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A geological reconnaissance of the dellwood seamount area, northeast pacific ocean, and its relationship… Bertrand, Wayne Gerrard 1972

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A GEOLOGICAL  RECONNAISSANCE OF THE DELLWOOD SEAMOUNT AREA,  NORTHEAST P A C I F I C OCEAN, AND  ITS RELATIONSHIP TO PLATE by  WAYNE GERRARD BERTRAND B.Sc,  University  A THESIS SUBMITTED  o f t h e West I n d i e s ,  1969  IN PARTIAL FULFILMENT  OF  THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  i n the  Department o f Geology I n s t i t u t e o f Oceanography  We  accept t h i s  required  thesis  as c o n f o r m i n g  to the  standard  THE UNIVERSITY OF B R I T I S H January,  1972  COLUMBIA  TECTONICS  In presenting  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r  an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree that permission f o r extensive f o r s c h o l a r l y purposes may by h i s representatives.  copying of t h i s thesis  be granted by the Head of my Department or I t i s understood that copying or p u b l i c a t i o n  of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission.  Department of  Geology  The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada  January  1972.  i ABSTRACT  The  D e l l w o o d Seamount A r e a , an a r e a o f a p p r o x i m a t e l y  10,000 s q u a r e km., Vancouver the  about  185 km.  west  o f the n o r t h e r n t i p of  I s l a n d i s l o c a t e d a t o r n e a r t h e n o r t h e r n m o s t end  J u a n de F u c a p l a t e .  The m a i n p u r p o s e  o f t h e s t u d y was  of to  t e s t t h e h y p o t h e s i s t h a t t h e D e l l w o o d K n o l l s mark t h e s i t e o f a s h o r t s p r e a d i n g segment c o n n e c t e d t o t h e E x p l o r e r S p r e a d i n g ment a t one  end by a t r a n s f o r m f a u l t  w e s t e r n s l o p e o f P a u l Revere Charlotte  right  lateral  An a n a l y s i s  shows t h a t  ( i ) the Revere  ing  segments.  zone  R i d g e ; and m e e t i n g  t h e Queen  a t t h e o t h e r end.  o f more t h a n 950 km.  profiles,  transform fault  t r e n d i n g a l o n g the s o u t h -  transform fault  reflection  Seg-  of continuous seismic  i n conjunction with other geophysical data, - Dellwood f a u l t  zone  c o n n e c t i n g the E x p l o r e r  ( i i ) The  Queen C h a r l o t t e  is a  dextral  and D e l l w o o d s p r e a d -  transform fault  dies  out at the s o u t h e a s t e r n end o f the S c o t t Channel n e a r the n o r t h e a s t e r n end o f t h e D e l l w o o d S p r e a d i n g Segment.  ( i i i ) I n the  channel between the Dellwood K n o l l s  (one o f two p o s s i b l e  of  the sediments  the Dellwood S p r e a d i n g Segment),  b a s e m e n t a r e c u t by n o r m a l teristic  c h a n n e l and i n t h e R e v e r e  ( i v ) The  Charlotte  a f e a t u r e which  o f s p r e a d i n g c e n t r e s w i t h median v a l l e y s .  flow i n this high,  faults,  and  lower c o n t i n e n t a l  Sound i s f a u l t e d  e x t e n s i o n o f the S c o t t contemporaneous  Islands  or recently  volcanic  i s characThe  - Dellwood f a u l t  s l o p e sediments west  and c r u m p l e d and may f a u l t , zone  be  locations  heat zone i s  o f Queen  the n o r t h e r l y  and a s i t e o f s l o w  ceased subduction.  The  deformation  ii  o f the t h i c k t u r b i d i t e sequence i n the Winona B a s i n may  a l s o be  due to s u b d u c t i o n . B a s a l t from the a r e a i s c h e m i c a l l y i n t e r m e d i a t e between t h o l e i i t i c and a l k a l i c t y p e s .  That from the Northwest Dellwood  K n o l l s , however, i s l e a s t d i f f e r e n t i a t e d and l e s s than 1 myr. o l d i n c o n t r a s t t o b a s a l t from the sediment-draped Southeast Dellwood K n o l l s , the l a t t e r b a s a l t h a v i n g Mn-coating up t o 50 t h i c k and i s thus r e l a t i v e l y o l d .  mm.  T h i s suggests t h a t s p r e a d i n g  may be o c c u r r i n g at the Northwest Dellwood K n o l l s and not i n the channel between the k n o l l s .  The t e x t u r e o f b a s a l t s from the  Dellwood Seamount Range v a r y depending on s i z e o f p i l l o w  and  depth below p i l l o w s u r f a c e , but the m i n e r a l o g y i s e s s e n t i a l l y similar.  An u n u s u a l rock p r o b a b l y b e s t d e s c r i b e d as a p l a g i o -  c l a s e - o l i v i n e b a s a l t p o r p h y r y was wood Seamount Range.  a l s o r e c o v e r e d from the D e l l -  Non-volcanic rocks recovered include  g l a c i a l e r r a t i c s , an a u t h i g e n i c sandstone c o m p r i s i n g g l a c i a l fragments i n an i r o n - r i c h cement, a l a m i n a t e d l i m o n i t i c  sediment  and manganese n o d u l e s . The Dellwood S p r e a d i n g Segment may have o r i g i n a t e d by l e f t l a t e r a l t r a n s c u r r e n t o f f s e t from the E x p l o r e r S p r e a d i n g Segment, the o f f s e t caused by a change i n the d i r e c t i o n o f motion: o f the Juan de Fuca p l a t e .  iii TABLE OF CONTENTS ABSTRACT  i  TABLE OF CONTENTS  i i i  L I S T OF TABLES  vi  L I S T OF ILLUSTRATIONS  v i i  ACKNOWLEDGMENTS I  INTRODUCTION  1  Location  1  Purpose II  xi  a n d Scope o f t h e I n v e s t i g a t i o n  A SUMMARY OF THE LITERATURE ON THE NORTHEAST P A C I F I C PLATES AND ON THE PETROLOGY OF OCEANIC BASALTS Regional Tectonics Gravity  Data  12 12  Heat Flow Data  15  Regional Tectonic H i s t o r y During the Cenozoic  19  Petrology  23  o f Oceanic  Types o f O c e a n i c  SHIPBORNE  Basalts  Basalts  O r i g i n of Oceanic III  5 5  and H e a t F l o w D a t a  Gravity  1  Basalts  AND LABORATORY INVESTIGATIONS  Shipborne  Operations  23 27 32 32  Introduction  32  Continuous  32  Seismic Reflection P r o f i l i n g  Dredging  34  Other Operations  34  L a b o r a t o r y Methods  34  CSP A n a l y s i s  34  Petrography  38  Chemical  38  Analysis  iv IV  S E I S M I C DATA.  41  Introduction  41  Major T e c t o n i c and P h y s i o g r a p h i c F e a t u r e s o f t h e D e l l w o o d Seamount A r e a Explorer  42  S p r e a d i n g Zone  42  D e l l w o o d Seamount Range  42  Southeast Dellwood K n o l l s  42  Northwest  43  Dellwood K n o l l s  D e l l w o o d S p r e a d i n g Zone  43  Scott  44  Channel  Queen C h a r l o t t e  Fault  Zone  45  Continental  Slope  45  P a u l Revere  Ridge  46  Winona B a s i n Revere  46  - Dellwood  F a u l t Zone  47  Other Features V  49  ANALYSIS OF DREDGE HAULS AND CORE  51  Petrography of Basalts  51  EN 70-025-2D  51  EN 70-025-3D  55  D e l l w o o d Seamount Range  58  Chemistry o f Basalts  .  70  Hyaloclastites Breccias  79  Chemical Weathering  § Alteration of Basaltic  Fragments  83  V e s i c l e L i n i n g s and F i l l i n g s  86  Post V o l c a n i c  Deposits  89  Ferromanganese C r u s t s and Nodules  89  Iron Deposit  93  Sediment  96  L o o s e l y C o n s o l i d a t e d Sediments  96  V  ANALYSIS OF DREDGE HAULS AND CORE  (Continued) 98  Mud Glacial JOIDES D r i l l  Erratics  98  H o l e No. 177 ( P a u l R e v e r e  Ridge)  100  VI  DISCUSSION: THE RELATIONSHIP OF THE DELLWOOD SEAMOUNT AREA TO THE JUAN DE FUCA PLATE  103  VII  SUMMARY AND CONCLUSIONS  118  VIII  BIBLIOGRAPHY  125  APPENDICES APPENDIX  APPENDIX  A  Summary o f m a j o r t e c t o n i c a n d p h y s i o g r a p h i c f e a t u r e s and t h e i r c h a r a c t e r i s t i c s as o b s e r v e d on CSP  B - Brief  description  o f dredge h a u l s  131 135  vi L I S T OF  I II  TABLES  A v e r a g e c o m p o s i t i o n and mean d e v i a t i o n s t h o l e i i t e s and a l k a l i b a s a l t s .  of oceanic 26  C h e m i c a l and n o r m a t i v e c o m p o s i t i o n s o r some b a s a l t s f r o m t h e D e l l w o o d Seamount A r e a .  57  III  Chemical compositions of b a s a l t s Seamount A r e a .  71  IV  C h e m i c a l c o m p o s i t i o n s o f b a s a l t s f r o m known s p r e a d i n g c e n t r e s , seamounts and o c e a n i c i s l a n d s .  72  V  Chemical Dellwood  81  VI  T h i c k n e s s o f f e r r o m a n g a n e s e c o a t i n g s and e s t i m a t e d age r a n g e f o r r o c k s o f e a c h d r e d g e h a u l .  90  Elemental chemical composition post deposits.  92  VII VIII IX X  from the Dellwood  compositions of h y a l o c l a s t i t e s Seamount A r e a  from the  volcanic  P a r t i a l c h e m i c a l c o m p o s i t i o n o f some deep s e a iron deposits. Types o f g l a c i a l Seamount A r e a .  erratics  95  from the Dellwood  D e s c r i p t i o n o f JOIDES P a u l R e v e r e R i d g e  100 core.  101  Vll  L I S T OF  ILLUSTRATIONS  FIGURES  1.  L o c a t i o n of the Dellwood  Seamount A r e a  2.  Map o f e a r t h q u a k e 1954 and 1963  3.  I n d e x a n o m a l y map o f t h e t o t a l m a g n e t i c i n t h e N o r t h e a s t P a c i f i c Ocean  epicentres occurring  between field  ;  4.  B a t h y m e t r y o f t h e deep s e a f l o o r o f f and B r i t i s h C o l u m b i a  Washington  5.  B o u n d a r i e s o f t h e J u a n de F u c a . P l a t e  6.  R e l a t i o n s h i p between s p r e a d i n g r i d g e s , s u b d u c t i o n z o n e s and Q u a t e r n a r y a n d e s i t i c volcanoes i n the N o r t h e a s t P a c i f i c  7.  G e n e r a l i z e d map o f t h e Cape M e n d o c i n o A r e a s c h e m a t i c a l l y showing major t e c t o n i c f e a t u r e s  8.  F r e e - a i r g r a v i t y a n o m a l y map, w e s t c o a s t o f W a s h i n g t o n and B r i t i s h C o l u m b i a  9.  F r e e - a i r g r a v i t y a n o m a l y map, Oregon  west c o a s t of  10.  F r e e - a i r g r a v i t y a n o m a l y map, Northern C a l i f o r n i a  west c o a s t o f  11.  Summary o f h e a t Pacific  12.  H e a t f l o w v a l u e s i n t h e D e l l w o o d Seamount E x p l o r e r Trench Area  13.  Some m a j o r Ame r i c a  14.  Magnetic  15.  S c h e m a t i c m o d e l o f p l a t e i n t e r a c t i o n s and e v o l u t i o n w i t h time o f boundary regimes a l o n g the west c o a s t o f N o r t h A m e r i c a assuming a model o f c h a n g i n g motions,  16.  R e c o n s t r u c t i o n o f p l a t e e v o l u t i o n and d e f o r m a t i o n r e l a t e d to l a t e Cenozoic i n t e r a c t i o n o f the North A m e r i c a n and P a c i f i c P l a t e s  f l o w v a l u e s i n the N o r t h e a s t  t e c t o n i c f e a t u r e s of Western  anomalies  i n the N o r t h e a s t  North  Pacific  vm L I S T OF  ILLUSTRATIONS  (Continued)  FIGURES 17.  Location of p l a t e boundary regimes w i t h r e s p e c t to p o i n t s i n western North America assuming m o t i o n s and d e f o r m a t i o n s d e s c r i b e d i n F i g u r e 16  18.  Major types of  19.  R a r e - e a r t h p a t t e r n r e l a t i o n between t h o l e i i t i c basalts of shiel v o l c a n o e s and o c e a n r i d g e tholeiites.  20.  D i a g r a m m a t i c summary o f t h e e f f e c t s and d i r e c t i o n s of f r a c t i o n a t i o n o f b a s a l t i c l i q u i d s at moderate to h i g h p r e s s u r e  21.  Model o f magmatic e v o l u t i o n Ridge  22.  Shipborne Operations - Dredging  23. - L o c a t i o n  o f CSP  basalt  of the  Mid-Atlantic  lines  24.  C o n s t r u c t e d p r o f i l e a l o n g the Dellwood b a s i n b e t w e e n t h e D e l l w o o d Seamount Range and t h e Dellwood K n o l l s  25.  Location  26.  Basalts Knolls  27.  Photomicrographs of o l i v i n e - p l a g i o c l a s e g l o m e r o p o r p h y r i t i c b a s a l t from the Northwest Dellwood K n o l l s  28.  Basalts  29.  C h a r a c t e r i s t i c features of b a s a l t i c p i l l o w f r a g m e n t s f r o m t h e D e l l w o o d Seamount Range  30.  Photomicrographs o f b a s a l t s from the Dellwood Seamount Range. Dredge H a u l No. EN 70-025-7D  31.  Photomicrographs o f b a s a l t s from the Seamount Range. Dredge H a u l Nos. EN and EN 70-025-9D  o f Dredge  Stations  r e c o v e r e d from the Northwest  from the Southeast Dellwood  Dellwood  Knolls  Dellwood 70 025-8D :  32.  P h o t o m i c r o g r a p h s showing changes i n t e x t u r e depth i n t o p i l l o w fragment  33.  R e l a t i o n s h i p b e t w e e n o b s e r v e d groundmass p i l l o w s i z e and c o o l i n g r a t e  with  textures,  ix L I S T OF ILLUSTRATIONS  (Continued) t  FIGURES 34.  H o l o c r y s t a l l i n e block lavas Seamount Range  from the Dellwood  35.  Porphyritic plagioclase basalt D e l l w o o d Seamount Range  36.  S i l i c a v a r i a t i o n diagrams D e l l w o o d Seamount A r e a  37.  T r i a n g u l a r diagram f o r basalts D e l l w o o d Seamount A r e a  38.  S . I . v a r i a t i o n diagrams D e l l w o o d Seamount A r e a  39.  H y a l o c l a s t i t e B r e c c i a fragments D e l l w o o d Seamount A r e a  40.  Weathered zones i n b a s a l t s Seamount A r e a  41.  V e s i c l e l i n i n g s and a m y g d u l e s i n b a s a l t s t h e D e l l w o o d Seamount A r e a  42.  F e r r o m a n g a n e s e n o d u l e s and c r u s t s D e l l w o o d Seamount Range  43.  Iron deposit  44.  Authigenic loosely consolidated t h e D e l l w o o d Seamount A r e a  45.  G l a c i a l e r r a t i c s r e c o v e r e d from the Dellwood Seamount A r e a  46.  V i n e ' s t o t a l f i e l d m a g n e t i c a n o m a l y map D e l l w o o d Seamount and a d j a c e n t a r e a s  47.  I n t e r p r e t a t i o n of t o t a l f i e l d magnetic anomalies a s s u m i n g t h e R e v e r e - D e l l w o o d F a u l t zone o r i g i n a t e d as a l e f t l a t e r a l t r a n s c u r r e n t f a u l t  48.  I n t e r p r e t a t i o n of t o t a l f i e l d magnetic anomalies assuming t h a t the Dellwood Spreading Centre o r i g i n a t e d i n S i t u l e s s . t h a n 2 myr. ago  49.  Summary o f m a j o r t e c t o n i c f e a t u r e s D e l l w o o d Seamount A r e a  50.  Symbols used i n i n t e r p r e t a t i o n o f S e i s m i c P r o f i l e s shown i n P l a t e s I t o X I I I  from the  f o r b a s a l t s of the o f the  f o r b a s a l t s of the from the  from the Dellwood  from the Dellwood  from  from the  Seamount Range sediments  from  of the  o f the  X  L I S T OF ILLUSTRATIONS  (Continued)  PLATES I  CSP a n d M a g n e t o m e t e r l i n e s  IOUBC.70-16-15  II  CSP a n d M a g n e t o m e t e r  IOUBC 70-16-16  III  lines and  IOUBC 70-16-17  CSP a n d M a g n e t o m e t e r l i n e s  IOUBC  and IV  CSP a n d M a g n e t o m e t e r l i n e s  V  CSP l i n e  VI  CSP a n d M a g n e t o m e t e r l i n e s and CSP a n d M a g n e t o m e t e r l i n e s and  VII  EN 70-025-3  139  140  70-16-18  IOUBC 70-16-19  141  IOUBC 70-16-20  142 .14 3  IOUBC  70-16-21A  IOUBC 70-16-21B  144  IOUBC 70-16-23 IOUBC 70-16-26  145  VIII  CSP l i n e  EN 70 -025 -1  IX  CSP l i n e  EN 70 -025 -2  X  CSP l i n e  EN 70 -025 -9  XI  CSP l i n e s EN 70 -025 -10 and  XII  CSP l i n e  B I 69 -050 -HUDSON EN 70-025-11  149  XIII  CSP L i n e  BI 69 -050 HUDSON 3  ISO  6  151.  146 14 7 148  xi  ACKNOWLEDGMENTS  T h i s t h e s i s was. u n d e r t a k e n u n d e r t h e s u p e r v i s i o n o f Dr.  R.L. Chase t o whom t h e a u t h o r  advice  i s greatly indebted.  and a s s i s t a n c e t h r o u g h o u t the p r o j e c t i s a p p r e c i a t e d . T h a n k s a r e due t o D r . W.K.  F l e t c h e r and t o Miss  Barr f o rt h e i r a s s i s t a n c e i n the chemical The  use o f t h e atomic  analyses  co-operation  of the.officers  HUDSON, o f t h e s c i e n t i s t s (Bedford  chemical  The e n t h u s i a s t i c  a n d c r e w o f CNAV ENDEAVOUR and. CSS  o f the A t l a n t i c Oceanographic  Laboratory  I n s t i t u t e ) , a n d o f t h e t e c h n i c i a n s a n d s t a f f o f t h e UBC  Geology Department,is a l s o Dr. the manuscript  appreciated.  R . L i Chase and D r . P.B. Read a n d made many h e l p f u l  Financial  support  critically,reviewed  suggestions.  f o r t h i s p r o j e c t was p r o v i d e d  G r a n t No. A - 7 0 3 2 , DRB G r a n t No. 9511-95  b y NRC  ( b o t h t o D r . R.L: C h a s e ) ,  f r o m s e v e r a l o i l c o m p a n i e s and a UBC G r a d u a t e F e l l o w s h i p .  Funds f r o m A t l a n t i c O c e a n o g r a p h i c L a b o r a t o r y of rock  Sandra  of the rocks.  absorption u n i t i n Dr. G r i l l ' s  o c e a n o g r a p h y l a b o r a t o r y was most w e l c o m e .  grants  His  supported  s a m p l e s c o l l e c t e d d u r i n g H u d s o n 70 p h a s e V I I .  cataloguing  CHAPTER  ONE  INTRODUCTION LOCATION The and  51°15'  North  longitude, by  Dellwood  latitude  shelf  n o r t h and n o r t h e a s t ,  Fault  Zone on t h e e a s t ,  south  and t h e S c o t t  margin Juan  o f the American  de  Fuca  P U R P O S E AND  offset along  (Talwani  bounded  and S c o t t  Islands  S p r e a d i n g Z o n e on  plate,  the  (Figure 1).  Seamount A r e a  and near  near  i s situated  the southwestern  t h e n o r t h e r n end o f the  INVESTIGATION suggested  end o f t h e Dellwood be  a short  the Explorer  or parallel  earthquake  plate  e t a l (1968)  s l o p e may  from  of the P a c i f i c  SCOPE OF THE  northwest  tinental  the Dellwood  West  Queen C h a r l o t t e S o u n d on  on t h e w e s t  1  50°15"  a n d 131°00'  kilometers  by t h e Winona Ridge  Range  between  Plate.  Ewing the  and s l o p e o f f  Seamount  the e a s t e r n margin  square  by t h e E x p l o r e r  Tectonically, at  and b e t w e e n 129°40'  i s a n a r e a o f some 1 0 , 0 0 0  the continental  the  Seamount A r e a , s i t u a t e d  Seamount  S p r e a d i n g Segment  near  a ridge Range  running  toward  Seamount  by a f r a c t u r e Range.  Rise zone  A cluster  the n o r t h end o f the E x p l o r e r  e t a l , 1965; W e t m i l l e r ,  from  the con-  segment o f the E a s t P a c i f i c  t o the Dellwood  epicentres  that  1969) s u p p o r t s t h i s  Segment  interpreta-  tion . The p u r p o s e that  the Dellwood  o f t h e s t u d y was  Knolls  mark  such  to test  the hypothesis  a segment, o f f s e t  of  from the  T h e S c o t t S e a m o u n t R a n g e i s a new name c h o s e n b y t h e a u t h o r b e c a u s e i t i s t h e l a r g e s t unnamed seamount r a n g e s i t u a t e d on the s o u t h bank o f t h e S c o t t C h a n n e l .  2  3  Explorer Spreading Segment by the Revere - Dellwood Fault Zone, and meeting the Queen Charlotte r i g h t - l a t e r a l transform f a u l t , thus forming the northwesternmost boundary of the Juan de Fuca plate.  If this i s true, then the Dellwood Seamount Area may  be  a t r i p l e junction between the P a c i f i c , American and Juan de Fuca plates, i . e . between the Dellwood Spreading  Zone, the Queen  Charlotte transform fault and the northern end of the zone of subduction which marks the eastern margin of the Juan de Fuca plate. In this thesis, geophysical data (seismic r e f l e c t i o n and magnetic p r o f i l e s ; heat flow, gravity and earthquake epicentral d i s t r i b u t i o n data) were used to produce a tectonic map area.  of the  Basalts from the Dellwood Seamount Range and Dellwood  Knolls were compared petrographically and chemically with similar rocks from known ocean ridge spreading centres, transform fault zones and seamounts,. especially, those of the northeast P a c i f i c , to determine whether or not they represent ocean ridge basalts. Due  to i n s u f f i c i e n t shiptime, extensive sampling was  and although about  one ton of rocks  was  impossible  recovered, they came  only from s i x dredge sites which, however, represent a l l the main seamounts of the area. Due to lack of unequivocal data resulting from i n s u f f i c i e n t shiptime, equipment malfunction, seismic r e f l e c t i o n records with low signal to noise ratio and inaccurate locations of some seismic and magnetic p r o f i l e s and earthquake epicentres, the study became a geological and geophysical reconnaissance of the area with special reference to the tectonics, and only tentative conclusions could be  reached.  4  FIGURE 2. I/.ap of earthquake epicenters, occuring between 1954 and 19o3. (f roin Tbbin and Sykes, 1 9 6 8 . )  5  CHAPTER  TWO  A SLMMARY OF THE LITERATURE ON THE NORTHEAST PACIFIC PLATES AND ON THE PETROLOGY OF OCEANIC BASALTS  REGIONAL TECTONICS The ental the  s l o p e and  a r e a t o be  1968;  adjacent  s e a f l o o r west o f B r i t i s h  tectonically  W e t m i l l e r , 1969).  epicentres tion  h i g h degree o f s e i s m i c a c t i v i t y below the c o n t i n -  and  shows t h e s e  along  segments.  active  The t o be  located mainly connecting  from Tobin  and  of e p i c e n t r e s of major earthquakes  and  i n the n o r t h e a s t Wilson  ocean r i d g e  (1965), Vine  and W i l s o n  C a l i f o r n i a has and  spreading  Hayes  Work by  (1968) Mason  the 1954  and (1961)  several other  (1968), S r i v a s t a v a et a l  Thus f r o m m a g n e t i c and  and  extended  the  seismic data,  C o l u m b i a , W a s h i n g t o n , O r e g o n and  the  Northern  been p o s t u l a t e d to c o n t a i n l a r g e t r a n s f o r m  faults  ocean r i d g e s .  Bathymetric Mammerickx and  shows  o c c u r r i n g between  E m i l i a e t a l (1968), have c o n f i r m e d  ocean f l o o r o f f B r i t i s h  spreading  (1968),  (1965), Vine  i n terms o f s e a f l o o r s p r e a d i n g .  d a t a o f R a f f and Mason.  subduc-  Pacific.  a u t h o r s , i n c l u d i n g P i t m a n and ( 1 9 7 1 ) and  Sykes,  earthquake  of  o t h e r s h a v e i n t e r p r e t e d t h e m a g n e t i c d a t a o f R a f f and ( F i g u r e 3)  and  of  i n areas  Sykes  location 1963  Tobin  worldwide d i s t r i b u t i o n  transform faults  F i g u r e 2, t a k e n  ( M i l n e , 1967;  C o l u m b i a shows  Taylor  features i d e n t i f i e d degree of c l a r i t y  c h a r t s by M e n a r d (1971),  and  (1967),  Chase e t a l (1970) show m a j o r  f r o m s e i s m i c and  magnetic data w i t h v a r y i n g  ( F i g u r e 4 ) , as w e l l  seamounts, t r e n c h e s , canyons, fans  (1961) , McManus  and  as m i n o r f e a t u r e s s u c h plains.  as  6  FIGURE 3 . I n d e x anomaly map o f t h e t o t a l m a g n e t i c f i e l d ir>„ the N o r t h e a s t P a c i f i c O c e a n . T h e p o s i t i v e a n o m a l i e s a r e shovm i n b l a c k . (from Raff and Kason, 1961.)  7 FIGURE 4  BATHYMETRY of the PIONEER SURVEY  AREA  NORTH of 45 N LAT. OY  J. UM!:>rR:C\X ana . L. JAYLCff Gfrt.CP>l'*L M M CENTIA SCfcPPS INSTITUTION of C \ f ANCGPAPMY St I C:AL C«»»T VJ I  8  Morgan  (1968)  referred  to the s m a l l a r e a between the  w e s t e r n m a r g i n o f N o r t h A m e r i c a and t h e J u a n de F u c a and  Gorda  r i d g e s as t h e J u a n de F u c a b l o c k .  this  J u a n de F u c a b l o c k o r p l a t e  consists  c e n t r e s and t r a n s f o r m f a u l t s these are:  The w e s t e r n m a r g i n o f  of a series of spreading  (Figure 5).  t h e D e l l w o o d S p r e a d i n g Segment ( E w i n g e t a l , 1968)  c o n n e c t e d by t h e R e v e r e  - Dellwood f a u l t  Segment  Ewing  the  ture  ( W i l s o n , 1965).  East P a c i f i c  zone  e t a l , 1968)  ( P a v o n i , 1966)  t o the  Explorer  i n turn connected  t o t h e J u a n de  Rise which i s connected v i a the transform fault  Rise i n the Gulf of C a l i f o r n i a .  series of transform faults  connected to the A l e u t i a n  by  Fuca  T h i s i s connected v i a the B l a n c o  Zone t o t h e San A n d r e a s  end o f t h i s is  Zone  Zone t o t h e G o r d a  Fracture the  (McManus, 1967;  Sovanco F r a c t u r e  segment  From n o r t h t o s o u t h  Frac-.  Mendocino  and t h u s t o The n o r t h e r n  and s p r e a d i n g s e g m e n t s  Island Arc v i a right  f o r m movement a l o n g t h e Queen C h a r l o t t e  lateral  and r e l a t e d  trans-  faults  ( T o b i n and S y k e s , 196 8 ) . The  l o c a t i o n of the e a s t e r n margin of t h i s p l a t e i s  u n c e r t a i n , though ental the  i t i s assumed t o be a t t h e b a s e  o f the  s l o p e o f f w e s t e r n N o r t h A m e r i c a b e t w e e n Cape M e n d o c i n o  s o u t h and t h e S c o t t I s l a n d s  several (i)  lines  of evidence which  A zone  Washington,  i n the n o r t h ; t h i s based  (ii)  s o u t h e r n B r i t i s h C o l u m b i a and V a n c o u v e r  Oregon,  Island  with  km.  1968).  D e f o r m a t i o n i n P l i o c e n e and P l e i s t o c e n e  continental  on  of moderate s e i s m i c i t y near the c o a s t o f  ( T o b i n and S y k e s ,  in  include:  some s e i s m i c e v e n t s h a v i n g h y p o c e n t r e s t o d e p t h s o f 60  the  contin-  sediments  s h e l f and s l o p e and i n W i n o n a B a s i n ( B a r r ,  on 1971,  SCAL€ a  so'H  10  personal (iii)  communication; S i l v e r , The  existence  1 9 6 9 , and p r e s e n t  of Pliocene  v o l c a n o e s n e a r the c o a s t o f Oregon Garibaldi ornia  in British  study).  and P l e i s t o c e n e and W a s h i n g t o n  andesitic  f r o m Mt.  C o l u m b i a t o Mt. L a s s e n i n N o r t h e r n C a l i f -  ( M o r g a n , 1 9 6 8 ; Hays and N i n k o v i c h ,  1970;  Figure  6).  M c K e n z i e and M o r g a n (1969) i n t e r p r e t e d t h e Cape Mendocino tion  a r e a as a t r i p l e  j u n c t i o n between  along the c o n t i n e n t a l  Mendocino  Fracture  margin north  t h e J u a n de F u c a p l a t e  the  o f Cape M e n d o c i n o .  fault-plane  Mendocino  regional ring  possible the  o f the. m a g n e t i c a n o m a l y  F a u l t by S i l v e r  c o m p r e s s i o n as w e l l  a t Cape M e n d o c i n o  Mendocino  fault.  as b e i n g consumed  First-motion  the  along  studies  and  s o l u t i o n s by B o l t e t a l ( 1 9 6 8 ) , S e e b e r e t a l ( 1 9 7 0 ) ,  as w e l l as an a n a l y s i s the  subduc-  o f Cape M e n d o c i n o ,  Zone and t h e San A n d r e a s t r a n s f o r m  They c o n s i d e r e d coast north  t h e zone o f  Fault that  Mendocino  (1969) i n d i c a t e t h a t as s t r i k e - s l i p  along  north-south  m o t i o n may  be  occur-  and p e r h a p s a l o n g t h e r e s t o f t h e  t o the Gorda Ridge  (Figure  7) and t h u s i t i s  c o n s u m p t i o n o f the Gorda B a s i n Fault  pattern  as w e l l  i s occurring  as a l o n g t h e w e s t e r n  along  continental  margin. The solutions within the  evidence from f i r s t - m o t i o n s t u d i e s  suggests that  a new  t h e J u a n de Fuce p l a t e  Gorda B a s i n  fault-plane  t e c t o n i c regime i s d e v e l o p i n g involving internal  deformation of  and n o r t h - s o u t h c o m p r e s s i o n a l o n g t h e  F a u l t e a s t o f the Gorda Ridge The  and  (Seeber et a l , 1970).  J u a n de F u c a p l a t e may  a series of smaller  plates  to the American c o n t i n e n t  Mendocino  t h u s be b r e a k i n g  p e r h a p s due as p a r t  up  to i t s becoming  o f the American p l a t e  into  welded or  due  11  ?  A  O  C  C  I  E  A N  —M  FIGURE 6* R e l a t i o n s h i p between spreading; r i d g e s , sv.bd*aotlch zones and Quaternary A n d e s i t i c v o l c a n o e s i n t h e N o r t h e a s t P a c i f i c * (from Hays and ITinkovich, 1970.)  OREGON  T  CALIFORNIA  ^ //GORDA BASIN\ \ X  , v  39"  } "  :  . Mfc ND  O C • f*0  .,^r  j  NORTH AMERICANI PLATE  PACIFIC, P L A T E AS FAULT  iGURE 7. G e n e r a l i z e d map o f Cape Mendocino A r e a s c h e n a t i c a l " : y showing major t e c t o n i c f e a t u r e s . . (from Seeber et a l . , 1970.)  12  t o a t e n d e n c y f o r s t r i k e - s l i p m o t i o n t o become c o n t i n u o u s the  c o n t i n e n t a l margin j o i n i n g  the  Queen C h a r l o t t e f a u l t  GRAVITY AND Gravity  (1967),  L o v e l l (1967),  o b s e r v e d t h a t the  features  implying  i b r i u m and  that  activity  Charlotte  with  fault  t o the the  e n t i r e r e g i o n and the  to  area  g r a v i t y w o r k done  and  area  Dehlinger  has  many m a j o r  is essentially  readjustment occurs  adjacent  P u g e t Sound a r e a , continental slope  Many o f t h e  e f f e c t s o f t o p o g r a p h y as  M e n d o c i n o and  local  1  in isostatic  equil-  f a r more r a p i d l y Regions  the B l a n c o and  the  free-air  of tec-  fault,  Queen  anomalies  f o r example t h o s e  G o r d a e s c a r p m e n t s and  zero-  structural  anomalies which r e s u l t from s t r o n g  i n c l u d e the  zone.  et a l  essentially  t h a n does t e c t o n i c u p h e a v a l .  free-air  and  Couch ( 1 9 6 9 ) ,  g r a v i t y i n the  isostatic  negative  Winona B a s i n  due  that  these features  tonic  system  zone.  e t a l (1970) , r e p o r t i n g on  average over both the  strong  Andreas f a u l t  Data  G e m p e r l e and  for  San  HEAT FLOW DATA  Dehlinger by  the  along  w i t h the  are  associated numerous  seamounts. A f r e e - a i r anomaly o f associated with trough.  Off  the n o r t h  anomaly g r e a t e r topographic  the p a r t i a l l y end  t h a n -150  trough  and  approximately  sediment - f i l l e d  -100  Queen  of Vancouver I s l a n d , a milligals  i s not  indicates that  this  milligals  Charlotte  free-air  associated with area  is  a  (the Winona  ^'he S c o t t I s l a n d s f r a c t u r e zone o f C o u c h , D e h l i n g e r , and i n c l u d e s t h e W i n o n a B a s i n and a d j a c e n t c o n t i n e n t a l s l o p e .  others  FIGURE 8. Free-air gravity anomaly map, west coast of Washington and B r i t i s h Columbia. Contour Interval 50 m i l l i g a l s . (after Couch, 1969.)  FIGURE 9. F r e e - a i r g r a v i t y anomaly map, west c o a s t o f Oregon. Contour I n t e r v a l 50 m i l l i g a l s . ( a f t e r D e h l i n g e r e t a l . , 1970.)  1-32  130  . 128  126  124  FIGURE 10, F r e e - a i r g r a v i t y anomaly map, west coasx o f N o r t h e r n C a l i f o r n i a . Contour I n t e r v a l 50 m i l l i g a l s . ( a f t e r D e h l i n g e r e t a l . , 1970.)  15  Basin  and a d j a c e n t  filled  downfaulted  gravity plate Heat  continental slope) structure.  anomaly maps o v e r  and a d j a c e n t Flow  areas,  Figures  the e n t i r e a l l taken  a sediment-  8, 9, and 10 a r e f r e e - a i r  r e g i o n o f t h e J u a n de F u c a from  Dehlinger  et al  (1970).  Lata Dehlinger  e t a l (1970) have  f l o w measurements made (Figure  may r e p r e s e n t  a l s o summarised  the heat  i n t h e a r e a between 1962 and 1970  11) as f o l l o w s :  "The h e a t f l o w i n tiie a r e a i s g e n e r a l l y h i g h f o r o c e a n i c r e g i o n s a v e r a g i n g 2.01 u c a l s / c m . s e c w h i c h i s a b o u t 60% h i g h e r t h a n t h e a v e r a g e f o r o c e a n b a s i n s (1.28 u c a l s / c m . s e c ) H i g h h e a t f l o w v a l u e s a r e s e e n t o be r e l a t e d to the Mendocino escarpment e a s t o f t h e Gorda Ridge, to t h e Gorda B a s i n , Gorda R i d g e , J u a n de F u c a R i d g e , C a s c a d i a B a s i n and D i x o n E n t r a n c e . The a v e r a g e v a l u e f o r 31 s t a t i o n s a l o n g t h e s e f e a t u r e s i s 2.95 u c a l s / c m . s e c a p p r o x i m a t e l y 601 h i g h e r t h a n t h e average f o r ocean r i d g e s A s t r i k i n g observat i o n on t h e h e a t f l o w map ( F i g u r e 11) i s t h a t h e a t f l o w v a l u e s a r e below n o r m a l a t r e l a t i v e l y s h o r t d i s t a n c e s west o f t h e r i d g e s , whereas t h e h i g h h e a t f l o w e x t e n d s f r o m the r i d g e s a c r o s s t h e p l a i n s t o the e a s t . The low h e a t f l o w i s a s s o c i a t e d w i t h n o r m a l t o above n o r m a l m a n t l e v e l o c i t i e s and t h e h i g h heat flow w i t h below normal mantle v e l o c i t i e s . ' 2  2  2  1  This ities  i s supported  (1968). Paul  relationship  Heat  Revere  Lister  by s e i s m i c  flow values  Ridge  and E . D a v i s  Circumnavigation  the  relation  aboard  o f these  i n the Dellwood  Discussion)  and m a n t l e  o f the Americas values  veloc-  Area  Seamount A r e a and were m e a s u r e d by L.  t h e CSS Hudson d u r i n g  the t e c t o n i c s o f the area  (See  flow  r e f r a c t i o n work by S h o r e t a l  - E x p l o r e r Trench  the  to  between heat  i n 1970.  to topography. i s discussed  Phase V I I o f  Figure  Their  12 shows  significance  i n a later section.  16  |12"  |.10*  133*  136'  134°  132'  130*  128*  126*  124*  122*  120'  FIGURE I I . Sunrarvry of heat flow values ( i n pcal/cr. .sec) i n t h e northeast P a c i f i c . (fras D'ehiinger et al. ,1970.) 2  CONTOUR INTERVAL 200 METRES  18  'IGUR5 1 3 . Some m a j o r t e c t o n i c f e a t u r e s o f W e s t e r n N o r t h America,, Host t h r u s t s a r e o m i t t e d . Quaternary v o l c a n l c s a r e b l a c k , g r a n i t i c plutonics are gray. (from Atwater, 1970.)  F i - u r e li}..Magnetic anomalies in the northeast Pacific from Atwater and Menard (1970). Numbering of anomalies and their ages shown i n the scale follow l U i r t z l e r and others (196S); ages of geologic epochs follow Bcrggren (1969).  19  REGIONAL TECTONIC HISTORY DURING THE Using America  the major  (Figure  northeast of.plate  13)  Pacific  and  North America.  The  first  (Figure  assuming  that  relative  t o one  the  15B)  ago  interactions  (Figure  a n o t h e r between 30 myr.  when the N o r t h A m e r i c a n  apart  and began  t o move p a s t  Prior  t o 30 myr.  ago,  this  one  15A)  and  and  Plates  models  5 myr,  Pacific  of  fixed i . e . that  fault  Plates  shows t h e c o a s t  tectonic  America,  ago;  as a s t r i k e - s l i p and  .15 w h i c h  were  a n o t h e r a t the r a t e  model  two  by, F i g u r e  of western North  and P a c i f i c  initiated  i n the  (1970) a p p l i e d  is illustrated  along the.coast  F a u l t was  North  Cenozoic h i s t o r y , o f w e s t e r n  the  the N o r t h American  San A n d r e a s  5 myr.  model  of western  anomaly p a t t e r n  14), Atwater  to e x p l a i n  shows s c h e m a t i c a l l y p l a t e history  features  the m a g n e t i c  (Figure  interactions  tectonic  CENOZOIC  only  broke o f 6 cm/yr.  California  as a s u b d u c t i o n zone. In A t w a t e r ' s is  second model,  assumed c o n s t a n t f o r s e v e r a l  this  motion  i s assumed t o be  the  coast.  Figure  and  deformation related  the N o r t h American Figure  17  the  plate  Pacific  amount  tens of m i l l i o n s  t a k e n up by  i s a reconstruction to m i d d l e  and P a c i f i c  - late  plates  of years  t r a n s f o r m motion of plate  motion and' along  evolution  Cenozoic i n t e r a c t i o n  under  such assumptions  of and  shows the t e c t o n i c h i s t o r y , a l o n g t h e , c o a s t o f w e s t e r n  North America American  16  the P a c i f i c - A m e r i c a n  during  t h e same p e r i o d .  is arbitrarily  plate  held  is horizontally  In F i g u r e  fixed  and  16,  the North  g o i n g back  moved t o t h e r i g h t  by  i n time, the  indicated. A late  Mesozoic  - early  C e n o z o i c e x i s t e n c e -of a K u l a  20  •  ^  <-  PRESENT  QUEEN CHARLOTTE  5M 300 im  ISLANDS STR.KE SLIP  1 S. F  ' 71 / \ / %  10 Ml  LA fjORTH OS AMERICANPACIFIC PLATE  SF LA 20 KT  N^.  */  J  SEATTLE  SAN  LOS  FRANCISCO  ANGELES  STRIKE  GUMMAS  MAZAT AN L  SLIP  1 NO RELATIVE MOTION BEING T A K E N UP  —  AT MARGIN  /  i •/-  GS • WZ "" v '"  SF  1  LA  NORTH AMERICAN PLATE1 -  30 NT.  FIGURE 15.  A - Schematic model of plate interactions assuming that the North American and Pacific plates were fixed to one another u n t i l 5 m.y. ago, at which time they broke apart and began, to move at a rate of 6 cm/vr. B - Evolution with time of boundary regimes along the coast <3f North .America assuming the model of. changing motions described i n Av (from Atwater, 1970.)  NOTE: In figures 15 and 16, single lines are transform faults, double lines are spreading centers and hatched lines are subduction zones. Large arrows show motion of the plates with respect to the P a c i f i c plate i n figure 15 and the North American plate i n figure 16. Small arrows show r e l a t i v e motions at points along plate boundaries. I n i t i a l s are places l i s t e d i n figure 17.  21  20MX  I200KM.  /  FIiVP.3  16.  R e c o n s t r u c t i o n o f p l a t e e v o l u t i o n a n d d e f o r m a t i o n r e l a t e d t o l a t e C e n o t o i c i n t e r a c t i o n of the ! i o - t h A n c r i c a n and P a c i f i c p l a t e s . D i a r . r a n s i n G show t h e d e r i v a t i o n o f v a r i o u s v e c t o r s . C a p t i o n s e i v e r - i l l l o n s o f y e a r s b e f o r e p r e s e n t and a r . o u n t o f o f f s e t w h i c h must s u b s e q u e n t l y o c c u r t o b r i n i ? P a c i f i c and I n n e r N o r t h A r - . e r i c a n p l a t e s b a c k t o t h e i r p r e s e n t r e l a t i v e p o s i t i o n s . P a c i f i c N o r t h A m e r i c a n m o t i o n (P ) i s a s s u m e d c o n s t a n t a t 6 c r - , / y r . i n a h o r i z o n t a l direction. F o r t h e l a s t 2 0 r y r . , 4 c n / y r . i s a s s u r e d t a k e n up on c o a s t a l f a u l t s w h i l e 2 c n / y r . I s a c c o m m o d a t e d by i n l a n d f a u l t s . T h u s C a l i f o r n i a was r . o v i n g n o r t h w e s t a t 2 c n / y r . P r i o r t o 2 0 n y r . a l l m o t i o n i s presumed t a k e n u p a l o n r ; t h e c o a s t . B l a c k r e g i o n s a r e u n a c c e p t a b l e o v e r l a p s of o c e a n i c a n d continental c r u s t , ( a f t e r Atwater, 1970). A  J J .!< P C„ t  A  A  » • " •  J u a n de F u e a - F . n c i f i c r o t l o n . ' u a n de ? u c a - A n o r i c a n n o t i o n . . ' u a n de F u c a - C a l i f o m i a m o t i o n . raci fi c-Anorican notion. Callfomia-Anerican notion.  F, • F a r a l l o n - F a c i f l c motion. F< • F a r a l l o n - A m e r l c a n n o t i o n . K» - X u l a - P a c i f i c n o t i o n . K» • K u l a - A n e r i c a n m o t i o n .  22  C  5  SP  H  B  SF SL CC  LV D LA PH  EP CI GS CH  HZ BC  GU  Figure 17. Location of plate boundary regimes with respect to points in western North America, assuming motions and deformations described for Figure 16. Inland cities are raised above the line. They have been projected to the coast vertically in the projection of Figure 16. roughly parallel to the direction of Farallon-North American underthrusting. Fine lines trace the shifting locations of the cities as the continent deforms. Gray areas show times and places where tectonic and igneous activity related to subduction are predicted. White areas show times and places where North America was in contact with the Pacific plate or with the Kula plate »  (from Atwater, 1970.)  23  P l a t e has b e e n p o s t u l a t e d 1970  ( P i t m a n and H a y e s , 1 9 6 8 ;  and o t h e r s ) t o e x p l a i n t h e E a s t - W e s t  anomalies  and  plates  t o generate these East-West  as t h e most p r o b a b l e o n e , i s correct.  m o t i o n s ) , the n o r t h e r n t r i p l e  this  c o a s t o f S o u t h e r n A l a s k a and B r i t i s h  Vancouver  Island  b e t w e e n 5 myr. fault triple the  was  5 myr.  ago  model  (changing  Columbia  the Dellwood  since before  just o f f northern Seamount  area)  and p r e s e n t , d u r i n g w h i c h t i m e t h e San In the second model  remained  o f f Vancouver  i n the f i r s t  Andreas  (constant motions), this  I s l a n d d u r i n g the whole  m i d d l e t o l a t e T e r t i a r y b u t m i g r a t e d n o r t h {not  proposed  Pacific  F u c a P l a t e ) moved r a p i d l y , down  and t h e n r e m a i n e d  (probably w i t h i n  active.  point  ago  de  patterns.  definitely  p o i n t between the A m e r i c a n ,  the Juan  myr.  second model o f c o n s t a n t  In the f i r s t  the  until  anomaly  i t i s n o t as y e t  Farallon Plate  ago  Farallon  t o u n r a v e l , as s u b d u c t i o n  and  30 myr.  (now  Aleutian  P r i o r t o 40  destroyed the magnetic  Although Atwater p r e f e r r e d  e s t a b l i s h e d which  south o f the  anomalies.  is difficult  t h e A l e u t i a n T r e n c h has  motions  magnetic  r i d g e l y i n g b e t w e e n t h e K u l a and  ago, however, the h i s t o r y of  trending  the Great Magnetic B i g h t l y i n g  Trench, with a t h i r d  Atwater,  model) from C a l i f o r n i a  south  d u r i n g the  of  as early  Tertiary.  PETROLOGY OF OCEANIC BASALTS Types o f Oceanic  Basalts  Oceanic b a s a l t s tholeiites Engel e t . a l  and  comprise  alkali-rich basalts.  (1965)  studied basalts  two m a i n t y p e s - o c e a n i c E n g e l and E n g e l from i s l a n d s  and  (1964)  and  seamounts  24 Di  Cpx  01  Ol Alkali  Bosolt  cpx  Group  (cpx)  Cpx  Cpx  .  Olivine  Tholeiite  Group  Tholeiite'  Group  FIGURE 18. M a j o r t y p e s o f b a s a l t . • (fro*: Y o d e r and T i l l e y , 1962.) A — Generalized normative b a s a l t tetrahedron. B — E x p l o d e d v i e w o f g e n e r a l i z e d s i m p l e b a s a l t system i l l u s t r a t e d i n A.  25  of  the E a s t P a c i f i c  that t h o l e i i t i c volcanic  R i s e and  submerged  f e a t u r e s i n the oceans a l o n g s c a r p l i k e  ridges of  zones and on d e e p e r f l a n k s o f t h e v a s t number o f  submarine v o l c a n o e s . basalts  cap  tholeiitic  normative  t o t a l - i r o n contents.  Kay  rocks are  depths  Aumento  the M i d - A t l a n t i c  of the median r i f t  t h e r i d g e and  al  oliyine  characterised  and  A1 0 2  3  alkali  R i d g e , y e t even h e r e ,  v a l l e y , w h i l e on t h e h i g h e r  olivine  t h e two  and  alkali  and  i z e d normative  basalt  tholeiites  olivine  contain normative between o l i v i n e  t e t r a h e d r o n by t h e c r i t i c a l  and h y p e r s t h e n e ,  olivine  tholeiites  and E n g e l  Y o d e r and  alkali  composition.  plane  of  tholeiites contain-  while a l k a l i  and n e p h e l i n e . and  Tilley  are d i v i d e d i n the g e n e r a l -  undersaturation, (Figure 18), o l i v i n e  normative  characteristics  them on t h e b a s i s o f n o r m a t i v e  olivine  transition-  basalts.  types of oceanic b a s a l t .  (1962) d i s t i n g u i s h e d basalts  reaches  on o c e a n i c i s l a n d s , t h e r e o c c u r a l s o ,  tholeiites  distinguish  by E n g e l  e t a l (1970)  (1967) r e m a r k e d t h a t a v a r i e t y  S e v e r a l c h e m i c a l and p e t r o l o g i c a l  silica  the  are t h e . o n l y t y p e . r e p o r t e d to have e x t r u d e d i n the  of  Alkali  et a l  composition with variable  v o l c a n i c e x t r u s i v e s i n c l u d i n g both t h o l e i i t e s  tholeiites  alkali-rich  Nicholls  I n d i a n oceans are t h o l e i i t i c .  b a s a l t s o c c u r on  ing  that  from the r i d g e s o f  t h a t mid-ocean r i d g e v o l c a n i c  by o l i v i n e  of  i s l a n d volcanoes.  t h a t most o f t h e b a s a l t s  m i d - A t l a n t i c and concluded  In c o n t r a s t , they found  s u b m a r i n e and  (1964) n o t e d  and  concluded,  f o r m most o f t h e d e e p l y  oceanic r i f t  basalts  t h e o c e a n b a s i n s and  Chemical  basalts distinction  b a s a l t s have been r e p o r t e d  ( 1 9 6 4 ) , E n g e l e t a l (1965) and o t h e r s .  Such  ..  I, , M U T i l ' H i II > n :  X.  \\i.u\..i ,L.*v  C  26  0 >MI'i".| 1) 1 1NN  l l l l M I ' V U I 11 U | I'll  lKlv.ll!  Ha Co Cr Cu  II *2 297 77 17 < SO 9 < 30 97 < 10 CI 130 292 •13 5 95  C,:i I.a Li Nh Ni Kb Sc Sr V Y Yb Zf  49.34 1.49 17.04 1.99 6.82 .17 7.19 11.72 2.73 .16 .(>9 .5S .16 . 29 1300" 130* 16 14 121 ' 4  SiOj TiOj M2O3  1-cO  M11O  Mi;0  oo  \:.;0 K O H;0 + a  H2O-  i\-Oi  i  K/i<!i • Sr/Rb Na/K K/Zr K/Ba K/Cr  l i l M I  h  1)  VI \ T I ' i V s  Sl.\M  1 !tu\l  Mi-aii deviation  lliolriitii: Cumjxml ion  V M I NI 1 S \  Al.k M l  6 19 19 21 57 10 1.5 15 (wciglit per cent) .54 .39 1.78 .65 1.50 .03 .67 .69 .20 .06  .05  A S H  Ki sit*. .  (ICVKII  49H 25 67 36 22 90? 11 72 51 33 26 H15 252 54 4 333  •>  1  Men 1  AU..M basalt  (pans per million) 7 3 73 6  HAI' !  '.on  136 5 57 13 2 5 9 .33 4 375 32 7 1 48  47^41 2.87 IS.02 4.17 5.80 .16 4.79 8.65 3.99 1.66 .79 .61 '" .92  3.08 .24 1.71 1.16 1.17 .03 1.35 .91 .41 .38  .22  ' .72 418 25 2 .4  28 206  ...  •  (  from En-el et a l . , 1965.)  i r  1  y 30  10 ._L_J  (Y)  L_J L  (ft) ~  L_J L L a C o P r N d P m S m E u G d T b D y H o E r T m Yl> L u 60 70 _ l  atomic number FIGURE  1 9 . Rare-earth  pattern  relation between  (o) t h o l e i i t i c basalts  o f s h i e l d v o l c a n o e s a n d (o) s p a t i a l l y  r e l a t e d m i d - o c e a n r i d g e t h o l e i i t c s . N o t e the l i g h t r ; c . e n r i c h m e n t for s h i e l d v o l c a n o e s i n c o n t r a s t to the h e a v y r a r e earths w h i c h a r e s i m i l a r for b o t h the s h i e l d v o l c a n o a n d t h e m i d - o c e a n r i d g e , (a) J c b c l T c i r t h o l e i i t e a n d a v e r a g e o f five R e d S e a a x i a l t r o u g h b a s a l i s ; (b) C u l p e p p e r t h o l e i i t e a n d a v e r a g e o f s i x E a s t P a c i f i c rise tholeiitcs.  .  .(frop S c h i l l i n g , 1971.)  27  distinguishing  f e a t u r e s a r e summarised i n Table  I taken  from  Engel e t a l (1965). Schilling  (1971) a l s o shows t h a t on t h e b a s i s o f r a r e  e a r t h d i s t r i b u t i o n p a t t e r n , mid-ocean r i d g e t h o l e i i t e s a r e distinguishable of  tholeiitic  enrichment volcanoes alts,  from s p a t i a l l y  composition  of the light relative  related oceanic s h i e l d  volcanoes  ( F i g u r e 1 9 ) , f o r t h e r e i s "a n o t i c e a b l e  r . e . content f o r the s u b a e r i a l  to the s p a t i a l l y  shield  r e l a t e d mid-ocean r i d g e bas-  w h i l e t h e h e a v y r . e . c o n t e n t s s t a y more c o n s t a n t . "  (1971) d e m o n s t r a t e d  that oceanic t h o l e i i t e  Gast  b a s a l t s had about  t h e same p r o p o r t i o n s o f r a r e e a r t h s a s c h o n d r i t i c m e t e o r i t e s except  fora slight  the a l k a l i  basalts  deficiency  i n the l i g h t e r elements,  o c c a s i o n a l l y produced  greatly enriched i n the l i g h t  while  a t t h e r i d g e were  rare earths.  O r i g i n o f Oceanic B a s a l t s Yoder and T i l l e y of  b a s a l t s , concluded  ( 1 9 6 2 ) , from  an e x p e r i m e n t a l  study  that  "The two p r i n c i p a l magma t y p e s r e c o g n i s e d by f i e l d i n v e s t i g a t o r s - t h o l e i i t i c a n d a l k a l i b a s a l t t y p e s - a p p e a r t o be s e p a r a t e d b y e q u i l i b r i u m t h e r m a l d i v i d e s a t 1 atm. The p r i n c i p a l d i v i d e s were f o u n d b y e x p e r i m e n t a t e l e v a t e d p r e s s u r e s to g i v e way t o a new s e t o f e q u i l i b r i u m t h e r m a l d i v i d e s r e s u l t i n g f r o m a new m i n e r a l o g y . The change of t h e e q u i l i b r i u m thermal d i v i d e s w i t h p r e s s u r e l e a d s t o t h e d e r i v a t i o n o f t h e two p r i n c i p a l magma t r e n d s f r o m t h e same b u l k c o m p o s i t i o n In g e n e r a l , a l k a l i b a s a l t - t y p e magmas a r e t o be e x p e c t e d t o be g e n e r a t e d a t g r e a t e r d e p t h s t h a n t h o l e i i t i c t y p e magmas f r o m t h e same p r i m a r y s o u r c e r o c k , " Kuno  ( 1 9 5 9 ) w o u l d d e r i v e t h e s e two magma t y p e s  from  d i f f e r e n t p a r e n t m a t e r i a l s m e l t i n g under d i f f e r e n t c o n d i t i o n s at  d i f f e r e n t l e v e l s beneath  the crust.  Macdonald  ( 1 9 5 9 ) , and  28  Engel  and Engel  (1964) , f r o m a n a l y t i c a l  data  r e l a t i o n s h i p s o f the p r i n c i p a l b a s a l t types Islands  and E a s t  alkali-rich  rocks  Pacific  coupled  with  on t h e H a w a i i a n  Rise r e s p e c t i v e l y , concluded  are d e r i v a t i v e rocks  tholeiites  by p r o c e s s e s  tholeiites  are the p r i n c i p a l  that  f r a c t i o n a t e d from  o f magmatic d i f f e r e n t i a t i o n  Schilling  oceanic  and o c e a n i c  o r o n l y magma g e n e r a t e d  upper mantle beneath t h e oceans.  field  i n the  (1971) r e p o r t e d  that  " T h o l e i i t i c s h i e l d volcanoes which are p r e s e n t l y o r were once l o c a t e d o v e r t h e c r e s t o f m i d - o c e a n r i d g e s a r e n o t common. Most o c e a n i c i s l a n d s a r e c h a r a c t e r i s e d by l a v a s o f t h e a l k a l i s e r i e s a t l e a s t subaerially. Such o b s e r v a t i o n s p r o b a b l y have g e n e t i c implications. Dredge h a u l s f r o m f l a n k s o f v o l c a n i c i s l a n d and seamounts a r e t o o s c a r c e t o d e t e r m i n e c r i t i c a l l y whether a g r a d a t i o n e x i s t s between seaf l o o r t h o l e i i t i c b a s a l t s over t h e r i d g e and a l k a l i b a s a l t s towards t h e top o f such v o l c a n i c e d i f i c e s . " Green and Ringwood pressure al  (1967) d e m o n s t r a t e d t h a t c h a n g e s i n  may be t h e c o n t r o l l i n g  m e l t i n g ; magma s e g r e g a t i o n  t a l l i z a t i o n , o f a parent olivine alkali  tholeiite  f a c t o r i n the trend of f r a c t i o n -  from r e s i d u a l  p y r o l i t e mantle producing  from a p a r t i a l  b a s a l t from f r a c t i o n a l  magma g e n e r a t i o n b e g i n n i n g correspond  to the f i e l d  Green and Ringwood  pyrolite tholeiite  at pressures  alumina  m e l t i n g at g r e a t e r depths.  Aumento  i n t e r r u p t e d sequence o f  w i t h t h e i n c o r r e c t magma t y p e s  does  observations."  N e v e r t h e l e s s , Aumento by  high  m e l t a t a d e p t h o f 30 km. a n d  (1967) r e m a r k e d , h o w e v e r , t h a t " t h i s  not  c r y s t a l s , and c r y s -  (1967),  used e x p e r i m e n t a l  (1967) - " t h a t 30% p a r t i a l  melting of  o f 12-18 k b . (35-60 km.) w i l l  magma .... a l e s s e r  degree o f p a r t i a l  will  p r o d u c e an a l k a l i - r i c h b a s a l t l i q u i d " ,  tion  that " o l i v i n e - r i c h  data  yield  olivine  m e l t i n g (201)  and t h e i r  demonstra-  t h o l e i i t i c magma may f r a c t i o n a t e t o  29 CLOSED  SYSTEM  FRACTIONATION AT  VARIOUS  ALKALI OlIVINE BASALT High  OF  BASALTIC  M A G M A  PRESSURES  ALKALI OLIVINE BASALT  Al,q&  OLIVINE THOLEIITE K$h AljOj 5-15% nor motive olivine & 5-15% hypenrhenc  High AljOj  normative  Enslatit* + Ctino pyroxene  CfinopyroJtena  OLIVINE &ASANITE normative nephdine  AUCAU OLIVINE BASALT Low A l , 0 , ; 25% normative olivine; + Aluminous 1*2% normative r>eph»Cn« Erotatire  Aluminous G'nopyroxen©  i  AIum-ncHJi Eniratite  OLIVINE BASALT Low A i p ; 25%  Ahjrninouf En italic  9 Kb  low AljO, EtutaHte  OLIVINE  THOLEIITE  Low A l p ,  13-18 Kb  3  20-25% nor ma live olivine ;5-I5% norma' five hypenthene  normative otvinc; AJuminoui & lub-caick ^5% orthopyroxene cGno pyroxene  l + Mgh A l f t • Eratatite ? PICRITE  FIGURE 20. DiagraiiJiiatic summary of. the e f f e c t s and d i r e c t i o n s of f r a c t i o n a t i o n of b a s a l t i c l i q u i d s at moderate to high pressures, (from Green and Ringwood, 1967,) MEDIAN VALLEY  CREST MTNS.  W  5 km. sea level RECENT  - 1 km. - 2km. ALKALI  •1  BASALT  TRANS  THOLEIITES  OLIVINE  ppt.  of  7  3 km.  rIOLEIITES  olivine  — 15 km-  ppt  of olivine  low  Co  ppt  of  a  pyroxene  • 35 km. • ALKALI OLIVINE BASALT  Mg - Al  pyroxene  %  fractional  30%  25%  20%  melting  25% • 60km.-  0 =  PYROLITE ••  = PYROLITE =  convection  convection  =PYROLITE==C>  FIGURE 21., Model of magmatic evolution, of the Mid-Atlantic (from Aumento, 1967.)  Ridge,  30  yield  distinctive  (Figure  b a s a l t i c magma t y p e s a t d i f f e r e n t  20) t o p r o v i d e  Mid-Atlantic  Ridge.  pressures"  a model o f m a g m a t i c e v o l u t i o n  O b s e r v a t i o n s by s e v e r a l  f o r the  a u t h o r s h a v e shown  that "a v a r i e t y o f v o l c a n i c e x t r u s i v e s i n c l u d i n g t h o l e i i t e s , h i g h a l u m i n a a n d a l k a l i b a s a l t s and t h e i r d i f f e r e n t i a t e s o c c u r on t h e M i d - A t l a n t i c R i d g e .... i n c o n t i n u o u s r e p e a t e d v o l c a n i c c y c l e s commencing w i t h t h o l e i i t e s and e n d i n g w i t h a l k a l i b a s a l t s .... - t h o l e i i t e s e x t r u d i n g on t h e f l o o r o f t h e m e d i a n r i f t v a l l e y ; subsequent e x t r u s i o n s capping the t h o l e i i t e s are progressively enriched i n a l k a l i s . " Aumento's model  (Figure  21) i s as f o l l o w s :  "Sudden s t r e s s r e l e a s e due t o f a u l t i n g on t h e median r i d g e v a l l e y r e s u l t i n c o n s i d e r a b l e partial m e l t i n g o f a p y r o l i t e mantle which i n i t i a t e s a v o l canic c y c l e w i t h subsequent e x t r u s i o n o f t h o l e i i t i c lava. As t h e o r i g i n a l e n e r g y i s c o n s u m e d , t h e e x t e n t o f p a r t i a l m e l t i n g p o s s i b l e i s g r a d u a l l y r e d u c e d so t h a t s m a l l e r q u a n t i t i e s o f magma p r o g r e s s i v e l y enriched i n a l k a l i s are generated. The l a s t e x t r u sions of a volcanic cycle consist of small quantities of a l k a l i o l i v i n e b a s a l t . S i n c e t h e magmas e x t r u d e o n t o an a c t i v e l y s p r e a d i n g f l o o r .... b y t h e t i m e a v o l c a n o reaches t h e end o f i t s c y c l e e x t r u d i n g t h e l a s t o f t h e a l k a l i l a v a s , i t w i l l h a v e moved l a t e r a l l y a f e w km. f r o m i t s o r i g i n a l a x i a l p o s i t i o n ..... H i g h a l u m i n a e q u i v a l e n t s o f t h e s e magmas w i l l be p r o d u c e d by d i f f e r e n t i a t i o n o f t h e r i s i n g magmas a t l o w e r p r e s s u r e and/or by p a r t i a l m e l t i n g o f p y r o l i t e a t shallower depths." Thus due t o d i f f e r e n t amounts o f p a r t i a l a p y r o l i t e mantle, coupled with spreading seafloor basalt to  the f i e l d  will  take place  from t h o l e i i t i c  to a l k a l i  w h i c h c a n be c o r r e l a t e d  e v i d e n c e o f a b u n d a n c e s and s p a t i a l d i s t r i b u t i o n s "  along the mid-ocean Gast patterns  magmatic d i f f e r e n t i a t i o n and a  "a c o n t i n u o u s c y c l e  magma g e n e r a t i o n  melting of  ridge.  (1971) o n t h e b a s i s  i n tholeiites  i n contrast  of rare  earth d i s t r i b u t i o n  to a l k a l i  basalts  suggested  31  (like  G r e e n a n d R i n g w o o d , 1 9 6 7 , f r o m e x p e r i m e n t a l d a t a on  basalts)  t h a t o c e a n i c ' t h o l e i i t e s may be t h e r e s u l t o f e x t e n s i v e  melting o f the parent m a t e r i a l , while a l k a l i  basalts represented  a l e s s e r degree o f m e l t i n g . Yoder the P e t r o l o g i c  (1971), r e p o r t i n g proceedings  o f a meeting  Implications o f Plate Tectonics, stated that  " P r o d u c t i o n o f magma b e n e a t h t h e r i d g e may r e s u l t from the ( c o n v e c t i v e ) r i s e (from a h i g h - t e m p e r a t u r e , high-pressure environment) o f s o l i d garnet p e r i d o t i t e without l o s s o f heat i n t o a lower pressure e n v i r o n ment where m e l t i n g c a n b e g i n . Generation o f the d i f f e r e n t t y p e s o f magma a p p e a r s t o d e p e n d on s e v e r a l factors ( i ) the composition of the parental m a t e r i a l ( i i ) t h e d e p t h a t w h i c h t h e magma i s s e p a r a t e d f r o m the p a r e n t a l m a t e r i a l , ( i i i ) the degree o f p a r t i a l melting achieved ( i y ) the physiochemical c o n s t r a i n t s t h a t l e a d t o r e p e t i t i v e magma t y p e s ( v ) t h e w a t e r c o n t e n t s t o r e d i n hydrous phases and ( v i ) t h e e x t e n t o f f r a c t i o n a t i o n en r o u t e t o t h e s u r f a c e . "  on  32 CHAPTER THREE SHIPBORNE AND LABORATORY  INVESTIGATIONS  SHIPBORNE OPERATIONS Introduction Work i n t h e a r e a was c a r r i e d o u t d u r i n g two c r u i s e s i n t h e summer o f 1 9 7 0 , b o t h first  aboard  CNAV ENDEAVOUR  f r o m May 25 t o J u n e 14 a n d t h e s e c o n d  A u g u s t 5. project  The s e c o n d  22E); the  f r o m J u l y 13 t o  c r u i s e was P h a s e V I I o f t h e HUDSON '70  ( a l s o c a l l e d B I 69-050) d u r i n g w h i c h  circumnavigated  (Figure  the Americas.  t h e CSS HUDSON  D u r i n g Phase V I I ( a l s o  called  BI 6 9 - 0 5 0 ) , t h e CSS HUDSON and CNAV ENDEAVOUR w o r k e d t o g e t h e r on a s e i s m i c r e f r a c t i o n experiment independently (Srivastava Continuous  on a g e o l o g i c a l  o f f Queen C h a r l o t t e  reconnaissance  I s l a n d s , and  of the region  e t a l , 1971). Seismic Reflection  Profiling  CSP p r o f i l e s IOUBC 70 -16-15-*21 , 23 and 26 w e r e in  the area d u r i n g the f i r s t  c r u i s e , w h i l e p r o f i l e s EN 7 0 - 0 2 5 - 1 ,  2,3,9,10,11 were r e c o r d e d on t h e s e c o n d 050and  Hudson 3 a n d 6 w e r e o b t a i n e d a b o a r d Barrett.  recorded  cruise.  P r o f i l e s B I 69-  t h e CSS HUDSON by Keen  Bathymetric p r o f i l e s o f these  l i n e s were  also  recorded. These p r o f i l e s o f s e a b o t t o m and a c o u s t i c a l b e l o w i t were f i l t e r e d Recorder  except  reflectors  a n d r e c o r d e d on a wet p a p e r G i f f t  f o r t h e two Hudson p r o f i l e s w h i c h  were  Graphic  recorded  b o t h on an EPC d r y p a p e r r e c o r d e r a n d on an A l d e n w e t p a p e r cision  Graphic  (Model  6 0 0 B , 5-40 c u . i n .  and  Recorder.  a 300 c u . i n .  Bolt  Bolt  a i r g u n s w e r e u s e d as s o u n d  Pre-  source  a t 1400 - 2000 p s i . on CNAV ENDEAVOUR  a i r g u n on CSS HUDSON).  The  returning  34 e c h o e s were r e c e i v e d on a l i n e a r M-7) t o w e d 200 f e e t a f t .  a r r a y o f 20 h y d r o p h o n e s  (Geospace  ( F o r t e c h n i c a l d e t a i l s , see T i f f i n ,  1969).  Dredging A pipe  d r e d g e was u s e d d u r i n g  the f i r s t  cruise  (when  o n l y one h a u l , IOUBC 70-16-12D was made i n t h e a r e a ) and c h a i n b a g dredges  ( F i g u r e 22) s u p p l i e d b y B e d f o r d  second c r u i s e . metric  chart  Institute The  Institute  during the  E a c h s i t e was s e l e c t e d w i t h t h e a i d o f a b a t h y -  (Mammerickx, 1969, S p e c i a l C h a r t  No. 1, S c r i p p s  of Oceanography), echosounder p r o f i l e s  and CSP p r o f i l e s .  d r e d g e was l o w e r e d f r o m t h e s h i p ' s bow, and when t h e m e t e r e d  wirelength  i n d i c a t e d t h e d r e d g e t o be on t h e b o t t o m , t h e s h i p  moved s l o w l y a s t e r n , p a y i n g  out a d d i t i o n a l wire  approximately  50% o f w a t e r d e p t h t o p e r m i t  angle  f r o m 0° t o 45°.  ranging  l o w t o p o g r a p h i c a l l y and drawn  Other  Operations Profiles  field  were r e c o r d e d  o f the t o t a l during  u s e d was a V a r i a n p r o t o n  dredging  At a l l s i t e s ,  placed  i n amounts o f  uphill.  i n t e n s i t y o f the earth's  the f i r s t  by L i s t e r  wire  t h e d r e d g e was  cruise.  The  p r e c i s i o n magnetometer.  m e a s u r e m e n t s were o b t a i n e d  with  and D a v i s  magnetic  instrument Heat  flow  a b o a r d t h e CSS  HUDSON d u r i n g P h a s e V I I Hudson 70 ( F i g u r e 1 2 ) . N a v i g a t i o n was by b a t h y m e t r i c tial  fixes,  LABORATORY  dead r e c k o n i n g  c h a r t , L o r a n A, c e l e s -  and S a t e l l i t e  Navigator.  METHODS  C.S.P. A n a l y s i s Tiffin technique  (1969) d i s c u s s e d  i n detail  a n d t h e a n a l y s i s o f CSP r e c o r d s .  t h e CSP Side  recording  by s i d e  record-  35 ing  of each shot of the a i r g u n  its  subsequent echoes produced a p r o f i l e  subbottom s t r u c t u r e s . of  a c o u s t i c impedance  (frequency ^ 1 shot/5 sec.)  Acoustic reflections (i.e.  changes  and c o m p r e s s i o n a l wave v e l o c i t y ) .  affect  depends.  density composi-  depth of b u r i a l  as w e l l  of materials  upon  S i n c e a c o u s t i c impedance  t o g e o l o g y and s i n c e CSP  impedance,  and  changes  Grain s i z e , mineral  the e l a s t i c p r o p e r t i e s  w h i c h a c o u s t i c impedance intimately related  occur at  of the product of  t i o n , p o r o s i t y , degree of l i t h i f i c a t i o n , as o t h e r f a c t o r s  of the seabottom  and  geological  records  is  reflect  changes  in this  interpretations  records  c a n be made, t h o u g h s e v e r a l p r o b l e m s must be  of  CSP  overcome.  F i r s t , w i t h o u t d e c o n v o l u t i o n , the d u r a t i o n o f the o u t g o i n g soundwave t e n d e d t o r e d u c e r e s o l u t i o n The w i d t h o f t h e r e t u r n i n g of  the band o f p a r a l l e l  echo was  lines  r e c o r d e d as bands  representing  and s h a r p i n t e r f a c e . the  The  t r u e two-way t r a v e l  tended to o b s c u r e echoes tors. whether or  Thus,  first  Subbottom  r a t h e r than a  of these l i n e s  reflectors discreet  corresponded to  time to the r e f l e c t o r .  The o t h e r  from u n d e r l y i n g c l o s e l y  spaced  to the w i d t h o f the band o f l i n e s subbottom  S e c o n d , soundwaves r e f l e c t e d  seafloor  representing  the  from the seabottom are be r e f l e c t e d  t o t h e s e a b o t t o m and  a g a i n and a g a i n f r o m t h e s e a f l o o r .  reflec-  reflector.  o n l y p i c k e d up by h y d r o p h o n e s , b u t may  a g a i n by t h e a i r - w a t e r i n t e r f a c e  lines  i t i s n o t known  s u b b o t t o m r e f l e c t o r o u t c r o p s on t h e  s e a f l o o r o b s c u r i n g the f i r s t  not  the s e a f l o o r or  f o r e x a m p l e , i n IOUBC 1 7 - 1 6 - 2 3 ,  the f i r s t  n o t , due  of l i n e s  record.  f o u n d by m e a s u r i n g t h e w i d t h  where p o s s i b l e , t h e a i r - w a t e r i n t e r f a c e . were a l s o  on t h e CSP  Such r e v e r b e r a t i o n  back  returned produced  36 multiples  on t h e r e c o r d  sometimes o b s c u r e d profiles  across  record.  the c o n t i n e n t a l  occasional records  c r o s s i n g the steep  Seamounts,  Hyperbolae  slopes.  Even  or  slope,  steep  still  tend  t o p r o d u c e h y p e r b o l a e on  exist  near the ship's  t o the sediment  (as f o r e x a m p l e ,  are present.  See, f o r example, the  and i r r e g u l a r  slopes  o f t e n have  i f a ship  a s , f o r example, i n the  slopes  internal  large boulders)  'tails'  does n o t p a s s  o f the Dellwood  which  directly  obscure over  as a s i d e  echo  true  a pinnacle  b u t t o one s i d e o f i t , a h y p e r b o l i c  a p p e a r on the r e c o r d  energy,  a r e common where t o p o g r a p h y i s  where s t e e p  o r where s o u r c e s  greater  slope.  reflectors  Such h y p e r b o l a e  r o u g h and i r r e g u l a r , track,  of their  subbottom r e f l e c t o r s  Third, point the  which because  pattern  may  above o r below t h e  seafloor  surface  the  side  echo.  ing  IOUBC 70-16-15, IOUBC 70-16-21A and EN 70-025-9, t h e l a s t  having  d e p e n d i n g on t h e p o s i t i o n o f t h e o b j e c t Side  echoes  a subbottom side  data  material  experience,  traversed  Thus  include  of v o l c a n i c  as specific evidence samples  t h e general  may be s u r m i s e d  the broad d i s t i n c t i o n  the v o l c a n i c s .  and l a c k  only.  includ-  are necessary.  g e o l o g i c a l nature of character  basement  by s e v e r a l c h a r a c t e r i s t i c s from p o i n t  of penetration  Different reflectors  may be due t o d e g r e e o f l i t h i f i c a t i o n ,  types Additional  from t h e r e c o r d  t h e abundance o f h y p e r b o l a e  topography  rock  between v o l c a n i c  s e d i m e n t s i s made on t h e r e c o r d s  which  into  of seismic  i n t h e f o r m o f s e a f l o o r and c o r e  itself. and  of reflectors  be made on t h e b a s i s  However, f r o m p a s t the  a r e shown on s e v e r a l p r o f i l e s  echo.  Identification cannot  producing  or  reflectors  o f sound  within  energy  the sediments  changes  i nlithology.  37 Faults, folds, discontinuities determined  and  other structures  c o u l d be  from  1) l a t e r a l c o n t i n u i t y o f r e f l e c t o r s 2) l a t e r a l change i n c h a r a c t e r o f r e f l e c t o r s 3) a t t i t u d e o f r e f l e c t o r s w i t h r e s p e c t t o o v e r l y i n g and n e i g h b o u r i n g r e f l e c t o r s 4) n a t u r e o f t h e u p p e r c o n t a c t s o f a s e q u e n c e of r e f l e c t o r s 5) t h i c k n e s s o f u n i t s , b o t h i n d i v i d u a l l y and i n sequence It  s h o u l d be n o t e d t h a t  faults  c a n o n l y show a p p a r e n t  movement on s e i s m i c r e c o r d s a n d , on it  i s i m p o s s i b l e to t e l l  it  i s also  o n l y one  the b a s i s o f a s i n g l e  the type o f f a u l t  impossible to t e l l  dip-slip  the a t t i t u d e  profile,  or i t s a t t i t u d e ,  as  o f any  from  structure  profile.  Petrography Each sample i n a dredge i n t o one of  of s e v e r a l groups  texture  i n t o one  i s e s t h e s e t e x t u r e s and r e l a t e s were t a k e n o f a l l major X-ray  diffraction  the f o s t e r i t e  t i o n work was and  iron  also  crusts  and  another.  were  these  basis.  The  them t o r a t e o f c o o l i n g .  Photo-  textural  features observed.  on a s e l e c t  of minor  few  s a m p l e EN  basalt  m i n e r a l phases  and  X-ray  diffrac-  7 0 - 0 2 5 - 7 0 - 7 2 , manganese  and n o d u l e s , h y a l o c l a s t i t e s ,  and  a  sandstone  s a m p l e IOUBC 70-16-12D-3 m a i n l y f o r i d e n t i f i c a t i o n o f t h e tained clay minerals.  fur-  summar-  c o n t e n t o f the o l i v i n e s .  done on mud  description  F i g u r e 33  analysis  samples a i d e d i n i d e n t i f i c a t i o n determined  group  c l a s s i f i e d , m a i n l y on a t e x t u r a l  t e x t u r e s a l l grade  classified  Thin sections  o r t h r e e samples from each  t h e r d e s c r i b e d and  graphs  c h i p p e d and  on a b a s i s o f h a n d - s p e c i m e n  and m i n e r a l o g y o f p h e n o c r y s t s .  t h e n made o f two  observed  h a u l was  con-  38 Chemical  Analyses Three  wet-chemical these,  determinations  together  provided as  the  with  f o r whole  o f major oxides  rock  chemical  personal  communication)  with  gm.  0.8  lithium  0.1  gm.  metaborate  (see Petrology) and l o c a l  analyses  modified  (1971 - p e r s o n a l  after  t h a t by M e d l i n  diluted  stirrer.  t o 1000 y g / m l .  c o n t a i n i n g Lanthanum  of  A1 0  Si0 , 2  2  3  1:9.  ation  (each The  i n ratio  solution  The Fletcher  oxides,  oxide  and,silicon,  was  while  an  then  a n d MnO, t h e  2  For the determination  c o n c e n t r a t i o n o f 400 i n the .ratio again  f o r the  determin-  a concentration of 5 Lanthanum  f o r determination  and caesium  o f MgO  and Na 0. 2  a n d c a e s i u m was t o c o r r e c t t h e i n t e r during  standard  (1971 - p e r s o n a l  3  c o n t a i n i n g both  1:9) w a s u s e d  by o t h e r  of Ti0  o f L a n t h a n u m was u s e d Fe 0 ,  mixed  f o r about h a l f  containing caesium  2  (1971 -  dissolved  c o n c e n t r a t i o n o f 50 y g / m l .  iron  a d d i t i o n o f Lanthanum  ference  inum  ratio  and t o t a l  o f sample  solution  solution  t h e same  o f CaO  yg/ml.  this  then  solution  1:9.  solution  2  A sample  containing  i n ratio  and K 0 , a sample  y g / m l . was u s e d , of  The sample  et a l  ( 1 0 -15 m i n . a t 1000°  by s t i r r i n g  f o r determination  solution  and B a r r  o f -100 mesh s a m p l e was  aided  a magnetic  used  oxides,  in  hour with  were  o f the major  c r u c i b l e T h i s was  acid  standards  absorp-  communication)  and fused  and  by atomic  C) i n a p r e i g n i t e d g r a p h i t e 50 m l . o f 5% n i t r i c  f o r accurate  communication),  For determination  m e t h o d u s e d was s l i g h t l y Fletcher  to Japan  a USGS b a s a l t s t a n d a r d  spectrophotometry.  (1969),  sent  by F l e t c h e r (1971 - p e r s o n a l  standards  tion  b a s a l t samples were  aspiration.  s o l u t i o n s used were  communication),  w h i c h w e r e made f r o m  except  obtained those  recipes taken  from  o f alum-  from  39 Langmyhr and Paus  (1968) .  Sample and s t a n d a r d an a i r - a c e t y l e n e f l a m e  s o l u t i o n s were t h e n  except  for A1 0 , Si0 2  were a s p i r a t e d i n a n i t r o u s o x i d e solutions  diluted  3  2  - acetylene  aspirated i n  and T i 0  2  which  flame, the standard  t o v a r i o u s c o n c e n t r a t i o n s so t h a t  absorbance  v a l u e s when s a m p l e s o l u t i o n was a s p i r a t e d l a y b e t w e e n two c l o s e l y s p a c e d v a l u e s o f a b s o r b a n c e r e a d i n g when s t a n d a r d different  c o n c e n t r a t i o n s were a s p i r a t e d .  l i n e b e t w e e n t h e two s t a n d a r d tion  solutions of  Assuming a s t r a i g h t  absorbance r e a d i n g s , the concentra-  C ( i n ug/ml.) o f t h e o x i d e  i n t h e sample s o l u t i o n  being  aspirated i s C = A + K  E E  where  A K E E E  = = x 2  l  The then  = = =  x  2  1  -  E l  c o n c e n t r a t i o n o f l o w e r s t a n d a r d i n g/ml. d i f f e r e n c e i n c o n c e n t r a t i o n s between upper and l o w e r s t a n d a r d s absorbance r e a d i n g f o r sample s o l u t i o n absorbance r e a d i n g f o r upper s t a n d a r d absorbance reading f o r lower standard  percentage  by w e i g h t  o f the oxide  i n the rock i s  C/Co x 100 where Co i s t h e c o n c e n t r a t i o n ( i n ug/ml.) o f t h e  sample s o l u t i o n used. times  F o r e a c h o x i d e , a s p i r a t i o n s were done  and t h e a r i t h m e t i c mean c a l c u l a t e d .  were done i n some c a s e s . the  -Ei  sample s o l u t i o n  Duplicate  analyses  The c o n c e n t r a t i o n C o f t h e o x i d e i n  c o u l d a l s o be f o u n d  graphically  assuming a  straight  l i n e b e t w e e n a b s o r b a n c e r e a d i n g f o r u p p e r and l o w e r  standard  s o l u t i o n s and t h i s was done i n some Trace  a very -100  cases.  e l e m e n t c o n c e n t r a t i o n s were d e t e r m i n e d  few s a m p l e s , m a i n l y  four  f o r economic purposes.  i n only  A 0.5 gm o f  mesh s a m p l e was d i s s o l v e d i n 25 m l . o f 1.5 m o l a r  hydro-  40 chloric  acid  according  communication) water,  acid.  necessary with  and a f t e r  2 ml, n i t r i c  fluoric  unit  solutions  - personal  to d r y n e s s , mixed  w i t h 3 ml.  ml. p e r c h l o r i c (concentration  acid  i n the a i r - a c e t y l e n e o f F e , Mn,  and 5 m l . h y d r o -  20 mg/ml.) o r when  then a s p i r a t e d  p r o v i d e d by F l e t c h e r  (1971  together  - personal  f l a m e o f an a t o m i c  absorption  Co, N i , Cu, Pb, Zn were  In t h e d e t e r m i n a t i o n o f Co, N i and Pb, a h y d r o g e n  lamp was u s e d i n a d d i t i o n background  absorption.  calculated  graphically  be  (1970  p o r t i o n o f i t , was  and c o n c e n t r a t i o n s  determined.  0.5  solution  a diluted  communication)  evaporation  acid,  This  standard  t o t h e method o f F l e t c h e r  to the element  lamp  The c o n c e n t r a t i o n s and d u p l i c a t e  to correct f o r  o f the elements  analyses  were  showed r e s u l t s t o  reproducible. In  basalts,  w a t e r was  d e t e r m i n e d as f o l l o w s :  0.2500  - 0.3000 gm sample powder was m i x e d i n a h a r d g l a s s t e s t t u b e with preignited weight  sodium  o f sample.  weighed  sample  utes, in  A weighed  flux  piece  equivalent  of f i l t e r  i n a w e i g h i n g b o t t l e ) was p l a c e d  w h i c h was w r a p p e d The  tungstate  i n a wet p a p e r  the f i l t e r  paper  was t h e n t r a n s f e r r e d  towel around  vapour being  the upper  condensed  to the w e i g h i n g b o t t l e  t h e amount o f w a t e r  only  gave  a negligible  released.  increase  (previously  i n t h e top o f the tube  at the top o f the tube.  give  Duplicate  paper  and t u b e were t h e n h e a t e d f o r a b o u t  the r e l e a s e d water  to s i x times  five  t o t e n min-  and c o l l e c t e d  The f i l t e r  of f i l t e r  a n a l y s e s were made on a l l s a m p l e s .  paper  and r e w e i g h e d t o  A determination with  i n weight  part.  flux  paper.  41 CHAPTER FOUR SEISMIC DATA  INTRODUCTION The sented  seismic data obtained during t h i s  i n P l a t e s I. t o X I I I , w h i c h c o m p r i s e  original  recorded p r o f i l e s  and  the form o f l i n e drawings.  on  F i g u r e 23  nautical miles  (951 km)  Tracks  profiles having les on  the l i n e  exaggeration  speed. for  by  a sound v e l o c i t y  varies  exaggeration  The  50.  The  on  slope  513  the  ang-  Nomographs vertical  sometimes v a r i e s  v a r i a t i o n being  caused  t o changes i n s h i p ' s  km/sec.  calculated  S i n c e sound  velocity  i n b e d r o c k , t h e npmo-:  be u s e d t o m e a s u r e s e a f l o o r  v e l o c i t y o f s o u n d i n u n c o n s o l i d a t e d wet  symbols used i n the  indicated  exaggerated  and nomographs a r e  i n w a t e r o f 1.5  ment v a r i e s b e t w e e n a b o u t 1.5  Figure  s c a l e due  i n d i f f e r e n t . t y p e s o f s e d i m e n t and  slopes only.  are  being exaggerated.  record; this  graphs p r o v i d e d should s t r i c t l y  the  angles  lines  the  s c a l e , angles  v a r i e s f r o m r e c o r d t o r e c o r d and  vertical  total  representing  slopes, while steeper  changes i n h o r i z o n t a l  The  Low  are  Because o f  d r a w i n g s show t h e e x a g g e r a t i o n .  the l e n g t h o f a s i n g l e  mainly  area.  and h o r i z o n t a l  appearance of steep  of.the  lines  Eighteen p r o f i l e s  are compressed though s t i l l  over  o f the survey  are g r e a t l y d i s t o r t e d .  the  the  a r e shown w i t h t h e CSP  t r a v e r s e the  d i f f e r e n c e between v e r t i c a l  pre-.  photographs of  In a d d i t i o n , p r o f i l e s  (see page 137) .  are  the g e o l o g i c a l i n t e r p r e t a t i o n i n  i n t e n s i t y of earth's magnetic f i e l d f r o m C r u i s e IOUBC 70-16.  study  km/sec and  line-drawn  2.2  sedi-.  km/sec.. A key  to  interpretations is,given in  42 MAJOR TECTONIC  AND PHYSIOGRAPHIC  The d a t a o b t a i n e d are p r e s e n t e d  graphic they  i n the p r o f i l e s  with reference  features o f the area. features  this  ment d r a p i n g ing  Zone Zone i s shown on o n l y one p r o A magnetic high  basin which contains only a t h i n  a v o l c a n i c basement b u t h a v i n g  t h i s basement t o p o g r a p h y .  a f f e c t i n g both  thin  D e l l w o o d Seamount  sediment cover  basically  a little to and  layer of sedi-  similar  seems t o be p r e s e n t  and v o l c a n i c basement.  other p r o f i l e s  t h e D e l l w o o d Seamount  to the topographic  t o the southeast  profile  o f the topographic i n the area.  ( A p p e n d i x A)  profile  Profile  show t h i s  b e t w e e n them i n p l a c e s up t o 0.2 s e e s , ment l a y e r may c o v e r  due p r o b a b l y  IOUBC 70-16-15  range t o c o n s i s t  thick.  A very  pockets thin  sedi-  most o f t h e Seamount R a n g e , b u t i s n o t  r e s o l v a b l e by t h e l o n g p u l s e  of the airgun.  Dellwood K n o l l s The S o u t h e a s t  r i d g e s and peaks c o v e r e d most a r e a s  Range  but i s s h i f t e d  o f rugged v o l c a n i c peaks w i t h sediment f i l l i n g  Southeast  o f smooth-  Range  the magnetic i n c l i n a t i o n  mainly  (>56400 gammas)  the e f f e c t  Normal f a u l t i n g  The m a g n e t i c p a t t e r n o v e r is  on w h i c h  profile.  - IOUBC 70-16-15 ( P l a t e I ) . over  the p r o f i l e s  r e m a r k s a b o u t t h e f e a t u r e s as s e e n on  The E x p l o r e r S p r e a d i n g  occurs  t h e t e c t o n i c and p h y s i o -  (discussed following),  Explorer Spreading  file  of Plates I - XIII  to t h e t e c t o n i c and p h y s i o g r a p h i c  Appendix A l i s t s  are l o c a t e d and b r i e f  the r e s p e c t i v e  FEATURES  g r e a t e r than  Dellwood K n o l l s i s a s e r i e s o f v o l c a n i c w i t h sediments o f v a r y i n g t h i c k n e s s i n 0.1 s e e s t h i c k .  CSP l i n e  IQUBC 70-16-20  which  traverses  to  relatively  be  indicate  that  this flat  the Northwest  (EN  70-025-9, P l a t e  The  and  X)  Northwest  slope  CSP  IOUBC 7 0 - 1 6 - 1 6  This  line  along the  line  and  side  acting  seamount.  of  sediment  Dellwood  cover  The the  channel  70-16-20 tary by  normal  been  Plate over  IV the  volcanic  EN  about  0.4  sec.  of  slopes.  trends  north-  Knolls.  presumably  i t s head  in  Channel.  shows t h e  on  A)  the-summit  contrasting  of  the  this  CSP  (see Appendix  sediment  IV)  faulted.  Dellwood  the ScOtt  sees)  nature  Dellwood  Most  to the  thick  of this  a r e a by  (Plate i n the  sediment  turbidity  (see D i s c u s s i o n ) .  between site  Zone" i s here  Knolls.  70-025-3  shows, h i g h e s t i n t e n s i t y  the  t o be  (>30°) w h i c h  Spreading  and  Pleistocene  c h a n n e l were  southwest  I I - BC)  topography  IV)  channel  example,  Knolls.  Zone  faulting.  the  seems  channel having  also  Dellwood  transported  during  line  must  along these  other lines  the  (Plate  (Plate  (<0.1  name " D e l l w o o d  between  material  as  little  and  Spreading  faulting  a tributary  This  the  summit  (IOUBC 7 0 - 1 6 - 2 0 , P l a t e  fault  a small  as w e l l  show o n l y r e l a t i v e l y this  of  as  IOUBC 7 0 - 1 6 - 2 0  of  of  slope of Northwest  crosses a very steep  This  compared, f o r  (IOUBC 70-16-20) a l s o Knolls  shows t h e  sediment.  steepness  indicate  across the northwest  seamount  The  and n o r t h w e s t  east  trends  o l d as  Dellwood line  direction  covered with  Knolls.  (>15°) p r e s u m a b l y  southeast  i n a NW  i t is relatively  with  slopes  seamount  over  the k n o l l s  CSP  given  profiles  V)  IOUBC  show t h a t  channel  is  The  Dellwood  as w o u l d  o f a s p r e a d i n g segment  and  magnetic  be  Knolls  sedimen-.  disturbed  i s believed currents  to  have  ice  rafting  profile SE  expected  (see  to  and  of  not  i f this  Discussion).  44 Scott  Channel  .  In the into  two  sections:  northeast slopes slope  and  Zone  o f the  D e l l w o o d K n o l l s , and  (see n e x t s e c t i o n ) .  Plate  this  I I - CD)..  northeast slopes  Other p r o f i l e s  of  slide  the  s u c h by  comparison w i t h  similar  (1967) and  Emery e t  o f f Eastern  are  features  a l (1970) on  North America.  by  profiles  Sediment  a b o u t 1.5  Scott  slope  of  the  turbidity  North American p l a t e  n o r t h w e s t moving P a c i f i c P l a t e .  the  southeast,slopes of  e n c o u n t e r e d on  line  along a t r i b u t a r y of west slope  of  IOUBC 70-16-16 the  Scott  may  be  to the  :  south-  expected  exists  onto  below  same as  that  trending  transecting  the . N o r t h w e s t D e l l w o o d K n o l l s .  XIII.  continental  the  ( P l a t e I I - BC)  C h a n n e l and  contin-  stationary)  A fault-zone  c h a n n e l and  and  migrating  o f f the  (assumed h e l d  the  this  indicate a  flowing  as-  C h a n n e l i s shown  S u c h a . s i t u a t i o n w o u l d be  currents  the:  Rona  sees, i n Plate  p r e s e n t c h a n n e l l y i n g a.few k i l o m e t e r s  a r e s u l t of  the  thickness,varies  c h a n n e l , the  as  of  of the  Here subbottom r e f l e c t o r s  channel.  high  interpreted  obtained  CSP  n o r t h w e s t s e c t i o n o f the  earlier  south-  continental  i n P l a t e V.  e a s t o f an  Dellwood  Charlotte  base of the  structures  Scott,Channel reaching The  the.Queen  across t h i s part  c h a n n e l at the slide  the  continental  structures, especially,along  T h e s e s l u m p and  in  the  the  here produces a magnetic  slope,  rise  divided  Basement c r o p s o u t , o n the  c h a n n e l and  c h a n n e l show s l u m p and  ental  be  the n o r t h e a s t s e c t i o n l y i n g between  northeast section contains  west s l o p e - o f  Clay  Channel can  Knolls.  The  (see  Scott  the northwest s e c t i o n l y i n g northwest of the  Seamounts and  Fault  a r e a of s t u d y , the  the  Beneath the  northsouth-  45  east  slopes  of  more r e c e n t structures area be  and  due  part The  the  slump  the  on  the  XIII. this  1.5  apparent  are  dip-slip  (MN),  VIII  the  i s mainly  southwest  zone, presumably  because  form  out  The  Queen C h a r l o t t e  dip-slip  faults  of  Zone  the  may  (HH')  reach  (except  XIII,  may  also  northwest  are  the  zone  surface  only  by  channels.  for  that  on  the  the  which  deepest  cross  HH'  ( P l a t e VI)  do  the  Queen C h a r l o t t e  continental part  the  of  channel  to  f a u l t , being  a  (see the  the  northeast,  fault  include  continental slopes  In<  show t h e  direction not  the  not  part  fault  into  of  VIII  faulted,.showing  t h e , f a u l t i n g i s on  z o n e may  be  cut  side  lines  also  in this  strata  have been  i n a southwest fault  this  i s shown i n P l a t e s  VI  lower  Faults  that  of p r o f i l e  dies  the  southwest  I t i s noteworthy  sediments  Slump  sees..thick.  in Plate  faulting  in Plate  in  in this  sediment, t h i c k n e s s  sediments  the  by  Channel.  channel  Sediments 0.6  is buried  Scott  underlying  Fault  movements.  on  whereas  fault,  of  the  s i d e -of. t h e  than  seen  The  the  fault-zone  Zone  sees.,.o£ w h i c h  Plate  side.  Fault  zone.  recent  channel,  more  faulting  w h e r e more  slope)  nature  Queen C h a r l o t t e  fault  reaches  northwest  :  channel  The  this  and cut-and-fill.  Queen C h a r l o t t e  and  Channel  transported.along  disturbed  The  of  Scott  sediments occur  to  of  the  trans-  Discussion). apparent  o f f Queen. C h a r l o t t e  Sound. Continental  Slope  The  seismic  profiles  edge o f f Queen C h a r l o t t e , S o u n d (i)  Upper  continental  seaward slope .  are  slope  truncated  which  traverse  show s e v e r a l sediments  by, f a u l t s  the  features,of  dipping  along  slope  the  gently  and  shelf  interest, (^2°)  continental  46 (ii)  Structural  features,  clines,  intrusions  slopes  or and  dams are  (iii)  s i m i l a r to  Lower s l o p e  sediments  Slump  Paul  Revere  onto  the  Revere  Ridge  the  fault  end  - EF).  i s not  of  adjacent seen out  part  southern part,  (1969)  margins. crumpled  continental  of  the  Scott  slope  Channel.  the  the  VII  the  and  is a fault  trace  the  scarp,  very  ridge  has  very  ridge  of  f a u l t e d nature This  (KK'), presumably low  the  slightly  of  of  of  faultthat  the  a cuesta  (^1°)  in a  the  severe  over  the  (Plate  lack  indicating  occurs  form  at  basement  because  Winona B a s i n .  (see  though  the  volcanic  Winona B a s i n the  comprising  basalts  o v e r most o f  A magnetic  dipping  structure  ridge.  with  northeast.  Basin  Ridge.  northwest (Plate  to  southwards.  apparently  The Revere  of  in Plate  In  Winona  slopes  zone e x t e n d s  sound waves and  die  sediments  Emery  lower  turbidites,  slope  d i r e c t i o n beneath  faults the  the  i s a complex  It i s d i f f i c u l t  penetration  ing  along  including indurated  northern  and  by  tectonic  deformed, appearing  northeast  southwest  ridge  are  occur  The  northeast  described  Such  o f many c o n t i n e n t a l  Petrology).  III  them.  lower  Ridge  Paul sediments,  u p p e r and  anti-  VIII).  structures  advancing  basement h i g h s ,  l i e b e n e a t h the  those  slopes  Plate  be  sediments behind  b e n e a t h the  (see (iv)  dam  w h i c h may  XII  end  southern part The of  - LL')  w i s e known as  the  basin  the  sediments  ridge  traverses Scott  o f Winona B a s i n  show s e v e r e  ( P l a t e VII the  Islands  i s adjacent  - JJ').  northern Fault  part  to  Paul  faulting  near  Only  profile  of  the  one  basin  Zone - Couch, 1969  and  the  (otherothers) ,  47 showing  a s e r i e s o f f o l d e d and f a u l t e d  sees, t h i c k . gravity  Couch  interpreted  the negative  zone  thick  sediment  as t h e e x p r e s s i o n o f a g r a b e n  gm/cm .  The f o l d i n g  3  attitude  filled  s e c t i o n s o f average d e n s i t i e s and f a u l t i n g  with  Island two 3 km  2.0 gm/cm a n d 3  o f t h e sediments  some component o f c o m p r e s s i o n a f f e c t i n g The  free-air  a n o m a l y o f more t h a n 150 m g a l s o v e r t h e S c o t t  fault  2.4  (1969)  s e d i m e n t s , more t h a n 3  the area  indicate  (see  Discussion).  o f these sediments n e a r t h e base o f t h e c o n t i n e n t a l  s l o p e c a n n o t be d e t e r m i n e d f r o m t h e r e c o r d w h i c h i s p o o r i n t h i s area.  No s h a r p c o n t a c t e x i s t s b e t w e e n t h e v o l c a n i c  Knolls  and t h e Winona B a s i n sediments  indicate  that t h i s  and v o l c a n i c s . sediments  contact consists  (See T i f f i n  and may  The most r e c e n t  i n t h e a r e a a r e n o t a f f e c t e d by t h e f o l d i n g -  and f a u l t -  ..  - Dellwood- F a u l t ZoneThe  west  line  o f i n t e r b e d d e d sediments  and C a m e r o n , 1 9 7 2 ) .  i n g and a r e h o r i z o n t a l . Revere  along t h i s  Dellwood  Revere  - Dellwood F a u l t  s l o p e s o f P a u l Revere  Zone t r e n d s a l o n g t h e s o u t h -  Ridge and S o u t h e a s t D e l l w o o d  Knolls,  and e x t e n d s i n t o t h e b a s i n b e t w e e n t h e D e l l w o o d Seamount Range and west  the Dellwood K n o l l s . of, but including, W  A l l profiles  crossing t h i s basin south-  ( P l a t e X I I I ) show some d e g r e e o f  f a u l t i n g w h i c h i s most i n t e n s e a l o n g p r o f i l e  EF ( P l a t e  d i e s o u t b o t h i n n o r t h w e s t and s o u t h e a s t d i r e c t i o n s . example, KK'  i t i s absent from p r o f i l e  (Plate VII) i t i s r e s t r i c t e d  P a u l Revere  Ridge.  t o t h e southwest  i nprofile  along this  slope.  Thus, f o r  I I ) a n d on p r o f i l e slope of  The s t e e p n a t u r e o f t h e s o u t h w e s t  the S o u t h e a s t D e l l w o o d K n o l l s a b l y due t o f a u l t i n g  BC ( P l a t e  I I I ) and  slope of  RS ( P l a t e X) i s p r e s u m The s e d i m e n t  i n the basin  j5 N a u t i c a l M i l e s  2.0  _J.0  Kilometers  3.0  I  I  w 4.0 to V O L C A N I C S 5.0  4  16  H- 6  f  C.S.P .  21B  LINE  I  H-3  18  9  19  CO  16  H- 6  21B  H- 3  18  9  19  DEPTH TO SEDIMENT (SEC. )  3.38  3. 33  3.33  3. 33  3.33  3. 41  3.44  DEPTH TO  3.63  3. 90  4.00  4. 33  3.70  3. 63  3.60  FIGURE 24  BASEMENT (SEC. )  Profile  ZZ" a l o n g b a s i n b e t w e e n t h e D e l l w o o d Seamount Range and D e l l w o o d  .Knolls, constructed  from data  obtained  from p r o f i l e s  which cross  the basin.  49 b e t w e e n D e l l w o o d Seamount Range and (^1  Dellwood K n o l l s  i s thickest  s e c . L L ' P l a t e X I I ) a t end o f c h a n n e l t r e n d i n g b e t w e e n t h e  D e l l w o o d K n o l l s where t h e b a s e m e n t i s a l s o d e e p e s t  (Figure  24)  and d e c r e a s e s i n t h i c k n e s s t o w a r d b o t h t h e n o r t h w e s t and s o u t h east  ( p r o f i l e BC  sec). in  Such  - Plate  I I - shows t h i c k n e s s o f l e s s  a sediment d i s t r i b u t i o n would  result  t h e d e e p e s t p a r t o f t h e b a s i n by s e d i m e n t s  mainly turbidites continental  than  from  0.2  ponding  ( b e l i e v e d t o be  and i c e r a f t e d d e b r i s ) t r a n s p o r t e d f r o m t h e  s h e l f and s l o p e a c r o s s t h e S c o t t C h a n n e l  c h a n n e l between the D e l l w o o d K n o l l s  and i n t o  the b a s i n  t h e D e l l w o o d Seamount Range and D e l l w o o d K n o l l s . p o r t i n a southwest d i r e c t i o n  a l o n g the  i s blocked i n this  between  Further transa r e a by  the  D e l l w o o d Seamount Range. Other Features Profile  VV  (Plate  X I I I ) shows t h e s e d i m e n t  between  t h e S c o t t Seamount Range and t h e D e l l w o o d Seamount Range i s a b o u t 0.5  s e c . t h i c k , w h i l e t o t h e s o u t h w e s t o f t h e S c o t t Seamount R a n g e ,  the sediment  i s about  n e a r e r t o the S c o t t  0.64  sees, t h i c k , presumably  Channel.  This thick  b e l i e v e d to comprise mainly t u r b i d i t e s the S c o t t Channel.  sequence  since i t i s of sediments i s  t r a n s p o r t e d to the a r e a v i a  Also of i n t e r e s t i n p r o f i l e V V  i s the  steplike  a s c e n t o f the o c e a n i c basement l a y e r i n a n o r t h e a s t d i r e c t i o n f e a t u r e which l e d Ewing  e t a l (1968)  segment i n t h e D e l l w o o d R e g i o n  to postulate a short spreading  (see D i s c u s s i o n ) .  The  ascent of  t h e o c e a n i c basement l a y e r i s t h e r e v e r s e o f t h e n o r m a l d i p o f o c e a n i c basement t o w a r d t h e  - a  continent.  &0R£D6£ EM 70-Ott-io 3»DR£DG£  EN70~OE5'3i,  7*DREDGE EN 70-025-lj, 8*DREPCE EN 70-025-% 9-CREDGE EN 70-025-%  5/H  -51'  IZ'DREDGE IOUBC 70-16-fy  •'  omu  JOIOES M*ITT.  50H  40 KM. NAUTICAL kH.ES  DREDGE CORE FIGURE  STATIONS  STATION 25  l-l •  SITE  51  CHAPTER FIVE ANALYSIS OF  Figure obtained by  during  25  shows the  l o c a t i o n of  the  summer o f  1970  JOIDES f r o m the  mer  o f 1971.  the  rock  are  f r o m so  made as ical  to  drill  These  types  of  few  ship  recovered  the  recovery  distribution  these  The f r o m any texture  one  the  metre h o l e  drilled  data  Seamount A r e a  of major rock  and  the and  only  although  sum-  types;  types;  t e x t u r a l and  thickness  seafloor  and  and  on  they  c e r t a i n g e n e r a l i s a t i o n s can  amount o f w e a t h e r i n g ;  absence  be  chem-  distribution  the r e l a t i o n s h i p  spreading.  of m i n e r a l o g i c a l v a r i a t i o n  dredge h a u l , the  f a r from  a talus slope. during  500  BASALTS  o f most o f  transported  one  hauls  samples p r o v i d e  sites,  observations  PETROGRAPHY OF  s i x dredge  the  d i f f e r e n c e s between b a s a l t  between  and  CORE  GLOMAR CHALLENGER d u r i n g  Dellwood  o f manganese c o a t i n g ;  A  and  basalt  their  catalogue  summer c r u i s e EN  Thomlinson, Bertrand EN  DREDGE HALLS AND  and  the  a n g u l a r i t y and  samples  source  suggest  areas  and  d e s c r i p t i o n of 70-025  Chase  i s the  among  samples  rough  surface  that  may  they  be  the  not  fragments  rocks  subject  were  from  recovered  of  a volume  by  (in press).  70-025-2D All  the  haul  taken  line  IOUBC 70-16-20, P l a t e  described  from  basaltic  as  Northwest  i s common  IV)  are  26A).  Knolls  fragments  olivine  p i l l o w f r a c t u r i n g with (Figure  recovered  Dellwood  glomeroporphyritic  Characteristic face  the  fragments  . The  from t h i s (Figure  curved  26  of p i l l o w s  basalts  dredge and and  (Figure  glassy  b a s a l t fragments  outer  CSP are  27B). sur-  are a l l  52  B - Glotneroporphyritic olivine - plagioclase basalt. Specimen NO. 3T 70-025-2D-1. FIGUR3 26 Basaltic fra^jnents from the Northwest Dellwood I'nolls. Dredge Haul NO. Si 70-025-2D.  S3  vesicular with  vesicles generally  Both i n hand specimen (Figure  27),  <1. mm i n d i a m e t e r .  (Figure  26B) a n d i n t h i n  the rock i s glomeroporphyritic  with  section  phenocrysts  comprising mainly c l u s t e r s of interpenetrating piagioclase (AnsH-ss) and/or o l i v i n e ( F 0 9 0 ) , olivine B). The  the percentage p l a g i o c l a s e to  i n the phenocrysts varying  considerably  (Figures  Single phenocrysts of o l i v i n e or plagioclase o l i v i n e s are euhedral  hedral.  along cracks  a n d may c o n t a i n  clinopyroxene  opaque i n c l u s i o n s  also occur  and opaqiies  (mainly  from p l a g i o c l a s e roxene b e l i e v e d  and a l s o  microlites; this  f5  l a t t e r habit  crystallised  The c l i n o p y -  of the c l i n o p y -  o f the b a s a l t i c glass. crystallised  ores also occur  the rocks from t h i s  dredge haul  amount o f , n o r m a t i v e n e p h e l i n e 0 , 9 1 , 20% o l i v i n e ,  A1 0  and thus a r e c l a s s i f i e d  3  complete chemical a n a l y s i s rock contains and  a little  i s thus i n t e r m e d i a t e  within  minerals.  small 2  o r e min-  Some o f t h e g r o u n d m a s s p l a g i o c l a s e i s  s a u s s u r i t i z e d y i e l d i n g epidote-group Chemically,  matrix  i n f a n s and sheaves g r o w i n g o u t  f a n s a n d s h e a v e s encompass p r e v i o u s l y  some o l i v i n e p h e n o c r y s t s .  60  magnetite) l y i n g i n a  due t o d e v i t r i f i c a t i o n  These p r e v i o u s l y  consist-  m i c r o l i t e s (An , _ ) , o l i v i n e ,  o f b a s a l t i c g l a s s p a r t l y a l t e r e d and d e v i t r i f i e d . roxene occurs i n g r a i n s  (Figure  (Figure 27C).  groundmass o f t h e s e r o c k s i s h y a l o p i l i t i c ,  i n g o f an a b u n d a n c e o f p l a g i o c l a s e  erals.  occur.  t o a n h e d r a l i n s h a p e , most b e i n g s u b -  L o c a l l y zoned p l a g i o c l a s e s The  The  also  2 7A a n d  Some o f t h e a n h e d r a l o l i v i n e s show r e a c t i o n r i m s a n d  alteration 27B).  laths  contain  a  a n d >17%  as h i g h - a l u m i n a o l i v i n e b a s a l t .  A  i n T a b l e I I shows t h a t , w h i l e t h e  normative nepheline, between s a t u r a t e d  i t i s low,in  alkalis  o l i v i n e t h o l e i i t e and  54  Plagioclase (Bytownite An-8S) phenocryst i n glomeroporphyritic basalt. The grounduass i s hyalopilitic. Specimen NO.EH 70-025-2D-1. (X50).  Olivine and zoned, plagioclase phenocrysts i n glomeroporphyritic basalt. The groundmass i s hyalopilitic. Specimen NO.EN 70-025-2D-8. (X50). 27 Photomicrographs of olivine - plagioclase gloaieroporphyritio basalt from the Northwest Dellwood 'nolls. T  55 alkali  olivine basalt.  between p l a g i o c l a s e tive plagioclase  (See C h e m i s t r y . )  and o l i v i n e  and o l i v i n e  phenocrysts are i n fact  The l a r g e  discrepancy  p h e n o c r y s t c o m p o s i t i o n a n d norma-  c o m p o s i t i o n may i n d i c a t e t h a t t h e  xenocrysts.  EN,70-025-3D This the  dredge h a u l  was t a k e n f r o m a f a u l t  Southeast Dellwood K n o l l s  16-20, P l a t e original  IV).  The b a s a l t  (Figure  IOUBC 70-  t e x t u r e , i s p r e s e r v e d enough t o be c l a s s i f i e d i n t o two  hyalopilitic  basalt  the b a s a l t  vesicles  25 a n d CSP l i n e  o f t h e groundmass, namely a  a n d an i n t e r s e r t a l b a s a l t  (Figures  samples r e c o v e r e d are v e r y v e s i c u l a r  28A a n d B ) .  (Figure 28D),  r a n g i n g f r o m a b o u t 0.2mm t o 5 mm i n d i a m e t e r a n d c o a t e d  w i t h manganese o x i d e up t o 50mm t h i c k on one s p e c i m e n 28C).  along  fragments are a l t e r e d but the  g r o u p s d e p e n d i n g on t h e t e x t u r e  All  scarp  (Figure  Some o f t h e f r a g m e n t s a r e p o r p h y r i t i c ( F i g u r e 2 8 D ) . The  h y a l o p i l i t i c basalt  a b o u t 5% p l a g i o c l a s e p h e n o c r y s t s  i sporphyritic (An  9 2  ) i n a h y a l o p i l i t i c ground-  mass o f s a u s s u r i t i z e d p l a g i o c l a s e m i c r o l i t e s clinopyroxene  and m a g n e t i t e l y i n g  The  intersertal  olivine  (Anj+o-so)*  i n a tachylyte  sional microphenocrysts of o l i v i n e  containing  also basalt  matrix.  contains  tial  Saussuritized plagioclase  28B).  are  common a n d t h e r o c k a l s o  and  i n t h e groundmass.  diffraction pattern about Fogg. The  contains  olivine  shows t h e o l i v i n e  Fe 0 2  only  interstimicrolites  as m i c r o p h e n o c r y s t s  The p o s i t i o n o f t h e .130 p e a k on an X - r a y m i c r o p h e n o c r y s t s t o be  M a g n e t i t e i s t h e m a j o r opaque high  with  l e s s pheno-  clinopyroxene  (Figure  Occa-  occur.  c r y s t s b u t much more g r a n u l a r tachylyte  olivine,  3  content  mineral.  (>2.0V), and h i g h  Fe 0 /FeO 2  3  56  A - Anor l-hite phenocryst (Au-92) i n hyalopilitic: basalt. (X50) Specimen No. 3N70 - 025 - 3D - 1  C - Thiol: ferro-anao, arxese crust (~50ffim) on weathered i n t e r s e r t a l basalt. Speciifeen No. SR 70 - 025 - 3D - 4.  3 - Phocondcrocraph o f i n t e r s e r t a l basalt. D - P o r p h y r i t i c and / e s i c u l a r b a s a l t s Specimen " o . 3! 70 - 025 - 3D - 3. 'X50) as seen i n hand specimen. F10TJRS.28  Basaltr; from the Southeast DelP./ood Knolls. Bred- e P a u l "o.3T TO-025-3D.  57 TABLE  II  C h e m i c a l and N o r m a t i v e c o m p o s i t i o n s o f some b a s a l t i c r o c k f r a g m e n t s f r o m t h e D e l l w o o d Seamount A r e a .  SAMPLE NO.  EN 70-025-2D-1 EN 70-025-3D-1  ROCK TYPE  EN 70-025-8D-121  High Al-01.Altered Basalt Vesicular Basalt 1  OXIDE Si02 Ti02 AI2O3  Fe 0 FeO MgO MnO CaO Na 0 K 0 2  3  2  2  P2O5  CO H 0 H 02  2  2  TOTAL  WEIGHT %  WEIGHT %  47 .34 1 .24 17 .65 1 .19 7 .70 10 .45 0 .14 11 .39 2 .64 0 .16 0 .06 0 .140 .38 0 .24  50 .04 2 .37 16 .29 2 .70 7 .09 5 .28 0 .15 11 .77 3 .49 0 .52 0 .19 0 .05 0 . 53 0 .28  100 .72  100 . 75  Olivine Tholeiite WE" IGHT 49 .70 1 .58 15 .91 1 . 78 7 .78 7 .14 0 .16 12 .50 3 .11 0 .23 0 .11 0 .15 0 .39 0 .20 100 .74  MINERAL  -  Quartz Nepheline Orthoclase Albite Anorthite  0 .91 0 .95 20 .67 35 .84  Wo D i o p s i d e En Fs Hypersthene Olivine  ^° Fa Magnetite Ilmenite Apatite Calcite Water TOTAL NOTE:  8 .10 5 .25 2 . 29 En p  s  14 .56 7 .01 1 .73 2 .36 0 .14 0 .32 0 .38 100 .48  -  -  —  —  3 .07 29 .53 27 .25  1 .36 26 .32 28 .77  12 . 35 7 .55 4  13 .18 7 .86 4 .64  1 .97 1 .07  0 .83 0 .49  2 .55 1 .53 3 .91 4 . 50 0 .44 0 .11 0 .53  6 .37 4 .15 2 .58 3 .00 0 .25 0 .34 0 . 39  100 .47  100 .54  The chemical compositions quoted above were determined by Japan A n a l y t i c a l C h e m i s t r y R e s e a r c h I n s t i t u t e . Glomeroporphyritic olivine - plagioclase  basalt  of F i g u r e s 27 A and B.  58 (>0.3 H e k i n i a n , 1971 and o t h e r s ) i n d i c a t e weathering line  o f the rock.  The r o c k c o n t a i n s no n o r m a t i v e 2  However, t h e T i 0  stant during weathering this  2  as t h e l o w MgO c o n t e n t may be t h e r e s u l t o f c h e m i c a l a l -  teration.  content i s b e l i e v e d t o remain  2  ( H e k i n i a n , 1 9 7 1 ) and i t s h i g h  r o c k may i n d i c a t e  and a l k a l i b a s a l t .  to remain  constant during weathering  h i g h >16%.  The A l 0 3  compositions  content  content, also believed  2  ( H e k i n i a n , 1971"), i s f a i r l y  The d i s c r e p a n c y b e t w e e n t h e p l a g i o c l a s e  o l i v i n e microphenocryst  normative  con-  t h a t the rock i s i n t e r m e d i a t e between  tholeiite  and  nephe-  ( T a b l e I I ) and t h e r e l a t i v e l y h i g h c o n t e n t s o f N a 0 a n d K 0  as w e l l  in  a l t e r a t i o n by c h e m i c a l  phenocryst  c o m p o s i t i o n s and t h e i r r e s p e c t i v e  indicates  t h e s e p h e n o c r y s t s may be x e n o -  crysts. Dellwood  Seamount Basaltic  Range fragments  EN 70-025-8D  a n d EN 70-025-9D  16-15, P l a t e  I) have s e v e r a l  f r o m Dredge H a u l s  f e a t u r e s i n common.  are p a r t s o f p i l l o w b a s a l t s  teristic  glassy curved s u r f a c e , r a d i a l  block lavas  70-025-7D',  ( F i g u r e 25 and CSP l i n e  fragments  A few fragments  EN  do n o t show t h e s e  lOuBC 70-  Most o f t h e  ( F i g u r e 29) and show fracturing  charac-  and v e s i c u l a r i t y .  f e a t u r e s and a r e here termed  (Figure 34).  From t h i n s e c t i o n d e s c r i p t i o n s , t h r e e m a i n t y p e s c a n be d i s t i n g u i s h e d wood Seamount.Range.  i n the p i l l o w  fragments  textural  of the.Dell-  They a r e  (i)  Hyalopilitic.Olivine Basalt  (ii)  Intersertal Olivine Basalt  (iii)  Subophitic Olivine Basalt  These t h r e e t y p e s g r a d e  i n t o one a n o t h e r e v e n w i t h i n  59  A - Characteristic fracturing i n pillo'.v lavas.  3 - Pounded top surface o f pillow fragments.  C - Rounded top surface and radial fracturing i n pillow fragments.  D - ("lassy surface of pillow fra; tnents.  FIGTRE 29  Characteristic features of basaltic pillow fragments froc the Dellwood Eean.ount Range.  . the on  same r o c k f r a g m e n t the  condition  tachylyte fibrous  and  or  (Figure  o f the  the  32)  tachylyte  habit  of  the  the  of  the  fragments are  The  feathery  tachylyte;  as  the  upper  due  an  single crystals.  magnetic. t e x t u r a l features Within  the  group of  30B)  amounts i n t h e microlites granular lyte.  f i b r o u s p y r o x e n e grow o u t  in  fans  m i c r o l i t e s and  enclose.previously  (mainly magnetite).  to d e v i t r i f i c a t i o n  explanation o f MAR  and  also offered 1  basalts.  I n some r o c k s ,  l  hyalopilitic  This habit deuteric  by  the  Uid-Atlantic  the Ridge  and  laths  to  magnetite,lying  30B  texture  and  (Anso-6o)»  (Figure and  oli-  varying  plagioclase  clinopyroxene, i n a m a t r i x of  p l a g i o c l a s e . m i c r o l i t e s are  Tilley  hyalopilitic,  s k e l e t a l occur i n  fibrous  of  altera-  M u i r and  Figures  groundmass c o m p r i s i n g  (An^-ss) , feathery  Some o f  habit  and  which i s l o c a l l y  clinopyroxene  the  the  Microphenocrysts of p l a g i o c l a s e (Figure  are  hyalo-  of  b a s a l t : m a y have a n a r r o w zone showing v a r i o l i t i c  vine  distinguish  devitrification  show t h i s f i b r o u s h a b i t .  31B).  surface.  e x t e n t of  (1964) f o r s i m i l a r f e a t u r e s 3.1C  on  the  opaque m i n e r a l s  pyroxene i s b e l i e v e d  r a r e r o l i v i n e pheno-  8  chilled  slightly  sheaves from p l a g i o c l a s e  crystallised  An o-9o  main d i s t i n g u i s h i n g f e a t u r e s  c l i n o p y r o x e n e and  t i o n of  of  generally,  similar basalts.  b a s a l t s , the  tachylyte. and  amount  p i l l o w fragments are  occur i n c l u s t e r s or  mineralogically  pilitic  mainly  feathery,  In t h i n s e c t i o n , s e v e r a l the  distinguished  clinopyroxene whether  weathered rims u s u a l l y  p h e n o c r y s t s may  Most o f  are  m e s o s t a s i s , the  showing sparse p l a g i o c l a s e  c r y s t s and The  and  granular. In hand specimen, the  similar  60  olivine, tachy-  saussuritized  and  61  A - Bytownite (An-8 i) phenocryst i n h y a l o p i l i t i c basalt. Specimen No. EN 7 0 - 0 2 5 ~ JD - 1 3 .  C - Lath-shaped plagioclase, skeletal o l i v i n e and occasional clinopyroxene microphenocrysts i n i n t e r s e r t a l basalt. Specimen No.EN 70-025-7D-1A.  B - H y a l o p i l i t i c basalt with feathery D - O l i v i n e and plagioclase microphenocryst i n i n t e r s e r t a l basalt. to fibrou:; groundmass clinopyroxene Specimen No. EN 70-025-7D-6. Specimen No. EN 7 0 ^ ) 2 5 - 7 D - l l . FIGURE 30  Photomicrographs of basalts from the Dellwood Secu.ount Range.  Dredge Raul No. SN 7 0 - 0 2 5 - 7D. (NOTIFICATION 5 ' 3 X )  62  A - B y t o w n i t e (An-87)—Olivine nd. j r o phenocryst i n h y a l o p i l i t i c basalt.  B - S u b v a r i o l i t i c Basalt. Specimen No. 3J 70-025-9D-2.  C - F y a l o p i l i t i c to i n t e r s e r t a l b a s a l t  D - P l a g i o c l a s e microphenocryst i n  Specimen No. 3T 7 0 - 0 2 5 - 9 D - 1 .  w i t h f i b r o u s clinopyroxene. Specimen No. 3T 7 0 - 0 2 5 - 9 D - 2 2 .  fine-drained i n t e r s e r t a l basalt. Specimen No. M 70-025-8D-4.  (MAGNIFICATION  50X )  FIGURE j l Fhotomicro graphs of basalts from the Dellwood Seamount Ran.e. ;  Dredge P a u l Nos. B I  70-025-8D  and  B I 70-O25-9D  63  some o f t h e h y a l o p i l i t i c  basalts  are also  glomeroporphyritic  (Figure 31A). The  intersertal  basalt  i s distinguished  from the  h y a l o p i l i t i c b a s a l t m a i n l y i n t h e l e s s e r amount o f t a c h y l y t e , t h i s b e i n g r e s t r i c t e d t o i n t e r s t i c e s i n t h e groundmass o f t h e intersertal basalt.  Mineralogy i s s i m i l a r to the h y a l o p i l i t i c  basalt but clinopyroxene 30C).  In the groundmass, t h e c l i n o p y r o x e n e  (Figures  31D a n d 3 0 C ) ,  feathery. the  a l s o o c c u r s as m i c r o p h e n o c r y s t s  i n places  fibrous  S k e l e t a l o l i v i n e (Figure  intersertal basalt  sertal basalts  i s mostly  (Figure  granular  31C),  but never  30D) i s much more common i n  as m i c r o p h e n o c r y s t s .  are very fine-grained  microphenocrysts of plagioclase  (Figure  Some o f t h e i n t e r -  (Figure  31D) a n d may  contain  a n d o l i v i n e i n c l u s t e r s o r as  single crystals. The  subophitic  stage  i n which the pyroxene i s l a t h  ( i n which there shaped, b u t s t i l l  begin to enclose the plagioclase in  the samples s t u d i e d  subophitic  texture  u r e s 32E a n d F.  i n a pillow basalt  glassy pilotic  f r a g m e n t i s shown, i n F i g -  c a n change w i t h i n  Going from t h e d e v i t r i f i e d  32 were  3 cms. o f t h e s u r f a c e  glassy  surface  tothe  changes g r a d a t i o n a l l y  from  a few m i c r o l i t e s a n d s p a r s e p h e n o c r y s t s t h r o u g h  and i n t e r s e r t a l  o c c u r .throughout. clase  encountered  f r o m s a m p l e EN 70-025-8D-6 a n d shows  of the p i l l o w , the texture  with  enough t o  One e x a m p l e o f a  A l l t h e p h o t o g r a p h s shown i n F i g u r e  how d r a s t i c t h e t e x t u r e s  interior  large  l a t h s ) was n o t o f t e n  under the microscope.  t a k e n o f one t h i n s e c t i o n  of a p i l l o w .  i s no g l a s s a n d  to subophitic.  hyalo-  P h e n o c r y s t s and v e s i c l e  The p h e n o c r y s t s a r e m a i n l y o l i v i n e a n d p l a g i o -  i n c l u s t e r s o r as s i n g l e c r y s t a l s .  6  A - L e v i t r i f i e d glassy (plane l i g h t X 5 0 )  surface,  C - O l i v i n e and p l a g i o c l a s e p h e n o c r y s t s i n h y a l o p i l i t i c grourxlmass. ( p l a n e l i g h t X50)  E - P l a g i o c l a s e p h e n o c r y s t s i n subo p h i t i c g r o u n d m a s s . ( p l a n e l i g h t X50) F I G U R E 32  4  3 - O l i v i n e and p l a g i o c l a s e p h e n o c r y s t s i n d e v i t r i f i e d g l a s s y groundmass. ( X-Nicols x50)  D - Intersertal texture, (plane l i g h t X 5 0 )  F - Plagioclase phenocrysts i n subophitic grourylmass. ( X - N i c o l e x50)  Photomicrographs shoving changes i n t e x t u r e f r a g m e n t . S p e c i m e n NO. EfT 70-025-8D-6.  with depth i n t o p i l l o w  .Hyalopilitic + feathery cpx. ± granular cpx. Glassy-*— H y a l o p i l i t i c no c p x .  Hyalopilitic + fibrous to a c c i c u l a r cpx. +  u a  with  rH  r*  .Hyalopilitic + granular cpx. -Decrease  margin  R=20cm.  10 15 Z (cm.) FIGURE 3 3  rH  Subophitic  (J •rH  c o crj  Pillow  I-l  —'-Or—  o CS Ihtersertal^__iJntergranular _  i n rate of cooling-  -Pillow  core  Time (T) r e q u i r e d f o r c o n d u c t i o n c o o l i n g t h r o u g h t h e i n t e r v a l 1200°C t o 900°C a t a d e p t h Z b e n e a t h t h e s u r f a c e o f a b a s a l t s p h e r e ( i d e a l i z e d p i l l o w ) " o f r a d i u s R. T h r e e c a s e s a r e shown f o r p i l l o w s o f r a d i u s 5, 10,, 20 cm. C o n s t a n t t h e r m a l d i f f u s i v i t y o f 0.007 a n d a s u r f a c e t e m p e r a t u r e o f 0°C a r e a s s u m e d , ( a f t e r M a r s h a l l a n d C o x , 1971).  20  O b s e r v e d groundmass t e x t u r e s i n b a s a l t s f r o m t h e D e l l w o o d Seamount A r e a a n d t h e i r r e l a t i o n s h i p t o c o o l i n g r a t e and p i l l o w s i z e .  66  It  i s believed  that  the textures  encountered i n these  p i l l o w f r a g m e n t s d e p e n d on t h e p o r t i o n o f t h e p i l l o w t h a t was examined under t h i n s e c t i o n , t h e r a t e o f c o o l i n g o f t h e p i l l o w as  a whole and t h e r a t e o f c o o l i n g o f t h a t p o r t i o n o f t h e p i l l o w  w h i c h was s e c t i o n e d . (Marshall  This  r a t e o f c o o l i n g depends on p i l l o w  and Cox, 1971) and F i g u r e  33 shows t h e r e l a t i o n s h i p  between r a t e o f c o o l i n g , s i z e o f p i l l o w and b a s a l t  texture.  Some f r a g m e n t s r e c o v e r e d f r o m t h e D e l l w o o d Range showed no f e a t u r e s 34).  Seamount  c h a r a c t e r i s t i c of p i l l o w lavas  I n hand specimen, they a r e n o t i c e a b l y - c o a r s e r  the rocks  stitial  granular  beginning  to enclose  may be p o r p h y r i t i c w i t h p h e n o c r y s t s o f o l i v i n e  34B) o r p l a g i o c l a s e A n  8 0  .  as i n F i g u r e s  the p l a g i o -  34D a n d E. Fo  The r o c k s  is  Most fragments a r e a l s o  vesicular.  These b l o c k  lavas  crysts  as t h e p i l l o w l a v a s  slowly  c r y s t a l l i s e d parts  p i l l o w lavas The (Anso-90) and  a  n  described very  9 0  (Fig-  a r e m a g n e t i c and m a g n e t i t e finely,  show the.same m i n e r a l o g y a n d pheno-  a n d may be t h e l o w e r p a r t s o f t h e - same f l o w s  o r more  that produced the  above.  c a l c i c nature of the,plagioclase  d magnesia-rich nature of the o l i v i n e  microphenocrysts  The  O l i v i n e a l s o occurs i n the ground-  mass a n d as m i c r o p h e n o c r y s t s . t h e common opaque m i n e r a l .  (inter-  34B o r s u b o p h i t i c  rocks ure  laths) texture  as i n F i g u r e  [An  6 0  ]  clinopyroxene  i n sample  either a diabasic  clase  5 0  _  below) w i t h  clinopyroxene)  (with lath-shaped  ,In t h i n  are almost h o l o c r y s t a . i l i n e (except  IOUBC 70-16-12D-1 d e s c r i b e d  (Figure  grained  t h a n p i l l o w f r a g m e n t s , and a l l have a w e a t h e r e d r i m . section,  size,  (Fo  g o  ) when c o m p a r e d w i t h  phenocrysts  phenocrysts  the A n o r t h i t e con-  67  CMS  A - Diabasic b a s a l t . Specimen NO. EN 70-025-8D-85.  3 - P h o t o m i c r o g r a p h showing o l i v i n e pl.enoc r y s t i - i n d i a b a s i c b a s a l t . Specimen NO. EN 70-025-8D-85. (] 50  INCHES 4  5  C M :  C - Plagioclase p h e n o c r y s t s i n s u b o p h i t i c b a s a l t . Specimen NO. EN 70-025-7D-69.  D - Photomicrograph of subophitic basalt. Specimen No.iiJN 70-025-7D-69. (plane l i g h t }50 )  - Photomicrograph of s u b o p h i t i c Specimen NO.EN 70-O25-7D-69. (X-Nicols X50)  FIGURE 34 H o l o c r y s t a l l i n e black lavas from the Dellwood Seamount Range.  basalt.  68 tent of  the  and  normative p l a g i o c l a s e  the  tion  groundmass and  (Anss)  (Table II) i n d i c a t e s that  o l i v i n e p h e n o c r y s t s and and  microphenocryst plagioclase  block  lavas  of the  and  olivine  the p l a g i o c l a s e  (Ani+s.gn)  (Fogn) c o m p o s i -  phenocrysts  m i c r o p h e n o c r y s t s o f the  pillow  D e l l w o o d Seamount a r e a may  and  basalts  in fact  be  xenocrysts . O n l y one tioned  and  fragment l a r g e  o t h e r w i s e a n a l y s e d was  IOUBC 70-16-12D. plagioclase gioclase  basalt  obtained  In hand specimen, t h i s  - olivine basalt  (An8o-85)  a b u n d a n t and  enough t o be  (Figure  from dredge  smaller  rock i s a p o r p h y r i t i c  35A)  o l i v i n e phenocrysts resorption  (Figure  f i n e l y v e s i c u l a r glassy.groundmass.  with  35B)  On t h e  surface  look  Thin section  basaltic t o the  opaque i n c l u s i o n s  glass)  crystal  f a c e s ) as  and  of  shows t h e  and  larger  growth zones  shown i n F i g u r e s  t o 1 cm.  and  35B  and  are  euhedral  to.subhedral,  and  most show p a r t i a l  (Figure the  35D).  The  o l i v i n e s are  resorption  (Figure  brown  (subparallel  C;  smaller,  larger  ground-  plagioclases  subhedral to  35B).  Some o f  l a r g e r p h e n o c r y s t s are  fractured  h i g h l y weathered matrix  plagio-  i n a mesostasis  compositionally  compared to the  plagioclases  vesicular  p l a g i o c l a s e m i c r o p h e n o c r y s t s are intensely  and  frag-  rock  i n l a r g e s t d i m e n s i o n ; and  perhaps other m i n e r a l s  a l t e r e d b a s a l t i c glass  o f the  making the  o l i v i n e microphenocrysts i n a f i n e l y  mass o f p l a g i o c l a s e  less  ( p r e s u m a b l y m a g n e t i t e and  o u t l i n i n g twinning  o l i v i n e p h e n o c r y s t s up clase  zoned p l a -  i n a weathered  p h e n o c r y s t s weather out  containing  large  ( F o s a ) , many s h o w i n g  ment, the p l a g i o c l a s e a breccia.  sec-  haul  p h e n o c r y s t s (< 5 cm., i n d i a m e t e r ) and  evidence of p a r t i a l  like  thin  anhedral the  zoned.  very fresh  where-all  the  A l l the as  vesicles  B - B y t o w n i t e phenocryst with o p a q u e s o u t l i n i n g g r o w t h zones "md a p a r t i a l l y r e s o r b e d olivine (Fo-83) p h e n o c r y s t i n p o r p h y r i t i c p l a g i o c l a s e b a s a l t . (X50)  FIGURE 35  P o r p h y r i t i c p l a g i o c l a s e basalt Seamount  Range.  D - Weathered v e s i c u l a r , l a s s y groundmass o f p o r p h y r i t i c plagioclase basalt.(X50)  'IOUBC 70-16-12D-1) f r o m t h e D e l l w o o d  70 are  l i n e d with The  fibropalagonite  (Figure 35D).  opaque i n c l u s i o n s i n t h e l a r g e p l a g i o c l a s e s a r e  c o n c e n t r a t e d i n random a r e a s o f t h e p l a g i o c l a s e , o u t l i n i n g e i t h e r twinning  o r growth zones p a r a l l e l  Compositional zoning i s generally  to the c r y s t a l outline.  rare.  Most o f t h e opaques a r e e u h e d r a l t o s u b h e d r a l i n shape, due  t o t h e i r p o s i t i o n along twin planes.  Several  plagioclase  p h e n o c r y s t s f r o m t h e o t h e r d r e d g e h a u l s o f t h e D e l l w o o d Seamount Range a l s o c o n t a i n  opaque i n c l u s i o n s o u t l i n i n g g r o w t h z o n e s a n d  twinning. This  very p o r p h y r i t i c plagioclase  i sbelieved  to repre-  sent i n i t s phenocrysts a semi-cumulate mainly o f p l a g i o c l a s e and  l e s s e r o l i v i n e w h i c h was b e i n g f o r m e d n e a r t h e b o t t o m o f a  magma c h a m b e r , b u t a change i n c o n d i t i o n s p h e n o c r y s t s t o be e x t r u d e d w i t h to give  the glassy  (hut  later  caused these  large  t h e magma w h i c h r a p i d l y  altered)  cooled  groundmass.  CHEMISTRY OF BASALTS C h e m i c a l c o m p o s i t i o n s o f 14 b a s a l t  specimens from t h e  D e l l w o o d Seamount A r e a a r e shown on T a b l e I I I . compared w i t h and  a n a l y s e s f r o m known o c e a n i c r i d g e s ,  shows t h e D e l l w o o d Seamount A r e a b a s a l t s  between t h o l e i i t e s  and a l k a l i  basalts  t o be t r a n s i t i o n -  h a v i n g more  b o t h N a 0 a n d K 0 a n d l e s s MgO, t h a n o c e a n i c t h o l e i i t e s 2  2  spreading centres but  islands  s e a m o u n t s shown on T a b l e I V . A v i s u a l c o m p a r i s o n o f t h e  tables al  selected  T h e s e c a n be  i n the A t l a n t i c , Indian  g e n e r a l l y .less a l k a l i s  basalts  and P a c i f i c  alkalis, from oceans  e s p e c i a l l y K 0 , than the a l k a l i  from seamounts and o c e a n i c  2  islands.  71  TAB LI: SAMPLE NUMBER AND ROCK TYPE EN 70-02S-2D-1 . Gloneropo r p h y r i t i c "Ol-Plag. B a s a l t  III  CllliMICAI. COMPOSITION' OF BASALTS FROM Till: DLLLWOOI) SEAMOUNT ARF.A CHEMICAL COMPOS ITION IN WT. \  LOCATION Si0 Northwest Dellwood K n o l l s  2  47.34  Ti0  2  1.24  Al 0 2  3  17.65  Fe 0 2  3  1.19  FeO  MnO  7.70  0.14  KgO  CaO  10 .45 11.39  Na 0 2  2 .64  K 0  ll 0  0.16  0.62 100.52  2  2  TOTAL !  i  1  EN-70-025-3D-1 Hyalopilitic  Southeast Dellwood K n o l l s  50.04  2.37 16.29  2.70  7.09  0.15  5.28 11.77  3.49  0.52  0.81 100.51  EN 70-02S-8D-121 Intersertal Diabasic Basalt  Dellwood Seamount Range  49.70  1.58 15.91  1.78  C .16 7.78 ...  7.14 12.50  3.11  0.23  0.59 100.48  0.8 ± .01  A  EN 70-025-2D-8 Glor.eroporphyritic Ol-Plag. Basalt  Northwest Dellwood K n o l l s  46.1 ±1.0  EN 70-025-3D-2 Intersertal Basalt (weathered)  Southeast Dellwood K n o l l s  47.1 ±1.0  2.23 14.3 ± .08 .2  EN 70-025-7D-25 Intersertal Basalt  Dellwood Seamount Range  47.9 ±1.8  1.80 ± .07  Dellwood EN 70-02S*7-D~38 H y a l o p i l i t i c B a s a l t Seamount Range  46.6 ±1.0  EN 70-02S-8D-4 Intersertal Basalt  Dellwood Seamount Range  EN 70-02S-8D-6 Supophitic Basalt  EN 70-025-8D-25 Diabasic Basalt  1 .24 16.3 ±0.08 ±0.2.  Fe as Fej.Oj 9.2±0.3  0.12 + .01  8.76 11.0 ± .13 ± .1  3.2 + .1  0.19 ± .02  10.2±0.2  0.11 ± .01  5.54 10.6 + .04 ±•2.  3.4 + .1  0.5 ± .1  1.6 ±0.3  9S.6  10.3+0.2  0.13 ± .01  6.88 10.7 ± .07 t O . l  3.2 ± .2  0.33 0.5 + .05 ±0.1  96.4  1.38 15.7 ±.08 ±0.3  9.1+0.1  0.12 ± .01  6.70 11.4 ± .05 + .3  3.1 ± .1  0.16 0.9 95.2 ± .03 + 0.2 •  48.0 ±1.0  1.40 14.6 ±.07 ±.4  9 . 3 ±0 .1  0.13 ±.01  6 .94 L1.7 ±.09 ±.2  3.2 ±.1  0.7 0.19 ±.02 ±0.1  Dellwood Seamount Range  48.9 ±1.0  1.35 15.4 ± .04 ±.2  9.6±0.1  0.12 ±.01  6 .75 L1.6 ±.05 ±.1  3.3 ± .1  0.17 1.0 ±.02 ±0.2'  98.2  Dellwood Seamount Range  50.2 ±1.3  1.50 13.7 ± .07 ±•4  8.9±0.1  0.13 ±.01  6.40 11.9 + .03 ± .1  3.3 ±.1  0.22 0.6 ±.03 ±0.1  98.8  EN 70-025-9D-1 Dellwood H y a l o p i l i t i c B a s a l t Seamount Range  46.9 ±2.2  1.5 + .1  14.7 ±.2  9.8+0.2  0.13 + .01  6.94 11.5 + .09 + .2'  4.5 ± .1  0.16 1.3 + .03 + 0.2  97.4  EN 70-02S-9D-13 Dellwood H y a l o p i l i t i c B a s a l t Seamount Range  46.4 ±.5  1.48 14.6 ±.08 ±.2  9.6+0.3  0.13 ±.01  6.40 11.9 + .06 ±.1  3.3 ± .1  0.18 1.4 ±.03 ±0.2  95.4  EN 70-025-9D-33 Hyalopilitic  Dellwood Seamount Range  47.9 ±3.0  1.53 14.3 ±.03 ±.1  9.7±0.2  0.12 ±.01  6.2 ± .1  11.5 + .1  3.2 ± .1  0.23 1.9 + .02 ±0.3  96.6  IOUBC 70-16-12D-1 Porphyri t i c Plag-6l. Basalt  Dellwood Seamount Range  43.5 ±3.0  0.4 ±.1  3.4±0.3  0.04 ±.01  4.3 ±.1  15.3 ±.5  2.2 ± .2  0.11 2.0 ±.02 + 0.3  96.8  i  14.7  ±0-3  i25.5  * A n a l y s e s done by J a p a n A n a l y t i c a l R e s e a r c h C h e m i s t r y I n s t i t u t e (See Table I I ) . A l l e r r o r s shown a r e maximum d e v i a t i o n s from t h e nean and a r e n o t r e l a t e d to a c c u r a c y o f the estimates.  96.9  '96.1  72  TAnU  IV  SAMPLE NO. AND BASALT TYPE  CIILMICAL COMPOSITIONS OF HAS ALT IC HOCKS OF KNOWN SKAMOUNTS, OCLANIC ISLANDS S OCEANIC RIDGES  CHEMICAL COMPOSITION KT. t  LOCATION SiOj  1. A l k a l i  Basalt  Bowio Seamount  48.0  Ti0  2  2.43  AljOj [ F e 0 j ! FcO 2  18.S  l.S  7.5  M/iO 0.1S  MgO  CaO  S.O  B.S  NajO ! K,0  i  11,0  I  ! P,0<  4.0  1.6  0.6  0.07  1  2. A l k a l i  Basalt  Bowie Seamount  45.2  J.l  16.4  0.6 .  10.3  0.18  6.9  8.1  3.8  2.4  0.6  0.71  3. A l k a l i  Basalt  Bowie Seamount  4S.33  J.S3  1S.0  1.81  10.64  0.23  6.77  8.S  4.3  2.36  0.21  0.73  4. A l k a l i O l i v i n e Basalt  Polulu Series, Kohala, Hawaii  •47.98  J.S3  IS.32  2.49  8.86  0.12  6.16  10.28  3.56  1.08  0.87  0.22  5. T h o l e i i t e (Avg. of 10 b a s a l t s )  Koolau S e r i e s , Oahu, Hawaii  I S0.4S ! 2.33 j  14 .94  3.38  7.SS  0.08  7.67  9.17  2.84  0.3S  0.96  0.27  6. T h o l e i i t e (Avg. of 24 b a s a l t s )  Mauna Loa, Hawaii  SO.42  2.97  11.62  2.71  9.07  0.10 10.11  9.74  2.09  0.39  7. T h o l e i i t e (Avg. of 4 analyses)  Carlsberg Ridge, Indian Ocean  SI.9  1.8  1S.S  3.6  6.4  7.3  9.S  3.9  0.1  8. High A l - O l T h o l e i Mid- • i t e (Avg. 2 a n a l . ) A t l a n t i c Ridge  48.2  0.7  17.3  1.2  8.6  10.2  11.3  2.4  0.1  9. O l i v i n e T h o l e i i t e (Avg. of 3 a n a l . )  SO.6  1.1  16.2  1.6  7.8  8.7  11.3  2.6  0.1  7.68  10.87  2.63  0.20  MidA t l a n t i c Ridge  1 48.61  1.S4  IS.31  ..A-1 ll Fe as Fe,0« 10.61  Juan de Fuca Ridge  49.82  2.12  13.77  12.66  6.49  10.90  2.73  0.12  12. T h o l e i i t e (Avg. of 7 analyses)  Gorda Ridge  49.62  1.S2  IS.78  9.90  7.29  11.78  2.42  0.1S  13. T h o l e i i t e (Avg. of 3 analyses)  East P a c i f i c Rise 49.17  1.S1  16.23  9.3S  7.00  11.83  2.S7  0.12  10. T h o l e i i t e (Avg. of 7 analyses)  Mid-Atlantic Ridge near 30°N.  11. T h o l e i i t e (Avg. of 7 analyses)  .  0.27  .  14. T h o l e i i t e  E x p l o r e r Seamount 48.10  1.2S  18.30  Rc ferences 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. )1. 12. 13. 14.  I l e r i c r , 1970 l i e n o r , 1970 Engel and l i n g e l , 1963 Macdonald, 1949 h'vntvorth and W i n c h e l l , 1947; Turner and Vcrhoogen, Macdonald, 19-19; Turner and Vcrhoogen, 1960 N i c h o l l s c t a l , 1964 Nicholls c f 1964 N i c h o l l s c_t aT, 1964 • Average obtained from analyses quoted by Kay e_t al , Average obtained from analyses quoted by Kay o_t aT, Average obtained from analyses quoted by Kay ct^ aT, Average obtained from analyses quoted by Kay ct aT, Kay c t a l ^ 1970 "  1960  1970 1970 1970 1970  9.SO  8.30  11.SO  2.81  0.09  0.40  73 Silica the  atomic  alumina  than t h e i r  the,author.  by,the  16.3%  author  by  show s t r i k i n g  atomic  absorption  Si0  2  and  2  and  compositions  author.  b e l i e v e d to  2  be  The  ing  the  3  silica  3  analyses  wt.  analyses  of  no  calculated  from  alumina  low  Because of  Fe 0 /FeO 2  3  the  ratios,,  f o r the r o c k s  e r r o r s , and  to  2-4%).  f o r the  o f a l l the o t h e r elements the quoted  error  analysed  are can  be  results. 2  and  Al 0  d i a g r a m s o f F i g u r e 36.  Sample EN  more magnesium t h a n  ( i . e . an  % (an e r r o r o f  and  e r r a t i c n a t u r e o f the S i 0 variation  while  s i m i l a r l y proved  III.  were n o t  the  analyses  column o f Table 2  gave o n l y  3  T h u s , i t seems  account  A1 0  For  3  absorption analyses of  1-2  p e r t i n e n t o b s e r v a t i o n s c a n be (i)  2  gave a v a l u e  3  values probably  accurate within  used i n i n t e r p r e t i n g The  % A1 0 .  A USGS s t a n d a r d b a s a l t  author.  silica  o n l y by  shown i n t h e l a s t  inaccuracy of S i 0  the  A1 0  atomic  The  low, but  analysed  ( i . e . an e r r o r o f a b o u t 7 . 5 % ) ,  when a n a l y s e d by t h e  a b o u t 6-10%.  classical  those  gave o n l y 1 2 . 8 5 % a l u m i n a  3  comparisons t h a t the  normative  I I I ) and  by  Chemistry  d i f f e r e n c e i n t h e wt.  (an e r r o r o f a b o u t 1 0 % ) .  consistently  totals  Research  2  o f a b o u t 6%)  These l o w  of Table  consist-,  analysed  2  2  l o w by  are  70-025-2D-1 c o n t a i n i n g .17,65% A 1 0  c o n t a i n i n g 13.65% A 1 0  these  oxides  70-025-3D-1 c o n t a i n i n g 16.29% A 1 0  o n l y 14.6%  in  two  values f o r standards  ( t h e . f i r s t 3 analyses  s a m p l e EN  by  of these  compared because  A c o m p a r i s o n b e t w e e n s a m p l e s a n a l y s e d by  e x a m p l e , s a m p l e EN  be  quoted  directly  c h e m i c a l methods by J a p a n A n a l y t i c a l  Institute  are  c a n n o t be  absorption analyses  e n t l y lower  wet  and  iron.  2  3  analyses  Still,  follow-;  made:  70-025-2D-1 w i t h 4 7 . 3 4 % S i 0 This  the  shows  i s t o be  expected,  2  contains  since  this  74 25 FIGURE 3 6 S i l i c a V a r i a t i o n D i a g r a m s f o r b a s a l t s o f t h e D e l l w o o d Seamount Area.  20  15  A1 0 2  +  A1 0  v  CaO  A  Total  a  MgO  -  Total Alkalis  o  Ti0  2  3  I r o n as F e 0 2  5  = Na 0 + K 0 2  2  2  3  to w  Q  i—i  X  o  12  CaO 10 Total  I r o n as Fe203  MgO  -•Boundary b e t w e e n ..•^"H'awaiian T h o l e i i t e s a n d , A l k a l i B a s a l t s on t o t a l A l k a l i s vs S i l i c a p l o t . Na 0 + K 0 2  2  8^ TiO, I 40  45  WT  % .STT.TfA  75  specimen i s a g l o m e r o p o r p h y r i t i c p l a g i o c l a s e  - olivine  with o l i v i n e phenocrysts having a high f o s t e r i t e (ii)  The s e m i - c u m u l a t e  diagram.  content  a l u m i n a , a n d l i m e a n d v e r y l o w i n MgO  (43.5%  s c a t t e r and t h e H a w a i i a n into  tholeiitic (iv)  plot  2  >FeO.  as t h i s  (An^) with lesser olivine  Plot of total  alkali  vs s i l i c a  and a l k a l i  rock  Fo  8 3  .  shows a w i d e  B o u n d a r y l i n e BB' d i v i d e s  (below the l i n e )  ).  Si0 ) high i n  a n d FeO w i t h MgO  S u c h a c o m p o s i t i o n i s s u p p o r t e d by t h e m i n e r a l o g y  (iii)  9 0  t r e n d shown by t h e  This rock i s u l t r a b a s i c  contains mainly p l a g i o c l a s e  (Fo  IOUBC 70-16-12.D-1 ( F i g u r e 35A)  does n o t f o r m p a r t o f any d i f f e r e n t i a t i o n variation  basalt  the b a s a l t s  types.  The v e r y w i d e s c a t t e r i n t h e a l u m i n a v s . s i l i c a  i s m a i n l y due t o t h e t o o l o w e s t i m a t e s o f A I 2 O 3 by t h e  atomic  a b s o r p t i o n method. The t r a n s i t i o n a l  the Dellwood 37, w h i c h  to a l k a l i n e nature of the basalts of  Seamount A r e a  i s shown more c o n v i n c i n g l y on F i g u r e ,  i s an AFM d i a g r a m  are n o t c o n s i d e r e d . unusual p l a g i o c l a s e  where t h e p e r c e n t a g e  Here t h e p l o t o f b a s a l t s semi-cumulate basalt  A1 0 2  3  and  Si0  (except f o r the  IOUBC 70-16-12D-1) f o l l o w  the a l k a l i  tiation  t r e n d s shown i n F i g u r e 40 w e r e t a k e n f r o m M a c d o n a l d and  Kuno tion of  diagram  well, here  (The d i f f e r e n -  5.)  (1968) p o i n t e d o u t t h a t w h i l e t h e s i l i c a  has the d i s a d v a n t a g e  of emphasizing  f r a c t i o n a t i o n , the SI ( S o l i d i f i c a t i o n  c a n be u s e d  trend.  more  closely  K a t s u r a , 1964, F i g u r e  differentiation  2  t o show e a r l y  and m i d d l e  s i n c e SI i s t h e p e r c e n t a g e i n any f r a c t i o n a t i o n  MgO  varia-  the l a t e  Index) v a r i a t i o n  stage diagram  stages of f r a c t i o n a t i o n i n t h e AFM d i a g r a m ,  as  and  t r e n d p l o t t e d , c o m p o s i t i o n o f t h e magma  76  Dellwood Seamount Area ° Basalts. o IOUBC 70-16-12D-1  77 FIGURE 38  SI V a r i a t i o n Diagrans f o r b a s a l t s o f the D i U u o o d Searaouiit A r e a .  CaO  \  . _ _ I o t a l _ Iron as-FeO  1  MgO  5L  Tin,  JS  2S  Na O  —•—" '  a  0.5 0.4 0.3 0.2  •  K.a  --  0.1  S10j__  ;  '  45  •  AljO.  IS  10  40  4 S  Mgo-100 /(Mgo  • FeO  35 (total)  • Na,0  • K O) a  I 30 - S o l i d i f i c a t i o n Index ( S I ) .  25  78  invariably  c h a n g e s so as t o d e c r e a s e  proceeds.,  F i g u r e 38 shows SI v a r i a t i o n d i a g r a m s f o r t h e  of the Dellwood  Seamount A r e a .  t h e SI v a l u e  as'fractionation  Several observations  basalts  c a n be made  from these diagrams. 1  (i)  T h e r e i s much l e s s s c a t t e r t h a n on  v a r i a t i o n d i a g r a m s and (ii)  The  trends  plagioclase  o f the d i f f e r e n t i a t i o n (iii)  can.be  trends  Of p r i m a r y  zone.  expected  drawn.  c u m u l a t e a g a i n does n o t  importance  i f the k n o l l s  are  the l e a s t  are p r o x i m a l  and  39.2.  a r o u n d 26. Southeast  T h i s low Dellwood  i n g r a t h e r than (iv)  the  amount o f I n o n l y two (EN  and  The  and  age  and  old rocks, values the  degree of weather-  s p e c i m e n s shown i n F i g u r e 41 70-025-7D-25) and  a t i o n diagrams are reasonable  rocks r e l a t i v e  and  expected  g e n e r a l s l o p e s o f the  35  Dell-  f o r the r e l a t i v e l y . o l d rocks of  differentiation  g e n e r a l l y what w o u l d be  spreading  K n o l l s h a v e SI  26.6  >CaO p r e s u m a b l y r e p r e s e n t i n g a more i r o n - r i c h  (v)  to a  differentiation.  c l i n o p y r o x e n e phase i n these  The  Dellwood  K n o l l s may, r e f l e c t  w i t h SI v a l u e s o f 31.5 FeO  Southeast  SI v a l u e  any  differentiated,  Rocks o f t h e  wood Seamount Range h a v e SI v a l u e s b e t w e e n 30 s c a r p on  l i e on  i s the o b s e r v a t i o n t h a t  Knolls  These h a v e SI v a l u e s o f 44.9  from a f a u l t  silica  shown.  r o c k s o f the Northwest Dellwood w h i c h i s t o be  the  groundmass  to the  surprises  others. these  SI  and  are  from a f r a c t i o n a t i o n  trends of the o x i d e s  those  (EN„70 - 025 - 3D-2),.  t r e n d s shown by show no  -  vari-  process.  ( i . e . whether  ;  79 positive  or negative)  HYALOCLASTITE  a g r e e w i t h t h o s e shown by Kuno  BRECCIAS  Hyaloclastite breccias tuffs  (Nayudu,  fragment fragments  ( S i l v e s t r i , 1963) o r p a l a g o n i t e  1964) w e r e r e c o v e r e d  f r o m two d r e d g e  h a u l s (one'  f r o m EN 70-025-2D a n d s e v e r a l f r o m EN 7 0 - 0 2 5 - 9 D ) . f r o m t h e l a t t e r h a u l were a l l s i m i l a r  but d i f f e r e n t specimen  (1968) .  i n hand-specimen  to each  The  other,  and X - r a y a n a l y s i s f r o m t h e one  f r o m EN 70-025-2D. The h y a l o c l a s t i t e  fragment  recovered  from dredge  EN 70-025-2D c a n b e s t be d e s c r i b e d as a p a l a g o n i t e ( F i g u r e 39A) c o n t a i n i n g b a s a l t i c  haul  tuff breccia  g l a s s f r a g m e n t s ; f r a c t u r e d and  s h a t t e r e d fragments o f g l a s s y p i l l o w s sometimes rounded p a l a g o n i t i z a t i o n o f t h e g l a s s y s k i n , . b u t more o f t e n  by  angular;  and o c c a s i o n a l p l a g i o c l a s e g r a i n s i n a g r e e n t o d a r k b r o w n m a t r i x . The whole, f r a g m e n t , i s  c o v e r e d w i t h a t h i n r i n d o f manganese -  iron oxides which penetrates (  The i n d i v i d u a l size  glassy basaltic  from m i c r o s c o p i c  to pieces  these l a r g e r fragments being The f r a g m e n t  into  the fragment  fragments vary  i n some p a r t s . considerably i n  2.5 cm. i n l a r g e s t d i m e n s i o n ;  rounded  due t o p a l a g o n i t i z a t i o n .  i s only l o o s e l y consolidated, tending  t o crumble  when d r i e d , t h e l a r g e r g l a s s and g l a s s y b a s a l t f r a g m e n t s in  resting  a m a t r i x o f p a l a g o n i t e and c l a y m i n e r a l s , shown by X - r a y  diffraction  t o be m a i n l y  montmorillonite.  The h y a l o c l a s t i t e  fragments  EN 70-025-9D a r e n e a r l y a l l f l a t , c r u s t on,one s u r f a c e o n l y from the fragment  recovered  from dredge  some w i t h a t h i n  (Figure 39C).  haul  ferromanganese  The m a i n d i f f e r e n c e s ,  already discussed include:  A - Eyaloclastite Breccia. Specimen No. EN 70-025-2D-24.  B - Photomicrograph of hyaloclastite breccia showing pala ;onitized glass shards i n a dark ferruginous matrix, (plane l i g h t 750) Specimen No. EN 70-025-9D-27. r  C - Hyaloclastite Breccia fragments  fro.i.  Dredge Haul No.EN 70-O25-9D.  IGURE 39 Hyaloclastite Breccia fragments from the Dellwood Seamount Area.  81  TABLE  V  C h e m i c a l C o m p o s i t i o n o£ H y a l o c l a s t i t e B r e c c i a s f r o m t h e D e l l w o o d Seamount A r e a  CHEMICAL COMPOSITION I N WT.  OXIDES  EN 70-025-9D-27  EN 70-025-2D-24 Si0  2  Ti0  2  37.2  A1 0  3  All  I r o n as F e 0  2  2  3  46.7  ±1.0  ±0.7  0.6 ±0.1  0.7 ±0.1  7.7 ±0.5  10 .6 ±0.6  18 . 23±0.05  11.08±0.05  MnO  0.16 + 0 .01  0 .49±0 .01  MgO  5.56±0 .11  4 .44±0 .12  CaO  3.85±0 .09  2 .64±0.10  Na 0 2  1.8 ±0.1  4.2 ±0.1  K 0  1.4 ±0.1  1.9 ±0.1  2  H 0, e t c .  17.8  1  2  12.5  ±0.5  ±0.5  Cu  0 .0045  0 .0060  Ni  0.0085  0 .0163  Co  0.0025  0 .0040  Pb  0 .0315  0 .0000  Zn  0 .0150  0.0175  NOTES:  E r r o r s q u o t e d above a r e maximum d e v i a t i o n s !  H 0, 2  hours  etc. represents a t 700° C.  volatiles  lost  f r o m t h e mean.  on h e a t i n g  f o r 24  82 (i) surface)  The f e r r o m a n g a n e s e c r u s t on one s u r f a c e  only. (ii)  The a b s e n c e o f l a r g e r o u n d e d f r a c t u r e d a n d s h a t -  t e r e d g l a s s y p i l l o w fragments w i t h p a l a g o n i t i z e d rims. all  the fragments are submicroscopic  mainly  (upper  palagonitized glass  comprising  shards..  (iii)  The f l a t  (iv)  Mineralogy:  diffraction  to microscopic  Instead,  shape o f t h e f r a g m e n t s . Thin  s e c t i o n ( F i g u r e 39B) a n d X - r a y  a n a l y s i s shows t h e h y a l o c l a s t i t e s  a t l o c a l i t y EN 70-  025 -9D t o c o n t a i n y e l l o w - b r o w n p a l a g o n i t i z e d g l a s s . s h a r d s , q u a r t z , and p l a g i o c l a s e i n a green m a t r i x o f p a l a g o n i t e and c l a y minerals  mainly (v)  montmorillonite but also c h l o r i t e Chemistry:  Table  by w e i g h t i n a l m o s t e v e r y hyaloclastites,  oxide  reflecting  also different origin  and i l l i t e .  V I shows d i f f e r e n t analyzed  percentage  f o r t h e two t y p e s o f  the d i f f e r e n t mineralogy  (discussed following).  and perhaps  Sample EN-70-025-  2D-24 c o n t a i n s no q u a r t z , b u t p e r h a p s more c a l c i c p l a g i o c l a s e ; contains  less  silica  a n d more c a l c i u m a n d i s l o w i n a l k a l i s .  Sample EN 70-025-9D-27 c o n t a i n s q u a r t z more p l a g i o c l a s e silica,  alumina The  (perhaps d e t r i t a l ) , and  (some o f w h i c h may be d e t r i t a l ) , c l a y m i n e r a l s , and a l k a l i i s .  formation  of hyaloclastite breccias i s genetically  r e l a t e d t o submarine v o l c a n i c e r u p t i o n s . summarised t h i s  relation  Silvestri  (1963)  as f o l l o w s :  "Immediately a f t e r the opening o f a f i s s u r e , the s e a w a t e r p e n e t r a t e s i n t o i t , comes i n t o c o n t a c t w i t h t h e r i s i n g magma a n d c h i l l s i t . T h u s , a s o l i d c r u s t i s formed, b u t i s r a p i d l y b r o k e n t o p i e c e s by t h e u p w a r d p u s h i n g magma w h i c h i s r e p e a t e d l y c h i l l e d a n d . s h a t t e r e d .... The e r u p t i n g magma may p a r t i a l l y , i n t r u d e between t h e s e a bottom and t h i s i n i t i a l  83  ( h y a l o c l a s t i t e ) b r e c c i a l i k e a s i l l , b u t more o f t e n i t w i l l perforate the covering b r e c c i a , pushing i t a s i d e and f l o w i n g o u t ( f o r m i n g p i l l o w l a v a s sometimes w i t h h y a l o c l a s t i t e b r e c c i a between the p i l l o w s ) . . . . A t t h e s u r f a c e o f t h e l a v a , g l a s s y f r a g m e n t s accumul a t e t o b u i l d up h y a l o c l a s t i t e s w h i c h may d e r i v e a l s o f r o m t h e s u r f a c e o f t h e l a v a f l o w i t s e l f , as w e l l as from the g l a s s y c r u s t s o f t h e growing p i l l o w s . " 1  l  The  p a l a g o n i t i z a t i o n o f the b r e c c i a s  p r o c e s s due t o c h e m i c a l and  i s a secondary  a l t e r a t i o n by r e a c t i o n between  h o t l a v a and t o h y d r o t h e r m a l a c t i v a t i o n by h e a t e d  w h i c h has p e n e t r a t e d  seawater  i n t o t h e h y a l o c l a s t i t e s and t h e r e  g a s e s r e l e a s e d by t h e l a v a .  The c l a y m i n e r a l s  t i o n phase i n t h e c o n t i n u i n g h y d r a t i o n  seawater  mixed  are a l a t e r  o f the b a s a l t i c  with  altera-  glass  s h a r d s by s e a w a t e r . Because o f i t s low S i 0 minerals,  and h i g h  CaO c o n t e n t ,  2  content,  absence o f d e t r i t a l  t h e sample r e c o v e r e d  025-2D i s b e l i e v e d t o be p a r t o f an i n i t i a l clastite  breccia, while  samples r e c o v e r e d  f r o m EN 70-  or interpillow  hyalo-  from dredge h a u l  EN 70-  025-9D a r e p a r t o f t h e h y a l o c l a s t i t e b r e c c i a f o r m e d above t h e lava  flow perhaps i n p a r t  as a pavement c o v e r  c o a t i n g on t h e u p p e r s u r f a c e and  only).  Detrital  (ferromanganese quartz  and f e l d s p a r  p e r h a p s a l s o p l a n k t o n i c o r g a n i s m s c o u l d t h e n e a s i l y have b e e n  added t o t h i s h y a l o c l a s t i t e b r e c c i a pavement.  CHEMICAL WEATHERING AND ALTERATION OF BASALTIC FRAGMENTS In hand specimen, the v a r y i n g shown by c o l o u r fragment  changes from core  degrees o f weathering are  to r i m (Figure 40).  A weathered  ( F i g u r e 40B) w o u l d t h u s show a h i g h l y a l t e r e d y e l l o w t o  red-brown l a y e r immediately below t h e , o u t e r  manganese  coating,  S t a t e m e n t s i n p a r e n t h e s e s do n o t f o r m p a r t o f t h e q u o t e , b u t a r e a d d e d by t h e a u t h o r .  84  A - Intensely weathered basalt fragments.  Basalt fragments with weathered zones r e s t r i c t e d to the rim.  FIGURE 40  3 - Weathered zones along fractures  i n basalt fra, iuents.  B - Moderately weathered basalt fragmen" Specimen NO.HJ 70-O2;~-9B- 22.  Weathered zones i n basalts of the B e l l wood Seamount Area.  85 then a yellow-green l a y e r s and may  l a c k the  ments may face  finally grey  a grey core  l a c k the  l a y e r and  surrounding  l a y e r f o l l o w e d by core.  and  red-brown or y e l l o w  show o n l y  a core.  the b l a c k  within  2 cm.  of the  may  and  black  fragments  s l i g h t l y weathered  frag-  i n t e n s e l y weathered  or g r e e n i s h b l a c k  Weathering i s mainly  r i m o f f r a g m e n t s and  thered  I n t e n s e l y weathered  ( F i g u r e 40A)  to the  relatively  a greenish-black  layers  restricted,  show t h e v a r i o u s  sur-  however,  colour  changes  s u r f a c e , the w e a t h e r e d r i m s u r r o u n d i n g  f r e s h l a r g e grey  core  r i m , c o l o u r c h a n g e s may  ( F i g u r e 40C).  be  sharp,  but  are  Within  the  the.wea-,  often gradational.  A sharp c o n t a c t , however, o f t e n e x i s t s between w e a t h e r e d r i m fresh interior. into the  the  interior  In f r a c t u r e d f r a g m e n t s , w e a t h e r i n g o f the  fragment along  colour  zonation  on  r i m o f the  fragment  (Figure  The mainly  the  also hematite,  l i m o n i t e , and  from h y d r a t i o n of b a s a l t i c  outer yellow  l a y e r i s mainly  the p i l l o w .  The  layers  g l a s s by  a l t e r a t i o n products  and  the  p a l a g o n i t e , but  hematite,  also iron  converting  i t to p a l a g o n i t e , i r o n oxides  minerals.  In h i g h l y weathered zones, v e s i c l e s are  p a r t s o f the  minerals  iron oxides.  specimens, chemical  limonite  In the  alteration  s a u s s u r i t i z a t i o n of p l a g i o c l a s e microlaths  The of and  black as  the t a c h y l y t e . and lined  clay and  l e s s weathered  i s , when (due  and  oxides,  mesostasis  and  the  of  clay  greenish black  Weathering a f f e c t s mainly  with palagonite  to  sea water.  a l t e r a t i o n products.  filled  shows  the p a l a g o n i t i z e d g l a s s y s u r f a c e  r e d - b r o w n zone c o n t a i n s  contain mainly  itself parallel  t h e v a r y i n g amounts  which r e s u l t  palagonite  and  40B).  c o l o u r changes r e f l e c t  p a l a g o n i t e , but  extends f a r  f r a c t u r e planes  f r a c t u r e plane  and  to  present,  deuteric  86  alteration) of  and  chemical weathering  the t a c h y l y t e v e s i c l e  lyte  linings  i n t h e groundmass a r o u n d P a l a g o n i t e may  tachy-  vesicles.  o c c u r as t h e i n i t i a l of b a s a l t i c  c l a y minerals being l a t e r phases;  of  palagonitization  and o f t h e i n t e r s t i t i a l  the  the g r a d u a l c h e m i c a l weathering  s y n g e n e t i c h y d r a t i o n and  i s mainly  h y d r a t e d phase i n  g l a s s by.sea  o r p a l a g o n i t e may  alteration  be  water,  due  (deuteric a l t e r a t i o n ) .  t h e p a l a g o n i t e i n t h e s a m p l e s s t u d i e d i s b e l i e v e d due  ical  a l t e r a t i o n by s e a w a t e r  since i t s distribution  t h a t i t i n c r e a s e s i n amount by inward from vesicles.  the w a l l s  Replacement p r o b a b l y c o n t i n u e s u n t i l  manganese and fragment  from  Most  t o chem-  indicates  r e p l a c i n g the b a s a l t i c  t h e o u t e r s u r f a c e and  to  glass  of cracks  precipitated  i r o n o x i d e s f o r m enough o f a c r u s t o v e r t h e  to p r e v e n t  and  f u r t h e r c o n t a c t between sea water  basalt  and  basaltic  glass. Weathering of  the b a s a l t s  i s also reflected  as r e p o r t e d by H e k i n i a n  r o c k s show an F e 0 : F e O r a t i o 2  Fe 0 2  3  and  3  a decrease  However, T i 0 mentioned  2  i n MgO  and A 1 0 2  >0.3;  and  show no  3  FeO  i n chemical (1971).  composition  Deeply  i n c r e a s e i n H 0,  weathered  K 0  2  2  and  compared to f r e s h r o c k s .  d e t e c t a b l e change.  Hart  (1970)  t h a t exchange between sea water  and o c e a n i c  tholeiites  c o u l d produce chemical compositions which  are s i m i l a r  to  basalts. Dellwood  The  transitional  Seamounts may  weathering  by s e a  V E S I C L E LININGS AND Two  to a l k a l i  t h e r e f o r e be  alkali  n a t u r e o f the b a s a l t s o f due  at. l e a s t  the  i n p a r t to  water.  AMYGDULES  types of v e s i c l e  linings  and  amygdules o c c u r  commonly  FIGURE  41  A - Calcite Specimen B - Calcite Specimen  V e s i c l e l i n i n g s and a m y g d u l e s i n b a s a l t s f r o m t h e D e l l w o o d Seamount A r e a .  lining vesicle NO.  EN 70-025-7D-11.  filling NO.  vesicle  NO.  (X - N i c o l s  X50)  i n hyalopilitic basalt.  EN 70-02.5 -7D-1.  C - Segregation vesicles Specimen  i n hyalopilitic basalt.  (X - N i c o l s  X50)  i n intersertal basalt.  EN 70-025-3D-4.  (Plane l i g h t  X50)  D - Palagonite l i n i n g subsidiary surface of segregation whose p r i n c i p a l s u r f a c e i s l i n e d w i t h t a c h y l y t e . Specimen  NO.  EN 70-025-8D-1.  E - Fibro-palagonite lining basalt. Specimen  NO.  (Plane l i g h t  segregation  EN 70-025-7D-6.  vesicles  (X - N i c o l s  vesicle  X50) in intersertal XSO)  F - Palagonite l i n i n g subsidiary surface of segregation vesicle whose p r i n c i p a l - s u r f a c e i s l i n e d w i t h d e v i t r i f i e d t a c h y l y t e . Specimen  NO.  EN 70-025-7D-11.  (Plane l i g h t  X50)  87  FIGURE 41 Vesicle linings and an.ygdules i n basalts froa. the Dellwood Seamount Area. (MAGNIPICATION X 5 0 )  88 in  the b a s a l t i c  rocks o f the Dellwood  Seamount  1)  Chemically p r e c i p i t a t e d ( F i g u r e s 41A a n d B)  linings  2)  S e g r e g a t i o n v e s i c l e s and t h e i r ( F i g u r e s 41C, D, E a n d F)  and  fillings  alteration  The c h e m i c a l l y p r e c i p i t a t e d l i n i n g s prise  red-brown h y d r a t e d  iron oxides  l i m o n i t e ) b l a c k manganese o x i d e s  Area,  products  and f i l l i n g s  (mainly hematite  and  and s p a r r y c a l c i t e .  Both  iron  and  manganese o x i d e s o c c u r  the  surface of the fragment, t h e i r p r e c i p i t a t i o n  ing  o f Mn and Fe and o t h e r e l e m e n t s f r o m t h e l a v a by r e a c t i o n  w i t h sea water.  i n vesicles  com-  i n the weathered r i m near  The f o r m a t i o n o f s p a r r y c a l c i t e  r e a c t i o n o f sea water trapped  a i d e d by l e a c h -  may be due t o  i n the v e s i c l e s o f a c o o l i n g l a v a  with the lava. The s e g r e g a t i o n v e s i c l e s ( F i g u r e 41) a r e s i m i l a r t o t h o s e representing s o l i d i f i e d formed v e s i c l e s b e f o r e being  i n thin section  d e s c r i b e d by S m i t h  c o n s o l i d a t i o n o f the l a v a , " t h i s  due t o "an i n c r e a s e i n c o n f i n i n g p r e s s u r e Partial  l a v a f o l l o w e d by c o m p l e t i o n  crystallisation  of c r y s t a l l i s a t i o n  c o u l d produce" the s e g r e g a t i o n v e s i c l e s . segregation vesicles  are thus  early movement  a p p l i e d t o the  c o n f i n i n g p r e s s u r e , f o r example, a t a deeper marine  of these  (1967) "as  r e s i d u a l m e l t w h i c h moved i n t o  f l u i d w i t h i n the v e s i c l e s . lar  observed  of a vesicu-, at a higher environment,  The p r i n c i p a l  surface  lined with basaltic  glass  ( t a c h y l y t e ) and s u b s i d i a r y s u r f a c e s may be l i n e d w i t h p a l a g o n i t e due  to a l t e r a t i o n  n i t e may lines  fill  or f i l l s  o f t h e t a c h y l y t e ( F i g u r e s 41D and E) o r p a l a g o -  the w h o l e . v e s i c l e . v e s i c l e s occurs  low b i r e f r i n g e n t m i n e r a l s  Most o f t h i s p a l a g o n i t e w h i c h  as a g r e e n i s h , . a n i s o t r o p i c f i b r o u s  ( F i g u r e s 41D a n d E) d e s c r i b e d by P e a c o c k  89 (1928)  as f i b r o p a l a g o n i t e .  The l e s s  tropic variety.which replaces  fibrous yellow-green iso-  the i n t e r s t i t i a l  glass of the  groundmass o f t h e s e b a s a l t s was d e s c r i b e d by. P e a c o c k palagonite.  Devitrification  o f theb a s a l t i c  vesicles  can cause m i c r o l i t e s  vesicles  (Figure  as g e l  glass i n segregation  and c r y s t a l l i t e s t o f i l l  or line  41F).  POST-VOLCANIC DEPOSITS Ferro-Manganese  Nodules  Figure the  and C r u s t s  42 shows f e r r o m a n g a n e s e  D e l l w o o d ' S e a m o u n t Range, w h i l e  manganese c r u s t  Figure  each dredge  b a s a l t from t h e  The maximum t h i c k n e s s  g i v e some measure o f t h e r e l a t i v e  from  28C shows a t h i c k  (<_ 50 mm.) o n an i n t e r s e r t a l  Southeast Dellwood K n o l l s . crusts  n o d u l e s and c r u s t s  of.manganese  age o f s p e c i m e n s  from  h a u l , t h i c k e r c r u s t s o c c u r r i n g on o l d e r r o c k s .  Some  r o u g h e s t i m a t e s o f t h e age o f t h e r o c k s a r e shown i n T a b l e V I , b a s e d o n e s t i m a t e d r a t e s o f growth, o f manganese c r u s t a n d n o d u l e s for  theNorth P a c i f i c  1967).  ( B e n d e r e t a l , 1970;  Barnes  For p e l a g i c n o d u l e s , t h e e s t i m a t e d growth r a t e  North P a c i f i c  i s 2.5 t o 3 mm/10  6  yr.  c r u s t s here would  also contain  age o f t h e r o c k .  6  contin-  t h e nodules and  continental debris l i k e quartz  and c l a y , as i n t h e D e l l w o o d Seamount A r e a . b a s e d on a v a l u e o f 2.5 mm/10  i n the  For.nodules nearer  e n t s j g r o w t h r a t e s w o u l d be much h i g h e r s i n c e  of  a n d Dymond,  T h u s , any e s t i m a t e  y r . i s p r o b a b l y , a maximum e s t i m a t e  The maximum q u o t e d r a t e o f g r o w t h o f  manganese n o d u l e s i s 40 mm/10 That ferro-manganese  6  y r . ( B a r n e s a n d Dymond, 1967) . c r u s t on r o c k s f r o m t h e d r e d g e  h a u l from the Southeast Dellwood K n o l l s  i sthicker  than the  90 manganese r i n d on r o c k s f r o m special  interest.  TABLE V I  o f F e r r o - M a n g a n e s e C o a t i n g a n d E s t i m a t e d Age Remarks on T h i c k n e s s Coating  Dredge H a u l No and L o c a t i o n  EN 70-025-3D Southeast Dellwood K n o l l s  o f Mn-Fe  EN 70-025-8D Dellwood Seamount Range  V a r i a b l e , up t o 12 mm.  EN 70-025-9D Dellwood Seamount Range  L a y e r e d c r u s t s up t o 80 mm. t h i c k , and n o d u l e s .  1+70 myr  thick.  0.1+2 myr  thick,  0.3+4.8 myr,  2+32 myr,  M a i n l y manganese r i n d a n d f r a g ments o f a l a m i n a t e d , i r o n - r i c h deposit < thick.  The c r u s t , when w e l l  developed,  i sthinly layered  ( F i g u r e 42B) a n d t h e s u r f a c e may be p i t t e d a n d f u r r o w e d 42C),  probably  1  0.02+1 myr,  M a i n l y a r i n d on g l a c i a l e r r a t i c s On b a s a l t f r a g m e n t s , i t i s 3-6 mm. t h i c k , b u t becomes 50 mm. t h i c k on p a r t s o f one s p e c i m e n where a g a i n t h e Mn-Fe o x i d e s a r e associated with detritus.  V a r i a b l e , up t o 5 mm.  IOUBC 70-16-12D  Estimated Age  Manganese R i n d <_ 1 mm. on 5 3 o u t o f 54 s p e c i m e n s . The l a s t s p e c i men h a s a c o a t i n g a v e r a g i n g 1 mm. b u t l o c a l l y r e a c h i n g 3 mm. where i t c o m p r i s e s Mn-Fe o x i d e s t o g e t h e r with d e t r i t a l debris.  EN 70-025-7D Southeastern end o f D e l l w o o d Seamount Range  Northwestern end o f . D e l l w o o d Seamount Range  Knolls i s of  (See D i s c u s s i o n . )  Thickness  EN 70-025-2.D Northwest Dellwood K n o l l s  the Northwest Dellwood  due t o s o l u t i o n  l a y e r e d around a nucleus  o f t h e manganese.  The n o d u l e s a r e  commonly a b a s a l t o r h y a l o c l a s t i t e  Age e s t i m a t e d u s i n g maximum v a l u e s o f 40 mm/10 v a l u e s o f 2.5 mm/10 y r . 6  (Figure  6  frag-  y r . a n d minimum  91  - Ferron.anganese crust (~30mm thick) unconfoni.ably overlying a bedded H y a l o c l a s t i t e Breccia. Specimen No.EN 70-025-9D-71. j  C - P i t t e d and furrowed ferromanganese crust. FIGURE 42 Ferromanganese nodules and crusts from the Dellwood Seamount Range.  TABLE  SAMPLE ROCK  NO.  LOCATION  TYPE  VII  ELEMENTAL CHEMICAL ANALYSES OF POST VOLCANIC DEPOSITS  ELEMENT COMPOSITIONS  IN WT. h  Na  Mg  Al  Si  K  Ca  Ti  Mn  Fe  41.1  26.6  MAXIMUM (Mero, 1964)  PACIFIC  4.7  2.4  6.9  20.1  3.1  4.4  1.7  MINIMUM (Mero, 1964)  OCEAN  1.5  1.0  0.8  1.3  0.3  0.8  0.11  8.2  2.4  AVERAGE (Mero, 1964)  Mn-NODULES  2.6  1.7  2.9  9.4  0.8  1.9  0.67  24 .2  14.0  Dellwood Seamount Range  1.6  o.8  3.0  10 .7  0.7  1.8  0.23  14.5  Southeast Dellwood KnolIs  1.4  1.8  2.2  8.1  r.i  1.2  0.16  22.1  Dellwood Seamount Range  1.5  0.7  1.0  8.6  0.3  1.3  Southeast Dellwood Knolls  3.0  1.7  3.9  16.8  1.0  2.9  0.19  9.0  7.2  IOUBC 70-16-12D-3 Sandstone  Dellwood Seamount Range  2.1  1.4  4.1  24 .1  1.5  3.4 .  0 .34  0.12  Mn-Nodule ( G r i l l , 1968)  Jervis Inlet  0.95  1.82  1.7  ND  0.98  1.33  0.096  32.72  EN 70-025-9D-92 Mn-Nodule EN 70-025-3D-4 Mn-Fe C r u s t IOUBC 70-16-12D-2 Iron Deposit EN 70-025-3D-22 Mn-impregnated Sediment  1  0  2.05  Co  Cu  Zn  2.3  2.0  1.6  0.08  0.36  0.014  0.16  0.028  0.04  0.02  0.35  0.99  0.53  0.047  0.09  7.75  0 .048  0.23  0.041  0.073  0.019  6.13  0.0052  0.049  0.013  0.035  0.0028  0  0.006  0.0015 0.0076  0  0 .0015  0.006  0.0035 0.013  0  9.13  0.0012  0.002  0.0015 0.0053  0  5 .01  0.013  0.026  0.0055 0.0019  ND  28.5  1 1  ND  - Not  Determined  Pb  1  93 ment.  I n F i g u r e 42A, a t h i c k f e r r o m a n g a n e s e c r u s t , 35 mm.  occurs over  a d i p p i n g bedded h y a l o c l a s t i t e  X-ray todorokite  analysis  thick,  breccia.  o f t h e f e r r o m a n g a n e s e c r u s t s shows  (a h y d r a t e d manganese o x i d e )  as t h e p r i n c i p a l  mineral  o f manganese, b u t t h e c r u s t s a l s o c o n t a i n m o n t m o r i l l o n i t e , c h l o r ite,  quartz, plagioclase  and g o e t h i t e .  Elemental  air-dried post-volcanic deposits, including crusts and  and n o d u l e s ,  average analyses  Grill  a r e shown i n T a b l e  the ferro-manganese  V I I . Maximum, minimum  ( M e r o , 1964) as w e l l  (1968) f o r a n o d u l e  analyses.of  as one a n a l y s i s b y  from J e r v i s • I n l e t , B r i t i s h  Columbia  a r e a l s o shown f o r c o m p a r i s o n . Iron  Deposit S e v e r a l fragments  consolidated deposit IOUBC 70-16-12D.  of a red thinly layered loosely,  ( F i g u r e 43) were r e c o v e r e d  The a d j a c e n t l a y e r s o f t h e s e  from  fragments  slightly  i n c o l o u r ; the l a y e r s  probably  due t o d e p o s i t i o n on an i r r e g u l a r b o t t o m .  shows t h e o c c a s i o n a l r e l i c t  dredge h a u l vary  are u n d u l a t i n g or s l i g h t l y f o l d e d ,  detrital  Thin  section  heavy m i n e r a l s , e.g., sphene,  b u t more i m p o r t a n t , shows a c o m p l e x l a y e r e d t e x t u r e , some l a y e r s composed o f r e d ' r i b l i k e ' tites  (Figure 43B).  i s o t r o p i c material resembling  X-ray  stalac-  d i f f r a c t i o n w i t h Cuka r a d i a t i o n  shows  t h e m a t e r i a l t o be amorphous and t h e d e p o s i t i s t h u s b e l i e v e d t o consist mainly of a hydrated crystalline  goethite).  i r o n oxide  A partial  chemical  (IOUBC 70-16-12D-2) i s g i v e n i n T a b l e of s i m i l a r Joensuu,  d e p o s i t s from  (1966).  given i n Table ic deposits.  the South  An e l e m e n t a l  VIII  analysis of this together with  deposit  analyses  P a c i f i c by B o n a t t i and  chemical  VII w i t h chemical  (e.g., limonite or crypto-,  composition o f the rock i s  compositions  of other Post  Volcan-  94  CMS  A - Layered Iron Deposit.  B -Photo..!crograph of iron deposit sho-,ving layers composed of r i b - l i k e limonite resembling stalactites, (plane light J 0) r  FIGURE 43 Iron Deposit (I0U3G 70-16-12D-2) from the Dellwood Seamount Range.  95 TABLE V I I I  P a r t i a l C h e m i c a l C o m p o s i t i o n o f Some Deep S e a I r o n Deposits  Oxide o r Element Si0 A1 0 CaO MgO K 0 Fe Mn  Sample a n d C o m p o s i t i o n i n a 17 .6 1.0 2.6 1.5 0.39 32 .5 1.94  2  2  3  2  3  IOUBC 70-16-125-2  12.4  18.4 ±0.5 1.9 ±0.3 1.82+0.01 1.16±0.09 0.36±0.02 28.5 ±0.1 2 .05±0.05  a 2  13 .9 1.0 2.3 0 . 85 0.45 28.8 2 .43  t. %  1.0  2.7 0.80 0.38 31 .1 0.58  C o m p o s i t i o n i n ppm. Ni Co Cu  400 35 74  NOTE -  ai,a , 3 a n a l y s e s o f South P a c i f i c by B o n a t t i a n d J o e n s u u , 1966. > a  a  r  e  2  The lar  62 0 15  90 32 60  460 120 120  origin of this  fragment  iron  is.believed  deposits  t o be s i m i -  t o t h a t o f manganese c r u s t s , n a m e l y b y c h e m i c a l d e p o s i t i o n  at the sediment-water  interface.  The s o u r c e o f t h e i r o n ,  t h e s o u r c e o f t h e manganese, i s a p r o b l e m . nodules  ( e . g . , those from J e r v i s  like  In shallow-water  Inlet, British  Columbia), the  manganese i s p r o b a b l y o b t a i n e d f r o m c o n t i n e n t s b y w e a t h e r i n g a n d oceanic transport. its  emanations  (rich  I n t h e deep s e a , s u b m a r i n e  i n Fe a n d o t h e r e l e m e n t s ) , a n d t h e l e a c h i n g  o f Fe a n d Mn f r o m s u b m a r i n e w a t e r and s u b m a r i n e and  basalts  due t o r e a c t i o n b e t w e e n s e a  l a v a may be t h e p r i m e  sources of the i r o n  manganese. Iron-rich deposits  crystalline  formed  consisting mainly of crypto-  g o e t h i t e have been r e p o r t e d from t h e South  by B o n a t t i a n d J o e n s u u was  volcanism with  (1966) , who b e l i e v e d  by f r a c t i o n a l  precipitation  Pacific  that "the deposit  o f Fe a n d Mn w h i c h h a d  96 b e e n i n t r o d u c e d i n t o t h e b o t t o m w a t e r by h y d r o t h e r m a l of volcanic o r i g i n S u c h an o r i g i n  solutions  and by l e a c h i n g o f deep s e a b a s a l t i c  lavas  i s a l s o a p p l i c a b l e t o the i r o n deposit o f the  D e l l w o o d Seamount Range a t l o c a l i t y very weathered nature  IOUBC 70-16-12D w h e r e t h e  o f t h e g r o u n d m a s s and l o w i r o n  content  o f t h e a s s o c i a t e d b a s a l t s ( s a m p l e IOUBC 70-16-12D-1) may cate  indi-'  a d d i t i o n o f i r o n t o t h e b o t t o m w a t e r by l e a c h i n g o f t h e  basaltic  rocks.  SEDIMENTS Loosely  Consolidated  Sediments  From d r e d g e h a u l  IOUBC 70-16-12D, s e v e r a l  of a green l o o s e l y c o n s o l i d a t e d sandstone recovered. cobble  ( F i g u r e 44A) were  I n hand specimen, the o c c a s i o n a l g l a c i a l p e b b l e o r  i s f o u n d s u r r o u n d e d by a s a n d - s i z e d  t h i n manganese r i n d o c c u r s Thin  green m a t r i x .  i n some p a r t s o f some  s e c t i o n ( F i g u r e s 44C and D) shows t h e r o c k  f o r a m s and d e t r i t a l  (glacial) rock  subangular  to contain  to rounded  hornblende,  s p h e n e , z i r c o n and e p i d o t e , a l l f l o a t i n g  shown by X - r a y d i f f r a c t i o n and  fragments w i t h l e s s e r  quartz,  and a l t e r e d  o r no g r a i n t o g r a i n c o n t a c t )  illite.  An e l e m e n t a l  composition  (IOUBC 70-16-12D-2) i s shown i n T a b l e t o be v e r y  iron  amounts o f (i.e.,  i n a green c l a y - r i c h  to c o n s i s t of c h l o r i t e , chemical  A very  fragments.  plagioclase  little  fragments  with  matrix  montmorillonite  of this  rock  V I I w h i c h shows t h e r o c k  rich.  The s a n d s t o n e f r a g m e n t s  (IOUBC 70-.16-12D-2) a r e  b e l i e v e d t o be a u t h i g e n i c , c o m p r i s i n g  mainly  glacial  detritus  C os D — Photomicrographs of authigenic sandstone showing angular to rounded quarts, plagioclase, forams and rock fragments i n a dark ferruginous matrix. Specimen NO. I0U3C 70-16-12D-3. (X50) FIGURE 44 Authigenic loosely consolidated sediu.ents from the Dellwood Seamount Area.  98 being  c o n s o l i d a t e d and  w h i c h may  be p a r t l y  from the  o f a v o l c a n i c o r i g i n , as  same l o c a l i t y .  fragments are settling  Foram t e s t s  a l l p e l a g i c and  to the bottom a f t e r One  44B)  c e m e n t e d i n p l a c e by  Detrital  sand-sized  be  the p r i n c i p a l  80%  fragments,  chlorite  montmorillonite).  to  the  is  shown i n T a b l e  s u r f a c e of the  i s impregnated  cementing  fragments.  More  clay minerals  Foram t e s t s  fragments.  An  hornthan  manganese (mainly  are m a i n l y  elemental  agent.  and  illite,  restricted  chemical  analysis  VIII.  . The  chain-bag  h e n c e o n l y one  diffraction  and  sample  dredges used d i d not (EN  70-025-7D-72) was  r e c o v e r much examined.  mud X-ray  showed i t t o c o n t a i n q u a r t z , p l a g i o c l a s e , c a l c i t e  ( f o r a m s ) and ite  c o n t a i n s more  however, c o n s i s t of h y d r a t e d  ( m a i n l y t o d o r o k i t e ) and  and  by  (Figure  grains include p l a g i o c l a s e , quartz,  the o c c a s i o n a l a l t e r e d r o c k  iron oxides  deposit  sandstone  70-025-3D  d e r i v e d d e t r i t u s , and  b l e n d e and of the  iron  death.  i s a l s o a l o o s e l y c o n s o l i d a t e d sediment, but glacially  cement  were a d d e d t o t h e s e d i m e n t  w i t h manganese o x i d e w h i c h may  and  i s the  found i n these  f r a g m e n t f r o m d r e d g e h a u l EN  foram t e s t s , l e s s  Mud  a ferruginous  c l a y m i n e r a l s , again mainly  illite.  Most o f t h i s  i s prpbably  chlorite,  montmorillon-  glacially  derived  material. Glacial  Erratics G l a c i a l e r r a t i c s were r e c o v e r e d  sites  except  ental  source.  composition.  EN  from a l l dredge  70-025-7D w h i c h i s f u r t h e s t away f r o m a c o n t i n The  glacial  erratics  vary  They r a n g e f r o m p e b b l e s  in size,  to boulders  shape >60  and  lb. in  S3  C  FIGURE 45  D  Glacial Erratics recovered from the Dellwood Seamount Area.  100 weight are  (Figure  45E), they are subangular  m a i n l y igneous o r metamorphic.  granodiorites, diorites,  Dellwood  schists  erratics  Mountains  IX  rocks include  Columbia  Glacial Erratics  F i g u r e 45 shows h a u l s from t h e  the constituent  indicate  rock  t h a t t h e Coast  i s the probable source  from the Dellwood  granites,  and d i a b a s e s .  o b t a i n e d i n dredge  The r o c k t y p e s l i s t e d  of British  rounded, and  and g n e i s s e s .  Seamount A r e a a n d T a b l e IX l i s t s  types found.  TABLE  Igneous  amygdaloidal basalts  Metamorphic rocks i n c l u d e some o f t h e g l a c i a l  to well  area.  Seamount  Area  D r e d g e Number a n d Number o f S p e c i m e n s  ROCK  EN 70025-2D  TYPE  EN 70025-3D  EN 70025-8D  EN 70025-9D  IOUBC 70 12-12D.  Igneous Volcanic Igneous Plutonic  g  Metamorphic  8  4  2  1  1  Sedimentary  -  -  -  Undifferentiated  *  -  '-  * - Several pebbles NOTE - T h e r e j  and c o b b l e s , m a i n l y  w e r e no g l a c i a l  Most o f t h e g l a c i a l  Inese r i n d ,  at least  JOIDES D r i l l  i n parts.  erratics erratics  4 1  4 -  1 *  igneous.  r e c o v e r e d f r o m EN 70-025-7D a r e c o v e r e d w i t h a manga-.  Some a l s o  show g l a c i a l  striations.  H o l e No. 177  T a b l e X I shows a l o g t y p e d e s c r i p t i o n o f a c o r e by. J O I D E S on t h e n o r t h w e s t and give  total  end o f P a u l Revere  t h i c k n e s s o f the sediment  Ridge..  drilled  The age  column a r e noteworthy and  some i d e a o f s e d i m e n t a t i o n r a t e s .  These a v e r a g e  about  4  101 TABLE X  D e s c r i p t i o n o f c o r e l o c a t e d a t 50 28.18'N. 130 12.30'W. on t h e n o r t h w e s t end o f t h e P a u l R e v e r e R i d g e a t w a t e r d e p t h o f 2006m. ( a f t e r Kulm and Von Huene,19 7 1 ) .  Depth i n core junitjThicknessi D e s c r i p t i o n o f u n i t (meters) | No., o f u n i t J 62  • O l i v e - g r a y to dark I g r e e n i s h - g r a y s i l t y muds.  j UUppppeerr Pleistocene  T h i n , o c c a s i o n a l l y graded s a n d and s i l t t u r b i d i t e s interbedded w i t h hard f i s s i l e muds.  Lower Pleistocene  i  4  rO-6  100 128  1-9 0i  1  200  r  — 2-2 2  r  3  I  32  300  -3 ~3"8".  4-  6  W e l l - d e f i n e d graded sand and s i l t t u r b i d i t e s .  Dark-olive Nannofossil muds w i t h no s a n d o r s i l t beds.  ' 68  f >56  5071  and c a r b o n a t e . ] U p p e r I Pliocene  I^TBas-aTt -Si41-  -4-Si  500  Nannofossil r i c h mud.  156  400  j Geological , -age ;  ' Lower I Pliocene  r Lower Pliocene  Indurated f i n e grained m o d e r a t e l y s o r t e d m a s s i v e ' Lower fan or c o n t i n e n t a l r i s e | Pliocene sediments a l t e r n a t i n g w i t h hemipelagic sediments.  102  cm/1000 y r . f o r the P l i o - P l e i s t o c e n e p e r i o d and about 10 cm/1000 y r . f o r the P l e i s t o c e n e .  The d e s c r i p t i o n o f t h e sedimentary  u n i t s i n d i c a t e d e p o s i t i o n by t u r b i d i t y c u r r e n t s , and, p e r i o d s o f q u i e s c e n c e d u r i n g which o n l y p e l a g i c muds were d e p o s i t e d .  This  p r o b a b l y r e f l e c t s the d i s t u r b e d h i s t o r y o f the c o r e - s i t e , i n the middle o f a f a u l t zone.  I t i s believed that sedimentation  rates  i n t h e a r e a o f the proposed Dellwood S p r e a d i n g Segment i s much greater  (see D i s c u s s i o n )  e n t a l slope  because i t i s a t the base o f t h e . c o n t i n -  and thus much n e a r e r t o a c o n t i n e n t a l source than  the P a u l Revere R i d g e , and a l s o because i t i s t o p o g r a p h i c a l l y much l o w e r than the P a u l Revere Ridge.  103 CHAPTER SIX DISCUSSION THE  RELATIONSHIP OF THE DELLWOOD SEAMOUNT AREA TO THE JUAN DE FUCA PLATE  The  e x i s t e n c e of the E x p l o r e r Spreading  established others).  Zone has been  (Ewing et a l , 1968; Morgan, 1968; Atwater, 1970 and  T h i s spreading  F a u l t Zone (Thomlinson,  zone terminates  at the Revere - Dellwood  1971, p e r s o n a l communication and present  s t u d y ) , along the southwest slope o f the Paul Revere The  Queen C h a r l o t t e r i g h t  lateral  Ridge.  transform f a u l t trends  along  the c o n t i n e n t a l slope o f f Queen C h a r l o t t e I s l a n d s (Chase and Tiffin,  i n press) and i n t o the n o r t h e a s t e r n s e c t i o n o f the S c o t t  Channel o f f Queen C h a r l o t t e Sound (MN - P l a t e VIII and V V Plate XIII).  F a u l t i n g a l s o occurs on the lower  slope and i n  the Winona Basin f u r t h e r south o f f Vancouver I s l a n d but t h i s faulting of  may be a p r e v i o u s l y a c t i v e more s o u t h e r l y e x t e n s i o n  the Queen C h a r l o t t e f a u l t or may be due to subduction  Juan de Fuca P l a t e i n the r e g i o n ,  The problem then i s what  k i n d o f boundary e x i s t s between the P a c i f i c  and Juan de Fuca  P l a t e s i n the r e g i o n between the E x p l o r e r Spreading the Queen C h a r l o t t e t r a n s f o r m Only  of the  Zone and  fault.  three types of p l a t e boundaries  are p r e s e n t l y  r e c o g n i s e d - transform f a u l t s , . s p r e a d i n g c e n t r e s , and subduction zones.  The bathymetry, v e c t o r geometry, p o s i t i o n and o r i e n t a -  t i o n o f known spreading centres and transform f a u l t s de Fuca - P a c i f i c P l a t e boundary and the d i s t r i b u t i o n  of the Juan o f sea-,  mounts i n the area a l l seem t o preclude e i t h e r a subduction or t r a n s f o r m f a u l t t r e n d i n g n o r t h e a s t  zone  from the Dellwood Seamount  104 Range t o t h e s o u t h e r n e n d o f t h e Queen C h a r l o t t e C h a r l o t t e S o u n d , as t h e t y p e o f b o u n d a r y and J u a n de F u c a P l a t e s i n t h e a r e a . exist 1.  as  i n the a r e a , making  (too  Fault  the boundary  P l a t e s v e r y complex  boundary  between the P a c i f i c other p o s s i b i l i t i e s  follows:  E i t h e r t h e Queen C h a r l o t t e  Pacific  Two  F a u l t o f f Queen  Zone becomes v e r y  diffuse  between the N o r t h American  and  i n t h e D e l l w o o d Seamount A r e a , t h e  comprising a series of very small spreading centres  small  t o be d e l i n e a t e d by t h e m a g n e t i c  by s m a l l t r a n s f o r m f a u l t s . distribution  anomalies)  joined  T h i s i s s u p p o r t e d by t h e d i f f u s e  o f earthquake e p i c e n t r e s  i n the area (Figure 2 ) ,  However, t h e > l o c a t i o n s o f t h e e p i c e n t r e s a r e n o t v e r y a c c u r a t e , each l o c a t i o n h a v i n g a l a r g e c i r c l e o f e r r o r  {>_ 10 km  radius,  T o b i n and S y k e s , 1 9 6 8 ) ; o r 2.  A w e l l - d e f i n e d spreading c e n t r e l i e s w i t h i n the Dellwood  Seamount A r e a c o n n e c t i n g t h e E x p l o r e r S p r e a d i n g segment v i a t h e Revere  - D e l l w o o d T r a n s f o r m F a u l t t o t h e Queen C h a r l o t t e  form F a u l t . this  Trans-  From t h e b a t h y m e t r y , t h e most o b v i o u s l o c a t i o n f o r  s p r e a d i n g c e n t r e w o u l d be t h e c h a n n e l b e t w e e n t h e D e l l w o o d  Knolls, hereafter called  the Dellwood  Channel.  I f t h e D e l l w o o d K n o l l s do mark t h e s i t e o f a s p r e a d i n g centre quences 1.  - the Dellwood Channel  - then several points  and conse-  o f t h i s h y p o t h e s i s must be c o n s i d e r e d as f o l l o w s : .  The D e l l w o o d Seamount A r e a may mark t h e t r i p l e  junction  b e t w e e n t h e P a c i f i c , N o r t h A m e r i c a n , a n d J u a n de F u c a  Plates.  T h i s w o u l d be t h e t r i p l e p o i n t w h e r e t h e D e l l w o o d S p r e a d i n g  Seg-  m e n t , t h e Queen C h a r l o t t e T r a n s f o r m F a u l t and t h e s u b d u c t i o n zone  o f t h e J u a n de F u c a P l a t e  a l l meet.. T h i s s u b d u c t i o n zone  105 is  represented  the de  other  i n t h e a r e a by t h e S c o t t  hand, subduction  Fuca P l a t e i n t h i s  somewhere t o t h e s o u t h  F a u l t Zone.  On  may n o t p r e s e n t l y be a c t i v e and J u a n  r e g i o n may be f u s e d  the N o r t h American p l a t e  represent  Islands  t o , and moving  - i n which case the t r i p l e  with,  point i s  a n d t h e D e l l w o o d S p r e a d i n g Zone w o u l d  the boundary between the P a c i f i c  and N o r t h  American  represent  a right  Plates, i n the area. 2.  The Queen C h a r l o t t e  lateral 1965)  transform  joining  and r e l a t e d f a u l t s  fault  zone o f t h e r i d g e t o a r c t y p e  the A l e u t i a n I s l a n d A r c to the East  in  the Dellwood Region.  in  the northeastern  continuous seismic  This  transform  reflection profiling  ends q u i t e  ( P l a t e X I I I ) and HH'  the  s o u t h e r n e n d o f t h e Queen C h a r l o t t e  f u r t h e r to the south,  i n the area  While p r o f i l e s  W  like  NO  F a u l t has d i e d out s o u t h e a s t  MN  (Plate  VIII),  F a u l t Zone, p r o f i l e s  ( P l a t e I X ) , ST a n d TU ( P l a t e X I ) , i n d i c a t i n g t h a t t h e Queen o f the S c o t t  Channel.  Charlotte  Further  south  shown  J J ' ( P l a t e V I I ) and L L ' ( P l a t e X I I ) i n d i c a t e c o m p r e s -  sion probably  due t o s u b d u c t i o n .  cause o f the c r u m p l i n g MN  (Plate VIII).  in  the Winona B a s i n  in  the S c o t t  sedimentation  abruptly  (see Seismic  t h e Winona B a s i n , however, t h e f o l d i n g and f a u l t i n g  on p r o f i l e s  Rise  ( P l a t e V I ) show f a u l t i n g b e l i e v e d t o be  do n o t show any s u c h f a u l t i n g  and  Pacific  s e c t i o n o f t h e S c o t t C h a n n e l as i s shown by  Data -Queen C h a r l o t t e F a u l t ) .  in  fault  (Wilson,  S u b d u c t i o n may a l s o be t h e  of lower slope  s e d i m e n t s shown on p r o f i l e  The f a c t t h a t t h e t o p m o s t l a y e r s a r e u n d e f o r m e d and t h a t many o f t h e f a u l t s  C h a n n e l do n o t r e a c h i s going  the surface, i n d i c a t e s that  on a t a much f a s t e r r a t e  that r e l a t i v e l y quiet  i n t h i s b a s i n and  tectonic conditions  than  deformation  e x i s t e d i n the very  106  recent past.  A l t e r n a t i v e l y , s t r i k e - s l i p m o t i o n may  have been  so much more i m p o r t a n t t h a n d i p - s l i p m o t i o n a l o n g t h e Queen Charlotte  transform fault  area', t h a t f a u l t i n g  i n the r e c e n t t e c t o n i c h i s t o r y o f the  i n the area i s u n r e c o g n i s a b l e i n a v e r t i c a l  s e c t i o n s i n c e s e d i m e n t s on b o t h s i d e s o f t h e f a u l t lar  i n a c o u s t i c i m p e d a n c e t o show t h e p r e s e n c e o f  d i s p l a c e m e n t on a CSP 3.  1  The  Revere  simi-  strike-slip  section.  - D e l l w o o d F a u l t Zone i s a r i g h t  f a u l t o f the r i d g e  are too  l a t e r a l transform  to r i d g e t y p e , d y i n g out i n a n o r t h w e s t e r l y  d i r e c t i o n n e a r t h e s o u t h w e s t end o f , t h e D e l l w o o d S p r e a d i n g Segment. T h i s i s a g a i n s u p p o r t e d by s e i s m i c d a t a w h i c h shows e v i d e n c e o f faulting  a l o n g the southwest s l o p e s o f P a u l Revere  R i d g e and  S o u t h e a s t D e l l w o o d K n o l l s , and i n t h e b a s i n b e t w e e n t h e  the  Dellwood  Seamount Range and t h e D e l l w o o d K n o l l s , h e r e a f t e r r e f e r r e d t o as the D e l l w o o d B a s i n . EF  (Plate  faulting  III),  JJ'  Such f a u l t i n g  i s shown on p r o f i l e s  ( P l a t e V I I ) and RS  (Plate X).  DD'  and  However,  i s n o t o b s e r v e d on t h e s o u t h w e s t s l o p e o f t h e n o r t h w e s t  Dellwood K n o l l s o r i n the b a s i n between the Dellwood K n o l l s  and  t h e D e l l w o o d Seamount Range  IOUBC  70-16 -16 4.  The  (BC  (the Dellwood B a s i n ) a l o n g l i n e  - Plate I I ) .  a r e a s h o u l d have h i g h h e a t f l o w .  v a l u e s i n t h e a r e a ( F i g u r e 12) n e l between the Dellwood K n o l l s  a r e 4.8 and 4,0  b a s i n between the D e l l w o o d K n o l l s  The  Review  than t w i c e the average  chan-  2  y c a l s / c m - s e c i n the 2  and t h e D e l l w o o d Seamount Range. f o r t h e J u a n de  and g r e a t e r t h a n t h r e e t i m e s t h e a v e r a g e  (see L i t e r a t u r e  flow  y c a l s / c m - s e c i n the  These v a l u e s are a t l e a s t t w i c e the average Plate  two h e a t  - Chapter I I ) .  The  f o r oceanic ridges  f o r ocean b a s i n s  v a l u e s are a l s o (1.82  Fuca  greater  ycals/cm -sec) 2  and  107 about t w i c e the average - s e c - Lee  f o r the E a s t P a c i f i c  and U y e d a , 1 9 6 5 ) .  Rise  (2.13 y c a l s / c m  Also note that the heat flow value  i s h i g h e r ( 4 . 8 ) w i t h i n t h e p r o p o s e d s p r e a d i n g zone the s o u t h e a s t o f i t .  The  2  h i g h v a l u e o f 16.1  t h a n (4.0) t o  y c a l s / c m - s e c i n the 2  E x p l o r e * S p r e a d i n g Segment i s a n o m a l o u s b u t b e l i e v e d due p r o d u c e d b o t h by r i s i n g magma i n a s p r e a d i n g t r e n c h and h e a t p r o d u c e d by movement a l o n g t h e R e v e r e  - Dellwood  to heat frictional  Transform  -Fault. 5. no  U s u a l l y , a c t i v e s p r e a d i n g zones  are covered w i t h l i t t l e  s e d i m e n t s , b e i n g v e r y y o u n g and f a r f r o m c o n t i n e n t s .  thick  sediment  especially posed  The  c o v e r i n p a r t s o f t h e D e l l w o o d Seamount A r e a ,  i n the c h a n n e l between the Dellwood K n o l l s  and d e p o s i t i o n o f s e d i m e n t s by t u r b i d i t y from the nearby N o r t h American  c u r r e n t s and  c o n t i n e n t d u r i n g the  transport  ice.rafting  Pleistocene.  S u c h r a p i d d e p o s i t i o n has b e e n c a l l e d upon by Moore (1970) e x p l a i n the t h i c k 15 km.  wide  Here the sediment several  sediments  faults.  cover averages A 390 m e t r e  6.  As  the sediments showing  t r e s w i t h median 7.  trough comprised  and Moore e s t i m a t e d t h a t t h e r a t e 3  faulting  of  yr.  and v o l c a n i c b a s e m e n t a r e c u t by s e v e r a l  Normal  Rise.  t h i c k and i s c u t by  T r o u g h , so t o o i n t h e D e l l w o o d  d i p - s l i p movements  Plate V).  core from t h i s  c a . . 3 5 0 cm/10  i n the Escanaba  500 m e t r e s  to  - a median  t h a t f o l l o w s the a x i s o f the Gorda  only Quaternary sediments s e d i m e n t a t i o n was  i n the Escanaba.Trough  and  (the pro- .  s p r e a d i n g a r e a ) , c a n e a s i l y be e x p l a i n e d by r a p i d  valley  or  (profiles  FG  - Plate  Channel, faults  I V and PQ  -  i s c h a r a c t e r i s t i c of s p r e a d i n g cen- ,  valleys..  B a s a l t Types i n the A r e a :  C h e m i c a l a n a l y s e s ( T a b l e I I I ) and  108 differentiation  diagrams  c a n i c s o f the Dellwood  ( F i g u r e s 37  and  Seamount A r e a  38)  are, i n g e n e r a l , i n t e r m e d i a t e  b e t w e e n a l k a l i and  tholeiite  Table  I shows tha.t t h e t o t a l  of  IV and T a b l e  show t h a t t h e v o l -  types.  Comparing Table  I I I with  a l k a l i v a l u e s f o r most  the r o c k s a n a l y s e d are i n t e r m e d i a t e between v a l u e s f o r  ites  and  f r o m EN  alkali basalts.  However, T i 0  70-025-3D a r e l o w and  v a l u e s , except  2  typically  tholeiitic  tholei-'  f o r those  Whether  then,  the i n t e r m e d i a t e n a t u r e o f the b a s a l t s i s t r u e , o r whether i t r e ; fleets  the degree o f w e a t h e r i n g  (Hart, 1970),  S i n c e , however, o n l y r e l a t i v e l y for  chemical  analysis  ( e x c e p t f o r s a m p l e s f r o m EN chemical  and T i l l e y  t h a t most, o f t h e b a s a l t s t h e y e x a m i n e d f r o m Mid-Atlantic also  analyses  Ridge  the  inter-  uncharacterfound  zone o f  were i n t e r m e d i a t e , though t y p i c a l  the  tholeiites  existed. N e v e r t h e l e s s , some more c o n c r e t e s u p p o r t  ing  This  (1964)  rift  which,  probably  of basalts,,however,.is-not e s p e c i a l l y  of spreading c e n t r e s , since Muir  sample  70-025-3D  the t r u e i n t e r m e d i a t e nature o f the b a s a l t s .  mediate nature istic  problem.  f r e s h p a r t s o f p i l l o w s were  were a l l v e r y w e a t h e r e d ) then t h e s e reflect  is a  c e n t r e i n the r e g i o n of the Dellwood  v a r i a t i o n d i a g r a m s o f F i g u r e 38, w h i c h  for a  spread-  K n o l l s comes f r o m  the  show t h a t t h e l e a s t  differ-  e n t i a t e d r o c k s i n t h e . a r e a come f r o m t h e N o r t h w e s t D e l l w o o d and h a v e SI v a l u e s o f 44.9  and  39.2,  w h i l e rocks from  wood. Seamount Range h a v e l o w e r S I v a l u e s t h e y a r e more d i f f e r e n t i a t e d t h a t i n i t i a t e d them.  and  I t w o u l d be  thus  centre that-produced  them.  f u r t h e r away f r o m  closest  A problem  Dell-  (30-35), i n d i c a t i n g  expected  e n t i a t e d r o c k s i n t h e a r e a w o u l d be  the  Knolls  the r i d g e  t h a t the l e a s t to the  that  differ-  spreading  arises,'however,  when  we  109 consider rocks  f r o m d r e d g e h a u l EN  a r o u n d 26, b u t  s i n c e these  b o t h by p e t r o g r a p h y v a l u e s may inal  reflect  nature  decreases  and  a n a l y s i s (Table  of the b a s a l t .  in.that  8,  Profile  basement  W  thus  A problem  i s p r o p o r t i o n a l to old.  ( l a y e r 2) r i s e s  toward  i n the Dellwood  dips i n a northeast  However,  these  talus  slope  direction  the c o n t i n e n t , r e a c h i n g i t s Seamount A r e a  and  then  i n the S c o t t Channel. the  suddenly  This  step-  continent i s  the o p p o s i t e o f the normal d i p o f o c e a n i c basement toward  a spreading  this  ( F i g u r e 46)  easterly  direction  Seamount A r e a , one northeasterly thus  two  of the 9.  Dellwood  Mason's 1961  Seamount A r e a .  The  m a g n e t i c a n o m a l y map  shows t h a t p r o f i l e  v e r s e y o u n g e r and  the.  f e a t u r e l e d E w i n g e t a l (1968) t o p o s t u l a t e  segment i n t h e  t a t i o n o f R a f f and 1968  age,  in.the area..  r i s e o f the o c e a n i c basement l a y e r t o w a r d  c o n t i n e n t and  VV  interpre-  by  Vine,  (Plate X I I I ) would  tra-  younger o c e a n i c v o l c a n i c basement i n a n o r t h and  thus  even w i t h o u t  would expect  direction  a rise  as o b s e r v e d  spreading  in. t h e  Dellwood  i n basement l a y e r i n a  on t h e CSP  p o s s i b l e e x p l a n a t i o n s f o r the observed  line.  There  steplike  are  ascent  basement.  Vine's  SI  ( P l a t e X I I I ) shows t h a t t h e o c e a n i c v o l c a n i c  shallowest level  like  orig-  content  and  70-025-3D were d r e d g e d f r o m a f a u l t e d  which.may have e x p o s e d the o l d e r r o c k s  the  t h a t MgO  with increased weathering.  t h a t the rocks are r e l a t i v e l y  f r o m EN  111) , t h e SI .  ( H e k i n i a n , 1971)  the degree o f w e a t h e r i n g  values  shown  r a t h e r than  I t s h o u l d be n o t e d  with increased weathering  indicating rocks  chemical  a r e v e r y w e a t h e r e d as  the degree o f w e a t h e r i n g  values would decrease arises  rocks  70-025-3D w h i c h h a v e SI  i n t e r p r e t a t i o n o f R a f f and Mason's m a g n e t i c  anomaly  Ill map  ( F i g u r e 3) f o r t h e D e l l w o o d  46,  Seamount A r e a  T h i s i n t e r p r e t a t i o n was made b e f o r e  Revere  - Dellwood  shown b y t h i s  i s shown i n F i g u r e  i t was known t h a t t h e  F a u l t Zone e x i s t e d a n d i s a t r a n s f o r m f a u l t as  study,.  Using  this  data, modified  interpretations  o f t h e m a g n e t i c anomaly map a r e shown i n F i g u r e s 47 a n d 48 where t h e m a i n d i f f e r e n c e i s t h e age o f t h e p o s i t i v e Dellwood  Seamount A r e a .  I n Vine's  anomaly 2 w h i c h i s g r e a t e r t h a n  anomaly i n t h e  interpretation,  2 myr. o l d .  this i s  I n the author's  i n t e r p r e t a t i o n , t h a t p a r t o f t h e anomaly t o t h e n o r t h e a s t o f the Revere l e s s than on  - Dellwood  F a u l t Zone i s a n o m a l y 1, a l l o f w h i c h i s •  2 myr, o l d a c c o r d i n g t o t h e a n o m a l y t i m e  t h e f i g u r e s . • The y o u n g e s t p a r t o f t h i s  t o be l e s s supported  than  700,000 y r . o l d .  wood K n o l l s as shown i n T a b l e Figures  47 a n d 48 s u p p o r t  i n the Dellwood  fault 10.  interpretation i s  from the Northwest  connecting  f r o m i t by t h e R e v e r e  of a spreading the Explorer - Dellwood  centre Spreading  Transform  t o t h e Queen C h a r l o t t e F a u l t Zone. I f the spreading  K n o l l s , then  this  centre i s the channel-between the Dellwood  channel  s h o u l d have h i g h h e a t  f a u l t i n g , y o u n g r o c k s on b o t h  n e t i c i n t e n s i t y over  f l o w , normal  s i d e s o f the channel  i n c r e a s i n g w i t h d i s t a n c e away f r o m t h e c h a n n e l  and  the c h a n n e l .  The p r e s e n c e  w i t h age  and s t r o n g e s t mago f . h i g h heat  normal f a u l t i n g has a l r e a d y been e s t a b l i s h e d (above).  study, suggests  age i n c r e a s i n g w i t h d i s t a n c e o n . t h e  flow  The  m a g n e t i c anomaly i n t e r p r e t a t i o n e i t h e r by V i n e , o r i n t h i s ent  Dell-  Thus t h e i n t e r p r e t a t i o n s i n  the hypothesis  Seamount A r e a  Segment b u t o f f s e t  VII.  anomaly 1 i s b e l i e v e d  This l a t t e r  b y t h e e s t i m a t e d age o f r o c k s  s c a l e shown  pres-  northwest  side., o f t h e c h a n n e l , b u t more d e t a i l e d m a g n e t i c m a p p i n g i n t h e  FIGURE  47  I n t e r p r e t a t i o n of magnetic anomalies assuming the Revere - Dellwood f a u l t zone o r i p i n a t e d as l e f t - l a t e r a l t r a n s c u r r e n t f a u l t .  FIGURE  48 ,  I n t e r p r e t a t i o n of magnetic anomalies assuming the p e l l w o o d S p r e a d i n g C e n t r e o r i g i n a t e d i i i s i t u l e s s t h a n 2 myr. ago  Winona B a s i n i s n e c e s s a r y t o d e l i n e a t e alies On  t h a t may  any  l i n e a r magnetic  anom-  e x i s t on t h e s o u t h e a s t s i d e o f t h e D e l l w o o d  the other-hand, magnetic  anomalies  t h a t may  Channel.  have e x i s t e d i n  t h e . p a s t i n the a r e a o f the Winona B a s i n have s i n c e been subdued by t h e t h i c k s e d i m e n t As intensity  cover.  shown on l i n e  IOUBC-70-16-20, t h e s t r o n g e s t m a g n e t i c  i s n o t - o v e r the Dellwood C h a n n e l , b u t . s l i g h t l y  southeast of i t .  A g a i n on l i n e  IOUBC-70-16-15, t h e  to the  magnetic  highs are d i s p l a c e d to the s o u t h e a s t o f the t o p o g r a p h i c h i g h s , b u t t h e g e n e r a l shape o f t h e t o t a l m a g n e t i c similar  to the t o p o g r a p h i c p r o f i l e .  o f the magnetic the magnetic  anomaly r e l a t i v e  inclination  measured.  profile-is  This southeast displacement  to the topography  may  be due  to  i n the a r e a ; the t o p o g r a p h i c e f f e c t ; ,  and t h e d i s t a n c e above t h e s e a f l o o r was  intensity  T h u s , on l i n e  at which the magnetic  IOUBC 7 0 - 1 6 - 2 0 , t h e m a g n e t i c  to the s o u t h e a s t of the Dellwood  C h a n n e l may  have been  field high  produced  by r o c k s i n t h e c h a n n e l . 11.  The  e x t e n t o f t h e w e a t h e r i n g and  c o a t i n g on r o c k s f r o m EN  t h i c k n e s s o f t h e manganese  70-025-3D s u g g e s t s t h a t t h e  Dellwood K n o l l s are o l d e r than the Northwest when t h e y s h o u l d be a b o u t  t h e same age  i s s u p p o r t e d by  ment c o v e r and s u b d u e d t o p o g r a p h y and RS and  (Plate X).  this  tailed knolls.  D r e d g e EN  f a u l t i n g may  ;  Dellwood  Knolls  i f t h e y were p r o d u c e d  a s p r e a d i n g c e n t r e i n the Dellwood Channel. the S o u t h e a s t Dellwood K n o l l s  Southeast,  T h i s o l d e r age the t h i c k e r  shown on p r o f i l e s  FG  d r e d g i n g i s needed to e s t a b l i s h the youngest  of  sedi-  (Plate  70-025-3D i s f r o m a f a u l t e d  h a v e e x p o s e d much o l d e r r o c k s .  by  IV)  slope,  .More  de-  age o f t h e s e  115 12.  Origin  o f the Dellwood  seamounts o f t h e D e l l w o o d near to  Seamounts and K n o l l s :  Seamount Range was p r o b a b l y  the a x i s o f t h e E x p l o r e r S p r e a d i n g  grow as t h e y moved w i t h  Revere  - Dellwood  seamount o f t h i s Spreading age  fault, zone.  range  centre.  This o r i g i n  age i n c r e a s e s w i t h  seafloor  (Menard,  Hence t h e s h a l l o w e s t  i s also  away  from  supported  b a s a l t s from  d i s t a n c e from  1969),  t o a zone o f weakness -  i s t h e one f u r t h e s t  o f the r e c o v e r e d p i l l o w  that  adjacent  initiated  Segment, b u t c o n t i n u e d  the spreading  p e r h a p s due t o t h e i r p o s i t i o n the  Each o f the  this  (highest)  the E x p l o r e r  by t h e e s t i m a t e d  range w h i c h  show  the E x p l o r e r Spreading  Seg-  ment. There Spreading Knolls.  i s at present.no  Zone i n t h e Winona B a s i n s o u t h e a s t How,  then,  was  i n the p a s t  and  the f o r m a t i o n  continuation is  related  Northwest ones. cate  d i d the k n o l l s  such  i n much t h e same way  then,  direction  along  than  I f the k n o l l s Channel,  the s p r e a d i n g the middle  produce o l d e r k n o l l s centre  dredging  they  the younger northwest  knolls.  this  the r o c k s  t h e same age. in- a . n o r t h e a s t  knolls.  further  away  This from  could  the spread-  The m a g n e t i c anomaly  possibility.  obtained  indi-  by a s p r e a d i n g  somewhere  o f the northwest  Range  the southeast  on t h e k n o l l s  to the s o u t h e a s t  as a l r e a d y m e n t i o n e d ,  Seamount  s h o u l d be a b o u t  zone t r e n d s  to this  I f s o , then the  were p r o d u c e d  p a t t e r n , h o w e v e r , seems t o p r e c l u d e then,  Segment.  there  subduction,  related  K n o l l s s h o u l d be o l d e r t h a n  the o p p o s i t e .  Perhaps,  Perhaps  as t h e D e l l w o o d  As s t a t e d a b o v e , t h e s p a r s e  Dellwood  d e s t r o y e d by  K n o l l s was  to the E x p l o r e r S p r e a d i n g Dellwood  o f the  originate?  a c o n t i n u a t i o n now  o f the Dellwood  zone i n t h e D e l l w o o d  ing  c o n t i n u a t i o n o f the E x p l o r e r  from  EN  Perhaps, 70-025-3D  116 come f r o m  a f a u l t e d slope  representative wood  of  the  that  youngest  exposed  old  extrusives  rocks of  which  the  are  not  Southeast.Dell-  ,  Knolls. The  spreading further  evidence  zone  work  presented  thus  does- e x i s t w i t h i n  i s needed  to  the  seems t o Dellwood  determine  indicate  that  a  Seamount A r e a ,  i t s precise  nature  and  but  loca-  ,  tion. One Dellwood  Spreading  proposed  that  established - Figure  "that  the  probably 4 myr.  8-12  In  myr.  to  formed?  ago..  d i r e c t i o n of suffered  remains  at  After  This of  and  least the  and  w h e n was  Heinricks  Plate  i s s u p p o r t e d by  oceanic  motion  overlap  a minor  change  was  Atwater  motions produces which  (1970  areas  of  indicates (P^)  sometime between  P l a t e m o t i o n was  the  (1971)  - North American motion  Pacific  C o u c h and.  and  Pacific  constant  Pacific  - How  Couch  present northwest  continental  20  and  established,  then,  Heinrichs  ".... t h e San A n d r e a s and Queen C h a r l o t t e Fairweather F r a c t u r e Zones became a c t i v e t r a n s f o r m f a u l t s , p o s s i b l y a l o n g o l d l i n e s o f w e a k n e s s .... Because of the d i r e c t i o n o f s e p a r a t i o n , the s h e a r e n e r g y i n v o l v e d , and the c u r v a t u r e o f t h e c o n t i n e n t a l m a r g i n , t h e J u a n de F u c a r i d g e began m i g r a t i n g n o r t h w e s t e r l y and r o t a t i n g by g r o w t h and f r a c t u r e t o w a r d an a l i g n m e n t n o r m a l t o t h e t r a n s f o r m f a u l t s y s t e m s as t h e P a c i f i c P l a t e p u l l e d s l o w l y away f r o m t h e c o n t i n e n t a l m a r g i n o f f V a n c o u v e r Island. I n i t i a l l y t h i s was a c c o m m o d a t e d b y c r u s t a l e x t e n s i o n , b u t a f t e r 5 - 6 , m i l l i o n y e a r s , a new ridge - t h e E x p l o r e r R i d g e was r e q u i r e d a n d f o r m e d . In the l a s t 1 myr. a d d i t i o n a l s h o r t segments of r i d g e have b e e n r e q u i r e d and f o r m e d n o r t h w e s t o f the Explorer R i d g e " ( F i g u r e 48) . ' Thus  the  Segment  whose model  ago."  according  '  the  16),  unacceptable  ,  additional question  DellWood Atwater's  Couch  and  Spreading  Heinrichs  account  Segment n o r t h w e s t  (1970) models  (Figures  15  of  and  for the  the  formation  Explorer  of  Ridge.,  16)," r o t a t i o n o f  the  117 J u a n de F u c a r i d g e t o w a r d an a l i g n m e n t n o r m a l fault of  systems  to the transform  i s a c c o m p l i s h e d by m e r e l y a change i n t h e d i r e c t i o n  u n d e r t h r u s t i n g o f t h e J u a n de F u c a P l a t e , t h i s  rotation  ing  t h e f o r m a t i o n o f t h e E x p l o r e r a n d p r e s u m a b l y , more  the  D e l l w o o d S p r e a d i n g Segments.  Fuca P l a t e  caus-  recently,  T h i s r o t a t i o n o f t h e J u a n de  i s shown by t h e f a n - s h a p e d p a t t e r n o f t h e m a g n e t i c  anomalies i n the area. P e t e r a n d L a t t i m o r e (1969) using a magnetic  a n d P e t e r a n d DeWald  anomaly and f r a c t u r e p a t t e r n o f P a v o n i  proposed a r e c o n s t r u c t i o n r i d g e s form a s i n g l e  continuous north-south trending  weakness, c l o c k w i s e r o t a t i o n  feature."  o f a NW-SE zone o f  c a u s e d by NE-SW c o m p r e s s i o n  transcurrent faulting  ridge crest  current  f a u l t s , once i n i t i a l  as r i g h t - l a t e r a l individual the  and magnetic  anomalies  i n the area.  continu-  The t r a n s -  d i s p l a c e m e n t has taken p l a c e , a c t  transform faults  segments o f r i d g e .  caused  ( s i n c e Anomaly 5 - i . e . l e s s  t h a n 10 myr. a g o ) a n d d i s p l a c e m e n t o f p a r t s o f t h e o n c e ous  (1966),  " i n w h i c h t h e J u a n de F u c a a n d G o r d a  A c c o r d i n g t o them, f o l l o w i n g t h e development  left-lateral  (1971) ,  due t o a c t i v e  growth o f t h e  I f thehypothesis i s correct,  D e l l w o o d S p r e a d i n g Segment c o u l d a l s o h a v e b e e n  similarly  f o r m e d by l e f t - l a t e r a l  t r a n s c u r r e n t motion  Ridge a l o n g t h e Revere  - D e l l w o o d F a u l t and then t h e sense o f  movement a l o n g i t c h a n g e d in  to dextral  the region o f the Dellwood K n o l l s  from t h e E x p l o r e r  by c o n t i n u e d a c t i v e (Figure 47).  growth  118  CHAPTER SEVEN SUMMARY AND CONCLUSIONS  Continuous seismic p r o f i l i n g Area indicates  that:  1.  - Dellwood Fault  The R e v e r e  i n • t h e D e l l w o o d Seamount  Zone i s a r i g h t l a t e r a l  form f a u l t o f the ridge t o ridge type. southwest Knolls  s l o p e s o f P a u l Revere  and i n t o  tion  I t trends along the  Ridge and S o u t h e a s t  Dellwood  t h e Dellwood B a s i n between t h e Dellwood  Range a n d D e l l w o o d K n o l l s .  trans-  Seamount.  I t dies out i n a northwesterly  and i s n o t o b s e r v e d i n t h e n o r t h w e s t end o f t h i s  direc-  Dellwood  Bas i n . 2.  The Queen C h a r l o t t e r i g h t l a t e r a l  die out i n a s o u t h e a s t e r l y , d i r e c t i o n Channel n e a r i t s s o u t h e a s t end. r e p l a c e d by S c o t t 3.  Islands  transform fault  appears t o  i n the region o f the Scott  Further to the southeast, i t i s  F a u l t Zone a n d t h e W i n o n a B a s i n .  The W i n o n a B a s i n c o n t a i n s g r e a t e r t h a n 3 s e c o n d s  o f f o l d e d and f a u l t e d s e d i m e n t s , t h e f o l d i n g  3000 m.)  and f a u l t i n g p r o b a b l y  b e i n g due t o some component o f c o m p r e s s i o n i n t h e a r e a p r o d u c e d by s u b d u c t i o n o f t h e J u a n de F u c a Plate„ have c e a s e d o r . c h a n g e d 4.  to s t r i k e - s l i p  faulting  i n the recent past.  The E x p l o r e r S p r e a d i n g S e g m e n t , c o n t a i n i n g o n l y a t h i n  o f s e d i m e n t s , shows d i p - s l i p v o l c a n i c basement. a t t h e P a u l Revere transform fault 5.  T h i s s u b d u c t i o n may  a f f e c t i n g b o t h sediment and  T h i s s p r e a d i n g segment a p p e a r s Ridge  - the s i t e  o f t h e Revere  t o end a b r u p t l y - Dellwood  i n the area.  Normal f a u l t i n g  ment e x i s t s  faulting  veneer  a f f e c t i n g b o t h sediments and v o l c a n i c  i n t h e Dellwood Channel between t h e Dellwood  baseKnolls.  119  This channel t o be  The  Pliocene  The  faulted  (400 m.)  turbidity.currents  P a u l Revere Ridge and  i s a complexly  P l e i s t o c e n e sediments  believed  the  faulted ridge sills  l o w o c c u r s o v e r t h e n o r t h w e s t e r n end  lower c o n t i n e n t a l  area  and  t h i s may  be  the n o r t h e r l y  T e c t o n i c sediment  the s l o p e .  the S c o t t Channel.  p a r t o f the S c o t t Channel t h e Queen C h a r l o t t e sediment  i s prominent  The  faulting  8.  The  has  subdued the topography  seen  the  occur and  northwestern  i n the n o r t h e a s t e r n  the southern.end  of  zone.  c o v e r o v e r much o f t h e S o u t h e a s t and  sub-  on t h e l o w e r s l o p e  i s b e l i e v e d t o be  transform fault  ceased  t r a p s (? d i a p i r s )  F a u l t i n g occurs beneath  p g r t o f the S c o t t Channel.  Sound i s  of present or r e c e n t l y  Slumping  ridge.  e x t e n s i o n of the S c o t t  d u c t i o n i n the  area.  comprising and f l o w s .  of the  s l o p e o f f Queen C h a r l o t t e  a site  in  into  and b a s a l t i c  I s l a n d F a u l t Zone and  beneath  of sediments  Pleistocene.  A magnetic 7.  sees.  t r a n s p o r t e d m a i n l y by  d u r i n g the 6.  c o n t a i n s >0.4  indicates  Dellwood  Knolls  t h a t t h e s e k n o l l s may  be  relatively old. From an a n a l y s i s  of the rocks dredged  Seamount A r e a , t h e f o l l o w i n g A.  Most:of  the fragments  c o n c l u s i o n s c a n be  are p i l l o w b a s a l t s  c h a r a c t e r between t h o l e i i t e s B.  The  m i n e r a l o g y o f the b a s a l t s -9o)  - bytownite  (An  labradorite  (An o-6o)  8 0  5  and  alkali  remains  phenocrysts  from  the  Dellwood  drawn:  intermediate i n basalts.  essentially  t h e same  (probably x e n o c r y s t s ) ;  microphenocrysts; andesine-labradorite  (An^g.go) g r o u n d m a s s ' m i c r o l i t e s • o l i v i n e b o t h ( p o s s i b l y x e n o c r y s t s ) F o q , and 9  as  phenocrysts  i n groundmass c l i n o p y r o x e n e  having a feathery, fibrous or granular habit  and  restricted  120 to  the  groundmass;  various In  the  minerals  tachylyte  - glassy  intergranular  the  rate  of  and  depth below  glass.  The  p r e s e n t , however, vary  pillow basalts,  encountered to  and  cooling  d i f f e r e n t groundmass  subophitic which  surface  of  textures  and  - depending  further  depends  pillow  the  considerably.  through h y a l o p i l i t i c  and  amounts o f  intersertal essentially,on  on  at which  are  size  of  pillow  texture  was  observed. Block  lavas  talline  of  with  s i m i l a r m i n e r a l o g y , but  diabasic  or  subophitic  essentially  textures,  were  holocrysalso  recovered. The  rocks  of  and  least  d i f f e r e n t i a t e d rocks  relatively  the  Northwest.Dellwood  recent  ridge  type  in  Knolls  are  the  youngest;  the.area  and  may  represent  extrusions.  These  also  glomeroporphyritic  olivine - plagioclase  most  of  i n the  crysts The  the of  other  rocks  plagioclase  feathery  to  r o c k s may  alteration  basaltic  of  Dredge H a u l mount o f  assortment clase  of  basalt  accumulating phenocrysts (tachylyte) iron  Dellwood  deposit  rock  only  and/or  8  devitrification  to  while pheno-  olivine.  be  due  the  are  sparse  of  clinopyroxene'in and  deuteric  glass. the  northwesternmost  Seamount Range c o n t a i n s  types  including  whose p h e n o c r y s t s as  basalts  character  IOUBC 7 0 - 1 6 - 1 2 D f r o m  the  contain  An o-9o)  (bytownite  fibrous  many o f . t h e s e  area  rocks  a plagioclase  containing  containing  semicumulate, (magnetite)  zones  greater  curious  (i) a porphyritic  were p r o b a b l y  opaques  o u t l i n i n g growth  a  and  than  the and  Fe,  plagio-  originally plagioclase semiopaques.  twinning,  28%  sea-.  (iii)  ( i i ) an an  iron-  r i c h a u t h i g e n i c sandstone H.  and  erratics.  Ages e s t i m a t e d from  t h i c k n e s s o f manganese c r u s t s ,  w i t h the topography  o f the Dellwood  t h a t the seamounts o f t h i s near to  grow f o r d i f f e r e n t  indicate  Two  r a n g e were p r o b a b l y  l e n g t h s o f time  the N o r t h w e s t  JOIDES - P a u l  K n o l l s may  and p r o b a b l y  the s e i s m i c p r o f i l e s ,  indicate  that turbidity  also  and  Core,  and  The  c r u s t and  the r e c o v e r e d g l a c i a l  i r o n and manganese i n t h e  sources glaciers basalts  - c o n t i n e n t a l weathering and  turbidity  important  been  rivers,  c u r r e n t s ; l e a c h i n g o f Fe and Mn, f r o m  from submarine v o l c a n i c  by  oceanic  sea water;  and  emanations.  s e i s m i c and p e t r o l o g i c d a t a when c o m b i n e d w i t h  o t h e r d a t a on h e a t conclude  sediment  from s e v e r a l  t r a n s p o r t a t i o n by  during progressive chemical weathering  The  erratics  ferromanganese  i t precipitated)  and  area.  only during  i n t h e i r o n d e p o s i t had p r o b a b l y (from which  genetically  i n the  c u r r e n t s are the major agent o f  added to the sea w a t e r  much  the slump f e a t u r e s  and p e l a g i c s e d i m e n t a t i o n p r o b a b l y b e i n g i m p o r t a n t  nodules  be  i n t h e a r e a , i c e r a f t i n g b e i n g somewhat l e s s  "quiet" periods.  the  matrix.  Revere Ridge  shown on  transport  continued  as t h e y moved w i t h  types of h y a l o c l a s t i t e b r e c c i a s occur  B o t h , h o w e v e r , , h a v e an i r o n - r i c h The  Segment b u t  ones.  chemically-, p e t r o g r a p h i c a l l y  different  a l l initiated  t h i c k n e s s o f manganese c r u s t s a l s o  t h a t the Southeast.Dellwood  o l d e r than  together  Seamount R a n g e , i n d i c a t e  the a x i s o f the E x p l o r e r S p r e a d i n g  s p r e a d i n g c r u s t . ' The  I.  (iv) g l a c i a l  flow, magnetics,  e t c . , l e a d s the author  t h a t a s p r e a d i n g , s e g m e n t does e x i s t w i t h i n  to  the,Dellwood  122 Seamount A r e a , Revere right  - Dellwood lateral  nature  and  further flow  data  transform  location  and  based  (i)  The  (ii)  fault,  of this  the  author  shown i n F i g u r e 49.  Dellwood  Spreading  dredging  fission  faulting  and  h i g h heat  Trending  northeast  Dellwood  Knolls with  and  are  Segment  between the  detailed  The  precis  Segment r e q u i r e s magnetic  subsequent  and  heat  accurate  age  t r a c k d a t i n g method.  b e l i e v e s there  Spreading  channel  as  Segment v i a t h e  Queen C h a r l o t t e ,  Zone t o the  seismic p r o f i l i n g ,  on  Dellwood  E x p l o r e r Spreading  Fault  more d e t a i l e d  The this  the  Transform  continuous  estimates  for  connecting  along  the  possible locations  - either  Dellwood flow,  two  Knolls with  i t s normal  or c e n t r e o f the  i t s young, r e l a t i v e l y  Northwest undifferentiated  basalts. Figure major t e c t o n i c  49  features of  f e a t u r e named t h e lands  and  indicated.  may,  The  based  on  Pacific others.  - J u a n de The  of  anomaly 1.  author's  Dellwood  interpretation  Seamount A r e a . Zone i s t h e  (1969),.and o t h e r s .  values  and  Fuca  plate  slightly  less  m o t i o n by  than  Atwater  E x p l o r e r Spreading  flow  area.  Scott Is-  Its width  and  at about  o f a b o u t 6 cm/yr. f o r  anomaly p a t t e r n i n the  i n the  The  is than  o f u n d e r t h r u s t i n g i s u n c e r t a i n , but  motion  h i g h heat  of  i n c l u d e more o f the Winona B a s i n  c l o s e to a n o r t h e r l y d i r e c t i o n  shape o f t h e  the m a g n e t i c  of extremely  in fact,  estimated  - American p l a t e  the  Scott I s l a n d Subduction  direction  b e l i e v e d t o be  - this  on  the  F r a c t u r e Zone o f Couch  uncertain  is  summarises  area  (1970) , and  the  f r e s h b a s a l t s i n the  Spreading  Pacific  6 cm/yr. f o r  Segment and  2 cm/yr  is  based  existence left  i s b e l i e v e d t o have  arm recent-  124 ly  ceased in, the area o f the r i g h t  became a c t i v e  arm o f t h i s  anomaly, b u t  i n t h e a r e a o f t h e l e f t arm p e r h a p s  t i m e t h a t t h e D e l l w o o d S p r e a d i n g Segment came i n t o in  its,present The  a t about the existence  location. D e l l w o o d S p r e a d i n g Segment may h a v e o n c e b e e n  c o n t i n u o u s w i t h , t h e E x p l o r e r S p r e a d i n g Segment, b u t was f r o m i t by l e f t - l a t e r a l yr.  ago and p r o b a b l y l e s s  Dellwood Fault  transcurrent. faulting  (less  offset  t h a n 10 m.  t h a n 2 m. y r . ago) a l o n g t h e , R e v e r e •  Z o n e , due t o r o t a t i o n o f t h e J u a n de F u c a  Plate  c a u s e d by a change i n t h e d i r e c t i o n o f t h e p l a t e movement as evidenced by,the fan-shaped p a t t e r n o f magnetic the  area.  changed  Continued active  growth i n the s p r e a d i n g c e n t r e s  the c h a r a c t e r o f the Revere  that of a transform fault  anomalies i n  zone.  - Dellwood Fault  Zone  into  125 CHAPTER EIGHT BIBLIOGRAPHY  A t w a t e r , T., 1 9 7 0 , I m p l i c a t i o n s o f p l a t e t e c t o n i c s f o r t h e Cenoz o i c t e c t o n i c e v o l u t i o n o f Western N o r t h America: B u l l . 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N o w r o o z i , 1 9 7 0 , M i c r o e a r t h q u a k e s e i s m i c i t y and t e c t o n i c s o f c o a s t a l n o r t h e r n C a l i f o r nia: B u l l . S e i s m o l . S o c Am., 6 0 , 1 6 6 9 - 1 6 9 9 . S h o r , G.G. J r . , P. D e h l i n g e r , H.U. K i r k $ W.S. F r e n c h , 1 9 6 8 , S e i s m i c r e f r a c t i o n s t u d i e s o f f Oregon a n d N o r t h e r n California: J . G e o p h y s . R e s . , 7_3, 2175-2194 . ;  S i l v e r , E.A., 1 9 6 9 , L a t e C e n o z o i c u n d e r t h r u s t i n g o f t h e c o n t i n e n t a l margin o f f northernmost C a l i f o r n i a : Science, 166, 1 2 6 5 - 1 2 6 6 . Silvestri, Smith,  S., 1 9 6 3 , P r o p o s a l f o r a g e n e t i c c l a s s i f i c a t i o n o f hyaloclastites: B u l l . V o l c a n o l . , 25_, 3 1 5 - 3 2 1 .  R.E., 1 9 6 7 , S e g r e g a t i o n v e s i c l e s Am..J. S c i . , 2 6 5 , 6 9 6 - 7 1 3 .  i n basaltic.lava:  S o l o m o n , M., 1 9 6 9 , N a t u r e a n d p o s s i b l e o r i g i n o f p i l l o w l a v a s and h y a l o c l a s t i t e b r e c c i a s o f f K i n g I s l a n d , A u s t r a lia: Q u a r t . J o u r . G e o l . S o c Lond., 124, 153-169. S r i v a s t a v a , S.P., D.L. B a r r e t t , ,W.G, B e r t r a n d , R.L. C h a s e , E.E. D a v i s , C.E. K e e n , C.R.B. L i s t e r , K.S. M a n c h e s t e r , D. I . R o s s , K.G. S h i h , A.G. T h o m l i n s o n § D.L. T i f f i n , 1 9 7 1 , G e o p h y s i c a l d a t a c o l l e c t e d d u r i n g Hudson 70 Phase V I I o f f B r i t i s h C o l u m b i a , A t l . Oceanogr, Lab D a t a S e r i e s No. 1971-5D. S r i v a s t a v a , S.P. , D.L. B a r r e t t , C.E. K e e n , K.S. M a n c h e s t e r , K.G. S h i h , D.L. T i f f i n , R.L. C h a s e , A.G. T h o m l i n s o n , E. E. D a v i s , C.R.B. L i s t e r , 1.971, P r e l i m i n a r y a n a l y s i s o f g e o p h y s i c a l m e a s u r e m e n t s n o r t h o f t h e J u a n de F u c a Ridge: Can. J . E a r t h S c i . , 8_, 1265-1281 . T a l w a n i , M., X. Le P i c h o n § J.R. H e i r t z l e r , 1 9 6 5 , E a s t P a c i f i c R i s e - The m a g n e t i c p a t t e r n a n d f r a c t u r e z o n e s : S c i e n c e , 1 5 J V 1109-1115. T h o m l i n s o n , . A . G . , W.G. B e r t r a n d § R.L. C h a s e , 1 9 7 2 , C a t a l o g u e d e s c r i p t i o n o f r o c k s d r e d g e d d u r i n g H u d s o n 70 P h a s e V I I , A t l . Oceanogr. Lab Data S e r i e s ( i n p r e s s ) .  130 T i f f i n , f y . L . , 1968, C o n t i n u o u s S e i s m i c R e f l e c t i o n P r o f i l i n g S t r a i t o f G e o r g i a , Ph.D. T h e s i s , U n i v e r s i t y o f B r i t i s h Columbia. Tiffin,  in  D.L., J.W. M u r r a y § B. Cameron, 1972, T e c t o n i c and d e p o s i t i o n a l h i s t o r y of the c o n t i n e n t a l margin.west of Vancouver I s l a n d : Can. J , E a r t h S c i . ( i n p r e s s ) ,  T o b i n , D.G.  § L.R. S y k e s , , 1 9 6 8 , S e i s m i c i t y and t e c t o n i c s o f t h e Northeast P a c i f i c : J . G e o p h y s . R e s . , 7_3, 3821-3846.  V i n e , F . J . , 1968, M a g n e t i c a n o m a l i e s a s s o c i a t e d w i t h m i d - o c e a n r i d g e s i n The H i s t o r y o f t h e E a r t h ' s C r u s t - A s y m p o s i u m e d i t e d by.R.A. P h i n n e y , P r i n c e t o n U n i v e r s i t y Press ;  V i n e , F . J . § T . J . W i l s o n , 1965, M a g n e t i c a n o m a l i e s o v e r a y o u n g oceanic ridge o f f Vancouver.Island: S c i e n c e , 150, 485-489. W e t m i l l e r , R . J . , 1969, An E a r t h q u a k e Swarm on t h e Queen C h a r l o t t e I s l a n d F r a c t u r e Zone: M.Sc. T h e s i s , U n i v e r s i t y o f British Columbia. W i l s o n , T . J . , 1965, anomalies 482-485.  T r a n s f o r m f a u l t s , o c e a n i c r i d g e s and m a g n e t i c southwest o f Vancouver I s l a n d : S c i e n c e , 150, ~~  Y o d e r , H.S,  § T.G. Sahama, 1957, O l i v i n e - X - r a y d e t e r m i n a t i o n curve: Am. M i n e r a l o g i s t , 4_2 , 4 7 5 - 4 9 1 .  Y o d e r , H.S.  § C E . T i l l e y , 1 9 6 2 , O r i g i n o f b a s a l t magmas: an e x p e r i m e n t a l s t u d y o f n a t u r a l and s y n t h e t i c . r o c k s y s t e m s : , J . P e t r o l . , 3_, 342-532.  Y o d e r , H.S., 1971, P e t r o l o g i c i m p l i c a t i o n s o f p l a t e S c i e n c e , . 1 7 3 , 464-466.  ;  tectonics:.  APPENDIX  A  TECTONIC AND PHYSIOGRAPHIC FEATURES EXPLORER SPREADING ZONE  DELLWOOD SEAMOUNT RANGE  SOUTHEAST DELLWOOD KNOLLS  NORTHWEST DELLWOOD KNOLLS  SUMMARY OF TECTONIC AND PHYSIOGRAPHIC FEATURES AND THEIR CHARACTERISTICS AS SHOWN ON C.S.P. PROFILE ON WHICH FEATURE IS LOCATED PLATE LETTER PROFILE  CHARACTERISTICS OF FEATURE AS SHOWN ON PROFILE  I  AB  IOUBC 70-16-15  Very t h i n sediment c o v e r on v o l c a n i c basement. Apparent d i p - s l i p f a u l t i n g .  I  AB  IOUBC 70-16-15  Magnetic i n t e n s i t y p r o f i l e i s s i m i l a r to t o p o g r a p h i c p r o f i l e , b u t appears s h i f t e d t o t h e s o u t h e a s t o f t h e topographic p r o f i l e .  II  BC  III  DD  VI  II '  X  RS  XIII  W  BI 69- 050-HUDSON 6  III  DD'  IOUBC  Sediment  IOUBC 70-16-16 1  1  IOUBC 70-16-18 IOUBC 70-16-21B EN 70- 125-9  A l l p r o f i l e s show t h e Range t o be m a i n l y v o l c a n i c peaks f o r m i n g rugged t o p o g r a p h y w i t h s e d i m e n t i n p o c k e t s between peaks r e a c h i n g 0.2 s e e s , t h i c k .  c o v e r s most o f seamount.  IV  FG  IOUBC  R e l a t i v e l y f l a t t o p o g r a p h y due t o sediment c o v e r ; f a u l t e d NW § SE s l o p e s , m a g n e t i c p r o f i l e shows h i g h n e a r NW s l o p e o f k n o l l s .  IX  NO  EN 70  Sediment i n p o c k e t s between v o l c a n i c peaks smoothes o u t topography.  V  PQ  EN 70  Sediment i n p o c k e t s between v o l c a n i c p e a k s . SE end o f l i n e .  X  RS  EN 70  F a u l t e d SW s l o p e o f k n o l l s ,  XII  LL'  BI 69  Relatively  II  BC  IOUBC  Steep f a u l t i n t e r s e c t i n g NW s l o p e o f k n o l l s , and o v e r l y i n g sediment c o v e r . P o s s i b l e f a u l t i n g n e a r NE end o f t h i p r o f i l e may be r e l a t e d t o the Queen C h a r l o t t e , f a u l t zone.  IV  FG  IOUBC  VIII  MN  EN 70  V XIII VI  PQ W* HH'  EN 70 BI 69 IOUBC  •20  flat  relatively flat  Faulted at topography.  topography.  Note c o n t r a s t i n g t o p o g r a p h y and s e d i m e n t d i s t r i b u t i o n r e l a t i v e t o the Southeast Dellwood K n o l l s .  Cross t h e s o u t h e a s t e r n s l o p e o f K n o l l s ,  APPENDIX  A  continued  TECTONIC AND PHYSIOGRAPHIC FEATURES  DELLWOOD SPREADING ZONE  SCOTT CHANNEL  QUEEN CHARLOTTE FAULT ZONE  PROFILE ON WHICH FEATURE IS LOCATED PLATE LETTER PROFILE IV  FG  IOUBC 70-16-20  V  PQ  EN  II  CD'  IOUBC 70-16-17  70-•025-3  CHARACTERISTICS OF  FEATURE AS SHOWN ON  PROFILE  M a g n e t i c h i g h i s not o v e r the z o n e , but t o the s o u t h e a s t o f i t . B o t h p r o f i l e s show s e d i m e n t s i n the zone o f t h i c k n e s s ^ 0.4 s e e s , d i s t u r b e d by a p p a r e n t d i p - s l i p faults. Basement i s n o t shown due to l a c k o f sound penetration. Outcrop o f o c e a n i c netic high.  v o l c a n i c basement l a y e r p r o d u c e s mag-  VIII  MN  EN  70- •025-1  Contains  faults  r e l a t e d t o the Queen C h a r l o t t e f a u l t  zone  VI  HH'  IOUBC 70-16-21A  Contains  faults  r e l a t e d t o the Queen C h a r l o t t e f a u l t  zone  XIII  W  BI 69- •OSO-HUDSON  C o n t a i n s f a u l t s r e l a t e d to the Queen C h a r l o t t e f a u l t Sediment t h i c k n e s s ^ 1 . 5 sees.  zone  IX XI XI  NO ST TU  EN 70- 025-2 EN 70- 025-10 EN 70- 025-11  Slump and faulting.  V  PQ  EN  70- 025-3 .  Channel i n subbottom r e f l e c t o r s , s e d i m e n t t h i c k n e s s > 0.8 s e e s . , f a u l t s below SE s i d e o f c h a n n e l slump s t r u c t u r e s on NW s i d e o f c h a n n e l .  VIII  MN  EN  70- 025-1  Apparent d i p - s l i p f a u l t i n g Scott Channel.  VI  HH  XIII  1  W  s l i d e s t r u c t u r e s on NE  on SW  slopes o f channel.  No  s i d e o f deepest p a r t  of  IOUBC 70-12-21A  Apparent d i p - s l i p  BI 69- 050-HUDSON  Apparent d i p - s l i p f a u l t i n g on NE s i d e o f deepest p a r t channel. Sediment t h i c k n e s s ^ 1.5 s e c .  of  faulting.  VIII  MN  EN  70- 025-1  T e c t o n i c dam below base o f s l o p e ; slump and s l i d e s t r u c t u r e s , t e c t o n i c dam below upper s l o p e , upper c o n t i n e n t a l s l o p e s e d i m e n t s are g e n t l y s l o p i n g ^ 2 and t r u n c a t e d by c o n t i n e n t a l slope f a u l t s . T e c t o n i c dams a c t as s e d i m e n t traps..  IX  NO  EN  70- 025-2  S i m i l a r s e d i m e n t d i s t r i b u t i o n as p r e v i o u s p r o f i l e , e x c e p t t e c t o n i c dam below base o f s l o p e n o t d i s t i n g u i s h e d .  XIII XII  W LL'  BI 69- OSO-HUDSON BI 69- OSO-HUDSON  CONTINENTAL SLOPE  Gently d i p p i n g c o n t i n e n t a l s h e l f sediments.  .APPENDIX  A  continued  TECTONIC AND PHYSIOGRAPHIC FEATURES  PROFILE ON MUCH FEATURE IS LOCATED PLATE LETTER PROFILE  CHARACTERISTICS  OF FEATURES AS SHOWN ON PROFILE  III VII  EF JJ'  IOUBC 70-16-19 IOUBC 70-16-23  F a u l t e d s e d i m e n t s and s e d i m e n t a r y r o c k o v e r rugged c a n i c basement. M a g n e t i c low o v e r R i d g e .  VII  KK'  IOUBC 70-16-26  R e l a t i v e l y u n d i s t u r b e d s e d i m e n t s o v e r rugged basement. M a g n e t i c l o w o v e r R i d g e .  VII  JJ'  IOUBC 70-16-23  F a u l t e d s e d i m e n t s a d j a c e n t t o P a u l Revere R i d g e . ments t h i c k e n toward c o n t i n e n t . Folded sediments NE end o f l i n e .  V  KK'  IOUBC 70-16-26  R e l a t i v e l y u n d i s t u r b e d sediments which t h i c k e n continent.  XII  LL'  BI 69-050-HUDSON 3  F o l d e d and f a u l t e d s e d i m e n t s g r e a t e r than 3 s e e s , t h i c k . Upper l a y e r s o f sediment a r e u n d i s t u r b e d .  III  DD  IOUBC 70-16-18  I n t r u s i o n i n b a s i n p r e s u m a b l y f a u l t bounded as t h e r e i s apparent d i s p l a c e m e n t o f r e f l e c t o r on b o t h s i d e s o f i n t r u sion. F a u l t i n g a l s o a l o n g SW s l o p e o f k n o l l .  III  EF  IOUBC 70-16-19  Shows w i d t h o f f a u l t zone o v e r P a u l Revere ment t h i c k n e s s i n b a s i n ^ 0.16 s e e s .  X  RS  REVERE - DELLWOOD FAULT ZONE  VI  HH'  IOUBC 70-16-21A  Sediment t h i c k n e s s i n b a s i n ^ 0 . 4 s e e s . faulting.  No e v i d e n c e o f  AND  VI  II'  IOUBC 70-16-21B  Sediment t h i c k n e s s i n b a s i n ^ 0.7 s e e s . faulting.  No e v i d e n c e o f  BASIN BETWEEN DELLWOOD SEAMOUNT RANGE AND DELLWOOD KNOLLS  VII  JJ'  IOUBC 70-16-23  F a u l t i n g a l o n g SW s l o p e o f P a u l Revere Ridge may n o t be r e l a t e d t o t h a t i n Winona B a s i n . F a u l t i n g i n area at base o f s l o p e o f P a u l Revere Ridge where s e d i m e n t < 0.15 sees, t h i c k .  XIII  W  BI 69-050-HUDSON 6  F a u l t i n g i n b a s i n between D e l l w o o d K n o l l s and D e l l w o o d Seamount Range where sediment t h i c k n e s s > 0.5 s e e s .  XII  LL'  BI 69-050-HUDSON 3  Sediment t h i c k n e s s i n b a s i n * 1 s e c .  BC  IOUBC 70-16-16  No Revere - D e l l w o o d F a u l t . ^ 0.3 s e e s .  ZZ*  F i g u r e 24  Shows sediment t h i c k n e s s i n b a s i n and p r o f i l e o f v o l c a n i c basement and s e d i m e n t - w a t e r i n t e r f a c e .  PAUL REVERE RIDGE  WINONA BASIN  II  1  EN 70-025-9  vol-  volcanic  Sedinear  toward  Ridge.  Sedi-  F a u l t e d SW s l o p e o f k n o l l i s o n l y e v i d e n c e o f Revere Dellwood f a u l t . Sediment t h i c k n e s s i n b a s i n > 0.15 s e e s .  Sediment t h i c k n e s s i n b a s i n  APPENDIX  A  TECTONIC PHYSIOGRAPHIC  OTHER  continued  FEATURES  FEATURES  PROFILE ON WHICH FEATURE IS LOCATED PLATE LETTER PROFILE  XIII  BI  69-050-HUDSON 6  CHARACTERISTICS  OF FEATURE AS SHOWN ON PROFILE  S t e p l i k e a s c e n t o f basement l a y e r between a r e a SW o f S c o t t Seamount Range and Queen C h a r l o t t e f a u l t zone. T h i c k n e s s o f sediment above basement l a y e r - t h i c k e r (0.64 s e c . ) southwest o f S c o t t Seamount Range than between S c o t t Seamount Range and D e l l w o o d Seamount Range where i t i s 0.5 s e c . t h i c k .  APPENDIX  B  DREDGE  IOUBC  EN  EN  EN  SITE  70-16-12D  70-025-1D  70-025-2D  70-025-3D  DREDGE HAUL ROCK N.  Latitude  DESCRIPTION LOCATION W. Longitude  Geographic Feature  DEPTH  (Meters)  From  To  BRIEFDESCRIPTION AND REMARKS •  50°  45.7'  130°  S3.0'  Dellwood Seamount Range NW Seamount  800  600  ^ 23 kg. total. Several distinct rock types. IOUBC 70-16-12D-1, One large fragment of a porpliyritic plagioclase-olivine basalt with a very weathered vesiculargroundmass. IOUBC 70-16-12D-2, Several small fragments of a red laminated iron deposit. IOUBC 70-16-12D-3, Several small fragments of a green loosely consolidated sandstone. Glacial erratics >v 9 kg. of various sizes and rock types  50°  S2.1'  130°  35.1'  Northwest Dellwood Knolls  ...  ...  Dredge did not touch  50°  50°  S3.7'  46.0'  130°  130°  36.6'  24.0"  Northwest Dellwood Knolls  Southeast Dellwood Knolls  2000  2100  bottom.  1600  ^ 114kg. total. ^ 9 0 % , p i l l o wf r a g m e n t s o f g l o m e r o p o r phyritic olivine-plagioclase vesicular basalt with hyalopilitic groundmass, manganese rind only. One fragment of hyaloclastite breccia. One large glacial fragment^ 2 kg. and several pebble-size and cobble-size glacial erratics.  1700  ^ 30 kg. total. Seven large weathered vesicular pillow fragments, one with thick manganese c r u s t^ S O m m . Several glacial erratics of various sizes and rock types. One fragment of a manganese impregnated loosely consolidated sediment.  APPENDIX  B  DREDGE  EN  EN  EN  SITE  70-025-7D  70-02S-8D  70-025-9D  NOTE:  continued™" LOCATION N.  Latitude  50° 18.3*  50°  50°  28.0'  37.6'  W. Longitude  130°  130°  130°  25.3'  32.5'  48.6'  Geographic Feature  Dellwood Seamount Range Southeastern end  Dellwood Seamount Range SE Seamount  Dellwood Seamount Range Middle Seamount  DEPTH  (Meters)  From  To  2000  1600  1900  BRIEF DESCRIPTION AND  REMARKS  1900  ^ 230kg. total. Mainly vesicular basaltic pillow fragments with hyalopilitic to intersertal textures. A few fragments of basaltic block lavas with holocrystalline textures. A 0.5 kg. mud sample. No glacial erratics. Variable thickness of manganese crust (< 5 mm. thick) .  1300  ^ 275kg. total. Several fragments of basaltic pillow lavas with hyalopilitic to subophitic textures and block lavas with diabasic textures. Fragments vary considerably in size from about 0.5 kg. to 40- kg. Variable thickness of manganese crust (< 12 mm. thick). One very large (^ 30 kg.) and a few smaller glacial erratics.  1600  ^ 185kg. total. Mainly fragments of basaltic pillow lavas with hyalopilitic to intersertal textures. Several fragments of hyaloclastite breccia. Several fragments of manganese nodules. Layered manganese crusts up to 80 mm. thick. A few glacial erratics.  A more detailed description of the recovered rock specimens is the subject of a volume Bertrand and Chase in Atlantic Oceanographic Laboratory Data Series Reports.  by  Thomlinson,  FIGURE CONTOUR  INTEff.'AL  ?00  l,'FTPF<:  •  23  138  FIGURE  50  Key  to Seismic  Profiles  Plates  VOLCANIC BASEMENT,  GOOD R E F L E C T O R  IN  MODERATE R E F L E C T O R  POOR R E F L E C T O R  IN  I to XIII  dashed where  SEDIMENTS  IN  SEDIMENTS  SEDIMENTS  FAULTS AFFECTING VOLCANIC  FAULT  IN  SEDIMENTS  S I D E ECHO  •  V  TECTONIC  UNCERTAIN  DAM  uncertain  BASEMENT  LENGTH  OF  LINE  30  NAUT.  AVERAGE  SPEED  VERTICAL  EXAGGERATION  O  4-6  KNOTS  lOkm.  F DELLWOOD  20 DELLWOOD  KNOLLS  (SE)  SPREADING ZONE  DELLWOOD KNOLLS  Ml.  WW)  12 3 J I  -146  +  4-0  40  149  6-or LENGTH  OF  LINE  13-5  AVERAGE  SPEED  4-9  VERTICAL  EXAGGERATION 10 km.  NAUT.  Ml.  LENGTH  OF  LINE  12-5  KNOTS  AVERAGE  SPEED  13 ! l'  VERTICAL  EXAGGERATION  0  6-3  10 km.  NAUT. KNOTS 17 I I  Ml.  AWARDS: Shell Trinidad Scholarship  1966-1969  U.B.C. Graduate F e l l o w s h i p  1970-1971  T h i s form i s to be completed by candidates f o r the Master's or h i g h e r degree and submitted to the U n i v e r s i t y L i b r a r y S p e c i a l C o l l e c t i o n s D i v i s i o n w i t h the t h e s i s .  

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