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UBC Theses and Dissertations

Study of tectonic processes and certain geochemical abnormalities in the Coast Mountains of British Columbia Culbert, Richard Revis 1971

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A STUDY OF TECTONIC PROCESSES AND CERTAIN GEOCHEMICAL ABNORMALITIES IN THE COAST MOUNTAINS OF BRITISH COLUMBIA by RICHARD REVIS CULBERT B A S c , U n i v e r s i t y of B r i t i s h C o l u m b i a , 1963 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF •'. DOCTOR OF PHILOSOPHY i n the Department . of : '. GEOPHYSICS ;. VJe accept t h i s t h e s i s as conforming t o the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA F e b r u a r y , '1971 In present ing th i s thes is in pa r t i a l f u l f i lmen t o f the requirements fo r an advanced degree at the Un ive rs i t y of B r i t i s h Columbia, I agree that the L ib ra ry sha l l make it f r ee l y ava i l ab le for reference and study. I fu r ther agree that permission for extensive copying o f th i s thes is fo r s cho la r l y purposes may be granted by the Head of my Department or by h is representat ives . It is understood that copying or pub l i ca t i on o f th i s thes is fo r f inanc ia l gain sha l l not be allowed without my wr i t ten permiss ion. Department of (j-egpAySris The Un ivers i ty o f B r i t i s h Columbia Vancouver 8, Canada Date /H<wZ U . / ?7l i ABSTRACT An examination was made of the d i s t r i b u t i o n of potassium, rubidium and strontium i n rocks of the Coast Mountains b a t h o l i t h i c complex south of Nass R i v e r , and of the form of tectonism a f f e c t i n g t h i s regime as revealed by morphological a n a l y s i s and geophysical evidence. The r a t i o K/Rb i n most p l u t o n i c s u i t e s of the Coast Mountains i s d i s t i n c t l y higher than values g e n e r a l l y associated w i t h rocks of the Co n t i n e n t a l C r u s t . This might be explained e i t h e r by assuming that these a l k a l i s have been de r i v e d i n pa r t from d e s t r u c t i o n of an oceanic c r u s t (of t y p i c a l l y higher K/Rb val u e s ) or that the b a t h o l i t h i s a regime from which a v o l a t i l e a l k a l i n e phase has been removed. Igneous rocks w i t h K/Rb values greater than 400 are widespread i n the c e n t r a l and southern p o r t i o n s of the p r o j e c t area, but i n the northern r e g i o n they are l e s s abundant and appear to c o r r e l a t e w i t h zones of thermal a c t i v i t y . In southern B r i t i s h Columbia, the unusual K/Rb values terminate a b r u p t l y on the eastern margin of the Coast Mountains. Average strontium c o n c e n t r a t i o n i n the Coast Mountains p l u t o n i c complex i s approximately 720 ppm, which i s unusually high. Strontium content appears to be r e l a t e d to p l a g i o c l a s e content and l i k e l y c o n t r o l l e d by magmatic f r a c t i o n a t i o n . High strontium c o n c e n t r a t i o n proved to be t y p i c a l of p l u t o n i c rocks across the C o r d i l l e r a of southern B r i t i s h Columbia, r a t h e r than being confined to the Coast Mountains. The frequency d i s t r i b u -t i o n f or strontium c o n c e n t r a t i o n i s bimodal for both the p l u t o n i c rocks of the southern Coast Mountains and those of the adjacent i n t e r i o r of the prov i n c e ; furthermore, the modes match. This suggests a s i m i l a r e a r l y * i i h i s t o r y for p l u t o n i c magmas i n these two r e g i o n s , while the h i s t o r y of t h e i r more mobile a l k a l i s o bviously has been d i f f e r e n t . The o v e r a l l r a t i o of rubidium to strontium i n the Coast Mountains b a t h o l i t h i c complex i s only 0.047. The Sr /Sr r a t i o i n t h i s environment i s consequently changing by approximately 0.001 every 550 m.y. A few measurements were made of t h i s r a t i o for p l u t o n i c rocks and gneisses i n the Coast Mountains. These ranged from 0.7031 to 0.7068, the v a r i a t i o n being expected i n view of metamorphic rocks having been digested during formation of some of the p l u t o n i c s u i t e s . In the measurement of rubidium and strontium concentrations f o r whole rock powders by X-ray fluorescence, an extension of the Compton s c a t t e r i n g technique was developed which allowed c o r r e c t i o n not only for matrix absorption but a l s o f o r background. This system employs l i n e a r r e g r e s s i o n a n a l y s i s to o b t a i n the parameters of a l a r g e l y e m p i r i c a l equation for the c o r r e c t i o n of readings. An apparent e r o s i o n surface of raid-Tertiary age i s s t i l l evident i n the s i m i l a r i t y of summit heights over wide areas of the Coast Mountains, e s p e c i a l l y i n the western p o r t i o n of the range. On the theory that any l i n e s of v e r t i c a l movement a c t i v e since development of the surface should have caused d i s c o n t i n u i t i e s i n t h i s summit envelope, a computer a n a l y s i s was made of summit e l e v a t i o n s to l o c a t e d i s l o c a t i o n s . The r e s u l t s showed tha t much of the Coast Mountains and Vancouver I s l a n d appears to be broken i n t o blocks by such l i n e s . Some of the major d i s c o n t i n u i t i e s a l s o mark the l o c a t i o n of other signs of Tectonic a c t i v i t y such as thermal centers ( h o t s p r i n g s and Quaternary volcanoes), strong lineaments, metamorphic screens, and abrupt changes i n f j o r d depths. One zone running up the Coast Mountain chain for almost the e n t i r e 500 mile length of the p r o j e c t area shows the above features as w e l l as seismic a c t i v i t y i n i t s southern p a r t . In the north i t separates regions of d i f f e r e n t potassium-argon ages and forms one of the b e l t s of anomalous K/Rb r a t i o s i n p l u t o n i c r o c k s . I t i s suggested that the deepest Coast Mountains f j o r d s are drowned fe a t u r e s , t h i s outlook being supported by apparent t e c t o n i c c o n t r o l of the terminations of deep f j o r d segments and i n a bimodal frequency d i s t r i b u t i o n of depths for fjords tr&nm'e'rsk i.6. •tbe&_teict.onic .t.rendi. An a n a l y s i s of secondary e r o s i o n surfaces along two major summit envelope d i s c o n t i n u i t i e s was undertaken to f i n d i f movement postdated u p l i f t . The best c o r r e l a t i o n a v a i l a b l e was for a l l movement f o l l o w i n g u p l i f t , but the r e s u l t s were not e n t i r e l y s a t i s f a c t o r y . An attempt to make a q u a n t i t a t i v e i n t e r p r e t a t i o n of lineament p a t t e r n s by l a s e r a n a l y s i s of contour maps d i d not prove f r u i t f u l . The general t e c t o n i c h i s t o r y suggested f o r the Coast Mountains i s f o r e a r l y T e r t i a r y u p l i f t of at l e a s t p a r t of the b e l t , l i k e l y as the r e s u l t of a c t i v e subduction. This was followed by the development of an e r o s i o n surface and then resumed u p l i f t i n the P l i o c e n e or l a t e Miocene. B»th t e c t o n i c and igneous s t y l e of the l a t e T e r t i a r y however, suggest r e l a x a t i o n and q u i t e l i k e l y block subsidence of the f j o r d zone. i v CONTENTS ABSTRACT LIST OF TABLES LIST OF FIGURES, PLATES AND MAPS ACKNOWLEDGEMENTS INTRODUCTION 1 CHAPTER I ANALYTIC PROCEDURES 5 CHAPTER I I DISTRIBUTION OF POTASSIUM, RUBIDIUM AND .10 STRONTIUM Trace element p a r t i t i o n i n g 10 Rubidium d i s t r i b u t i o n 13 I n t e r p r e t a t i o n of anomalous K/Rb r a t i o s 17 Potassium and rubidium d i s t r i b u t i o n f or 26 Coast Mountains rocks Strontium abundance and d i s t r i b u t i o n kk Strontium d i s t r i b u t i o n i n Coast Mountains rocks 45 Summary 51. CHAPTER I I I STRONTIUM ISOTOPIC RATIOS 5k Values and s i g n i f i c a n c e 5k Strontium m i g r a t i o n and apparent i s o t o p i c 58 f r a c t i o n a t i o n Strontium isotope r a t i o s for Coast Mountains 6k rocks Summary ^ V CHAPTER IV GEOLOGY AND MORPHOLOGY OF THE COAST MOUNTAINS £Q T e r t i a r y h i s t o r y 68 P e t r o l o g y 69 S t r u c t u r e and age 78 Coast Mountains morphology 8 l Summary 93 CHAPTER V TECTOMORPHIC ANALYSIS 95 Summit l e v e l d i s c o n t i n u i t i e s 95 D i s t r i b u t i o n of thermal centers 107 D i s t r i b u t i o n of ages 108 G r a v i t y a n a l y s i s 1 0 9 D i s t r i b u t i o n of K/Rb anomalies 111. D i s t r i b u t i o n of e p i c e n t e r s 1 1 1 I n t e r p r e t a t i o n of f j o r d s H i f Summary of r e s u l t s 119 CHAPTER VI DISCUSSION AND CONJECTURE R e l a t i o n s h i p of Coast Mountains b a t h o l i t h to 1 2 2 c o n t i n e n t a l development I n t e r p r e t a t i o n of abno r m a l i t i e s i n strontium and rubidium d i s t r i b u t i o n " 1 2 ^ I n t e r p r e t a t i o n of t e c t o n i c form and h i s t o r y 128 Summary of evidence f o r T e r t i a r y h i s t o r y v i APPENDIX I RESULTS OF' CHEMICAL ANALYSIS 13k APPENDIX II SELECTION AND HANDLING OF SAMPLES 150 APPENDIX III ATOMIC ABSORPTION ANALYSIS 158 APPENDIX IV X-RAY FLUORESCENCE ANALYSIS I63 APPENDIX V COMSCAT I COMPUTER PROGRAM 180 APPENDIX VI COMSCAT II COMPUTER PROGRAM 1-83 APPENDIX VII USE OF THE MACROPROBE IN MICROANALYSIS 187 APPENDIX VIII MASS SPECTROMETERY 1.94 APPENDIX IX SCARPFILTER COMPUTER PROGRAM 196 APPENDIX X CORRELATION OF SECONDARY EROSION SURFACES 201 APPENDIX XI LASER ANALYSIS AND ZONING OF LINEAMENT PATTERNS 207 v i i LIST OF FIGURES Figure T i t l e Page 1 C o n t i n e n t a l and oceanic K/Rb trends -j,g 2 D i s t r i b u t i o n of K and Rb f o r igneous rocks and gneisses ^3 of the Coast Mountains b a t h o l i t h 3 D i s t r i b u t i o n of K and Rb for igneous rocks and gneisses ^ of the southern B.C. I n t e r i o r 4 D i s t r i b u t i o n of K and Rb for sedimentary rocks ^ 5 Frequency d i s t r i b u t i o n for K/Rb values from igneous rocks from the B.C. C o r d i l l e r a 6 D i s t r i b u t i o n of K, Rb, and Sr across the southern C o r d i l l e r a of B.C. 7 Comparison of strontium c o n c e n t r a t i o n w i t h p l a g i o c l a s e i+y content f o r the p l u t o n i c rock s e r i e s 8 Comparison of strontium c o n c e n t r a t i o n w i t h p l a g i o c l a s e Zfg content i n p l u t o n i c rocks 9 Frequency d i s t r i b u t i o n s f o r strontium c o n c e n t r a t i o n ^0 10 Rates of change of the strontium i s o t o p i c r a t i o 56 11 Contours on the summit envelope near Waddington Dome 12 Frequency d i s t r i b u t i o n f o r maximum depths of 108 0,1 Coast Mountains f j o r d s 13 E l u t i o n c a l i b r a t i o n curves for i o n exchange 2137 14 Sample c a l i b r a t i o n f o r potassium by atomic absorption 1B0 15 R e l a t i o n s h i p s of Compton s c a t t e r i n t e n s i t y to absorbance and background 1-9,2 16 Macroprobe r e s u l t s 17 Matching of secondary e r o s i o n l e v e l s across the 20^ southern a x i a l f r a c t u r e 18 Attempted matching of secondary e r o s i o n surfaces 205 across the B e l l a Coola River 19 Schematic o u t l i n e of l a s e r o p t i c a l bench 211 v i i l . LIST OF TABLES Table T i t l e Page 1 Comparison of twin sample p a i r s from ei g h t outcrops of 6 the S e c h e l t p l u t o n 2 U.S.G.S. standard rocks - values used 7 3 Average K, Rb, Sr, and S r 8 7 / S r 8 6 values for v a r i o u s lk rock types and p o r t i o n s of the e a r t h 4 D i s t r i b u t i o n of Rb, Sr and K i n v a r i o u s l i t h o l o g i e s 30 of the B r i t i s h Columbia C o r d i l l e r a 5 V a r i a t i o n of K/Rb with potassium mineral content 38 6 E f f e c t s of a l t e r a t i o n on Rb, S r , and K d i s t r i b u t i o n 39 7 Rb, S r , and K d i s t r i b u t i o n across the C o r d i l l e r a of h2 southern B r i t i s h Columbia 8 A c t i v a t i o n energy and d i f f u s i o n of S r 8 7 6 l 9 Mass spectrometery r e s u l t s f o r strontium 65 10 C l a s s i f i c a t i o n of igneous rocks 71 11 L i t h o l o g i c a l composition of the Coast Mountains 72 b a t h o l i t h i c complex 12 Atomic absorption t e c h n i c a l data 159 13 Curve f i t t i n g f or atomic absorption c a l i b r a t i o n 162 14 X-ray fluorescence a n a l y s i s - instrument s e t t i n g s loh • 15 Comparison of X-ray fluorescence a n a l y s i s of f i v e rock 166 samples with r e s u l t s from more f i n e l y p u l v e r i z e d s p l i t s 16 Comscat 1 Quadratic f i t t i n g 17^ + 17 Comscat 1A Linear r e g r e s s i o n 176 18 Comscat 2 Linear r e g r e s s i o n 17.8 i x LIST OF PHOTOGRAPHIC PLATES P l a t e T i t l e Page 1 Metamorphic screen forming from r o o f pendant 7.6 2 Waddington Range from northeast, showing d i s s e c t e d dome 86 3 Mt. Waddington from northwest, showing t r u n c a t i o n of 87 dome by a x i a l f r a c t u r e 4 Sample contact p r i n t from contour map of Burroughs 21k I n l e t area 5 F o u r i e r transform of contour p a t t e r n , Burroughs I n l e t ,215" 6 Fo u r i e r transform of contour p a t t e r n , Waddington area 216 LIST OF MAPS Map T i t l e Page 1 Rock, sample and age dates s i t e s , northern p r o j e c t area 27 2 Sample l o c a t i o n s , southern c o a s t a l ranges 28 3 Sample l o c a t i o n s , Fraser R. and southern I n t e r i o r 29 4 T e c t o n i c — m o r p h o l o g i c a l d i v i s i o n s of the southwestern 82 p o r t i o n of B.C. 5 Thermal centers and zones of the Coast Mountains 102 • 6 Summit l e v e l d i s l o c a t i o n s , northern p r o j e c t area 103 7 Summit l e v e l d i s l o c a t i o n s , southern p r o j e c t area 10^ 8 D i s t r i b u t i o n of e p i c e n t e r s , 51°30« to 50° N l a t . 11.3 9 Owikeno—Holberg t e c t o n i c r e g i o n Q X ACKNOWLEDGEMENT'S This p r o j e c t has been financed i n par t by Natio n a l Research Council of Canada grants to Dr. W.F. Slawson and Dr. R.D. R u s s e l l , both of whom I wish to thank f o r advice and a s s i s t a n c e . N a t i o n a l Science Foundation grant GA737 to Dr. Slawson was als o used i n support of t h i s work. The p r o j e c t has been g r e a t l y a s s i s t e d by the ki n d co-operation of Drs. J.A. Roddick, W.W. Hutchison, and J . Souther, of the G e o l o g i c a l Survey of Canada. Also g r e a t l y appreciated was advice on problems p e r t a i n i n g to chemistry from Dr. R.E. Delav a u l t and Dr. M. Barnes; and on matters p e r t a i n i n g to geology and geomorphology from Dr. W. Mathews and Dr. W. Barnes. Many of the analyses reported here have been made on atomic absorption or X-ray fluorescence u n i t s of the Department of Geology, U.B.C., or on a mass spectrometer constructed by J . Blenkinsop. 1 INTRODUCTION The Coast Mountains l i e along the western edge of mainland B r i t i s h Columbia, from near the Washington border north i n t o the Yukon T e r r i t o r y . This p r o j e c t studied only that p a r t of the mountain chain south of the southeastern t i p of Alaska, or roughly h a l f of the Coast Mountains l e n g t h of approximately 1000 m i l e s . The Coast Mountains are l a r g e l y u n d e r l a i n by a complex of p l u t o n i c rocks (Roddick et a l ^ 1967 j Hutchison, 1970), dominated by g r a n o d i o r i t e and quartz d i o r i t e . These range i n age from Cretaceous through T e r t i a r y , and at l e a s t a major p o r t i o n were emplaced or u p l i f t e d during the p e r i o d when subduction and d e s t r u c t i o n of an oceanic c r u s t a l p l a t e i s thought t o have been o c c u r r i n g beneath the western margin of North America (McKenzie and Morgan, 1969; Atwater and Menard, 1970). The Coast Mountains b a t h o l i t h hence provides an opportunity to study the geochemical character of a major T e r t i a r y orogenic b e l t which was presumably associated with c r u s t a l d e s t r u c t i o n . Furthermore a system of c l e a r lineament patt e r n s i n the Coast Mountains and a w e l l developed summit envelope representing a mid-T e r t i a r y e r o s i o n surface or surfa c e s , allows a n a l y s i s of present t e c t o n i c s t y l e . Geochemical work was concerned mainly with d i s t r i b u t i o n of potassium, rubidium and strontium, and to a l e s s e r extent w i t h the i s o t o p i c composition of strontium. Considerable data has been published on the subject of K/Rb r a t i o s i n rocks ( f o r example Heir and Adams, 1964; Shaw, 1968), and i t has been demonstrated t h a t there are d i s t i n c t l y higher values of t h i s r a t i o i n oceanic c r u s t a l m a t e r i a l s than i n almost a l l rocks of the c o n t i n e n t a l c r u s t . 2 If the a l k a l i s i n some of the Coast Mountains igneous suites were derived from destruction of oceanic c r u s t a l material, t h i s might show up i n t h e i r K/Rb r a t i o s . With t h i s i n mind, a study was made of the d i s t r i b u t i o n of K/Rb values i n rocks of the Coast Mountains and of the p e t r o l o g i c a l and tectonic features which appeared to influence t h i s parameter. The r a t i o Rb/Sr i s of importance i n that i t controls i n any environment the rate of change of strontium's i s o t o p i c composition, strontium-87 being the daughter product i n radioactive decay of rubidium-87. This rate i s of p a r t i c u l a r i n t e r e s t i n considering the o r i g i n of material from which g r a n i t i c rocks have formed. At time of s o l i d i f i c a t i o n , most suites of igneous rocks did not contain as much radiogenic strontium as might ba expected i f these rocks had been produced by fusion of older c r u s t a l material (whose Rb/Sr r a t i o would average much higher than that of the mantle). This problem has been discussed by Hurley e_t (1962) and Hurley (1968a). The Coast Mountains were known to be a region of potassium-poor i n t r u s i v e rocks when compared to adjacent older suites, and also to be an area r i c h i n strontium. It was hoped that the regional d i s t r i b u t i o n and t e r r i t o r i a l l i m i t s of these anomalies might shed some l i g h t on the r e l a t i o n of the Coast Mountains b a t h o l i t h to i t s surroundings. Samples of igneous rocks from both Vancouver Island and the southern i n t e r i o r of B r i t i s h Columbia were analysed for comparison with r e s u l t s from the southern Coast Mountains. Some work was done on obtaining increased accuracy from X-ray analyses of powdered rock for rubidium and strontium through an extension of the Compton scattering technique (Reynolds, 1963). This method i s used to correct for absorption of r a d i a t i o n by the sample, but was found also to be a measure of background i n t e n s i t y , and through l i n e a r regression analysis very good 3 c o r r e c t i o n a l f a c t o r s were obtained. This technique r e q u i r e s only three measurements f o r the determination of both rubidium and strontium, and appears accurate over a wide range of v a r i a t i o n i n c o n c e n t r a t i o n and matrix absorption f a c t o r s . Regions of deep earthquakes (Barazangi and Dorman, 1969) along the eastern rim of the P a c i f i c Ocean correspond to p a r t s of the C o r d i l l e r a which reach the g r e a t e s t a l t i t u d e and which g e n e r a l l y show signs of Quaternary u p l i f t . Furthermore, those p o r t i o n s w i t h deep earthquakes do not have deep f j o r d s . The r e l a t i o n s h i p between deep earthquakes and r a p i d c r u s t a l subduction i s w e l l documented (Morgan, 1968), and the l i k e l i h o o d of p o s i t i v e r e l i e f r e s u l t i n g from subduction beneath a c o n t i n e n t a l margin i s developed by Danes (1969) from t h e o r e t i c a l c o n s i d e r a t i o n s . No r a p i d subduction or deep earthquake b e l t p r e s e n t l y occurs beneath the Coast Mountains, and the c a l c u l a t i o n s of Danes (1969) and of Bostrom (1968b) suggest that the range may not be i s o s t a t i c a l l y or s t r u c t u r a l l y s t a b l e without c r u s t a l underflow. Souther (1970) has pointed out that the present t e c t o n i c and v o l c a n i c regime i n the C o r d i l l e r a of B r i t i s h Columbia might be explained by block t e c t o n i c s and a r e l a x a t i o n of compressional f a r c e s . A l l t h i s suggests that l a r g e - s c a l e block subsidence i n the Coast Mountains might w e l l be t a k i n g p l a c e , and the above-mentioned r e l a t i o n between deep f j o r d s and deep e p i c e n t e r s might then be due to the major f j o r d s being drowned v a l l e y f e a t u r e s , only modified and cleaned of sediments during P l e i s t o c e n e g l a c i a t i o n . A p a t t e r n of l i n e a r d i s c o n t i n u i t i e s i n the summit envelope height was o u t l i n e d by computer a n a l y s i s of summit e l e v a t i o n s , and t h i s p a t t e r n s t r o n g l y suggests block t e c t o n i c s . Some of the major l i n e s of d i s l o c a t i o n show signs of having been a c t i v e p r i o r to formation of the summit envelope and some s t i l l appear to be t e c t o n i c a l l y a c t i v e at present. Geophysical and morphological f e a t u r e s studied are c o n s i s t e n t w i t h subsidence of the f j o r d zone of the Coast Mountains f o l l o w i n g r e g i o n a l u p l i f t i n the P l i o c e n e ox l a t e Miocene. a. Features suggesting d i f f e r e n t i a l block movements since the Miocene: i ) B locks o u t l i n e d by summit envelope d i s l o c a t i o n s (SEDs). i i ) Apparent block t i l t i n g , i i i ) Secondary e r o s i o n surface c o r r e l a t i o n across SEDs. b. Features suggesting d i f f e r e n t i a l movement i n e a r l y T e r t i a r y : i ) Apparent c o n t r o l of r e g i o n a l age-date p a t t e r n s by an SED. i i ) Regions of d i f f e r e n t t e c t o n i c s t y l e bounded by SEDs. c. Features i n d i c a t i n g that the p a t t e r n i s s t i l l a c t i v e : i ) Continuing seismic a c t i v i t y along an SED. i i ) Hotsprings and Quaternary volcanoes along SEDs. d. Features i n d i c a t i n g f j o r d zone subsidence: i ) C o n t r o l of f j o r d heads by strong lineaments and SEDs. i i ) C o n t r o l of oceanward termi n a t i o n s of deep f j o r d channels by lineaments and SEDs. i i i ) Major ocean channels p a r a l l e l w i t h the Coast Mountains, i v ) Bimodal frequency d i s t r i b u t i o n for depths of f j o r d s t r a v e r s e to the Coast Mountains a x i s . 5 CHAPTER I ANALYTIC PROCEDURES The o b j e c t of analyses i n t h i s program has been to l o c a t e rocks of d i s t i n c t l y anomalous K/Rb r a t i o s and o b t a i n r e g i o n a l averages f or potassium, rubidium, and strontium content. There i s hence no need for accuracy i n i n d i v i d u a l analyses that i s s u b s t a n t i a l l y greater than the d e v i a t i o n i n those parameters t h a t might be expected i n the v i c i n i t y of i t s sample s i t e . A considerable amount has been published regarding the v a r i a t i o n of chemical and p h y s i c a l parameters to be expected w i t h i n bodies of rock ( f o r example Ahrens, 1963; B u t l e r , 1964) and the Coast Mountains p l u t o n i c rocks are commonly v i s i b l y heterogeneous. Analyses f o r e i g h t p a i r s of samples i n which each p a i r was taken from an outcrop of reasonably homogeneous appearance are compared i n Table 1. Average v a r i a t i o n was j u s t over 1% of the mean for K/Rb values and s i g n i f i c a n t l y higher for other parameters. With t h i s i n mind, the techniques employed i n a n a l y s i s were s e l e c t e d to process l a r g e numbers of samples q u i c k l y , r a t h e r than maintain a high l e v e l of accuracy on i n d i v i d u a l specimens. Care was taken, however, to pr o p e r l y standardize the r e s u l t s so that i n a c c u r a c i e s d i d not take the form of an o v e r a l l b i a s . U.S.G.S. standard rocks W-1,GSP-1, BCR-1 and AGV-1 were employed to t h i s end, concentrations f o r the v a r i o u s elements i n v o l v e d being taken from Flanagan (1969), and given i n Table 2. A t o t a l of 313 rock samples were analysed f o r potassium, rubidium, and strontium, and r e s u l t s are given i n Appendix I . The techniques i n v o l v e d Table 1 Comparison of Twin Sample Pairs from Eight Outcrops of the Sechelt Pluton pa i r #1 2 3 4 5 6 7 8 Average Rb variation 2.3ppm 8.6 9 .6 5.9 1.3 3.4 3.3 3.5 5.4ppm % of mean 8.5 20.0 17.5 16.9 2.0 8 . 9 13.2 9.2 13.8% Sr variation 262ppm 148 3 23 27 31 84 29 76ppm % of mean 29.1 17.5 . 7 7.0 7.0 5 . 4 15.7 7.0 11.2% K variation 0.29% .11 .17 .25 .13 .11 .31 .12 0.18% % of mean 20.0 5.6 7.5 1^.7 8.1 7.4 27.4 8.5 12.4% K/Rb variation 61 47 42 10 15 9 65 2 45 % of mean 11.7 10.0 10.1 2.1 5.8 2 .3 14.8 .5 7.2% Rb/Sr variation 0.006 .020 .024 .026 .008 .010 .001 .015 0.014 % of mean 24.0 18.2 18.5 23.6 M 15.2 2.1 16.3 15.3% Measurements of Rb, Sr and K were made f o r eight p a i r s of samples, eash p a i r r e p r e s e n t i n g a reasonably homo-geneous outcrop. D i f f e r e n c e s i n composition f o r each p a i r are given, and these d i f f e r e n c e s are recorded as a percentage of the mean of the two values* Table 2 U.S.G.S. Standards -- Values Used (Flanagan et a j , 1969) Standard Rb ppm Sr ppm % k W-1 22 190 0.5*» BCR-1 1*9 JkO Uk3 AGV-1 70 660 2.k GSP-T 268 280 **.7 Values are f o r the K s Rb and Sr contents of four U«S« G e o l o g i c a l Survey standard rocks used to standardize X-ray fluorescence and atomic a b s o r p t i o n measurements» 8 i n s e l e c t i o n and preparation of these specimens are discussed i n Appendix I I . Atomic absorption was used for the analysis of potassium and for a set of calcium analyses on samples from the northern Coast Mountains. A d e s c r i p t i o n of t h i s technique i s presented i n Appendix I I I . X-ray fluorescence was employed i n determining the rubidium and strontium contents of most rocks examined, and considerable work was done on the use of Compton scattering to improve accuracy. This i s documented i n Appendix IV, with the r e l a t e d computer programs outlined i n Appendices V and VI. An additional study into the possible uses of an X-ray fluorescence macroprobe i n microanalysis i s outlined i n Appendix VII. Mass spectrometery was employed i n determining;thgisotppic composition of several strontium samples and i n isotope d i l u t i o n analysis for rubidium i n c e r t a i n basic rocks. This technique i s t r e a t e d i n Appendix VIII. The measurements of potassium, rubidium and strontium were done across a span of four years, using d i f f e r e n t instruments and somewhat d i f f e r e n t techniques. For t h i s reason, there are d i f f e r e n t l e v e l s of accuracy involved. Measurements on rocks from southern B r i t i s h Columbia generally are the most accurate. For rubidium and strontium measurements run by X-ray fluorescence using Compton scattering for c o r r e c t i o n , the standard errors for nine standard rocks were 0.57 ppm for the rubidium and 0.72 ppm for strontium. For samples run without Compton scattering c o r r e c t i o n , the average difference between X-ray fluorescence and isotope d i l u t i o n measurements was 7%, and errors as great as 15 ppm were observed i n some runs on strontium standards. Repeated analysis for potassium were consistent to within 8% i n a l l runs. Analyses for potassium for the southern Coast Mountains was improved by use of a 9 sodium a d d i t i v e and systematic data handling. The average d e v i a t i o n from the mean for repeated a n a l y s i s of rocks from the southern Coast Mountains was j u s t over 0.05% potassium. The r e s u l t s i n Table I were obtained by the most accurate methods mentioned above. 10 C H A P T E R II DISTRIBUTION OF POTASSIUM, RUBIDIUM, AND STRONTIUM Trace Element P a r t i t i o n i n g General Theory. I f i n a cooling magma a l i q u i d phase i s i n cheraical equilibrium with a s o l i d one, then each component of that system w i l l be d i s t r i b u t e d between the two phases so that i t s chemical p o t e n t i a l i s the same i n both. I f the component i s present as a trace element, then the r a t i o of i t s concentrations i n the two phases w i l l remain constant. This i s the Be r t h e l o t — N e r n s t D i s t r i b u t i o n Law, and as a subsequent c o r o l l a r y the r a t i o of concentrations of a trace element i n two minerals p r e c i p i t a t i n g simultaneously from a melt should also remain constant. A modification of t h i s r u l e due to Henderson and Kracek, (1927), i s useful when the trace element i s present i n su b s t i t u t i o n for a l a t t i c e element or " c a r r i e r " . If the r a t i o "R" for phase "p" i s defined as concentration of trace element Rp = concentration of c a r r i e r element then for two phases "A" and "B" e q u i l i b r a t e d during formation, ( R A / R b ) = D ^ where D^g i s a constant defining the p a r t i t i o n i n g c o e f f i c i e n t for the two phases. For the case of a mineral phase "A" forming from melt "B", i f D i s le s s than unity, the r e l a t i v e concentration of trace element to c a r r i e r w i l l increase i n the melt as s o l i d i f i c a t i o n proceeds; and i f the f l u i d escapes after p a r t i a l f r a c t i o n a t i o n i t w i l l be enriched i n t h i s trace element with respect to i t s c a r r i e r . In t h i s manner trace elements tend to be concen-tr a t e d i n l a t e stage hydrothermal f l u i d s and pegmatites. This i s by no 11 means always the case, however, for i n some si t u a t i o n s the trace element i s accepted p r e f e r e n t i a l l y to i t s c a r r i e r . P e t r o l o g i c a l L i m i t a t i o n s . The Berthelot-.-rNernst D i s t r i b u t i o n Law may be applied to a cooling magma only with caution. D^g i s a function of temperature and of phase composition, both of which vary during cooling. Furthermore, the i n t e r i o r of a s i l i c a t e c r y s t a l does not necessarily remain i n equilibrium with the melt from which i t i s growing. A t o t a l f a i l u r e of c r y s t a l and melt to e q u i l i b r a t e leads to a logarithmic d i s t r i b u t i o n of trace element concentrations outward from the center of the c r y s t a l , and t h i s i s not uncommon i n rock minerals. Interpretation of D^g values from r e l a t i v e concentration of trace and c a r r i e r elements i n two co-existing minerals i s further obscured by incomplete knowledge of paragenesis, by the often . questionable assumption of a closed system, and by v a r i a t i o n of melt composition through simultaneous p r e c i p i t a t i o n of other minerals. Physical and Chemical Factors Affecting D i s t r i b u t i o n . Although the p a r t i t i o n i n g c o e f f i c i e n t D^g for a trace element may be sens i t i v e to a va r i e t y of chemical and physical parameters of i t s environment, the v a r i a t i o n w i l l be much l e s s s i g n i f i c a n t i f the element i s placed by s u b s t i t u t i o n for a c a r r i e r ion of the same valence and sim i l a r radius. D i s t r i b u t i o n of the two i on species w i l l then vary i n a similar manner, so that D ^ w i l l not be gre a t l y affected. This was found to be true for rubidium and potassium as chlorides i n aqueous sol u t i o n by Mclntyre (1962) for temperature v a r i a t i o n s o of 100 C, and for potassium and cesium d i s t r i b u t i o n between sanidine and a molten phase (Eugster, 1955) i n the range 500°C to 800°C. Eugster also found 12 no detectable change i n D^g between one and two ki l o b a r s pressure despite a 2b% d i f f e r e n c e i n the size of potassium and cesium ions. Composition of a system w i l l influence p a r t i t i o n i n g c o e f f i c i e n t s between the components, but once again i f a trace ion and i t s c a r r i e r are of roughly the same size and carry the same charge, v a r i a t i o n s w i l l be small. Elements forming more than roughly one percent of an assemblage cannot be considered trace elements i n t h i s context (Mclntyre, 1963) and may have a p a r t i t i o n i n g c o e f f i c i e n t dependent on concentration. Trace elements which proxy for a c a r r i e r of d i f f e r e n t valency w i l l have p a r t i t i o n i n g c o e f f i c i e n t s s e n s i t i v e to changes i n melt composition, temperature, and possibly pressure. Furthermore, such substitutions depend on a v a i l a b i l i t y of suitable ions for n e u t r a l i z i n g l a t t i c e charge discrepancies and are poorly defined by the Be r t h e l o t — N e r n s t D i s t r i b u t i o n Law. Equally i l l - d e f i n e d are those cases of s u b s t i t u t i o n for more than one c a r r i e r . As ++ + ++ Sr may both proxy for K and substitute for Ca , i t i s not surprising that i t s r e l a t i o n to c a r r i e r ions i s often unpredictable. The d i s t r i b u t i o n law assumes incorporation of a trace element by d i r e c t s u b s t i t u t i o n into the l a t t i c e for a c a r r i e r and may be meaningless i f concen-t r a t i o n i s co n t r o l l e d instead by other mechanisms. DeVore (1955) has studied t h i s problem and concluded that incorporation of foreign material by absorption of complexes on the surface of forming c r y s t a l s may well be important i n trace element d i s t r i b u t i o n . It seems l i k e l y , however, that t h i s w i l l be a c o n t r o l l i n g factor only when the trace element i s indeed foreign to the l a t t i c e , and not when there i s a suitable c a r r i e r present. 13 Summary.. P a r t i t i o n i n g of a trace element between mineral phases w i l l be approximately independent of physical and chemical conditions only i f a single c a r r i e r element i s present and i f t h i s c a r r i e r has the same valency and approximately the same size as the trace ion. D i s t r i b u t i o n of rubidium between co-magmatic b i o t i t e and potash feldspar would be one good example. For a magmatic suite to maintain a constant trace element to c a r r i e r r a t i o for whole rocks requires either that the p a r t i t i o n i n g c o e f f i c i e n t s be unity for a l l minerals bearing these elements, or that mineral f r a c t i o n a t i o n be minimal. For more detai l e d models, see Cast (1968). Rubidium D i s t r i b u t i o n Abundance. Rubidium forms no minerals of i t s own, occurring e n t i r e l y i n s u b s t i t u t i o n for potassium. E a r l y work on the abundance of rubidium was c a r r i e d out by Goldschmidt et a.1 (1.934), but t h e i r averages of 310 ppm for igneous rocks and 300 ppm for sedimentary rocks were found to be somewhat high by l a t e r workers. A reasonably thorough i n v e s t i g a t i o n of rubidium abundance i n rocks was published by Horstman (1957), but h i s concentrations tend to be lower than those reported i n recent studies. Two of the most r e l i a b l e and comprehensive sources of rubidium measurements for a wide range of rocks are reported i n the studies of Ahrens and Taylor (i960), and Heier and Adams (1964). Table 3 shows estimates of rubidium concentration by some authors whose work dealt with rocks from a wide s,pectrum of geological provinces. Igneous rocks are roughly subdivided, and some of the v a r i a t i o n i n t h e i r estimated contents undoubtedly a r i s e s from d i f f e r e n t systems of rock c l a s s i f i c a t i o n . 14. TABLE 3 Average K, Rb, K/Rb, Rb/Sr and S r 8 7 / S r 8 6 Values f o r V a r i o u s P o r t i o n s of the E a r t h Rb K/Rb Rb/Si S T 8 7 / * " C r u s t upper c o n t . lower c o n t . I l l A * ; 53N 437A*; 365N 229A* 23A* c o n t i n e n t a l 9 0 K ; 150B 113C; 87E oceanic T o t a l Mant le 21A* ; . 35C 57A*; 91C 90Q; 74E 3 .6C ; 0.38N 518A* 267 A * 0 .33P; 0.145N 0 .25A* ; 0.25M 0.03A 375K; 340B 232K; 167B 0 .15N; 0.24K 442E; 461A* 230C 0.44B; 0 .2E 700A* 249C 0 .03A* 36N 460A; 305C 0.020A 0 .01IN 0.7205A 0.7045A 0.72E 390A; 441E 236A*; 230C 0.115A; 0 .17E 0.709A 0.7O15F 0.7.035A 0.70271 0.7025N Whole E a r t h 0 . 4 A * ; 2 . 9 C 12A* 350A; 293C 0 .033A* A. H u r l e y (1968a) A * H u r l e y (1968b) B . Vinogradov (1962) C . H e i e r and Adams (1964) D. Horstman (1957) E . H u r l e y et a l (1962) F . Engel et a l (1965) G . T u r e k i u n and Wederpohl (1961) H. Tatsumoto and Hedge (1965) I . Canney (1952) J . Hedge (1967) K . T a y l o r (1964) L . Hedge and W a l t h a l l (1963) M. Faure and H u r l e y (1964) N . Armstrong (1968) P . Cast (1960) Q. T a y l o r (1965) T 5 TABLE ' 3 : Estimations of Rb, S r , and K/Rb Content of Rocks by Various Authors Rb Sr K/Rb Rb/Si Grani te Syeni te Granodi or i te Granodi or i te & gran i te Intermediate i.ntrusi ves Qtz . d i o r i t e D i p r i t e •'' J&ibbro S3 ^ Ul t rabas ic Rhyol i te Trachyte Dac i te Andesite Basalt T70C; T70D 196E; T30H 150a 110Q; 124C 110G; I36E 99C; 122E 120Q. 200B; 170G 110D; 60H 76C 40A; 100B 77Cj 88E 45B; 28C 30D; 32 E 2B; 0 .03C 10D; 0 . 5 E 0.2G 217C 238C 97C 73Cj 88E kSB; 4 7 C 30Dj 32E 30G; 30H 197E; 400H 200G* 156E 440 E 300B ; 100G 600H 975A; 800B 500E 440B; 440E 10B; 49E 1G 500E 4 4 0 B ; 440E 465G; 600H 200C; 290H I.OEj 0.2H 300Cj 445G 0.55G; O.87E 230c 300H 23OC 23OC 23OC 0.28E 167B; 245G 0.645B} 1.7G 0.1H 210B; 230C 0.04Aj 0.18E 0.135B 185B; 270C 0.102B; 0.07E 155B; 300C 0.2B; 0.01E 200G 0.2G 175C 200C 0.176E 185B; 270C 0;102B} 0.073E 275G; 400H 0.065G; 0.05H 16 TABLE 3 ( cont inued) Rb Sr K/Rb Rb/Si Oceanic b a s a l t s S ha 1es Greywacke Limestone Sedimentary average 5A; 1.2H 200B; 149E 140G 1200. 5 E ; 3G o . s a IIODj 2801 180A 200A; 115H kSOB; 300G 61OG 200A 1500-2000F 140CH 114B; 190G 900G 0.025A; 0.01H O.khB; 0.5E 0.47G} 0 .32 J 0.008E; 0.003G 0.90A 17 Coherence of Rubidium and Potassium. The r a t i o of rubidium concentra-t i o n to that of i t s c a r r i e r element potassium i s remarkably constant through almost a l l continental rock s u i t e s . This coherence was f i r s t demon-strated by Ahrens et_ al, (1952) for both rocks and c h r o n d r i t i c meteorites. A considerable amount of l i t e r a t u r e has now been compiled on t h i s subject, and Shaw (1968) gives a bibliography of many of the works to that date. The issue has been clouded by poor analyses, and inadequate at t e n t i o n paid to the margins of error i n K/Rb r a t i o s reported. The most caref u l work, however, has shown that K/Rb values for continental whole rocks almost always f a l l within d e f i n i t e l i m i t s ; the exceptions are l o g i c a l ones and w i l l be discussed. The range 160—300 (Ahrens and Taylor, 1960) w i l l be con-sidered normal for continental rocks i n t h i s study, and i s shown on Figure 3. Shaw (1968), on the basis of a s t a t i s t i c a l analysis of published data for 51 rock suites, finds a s l i g h t v a r i a t i o n of K/Rb values with concentration of'these a l k a l i s ; and h i s estimation of t h i s trend i s also shown i n Figure 1. Interpretation of Anomalous K/Rb Ratios V a r i a t i o n by Mineral, Discrimination. As the rubidium ion i s approxi-mately 10% larger than that of potassium, i t w i l l substitute more r e a d i l y for potassium i n minerals with an open l a t t i c e . As the co-ordination number for potassium i n micas i s 12 (compared to 10 i n feldspar) i t i s not s u r p r i s -ing that rubidium i s most r e a d i l y accepted by b i o t i t e and muscovite. The p a r t i t i o n i n g c o e f f i c i e n t between a micaceous phase (m) and potash feldspar ( f ) may be espressed i n the form K/Rb f i n feldspar 1) . D m f = K/Rb ( i n mica) 18 Figure 1. The normal range i n v a r i a t i o n of K/Rb values i n whole rocks of the continental crust i s shown by a l a b e l l e d zone, and Shaw's estima-t i o n of t h i s trend i s shown by a dashed l i n e . Results from analysis of oceanic rocks as reported by various authors are also p l o t t e d . i 20 Heier and Adam (1964) have c o l l e c t e d data on co-existing b i o t i t e — p o t a s h feldspar p a i r s and found D^f varied from 1.6 to 5.3. I t i s of i n t e r e s t that the feldspars gave K/Rb values which showed over twice as great a spread as did D^. Trace element p a r t i t i o n i n g theory p r e d i c t s that should remain reasonably constant throughout a magmatic series i f the potassium minerals formed i n equilibrium. Zartman (1963) showed that for a suite of plutonic rocks near Llano, Texas, D^f was l i m i t e d to the range 3.9—4.4 i n a l l rocks which gave a concordant isochron. Considerable data on the p a r t i t i o n i n g c o e f f i c i e n t s for potassium, rubidium, and strontium during cooling of a magma has been published by P h i l p o t t s and Schnetzler (1970), who show that K/Rb values should be somewhat higher i n the early forming members of a f r a c t i o n a t i n g magmatic su i t e . Diopside and amphiboles have both been shown to discriminate strongly against rubidium i n comparison to potassium. Minerals which do not carry potassium as a l a t t i c e element cannot be expected to obey trace element p a r t i t i o n i n g laws for rubidium, and, as mentioned previously, the acceptance of both rubidium and potassium may depend on unknown mechanisms of trace ion incorporation. Hart and A l d r i c h (1967) i n an analysis of 50 amphiboles found K/Rb r a t i o s ranging from 100 to 5000 and averaging 1120. These averaged f i v e times greater than for pyroxenes. Other analyses of amphiboles (Gast, 1967; G r i f f e n et, al., 1968) have obtained comparable r e s u l t s . Diopside has also been shown to discriminate against rubidium, and contains the bulk of both a l k a l i s i n some ultr a b a s i c rocks. Sen (1959) has shown that the amount of potassium which w i l l f i t into c r y s t a l l i z i n g plagioclase by s u b s t i t u t i o n i s dependent on the openness of 21 the l a t t i c e , and hence increases with temperature and with aluminum— s i l i c o n disorder. As the rubidium ion i s larger than that of potassium, s e l e c t i v e d i s c r i m i n a t i o n against rubidium i s to be expected where incorpo-r a t i o n of these ions i s governed by l a t t i c e s u b s t i t u t i o n . High K/Rb values i n some cases have been confirmed (Erlank et j l . , 1969) but t h i s does not appear to be common, possibly because much of both a l k a l i s i s present i n a l t e r a t i o n products or p e r t h i t i c intergrowths ( H a l l , 1967; Nockolds and M i t c h e l l , 1942). V a r i a t i o n by Fra c t i o n a t i o n . The most commonly observed deviation from normal K/Rb values i n continental whole-rocks involves a decrease i n t h i s r a t i o due to excess rubidium i n late-stage magmatic d i f f e r e n t i a t i o n . Pegmatites and areas of a l k a l i metasomatism often show t h i s e f f e c t . An increase i n rubidium concentration i n late-stage f l u i d s i s to be expected i f potassium i s accepted p r e f e r e n t i a l l y to rubidium i n formation of potassium minerals. Extreme cases of pegmatite feldspars containing up to 2.8% rubidium (Borovik-Romanova and K a l i t a , 1958) or of metasomatism increasing rubidium concentration by a factor of four without potassium increase (Voskrensenskaya and Fel'dman, 1964) have been reported. In general the e f f e c t s of f r a c t i o n a t i o n and a l t e r a t i o n have not been so prominent, however, and are n e g l i g i b l e i n some rock s u i t e s . Papers dealing with t h i s general subject include Taylor et, j l . (1956), Taylor and Heier (1958), Beus and Oyzerman (1965), and Taylor (1965). In rocks where the bulk of potassium i s held i n minerals such as diopside or amphiboles which discriminate against rubidium, f r a c t i o n a t i o n i s bound to y i e l d whole rocks with a high K/Rb r a t i o . Such rocks have been i d e n t i f i e d i n several areas and excluding syenites (Payne and Shaw, 1967) and 22 c e r t a i n m i g m a t i t e s ( W h i t n e y , 1969) , t h e y a r e b a s i c or u l t r a b a s i c i n n a t u r e . E x a m p l e s i n c l u d e p e r i d o t i t e from S t . P a u l Rocks ( C a s t , 1 9 6 7 ) , a m p h i b o l i t e s o f M i n n e s o t a ( G r i f f i n et. §1, 1968) and the B u s h v e l d complex ( E r l a n k e_t a l , , 1 9 6 9 ) . O t h e r b a s i c r o c k s have y i e l d e d normal o r o n l y s l i g h t l y anomalous K / R b v a l u e s , p r e s u m a b l y because o f c o n t a m i n a t i o n by h y d r o t h e r m a l a l t e r a t i o n o r l a c k o f s t r o n g m i n e r a l f r a c t i o n a t i o n i n t h e i r g e n e s i s . I n o t h e r c a s e s o f u l t r a b a s i c r o c k s w i t h normal r a t i o s , the a l k a l i s were found to be h e l d m a i n l y i n p y r o x e n e s , w h i c h do n o t d i s c r i m i n a t e a g a i n s t r u b i d i u m . I f d u r i n g t h e s o l i d i f i c a t i o n o f a m e l t no m i n e r a l forms which i s s u i t -a b l e f o r c a r r y i n g r u b i d i u m , and i f t h e r e i s no l o s s o f l a t e s tage f l u i d s , t h e n r u b i d i u m may t e n d t o be p l a c e d i n a c c e s s o r y m i n e r a l s or a l o n g g r a i n b o u n d a r i e s where i t i s s u b j e c t t o l e a c h i n g . I n t h i s r e g a r d i t i s o f i n t e r e s t t h a t E r l a n k e £ §1. (1969) i n t h e i r s tudy o f t h e B u s h v e l d complex c o u l d o n l y a c c o u n t f o r h a l f o f t h e r u b i d i u m o b s e r v e d i n some whole r o c k s when t h e c o n s t i t u e n t m i n e r a l s were a n a l y s e d . S u s c e p t i b i l i t y o f K / R b r a t i o s i n b a s i c r o c k s to l e a c h i n g has a l s o been e x p l o r e d by G r i f f i n and M u r t h y ( 1 9 6 8 ) . I n t h e p r e s e n t C o a s t M o u n t a i n s s t u d y , most o f t h e r o c k s found to have anomalous K / R b r a t i o s c o n t a i n s u f f i c i e n t b i o t i t e o r p o t a s h f e l d s p a r t h a t t h e amounts o f t h e s e a l k a l i s h e l d i n o t h e r m i n e r a l s w i l l not be an i m p o r t a n t i n f l u e n c e . G a b b r o s form o n l y about 4% o f t h e C o a s t M o u n t a i n s p l u t o n i c com-p l e x and have been e x c l u d e d from t h e c o r r e l a t i o n o f K / R b a n o m a l i e s w i t h t e c t o n i c s t r u c t u r e , as t h e i r r a t i o s may r e f l e c t m i n e r a l d i s c r i m i n a t i o n r a t h e r t h a n t h e s o u r c e o r h i s t o r y o f t h e s e a l k a l i s . T r u e g r a n i t e s and p e g m a t i t e s c o m p r i s e a n e g l i g i b l e p e r c e n t a g e o f C o a s t M o u n t a i n s i n t r u s i v e r o c k , and as t h e y a r e l i k e l y end members i n a f r a c t i o n a t i o n p r o c e s s t h e y have a l s o been e x c l u d e d i n t h i s t e c t o n i c c o r r e l a t i o n . 23 Data on the p a r t i t i o n i n g c o e f f i c i e n t s for potassium and rubidium between rock minerals and melts suggests that a magma d i f f e r e n t i a t i n g by f r a c t i o n a l c r y s t a l l i z a t i o n w i l l have a somewhat lower K/Rb r a t i o i n the ' melt than the early forming s o l i d phase (Philpotts and Schnetzler, 1 9 7 0 ) . High K/Rb values such as observed i n the Coast Mountains might hence be i n res i d u a l material, providing that a major portion of these a l k a l i s was t i e d up i n minerals such as hornblende and plagioclase during f r a c t i o n a t i o n . Gast ( 1 9 6 9 ) has made some estimations of the e f f e c t of anatexis on the K/Rb r a t i o s for a hornblende bearing rock. The Oceanic Trend. Oceanic Basalts tend to show much higher K/Rb values than t h e i r continental counterparts. Ratios i n excess of 2 0 0 0 have been reported by Gast ( 1 9 6 5 ) , Tatsumoto et al. ( 1 9 6 5 ) , and Engel et j jL . ( 1 9 6 5 ) . The term " t h o l e i i t e " has come to be associated with anomalous oceanic rocks i n the l i t e r a t u r e . This i s unfortunate, as the term i s poorly defined and implies a p e t r o l o g i e a l cause for the anomalies, which studies such as that of Lessing et al. ( 1 9 6 3 ) have shown to be c h a r a c t e r i s t i c of a wide range of oceanic volcanic rocks. Data from the four above-mentioned papers constitute the oceanic trend as shown on Figure 1 . Some normal K/Rb values have also been reported from oceanic volcanic rocks, but there i s a strong p o s s i b i l i t y that t h i s may be the r e s u l t of contamination, caused dominantly by the rapid a l t e r a t i o n of these volcanic rocks by sea water (Hart, 1 9 6 9 ) , as may the trend i t s e l f . Achrondritic meteorites contain very non-radiogenic strontium and K/Rb values which are scattered through a range si m i l a r to those of oceanic b a s a l t s . This has been c i t e d as evidence for a mantle of achrondritic 2h composition, but that view has been attacked on several grounds and Hurley (1969) has shown on the basis of mass balance c a l c u l a t i o n s for radiogenic decay processes of geological importance that a potassium to rubidium r a t i o for the whole earth of greater than 400 i s u n l i k e l y . There must then be extensive f r a c t i o n a t i o n of some unusual sort involved i n d e r i v a t i o n of oceanic eruptives from the mantle. This process remains obscure (for example, Gast, 1968), but Gast (1967) has suggested a scheme of f r a c t i o n a -t i o n which uses the reluctance of amphiboles to accept rubidium as a possible method of maintaining a mantle K/Rb r a t i o lower than that of derived oceanic c r u s t . In view of t h i s question concerning K/Rb r a t i o s of the mantle and of rocks derived therefrom, there has been considerable interest In K/Rb values for e c l o g i t e s . Studies by Heier and Compston (1966) and Compstusn and Lovering (1969) have found that e c l o g i t e s r e t a i n r a t i o s within the region considered normal for continental rocks. Allsopp et, aj, (1968), however, observe K/Rb r a t i o s i n the pyroxenes of e c l o g i t e which are as high as those i n oceanic volcanic s u i t e s . They suggest the lower K/Rb values for whole rock samples i s the r e s u l t of a l t e r a t i o n , and the issue i s s t i l l i n doubt. In summary i t may at best be said that continental whole rocks (other than u l t r a b a s i c rocks and syenites) showing anomalously high K/Rb values have a p r i m i t i v e or oceanic character. The a l k a l i s i n these rocks were eith e r derived i n part from an oceanic regime or through a form of f r a c -t i o n a t i o n s i m i l a r to that by which oceanic basalts are derived from the mantle. The p o s s i b i l i t y of a t t a i n i n g anomalous regional K/Rb values through some l a t e form of a l t e r a t i o n w i l l be discussed next. 25 R u b i d i u m M o b i l i t y D u r i n g A l t e r a t i o n * R u b i d i u m i s v u l n e r a b l e to l e a c h i n g as p o t a s s i u m m i n e r a l s a r e o f t e n t h e most s u s c e p t i b l e t o a l t e r a t i o n . R u b i d i u m , however , i s more r e a d i l y a d s o r b e d t h a n p o t a s s i u m and so l e s s m o b i l e , a t l e a s t under t h e c o n d i t i o n s o f w e a t h e r i n g . K / R b v a l u e s f o r c l a y m i n e r a l s such as k a o l i n i t e and m o n t m o r i l l i n i t e t e n d t o be low (.Weaver, 1953) as a r e s u l t o f a d s o r b e d r u b i d i u m ( R e y n o l d s , 1963; C a n n e y , 1 9 5 3 ) . T h i s a l s o e x p l a i n s why s e d i m e n t a r y r o c k s t e n d to have normal K / R b r a t i o s even t h o u g h t h i s v a l u e i s about 3130 i n sea water (Amales and W e b s t e r , 1 9 5 7 ) . M i c a s as w e l l as c l a y s have base exchange p r o p e r t i e s , and K u l p and E n g e l (1963) found t h a t t h e i r p o t a s s i u m and r u b i d i u m c o n t e n t i s q u i t e s u s c e p t i b l e t o a l t e r a t i o n by p a s s i n g ground w a t e r . They o b s e r v e d t h a t e l u t i o n by 1 ppm r u b i d i u m s o l u t i o n a l t e r e d t h e r u b i d i u m c o n c e n t r a t i o n o f b i o t i t e by 21% i n a week a t room t e m p e r a t u r e . T h i s s o r t o f p r o c e s s may e x p l a i n t h e d i f f e r e n c e i n c o n c l u s i o n s r e a c h e d by v a r i o u s a u t h o r s on t h e e f f e c t o f w e a t h e r i n g on a p p a r e n t r u b i d i u m — s t r o n t i u m a g e - d a t e s ( see f o r example Zartman (1963) and G o l d i c h and G a s t ( 1 9 6 6 ) ) , b u t i t s e f f e c t on t h e o v e r a l l e r o s i o n c y c l e a p p e a r s to be t r a n s i e n t . K / R b v a l u e s f o r s e d i m e n t a r y and m e t a s e d i m e n t a r y r o c k s are a l m o s t i n v a r i a b l y normal and g e n e r a l l y s l i g h t l y lower t h a n a s s o c i a t e d i g n e o u s r o c k s as a r e s u l t o f t h e f o r e m e n t i o n e d r u b i d i u m a d s o r p t i o n . An e r o s i o n c y c l e t h u s t e n d s t o n o r m a l i z e t h i s r a t i o , and s e d i m e n t a r y r o c k s o f t h e C o a s t M o u n t a i n s a r e m a i n l y normal as F i g u r e 8 shows. S u r p r i s i n g l y l i t t l e work seems t o have been done on t h e e f f e c t o f v a r i o u s forms o f h y d r o t h e r m a l a l t e r a t i o n on K / R b r a t i o s . R e s u l t s from a n a l y ^ s i s o f a l t e r e d r o c k s i n t h e s o u t h e r n C o a s t M o u n t a i n s show t h a t t h i s form 26 of molesting can s u b s t a n t i a l l y increase K/Rb values, although whether t h i s i s of regional importance i s doubtful. The evidence w i l l be discussed l a t e r . Under a thermal gradient, rubidium i s usually more mobile than potas-sium. Furthermore, work by Ferrand (1960) on penetration of a l k a l i s into i n c l u s i o n s showed that rubidium was more mobile than concomitant potassium under at l e a s t some conditions of metasomatism. There i s hence l i t t l e doubt that K/Rb r a t i o s can be disturbed by metamorphic events, but a major region-al increase i n these r a t i o s due to metasomatism or thermal gradients has not been demonstrated. A higher thermal gradient than those studied by Horstman (1957) might give s i g n i f i c a n t f r a c t i o n a t i o n , but such cases could be only of l o c a l importance. Curves constructed by Hansen and Gast (1963) for mobility of ions under various a c t i v a t i o n energies show that a higher temperature gradient does not necessarily increase the mobility d i f f e r e n t i a l between two ion species. Potassium and Rubidium D i s t r i b u t i o n for Coast Mountains Rocks Potassium and rubidium measurements were made on 77 rock samples from the northern Coast Mountains ( l o c a t i o n s shown on map 1), on 77 rocks from the Coast Mountains between l a t i t u d e s 50° 30' and 52° N (central Coast Mountains c o l l e c t i o n , map 2). There were also 47 samples analysed from rocks of B r i t i s h Columbia's southern i n t e r i o r (map 3) and 22 samples from Vancouver Island (map 2). Appendix I gives rock c l a s s i f i c a t i o n and analysis r e s u l t s for each specimen. Averages are tabulated for regions and rock types i n Table 4. Intrusive averages given there take into account composition of the b a t h o l i t h i n terms of rock type, as presented i n Table 11;. Giving equal weight to each R O C K S A M P L E and A G E D A T E S I T E S Table 4 Distribution of Rb, Sr, and K in Lithologies of Northern and Central Coast Mountains Northern Regi on No. of Samples Rb ppm S rppm K% K/Rb Rb/Sr Quartz monzonite Granodiorite Quartz dior i te Diorite 7 1 7 3 76 50 36 29 682 995 942 375 1.95 1 .47 1.16 0.82 256 295 322 2fc3 0.11 0«°5° 0.038 0.077 weighted intrusive averaqe 39 • 838 1.23 316 0.046 Central Region Quartz monzonite Granodiorite Quartz dior i te Diorite 5 19 16 5 74 41 23 21 450 705 1006 601 2.36 I . 6 3 0.95 0.80 320 397 412 381 0.165 0.058 0.023 0.035 ^ ; wei ghted intrusive average 31 803 1.19 384 0.039 Northern and Central Reqions Combined Granite & pegmatites Gabbro Gnei ss Conglomerates Volcanic rocks & greenstones Metamorphic rocks Sedimentary rocks 7 7 16 8 9 21 17 150 4 .3 33 20 27 93 74 250 ..... 405 815 380 208 270 285 3.40 0.27 1,15 0.95 1.03 2.15 1.38 225 628 350 475 382. 230 185 0.60 0.011 0.040 0.053 0.13 0.34 0.26 Table 4 i(continued) Distribution of Rb, Sr, and K in Lithologies bf the Southern Cordil lera Southern Coast Mountains No. of Rb Sr K(%) K/Rb Rb/Sr Samples ppm ppm Quartz monzonite & granodi ori te 3^ 42 483 1.55 368 0.087 Quartz dior i te 36 28 562 0.97 346 .050 Diorite & gabbro 9 13 520 0.48 367 .025 weighted 520 1.04 0.056 intrusive averaqe 359 Volcanic rocks 11 . . 29 383 0.88 302 0.076 Vancouver Island Granodi ori te 7 60 407 1.70 283 0.15 Quartz dior i te 6 33 327 0.88 266 .10 Diorite 3 20 516 0.70 350 .039 Volcanic rocks 6 10 354 0.23 230 0.028 Southeastern Cordillera Quartz monzonite 10 230 590 3.43 149 0.39 G ranodi ori te 10 101 623 2.20 2*8 .16 Quartz diorite 6 76 554 1.53 201 .13 Diorite 3 53 560 1.31 247 .095 Syeni te 7 105 1113 3.43 326 .092 Volcanic rocks 6 60 450 1.81 301 .13 Sedimentary & metamorphic 5 83 199 1.65 200 0.42 32 Figures 2.3 and 4. The normal range of K/Rb values which was shown i n Figure 1 i s outlined by diagonal l i n e s . Results of analyses for various l i t h o l o g i e s of the western C o r d i l l e r a of B r i t i s h Columbia are p l o t t e d . '33; Fi e u r o s DISTRIBUTION Of POTASSIUM AND RUBJO IUM IGNEOUS ROCKS and GNEISSES' CJOAST MOUNTAINS BATHOLITH. Figure 3 DISTRIBUTION OF POTASSIUM AND RUBIDIUM FOR IGNEOUS ROCKS AND GNEISSES I I I s - s y e n i t i c or ultrabasic v - metavolcanic of the three c o l l e c t i o n s from the Coast Mountains, the average material of the b a t h o l i t h i c complex has a rubidium content of 33 ppm and a K/Rb r a t i o of approximately 360. This i s s i g n i f i c a n t l y outside the range of 150—300 considered normal for continental material, and as a comparison of Figures 1 and 2 i n d i c a t e s , the K/Rb r a t i o of Coast Mountains i n t r u s i v e samples appear to l i e mainly on the oceanic trend. Some other i n t e r e s t i n g points shown i n Table 4 include: i ) Volcanic rocks and greenstones generally have K/Rb r a t i o s which are anomalous, although the few samples obtained of more recent acid lavas did not. Basic lavas c o l l e c t e d usually had rubidium concentrations too low for X-ray fluorescence analysis and are not reported. i i ) Sedimentary and metasedimentary rocks f a l l mainly within the normal spread of continental K/Rb values, as did acid d i f f e r e n t i a t e s such as granites and pegmatites. (Figure 4) i i i ) Gabbros (whose rubidium contents were mainly obtained by isotope d i l u t i o n ) and syenites showed high K/Rb r a t i o s as expected. i v ) Conglomerate samples, which presumably represent an igneous t e r r a i n predating the present one, tend to have high K/Rb values. F r a c t i o n a t i o n has apparently had some e f f e c t on d i s t r i b u t i o n of K/Rb r a t i o s through the Coast Mountains b a t h o l i t h . This i s evident both i n v a r i a t i o n s within the i n t r u s i v e series ( i e . granite to gabbro), and i n a c o r r e l a t i o n between these r a t i o s and the type of potassium mineral involved, (Table 5). Rocks i n which feldspar i s the dominant potassium c a r r i e r have higher K/Rb r a t i o s than those dominated by b i o t i t e , as might be expected i f mineral f r a c t i o n a t i o n had taken place i n view of the p a r t i t i o n i n g factors for these minerals as discussed previously. The extent of v a r i a t i o n i n K/Rb values with a change i n mineralogy, or even with absence of potassium minerals i s not large compared to the regional tendency for Coast Mountains values to be high. The same may be said of the v a r i a t i o n with respeet to plutonic rock species. F r a c t i o n a t i o n was apparently important i n setting i n d i v i d u a l K/Rb values, but i f i t i s to explain the general b a t h o l i t h anomaly there must have been d i f f e r e n t i a t i o n with respect to a phase which i s not now apparent. Another i n t e r e s t i n g c o r r e l a t i o n i s one between K/Rb values and forms of a l t e r a t i o n . This i s tabulated i n Table 6. A l t e r a t i o n may c l e a r l y be seen to a f f e c t K/Rb r a t i o s , e s p e c i a l l y where c h l o r i t i z a t i o n i s involved. (Two samples of pink hydrothermal a l t e r a t i o n were involved, and both showed K/Rb r a t i o s over 500.) At t h i s point i t should be noted that c h l o r i t i z a t i o n , epidote a l t e r a t i o n , and d i o r i t i z a t i o n are a l l r e l a t e d i n Coast Mountains petrology and occur i n rock complexes which appear to be more p r i m i t i v e than (as opposed t© being altered from) surrounding plutonic rocks. Intrusive suites with appreciable amounts of potassium minerals seldom show much of t h i s form of a l t e r a t i o n . I f c h l o r i t i z a t i o n represents stripping of a l k a l i s from previously formed potassium minerals, t h i s event was l i k e l y before or during the l a t e stage formation of potassium minerals i n the b a t h o l i t h i c complex. A l t e r a t i o n may be a clue to the process which caused a K/Rb anomaly i n the Coast Mountains, but only about one h a l f of the rock samples i n which t h i s r a t i o i s over 400 show a l t e r a t i o n , and the anomalous regional d i s t r i b u t i o n of these a l k a l i s cannot simply be attributed to -38' Table Variation of K/Rb with Potassium Mineral Content for Quartz Diorites and Diorites of Southern Coast Mountains and Vancouver Island ^ . . b iot i te R a t , ° K feldspar No. of Specimens Average K/Rb 0 - 1 / 3 6 403 1/3 - 1 7 373 1 - 3 7 346 3+ ! 3 346 both potassium mi nerals negligible 9 390 K/Rb ratios are shown to be somewhat dependent on the mineral holding these allealise Variation i s i n the direction to be expected i f i t were the result of mineral fractionation* A l l groupings, however, have substantially higher K/Rb averages than normal continental rocks. Table 6 E f f e c t s of A l t e r a t i o n on Rb, S r , and K D i s t r i b u t i o n i n D i o r i t e s and Quartz D i o r i t e s of the Southern Coast Mountains and Vancouver I s l a n d Form of A l t e r a t i o n Rb Sr K{%) K/Rb Rb/Sr ppm ppm c h l o r i t i z a t i o n 16 554 0.71 443 0.029 ep idote ( w i t h c h l o r i t e ) 26 582 1.07 411 .045 d i o r i t i z a t i o n .20 410 0 .80 400 .049 k a o l i n i z a t i o n 24 552 0.98 407 .043 u n a l t e r e d 27 670 0.91 337 0.040 ko l a t e stage hydrothermal leaching. Another i n t e r e s t i n g r e s u l t of the analyses i s shown i n the frequency d i s t r i b u t i o n of K/Rb values for igneous rocks (Figure 5). The d i s t r i b u t i o n i s bimodal for Coast Mountains c o l l e c t i o n s , although not d i s t i n c t l y so i n the case of the central sample region. In each case one mode l i e s i n the continental normal range (as does the single mode for samples from the I n t e r i o r ) and the upper mode i s d i s t i n c t l y anomalous, occurring between 350 and 450. The lower mode i s the more prominent i n the Northern Coast Mountains, where there i s also evidence of a basement complex, or at l e a s t a metamorphic t e r r a i n predating the b a t h o l i t h and represented by the Central Gneissic Complex. Some of the gneisses fram t h i s had very high K/Rb r a t i o s , p ossibly representing metaplutonic greups, but much of the complex i s composed of metasedimentary rocks which may have provided a source of a l k a l i s with normal continental K/Rb values. Whether the two modes i n these frequency diagrams a c t u a l l y represent two d i s t i n c t populations i s not c l e a r . A b r i e f examination of the rock specimens has shown no obvious d i v i s i o n . The bimodal character i s weak or absent i n frequency d i s t r i b u t i o n s for rubidium concentration alone. Table 7 and Figure 6 show v a r i a t i o n i n rubidium content of igneous rocks and K/Rb r a t i o s for various parts of the southern B r i t i s h Columbia C o r d i l l e r a from Vancouver Island to the West Kootenay region. Some of these groupings are not based on very large sample populations, and there i s no data on composition of ba t h o l i t h s outside the Coast Mountains on which to base i n t r u s i v e rock averages weighted by rock type. The general o u t l i n e of a l k a l i d i s t r i b u t i o n i s c l e a r , however, with an abrupt increase F IGURE 5 FREQUENCY D I S T R I B U T I O N OF K/Rb VALUES FOR IGNEOUS ROCKS FROM THE C O R D I L L E R A OF B. C . ( g a b b r o s & s y e n i t e s e x c l u d e d ) to S o u t h e r n C o a s t M o u n t a i n s S o u t h e r n I n t e r i o r - Table 7 Rb, S r , and K D i s t r i b u t i o n Across the C o r d i l l e r a of Southern B . C . Average Content of I n t r u s i v e Rock S e n i l e s Regi ori Vancouver I s l a n d Hoiva Sound - Seche.lt South C e n t r a l Coast Mtns S o u t h e a s t e r n Coast Mtns . ( cos t of L i 1 l o o e t R . , Ha r r i sen L k . ) Thompson P l a t e a u , Cascade Range ( B . C . ) Okanagan I n t e r i o r Ranges, Kootenays Rb ppm Sr. ppm 37 3k 3 0 " . 31-.-71 170 1**3 425 <*75 528 570. 502 670 676 K(%) 1.16 1.24 1.23 1.04 1.76 2 . 9 0 2.50 K/Rb 3! 4 364 4 1 0 ... 336 248 171 180 Rb/Si 0 . 0 8 7 .071 . 0 5 7 . 0 5 4 . 1 4 . 2 5 0 . 2 7 h'o. of Samples 17 40 21 20 14 7 10 V a r i a t i o n s i n geochemical parameters are observed f o r rough r e g i o n a l d i v i s i o n s ac ross the southern-C o r d i l l e r a from Vancouver I s l a n d t o the Kootenay D i s t r i c t o V a l u e s g i v e n are an average of samples only> w i t h o u t w e i g h i n g by r o c k t y p e , the average d i s t r i b u t i o n o f l i t h o l o g i e s not b e i n g a v a i l a b l e . 43 FIGURE 6 DISTRIBUTION OF POTASSIUM, RUBIDIUM AND STRONTIUM ACROSS THE SOUTHERN CORDILLERA OF B. C. i n both a l k a l i s and a reversion to continental normal K/Rb values at the eastern edge of the Coast Mountains. Vancouver Island tends to have K/Rb r a t i o s intermediate between those of the Coast Mountains and those of the I n t e r i o r . Strontium Abundance and D i s t r i b u t i o n Strontium most commonly occurs i n rocks by s u b s t i t u t i o n for calcium, despite calcium's 20% smaller i o n i c radius. Furthermore, s u b s t i t u t i o n i s almost e n t i r e l y i n feldspars where strontium i s accepted i n preference to i t s c a r r i e r ( B e r l i n et_ al,, 1968; P h i l p o t t s and Schnetzler, 1970), with very l i t t l e occurring i n mafic minerals despite the more open l a t t i c e p o s i t i o n i n b i o t i t e . S u b s t i t u t i o n for potassium also occurs, again mainly i n feldspar. V a r i a t i o n i n strontium concentration and i n the Sr/Ca r a t i o during f r a c t i o n a t i o n i s notably e r r a t i c . A few rock sui t e s , including the Saanich granodiorite of southern Vancouver Island (Turekian and Kulp, 1956) show a c o r r e l a t i o n between calcium and strontium concentrations as might be expected. Other suites (such as the Columbia Basalts) show a d i s t i n c t l y inverse c o r r e l a t i o n . Many rock groups show no trend at a l l . Calcium analyses were c a r r i e d out on rock samples from the northern and central Coast Mountains, but Sr/Ca r a t i o s showed no f r a c t i o n a t i o n trends and t h i s l i n e of study was dropped. Strontium i s considerably more concentrated i n the intermediate rocks of a plutonic s e r i e s ( i . e . quartz d i o r i t e and d i o r i t e ) than i n either the more acid or basic members. The most l i k e l y explanation seems to be that t h i s i s where plagioclase i s concentrated during f r a c t i o n a t i o n . k5 Table 3 tabulates estimates of strontium concentration i n various rock, types and parts of the crust. The element does not appear to be r e g i o n a l l y mobile i n terms of l a t e hydrothermal a l t e r a t i o n , at l e a s t , when compared to the a l k a l i s . This may i n part be due to the everpresent plagioclase component of rocks acting as a sink. Mobility i s of concern mainly i n considering the problem of radiogenic strontium, and w i l l be discussed i n d e t a i l i n the next chapter. gtrontium D i s t r i b u t i o n i n the Coast Mountains Strontium analyses were run on the same sample groups as described for potassium and rubidium. Individual r e s u l t s are given i n Appendix I and group averages are compiled i n Table 5. Average strontium content for the Coast Mountain b a t h o l i t h i s about 720 ppm, and runs over 100 ppm higher for the northern section. Volcanic and metamorphic rocks tend to be d i s t i n c t l y lower. An average of 720 ppm i s well above most estimates of strontium concentration for even the intermediate plutonic rocks on a world scale. Hurley (1969), however, gives 975 ppm for a t y p i c a l d i o r i t e , which i s close to t y p i c a l averages for d i o r i t e and quartz d i o r i t e i n the northern Coast Mountains. There i s a close c o r r e l a t i o n between strontium content and plagioclase content of rocks through the plutonic s e r i e s . This i s shown i n Figure 7 and suggests that mineral f r a c t i o n a t i o n may have played a major r o l e i n stron-tium d i s t r i b u t i o n . When strontium content i s plo t t e d against the percent plagioclase for i n d i v i d u a l specimens (Figure 8) the r a t i o of 25 ppm strontium per percent plagioclase forms a minimum. k6 Figures 7 and 8. The r e l a t i o n s h i p between p l a g i o c l a s e content and strontium content i s examined f o r igneous rocks of the c o a s t a l batho-l i t h . A c l o s e c o r r e l a t i o n between these parameters i s shown through the p l u t o n i c rock s e r i e s (Figure 7), and while t h i s does not hold f or i n d i v i d u a l specimens (Figure 8), there does appear to be a minimum strontium to p l a g i o c l a s e r a t i o . kl FIGURE 7 COMPARISON OF STRONTIUM CONCENTRAT ION WITH P L A G I O C L A S E CONTENT FOR PLUTON IC ROCKS OF NORTHERN AND CENTRAL COAST MOUNTAINS B A T H O L I T H P e r c e n t a g e P l a g i o c l a s e 1 • I <5 I I i G R A N I T E QUARTZ IMONZONITE GRANO- 1 QUARTZ D I O R I T E D I O R I T E D I O R I T E GABBRO D i s t r i b u t i o n o f S t r o n t i u m F IGURE ,8 COMPARISON OF STRONTIUM CONCENTRAT ION AMD P L A G I O C L A S E CONTENT • FOR PLUTONIC ROCKS OF NORTHERN AND CENTRAL COAST M T N S . 80 Co o o o o o o o < M cr N O oo o C M j -ppm Strontium 49 One surprising r e s u l t of the analyses for southern B r i t i s h Columbia was that the highest strontium concentrations are not i n the Coast Mountains but farther east. Figure 6 and Table 7 show samples from Vancouver Island have the lowest strontium content and those from West Kootenay area the highest, despite the fact that the l a t t e r were commonly more acid rocks such as quartz monzonites. Another surprise was that frequency d i s t r i b u t i o n s for strontium concentration i n plutonic rocks (Figure 9) are bimodal for both the southern Coast Mountains and the Int e r i o r c o l l e c t i o n s , and these modes match. The d i s t r i b u t i o n of strontium across the southern C o r d i l l e r a i s thus quite s i m i l a r , while that of the more mobile a l k a l i s i s not. The higher mode (550-650 ppm Sr) of the southern sample areas may also be observed i n the northern Coast Mountains, but the lower mode (350-450ppm) i s absent. It i s not clear whether t h i s bimodal d i s t r i b u t i o n represents two d i s t i n c t genetic populations. There i s no sample c o r r e l a t i o n with the two modes shown for K/Rb values. The r a t i o Rb/Sr for the Coast Mountains b a t h o l i t h i s approximately 0.047, which i s very low for a large region of continental cr u s t . Almost a l l of the volcanic rocks analysed, except for those of Vancouver Island, have s u b s t a n t i a l l y higher Rb/Sr averages. Metasedimentary samples average close to what i s considered usual for continental crust (Table 5), and plutonic rocks of the southern I n t e r i o r are closer to t y p i c a l c o n t i n e n t a l -crust values than to Coast Mountains r a t i o s . The change i n Rb/Sr values i s quite abrupt at the eastern edge of the Coast Mountains (Figure 6). FIGURE 9t FREQUENCY DISTRIBUTIONS FOR STRONTIUM CONCENTRATIONS IN PLUTONIC ROCKS Northern and centra l Coast Mtns, tllUitmiiiiimiillllllimiin o LA -3-o LA I I I , Southern 'Coast tatns. | I I I I ! S 0 J 1 thern J n t e r i o r I wwwwwwwwwwwwwwwww \\\\\\\\\\v o IA VO \wm\ Strontium Content (ppm) 51 Summary Theory and Background i ) If a trace element and i t s c a r r i e r have the same charge and simi l a r i o n i c radius, t h e i r p a r t i t i o n i n g c o e f f i c i e n t s are affected i n a similar manner by changes i n physical and chemical properties of t h e i r environment. In geological materials, rubidium has such a c a r r i e r (potassium), strontium does not. i i ) During f r a c t i o n a t i o n of a magma, the r a t i o of a trace element t© i t s c a r r i e r i s sim i l a r i n the various phases only i f t h e i r p a r t i t i o n i n g c o e f f i c i e n t s for these phases are near unity. This requirement i s not f u l f i l l e d i n the case of rubidium and potassium. i i i ) Despite considerable v a r i a t i o n of K/Rb values between co-e x i s t i n g minerals, the range of t h i s r a t i o for continental whole-rocks i s quite l i m i t e d (generally 160—300). Exceptions include obviously d i f f e r e n t i a t e d suites such as pegmatites and also c e r t a i n basic rocks i n which the a l k a l i s are dominantly held i n minerals such as amphiboles, diopside and pla g i o c l a s e which discriminate against rubidium. i v ) Oceanic basalts have much higher K/Rb r a t i o s than continental b a s a l t s . Unaltered e c l o g i t e s may also be anomalous. Whether t h i s r e f l e c t the mantle r a t i o or some system of oceanic or deep-seated f r a c t i o n a t i o n i s not known. v) Strontium i s generally most concentrated i n the intermediate rock of a plutonic s e r i e s , and more p l e n t i f u l i n plutonic than volcanic s u i t e s . 52 Observations i ) In the Coast Mountains b a t h o l i t h i c complex, the average r a t i o of potassium to rubidium i s 360, which l i e s outside the l i m i t s considered normal for K/Rb values i n continental rocks. Almost a l l of the sedimen-tary rocks f a l l within the normal continental range. i i ) The majority of rocks showing anomalous K/Rb values contain s u f f i c i e n t b i o t i t e and potash feldspar that only a minor portion of the rubidium and potassium i s i n minerals discriminating against rubidium. There i s some v a r i a t i o n of K/Rb with domination of b i o t i t e as the potassium c a r r i e r but t h i s does not explain the regional anomaly. i i i ) C e r t a i n forms of a l t e r a t i o n , notably c h l o r i t i z a t i o n , cause unusually high K/Rb values, but t h i s again does not d i r e c t l y explain regional rubidium paucity. i v ) In both the southern and northern portions of the Coast Mountains study area, d i s t r i b u t i o n s of K/Rb values are bimodal. The lower modes f a l l within the range considered continental normal. The lower mode i s the major one for the northern Coast Mountains samples, and t h i s i s the part of the Coast Mountains which appear to have a basement or older g n e i s s i c complex. v) On the east of the Coast Mountains there i s a f a i r l y abrupt reversion of igneous K/Rb values to continental normal, along with an increase i n both a l k a l i s . Vancouver Island also has a lower K/Rb average than the adjacent mainland. 53 v i ) Strontium content of the Coast Mountains b a t h o l i t h i s high ( c i r c a . 720 ppm) by standards for igneous rocks, but perhaps not extra-ordinary for dominantly quartz d i o r i t e t e r r a i n . v i i ) In the C o r d i l l e r a of southern B r i t i s h Columbia, strontium content of plutonic rocks appears to increase eastward. The frequency d i s t r i b u t i o n of concentrations i s bimodal i n both the southern Coast Mountains and the southern I n t e r i o r . Furthermore, the modes for these two d i s t r i b u t i o n s match. v i i i ) The r a t i o Rb/Sr i n the Coast Mountains b a t h o l i t h i s i n the neighborhood of 0.047. Associated volcanic rocks and i n t r u s i v e rocks of the B r i t i s h Columbia In t e r i o r have higher average values. 5k CHAPTER III STRONTIUM ISOIOPIC RATIOS Values and S i g n i f i c a n c e Rubidium 87 decays to strontium 87 with a h a l f l i f e of approximately 5 x 10*^ years, and the r a t i o S r 8 7 / S r 8 ^ i s the one t r a d i t i o n a l l y used as a measure of the radiogenic component present i n a strontium occurrence. The l e a s t radiogenic (lowest) r a t i o s known are for chon d r i t i c meteorites, which y i e l d i n i t i a l values as low as 0.689 (Gast, 1960). 87 / 86 The rate of change of Sr /Sr i n any closed environment w i l l depend on the r a t i o of rubidium to strontium therein, and i s given i n Figure 10 for several Rb/Sr values of geological s i g n i f i c a n c e . The r a t i o S r 8 7 / S r 8 ° of strontium i n an igneous rock at time of i t s formation (or at l e a s t strontium homogenization) i s r e f e r r e d to as i t s i n i t i a l strontium i s o t o p i c r a t i o , which w i l l here be abbreviated ISIR. Assuming the mantle to be reasonably homogeneous, i t s Rb/Sr value should be r e f l e c t e d by an increase with time of the ISIR i n derived igneous rocks. Hedge and Peterman (1970) and other authors have cast doubt an the homogeneity of the mantle, but the v a r i a t i o n may be considered small compared to the difference i n Rb/Sr values between the mantle and regimes of the continental c r u s t . There have been some attempts to observe S r 8 7 / S r 8 ^ change with time i n the mantle d i r e c t l y from the v a r i a t i o n of lowest published values of ISIR. The best estimates appear to be for an increase of about 0.5% (or 0.0035) i n the value of S r 8 7 / S r 8 6 for mantle strontium i n the l a s t 3 b.y. 55 (Hedge and Walthall, 1963; Hurley, 1968). By any model, however, there has been l i t t l e change i n i s o t o p i c composition of strontium i n the source region of b a s a l t i c rocks over geological time, although about 7% of t e r r e s t r i a l rubidium must have changed to strontium 87 i n the l a s t 4.5 b.y. The mantle by inference and the oceanic crust by measurement both have a low average Rb/Sr value (see Table 10) compared to estimates for s i a l i c crust as derived from considera-t i o n of shales and shield igneous rocks. The r a t i o of Rb/Sr values i n s i a l to those of the basalt source region i s generally estimated to be i n the neighbourhood of 30, hence the ISIR for an igneous rock should be an indicat o r of the residence time of i t s parent material i n a s i a l i c regime, or simply i t s w c r u s t a l prehistory". In f a c t , however, even s h i e l d granites commonly have ISIR values le s s than 0.71 and often s u b s t a n t i a l l y lower. As an example, a change i n S r 8 7 / S r ^ from a value t y p i c a l of modern oceanic basalts ( c i r c a 0.704) to 0.710 would allow only about 250 m.y. c r u s t a l prehistory. This tendency toward low ISIR values for igneous rocks i s interpreted as meaning that igneous events have access to a supply of p r i m i t i v e or subcrustal strontium. That i n turn suggests continuous evolution of s i a l (Hurley et &1, 1963), which i s not supported by models based on lead isotopes. Furthermore, the concept of subcrustal d e r i v a t i o n i s embarrassing when the rocks are paragneisses or other suites not e a s i l y compromised with a major i n f l u x of foreign strontium. This problem w i l l be discussed i n d e t a i l i n the f i n a l chapter. 56 Figure 10. The rates for change of the r a t i o Sr /Sr i n environ-ments of various Rb/Sr values are given, and net changes i n S r 8 7 / S r ; over various periods of time are displayed. 58 gtrpntium Migration and Apparent, Isotppic F r a c t i o n a t i o n Migration, During A l t e r a t i o n . Although no measurable f r a c t i o n a t i o n of strontium isotopes by natural chemical processes has been observed, the s i t u a t i o n i n which radiogenic strontium appears i n a potassium l a t t i c e s i t e allows i t greater mobility (under c e r t a i n conditions) than i s c h a r a c t e r i s t i c of non-radiogenic strontium i n that mineral. I t i s hence not surprising that i n the majority of cases where discordant rubidium—strontium mineral ages have been investigated, the cause has proved to be.^migration'of irladio-genic strontium from potassium minerals. Plagioclase provides the l a t t i c e most commonly re c e i v i n g strontium, as i t accepts i t p r e f e r e n t i a l l y to calcium ( B e r l i n et jjl_, 1968). As the c o e f f i c i e n t s of d i f f u s i o n for normal and radiogenic strontium w i l l not d i f f e r s i g n i f i c a n t l y , t h e i r d i f f e r e n c e i n mobility must r e f l e c t i n i t i a l l a t t i c e bonding, or e f f e c t i v e l y , t h e i r a c t i v a t i o n energy. B i o t i t e i s e s p e c i a l l y susceptible to leaching of radiogenic strontium as strontium does not r e a d i l y substitute into i t s twelve-fold co-ordination s i t e s for potassium; for the same reason most common strontium i n b i o t i t e s i s occluded i n accessory minerals (mainly apatite) which are comparatively r e f r a c t o r y . The s i t u a t i o n i s somewhat d i f f e r e n t for potash feldspar. Here stron-tium seems more r e a d i l y accepted, but i t has been shown that an increase i n t r i c l i n i c i t y of t h i s feldspar may lead to expulsion of S r 8 7 (Arriens, 1966; Brooks, 1966). Increasing t r i c l i n i c i t y has i n turn been observed to r e s u l t from shearing stress (Parsons, 1965). A phase change may also be important i n expulsion of radiogenic stron-tium from b i o t i t e s . Muscovite (with a s i m i l a r l y open l a t t i c e and lack of 59 common strontium s u b s t i t u t i o n for potassium) usually r e t a i n s radiogenic strontium and may even act as a sink for i t during periods of i t s migration. B i o t i t e , being an i r o n mineral, i s e s p e c i a l l y s e n s i t i v e to the oxygen fugacity of i t s environment (Eugster and Wones, 1962), and t h i s might well 87 be a c r i t i c a l factor i n expulsion of Sr . In several cases of mineral age discrepancies reported for rubidium— strontium dating, there has been l i t t l e or no v i s i b l e a l t e r a t i o n of the minerals. Furthermore, the order of mineral s t a b i l i t y with regard to reten-t i o n of radiogenic strontium turns out to be quite d i f f e r e n t i n d i f f e r e n t geological environments. It seems l i k e l y that temperature, temperature gradients, phase changes, deformation, and various forms of chemical a l t e r a -t i o n (including weathering) may a l l be important under s p e c i f i c circumstances. Thermal D i f f u s i o n . There have been a few attempts to calculate the e f f e c t i v e a c t i v a t i o n energy of radiogenic strontium i n b i o t i t e s from i t s observed mobility i n the f i e l d . Temperature—time curves may be constructed for an i d e a l country rock adjacent to a non-convecting dyke through the c a l c u l a t i o n s of Jaeger (1965). If i t i s assumed that the d i f f u s i o n coef-f i c i e n t "D" i s of the form D = A g ~ ^ R T , where "Q" i s the a c t i v a t i o n energy, "R" i s the perfect gas constant, WT" i s the temperature as a function of time, and where **A" i s a constant, then the equation can be integrated numerically for the assumed temperature—time d i s t r i b u t i o n . For a measured t o t a l l o s s of daughter isotopes from mineral grains of known si z e , a value of "Q" may then be found. The unknown "A" i s removed from the equations by using only r a t i o s of these i n t e g r a l s . This technique i s set fo r t h and solved by Hansen and Gast (1967) and t h e i r r e s u l t s are given i n 60 Table 8, along with two other estimates. There are a number of questionable assumptions inherent i n t h i s approach, the more important of which are: i ) That the a c t i v a t i o n mechanism was e n t i r e l y temperature dependent and c o n t r o l l e d by d i f f u s i o n . The possible r o l e of oxygen fugacity has already been mentioned, and b i o t i t e s t a b i l i t y i s known to be sen s i t i v e to shear s t r e s s . i i ) That the latent heat of c r y s t a l l i z a t i o n of the magma may be accounted for by an equivalent r i s e i n temperature of the i n t r u s i o n . This i s obviously not going to be a good approximation close to the contact. i i i ) That a l l heat was c a r r i e d by conduction. Heat sinks and sources such as reactions, phase changes, or f l u i d phases are not considered. i v ) That there was no convection i n the i n t r u s i v e , which may well not have been the case. Cooling i s assumed l a t e r a l , rather than p a r t l y toward the surface, and physical shape of the magma body underground or i n the eroded (absent) continuation are not known. v) That there was an i n f i n i t e strontium sink outside the b i o t i t e flakes, and that no ba r r i e r such as an adsorbed f i l m caused interference. v i ) That the parameter "A" i s constant under a l l temperature and phase v a r i a t i o n s , which i s not l i k e l y . v i i ) That the expulsion of material from b i o t i t e obeys the model of c y l i n d r i c a l d i f f u s i o n , with los s only about the edges. This was not substantiated by Hart (1964), and i t i s l i k e l y that a mica c r y s t a l bahaves more l i k e a mosaic i n d i f f u s i o n . This compilation gives some idea of the problems involved i n tr y i n g to Table 8 cry A c t i v a t i o n Energy and D i f f u s i o n of S r ° ' Source L o c a t i o n Mechanism M i n e r a l Energy (Q) Compared to A r 4 0 Temperature of A c t i v a t i o n i n v o l v e d Hansen & Gast (1967) Snowbank p l u t o n & Duluth Gabbro c y l i n d r i c a l d i f f u s i o n zero order r e a c t i o n 1st order r e a c t i o n d i f f u s i o n b i o t i t e 50-75 K c a l / m o l e b i o t i t e 30 b i o t i t e 50 hornblende 100 Q s i m i l a r but d i f f u s i o n c o e f f i c i e n t about t e n t imes l a r g e r for Ar^O a c t i v a t i o n at 150°-220°C & complete Sr l o s s 300°C h igher temp. Har t (1964) Front Range Colorado d i f f u s i o n r e a c t i o n b i o t i t e 25 b i o t i t e <25 as above as above H u r l e y et. a l . (1962) A l p i n e F a u l t N . Z . d i f f u s i o n b i o t i t e 27 d i f f u s i o n c o e f f i c i e n t & Q both s i m i l a r leakage at 100°C G . S . A . memoir 73 l a b d i f f u s i o n r e a c t i o n b i o t i t e b i o t i t e 30 80-150 62 make quantitative estimates of Sr° mobi l i t y . Many of the same doubts are r a i s e d i n a sim i l a r study by Hart (1964) i n the Front Range of Colorado. It w i l l be observed that he obtained a much lower value of a c t i v a t i o n energy than did Hansen and Gast. A d i f f e r e n t approach was taken by Hurley et a l (1962) who studied 87 argon and Sr leakage i n u p l i f t e d rock along the Alpine Fault i n New Zea-land. A better case might be made for control of thermal gradient here, but rocks i n the immediate v i c i n i t y of a major zone of shearing and tec t o n i c a c t i v i t y would seem a poor place to search for a simple time—temperature d i f f u s i o n model. While the r e s u l t s of these studies are understandably i n poor agreement, the data (Table 8) does serve to show that by one means or another, thermal events can cause expulsion of radiogenic strontium from potassium minerals at s u r p r i s i n g l y low temperatures. This i s substantiated by several reports 87 of inter-mineral Sr movement i n rocks which show l i t t l e or no apparent a l t e r a t i o n of the minerals concerned (for example, Lanphere et. j l . , 1964). Most metamorphic events i n the Coast Mountains appear to have been accompanied by metasomatism, and the f r a c t i o n a t i o n of strontium isotopes under these conditions i s poorly understood. C e r t a i n l y radiogenic strontium may be stripped p r e f e r e n t i a l l y from some potassium minerals, however, as observed during c h l o r i t i z a t i o n (Brooks, 1966). Table 6 shows that several forms of a l t e r a t i o n caused some loss of strontium from Coast Mountains quartz d i o r i t e s . The E f f e c t s of Fractionation on ISIR. The next important question i s whether radiogenic strontium, when l o s t from a potassium mineral, may have 63 regional m o b i l i t y . I f Sr°' may be s e l e c t i v e l y mobilized either by i t s lower a c t i v a t i o n energy and s e n s i t i v i t y to phase changes or through meta-somatism or destruction of potassium minerals, then the non-radiogenic nature of strontium at formation of so many igneous rock suites might simply 87 r e f l e c t l o s s of Sr i n a mobile phase p r i o r to homogenization. The p o s s i b i l i t y of anomalous strontium i s o t o p i c r a t i o s being caused by anatexis was discussed by Heier (1964), and since then some apparent ex-87 amples of Sr enrichment have been reported. Perhaps the most dramatic of these i s from the northern Baikal region of Russia (Yashchenko and Varshav-skaya, 1965) where ISIR values as high as 1.25 were recorded where there had been a l k a l i a l t e r a t i o n or rocks with a normal ISIR of 0.8031 0.023. It can-not be proven that the phase which caused metasomatism here derived i t s r i c h store of radiogenic strontium by s e l e c t i v e s t r i p p i n g of a t e r r a i n , but t h i s i s the environment where such a component might be expected to appear. What e f f e c t the s t r i p p i n g of Sr w i l l have on the t o t a l Sr /Sr ^ r a t i o of the material l e f t behind can only be surmised, but i t i s not inconceivable that a major part of the radiogenic strontium formed since c r y s t a l l i z a t i o n of potassium minerals might be l o s t , and further heating then y i e l d a magma and igneous suite with values of ISIR which are low or of p r i m i t i v e appearance. Inherited Oceanic Strontium. F i n a l l y there i s the problem of strontium i s o t o p i c content of sea water, and what e f f e c t t h i s may have on the ISIR values of rocks incorporating fused sediments. Although comparison of Sr /Sr r a t i o s i n modern and f o s s i l s h e l l s (Faure et. al., 1963) did not 6k show a recognizable trend with time, a more exacting study by Peterman e£. sX. (1970) demonstrated that there i s some v a r i a t i o n , p ossibly c o n t r o l l e d by periods of global tectonics introducing new supplies of p r i m i t i v e strontium. (The i s o t o p i c r a t i o for oceanic strontium i s approximately 0.709.) To a major extent the strontium i s o t o p i c character of a fin e grained oceanic sedimentary rock w i l l be normalized to the oceanic value. This has been studied not only because of i t s e f f e c t on the ISIR of rocks formed on the continental rim, but due to i t s importance i n creating strontium isotope homogeneity necessary for dating sediments by the rubidium-strontium tech-nique. The problem has been discussed by Whitney and Hurley (1964) for p e l i t i c sediments by Dasch et j l . (1966) for pelagic clays, and by Peterman e i al. (1967) for greywackes of Oregon and C a l i f o r n i a . Strontium Isotopic Ratios, for the Coast Mountains Table 9 gives the r e s u l t s of seven S r ^ / S r ^ measurements made on igneous rocks and gneisses of the Coast Mountains. Samples were selected with s u f f i c i e n t l y low Rb/Sr values that a measured S r ^ 7 / S r 8 ^ r a t i o may be considered approximately equivalent to an ISIR. Both basic and intermediate i n t r u s i v e rocks had rather p r i m i t i v e i s o t o p i c r a t i o s for plutonic material. The values were scattered, quite possibly as a r e s u l t of strontium from digestion of metasedimentary rocks. In t h i s respect i t i s of i n t e r e s t that the two gneiss samples, which are more obviously associated with metamorphic complexes, had somewhat higher 87 86 Sr /Sr r a t i o s . This r e l a t i o n s h i p was also shown by Menter (1970) i n the Okanogan Range where material predating metamorphism had an ISIR of 0.7039, while synmetamorphic gneisses were s u b s t a n t i a l l y higher (0.7066 and 0.7080) 65 Table 9 Mass Spectrometry Results fo r Strontium No. of Sample Descrf p t i on ~ 87 . 86 Sr /Sr Standard Dev ia t i on Rb/Sr 354 Qtz . d i o r i t e 0.7033 ;o: 001:3 0.031 24 Granodior i te .7031 .0015 .012 211 0_tz. d i o r i t e .7056 .0010 .013 57 Conglomerate .7048 .0019 .023 62 Gnei ss Nass R. .7068 .0004 .026 227 Gneiss Waddington .7060 .0017 .035 596 Gabbro .7040 .0020 0.040 Ei mer & Amend SrCO 3 0.7077 0.0005 ——. A l l rocks analysed are from the Coast Mountains. A l l r a t i o s were nor-malized to S r 8 6 / S r 8 8 = 0.1194. 66 with postorogenic granites y i e l d i n g intermediate values. Hedge e£. aJL (1970) have measured the strontium i s o t o p i c r a t i o for several Cenozoic lavas of Oregon and Washington. Twelve samples of Andesite and dacite from the western Cascade Range had S r 8 7 / S r 8 ^ r a t i o s i n the reasonably narrow range of 0.7032Ito :Q.7039,'. which:seems>to approximate the l e v e l of the more p r i m i t i v e Coast Mountains plutonic rock strontiums. It i s also t y p i c a l of values measured for t h i s r a t i o i n oceanic basalts, although those of the Gordo and Juan de Fuca Rises (the r i s e s most c l o s e l y associated with the Cascade Range and Coast Mountains) have s l i g h t l y lower values, ranging from 0.7012 to 0.7031 (Hedge and Peterman, 1970). 87 86 Average Sr /Sr r a t i o s i n the Coast Mountains b a t h o l i t h i c complex are changing very slowly as a r e s u l t of the unusually low Rb/Sr r a t i o s i n t h i s environment. Its growth rate i s shown on Figure 10, and i s approximately one f i f t h or one s i x t h that assumed for t y p i c a l continental s i a l (Table 3). On the average, strontium i n the Coast Mountains 87 / 86 b a t h o l i t h i s a l t e r i n g i t s Sr /Sr r a t i o by 0.001 every 500 m.y. Summary i ) The rate of change of S r 8 7 / S r 8 6 i n any environment depends on the r a t i o Rb/Sr t h e r e i n . As there i s a very pronounced difference between Rb/Sr r a t i o s i n the s i a l i c crust and mantle (or source region for the crust"), the strontium i s o t o p i c r a t i o of an igneous rock at time of i t s formation would appear to be a measure of the length of s i a l i c prehistory of i t s strontium. i i ) The majority of igneous rock suites cannot have had much c r u s t a l 67 prehistory by the above c r i t e r i o n . i i i ) I t seems p l a u s i b l e that the s e l e c t i v e destruction of potassium minerals might s t r i p a t e r r a i n of much of i t s radiogenic strontium, at l e a s t p a r t i a l l y explaining low ISIR values. i v ) Investigations of the mechanism and extent of mobility for radio-genic strontium i n a metamorphic event have shown that i t may become mobile at temperatures as low as 100°C, and under c e r t a i n unspecified conditions of mineral stress or a l t e r a t i o n . v) Coast Mountains plutonic rocks have ISIR values as low as many oceanic rocks, and similar to those of Cenozoic andesites from the Cascade Range. v i ) A scatter i n ISIR values for plutonic rocks i n the Coast Mountains-; and higher values for gneisses suggest that the d i g e s t i o n of metamorphic rocks may have affected t h i s r a t i o . v i i ) Rb/Sr values for the Coast Mountains are so low that the i s o t o p i c r a t i o of strontium i n that environment i s changing at only about one f i f t h or one s i x t h the rate that i t i s i n t y p i c a l s i a l i c material. 68 CHAPTER IV GEOLOGY AND MORPHOLOGY OF THE COAST MOUNTAINS The Coast Mountains as defined by Holland (1964) extend from Fraser River northward approximately one thousand miles to beyond the Yukon Border. This research project has examined only that part of the mountain chain south of Nass River and the southern t i p of Alaska, thus including the P a c i f i c Ranges and the Kitimat Ranges, whose l i n e of d i v i s i o n i s the B e l l a Coola Valley, (map 4). Te r t i a r y History In the early T e r t i a r y , rapid subduction of an oceanic c r u s t a l p late known as the F a l l e r o n plate took place along the western margin of North America (McKenzie and Morgan, 1969). Rapid subduction beneath a continental margin tends to cause strong u p l i f t . This may be shown on t h e o r e t i c a l grounds (Danes, 1969) and observed throughout the C o r d i l l e r a i n the c o r r e l a -t i o n between deep earthquake zones (which are g l o b a l l y r e l a t e d to rapid subduction l i n e s ) and parts of the C o r d i l l e r a which are of greatest eleva-t i o n and which have sustained recent u p l i f t (21,000 feet for Pliocene se d i -ments i n the v i c i n i t y of Malaspina, Alaska). Early T e r t i a r y u p l i f t appears to have been strongest along the axis of the Coast Mountains, and the d i s t r i b u t i o n of T e r t i a r y potassium—argon age dates (to be discussed) i n the core of the Kitimat Ranges suggests that t h i s axis was r e g i o n a l l y u p l i f t e d through the c r i t i c a l potassium—argon isotherms during subduction. Not s u r p r i s i n g l y , andesitic volcanism was common i n the C o r d i l l e r a of 69: B r i t i s h Columbia during t h i s period. This volcanism died out by the Oligocene, however, (Souther, 1970) and sometime during the mid-Tertiary an erosion surface or surfaces formed over the Coast Mountains. The next volcanic episode was the eruption i n l a t e Miocene or early Pliocene times of plateau basalts on the eastern side of the range. Pliocene u p l i f t elevated parts of these sheets as high as 8500 feet (Tipper, 1966) i n a portion of the range where the highest summits are about 10,000 feet i n e levation. This means that the r e l i e f of the Coast Mountains was only 1500 feet maximum with respect to the i n t e r i o r plateau i n the l a t e Miocene, even i f there was no d i f f e r e n t i a l e levation between the basalts and the highest sections of the range during Pliocene u p l i f t . This low r e l i e f , and the erosion surfaces mentioned, suggest that the mid-T e r t i a r y was not a time of much tectonic a c t i v i t y i n the Coast Mountains. U p l i f t of the present mountain range took place mainly i n the l a t e Pliocene. The most recent s t y l e of igneous a c t i v i t y includes extrusion of acid and intermediate volcanics and i n t r u s i o n of high l e v e l , discondant stocks of granite and syenite. Petrology The Coast Mountains of B r i t i s h Columbia comprise what i s l i k e l y the largest Phanerozoic b a t h o l i t h i c complex i n the world (Roddick and Hutchison, 1968), and the i n i t i a l geological mapping i s presently being undertaken by the Geological Survey of Canada. One hundred six t y of the rock samples whose analyses are l i s t e d i n Appendix 1 were donated by Dr. J.A. Roddick and Dr. W.W. Hutchison from t h e i r c o l l e c t i o n s made during mapping of the Prince Rupert, Douglas Channel, Laredo Sound, Hecate S t r a i t , Rivers I n l e t , Mt. 70 Waddington, and Ale r t Bay map sheets as part of the Government's Coast Mountains Pr o j e c t . The writer worked as a technical o f f i c e r on t h i s program during the f i e l d seasons of 1965 and 1967, and during the F a l l and Winter of 1965. Recent pu b l i c a t i o n s concerning the geology of the Coast Mountains include Hutchison (1970), Hutchison (1967), Baer (1967), Baer (1968), Roddick e l a i (1967), Roddick (1965), Roddick (1966), Tipper (1968) and Roddick and Hutchison (1968). Plutonic rocks. Table 10 outlines the plutonic rock c l a s s i f i c a t i o n system used i n subdividing the b a t h o l i t h i c complex. This i s the system adopted by the forementioned Coast Mountains Pr o j e c t , and the method used to estimate mineral percentages i s discussed under laboratory techniques. Gabbros are defined on the basis of s p e c i f i c g r a v i t y , which i s determined by f i r s t weighing a dry rock specimen and then soaking i t i n water for at lea s t half an hour before determining i t s volume by recording the change i n weight when suspended i n water. Table 11 gives the approximate percentages of the various plutonic rocks i n the b a t h o l i t h i c complex. This was obtained for the northern and central Coast Mountains by g r i d counting on a geological map, and for the southern Coast Mountains from Roddick (1965). Granodiorites and quartz d i o r i t e s are seen to comprise over two-thirds of the plutonic rocks i n the Coast Mountains, and would l i k e l y be closer to three-quarters i f one con-siders that much of the material i n the gneisses and migmatites i s of t h i s composition. Individual plutons i n the Coast Mountains show a wide v a r i e t y of s i z e , Table i o Classif icat ion of Igneous Rocks Quartz Content K feldspar Rock Name (%) (as % of total feldspar) Granite >5 >67 Quartz Monzonite >5 33-67 Granodiorite >5 5-33 Quartz Diorite >5 0-5 Diorite 0-5 0-5^ ,' Gabbrb is here defined as a plutonic rock of specific gravity >2.905 Td Table 11 Ccmposi t i on of Coast Mountains Ba tho l i th i c Complex A. Between Nass and Homathko Rivers Grani te and Quartz Monzonite 3«5% Granodior i te . . . . 2 9 . 0 Quartz D i o r i t e . . . . . 3 8 . 0 Di o n te • .11.5 Gabbro ... 1.0 Gneiss and M i g m a t i t e s . . . . . ......17.0 B. Vancouver and Coquitlam Region (Roddick, I965) Granite 2.4% G r a n o d i o r i t e . . . . . . . 26.5 Quartz D i o r i t e 51.4 Gabbro, D i o r i t e , Migmatite. • 19.7 73 shape, structure, boundary r e l a t i o n s , and degrees of homogeneity. Granites and syenites are rare, occurring only i n a few stocks which are usually associated with tectonic lineaments. They have the appearance of permissive i n t r u s i o n and are usually homogeneous, with d i s t i n c t boundaries* Quartz monzonite bodies are t y p i c a l l y larger, l e s s d i s t i n c t , and les s homogeneous. B i o t i t e i s t h e i r p r i n c i p a l mafic mineral. Quartz monzonite occurs r i g h t out along the coast, so that the "quartz d i o r i t e l i n e " i s l e s s well-defined than elsewhere on the P a c i f i c rim (Moore, 1959). In rocks more basic than quartz monzonite there i s a d e f i n i t e trend . i n character and form of plutonism which p a r a l l e l s increasing color index and decreasing a c i d i t y . This trend includes: Increasing heterogeneity. More d i r e c t i v e f a b r i c s and textures. More i n c l u s i o n s . Increased hornblende/biotite r a t i o Boundary r e l a t i o n s h i p s which are l e s s d i s t i n c t and quite v a r i a b l e . These trends appear to follow color index (mafic content) more c l o s e l y than the feldspar r a t i o on which rock c l a s s i f i c a t i o n i s based. Contacts between plutonic rock species are commonly gradational or marked by a zone of migmatic textures but they also may be abrupt and d i s t i n c t . The same may be said for t h e i r contacts with metamorphic rocks, and i t i s not uncommon to f i n d a contact appearing d i s t i n c t l y i n t r u s i v e i n one point, yet at another showing progressive g r a n i t i z a t i o n structures i n place. The more acid plutons or parts of plutons may have d i a p i r i c struc-tures or evidence of permissive i n t r u s i o n , but there seems l i t t l e reason 1 i i i i i i v v 74 to believe that the majority of the coastal b a t h o l i t h i c rocks were emplaced by major upward movements of i n d i v i d u a l magma bodies (as opposed to either a l k a l i n e v o l a t i l e s or tectonic blocks) with respect to surrounding rocks. In considering the genesis of i n t r u s i v e suites i n the Coast Mountains, one of the most s t r i k i n g features i s the appearance of increasing a c i d i t y (addition or l a t e formation of quartz and potassium minerals) during t h e i r development. With the exception of alpine u l t r a b a s i c s , two plutonic rock species with a d i s t i n c t contact w i l l almost i n v a r i a b l y be rela t e d i n such a way that the more acid one seems younger. E i t h e r i t has been intruded i n t o , or formed by a l t e r a t i o n of, the more basic rock. Furthermore, i t i s not uncommon to observe plutonic rocks which have either formed by fusion and metasomatism of country rocks, or at least digested a major amount of them. Petrogenesis of the Coast Mountains b a t h o l i t h i c rocks near Vancouver i s treated i n d e t a i l by Roddick (1965). In addition to the forementioned time trend toward more acid i n t r u s i o n s i n the Coast Mountains, acid lava eruptions and permissive i n t r u s i o n of small granite and syenite plugs has been the most recent s t y l e of igneous a c t i v i t y , or more properly the most recent events that have been exposed at the surface. On the other hand, most of the material found i n boulder conglomerates or i n the "basement" gneisses of the Kitimat Ranges i s not very basic. Apparent increase i n the a c i d i t y of plutonic rocks may well be simply a function of the mode of development of i n t r u s i v e suites through the acti o n of v o l a t i l e s , and need not r e f l e c t a time trend toward more acid or s h i e l d - l i k e magmas. 755 Metamorphic and sedimentary rocks. Most sedimentary, metasedimentary, and metavolcanic rock units associated with the Coast Mountains are found along the i n t e r i o r side. These are mainly Mesozoic i n age, and have been studied by several workers including Tipper (1968), Tipper (1969), D u f f e l l (1959), D u f f e l l and Souther (1964), and D u f f e l l and McTaggart (1952). A few T e r t i a r y volcanic and sedimentary units are found along the coast, but within the western ha l f of the b a t h o l i t h i c complex metamorphic rocks usually occur either i n screens or as part of complicated gn e i s s i c b e l t s . The l a t t e r are varied zones of migmatites with some of the c h a r a c t e r i s t i c s of a basement complex, and represented i n the northern Coast Mountains by what Hutchison (1970) r e f e r s to as the Central Gneissic Complex. The term "screens** i s applied to high-angle sheets of metamorphic rock, usually of considerable horizontal continuity, which plunge downward for at l e a s t the few thousand feet over which Coast Mountains r e l i e f allows observation. The mode by which a screen becomes incorporated into or between plutons i s puzzling. They are by no means confined to the Coast Mountains, and Pl a t e 1 shows one i n the Mt. Everest region of Nepal which i s derived from a pluton roof. Metamorphic rocks within the coastal b a t h o l i t h i c complex are mainly greenstones, a r g i l l i t e s , graywackes, t u f f s , and some limestone u n i t s . The metasedimentary rocks grade into s c h i s t s , amphibolites, skarns, and gneisses. A wide assortment of migmatite was observed. Metamorphic grade i n the Coast Mountains i s generally low, although a few regions exhibit s i l l i m i n i t e or c o r d i e r i t e . This i s treated by Hutchison (1970). 5 P l a t e 1 Metamorphic Screen Forming from Roof Pendant Mt . Nuptse , Nepal photo by A. C u l b e r t 77: Volcanic Rocks. Volcanism was common along the margins of the Coast Mountains before, during, and aft e r the period of orogenesis, and a large portion of the metamorphic rocks within the b a t h o l i t h i c complex are green-stones. D i o r i t i z a t i o n of these i s commonly observed. The metavolcanics of the Coast Mountains appear to be d i s t i n c t l y more basic than Pleistocene volcanics, although the nature of acid eruptions leave t h e i r lavas more vulnerable to erosion. Souther (1970) observes that r e l a x a t i o n of com-pressive stresses since the :locene has led to acid volcanism, and these rocks have been studied by Mathews (1958) and Souther (1967). An important point made by Souther i s that there appears to be no v a r i a t i o n i n volcanic type inland as described on other active continental margins by Kuno (1966). In conjunction with the lack of deep earthquake f o c i under the Coast Mountains, t h i s supports the view that there presently i s no very active zone of deep c r u s t a l subduction under t h i s part of the P a c i f i c rim. Summary. i ) The Coast Mountains form what i s l i k e l y the largest Phanerozoic b a t h o l i t h i c complex i n the world. Lithology i s dominantly quartz d i o r i t e and granodiorite. i i ) Potassium minerals were the l a s t to form i n the coast plutonic rocks, and mobility of late-stage a l k a l i n e phases i s evident. Signs of diges t i o n of metamorphic country rock are also widespread. i i i ) Those rocks with greater potassium content tend to be l e s s f o l i a t e d , more homogeneous, and contain fewer i n c l u s i o n s . i v ) Much of the matrix of the Coast Mountains b a t h o l i t h i c complex 78 appears to have been ra i s e d r e g i o n a l l y or i n blocks, although the more acid (potassium-rich) plutons tend to show d i s t i n c t l y d i a p i r i c or i n t r u s i v e r e l a t i o n s h i p s . v) Where contacts between plutonic rock species are d i s t i n c t , the more acid usually appears to be l a t e r . A series of small, discordant plugs of granite and syenite do form the l a s t recognized i n t r u s i v e event, but the apparent regional time trend toward more acid i n t r u s i o n s may well be a function of the mobility of the l a t e stage f l u i d s which formed most of the quartz and potassium minerals. v i ) Several metamorphic screens of considerable depth and continuity are observed i n the Coast Mountains b a t h o l i t h i c complex. The mode of t h e i r emplacement i s not obvious. v i i ) Acid volcanism has been common i n the Coast Mountains since the T e r t i a r y . Lava composition does not show the v a r i a t i o n inland observed i n other v o l c a n i c a l l y active continental margins. Structure and Age The dominant trend of both tex t u r a l and tectonic structures i n the Coast Mountains i s p a r a l l e l to the axis of the range i t s e l f . Lineaments, screens, elongation of plutons, and f o l i a t i o n a l l strongly exhibit t h i s trend, and lack of useful s t r a t i g r a p h i c or s t r u c t u r a l control traversing t h i s o r i e n t a t i o n has almost completely obscured the extent of movements along northwesterly f r a c t u r e s . A major system of transcurrent f a u l t s p a r a l l e l the Coast Mountains on t h e i r i n t e r i o r side (White, 1959; Tipper, 1968) and Stratigraphic-. control i n that case allows the deduction of large r i g h t -l a t e r a l displacements of Mesozoic and perhaps early T e r t i a r y age. Whether 79 any similar systems have operated within the Coast Mountains proper i s not known. Faults transverse to t h i s northwest trend usually have a v e r t i c a l displacement where seen i n the i n t e r i o r , and perhaps for t h i s reason cannot be observed c l e a r l y i n the- generally v e r t i c a l structures of the Coast Mountains b a t h o l i t h i c complex. One exception may be the Owikeno lineament which possibly o f f s e t s a limestone band i n the v i c i n i t y of Owikeno Lake!by 18 miles (Roddick and Hutchison, 1968). Although l i t t l e may be said about the extent of f a u l t movements i n the Coast Mountains, f a u l t i n g has been extensive both i n the adjacent i n t e r i o r and on Vancouver Island (Muller, 1967). There have very d e f i n i t e l y been extensive v e r t i c a l displacements associated with the Coast Mountains, and the form and s i g n i f i c a n c e of some of the more recent v e r t i c a l movements w i l l be discussed i n d e t a i l l a t e r . Secondary f o l i a t i o n s , f o l d s , and a few lineaments trending north or north-northeast are observed i n the Kitimat Ranges. Fold a x i a l surfaces with the NNE trend t i l t i n either d i r e c t i o n , but those with the NW o r i e n t a t i o n are overturned to the west (Hutchison, 1970). The r e l a t i o n s h i p of these t e x t u r a l trends to the dominant northwesterly one suggests that the former i s of greater age. This sequence i s similar to the f i r s t two phases of deformation outlined by Ross (1968) and Ross and K e l l e r h a l s (1968) i n south-central B r i t i s h Columbia. The t r a n s i t i o n between tectonic d i r e c t i o n s , which there appears to f a l l near the Mesozoic—Paleozoic boundary, con-veniently marks the f i r s t time the Coast Mountains axis made i t s e l f evident i n surrounding geology. Peacock (1935) made a d i r e c t i o n a l analysis of Coast Mountains l i n e a -8o ments and found that there were two dominant sets of orthogonal components. One of these had axes which were everywhere between N 10° W and N 4° E and between due east and N 78° E. The other set of axes was concordant with the major trend of the Coast Mountains, the l o n g i t u d i n a l member swinging from about N 72° W at l a t i t u d e 48° to due north at l a t i t u d e 52°. In the Kitimat Ranges i t was more constant, at approximately N 54° W. D i s t i n c t breaks i n the trend of these conformal lineaments were observed at approximately the l a t i t u d e s of the B e l l a Coola River and the Skeena River. Bostrom (1968) has sought to r e l a t e these lineament d i r e c t i o n s to a stress pattern, but as previously mentioned, they represent d i r e c t i o n s of s t r u c t u r a l and t e x t u r a l weakness and t h i s anisotropy makes s t r e s s - s t r a i n analysis dubious. Further subdivision of the Coast Mountains by regional l i n e a t i o n patterns, and the use of laser analysis i n t h i s work i s discussed i n Appendix XI. Rubidium/strontium r a t i o s of Coast Mountains igneous rocks are much too low to use rubidium-strontium age dating on whole rocks, and the extensive migmatization and a l k a l i n e mobility observed i n the f i e l d and when staining potassium minerals leaves l i t t l e hope for mineral isochrons. With almost no f o s s i l s preserved along the axis of the Coast Mountains, chronology r e l i e s heavily on potassium-argon. This y i e l d s a v a r i e t y of ages, mainly Laramide, but ranging roughly from 40 m i l l i o n years to 140 m i l l i o n years with a few discordant acid i n t r u s i o n s d i s t i n c t l y younger. Rock ages i n the Kitimat Ranges appear to f a l l into episodes with some tectonic control (map 1), and older ages out along the coast. This rather strange arrangement w i l l be discussed l a t e r . 81 Although T e r t i a r y orogeny has destroyed almost a l l memory of preceding events i n the Coast Mountains b a t h o l i t h , the region appears to have been at le a s t p e r i o d i c a l l y an area of elevation and l i k e l y i n t r u s i o n since the T r i a s s i c . This i s la r g e l y based on evidence i n Mesozoic rocks to the east, but there are also g r a n i t i c cobbles i n metaconglomerates of the screens with-i n the present b a t h o l i t h s and the abovementioned gne i s s i c complexes which have some features of a basement. These gneisses may unconformably underlie the Permian i n the Whitesail Lake map area. Furthermore, early Paleozoic rocks are found along the coast of southeastern Alaska, where dates as old as the l a t e Precambrian are reported for hornblende and zircons i n basic rocks (Lanphere, 1968). Southeastern Alaska may represent an e n t i r e l y d i f f e r e n t geological province, but i t may also represent an e a r l i e r regime overprinted by the Coast Mountains tectonic axis. Coast Mountains Morphology One of the most d i s t i n c t and widespread features of Coast Mountains morphology i s the tendency of peak elevations to be similar over large areas. This was observed by G.M. Dawson as early as 1896 and by many authors since, being interpreted as representing a dissected erosion surface or surfaces of mid T e r t i a r y age. Its preservation i s perhaps not surprising i n view of the regional homogeneity of much of the plutonic rock i n the Coast Mountains to erosion when compared to mountain ranges composed of sedimentary units. The P a c i f i c Ranges, and to a lesser extent the Kitimat Ranges, may r e a d i l y be divided into three morphological provinces. Proceeding from the 83 east these comprise an elevated area of rugged summits, g l a c i e r s , and snow-f i e l d s which w i l l be r e f e r r e d to as the eastern u p l i f t ; a l e s s spectacular b e l t of deep v a l l e y s , ridges, i s l a n d s , lakes and i n l e t s which w i l l be r e f e r r e d to as the f j o r d zone; and on the coastal fringe between approxi-mately l a t i t u d e s 51° and 54° l i e s the Milbanke S t r a n d f l a t . (map 4) Eastern U p l i f t . This region constitutes the most elevated portion of Coast Mountains and i n the P a c i f i c Ranges i s the well-defined region between the heads of major f j o r d s and the eastern rim of the mountain chain. In the Kitimat Ranges i t s western boundary i s not everywhere d i s t i n c t . Summit elevations reach 13,104 feet i n Mt. Waddington, and several other areas south of B e l l a Coola River a t t a i n heights over ten thousand fe e t . G l a c i e r i -z a tion i s extensive here, and a series of major snowfields dominate much of the western rim of the u p l i f t . North of B e l l a Coola River the highest summits reach j u s t over nine thousand feet, and although g l a c i e r s are present there are no large snowfields i n the Kitimat Ranges. The eastern u p l i f t i s comprised dominantly of g r a n i t i c rocks on the west and Mesozoic metasedimentary and metavolcanic units on the east. The landform i s t y p i c a l l y deep v a l l e y s and jagged summits. Peaks are seldom joined by ridges which approach the summit elevation, d i f f e r i n g i n t h i s respect from landforms t y p i c a l of the western Coast Mountains and Vancouver Island. This i n d i v i d u a l character and jaggedness of summits on the eastern u p l i f t gives the impression that a l l record of an o r i g i n a l erosion surface may have been l o s t . Many of the sharp peaks i n fact do not reach the main summit envelope, but the highest peaks conform to an e a s i l y contoured surface whose main features are gentle, continuous v a l l e y s and domes. The 8k highest and most rugged region of the Coast Mountains i s the Waddington Range, and even here the summit envelope may be seen both from the con-touring (Figure 11) and from Photo Plates 2 and 3 to conform to a smooth dome, which has been abruptly truncated on the west by the edge of the eastern u p l i f t . Fjord gone. In the P a c i f i c Ranges, t h i s constitutes the region westward from the eastern u p l i f t to the Coastal Trough or s t r a n d f l a t s adjacent thereto. Mountains are of lower elevation than farther east and have a greater tendency to form summits of subdued r e l i e f with respect to high connecting ridges. Few peaks stand out as singular when observing a skyline i n t h i s region; the most pronounced being commonly alpine u l t r a -basic i n t r u s i o n s . Valleys are deep and of r e l a t i v e l y gentle gradient; lakes are very common. In the Kitimat Ranges, the d i v i s i o n between f j o r d zone and eastern u p l i f t i s not everywhere sharply defined. Dean Channel and Gardiner Canal cut deeply into the Coast Mountains, and the K i t i m a t — T e r r a c e trench was also flooded during the Pleistocene. Elevations of greater than eight thousand feet and topography t y p i c a l of the eastern u p l i f t elsewhere are confined to the eastern rim of the main range and l i e dominantly i n Meso-zoic volcanic and metasedimentary rocks. Genesis of fj o r d s on the high-latitude mountain coastl i n e s of the world has been va r i o u s l y attributed to drowning of v a l l e y s , emergence of submarine canyons, submarine g l a c i a l overdeepening, and tectonic r i f t i n g . As there i s an almost complete global correspondence between the l o c a t i o n of fjordlands and those mountain c o a s t l i n e s which sustained continental 85 F igure 11 CONTOURS ON THE SUMMIT ENVELOPE NEAR WADDINGTON DOME S c a l e : 1 i n c h / 10 mi les ooooooo A ^ x i a l F rac ture K Knight F rac ture 0 10 P l a t e 2 Waddington Range from N o r t h e a s t , Showing D i s s e c t e d Dome phote by R. Hagen P l a t e 3 Mt . Waddington from Nor thwes t , Showing T r u n c a t i o n of Dome by the A x i a l F r a c t u r e Summit envelope i n d i c a t e d 88 g l a c i a t i o n , i t might appear that a g l a c i a l o r i g i n i s mandatory. Further-more, fjords have cross-sectional shapes t y p i c a l of g l a c i a l v a l l e y s and g l a c i e r s are known to be capable of overdeepening. There are a number of problems i n a purely g l a c i a l theory of f j o r d genesis, however, and most of these have been compiled by Windslow (1965). The most important objections are those concerned with the extreme depth of some f j o r d s . Although the greatest recorded depth for an i n l e t of the B r i t i s h Columbia coast i s approximately 2500 feet i n Finlayson Channel, depths greater than 4000 feet are reported i n Norway, and over 5000 feet i n Patagonian C h i l e . Considering that even the outer edge of the Continental Shelf of the B r i t i s h Columbia coast i s i n the neighbourhood of only 600-700 feet deep (and t h i s edge i s considerably shallower on a world average), f j o r d depths are phenomenal. Furthermore, bedrock i n f j o r d s may be con-siderably deeper than bottom soundings. G l a c i a l overdeepening of v a l l e y s has been demonstrated, for example i n the Yosemite Valley of C a l i f o r n i a , where a rock basin some 450 meters deep e x i s t s i n g r a n i t i c bedrock (Guten-berg e£ §1, 1956). Much of the c l a s s i c a l work on genesis of g l a c i a l v a l l e y s has, i n fa c t , been c a r r i e d out i n the v i c i n i t y of Yosemite (Matthes, 1930), and Yosemite i s most c e r t a i n l y a c l a s s i c a l g l a c i a l v a l l e y . Whether i t i s a t y p i c a l one, however, i s dubious. The spectacular succession of truncated ridges and the great hapging v a l l e y of the Merced River represent a landform seen occasionally i n Prince Rupert area and northward, but seldom i n the coastal ranges farther south. G l a c i e r s have cut deeply into a few v a l l e y flanks to produce i s o l a t e d features such as seen at the town of Squamish, 30 miles northwest of Vancouver. Here g l a c i a l action (with the assistance 89 of prominent lineaments) has carved a granite wall 1500 feet high and l e f t the adjacent v a l l e y of Shannon Creek hanging by 800 feet. Shannon Creek i s a true hanging v a l l e y , but these are not common i n the P a c i f i c Ranges, most formations so termed being simply cirques. It would be much more convenient to a t t r i b u t e f j o r d genesis to drown-ing of g l a c i a l v a l l e y s , and f j o r d s have i n fact been referred to i n that manner. This, however, requires extensive Pleistocene and Recent subsi-dence, whereas evidence supports general u p l i f t due to i s o s t a t i c adjustment following r e t r e a t of continental g l a c i a t i o n . The o r i g i n of f j o r d s w i l l be discussed i n d e t a i l l a t e r , but at t h i s time i t would be h e l p f u l to recognize three reasonably d i s t i n c t classes of Coast Mountains f j o r d s and define them. i ) Master Fjords These comprise the major i n l e t s that reach well back into the Coast Mountains. They tend to be deep and display a reasonably gentle bottom gradient sloping seaward to the zone of coastal i s l a n d s . Both th e i r heads and t h e i r seaward termination of deep channels appears to be t e c t o n i c a l l y c o n t r o l l e d , as w i l l be o u t l i n e d . Master fjords are 1 - 2 miles wide and tend to maintain an even width despite angular o f f s e t s i n d i r e c t i o n , i i ) Longitudinal Channels These are channels, usually open at both ends, which run p a r a l l e l or sub-parallel with the Coast Mountains s t r u c t u r a l trend. Control by l i n e a -ments i s commonly obvious, and hence these channels are t y p i c a l l y straight or i n broad arcs. Their width varies greatly and the bottom p r o f i l e i s usually i r r e g u l a r , tending to exhibit arches and basins. This form of 90 waterway i s best developed along the north coast, G r e n v i l l e and Princess Royal Channels being major examples. Channels such as these would form i f subsidence occurred along the same fractures on which the front of the Coast Mountains was u p l i f t e d , provided a period of slope r e t r e a t or stream erosion of the fracture system separated u p l i f t and subsidence. It i s of in t e r e s t that the channels form sub-parallel troughs which become wider westward, and submerged versions appear beyond the s t r a n d f l a t . The narrower inland channels tend to display i n l e t s branching eastward, and lakes on the west side, whereas the outer channels tend to be flanked on the west by drowned r e l i e f , and by smooth shorelines on eastern edges. Both landforms suggest westward t i l t i n g of inter-channel blocks. South of Johnstone S t r a i t the master f j o r d s empty not into a region of lo n g i t u d i n a l channels but into a series of c i r c u l a r i s l a n d — c h a n n e l patterns such as observed i n Howe Sound or Toba I n l e t . i i i ) Scoop In l e t s and Lakes The majority of coastal i n l e t s appears to have formed by scooping out of basins within deep v a l l e y s . With a few exceptions, these do not form i n the eastern part of the f j o r d zone. One common feature i s a shallow, con-s t r i c t e d o u t l e t r e f e r r e d to as the threshold or "rock bar". Scoop i n l e t s are l i k e l y i d e n t i c a l i n o r i g i n to the many v a l l e y lakes ( as opposed to cirque lakes) of t h i s region. In the Kitimat Ranges e s p e c i a l l y , both lakes and i n l e t s occur i n low, m i s f i t v a l l e y s which are i n part lineament c o n t r o l l e d , but often very tortuous i n plan. Thresholds and rock bars are common at the mouths of small i n l e t s , and there seems to be a continual progression from i n l e t s through t i d a l lagoons to lakes as the threshold becomes more prominent. Maximum Fjord depth in fathoms 92' O r i g i n of both the lakes and the i n l e t s i s l i k e l y g l a c i a l gouging i n con-f i n e d v a l l e y s , and t h e i r form of t h r e s h o l d should not be confused w i t h depth d i s c o n t i n u i t i e s i n wide channels, such as give seaward t e r m i n a t i o n to deep zones of master f j o r d s . A bimodal d i s t r i b u t i o n of maximum i n l e t depths (Figure 12) supports the suggestion of two d i s t i n c t types of f j o r d s . In t h i s c o m p i l a t i o n l o n g i t u d i n a l channels and i n l e t s were excluded, only those f j o r d s t r a v e r s e to the a x i s of the Coast Mountains being considered. Also excluded were bays without a d i s t i n c t maximum depth, deepening continuously i n t o a more dominant body of water. Mi1banke S t r a n d f l a t . S t r a n d f l a t s are b e l t s of subdued r e l i e f and low a l t i t u d e which f l a n k some f j o r d regions on the seaward s i d e . Their o r i g i n i s p e r p l e x i n g ( H o l t e d a h l , 1960) as they appear to postdate excavation of the f j o r d s and are rather wide to be wave-cut benches, reaching 50 ki l o m e t e r s width i n Norway. Along the Coast Mountains, a s t r a n d f l a t extends from approximately Drury I n l e t to Porcher Islan d and has a d i s t i n c t i v e morphological t e x t u r e , f e a t u r i n g knobby h i l l s and lineaments which are c l e a r l y etched despite the low r e l i e f . This morphology, together with the deep weathering i n places missed by o v e r - r i d i n g g l a c i e r s (Roddick, 1969), suggests that the s t r a n d f l a t represents an o l d e r o s i o n surface. Lakes and the few i n l e t s found on the Milbanke S t r a n d f l a t tend to be shallow, angular, and narrow. The western edge of t h i s r e g i o n i s i n many pl a c e s d i s t i n c t , f o l l o w i n g major lineaments or summit l e v e l d i s c o n t i n u i t i e s which may be traced beyond the s t r a n d f l a t . In some l o c a l i t i e s these l i n e s 93 have been t e c t o n i c a l l y a c t i v e r e c e n t l y , as w i l l be m e n t i o n e d . Even where t h e s t r a n d f l a t i s bounded by o b v i o u s l i n e s o f u p l i f t , however , t h e r e i s e v i d e n c e t h a t i t s l e v e l has been b e v e l l e d i n t o a d j a c e n t v a l l e y s , l i k e l y by t r a n s g r e s s i o n o f t h e s e a . The s t e e p - s i d e d , knobby s t r a n d f l a t h i l l s may v e r y w e l l r e p r e s e n t a mature e r o s i o n p a t t e r n f o r g r a n i t i c t e r r a i n , m o d i f i e d by wave a c t i o n . The w e s t e r n edge o f t h e C o a s t M o u n t a i n s s t r a n d f l a t i s t y p i c a l l y s u b -t e n d e d by a l o n g i t u d i n a l c h a n n e l , and a n o t h e r l i n e o f s h o a l s f a r t h e r west may r e p r e s e n t a submerged c o n t i n u a t i o n . Some p a r t s o f t h e p r e s e n t s t r a n d f l a t s i n f a c t appear t o be s u b m e r g i n g , and t h e f o r e m e n t i o n e d r e g i o n s o f d r o w n i n g a l o n g t h e e a s t e r n edge o f l o n g i t u d i n a l c h a n n e l s a r e e a s i l y c o n f u s e d w i t h s t r a n d f l a t s e x c e p t f o r t h e i r m o r p h o l o g i c a l p a t t e r n s o f submergence . Summary o f S t r u c t u r e . ,Age. and M o r p h o l o g y i ) The dominant s t r u c t u r a l t r e n d o f t h e C o a s t M o u n t a i n s i s n o r t h -w e s t e r l y , and c o n c a v e t o t h e e a s t . I n t h e K i t i m a t Ranges t h i s d i r e c t i o n i s o v e r p r i n t e d o n an o l d e r , more n o r t h e r l y t r e n d . T h e r e has been t r a n s c u r r e n t movement a l o n g f a u l t systems b o u n d i n g t h e P a c i f i c Ranges on t h e e a s t , b u t l i t h o l o g i c a l c o n t r o l does not a l l o w much to be s a i d about the p o s s i b i l i t y o f such d i s l o c a t i o n s w i t h i n the b a t h o l i t h . i i ) P o t a s s i u m — a r g o n a g e - d a t e s i n t h e K i t i m a t Ranges f a l l i n t o the r a n g e 40—140 m . y . and become younger i n l a n d from t h e c o a s t . A few d i s c o r d a n t a c i d p l u g s a r e d i s t i n c t l y y o u n g e r . i i i ) C o a s t M o u n t a i n s morpho logy may be r o u g h l y d i v i d e d i n t o a c o a s t a l s t r a n d f l a t ; a b e l t o f deep f j o r d s , r i d g e s , and l a k e s ; and a r e g i o n o f h i g h 9k peaks and alpine t e r r a i n . Summit l e v e l s are t y p i c a l l y similar over large areas, suggesting d i s s e c t i o n of an upland surface of mid-Tertiary. i v ) Fjords f a l l roughly into two categories, d i f f e r e n t i a t e d by depth, width, o r i e n t a t i o n , bottom p r o f i l e , and character of t h e i r terminations. v) The prominent channels which p a r a l l e l the B.C. coast also appear to be t e c t o n i c a l l y c o ntrolled and westward t i l t i n g of the interchannel blocks i s suggested. v i ) The Milbanke S t r a n d f l a t has the morphology of a mature erosion surface modified by wave action. 95 CHAPTER V TECTOMORPHIC ANALYSIS gummit Level D i s c o n t i n u i t i e s S i o n i f i n a n c e * The s i m i l a r i t y i n summit l e v e l s over l a r g e regions of the Coast Mountains and Vancouver I s l a n d has already been mentioned, together w i t h i t s i n t e r p r e t a t i o n as a d i s s e c t e d e r o s i o n surface or sur-faces of m i d - T e r t i a r y age. Some l i n e s of abrupt d i s c o n t i n u i t y are obvious i n t h i s summit enve-lope, and a computer a n a l y s i s was undertaken to l o c a t e and map such f e a t u r e s . In the S i b e r i a n s e c t i o n of the c i r c u m - P a c i f i c mobile b e l t , a P l i o c e n e l e v e l l i n g of Kamchatka Peninsula has given the necessary c o n t r o l to map P l i o c e n e and Recent d i s t o r t i o n s and block movement, and r e l a t e these t o v o l c a n i c a c t i v i t y ( E r l i c h , 1968). C o n t r o l there was s t r a t i g r a p h i c however, and before attempting a s i m i l a r a n a l y s i s by assuming a summit envelope, a d i s c u s s i o n of p o s s i b l e o r i g i n s of these l i n e s of d i s c o n t i n u i t y , other than by t e c t o n i c d i s l o c a t i o n , i s r e q u i r e d . The most obvious a l t e r n a t i v e i s d i r e c t i n h e r i t a n c e from the o l d e r o s i o n surface. This i s e s p e c i a l l y a t t r a c t i v e along the i n t e r i o r edge of the Coast Mountains, where i f a summit envelope i s preserved at a l l , i t c o n s i s t s only of widely s c a t t e r e d summits. McCann (1922) has i n f a c t suggested th a t d i f f e r e n t i a t i o n of the mountains from the I n t e r i o r P l a t e a u preceded P l i o c e n e u p l i f t , although Tipper r e p o r t s Late Miocene or P l i o c e n e p l a t e a u b a s a l t s r i s i n g smoothly from the I n t e r i o r P l a t e a u to 8500 feet i n the Coast Mountains (quoted by Roddick, 1966). 96 Stepped e r o s i o n surfaces have been a t t r i b u t e d elsewhere to the r e t r e a t of pediments ( f o r example, Holmes, 1965) and evidence w i l l be presented t h a t some of the steps i n the Coast Mountains appear to have r e t r e a t e d from the obvious lineaments along which they were l i k e l y i n i t i a t e d . Furthermore, e r o s i o n surfaces of d i f f e r e n t a l t i t u d e s may be caused by e r o s i o n to d i f f e r i n g base l e v e l s . To be proven t e c t o n i c a l l y s i g n i f i c a n t a p a t t e r n of summit l e v e l d i s c o n t i n u i t i e s must th e r e f o r e be shown to c o r r e l a t e with other signs of t e c t o n i c a c t i v i t y . These signs w i l l be shown to i n c l u d e a v a r i e t y of geophysical and g e o l o g i c a l phenomena. Evidence w i l l a lso be discussed fo r some of these t e c t o n i c l i n e s having been a c t i v e i n the e a r l y T e r t i a r y . In t h i s r e s p e c t , r e g i o n a l l i n e a t i o n p a t t e r n s t r e a t e d i n Appendix XI suggest that there has been some r e t r e a t of summit envelope d i s l o c a t i o n s from mar-gins of what appear to be l a r g e b l o c k s of d i f f e r i n g t e c t o n i c s t y l e . Major lineaments bordering these blocks were presumably boundaries to s t r e s s pat-t e r n s and hence s t r a i n p a t t e r n s . Of greater s i g n i f i c a n c e i n d i f f e r e n t i a t i n g between pediments and t e c t o n i c scarps, however, i s the c o r r e l a t i o n of these d i s l o c a t i o n s w i t h present geophysical phenomena and w i t h features asso-c i a t e d w i t h P l i o c e n e u p l i f t . These features i n c l u d e f j o r d s , and secondary e r o s i o n surfaces (Appendix X). 97 Wahrhaftig (1965) has presented evidence that stepped erosion surfaces on g r a n i t i c t e r r a i n of C a l i f o r n i a were caused by a process which w i l l here be r e f e r r e d to as r e g o l i t h corrosion. Areas covered by s o i l s hold water against the rock i n t e r f a c e , causing breakdown of the granite into p a r t i c l e s which may be transported. The r e s u l t i s downward corrosion of areas holding r e g o l i t h , while steeper bands remain as c l i f f l i n e s . The steps a t t r i b u t e d to t h i s process reach considerable height, but do not have the continuity of the d i s l o c a t i o n s observed i n the Coast Mountains summit envelope. Nevertheless, r e g o l i t h corrosion appears to be very active here presently, and may have had an important r o l e i n r e t r e a t of scarp l i n e s . It i s common at the base of coastal granite c l i f f s -to find a zone of corroded rocks and subsequent formation of overhangs (which work upward by collapse) near the r e g o l i t h l i n e . Even small cracks i n g r a n i t i c b l u f f s provide s i t e s for corrosion, and i t appears that these i n turn may i n i t i a t e e x f o l i a t i o n . Regolith corrosion under steep forested slopes seems important i n i n i t i a t i n g debris s l i d e s , judging by the weathered condition of much of the material so loosened. The present importance of these mechanisms may be tr a n s i e n t , a r e s u l t of g l a c i a l over-steepening, so that t h e i r long-range effectiveness i n maintaining both steep slopes and r e t r e a t i n a wet climate i s not known. While they do not detract from the tectonic s i g n i f i c a n c e of regional summit envelope d i s c o n t i n u i t i e s , they j o i n pediment r e t r e a t and wave action as possible causes of the r e t r e a t of scarps from l i n e s of move-ment preceding Pliocene u p l i f t . I t w i l l be observed that summit envelope d i s c o n t i n u i t i e s not uncommonly p a r a l l e l a major lineament on the side of 98 r e l a t i v e u p l i f t . B r i e f l y , then, the l i n e s of d i s l o c a t i o n being sought are l i k e l y to be of tectonic s i g n i f i c a n c e i f they may be shown to co r r e l a t e with other t e c -t o n i c features or to displace structures other than the summit envelope. Computer Analysis Technique. The summit envelope for the Coast Mountains and Vancouver Island between l a t i t u d e s 49° and 55° was repre-sented for analysis by an array of elevations representing the highest points within g r i d squares f i v e miles on edge. A l t i t u d e data was taken mainly o f f government topographic maps with a contour i n t e r v a l of 500 feet, representing rather crude ele v a t i o n a l control but the best available for most of the Coast Mountains. The f i v e mile g r i d spacing was a compromise between the necessity of having at l e a s t some part of the summit envelope i n almost every square, and the requirement of s u f f i c i e n t l y small spacing for good control and d e t a i l . Grid squares which did f a l l e n t i r e l y within major v a l l e y s or depressions required a decision as to whether they should be smoothed over or assumed an actual trough i n the old erosion surface. These decisions a f f e c t somewhat the shape of the contours on the reconstructed surface, but the computer analysis program used subdues the e f f e c t s of ridges and trenches when searching for scarps. Another problem i n the data generation stage a r i s e s from Pleistocene volcanic p i l e s l y i n g on the old erosion surface, but these are only of l o c a l s i g n i f i c a n c e i n topographic a n a l y s i s . The old erosion surface when contoured i s reasonably smooth as would be expected from observations of summit heights. 99 With the establishment of a d i g i t a l array representing the summit enve-lope, the next problem was evolving a technique to trace l i n e a r d i s c o n t i n u i -t i e s . As t h i s f i l t e r must respond to d i s l o c a t i o n s and changes i n slope angle, rather than the slopes themselves, second-derivative analysis was an obvious choice. This operation was c a r r i e d out using the weighting factors suggested by F u l l e r (1966). Second-derivative technique, however, proved too blunt an instrument, magnifying roughnesses i n the summit envelope without any r e a l allowance for the form or continuity of these disruptions, and without very precise l o c a t i o n a l c o n t r o l . In designing a new a n a l y t i c system, the following objectives were viewed: i ) Slopes ( f i r s t d e r i v a t i v e s ) on the summit envelope should not show, i i ) D i r e c t i o n a l continuity of a d i s l o c a t i o n i s important, i i i ) Individual highs and lows, or troughs and ridges i n the envelope, should not show as d i s c o n t i n u i t i e s when looking for fractures, i v ) The i d e a l shape of the l i n e s being sought i s a scarp or step function. This i s tenable mainly because of the coarseness of the analysis where a f i v e mile g r i d spacing and 500 foot contour i n t e r v a l are used. The program evolved for the above purpose w i l l be r e f e r r e d to as a s c a r p - f i l t e r and i s given i n Appendix IV with explanations. For each g r i d square the program t e s t s for d i s c o n t i n u i t i e s i n eight d i r e c t i o n s . The magnitude of the number assigned to a scarp i n any one of these d i r e c t i o n s for any g r i d space i s proportional to the height of the scarp, but the f u l l value i s given only i f the d i s l o c a t i o n i s a step function of minimum length twenty miles (centered on the t e s t square). Sloping surfaces on either side 100 of the scarp reduce the assigned value i n such a way t h a t a constant slope of width twenty m i l e s or more w i l l g i v e a value of zero. The e f f e c t s of r i d g e s , troughs, or e r r a t i c p o i n t s i n the summit surface i s g r e a t l y subdued. Two major problems arose i n use of t h i s s c a r p - f i l t e r . One was that d i s l o c a t i o n s proved d i f f i c u l t to f o l l o w where the summit envelope i s rough, and the other t h a t a more or l e s s s t r a i g h t scarp l i n e was r e q u i r e d . To over-come these drawbacks, two more computer p r i n t o u t s were added to the program. One of these represents e l e v a t i o n a l d i f f e r e n c e along a t w e n t y - f i v e mile l i n e , again t e s t e d for eight d i f f e r e n t o r i e n t a t i o n s at each g r i d square. This c a l c u l a t i o n i s weighted to give g r e a t e s t importance to d i s l o c a t i o n height at the c e n t r a l p o i n t , and the r e s u l t s were used t o t r a c e scarps through rough s e c t i o n s of the array surface, where slope p e n a l t i e s i n the main s c a r p - f i l t e r had obscured the d i s l o c a t i o n . The other secondary p r i n t -out (ten-mile s c a r p - f i l t e r ) i s s i m i l a r to the main program, but r a t h e r than t e s t i n g for d i s c o n t i n u i t i e s i n e l e v a t i o n between adjacent g r i d squares, i t makes comparison of s t r i p s f i v e m i l e s apart. This serves to define broader or l e s s abrupt d i s c o n t i n u i t i e s i n e l e v a t i o n and to catch scarps which are e i t h e r not very s t r a i g h t or which trend between two of the eight o r i e n t a t i o n s t e s t e d . The f i n a l step i n use of the s c a r p - f i l t e r was c o r r e l a t i o n of l i n e s generated w i t h a c t u a l contour maps. Those l i n e s of summit l e v e l d i s c o n t i n u i t y being sought were s u b s t a n t i a l l y sharper than n e c e s s a r i l y represented by a f i v e - m i l e g r i d system. F i n a l r e s u l t s are shown on maps 6 and 7. Almost without exception, computer-generated l i n e s which were strong for t h i r t y m i l e s ( s i x g r i d squares) or more were found to be d i s t i n c t on the maps. 101 3 Those obtained from the ten mile s c a r p - f i l t e r were l e s s often observable. These l e s s - d i s t i n c t zones are not shown on the maps, although some may be s i g n i f i c a n t as axes of warping, d i s l o c a t i o n along multiple fractures, or as older scarps made i n d i s t i n c t by d i s s e c t i o n or erosion. Interpretation of Results. The major d i s l o c a t i o n s i n summit elevations were found to c o r r e l a t e with several other phenomena. These include termination of f j o r d s , Pleistocene volcanic centers, hotsprings, metamor-phic screens, lineaments, anomalous potassium/rubidium r a t i o s i n nearby igneous rocks, and earthquake epicenters. A prominent b e l t of these features runs from the head of Howe Sound about 470 miles to the north end of the project area at Nass River. This w i l l be r e f e r r e d to as the " a x i a l fracture zone", and i s shown on map 5. The gross o u t l i n e i s approximately a great c i r c l e , but i n d e t a i l i t i s comprised of a series of fractures o f f s e t by cross-lineaments (see maps 6 and 7). A second prominent and reasonably continuous l i n e i s the edge of the forementioned elevated portion of the Coast Mountains, the eastern u p l i f t . In the south, t h i s coincides with (or i s ) the a x i a l fracture, but north of the Owikeno Lineament i t l i e s farther east. The u p l i f t l i n e tends to follow metasedimentary screens, but appears mainly as a prominent d i s l o c a t i o n i n the summit envelope with l i t t l e or no thermal s i g n i f i c a n c e . In the Kitimat Ranges i t moves well to the east and another l i n e of lineaments, thermal centers, and anomalous potassium/rubidium r a t i o s appears between. This i s denoted as the Terrace Fracture. l o 5 i ) Axial Fracture, southern part. As map 5 demonstrates, the a x i a l fracture zone may be extended to the United States as a straight l i n e to in t e r s e c t the two most northerly Pleistocene volcanoes i n western Washington, Mt. Baker and Glacier Mtn. The zone crosses the Fraser River Valley at a point where t h i s i s cons t r i c t e d by protrusion of Mts. Sardis and Vedder through the a l l u v i a l covering. This southward p r o j e c t i o n i s only t e n t a t i v e , however, and the ax i a l fracture does not take on the form of a major scarp l i n e for more than a short distance south of Howe Sound. Along the 165 miles between Howe Sound and the Owikeno Lineament, which i s the zone's f i r s t major o f f s e t , average e l e v a t i o n a l d i f f e r e n c e i n the summit envelope between adjacent f i v e mile g r i d squares across t h i s l i n e i s 1300 feet. By comparison, the summit envelope of the adjacent f j o r d zone has a slope of approximately 55 feet per mile, and the eastern u p l i f t s u b s t a n t i a l l y l e s s . Slopes on the l a t t e r are often downward to the east when near the a x i a l f r a c t u r e . Five f j o r d s terminate on the southern part of the a x i a l fracture, and only the minor, c i r q u e - l i k e Princess Louisa Inlet extends beyond. River drainages are arranged so that no r i v e r s cross the main fracture along the forementioned 165 miles. Map 7 shows that the fracture follows metasedi-mentary screens with very few exceptions, wherever the geology of i t s route i s known. i i ) Axial Fracture, central portion. In the region between Owikeno Lake and Gardiner Canal, the ax i a l fracture i s l a r g e l y d i s t i n c t from the western edge of the eastern u p l i f t . The rather abrupt o f f s e t at the Owikeno Lineament i s i n t e r e s t i n g i n view of the possible eighteen mile o f f s e t suggested here from geological evidence by 106 Roddick (1968). Between t h i s lineament and the B e l l a Coola cross-structure, a trough i n the summit envelope l i e s between the eastern u p l i f t and the a x i a l fracture, which i s i t s e l f a prominent trench. In the region north of Dean Channel, neither the front of the u p l i f t nar the a x i a l l i n e are d i s t i n c t . The l a t t e r may well be o f f s e t at l e a s t as far west as Cascade I n l e t ; the ten-mile s c a r p - f i l t e r suggests i t runs on up through the heads of Kynoch and Mussel I n l e t s . In any case, the zone may be picked up by thermal and geochemical evidence farther northwest i n the v i c i n i t y of Sheep Passage. i i i ) Axial and Terrace zones, northern section. Continuation of the a x i a l fracture between Douglas Channel and Nass River i s mainly on the grounds of a prominent scarp l i n e i n the summit envelope and strong lineaments along the general l i n e of pro j e c t i o n of the fracture northward. This i s also found to divide rock suites of d i f f e r i n g age, as w i l l be discussed. The Terrace zone i s reasonably well defined u n t i l i n the v i c i n i t y of Gardiner Canal, but from there southward i t s course i s speculative. i v ) Bella-Coola cross-zone. An east-west b e l t of thermal centers crosses the Coast Mountains j u s t north of the B e l l a Coola River, as was observed by Souther (1970). This i s the d i v i s i o n between Kitimat and P a c i f i c Ranges, which i s accompanied by a pronounced change i n tectonic form as shown both through the summit enve-lope analysis and the above mentioned lineament analysis of Peacock (1935). This d i v i s i o n i s also a change i n morphological form — the coastal region 107 northward displaying a complex of islands and i n l e t s extending much farther i n t o the mountains than to the south. Dean Channel and ..Gar.dlner_Canal are exceptional i n t h i s respect. The general coastal topography has the appearance of p r e - g l a c i a l drowning ( r e l a t i v e to the region on the south) of the area inland from the s t r a n d f l a t . The greatest i n l e t depths i n B r i t i s h Columbia occur i n t h i s region. Both summit envelope analysis and coastal topography thus point to r e l a t i v e movement ( i n the neighbourhood of 1500 feet) downward on the north side of the B e l l a Coola River, v) Waddington axis. Between the depressions of Hecate S t r a i t and the S t r a i t of Georgia, Vancouver Island i s almost joined to the mainland by what i s termed the Seymour Arch at approximately l a t i t u d e 50° 30' N. This i s part of a l i n e of high elevations; (map 7), including the highest summits of Vancouver Island (Hinde block), the greatest elevation i n the Coastal Trough (Hkusam block), the highest summits west of the a x i a l fracture (Franklin block) and the highest mountains i n the project area (Waddington dome). This l i n e does not c o r r e l a t e well with other features, and i s a seri e s of i s o l a t e d block u p l i f t s rather than a swell. I t s s i g n i f i c a n c e i s not obvious. D i s t r i b u t i o n of Thermal Centers Forty-four of the Quaternary volcanoes and 18 hotsprings known to l i e within or immediately adjacent to the Coast Mountains project area are shown on map 5. This data i s derived l a r g e l y from Souther and Halstead (1969), Holland (1964), White(l966), and Souther (1970). A l l of these thermal cen-t e r s l i e within one or more of f i v e well defined zones. 1 0 8 The best developed thermal zone runs north from near the town of Squamish at the head of Howe Sound, and e n t a i l s more than 30 volcanic cen-t e r s . I t s shape i s not obvious on the maps of White (1966) or Holland (1964), who have not included the centers clo s e s t to Squamish townsite (see Mathews, 1958). This b e l t of thermal a c t i v i t y i s terminated on the south by the ax i a l fracture and on the north by the forementioned Taseko Fault system along the eastern margin of the Coast Mountains. Both of these may be s c l a s s i f i e d as l i n e s of c r u s t a l weakness. A l k a l i f r a c t i o n a t i o n p l o t s of the composition of volcanic rocks from t h i s b e l t (from analyses by Mathews, 1958) suggest d i f f e r e n t i a t i o n from a magma t y p i c a l of plateau basalts (Souther, 1969). The zone i s therefore p o s s i b l y a tensional r i f t between two l i n e s of lon g i t u d i n a l weakness. A subparallel thermal l i n e which follows the L i l l o o e t River and Harrison Lake may well be a similar feature. I f the Pleistocene volcanic p i l e s are ignored, both the Squamish and L i l l o o e t thermal b e l t s are followed by shallow trenches i n the summit envelope. The remaining three thermal zones have already been introduced. They are the a x i a l fracture with eighteen thermal centers, the Terrace fracture with three centers, and the B e l l a Coola cross-zone with seven. Another i n t e r p r e t a t i o n of thermal zones i n the C o r d i l l e r a of B r i t i s h Columbia i s given by Souther (1970), who suggests two major b e l t s of Quaternary volcanism approximating the Squamish and B e l l a Coola zones and possibly representing the beginnings of a r i f t and a transform f a u l t respect-i v e l y . D i s t r i b u t i o n of Age-Dates. Map 1 gives age groupings for potassium-argon dates on plutonic rocks from the Kitimat Ranges (Hutchison, 1970). 109 A l l of the older (84—139 m.y.) ages observed are for rocks from the western edge of the Coast Mountains, generally close to the edge of the s t r a n d f l a t . Three rocks f a l l into the 74—79m.y. category, a l l l y i n g close to either the a x i a l fracture or B e l l a Coola thermal zone. Two other samples from along or immediately adjacent to the a x i a l fracture were dated at 64 m.y. and 67 m.y. and a sample l y i n g d i r e c t l y on the a x i a l fracture yielded 57 m.y. A l l ten samples l y i n g east of the a x i a l fracture within the Kitimat Ranges have ages i n the s u r p r i s i n g l y narrow range of 43—50 m.y. As previously mentioned, most of the Coast Mountains b a t h o l i t h i c com-plex has l i k e l y been u p l i f t e d by block tect o n i c s or at l e a s t r e g i o n a l l y , rather than by upward i n t r u s i o n of i n d i v i d u a l plutons. Hence the region east of the a x i a l fracture appears to have r i s e n somewhat faster or farther than that to the west, exposing rocks which more recently came through the c r i t i c a l potassium—argon isotherm. By t h i s reasoning, the a x i a l fracture has been a feature of importance i n the Kitimat ranges since at l e a s t p r i o r to formation of the surface which i s now a summit envelope. There have not as yet been enough age dates published for the P a c i f i c Ranges to make a similar a n a l y s i s . Gravity Analysis A Bouguer gravity map of Vancouver Island and the adjacent f j o r d zone of the Coast Mountains has been compiled by Walcott (1967), and some data i s also a v a i l a b l e for the northern coast (Stacey et a l , 1969). A more d e t a i l e d map of gravity i n the Coast Mountains i s being compiled by the Dominion Government. 110 The gross aspect of Bouguer gravity on the coast i s a region of p o s i -t i v e anomaly (to 60 m i l l i g a l s ) over Vancouver Island and a strong b e l t of negative over the Coast Mountains. The n u l l axis c l o s e l y follows the coastal trough and S t r a i t of Juan de Fuca. These s t r a i t s and the Fraser V a l l e y show up abruptly on the gravity map. Less d i s t a n t cross structures include the Leech River f a u l t , and the B e l l a Coola and Owikeno lineaments. Danes (1970) has studied the negative g r a v i t y trend which extends south into the northern Cascade Range, and finds that a l l the mountain groups i n northwestern Washington have a free a i r anomaly representing an excess mass such as might be expected to cause the ranges to almost com-p l e t e l y sink i n a quarter m i l l i o n years i f other factors were not operating. Danes has calculated that the subduction zone of a convection c e l l beneath a continental margin would f i r s t cause a trough there, but l a t e r would develop p o s i t i v e r e l i e f due to counter-flow i n the lower cru s t . He estimates from theory a 50-100 m i l l i g a l free a i r negative anomaly associated with t h i s upwarping, and t h i s i s approximately what i s now observed. If the region of p o s i t i v e r e l i e f i s subject to erosion and mass lo s s , i t w i l l continue to be pushed up. That p r e d i c t i o n f i t s well with the d i s t r i b u t i o n of ages as observed i n the northern Coast Mountains, and suggests one possible mechanism for the c o r r e l a t i o n between coastal elevation and active subduction zones, which w i l l be discussed. Bankes (1969) has done free a i r reduction of g r a v i t y data for the coast of B r i t i s h Columbia, and observes that there i s an anomaly at the head of the i n l e t s . As t h i s i s near the edge of available gravity data as well, i t quite possibly applies to the region east of the a x i a l f r a c t u r e . I l l Danes (1970) has calculated that a convective pressure of 1.2 x 10 dynes/cm 2 would be required to prevent s e t t l i n g of the Cascade and Olympic Ranges, hence reaching through gravity analysis the same conclusion that Bostrom (1968b) did by str u c t u r a l analysis of the Coast Mountains, namely that the coastal p o r t i o n of the C o r d i l l e r a here could not be stable without l a t e r a l pressure. D i s t r i b u t i o n of Potassium/Rubidium Anomalies As map 1 demonstrates, most of the igneous rock samples analysed from the Kitimat Ranges that were found to have potassium/rubidium r a t i o s over 400 occur along or near either the a x i a l fracture of the Terrace f r a c t u r e . (Gabbro samples are excluded as previously mentioned.) This does not appear to be the r e s u l t of rock a l t e r a t i o n s . In the P a c i f i c Ranges (map 2) t h i s clear r e l a t i o n s h i p does not hold, not because the rocks from near major fractures have l e s s tendency to be anomalous, but because a major number of those distant for obvious fractures also show high r a t i o s . Considering al t e r e d samples separately does l i t t l e to improve the r e s o l u t i o n . The s i g n i f i c a n c e of t h i s w i l l be explored i n the f i n a l t hesis discussion. D i s t r i b u t i o n of Epicenters There i s s u f f i c i e n t seismic control to locate the f o c i of some of the small earthquakes within the southwestern Coast Mountains. D i s t r i b u t i o n of epicenters as reported by Milne and Lucas (1961), Milne and Smith (1960, 1961, 1962), and Milne (1970) are given for the mainland north of 50° N l a t i t u d e on map 8. S o l i d c i r c l e s show epicenters located with greater accuracy, l i k e l y f a l l i n g within the radius of the c i r c l e . 1 1 2 On the mainlands the most obviously active zone i s a b e l t of seismic a c t i v i t y along the a x i a l fracture and out toward Knight I n l e t fracture which bounds the outer edge of the F r a n k l i n block. Several epicenters are also observed i n the region southwest of Chilko Lake and a few along the Inland Passage fracture zone. North of the region shown, control i s poor, although the establishment of a seismograph at Port Hardy on northern Vancouver Island should eventually allow accumulation of data for part of t h i s region. South of l a t i t u d e 49° 45', epicenters are scattered through a broad region l y i n g southwest of the approximate extension of the a x i a l f r a c t u r e . Earthquakes deeper than 100 km do not occur beneath the Coast Moun-ta i n s or adjacent P a c i f i c Basin rim. They are observed, however, north-west of the Denali f a u l t i n south-central Alaska and along the western rim of South America down to the f j o r d region of Patagonian C h i l e (see for eg. Barazangi and Dorman, 1969). These portions of the eastern P a c i f i c margin which exhibit deep earthquake f o c i also generally show signs of recent u p l i f t of the continental margin (21,000 feet since the Pliocene i n the case of the St. E l i a s area west of Denali f a u l t ) . Deep earthquake sections tend to reach elevations several thousand feet greater than the summits (neglecting volcanic p i l e s ) on other parts of t h i s rim, and they do not have the s t y l e of deep f j o r d formation seen i n the Coast Mountains or Patagonia. If deep earthquake f o c i are taken as evidence of active subduction, t h i s f i t s Danes' prediction(l970) of c e n t r a l u p l i f t during that process. DISTRIBUTION OF EARTHQUAKE EPICENTERS Ilk C o r r e l a t i o n of Fractures with Screens In the central and western parts of the Coast Mountains b a t h o l i t h i c complex, metamorphic and migmatitic rocks commonly occur i n elongated bands of regional continuity extending downward into the plutonic matrix as far as the r e l i e f allows observation. The more prominent screens are shown on map 7 and a close c o r r e l a t i o n with major summit-envelope d i s l o -cations i s e s p e c i a l l y obvious i n the southern Coast Mountains. What d i s -c o n t i n u i t i e s do appear i n the screens along the a x i a l fracture may be at t r i b u t e d i n part at l e a s t to lack of geological mapping between the i n l e t s . I t i s not obvious whether the screen to fracture c o r r e l a t i o n e x i s t s because both were formed by the same mechanism (such as subductional forces on a p l a s t i c matrix) or i f the screens are simply l i n e s of weakness through a b a t h o l i t h i c t e r r a i n which might otherwise e x h i b i t considerable s t r u c t u r a l strength. In the northwestern p o r t i o n of the study area, the Kemano Gneiss of the Central Gneissic Complex i s r e g i o n a l l y prominent and the many heavily f o l i a t e d zones i n t h i s greatly reduce the difference i n competency between metamorphic screens and t h e i r surroundings. "Either the fractures have les s tendency to follow screens i n t h i s region, or else the screens are not as obvious i n t h i s complex and migmatitic t e r r a i n . I nterpretation of Fjords One of the more surp r i s i n g observations i s that most master f j o r d s terminate on either a summit l e v e l d i s c o n t i n u i t y or strong lineament. The a x i a l fracture i n the southern Coast Mountains turns out to be almost p r e c i s e -l y the l i n e bounding the major i n l e t s . This r e l a t i o n s h i p i s not s e n s i t i v e to 115 changes i n sea l e v e l . A t y p i c a l master f j o r d near i t s head i s a mile wide and a thousand feet deep. Considering the rough manner i n which the a x i a l fracture zone i s defined, i t s c o r r e l a t i o n with the i n l e t head w i l l not be much influenced by lowering of sea l e v e l or delta formation during the period since g l a c i e r s l a s t occupied the i n l e t . Raising of sea l e v e l would extend most i n l e t s considerably, and t h i s has apparently occurred i n some v a l l e y s i n the past. Such an extension, however, would be e a s i l y i d e n t i f i e d by i t s shallow depth and would be subject to f i l l i n g with sediments. Another observation of i n t e r e s t i s the arrangement of drainage so that only a very few r i v e r s cross the a x i a l fracture zone. In part t h i s i s the r e s u l t of master f j o r d s c o l l e c t i n g drainage, but to a large extent i t stems from strong lineaments p a r a l l e l to the zone which d e f l e c t s drainage. If i t i s to. be suggested that the major coastal f j o r d s owe t h e i r depth t o sinking of the f j o r d zone, some western l i n e of fr a c t u r i n g between t h i s and the s t r a n d f l a t s or Vancouver Island i s to be expected. The summit l e v e l analysis shows only a few reverse (east facing) scarp l i n e s i n t h i s region, but then sinking might be expected to follow the same l i n e s of fracture as u p l i f t d i d , so that summit envelope study i s a poor subsidence i n d i c a t o r . The oceanward terminations of deep f j o r d s , however, should c l e a r l y o u t l i n e the western boundary of a sinking area. The outer end of deep i n l e t channels i s usually reasonably abrupt, or at l e a s t occurs i n steps. These locati o n s are marked on maps 6 and 7. This type of termination i s f i n a l , i n that the channels farther west do not again reach the depths of the main f j o r d s . In t h i s way the terminations d i f f e r from the thresholds and rock bars that occur i n many i n l e t s , e s p e c i a l l y near t h e i r mouths. 11.6 Oceanward terminations of deep fj o r d s were found to o u t l i n e a f a i r l y broad zone between the s t r a n d f l a t and the true f j o r d zone. This has been termed the Inland Passage fracture b e l t and i s shown on map 4. As maps 6 and 7 show, most of these deep f j o r d terminations or steps occur on or near l i n e s of summit l e v e l d i s c o n t i n u i t y , usually with the summit envelope scarp facing west and hence i n the opposite d i r e c t i o n from the movement indicated by change i n i n l e t depth. This again suggests a cycle of emergence, d i s s e c t i o n , and subsidence. For one section, the Inland Passage fracture b e l t contracts and the s t r a n d f l a t margin crosses onto the mainland. This i s at the Seymour—Belize Inlet complex (see map 9), and while the narrowness of the fracture zone may 'simply be due to lack of water depth data for the i n l e t group, sinking along the s t r a n d f l a t margin has very abruptly terminated i n l e t s and lagoons to produce a unique pattern. The v a l l e y which i s now B e l i z e I n l e t once emp-t i e d into the ocean d i r e c t l y and there i s s t i l l obvious a large open beach between the rocky coastal headlands (Burnett Bay) with sand h i l l s leading back into swampland. Termination of the major f j o r d s by fractures and lineaments does not i n i t s e l f preclude the p o s s i b i l i t y of t h e i r o r i g i n being e n t i r e l y by g l a c i a l over-deepening. I t could be argued that t h e i r heads are c o n t r o l l e d by l i t h o l o g i c a l weakness at a zone of f r a c t u r i n g , or by j o i n i n g of g l a c i e r s as the r e s u l t of lineament c o n t r o l . The westward terminations have been suggested (Burwash, 1918) to r e s u l t from release of major g l a c i e r s from confinement of t h e i r v a l l e y s , which to some extent correlates with summit l e v e l d i s c o n t i n u i t i e s . It seems too much of a coincidence, however, that 117 many of the major fjords have t h e i r heads along summit envelope d i s l o c a t i o n s of the same general magnitude as apparent f j o r d depth. This, and the pre-v i o u s l y mentioned patterns of l o n g i t u d i n a l channels and of i n l e t truncations on the i n t e r i o r margin of the s t r a n d f l a t , support the proposal that the major fjords owe t h e i r depth to block subsidence. The bimodal frequency d i s t r i b u t i o n for depths of i n l e t s traverse to the Coast Mountains axis has already been mentioned (Figure 12). Two i n l e t s whose depths l i e between the modes are unusual. One i s Howe Sound, whose depth near i t s head i s t y p i c a l of master f j o r d s , but the deep channel ends at a submerged terminal moraine. This i n l e t i s on the southern extremity of the f j o r d zone, and i t i s proposed that the l a s t period of g l a c i a t i o n was not s u f f i c i e n t l y f o r c e f u l here to e n t i r e l y clear out the i n l e t . Another unusual case i s the f o s s i l i n l e t of Powell Lk. (Mathews, 1962). This terminates oceanward on an apparent fracture l i n e , but there i s no obvious one at i t s head. Furthermore i t contains s i l l s , which true master fjords do not. The c l a s s i c deep f j o r d systems of the P a c i f i c Coast of the Americas end rather abruptly at three l o c a t i o n s . Two of these mark approximately the ends of deep earthquake zones (which l i e i n the regions without master f j o r d s ) , and the t h i r d (near Vancouver) i s l i k e l y a l i m i t of e f f e c t i v e con-t i n e n t a l g l a c i a t i o n . The apparent r e l a t i o n s h i p between deep earthquakes and recent u p l i f t on t h i s continental margin has already been ou t l i n e d . It seems p l a u s i b l e that both g l a c i a t i o n and submergence may be required for the formation of deep f j o r d s . In t h i s regard i t i s of i n t e r e s t that Crary (1966) i n h i s study of an i c e covered f j o r d i n Antarctica found that the f j o r d was 118 indeed f i l l e d with i c e , but that a gravity anomaly near i t s head suggested te c t o n i c control may have been present. The Problem of In l e t Patterns Two obvious problems i n considering deep fjords as downfaulted v a l l e y segments i s the lack of major v a l l e y continuations beyond the heads of some fj o r d s (notably J e r v i s I n l e t ) and shapes of master fj o r d s which do not form a drainage-like pattern. Contours on the summit envelope show that J e r v i s I n l e t did have a trough leading to i t , the drainage having been apparently diverted southward by the Elaho River. On the problem of oceanward branch-ing of the main f j o r d s , i t has been shown that t h i s i s a zone of cross-f r a c t u r i n g , the b e l t of is l a n d s being also that of f j o r d depth termination. There s t i l l remains a problem i n the lack of f j o r d branching i n the semblance of a drainage pattern. Adjacent r i v e r s usually have deep v a l l e y s with gentle p r o f i l e s leading to present sea l e v e l , and a future subsidence would produce an i n t r i c a t e pattern very unlike the present one. These deep v a l l e y s , however, are products of g l a c i a l gouging along with t h e i r scooped lakes and i n l e t s . .The period of u p l i f t during which master f j o r d v a l l e y s were cut must have been l i m i t e d , allowing time for major r i v e r s c u t t i n g across the f j o r d zone to approach a base l e v e l , but not allowing destruction of the summit envelope. There i s no evidence of any period of s t a b i l i t y following u p l i f t which might have allowed maturing of the major erosion features i n the f j o r d zone. This period of u p l i f t i s d i s t i n c t from that which caused the forementioned d i s t r i b u t i o n of age dates i n the Coast Mountains, and a period of s t a b i l i t y must have intervened as demonstrated by existence of the erosion surface which i s now a summit envelope. 119 It should be mentioned that the problem of f j o r d s not resembling drainage patterns i s also avoided i f they are a t t r i b u t e d to r a i s e d sub-marine canyons (Windslow, 1965) or fractures (Bostrom, 1968b). Neither of these f i t the observations quite as well, however, as deep f j o r d zones terminate against the s t r a n d f l a t which would not be expected of submarine canyons, and the summit envelope i s usually continuous across f j o r d s , which seems u n l i k e l y i f they are major fractures i n a region of block t e c t o n i c s . Summary of Results i ) At l e a s t some of the l i n e s of d i s l o c a t i o n i n the summit envelope are l i k e l y to be of tectonic s i g n i f i c a n c e and a computer analysis was under-taken to o u t l i n e them. i i ) This analysis located several d i s l o c a t i o n s of surprising continuity, often corresponding to other tectonic features. A major b e l t of these phenomena runs 470 miles up the Coast Mountains and i s r e f e r r e d to as the " a x i a l fracture zone". i i i ) The i n d i v i d u a l fractures of the a x i a l zone are repeatedly o f f s e t at prominent lineaments. One of these i s the Owikeno lineament where there i s also some geological evidence of transcurrent movement. Another i s the B e l l a Coola cross-fracture where evidence i s presented for 1500 f t . r e l a t i v e movement downward on the north side. i v ) Hotsprings and Pleistocene or Recent volcanoes i n the part of the Coast Mountains studied l i e along one or more of f i v e thermal b e l t s . In the Kitimat Ranges these are also the locati o n s of most rock samples found to 120 have potassium/rubidium r a t i o s over 400. v) In the kitimat Ranges the a x i a l fracture also divides rocks of d i f f e r i n g ages, strongly suggesting that the region on the east of i t has been u p l i f t e d more r a p i d l y . v i ) In the P a c i f i c Ranges there i s a tendency for summit envelope d i s -locations to follow metamorphic screens. v i i ) The a x i a l fracture zone between l a t i t u d e s 50° and 51° 30' (and quite possibly elsewhere) i s s e i s m i c a l l y a c t i v e . v i i i ) Along the P a c i f i c rim of North America, master fjords e x i s t where there has been continental g l a c i a t i o n and there are no deep earthquakes. The rim sections which do display deep f o c i tend to have higher topography and show signs of continuing u p l i f t . i x ) The Coast Mountains i s a b e l t of negative B:ouguer gr a v i t y . Both s t r u c t u r a l and gravity c a l c u l a t i o n s have been published to show that the coastal ranges would not be stable without l a t e r a l pressure, presumably due to motion of the ocean floo r against the continent. x) The deep channels of master fjords tend to terminate at both ends on fractures which are also summit envelope scarps. Oceanward terminations occur i n a b e l t of islands and channels termed the Inland Passage fracture b e l t . x i ) The o v e r a l l tectonic pattern i s one of block f a u l t i n g and subsidence, and hence presents a f a b r i c not unlike that described as t y p i c a l of the P a c i f i c rim by several Russian authors (for example, Beloussov and Kosmin-skaya, 1968). x i i ) Preservation of a summit envelope and the youthful appearance of i t s 1 2 1 . d i s s e c t i o n pattern suggests that the period of strong u p l i f t which preceded the above mentioned p a r t i a l subsidence was not lengthy. x i i i ) Attempted c o r r e l a t i o n of secondary erosion surfaces suggests that a l l movement on the southern a x i a l fracture and the B e l l a Coola cross-lineament post-date the formation of the erosion surface, but more de t a i l e d work and more maps are required. 122 CHAPTER VI DISCUSSION AND CONJECTURE Relationship of the Coast Mountains Ba t h o l i t h to Continental Development D i s t r i b u t i o n of lead isotopes i n continental material implies that the bulk of North America was formed between 3500 and 2500 m i l l i o n years ago (Patterson and Tatsumoto, 1964), or more properly that most of the lead was placed i n the crust during or before t h i s period. This p i c t u r e of early lead concentration contrasts sharply with the apparent history of strontium p a r t i t i o n i n g between crust and mantle, as i n i t i a l strontium i s o t o p i c r a t i o s (ISIR) for most igneous rocks suggest that the major portion of strontium involved i n each igneous event was derived from some s u b - s i a l i c source with a low Rb/Sr r a t i o . The average Rb/Sr for Coast Mountains plutonic rocks i s 0.047, or roughly o n e - f i f t h that estimated for continental s i a l , and the copious 87 86 strontium i n t h i s complex i s changing i t s Sr /Sr r a t i o by only 0.001 every 550 m.y. A future magmatic event deriving strontium from t h i s regime or in v o l v i n g a l k a l i n e metasomatism of the present b a t h o l i t h could conceivably produce acid i n t r u s i v e rocks with low ISIR values such as are commonly observed. In view of t h i s and of the Coast Mountains comprising the largest Phanerozoic b a t h o l i t h i c complex known, the regime might appear a natural model for the developmental stage or e f f e c t i v e l y the c r u s t a l pre-history of older shields and cratonal i n t r u s i v e complexes. On the other hand, the period l a s t i n g from roughly 3£ b.y. ago to 1 b.y. ago saw establishment of the great shield areas, whose range i s s t i l l being 1.33 o u t l i n e d beneath younger orogenic regions by zi r c o n and lead isotope studies. There seems l i t t l e firm evidence that the form of continental development during that time i s d i r e c t l y comparable to the present regime of global t e c t o n i c s , either i n chemical or physical processes. It might, i n f a c t , be questioned whether the continents are now accreting at a l l . Observations i n the Coast Mountains suggest that the t e r r a i n preceding subduction was p a r t i a l l y incorporated and digested, but mainly removed by u p l i f t and erosion. The balance of v o l a t i l e a l k a l i s may yet be restored by v o l i t i z a t i o n of mobile elements from the new root zone as isotherms are r e -established following subduction. While such a process could conceivably erase the present geochemical abnormalities, there seems no reason to believe that a subductional zone beneath a continent produces a wound which heals with a more stable or c r a t o n - l i k e crust than had been removed. In t h i s view the Coast Mountains b a t h o l i t h may be simply a t r a n s i t o r y regime i n which the plutonic l e v e l of an orogenic b e l t associated with sub-duction has been exposed, but post-orogenic processes have not yet completed t h e i r work. Much of the power of the lead isotope technique stems from two isotopes of lead being derived from uranium isotopes which may be presumed to occur i n a l l environments at a set r a t i o for any given time. Coherence of potassium and rubidium, both of which have natural radioactive isotopes, also gives a decay p a i r which i s not as convenient as uranium, but may neverthe-l e s s be used to set c e r t a i n l i m i t a t i o n s . Hurley (1968a, 1968b) has used t h i s system to find l i m i t s for the K/Rb r a t i o of the earth, but h i s model contains several uncomfortable assumptions, such as an absence of Argon-40 on earth 12b 4.5 b.y. ago ( u n l i k e l y i f earth was a cold accretion body), a single stage m a n t l e — c r u s t f r a c t i o n a t i o n process without r e c y c l i n g ( u n l i k e l y i n view of f r a c t i o n a t i o n at subduction zones), complete mantle mixing (requiring pre-sumably a convection c e l l to bottom of the mantle) and a rate of c r u s t — mantle exchange for any element which i s time dependent only i n that i t i s proportional to concentration of that element i n the mantle. A more com-plex model by Armstrong (1968) takes i n several other elements and tackles some of the above-mentioned problems, but t h i s requires estimation of several parameters which are not r e a l l y well understood. In a l l models there remains the assumption that c r u s t a l development has been continuous and has not changed s t y l e . Even i f sh i e l d development may be attributed to the sort of tectonic regime presently observed, t h i s s t i l l leaves a f u l l b i l l i o n years of tectonic mystery between the ubiquitous event of 4.5 b.y. ago and the f i r s t record of continental n u c l e i . At best, then, i t may be said that the geochemical abnormalities of the Coast Mountains t e r r a i n a s s i s t s i n modelling of continental development only i n providing a major c r u s t a l regime which i s preserving strontium of p r i m i t i v e i s o t o p i c character and i s hence an a l t e r n a t i v e to the mantle as a type source for such strontium during future orogenesis. Whether Coast Mountains geochemistry sheds any l i g h t on the f r a c t i o n a t i o n a l processes associated with subductional zones w i l l be discussed next. Interpretation of Abnormalities i n Strontium and Rubidium D i s t r i b u t i o n . The high strontium concentrations observed i n i n t r u s i v e rocks of the B r i t i s h Columbia C o r d i l l e r a are most e a s i l y explained by assuming these 1 2 5 rocks to have been derived by f r a c t i o n a t i o n (or subjected to anatexis) with los s of a more al k a l i n e phase. If the present plutonic rocks or t h e i r parent material were accumulates of (dominantly) plagioclase and amphiboles, then the high strontium concentration (which follows p l a g i o -clase, see Figure 11) and to some extent the high K/Rb r a t i o s might be ex-plained by simple trace element p a r t i t i o n i n g . ( P h i l p o t t s and Schnetzler, 1970; Gast, 1968) The mobile phase, which might be expected to carry much of the a l k a l i s (and possibly any radiogenic strontium involved i f the l i q u i d phase was due to anatexis), presumably moved up to form acid extrusive rocks, pegmatites, or high l e v e l i n t r u s i o n s since removed by erosion. The observed d i f f e r e n c e between strontium content of volcanic and plutonic rocks supports the view that strontium concentration i n the l a t t e r i s by accumulation or r e t e n t i o n of the more r e f r a c t o r y minerals. In a l l l i k e l i h o o d then, the Coast Mountains are a root zone of an older i n t r u s i v e province, which i s not surprising i n view of the evidence for central u p l i f t i n the T e r t i a r y , older ages for i n t r u s i v e suites flanking the Coast Mountains, and cobbles of plutonic rocks i n metamorphic screens. Stron-tium concentration i s also evident i n the rock east of the Coast Mountains, although the h i s t o r y of the a l k a l i s there has obviously been d i f f e r e n t . Two models might be used to explain the high K/Rb r a t i o s of Coast Moun-ta i n s igneous rocks. The most obvious theory i s that these a l k a l i s were derived i n part from the destruction of oceanic crust, or possibly through a form of the same process by which oceanic c r u s t a l fractures obtain rocks of anomalous K/Rb r a t i o s from (presumably)the mantle. These suggestions are 126 supported i n preference to a simple theory of mineral f r a c t i o n a t i o n by anomalous K/Rb r a t i o s found, i n some of the Coast Mountains volcanic rocks, and control of anomalies i n the Kitimat Ranges by major fractures. This l a t t e r feature, however, and the c l e a r l y binormal frequency d i s t r i b u t i o n of K/Rb values i n that region, are l i k e l y the r e s u l t of the Coast Mountains orogenic b e l t there being over-printed on an older regime whose metamorphosed remnants influence the regional geochemistry. A case may also be made for K/Rb anomalies being a r e s u l t of f r a c t i o n a -t i o n and a l t e r a t i o n . Although i n the present Coast Mountains i n t r u s i v e rocks these a l k a l i s are not held dominantly i n minerals which discriminate against rubidium, a t y p i c a l d i o r i t e elsewhere (see for example Clark, 1966) i s approximately as r i c h i n potassium as an average Coast Mountains quartz monzonite, and i t i s possible that an o r i g i n a l d i o r i t e (amphibole— plagioclase rock) with an anomalous K/Rb r a t i o due to f r a c t i o n a t i o n or ana-t e x i s , simply donated a l k a l i s to l a t e forming potassium minerals. As the Coast Mountains were u p l i f t e d r e g i o n a l l y , some clues as to the formation of these rocks should s t i l l be i n place. These clues include a l t e r a t i o n , heterogeneity, and comparative lack of mobility among the more basic members of the plutonic rock s e r i e s . D i o r i t i z a t i o n of greenstones i s an e s p e c i a l l y heterogeneous process, producing dominantly hornblende— plagioclase rocks, but often of widely d i f f e r i n g grain size and including areas of basic pegmatite. The most obvious explanation for t h i s d i f f e r e n c e i n apparent ion mobility i s the a v a i l a b i l i t y of water, and t h i s i s also the l i k e l y reason for the d i f f i c u l t y some plutons have had i n digesting the limey units of metamorphic groups, these requiring more water to assimilate 127 than other metasediments. Furthermore, c h l o r i t i z a t i o n i s common i n the Coast Mountains d i o r i t e and quartz d i o r i t e complexes, and t h i s may be correlated with high K/Rb values, although not d i r e c t l y with tectonic features. Considering a l l t h i s , i t seems possible that the anomalous K/Rb values for Coast Mountains rocks originated through p a r t i a l v o l a t i l i z a t i o n and l o s s of these a l k a l i s during a magmatic or metamorphic stage. High r a t i o s might then be prevalent along fractures where high thermal gradients, an escape route, and perhaps a v a i l a b i l i t y of water, aided i n escape of a v o l a t i l e phase. Anomalous K/Rb r a t i o s i n the Coast Mountains may hence be attributed either to destruction of an oceanic crust or to f r a c t i o n a t i o n within the root of an orogenic zone. E i t h e r view f i t s well with the concept of plate tectonics and subductional zones. Deep incorporation of metamorphic screens into a b a t h o l i t h i c complex of otherwise p r i m i t i v e S r ^ / S r ^ and K/Rb r a t i o s might also be expected of a subductional zone. Quite possibly then, t h i s has been the source area for a period of andesitic volcanism, although the great numbers of synplutonic dykes within the b a t h o l i t h i c rocks suggest that the extrusive systems have been more complex, as the dykes are t y p i c a l l y more basic than the surrounding rock. One other very i n t e r e s t i n g observation i s that the most recent s t y l e of igneous a c t i v i t y i s represented by acid volcanism (which does not r e -semble arc andesites of subductional zones) and high i e v e l , permissive i n t r u s i o n s of granite and syenite. These young, acid rocks have normal K/Rb r a t i o s and quite possibly a l k a l i n e metasomatism i s accompanying them at depth. A more t y p i c a l continental d i s t r i b u t i o n of potassium and 128 rubidium may well already be e s t a b l i s h i n g i t s e l f . The most obvious source of these a l k a l i s i s v o l a t i l i z a t i o n at depth due to establishment of new isotherms across a subductional zone which has ceased to be a c t i v e . The normal K/Rb r a t i o of these rocks i s to be expected, as they are the mobile a l k a l i n e phase and hence enriched i n rubidium by p a r t i t i o n i n g . Whether t h i s addition of a l k a l i s to a regime high i n strontium might produce at some l e v e l a plutonic system whose geochemistry i s similar to i n t r u s i v e rocks of the B.C. I n t e r i o r seems at l e a s t s u p e r f i c i a l l y p o s s i b l e . Regional potassium metasomatism of the required nature appears to have taken place i n the Athabasca mobile zone. The geochemistry of t h i s metasomatism and the tendency for upward migration of a l k a l i n e phases i n the crust are discussed by Burwash and Krupicka (1969). Interpretation of Tec.tonic Form and History The model of global tectonics which deals with boundary i n t e r a c t i o n s between large c r u s t a l p l a t e s , has been very successful i n explaining geo-physical and morphological features of the ocean basins and continental margins. Recognition of zones of c r u s t a l r i s i n g and subduction has led to speculation as to the p o s s i b i l i t y of f o s s i l subduction b e l t s or i n t e r p l a t e j o i n i n g l i n e s on the continents and how these might be recognized. The Coast Mountains of B r i t i s h Columbia are presently i n a somewhat debatable p o s i t i o n i n t h i s global tectonic framework. During much of the T e r t i a r y , a major subductional zone appears to have extended along the e n t i r e western coast of North America, the evidence from ocean f l o o r mag-neti c patterns having been discussed by Atwater and Menard (1970), Morgan (1968), and Menard and Atwater (1968). At present there i s an apparent 129 termination of a dissected ridge system (Gordo and Juan de Fuca Ridges) to the west of Vancouver Island, and an active f a u l t system (Queen C h a r l o t t e — Fairweather Fault) running northward along the margin of the continental r i s e . Despite the proximity of r i s e s , there are no deep earthquakes beneath the western edge of North America, nor i s the recent volcanism within the Coast Mountains t y p i c a l of arc andesites. Subduction beneath the Coast Mountains has almost c e r t a i n l y been greatly reduced from the rate of 7 cm/yr estimated for early T e r t i a r y underflow. It has been suggested by various authors (Caner and Cannon, 1965; Souther, 1970; Bostrom, 1968a) that an extension of the oceanic ridge system runs beneath or near the Coast Mountains. This suggestion cannot be l i g h t l y dismissed, although lack of a well defined r i f t system confines t h i s p o s s i -b i l i t y to a f a i r l y recent development, and the most recent tectonic form i s major block subsidence. The period of u p l i f t which produced the rock age d i s t r i b u t i o n pattern observed i n the Kitimat Ranges, appears to be that period of subduction which marked the consumption of the Fa l l e r o n Plate as outlined by McKenzie and Morgan (1969). Evidence, both observational and t h e o r e t i c a l , for strong u p l i f t of coastal margins during subduction, has already been discussed. The youngest zone of the Kitimat Ranges dates, i n fa c t , from the period when the F a l l e r o n subduction l i n e was active there. Subduction must have ceased or been greatly reduced sometime i n the mid T e r t i a r y , allowing formation of an erosion surface i n the Coast Moun-ta i n s , which i s now the summit envelope. U p l i f t was re-instated during the Pliocene, a r i s e of at least 6000 feet having occurred since deposition of 130 Pliocene lavas i n the Taseko area. Cause of t h i s elevation i s perplexing. It may be associated with the suggested change i n d i r e c t i o n of the Juan de Fuca ridge system through the period of 7.5 m.y. to 3 m.y. ago (Menard and Atwater, 1968). This f i n a l u p l i f t , and the period of r e l a x a t i o n and subsidence which i s following, are accompanied by acid igneous events, however, and both may have resulted d i r e c t l y from re-establishment of isotherms across the old zone of subduction. 1 3 1 Summary of Supporting Evidence, for T e r t i a r y History of tme Coast Mountains a. E a r l y T e r t i a r y orogeny i n the Coast Mountains was associated with the subduction of oceanic cru s t . i ) Interpretation of ocean f l o o r magnetic-patterns (Mackenzie and Morgan, 1969) i i ) E a r l y T e r t i a r y andesitic volcanism i n the C o r d i l l e r a of B r i t i s h Columbia (Souther, 1970) i i i ) Anomalous K/Rb r a t i o s i n igneous r o c k s — i n t e r p r e t a t i o n as a l k a l i s derived from oceanic crust ( t h i s work, p 3 6 , 1 2 5 ) i v ) Anomalous K/Rb r a t i o s — i n t e r p r e t a t i o n as an u p l i f t e d root zone ( t h i s work, p 5 7 v 125) v) Comparison of strontium and potassium d i s t r i b u t i o n s i n the southern C o r d i l l e r a — i n t e r p r e t a t i o n of Coast Mountains o r i g i n as an u p l i f t e d root zone ( t h i s work, p 4.9, 125) v i ) P r i m i t i v e S r 8 7 / S r 8 ^ r a t i o s i n igneous rocks ( t h i s work, p 64 > v i i ) Interpretation of age-date d i s t r i b u t i o n as central u p l i f t i n Kitimat Ranges ( t h i s work, p 1091 b. Lines of u p l i f t (as noted above)may be caused by rapid subduction beneath a continental margin. i ) From purely t h e o r e t i c a l c a l c u l a t i o n s (Danes, 1970) i i ) C o r r e l a t i o n of deep earthquake zones beneath the C o r d i l l e r a with elevation of C o r d i l l e r a and strong u p l i f t ( t h i s work, p 1 1 2 ) c. .Block tectonics were active i n the Coast Mountains i n the early T e r t i a r y . i ) Apparent blocks of d i f f e r i n g lineament ( s t r e s s ) patterns ( t h i s work, 132 Appendix XI ) i i ) F r a c t u r e boundary to an age-date p a t t e r n ( t h i s work, p 109) d . The m i d - T e r t i a r y was a t ime of comparative t e c t o n i c quiescence i n the Coast Mounta ins . i ) C e s s a t i o n of v o l c a n i s m i n the C o r d i l l e r a of B r i t i s h Columbia (Souther , 1970) i i ) Development o f an e r o s i o n sur face or s u r f a c e s , or an upland s u r -face across the Coast Mountains ( f o r example, Peacock, 1935) i i i ) Smal l r e l i e f of the Coast Mountains w i t h r e s p e c t t o I n t e r i o r P l a t e a u (based on T i p p e r , 1966; see t h i s work, p gg) e . At l e a s t some of the l i n e a r summit envelope d i s c o n t i n u i t i e s (SED's) of the Coast Mountains r e s u l t from b l o c k f a u l t movements. i ) B l o c k p a t t e r n s formed by SED's and l i n e a r c o n t i n u i t y of scarps (maps 6 and 7) i i ) C o r r e l a t i o n of SED*s w i t h thermal centers (map 5) i i i ) Se i smic a c t i v i t y a long an SED (map 8) i v ) C o r r e l a t i o n of SED's w i t h anomalous K/Rb r a t i o s i n igneous r o c k s (map 1) v ) Apparent b l o c k t i l t i n g ( t h i s work, p 90) v i ) C o r r e l a t i o n of secondary e r o s i o n sur faces across SED*s ( t h i s work, Appendix X) v i i ) C o n t r o l of abrupt changes i n f j o r d depths by SED's (maps 6 and 7) v i i i ) C o n t r o l of SED's by major metamorphic screens , which are l i k e l y zones of c r u s t a l weakness (map 7) 133 f. The deepest fjords of the Coast Mountains r e s u l t from drowning of v a l l e y s through the subsidence of the f j o r d zone following Pliocene u p l i f t . i ) I s o s t a t i c i n s t a b i l i t y of Cascade and Olympic Ranges without subductional forces (Danes, 1969) i i ) S t r u c t u r a l i n s t a b i l i t y of Coast Mountains without pressure from the ocean side (Bostrom, 1968b) i i i ) C o r r e l a t i o n of deep f j o r d zones throughout the C o r d i l l e r a with coasts which have been glaciated but do not have the support of a rapid subduction (deep earthquake) zone ( t h i s work, p 112) i v ) Control of the abrupt headward commencement of deep fjords by SED*s and lineaments (maps 6 and 7) v) Gravity changes at f j o r d heads (Bankes, 1964; Crary, 1966) v i ) Abrupt or stepwise seaward termination of the deep zone of fjords and c o r r e l a t i o n of these with SED's arid tectonic features (maps 6 and 7) v i i ) Interpretation of l o n g i t u d i n a l channels as fractures on which Pliocene u p l i f t was reversed ( t h i s work, p qo) v i i i ) Interpretation of the s t r a n d f l a t as an erosion surface and i t s control of transverse channels ( t h i s work, P 9 2 , map 6) i x ) Bimodal frequency d i s t r i b u t i o n of Coast Mountains fjords trans-verse to the tectonic axis ( t h i s work, P91) 134 R e s u l t s N o r t h e r n C o a s t M o u n t a i n s A P P E N D I X I o f C h e m i c a l A n a l y s i s N o . o f S a m p l e D e s c r i p t i o n Rb * ? V p p m (% )K K/Rb R b / S r (%)c« 1 S k a r n — 43 0.07 — 17.5 2 Q . t z . d i o r i t e 14 626 .16 115 0.022 8 .6 3 S c h i s t 96 312 2 .4 250 .308 3.2 4' S c h i s t 130 381 3 . 9 300 .34 1.5 5 C i t z . m o n z . 58 890 I . 6 5 280 .066 1.7 6 G a b b r o 9 760 0.33 365 .012 7.0 7 D i o r i t e i i 711 1.2 j | - . 320 .053 4 . 6 8 Q . t z . d i o r i t e 15.9 1290 0.79 495 .012 5 .8 9 G r a n o d i o r i t e 36 702 1.05 290 .051 4.1 10 S c h i s t 94 116 2 .6 275 .81 1.2 11 S c h i s t 109 840 2.3 210 .13 2 . 0 12 G r a n o d i o r i t e 68 783 2.1 325 .087 — 13 G r a n i t e 116 22 3.45 295 5:..3!> 0.8 14 G r a n i t e 116 587 3.8 330 J 9 8 1.4 15 G r e e n s t o n e 10 90 0.42 420 .11 2 .7 16 P e g m a t i t e 253 239 3.2 125 1.06 0.7 17 S c h i s t 138 238 2.3 165 .58 0.8 18 S c h i s t 60 943 1.9 315' .064 7.0 19 S c h i s t 69 15 2 . 0 290 4 . 6 0.8 20 Q_tz . m o n z . 152 109 1.2 80 1.39 1.0 21 S c h i s t 56 271 1.45 260 .21 4 . 9 22 Q_ tz . d i o r i t e 43 ?76 1.05 245 .16 1.8 * values underlined are by i sotope^di lut ion; 135 A P P E N D I X 1 ( c o n t i n u e d ) N o . o f S a m p l e D e s c r i p t i on R b p p m S r ppm (% )K K/Rb R b / S r 23 Q t z . d i o r i t e 950 1.2 352 0 . 0 3 7 5 . 5 24 G r a n o d i o r i t e 19 1580 0 . 9 475 .012 4 . 6 25 G r a n i t e 159 84 3 . 0 190 1.81 0 . 6 26 L i m e s t o n e 94 — — — — 27 Q t z . d i o r i t e 56 573 2 . 0 355 .098 3 . 6 28 Q t z . m o n z . 44 993 1.7 385 .043 2 . 8 29 M e t a m o r p h i c 116 654 1.9 165 .117 2 . 6 30 L i m e y s e d . 9 393 0 .22 245 .023 1 5 . 6 31 Q t z . m o n z . 66 499 2 . 2 330 . 1 3 1.2 32 S e d i m e n t a r y 72 103 2 . 1 290 . 7 0 2 . 1 33 Q t z . m o n z . 82 754 3 .3 400 .106 1.1 3*» G r a n o d i o r i t e 62 1240 1.6 260 . 0 1 0 6 . 4 35 S c h i s t 49 22 1.7 345 2 . 2 3 2 . 3 36 Q t z . d i o r i t e 50 1190 1.0 200 .042 4 . 8 37 A r k o s e 133 138 3 . 0 225 . 9 6 1.3 38 L i m e s t o n e 66 >54 2 . 6 395 1222. 17 .5 39 S c h i s t 266 210 3 . 6 135 1.27 4 . 2 40 S c h i s t !§£ 203 3 .5 190 .91 6.5 41 Q t z . m o n z . 55 844 I . 6 5 300 .065 2 . 7 42 S e d i m e n t a r y 95 228 O .38 40 .42 2 . 9 43 G r e e n s t o n e 28 326 1.48 520 . 0 8 6 2 . 1 44 S e d i m e n t a r y 20 677 0 .65 325 . 0 3 0 3 .2 k$ S e d i m e n t a r y 118 261 2 . 8 240 0.145 1.8 136 - , D e s c n p t i S a m p l e 48 S e d i m e n t a r y 49 G r a n o d i o r i t e 50 G r a n o d i o r i t e 51 D i o r i t e 52 G n e i s s 53 D i o r i t e 54 G n e i s s 55 G n e i s s 57 C o n g l o m e r a t e 58 C o n g l o m e r a t e 59 C o n g l o m e r a t e 60 G n e i s s 61 G n e i s s 62 G n e i s s 63 G n e i s s 64 G n e i s s 65 G n e i s s 66 G a b b r o 67 S c h i s t 68' : G n e i s s 69 a 1 t e r a t i on s a m p l e ( 0 _ t z . d i o . ) A P P E N D I X 1 ( c o n t i n u e d ) Rbnnm S r (% )K ppm ppm _ 80 160 1.6 44 1196 1.55 72 1040 1.6 41 316 1.35 3 8 . 6 479 1.0 32 190 0 . 9 6 28 116 0 . 9 6 28 109 1.20 12 744 0.65 30 413 1.36 53 1392 2 . 0 31 1015 — 1 1 . 6 489 0 .78 2 3 . 7 1320 1.15 35 821 1.1 30 251 1.2 32 239 1.2 10.1 152 0.46 72 336 1.1 24 1233 1.15 31 1363 1.70 K/Rb R b / S r ( % ) C a 200 0 . 5 0 2 . 3 350 . 0 3 7 4 . 1 220 . 0 6 9 3.8 320 . 1 3 5 . 3 260 .084 3 . 0 300 . 168 5.1 345 .24 5 . 3 430 . 2 5 7 5 . 9 $4 0 . 0 1 6 4 . 1 450 .073 3 .0 380 . 038 1.7 455 .031 — 670 .024 6 . 2 485 . 0 0 6 3 .3 315 .043 2 . 6 400 . 12 5 . 0 380 . 1 3 ^ 5 . 5 455 . 0 6 6 — 155 .21 3 .0 480 . 019 — 545 0.023 3 .5 137 A P P E N D I X 1 ( c o n t i n u e d ) D e s c r i p t i o n R b p p m S r (% )K K/Rb Rb/S r ( % )Ca 70 Q_tz . m o n z . 9k 950 3 . 0 320 0 .099 : .2 .8 71 G n e i s s 31 921 1.3 420 . 0 3 4 5 . 5 72 L a m p , d y k e 28 538 0 .78 280 .052 74 C o n g l o m e r a t e 15 378 . 6 7 445 .040 2 . 4 75 C o n g l o m e r a t e 16 187 0 .75 470 . 0 8 6 1.9 76 C o n g l o m e r a t e 10 413 0 . 3 6 360 .024 ; 1v7 77 C o n g l o m e r a t e kk 508 1.85 420 . 0 8 7 1.-6 78 C o n g l o m e r a t e ,9. 312 . 9 6 505 .061 ? . 3 80 G n e i s s 17 384 0 .85 500 .044 2 . 7 81 V o l c a n i c 7 1 . 6 391 2 . 5 0 349 .183 82 G r a n o d i o r i t e 14 . 4 576 0 . 5 7 395 0 .028 — C e n t r a l C o a s t M o u n t a i n s 155 L a m p , d y k e 20 — 0.51 255 0 .103 4 . 9 156 G r a n o d i o r i t e 24 165 1.18 490 .15 3 .5 157 G r a n o d i o r i t e 24 1095 1.25 520 .022 4 . 8 158 G r e e n s t o n e 162 0 .38 445 .083 8 . 3 159 M e t a s e d . 52 384 1.7 325 .135 2 . 7 160 Q . t z . m o n z . 86 264 2 . 6 300 .325 2 . 4 161 M i g m a t i t e 55 566 1.15 210 . 0 9 7 4 . 4 162 G a b b r o hi 551 0 .33 945 .0.006 4 . 6 138 A P P E N D I X J ( c o n t i n u e d ) row. o r v S a m p l e D e s c r i p t i o n ppm S r ppm (% )K K/Rb R b / S r ( % ) C a 163 Q t z . d i o r i t e 10 566 0.49 490 0.018 5.5 164 L i m e s t o n e 16 136 0.14 90 .12 — 166 G r a n o d i o r i t e 43 515 1.2 280 . 083 4.1^ 167 G a b b r o — 537 0.26 — — 9.1 168 V o l c a n i c 19 515 0 .79 415 .035 5.0 k 169 Q t z . d i o r i t e 26 667 O . 8 9 350 . 0 3 9 5.2 170 Q f z . d i o r i t e 17 798 0.81 475 .021 5.3 171 G n e i s s , M i g . 35 783 1.0 285 .045 — 172 Q t z . m o n z . 48.7 392 2.05 20 .124 1.8 173 Q t z . d i o r i t e 20 635 0 .70 350 .031 4.6 174 G r a n o d i o r i t e 56 123 2.1 375 .455 4.6 175 G a b b r o (5) 870 0.2 (400) (.006) 7.4 176 S k a r n — 75 0.11 — — 2.5 177 M e t a s e d . 36 528 1.3 360 . 068 — 178 S e d i m e n t a r y 35 235 0 .63 180 .149 — 179 S e d i m e n t a r y 101 232 2.2 220 .435 1.5 180 G r a n o d i o r i t e 29.2 1616 1.2 410 .018 3.9 181 D i o r i t e 27 507 1.0 370 .053 6.6 182 S c h i s t 94 153 2.6 275 .61 — 183 G r a n o d i o r i t e 35 1138 1.75 500 .031 1.7 184 V o l c a n i c 63 120 2.3 365 .53 1.1 185 S e d i m e n t a r y 65 170 1.35 205 O . 3 8 0.5 139 A P P E N D I X 1 ( c o n t i n u e d ) N o . o f S a m p l e D e s c r i p t i on R b p p m S r p p m (%)K K/Rb R b / S r ( % )Ca 186 G r e e n s t o n e 27 319 0 .58 215 0 .085 0.7 187 D i o r i t e 36.3 667 0 . 96 375 .054 6.0 188 Q t z . m o n z . 70 70 2.7 385 1.0 3.0 189 G r a n o d i o r i t e . 3 8 928 1 .65 435 .041 4.8 190 G r a n o d i o r i t e 89 304 2.7 305 . 2 9 0.8 191 G r a n o d i o r i t e 22.5 718 1 .35 600 .031 4.6 192 M e t a s e d . 51 131 1.05 205 .39 1.7 193 G a b b r o — 203 0.10 — — 3.8 194 D i o r i t e 13.3 54 0.60 451 . 25 5.3 195 G r a n o d i o r i t e 58 725 2.1 360 .080 2.3 196 G a b b r o 20 827 0.42 210 .024 1.3 197 G r a n o d i o r i t e 62 316 1.85 300 .20 3.1 198 S e d i m e n t a ry 34 400 1 .05 310 . 0 8 5 0.6 199 S k a r n 15 718 0.22 145 .021 — 200 S c h i s t 57 307 2 . 5 9 385 .19 4.9 201 0_tz . d i o r i t e 18 979 0.64 355 0 1 8 5.0 202 S c h i s t 43 323 1.40 320 . 1 3 0.5 203 ; . S c h i s t 129 196 3.0 230 .66 1.0 204 P e g m a t i t e 22 653 0.64 290 . 0 3 4 2.5 205 G r a n u l i t e 35 468 0.88 250 . 075 5.0 206 A p l i t e 130 94 3.1 240 1 .38 0.8 207 Q t z . d i o r i t e 27 1095 1.3 480 . 025 4.4 140 A P P E N D I X 1 ( c o n t i n u e d ) N o . o f S a m p l e D e s c r i p t i o n R b p p m S r ppm (%)K K/Rb R b / S r ( % ) C a 208 Q t z . d i o r i t e 22 858 0 .88 400 0 .026 2 . 9 209 G r a n o d i o r i t e 78 241 1.6 205 .32 1.2 210 Q t z . d i o r i t e 38 1479 1 .40 370 . 027 4 . 7 211 Q t z . d i o r i t e 2 0 . 9 1580 1.0 480 . 0 1 3 6 .2 212 G r a n o d i o r i t e 36 913 1.55 430 . 0 3 9 3.3 213 G r a n o d i o r i t e 38 255 1.5 395 .149 2 . 4 214 . > . Q t z . d i o r i t e 39 587 1.05 270 .144 4 . 9 215 G r a n o d i o r i t e 62 1030 1.95 315 .061 2 .6 216 D i o r i t e 25 866 O.96 385 .029 3.5 217 Q t z . d i o r i t e 23 1160 1.0 445 . 0 2 0 4 . 6 218 G r a n o d i o r i t e 34 587 1.2 350 .058 4 . 8 219 Q t z . d i o r i t e 18 1450 0 .95 535 .012 5 .7 220 G r a n o d i o r i t e 38 866 1.35 350 .044 3.9 221 Q t z . d i o r i t e 32 1124 1.40 440 . 028 5.2 222 Q t z . m o n z . 71 579 1.45 200 .122 1.2 223 G r a n o d i o r i t e 30 1131 1.8 600 . 0 2 7 1.8 224 G n e i s s 40 914 1.3 325 .044 5.1 225 Q t z . d i o r i t e 14.2 1117 0 . 7 3 515 .013 5 .6 226 G r a n o d i o r i t e 39 196 1.25 320 .199 *».3 227 G n e i s s 3 5 ^ 1450 0 .88 250 .024 — 228 G n e i s s 50 1537 1.25 250 . 0 3 3 2 . 8 * 229 V o l c a n i c 8 7 . 6 531 2 .68 306 0 .165 — 141 A P P E N D I X 1 ( c o n t i n u e d ) N o . o f S a m p l e D e s c r i p t i o n R b p p m S r ppm (% )K K/Rb R b / S r ( % ) C a 230 E p i d o t e 7 2 . 3 3936 1.43 198 0 . 0 1 8 — 234 C o n g l o m e r a t e 28 373 0 .78 280 . 0 7 5 1.6 235 Q t z . d i o r i t e 15 659 O .63 421 . 0 2 3 — 236 D i o r i t e 11 486 0 . 2 5 227 .023 S o u t h e r n C o a s t M o u n t a i n s N o . o f S a m p l e D e s c r i p t i on ppm S r p p m (% )K K/Rb Rb/S r 301 Q t z . d i o r i t e 24 . 0 500 0 .79 329 0.048 302 Q t z . d i o r i t e 2 5 . 9 439 1 .19 459 . 0 5 9 303 Q t z . d i o r i t e 1 5 . 9 670 0 . 5 0 314 .024 304 Q t z . d i o r i t e 12.1 481 0 .53 438 .025 305 Q t z . d i o r i t e 21 .0 457 0 . 9 4 448 .046 306 G r a n o d i o r i t e 3 5 . 0 424 1 .36 389 . 083 307 G r a n o d i o r i t e 2 6 . 7 770 1.31 491 . 022 308 G r a n o d i o r i t e - 4 7 . 3 492 2.01 444 . 0 9 6 309 G r a n o d i o r i t e 5 9 . 5 426 2 .34 393 .141 310 G r a n o d i o r i t e 3 8 . 4 318 1.84 479 . 0 9 5 311 G r a n o d i o r i t e 6 3 . O 372 1.71 251 . 1 6 9 312 G r a n o d i o r i t e 3 9 . 7 558 1.53 383 .071 313 G r a n o d i o r i t e 2 3 . 7 491 0 . 9 7 409 .048 314 G r a n o d i o r i t e 40 .2 401 1.48 368 . 1 0 0 316 G r a n o d i o r i t e 3 0 . 5 630 0 .62 193 0.048 142 A P P E N D I X 1 ( c o n t i n u e d ) N o . o f S a m p l e D e s c r i p t i o n R b p p m S r p p m (% )K K/Rb R b / S r 317 G r a n o d i o n * t e 42 .5 426 2.01 473 0 . 1 0 0 318 D i o r i t e 34.1 326 1.39 408 .104 319 Q t z . d i o r i t e 4 7 . 5 245 1.62 341 .193 320 M e t a v o l c . 7 1 . 6 201 2 . 9 4 411 . 157 321 Q t z . d i o r i t e 20.1 401 0.71 353 . 0 5 0 322.- ^ " G r a n o d i o r i t e 18.1 882 O .58 320 . 0 2 0 323 Q t z . d i o r i t e — 725 0.31 — — 324 Q t z . d i o r i t e 32.A 647 0 .70 216 . 0 5 0 325 Q t z . d i o r i t e 2 7 . 0 309 1.12 415 . 087 326 G r a n o d i o r i t e 95.4 247 2.61 2 7 4 , .382 327 G r a n o d i o r i t e 4 9 . 0 468 1.66 339 .105 328 M e t a v o l c . 18.1 562 O .38 210 . 032 329 M e t a v o l c . 19 .3 539 0.31 161 . 036 330 Q t z . d i o r i t e 2 0 . 6 413 0 .55 267 . 0 5 0 331 G r a n o d i o r i t e 4 5 . 3 660 1.22 269 . 0 6 9 332 Q t z . d i o r i t e 2 7 . 4 399 0 . 6 6 267 .062 333 Q t z . d i o r i t e 40 .8 589 1.70 416 . 069 33k G r a n o d i o r i t e 46 . 3 294 1.52 328 .158 335 Q t z . d i o r i t e 5 0 . 7 386' 1.39 274 .131 336 M e t a v o l c . 5 5 . 7 570 1.25 224 . 0 9 8 337 G r a n o d i o r i t e 24 .3 637 0 . 9 9 408 . 0 3 7 338 G r a n o d i o r i t e 3 9 . 0 608 1 .62 415 0 . 0 6 4 143 A P P E N D I X 1 ( c o n t i n u e d ) N o . o f S a m p l e D e s c r i p t i o n Rb m ppm S r ppm (% )K K/Rb R b / S r 339 Q t z . d i o r i t e 3 8 . 4 598 0 . 9 0 234 0.064 340 M e t a v o l c . 40 .0 704 1.12 280 . 0 5 7 341 G r a n o d i o r i t e 2 6 . 6 229 -1.20^ 470 .116 342 G r a n o d i o r i t e 4 7 . 3 425 1.74 368 .111 343 Q t z . d i o r i t e 3 5 . 9 631 1.44 401 . 057 345 G r a n o d i o r i t e 35 560 1.66 474 .063 346 E p i d o t e 30 602 1.67 557 . 0 5 0 347 D i o r i t e 12 36O 0 . 6 0 500 .033 348 D i o r i t e 9 .2 354 0 . 13 141 . 0 2 6 349 G r a n o d i o r i t e 5 0 . 9 416 1.75 343 . 122 350 B a s a l t 2 8 . 5 0 . 1 0 — — 351 Q t z . d i o r i t e 19 287 0 . 9 4 495 .066 352 Q t z . d i o r i t e 14 .6 313 0 .57 390 .047 353 Q t z . d i o r i t e 2 7 . 5 265 1.10 400 .104 354 Q t z . d i o r i t e 24.1 781 0 .62 257 .031 355 Q t z . d i o r i t e 3 1 . 4 58O 1.66 529 . 0 5 4 356 B a s a l t 1 9 . 7 555 1.14 578 .036 357 Q t z . d i o r i t e 3 7 . 7 556 1.44 374 . 0 6 8 358 A n d e s i t e 14 .6 507 0 . 2 9 3:99 . 0 2 9 359 Q t z . d i o r i t e 26.1 967 0 .65 249 . 027 360 Q t z . d i o r i t e 21.7 869 0 .55 253 . 025 361 Q t z . d i o r i t e 18 .5 788 0 . 9 8 530 . 0 2 3 362 Q t z . m o n z . 8 5 . 4 141 2 .7 320 , 0 . 6 0 6 144 A P P E N D I X 1 ( c o n t i n u e d ) N o . " o f S a m p l e D e s c r i p t i o n ppm S r ppm (%)K K/Rb R b / S r 563 G r a n o d i o r t t e 35.2 463 1.48 420 0.016 564 Q t z . d i o r i t e 10.4 440 0 .32 307 .024 565 G r a n o d i o r i t e 40.5 480 1.35 333 .084 566 Q t z . d i o r i t e 22.5 584 1.02 453 . 038 567 Q t z . d i o r i t e 39.4 567 1 .98 502 .069 56$ Q t z . d i o r i t e 20.5 247 0.68 332 .082 570 G r a n o d i o r i t e 41.0 160 1 .56 380 . 2 5 6 571 A n d e s i t e 27.2 259 0 .76 279 . 105 572 D i o r i t e 9 .65 302 0 .32 332 .032 573 A n d e s i t e 9.68 336 0 .25 260 . 0 2 9 574 G r a n o d i o r i t e 37.2 628 1 .07 288 . 0 5 9 575 Q t z . d i o r i t e 2 9 . 8 630 1.20 403 .047 576 G r e e n s t o n e 12.6 145 0.15 119 .087 577 Ba s a 11 14.6 158 0.62 425 . 093 578 A r k o s e 15.6 68.4 0.61 391 .228 579 G r a n o d i o r i t e 43.2 239 1 .72 400 .181 580 M e t a v o l c . 29.7 138 0.57 192 .216 581 Q t z . d i o r i t e 27.9 596 1.12 40! .047 583 Q t z . d i o r i t e 59.3 592 1.52 256 .10 584 G r a n o d i o r i t e 32.5 672 1.68 517 .048 585 Q t z . d i o r i t e 49.1 672 1.02 208 . 0 7 3 586 Q t z . d i o r i t e 26.0 571 1.02 392 0.045 145 A P P E N D I X t ( c o n t i n u e d ) N o . o f S a m p l e D e s c r i p t i o n R b P P m S r p p m (% )K K/Rb R b / S r 587 Q t z . d i o r i t e 17 .0 950 0 .59 3k7 0 . 0 1 8 588 D i o r i t e 2 2 . 3 910 0 .69 309 . 025 589 Q t z . m o n z . 24 936 0 . 9 0 375 . 026 590 Q t z . d i o r i t e 18 860 0.61 340 .021 591 G r a n o d i o r i t e 31.^ 730 1.07 341 .043 592 Q t z . d i o r i t e 41 . 4 422 1.91 461 . 098 593 S c h i s t 8 3 . 4 225 2.21 265 .371 594 C o n g l o m e r a t e 2 9 . 5 329 0 .43 146 . 0 9 0 595 C o n g l o m e r a t e 51 906 O.58 115 . 056 596 G a b b r o 1 6 . 9 424 0 .25 148 .040 597 G a b b r o 11 379 0 .37 336 . 0 2 9 146 A P P E N D I X 1 ( c o n t i n u e d ) S o u t h e r n I n t e r i o r N o . o f S a m p l e D e s c r i p t i o n Rb ppm S r ppm (% )K K/Rb R b / S r 402 Q t z . d i o r i t e 41 . 0 656 0.94 229 0 .062 403 G r a n o d i o r i t e 6 7 . 3 331 1.82 210 . 2 0 3 404 Cr. ' h j a G n e i s s 259 180 4 . 5 5 175 1.43 405 Q t z . d i o r i t e 135 391 1.43 106 . 3 5 406 Q t z . m o n z . 268 308 4 . 0 0 149 . 8 7 407 Q u a r t z i t e 52 50 0 .89 171 1.04 408 S c h i s t 178 68 3.86 217 2.61 409 G r a n o d i o r i t e 151 1118 3.22 213 .14 410 D i o r i t e '61 819 1.40 230 . 0 7 411 Q t z . m o n z . 248 137 3 .06 123 1.81 412 Q t z . m o n z . 311 101 3 .67 118 3 .08 413 G r a n o d i o r i t e 144 742 2 . 5 0 174 .19 414 Q t z . m o n z . 126 1730 2 . 2 8 181 . 0 7 3 415 Q t z . d i o r i t e 64 423 0.94 147 .15 416 U l t r a b a s i c 16 358 0 .62 388 .04 417 G r a n o d i o r i t e 77 960 1.44 187 . 0 8 418 G r a n o d i o r i t e 154 455 2 .83 184 . 3 4 419 S y e n o d i o r i t e 103 1802 2 . 8 3 275 . 0 6 420 Q t z . p o r p h . 80 801 1.97 246 . 1 0 421 G r a n o d i o r i t e 7 9 . 2 408 1.21 153 . 1 9 4 422 G r a n o d i o r i t e 6 6 . 3 586 1.57 237 .113 423 D i o r i t e 45 306 0 . 9 7 215 0.15 147 A P P E N D I X 1 ( c o n t i n u e d ) N o . o f S a m p i e D e s c r i p t i o n Rb ppm S r ppm (% )K K/Rb R b / S r 424 Q t z . d i o r i t e 20 214 0 . 4 7 235 0 .09 425 V o l c a n i c 5 6 . 6 171 1.99 350 .331 426 D i o r i t e 51 .8 552 1.56 301 . 0 9 4 427 G r a n i t e 104 191 2 . 7 0 259 .64 428 G r a n o d i o r i t e 4 9 . 7 267 1.93 388 . 175 429 G r a n o d i o r i t e 98 799 2.40 245 . 12 430 G r a n o d i o r i t e 78 435 2 . 1 0 269 .15 431 0_ tz . d i o r i t e 50 h\S 1.12 224 . 1 0 432 G r a n o d i o r i t e 120 564 2 . 7 8 231 .212 433 Sy e n i t e 135 I 698 4 . 9 8 368 . 0 7 9 434 S y e n i t e 9 0 . 6 814 4 .02 443 .111 435 Q t z . d i o r i t e 60 713 1.53 255 . 0 8 436 A r k a s e 25 101 0 .43 228 .25 437 Q t z . d i o r i t e 72 556 1.87 260 . 1 3 438 Q t z . m o n z . 409 59 3.24 IT,- 6 . 9 439 Q t z . d i o r i t e 71 574 1.30 215 .12 440 S y e n i t e 86 760 2 . 6 6 309 .11 441 G r e e n s t o n e 83 95 2 . 7 3 384 . 8 7 442 G r a n i t e 183 = 1339 4 . 3 5 238 .14 443 Q t z . m o n z . 107 520 2 . 5 0 234 . 2 0 444 Q t z . m o n z . 187 776 3.90 202 .24 445 Q t z . m o n z . 2 3 6 : , 686 3.72 156 ,3kk 446 R h y o l i t e 718 153 4 . 0 5 56 4 . 7 447 S y e n o d i o r i t e 113 598 2 .72 196 0.19 148 A P P E N D I X 1 ( c o n t i n u e d ) N o . o f S a m p l e D e s c r i p t i on R b P P m S r p p m (%)K K/Rb R b / S r 448 Q t z . d i o r i t e 72 667 1.93 250 0.11 449 V o l c a n i c 31 752 1.05 339 .041 450 B a s a l t 22 352 0 .53 241 .062 451 E p i d o t e — 1105 0 .08 — ~ V a n c o u v e r I s l a n d N o . o f S a m p l e D e s c r i p t i on Rb ppm S r ppm (% )K K/Rb R b / S r 501 Q t z . d i o r i t e 3 8 . 4 399 1.78 462 0 .096 502 D i o r i t e 16.1 441 0 . 5 9 366 . 037 503 Q t z . d i o r i t e 25 .6 568 0 . 9 9 387 .045 504 M e t a v o l c . 7.7 165 0.021 273 .046 505 Q t z . d i o r i t e 5.3 128 0.11 207 .041 506 G r e e n s t o n e 9 . 5 818 0 . 3 9 410 . 012 507 Q t z . d i o r i t e 31 .6 337 0 .95 301 . 0 9 4 508 G r a n o d i o r i t e 90 743 1.78 118 .121 509 G r a n o d i o r i t e 38 369 1.21 363 . 1 0 3 510 G r a n o d i o r i t e 7 1 . 8 456 2 . 4 9 347 . 1 5 7 511 M e t a v o l c . 8 . 4 186 0.11 131 .045 512 V o l c a n i c 9.15 815 0 . 2 0 220 .011 513 V o l c a n i c 10 108 0.15 150 . 0 9 3 51^ Q t z . d i o r i t e 2 7 . 9 491 0.94 337 . 0 5 7 515 G r a n o d i o r i t e 3 4 . 2 330 1.13 38O 0.104 149 A P P E N D I X 1 ( c o n t i n u e d ) N o . o f S a m p l e D e s c r i p t i o n R b p p m S r p p m (%)K K/Rb R b / S r 516 E p i d o t e 2 2 . 9 1037 0 .35 153 0 .022 517 H y d r o t h e r m a l a l t e r a t i o n 3 2 . 9 295 1.38 419 .111 518 A n d e s i t e 1 2 . 6 180 0 .33 270 . 0 7 0 519 V o l c a n i c 9 . 9 112 0.13 131 . 0 8 8 520 G r a n o d i o r i t e 6 3 . 2 320 2.31 366 . 1 9 7 521 Q t z . m o n z . 6 6 . 5 354 2.48 373 .188 522 Q t z . d i o r i t e 14 .8 251 0 . 5 5 371 . 0 5 9 523 G r a n o d i o r i t e 3 2 . 0 356 0 .95 297 . 0 9 0 524 D i o r i t e 19 .5 542 0.51 262 . 036 525 G r a n o d i o r i t e 5 5 . 4 287 185 .193 526 G r e e n s t o n e 13 .3 440 0.42 316 0 . 0 3 0 150 APfEN.pl* ,11 S e l e c t i o n and Handling of Samples The 313 samples analysed for potassium, rubidium, and strontium during the course of t h i s project may be subdivided into two major groups, examined at d i f f e r e n t times and by somewhat d i f f e r e n t techniques. The f i r s t con-s i s t e d of rock samples obtained from c o l l e c t i o n s made by the writer and others for the Coast Mountains Project of the Geological Survey of Canada during the 1965 and 1967 f i e l d seasons. Specimens analysed were chipped from larger samples retained by the forementioned project with the kind permission of Dr. J . Roddick and Dr. W. Hutchison. The region covered by t h i s c o l l e c t i o n i s roughly the Coast Mountains from Nass River south to l a t i t u d e 53° (see maps 1 and 2)3 and w i l l be r e f e r r e d to as the northern and central Coast Mountains c o l l e c t i o n s . Samples were selected to study both the areal and l i t h o l o g i c a l d i s t r i b u t i o n of the elements concerned. A l a t e r c o l l e c t i o n (159 rocks) made during 1969 and 1970 involved the southern part of B r i t i s h Columbia, from the West Kootenay d i s t r i c t to Vancouver Island. In t h i s group mainly igneous rocks were involved, and c o l l e c t i o n was dominantly from roadside outcrops and i n l e t shorelines, care being taken to sample unweathered material. This mode of c o l l e c t i o n has the advantage of allowing a larger specimen to be taken and of being able to observe regional geology to avoid selecting obviously l o c a l i z e d br d i f f e r e n t i a t e d l i t h o l o g y . There i s , however, the d i s t i n c t disadvantage that both a r t e r i a l roads and some ocean channels tend to follow zones of geo-l o g i c a l d i s l o c a t i o n or major lineaments, quite p o s s i b l y the same l i n e s as might show anomalous geochemical c h a r a c t e r i s t i c s or a l t e r a t i o n . By compari-151' son, most of the specimens obtained from the Coast Mountains Project originated with helicopter-supported g r i d sampling or ridge traverses. Handling and Standard Chemical Procedures Etching and S t a i n i n g . C l a s s i f i c a t i o n of plutonic rocks (see Table 15) i s based on the r a t i o of potassium feldspar to pl a g i o c l a s e , and the per-centage of quartz present. It i s almost always d i f f i c u l t , and frequently impossible, to v i s u a l l y i d e n t i f y potash feldspar i n Coast Mountains plutonic rocks. Furthermore i t i s often not fe a s i b l e to make a good estimate of quartz i n hand specimen. A l l plutonic rocks were hence etched and stained to allow easy i d e n t i f i c a t i o n of minerals. In t h i s procedure, the sample face on which estimation i s to be made i s f i r s t submerged for approximately two minutes i n 49% hydrofluoric acid i n a p l a s t i c bowl. This step i s per-formed i n a fume c l o s e t , and p l a s t i c or rubber gloves are a recommended safety precaution. A l l acid i s then rinsed o f f and the rock dipped for a further two minutes i n a saturated so l u t i o n of sodium c o b a l t i n i t r i t e . F i n a l l y the specimen i s flushed under a stream of water u n t i l a l l soluble c o b a l t i n i t r i t e i s removed, and then allowed to dry. Mineral i d e n t i f i c a t i o n i s possible only when the treated sample i s thoroughly dry. Minerals which contain potassium are stained a bright yellow by i t s insoluble c o b a l t i n i t r i t e s a l t . B i o t i t e flakes may be yellow at t h e i r edges, but are e a s i l y d i f f e r e n t i a t e d from potash feldspar, on whose abundance the rock c l a s s i f i c a t i o n depends. Plagioclase has a d i s -t i n c t i v e white, chalky texture, and quartz remains c l e a r . Occasionally pl a g i o c l a s e a t t a i n s a l i g h t yellow c o l o r a t i o n , presumably due to minor potassium content by a l t e r a t i o n or p e r t h i t i c intergrowth. An o v e r a l l 1 5 2 yellowish caste, however, usually s i g n i f i e s i n s u f f i c i e n t washing before drying the sample. This process may be shortened by keeping the hydrofluoric acid warm i n a water bath. Cloudy quartz and deep encrustations on plagioclase in d i c a t e too intense an acid attack, while poor p l a g i o c l a s e — q u a r t z d e f i n i t i o n signals weakening of the acid or i n s u f f i c i e n t time allowed for etching. As these judgments can only be made on a completely dry surface, i t i s convenient to dry rocks quickly by heating during batch runs so that appropriate adjustments may be made to the process. Following staining, estimation of mineral percentages was made with the assistance of charts simulating areal coverage by randomly scattered material. Besides mineral i d e n t i f i c a t i o n , staining provides considerable information about rock textures and a l t e r a t i o n , e s p e c i a l l y regarding the action of l a t e v o l a t i l e phases which tend to be potassium-rich and which may have been important i n the d i s t r i b u t i o n of a l k a l i s i n many Coast Mountains rock s u i t e s . Crushing and S p l i t t i n g . Rock specimens obtained from the Geological Survey of Canada were too small to be crushed i n the available machines without sustaining s i g n i f i c a n t contamination. They were hence crushed by hand to a grain size of a few millimeters and then s p l i t , a few grams being further reduced by hand. Many of the samples contained r e s i s t a n t b i o t i t e flakes, and i t was generally not possible to reduce these as com-p l e t e l y as other minerals. This i s one apparent source of error as i t allows development of inhomogeneity i n the powder by a g i t a t i o n , and i t causes problems during X-ray fluorescence analysis as w i l l be discussed. 153 With care f u l handling, however, the errors did not prove to be so great that a c q u i s i t i o n of a b a l l m i l l was f e l t to be necessary. No attempt was made to screen the samples or reduce them to a s p e c i f i c g rain s i z e . Very fine powders were found to have s i g n i f i c a n t non-reproducability during X-ray fluorescence analysis due to compaction. The larger samples obtained i n southern B r i t i s h Columbia were pulver-ized mechanically and then further reduced by hand. The Acid Attack. For a l l a n a l y t i c a l procedures requiring destruction of the s i l i c a t e matrix, attack by hydrofluoric acid was employed. Usually t h i s was combined with sulphuric acid, although p e r c h l o r i c acid was s u b s t i -tuted where calcium analyses were involved. The r e a c t i o n of sulphuric acid on a l k a l i perchlorates i s explosive, and care was taken to clean the fume hood between i t s use i n techniques involving sulphuric and p e r c h l o r i c acids. The following procedure was used for a l l attacks: i ) Approximately one-quarter gram of powdered rock i s weighed out on a Mettler Micro-gram-atic balance and transferred into a 50 ml. Teflon beaker. i i ) Roughly 5 ml. of 50% sulphuric acid or 70% p e r c h l o r i c acid i s added to the sample. If a spike i s involved, i t i s pipetted into the beaker before the a c i d . i i i ) Approximately 15 ml. of 48% hydrofluoric acid i s added, the Teflon beaker covered, and placed i n a tray of quartz sand on a hotplate. It i s held at 120°C for at least eight hours. This dissolves a l l of the rock with the exception of a few minor accessory minerals and graphite, which was seldom present. 13k i v ) Beaker covers are removed and the acids> together with v o l a t i l e f l u o r o s i l i c a t e s , fumed o f f at approximately 200°C. Samples to be used i n an ion exchange column are best treated again with a small amount of sulphuric acid and the fuming step repeated to ensure removal of a l l X f l u o r i d e i o n . i v ) The dry residue i s taken up i n a few m i l l i l i t e r s of hydrochloric a c i d . This w i l l not dissolve a l l of the residue i f i t i s present as sulphates; a considerable portion of the a l k a l i n e earths remain undis-solved i f 2N acid i s employed. They are considerably more soluble i n 6N hydrochloric a c i d . The Teflon beakers are cleaned i n Fisher laboratory cleaning reagent followed by b o i l i n g i n 30% n i t r i c a c i d . P e r i o d i c a l l y , they are further cleaned with acetone or an abrasive. In spite of t h i s the beakers occlude material, which appears as a brownish residue during blank runs. This material does not seem to contain s i g n i f i c a n t strontium or rubidium, however. Ion Exchange Columns. A l l work dealing with i s o l a t i o n of rubidium and strontium by ion exchange used Dowex-50W-X, 200-400 mesh cation exchange r e s i n . The columns were made by annealing 200 ml. round bottom f l a s k s to the tops of 12-inch chromatographic columns of 3/8-inch inside diameter. Height of r e s i n i n these columns va r i e d with normality of the hydrochloric acid wetting i t , being approximately 6 inches for 6.2N acid and 7% inches for 2N. The basic technique for separation of rubidium and strontium from rocks i s given by Allsopp (1961). Columns were used mainly i n preparing 155 samples for running on the mass spectrometer, and were c a l i b r a t e d by drying successive portions of the elutant onto c e l l u l i t e and running these on X-ray fluorescence. In such procedures, i t was found best to use r e a l rocks rather than chemical reagents as standards, as there i s a s i g n i f i c a n t l y d i f f e r e n t response. C a l i b r a t i o n curves are given i n Figure 13. In rubidium-strontium age-dating work, i t i s generally not necessary to p u r i f y the rubidium on columns. Rubidium l e v e l s i n Coast Mountains rocks are so low, however, that i t was found advantageous to do so, a cut between 45 ml. and 70 ml. being employed with a 2N elutant. The p u r i f i c a t i o n of strontium, e s p e c i a l l y with regard to removing rubidium, i s e s s e n t i a l for mass spectrometric work. Three d i f f e r e n t systems were used at various times for separating rubidium and strontium p r i o r to f i n a l separation on the column: i ) P r e c i p i t a t i o n of rubidium (dissolved i n 2N HCl) with a strong s o l u t i o n of sodium tetraphenylboron. This i s rapid and simple, but introduces the possible contamination of another reagent, and much strontium remains undissolved i n 2N a c i d . This was s u i t a b l e , however, for Coast Mountains rocks r i c h i n strontium, and i t i s t h i s procedure which was used for the blank run. i i ) Leaching of sulphates with 100 ml. of hot, d i s t i l l e d water. This technique i s very clean and r a p i d . X-ray fluorescence t e s t s show that approximately 90% of the rubidium i s l o s t and 65% of the strontium i s retained i n the residue. i i i ) S t r i p p i n g of rubidium on an ion exchange column using 12N a c i d . The a l k a l i n e earths are almost immobile i n Dowex-50 when 12N hydro-15'6 c h l o r i c acid i s used as an elutant, while rubidium and almost everything else i s flushed through. Hydrochloric acid cannot be d i s t i l l e d , however, at 12N concentration and so must f i r s t be p u r i f i e d by running through a column to remove any strontium. As the a l k a l i n e earths have very l i t t l e s o l u b i l i t y i n 12N hydrochloric acid, material i s transferred to the columns i n 5 ml. of 6.2N ac i d . The column has previously been adjusted to 12N, and a further 30 ml. of 12N acid are then added. Following t h i s , the strontium i s mobilized with 6.2N acid, Figure 13 giving the c a l i b r a t i o n curve. For the rocks used, strontium was present i n copious quantities and generally only a 10 ml. sample between 25 ml. and 35 ml. elutant i s c o l l e c t e d . On both 12N and 2N runs i t was found advantageous to prevent band spreading of rubidium concentrate at the top of the column by i n i t i a l a d dition of elutant as two 5 ml. aliquots followed by addition of the remaining a c i d . Columns were cleaned by flushing with 100 ml. of d i s t i l l e d 6N hydro-c h l o r i c acid and then 50 ml. of 2N a c i d . P e r i o d i c a l l y they were back-aspirated to allow r e s e t t l i n g of the r e s i n bed, which becomes compacted during shrinkage and expansion r e s u l t i n g from v a r i a t i o n i n the normality of elutants. In order to speed the ion exchange separation, elutants were forced through the columns under pressure. A monometer was used to prevent t h i s pressure becoming greater than 5 inches of mercury. 157 Fi gure "! 3 ELUTION CALIBRATION CURVES FOR ION EXCHANGE (column, r e s i n , and elutant parameters in text) E lu t ion with 6 N HCl fo l low ing 30 ml of 12 N HCl 100% STRONTIUM ""I \ < I I 1 i • I » i LO O LA O LA O LA O LA O *TT- •— CM CM OA CO -CT LA ml. of e lutant E lu t ion with 2 N HCl OA -3- LA NO P-. CO GN O — CM OA 158 A P P E N D I X I I I Atomic A b s o r p t i o n A n a l y s i s B o t h p o t a s s i u m and c a l c i u m a n a l y s e s were made o n t h e T e c h t r o n AA-4 a t o m i c a b s o r p t i o n s p e c t r o p h o t o m e t e r u n i t o f t h e Department o f G e o l o g y . T a b l e 12 l i s t s t h e s e t t i n g s used f o r t h e s e two e l e m e n t s . Samples o f a p p r o x i m a t e l y 0 . 2 g s i z e were d i s s o l v e d by t h e u s u a l a c i d a t t a c k , p e r c h l o r i c a c i d b e i n g used r a t h e r t h a n s u l p h u r i c when c a l c i u m a n a l y s e s were t o be p e r f o r m e d . The s a m p l e s , as s o l u t i o n s i n d i l u t e h y d r o -c h l o r i c a c i d , were s t o r e d u n t i l a p p r o x i m a t e l y s e v e n t y had a c c u m u l a t e d . E a c h was t h e n d i l u t e d t o one l i t e r i n a v o l u m e t r i c f l a s k , and a p o r t i o n s p i k e d w i t h l an thanum i f c a l c i u m a n a l y s e s were i n v o l v e d , and sodium as s p e c i f i e d i n T a b l e 12 . T h i s d i l u t i o n r e d u c e s c o n c e n t r a t i o n o f t h e s o l u t i o n s t o a few ppm, p l a c i n g them i n t h e most s e n s i t i v e r a n g e f o r a tomic a b s o r p -t i o n a n a l y s i s . At such low c o n c e n t r a t i o n s , however , i t i s n e c e s s a r y t o p e r f o r m t h e a n a l y s e s w i t h i n a few h o u r s a f t e r d i l u t i o n . O n l y a few m i l l i -l i t e r s o f each s o l u t i o n i s r e q u i r e d f o r a r e a d i n g . The l a n t h a n u m and sodium a d d i t i v e s were employed t o p r e v e n t i n t e r -f e r e n c e from o t h e r e l e m e n t s ( see E l w e l l and G i d l e y , 1 9 6 2 ) . Lanthanum s o l u -t i o n was p r e p a r e d by d i s s o l v i n g t h e o x i d e i n h y d r o c h l o r i c a c i d , and i s r e q u i r e d t o i n h i b i t sodium and aluminum i n t e r f e r e n c e i n c a l c i u m measurement . The sodium a d d i t i v e i s b a s i c a l l y used t o f l o o d t h e sys tem so t h a t p o t a s s i u m measurements w i l l not be dependent o n t h e amount o f sodium i n t h e r o c k s . S e v e r a l a v a i l a b l e sodium r e a g e n t s were c h e c k e d t o f i n d t h e one w i t h t h e l o w e s t K / N a r a t i o , sodium n i t r a t e b e i n g c h o s e n . S t a n d a r d i z a t i o n was made i n two s t e p s . The f i r s t o f t h e s e i n v o l v e d Atomic Table Absorpti on 12 Technical Data Potassium Calcium Lamp current 5ma 10ma Wave length 7665A 4227A S l i t width 300 microns 25 microns Flame blue, acetylene blue, acetylene Additive La-5n0ppm Na-50ppm 50% absorption circa 6ppm circa 15ppm H Figure 14 Sample Calibration for Potassium by Atomic Absorption 70 o JQ < 00 6 i I ~ T ~ 5 T 7 o1 9 T o ppm potassium in solution 161 a set of six potassium and calcium chemical standards over the approximate range 0-60% absorbance. These were used to obtain the slope of the concen-tration-absorbance curve. Four U .S.G .S . standard rocks were used to normal-i z e t h i s curve, an example being given i n Figure 14. Both polynomial and exponential curve f i t t i n g were t r i e d , the former being preferred. The f i t was poor at low concentration, however, and the standardization employed therefore assumed that absorbances of l e s s that 22% were l i n e a r l y r e l a t e d to concentration, and those above were f i t t e d as a cubic polynomial. Parameters and errors are given i n Table 13. 1 6 2 T a b l e 13 C u r v e F i t t i n g f o r A t o m i c A b s o r p t i o n C a l i b r a t i o n Kppm = C 0 + C | A + C 2 A 2 + C ^ A ^ j A = a b s o r b a n c e B e s t F i t : C Q = - 0 . 3 2 C . = 1 3 .2 C 2 = - 2 6 . 2 6 C 3 = 5 2 . 9 Sum o f S q u a r e s = 0 . 0 4 9 C h e m i c a l S t a n d a r d % E r r o r i n A b o v e E q u a t i o n O.Oppm 0 .5 1.0 2 . 0 5 . 0 1 0 . 0 —"A N o t a c c e p t a b l e - 1 3 . 4 S t r a i g h t l i n e - 1 1 . 7 f i t u s e d 7'7J for t h i s r a n g e . 0 . 9 9 0 . 1 4 1 6 3 APPENDIX IV X-ray Fluorescence Analysis X-ray fluorescence analysis of rock powders provides j u s t the sort of rapid, semi-quantitative technique required for t h i s p r o j e c t . Furthermore, both rubidium and strontium show good response i n t h i s method, and are s u f f i -c i e n t l y concentrated i n most rocks for i t to be applicable. Technical data for running rubidium, strontium and potassium on the P h i l l i p s PW 1540 model are given i n Table 14. When a material i s submitted to an X-ray source, e x c i t a t i o n of electrons causes each element involved to fluoresce with a d i s t i n c t i v e spectrum of secondary X-radiation. The i n t e n s i t y of secondary r a d i a t i o n at any wave-length (or "line*") i s proportional to the concentration of the corresponding element, modified by absorption, background, and matrix e f f e c t s to be men-tioned. The secondary X^ray spectrum i s d i f f r a c t e d by a c r y s t a l and moni-tored by a s c i n t i l l a t i o n counter. The angle of d i f f r a c t i o n i s c h a r a c t e r i s t i c for a given c r y s t a l and wave-length and i s c a l l e d the Bragg angle. The longer wave-lengths of fluorescence evolved from the l i g h t e r elements (such as potassium) require a vacuqm path and are measured with a flow meter using P-10 gas. Sources of .Error. In addition to minor instrumental problems such as d r i f t or - i n s t a b i l i t y and f i n i t e counting time, the following problems are inherent i n X-ray fluorescence a n a l y s i s . i ) Absorption Each element has a c e r t a i n c o e f f i c i e n t of absorption for any given Table 14 X-Ray Fluorescence Analysis Instrument Settings for Alkalfs To Measure Compton Scatter Standard Unit Rb Sr K Rb Macroprobe Sr K L ine Monitored — K 0 C 3 " Y Angle Monitored 21.05 26.65 25.15 20.50 16.05 15.13 68.02 Attenuation 5 • 5 5 3 5 5 3 Window Width open 100 100 120 200 200 90 Lower Level threshold 400 400 275 400 420 150 Crystal Li F 7 LiF Li F E0DT L iF LiF EDDT Counter sc int i l l a t ion scinti1fation sc in t i l l a t ion flow scint i1lat ion sc int i1 la t i on flow Pressure atmospheric atmospheric atmospheric vacuum atmospheric atmospheric vacuum On a l l work: tube voltage.. .50kv Measuring systems: sc in t i1 la t ion . . .2 . 6 7 5 k v cur rent . . . . . . . .3 0 m a f l o w . . . . . . . . . . . . 4 . 4 6 5 k v Samples using Compton scatter correction are run for Rb and Sr with pulse height analyser at threshold. 165 wave-length of r a d i a t i o n . This form of matrix interference may be cor-rected for i f there i s s u f f i c i e n t data available on the composition of the sample (see Lucas-Tooth and Pyne, 1963), but a much more fe a s i b l e method involves the use of Compton scat t e r i n g , which w i l l be discussed i n d e t a i l l a t e r . Absorption v a r i a t i o n s may also be reduced by use of a heavy absorbent (for example, Rose et, <jl_, 1963). i i ) Density and Matrix Corrections The e f f e c t s of v a r i a b l e sample compaction, percentage voids (pack-ing), and v a r i a t i o n s i n the structure of the s i l i c a t e matrix may be l a r g e l y avoided by grinding the powder very f i n e l y (to at l e a s t 100 mesh) and then p e l l e t i z i n g . Fusion may also be employed, but t h i s tends to v o l a t i l i z e the a l k a l i s , including rubidium. Various matrices have been suggested to aid the process of p e l l e t i z i n g , ranging from heavy absorbents such as lanthanum oxide (Rose et. ajL., 1963) designed also to cut down on background scatter and absorbance v a r i a t i o n , to l i g h t materials such as c e l l u l o s e ( B a l l , 1965), which give a minimum of signal attenuation. In addition to the problems of p e l l e t formation, p e l l e t i z i n g requires weighing and mixing procedures, and i n view of the accuracy requirements of t h i s project, purchase of p e l l e t i z i n g equipment was not considered necessary. This may have been a mistake, as i t w i l l l i k e l y be required to supplement the use of Compton scattering for rubidium—strontium dating, i i i ) Homogeneity and Orientation The main source or inaccuracy i n t h i s category arises from the forementioned b i o t i t e flakes which cannot be e n t i r e l y reduced. Although Table 15 Comparison of X-Ray Fluorescence Analysis of Five Rock Samples with Results from More Finely Pulverized (-100 mesh) S p l i t s * Sample ppm Rbn-Rbf % of mean* ppm S r n - S r f % of mean* (Rb/Sr) -(Rb/Sr) f % of mean* #1 1.5 14.3 3 0.31 0.002 18.1 2 3.1 5.7 2 .54 .004 2.7 3 0.3 1.6 -7 -.80 .000 0.0 4 -3.2 -14.5 14 2.5 -.007 ^17.5 5 3.5 11.3 -15 -2.0 .005 11.9 Average 1.0 3.7 -0.6 .11 .0008 3.0 Average of Absolute Values 2.3 9.5 8.2 1.23 0.0035 11.1 The e f f e c t of complete p u l v e r i z a t i o n to les s than 100 mesh i s shown for Rb and Sr measurements on whole rock powders. The subscripts "n" and " f * r e f e r to values measured i n normal and f i n e l y ground s p l i t s r e s p e c t i v e l y . The differences i n readings are given as a percentage of the mean value for each p a i r . 167 small, these are capable of separating from the remainder of the powdered rock under s u f f i c i e n t a g i t a t i o n , and they furthermore tend to a l i g n them-selves p a r a l l e l to the face of the i r r a d a t i o n diaphragm of the sample holder. This only involves the flakes immediately against the diaphragm, but these are obviously the most important. The alignment means that bio-t i t e i n t e r s e c t s an:iunrepresentatively large proportion of the r a d i a t i o n , and the net e f f e c t w i l l be an increase i n the apparent rubidium from such a rock. This w i l l not tend to create f a l s e K/Rb or Rb/sr anomalies, and i n fact w i l l have the opposite e f f e c t . Table 15 compares analyses of some rocks with r e s i s t a n t b i o t i t e s with the r e s u l t s upon complete p u l v e r i z a t i o n to pass 100 mesh. The average difference i s 3.7% of the mean for rubidium and 0.11% for strontium. Errors a r i s i n g from inhomogeneity and alignment are kept to t h i s l e v e l only by ca r e f u l loading and handling of the sample to avoid l a t e r a l movements of material i n the sample holder, i v ) Dead Time Correction This c o r r e c t i o n i s based on the time required for the counter to process an incoming pulse and during which i t i s not receptive to other a r r i v a l s . S p e c i f i c a t i o n s for the P h i l l i p e l e c t r o n i c counting system used give the dead time as about two microseconds. The c o r r e c t i o n i s systematic and of the form: S = S m / ( l - c p s . d t c ) where S i s the r e a l s i g n a l , S m the measured one, cps the signal strength i n counts persecond, and dtc the dead time. This c o r r e c t i o n i s not important when a pulse height analyser i s em-ployed to f i l t e r the si g n a l , but when the. Compton scattering technique i s 1 6 8 being used the counting rate i s s u f f i c i e n t l y high and the necessary pre-c i s i o n s u f f i c i e n t l y great that i t cannot be ignored. The cor r e c t i o n may be made assuming the two microseconds for dead time, but i t may be observed that equation 1 i n binomial expansion takes the form: S = Snj(l + cps.dtc + ( c p s . d t c ) 2 + . . . ) 2 and may be f i t t e d by the quadratic modelling to be presented i n conjunction with Compton scattering c o r r e c t i o n programs, v) Background L i k e l y the largest source of error i n the X-ray fluorescence measurements i s i n estimation of background. Both strontium and rubidium have t h e i r K-alpha l i n e s near a prominent l i n e of tungsten, and hence i n a region of high interference when a tungsten target tube i s being used. Furthermore, the background i n t e n s i t y changes r a p i d l y and non-linearly with Bragg angle. This s i t u a t i o n i s improved greatly with use of a molybdenum target X-ray source, but there i s s t i l l the problem of interference of other elements at the angle where background i s measured, and the necessary approximations for extrapolating background height where measured to that beneath the rubidium and strontium peaks. Methods of reducing the error i n t h i s approximation w i l l be discussed under Compton scattering correct-i o n a l programs. Compton Scattering Technique. X-ray fluorescence analysis of rubidium and strontium i n whole rocks may be made quantitative (as opposed to semi-quantitative) through the use of a molybdenum target X-ray source and a co r r e c t i o n a l technique based on Compton scat t e r i n g . Peterman and Hedge (1968) used t h i s system i n rubidium—strontium age-dating of Precambrian 1 6 9 events i n northeastern Colorado, obtaining Rb/Sr values with a p r e c i s i o n of 3.3% (2 sigma). Powell et al_ (1969) i n t h e i r study of the S t i l l w a t e r complex report an average deviation of only 3.31% between X-ray f l u o r -escence and mass spectrometer r e s u l t s for rubidium and 4.01% for strontium. The Compton scattering technique i s based on work of Hower (1959), who showed that the absorption c o e f f i c i e n t s of two materials w i l l be at a con-stant r a t i o at a l l wave-lengths, provided the range i n wave-lengths does not cross the absorption edge of a matrix element. In common rocks, i r o n i s the heaviest element whose abundance makes i t s i g n i f i c a n t . It has an absorption edge at a wave-length of 1.74 between K-alpha frequencies of cobalt and n i c k e l so the Compton scattering technique i s useful for elements heavier than n i c k e l i n rocks. Reynolds (1963) further demonstrated that the absorption c o e f f i c i e n t for a p a r t i c u l a r wave-length i s l i n e a r l y r e l a t e d to the r e c i p r o c a l of Compton scattering i n t e n s i t y . The Compton (or incoherent) scattering peak occurs at a wave-length s l i g h t l y longer than that of the primary r a d i a t i o n , and hence i s measured at a Bragg angle s l i g h t l y greater than that of the K-alpha l o c a t i o n of molybdenum, when using a molybdenum target X-ray source. With a l i t h i u m f l u o r i d e c r y s t a l and the P h i l l i p s unit, a two-theta angle of 21.05° was employed. Once the r e l a t i o n s h i p between Compton scattering i n t e n s i t y and absorbance has been established, the absorbance of any matrix i s e a s i l y c a l -culated and concentration of an unknown element determined by comparison to a standard through the equation R c = R s * R a 3 where each H R " has the form of a r a t i o R = sample parameter 4 standard parameter 170 and the parameter subscripts r e f e r : "c" to the concentration of the element being analysed, " s " to signal strength for the K-alpha peak of that element, and "a" to the mass absorption c o e f f i c i e n t s . The a p p l i c a t i o n of equation 4 to the analyses of rocks was observed to be rather poor for elements at low concentrations. This i s because of the forementioned d i f f i c u l t i e s i n estimating background under peaks, even when using a molybdenum target source. It was found, however, that a reason-ably good estimation of background could be made by assuming i t to be qua d r a t i c a l l y r e l a t e d to incoherent scattering i n t e n s i t y , that i s , to the Compton scatter peak height (see Table 16). This r e l a t i o n s h i p y i e l d s as great an accuracy as might be expected from d i r e c t reading of the background, considering the forementioned problems of interference. Furthermore, one l e s s reading i s needed for each sample, i f background i s estimated from Compton scat t e r i n g . The f i r s t computer program (Comscat 1) evolved for Compton scattering c o r r e c t i o n i s based on the above p r i n c i p l e and takes the following steps (see also Appendix V): i ) A quadratic r e l a t i o n s h i p i s established between absorbance and the inverse of Compton scatter i n t e n s i t y . This was done using chemical standards (for which absorbance c o e f f i c i e n t s may be calculated) p r i o r to commencement of analysis program, and the parameters from least square f i t t i n g of t h i s master curve i s read into Comscat 1 program. The quadratic component i n t h i s f i t t i n g i s mainly a r e s u l t of the forementioned dead-time error (see equation 2). i i ) Four rocks or chemicals used i n est a b l i s h i n g the above master curve 172 are used to adjust readings to the curve on the day of ana l y s i s . With t h i s adjustment, absorbance c o e f f i c i e n t s of a l l rocks and standards are calculated after d r i f t c o r r e c t i o n s . i i i ) X-ray fluorescence readings are made on a group of standards (for which rubidium and strontium concentrations are known) to determine four parameters. These are the K-alpha i n t e n s i t i e s for rubidium and strontium, Compton scattering peak height, and the background at two-theta of 26.2°. This background l o c a t i o n was chosen to avoid interference from other elements as much as possible, and to be clear of the t a i l s of the often quite sub-s t a n t i a l strontium peaks. The parameters are read into the program and corrected for instrumental d r i f t . i v ) Each set of readings for each parameter of both the standards and samples consists of three specimens with a reading of IhS.G.S. standard rock W-1 both before and after the set. In t h i s manner, d r i f t c o r r e c t i o n may be made for changes during the running of the set, and normalized to correct for d r i f t throughout the ana l y s i s . It i s assumed that the d r i f t corrections are proportional to the absolute values of the readings, which appears a v a l i d assumption from observation of the r e l a t i o n of the time for unit warm-up and the observed absorbance. v) The r e l a t i o n s h i p between Compton scattering i n t e n s i t y and back-ground at a two-theta of 26.2° i s established by means of a least-squared-f i t t i n g subroutine (see Table 16). v i ) An estimate of the r a t i o of background i n t e n s i t y at two-theta of 26.2° to that beneath the rubidium K-alpha (26.65°) and strontium K-alpha 25.15°) p o s i t i o n s i s made. This estimate i s based on readings made on 1 7 3 chemical reagents i n which the element concerned i s expected to be absent, and i s approximately 1.09 for rubidium and 0.84 for strontium. It was hoped that the f i n a l r e s u l t s could be made somewhat les s s e n s i t i v e to these extrapolations of the background by using quadratic modelling i n the next step. v i ) Peak heights for rubidium and strontium K-alpha are obtained by subtracting background from the t o t a l i n t e n s i t y readings for the standards. This i s corrected for matrix absorbance and by the best quadratic f i t between these corrected peak heights and the concentration of rubidium and strontium determined for the standards. v i i ) The raw data for the samples are read i n , backgrounds and absorbances computed as for the standards, and then rubidium and strontium concentrations determined by the foregoing model. While the r e l a t i o n s h i p s of mass absorbance and background to Compton scattering proved to be very good, considering the data was based on one-minute counting times, modelling the f i n a l values of element concentration as i f r e l a t e d q u a d r a t i c a l l y to the corrected K-alpha peak i n t e n s i t y was not so promising (see Table 16). It was suspected that the reason for t h i s poor c o r r e l a t i o n lay i n the form of error caused by inaccuracies i n the foremen-tioned background extrapolation f a c t o r s . E r r o r s of t h i s type are a function of background, and hence of Compton scattering, and the f i n a l model might better be constructed by considering equation 4 i n the form: concentration of unknown _ absorbance of unknown ~ A l ' K a l P n a intensity—(e).Background) + A 2. 5 where "e" i s the unknown extrapolation factor and the "A's" are constants. Table 1 6 Comscat 1 Quadratic Fitt ing No. of Standards Independent Variable (x) Dependent Variable (y) a 0 a 1 a 2 Rmse a o Rmse a 1 Rmse a 2 Sum of Squares 9 absorpti on coefficient inverse of compton scattering - 2 . 5 5 14.45 - 2 . 5 2 6 . 1 3 1 9 . 4 7 14.05 0 . 1 0 6 12 background 29 = 2 6 . 2 ° compton scattering 0.0672 0 . 0 6 7 9 - 0 . 2 7 8 x ItT1* 3.08 4.61 1.50 0.219 x 10~3 7 rubi dium corrected K-*1phe - 4 7 . 9 1 7 0 7 . 4 - 2 1 5 0 . 2 1.72 30.1 9 5 . 2 2 2 . 8 * 7 strontium corrected K-alpha - 6 . 3 4 781 .7 53.1 0 . 9 3 5 .76 6 . 3 9 7 6 . 9 * * not acceptable Rmse = root mean square stat ist ica l error of parameter estimate To f i t : y = a Q + a,x + a 2x? 175 A l t e r n a t i v e l y , C x / u x = a Q + a xK x + a 2 B x 6 where C, u, K, and B r e f e r to concentration, absorbance, K-alpha i n t e n s i t y , and the background r e s p e c t i v e l y , and the unknown c o e f f i c i e n t s are determined by l i n e a r regression. This system, referred to as Comscat IA , i s given i n Appendix V, and the r e s u l t s from f i t t i n g a set of standards are shown i n Table 17. They are not p a r t i c u l a r l y encouraging, c/u for strontium having a standard error of 1.09 or 2.7% of the mean, while the corresponding parameters for rubidium were 2.14 and 14.3%. The f i n a l form of Compton scattering c o r r e c t i o n used i s based on equation 6 i n the form: C x ^ (R x - B x) ( u x ) . 7 As mentioned, the absorbance may be modelled q u a d r a t i c a l l y to the inverse of the Compton scattering i n t e n s i t y "Q". u = b 0 + bx/Q + b 2/(Q') 2 8 where the quadratic term i s not very s i g n i f i c a n t (see Table 16). It i s mainly the r e s u l t of dead time c o r r e c t i o n and may be neglected i f t h i s c o r r e c t i o n i s approximated. On the other hand, "bo" accounts for roughly 10% of the t o t a l magnitude and hence, r e c a l l i n g the good f i t for background as a quadratic expression of Compton scattering i n t e n s i t y , the equation may be written: C x<* (R x " d Q - d xQ - d 2Q 2) ( b 0 + bj/Q). 9 The values of d 0 , d^ and d2 are not known exactly due to the fore-mentioned problem of estimating background under the K-alpha peaks. Table 17, Comscat IA Linear Regression No. of Standards Dependent Variable Intensity Background (B) Background^ •o Standard Error in (y) Mean (y) 7 rubidium absorbance correlations 0.9^ 3 0.375 0.332 — — 7 rubidium absorbance coefficients 163.0 118.0 — -34.7 2.14 14.9 8 strontium absorbance correlations 0.984 -0.376 -0.412 — — — 8 strontium absorbance coefficients 134.9 157.9 -44.7 2.96 40.5 To f i t : • - concent rati on , „ x , o \ y " absorbance = a 0 + a l < K ° ° + a2<B) + a3 ( B } Fit not acceptable 177 Using the form: C x = p 0 + p^R/Q) + P2/Q + P 3R + P 4Q + P 5 Q 2 10 however, a rather good f i t should t h e o r e t i c a l l y be po s s i b l e . Despite the seeming complexity of t h i s model, three readings are s t i l l a l l that are necessary to measure both rubidium and strontium, and the re s t may be handled by the Comscat 2 program (Appendix VI) which models the above equation from standards by l i n e a r regression. Quantitatively, the term HR/Q" w i l l obviously dominate the foregoing approximation, but the almost complete c o r r e l a t i o n (see Table 18) between i t and element concentration was not expected. This explains the success of Damon and others (1966) i n using that parameter d i r e c t l y for rubidium and strontium a n a l y s i s . Other terms become important, however, under c e r t a i n circumstances. When measuring concentrations where a high peak-to-back-ground r a t i o i s encountered, the"p3R" term i s s i g n i f i c a n t . When peak-to-background r a t i o i s low, as i s usually the case with rubidium measurements for Coast Mountains plutonic rocks, the "pQ" and '^/Q" terms become im-portant. It was found, i n fac t , that a considerably more accurate f i t was possible for rubidium i f standards with over 150 ppm concentration were excluded from the c o r r e l a t i o n . S i m i l a r l y , standards with le s s than 30 ppm strontium were excluded to give a better f i t over the concentration range t y p i c a l of Coast Mountains i n t r u s i v e s u i t e s . Results from a t y p i c a l run on a set of standards are given i n Table 18, the input data being weighted i n favour of the four U.S.G.S. standard rocks. Regression analysis also showed that i f a large range i n Compton scattering i n t e n s i t i e s i s involved, the term "p4Q" may be s i g n i f i c a n t . Table 18 Comscat 2 Linear Regression Results No. of Standards Dependent Variable (y) *1 fi2 S 3 s 9 5 ao Standard Error in (y) Mean (y) 9 Rb ppm correlations 0.95** 0 . 7 4 7 - 0 . 2 5 7 0 .197 0 . 1 6 0 — — --coefficients 1 5 1 0 . 9 - 2 2 1 . 7 — 4 9 . 8 — - 2 0 7 . 5 0 .566 46.2 9 S rppm correlations 0 .9996 0 . 9 6 6 0 .369 - 0 . 4 6 3 - 0 . 5 0 7 — coefficients 1 2 1 0 . 9 - 2 2 9 . 6 — 1 7 2 . 2 - 3 3 . ^ - 2 9 0 . 6 0 . 7 2 3 294 To f i t : v = a _ + 7 ppm o a . (KV0_ ) + a 2 (K°() + a3/a + a^Q + a 5 « 2 where Q. is Compton scattering intensity 179 (For rocks. Compton s c a t t e r i n g i n t e n s i t y to a major extent f o l l o w s sodium c o n t e n t ) . I t i s hence important to s e l e c t standards which are s i m i l a r to the samples concerned both i n the range of mass absorbance and c o n c e n t r a t i o n of the unknowns. A P P E N D I X V COMSCAT I PROGRAM D I M E N S I O N S T R ( 5 0 ) , S T S ( 5 0 ) , A ( 5 ) , B (.5 ) , R ( 5.), S ( 5 }, 8 G ( 2 0 0 ) , C A ( 2 0 0 ) . D I M E N S I O N . X ( 5 0 ) , Y ( 5 0 ) , Y F ( 5 0 ) ,W<50) , F 1 ( 5 0 ) . £ 2 . ( 5 0 ) , P ( 5 ) , U ( 2 0 0 ) , I T ( 2 0 0 ) , L N ( 2 0 0 ) , L Q ( 2 0 0 ) , E R ( 2 0 0 ) , E S ( 2 0 C ) . R E A D ( 5 , 1 1 8 ) Z 1 , Z 2 , Z 3 — "* . "-.'5 R E A D ( 5 , 1 1 8 ) R S . C S . C S C . R F - - , , „ . . . . R E A D ( 5 , 1 1 8 ) V A , V 6» V R » V S :\ ' •" ••' : - R E A D ( 5 , 1 1 4 ) N S T . N S A ', • ' : :„NAT=- 3 # N S A Ai,'.: ../:..... .^• • \ . i : . . .L.7 -^ .^ . .^ /^ l .C.^_. : i - . . . . . . . N T T = 3 * N S T + I . •., ,.: R E A D ( 5. 1 1 8 ) B C R . R C S ' " :; " /:: •VQP.= V R - ( V B » B C R ) ' , . . '' . . ' ' :-'• - • V Q S = V S - ( V R * B C S ) ' N A = 2 • ••• •• "•, •: '•. • _ R E A C ( 5, 1 1 8 ) . . ( S T R C I ).tI = l » N T T ) •_':-^ ..-./.l..= ' ... .• 'I,.,.' '.'•.:;1^:7 R E A D ( 5 , U 8 ) ( S T S ( I ) , 1 = 1 , N T T ) W R I T E ( 6 , 3 0 0 ) 3 0 0 ^ F O R M A T ( 4 2 H COR R E L A T I O N O F B A C K GROUN C TO S C A T T E R I N G ) • . DO 2 0 L = l , N S T .... .'. R E A D ( 5 , 1 1 8 ) ( A< I ) ,1=1, 5 ) , < B ( I ) ,1 = 1 , 5 ) •• R E AD ( 5 , 1 1 . 8 ).;_{.R.UJ , .1=1., 5 U J S J J )_»J=1 »„5J...:-0 0 1 8 K = l , 5 • . • .. ;•, A ( K ) = A ( K ) * R F . :." '. B ( K ) = B ( K ) * R F ' : . v • R ( K ) = R ( K ) * R F 1 8 S ( K ) = S ( K ) * R F ..... DO 2 0 J = 2 , 4 .., _.r..„:_...i.::.: Z J = F L O A T ( J 1 - 1 . 0 A ( J ) = A ( J ) * A ( 1 ) / ( A ( 1 •) '+ ( M l ) - A ( 5 ) ) * Z J / 4 . 0 ) ~v B ( J ) = B ( J ) * B ( l ) / ( B ( l ) + ( B ( l ) - 6 ( 5 ) ) * Z J / 4 . Q ) '• • .R.JJ ) = R ( . J ) * R ( 1 ) / ( R U ) + ( R ( 1 > - R ( 5 ) ) * Z J / 4 . 0 ) : S ( J ) = S ( J ) * S ( 1 ) / < S U ) + ( S U ) - S ( 5 ) ) * Z J / 4 . 0 ) \9 :• : x.(NA ).=A( J.)*VA/A.U).„£.,;• • ••• ,/ '•• ,.; • ,uj Y I N A ) = 3 ( J ) * V B / B < T ) U { N A ) =R( J ) * V R / R U ) T ( N A ) = S ( J >.*vs/su ) :• • ' • • • •'• ; 2 0 N A = N A + I '•>'•'•;' ! . . x ( D = VA . . • . ._ Y { 1 ) = V 3 . / . ! _ _ 1 _ J L J _ _ • : U U >=VR '.' V,v.\-: •'• '• • j ; T( 1 ) = V S ' •j ;- COMMON M, P, Y F :'. •'')••••-• .• ••' '' i: • • • j.v; . ' N = N T T • E P = O . o o i • . .:. : ;' '.-•..•=••• P ( 1) = o. o • l 8 l ; ; ' WR ITE (6, 301) •" ; 301 • FORMAT (17H INPUT DATA X, Y ) '•/'.• 00' 75 1=1, M i l . . • G . 7 5 WRITE (6,5 ) X{ I ) , Y ( I) EXTERNAL. AUX : • • " / ' • ' • ' CALL L Q F ( X ,Y ,YF,W,E1 ,E 2 ,.P , 0 . 0 , N, M • NI t NO » E P , AUX ) WRITE (6 ,302) • : ••' WRITE (6,5) ( E l ( I ) ,I=L,M) L.G^GJ-l G.G:\G':.G,,,_ v.. ... WR ITE ( 6, 303) "• GG • '• «':•• -DO 7 1 = 1 , N •; • E2( I ) = ( Y ( I ) - Y F ( I) )»1Q0.0 / Y (I) : : : v 7 WRITE (6, 5 ) X( I ) , Y ( I) > E2( I J • .. . / '•' B l =P( l ) -• ' .LG' B2=P( 2 ) :. \ . : . . _ G . _ _ • B3=P(3) ' WRITE (6,304) .' ; ' G " 304 FORMAT (22H RUBIDIUM .CORRELATION . . ) :i - ••' .-'rG DG 60 L = l , NTT : : i • : X ( 1. ) = 1 . 0 / X ( L ) • CA(L)=Zl+Z2*X(L ) + Z 3 * X < L ) * * 2 ' •'" h ' : U<L) = (U(L)-YF(L)*BCR)*CA(L)/CSC -C'-^/vG" 6 0 T(L) = ( T(L)-YF(L)*BCS)*CA(L)/CSC •I.. . WRITE (6 ,305) ' ' ',- . ; " - ' • -V . •. . 3 0 5 FORMAT (24H CORRECTED Y, ABSORB., X ) : . oo 61 L= l, N T T ."v W RI TE. (6,5) Y F ( L) , CA (L > tUJL ) V: - G> yi ±__ - Y { L ) = S T R ( L ) •: ' •' • ) 6 1 -.. x ( L )=u (L ) y P( 1 ) =0.0 • - • ••• 1 • ' ' ' - ' •- ' -P i 2> = Y( 1 )/X( l ) • P (3 ) = 0 .C ':<. '• ,;• CALL LQF ( X,Y. , Y F . , , W , E L , E2, P. ,0 AUX ) V: . WR i T E ( 6 , 3 0 2 ) G GG-- G | •••• • WRITE (6,5) (E1 ( D , I=1,M) :' •/ : •- •• WRITE ( 6,303) , - V " " . • • ;- ' ': : J" ' - ' ' . T D O 8 1 = 1,N • ' : E2( I ) = ( Y { I ) - Y F ( I ) ) * L 0 0 . 0 / Y ( I ) tJ8__.l_.WR I TE ( 6 ,5) XU) ,V( I) , E 2 ( T ) ^.;£_lil.i_L:^: . R1=P<1) ' • R2=P<2) . • • R 3 = P C 3 ) ' ••. ... . ' • . . • • : -.: DO 62 L = 1 ? NTT V -v. '•• Y(L) = STS( L) . •". 6 2 _ X ( L ) = T(L) •; -> . : : • ' ... •• - - • ' j__ P( 1 )=0 .0 P( 2)=Y( 1)/X(1 ) p(3)=o.o. . , WRITE (.6 ,306) •: 306 • FORMAT (2.3H STRONTIUM CORRELATION ) . '______C ALL LQF ( X, Y , Y F » W , E l.,.E2,P., 0.. 0 , N t.M, N I , ND., E.P..,AUX) . WRITE (6,302 ) •'. ; - WRITE (6,5) ( E1 ( I ) ,1 = 1 ,M) • WRITE(6, 303) - • '.'V •• : . ; -* D O 9 1 = 1 , N :-. .':;./,,.. ': E2( I ) = ( Y ( I ) - Y F ( I ) ) * 1 0 0 . 0 / Y ( I ) 9 . . WRITE.(6 ,5.1.X.( I j ,Y . ( I ) t E 2 J J j j ^ ^ l L i l X ,. '.si=p< i ) • • • v :;. • ; / - S 2 = P ( 2.) . •. ••. • '•• v:.. "•" :: " " s3=p<3) ' . •: • - ' • ... 182 •'. •' - NA= i •• ; " • ' " " •  • ". • W R I T E (6 , 3 0 7 . ) ' . 3 0 7 . . F O R M A T { 2 I H S I M P L E X R8 , SR, A B S ). . •• DO 7 0 L = 1 » N S A . . . R E A D ( 5 , 1 1 9 ) ( L O C I ) , 1 = 2 , 4 ) , ( A ( I ) , 1= 1 , 5 ) RE A D ( 5 , 1 18) (R ( I ) , I = 1 ,5) , { S ( I ),1=1,5) ( DO 63 K = I ,5 <;:• A ( K ) = A ( K ) * RF 1 R ( K ) = R ( K )«RF ..... 1; 6 3 . S ( K ) = S (K )*RF .' : DO 7 0 J = 2»4 • " Z J = F L O A T (J ) - l . 0 A ( J ) = A ( J ) * V A / ( A (1 > + ( A ( 1 ) - A ( 5 ) ) * Z j / 4 . 0 ) . R ( J ) = R < J ) * V R / ( R ( 1 ) + ( R ( l ) - R ( 5 ) ) * Z J/A .O ) S ( J ) = S ( J ) * V S / ('S (1 ) + ( S { 1 ) - S ( 5) ) * Z J / 4 . 0 ) B G ( J ) = B l + B 2 * A t J ) + B 3 * A ( J ) * * 2 . . • A ( J )= 1 . 0 / A ( J ) . ' : C M J) =Zl+Z2 * A (J ) + Z 3 * A ( J ) **3. • .'• L N ( N A ) = L 0 ( J ) . U ( N A ) = ( R ( J ) - B G ( J ) * B C R ) * C A ( J ) / C S C '•"••/.':"'',•. ... T ( N A ) = ( S ( J ) - B G ( J ) *BCS ) * C A (J ) / C S C . . . . R{ J ) = U ( NA ) * R S / V Q R . . - ; S ( J } = T { N A ) * C S / V Q S R S R = R ( J ) / S ( J ) : • W R I T E ( 6 , 6 ) L N ( N A ) » R ( J ) , S ( J ) , C A ( J ) , R S R U ( N A ) = R 1 + R2*U ( N A ) + R 3 * U ( N A ) * * 2 v T ( NA). = S 1+.S2* T ( NA.) + S 3 * T ( N A J **.2 l_i_:„'„_. .'. E S ( N A ) = ( S ( J ) - T ( N A ) 3 * 1 0 0 . 0 / T ( N A ) E R ( N A ) = ( R ( J ) - U ( N A ) ) * 1 G 0 . 0 / U ( N A ) 7 0 N A = N A + 1 WRITE ( 6 , 100 ) . . 100 FORMAT(31H RUBIDIUM AND STRONTIUM CONTEN I DC! .80 L= 1, NAT' a _ l ' . L i J . i . l l ^ . ' . : -RSR=U(L)/T(L) 80 WRI TF ( 6,6) L N ( L ) , U(L) , T (I.) , RSR' .. . WRITE (6, 308) ;' •• "• ' "• 308 FORMAT (20H PERCENT-DEVIATIONS ) DO .81 L = 1» NA T ' 81 WR ITE. (6,6 ).. LN ( L ) , ER (.L ), ES(.U _... < 5 'FORMAT {1X,8G15.5 ) 6 .FORMA T( 1X,I6,7G15.5) - . 114 • FORMAT(215) ' • • . •118 FORMAT( 1CF6.0) . 119 FORMAT (316, 5F6-C) -•3:.02_.__F.0RMA.T.. .(18tL ST.AT.I ST.I.CAL. ERROR. >_.___ 303 . FORMA T(2 5H X, Y , PERCENT DEVIATION ) ' V. ' " STOP • •' '• '•' . END ! I F U N C T I O N A U X ( P , D , X , L ) . , : D I M E N S I O N P ( 5 ) , D( 5 ) , Y F { 50 ) ; T v.. • . . C O M M O N M , P Y F •' '"' ' '" ' D< 1 >-l .0 - / : " • - ' • ! • ' -.\:.. . AUX= • p t i ) . .. D O 10 j=2 , M :. \ D ( J )= D( J-1)*.x.:\. 10 A U X = A U X + P ( J ) * D ( J ) • ! , R E T U R N • • E N D I:,.: -183 APPENDIX VI Comscat I I — Program O r g a n i z a t i o n The f i r s t p a r t of the Comscat I I program makes c o r r e c t i o n s tto the s t a n d a r d i z a t i o n readings and generates parameters f o r r e g r e s s i o n a n a l y s i s . I t i s designed to use d i r e c t l y as a TDATA input subroutine. Statement # 2 NTT i s the number of standards; RF i s the r e d u c t i o n f a c t o r for conversion of readings to counts per second. 3-7 STR, STS are readings on Rb K-alpha and Sr K-alpha, r e s p e c t i v e l y . SQR and SOS are the corresponding sample numbers;CMS i s a reading of Compton s c a t t e r i n g i n t e n s i t y . 9-11 This process converts readings to counts per second and makes dead time c o r r e c t i o n . 13 An input data w r i t e o u t , for reference only 17, 18 Generation of (K-alpha/Compton s c a t t e r ) r a t i o s 19,. 20 Generation of other Compton s c a t t e r parameters. 21 P r i n t - o u t of r e g r e s s i o n parameters. The second p a r t of Comscat I I program c o r r e c t s the a c t u a l sample data and computes rubidium and strontium content from r e g r e s s i o n output parameters. Input readings are taken i n sets of f i v e which s t a r t and f i n i s h with a standard. There are hence three unknown samples i n each set, or batch. COMSCAT II GENERATION OF PARAMETERS FOR REGRESSION A N A L Y S I S DT MENS I UN STR(50) ,STS(50) ,SOR(50) ,S0S(50) ,CMS ( 5 0 ) ,CSS(4) , rJMS( 50) 1 A B S ( 5 0 ) , X 3 ( 5 0 ) , X 2 ( 5 0 ) , A R ( 5 0 ) READ(5,12C) NTT , RF .. ..:.,',:.'./ . READ(5,118) (STR(I),1=1,NTT) READ(5,118) (STS ( I ) , 1 = 1 ,NTT)•-.'.•/ ' . .. R E A D ( 5 , U 8 ) ( SOR ( I ) , I =1, NTT ) . - ' ' R.EAD(5,I18) .(SOS ( I )-,T=l,iMTT) READ(5,118) (CMS '( I )•, I = 1, NTT )' DO 14 L = 1.,NTT ;.:..„.::..:::.:..::.; v. ,. - V . ' . . . . . STR ( L ) = S T R ( L ) - R F / ( 1 . 0 - S T R ( L )•-:--0.02---RF ) ; S T S ( L ) = S T S ( L ) * R F / ( 1 . 0 - S T S ( L ) * 0 . 0 2 * R F ) 1 4 C MS- ( L ) =Q'iS ( L ) *R F / ( 1 .O-CM S ( L ) * 0.0 2»R F ) _ _ _ _ _ DO 180 J = l , NTT . J"' 180. ' ' WRITE (6 ,5 ) STR.( J ) , S TS ( J ) , CM S ( J ) WRITE (6 ,200) '. . 1/ .. •': ' 2 0 0 FORMAT(63H REGRESSION PARAMETERS RPPM, SPPM, R, S, R/C, S/C, 1/C, i c , 02 )•'•'. . .•• .; . . DO 15 L = l ,MTT ' • : ' ' •.: ' ••' ' ABS ( L ) =S TR ( L ) / CMS ( L )- . .... , V'./" B MS ( L ) = S T S ( L ) / C M S ( L ) . • ..-...•I ..AR (L ) =1 .O/CMS (I. ) 7 V:.^.l._...;. •'• . .. .. x 2 ( L ) = c i-. s i L ) ••• 2 • .• 1 5 WRITE (6,5 )' SQR (L ) ,SQS (L ) , STR (L) , STS ( L ) , ABS( L ) , 6MS( L ) , AR( L) , CMS (L ) ' _ 1 X 2 ( L l • • • • v • •  FORMAT (1 X , 10 G1 2 . 5 ) . FORMAT ( 10F6 .0-) : ' :• = •'•.,"•"• ; ' FORMAT (I 5 , I F 5 . 0 ) / '_L,_LL.._^ !__;-_1L^ .. J. , ' . ' V _ STOP • 5 , 1 1 8 1 2 0 185 Statement # 2 Rubidium and Strontium parameters as obtained by r e g r e s s i o n a n a l y s i s of the standards are read i n . Observe that only four parameters were found necessary. (Table 9) 3 These r e f e r to Rb K-alpha, Sr K-alpha, and Compton s c a t t e r i n t e n s i t y readings for the batch standard. RF i s the r e d u c t i o n f a c t o r . 4 NSA i s the number of batches or sets of samples. 8, 9 For each batch, the sample number, Compton s c a t t e r r eading, and K-alpha readings are taken i n . 11-18 Dead time c o r r e c t i o n and s t a n d a r d i z a t i o n . 19-22 D r i f t c o r r e c t i o n . 23, 24 Computation of (K-alpha/Compton s c a t t e r ) r a t i o s . 24-28 Computation of rubidium and strontium c o n c e n t r a t i o n and Rb/Sr r a t i o s . 31-34 Output. COMSCAT I I PROCESS ING OF SAMPLE D A T A . S C C I M P I L F . n I .v-ENS I O N R ( 5 ) , S ( 5 ) , A ( 5 ), ROC ( 5 ) , SOC ( 5 ) , I N I 5 ) , U ( 2 0 0 ) , T( 2CC) , i , R S ( 2 C 0 . . N T U & o , "•••j • ' _ ,; R F A D ( 5 r i l 8 ) R X n , R X I , R X 2 , R X 3 , S X O , S X l » S X 2 , S > < 3 . R L A D ( 5 , T 1 8 ) V A , V R > V S , R F . R F A O ( 5 , 1 1 9 ) N S A \ . ' • N A T = 3 « N S A NA =1 ••• n f ; 7 0 L = l ,NSA R E A 0 ( 5, 117) ( IN( iY , I = 2fA' ) V (A( I ) , 1 = 1 , 5 ) " ""• • • ~ " . "Y ' R c A D ( . 5 . 1 i 8 ) ( S( I ) , 1 = 1 ,5 ) , (R ( I ) , 1 = 1 , 5 ) . . . n o 3 0 0 M=1,5 A ( M ) = A ( M ) / L O G O . 0 ; R(M)=R(M) / 1 C 0 0 . 0 _ i _ 0 _ _ : _ . S ( M ) = S ( M ) / 10 0 0 . 0 , DC 7C J=2 ,4 Z J = F L G A T ( J ) - 1 . 0 A{ J ) = A( J ) - * R F / ( 1.0-A< J ) # C . 0 2 * R F ) . R( J ) = R( J M : R F / (1 , 0 - R ( J ) * 0 . 0 2 * R F ) S( J ) = S U ) * R F / < 1 . 0 - S < J } v C . . 0 2 * R F ) , Y- . ./•• A ( J ).= A (J ) * A ( 1 ) / ( A ( I ) + ( A ( 1 ) ~ A ( 5 ) ) S--ZJ / 4 . 0) • Y r -R < J ) = R ( J ) * R ( 1 ) / ( R ( i ) + ( R ( 1 > - R ( 5 ) ) * Z J / 4 . C ) S ( J ) = S ( J )-S( 1 ) / ( S ( 1) + <S( i ) - S ( 5) )> : Z J/4 .C ) . . Y R C C ( J ) = R ( J ) / A ( J ) SOC ( J ) =S ( J) /A ( J ) U ( NA ).= RX0 + RX1*R0C { J )+RX2*R{ J )+RX3*A { J) U(NA) =1 . 07-'-U£\A) T(NA.)='SXO+SX1*SOC ( J ) + S X 2 * S ( J)+SX3*A'( J } - 3 3 . 4 * A U ) * * 2 ' . ,T ( N A ) = 0 . 9 5 * T ( N A ) . .'• R S (NA )= L: ( N A ) / T { N A) . \' •' N I ( N A ) = IN ( J ) 7C NA=NA+1 ' '• . . . WRITE ( 6 , 1 0 2 ) .' '102""" FORMAT ( 31H R U B I D I U M , ' S T R O N T I U M ' , A N D R B / S R ) ; DO 80 L = l , NAT ' ' • 8C WRITE ( 6 , 5 ) N H L ) , U ( L ) , T ( L) , RS ( L ) 5 FORMAT.( 16 , 7 G 1 5 . 5 ) : i i 9 F'CRMAT ( 15) " , . Y-: . 117 ;'. u s FORMAT! 31 6 , 5 F 6 . C) : Y ' -V .' •'•V.Y- ' Y " - " • Y FORMAT (10F6 .0 ) S T O P ' '•: • Y .. : ' /\ Y.V - Y Y Y Y Y E N D • ,' :•" _8?7 APPENDIX VII Use of the Macroprobe i n Microanalysis With the establishment of an X-ray fluorescence macroprobe i n the Department of Geology i n 1967, a program was undertaken to adapt t h i s instrument to semi-quantitative micro-analysis of rubidium, strontium, potassium, and other elements derived from geological materials. Theory. As previously mentioned, X-ray fluorescence analysis of whole rock powders e n t a i l s the following sources of inaccuracy: i ) Inter-element interference and absorption of r a d i a t i o n , i i ) Matrix e f f e c t s inherent i n d i f f e r i n g mineral structures, i i i ) Packing of rock powders to give density v a r i a t i o n s , i v ) Lack of an i n t e r n a l standard and a blank to check background, v) I n s u f f i c i e n t concentration of many elements of geological i n t e r e s t . A l l of the above problems are avoided i f the elements of i n t e r e s t are extracted from the rock and mixed with an i n t e r n a l standard. They may then be presented to the X-ray unit dried onto an absorbent d i s c of f i l t e r paper or laboratory cleaning t i s s u e . Techniques of t h i s type have been described for s p e c i f i c non-geological applications (for example, Natelson et j l . , 1962). I t seemed f e a s i b l e to extend t h i s general method by means of the macroprobe, i n which the X-ray source i s masked to i r r a d i a t e an area as small as 100 microns, while s e n s i t i v i t y i s aided by the concentra-t i o n of r a d i a t i o n through a curved mica c r y s t a l . The macroprobe i s described by Hermes and Ragland (1968) with 188 c e r t a i n a p plications to measurement of major rock-forming elements. Lack of other reports from projects using t h i s instrument was considered l i k e l y due to i t s recent introduction, but i t has since been learned that other workers have found i t unsuitable for trace element a n a l y s i s . The major requirements of chemical techniques to be used i n concen-t r a t i n g elements for the macroprobe, are that they i s o l a t e a l l of the e l e -ments to be measured and that contamination be kept low due to the small quantities involved. Instrument s e n s i t i v i t y required that any element to be measured semi-quantitatively be 0.5% or more of the t o t a l loaded sample, which required removal of rock forming elements not of d i r e c t i n t e r e s t . Those elements allowed to remain i n the sample must furthermore be con-sidered so that no major sample constituent had i t s absorption edge between the K-alpha p o s i t i o n s of the i n t e r n a l standard and the elements to be analysed. Once separated, the sample must be made homogeneous and mounted i n a form which need be no more than 100 microns i n diameter and 70 microns deep. Based on these parameters, no more than a nanogram of the element need be extracted from the rock for semi-quantitative a n a l y s i s . I t was on t h i s a l l u r i n g prospect that the program was i n i t i a t e d . Work on t h i s project was c a r r i e d out over several months, but as there was only marginal success i n a few areas, the various experiemnts and complications w i l l not be described i n d e t a i l . Problems f e l l broadly into the following categories: i ) Machine non-reproducability. Despite a curved c r y s t a l focusing system i n the macroprobe, sensi-t i v i t y was not as good as had been hoped. D r i f t and long period i n s t a b i l i t y 189 made long counting times d i f f i c u l t to standardize, and background was noisy, i i ) Inhomogeneity. Obtaining and mounting a very small amount of material was complicated by the requirement that i t be homogeneous. This was e s p e c i a l l y important as centering the sample i n the X-ray beam must be done by maximizing a reading on the element to be analysed. The amount of trouble involved i n obtaining a homogeneous specimen was su r p r i s i n g ; the solutions are described under the chemical groups. i i i ) Chemical f r a c t i o n a t i o n . Several chemical reactions purporting to p r e c i p i t a t e two or more e l e -ments q u a n t i t a t i v e l y were a c t u a l l y found to fractionate the r a t i o s of these elements quite noticeably. Furthermore, i n d i s s o l v i n g and tre a t i n g sub-s t a n t i a l amounts of rock to i s o l a t e trace element groups, contamination was an ever-present problem. Ppta.ssium and Rubidium. As several a n a l y t i c schemes reported to pre-c i p i t a t e both of these elements q u a n t i t a t i v e l y , they appeared to be an easy pair to t r e a t . P r e c i p i t a t i o n by sodium tetraphenylboron did preserve the K/Rb r a t i o , and cesium may be used as an i n t e r n a l standard. (Spectrograde cesium chloride was obtained for t h i s purpose.) The tetraphenylboron r a d i c a l , however, was too heavy, d i l u t i n g the sample beyond usefulness. Furthermore, these compounds are not stable under strong X-rays. No sys-tem was found to further concentrate the a l k a l i s without tampering with t h e i r r a t i o . C o b a l t i n i t r i t e p r e c i p i t a t i o n also yielded a heavy compound, and discriminated against rubidium. After several leaching and ion-exchange procedures had also f a i l e d , a 190 method was found using fusion. The rock samples were f i r s t digested i n a mixture of hydrofluoric and n i t r i c acids, and t h i s evaporated to dryness. The residues were then transferred to a furnace and kept for six hours at 900°C i n a nitrogen atmosphere. A l l detectable potassium and rubidium were removed from feldspar and b i o t i t e i n t h i s manner, and washed from the fusion tube with d i l u t e HCl. Homogeneity was achieved by melting the a l k a l i s as n i t r a t e s and cooling quickly. As several grams of rock may be treated at once i n t h i s manner, i t might be used with a standard X-ray fluorescence unit to obtain K/Rb values for basic rocks. Strontium. Barium and Calcium. Various forms of chromate, sulphate, rhodizonate, oxalate, and carbonate p r e c i p i t a t i o n s were t r i e d , without obtaining one which appeared to give complete recovery of a l l the a l k a l i n e earths without complications due to f r a c t i o n a t i o n or i n c l u s i o n of other elements. The best system devised was similar to the 12 N HCl elutant method described under ion exchange procedures (see also Figure 1). There i s one difference i n that only 25 ml. of the concentrated acid may be used to bring other elements out of the column i f barium i s to be included i n the analysis, as i t i s s l i g h t l y mobile at t h i s a c i d i t y . Alkaline earths were handled as hydroxides for macroprobe analysis, as the chlorides are hygroscopic. No e f f e c t i v e method was found of forming them into small, homogeneous dots. Heavy Metals. Separation of a n a l y t i c goups I and II by hydrogen sulphide p r e c i p i t a t i o n was one of the more obvious techniques of geochemical 191 i n t e r e s t . A sweeping agent was usually required because of the low con-centration of these elements i n most rocks. Cadmium was generally employed both as a sweep and as an i n t e r n a l standard. When the sample loaded i s only a few micrograms, however, the p r e c i p i t a t i n g agent must be removed. Although such small samples were not used i n these t e s t s , an experiment was run which showed that t h i s could be accomplished using mercury for the sweeping agent. Almost a l l mercury was then l e f t behind by leaching with n i t r i c acid, i n which the other sulphides are soluble. Normally mercury was avoided due to the tendency of i t s sulphide to vaporize when exposed to strong X-radiation i n a vacuum. For the most part, sulphide p r e c i p i t a t i o n s worked well for chemicals and reasonably well for rocks, e s p e c i a l l y when a strong solution of ammon-ium acetate was employed to keep lead i n so l u t i o n p r i o r to introduction of the sulphide i o n . Heavy metal p r e c i p i t a t e s were made homogeneous by d i s -solving them i n a drop of d i l u t e acid and placing t h i s on a hot m e t a l l i c sur-face where the drop " s k i t t e r s " on a steam pad, f i n a l l y depositing i t s con-tents as a small, homogeneous f l e c k . It was found that reasonably good semi-quantitative analysis for lead, s i l v e r , bismuth and copper could be c a r r i e d out on a microgram of each element using four minutes counting on both peak and background (Figure 16). Accuracy was i n the neighbourhood of ± 10% and better for bismuth and lead than for the other elements. Using standard X-ray fluorescence equipment, other workers (for example, Natelson et a l , 1962) have obtained better accuracy for not much loss i n s e n s i t i v i t y . Considering that the dots of sample material used were not very e f f i c i e n t (too deep), and allowing 30 min. F i g u r e 1 6 Macroprobe Results 6 193 counting time, i t seems p o s s i b l e that the l i m i t of a n a l y s i s for heavy e l e -ments would be i n the order of a few tenths of a microgram. This i s a f u l l order of magnitude below other X-ray fluorescence methods reported, but s t i l l d i s a p p o i n t i n g . There i s even l e s s advantage for l i g h t e r elements, and long counting times are of dubious value because of i n s t a b i l i t i e s p r e v i o u s l y mentioned. Conclusions f o r Macroprobe P r o j e c t . No e f f e c t i v e method was developed f o r adapting the macroprobe to s e m i - q u a n t i t a t i v e m i c r o a n a l y s i s of r o c k s . The major use of t h i s instrument appears to be i n t r a c i n g major element v a r i a t i o n s across small specimens such as rock c r y s t a l s . The macroprobe i s a new device, and i t i s not u n l i k e l y t h a t improvements i n ins t r u m e n t a t i o n w i l l a llow the p o s s i b i l i t i e s discussed here to be r e a l i z e d . A method of a l k a l i v o l a t i l i z a t i o n was developed which might be employed with a standard X-ray fluorescence u n i t to o b t a i n K/Rb r a t i o s of rocks poor i n these a l k a l i s . Measurement of potassium by X-ray fluorescence, however, r e q u i r e s use of the flow; counter, and as the r a d i a t i o n i n v o l v e d i s at a wave-length below the absorption edge of some major rock m i n e r a l s , Compton s c a t t e r i n g cannot e a s i l y be a p p l i e d as a c o r r e c t i o n . I9h APPENDIX VIII Mass Spectrometry The strontium isotope measurements reported i n Chapter I I I , and several isotope d i l u t i o n analyses of rubidium were c a r r i e d out on a 12", single-focusing mass spectrometer, using t r i p l e filament technique. This machine was constructed by J . Blenkinsop under the supervision of R.D. Ru s s e l l . Blenkinsop also made several of the rubidium measurements by isotope d i l u t i o n . Both strontium and rubidium were p u r i f i e d by use of ion exchange columns before loading for mass spectrometry. In the case of strontium t h i s was to prevent interference by rubidium, and i n the case of rubidium because of i t s low concentration i n the samples being analysed. Rhenium filaments were employed i n a l l runs. These were out-gassed i n vacuum at white heat p r i o r to loading, and the loaded sample taken to a d u l l red heat i n a i r . Loading was accomplished using water as a solvent i n the case of rubidium, and 2 N HCl for strontium. Center filament currents were t y p i c a l l y i n the range of 3.0 to 3.5 amps for rubidium measurements and 4.0 to 4.5 amps for strontium. Use of currents higher than t h i s tended to cause evaporation of rubidium from surrounding parts of the source. Readings were made easier to record i n the case of the strontium isotope work by i n s t a l l a t i o n of a computer i n t e -grating system to smooth fl u c t u a t i o n s i n output. Several measurements made of the rubidium content of U.S.G.S. standard rock W-l gave 21.7 ppm concentration with a standard deviation of 0.2 ppm. 195 This concentration i s s l i g h t l y lower than the values generally quoted for that standard, but f i t s well with the more recent isotope d i l u t i o n measurements from other l a b o r a t o r i e s as compiled by Flanagan (1969). The measured Rb^ 5/Rb^ 7 r a t i o was 2.59T~± 0.001 for normal rubidium, com-pared to 2.593 reported by Catanzaro et j l . (1969). The rubidium blank was approximately 0.1 micrograms. Those rubidium measurements made by isotope d i l u t i o n are underlined i n Appendix I. 87 / 86 A. few Sr /Sr measurements were made for strontium i n Coast Moun-tain s igneous rocks, and these are discussed i n Chapter I I I . Measurement of t h i s r a t i o i n the Elmer and Amend standard strontium carbonate gave 0.7077 - 0.0005. The accepted r a t i o of 0.7080 i s within the standard deviation, and normalization to t h i s value was not c a r r i e d out for the rock strontium r a t i o s . Correction was, however, made for f r a c t i o n a t i o n assuming 88 that S r 8 6 / S r O T i s 0.1194. In a l l but two samples the standard deviation 86 , 8 8 87 , 86 i n the Sr /5Sr value, although smaller than that for Sr /Sr , made a 87 86 larger c o n t r i b u t i o n to the uncertainty i n the f i n a l Sr /Sr r a t i o reported. A blank run for strontium showed 1.1 micrograms, which i s poor. This i s l i k e l y the r e s u l t of the large amounts of strontium being processed i n the rock samples being studied and the use of unpurified sodium tetraphenyl-boron to p r e c i p i t a t e rubidium. In view of the high strontium content of a l l rocks involved and the l i m i t e d v a r i a t i o n of t h e i r strontium i s o t o p i c compo-s i t i o n , t h i s l e v e l of contamination does not make a s i g n i f i c a n t addition to the e r r o r . 196 APPENDIX IX  S c a r p - f i l t e r Program and O u t l i n e The purpose of the s c a r p - f i l t e r computer program i s to o u t l i n e l i n e a r d i s l o c a t i o n s through the values of a numerical g r i d array. The meaning of output f o r the f i v e - and ten-mile s c a r p - f i l t e r s has been defined i n the t e x t . The language i s F o r t r a n . Dimensions and Input. Statements 1-3 i n the included program r e p r e -sent a very simple data input system. The f i r s t two values are the num-bers of rows and columns (NROW, NCOL) i n the g r i d . G r i d values ( e l e v a t i o n s ) are then read i n 20F4.0 format, row by row. Where the value 80 i s met i n the dimension statement, t h i s r e f e r s to maximum g r i d s i z e and must be a l t e r e d f o r l a r g e r a r r a y s . As a n a l y s i s r e q u i r e s use of two g r i d spaces on every side of the p o i n t being t r e a t e d , the a c t u a l o p e r a t i o n i s on a g r i d four rows and columns smaller than i n p u t . Statements 4 and 5 define these boundaries f o r array operators. Establishment of a G r i d . Statements 6 through 15 i n i t i a t e the DO-loops fo r two dimensional o p e r a t i o n , and e s t a b l i s h about each p o i n t ( l , J ) a f i v e by f i v e g r i d of the e l e v a t i o n s surrounding that p o i n t . Direct, D i f f e r e n c e Output. The magnitude of e l e v a t i o n a l d i f f e r e n c e s between adjacent squares or the diagonal e q u i v a l e n t s are computed i n statements 24—27 f o r the four primary d i r e c t i o n s . These are p r i n t e d out but have proved of l i t t l e value i n t h i s form. Statements 16—23 check to make sure t h a t a s u f f i c i e n t part of the surrounding g r i d i s complete to make the measurements v a l i d , and p r i n t s -0.0 i f t h i s i s not so. Negative 197 e l e v a t i o n s should be fed i n f o r g r i d p o i n t s which are not to be t r e a t e d , as i n areas of ocean, e t c . 1 Primary S c a r p - f i l t e r s . Statements 29 to 67 e s t a b l i s h the values for the f i v e - m i l e and ten-mile s c a r p - f i l t e r s , and average e l e v a t i o n a l d i f f e r e n c e s between p a r a l l e l s t r i p s of topography. For each d i r e c t i o n i n t u r n , the des i g n a t i o n s V,W,X,Y,Z stand f o r weighted average e l e v a t i o n s along s t r i p s p a r a l l e l to the d i r e c t i o n being t e s t e d . The s c a r p - f i l t e r outputs are stored under B(LQ,I,J) where LQ i s a number which i n d i c a t e s i t s d i r e c t i o n and width. In i n t e r p r e t i n g the output, the scarp i n d i c a t e d runs below or to the r i g h t of the g r i d p o i n t i n question. Output Adjustments. Statements 6 8 — 8 0 adjust the output so that each p o i n t i s represented by a s m a l l , whole number. Only anomalously high values are not zero, which makes the output easy to read. Statements 81—86 add a l a r g e number to the f i r s t output g r i d value to t e l l which data set ( d i r e c t i o n ) and f i l t e r type) i s represented. The remainder of the program i s p r i n t - o u t i n s t r u c t i o n s . 1.9.8 PRIMARY SCARP-FILTER PROGRAM 6 0 0 0.1 MEMS I OA! A ( B 0 , - 8 0 ) , 8 ( 1 0 , 8 0 , 8 0 ) , 0 ( 1 0 , 8 0 , 8 0 ) READ ' (.5 , 60 0 ) MPO.W,NCQL » (•( A ( K , 1. ) , 1 = 1 , N C O L ) ,K = 1 , FORMAT (2 T5 / ( 20.F4 . 0 ) } ' •JK: = NC0L .- ? • "' ' . ' • NRGW ) •- • D G 1 0 J=3 , J N '•: ' M=J + 1 ' ' ' " '' ' ."'. . '•_ / " .\;-J-1 . ' '• ' ' ' R ] " : M M = J + 2 N\'= J - 2 • • on <3 1 = 3 , iN ... • • K A = T + 1 • ... . L A= I- L . 0..' ' 1 _ •_ _. ; K K = I + 2 ' ' ' " ' . ' . . \ . . . . ., LL=.T-2 I F ( A ( T , J ) ) 5 , 1 T 1 . 1 2 ; '•• 3 1 0 0 • I F ( A ( I ,M) 1 5 , 2 , 2 I F ( A ( K A , J ) ) 5 , 3 , 3 I F ( A ( I, N ). ) 5 , I 01 ,.1 01 '• . j ' ., ;  0 0 ' l O O JQ = 1. , 4 L Q = 2 * J Q Of I. Q . J , J ) = - 0 . 0 - —— .• • '• 101 i ]'•••;• 1 2 GO TO . 1 2 . ' . . 0 ( 2 , I , J ) = ( A { I ,M . ) ' -A ( I , J ) ) / 2 . 0 '' 0 ( 4 , I , J ) = . ( A (• F , J ) - A ( K A , J ) ) / 2 . 0 . : . 0 ( 6 , 1 , , J )..= 0 . 5--= ( A { I , J ) ) - 0 . 2 5- ( A ( I •» M ) +A { KA , J") ) 0( 8 , I, J )= 0 . 5 * < A { T , J ) ) -0 . 2 5 * ( A < I , N )'+A { K A , J ) ) L 0 = 1 . V = A ( I, NN )+A ( K A , NN ) + 0 . 5 - ( A ( LJ. , N N ) +A ( KK , N N ) ) !••..;•_:.• w_ A ( I , N ) + AC K A , N ) + 0 . 5 * ( A <L A , N ) + A ( K K , N ) ) !''.'•; • X = A ( I , J ) + A< KA , J )+0 . 5* ( A ( LA , J ) +A { K K , J ) ) • Y= A ( I , M ) + A ( K A , M ) + 0. 5 * ( A ( L A , M ) + A ( K K , M ) ) Z = A ( I ,-M.M ) +A ( KA , MM ) + 0 . 5 * ( A ( L A , MM ) +A ( K K , M M ) ) B ( L O , I , J ) •= 0 . 1*{ A R S ( X - Y ) )-0.65*{ A 8 S ( Z-Y ) +ABS ( W-x n - i . 0 D t L O t l i J ) = ( Y - X ) / 5 . 0 LO=LQ+1 B( L Q , I , J.)•= 0 . 1 * ( ABS ( W-Y) ) - 0 . 05*.< A S S ( V - W ) + A B S ( Y -Z ) ) - 1 . 0 L 0 = L C + 1 .' V= A { L L , J ) +A ( L L , M) + 0 ' . 5 * (A ( LL , M.) + A ( L L ,MM) ) •'• . '«.' = A ( L A , J ) + A (1. A , M ) +0 . 5* (A ( L A , N ) + A ( L A , M M ) ) X= A { I , J ) +AC I , M ) + 0 . 5 * ( A ( I , N ) + A ( T., MM ) .) . Y= A ( K A , J ) +A ( K A , M ) + 0 . 5 * ( A. ( KA , N) + A ( K A , M M ) ) . Z = A ( K K , J ) +A ( KK-, M ) + 0 . 5 * ( A { KK , N ) + A ( K K , M_,^ ) ) _ • \ S ( L 0 , T , J ) = 0 . 1 * ( A B "S T'X - Y')")' - 0 7 0 5 *~{ A B S 1 Z - Y ) + A B S'("w - xT Pl".' "6" D'( L C , I, J )= ( Y - X ) / 5 . 0 ' • L 0 = L 0 + 1 . : • ' • • B ( L Q , I , J ) = 0 . 1* ( A.BS ( W-Y ) . ) - 0 . 0 5 * . ( A 3 S ( V-W) .+ A 3 S . ( Y - Z ) ) -1 . 0 L ' « = L Q + I . 199 v - A ( i , N) +.A ; L \ ) + A (i i, j j '7 077 _ •• •' 'J ' 'w = A( I . \ ) + A ( 1. A , J ) + 0. 5 * ( A (' K A ,. N N ) + A ( L L V MT ) '7"' .r~~7; 7.77 . X = A (. I , J )+0.5*(A (KK, NN)+A(KA,N ) + A (LA » M ) + A ( LL,MM) ) ' 'Y-A ( K A , J ) + A ( I , H ). + f) . 5 * ( A ( KK , M ) + A ( LA, MM.) ) • .'.. ; .' 7 = A ( K K , J ) + A (!< A , M.) + A ( I ».M.M ) •R ( L. Q.» T» J ) = 0 . I * ( A R.S (X-Y'). )-,0 .05*( ABS( Z-Yl+ARS (W-X) )-1.0 : .0 ( LQ » I » J ) '=.•( Y-X ) /5 .0 '. L(-) = LQ+ i 7. • . '-.) • 77 • '; R ( LQ., T ,.J ) = 0 .1 * ( AR S ( W-.Y ) }-0.05*'(AB.S( V-W).+ ABS( Y-Z) ) - 1 . 0-• •' LCv' = LQ+l_'x ;"'-' . V = A ( L L . J~)+A ( L A. M ) 4-A (I , MM) ' "'..''' . ..,••'' ,' -W = A ( I A t J •) + A ( I ,M ) +0 . 5*( A ( LL , N ) +A,( KA ,m ) ) X = A ( I , J 1 +0 . 5.* ( A ( L A , M ) + A ( K K , MM ) + A ( K A , M.) + A (L-L--, NM ) > .7 „ £ „/.... Y/= A ( I ,M )+A( KA ,'J.) +0.5* { A J LA , NN ) + A (KK , M )•) ' • ' '• 7... • Z-= A.( '[ , NN ) + A ( K A , N ) + A ( K K,, J ) " V : • . • '-7 '7.• 7-.: R ( LQ, T , J) =0. ] #"( ARS.(X-Y ). )~6 .05* ( A3S { Z.-Y ) +ABS (W-X ) J-1. 0. .. ' ': D ( L C), I , J ) — ( Y- X ) / 5 . 0 ' . "" ' • • : ' • -• . (.(:•= LC+l ' R< LO, I , J l =0. 1*.{ A 6 S ( W—Y ) ) -0 • 05 ( AB S. ( V-VI ) .+ABS ( Y- L ) ) - l .0 '• ..'DO 4 LQ=1,8 • "'• '•• 1 7 '•'..;.- ; . -7 I F ( B ( I. Q » T , J.) ). 8,4,4* \ , - - • 8 • R ( LO , I , J) =0. . 4 •• f.nNT \ NUF ' •  , '•' ••••.'' IF ( A ( LL , M M ) ) 7.:, 6,6' : :7.I F ( A(KK,MN) 17,0,9 ^ '• -.' 7'' • "I •, : .'.-'7 •'' oo 11 i.o= r, e: " 7; :' : :'. 7 ; - ' l l ' 7 7i( LC, I , J)=-0.0 00 1.5 T Q~ 1.4 ' .' L0=2*T0-1 . . 15 0 ( i.. 0 , ' , J) =-0.0 9 • .' : CO NTT MO E '• •'• .'7 10 ... . C O M I NO P --77 '' ''7..:. ''J 7...T. ', DO 20' L0= 1, 8 AL=FLOAT(LO) o ( L 0 , 3 ,.3.) = B ( L 0, 3 , 3 ) + ( A L * 100.0) .. IF ( D( LQ ,3 , 3 ) ) 19, 20,20 19 :. . DM. Q, 3 t 3 )'= (• 100..0..6*Al. ),-D( LQ,3, 3 ) 20 • 0(LQ,3,3)=D(.L0 ,-3 , 3 ) + ( 10 0 0 .0 * A L )'. .. or: 651 1.0 = 1 ,8 , . . ;7 " " ' .' DO .649 K = 3,.IN ' 649 WR I T.E (6 , 7 00) ( 0 ( LQ , K , L ) , L=3 , J.N ) WR I T F { 6 , 7 0 1 ) DO 650 K = 3 , I N. .' • _ 6 50 W R I T E ( 6 , 700) ( B ( LQ, K , L ):, L=3 , JM. • ' ,.' : ' 651 WR ITE ( 6 , 7 0 1 ) , • . "A "~ \ •': , 7 00 FORMAT ( 1 H 0 , 2 5 F 5 . 0 ) .'•' i,. . 701 FORMAT ( 1 H 1 ) STOP ... .••'.,..• END - •. • •: . • 7'• • " i . 7 : ; 200 SECONDARY SCARP-FILTER PROGRAM (For d i r e c t i o n s oblique to those tested by primaryrprogram) OIMFNSION A(80,SO)., .8(10,86,80), 0 ( 1 0 , 8 0 , 8 0 ) ' .. READ ( 5 , 6 0 0 ) MR0W,MC0L , ( ( A ( K , L ) , L = 1,MC0L) ,K=1,NROW) 600 FORMAT ( 2 I 5 / ( 2 0 F 4 . 0 / 4 F 4 . 0 ) ) s j M = N C 0 L - 2 ' ' ' • . .' • . ~ I N=IMR0W-2 ' • ' " ' ~ ~ " ' DO 10 J=3, J.N ' . •M = J+1 ' ' ,. ;. •. . .... .;" . .. . . ,N = J - 1 • : MM=J+? - ' NN=J-? ' ' - " 1 • •- ' • '• :' -• ;DO 9 1=3,IN KA=I + 1 ' . ' v . • i. A =1—1 : . . ..... • ;. ... \ ; ....: KK'=.T+2 ,'. . • L L = I - 2 •' ' ' ' ' " T F ( A ( I, J ) ) 5 , 1 , 1 1 I F ( A ( I , M ) ) .5 , 2 , 2 2 . . I F ( A ( K A , J ) ) 5 , 3 , 3 '' 3 T F ( A { I., N ) ) 5 , 1 0 1 , 1 0 1 " 5 .• : on i o n 'JO=.I ,4'. ; 1 0 0 • 0 ( 1 . 0 , I , J ) = - 0 . 0 .GO TO 9 1 0 1 0 ( 1 , I , J ) = .( A( .1 , J ) -A ( K A , J.) - A ( L A , M ) + ( A ( K K , N ) + A ( L L , M ) ) / 2 .0 ) 1 5 . 0 ,0(2., I , J ) = ( A ( I , J ) - A ( . K A , N ) - A ( I , M ) + ( A IKA,NN)+A(L A , M M ) ) / 2 . 0 ) / 5 . 0. 0 ( 3 , I , J ) = ( A ( I , J.) - A ( L A,, N ) -( T , M ) + ( A ( L A , N N ) + A ( K A , M M ) ) / 2 .0 ) 7 5 . 0: 0 ( 4 , I , J ) = ( A ( I , J ) - A ( L A , J ) - A ( K A , M } + ( A ( L L » N ) + A ( K K , M ) ) / 2 . 0 ) / 5 . 0 : ' 9 C O N T [ N U E ' • 1 0 . C O N T I N U F 0 0 6 5 1 LQ = 1 ,4 .. ' 0 0 6 4 9 K = 3 , I N > 6 A 9 ..' WR I T F ( 6, 7 0 0 ) ( 0 ( L O , K, L ) ,.L = ; • •' 6 5 1 1 <" I T F ( 6 , 7 01 ) . .:: 7 0 0 F O R M A T ' ( I HO , 2 5 F 5 . 0 ) !•"• 7 0 1 F O R M A T ( 1 H 1 ) S T O P •; ' E N D ,• 201. APPENDIX 'X C o r r e l a t i o n , of Secondary E r o s i o n Surfaces S c a r p - f i l t e r a n a l y s i s performed a reasonably good job of d i v i d i n g the Coast Mountains i n t o regions of f a i r l y smooth and continuous summit l e v e l s . There remains the question of whether these s e c t i o n s represent an e r o s i o n surface which was once continuous from the s t r a n d f l a t s to the I n t e r i o r P l a t e a u , or i f the d i s c o n t i n u i t i e s predate u p l i f t . An attempt to solve t h i s problem was made through a technique known as the shoulder and summit method (Geyl, 1961). This i s based on the o b s e r v a t i o n t h a t periods of s t a b i l i t y during u p l i f t of a r e g i o n may allow r i v e r s to cut to a base l e v e l and broaden t h e i r v a l l e y s . L e v e l s so formed w i l l be preserved as shoulders on some r i d g e s a f t e r continued u p l i f t causes f u r t h e r d i s s e c t i o n . I t may be p o s s i b l e to c o r r e l a t e these secondary e r o s i o n l e v e l s across a summit enve-lope d i s c o n t i n u i t y , provided there has been no r e l a t i v e movement along t h i s l i n e during r e g i o n a l u p l i f t , and provided the shoulders present a c t u a l l y represent widespread e r o s i o n l e v e l s . The usual peak and shoulder technique was modified to avoid the problem inherent i n t r u n c a t i o n of lower e r o s i o n l e v e l s by g l a c i e r s during reshaping of v a l l e y s . Ridges were marked from summits down to where they l o s t expres-s i o n due to t h i s process. The e l e v a t i o n of each summit and shoulder was a l l o t t e d e i t h e r one or two p o i n t s , depending on prominence, and the number of p o i n t s f o r each e l e v a t i o n was d i v i d e d by the number of r i d g e s which crossed t h a t l e v e l . As these p o i n t s are a l l o t t e d not on the b a s i s of abso-l u t e width of the contour spacing, but r a t h e r on r e l a t i v e width w i t h respect 202 to surrounding contours, upland surfaces do not show on the compilation. Rather, one sees l e v e l s of greatest, b e v e l l i n g with respect to the surround-ing slope, and must make use p r i m a r i l y of the distances between these i n the f i n a l c o r r e l a t i o n . Obviously, only small areas may be treated i n any one compilation, to r e t a i n the necessary r e s o l u t i o n on what may well be a t i l t e d or uneven secondary erosion surface. One problem with t h i s technique i s that the l e v e l of the highest sum-m i t s ) always has a r a t i n g of unity, and i t i s necessary to decide from the number of peaks reaching that height and t h e i r sharpness whether i t i s t r u l y a l e v e l of s i g n i f i c a n c e . Figures 17 and 18 show compilations for secondary erosion surfaces across the southern a x i a l fracture and the B e l l a Coola fra c t u r e , and parts of the p r o f i l e which are not defined by at l e a s t f i v e summits or ridges have been only dotted i n . Another problem i s g l a c i a l scouring has not l e f t enough shoulders at lower l e v e l s to e s t a b l i s h erosion l e v e l s there despite the adapted technique. This r e s t r i c t s g r e atly the elevations across which c o r r e l a t i o n can be made. The most unfortunate problems to a r i s e during the compilation stage were inherent i n the topographical maps themselves. It was found that one hundred foot contours were required to make meaningful i n t e r p r e t a t i o n s , and these are published for only a minor part of the project area. Further-more, the contour r e n d i t i o n of topography i s known to be quite poor i n some of the more i n t e r e s t i n g map sheets. Results of the shoulder and summit analysis had two unexpected r e s u l t s , which may be observed i n Figures 17 and 18. The f i r s t i s r e s o l u t i o n of secondary erosion surfaces that i s considerably better than had been 203 Figures 17 and 18» Suggested c o r r e l a t i o n s are shown for secondary e r o s i o n l e v e l s across major d i s c o n t i n u i t i e s i n the summit envelope. Note t h a t the distance between peaks, r a t h e r than peak h e i g h t s , i s the most r e l i a b l e means of c o r r e l a t i o n . P r o f i l e s not defined by f i v e or more r i d g e s or summits are shown dashed. In both f i g u r e s , the best c o r r e l a t i o n i s that shown, and corresponds to a l l the movement i n d i c a t e d by summit envelope d i s l o c a t i o n having postdated r e g i o n a l u p l i f t . MATCHING OF SECONDARY EROSION LEVELS ACROSS THE SOUTHERN F i Q m - C I f AXIAL FRACTURE ZONE ELEVATION ATTEMPTED MATCHING OF SECONDARY EROSION SURFACES ACROSS THE BELLA COOLA RIVER 206 expected, and the second i s t h a t these show a frequency of about four to seven hundred f e e t , which does not seem n a t u r a l . This apparent frequency l i k e l y o r i g i n a t e s i n the b a s i c method of marking l e v e l s , which tends to a l l o t a p o i n t t o the widest contour spacing with respect to immediate sur-roundings. This may not make such l e v e l s l e s s r e a l , but tends to show up even small shoulders i f there i s nothing l a r g e r about (which i s what the technique was designed to do i n order to catch e r o s i o n l e v e l s below the l i n e of g l a c i a l s c o u r i n g ) . Assuming the r e s u l t s to be meaningful, the u n i f o r m i t y of e r o s i o n l e v e l separations makes c o r r e l a t i o n q u i t e d i f f i c u l t , and as mentioned i t i s the s e p a r a t i o n a l d i s t a n c e s r a t h e r than the a r e a l importance ( i . e . , p l o t height) that i s expected to y i e l d meaningful r e s u l t s . In both cases studied (southern a x i a l f r a c t u r e and B e l l a Coola R i v e r ) , a reasonable f i t may be made f i t t i n g the assumption t h a t a l l d i f f e r e n t i a l movement was l a t e r than formation of the secondary e r o s i o n l e v e l s observed. The magnitude of the d i s l o c a t i o n s represented i s c l o s e to t h a t expected from summit l e v e l i n t e r p r e t a t i o n , being 2000 f t . i n the case of the southern a x i a l f r a c t u r e adjacent to Tantalus-; Range (whose highest summit does not quite reach the o l d e r o s i o n s u r f a c e ) , and 1400 f t . across the B e l l a Coola R i v e r . These r e s u l t s are somewhat unexpected, as the general p o s i t i o n of o l d upland surfaces tend to c o r r e l a t e across these f e a t u r e s , suggesting that most f r a c t u r e movement had preceded u p l i f t . Further work along these l i n e s i s recommended when more one hundred foot contour maps are a v a i l a b l e , and i t would be dangerous to draw any f i r m conclusions regarding the r e l a t i v e ages of r e g i o n a l u p l i f t and scarp development from the data now a v a i l a b l e . 2G7 APPENDIX XI Regional, .Analysis and the Zoning of L i n e a t i o n P a t t e r n s Map 9 shows a good example of a r e g i o n o u t l i n e d by d i r e c t i o n and d e n s i t y of l i n e a t i o n p a t t e r n s . These regions tend to be much l a r g e r than the i n d i v i d u a l b l o c k s shown by summit l e v e l a n a l y s i s . As t h i s example shows, these d i r e c t i o n a l regions are approximately bounded by summit enve-lope scarps, but these tend to be somewhat o f f s e t i n the d i r e c t i o n of higher summit e l e v a t i o n from major lineaments ( i n t h i s case the Owikeno and the Holberg—Johnstone S t r a i t lineaments) which more n a t u r a l l y bound the r e g i o n . This may represent scarp r e t r e a t from an older l i n e of movement. In the case demonstrated, the eastern boundary i s l e s s d i s t i n c t but shows reverse throw, being e i t h e r a summit envelope scarp f a c i n g east or the mar-g i n of a broad t r e n c h . This example i s included dominantly to show the use of lineament f a b r i c a n a l y s i s as another method of tectomorphic zoning. The p o s s i b i l i t y of q u a n t i z i n g such f a b r i c (both d i r e c t i o n and d e n s i t y ) by l a s e r a n a l y s i s was i n v e s t i g a t e d . Laser A n a l y s i s of Contour Maps A b r i e f i n v e s t i g a t i o n was undertaken to determine i f a s i g n i f i c a n t amount of tectomorphic data could be derived from Coast Mountains topographic maps by l a s e r a n a l y s i s . The theory of l a s e r treatment of graphic data has been given by a number of authors, ('for exampT;.^-v[?3PK§PI:h>. '('1^ 65'),)?..;, Bothy the p o s s i b i l i t y of d i r e c t i o n a l f i l t e r i n g , and the F o u r i e r transform method of d i s p l a y i n g d i r e c t i o n a l character appeared a p p l i c a b l e to the problems at hand. 2 0 8 Map, 9. A r e g i o n a l t e c t o n i c block i s d i s t i n g u i s h e d by a d i s t i n c t i v e lineament p a t t e r n . S o l i d l i n e s are summit envelope d i s c o n t i n u i t i e s g e n e r a l l y l y i n g somewhat i n l a n d from major lineaments which appear bound the blo c k . 210 Two p o s s i b i l i t i e s were i n v e s t i g a t e d : i ) As contours i n a rugged t e r r a i n w i l l tend to have a p r e f e r r e d o r i e n t a t i o n approximating v a l l e y (and lineament) d i r e c t i o n s , such trends should be d i s p l a y e d as rays on a F o u r i e r transform of the contour map. This technique would remove the personal b i a s inherent i n the usual method of drawing i n apparent lineaments and then performing a manual a n a l y s i s of t h e i r d i r e c t i o n s . i i ) B e l t s of c r u s t a l f a i l u r e might be expected to have an unusually high percentage of lineaments and v a l l e y s i n the d i r e c t i o n of s t r a i n . I f the contour p a t t e r n i s f i l t e r e d so that only high-frequency d i r e c t i o n a l data of the o r i e n t a t i o n being examined i s allowed to pass, then the zone of f a i l u r e might become apparent even on an otherwise complex contour map. I f necessary, a microdensitometer could be used to make t h i s q u a n t i t a t i v e . The f i r s t major o b s t a c l e i n t h i s p l a n proved to be o b t a i n i n g a high c o n t r a s t r e n d i t i o n of the contours. Even using high c o n t r a s t copy f i l m and f i l t e r s , the l i g h t brown contours of the 4 m i l e s / i n c h topographic maps d i d not come through d i s t i n c t l y enough. This problem was solved by making paper contact negatives d i r e c t l y from the maps. The map i s pressed against the emulsion of a number s i x c o n t r a s t photographic paper (8" x 10") by a heavy g l a s s p l a t e . This i s exposed to an even l i g h t source and the paper developed i n double strength developer. The r e s u l t i s extreme c o n t r a s t , (see P l a t e 4) as the paper has almost no response to the brownish l i g h t beneath contours. Contour l i n e s are somewhat widened i n t h i s process, which i s u s e f u l as i t i s then p o s s i b l e to analyse the maps e i t h e r i n p o s i t i v e or negative form. C u l -t u r a l and p o l i t i c a l f e atures which form s t r a i g h t l i n e s not governed by topography are removed by bleaching or i n k i n g i n . A negative i s prepared by Figure 19 SCHEMATIC OUTLINE OF LASER OPTICAL BENCH T — P o s i t i o n at which transform i s photographed or f i l t e r e d . R — F i l t e r e d reconstruction photographed here. ray path - d i f f r a c t e d ray path H H Laser Light Source Negative t o be Analysed Lens Lens Adjustable Diaphragm 212 photographing the contact p r i n t , using high contrast copy f i l m . This was shot at an ASA of 12 rather than the recommended 64 and i s best developed i n high-strength Acufine developer. Centering and focusing of the laser system has been described by James (1970). Figure 19 shows p o s i t i o n i n g of lenses and camera for photo-graphing Fourier transform and f i l t e r e d data. An adjustable diaphram was used to cut down the beam diameter so that i t does not i n t e r s e c t any boun-daries of the negative being analysed. A 35mm Practina camera without lens was used to obtain the photographs, t h i s instrument being recommended be-cause of i t s waist l e v e l view-finder and lack of glare on the ground glass viewer. As a neon-argon laser was employed, the l i g h t involved was red and hence photographs were taken with a high speed panchromatic f i l m , Kodak night s u r v e i l l a n c e f i l m 2475. The a v a i l a b l e information covers a considerably greater range of l i g h t i n t e n s i t y than the f i l m w i l l respond to, so that three or four photographs i n the i n t e r v a l l/5 s e c . — 4 sec. were taken for each transform or f i l t e r e d data reconstruction. F i l t e r i n g of the Fourier transform was accomplished by means of aluminum f o i l from which wedges of approximately 10° arc were cut to permit passage of transform rays i n selected d i r e c t i o n s . The f i l t e r was mounted on a glass plate and employed i n an adjustable holder. The f i l t e r e d data image proved very weak, re q u i r i n g 4-8 seconds exposure, and during t h i s time care must be taken to maintain a darkened room i n view of the s e n s i t i v i t y of the f i l m . Results Fourier transforms r e s u l t i n g from laser treatment of contour patterns 213 tended to show the obvious t e c t o n i c d i r e c t i o n s , and u s u a l l y secondary rays r e s u l t i n g from s i n g u l a r f r a c t u r e s such as i n l e t or major v a l l e y segments. Two examples are given i n P l a t e s 4 and 5. The technique does appear to have some promise, although i t i s not o b v i o u s l y more e f f e c t i v e than a study of lineament d i r e c t i o n s on a i r photos or s m a l l - s c a l e contour maps. Laser a n a l y s i s appears to be much f a s t e r than lineament a n a l y s i s and allows l e s s personal b i a s , but there are very r e a l problems i n t r e a t i n g major f e a t u r e s whose prominence on maps may be out of a l l p r o p o r t i o n to t h e i r t e c t o n i c s i g -n i f i c a n c e . S i n g u l a r t opographical f e a t u r e s a l s o proved to be what the f i l t e r e d image r e c o n s t r u c t i o n showed up best. Contour maps f i l t e r e d f or a c e r t a i n d i r e c t i o n showed up zones of that o r i e n t a t i o n only where these were already obvious to the eye on the o r i g i n a l map, and the most prominent l i n e s were the l a r g e , obvious v a l l e y segments running i n the d i r e c t i o n concerned. 215 P l a t e 5 Laser F o u r i e r Transform f o r Contour Map of Burroughs I n l e t Region (Map shown i n P l a t e 4) P l a t e 6 Laser Fourier Transform for Contour Map, Mt. Waddington mpa area. 217 BIBLIOGRAPHY Ahrens L.H. (1963) Lognormal type d i s t r i b u t i o n i n igneous rocks - IV. Geochim. Cosmochim. Acta 2 I » 333. Ahrens L.H. (1966) "Element d i s t r i b u t i o n s i n s p e c i f i c igneous rocks - VIII. Geochim. Cosmochim. Acta 3_0, 109. Ahrens L.H., Pinson W.H. and Kearns M.M. 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