o u s  Vancouver  unpublished  data),  most o f  c o l l e c t e d from t h e  and  lithological  Charlotte rocks  has  Islands  and and  been  noted  of t h e Vancouver  Island  a n a l y s i s more m e a n i n g f u l when o n l y  o f samples from  equivalent  units  on  t h e Queen  C h a r l o t t e I s l a n d s were a v a i l a b l e .  Statistical  Analysis Frequency d i s t r i b u t i o n  bilities  h i s t o g r a m s o f measured  suscepti-  (on l o g a r i t h m i c s c a l e ) a r e p r e s e n t e d i n F i g . 24 and r e l a t e d  98  35T  30  MASSET (Q.C.I.)  MASSET (Q.C.I.) AND METCHOSIN (V.I.)  METCHOSIN (V.I.)  N = 44  25  TERTIARY VOLCANICS:  EARLY TERTIARY  EARLY—MIDDLE TERTIARY  N = 71  r  35 -30  N = 115  20+  -25 L  20  15 10 -  -10  5-  -5  •  0  35-r JURASSIC VOLCANICS 30-  >-  YAKOUN (Q.C.I.) AND BONANZA (V.I.)  [TTT  0  TRIASSIC  N = 30  r35  TRIASSIC  KARMUTSEN (V.I.)  KARMUTSEN (V.I. & O.C.I.) N = 152  N = 136  -30 -25  25-  u 20-z  -20  LU  -15  3 O  -10  LU CC  rlI_n£xL: 35-j 3025-  EARLY—MIDDLE TERTIARY POST TECTONIC PLUTONS (O.C.I.)  N = 27  in-  (v.i. a Q.C.I.)  N = 37  N = 43  -20 -15  15-  10-5100  1000  10000  10  100  1000  10000  SUSCEPTIBILITY K, EMU/cm  F i g . 24  30 -25  20-  10  0  •35  JURASSIC INTRUSIONS  JURASSIC  ISLAND INTRUSIONS (V.I.)  -5  3 3  10  u  -10  -5  EEL  100  1000  10000  - 10 m-« x  Frequency d i s t r i b u t i o n histograms of magnetic s u s c e p t i b i l i t y of Queen C h a r l o t t e Islands and Vancouver Island v o l c a n i c and P l u t o n i c rocks.  TABLE VII  MAGNETIC SUSCEPTIBILITY OF QUEEN CHARLOTTE ISLANDS AND VANCOUVER ISLAND ROCKS  1  2  3  4  5  6  7  8  TOW HILL SILLS (Q.C.I.)  3.10  0.12  3.11  1296  321  1260  6  MASSET (Q.C.I.)  3.11  0.32  3.13  1686  1309  1306  44  METCHOSIN (V.I.)  3.35  0.40  3.39  3016  2030  2255  71  TERTIARY VOLCANICS (T)  3.26  0.39  3.30  1863  2166  1830  115  POST TECTONIC PLUTONS (Q.C.I.)  3.08  0.62  3.23  1977  1537  1191  27  YAKOUN (Q.C.I.)  2.95  0.84  3.08  2809  3134  895  12  BONANZA (V.I.)  2.40 0.77  2.50  724  818  249  18  JURASSIC VOLCANICS (T)  2.62  0.83  2.75  1558  2280  416  30  SYNTECTONIC  3.19  0.20  3.25  1708  764  1566  6  ISLAND INTRUSIONS (V.I.)  2.95  0.64  3.20  1675  1277  886  37  JURASSIC INTRUSIONS (T)  2.98  0.60  3.23  1680  1211  959  43  KARMUTSEN (Q.C.I.)  2.73  0.57  2.89  953  848  540  16  KARMUTSEN (V.I.)  2.91  0.71  3.17  1817  1767  816  136  KARMUTSEN (T)  2.89  0.70  3.16  1726 .1712  781  152  KARMUTSEN MODE A  3.24  0.32  3.28  2241  1650  1738  116  KARMUTSEN MODE B  1.76  0.24  1.73  69  46  58  36  PLUTONS (Q.C.I.)  1  = Formation  2,3  = Arithmetic mean and standard deviation of the logarithm of susceptibility  k  = Median of logarithm of susceptibility  5,6  - Arithmetic mean and standard deviation of susceptibility  7  = Antilogarithm of mean susceptibility  8  = Number of samples _g (Susceptibilities i n units of 10 emu.)  TOO  statistical  parameters i n T a b l e  VII.  constructed  for  sills,  the  Tow  Hills  H i s t o g r a m s have syntectonic  not  been  plutons  and  Karmutsen v o l c a n i c s because o f t h e l i m i t e d number o f sample measurements  from  each  of  these  units.  Similarly,  because  of  a  small  number o f measurements t h e J u r a s s i c Yakoun and Bonanza v o l c a n i c s o f the Queen C h a r l o t t e and Vancouver I s l a n d s have been combined i n t o a single  histogram. Susceptibilities  Queen  Charlotte  samples  only  interval grams. were  Islands  when  of  were  cores  considered  measurements  (log susceptibility Measurements t h a t  averaged, r e s u l t i n g  from the  differed  o f 0.2)  by  site  represent  more  than  used t o c o n s t r u c t  d i d not d i f f e r i n 59  to  same  by t h i s  on  the  discrete the  group  the  histo-  arbitrary  amount  " d i s c r e t e " sample measurements  from  the 214 c o r e s . The  statistical  s u s c e p t i b i l i t y measurements geographical  distribution  representativeness  and  (Table V I I ) i s d i f f i c u l t t o a s s e s s . o f rock  and  Queen C h a r l o t t e  and  i s therefore s t a t i s t i c a l l y  Islands  plutons  i s neither systematic unsatisfactory.  f o r the  Yakoun  nor t r u l y  The  random  In a d d i t i o n , not a l l  volcanics  by  susceptibility  and  syntectonic  and, t o a l e s s e r d e g r e e , t h e p o s t - t e c t o n i c p l u t o n s , must  considered for  Results  of  samples c o l l e c t e d f r o m Vancouver  rock t y p e s from each g e o l o g i c u n i t a r e r e p r e s e n t e d measurements.  accuracy  p r e l i m i n a r y because o f s m a l l sample p o p u l a t i o n s .  be  Results  t h e Masset (N = 4 4 ) , M e t c h o s i n (N = 7 1 ) , and t h e Karmutsen (N =  152) are c o n s i d e r e d an e s t i m a t e d  however t o be r e p r e s e n t a t i v e and a c c u r a t e  within  5-10%. The  tendency  of  a  susceptibility  distribution  to  101  approximate a l o g normal (Gaussian) d i s t r i b u t i o n has been noted by a number of workers  (eg. T a r l i n g ,  1971, p.89; Puranen e t a l , 1974).  The d i s t r i b u t i o n s o f t h e l a r g e r sample p o p u l a t i o n s tend  t o confirm  tions  are b e s t  this  compared  standard  deviation  Although  i t has been  statistical  observation.  For t h i s  on t h e b a s i s  of the logarithm suggested  shown i n F i g . 24  reason,  the d i s t r i b u -  of the a r i t h m e t i c  of s u s c e p t i b i l i t y  that  t h e median  measure than t h e mean ( P l a t o u ,  mean and  (Table V I I ) .  i s a more  valid  1974) t h e d i f f e r e n c e i n  v a l u e s i s minimal when t h e lognormal d i s t r i b u t i o n s are a p p r o x i m a t e l y symmetric ( F i g . 24 and T a b l e V I I ) .  Frequency Di s t r i but i o n s The h i s t o g r a m s o f f r e q u e n c y d i s t r i b u t i o n and means o f l o g s u s c e p t i b i l i t y  i n d i c a t e t h a t , f o r t h e Queen  I s l a n d s , t h e T e r t i a r y Masset v o l c a n i c s and p o s t - t e c t o n i c Upper  Jurassic syntectonic  magnetic  susceptibilities.  susceptibilities the  greater  butions  of these  plutons,  have  Although units  the  the  Charlotte  plutons  highest  difference  is statistically  rocks  suggests  a  i n mean l o g  not  larger  significant,  number  s u s c e p t i b i l i t i e s f o r t h e s e u n i t s t h a n f o r t h e Masset. Island  t h e Karmutsen  volcanics  and I s l a n d  and  associated  l o g median v a l u e s and more l e p t o k e r t i c (peaked)  f o r the plutonic  Vancouver  arithmetic  On  distriof  high  northern  I n t r u s i o n s are  the dominant magnetic r o c k s ( C o l e s and C u r r i e , 1977). The M i d d l e J u r a s s i c Yakoun (Queen C h a r l o t t e Lower J u r a s s i c Bonanza (Vancouver I s l a n d ) magnetic number  susceptibi1ites of  sample  and w i d e s t  measurements  volcanics  range  and  high  Islands)  and  have t h e lowest  i n values. relative  The  small  dispersion  102  (indicated  by l o g s t a n d a r d  comparison  with  younger  Yakoun  other  the  result  units  volcanics  Bonanza v o l c a n i c s .  deviations)  meaningless.  a r e somewhat  Although t h i s  o f sample  bias,  p o r p h y r i t i c andesite  f i n e r grained  andesite,  Magnetic (syntectonic  plutons,  slight  than  coeval  volcanic  than  the  Karmutsen  higher  than  differences  those  susceptibilities  Intrusions)  volcanics.  those  of  quartz  plutonic  are s i g n i f i c a n t l y  Bonanza)  Syntectonic  diorite  susceptibilities  of  highly  samples  magnetic  the  composition.  Island are  of  comprise  and r h y o d a c i t e .  of the older  (Yakoun,  and  are predomi-  volcanics  rocks  of  Intrusions quartz  The  rocks greater  and s l i g h t l y  d i o r i t e c o m p o s i t i o n have s u s c e p t i b i 1 i t e s two t o t h r e e than  of the  i n compostion  The Yakoun v o l c a n i c s  b a s a l t i c andesite  rocks  quantitative  S u s c e p t i b i l i t i e s of the  whereas t h e Bonanza  Island  make  apparent d i f f e r e n c e may s o l e l y be  g r a i n s i z e may a l s o be a f a c t o r . nantly  however,  greater  hornblende  times  greater  d i s t r i b u t i o n of  i s bimodal; diorite  or  t h e more  granodiorite  c o m p o s i t i o n and t h e more weakly magnetic samples are o f more a c i d i c v a r i e t i e s (eg. quartz monzonite). Like histogram  the Island  of t h e Karmutsen  Intrusions, volcanics  i s bimodal  population  (A) of high  population  (B) o f low s u s c e p t i b i 1 i t e s .  Currie  and  Muller  "holocrystalline than  fine  hypocrystalline  the frequency d i s t r i b u t i o n  susceptibilities  (1976) grained medium  who  distinct  having  grained  a large  sub  from  a small  sub  This bimodality  attributed  rocks  with  rocks".  was noted by  the  distribution to  higher  susceptibilities  The  approximate l o g  normal d i s t r i b u t i o n o f both A and B modes i s expected s i n c e bution  of  susceptibilities  i s often  a  function  of  grain  distrisize,  103  which  i n any  rock  type  i s lognormally  distributed.  On  Queen  C h a r l o t t e I s l a n d s , f o r which o n l y 16 " d i s c r e t e " c o r e sample measurements  were  with  both  available, pillow  and  high  magnetic  massive  s u s c e p t i b i l i t y with c h l o r i t i z e d mean magnetic s u s c e p t i b i l i t y  susceptibility  basaltic  lavas  i s associated  and  low  magnetic  equivalents ( i . e . greenstones).  The  o f t h e B mode i s lower than any u n i t on  Vancouver and Queen C h a r l o t t e I s l a n d s r e p o r t e r h e r e ; t h e mean o f t h e A mode i s not s i g n i f i c a n t l y  different  ( a t 95% c o n f i d e n c e )  than t h e  more h i g h l y magnetic u n i t s (Masset, post and s y n t e c t o n i c p l u t o n s ) on the Queen C h a r l o t t e I s l a n d s . Magnetic (Louise  susceptibilities  P l u t o n and S a n d s p i t  Group) a r e r e l a t e d  more a c i d i c rock t y p e s having is  generally  diorite  gradational  (Sandspit  lower  from  Pluton)  of  t o composition  susceptibilities.  t h e more  highly  The  The low magnetic  ( F i g . 24) a r e from  t h e East Kano B a t h o l i t h .  quartz  to  quartz  susceptibilities  h i g h l y weathered  Excluding these  with  decrease  magnetic  t o g r a n o d i o r i t e (Chinukunkl)  monzonite ( L o u i s e and Cumshewa). shown on t h e h i s t o g r a m  of the p o s t - t e c t o n i c plutons  samples  samples  increases the  mean l o g s u s c e p t i b i l i t y from 3.08 t o 3.27. Susceptibility restricted facies were  t o basalt flows  (Graham  found  similarity  measurements o f t h e Masset v o l c a n i c s were  Island).  ash f l o w s  R h y o l i t e samples,  t o be s l i g h t l y  more magnetic  i n age and c o m p o s i t i o n  Moresby I s l a n d  of the Tartu  (see f o l l o w i n g than  t h e Kootenay  l i k e l y have r e l a t i v e l y  s i m i l a r t o the Tartu f a c i e s . pyroclastic  and r h y o l i t e  basalt.  section)  Because o f  and Dana f a c i e s o f  h i g h magnetic  susceptibilities  However, much o f t h e a r e a o c c u p i e d by  b r e c c i a s o f t h e Dana f a c i e s  has been metamorphosed by  104  post  tectonic  intrusions,  so  resulting  chloritization  may  have  reduced s u s c e p t i b i l i t y o f t h e s e r o c k s . The insignificant similar  magnetic Tow  Hill  susceptiblity sills  t o t h a t o f t h e Masset  samples  from  aphanitic  sill  interiors  olivine  Vancouver  Island,  somewhat  higher  than  volcanics.  chill  those  volumetrically  Graham  Medium  slightly  Island  grained  more  margins.  basaltic  i n c l u d e d here  the  north-eastern  are  b a s a l t s from  t h e Lower T e r i t a r y M e t c h o s i n  are  of  of  diabase  magnetic  than  Susceptibilities  to dacitic  lavas of  ( F i g . 24) f o r comparison of the T e r t i a r y  is  of  southern purposes,  volcanics  o f the  Queen C h a r l o t t e I s l a n d s .  REMNANT MAGNETIZATIONS  Results  of  measurements  of  remnant  intensities  of  o r i e n t e d c o r e s from t h e Queen C h a r l o t t e I s l a n d s are r e p o r t e d here t o e n a b l e t h e r e l a t i v e magnitudes o f remnant and induced to  be  field The  assessed,  i n conjunction with  demagnetization, initial  remnant  w i t h paleomagnetic Spinner were  and,  to consider intensities-j  study  made  using  results  the  stabilities  were  measured,  ( H i c k e n and I r v i n g ,  Magnetometer SMI. apparatus  Alternating described  of of  (AF)  remnances.  Schonstedt  demagnetizations  Roy e t a l  I n i t i a l remnant i n t e n s i t i e s used t o c a l c u l a t e means of reverse orientation intensity individual cores.  alternating  i n conjunction  1977), on a  field by  magnetizations  (1973).  The  Q r a t i o s are t h e measurements on  105  r e s u l t s , p r e v i o u s l y u n p u b l i s h e d , were s u p p l i e d by E. communication,  Feb.  Irving  (written  1978).  Remnant I n t e n s i t i e s The remnant  relationship  magnetizations  shown  i n F i g . 25.  ratio  Q  between  (before  The  the  between  z a t i o n , d e f i n e d as Q = R/kH, the  ambient  A/m).  geomagnetic  any  sloping  remnant  susceptibilities explicit  lines  natural  demagnetization)  indicate  magnetization  and  R  the  and  Koenigsberger  induced  magneti-  where k i s the s u s c e p t i b i l i t y and  field,  taken  here  to  be  0.565  The plutons,  Oe  Koenigsberger  both  respectively.  major  The  o n l y ) are  range  from  t h e Tow  ratios  contributors  f o r the  to  0.3  Hill  less  than  t o 9.0  sills  the  post  and  magnetic  1.0.  Q  ratios  f o r the  w i t h most g r e a t e r than  range from 0.7  anomaly f i e l d .  Of  stable  directions  remnant  syntectonic  anomaly  t o 1.8.  eight  sites  Masset remnant  (Susceptibilities basalts.)  and  0.5  1.0,  rhyolites  were  intensities of r h y o l i t e s  and  San  Christoval  volcanics  w h i l e those f o r Tertiary  component of the t o t a l  magnetic  Masset  measured,  volcanics  four  sites  generally  found  Q  than  ratios  were a l s o  Q r a t i o s f o r hornblende  syntectonic  field  R e s u l t s f o r the  i n the  were  Masset  p o l a r i t i e s and f o u r had r e v e r s e d ( H i c k e n and I r v i n g ,  initial  core  Q r a t i o s f o r t h e Karmutsen v o l c a n i c s ( s i n g l e c o r e  v o l c a n i c s i n d i c a t e a s i g n i f i c a n t NRM  the  (45.2  sites.  because o f h i g h s u s c e p t i b i l i t i e s are g e n e r a l l y l e s s t h a n 0.3  site  H is  C l u s t e r i n g o f d a t a p o i n t s i n F i g . 25 g e n e r a l l y r e f l e c t s  measurements from i n d i v i d u a l  is  Batholith  and are  which  had  normal  1977). to  have  Masset  h i g h e r than  diorite  for  higher basalts.  those  of  quartz d i o r i t e similar.  As  the from  remnant  106  F i g . 25  Comparison o f remnant and i n d u c e d m a g n e t i z a t i o n s f o r c o r e samples from t h e Queen C h a r l o t t e I s l a n d s . S l o p i n g l i n e s i n d i c a t e the v a r i a t i o n o f Koenigsberger Q r a t i o s .  107  i n t e n s i t i e s were a v a i l a b l e o n l y f o r the L o u i s e p l u t o n , i t c o u l d be  determined  i f Q ratios  varied with composition  not  of p o s t - t e c t o n i c  intrusive rocks.  Alternating Field All 1977)  Demagnetization  c o r e specimens a n a l y z e d f o r NRM  were s u b j e c t e d t o AF  relaxation (8 x  10  A/m)  time A/m)  4  steps.  demagnetization,  remnance. for pilot  Fields  to  reduce  the  g r a p h i c a l l y ) are g i v e n ' i n T a b l e  NRM  f o r Masset  samples (CM2, (CP7,  i n 50  intensity  v a r i e d from  In a number of cases  V I I I ) , the remnances were u n s t a b l e and possible after  used  AF  by  quartz d i o r i t e ;  Karmutsen  coherent  (4  50%  Oe  x  10  CP8,  10,  (estimated  with those  These  measurements were included  11, q u a r t z monzonite) and  low-peak 50% f i e l d s and v o l c a n i c s and  2  Masset  plutonic  sample  quartz d i o r i t e ) .  low K o e n i g s b e r g e r rocks  one  indiates  ratios for that  stable  remnant m a g n e t i z a t i o n does not c o n t r i b u t e s i g n i f i c a n t l y The  number of t h e s e samples suggests remnant m a g n e t i z a t i o n s and  hornblende  Currie quartz  h i g h magnetic  susceptibility  however t h a t low c o e r c i v i t y  c o u l d produce a s m a l l coherent  (1977)  3  r h y o l i t e ) , 4 samples of the L o u i s e p l u t o n  the magnetic anomaly f i e l d .  Coles  Oe,  1000  55 t o 120 Oe  from t h e San C h r i s t o v a l B a t h o l i t h (CP16, hornblende  the  to  (not i n c l u d e d i n Table  meaningful  demagnetization.  b a s a l t ; CM9  The  up  v o l c a n i c s samples c o n s i d e r a b l y h i g h e r than  of a l l o t h e r specimens.  not  fields  low  VIII.  In g e n e r a l the 50% f i e l d s fields  Irving,  i n o r d e r t o remove  Peak demagnetizing specimens were  ( H i c k e n and  found  diorite)  for of  two high  samples  a  viscous  contribution.  (gabbro,  magnetic  of  to  biotite-  susceptibility  108  TABLE VIII MAGNETIC HARDNESS OF QUEEN CHARLOTTE ISLANDS CORE SAMPLES ROCK TYPE  FIELD TO REMOVE 50% of NRM (Oersted peak AF)  KOENIGSBERGER RATIO Q  60  1.17  1480  85 95 105 105 115 115 200 120 120 120 165  0.96 0.29 2.30 2.80 1.82 2.18 12.08 5.71 1.46 0.99 0.63  1040 2580 460 280 870 1230 2560 1760 2310 860 1140  0  SUSCEPTIBILITY k emu/cm x I O 30  TOW HILL SILLS CP4-7A  Diabase  MASSET VOLCANICS CM1-4C CM3-5A CM4-7A CM5-2A CM6-1A CM7-1A CM8-1A CM10-3A CM11-1A CM12-1A CM13-1B  Basalt Basalt Basalt Basalt Basalt Basalt Rhyolite Basaltic breccia Rhyolite Rhyolite Rhyolite  KARMUTSEN VOLCANICS CP12-1A  Basalt  70  0.60  2130  POST TECTONIC PLUTONS CP9-3A CP13-1A  Quartz Monzonite Quartz Monzonite  85 65  0.46 1.18  910 500  SYNTECTONIC PLUTONS CP1-1A CP2-2C CP3-1A CP3-4A CP3-5A CP14-1A CP15-1A  Hornblende Diorite Hornblende Diorite Hornblende Diorite Hornblende Diorite Hornblende D i o r i t e Quartz Diorite Quartz Diorite  90 85 70 80 85 80 55  0.20 0.22 0.27 0.18 0.24 0.22 0.28  1680 2080 2730 3100 3090 910 830  a  Core s i t e and laboratory sample number assigned by Division of Geomagnetism, Earth Physics Branch  b  1 Oe = 80 A/m 3 1 emu/cm - 12.56 i n SI.  c  - 6  109  f r o m t h e Coast P l u t o n i c Complex, t h a t r a t e s o f v i s c o u s b u i l d u p such  that  a  viscous  component  could  add  were  a c o n t r i b u t i o n equal  to  about 30% o f t h e i n d u c e d m a g n e t i z a t i o n t o t h e anomaly f i e l d . The Koenigsberger  high  peak  alternating  fields  coupled  with  high  r a t i o s o f t h e Masset v o l c a n i c s i n d i c a t e s t h a t t h e  i s s t a b l e ( h i g h c o e r c i v i t y ) and c o m p r i s e s anomaly f i e l d t h a n does i n d u c e d  a higher percentage  NRM  of the  magnetization.  DISCUSSION  Previous remnant  d i s c u s s i o n on  magentization  magnetic  has  properties of  Charlotte  Islands.  susceptibility  pointed  volcanic  A general  to  and  the  Hill)  (Yakoun,  tending  inverse correlation  t o have h i g h e r  Karmutsen  B  following  p l u t o n i c rocks  b i l i t y and age o f v o l c a n i c s i s o b s e r v e d , Tow  distributions  Mode).  features of  the  w i t h younger rocks  younger  in  Queen  between s u s c e p t i -  susceptibilities The  and  than  (Masset,  older  rocks  also  have  volcanics  a p p r e c i a b l y h i g h e r remnant i n t e n s i t i e s and Q r a t i o s . The  magnetic  susceptibility  of  intrusive  rocks  r e l a t e d t o c o m p o s i t i o n , w i t h more b a s i c r o c k s h a v i n g  higher  ibilities.  a l , 1968)  A  number  of  authors  ( e . g . Puranen e t  suscept-  r e c o g n i z e d t h e dependance o f s u s c e p t i b i l i t y on t h e m a g n e t i t e of  a rock  expressed  FeO p e r c e n t a g e s . model higher  percent  either  As e x p e c t e d  of magnetite  i n Masset  as  basalts  a  volume  percent  from s u s c e p t i b i l i t y  (the chief and  of  a n d e s i t e s o r Karmutsen c h l o r i t i z e d b a s a l t i c  than  have  content  Fe2C"2 and  measurements, t h e  ferro-magnetic  rhyolites  as  is  component) i s  Yakoun  porphyritic  lavas (Sutherland  Brown,  110  1968).  Gabbroic  Karmutsen study, types FeO  and Masset  have  higher  and would ^^2^3  and  Brown,  and  diabasic  associated  v o l c a n i c s , though  modal  magnetite  be expected  of  not  higher  A-mode  than  both  the  f o r magnetic  t h e above  rock  susceptibilities.  The  Karmutsen  e t a l , 1974) exceed  with  sampled  contents  t o have  percentages  1968, M u l l e r  dykes  those  lavas  (Sutherland  of analyzed  Masset  f l o w s though Fe202/Fe0 r a t i o s a r e l e s s . The  magnetic s u s c e p t i b i l i t i e s and remnant i n t e n s i t i e s o f  Masset r h y o l i t e s and b a s a l t s might be c o n s i d e r e d more h i g h l y s u s c e p t i b l e r h y o l i t e f l o w s magnetite 1968). highly  and  FeO  Haggerty oxidized  increases withn magnetic  Fe^O^  have a p p r e c i a b l y  concentrations  and more magnetic increasing S ^ i n acidic  phases  have  than  basalts.  and although  suites  bulk  i s relatively  large magnetically  lower  (Sutherland  (1979) shows, however, t h a t r h y o l i t e s  minerals  volume) these  and  anomalous s i n c e t h e modal Brown,  may  be more  Oxidation  state  concentration of small  ( 1 - 3 % by  s t a b l e components of  3+ Fe  in  solid  solution.  Conversely  advanced  high  temperature  o x i d a t i o n , commonly observed i n s u b a e r i a l b a s a l t s , i s a m a g n e t i c a l l y destructive mineral transformation  process.  Ill  CHAPTER VI  AEROMAGNETIC MAPS OF THE QUEEN CHARLOTTE ISLANDS  INTRODUCTION A  discussion  of  aeromagnetic  survey  maps  covering  n o r t h e r n Moreby I s l a n d , s o u t h e a s t e r n Moresby I s l a n d and n o r t h e a s t e r n Graham I s l a n d i s p r e s e n t e d t o known geology  here i n o r d e r t o r e l a t e magnetic  and magnetic p r o p e r t i e s o f rock  response  u n i t s reported i n  the  previous chapter.  D e l i n e a t i o n o f magnetic t r e n d s  and p a t t e r n s  and  s i z e and i n t e n s i t y o f magnetic f e a t u r e s i s used t o e x t r a p o l a t e  g e o l o g i c a l and s t r u c t u r a l d a t a t o o f f s h o r e Hecate S t r a i t . Location netic  surveys  and p a r t i c u l a r s  are given  29,32, and 33 i n pocket)  maps  of  Triassic have  Karmutsen,  been  types. are  Sutherland  divided  Jurassic  traverses  In o r d e r  The  contoured  superimposed on t h e r e g i o n a l g e o l o g i c (1968).  Volcanic  rocks,  Yakoun and T e r t i a r y  sub-facies  to  to simplify  a r e not i n c l u d e d  IX.  aeromag-  a t a s c a l e o f 1:125,000 ( F i g s .  indicate  D i s t r i b u t i o n o f non-magnetic T r i a s s i c  not shown.  reduced.  Brown  into  t o the three  i n F i g . 26 and T a b l e  aeromagnetic d a t a has been reproduced 28,  related  namely  Masset  the i l l u s t r a t i o n s  and t h e c o n t o u r  Formations  predominant  to Tertiary  intervals  the  rock  sediments the f l i g h t have  been  The r e a d e r i s r e f e r r e d t o t h e o r i g i n a l maps ( s e e i n d i c a t e d  map s o u r c e s i n T a b l e IX) f o r a d d i t i o n a l  detail.  112  F i g . 26  L o c a t i o n o f Queen C h a r l o t t e I s l a n d s a e r o m a g n e t i c maps.  TABLE IX AEROMAGNETIC SURVEY DATA - QUEEN CHARLOTTE ISLANDS NORTHERN MORESBY ISLAND AREA, APPROX. (Mn ) 2  AIRCRAFT MAGNETOMETER HORIZONTAL CONTROL TERRAIN CLEARANCE  FLIGHT LINE SPACING  800  SOUTHEASTERN MORESBY ISLAND  NORTHEASTERN GRAHAM ISLAND  750  1150  Cessna 180  Fixed wing aircraft  Fluxgate  Fluxgate  Airphoto laydown 1) 3850 ft (1173 m) constant elevation 2) 500 ft (152 m) mean terrain clearance 1320 ft (402 m)  Airphoto laydown 500 ft (152 m). mean terrain clearance  1320 ft (402 m)  FLOWN BY  Canadian Aero Service Ltd. (now Geoterrex Ltd.)  Hunting Survey Corp. Ltd. (now Lockwood Survey Corp.)  ORIGINAL MAP SCALE'  1 inch = 2640 ft (>s mile) 1 : 31,680  1 Inch = 1320 ft [h mile) 1 : 15,840  ORIGINAL CONTOUR INTERVAL DATE FLOWN BACKGROUND LEVEL (BASE INTENSITY) DATA SOURCE  25 nT Aug.-Oct., 1959  20 nT  Fluxgate Airphoto laydown 1500 ft (457 m) constant elevation  5280 ft (1609 m)  1 Inch = 5280 ft (1 mile) 1 : 63,360 10 nT  June-Aug., 1961  Arbitrary  3000 nT  B.C. Dept. Mines Aeromagnetic Maps Series AM 59-1 to AM 59-4  Dennlson Mines Ltd. Airborne Magnetic Survey (four maps), unpublished data  Arbitrary Grlnsfelder D., 1960, Report of Airborne Magnetometer Survey, Graham Island Onshore Area; B.C. (Richfield Oil Corp.), B.C. Dept. Mines and Petroleum Resources, Pet. Res. Br. Open File 861.  114  HIGH LEVEL AEROMAGNETIC MAP OF BRITISH COLUMBIA  In ometer  survey  Pacific 1974;  residuals with  was  Ocean Coles  1969, a h i g h - l e v e l ,  (Haines  over  British  1977).  A  contour  p o r t i o n o f t h e Coast  by a h i g h  amplitude  positive  anomalies  central  Moresby  succession  centered  positive  Island.  The  of m i d - T e r t i a r y  while  t h e second  a  p o s s i b l e source  have  been  f o r deep  the l o c i i  rocks,' or  higher  Because t h e thermal  of  oxygen  of v e r t i c a l  i n F i g . 27.  Graham  anomaly facies  east-  overlies  a  thick  basalts  and  rhyo-  f o r t h e most p a r t , Masset  (Sutherland  crustal  viscous  Brown, 1966) suggests  magnetization. enhancement,  fugacity  Dana  P r o x i m i t y o f t h e anomalies t o  to  The vents  increasingly  precipitate  iron  may mafic  oxides.  p a t t e r n o f high heat f l o w a s s o c i a t e d w i t h Masset  deeper  magnetizations  critical  Compared  and  have remained f o r s e v e r a l m i l l i o n s  detected  field  Island  volcanic a c t i v i t y w i l l more  Haines,  a r e two l a r g e ( 400 nT)  Tartu  f a c i e s b a s a l t and r h y o l i t e b r e c c i a s . i n d i c a t e d Masset e r u p t i o n c e n t e r s  and  anomaly, t h e I n s u l a r B e l t i s  first  overlies,  adjacent  P l u t o n i c Complex, which i s  western  Masset  and t h e  map  Exceptions  over  a i r b o r n e magnet-  1972; Hannaford  r e l a t i v e t o t h e IGRF i s reproduced  regionally magnetically quiet.  lites,  Columbia  and Hannaford,  and C u r r i e ,  t h e western  outlined  flown  three-component  intense  i n an a r e a  of r e l a t i v e l y  could quiet  only  persist  magnetization  C u r r i e i s o t h e r m a t depth had been passed.  of years, and  be  a f t e r the  115  . 27  Map o f v e r t i c a l component m a g n e t i c f i e l d r e s i d u a l s f o r s o u t h w e s t e r n B r i t i s h Columbia and c o n t i n e n t a l s h e l f a t OfjnT c o n t o u r i n t e r v a l . B a t h y m e t r i c depths a r e i n m e t e r s , eproduced from C o l e s and C u r r i e (1977, F i g . 1 ) .  116  NORTHERN MORESBY ISLAND  Two a i r b o r n e  s u r v e y s o f n o r t h e r n Moresby  Island  (Figs.  28 and 29) were f l o w n i n 1959 f o r t h e B r i t i s h Columbia Department o f Mines:  one a t a c o n s t a n t f l i g h t a l t i t u d e o f 1173 m (3,850 f t ) and a  second  a t an average  terrane  aeromagnetic d a t a formed Queen  Charlotte  relationship  of  c l e a r a n c e o f 152 m  (500 f t ) . The  p a r t o f t h e o v e r a l l mapping p r o j e c t o f t h e  Islands  (Sutherland  magnetic  response  Brown, to  1968),  mapped  though  the  geology  was not  response  produced  discussed. In  order  t o evaluate  t h e magnetic  s o l e l y by t o p o g r a p h i c e f f e c t s , both c o n t o u r e d aeromagnetic maps were compared w i t h (Figs.  National  Topographic S e r i e s Maps.  30 and 31) were c o n s t r u c t e d  Two c r o s s - s e c t i o n s  to illustrate  effect  of topo-  graphy and g e o l o g y on draped and c o n s t a n t l e v e l s u r v e y s . N o r t h e r n Moresby I s l a n d peaks  and r i d g e s , formed  primarily  i s characterized of p l u t o n i c  include  deep  northwest-southeast  straits  structural  sharp c o n t a s t i n topography be  a relatively  attenuated  stronger  trend.  that  constant elevation  the  ridge-valley  suggesting  s e c t i o n A-A  1  magnetic  topography a  c u t t h e predominate  on t h e c o n s t a n t e l e v a t i o n  response  over  curve  t h e peaks  on  significant  both  east  strong  survey  would  In F i g . 31  resemblance t o  and west  topographic  of t h i s  and r i d g e s and  and i n l e t s .  bears  rocks,  The mountainous  The expected e f f e c t  o r weaker response over v a l l e y s  the  profile  and i n l e t s  mountainous  and v o l c a n i c  r i s i n g t o e l e v a t i o n s as g r e a t as 1130 m (3,700 f t ) . regions  by  effect.  ( F i g . 30) however, t h e c o n s t a n t e l e v a t i o n  ends On  of the cross-  c u r v e , here  SEWELL INLET  LOUISE ISLAND  3000-q  LOWER-MIDDLE TERTIARY MASSET FORMATION: KOOTENAY FACIES Rhyolitlc lull, mixed volcanics UPPER CRETACEOUS ™ HONNA FORMATION: Conglomerate  MIDDLE JURASSIC YAKOUN FORMATION: And08ltlc agglomerate, volcanic sandstone  M  UPPER TRIASSIC - LOWER JURASSIC KUNGA FORMATION: Limestone, argllllte  UPPER CRETACEOUS HAIDA FORMATION: Shale, sandstone  UPPER TRIASSIC ^ y y j l KARMUTSEN FORMATION v v v v l Basaltic lava, greenstone  Vertical exaggeration: x 3.8  LOWER CRETACEOUS LONGARM FORMATION: Siltstone, sandstone  LOWER TERTIARY I POST TECTONIC PLUTON: 1 Quartz monzonite  Horizontal scale:  F i g . 30  E3!  Geology modllled after Sutherland Brown (1966, Fig. 6., Cross Section H-H)  5  10  Kilometres  G e o l o g i c c r o s s - s e c t i o n o f n o r t h e r n Moresby I s l a n d a l o n g A-A' w i t h mean t e r r a i n c l e a r a n c e and c o n s t a n t f l i g h t a l t i t u d e t o t a l m a g n e t i c f i e l d p r o f i l e s .  u  o z  B  B'  Ul  S 3400 u.  (-1800  Ul  3200  g IS  3000  1400  2800  1200  I  2600  P £  1000 800  2400-|  o Ul  [Z  1-600  2200-|  2  I  p Q -J ui tZ  o  e < x_i  1800  < S  -  oc (9  5 z  9 2000 Z  5  1600  "  1600 -100  o ITALUNKWAN SAN CHRISTOVAL  o  IS.  BATHOLITH  Z  o  P S E A LEVEL  <  L O W E R — M I D D L E TERTIARY FORMATION: - • MASSET DANA FACIES Mixed d a s ! breccias  UPPER TRIASSIC — LOWER JURASSIC K U N G A FORMATION: Limestone, argllllte  UPPER  UPPER TRIASSIC ~ W V VI K A R M U T S E N F O R M A T I O N : Basaltic lava, greenstone, amphlbollte VVV1  • *  CRETACEOUS HONNA FORMATION: Conglomerates  UPPER C R E T A C E O U S I HAIDA F O R M A T I O N : Shale, Sandstone MIDDLE J U R A S S I C YAKOUN FORMATION: Andesitic agglomerate  g.  31  T•EcRnT I•Am RY i IPOST TECTONIC PLUTON: I Quartz monzonite  E3!  UPPER JURASSIC SYNTECTONIC PLUTON: Hornblende diorite  G e o l o g y modified alter Sutherland Brown ( 1 9 6 8 , Fig. 6, C r o s s - S e c l l o n G - G ) Vertical exaggeration: x 3.8  Horizontal scale: 5  10  G e o l o g i c c r o s s - s e c t i o n o f n o r t h e r n Moresby I s l a n d a l o n g B-LV w i t h mean t e r r a i n c l e a r a n c e and c o n s t a n t f l i g h t a l t i t u d e t o t a l magnetic f i e l d p r o f i l e s .  119  more subdued, bears effect  s i m i l a r i t y t o topography  appears s m a l l compared t o t h a t from  On both be  little  c a u s a t i v e rock  c r o s s - s e c t i o n s , t h e smoother, c o n s t a n t  considered  clearance  a  simple  magnetic  observation  in  filtered  curve  itself  version  elevation  of  the  because o f s i m i l a r i t y suggests  that  and any t e r r a i n  terrain  bodies.  curve  mean  terrain  i n response. effects  may  This  are  small  compared t o g e o l o g i c e f f e c t s . The predominant magnetic t r e n d  i n the northern  Island survey area i s o r i e n t e d northwest-southeast, main  structural  west  trends  elements.  Secondary  arcuate  northwest-southeast  magnetic  eastern  splay  of  Louise Island.  or extension  of  and  southern  trough  t h e Rennel  and e a s t -  portions.  corresponds Fault  on  with  An an  east-central  C o n t i n u a t i o n o f t h i s trough o f f s h o r e , t o the east o f  L o u i s e I s l a n d suggests expression  p a r a l l e l t o the  northeast-southwest  c h a r a c t e r i z e the c e n t r a l  Moresby  the  a submarine e x t e n s i o n of t h e f a u l t .  north-northwest  trending  Louscoone  Magnetic Fault  is  l i m i t e d , on t h e c o n s t a n t t e r r a i n c l e a r a n c e magnetic map, t o a s m a l l , low  relief,  magnetic t r o u g h  i n t h e v i c i n i t y of L o u i s e Narrows and  c u r v a t i v e o r i n f l e c t i o n o f magnetic c o n t o u r s near  Dana Passage.  As  s i m i l a r rock t y p e s a r e j u x t a p o s e d on e i t h e r s i d e o f t h e f a u l t t r a c e through much o f t h e s u r v e y part t o a topographic A clearance lies,  effect. magnetic  plateau  s u r v e y ) , c h a r a c t e r i z e d by h i g h  covers  Passage,  broad  a r e a , magnetic e x p r e s s i o n may be due i n  the eastern  (on  the  amplitude  p o r t i o n o f Moresby  e a s t e r n Talunkwan I s l a n d , and southern  constant magnetic  Island Louise  west  terrain anomao f Dana  Island.  The  m a j o r i t y o f t h i s a r e a i s u n d e r l a i n by Masset Dana f a c i e s mixed c l a s t  120  tuff  breccias, feldspar  plateau  corresponds  previously  from  to  the  porphyries the  high  and  positive  level  rhyolites. magnetic  vertical  The  magnetic  anomaly  field  described  aeromagnetic  map  ( F i g . 27). The facies  magnetic  volcanics  on  subdued than t h o s e ridges  and  Kootenay  anomalies  western  Moresby  trending  roughly  volcanics, contrast of  east-west  and  Island  Masset  flanking  with  Karmutsen  Kootenay  ( F i g . 29)  a s s o c i a t e d w i t h the Dana f a c i e s .  troughs,  anomalies  characterizing  are  Short  magnetic  northwest-southeast  east-west  trending  volcanics.  A  more  over low  fault  the  relief trending  bounding the Kootenay r o c k s south of Douglas I n l e t i s  marked by a steep magnetic g r a d i e n t . Coarse g r a i n e d  gabbroic  Masset  l a r g e l i n e a r body e a s t of B a r r i e r Bay)  intrusives  (such  as  the  have a s s o c i a t e d h i g h magnetic  values. The either have  Masset  T e r t i a r y p o s t - t e c t o n i c p l u t o n s where i n c o n t a c t w i t h or  Karmutsen  associated  associated  with  high the  v o l c a n i c s or  magnetic  Louise  Pluton  flank  where Karmutsen  greenstones  tuffs  and  rock  Louise  hornfelsic  P l u t o n of  values,  and  enveloped  by  have  the  Highest  are  situated  and  Yakoun  been  quartz monzonitic  suggests more  relief.  metamorphosed  intruded.  that  highly susceptible basic  magnetic along  The has  i t may intrusive  core lower be  border  types  p.138]  more  Alternatively,  basic the  rock  high  magnetic  (Sutherland values  may  of  zoned  Island  Brown, be  the  magnetic  rocks.  n o r t h e a s t e r n Moresby  of  western  sandstones,  q u a r t z monzonite Cumshewa P l u t o n on phases  values  its  volcanic  composition,  possibility  equivalents  and [The has 1968,  associated  121  w i t h m i n e r a l i z a t i o n near t h e i n t r u s i v e c o n t a c t zone, s i m i l a r syntectonic batholith a c r o s s Selwyn I n l e t are  part  along  (see below).  o f t h e same  tuffs  C o n t i n u a t i o n o f a magnetic t r e n d  i n d i c a t e s t h a t t h e L o u i s e and Talunkwan  t h e same t r e n d  Yakoun  t o the  intrusive cross  body.  a belt  Northward,  magnetic  o f metamorphosed  and v o l c a n i c sandstones.  The high  Plutons highs  (hornfelsic)  magnetics  suggest  s h a l l o w b u r i a l o f a y e t unroofed p o r t i o n o f t h e L o u i s e P l u t o n . The quartz  magnetic  monzonite  Pluton.  Highest  composition) magnetic  s u r v e y map a r e r e c o r d e d tuffs.  character  o f t h e Lagoon  i s similar  values  on  Pluton  to that  t h e mean  (also  of the  terrain  near c o n t a c t s w i t h Kootenay f a c i e s  of  Louise  clearance rhyolitic  The anomaly p a t t e r n on t h e c o n s t a n t e l e v a t i o n survey map i s  represented  by a s i n g l e  broad  magnetic  high  with  three  separate  magnetic peaks. The  broad  NE-SW t r e n d i n g  Lagoon P l u t o n , near Sewell  I n l e t , covers  most p a r t by Upper Cretaceous The signature magnetic Barrier magnetic  as  Yakoun would  be  volcanic  rocks  expected  by  Volcanic  Bay and a t t h e head  f r o m Cretaceous  and cannot sediments.  low, south  display  t h e wide sandstones  o f Selwyn  Inlet  t h a t Yakoun p o r p h y r i t i c t h e exposure  appears as a magnetic low.  range  magnetic  i n measured  and t u f f s  east  of  o r no maps  A magnetic high does however c h a r a c t e r -  be  values,  varying  be d i s t i n g u i s h e d on t h e magnetic  Yakoun r o c k s west o f L o u i s e Narrows.  magnetic  sediments.  display l i t t l e  ize similar expected  of the  an area u n d e r l a i n f o r t h e  Queen C h a r l o t t e Group  susceptibilities.  relief  magnetic  Although  a n d e s i t e s would  on t h e e a s t  side  i t might  d i s p l a y higher  of Louise  Island  122  Magnetic  relief  over  Karmutsen v o l c a n i c r o c k s  a l l y subdued w i t h c o m p a r a t i v e l y northern  Vancouver  relief  and  1976).  On  low magnetic v a l u e s , i n c o n t r a s t t o  I s l a n d where the  higher  magnetic  i s gener-  Karmutsen d i s p l a y s both  values  above  background  higher  (Eastwood,  Moresby I s l a n d , somewhat h i g h e r magnetic v a l u e s  are more  commonly a s s o c i a t e d w i t h massive f l o w s than w i t h p i l l o w l a v a s . High r e l i e f  and  high magnetic v a l u e s are a s s o c i a t e d w i t h  Karmutsen massive l a v a s and Christoval  Batholith  southwestern have  on  that  as  Karmutsen  Vancouver  magnetite. tions  a l s o c r o s s - s e c t i o n B-B',  p o r t i o n of the s u r v e y  shown  zones  (see  a m p h i b o l i t e s where i n t r u d e d by  volcanic  Island  Amphibolite indicated  area.  commonly  derivatives  by  magnetic  in  contain  may  F i g . 31)  Kuniyoshi  rocks  thus  values  and  San  i n the  Liou  contact  (1976)  metamorphic  abundant have  near  the  secondary  high  magnetiza-  San  Christoval  the  Batholith. Intense  localized  magnetic  c o n s t a n t t e r r a i n c l e a r a n c e s u r v e y map) i r o n - c o p p e r d e p o s i t s a t Tasu and anomaly Mine. are  located  Kunga  above  limestones.  magnetite  replacement,  included  emplacement  showings  and  Garnet ore  top  of  the  Skarnification  the  San  at  bodies  Karmutsen, and  No the  Christoval  on  magnetite  Old  Townsite  is similar;  and  igneous  replace  both  massive including  intrusion  Batholith  the  appreciable  mineralization,  r e s u l t e d from repeated of  seen  are a s s o c i a t e d w i t h  Tasu  the  (best  Garnet mine s i t e s .  i s a s s o c i a t e d w i t h magnetite Geology of the  highs  that  (Sutherland  Brown, 1968). A l o c a l magnetite  high i s a s s o c i a t e d with magnetite  ore a t t h e I r o n Duke p r o p e r t y on n o r t h e r n L o u i s e I s l a n d .  iron  123  The  syntectonic  San C h r i s t o v a l  Batholith  c h a r a c t e r s i m i l a r t o t h a t o f t h e Karmutsen v o l c a n i c s .  has  magnetic  Magnetic  lows  predominate  i n most areas e x c e p t i n g over i n t r u s i v e c o n t a c t s w i t h t h e  Karmutsen.  The  Batholith  orientation  or i t s enclosing  o f magnetic  features  r o c k s are o r i e n t e d  related  t o the  northwest-southeast,  s i m i l a r t o s t r i k e d i r e c t i o n , contact orientation  and t r e n d o f minor  faults.  SOUTHEASTERN MORESBY ISLAND  An was f l o w n  ation  survey  i n 1961 f o r Denison  southeatern Island  aeromagnetic  Moresby  ( F i g . 32). program  Island  with constant  Mines  from  Burnaby  The s u r v e y formed  f o r iron  L t d . along  clearance  a 50 km  s t r i p of  to  Kunghit  p a r t o f an i n t e n s i v e  explor-  ore d e p o s i t s  Island  terrain  south  (see Sutherland  Brown  pp.  194-197, B.C., Ann.Rept., 1963, pp. 18-21). The  major  features  relationships  of magnetic  block  and magnetic  faults  of  troughs highs  t h e aeromagnetic t o major  map  transcurrent  t o Southern  Group  are t h e and  minor  post-tectonic  p l u t o n s and m a g n e t i t e i r o n o r e d e p o s i t s . A  north-northwest  trending  linear  magnetic  trough  c o r r e s p o n d s t o t h e t r a c e o f t h e Lousconne F a u l t from Kunghit south through Luxana Bay. o v e r Rose I n l e t suggest  C i r c u l a r t o l o b a t e magnetic  lows  a s o u t h e r n e x t e n s i o n t o a minor  Island located  fault  that  t r e n d s n o r t h from t h e head o f t h e i n l e t . Elongate depressions,  oriented  east-west roughly  to  northeast-southwest  perpendicular  to  the  magnetic predominant  124  magnetic t r e n d c h a r a c t e r i z e S k i n k u t t l e I n l e t , and t o a l e s s e r Carpenter  Bay  and  Stewart  Channel.  The  structure  of  degree  Skinkuttle  I n l e t c o m p r i s e s g e n t l y d i p p i n g p a n e l s of Karmutsen, Kunga and  Yakoun  r o c k s , r a r e l y f o l d e d , which t r e n d e a s t t o n o r t h - e a s t  north-  ward, c u t by a number of steep b l o c k f a u l t s p.  (Sutherland  dip  Brown,  1968,  195). The  magnetite and is  and  major  iron  ore  Jedway south similar  minesites  deposits  that  the  monzonitic  highs  major  relief Jib  suggests  of  that  Jib the  two  a l s o be  related  Brown, 1968,  p. 194; B.C.,  P o i n t Langford  slightly these  more  located short form  Pluton on  the  distance part  Collision  of Bay  has  lower  granitic  to  quartz  offshore Point  plutons  are  Burnaby  Tasu be  nT,  of  Garnet  younger.  of of  peaks  deposits  extend  one  the  Island  and  dioritic  presence  magnetite  of  northeast  the  drilling  are  no  and  to extensive  p l u t o n s compared t o the  Carpenter  1,000  The  over  to the  the  quartz magnetic  magnetite  east  of  the  and main  m i n e r a l i z a t i o n (Sutherland  a s s o c i a t e d w i t h the  plutons  acidic  the  phase may  the  to  Ann.Rept. 1963).  Magnetic highs and  for  than  confirmed  part  g e o l o g y of t h e s e  Burnaby)  smaller  anomaly may  The  intrusive greater  in  southeastern  previously  Offshore  has  correspond  J i b on  (south  Jedway s t o c k s .  south  at  described  highs, with  dioritic  highs  of H a r r i e t Harbour.  although  magnetic quartz  to  magnetic  relief  Jedway and  magnetic corner overlies Langford roughly  a  and  the  composition  of  The  Island  partly  exposed The  o u t l i n e d by  The  granitic  magnetic and  high  extending  stock  Point the  Carpenter, reflect  J i b plutons.  Kunghit  Pluton.  may  monzonitic  expression.  of  Collision,  that  Langford  2900 and  3200  a may and nT  125  countour  lines.  The Upper J u r a s s i c  Burnaby  Island Pluton of mafic  r i c h q u a r t z monzonite, though o n l y p a r t i a l l y covered  by t h e aeromag-  n e t i c s u r v e y , would be expected t o d i s p l a y high magnetic Migmatites exposed  on K u n g h i t  low-moderate  magnetic  generally  Island.  hornblende  I s l a n d , west  v o l c a n i c s comprises of  o f mixed  relief.  circular  low magnetic  Boundaries  diorite  o f Luxana  pattern  t o l o b a t e magnetic  o f Karmutsen  l i m e s t o n e s cannot be determined  similar  lavas  and a m p h i b o l i t e  Bay, have  The magnetic  values,  relief.  associated  of  Karmutsen  r i d g e s and t r o u g h s  to  northern  o r greenstones  Moresby  and  Kunga  from magnetic d a t a .  NORTHEASTERN GRAHAM ISLAND  A (Fig. Oil  constant  33) was f l o w n Corporation  terrain  over  northeastern  (Grinsfelder,  s t r u c t u r e o f t h e northwest  1960)  airborne  Graham  magnetic  rocks  wells  included  Island f o r R i c h f i e l d  i n order  to  map  penetrated volcanic  by  four  breccias  Richfield and  and  cores  Magnetic  indicated  basement  property a n a l y s i s of Tartu  high magnetic s u s c e p t i b i l i t y  e t aj_  conglomerate,  r h y o l i t e and massive b a s a l t s o f t h e Masset T a r t u f a c i e s Brown, 1968).  survey  p o r t i o n o f t h e Queen C h a r l o t t e B a s i n .  Basement exploratory  clearance  (Sutherland  v o l c a n i c samples  and s t a b l e remnant  magnetization. The comprise  shorter  northern  portion  amplitude  magnetic  pattern  wavelength,  higher  of the survey  anomalies  in  the  of  area  northeastern amplitude and  southern  Graham  anomalies  longer portion.  Island i n the  wavelength,lower The  magnetic  126  ' p r o v i n c e s ' c o r r e s p o n d i n p a r t t o two major a  'magnetic'  Masset No. Pliocene  r i d g e t h a t extends  1 well. time  eastern  southeastward from  vicinity  G e o l o g i c d a t a ( S u t h e r l a n d Brown, 1968)  structure  portion  s u b - b a s i n s s e p a r a t e d by  of  map  Graham  (Grinsfelder,  Island  also  1960)  indicate  that the  of  the  and a ( ? ) covers  presence  the of  a  basement r i d g e . In the n o r t h e r n s u b - b a s i n , a p a t t e r n of h i g h - a m p l i t u d e , l o b a t e and b i f u r c a t i n g source  rocks  pattern  and  anomalies i n d i c a t e s  possible  i n the western  basement  portion  of  s h a l l o w depths t o  faulting. the  remnant  (normal  c i r c u l a r magnetic Hill, on  reverse)  sediment  basement f l e x u r e .  c o v e r as t h i n  t h e nearby Tow H i l l In  the  reflect  topography  that  and  field  induced  dipole  reflects  by  partial  vector addition  magnetizations.  A  h i g h w i t h r e l i e f of 250 nT c o r r e s p o n d s t o Argonaut  a Pleistocene glacial  a local  relief  or  magnetic  sub-basin  c a n c e l l a t i o n o r r e i n f o r c e m e n t of the t o t a l of  A  Masset  as  f e a t u r e t h a t appears t o have developed Depth t o basement e s t i m a t e s suggests  2000' compared t o g r e a t e r than  6000'  at  well. southern  thicker  s u b - b a s i n magnetic  sediment  infill  s l o p e s eastward  toward  over the  an  anomalies  of  irregular  central  lower  basement  portion  of  the  Queen C h a r l o t t e B a s i n .  RELATIONSHIP OF MAGNETIC ANOMALIES TO MAGNETIC ROCK PROPERTIES  The patterns  and  preceeding  magnetic  correspondences  to  rock  the  discussion properties  geologic  on  aeromagnetic  suggests  units,  rock  a  number types  anomaly of  and  basic major  127  structures  on  the  Queen  Charlotte  Islands.  Generalized  anomaly  t y p e s and magnetic c h a r a c t e r i s t i c s are summarized i n T a b l e X. As  expected  from  measurements the h i g h e s t with  the  Tertiary  susceptibility  Masset  and  anomaly f i e l d ,  reverse  polarities  prominently  volcanics  extent  of the  high  is  a  ties  rock  and  volcanics, relief  and  intensity  magnetic rock  appear t o  ity.  A l t e r a t i o n and  addition  to  signature  high  S iO ^  constrained  relative  the  content  and  lateral  a m p l i t u d e of  magnetic  the  v a r i e t y of  A n a l y s i s of  rock  the  proper-  v a r i e t i e s to  have  susceptibilities. associated  with  the  Karmutsen  i n t r u s i v e contacts,  are  than  what  might  from  be  In p a r t i c u l a r , the  weaker  'B'  expected the  may  explain  the  of  aeromagnetic  mode magnetic  p o s s i b l e demagnetization bias  The  the  depends on  rock.  normal  of  near  reflect  sample  of  the  volcanics.  those  properties.  would  plutons.  reflecting  showed the more b a s i c  anomalies  excepting  pattern  has  The  invaded  of the p l u t o n i c rocks  Magnetic  that  the p l u t o n s  t y p e of  somewhat h i g h e r magnetic  associated  post-tectonic  response  function  plutons.  anomalies a s s o c i a t e d w i t h intrusive  dipole  aeromagnetic  viscosity  epizonal  and  i s o f t e n a s s o c i a t e d w i t h the  plutons  correspondingly  intensity  c o m p r i s e s the l a r g e r p e r c e n t a g e of  a magnetic  developed  post-tectonic  remnant  a m p l i t u d e magnetic anomalies are  Because remnant m a g n e t i z a t i o n Masset  and  due  to  discrepancy.  lower  measured patterns  susceptibilreheating,  in  Because  of  similarity  i n remnant m a g n e t i z a t i o n  d i r e c t i o n s t o Masset v o l c a n i c s ,  H i c k e n and  I r v i n g (1977) suggested t h a t the Karmutsen v o l c a n i c s  may  have been w e a k l y r e m a g n e t i z e d d u r i n g T e r t i a r y t i m e . The  low  amplitude  subdued  aeromagnetic  pattern  of  the  128  TABLE X RELATIONSHIP OF MAGNETIC ANOMALIES AND MAGNETIC ROCK PROPERTIES TO GEOLOGIC UNITS QUEEN CHARLOTTE ISLANDS  i  FORMATION/UNIT  MAGNETIC ROCK PROPERTY  MAGNETIC ANOMALY CHARACTERISTICS  PIio-Pleistocene Tow H i l l S i l l s  High S u s c e p t i b i l i t y High Q  Not e s t a b l i s h e d  Lower-Middle  High S u s c e p t i b i l i t y  High amplitude, mediumshort wavelengths; Magnetic d i p o l e s  Middle J u r a s s i c Yakoun Volcanics  Variable S u s c e p t i b i l i t y Generally Low  Low amplitude Long wavelength  Upper T r i a s s i c  High o r Low S u s c e p t i b i l i t y  Low-medium amplitude, medium wavelength (High amplitudes near i n t r u s i v e contacts)  Cretaceous-Tertiary Post Tectonic Plutons  High S u s c e p t i b i l i t y Low Q ( V a r i a t i o n s due to rock type)  Medium-high amplitude Medium-short wavelength (Higher amplitudes associated with more basic rock types)  Upper J u r a s s i c Syntectonic Plutons  Medium-High S u s c e p t i b i l i t y Low Q ( V a r i a t i o n s due to rock type)  Low-medium amplitude Medium wavelengths  Tertiary  129  Yakoun v o l c a n i c s i s e x p e c t a b l e bilities. sive  The  rocks  from g e n e r a l l y low magnetic s u s c e p t i -  low-medium a m p l i t u d e  reflects  magnetic  response  of  intensities  syntectonic  somewhat  intru-  weaker  than  i n d i c a t e d by medium-high s u s c e p t i b i l i t i e s . Major maps by  a  linear  e l o n g a t e magnetic A relate specific ical and  wrench  pattern,  of  rock  geological  complexities  cation however,  solutions.  the  indicated  as  a  uncertainties properties  and  steep  the  arise  and  on  the  aeromagnetic  magnetic  gradient  or  of  plutons)  magnetic  data  with can  attempting  to  patterns  to  aeromagnetic  both  ( i . e . Karmutsen w i t h  Combined  when  Queen C h a r l o t t e  similarity  post-tectonic  difficult.  either  u n i t s on  magnetic p a t t e r n s  Masset w i t h  are  trough.  number  magnetic  faults  magnetic  constrain  rock  syntectonic  make unique other  Islands.  rock  the  properties plutons  type  geophysical number  Geolog-  and  identifiinformation  of  possible  130  CHAPTER VII  MAGNETIC ANOMALIES OF WESTERN HECATE STRAIT AND  NORTHWESTERN QUEEN CHARLOTTE SOUND  INTRODUCTION Total  magnetic f i e l d  intensity  was  km  of ships t r a c k during  I.O.U.B.C. C r u i s e No.  of  the  run  magnetic  seismic  profiling  r o c k s and Basin. data  survey,  (chapter  in conjunction  VIII),  was  s t r u c t u r e a l o n g t h e western  Acquisition,  1.  76-10. with  along The  high  a i d mapping  1287  purpose  resolution of  basement  margin of the Queen C h a r l o t t e  reduction, correction  are d e s c r i b e d i n Appendix  f i e l d map  to  measured  The  and  error  contoured  assessment  residual  of  magnetic  ( w i t h r e s p e c t t o I.G.R.F.) i s shown i n F i g . 34 ( i n pocket)  and magnetic anomaly p r o f i l e s i n F i g . 35. The  data c o l l e c t e d f o r t h i s  study  by marine magnetic s u r v e y d a t a from  Queen  1974;  F i g . 34)  Tiffin  adjacent al,  and  Currie,  1976;  see  t o Queen C h a r l o t t e Sound  1971;  S r i v a s t a v a , 1973).  As  a  constant  correction  to  Cruise Fig.  No.  minimize  Murrary  75-22) have a l s o been  and  the  1971;  (Tiffin,  oceanic  area  S r i v a s t a v a et  l a r g e d i s c r e p a n c i e s (80-100  R e l e v a n t p o r t i o n s of a s u r v e y conducted Queen C h a r l o t t e Sound by J.W.  been supplemented  C h a r l o t t e Sound  (Srivastava,  were found when t h e o c e a n i c s u r v e y d a t a was data  has  compared t o l a t e r error  i n 1975 and R.D.  was  survey  introduced.  i n Hecate S t r a i t Macdonald  included ( f o r line  nT)  and  (I.O.U.B.C.  location,  see  1). The n o r t h e r n and s o u t h e a s t e r n Moresby I s l a n d  aeromagnetic  131  s u r v e y d a t a ( s e e p r e v i o u s d i s c u s s i o n ) has been i n c o r p o r a t e d i n t o t h e r e s i d u a l magnetic f i e l d made t o s t r i c t l y airborne  data  elevation  map ( F i g . 3 4 ) , a l t h o u g h no attempt  reconcile  sets.  the d i f f e r e n t  For northern  ( r a t h e r than  constant  integrated  with  t h e marine  peak f i e l d  s t r e n g t h over c o n t i g u o u s  by s i m p l e s h i f t t o l e v e l  data  e l e v a t i o n s o f marine and  Moresby  terrain because  was  filtered  by s i m p l e  data  areas.  d a t a was  i n peak t o  Data s e t s were combined  data  (1600 nT c o n t o u r  = 0  along boundary p o i n t s .  f o r southeastern  nonweighted  the constant  of s i m i l a r i t y  o f aeromagnetic  aeromagnetic  Island,  clearance) survey  nT, r e l a t i v e t o IGRF) t o p r o v i d e coherency The  has been  smoothing  over  Moresby a 0.5  Island  inch sq.  g r i d b e f o r e b e i n g combined w i t h t h e marine d a t a (2750 nT c o n t o u r = 0 nT,  r e l a t i v e t o IGRF).  was  required  represented  because  survey type,  procedure airborne  would data  aeromagnetic 1978). sets  a i r b o r n e survey  and  greater  does n o t r e f l e c t  sample d e n s i t y , and e l e v a t i o n . r e q u i r e an e q u i v a l e n t source before  data,  c o n t i n u a t i o n , removal  and boundary  detail differ-  southeastern  i n integrating Moresby  integration  r e p r e s e n t a t i o n of the o f t h e IGRF  the airborne  Island  and  Hecate  procedure  g r a d i e n t and c u r v a t u r e o f t h e magnetic  s e t s near t h e i r common boundary.  Strict  from t h e  c o r r e c t i o n s (Bhattacharyya  e x p l a i n e d by t h e s i m p l e i n t e r g r a t i o n in  wavelength  data  t o t h e a d j o i n i n g marine area but o n l y d i f f e r e n c e s  Difficulties of  the shorter  by t h e draped  ences i n geology in  Upward c o n t i n u a t i o n o f t h e aeromagnetic  and marine Strait  employed  fields  e_t _al_, data  can be  and changes  i n t h e two d a t a  132  INTERPRETATION PROCEDURE  The completely ties,  obscured  partly  method  use of marine magnetic d a t a t o i n f e r t h e geology o f basement  and p a r t l y  from  and  of t h e manyfold  types.  Magnetic  Charlotte  Islands  and t h e i r  associated  of t h e g e o p h y s i c a l  property does  magnetic  Sound  makes  pondences but a l s o r e l i e s from nearby defined  constrained  land.  use o f such  on e x t e n s i o n  gross  structural and g e o l o g i c  trends,  fields.  combined  with  seismic magnetic  p r e d i c t i o n of gross must  be  considered  r e f i n e the present  inter-  northwestern corres-  distributions  c o n t i n u a t i o n of  t h e i n t e r p r e t a t i o n i s more  closely  u n i t s have been mapped w i t h some degree of  s h e l f and b a s i n p o r t i o n s o f t h e survey seismic,  and  i s direct  units  The  1ithology-anomaly  c e r t a i n t y t o t h e i n n e r s h e l f edge, and beyond.  lution  considerable  geologic  of known rock  In areas where t h e r e  between  and aeromagnetic  provide  o f t h e g e o l o g y of western Hecate S t r a i t  Queen C h a r l o t t e  well  rock  uncertain-  correspondences  on e m p i r i c a l c o r r e l a t i o n s between  structures  pretation  ambiguity  because  t h e Queen  information  involves considerable  because o f the i n h e r e n t  anomalies and rock data  rock  refraction, data  lithology.  area, bathymetric, gravity,  provide  and  addtional  Speculation  preliminary.  F o r both t h e i n n e r high  reso-  data  when  evidence  for  well  about age and s t r u c t u r e  Additional  data  will  certainly  interpretation.  DEPTH TO BASEMENT ESTIMATES  Depth  t o basement  estimates  have  been  calculated  from  133  the t o t a l f i e l d s t r u c t u r e map (Fig.  of t h e western  36 i n p o c k e t ) .  isopach Fig.  magnetic d a t a t o a i d i n c o m p i l a t i o n o f a s i m p l i f i e d  map  of  p o r t i o n of t h e Queen  A d d i t i o n a l data  Neogene  Skonun  sources  sediments  Charlotte Basin  include a  (Shouldice,  1 8 ) , a b a s i n model d e r i v e d f r o m i s o s t a t i c g r a v i t y  (Stacey,  1973;  see  anomaly d a t a  1975, see F i g . 1 9 ) , basement depths from e x p l o r a t o r y w e l l s  (Shouldice,  1973; S h e l l  refraction (Chapter  simplified  profiles VIII),  Canada  (Mahannah,  limited  Well  H i s t o r y Reports)  1965).  because o f  Seismic  shallow  and  seismic  reflection  depth  profiles  of p e n e t r a t i o n ,  were used t o d e f i n e t h e b a s i n edge. Depths number (Am,  of g r a p h i c  1972).  t o magnetic  basement  were  calculated  using  ( e m p i r i c a l ) e s t i m a t o r s and c h a r a c t e r i s t i c  Where t h e azimuth  o f magnetic  profiles  curves  deviated  p e r p e n d i c u l a r t o t h e s t r i k e o f t h e magnetic body, t h e depth was m u l t i p l i e d by t h e c o s i n e o f t h e d e v i a t i o n . that  the d i r e c t i o n  of magnetization  ation:  26°E, d e c l i n a t i o n :  71°N,  from  estimate  I t has been assumed  does not d e p a r t  from t h a t o f t h e c u r r e n t e a r t h ' s f i e l d  significantly  ( f o r the survey area,  total  a  intensity  (F):  inclin-  56,500 nT;  Dawson and N e w i t t , 1977). Comparison with  control  points  of a  s u b j e c t i v e average  provided  by o t h e r  data  sources  most e s t i m a t e s s h o u l d be a c c u r a t e w i t h i n +10-15%. magnetic effects  features, or  where  interpreted  pre-Skonun subcrop  non-magnetic ( e . g . s o u t h e r n not  mappable  ciliation  from  strong  of a l l data  sources  data.  i s known  was  Final  estimates  suggests  that  In areas o f broad  supra-basement  Hecate s u b - b a s i n )  magnetic  o f depth  or  magnetic  assumed  to  be  basement s t r u c t u r e was integration  and  necessarily interpretative.  reconThe  134  placement  and o r i e n t a t i o n  o f major depocentres  and basement r i d g e s  i s c o n s i d e r e d a c c u r a t e a l t h o u g h s m a l l changes i n basement r e l i e f and f a u l t s are not shown on t h e s t r u c t u r e map.  INTERPRETATION OF MARINE MAGNETIC ANOMALIES  Interpretation  of  marine  f o l l o w s , based on d a t a a c q u i r e d from: of  magnetic  anomaly  patterns  1) t h e i n n e r s h e l f r e g i o n e a s t  s o u t h e r n Queen C h a r l o t t e I s l a n d s , 2) Moresby r i d g e and Hecate and  Charlotte Strait),  subbasins  Charlotte Basin  3) n o r t h w e s t e r n Queen C h a r l o t t e  immediately Interpreted Neogene  o f t h e Queen  adjacent basement  sediments  to  and  Queen  Charlotte  on t h e i n n e r s h e l f ,  basement  Hecate  Sound, 4) t h e , o c e a n i c a r e a  northwestern  seacrop  (western  structure  Sound.  subcrop  contours  of  beneath  t h e Queen  C h a r l o t t e B a s i n a r e shown i n F i g . 36.  Inner S h e l f  The Cenozoic onshore Basin  inner  sedimentary  shelf  region,  and c r y s t a l l i n e  exposes  Mesozoic-mid  r o c k s as s e a c r o p , extends  from  Queen C h a r l o t t e I s l a n d s t o t h e edge o f t h e Neogene C h a r l o t t e ( F i g . 3 6 ) . The edge o f t h e b a s i n does not c o r r e s p o n d  change i n submarine topography, Fig.  which  except  36 t o F i g . 41) but marks t h e l i m i t  o f f Kunghit o f landward  Island  with a (compare  encroachment o f  Neogene Skonun sediments. From  Louise  Island  'basement' (pre-Skonun) seacrop  south  to  Kunghit  Island  pattern of the inner shelf  the  has been  135  mapped data  ( F i g . 36)  and  channels  onshore geology and  survey  f r o m magnetic  inlets  area,  concerning  are  of  also  ( F i g . 34)  ( F i g . 42).  The  the c o a s t a l geology  bathymetric  Expected  e a s t e r n Moresby shown.  and  seacrop  patterns  Island, outside  following  ( F i g . 41)  general  the  in  marine  observations  have a i d e d p r e d i c t i o n and  mapping  of  seacrop. 1)  Upper J u r a s s i c  Yakoun a n d e s i t i c  competent rock  type,  c o a s t of s o u t h e r n  2)  exposed  on  small  Laskeek  Bay).  Ice-deepened  bathymetric  Paleozoic-Mesozoic  Upper  (e.g.  deeper  o l d e r r o c k s as  small  ridges  Juan  Karmutsen  4)  Structural fault  Overlying  not be  system  strike-slip  faults  the  in  cut  ?Upper  succession  v o l c a n i c s are  and  exposing  exposed  anticlinal  flanking  (with faults)  rock  along an has  outcrop  the  and  sediment  as  the  homoclinal cover  and  Rennel-Louscoone  echelon  folds  produced pattern  commonly f o l l o w Kunga  thin-bedded  likely  may  preserved.  response  predictable  is  east  Channel)  into  stratigraphic  the  (particularly  Perez  westward  eroded c o r e s of w r e n c h - r e l a t e d  o r may  along  a more  seacrop.  Triassic  structures.  islets  as  Queen C h a r l o t t e I s l a n d s and  channels  progressively  3)  forms  agglomerate,  carbonaceous  in  and  conjugate  some  areas  (Chapter  limestones nature  wrench  X).  a  Wrench  because  of i t s  ( S u t h e r l a n d Brown,  1968, p. 5 6 ) . From L o u i s e I s l a n d south  to Lyell  I s l a n d seacrop  patterns  represent  136  an e x t e n s i o n of c o a s t a l geology sub-basin  edge.  The  most  and  s t r u c t u r e e a s t toward  characteristic  anomaly p a t t e r n o f f L o u i s e I s l a n d trough  t h a t extends  a c r o s s the  feature  of  i s a southeast  inner shelf  the Hecate  the  magnetic  t r e n d i n g magnetic  t o a p o s s i b l e submarine  e x t e n s i o n of the S a n d s p i t F a u l t i n Hecate s u b - b a s i n  ( F i g . 36).  trough  offshore exten-  sion  ( w i t h magnetic  of  major  the  Rennel  through  lows of -lOOnT) r e p r e s e n t s an  wrench f a u l t  going  of L o u i s e  Island,  the  magnetic c o n t o u r s t r e n d i n a more s o u t h e r l y d i r e c t i o n r e f l e c t i n g  the  notable d e f l e c t i o n  structures.  at Louise  Island  South  ( e a s t of the L o u i s e P l u t o n ) i n  the main s t r a n d of the Rennel-Louscoone The 31)  g e o l o g y of Laskeek Bay  i s c h a r a c t e r i z e d by  a  series  and  includes a to  fold  fault  that  parallel  and  lateral  ( F i g . 61)  related  subparallel fault  right  system  The  system. (see c r o s s - s e c t i o n B-B ,  of  small  related folds.  E a s t of the Louscoone f a u l t  southern  Island  of  Louise  Karmutsen  to northern L y e l l  greenstones  exposed as o u t c r o p and fault  bounded  erates  are  Islands.  as  Yakoun seacrop  Towards the c e n t r a l  I s l a n d ) s t r u c t u r e and extension  of  the  anticline  southwest  s o u t h e a s t toward  Kunga  seacrop.  sync!ine,  exposed  and  seacrop  Rennel  fault  Island  limestones  pyroclastics as  bounded  zone and  Further east  and  an  from  anticlinal  belt  and  argillites  i n Laskeek and  outcrop  on  fault  bounded,  Reef  of the main s t r a n d , extends  from  in a  agglomand  (west  doubly  are  Bay,  andesitic  p a t t e r n s are r e l a t e d t o the A  wrench  extending  p o r t i o n of Laskeek Bay  Fault.  Fig.  1  Lost  of Reef southeast plunging  Louise  Reef I s l a n d , e x p o s i n g Karmutsen v o l c a n i c s and  Island Kunga  Limestones. The  c o m p a r a t i v e l y low magnetic v a l u e s i n the Laskeek  Bay  137  region  partially  bilities)  associated  greenstones. could  be  reflects  the  with  Partial  weak  magnetization  (low  suscepti-  pyroclastics  and  Karmutsen  primary  magnetite)  Yakoun  demagnetization  (loss  a s s o c i a t e d w i t h the s h e a r i n g and  of  cataclasis  of w a l l  rocks  along the major wrench f a u l t s and s u b s i d i a r y s p l a y s . North  of  the  Rennel  e l a s t i c s of the Haida Formation belt  t h a t extends  Island been  and cut  from  Graham  Hecate S t r a i t . into  Haida  Albian-Turonian  are exposed Island  northern  Seacrop  (subbasin  edge) i s p r o b a b l y d i s c o n t i n u o u s .  volcanoes  may  time  Louise  of  east  Island  marine  within  ( S u t h e r l a n d Brown, p. 92) t o i n t e r v e n i n g On  the  inner shelf,  of the mapped f o l d indented  1968,  belts,  s h e l f edge.  of  Sandspit  by  a thin  p.  probable  92).  The  Yakoun r o c k s  low  has  agglomerates amplitude  is similar  of  Fault  the  cover  themselves  Skidegate  of  have Basin  lows.  south of the Rennel  Island  have  elastics,  Fault  and  Yakoun v o l c a n i c s p r o b a b l y seacrop  Reef  Yakoun a n d e s i t i c  to  marine  the  Louise  Remnants of o l d Yakoun  have been b l a n k e t e d  deposition  continuous  appears  the to  marine  northern  sediments, s i n c e eroded, o r the v o l c a n o e s may  restricted  vent  to  Most of Cumshewa I n l e t  sediments.  a t one  i n an almost  southeast  extending  marine  of  Fault,  been i n d i c a t e d and  tuffs  magnetic  t o the  as a  east  to  the  possible  ( S u t h e r l a n d Brown, anomalies  aeromagnetic  over  response  the over  the v o l c a n i c s on n o r t h e r n Moresby I s l a n d . South indicate  of Cumshewa P o i n t h i g h magnetic  a submarine e x t e n s i o n o f  the  h i g h a m p l i t u d e anomaly i s p a r t i c u l a r l y total  magnetic  intensity  map  of  values  ( 900  nT)  Cumshewa P l u t o n .  A  n o t i c e a b l e on  simplified  the  Queen  the  Charlotte  similar  Basin  138  (Shouldice, suggest  1973;  see  F i g . 20).  High  magnetic  values  a p o s s i b l e s m a l l p l u t o n u n d e r l y i n g Laskeek Bay  ( 650  nT)  southwest  of  Reef I s l a n d . Seacrop Ramsay  Islands  coverage  region.)  On  from These  narrow  does  not  the  volcanics dip  of  the  over  east  of  Masset  the  I s l a n d , the  the  dates  Tar  east Tar  of  21+1  Lyell  Dana  inner Tar  porphyries  and  and  I s l a n d s ; see to  shelf  Islands  and  facies. in  this  (east  Islands  and  dykes  (Masset  27+2 Ma  were  of  obtained  d i s c u s s i o n Chapter  southeast  Ramsay I s l a n d ( S u t h e r l a n d Brown, 1968, feldspar  shelf  most of Ramsay I s l a n d Dana v o l c a n i c b r e c c i a s are  samples f r o m  on  extend  Lyell  (Whole rock K-Ar  sub-basin  inner  volcanics  northeastern  I s l a n d ) and  exposed.  the  comprises  (Magnetic  Lyell  on  (20-30°) toward north-northeast F i g . 5).  the  Hecate  (15-25°)  Intrusive  hypabyssal  III.)  on  biotitic  equivalents)  are  exposed on s o u t h e a s t e r n L y e l l I s l a n d .  Fig.  36  as  volcanics  The  southern  limit  the  northern  edge of  probably  rest  seacrop  normally  channel  Wall  of L y e l l  Perez  rock  exposure  Perez  Channel.  Karmutsen  sandstone and  Here  do  not  extend  in  Masset  volcanics.  Island indicate  Channel  has  been  cut  The  t h a t Masset  northwards  into  as  exposure  the  predominately  of Karmutsen v o l c a n i c s and along  the  southern  i n c l u d e s Kunga l i m e s t o n e s , Lower Cretaceous  e r a t e s and  i s indicated  Bay.  southwesterly d i p p i n g panels equivalents.  Juan  h i g h l y magnetic,  i n s o u t h e r n Laskeek Juan  Masset  unconformably on  low magnetic v a l u e s n o r t h e a s t volcanics,  of  Upper J u r a s s i c  metamorphic  p o r t i o n of  the  Longarm conglom-  Burnaby  Island Pluton.  D e p o s i t i o n and t u r b i d i t y r e d i s t r i b u t i o n o f Longarm e l a s t i c s  in fault  139  troughs  e a s t of  basin f i l l  the  Louscoone f a u l t  probably  represented  extensive  t h a t o r i g i n a l l y covered much o f the o u t e r p o r t i o n o f Juan  Perez  Channel.  trend  roughly  Magnetic  contours  east-southeast,  east  of  parallel  the  to  Louscoone  structural  Fault, elements  r e l a t e d t o the wrench system. On  the  h i g h amplitude acterize  wide  ( 900  basement  inner  shelf,  northeast  of  nT), s h o r t wavelength magnetic  seacrop.  The  anomaly  pattern  e a s t over the n o r t h e a s t t r e n d i n g Moresby r i d g e . of  these  linear  anomalies  i s discussed  in  the  continues  char-  further  (A p o s s i b l e  following  source  section.)  Kunghit  Island  Karmutsen  north-  and  i n n e r s h e l f from Burnaby I s l a n d south  comprises  Yakoun  easterly  trending homoclinal persist  titled  v o l c a n i c s and  by  anomalies  ?Upper  gently  deformed  Jurassic  to  the  been  Southern panels  patterns  inferred  mainly  volcanic  sandstones  discriminated of  on  the  Yakoun vents  and  from  Karmutsen Kunga  b a s i s of  Group  I s l a n d s , seacrop  of  of  intruded  and  indicated edge  The  arcuate  by  magnetic  and  beyond  Moresby  coastal  and  magnetic  Kunghit  geology  v o l c a n i c s and  and  (Chapter  of  Islands  bathymetric  nonmagnetic  anomaly  cones out  Yakoun  are  system.  VI)  Yakoun  cannot  patterns.  the  middle  If  rocks  may  be  more  be the  Jurassic  a l o n g the e a s t c o a s t t o s o u t h e r n of  to  panels  plutons.  t h a t , as  limestones  that b u i l t  s h a l l o w marine b a s i n extends Charlotte  east  folded  limestones,  C h a r l o t t e sub-basin  Seacrop  Weekly magnetic  and  Kunga  r e l a t e d t o the Louscoone wrench f a u l t  data.  The  indicate faults. Seacrop on the  line  anomalies  t r e n d of steep magnetic g r a d i e n t s t h a t t r e n d n o r t h and  west may  have  Burnaby I s l a n d ,  Queen  extensive  140  than  indicated  Formation shelf.  in Fig.  36.  Thin  a r e i n f e r r e d t o seacrop  bedded  limestones  o f t h e Kunga  over much o f t h e s o u t h e r n  F a u l t s and t i g h t f o l d s , e a s i l y p r e s e r v e d  inner  i n t h e s e r o c k s , may  c h a r a c t e r i z e much o f t h e r e g i o n . South o f K u n g h i t  I s l a n d magnetic anomalies t r e n d  e a s t , p a r a l l e l t o trend of c o a s t a l geology.  High a m p l i t u d e magnetic  anomalies may be a s s o c i a t e d w i t h an o f f s h o r e e x t e n s i o n sive  contact  volcanics. pluton,  of  The  the  San  southern  characterized  Christoval  extent  by  Batholith  of the J u r a s s i c  low-moderate  south-  magnetic  of the i n t r u and  Karmutsen  Luxana  relief  migmatic  on  Kunghit  I s l a n d , i s not known. Sediments o f t h e Lower C r e t a c e o u s Longarm F o r m a t i o n and Upper Cretaceous Queen C h a r l o t t e their  occurrence  on t h e s o u t h e r n  Group a r e absent inner  shelf.  or r e s t r i c t e d i n Non-deposition  e r o s i o n o f t h e s e sediments i s i n d i c a t e d by l i m i t e d Longarm  elastics  on  resistence t o erosion rocks.  During  Islands  probably  southern  Queen  Charlotte  compared t o Kunga  exposure o f o n l y  Islands  limestones  a t e c t o n i c highland  t o r e s t r i c t e d f a u l t bounded t r o u g h s along l i n k a g e and t h e S k i d e g a t e  that  and  weaker  and c r y s t a l l i n e  t h e C r e t a c e o u s much o f t h e s o u t h e r n formed  or  Queen  Charlotte  supplied d e t r i t u s  t h e Rennel-Louscoone f a u l t  Basin t o the north,  bypassing  much o f t h e  e a s t e r n p o r t i o n o f s o u t h e r n Queen C h a r l o t t e I s l a n d s .  Queen C h a r l o t t e  The Moresby Ridge  Basin  pattern  of  magnetic  and Hecate and C h a r l o t t e  anomalies  that  sub-basins  characterize  i s a p r o d u c t of  141  depth  to  magnetic  basement that the  changes  "the  source in  pattern  rock,  rock  of  structure,  magnetizations.  broad  lobate,  Queen C h a r l o t t e B a s i n was  the  and  intra  Shouldice  and  and  supra-  (1973)  noted  b i f u r c a t i n g anomalies  r e s u l t of v a r i a t i o n s i n  over  thickness  of T e r t i a r y sediment o v e r l y i n g v o l c a n i c basement".  Hecate  Sub-basin:The  Hecate  Moresby R i d g e ( F i g . 36) contain by  basin  indented  of  terizes  the  35)  thick  saddles  possible  broad,  or  fault  low  relief  origin  Neogene  relief  that  survey  area.  attenuation  sediment  source  values  of  550  A nT  graben-like the  southeast  of  cover  rocks.  exceed  A sediments  low  are  east  of  separated  ridges.  located  magnetic  w e s t e r n p o r t i o n of the  reflects  basement  Island  and  Steepest  east  of  the  that  charac-  s h e l f edge o f f L y e l l and Ramsay I s l a n d s . The  and  north  of Neogene nonmarine s e d i m e n t s ,  nose-shaped  slopes  located  c o m p r i s e s a number of major d e p o c e n t e r s t h a t  g r e a t e r than 4 km  elongate,  sub-basin,  Queen C h a r l o t t e B a s i n  the  and  broad  total  magnetic  nonmagnetic magnetic  covers  the  trough  containing  Cretaceous  pattern  As  due  to  magnetic  with  magnetic  plateau  Basin  field  34  weakly  northeastern  Skidegate  i n t o Hecate S t r a i t .  or  (Figs.  portion  of  the  predominately  marine  extends  Louise  discussed  from  previously,  the  t r e n d of magnetic anomalies i s c o n s i s t e n t w i t h the i n t e r p r e t a t i o n of an  offshore  associated shelf  extension with  edge the  the basin  of Rennel  the  wrench  extends  v i c i n i t y of the Sockeye E-66  marine  at  and  basin  fault least  B-10  and  faults  and  folds  From  the  inner  system. 30  wells.  km  along The  trend  to  Sockeye E-66  the well  142  KILOMETRES  Fig.  35  M a g n e t i c anomaly p r o f i l e s a l o n g s h i p ' s Hecate S t r a i t .  t r a c k i n southwestern  143  penetrated  152  meters  of  F o r m a t i o n ? ) , bottoming while  the  Shell  Canada  1975;  B-10  well Ltd.,  see F i g . 19)  presence  of  Cretaceous  nonmarine  i n Yakoun v o l c a n i c s ( S h e l l bottomed  i n Cretaceous  1968b).  Isostatic  (Skidegate  Canada L t d . 1968c)  elastics  gravity  (152+  meters;  anomalies  (Stacey,  i n t h e v i c i n i t y o f t h e Sockeye w e l l s suggest  l e s s dense Cretaceous  rocks.  of the Hecate s u b - b a s i n t h e Tyee N-39 Cretaceous  elastics  ( I n the  the  northern p o r t i o n  w e l l penetrated  101 meters of  s e c t i o n ( S h e l l Canada L t d . , 1968a).) Near t h e c e n t r a l p o r t i o n o f s o u t h e r n Hecate s u b b a s i n  trend  of  magnetic  parallelling lelling  the  anomalies  Skidegate  the t r e n d of  Fault.  Although  Sandspit  trend  changes Basin  from  to  an  of  of  evidence  of  late  Neogene  has  not  (chapter V I I I ) ,  or  to  connecting  Moresby I s l a n d (azimuth  144°)  the may  paral-  faulting  Sandspit  along  been r e c o g n i z e d  the  on  high  a basement d i s c o n t i n u i t y  Sandspit be  118°,  146°,  a p o s s i b l e o f f s h o r e e x t e n s i o n of the  i n Hecate s u b - b a s i n  zone  azimuth  azimuth  resolution seismic p r o f i l e s fault  an  the  Fault  present  on  in this  northeastern area.  I f so,  i t would l i k e l y be l o c a t e d along t r e n d of a magnetic t r o u g h , 5-10 wide t h a t extends Ridge.  65 km f r o m e a s t of L o u i s e  A similar  magnetic  trough  zone where i t c r o s s e s S k i d e g a t e wrench  displacement  has  rocks  occurred  displaced  southeast  fault  and  i t s o f f s h o r e e x t e n s i o n , which  the  south,  probably  ( S u t h e r l a n d Brown, 1968).  the  the  Basin  the  of  on  ( F i g . 34).  Skidegate  of  east  I s l a n d south t o Moresby  c h a r a c t e r i z e s the  Inlet  basin  predates O f f s e t of  Fault  fault  Movement  Rennel  on  lateral  trace on  the  fault  extension, may  the  bounds S k i d e g a t e  movement the  Sandspit  If right  Sandspit  presumed  trend.  km  be  Rennel  Basin  to  Sandspit  Fault i s therefore  144  i n d i c a t e d u n l e s s i t t e r m i n a t e s a t or near t h e S a n d s p i t e x t e n s i o n . Subcrop south of t h e Rennel f a u l t s u b - b a s i n may  l a r g e l y comprise  ments.  The  high  Masset  Dana  Islands 34).  does  not  magnetic  volcanics  extend  on  any  anomaly  Cretaceous  that  offshore  southwestern  (Mahannah, 1965). obtained  from  Hecate  (see  and  Lyell  Figs.  29  or  refraction  volcanic  profiles and  rocks  t o 4 km  across  4.01  and  probable  t h e r e f o r e may  rocks.  s u b b a s i n edge e a s t of L y e l l Mesozoic  are  Normal  4.91  km/sec  faults  Mesozoic along  to  the  east  and  sedi-  the  and Ramsay I s l a n d s have dropped  depth  those  Masset v o l c a n i c s  indicate  step  and  profile  These v e l o c i t i e s are c o n s i d e r a b l y l e s s than  C h a r l o t t e sub-basin  mentary  sub-basin  sedi-  characterizes  e a s t - c e n t r a l Moresby  distance  Hecate  Basement v e l o c i t i e s from a r e v e r s e d s e i s m i c r e f r a c t i o n  across  in  Yakoun v o l c a n i c s and  amplitude  facies  i n southwestern  uplifted  steep  probable  subaqueous  p y r o c l a s t i c s and v o l c a n i c b r e c c i a s of t h e Dana f a c i e s t o the west. Isostatic gravity suggests may  t h a t p a r t of the n o r t h e r n  (Stacey,  rocks  t o 6.49  sion.  These  could  Stacey  o r Masset b a s a l t s .  l e s s dense d i o r i t i c  be  High  (Mahannah, 1965) Karmutsen  The  1975;  p o r t i o n of the  be u n d e r l a i n by dense v o l c a n i c r o c k s .  which range from 4.14  and  anomalies  well  Fig.  Hecate  support  velocities  this conclu-  as  suggested  bottomed  r o c k s o f ?Upper P a l e o z o i c age  19)  sub-basin  basement  volcanics  Tyee N-39  see  by  i n gabbroic  (Shell  Canada  L t d . , 1968a).  Moresby Island  Ridge: N55°E  Moresby to  Ridge,  central  basement f e a t u r e , 20-30 km  Hecate  which  extends  Strait  55  ( F i g . 36)  i n width, that separates  km  from  Burnaby  is  a  positive  the  Hecate  and  145  Charlotte 1 km on  sub-basins.  while  Depth t o the  r e l i e f exceeds 2.5  Skonun  sedimentation  northward  transgressing  much  southern  of  km.  Hecate  was  shown by  Fig.  19)  who  Shouldice  shallow  as  ridge  had  i s less  a major  a  partial  marine  (Charlotte  The  seas  Fig.  free-air  20)  barrier  that  subbasin)  and  and  to  occupied and  Stacey  isostatic  than  influence  Queen  approximate p o s i t i o n of the  (1973; see  a t t r i b u t e d high  the  ridge  acting  Strait  C h a r l o t t e Sound (Chapter I V ) .  of  The  patterns, Neogene  top  ridge  (1975;  gravity  see  anom-  a l i e s o v e r the r i d g e t o dense Karmutsen v o l c a n i c s . The  magnetic e x p r e s s i o n  comprises elongate t o v a r i e s from g r e a t e r Island trend  to  than 800  350-650 nT  roughly  continuation  of  the  and  may  marine as  ( F i g s . 34  amplitude  the  inner  basin  data  the t o t a l  and  anomalies.  s h e l f east  edge.  indicate  magnetic  seen on  high magnetic v a l u e s  magnetic s u s c e p t i b i l i t y , post-tectonic  highs that structure that  the  ridge  fault  would  Relief  of  Elongate  35)  Burnaby  anomalies  trends. likely  Upward  produce  i n t e n s i t y aeromagnetic  a map  20). The  or  of  the  high  nT on  east  north-south  broad magnetic high (Fig.  subrounded  of  i s comprised  magnetic  i . e . Karmutsen  i n t r u s i v e rocks.  characterize  the of  ridge volcanic  anomaly p a t t e r n s of  low  are a t t r i b u t e d t o r o c k s (A mode), Masset  Coincident would  are  generally  the  r i d g e t o o u t c r o p of Masset v o l c a n i c s  and Ramsey I s l a n d s and Murrelet  L-15  i n d i c a t e that  rocks.  associated  with  and  up  Masset "basement" rock  to  1.5  magnetic  much of  Karmutsen  relief.  high  volcanics,  Aeromagnetic  t o medium a m p l i t u d e and  w e l l s (northern  gravity  of  the  maps show volcanics  Proximity t h i c k on  i n the A u k l e t  G-41  of  Lyell and  C h a r l o t t e s u b - b a s i n ) s u g g e s t s t h a t much  146  of  the  r i d g e might, t h e r e f o r e ,  volcanics.  If  'core'  of  Stacey  (1975).  the  capped  slightly  inner  an  composed of  Masset  rocks,  high  may  amplitude,  result  produced  by  possible  suprabasement  Moresby  offshore  short  capped Ridge  from  extension magnetic  wavelength  intrabasement of  the  The  age  and  on  the  basis  of  by  volcanoes  deposited  from  over n o r t h e r n  b a s a l t p o r p h y r y , 206 and  which  by  anomalies  on  and  C h a r l o t t e sub-basin  m from the top  p y r o c l a s t i c s in Auklet  G-41  of  and  mineralization  intrusion.  a v a i l a b l e geophysical  flows  effects  Pluton  of Moresby Ridge must be  basaltic  considered  data.  If  com-  be one  pyroclastics  or  were  i n Lower O l i g o c e n e .  a s e c t i o n of Masset  gave a K-Ar  a  suggested  p r i s e d p a r t i a l l y or e n t i r e l y of Masset rocks the r i d g e may more  Masset have  magnetic  e f f e c t s produced  origin  by  may  Burnaby I s l a n d  a s s o c i a t e d w i t h i r o n ore b o d i e s r e l a t e d t o the  speculative  or  more dense Karmutsen v o l c a n i c s , as  The  shelf  by  be  age  of  36+  (A  basalts  4 Ma.)  If  the r i d g e i s comprised l a r g e l y of Upper T r i a s s i c Karmutsen l a v a s , i t may  have formed  a physiographic  w i t h i n the Cretacous S k i d e g a t e Moresby Ridge oblique  to  western  portion  transverse California;  major  element, the see  associated with Charlotte any  great  the  B a s i n t o the  on  the  Charlotte  Stockton  arch,  Dickinson  and  trend  distance  east  is a of  similar the  (A  segments the  Seely,  1979.)  similar  fault  and major  Great V a l l e y  Although  system on  lies  Islands  of  structures  s o u t h e r n Queen  d i r e c t i o n t h e y do  main  depostion  i t s trend  Charlotte  Basin.  the Louscoone wrench f a u l t  Islands  because  Queen  Queen  restricted  north.  remains e n g i m a t i c  structures of  barrier that  trace.  not If  extend appears  u n l i k e l y t h e r e f o r e t h a t s t r e s s systems r e l a t e d t o the major wrenches  147  could the  have i n f l u e n c e d t h e development of Moresby R i d g e . importance  of  major  crustal  dislocations  and  Because of  block  rotations  ( r e l a t e d t o l i t h o s p h e r i c p l a t e i n t e r a c t i o n s ) i n the g e o l o g i c h i s t o r y of the Queen C h a r l o t t e I s l a n d s and  Insular Tectonic Belt, a tectonic  o r i g i n c a n n o t , however, be d i s c o u n t e d .  Charlotte  Sub-basin:  The  C h a r l o t t e sub-basin  Moresby r i d g e t o t h e west c e n t r a l The  deepest  p o r t i o n s of  immediately that  south  trends  contours  the  N40°W  near  ( F i g . 36)  at  r i d g e and  the  indicate  south  from  p o r t i o n o f Queen C h a r l o t t e Sound.  sub-basin  o f Moresby  extends  g r e a t e r than  northwest  Harlequin that  the  of  D-86  3.5  a short ridge  well.  sub-basin  km l i e  Structure  floor  east  of  s o u t h e r n Moresby I s l a n d and along e a s t e r n Hecate S t r a i t s l o p e g e n t l y toward mately  the c e n t r a l 2  km  p o r t i o n of t h e s u b - b a s i n which  depth.  The  sub-basin  edge  is  lies  not  at approxi-  faulted  except  p o s s i b l y a g a i n s t Moresby Ridge. The  magnetic p a t t e r n c h a r a c t e r i z i n g  of t h e C h a r l o t t e s u b - b a s i n east  t r e n d i n g magnetic  and  Kunghit  and  south  changesto  Islands. of  northwest,  ( F i g . 34) c o m p r i s e s  r i d g e s and  troughs  Towards t h e c e n t r a l  Kunghit  t h e western  Island  the  parallelling  broad  east  of  portion  trend  of  arcuate northsouthern  of  the  magnetic  t h e t r e n d of the  portion  Morsby  sub-basin anomalies  southern  end  of  troughs, with r e l i e f  of  a p p r o x i m a t e l y 20 km e a s t of Moresby I s l a n d ,  15  the Louscoone and S a n d s p i t f a u l t s . The  a r c u a t e magnetic r i d g e s and  up t o 250 nT, extend km  e a s t of t h e s u b - b a s i n edge.  of  folds  and  monoclinal  panels  They r e f l e c t on  southern  an o f f s h o r e e x t e n s i o n Moresby  and  Kunghit  148  Islands wrench  and  the  fault  inner  system.  I s l a n d may  represent  an  P o i n t Langford  of  reflect  the  oblique  values  Jurrasic  east  trend  magnetic  Moresby  likely  that  High  southern  ridge  shelf  Pluton.  Low  f o l d e d panels  sub-basin  edge.  to  (  the  500  extension  Louscoone  nT) of  east  the  of  ?Upper  magnetic v a l u e s t h a t f l a n k of Kunga  Windows  limestones  may  expose  that  older  the  extend  Karmutsen  volcanics. Subcrop well  results  is  M u r r e l e t L-15 and  over  the  largely  comprised  and A u k l e t G-41  bottomed  flows.  in  similar  p r o f i l e s (Mahannah, 1965) t o measured  interval  H a r l e q u i n D-86 with  the  short  troughs  suggests  source  rock extends  Over  low-density  Tertiary  a  ( S t a c e y , 1975;  indicated  volcanics.  At  by the  the  Ma)  reversed  Harlequin  D-86  pyroclastics  and  seismic  t o 5.55  refraction  km/sec, comparable  v o l c a n i c s i n the  nearby  lows  magnetically  high  with  adjoining  sub-basin  uniform  (Masset?)  basement  p o r t i o n of the s u b - b a s i n ,  effect  associated  with  the  the  volcanics  reduced. southwestern  p o r t i o n of  g r a v i t y anomalies  Neogene  granitic  (42  Masset  over the s o u t h e r n  the  negative i s o s t a t i c  of  magnetic  s i g n i f i c a n t ' remnant magnetic being c o n s i d e r a b l y  as  approximate c o i n c i d e n c e of a magnetic  and  that  Eocene  range from 4.85  The  ridge  Masset  from t h r e e  velocities  well.  of  F u r t h e r south  Upper  Basement v e l o c i t i e s  sub-basin  w e l l s , Upper Eocene or younger b a s a l t s  p y r o c l a s t i c s were p e n e t r a t e d .  well  by  Charlotte  or  sediments  sedimentary  see F i g . 19).  the  cannot be and  suggest  rocks  In t h i s  may  sub-basin  accounted that  underlie  for  large solely  Mesozoic-mid Skonun  rocks  a r e a Masset v o l c a n i c s may  be  149  absent o r c o n s t i t u t e o n l y a t h i n c o v e r over the low d e n s i t y r o c k s .  Oceanic A r e a A d j a c e n t t o Queen C h a r l o t t e Sound  Major base  of  the  p h y s i o g r a p h i c f e a t u r e s o f the o c e a n i c a r e a a t the  continental  Sound  i n c l u d e Tuzo W i l s o n  fault  zone,  (southern  Moresby  portion).  and  slope  off  and  Delwood  S c o t t deep  L o c a t i o n and  f e a t u r e s i s shown i n F i g . 41. region  ( F i g . 34)  acquired  in  (Tiffin,  1974;  a  has  been  and  knolls,  sea  survey  Currie,  coverage 1973)  1971b,  r e p o r t e d by  1976)  Srivastava  et  Pitman  Hayes  and  of  aU  Charlotte  Queen C h a r l o t t e and  Oshawa  expression of  primarily  o b t a i n e d d u r i n g I.O.U.B.C. C r u i s e 76-10 (Srivastava,  channels  t o t a l magnetic  compiled^  Queen  the  bathymetric  The  multiparameter Tiffin  north-central  field from  Queen  map  f o r the  Charlotte by  ( t h i s s t u d y ) and  (1968),  these  magnetic  supplemented  1971).  Rise  Sound  profiles  Hudson  Sparse  Naugler  data  and  '70  magnetic Wageman  and Couch (1969) has not been i n c o r p o r a t e d . The  p a t t e r n of magnetic  shows.a c l o s e correspondence l a r g e p o s i t i v e magnetic two s e p a r a t e magnetic  anomalies  over the o c e a n i c  area  t o t h e major p h y s i o g r a p h i c f e a t u r e s .  p l a t e a u t h a t t r e n d s r o u g h l y W-SW  peaks of g r e a t e r t h a n 800  p o s i t i o n of t h e Tuzo W i l s o n k n o l l s . James r i d g e , the k n o l l s r i s e 0.7  A  comprises  and 850 Nt marks the  Located 60 km south of Cape S t .  km above t h e ocean f l o o r a t 2.1  C o m p i l a t i o n of magnetic f i e l d d a t a from surveys southwest of the (Riddihough et a]_ 1980; Currie incorporated.  km  was completed b e f o r e d a t a Queen Charlotte Islands et jH, 1980) could be  water d e p t h .  Dredge h a u l s from one of the seamounts r e c o v e r e d f r e s h  h a w a i i t e and photographs cooling  fractures  Chase, K/Ar  1977).  date  samples  and  The  of  showed c l e a r l y negligible  young  age  of  than  0.05  Ma  less  fresh  lava flows,  sediment  the  cover  seamounts was  o b t a i n e d from  tensional  (Tiffin,  1974;  confirmed  by  one  of  the  a  dredge  (Chase, p e r s o n a l communication). According  t o Chase ( 1 9 7 7 ) , g e o m e t r i c , c h r o n o l o g i c a l  and  p e t r o l o g i c e v i d e n c e s u g g e s t s t h a t the seamounts form the a c t i v e  end  of  the  northeastern  recent the  Pacific  c h r o n o l o g i c and  Kodiak-Bowie  geochemical  evidence  seamount  chain.  More  however,  predicts  that  p r e s e n t hot s p o t l o c a t i o n i s 270-360 km northwest of Tuzo W i l s o n  knolls,  40-130 km  1980).  R i d d i h o u g h e t a ^ (1980) suggest t h a t t h e Tuzo W i l s o n k n o l l s  are  the  similar  s o u t h e a s t of  l o c u s of a c t i v e to that  the  Bowie  s p r e a d i n g which  of the Delwood  knolls  seamount  (Turner e t a l _ ,  i s both complementary  i n providing  and  the c o n n e c t i o n  between t h e E x p l o r e r Ridge and Queen C h a r l o t t e F a u l t (see F i g . 12). The able  to  ' s i m p l e ' magnetic p a t t e r n o v e r t h e k n o l l s  patterns  (Francheteau  e_t _al_,  r e s p e c t t o the l o c a l the  observed 1970).  over Slight  e l e v a t i o n s can  current earth's f i e l d  Pacific offset  of  midplate magnetic  i s comparseamounts peaks  with  be e x p l a i n e d by i n c l i n a t i o n  of  and non-homogenous magnetic e f f e c t s o f the  source rock. The the  strong p o s i t i v e  Tuzo W i l s o n k n o l l s  polarity  epoch  (0.7  magnetic  field  that  characterizes  ( F i g . 34) i s t h e product of t h e most r e c e n t  Ma).  Francheteau  e t ^1_ (1970)  seamounts such as t h e Tuzo W i l s o n k n o l l s p e r i o d of 0.01-0.1 Ma y e a r s and w i l l  indicate  are n o r m a l l y b u i l t  be magnetized  that  over  a  predominately i n  151  one  direction,  ently  during  a single  l i e on o c e a n i c c r u s t  1971; R i d d i b o u g h , 1977). strong  lineation  netics related effect the  which  runs  might  that  The k n o l l s  with  line  floor.  et  of termination  spreading suggests that  represent  a  former  of the P a c i f i c  the region  Queen  'block' t o the east of t h i s  t h e magmagnetic  and t h e r e f o r e would  would  be t h a t  lineations,  o f t h e Delwood  Charlotte  fault  Plate  Fault  aj[,  symmetry o r  An a l t e r n a t e e x p l a n a t i o n might  from  appar-  i s 5-6 Ma o l d ( S r i v a s t a v a  t o t h e seamounts has d e s t r o y e d t h e remnant  northwestwards  America p l a t e  epoch.  The l a c k o f any i d e n t i f i a b l e  associated  o f t h e ocean  apparent  polarity  knolls,  position.  The  have been a t t a c h e d t o t h e  n o t have been t h e s i t e  o f ocean  c r u s t and magnetic anomaly g e n e r a t i o n ( R i d d i h o u g h e t aj_, 1980). Delwood knolls,  have  been  knolls,  which  l i e 80 km  S-SE  proposed  as a  spreading centre connecting the  E x p l o r e r Ridge t o t h e Juan de Fuca p l a t e systems 1971; The  B e r t r a n d , 1972; Chase e t a_U pattern  o f magnetic  p a r t i c u l a r l y complex, the  ridge  crest  anomalies  o f t h e Juan  f i t observed  detailed uniformly  magnetic  by magnetic  over  Fuca  anomalies,  bodies  m a g n e t i z a t i o n s a r e comparable seamounts  1975; R i d d i b o u g h e t a l _ , 1980). the knolls  ( F i g . 37) i s  Explorer  mapped  to a series and  ridge  system.  on  the basis  o f model anomalies  determined  that  1)  of a from  calculated  t o mean v a l u e s determined f o r P a c i f i c  anomaly f i t t i n g  z a t i o n s o f dredge samples  -  a t o r near  three-dimensional modelling techniques  survey of the k n o l l s , magnetized  de  Wilson  ( S r i v a s t a v a et cH,  c h a r a c t e r i s t i c o f seamounts formed  R i d d i h o u g h e t a ^ (1980) used to  o f Tuzo  and measured  bulk  magneti-  from t h e k n o l l s and t h e E x p l o r e r and Juan  de Fuca r i d g e s , and 2) t h e k n o l l s were almost e n t i r e l y  produced by  MAGNETIC ANOMALIES - QUEEN CHARLOTTE SOUND  » Fiq. 37  km  j  Magnetic anomaly map of Queen Charlotte Sound and adjacent Pacific Ocean. Dk = Delwood knolls, TWK = fuzo Wilson knolls, QCfz = Queen Charlotte fault zone, CJr - Cape St. James ridge, OR = Oshawa Rise, SC = Scott Channel, CS = Cape Scott. Redrawn from T i f f i n and Currie (1976).  153  n o r m a l l y magnetized b a s a l t s d u r i n g the l a s t p o l a r i t y epoch. A  magnetic  between Tuzo W i l s o n ( F i g . 34)  marks the  transform  fault  65°,  north  of  accumulation west  trough,  k n o l l s and  km  the  wide,  zone. Tuzo  A  short  Wilson  magnetic  S r i v a s t a v a e t ^1_; 1971  Cape S t .  (25  knolls, of  relief  km)  (see  the  Queen  elevated  ridge  thick  Couch,  azimuth  sedimentary  To  the  1969,  north-  Fig.  21;  F i g . 5) c h a r a c t e r i z e s s o u t h e r n Oshawa R i s e , a  extension  k n o l l s t o Bowie Seamount.  of the Tuzo W i l s o n  Charlotte basement  a  ridge,  Channel.  also  located  a c t i v e Queen C h a r l o t t e  magnetic  Moresby  140°,  James magnetic  overlies  broad basement s w e l l t h a t c o n n e c t s the southeastern  azimuth  p r o b a b l e l o c a t i o n of the  i m m e d i a t e l y south  subdued  10  fault  trough  foundation  t r e n d of low magnetic v a l u e s  (Fig.  that  magnetic p l a t e a u , 34)  connects  suggests to  a  Oshawa  west  A of  possible  Rise.  The  n o r t h of the Delwood k n o l l s i s a p p r o x i -  m a t e l y c o i n c i d e n t w i t h S c o t t Channel.  Tectonic  I m p l i c a t i o n of Magnetic Anomalies Over Western  Queen C h a r l o t t e Sound Magnetic anomalies over the  outer  continental shelf  s l o p e of Queen C h a r l o t t e Sound r e f l e c t major g e o l o g i c and elements whose o r i g i n opment  of  the  anomalies that  northern major  Insular  ( F i g s . 34  joins  southern  Vancouver  bathymetric  is critical  and  Tectonic 37)  Queen Island.  re-entrant  C h a r l o t t e Sound s h e l f .  t o an u n d e r s t a n d i n g Belt.  displays  a  Charlotte A  structural  of the  pattern  of  (Cape  St.  magnetic, p a t t e r n  central  portion  of  devel-  magnetic  discontinuous,1inear  Islands  subdued i n the  The  and  trend  James)  to  overlies a the  Queen  154 Various observed  g e o l o g i c a l models have been proposed t o  geophysical  anomalies.  Srivastava  (1973) suggested  anomaly on  the  that  reflects  convergence that  outer a  Srivastava  that  continental  an  active  a c o n t i n u o u s r i d g e may,  shelf  and  S t a c e y and  margin. at one  Stephens  Cretaceous  and  "shelf  Shouldice  anomaly"  and  possible  (1973)  speculated  time ( p o s s i b l y e a r l y Queen C h a r l o t t e  across  that  Tertiary),  Islands.  On  Stacey  overlying  Sound  in  is  earlier  the  (1975)  a c e n t r a l gap  Queen C h a r l o t t e  sediments,  and  edge  transition  (1969) suggested  Tertiary  (1971)  p o s i t i v e magnetic  i s o s t a t i c g r a v i t y anomaly d a t a ,  otherwise continuous u p l i f t by  is a  crustal  have e x i s t e d between Vancouver and b a s i s of f r e e - a i r and  aj_  a discontinuous  continent-ocean  along  et,  explain  an  filled  volcanic  rocks. In  order  to  explain  the  S t a c e y (1975) suggested t h a t the  gap  i n the  shelf  Queen C h a r l o t t e  edge  Islands  ridge,  could  have  been r a f t e d northwards w i t h r e s p e c t  t o Vancouver I s l a n d , p o s s i b l y i n  a manner s i m i l a r t o  of  Mexican m a i n l a n d . may  have  Fault.  occurred  and  (azimuth to  more  adjacent  140°) head  with  the  Queen C h a r l o t t e  a  blind  Islands to  southern  California  recently  along  the  line  t h a t the heads of t h r e e  southern without  extension apparent  of  They f u r t h e r s p e c u l a t e d  west  of  platform  the north  Sound from the  fault of  the  source  the  separation  the  Sandspit  on  Sound, c o - l i n e a r Sandspit the  Fault,  continental  t h a t p a r t of the Queen  extension Vancouver  Pacific.  of  from  submarine canyons at  Goose I s l a n d Banks i n Queen C h a r l o t t e  s h e l f (see F i g . 4 1 ) . Charlotte  separation  Chase e t a]_ (1975) suggested t h a t such  They r e c o g n i z e d  Mitchell  appear  the  may  once  Island,  have  closing  Subsequent movement  lain off along  155  the  Sandspit  ocean  and  or r e l a t e d f a u l t s  moved  position.  New  sediments of  Queen  Charlotte  ocean f l o o r the  would  outer  have opened the  mountains  thus created  north  would  c o n t i n e n t a l s h e l f and  Sound t o  to  be  their  deeply  slope,  have  suggested  that  Queen C h a r l o t t e I s l a n d s  et  aj_ (1979) and  northward  i n Neogene t i m e f o l l o w e d with  of  further  Anahim  F i g s . 12 and  hot  by  subsequent  spot  (see  Yorath  Masset  and  the  a rifting  volcanism  discussion,  Queen  event i n  and  passage  Chapter  Sound  v o l c a n i c s ) may  be  ations  explained  be  (1970) has basalt  (or  l i m i t e d , the by  shown t h a t the  to  l a c k of  magnetic  Curie  the  c e n t r a l gap  Basin  (Galloway,  would  be  identifiable rock  Queen  Charlotte  at  1979) 5  Delwood k n o l l s and  depth  of  (Higher  p o s s i b l e hot  burial.  magnetic  line-  Carmichael  unaltered  submarine  Sound.  that  s h e l f and Using  an  s o u t h e r n Queen  slope average  Charlotte  a minimum ambient t e r m p e r a t u r e of  km.  Total magnetization  older  S t a c e y (1975) showed  of 3.0°C/100 m f o r the  1974;  expected  in  basalts  from  properties.  temperature of  because of the p r o x i m i t y of the gap  knolls).  them  o f T e r t i a r y sediment u n d e r l i e s the  geothermal g r a d i e n t  this  distinguish  i s t y p i c a l l y about 200°C or l e s s .  as much as 5 km near  III,  13).  Charlotte  can  Case  western  A l t h o u g h our a b i l i t y t o d e t e c t young ocean f l o o r in  by  presumably  d i s l o c a t i o n of  Queen C h a r l o t t e Sound a s s o c i a t e d the  buried  burial.  More r e c e n t l y , B e v i e r (1981)  present  and  magnetic anomalies would, i f ever formed, be d e s t r o y e d h e a t i n g r e l a t e d t o depth of  the  t o a recent  spot i n the  could  Irving  temperature  et  t h u s be  may  be  spreading  expected centre  v i c i n i t y of Tuzo reduced by  a}_ (1970)  have  150°C  Wilson  reheating  shown  at  that  at the  156  i n t r u s i o n o f magma i n t o sediments r e s u l t s i n s l o w e r c o o l i n g and t h u s a  coarser  basaltic  grain sill  s i z e and  lower  encountered  e x t r e m e l y low t o t a l  i n DSDP  magnetization  ( R i d d i h o u g h e t a l , 1980). crust could  natural  remnant  hole  177  magnetization.  (Winona  Basin)  compared t o average ocean  The above e v i d e n c e  has  basalts  indicates that  u n d e r l i e t h e gap i n Queen C h a r l o t t e  A  ocean  Sound as suggested  by Chase e t aj_ 1975). Any spreading events  model  recorded  Charlotte  Islands  crustal  o f Vancouver  h i s t o r y o f Vancouver  ( s e e Chapter  d i s l o c a t i o n s or  I) show  and Queen Island  a  by t e c t o n i c  gradual  Charlotte  and t h e Queen divergence  in  and f a c i e s a f t e r t h e Lower Cretaceous t h a t might be accounted  for  by t h e p r e s e n t  on  Vancouver I s l a n d  separation  records  the f i n a l  islands,  Triassic  Cretaceous  have been d e p o s i t e d  Islands  volcanism Islands  t h e western margin o f t h e Vancouver  Lower  Queen C h a r l o t t e Sound. Charlotte  Andesitic  Basin  major t e c t o n i c event t h a t was synchronous on t h e  although  F o r m a t i o n ) may  of the i s l a n d s .  (Bonanza F o r m a t i o n ) and Queen C h a r l o t t e  (Yakoun F o r m a t i o n ) along  Bay,  large  Sound must be c o n s t r a i n e d  i n i n s u l a r rocks  The g e o l o g i c  the  invokes  t o open C h a r l o t t e  Islands.  timing  that  Kunga Formation  in fault  sediments  (Longarm  bounded t r o u g h s  across  The mountainous s p i n e o f Vancouver and Queen  comprises  "Wrangellia"  marine  l a r g e l y the o l d e r  succession (Queen  that  Charlotte  Upper  Paleozoic-Upper  includes  Karmutsen  Islands)  and Q u a t s i n o ,  and Harbledown F o r m a t i o n s (Vancouver  Island).  e x t e n s i v e l y exposed on s o u t h e r n Queen C h a r l o t t e Vancouver I s l a n d , and l i k e l y form t h e f o u n d a t i o n edge o f t h e s h e l f i n Queen C h a r l o t t e Sound.  volcanics, Parson  These r o c k s are  Islands  and  northern  of the ridge at the  157  Major  Sandspit  and  Rennel-Louscoone systems (Chapter X ) , have p l a y e d a s i g n i f i c a n t  role  in  Belt  the  geological  (Sutherland faults  right  ciated  have  with  Wrangellia Charlotte  wrenches,  development  Brown,  may  lateral  1966;  1968;  developed  translation  terrane  in  of  including  the  Tectonic  1970).  Some  Jeletzky,  over  old  and  juxtapositon  Upper  Insular  lines  of  of  Jurassic-Lower  I s l a n d s have been r a f t e d  crustal  of  these  suture  asso-  the  allochtonous  Cretaceous.  north with  If  respect to  Queen  Vancouver  I s l a n d , combined movement l i k e l y o c c u r r e d on a number o f t h e s e major faults. Subsidence tectonic result  of  readjustments, of  the  or  translation  shelf  edge  opening  and  ridge, related  Queen  C h a r l o t t e Sound  possible  ocean  spreading  segments  must  T h i s would appear t o argue a g a i n s t a  which  formed  only  in  the  as  last  a  have  deposition in  r i d g e i n Queen C h a r l o t t e Sound being r e l a t e d t o the ridge  local  of  preceeded Neogene s h a l l o w t o deep marine c l a s t i c Charlotte sub-basin.  to  the  spreading  Explorer-Delwood  few  million  years  ( R i d d i h o u g h e t al_, 1980). The supports  the  (1969) and  pattern  of  observations  Shouldice  of  anomalies  Stacey  (1975),  (1973) t h a t a more o r  predominately  Mesozoic  Vancouver  Queen  and  magnetic  rocks  forms  an  Charlotte Islands.  (Figs. Stacy  34  and  and  37)  Stephens  l e s s continuous  belt  arcuate  between  From  the  ridge Queen  of  Charlotte  Islands  (Cape S t . James), a magnetic r i d g e , w i t h v a l u e s t h a t exceed  850  extends  nT,  form,  bounded  Charlotte  fault  65 to  km the  zone,  southeast. west and  by to  A the  the  narrow e l e v a t e d continental east  by  shelfal  slope  Moresby  and canyon,  platQueen and  158  characterized  by  a  coincident  positive  free  a i r gravity  anomaly  ( F i g . 21) extends 45 km from Cape S t . James a l o n g the same t r e n