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Structural geology and Rb-Sr geochronology of the anarchist mountain area Southcentral British Columbia Ryan, Barry Desmond 1973

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C. i STRUCTURAL GEOLOGY AND RB-SR GEOCHRONOLOGY OF THE ANARCHIST MOUNTAIN AREA SOUTHCENTRAL BRITISH COLUMBIA by Barry Desmond Ryan, B.Sc, University of British Columbia, 1967. A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of Geology We accept this thesis as conforming to. the required standard UNIVERSITY OF BRITISH COLUMBIA December (973 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission fo r extensive copying of t h i s thesis fo r scholarly purposes may be granted by the Head of my Department or by h i s representatives. It i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of The University of B r i t i s h Columbia Vancouver 8, Canada Date 7 < ABSTRACT . High grade metamorphic rocks belonging to the Shuswap Complex crop out in the southern Okanagan region of British Columbia. An area of these rocks previously mapped by Bostock (1940) as the Vaseaux Formation was studied. A local structural lithologic succession is postulated compris*n|. of four units, whose present thicknesses are variable but do not generally exceed 100 f t . Four phases of penetrative deformation are recognized. The f i r s t , recumbent i s o c l i n a l with northerly trends, was succeeded by a second re-cumbent i s o c l i n a l phase, with northwesterly trends. Phase 3 produced easterly trending upright close folds, and later open upright north-westerly and northerly trending folds characterize phase 4. Five intrusive events punctuate the structural history. Two pre-cede phase 2 and three postdate i t . Rb-Sr isotopic dating of these i n -trusions provides a Tertiary age for phase 4, and a pre-mid-Jurassic age for phase 2. The existence of a mid-Jurassic metamorphism can also be inferred from the isotopic data. Based on interpretations of data from adjacent areas i t appears that phases 1, 2 and 3, and related events are a l l facets of the Lower Mississippian Caribooan Orogeny. i i i T A B L E OF CONTENTS P a g e ABSTRACT i i T A B L E OF CONTENTS i i i L I S T OF T A B L E S v i i L I S T OF FIGURES . i x L I S T OF P L A T E S IN POCKET ; xv SECTION ONE INTRODUCTION 2 1-1 GENERAL INTRODUCTION . . . . . . . . 2 1-2 GENERAL GEOLOGY OF .THE THESIS AREA LO 1- 3 AKNOWLEDGEMENTS 12 SECTION TWO STRATIGRAPHY 14 2 - 1 STRUCTURAL SUCCESSION , . . . 14 2 -2 UNIT I AMPHIBOLITE 18 2 -3 UNIT I I QUARTZITE 22 2 -4 UNIT I I I P E L I T E 22 2 -5 UNIT IV AMPHIBOLITE 23 2 -6 UNIT V EARLY GRANODIORITE 23 2-7 UNIT VI B I O T I T E QUARTZ MONZONITE 25 2 -8 UNIT V I I MUSCOVITE QUARTZ MONZONITE . 26 2 -9 UNIT V I I I L A T E KINEMATIC QUARTZ MONZONITE . 26 2 -10 UNIT IX LEUCOCRATIC B I O T I T E A L B I T E QUARTZ MONZONITE ;27 2-1 i BRECCIA . 28 2-12 DYKES AND VEINS . ... 28 2-13 ORIGIN OF ROCK UNITS 28 2- 14 STRATIGRAPHIC EQUIVALENTS 29 SECTION THREE STRUCTURE ... 36 3- 1 INTRODUCTION 36 3-2 MESOSCOPIC STRUCTURAL DATA . . . . ........ . . .• 37 3-3 STRUCTURAL ANALYSIS FORMAT • . •;••/; ... .. . 39 3-4 PHASE 2 DEFORMATION .............. 42 3-5 PHASE 1 DEFORMATION 57 3-6 SLIDES AND MYLONITES .' 62 3-7 PHASE 3 DEFORMATION • 69 3-8 PHASE 4 DEFORMATION 75 3-9 POSITION IN THE STRUCTURAL SUCCESSION OF INTRUSIVE UNITS 77 3-10 PHASES OF DEFORMATION SOUTH OF LONG JOE CREEK .. 82 3-11 FRACTURES . . . 91 3- 12 SUMMARY 95 SECTION FOUR METAMORPHISM 96 4- 1 INTRODUCTION 96 4-2 ISOGRADS 98 4-3 METAMORPHIC MINERALOGY RESULTING FROM METAMORPHISM M2 99 4-4 METAMORPHIC REACTIONS AND P T CONDITIONS OF M2 . 103 4-5 RELATIVE AGE OF M2 WITH RESPECT TO PHASES OF DEFORMATION AND INTRUSIVE UNITS 108 4-6 METAMORPHISM M3 109 4-7 METAMORPHISM Ml 112 V 4-8 CONTACT METAMORPHISM 114 4-9 RELATIONSHIP OF DEFORMATION TO METAMORPHISM ... 1 1 4 4MO DYNAMIC METAMORPHISM 1 1 9 4- 11 SUMMARY 1 2 3 SECTION FIVE GEOCHRONOLOGY 1 2 5 5- 1 INTRODUCTION 1 2 5 5-2 PREVIOUS ISOTOPIC WORK WITHIN AND ADJACENT TO THE SHUSWAP TERRANE, 1 2 6 5-3 DATA SUMMARY 1 2 8 5-4 GEOCHEMISTRY 1 3 1 5-5 GEOCHEMISTRY OF UNIT I • 1 3 9 5-6 GEOCHRONOLOGY OF INTRUSIVE UNITS 1 4 4 '5-7 GEOCHRONOLOGY OF METASEDIMENTARY UNIT I I I 151 5-8 GEOCHRONOLOGY OF THE VASEAUX LAKE AREA 157 5- 9 ISOTOPIC AND GEOLOGIC DATA SYNTHESIS 158 SECTION SIX DISCUSSION 162 6- 1 INTRODUCTION 162 6-2 STRUCTURAL SYNTHESIS 162 6-3 STRUCTURAL SYNTHESIS SOUTHERN OKANAGAN VALLEY . 167 6-4 REGIONAL SYNTHESIS 171 REFERENCES CITED • 177 APPENDIX :1A A DETAILED CONSIDERATION OF THE RB-SR ISOTOPIC CLOCK . 188 1A-1 INTRODUCTION 188 1A-2 EFFECTS OF SEDIMENTARY PROCESSES ON THE RB-SR ISOTOPIC CLOCK 188 v i 1A-3 EFFECTS OF METAMORPHISM ON THE RB-SR CLOCK 195 1A-4 DETAILED INVESTIGATION OF RESULTS AND PROCESSES OF ISOTOPIC MIGRATION 200 1A-5 SUMMARY . 212 APPENDIX 2A RB-SR CHEMISTRY AND MASS SPECTROMETER TECHNIQUES ... 214 2A-1 INTRODUCTION 214 2A-2 SAMPLE PREPARATION TECHNIQUES ..... 214 2A-3 ISOTOPIC SPIKING THEORY AND SPIKE DATA 221 2A-4 ERRORS AND CORRECTIONS IN MASS SPECTROMETER WORK 227 2A-5 MASS SPECTROMETER TECHNIQUES 231 2A-6 RB DECAY CONSTANT 231 APPENDIX 3A X RAY FLUORESCENCE TECHNIQUES 233 3A-1 INTRODUCTION 233 3A-2 THEORY OF THE X RAY FLUORESCENCE PROCEDURE ... 233 3A-3 CORRECTIONS AND ERRORS IN X RAY FLUORESCENCE WORK 235 3A-4 ANALYSIS PROCEDURES 239 3A-5 PRECISION OF THE METHOD .. 245 3A-6 COMPARISON OF THE PRESENT PROCEDURE WITH THAT OF OTHER LABORITORIES 249 3A-7 SUMMARY 250 APPENDIX 4A THEORY OF RB-SR GEOCHRONOLOGY 251 APPENDIX 5A ATOMIC ABSORPTION SPECTROPHOTOMETRY 254 v i i LIST OF TABLES Pages Table 2-1 Rock u n i t s 17 Table 2-II Modes of some u n i t s estimated from t h i n s e c t i o n s 19 Table 2-IH Chemical a n a l y s i s of u n i t V 24 Table 3-1 S t r u c t u r a l elements and nomenclature ... 35 Table 4-1 Some M2 mineral assemblages . . 100 Table 4-H R e l a t i v e ages of i n t r u s i v e s , phases of deformation and metambrphisms 107 Table 5-1 I s o t o p i c and geochemical data, a l l s amp l e s 129 Table 5-H Unit V, g r a n o d i o r i t e , i s o t o p i c and 138 Table 5-IH Unit I, amphibolite, i s o t o p i c and geochemical data 140 Table 5-IV Average K and Rb c o n c e n t r a t i o n s and Sn values f o r a n d e s i t e s ; i s o t o p i c and geochemical data 140 Table 5-V I n i t i a l Sr r a t i o s and ages f o r i n t r u s i v e u n i t s . . 14 3 Table 5-vt U n i t V I I I , l a t e quartz monzonite, i s o t o p i c and geochemical data 143 Table 5-VII Unit VII, muscovite quartz monzonite, i s o t o p i c and geochemical data 145 Table 5-VIH Unit VI, b i o t i t e quartz monzonite, i s o t o p i c and geochemical data 148 Table 5-IX Unit III, p e l i t e , i s o t o p i c and geochemical data 150 Table 5-X M i n e r a l and i s o c h r o n ages from u n i t I I I . 150 Table 5-XI Igneous and metamorphic samples from north of the map area; i s o t o p i c and geochemical data 156 Table 1A- 1 Isotope samples of boulder 189 v i i i Table 1A-I A r g i l l i t e samples of the Creston Formation, B e l t P u r c e l l Supergroup .... 193 Table 1A-II Excess ages i n b i o t i t e s caused by d i f f u s i o n back-log 197 Table 1A-IIIIsotope m i g r a t i o n study, i s o t o p e data ... 199 Table 1A-IV Secondary i s o c h r o n and muscovite ages .. 203 Table 1A-V D i f f u s i o n model diagram and terms 203 Table 1A-V-I Size data and ages of muscovites 208 Table 1A-VII Isotope balance sheet f o r whole rock sample T9 208 Table 2A-I Rb and Sr i s o t o p e spike equations 220 Table 2A-I.I Rb and Sr s h e l f standard data 222 Table 2A-III Spike c a l i b r a t i o n data 223 Table 2A-IV Blank contamination and d u p l i c a t e mass spectrometer runs 228 Table 3A-I X-ray f l u o r e s c e n c e b a s i c equations .... 234 Table 3A-H X-ray f l u o r e s e e n c e equipment and s e t t i n g s used 246 Table 3 A - I I I P r e c i s i o n and accuracy of X-ray a n a l y s i s 248 Table 3A-IV U.S.G.S. standard rock samples 248 Table 5 A-I. Method of c a l c u l a t i n g potassium c o n c e n t r a t i o n s 253 Table 5A-PI D u p l i c a t e spectrophotometer analyses . . 253 i x LIST OF FIGURES Page F i g u r e 1-1 L o c a t i o n of t h e s i s area 1 Fig u r e 1-2 G e n e r a l i z e d geology B.C 3 Fig u r e 1-3 Summary of d e t a i l e d work i n the Shuswap .Terrane 6 Fig u r e 2-1 L i t h o l o g y , g e n e r a l i z e d d i s t r i b u t i o n of u n i t s 13 Fi g u r e 2-2 S t r u c t u r a l s u c c e s s i o n s e c t i o n s ^5 Fig u r e 2-3 Diagramatic i l l u s t r a t i o n of e a r l y s t r u c t u r e s and l o c a t i o n of s t r u c t u r a l s u c c e s s i o n s e c t i o n s 17 Fig u r e 2-4 S t r u c t u r e from, u n i t I b e l i e v e d to be csed-=. imentary and p o s s i b l y v o l c a n i c ; L e n s e .cap^. 21 Figure 2-5 P o r p h y r o c l a s t of O l i g o c l a s e i n u n i t I, plane p o l a r i z e d l i g h t . V e r t i c a l f i e l d 5 . 2 mm 21 Fi g u r e 2-6 S t r u c t u r a l and s t r a t i g r a p h i c c o r r e l a t i o n s of t h e s i s rocks with rocks i n adjacent areas 31 Figure 3-1 A x i a l t r a c e s and s t r u c t u r a l domains ... 34 Figure 3-2 Mesoscopic s t r u c t u r a l data from domains 9 and 10 f o r f o l d 2a 40 Figure 3-3 Macroscopic hinge r e l a t e d to tr a c e 2a . 41 F i g u r e 3-4 Mesoscopic s t r u c t u r a l data from domain 8 4 3 Figure 3-5 Mesoscopic s t r u c t u r a l data from domains 7 and 8 45 Figure 3-6 P l o t of 100 hornblende C-axes from domain 8 47 Fig u r e 3-7 Mesoscopic s t r u c t u r a l data from domain 12 49 Figure 3-8 Mesoscopic s t r u c t u r a l data from domain 12 50 Figure 3-9 Mesoscopic s t r u c t u r a l data from domains 5 and 6 52 Fig u r e 3-10 Phase 2 f o l d r e f o l d i n g a phase 1 f o l d . 54 X F i g u r e 3-•11 Phase 1 a x i a l s u r f a c e t r a c e s 55 Fig u r e 3-•12 Mesoscopic s t r u c t u r a l data from domains 56 Fig u r e 3-•13 Mesoscopic s t r u c t u r a i r data from 58 Fig u r e 3-•14 L o c a t i o n of s l i d e s and mesoscopic data . 59 F i g u r e 3-•15 Decollement f o l d i n g i n domain 11 61 Fig u r e 3- 16 D e t a i l e d map of domains 9 to 13 63 Fig u r e 3- 17 Ribbon quartz C-axes from mylonite .... 67 Figure 3- 18 Phase 3 a z i a l s urface t r a c e s and 68 Figure 3- 19 Phase 3 f o l d r e f o l d i n g a phase 2 f o l d 70 Figure 3- 20 70 Figure 3- 21 Mesoscopic s t r u c t u r a l data from 71 Fig u r e 3- 22 Phase 4 a x i a l s u r f a c e t r a c e s and 73 Fig u r e 3- 23 B r e c c i a under plane p o l a r i z e d l i g h t (A) and crossed n i c o l s (B) . V e r t i c a l 74 Fig u r e 3- 24 Phase 1 and 2 f o l i a t i o n s i n .'.unit V ... 76 Fig u r e 3- 25 76 Fig u r e 3- 26 Garnets during emplacement of u n i t VIII and p o s t d a t i n g phase 3 80 Fig u r e 3- 27 83 Fig u r e 3- 28 Mesoscopic s t r u c t u r a l data from the 84 Fig u r e 3- 29 Tight phase 2 f o l d i n u n i t I •, ••' domain 18 85 Fig u r e 3- 30 I s o c l i n a l phase 2 f o l d i n u n i t I I I 85 Fig u r e 3- 31 Rootless f o l d s assumed to be phase 1 i n u n i t II (domain 19) , plane p o l a r i z e d 85 x i F i g u r e 3-32 C r e n u l a t i o n cleavages , domains 17, 21 and 22 : 88 Fig u r e 3-33 F r a c t u r e data ; 90 FiguEe 3-34 020* t e n s i o n j o i n t t r u n c a t i n g two shear j o i n t s (sets C and D) 92 Fig u r e 4-1 Metamorphic mineral isograds 97 F i g u r e 4-2 S t a u r o l i t e c r y s t a l with a l t e r a t i o n margin of white mica (muscovite ?), plane p o l a r i z e d l i g h t . V e r t i c a l f i e l d 3.0 mm. . 102 Figure 4-3 Diopside g r a i n (D) c o n t a i n i n g c a l c i t e (C) and i n contact with t r e m o l i t e (T), plane p o l a r i z e d l i g h t . V e r t i c a l f i e l d 3.8 mm . 102 Fig u r e 4-4 A x i a l s u r f a c e mica f o l i a t i o n p o s t d a t i n g formation of phase .1 . f o Id cr o s s ed n i c o l s . V e r t i c a l f i e l d 4.9mm. 102 Figure 4-5 F l a t t e n e d M2 garnet, plane p o l a r i z e d l i g h t V e r t i c a l f i e l d 5.2 mm ,106 Fig u r e 4-6 Undeformed s t a u r o l i t e c r y s t a l s , plane p o l a r i z e d l i g h t . V e r t i c a l f i e l d 5 . 2 mm. . 106 Fig u r e 4-7 Coarse b i o t i t e (white f l a k e s ) o u t l i n i n g ' a f o l i a t i o n which postdates c r e n u l a t i o n cleavage, crossed n i c o l s . V e r t i c a l f i e l d 5.2 mm 110 F i g u r e 4-8 E a r l y f o l i a t i o n o u t l i n e d by f i n e b i o t i t e •;. . and l a t e r f o l i a t i o n o u t l i n e d by coarse b i o t i t e , plane p o l a r i z e d l i g h t . V e r t i c a l f i e l d 5.2 mm. ... 110 Fig u r e 4-9 Mica: c r e n u l a t i d by phase 3, plane p o l a r i z e d l i g h t . V e r t i c a l f i e l d 5.2 mm. . 113 Fig u r e 4-10 Euhedral tourmaline c r y s t a l , plane p o l a r i z e d l i g h t . V e r t i c a l f i e l d 5.2 mm. . 113 Fig u r e 4-11 F l a t t e n e d p a r a l l e l phase 1 f o l d 118 Fig u r e 4-12 E l l i p t i c a l r o t a t e d p o r p h y r o c l a s t of f e l d s p a r , crossed n i c o l s . V e r t i c a l f i e l d 1.8 mm. . • 118 Fig u r e 4-13 P o r p h y r o c l a s t of f e l d s p a r with pressure shadow (A), crossed n i c o l s . V e r t i c a l f i e l d 1 . 8 mm. .MM 118 x i i F i g u r e 4-14 Ribbon quartz from u n i t Vim, crossed ; n i c o l s . V e r t i c a l f i e l d 1.6 mm 120 Figu r e 4-15 Polygonized quartz from u n i t Vim, crossed n i c o l s . V e r t i c a l f i e l d 1.8 mm. 120 Figu r e 4-16 Myrmekite from u n i t VI, crossed n i c o l s . V e r t i c a l f i e l d 1.1 mm. .~ 120 Fig u r e 4-17 Kinked muscovite i n mylonite d e r i v e d from l a y e r e d u n i t s , crossed n i c o l s . V e r t i c a l f i e l d 2.1 mm 122 Figure 5-1 I s o t o p i c and geochemical data sample l o c a t i o n s 130 Figu r e 5- 2 132 Figure 5- 3 Rb, K d i s t r i b u t i o n of i n t r u s i v e rocks ... 134 F i g u r e 5- 4 ,Rb,~.Sr,K d i s t r i b u t i o n of i n t r u s i v e samples. 134 Figure 5- 5 138 Figure 5- 6 Unit V,histogram of i n i t i a l Sr r a t i o s ... 138 F i g u r e 5- 7 140 F i g u r e 5- 8 Unit V I I I , l a t e quartz monzonite, 143 Figure 5- 9 Unit VII,muscovite quartz monzonite, 145 F i g u r e 5- 10 Unit V I , b i o t i t e quartz monzonite, 148 F i g u r e 5- 11 Unit I l l j W h o l e rock samples,isochron 150 F i g u r e 5- 12 Unit I I I , p e l i t e samples,isochrons f o r 152 F i g u r e 5- 13 Average i s o t o p e systems represented by samples S1+S2 and S7+S8 152 Figure 5- 14 Unit I I I , m i n e r a l samples,isochron diagram. 154 F i g u r e 5- 15 Unit I I I j mineral sample,isochron diagram . 154 Figure 5- 16 Samples from the Vaseaux Lake area, 156 Figure 6- 1 G e n e r a l i z e d north-south s e c t i o n t h e s i s 161 x i i i F i g ure 6-2 G e n e r a l i z e d north-south s e c t i o n , s o u t h e r n Okanagan 161 Figu r e 6-3 Diagramatic i l l u s t r a t i o n o f . e a r l y s t r u c t u r e s and I d e a t i o n of s t r u c t u r a l s u c c e s s i o n s e c t i o n s 164 Fi g u r e 6-4 S t r u c t u r a l geology of the southern Okanagan 16 6 F i g u r e 1A-1 P l o t of i s o t o p e data f o r boulder 189 Figu r e 1A-2 Percent mineral v Sr p l o t f o r marine c l a y s 191 Figure 1A-3 Isochron diagram ; a r g i l l i t e samples from Creston Formation,Belt P u r c e l l Supergroup 193 Figure 1A-4 Isotope m i g r a t i o n study, muscovite data, i s o c h r o n diagram 201 Figu r e 1A-5 Isotope m i g r a t i o n study,whole rock and mine r a l data, i s o c h r o n diagram 201 Figure 1A-6 D i f f u s i o n model, p l o t of Ad v 6t m.yr. .. 206 Figu r e 2A-1 Diagramatic plan of a n a l y s i s procedure .. 213 F i g u r e 2A-2 Dowex 50w x 8% Sr e l u t i o n c h a r a c t e r i s t i c s . 217 Figu r e 2A-3 Rb and Sr mass d i s t r i b u t i o n c o e f f i c i e n t s f o r dowex 50 r e s i n 217 8 6 Figure 2A-4 Optimum s p i k i n g f o r Sr spike 225 84 Figure 2A-5 Optimum s p i k i n g c h a r a c t e r i s t i c s of Sr spike 225 8 7 F i g u r e 2A-6 Optimum s p i k i n g f o r Rb spike 225 8 7 86 F i g u r e 2A-7 E f f e c t s of Sr contamination on Sr/ Sr . 230 Figu r e 3A-1 Long term X-ray f l u o r e s c e n c e s t a b i l i t y ... 236 Figu r e 3A-2 Dead time c o r r e c t i o n curve ..." 236 Figu r e 3A-3 P e l l e t weight c a l i b r a t i o n 238 Figu r e 3A-4 C a l i b r a t i o n of pulse height analyser f o r Rb .......... 240 Figure 3A-5 C a l i b r a t i o n of pulse height analyser f o r Rb and Sr 240 X-irV F i g u r e 3A-6 P l o t of mass a b s o r p t i o n c o e f f i c i e n t s f o r chemical standards a g a i n s t 1/MeKocscattered . 242 Figure 3A-7 X.R.F. data sheet 244 Figu r e 5A-1 Atomic a b s o r p t i o n standard curves f o r K and L i 255 X V LIST OF PLATES IN POCKET PLATE A Geology Oliver-Osoyoos Area, l i t h o l o g y PLATE B Geology Oliver-Osoyoos Area, phase 1 and 2 s t r u c t u r a l geology PLATE C Geology Oliver-Osoyoos Area, phase 2, 3, 4 and 5 s t r u c t u r a l geology PLATE D G e o l o g i c a l s e c t i o n s , Oliver-Osoyoos Area \ i FIGURE I - J GENERALIZED GEOLOGY SOUTHEASTERN B.C. Okanagan Lake Osoyoos Granites A/liles 50 • Koote nay Lake B X , U.S . A . M Tertiary Volcanics Mesozoic Upper Paleozoic rocks Sbuswop Terrene Lower Paleozoic and Windermere rocks Belt Puree!! 2 SECTION I INTRODUCTION 1-1. General Introduction In British Columbia there are two zones of complexly folded highly metamorphosed rocks forming cores of the Eastern Cordilleran Fold Belt and of the Western Cordilleran Fold Belt (Wheeler, 1970). The core zone of the Eastern Belt is known as the Ominica Geanti-cline and is composed of a number of disconnected northerly elongate areas of metamorphic rocks (generally of amphibolite facies). The southernmost part of the belt within Canada is known informally as the Shuswap Metamorphic Complex. The metamorphic rocks together with associated intrusives are termed the Shuswap Terrane (Figure 1-1). The thesis area is located within, but near the western margin of the Shuswap Terrane. The Shuswap Terrane is bounded on the east by complexly folded rocks of the Kootenay arc which are more heterogeneous in rock type and older than those of the dominantly volcanic sequence of the Intermontane Zone which bounds the Shuswap Terrane on the West. The extent and chara-cter of metamorphic rocks in the Canadian Cordillera is illustrated by Monger and Hutchison (1971). Since 1950, small scale mapping within the Shuswap Terrane, by a number of workers, has provided a patchwork of detailed information serving to focus attention on immense problems of correlating structural successions, stratigraphy, and absolute geochronology of events from area to area. Before presenting the ideas of these workers the evolution of some theories concerning the Shuswap Terrane are traced through the work of early contributors. Dawson (1879) explored the area around and south of Shuswap Lake. 3 In part his conclusions were that "the rocks seen on the Shuswap Lakes are so distrubed and altered that though about two weeks were given to their examination, much uncertainty yet remains with regards to their relationship among themselves" (Dawson, 1879 p. 33). On his map Dawson (1898) named these "disturbed metamorphics", the Shuswap Series, after Shuswap Indians and believed i t to be Archean and much like the Gren-v i l l e of Eastern Canada. Daly (1915) introduced the term Shuswap Ter-rane and his mapping in Albert Canyon on the Illecillewaet River, east-ern British Columbia, suggested that Precambrian Belt sedimentary rocks rest unconformably on the Shuswap Terrane. From the work of these two geologists grew the idea that the Shu-swap Terrane must represent a very ancient mass of metamorphosed Pre-cambrian rock (probably Archean). Although the work of Gunning (1928) discredited Daly's Precambrian unconformity, Dawson's idea.of an ex-tensive Precambrian metamorphic terrane was not seriously questioned unt i l 1939. Cairnes (1939) summarizing work started in British Colubia in 1928, discussed the growing conflict of opinions concerning the age of Shuswap metamorphism. He considered the Shuswap Complex to consist of rocks of several ages a l l metamorphosed in Mesozoic times by numerous plutons. Two schools of thought, Dawson's and Cairnes" concerned with sedimentary age of Shuswap rocks and age of their metamorphism, have persisted right up to the present time. Other proposals about the Shuswap Terrane have precipitated contro-versy. Daly suggested that Shuswap rocks had. experienced "static load metamorphism" (paly, 1917). On the basis of petrofabric data, Gilluly (1934) questioned Daly's idea of load metamorphism and suggested i n -stead that metamorphism was dynamic in nature. Current opinion holds 4 FIGURE 1 - 2 Summary of detailed work in the Shuswop Terrane 5 FYSON I FYLES S Me D, Oi D, D* cr D h h v M P PC 6 Christie ED SOUTHERN B C o> S Me 0/ 0 Z D, o M ! 1 1 V p PC , 7 RYAN S Mil 0/ Oi D t D* 0> o M 1 V P 1 PC PRETO M PC S M« 0/ o 2 \ Le g e n d PC S M. D, D*. D* 2 REESOR M PC S M« D/ Dz 0^ 1 t 3 ROSS S Me 0/ D 3 t» o M h 1 % •4 P PC Amphiboli te f a c i e s Gronitic rocks Greenschist f a c i e s Low g r o d e f a c i e s Unmetamorphosed rocks Prehnite PumpellyHe Metoyreywacky facies S Sediment oge M< Metamorphic ages D Mom phoses of deformation ^ Fold axis trend for each phase and associated axial ' surface steep(VJ| or shollow dipping ( h ) 5 that the Shuswap rocks have experienced regional dynamothermal meta-morphism. Evolution of opinion is related to increasing appreciation of the structural complexity of the Shuswap Complex. Previous detailed work in a number of areas of the Shuswap Ter-rane has now brought to light the complexity of structural and meta-morphic events that exist to hamper correlations with less metamor-phosed rock of known stratigraphic age. Rocks considered to be part of the Shuswap Complex have now been correlated in a number of areas with sedimentary sequences of known stratigraphic age, permitting age limits to be placed on some of the metamorphic and deformational events. Figure 1-2 pinpoints some of the areas from within the Shuswap Ter-rane that have been studied in detail. The area underlain by metamor-phic rocks of amphibolite facies grade shown in the reference map in Figure 1-2, generally corresponds to the Shuswap Terrane as outlined in Figure 1-1. An attempt is made in Figure 1-2 to precis the opinions of a few authors on the age and number of metamorphic and deformational events experienced by Shuswap Complex rocks, and on the sedimentary age of these rocks. The work of authors mentioned in Figure 1-2 and others, is b r i e f l y discussed in approximate chronologic order. Near Vernon, British Columbia, Jones (1959) mapped the Shuswap Com-plex as unconformably overlain by, or in fault contact, with the Permian Cache Creek Group. He considered the metamorphism of the Shuswap Complex to be pre-Mesozoic, possibly Precambrian in age, but not of the "static load" type suggested by Daly (1917). Hyndman (1968) stated that low grade Triassic rocks of the Slocan Group, cropping out near the eastern margin of the Shuswap Terrane, had experienced the same phases of de-formation as adjacent Shuswap rocks. He suggested, therefore that 6 the eastern margin of the Shuswap Terrane, had experienced the same phases of deformation as adjacent Shuswap rocks. He suggested, there-fore, that along i t s eastern margin the Shuswap Complex had experienced Triassic metamorphism and deformation. The Shuswap Complex extends east of the Columbia River near Revel-stoke. Here, Ross (1968) identified three phases of deformation in meta-morphosed sedimentary rocks included in the Shuswap Complex, but known to be of Late Proterozoic and Early Paleozoic age. Ross (1970) in a paper which included work to the south, suggested that two synmetamorphic phases of deformation predate the Triassic, and therefore, that some of the Shuswap metamorphism and deformation was pre-Mes.ozoic. An area of Shuswap rocks near Grand Forks, British Columbia, was mapped by Preto (1967), who correlated local Shuswap rocks with Late Precambrian to Early Paleozoic metasediments found to the east. Accord-ing to Preto, these Shuswap rocks had experienced low pressure, high temperature metamorphism, and deformation in post-Lower Jurassic times. Reesor (1970) mapped a north-south line of gneiss domes that crop out within, but near the eastern margin of the Shuswap Terrane. He considered the gneiss domes to be metasomatically derived from sediments as old as Late Precambrian, and to have been metamorphosed and deformed in post-Mississippian, possibly post-Triasic, times. The rocks which mantle the domes have experienced at least two phases of deformation, the f i r s t accompanied by sillimanite - almandine - orthoclase subfacies meta-morphism. A number of geologists have worked near the western margin of the Shuswap Terrane. Fyson (19 70) considered Shuswap rocks which crop out near Shuswap Lake, British Columbia, to be of Upper Paleozoic to Lower 7 Mesozoic age. Metamorphism and four phases of deformation have affected these rocks. Ross and Christie (1969) working ten miles north of the thesis area, and south of the area mapped by Fyson, outlined three i n -tense phases of recumbent deformation. Some generalizations can be made by the present author about the geology of the Shuswap Complex. Shuswap rocks are generally enclosed by the sillimanite isograd. The metamorphism responsible for this isograd was not Precambrian. Amphibolite grade metamorphism was definitely post-Triassic in many places but pre-Mesozoic in others. Thus, Shuswap Complex rocks experienced more than one metamorphic event and the exact ages and regional extent of these events are at present among the more controversial questions concerning the Shuswap Complex. Detailed mapping of various areas of the Shuswap Terrane indicate that a l l areas experienced at least one deformation which produced prominent re-cumbent folds. This deformation is not always synchronous throughout the Shuswap Terrane nor is i t the only deformation recognized in the various areas. With this •jj.n mind, i t is s t i l l useful to outline the trend of these prominent recumbent folds, as mapped in ..different parts of the Shuswap Terrane. In the northeast the hinge trend is southeasterly, in the south northerly, in the south-centre easterly and along the western margin of the Shuswap Terrane fold hinges trend southeasterly. The thesis area is located adjacent to the western margin of the Shuswap Terrane near Oliver where a number of detailed mapping projects have been completed, (Ross and Christie, 1969), (Okulitch, 1970), Christie, 1973) and Ross (1973). Because of this concentration of detailed infor-mation, i t may be possible to correlate lithologic units, geochronologic isotope data and structural histories over an"extended area. After such 9 correlations the relationship of the structural history of this part of the Shuswap Terrane to that of the adjacent low grade metamorphic rocks may become apparent, and the absolute age of the.." events comprising this history may also emerge. These correlations are made using the three parameters of lithology, isotopic data and structure. It i s anti-cipated that correlation of each parameter w i l l produce the same geo-logic picture. With this in mind the area located in Figure 1-3 was mapped in detail and samples collected for a geochronologic study. In the present study the Rb-Sr technique is emphasized because results based on K-Ar work in the southern Okanagan are too susceptible to the resetting of the radiometric clock by late tectonic events. A number of geologists have worked in the vici n i t y of the thesis area. The most recent regional geologic map incorporating the thesis area was compiled by L i t t l e (1961). L i t t l e refers to high grade meta-morphic rocks cropping out in the thesis area as the Monashee Group,(a name used by Jones (1959) for metamorphic rocks considered to be Precam-brian or younger). Previously, Bostock (1940) had referred to the high grade metasediments as the Vaseaux Formation, which he considered to be older than the less metamorphosed sediments of the Kobau Group of Car-boniferous (?) age. Similar low grade metamorphosed sediments in the thesis area L i t t l e (1961) mapped as the Anarchist Group. This latter name was introduced by Daly (1912) for sedimentary rocks encountered between Grand Forks and the Okanagan Valley. Waters and Krauskopf (1941), mapping south of the thesis area, divided the Anarchist Group into three parts. On the basis of poorly pre-served fossils they assigned the Anarchist Group a Carboniferous or probably Permain age. 10 Rinehart and Fox (1972) who mapped part of the area previously mapped by Waters and Krauskopf (1941) divided the Anarchist Group into two formations. One of these formatiors was found to contain a Permian, possibly Late Permian fauna. Southwest of the thesis area they mapped the Kobau Formation of post-Anarchist, possibly Late Permian age. This .'".formation they considered to be stratigraphically continuous with the Kobau Group defined by Bostock, (1940). L i t t l e (1961) mapped the oldest intrusive in the thesis area (unit V, plate A) as the Nelson Plutonics, and of Mesozoic age, and those i n -trusives slightly younger (units VI to VII) as the Valhalla Plutonics (after McConnell and Brood, 1904). Daly (1912) called one area of i n -trusive Unit V, the Osoyoos Granodiorite. This area of unit V was re-mapped by Krauskopf (1941), as part of a survey of intrusives cropping out in the Okanagan Valley. 1-2. General Geology of the thesis area. The thesis area is located along the eastern flank of the southern Okanagan Valley, about 270 miles east of Vancouver. It is crossed by the British Columbia Highway No. 3. The area mapped lie s between the Okanagan Valley to the west and longitude 119°15' on the east, and between latitude 49°10' and the 49th parallel. Oliver and Osoyoos are in the northwest and southwest corners of the map area respectively (Figure 1-3). Physiographically the map area is located in the southwestern corner of the Okanagan Highland, part-of the Interior Plateau division which re-presents an uplifted and dissected Late Tertiary erosion surface (Holland, 1964). Maximum re l i e f in the thesis area is 3700 f t . (1100 m) . Apart from steep c l i f f s east of the Okanagan Valley r e l i e f is generally moderate. Much of the mapped area is occupied by synkinematic quartz monzonite 11 intrusions. These intrusions partially enclose layered rocks which outline a broad dome. This dome was formed by the latest penetrative phase of deformation (phase 4). The layered rocks are amphibolites, quartzites and pelites and they comprise a structural succession com-posed of four units. The layered rocks exhibit evidence of three phases of deformation (phases 3, 2 and 1), a l l earlier than phase 4. Phase 3 is represented by east-west traces and by mesoscopic chevron folds approximately parallel in style and with nearly vertical axial surfaces. Most of the spectacular folds of mesoscopic and macroscopic scale which are seen in the layered rocks formed during phase 2. This phase formed i s o c l i n a l recumbent f l a t -tened parallel folds whose axes plung northerly or southeasterly. There is inconclusive evidence for the existence of an even earlier phase of deformation, (phase 1) now represented by is o c l i n a l recumbent flattened parallel folds, with variable northerly plunging fold axes. Three sepa-rate intrusive units were emplaced prior to, or during phase 2, and em-placement of two more intrusive units post-dated phase 2. Three metamorphic events have combined to produce the metamorphic rocks mapped. These events accompanied phases 1, 2 and 4. Combined meta-morphic grade reached middle amphibolite facies in the middle and northern parts of the area, but the grade decreased sharply to lower greenschist facies in the south. The most intense metamorphism which accompanied phase 2 was responsible for this sharp gradient. Rb-Sr isotopic data provides Tertiary ages for the metamorphism that accompanied phase 4, and Jurassic or older ages for the intrusive units whose emplacement preceded or accompanied phase 2. A fourth metamorphic event of Jurassic age is suggested by the Rb-Sr isotopic data. 12 1-4. Acknowledgements Dr. J . V. Ross suggested the p r o j e c t and provided a continuous source of ideas and enthusiasm. Close cooperation w i t h Dr. J . B l e n -kinsop during our j o i n t t h e s i s research was i n v a l u a b l e to the author, as was the a s s i s t a n c e and encouragement of Dr. W. F. Slawson. A N a t i o n a l Research Committee s c h o l a r s h i p i s g r a t e f u l l y acknowledged. 14 SECTION 2 STRATIGRAPHY 2-1. Structural succession Amphibolites and metasedimentary rocks in the thesis area were previously mapped by Bostock (1940) as was the VaseauxFor-mation, which L i t t l e (1961) included in the Monashee Group. No evidence for stratigraphic top was found in any of these layered rocks. This is not unexpected considering their deformational his-tory, and as a result no attempt is made to define a stratigraphic succession. The postulated structural succession is derived from two assumptions. The f i r s t is that limited evidence supports the existence of phase 1 deformation,and the second that rocks coring phase 1 antiforms are structurally the lowest. A structural syn-thesis (Section 6-1) illustrates how rocks coring phase 1 folds can be unfolded to obtain the postulated structural succession. Layered rocks are divided into four units, (units I toIV) com-prising a structural succession varying in present thicknes. from less than 100 f t (30 m) to approximately 1000 f t (300 m). Tectonic slides and recumbent folds produce numerous repetitions and are re-sponsible for an unknown amount of thinning of the structural suc-cession. The top and bottom of the succession are represented by con-tacts with intrusive units. An age of the succession is pre-Jurassic based on geochronology and f i e l d relations. Granitoid rocks have been divided into five units (units V to IX) representing five intrusive events which can be arranged in relative chronologic order. The youngest unit which comprises Tertiary basic volcanics brings the total number of units recognized to ten. Fig. 2-1 section 2 section I V t i l l sea I a U l o o / / > / / section 3 •* -» a g ar o o o rt o o ye -* 3 0 A 3 3 Iff o C M o 3 a o 3 cr w a o u C l on loc re w u otio ^ » 3 3" an Plo o to Ci O « -* o > o CD 3 T3 44 *1 P _ 3 3 U l a 3 1 -* CD CL c cr •< n ro U l O .A* section 5 : r - 7 i A? •f f section 6 f / / f f / f / I / f / f -\ \ f f o f Section 4 I -c m IN) I C o H C > r c o o rn 0) </> o z w m o H O Z w ST 16 illustrates the generalized distribution of most of these ten units but not of the volcanic unit. In a number of areas mylonitization has produced distinctive mappable phases of the recognized units. Three areas of mylonite (unit IV m) derived from unit IV and two areas of mylonite (unit A m) not derived from recognized intrusive units are delineated on plate A. The mylonites are described in Section 3-6 under the general heading of slides. The slides are probably related to, and developed at the same time as, the mylonites. An area of breccia (unit IX b) derived from a number of parent rock units, is delineated on plate A and Fig. 2- 1. The breccia is described in Section 3-8 in conjunction with the Tertiary deformation (phase 4) which was probably responsible for the brecciation. Figure 2-2 contains six structural succession sections which traverse different parts of the four phase 1 folds described in Section 3- 5. The sections are located in figure 2-1 and positioned with respect to the main structures, in a diagramatic way 4in figure 2-3. Figure 2-3 is a pi c t o r i a l three dimentionajl view of the main structures. The units are named in table 2-1. Emphasis in figures 2-2 and 2-3 is placed on the four layered units whose present thicknesses rarely exceed 500 f t . (90 m), and are often less than 50 f t . (15 m). Thicknesses in figure 2-2 are average thicknesses from the vicinity of the section lines. The structurally lowest amphibolite (unit I) is overlain by quart-zite (unit II) and pelite (unit III). A second amphibolite unitt (unit IV), thinner and less persistent but identical in a l l other respects to unit I, appears to structurally overly unit III. The structural F I G U R E 2- 3 Diagramatic illustration of early structures and location of structural succession sections a B ttruclurol tuciossion tection * . olso locoted in figure 2-1 TABLE 2-1 ROCK UKITS • i Unit X Volcanic breccia Unit IX Leucocratic Biotite Albite Quartz Monzonite Unit VIII Late Kinematic Quartz Monzonite Unit VII Muscovite Quartz Monzonite Unit VI Biotite Quartz Monzonite Unit V Early Granodiorite Unit IV Amphibolite Unit III Pelite Unit II" Quartzite Unit I Amphibolite 18 geometry suggests that unit IV is distinctive from unit I but the many uncertainties in the structural interpretation, mean that justification for this separation is minimal. In the south where outcrop is sparse,layered rocks have not been sub-divided, and on plate A they are described simply as undivided layered rock (unit A) . The ten rock units separated,are described in subsequent sections, Lithologic descriptions and a discussion of metamorphism (Section 4) were aided by examination of over 100 thin sections. A l l thin sections were stained to f a c i l i t a t e estimation of quartz, plagioclase and K feld-spar contents. Plagioclase composition in most thin sections was de-termined on a universal stage using the "a" normal method. Table 2-11 l i s t s visually estimated mineral modes for thin sections from some units. Thin section numbers are grid references which give the approximate position of the parent sample on figure 2-1 which has a lettered and numbered grid. 2-2. Unit I. Amphibolite Unit I forms a narrow northerly striking band extending from the 49°th parallel northwards to Inkaneep Creek (figure 2-1). The northern part of the band has been metamorphosed to amphibolite facies whereas south of Long Joe Creek metamorphic grade reached only greenschist facies. The character of unit I north of Long Joe Creek is described f i r s t . Here, unit I which weathers dark grey to black,is usually easy to recog-nize in the f i e l d because of i t s close association with the rusty weath-ering schist of unit III. The present thickness of unit I rarely exceeds 500 f t . (150 m). A medium to coarsely banded appearance, caused by dif -fering proportions of hornblende and plagioclase, is further accentuated by synkinematic alaskitic s i l l s . Near hinges of macroscopic folds TABLE 2 -JT M O P E ' S O K SOHK I IM1TS E S T I M A T E D ' F R O M T H I N S E C T I O N ? ; U N J T I A H I ' H ) B O L 1 T E S A J - T L E UTZ K PI ay An% AMP DIO 10 .15 33 70 M 15 8 37 75 M 5 40 36 50 10 30 77 50 10 10 40 38 40 25 10 52 40 . 10 60 35 5 10 30 7 • 60 M 30 7 60 ESTIMATED MODES SC ALU CliL EP DIO S I L STA O t h e r C .5 , 6 . 8 A . 4 , 1 3 . 7 B. 8 , 1 0 . 7 B .2 , 1 0 . 7 B. 2 , 10. 7 10 40 38 40 " M s A . 7 ,14 . - - - 3 C . 4 ,10 E .2 , 2 . 1 E . 6 , 1 . 5 M M ' M 65 10 UNIT I I I FF.LITE ESTIMATED MODES SAMPLE QTZ K P l a g An% AMP BIO .MUSC ALM CHL B.7 ,10 60 15 31 15 10 B.7 ,10 20 10 50 36 15 5 D. 3 , 4 . 6 40 20 42 30 5. D.4 ,6 60 15 46 15 5 D. 3 , 6 . 1 35 40 4 4 • 25 H 6 .6 , 6 . 5 60 U 30 45 7 H M D.8 , 6 . 1 70 H 15 15 E . 5 .6 30 40 60 M 25 5 D 7 .7 60 20 39 15 5 C .6 , 5 . 5 35 10 • 36 40 15 M C .6 , 5 . 5 75 M M 10 10 D ,5 20 50 31 . 5 5 D.2 , 4 . 7 20 30 36 35 10 M D.2 . 9 . 7 20 15 . 42 25 40 D.3 , 9 . 6 50 5 15 35 15 15 a E.2 , 8 . 7 10 . M 10 27 10 10 , E .2 , 3 . 4 35 35 15 M M E .3 , 3 . 4 25 25 40 M G.2 , 3 . 1 30 30 36 15 15 G.2 , 3 . 1 40 20 15 5 H E.4 ,3 45 20 25 5 M F . l , 2 . 6 ? 7 5 30 B.8 ,10 .1 35 M 45 38 15 M M D , 1 0 . 1 40 M 20 . 2 6 20 20 B .7 ,10 .7 45 25 40 20 5 M EP DIO S I L STA O t h e r 5 10 M 15 5 UNIT V EARLY GRANODIORITE ESTIMATED MODES SAMPLE "QTZ ~ ' K P i n g An% " " AMP '.' B I O MUSC ALM CHL EP C . 2 , 6 . 5 30 10 45 37 '2 10 1 2 E ,15 - 20 5 60 37 25 10 5 H ,13 .4 30 5 50 38 10 M 2 F . 8 ,14 30 10 40 37 1 5 5 F . 6 , 1 3 . 8 20 10 55 33 10 5 M H A ,13 30 10 40 38 2 7 1 C , 9 . 6 30 10 55 45 5 M M • M C 3 ,11 , 40 10 45 33 5 M E , 1 .1 30 3 50 30 5 M M DIO S I L STA O t h e r UNIT VI BIOTITE QUARTZ MONZONITE ESTIMATED MODES SAMPLE QTZ K P l a g An% AMP BIO MUSC ALM CHL EP C , 16 .2 35 10 35 33 5 5 H M E , 8 . 3 .•v30 15 40 36 2 10 D . l , 1 5 . 2 30 30 30 33 5 M M M F . S ,3 30 15 45 27 lOsericite DIO S I L STA O t h e r UIUT V I I I MUSCOVITE QUARTZ MONZONITE . 1 ESTIMATED MODES ' O t h e r SAMPLE QTZ K P l a g A n l • AMP BiO MUSC ALM CHL EP DIO S I L STA 11 , 1 9 . 3 35 1.2 , 9 . 3 50 30 20 . 35 20 25 25 5 M M M M M M=MJ.nor QTZ«qii. irt .s!. K • K fnld.'; i iar. P l n g . p l . T l i o c i a s " . AMHi ;nn|,h i L/,]e, IMOt hi r.f. i I".. MUPC,muncovi t o . . C I I L « c h l o r i t c . E P s c p l d o t c . D lOrd iop i i i t Jc . HI.l,r:i i i 1 i i U:. :;'J'Asr;'.. :iur'jl i AI,M«<|.iri)<!t.. 20 layering is discontinuous and appears as streaks which are hornblende or feldspar rich. Minor folds are apparent in the banding in some areas and are numerous near macroscopic fold hinges. Fine lamination or foliation parallels coarse banding and penetrative hornblende line-ations are developed in a l l outcrops. Occasional diospside rich streaks are the main variation from the common amphibolite. The texture, in thin sections of unit I from north of Long Joe Creek, is medium grained nematoblastic to granoblastic. Amphibole accounts for over 50% of the samples; plagioclase (anorthite content variable, but greater than 35%) and quartz are also present. Visually estimated min-eral percentages are given in table 2-1L. South of Long Joe Creek unit I attains a present thickness of 1500 ft (450 m). Here, the unit experienced greenschist facies metamorphism and has the appearance of a typical greenstone. Granitic synkinematic s i l l s are absent from outcrops of the unit which.has an aphanitic tex-ture. Extensive development of parallel folds has in some localities accentuated foliation giving the unit a p h y l l i t i c look. In one locality (figure 2-4) a structure believed to be non-deformational and possibly a volcanic block has apparently survived a l l the deformation. Outcrops of pure white quartzite, sometimes fine banded, are found in unit I. One such area of quartzite (unit I b) is delineated on plate A. " In the extreme south porphyroclasts of amphibole and oligoclase (figure 2-5) have survived deformation. They s i t in a nematoblastic fine grained groundmass of actinolite,(identified by X-ray diffraction) chlorite, quartz and feldspar. Chlorite also occurs as porphyroblasts. In upper chlorite facies, the nematoblastic texture is less prominent, 2 1 Figure 2-5 Porphyroclasts of oligoclase i n unit I, plane polarized l i g h t . V e r t i c a l f i e l d 5.2mm. 22 i porphyronlasts are absent and the average grain size tripled, being in the order of .5 mm in diameter. • 2-3. Unit II. Quartzite The limited extent of unit II, which rarely exceeds 50 ft (15 m) in present thickness, is indicated in plate A, but not in figure 2-1. In the north, unit II is a grey to white medium-banded quartzite containing minor amounts of biot i t e and hornblende. One outcrop of unit II is engulfed i n a breccia (unit IX b). This quart-zite i s light grey and fine-banded and i t contains minor micaceous material. In the south, unit II is a fine-banded black to dark grey quartzite with argillaceous partings. Unit II forms sharp contacts with Unit I . In thin sections', samples have a fine grained granoblastic to weakly foliated texture. Quartz generally composes more than 50% of samples and occurs as fine (less than .1 mm. diameter) strained grains. Inorder of decreasing abundance, actinolite, biotite, chlorite and feldspar account for the rest of the samples. 2-4. Unit III.. Pelite Despite i t s limited thickness, ( i t rarely exceeds 100 f t ( 30 m) in present thickness) unit III is the most distinctive rock unit in the thesis area and can be traced from east of Osoyoos Lake near the 49th par a l l e l to a point east of the northern end of the Lake (Fig. 2-1). As metamorphic grade increases to the north, unit III changes from ar— g i l l i t e , to slate, phyllite and f i n a l l y schist. Generally rusty weath-ering outcrops contrast strongly with the grey appearance of most of the granitoid units. Contacts of unit III with unit II are gradational. In the north, where metamorphosed to amphibolite facies, much of the volume of unit III is made up of synkinematic pegmatite and alaskite s i l l s . Here, unit III is a quartz - mica - almandine schist. Table 2-11 illustrates the mineralogy and approximate modes of samples studied in thin section. The texture is lepidoblastic, with occasional porphyroblasts of almandine. Staurolite, which occurs as porphyroblasts, and sillimanite, which occurs as fine needles, are useful metamorphic grade index minerals. Micas, usually biotite and to a lesser extent muscovite, outline several foliations, the best developed of which is usually parallel to com-positional layering and s i l l s . In the south, where metamorphosed to greenschist facies, unit III is an a r g i l l i t e or phyllite, depending on degree of recrystallization. The unit weathers grey or dark brown and often exhibits several gene-rations of well developed crenulation cleavages, which in places ob-scure the trend of compositional layering. No sedimentary structures were observed. In thin section the phyllite has a fine grained ( .1mm diameter). lepidoblastic texture. 2-5. Unit IV. Amphibolite In two l o c a l i t i e s north of Mica Creek, amphibolite structurally overlies unit III. If the structural interpretation in these two areas is correct, then this amphibolite represents a second amphibolite unit structurally higher than unit I, but identical in a l l other respects. Unit IV forms sharp contacts with unit III. 2-6. Unit V. Early Granodiorite Anarchist Mountain, east of Osoyoos Lake, is underlain by a f o l i -ated granodiorite, unit V. Massive grey outcrops of this unit are de-1. lineated by well developed northeasterly trending fractures. The unit 24 TABLE 2-I-JI CHEMICAL ANALYSIS OF UNIT V EARLY GRANODIORITE After Daly (1912) Element Element SiO 68.43 K 0 2.51 2 2 Al 0 15.8 Na 0 3.47 2 3 2 Fe 0 • 1.06 H 0 .58 2 3 2 FeO 1.55 CO N.D. 2 TiO .2 P 0 .07 2 2 5 MnO .1 BaO .09 CaO 4.08 SrO .02 MgO 1.46 25 can be traced to the north, but effects of metamorphism and defor-mation make separation of unit V from other granitoid units d i f f i -cult. Separation is possible in the northwest but becomes nearly impossible to the northeast because of sparse outcrop. An intrusive origin for unit V is suggested by i t s uniform composition, sharp con-87 86 tacts with layered units and low Sr/ Sr i n i t i a l ratio (Section 5-4). Deformation and metamorphism have destroyed any grain size variations near contacts with layered rocks. Unit V is a foliated medium-grained hypidiomorphic granular bio-t i t e hornblende granodiorite (table 2-VT) . Anorthite content of plagio-clase is about 37%. Epidote is the major accessory mineral. Myinmekite, is present in a number of thin sections, and quartz is strained and has serrated boundaries. A single chemical analysis (table 2—1LJ) of a sample from unit V was given by Daly (1912). A more complete petrographic de-scription of unit V is given by Krauskopf (1941) who refers to i t as the Osoyoos Granodiorite,after Daly (1912). The dominant foliation of the unit is outlined by quartz and feld-spar lenses and is parallel to contacts with layered rocks. A more subtle foliation,outlined by hornblende crystals^is also present. Near tectonic slides, the unit is extensively granulated. The intrusive re-lationships and tectonic fabric of unit V are discussed in Section 3-9. 2-7. Unit VI. Biotite Quartz Monzonite Much of the area mapped is underlain by unit VI, a medium grained hypidiomorphic granular, biotite or hornblende quartz monzonite. Locally the unit is a strongly foliated and lineated medium grained alaskite. The unit weathers grey or pink. Quartz usually has a measurable foliation 26 which is distinctly better developed near contacts with layered rocks, and in areas that experienced amphibolite facies metamorphism. Con-tacts with layered units are sharp, suggesting an intrusive origin \or the unit, although even in the south no chilled margin could be found. Mineralogy and approximate modes of samples from unit VI are listed in table 2-1-1. Feldspar proportions define the unit as a quartz monzonite. Anorthite content of plagioclase, which displays abundant albite twinning, is about 34%. Microcline is more common than ortho-clase, biotite is the main mafic mineral; epidote and pink garnet are the main accessory minerals. Myrmekite, and straining of quartz grains are common micro-textures. 2-8. Unit VII. Muscovite Quartz Monzonite Unit VII is a pink weathering leucocratic foliated quartz monzon-ite with a medium grained hypidiomorphic granular texture. It is char-acterized by small pink garnets and p o i k i l i t i c muscovite flakes, both of which make i t easy to distinguish from unit VI, whjLch is texturally similar. S i l l s of unit VII intrude unit VI indicating that unit VII is intrusive and post-dates unit VI. Unit VII is not in contact with layered units but i t s foliation appears to parallel contacts with unit VI. Feldspars of unit VII are oligoclase, orthoclase and microcline, and accessory minerals are biotite, epidote and chlorite. Microtextures are igneous, but evidence of post-crystallization deformation is ubiquitous. 2-9. Unit VIII. Late' Kinematic Quartz Monzonite Unit VIII is a medium to coarse grained hypidiomorphic granular, or occasionally porphyritic, biotite quartz monzonite which generally has a 27 poorly developed foliation. It crops out in two extensive areas (figure 2-1). Contacts with other units have not been observed but the uniform nature and porphyritic texture of the unit suggest an intrusive origin. Plagioclase in unit VIII (anorthite content on average 27%) is zoned. Zoned plagioclase crystals are rare in units V to VII. K feldspar in unit VIII is orthoclase. Biotite is the dominant mafic mineral. 2-10. Unit IX. Leucocratic Biotite Albite Quartz Monzonite A stock called Oliver Granite by Bostock (1940) and also mapped by Richards (1968) and Okulitch (1970), crops out northwest of Oliver and in the northern part of the map area where i t is referred to as unit IX. Unit IX is a porphyritic to hypidiomorphic granular biotite quartz monzonite. Pink, 1 to 3 cm. diameter, subhedral phenocrysts of K feldspar, generally microcline, l i e in a groundmass of quartz, albite and biotite whose grain size is 3 to 10 mm. Accessory minerals include muscovite, chlorite and epidote. Grains exhibit some strain but boundaries are not granulated. In the extreme southwest of the map area outcrops of a non-foliated porphyritic quartz monzonite have been included in unit IX, as have oc-casional large outcrops of non-foliated quartz-feldspar pegmatite not part of dyke or vein systems. These pegmatites crop out one mile north of Mica Creek (plate A). Contacts of unit IX,in the thesis area,have not been observed; in other areas they are intrusive and discordant. 28 2-11. Unit X. Volcanic Breccia Three small outcrops of basic volcanic material (unit X) rest unconformably on a l l other units. Unit X was mapped by L i t t l e (1961) as being of Eocene to Oligocene age. It forms brown weathered, partly disaggregated outcrops of volcanic breccia,or reworked basic volcanic debris. 2-12. Dykes and Veins. Postkinematic dykes and veins were mapped in the f i e l d but are not shown on plate A. Discordant vertical quartz^feldspar-muscovite pegmatite veins up to 50 ft (15 m) wide predate a set of vertical 1am-prophyre dykes. The lamprophyre dykes, commonly in the order of 10 ft (3 m) in width, contain phenocrysts of plagioclase, biotite andpccasionally olivine and pyroxene, and classify approximately as vogesites. Ages of these dykes are probably similar to that of a biotite, pyroxene lam-prophyre which is 53 myr. (White, et al., 1968). This 53 myr. old dyke cuts the Oliver Stock (unit IX). 2-13. Origin of rock units No whole rock chemical analyses of rock units were made, so that any inference about origin of units is based on textural or mineralogic data. A few comments can be made about the origin of units I and IV. If indeed, Unit I containsa volcanic block (figure 2-4), then this implies that units I and IV were at least in part extrusive. An andesitic com-position is compatible with the presence of amphibole and oligoclase phenocrysts, though oligoclase is a l i t t l e more sodic than most feldspar phenocrysts in andesite, however this feldspar composition may have been affected by metamorphism. Further comments concerning the origin of 87 86 unit I are made in conjunction with an analysis of Rb, K and Sr/ Sr 29 data for the unit (Section 4-4). Christie (1973) favoured a greywacke suite a f f i n i t y for the units that he recognized within the Vaseaux Fromation. Units I to IV also included in the Vaseaux Formation of Bostock (1940) do not contain ex-tensive outcrops of metachert, so that a greywacke suite a f f i n i t y i s possible. 2-14. Stratigraphic Equivalents High grade Shuswap rocks, in the southern Okanagan Valley, mapped by L i t t l e (1961) as Monashee Group (Precambrian or later) are shown to be structurally continuous with rocks adjacent to the southern limit of the thesis area, mapped by Waters and Krauskopf (1941) as the Upper An-archist Series. The northerly trending band of layered rock (units I to III), cropping out along the eastern margin of the Okanagan Valley ? joins the areas mapped by these two authors. Waters and Krauskopf- (1941) divided the Anarchist Series (Daly, 1912) into Upper, Middle and Lower Anarchist Series. They found Car-boniferous or Permian fos s i l s in the Middle Anarchist. More recently L i t t l e and Thorpe., (1965) have re-defined the Anarchist as a Group and divided i t into six Permian or younger units. In the Loomis Quadrangle, Washington, Rinehart and Fox(1972) mapped an unconformity between the Middle and Upper Anarchist Series (Waters and Krauskopf, 1941). They assigned rocks below this unconformity to the Anarchist Group and rocks above to the Kobau Formation which they fel t was continuous with the Kobau Group. Rinehart and Fox (1972) found a Permian, possibly Late Permian fauna, in the Anarchist Group. The Kobau Group which crops out southwest of Oliver and north of the 49th parallel has been mapped by Bostock (1940)and Okulitch (1970). 30 Bostock considered the Kobau Group to be of questionable Carboni-ferous age whereas Okulitch considered i t to be of pre-Permian pos-sibly pre-Pennsylvanian age. These age assignments are in contrast to the post-Late Permian age assigned to the Kobau Group by Rinehart and Fox (1972). Okulitch (1970) on the basis of comparisons of structural his-tories, suggested that the Kobau Group was deposited on the previously folded and metamorphosed Vaseaux Formation (part of the Monashee Group). The Vaseaux Formation which crops out a few miles northeast of Oliver has been mapped by Ross and Christie (1969) and Christie (1973) who de-fine two phases of iso c l i n a l recumbent deformation in these rocks. Okulitch mapped only one phase in Kobau Group rocks, a few miles to the southwest. The present author tentatively identifies two phases of i s o c l i n a l recumbent folding in the Oliver-Osoyoos area. Thus, rocks in the Oliver -Osoyoos area appear to have a structural history similar to Shuswap Com-plex rocks (Vaseaux Formation) to the north, and are structurally older than Kobau Group rocks mapped by Okulitch (1970). Okulitch (1970) based on his estimate of the age of the Kobau Group, assigned an age of pre-Permian possibly pre-Carboniferous to the Kobau-Vaseaux unconformity. Ross and Barnes (1973) working ten miles north-west of Oliver mapped a second unconformity which separates rocks con-taining the later of the two phases of i s o c l i n a l recumbent deformation from overlying, l i t t l e deformed, probable Late Paleozoic rocks. This second unconformity must be separate from and post-date the Kobau-Vas-eaux unconformity suggested by Okulitch, which therefore, has to be at least as old as Carboniferous. • 1 31 > FIGURE 2-6 Structural and stratigraphic correlations of thesis rocks with rocks i n adjacent areas Stratigraphic correlation Late Permian Permian t or younger ^ -o DH °8 Kobau Group Kobau Formation Anarchist Group Upper Anarchist Series Units I to IV CM . V C V X) O r>-C & . rH ON co rH to .M *H •«—* CO CO -3- X r H 2 ON o CO Fn Q> —* —" s: O O C I s - r>- CM 0) • •P ON ON • cu $-1 rH <U w <H u — CU rt cu <u si ON CO « •P o rH w w •rl +•> +» v o • H « w co \ i i - i • H (0 i a u 10 PQ .c j>4 x: O fH 1 o | o i a | e-t o o « Structural correlation mid-Carboniferous or older <u w rt C/] rt (0 rt s: P, Old Tom Shoemaker Formations Vaseaux Formation Vaseaux Formation Kobau "Group Units I to IV Based on structural correlations with the work of,Christie (1973), Ross and Barnes (1973) and Okulitch (1970), rocks in the Oliver -Osoyoos area are older than the Kobau Group which i s pre-Late Paleo-zoic in age; but based on stratigraphic correlations with the work of^Waters and Krauskopf (1941) and Rinehart and Fox (1972), rocks in the Oliver-Osoyoos area are equivalent to the Kobau Group which is post-Late Permian in age. Geochronologic isotope data does not help to resolve this conflict. It provides an age of greater than 170 myr. for units I to IV (Section 5) and an age.of greater than 194 myr. for Anarchist Group rocks (Rinehart and Fox, 19 72). The dilemma is i l l u s -trated in figure 2-6. In the absence of conclusive data the present author prefers to accept the structural rather than the stratigraphic correlation, though no convincing explanation for the conflict between the two can be given. It . i s pointed out that, though rocks in the southern end of the thesis area were mapped by Waters and Krauskopf (1941) as Upper Anarchist, this area of Upper Anarchist is isolated from other areas of Anarchist rock by the Colville Batholith (Waters and Krauskopf, 1941). The conclusions based on the structural correlation are summarized. There is evidence for two unconformities - one pre-Late Paleozoic, pos-sibly related to the Caribooan Orogeny (Ross and Barnes, 1973), and an earlier one (Okulitch,1970). The three earliest phases of deformation in the thesis area,which are equivalent to the f i r s t three phases recog-nized by Christie (1973) and Ross (1973). are at least as old as the Car-boniferous Caribooan Orogeny. The extent and age of the earlier uncon-formity is unknown. It could be intra-Caribooan and of only local extent. Units I t© IV are older than mid-Carboniferous. The structural succession 33 in the thesis area of amphibolite (unit I), quartzite (unit II), pelite (unit III) and amphibolite (unit IV) does not include suf-ficient rock types to make possible comparison with otherstruc-tural successions,on a unit to unit basis. 34 TABLE 3-1 STRUCTURAL ELEMENTS AND NOMENCLATURE EVEKT D5. F i f t h d e f o r m a t i o n ; n o n p e n e t r a t i v e . D4. F o u r t h d e f o r m a t i o n ; p e n e t r a t i v e . D3. T h i r d d e f o r m a t i o n ; p e n e t r a t i v e . DESCRIPTION F r a c t u r e s e t s : SYMBOL F5-l,F5-2,F5-4,F5-5, Large wavelength f o l d s w i t h s t a t i s t i c a l l y d e f i n e d f o l d axes: C r e n u l a t i o n c l e a v a g e : F o l d h i n g e s & c - r e n u l a t i o n l i n e a t i o n s : D4 ( F3 L3 D 2 ( s ) . N o n p e n e t r a t i v e d e f o r m a t i o n T e c t o n i c s l i d e s : r e l a t e d t o D2. Sa,Sb,Sc,Sd, D2. Second d e f o r m a t i o n ; p e n e t r a t i v e . A x i a l p l a n e c l e a v a g e : F.old. .hinges , ' m i n e r a l , ir.ic'a edge and s t r e a k l i n e a t i o n s : F2 L2 co D l . F i r s t d e f o r m a t i o n ; p e n e t r a t i v e . A x i a l p l a n e c l e a v a g e : F o l d h i n g e s , m i n e r a l , mica edge and s t r e a k l i n e a t i o n s : FL LI Do. D e p o s i t i o n . C o m p o s i t i o n a l l a y e r i n g : Fo 36 SECTION 3 STRUCTURE 3-1. Introduction Layered rock units I to IV and intrusive unit V have been re-peatedly folded and partly engulfed by synkinematic and post-synkine-matic intrusive units VI to IX. A l l that now remains of the s t r a t i -graphic succession is a stack of is o c l i n a l recumbent fold hinges, out-lined by remnants of layered units, and separated by tectonic slides. Later folding has formed a domal structure cored by units VI to IX and flanked by the iso c l i n a l l y folded.- layered units (figure 2-1) . The profusion of structures can best be described in an organized way i f they are related to a number of fold sets; each set in turn representing evidence for a unique phase of deformation. The basic premise would appear to be that the earliest recognized deformation (phase 1) occurred at the same time in a l l places and preceded phase 2. Obviously no such rigid constraint can be envisaged. A single phase may not be synchronous throughout an area and therefore could be affect-ing rocks in one area while an earlier phase was s t i l l affecting rocks in an adjacent area a few miles distant. Constraints can be placed on the degree to which phases overlap in time,within areas occupied by single refolded macroscopic structures. Phases in the thesis area are considered to represent,within reason, temporally distinct events. Five distinct phases are recognized (table 3-1). Isoclinal recumbent fold hinges appear to belong to two phases (phase 1 and 2) with axes of both phases trending nearly parallel to the Okanagan Valley, that i s , north to northwest. Phase 3, which is sponsible for nearly vertical east-west axial surfaces, succeeded rest 37 phase 2, probably with l i t t l e delay. Phase 4 is responsible for the domal structure previously mentioned and for north to northwest trending near vertical axial surfaces. Phase 5 produced fracturing. Both phase 4 and 5 occurred in the Tertiary, long after the end of phase 3. 3-2. Mesoscopic structural data Structural analysis of structurally complex areas starts with an understanding of the fold geometry and structural sequence on the meso-scopic scale. With this in mind, careful attention was paid to meso-scopic structural elements during mapping. Such data is much more .^plentiful in layered units than intrusive units. Compositional layering (Fo) measured in units II and III is probably sedimentary in origin and is now nearly completely trans-posed into parallelism with the earliest recognized axial surface fo-lia t i o n (FI) described in Section 3-4). Layering (Fo) in unit I, which is parallel with FI in units II and III, has been accentuated by meta-morphic segregation but owes i t s origin to events prior to, or contem-poraneous with, phase 1. In units I to IV the well developed foliation (FI) parallel to Fo represents the earliest tectonic feature measured. The term foliation is used to describe penetrative surfaces outline by foliate minerals (Whitten, 1966). Later foliations, more subtle than FI, and generally intersecting Fo at acute angles can sometimes be measured in unit III and occasionally in units I, II and IV. It can often be demonstrated that axial surfaces of mesoscopic phase 2 folds are parallel to these later foliations which are therefore, called F2. Crenulation and strain-slip cleavages are considered by the present 38 author to be recognizably different and not in the s t r i c t sense foliations as described by Whitten (1966). Strain-slip cleavage, implying s l i p along micro-axial planes which form crenulation clea-vages, is not as extensively developed in the thesis area as crenu-lation cleavages. Most crenulation cleavage formed during phase 3 and is rreferfed a€oFas F3. Minor folds of many generations are present in layered units. Rarely could sequential interference patterns be identified,so that assignment of a particular minor fold to a related phase depended largely on i t s style and orientation. Four descriptive types of lineations are recognized in the f i e l d : (a) mineral lineations, generally produced by alignment of quartz or horn-blende; (b) mica edge, or intersection lineations, formed by t i l t i n g or breaking of mica flakes or by intersections of two micaceous f o l i -ations; (c) crenulation lineations, which are micro-hinges formed by crenulation cleavages; and (d) streak or smear lineations not obviously mineral alignments and generally found in mylonites. Most of the intrusive units mapped are foliated, with occasionally more than one foliation being recognized. Mineral lineations are also present. The relationships of these structural elements to those measured in the layered rocks are discussed in Section 3-9. Fractures present in both layered and intrusive units represent the most recent structural elements systematically measured. Table 3-1 gives a brief description of structural elements and nomenclature used to refer to these elements. Mesoscopic structural elements are plotted on plates A, B and C. Orientation of structural elements is represented on lower hemisphere equal area projections. 39 The lowest contour on contoured diagrams (Jigure 3-3 to figure 3-33) is defined using the Mellis Circle method, higher value con-tours are defined using the Schmidt method (Turner and Weiss, '1963). Contour values expressed as percentages on diagrams refer to concen-trations of data per 1% of projection. Statisically defined fold axes, that i s , poles to great circle distributions of foliation data, are labelled on diagrams (figure 3-2 to figure 3-33) as Dl, D2 etc., according to the associated phase. On most diagrams lineations are differentiated on the basis of descriptive type. On some diagrams lineations are differentiated on the basis of generation as LI or L2 implying relationship to phase 1 or phase 2. 3-3. Structural analysis format Axial traces related to each phase, and structural domains used as an aid in describing the structural geometry, are both illustrated in figure 3-1. Structural domains are sub-areas of the map, selected such that a particular structural element has a consistency of orien-tation within them. This consistency provides information about a single structural event which would not be apparent i f orientation of structural elements was considered en masse. The dimensions of folds illustrated in figure 3-1, are not great, and there is a limited volume of layered rock to define these folds. For these reasons, despite de-tailed mapping, considerable ambiguity remains, in the structural i n -terpretation presented. It is believed to be the most lik e l y , but could be one of many consistent with the data collected. The discussion of the deformational history is organized as follows. First, in section 3-4, the second or most obvious phase is discussed and evidence for each phase 2 macroscopic fold, summarized. The same 4Q.: FIGURE 3-2 Mesoscopic s t r u c t u r a l data from domains 9 and 10 f f o r f o l d 2a V ill • • • B . Domain lO-i'op limb 51 poles to Fo so l i d line 4% contour plus Domain 9ondlO 31 polos to f g 6 % conlour _L i_n ea t_[ °_n s  o Horn blend e Quartz • Mica e d g e and isoclinol minor fold axes LOWER H E M I S P H E R E E Q U A L A R E A P R O J E C T I O N S 41 F i g u r e 3-3 M a c r o s c o p i c h i n g e r e l a t e d t o t r a c e 2a 42 procedure is followed for phase 1 in section 3-5. Tectonic slides contemporaneous with phase 2 are discussed in section 3-6. Evi-dence for phases 3 and 4 is considered i n sections 3-7 and 3-8, respectively. Intrusive units do not exhibit the same profusion of mesoscopic structures as do layered rocks. The position of intrusive units in the structural succession, as determined with data available, is dis-cussed in section 3-9. It is apparent from figure 3-1 that some macroscopic fold traces do not extend into the southern part of the map area,where metamorphic grade is greenschist facies in contrast to the amphibolite facies in the north. Correlation of mesoscopic structures from high to low grade metamorphic areas,and a general discussion of the deformational history in low grade metamorphic areas, is contained in section 3-10. Phase 5 which includes a l l non-penetrative late fracturing identi-fied in the map area is discussed in section 3-11. This is followed by a short summary of the deformational history in section 3-12. 3-4. Phase 2 deformation Phase 2 appears to be responsible for four macroscopic folds, (represented by traces 2a, 2b, 2c, and 2d; figure 3-1) of which fold 2a is the best substantiated. Domains 10 and 9 (figure 3-1) occupy the top and bottom limbs of fold 2a, respectively. The geometry of fold 2a in domains 10 and 9 is illustrated in figure 3-2 in which poles to Fo are contoured with a solid line and quartz,hornblende and mica edge lineations are plotted as points. Isoclinal minor fold axes are plotted with the same symbol as mica edge lineations, and poles to F2 are con-toured with a dashed line (figure 3-2B). Fold 2a is is o c l i n a l as 4.3 FIGURE 3-> Mesoscopic structural data from domain 8 £02" Fold 2 o Hingo Grea Domain 8 — poles to Fo Lineat io ns <• hornblende qoai tz • + isoclinal fold axes / great circle to ' poles to Fo D2 pole to great circle = LOWER H E M I S P H E R E E Q U A L A R E A P R O J E C T I O N S indicated by average orientations of the top, (figure 3-2B) and bottom (figure 3-2A) limbs which are the same. The distrubution of poles to Fo from both limbs does not define a fold axis for fold 2a, but horn-blende lineations consistently plunge more northerly than quartz and mica edge lineations. The two bands of unit I cropping out in domains 10 and 9, project across Inkaneep Valley into a single mass of unit I cropping out in do-mains 7 and 8. Layering here is contorted and.streaky i n appearance, and minor folds are abundant. In one locality (figure 3-3) the macro-scopic i s o c l i n a l recumbent hinge of.fold 2a crops out. Compositional layering measurements (Fo) across the hinge of fold 2a define a fold, axis(D2 /figure 3-4A) oriented 315°/00°. From figure 3-4A and figure 3-2, i t is apparent that the fold 2a is approximately cylindrical and coaxial with mica edge and quartz lineations and is o c l i n a l minor fold hinges, measured in domains 7 to 10. Summarizing data from domains 7 to 10, i t can be said that fold 2a is i s o c l i n a l , recumbent, closes to the southwest and plunges shallowly northwest. Fold profiles of mesoscopic folds associated with fold 2a were not systematically measured, but f i e l d observations suggest that in the various lithologies they generally have class IC style (Ramsay, 1967). This notation of fold style is used in succeeding sections. Fold 2a is prominent in sections ,D, E and F of plate D. The next problem i s to justify calling fold 2a a phase 2 structure. In domains 9 and 10 (figure 3-2) hornblende lineations measured in units I and IV are generally not parallel to quartz or mica edge lineations measured in adjacent outcrops of unit II or III. Quartz lineations are found on surfaces of concordant pegmatite veins intruded during high grade 45 F I G U R E 3-5, Mesoscopic structural data from domains 7 and 8 N 0^2 0 Domain 7 6 6 poles to Fo 3 % contour l ineat ions • = L t ' -D2 = 3I5700" metamorphism, at which time micas would be c r y s t a l l i z i n g or r e c r y -s t a l l i z i n g . The quartz and mica, edge l i n e a t i o n s may have been frozen i n the rock,-by e i t h e r of two events. (a) The l i n e a t i o n s may be expressions of deformation that occurred during a metamorphic climax. In t h i s case, hornblende l i n e a t i o n s could be o r i e n t e d along d i f f e r e n t d i r e c t i o n s character-i s t i c of an e a r l i e r deformation (phase 1). The map outcrop p a t t e r n of u n i t s I , I I and I I I can be explained i f an e a r l y phase (phase I) i s assumed, as can rare examples of i s o c l i n a l l y r e f o l d e d f o l d s . (b) An a l t e r n a t i v e e x p l a n a t i o n i s that quartz and mica edge l i n e a t i o n s were frozen i n the rock a f t e r phase 2, and during l a t e r de-formation that closed up phase 2 f o l d s . Hornblende l i n e a t i o n s were mechanically r e o r i e n t e d during t h i s l a t e r event. Phase 3 could represent such an event but i s not intense i n the t h e s i s area,and t h e r e f o r e , though i t might accentuate phase 2 l i n e a t i o n s , i t i s un-l i k e l y to mechanically r e o r i e n t hornblende l i n e a t i o n s by movement w i t h i n Fo. Explanation (a) i s preferred<and i s discussed i n d e t a i l . The hornblende l i n e a t i o n s formed during low-grade metamorphism along d i r e c t i o n s c h a r a c t e r i s t i c of phase 1. This o r i e n t a t i o n was r e -tained during subsequent higher grade metamorphism which accompanied phase 2. Folds,whose axes are p a r a l l e l to mica edge or quartz l i n e -a t i o n s , t h e r e f o r e appear to be r e l a t e d to the second of two phases of recumbent i s o c l i n a l deformation. Hornblende l i n e a t i o n s should i l l u s -t r a t e e f f e c t s o f . r e f o l d i n g by phase 2. The s t y l e of macroscopic phase 2 f o l d s i s not known but the near p a r a l l e l i s m of hornblende L I l i n e -ations and L2 l i n e a t i o n s i s compatible w i t h extensive e l o n g a t i o n p a r a l l e l to phase 2 hinges. 1 .47 F I G U R E 3 - 6 Plot of 100 Hornblende C-axes from domain 8 Contours ?.% 4% 8% 16% Plane of 1 hin section horiz.ontal /'= PI one of Fo I m = Field measured LI hornblende lineotion 2 m = w *. 1-2 * * 2o ^Average orientation of hinge 2o 315/00 LOWER HEMISPHERE EQUAL AREA P R O J E C T I O N 48 Within domains 7 and 8 (figure 3-4 and 3-5) separation of hornblende lineations from quartz and mica edge lineations is again apparent. In some localities in these domains, two hornblende lineations are identi-fied. One, a coarse hornblende crystal lineation is parallel to mica edge and quartz lineations, whereas a second fine hornblende crystal lineation is not parallel to these lineations. Thus, the assumption is made in figures 3-4B and.3-5A, that hornblende lineations, unless two are present, are LI lineations and..that quartz and mica edge lineations and i s o c l i n a l minor folds are>L2 linears. These L2 linears are coaxial with fold 2a. An oriented thin section was cut from a sample of unit I collected in the region of the hinge of fold 2a (figure 3-3 and domain 7). Orien-tations of 100 hornblende C-axes were measured (figure 3-6). Hornblende crystals aligned but the distribution does not correlate verywell with the LI and L2 hornblende lineations measured near the f i e l d location of the thin section. This may be because of inaccuracies in the measue-ment of the C-axes^ or in the reorientation of the sample. It must be mentioned that domains 7 and8 are situated on either side of a phase 4 axial surface trace (trace 4a, figure 3-1). Fold 4a has re-folded (Fo/Fl) and F2 about an axis (D4, figure 3-5B) which is almost paral-l e l with the pre-existing _ - fold 2as axis (D2, figures 3-4A and 3-5B). Thus, phase 4 folding in domains 7 and 8 has had minimal effect on the o r i -entation of LI and L2 linears. Fold 2b (figure 3-1), a second antiform structurally below fold 2a, closers to the southwest (section F and G, plate D) . In the northern part of domain 12, unit I crops out in the hinge of fold 2b. Measurements from this region,plotted in figure 3-7B,indicate that the fold is cylindrical 49 F I G U R E 3 -7 Mesoscopic structural data from domain 12 Domain (2 145 poles to Fo l»3 % e-ontour D4= 1 3 0 / 9 ° B Fold 2 b Hinge area, domain 12 II po les to Fo 10% contour D2 = 3 0 7 ° / l 0 O L ineo ti o n s _ +tiso c lino I fold axes .^quartz,mica edge oshorn blende LOWER H E M I S P H E R E E Q U A L A R E A P R O J E C T I O N S 50 FIGURE 3-8 Mesoscopic structural data from domain 12 Domain 12 23 p o l e s fo units Ijtolll A % contour 0 4 fold axis shown defined by po les to Fj. B Domoin 12 Fold 2 b . - L i top limb o ' L i bo t tom limb 02. fo ld axis trend e © LOWER H E M I S P H E R E . E Q U A L A R E A P R O J E C T I O N S 51 and that the hinge is coaxial with phase 2 mesoscopic linears. Hornblende lineations from unit I }plotted in figure 3-7Ajdo not scatter much from the 2b fold axis,defined by poles to Fo and phase 2 mica edge and quartz lineations. It appears that in the vicinity of this phase 2 hinge hornblende has crystallized o: recrystallized or been mechanically reoriented, along L2 directions. Domain 12 is traversed by two phase 4 traces, one phase 3 trace, one.phase 2 trace and two phase 1 traces, and the structure is there-fore, complex. The two phase 4 traces (4a and 4b) disperse (Fo/Fl) and F2 about an axis D4 (figures 3-7A and 3-8A). The phase 3 trace (3b), which trends east-west, is responsible for the dispersion of lineations seen in figure 3-7A. Despite the multiplicity of traces in domain 12, i t remains apparent that fold 2b changes from is o c l i n a l recumbent in domain 12, to open upright south of domain 12 (sections G, H and I, plate D). Lack of outcrop of layered rocks north of Inkaneep Creek makes i t d i f f i c u l t to outline macroscopic folds. However, the outcrop pattern in domain 5 suggests the existence of one phase 2 fold. This fold (trace 2c on figure 3-1) is a nearly i s o c l i n a l recumbent synform. closing to the northwest. The parts of the limbs of fold 2c, outline by layered rock, are nearly parallel so that plots of (Fo/Fl) do not define a macroscopic hinge for the fold 2c. Abundant L2. quartz and mica edge lineations in the vi c i n i t y of fold 2c, and the presence on the top limb of a mylonitic band (unit VI m) also exhibiting L2 lineations, both im-ply that fold 2c is in fact a phase 2 fold. The axis of ..the fold plunges shallowly northwest and the axial surface dips towards northeast. 52 FIGURE. 3- 9 Mesoscopic structural data from domains 5 and 6 . N 1 Domoin 6 12 0 po les to composition loyering Fo in unit I to III and foliation F t in units V to VIII 1*5 % contour B Domain 5 130 p o l e s to F0 units I to III ond F^ units V to VIII combined dota 1-5 % contour _Lm ea_tj o_n_s_ o "hornblende . =quartz and in ica edge LOWER H E M I S P H E R E E Q U A L A R E A P R O J E C T I O N S 53 Data collected from domain 5, which is traversed by trace 2c, is illustrated in figure 3-9B,in which i t is apparent that hornblende lineations are again displaced from quartz and mica edge lineations. Planar data plotted includes (Fo/Fl) measured in units I and III and the dominant foliation from intrusive units V, VI and VII. The f o l i -ation in the intrusive units is considered to be an F2 foliation, (section 3-9). A band of unit II, containing is o c l i n a l mesoscopic folds, crops out in domain 1. This band occupies the same structural level as a sediment band to the northeast (domain 22) which is under, and overlain by,unit V. It is suggested that the sediment band defines the core of a phase 2 isoclinal antiform (fold 2d, sections A, B and D, plate D). L2 lineations plunge to the northwest in domain 6 (figure 3-9A) where unit VI overlies unit V. This implies that the hinge of fold 2d, in unit V, is antiformal and has plunged below outcrop level. If fold 2d is real then i t is structurally the highest phase 2 fold identified. Four phase 2 folds have been described. Folds 2a and 2b are sub-stantiated by mapping, whereas fold 2c is only partially substantiated by mapping. Fold 2d is speculative but can be coordinated easily into a general structural section, the appearance of which is defined by folds whose existence is less speculative. Phase 2 folds are recumbent, iso-c l i n a l and generally plunge northwest with axial surfaces dipping north-east. A l l of these folds are separated from each other by slides der scribed in section 3-6. No macroscopic phase 2 trace can be projected, with confidence,south of Long Joe Creek into the lower grade metamorphic rocks. Evidence for phase 2, south of Long Joe Creek^is presented in section 3-10. 54 55 56 FIGURE 3-12 Mesoscopic structural data from domains 15 & 1 Domain 15 4 5 p o l e s to F, 4 % c o n t o u r L ineat ions + isoclinal fold axes . = U D4= 145/20 0 1 = 1457 20° B Domain II (Klippe) 4 3 po les to Fo 4 % contour L ineat ions P = h 0 r n b I e n d e + isoclinal fold axes — poles to Fjt. D» -' 136740° is pole to small circle through Fo data 57 3-5. Phase 1 deformation In Shuswap rocks north of the thesis area, Ross and Christie (1969) and Christie. (1973) have found evidence for a phase of deformation pre-ceding the prominent and correlable phase.referred to as phase 2 in the thesis area. On the mesoscopic scale the presence of phase 1 in the thesis area is suggested by the consistent divergence of hornblende l i -neations from quartz and mica edge,L2 lineations. Also, i s o c l i n a l l y re-folded folds interpreted as phase 1 folds, refolded by phase 2 folds have been observed in a few locations (figure 3-10). Despite the paucity of macroscopic evidence for phase 1, four folds (la, lb, l c and Id, figure 3-11) are assigned to this phase. These folds,which are not completely substantiated by mappingjare more easily interpreted as phase 1 folds than phase 2 folds. Evidence for fold l a i s discussed f i r s t . In domain 15 (figure 3-11 and plate A) units II and III appear to wrap around unit I to form an i s o c l i n a l antiform (trace l a ) , the axis of which is poorly defined on figure 3-12A, as Dl. Unit III in domain 15, exhibits i s o c l i n a l minor folds and two mica edge lineations classified in the f i e l d as LI and L2. Hinges of i s o c l i n a l folds are parallel to LI and clustered around the Dl axis whereas L2 lineations are scattered (figure 3-12A). Fold l a is probably a phase 1 structure. L2 lineations are formed by the inter-section of F2 with the previously folded surface Fo. L2 lineations are therefore scattered within the F2 surface. It is unlikely that F2 has been confused with F3 in domain 15. This is because F3 is a steep dip-ping crenulation cleavage, whereas F2 is a micaceous foliation in this domain. The geometry in domain 15 is complicated by a phase 4 fold (trace 58 FIGURE 3-13 Mesoscopic structural data from domain 13 N 5? AiDomain Lineations i n units VI & VII: • sLineations in. myloniiic band A.-BtDomains 7 & 8; 19 poles to lamination i n mylonites,. contour and associated lineations - : i C:Lineation measurements;domain 9> +»belov- lb axial trace.-• «above slide Sa: ••above lb axial trace and belov.. slide Sa« 60 4b, figure 3-1 and 3-12A) but as axes of folds 4b and l a are locally parallel, plunging shallowly southeast, the LI lineations are not dis-persed much by fold 4b. Antiform la can be traced northward into domain 13 where unit I is locally cylindrically folded on the macroscopic scale. Measurements of Fo made across the hinge region define an axis plunging northwest for fold l a (Dl, figure 3-13A). Hornblende lineations are parallel to this axis and throughout domain 13, L2 mica edge and quartz mineral lineations trend more easterly than these LI hornblende lineations (figure 3-13B). Fold l a is an i s o c l i n a l recumbent antiform (section C, plate D) whose hinge plunges northwest in the north and southeast in the south. The axial surface dips northeast. Antiform l a must be separated from fold 2a by a slide (designated as Sd in figure 3-14) as i t does not ap-pear to form part of the upper limb of fold 2a. Two bands of unit III cropping out just below slide Sa (figure 3-14) appear to converge northwards (plate A) to form the hinge of fold lb. This hinge is not completely substantiated by mapping. After considering the limited f i e l d data i t is the opinion of the author that the outcrop pattern represents a phase 1 fold (fold lb, figure 3-11). The macro-scopic hinge orientation for fold lb cannot be calculated, but i t s ex-tremely oppressed nature is consistent with a phase 1 origin. Fold lb must be separated from the lower limb of fold 2a by a slide (Sa, figure 3-14) to account for the extension northwards of this lower limb. There is some evidence for such a slide. LI hornblende lineations in domain 9 (figure 3-14C) measured above the postulated slide position, are differently oriented from measurements taken below the slide. F i g u r e 3-15 D e c o l l e m e n t f o l d i n g i n d o m a i n 11 62 Similarly, measurements from above and below trace lb are separated, possibly due to post-phase 1 preferential flatfenning of one limb of fold lb. The upper limb of fold lb, defined by units I to III, ex-tends southwards across Mica Creek separating units V and VI. Unit III outlines a closure in domain 12,(figure 3-11 and plate A) interpreted as part of fold lc.;,. which closed to the northeast. Closure about L2 directions necessitates an antiform closing to the southwest which implies that the underlying phase 2 fold Qb) would have to be a synform closing to the northeast, which i t is not. Trace lc is therefore considered to represent a phase 1 synform that reappears below trace 2b, as trace Id. LI hornblende lineations associated with fold lc have been reoriented by fold 2b such that they now have'different orien-tations on the top and bottom limbs of fold 2b (figure 3-8B). The flip bf LI lineations across trace 2b is in accord with the suggestion that phase 2 folds are class l c . LI lineations on opposite limbs of fold 2a do not flip and this can be explained i f fold 2a is class 2 in style, and has undergone extensive flattening with X axis of the strain ellipsoid parallel hinge 2a. 3-6. Slides and mylonites The fragmentation of some of the macroscopic fold sets has already been mentioned and in this tectonic environment fold thrusts can be sus-pected a s a causei A better name for such faults is slides, a term described and defined by Fleuty (196+). Analysis suggests the presence of a numberof slides (Sa to 8d; figure 3-14) of which Sa leaves the most obvious mark. 63 64 This slide separates phase 2 antiform 2a from the underlying phase 2 antiform 2b, and is responsible for removing the intervening phase 2 synform. Evidence for slide Sa can be found in domain 11, figure 3-14, in which decollement folding in unit I (figure 3-15) cannot be traced below a mylonitic zone which therefore occupies the surface of slide Sa. In domain 11 the Klippe of unit I which rests on the slide surface is interpreted as being part of the hinge of fold 2a. Surfaces Fo/Fl and F2 in unit I (domain 11) are both re-folded about the phase 2 axis to define a new fold axis(Ds, figure 3-12B). This decollement folding cannot be confused with phase 4 fold-ing which has sub-parallel trends, for two reason. F i r s t , decolle-ment folding is too tight to represent phase 4 folding, and secondly, the folds do not project below the slide which pre-dates phase 4. Structural analysis suggests that slide Sa follows the bottom limb of fold 2 a (figure 3-16; , section A, B and figure 3-14V The area in domains 8 and 9 (figure 3-14) through which the slide is postulated to traverse is occupied b,y a protomylonite formed from an alaskitic phase of unit VI. Discrete bands of mylonite less than 5 f t , (2m) wide were located within the protomylonite, but could not be mapped as outcrop of 65 a single unit. Lamination in mylonite bands is essentially parallel to foliation in adjacent, less mylonitized rock (compare figures 3-2 and 3-4 with figure 3-14B). It is inferred from the position of slide Sa along the lower limb of fold 2a that the slides are related to phase 2. Generally in the mylonite bands, lineations are parallel to isoc l i n a l minor fold hinges (figures 3-14A and B). Although displaced somewhat to the west, both these features are nearly parallel to> phase 2 lineations in adjacent units. The rotation of lineations in the mylonites towards parallel-ism with phase 3 trends, implies that slide development occurred in the interval between phase 2 and phase 3. In domain 9 lineations from above and below slide Sa have slightly different orientations suggesting some rotation across the slide surface. An area of mylonite north of Inkaneep Creek (area A on the map in figure 3-14) is considered to have formed from unit VI during develop-ment of a second slide, Sb, which follows the bottom limb of fold 2c. Lineations in the mylonite band trend more westerly than lineations in adjacent un-mylonitized outcrops of units VI and VII (figure 3-14A). The evidence for the third slide (Sc) is sparse. The lower contact of the mass of unit VII which straddles Inkaneep Creek is mylonitized and a slide is postulated to follow this lower contact. The structural interpretation given for the geometry of phase 1 and phase 2 folds requires that a slide (Sd) separate folds l a and 2a. This slide is illustrated in figure 3-16 despite the fact that no direct evi-dence for i t s existence could be found in the f i e l d . It is reasonable to infer that, as slide development is related in 66 time to phase 2, so also are slide movement directions related to phase 2 movement directions. The present position of phase 2 folds suggests that rocks were thrust in a southwesterly or southerly d i -rection during slide development. Mylonites developed within the slides are of two distinct paren-tages. Three extensive areas of mylonite developed from unit VI were mapped and are designated as unit VI m, on plate A. Other thinner bands of mylonite, not obviously of igneous parentage, were recognized in the f i e l d but only mapped in the south (unit Am, plate A). The three areas of mylonite of igneous parentage are indicated in figure 2-1 and plate A. They are black to grey and generally aphanitic, with 30 to 50% porphyroclasts of feldspar and quartz ( 1 to 5 mm in dia-meter). The southernmost of the three areas , J ( domains 8 and 9)is of protomylonite apparently derived from an alaskitic phase of unit VI. This protomylonite is a pink quartz-feldspar augen granulite. Contacts of these mylonitic rocks with their parent units have not been observed. In thin section elLiptical porphyroclasts are surrounded by fine grained poj^gonized quartz or ribbon-quartz. Most of the mylonite bands of non-igneous parentage are aphanitic cherty in appearance, and grey-brown or black.u . * Lamination"is well developed and often mesoscopically deformed into folds ranging from open to i s o c l i n a l in style. The bands mapped in the south are grey, p h y l l i t i c and contain subhedral porphyroclasts of hornblende and zoned feldspar, (more calcic than albite). These bands (denoted as unit Am on plate A) are now apparently conformable with the phyllite or quartzite country rock, though they are not of the same composition. The r e l i c t large crystals suggest that tuffs, dykes, or s i l l s , may actually have been 1 67 FIGURE 3 - / 7 RIBBON QUARTZ C - A X E S FROM MYLONITE (unit Vim domop 6> Equal area lower hemisphere plot of 118 C-axes l«7and 4«7% contours L Z Phose 2 lineolion \ Foliotion ( F z ) 68 phase 3 traces"^* ft synformol } L anfiformol A:Inkaneep Cr. to Mica Cr. 33 poles to F3 6% contour. BiMica Cr. to Long Joe Cr. 28 poles to F; 7% contour. C. South of Long Joe Cr, 83,poles to F3; 2% contour. D;Phase 3 fold axes from domains 1, 2 & Dal6» 0* DoA* 8//10" DQ2» 90/10° 69 their parent rock. Quartz grains in most of the mylonites are optically aligned and the relationship between the orientation of this crystalographic alignment and mesoscopic linears was investigated. An oriented thin section from unit VI m (area A on map i n figure 3-14) was studied and 200 ribbon-quartz C-axes were measHred (figure 3-17). Ross (1973) discussed the significance of polygonized quartz and ribbon-quartz. The quartz C-axes measured, near the foliation F2, and approximately on a small c i r c l e girdle about the mesoscopic lineation. This pattern i s not unlike that obtained by Ross (1973) for ribbon-quartz. If the s l i p systems along which the quartz deforms are sub-parallel to (0001), as suggested by Heard and Carter., (1968), Carter (1971) and T u l l i s et al.? (1973), then these s l i p surfaces must be oriented at large angles to the fo l i a t i o n . Experimental deformation of quartz (Tullis et a l . , 1973) has produced small-circle C-axis distributions centred on the max-imum principal stress direction. It appears therefore, that during the f i n a l stages of mylonite development the lineation direction was one of compression. This is in accord with the suggestion that movement along the slide plane was at 90 degrees to the lineation and was not accom-panied by development of another lineation. 3-7. Phase 3 deformation A number of macroscopic and mesoscopic structures trend easterly through the thesis area. These structures are considered to be com-ponents of a third phase of deformation. On the macroscopic scale they consist of three traces (3a-, 3b and 3c on figure 3-18) , and on the Figure 3-19 Phase 3 f o l d r e f o l d i n g a phase 2 f o l d 7i FIGURE 3 - 2 ( . Mesoscopic structural data from domains 1 & 2 Domoin 1 4 5 p o l e s to F 0 i F i 4 % contour. 03 = Q7°/\0° Domoi n 2 1 1 2 p o l e s to F t 2 % c o n t o u r 0 3 = 90°/1 0* L i n e a t i o n s • =~^u~o"rll: o - hornblende LOWER H E M I S P H E R E E Q U A L A R E A P R O J E C T I O N S 72 mesoscopic scale of crenulation cleavages (figure 3-20) chevron folds and lineations. Phase 3 crenulation cleavage measurements are plotted in figure 3-18, from which i t is apparent that this cleavage is developed throughout the map area. Greater dispersion of measurements in the south may be caused by confusing phase 2, 3 and 4 cleavages. This problem is discussed in section 3-11. Because crenulation cleavage is a semi-brittle type of deformation, i t s presence in rocks that were metamorphosed to amphibolite facies, during phase 2, is evidence that phase 3 post-dates phase 2 and i t s accompanying metamorphism. More direct evidence can be found in the form of phase 3 folds refolding phase 2 folds (figure 3-19). It is also apparent that phase 3 in part, pre-dates contact metamorphism caused by unit VIII, as discussed in section 3-9. The best defined macroscopic phase 3 fold (trace 3a on figure 3-18) traverses domains 1 and 2 in which i t folds (Fo/Fl) in unit II and F2 in units V to VIII. Foliation measurements from these two domains, plotted separately, are redistributed by phase 3 along l o c i approaching great circles which define two phase 3 axes (D3, figures 3-21A and B). Earlier lineations are scattered by phase 3 but no locus can be assigned to the plot of scattered lineations. Theinterlimb angle of fold 3a cannot be ascertained, but on the basis of i t s westerly trend and steeply dipping axial surface i t is considered to have formed at the same time as meso-scopic phase 3 chevron folds and crenulation cleavages. Within the central area of the map (Fo/Fl) strikes nearly perpen-dicular to phase 3 traces. The effects of phase 3 on (Fo/Fl) on the macroscopic scale are therefore minimized. Dispersion of the L2 plunge direction (plate B) defines two easterly trending traces (3b and 3c 73 Phase 4 axial surface traces mop' area N Legend |phase 4 troces*sv % synformol y antiformol A_ Phase 4 f o l d axes i n domains 3 .^ ,6 ,8 ,12 ,15 , & 21+22. Do3*3^07l5* Do.i-006^22' Do.6=002°/20' DQ8«318>V" DCL12=1^72C| DQ22+21 «1277l3° v ^ : Figure 3-23 Breccia, under plane polarized l i g h t (A), and crossed n i c o l s . V e r t i c a l f i e l d 5.2mm. 75 figure 3-18) which are considered to represent phase 3 folds. 3-8. Phase 4 deformation A number of northerly to northwesterly trending gentle, low-amplitude folds (4a, 4b, 4c and 4d on figure 3-22), probably class lb, in style, are outlined by (Fo/Fl) and F2 in most units. These folds are evidence of a fourth phase of deformation (phase 4). Phase 4 is dated as Tertiary, (section 3-10), and therefore, post-dates phase 3, which took place before or during the emplacement of unit VIII, which is isotopically dated as Jurassic (section 5). Mesoscopic evidence for phase 4 is limited. Weakly developed, closely spaced fracture cleavage probably formed during phase 4. A few mesoscopic, open,class lb folds with northwesterly trends were seen, and these folds probably also formed during phase 4. Christie (1973) identi-fied two phases of penetrative deformation dated as Tertiary. In the thesis area a l l Tertiary penetrative deformation is assigned to phase 4. Phase 4 deformation and Tertiary fracturing were accompanied by hy-drothermal alteration (Christie, 1973). A breccia which surrounds the southern end of unit IX probably formed at this time and can therefore be considered a phase 4 breccia This breccia (unit IX b, plate A) is com-posed chiefly of 1 to 50 mm diameter angular, extremely altered igneous rock and pink feldspar fragments (figure 3-23) which together make up more than 90% of the rock and form crude lamination. In thin section, quartz and feldspar (anorthite content 26 to 37%) in some of the frag-ments ar.e highly strained,whereas epidote is unstrained and restricted to the groundmass. Pink feldspar (microcline) in the breccia was derived from unit IX, but his unit could not have provided the plagioclase, 76 77 Which could have been derived from units V or VI. The strained min-eral fragments could have been derived from the mylonitized area (unit VI m) . Contacts of the breccia with unit II are sharp, but appear to be gradational with units V and VI. Contacts with unit IX are not exposed. In an area of poor outcrop near the southern contact of unit VI, a single outcrop of breccia similar to unit IX b, was found. 3-9. Position of intrusive units in the structural succession Intrusive units do not exhibit .the same abundance of mesoscopic structures as do the layered units. Despite this handicap the intrusive units can be assigned positions in the structural succession, and there-fore relative ages. This is done by careful analysis of the significance of foliations and.lineations exhibited by some intrusive units, and by re-lating these structures to their counterparts within the layered units. Five distinct intrusive events can be fi t t e d into the structural suc-cession. Unit V is the oldest intrusive unit identified. Two foliations can be distinguished in this unit, one outlined by lenses of quartz and feld-spar (quartz-feldspar foliation) and a second, less well-developed fo-li a t i o n , which contains coarse hornblende crystals (hornblende foliation). In places the hornblende foliation is seen to post-date and cut across the earlier quartz-feldspar foliation (figure 3-24). Both foliations are crenu-lated by phase 3 cleavage. Thus, i t appears likely that the hornblende foliation is F2 and the quartz-feldspar foliation is F l . Unit V was in-truded during or before phase 1 and could represent basement upon which the layered rocks were deposited. The presence of structures in unit V 78 pre-dating the earliest structures in the layered rock and the absence of a contact metamorphic aureole surrounding unit V would support this suggestion. Sheared mafic dykesrare present in unit V and were not seen in the enveloping rocks but this may be because of poorer outcrops of the lay-ered rocks (extensive road cuts expose unit V). These dykes contain a concordant foliation parallel to F l M in unit V, and are.therefore, as old as phase 1. Occasionally, folds were seen in the dykes but in a l l examples i t appeared that the folds post-dated F l . There i s , therefore no evidence suggesting that the dykes have a structural history pre-dating phase 1, and formation of F l in unit V. Mesoscopic xenoliths in unit V are foliated parallel to F l , but do not appear to have a struc-tural history pre-dating formation of F l . No obvious remnant contact metamorphic effects associated with unit V were identified. In the north such effects would not have sur-vived regional metamorphism and two phases of intense deformation. In the south, where regional metamorphic grade is lower, contact metamor-phic effects may have survived. Unfortunately, the rocks enveloping unit V in the south are mostly non-reactive amphibolites. In one loca-l i t y near the 49th parallel coarse,disoriented amphibole crystals are developed in unit I adjacent to unit V. This is possible evidence of contact metamorphism. Krauskopf (1941) considered unit V to be intrusive into enveloping rocks in which he saw evidence for a contact aureole and locally discor dant contacts. He also suggested that the dominant quartz-feldspar foliation formed as unit V crystallized. Present work indicates that contacts of unit V are regionally concordant with respect to F l in unit 79 and Fo in the layered units. Unit V was involved in phase 1, but there is no evidence to suggest that i t has a structural history pre-dating phase 1, or that i t formed a basement to units I to IV. Its present structural posi-tion is as s i l l s or as cores to phase 1 folds (section 6). Emplacement of unit VI post-dates emplacement of unit V, as i n -dicated by the identification of an inclusion of unit V in unit VI, (figure 3-25). Only one foliation, a biotite foliation^is identified in unit VI. In the north, (domains 4 and 5) with one exception, this foliation is parallel to the axial surface of tight folds outlined by ill-defined layering. These folds have the style and orientation of phase 2 folds. The foliation in unit VI is therefore, a structural feature and is parallel to F2. In the case of the exception noted above, the biotite foliation outlined a phase 2 fold. H e E the f o l i -ation apparently developed before phase 2 and could be partly magmatic in origin. Unit VI was emplaced after phase 1 and during, or a l i t t l e before phase 2. Emplacement of unit VI during or before phase 2 is supported by the absence of a contact metamorphic aureole surrounding the unit. The aureole, i f i t ever existed, has been destroyed by the regional meta-morphism that accompanied phase 2. The scarcity of zoned plagioclase in unit VI can also be attributed to the effect of this regional meta-morphism. Mesoscopic structures are not abundant in unit VI. Near contacts with layered units F2 in unit VI is nearly parallel to (Fo/Fl) in layered units; further from contacts, F2 i n unit VI is not well developed. The unit has a quartz lineation which is parallel to L2 in adjacent layered units. In the south, foliations and lineations in unit VI are less 80 Figure 3-26 Garnets c r y s t a l l i z e d during emplacement of unit VIII and postdating phase 3 crenulation cleavage. 81 pervasive than in the north, and unit VI has an augen texture with strongly developed L2 lineations. This texture may have developed during phase 2 or during subsequent reactivation of the contact. The former hypothesis is preferred. In the extreme south, the f o l i -ation in unit VI is discordant to layering in units I to IV, and the contact is marked bya zone of breccia formed from unit VI. Unit VII has a muscovite foliation and quartz and mica edge l i -neations. These features are parallel to their counterparts in unit VI. Unit VII was, therefore, involved in phase 2, and the foliation and l i -neations are phase 2 elements. S i l l s of unit VII intrude unit VI indi-cating that unit VII post-dates unit VI. Unit VII was emplaced during the f i n a l stages of phase 2,along the sites of developing slides whose formation bridges the time gap betwee/i phase 2 and phase 3. Unit VIII is porphyritic, weakly foliated and i t s feldspars are zoned. This unit escaped the amphibolite grade metamorphism in the north which was associated with phase 2. No contacts with other units were seen, but in the south, (domain 15, figure 3-1) a small crescent-shaped screen of layered rock i n unit VIII exhibits effects of recrystal-lization contemporaneous with emplacement of unit VIII. This recrystal-lization post-dates a phase 3 cleavage (figure 3-26). Apparently unit VIII, post-dates phase 3 in part, but i t s weak foliation is probably re-lated to phase 3. Unit IX post-dates a l l major penetrative deformation. Its contacts with other units are obscured by intense hydrothermal alteration or brec-cia zones. The unfoliated igneous texture of unit IX indicates that i t post-dates unit VII. Other intrusive events not represented as map units include,vertical 82 pegmatite veins intruded into easterly trending fractures which are probably related to phase 3, and lamprophyre dykes intruded into north-erly trending fractures of probable Tertiary age. Summarizing intrusive events, Unit V, the oldest intrusive, i s con-temporaneous or older than phase 1 but not structurally older than the layered rocks. Initiation of phase 2 was accompanied by intrusion of large volumes of unit VI. The f i n a l stages of phase! 2 were accompanied by intrusion of unit VII. Culmination of the metamorphic event which accompanied phase 2 was followed within a short time by phase 3 and intrusion of unit VIII. Unit IX was intruded next. Slides developed sometime during the interval phase 2 to phase 3. Pegmatites represent later intrusive activity and lamprophyre dykes were emplaced during Tertiary metamorphism which accompanied .phase 4. 3-10. Phases of deformation south of Long Joe Creek The grade of metamorphism accompaning phase 2 decreases to the south,and the resulting change i n character of phase 2 folds in the south i s responsible for some uncertainty in the correlation of phases seen in the north with those seen in the south. In the north, where rocks experienced amphibolite facies metamorphism during phase 2, four phases of folding can be recognized. Data from the southern part of the map area, where rocks experienced amphibolite to lower greenschist metamorphism during phase 25 iar. analysed by domains, and evidence for the presence of phases 1 to 4 in each domain is discussed. 83. Mesoscopic structural data from the southern port of Ihe mop area. D o m o i n 19 71 p o l e s t o . Fo 3 % c o n t o u r Domoin 17 7 3 p o l e s to F o 3 % c o n t o u r L m e o t i o n s _ o c h o r n b l e n » ~ mico edge • »• q u o r t z + = minor f o l d a x e s D Oorr.oins 2 2 ond j 1 0 % c o n t o u r d o m a i n 21 2 0 p o l e s to Fo / 8% c o n t o u r d o m o i n 2 2 2 4 p o ! e s to Fo, D 4 - \ZS>'/\€ B Domoin 18 AO p o l e s to F o 5 % c o n t o u r 8 5 Figure 3-30 I s o c l i n a l phase 2 f o l d i n unit III, domain 18. Figure 3-31 Rootless folds assumed to be phase 1 i n unit I I , domain 19, plane polarized l i g h t . V e r t i c a l f i e l d 4.5mm. 86 In domain 17 (figure 3-1) which includes rocks that experienced amphibolite facies metamorphism during phase 2, evidence for phase 3 is more abundant than evidence for phases 2 and 1. Phase 3 crenulation cleavages and minor folds are distinctive (figure 3-20 and 3-27). On the local scale(Fo/FL) i s folded and the distribution of plots of (Fo/Fl) in figure 3-28A, could define an average fold axis for domain 17, which trends east to southeast. This axis i s certainly caused i n part by phase 3 folding but could also be attributed to open folding associated with phase 4. Phase 3 i s responsible for dispersing pre-phase 3 lineations (figure 3-28A) but despite this, hornblende lineations which are presum-ably LI, are displaced more to the north or south than L2 quartz and mica edge lineations. Mesoscopic phase 2 folds, identified in domain 17 by their relationship to L2 lineations, are tight to i s o c l i n a l =arid__o"f class l c style. Phase 1 folds, parallel to the LI hornblende lineations^were not found. The volume of layered rock from which the structural data can be collected is so limited in this domain, that i t is d i f f i c u l t to extract evidence for each phase, but data is consistent with two phases pre-dating phase 3. In domain 18 there is evidence that the geometry of mesoscopic phase 2 folds changes as the metamorphic grade decreases. This domain includes rock which experienced lower amphibolite facies metamorphism during phase 2. In unit I, tight to isoc l i n a l class lb folds (figure 3-29) with 87 rounded hinges have eas t er ly trends s u b p a r a l l e l to phase 3 or 2. I s o c l i n a l c lass l c fo lds ( f igure 3-30) i n uni t I I I have s i m i l a r trends. I t i s assumed that both these folds are phase 2 fo lds because they d i f -fer i n s t y l e from obvious phase 3 fo lds seen i n uni t I i n domain 17, ( f igure 3-27). I f th i s i s the case, phase 2 fo lds which i n high grade rocks had c lass l c s ty le ,have c lass lb s t y l e i n uni t I i n domain 18. Hinges of t ight c lass l c fo lds i n uni t I II are p a r a l l e l to quartz and mica edge l i n e a t i o n s which are presumed to be L2 l i n e a t i o n s . There i s no evidence for a separat ion of hornblende l i n e a t i o n s from other l i n e a t i o n s i n domain 18 ( f igure 3-28B). E i t h e r phase 1 and 2 trends are p a r a l l e l to one another ,or hornblende l i n e a t i o n s are no longer p a r a l l e l to phase 1 d i r e c t i o n s . No f o l d s , t h a t could be d e f i n i t e l y assigned to phase l ,were seen i n domain 18. In domain 18, phase 4 traces and crenu la t ion cleavages undergo a r o t a t i o n to a more northwesterly trend. The trends of e a r l i e r phases are also rotated, and th i s adds to the d i f f i c u l t y of i d e n t i f y i n g evidence of phases 1 to 3. Evidence for phases 3 and 2 could be found, but no e v i -dence for phase 1 was found. Domain 19 includes the area i n which the metamorphic isograds are c loses t together. In the north of th i s domain, u n i t I I I contains s tauro-l i t e , whereas i n the south, c h l o r i t e i s c h a r a c t e r i s t i c . Rocks i n domain 19 e x h i b i t a profus ion of mesoscopic c lass lb chevron fo lds and crenu-l a t i o n cleavages of many trends. Pre -da t ing a l l these s tructures are c lass l c or c lass 2 r o o t l e s s , i n t r a f o l i a l , i s o c l i n a l folds ( f igure 3-31). As phase 2 fo lds are i n f e r r e d to change s t y l e to c lass lb i n the south, these root less folds must represent phase 1 f o l d s . I t i s u n l i k e l y that phase 1 fo lds change s t y l e i n the south as evidence suggests that phase 1 88 F I G U R E 3- 32 Crenulat ion C l e a v a g e s , domains 17, E l and 2 2 . J 8% Contour, 28 measurements ^  domoin 17 I 2 % ' » , l 5 ^ , " . 2 1 / 17 % « . •, 6 » i •' ' «' 22 50* Smoll circle centred on D4 Dozyz\< LOWER H E M I S P H E R E E Q U A L A R E A P R O J E C T I O N 89 was accompanied by uniform low grade metamorphism throughout the map area. Class lb chevron folds with northerly to northeasterly phase 4 trends refold mineral lineations,which must predate phase 3- as phase 3 did not produce mineral lineations. These lineations must be phase 2 as they postdate the rootless isoclinal,class lc or class 2 phase 1 folds. There is evidence in domain 18 for phase 1 microscopic folds and ..phase 2 lineations. The profusion of crenulation cleavages and chevron folds that postdate phases 1 and 2 cannot be resolved confi-dently into phase 3 and 4 features. Domains 21 and 22 include respectively the west and east flanks of the southern end of the dome cored by unit VI. The nose of the dome, as outlined by (Fo/Fl) plunges southeasterly (figure 3-28D) . Crenulation cleavages probably related to phase 3 appear to be folded about the same axis as (Fo/Fl). This is shown in figure 3-32 in which crenulation clea-vages from domains 17,'21 and 22 are plotted. Many of the measurements spread along a small circle centered on the nose of the dome as defined by (Fo/Fl) in domains 22 and 21 (figure 3-28D). The dome apparently postdates phase 3 and is therefore a phase 4 feature. Near the 49th parallel phase 4 appears to have a southeasterly to easterly trend. In this area lineations and isoc l i n a l i n t r a f o l i a l folds, predating phase 4, plunge northerly or northwesterly. Because of sparse outcrop no analysis was made of these lineations and folds. Though phase 1, 2 or 3 macroscopic folds cannot be identified south of Long Joe Creek, evidence for these 3 phases can s t i l l be found in the ro cks. 90 Domains .~3 and 4 9 7 joint m e a s u r e m e n t s 2 % c o n t o u r Domains 16 and 2 0 6 9 joint measurements; 3 % contour . Prmcipa I for joint stress sets. Tota l area 23 pegmat i t c veins 6 % contou r ^ s l n k e of lampropliyr^ dykes • * jomt m e a s u r e m e n t s in dykes. axes EQUAL AREA LOWER HEMISPHERE PROJECTIONS 91 3-11. Fractures From air photos, i t is apparent that on the macroscopic scale north-trending lineaments accentuated by glaciation are abundant in the map area. On the ground, because layered rocks are scarce and often strike parallel to lineaments, fault offset related to a parti-cular lineament can rarely be proved. In plate A, only faults with mapped offset are shown. Many lineaments probably represent vertical faults with small offset. Mapped faults trend northerly or northeast-erly, generally approximately 040°. They are certainly late features of probable Tertiary age, as are most joint sets. It is d i f f i c u l t to measure joints systematically in the f i e l d . For example, i f two joint sets, forming a conjugate pair are developed, only one set is likely to fracture in a single outcrop. Measurement of two joints per outcrop could easily produce up to 50% spurious data. It is better to make single joint measurements on adjacent outcrops. Analysis of mesoscopic fractures with no offset (joints) suggests five distinct fracturing events. Figure 3-33B, is a synoptic diagram of a l l joint measurements. Flat-lying minor thrusts or joints (F5-1), with heavily chloritized surfaces represent the earliest event (concen-tration A, figure 3-33A). They are found mainly in northern outcrops of unit VI (see concentration A, figure 3-33C) and are sub-parallel to the phase 2 slides previously discussed. In one localit y , a minor thrust is cut by a pegmatite vein with an easterly phase 3 strike. Apparently the thrust predates phase 3. Steeply dipping joints ,which postdate fractures. Set A..,can be as-signed to four distinct fracturing events which are represented in order of decreasing age by joint sets F and G (F5-2), set B, (F5-3), sets C 92 j o i n t s ( s e t s C a n d D ) . 93 and D (F5-4) and fin a l l y the youngest set E (F5-5). The orientation of sets F and G (figure 3-33B) is such that they appear to be a-c shear joints related to phase 3. East-west vertical joints (set B, figure 3-33B) , sometimes occupied by pegmatitie dykes, (figure 3-33F), appear to be a-b joints associated with phase 3. Two areas of extensive outcrop of intrusive units are,domains 3 and 4 in the north, and domains 16 and 20 in the south,(figure 3-1). Joints from these two areas are plotted separately (figure 3-33C and D). With the exception of flat-lying joints found only in the north (concentration A), joint concentrations in the two areas, which are ten miles apart, are remarkably similar. Concentrations C and D (figure 3-33B and D) apparently represent conjugate shear joint sets (F5-4). Surfaces of these joints are chlori t i c and sometimes striated. In one locality, joints from both sets are truncated by a later 020° extension joint (figure 3-34). Centers of joint concentrations are approximately located on figures 3-33C and D for the southern and northern areas respectively. Joint sets C and D can best be explained as a-c shear joints formed by east-west compression and re-lated to the north-south trending traces of phase 4. Well-developed tension joints (concentration E, figure 3-33B) paral-l e l the Okanagan Valley. These joints, which are noticably more abundant near the Okanagan Valley, are often represented by closely spaced frac-tures, or en echelon discontinuous fractures. Fracture surfaces are clean. These joints could be a-b joints related to north-south trending phase 4 traces and they represent the f i f t h and youngest fracturing event identified , (F5-5). Lamprophyre dykes occupy joints of set E (figure 3-33F). Joints in the dykes do not have orientations 94 markedly different from joints in the surrounding rocks (compare f i g -ures 3-33F and D). Figure 3-33E, illustrates the possible principal stress axis o r i -entations associated with the joints. The convention used is cr 1 = minimum principal compressive stress direction. A plausible kinematic interpretation of the fracture data is presented. I n i t i a l l y , north-south compression associated with phase 3 produced joint set F and G. Relaxation about this north-south direction produced extension joints (set B) which controlled emplacement of pegmatite veins. Compression then started acting in an easterly direction at close to 90° to the previous compressive direction associated with phase 3. This renewed compression formed shear joint sets C, A and D, and could be associated with phase 4. Relaxation of this stress f i e l d caused the direction of cr 3, related to shear joints C and D, to become the cr 1 d i -rection related-to extension joint set E, which controlled emplacement of the lamprophyre dykes. It cannot be assumed that joint sets F, G and B, which are related in orientation to phase 3, formed at about the same time as phase 3; they could have formed considerably later. Joint sets C, D and E appear to be components of Tertiary fracturing which has been documented in southern,British Columbia by Monger (1968). Axes of northerly trending folds are nearly parallel to the cr 1 direction for shear joints C and D. Using this fact and the known existence of an early Tertiary metamorphism (section 4) i t can be suggested that phase 4 occurred at the same time as the Tertiary metamorphism and fracturing, and is therefore also Tertiary in age. 95 3-12. Summary Four distinctive fold sets have been postulated to explain the structural f i e l d data. The fold sets may be ordered in time to rep-resent four distinctive phases of deformation. There is limited evi-dence in rocks of a l l metamorphic grades for an early phase (phase 1) of recumbent folding, but there is abundant evidence in high grade meta-morphic rocks for a second phase (phase 2) of recumbent folding. Phase 2 folds probably have different styles in low grade metamorphic rocks where evidence for phase 2 is not so conclusive. Mesoscopic chevron folds, crenulation cleavages and macroscopic easterly trending.traces, found in rocks of a l l metamorphic grade, are a l l considered to have formed during phase 3, which clearly postdates phase 2. Open folds with northerly or northwesterly trends are considered to have formed during phase 4 Tertiary deformation. Christie (1973) was able to distinguish two separate Tertiary phases of deformation. The relationship of metamorphism to these phases is discussed in the next section, following which, an attempt is made to assign absolute ages to the various metamorphic and def ormational events. 96 SECTION 4 METAMORPHISM 4-1. Introduction Evidence for five phases of deformation can be found in rocks from the thesis area. As mentioned in section 3, the accumulative grade of layered rocks varies from amphibolite facies in the north,to greenschist in the south. Largely as a result of thin section workjit appears that the accumulative metamorphic grade of rocks in the thesis area is the re-sult of three distinct periods of regional metamorphism which accompanied phases 1, 2 and 4, plus 5. The earliest period of metamorphism is related to phase 1 and could be considerably older than Carboniferous. If i t was of regional extent, then there is no evidence to suggest that i t exceeded lower greenschist facies, which is the lowest accumulative grade of metamorphism now exhi-bited by the layered rocks. The second period of regional metamorphism which was contemporaneous with phase 2, predates the mid-Carboniferous and apparently reached the highest grade of the three periods of regional metamorphism. It produced upper amphibolite facies metamorphism of the Barrovian type in the north. Grade achieved in the south was considerably lower. Locally dynamic metamorphism affects rocks adjacent to the tectonic slides which developed soon after phase 2. Units VIII and IX were intruded after regional metamorphism which accompanied phases 1 and 2. These units are responsible for contact meta-morphism for which evidence in the thesis area is sparse. The third period of regional metamorphism occurred in the Tertiary and was contemporaneous with phases 4 and 5. It probably did not exceed 97 98 middle greenschist facies in grade, and could have been accompanied by extensive hydrothermal alteration in the north. The three regional metamorphic events are referred to as Ml, M2 and M3. It should be noted that whereas Ml and M2 are broadly contem-poraneous with phases 1 and 2 respectively, M3 is related to phases 4 and- 5. Some geochronologic data, analysed in section 5, is best explained by postulating the existence of a Jurassic metamorphism. There is no indisputable petrographic evidence in the thesis area for Jurassic meta-morphism, but elsewhere, such evidence is abundant. 4-2. Isograds The most striking feature of the metamorphic rocks in the thesis area is the diversity of metamorphic grade exhibited by them. This diversity of grade is the result of the metamorphism (M2) and can be represented by biotite, garnet, staurolite and sillimanite mineral isograds. Figure 4-1 illustrates the approximate location of, key metamorphic minerals, and the mineral isograds defined by the f i r s t appearance of these minerals. Only mineral identifications checked by thin section work or X-ray d i f -fraction are shown in figure 4-1, and used to position the isograds. Obviously, key minerals were noted in the f i e l d in many more l o c a l i t i e s . Some comments should be made about the temperature gradients required to produce the observed isograd spacing. The metamorphic grade of rocks changes from chlorite to sillimanite over a distance of about 3 miles (5km-). A high geothermal gradient can be suspected. In semi-quanti-tative terms, a horizontal geothermal gradient of 60° to 80°C/Km is suggested, i f the isograds were formed by a conductive geothermal frozen in time. This is the minimum, gradient which equals the true gradient 99 only i f the isograds are vert i c a l . Phase 4 folding, which was respon-sible for the broad dome occupying the southern half of the area map-ped, folded the isograds and probably steepened them. Unfortunately, there is no way that these isograd surfaces can be located accurately enough in space to define their orientation. The position of the isograds with respect to the trend of various units and fold traces is considered. The isograds are not parallel to unit contacts. They do not appear to be locally related to boundaries of unit VI which is the most voluminous intrusive unit. Regionally, the isograds shown in figure 4-1, form the southern end of a domal metamor-phic high, which extends northwards, generally elongate parallel to phase 4 traces. Many other areas of Shuswap rocks are bounded by closely spaced isograds. Sometimes the isograds are stratigraphically controlled (Cam-b e l l , 1970), (Fyson, 1970), and other times they are steeply dipping. (Fletcher, 1971), (Reesor, 1970). A pattern of isograds remarkably simi-lar to that of the thesis area was obtained by James (1955). 4-3. Metamorphic mineralogy resulting from metamorphism M2 As rock units are traced from south to north, the metamorphic min-eral grain size increases, and there is an attendant development of meta-morphic foliation. Both features suggest an increase in metamorphic grade, which is substantiated by the appearance in the expected order of key metamorphic minerals (figure 4-1) and pegmatite veins. The mineralogy of most units illustrates the increasing grade of this metamorphism (M2). Unit III is particularly sensitive to metamorphic recrystallization. In the south i t is a siliceous a r g i l l i t e . Along strike to the north, i t is transformed successively into slate, phyllite and fin a l l y schist. TABLE 4-1 SOME M2 MINERAL ASSEMBLAGES G r e e n s c h i s t f a c i e s Calc s i l i c a t e s P e l i t i c rocks Musc+Bio+Qtz+Alb+Chl Bio+Qtz+Garn+Alb Amphibolites Act+Alb+Qtz+Ep+Chl+Sph Amphibolite f a c i e s Dio+Trem+Cal+Plag+Qtz Dio+Qtz+Plag Bio+Staur+Qtz+Plag Bio+Musc+Qtz+Flag+K F e l d B i o +Amp+Q t z +P1ag+Garn Bio+Garn+Qtz+Flag+Musc Bio+Garn+Sil+Qtz+Plag Amp+Plag+Qtz+Bio+Sph+Dio+Plag Act=A c t i n c a l i t e A l b = A l b i t e B i o = B i o t i t e C a l = C a l c i t e C h l = C h l o r i t e Dio=Diopside Ep=Epidote Garn=Garnet Musc=Muscovite P l a g = P l a g i o c l a s e Qtz=Quartz S t a u r = S t a u r o l i t e S i l = S i l l i m a n i t e Trem=Tremolite . . . 101 The foliation of the phyllite, defined by microscopic flakes of white mica, is characteristic of the lower greenschist facies of dynamother-mal metamorphism. The middle and upper greenschist facies can be dis-tinguished by the appearance of biotite and garnet, respectively. Staurolite, identified in a number of thin sections (figure 4-1), charac-terizes the lower amphibolite facies. The presence of f i b r o l i t e , iden-t i f i e d in thin section \and by X-ray diffraction, indicates that M2 reached upper amphibolite facies. Middle amphibolite facies i s repre-sented by the presence of andalusite or kyanite. Because of, either un-favourable rock chemistry, or lack of outcrop combined with compressed isograd spacing, neither of these minerals were found. Units I and IV underwent minimal transformation with increasing M2 grade. Some useful indicators of M2 grade include the disappearance of actinolite and the appearance of hornblende at the beginning of the am-phibolite facies; the disappearance of epidote in the upper amphibolite facies, and the crystallization of diopside at the beginning of the am-phibolite facies. The fine-grained green pleochroic amphibole^character-i s t i c of unit I in.the south,gives an actinolite X-ray diffraction trace. Thin sections of samples of unit I from between Mica Creek and Long Joe Creek contain, predominantly, hornblende and calcic plagioclase, but rare grains of a non-pleochroic clinoamphibole could be actinolite. Epidote that crystallized during M2 was identified in samples of unit I from the south, but most of the epidote identified in samples from the north ap-peared to have crystallized later than M2. Diopside was noted in the fi e l d in many outcrops of unit I in the north. Two small outcrops of calc-silicate in unit III (figure 4-1), lo-cated one mile north of Long Joe Creek,are composed of diopside, . 1 0 2 Figure'4-2 Staurolite c r y s t a l with a l t e r a t i o n margin of white mica ( muscovite ? ), plane polarized l i g h t . V e r t i c a l f i e l d 3.0mm. Figure 4-4 Axia l surface mica f o l i a t i o n postdating formation, of phase 1 f o l d , crossed n i c o l s . V e r t i c a l f i e l d 4.9mm. 103 tremolite, quartz, feldspar and calcite. 4-4. Metamorphic reactions and P, T, conditions of M2 Some metamorphic mineral assemblages of the layered units are lis t e d in table 4-1 from which i t can be seen that chlorite, biotite, garnet, staurolite and sillimanite represent useful index minerals. As no chemical analyses were made of samples, equilibrium assemblages or mineral reactions are not discussed indetail. Metamorphic reactions helpful in determinining the grade and P, T, conditions of M2 occurred in unit III which appears generally to be im-poverished in K andAl and rich in Fe. Biotite is one of the minerals crystallized in the greenschist facies. Fletcher (1972) considered bio-tite in similar low K pelites to have formed by the reaction: K rich muscovite + chlorite + quartz = biotite + less K rich muscovite + H20, (Tilley, 1926). equation A . Despite the high Fe content and low Al content of unit III which are favourable for the growth of stilphnomelane, this mineral was not found in thin sections. The boundary of the amphibolite facies is defined by the f i r s t ap-pearance of staurolite and presence of garnet. The f i r s t appearance of garnet was noted in the f i e l d in greenschist facies rocks and samples from amphibolite facies rocks gave an almandine X-ray diffraction pattern. Thin section observations support Winkler's (1967) suggestion that staurolite formed from the reaction: Fe rich chlorite + muscovite = staurolite + biotite + almandine +H20, equation B. Staurolite appears to form stable crystal boundaries with biotite, where-as i t is partially altered to white mica (muscovite ?) (figure 4-2) in one thin section. No thin sections contain both chlorite and staurolite 104 crystallized during M2. These three observations can be predicted using equation B. The attainment of upper amphibolite grade is suggested by the pres-ence of sillimanite. Sillimanite can form by a number of reactions but i t is unlikely that the f i b r o l i t e , identified by X-ray diffraction as sillimanite, formed from kyanite. Muscovite and sillimanite are not found in the same thin sections,in which sillimanite is invariably in con-tact with biotite and almandine. A number of reactions require the growth of sillimanite at the expense of muscovite. One such plausible reaction discussed by Garmichael (1970) i s ; staurolite + muscovite + quartz = sillimanite + garnet + biotite + H20; equation C. Because using staining techniques, no K feldspar was found in thin sections containing sillimanite, the reaction; muscovite + quartz = sillimanite + K feldspar +H20; equation D, is unlikely. The calc-silicate outcrops locate the diopside isograd which lies within the amphibolite facies. Thin sections of calc-silicates from unit III, located in figure 4-1,contain diopside and calcite (figure 4-3). The coexistence of these minerals indicates that the reaction: tremolite + cal-cite + quartz = diopside; equation E, has not gone to completion,and that the thin section must come from an out-crop which occupies the zone of the diopside isograd. Reaction E occurs at temperatures higher than that at which staurolite crystallizes (Winkler,-1967,). (Fletcher (19 72) found that the diopside isograd occurred in the sillimanite zone where crystallization of fibrous sillimanite by the re-action: muscovite + garnet = sillimanite + biotite + albite + quartz +H20; equation F, eliminated garnet from the rocks. Carmichael, on the other hand, placed 105 the diopside isograd above the (sillimanite, garnet, h,iotite) isograd defined by equation C. The diopside isograd in the thesis area appears to occur within the sillimanite isograd which probably formed by reaction C. The grade of M2 reached upper amphibolite facies as proved by the presence of sillimanite which probably formed in part by re-' action C. The lower boundary of the upper amphibolite facies could not have been exceeded by much, because muscovite is found in unit III within the sillimanite isograd (figure 4-1). The reaction C could not have gone to completion. The presence of epidote and microcline in in-trusive units, which experienced M2 amphibolite grade also restricts the upper limit of M2 metamorphism attained to lower,upper amphibolite facies. It is dangerous to assign specific pressure and temperature values to M2, but the: break-down of epidote occurs at about 680"degrees and is pressure insensitive (Winkler,1967), whereas reaction C is pressure sen-sitive and occurs at 690 degrees above a pressure of 4 Kb. Rocks capable of crystallizing staurolite could almost certainly crystallize cordierite under different conditions. The absence of cordierite in thesis rocks therefore implies a pressure i n excess of 3.5 Kb (fiichardson,1968). Thus, in general terms metamorphism M2 reached a temperature of nearly 680 de-grees and a pressure in excess of 3.5 Kb. If this pressure can be equa-ted with load pressure then a lithostatic column of 3500 f t , or 14 Km- is suggested. Temperatures and lithostatic columns of these magnitudes pre-dict a geothermal gradient similar to that suggested by the isograd spacing. Many arguments can be used to show that the suggested pressure need not be formed solely by overburden of a column of horizontal sediments. Stacking of recumbent folds could have increased the pressure accompany-ing M2. Whatever the stratigraphic thickness of sediments responsible 106 Figure 4-5 Flattened M2 garnet , plane polarized l i g h t . V e r t i c a l f i e l d 5»2mm. Figure 4-6 Undeformed st a u r o l i t e crystals , plane polarized l i g h t . V e r t i c a l f i e l d 5.2mm. TABLE 4-2 Relative ages of intrusives,phases of deformation and metamorphisms* pre-mid-Carboniferous ? Jurassic ? Ter t i a r y ? Unit X j ' — = Phase 5 :— Dykes M 3 Unit IXb • Phase 4 Unit IX Metamorphism ? Unit VIII Phase 3 Unit VII Unit Vim • Phase 2 ( s l i d e s ) M 2 Phase 2 Unit VI M 1 Unit V Phase 1 108 for the 3.5 Kb pressure they are of pre-Pennsylvanina age. 4-5. Relative age of M2 with respect to phases of deformation, and i t s effect on intrusive units The relative age of M2 with respect to other deformational and meta-morphic events is illustrated graphically in table 4—22. It has been men-tioned in previous discussions that M2 was contemporaneous with phase 2. Evidence for this suggestion can be found in the fabric of the metamor-phic rocks. Micas crystallized during M2 outline phase 1 folds or axial surfaces of these folds (figure 4-4), but in both cases obviously grew after formation of the folds. Deformation of M2 staurolite crystals, by phase 3 crenulation cleavages, dates M2 as pre-phase 3. Concordant peg-matite and aplite veins become conspicuous in layered rocks within the staurolite isograd. These veins are folded by phase 2 and micas in them aligned parallel to phase 2 axial surfaces. Although not conclusive, these facts substantiate the conclusion that M2 was broadly contempora-neous with phase 2. On the local scale the relative age of M2 with respect to phase 2 varies. In the north some M2 garnets were flattened (figure 4-5), most probably during phase 2. Ross (1973) describes garnets in mylonitized Vaseaux Formation rocks that were flattened during deformation equivalent to phase 3. The garnets in figure 4-5 occur in a sample of unit III crenu-lated by phase 3, therefore, flattening is more reasonably attributed to phase 2 than phase 3. This suggests that phase 2 outlasted growth of M2 garnet in the north. In the south, adjacent to unit VIII, some stauro-l i t e crystals have not been deformed by phase 3 (figure 4-6). Here, ap-parently M2 crystallization outlasted phase 2 and may have continued 109 during the emplacement of unit VIII which occurred during or soon after phase 3. Phase 1 deformation was accompanied by emplacement of unit V, which therefore experienced M2. Obvious effects of M2 on Unit V are minimal. Generally feldspars in samples of unit V are unzoned and in the north the presence of epidote, microcline and apparently rare grains of diopside are compatible with attainment of middle amphibolite facies during M2. It has already been stated (section 3) that emplacement of unit VI, in part, predates phase 2, and the absence of any contact metamorphic aur-eole surrounding unit VI implies that the unit was also emplaced before the end of M2. Zoned feldspars are present in some samples from north of Inkaneep Creek but are absent in samples of unit VI from elsewhere. Rare, small, pink garnets, seen in thin section, could be metamorphic, as also could epidote and a non-pleochoric clinoamphibole, but generally M2 has produced minimal change in the mineralogy of unit VI. Unit VII was emplaced before the end of phase 2 and,.therefore, prob-ably during the waning stages of M2. A number of factors suggest that unit VII escaped the brunt of M2. Poorly preserved feldspar zoning, presence of orthoclase and microcline, and absence of epidote, could a l l suggest, either that M2 grade reached upper amphibolite facies,or that grade did not increase sufficiently to anneal feldspars, invert ortho-clase to microcline or crystallize epidote. Small pink garnets in unit VII appear to postdate phase 2. They are not deformed and probably grew during the waning stages of M2. 4-6. Metamorphism M3 Metamorphism M2 was probably pre-mid-Carboniferous; there is no evidence for any other metamorphism unt i l the Jurassic. Isotopic data, 110 Figure 4 - 7 Coarse b i o t i t e ( white flakes ) outlining a f o l i a t i o n which postdates the crenulation cleavage, crossed n i c a l s . V e r t i c a l f i e l d 5»2mm. Figure 4 - 8 Early f o l i a t i o n outlined by fine b i o t i t e and a l a t e r f o l i a t i o n outlined by coarse b i o t i t e , plane polarized l i g h t . V e r t i c a l f i e l d 5.2mm. I l l (section 5) can be interpreted to support the existence of a Jurassic metamorphism. Mineralogical data, as evidence for this event, which is discussed in section 5, is absent in the thesis area. There is mineralo-gical and structural data to support the suggestion of a Tertiary metamor-phism M3,which did not exceed middle greenschist facies. A sample of unit III from the south of Long Joe Creek contains biotite which clearly post-dates formation of crenulation cleavages and outlines a foliation (figure 4- 7). This M3 biotite has been dated at approximately 35 m. yr. (section 5- 7, sample Sb7) and defines a grade for M3 of at least middle greenschist facies . Other mineralogic evidence for M3 is not abundant. In the samples of unit III which experienced M2 amphibolite grade, i t is d i f f i c u l t to sepa-rate retrograde M2 effects from prograde M3 effects. In one sample con-taining staurolite, biotite is of two generations (figure 4-8). The later generation outlines a foliation which is not parallel to F3 and,therefore, is probably later artd related to Tertiary metamorphism M3 and Phase 4. Some micas from samples of unit III appear to predate phase 3 crenulation clea-vages (figure 4-9) but have'Tertiary Rb-Sr ages (section 5-7). Metamor-phism M3 did not totally recrystallize these micas but i t s effects are registered by their isotopic data. There is no conclusive data that de-fines the upper limit of M3, but a l l the garnets in unit 3 appear to be of one generation, so that apparently M3 did not reach upper greenschist facies. A l l the intrusive units experienced M3 but i t s effects on these units were restricted largely to partial recrystallization of minerals. Isotopic data for minerals from intrusive units (discussed in section 5-6) registers M3. The outer zone of zoned epidote crystals seen in unit VI may have grown during M3 which was not intense enough to anneal feldspar zoning 112 in unit IX. The hydro-thermal alteration of unit IX and the breccia sauth of unit IX are extensions of the alteration in the Vaseaux Lake area con-sidered by Christie (1973) to be Tertiary in age. He suggested that i t was related to Tertiary volcanism which predated deposition of the White Lake Basin sediments cropping out a few miles to the west of Vaseaux Lake (Church ,^1967). K-Ar data provides the best estimate of the age of M3. Lamprophyre dykes (White,1968) and rhomb porphry dykes which are related to volcanism in the White Lake Basin (Church,1967) have Early Tertiary ages,as do micas in the thesis area which were apparently ef-fected by M3. The rhomb porphyry dykes are found undeformed and unrecry-stallized in some loca l i t i e s and extensively deformed and recrystallized in others. Because they have identical Tertiary ages of 44 m. yr. at both loc a l i t i e s (Ross and Barnes,1973) deformation,probably equivalent to Phase 4, must have accompanied emplacement. Christie (1973) found evidence for an Early Tertiary metamorphism which accompanied open folding in the Vaseaux Lake area. This metamor-phism is equivalent to M3 whose grade in the thesis area did not exceed middle greenschist facies. Christie's deformation is equivalent to phase 4. There is no information concerning the pressure operatingg during M3, but on stratigraphic grounds i t was probably low. 4-7. Metamorphism Ml L i t t l e evidence for a metamorphism (Ml) earlier than M2 remains. Contact metamorphism caused by emplacement of unit V would be a part of Ml. Krauskopf (1941) believed that he could recognize, south of thesis area, an extensive contact metamorphic aureole associated with unit V. 113 Figure 4 - 9 Mica crenulated by phase 3 » plane polarized l i g h t . V e r t i c a l f i e l d 5.2mm. Figure 4-1C Euhedral tourmaline c r y s t a l , plane polarized l i g h t . V e r t i c a l f i e l d 5.2mm. 114 If Ml represents a regional metamorphism then i t did not exceed, by much, the lowest grade (chlorite) attributed to M2. No data remains to sug-gest that locally Ml reached a high grade, but in the north the develop-ment of LI hornblende lineations indicates middle greenschist facies. Christie (19 73) believed that metamorphism which accompanied defor-mation equivalent to phase 1, in the Vaseaux Lake area, reached middle to upper greenschist facies and was of a progressive nature. In the thesis area there is no data suggesting that either a long or short period of time separated Ml from M2. 4-8. Contact metamorphism Any contact metamorphism that was caused by intrusive units V, VI and VII, whose emplacement predates M2, has been obliterated. Extensive contact metamorphic aureoles are not developed around the two intrusive units, VIII and IX, whose emplacement postdates M2, phase 2 and phase 3. Some recrystallization caused by unit VIII was observed in the small crescent of layered rock engulfed by unit VIII near Long Joe Creek. Eu-hedral garnets and coarse unoriented muscovite are present (figure 3-26). Also near Long Joe Creek, tourmaline crystals (figure 4-10) and cunori-ented muscovite flakes may have crystallized during contact metamorphism caused by unit VIII. The grade of contact metamorphism caused by unit VIII cannot be determined; in fact at the time of emplacement the li t h o -static column may have been such that no clear-cut aureole ever existed. No contact metamorphism caused by unit IX was found. To the west, Okulitch (1970) mapped the extension of unit IX and described a restricted aureole,that just attained the hornblende hornfels facies. 4-9. Relationship of deformation to metamorphism Phase 2 was broadly contemporaneous with M2 and therefore acted on 115 rocks that were experiencing different grades of metamorphism. Some discussion is warranted of the exact timing of phase 2, with respect to M2, in different areas, and of the effect of different grades of metamor-phism on the style of phase 2 folds. It is unlikely that a l l rocks experiencing M2 metamorphism attained their maximum M2 temperatures at the same time. If M2 was caused by a locallized heat source which produced an outward moving heat wave, then rocks at different distances from the source must have experienced d i f -ferent temperature peaks of different magnitudes, at different times. If this was the case, two possibilities exist. The climax of phase 2 defor-mation could have migrated in time and space with the heat wave, decreas-ing in intensity as the magnitude of the temperature peak of the heat wave decreased. Alternatively, phase 2 could have been synchronous throughout the thesis area occurring in a specific area,before, during, or after attainment of the local temperature peak. Secondary creep rates are very temperature dependent. A rise in tem-perature of 100° C can cause a three-fold increase in the strain rate of carbonates, i f differential stress remains constant (Heard,1963). With this in mind, i t is probable that total strain associated with phase 2 is less in rocks that experienced low grade M2 metamorphism,than i t is in rocks that experienced high grade M2 metamorphism. Also, because of the relationship of strain to temperature, high grade metamorphic rocks were probably deformed earlier than low grade rocks. Possibly, on the macroscopic scale, the upright axial surfaces of phase 2 folds in greenschist facies rocks in the south represent less total strain than the recumbent phase 2 axial surfaces in amphibolite facies rocks in the north. A similar change of style and intensity of 116 i deformation,with metamorphic grade is discussed in a model, presented by Fyson (1971). Phase 2 could not have been completely synchronized with the M2 temperature peak. It is argued in section 4-5, that in the north, phase 2 , in part postdates M2. This possibility is certainly suggested by parallel folding and development of a micaceous F2 foliation in aplite veins, injected into amphibolite facies rocks during M2. In the south, i t appears that phase 2 might have predated M2. It has been suggested by Campbell (1970) that multiple fold sets are formed in high grade rocks as a result of metmorphism and not necessarily as a result of more regional forces which form fold sets in both high and low grade rocks. There is no evidence in the thesis area that high grade M2 rocks exhibit more than one set of folds formed in the time span of phase 2. Nor, apart from the change in orientation of axial surfaces, does there appear to be a drastic change in the orientation of phase 2 structures from high to low grade M2 facies rocks. In general terms, i t is interesting to consider, in the thesis area, the correlation between metamorphic environment on the one hand, and phy-si c a l properties of rocks and the resulting deformation, on the other hand. Holland and Lambert (1969) discuss the relationship of rheology to meta-morphic grade. They define five regimes characterized by different rhe-ologies and strain patterns. The f i r s t regime starts below the level of diagenesis. A sixth regime may be considered to operate before diagenesis under high H20 pore pressure and rock porosity. In this environment soft sediment folding can occur and as viscosity contrasts between rocks would be at a minimum,folding could be similar in style (Biote,1962). Such folding, i f similar in style is often accompanied by formation of 'a' 117 lineations and slatey cleavages (Maxwell,1962). In the thesis area large phase 1 folds are outlined by unit I, which under non-metamorphic conditions would not have a viscosity sim-i l a r to that of unit III, and as phase 1 appears to have been accom-panied by at least lower greenschist facies, i t is improbable that these folds developed in a soft sediment regime. It is also unlikely that they developed in the f i r s t regime of Holland .efrfa1-!!. which is character-ized by primary creep (Ramsay,1967). Regime two of Holland, et a l . -equivalent, to greenschist .facies charac- t terized by reactions which release water into the rock. Strain is proba-bly by secondary creep (Ramsay,1967) and tight folds often similar in style are formed. Mesoscopic phase 1 folds in the thesis area are class l c in style (figure 4-11) with flattening ratios (t) greater than 5 (Ram-say, 1967). There is no evidence to suggest that Ml exceeded greenschist facies andftherefore,phase 1 probably operated under rheologic conditions of regime 2 as did phase 2 in the south. In the north, phase 2 probably operated under rheologic conditions approaching those of regime 4, in which partial melting and breakdown of hydrous minerals decrease the competence of the rocks. Because fold 2a is cored by phase 2 intrusive unit "VT, i t did not ex-perience the f u l l effect of the M2 gradient and i t remains iso c l i n a l for a l l i t s tracable length. Fold 2b, is cored by phase 1 intrusive unit V, which could not offset the effects of-the M2 gradient on the style of this fold, which changes from iso c l i n a l in the north to open in the south. There is insufficient outcrop to trace either of these folds south of Long Joe Creek. Phase 3 occurred under low temperature conditions when units were 118 I Figure 4-11 Flattened p a r a l l e l phase 1 f o l d . Figure 4-12 E l l i p t i c a l rotated porphyroclast of feldspar, crossed n i c o l s . V e r t i c a l f i e l d 1.8mm. Figure 4-13 Porphyroclast of feldspar with pressure shadow (A), crossed n i c o l s . V e r t i c a l f i e l d 1.8mm. 119 relatively dehydrated and in most cases fol . i ated by earlier deformation. These factors controlled the style of phase 3 which in the thesis area produced class lb chevron folds and crenulation cleavages which are no-ticably more abundant in the south. Further north, in the area mapped by Christie (1973) the equivalent deformation appears to have occurred under higher metamorphic conditions and is in part similar in style. Phase 4 occurred under low grade metamorphic conditions that did not exceed middle greenshcist facies. Mineral ages in the north are older than mineral ages in the south; possibly the intensity of M4 decreased northwards. In the north where foliation is flat-lying, phase 4 produced approximately 10% shortening, warping the foliation into macroscopic, up-right open folds. In the south where foliation in intrusives is steeply dipping:it appears that much of the overall shortening was taken up in the layeresL units by development of numerous mesoscopic upright class lb chevron folds. 4-10. Dynamic Metamorphism Dynamic metamorphism, generally contemporaneous with slide develop-ment has produced some zones of mylonite. Two extensive zones of mylon-ite (unit VI m, plate A), apparently developed from unit VI, crop out north of Inkaneep Creek. The porphyroclastic texture of these mylonites was ex-amined in thin section. Porphyroclasts of plagioclase, microcline and quartz s i t in an apha^ -n i t i c matrix of quartz, epidote, biotite, chlorite and feldspar. Por-phyroclasts are e l l i p t i c a l in cross section (figure 4-12) and in the case of feldspars, sometimes have circularly zoned strained extinction. This extinction does not appear to be igneous in origin and may result from inward migration of effects of flattening on the porphyroclasts. Some . 12a . Figure 4-14 Ribbon quartz from unit Vim , crossed n i c o l s . V e r t i c a l f i e l d 1.6mm. Figure 4-15 Polygonized quartz from unit Vim , crossed n i c o l s , V e r t i c a l f i e l d 1.8mm. Figure 4-16 I'/iyrmekite from unit VI , crossed n i c o l s . V e r t i c a l f i e l d 1.1mm. 121 porphyroclasts are rotated (figure 4-12). This rotation could result from flattening of the porphyroclasts into the foliation,or simple shear rotation of the porphyroclasts out of the foliation. Pressure shadows around the porphyroclasts are also common (figure 4-13). The aphanitic groundmass is composed in part of quartz which where strained, forms groups of elongate optically aligned grains with serrate grain boundaries (ribbon-quartz, figure 4-14) or where deformed into sub-grains, groups of subhedral unstrained optically aligned grains (polygon-ized quartz,figure 4T-15) . Biotite occurs as a fine mat of recrystallized grains. Epidote crystals are invariably zoned; outer zones could repre-sent growth during dynamic metamorphism or during M3. Myrmekite (figure 4-16) which consists of quartz rods in an albite host is common in the mylonites and generally in intrusive units which have been deformed. The myrmekitic host usually grows off a more calcic feld-spar (Baker, 1970). This texture is believed to have formed during mylon-itization of the rock by recrystallization of fine grains of feldspar and quartz (Shelly, 1964). It must have formed when the temperature was at least as high as that corresponding to greenschist facies. Mylonites not developed from unit VI have similar porphyroclastic tex-tures. These mylonites, except for those in the south (unit A m, plate A), appear to be developed from unit III. They contain muscovite porphyro-clasts which are e l l i p t i c a l and often kinked or bent (figure 4-17). Dynamic metamorphism,produced temperatures sufficient to., recrystal-l i z e quartz and biotite, and crystallize myrmekite, and therefore probably attained middle greenschist grade. The presence of chlorite which appears to have grown soon after mylonitization limits the maximum possible grade to upper greenschist. The dynamic metamorphism was contemporaneous with 122 Figure 4-17 Kinked muscovite i n mylonite derived from layered units, crossed n i c o l s . V e r t i c a l f i e l d 2.1mm. 123 slide development which occurred a.-frer phase 2, and before phase 3, (table 4-2). There are a number of possible explanations for the fact that lami-nation of unit Vim is parallel to F2 in adjacent outcrops of unit VI. The lamination could have formed^at 45 degrees to F2,by extensive simple shear in unit Vim. Alternatively, the lamination and F2 may have been formed by the same mechanism. This mechanism could be flattening within the X Y plane of a common oblate strain ellipsoid, as suggested by Ross (1973). The preservation in the mylonite zones of phase 2 i s o c l i n a l minor folds and L2 lineations indicates that within the mylonites extensive simple shear at large angles to L2 did not occur. The mylonite lamination therefore probably formed in the X Y plane of a pure shear strain e l l i p -soid. Certainly some simple shear occurred as illustrated by rotation of a few porphyroclasts. 4-11. Summary Rocks provide evidence for a metamorphic history extending from the mid-Paleozoic to the Tertiary. The f i r s t two metamorphisms5which may or may not be part of a protracted progressive event, were pre-Pennsylvanian. Locally, dynamic metamorphism is associated with the f i n a l stages of the second event which imprinted on the rocks, isograds outlining upper am-phibolite to lower greenschist facies of the Barrovian type. Because i n -trusion of unit VIII was broadly contemporaneous with phase 3, i t too, predates the Pennsylvanian, as must the contact metamorphism associated with i t . A hundred million years passed, apparently, without incident, u n t i l the J'Jwassic. Although, in the thesis area, petrographic evidence for a ,'JiUrassic metamorphism is absent, i t certainly exists elsewhere. Bearing this in mind, Rb-Sr isotope data discussed in the next section can be 124 interpreted to support the existence of a Jurassic metamorphism which was accompanied by intrusion of unit IX. The grade of this event was certainly not high, but i t provided sufficient energy to profoundly affect the isotopic history of the rocks and minerals in the. thesis -area. Another period of quiescence extended to the Tertiary, at which time a multitude of near surface events can be coordinated under the general description of a Tertiary metamorphism. Dykes were intruded, hydrothermal activity occurred and minerals were recrystallized. A grade not exceeding middle greenschist facies can be inferred from these events. 125 SECTION 5 GEOCHRONOLOGY 5-1. Introduction A protracted geologic history has been outlined in the preceding sections. Isotopic and geochemical data can help to substantiate and amplify this history in three ways. One of the simplest uses of isotopic and geochemical data is to finger-print various intrusive units. Much of the thesis area is underlain by intrusive rocks which reveal l i t t l e compositional variation yet must be separated with confidence into a number of distinctive intrusive units. Section 5-4 discusses the K , Rb and Sr geochemistry of the units and indicates how geochemical data supports division of intrusive rocks into the units described in section 2. The ^ S r / ^ S r present ratio is used as an aid in separating unit V from other intrusive units. Strontium isotopic data strengthens the discussion of the origin of some rock types. Thus in this thesis ^ S r / ^ S r i n i t i a l ratios and K/Rb ratios help in deciphering the origin of unit I (section 5-5). The third use of isotopic data is for dating. Attempts were made, with limited success, to date intrusive units VI, VII, VIII, and metasedimentary unit III. The structural history is punctuated by intrusive and metamorphic events both of which can be dated. Isotope work can provide absolute ages for these events; but in practice i t usually provides only minimum ages. These ages may s t i l l support the postulated sequence of events but they must be interpreted with care. 126 It is not surprising, considering the complexity of the geologic history within the thesis area, that the isotope data does not submit to a simple interpretation. Apparent ages,read from the data^must be explained within the context of the geologic history. If this cannot be done,and a conflict exists between the proposed geologic history (section 1 to 4) and the apparent ages calculated from isotopic data (section 5), then probably the geologic history should be reformulated. 5-2. Previous isotopic work within and adjacent to the Shuswap Terrane. Most Shuswap rocks, which occupy the core zone of the Eastern Cordilleran Fold Belt, have experienced many metamorphic and deformational events. The ages of these events probably changed from locality to locality. I n i t i a l attempts at radiometric dating of Shuswap events assumed one regionally synchronous metamorphic event. Gabrielse and Reesor. (1964) and Baadsgaard et a l . , (1961) compiled earlier mineral K-Ar ages for the Shuswap Terrane. Gabrielse et a l . concluded that the age of Shuswap metamorphism was 102 m.yr., or older. The Nelson Batholith intrudes Shuswap rocks cropping out along the eastern margin of the Eastern Cordilleran Fold Belt. Emplacement of the batholith postdates the most intense deformation and metamorphism affecting the Shuswap country rocks. Numerous K-Ar dates on micas and amphiboles from the batholith (Gabrielse et a l . , 1964) (Nguyen et a l . , 1968) range from 55 to 171 m.yr. Nguyen et a l . (1968) obtained apparent K-Ar ages on Valhalla Plutonics indistinguishable from those of the Nelson Batholith. L i t t l e - (1960) described the Valhalla Plutonics as contemporaneous and in part younger than the Batholith but abundant throughout the Shuswap Terrane. On the western flank of the Shuswap Terrane undeformed stocks that 127 intrude Shuswap rocks apparently escaped and therefore postdate the more intense deformation (phase 2 in this thesis). One of these stocks, Unit IX, has a K-Ar age of 144 m.yr. (White et a l . , 1968). Other intrusions further west of the thesis area include the Copper Mountain stock, 194 m.yr. (Preto, 1972); the Guichon Batholith, 200 m.yr. (White et a l . , 1967); the Brenda stock, 168 m.yr. (White et a l . , 1968); the Okanagan Complex, 180 m.yr. and the Similkameen Complex, 155 m.yr. (Roddick et a l . , 1972). Possible correlatives to Shuswap rocks exist in the State of Washington. Synmetamorphic actinolite from metamorphosed Permian rocks yielded a Triassic age of 190 m.yr. (Hibbard, 1971). Rinehart and Fox (1972) quote ages of 194 and 179 m.yr.for coexisting hornblende and biotite from the Loomis Pluton,which crops out 15 miles southwest of the thesis area. This pluton has discordant contacts with metamorphic rocks, assigned by them,to the Anarchist Group. Only recently have Rb-Sr techniques been applied to dating problems in the Shuswap Terrane. Menzer (1970) determined a minimum age of 129 m.yr. for a synmetamorphic orthogneiss from the Okanagan Range, Washington. Blenkinsop (1972) obtained 740 m.yr. and 240 m.yr. whole rock isochron ages from a granitic gneiss in the Revelstoke area. The gneiss (granite gneiss of Ross5 1968) cores a fold developed early in the structural succession of this area. A 58 m.yr. isochron was obtained from granitic rocks in southern British Columbia (Fairbairn et a l . , 1964). Coryell intrusives of Early Tertiary age (Fyles et a l . , 1973) crop out throughout the Shuswap Terrane ( L i t t l e , 1960). These syenitic intrusions are part of a widespread intrusive and extrusive Tertiary episode also represented by the Marron Volcanics (Mathews, 1963) which crop 128 out in the Greensood area (southern British Columbia). This Tertiary event has reset many K-Ar and fission track ages determined in geologically older rocks, for example Medford (in preparation) obtains Early Tertiary K-Ar and fission track ages for Shuswap rocks cropping out east of Okanagan Lake. In summary, K-Ar and Rb-Sr geochronologic data from within the Shuswap Terrane substantiates an Early Tertiary episode of intrusion and extrusion correlatable with M3. Shuswap rocks and mineral ages, not completely reset by this Tertiary event, are generally younger than Triassic and may be reflecting an episode of Early Jurassic deformation and metamorphism (The Columbian Orogeny). Possibly because of the effect of the Tertiary event, no pre-Pennsylvanian Caribooan ages have been obtained. 5-3. Data summary. Appendix 4A describes the theory of Rb-Sr geochronology and appendixes 2A and 3A describe the Rb-Sr analytical procedures. The atomic absorption technique for measuring K concentrations is described in appendix 5A. Single sample error bars at the 2a level are drawn in each isochron diagram. The length of the error bar corresponds to the 2o- error for samples plotted at the position of the error bar. Slopes and intercepts of isochrons were calculated using the method proposed by York (1969). In a recent paper, Brooks et a l . (1972) emphasize the difference between isochrons defined by samples that only contain experimental error and errorchrons defined by samples whose scatter about the line is greater than can be explained by experimental error alone. In this study, because of the complex geologic history, none of the 129 • TABLE 5 - I ISOTOPIC AND SAMPLE Sr / Sr Rb / Sr Rb ppm (Kn) (r) A l . 7058 .086 4,9 A2 . 7060 . 123 7.7 A3 . 7088 . 384 4] A4 . 7071 . 384 • 22 A5 15 A6 20 GEOCHEMICAL DATA ALL SAMPLES Sr ppm K % Rb / Sr K % UNIT I .165 .3 .03 610 181 .23 .043 300 309 . 8 • .13 200 166 . 5 . 13 440 171 .23 .09 152 153 .41 .13 204 S l .7156 3.854 145.6 S2 .7139 1. 308 122.0 54 . 7250 4. 356 126.9 P2 .7082 .1892 34 . 00 S5 .7115 . 8613 54 . 20 S6 . 7278 1.51.1 142. 3 S7 . 7131 1. 416 80.4 S8 .7136 2. 107 89.10 Sbl .8577 207.1 568 . 1 Sml . 7206 13.4 5 293.0 Sb2 . 7413 57.15 416 . 2 Pm2 .7106 4 . 819 232.0 Sb4 . 7937 184.4 550 Sm4 . 7335 17. 31 247.0 Sb5 . 7287 47.08 223.0 Sb7 .7177 . 10. 21 233.8 Pml2 . 7511 74.70 462. 2 UNIT III 109.4 3.2 1.3 • 220 270.0- 2.4 .45 200 86.70 3.3 1.5 260 519.6 . .9 .065 260 182 . 1 1.8 . 3 330 273. 1 1.9 . 52 134 164 . 3 3.0 .49 375 122 . 4 2.1 .73 240 8.053 7.2 71 130 63.00 11.0 47 375 21. 14 5.9 20 140 139 . 3 6 .1 1.7 260 8 . 702 5.1 63 93 41. 38 6.1 6.0 248 13.74 5.9 16 264 66 . 34 5.6 3.5 240 17.98 8.1 86 175 FI .7074 F2 .7054 F3 .7050 F4 .7066 F5 .7045 F6 ' •. .7054 F7 . 7048 F8 .7070 T9 .7045 F10 .376 63.2 .468 74.38 .296 56.27 .373 69.1 .401 63.7 .487 71.11 .474 74.6 •484 76,9 .257 54.7 62.8 UNIT V 487.3 1.8 459.8 2.4 549.3 1.6 536.2 1.7 458.9 1.6 442.8 2.1 455.3 2.2 459.7 2.1 61G.5 1.5 520.8 1.2 .13 280 .16 320 .10 280 .13 250 . 14 250. .17 . 300 .16 290 .17 . 2 7 0 .09 270 .12 190 E l • .7081 . 4707 103. 8 E2 •: . 7128 2.628 281.5 E3 .7088 .3087 79.0 E4 1.166 181.8 344.1 E5 108.2 E6 76 . 4 E7 •' * 108.4 E8 - 102.4 Eb2 ' . 7220 12.69 840 Em2' •.' .7182 8.347 658. 3 Dl ' .7186 5.022 175.1 D2 .7168 5.238 180.5 D3 . .7134 3.474 160.6 D4 . 7083 1.041 . 92.72 D5 .7079 1.188 100 . 0 D.G 138.2 Dml .7622 49.23 • 615.8 Dm2 . 7562 41.2 • 596 . 6 C l . .7070 . 142 51.1 C2 .7092 .9631 151.7 C3 .7119 • .1916 66.4 Cbl .7169 5.181 804 UNIT v i 637.8 2 .7 .16 260 310.1 3 .2 .91 1 110 740. 2 3 .0 .11 ' 380 5.72 3 .9 60 ' 113 619 . 3 1 .8 .18 167 .641.9 2.1 .12 274 609 . 6 2. .5 \ 18 231 70 3. 3 2, .7 .15 275 192 4, ,7 4.4 56 223 4 , •6 2.9 70 UNIT VII 101.0 3, .2 1.7 180 99.77 3. .6 . 1.8 200 133. 8 3. .4 1.2 210 257 . 7 2, .9 • . 36 310 243.5 2. .5 .41 250 332.2 4, .0 .42 • . i 290 36 .38 • 7. 2 17 120 42 . 09 7. 7 14- 130 UNIT VIII 1041 1. 9 .0 49 372 456 4. 4 .33 290 1003 2. 9 .066 436 449 .4 4. 8 1.8 60 130 e 131 suites of samples representing particular units define isochrons. The ages of errorchrons defined by a l l or some of the samples in each suite have been calculated using York's (1969) method. Reasonable s t a t i s t i c a l or geologic uncertainties cannot be attached to these ages. The ages provided by these errorchrons in most cases reflect the effect of at least two unique events and ,therefore,may not provide the exact age of either event. Rb-Sr analyses were made on 47 samples representing most of the units in the thesis area. An additional 5 samples from the VaseauxLake area were analysed. Analysis of another 27 samples collected from outside the thesis area are reported in Appendix 1A. In Appendix 1A are discussed, in detail, some aspects of the problems of Rb-Sr open system behaviour. Emphasis is placed on the many uncertainties involved in reading absolute ages from Rb-Sr isotope data. Location of samples collected in the thesis area are indicated in figure 5-1,and a l l analytical data for samples compiled in table 5-1. Most of the samples were analysed for ^ ^Sr/^^Sr(present) and K % and a l l were analysed for Rb ppm, and Sr ppm. In the discussion some abbreviations are made. The ratios ^ S r / ^ S r (present) and ^ S r / ^ S r (initial) are referred to as Sn and Si respectively, and the ratios ^Rb/ 86 Sr present and K/Rb are referred to as r and R respectively. The origin of these terms, in the context of the development of Rb-Sr dating equations, is explained in Appendix 4A. 5-4. Geochemistry. The simplest use for R, r, Si and-Sn ratios is for finger-printing different intrusive units. Four foliated granitic units (unit V, VI, VII, and VIII) have been separated on the basis of f i e l d data. It i s 132 133 desirable to substantiate this separation with geochemical data which may be easier than f i e l d data to evaluate. Before discussing the Rb, K and Sr geochemistry of units, i t is useful to summarize some of the background theory of Rb-K partitioning in rocks which is discussed in detail by Culbert (1972). To summarize here Rb has a slightly larger ionic radius (1.47°A) than K (1.39°A). Rb is a trace element in rocks and never forms i t s own minerals. Normal continental rocks have R values of 300 to 160 (Shaw, 1968) whereas oceanic rocks and rocks which have undergone fractional crystallization have different value's. The ranges of R values for different rock types are indicated in figure 5-2. The ratio of R for a crystal over R for a coexisting liquid is the partitioning coefficient for a crystal liquid system. This ratio is indicative of the relative preference of a crystal for K as compared to that of a liquid. Numbers greater than 1 indicate discrimination by crystals against Rb; this Rb i s concentrated in the residual liquid which w i l l later form crystals with low R values. The partitioning coefficient for two coexisting minerals is related to difference of ease with which Rb can f i t into the two crystal structures. Because of large ionic radius Rb prefers to occupy crystal sites with high atomic co-ordination numbers. For example Rb prefers the 12 fold co-ordinated K sites of micas more than the 8 fold co-ordinated K sites of amphiboles. A series of increasing Rvalues for minerals, implying increasing discrimination against Rb would be, biotite (1); muscovite (2); K feldspar (3); plagioclase (5); and amphibole (10). The numbers in brackets are relative partitioning coefficients calculated taking R for biotite as 1. This series is also • O S . FIGURE 5- + 135 in order of decreasing co-ordination number for K. Units V to VIII have a range of R and r values; Rb and K vary sympathetically sample to sample,indicating coherence of these elements. On a log Rb v log K graph (figure 5-3) most samples plot on Shaw's (1968) normal f i e l d , that is with R values in the range of 160 to 300. R values of samples from each unit (figure 5-3) tend to form clusters. Clusters for each unit partially overlap but are reasonably distinct. Obviously geochemical data supports, to some extent, f i e l d differentiation of units V to VIII. For a comagmatic series the R values of different phases usually decrease with decreasing age of the phases (Butler et a l . , 1961) . Although based of minimal data average R values for units V to VIII increase from 266 for unit V to 366 for unit VIII; a trend opposite that expected for a comagmatic series. The geochemical data cannot be used to support the suggestion that units VII or VIII are differentiated phases of unit VI. It can be inferred from the orientation of clusters for units VI, VII and VIII (figure 5-3) that low R values correlate with high Rb and K concentrations. This is normal fractionation trend for samples of each unit. The geochemical data from units VI and VIII was probably affected by the range of intensity of M2 experienced by these two units. Samples of unit VI from north of Mica Creek tend to have lower r values and higher R values than samples from south of the creek. There appears to be no correlation of R values from unit III with metamorphic grade. This implies that, in unit III, K and Rb behaved similarly during increasing metamorphic grade. The average R value of unit III is 250 (based on 8 values). This value is higher than values of 144 and 190 for shales 136 quoted by Vinogradov (1962) and Turekium and Wederpohl. (1961) respectively. On a regional scale the average Rb/Sr ratios of intrusions may be useful for identifying intrusions of a certain age. Culbert (1972) found that intrusions in the Coast Range Mountains, British Columbia, had abnormally low Rb/Sr ratios. Average Rb/Sr values for granites of 1.0,and for granodiorites of .28,have been calculated by Hurley et al.. (1962). With the exception of unit VII (average Rb/Sr = 1.01) units have Rb/Sr ratios significantly lower than these values (unit V, granodiorite, Rb/Sr = .13; unit VI, quartz monzonite, Rb/Sr = .41; unit VIII, quartz monzonite, Rb/Sr = .11). The average Rb/Sr ratio of 22 post-Jurassic granitic rocks, from southern British Columbia, is .56 (Fairbairn et a l . , 1964). Average Rb/Sr ratios significantly lower than .56,for intrusions from southern British Columbia, may be characteristic of pre-post-Jurassic intrusions. There exists here a possible way of separating Caribooan intrusives from younger intrusives. Rb/Sr data for the intrusive units is plotted in figure 5-4. The Si value of units can be used to justify separation of the units and in a discussion of their origin. Unfortunately, because of the complex isotopic history of intrusive units, l i t t l e significance can be attached to their Si values. They are unlikely to be true i n i t i a l Sr/ Sr ratios fixed at the time of crystallization of the units and should really be regarded simply as intercept ratios. The Si values of the intrusive units are given in table 5-V. The Si value for unit VIII was calculated using mineral data and therefore cannot be considered a true whole rock Si value. The apparent Si values for 137 units VI, VII, and VIII tend to be low but no overall trend is apparent. The average Si value obtained by Fairbairn et a l . 4 (1964) for post-Jurassic rocks from the Okanagan Valley is .7066 (based on 6 values). Menzer (1970) obtained Si values of .706 for an Upper Cretaceous intrusion and .704 to .708 for a., synorogenic orthogneiss (age in excess of 129 m.yr.). Apparent Si values for intrusive rocks i n the thesis area cover the range .704 to .707. No useful pattern is apparent in Si values of intrusions from the Okanagan Valley. Not much can be said about the Si geochemistry of pegmatites injected during M2. A sample of a muscovite, quartz, albite pegmatite provided a whole rock, and muscovite sample. . The isochron obtained from these two samples (figure 5-12) provided an age of 40 m.yr. and an Si value of .708- At the time of M2 (possibly Carboniferous) this Si value could have been .707. Strontium with this ratio was not available from unit V but a value of .707 is more characteristic of intrusive rocks than pelites which generally have higher S i values (see Appendix 1A). Samples of unit V have very low r values, thus their Si values have changed l i t t l e through time. In fact in 400 m.yr., Si values would 138 TADLK 5 -11 UNIT V GRANODIORITE ISOTOPIC AND GEOCIILMICAL DATA SAMPLE 8' /Zl (Sn) At (r) Rb ppm Sr ppm K % Rb/ / s r K % / • /Rb F l .7074 .376 63.2 487. 3 1 8 .13 280 F2 .7054 .468 74.38 459. 8 2 4 • 1 6 .320 T3 . 7050 .296 56.27 549. 3 1 6 .10 280 F4 . 7066 .373 69.1 5 36. 2 1 7 .13 250 F5 .7045 .401 63.7 458. 9 1 6 .14 250 F6 .7054 .487 71.11 442. 8 2 1 .17 • 300 F7 .7048 .474 74.6 455 3 2 2 .16 290 F8 .7070 . .484 76.9 459 7 2 1 .17 270 F9 .7045 .257 54.7 616 5 1 5 .09 270 F10 62.8 520 8 1 2 .12 190 F average 67 499 1 8 .13 270 F I G U R E S - 5 - «TOT8 U N I T V I S O C H R O N D I A G R A M o p p r o m m o l e m o m m u m O n 2> e r ror ..%|_ •<708P © ft o F fp 0 F 7 87 - ' S r • 7000 , | L . .2 . J i 1 1 ^ B • Sr FIGURE 6 - 6 UNIT V H I S T O G R A M OF INITIAL Sr R A T I O S » 7O0O 139 change by about .0025. Values of Sn may therefore be useful in identifying unit V, which because of i t s complex history is often d i f f i c u l t to distinguish, solely on the basis of f i e l d data, from other units. Ten whole rock samples were analysed for Rb ppm, Sr ppm. and K%. Nine of these samples were also analysed for Sn. Sample locations are plotted in figure 5-1. Data is tabulated in table 5-II and plotted in figure 5-5. Values of Sn for unit V are significantly lower than Si values for other intrusive units. This fact aids in recognition of unit V. The most frequent Sn value is in the range .7045 to .7055 but the actual distribution of Sn values is bimodal (figure 5-6). There is no correlation between location of the samples and their Sn values. It can be inferred from these low Sn values that,either unit V is considerably younger than the Carboniferous,or that i t has suffered variable Q n radiogenic Sr loss. Data for unit V does not plot on an isochron 87 (figure 5-5), so that radiogenic Sr loss can be suspected. The simplest use of isotopic data,that of labelling rock types,is exemplified by unit V. The Sn values of unit V are consistently lower than Sn values of other intrusive units. This adds credence to the separation of unit V, as a distinct intrusive unit, from units VI to VIII which are themselves separated in part on the basis of geochemical data. 5-5. Geochemistry of unit I. On the basis of petrography i t has been suggested that unit I is a meta-andesite. Isotopic data and geochemical data can help substantiate this claim, as well as strengthening speculation about the ultimate origin of andesites. The effects on samples of unit I of varying degrees of 140 TABLE -in UNIT AMPHIBOLITES S.V TLB ISOTOPIC AND GEOCHEMICAL DATA 6/ s Er ISn) / g r (r) Rb ppm Al" .7058 . A2* .7060 A3" .7088 A4* .7071 A5' .AS4" average sample .7073 amphibolite facies .086 .123 .384 .384 4.9 7.7 41 22 15 20 21.4 Sr ppm 165 181 309 166 171 153 207 samples from greenshist facies ' samples from amphibolite facies K % . 3 . 23 . 8 .5 .23 .41 .44 / s r .03 .043 .13 .13 ;09 .13 .1 K % 610 300 200 440 152 204 206 AVERAGE K AND RB CONCENTRATIONS AND Sn VALUES POR ANDESITES SAMPLE ISOTOPIC AND GEOCHEMICAL DATA ir Sr. 5 r / w / S r Sr (Sn) Andasito 7055 Calfc Alk Andosite T h o l e i i t i c Andesite V S r (r) Rb ppm 50 30 6 Sr ppm 243 385 220 K 1.25 1.29 .52 Rty / S r 250 A .430 B 890 B Ewart et a l . (L96S) Jakes et al. 6.972) F I O U R E 5 - 7 UNIT | S A M P L E S ISOCHRON D I A G R A M 141 metamorphism have also to be considered. Numerous authors have studied the K and Rb geochemistry and Sn values of basic volcanics in the context of their position with respect to the Benioff zone. In summary volcanism across an active subduction zone is characterized by a l k a l i basalts on the ocean side of the subduction zone, changing to progressively more potassic andesites on the continent side (Dickinson, 1970). Peterman et a l . . (1970), Ewart and Stipp, (1968) and Jakes and White, (1972) are three of the more recent studies of andesites. Table 5—IVrepresents a compilation of their data and values from table 5-IV are plotted in figure 5-2. The Sn values of intra-oceanic and andesitic volcanic rocks are generally similar (.7038+ .01,Dickinson, 1970). Intra-oceanic volcanic rocks generally have higher Sr ppm. and R values but lower Rb ppm and K% than volcanics on the continent side of the subduction zone. Six small (less than 1 Kg.) whole rock samples of unit I were analysed for Rb ppm , Srppm and K% and in addition four were also analysed for Sn. Data is presented in table 5-IIJand sample locations indicated in figure 5-1. Samples represent the range of metamorphism experienced by unit I. The single sample which experienced greenschist metamorphism has an Sn value too low and an R value too high for the amphibolite to have formed from a limey pelite or dolomite. The low Sn value tends, to confirm the opinion expressed in section 2 that unit I was originally a basic extrusive. Jones et a l . (1973) who measured Sn values of amphibolites concluded on the basis of low Si values of .7033 to .7068 that they formed from andesites. Comparison of tables 5-III and 5-JV indicates that on the basis of Rb and Sr concentrations and R values the 142 samples of unit I have a f f i n i t i e s with andesites found on the continental side of a subduction zone. K% content of the samples,if they represent meta-andesites, suggests proximity to a subduction zone (Dickinson, 1970). The Sn values of unit I are on the high side for andesites. Similar high Sn values of andesites in New Zealand (.7055) have been taken by Ewart and Stipp (1968) to indicate that these andesites formed by, partial assimilation of sedimentary material, by basaltic magma. The Sn values of unit I vary significantly and this variation is not related to development of an isochron (figure 5-7), but could be related to the different intensities of metamorphism suffered by the samples. The three samples metamorphosed to amphibolite facies grade during M2 have an average Sn value of .7073. If indeed variation in Sn values of unit I was caused by introduction of Sr during M2, then i t is possible to calculate the Sn value of the introduced Sr which is .7136. Strontium with this isotope ratio was probably never available from unit V which has on average low Sn values,but could have been available from unit III. Studies of thin section of samples Al, A2 and A3 suggest a correlation of high amphibole content with high R and low Rb ppm. independent of metamorphism. This is a reflection of the high R values usually associated with amphiboles. A similar correlation has been suggested by Shaw (1968) and used by Jakes and White (1972) to correlate different R values with depth of generation of andesite from the down going oceanic slab. High R values are generated at shallow depths. Geochemical data is in accord with petrographic data in indicating that unit I could originally have been an andesite. Isotopic data suggests migration into unit I of Sr enriched in a radiogenic component. This Sr was probably introduced during M2 and derived from unit III. 143 TADLE 5 - V INITIAL Sr / Sr RATIOS ( SJ ) AND AG):S TOR IHTUS.TVE UNITS UNIT Unit Unit Unit Unit Si V VI VII VIII ,705 ,706 ,706 ,707 Synkinematic s i l l . 70<i AGE 170 myr. 3.-10 rayr. 135 ir.yr. 35. inj'r. AVERAGE R b / S r .14 . .26 .98 .11 .037 TABLS 5 -V?< UNIT VW LATE OLARTZ MONZONITE SAMPLE Cl C2 C3 Cbr C average ICOVOriC AND GEOCHEMICAL DATA .7070 .7092 .'7119 ;7169 Rb ppm Sr ppm K % Rb/ / S r K « / . / s b % .142 51.1 1041 1.9 .049 372 .9631 . 151.7 456 4.4 .33 290 .1916 66.4 1003 2.9 .066 . 436 s.m 604 449.4 4.8 1.8 60 • 93 620 3.1 .11 366 FIGURE 5 - 8 UNITV/77 UATE QUARTZ MONZONITE 144 5-6. Geochronology of Intrusive units The most extensive use of isotope data is for dating. The more protracted the history of the rock analysed,the more ambiguous the story provided by the isotope data. The isotope data for intrusive units is therefore discussed in order of increasing age, that is unit VIII, then unit VII and fi n a l l y unit VI. Unit VIII was probably emplaced during phase 3. It is structurally the youngest intrusive unit dated and should therefore provide the simplest isotopic picture. Three large (greater than 5 Kg) whole rock samples were collected from unit VIII. Sample locations are indicated in figure 5-1 and analytical results presented in table 5-V/. Samples Cl and C3 are of fresh rock; sample C2 is altered material collected from near the contact with unit VI. Biotite Cb2 was separated from sample Cl. The three whole rock samples do not distribute along an isochron (figure 5-8) but a biotite,whole rock isochron can be drawn. This isochron is in reality a single mineral age analogous to a K-Ar age,which is generally also a single mineral age in which assumptions about the i n i t i a l ^Ar/~^Ar ratio are implicit. The isochron has an apparent age of 135 m.yr. and an Si value of .707. Sample C2 has suffered saussuritization and fracturing which are both probably related to, either formation of mylonites (unit VIm)y or phase 4 breccia (unit IXb). The effects of these events on the isotope data from sample C2 are unknown. Sample C3, in contrast to samples C2 and Cl, appears to be enriched in 8 7 S r . Unit VIII which postdates phase 2 and M2 has been deformed by phase 3. Thin sections indicate some cataclasis which has deformed the biotite. Metamorphism M3 must also have affected unit VIII but has not totally 145 TABLE 5 -VII SAMPLE UNIT VII... MUSCOVITE QUARTZ MONZONITE ISOTOPIC AND GEOCHEMICAL DATA -8' S5/M(Sn) *b/et (r) / S r /Sr ' Rb ppm Sr ppm K % Rb/ / S r K % Dl D2 D3 D4 D5 D6 Daverage Dml Dm2. .7186 .7168 .7134 .7083 i7079 .7622 .7562 5.022 5.238 3.474 1.041 1.188 49.23 41.2 175.1 180.5 160.6 92.72 100.0 138.2 141 615.8 596.6 101.0 99.77 133.8 257.7 243.5 332.2 195 . 36.38 42.09 3.2 3.6 3.4 2.9 2 .5 4 3 .3 7.2 7.7 1.7 1.8 1.2 • 36 .41 .42 .98 17 .14 180 200 210 .310 250 290 240 120 130 146 recrystallized the biotite. The 135 m.yr. age of unit VIII is therefore a minimum age of crystallization which has suffered an unknown amount of updating by M3. The Si value of the isochron i s not necessarily the i n i t i a l 87 86 Sr/ Sr ratio of sample Cl, 135 m.yr. ago. In a l l probability 87 updating of the biotite occurred by loss of radiogenic Sr, causing the plotted sample position Cbl to move steeply down to the l e f t (figure 5-8). This i n turn produces an arbitrary intercept ratio of the line Cbl to Cl, which is higher than the original Si intercept. Unit VII was emplaced during the f i n a l stages of phase 2 and therefore has experienced at least two events (phase 2 and M3) subsequent to i t s crystallization. Samples from unit VII analysed include three large (greater than 5 Kg) samples, D2, D3 and D4 and two small (less than 1 Kg) samples, Dl and D5. Two muscovites separates^Dial and DTI12, were obtained from sample D2. Data for samples,plus an additional two not analysed for Sn} is presented in table 5-VJJ. Isotopic data is plotted in figure 5-9. Consideration of single sample errors indicates that samples D4, D3 and D2 distribute along an isochron,but the whole suite of sample, points (Dl to D5) distribute along an errorchron. The isochron defined by the three large sample points D2, D3 and D4 has an age of 138 m.yr. and an Sn of .706. The errorchron defined by the whole suite has an age of 168 m.yr. Individual ages of Dml and Dm2, calculated using D2 their parent rock,are 70 m.yr. and 73 m.yr. respectively. Samples of unit VII have experienced isotopic open system behaviour. 87 Apparent ages of muscovites Dml and Dm2 have been lowered by Sr loss 147 (addition of Rb is unlikely; see Appendix LA), whereas whole rock 87 samples have retained older ages. If Sr was lost from muscovites during a single period of isotope migration }then this event occurred in the time range 70 to 0 m.yr. and was probably M3. The more recent 8 7 the event the less the percentage of total Sr lost from the muscovites. 87 Sr lost by the muscovites probably was partially incorporated in feldspars. Appendix 1A discusses: this type of migration. If migration of ^ S r i n t o feldspars has occurred, then small whole rock samples with unrepresentatively high feldspar contents should 87 have gained Sr during the migration event, and small whole rock samples with unrepresentatively high muscovite contents should have lost radiogenic Q 7 Sr. Small whole rock sample points DI and D5 in fact do scatter from the isochron drawn through the larger whole rock sample points D2, D3 and D4. The above argument j u s t i f i e s using the isochron drawn through these three large sample points to provide the best estimate of the whole rock age^ rather than using the errorchron drawn through a l l the sample points. Retention of the D2 to D4 isochron implies that M3 caused open 8 7 system behaviour of Sr in minerals and small rock samples, but did not affect the isotopic make up of larger whole rock samples which s t i l l register a 140 m.yr. age. If open system behaviour occurred approximately 70 m.yr. ago, then for the time span 140 m.yr. to 70 m.yr. the Sn value for sample D2 developed from .706 to .7115; (.706 is the Si value for the 140 m.yr. isochron, and .7115 is the Si value for the 71.5 m.yr. muscovite mineral isochron). This is a change of Si values of .0055. The calculated change in the Sn value for sample D2, using the Rb and Sr 148 .TADLli 5 -VIII •' UNIT V I BIOTITE QUARTZ MONZONITE ISOTOPIC AND GEOCHEMICAL DATA . SAMPLE J' / S r <8«> ^ ' ( r ) Rb ppm Sr ppm K El .7081 / .4707 . . 103.8 637.8 2.7 E2. .7128 .; 2.628 , 281.5 310.1 3; 2 E3 .7088 .3087 :' \ 79.0 . 740.2 •3.0 E4 • / 181.8 344 .1 . 5.72 3,9 E5 108.2 619.3 . 1.8 E6 ' vi 76.4 641.9 2.1 E7 108.4 609.6 2.5 re 102.4 703.3 2.7 Eaverago 150 608 2.8 Eb2 .7220 12.69 840 192 * • 4.7 tn2 i7183 8*347 ' 658.3 223 4.6 Rb/ / s r .16 .91 .11 60 .18 .12 .18 ;i5 .41 4.4 2.9 K % 260 •110 380 113 167 274 231 275 242 56 70 149 concentrations of sample D2 and time span 70 m.yr. is .005. Agreement between predicted and calculated increments of Sn supports a model of complete re-equilibration 140 m.yr. ago and temporary open system behaviour of minerals, leading to near complete re-equilibration of the minerals, 70 m.yr. ago. The 140 m.yr. age, in that i t appears to represent a near complete setting of the whole rock Rb-Sr clock, may represent crystallization of unit VII. On the other hand,structural data indicates that unit VII was emplaced into i t s present position before the end of phase 2;which is pre-mid-Carboniferous (Ross and Barnes, 1973). The 140 m.yr. age may be evidence of a thermal event not represented by metamorphisms Ml, M2 or M3. This important thesis is developed in section 5-9. Unit VI predates unit VII and has therefore experienced a more protracted geologic history which is reflected in i t s isotopic data. Unit VI suffered differing intensities of metamorphism during M2, and samples were collected from a l l metamorphic grades. Four large (greater than 5 Kg) whole rock samples El to E4 were analysed for Rb ppm., Sr ppm and Sn. Biotite Eb2 and muscovite Em2 were separated from sample E2. Additional samples E5, E6, E7 and E8 were analysed for Rb ppm Sr ppm and K%. Analytical data is tabulated in table 5-Wand plotted in figure 5-10. Whole rock sample points El to E4 scatter along a 171 m.yr. errorchron which has an Si value of .707. If sample E3 is omitted and samples E l , E2 and E4 used to define a three point isochron, then the age remains unchanged but a lower Si value of .706 is obtained. It is this isochron which is actually drawn in figure 5-10. The isochron age is heavily weighted by sample E4, an alaskitic phase of unit VI. Minerals 150 TAHI .1J 5 - IX S A M P L E SI S2 P2 S4 S5 S6 S7 S8 S b l Sml • Sb2 Pm2 Sb4 Srn4 SbS Sb6 Pm6 Sb7 Pml2 UNIT I I I :pE{,lrB ISOTOPIC AND GEOCHEMICAL DATA tr tr 1 / S r (Sn) ( r ) Rb ppm Sr ppm K % R b / / S r K » / .7156 .7139 '• . 7082 3.854 1.308 ' .1892 145.6 122 34 109.4 270 519.6 3.2 2.4 . 9 1/3 .45 .065 220 200 . 260 . 7250 .7135 4.356 . .8613 126.9 51. 2 86.7 182.1 273.1 3.3 1.5 260 . 7278 1.511 142.3. 1. 8 1.9 • .3 .52 330 134 . 7131 .7136 . 8577 1.416 2.107 207.1 80.4 89.1 568.1 164 . 3 122.4 8.053 3.0 2.1 7.2 .49 .73 71 ' 375 240 130 . 7206 .7413 .7106 13.45 57.15 4.819 293 416.2 232.0 63.0 21.14 139.3 11.0 5.9 6.1 . 47 20.0 1-7 375 140 260 . 7937 .7335 . 7287 184.4 . 17.31. 47.08 550 247 223 467 8.702 41.38 13.73 5.1 6.1 5.9 •> c 63 6.0 16 93 246 264 .7177 .7511 1894 77 ' . 10.21 74 .7 . 233.8 462.2 66.34 17.98 6. 8 5.6 8.1 3.5 .85.71 360 240 . 175 TABLE MINERAL AND ISOCHRON AGES FROM UNIT I I I ' Whole r o c k . M u s c o v i t e . B i o t i t e . P e g m a t i t i c m u s c o v i t e . Average age FIGURE •7300 50 £0 • 35 40 55 ' 45 25 40 50 25 45 35 52.5 .52.5 33 40 5 - / / UNIT Ml W H O L E R O C K S A M P L E S Isochron d . o g r o m Rb * (R) 17 S r '86 S r o p p r o x i m o t e m o x i m u m : 2 t r e f r ° r . .%L_ 3-% 0 S 4 V - 7 2 0 0 S Z r e f e r e n c e . s o c h r o n ^ n ^ -SI •7/0O S 5 0 S 7 'SO 87 Rb S r 151 Em2 and Eb2 def ine a 62 m.yr. minera l isochron which p r o j e c t s through parent rock sample point E2. The isotopic h i s t o r y of un i t VI i s s i m i l a r to that of un i t V I I , except that whole rock data for un i t VI i s more s c a t t e r e d . Again the ac tua l d i f f e r e n c e of the S i values of the whole rock and minera l isochrons fo r un i t VI i s s i m i l a r to the d i f f e r e n c e c a l c u l a t e d us ing the d i f f e r e n c e i n age of the two isochrons and composit ion of sample E2. A model of near complete r e - e q u i l i b r a t i o n of minerals 60 m.yr. ago i s supported. It i s u n l i k e l y that the 170 m.yr. age i s the age of c r y s t a l l i z a t i o n of un i t VI . It could approximate the age of some l a t e r J u r a s s i c event which a lso a f fec ted un i t VI I . The un i t VI minera l isochron evidences a T e r t i a r y event probably M3. In t rus ive un i ts VII and VI have at l e a s t two stage i s o t o p i c h i s t o r i e s . Minera ls from both i n t r u s i o n s r e g i s t e r a T e r t i a r y event whereas whole rocks appear to r e g i s t e r a J u r a s s i c event. B i o t i t e from i n t r u s i v e un i t VII I a l s o p o s s i b l y r e g i s t e r s t h i s e a r l i e r event . A l l these ages are co-ord inated with the postu la ted geo log ic h i s t o r y i n s e c t i o n 5-9. 5-7 . Geochronology of the metasedimentary u n i t I I I I so top ic data .obtained from metasediments may provide the age o f , the provenance, sedimentat ion, or of subsequent metamorphism (Appendix 1A). Data fo r uni t I I I , i n accord with data from i n t r u s i v e u n i t s , dates an Ear ly T e r t i a r y event and can be in te rp re ted to imply the ex is tence of an e a r l i e r J u r a s s i c event . No ages o lder than J u r a s s i c can be read from the da ta . Whole rock samples of un i t III were c o l l e c t e d 152 153 -from a l l metamorphic grades. Micas were separated from some of these samples. Analytical data is tabulated in table 5-IX and sample locations plotted in figure 5-1. If the two sample points S6 and S4 are ignored, then a 76 m.yr. errorchron can be drawn through the rest of the whole rock sample points (figure 5-11). Samples Sl and S2 were collected from adjacent outcrops less than 1000 f t apart as were samples S7 and S8. If each pair (S1-S2 and S7-S8) is used to define a two point isochron then ages of 50 and 55 m.yr. are obtained for the two isochrons(figure 5-12). Thus i t appears that whole rock samples of unit III exhibit inconclusive evidence of the Early Tertiary event (M3). Adjacent volumes of unit III appear to have been re-equilibrated during M3,that is isotopically reset to the same Tertiary Si value. This re-equilibration has affected low grade as well as high grade metamorphic samples and has operated over distances of up to 1000 f t . Isotopic re-equilibration caused widely separated outcrops to provide isochrons of similar ages but different Si values. Similar re-equilibration of sediment volumes has been demonstrated in Belt-Purcell a r g i l l i t e s (Appendix IA). Sediment volume (S7+S8) represented by samples S7 and S8 had an Si value of .712,50 m.yr. ago (the Si value for the S7 to S8 isochron; figure 5-12). If the data for samples S7 plus S8 is used to provide average Rb and Sr concentrations for sediment volume (S7+S8), then to a f i r s t approximation the isotopic values 50 m.yr. ago for sediment volume (S7+S8) can be plotted on an isochron diagram. If this i s done for S7 plus S8,and also Sl plus S2 (figure 5-13), a second two point isochron is obtained that extends back to the time when a l l samples of unit III 154 F I G U R E 6 - / 5 UNIT III M I N E R A L 8 A H P L E ISOCHRON D I A G R A M f 7 2 0 0 155 (represented by widely separated samples Sl plus S2 and S7 plus S8) had the same Si value. An age of 80 m.yr. for this second isochron sets the time of pre-Tertiary equilibration of unit III at 50+80 m.yr. = 130 m.yr. The above analysis is theoretically correct but with so l i t t l e data results can only be considered an extremely crude approximation. Nevertheless,an age of 130 m.yr. is in reasonable agreement with the age of the Early Jurassic event,suggested by the isotopic data of intrusive units VI, VII and VIII. In contrast to igneous micas,metamorphic micas may crystallize or recrystallize incorporating strontium whose isotopic ratio is not the same as that of their parent rock. Some value of Si has to be assumed, i f an age is to be calculated from isotopic data of a metamorphic mica. Ages of biotites and muscovites from unit III have been calculated from two point isochrons drawn through the mica and parent sample points. In two cases biotite ages are calculated from biotite, muscovite isochrons. The Si value of two mica isochrons i s probably a better estimate of the real i n i t i a l Sr ratio of the micas than is the Si value of a mica parent rock isochron. This is because the micas probably incorporated Sr with the same Si value during their crystallization or recrystallization. Mica isochrons are drawn in figures 5-14 and 5-15 and data for these isochrons -is tabulated in table 5-X J. The muscovites from unit III have an average apparent age of 52.5 m.yr.} whereas the average pegmatite mica age is slightly younger (40 m.yr.) and the average age of biotites (33 m.yr.) is youngest (table 5-X.)). Obviously micas register the Early Tertiary event M3. An obvious explanation of the spread- in ages is 87 incomplete re-equilibration by M3 and radiogenic Sr loss from some micas subsequent to M3. 156 TABLE 5 -*l I G N E O U S AND M E T A M O R P H I C S A M P L E S TROM .NORTH OF T H E M A P AREA SAMPLE I S O T O P I C A N D G E O C H E M I C A L D A T A SXr" «n> - (r, Ro ppm Sr ppra K * / S r S9 SLO SmIO S U G I Cbl .7673 . 7467 .76*0 .704 1 .7058 2.039 3.683 23.21 .1075 2.826 116.1 148.7 310.3 85.2 28.9 256.2 165.7 117 38. 89 918. 4-777 .3 262.2 2.3 3.5 3.3 1.1 5.9 .7 1.3 6--.093 .037 .98 .200 235 387 230 r- « 8 0 O 0 87 F I G U R E 5 - / 6 S A M P L E S FROM THE V A S E A U X L A K E A R E A somples locations figure 6-4 ISOCHRON D I A G R A M S • • A S C H I S T 5 r / , 2 o- error / S r • ! % ' -3-% S9 • 7 5 0 0 in ierce£!_ Sm 10 • SIO 87 Rb '86 Sr •7 250 10 —i . 15 20 ( 25 •7100 SYN K I N EM A TI C Q U A R T Z M O N Z O N I T E SJ-LL 87 Sr ^86 Sr -7 050 he — Gl intercept '70 4 v 3 5 m.yr. 2 cr e rror 3-% Gbl •7000 •5 Rb / ' S r I'5 2- 2-5 i 157 The precise age of M3 is probably indicated best by the K-Ar ages. A pegmatite muscovite (sample Pm6) in the thesis area has an age of 48 m.yr., and basic dykes in the Oliver area have ages of 44 m.yr. (Ross and Barnes, 1973). An age of approximately 45 m.yr. for M3 is significantly lower than the mineral ages of units VI, VII and VIII. Unit III provides no substantial isotopic evidence for any events older than M3. It appears that metasediments and metasedimentary minerals are less resistant to updating than intrusive rocks and minerals. 5-8. Geochronology of the Vaseaux Lake area. In order to see whether an age pattern similar to that in the thesis area exists in Shuswap rocks to the north, five samples were collected and analysed from the Vaseaux Lake area mapped by Ross (1973) and Christie (1973). The location of these five samples is indicated in figure 6-3 and analytical data tabulated in table 5-XI . Two whole rock samples (S9 and S10) and muscovite sample SmlO were collected from an outcrop of quartz mica schist. This schist outlines a phase 2 fold cored by a concordant synkinematic phase 2 quartz monzonite sill,which provided rock sample Gl and biotite sample Gbl. A parent rock, muscovite isochron age of 60 m.yr. obtained from the schist (figure 5-16A), is similar to metasedimentary ages from the thesis area; however the schist whole rock samples (S10 and S9) have higher Sn values than samples of unit III. The isotopic data therefore does not provide grounds for suggesting that the two p e l i t i c units are stratigraph-i c a l l y equivalent. A biotite, parent rock isochron for the s i l l has an age of 35 m.yr. 158 and an Si value of .704 (figure 5-16B). Low r values for samples Gl and GB1 produce large errors in this age. Rb-Sr analyses of samples from north of the thesis area indicate that effects of the Tertiary event (M3) are registered by Rb-Sr data at least as far north as the Vaseaux Lake area. 5-9. Isotopic and geologic data synthesis. In this subsection ages resulting from the interpretation of the isotope data are co-ordinated with the structural and metamorphic history described in the previous sections. The geologic history is composed in part of intrusive,metamorphic and deformational events. Rb-Sr geochronology is capable of dating the f i r s t two events but,only in specific circumstances such as dating of mylonites (Abbott, 1972) can Rb-Sr geochronology data a phase of deformation. No isotope analyses were made of mylonites during this study. Phases of deformation are therefore dated indirectly by relating them to an intrusive or metamorphic event. Intrusive activity accompanied the three metamorphisms Ml, M2 and M3. Rb-Sr work dates the youngest metamorphism M3 as Early Tertiary. Metamorphism M3 was accompanied by intrusion of syenites and extrusion of basic volcanics outside the thesis area, and by intrusion of lamprophre dykes in the thesis area. Phase 4 which accompanied M3 is therefore dated as Early Tertiary. Most mineral ages have been reset by M3, in other words they lost a l l 87 of their accumulated radiogenic Sr during M3 which reached middle greenschist facies. An average age of 45 m.yr. for M3 can be inferred from analyses of micas from unit III. Micas from intrusive units have 159 older ages of 60 to 73 m.yr. The difference between igneous and metamorphic mica ages is considered to be caused by incomplete re-equilibration of igneous micas and updating of the ages of micas from unit III subsequent to M3. The difference of ages cannot be taken as evidence for a distinct Late Cretaceous event. Phase 2 accompanied M2. Based on the unconformity mapped by Ross and Barnes (1973), phases 1 and 2 and intrusive units V, VII, and VIII are a l l older than the mid-Carboniferous. Isotope ages are a l l much younger than mid-Carboniferous and therefore do not date M2. Apparent whole rock ages of units VI and VII are 170 m.yr. and 140 m.yr. respectively. A Jurassic event i s suggested by these ages. Structural and petrographic data from the thesis area provides no evidence for a metamorphic or structural event in the time interval M2 to M3 which brackets the Jurassic. If units VI, VII and VIII are older than mid-Carboniferous then either M3 accounted for over 50% loss 87 of radiogenic Sr from whole rock.samples of units VI and VII, or there is a Jurassic metamorphism which affected these whole rock samples. Sample data from unit VHdefines an isochron composed of sample points D2, D3 and D4. This linear array is more lik e l y to be formed by 87 complete flushing of a l l radiogenic Sr 140 m.yr. ago than by partial 87 loss of radiogenic Sr during M3. Complete re-equilibration of rocks and minerals in the Jurassic is also suggested by the correspondence of the biotite age of unit VIII with the whole rock age of unit III. More indirect evidence supporting the existence of a Jurassic metamorphism can be found. Unit IX has a K-Ar age of 144 m.yr. (White et al.,1968). It i s unlikely that M3 would reset Rb-Sr Caribooan whole rock isochrons and update K-Ar mineral ages to the same intermediate age. 160 A more plausible suggestion is that unit IX was intruded about 144 m.yr. ago (somewhat older after adjusting for the effects of M3). Intrusion of unit IX is responsible for, or is the expression of, a more regional metamorphic event which reset whole rock ages of units VI, VII and VIII. The K-Ar sample of unit IX was collected from west of the Okanagan Valley and may therefore come from an area which experienced a lower intensity of M3 metamorphism than the thesis area. If this is true i t complicates the above argument. In summary Rb-Sr mineral isotope data dates M3 and hence by inference the contemporaneous deformation, phase 4. Based on structural correlations M2 and phases 1, 2 and 3 have to be pre-mid-Carboniferous. The Jurassic whole rock isotope ages of units VI, and VII, and the mineral age of unit VIII may be imaginary formed by partial updating caused by M3, or real ages dating a Jurassic metamorphism. There is considerable evidence outside the thesis area for a Jurassic, Columbian Orogeny affecting Shuswap rocks. In the thesis area unit IX can be equated with the Columbian Orogeny, but there remains an embarrassing lack of structural or petrographic data to equate with this Jurassic Orogeny. FIGURE 6 - 1 GENERALIZED NORTH SOUTH SECTION THESIS AREA Rock types F igures |" " y | late intrusives}^] r^ la | ; ; ;| phase 3 « IVIli) [ 7 ^ 1 P f « « e 2 » (vy) [::::! phose i » Cv) r > P . I t — V J N mt to B G d • monts | oiher then pMifa] AV\ (tld 4 oxiol m r f o c e traces | phac«s 3 and 4 ^ • ^ p f c o i e 2 „* pfi c « « i FIGURE 6-2 NORTH SOUTH SKETCH S E C T I O N SOUTHERN OKANAGAN ^ " V V V e / < ' V * / e / w , / ^ . / v esit ot Voiaui lake 0 Miles I e c u of Oioycci toko (Tl 162 SECTION 6 DISCUSSION 6-1. Introduction Four layered rock units have been defined and described, and four sets of macroscopic folds have been outlined. Mesoscopic structural data has permitted ordering of these sets in time, leading to the de-scription of four distinct phases of deformation. Penetrative defor-mation was followed by fracturing. Rocks in the thesis area have experienced differing intensities of metamorphism. The f i n a l metamorphic character of the rocks is the sum-mation of effects originating from three, possibly four separate meta-morphisms. It can be inferred from petrographic data that Ml was coin-cident with phase 1, M2 was coincident with phase 2 and M3 was coinci-dent with phase 4. The most intense metamorphism, (M2)^  formed a series of closely spaced isograds that strike across the structural trends of the contemporaneous phase 2. and across the trend of layered units. Isotopic data can be more easily explained i f another metamorphism is postulated. This metamorphism has not been dated but i t might be expected to be mid-Jurassic in age. 6-2. Structural synthesis The f i r s t step to unravelling the structure is to remove the effect of the slides from the generalized section 6-1 which represents the northern half of the thesis area. A number of phase 1 and 2 folds separated by slides are depicted in section 6-1 in which units I to IV are combined. The section is not complicated by open folds that belong to phases 3 and 4. Displacement along the slides towards the southwest can be inferred i f the layered units are considered to form part of a 163 single band now disrupted by movement along the slides. As discussed in section 4 the mylonites that occupy the sites of the slides were probably formed largely by flattening, however, some displacement along the slides is indicated by rotation of porphyroclasts in the mylonites. When segments of layered rock are moved back.along the slides so as to make, as far as possible, a continuous band, then three southwest verging phase 2 antiforms dominate the section (figure 6-1). The lowest is represented by trace 2b which is separated from the struc-turally higher antiform 2a, by a phase 2 synform that has been com-pletely removed by slide Sa (figure 6-1). The third antiform, re-presented by trace 2d, is separated from antiform 2a by at least syn-form 2c and possibly three slides (Sd, Sc and Sb). The slide Sd, pos-tulated to separate antiform 2a from fold l a , may have removed a phase 2 synform in the same manner as slide- Sa. It is now possible to visualize more accurately the structural position of intrusive unit VI, which forms conformable contacts with the layered rocks over most of the area. It is apparent from plate A that i t contacts both unit I and III and was therefore not intruded into a particular stratigraphic level during development of phase 2 folds. It appears 'that unit VI was emplaced into the country rock as s i l l s , either during or just before phase 2 deformation. It is clear from figure 6-1 that unit VI predominates at higher structural levels. On the basis of present orientation, the three phase 2 traces, 2a, 2b and 2d, represent antiforms. In order to derive a structural succes-sion these antiforms are unfolded so that rocks in their cores are struc-turally lowest. This unfolding is done by rotating the limbs open to 164 F I G U R E 6-3 Diagramatic i l l u s t r a t i o n of early structures ' "and location of structural succession sections a S tlructurol tucsoesion soction " .. . olso locotod in ( i g u r o Z - l 165 compensate for parallel phase 2 folding. The location of phase 1 folds, with respect to the phase 2 folds, is depicted diagramatically in figure 6-3. Phase 1 fold la is probably separated from fold lb by two slides and two missing phase 2 synforms, but i t is possible to unfold these phase 2 structures so that folds la and lb form a single antiform. Fold Id becomes part of synform l c when phase 2 antiform 2b is unfolded. Thus, after unfolding phase 2 struc-tures, a phase 1 antiform-synform pair is formed in which the antiform is cored by unit I. Amphibolite is restricted to the base of the structural succession except on the lowest limb of fold lc where a second segment of amphibo-l i t e (unit IV) overlies unit III. The predominance of amphibolite struc-turally below unit III might suggest that unit IV is a segment of unit I and that i t s structural position has not been correctly interpreted. Cer-tainly this is possible, but the simpler expedient of forming another unit (unit IV) has been followed. Phase 1 lineation trends are not sufficiently defined to permit detailed discussion of phase 1 orientation prior to phase 2. Unit V generally contacts unit I and cores phase 1 antiforms, a l -though i t is not restricted to these structural positions and could hot therefore have been basement to the sediments. It was probably intruded in part as s i l l s during phase 1. It can be inferred from petrographic and geochemical data that units V and VI are distinct intrusions rather than unit VI being a differentiated phase of unit V. This inference is in accord with the structural history described in section 2 which suggests than an unconformity was created after emplacement of unit V and before emplacement of unit VI. The regional ex-tent of this unfonformity is unknown. Unit VII, whose structural position 166 167 along slides is simple, could be a differentiated phase of unit VI. The relative volumes of the two units support such a suggestion although the geochemical data does not. Unit VIII, whose contacts in areas that experienced high grade metamorphism during M2 are broadly conformable, is distinguished from unit VII by i t s high Sr content (section 5). It appears unlikely that unit VIII is another and later phase differen-tiatedfrom unit VI; in fact, unit VIII is geochemically more like the phase 2 synkinematic s i l l mapped by Christie (1973) (section 5-9). 6-3. Structural synthesis for the southern Okanagan Valley. Three areas adjacent to the thesis area have been mapped in detail. To the west Okulitch (1970) mapped the Mt. Kobau region. On the north, Christie (1973) mapped and area east of Vaseaux Lake,and Ross (1973) has mapped west of Vaseaux Lake. Figure 6-4 covers parts of these areas and illustrates the general geology of the region. It is on the same scale and overlaps the northern end of figure 3-1. Some of the contacts and axial traced in figure 6-4 have been extrapolated between the various areas by the present author. Not included in figure 6-4, are two areas mapped by the author; one contains part of the Shoemaker Formation six miles southwest of Keremeos and another, contains part of the Hedley Group near Hedley, British Columbia. Some general comments can be made about the regional geology. Folds similar to phase 2 and 3 folds in the thesis area, can be identified in the high grade metamorphic rocks mapped by Ross (1973) and Christie (1973) north of the thesis area near Vaseau Lake. These folds are illustrated in figure 6-4 in which trace numbers refer to phases as recognized in the thesis area. They are also illustrated in figure 6-2 which is a north-south cross section extending along the eastern side of the Okanagan Valley. 168 The o r i e n t a t i o n and s t y l e of these f o l d s from north of the t h e s i s area j u s t i f i e s r e l a t i n g them to phase 2 and 3 f o l d s as defined i n the t h e s i s area. Rocks west of the t h e s i s area mapped by Bostock (1939) as Kobau, Shoemaker and Old Tom Formations are g e n e r a l l y of low metamorphic grade. North of Keremeos, Ross and Barnes, (1973) demonstrated the l a t t e r two formations experienced pre-mid-Carboniferous deformation s i m i l a r to that of rocks i n the Vaseaux Lake area and apparently equivalent to phases 2 and 3 i n the t h e s i s area. S i x miles southwest of Keremeos Shoemaker rock s , apparently s t r u c t u r a l l y e q uivalent to those mapped by Ross and Barnes, ex-h i b i t northeast t r e n d i n g i s o c l i n a l recumbent f o l d s , a l s o probably equiva-v a l e n t to phase 2 f o l d s . These f o l d s are r e f o l d e d by open upright f o l d s t rending northeast which may be equivalent to phase 3 f o l d s but have d i f -f e r e n t o r i e n t a t i o n s . Further to the west at Hedley, the Hedley Formation, which i s known to be T r i a s s i c (Bostock, 1940) doffi not cont a i n i s o c l i n a l r e -cumbent f o l d s t r e n d i n g northwest. Apparently phase 2 can be i d e n t i f i e d west of Keremeos i n rocks o l d e r than mid-Carboniferous. The two phase 3 synforms ( f i g u r e 6-4) appear to r e s u l t from i n t r u s i o n of a southward d i p p i n g sla b of u n i t V I I I . The most n o r t h e r l y phase 3 syn-form i s overturned to the south and r e f o l d s an e a r l i e r phase 2 f o l d which o r i g i n a l l y closed to the southwest. The most so u t h e r l y phase 3 f o l d s , which i s an open upright synform ( t r a c e 3a i n the t h e s i s a r e a ) , marks the southernmost contact of the slab of phase 3 i n t r u s i v e ( u n i t V I I ) . I t appears from the form of these phase 3 f o l d s ( f i g u r e 6-2) that the slab has pushed i t s way upwards through s t r u c t u r a l l y lower phase 2 f o l d s to the south and folded the higher phase 2 f o l d s to the north. The p o s s i b i l i t y that f o l d s i n the north are s t r u c t u r a l l y higher than 169 folds in the south has important implications It does not necessarily mean that rocks to the south are lower in the structural succession but i t certainly suggests i t . If rocks to the south are structurally older than rocks in the north then they must have experienced the earliest deformation evident in rocks to the north. This deformation is phase 1 which is well documented in rocks around Vaseaux Lake (Christie, 1973) but not so well documented in the thesis area. If rocks in the thesis area are structurally older han rocks near VaseauxLake, then they must also be structurally older than Kobau Group rocks that crop out on the west flank of the Okanagan Valley. These rocks mapped by Okulitch (1970) do not contain phase 1 folds. Rocks in the thesis area should therefore project structurally below rocks in the Mt. Kobau area. Okulitch mapped folds belonging to three phases. Folds of the f i r s t phase resemble phase 2 folds in the thesis area, in style and orientation. Of the three earliest nappes described by Okulitch (1969). the synformal nappe No. 2 closes in the same direction as fold 2a and is a possible correlative of i t . The axial trace of this nappe however appears to crop out topographically about 1500 f t . (455 m.) above the axial trace of fold 2a. The relationship between the two traces is confused by later folds and the absence of outcrops in the Okanagan Valley. Rocks in the Mt. Kobau area may overlie rocks in the thesis area but the data in inconclusive. Later structures in the Mt. Kobau area can be correlated with struc-tures in the thesis area. An overturned synform denoted as phase 2 Okulitch (1969) appears to be continuous in the thesis area with synorm 3a which is upright. The two folds are represented by the single most southerly phase 3 trace in figure 6-4. The tightening of this fold to 170 the west could be explained by i t s position between the Fairview and Oliver Stocks mapped by Okulitch (1970). The antiform, mapped by Okulitch complementary to this phase 3 synform (3a), either opens out or projects down the Okanagan Valley parallel to phase 4 trace 4a as inferred in figure 6-4. In summary, phase 2 in the thesis area represents an event that can be recognized in rocks of the appropriate age, cropping out in the rest of the southern Okanagan Valley. Unfortunately, specific phase 2 traces cannot be projected from the thesis area into adjoining areas. The style of macroscopic phase 2 folds in the Mt. Kobau area, where the grade of metamorphism that accompanied phase 2 did not exceed middle greenschist facies, is similar to the style of phase 2 folds in the northern part of the thesis area where the metamorphic grade was higher. Thus, there were not drastic changes in style or orientation of phase 2 folds with the decrease in metamorphic grade. Some phase 3 folds appear to be the results of, or at least were closed up by, intrusion of a slab of unit VII. To the north and under the slab axial surfaces of phase 3 folds are overturned, and the folds are similar in style. To the south and above the slab phase 3 folds are upright, parallel in style and accompanied by crenulation cleavages. Phase 3 folds exist in areas where no rock equivalent to unit VIII has been mapped. These folds are identified in the Keremeos area (Ross and Barnes, 1973) and in the area mapped by Okulitch (1970). Open northwest trending folds southwest of Keremeos may be phase 3 structures. Obvious-ly phase 3 deformation was not a l l caused by intrusion of unit VII and equivalent rocks. 171 It can be inferred from the distribution of intrusives of different relative ages, and the form of a generalized north-south section, that rocks in the thesis area are structurally lower than rocks in the Vaseaux Lake area. The most prominent fold in the thesis area (phase 2 fold 2a) appears to project significantly below i t s most likely counterpart in the Mt. Kobau area to the West. 6-4. Regional syntheses. A coherent picture of the deformation history of the southern Oka-nagan Valley has been described. Projecting onto a larger stage, local events which contributed to this deformational history can be related to events comprising the tectonic history of British Columbia. Many authors have stressed the relationship between subduction and such geologic c r i -teria as upli f t in the arc-trench gap, andesitic arc volcanism, thrust faulting, and formation of paired metamorphic belts. Dickinson (1970) summarized geologic c r i t e r i a for plate tectonic events using examples from the western U.S.A. The youngest events documented in the southern Okanagan Valley are represented in the thesis area by phase 4 folding, phase 5 fracturing and M3, the age of which is established at about 45 m.yr. These events are part of the Laramide Orogeny, of Late Cretaceous to Early Tertiary age (Douglas, 1970). This Orogeny caused thrusting in the Rocky Mountains, and to the west of the Rockies, extensive north-south normal faulting, intrusion and open folding. The Coast Mountains Batholithic Complex experienced upl i f t during the Laramide Orogeny (Culbert, 1971) and meogeoclinal Upper Jurassic and older sediments were thrust eastwards from the area now occupied by the 172 core zone of the Eastern Cordilleran Fold Belt (Price, 1970). These regional Laramide events predate Eocene or Oligocene basic volcanics (unit X in the thesis area), which rest unconformably on Shuswap rocks in the southern Okanagan Valley ( L i t t l e , 1961). Extrusion of the Eocene calcalkaline or acid volcanics was followed in the Miocene by extrusion of olivine basalts. Souther (19 70) suggested that this change of extrusive rock type is related to a succession of subduction to the west. The plate tectonic model of Atwater (1970) proposes sub-duction off the southern coast of British Columbia, most recently of the Juan de Fuca Plate and in Mid-Tertiary times of the Farallon Plate. In the U.S.A. migration of a transform fault-continental plate inter-section point both up and down the west coast caused the end of sub-duction at different latitudes at different times. Cessation of sub-duction off the west coast of the U.S.A. is evident in the change from andesitic to basaltic volcanism within the continental plate (Christi-ansen and Lipman, 1972) in accord with the suggestion of Souther (1970). In terms of plate tectonics, the Laramide Orogeny appears to be the superficial expression of subduction off the west coast of Vancouver Island. The north-south trend of phase 4 folding and phase 5 fracturing is characteristic of Tertiary Laramide deformation throughout much of the Cordillera and probably parallels the average trend of the uplifting continental margin. The deformation occurred as the margin was uplifted. Relative to the Tertiary subduction zone, the thesis area occupies the area of the low pressure metamorphic belt in the context of Miya-shiro's (1972) paired metamorphic-belt model. Metamorphic grade of M3 is too low to be assigned to a particular baric type. In the eastern 173 part of the Shuswap Terrane a late transition to low-pressure meta-morphism has been reported by Reesor (1970) who observed cordierite overgrowths on sillimanite. The age of this transition is not known. Phases 1, 2 and 3 and metamorphisms 1 and 2 are pre-Pennsylvanian. There is therefore an interval of nearly 300 m.yr. during which no major deformation or metamorphism is registered by rocks in the southern Okanagan Valley. The rest of the core zone of the Eastern Cordilleran Fold Belt did not have .such a protracted holiday, and i t is instructive to outline a possible tectonic history for British Columbia extending to the Pennsylvanian. Monger et a l . - (1972) discuss a model for the evolution of the Canadian Cordillera, the highlights of which are out-lined here. The Jurassic to Cretaceous Columbian Orogeny represents part of the continuing episode of subduction west of the Coast Mountains Batholithic Complex. During this Orogeny some parts of the Shuswap Complex experienced intense deformation. In the area near Shuswap Lake Late Triassic rocks are complexly deformed (Okulitch, 1973, oral com-munication) , and near the Upper Arrow Lake, Triassic rocks have ex-perienced three phases of deformation (Hyndman, 1968). K-Ar ages throughout the Shuswap Terrane indicate considerable intrusive ac-t i v i t y through the Late Jurassic to the Cretaceous (Monger et a l . , 1972) , and the Coast Mountains Batholithic Complex (Hutchison, 1970) is Columbian in age. In the southern Okanagan Valley there is isotopic evidence (section 5) for Columbian metamorphism but no clear evidence of deformation. Unit IX could have been emplaced during the Columbian Orogeny on the basis of i t s 144 m.yr. K-Ar age. No major deformation occurred at this time 174 in the southern Okanagan Valley, but 25 miles west of Oliver the Triassic Hedley Formation is deformed. This deformation, represented by northwest trending close folds, does not appear to equate with phase 4, and therefore could represent Columbian folding. As expected, based on Triassic age of the Hedley Formation, i t does not contain isoc l i n a l folds that could be correlated with phases 1 or 2. South of the 49th parallel in the Loomis Quadrangle Permian Anarchist rocks are intensely deformed (Rinehart and Fox, 1972). The Coast Mountains Batholithic Complex probably became an i n -tegral part of southern British Columbia in Latest Triassic times (Monger et a l . , 1972). Prior to Late Triassic times subduction probably occurred east of the present location of the Coast Mountains Batholithic Complex. In Triassic times subduction could have been active along the present site of the Fraser-Yalokum fault zone. Intrusion adjacent to the thesis area, possibly associated with this subduction, is evidenced by Late Triassic ages obtained for the Similkameen Batholith (Roddick et a l . , 1972). There is no evidence of deformation or metamorphism in the thesis area at this time. In Permo-Triassic times subduction porduced blueschist metamorphism along the Pinchi Fault. This zone would project southwards along the west flank to the Okanagan Valley where there is no evidence for a c t i -vity at this time. The same zone appears to be the location of the pre-Pennsylvanian subduction or obduction zone that caused the Caribooan Orogeny. Surviving evidence for the Caribooan Orogeny in the Shuswap Terrane is spotty but convincing (Douglas, 1970). In the southern Okanagan Valley i t is this orogeny, and associated subduction or obduction to the 175" west, that was responsible for most of the metamorphism and deformation seen in the Shuswap rocks. Generally the Caribooan Orogeny does not appear to have been associated with much andesitic volcanism. Phase 2 has a trend sub-parallel to the projected trace of the subduction zone. The same is certainly not true for phase 3 whose trend on the local scale could in part be related to emplacement of unit VIII. East-west trending folds are common in the Shuswap Terrane and on the regional scale the trend could be related to cessation of subduction or i n i t i a t i o n of strike-slip movement along many different subduction zones. The unconformity, which separates rocks that experienced phase 1 from those that did not, is probably intra-orogenic though i t could separate two unrelated orogenies. In the Kootenay Arc, east of the core zone of the Eastern Cordilleran Fold Belt, there is no evidence for a separate and distinct pre-Caribooan Orogeny. This leaves the East Kootenay Orogeny (White, 1959) of Late Proterozoic age, as a possible, but unlikely, parent for phase 1 deformation. The tectonic history of British Columbia is complex in terms of plate tectonics. A broad north to north-east trending zone has been an interplate margin for at least the entire Phanerozoic Era, and the specific location of the plate boundary has migrated westward from early Phanerozoic to the present. The general parallelism of successive sub-duction zones probably produced successive phases of deformation of similar trends in the Shuswap Terrane. Separation or even recognition of these phases may now be impossible. 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C., ( 1 9 6 8 ) , P o t a s s i u m - a r g o n ages o f some i g n e o u s r o c k s i n '(northern Stevens:s C o u n t y , W a s h i n g t o n : U. S. G e o l . S u r v . P r o f . P a p e r , 6OOP,D242-D247. Y o r k , D., ( 1 9 6 9 ) , L e a s t - s q u a r e s f i t t i n g o f a s t r a i g h t l i n e w i t h c o r r e l a t e d n e r r o r s : E a r t h P l a n e t . S c i . L e t t e r s , 5^ , 320-324. Z a r t m a n , R. E., ( 1 9 6 9 ) , A g e o c h r o n o l o g i c s t u d y of t h e Lone G r o v e P l u t o n f r o m t h e L l a n e U p l i f t , T e x a s : J o u r . P e t . , 5, 359-408. 188 APPENDIX IA A DETAILED CONSIDERATION OF THE RB-SR ISOTOPIC CLOCK 1A-1. Introduction In this appendix some of the discrepancies between real geologic processes and the Rb-Sr isotopic clock model held to be analogous to these processes,are considered. The effects of sedimentary processes and metamorphism on the isotopic clodk are examined, and a detailed i n -vestigation is made of the results and possible processes of Sr iso-topic migration in a granodiorite stock. 1A-2. Effects of sedimentary processes on the Rb-Sr isotopic clock The event that the whole rock Rb-Sr dates is equilibration of Si and dispersion of Rb/Sr in a rock volume which is represented by a number of samples. This event is analogous to crystallization of a magma, but the degree to which i t is approximated by geologic processes, involved in sediment formation and metamorphism, is obscure. If a sedi-mentary unit i s - t o be dated, then i t must have a uniform, Si value at the time of sediment formation. This means that variations in the Sn value of provenance rocks must f i r s t be destroyed, most probably by weathering. The effects of weathering,on the Rb-Sr geochemistry of rocks and minerals,have been studied by a number of authors. Dasch (1969) found that weathering produced increases in r values but l i t t l e change in the Sn values of granites and basalts. Bottino and Fullagar'. (1968) obser-ved an increase of up to 70% in r value caused by both loss of Sr and gain of Rb, in weathered rocks. The net effect of this was an age re-duction of 0 to 15%. Most of the Sr was lost from plagioclase which was undergoing alteration. Unless plagioclase has been enriched in 87 radiogenic Sr (Brooks, 1969) Sn values of provenance rocks w i l l not 189 TABLE /A-1 Sample core ISOTOFE SAMPLES Of BOULDER 87 Sr .7506 Partially weathered .7544 Weathered rim .7577 87 1.41C i;500 1.663 Rb ppm 30.8 33.6 37.3 Sr ppm 63.2 65.7 65.1 190 be reduced to a uniform value. Weathering effects on individual minerals have been studied directly (Zartman, 1964) (Goldich and Gast,1966) and experimentally (Kulp and Engels, 1963). The effect of weathering is to decrease but not reduce to zero the Rb-Sr ages of minerals. Absorption of Rb, ion 87 exchange, loss of radiogenic Sr, and alteration, are a l l important processes that contribute to this age reduction. The author analysed samples from:a f o s s i l weathered biotite, feld-spar gneiss boulderj originating from a 700 myr. old metaconglomerate. A weathered shell emphasized by iron staining provided three samples (table 1A-I),each representing a different intensity of weathering. The r values and Rb and Sr concentrations of the samples a l l increased with degree of weathering . The Sn value increased 17% suggesting ad-dition, during weathering, of Sr with a Sn value of .975. This addition 87 of radiogenic Sr is unusual. Late carbonate minerals in the boulder 87 may have scavenged radiogenic Sr from altering minerals i n the sur-rounding rock. This process could have occurred during the low grade metamorphism that has affected the boulder. The R value also undergoes modification during weathering and sedi-mentation. Ion exchange capacities of some clays are responsible for low-ering R. value.'t and increasing the Rb content of the clays. The high R 5 value (3170) and shorter residence h a l f - l i f e of Rb (2.7 x 10 yr) in sea 7 water, as compared to that of K (1.1 x 10 yr.) (Mason, 1966), result from the above absorption and exchange phenomena. Studies of provenance rocks indicate that these rocks are generally incapable of providing material with uniform Si values for sediment for-mation. This conclusion can be supported by studies of recent sediments. 191 FIGURE M-a P e c c , n r M i n e r a l v Sf p l o t for M a r i o n c l o y s * l l l i i e 60 40 20 U_J I U -70 .74 40 I Kaolin i to CO J I •74 80 60 40 Kaolinito -t- i l l i t e 7 ~ — I L 1 1 _ 79 -74 60 40 20 Monrmori 11 on i t a - - L . — I I J 70 .74 20 C h l o r i t e •70 •74 c i L is r/Vr Ooto from Ootch e t o I. (l 9 6 6J 192 Murphy and Beiser (1968) measured Sn values of recent deep sea sedi-ments and obtained a poor isochron whose age was that of the proven-ance rocks. Data of Dasch (1967),(1966) indicates a positive correla-87 tion of inherent radiogenic Sr w i t h t i l l i t e and kaolinite content of recent marine clays (figure 1A-2). It appears that generally weather-ing cannot be relied upon to produce uniform Si values in juvenile sediments. Diagenesis could be capable of resetting the Rb-Sr isotopic clock. The juvenile sediment is in contact with a circulating isotopically ho-mogeneous pore f l u i d for a considerable time. Clays and authigenic min-erals such as i l l i t e and glauconite undergo slow ordering with time and as depth of burial increases (Maxwell and Hower, 1967). Ordering is accompanied by increase in K and Rb contents causing a concomitant de-crease i n mineral age (Goldich,1959). Upgrading of mineral ages, and therefore sediment age, during diagenesis, could fortuitously balance effects of inheritedpibvenance age, but diagenesis does not produce uni-form Si values i n the juvenile sediment. Despite the apparent i n a b i l i t y of sediment forming processes, of which weathering and diagenesis are the most interesting, to produce sediments with uniform Si values a number of authors have attempted to date ancient sediments by Rb-Sr geochronology. Compston and Pigeon, (1962) f i r s t to tackle the problem were optimistic after obtaining a r e a l i s t i c age from one of three sedimentary rock suites analysed. A detailed examination of the problems of datirg ancient sediments was 87 made by Whitney and Hurley (1964). Radiogenic Sr in i l l i t e s caused them to obtain ages 15% i n excess of the true sediment age. A larger excess age might have resulted i f the provenance age had been consider-193 TADLE I A-11 -'• . ' ARGILLITE SAMPLES OF THE CRESTON FMTN BELT FURCELL SUPERGROUP ISOTOPE DATA Sample ' Sr Rb ppm Sr ppm BP1 ' .7442 .8969 78 252.5 BP2 .7578 1.973 90. 6 133.5 BP 3 1.098 20.94 200 .1 28.7 BP4- 1.027 21.51 263 .2 36.5 BPS .7569 2.727 95. 4 101.7 BP6 .9710 14.96 165 .4 32.8 BP7 1.748 79.5 .365 .2 16.8 BP8 1.398 45.5 294 .7 20.0 BP9 ". ' . 1.088 18.49 213 .2 34.6 BP10 1.168 24.89 247 30.0 194 ably, older than the sediment age. Enthusiasunfor sediment dating pro-jects was maintained by an interesting reinterpretation of Whitney's paper by BoifLnger and Compston. (1967) who showed that a younger, stratigraphically acceptable age could be obtained by f i t t i n g two paral-l e l isochrons through Whitney's data. This implies a dual provenance for the samples. Rb-Sr analyses made by the author of Late Precambrian sedimentary samples can be used to il l u s t r a t e some of the problems of interpreting Rb-Sr data from sediments. A r g i l l i t e samples of the Creston Formation) collected by W. Barnes from near Moyie Lake, British Columbia, were used in the study. Equivalents of this Precambrian Formation of the Belt-Purcell Supergroup have been dated by Obradovich and Peterman (1968)^ who obtained an age of 1030 + 53 m.yr. Ten samples representing from 2" to 4" of stratigraphic thickness were analysed (table lA-JI) . The data spreads on an isochron plot ( f i g -ure 1A-3) but is contained by 1295 and 865 m.yr. isochrons. The spread of data is probably, in part, caused by variation of Si values of the samples. Adjacent samples (BP1, BP5 and BP4, BP6) 1" to 3" apart were analysed and these provide two, two point isochrons (dashed lines in figure 1A-3). The Si values for these isochrons are different and their ages much younger than the average 1000 m.yr. age of a l l the samples. It appears that small volumes of rock have been partially reequi-librated probably during an Early Phanerozoic metamorphic event. Widely separated larger volumes of rock have acted as nearly closed systems, retaining true age and nearly uniform original Si values. The data illustrates the effects of variations of Si on sedimentary isochrons 195 and the sensitivity of the Rb-Sr clock of sediments to subsequent events such as low grade metamorphism. Whole rock Rb-Sr dating of ancient sediments is a hit and miss proposition.. Until considerable work has been done,one does not know i f variable Si values of samples, excess age problems, or post-dia-genetic open system behaviour, w i l l n u l l i f y the usefullness of results. A new approach to the problem of dating sediments by Boffinger et a l . , ( 1968 ) employs acid leaching to isolate two separate isotopic systems from a single whole rock sample. A single sample can then pro-vide a two point isochron. Results of Boffinger et a l . were promising. In a paper by Chaudhuri and Brookins (1969), the leach residue gave a stratigraphically acceptable age but for ..obscure, possibly fortuitous reasons. Acid leaching provides a useful way to increase data spread along an isochron; a more detailed interpretation of the results of acid leaching needs considerable supportive data. 1 A - 3 . Effects of metamorphism on the Rb-Sr isotopic clock Metamorphism could easily reequilibrate the Rb-Sr isotopic clock. Increasing metamorphic grade initiates processes such as, solid d i f -fusion, mineral growth and fl u i d transport, that must a l l play a part in resetting the isotopic clock. When a suite of sedimentary samples i s metamorphosed?the rock volume represented by the suite is usually isotopically reequilibrated to provide a new metamorphic age. It can be inferred from the data in this study (section 5) } that by middle green-schist facies resetting of the Rb-Sr clock is nearly complete. A l l whole rock pelite data (unit III) appears to record M3 which did not exceed middle greenschist. facies. Metamorphism could produce regional changes in R or Sn values. 196 Long range migration of Rb during metmorphism would be indicated by systematic changes in R values of unit III. No such systematic changes of R values related to metamorphism are observed. An increase .'. in R value caused by loss of absorbed Rb dlays might be ./expected. 87 Systematic loss of radiogenic Sr from sediments during high grade metamorphism would be evidenced by^lower Si values for meta-sediments as opposed to sediments. An average Si value of .7064 (based on nine values) for metasediments can be obtained from data compiled by Hurley et^al. (1962). An average Si value for sediments of .7153 is obtained from nine papers dealing with Rb-Sr sedimentary isochrons, known to the author. The above averages ignore bias in rock type, age 87 and experimental error, but despite this the inference ,that radiogenic Sr is lost during metam.orphism.jis clear. Data from unit III is incon-87 elusive on this point though migration of radiogenic Sr out of unit III during high grade metamorphism is suggested by data from unit I. Solid diffusion probably plays an important role in isotopic re-87 equilibration during metamorphism. Solid diffusion loss of radiogenic Sr has been demonstrated by Hart et a l . (1968), Hurley (1962), McNutt (1964) and Baadsgaard and Breemen (1970). An earlier paper, (Senftle and Baacken,1955) considered the possibilities of diffusion controlled isotope fractionation in nature. Such effects are probably minimal, and would be hard to separate from mass spectrometer experimen-tal fractionation,which is corrected for (Appendix 2A). 87 It i s often f e l t that solid diffusion loss of radiogenic Sr is greater at high temperatures than low temperatures. Using data from Hart et a l . (1968) on Sr diffusion from biotite, i t can be shown that a three fold decrease in grain radius, increases the rate of diffusion 197 T A B L E IA-m Excess ages i n B i o t i t e c a u s e d by d i f f u s i o n b a c k l o g D/a 3" 4 e q u i v a l e n t t e m p e r a t u r e " ^ e x c e s s age f a c t o r n\yr„ 1 0 1 3 520 .027 1Q-14 ,. 430 .27 1Q-15 365 2.7 10-16 300 "27 10-17 . 250 270 198 loss of Sr to the same extent as a 100° C increase in temperature. It is possible that i f the radius of micas in a metasediment increases three fold from middle greenschist to middle amphibolite facies (equi-87 valent to a 100° C temperature increase) } then the rate of radiogenic Sr diffusion lossffrom the micas could remain about the same. Rocks probably experience greenschist facies temperatures for a longer time than amphibolite facies temperatures during a metamorphic cycle, and therefore isotopic reequilibration can be expected to occur at reasonably low temperatures. Deformation acting on low grade meta-morphic grade rocks can affect mechanical mixing and grain size re-duction aiding isotopic reequilibration. Simple radiometric models assume an instantaneous starting of the isotope clock. During metamorphism, when solid diffusion probably con-87 trois the rate of radiogenic Sr migration, rocks or minerals are not reequilibrated at an instant in time. An example of a mica which is experiencing metamorphism is dis-87 87 cussed. Radiogenic Sr is forming in the mica from Rb decay and some 87 of this Sr is diffusing out. However fast diffusion loss of Sr a cer-87 tain concentration of radiogenic Sr remains in the mica to maintain this diffusion loss. The mica is at no time completely flushed of radio-87 genie Sr. Simple radiometric equations not considering this backlog 87 of radiogenic Sr w i l l predict ages in excess of the end of the meta-morphic event. Assuming a state analogous to transient equilibrium of a double radioactive decay series, an excess age factor for biotite can be cal-culated (table 1A-JJB . Diffusion constants were obtained from Hartet a l . (1968); who calculated Sr diffusion parameters for coarse grained biotite. 199 ISOTOPE MIGRATION STUDY Sample Mineralogy Analysed isotpic and geochemical data Ab Or M Q O 8Vss s<; J Rb ppm Sr pprc 3 K K/Rb T9 65 i 10 22 2 1.957 • 48.27 137.6 8.259 .92 67 F2 82 .5 0 17 .5 1.382 3.789 12.5 10 . 13 .16 130 FL2 82 .5 0 17 .5 1.384 5.211 16.93 9.983 F3 74 12 0 14 0 1.-162 12.53 61.45 15.11 .64 104 F4 95 7.76 392.8 1367 17.01 13 99 M9 100 28.87 1651 2128 J.3.8 8.5 40 ML9 100 35.92 2111 2125 12.93 M10 5 0 94 1 0 " 25.14' .1859 1433 7.55 7.6 53. T10 38 13 5 43 1 .8723 6.856 73.4 31.5 Sample Purity grain size dia Mil' 100 .35 cm 4.209 M12 100 .6 cm 3.161 M13 100 .4 cm 73.75 M14 100 1.2 cm 70.64 M15 100 6.0 cm 32.32 Calculated isotopic Ab Or K Q O TP9 71 1 8.8 16.2.2 1.96 Fl>2 100 1. 376 FP3 100 1.587 MP10 100 33.27 LF ,1.25 I,M 2.14 330.6 581.1 6.83 232.6 554 .7 8.56 4298 1539 8.454 4208 1724 9.297 1906 . 150Q 9.317 leochemical . d ata for pure phases 49 147 9.76 .83 56 3.211 12.59 12.1 .17 137 26.29 434 .4 . 51.92 4.3 99 ' 2493 1523 7.4 7.6 50 3G.9 11.9 256 69.8 Ab = albite Or = microcline M = muscovite O = quartz O = other mostly tourmaline 200 With reference to tablel/WJJ, results translate as follows; a coarse grained biotite maintained at 365°C for a time in excess of 2.7 m.yr. w i l l age of 2.7 m.yr. in excess of succession of metamorphism, i f dated today. Parent rock, mineral isochrons can therefore be ex-pected to record ages in excess of end of metamorphism. 1A-4. Detailed investigation of results and processes of isotopic migration. A previous paper (Ryan and Blenkinsop, 1971) presented Rb-Sr data obtained from a stock,which subsequent to i t s crystallization exper-ienced a low grade metamorphic event. The stock is about 1260 m.yr. old and has been affected by a later 700 m. yr. old orogeny, (the East Kootenay Orogeny, White, 1959). It is used here as a simple example of multi-stage isotopic history apparent in the thesis area. Additional samples from the stock were analysed during the present study, and data used to investigate the effects of the subsequent meta-morphism on the Rb and Sr distribution i n , whole rock.-and mineral sam-ples from the stock. Minerals were leached to gain information about isotopic redistribution,and muscovites of different sizes analysed to 87 test for diffusion controlled^retention Sr. The stock is a coarse grained, to porphyritic, muscovite, albite, granodiorite with tourmaline as a prominent accessory mineral. Isotopic data for the stock is in table 1A-IV Two whole rock samples (T9 and T10) were analysed.. One, T9 was s p l i t into several component minerals; (al-bite, F2, muscovite M10 and an albite-microcline mixture F3). Two mus-covites Mil and M12^ of: dif f erent .averagel.grain sizes, were separated from whole rock sample T10. Additional mineral samples, microcline F4 and muscovites M9, M13, M14 and M15, were obtained from the outcrop area 201 F I G U R E iA-<h 5 0 - " r / ISOTOPF. MIGRATION S T U D Y M U S C O V I T E DATA isochron diagram - / / / F I G U R E /A-S I S O T O P E M I G R A T I O N S T U D Y W H O L E ROCK A N D M I N E R A L D A T A i s o c h r o n d i o 9 r a n 86_ Sr 10 _ i _ 20 I 30 L _ 40 _J 202 that provided whole rock sample T9. Muscovites M13, M14 and M15 were separated on the basis of original grain size. Splits of mus-covite M9 and albite F2 were leached for six hours, in 2 molar dis-t i l l e d HCL, at room temperature,and analysed to provide samples ML9 and FL2. Isotopic and geochemical data for pure mineral separates ideal rock, and disolved leached phases (pure phases, table 1A-IV) wereccalculated.from real sample data. Real data is plotted as crossesaand calculated data as dots in figures 1A-4 and 1A-5. The 1260 m.yr. errorchron^ previously obtained for the stock (Ryan and Blenkinsop, 1971) is shown as a dashed line. Also, borrowed from this paper is data for muscovite Ml and i t s parent whole rock T4. Three mineral, rock isochrons, T4 to Ml (900 m.yr), T9 to F2, F3, M10 (868 m.yr.) and T10 to Mil, M12 (700 m.yr), are shown as solid lines in figure 1A-5. They a l l have ages less than 1260 m.yr. Obviously minerals have been affected by the East Kootenay Orogeny. The problem is to investigate the degree and mechanism of isotope migration that occurred during the East Kootenay Orogeny. The effect of the East'Kootenay Orogeny on muscovites is dis-87 cussed f i r s t . Loss of Sr rather than gain of Rbjby muscovitejis i n -dicated by the non correlation of muscovite ages with their R values (compare table 1A-IV and 1A-V). If present, such a correlation would imply that addition of Rb had decreased muscovite ages and at the same 87 time decreased their R values. Loss of radiogenic Sr by solid dif-fusion from the muscovites is also suggested by the unaltered and un-recrystallized nature of the muscovite. 87 A model of radiogenic Sr diffusion loss from muscovites is diagramatically presented in table 1A-VI. In table LA-Vf the age of the 203 TABLE IA-% Secondary Isochron and Muscovite ages Samples age myr. S i i n t e r c e p t T4 to Ml 900 .765 T9 toF2 F3 M10 86 8 1.33 T10 to M11M12 700 119 1151 M13 1146 M14 1121 M15 1119 TABLE /A-VI 79 5 71 assumed DIFFUSION MODEL DIAGRAM AND TERMS _^Terms T = age of stock Known t = age to end of d i f f u s i o n event Unknown St = duration of d i f f u s i o n event Unknown Muscovite Ma muscovite Mb muscovite Mc apparent age ta tb t c known s i z e radius ra rb re known d i f f u s i o n escape Ada A db ^ d c Unknown constant Time diagram Age of stock d i f f u s i o n event - present T . = A : to 16-204 stock (1260 m.yr- = T m.yr.) is the time of crystallization of the muscovite samples (Ma, Mb, Mc,) which subsequently experienced a 87 period of radiogenic Sr loss. The^:(jl£h'gtrr of time yduring which the muscovites lost Sr (isSt m. yr. This time interval is interpreted as being b\ie.'ctuc*.hon: 6:L the East Kootenay Orogeny. Strontium loss from the muscovites ended t m.yr. ago and this time is interpreted to be the same as the end of the East Kootenay Orogeny. During St m.yr. 87 muscovites lost differing total amounts of radiogenic Sr} depending on their sizes (ra, rb, rc; table lA-VJD . Now muscovites register d i f -ferent ages (ta, tb, tc m.yr.) a l l older than t m.yr. because no mus-87 covite lost a l l i t s radiogenic Sr, by diffusion. ConstantsXda, Adb, andXdc (table 1A-VZ) are diffusion escape constants analogous to radio-active decay constants. They allow diffusion to be treated as equi-87 valent to radioactive decay of Sr out of mica (Damon, 1968). It is assumed that the external environment i n i t i a t i n g diffusion, largely temperature, is the same for a l l muscovitesf and that,therefore, different muscovite ages, representing different amounts of radiogenic 87 Sr loss, are caused by different grain sizes. The diffusion escape constant i s related to grain size by the equation; 2 Ad = 12.5 D/ r ; (Damon, 1968) in which r is grain radius and D is the diffusion coefficient. This equation assumes cylindrical diffusion and the value of D is assumed to be the same for a l l muscovites. The model presented in table lA-VIhas as unknowns t. myr. St m.yr. and Ad for each muscovite. The problem is to formulate equations which can be solved for these unknowns. Such an equation for a single musco-vite, adapted from Damon (1968) i s : 205 - . ( \r.St -Xd.te) in » 5;e + W - A r l e — e /; Equation 1. 87 Sn = radiogenic Sr present at t m.yr . ago, immediately a f t e r 87 the period of d i f f u s i o n loss of Sr from the muscovite. 87 Rn = Rb present i n the muscovite immediately a f t er d i f f u s i o n 87 loss of radiogenic Sr at t m.yr. ago. 87 S i = radiogenic Sr present i n the muscovite immediately before d i f f u s i o n at t + ft m.yr. ago. 87 R i = Rb present i n the muscovite immediately before d i f f u s i o n at t + 6t m.yr. ago. 87 -1 Xr = decay constant for Rb expressed i n sec -1 87 Ad = d i f f u s i o n escape constant i n sec for Sr from the muscovite. Suffixes a , b and c re f er to the three separate muscovites.. ( table 1A-VD . The unknowns Sn and S i can be expressed i n terms of of the ages for the muscovites, for example for muscovite Mc. _ Ar (tc -t) _ \r.xc 5n = Kn e — e j equation 2. c a . „ \r(T-(t+&0) D W T - f c c + x c -St) Si = Ki e = Ki e ; equation 3. In these equations xc m.yr . i s the excess age fac tor i n the youngest and smallest muscovite; that i s tc m.yr. - t m.yr. I f St m.yr. i s short then R i i s nearly equal to Rn. Equations s i m i l a r to equation 1^which have as unknowns Sn, S i , a d i f f u s i o n escape constant (Ada or Adb e tc . ) and time terms such as t , t c , St and xc m.yr.j can be w r i t t e n for each muscovite^Ma, Mc and Md), Using equations s i m i l a r to 2 and 3, terms S i and Sn can be replaced by terms R i , Rn, T , t and St i n equations s i m i l a r to equation 1. 207 Using the r e l a t i o n s h i p 4--x^  Xdc = r a equation 4. equations for each muscovite can be rewri t ten such that they contain only one unknown d i f f u s i o n escape constant. Equation 4, assumes that the radius term i n the d i f f u s i o n equation i s equivalent to the p h y s i c a l gra in r a d i u s . The equation for muscovite Ma then becomes: _ /\r (ta.-tz-acc) .\ _ / Ar (T-bc + xc-St) A -Xda..6t JWe - l J = R i ( e - l).e + A d * - Ar (e - e ) equation 5. Using the approximations, e - /feSxand Rn*Ri, produces an equation with Ad a xc m.yr . and Si m.yr. as unknowns. I f a s i m i l a r equation i s w r i t t e n for muscovite Mc and the two equations for muscovitesMc and Ma combined, then the term xc m.yr . can be e l iminated . The r e s u l t i n g master equation has two unknowns Ada and gt m.yr. and provides a curve on a Ada v St m.yr. p lo t ( f igure lA-Vi) . I f data i s c o l l e c t e d from a number of muscovites of d i f f e r e n t s i z e s , then a number of master equations , combining data from two mus-c o v i t e s , can be w r i t t e n . These master equations should i n t e r s e c t on a A d , £ t m.yr . p lo t to provide unique so lut ions for these two terms. Terms xc m.yr. and t m.yr. could then be ca l cu la ted from equations of the form of equation 5. Solut ions for the terms of i n t e r e s t can be obtained i f a number of muscovite samples of d i f f e r e n t average s izes are analysed. Average gra in s i zes of muscovite samples M i l to M15 were obtained by d i r e c t measurement of a representat ive number of gra ins , and average gra in s i zes of muscovite samples M l , M9 and M10 were estimated by eye (tables lA- /y and lA-VIl). Data from muscovites M9, M10 and M i l was used to 208 TABLE /A-Vll Size data and a g e s ( c a l c u l a t e d using S i = .71) of muscovites Muscovite sample r a d i u 8 { n m i ) 2 a g e ^ . ^  ^ ^ Ml 4 M9 3 6 M10 9 m M i l ' 3 900 1151 27.5 36 888 6.25 718 4 4 Ml 2 Ml 3 6 Ml 4 36 6 717 ' 4 1146 Ml! 1121 900 1119 r i '7\BLE IA -VIII Isotope balance sheet f o r whole rock sample T9 8 7 c o n s i d e r i n g m i g r a t i o n of Si" r a d i o g e n i c o n l y 87 87 Sample S r ( r ) added ugm/ gm Sr (r) s u b t r a c t e d ugm / gm FP2 .56 .40 FP3 1.45 . 0145 MP 10 + .4145 T£9 8 Ir <r) gained - .24 •' 2.56 .226 t o t a l ^ - t o t a l - .226 209 calculate curves for master equations M9 + M10 and M9 + Mil. ,. Size data used in the calculations is shown in.table 1A-VU and the resulting curves in figure 1A-6. Curves are nearly straight lines and do not intersect, however, within reasonable estimates of grain size they can be made to overlap. Two master curves for the pair M9 + MIO^  based oil different estimates of grain size^ are shown in figure 1A-6. Obviously an intermediate curve would overlap M9 + Mil master curve. The muscovite ages do not a l l correlate with grain size (table 1A-VII so that in this case the isotopic data does not completely sup-port the diffusion model. The model is capable of providing unique solutions for the terms Ad, it:: m.yr and t m.yr. i f an independent estimate of xc m.yr. is available. The youngest muscovite K-Ar age for the stock (Leech,1962) is 45 m.yr. younger than the youngest Rb-Sr age. 45 m.yr. must therefore be a minimum estimate of xc m.yr. (ignoring ambiguities in the value of the various decay constants). A curve of xc m.yr. v Ad is plotted in figure 1A-6 and on this curve a value of 45 m.yr. for xc m.yr. predicts*St m.yr. of 1 m.yr. and a -14 -1 Ad of 8.0 x 10 sec . Had the Rb-Sr data supported the model better a similar model could have been used for K-Ar data from muscovites and unique solu-tions for t m.yr. and it m.yr. obtained, afterrmaking some assumptions about ratio of Ar diffusion constants to Sr diffusion constants in mus-covites . The model emphasizes some interesting points. No muscovite registers exactly the age of the East Kootenay Orogeny. The Orogeny lasted for St m.yr. and this value is built into the diffusion 210 equations. I f simple s o l i d d i f f u i o n h o l d s , then knowledge of Ad provides i n f o r m a t i o n about:1 the average operating temperatures of the Orogeny. Unfortunately the model cannot be complete. Some major f a c t o r s have not been considered i n the model. The geologic s i t u -a t i o n could be more complex and s p a t i a l l y v a r i a b l e . The e f f e c t i v e d i f f u s i o n g r a i n s i z e may not equal p h y s i c a l g r a i n s i z e . A r e a l tem-perature-time p l o t may not be approximated by a f l a t peak as i m p l i e d i n the model. Deformation may a f f e c t Ad by a l t e r i n g the a c t i v a t i o n energy of d i f f u s i o n . 87 Muscovites have l o s t r a d i o g e n i c Sr p o s s i b l y by s o l i d d i f f u s i o n . 87 I t remains to i n v e s t i g a t e r e l o c a t i o n of the Sr i n other minerals. Sample data f o r f e l d s p a r s F2 and F3 p l o t s above the whole rock e r r o r -chron. This suggests that w i t h i n whole rock sample T9 feldspar? sam-87 p i e s F2 and F3 have taken up r a d i o g e n i c Sr l o s t by muscovite. I t i s u n l i k e l y that the apparent p o s i t i o n of f e l d s p a r sample p o i n t s F2 and F3,in f i g u r e lA-5,can be explained by l o s s of Rb from the f e l d s p a r s , as t h i s i m p l i e s an unreasonably l a r g e 30% l o s s of Rb from t h e i r parent rock T9. Using the 1260 m.yr. errorchron f o r reference, a balance sheet 87 of radiogenic Sr f o r whole rock sample T9 can be c a l c u l a t e d (Table 87 lA-VIIl). Points above the errorchron have rece i v e d .'Sr and p o i n t s 87 below l o s t Sr. Whole rock sample T9 has received approximately .24 87 87 ugm.' Sr/gm rock,during the East Kootenay Orogeny. This Sr must have been donated by muscovite from other parts of the stock. A d d i t i o n of Sr to f e l d s p a r s during isotope migration.has been documented by a num-87 ber of authors. Wasserburg et a l . (1964) demonstrated additon of Sr 87 and Rb to a l t e r e d p l a g i o c l a s e and l o s s of>- Sr and Rb from K f e l d s p a r . 211 Acid leaching removes loosely held adsorbed ions or carbonate material. In reality i t checks for low temperature migration of Rb-87 or Sr. Leached muscovite ML,9 (table 1A-J\0 has lost Sr, either as a distinct phase characterized by an Sn value of 2.14 or by preferen-87 t i a l extraction of common Sr over radiogenic Sr in the ratioj;20 to 1. 87 Work of Deuser and Herzog, (1963) indicated that radiogenic Sr, which occupies K sites in the crystal lattice, was more strongly held than common Sr. The results of leaching feldspar F2 are equivocal due to a small contamination of muscovite grains in the feldspar separate, 87 but albite F2 does not contain an easily leached radiogenic Sr phase. To check that heavy liquids, used to.-separate albite F2, did not re-87 move Sr a second separate was obtained by air suction, analysis of 87 which indicated no removal of Sr by heavy liquids. Leaching provided l i t t l e positive information except to show 87 that migrating Sr has permeated acceptor feldspars, by solid d i f -fusion, as indicated~;by the absence of secondary minerals or recrystal-lization in the feldspars. Solid diffusion into minerals may put some constraints on closed system behaviour. Only i f diffusion gain of acceptor minerals can keep pace with diffusion loss of donar minerals can a rock remain an isoto-87 pically closed system. Feldspars in rock T9 have accepted Sr at .a faster rate than muscovites in rock T9 could provide i t . Rock T9 has 87 therefore stolen Sr from rocks of different compositions and has not remained a closed system^during low grade metamorphism of the East Kootenay Orogeny. 212 1A-5. Summary Rb-Sr dating of sediments and metasediments is unlikely to provide conclusive results. Attempts to date sediments w i l l often be thwarted by variable Si values and uncertainties as to what event reset the isotopic clock. Metamorphism of sediments may be easier to date but a simple isotope clock model, is misleading. Solid diffusion can control mineral rock isochrons, and solid diffusion properties of minerals in a single rock may in part control the rocks ab i l i t y to remain an isotopically closed system. 213 FIGURE 2A - / ' • ' • . Diagramatic plan of analysis procedure Sn = 87 Sr S r -i c 3 c r for • O • to -» « a C 3 Z) c. or o in o -t» 4» © -> —' 39 to » o V 1 -1 _' 3 ? - T I M M j ! » -* o a. ei « a < o f 6 *\ ° ° x o P 3 -w 3 o O ™ \ ~ 3 1 W o -» u -* 1 7 :r o a» o cr sc o 3 -n w o O « o "-•j o O : r -n a on o r -0-O ID O a o w K O O 3 40-0° "O < o P CO c IS O O J n c CO fo cr 3 o *> o S * -P ° 3 w 5 « f a * « * _ ~ T) re v. Z~ -- „ M <9 \ - • S '2 ol O O 3 O t/5 * • « o rt 3 o <D n a P - * 3 0 •> 0 < 3 •o o © ^ 3 T I - * - 3 • 3 o 3 214 APPENDIX 2A Rb-Sr CHEMISTRY AND MASS SPECTROMETER TECHNIQUES 2A-1. Introduction: Rb-Sr geochronology requires the accurate measurement of Rb and Sr concentrations, and of Sn (the ^ S r / ^ S r present ratio). The latter measurement requires the use of a mass spectrometer, whereas the other two may or may not. Figure 2A-1 is a diagramatic outline of how different samples were analysed. Procedures evolved during the study so that the outline is not true for a l l samples. X-ray fluorescence procedures are described in Appendix 3A. This appendix discusses the chemical and mass spectrometer techniques involved in Rb-Sr geochronology. 2A-2. Sample preparation techniques. An outline of the present procedure which evolved from the U.S.G.S. procedure (Petermen et al., 1967) is as follows. Rock samples are crushed to fine sand size, and a representative 100 gram portion removed. This 100 gram portion is crushed to 100 mesh size and a representative 10 gram portion crushed to less than 200 mesh size. The f i n a l 10 gram portion provides a sample for Rb-Sr chemistry and for making a rock pellet for X-ray fluorescence analysis. The remaining crushed rock can be used for mineral separation. Rb and Sr concentrations of the samples are estimated using preliminary X-ray fluorescence analysis, or previous experience. After this sufficient weight of sample is weighed out, such that i t contains at least 15 micrograms (ugm.) Sr, and 5 ugm. Rb. This sample powder is 215 dissolved over a period of one to four days in a solution of HF and H 2 S O 4 . When dissolved the sample solution is taken to dryness and more H 2 S O 4 added before i t i s dried again. The resulting sample residue is dissolved in 50 ml of 6 molar HCL. This solution is accurately divided by weighing into two portions. One portion (Sr split) contains at least 10 ugm. of Sr. The other portion (Rb split) contains at least 2 ugms. of Rb. At this stage Rb spike solution i s added to the Rb sp l i t and Sr spike solution to the Sr s p l i t . Spike solutions are standard solutions and are described in section 2A-3. The Sr s p l i t contains Rb which is separated from Sr in a cation exchange column. The Sr sp l i t is f i r s t evaporated down to 7 ml and washed through a cation exchange column with 6 molar HCL and a Sr cut collected. This Sr cut is then washed with 2 molar HCL through the cation exchange column a second time and a second Sr cut collected. This second cut when dried is ready for analysis on the mass spectrometer for Sr. The same procedure is followed when an analysis of Sn is required except that i t may be advantageous not to add any Sr spike solution. The Rb s p l i t is taken to dryness redissolved in 5 ml of 2 molar HCL, and washed through a cation exchange column with 2 molar HCL. The Rb cut is collected and dried in preparation for analysis with the mass spectrometer. This outline describes how Rb and Sr samples are prepared for mass spectrometer analysis. When sample Rb and/or Sr concentrations and available sample weights combine to make X-ray fluorescence analysis 216 possible then the above procedure is modified, as is inferred in figure 2A-1, to minimize the number of mass spectrometer analyses. Those parts of the outline dealing with rock dissolution and cation exchange column behaviour,are discussed in more detail. Complete dissolution of samples is essential before meaningful measurements of Rb and Sr concentrations can be made. HF attacks silicates by the reaction SiC>2 + 4 HF S1F4 + 2H2O. Ideally 3 cc. of HF dissolves.1 gm. of quartz. Unfortunately, because of evaporation, about 30 cc. of HF are usually required to dissolve the .2 to 1 gm. samples used. The residue l e f t after samples are dissolved in HF, is composed of fluoride salts, which in subsequent procedures w i l l dissolve glassware. The residue is composed of sulphate or perchlorate salts i f either of the related acids is added to the HF solution. Sulphuric acid is safer and has a higher boiling point than perchloric acid, and for these reasons is used in rock dissolution. One gm. of muscovite requires about 1.3 cc. of 1 to 1 H2SO4 to precipitate a l l i t s cations as sulphates. One gm. of muscovite contains more cations than most actual samples therefore 4 cc. of 1 to 1 H2SO4 is ample to ensure precipitation of a l l cations in sample as sulphates. Rb must be removed completely from Sr split s because i f present in the mass spectrometer i t w i l l ionize very easily and cause isotopic interference with one of the Sr isotope peaks. If samples are to be successfully analysed in the mass spectrometer a high retention of Sr plus i t s complete separation from Rb must be achieved in cation exchange column, separation, procedures. The columns used for Sr separation are 1.1 cm. FIGURE 2 A - 2 Dowex 50w x 8 % Sr elution chorocter ist ics e x p e r i m e n t a l d o t * \ - 3 0 -• 1 0 - 1 0 10 2 M O L A R E L U T I O N s / ' • a' 100 sample • w ie jh t S r load % recovery M 1 -82 3 ugm 6 0 1 • . "J QUI 1 - S I 23 e o 8 1 -34 9 3 0 . 10 e s t t m a f e d e r r o r s in da < a p o i n * s a n d r e c o v e r y v a l u e s 1 0 % x< 120 -5-140 I ' -~ ml o f e lo f oat 6 M O L A R E L U T I O N /I I V . t 'I r! ''ft' 3 0 X \ X \ \ \K \ " N N ^ \ 50 ^ ^ f ; M 1 • 8 2 1° . 6 0 BI • S 4 e 3 0 QM 2 • 2 3 125 6 0 Q M 1 •31 3 0 5 0 Q S 1 • 31 8 0 7 5 M m u s c o v i t e B b i o t i t e Q M quorfx m o n z o n i t e S s h u t F I G U R E 2 A - 3 8 0 Rb and Sr mass d is t r ibut ion coe f f i c ien ts for Dowex SO resin d i f f e r e n t c r o s s ; l inkage percentages ^ doto f rom O i b m o n d (|95 5) • H '• ^ •'• ^ 2 0 . -\ ^ \ V \ • \ \ \ S.\ N , X , 6 0 ml of • t u l a n t _L2_ H C L M o l a r i t y i 218 diameter x 22 cm. long and contain 6.5 to 7 gms. of Dowex 50 x 200 mesh resin. Sample Sr splits are dissolved in 7 ml of 6 molar HCL. The high molarity of acid ensures that a l l the sample is maintained in solution during separation into Rb and Sr splits and subsequent ion column procedures. Sample Sr splits are eluted in 6 molar HCL through the columns. After 25 ml of elutant has passed through the column the next 40 ml is collected and provides the f i r s t Sr cut. This f i r s t column separation changes the Sr sp l i t from a solution of sulphate salts to a solution of soluble chloride salts and performs a partial separation of Al, K, Fe, and some Rb, from the sample Sr s p l i t . The 40 ml Sr cut is taken to dryness and easily redissolved in 1 to 2 ml of 2 molar HCL. Elution in 2 molar HCL through a second column similar to the f i r s t affects a clean separation of Sr. The actual position of the second Sr cut varies with Rb and Sr concentrations of the sample, as indicated in figure 2A-2 which i s based on data obtained during this study. Rb splits are eluted through cation exchange columns in 2 molar acid providing a clean sample cut composed of chlorides. Both factors increase the st a b i l i t y of Rb mass spectrometer runs. Fundamental properties of Dowex 50 resin were f i r s t described by Bauman and Eichhorn (1947) and the theory of cation separation by Mayer and Tomkins (1947). Dowex 50 is a sulphonated polystyrene resin, in which SO3 anions are attached to a polymeric skeleton of polystyrene chains linked by divinglbenzene. H + ions are loosely bonded to the structure to neutralize charge. During elution a cation C + forms an equilibrium reaction with the resin. (Res SO3) H+ + C + (Res SO3) C + + H + (1). If flow of electrolyte (HCL) i s maintained through the resin, cations w i l l be dislodged from their sites and move further down the resin column. The resin has an ion exchange capacity, usually given in m i l l i -equivalents per gm. of wet resin. For separation of cations each cation load should be considerably less than 1% of the total exchange capacity of the resin. Concentrated acids push the cation exchange reaction (1) to the l e f t for a l l cations, and cation separation in elutant decreases. Exchange reactions w i l l maintain equilibrium i f a flow rate of 1 to 2 ml of elutant per minute is not exceeded. High temperatures increase cation separation a b i l i t i e s of the resin. In this study elutions were always performed at room temperature. Mass distribution coefficients (Dc) are resin parameters that describe resin behaviour. Mass distribution coefficient, Dc = cations/gm resin^cations/ml elutant. Values of Dc are calculated using a single cation. When a mixture of cations is introduced into the cation exchange column previously calculated values of Dc for each cation are changed. If two cations are introduced one (B) in trace quantities compared to the other (A) then the value of Dc for B is controlled by concentration of major element A and is given by, Dc = R/(A)b/^ ; (2). R is a constant and a and b are valencies of elements A and B. Equation (2) mc/zca^ es that B elutes earlier as concentration of A increases. If a l l cations are in trace quantities,then the elution peak position for each cation i s given by, V ml = (mass of resin) x Dc + Vo ml; (3). Vo i s the pore volume of the resin column. The Dc values of a resin provide an approximate idea of elution characteristics of a particular resin. A large difference in Dc values for two elements implies a good separation of the elements ;in the cation exchange column. 220 TABLE - 2A-/ Rb AND Sr ISOTOPE SPIKE EQUATIONS CONSTANTS 86 / S r / = .1194 / S 8 S r 8 4 s 5 ^ 6 S r = ' ° 5 6 R  8 5 R b / 8 7 = 2.593 86„ SPIKE Sz' 86 moles Sr s p i k e 8 Sr u moles sample = , . (l - 88s--/ «.•> v 8 6 < = ^ / ^ PVs3Srm.- - 1 1 D 4 j 7 S r noles sample - 8 6 S r ? moles Spike ( " s r / g ^ m - ^Sr/g^sp) + 8 6 S r ; 1 „ 0 i c s sampleFsr^  n m r e f e r s ' t o r a t i o of sp i k e + sample i s o t o p e mixture S P " " " •• i s o t o p e s i n sp i k e s o l u t i o n s •' • '• » >• i s o t o p e s i n common Sr 84 Sr SPIKE 8 6 S r moles sample =(l ~ S p * ^Sr/aSf. *) * ? ^ L " " S r s P i k e N o r m a l i z a t i o n e q u a t i o n "s/n^* ( " s r / g ^ m - ^ S r / ^ ^ s p ) ( l - 8 4 s r / 8 8 ^ s x " s r ^ j ^ 37 . Rb SPIKE Mgros. Rb t o t a l = 307.4 x (•/)p m o l e s 7 Rb GENERA!, EQUATIONS R = c o n c e n t r a t i o n r a t i o by X R F S Z 86 i s o t o p i c r a t i o ' Sr -(827.8 + 87 Sn) -FRACTIONATION » S r / g f l ^ (true) / 221 The Dc values and cation exchange capacity of Dowex 50 resin change with degree of cross linking of polystyrene chains. Larger Dc values are obtained from resins with a high percentage of cross-linking (figure 2A-3, data from Diamon, 1955). Values from figure 2A-3 predict an elution position of 40 ml and 85 ml for Sr in 6 and 2 molar HCL respectively. These values compare with elution positions found experimentally (figure 2A-2) of 40 ml and 110 ml for Sr in 6 and 2 molar HCL respectively. The effective use of cation exchange resins requires careful calibration of resin properties using real rock samples. Cation exchange columns used in this study were calibrated with dissolved rocks and minerals of known Rb and Sr concentrations. Twenty ml portions of elutant were analysed for Sr by atomic absorption and for Rb by X-ray fluorescence procedures. 2A-3. Isotopic spiking theory and spike data. Mass spectrometers measure isotopic ratios. To determine the concentration of Rb or Sr in a sample, a spike containing a known amount of Rb or Sr ;of known isotopic content, must f i r s t be added to the sample. The isotopic content of the spike is different from that of the sample. Isotopic ratios )resulting from mixture of spike plus sample^are measured in the mass spectrometer. These ratios in conjunction with knowledge of a sample weight and spike isotopic content, permit calculation of Rb or Sr concentrations of the sample. Equations and terms used to make such calculations are in table 2A-1. Spike solutions are calibrated using a solution of common Sr or Rb (shelf solution) whose concentration is accurately determined. Data for I 222 TABLE 2 A -J-l Rb AND Sr SHELF STANDARD DATA " Kb SHELF DATA Concentration = 99 8 ppm Rb t o t a l 8 7 R b / c = . 3857' / 8 5 R b Sr SHELF DATA Concentration = 991 ppm Sr t o t a l 8 7 S r / , . r = .71033 ±.0005 1 CT 8 4 S r / , = .05G8 8 4 S r / . o = -006782 8 4 S r / „ = .07995 / 8 6 S r / 6 8 S r / 8 7 S r Weight proportion of isotopes (%) molar proportions of isotopes (%) • - p c Sr 82.85 82.571 8 7 S r 6.948 7.004 8 6 S r 9.66 8 9.859 8 4 S r .536 .56 Reference Catanzaro et a l . fl969) 223 TABLE 2^ -JJT SPIKE CALIBRATIOU DATA Sr spike data 86 86, Sr p moles/ ml 1 .1195 2 .1198 concentration determinations 3 .1203 4 .1200 average .1199 ± .27 % lcr Sr spike (concentrated sgike J_ 87-Sr/ 8G Sr calculated .7150 .7118 .7058 .7144 . 7113 normalized correction to 87 Sr/ 86 Sr 8 6 , corrected concentration = .1192^1 moles Sr/ral 86 86 of .7113 gives .71033 Sr suike Sr u mo les/nl ( dilute spike ) 87 Sr, 86 calculated Sr concentration determinations average 1 .01790 2 .01766 3 .01796 4 .01789 5 .01796 .01737 ± .75 % 1 CT 87, .7167. .7117 .7142 normalized correction to "'Sr/gg of .7142 gives .71033 Sr 86 / corrected- concentration =• .ol758 yx moles Sr/ml 86 88, 5 ^ S r = .01721 ± .00007,1 cr Sr _spike isotope ratios 87 Sr/ 86 Sr 006894 i .000055^  1 o" 84 Sr spike_ calibrations 84 average Sr yx moles/ gm .02346 .02354 .02342 .02347 i .2 I lo spike composition 84, Sr 86 Sr 87 88 Sr Sr p gm/ gm 1.972 .0386 .0904 .3117 86 = . 0443 ± .3% lcr 87 84„ , Sr spike isotope ratjps_ Sr. 84 .01892 i .21 1 c Sr 8 V 8 84 wei.ght % 81.8 ' 1.6 3.7 12.9 .1509 i .1% lcr Sr 87 Rl) soike average 87 calibra tions PI) p moles/ml .2825 ' .2815 .2786 . 2307 .2808 +.6 % 1 cr Rb spike isotope ratios 87 Rb/ 85 = .00798. ± I-' % 1 o" Rb shelf solutions is in table 2A-JI. Errors in concentrations are considered to be less than .5%. I n i t i a l l y two Sr^^ spikes were used with concentrations of 86 86 approximately 1.5 ppm. Sr/ml and 10 ppm. Sr/ml (table 2A-UI) . Sr spikes were added to Sr splits with pipettes. Spike volumes of 1 ml could be added to Sr splits with an accuracy of + .3% (lcr ), 2 ml with an accuracy of + .2% ( l c ) and 5 ml with an accuracy of + .1% ( l j r ) . 84 Data for the Sr spike used for some determinations is in table 3A-UL ^ S r spike was added to samples using a 2.5 cc. syringe weighed before and after delivery of spike. Errors in delivery of ^ S r spike are considered to be negligible. o -j Calibration data for the Rb spike used is in table 3A-3. 8 7 Pipettes were used for delivering Rb spikes. The sample concentration can only be calculated i f addition of spike to sample produces a significant change in the sample isotopic ratios,as measured in the mass spectrometer. If the sample plus spike mixed ratio (M), is not very different from the original sample ratio (S) then small errors in measuring the former ratio (M) produce large errors in the calculated concentrations. For a particular spike there is an optimum mixture of spike plus sample which ensures that effect of measurement errors is kept to a minimum. The theory of optimum spiking and error magnification investigates the choice of optimum sample plus spike mixture. Error magnification (Em) is defined as error in sample concentration (Ec),divided by sample concentration (Sc), a l l over, error in mass spectrometer ratio (Er) } 225 226 divided by mass spectrometer ratio (R); or Es/Sc^Er/R = Em. The Em characteristics were calculated for a number of spikes (figures 2A-4 to 2A-6). The Em characteristics of a ^ S r spike are illustrated in figure 2A-4. Curve A gives error magnification associated with different sample plus spike mixed ratios (^Sr/^Sr M); for the ^ S r Spike solution used during this study ( 8 8Sr/ 8^Sr spike = . 0172, table 2A-IID . If spike is added such that this mixed ratio is between 1 and 10 then error in mass spectrometer measurement of the mixed ratio is amplified by a factor of 1 to 1.53when translated into error in calculated Sr concentration. Curve B gives Em values obtained when different spikes of different Sr/ Sr (spike) values (as indicated on the curve) are used, in the particular case when spike plus sample mixed ratio is optimum. It can be seen that in this case Em is large when Sr/ O DSr (spike) is large. Curve C (read using right hand cordinate) predicts amount of spike used at optimum spiking for different spikes. If the spike used has a ^ S r / ^ S r (spike) ratio of .1 (curve B) then optimum spiking occurs at a mixed ratio of 1 (ordinate scale). A mixed ratio of 1 predicts a Sr spike to sample ratio of about 1 (curve C right hand co-r-ordinate) . Equivalent data for ^Rb spike is presented in the form of similar curves in figure 2A-6. Spiking with 8 4 S r is more complicated. Both 8 4 S r and 8^Sr act as spike isotopes and each of the ratios 8 4 S r / 8 6 S r (M) and 8 4 S r / 8 6 S r (M) have optimum values. Figure 2A-5 illustrates data for the Sr spike used in this study. Curves A and B are plots of sample plus spike mixed ratios (bottom ordinate) against Em (right hand co-ordinate). The two 84 86 mixed ratios are not independent; curve C equates Sr/ Sr (M) l e f t O A g g co-ordinate with 4Sr/ Sr (M) top ordinate. Consideration of the three curves indicates that Em is less than 1.5 i f 8 4 S r / 8 ^ S r (M) is in the range 10 to .1. Ratios 8 4 S r / 8 6 S r (M) or 8 4 S r / 8 8 S r (M) can be used separately to calculate Sr concentration of sample. The two equations used can be combined so that ^Sr/o^Sr ( S) c a n b e calculated (equation in table 2A-1). Because of machine fractionation the calculated value of 8 6 S r / 8 8 S r (S) is rarely .1194 (the accepted value). Ratios 8 4 S r / 8 6 S r 84 88 (M) and Sr/ Sr (M) are corrected for fractionation (equation in table 2A-1) until a value of .1194 for 8 6 S r / 8 8 S r (S) is calculated. Sample concentrations and Sn values free of fractionation can then be calculated. The above correction cannot be made i f Sr spikes or Q -j Rb spikes are used. Optimum 8 4 S r spiking requires a spike sample ratio of .12 whereas Q £ optimum °Sr spiking requires a spike sample ratio of .8. The economic use of 8 4 spike offsets i t s high cost. 2A-4. Errors and corrections in mass spectrometer work. Errors in mass spectrometer work originate in a number of ways. A prime source of error is isotope fractionation which to a greater or lesser degree effects a l l isotope ratios and occurs in a l l source configurations. As a sample is analysed, measured values of Sn ratio change with time, generally increasing. This implies that the lighter O D S r isotope is being removed preferentially from the source. This 86 88 fractionation effect also changes Sr/ Sr (S) value of .1194. Table 2A-1 gives the isotope fractionation correction equation. Isotopic fractionation effects can be as much as .5% in O D S r / Sr ratio and half as much in Sn. 228 TABLE 2/4 - IV BLANK CONTAMINATION AND DUPLICATE MASS SPECTROMETER RUNS Sr Blanks 8 6 determinations p moles Sr A undistilled acid HCL .0015 B distilled acid HCL .00059 C ion column HCL .000013 A and B represent total blanks C represents blank from ion column only Rb Blanks Sr total p gms .13 .05 .01 determination 1 8 7 ji moles Rb .00028 .00038 Rb total yx gms .087 .118 sample 1 sample 2 Sr concentration duplicates  8 6Sr spike 8 4Sr spike % difference 223 ppm 269 and 271 ppm 22 8 ppm 2 % .7 % Rb concentration duplicates 87 sample 1 sample 2 Rb!spike • % difference 2379 ppm 2354 ppm 1 % 175ppm 174ppm .6% sample 1 sample 2 sample 3 sample 4 87 / Sy86 duplicate determinations ' Sr unspiked .7088 and .7088 .7060 and .7070 .7181 .7622 84-, Sr spiked .7182 .7600 difference 0 % .14 % .01 % .29 % 229 87 85 The maximum measured change in Rb/ Rb ratio of a Rb sample caused by isotope fractionation was .5%. An error of less than .5% attributable to isotope fractionation may exist in Rb concentrations, and in Sr concentrations determined using a Sr spike. Sample concentrations were determined by X-ray fluorescence, or by mass spectrometry using a ^ 4Sr, ^ S r , a n c j ^Rb spikes. The method of concentration determination has not been indicated for individual samples. Concentrations determined by X-ray fluorescence (Appendix 3A) are considered precise to + 1.7% (lcr) for Rb and + 1-5% ( l c ) for Sr. Mass spectrometer determinations are more precise than this. Blanket uncertainties in concentrations are set at + 1.7% (lcr) for Rb and + 1.5% ( l c ) for Sr. Values of Sn were measured from unspiked or 8 4 S r spiked mass spectrometer runs. As improvements were made to the mass spectrometer and analysis procedure, standard deviation of Sn measurements decreased. Over the duration of the study Sn values for rocks are considered precise to + .05% (lcr) and for micas to + .1% ( l c r ) . Duplicate mass spectrometer runs were made and chemical blanks analysed (table 2A-IV) . Consistent contamination of samples by common Sr does not affect calculated ages,but does change measured Sn values. Sr splits from mica samples usually contain 1 to 10 ugm. of Sr, when loaded into the mass spectrometer. A ratio of contaminant Sr to sample Sr of .01 is therefore possible and i f the Sn values of the contaminant and sample differ by .1 then the measured Sn value for the sample would be in error by .001 (figure 2A-7). This demonstrates the extreme case, usually Sr contamination alters Sn values much less. A l i s t of errors at l c contributing to overall error (lcr) in mass 230 spectrometrically determined Rb and Sr concentrations is as follows: total error includes error in shelf concentration (.5%); fractionation errors (.5%); measurement errors x Em (.1%); errors in spike delivery and weighing sample (.3%); errors derived from contamination (.1%); errors in spike concentration (.75%). The value of the square root, of the sum of the squares, of the individual 1 errors indicates that a total 1 cr error of 1% is reasonable. 2A-5. Mass spectrometer techniques. A 30 cm. 90 degree single focussing mass spectrometer was used for a l l analyses. The machine was built by the Geophysics Department, at The University of British Columbia,largely by John Blenkinsop as part of his thesis research. The operating procedures and specifications of the mass spectrometer are described by Blenkinsop (1972). The samples were analysed using t r i p l e rhenium filaments. Most analyses were made using a pre-set peak selection technique (peak hopping). About 30 scans of the spectrum were completed and in sequence group of 10 scans used to calculate isotope ratios. Rb was a problem in Sr analyses of micas but could usually be almost completely burned off during Sr analyses of rock samples. 2A-6. Rb decay constant. 8 7 It is d i f f i c u l t to measure the decay constant of Rb accurately. Ambiguity as to the correct value has led to use of two values. One of 1.47 x 10 ^ y r ^  was measured experimentally by Flynn et a l . , (1959), and supported by K-Ar and Rb-Sr comparisons made by Kulp and Engels, (1963). A second value of 1.39 x lO ^ ^ y r ^ was determined by Aldrich et al., (1956) by comparison of Rb-Sr and uranium lead ages. Kulp, (1961) when constructing his geologic time scale used 1.47 x 10 " L ±yr 1, as does the Geological Survey of Canada laboratory (Wanless et a l . , 1968). The author decided to use 1.47 x l O ' ^ y r ^. Obviously when comparing Rb-Sr ages i t is imperative to ensure that the same decay constant is used to calculate each age. A l l Rb-Sr ages quoted have been recalculated using a 1.47 x l O ^ ^ y r ^ decay constant. 233 APPENDIX 3A  X-RAY FLUORESCENCE TECHNIQUES 3A*--1. Introduction Rb-Sr geochronology requires the accurate determination of Rb and Sr concentrations. Usually these concentrations can be determined with sufficient accuracy by either mass spectrometer techniques, or the quicker X-ray fluorescence techniques. An X-ray fluorescence procedure for the precise determination of Rb and Sr concentrations was established. 3A-2. Theory of the X-ray fluorescence procedure The concentration of a particular element in a rock sample can be related to the intensity of a line in the fluorescent spectra generated by that element (equation A,table 3A-1). It is necessary to know the value of the mass absorption coefficient ( u ) to solve equation A. The value of u must be determined from some parameter in the X-ray spectra that is proportional to u. Not a l l X-ray photons incident on a sample cause the elements to fluoresce. Some, photons are scattered by co l l i s i o n with electrons. Scattering may occur without loss of energy (elastic or coherent scat-tering called Rayleigh scattering), or photons may suffer loss of en-ergy in which case their wavelength must increase (inelastic, inco-herent or Compton scattering, Comptbn and Allison., (1935)). The probability of Compton scattering increases as the energy of the electron with which the photon collides decreases. Electrons in particular shell in a light element have less energy than electrons in an equivalent shell in a heavier element. Therefore samples composed TABLE 3A-1 X RAY FLUORESCENCE BASIC EQUATIONS General equation x = u I / K (A) a ax xa. x = concentration of a particular element in sample a. a u = mas?-absorption coefficient at X of sample a . ax I = intensity (cps) of X ray peak generated by element x, xa K in sample a at wave-length A <• K = a constant x ppm = u I /K (B) a ax xa x ppm = u I A (C) s sx xs s = a standard in which concentration of x is known . (A)/(B) x ppm/x ppm-u I^xc/u I a s sx sx The relationships/derived by Hower (1959) and Reynolds (1963) u /u =u / u (D) ax sx a x (Mo K«*.) s x (Me K<*) u = m+n/CS u =ra+n/CS (E) ax (Mo Kct) a S A (Mo K*-) s CS = intensity (cps) of Compton scattered Mo Ketpeak,m and n are constants for the u v l/CS calibration line (see figure 3A-0) x ppm/x ppm = (m+n/CS )I / (m+n/CS ) i (F) a s a xa x; xs Equation (F) can be solved for concentration x i n sample a after constants m and n have been determined . 235 of l i g h t elements generate more Compton scat tered r a d i a t i o n than samples composed of h e a v i e r e lements. A measure of Compton s c a t t e r e d r a d i a t i o n from a sample i s r e l a t e d i n a general way to i t s chemical composi t ion and t h e r e f o r e to u . A molybdenum X - r a y tube emits a s t rong X - ray peak (MoK«) which i s i n - p a r t s c a t t e r e d by the sample as a Compton s c a t t e r e d Mo Kc< peak. Reynolds , (1963) showed exper imenta l ly that the Compton s c a t t e r e d MoKt* peak i n t e n s i t y ( 1 / C . S . tab le 3A-1) was p r o p o r t i o n a l to u. " ~ P r e v i o u s l y Hower (1959) had shown that i n the reg ion .4A to 1.7°A, f o r any two rock sampleSjthe va lue of the r a t i o of t h e i r u va lues was a -constant independent of wave - length . Reynolds was t h e r e f o r e ab le to w r i t e equations. B, C, D, E and F ( tab le 3A-1) . Equat ion F conta ins on ly one unknown; the concent ra t ion of element x i n the sample a. The c o n -c e n t r a t i o n of x can there fo re be c a l c u l a t e d . The method used i n t h i s study i s based on the above theory . 3A-3 . Cor rec t ions and e r r o r s i n X - r a y f luorescence work Under i d e a l o p e r a t i n g c o n d i t i o n s , r e p e a t e d measurement of a p a r -t i c u l a r s i g n a l over a shor t time span produces a fami ly of counts whose va lues d i s t r i b u t e a long a gaussian curve. I f the value o f a s i n g l e count (N) i s l a r g e then i t can be shown that the percentage s tandard d e v i a t i o n (%o-) o f a s i n g l e count i s 1000 %. This holds f o r a l l counts and d e -r i v e s from the f a c t that genera t ion of X-rays i s a random p r o c e s s . Th is d e v i a t i o n i s there fore the l i m i t i n g e r r o r i n a l l X - ray work and i s o f t e n masked by machine or sample e r r o r s . E r r o r s i n s i g n a l measurement may r e s u l t from shor t o r long term p r o c e s s e s . Machine e r r o r s c o n t r i b u t i n g to short term i n s t a b i l i t y r e s u l t from generator i n s t a b i l i t y and s i g n a l p rocess ing equipment. T o t a l shor t • 236 FIGURE 3 A - / L o n g l o r m X roy f l u o r e s c e n c e s l o b i l i l y plot cf r e p e a l e counts v s t i m e band ind ica tes lcr for i n d m d u o l •2% •4% 2 time fiou r 3 • I Z 5 * 5 -6 FIGURE Z A-i 237 term e r r o r i n s i g n a l at 1 cr can be w r i t t e n as e = e + e ^where e g s s i s the e r r o r from counting s t a t i s t i c s and e i s the machine e r r o r , g mostly r e s u l t i n g from generator f l u c t u a t i o n s . E decreases as the s number of counts increases,whereas e i s f i x e d q u a n t i t y , and when g count numbers are high becomes the l i m i t i n g f a c t o r c o n t r o l l i n g t o t a l short term e r r o r . The e r r o r i n s i g n a l measurement caused by generator i n s t a b i l i t y i s l e s s than .5% f o r the equipment used. Analyses of a batch of samples may take 10 hours or more during which time the machine must have rep r o d u c i b l e c h a r a c t e r i s t i c s . Long term d r i f t o r i g i n a t e s i n s i g n a l processing c i r c u i t s and the X^-ray tube, and can be kept to a minimum by a l l o w i n g adequate warm up time f o r the machine. At l e a s t two hours warm up time preceeded analyses and when p o s s i b l e the machine was switched on 24 hours p r i o r to a n a l y s i s . Long term d r i f t e f f e c t s were checked by repeatedly r e l o a d i n g a n a l y s i n g a s i n g l e bakelite» d i s c ( f i g u r e 3A-1). This produced a f a m i l y of counts whose average value was n. A .5% d r i f t i n count i n t e n s i t y was measured over a 7 hour p e r i o d . B e t t e r than 68.3% of the i n d i v i d u a l counts p l o t i n a band width of .13% of n ( f i g u r e 3A-1) suggesting a .065% standard d e v i a t i o n f o r a s i n g l e count which agrees w e l l w i t h the c a l c u l a t e d 100/jR" value. No long term d r i f t c o r r e c t i o n s were a p p l i e d to data during subsequent analyses and i f d r i f t was s i g n i f i c a n t the machine was e i t h e r allowed a longer warm up time or ^ .analyses were repeated at some other time. S i g n a l counters have a f i n i t e response time which means that i t takes them a few micro seconds to r e g i s t e r one photon during which time they cannot r e g i s t e r other in-coming photons. This time i s r e f e r r e d to as dead time. The r e s u l t of counter dead time i s ; t h a t count number 238 239 recorded is always less than the true total count. Most measurements were correctedffor dead time. The correction in micro seconds is given by the manufacturer. Effect of dead time correction is graphically i n -dicated in figure 3A-2. 3A-4. Analysis Procedures Samples can be analysed as unconsolidated fine rock powder but this introduces matrix problems. A relatively quick and reproducible method of preparing samples involves grinding rock samples to finer than 200 mesh size and then compacting the rock powder into 2.5 cm diameter discs with a press. For this study samples were compacted into pellets backed by a mixture of boric acid and bakelite. Rock powder was bonded with a few drops of-mowiel, an organic solution. Mowiel and boric acid were checked and found to be free of Rb and Sr contamination. A series of pellets containing increasing weights of a low absor-ption rock standard were analysed (figure 3A-3). These analyses i n d i -cated that 5 gms. of material totally absorbs the primary X-rays and is sufficient rock powder for a pellet. Ai mould designed to deliver at least 6 gms. of rock was used to make pellets. The pulse height discriminatdrjr? (P.H.A.) is used to improve the machine's performance. X-rays diffracted by the analysing crystal at a particular angle do not a l l have the same energy. The pulse height dis-criminator circuit acts as an energy f i l t e r and can be adjusted to dis-criminate against photons of certain energies, originating from elements not of interest. An energy s i l l below which no photons are registered is referred to as the lower level voltage. An upper limit of regis-tration can be fixed to form an energy window or channel width expressed 240 FIGURE 5A-+-Colibretion of pjlsu height" analyxer let Rb 241 in volts. The P.H.A. is adjusted to register photons generated by Rb and Sr. The machine is set up to count on the Rb or Sr peak and then with a narrow window (7 volts) the lower level is adjusted until a maximum reading is registered from the incoming signal. The lower level reading is then approximately proportional to the energy of incoming photons from Rb or Svff-y* 3A-S). Data from pulse height calibration for Rb and Sr is in figure 3A-5. Window width for general operation is 2.5x (peak width at 1/2 max-imum height)}or 2.5 x 160 = 400 volts,centered on a lower level setting of 470 volts, giving an actual lower level setting,oa half window width lower, of 270 volts. The lower level voltage span in figure 3A-4 cor-responding to the steep part offthe slope is approximately equal to op-timum window width. Center of the steep curve corresponds to lower level energy value equivalent to Rb photon energy. Pulse heights discriminator has two effects on the Rb and Sr peak signals. It decreases their absolute intensity and increases their peak to background ratio.. As already mentioned the error in a single count is given by 100//N\ It is therefore important to check that the s t a t i -s t i c a l advantages of a greater peak to background ratio resulting from use of the P.H.A. are not n u l l i f i e d by the higher 1 0" error associated with smaller peaks also resulting from use of the P.H.A. The P.H.A. can be used to advantage as long as the window allows 60% of the signal to pass. An alternate method of calibrating the P.H.A. is to increase the lower level voltage setting while keeping the window width at in f i n i t y . Figure 3A-4 illustrates P.H.A. calibration for Rb using this technique. Before routine analysis of samples can commence an accurate method 242 FIGURE 3A-<? Plot of moss absorption coefficients for chemical .'2 *4~ «6 '8 x 10 243 of determining u of samples and rock standards must be found. A number of chemical standards were made and u at .75° A calculated for each. Measurements were made on background, Mo K^and Mo KjuComp-;ton scattered (CS.) peaks for these standards. Data was plotted against u and i t was found that 1/QS. provided the best correlation with u, although Mo K*/ QS. and 1/background also formed linear plots against u. . Values of 1/C.S. for chemical standards are plotted against u calculated at .75°A (figure 3A-6). Rock standards and chemical stan-dards were run as a batch and a similar plot used to define u values for a l l rock standards. Baseline characteristics of a number of rocks were investigated by scanning. It was found that only one baseline position in the region of Rb and Sr peaks was free from interference. It was also evident that base-lines were of different intensities but a l l could be represented by a single curve. Using this curve and a single baseline position, baseline correction factors for Rb•and Sr peak positions were calculated. Samples and standards were analysed in batches. Peaks were ac-curately located before each batch of analyses. Samples and at least four standards were run in each batch. Analysis of each sample was pre-ceded by a 50 sec. count on a bakelite disc,kept in one sample holder. Comparison of these counts during analyses revealed any unusual insta-b i l i t y or d r i f t of the machine. A l l samples and standards were placed in the same holder and same loading slot. Analysis sequenceaand count times on samples are indicated in the data sheet (figure 3A-7). Counts were performed in sequence, l e f t to right on the data-sheet. Single sample analysis time is just over 7 244 51 1 A — 2 ± vl -4J I v. 1* 1 sl I •L ol V V 0 VJ s k Vj I V , ill Ul I v. V < 1.1 IS 245 minutes. Operating parameters and machine specifications are in table 3A-II. Rb and Sr concentrations were calculated from raw data as follows: a. A l l counts dead time corrected: b. Rock standards used to define a u v 1/C. S. calibration line; c. u for samples calculated; d. Rb and Sr peaks corrected for background; e. Rb and Sr corrected peak intensities for standards multiplied by u and plotted against concentration; f. u times Rb and Sr corrected peak intensities for samples used to determine Rb and Sr concentration for samples. This reduction procedure i s accomplished by a computer program written by John Blenkinsop (1972). Rock standards used include U.S.G.S. standards and samples pre-viously analysed by isotope dilution,during the present study. Cross-checks betweenU.S .G.S. and U.B.C. standards were made and no significant discrepencies found. Concentration values of U.S.G.S. standards used are l i s t e d in table 3A-IV. Values used are close to those used by other laboratories except in the case of G.S.P. I where the U.B.C. checks consistently predicted a higher Rb concentration. 3A-5. Precision of the method Samples were analysed using fixed time counting conditions (Jenkins, 1969). Error associated with fixed time counting at lcr % = lOO.Ji/rf'JRp-Rb R is count rate, p and b are peak and base and T is total count time on .peak plus base. A l l subsequent error values given are one standard de-viation errors. Using the above formula and count rates characteristic of the machine i t can be shown t h a t for a sample concentration of 20 ppm counting error is approximately 1.7% and at 100 ppm is approximately .5%. TABLE 3A-JJ X RAY FLUORESCENCE EQUIPMENT AND SETTINGS USED P h i l i p s equipment Voltage g e n e r a t o r PW 1011/60 X ray generator Pw 1050/85 S c i n t i l l a t i o n counter PW 4025 S c a l a r PW4231 Timer PW4261 Pulse shaper PWI365 A m p l i f i e r a n a l y s e r PW 4280 Rate meter PW1362 X ray tube Mo Operating parameters X ray tube v a l t a g e 50 Kv X ray tube amperage 30 Ma Pulse height d i s c r i m i n a t e r A t t e n u a t i o n 5 Window 400 V Lower l e v e l v o l t a g e 270 v firne constant .5 sec C r y s t a l L i t h i u m f l o u r i d e ('^200 C o l l i m a t o r s e t t i n g f i n e 247 These errors represent the smallest values that can be attained. Practical error expected can be calculated by considering errors accumulated at each measurement step. For a sample, error in measurement of 1/C.S. is .7% and error in u calibration curve is 1.2% (table 3A-IH) . Absorption is therefore determined with an error of 1.3%. Slope errors for Rb and Sr concentration curves are respectively 1% and .6% (table 3A-ffl) . Using these values ...the prac-t i c a l expected error for a sample with a concentration of 100 ppm Rb is 1.75% and for a concentration of 20 ppm Rb i t is 2.4%. The cor-responding errors for Sr are at 100 ppm,1.5% and at 20 ppm,2.3%. \ The value of Rb/Sr ratio is determined without using an absorption correction and is therefore generally determined more accurately than concentrations. A number of checks on precision of the X-ray fluorescence pro-cedure were made (table 2>k-JB) . Two pellets were made from the same sample and both pellets analysed. Results were compared and repro-ducibility was generally about 1%. A single standard was repeatedly loaded and analysed...during a •single batch of analyses. The 1 cr stan-dard deviation of the duplicate analyses was generally about 1%. The standard deviation of a l l individual errors, calculated using the ac-cepted accurate concentration was less than 1.5%. Most batches of analyses contained standards run as unknowns. For concentrations of 10 ppm to 40 ppm calculated concentrations/deviated from accepted con-centration by an average of 4%. Calculated concentrations greater than 40 ppm^on average.^deviated from accepted concentration by 1%. If concentrations of standards used are considered to be ac-curate, then in general the accuracy at 1 cr as determined experimen-t a l l y , for concentrations greater than 40 ppm is about 1.5% and this 248 T A B L E 5A-QI PRECISION AND ACCURACY OF X RAY FLU PRESENCE ANALYSTS pellet sample A 1 2 sample B 1 2 sample C 1 2 Dupl .icate U.S.G.S standard: . G.S. P. I Kb ppm Sr ppm ^Ar values used 261 235 1. 1106 1 266 237 1. 122 2 265 238 1. 110 3 26G 233 1. 118 4 265 237 1. 118 5 264 238 1. 109 average 265 233 1. 115 Pupli cate analyses separate pellets Rb 77.3 77.9 37.7 36.8 42.3 42.0 Sr difference 1 2.5 465.9 459.7 65.8 66.4 12.1. 7 121.9 % . di f f crcrice 1 same pellet^ same analysis hatch U.S.G.S.standard G.2, Rbppm Srppm F/Sr G.S. Kb ppm Sr ppm r atio Rb ppm Sr ppm values used 171 4S0 .3563 1 171 4 74 .3613 2 169 472 . 3533. 3 171 476 .3585 4 171 477 .3589 5 171 475 .3587 average 171 475 .3591 S.G,S value average % difference 1 cr 261 265 1.5 .35 235 235 1 .25 1.3 1.1106 1.115 .4 .7 171 171 0 .6 4 80 475 1 1.3 . 3563 .3591 .8 .5 sample Rbppm error U.B.C-l 99.1 1 A.G.V. 65.7 1.9 G.S.P. 1 262.2 .4 G.2 170.3 .6 U.B.C-l 98.9 1 . G .. 2 170.7 .2 G.S.P.I 261.3 .1 B.C. R. 48 .2 average error .7 Standards _run_ _as unknowns^  Srppm 11.3 662.6 233.8 478.8 11.7 480.5 234 .9 334.5 1 o" range of error 0 to 1.3 Slooe rrors 2 I ;i v Mo K<scattered = 1 Rb peak v Rb concentration Sr peak v Sr concentration 2.7 .6 .2 .25 1.7 .1 0 1.1 .8 to 1.4 error in 1.5 1.8 .9 .2 .8 .2 .1 1.2 0 to 1.4 Jiverage _of _13 values = 1 % .6 I TABr.K 3A-/V JiLS.^.J_^A2iDMp_^OCLJAMPIiES sample G. S .P. 1 1 R b ppm 261 Sr ppm 235 M- experi 6. 76 02 2 251 236 1 171 480 6.075 2 171 479 A.G.V 1 67 603 7.412 2 68 661 B. C. P. .1 1 48.2 331 9.61 W.l 2 48.3 3 34 1 21.G 190 9.225 p calculated 6.58 5.99 7.31 9.43 1 = Values found to be most internally consistent- by tbe author 2 = Values used by Fairbairn and Hurley (1973) t " r 249 is the accuracy assigned to the method. The theoretical maximum pre-cision for the same concentration range is about .5%. The expected practical precision found by summing errors incurred at each stage is about 2%. 3A-6. Comparison of present procedure with that of other laboratories A number of laboratories determine Rb and Sr concentrations and r values by X-ray fluorescence for routine Rb-Sr geochronologic work. Peterman et a l . (1968) determined r values by X-ray fluorescence and achieved a precision of 2.2% at 2 cr for a range of r values. Powell et a l . (1969). using a method very similar to that used in the present study quote a 1 cr precision of 1.9% and 1.46% for Rb-.and Sr concen-trations respectively. The U.S.G.S. X-ray flourescence technique for measuring r values is described in detail by Doering (1968) who quotes a 2 cr precision of 3%. A detailed reinvestigation of Reynolds (1963) linear u v 1/C.S. relationship by Fairbairn and Hurley (1971) convinced them that the re-lationship was linear over short segments of .the plot only. Background intensity is inversely propoetional to u. This has been used by many people to make a quick semi-quantative determination of u (Andermann and Kemp, 1958). Fairbairn and Hurley (1971) averaged u values cal-culated, for a single sample, using background and 1/C.S. to derive a single more accurate value for u. In the authors experience u v 1/C.S. is probably not a straight line over an extended range of u values but for range of u values of granitic rocks i t is safe to con-sider i t linear. The author used background v u relationship in a correction 250 procedure when analysing rock powder as opposed to pellets. Both 1/C.S and 1/background are proportional to u therefore a plot of 1/C.S v 1/background should be a straight line. Points not on the line must represent values of 1/C.S. or 1/background that do not predict a correct u. Such points can be corrected to the line and new u values calculated, or samples they represent reanalysed. The procedure is one of internal correction and i t appeared to have po s s i b i l i t i e s , but was not developed further. 3A-7. Summary An accurate rapid method of determining Rb and Sr concentrations and r values by X-ray fluorescence was developed. Total preparation time amounts to approximately 30 minutes, with analysis time an ad-ditional 20 minutes. The time required to determine concentrations by mass spectrometry is much longer. Precision of the X-ray fluorescence procedure at 1 cr is about 1.5% for most concentrations and r values. A 1% precision for con-centrations could be obtained by mass spectrometry over an extended concentration range but the r values would s t i l l be determined with an errorof greater than 1%. There are some practical constraints of the X-ray procedure. a. 6 gm of a sample are required. b. The u value of the sample must be in a limited range. c. Rb and Sr concentrations must be greater than 40 ppm. 251 APPENDIX 4A THEORY OF RB-SR GEOCHRONOLOGY 8 7 8 7 | IQ Rb decays to Sr with a h a l f - l i f e of 4.7x10 years . The decay can be d e s c r i b e d by the simple equation, 87Rb.(N) = 8 7 R b ( I ) e " A t ; equation 1 N = number of atoms at t = present; I = number of atoms at t = 0. T h i s equation can be r e w r i t t e n i n the form, 8 7 S r ( r a d i o g e n i c ) = 8 ? S r ( N ) - 8 7 S r ( I ) = 8 ? R b ( I ) - 8 ?Rb(N) = 8 7 R b ( N ) ( e A t - 1); equation 2 86 Sr i s a non r a d i o a c t i v e i s o t o p e unchanged i n c o n c e n t r a t i o n through-out time. Equation 2 can t h e r e f o r e be rewritten:'in the formj Sn - S i = r ( e A t - 1) equation 3 Sn = 8 7 S r / 8 6 S r ( N ) , S i = 8 7 S r / 8 6 S r ( I ) , r = 8 7 R b / 8 6 S r ( N ) . Terms Sn and r can be c a l c u l a t e d from mass spectrometer measurements. If a value f o r S i i s assumed then a s i n g l e sample provides a s o l u t i o n to equation 3. When a value f o r S i cannot be assumed, a s u i t e of cogenetic samples i s analysed and the r e s u l t s are presented g r a p h i c a l l y i n such a way that i f S i i s constant f o r the s u i t e t m.yr. (common age of s u i t e of samples) can be c a l c u l a t e d . Two g r a p h i c a l methods have been used. ThepGompston J e f f e r y p l o t and the Bernard P r i c e i n s t i t u t e , (B.P.I.) or i s o c h r o n p l o t . The Compston J e f f e r y p l o t (Compston and J e f f e r y , 1959) d e s c r i b e d i n d e t a i l by R i l e y and Compston, (1962) i s developed from equation 3 which can be r e w r i t t e n as; Xt. 8 7 8 7 (Sn - S i ) l / r = (e - 1) = Sr ( r a d i o g e n i c ) / Rb(N) equation 4. 252 8 7 8 6 8 7 87 On a Sr/ Sr v Sr ( r a d i o g e n i c ) / Rb p l o t each sample i s represented by a s t r a i g h t l i n e . The..gradient and the i n t e r c e p t 8 7 86 on the Sr/ Sr axis of each sample l i n e are known. If a l l samples a l s o had the same S i value then l i n e s i n t e r s e c t at t h i s S i value and the^x common age can be c a l c u l a t e d from equation 4 . An a l t e r n a t i v e method, the Bernard P r i c e I n s t i t u t e (B.P.I.) method was f i r s t i n t r o d u c e d by Hales (1960). 8 7 86 Equation 3, on a Sr/ Sr v r p l o t , i s a s t r a i g h t l i n e i f S i and t are constant f o r a l l samples. A number of oogenetic samples t h e r e f o r e p l o t as p o i n t s on a l i n e of constant age (isochron) whose grad i e n t i s ( e - 1). Most pap ers t h i s t h e s i s i n c l u d e d use the B.P.I, or i s o c h r o n diagram. Two events f o r example c r y s t a l l i z a t i o n (to m.yr.) and l a t e r metamorphism (tlm.yr.) may be recorded by i s o t o p e data. Rock samples which at to m.yr. had i d e n t i c a l S i .values d i s t r i b u t e along an i s o c h r o n l i n e (slope = ( e A t - 1)) on an i s o c h r o n diagram . This i s a whole rock i s o c h r o n . E q u i l -i b r a t i o n of mineral Sn values i n a s i n g l e parent rock sample at t l m.yr. may occur without d i s t u r b i n g the Sn value of Rb c o n c e n t r a t i o n of the parent rock sample. A second or mineral i s o c h r o n whose slope provides an age of t l m.yr. i s thereby formed U s u a l l y one or two micas plus a parent rock sample are s u f f i c -i e n t to d e f i n e a mineral i s o c h r o n , and provide an age f o r t h i s second event. As explained i n Appendix 1A there i s at best only a f i r s t order f i t of i s o t o p e data to t h i s geometric model. 253 TABLE 5 - A - 1 METHOD OF CALCULATING POTASSIUM CONCENTRATIONS . Terms W - weight of sample, w =v^i-ght of spike-- L - L i concentration of spike i n ppm. R = K ppm / L i ppm r a t i o for spike „ C = K ppm / K a b s L i p p m / L i abs for standard A = K / L i absorption (abs) r a t i o for a sample . K i n sample + spike = C. x A.x L.x w. K ppm in sample - * ( C.A.L.w -R.'L.w ) / W K ppm i n sample = w.L(CA - R) / W (1) Spike c h a r a c t e r i s t i c s L i concentration = 1649 ppm K ppm / L i ppm = .001 Na / L i = 20 TABLE S-A-Z Duplicate spectrophotometer analyses rock K % calculated K % accepted % difference G 2 3.48 3.69 6 G 2 3.91 6 G 2 3.62 2 G 2 3.75 2 G 2 3.27 11 G S P 4.65 4.56 2 254 APPENDIX 5A ATOMIC ABSORPTION SPECTROPHOTOMETRY Most samples were analysed f o r potassium . Analyses were made on a Tectron A. A. 4 atomic a b s o r p t i o n s p e c t r o -photometer belonging to the geology department. Samples of .1 to .5 gms were weighed out and d i s s o l v e d i n HF+H2So4. A f t e r d i s s o l u t i o n .the usual A. A. procedure i s to t r a n s f e r sample s o l u t i o n to a v o l u m e t r i c f l a s k ; d i l u t e to a known c o n c e n t r a t i o n range, and add a f i x e d amount of Na b u f f e r , before a n a l y s i n g j.the sample on the spectrophotometer. In t h i s study a f t e r d i s s o l u t i o n a known amount of Na b u f f e r e d L i spike s o l u t i o n ( t a b l e 5A-1) was added to each sample such that the r e s u l t i n g K / L i r a t i o was about one. Sample s o l u t i o n s were then d i l u t e d to any measureable c o n c e n t r a t i o n and the L i / K r a t i o measured on the spectrophotometer. The sample K c o n c e n t r a t i o n was c a l c u l a t e d from L.the K / L i a b s o r p t i o n r a t i o ( t a b l e 5A-1). K c o n c e n t r a t i o n s of samples were estimated p r i o r to s p i k i n g by using t h e i r Rb c o n c e n t r a t i o n s (250xRb = K) • .'. t Averaged flame photometer a n a l y s i s values of F l i e s e r (1962) were useddto provide K c o n c e n t r a t i o n s f o r U.S.G.S. standards G.2 and G.S.P.I. A sample of G.2 was spiked with L i d i s s o l v e d and d i l u t e d to known c o n c e n t r a t i o n s to provide a s e r i e s of absolute standards. These were used to d e f i n e L i and K c a l i b r a t i o n curves ( f i g u r e 5A-1). Other samples of G.2 were d i s s o l v e d and spiked to K / L i r a t i o s ranging from .5 to 3 and these plus a sample of G.S.P.I were t r e a t e d as unknowns. 256 A n a l y s i s o f t h e s e s a m p l e s ( t a b l e 5A-ff) i n d i c a t e d t h a t whan t h e K / L i r a t i o r a n g e s f r o m .5 t o 2 t h e a v e r a g e e r r o r i s 4%. The lcr e r r o r f o r t h e f i r s t f o u r G.2 a n a l y s e s ( t a b l e 5A-H) i s 5%. The mean of.t-he'::results,' i s . c l o s e t o t h e a c c e p t e d v a l u e . U s i n g a 5% s t a n d a r d d e v i a t i o n f o r K a n a l y s e s and a 2% s t a n d a r d d e v i a t i o n f o r Rb a n a l y s e s (assumed c o n c e n t r a t i o n g r e a t e r t h a n 40 ppm.) t h e n t h e lcr e r r o r f o r R v a l u e s i s 5.5%. The s p i k i n g method o f K a n a l y s e s r e q u i r e s l e s s l a b o r i t o r y work b u t ; i n v o l v e s more s p e c t r o p h o t o m e t e r m e asurements t h a n t h e t o t a l r e t e n t i o n and d i l u t i o n method. W i t h t h e s p i k i n g method s p i k e c a n be added v e r y • a c c u r a t e l y and s a m p l e s a r e a n a l y s e d i n n e a r l y i d e n t i c a l s o l u t i o n s so t h a t e r r o s s c a u s e d by v a r y i n g f l a m e i n t e r e f e r e n c e e f f e c t s a r e removed. . I n the 5; s i t u a t i o n where o n l y K m e a s u r e m e n t s a r e r e q u i r e d and K c o n c e n t r a i o n c a n be e s t i m a t e d b e f o r e h a n d t h e s p i k i n g method i s p r o b a b l y q u i c k e r and has t h e p o t e n t i a l f o r b e i n g more a c c u r a t e t h a n t h e t o t a l r e t e n t i o n and d i l u t i o n method. P L A T E B GEOLOGY OLIVER OSOYOOS AREA PHASE I AND 2 S T R U C T U R A L GEOLOGY >*" Axiol surfoce t race approximate inferred » l ^ " " p h a s * I t race Phase 2 (trace Synform Ant i form ^Wfvfv» S l ides approx imate i n f e r r e d •» ~ Hornblende minerol l i nea t ions general ly re la ted to phase I . Mico edge quorlz minerol and streak lineations generally phase 2 *"•£*— Isoclinal to light minor fo ld axis PLATE P L A T E D GEOLOGICAL SECTIONS OLIVER OSOYOOS AREA An north Bn north south VI Cn north south c Co tost 0 w west Ew west oast Fw ^ * T V""*"---. - . J • - t west • I VI VI .VIM oast Fo 2 " S Gw west oast Hw west VI VI ' • .N V oast Ho tw west oast lo 1 '/ Am I / * / III / II / l l / { / \ t i \ Kw west oast Ko LEGEND scale All sections start at sea level S O O O F t 4 0 0 0 3 0 0 0 2000 1000 0 '  I mile contacts approximate «*•« inferred approximate •-axiol plane traces r r . - ? -inferred 1 faults approximate inferred 


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