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Geology and geochronometry of the Eagle Plutonic Complex, Coquihalla area, southwestern British Columbia… Greig, Charles James 1989

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GEOLOGY AND GEOCHRONOMETRY OF THE EAGLE PLUTONIC COMPLEX, COQUIHALLA AREA, SOUTHWESTERN BRITISH COLUMBIA (92H/6,7,10,11) by CHARLES JAMES GREIG B.Comra., The University of B r i t i s h Columbia, 1981 B.Sc, The University of B r i t i s h Columbia, 1985 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Geological Sciences) We accept t h i s thesis as conforming to the required standard-THE UNIVERSITY OF BRITISH COLUMBIA JUNE, 1989 Charles James Greig, 1989 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Gc € P I €> CiJ Cg\ fE>e-» € ^ CeJ^> The University of British Columbia Vancouver, Canada DE-6 (2/88) ABSTRACT The Eagle plutonic complex forms the southern half of the 200 kilometer long, north-northwest trending Mt. Lytton-Eagle plutonic complex, which parallels the" regional structural grain in southwestern British Columbia and extends from south of the forty-ninth parallel to near Lytton (50° 30'N). The Mt. Lytton-Eagle complex lies along the westernmost margin of Quesnellia (Intermontane Belt), separating i t from terranes of the Coast-Cascade belt. In the Coquihalla area, the Eagle complex is bounded on the east by a west-dipping, syn-deformational intrusive contact against intensely foliated rocks of the Upper Triassic Nicola Group. On the west, the Eagle complex is in fault contact with Jurassic to Middle Eocene sedimentary rocks of the Methow-Pasayten trough. Four map-units have been distinguished within the Eagle complex in the Coquihalla area. Foliated Late Jurassic Eagle tonalite (155 + 4 Ma, U-Pb) at the eastern margin of the Eagle complex intrudes mylonitic Upper Triassic Nicola Group rocks and structurally overlies them along the moderately southwest dipping Eagle shear zone, which has a structural thickness of >1 kilometer and a strike length of >100 kilometers. Kinematic indicators suggest a top-to-the-east sense of shear. Locally, randomly oriented, strongly foliated Nicola Group inclusions occur in Eagle tonalite, indicating that deformation in part pre-dated emplacement of Eagle tonalite. More commonly, Nicola Group inclusions in Eagle tonalite are concordant, oblate and may contain foliated, boudined, ia or f o l d e d Eagle t o n a l l t e apophyses, suggesting t h a t deformation a l s o post-dated emplacement of Eagle t o n a l i t e . Contact r e l a t i o n s are i n t e r p r e t e d to represent e a s t - d i r e c t e d syn-kinematic emplacement of Eagle t o n a l i t e i n t o the N i c o l a Group i n Late J u r a s s i c time. In the c e n t r a l and western Eagle complex, Eagle t o n a l i t e grades i n t o w e l l - l a y e r e d t o n a l i t e o r t h o g n e i s s of Eagle g n e i s s , which a l s o comprises subordinate a m p h i b o l i t e and r a r e c a l c - s i l i c a t e . Eagle t o n a l i t e and gneiss are c r o s s c u t by mid-Cretaceous, muscovite-b e a r i n g , peraluminous plutons of the F a l l s l a k e p l u t o n i c s u i t e (110.5 +0.4 Ma, U-Pb), which have e x t e n s i v e l y r e s e t K-Ar and Rb-Sr sy s t e m a t i c s i n t h e i r host r o c k s . F a l l s l a k e s u i t e rocks c l e a r l y c r o s s c u t Late J u r a s s i c f a b r i c s i n Eagle t o n a l i t e and g n e i s s , but are themselves v a r i a b l y deformed. Near t h e i r western margin, a west-northwest t r e n d i n g f o l i a t i o n i s developed t h a t i n c r e a s e s i n i n t e n s i t y to the southwest, where i n t e n s e l y f o l i a t e d muscovite-bearing plutons are juxtaposed with Late J u r a s s i c Zoa complex hornblende quartz d i o r i t e (153 +. 10 Ma, U-Pb) along the Pasayten f a u l t . Kinematic i n d i c a t o r s from d u c t i l e l y s t r a i n e d rocks i n the Pasayten f a u l t give a c o n s i s t e n t s i n i s t r a l sense of shear with an e a s t - s i d e - u p component. Rubidium-Strontium and K-Ar muscovite dates from i n t e n s e l y deformed rocks y i e l d mid-Cretaceous dates of 97.2 + 2.1 and 105 + 4 Ma. Mid-Cretaceous c o o l i n g dates from l e s s deformed rocks of the F a l l s l a k e s u i t e are concordant with dates from the deformed r o c k s . Together with provenance t i e s between the Eagle complex and the l a t e A l b i a n to Cenomanian Spences Bridge and Pasayten groups, the dates i n d i c a t e t h a t the Eagle complex was unroofed approximately 10 to 15 Ma a f t e r i n t r u s i o n of the F a l l s l a k e s u i t e . U p l i f t and un r o o f i n g was probably accommodated by movement on the Pasayten f a u l t . On the west s i d e of the Eagle complex, Middle Eocene sedimentary rocks of the Pasayten trough o v e r l i e the Zoa complex along a moderately west d i p p i n g sheared contact that i s i n t e r p r e t e d as a nonconformity d i s r u p t e d d u r i n g east-vergent t h r u s t f a u l t i n g . In the so u t h , the Middle Eocene c l a s t i c sequence i s s t r u c t u r a l l y o v e r l a i n on i t s west s i d e by middle Cretaceous c l a s t i c r o c k s ; i n the n o r t h , Middle Eocene rocks are intr u d e d on t h e i r west s i d e by the Middle Eocene Needle Peak p l u t o n (46.0 + 1.6, 45.8 + 1.6 Ma, K-Ar Hb, B i ) , which c o n s t r a i n s east-vergent t h r u s t f a u l t i n g i n v o l v i n g the Middle Eocene sequence to Middle Eocene time. Up to 10 k i l o m e t e r s of d e x t r a l s t r i k e - s l i p movement occurred on the no r t h - n o r t h e a s t t r e n d i n g Zoa f a u l t i n post-Middle Eocene time. Movement on the Zoa f a u l t may be coeva l with post-Middle Eocene to E a r l y Miocene movement on the northeast t r e n d i n g , southeast-side-down, d e x t r a l C o q u i h a l l a f a u l t . i i i TABLE OF CONTENTS ABSTRACT i a TABLE OF CONTENTS iv LIST OF FIGURES ix LIST OF TABLES xix LIST OF APPENDICES xx LIST OF PLATES xxi CHAPTER 1: INTRODUCTION 1 I. INTRODUCTION 1 I I . LOCATION AND ACCESS 2 I I I . PHYSIOGRAPHY, CLIMATE AND VEGETATION 2 IV. FIELDWORK AND METHODS 6 V. ACKNOWLEDGEMENTS 6 CHAPTER 2 : TECTONIC SETTING 8 I. INTRODUCTION 8 I I . QUESNELLIA, WRANGELLIA, AND THE SUPER- AND MEGATERRANES 1 0 A. QUESNELLIA 1 0 B. WRANGELLIA 1 4 C. INSULAR-INTERMONTANE SUPERTERRANE BOUNDARY . . . 1 4 I I I . SMALLER TERRANES OF THE COAST-CASCADE BELT . . . . 1 6 A. TYAUGHTON-PASAYTEN-METHOW TROUGH 1 6 1 . PASAYTEN TROUGH 1 7 2 . METHOW TROUGH 1 8 3 . TYAUGHTON TROUGH 1 9 B. BRIDGE RIVER-HOZAMEEN AND CADWALLADER TERRANES . 2 0 C. SKAGIT SUITE* 2 1 D. NORTHWEST CASCADES SYSTEM (NWCS) 2 2 IV. CONCLUSIONS 2 3 CHAPTER 3 : PREVIOUS WORK 2 4 I. INTRODUCTION 2 4 I I . EAGLE PLUTONIC COMPLEX 2 4 A. H. BAUERMAN 26 B. G.M. DAWSON 2 7 C. R.A. DALY 3 0 D. G.C. SMITH AND F.C. CALKINS 3 2 E. CHARLES CAMSELL 3 3 F. C.E. CAIRNES 3 5 G. H.M.A. RICE 4 0 H. GEOCHRONOMETRY OF THE 1 9 6 0'S AND EARLY 1 9 7 0 ' S . 4 1 I. J.A. COATES 4 3 J. PHILLIP ANDERSON 4 4 iv K. "THE CHIEF" 45 I I I . MT. LYTTON PLUTONIC COMPLEX 46 IV. NICOLA GROUP ROCKS IN CONTACT WITH THE EAGLE COMPLEX 48 A. G.M. DAWSON 49 B. CHARLES CAMSELL 51 C. C.E. CAIRNES 53 D. H.M.A. RICE 54 E. G.E.P. EASTWOOD 55 F. D.C. FINDLAY 57 G. PHILLIP ANDERSON 58 H. -J-; NELSON 58 I. G.T. NIXON AND V.J. RUBLEE 59 CHAPTER 4: MAP UNITS 60 I . INTRODUCTION 60 II . NICOLA GROUP 6 0 A. INTRODUCTION AND SUMMARY 60 B. Dl STRIBUTI ON . 6 2 C. LITHOLOGY AND COMPOSITION . 6 2 D. PETROGRAPHY 68 E. GENERAL STRUCTURE . 71 F. DISCUSSION 71 III . ZOA COMPLEX 73 A. INTRODUCTION AND SUMMARY 7 3 • B. DISTRIBUTION 74 C. METAVOLCANIC ROCKS 74 1. INTRODUCTION AND SUMMARY 7 4 2. DISTRIBUTION 75 3. LITHOLOGY AND COMPOSITION 75 4. GENERAL STRUCTURE 76 5. PETROGRAPHY 7 8 6. DISCUSSION 7 78 D. ZOA COMPLEX PLUTONIC ROCKS--HORNBLENDE (QUARTZ) DIORITE 80 1. INTRODUCTION AND SUMMARY 80 2. DISTRIBUTION 80 3. NORTHERN BELT 81 4. SOUTHERN BELT 9 0 E. DISCUSSION 95 IV. EAGLE TONALITE 9 6 A. INTRODUCTION AND SUMMARY 9 6 B. LITHOLOGY AND COMPOSITION 9 7 1. INTRODUCTION AND SUMMARY 9 7 2. DESCRIPTION 97 3. GRAIN SIZE AND GRAIN SIZE VARIATIONS . . . 98 4. INCLUSIONS 98 C. GENERAL STRUCTURE 101 D. PETROGRAPHY 104 E. CONTACT RELATIONS 108 F. DISCUSSION 112 V. FALLSLAKE PLUTONIC SUITE 114 v A. INTRODUCTION AND SUMMARY 114 B. DISTRIBUTION 114 C. CORRELATIVE ROCKS 115 D. LITHOLOGY AND COMPOSITION 116 1. INTRODUCTION AND SUMMARY 116 2. LARGE INTRUSIONS 118 3. SMALLER MUSCOVITE-BEARING INTRUSIONS—FORM AND'COMPOSITION 119 E. CONTACT RELATIONS 123 1. EXTERNAL CONTACT RELATIONS 123 2. INTRA-PLUTON CONTACT RELATIONS 132 F. GENERAL STRUCTURE 137 G. PETROGRAPHY 138 1. INTRODUCTION AND SUMMARY 138 2. LARGER INTRUSIONS 138 3. SMALLER INTRUSIONS 140 4. FINE-GRAINED TONALITE INCLUSIONS AND FINE-GRAINED "CONTACT PHASE" 140 H. DISCUSSION 145 VI. EAGLE GNEISS 146 A. INTRODUCTION AND SUMMARY 146 B. DISTRIBUTION 146 C. LITHOLOGY AND COMPOSITION 147 1. TONALITE ORTHOGNEISS AND AMPHIBOLITE . . . 147 2. MARBLE AND CALC-SILICATE 151 D. CONTACT RELATIONS 151 E. GENERAL STRUCTURE 157 F; PETROGRAPHY 157 G. DISCUSSION 160 VII. MIDDLE CRETACEOUS SEDIMENTARY ROCKS 161 VIII. UNDIVIDED TERTIARY INTRUSIONS 162 A. EOCENE STOCKS 162 B. TERTIARY DIKES 164 IX. MIDDLE EOCENE CLASTIC ROCKS 170 A. INTRODUCTION AND SUMMARY 170 B. LITHOLOGY AND COMPOSITION 171 X. NEEDLE PEAK PLUTON 175 XI. COQUIHALLA VOLCANIC COMPLEX 180 CHAPTER 5: GEOCHRONOMETRY 183 I . INTRODUCTION 183 I I . U-PB DATING, ANALYTICAL RESULTS AND INTERPRETATIONS 184 A. ZOA COMPLEX 184 B. EAGLE TONALITE AND GNEISS 187 C. FALLSLAKE PLUTONIC SUITE 198 I I I . K-AR AND RB-SR DATING, ANALYTICAL RESULTS AND INTERPRETATIONS '. 204 A. INTRODUCTION 204 B. NICOLA GROUP 205 C. ZOA COMPLEX 213 D. EAGLE TONALITE AND GNEISS . 215 v i E. FALLSLAKE PLUTONIC SUITE 220 F. EARLY EOCENE INTRUSIONS 224 G. NEEDLE PEAK PLUTON 227 H. MIDDLE EOCENE ANDESITE DIKES 228 I. COQUIHALLA VOLCANIC COMPLEX 228 IV. DISCUSSION AND SYNTHESIS 232 A. INTRODUCTION 232 B. MAGMATIC EPISODES 232 C. MIDDLE CRETACEOUS PLUTONISM AND RESETTING . . . 234 D. GEOCHRONOMETRIC CONSTRAINTS ON DEFORMATIOM . . . 235 E. STRONTIUM ISOTOPIC COMPOSITIONS 237 CHAPTER 6: GEOCHEMISTRY 240 I. INTRODUCTION 240 II . MAJOR ELEMENT GEOCHEMISTRY 240 II I . TRACE AND RARE EARTH ELEMENT (REE) GEOCHEMISTRY . . 250 A. MAFIC ROCKS 250 1. AMPHIBOLITE 251 2. BASALT DIKES OF COQUIHALLA VALLEY 252 B. "TONALITE" SUITE AND FALLSLAKE PLUTONIC SUITE . 254 IV. FALLSLAKE PLUTONIC SUITE: DISCUSSION OF I-TYPE AND S-TYPE AFFINITIES AND POSSIBLE ORIGIN 260 CHAPTER 7: STRUCTURAL GEOLOGY 265 I. INTRODUCTION AND SUMMARY 265 II . UPPER TRIASSIC NICOLA GROUP 267 A. INTRODUCTION AND SUMMARY . . 2 6 7 B. DESCRIPTION 268 C. DISCUSSION 274 II I . ZOA COMPLEX 276 A. INTRODUCTION AND SUMMARY 276 B. DESCRIPTION 276 C. DISCUSSION 283 IV. FALLSLAKE PLUTONIC SUITE 284 A. INTRODUCTION AND SUMMARY 284 B. DESCRIPTION 285 C. DISCUSSION 296 V. EAGLE TONALITE AND GNEISS 297 A. INTRODUCTION AND SUMMARY 297 B. DESCRIPTION 298 C. DISCUSSION 310 VI. MIDDLE EOCENE SEDIMENTARY ROCKS 318 A. DISCUSSION 322 VII. OTHER TERTIARY STRUCTURES 326 A. INTRODUCTION AND SUMMARY 326 B. ZOA FAULT 328 C. COQUIHALLA FAULT 329 D. PASAYTEN FAULT 330 E. ANDES I TE DIKES 333 CHAPTER 8: GEOLOGIC EVOLUTION OF THE COQUIHALLA AREA . . . . 334 A. LATE TRIASSIC-EARLY JURASSIC 334 v i i B. MIDDLE TO LATE JURASSIC 334 C. CRETACEOUS 336 D. TERTIARY 338 REFERENCES CITED 339 APPENDICES 358 APPENDIX 5.1: ANALYTICAL RESULTS, GEOCHRONOMETRY . . . 358 APPENDIX 5 . I I : ANALYTICAL PROCEDURES . . 410 APPENDIX 5.IIA: U-PB ANALYTICAL TECHNIQUES . . . . 410 APPENDIX 5.IIB: K-AR ANALYTICAL TECHNIQUES . . . . 412 APPENDIX 5.IIC: RB-SR ANALYTICAL TECHNIQUES . . . 413 APPENDIX 6.IA: WHOLE ROCK GEOCHEMISTRY SAMPLE LOCATION AND LITHOLOGY 415 APPENDIX 6 .IB: ANALYTICAL RESULTS, GEOCHEMISTRY 416 APPENDIX 6 . I I : GEOCHEMICAL TECHNIQUES 422 v i i i y LIST OF FIGURES F i g u r e 1.1: View east-southeast to I n t e r i o r P l a t e a u from r i d g e 1 k i l o m e t e r southwest of C o q u i h a l l a Mtn.; view from same p o i n t as F i g u r e 1.2. 4 F i g u r e 1.2: View northwest to Coast-Cascade mountains from r i d g e 1 ki l o m e t e r SW of C o q u i h a l l a Mtn.; view from same po i n t as F i g u r e 1.1 5 F i g u r e 2.1: G e n e r a l i z e d t e r r a n e map of the Canadian C o r d i l l e r a ; i n s e t s show f i v e g e o l o g i c - p h y s i o g r a p h i c s u b d i v i s i o n s of the Canadian C o r d i l l e r a and area d e p i c t e d i n F i g u r e 2.2 ' 11 F i g u r e 2.2: Terrane map of SW BC & NW Wash.; M=Methow, TY=Tyaughton, P=Pasayten, HZ=Hozameen, HA=Harrison, NWCS=Northwest Cascade, BR=Bridge R i v e r , CD=Cadwallader, SK=Skagit ( i n c l u d e s CM,NS,SW,I,LJ, see t e x t ) , CZ=Cenozoic, f o r others see F i g u r e 2.1 12 F i g u r e 3.1: L o c a t i o n map f o r previous work, Eagle and Mt. L y t t o n p l u t o n i c complexes 25 F i g u r e 4.1: S i m p l i f i e d geology, C o q u i h a l l a area 61 F i g u r e 4.2: P a r t i a l l y u r a l i t i z e d clinopyroxerie p o r p h y r o c l a s t i n a m p h i b o l i t i c s c h i s t , N i c o l a Group, Skwum Creek. Width of f i e l d of view i s 7 mm 64 F i g u r e 4.3: Weakly-developed c o m p o s i t i o n a l l a y e r i n g i n N i c o l a Group a m p h i b o l i t e ; f o l i a t i o n p a r a l l e l t o l a y e r i n g . Width of f i e l d of view i s 2 mm 64 F i g u r e 4.4: F o l i a t e d marble, N i c o l a Group, Murphy Lakes. . 66 F i g u r e 4.5: C a l c - s i l i c a t e at the contact between N i c o l a Group marble and f o l i a t e d s i l l , Tulameen R i v e r 66 F i g u r e 4.6: I n t e r l a y e r e d q u a r t z o f e l d s p a t h i c s c h i s t (pale c o l o u r ) and a m p h i b o l i t e , N i c o l a Group, Tulameen R i v e r road 67 F i g u r e 4.7: Stained s l a b of q u a r t z o f e l d s p a t h i c s c h i s t ( d u c t i l e l y s t r a i n e d s i l l ) , N i c o l a Group, Law's Camp. . . 67 F i g u r e 4.8: P r e f e r r e d g r a i n shape o r i e n t a t i o n of c a l c i t e t y p i c a l of f o l i a t e d marble, N i c o l a Group, Skwum Creek. Width of f i e l d of view i s 5 m i l l i m e t e r s 70 F i g u r e 4.9: Hand specimen of amygdaloidal metavolcanic r o c k , Zoa complex, near Highway 5 summit 77 F i g u r e 4.10: Weakly s t r a i n e d fragmental metavolcanic r o c k s , Zoa complex, between Romeo and Iago, abandoned KVRR grade, C o q u i h a l l a V a l l e y 77 F i g u r e 4.11: D i o r i t e i n j e c t i o n complex, Zoa complex, Thar Peak; note g r a i n s i z e v a r i a t i o n s between "phases." L a y e r i n g i s igneous i n o r i g i n and u n r e l a t e d to d u c t i l e s t r a i n 82 F i g u r e 4.12: Hand specimen ( s t a i n e d ) showing g r a i n s i z e v a r i a t i o n i n hornblende quartz d i o r i t e ; Zoa complex, Zoa Peak ~. 83 F i g u r e '4.13: Hornblende d i o r i t e i n j e c t i o n complex, Zoa complex, Zoa Peak; outcrop shows e a r l y u n f o l i a t e d medium-grained phase and c r o s s - c u t t i n g v e r y f i n e - g r a i n e d i x (1) and f i n e - to medium-grained phases (2) of s i m i l a r composition 84 F i g u r e 4.14: Oblate and concordant very f i n e - g r a i n e d metavolcanic i n c l u s i o n s i n weakly f o l i a t e d hornblende quartz d i o r i t e , Zoa complex, Thar Peak. Outcrop s u r f a c e i s at an acute angle to the f a b r i c 86 F i g u r e 4.15: D i o r i t e agmatite with v e r y f i n e - g r a i n e d d i o r i t e i n c l u s i o n s i n a f i n e - g r a i n e d d i o r i t e m a t r i x , Zoa complex, Coldwater R i v e r V a l l e y 86 F i g u r e 4.16: U n f o l i a t e d hornblende quartz d i o r i t e , Zoa complex, Thar Peak 87 F i g u r e 4.17: S u i t e of samples of v a r i a b l y s t r a i n e d hornblende quartz d i o r i t e from NE margin of the Zoa complex, western slop e s of Dear Mtn.; p r o g r e s s i v e i n c r e a s e i n s t r a i n from bottom (protomylonite ) to top ( u l t r a m y l o n i t e ) 92 F i g u r e 4.18: Stained s l a b of f o l i a t e d Eagle t o n a l i t e with f o l i a t i o n o u t l i n e d by p r e f e r r e d g r a i n shape o r i e n t a t i o n of p l a g i o c l a s e f e l d s p a r and b i o t i t e ; note a l t e r a t i o n selvages along f r a c t u r e - v e i n l e t s h i g h l i g h t e d by s t a i n i n g . 99 F i g u r e 4.19: B i o t i t e - m e g a c r y s t i c Eagle t o n a l i t e , near Eagle t o n a l i t e / n o r t h e r n F a l l s l a k e p l u t o n c o n t a c t , J u l i e t Creek 99 F i g u r e 4.20: Stained specimen of b i o t i t e megacrystic Eagle t o n a l i t e (or g r a n o d i o r i t e ) with u n u s u a l l y high potassium f e l d s p a r content; near Eagle t o n a l i t e / n o r t h e r n F a l l s l a k e p l u t o n c o n t a c t , J u l i e t Creek; sample cut p e r p e n d i c u l a r to f o l i a t i o n 100 F i g u r e 4.21: P y t g m a t i c a l l y f o l d e d t o n a l i t e apophyses w i t h i n meter-scale a m p h i b o l i t e s c r e e n , Eagle t o n a l i t e , s e v e r a l 100 meters southwest of Upper Coldwater e x i t ramp, Highway 5 102 F i g u r e 4.22: G n e i s s i c Eagle t o n a l i t e , Tulameen R i v e r , showing f a b r i c d e f i n e d by narrow continuous b i o t i t e f o l i a . . . . 103 F i g u r e 4.23: W e l l - f o l i a t e d Eagle t o n a l i t e , J u l y Mtn.; f o l i a t i o n p a r a l l e l to hammer handle 103 F i g u r e 4.24: F o l i a t e d Eagle t o n a l i t e with t y p i c a l weakly-developed "augen" or f l a s e r t e x t u r e and weakly ribboned quartz aggregates wrapping around p l a g i o c l a s e f e l d s p a r " p o r p h y r o c l a s t s . " 106 F i g u r e 4.25: Eagle t o n a l i t e , showing zoned primary epidote with a l l a n i t e c o r e , Tulameen R i v e r ; crossed p o l a r i z e r s , width of f i e l d of view 7 mm 106 F i g u r e 4.26: Eagle t o n a l i t e , showing embayed and i n c l u s i o n - r i c h primary e p i d o t e ; J u l i e t Creek; crossed p o l a r i z e r s , width of f i e l d of view i s 6 mm 107 F i g u r e 4.27: Eagle t o n a l i t e , showing primary epidote i n c o n t a c t with l a t e r b i o t i t e ; J u l i e t Creek; crossed p o l a r i z e r s , width of f i e l d of view i s 6 m 107 F i g u r e 4.28: I n t e n s e l y f o l i a t e d a m p h i b o l i t e i n c l u s i o n concordant with w e l l - f o l i a t e d (upper r i g h t to lower l e f t ) x Eagle t o n a l i t e , note f o l i a t e d and boudlned t o n a l i t e apophyses near hammer; near Murphy Lakes 110 F i g u r e 4.29: D e t a i l of F i g u r e 4.28 showing f o l i a t e d and boudined t o n a l i t e apophyses w i t h i n i n t e n s e l y f o l i a t e d a m p h i b o l i t e i n c l u s i o n , Murphy Lakes area 110 F i g u r e 4.30: F o l i a t e d marble and amphibolite i n c l u s i o n s i n u n f o l i a t e d to weakly f o l i a t e d Eagle t o n a l i t e , Murphy Lakes I l l F i g u r e 4.31: Stained hand specimen of b i o t i t e muscovite g r a n o d i o r i t e / t o n a l i t e , c e n t r a l F a l l s l a k e p l u t o n , near F a l l s l a k e e x i t , Highway 5; note mottled d i s t r i b u t i o n of potassium f e l d s p a r ( y e l l o w ) . 117 F i g u r e 4.32: Stained specimen of m y l o n i t i c muscovite t o n a l i t e from the southwest margin of the northern F a l l s l a k e p l u t o n , upper East Anderson R i v e r ; note the potassium . f e l d s p a r - p o o r n a t u r e . Width of f i e l d of view i s 8 cm. . 120 F i g u r e 4.33: F i n e - g r a i n e d "contact phase," J u l y Mtn.; note potassium f e l d s p a r enrichment along v e i n 120 F i g u r e 4.34: F o l i a t e d garnet muscovite monzogranite i n t r u s i o n of the F a l l s l a k e p l u t o n i c s u i t e , Eagle g n e i s s , J u l y Mtn. area 121 F i g u r e 4.35: Muscovite monzogranite pegmatite, "pink pegmatite," F a l l s l a k e p l u t o n i c s u i t e , Highway 5 t o l l b o o t h . 121 F i g u r e 4.36: "Pink pegmatite" of the F a l l s l a k e p l u t o n i c s u i t e c u t t i n g t o n a l i t e o r t h o g n e i s s o£ the Eagle g n e i s s , Highway 5 t o l l b o o t h . 122 F i g u r e 4.37: Pale-weathering muscovite monzogranite pegmatite dike (roughly 2-3 m wide) of the F a l l s l a k e p l u t o n i c s u i t e c u t t i n g t o n a l i t e o r t h o g n e i s s of Eagle g n e i s s , Highway 5, approximately 2 km SW of t o l l b o o t h 125 F i g u r e 4.38: A p l i t i c to p e g m a t i t i c garnet muscovite monzogranite i n t r u s i o n of the F a l l s l a k e s u i t e c u t t i n g Eagle g n e i s s , approx. 1 km south of C o q u i h a l l a Lakes. . 126 F i g u r e 4.39: White-weathering b i o t i t e muscovite monzogranite dik e of the F a l l s l a k e s u i t e i n t r u d i n g and c r o s s - c u t t i n g the f a b r i c (upper l e f t to lower r i g h t ) i n t o n a l i t e o r t h o g n e i s s of Eagle g n e i s s , J u l y Mtn. area 126 F i g u r e 4.40: Migmatite f a b r i c i n Eagle g n e i s s , showing extreme m o b i l i t y and v a r i a b l e compositions of Eagle gneiss and h y b r i d ( ? ) phases near northern F a l l s l a k e p l u t o n / E a g l e gneiss c o n t a c t , J u l y Mtn 128 F i g u r e 4.41: Migmatite f a b r i c , Eagle g n e i s s ; c r o s s - c u t t i n g l e u c o c r a t i c h y b r i d ( ? ) phase and mobile Eagle g n e i s s , near northern F a l l s l a k e pluton/Eagle gneiss c o n t a c t , J u l y Mtn. . .' . 128 F i g u r e 4.42: Migmatite f a b r i c , Eagle g n e i s s ; mobile l a y e r e d Eagle g n e i s s / n o r t h e r n F a l l s l a k e p l u t o n h y b r i d ( ? ) phase c r o s s - c u t t i n g f o l d e d Eagle g n e i s s , J u l y Mtn 129 F i g u r e 4.43: L i t - p a r - l i t s i l l s of pale weathering b i o t i t e m u s c o v i t e g r a n o d i o r i t e / m o n z o g r a n i t e i n t r u d i n g x i n o r t h e a s t - d i p p i n g Eagle g n e i s s , J u l y Mtn. F i g u r e 4.44 i s a c l o s e - u p of Eagle gneiss from t h i s outcrop 129 F i g u r e 4.44: Close-up of Eagle gneiss from F i g u r e 4.43, showing development of o b l a t e and concordant b i o t i t e c l o t s or lozenges i n o r t h o g n e i s s l a y e r sandwiched by F a l l s l a k e s u i t e s i l l s ; J u l y Mtn 133 F i g u r e 4.45: Eagle gneiss i n c l u s i o n i n u n f o l i a t e d b i o t i t e t o n a l i t e h y b r i d ( ? ) phase near northern F a l l s l a k e / E a g l e t o n a l i t e / E a g l e g n e iss c o n t a c t , J u l y Mtn 133 F i g u r e 4.46: Rare muscovite-bearing i n c l u s i o n i n weakly f o l i a t e d b i o t i t e t o n a l i t e h y b r i d ( ? ) phase, northern F a l l s l a k e p l u ton/Eagle t o n a l i t e c o n t a c t , J u l y Mtn. . . . 134 F i g u r e 4.47: Complex disharmonic f o l d i n g i n l a y e r e d Eagle g n e i s s , lower Jim K e l l y Creek 134 F i g u r e 4.48: B i o t i t e r e s t i t e ( ? ) at contact between pale weathering u n f o l i a t e d b i o t i t e muscovite g r a n o d i o r i t e of the northern F a l l s l a k e p l u t o n (bottom, l e f t ) and weakly f o l i a t e d Eagle t o n a l i t e ( t o p , r i g h t ) , J u l y Mtn; note lack of c h i l l e d c o n t a c t s . 135 F i g u r e 4.49: I n t e r f i n g e r i n g u n f o l i a t e d f i n e - g r a i n e d t o n a l i t e "contact phase" and pale weathering b i o t i t e muscovite g r a n o d i o r i t e , northern F a l l s l a k e p l u ton/Eagle t o n a l i t e ' c o n t a c t , J u l y Mtn. 135 F i g u r e 4.50: A g m a t i t i c i n t r u s i v e c o n t a c t showing r o t a t e d blocks of Eagle gneiss i n matrix of F a l l s l a k e s u i t e b i o t i t e muscovite g r a n o d i o r i t e ; J u l y Mountain 136 F i g u r e 4.51: I n t r u s i v e stockwork with pale weathering F a l l s l a k e s u i t e b i o t i t e muscovite g r a n o d i o r i t e or monzogranite i n t r u d i n g Eagle g n e i s s , J u l y Mtn; view l o o k i n g northwest 136 F i g u r e 4.52: Pink pegmatite of the F a l l s l a k e s u i t e i n t r u d i n g and p y t g m a t i c a l l y f o l d e d with t o n a l i t e o r t h o g n e i s s of Eagle g n e i s s , Highway 5 t o l l b o o t h 141 F i g u r e 4.53: White-weathering monzogranite pegmatite dike of the F a l l s l a k e s u i t e i n t r u d i n g o r t h o g n e i s s and a m p h i b o l i t e of Eagle g n e i s s ; i t s e l f o f f s e t on d i s c r e t e l a y e r - p a r a l l e l d u c t i l e shear zones; KVRR abandoned grade, C o q u i h a l l a canyon 142 F i g u r e 4.54: B i o t i t e muscovite g r a n o d i o r i t e / t o n a l i t e , c e n t r a l F a l l s l a k e p l u t o n ; note c o e x i s t e n c e of b i o t i t e with muscovite; crossed p o l a r i z e r s , f i e l d of view i s 6 mm. . 142 F i g u r e 4.55: M y l o n i t i c muscovite t o n a l i t e of the northern F a l l s l a k e p l u t o n , showing h i g h l y elongate quartz r i b b o n g r a i n s and i n t e n s e l y a l t e r e d p l a g i o c l a s e ; plane l i g h t , width of f i e l d of view i s 1 cm 143 F i g u r e 4.56: Muscovite monzogranite pegmatite showing gr a p h i c intergrowths of muscovite and q u a r t z ; approximately 1.5 km SW of Highway 5 t o l l b o o t h ; c r ossed p o l a r i z e r s , f i e l d of view i s 6 mm 143 F i g u r e 4.57: F i n e - g r a i n e d "contact phase," showing unzoned a l b i t i c overgrowths with quartz i n c l u s i o n s on zoned x i i p l a g i o c l a s e g r a i n ; J u l y Mountain; crossed p o l a r i z e r s , f i e l d of view i s 6 mm F i g u r e 4.58: Folded apophyses of t o n a l i t i c o r t h o g n e i s s i n amphib o l i t e l a y e r , Eagle g n e i s s , 1 km west of Highway 5 t o l l b o o t h F i g u r e 4.59: Refolded i s o c l i n a l f o l d i n augen-rich ( b l a s t o m y l o n i t e ) contact l a y e r between amph i b o l i t e and t o n a l i t e o r t h o g n e i s s , Eagle g n e i s s , abandoned KVRR grade, C o q u i h a l l a R i v e r canyon F i g u r e 4.60: Stained hand specimen from augen-rich c o n t a c t zone between amph i b o l i t e and t o n a l i t e o r t h o g n e i s s , Eagle g n e i s s , approx. 1 km west of Highway 5 t o l l b o o t h . . . F i g u r e 4.61: Amphibolite boudins i n t o n a l i t e o r t h o g n e i s s , Eagle g n e i s s F i g u r e 4.62: T o n a l i t e leucosome i n amphi b o l i t e l a y e r , Eagle g n e i s s , approx. 1 km west of Highway 5 t o l l b o o t h ; s t a i n e d specimen on l e f t hand s i d e F i g u r e 4.63: T o n a l i t e o r t h o g n e i s s of Eagle g n e i s s , near Dry Gulch on Highway 5; s t a i n e d specimen on r i g h t hand s i d e F i g u r e 4.64: W e l l - l a y e r e d t o n a l i t e o r t h o g n e i s s ( s t a i n e d specimen on r i g h t hand s i d e ) showing c o m p o s i t i o n a l l a y e r i n g o u t l i n e d by v a r i a t i o n s i n abundance of mafic and f e l s i c m i n e r a l s , Eagle g n e i s s , J u l i e t Creek 153 Fi g u r e 4.65: Folded c o m p o s i t i o n a l l a y e r i n g i n s t a i n e d hand specimen of t o n a l i t i c o r t h o g n e i s s , Eagle g n e i s s , Highway 5 t o l l b o o t h 154 Fig u r e 4.66: Discontinuous l a y e r s i n t o n a l i t e o r t h o g n e i s s , Eagle g n e i s s , Highway 5 t o l l b o o t h 154 Fi g u r e 4.67: U n f o l i a t e d t o n a l i t e from meter-scale l a y e r i n Eagle g n e i s s , J u l i e t Creek; s t a i n e d specimen on r i g h t hand s i d e 155 Fi g u r e 4.68: Augen o r t h o g n e i s s , Eagle gneiss 155 Fi g u r e 4.69: Augen t e x t u r e ( b l a s t o m y l o n i t e ) i n g n e i s s i c t o n a l i t e o r t h o g n e i s s , Eagle g n e i s s , Dear Mtn 156 F i g u r e 4.70: White 3-4 cm t h i c k marble and c a l c - s i l i c a t e boudin (beneath s c a l e ) i n t e r l a y e r e d with a m p h i b o l i t e and c r o s s c u t by F a l l s l a k e s u i t e pegmatite, Eagle g n e i s s , abandoned KVRR grade, C o q u i h a l l a R i v e r Canyon 156 Fi g u r e 4.71: well-developed quartz r i b b o n g r a i n s i n augen-rich o r t h o g n e i s s , Eagle g n e i s s , near Dry Gu l c h , Highway 5; plane l i g h t , width of f i e l d of view 6 mm. . . 158 Fi g u r e 4.72: Randomly o r i e n t e d b l o c k s of i n t e n s e l y f o l i a t e d N i c o l a Group r o c k s , agmatite at east margin of e a r l y T e r t i a r y I l l a l s t o c k , B r i t t o n (Eagle) Creek 165 Fi g u r e 4.73: I n c l u s i o n s of Eagle gneiss i n u n f o l i a t e d e a r l y T e r t i a r y Tulameen " f a l l s " s t o c k , upper Tulameen R i v e r . . 165 Fig u r e 4.74: View to NNE of NNE t r e n d i n g , s t e e p l y east d i p p i n g a p h a n i t i c a n d e s i t e d i k e s , J u l y Mtn. a r e a . . . . 166 Fi g u r e 4.75: S i l l s and di k e s of Middle Eocene(?) hornblende f e l d s p a r porphyry ( l i g h t grey) i n t r u d i n g Middle Eocene(?) x i i i 144 148 148 149 149 152 c l a s t i c r o c k s , Guanaco Peak. Large s i l l i s approximately 60 meters t h i c k . 168 F i g u r e 4.76: Meters-wide r e c e s s i v e weathering diabase d i k e c u t t i n g c e n t r a l F a l l s l a k e p l u t o n g r a n o d i o r i t e ; abandoned r a i l w a y grade, C o q u i h a l l a River v a l l e y . Arrow p o i n t s to g e o l o g i s t s l i g h t l y above and to r i g h t of c e n t e r . . . . 169 F i g u r e 4.77: A n d a l u s i t e ( c h i a s t o l i t e ) and c o r d i e r i t e p o r p h y r o b l a s t s i n Middle Eocene(?) c l a s t i c r o c k s , c o n t a c t a u r e o l e of Needle Peak p l u t o n , Nak Peak; crossed p o l a r i z e r s , width of f i e l d of view 6 mm 172 F i g u r e 4.78: Conglomeratic " g r i t " with angular and subangular-g r a n i t i c c l a s t s , Nak Peak. 172 F i g u r e 4.79: Middle Eocene t h i n - to medium-bedded g r i t t y s i l t s t o n e , Vuich Creek. 173 F i g u r e 4.80: Middle Eocene coarse conglomerate, with rounded g r a n i t i c c l a s t s i n mauve g r i t m a t r i x , Vuich Creek. . . . 173 F i g u r e 4.81: Pod-shaped bodies of c a l c - s i l i c a t e (contact metamorphosed c a l c a r e o u s c o n c r e t i o n s ) i n pale grey weathering Middle Eocene(?) s i l t s t o n e , Nak Peak; hammer l i e s on bedding plane 174 F i g u r e 4.82: View west from study area to Alpaca and Steinbok peaks, u n d e r l a i n by middle Eocene monzogranite of the Needle Peak p l u t o n 176 F i g u r e 4.83: Medium- to c o a r s e - g r a i n e d monzogranite of the middle Eocene Needle Peak p l u t o n , Highway 5 177 F i g u r e 4.84: Stained specimen of medium- to c o a r s e - g r a i n e d monzogranite of the middle Eocene Needle Peak p l u t o n , showing megacrystic potassium f e l d s p a r g r a i n s ; Highway "5 178 F i g u r e 4.85: F i n e - g r a i n e d c h i l l margin of Needle Peak p l u t o n at c o n t a c t with Middle Eocene(?) sedimentary r o c k s , Zum Peak 179 F i g u r e 4.86: View to north of e a r l y Miocene C o q u i h a l l a v o l c a n i c complex, with C o q u i h a l l a Mtn. composite stock on l e f t , v o l c a n i c dome on r i g h t , v o l c a n i c rocks i n foreground 181 F i g u r e 5.1: S i m p l i f i e d geology, C o q u i h a l l a a r e a , showing U-Pb dates . 186 F i g u r e 5.2: U-Pb c o n c o r d i a diagram f o r z i r c o n s from sample 1002, Zoa complex, Thar Peak p i p e l i n e 188 F i g u r e 5.3: U-Pb c o n c o r d i a diagram f o r z i r c o n s from sample MV-83-9, Eagle g n e i s s , C o q u i h a l l a canyon. 190 F i g u r e 5.4: U-Pb c o n c o r d i a diagram f o r z i r c o n s from sample 1001, Eagle t o n a l i t e , Coldwater e x i t ramp, Hwy. 5. . . . 192 F i g u r e 5.5: U-Pb c o n c o r d i a diagram f o r z i r c o n s from sample 997, Eagle t o n a l i t e , Murphy Lakes 194 F i g u r e 5.6: U-Pb c o n c o r d i a diagram f o r z i r c o n s from samples 997, 1001 and MV-83-9, Eagle t o n a l i t e and g n e i s s , C o q u i h a l l a area 195 F i g u r e 5.7: U-Pb c o n c o r d i a diagram f o r z i r c o n s from sample 86-1, Eagle t o n a l i t e , Hope-Princeton Highway 197 xiv F i g u r e 5.8: U-Pb c o n c o r d i a diagram f o r zircons and monazlte (Ml and M3) from sample 1003, c e n t r a l F a l l s l a k e p l u t o n , F a l l s l a k e e x i t , Hwy. 5; F i g u r e 5.9 shows enlargement of upper data p o i n t c l u s t e r from t h i s diagram 201 F i g u r e 5.9: Enlargement of part of U-Pb c o n c o r d i a diagram f o r z i r c o n s from sample 1003 (Figure 5.8) showing upper data p o i n t c l u s t e r , c e n t r a l F a l l s l a k e p l u t o n , F a l l s l a k e e x i t , Hwy. 5 202 F i g u r e 5.10: S i m p l i f i e d geology, C o q u i h a l l a a r e a , showing N i c o l a Group, Zoa complex, Eagle t o n a l i t e and Eagle g n e i s s Rb-Sr and K-Ar dates 210 F i g u r e 5.11: Randomly-oriented post-kinematic "Hollywood" hornblende i n N i c o l a Group g a r b e n s c h i e f e r , Hope-Princeton Highway; sample slabbed p e r p e n d i c u l a r to f o l i a t i o n . . . 212 F i g u r e 5.12: Sample 1002, hornblende quartz d i o r i t e , Zoa complex, Thar Peak p i p e l i n e , showing s l i g h t l y a l t e r e d ( l e f t ) and completely a l t e r e d ( r i g h t ) hornblende; a l t e r a t i o n assemblage i s e p i d o t e , c h l o r i t e and magnetite 214 F i g u r e 5.13: Rb-Sr whole-rock--mineral separate i s o c h r o n f o r Eagle t o n a l i t e and gneiss ( e x c l u d i n g r e s e t b i o t i t e from samples 992 and 1001), C o q u i h a l l a area; lower diagram i s d e t a i l showing whole-rock data (and epidote from sample 997); MSWD=2.1. 217 F i g u r e 5.14: S i m p l i f i e d geology, C o q u i h a l l a a r e a , showing Rb-Sr and K-Ar dates f o r the F a l l s l a k e p l u t o n i c s u i t e and f o r T e r t i a r y i n t r u s i o n s . 221 F i g u r e 5.15: Rb-Sr w h o l e - r o c k — m i n e r a l separate i s o c h r o n f o r the F a l l s l a k e p l u t o n i c s u i t e , C o q u i h a l l a area 225 F i g u r e 5.16: U n a l t e r e d , undeformed E a r l y Miocene col u m n a r - j o i n t e d b i o t i t e f e l d s p a r p o r p h y r i t i c r h y o l i t e d i k e (sample 774) i n t r u d i n g i n t e n s e l y f r a c t u r e d and a l t e r e d c e n t r a l F a l l s l a k e p l u t o n i n the C o q u i h a l l a f a u l t ; abandoned KVRR grade, C o q u i h a l l a canyon 229 F i g u r e 5.17: Rb-Sr whole-rock i s o c h r o n f o r the C o q u i h a l l a v o l c a n i c complex; r e c a l c u l a t e d from t h a t of Berman and Armstrong (1980) and i n c l u d i n g analyses of E a r l y Miocene i n t r u s i o n s (655 and 774 ) from t h i s study 231 F i g u r e 6.1: A l k a l i s - s i l i c a p l o t ( I r v i n e and Baragar, 1971) f o r r e p r e s e n t a t i v e samples from the C o q u i h a l l a area; Eagle t o n a l i t e = c l o s e d t r i a n g l e s , F a l l s l a k e p l u t o n i c s u i t e = open squares 242 F i g u r e 6.2: AFM p l o t ( I r v i n e and Baragar, 1971) f o r r e p r e s e n t a t i v e samples from the C o q u i h a l l a a r e a ; Eagle t o n a l i t e ( c l o s e d t r i a n g l e s ) , F a l l s l a k e p l u t o n i c s u i t e (open s q u a r e s ) ; (A=Na20+K20, F=FeO+0.8998*Fe203, M=MgO; a l l i n wt%) • 243 F i g u r e 6.3: Si02 vs. Zr/Ti02 p l o t (Winchester and F l o y d , 1977) f o r samples from the C o q u i h a l l a area; Eagle t o n a l i t e = c l o s e d t r i a n g l e s , F a l l s l a k e s u i t e (except 1004, f o r which Zr i s below d e t e c t i o n ) = open squares 244 xv F i g u r e 6.4: Major element c o m p o s i t i o n a l v a r i a t i o n (Harker) diagrams f o r Eagle t o n a l i t e ( c l o s e d t r i a n g l e s ) and the F a l l s l a k e p l u t o n i c s u i t e (open squares) 245 F i g u r e 6.5: Shand index histogram showing degree of alumina s a t u r a t i o n f o r samples from the C o q u i h a l l a area; (peraluminous = molar A/C+N+K>1; metaluminous = molar A/C+N+K<1; where A=Al203, C=CaO, N=Na20 and K=K20). . . 247 F i g u r e 6.6: Normative d i o p s i d e or corundum versus Si02 f o r p l u t o n s from the C o q u i h a l l a area; Eagle t o n a l i t e = c l o s e d t r i a n g l e s , F a l l s l a k e s u i t e = open squares 248 F i g u r e 6.7: Normative quartz (Q), p l a g i o c l a s e (P) and a l k a l i f e l d s p a r (K) f o r C o q u i h a l l a area plutons p l o t t e d on a S t r e c k e i s e n (1976) c l a s s i f i c a t i o n diagram f o r p l u t o n i c r o c k s ; Eagle t o n a l i t e = c l o s e d t r i a n g l e s , F a l l s l a k e s u i t e = open squares 249 F i g u r e 6.8: Ocean r i d g e g r a n i t e (ORG) normalized geochemical p a t t e r n s f o r Eagle t o n a l i t e ( c l o s e d t r i a n g l e s ) , the F a l l s l a k e p l u t o n i c s u i t e (open squares) and v o l c a n i c arc g r a n i t e s ( a f t e r Pearce et a l . , 1984) 255 F i g u r e 6.9: Rb vs. Si02 diagram with v o l c a n i c a r c and s y n - c o l l i s i o n g r a n i t e f i e l d s (Pearce et a l . , 1984; >90% of data w i t h i n dashed l i n e ) and showing data f o r Eagle t o n a l i t e ( c l o s e d t r i a n g l e s ) and the F a l l s l a k e s u i t e (open squares) 257 F i g u r e 6.10: Normalized t r a c e and r a r e e a r t h element p a t t e r n s f o r Eagle t o n a l i t e ( t r i a n g l e s ) , and f o r normal c o n t i n e n t a l a r c s and p r i m i t i v e i s l a n d and c o n t i n e n t a l a r c s from Brown et a l . (1984); s i n g l e a n a l y s i s only (1001) f o r Th and Nb 259 F i g u r e 7.1: S t e r e o p l o t s of N i c o l a Group s t r u c t u r a l f e a t u r e s ; a) poles to f o l i a t i o n , study area; b) l i n e a t i o n s ( c i r c l e s ) , minor f o l d axes (diamonds), poles to f o l i a t i o n ( c r o s s e s ) , Law's camp and to south (see P l a t e 1 ) . . . . 271 F i g u r e 7.2: S t e r e o p l o t s of N i c o l a Group s t r u c t u r a l f e a t u r e s ; a) poles to f o l i a t i o n , Skwum Creek-Independence p r o p e r t y , north of Law's camp; b) poles to f o l i a t i o n , Coldwater V a l l e y and northwest (see P l a t e 1) 272 F i g u r e 7.3: S t e r e o p l o t of poles to f o l i a t i o n ( c r o s s e s ) and poles to bedding ( s q u a r e s ) , N i c o l a Group, Lawless Creek a r e a . Compiled from Eastwood (1961) 273 F i g u r e 7.4: S t e r e o p l o t s of Zoa complex s t r u c t u r a l f e a t u r e s ; a) poles to f o l i a t i o n , metavolcanic r o c k s , Highway 5 summit; b) po l e s to igneous f o l i a t i o n , hornblende quartz d i o r i t e , d i o r i t e - m e t a v o l c a n i c contact 278 F i g u r e 7.5: S t e r e o p l o t s of Zoa complex s t r u c t u r a l f e a t u r e s ; a) poles to igneous f o l i a t i o n , hornblende quartz d i o r i t e , Zoa complex north b e l t ; b) p o l e s to igneous f o l i a t i o n , hornblende quartz d i o r i t e , Zoa complex south b e l t . . . . 280 F i g u r e 7.6: S t e r e o p l o t s of Zoa complex s t r u c t u r a l f e a t u r e s ; a) p o l e s to m y l o n i t i c f o l i a t i o n , NE margin, north b e l t ; b) poles to m y l o n i t i c f o l i a t i o n ( c r o s s e s ) , NE margin, x v i south b e l t , and poles to d i s c r e t e d u c t i l e shear zones (diamonds), south b e l t 281 Fi g u r e 7.7: Sample 1060, m y l o n i t i c Zoa complex hornblende quartz d i o r i t e , showing r i b b o n quartz g r a i n s wrapping around p l a g i o c l a s e f e l d s p a r and hornblende p o r p h y r o c l a s t s ; plane l i g h t , width of f i e l d of view i s 5 mm 2 82 F i g u r e 7.8: S t e r e o p l o t of poles to f o l i a t i o n , n orthern F a l l s l a k e p l u t o n . - . 286 F i g u r e 7.9: S t e r e o p l o t of poles to f o l i a t i o n , F a l l s l a k e s u i t e i n t r u s i o n s i n Eagle g n e i s s , Coquihalla-Tulameen a r e a . . 288 Fi g u r e 7.10: S t e r e o p l o t of poles to F a l l s l a k e s u i t e pegmatite d i k e s , Eagle g n e i s s , Coquihalla-Tulameen a r e a . Equal area net contoured u s i n g the method of Kamb (1959), contours are 1, 4, 7 and 10% 289 Fi g u r e 7.11: Elongate deformation bands, subgrains and r e c r y s t a l l i z e d new g r a i n s w i t h i n ribboned quartz aggregates, sample 1059B, southwest margin, northern F a l l s l a k e p l u t o n (Pasayten f a u l t ) 292 Fi g u r e 7.12: 120 g r a i n boundary i n t e r s e c t i o n s of r e c r y s t a l l i z e d s t r a i n - f r e e new g r a i n s w i t h i n ribboned quartz aggregates, sample 16-1, southwest margin, northern F a l l s l a k e p l u t o n (Pasayten f a u l t ) 293 Fi g u r e 7.13: I n t r a g r a n u l a r f r a c t u r e i n p l a g i o c l a s e f e l d s p a r i n f i l l e d with q u a r t z , sample 1059B, southwest margin, northern F a l l s l a k e p l u t o n (Pasayten f a u l t ) 295 Fig u r e 7.14: Comparative s t e r e o p l o t s of poles to f o l i a t i o n i n Upper T r i a s s i c N i c o l a Group (a) and Late J u r a s s i c Eagle t o n a l i t e (b) along t h e i r c o n t a c t (Eagle shear z o n e ) , Coquihalla-Tulameen a r e a . 301 Fi g u r e 7.15: Comparative s t e r o p l o t s of N i c o l a Group and Eagle t o n a l i t e s t r u c t u r a l f e a t u r e s along t h e i r c o ntact (Eagle shear z o n e ) , Law's camp and to sou t h , (a) +=poles to f o l i a t i o n ; c i r c l e s = l i n e a t i o n s , diamonds=minor f o l d axes; (b) c i r c l e s = f o l i a t i o n 302 Fi g u r e 7.16: Comparative s t e r e o p l o t s of poles t o f o l i a t i o n i n Upper T r i a s s i c N i c o l a Group (a) and Late J u r a s s i c Eagle t o n a l i t e (b) along t h e i r c o ntact (Eagle shear zone), Skwum Creek-Independence p r o p e r t y , north of Law's camp (see P l a t e 1) 303 Fig u r e 7.17: Comparative s t e r e o p l o t s of poles to f o l i a t i o n i n Upper T r i a s s i c N i c o l a Group (a) and Late J u r a s s i c Eagle t o n a l i t e (b) along t h e i r c o n t a c t (Eagle shear z o n e ) , Coldwater V a l l e y and northeast 304 Fig u r e 7.18: S t e r e o p l o t s of poles to f o l i a t i o n f o r Eagle t o n a l i t e on r i d g e immediately north-northwest of upper Coldwater R i v e r . Equal area net contoured u s i n g method of Kamb (1959), contours are 1, 4, 7, 10, 13, 16 and 19% 306 Fig u r e 7.19: Disharmonic minor f o l d o u t l i n e d by l e u c o t o n a l i t e " v e i n " i n a m p h i b o l i t e , Eagle gneiss 308 xv i i Figure 7.20: Stereoplot of minor fold axes, Eagle gneiss, Highway 5 and v i c i n i t y 309 Figure 7.21: Annealed quartz ribbon grains, blastomylonitic or "augen" t o n a l i t e orthogneiss, Eagle gneiss, Dry Gulch. F i e l d of view 6 mm 314 Figure 7.22: Stereoplot of poles to bedding, Middle Eocene sedimentary rocks, Coquihalla-Tulameen area 319 Figure 7.23: View looking north to east-verging outcrop-scale f o l d in hornfelsed Middle Eocene(?) s i l t s t o n e , s t a t i o n 86-542, base of Zum Peak 320 Figure 7.24: Strained Middle Eocene(?) g r i t , Zoa complex contact, Zoa Peak. 321 Figure 7.25: Gradational contact between Zoa complex d i o r i t e (lower right) and Middle Eocene(?) conglomeratic g r i t (upper l e f t ) , note concordance of f a b r i c and gradation between d i o r i t e and matrix of g r i t (top of hammer handle); Nak and Thar Peaks 321 Figure 7.26: Meso- and microscopically unstrained Middle Eocene (?) g r i t , showing poorly sorted, sub-rounded to angular d u c t i l e l y strained g r a n i t i c c l a s t s set in a very fine-grained matrix. Width of f i e l d of view i s 6 mm. . 323 Figure 7.27: Strained Middle Eocene g r i t at basal contact with Zoa complex, Vuich Creek. Note strong f o l i a t i o n p a r a l l e l to long dimension of pulled-apart d u c t i l e l y strained quartz c l a s t . Crossed n i c o l s , width of f i e l d of view i s 6 mm 323 Figure 7.28: Strained Late Jurassic Zoa complex hornblende quartz d i o r i t e at contact with overlying Middle Eocene sedimentary rocks, Vuich Creek. Matrix i s very fine-grained c h l o r i t e and white mica(?). Crossed n i c o l s , width of f i e l d of view is 6 mm 324 Figure 7.29: Simplified geology map, Coquihalla area. . . . 327 Figure 7.30: View northwest across Coquihalla Valley to Dry Gulch and Highway 5 331 Figure 7.31: Stereoplot of poles to andesite dikes, Coquihalla-Tulameen area. . . , 333 x v i i i LIST OF TABLES Table 5.1: U-Pb ANALYTICAL DATA, EAGLE PLUTONIC COMPLEX. . . 185 Table 5.II: U-Pb ANALYTICAL DATA, FALLSLAKE PLUTONIC SUITE . 199 Table 5 . I l l : K-Ar ANALYTICAL DATA, COQUIHALLA AREA. . .. . . 206 Table 5.IV: EAGLE TONALITE, AND GNEISS: Rb-Sr ANALYTICAL DATA, CALCULATED 0 Sr/ Sr RATIOS AND Rb-Sr WHOLE-ROCK--MINERAL SEPARATE ISOCHRONS 207 Table 5.V: FALLSLAKE PLUTONIC, SULTJS: Rb-Sr ANALYTICAL DATA, CALCULATED INITIAL Sr/ Sr RATIOS AND Rb-Sr WHOLE-ROCK—MINERAL SEPARATE ISOCHRONS 208 Tablef t 75.VI^ Rb-Sr ANALYTICAL DATA, CALCULATED INITIAL Sr/ Sr RATIOS AND Rb-Sr WHOLE-ROCK--MINERAL SEPARATE ISOCHRONS, MISCELLANEOUS SUITES/SAMPLES, COQUIHALLA AREA 209 Table 6.1: TRACE AND RARE EARTH ELEMENT DISCRIMINANT DIAGRAMS, SUMMARY OF RESULTS FOR MAFIC ROCKS 2 53 x i x LIST OF APPENDICES APPENDIX 5.1: ANALYTICAL RESULTS, GEOCHRONOMETRY 358 APPENDIX 5.II: ANALYTICAL PROCEDURES 410 APPENDIX 5.IIA: U-PB ANALYTICAL TECHNIQUES 410 APPENDIX 5.IIB: K-AR ANALYTICAL TECHNIQUES 412 APPENDIX 5.IIC: RB-SR ANALYTICAL TECHNIQUES 413 APPENDIX 6.IA: WHOLE ROCK GEOCHEMISTRY SAMPLE LOCATION AND LITHOLOGY 415 APPENDIX 6.IB: ANALYTICAL RESULTS, GEOCHEMISTRY 416 APPENDIX 6.II: GEOCHEMICAL TECHNIQUES 422 XX LIST OF PLATES •(Dock- pockot-) J£w SjPc. PLATE 1: GEOLOGICAL MAP OF THE COQUIHALLA AREA PLATE 2: SAMPLE AND STATION LOCATION MAP PLATE 3: GEOLOGICAL CROSS-SECTIONS x x i INTRODUCTION / 1 CHAPTER 1: INTRODUCTION I. INTRODUCTION This study focuses on the geology of the Eagle plutonic complex at the boundary between the Intermontane and Coast belts of the Canadian C o r d i l l e r a . In southwestern B r i t i s h Columbia, th i s boundary i s marked by the Pasayten f a u l t , which separates the large allochthonous terrane, Quesnellia, of the Intermontane Belt, from smaller terranes of the Coast Belt (Figures 2.1 and 2.2). The southwestern margin of Quesnellia i s underlain by the Mt. Lytton-Eagle plutonic complex, within which i s preserved a record of plutonism and deformation that may r e f l e c t the interaction of Quesnellia with outboard terranes. The northern half of the complex, the Mt. Lytton plutonic complex (Monger, 1981), extends south to 50°N. It i s of early Mesozoic age, i s l o c a l l y crosscut by T r i a s s i c - J u r a s s i c plutons, and i s considered by Monger (1985) to represent a lower s t r u c t u r a l l e v e l of the Upper T r i a s s i c Nicola volcanic arc. The Eagle plutonic complex, which forms the southern half of the Mt. Lytton-Eagle complex, i s a deformed intrusive complex comprising pre-Late Jurassic, Late Jurassic, Early Cretaceous and middle Cretaceous rocks. It i s bounded on the east by a syn-deformational Late Jurassic intrusive contact with the Upper T r i a s s i c Nicola Group, and bounded on the west by the mid-Cretaceous and Te r t i a r y Pasayten f a u l t . The Pasayten f a u l t separates the Eagle complex from the predominantly sedimentary rocks of the Methow-Pasayten trough. U p l i f t during late Early Cretaceous to early T e r t i a r y time provides the disparate parts of INTRODUCTION / 2 the Mt. Lytton-Eagle complex with their regional s t r u c t u r a l i n t e g r i t y . The purpose of the study was to c l a r i f y the intrusive and s t r u c t u r a l h i s t o r y of the poorly-understood Mt. Lytton-Eagle complex as a contribution to a better understanding of the tectonic history of southwestern B r i t i s h Columbia. The study involved mapping of the Eagle plutonic complex in the Coquihalla area and supporting geochronologic, geochemical and petrographic work. Preliminary accounts of the work are found in Greig (1988a,b,1989) and Greig and van der Heyden (1988). II. LOCATION AND ACCESS The study area, which encompasses roughly 400 square kilometers between J u l i e t Creek on the north and the Tulameen River on the south, i s located approximately 150 kilometers east-northeast of Vancouver near the center of the Hope (92H) map-area (see Figure 3.1 and Plates 1 and 2). Access i s via the new (completed in 1986) Coquihalla t o l l highway (Highway 5), which traverses the study area and li n k s the towns of Hope and M e r r i t t , which l i e s 108 kilometers to the north-northeast of Hope. The Highway 5 tollbooth, 55 kilometers from Hope, i s located in the center of the study area. Secondary access i s provided by an extensive network of logging roads (Plate 2). I I I . PHYSIOGRAPHY, CLIMATE AND VEGETATION The Eagle complex in the study area straddles the t r a n s i t i o n between the Hozameen Range of the Cascade mountain system and the INTRODUCTION / 3 southern part of the Interior Plateau (the Thompson Plateau, Holland, 1976). To the east, the Interior Plateau i s characterized by subdued topography and accordant summits (Figure 1.1). To the west, the Cascade and Coast mountain systems e x i h i b i t greater topographic r e l i e f and more rugged topography (Figure 1.2). Parts of the study area underlain by the Interior Plateau range in elevation up to 1800 meters, with ridges commonly averaging 1500 meters. Relief may be as great as 750 meters but i s t y p i c a l l y on the order of 450 to 500 meters. This i s in contrast to the west side of the map-area, in which elevations greater than 1900 meters are common and r e l i e f reaches 1300 meters. The physiographic t r a n s i t i o n from the Coast and Cascade mountain systems to the Interior Plateau lar g e l y controls variations in climate and vegetation. Climatic and f l o r a l differences between the physiographic belts are s t r i k i n g , even across the width of the study area. For example, annual p r e c i p i t a t i o n on the west side (100-150 centimeters/year) is s i g n i f i c a n t l y greater than on the east side (50-75 centimeters/year, Farley, 1979). As well, east of the physiographic change, the climate i s somewhat more seasonal, with colder winters and hotter summers. Differences in f l o r a mirror the clima t i c changes. For example, on the west, balsam, hemlock, Douglas f i r and red cedar are common, while on the east, spruce, pine, balsam and Douglas f i r predominate, with hemlock and red cedar being less common. Superimposed on the broader changes between physiographic belts are changes in climate and vegetation INTRODUCTION / 4 F i g u r e 1.1: View east - s o u t h e a s t to I n t e r i o r P l a t e a u from r i d g e 1 kilometer southwest of C o q u i h a l l a Mtn.; view from same p o i n t as Fi g u r e 1.2. INTRODUCTION / as Figure 1.1. INTRODUCTION / 6 with a l t i t i u d e . Treeline ranges from approximately 1500 to 1800 meters elevation. Above the t r e e l i n e , stunted alpine f i r and juniper are common. IV. FIELDWORK AND METHODS F i f t y days in June, July and August, 1986 and a further twenty-nine days in September and October, 1986 and August and September, 1987 were spent on fieldwork in the study area. Seventeen other days were spent on regional mapping traverses in the Mt. Lytton-Eagle complex outside the study area or on f i e l d t r i p s examining adjacent rock units. Fieldwork consisted of 1:25,000 scale mapping and sample c o l l e c t i o n for geochronologic, geochemical and petrographic study. Field-maps consisted of enlargements of 1:50,000 federal government topographic maps and ground control was supplemented by 1:50,000 scale airphotos. Over 350 slabbed hand samples of plutonic rock were stained for potassium feldspar and 200 samples were examined in thin section. Conventions used throughout t h i s study include plutonic rock names of Streckeisen (1976), the time scale of Palmer (1983), and decay constants for isotopic dates of Steiger and Jager (1977). V. ACKNOWLEDGEMENTS I would l i k e to thank thesis supervisor R.L. Armstrong and the other members of my thesis committee, R.G. Anderson and J.W.H. Monger of the Geological Survey of Canada and J.K. Russell of the University of B r i t i s h Columbia, for support and advice during t h i s INTRODUCTION / 7 p r o j e c t . Fieldwork i n summer 1986 was funded by the G e o l o g i c a l Survey of Canada and d i r e c t e d by J.W.H. Monger, who a l s o suggested the p r o j e c t . A l l c o s t s i n the geochronometry l a b o r a t o r y at U.B.C. were funded by an NSERC o p e r a t i n g grant to R.L. Armstrong. Argon, potassium, and uranium-lead analyses were performed by J . H a r a k a l , D. Runkle, and P. van der Heyden, r e s p e c t i v e l y . Thanks are a l s o due t o : R.G. Anderson and D.C. Murphy f o r advice and encouragement on many aspects of t h i s s t u d y , B. G r e i g , M. Gunning and K. Hancock f o r a s s i s t a n c e i n the f i e l d , J . H a r a k a l , D. Runkle, P. van der Heyden, R. P a r r i s h and R.M. Friedman f o r guidance i n the l a b o r a t o r y , G.E. Rouse f o r p a l y n o l o g i c a l work, H. Hurlow and J.M. Journeay f o r advice on m i c r o s t r u c t u r e s , Y. Douma f o r t h i n s e c t i o n s , and P. C h r i s t o p h e r , G. Richards and A.E. S o r e g a r o l i f o r access to p r i v a t e company r e p o r t s . As w e l l , d i s c u s s i o n s with J.A. O'Brien, N. Mortimer, W.H. Mathews, J . F i l l i p o n e , K. S t o f f e l , R.A. Haugerud, J . I . Garver, M. McGroder and many c o l l e a g u e s at U.B.C. provided me with v a l u a b l e i n s i g h t s . S p e c i a l thanks are due to U.B.C. Department of G e o l o g i c a l Sciences t e c h n i c i a n s Gord Hodge and Bryon "the Dukester" Cranston f o r advice r e g a r d i n g photography and d r a f t i n g , as w e l l as f o r p l a y i n g i n and o r g a n i z i n g many s e s s i o n s of morning hockey. My deepest thanks are rese r v e d f o r my wife B e r n i c e , f o r her never-ending love and support throughout t h i s somewhat t r y i n g p r o j e c t , and f o r b r i n g i n g our son Roy i n t o the world to add some much-needed joy to the l a t t e r stages of the t h e s i s work. TECTONIC SETTING / 8 CHAPTER 2: TECTONIC SETTING I. INTRODUCTION Since the advent and general acceptance of plate tectonic theory, much of the Canadian C o r d i l l e r a has been considered to be composed of allochthonous tectonostratigraphic terranes accreted to the margin of continental North America during the Mesozoic and Cenozoic (e.g. Monger et. al., 1972, Coney et. al., 1980). Paleontologic (Smith and Tipper, 1986), paleomagnetic (Monger and Irving, 1980; Irving et. al., 1985) and stratigraphic signatures of individual terranes suggest that to a large extent they evolved separately during Paleozoic and early Mesozoic time and that they may have originated up to thousands of kilometers from th e i r s i t e of accretion. Terrane transport and eventual c o l l i s i o n has resulted from convergent r e l a t i v e motion between the North American continental lithospheric plate and the P a c i f i c Basin oceanic lithospheric plates, of which the terranes were once a part. Extreme mobility i s i m p l i c i t in the fact that approximately 11,500 kilometers of oceanic lithosphere has been subducted beneath western North America since the Jurassic (Engebretson et. al., 1988). Evidence for accretion to continental North America and pre-accretion amalgamation of terranes i s provided by sedimentologic, s t r u c t u r a l , metamorphic or intrusive l i n k s across the bounding fault s of the terranes. Although there i s now general agreement that much of the Canadian C o r d i l l e r a i s comprised of allochthonous terranes, there i s considerably less agreement on the paleogeography of terranes TECTONIC SETTING / 9 and the t i m i n g of t e r r a n e amalgamation and a c c r e t i o n . D i f f e r e n c e s of o p i n i o n and i n t e r p r e t a t i o n r e g a r d i n g these aspects of t e r r a n e h i s t o r y have a r i s e n p r i m a r i l y because no s i n g l e model f o r the t e c t o n i c e v o l u t i o n of the C o r d i l l e r a e x i s t s t h a t s u c c e s s f u l l y s a t i s f i e s the complex and o f t e n c o n f l i c t i n g p a l e o n t o l o g i c , paleomagnetic and g e o l o g i c d a t a . L a r g e r - s c a l e t e c t o n i c models are i n disagreement on many fundamental p o i n t s ( c f . Monger, 1984; Umhoefer, 1987; Smith and T i p p e r , 1986; van der Heyden 1989; Wernicke and K l e p a c k i , 1988), while s m a l l e r - s c a l e s t u d i e s seem to add more complexity to the l a r g e r p i c t u r e r a t h e r than r e s o l v e d i f f e r e n c e s (e.g. Coates, 1970, 1974; B a r k s d a l e , 1974; Anderson, 1976; Cole and Tennyson, 1977; T r e x l e r and B ourgeois, 1985; K l e i n s p e h n , 1985; Ray, 1986; O'Brien, 1987; and Garver e t . a l . , 1988 with r e s p e c t to the e v o l u t i o n of the Tyaughton-Pasayten-Methow t r o u g h ) . In the Canadian C o r d i l l e r a , major t e r r a n e boundaries g e n e r a l l y do not correspond with the t r a d i t i o n a l f i v e - f o l d s u b d i v i s i o n of g eologic/morphologic b e l t s (Figure 2.1). The present study area i s l o c a t e d along the southernmost part of the Intermontane B e l t - C o a s t B e l t boundary (Figure 2.1). The southern Coast B e l t i s commonly r e f e r r e d to as the Coast-Cascade B e l t because of g e o l o g i c s i m i l a r i t i e s among r o c k - u n i t s i n the southern Coast and North Cascade mountains. The Coast-Cascade B e l t comprises a c o l l a g e of small t e r r a n e s t h a t i n c l u d e s the composite Northwest Cascades system and Skagit s u i t e of Brown (1987), the Cadwallader and Bridge River-Hozameen t e r r a n e s (Rusmore et. a l . , 1988 ) , the H a r r i s o n t e r r a n e TECTONIC SETTING / 10 (Wheeler and McFeely, 1987) and the Tyaughton-Pasayten-Methow trough (Figure 2.2). This complex system of small t e r r a n e s forms a n o r t h w e s t - t a p e r i n g wedge-shaped r e g i o n t h a t separates two much l a r g e r t e r r a n e s , W r a n g e l l i a and Q u e s n e l l i a . W r a n g e l l i a u n d e r l i e s much of the western Coast Mountains and Vancouver I s l a n d a c r o s s the Co a s t - I n s u l a r b e l t boundary i n southern B r i t i s h Columbia. Q u e s n e l l i a u n d e r l i e s the Intermontane B e l t and much of the Omineca B e l t i n southern B r i t i s h Columbia. The f o l l o w i n g d i s c u s s i o n of the major l i t h o - t e c t o n i c components of the Coast-Cascade B e l t ignores the important Late Cretaceous to T e r t i a r y s t r u c t u r a l , p l u t o n i c and metamorphic o v e r p r i n t t h a t i s well-developed a c r o s s a l l the t e r r a n e s of t h i s r e g i o n (e.g., the north t r e n d i n g F r a s e r - S t r a i g h t Creek f a u l t , a s t r i k e s l i p f a u l t with approximately 100 k i l o m e t e r s of d e x t r a l o f f s e t t h a t e s s e n t i a l l y b i s e c t s the r e g i o n under d i s c u s s i o n (Figure 2 . 2 ) ) . Greater emphasis i s placed on Q u e s n e l l i a and the Tyaughton-Pasayten-Methow trough because they are juxtaposed i n the study a r e a . I I . QUESNELLIA, WRANGELLIA, AND THE SUPER- AND MEGATERRANES A. QUESNELLIA Q u e s n e l l i a comprises d i s c o n t i n u o u s and heterogeneous basement of P a l e o z o i c marine sedimentary and v o l c a n i c rocks of probable oceanic and i s l a n d a r c a f f i n i t y (Harper Ranch Group and A n a r c h i s t assemblage; Monger, 1982; Wheeler and McFeely, 1987) in t r u d e d by Late T r i a s s i c to E a r l y J u r a s s i c plutons and o v e r l a i n unconformably TECTONIC SETTING / 11 GENERALIZED TERRANE MAP OF THE CANADIAN CORDILLERA NA: North American craton TERRANES Displaced continental margin CA: Cassiar NS: Nisling Pericratonic terranes KO: Kootenay Accreted terranes Intermontane Superterrane • • : Slide Mountain QN: Quesnellia DY: Dorsey CC: Cache Creek ST: Stikinia Coast-Cascade Belt (see Figure 2.2) insular Superterrane AX: Alexander WR: Wrangellia O: Outer terranes (undifferentiated) CPC: Coast Plutonic Complex (alter Wheeler and McFeely, 1987) (C.CANADA \ U . S . A . " ~ N - — 4 9 ' N >see Figure 2.2 Figure 2.1: Generalized terrane map of the Canadian C o r d i l l e r a ; insets show f i v e geologic-physiographic subdivisions of the Canadian C o r d i l l e r a and area depicted in Figure 2 . 2 . TECTONIC SETTING / 12 Figure 2.2: Terrane map of SW BC & NW Wash.; M=Methow/ TY=Tyaughton, P=Pasayten, HZ=Hozameen, HA=Harrison, NWCS=Northwest Cascade, BR=Bridge River, CD=Cadvallader, SK=Skagit (includes CM,NS,SW,I,LJ, see t e x t ) , CZ=Cenozoic, for others see Figure 2.1. TECTONIC SETTING / 13 (Read and Okulitch, 1977) by Upper ( l o c a l l y Middle) T r i a s s i c to Lower Jurassic marine and non-marine c a l c - a l k a l i n e to alkaline arc volcanic and sedimentary rocks, Nicola-Rossland and Slocan groups, respectively (Schau, 1970; Preto, 1979; Mortimer, 1986,1987). Quesnellia was amalgamated with the oceanic Slide Mountain terrane by Late T r i a s s i c time because the Nicola Group and Slocan Group interfinger and the Slocan Group rests unconformably on the Slide Mountain terrane (Monger, 1984). Evidence from southeastern B r i t i s h Columbia indicates that Quesnellia and the Slide Mountain terrane were emplaced onto the North American continental margin at least by late Early to early Middle Jurassic time (Monger, 1984); however, sedimentologic t i e s between Quesnellia and the peri-cratonic Kootenay terrane exist as early as the Carboniferous (Wernicke and Klepacki, 1988), and s t r u c t u r a l t i e s between the Slide Mountain and Kootenay terranes exist by the Early Permian (Klepacki and Wheeler, 1985). In southwestern B r i t i s h Columbia, Quesnellia i s juxtaposed along i t s northwest margin with the Permian to Middle Jurassic Cache Creek terrane, which contains Permian faunas of Tethyan a f f i n i t y and i s interpreted as an accretionary prism. The Cache Creek terrane contains evidence for a Late T r i a s s i c link with Quesnellia (exchange of c l a s t s ; Monger, 1981, 1982), but assembly of Cache Creek and Quesnellia did not end u n t i l Middle or Late Jurassic time (Cordey et. a l . , 1987). It also suggests that the composite Intermontane superterrane (Price et. al., 1985), or "Terrane I" (Monger et. al., 1982), comprised of Quesnellia and the TECTONIC SETTING / 14 S l i d e Mountain, Cache Creek and S t i k i n e t e r r a n e s , was not completely amalgamated by the Late T r i a s s i c . S t r a t i g r a p h i c t i e s between Q u e s n e l l i a and the Tyaughton-Pasayten-Methow trough are d i s c u s s e d below. B. WRANGELLIA In southern B r i t i s h Columbia, W r a n g e l l i a i s composed of Devonian-Permian a r c v o l c a n i c , sedimentary and i n t r u s i v e rocks of the S i c k e r Group, and by voluminous t h o l e i i t i c f l o o d b a s a l t s of the Upper T r i a s s i c Karmutsen Formation, which i s capped by Upper T r i a s s i c l i m e s t o n e . The S i c k e r Group and Karmutsen Formation are o v e r l a i n and i n t r u d e d by E a r l y to Middle(?) J u r a s s i c Bonanza Group v o l c a n i c r o c k s , and coeva l I s l a n d i n t r u s i o n s and p l u t o n i c and metamorphic rocks of the Westcoast C r y s t a l l i n e Complex (Isachsen, 1987). W r a n g e l l i a and the Alexander t e r r a n e (Figure 2.1) together comprise the composite I n s u l a r superterrane ( P r i c e et. a l . , 1985), or "Terrane I I " of Monger et. a l . (1982). C. INSULAR-INTERMONTANE SUPERTERRANE BOUNDARY In B r i t i s h Columbia, the I n s u l a r superterrane-Intermontane su p e r t e r r a n e boundary i s one of the more e l u s i v e , enigmatic and c o n t r o v e r s i a l f e a t u r e s of the C o r d i l l e r a because the boundary i s obscured by the intense p l u t o n i c and metamorphic o v e r p r i n t of the Coast P l u t o n i c Complex. In southwestern B r i t i s h Columbia, some workers c o n s i d e r W r a n g e l l i a may extend as f a r east as the Bridge R i v e r t e r r a n e and Tyaughton trough (e.g. T i p p e r , 1984; K l e i n s p e h n , TECTONIC SETTING / 15 1985; Wernicke and Klepacki, 1988), but l i k e l y i t i s much less extensive and extends only marginally into mainland B r i t i s h Columbia at i t s southern end (Figures 2.1 and 2.2; Wheeler and McFeely, 1987). Only i n d i r e c t evidence exists for the timing of accretion of the Insular superterrane to North America. Monger et. al. (1982) view the deformation, metamorphism, g r a n i t i c magmatism and u p l i f t which exposes the Cordilleran " i n f r a s t r u c t u r e " in the Coast Plutonic Complex as r e s u l t i n g from compressional thickening of the crust related to accretion of the Insular superterrane to the Intermontane Belt at the superterrane boundary. Cretaceous and Early T e r t i a r y ages of Coast Plutonic Complex, and Cretaceous sedimentary provenance reversals, roughly coeval thrust f a u l t i n g , and regional metamorphism and plutonism in the North Cascades were believed to provide evidence for timing of the accretion. Accretion may have occurred e a r l i e r . Arthur (1987) suggests Lower Cretaceous Peninsula and Brokenback H i l l Formations of the Harrison Lake area are co r r e l a t i v e with the Gambier and F i r e Lake groups to the west and northwest as an e a r l i e s t Cretaceous overlap sequence on Wrangellia and on Jurassic and older rocks of the Harrison Lake area. Middle Jurassic shale basins common to Wrangellia, S t i k i n i a , Quesnellia and cratonal North America suggest to Tipper (1984) that the terranes were together and adjacent North America by that time. A magmatic l u l l from 150 to 130 Ma in southern B r i t i s h Columbia (Armstrong, 1988) may have been caused by choking of the TECTONIC SETTING / 16 Jurassic subduction zone along the North American margin by accretion of Wrangellia. By 127 Ma, in Early Cretaceous time, a vigorous magmatic arc had been established across a l l terranes in B r i t i s h Columbia, sealing a l l possible sutures. Pre-early Late Jurassic deformation in the western Cache Creek terrane (Mortimer et. al., in press; Cordey et. al., 1987) suggests that t h i s may record accretion of the Cadwallader and Bridge River-Hozameen terranes to Quesnellia and S t i k i n i a (Potter, 1986; Rusmore et. al., 1988). Van der Heyden (1989) argues that t h i s deformation represents pre-late Middle Jurassic accretion of a composite Wrangellia-Alexander-Stikinia "Megaterrane." I I I . SMALLER TERRANES OF THE COAST-CASCADE BELT Numerous small northwest trending terranes in the Coast-Cascade Belt are linked by common Cretaceous plutonic, metamorphic and deformational h i s t o r i e s (Tabor et. al., in press). Displacements on terrane-bounding faul t s are generally poorly constrained, but s i g n i f i c a n t differences in pre-Cretaceous geology suggest wide separation of terranes in e a r l i e r Mesozoic time. A. TYAUGHTON-PASAYTEN-METHOW TROUGH The Tyaughton-Pasayten-Methow trough comprises an assemblage of dominantly sedimentary rock disrupted by Early T e r t i a r y Fraser-Straight Creek dextral s t r i k e - s l i p f a u l t i n g . The Tyaughton trough l i e s northwest of the fa u l t and the Methow-Pasayten trough l i e s to the southeast (Pasayten to the north of the International TECTONIC SETTING / 17 border and Methov to the south). The potential of the Tyaughton-Pasayten-Methow trough to record tectonic assembly of nearby Quesnellia, S t i k i n i a , Wrangellia and Cache Creek terranes has motivated numerous studies of the sedimentary rocks (Tyaughton: Kleinspehn, 1985; Umhoefer, et. al., 1988; Garver et. al., 1988; Pasayten: Coates, 1970, 1974; Anderson, 1976; Ray, 1986; O'Brien, 1987; Methow: Cole and Tennyson, 1977; Tennyson and Cole, 1978; Trexler, 1985; Trexler and Bourgeois, 1985; McGroder, 1988). 1. PASAYTEN TROUGH Lower T r i a s s i c ( ? ) to Eocene sedimentary rocks make up the Pasayten trough. Pre-Cretaceous breaks in the succession include: sub-Lower Jurassic unconformity between the Lower to Middle Jurassic Ladner Group and metavolcanic rocks of the Lower Tr i a s s i c ( ? ) Spider Peak Formation (Ray, 1986; Anderson, 1976), and a sub-Kimmeridgian disconformity between the Upper Jurassic Thunder Lake sequence and Bajocian Ladner Group rocks (O'Brien, 1987). Ladner Group rocks have been interpreted as forearc sedimentation u n t i l Middle Jurassic termination by accretion of Wrangellia (Anderson, 1976), or as tur b i d i t e s deposited along the margin of an ocean basin (Ray, 1986). O'Brien (1987) suggests that Ladner Group rocks contain an arc component and that volcanic and v o l c a n i c l a s t i c rocks of the Dewdney Creek Formation of the Ladner Group represent c a l c - a l k a l i n e volcanic centers active in the trough in Aalenian to Bajocian time (187 to 176 Ma). In the Late Jurassic and Cretaceous, the Pasayten trough was an interarc successor basin TECTONIC SETTING / 18 (Anderson, 1976). The Thunder Lake sequence and rocks of the H a u t e r i v i a n (131 to 124 Ma) part of the o v e r l y i n g Lower Cretaceous Jackass Mountain Group c o n t a i n the e a r l i e s t h i n t s of a p l u t o n i c provenance i n , and the f i r s t h i n t s of an e a s t e r n margin t o , the Pasayten trough (O'Brien, 1987). O'Brien i n t e r p r e t s t h e i r source as a t r a n s i t i o n a l a r c . Barremian to A l b i a n (124 to 97.5 Ma) Jackass Mountain Group, p a r t l y non-marine, was d e r i v e d from a d i s s e c t e d a r c . Mainly non-marine l a t e A l b i a n to Cenomanian Pasayten Group was d e r i v e d from a r e c y c l e d orogen (O'Brien, 1987). Two d i v e r g i n g views of the a c c r e t i o n of W r a n g e l l i a are h e l d . Ray (1986) suggests t h a t the Hozameen Group, Spider Peak Formation and b a s a l u n i t s of the Pasayten trough were d e p o s i t e d i n a s i n g l e l o n g - l i v e d b a s i n t h a t was t e l e s c o p e d d u r i n g E a r l y or middle Cretaceous d e f o r m a t i o n . O'Brien (1987) suggests that d i f f e r e n t geochemical s i g n a t u r e s f o r Hozameen Group and Spider Peak Formation v o l c a n i c basement rocks precludes t h e i r c l o s e a s s o c i a t i o n p r i o r to J u r a s s i c time. In the absence of compelling t i e s between the b a s i n and other Coast-Cascade B e l t t e r r a n e s or to Q u e s n e l l i a i n the E a r l y J u r a s s i c , Upper Middle and Upper J u r a s s i c c l a s t i c rocks are viewed as the f i r s t o v e r l a p assemblage (O'Brien, 1987). 2. METHOW TROUGH Age c o n t r o l on pre-Cretaceous rocks i n the Methow trough i s g e n e r a l l y poorer than i n the Pasayten t r o u g h . Jura-Cretaceous u p l i f t of an e a s t e r n T r i a s s i c - J u r a s s i c arc and metamorphic complex ( Q u e s n e l l i a ) s u p p l i e d d e t r i t u s to the trough i n a f o r e a r c s e t t i n g TECTONIC SETTING / 19 (Tennyson and C o l e , 1978; Cole and Tennyson, 1977; Anderson, 1976). There i s no evidence i n the b a s i n f i l l f o r tectonism to the west u n t i l the Cenomanian-Turonian(?) (97.5 to 88.5 Ma; Tennyson and C o l e , 1978; Cole and Tennyson, 1977). A l b i a n to Campanian (113 to 74.5 Ma) V i r g i n i a n Ridge Formation rocks r e c o r d middle to Late Cretaceous e v o l u t i o n of the Methow trough as a wrench-fault b a s i n ( T r e x l e r , 1985; T r e x l e r and Bourgeois, 1985). Truncated sedimentary facies-'""at""-"-the b a s i n margins i n d i c a t e p o s t - d e p o s i t i o n a l r e a c t i v a t i o n of the basin-bounding Ross Lake and Pasayten f a u l t s , but se d i m e n t o l o g i c evidence suggests that the Cretaceous e a s t e r n b a s i n margin was t e c t o n i c a l l y q u i e t e r than the western margin ( T r e x l e r and Bourgeois, 1985). 3. TYAUGHTON TROUGH Sedimentary rocks of the Tyaughton trough range i n age from Middle J u r a s s i c to Late Cretaceous. The Mt. Lytto n - E a g l e complex has been suggested as the source- f o r voluminous g r a n i t i c conglomerate of the Lower Cretaceous Jackass Mountain Group ( D u f f e l and McTaggart, 1952; K l e i n s p e h n , 1985). Dates f o r three c l a s t s range from l a t e Middle J u r a s s i c to e a r l i e s t Cretaceous (K-Ar, 160 +/- 11 Ma, 134 +/- 16 Ma and 133 +/- 16 Ma; K l e i n s p e h n , 1985). Jackass Mountain Group rocks r e s t unconformably on S t i k i n i a n ortheast of the b a s i n and on rocks forming the southwest b a s i n margin, which Kleinspehn (1985) considered to be of Wran g e l l i a n a f f i n i t y . On t h i s b a s i s Kleinspehn (1985) suggested TECTONIC SETTING / 20 pre-Hauterivian (131 to 124 Ma) accretion of Wrangellia to inboard terranes. She attributed the absence of a pre-Cenomanian western sediment source to lack of uplift of accreted terranes to the west (Kleinspehn, 1985). Garver et. al. (1988) suggest that Jura-Cretaceous sedimentation in the Tyaughton trough reflects a transition from pre-Albian slow sedimentation in a forearc setting to rapid sedimentation and two-sided basin f i l l i n g in an Albian (113 to 97.5 Ma) collisional setting. Collision implies telescoping of terranes to the west (Garver et. al., 1988). B. BRIDGE RIVER-HOZAMEEN AND CADWALLADER TERRANES The Bridge River complex and Hozameen Group comprise a disrupted Permian to Middle Jurassic oceanic assemblage offset across the Fraser-Straight Creek fault. The Bridge River-Hozameen terrane comprises metabasaltic rocks (pillow basalt, massive lava, tuff and breccia), chert and a r g i l l i t e , and lesser limestone, gabbro, serpentinite and greywacke in fault contact with terranes west and east (Figure 2.2; McTaggart and Thompson, 1967; Ray, 1986; Rusmore et. al., 1988). Rusmore et. al. (1988) suggest that the Bridge River-Hozameen terrane represents remnants of a small ocean basin formed in an arc to back-arc setting. Ray (1986) draws essentially the same conclusion, but believed that the Bridge River-Hozameen terrane and Tyaughton-Methow-Pasayten trough were part of the same basin in the Early Jurassic. Rusmore et. al. (1988) considered the earliest link between the terranes to be in the late Middle Jurassic. TECTONIC SETTING / 21 Upper T r i a s s i c to Middle Jurassic island arc-related basalt and c l a s t i c rocks make up the Cadwallader terrane, which i s faulted against the west and northwest margins of the Bridge River-Hozameen terrane (Figure 2.2; Rusmore, 1987; Rusmore et. al., 1988). No firm t i e s between Cadwallader and Bridge River terranes exist prior to overlap by the late Middle Jurassic to Lower Cretaceous Relay Mountain Group, but deformation a f f e c t i n g both terranes in pre-Callovian (169 to 163 Ma) time was inferred to represent their amalgamation and accretion to the Intermontane superterrane to the east (Rusmore et. al., 1988). C. SKAGIT SUITE The varied terranes of the Skagit suite (Brown, 1987) (Figure 2.2, L i t t l e Jack (LJ), Chelan Mountains (CM), Nason (NS), Swakane (SW) and Ingalls ( I ) , and their sub-terranes) are characterized by an intense Late Cretaceous to T e r t i a r y metamorphic, plutonic and deformational overprint (Tabor et. al., in press). The Skagit suite is in f a u l t contact with the Northwest Cascades system to the west and with the Bridge River-Hozameen terrane and the Tyaughton-Pasayten-Methow trough to the east. L i t t l e i s known of the age or s t r a t i g r a p h i c a f f i n i t y of metamorphosed Skagit suite rocks, although inferred p r o t o l i t h s suggest s i m i l a r i t i e s to several adjacent terranes (e.g. Monger, 1986). TECTONIC SETTING / 22 D. NORTHWEST CASCADES SYSTEM (NWCS) The NWCS comprises an Early Cretaceous, large-scale tectonic melange of metamorphosed (high pressure/low temperature) Paleozoic to Mesozoic oceanic sedimentary and volcanic terranes which were juxtaposed along a series of high- and low-angle faults (Brown, 1987). In Brown's (1987) view, NWCS terranes are accreted to North America then carried northward by dextral s t r i k e - s l i p f a u l t s driven by oblique convergence between P a c i f i c basin plates and North America. The NWCS attains i t s pre-Tertiary configuration when thrust against the northern margin of a reentrant created by pre-middle Cretaceous c o l l i s i o n of Wrangellia with inboard terranes (Brown, 1987). The NWCS of Brown (1987) e s s e n t i a l l y corresponds to the San Juan-Cascades nappe system of Brandon et. al. (19 88) and to terranes west of the Straight Creek f a u l t described by Tabor et. al. (in press). Based on the common presence of similar Upper Jurassic-Lower Cretaceous c l a s t i c sequences, Brandon et. al. (1988) infer that Wrangellia and the San Juan-Cascades nappes were close together and close to North America by the Late Jurassic. Late Cretaceous and e a r l i e r ( ? ) thrust f a u l t i n g , attributed either to increased coupling between overriding and subducting plates or to c o l l i s i o n of northward-moving terranes with a reentrant in the continent margin, af f e c t s San Juan-Cascades terranes which were previously accreted to North America (Brandon et. al., 1988). Monger (1986) and Arthur (1987) suggest a Toarcian (193 to 187) provenance link between the Harrison terrane and part of the TECTONIC SETTING / 23 NWCS (the Chilliwack Group). This suggests that parts of the NWCS were amalgamated with rocks to the north prior to the Late Cretaceous and that the Harrison terrane is part of the NWCS. Arthur (1987) considers Lower Cretaceous rocks of the Harrison terrane to represent an overlap sequence with Wrangellia, suggesting that Wrangellia and the NWCS were amalgamated by the Early Cretaceous. IV. CONCLUSIONS There is essentially unanimous agreement that terrane assembly in the Coast-Cascade Belt was accomplished by middle to Late Cretaceous time. There is no hard evidence for ties between Quesnellia and the Tyaughton-Pasayten-Methow trough even in the Cretaceous, but there is a consensus that an arc to the east was the primary sediment source. An uplifted Quesnellia is generally invoked as that source. Pre-Early Cretaceous relationships between most terranes are s t i l l disputed. There are hints within most terranes of Middle to Late Jurassic terrane interactions, suggesting that this was an important period for amalgamation and(or) accretion in the Coast-Cascade Belt. Opinions differ as to the driving force behind the Middle to Late Jurassic "event," but accretion of the Insular superterrane plays a leading role in most models. PREVIOUS WORK / 24 CHAPTER 3: PREVIOUS WORK I. INTRODUCTION In southwestern B r i t i s h Columbia, the geology of the southern Interior Plateau and northernmost Cascade Mountains has been studied intermittently since 1859 (Bauerman, 1885), when the i n i t i a l International Boundary Survey was undertaken by the governments of B r i t a i n and the United States of America. The Mt. Lytton-Eagle plutonic complex has been examined in the context of a number of t o p i c a l and regional studies, mostly in areas surrounding i t s southern half, the Eagle complex. Previous work for the Mt. Lytton complex and for the Eagle complex i s described separately. Because geology of Nicola Group rocks along the east margin of the Eagle complex i s integral to an understanding of the evolution of the complex, a separate review of previous work on the Nicola Group i s included. Study areas, geographic features and settlements referred to in the text are shown in Figure 3.1. II. EAGLE PLUTONIC COMPLEX In previous studies, external intrusive relations and age of the Eagle complex was the primary focus. The west contact of the Eagle complex, with sedimentary and subordinate volcanic rocks of the Pasayten trough, has been variously interpreted as intrusive, unconformable and faulted. The east contact, with rocks of the Upper T r i a s s i c Nicola Group, has been interpreted as both "metamorphic" and intr u s i v e . PREVIOUS WORK / 25 (SJV BRITISH I o \ \ C O L U M B I A | I A L B E . 821 / • / 8 2H ! Hopi • < > < ^FIGl 1 U.S.A. IRE 3.1 49* 3 0 ' N 49 .oo-N-£^ , l L c fU"^: vi WBShlnoton Stat* Figure 3.1: Location map for previous work, Eagle and Mt. Lytton plutonic complexes. PREVIOUS WORK / 26 A. H. BAUERMAN H i l a r y Bauerman, the g e o l o g i s t attached to the B r i t i s h c o n t ingent of the o r i g i n a l F o r t y - n i n t h P a r a l l e l Boundary Survey, conducted h i s f i e l d w o r k d u r i n g the 1859-1861 f i e l d seasons, but h i s work went unpublished u n t i l 1885 (Bauerman, 1885). Bauerman's geology, due to l o g i s t i c a l d i f f i c u l t i e s , was, of n e c e s s i t y , very g e n e r a l . References to Eagle complex rocks encountered along the Similkameen and Pasayten r i v e r s are sketchy: "...they [sedimentary rocks] are succeeded by a small mass of grey s y e n i t e which preserves i t s massive c h a r a c t e r f o r a mile and then becomes g n e i s s i c . " (Bauerman, 1885, p.l4B) Bauerman (1885, p. 15B) a l s o mentions rocks along the I n t e r n a t i o n a l boundary t h a t c o n s t i t u t e , i n p a r t , the southward c o n t i n u a t i o n of the Eagle complex. He r e f e r r e d to them as the "Ashtnoulou g r a n i t e , " and d e s c r i b e d them as being "...of an e x c e e d i n g l y v a r i a b l e composition." This d e s c r i p t i o n remains q u i t e a c c u r a t e , even i n l i g h t of more recent work, because he a p p a r e n t l y used the term "Ashtnoulou g r a n i t e " to encompass a l l p l u t o n i c rocks along the I n t e r n a t i o n a l boundary, from the Pasayten River almost to the Okanagan v a l l e y . PREVIOUS WORK / 27 B. G.M. DAWSON G.M. Dawson (1879) f i r s t p u b l i s h e d d e s c r i p t i o n s of Mt. Lytt o n - E a g l e complex rocks based on 1875 and 1876 g e o l o g i c a l reconnaissance along four t r a n s e c t s . One of the t r a i l s , the government c a t t l e t r a i l between the N i c o l a V a l l e y and Hope, crossed the Eagle complex through the center of the present study a r e a , along the C o q u i h a l l a and Coldwater r i v e r v a l l e y s . His other t r a n s e c t s were along the Thompson R i v e r , near the north end of the Mt. L y t t o n complex; along U t z l i u s and Spius (Maka?) c r e e k s , roughly ten k i l o m e t e r s north of the present study a r e a , near the p o o r l y d e f i n e d Eagle/Mt. L y t t o n c o n t a c t ; and across Hope Pass, at the d i v i d e between the S k a i s t R i v e r and Whipsaw Creek, approximately t h i r t y k i l o m e t e r s south of the study a r e a . Only sketchy d e s c r i p t i o n s of Mt. Lyt t o n - E a g l e complex rocks are given by Dawson i n r e s p e c t of h i s Thompson, U t z l i u s and C o q u i h a l l a t r a n s e c t s and h i s i n t e r p r e t a t i o n s of t h e i r age, o r i g i n and r e l a t i o n s h i p s with adjacent u n i t s appear to be based l a r g e l y on h i s more d e t a i l e d d e s c r i p t i o n s of the Skaist-Whipsaw t r a n s e c t . Dawson rec o g n i z e d many of the e s s e n t i a l c h a r a c t e r i s t i c s of the Mt. Ly t t o n - E a g l e complex and adjacent rock u n i t s and the r e l a t i o n s h i p between them. He c o r r e l a t e d (p.73B) the c r y s t a l l i n e ( g r a n i t i c or g n e i s s i c ) rocks he examined along h i s U t z l i u s , C o q u i h a l l a and Whipsaw t r a n s e c t s with one another, r e f e r r i n g to them as the " c r y s t a l l i n e a x i s " of the Coast or Cascade Range. F u r t h e r , Dawson suggested that a c o r r e l a t i o n be made between rocks of h i s N i c o l a s e r i e s i n t h e i r type-area and the metavolcanic and PREVIOUS WORK / 28 l e s s e r metasedimentary rocks t h a t he found along Whipsaw Creek and the Coldwater R i v e r , along the e a s t e r n margin of the Eagle complex. He a l s o f i r s t r ecognized the s t r u c t u r a l concordance of f o l i a t i o n s i n the Eagle complex and the N i c o l a b e l t and c o r r e c t l y i d e n t i f i e d the f a u l t between Eagle complex rocks and sedimentary rocks to the west (p.43B). Although Dawson a p p a r e n t l y favoured a " g r a n i t i z e d N i c o l a Group" o r i g i n f o r Eagle complex r o c k s , he n e v e r t h e l e s s l e f t open the p o s s i b i l i t y t h a t they were i n t r u d e d i n t o N i c o l a r o c k s . As noted, Dawson d e s c r i b e d the Eagle complex and neighbouring N i c o l a s e r i e s rocks near the headwaters of the S k a i s t R i v e r and Whipsaw Creek i n somewhat gr e a t e r d e t a i l than i n h i s other t r a n s e c t s (p.63B f f ) . T h i s t r a n s e c t , which followed the route of the o l d Dewdney T r a i l , e s s e n t i a l l y r e p r e s e n t s a c r o s s - s e c t i o n through N i c o l a and Eagle r o c k s , as i t runs p e r p e n d i c u l a r to the g eneral s t r i k e of l a y e r e d rocks of the r e g i o n . Dawson's d e s c r i p t i o n s of Whipsaw Creek rocks are c o n s i s t e n t with more re c e n t work ( c f . Anderson, 1971, see d i s c u s s i o n below), and with the present author's o b s e r v a t i o n s of the rocks i n t h a t a r e a . Some of h i s i n t e r p r e t a t i o n s as to the o r i g i n of the Eagle complex and i t s r e l a t i o n s h i p to N i c o l a Group rocks a r e , however, c o n t r a d i c t o r y . Dawson's view was t h a t the g n e i s s i c rocks of the Eagle complex were d e r i v e d by metamorphism from s t r a t i f i e d rocks of the N i c o l a s e r i e s . He r e f e r s to g n e i s s i c l a y e r i n g i n the complex as "beds" tha t form part of a "continuous descending sequence." Presumably, he c o n s i d e r e d them to be continuous with metamorphosed N i c o l a r o c k s . On Whipsaw Creek, lack of exposure prevented Dawson from PREVIOUS WORK / 29 observing the a c t u a l contact between Eagle and N i c o l a r o c k s . He i n t e r p r e t e d the contact as a metamorphic one (1879, p.65B and c r o s s - s e c t i o n ) , but went on to q u a l i f y h i s i n t e r p r e t a t i o n as f o l l o w s : "...the probable d i v e r s i t y of the two s e t s of rocks i s i n d i c a t e d by the c l o s e j u n c t i o n of c o a r s e l y g n e i s s i c m a t e r i a l s with the f i n e l y laminated h o r n b l e n d i c and micaceous s c h i s t s which a p p a r e n t l y d i p beneath them." On the Coldwater R i v e r , Dawson d e s c r i b e d the E a g l e - N i c o l a contact as f o l l o w s : "the l i n e between the s c h i s t o s e and coarse g n e i s s i c r o c k , i s i n both cases q u i t e sharp. The comp a r a t i v e l y l i t t l e a l t e r e d c h a r a c t e r of the s c h i s t s , tends to throw doubt on the theor y of t h e i r i n t i m a t e connection with the g n e i s s i c r o c k s , and i t i s p o s s i b l e t h a t an unconformity too s l i g h t to be detected i n beds at such high angles ( i n t h i s p l a c e <80°), or tha t the seemingly g n e i s s i c rock i s r e a l l y i n t r u s i v e , i t s apparent bedding being due to p r e s s u r e , or the p o s i t i o n of the plane of c o o l i n g . " However, Dawson appeared u n c e r t a i n about the nature of the contact between the Eagle complex and the N i c o l a Group. His u n c e r t a i n t y i s r e f l e c t e d i n h i s assignment of Eagle complex rocks to the PREVIOUS WORK / 30 a p p a r e n t l y all-encompassing "Cascade c r y s t a l l i n e s e r i e s " of Selwyn's (1872) p r o v i s i o n a l c l a s s i f i c a t i o n , to which Dawson (1879, P.172B), a s s i g n s a P a l e o z o i c age. C. R.A. DALY In h i s c l a s s i c study of the geology along the f o r t y - n i n t h p a r a l l e l , R.A. Daly (1912) mapped the southern e x t e n s i o n of the Eagle complex. He named the body the Remmel b a t h o l i t h and assigned i t a J u r a s s i c ( ? ) age. The Remmel b a t h o l i t h formed the western margin of Daly's Okanagan composite b a t h o l i t h , which extended from the Okanagan v a l l e y on the east to the Pasayten River on the west and which i n c l u d e d the Osoyoos b a t h o l i t h , the Similkameen b a t h o l i t h and the C a t h e d r a l b a t h o l i t h . Within the Remmel b a t h o l i t h , Daly recognized two phases of what he cons i d e r e d a s i n g l e i n t r u s i o n . His narrower e a s t e r n " a c i d " phase (1 to 2 k i l o m e t e r s wide at the I n t e r n a t i o n a l boundary) he d e s c r i b e d as c o n t a i n i n g a bette r - d e v e l o p e d " g n e i s s i c and banded" s t r u c t u r e than the more ext e n s i v e western phase, which u n d e r l i e s the 20 kil o m e t e r wide area between the Pasayten and Ashnola r i v e r s at the Canada-U.S.A. border. The western phase, although d e s c r i b e d by Daly as somewhat v a r i a b l e i n c o m p o s i t i o n , has a "sheared g r a n o d i o r i t e " as i t s most common l i t h o l o g y . T h i s rock-type has a mode of 27% q u a r t z , 51% andesine, 7% o r t h o c l a s e and 6% b i o t i t e , and i n f a c t p l o t s as a t o n a l i t e i f the IUGS c l a s s i f i c a t i o n of S t r e c k e i s e n (1976) i s used. L i k e the Eagle t o n a l i t e i n the present study a r e a , i t i s c h a r a c t e r i z e d by " l u s t r o u s " b i o t i t e phenocrysts that commonly make PREVIOUS WORK / 31 up >1 centimeter f o i l s . As opposed to the e a s t e r n phase of the Remmel, which Daly d e s c r i b e d as "wholly r e c r y s t a l l i z e d , " the western phase was d e s c r i b e d as being " s t r o n g l y g r a n u l a t e d " or "crushed" and not r e c r y s t a l l i z e d . Daly a t t r i b u t e d the " c r u s h i n g " i n the western Remmel and the formation of g n e i s s i c and banded s t r u c t u r e i n the e a s t e r n Remmel to the same episode of "dynamic and hydrothermal metamorphism." He maintained t h a t r e c r y s t a l l i z e d g n e i s s i c and banded rocks of the e a s t e r n phase had undergone more intense dynamic and hydrothermal metamorphism than crushed rocks of the western phase. He i n t e r p r e t e d c ontact r e l a t i o n s between the Remmel b a t h o l i t h and the C a t h e d r a l b a t h o l i t h t o the east as i n d i c a t i n g t h a t deformation and metamorphism tha t a f f e c t e d the Remmel predated i n t r u s i o n of the C a t h e d r a l b a t h o l i t h (to which he assigned a T e r t i a r y a g e ) . Within the western phase of the Remmel b a t h o l i t h , Daly mapped two l a r g e pendants. He d e s c r i b e s the l a r g e r western pendant, which he termed the " b a s i c complex," as c o n t a i n i n g d i v e r s e rock-types with complex s t r u c t u r e s . Daly assigned the rocks i n the pendants a Late P a l a e o z o i c ( ? ) age and recognized them as evidence f o r pre-Remmel i n t r u s i o n and d e f o r m a t i o n . Although these rocks have been r e f e r r e d to i n subsequent s t u d i e s (e.g., "hornblende gneisses of Sheep Mountain" of S t a a t z et. al . , 1971), no work which has the complex as i t s primary focus has been p u b l i s h e d s i n c e Daly's study. Daly thought th a t a l t e r e d rocks of the western phase of the Remmel b a t h o l i t h along t h e i r west co n t a c t represented a paleo-weathering s u r f a c e and he i n f e r r e d t h a t t h e i r c o ntact with PREVIOUS WORK / 32 v o l c a n i c agglomerate was unconformable. He i n c l u d e d the agglomeratic rocks i n h i s mainly sedimentary "Pasayten S e r i e s , " which Daly i n t e r p r e t e d as a g i g a n t i c monocline and to which he assigned a Cretaceous age. The J u r a s s i c ( ? ) age that Daly assigned to the Remmel b a t h o l i t h was based presumably on t h i s i n t e r p r e t a t i o n . Deformation manifest as c r u s h i n g and g n e i s s i c s t r u c t u r e i n the Remmel b a t h o l i t h and as f o l d i n g i n the sedimentary rocks was a t t r i b u t e d by Daly- to the same pos t - C r e t a c e o u s , p r e - T e r t i a r y event. The d i f f e r e n c e i n s t r u c t u r a l s t y l e he a t t r i b u t e d to the d i f f e r e n c e i n depth of b u r i a l . Daly's Pasayten S e r i e s encompasses rocks now r e f e r r e d to the Methow-Pasayten tr o u g h . In the area between the I n t e r n a t i o n a l Boundary and the C o q u i h a l l a R i v e r the b e l t i n c l u d e s sedimentary rocks of known E a r l y J u r a s s i c , lower Middle J u r a s s i c , Late J u r a s s i c , E a r l y C r etaceous, Late Cretaceous (O'Brien, 1987) and Middle Eocene age. D. G.C. SMITH AND F.C. CALKINS Smith and C a l k i n s (1904) undertook a one season g e o l o g i c survey f o r the U.S. government c o i n c i d e n t with Daly's s t u d y . Although t h e i r study i s much l e s s d e t a i l e d than D a l y ' s , they recognized many of the map-units d e t a i l e d by him. They a l s o note the presence of two-mica g r a n i t e c o n t a i n i n g pink garnets ( F a l l s l a k e p l u t o n i c s u i t e of t h i s study?) w i t h i n the Remmel b a t h o l i t h and extending s e v e r a l miles to the south- s o u t h e a s t , and note th a t s t r a i n t e x t u r e s are present w i t h i n t h i s two-mica g r a n i t e . PREVIOUS WORK / 33 E. CHARLES CAMSELL Charles Camsell spent p a r t s of s e v e r a l f i e l d seasons between 1906 and 1911, as w e l l as 1918, mapping the Similkameen, Tulameen, and C o q u i h a l l a d i s t r i c t s of southwestern B r i t i s h Columbia f o r the G e o l o g i c a l Survey of Canada (GSC). He produced a r e g i o n a l map of the Tulameen area (Camsell, 1913), which encompasses part of the Eagle complex, but because the emphasis of h i s r e p o r t s i s on miner a l o c c u r r e n c e s , h i s d i s c u s s i o n s of the r e l a t i v e l y mineral-poor main mass of the Eagle complex are t y p i c a l l y s h o r t and h i g h l y g e n e r a l i z e d . Camsell d i d , however, make a number of notable o b s e r v a t i o n s . He f i r s t r e c o gnized the c h a r a c t e r i s t i c a c c e s s o r y epidote i n Eagle complex r o c k s , although he a s c r i b e d i t s presence to "decomposition." He a l s o noted the well-developed f o l i a t i o n i n Eagle complex r o c k s , and a t t r i b u t e d i t s o r i g i n to "...some movement along the c o n t a c t s at the time of i n t r u s i o n , when the rock was s o l i d i f y i n g from a s t a t e of f u s i o n ( C amsell, 1913, p.78)." In a d d i t i o n , Camsell examined the c o n t a c t s of the Eagle complex i n the southern p a r t of the present study a r e a , and was the f i r s t to recognize the unconformity between sedimentary and g r a n i t i c rocks along the west co n t a c t of the complex (Camsell, 1910, 1911, 1913). He a l s o r e cognized (p.53, C a m s e l l , 1907) tha t the east contact of the Eagle complex was i n t r u s i v e , with a " b e l t of l i g h t c o l o u r e d g r a n i t e " (Eagle t o n a l i t e of the present study) i n t r u s i v e i n t o " s c h i s t s " ( N i c o l a Group) exposed along the Tulameen R i v e r and Eagle ( l a t e r B r i t t o n ) Creek. He a l s o reexamined the Whipsaw Creek area which Dawson had d e s c r i b e d and found t h a t " g n e i s s i c g r a n o d i o r i t e " PREVIOUS WORK / 34 (Eagle complex) int r u d e d "hornblende and c h l o r i t e s c h i s t s " ( N i c o l a Group) (Camsell, 1912). Camsell l a t e r designated the Eagle ( B r i t t o n ) Creek l o c a l i t y the "type" area f o r h i s "Eagle g r a n o d i o r i t e " ( C amsell, 1913). This same l o c a l i t y , which Camsell d e s c r i b e s i n some d e t a i l (p.78), was examined by the present a u t h o r . The g r a n o d i o r i t e he d e s c r i b e d i s part of an e a r l y T e r t i a r y s t o c k , the I l l a l stock (Chapter 4 ) , which d i f f e r s fundamentally from Eagle t o n a l i t e . The most s i g n i f i c a n t of these d i f f e r e n c e s , apart from t h e i r r e l a t i v e emplacement ages, i s the complete lack of f a b r i c i n the I l l a l s t o c k . F u r t h e r , the I l l a l stock has an a g m a t i t i c e a s t e r n c o n t a c t , where i t forms the matrix to r o t a t e d b l ocks of highly-deformed N i c o l a Group r o c k s . Both these a t t r i b u t e s are hallmarks of p o s t - t e c t o n i c i n t r u s i o n , and although Camsell c o r r e c t l y d e s c r i b e d the Eagle as i n t r u s i v e i n t o N i c o l a Group r o c k s , the outcrops i n h i s "type area" are not t y p i c a l of the nature of i n t r u s i o n of the Eagle t o n a l i t e i n t o N i c o l a Group r o c k s . C a m s e l l , i n part f o r t u i t o u s l y , c o r r e c t l y estimated a J u r a s s i c age f o r the "Eagle g r a n o d i o r i t e . " From i n t r u s i v e r e l a t i o n s with Upper T r i a s s i c N i c o l a Group rocks along i t s east margin, he was able to place an o l d e r l i m i t on the age of emplacement of the E a g l e . His Cretaceous younger l i m i t was based on r e c o g n i t i o n of the unconformity between what Camsell thought were Cretaceous sedimentary rocks and what he i n t e r p r e t e d to be g r a n i t i c rocks c o r r e l a t i v e with other Eagle r o c k s . In l i g h t of new m i c r o p a l a e o n t o l o g i c and geochronometric data and bedrock mapping PREVIOUS WORK / 35 from t h i s s t u d y , Camsell had a c t u a l l y placed a Middle Eocene younger l i m i t o n l y on the age of the Late J u r a s s i c Zoa complex, which was f a u l t e d a g a i n s t Eagle t o n a l i t e and g n e i s s i n mid-Cretaceous time. F. C.E. CAIRNES A c t i v e e x p l o r a t i o n and development of mineral p r o p e r t i e s along the C o q u i h a l l a s e r p e n t i n e b e l t and c o n s t r u c t i o n from 1910 to 1916 of the K e t t l e V a l l e y Railway l e d to the renewal of g e o l o g i c a l work i n the C o q u i h a l l a and a d j o i n i n g r e g i o n s . This renewal of work was i n i t i a t e d by Charles Camsell ( C a m s e l l , 1919), but was c a r r i e d on by C.E. C a i r n e s , who p u b l i s h e d s e v e r a l p r e l i m i n a r y r e p o r t s ( C a i r n e s , 1921, 1923, 1924a) and a summary Memoir ( C a i r n e s , 1924b) on the C o q u i h a l l a a r e a . C a i r n e s , l i k e e a r l i e r g e o l o g i s t s , emphasized the c o n t i n u i t y of the Eagle g r a n o d i o r i t e i n the C o q u i h a l l a area with rocks to the s o u t h . He suggested (1924a, p.62A) that the Eagle g r a n o d i o r i t e exposed along the Similkameen and Pasayten r i v e r s was continuous with and part of the Reramel b a t h o l i t h of D a l y , and t h a t both were c o r r e l a t i v e with Eagle rocks i n the Whipsaw Creek, Tulameen River and C o q u i h a l l a R i v e r a r e a s . Although Cairnes a l l u d e d to a g r a n i t i z a t i o n o r i g i n f o r p a r t s of the Eagle g r a n o d i o r i t e , as suggested i n the e x t r a c t below: " .. . the great r e g u l a r i t y of the banding and the m i a r o l i t i c s t r u c t u r e [nowhere observed by the present author] "of the PREVIOUS WORK / 36 i n t r u s i v e suggest th a t there may a c t u a l l y have been some replacement of an e a r l i e r s t r a t i f i e d formation . . . (p.94, 1924b)," he regarded i t s c o n t a c t with N i c o l a rocks as i n t r u s i v e and recognized the r e g i o n a l l y concordant form of the E a g l e : " . . . t h i s body of g r a n o d i o r i t e much resembles a huge s i l l , between 4 and 5 miles wide, extending i n a d i r e c t i o n a few degrees west of n o r t h . . . ( C a i r n e s , 1923, p.92A)" However, u n l i k e e a r l i e r g e o l o g i s t s , Cairnes spent c o n s i d e r a b l e time examining the i n t e r n a l s t r u c t u r e of the Eagle g r a n o d i o r i t e . In the C o q u i h a l l a a r e a , h i s work r e f u t e d Camsell's (1913) view th a t f o l i a t i o n was more prominent i n the Eagle g r a n o d i o r i t e near c o n t a c t s with the Tulameen S e r i e s ( C a i r n e s , 1924b, p.95). C a i r n e s observed t h a t the f o l i a t i o n i n the Eagle g r a n o d i o r i t e , though widespread, was not present everywhere, nor uniform i n o r i e n t a t i o n throughout. Cairnes regarded the f o l i a t i o n as: "...not a type such as would r e s u l t from crush metamorphism of an o r i g i n a l l y massive r o c k , but from i t s r e g u l a r i t y , the l i n e a r arrangement of the mineral c o n s t i t u e n t s , and an absence of i n t e n s e g r a n u l a t i o n , seems to be r a t h e r the r e s u l t of pressure exerted on, or movement e f f e c t e d i n , a v i s c o u s or semi-molten magma." ( C a i r n e s , 1924b, p.95) PREVIOUS WORK / 37 He b e l i e v e d t h a t f a b r i c s i n Eagle g r a n o d i o r i t e were r e l a t e d to "pressure . . . set up by the i n t r u s i o n ..." of the Needle Peak p l u t o n " . . . while the g r a n o d i o r i t e was s t i l l v i s c o u s " ( C a i r n e s , 1924b, p.95). C a i r n e s was of the o p i n i o n t h a t the Needle Peak p l u t o n , r e f e r r e d to by him under the heading "complex of Cretaceous b a t h o l i t h s , " was only s l i g h t l y younger than the Eagle g r a n o d i o r i t e . Cairnes a l s o noted the c o m p o s i t i o n a l v a r i a b i l i t y of those rocks that he and others had mapped as Eagle g r a n o d i o r i t e . He remarked on m u s c o v i t e - r i c h v a r i e t i e s ( C a i r n e s , 1923, p.92A) and pegmatites ( C a i r n e s , 1924b, p.94) and noted the presence w i t h i n h o r n b l e n d e - r i c h rocks of "very conspicuous" epidote (p.94, C a i r n e s , 1924b) w i t h i n the C o q u i h a l l a a r e a . F u r t h e r , Cairnes noted the presence of more mafic g r a n i t i c rocks along the western f l a n k of the Eagle g r a n o d i o r i t e (Zoa complex hornblende quartz d i o r i t e of the present study) and found them " . . . s u f f i c i e n t l y d i s t i n c t . . . to be mapped s e p a r a t e l y as the Eagle d i o r i t e formation" (1923, p.23A). Although he never a c t u a l l y observed t h e i r c o ntact (p.96, C a i r n e s , 1924b), Cairnes considered Eagle d i o r i t e to be a border phase of Eagle g r a n o d i o r i t e , being " . . . i n t r u d e d s l i g h t l y i n advance of the l a r g e r bulk of the g r a n o d i o r i t e ..." or " . . . being a d i f f e r e n t i a t e i n p l a c e , developed near the base of the huge s i l l - l i k e body of the g r a n o d i o r i t e Cairnes wrongly b e l i e v e d t h a t the Eagle d i o r i t e i n t r u d e d sedimentary rocks t h a t border Eagle or Zoa complex rocks on t h e i r west s i d e . Because of t h i s , and because he r e f e r r e d the PREVIOUS WORK / 38 sedimentary rocks to the Lower Cretaceous (they are now known to be Middle Eocene i n a g e ) , he i n c o r r e c t l y assigned a post-Lower Cretaceous age to the Eagle d i o r i t e and g r a n o d i o r i t e . Cairnes b e l i e v e d he had s u f f i c i e n t evidence to support the presence of an i n t r u s i v e c o n t a c t . This evidence i n c l u d e d h o r n f e l s e d sedimentary rocks near the Eagle d i o r i t e c o n t a c t and " f i n e r - g r a i n e d or p o r p h y r i t i c v a r i e t i e s " of Eagle d i o r i t e , regarded by Cairnes as border phases, near i t s co n t a c t with sedimentary rocks ( C a i r n e s , 1924b, p.90). He a l s o c o n s i d e r e d the i n c r e a s i n g abundance of p o r p h y r i t i c i n t r u s i v e s w i t h i n the sedimentary rocks toward the Eagle d i o r i t e c o n t a c t as evidence of i n t r u s i o n : "Within a mile or so of the Eagle g r a n o d i o r i t e c o n t a c t the sediments i n c l u d e d with the Cretaceous rocks are i n t e r s e c t e d by porphyry dykes which become both l a r g e r and more abundant i n approaching the g r a n o d i o r i t e , and lend some support to the view th a t they r e p r e s e n t a l a t e phase i n the i n t r u s i o n of t h i s g r a n o d i o r i t e . " ( C a i r n e s , 1923. p.99A) The f i n e r - g r a i n e d rocks are now known, at l e a s t i n p a r t , to be pre-Late J u r a s s i c metavolcanic r o c k s . As w e l l , the sedimentary rocks have been h o r n f e l s e d not by C a i r n e s ' Eagle d i o r i t e , but by the Middle Eocene Needle Peak p l u t o n , the c o n t a c t of which c o i n c i d e s c l o s e l y with the co n t a c t between the narrow b e l t of sedimentary rocks and Eagle d i o r i t e i n the C o q u i h a l l a a r e a . PREVIOUS WORK / 39 Despite t h i s e v i d e n c e , C a i r n e s ' a s s e r t i o n t h a t the contact between sedimentary rocks and Eagle d i o r i t e i s i n t r u s i v e i s somewhat p e r p l e x i n g i n l i g h t of the f a c t t h a t , l i k e C a m s e l l , he had examined the contact near Jim K e l l y , R a i l r o a d and Vuich creeks near the south end of the present study area and had found i t unconformable: "On the R a i l r o a d - [ J i m ] K e l l y Creeks d i v i d e . . . T h e b a s a l " bed i s a b r e c c i a interbedded with grey f e l d s p a t h i c beds. The p e c u l i a r l y f r e s h appearance of these rocks on t h i s d i v i d e , t h e i r evident unconformable r e l a t i o n with the o l d e r g r a n o d i o r i t e . . . (1923, p.98A)" That he chose to d i s r e g a r d t h i s evidence suggests t h a t C a i r n e s may have suspected t h a t the sedimentary rocks were younger, or the g r a n o d i o r i t e o l d e r , than rocks along s t r i k e , and that t h i s l o c a l i t y was not r e p r e s e n t a t i v e of the true contact r e l a t i o n s . In h i s examination of the west co n t a c t of the Eagle g r a n o d i o r i t e i n other a r e a s , Cairnes seems to have been swayed by h i s o r i g i n a l i n t e r p r e t a t i o n . Near Whipsaw Creek, he i n t e r p r e t e d the contact of the Eagle with sedimentary rocks to the west as i n t r u s i v e , but acknowledged th a t the contact i s not d i r e c t l y exposed and may have l a t e r been f a u l t e d , and t h a t h i s i n t e r p r e t a t i o n i s based on o b s e r v a t i o n s made i n the C o q u i h a l l a a r e a . Along the present route of the Hope-Princeton highway (Highway 3 ) , about 25 k i l o m e t e r s south of the Whipsaw Creek area PREVIOUS WORK / 40 and 50-60 k i l o m e t e r s south of the C o q u i h a l l a a r e a , C a i r n e s again favoured an i n t r u s i v e c ontact between the Eagle and the sedimentary rocks to the west. His evi d e n c e , which i n c l u d e d the presence of di k e s s i m i l a r i n composition to the Eagle w i t h i n the s t r a t i f i e d r o c k s , the presence on the western margin of the Eagle of a " b a s i c border phase" of somewhat more mafic composition than the average g r a n o d i o r i t e , and the northward t r u n c a t i o n of a v o l c a n i c u n i t o c c u r r i n g at the base of the s t r a t i f i e d rocks along the Pasayten R i v e r , i s , as he puts i t , "not c o n c l u s i v e ( C a i r n e s , 1923)." Despite n o t i n g the lack of any contact e f f e c t s i n the sedimentary rocks from t h i s r a t h e r l a r g e i n t r u s i v e body, Cairnes again noted the evidence of i n t r u s i o n he found i n the C o q u i h a l l a area and appears to have been swayed i t . G. H.M.A. RICE H. M.A. R i c e , i n h i s Memoir on the P r i n c e t o n map-sheet ( R i c e , 1947), i n c l u d e d the Eagle g r a n o d i o r i t e under the heading "Coast i n t r u s i o n s , " to which he assigned a J u r a s s i c or e a r l y E a r l y Cretaceous age (p. 43, Rice 1947). On the b a s i s of the IUGS c l a s s i f i c a t i o n o f S t r e c k e i s e n (1976), the average mode of e i g h t specimens of Eagle g r a n o d i o r i t e examined by Rice (page 37, R i c e , 1947) p l o t s i n the f i e l d f o r t o n a l i t e . Rice noted the conformity between s t r u c t u r e s i n the Eagle and the N i c o l a Group, observed that f o l i a t i o n w i t h i n the Eagle was g e n e r a l l y p a r a l l e l to i t s long dimension and f i r s t remarked on the c l o s e a s s o c i a t i o n between s c h i s t o s e N i c o l a Group rocks and the Eagle g r a n o d i o r i t e (marginal PREVIOUS WORK / 41 notes to Map 888A, R i c e , 1947). Near the i n t e r n a t i o n a l border and at the southern end of the E a g l e , he mapped the "synform" t h a t i s o u t l i n e d by a change i n trend of the e l o n g a t i o n of the i n t r u s i o n and by the changing o r i e n t a t i o n of i t s f o l i a t i o n . Rice b e l i e v e d t h a t the Eagle was ". . . i n t r o d u c e d along the bedding of the N i c o l a , perhaps i n l a r g e p art by g r a n i t i z a t i o n " ( R i c e , 1947, p.36). H. GEOCHRONOMETRY OF THE 19 60'S AND EARLY 19 70'S In the 1960's and e a r l y 1970's, a number of potassium-argon dates f o r the Eagle complex were determined by the GSC l a b o r a t o r y (Leech et. al . , 1963; Wanless et. a l . , 1967) and the l a b o r a t o r y at Queen's U n i v e r s i t y (Roddick and F a r r a r , 1972). None of the d a t i n g s t u d i e s i n v o l v e d g e o l o g i c mapping w i t h i n the Eagle complex i t s e l f , but were conducted to support s t u d i e s on rocks of the Tulameen u l t r a m a f i c complex to the east (Leech et. al . , 1963; Roddick and F a r r a r , 1972) and the Pasayten trough to the west (Wanless et. a l . , 1967). A l l dates i n the f o l l o w i n g d i s c u s s i o n have been r e c a l c u l a t e d to decay constants recommended by S t e i g e r and Jager (1977) . A f r e q u e n t l y c i t e d 146 +/- 12 Ma K-Ar (2 sigma) b i o t i t e date-determined by Leech et. a l . (1963) f o r Eagle " g r a n o d i o r i t e " near the confluence of McGee Creek and the Tulameen R i v e r was the f i r s t i s o t o p i c date determined f o r the Eagle complex. Because no c o r r e c t i o n was made f o r atmospheric argon i n t h i s a n a l y s i s and because such an o l d date has not been confirmed by l a t e r K-Ar b i o t i t e dates f o r the Eagle complex, t h i s date has been d i s c r e d i t e d PREVIOUS WORK / 42 (R.L.Armstrong, p e r s o n a l communication, 1988). Wanless et. al. (1967) obtained a 101 +/- 6 Ma (2 sigma) date f o r f o l i a t e d hornblende b i o t i t e quartz d i o r i t e from Highway 3 (the Hope-Princeton highway) tha t was c o l l e c t e d and i n t e r p r e t e d by J.A. Coates, who was s t u d y i n g rocks of the adjacent Pasayten t r o u g h . Roddick and F a r r a r (1972) dated eleven mineral separates from e i g h t samples of the Eagle complex. A l l Queens e r r o r s quoted are one sigma. F i v e of the samples were c o l l e c t e d from the Tulameen Ri v e r (the southern end of the present study a r e a ) , two were c o l l e c t e d from an area adjacent to the southern end of the Tulameen complex (see Roddick and F a r r a r (1972), t h e i r F i g u r e 1) and a s i n g l e sample was c o l l e c t e d from along Highway 3. The sample from Highway 3 y i e l d e d concordant hornblende and b i o t i t e dates of 114.5 +/- 1.2 Ma and 115.1 +/- 1.8 Ma r e s p e c t i v e l y , s u g g e s t i n g t h a t the sample cooled r a p i d l y through the r e s p e c t i v e b l o c k i n g temperatures f o r argon i n hornblende and b i o t i t e . Muscovite from a pegmatite dike c u t t i n g the g r a n o d i o r i t e y i e l d e d a 73.7 +/- 1.2 Ma ( l a t e s t C retaceous, two analyses y i e l d e d i d e n t i c a l dates) date and b i o t i t e from a v e i n ' c u t t i n g g r a n o d i o r i t e y i e l d e d a 87.6 +/- 1.4 Ma d a t e . Both were considered to be r e l a t e d to l a t e hydrothermal a c t i v i t y . Of the seven remaining d a t e s , one was a hornblende date of 107.2 +/- 1.7 Ma, two were from a d u p l i c a t e a n a l y s i s of b i o t i t e t h a t y i e l d e d 97.8 +/- 1.2 Ma and 100.4 +/- 1.2 Ma d a t e s , two were analyses of d i f f e r e n t mesh s i z e s of b i o t i t e from the same rock and y i e l d e d 105.8 +/- 1.6 Ma and 109.0 +/- 1.7 Ma d a t e s , and two were b i o t i t e dates from separate samples of 104.7 +/- 1.6 Ma and PREVIOUS WORK / 43 109.1 +/- 1.2 Ma. Roddick and F a r r a r (1972) i n t e r p r e t e d the dates as i n t r u s i v e ages and suggested that the Eagle g r a n o d i o r i t e was i n t r u d e d over a p e r i o d of 10 Ma, with the peak of i n t r u s i v e a c t i v i t y o c c u r r i n g at approximately 104 Ma. I . J.A. COATES In the Manning Park area (at the l a t i t u d e of Highway 3 ) , J.A. Coates (1970, 1974) s t u d i e d the s t r a t i g r a p h y and s t r u c t u r e of sedimentary rocks of the Jura-Cretaceous Pasayten trough (Methow-Pasayten-Tyaughton t r o u g h ) . Because the east margin of the trough had been i n f e r r e d by previous g e o l o g i s t s to be e i t h e r a f a u l t (Bauerman, 1884; Dawson, 1879) or an unconformity (Camsell, 1913; Daly, 1912; R i c e , 1947), and because s e d i m e n t o l o g i c a l data suggested an e a s t e r n provenance f o r much of the Cretaceous s e c t i o n i n the t r o u g h , Coates spent c o n s i d e r a b l e e f f o r t examining the west contact of the E a g l e . He examined four l o c a l i t i e s i n p a r t i c u l a r d e t a i l (1974, p.61-63), and i n the Manning Park area he concluded th a t the contact was a f a u l t . Coates d e s c r i b e d h o r i z o n t a l and s h a l l o w l y southeast plunging l i n e a r f a b r i c s on f a u l t planes at two of the l o c a l i t i e s and noted t h a t they were sug g e s t i v e of s t r i k e - s l i p or o b l i q u e - s l i p movement. However, on the b a s i s of Camsell's and C a i r n e s ' well-known Jim K e l l y - R a i l r o a d - V u i c h creeks unconformity, which he re-examined (1974, p.62), Coates concluded th a t the f a u l t must have been a c t i v e d u r i n g d e p o s i t i o n of the Cretaceous sediments. PREVIOUS WORK / 44 J . PHILLIP ANDERSON Of a l l the previous g e o l o g i c work tha t has i n v o l v e d the Eagle complex, only the study of Anderson (1971) had the Eagle complex as i t s primary main f o c u s . Anderson mapped an area i n the v a l l e y of Whipsaw Creek th a t s t r a d d l e d the contact of the Eagle complex and the Upper T r i a s s i c N i c o l a Group. He noted t h a t most Eagle rocks were t o n a l i t i c i n c o m p o s i t i o n , t h a t g n e i s s i c l a y e r i n g i n the Eagle was more pronounced to the west and that abundant l e u c o c r a t i c " a l a s k i t e " ( g r a n o d i o r i t e , quartz monzonite and g r a n i t e ) , a p l i t e and pegmatite i n t r u s i o n s c r o s s - c u t the t o n a l i t i c r o c k s . Based on these o b s e r v a t i o n s , Anderson suggested t h a t the Eagle " g r a n o d i o r i t e " be renamed "Eagle t o n a l i t e - g n e i s s complex." Within the N i c o l a Group, Anderson documented a westward i n c r e a s e i n metamorphic grade from g r e e n s c h i s t to amphibolite f a c i e s as the Eagle complex was approached. He a l s o recognized t h a t primary f a b r i c s i n N i c o l a Group v o l c a n i c rocks had been o v e r p r i n t e d as the metamorphic grade inc r e a s e d and f o l i a t i o n became more pronounced toward the E a g l e . Anderson i n t e r p r e t e d the metamorphic g r a d i e n t as a r e g i o n a l f e a t u r e u n r e l a t e d to contact metamorphism of the N i c o l a Group by the Eagle and f a i l e d to r e c o g n i z e the m y l o n i t i c c h a r a c t e r of f o l i a t e d rocks at the Eagle complex-Nicola Group c o n t a c t , thus deemphasizing the t e c t o n i c c h a r a c t e r of the c o n t a c t . Anderson's view was t h a t the Eagle complex was d e r i v e d through a n a t e x i s of the N i c o l a Group. PREVIOUS WORK / 45 K. J.W.H. "THE CHIEF" MONGER In 1984, the GSC, as part of i t s ongoing regional mapping program, began re-mapping the Hope map-sheet at 1;250,000 scale (Monger, 1985). The present study, begun in 1986, has been supported by that project. Monger (1985), in a review of the structures in the southwestern Intermontane Belt, b r i e f l y summarized what was known to date about the Mt. Lytton plutonic complex (in which he had included the Eagle granodiorite). He noted that the older northern part (mainly in Ashcroft map-area and referred to herein as the Mt. Lytton plutonic complex) did not contain the r e l a t i v e l y uniformly-oriented f a b r i c seen in the southern part, the Eagle granodiorite. Like e a r l i e r geologists, Monger recognized the concordant nature of f o l i a t i o n s in the Eagle granodiorite and the Nicola Group and suggested that they were genet i c a l l y related. A preliminary 135 Ma U-Pb zircon date ( e a r l i e s t Cretaceous) for "migmatite" in Eagle granodiorite reported by Monger (1985; in the present study, further U-Pb analyses on zircon from the same sample have yielded a Late Jurassic date (Chapter 5) was taken as the age of emplacement of the Eagle and as the time of formation of st r u c t u r a l fabrics along i t s east margin. Monger correlated the southwest dipping f o l i a t i o n s with east-vergent structures, f i r s t recognized by Travers (1978), which bring the Nicola and Cache Creek groups over the Ashcroft Formation in the Ashcroft map-area to the north. PREVIOUS WORK / 46 I I I . MT. LYTTON PLUTONIC COMPLEX To the north of the C o q u i h a l l a a r e a , i n northern Hope map-area (92H) and southern A s h c r o f t map-area (921), the Eagle complex i s continuous with the Mt. L y t t o n p l u t o n i c complex (Monger and M c M i l l a n , 1984). The Mt. L y t t o n complex was o r i g i n a l l y named the Mount L y t t o n b a t h o l i t h by D u f f e l l and McTaggart (1952) i n t h e i r Memoir on the A s h c r o f t map-area. As d e s c r i b e d by them, the b a t h o l i t h encompassed the heterogeneous mass of p l u t o n i c and l e s s e r metamorphic rock exposed east of the F r a s e r River and south of L i l l o o e t , as w e l l as s e v e r a l s t o c k s along s t r i k e to the northwest (e.g., the Mt. M a r t l e y and P a v i l i o n Lake s t o c k s ) . D u f f e l l and McTaggart recognized that the main body of the Mount L y t t o n b a t h o l i t h was composed of p l u t o n i c phases of s e v e r a l ages t h a t on s t r a t i g r a p h i c evidence were of J u r a s s i c to E a r l y Cretaceous age (phases east of L y t t o n i n t r u d e Upper T r i a s s i c N i c o l a Group e q u i v a l e n t s and the b a t h o l i t h i s o v e r l a i n on i t s east margin by v o l c a n i c rocks of the Lower Cretaceous Spences Bridge Group, D u f f e l l and McTaggart, 1952, p.81). In a d d i t i o n , they recognized t h a t much of the mass of the Mount L y t t o n b a t h o l i t h i n the southern part of the A s h c r o f t area resembled and was continuous with the Eagle g r a n o d i o r i t e . Near the northernmost end of the main body, north of the Thompson R i v e r , D u f f e l l and McTaggart d e s c r i b e d a heterogeneous p l u t o n i c complex c o n t a i n i n g phases of gabbro and h o r n b l e n d i t e . South of the Thompson R i v e r , they found the Mount L y t t o n b a t h o l i t h dominated by hornblende and b i o t i t e g r a n o d i o r i t e and quartz d i o r i t e PREVIOUS WORK / 47 that they considered younger than the more b a s i c rocks to the n o r t h . D u f f e l l and McTaggart a l s o noted that rocks along the west margin of the b a t h o l i t h south of the Thompson Ri v e r c o n t a i n a f o l i a t i o n o u t l i n e d by mafic minerals t h a t p a r a l l e l s the f a u l t e d north-northwest t r e n d i n g west contact of the b a t h o l i t h . From the time of D u f f e l l and McTaggart (1952) u n t i l re-mapping of the A s h c r o f t map-area by the GSC i n the 1980's, the Mt. L y t t o n complex was the focus of l i t t l e or no g e o l o g i c mapping. Mapping and geochronometry by the GSC s i n c e 1980, though mainly of a reconnaissance n a t u r e , has e l a b o r a t e d on the age, composition and d i s t r i b u t i o n of s e v e r a l c o n s t i t u e n t plutons w i t h i n the Mt. L y t t o n complex (Monger, 1981; Monger, 1982; Monger and M c M i l l a n , 1984). As w e l l , a more d e t a i l e d study of metamorphic and p l u t o n i c rocks near the n o r t h end of the Mt. L y t t o n complex along the Thompson Riv e r ( " s c h i s t and g n e i s s , " i n p a r t , of D u f f e l l and McTaggart (1952) and " L y t t o n g n e i s s " of Monger (1981)) was undertaken (Brown, 1981). Brown d e s c r i b e d l o c a l l y w e l l - l a y e r e d amphibolite-grade q u a r t z o f e l d s p a t h i c g n e i s s , amphibolite and l o c a l mylonite of the " L y t t o n g n e i s s " and d i s t i n g u i s h e d four map-scale i n t r u s i v e phases ranging i n composition from g a b b r o / d i o r i t e to g r a n o d i o r i t e . Due to d i f f i c u l t i e s of a c c e s s , the r e l a t i v e ages of i n t r u s i v e u n i t s could not be determined, but a l l were cons i d e r e d to post-date formation of the f a b r i c i n the gneiss (Brown, 1981). On the b a s i s of l i t h o l o g i c s i m i l a r i t y and three E a r l y J u r a s s i c K-Ar dates obtained f o r g r a n o d i o r i t e of the Mt. L y t t o n complex south of the Thompson R i v e r , Monger and McMillan (1984) su b d i v i d e d PREVIOUS WORK / 48 plutonic rocks of the Mt. Lytton complex into T r i a s s i c and (?) Jurassic d i o r i t e (and l o c a l amphibolite) and e a r l i e s t (?) Jurassic granodiorite. A Late T r i a s s i c - E a r l y Jurassic U-Pb zircon date has since been determined for the granodiorite (J.W.H. Monger, personal communication, 1988). As well, the Lytton gneiss has yielded a preliminary U-Pb zircon date of approximately 252 Ma (Late Permian, Monger, 1985 and P. van der Heyden, personal communication, 1988). This data suggested to Monger (1985) that rocks in the Mt. Lytton complex record post-Permian deformation and metamorphism and were u p l i f t e d in Early Jurassic time. Monger (1985) also speculated that rocks in the northern Mt. Lytton complex represented a lower st r u c t u r a l panel formed by underplating during late T r i a s s i c subduction of Cache Creek Group rocks beneath the Nicola arc. IV. NICOLA GROUP ROCKS IN CONTACT WITH THE EAGLE COMPLEX In southwestern B r i t i s h Columbia, the close association of the Nicola Group with important ore deposits and i t s r e l a t i v e l y great areal extent have made i t the focus of many regional and l o c a l geologic studies. Several studies that have focused, in part, on Nicola Group rocks adjacent to the Eagle complex are summarized here. Other studies relevant to the regional geology and tectonic setting of the Nicola Group have been referred to in Chapter 2. PREVIOUS WORK / 49 A. G.M. DAWSON Dawson (1879) was the f i r s t to recognize the s i m i l a r i t y of rocks that form the east margin of the Eagle complex to rocks he dubbed "Nicola s e r i e s " in their type-area along Nicola Lake. During fieldwork in 1875-77, he made four separate transects across the Mt. Lytton-Eagle complex (see discussion above). Dawson r e c o g n i s e d the s i m i l a r i t i e s between transects of both Nicola Group and Eagle complex rocks and i d e n t i f i e d many of their most fundamental c h a r a c t e r i s t i c s . For example, he described the consistent and concordant northwest s t r i k i n g , southwest dipping fabrics seen in Nicola Group and Eagle complex rocks and noted the sheared nature of the belt of Nicola Group rocks adjacent to the Eagle complex. In a br i e f description of the poorly exposed Nicola Group rocks along the Coldwater River, he noted the presence of dark green schistose c h l o r i t i c and talcose rocks, some of which contain feldspar phenocrysts in a matrix of feldspar and subordinate hornblende. According to Dawson, these l i e in a "synclinal ( s i c ) . " In a more extensive examination of Nicola Group rocks along Whipsaw Creek, Dawson described an eastward overturned tight synform or antiform of metamorphosed and deformed volcanic-derived rocks in which a l l l i t h o l o g i e s exhibit similar northwest-trending, southwest-dipping f a b r i c or layering. Rocks in t h i s belt include (from west to east): "bedded d i o r i t e ; " hornblendic, micaceous, and feldspathic s c h i s t ; fragmental volcanic rocks with l e n t i c u l a r "squeezed" fragments; red schistose "altered and compressed" PREVIOUS WORK / 50 amygdaloid; black schisty or slatey a r g i l l i t e (which l i e in the core of his structure and in which he found poorly-preserved f o s s i l s of Monotis subcircularis); greenish to blackish d i o r i t e ; s l i g h t l y calcareous "spotted" f e l s i t e ; and reddish-grey conglomerate. By Dawson's description, the width of rocks in the Whipsaw Creek area that display a consistent northwest trending, southwest dipping fab r i c and/or layering appears to be approximately f i v e kilometres. Downstream and to the east-northeast along Whipsaw Creek and beyond a covered i n t e r v a l , he noted the presence of grey and greenish d i o r i t e , compact bluish-grey and greenish feldspathic rocks, and grey volcanic breccia or agglomerate. These rocks appear to lack the consistent f a b r i c common to Nicola Group rocks west of t h i s point because Dawson described them as being "... of such a character as to afford l i t t l e i ndication of their a t t i t u d e . " Dawson (1879) favoured derivation of Eagle complex rocks from rocks of the Nicola Group. However, he discussed the p o s s i b i l i t y of t h e i r contact being interpretable as either intrusive, unconformable or "metamorphic" (p.67B, p.70B), and thus appeared to be uncertain as to their true r e l a t i o n . This uncertainty i s perhaps r e f l e c t e d in his inclusion of Eagle complex rocks (which he concluded were derived from Upper T r i a s s i c Nicola Group rocks) in the "Cascade C r y s t a l l i n e s e r i e s " to which he assigns an older and therefore contradictory Upper Palaeozoic age. PREVIOUS WORK / 51 B. CHARLES CAMSELL Charles Camsell of the GSC was the next geologist to map Nicola Group rocks in the v i c i n i t y of the present study area. He spent parts of the 1906 and 1908 and a l l of the 1909 and 1910 f i e l d seasons mapping in the Similkameen r e g i o n and in the Tulameen map-area, which overlaps the southeast margin of the present study area. Camsell published a number of preliminary reports (Camsell, 1907, 1909, 1910, 1911, 1912) during ongoing fieldwork and a Memoir summarizing his work in the Tulameen region (Camsell, 1913). In 1906, Camsell (1907) spent some time examining Nicola Group equivalents near the South Similkameen (formerly Roche) and Pasayten r i v e r s . Rocks upstream of Similkameen F a l l s , which correspond with the belt of strained Nicola Group rocks p a r a l l e l i n g the Eagle complex, he distinguished as the oldest rocks in the area and informally named "Roche River s c h i s t s . " Along the South Similkameen (Roche) r i v e r , he described the Roche River s c h i s t as c h l o r i t i c schist with smaller bands of graphitic and t a l c s c h i s t . Along the Pasayten River he noted "micaceous and hornblende s c h i s t s , frequently very s i l i c e o u s and becoming gneissic and holding bands of greyish c r y s t a l l i n e limestone." Later in the same season, Camsell made a reconnaissance of the Nicola Group near the present study area. He described "... a series of metamorphosed sedimentaries, limestone, quartzite and s c h i s t s , " and noted that rocks east of the Tulameen ultramafic complex were mainly volcanic. No s t r i c t correlations or age assignments were made, although he did infer that the Roche River schist may have been more highly PREVIOUS WORK / 52 metamorphosed e q u i v a l e n t s of the rocks he had d e s c r i b e d near the present study a r e a . Camsell spent more time i n the Tulameen D i s t r i c t d u r i n g the 1909 f i e l d season (Camsell, 1910). However, he provides only a b r i e f d e s c r i p t i o n of the N i c o l a Group rocks exposed along the Tulameen R i v e r : " . . . limestone interbedded with hornblende s c h i s t s i s succeeded by great t h i c k n e s s e s of v o l c a n i c rocks i n which some narrow bands of a r g i l l i t e and limestone are i n t e r c a l a t e d . V o l c a n i c rocks are agglomerates and b r e c c i a s , with a n d e s i t e and diabase f l o w s , the l a t t e r being metamorphosed to c h l o r i t i c and other s c h i s t s . The p r e v a i l i n g s t r i k e i s roughly i n a north and south d i r e c t i o n , with d i p s v a r y i n g from 20 to 90 degrees. The rocks have passed through severe orogenic d i s t u r b a n c e s . . . " Camsell (1912), i n d e s c r i b i n g s e v e r a l mineral prospects along the Eagle complex-Nicola Group c o n t a c t i n the Whipsaw Creek area noted the i n t r u s i v e nature of " g n e i s s i c g r a n o d i o r i t e " of the Eagle complex i n t o "metamorphosed hornblende and c h l o r i t e s c h i s t s of the N i c o l a Group. However, f o l l o w i n g a b r i e f examination of t h i s same a r e a , i t i s suspected t h a t at l e a s t some, and probably a c o n s i d e r a b l e amount, of the "many apophyses" that Camsell a t t r i b u t e s to the Eagle complex may i n f a c t be s i g n i f i c a n t l y younger i n age. Camsell (1913) employed the name Tulameen group f o r rocks i n the Tulameen area t h a t Dawson (1879) had t e n t a t i v e l y c o r r e l a t e d PREVIOUS WORK / 53 with h i s own N i c o l a s e r i e s . The same c o r r e l a t i o n v/as a l s o made by C a m s e l l , but he proposed the d i f f e r e n t name because of a lack of d i a g n o s t i c f o s s i l s w i t h i n the Tulameen group rocks he mapped. Camsell's (1913) summary d e s c r i p t i o n of the Tulameen group i s of an " . . . enormous development of v o l c a n i c r o c k s , with which are interbedded one or two t h i n s t r a t a of limestone and some a r g i l l i t e . " Camsell d e s c r i b e d the s e c t i o n exposed along the Tulameen R i v e r as being r e p r e s e n t a t i v e of the group as a whole. L i t h o l o g i e s d e s c r i b e d i n t h i s s e c t i o n i n c l u d e : s i l i c e o u s and a r g i l l a c e o u s s c h i s t , a n d e s i t e and " p o r p h y r i t e , " a n d e s i t e b r e c c i a , c h l o r i t e and t a l c s c h i s t , and banded a r g i l l i t e and l i m e s t o n e . Camsell noted that the m a j o r i t y of the v o l c a n i c r o c k s , which make up g r e a t e r than 90% of the Tulameen group, have a well-developed " s c h i s t o s e s t r u c t u r e , " t h a t c h l o r i t e , epidote and c a l c i t e are abundant, and t h a t the rocks are commonly " a l t e r e d " to a c h l o r i t e s c h i s t . He a l s o observed th a t metamorphosed a r g i l l i t e s develop i n t o mica and hornblende sillimanite s c h i s t . C. C.E. CAIRNES Cai r n e s (1923), b r i e f l y d e s c r i b e d N i c o l a Group rocks along the K e t t l e V a l l e y Railway grade between C o q u i h a l l a and Canon House ( T h a l i a ) s t a t i o n s and along the Dewdney T r a i l i n the Whipsaw Creek-Hope Pass a r e a . He noted the s c h i s t o s e nature of the rocks i n both areas and r e f e r r e d them to Camsell's (1913) "Tulameen S e r i e s . " In PREVIOUS WORK / 54 1923, Cairnes (1924a) examined N i c o l a rocks along the present route of Highway 3 (Similkameen R i v e r ) . In t h i s s t u d y , he su b d i v i d e d N i c o l a rocks (Tulameen S e r i e s ) i n t o s c h i s t o s e (between Eagle g r a n o d i o r i t e and confluence of Pasayten and Similkameen r i v e r s ) and non-schistose v a r i e t i e s (east of s c h i s t o s e v a r i e t y ) . Cairnes suggested t h a t s c h i s t o s e and non-schistose rocks were f a u l t e d a g a i n s t one another, but noted t h a t non-schistose rocks were the probable p r o t o l i t h to s c h i s t o s e r o c k s . D . H . M . A . RICE In h i s r e g i o n a l map of the P r i n c e t o n a r e a , Rice (1947) f i r s t a s signed N i c o l a rocks t h e i r "Group" s t a t u s and f o r m a l l y c o r r e l a t e d l i t h o l o g i e s from throughout the P r i n c e t o n map-sheet with N i c o l a rocks i n t h e i r type-area on N i c o l a Lake. He a l s o d i s c o v e r e d Halobia-bear ing f o s s i l l o c a l i t i e s j u s t east of Lawless Creek, c o n f i r m i n g e a r l i e r work which suggested t h a t the u n f o s s i l i f e r o u s rocks of the Lawless Creek-Tulameen River area were Upper T r i a s s i c i n age. Rice was perhaps the f i r s t to e x p l i c i t l y r e c o g n i z e the b e l t of s t r a i n e d N i c o l a Group rocks along the e a s t e r n margin of the Eagle complex. In the marginal notes to the map that accompanies h i s Memoir on the P r i n c e t o n map-sheet, Rice (1947) noted t h a t "Most of the N i c o l a rocks are not s t r o n g l y metamorphosed, but they are sheared i n t o c h l o r i t e and s e r i c i t e s c h i s t s along a b e l t as much as four miles wide p a r a l l e l i n g the east margin of the Eagle P R E V I O U S WORK / 55 g r a n o d i o r i t e b o d y . . . . " He w a s a l s o t h e f i r s t t o r e c o g n i z e t h e s i m i l a r i t y o f r o c k s i n c l u d e d i n t h e Z o a c o m p l e x i n t h e p r e s e n t s t u d y w i t h r o c k s o f t h e N i c o l a G r o u p . R i c e ( 1 9 4 7 , Map 888A) s h o w s N i c o l a G r o u p o n t h e r i d g e b e t w e e n R a i l r o a d a n d J i m K e l l y c r e e k s a n d i n a l a r g e r t r i a n g u l a r a r e a n e a r t h e c o n f l u e n c e o f P o d u n k C r e e k a n d t h e T u l a m e e n R i v e r , j u s t s o u t h o f t h e p r e s e n t s t u d y a r e a . E . G . E . P . EASTWOOD T h e m o s t d e t a i l e d m a p p i n g a n d t h o r o u g h d e s c r i p t i o n o f N i c o l a G r o u p r o c k s a d j a c e n t t o t h e t h e s i s a r e a w a s t h a t u n d e r t a k e n b y E a s t w o o d ( 1 9 6 1 ) . U n l i k e m a n y e a r l i e r a n d l a t e r w o r k e r s i n t h i s r e g i o n , w h o s e p r i m a r y f o c u s h a s b e e n t h e m a f i c - u l t r a m a f i c T u l a m e e n c o m p l e x , h e . m a p p e d e x c l u s i v e l y t h e N i c o l a G r o u p r o c k s i n t h e L a w l e s s C r e e k a r e a w h i c h h o s t m a n y m i n e r a l s h o w i n g s . H i s map e s s e n t i a l l y f o l l o w s L a w l e s s C r e e k , w h i c h f l o w s i n a s o u t h -s o u t h e a s t e r l y d i r e c t i o n a p p r o x i m a t e l y p a r a l l e l t o , b u t t w o t o f i v e k i l o m e t r e s n o r t h e a s t o f , t h e E a g l e - N i c o l a c o n t a c t . L a w l e s s C r e e k f l o w s i n t o t h e T u l a m e e n R i v e r a s h o r t d i s t a n c e d o w n s t r e a m o f t h e T u l a m e e n c o m p l e x a n d r o u g h l y f i v e k i l o m e t r e s e a s t o f t h e E a g l e c o m p l e x . E a s t w o o d ( 1 9 6 1 ) w a s f r u s t r a t e d i n h i s m a p p i n g b y a n u m b e r o f f a c t o r s t h a t t o g e t h e r r e s u l t e d i n h i m d e s c r i b i n g a " k a l e i d o s c o p i c " g e o l o g i c p a t t e r n . T h e s e f a c t o r s i n c l u d e d h e a v y o v e r b u r d e n a n d h e a v i l y t i m b e r e d s l o p e s ; h i g h l y v a r i e d l i t h o l o g i e s w h i c h e x h i b i t e d PREVIOUS WORK / 56 "...marked changes over s h o r t d i s t a n c e s , along the s t r i k e as w e l l as a c r o s s i t . . . ; " rocks which had been "...squeezed and probably c l o s e l y f o l d e d , with p r o d u c t i o n of a coarse r e g i o n a l cleavage or f o l i a t i o n . . . ; " and a network of b r i t t l e f a u l t s which prevented him from developing a coherent s t r a t i g r a p h y f o r the N i c o l a Group i n the Lawless Creek a r e a . However, h i s l i t h o l o g i c d e s c r i p t i o n s appear thorough. L i t h o l o g i e s recognized by Eastwood were d i v e r s e but dominated by dense, dark g r e y i s h - g r e e n , f i n e - g r a i n e d "greenstones," tha t i n c l u d e d " . . . l a v a s , flow b r e c c i a s , p y r o c l a s t i c s , greywacke, and mixed p y r o c l a s t i c s and greywacke." Eastwood a l s o noted subordinate " . . . d a c i t e , r h y o l i t e , f i n e - g r a i n e d dark sediments [ a r g i l l i t e s , s i l t y a r g i l l i t e s , p h y l l i t e s , s i l t s t o n e s and impure q u a r t z i t e s ] , sedimentary s c h i s t s , l i m e s t o n e , and pebble and granule conglomerate." Primary v o l c a n i c and/or sedimentary f e a t u r e s , such as r a r e p i l l o w - l i k e s t r u c t u r e s , r i p - u p c l a s t s , and p o r p h y r i t i c , fragmental and p o s s i b l e amygdaloidal t e x t u r e s are d e s c r i b e d , but Eastwood d e s c r i b e s f o l i a t i o n as " . . . commonly... the only s t r u c t u r a l f e a t u r e apparent." From the r e l a t i v e p a u c i t y of bedding symbols r e l a t i v e to f o l i a t i o n symbols shown on h i s sketch-maps, t h i s indeed appears to be the c a s e . Furthermore, where bedding i s observed, i t almost i n v a r i a b l y appears to be concordant with f o l i a t i o n measurements i n neighbouring r o c k s . Thus, d e s p i t e the d i v e r s i t y seen i n the N i c o l a Group i n the Lawless Creek a r e a , the rocks bear a u n i f y i n g PREVIOUS WORK / 57 northwest t r e n d i n g , southwest d i p p i n g f a b r i c or l a y e r i n g . T h i s f a b r i c or l a y e r i n g i s i n part primary, but i s l a r g e l y a superimposed f o l i a t i o n or s c h i s t o s i t y . From Eastwood's d e s c r i p t i o n s , i t i s evident t h a t t h i s f a b r i c i n c r e a s e s i n i n t e n s i t y toward the west and toward the Eagle complex, where h i s "coarse cleavage or planar p a r t i n g " grades i n t o a "close-spaced s c h i s t o s i t y . " Where the o r i e n t a t i o n v a r i e s g r e a t l y from i t s normally uniform northwest t r e n d and southwest d i p , Eastwood a s c r i b e s the changes to l a t e r f a u l t i n g . He d e s c r i b e s the few f o l d s observed as s m a l l , v a r i a b l e i n plunge (on average g e n t l e to the southeast) and t y p i c a l l y i n d i c a t i n g a sense of movement of southwest over n o r t h e a s t . F. D.C. FINDLAY F i n d l a y (1969), i n re-examining the Tulameen u l t r a m a f i c - m a f i c complex, mapped an envelope of N i c o l a Group country rocks i n t r u d e d by t h a t body. He i n t e r p r e t e d the Tulameen complex as being i n t r u d e d contemporaneously with a p o s t u l a t e d l a t e T r i a s s i c deformation a f f e c t i n g the N i c o l a Group and a t t r i b u t e d the lack of observed primary i n t e r n a l s t r u c t u r e s to t h a t event. His c r o s s -s e c t i o n s i n d i c a t e t h i s deformation to be east - s o u t h e a s t v e r g i n g . P a r a l l e l i s m of the long a x i s of the Tulameen complex with the r e g i o n a l s t r u c t u r a l g r a i n was noted by F i n d l a y . I n t e r n a l f a b r i c s , where p r e s e n t , are re p o r t e d as being p a r a l l e l or s u b - p a r a l l e l to PREVIOUS WORK / 58 u l t r a m a f i c - g a b b r o i c c o n t a c t s , which are i n t u r n p a r a l l e l to the margins of the body and t h e r e f o r e to the r e g i o n a l f a b r i c as w e l l . N i c o l a Group rocks are d e s c r i b e d by F i n d l a y as metasedimentary and metavolcanic a l b i t e - e p i d o t e - a m p h i b o l e s c h i s t s , c a l c a r e o u s g r e e n s c h i s t s , a r g i l l a c e o u s q u a r t z i t e s , q u a r t z - m i c a - p l a g i o c l a s e s c h i s t s and c r y s t a l l i n e limestone bands, with t h e i r r e g i o n a l metamorphic grade being r a i s e d from g r e e n s c h i s t to e p i d o t e -a m p h i b o l i t e near the Tulameen complex c o n t a c t . G. PHILLIP ANDERSON Approximately 20 k i l o m e t e r s south of the present study a r e a , near the headwaters of Whipsaw Creek, Anderson (1971) d e s c r i b e d the contact between N i c o l a Group rocks and the Eagle complex. Contact r e l a t i o n s and l i t h o l o g i e s appear remarkably s i m i l a r to those observed i n the C o q u i h a l l a r e g i o n . Anderson i n t e r p r e t e d the contact i n the Whipsaw Creek area as g r a d a t i o n a l , with the "Eagle T o n a l i t e - G n e i s s complex" owing i t s o r i g i n to in s i t u a n a t e x i s of N i c o l a Group rocks that i n c r e a s e d i n metamorphic grade from g r e e n s c h i s t to a m p h i b o l i t e f a c i e s west toward t h e i r c o n t a c t with rocks of the Eagle complex. H. J. NELSON Approximately 30 k i l o m e t e r s southeast of the study a r e a , near Gr a n i t e Mountain, amp h i b o l i t e grade rocks were i d e n t i f i e d i n the PREVIOUS WORK / 59 N i c o l a Group near t h e i r c o n t a c t with rocks of the Eagle complex (Nelson in Brown, 1980). M i n e r a l assemblages i n c a l c - s i l i c a t e and meta-volcanic rocks i n d i c a t e d temperatures of g r e a t e r than 5 5 0° and p r e s s u r e s g r e a t e r than 2-3 k i l o b a r s (Nelson in Brown, 1980). I. G.T. NIXON AND V.J. RUBLEE Nixon and Rublee (1988), i n a r e e v a l u a t i o n of the Tulameen u l t r a m a f i c complex, observed that rocks w i t h i n the complex were v a r i a b l y deformed, but t h a t m y l o n i t i z e d mafic and u l t r a m a f i c rocks were common. P r e l i m i n a r y i n t e r p r e t a t i o n s by Rublee of kinematic i n d i c a t o r s i n d u c t i l e l y s t r a i n e d rocks suggested d e x t r a l s t r i k e - s l i p movement (Nixon and Rublee, 1988). MAP UNITS / 60 CHAPTER 4: MAP UNITS I. INTRODUCTION Ten map u n i t s have been recognized i n the study area ( F i g u r e 4.1, P l a t e 1 ) . The Eagle p l u t o n i c complex, f o r m e r l y known as the Eagle g r a n o d i o r i t e , comprises four d i s t i n c t , predominantly p l u t o n i c map u n i t s t h a t l i e both west (Late J u r a s s i c Zoa complex) and east (Late J u r a s s i c Eagle t o n a l i t e , J u r a s s i c and Cretaceous Eagle gneiss and middle Cretaceous F a l l s l a k e p l u t o n i c s u i t e ) of the Pasayten f a u l t . The Upper T r i a s s i c N i c o l a Group f l a n k s the Eagle complex on the east and middle Cretaceous and Middle Eocene sedimentary rocks f l a n k i t on the west. The Eagle complex i s int r u d e d by numerous e a r l y Eocene stock s and the Middle Eocene Needle Peak p l u t o n , and i s nonconformably o v e r l a i n by the E a r l y Miocene C o q u i h a l l a v o l c a n i c complex. I I . NICOLA GROUP A. INTRODUCTION AND SUMMARY The Eagle complex i n t r u d e s or i s f a u l t e d a g a i n s t a 1 ki l o m e t e r wide or wider b e l t of deformed Upper T r i a s s i c N i c o l a Group rocks ( R i c e , 1947) throughout i t s 100 k i l o m e t e r e a s t e r n margin i n southwest B r i t i s h Columbia. N i c o l a Group metavolcanic and metasedimentary rocks adjacent to the Eagle complex are c h a r a c t e r i z e d by the presence of a northwest t r e n d i n g , southwest d i p p i n g p e n e t r a t i v e f o l i a t i o n . In the study a r e a , dark green, r u s t y weathering s c h i s t o s e b i o t i t e a m p h i b o l i t e i s i n t e r l a y e r e d with MAP UNITS / 61 TERTIARY MIOCENE I COQUIHALLA VOLCANIC M c v COMPLEX EOCENE Emg | NEEDLE PEAK PLUTON MIDDLE EOCENE SEDIMENTARY ROCKS Es mKg Ei UNDIVIDED INTRUSIVE ROCKS CRETACEOUS „ . MID-CRETACEOUS I SEDIMENTARY ROCKS EARLY CRETACEOUS FALLSLAKE PLUTONIC SUITE JURASSIC AND CRETACEOUS •^IrnKgrj EAGLE GNEISS LATE JURASSIC | L)t | EAGLE TONALITE LATE JURASSIC AND OLDER I LJZ I ZOA COMPLEX TRIASSIC UPPER TRIASSIC | TrN | NICOLA GROUP Geological contact - ' High angla fauh Thruat laull Figure 4.1: S i m p l i f i e d geology, Coquihalla area.. MAP UNITS / 62 subordinate f o l i a t e d marble and micaceous quartzofeldspathic s c h i s t . Primary textures are rare. Mineral assemblages indicate upper greenschist or lower amphibolite metamorphic grade. A decrease in in t e n s i t y of f a b r i c and metamorphic grade to the northeast, away from t o n a l i t e of the Eagle complex, suggests that deformation and metamorphism were cogenetic with emplacement of Eagle t o n a l i t e , which contains a concordant f a b r i c . B. DISTRIBUTION Nicola Group rocks occur along the eastern border of the area mapped (Figure 4.1, Plate 1). Typical and accessible exposures occur on the Tulameen River road, north of the confluence of Champion Creek with the Tulameen River. G l a c i a l d r i f t and poor exposure l i m i t the number of good exposures of Nicola Group rocks in the study area. Several early T e r t i a r y intrusions are l o c a l i z e d along the Eagle complex-Nicola Group contact. These intrusions are surrounded by a l t e r a t i o n , mineralization and fracturing that overprints Nicola Group rocks. The res u l t i s that many of the Nicola Group rocks seen are highly fractured and l i m o n i t i c , with textural d e t a i l s obscured by an assemblage that may include py r i t e , quartz, c a l c i t e , c h l o r i t e and epidote. C. LITHOLOGY AND COMPOSITION Nicola Group l i t h o l o g i e s include amphibolite, marble, quartzofeldspathic schist and mafic-ultramafic rocks. The most common Nicola Group rock type in the study area i s medium to dark MAP UNITS / 63 green, r u s t y weathering, f i n e - g r a i n e d s c h i s t o s e b i o t i t e a m p h i b o l i t e . A p e r v a s i v e m i l l i m e t e r to s u b - m i l l i m e t e r s c a l e f o l i a t i o n and(or) l a y e r i n g c h a r a c t e r i z e s a m p h i b o l i t e . L o c a l l y , p o r p h y r o c l a s t s of medium- to f i n e - g r a i n e d p l a g i o c l a s e or blocky pyroxene(?) are present (Figure 4.2). In one p l a c e , s l i g h t l y f l a t t e n e d q u a r t z - f i l l e d amygdules were noted. P o r p h y r o c l a s t s commonly have " t a i l s " (pressure shadows) and t h e i r long dimensions occur i n the plane of f o l i a t i o n ; many p o r p h y r o c l a s t s appear to have been r o t a t e d w i t h i n the f a b r i c . In some p l a c e s , l a y e r i n g may be evide n t i n s u b t l e , f i n e laminae of a l t e r n a t i n g amphibole and p l a g i o c l a s e - r i c h c o m p o s i t i o n a l l a y e r s ( F i g u r e 4.3). R a r e l y , f i n e c o m p o s i t i o n a l l a y e r i n g o u t l i n e s c e n t i m e t e r - s c a l e , r o o t l e s s i s o c l i n a l f o l d s with limbs transposed i n t o the f o l i a t i o n . F o l i a t i o n planes are commonly b i o t i t e - r i c h ; l o c a l f i n e - g r a i n e d a c i c u l a r amphibole may d e f i n e a l i n e a t i o n or be randomly-oriented. Q u a r t z - p y r i t e - c h l o r i t e - e p i d o t e - c a l c i t e a l t e r a t i o n which i s pe r v a s i v e or occurs as v e i n l e t s o v e r p r i n t s the amph i b o l i t e and may be a s s o c i a t e d with m i n e r a l i z a t i o n . Marble and subordinate c a l c - s i 1 i c a t e are particularly"common at the Eagle complex-Nicola Group co n t a c t (Figure 4.4), where marble l a y e r s up to s e v e r a l meters t h i c k are i n t e r l a y e r e d with s c h i s t o s e a m p h i b o l i t e . Marble weathers pale grey to brown and i s white to grey on f r e s h s u r f a c e s . I t i s medium-grained and commonly co n t a i n s a s t r o n g f o l i a t i o n . The f a b r i c i s most notable on weathered s u r f a c e s , where i t i s o u t l i n e d by s l i g h t c o m p o s i t i o n a l or g r a i n s i z e d i f f e r e n c e s t h a t weather d i f f e r e n t i a l l y . MAP UNITS / 64 Figure 4 . 2 : P a r t i a l l y u r a l i t i z e d clinopyroxene porphyroclast in amphibolitic s c h i s t , Nicola Group, Skwum Creek. Width of f i e l d of view i s 7 mm. • i.-1.1 — - . i • i — — ... . . , - — — . — M. . - J Figure 4 . 3 : Weakly-developed compositional layering in Nicola Group amphibolite; f o l i a t i o n p a r a l l e l to layering. Width of f i e l d of view is 2 mm. MAP UNITS / 65 D i f f e r e n t i a l weathering a l s o o u t l i n e s r a r e , i s o c l i n a l and r o o t l e s s minor f o l d s . F i n e - g r a i n e d , s c a t t e r e d q u a r t z , p y r i t e , epidote and p i n k i s h brown garnet a c c e s s o r y minerals are v i s i b l e i n hand specimen. C a l c - s i l i c a t e minerals are most common i n r e a c t i o n rims along the margins of marble l a y e r s (Figure 4.5). De c i m e t e r - s c a l e , pale grey to cream-coloured " f e l s i c " l a y e r s of muscovite b i o t i t e q u a r t z o f e l d s p a t h i c s c h i s t (metaplutonic rock) are l o c a l l y i n t e r l a y e r e d with and i n p l a c e s s l i g h t l y d i s c o r d a n t t o , s c h i s t o s e a m p h i b o l i t e (Figure 4.6). Most c o n t a i n well-developed m i l l i m e t e r - or s u b - m i l l i m e t e r - s c a l e m y l o n i t i c f o l i a t i o n and(or) l a y e r i n g and many c o n t a i n p l a g i o c l a s e p o r p h y r o c l a s t s (Figure 4 . 7 ) . Most s t a i n e d , slabbed samples are t o n a l i t i c , although r a r e samples are potassium f e l d s p a r - r i c h . The presence of p o r p h y r o c l a s t s as w e l l as the geometry and contact r e l a t i o n s of the f e l s i c l a y e r s suggest an i n t r u s i v e o r i g i n . The absolute age of the f e l s i c i n t r u s i o n s i s unknown, but an ol d e r l i m i t i s provided by the Upper T r i a s s i c age of the N i c o l a Group rocks they i n t r u d e . A Late J u r a s s i c younger l i m i t i s suggested by l e s s h i g h l y deformed s i l l s of epidote b i o t i t e t o n a l i t e (Eagle t o n a l i t e ) t h a t are common i n the N i c o l a Group near i t s c o n t a c t with Eagle t o n a l i t e . In s e v e r a l i s o l a t e d exposures i n the drainage of Skwum Creek, coarse g r a i n e d , pyroxene-bearing mafic or u l t r a m a f i c rocks o c c u r . Contact r e l a t i o n s were not observed. The mafic rocks are s l i g h t l y s t r a i n e d compared with nearby a m p h i b o l i t e . MAP UNITS / 66 F i g u r e 4 . 5 : C a l c - s i l i c a t e at the con t a c t between N i c o l a Group marble and f o l i a t e d s i l l , Tulameen R i v e r . MAP U N I T S / 6 7 F i g u r e 4.6: I n t e r l a y e r e d q u a r t z o f e l d s p a t h i c s c h i s t (pa le c o l o u r ) and a m p h i b o l i t e , N i c o l a Group, Tulameen R i v e r r o a d . F i g u r e 4 .7: S t a i n e d s l a b of q u a r t z o f e l d s p a t h i c s c h i s t ( d u c t i l e l y s t r a i n e d s i l l ) , N i c o l a Group, Law's Camp. MAP UNITS / 68 D. PETROGRAPHY Four of the ten samples of schistose amphibolite examined in thin section contained medium-grained porphyroclasts of u r a l i t i z e d pyroxene (Figure 4.2). The remainder were uniformly f i n e - or very fine-grained. The strong f o l i a t i o n in most specimens was defined by the preferred orientation of amphibole and subordinate b i o t i t e and was in part outlined by poorly-defined sub-millimeter to millimeter-scale alternating amphibole- and plag i o c l a s e - r i c h layers (Figure 4.3). In one sample, millimeter-scale compositional layering i s i s o c l i n a l l y folded. With the exception of r e l i c t pyroxene porphyroclasts, few primary textures or r e l i c t fabrics survived r e c r y s t a l l i z a t i o n . Textures are t y p i c a l l y nematoblastic or l e p i d o b l a s t i c (dimensional preferred orientation p a r a l l e l to f o l i a t i o n defined by prismatic or micaceous minerals, respectively) depending on the r e l a t i v e quantities of amphibole (and lesser prismatic c l i n o z o i s i t e ) or b i o t i t e present. Textures are more nearly granoblastic in layers richer in plagioclase and(or) quartz. In most sections, amphibole has also l o c a l l y grown across the f o l i a t i o n . More mafic layers within the amphibolite are amphibole-rich (40 to 60% and up to 90% amphibole). Amphibole i s t y p i c a l l y u r a l i t i c to a c t i n o l i t i c in composition (pale straw to medium green to deep bluish-green pleochroism and other o p t i c a l properties match those of the Tschermakite group (Troger, 1979)). Anorthite content of plagioclase varies. Most specimens contain andesine-labradorite, but plagioclase of a l b i t e - o l i g o c l a s e composition was MAP UNITS / 69 i d e n t i f i e d in several sections. Amphibolite may or may not contain b i o t i t e . B i o t i t e makes up 5 to 10% of some layers of pyroxene-poor amphibolite. The c a l c - s i l i c a t e assemblage garnet, pyroxene (diopside?), and epidote, apparently stable with one another, are r e l a t i v e l y abundant in several layers in one thin section of amphibolite. C l i n o z o i s i t e occurs in most of the sections examined and millimeter-scale layers with up to 40% c l i n o z o i s i t e occur in several samples. A later generation of more i r o n - r i c h epidote, commonly associated with c a l c i t e , c h l o r i t e and opaque minerals may also be present. Quartz makes up nearly 20% of some layers, and most specimens contain approximately 1 to 3% accessory opaque minerals. Marble i s f i n e - to medium-grained, xenoblastic, and comprises greater than 95% c a l c i t e . C a l c i t e i s invariably twinned, commonly in several d i r e c t i o n s , and has a preferred grain shape orientation that p a r a l l e l s the f o l i a t i o n in the rock (Figure 4.8). Scattered accessory minerals in marble include diopside (up to 2% in one section), opaques (pyrite?), quartz, white mica and t i t a n i t e . One c a l c - s i l i c a t e sample contained intergrown, very coarse-grained (>8 millimeters) p o i k i l o b l a s t i c garnet and c l i n o z o i s i t e overgrowths on medium-grained c a l c i t e . M y l o n i t i c a l l y f o l i a t e d b i o t i t e muscovite quartzofeldspathic sch i s t i s uniformly f i n e - to very fine-grained, and dominated by allotriomorphic-granular or xenoblastic(?) textures; most evidence of sub-solidus d u c t i l e s t r a i n in mineral grains has been annealed. These rocks show millimeter-scale compositional layering, preferred MAP UNITS / 70 Figure 4.8: Preferred grain shape orientation of calcite typical of foliated marble, Nicola Group, Skwum Creek. Width of f i e l d of view is 5 millimeters. MAP UNITS / 71 orientation of micas, and t y p i c a l lens-shaped to highly elongate quartz layers ( r e l i c t ribbon grains?). Plagioclase ranges from An5 to Anl5. Vague r e l i c t zoning survived in scattered plagioclase grains. B i o t i t e and muscovite are present in a l l but one section. M u s c o v i t e i s t y p i c a l l y p o i k i l i t i c o r p o i k i l o D l a s t - i c , d i s c o r d a n t to the fab r i c in the rock, and interpreted to have formed later than b i o t i t e . Accessory minerals include epidote, p y r i t e , and rare garnet. E. GENERAL STRUCTURE Along the eastern margin of the Eagle complex, Nicola Group rocks are characterized almost everywhere by a well-developed northwest s t r i k i n g , southwest dipping mylonitic f o l i a t i o n concordant with the contact. Several kilometres to the northeast, in t e n s i t y of f a b r i c decreases, metamorphic grade diminishes from upper greenschist or lower amphibolite to greenschist facies (c h l o r i t e zone; Read, 1988) and primary textures survive (Eastwood, 1961). Ductile s t r a i n of large magnitude was responsible for the intense mylonitic f o l i a t i o n , r e l i c t porphyroclasts of pyroxene or plagioclase, and the l o c a l occurrence of rootless i s o c l i n a l minor folds. F. DISCUSSION Continuity of f o l i a t e d amphibolite with comparatively undeformed and unmetamorphosed mafic volcanic rocks of the Nicola Group to the east suggests that the volcanic rocks were the MAP UNITS / 72 p r o t o l i t h for the f o l i a t e d amphibolite near the Eagle complex. The metamorphic mineral assemblages are diagnostic of metamorphic facies but not of precise pressure-temperature conditions. Mineral assemblages observed in the amphibolite indicate that upper greenschist and(or) lower amphibolite facies conditions were attained along the eastern contact of the northern Eagle complex. The lack of metamorphic c h l o r i t e , presence of diopside and of clean, sharp grain boundaries and well-developed nematoblastic or l e p i d o b l a s t i c textures are more t y p i c a l of amphibolite grade metamorphism. However, the variations in the composition of amphibole and plagioclase in the amphibolite are permissive of conditions t r a n s i t i o n a l between greenschist and amphibolite grade. Although the observed metamorphic mineral assemblages provide some constraints on the temperatures reached in t h i s belt of rocks, pressure estimates are even more loosely constrained. Q u a l i t a t i v e l y , the extent of t h i s belt of rocks, along and across s t r i k e , and the regional (as opposed to contact) metamorphic character of mineral assemblages suggest that metamorphism may have occurred at several kilometers depth. Regionally, the Nicola Group is t y p i c a l l y of greenschist or sub-greenschist grade and i s unfoliated. Deformed and metamorphosed Nicola Group rocks in the belt p a r a l l e l i n g the Eagle complex are unmatched elsewhere in southwestern B r i t i s h Columbia. Thus, the belt of high s t r a i n and elevated metamorphic grade is uniquely related to the Eagle t o n a l i t e . MAP UNITS / 73 I I I . ZOA COMPLEX A. INTRODUCTION AND SUMMARY The Late Jurassic and older Zoa complex forms the westernmost unit of the Eagle complex and i s exposed in two elongate belts separated by the Zoa and Coquihalla Valley f a u l t s . It consists of hornblende (quartz) d i o r i t e , dated as Late Jurassic, that intrudes subordinate metavolcanic rocks. A greenschist grade metamorphic overprint and a strong magnetic signature characterizes both units. Hornblende (quartz) d i o r i t e is heterogeneous in grain size as well as development, i n t e n s i t y and orientation of gneissic f o l i a t i o n . Metavolcanic rocks, not d i f f e r e n t i a t e d in Plate 1 , are commonly dark green, massive, fine-grained and display rare amygdaloidal and porphyritic textures. Abundant fine-grained "greenstone" inclusions within d i o r i t e are evidence that i t intrudes the metavolcanic rocks. The contact between the diorite-metavolcanic Zoa unit and rocks of the Eagle complex that l i e to the east i s a f a u l t . B r i t t l e and d u c t i l e fabrics along the f a u l t suggest a compound history. The f a u l t contact and lack of mutual intrusive relationships with any other Eagle complex rocks suggest that the Zoa complex was probably not juxtaposed with the rest of the Eagle complex u n t i l mid-Cretaceous time. Regional c o r r e l a t i o n of the Zoa complex with other rock units in southwestern B r i t i s h Columbia i s uncertain, but metavolcanic rocks in the complex bear s i m i l a r i t i e s to rocks of the Upper T r i a s s i c Nicola Group, exposed approximately five kilometers to the east across the Pasayten f a u l t and on the MAP UNITS / 74 other side of the Eagle complex. On i t s west side, the Zoa complex is overlain by sedimentary rocks of Middle Eocene and probable Middle Eocene age along a moderately west dipping sheared st r a t i g r a p h i c contact. B. DISTRIBUTION With the exception of i t s northernmost part, the western margin of the Eagle plutonic complex in the study area is underlain by rocks of the Zoa complex (Figure 4.1, Plate 1). Zoa complex rocks occur in two elongate belts (the "northern" and "southern" belts) separated by the north-northeast trending Zoa f a u l t and northeast trending Coquihalla Valley f a u l t . Prior to movement on the f a u l t s , the two belts may once have been contiguous (Chapter 7). An isolated exposure of Zoa complex metavolcanic rocks occurs on the northwest side of the Coquihalla River v a l l e y between Romeo and lago stations (Plate 1). The best exposures of Zoa complex rocks occur in the northern b e l t , p a r t i c u l a r l y on Zoa Peak ridge (49°37'30", 121°05'00") and on Thar Peak. Good exposures in the southern belt are found on the west-northwest trending spur-ridge of Coquihalla Mountain and on the ridges south and west of the headwaters of Jim K e l l y Creek. C. METAVOLCANIC ROCKS 1. INTRODUCTION AND SUMMARY Metavolcanic rocks of the Zoa complex occur as two map-scale bodies and as inclusions in hornblende (quartz) d i o r i t e . Most MAP UNITS / 75 commonly, they are dark green, very fine-grained and massive, but they may r a r e l y possess amygdaloidal, porphyritic, or fragmental textures. In places, millimeter- to centimeter-scale compositional layering is v i s i b l e , but a greenschist to amphibolite grade metamorphic overprint commonly obscures primary textures. 2. DISTRIBUTION Although metavolcanic rocks are found in both the northern and southern be l t s , they are generally of too limited areal extent to be distinguished from the plutonic rocks at the scale of mapping. The only map-scale bodies of metavolcanic rocks in the study area occur near the summit of Highway 5 and along the northwest side of the Coquihalla River v a l l e y between Romeo and Iago stations (Plate 1). The Highway 5 exposures are superb and the majority of samples studied came from there. In the Coquihalla Valley, metavolcanic rocks occurring in a "pendant" along the margin of the Needle Peak pluton are r e l a t i v e l y inaccessible because of steep slopes. They were examined only in a few exposures along the abandoned Kettle Valley Railroad grade. 3. LITHOLOGY AND COMPOSITION Metavolcanic rocks in the Zoa complex, including those near the summit of Highway 5, are invariably very fine-grained, featureless and green (commonly dark green and r a r e l y pale green). Weathered surfaces and fractures may be rust-coloured from oxidation of p y r i t e ; cross-cutting chlorite-epidote veinlets are MAP UNITS / 76 common. Fine grain size hinders mesocopic observation. Most metavolcanic rocks appear massive in hand specimen, but may show a f a i n t millimeter- to centimeter-scale compositional layering. Rarely, metavolcanic rocks contain amygdules and mafic phenocrysts(?). Amygdules are commonly flattened (Figure 4.9) and may be elongate and subparallel in orientation. They t y p i c a l l y contain quartz or feldspar, subordinate amphibole and opaque minerals, and may range in size up to 1.5 centimeters. Millimeter-to 0.5 centimeter-scale c l o t s of very fine-grained mafic minerals, also commonly flattened, may represent r e c r y s t a l l i z e d mafic phenocrysts or possibly.mafic-rich amygdules. In outcrops along the abandoned Kettle Valley Railway grade between Iago and Romeo stations, metavolcanic rocks exhibit variable degrees of d u c t i l e deformation. Unstrained or weakly-strained fragmental volcanic rocks (Figure 4.10) as well as plagioclase- and pyroxene-phyric and(or) amygdaloidal rocks grade into strained protomylonitic equivalents. Metavolcanic rocks are mainly amphibolite (amphibole in part pseudomorphs . .i pyroxene?); quartz was r e l a t i v e l y abundant in one stained specimen. Secondary c h l o r i t e , epidote and c a l c i t e are abundant and pyrite is a common accessory mineral. 4. GENERAL STRUCTURE The s t r u c t u r a l geology of the metavolcanic rocks i s enigmatic because of the l i t h o l o g y and lack of marker horizons in the unit. Structures include b r i t t l e f a u l t s and fractures and the mesoscopic compositional layering or p r e f e r e n t i a l alignment of flattened amygdules or phenocrysts described e a r l i e r . MAP UNITS / 77 H i •1 ° F i g u r e 4.9: Hand specimen of a m y g d a l o i d a l m e t a v o l c a n i c r o c k , Zoa complex, near Highway 5 summit. F i g u r e 4.10: Weakly s t r a i n e d f r a g m e n t a l m e t a v o l c a n i c r o c k s , Zoa complex, between Romeo and Iago, abandoned KVRR grade, C o q u i h a l l a V a l l e y . MAP UNITS / 78 5. PETROGRAPHY Rocks of t h i s unit are almost as unrewarding to study in thin section as they are in hand specimen. In thin section, metavolcanic rocks are commonly very fine-grained and t y p i c a l l y composed of 40 to 50% randomly oriented a c i c u l a r amphibole in a matrix of granoblastic plagioclase feldspar. Gradational changes in the r e l a t i v e abundance of amphibole, plagioclase feldspar and b i o t i t e define the compositional layering. Within individual compositional layers, mineral grains are randomly oriented. Amphibole in the metavolcanic rocks i s fine-grained (up to 3 or 4 millimeters long but average grain size much less than 1 millimeter), has strong absorption, and i s pleochroic from pale green to a deep bluish-green. Plagioclase i s oligoclase-andesine, with anorthite content ranging from An23 to An44- Very pale brown to pale brown pleochroic b i o t i t e is a minor component except for quartz-rich samples. B i o t i t e occurs in discontinuous patchy zones which grade into more t y p i c a l amphibole-rich zones. Accessory minerals include opaques (mainly p y r i t e ? ) , t i t a n i t e and apatite. Secondary minerals, mainly in veinlets but also as a l t e r a t i o n products, include c h l o r i t e , c a l c i t e , epidote and magnetite. 6. DISCUSSION Mineral assemblages and textures in metavolcanic rocks of the Zoa complex indicate that they reached greenschist grade metamorphic conditions. A c t i n o l i t i c amphibole, abundant c h l o r i t e and epidote (commonly in veinlets) and r e l i c t igneous textures are MAP UNITS / 79 i n d i c a t i v e of g r e e n s c h i s t grade c o n d i t i o n s , as are the ragged min e r a l growth t e x t u r e s t y p i c a l of metavolcanic r o c k s . C o r r e l a t i o n of the pre-Late J u r a s s i c metavolcanic rocks with other l i t h o l o g i c packages i n southwestern B r i t i s h Columbia i s u n c e r t a i n . Any age from Late J u r a s s i c to Precambrian i s permitted by the hard evidence a v a i l a b l e . Zoa complex rocks are i n f a u l t c o n t a c t on t h e i r east margin with other rocks of the Eagle complex and t h e i r s t r a t i g r a p h i c r e l a t i o n t o pre-Middle Eocene sedimentary rocks to the west i s u n c e r t a i n . C o r r e l a t i o n i s a l s o hampered by the r e l a t i v e l y l i m i t e d exposures of Zoa complex metavolcanic r o c k s , by t h e i r c r y p t i c nature and by the lack of d i r e c t age c o n t r o l . The two most l i k e l y c o r r e l a t i v e rock u n i t s are the Upper T r i a s s i c N i c o l a Group to the east and the E a r l y T r i a s s i c ( ? ) Spider Peak Formation (Ray, 1986) to the west. L i t h o l o g i c s i m i l a r i t i e s of pyroxene- and p l a g i o c l a s e - b e a r i n g metavolcanic rocks i n the Zoa complex w i t h , and t h e i r p r o x i m i t y t o , rocks of the N i c o l a Group to the east suggest that there may be a b a s i s f o r c o r r e l a t i o n . In f a c t , t h i s c o r r e l a t i o n was made by Rice (1947), who i n c l u d e d rocks continuous with the southern b e l t of the Zoa complex with the N i c o l a Group on h i s map of the P r i n c e t o n a r e a . The other p o s s i b i l i t y f o r c o r r e l a t i o n , the E a r l y T r i a s s i c f ? ) Spider Peak Formation of Ray (1986), i s exposed on the e a s t e r n s i d e of the Hozameen f a u l t (Figure 2.2), which forms the western boundary of the Methow-Pasayten trough i n southwestern B r i t i s h Columbia. The Spider Peak Formation comprises a l t e r e d massive v o l c a n i c "greenstone," but c o n t a i n s l e s s e r p i l l o w b a s a l t , gabbro, MAP UNITS / 80 and v o l c a n i c l a s t i c r o c k s . The f a c t that Spider Peak greenstones have a d i s t i n c t i v e geochemical s i g n a t u r e (Ray, 1986) suggested the p o s s i b i l i t y that a c o r r e l a t i o n on geochemical grounds with metavolcanic rocks of the Zoa complex might be made. Meagre geochemical data (Chapter 6 ) , however, suggests t h a t N i c o l a Group a f f i n i t i e s are more p r o b a b l e . D. ZOA COMPLEX PLUTONIC ROCKS—HORNBLENDE (QUARTZ) DIORITE 1. INTRODUCTION AND SUMMARY I n c l u s i o n - r i c h d i o r i t e and quartz d i o r i t e i n t r u d e the Zoa complex metavolcanic rocks and make up the bulk of the Zoa complex. The d i o r i t e i s t y p i c a l l y heterogeneous i n g r a i n s i z e and f a b r i c development, i n t e n s i t y and o r i e n t a t i o n . A l b i t e and a near-p e r v a s i v e a l t e r a t i o n of hornblende i n d i c a t e g r e e n s c h i s t grade metamorphism. Intense d u c t i l e s t r a i n has been l o c a l i z e d i n p l u t o n i c rocks along the n o r t h e a s t margin of the Zoa complex and i s manifest i n a n o r t h w e s t - s t r i k i n g , moderately steep n o r t h e a s t -d i p p i n g m y l o n i t i c f o l i a t i o n . 2. DISTRIBUTION D i s t r i b u t i o n of the p l u t o n i c component of the Zoa complex m i r r o r s the d i s t r i b u t i o n of the complex as a whole: Zoa complex p l u t o n i c rocks make up much of the more well-exposed, a c c e s s i b l e and b e t t e r - s t u d i e d northern b e l t as w e l l as the more p o o r l y understood southern b e l t . MAP UNITS / 81 3. NORTHERN BELT Hornblende-bearing (quartz) d i o r i t e p r i n c i p a l l y occurs in the northern part of the northern belt, underlying Thar and Zoa peaks and the lowermost northern and eastern slopes of Zum Peak, from the summit of Highway 5 north to the v a l l e y of the Coldwater River. a. LITHOLOGY AND COMPOSITION Quartz d i o r i t e (most common), d i o r i t e (common), and t o n a l i t e (rare) make up the Zoa complex pluton. Extreme grain size variations are t y p i c a l of the plutonic rocks (Figures 4.11 and 4.12). Medium-grained v a r i e t i e s of d i o r i t e are common, fine-grained d i o r i t e i s less common, and coarse-grained or pegmatitic v a r i e t i e s are rare. Relations between phases may be gradational or cross-cutting. Seemingly paradoxical cross-cutting intrusive r e l a t i o n s may occur within a single outcrop, suggesting that the various phases are of similar age (Figure 4.13). Medium-grained protomylonitic to very fine-grained ultramylonitic meta-diorite occurs along the northeast margin of the Zoa complex in the v a l l e y of the Coldwater River. Well-developed f o l i a t i o n , plagioclase feldspar porphyroclasts and ribboned quartz grains are t y p i c a l . D i o rite weathers pale greenish grey to white and i s commonly greenish grey on fresh surfaces. More hornblende-rich v a r i e t i e s and finer-grained phases generally have a more greenish cast. Like the metavolcanic rocks discussed above, d i o r i t e i s commonly cut by millimeter-scale chlorite-epidote v e i n l e t s . MAP UNITS / 82 Figure 4.11: Diorite injection complex, Zoa complex, Thar Peak; note grain size variations between "phases." Layering is igneous in origin and unrelated to ductile strain. MAP UNITS / 83 Figure 4.12: Hand specimen (stained) showing g r a i n s i z e v a r i a t i o n i n hornblende quartz d i o r i t e ; Zoa complex, Zoa Peak . MAP UNITS / 84 Figure 4.13: Hornblende d i o r i t e i n j e c t i o n complex, Zoa complex, Zoa Peak; outcrop shows early unfoliated medium-grained phase and cross-cutting very fine-grained (1) and fine- to medium-grained phases (2) of similar composition. MAP UNITS / 85 Zoa complex plutonic rocks are i n c l u s i o n - r i c h compared with Eagle t o n a l i t e or most of the F a l l s l a k e suite. Inclusions, invariably dark green and very fine-grained, are d i f f i c u l t to distinguish from fine-grained d i o r i t i c phases or from common andesitic to b a s a l t i c dikes. Inclusions are p a r t i c u l a r l y abundant in d i o r i t e near i t s contact with metavolcanic rocks where they are oblate, elongate (>>10:1) and concordant with f o l i a t i o n in d i o r i t e (Figure 4.14). In the Coldwater River Valley at the northwest foot of Zoa Peak, rare agmatites or stockworks comprise irregular f i n e -to very fine-grained cognate d i o r i t e inclusions in a f i n e - to medium-grained d i o r i t e matrix (Figure 4.15). b. GENERAL STRUCTURE Although well-developed in places, planar fabrics are a less conspicuous at t r i b u t e of Zoa complex plutonic rocks than of the neighbouring F a l l s l a k e suite and Eagle t o n a l i t e and gneiss. Large tracts of d i o r i t e are unfoliated, in p a r t i c u l a r on Zoa Peak and on the lower slopes of Zum Peak, and less commonly on Thar Peak (Figure 4.16). Pervasive planar fabrics in d i o r i t e of the northern belt occur in two areas: the Coldwater River Valley along the northeastern margin of the complex and adjacent to metavolcanic rocks near the summit of Highway 5. Elsewhere, f o l i a t i o n i s variably oriented and discordant to planar fabrics developed in both the Zoa complex and in adjacent rock units. Structural c h a r a c t e r i s t i c s of the Zoa complex are discussed in further d e t a i l in Chapter 7. MAP UNI T S / 86 Figure 4.14: Oblate and concordant very f i n e -grained metavolcanic inclusions in weakly f o l i a t e d hornblende quartz d i o r i t e , Zoa complex, Thar Peak. Outcrop surface i s at an acute angle to the f a b r i c . Figure 4.15: Di o r i t e agmatite with very fine-grained d i o r i t e inclusions in a fine-grained d i o r i t e matrix, Zoa complex, Coldwater River Valle y . MAP U N I T S / MAP UNITS / 88 c. PETROGRAPHY The plutonic rocks commonly contain microstructural textures related to d u c t i l e s t r a i n which overprint t y p i c a l hypidiomorphic-granular, f i n e - to medium-grained and is o t r o p i c textures. F o l i a t i o n i s defined by preferred grain-shape orientation of hornblende and plagioclase feldspar. Alb i t e (An2 to Ani7)/ the predominant feldspar, i s everywhere altered to s e r i c i t e and saussurite. Many grains, p a r t i c u l a r l y in the deformed samples, have been completely altered. Rare zoning of a l b i t e is apparent from the p r e f e r e n t i a l replacement of more c a l c i c - r i c h ( ? ) zones by a l t e r a t i o n minerals. Amphibole, which appears to be the only primary mafic mineral present, i s of Tschermakitic composition in most sections, but common hornblende r a r e l y occurs. Chl o r i t e , b i o t i t e , c a l c i t e , magnetite, epidote, sphene and apatite are a l t e r a t i o n products of amphibole. Accessory minerals include t i t a n i t e , magnetite(?) and p y r i t e . d. CONTACT RELATIONS Zoa complex metavolcanic rocks are intruded by Zoa complex hornblende quartz d i o r i t e immediately north of the summit of Highway 5. Along their northeast, east and southeast margins, Zoa complex rocks are faulted against the mid-Cretaceous F a l l s l a k e plutonic s u i t e . On the west margin, Zoa complex rocks are overlain unconformably(?) and s t r u c t u r a l l y by c l a s t i c rocks of probable Middle-Eocene age. MAP UNITS / 89 The contact between metavolcanic rocks and d i o r i t i c rocks near the summit of Highway 5 summit i s poorly exposed. However, the presence of common oblate "greenstone" inclusions in d i o r i t e and the concordant nature of their respective fabrics strongly suggest that d i o r i t e intruded the metavolcanic rocks. The northern belt of the Zoa complex is in fa u l t contact along i t s east margin with Eagle gneiss and with muscovite b i o t i t e granodiorite of the central F a l l s l a k e pluton. The fa u l t i s a moderate to steeply west-dipping high-level b r i t t l e structure which may have had up to 10 kilometers of dextral s t r i k e - s l i p motion since Middle Eocene time. The covered northeastern contact, the Pasayten f a u l t , i s inferred to be a du c t i l e shear zone because of common sub-parallel d u c t i l e deformation fabrics in d i o r i t e on the northeasternmost side of the Zoa complex and in flanking muscovite granodiorite/tonalite on the southwesternmost side of the northern F a l l s l a k e pluton (see Chapter 7). To the northwest, along s t r i k e , the Pasayten f a u l t juxtaposes sedimentary rocks of probable Middle Eocene age with the northern F a l l s l a k e pluton. This r e l a t i o n s h i p suggests that the Pasayten f a u l t was reactivated in Middle Eocene or later time. On i t s west side, the northern belt of the Zoa complex is overlain by sedimentary rocks of probable Middle Eocene age along a moderately west-dipping sheared st r a t i g r a p h i c contact. The sharp discordance between planar fabrics in d i o r i t e and in strained c l a s t i c rocks at the base of the Middle Eocene section suggests that the respective fabrics were formed in two separate events. MAP UNITS / 90 4. SOUTHERN BELT The southern belt of the Zoa complex i s a somewhat discontinuous belt of metamorphosed and deformed plutonic and subordinate volcanic rocks that extends southeast from the Coquihalla River Valley south at least as far as Podunk Creek (see Figure 3.1). a. LITHOLOGY AND COMPOSITION Southern belt quartz d i o r i t e to d i o r i t e is l i t h o l o g i c a l l y s imilar to that of the northern b e l t . Undeformed d i o r i t e possesses the same heterogeneous grain s i z e , f a b r i c and the abundant "greenstone" inclusions as in the northern be l t , but d i o r i t e in the southern belt i s t y p i c a l l y more highly deformed. This at t r i b u t e i s l i k e l y a function of present exposure, not d i f f e r i n g geologic history. In the drainage of Jim K e l l y Creek, discrete meter-scale d u c t i l e shear zones in Zoa complex d i o r i t e and greenstone are commonly associated with narrow quartz and carbonate veins and are commonly mineralized with pyrite and lesser copper s u l f i d e s . Plutonic rocks in t h i s area are also characterized by the presence of rusty-weathering buff, cream, or pale green aphanitic r h y o l i t e intrusions. Most rh y o l i t e s are d i k e - l i k e bodies with irregular contacts. A p y r i t i c f e l s i c stock from t h i s suite crosscuts the contact between Zoa complex rocks and Middle Eocene sedimentary MAP UNITS / 91 rocks l o c a l l y , indicating that the f e l s i c suite is Middle Eocene or younger in age. D u c t i l e l y deformed l i t h o l o g i e s in the southern belt of the Zoa complex share many features of d u c t i l e l y deformed, northern belt d i o r i t e the v a l l e y of the upper Coldwater River: pervasively deformed d i o r i t e near the northeast margin of the complex; very fine to medium grain s i z e ; pale to dark green weathering colour; throughgoing f o l i a t i o n , ribboned quartz aggregates and plagioclase feldspar porphyroclasts in protomylonite and mylonite; and intense sub-millimeter scale layering c h a r a c t e r i s t i c of ultramylonite. Ductile s t r a i n textures are commonly masked by strong c h l o r i t e and pyrite a l t e r a t i o n and b r i t t l e fractures. b. GENERAL STRUCTURE Planar fabrics are variably represented in the southern belt of the Zoa complex. Where present, the f a b r i c ranges from a weak, commonly variably oriented primary or magmatic f o l i a t i o n to an intense sub-solidus mylonitic f a b r i c . Except for discrete meter-scale d u c t i l e shear zones within d i o r i t e along central Jim K e l l y Creek, mylonitic fabrics are limited to rocks along the northeast margin of the Zoa complex (Figure 4.17). The mylonitic f a b r i c has a consistent northwest s t r i k e and moderately steep northeast dip except in outcrops on the Tulameen River upstream of Tulameen F a l l s , where fabrics dip at low angles to the west and the east (Plate 1). MAP UNITS / 92 Figure 4.17: Suite of samples of v a r i a b l y s t r a i n e d hornblende quartz d i o r i t e from NE margin of the Zoa complex, western slopes of Dear Mtn.; progressive increase i n s t r a i n from bottom (protomylonite) to top ( u l t r a m y l o n i t e ) . MAP UNITS / 93 In the c e n t r a l p a r t of Jim K e l l y Creek, abundant shear f r a c t u r e s and l o c a l f a u l t b r e c c i a are developed i n d i o r i t e and i n Middle Eocene or younger f e l s i c i n t r u s i o n s . F a u l t b r e c c i a s are up to s e v e r a l meters or more i n t h i c k n e s s , c o n t a i n angular c l a s t s of d i o r i t e w a l l r o c k s e t i n a gougey green c h l o r i t i c m atrix and are mostly s t e e p l y d i p p i n g and v a r i a b l e i n s t r i k e . C. CONTACT RELATIONS Along the northernmost southern b e l t p l u t o n i c rocks Miocene C o q u i h a l l a v o l c a n i c v a l l e y s of Jim K e l l y Creek s t r a i n e d d i o r i t e i s i n f a u l t Pasayten f a u l t . Along t h e i r o v e r l a i n by Middle Eocene s t r a t i g r a p h i c c o n t a c t . Along the northernmost complex rocks are juxtaposed of the E a r l y Miocene C o q u i h a l l a v o l c a n i c complex along a steep f a u l t t h a t f o l l o w s Unknown Creek (the Jim K e l l y Creek f a u l t of Berman and Armstrong (1980)). I t was i n t e r p r e t e d to have been a c t i v e d u r i n g d e p o s i t i o n of C o q u i h a l l a v o l c a n i c complex r o c k s . A one meter f a u l t b r e c c i a and a meter-scale s l i v e r of dark grey a r g i l l a c e o u s rock c o n t a i n i n g i r r e g u l a r green a p h a n i t i c a n d e s i t i c ( ? ) d i k e s separate quartz d i o r i t e from C o q u i h a l l a complex rocks i n the lower reaches of Unknown Creek. F a u l t b r e c c i a c o n s i s t s of g r a n i t i c p a r t of t h e i r n o r t h e a s t margin, the are i n f a u l t c o ntact with the E a r l y complex. F a r t h e r s o u t h e a s t , i n the and the Tulameen R i v e r , d u c t i l e l y c o n t a c t with Eagle g n e i s s along the west margin, southern b e l t rocks are sedimentary rocks along a sheared part of t h e i r northeast margin, Zoa with t u f f a c e o u s and r h y o l i t i c rocks MAP UNITS / 94 c l a s t s (average <0 .5 cm, up to 20 cm) set in a c h l o r i t l c gouge. Disrupted and sheared a r g i l l i t e and boudined dikes indicate that both have been involved in movement along the f a u l t . Farther southeast, in the valleys of Jim Kelly Creek and the Tulameen River, d u c t i l e l y strained d i o r i t i c rocks are in probable f a u l t contact with Eagle gneiss along the Pasayten f a u l t . The actual contact i s covered by g l a c i a l d r i f t . D i o rite possesses a northwest trending, moderate to steeply northeast dipping protomylonitic to mylonitic fa b r i c that generally increases in int e n s i t y northeast toward the Pasayten f a u l t . The faulted nature of the contact i s inferred from the presence of coplanar d u c t i l e deformation fabrics present on both sides of the f a u l t (Chapter 7). S i m i l a r i t i e s between t h i s contact and i t s northern counterpart in the Coldwater-East Anderson River valleys suggest that movement along t h i s d u c t i l e shear zone occurred in mid-Cretaceous time. On i t s west side, the southern be l t , l i k e the northern b e l t , i s overlain by sedimentary rocks of Middle Eocene age along a moderately west-dipping sheared st r a t i g r a p h i c contact. Diorite s t r u c t u r a l l y and s t r a t i g r a p h i c a l l y beneath the sedimentary rocks is strongly c h l o r i t i z e d , varies from intensely f o l i a t e d to unfoliated, and contains discrete meter-scale and smaller du c t i l e shear zones that t y p i c a l l y trend north-northwest and dip steeply to the northeast. In contrast, sedimentary rocks are r e l a t i v e l y fresh and are affected only by high-level folding and f a u l t i n g . The contrasting s t r u c t u r a l s t y l e s , conditions of deformation and metamorphic grade confirm that the Zoa complex was deformed and MAP UNITS / 95 metamorphosed prior to deposition and deformation of the clastic rocks. E. DISCUSSION Similar lithologies and structural fabrics in the northern and southern belts of the Zoa complex as well as identical contact relations with adjacent map-units suggest strongly that the two may once have been contiguous prior to movement on the Zoa and Coquihalla Valley faults. Offset geologic contacts suggest as much as 10 kilometers dextral movement (Chapter 7). Structural, geochronometric and metamorphic evidence and a lack of mutual intrusive relations indicate that the Zoa complex is in fault contact with other Eagle complex rocks to the east and that juxtaposition likely did not occur until mid-Cretaceous time. Localization of ductile strain fabrics in the Zoa complex and in other Eagle complex units along the Pasayten fault strongly suggests that the structures are coeval. Formation of ductile fabrics occurred in mid-Cretaceous time (Chapter 5). Foliation or gneissosity within the Zoa complex is variably oriented compared with fabrics near the Pasayten fault and the summit of Highway 5. This is sharply dissimilar to Eagle tonalite and gneiss, which contain a pervasive fabric that is consistent throughout. This discordance suggests that pre-middle Cretaceous fabrics in the Zoa complex were likely not cogenetic with pre-middle Cretaceous fabrics in Eagle tonalite and gneiss and that the rock units may not have been near to one another prior to middle Cretaceous time. MAP UNITS / 96 C o n t r a s t i n g metamorphic grade a l s o suggests a d i f f e r e n t h i s t o r y f o r rocks of the Zoa complex and rocks of the r e s t of the Eagle complex. G r e e n s c h i s t grade metamorphism of rocks of the Zoa complex i s i n sharp c o n t r a s t t o the unmetamorphosed and g e n e r a l l y completely u n a l t e r e d appearance of rocks of the F a l l s l a k e s u i t e and Eagle t o n a l i t e and g n e i s s . The Zoa complex was probably 'metamorphosed between Late J u r a s s i c emplacement and mid-Cretaceous j u x t a p o s i t i o n with the F a l l s l a k e s u i t e and Eagle t o n a l i t e and g n e i s s . IV. EAGLE TONALITE A. INTRODUCTION AND SUMMARY W e l l - f o l i a t e d to g n e i s s i c Late J u r a s s i c hornblende b i o t i t e t o n a l i t e (Eagle t o n a l i t e ) forms the bulk of the Eagle complex, both i n the present map area and r e g i o n a l l y ( Figure 4 . 1 , P l a t e 1 ) . It i s h i g h l y elongate and trends approximately north-northwest for more than 100 k i l o m e t e r s from t h e - I n t e r n a t i o n a l border to near 50°N (Figure 3.1). A widespread b i o t i t e f o l i a t i o n and the presence of ac c e s s o r y primary epidote are c h a r a c t e r i s t i c of Eagle t o n a l i t e . I n t r u s i v e and s t r u c t u r a l r e l a t i o n s along i t s east c o n t a c t argue s t r o n g l y f o r l a t e syn-kinematic emplacement of Eagle t o n a l i t e i n t o rocks of the Upper T r i a s s i c N i c o l a Group i n Late J u r a s s i c time. MAP UNITS / 97 B. LITHOLOGY AND COMPOSITION 1. INTRODUCTION AND SUMMARY Late J u r a s s i c t o n a l i t e i s c h a r a c t e r i z e d by the presence of a moderate to s t r o n g l y developed planar f a b r i c , abundant b i o t i t e , and by the presence of a c c e s s o r y primary e p i d o t e . C h a r a c t e r i s t i c a c c e s s o r y minerals i n c l u d e hornblende and e p i d o t e . T o n a l i t e i s pale to medium gre y , pale grey to white weathering and mesocratic; i t i s t y p i c a l l y medium-grained and l a r g e l y i n c l u s i o n - f r e e . 2. DESCRIPTION More than f i f t y s t a i n e d s l a b s i n d i c a t e a t o n a l i t i c composition ( S t r e c k e i s e n , 1976), c o n t a i n i n g between 50 and 65 percent p l a g i o c l a s e , between 20 and 30 percent q u a r t z , and l e s s than 5 percent potassium f e l d s p a r (Figure 4.18). G r a n o d i o r i t e i s r a r e . Mafic minerals commonly make up between 7 and 15 percent but as much as 20 percent of the mode. B i o t i t e i s by f a r the most abundant mafic m i n e r a l but hornblende i s always present and r a r e l y may predominate. Primary e p i d o t e , although l e s s abundant (approximately 1 to 3 p e r c e n t ) , i s c h a r a c t e r i s t i c . Epidote i s c l e a r l y v i s i b l e i n most hand specimens and may occur as g r a i n s up to 4 m i l l i m e t e r s i n l e n g t h . The general u n a l t e r e d nature of Eagle t o n a l i t e , and the l i t t l e a l t e r e d f e l s i c and mafic m i n e r a l s suggest th a t epidote i s not a secondary m i n e r a l . MAP UNITS / 9 8 3. GRAIN SIZE AND GRAIN SIZE VARIATIONS T o n a l i t e i s t y p i c a l l y medium-grained but f i n e - g r a i n e d and coa r s e - g r a i n e d v a r i e t i e s o c c u r . Dikes of f i n e - g r a i n e d epidote hornblende b i o t i t e t o n a l i t e , commonly l e s s than 1 meter i n t h i c k n e s s , were noted at seven wi d e l y separate l o c a l i t i e s throughout the study a r e a . P e g m a t i t i c t o n a l i t e c o n t a i n i n g b i o t i t e , q u a rtz and p l a g i o c l a s e occurs i n one place as a 5 to 10 centimeter s e g r e g a t i o n w i t h i n s l i g h t l y g n e i s s i c t o n a l i t e . Near the headwaters of J u l i e t Creek, approximately seven k i l o m e t r e s due north of the Coldwater R i v e r — E a s t Anderson River d i v i d e and near the contact with the northern F a l l s l a k e p l u t o n , " b i o t i t e megacrystic" t o n a l i t e c o n t a i n s u n u s u a l l y l a r g e b i o t i t e g r a i n s (up to 2 c e n t i m e t e r s , averaging approximately 1 c e n t i m e t e r , F i g u r e s 4.19 and 4.20). This v a r i e t y i s probably of l o c a l extent o n l y . S c a t t e r e d " b i o t i t e m e g acrystic" t o n a l i t e outcrops a l s o occur i n i s o l a t e d exposures on the headwaters of Skwum Creek and on the Tulameen R i v e r a s h o r t d i s t a n c e upstream of i t s confluence with Champion Creek. 4. INCLUSIONS Eagle t o n a l i t e g e n e r a l l y l a c k s i n c l u s i o n s except near i t s co n t a c t with N i c o l a Group r o c k s , where i n t e n s e l y f o l i a t e d b i o t i t e a m p h i b o l i t e and subordinate f o l i a t e d marble i n c l u s i o n s are common. To the west, r a r e f i n e - to medium-grained e p i d o t e b i o t i t e a m p h i b o l i t e i n c l u s i o n s o c c u r . I n c l u s i o n s are commonly o b l a t e , f o l i a t e d p a r a l l e l t o t h e i r long dimensions, and t y p i c a l l y s l i g h t l y d i s c o r d a n t with f o l i a t i o n i n the host t o n a l i t e . T o n a l i t i c MAP U N I T S / 99 F i g u r e 4.18: S t a i n e d s l a b of f o l i a t e d E a g l e t o n a l i t e w i t h f o l i a t i o n o u t l i n e d by p r e f e r r e d g r a i n shape o r i e n t a t i o n of p l a g i o c l a s e f e l d s p a r and b i o t i t e ; note a l t e r a t i o n s e l v a g e s a l o n g f r a c t u r e - v e i n l e t s h i g h l i g h t e d by s t a i n i n g . F i g u r e 4.19: B i o t i t e - m e g a c r y s t i c E a g l e t o n a l i t e , near E a g l e t o n a l i t e / n o r t h e r n F a l l s l a k e p l u t o n c o n t a c t , J u l i e t Creek. MAP UNITS / 100 Tigure 4.20: Stained specimen of b i o t i t e megacrystic Eagle t o n a l i t e (or g r a n o d i o r i t e ) with unusually high potassium f e l d s p a r content; near Eagle t o n a l i t e / n o r t h e r n F a l l s l a k e pluton contact, J u l i e t Creek; sample cut perpendicular to f o l i a t i o n . MAP UNITS / 101 apophyses which i n t r u d e amphibolite i n c l u s i o n s are f o l d e d and(or) f l a t t e n e d and(or) boudined w i t h i n the f a b r i c of the i n c l u s i o n ( F i g u r e 4.21). I n c l u s i o n s are t y p i c a l l y l e s s than a meter wide and s e v e r a l meters l o n g , but rare amphibolite "screens" range up to 4 meters i n width and up to tens of meters i n l e n g t h . C . G E N E R A L S T R U C T U R E Eagle t o n a l i t e i s r a r e l y u n f o l i a t e d . Planar f a b r i c may be obscured i n areas of poor exposure or where l o c a l b r i t t l e f a u l t i n g , f r a c t u r i n g and a l t e r a t i o n o v e r p r i n t s . Two s u b u n i t s of Eagle t o n a l i t e may be d i s t i n g u i s h e d : s l i g h t l y g n e i s s i c v a r i e t i e s predominate i n the southwest and w e l l f o l i a t e d v a r i e t i e s i n the n o r t h e a s t . The t r a n s i t i o n between these v a r i e t i e s i s g r a d a t i o n a l and well-exposed i n continuous creek and r i v e r outcrops where n e i t h e r sharp change i n the nature of the planar f a b r i c nor c r o s s -c u t t i n g r e l a t i o n s h i p s between v a r i e t i e s are observed. The consanguineous nature of the g n e i s s i c and f o l i a t e d t o n a l i t e s i s confirmed by p e t r o g r a p h i c , geochemical, and geochronometric s t u d i e s . The d i s t i n c t i o n between " w e l l - f o l i a t e d " and " s l i g h t l y g n e i s s i c " f a b r i c s i n t o n a l i t e i s s u b t l e and somewhat s u b j e c t i v e . Both v a r i e t i e s are c h a r a c t e r i z e d by b i o t i t e f o l i a t i o n . G n e i s s i c v a r i e t i e s look more eq u i g r a n u l a r because of f i n e r - g r a i n e d b i o t i t e . G n e i s s o s i t y i s expressed as narrow (commonly 1 m i l l i m e t e r or l e s s ) but m e s o s c o p i c a l l y continuous b i o t i t e l a y e r s ( f o l i a ? ) s e p a r a t i n g 1 to 5 centimeter q u a r t z o f e l d s p a t h i c l a y e r s (Figure 4.22, MAP UNITS / 102 Figure 4.21: P y t g m a t i c a l l y folded t o n a l i t e apophyses w i t h i n meter-scale amphibolite screen, Eagle t o n a l i t e , s e v e r a l 100 meters southwest of Upper Coldwater e x i t ramp, Highway 5. MAP UNITS / 103 Figure 4.22: G n e i s s i c Eagle t o n a l i t e , Tulameen R i v e r , showing f a b r i c defined by narrow continuous b i o t i t e f o l i a . Figure 4.23: W e l l - f o l i a t e d Eagle t o n a l i t e , J u l y Mtn.; f o l i a t i o n p a r a l l e l to hammer handle. MAP UNITS / 104 cf. Figure 4.23). S l i g h t l y flattened or ribboned quartz grains also contribute to the f o l i a t e d appearance of both gneissic and we l l - f o l i a t e d v a r i e t i e s of t o n a l i t e . Flattened quartz grains are commonly v i s i b l e in hand specimen and in places form lens-shaped aggregates that wrap around plagioclase grains and y i e l d a vague protomylonitic or "augen" texture (Figure 4.24). T o n a l i t i c rocks r a r e l y display a strong b i o t i t e l i n e a t i o n , and, i f present, i t i s l o c a l and at the expense of a planar f a b r i c . Lineated rocks grade along and across s t r i k e into w e l l - f o l i a t e d but non-lineated rocks of i d e n t i c a l composition. In some slabbed, stained hand specimens, a very weak linear f a b r i c is outlined by the preferred shape f a b r i c of plagioclase and quartz. D. PETROGRAPHY Eagle t o n a l i t e i s compositionally and t e x t u r a l l y homogeneous. Grain size averages 2 to 3 millimeters (medium-grained), though rare fine-grained millimeter-scale layers occur within s l i g h t l y gneissic v a r i e t i e s . Allotriomorphic-granular textures predominate. Tonalites are also t y p i c a l l y inequigranular: larger plagioclase grains (ranging in size from 1 to 5 or 6 millimeters and averaging 3 to 4 millimeters) commonly rest in a finer-grained "groundmass" of quartz, b i o t i t e , amphibole, potassium feldspar and plagioclase. In some specimens, large b i o t i t e plates are composites of smaller grains. Essential and widespread minerals of Eagle t o n a l i t e are (in order of decreasing abundance): plagioclase, quartz, b i o t i t e , MAP UNITS / 105 potassium feldspar, amphibole and epidote. Accessory minerals include t i t a n i t e , apatite, p y r i t e , magnetite(?), a l l a n i t e ( ? ) (commonly as cores to primary epidote) and zircon. Primary igneous zoning in a l b i t e to oligoclase (Ano to An20) i s conspicuously absent in a l l but the largest grains. Plagioclase in a l l sections displays abundant a l b i t e , common p e r i c l i n e and lesser Carlsbad twinning. B i o t i t e i s the most abundant mafic mineral. It i s of uniform composition, with strong absorption and pale straw yellow to olive green to dark brownish-green pleochroism. Tschermakitic(?) amphibole also has strong absorption and X=pale straw yellow, Y=olive green and Z=deep bluish-green pleochroism. Microcline, along with quartz, i s invariably fine-grained and i n t e r s t i t i a l to plagioclase. Epidote, colourless and non-pleochroic except for common pale brown pleochroic a l l a n i t e ( ? ) cores, i s present in quantities of one to three percent, regardless of the rock's a l t e r a t i o n state (Figure 4.25). It i s commonly deeply embayed, has vermicular contacts with plagioclase, and contains numerous quartz inclusions (Figure 4.26). B i o t i t e commonly surrounds epidote along euhedral margins (Figure 4.27). Such textures, remarkably similar to textures described by Zen and Hammarstrom (1984) for magmatic epidote-bearlng plutons, suggest that epidote in Eagle t o n a l i t e was a liquidus mineral. The common association of primary epidote with s e r i c l t i z e d plagioclase, a yellowish-green pleochroic secondary epidote, and with secondary c h l o r i t e , magnetite, sphene, and apatite, suggests that epidote was not in equilibrium with the MAP UNITS / 106 Figure 4.24: F o l i a t e d Eagle t o n a l i t e with t y p i c a l weakly-developed "augen" or f l a s e r t e x t u r e and weakly ribboned quartz aggregates wrapping around p l a g i o c l a s e f e l d s p a r " p o r p h y r o c l a s t s . " Figure 4.25: Eagle t o n a l i t e , showing zoned primary epidote with a l l a n i t e core, Tulameen R i v e r ; crossed p o l a r i z e r s , width of f i e l d of view 7 mm. MAP UNITS / 107 Figure 4.26: Eagle t o n a l i t e , showing embayed and in c l u s i o n - r i c h primary epidote; J u l i e t Creek; crossed p o l a r i z e r s , width of f i e l d of view i s 6 mm. Figure 4.27: Eagle t o n a l i t e , showing primary epidote in contact with later b i o t i t e ; J u l i e t Creek; crossed p o l a r i z e r s , width of f i e l d of view is 6 m. MAP UNITS / 108 mineral assemblage present during f i n a l c r y s t a l l i z a t i o n of the to n a l i t e magma. Bi o t i t e and amphibole are l o c a l l y altered to some or a l l of c h l o r i t e , magnetite, t i t a n i t e , and secondary epidote even in the freshest samples. Feldspars in most sections display minor a l t e r a t i o n to very fine-grained white mica and/or epidote group minerals ( c l i n o z o i s i t e ( ? ) , z o i s i t e ( ? ) ) . E. CONTACT RELATIONS The eastern margin of the Eagle t o n a l i t e i s a syn-deformational intrusive contact with Upper T r i a s s i c Nicola Group rocks. On i t s west margin, the to n a l i t e grades into coeval t o n a l i t e orthogneiss of the Eagle gneiss. Eagle t o n a l i t e and gneiss were intruded along their west margin by mid-Cretaceous muscovite-bearing granodiorite of the Fa l l s l a k e plutonic s u i t e . On i t s east margin, Eagle t o n a l i t e intrudes and has been deformed with intensely f o l i a t e d rocks of the Upper T r i a s s i c Nicola Group. The coplanar t o n a l i t e and Nicola Group f a b r i c s , presence of f o l i a t e d t o n a l i t e s i l l s within the Nicola Group, and geometry of Nicola Group inclusions within t o n a l i t e indicate that the ton a l i t e intruded the Nicola Group syn-kinematically. The Nicola Group-Eagle t o n a l i t e contact i s covered for much of i t s extent in the study area. The contact i s also obscured by Early Eocene stocks (e.g., Keystone stock, Independence porphyry and I l l a l stock, Plate 1), abundant dikes and s i l l s of probable early T e r t i a r y age, mineralization (e.g., Independence camp, Law's camp, MAP UNITS / 109 Keystone property), and b r i t t l e f a u l t i n g and fracturing commonly cospatial with T e r t i a r y intrusions. Nonetheless, the nature of the Nicola Group-Eagle to n a l i t e contact is known from d i r e c t observation in a few places and can be inferred from s t r u c t u r a l and intrusive r e l a t i o n s observed in adjacent rocks. Tonalite s i l l s , up to tens of meters wide, are common within rocks of the Nicola Group near i t s contact with Eagle t o n a l i t e . Tonalite s i l l s contain abundant b i o t i t e and lesser amounts of primary epidote c h a r a c t e r i s t i c of Eagle t o n a l i t e . S i l l s are t y p i c a l l y w e l l - f o l i a t e d and contain fabrics p a r a l l e l with those in Nicola Group country rocks. Intensely f o l i a t e d oblate amphibolite inclusions are common in Eagle t o n a l i t e near i t s contact with the Nicola Group and are concordant with the pluton's f o l i a t i o n . In several places, larger inclusions are cut by decimeter- to centimeter-scale t o n a l i t e apophyses that are f o l i a t e d , uncommonly boudined (Figures 4.28 and 4.29) or r a r e l y t i g h t l y folded (Figure 4.21). F o l i a t i o n within, apophyses is p a r a l l e l to inclusion and to n a l i t e f a b r i c s . An important exception i s t o n a l i t e on the Lawless Creek Forest Service road overlooking Murphy Lakes. There, Eagle t o n a l i t e i s unfoliated and contains randomly-oriented but strongly f o l i a t e d marble and amphibolite inclusions c l o s e l y similar to Nicola Group rocks (Figure 4.30). MAP UNITS / 110 Figure 4.28: i n t e n s e l y f o l i a t e d amphibolite i n c l u s i o n concordant with w e l l - f o l i a t e d (upper r i g h t to lower l e f t ) Eagle t o n a l i t e , note f o l i a t e d and boudined t o n a l i t e apophyses near hammer; near Murphy Lakes. Figure 4.29: D e t a i l of Figure 4.28 showing f o l i a t e d and boudined t o n a l i t e apophyses w i t h i n i n t e n s e l y f o l i a t e d amphibolite i n c l u s i o n , Murphy Lakes area. MAP UNITS / 111 Figure 4.30: F o l i a t e d marble and amphibolite i n c l u s i o n s i n u n f o l i a t e d to weakly f o l i a t e d Eagle t o n a l i t e , Murphy Lakes. MAP UNITS / 112 F. DISCUSSION The presence of magmatic epidote in Eagle t o n a l i t e suggests high pressure derivation, perhaps corresponding to depths of at least 25 kilometers (Zen and Hammarstrom, 1984). Mineral assemblages in the adjacent Nicola Group, however, indicate that peak metamorphic conditions reached only upper greenschist or lower amphibolite grade and were r e s t r i c t e d to a r e l a t i v e l y narrow belt p a r a l l e l i n g the Eagle complex. Thus, pressures and temperatures for emplacement of Eagle t o n a l i t e were s u b s t a n t i a l l y lower than that inferred for genesis of the magmatic epidote (Zen and Hammarstrom, 1984). This suggests that either magmatic epidote may form at much lower pressures than proposed or that Eagle t o n a l i t e was c r y s t a l l i z e d at deep c r u s t a l levels before being emplaced at a higher l e v e l . Disequilibrium textures in Eagle t o n a l i t e , which suggest that magmatic epidote may not have coexisted stably with the mineral assemblage " present during f i n a l c r y s t a l l i z a t i o n , support the second p o s s i b i l i t y . Late syn-kinematic intrusion of Eagle t o n a l i t e i s suggested. P a r a l l e l f a b r i c s in Eagle t o n a l i t e and i t s country rocks suggest that a deformational event affected both. There i s l i t t l e or no microstructural evidence for sub-solidus d u c t i l e deformation, indicating that the strong f o l i a t i o n in Eagle t o n a l i t e formed large l y at high temperatures, perhaps during i t s emplacement. Evidence for pre- and post-tonalite deformation i s provided by Nicola Group inclusions within Eagle t o n a l i t e . Most commonly, inclusions are concordant with w e l l - f o l i a t e d t o n a l i t e and may MAP UNITS / 113 contain f o l i a t e d , boudined, or folded t o n a l i t e apophyses that are symptomatic of post-intrusive deformation. Rarely, such as at the Murphy Lakes l o c a l i t y discussed above, inclusions with a strong fabric are found within unfoliated t o n a l i t e , indicating that deformation in part preceded intrusion. Both pre- and post-intrusive deformation i s indicated in the t o n a l i t e s i l l s which intrude the Nicola Group. Pervasive f o l i a t i o n in to n a l i t e s i l l s and i t s concordance with regional fabrics suggest that the cause of f a b r i c formation was post-intrusive deformation. Pre-tonalite f a b r i c in the host rock may have guided l i t - p a r - l i t emplacement of to n a l i t e into Nicola Group rocks. The generally poorly s t r a t i f i e d nature of Nicola Group rocks in southwestern B r i t i s h Columbia, both l o c a l to the study area (Eastwood, 1961) and farther to the north and east (e.g., Schau, 1970; Preto, 1979), suggests that layering, i f present, was more l i k e l y deformation-related than primary. Remarkable concordance of planar fabrics in Eagle t o n a l i t e with f o l i a t i o n in Nicola Group country rocks and with the eastern margin of the Eagle complex occurs over a s t r i k e length of approximately 100 kilometers. The st r u c t u r a l s t y l e of deformed Nicola Group rocks contrasts sharply with c o r r e l a t i v e rocks elsewhere in southwestern B r i t i s h Columbia. MAP UNITS / 114 V. FALLSLAKE PLUTONIC SUITE A. INTRODUCTION AND SUMMARY Several large muscovite b i o t i t e granodiorite to t o n a l i t e intrusions and numerous oogenetic ( b i o t i t e ) muscovite monzogranite stocks, dykes and s i l l s make up the mid-Cretaceous F a l l s l a k e plutonic s u i t e . The F a l l s l a k e suite i s the youngest unit in the Eagle complex and i s found mainly along i t s west margin, up to the Pasayten f a u l t , but not on i t s west side. On i t s western margin, the F a l l s l a k e plutonic suite i s juxtaposed against Middle Eocene(?) c l a s t i c rocks and with late Jurassic and older rocks of the Zoa complex along the Pasayten f a u l t . F a l l s l a k e suite intrusions t y p i c a l l y contain a west-northwest trending, moderate to steeply dipping f o l i a t i o n that increases in character to protomylonite and mylonite southwest toward the Pasayten f a u l t . To the east, F a l l s l a k e suite rocks intrude Late Jurassic t o n a l i t i c rocks in a broad contact zone that in large part coincides with the d i s t r i b u t i o n of Eagle gneiss. B. DISTRIBUTION Several large muscovite b i o t i t e granodiorite to t o n a l i t e intrusions and numerous oogenetic ( b i o t i t e ) muscovite monzogranite stocks, dykes and s i l l s make up the mid-Cretaceous F a l l s l a k e plutonic s u i t e . They occur only east of the Pasayten f a u l t , where they intrude Eagle t o n a l i t e and gneiss (Figure 4.1, Plate 1). The smaller intrusions underlie a variable but s i g n i f i c a n t proportion MAP UNITS / 115 of the Eagle g n e i s s , but are d e s c r i b e d i n t h i s s e c t i o n because of t h e i r g e n e t i c r e l a t i o n to the l a r g e r i n t r u s i o n s . P r i o r to T e r t i a r y f a u l t i n g and v o l c a n i s m , the three l a r g e r muscovite-bearing i n t r u s i o n s , the n o r t h e r n , c e n t r a l , and southern F a l l s l a k e p l u t o n s , may have been cont Inuous. The type area f o r the s u i t e i s the area around F a l l s l a k e Creek, near the center of the study a r e a ; i t i n c l u d e s e x c e l l e n t exposures along Highway 5 and i n C o q u i h a l l a canyon, along the abandoned K e t t l e V a l l e y Railway grade. The n o r t h e r n F a l l s l a k e p l u t o n , an elongate body t h a t u n d e r l i e s the northwest-trending r i d g e system n o r t h e a s t of the headwaters of the East Anderson and Coldwater r i v e r s , i s the most e x t e n s i v e . I t i s o f f s e t along f a u l t s of probable T e r t i a r y age (Chapter 7) from the c e n t r a l F a l l s l a k e p l u t o n , which s t r a d d l e s the C o q u i h a l l a R i v e r V a l l e y south and east of Thar Peak, near the mouths of F a l l s l a k e and Baldwin c r e e k s . South of C o q u i h a l l a Mountain, around the headwaters of McGee Creek, the southern F a l l s l a k e p l u t o n comprises muscovite-bear i n g g r a n i t i c rock but has not been s t u d i e d i n any d e t a i l and w i l l not be d i s c u s s e d f u r t h e r . C . C O R R E L A T I V E ROCKS South-southeast of the study a r e a , c o r r e l a t i v e muscovite-b e a r i n g s t o c k s , d i k e s , and s i l l s i n t r u d e f o l i a t e d and g n e i s s i c t o n a l i t i c rocks along the southwest margin of the Eagle complex at l e a s t as f a r south as G r a n i t e Mountain (see F i g u r e 3.1). North of the study a r e a , somewhat more e x t e n s i v e but as yet u n d i f f e r e n t i a t e d or undated i n t r u s i o n s of muscovite-bearing g r a n i t i c rock occur MAP UNITS / 116 along the western margin of the Mt. Lytton-Eagle plutonic complex, at least as far north as Lytton (J.W.H. Monger, oral communication, 1988) . D. LITHOLOGY AND COMPOSITION 1. INTRODUCTION AND SUMMARY The largest F a l l s l a k e suite plutons are leucocratic, two-mica granodiorite (90% or more of the suite; Figure 4.31) and lesser t o n a l i t e (10% or less of the suite; Streckeisen, 1976). Muscovite-bearing stocks, dikes and s i l l s of the F a l l s l a k e suite form between 10 and 40% of the Eagle gneiss and are common in Eagle t o n a l i t e . They are more abundant and generally larger in size near the large plutons in the F a l l s l a k e suite and are c h a r a c t e r i s t i c a l l y heterogeneous in grain size and geometry, but are almost invariably monzogranite. The leucocratic nature of muscovite-bearing g r a n i t i c rocks i s mirrored in t h e i r white to pale-grey weathering colour. Fresh surfaces are white, cream or pale grey, and recently exposed j o i n t s and fractures, notably along Highway 5, are rusty or very pale green. Pale pink pegmatites are r e a d i l y distinguished from rusty-weathering, buff to cream pegmatitic muscovite granite. Larger muscovite-bear ing plutons are t y p i c a l l y medium-grained, but grade l o c a l l y into a p l i t i c and pegmatitic v a r i e t i e s , e s p e c i a l l y near contacts with gneissic and t o n a l i t i c rocks. Complex variations in grain size t y p i f y smaller a p l i t i c to pegmatitic muscovite monzogranite bodies in the Eagle gneiss. MAP UNITS / 117 1 1 2 3 4 5 centimetres Figure 4.31: Stained hand specimen o f b i o t i t e m u s c o v i t e g r a n o d i o r i t e / t o n a 1 i t e , c e n t r a l F a l l s l a k e p l u t o n , near F a l l s l a k e e x i t , Highway 5; note mottled d i s t r i b u t i o n of potassium f e l d s p a r ( y e l l o w ) . MAP UNITS / 118 Plutons of the F a l l s l a k e suite are mostly inclusion-free. Near contacts with gneissic and t o n a l i t i c rocks, the plutons are l o c a l l y r i c h in fine-grained t o n a l i t e inclusions and are commonly associated with a fine-grained "contact phase" that i s compositionally and t e x t u r a l l y i d e n t i c a l to the inclusions. 2. LARGE INTRUSIONS The northern F a l l s l a k e pluton i s the most extensive, well-exposed, homogeneous and best-known of the three large intrusions in the F a l l s l a k e plutonic s u i t e . Leucocratic granodiorite predominates over t o n a l i t e and t o n a l i t i c rocks are common only along the pluton's southwest margin. The northeast to southwest compositional change is mirrored by an increase in white mica r e l a t i v e to b i o t i t e and in the in t e n s i t y of the f o l i a t i o n within the pluton (Figure 4.32). The changes appear to r e f l e c t increased d u c t i l e s t r a i n along the margin of the pluton (Chapter 7). The central F a l l s l a k e Creek plut-onj also comprises granodiorite or t o n a l i t e , i s equally leucocratic and contains generally equal abundance of b i o t i t e and muscovite. Near contacts with t o n a l i t i c or gneissic rocks, a l l the large muscovite-bearing intrusions contain a fine-grained epidote hornblende muscovite b i o t i t e t o n a l i t e "contact phase" (see below). The contact phase i s t y p i c a l l y unfoliated or at most weakly f o l i a t e d . B i o t i t e i s always much more abundant than muscovite. The colour index of the contact phase appears greater than that of MAP UNITS / 119 granodiorite or to n a l i t e of the large intrusions (Figure 4.33), but th i s may be due to finer grain s i z e . 3. SMALLER MUSCOVITE-BEARING INTRUSIONS—FORM AND COMPOSITION Within Eagle gneiss, the smaller muscovite-bearing monzogranite intrusions form meter-scale dikes and s i l l s and highly irregular stocks that are up to many tens of meters across. Within Eagle t o n a l i t e , muscovite-bearing intrusions are less abundant, smaller, and almost invariably occur as pegmatite dikes or s i l l s . Although more heterogeneous in grain size and having more irregular intrusive geometries, the smaller intrusions are more compositionally homogeneous (invariably monzogranite) than the larger plutons. Muscovite i s commonly the sole mica or predominates over b i o t i t e . The presence of b i o t i t e appears to correlate with rare occurrences of granodiorite or to n a l i t e phases. Garnet, as fine-grained euhedral red grains, is a common but not essen t i a l accessory mineral (Figure 4.34). Two suites of pegmatitic muscovite-bearing intrusions, pink pegmatites and pegmatitic muscovite granites, were distinguished. The pink monzogranite pegmatite dikes (on average approximately 15 centimeters, ranging up to 2 or 3 meters thick) consist of grey quartz, pinkish potassium feldspar, white plagioclase, very pale greenish muscovite and scattered fine-grained red garnets (Figures 4.35 and 4.36). Dikes or s i l l s of pegmatitic muscovite granite resemble the pink pegmatite in composition and form but are MAP UNITS / 120 Figure 4.32: Stained specimen of mylonitic muscovite t o n a l i t e from the southwest margin of the northern F a l l s l a k e pluton, upper East Anderson River; note the potassium feldspar-poor nature. Width of f i e l d of view i s 8 cm. Figure 4.33: Fine-grained "contact phase," July Mtn.; note potassium feldspar enrichment along vein. MAP UNITS / 121 F i g u r e 4 . 3 4 : F o l i a t e d garnet muscovite monzogranite i n t r u s i o n of the F a l l s l a k e p l u t o n i c s u i t e , Eagle g n e i s s , J u l y Mtn. a r e a . F i g u r e 4 . 3 5 : Muscovite monzogranite pegmatite, "pink pegmatite," F a l l s l a k e p l u t o n i c s u i t e , Highway 5 t o l l b o o t h . MAP UNITS / 122 Figure 4.36: "Pink pegmatite" of the F a l l s l a k e plutonic suite cutting t o n a l i t e orthogneiss of the Eagle gneiss, Highway 5 tollbooth. MAP UNITS / 123 less widespread, much larger (average approximately 1.5 meters, ranging up to 10 meters thick; Figure 4.37) and lack the c h a r a c t e r i s t i c pink potassium feldspar. Pegmatitic muscovite granite i s also distinguished by i t s complex internal grain size variations among a p l i t i c , medium-grained and pegmatitic variants (Figure 4.38). The stocks near larger F a l l s l a k e plutons resemble pegmatitic variants that occur within the plutons. Pink pegmatite intrusions appear to be more common away from the larger muscovite-bearing plutons, and so are more common within Eagle t o n a l i t e than within Eagle gneiss. E . C O N T A C T R E L A T I O N S 1. E X T E R N A L C O N T A C T R E L A T I O N S a. I N T R O D U C T I O N A N D S U M M A R Y The central and northern F a l l s l a k e plutons are inferred to be faulted against Late Jurassic and older rocks of the Zoa complex and Middle Eocene(?) c l a s t i c rocks along their west and southwest margins. Along t h e i r eastern margins, the plutons and s a t e l l i t e phases of the F a l l s l a k e plutonic suite intrude Late Jurassic Eagle t o n a l i t e and gneiss. b . W E S T C O N T A C T The northern F a l l s l a k e pluton i s juxtaposed with Late Jurassic and older (?) Zoa complex and Middle Eocene(?) c l a s t i c rocks along the Pasayten f a u l t . Faulting i s inferred to be multistage: mid-Cretaceous d u c t i l e structures were reactivated in Te r t i a r y MAP UNITS / 124 time. The contact i s poorly exposed, but s t r u c t u r a l fabrics in juxtaposed units suggest a f a u l t contact (Chapter 7). C. CONTACTS WITH EAGLE TONALITE AND GNEISS Fa l l s l a k e plutonic suite c l e a r l y intrudes and is younger than Eagle t o n a l i t e and gneiss (Figure 4 . 3 9 ) . Probable hybrid phases at the contact have the e f f e c t , however, of obscuring intrusive r e l a t i o n s . Contact geometries are, as a rule, highly irregular in d e t a i l , and hybrid contact phases are heterogeneous in texture and composition, suggesting that phases on both sides of t h i s contact were very mobile during emplacement of the F a l l s l a k e s u i t e . Contacts between monzogranite-rich Eagle gneiss and gneissic i n c l u s i o n - r i c h F a l l s l a k e suite plutons are somewhat a r b i t r a r y , but drawn at the l i m i t s of inclusion-free, r e l a t i v e l y homogeneous, medium-grained, muscovite b i o t i t e granodiorite or t o n a l i t e . The convention excludes i n c l u s i o n - r i c h contact zones of the plutons and the map scale precludes d i f f e r e n t i a t i o n of smaller-scale F a l l s l a k e suite intrusions in Eagle gneiss; the extent of the large F a l l s l a k e suite intrusions i s therefore a minimum. Rocks in the contact zone have been included in Eagle gneiss, which i s in part t y p i f i e d by extreme heterogeneity. The complexity and along-strike v a r i a b i l i t y of the contact zone between the F a l l s l a k e and t o n a l i t e suites are best exemplified within a one kilometer radius of the flanks and peak of July Mountain. As well, evidence for the presence and mobility of hybrid phases is best displayed there. MAP UNITS / 125 Figure 4.37: Pale-weathering muscovite monzogranite pegmatite dike (roughly 2-3 m wide) of the F a l l s l a k e plutonic suite cutting t o n a l i t e orthogneiss of Eagle gneiss, Highway 5, approximately 2 km SW of tollbooth. MAP UNITS / 126 F i g u r e 4.38: A p l i t i c to p e g m a t i t i c garnet muscovite monzogranite i n t r u s i o n of the F a l l s l a k e s u i t e c u t t i n g Eagle g n e i s s , approx. 1 km south of C o q u i h a l l a Lakes. F i g u r e 4.39: White-weathering b i o t i t e muscovite monzogranite d i k e of the F a l l s l a k e s u i t e i n t r u d i n g and c r o s s - c u t t i n g the f a b r i c (upper l e f t t o l o v e r r i g h t ) i n t o n a l i t e o r t h o g n e i s s of Eagle g n e i s s , J u l y Mtn. a r e a . MAP UNITS / 127 The peak and much of the highest part of July Mountain are underlain by homogeneous Eagle t o n a l i t e with a strong, consistent f o l i a t i o n . P a r t i c u l a r l y along i t s steep and well exposed north-northeast flank, t o n a l i t e was intruded from below by two-mica granodiorite of the northern F a l l s l a k e pluton. At the map scale, the contact appears sub-horizontal, but in d e t a i l i t is highly i r r e g u l a r . This r e l a t i o n holds for the northeast, east and southern parts of the contact, where t o n a l i t e commonly caps the ridges ahd i s surrounded by two-mica granodiorite at lower elevations. On the margins of the t o n a l i t e "cap" on July Mountain and in the adjacent Eagle gneiss, intrusive relations between the F a l l s l a k e suite and Eagle t o n a l i t e and gneiss are t y p i c a l l y complicated, and, in places ambiguous where probable hybrid phases of the F a l l s l a k e suite and t o n a l i t e are developed. Hybrid rocks appear to have a f f i n i t i e s to both Eagle t o n a l i t e and the F a l l s l a k e suite but appear cogenetic with intrusion of the younger plutons. In some places they bear some of the hallmarks of migmatitic rocks (Thorpe and Brown, 1985, p.145 f f . ) , and in the s t r i c t sense they are migmatitic since they are "mixed rocks" (Figures 4.40, 4.41, and 4.42). Meter-scale a p l i t i c , medium-grained and pegmatitic l i t - p a r - l i t intrusions are common throughout Eagle gneiss (Figure 4.43). They intrude p a r a l l e l and sub-parallel to gneissic f a b r i c s , t y p i c a l l y have discordant dike- and v e i n - l i k e apophyses and generally lack c h i l l margins. In one place, west of the tarn on the north side MAP UNITS / 128 Figure 4.40: Migmatite f a b r i c in Eagle gneiss, shoving extreme mobility and variable compositions of Eagle gneiss and hybrid(?) phases near northern F a l l s l a k e pluton/Eagle gneiss contact, July Mtn. Figure 4.41: Migmatite f a b r i c , Eagle gneiss; cross-cutting leucocratic hybrid (?) phase and mobile Eagle gneiss, near northern F a l l s l a k e pluton/Eagle gneiss contact, July Mtn. MAP UNITS / 129 Figure 4.42: Migmatite f a b r i c , Eagle gneiss; mobile layered Eagle gneiss/northern F a l l s l a k e pluton hybrid(?) phase cross-cutting folded Eagle gneiss, July Mtn. Figure 4.43: Lit-par-lit s i l l s of pale weathering b i o t i t e muscovite granodiorite/monzogranite intruding northeast-dipping Eagle gneiss, July Mtn. Figure 4.44 i s a close-up of Eagle gneiss from t h i s outcrop. MAP UNITS / 130 of July Mountain, a meter-thick layer of f o l i a t e d Eagle t o n a l i t e i s sandwiched between two F a l l s l a k e suite s i l l s . Within the layer, unusual concordant "lozenges" of b i o t i t e , up to 10 centimeters long by 2 centimeters thick, have grown to give the appearance of a "bed" of black "clams" (Figure 4.44). Metamorphic fabrics such as t h i s , the lack of c h i l l e d margins and the unaltered appearance of t o n a l i t i c rocks in contact with the F a l l s l a k e suite attest to the emplacement of the suite into hot and(or) f l u i d - r i c h wall rocks. Concordant sheet- or s i l l - l i k e l i t - p a r - l i t intrusions and discordant dikes are the most common intrusive geometries of F a l l s l a k e suite intrusions in the contact zone, but agmatite and stockwork zones as well as hybrid(?) phases are also present l o c a l l y . Hybrid rocks, themselves variable in composition and texture, are very leucocratic granodiorite which contain b i o t i t e and subordinate muscovite. The presence and genesis of hybrid phases i s inferred from the following observations: compositions d i s t i n c t from yet sharing attributes of both F a l l s l a k e suite b i o t i t e muscovite granodiorite and Eagle b i o t i t e t o n a l i t e ; hybrid rocks are r e s t r i c t e d to the contact zone along the margins of F a l l s l a k e suite intrusions; general unfoliated nature of hybrid phases; presence of t o n a l i t i c gneiss inclusions in unfoliated hybrid rocks which otherwise resemble Eagle t o n a l i t e , unique to the contact zone (Figure 4.45); a two-mica bearing g r a n i t i c inclusion contained within weakly f o l i a t e d b i o t i t e - r i c h t o n a l i t e (Figure 4.46); complex disharmonic folding and migmatitic textures in Eagle gneiss MAP UNITS / 131 suggestive of extreme mobility (Figure 4 . 4 7 ) ; occurrence of b i o t i t e - r i c h r e s t i t e ( ? ) within two-mica granodiorite i s unique to the contact and i s commonly associated with fine-grained epidote b i o t i t e t o n a l i t e inclusions (Figure 4 . 4 8 ) ; and the lack of any textural evidence which suggests quenching of younger phases against gneissic or t o n a l i t i c rocks. An enigmatic fine-grained t o n a l i t i c "contact phase" i s developed l o c a l l y along the contact, and i s unique to contacts between larger plutons of the F a l l s l a k e suite and Eagle t o n a l i t e and gneiss. It i s a metre-scale border phase or occurs as inclusions within F a l l s l a k e suite granodiorite. The contact phase i s also most extensively developed and best exposed on and around July Mountain, p a r t i c u l a r l y on the lover and middle parts of the c l i f f s forming i t s northeast side. Inclusions of fine-grained t o n a l i t e , up to tens of meters across, occur in two-mica granodiorite of the northern F a l l s l a k e pluton. Near the top of the c l i f f s , a meter-scale layer or border of fine-grained contact phase t o n a l i t e commonly separates f o l i a t e d b i o t i t e t o n a l i t e capping the c l i f f s from younger F a l l s l a k e two-mica granodiorite below. Within a meter or so of the contact, medium-grained w e l l - f o l i a t e d b i o t i t e t o n a l i t e contains scattered, t y p i c a l l y discontinuous layers of centimeter- to decimeter-wide fine-grained t o n a l i t e that are commonly (but not always) concordant. The fine-grained layers appear massive and f o l i a t i o n in t o n a l i t e at t h e i r margins i s less well-developed (e.g., b i o t i t e appears less well-aligned). Unfoliated two-mica granodiorite adjacent to the fine-grained MAP UNITS / 132 border phase appears to interfinger with inclusions and " t a i l s " of weakly f o l i a t e d or massive fine-grained t o n a l i t e (Figure 4 . 4 9 ) . Rare agmatite and stockwork zones occur l o c a l l y along contacts between rocks of the F a l l s l a k e suite and Eagle t o n a l i t e and gneiss. Agmatites contain rotated blocks of both gneissic granodiorite and layered gneiss in a "matrix" of muscovite-bearing monzogranite or granodiorite (Figure 4.50) and may grade into stockvorks, in which there i s a smaller proportion of matrix and in which the gneissic blocks are more concordant (Figure 4.51). Isolated, meter-scale inclusions of gneiss are generally r e s t r i c t e d to the margins of the larger intrusions of the F a l l s l a k e s u i t e ; for example, on the southwest side of Dry Gulch, along Highway 5 and along the abandoned Kettle Valley Railway grade. 2. INTRA-PLUTON CONTACT RELATIONS Intrusive r e l a t i o n s among phases within the F a l l s l a k e plutonic suite are contradictory. Relations between the two pegmatite phases were observed at only one place, where a pink pegmatite dike intruding layered t o n a l i t e in Eagle gneiss i s likewise intruded by a muscovite monzogranite pegmatite s i l l . However, in the central F a l l s l a k e pluton, muscovite monzogranite pegmatite and/or a p l i t e variants Indistinguishable from muscovite monzogranite Intrusions in Eagle gneiss are l o c a l l y intruded by narrow (average less than 10 centimeters) pink pegmatite dikes. This suggests that pink pegmatite post-dates muscovite monzogranite pegmatite and the large plutons. Pink pegmatite dikes are rare in the central and northern MAP UNITS / 133 Figure 4.44: Close-up of Eagle gneiss from Figure 4.43/ shoving development of oblate and concordant b i o t i t e c l o t s or lozenges in orthogneiss layer sandviched by F a l l s l a k e suite s i l l s ; July Mtn. Tigure 4.45: Eagle gneiss inc l u s i o n in unfoliated b i o t i t e t o n a l i t e hybrid(?) phase near northern Fallslake/Eagle tonalite/Eagle gneiss contact, July Mtn. MAP UNITS / 134 Figure 4.46: Rare muscovite-bearing inclusion in weakly f o l i a t e d b i o t i t e t o n a l i t e hybrid(?) phase, northern F a l l s l a k e pluton/Eagle t o n a l i t e contact, July Mtn. Figure 4.47: Complex disharmonic folding in layered Eagle gneiss, lover Jim K e l l y Creek. MAP UNITS / 135 Figure 4.48: B i o t i t e r e s t i t e ( ? ) at contact between pale weathering unfoliated b i o t i t e muscovite granodiorite of the northern F a l l s l a k e pluton (bottom, l e f t ) and weakly f o l i a t e d Eagle t o n a l i t e (top, r i g h t ) , July Mtn; note lack of c h i l l e d contacts. Figure 4.49: Interfingering unfoliated fine-grained t o n a l i t e "contact phase" and pale weathering b i o t i t e muscovite granodiorite, northern F a l l s l a k e pluton/Eagle t o n a l i t e contact, July Mtn. MAP UNITS / 136 Figure 4.50: Agmatitic intrusive contact showing rotated blocks of Eagle gneiss i n matrix of F a l l s l a k e suite b i o t i t e muscovite granodiorite; July Mountain. Figure 4.51: Intrusive stockwork with pale weathering F a l l s l a k e suite b i o t i t e muscovite granodiorite or monzogranite intruding Eagle gneiss, July Mtn; view looking northwest. MAP UNITS / 137 Fa l l s l a k e plutons r e l a t i v e to Eagle t o n a l i t e and gneiss. Along Highway 5, large dikes of muscovite monzogranite pegmatite cut Eagle ton a l i t e and gneiss and appear to grade into smaller pink pegmatite apophyses. These intrusive relations suggest that the phases are cogenetic and supports the geochronometric and geochemical r e s u l t s (Chapters 5 and 6, res p e c t i v e l y ) . F. GENERAL STRUCTURE The F a l l s l a k e plutonic suite is f o l i a t e d over large areas, but the mesoscopic fab r i c i s not as c h a r a c t e r i s t i c as for Eagle t o n a l i t e and gneiss. The F a l l s l a k e suite crosscuts f o l i a t e d Eagle t o n a l i t e and gneiss. Fabric preserved in the F a l l s l a k e suite was formed in a younger deformational event. F o l i a t i o n within the three largest F a l l s l a k e suite intrusions varies in orientation and int e n s i t y . The northern F a l l s l a k e pluton contains a consistent west-northwest trending, moderately steep northeast dipping f o l i a t i o n that steepens somewhat and changes in character to protomylonite and mylonite southwest toward the Pasayten f a u l t . Close-spaced ribbon quartz and feldspar porphyroclasts are common in rocks adjacent to the f a u l t . Near Jim Kell y Creek, similar mylonitic fabrics were developed in muscovite monzogranite of Eagle gneiss adjacent to the Pasayten f a u l t . However, along the northeast margin of the northern F a l l s l a k e pluton, and within the two other large muscovite-rich intrusions, massive textures are common and the f o l i a t i o n i s less well-developed. F o l i a t i o n i s uncommon in the smaller F a l l s l a k e MAP UNITS / 138 suite intrusions within Eagle t o n a l i t e and gneiss, and mesoscopically, they appear l a r g e l y unaffected by d u c t i l e deformation associated with the Pasayten f a u l t . Pegmatite i s pytgmatically folded l o c a l l y (Figure 4.52) and muscovite-monzogranite dikes that c l e a r l y crosscut f o l i a t e d t o n a l i t e orthogneiss in Eagle gneiss are of f s e t along discrete millimeter-scale d u c t i l e shear surfaces (Figure 4.53). G . PETROGRAPHY 1. INTRODUCTION AND SUMMARY A l l eighteen samples of the F a l l s l a k e plutonic suite studied display some microfabric, even specimens with no apparent mesoscopic f a b r i c . This d i f f e r s s i g n i f i c a n t l y from the Eagle t o n a l i t e and gneiss which t y p i c a l l y contain a strongly-developed mesoscopic f a b r i c but limited microfabric. Microstructures related to d u c t i l e s t r a i n are described and discussed in greater d e t a i l in Chapter 7. 2. LARGER INTRUSIONS Oligoclase (Anl6 to An27) in the large F a l l s l a k e suite plutons commonly exhibits well-developed o s c i l l a t o r y zoning, a l b i t e twinning and subordinate p e r i c l i n e or rare Carlsbad twins. Potassium feldspar i s commonly microcline and i n t e r s t i t i a l to plagioclase. Quartz, also i n t e r s t i t i a l to plagioclase, displays ubiquitous undulatory extinction and i s almost invariably b i a x i a l . In a l l but the most Intensely deformed rocks, muscovite and b i o t i t e MAP UNITS / 139 are equally abundant. B i o t i t e i s pleochroic from pale green to olive green to deep brown. Muscovite i s larger, less ragged and better formed than b i o t i t e . Sharp grain boundaries between muscovite and b i o t i t e and few replacement textures suggest an equilibrium assemblage (Figure 4.54). S e r i c i t e and(or) saussurite a l t e r a t i o n products of plagioclase are p a r t i c u l a r l y well developed in the more deformed rocks and in the cores of large grains. Pale green c h l o r i t e a l t e r a t i o n of b i o t i t e occurs along cleavages and grain boundaries. Accessory minerals include zircon and monazite, and opaque minerals are generally absent, although pyrite was present in heavy mineral concentrates separated for geochronometry. Specimens of the central and northern F a l l s l a k e plutons are hypidiomorphic-granular, f i n e - to medium-grained, se r i a t e , weakly to moderately f o l i a t e d muscovite b i o t i t e granodiorite. Larger (up to 6 millimeters, average 3 millimeters) and better-formed plagioclase occurs in a matrix of finer-grained mica and s t i l l finer-grained anhedral to subhedral quartz and feldspar. Plagioclase is predominantly subhedral, and has irregular ( r e c r y s t a l l i z e d ? ) grain boundaries but regular compositional zoning. Grain boundaries among plagioclase, quartz and potassium feldspar are commonly myrmekitic. Lens- or pod-shaped quartz aggregates (2 to 5 millimeters long) are composed of individual fine-grained new grains or subgrains misoriented by less than 7° with respect to adjacent host grains (cf. B e l l and Etheridge 1973). Pre f e r e n t i a l l y - o r i e n t e d mica and aligned quartz aggregates outline MAP UNITS / 140 aggregates outline a micro- and mesoscopic f o l i a t i o n , and in more intensely deformed specimens, the aggregates form highly elongate ribbon-grains (Chapter 7, Figure 4.55). 3. SMALLER INTRUSIONS IN EAGLE TONALITE AND GNEISS Pink pegmatite at the Highway 5 tollbooth consists of graphically intergrown a l b i t e , quartz, microcline and muscovite, and scattered euhedral fine-grained garnet. A l l minerals except garnet are deformed. Muscovite monzogranite pegmatite c o l l e c t e d from a 1.5 meter thick dike approximately 1.5 kilometer southwest of the Highway 5 tollbooth consists of s t r i k i n g graphic intergrowths of coarse-grained quartz, a l b i t e , microcline and muscovite (Figure 4.56) but lacks microfabric. Specimens of muscovite monzogranite intrusions in Eagle gneiss have s i m i l a r mineralogy to pegmatite described above but vary more widely in grain s i z e . They are hypidiomorphic- to allotriomorphic-granular and s e r i a t e textured. Muscovite and the alignment of quartz aggregates outline a weak to moderate f o l i a t i o n in the specimens. 4. FINE-GRAINED TONALITE INCLUSIONS AND FINE-GRAINED "CONTACT P H A S E " Samples of the contact phase and of the fine-grained inclusions are petrographically i d e n t i c a l . Both units are epidote-bearing t o n a l i t e and the very ragged, biotite-rimmed primary epidote resembles epidote i n Eagle t o n a l i t e . Both units MAP UNITS / 141 Figure 4 .52: Pink pegmatite of the F a l l s l a k e suite intruding and pytgmatically folded v i t h t o n a l i t e orthogneiss of Eagle gneiss, Highway 5 tollbooth. MAP UNITS / 142 Figure 4.53: White-weathering monzogranite pegmatite dike of the F a l l s l a k e suite intruding orthogneiss and amphibolite of Eagle gneiss; i t s e l f o ffset on discrete l a y e r - p a r a l l e l d u c t i l e shear zones; KVRR abandoned grade, Coquihalla canyon. note coexistence of b i o t i t e with muscovite; crossed po l a r i z e r s , f i e l d of view i s 6 mm. MAP UNITS / 143 Figure 4.55: Mylonitic muscovite t o n a l i t e of the northern F a l l s l a k e pluton, shoving highly elongate quartz ribbon grains and intensely altered plagioclase; plane l i g h t , vidth of f i e l d of viev i s 1 cm. Figure 4.56: Muscovite monzogranite pegmatite shoving graphic intergrovths of muscovite and quartz; approximately 1.5 km SW of Highvay 5 tollbooth; crossed p o l a r i z e r s , f i e l d of viev i s 6 mm. MAP UNITS / 144 F i g u r e 4 . 57 : F i n e - g r a i n e d " c o n t a c t phase," shoving unzoned a l b i t i c overgrovths v i t h q u artz i n c l u s i o n s on zoned p l a g i o c l a s e g r a i n ; J u l y Mountain; c r o s s e d p o l a r i z e r s , f i e l d of v i e v i s 6 mm. MAP UNITS / 145 contain b i o t i t e and muscovite, but muscovite i s much less abundant and c r y s t a l l i z e d l a t e r . Irregular, unzoned a l b i t i c rims on an o r t h l t e - r i c h , oscillatory-zoned cores characterize the inclusions and the "contact phase." Circular quartz inclusions i n the a l b i t i c rims are aligned p a r a l l e l to grain boundaries (Figure 4.57). H . D I S C U S S I O N The cogenetic nature of intrusions included in the F a l l s l a k e plutonic suite i s suggested by their leucocratic nature, intermediate to f e l s i c composition, the common presence of muscovite and garnet, and the general lack of mutual intrusive r e l a t i o n s . Geochronometric and geochemical r e s u l t s confirm t h i s r e l a t i o n s h i p (Chapters 5 and 6, r e s p e c t i v e l y ) . An absence of c h i l l e d F a l l s l a k e suite rocks and the s p a t i a l association with F a l l s l a k e suite contacts of hybrid and p a r t i a l l y assimilated(7) (the "contact phase" and fine-grained inclusions) phases, migmatite, and disharmonically folded Eagle gneiss imply that Late Jurassic rocks were hot and mobile during emplacement of F a l l s l a k e suite intrusions in middle Cretaceous time. This i s compatible v i t h geochronometric evidence that indicates extensive re s e t t i n g of Rb-Sr and K-Ar systematics for Late Jurassic Eagle t o n a l i t e and gneiss in the mid-Cretaceous and suggests that the F a l l s l a k e suite vas emplaced at mesozonal depths and(or) vas v o l a t i l e - r i c h . MAP UNITS / 146 VI. EAGLE GNEISS A. INTRODUCTION AND SUMMARY Eagle gneiss is a discontinuous belt in central and western Eagle complex comprising a mixture of heterogeneous, recognizable p r o t o l i t h s of limited extent. Eagle gneiss encompasses the contact zone between Late Jurassic f o l i a t e d and gneissic t o n a l i t i c rocks and mid-Cretaceous muscovite-bearing granitoids of the F a l l s l a k e plutonic s u i t e . Well-layered orthogneiss, g e n e t i c a l l y related to Eagle t o n a l i t e to the east, i s interlayered with and in part intruded subordinate amphibolite and rare marble and c a l c - s i l i c a t e rocks. F a l l s l a k e plutonic suite s i l l s , dikes and stocks intruded the layered rocks, underlie from 10 to 40% of Eagle gneiss and are an integral constituent. Well developed layering, l o c a l folding, and scattered hybrid phases in Eagle gneiss suggest a complicated str u c t u r a l and intrusive history. Its heterogeneous nature and complicated structure are l i k e l y related in large part to emplacement of the mid-Cretaceous F a l l s l a k e plutonic s u i t e . B. DISTRIBUTION Eagle gneiss forms a discontinuous belt in central and western Eagle complex (Figure 4.1, Plate 1), between Eagle t o n a l i t e and the central and northern F a l l s l a k e plutons. Southeast of the southern F a l l s l a k e pluton, Eagle gneiss forms the western margin of the Eagle complex; F a l l s l a k e suite intrusions are abundant but are too small and discontinuous to distinguish from the gneiss. MAP UNITS / 147 C. LITHOLOGY AND COMPOSITION Eagle gneiss is a heterogeneous unit comprising four elements. Tonalite orthogneiss(1) gen e t i c a l l y related to Eagle t o n a l i t e to the east predominates. Orthogneiss is interlayered with and intruded subordinate amphibolite(2) and rare marble and c a l c -s i l i c a t e marble(3). Leucocratic, muscovite-bearing stocks, dikes and s i l l s of the F a l l s l a k e plutonic suite(4) intrude a l l other elements and are an integral part of Eagle gneiss. 1. TONALITE ORTHOGNEISS AND AMPHIBOLITE Layered rocks of the Eagle gneiss consist of t o n a l i t e orthogneiss and amphibolite. Amphibolite layers are subordinate in abundance to orthogneiss and vary in continuity and thickness (centimeters to perhaps tens of meters t h i c k ) . Thicker layers commonly contain millimeter- to centimeter-scale internal layering. Contact relations between amphibolite and orthogneiss vary from gradational to intrusive (where amphibolite i s crosscut by t o n a l i t e apophyses; Figure 4.58) to s t r u c t u r a l . The s t r u c t u r a l zones include contacts where plagioclase augen mark centimeter to decimeter thick high s t r a i n zones between amphibolite and orthogneiss (Figures 4.59 and 4.60). Locally, amphibolite boudins form discontinuous layers within orthogneiss (Figure 4.61). Orthogneiss and amphibolite are r e l a t i v e l y simple mineralogically and compositionally s i m i l a r . Variable amounts of plagioclase, amphibole, quartz, b i o t i t e and epidote are t y p i c a l but they are potassium feldspar-poor. Orthogneiss i s much more MAP UNITS / 148 Figure 4.58: Folded apophyses of t o n a l i t i c orthogneiss in amphibolite layer, Eagle gneiss, 1 km west of Highway 5 to l l b o o t h . Figure 4.59: Refolded i s o c l i n a l f o l d in augen-rich (blastomylonite) contact layer between amphibolite and t o n a l i t e orthogneiss, Eagle gneiss, abandoned KVRR grade, Coquihalla River canyon. MAP UNITS / 149 Figure 4.60: Stained hand specimen from augen-rich contact zone between amphibolite and t o n a l i t e orthogneiss, Eagle gneiss, approx. 1 km vest of Highvay 5 tollbooth. Figure 4.61: Amphibolite boudins in t o n a l i t e orthogneiss, Eagle gneiss. MAP UNITS / 150 leucocratic (less than 15% mafics) than amphibolite (more than 35% mafics). Disseminated pyrite (1 or 2% of rock) and rare dark red garnet also characterize amphibolite. Except for i t s greater amphibole content, orthogneiss i s composit i o n a l l y indistinguishable from Eagle t o n a l i t e . Tonalite leucosomes in amphibolite layers are more leucocratic than orthogneiss or Eagle t o n a l i t e (Figure 4.62). Orthogneiss contains a variable internal f a b r i c . Most commonly i t i s weakly gneissic, with discrete but continuous centimeter-spaced b i o t i t e f o l i a defining gneissosity. The f a b r i c in t h i s v a r i e t y i s much more apparent i n outcrop than in hand specimen (Figure 4.63, refer also to Figure 4.22 in Eagle t o n a l i t e s ection). Weakly gneissic t o n a l i t e grades into w e l l - f o l i a t e d t o n a l i t e , i n which the f o l i a t i o n i s defined by the dimensional preferred orientation of b i o t i t e . We11-developed compositional layering i s also common in orthogneiss. It comprises well-developed millimeter- to centimeter-scale alternating mafic and f e l s i c layers (Figures 4.64 and 4.65). Most layers are concordant but mesoscopically appear to be discontinuous (Figure 4.66). Local meter-scale t o n a l i t e layers are unfoliated (Figure 4.67). Except for b i o t i t e , minerals within orthogneiss are only weakly f o l i a t e d . Textures include ribbon quartz and plagioclase augen (blastomylonite(?); Figures 4.68 and 4.69). More pronounced augen textures are r e s t r i c t e d to t o n a l i t e orthogneiss-amphibolite contacts and some contacts between orthogneiss and F a l l s l a k e suite s i l l s . MAP UNITS / 151 Layers of amphibolite and included leucosome are commonly heterogeneous in composition and s t r u c t u r a l l y complex. Amphibolite i s commonly medium-grained (rarely fine-grained) and weakly nematoblastic or l e p i d o b l a s t i c . Discontinuous millimeter- to centimeter-scale t o n a l i t e leucosomes range from l e n t i c u l a r and concordant to discordant and i r r e g u l a r . Leucosomes outline l o c a l rootless i s o c l i n a l folds but, more commonly, folds within amphibolite-rich packages are disharmonic. B i o t i t e - r i c h layers in the amphibolite mimic the complex fabrics abundant in the leucosomes. 2. MARBLE AND CALC-SILICATE Marble and c a l c - s i l i c a t e occur within Eagle gneiss in the c l i f f above the north portal of a tunnel on the abandoned Kettle Valley Railroad (KVRR) grade (Figure 4.70). A discontinuous, concordant layer of elongate, 10 to 30 centimeter thick marble boudins with centimeter thick c a l c - s i l i c a t e reaction rims occur within meter-scale interlayers of amphibolite and orthogneiss. D. CONTACT RELATIONS Eagle gneiss occurs mostly along the contact zone between Late Jurassic Eagle t o n a l i t e to the east and the middle Cretaceous F a l l s l a k e plutonic suite to the west. Eagle orthogneiss grades into s l i g h t l y gneissic to f o l i a t e d Eagle t o n a l i t e . F a l l s l a k e suite intrusions, an integral part of Eagle gneiss, intrude the orthogneiss and amphibolite in a myriad of intrusive geometries. MAP UNITS / 152 0 1 2 3 4 5 c e n t i m e t r e s F i g u r e 4.62: T o n a l i t e leucosome i n am p h i b o l i t e l a y e r , Eagle g n e i s s , approx. 1 km v e s t of Highvay 5 t o l l b o o t h ; s t a i n e d specimen on l e f t hand s i d e . MAP UNITS / 153 Figure 4.63: Tonalite orthogneiss of Eagle gneiss, near Dry Gulch on Highvay 5; stained specimen on right hand side. Figure 4.64: Well-layered t o n a l i t e orthogneiss (stained specimen on right hand side) shoving compositional layering outlined by variations in abundance of mafic and f e l s i c minerals, Eagle gneiss, J u l i e t Creek. MAP UNITS / 154 Figure 4.65: F o l d e d c o m p o s i t i o n a l layering In stained hand specimen of t o n a l i t i c orthogneiss. Eagle gneiss, Highway 5 tol l b o o t h . MAP UNITS / 155 Figure 4.67: Unfoliated t o n a l i t e from meter-scale layer in Eagle gneiss, J u l i e t Creek; stained specimen on r i g h t hand side. Figure 4.68: Augen orthogneiss, Eagle gneiss. MAP UNITS / 156 Figure 4.69: Augen texture (blastomylonite) in gneissic t o n a l i t e orthogneiss, Eagle gneiss, Dear Mtn. Figure 4.70: White 3-4 cm thick marble and c a l c -s i l i c a t e boudln (beneath scale) inter layered with amphibolite and crosscut by F a l l s l a k e suite pegmatite, Eagle gneiss, abandoned KVRR grade, Coquihalla River Canyon. MAP UNITS / 157 E . GENERAL STRUCTURE Eagle gneiss i s s t r u c t u r a l l y complex. Although no map-scale folds vere recognized v i t h i n Eagle gneiss, minor fold v a r i e t i e s include open to i s o c l i n a l , disharmonic and ptygmatic. Minor folds v i t h i n orthogneiss are commonly r e s t r i c t e d to l o c a l layers. Displacements up- and dovn-structure seem to die out v i t h i n a fev meters and the orientation of s t r u c t u r a l l y overlying and underlying gneissic layers i s unaffected. Disharmonic and ptygmatic folds are p a r t i c u l a r l y common v i t h i n thick amphibolite layers and areas of abundant F a l l s l a k e suite intrusions. F. PETROGRAPHY Eagle orthogneiss and Eagle t o n a l i t e are mineralogically s i m i l a r . Orthogneiss i s s l i g h t l y more amphibole-rich and contains s l i g h t l y more c a l c i c plagioclase (oligoclase (Anil-18) in a l l samples of Eagle orthogneiss compared v i t h a l b l t e - o l i g o c l a s e (Ann-20) i n Eagle t o n a l i t e ) . The d i s t i n c t i v e primary epidote common in Eagle t o n a l i t e also t y p i f i e s Eagle orthogneiss. Fine- to medium-grained t o n a l i t e and rare medium-grained granodiorite of the orthogneiss contain microfabric analogues of the mesoscopic f a b r i c : veakly-developed compositional layering, strongly-developed b i o t i t e alignment and veak alignment of plagioclase grains and quartz aggregates. Except for ribboned quartz In augen orthogneiss (Figure 4.71), other evidence for sub-solidus d u c t i l e deformation the unit i s limited to ubiquitous MAP UNITS / 158 Figure 4.71: veil-developed quartz ribbon grains in augen-rich orthogneiss, Eagle gneiss, near Dry Gulch, Highvay 5; plane l i g h t , vidth of f i e l d of viev 6 mm. MAP UNITS / 159 undulatory extinction and very weakly-developed deformation bands in quartz, uncommon undulatory extinction in b i o t i t e and rare bent or tapering a l b i t e twins in plagioclase. Amphibolite from layers i n Eagle gneiss and from a layer in Eagle t o n a l i t e near the Upper Coldwater exit ramp on Highway 5 are f i n e - to medium-grained and have fine compositional layering and weakly nematoblastic textures. Amphibole (Tshermakite, from 25 to 55%) and plagioclase (oligoclase, An 10-17, from 45 to 70%) dominate. Accessory minerals apatite, opaques, quartz, t i t a n i t e and rare a l l a n i t e are t y p i c a l . One sample, from near the Highvay 5 tollbooth, a t y p i c a l l y contained about 5% p a r t l y u r a l i t i z e d r e l i c t clinopyroxene grains. Abundant epidote noted in many places i n the f i e l d vas not present in the sections examined. Granoblastic marble from a marble boudin consists of 95% very fine-grained to medium-grained c a l c i t e (vith bent lamellar tvinning) and approximately 5% scattered diopside. Trains of very fine-grained r e c r y s t a l l i z e d grains crosscut larger r e l i c t ( ? ) c a l c i t e grains. Granoblastic c a l c - s i l i c a t e along the margin of the boudin consists of millimeter-scale layers of quartz (vith <5% plagioclase) alternating v i t h layers containing c l i n o z o i s i t e , a l b i t e , amphibole and(or) quartz and t i t a n i t e . Quartz everyvhere exhibits undulatory extinction and contains scattered deformation bands. MAP UNITS / 160 G. DISCUSSION Amphibolite layers containing t o n a l i t e apophyses indicate that the layers are, at least in part, pre-Late Jurassic in age. R e l i c t pyroxene phenocrysts in one amphibolite sample suggest that pyroxene-phyric Nicola Group volcanic rocks are a l i k e l y p r o t o l i t h . Meagre geochemical evidence (Chapter 6) supports a Nicola Group p r o t o l i t h for amphibolite from Eagle gneiss. Rare marble in Eagle gneiss i s compatible v i t h a Nicola Group o r i g i n , as marble i s common in the Nicola Group near i t s contact v i t h the Eagle complex. Boudined amphibolite layers lacking t o n a l i t e apophyses could be pre-, syn- or post-tonalite but are d e f i n i t e l y pre-deformation. Compositional uniformity and simple internal structure of many boudined layers suggest an o r i g i n as mafic dikes. The boudined marble layer, hovever, implies that thin layers of amphibolite could also be more highly strained metavolcanic layers. Mafic-rich augen-textured layers at many orthogneiss-amphibolite contacts and some orthogneiss-Fallslake suite contacts also suggests the p o s s i b i l i t y that some amphibolite layers are r e c r y s t a l l i z e d zones of s t r a i n concentration. Evidence for d u c t i l e f l o v in Eagle gneiss i s videspread and an o r i g i n for much i t s layering in d u c t i l e f l o v i s suggested. Most gneiss layers, though concordant, are mesoscopically discontinuous, suggesting that sub-parallel d u c t i l e f l o v has strung out or cut off ind i v i d u a l layers. Boudinaged marble and amphibolite layers, presumably deformed in a d u c t i l e matrix, suggest that orthogneiss MAP UNITS / 161 behaved p l a s t i c a l l y and was at elevated temperatures during deformation. VII. MIDDLE CRETACEOUS SEDIMENTARY ROCKS Dark grey, t h i n - to medium-bedded s i l t s t o n e and shale in the southwest corner of the study area on Vuich Creek yielded late Albian to Cenomanian (approximately 100 Ma to 90 Ma: middle Cretaceous) palynomorphs (G.E. Rouse, personal communication, 1987; Plate 2). Newly recognized Middle Eocene sedimentary rocks located along the west margin of the study area were previously assigned to the Upper Cretaceous Pasayten Group. Their presence indicates that the depositional and deformational history of the Pasayten trough continued into T e r t i a r y time. Sedimentary rocks underlying the eastern margin of the Pasayten trough that are along s t r i k e from the Middle Eocene section but outside the study area have also been assigned to the Upper Cretaceous Pasayten Group (Coates, 1970, 1974; Monger, 1970). F o s s i l control for the easternmost Pasayten Group, i s extremely poor, however (see Coates, 1974, figure 12, and O'Brien, 1987, figure 25 (p.74)). Therefore, i t i s possible that many rocks previously included in the Pasayten Group may in fact be of Middle Eocene age. The e a r l i e s t firmly established sedimentologic t i e across the Pasayten f a u l t i s provided by d i s t i n c t i v e Eagle complex cl a s t s (e.g. d u c t i l e l y strained f o l i a t e d muscovite-bearing granite) in Middle Eocene basal conglomerate that i s well-exposed in the v i c i n i t y of MAP UNITS / 162 Vuich, Jim Kelly, and Railroad creeks. An e a r l i e r sedimentologic t i e might be established i f the probable Late Cretaceous age of sedimentary rocks exposed on the lower part of Sutter Creek could be substantiated. These rocks, which l i e less than a kilometer west of the southwest corner of the study area, were studied by MacClean (1986). They are shown by her as being continuous with c l a s t i c rocks exposed on Vuich Creek. The rocks on Vuich Creek are of similar l i t h o l o g y and have yielded late Albian to Cenomanian (approximately 100 Ma to 90 Ma: middle Cretaceous) palynomorphs (G.E. Rouse, personal communication, 1987). MacClean (1986) notes that the Sutter Creek beds contain abundant d e t r i t a l muscovite (up to 30%), an obvious source of which i s nearby rocks of the F a l l s l a k e plutonic s u i t e . If the unit's age were established, i t would provide a firm middle Cretaceous t i e across the Pasayten f a u l t and confirm that the F a l l s l a k e suite and Eagle t o n a l i t e and gneiss were ra p i d l y unroofed in the middle Cretaceous. VIII. UNDIVIDED TERTIARY INTRUSIONS A. EOCENE STOCKS The contact between the Eagle complex and the Nicola Group to the east appears to have l o c a l i z e d T e r t i a r y intrusions. F e l s i c to intermediate post-tectonic porphyritic dykes, s i l l s and stocks and attendant b r i t t l e fracture, a l t e r a t i o n and mineralization are e s p e c i a l l y common near the contact. Four large, unfoliated Early Eocene stocks in the study area (Figure 4.1, Plate 1) occur along important Mesozoic structures, but are post-tectonic. MAP UNITS / 163 For example, the "Granite Porphyry" (Camsell, 1913) i s an elongate composite intrusion along the Eagle-Nicola contact. The post-tectonic, high-level porphyritic dykes are associated with copper-gold mineralization near their north end at the Independence mineral property. The Independence porphyry has a weakly trachytic porphyritic or seriate texture and contains strongly zoned plagioclase and d i s t i n c t i v e acicular amphibole. Similar porphyritic s i l l s and dikes, commonly associated with mineralization, occur to the south along the Eagle complex-Nicola Group contact. The early T e r t i a r y (W.J. McMillan, personal communication, 1986) Keystone stock in the Coldwater River Valley i s an unfoliated, equigranular, medium-grained, hornblende b i o t i t e quartz d i o r i t e which intrudes rocks of the Eagle complex. The stock i s crosscut by a multiple-phase, steeply-plunging, pipe-like intrusive breccia which hosts base and precious metal mineralization (Saleken, 1979). To the northwest, on the south side of J u l i e t Creek valley, the undated, poorly exposed but similar "Rover stock" also intrudes rocks of the Eagle complex. The I l l a l stock, which was Camsell's (1913) "type" Eagle "granodiorite," is another post-tectonic stock, which straddles the Eagle complex-Nicola Group contact at the confluence of Brit t o n (formerly Eagle) and I l l a l Creeks. The stock i s unfoliated, l i g h t grey to dark grey (along i t s margins), weakly porphyritic b i o t i t e hornblende granodiorite. It lacks the t y p i c a l planar fabric and primary epidote of the somewhat compositionally-similar Eagle MAP UNITS / 164 t o n a l i t e , and i s much less b l o t i t e - r i c h . At i t s west contact, i t intrudes gneissic Eagle t o n a l i t e and at i t s agmatitic east contact, i t contains randomly oriented blocks of schistose Nicola Group rocks (Figure 4.72). The I l l a l stock i s f i n e - to medium-grained, porphyritic and contains strongly zoned plagioclase. Unfoliated hornblende b i o t i t e quartz monzodiorite or granodiorite of the Tulameen " f a l l s " stock, occurs along the Pasayten f a u l t , where i t juxtaposes Eagle gneiss and the Zoa complex, on the Tulameen River, several hundred meters upstream from i t s confluence with Vuich Creek. The contact with Eagle gneiss i s covered, but the stock contains inclusions of gneiss (Figure 4.73). To the south, near the l i p of Tulameen " f a l l s , " the stock intrudes protomylonitic hornblende quartz d i o r i t e of the Zoa complex. The stock i s hypidiomorphic-granular and medium-grained, and contains strongly zoned a l b i t i c plagioclase, aggregates of polygranular quartz, minor microcline and mildly c h l o r i t i z e d and(or) epidotized b i o t i t e and hornblende. B . T E R T I A R Y D I K E S Numerous d i s t i n c t i v e dike suites intrude the Eagle complex. By far the most abundant are green, fine-grained, aphyric to plagioclase- and ac i c u l a r hornblende-phyric andesite(?) dikes up to 2 meters wide that trend north-northwest and dip steeply to the east (Figure 4.74, see also Chapter 7). The dikes may represent more than one magmatic event. However, the Middle Eocene isotopic date for hornblende from a dike in the central F a l l s l a k e Creek MAP UNITS / 165 Figure 4.72: Randomly oriented blocks of intensely f o l i a t e d Nicola Group rocks, agmatite at east margin of early T e r t i a r y I l l a l stock, Britton (Eagle) Creek. Figure 4.73: Inclusions of Eagle gneiss in unfoliated early T e r t i a r y Tulameen " f a l l s " stock, upper Tulameen River. F i g u r e 4 .74 : V i e v t o N N E o f N N E t r e n d i n g , s t e e p l y e a s t d i p p i n g a p h a n i t i c a n d e s i t e d i k e s , J u l y M t n . a r e a . MAP UNITS / 167 pluton, concordant with dates for the nearby Needle Peak pluton, suggests that the dikes may be part of an extensive Middle Eocene magmatic event (Chapter 5). S i l l s and subordinate dikes of hornblende feldspar porphyry tens of meters thick are common within Middle Eocene(?) c l a s t i c rocks, p a r t i c u l a r l y in the belt adjacent to the Needle Peak pluton (Figure 4.75). If the c l a s t i c rocks are Middle Eocene in age, then the s i l l s must be coeval because they and their host are intruded and hornfelsed by the Middle Eocene Needle Peak pluton. Middle Eocene(?) s i l l s were intruded by a suite of white to cream-coloured, i r r e g u l a r , columnar-jointed aphanitic to sparsely quartz- and(or) potassium feldspar-phyric r h y o l i t e dikes. Coarse-grained potassium feldspar phenocrysts in the r h y o l i t e and the dikes' s p a t i a l association with the Needle Peak pluton suggest they are cogenetic. However, meter-scale r h y o l i t e plugs occur throughout the study area and l o c a l l y crosscut the Middle Eocene green andesite dikes. The r h y o l i t e may be post-Middle Eocene age as well. In the Coquihalla River Valley several other suites of younger intrusions, which crosscut Eagle complex rocks, are exposed along road and r a i l cuts. Mauve, meter-scale columnar-jointed, b i o t i t e feldspar porphyritic r h y o l i t e dikes, prominent in several places along the abandoned Kettle Valley Railway grade, yielded an early Miocene isotopic date (Chapter 5) that is concordant with dates for the nearby Coquihalla volcanic complex (Berman 1979, Berman and Armstrong -1980) and Podunk Creek volcanics (Mathews et al., 1981). MAP UNITS / 168 Figure 4.75: S i l l s and dikes of Middle Eocene(?) hornblende feldspar porphyry ( l i g h t grey) intruding Middle Eocene (?) c l a s t i c rocks, Guanaco Peak. Large s i l l i s approximately 60 meters thick. MAP UNITS / 169 Figure 4.76: Meters-vide recessive veathering diabase dike cutting c e n t r a l F a l l s l a k e p l u t o n granodiorite; abandoned r a i l v a y grade, Coquihalla River v a l l e y . Arrow points to geologist s l i g h t l y above and to right of center. MAP UNITS / 170 A small set of recessively weathering diabase dikes trend northeasterly p a r a l l e l to the Coquihalla Valley f a u l t and reach thicknesses of 10 to 15 meters (Figure 4.76). The diabase i s undated, but intrudes the Middle Eocene green andesite dikes. Intrusive r e l a t i o n s with Early Miocene b i o t i t e feldspar r h y o l i t e porphyry were not observed, but the diabase i s t y p i c a l l y sheared and fractured whereas r h y o l i t e is not. The diabase i s l i k e l y post-middle Eocene but pre-early Miocene in age. Fine- to medium-grained plagioclase (labradorite) laths, o l i v i n e , magnetite, pyrite and deuteric(?) b i o t i t e in the dikes are surrounded by medium- to coarse-grained p o i k i l i t i c clinopyroxene grains. IX. MIDDLE EOCENE CLASTIC ROCKS A. INTRODUCTION AND SUMMARY Middle Eocene c l a s t i c rocks exposed along the west side of the study area, previously assigned to the Cretaceous (Cairnes, 1924b), are characterized by the presence of red to mauve, g r i t t y a r g i l l i t e and arenite. Grits are interbedded with more common dark grey a r g i l l i t e , subordinate pale grey-weathering s i l t s t o n e and sandstone, and rare conglomerate. Rocks from a good section along Vuich Creek yielded Middle Eocene palynomorphs (G.E. Rouse, personal communication, 1987; Plate 2). C l a s t i c rocks elsewhere in the study area lack f o s s i l control. To the north, c l a s t i c rocks are intruded by abundant s i l l s of hornblende feldspar porphyry and both are intruded to the west by the Middle Eocene Needle Peak pluton. To the southwest, middle MAP UNITS / 171 Cretaceous c l a s t i c rocks s t r u c t u r a l l y o v e r l i e the Middle Eocene c l a s t i c rocks (Chapter 7). To the east, Middle Eocene c l a s t i c rocks s t r a t i g r a p h i c a l l y and s t r u c t u r a l l y overlie the Late Jurassic and older Zoa complex along a gently to moderately southwest-dipping unconformity reactivated during east-vergent thrust f a u l t i n g (Chapter 7). Within the Middle Eocene c l a s t i c section, deformation i s manifest as f a u l t s and rare east-vergent t i g h t to open fol d s . B. LITHOLOGY AND COMPOSITION Dark grey medium- or thin-bedded and r a r e l y thick-bedded s i l t s t o n e , s i l t y mudstone and lesser fine sandstone make up the sequence of Middle Eocene c l a s t i c rocks. Adjacent to the Needle Peak pluton, medium-grained porphyroblasts of andalusite and co r d i e r i t e are developed (Figure 4.77). Dark grey a r g i l l i t e i s interbedded with mauve to red g r i t t y arenite and a r g i l l i t e which not only characterize the section in the study area but may also d i s t i n g u i s h T e r t i a r y from pre-Tertiary c l a s t i c rocks to the vest. M G r i t s " are commonly thick-bedded and poorly-sorted, v i t h angular to rounded g r a n i t i c c l a s t s in a f i n e r -grained matrix (Figure 4.78). Subordinate pale mauve, buff or l i g h t green g r i t t y a r g i l l i t e , l o c a l red thin-bedded g r i t t y s i l t s t o n e (Figure 4^79) and coarse conglomerate v i t h a mauve g r i t matrix (Figure 4.80) also occur. Conglomerate, most common in the s t r u c t u r a l l y and s t r a t i g r a p h i c a l l y lowest part of the sequence, i s very poorly MAP UNITS / 172 Figure 4.77: Andalusite ( c h i a s t o l i t e ) and c o r d i e r i t e porphyroblasts in Middle Eocene(?) c l a s t i c rocks, contact aureole of Needle Peak pluton, Nak Peak; crossed p o l a r i z e r s , width of f i e l d of viev 6 mn. Figure 4.78: Conglomeratic " g r i t M v i t h angular and subangular g r a n i t i c c l a s t s , Nak Peak. MAP UNITS / 173 Figure 4.79: Middle Eocene t h i n - to medium-bedded g r i t t y s i l t s t o n e , Vuich Creek. Figure 4.80: Middle Eocene coarse conglomerate, with rounded g r a n i t i c c l a s t s in mauve g r i t matrix, Vuich Creek. MAP UNITS / 174 Figure 4.81: Pod-shaped bodies of c a l c - s i l i c a t e (contact metamorphosed calcareous concretions) in pale grey weathering Middle Eocene (?) s i l t s t o n e , Nak Peak; hammer l i e s on bedding plane. MAP UNITS / 175 sorted and contains rounded to angular c l a s t s that reach 0.5 meter in s i z e . Conglomerate c l a s t s are dominantly f o l i a t e d muscovite-bearing granodiorite, quartz d i o r i t e and gneiss. Buff to pale grey weathering medium- to thick-bedded poorly sorted muscovite-rich sandstone i s less common. Medium- to thick-bedded pale grey weathering s i l t s t o n e or fine sandstone containing unusual pod-shaped bodies of c a l c - s i l i c a t e only occurs along the east margin of the Needle Peak pluton. C a l c - s i l i c a t e pods are crudely e l l i p t i c a l , up to 1 meter long and several tens of centimeters thick, and are concordant with bedding planes (Figure 4.81). Their shape, mineralogy, and concordance with bedding suggest that they may be contact metamorphosed calcareous concretions. X . N E E D L E P E A K P L U T O N The Needle Peak pluton (Monger, 1970) of Eocene (40 Ma; Wanless et a l . , 1967), not Cretaceous (Cairnes, 1924b) age underlies granitoid mountains along the west-central margin of the map-area (Figure 4.82, Figure 4.1, Plate 1). The smooth surfaces and well-developed e x f o l i a t i o n j o i n t s are d i s t i n c t i v e . The pluton consists of massive, l i g h t grey, medium to coarse-grained b i o t i t e hornblende monzogranite that commonly contains euhedral, pinkish potassium feldspar phenocrysts (Figures 4.83 and 4.84). Scattered coarse-grained p e r t h i t i c potassium feldspar and intensely zoned plagioclase (Ani5 to An20) occur in a medium-grained groundmass containing undulose quartz, hornblende, b i o t i t e , feldspar and fine-grained accessory t i t a n i t e , opaques, apatite and MAP UNITS / 176 Figure 4.82: View west from study area to Alpaca and Steinbok peaks, u n d e r l a i n by middle Eocene monzogranite of the Needle Peak pluton. MAP UNITS / 177 Figure 4.83: Medium- to coarse-grained monzogranite of the middle Eocene Needle Peak pluton, Highvay 5. MAP UNITS / 178 Figure 4.84: Stained specimen of medium- t o c o a r s e - g r a i n e d monzogranite of the middle Eocene Needle Peak pluton, shoving megacrystic potassium feldspar grains; Highvay 5 . MAP UNITS / 179 Figure 4.85: Fine-grained c h i l l margin of Needle Peak pluton at contact v i t h Middle Eocene (?) sedimentary rocks, Zum Peak. MAP UNITS / 180 zircon. Internal features of the Needle Peak pluton were not mapped in t h i s study. Along i t s east and northeast contacts, the Needle Peak pluton intrudes (Figure 4.85) and metamorphoses Middle Eocene(?) c l a s t i c rocks. A l k a l i feldspar-phyric f e l s i c dikes, l i k e l y related to the Needle Peak pluton, commonly intrude c l a s t i c rocks near the pluton's contact. Along i t s southeast contact, the Needle Peak pluton intrudes narrow pendants of Zoa complex metavolcanic and c l a s t i c rocks. It is juxtaposed with older hornblende quartz d i o r i t e of the Zoa complex and muscovite b i o t i t e granodiorite of the central F a l l s l a k e pluton and possibly with p y r o c l a s t i c and r h y o l i t i c rocks of the Coquihalla volcanic complex rocks along the Coquihalla Valley f a u l t . XI. COQUIHALLA VOLCANIC COMPLEX The Miocene Coquihalla volcanic complex (Berman, 1979; Berman and Armstrong, 1980) underlies Coquihalla Mountain and the ridges radiating outward from i t (Plate 1). It consists of undeformed ca l c - a l k a l i n e f e l s i c to intermediate extrusive and intrusive rocks of which pale-weathering, flaggy, r h y o l i t i c p y r o c l a s t i c rocks are the most extensive. Pyroclastic rocks nonconformably overlie rocks of the Eagle complex and are intruded by andesitic to d a c i t i c domes, dykes and s i l l s , and by a late quartz d i o r i t e stock which forms the core of Coquihalla Mountain (Figure 4.86, Figure 4.1). Concordant K-Ar and Rb-Sr isotopic dates of 23 Ma for rocks from the Coquihalla complex indicate an e a r l i e s t Miocene age. MAP UNITS / 181 Figure 4 .86 : Viev to north of early Miocene Coquihalla volcanic complex, v i t h Coquihalla Mtn. composite stock on l e f t , volcanic dome on r i g h t , volcanic rocks in foreground. MAP UNITS / 182 In t h i s study, rocks of early Miocene or probable early Miocene age were recognized beyond the Coquihalla volcanic complex defined by Berman (1979). On the lower slopes of the northeast bank of Unknown Creek, tuffaceous rocks of the complex are overlain or intruded by well-jointed massive r h y o l i t e . These rocks confirm Cairnes* (1924b) placement of the contact between early Miocene and older rocks and indicate that early Miocene extrusive rocks occur in place near the f l o o r of the Coquihalla v a l l e y . An o u t l i e r of d i s t i n c t i v e flaggy l i t h i c t u f f occurs near exposures of muscovite-bear ing rocks of the F a l l s l a k e plutonic suite on the ridge between McGee and I l l a l creeks. These l o c a l i t i e s suggest that the Coquihalla volcanic f i e l d may have been deposited on a surface with considerable r e l i e f , possibly recently exhumed. Numerous intrusions s i m i l a r to those found within the bounds of the Coquihalla volcanic complex were also recognized during mapping of the surrounding area. Early Miocene isotopic dates were determined for a hornblende feldspar porphyry plug on the ridge overlooking B r i t t o n Creek approximately 4 kilometers west of Murphy Lakes and for a b i o t i t e feldspar porphyry dike in the Coquihalla River Valley (Chapter 5 ) . GEOCHRONOMETRY / 183 CHAPTER 5: GEOCHRONOMETRY I . INTRODUCTION Uranium-lead, potassium-argon and rubidium-strontium dating were undertaken to determine the age of emplacement and cooling of the main plutonic rock units i n the study area and to constrain the timing of deformation a f f e c t i n g rocks along the westernmost margin of the Intermontane Belt. Six U-Pb zircon dates, one U-Pb monazite date, twenty-nine K-Ar mineral dates, and one conventional K-Ar whole rock date were determined. Rubidium and strontium 87 86 content and Sr/ Sr r a t i o were analyzed for eighteen whole rock samples and eighteen mineral separates and twenty-two Rb-Sr dates were calculated from the analyses. A l l the U-Pb dates and a l l but eleven K-Ar dates and fi v e Rb-Sr dates were determined for rocks of the Eagle complex proper. Two K-Ar dates and two Rb-Sr dates were determined for metamorphosed Nicola Group rocks and the remainder of the dates were determined for Te r t i a r y intrusions. Sample locations are shown on Plate 2, and on si m p l i f i e d geological maps that accompany discussion of the re s u l t s (Figures 5.1, 5.10 and 5.14). Data are summarized i n Tables 5.1, 5.II, 5 . I l l , 5.IV, 5.V and 5.VI. Complete a n a l y t i c a l r e s u l t s are given for individual samples on data sheets in Appendix 5.1. An a l y t i c a l procedures are b r i e f l y outlined in Appendix 5.II. GEOCHRONOMETRY / 184 I I . U-PB DATING, ANALYTICAL RESULTS AND INTERPRETATIONS Five samples from the Eagle plutonic complex in the study area were selected for U-Pb dating: two from Eagle t o n a l i t e , one from the central F a l l s l a k e pluton, one from hornblende quartz d i o r i t e of the Zoa complex, and one from t o n a l i t e orthogneiss of the Eagle gneiss (Figure 5.1). One sample of Eagle t o n a l i t e from the Hope-Princeton highway (Highway 3; see Figure 3.1) was also dated. Twenty-one zircon and two monazite fractions were analyzed. Uranium-lead data are plotted on 2 0 6Pb/ 2 3 8U vs. 2 0 7Pb/ 2 3 5U concordia diagrams (Wetherill, 1956), which were plotted using an HP plotter driven by software written by Ludwig (1983) and modified for an HP 9845 computer. Uranium-lead dates are stated with 2 sigma errors (95% confidence l e v e l ) . Closure temperatures for zircon and monazite to d i f f u s i o n of radiogenic Pb are reported by Parrish and Roddick (198 5) to be more than 800 °C and more than 600 °C, respectively. A . ZOA COMPLEX Weakly f o l i a t e d hornblende quartz d i o r i t e (sample 1002) from the northern belt of the Zoa complex was coll e c t e d for U-Pb dating from the base of Thar Peak on the natural gas pipeline road that runs upslope of and p a r a l l e l to Highway 5 (Figure 5.1, Plate 2). Less than 0.5 kilometer to the southwest of the sample s i t e , quartz d i o r i t e intrudes metavolcanic rocks of the Zoa complex and within several hundred meters to the southeast, the Dry Gulch-Coquihalla GEOCHRONOMETRY / 185 Table 5.1: U-Pb ANALYTICAL DATA, EAGLE PLUTONIC COMPLEX. Saarjle* Ht U Pb^ Isotonic abundance3 6/4"* Isotogic r a t i o s1 3 +/- 2 sigaa errors f r a c t i o n6 1' 208 207 204 Dates (Ha)* +/- 2 sigaa errors " t i l : ? |AGLL§N§ISS +74-149 22.7 501 10.0 5.62 4.93 0.0024 11410 0.02099+/-18 0.14178+/-127 0.04898+/-7 NH 133.9+/-1.2 134.6+/-1-2 147. U/-3.3 +44-74 30.6 654 13.4 6.81 4.94 0.0021 7160 0.02138+/-19 0.14469+/-i30 0.04909+/-7 (1 136.4+/-1.2 137.2+/-1.2 152.3+/-3.4 +74-149 10.6 552 11.8 6.52 4.97 0.0059 12572 0.02219+/-8 0.14930+/-6 0.04BB2+/-6 NM ABR 141.5+/-0.5 141.3+/-0.5 139.1+/-2.7 1221 EASLE_T0NALIIE +74-149 10.4 597 14.6 10.40 7.33 0.1653 600 0.02337+/-28 0.15800+/-270 0.04903+/-57 NIC.1/1 148.9+/-1.8 148.9+/-2.4 149.3+/-27.5 +44-74 7.9 554 11.7 5.57 5.38 0.0314 2940 0.02208+/-8 0.14960+/-60 0.04915+/-9 NM2.1/1 140.8+/-0.5 141.6+/-0.5 155.0+/-4.1 +74-149 1.9 623 13.4 5.46 5.22 0.0206 3057 0.02256+/-5 0.15300+/-30 0.04919+/-5 NH2.1/1 ABR 143.8+/-0.3 144.6+/-0.3 157.0+/-2.6 997 +44-74 7.2 644 14.3 6.60 5.09 0.0114 7274 0.02303+/-8 0.15620+/-50 0.04920+/-3 NH2.1/1 146.8+/-1.0 147.4+/-1.0 157.4+/-3.2 +74-149 3.9 627 14.1 6.20 5.05 0.0094 6630 0.02336+/-5 0.15830+/-60 0.04914+/-16 NH2.1/1 ABR 148.9+/-0.6 149.2+/-1.0 154.7+/-15 1002 IQA_CQttPLEX_HORNBLENDE_QUA +74-149 3.9 207 4.9 13.57 5.30 0.0255 3159 0.02286+7-33 0.15520+/-240 0.04922+/-28 NH2.1/1 145.7+/-2.1 146.5+/-2.1 158.4+/-13.2 +74-149 23.7 201 4.8 15.65 6.23 0.0913 1059 0.02216+/-15 0.14910+/-22 0.04881+/-59 NH2.1/1 ABR 141.3+/-1.0 141.1+/-1.9 13B.9+/-28.6 +44-74 1.5 221 5.0 14.39 5.34 0.0296 2217 0.02193+/-16 0.14840+/-110 0.04907+/-14 H1.5/3,NHl/5 139.8+/-1.0 140.5+/-1.0 151.4+/-6.6 86-1 lONALITEiJOPEiPRINCEIOLHISHHAY (HHY._3) -74+44 9.2 286 5.1 7.11 5.43 0.0406 2112 0.01822+/-6 0.1214+/-4 0.04833+/-9 NH2.1/1 116.4+/-0.4 116.4+/-0.4 115.4+/-4.4 +74-149 11.0 171 3.1 6.76 5.21 0.0240 3007 0.01862+/-6 0.1248+/-4 0.04860+/-7 NH2.1/1 118.9+/-0.3 119.4+/-0.4 128.6+/-3.3 +74-149 2.9 187 3.4 9.24 5.43 0.0395 1401 0.0184B+/-3 0.1236+/-3 0.04852+/-9 NH2.1/1 ABR 118.0+/-0.2 118.3+/-0.3 124.5+/-4.1 Complete analytical data, including aeasured ^'cx?b/::x>,*?b errors, aole I blank Pb and Pb^ /tPb^ +Pb,...-,,,,,^ ,,) rat i o s , assuaed coaaon Pb ages (froa the curve of Stacey and Kraaers, 1975), and correlation coefficients for Pb/U rat i o s , are recorded on UBC Canadian Cordillera Geochronoaetry F i l e lab sheets in Appendix 5.1 of the thesis. Radiogenic + coaaon Pb. Radiogenic + coaaon Pb, corrected for 0.15X/aau fractionation and for 60-250 pg Pb blank with coaposition 208:207:206:204 = 37.0+/-0.75:15.50+/-0.34:17.75+/-0.19:1. "Measured 2 0 Rb/: 2 0 ,'*Pb corrected for 0.15X anu fractionation. ^Corrected for fractionation (0.121/aau for U, 0.151/aau for Pb), for blank Pb (see note 3 above), and for coaaon Pb using the growth curve of Stacey and Kraaers (1975); errors are 2 sigaa, and only the last digits are shown. &+74-149 = size range in a; II, NH = aagnetic, non-sagnetic on Frantz isodynaaic separator at indicated aaperage and side t i l t (e.g., 2.1/1 = 2.1 aaps at 1° side t i l t ) ; ABR = abraded. ^Decay constants used in calculations of dates: 3 3 0U = 1.55125xl0"~10, : 2 3 =U = 9.8485xl0~x o; ' " ^ d / 2 3 5 ^ = 137.88 (Steiger and Jager, 1977). Errors are 2 sigaa. GEOCHRONOMETRY / 186 - 4 9 M 5 ' TERTIARY M I O C E N E C O Q U I H A L L A V O L C A N I C M c v C O M P L E X E O C E N E Emg N E E D L E P E A K P L U T O N Es MIDDLE E O C E N E S E D I M E N T A R Y R O C K S UNDIVIDED INTRUSIVE R O C K S mKs mKg Lit CRETACEOUS M I D - C R E T A C E O U S SEOIMENTARY R O C K S E A R L Y C R E T A C E O U S F A L L S L A K E PLUTONIC SUITE JURASSIC AND CRETACEOUS L J m K g r E A G L E GNEISS L A T t I U R A S S I C E A G L E TONALITE L A T E J U R A S S I C A N D O L D E R I LIZ | Z O A C O M P L E X TRIASSIC U P P E R T R I A S S I C | TrN | NICOLA G R O U P y Geological contact -1 _ ' High angle fault ^ -*~ Thrust lault Figure 5.1: Simplified geology, Coquihalla area, showing U-Pb dates. GEOCHRONOMETRY / 187 fa u l t system juxtaposes Zoa complex rocks with the central F a l l s l a k e pluton. Three zircon fractions were separated from sample 1002. Stubby e l l i p t i c a l forms predominate (roughly 60%) over short to long prismatic forms. Zircons are c h i e f l y colourless, but very pale yellowish grains were also noted. The three zircon fractions from sample 1002 plot on concordia with overlapping, but very large, error envelopes (Figure 5.2). The d i s t r i b u t i o n of the unabraded f r a c t i o n s , with the fine f r a c t i o n overlapping in a n a l y t i c a l error with the coarse f r a c t i o n but p l o t t i n g s l i g h t l y down the chord, suggests lead l o s s . A mid-Cretaceous K-Ar hornblende date from t h i s sample, interpreted as reset (see below) might be coeval with an episode of lead loss. However, a f t e r abrasion, the re-analyzed coarse f r a c t i o n plotted closer to the fine f r a c t i o n , suggesting that large errors on the o r i g i n a l analysis may overemphasize the contribution of lead l o s s . Since a t i g h t l y constrained chord w i l l not f i t through the large error envelopes of the three points, a minimum age for t h i s sample of 153 + 10 Ma was calculated by assuming recent lead loss and f i t t i n g a chord through the points and the o r i g i n . B . EAGLE TONALITE AND GNEISS Zircon grains from three samples of Eagle t o n a l i t e and gneiss in the Coquihalla area were dated. The f i r s t sample dated, MV-83-9, was coll e c t e d in 1983 by P. van der Heyden and J.W.H. Monger. Two zircon fractions from t h i s sample yielded a 135 Ma date GEOCHRONOMETRY / 188 0.0255 0.0245|-0.0235 D CD cn (VI \ 0.0225 -Q D_ CO ° 0.0215 0.0205 0.0195 EHGLE PLUTONIC COMPLEX ZOfl HB QZ DIORITE THAR PERK P I P E L I N E MVG-8B-1002 1 5 4 0.135 74-149,NM +74-149.NH RBR ERRORS RRE 2 SIGMA -L _L 0.145 0.155 0.165 207P b /235u 0. 175 Figure 5.2: U-Pb concordia diagram for zircons from sample 1002, Zoa complex, Thar Peak pipeline. GEOCHRONOMETRY / 189 reported in Monger (1985). In thi s study, a t h i r d f r a c t i o n from sample MV-83-9 was analyzed and the date reinterpreted. Two other samples of Eagle t o n a l i t e and gneiss, 1001 and 997, were coll e c t e d and processed for t h i s study. Sample MV-83-9 consists of epidote hornblende b i o t i t e t o n a l i t e orthogneiss from approximately 0.5 kilometer upstream of Dry Gulch in the v a l l e y of the Coquihalla River (Figure 5.1, Plate 2). The orthogneiss was interlayered with subordinate amphibolite and rare marble and c a l c - s i l i c a t e . Two l i g h t l y abraded zircon fractions were o r i g i n a l l y dated and a 135 Ma date (without errors) was reported i n Monger (1985). In th i s study, remaining material from the coarser of the two fractions was reprocessed, more heavily abraded and reanalyzed. Zircons are clea r , colourless to very pale pink euhedral prisms. Greater than 50% of grains i n the fine f r a c t i o n but less than 5% of grains in the coarse f r a c t i o n contain small opaque inclusions. Results of analyses from both studies are shown on the concordia plot in Figure 5.3. The fact that reanalysis of the more highly abraded coarse f r a c t i o n plots both on and farther up concordia than the o r i g i n a l analysis implies that the sample has undergone grain boundary lead l o s s . Accordingly, a minimum date of 148 +/- 6 Ma was calculated by assuming recent lead loss and f i t t i n g a chord through the analyzed points and the o r i g i n . This date i s within error of the Pb-Pb dates for a l l three f r a c t i o n s . Sample 1001 consists of s l i g h t l y gneissic epidote hornblende b i o t i t e t o n a l i t e c o l l e c t e d from outcrops on the west side of the Upper Coldwater e x i t ramp on Highway 5 (Figure 5.1, Plate 2). GEOCHRONOMETRY / 190 0.024 0.019 6.132 0.136 0.140 0.144 0.148 0.152 0.1S6 0.160 2 0 7 P b / 2 3 5 u Figure 5.3: U-Pb concordia diagram for zircons from sample MV-83-9, Eagle gneiss, Coquihalla canyon. GEOCHRONOMETRY / 191 Eagle t o n a l i t e i n t h i s area varies from w e l l - f o l i a t e d , to s i g h t l y gneissic to l o c a l l y unfoliated but lineated v a r i e t i e s . S l i g h t l y to the southwest of the c o l l e c t i o n l o c a l i t y , t o n a l i t e intrudes meter-scale concordant screens of amphibolite. Folded t o n a l i t e apophyses in the screens indicate that t o n a l i t e and amphibolite have been deformed together following intrusion. Three zircon fractions from sample 1001 were dated. Zircons from both coarse and fine fractions are commonly colourless to very pale yellow, euhedral to subhedral and prismatic in form. Lesser stubby e l l i p t i c a l forms, commonly pale yellow in colour, are also present. Terminations on zircon grains are t y p i c a l l y not well-developed. Colourless bubble-shaped inclusions are common, opaque inclusions are rare, and s l i g h t l y cloudy core regions occur in some of the e l l i p t i c a l grains. Results from the analysis of the three fractions are shown in Figure 5.4. The position farther up concordia of the unabraded coarse f r a c t i o n r e l a t i v e to i t s abraded counterpart suggests that lead loss was r e l a t i v e l y unimportant in t h i s sample. Also, the degree of discordance of the fractions shows no co r r e l a t i o n with measured uranium content, suggesting further that lead loss may unimportant. Unfortunately, errors for t h i s point (+74-149, NM, see Figure 5.4) are large r e l a t i v e to errors for the other points, so the sig n i f i c a n c e of t h i s point i s uncertain. A minimum date based on the upper intercept of a chord f i t through the o r i g i n and the three points i s 156 +_ 4 Ma. Potassium-argon and Rb-Sr dating SEOCHRONDMETRY / 192 0.0255 i • i ERGLE PLUTONIC COMPLEX i5e ERGLE TONRLITE 0.0245 COLDWATER EXIT RRMP MVG-86-1001 J^l^ 0.0235 +74-149.NM 03 m CVJ \ 0.0225 Ji Q. 74-149,NM HBR ^ F ^ / +44-74, NM U) S 0.0215 138 134-< 0.0205 ERRORS RRE 2 SIGMA 0.0195 0. I . I . • 135 0.145 0.155 0. 207p b /235y 165 0. 175 F i g u r e 5.4.: U-•Pb c o n c o r d i a d i a g r a m f o r z i r c o n s f r o m s a m p l e 1 0 0 1 , E a g l e t o n a l i t e , C o l d w a t e r e x i t r a m p , Hwy. 5 . GEOCHRONOMETRY / 193 of sample 1001 indicates that in early Eocene time complete reset t i n g of these isotopic systems occurred in b i o t i t e whereas p a r t i a l resetting occurred in hornblende. Sample 997 consists of f o l i a t e d epidote hornblende b i o t i t e t o n a l i t e that was collected approximately 1 kilometer northwest of Murphy Lakes (Figure 5.1, Plate 2). Less than a kilometer to the northeast, Eagle t o n a l i t e intrudes and i s deformed with rocks of the Upper T r i a s s i c Nicola Group. Two zircon f r a c t i o n s , a coarse abraded f r a c t i o n and a fine unabraded f r a c t i o n , were analyzed (Figure 5.5). Zircon grains from both fractions are colourless to very pale yellow. Most are prismatic and euhedral but have poorly formed terminations. E l l i p t i c a l zircons are present in both fractions but are uncommon, and less than 10% of the grains contain colourless or opaque inclusions or have cloudy or cracked core regions. Based on a chord passing through the o r i g i n and the two points and interpreted to model a recent lead loss t r a j e c t o r y , a minimum age i s 157 + 4 Ma. Sample 997 has yielded a 130 + 4 Ma K-Ar hornblende date, a 108 + 4 Ma K-Ar b i o t i t e date and a 110.5 + 3.4 Ma Rb-Sr epidote-biotite-whole rock isochron date. Figure 5.6 i s a composite concordia plot including a l l eight points from samples of Eagle t o n a l i t e and gneiss in the Coquihalla area. A chord was f i t t e d to the eight points in an attempt to est a b l i s h a better minimum age for the s u i t e . It i s assumed that the bodies sampled were comagmatic because a l l three bodies contain d i s t i n c t i v e primary epidote, are otherwise similar GEOCHRONOMETRY / 194 0.025h 0.021 0.146 0.130 0.154 0.158 0.162 0.166 0.170 2 0 7 P b / 2 3 5 u F i g u r e 5 . 5 : U-Pb c o n c o r d i a d i a g r a m f o r z i r c o n s f r o m s a m p l e 9 9 7 , E a g l e t o n a l i t e , M u r p h y L a k e s . GEOCHRONOMETRY / 195 0.0243 0.0235 ZD CD 0.0225 cn CVI \ JQ to" 0.0213 O CM 0.0203 0.0193 EAGLE PLUTONIC COMPLEX ERGLE TONHLITE RND GNEISS COQUIHRLLR-TULRMEEN RRER i ecu ERGLE GNEISS (83-9), ERGLE TONALITE (997,1001) J L . ERRORS ARE 2 SIGMA X 0.136 0.140 0.144 0.148 0.152 0.156 0.160 0.164 2 0 7 P b / 2 3 5 u Figure 5.6.: U-Pb concordia diagram for zircons from samples 997, 1001 and MV-83-9, Eagle t o n a l i t e and gneiss, Coquihalla area. GEOCHRONOMETRY / 196 petrographically and compositionally, and do not display cross-cutting intrusive r e l a t i o n s . Discordance in K-Ar and Rb-Sr mineral dates for Eagle t o n a l i t e and gneiss demands a multi-stage thermal history and suggests r e l a t i v e l y complex lead loss, despite the lack of c o r r e l a t i o n in zircon fractions between measured uranium content and degree of discordance. The upper intercept of the chord, interpreted as the maximum age of emplacement of t o n a l i t i c rocks of the suit e , i s 168 +26/-16 Ma. The lower intercept, which could represent the time of lead loss or which could have no geological significance (Parrish and Roddick, 1985), i s 79 +44/-54 Ma. Errors on the intercepts are large because the chord has a shallow intersection with concordia in the age range for Mesozoic rocks. A more precise upper intercept i s obtained by forcing the discordia through the o r i g i n . This y i e l d s a minimum date for emplacement at 155 + 4 Ma, which i s within error of the minimum dates calculated for each in d i v i d u a l sample above. Sample 86-1 consists of f o l i a t e d hornblende b i o t i t e t o n a l i t e that was co l l e c t e d from a roadcut through Eagle t o n a l i t e on the Hope-Princeton highway (Highway 3) approximately 1 kilometer southwest of Goodfellow Creek in Manning Park. In the Manning Park area intrusive and s t r u c t u r a l r e l a t i o n s between the Eagle complex and the Upper T r i a s s i c Nicola Group to the east resemble those in the Coquihalla area. Three zircon fractions from sample 86-1 were analyzed (Figure 5.7). E l l i p t i c a l zircons predominate over prismatic GEOCHRONOMETRY / 197 0.0205 • i ' i • i • i ' i • y 0.0135 ERGLE PLUTONIC COMPLEX ERGLE TONALITE / HOPE-PRINCETON HHY. MVG-BB-l CO cn ru \ 0 .0185 -Q Q_ CO o CU >^+?4-14S.NM 1 1 8 ^ 0 ^ ^ » / * ^ 7 4 - l 4 9 , N M RBR »-44-74,Nr1 U 4 - / 0 .0175 ERRORS RRE 2 SIGMR O.OlgS i . i . i . i i 114 0 .118 0 .122 0 .126 0 . 1 3 0 0 .134 0 . 207 P b / 235u 138 F i g u r e 5 . 7 : U - P b c o n c o r d i a d i a g r a m f o r z i r c o n s f r o m s a m p l e 8 6 - 1 , E a g l e t o n a l i t e , H o p e - P r i n c e t o n H i g h w a y . GEOCHRONOMETRY / 198 zircons in sample 86-1, whereas in samples from the Coquihalla area, prismatic forms predominated over e l l i p t i c a l forms. Less than 5% of the grains contain colourless or opaque inclusions and less than 1% contain cloudy core regions. A minimum date based on the upper intercept of a chord f i t through the or i g i n and the three points i s 123 +_ 5 Ma. Sample 86-1 has also yielded a 110 + 4 Ma K-Ar hornblende date and a 107 + 4 Ma K-Ar b i o t i t e date (R.L. Armstrong, unpublished data). C. FALLSLAKE PLUTONIC SUITE Sample 1003 was the only sample from the F a l l s l a k e plutonic suite dated by U-Pb methods. The sample l o c a l i t y i s approximately 100 meters northwest of the F a l l s l a k e exit ramp on Highvay 5, i n unfoliated to weakly f o l i a t e d muscovite b i o t i t e granodiorite of the central F a l l s l a k e pluton (Figure 5.1, Plate 2). The central F a l l s l a k e pluton intrudes Eagle gneiss less than a kilometer to the northeast and i s juxtaposed against rocks of the Zoa complex along the Dry Gulch-Coquihalla f a u l t less than a kilometer to the northvest. Nine mineral fractions from t h i s sample vere successfully analyzed. Unfortunately, data for four add i t i o n a l fractions are meaningless, and are not reported here, because zircon in these fracti o n s vas not f u l l y dissolved during chemistry. Although i t vas assumed i n i t i a l l y that the fractions vere comprised e n t i r e l y of zircon, l a t e r SEM vork revealed that the four fractions vere GEOCHRONOMETRY / 199 Table 5 . 1 1 : U-Pb ANALYTICAL DATA, FALLSLAKE PLUTONIC SUITE Saagle 1 kit U Pb""1 Isotopk abundance3 6/4** Isotopk ratios 5 5 +/- 2 sigaa errors fraction 6" 208 207 204 Dates (Ha)7" +/- 2 sigaa errors QiNTRAL_FALLSLAKE_PLUTON 1203 +74-149 2.7 441 8.1 5.88 5.14 0.0158 4801 0.01926+/-14 0.1303+/-10 0.04909+/-9 NH2.1/1 CORES 123.0+/-0.9 124.4+/-0.9 152.0+/-4.3 +74-149 NH 2.6 363 6.4 5.99 4.99 0.0075 7135 0.01853+/-16 0.1247+/-11 0.04882+/-7 2/1 W/0 CORES 118.3+/-1.0 119.3+/-1.0 139.3+/-3.1 +44-74 22.7 543 11.7 8.83 5.99 0.0736 1334 0.02153+/-13 0.1456+/-10 0.04905+/-17 NM+H 137.3+/-0.8 13B.1+/-0.9 150.3+/-8.1 +74-149 NN 4.6 481 9.9 6.38 5.34 0.0284 2B35 0.02123+/-4 0.1442+/-3 0.04927+/-4 2.1/1 ABR 135.4+/-0.3 136.8+/-0.3 160.6+/-1.7 +74-149 M2.1/1 2.0 596 12.9 7.59 5.98 0.0697 1219 0.02184+/-7 0.1492+/-6 0.04956+/-8 NM1.5/3 ABR 139.3+/-0.5 141.2+/-0.5 174.2+/-4.0 +44-74 0.1 401 10.3 25.29 6.99 0.1409 215 0.02188+/-4 0.14B4+/-2B 0.04921+/-30 NN2.1/1 ABR 139.5+/-0.3 140.5+/-2.5 158+/-43 +44-74 M2.1/1 1.0 684 14.4 8.35 5.57 0.0436 1410 0.0212B+/-4 0.1448+/-4 0.04934+/-7 NH1.5/3 ABR 135.8+/-0.3 137.3+/-0.3 163.9+/-3.5 H0NAZ.+74-149 0.3 748 94.5 71.6 5.46 0.0480 784 0.01759+/-7 0.1154+/-7 0.04757+/-22 NN0.5/10,Hl/5 112.4+/-0.5 110.9+/-0.6 7B+/-11 M0NAZ.+74-149 0.3 844 135.3 72.1 21.33 1.1335 83 0.01731+/-5 0.1094+/-27 0.04585+/-104 NH0.5/10,Ml/5 110.6+/-0.3 105.4+/-2.5 -10+/-56 ACoaplete analytical data, including aeasured ' ^ ^ b l ^ ^ b errors, sole I blank Pb and P b ^ P b ^ + P b . ^ , ^ , } ratios, assuaed coaaon Pb ages (froa the curve of Stacey and Kraaers, 1975), and correlation coefficients for Pb/U ratios, are recorded on UBC Canadian Cordillera Geochronooetry F i l e lab sheets in Appendix 5.1 of the thesis. Radiogenic + coaaon Pb. Radiogenic + coaaon Pb, corrected for 0.157./aau fractionation and for 60-250 pg Pb blank with composition 208:207:206:204 = 37.0+/-0.75:15.50+/-0.34:17.75+/-0.19:1. "Measured :eo6T)b/::20*Pb corrected for 0.157. aau fractionation. "^Corrected for fractionation (0.12X/aau for U, 0.151/aau for Pb), for blank Pb (see note 3 above), and for coaaon Pb using the growth curve of Stacey and Kraaers (1975); errors are 2 sigaa, and only the last digits are shown. &+74-149 = size range in a; M, NM = aagnetic, non-aagnetic on Frantz isodynaaic separator at indicated aoperage and side t i l t (e.g., 2.1/1 - 2.1 aaps at l " side t i l t ) ; ABR = abraded. "Decay constants used in calculations of dates: : e 3 e U = 1.55125xl0~10, = 9.8485x10 Staaa/S3es\} = 137.88 (Steiger and Jager, 1977). Errors are 2 sigma. GEOCHRONOMETRY / 200 a c t u a l l y composed of mixed zircon and monazite. Seven zircon and two monazite fractions provided useful data. A l l zircon fractions from sample 1003 contain microscopic evidence for xenocrystic cores. Although many grains are transparent and appear to have undergone a single stage growth history, cores of the majority of grains are cloudy, i n c l u s i o n - r i c h , or more densely fractured than rims. In many grains, the boundary between core and rim i s d i s t i n c t . Most grains are prismatic (aspect r a t i o 3:1 to >20:1); subordinate e l l i p t i c a l grains are present. There i s no c o r r e l a t i o n between grain morphology and microscopic evidence of inheritance. Monazite, common in the more magnetic f r a c t i o n s , occurs as very pale yellow, stubby, poorly-formed prisms with a tabular to blocky habit. Prism faces on monazite grains vere neither as sharp nor as well terminated as on zircon grains and permitted d i s t i n c t i o n of the two mineral species. Dirty, orange-coloured inclusions and (or) oxide (?) fracture coatings were present in 30 to 40% of the grains and the same grains were commonly cloudy. Transparent monazite grains commonly contain colourless bubble-shaped inclusions. Data for the seven pure zircon and two pure monazite fractions from sample 1003 are plotted on concordia diagrams in Figures 5.8 and 5.9. The spread in data points indicates that U-Pb systematics in the central F a l l s l a k e pluton are complex. Petrographic evidence for abundant xenocryst cores in a l l zircon fractions suggest the spread in U-Pb data for zircon fractions i s due to inheritance of an older Pb component. The two unabraded coarse fractions have the GEOCHRONOMETRY / 201 0.024 1 1 i 1 1 ' 1 FALLSLAKE PLUTONIC SUITE CENTRAL FALLSLAKE PLUTON 0.022 MS-BI GRDR/T0NALITE Z +44-74.NM RBR . MVG-8B-1BB3 z +44-74.w |+M^^S*-**74-149,M RBR >^rZ +44-74,M RBR +74-149,NM RBR D 1 3 0 , ^ GO 0.020 cn O J sjc/i- +74-149, NM 'CORES* \ 120 . Q I +74-149,NM *N/t> CORES* Q J 0.018 MONHZ. H l . ^ O < = - 1 i n $ r (VI rioNHZ. na 0.016 E R R O R S R R E « 2 SI6MR 0.014 i 0. 10 0.11 0.12 0.13 0.14 O . I S 0. 16 2 0 7P b /2 3 5 y r i g u r e 5 . 8 : U—Pb c o n c o r d i a d i a g r a m f o r z i r c o n s a n d m o n a z i t e (Ml and M3) f r o m s a m p l e 1 0 0 3 , c e n t r a l F a l l s l a k e p l u t o n , F a l l s l a k e e x i t , Hwy. 5 ; F i g u r e 5 . 9 s h o w s e n l a r g e m e n t o f u p p e r d a t a p o i n t c l u s t e r f r o m t h i s d i a g r a m . GEOCHRONOMETRY / 2 0 2 0.0236 I • 1 • 1 ' 1 ' V 1 0.0232 FRLLSLHKE PLUTONIC SUITE / CENTRAL FHLLSLflKE PLUTON / MS-BI GRDR/TONflLITE l 4 6 / MVG-B6-1003 S 0.0228 m J T J 0.0224 / oi \ Si Q_ 0.0220 / . (0 o 0.0216 / +74-149.M RBR ^><(.44_74 t N M 4 f, >r \ ^ ^ ^ * « * - * « . H RBR 0.0212 / +74=149.MM RBR ERRORS RRE 2 SIGMR 0.0208 0. i i i i 140 0.144 0.148 0.152 0.136 0. 207pb/235u 160 F i g u r e 5 . 9 E n l a r g e m e n t o f p a r t o f U-Pb c o n c o r d i a d i a g r a m f o r z i r c o n s f r o m s a m p l e 1003 ( F i g u r e 5 . 8 ) s h o w i n g u p p e r d a t a p o i n t c l u s t e r , c e n t r a l F a l l s l a k e p l u t o n , F a l l s l a k e e x i t , Hwy. 5 . GEOCHRONOMETRY / 203 youngest U-Pb dates r e f l e c t i n g perhaps, the presence of a r e l a t i v e l y larger component of primary magmatic xenocryst-free zircon. Inexplicably, the unabraded fine zircon f r a c t i o n l i e s in a cluster (see Figure 5.9) with a l l the abraded fr a c t i o n s . The fiv e fractions in the cluster have c l o s e l y similar U/Pb dates that range from 136 to 141 Ma and Pb/Pb dates range from 150 to 174 Ma. This suggests that a large part of the inherited lead i s late Jurassic (144 to 163 (Palmer, 1983)), the age of to n a l i t e that hosts the central F a l l s l a k e pluton. The emplacement age of the central F a l l s l a k e pluton i s interpreted to be 110.5 +0.4 Ma, calculated from the weighted mean of the 2 0 7Pb/ 2^\j r a t i o s for monazite fractions analyzed from sample 1003. The Pb/ U dates of monazite have been found in many instances to c l o s e l y approximate the emplacement age of plutons in which the interpretation of emplacement ages from U-Pb zircon data is complicated by problems of Pb inheritance (R.R. Parrish, oral communication, 1988). A discordia f i t t e d to a l l but the monazite data points for sample 1003 yield s a lower intercept of 95 +11/-17 Ma close to but not quite concordant with the monazite date. Additional evidence in support of a mid-Cretaceous emplacement age for the central F a l l s l a k e pluton and the F a l l s l a k e plutonic suite includes abundant K-Ar and Rb-Sr dates that center on 100 Ma (see below). Four Rb-Sr and K-Ar mineral dates from sample 1003 range from 96.2 + 2.1 Ma (Rb-Sr b i o t i t e ) to 104 + 4 Ma (K-Ar muscovite). Discordance among K-Ar and Rb-Sr mineral dates GEOCHRONOMETRY / 204 in Eagle t o n a l i t e and gneiss (see below) i s also most e a s i l y explained by mid-Cretaceous emplacement of the Fa l l s l a k e s u i t e . Clustering of late Jurassic U/Pb dates for well-abraded zircon fractions suggests that was the age for the inherited Pb component. The upper intercepts of other discordia l i n e s , however, suggest that late Jurassic Pb may be mixed with an older component. A chord f i t to the zircon data and the 110.5 +_ 0.4 Ma concordia intercept (interpreted emplacement age) y i e l d s an upper intercept of 278 + 11 Ma (early Permian). The discordia that was f i t to the zircon data alone yielded a 221 +32/-26 Ma (late T r i a s s i c ) upper intercept. I I I . K-AR AND RB-SR DATING, ANALYTICAL RESULTS AND INTERPRETATIONS A. INTRODUCTION Potassium-argon and Rb-Sr sample locations and data are shown on Figures 5.10 and 5.14 and Plate 2, and l i s t e d in Tables 5 . I l l , 5.IV, 5.V and 5.VI. Selected Rb-Sr data have been plotted on 87 86 87 86 Sr/ Sr vs. Rb/ Sr isochron diagrams (Figures 5.13, 5.15, and 5.17). Potassium-argon and Rb-Sr dates and Sr i n i t i a l r a t i o s are assigned errors at the one sigma l e v e l (66% confidence l e v e l ) . Closure temperatures for mineral species, which are in part dependent on grain size and cooling rate, are reported by Parrish and Roddick (1985) to be: K-Ar hornblende (530 + 40 °C), K-Ar b i o t i t e (280 + 40 °C), K-Ar muscovite (about 350 °C), Rb-Sr b i o t i t e (320 + 40 °C) and Rb-Sr muscovite (500 °C or more). GEOCHRONOMETRY / 205 B. NICOLA GROUP Two samples of amphibolite s c h i s t from the Upper T r i a s s i c Nicola Group in the study area yielded amphibole separates. The age of formation of the metamorphic f a b r i c in Nicola Group rocks in the study area i s constrained by the minimum age of emplacement of the late syn-kinematic Eagle t o n a l i t e (155 +_ 4 Ma, 2 sigma e r r o r s ) . Potassium-argon and Rb-Sr dating of amphibolite indicates that Nicola Group metamorphic rocks adjacent to the Eagle complex were p a r t i a l l y degassed during mid-Cretaceous and (or) early T e r t i a r y thermal events. Sample 999 was extremely fine-grained and i t s amphibole separate was contaminated by approximately 3% b i o t i t e . I t was coll e c t e d near the Eagle t o n a l i t e - N i c o l a Group contact, within several hundred meters of the Early Eocene "Independence porphyry" (54.5 + 1.9 Ma K-Ar Hb, Figure 5.10, Plate 2). The sample yielded a 64.7 +_ 4.2 Ma date that i s interpreted as a hybrid of true K-Ar b i o t i t e and hornblende dates, both of which were at least p a r t i a l l y reset in ear l y Eocene time. Whole rock Rb-Sr analysis of sample 999 yielded a two-point Late T r i a s s i c Rb-Sr whole rock isochron with a date of 213 + 7 Ma assuming an i n i t i a l strontium r a t i o equal to that of Eagle t o n a l i t e (0.70365 + 0.00002, 1 sigma). This date i s interpreted as a minimum age for rocks of the Nicola Group in t h i s area. Assuming a r e l a t i v e l y low i n i t i a l strontium r a t i o equal to that of the Late T r i a s s i c Guichon batholith (0.70340 + 0.00002), thought to be GEOCHRONOMETRY / 206 Table 5 . I l l : K-Ar ANALYTICAL DATA, COQUIHALLA AREA. Sample Mineral 7. K Ar /. «r '_i T H r Date err o > Ma NICOLA GROUP 999 Hb 1 . 07 2. 741 88. 0 64.7 + / - 4. 1222 Hb 0 . 43 "> f)  rD O J I - a KJ y-J 90. i 117 + /- 4 ZOA COMPLEX 1002 Hb 1. 05 3.987 88. 9 95.2 + /- u J • 160 Hb 0 . 43 2. 869 91 . 3 145 + /.- 5 EAGLE TONALITE 992 Hb 0 . 76 3. 536 36. 1 118 + /- 4 Bi 4. 86 18.386 93. 1 97. 8 + /- N 4 396 Bi 7. •-tcr 28.843 88. 8 99. 6 + / - /-! O • 5 937 Hb 0 . 33 5. 171 91. 6 130 + / _ 4 Bi 7. 31 31.706 91. 4 108 + / - - 4 1001 Hb 0. 34 3. 163 93. / - I \_V 85. 0 + / - \-J m 0 Bi 7. 14 15.433 77. 1 55. 0 + / - 1. 9 1026 Bi 6. 86 27.534 72. 9 100 + /- 4 1110 Bi 6. 61 27.830 90. 9 105 + / - - 4 EAGLE GNEISS 1090 Hb 0. 30 1. 448 82. 1 120 +/- 4 FALLSLAKE PLUTONIC SUITE 395 M B a. 63 35.848 88. 9 104 + / - 4 Bi 6. 66 26.481 93. 6 99. 5 + / - \-J m 5 1003 Ms 8. 54 u J • vJ J D 88.4 104 + / - 4 Bi 6. 98 26.887 90. 1 96.5 + / - 4 1004 Ms 8. 53 30.321 86. 1 91.0 + / - *—i V-J ft 1005 Ms 8. 87 31.578 87. 0 89. 4 + / - /-> • 1 1059 Ms 7. 91 89. 7 105 + / - 4 ILLAL STOCK 201 Hb 0 . 54 1.213 80. 7 57. 3 + / - - !—! • 0 Bi 6. 29 14.312 89. 9 57. 6 + / - »_ • 0 INDEPENDENCE PORPHYRY 1000B Hb 0. 0. 742 62. 5 54. 5 + /- i . 9 TULAMEEN FALLS STOCK 122 Bi 6. 83 13*538 83. 5 50. 3 + / - i . 8 NEEDLE PEAK PLUTON 29 Hb 0. 93 1.675 SO. 0 46.0 + / - i . 6 Bi 6. 80 12.258 92. 1 45. 8 + /- i . 6 DIKES/PLUGS 1216 Hb 0. 55 1.015 85. 4 46.8 +/- 2. 1 655 Hb 0. 39 0.340 55. 6 22 • 2 + / - - 0. 8 774 WR 2. 60 2.246 76. 7 22. 1 + / - 0. 8 1. Radi ogeni c **°Ar C xlO "*cc/gram) 2. Radiogenic argon as percentage of total Ar. 3. Decay constants used in age cal c u l a t i o n : beta = 4.96x10--10 y r- 1 epsilon ~ 0 . 5 8 1 x l 0 ~l° yr"1; 40K/K = 0.01167 atom. 7. CSteiger and Jager, 1977). 4. Errors are one si qma. . GEOCHRONOMETRY / 2 Table 5.IV: EAGLE TONALITE AND GNEISS: Rb-Sr ANALYTICAL DATA, CALCULATED ^ S r / ^ r RATIOS AND Rb-Sr WHOLE-ROCK—MINERAL SEPARATE ISDCHRONS. Saaple1 HA'""* S r3 Rb B7Rb/86Sr 87Sr/86Sr Isochron Date+/-error* " I n i t i a l " HSHD nuaber (ppm) (ppa) (+/-2X) (+/- 1 sigaa)"5 or 2 pt. (Ha) 87Sr/86Sr FOLIATED TONALITE, MURPHY LAKES 997 a B UR ep bi 891 1720 33.1 19.3 0.0 158 0.064 0.70379+/-6 WR-ep-bi 0.000 0.70364+/-5 13.8 0.72532+/-9 110.5+/-3.4 0.70366+/-4 0.4 1026 11 UR bi 877 52.7 15.9 145 FOLIATED TONALITE, TULAMEEN RIVER 0.052 0.70375+/-3 HR-bi 7.97 0.71658+/-9 114.0+/-2.5 0.70367+/-3 1110 B UR bi 891 68.1 16.6 149 FOLIATED TONALITE, ILLAL CREEK 0.055 0.70381+/-9 HR-bi 6.34 0.71362+/-6 109.8+/-2.5 0.70372+/-9 996 B UR bi 558 25.6 31.2 251 BIOTITE HE8ACRYSTIC TONALITE, JULIET CREEK 0.162 0.70396+/-18 HR-bi 102.0+/-4.0 28.5 0.74504+/-11 0.70373+/-18 1001 B UR bi 922 25.3 15.3 156 GNEISSIC TONALITE, COLDWATER EXIT RAHP, HHY 5 0.049 0.70379+/-5 HR-bi 55.7+7-2.3 17.9 0.71792+/-11 0.70375+/-5 992 B UR bi 840 178 14.6 i l l GNEISSIC TONALITE, JULIET CREEK 0.049 0.70393+/-10 HR-bi 1.81 0.70560+/-24 . 66.8+/-10.5 0.703B8+/-10 1090 UR 224 3.8 TONALITE 0RTH06NEISS, HHY. 5 0.049 0.70365+/-2 A 12 PT. ISOCHRON FOR THE SUITE (EXCLUDING RESET BIOTITE FROH 86-992 AND 86-1001) YIELDS 111.2+/-2.1 Ha AT 0.70365+/-2 (HSUD=2.1). A 7 PT. ISOCHRON WITH ALL BIOTITE ANALYSES AND THE WHOLE ROCK ANALYSIS FOR SAHPLE 992 EXCLUDED YIELDS 152+/-87 Ha AT 0.70364+/-0.00007 (MSHD=0.3). 1Coaplete analytical data and saaple descriptions and locations are recorded on UBC Canadian Cordillera Geochronoaetry F i l e lab sheets in Appendix 5.1 of the thesis. ^HA - aaterial analyzed; UR = whole rock, as = suscovite, bi = b i o t i t e , ksp = potassiua feldspar. E r r o r s in Sr and Rb analyses are +/- 5L "*Dates and i n i t i a l ratios are calculated with the oodel of York (1967); errors are one sigaa; only the last d i g i t s are shown for i n i t i a l ratio errors; Rb decay c o n s t a n t s . 4 2 x l 0 ~1 0 y e a r "1. ^Within-run errors; where within-run errors<0.00005, between-run errors of 0.00010 were used in isochron calculations. GEOCHRONOMETRY / 208 T a b l e 5 .V: FALLSLAKE PLUTONIC S U I T E : R b - S r ANALYTICAL DATA, CALCULATED INITIAL 8 7 S r / e ' > S r RATIOS AND R b - S r WHOLE-ROCK- -MINERAL SEPARATE ISOCHRONS. Saaple1 NA52 S r3 Rb 87Rb/86Sr 87Sr/86Sr Isochron Date+/-error"* I n i t i a l MSHD nuaber (ppa) (ppa) (+/-2Z) (+/- 1 s i g a a )3 or 2 pt. (Ha) 87Sr/86Sr CENTRAL FALLSLAKE PLUTON 1003 UR 689 25.1 0.104 0.70398+/-5 UR-as-bi 100.2+/-3.7 0.703B4+/-12 5.9 B as 66.9 183 7.94 0.71551+/-3 UR-as 103.5+/-2.2 0.70384+7-5 B bi 48.7 304 18.1 0.72B59+/-19 UR-bi 96.2+/-2.1 0.70383+/-5 NORTHERN FALLSLAKE PLUTON 995 UR 526 30.6 0.168 0.70398+/-7 HR-as-bi 103.7+/-2.0 0.70373+/-7 . 0.8 B as 40.9 189 13.4 0.72375+/-B UR-as 105.1+/-2.7 0.70373+/-7 R bi 32.8 271 24.0 0.73B32+/-10 HR-bi 101.4+/-3.1 0.70374+/-7 PINK PEGMATITE DIKE—HHY. 5 TOLLBOOTH 1004 UR 13.9 150 31.4 0.75080+/-19 HR-ksp-as 105.4+/-4.9 0.703+/-4 0.5 a ksp 18.3 476 75.9 0.81301+/-6 HR-ksp 98.4+/-10.5 0.707+/-6 B as 1.89G ' 84B 1610 3.147+/-20 UR-as 106.9+/-5.5 0.703+/-4 PEGMATITIC MUSCOVITE 6RANITE DIKE--HHY. 5 1005 UR 47.1 128 7.BB 0.71545+/-2 UR-ksp-as 82+/-12 0.7063+/-12 0.5 a ksp 63.2 146 6.69 0.71418+/-2 HR-ksp 75+/-14 0.7070+/-13 • as 4.3 328 229 1.00620+/-41 UR-as 92+7-22 0.7051+/-25 MYLONITIC T0NALITE--N0RTHERN FALLSLAKE PLUTON 1059 UR 224 3.8 0.049 0.70438+/-5 HR-as 97.2+/-2.1 0.70431+/-5 as 46.7 202 12.5 0.72157+/-4 14 PT. ISOCHRON COMBINED FALLSLAKE SUITE YIELDS 101.8+/-2.2 Ha AT 0.70400+/-8 (HSHD=6.4). 5 PT. HHOLE-ROCK FALLSLAKE SUITE ISOCHRON YIELDS 102+/-12 Ma AT 0.70399+/-15 (HSHD=20). 1Coaplete analytical data and saaple descriptions and locations are recorded on UBC Canadian Cordillera Geochronoaetry F i l e lab sheets in Appendix 5.1 of the thesis. ^NA = aaterial analyzed; HR = whole rock, as = auscovite, bi = b i o t i t e , ksp = potassiua feldspar. E r r o r s in Rb and Sr analyses are +/- 51. "*Dates and i n i t i a l ratios are calculated with the aodel of York (1967); errors are one sigaa; only the last d i g i t s are shown for i n i t i a l r a t i o errors; Rb decay c o n s t a n t s . 4 2 x l 0 ~1 0 y e a r- 1. Within-run errors; where within-run errors<0.00005, between-run errors of 0.00010 were used in isochron calculations. ^MSID. GEOCHRONOMETRY / 209 T a b l e 5-V i s R b - S r A N A L Y T I C A L D A T A . C A L C U L A T E D I N I T I A L mrSr/mmSr R A T I O S AND R b - S r W H O L E - R O C K — M I N E R A L S E P A R A T E I S O C H R O N S . M I S C E L L A N E O U S S U I T E S / S A M P L E S , C O Q U I H A L L A A R E A . Saaple' Sr 3 Rb 87Rb/86Sr 87Sr/B6Sr Isochron Date+/-error"* Initial MSUD number (ppa) (ppa) (+/-2X) (+/- 1 s i g a a ) 3 or 2 pt. (Ha) 87Sr/86Sr NICOLA GROUP AMPHIBOLITE 999 UR 396 71.1 0.521 0.70521+/-4 sJR+IR 244+/-7.8 assuaed=0.70340* WR+IR 213+/-7.4 assuaed=0.70365' r ZOA COMPLEX HORNBLENDE BUARTZ DIORITE 1002 HR 846 33.5 0.116 0.70356+/-4 INDEPENDENCE PORPHYRY 1000B HR 1256 30.3 0.069 0.70385 0.703BO" NEEDLE PEAK PLUTON 29 UR 199 81.5 1.19 0.70436+/-5 WR-hb-bi 43.7+/-5.1 0.70363+/-12 0.14 n hb 18.0 15.4 2.50 0.70520+/-4 a bi 5.50 508 273 0.8637+/-3 COQUIHALLA VOLCANIC COMPLEX DIKES 655 UR 493 50.6 0.298 0.70390+/-15 UR 21.b>/-3.0* 0.70375+/-7 0.54 774 UR 351 73.2 0.605 0.70414+/-4 1Coaplete analytical data and saaple descriptions and locations are recorded on UBC Canadian Cordillera Geochronoaetry F i l e lab sheets in Appendix 5.1 of the thesis. ^ A = aaterial analyzed; HR = whole rock, as = auscovite, bi = biotite, ksp - potassiua feldspar. ^Errors in Rb and Sr analyaes are +/- 5X. "*Dates and i n i t i a l ratios are calculated with the aodel of York (1967); errors are one sigaa; only the last digits are shown for i n i t i a l ratio errors; Rb decay constants. 4 2 x l 0 - x o y e a r - 1 . Within-run errors; where within-run errors <0.00005, isochrons were calculated using between-run errors of 0.00010. "TJate calculated using an assueed i n i t i a l ratio equal to that of the Guichon batholith. 7Date calculated using an i n i t i a l ratio equal to that of Eagle tonalite. ^ I n i t i a l ratio calculated using an intrusive age of 54.5 Ma (K-Ar hornblende date). ^Date and i n i t i a l ratio calculated by coabining data froa this study with whole rock data (seven points) froa Beraan and Armstrong (1981). GEOCHRONOMETRY / 210 . 996 Bl: 99.6 +/- 3.5 I BMrYR: 102.0 +/- 4.0 v 992 Hb: 118 +/- 4 Bl: 97.8 +/- 3.4 BI-WR: 66.8 +/- 10.5 TERTIARY M I O C E N E I .... I COQUIHALLA VOLCANIC l M C V l C O M P L E X E O C E N E Emg | N E E D L E PEAK PLUTON MIDDLE E O C E N E 1001 Hb: 85.0 +/- 3.0 Bl: 55.0 +/- 1.9 BI-WR: 55.7 • / - 2.3 Es SEDIMENTARY R O C K S mKs mKg | Ei [ UNDIVIDED INTRUSIVE R O C K S C R E T A C E O U S MID-CRETACEOUS SEDIMENTARY R O C K S E A R L Y C R E T A C E O U S F A L L S L A K E PLUTONIC SUITE 997 Hb: 130 +/- 4 B1: 108 +/- 4 BI-Ep-WR: 110.5 • / - 3.4 y s  JURASS IC A N D C R E T A C E O U S lUrnKgrj E A Q L E GNEISS L A T E J U R A S S I C [ L i t | E A G L E TONALITE L A T E J U R A S S I C A N D O L D E R | L ) Z | ZOA COMPLEX TRIASSIC U P P E R T R I A S S I C TrN NICOLA GROUP . ! & I 1222 Hb: / | 1 1 7 • / - 4 Oeologlcal contact — ^ ^ High angle tault Thrust tault 1026 Bl: 100 • / - 4 BI-WR: 114.0 • / - 2.5 F i g u r e 5 . 1 0 : S i m p l i f i e d g e o l o g y , C o q u i h a l l a a r e a , s h o w i n g N i c o l a G r o u p , Z o a complex, E a g l e t o n a l i t e and E a g l e g n e i s s R b - S r and K-Ar d a t e s . GEOCHRONOMETRY / 211 comagmatic with part of the Nicola Group (Monger and McMillan, 1984), yie l d s an older 244 + 8 Ma date (Early to Middle T r i a s s i c ) that i s as maximum age for these Nicola Group rocks. The 244 to 213 Ma age range agrees with the biost r a t i g r a p h i c age of the Nicola Group. The second sample of Nicola Group amphibolite from the study area (1222) vas coll e c t e d several hundred meters from the contact with Eagle t o n a l i t e along a logging road south of the Tulameen River, near i t s confluence with Champion Creek (Figure 5.10, Plate 2). The 117 +. 4 Ma K-Ar amphibole date for sample 1222 i s interpreted to represent p a r t i a l degassing of radiogenic argon in mid-Cretaceous time, probably coincident with emplacement of the Fa l l s l a k e plutonic s u i t e . A sample of Nicola Group amphibolite possessing s t r i k i n g garbenschiefer texture (Figure 5.11) from near the Eagle to n a l i t e - N i c o l a Group contact along the Hope-Princeton highway (Highway 3, approximately 0.5 kilometers southwest of Goodfellow Creek) in Manning Park (see Figure 3.1) yielded a K-Ar amphibole date of 119 + 4 Ma (R.L. Armstrong, unpublished data). This date i s coeval with the minimum emplacement age (123 + 5 Ma) determined for nearby Eagle t o n a l i t e in the Manning Park area (see above) and because amphibole grows randomly within and across the f o l i a t i o n plane, the date places a younger l i m i t on the time of f o l i a t i o n formation in the Nicola Group. GEOCHRONOMETRY / 212 F i g u r e 5 . 1 1 : Randomly-oriented p o s t - k i n e m a t i c "Hollywood" hornblende i n N i c o l a Group g a r b e n s c h i e f e r , Hope-Princeton Highway; sample slabbed p e r p e n d i c u l a r to f o l i a t i o n . GEOCHRONOMETRY / 213 C. ZOA COMPLEX Greenschist grade Zoa complex hornblende quartz d i o r i t e intrudes constituent metavolcanic rocks and i s juxtaposed along the Pasayten f a u l t with the mid-Cretaceous F a l l s l a k e plutonic suite. Two samples of hornblende quartz d i o r i t e of the Zoa complex yielded hornblende separates and K-Ar dates. Sample 1002 was collected from the Thar Peak pipeline road, several hundred meters northwest of the Zoa and Coquihalla f a u l t s (Figure 5.10, Plate 2). Most amphibole grains exhibit a l t e r a t i o n to b i o t i t e , c h l o r i t e , epidote and magnetite and a number of grains have been completely replaced (Figure 5.12). Sample 87-160 has been affected to a lesser degree by metamorphism or a l t e r a t i o n . Amphibole in the sample shows approximately 10% a l t e r a t i o n to c h l o r i t e , epidote, magnetite, c a l c i t e and sphene. Sample 1002, from which a Late Jurassic minimum age was obtained by U-Pb zircon dating, has a K-Ar hornblende date of 95.2 + 3.3 Ma (mid-Cretaceous). Sample 160 has a K-Ar hornblende date of 145 +_ 5 Ma (latest Jurassic or e a r l i e s t Cretaceous). The mid-Cretaceous hornblende date for the most altered sample i s interpreted as a metamorphic date. The 145 Ma date from the less altered sample i s interpreted as a time of cooling. Minor radiogenic argon loss i s possible. Such loss probably accompanied a l t e r a t i o n or metamorphism in mid-Cretaceous time, when the Zoa complex was metamorphosed and deformed. GEOCHRONOMETRY / 214 Figure 5.12: Sample 1002, hornblende quartz d i o r i t e , Zoa complex, Thar Peak pipeline, shoving s l i g h t l y altered ( l e f t ) and completely altered (right) hornblende; a l t e r a t i o n assemblage i s epidote, c h l o r i t e and magnetite. GEOCHRONOMETRY / 215 Rubidium-strontium whole rock analysis of sample 1002 y i e l d s a 8 7 S r / 8 6 S r r a t i o of 0.70356 + 0.00004 at 8 7Rb/ 8 6Sr of 0.116 + 0.004 and an i n i t i a l strontium r a t i o of 0.70331 for Late Jurassic (153 + 10 Ma) quartz d i o r i t e of the Zoa complex. The strontium i n i t i a l r a t i o i s s i g n i f i c a n t l y lower than that for coeval Eagle t o n a l i t e (0.70365 +_ 0.00002), suggesting that the more compositionally primitive Zoa complex rocks were derived from a more primitive p r o t o l i t h . D. EAGLE TONALITE AND GNEISS Potassium-argon and Rb-Sr dates for Eagle t o n a l i t e and gneiss are mainly late Early Cretaceous, but several younger dates were also obtained in t h i s study (Figure 5.10, Tables I I I , IV). Strong discordance among dates from d i f f e r e n t isotopic systems and dates from d i f f e r e n t minerals for the same sample i s due to p a r t i a l degassing during mid-Cretaceous and early T e r t i a r y thermal events. Four mineral dates from Eagle t o n a l i t e and gneiss that are younger than Early Cretaceous are interpreted to have been wholly or p a r t i a l l y reset by early T e r t i a r y plutonism. Three of the reset dates are from sample 1001, collected near the southern end of the earl y Eocene Keystone stock. Concordance of K-Ar b i o t i t e (55.0 + 1.9 Ma) and Rb-Sr b i o t i t e (55.7 + 2.3 Ma) dates and K-Ar b i o t i t e dates for the Keystone stock (56.1 + 2.0 Ma and 53.5 +1.9 Ma, see below) suggests resetting occurred. The potassium-argon hornblende date for the same sample (1001; 85.0 + 3.0 Ma) i s anomalously young r e l a t i v e to other K-Ar hornblende GEOCHRONOMETRY / 216 dates for Eagle t o n a l i t e and gneiss (118-130 Ma), and r e f l e c t s p a r t i a l resetting by the Keystone stock. The other date that may have been reset i s a Rb-Sr b i o t i t e date of 66.8 + 10.5 Ma from sample 992, collected from a logging road on the south side of the v a l l e y of J u l i e t Creek, less than two kilometers from the early Tertiary(?) "Rover" stock. Five other K-Ar b i o t i t e dates for Eagle t o n a l i t e and gneiss from this study and three from previous studies range from 97.8 + 3.4 Ma to 108 + 4 Ma, average 103.1 + 3.8 Ma and show a strong positive c o r r e l a t i o n of distance from F a l l s l a k e suite intrusions with cooling age. Rubidium-strontium biotite-whole rock dates calculated for the samples from t h i s study, excluding the reset dates discussed above (samples 1001 and 992), average 109.1 + 3.1 Ma and range from 102.0 + 4.0 Ma to 114.0 + 2.5 Ma. Rb-Sr and K-Ar b i o t i t e dates are generally in agreement, but cor r e l a t i o n between Rb-Sr biotite-whole rock dates and distance to •Fallslake suite intrusions i s not as marked as i t i s for K-Ar b i o t i t e cooling dates. Except for the reset date for sample 1001, K-Ar hornblende dates for Eagle t o n a l i t e and gneiss (118 +_ 4 Ma, 120 + 4 Ma, and 130 + 4 Ma for samples 992, 1090 and 997), young toward mid-Cretaceous F a l l s l a k e plutonic suite intrusions and r e f l e c t variable p a r t i a l argon loss during mid-Cretaceous intrusion of the younger su i t e . Perhaps the best example of discordance among isotopic systems is provided by sample 997, collected near Murphy Lakes, not far from the east margin of Eagle t o n a l i t e (Figure 5.10, Plate 2). GEOCHRONOMETRY / 217 Uranium-lead dates for zircon from sample 997 are interpreted as a Late Jurassic (157 + 4 Ma) minimum age of emplacement; however, K-Ar hornblende, K-Ar b i o t i t e and Rb-Sr whole rock-biotite dates are 130 +_ 4 Ma, 108.5 + 4 Ma and 110.3 + 3.4 Ma. Assuming a simple cooling history, closure temperatures of the respective i s o t o p i c systems and mineral species require a minimum of 50 Ma for cooling of Eagle t o n a l i t e and gneiss at t h i s l o c a l i t y from >80O °C at 157 Ma (minimum date) to 280 °C at 108.5 Ma. This improbably slow cooling rate for an intrusion suggests a more complex thermal history. Intrusion of the F a l l s l a k e suite i s the suspected cause of the isotopic r e s e t t i n g . Sample 997, the sample farthest from any large F a l l s l a k e suite intrusion, shows the least complicated K-Ar and Rb-Sr systematics and the least evidence for mid-Cretaceous thermal disturbance. A l l of the K-Ar and Rb-Sr dates for sample 997 are at the old end of the range of dates for the t o n a l i t e suite for each mineral species. A composite 12 point, mineral-whole rock Rb-Sr isochron calculated for Eagle t o n a l i t e and gneiss yie l d s a 111.2 +_ 2.1 Ma date (Figure 5.13). The slope of the isochron and therefore the date are heavily weighted by the b i o t i t e analyses and i t represents the average date at which b i o t i t e in Eagle t o n a l i t e and gneiss became closed to d i f f u s i o n of radiogenic strontium. An isochron which excludes a l l b i o t i t e analyses and the whole rock analysis for sample 992 yi e l d s a 152 + 87 Ma date at an 8 7 S r / 8 6 S r i n i t i a l r a t i o of 0.70364 + 0.00007. GEOCHRONOMETRY / 218 0.75500 0.74500 (j) 0.73500 C D 00 \o.72500 CO 00 0.71500 0.70500 0.69500 0.70400 0.70390 CO CO 0.70380 0 0 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — p — 1 — 1 1 1—1—1 — 1 — 1 — 1 — 1 — 1 1 1— : L A T E J U R A S S I C E A G L E : T O N A L I T E A N D G N E I S S 9 9 6 : C o m b i n e d i s o c h r o n -^ x ^ B i 997 : - Bi 1 0 2 6 / ' • ; Bi 1 1 1 0 ^ ^ 111.2 + / - 2.1 Ma : 12 point Rb—Sr isochron Initial Sr = 0 .70365 + / - 2 ' Whole rock " analyses, see I detail below 1 1 1 1 1 1 1 1 1 1 L errors are 1 sigma i i i i i i i i i i i i i i i i i i 10 15 20 8 7 R b / 8 6 S r 25 30 CO oo 0.70370 0.70360 I.7035Q - i — n — i — r - i — n — i — i — i — i — r — l — r — l — r — i — n — r — i — i — i — i — i — i — i — i — i — i — i — i — r p _ 0 WR 992 W^R 1001 WR 1 1 1 0 0 0 P R "997 , WR 1 0 2 6 0 -WR 996 :Ep 997 WR 1090 0 1 2 p t . W R - m i n . s « p . = 1 1 1 . 2 + / _ 2 . 1 M o o t i n i t i a l S r - 0 . 7 0 3 6 S + / - 2 7 p t W R + 9 9 7 » p ( » x c l . 9 9 2 W R ) » 1 5 2 + / - 8 7 M a o r t i n i t i a l S r = 0 . 7 0 3 6 4 + / - 7 ( d a s h e d h ' n » ) ' ' ' i i i I i i — i — L _ i _ errors are 1 sigma -I I I I I I ' 1 • I I I I I I I I I I I L-.00 0.02 0.04 0.06 0.08 0.10 0.12 O.H 0.16 0.18 8 7 R b / 8 6 S r Figure 5.13: Rb-Sr whole-rock—mineral separate isochron for Eagle t o n a l i t e and gneiss (excluding reset b i o t i t e from samples 992 and 1001), Coquihalla area; lower diagram i s det a i l showing whole-rock data (and epidote from sample 997); MSWD=2.1. GEOCHRONOMETRY / 219 87 86 The Sr/ Sr r a t i o for the composite 12 point Eagle t o n a l i t e 87 86 and gneiss isochron i s 0.70365 + 0.00002 and Sr/ Sr ra t i o s for seven whole rock-biotite pairs from the to n a l i t e suite range from 0.70366 to 0.70388. Samples 992 and 1001, which have reset or 87 86 p a r t i a l l y reset T e r t i a r y mineral dates, have the highest Sr/ Sr 87 86 r a t i o s . Samples with the lowest Sr/ Sr r a t i o s are farthest from 87 86 Fa l l s l a k e suite plutons. I n i t i a l Sr/ Sr ra t i o s for samples 997 and 1001, calculated from th e i r U-Pb zircon minimum dates, are 0.70365 and 0.70368. The strong discordance in ages for Eagle t o n a l i t e and gneiss among d i f f e r e n t dating systems implies that the rocks have experienced a multi-stage cooling history. The F a l l s l a k e plutonic suite i s interpreted to have been emplaced circa 110.5 + 0.4 Ma (U-Pb). This date i s s i m i l a r , within error, to the combined Rb-Sr isochron for Eagle t o n a l i t e and gneiss and corresponds c l o s e l y to the younger l i m i t of K-Ar and Rb-Sr b i o t i t e dates for the units and to the younging trends in the Eagle t o n a l i t e and gneiss K-Ar b i o t i t e and hornblende data. The range of K-Ar and Rb-Sr b i o t i t e dates for Eagle t o n a l i t e and gneiss (97.8 and 114 Ma) corresponds with a similar range of Rb-Sr and K-Ar muscovite and b i o t i t e dates for the Fa l l s l a k e plutonic suite (cluster between 97 and 105 Ma). Resetting of Rb-Sr and K-Ar systems in Eagle t o n a l i t e and gneiss was complete or nearly complete during emplacement of the F a l l s l a k e plutonic suite and a l l three units cooled through the 280° isotherm (the b i o t i t e blocking temperature, Parrish and Roddick, 1985) within approximately 10 Ma. GEOCHRONOMETRY / 220 E. FALLSLAKE PLUTONIC SUITE Several large mid-Cretaceous b i o t i t e muscovite granodiorite to t o n a l i t e intrusions and numerous cogenetic ( b i o t i t e ) muscovite monzogranite stocks, dykes and s i l l s of the F a l l s l a k e plutonic suite are mainly r e s t r i c t e d to the west margin of the Eagle complex. On th e i r west side, d u c t i l e l y and b r i t t l e l y deformed F a l l s l a k e plutonic suite i s juxtaposed with the d u c t i l e l y deformed Late Jurassic and older Zoa complex and with b r i t t l e l y deformed middle Eocene c l a s t i c rocks along the Pasayten f a u l t . To the east, F a l l s l a k e suite rocks intrude Late Jurassic Eagle t o n a l i t e and gneiss. Uranium-lead dating of zircon and monazite from the central F a l l s l a k e pluton indicate that i t was emplaced in mid-Cretaceous time (110.5 +.0.4 Ma). Potassium-argon and Rb-Sr dates for the Fa l l s l a k e suite are invariably mid-Cretaceous and, except for dates from pegmatites, i n t e r n a l l y consistent (Figure 5.14). Dates also agree well with f i e l d r elationships and with geochronometric data for other rock units in the Coquihalla area. The Rb-Sr, K-Ar and U-Pb systematics suggest rapid u p l i f t and cooling, accompanying east-side-up motion on the Pasayten f a u l t , followed mid-Cretaceous emplacement of the F a l l s l a k e s u i t e . Potassium-argon and Rb-Sr muscovite and b i o t i t e dates were determined for sin g l e , r e l a t i v e l y undeformed samples of each of the central and northern F a l l s l a k e plutons, the largest of the Fa l l s l a k e suite plutons. Sample 1003, collected for U-Pb dating GEOCHRONOMETRY / 2 2 1 995 Ms: 104 • / - 4 Bl : 99.5 • / - 3.5 Ma-Br-WR 103.7 +/- 2.0 Me-WR: 105.1 • / - 2.7 BI-WR101.4*/-a.1 201 Hb. 57.3 • / - 2.0 Bl: 57.6 • / - 2.0 122 B l : 50.3 • / - 1.8 F i g u r e 5 . 1 4 : S i m p l i f i e d g e o l o g y , C o q u i h a l l a a r e a , s h o w i n g R b - S r a n d K - A r d a t e s f o r t h e F a l l s l a k e p l u t o n i c s u i t e a n d f o r T e r t i a r y i n t r u s i c m s . GEOCHRONOMETRY / 222 from the central F a l l s l a k e pluton near the Fa l l s l a k e exit on Highway 5, yielded K-Ar and Rb-Sr b i o t i t e dates of 96.5 +3.4 Ma and 96.2 +_ 2.1 Ma, and K-Ar and Rb-Sr muscovite dates of 104 + 4 Ma and 103.5 + 2.2 Ma. Sample 995, collected from the northern F a l l s l a k e pluton near the headwaters of J u l i e t Creek, gave K-Ar and Rb-Sr b i o t i t e dates of 99.5 + 3.5 Ma and 101.4 +3.1 Ma, and K-Ar and Rb-Sr muscovite dates of 104 + 4 Ma and 105.1 + 2.7 Ma. Closure temperatures for U-Pb, K-Ar and Rb-Sr isotopic systems for dated minerals from sample 1003 indicate a time-averaged cooling rate for the central F a l l s l a k e pluton of 37°C/Ma. On the southwesternmost margin of the northern F a l l s l a k e pluton, on the slopes above the headwaters of the East Anderson River, a sample (1059) of strongly altered, intensely deformed to n a l i t e was collected for dating to constrain the timing of duc t i l e s t r a i n on the Pasayten f a u l t . In thin section, the sample showed pervasive a l t e r a t i o n of plagioclase feldspar and an abundance of opaque a l t e r a t i o n products, but strained muscovite " f i s h , " interpreted to have been dynamically r e c r y s t a l l i z e d during d u c t i l e s t r a i n , appear unaltered. Rubidium-strontium an