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Structural relations between the Shuswap and "Cache Creek" complexes near Kalamalka Lake, southern British… Solberg, Peter Harvey 1976

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.STRUCTURAL RELATIONS BETWEEN THE SHUSWAP AND "CACHE CREEK" COMPLEXES NEAR KALAMALKA LAKE, SOUTHERN BRITISH COLUMBIA by Peter Harvey Sol berg Sc, Massachusetts Inst i tute of Technology 1974 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in the Department of Geological Sciences We accept th i s thesis as conforming to the required standard. THE UNIVERSITY OF BRITISH COLUMBIA (c) Peter Harvey Wfberg, 1976 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r ag ree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y pu rpo se s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Depar tment o f Cr- f o. ) £>«^ )~ a a | C \ <2 h r <P-S The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 i ABSTRACT Five phases of deformation are recognized in Shuswap metamorphics south of Vernon, B r i t i s h Columbia. Phase 1 and 2 deformations are i s o c l i n a l gently dipping folds which trend N and ESE respect ive ly. Some thermal a c t i v i t y may have occurred p r io r to phase 2 deformation but metamorphism culminated in the amphibolite fac ies during and fol lowing phase 2. Meta-morphism waned pr io r to the development of NE trending phase 3, folds of which are angular and moderately t i gh t with one steep and one shallowly dipping limb. Phase 4 and 5 deformations trend NE and N respect ive ly , and comprise open upright buckle folds and fractures which are contem-poraneous with abundant hydrothermal a l t e r a t i on . The 42- 10 m.y. B.P. s r/Rb whole rock age date secured from a phase 2 s i l l probably represents thermal upgrading. Low metamorphic grade "Cache Creek" metasediments west of Vernon have undergone 4 recognized deformational phases. Phase 1 fo lds are t i g h t , steeply dipping, and trend WNW. Phase 2 comprises E trending, angular mesoscopic fo lds . Phase 3 and 4 comprise NE and N trending fracture sets. A large amphibolite s i l l defines the "Cache Creek" albite-epidote-amphi-bo l i t e facies metamorphic culmination. Metamorphic hornblendes from the amphibolite y i e l d a 178 + 6 m.y. B.P. age date, using the K/Ar method. Hydrothermal a c t i v i t y occurred in associat ion with phase 3 and 4 deformations. The f i n a l four phases of Shuswap deformation appear to corre late with respective "Cache Creek" phases, based on s t ructura l s i m i l a r i t i e s . This suggests that the two complexes may be, at least in part , s t ructura l equivalents. TABLE OF CONTENTS ABSTRACT TABLE OF CONTENTS LIST OF .FIGURES AND TABLES ACKNOWLEDGEMENTS A. GEOLOGY OF THE KALAMALKA LAKE AREA 1) 4 - INTRODUCTION General Introduction General Geology 2 - STRATIGRAPHY Unit 1: Hornblende Gneiss Unit l a : Quartzite Unit II: Hornblende - B i o t i t e Gneiss Unit I I I: B i o t i t e Schist Unit IV: Calcareous Quartzite Unit V: Gran i t ic Dikes and S i l l s Unit VI: Limestone and S i l t s tone Unit VII: Sandstone and S i l t s tone Unit V i l a : S i l t s tone Unit V i i b : L i t h i c Arenite Unit VII I: Amphibolite Unit IX: Quartz Monzonite Bathol ith Unit X: Tert iary Vol cam'cs Unit Xa: Volcanic Breccia 3 - STRUCTURE Shuswap Structure Shuswap Phase T Shuswap Phase 2 Shuswap Phase 3 Shuswap Phases 4 and 5 i i i Page "Cache Creek" Structure 5 0 "Cache Creek" Phase 1 5 4 "Cache Creek" Phase 2 5 7 "Cache Creek" Phases 3 and 4 6 0 Amphibolite Structure 6 0 Quartz Monzonite Structure 62 4 - METAMORPHISM 6 3 Shuswap M2 6 3 Shuswap Ml 6 8 ("Cache Creek" Metamorphism 6 9 Tert iary Thermal A c t i v i t y 73 5 - DISCUSSION 7 4 Age, Or ig in , and Strat igraphic 74 Correlation of Shuswap Units Age, Or ig in , and Strat igraphic (' 75 Correlat ion of "Cache Creek" Units Shuswap - "Cache Creek" Structural 78 Correlat ion B. REFERENCES 84 C: APPENDIX 1 89 iv LIST OF FIGURES AND PLATES Page 1 - 1 Generalized geology of southeastern B.C. 2 1 - 2 Generalized geology of area of study 7 1 - 3 Location map of area of study 8 1 - 4 Photo of Kalamalka Lake area TO 2 - 1 Table of petrographic modes 1 4 2 - 2 Photo of phase 3 f o ld in Unit I 1 5 2 - - 3 Thin section of unit II 1 5 2 - 4 Photo of unit III 1 8 2 - 5 Thin section of un i t III 1 8 2 - 6 Thin section of unit IV 2 0 2 - 7 Thin section of f o s s i l s in un i t VII limestone 2 0 2 - 8 Photo of un i t V i l a 2 2 2 9 9 Thin section of un i t VIII 2 2 2 - 1 0 Thin section of unit X 2 6 2 - 1 1 Photo of un i t X 2 6 3 - 1 Shuswap phase 1 , 2 , and 3 folds in unit IV 2 9 3 - 2 Thin section of kinked muscovite in unit III 2 9 3>-3 Structural domain map 3 3 3 - 4 Photo of phase 4 folds in un i t III 3 1 3 r 5 Phase 1 i soc l ines refolded by phase 2 in unit I 3 1 3 - 6 Photo showing Shuswap phase 1 folds 3 5 3 - 7 Map showing Shuswap phase 1 structures 3 6 3 - 8 Stereoplot of Shuswap phase 1 structures 3 7 3 - 9 Map showing Shuswap phase 2 structures 4 0 3 - 1 0 Stereoplot of Shuswap phase 2 structures 4 1 3 - 1 1 Phase 2 decollement f o ld i n unit V 3 5 3 - 1 2 Stereoplot of structures in quartz monzonite s i l l , 4 3 unit V 3 - 1 3 Map showing Shuswap phase 3 structures 4 6 3 r l 4 Stereoplot of Shuswap phase 3 structures 4 7 3 - 1 5 Thin section of ca tac la s t i c breccia in unit V 4 9 3 - 1 6 Photo of s l ickensides on a phase 5 f a u l t 4 9 3 - 1 7 Map showing Shuswap phase 4 and 5 structures 5 1 3 - 1 8 Stereoplot of Shuswap phase 4 structures 5 2 V 3-•19 Stereoplot of Shuswap phase 5 structures 53 3-•20 Map showing "Cache Creek" structures 55 3-•21 Stereoplot of "Cache Creek" phase 1 structures 56 3-•22 Photo-of "Cache Creek" phase 2 f o l d . Hand specimen 58 3-•23 Stereoplot of "Cache Creek" phase 2 structures 59 3-•24 Stereoplot of "Cache Creek" phase 3 and 4 structures 61 3-•25 Thin section of un i t VIII 58 4-1 Table of metamorphic parageneses 64 4-2 Graph of Shuswap metamorphic equi l ibr ium reactions 66 4-3 Graph of "Cache Creek" metamorphic equi l ibr ium 7 2 4-'. reactions 5-1 Table of s t ructura l and metamorphic re lat ions between 80 Shuswap and "Cache Creek" complexes A- l Sr/Rb isochron. K/Ar geochronologic data 90 Plate A Geology of Kalamalka Lake area Plate B Structure of the Kalamalka Lake area Plate C Cross sections of the Kalamalka Lake area ACKNOWLEDGEMENTS The author would l i k e to thank Dr. J.V. Ross for suggesting the f i e l d problem and supplying funds through National Research Council of Canada Grant A-2134. Thanks are also extended to J . Harakal fo r performing the K/Ar analyses. The author would l i k e to express appreciation to a l l those who gave of time and in teres t during the preparation of the thes i s , espec ia l ly the technical s t a f f of the department. Support was obtained through Teaching Assistantships in the Depart-ment of Geological Sciences, 1974-1976; and a research grant from'Careers '75 for the summer of 1975. 1 1. INTRODUCTION General I n t roduc t i on The Shuswap Metamorphic Complex, which comprises the southern core of the Eastern C o r d i l l e r a Fold B e l t (Campbel l , 1973) c o n s i s t s o f s c h i s t s , gne i s se s , and a s s oc i a t ed i n t r u s i v e s which have undergone a complex deformat iona l h i s t o r y ( f i g u r e 1-1). H igh ly deformed rocks of the Kootenay Arc border the Shuswap Terrains) to the ea s t . Highly deformed although gene ra l l y much lower grade metasediments and v o l c a n i c s of the Intermontane Zone border the Shuswap T e r r a i n s ) t o the west. Numerous workers have mapped both the Shuswap Complex and the Intermontane Zone on a v a r i e t y o f s c a l e s . Although s t i l l i ncomplete , a u n i f i e d s t r u c t u r a l h i s t o r y across the Shuswap Complex i s being s yn thes i zed from d e t a i l e d s tud ies a t severa l l o c a t i o n s . The s t r u c t u r a l h i s t o r y of the Intermontane Zone remains l e s s c l e a r and major s t r a t i g r a p h i c r e v i s i o n s have r e c e n t l y been in t roduced (Oku l i t ch and Cameron, 1976:; Monger, 1975). The important ques t ion o f the s t r u c t u r a l r e l a t i o n s h i p s between the Shuswap and border ing Intermontone rocks remains unsolved. A b r i e f o u t l i n e of prev ious work i n these areas serves to i l l u s t r a t e the p o s s i b i l i t i e s and comp lex i t i e s i n v o l v e d . Dawson (1898) f i r s t mapped the rocks i n the Vernon a r e a , south of Shuswap Lake, in t roduced the name "Shuswap S e r i e s " f o r the deformed metamorphics, and ass igned them a Precambrian age. Daly (1912, p.168) accepted the use of Dawson's terminology and the p r o b a b i l i t y of an anc i en t o r i g i n o f the Shuswap metamorphics. He f e l t t ha t Shuswap rocks had undergone " s t a t i c load metamorphism" due to very deep b u r i a l . Work by Brock (1934) on Shuswap gneisses near Okanagan Lake, however, i n d i c a t e d tha t p l u t o n i c i n t r u s i o n s caused doming and a t tendant minera l l i n e a t i o n s 2 GENERAL I ZED GEOLOGY, SOUTHEASTERN B. C. ( f r o m M e d f o r d , 1 9 7 6 ) O k a n o g a n L a k e M Gran i t i c Rock T e r t i a r y V o l c a n i c s Mesozo ic — Upper P a l e o z o i c Rock Shu swap M e t a m o r p h i c C o m p l e x L o w e r P a l e o z o i c - W i n d e r m e r e S t r a t a Be l t P u r c e l l S t r a t a GNE ISS DON ES 1. F renchman ' s Cap 2. T h o r - O d i n . 3 V a l h a l l a FIGURE 1-1 of the gneisses and related s i l l s . He thus interpreted Shuswap metamor-phism as dynamic rather than s t a t i c in nature. G i l l u l y (1934) further substantiated th i s dynamic metomorphic hypothesis by petrofabr ic analysis of Daly's deformed samples. Following extensive more recent detai led work i t i s now generally accepted that Shuswap rocks have undergone several episodes of regional dynamo-thermal metamorphism and deformation^ (Chr i s t ie , 1973; Ross, 1973; Ryan, 1973; Medford, 1976). Cairnes (1939) f e l t the Shuswap Complexito be rocks of several ages ranging from Precambrian to Tr ia s s i c which a l l experienced common thermal metamorphism due to extensive Mesozoic plutonism. Cairnes also noted that meta-sediments and vol cam* cs of the Cache Creek Complex (Dawson, op . c i t . ) appeared to be s im i l a r l y deformed and metamorphosed though at a lower grade and that Shuswap - Cache Creek contacts were generally gradational on a small scale. The controvery between Dawson's Precambrian and Cairnes mult ip le age of Shuswap sediments hypotheses has yet to be completely resolved. Continuing work begun in 1945 by Rice; Jones (1959) compiled the d e f i n i t i v e summary of geology of the Vernon area on a scale of 'one inch to four miles in the Geological Survey of Canada Memoir 296 and accom-panying map sheet, Jones considered Shuswap rocks to be possibly of Pre-cambrian age and separable into three major s t rat igraph ic groups: The Monashee Group, 50,000 feet thickness, of dominantly high grade schists and gneisses; overla in by the Mount Ida Group, 60,000 feet thickness, composed of low grade meta-sediments and volcanics; capped by the Chapperon Group, about 5,000 feet thickness, of low grade a r g i l l i t e s , s ch i s t s , limestones and quartz i tes . He noted marked st rat igraphic s im i -l a r i t i e s between the Mount Ida and Chapperon Groups. Jones (1959) believed the Shuswap Complex to be unconformably over la in by Permian Cache Creek rocks which consist of a r g i l l i t e s , greenstone and limestone. He indicated f i ve possible l o c a l i t i e s where the upper Shuswap unconformity with overlying Cache Creek rocks i s observable. Preto (1964) mapped three of the suggested unconformities at Salmon River, Keefer Gulch and B.X. Creek. He concluded that although the Keefer Gulch and B.X. Creek contacts were probably along f a u l t s , there was strong evidence for an angular unconformity at Salmon River. The structura l re lat ions between the two^ l i t ho l o g i e s , however, have not been c l ea r l y establ ished. Preto (1967) l a te r correlated Late Precambrian - Early Paleozoic rocks to the east with Shuswap metamorphics, concluding that Shuswap rocks had undergone deformation and attendant metamorphism in Jurras ic time. Other attempts have been made at cor re lat ing high grade Shuswap Rocks with surrounding and included lower grade metasediments. Hyndman (1968) attempted to correlate structures between Tr ias s i c Slocan Group rocks east of the Shuswap Terrainkjand higher grade Shuswap rocks. He contended that a l l major deformation occurred in Tert iary time. Ross (1968, 1970) suggested cor re lat ing early phases of deformation in Shuswap rocks with deformation in low grade metasediments near Revel stoke, concluding that some Shuswap deformation occurred during the Paleozoic. After studying the ThorrOdin gneiss dome which comprises one of the Structural culminations of the Omenica Geant ic l ine, Reesor (1970, p.73) concludes: " . . . the locus of the gneiss domes i s not determined by superposed large scale f o l d s . " and "Deformation and metamorphism...is post Miss iss ippian and possibly post T r i a s s i c " . Although regional sty les and absolute ages of deformation in the Shuswap Complex remain in contention, i t is now c lear that a c t i v i t y occurred in 5 pre-Mesozoic time. Correlat ion of s t ructura l and metamorphic events in high grade Shuswap rocks has been greatly improved recently due to the combined e f fo r t s of several detai led studies: Ross and Chr i s t i e (1969), Chr i s t ie (1973), Ross (1973), and Ryan (1973). S im i la r l y deformed low grade metasediments in northern Washington were mapped by Waters and Krauskopf (1941) and L i t t l e (1961). Termed the Anarchist Group a f te r Daly (1912), they were tentat i ve ly assigned a Permian age from f o s s i l co r re la t ion . Another group of low grade meta-sediments, termed the Kobau Group by Bostock (1940), was investigated by Okulitch (1970) and assigned a pre-Cretaceous, l i k e l y post-Devonian age. Barnes and Ross (1975), however, suggest tectonic emplacement at a l a te r time. In l a te r papers Okulitch (1973) and Okulitch and Cameron (1976) discuss cor re lat ion of the Kobau Group with the Anarchist Group, the Chapperon Group west of Vernon, the Mount Ida $roup, the Nicola Group, and the Cache Creek Group. These eugeosynclinal, low grade meta^sedimentary and volcanic assemblages, show important s t rat igraph ic and structura l relat ionships and in a review paper Monger (1975) suggests a unifying c l a s s i f i c a t i o n . He separates the Cache Creek Group into two fundamen-t a l l y d i f fe rent rock types: The Cache Creek of the At l in^Terrace, Stuart Lake and Type l o c a l i t i e s , and the rock type near Kamloops, which correlates s t ra t i g raph i ca l l y with Chapperon, Ana rch i s t , ^ Kobau and Chi l l iwack metasediments. The former group i s characterized by basa l t i c to r h y o l i t i c vo lcanics , abundant pyroclastics;<,and volcanic sandstone, car -bonate and p e l i t e . The l a t t e r group comprises banded chert, p e l i t e , carbonate, basic volcanic rocks and associated gabbro and alpine type ultramafics. 6 General Geology Medium to high grade rocks of the Shuswap Complex have undergone a complex sequence of polyphase deformation and metamorphic events. At least the r e l a t i ve sequence and in some instances the absolute ages of these events have been establ ished. Surrounding and included low grade metasediments and volcanics of the Cache Creek Group have also undergone a complex deformational h istory. The st ructura l and metamorphic r e l a t i o n -ships between these high and low grade rocks has not been establ ished. The author has mapped an area of approximately twenty square miles near Vernon, B r i t i s h Columbia, on a scale of four inches to one mi le , in an endeavour to establ i sh structural re lat ions between these two complexes. Northerly trending KaTamalka Lake separates the two major rock types (figure 1-2, plate A). To the east medium to high grade metamor-phosed sediments have undergone f i v e recognizable phases of deformation. Gneisses, quartzites and schists comprise the four mapable layered un i t s , which contain numerous early g ran i t i c dikes and s i l l s . A l a te discordant diabase dike intrudes the layered rocks and the area i s capped in places with Tert iary volcanics and associated volcanic conglomerates. West and north of Kalamalka Lake s i l t s t one s , sandstones, limestone pods and minor chert of the Cache Creek Group have undergone low grade metamorphism, have been involved in three or possibly four deformational phases, and contain a large concordant amphibolite in t rus ion. Intruding Cache Creek sediments to the south are massive, highly weathered, monzoni-t i c to g ran i t i c int rus ives. Tert iary andesit ic volcanics cap the other units at various places. The map area locat ion , i l l u s t r a t e d in f igure 1-3, i s on the eastern flank of the south-central Okanagan Val ley, about 320 miles east of Vancouver. I t i s crossed by B r i t i s h Columbia highways Six and Ninety-Seven and l i e s immediately south and west of Vernon around the northern end of Kalamalka Lake. The area mapped l i e s between lat i tudes 50°15' and 50°20'and longitude 119°15' and 119°30'. The area i s located i n the Inter ior Plateau at the south-west boundary of the Shuswap Highland and Thompson Plateau. The topography was produced by Pliocene dissect ion of the Tert iary erosion surface (Holland, 1964). Re l ie f i s generally moderate, not greater than approxi mately 3,000 feet. Some rather large g l a c i a l l y carved scarps occur providing excel lent exposures. The best example of these, south facing c l i f f s to the north of Cozens Bay, Kalamalka Lake, are shown in f igure 1-4. Panoramic view of the area of study, facing north. Foreground i s Shuswap Terra in ; eastern background i s "Cache Creek" Group; western background i s quartz monzonite int rus ives . 2. STRATIGRAPHY. Jones (1959) mapped high grade metamorphic rocks to the southeast of Vernon as the Monashee Group of the Shuswap Complex. Although he found no recognizable marker horizons he estimated the tota l thickness of the group to be greater than the 50,000 foot section accoss Mount Thor in the Gold Range,50 miles to the east of Vernon. As noted prev-ious ly , Jones (1959) considered the Shuswap rocks in the Vernon area to be uncomformably over la in by Cache Creek Group metasedimends. These he subdivided into three units (Jones, 1959, p.g. 39): "The lowermost unit (Divis ion A) i s about 8,000 feet thick and i s pre-dominantly a r g i l l i te; the middle unit (Divis ion B) i s about 8,000 feet thick and consists of andes it ic lava, t u f f ^ a r g i l l i t e , quar tz i te , and limestone; the upper unit (Divis ion C) is at least 10,000 feet thick and consists of limestone, qua r t z i te , a r g i l l i t e , and volcanic rock. A rough estimate of the minimum thickness of the whole group i s 25,000 f e e t . " Recent work (Monger,, ;1975^/; Danner, personal communication) indicates that these low grade metasediments do not corre late with the Cache Creek Groupp of the type l o c a l i t y , therefore the present author w i l l refer to the assemblage as the "Cache Creek" Group for the remainder of th is study. The generalized d i s t r i bu t i on or rock units in the thesis area i s shown in f igure 1-2. No evidence for s t rat ig raph ic base, top, or correlat ions with other sections was found i n Shuswap rocks of the thesis area. Layered units I through IV comprise a structural succession ranging from 500 to 1,300 feet in tota l present thickness. Unit thicknesses are derived from the cross sections in plate C. Unit I consists of banded hornblende gneiss and although i t atta ins the maximum thickness of the succession, 600 fee t , i t i s at one locat ion t e c h n i c a l l y el iminated. Unit II i s a granular hornblende-biotite gneiss which attains a maximum thickness of 250 feet. Unit III i s a d i s t i n c t i v e l y rusty weathering well f o l i a t ed b i o t i t e sch i s t which varies from 20 to 300 feet in thickness. Unit IV, although the thinnest unit of the succession with a maximum 150 foot thickness, i s the most d i s t i n c t i v e , consist ing of l i g h t buff to white calcareous quartz i te . I t outl ines the geometry of the areas major phase 2 synform. A l l of these layered units were intruded by a series of g ran i t i c dikes and s i l l s , comprising unit V, pr io r to phase 3 deformation. The quartz monzonite s i l l at locat ion F-8, f igure 1-2, was dated at 42- 10 m.y. by the Sr/Rb whole rock method, appendix 1. "Cache Creek" rocks of the thesis area,which are composed of sand-stone, s i l t s tone and limestone, a t ta in a maximum overal l present thickness of 9,000 feet. Limited evidence of graded bedding in l i t h i c arenites implies that the sequence increases in age to the north. L i tho log ic repet it ions and dip var iat ions ind icate possible large scale fo ld ing but no megascopic folds were observed in the f i e l d . Cross sections of "Cache Creek" units are shown in plate C. North of Kalamalka Lake and west of Vernon "Cache Creek" meta-sediments, comprising unit VI, consist of limestone, s i l t s tone and minor vol cam"cs. These dip steeply southward and a t ta in a maximum present thickness of 3,000 feet . South of Vernon and west of Kalamalka Lake i s unit VII which also dips steeply southward. I t comprises two subunits: Ca) s i l t s t one , overla in by (b) an immature l i t h i c arenite containing minor chert bands. The subunits occur in bands of roughly s imi la r thickness ranging from 600 to 1,500 feet , and the overal l unit thickness, 13 assuming s t rat igraph ic not tectonic r epe t i t i o n , i s at most 6,000 feet . Included in unit VI are numerous limestone pods which reach one half mile in length. A large amphibolite s i l l , , un i t VI I I, forms the contact between "Cache Creek" units VI and VII north of the Vernon Arm of Okanagon Lake. It was dated by the l<0/Ar method at 178- 6 m.y., appendix 1. The largest plutonic body in the area, a f o l i a ted grarlodiorite -quartz) monzonite, unit IX, forms an igneous contact with the southernmost "Cache Creek" rocks. The contact l i e s roughly pa ra l l e l to the s t r i ke of "Cache Creek" bedding. F i na l l y , the ent i re map area has been involved in abundant Tert iary igneous a c t i v i t y , rocks of which comprise unit X. Andesit ic volcanics cover parts of a l l underlying groups and related dikes intrude Shuswap rocks; one i so lated outcrop of volcanic breccia caps underlying volcanics ju s t south of Vernon. Petrographic descriptions of indiv idual rock units comprise the remainder of th is chapter. Opt ica l l y estimated, representative modes are l i s t e d in f igure 2-1. Unit I - Hornblende Gneiss This unit comprises medium to coarse grained beige to dark brown banded hornblende gneiss. I t exhib its d i s t i n c t i v e banding on a scale of two to s ix inches produced by varying proportions of hornblende (figure 2-2), and fractures into equant blocks. I t i s composed of quartz, plagioclase (An 31), major hornblende and minor b i o t i t e . Hornblende generally dominates over quartz. Sphene and epidote are common access-or ies . Hornblendes are fractured but define a strong l i nea t i on contained Figure 2-1 PETROGRAPHIC MODES Station Locat. Unit Qz PI An Or Hb Bi Gar Chi Di Opq Ca Other 73 D-9 I 15 10' 37 TO 55 51 »-. 3 1 ep 2 7 F-9 I 35 25 26 10 20 2 2 1 sph 5 79 F-8 I 10 15 15 45 8 5 2 B-13 ErlOV la 70 10 ' ". 1 5 10 1 sph 3 2 F-7 II 24 34 36 23 8 8 .5 2 ap 5 9 F-9 III 70 5 29 5 10 5 3 ep 1; sph 1; cumm Tr 17 F-10 III 53 25 26. 15 10 1 2 ep 1; sph 1, mus 1 5 G-7 IV 40 10 30 45 1 sea 2; ep 1; sP% 1 56 G-7 IV 66 5 32 5 1 13 1 7 ep 1 10 F-9 IV 67 5 25 2 sph 1; ep 1, sea 1 22 F-9 IV 40 15 40 25 15 5 sea Tr 22k F-9 IV 45 1 Tr 15 35 sph 3; ep 1 60 F-8 IV 61 5 36 5 1 20 2 4 ep 1; sea 1 16 F-9 V 75 15 32 5 2 3 C-38 F-10 V 15 25 40 5 5 ep 10 64 F-8 V 30 25 31 30 3 10 1 sph 1 10s F-9 Hb s i l l 5 5 27 5 80 5 ap 5; ep 5 C-146 C-5 VI 1 11 98 C-51 E -6 VII 10 20 1? 1 8 rx frags 30; matrix 31 24 E - 5 VII 55 25 4 3 5 mus 10; l im 2 23 Er-7 VII 88 10 2 C-46 E - 5 VII 8 18 5 2 60 hem 2 C-139 CN-4 VIII 1? 1 7 55 3 Tr 4 ep 10; zo 23, sph Tr C-140 C-4 VIII 50 5 1 ep 10; zo 34 34 Fr4 IX 20 30 37 30 10 1 4 ep 4; sph 1 '.. 49 F-8 X 11 37 5 3 3 g.m. 73 18 DrJ X 40 36 2 3 glass 50, zeo Tr 15 2-2 Tight phase 3 folds in banded hornblende gneiss, unit I. 2-3 Photomicrograph showing roughly equal pro-portions of b i o t i t e and hornblende in un i t II. Plane polar ized l i g h t . F ie ld of view i s 3.2 m.m. across. ,16 in the phase 2 metamorphic f o l i a t i o n plane. Quartz exhibits a high degree of rec ry s ta l i za t i on and polygonization tending toward mortar texture. The texture in th in section is nematoblastic. Unit l a - Quartzite A diagnostic feature of unit I i s the common occurrence of d i s -continuous but mappable d i op s i d i c ' qua r t z i t e lenses. The quartz i te is f ine grained, o l i ve green to beige, nonf i s s i l e and highly f ractured. In outcrops i t i s structureless and often appears aphanit ic. Compositionally i t i s very quartz r i ch with minor plagioclase (An 25), d iops ide, and possible grossu lar i te garnet, b i o t i t e , and sphene. It does not contain c a l c i t e . The texture i s equigranular granoblast ic. r t Unit II - Hornblende r- B i o t i t e Gneiss This unit is f i ne to medium grained brown feldspathic hornblende-b i o t i t e gneiss. Granular even grained texture and lack of pronounced banding d i f f e r e n t i a t e i t from units I and III in the f i e l d . I t contains essential quartz,* plagioclase (An 36), orthoclase, and roughly equal amounts of hornblende and b i o t i t e though never over twenty percent tota l mafics. Quartz i s generally equant, undulose, and part ly rec ry s ta l i zed . Feldspars are commonly f ractured. Both hornblende and crenulated b i o t i t e out l ine a poorly developed l i nea t i on . A photomicrograph of Unit II i s shown in f igure 2-3. Unit III r- B i o t i t e Schist This un i t comprises medium grained beige to brown rusty weathering well f o l i a ted b i o t i t e sch i s t . I t i s composed of abundant quartz, 17 orthoclase, plagioclase (An 30), b i o t i t e and minor almandine garnet. Diopside and cummingtonite occur sporadical ly and sphene and epidote are common accessories. Texture varies from 1epidoblastic to grano-b l a s t i c depending on quartz content. Grain boundaries tend toward 120 degrees. B i o t i t e l i e s in the f o l i a t i o n plane. Quartz exhib its undulatory ext inct ion but only a low degree of preferred or ientat ion due to large grain s ize and generally equant shape. The appearance of unit III i s i l l u s t r a t e d in f igures 2-4 and 2-5. At several l o c a l i t i e s concordant hornblende s i l l s are enclosed in the b i o t i t e sch i s t . They are coarse grained ?dark green to black and consist ch i e f l y of vaguely aligned hornblende with minor b i o t i t e and quartz. Hornblende i s highly f ractured. Contacts with the surrounding schist are sharp. Unit IV - Calcareous Quartzite ^ This unit i s f ine to medium grained buff to blue-gray, l i neated, f o l i a t e d , and contains essential c a l c i t e . I t weathers to a p i t ted surface permitting accurate measurements of elongate minerals. In the cores of recumbent phase 2 fo lds one often finds segregations containing up to 50 percent diopside. This unit out l ines the highly conspicuous nearly three mile long phase 2 fo ld in the southeast portion of the map area, locat ion F-8. It i s composed of at least 50 percent quartz, e plagioclase (An 36), c a l c i t e , d ips ide, and accessory s capo l i te , sphene and epidote. Quartz tends to form undulatory ribbon grains subparallel to compositional layer ing. Feldspar and diopside are fractured and s im i l a r l y aligned although not nearly as rec ry s ta l i zed . Notably, 18 2-4 Prominent garnets l i e in b i o t i t e matrix of b i o t i t e s ch i s t , unit I I I. Scale bar = 1 c m . 2-5 Photomicrograph of unit III. Strong b i o t i t e alignment in phase 2 f o l i a t i o n plane. Plane polar ized l i g h t . F ie ld of view i s 3.2 m.m. across. 19 .. c a l c i t e i s everywhere f ine grained. Figure 2-6 i s a photomicrograph of Unit IV. Texture i n th'fn section i s granoblastic to poorly developed nematoblastic. Unit V - Granit ic Dikes and S i l l s A large number of l i g h t colored dikes and s i l l s ranging composit-i ona l l y from granodiorite to quartz monzbnitei intrude layered units I through IV. Although no c h i l l e d margins were i den t i f i ed contacts with intruded units are sharp down to a scale of a few mi l l imeter s , suggesting an intrus ive o r i g i n . Structural evidence, chapter 3, indicates that intrus ion predated phase 3 deformation. Petrographical ly, unit V i s medium to coarse grained hypidiomorphic to porphyr i t ic with an average monzonitic composition. Commonly myr-/ mekitic orthoclase predominates over normally zoned plagioclase (An 26-34), major quartz and minor b i o t i t e . Quartz exhibits undulatory ext inct ion and both quartz and feldspars are highly f ractured. B i o t i t e i s exten-s i ve ly c h l o r i t i z e d . The only int rus ive large enough to be shown on plate A exhib i ts a b i o t i t e alignment f o l i a t i o n pa ra l l e l to surrounding phase 2 metamorphic f o l i a t i o n . I t was dated by the Sr/Rb whole rock method at 42 - 10 m.y., appendix 1. Unit VI - Limestone and S i l t s tone West of Vernon and north of Kalamalka Lake massive limestone pods are imbedded in a s i l t s tone matrix. Although limestone appears to dominate over matrix, a d i f f i c u l t sampling problem exists due to the massive limestones r e l a t i ve resistance to weathering. This i s espec ia l ly true north of Kalamalka Lake where exposures are generally poor, often completely obscuring the less res i s tant s i l t s t one . 20 2-6 Unit IV. Calcareous quartz i te . Fine grained granular c a l c i t e and undulatory quartz envelope d io -pside porphyroblasts. Cross polarized l i g h t . F ie ld of view i s 2.3 m.m. across. 2-7 Crinoid stem and bryozoa in limestone pod of unit VII. Plane polarized l i g h t . F ie ld of view i s 4.6 m.m. across. 21; The limestone i s medium to f i ne grained, l i g h t to dark gray, massive weathering with bedding only recognizable as poorly defined parting planes and planar f o s s i l hash segregations. In th in section the limestone i s seen to be a recrys ta l i zed biomicr i te composed almost en t i r e l y of c a l c i t e . The s i l t s tone matrix i s described i n de ta i l as un i t VII a f below. Unit VII - Sandstone and S i l t s tone West of Kalamalka Lake a repeated sequence of immature l i t h i c arenite and s i l t s tone contains limestone pods. The limestone appears mineralogical ly i d e n t i c a l , both in f i e l d and deta i led study, with that of unit VI; but contains f a i r l y well preserved c r ino id stems, bryozoa, and rare enchinoids, f igure 2r-7. As the s i l t s tone and sandstone are separable in the f i e l d , they are described separately as units V i l a and V l l b . Unit V i l a - S i l t s tone In hand specimen uni t V i l a i s dark gray, aphanit ic, and highly fractured into small equant blocks. S t r a t i f i c a t i o n i s convoluted, broken, and discontinuous on a very small sca le, see f igure 2-8. This unit could be genet ica l ly c l a s s i f i e d as a s i l t s tone pseudoconglomerateg (Pettijohn, 1957, p.190). In th in section the unit i s extremely f i ne grained with a maximum ,grain s i ze of ten microns and is composed of angular, poorly sorted quartz grains, b i o t i t e , c a l c i t e , white mica, and ch l o r i t e . 22 2-8 Convoluted and microfaulted s t r a t i f i c a t i o n in s i l t s t one , unit V i l a . Cross polarized l i g h t . F ield of view is 4.6 m.m. across. 2-9 CIinopyroxene (at ext inct ion) cores complexely zoned hornblende of unit VIII. Cross polar ized l i g h t . F ield of view i s 4.6 m.m. across. 23 Unit VIlb - L i t h i c Arenite In the f i e l d unit VIlb i s dark gray-green f ine grained and highly fractured with prominent c a l c i t e f racture f i l l i n g s . Limited evidence of graded bedding in the f i e l d implies that age increases to the north. In thin section the rock consists of poorly sorted, s l i g h t l y rounded, angular l i t h i c fragments of a l b i t e and ru t i l a t ed quartz, possible volcanic shards, and c a l c i t e fragments f l oa t i ng in a micro^crystal ine ground mass. The largest grain s ize recognized i s 0,2 mi l l imeters . Quartz vein f i l l i n g exhibits: undulatory. 'extinction. Unit VIlb contains rare gray micro^crystal ine highly fractured banded chert lenses. In thin section the chert appears highly recrys ta l i zed with a l l grain boundary intersections approaching 120 degrees. I t i s quite d i r t y with ten percent kinked ch l o r i t e and small euhedral opaques. Unit VIII - Amphibolite This unit consists of a large hornblende r i ch body ly ing concord-antly between units VI and VII. I t i s bas i ca l l y a bimineralogical unit with medium grained dark green hornblendes p o i k a l i t i c a l l y enclosed in a subordinate anhedral apple-green epidote groundmass. Hornblendes are concentr ica l ly zoned, with a c t i n o l i t i c rims i den t i f i ed by X-ray d i f f r a c t i o n . Hornblendes contain ragged anhedral o l i v i ne and clinopyroxene remnants, f igure 2-9, and epidote contains rare a l b i t e (An 07) remnants. Thus un i t VIII appears to be an altered igneous s i l l . Because hornblende dominates over epidote in a l l cases an or ig ina l gabbroic composition i s suggested assuming mafics a l t e r to hornblende and plagioclase a l te r s to a l b i t e plus epidote.. Hornblendes show a poorly developed l inear alignment and the unit exhib i ts a macroscopic banded character although neither of 24-' these structures were investigated in d e t a i l . Because of i t s i n t r i gu ing compositional and structura l cha rac te r i s t i c s , and lack of possible s t r a t i g r aph i ca l l y co r re la t i ve un i t s , a K/Ar geochronologic study of th i s unit was undertaken. Hornblendes y ielded an age of 178- 6 m.y. (appendix 1), the s ign i f icance of which i s discussed in section 5. Unit IX - Quartz Monzonite Bathol ith The large C IlC 3plutonic body j u s t west of Kalamalka Lake was previously dated by f a i r b a i r n et . a l . (1964) at 58 m.y. using the Sr/Rb method. The present author did not redate the pluton but f i e l d evidence confirms a pre-Eocene o r i g i n as i t i s over la in by probable Eocene volcanics at l o c a l i t y G-6 (see f igure 1-2). Jones (1959) mapped the unit as part of the Cretaceous Coast Intrusives. I t i s in igneous contact with "Cache Creek" rocks to the north and commonly includes a l tered pods of country rock. In hand specimen the rock i s a medium grained f o l i a t ed highly altered quartz monzonite. In th in section i t i s seen to be porphyr i t ic with subhedral highly saussuratized plagioclase (An ;37), and anhedral dentate q u a r t z , p o i k a l i t i c a l l y enclosed in la te anhedral orthoclase. Abundant c a l c i t e veining and secondary ch l o r i t e and epidote, indicate extensive hydrothermal a l t e r a t i on . Unit X - Tert iary Volcanics Outcrops of Tert iary volcanics cap underlying rocks in i so lated areas throughout the map area (see plate A and f igure 1-2). Jones (1959) c l a s s i f i e d them as the Kamloops Group of Eocene to Miocene age. They appear s t ra t i g raph i ca l l y equivalent to Marron Formation volcanics 25 which Mathews (personal communication) has dated at 49- 2 m.y. using the K-Ar method. Plateau basalts of probable Miocene Age (Mathews, personal communication) encroach on the very south-east corner of the map area but were not considered in th i s study. The volcanics range from basalt to andesite in composition and rare ly include a ltered t u f f bands. They are aphanit ic , ves0cular to amygduloidal, and various shades of green in hand specimen. In th in section t rachyt ic texture i s well developed with f e l ted plagioclase (An 36) micro l i tes and glomeroporphyritic segr ations of zoned p lag io-c lase, clinopyroxene and possibly hornblende, f igure 2-10. The segre-gations are highly a l te red. Vesicles are c a l c i t e f i l l e d . At one locat ion , approximately F-8 (see plate A), a two inch thick lamprophyre dike occupies a north s t r i k i n g ve r t i c a l phase 5 f racture. The aphanitic groundmass contains glomeroporphyritic clumps of subhedral plagioclase (An 37), pyroxene, b i o t i t e and hornblende, and exhib i ts a vague flow banding pa ra l l e l to the s t r i ke of the d ike. Compositionally, the rock c l a s s i f i e s as a Spessartite and is probably genet ica l ly related to the overlying mafic vo lcanics, unit X. Ross (1974) has dated a s im i la r f o l i a ted phase 5 dike at 43- 2 m.y. using the K-Ar method. Unit Xa - Volcanic Breccia At one l o c a l i t y , C-9, a sequence of volcanic breccia over l ies volcanics of Unit XI. The outcrop exhib i ts poorly developed flow planes in which c lasts are vaguely al igned. The breccia consists of poorly sorted angular to well rounded volcanic and sedimentary fragments with maximum c l a s t s i ze of one centimeter, set in a buff to brown aphanit ic groundmass. The groundmass i s microcrystal ine p a r t i a l l y d e v i t r i f i e d 26 2-11 Vo l can i c and sedimentary fragments i n v o l c a n i c b r e c c i a , u n i t Xa. Plane p o l a r i z e d l i g h t . F i e l d o f view i s approx imate ly 3 c m . ac ro s s . 27 glass composed of quartz, fe ldspar, b i o t i t e , and r e l i c t shards. The matrix never comprises more than t h i r t y percent of the whole rock. Figure 2-11 i l l u s t r a t e s the character of unit Xa. 28 3, STRUCTURE Shuswap rocks have undergone f i v e and "Cache Creek" rocks four superposed deformational phases on scales ranging from mil l imeters to several kilometers. A l l outcrops contain abundant mesoscopic structures and at each s ta t ion s t r a t i f i c a t i o n or compositional layer ing and recognizable l a te r structures (minor f o ld axes and ax ia l planes, l ineations ; , f o l i a t i o n s , and fractures) were recorded. Superpos i t ion of up to three phases of deformation in one outcrop i s occas ional ly seen as i n f igure 3-1. This permits d i rec t assignment of f o ld sequences to par t i cu la r deformational styles and or ientat ions which are interpreted as comprising s ing le phases. L i tho log ic and mesoscopic structural data was used to i n fe r the pos i t ion and geometry of macroscopic s t ructura l elements. The results are not unique but represent the best estimate of the st ructura l h istory of the map area. S t r a t i f i c a t i o n in "Cache Creek" rocks comprises the e a r l i e s t recognizable structure and consists of f i n e l y spaced a l ternat ing l i g h t and dark layers i n both sandstone and s i l t s t one . Compositional layer ing on a scale of up to f i v e c m . i s well developed in Shuswap layered units I through IV and may represent s t r a t i f i c a t i o n but no r e l i c t primary structures were observed. A profusion of l a t e r mesoscopic structures occur throughout the map area. Shuswap rocks contain at least one penetrative metamorphic s ch i s toc i t y , cons ist ing of planar aligned b i o t i t e s , which pa ra l l e l s transposed compositional layer ing except near i s o c l i n a l f o l d cores where i t diverges to produce ax ia l plane f o l i a t i o n . Related mineral alignment l ineat ions (hornblende and diopside alignment along with 1 3-2 Kinked muscovite from the nose of a major phase 3 f o l d , in unit III. Cross polarized l i g h t . F ie ld of view i s 1.2 m.m. across. 30 ribbon quartz elongation in Units I, III and IV) are commonly, but not always pa ra l l e l to minor i soc l ine axes. Some i s o c l i n a l folds re fo ld ea r l i e r rootless i so l ines and the i r ax ia l plane f o l i a t i o n s ; others do not. Compositional layering surfaces in layered units almost always exh ib i t ribbon quartz and mica edge intersect ion l i neat ions . Cache Creek rocks contain a penetrative metamorphic f o l i a t i o n pro-duced by mica alignment but constituent c las t s do not exh ib i t recog-nizable preferred or ientat ion. Metamorphic micas pa ra l l e l s t r a t i f i c a -t ion except i n the cores of i s o c l i n ca l foldslwhere a weak ax ia l plane f o l i a t i o n i s occasional ly recognizable in the f i e l d . Quartz elongation in metachert lenses produces the only i d en t i f i a b l e mineral alignment l i nea t i on . Poorly defined l inear structures developed on s t r a t i f i c a t i o n surfaces are weathered s t r a t i f i c a t i o n - metamorphic f o l i a t i o n mica edge intersect ion l ineat ions. . Less pervasive minor structures occur throughout both rock types related to l a t e r , more b r i t t l e , phases of deformation. Microscopical ly kinked micas produce a crenulation cleavage and l i neat ion (f igure 3-2) in layered Shuswap units near some major fo ld hinges. Crenulation cleavage in "Cache Creek" rocks i s developed by kinking of the mietamor-phic f o l i a t i o n on a scale of one to f i v e centimeters. Both Shuswap and "Cache Creek" rocks develop nonpenatrative f racture cleavages pa ra l l e l to ax ia l planes of minor buckle fo ld s , f igure 3-4. A l l Mesoscopic structural data i s plotted on lower hemisphere equal area project ions. The map area i s subdivided into a number of s t ructura l domains, chosen such that par t i cu la r deformational character i s t i c s are homogenous throughout that domain. Differences in mesoscopic structures 31 3-4 Phase 4 buckle folds with fracture cleavage developed along ax ia l planes. In b i o t i t e s ch i s t , facing N.E. 3-5 Phase 2 refolding rootless phase 1 i soc l ines in hornblende gneiss, unit I. Distorted phase 1 l ineat ions f a i n t l y v i s i b l e . 32 between domains are used to substantiate large scale structural features. Structural domains are shown in f igure 3-3, Structural elements of Shu-swap and "Cache Creek" Complexes are described separately. Possible st ructura l corre lat ions between the two groups are discussed in Section 5. Shuswap Structure Shuswap rocks appear to have undergone f i ve phases of deformation. The most eas i l y recognized, phase 2, produced gently northerly dipping subhorizontally easterly plunging i s o c l i n a l fo ld s . These refo ld e a r l i e r gently northerly dipping and plunging rec l ined i soc l ines defined as_ Phase 1. Some l i t h o l o g i c repet i t ions and mixed vergences are unexplain-able in terms of phase 2 fo ld ing alone. Phase 3 folds plunge subhorizon-t a l l y to the northeast with var iably dipping ax ia l planes. Unusual phase 3 geometry consists of sharp hinged angular folds with one steep and one gently dipping limb. Phase 4 and 5,which trend northeasterly and northerly respect ive ly , are la te b r i t t l e events characterized by upright buckle folds and abundant f ractures. Igneous a c t i v i t y , which occurred contemporaneously with phase 2 and 5 deformations, i s discussed below. Metamorphism, discussed in sec-t ion 4, may have occurred during phase 1 deformation and culminated in amphibolite facies during and fol lowing phase 2 deformation. Widespread hydrothermal a l te ra t i on occurred in Tert iary time, contemporaneous with phase 4 and 5 deformation. .34 Shuswap Phase 1 Shuswap rocks contain evidence for a northerly trending i s o c l i n a l recl ined phase of deformation, folds of which never re fo ld any structures other than compositional layer ing. These ea r l i e s t recognizable structures are defined as phase 1. In some instances southeast.trending; J " ' " : ( f ^ ^ p h a s e 2 folds refo ld north trending phase 1 i soc l ines as in f igure 3-5, which i l l u s t r a t e s the r e l a t i v e dating of the age of phase 1. This ear ly phase in high grade Shuswap rocks has been recognized by previous workers to the south of the thesis area (Ross and Ch r i s t i e , 1969; Ch r i s t i e , 1973; Ross, 1973; Ryan, 1973). Mesoscopic phase 1 i s o c l i n a l f o l d s , although not p l e n t i f u l , are found in a l l layered Shuswap units throughout the map area (f igure 3-6). In calcareous quar tz i te , unit IV, elongate quartz produces a penetrative l ineat ion pa ra l l e l to fo ld axes. Penetrative f o l i a t i o n s are well developed by planar b i o t i t e alignment in units II and I I I , and l i near hornblende alignment in units I and II. Because phase 1 f o l i a t i o n s pa ra l l e l mesosco-pic ax ia l planes and phase 1 l ineat ions pa ra l l e l minor fo ld axes, they are interpreted as ax ia l plane f o l i a t i o n s and ax ia l l i nea t i on s , respect ive ly. Mesoscopic s t ructura l data for phase 1 deformation i s plotted in plan view, f igure 3-7, and an equal area project ion, f igure 3-8. Minor fo ld axes and ax ia l l ineat ions concentrate at '000 o /16°. Poles to phase 1 ax ia l planes and ax ia l plane cleavage f a l l on a great c i r c l e locus. Axial plane cleavage appears to c lose ly pa ra l l e l minor f o l d ax ia l planes and the pole to the great c i r c l e locus coincides with the average phase 2 fo ld axis discussed below. The spread of poles to ax ia l planes is interpreted as a resu l t of refo ld ing by phase 2 deformation. The average ax ia l plane 3-6 North trending phase 1 fo ld which folds com-pos it ional layering in calcareous qua r t z i te , un i t IV. 3-11 Decollement s ty le phase 2 fo ld in a g ran i t i c s i l l , unit V. 37 FIGURE 3-8 in Shuswap Phase 1 • Phase 1 mineral lineations O Phase 1 fold axes showing vercjence + PoIes to Phase 1 ax ia I pIanes 38 :.. o r i en ta t i on , 132°/20°N, contains the concentration of minor f o l d axes and l ineat ions . Because of the present i s o c l i n a l geometry, refo ld ing by phase 2, and the r e l a t i v e l y small amount of s t ructura l data, o r i g ina l phase 1 s ty le and or ientat ion is indeterminate. Mesoscopic phase 1 folds have consistent counter-clockwise vergence in domains D2 through D6, D7 and D9, as shown in f igure 3-3. Phase 1 exhib its clockwise vergence with in domains Dl and D8 which define- a south east trending s t r i p of reversed phase 1 vergence. The l i t h o l o g i c succes-sion with the ef fects of phase 2 deformation removed s t i l l shows l i t h o l o g i c repet i t ions . The large ae r i a l extent of mesoscopic phase 1 f o l d s , the macroscopic band of reversed phase 1 vergence and l i t h o l o g i c repet i t ions unexplained by phase 2 fo ld ing indicate widespread and possibly large scale effects of early phase 1 fo ld ing . Shuswap Phase 2 Phase 2 deformation of Shuswap rocks i s the best developed i n the map area. I t produces well defined structures on a l l scales up to the prominent gently northerly dipping i s o c l i n a l synform outl ined by ca lca r -eous quar tz i te , unit IV. Other major phase 2 folds to the north and south are defined by l i t h o l o g i c repet i t ions and vergence studies. Mesoscopic phase 2 folds are seen to re fo ld rootless phase 1 i soc l ines in f igure 3-5. Figure 3-1 i l l u s t r a t e s inter re lat ionsh ips of phase 1, 2, and 3 mesoscopic fo lds . Mesoscopic phase 2 folds cores commonly contain mineral segregations; diopside in unit IV and hornblende in units I and II. Diopside and horn-blende alignment plus l i near quartz elongation produce a penetrative ax ia l l i n e a t i o n ; b i o t i t e alignment produces a penetrative f o l i a t i o n pa ra l l e l to 39 minor f o ld ax ia l planes. Mica and quartz edge l ineat ions found on many compositional layering surfaces pa ra l l e l mesoscopic phase 2 fo ld axes. They are interpreted as compositional layering-metamorphic f o l i a t i o n intersect ion l i neat ions . In one instance where a phase 2 f o l d refolds phase 1 rootless i so -c l ines in unit 1, Figure 3-5, two penetrative hornblende l ineat ions are present. The most prominent pa ra l l e l s the phase 2 fo ld ax i s . The other i s curvil inear,wraps around the phase 2 hinge, and l i k e l y represents d i s torted phase 1 ax ia l l i nea t i on . Structural data for phase 2 deformations i s p lotted on plan view, f igure 3-9, and equal area project ion, f igure 3-10. Minor f o ld axes,which exh ib i t mixed vergences and penetrative l ineat ions described above, show a wel l defined concentration with or ientat ion 106°/06°. The pole of the great c i r c l e locus of poles to phase 1 ax ia l planes has or ientat ion 95°/10°, nearly coincedent with the s t a t i s t i c a l l y defined phase 2 ax i s . Poles to phase 2 ax ia l planes c lu s te r at a d i f fuse concentration. From t h i s , phase 2 ax ia l plane or ientat ion is s t a t i s t i c a l l y defined as 117 0/30° N. Phase 1 ax ia l planes and compositional layer ing have been transposed into near coincedence with phase 2 ax ia l plane o r ientat ion . Four macroscopic phase 2 folds are recognized in Shuswap rocks of the thesis area. Synform 2-1, outl ined by un i t IV i l l u s t r a t e s the extremely t i ght nature of macroscopic phase 2 fo ld ing . At the edge of Kalamalka Lake,location F-4 } f igure 1-2 and plate A, the two calcareous quartz i te limbs diverge exposing cores of b i o t i t e s ch i s t , unit I I I , and hornblende gneiss, un i t I. Unit IV limb separation at th is point is approximately 500 feet. Unit I pinches-out down plunge at locat ion F-8. At the end of outcrop, locat ion F-9, un i t III s t i l l separates the quartz-i t e l imbs, though tota l outcrop width i s less than 50 fee t . South of T Shuswap Phase 2 • Mineral Lineations o FoId axes )^ Fold axes with vergence + Poles to axial planes Cozens Bay the b i o t i t e sch i s t pinches out although the now s ing le coring quartz i te band continues eastward out of the map area fo r a distance of over three mi les! Mesoscopic phase 2 folds exh ib i t consistent clockwise vergence north of f o ld 2r l but counter-clockwise vergence to the south, f igure 3-9, confirming a synformal nature. The concentrations of poles to compositional layer ing on opposite sides of f o ld 2-1 cannot be dist inguished, ind icat ing i s o c l i n ca l macroscopic geometry. Evidence for antiforms 2-2 and 2-3 i s less conclusive. Hornblende gneiss, unit I, i s repeated around cores of hornblende-biotite gnesis, unit II. Reversed mesoscopic fo ld vergence around fo ld 2-2 confirms a n t i -formal geometry but evidence for fo ld 2-3 i s ambiguous. Fold 2-4 is only poorly defined by l i t h o l o g i c repet i t ions of units I and II around a core of b i o t i t e s ch i s t , unit III. Moreover, the s ingle vergence measurement, shown in f igure 3-9, i s consistent with a synformal nature. Poles to compositional layering around folds 2-2, 2-3, and 2-4 show , no recognizable divergence indicat ing i s o c l i n a l geometry. Numerous g ran i t i c dikes and s i l l s , petrographical ly described in sect ion 2, are related to phase 2 deformation. They contain mesoscopic phase 3 folds and decollement folded phase 2 fo lds ; f igure 3-11, but no e a r l i e r structures. The largest int rus ive s i l l shown on plate A at locat ion F-8 exhibits a wel l developed phase 2 b i o t i t e alignment f o l i a t i o n and la te b r i t t l e f ractures. Structural data for th i s unit i s shown in f igure 3-12. The s i l l was dated by the Sr/Rb whole rock method at 42+10 m.y., appendix 1. A possible thermal resett ing o r i g in for the Sr/Rb date i s suspected. Mathews secured s im i l a r Eocene ages from Shuswap gneiss of the T r i n i t y H i l l s at the north of the map area. He u t i l i z e d the K/Ar 43 UNIT V STRUCTURES • Mineral lineations ^ Poles to fractures Pol es to fol iat ion', o Domain D2 ® Doma i n D5 44' method which i s susceptible to thermal resett ing at r e l a t i v e l y low tempera-tures and pressures. He nonetheless concludes that the results are anomalous (Mathews, 1976, p.47): "Explanation of the very young apparent ages of the'gneisses remains e lu s i ve . " " The s u s cep t i b i l i t y of the Sr/Rb i sotop ic system to thermal resett ing i s at present v i r t u a l l y unknown. Contradictory resu l t s have two possible explanations: (1) The Tert iary date represents the time of phase 2 deformation in which case phases 2 through 5 a l l occurred in Tert iary time or l a t e r : (2) The 42 m.y. age represents a thermal event which updated the Sr/R(b i sotopic clock. Neither p o s s i b i l i t y seems read i ly acceptable. Speculat ively, however, thermal resett ing seems more compatible with large scale Cord i l leran tectonics and the resu lts of other workers than four deformational phases occurring in Tert iary time. Shuswap Phase 3 Phase 3 deformation produces mesoscopic structures throughout the map area but appears to have l i t t l e macroscopic e f fec t . L i tho log ic repe-t i t i o n s and mesoscopic s t ructura l evidence may suggest the existence of a large scale synform. Mesoscopic fo ld geometry and the development of microscopic phase 3 crenulation cleavages indicates less duct i l e con-d i t ions than for phase 2 deformation. Figure 3-1 i l l u s t r a t e s phase 3 refo ld ing both phase 1 and 2 mesoscopic fo lds . Unusual phase -3 f o ld geometry consists of a l ternate ly shallowly and steeply dipping planar limbs with angular hinges ; f igure 2-2. An interl imb angle of 70° was determined by averaging measurements of s i x mesoscopic fo ld s . Kinked micas, f igure 3-2 Jproduce crenulation cleavages and l ineat ions in phase 3 fo ld cores in units I, I I , and I I I. This 4.5 resu lts in d i scont inu i ty surfaces along mesoscopic ax ia l planes and l i n e a -tions on fo ld hinges pa ra l l e l to minor fo ld axes. Mesoscopic phase 3 data, shown in figures 3-13 and 3-14, is not amenable to simple in terpretat ion. Phase 3 ax ia l planes s t r i ke north-easterly but dips vary extensively. Because phase 1 and 2 ax ia l planes do not exh ib i t s imi la r var iat ions in o r i en ta t i on , the e f fec t cannot be due so le ly to l a te r re fo ld ing. Poles to phase 3 ax ia l planes may be in terpre-ted to define two concentrations, (see f igure 3-14). If so Shuswap phase 3 fo ld ing may comprise a pair of conjugate ax ia l planes, one dipping moderately northward, the other gently southward. Both Chr i s t ie (1973) and Medford (1976), arr ived at s im i l a r conclusions about a possible cor-re l a t i ve phase of deformation to the south, and assigned the conjugate ax ia l planes to subphases 3a and 3b. The l im i ted data of the present study does not permit such quant itat ive subdivis ion but is suggestive of s imi la r s t ructura l development. Axial l ineat ions and minor fo ld axes plunge gently northeastward but also exh ib i t considerable var ia t ion in or ientat ion. They are seen to l i e on a northeast centered, small c i r c l e locus (figure 3-14). Phase 2 l inear structures show a s imi la r north-south spread, ind icat ing possible pa ra l l e l s ty le refo ld ing by a l a te r deformational phase. North of Cozens Bay Shuswap l i t h o l o g i c a l contacts and macroscopic phase 2 ax ia l traces veer from northwesterly trends in the north to easterly trends in the south, out l in ing a probable macroscopic phase 3 fo ld (f igure 3-13). Locations of maximum l i t h o l o g i c curvature define the ax ia l trace pos i t ion. Orientational var ia t ion of compositional layering indicates synformal geometry. The change in mesoscopic phase 3 fo ld vergence from counterclockwise in the north to clockwise south of 47 1 Shuswap Phase 3 • Mi neraI I i neat i ons o FoId axes O Fold axes with vergence + Poles to axial planes 48 the f o l d , confirms such an interpretat ion. Mesoscopic phase 3 fo lds at locat ion F-7 exh ib i t no vergence, consistent with the major phase 3 f o l d hinge pos i t ion ing. It should be noted that the macroscopic phase 3 ax ia l trace i s gently cu rv i l i near probably as a r e su l t of l a t e r refo ld ing. Shuswap Phases 4 and 5 Phase 4 and 5 deformations are low temperature b r i t t l e events which l i k e l y occurred during the Tert iary. They are responsible for open buckle fo ld s , f ractures, and minor ca tac l a s t i c brecc ia. Some previous authors (Ryan 1973, Ross 1974) considered phase 4 and 5 to comprise a s ingle deformational event whereas others (Chr i s t i e , 1973) consider them separable but probably coeval in nature. In the thesis area north trending phase 5 post dates northeast trending phase 4. Phase 4 and 5 s t ructura l elements are c h a r a c t e r i s t i c a l l y non^pene-t ra t i ve and not well developed but occur throughout the map area. Gentle warping of compositional layering surfaces commonly produces minor upright buckle folds with f racture cleavage along ax ia l planes, f igure 3-4. Abun-dant ve r t i c a l fractures with v i r t u a l l y no o f f se t p a r a l l e l the f racture cleavage. Country rocks surrounding these fractures are hydrothermally a l tered. One north trending f racture at locat ion F-8, f i gure 1-2, con-tains an undeformed lamprophyre dike described in section 2. I t resembles fo l i a ted rhomb-porphyry dikes to the south dated by the K/Ar method at 43+2 m.y. (Ross, 1974). Catac last ic breccia (f igure 3-15, locat ion F-10) was probably produced during phase 4 or 5 deformation. Interference of minor phase 4 and 5 buckle folds sometimes imparted an undulatory dome and trough nature to compositional layering surfaces. At locat ion E-10 a ve r t i c a l north s t r i k i n g phase 5 f a u l t crosscuts phase 4 f ractures . The 49 3-15 Highly s e r i c i t i z e d plagioclase and granulated quartz i n ca tac la s t i c breccia (phase 4 or 5?) of unit V. 3-16 Slickensides on a v e r t i c a l l y dipping, N s t r i k i n g , phase 5 f a u l t which truncates phase 4 f ractures. '5.0 f a u l t surface contains v e r t i c a l l y plunging slicken_,sides, f igure 3-16, ind icat ing minor, dominantly d i p - s l i p movement. Structural data for phase 4 and 5 deformation in Shuswap rocks i s shown in f igures 3-17, 3-18, and 3-19. Poles to phase 5 ax ia l planes and fracture cleavage define average axia l plane or ientat ion of 002°/84°W. Average ax ia l or ientat ion defined by minor fo ld axes concentration i s 000°/14? Average phase 4 or ientat ion i s poorly defined but d i s t i n c t from phase 5. Minor axes concentrate at 053°/00°; fracture cleavages and fractures at 072°/80S. A possible northeast trending f a u l t pa ra l l e l s Cozens Bay Valley ( locat ion F-10 and plate B) and i s tentat ive ly assigned to phase 4 defor-mation. Fault geometry i s pecul iar with approximately 500 feet apparent l e f t l a t e r a l movement i n the west and 300 feet r ight l a te ra l movement in the east. Overall f a u l t movement i s probably less than 100 feet south-up d i p - s l i p with movement on a steeply dipping f a u l t plane. No other macroscopic phase 4 st ructura l elements are recognized. Four macroscopic phase 5 folds are shown on plate B and f igure 3-17. These were defined on the basis of var iat ions in compositional layering o r ientat ion , as i l l u s t r a t e d on plate A. The folds are upright, very gentle and discontinuous. "Cache Creek" Structure "Cache Creek" rocks of the thesis area have undergone four recognized deformational phases. The e a r l i e s t , phase 1, produced very t i gh t fo lds ax ia l planes of which dip steeply northward and which plunge subhorizon-t a l l y westward. These are sometimes refolded by moderately t i gh t steeply dipping southwest plunging folds of the next recognized phase. The f i n a l two deformations,phase 3 and 4, trend northeasterly and norther ly, produce abundant fractures with attendant hydrothermal a l t e r a t i o n , and a small 52 Shuswap Phase 4 o Fo I d axes a Poles to fractures + . Poles to axial pianes 53 I +. Poles to fractures A Poles to axial planes 5.4 number of minor upright buckle fo lds . Their r e l a t i ve timing in "Cache Creek" rocks i s indeterminate. Both the large amphibolite s i l l , un i t VII I, and the quartz; jtnonzonite piuton, unit IX, contain evidence of late b r i t t l e events but no e a r l i e r structures. "Cache Creek" Phase 1 The e a r l i e s t phase of deformation i n "Cache Creek" rocks, defined as phase 1, produced very t i ght mesoscopic folds whose ax ia l planes pa ra l l e l s t r a t i f i c a t i o n except in f o ld hinges. Metamorphic f o l i a t i o n due to planar b i o t i t e alignment pa ra l l e l s phase 1 f o l d ax ia l planes and is interpreted as ax ia l plane f o l i a t i o n . On a small number of fo ld hinges * s t r a t i f i c a t i o n - a x i a l plane f o l i a t i o n intersections produce mica edge l ineat ions pa ra l l e l to minor f o ld axes. The penetrative l i neat ion in "Cache Creek" metachert lenses is produced by l inear quartz alignment pa ra l l e l to phase 1 f o ld axes. Structural data for phase 1 deformation is p lotted on plan view, f igure 3-20, and equal area project ion f igure 3-21. Poles to phaseJ axia l planes concentrate nearly hor izonta l ly ,def in ing an average ax ia l plane or ientat ion of 107°/90° N. Phase 1 f o ld axes and ax ia l l ineat ions/ , scatter along the small c i r c l e locus shown in f igure 3-21. The average ax ia l o r i en ta t i on , assumed to be the intersect ion of the average ax ia l plane and l ineat ion locus, has or ientat ion 289°/20°. Poles to s t r a t i f i c a -t ion l i e on a steeply dipping surface with pole or ientat ion 288°/05°, approximately col inear with phase 1 ax ia l o r ientat ion . S t r a t i f i c a t i o n (see plate A) i s generally steeply dipping and c lose ly coplanar with phase 1 ax ia l plane or ientat ion. This s t ructura l data indicates that s t r a t i f i c a t i o n has been almost completely transposed toward the e a r l i e s t phase of "Cache Creek" deformation. Interlimb angles were never greater 0 L MILES IX Vila -Vila A ^ " ^ ^ vllb FIGURE 3-20 "CACHE CREEK" STRUCTURES ( l i t h o l o g i c l e g e n d s e e P L A T E A ) P h a s e 1 L i n e a t i o n s F o l d A x e s A x i a I P l a n e s D i p R e v e r s a l •>—-S t r u c t u r a l D i v e r g e n c e 5 6 Cache Creek Phase 1 e Li neations o FoId axes O • Fold axes with vergence + Poles to axial planes 57 than 10 degrees. Compositional layer ing within "Cache Creek" domain D10 generally dips steeply southward. However along an easterly trending band at l oca -t ion E-5, domain DlOa, layering dips steeply northward. Both compositional layering and phase 1 ax ia l plane or ientat ion diverge widely from the i r average or ientat ions in the v i c i n i t y of the large limestone pods, domain DIOb, f igure 3-20. The question of limestone emplacement i n "Cache Creek" e l a s t i c s i s discussed in Section 5. "Cache Creek" Phase 2 Phase 2 deformation in "Cache Creek" rocks consists of mesoscopic angular folds and kinking of phase 1 f o l i a t i o n producing crenulat ion cleavages and l ineat ions . Folds approach chevron s ty le geometry with planar limbs and angular hinges. As seen in f igure 3-22, planar structures are developed along ax ia l planes. These poorly developed, discontinuous surfaces do not appear penetrative in the f i e l d but micas in the fo ld cores are microscopical ly crenulated suggesting an intermediate s t y le between crenulation and fracture cleavages. No l inear structures other than fo ld axes were recognized associated with mesoscopic phase 2 f o ld s . Most early metamorphic f o l i a t i o n surfaces are crenulated on a scale of from 0.5 to 5 centimeters. Because of s i m i l a r i t i e s in s t y le and o r ienta -t i o n , crenulations and structures related to minor folds are both considered to be produced by phase 2 deformation. Structural data for phase 2 deformation is shown in f igure 3-23. Concentration of poles to ax ia l planes define an average phase 2 ax ia l plane or ientat ion of 066°/80° N. Minor f o ld axes and crenulat ion l i n e a -tions concentrate at 253°/36°. The center of the small c i r c l e locus of 3-25 Epidote veining in two direct ions in amphi-b o l i t e , unit VIII. Plane polarized l i g h t . F ie ld of view i s 3.3 m.m. across. 59 Cache Creek Phase 2 • Li neat i ons o FoId axes O* Fold axes with vergence + PoIes to axiaI pIanes 60 phase 1 l i near structures, 253°/00° coincides with phase 2 ax ia l trend, ind icat ing pa ra l l e l s t y le refo ld ing of phase 1 structures by phase 2. Interlimb angles averaged from f i ve mesoscopic phase 2 fo lds i s 60°. No macroscopic phase 3 structures were recognizable in "Cache Creek" rocks. "Cache Creek" Phases 3 and 4 Phase 3 and 4 deformation in "Cache Creek" rocks cons ist of v e r t i -cal fractures with no o f f set and very l i t t l e separation. Quartz and c a l c i t e vein f i l l i n g as well as c h l o r i t i z a t i o n and epidot izat ion of surrounding country rocks is common. In two instances, s t r a t i f i c a t i o n is warped into minor,upright,north trending buckle fo ld s . Structural data for phase 3 and 4 deformations is shown in f igure 3-24. Fractures a l l dip steeply. Data could be interpreted as comprising a s ingle deformation with widely varying f racture or ientat ions. Two separate concentrations are recognizable, however, and neither f racture set exhibits shear features. Furthermore, the two recognized mesoscopic folds trend northerly rather than at an or ientat ion intermediate between the two recognized concentrations. From th is evidence two deformational episodes, trending northeasterly and norther ly, are defined as phase 3 and 4. The r e l a t i ve timing of these episodes is unknown and no macro-scopic phase 3 or 4 s t ructura l elements are recognizable. Amphibolite Structure Amphibolite s i l l , unit VI I I, crops out at the northern t i p of the Vernon Arm of Okanagan Lake, locat ion C-3. I t contains abundant phase 4 and 5 fractures with quartz, c a l c i t e and epidote vein f i l l i n g , f igure 3-25, and c l ea r l y predates these structural events. No e a r l i e r structures were i d en t i f i a b l e . The K/Ar date on hornblendes from Unit VIII of .;*62| 178+6 m.y. appendix 1, probably represents a thermal event as the o r i g i n a l l y igneous s i l l was metamorphosed to albite-epidote-amphibol ite f a c i e s , the highest grade attained in "Cache Creek" rocks. It fol lows that metamorphism may have occurred at about 178 m.y. in "Cache Creek" rocks of the thesis area. Quartz Monzonite Structure The large granodiorite-quartz monzonite ba tho l i t h , unit IX, to the south of "Cache Creek" rocks and west of Kalamalka Lake, also contains evidence of phase 4 and 5 b r i t t l e deformation but no e a r l i e r structures were recognizable. Although of low precis ion and questionable accuracy, the 58 m.y. Sr/Rb isochron obtained by Fairbairn e t . a l . for th i s body i s in agreement with the present structural i n terpretat ion. / 63; ' 4. METAMORPHISM The thermal history of the thesis area, l i k e i t s deformational h i s tory, i s complex. Shuswap rocks reached a maximum cumulative metamor-phic grade of medium pressure amphibolite facies contemporaneous with and fol lowing phase 2 deformation. This metamorphic culmination i s termed M2. Extremely l im i ted data indicate that an early metamorphic episode may have occurred in.Shuswap rocks p r io r to phase 2 deformation. Although i t i s unknown i f th is was a prograde stage of metamorphism accompanying phase 2 deformation or a separate e a r l i e r event, conditions were probably lower than the metamorphic culmination. This tentative early event is termed Ml. Regional metamorphism also occurred in "Cache Creek" rocks but attained a maximum grade of only greenschist to a lb ite-epidote-amphibol i te fac ies . Amphibolite s i l l , un i t VII I, i s o top i ca l l y dated at 178+ 6m.y.3 appendix 1, underwent regional metamorphism pr io r to phase 4 deformation. This date probably represents thermal upgrading rather than the c r y s t a l i -zation age, and could be related to the Colombian Orogeny- Abundant hydrothermal a c t i v i t y occurred during Tertiary time causing a l t e ra t i on in the v i c i n i t y of f ractures , quartz and c a l c i t e vein f i l l i n g , and i n some cases ca tac la s t i c brecc iat ion. This l a te thermal event i s recognized i n both Shuswap and "Cache Creek" rocks. In the remainder of th i s chapter metamorphic parageneses, react ions, and physical conditions for metamorphic episodes£T}^^ " T | a r e d iscussed,start ing with the metamorphic culmination. Shuswap M2 Useful M2 parageneses are l i s t e d in f igure 4-1. Due to the widely varied mineralogy of units I through IV, amphibolite fac ies Shuswap 64 FIGURE 4-1 METAMORPHIC PARAGENESES Shuswap Complex 1) orthoclase + plagioclase + quartz + c a l c i t e (unit I I I) 2) quartz + z o i s i t e + plagioclase (unit IV) 3) grossu lar i te + quartz + c a l c i t e (unit IV) 4) c a l c i t e + quartz + diopside (unit IV) 5) plagioclase + octhoclase + diopside + sphene (unit IV) 6) quartz + muscovite + diopside + magnetite (unit I I I) 7) quartz + z o i s i t e + diopside + magnetite (unit IV) 8) quartz + scapol i te + diopside (unit la) 9) cummingtonite + hornblende + plagioclase (unit I) 10) diopside + c a l c i t e + sphene (unit IV) 11) quartz + orthoclase + plagioclase + b i o t i t e (unit II) 12) almandine + b i o t i t e + plagioclase (unit I I I) 13) muscovite + quartz + plagioclase (unit I I I) "Cache Creek" Complex 14) b i o t i t e + ch lo r i t e + quartz - (unit VII) 15) quartz + b i o t i t e + muscovite (unit VII) 16) plagioclase + quartz + ch l o r i t e (unit VII) 17) hornblende + i lmenite (unit VIII) 19) epidote + a c t i n o l i t e + opaque (unit VIII) 20) epidote + plagioclase (unit VIII) metamorphism is, quite wel l defined and i s discussed f i r s t . Orthoclase and plagioclase are commonly found i n contact in Shuswap rocks of the map area. A lb i te subst i tut ion in coexist ing orthoclase and plagioclase was therefore used, fol lowing the technique described by Stormer (1975), to establ i sh a geothermcimeter or more s p e c i f i c a l l y a P/T coexistence l i ne in Shuswap rocks. A lb i te subst i tut ion in three plagioclase grains coexist ing with two orthoclase grains was determined using the ARL e l ec -tron microprobe. A lb i t e subst i tut ion averaged 71% in plagioclase (An 29) and 23% in orthoclase. Using the equi l ibr ium equation: NaA lS i 3 0 8 (AF) = NaAlSi 30e (PF) (1) (where (AF) and (PF) indicate a l k a l i feldspar and plagioclase mineral phases) and graphs of Stormer (1975), the pressure - temperature coexistence v l i n e (1), f igure 4-2, was deduced, with 50°C uncertainty. I t was of in teres t to determine the pore f l u i d composition during M2. Calcareous quartz i te , un i t IV, was chosen for deta i led analysis because of the strong dependence of reactions in carbonate rocks on C0 2 concentration in the pore f l u i d (Greenwood, 1962). The occurrence of parageneses 2 and 3 indicates that XCO2 was very low in these rocks and occurred between i sobar ic invar iant points: , Gr + Qz + Pr + Ca (I) investigated by Gordon and Greenwood (1971) and Zo + Gr + Qz + An + Ca (I I) investigated by Winkler (1974) in the magnesium free system. Assuming s ix and two ki lobars as upper and lower pressure (Bounds*, i sobar ic i n -variant points (I) and (I I) indicate the fol lowing brackets for the proportion of CO2 i n the pore f l u i d : 5% + 15% <XC0 2 ^23% +-5% (2) * Six and two ki lobars are common upper and lower experimental pressure conditions. 66 Equilibria for the metamorphic culmination in Shuswap rocks of the study area. FIGURE 4-2 67 The low XC02 value i s expected due to the r e l a t i v e l y small volume and low ca l c i t e content of unit IV, Analysis of pore f luids was also attempted d i r e c t l y using the crushing stage technique of Roedder 0970 d) on f l u i d inclusions i n quartz. Although inclusions are numerous, giving the quartz i t s milky appearance, they are so smal l , never larger than a few microns, that no quant itat ive resu lts were obtained. Fortu i tous ly, the determination of abundant low XC02 pore f l u i d s proved useful in e s tab l i sh -ing upper bounds on M2 pressure and temperature. As seen from paragenesis 2 quartz occurs in contact with z o i s t i t e in unit IV. Equil ibrium i s therefore to the l e f t of the equation: 43.P+ lQz= 1 Gr + 5 An + 2 H20 +(Mag.) (3) experimentally studied by Liou (1973). Because magnetite was commonly observed in unit IV, parageneses 6 and 7, results obtained for equation (3) using a QFM rather than an NNO buffer seem appropriate. Equation (3) defines maximum temperature and minimum pressure because of i t s pos i t i ve slope, f igure 4"2. Conditions of P(total) = PH20 or XC0 2 = 0 were chosen as XC02> 0 would only s h i f t the curve upward and to the l e f t , further r e s t r i c t i n g pressure and temperature condit ions. Equation (3) establishes a lower bound to the P/T l i ne defined by equation (1). Although not common; muscovite i s found in a l l Shuswap un i t s . The coexistence of muscovite, plagioclase plus quartz, paragenesis 13, and the lack of any a luminos i l icates, ind icates that equi l ibr ium l i e s to the l e f t of the equation: Ab + Mus + Qz+ H20 = Melt + A l 2 S i 0 5 (4)' studied experimentally by Storre and Karotke (1971), Combination of equation (4) with the P/T coexistence l i ne defined by equation (1) define upper pressure and temperature conditions fo r cumulative Shuswap meta-morphism. . 68 Equations (1), (3) and (4), shown in f igure 4-2, indicate that maximum cumulative metamorphic conditions in Shuswap rocks were approximately 610°C and 5.2 ki lobars with a low C0 2 concentration in the pore f l u i d . Parageneses 4 through 8 in Shuswap rocks imply that equi l ibr ium l i e s to the r i gh t of equation:. 1 Tr + 3 Cd + 2Qz= 5Di + 3C0 2 + 1 H20 (6) investigated experimentally by Skippen (1974). Diopside alignment i n un i t IV produces southeast phase 2 l ineat ions but no north trending phase 1 diopside l ineat ions were observed in un i t IV. Phase 2 f o l d cores commonly contained diopside segregations but phase 1 cores do not. This indicates that M2 metamorphism i s at least contemporaneous with phase 2 deformation. Hornblendes def ining phase 2 l ineat ions in units I and II exh ib i t l i t t l e f ractur ing or other deformation features. Phase 3 ax i a l plane cleavage however, i s dominantly b r i t t l e i n nature, therefore M2 metamorphism was e i ther retrograde or had ceased en t i r e l y by the time of phase 3 deformation. M2 in Shuswap rocks was broadly contemporaneous with and continued fol lowing phase 2 deformation, thus the annealing stage enhanced the fabr i c produced during deformation. Shuswap Ml The o r i g ina l geometry of ear ly phase 1 deformation in Shuswap rocks i s unknown due to i s o c l i n a l phase 2 refo ld ing^ and l a te r t ightening necessitated by phase 3. Theoret ical ly phase 1 could have been a b r i t t l e f l e x - s l i p event with no attendant metamorphism. Extremely l im i ted e v i -dence suggests that this i s not the case. As noted previously?u'nit IV contains marked diopside alignment pa ra l l e l to phase 2 axes. No diopside alignment in phase 1 ax ia l d i rec t ion was observed although minor phase 1 69 : ? folds in un i t IV were common (f igure 3-6). Although mesoscopic phase 1 folds were observed in a l l layered Shuswap 1 i t h o j o g i e s , only s i x recog-nizable phase 1 l ineat ions were observed. These l ineat ions were produced by hornblende mineral alignment and occur only in units I and II; horn-blende-biot i te gneiss and hornblende gneiss, not units III and IV. This l im i ted evidence suggests that an early metomorphic event, termed Ml, occurred e a r l i e r than M2. Metamorphic grade, although probably lower than M2, and relat ionships with deformations and l a t e r metamorphic e p i -sodes, are unknown. "Cache Creek" Metamorphism Petrographic invest igat ion of "Cache Creek" metamorphic mineralogy proved d i f f i c u l t due to the ubiquitous f ine grain s i ze so |k;fray d i f f r a c -t ion studies of units V i l a , VI lb, and VIII were conducted to provide addit ional information. Results indicate that these rocks (have undergone s i gn i f i c an t metamorphism of greenschist to albite-epidote-amphibol ite fac ies . Rocks north of the Vernon Arm of Okanagan Lake may have undergone s l i g h t l y higher grade conditions than those to the south. L i t h i c a ren i t i e s , unit V i l a , contain abundant angular plagioclase fragments which exh ib i t negative r e l i e f and a l b i t e X-ray d i f f r a c t i o n l i ne s . Fine grained metamorphic b i o t i t e and white mica i s abundant in s i l t s t o n e , unit VIIef,and occurs in the matrix of sandstonejUnit V l l g . Although not often o p t i c a l l y recognizable in the microcrystal ine matrices both units produce ch lo r i t e X-ray patterns. Relevant metamorphic parageneses from unit VII are l i s t e d in f igure 4-1. 70. Paragenesis 14 indicates that equi l ibr ium in unit VII l i e s to the r i ght of the equation: Jstilp + Phen = Bi + Chi + Qz + H20 (.5) (Winkler, 1974, p. 202) i l l u s t r a t e d in f igure 4-3? Unit VII therefore attained greenschist fac ies metamorphic conditions with temperature great-er than approximately 450°C. Calcareous f o s s i l s in limestone pods con-tained in un i t VII, f igure 2-7, are part ly recrys ta l i zed but recognizable. B iot i tes are aligned in the phase 1 f o l i a t i o n plane which wraps around b r i t t l e phase 2 ax ia l plane cleavage, f igure 3-22, suggest^'that metamor-phism culminated pr io r to phase 2 deformation. The large amphibolite s i l l j u s t north of the Vernon Arm of Okanagan Lake provides informative metamorphic mineralogy. Ragged a l b i t e remnants occur with in abundant granular to f ibrous manganiferous epidote (piedmon-t i t e ) and possible c l i n z o i s i t e . . Rare clinopyroyene and possible o l i v i n e remnants form cores within subhedral complexly zoned aluminous hornblende, f igure 2-9... X-ray d i f f r a c t i on study indicates pale green hornblende rims to be a c t i n o l i t i c . Ch lo r i t e , magnetite and spene are common accessories with occasional minor quartz. The common associat ion of epidote and a c t i n o l i t e , parageness 19, indicate that equi l ibr ium l i e s to the r i gh t of the equation: Pre/PU + Chi + Qz = Ep + Act + H20 (6) (Winkler, 1974, p. 70). This temperature dependent equation, shown in f igure 4-3, indicates a 0 temperature in excess of approximately 350 C. A c t i n o l i t i c rims on com-plex ly zoned hornblendes suggest that the causative thermal event was protracted in nature with a pronounced retrograde stage. Winkler (1974), p. 166, states that: 7 1 "the change from a c t i n o l i t e to hornblende w i l l probably take place at about 500OC, r i s i n g only s l i g h t l y with increasing pressure." Liou (1973) experimental l y^ inves t i gated metamorphic reactions concerning epidote and in pa r t i cu la r the equations; Ep + Qz = Gr + An. + (Mag) + F (7.) and Chi + Sph + Qz = (A l r ich) Hb + II + H20. (8) Paragenesis 18 indicates that equi l ibr ium l i e s to the l e f t of equation (7) shown in f igure 4-3, whereas paragenesis 17 l i e s to the r i gh t of equation (8), as hornblende i s i n contact with i lmeni te. The metamorphic culmination in "Cache Creek" rocks reached a l b i t e -epidote-amphibolite facies conditions with pressure in excess of 3 Kb and temperature of about 550°C, Liou (1973). The highly recrys ta l i zed nature of the limestone in unit VI and the metamorphic parageneses of the associated amphibolite s i l l , unit VII I, suggest that metamorphism may have been more intense north of the Vernon Arm of Okanagan Lake than in un i t VII to the south. Lack of d e f i n i t i v e parageneses in unit VII precludes d i rec t assignment of a par t i cu la r isograd. Mineralogical and textural re lat ionships in the amphibolite strongly suggest an igneous parentage. CIinopyroxene and o l i v i ne remnants coring subhedral hornblendes and remnant plagioclases in the epidote matrix indicate an o r i g ina l gabbroic composition assuming s i m p l i s t i c a l l y that mafics a l t e r to hornblende and plagioclase a l te r s to a l b i t e plus epidote. Unfortunately, contacts with surrounding metasedimentary units VI and VII were not observed. Hornblendes from unit VIII were dated by the K/Ar method at 178+6 m.y., appendix 1. The secondary replacement nature of the horn-blendes, the hypothesized!original igneous composition, and the super-3 Temperature C Equilibria for the metamorphic culmination in "Cache • Creek* rocks of the study area. FIGURE 4-3 73, posed albite-epidote-amphibol ite fac ies metamorphism a l l point to thermal upgrading of the K/Ar radiogenic c lock. The-178 t_6 m-,y."'date, represents; a metamorphic event rather than c r y s t a l i z a t i on of the or ig ina l igneous body. Unit VIII contains abundant phase 3 and 4 f ractures , attendant hydrothermal a l t e ra t i on and possible open warping. No e a r l i e r structures were recognized. Unit VIII s t ruc tu ra l l y predates b r i t t l e deformation and hydrothermal a l te ra t i on of probable Tert iary age and underwent a regional metamorphic episode, poss ibly/attaining albite-epidote-amphibol ite fac ies condit ions, at about 178 m.y. Regional implications of "Cache Creek" structural and metamorphic h istory are discussed in section 5. Tert iary Thermal A c t i v i t y Abundant hydrothermal a c t i v i t y occurred during Tert iary time related to late b r i t t l e deformations. Ch lo r i te , epidote, and c a l c i t e veins occupy steeply dipping northerly and northeasterly s t r i k i ng fractures in both Shuswap and "Cache Creek" rocks, f igure 3-25, and Mafics and feldspars in surrounding country rocks are highly a l tered. In one1; instance, a north-east trending band of hydrothermally a ltered c a t c l a s t i c breccia was observed at s tat ion C-38, f igure 3-15. Abundant igneous a c t i v i t y at th i s time may have provided the heat necessary for this l oca l i zed thermal event, however, the vast areal extent of Tert iary hydrothermal a c t i v i t y suggests alternate heat sources. This could be f r i c t i o n a l heating, due to easter ly directed tectonic underthrusting during Tert iary time. t74 5. DISCUSSION Age, Or ig in , and Strat igraphic Correlat ion of Shuswap Units Any statement concerning the o r i g in of Shuswap rocks in the thesis area i s en t i r e l y speculative as no whole rock chemical analyses were per-formed and no r e l i c t structures observed. The ubiquitous layered nature of units I through IV probably re f l ec t s metamorphically accentuated s t r a t i f i c a t i o n . Chr i s t ie (1973) suggested a possible graywacke suite o r i g i n for high grade Shuswap metamorphics near Vaseaux Lake based on mineralogy. Ryan (1973), however, favored a vo lcanic, possibly andes it ic o r ig in from Sr/Rb i sotopic and mineralogical data. Neither the base nor top of the loca l Shuswap sequence i s exposed in the thesis area. The present author has i den t i f i ed two phases of i s o -c l i n a l fo ld ing in layered units I through IV. S imi lar high grade rocks to the south, in the Oliver-Osoyoos area (Ryan 1973), and the VaseauV Formation (Ross and Ch r i s t i e , 19,69; Ch r i s t i e , 1973) have also undergone two i s oc l i na l deformational phases. Mineralogical s i m i l a r i t i e s of amphibolite gneiss, b i o t i t e sch i s t , and calcareous quartz i te in the thesis area to s imi la r l i t ho log ie s in the south are s t r i k i n g . Actual l i t h o -log ica l co r re l a t i on , however, i s not possible. The controversy over the o r i g in and age of the Shuswap metamorphic complex Ha s continued since Dawson (1898) f i r s t mapped the rocks (see section 1). White (1959) presents an entertaining review of the rapid evolution of ideas pr io r to 1959. Ross (1970, p.64) studied the s t ruc -tural evolution of the Kootenay Arc, east of the thesis area and notes that: "the northerly extension of the arc trends i n to ; and becomes an integral part of the Shuswap complex." He suggests that parautochthonous g ran i t i c gneiss basement of possible ; 75 Hudsonian age was act i ve ly involved in the corej>tythe Frenchman's Cap gneiss-dome; one of the Shuswap structural culminations. The e a r l i e s t causative Shuswap deformation occurred in pre-Meso]zo'ic time. To the east major allochthonous f o ld cores produced by the same early deformation override passive Puree!! basement. Campbell (1973), in a study of Cordi l leran tecton ics , amplif ies Ross' contentions. He concludes that " th ick skinned" tectonics with ac t i ve l y involved basement and dominantly ve r t i ca l movements dominate in the Omineca Crystalline Belt (Shuswap Complex). To the east however, " th in skinned" tectonics dominate, causing horizontal thrust ing to the east over a passive, non-involved basement. Lead isotope analyses of zicons from the Shuswap Terrain have provided promising results which "see through" the thermal events which have consistently confounded other radiogenic dating techniques. Wanless and Reesor (1974) derive a 1960 m.y. Proterozoic age for " c r y s t a l i z a t i o n " of zircons from granodiorite of the core zone of the Thor-Odin gneiss dome northeast of the thesis area. Based on l im i ted evidence they suggest an igneous o r i g in of the granodiorite not repres-entative of the Shuswap Complex as a whole on which they comment (Wanless and Reesor, 1974, pg 331): V "The mantling gneisses of great area! extent throughout the Shuswap, have been derived from rocks ranging in age from probable Cambrian to Tr ias s i c age." They further suggest that the 175 m.y. lead isotope lower intercept represents the metamorphic and deformational culmination of the Colombian Orogeny. Okulitch e t . a l . (1975) f i nd a 375 m.y. Devonian minimum crysta l i za t i on age of zircons frorrTthe Mount Fowler Bathol ith northeast of the thesis area. They suggest that th i s plutonism may be related to the Late Devonian-Early Miss iss ippian Caribooan or Antler - 7 6 Orogeny (Ross and Barnes, 1972; Wheeler e t . a l . , 1972; White, 1959). In the most recent study to date Wanless and Okulitch (1976, p.47) summarize the i r ex i s t ing geochronologic data concluding: "The Shuswap Metamorphic Complex, f loored by mid-Proterozonic gneiss, was formed from late Proterozoic to Late Tr ias s i c sedimentary and volcanic rocks during the Jura-Cretaceous Columbian Orogeny." In conclusion the present state of knowledge indicates complex Precambrian through Mesozoic o r i g i n and deformation of rocks const i tut ing the Shuswap Metamorphic Complex. The present study, other than reaff irming Paleozoic, Mesozoic and Cenozoic deformational and Metamorphic events provides no new information concerning the o r i g in and s t rat igraph ic corre lat ion of the complex. Age, Or ig in , and Strat igraphic Correlat ion of "Cache Creek" Units No whole rock chemical analyses were performed on "Cache Creek" rocks. L i t h i c arenites are very immature,containing up to t h i r t y percent of f i ne grained matrix. They occasionally exh ib i t graded bedding and contain metachert lenses. Fine (1 m.m.) compositional layering i n s i l t s t one , Unit V l l b , i s convoluted and discontinuous with abundant microfaults (f igure 2-8) i nd icat i ve of early sof t sediment deformation. This evidence is suggestive of a d i s ta l t u r b i d i t e , marine graywacke suite o r i g i n . Massive limestone pods in Unit VII form sharp contacts with surrounding e l a s t i c s down to a scale of a few milimeters. S t r a t i f i c a t i o n and a l l l a te r structures except b r i t t l e phase 3 and 4 fractures in s i l t s tone and sandstone in the v i c i n i t y of the limestone pods, domain D10b,are disrupted from the i r average or ientat ions. This s tructural disruption was noted in section 3. No structures other than phase 3 77 and 4 fractures were recognized in the limestone. Absence of penetrative structures in the limestone pods, coupled with the abundance of d i s -rupted early structures in surrounding sediments, suggests possible tectonic emplacement of the limestone into surrounding previously deformed sediments. Okulitch (1974) assigned complexely fo lded, low grade meta-sediments northwest of Okanagan>Lake to the Pennsylvanian-Permian Cache Creek Group, based on re-evaluation of the f o s s i l l o c a l i t y o r i g i n a l l y indicated by Jones (1959). He correlated these with "Cache Creek" rocks of the thesis area, southeast of Okanagan Lake,apparently on the basis of l i t h o l o g i c s i m i l a r i t i e s . "Cache Creek" e l a s t i c s of Unit VII consist of inter layered s i l t -stone and f ine grained poorly sorted sandstone containing angular rock, quartz, and feldspar fragments. This sequence shows marked s i m i l a r i t i e s to the basal d i v i s i on of the Pennsylvanian-Permian Chi l l iwack Group which Monger (1970, p.6-7) describes as, ' p e l i t e s i l t s t o n e , and f ine grained sandstone ... composed of poorly sorted angular fragments.' The present author suggests that these groups are possible s t rat ig raph ic equivalents based on l i t h o l o g i c s i m i l a r i t i e s . Def in i t i ve f o s s i l evidence in "Cache Creek" rocks of the thesis area i s lacking but ten L miles to the northwest along the same structura l trend Danner (personal communication) has i den t i f i ed Pennsylvanian-Permian fu su l i n i d s . He speculates that poorly preserved bryozoa from limestone pods of Unit VII, f igure 2-7, may be Devonian in age. In his discussion of cor re lat ion of eugeosynclical assemblages in the Co rd i l l e r a , Monger (1975) subdivides upper Paleozoic rocks into three d i s t i n c t north-south trending be l t s . The middle belt in Canada 78 consists of the Mount Roberts, Cache Creek near Kamloops, Chapperon, Anarchist, Kobau and Chi l l iwack Groups. Danner (1976, p.68) has con-sidered depositional environments of these rocks and f inds : "Late Paleozoic Cache Creek,Chilliwack,and Sicker Groups i n south western B r i t i s h Columbia and the i r counterparts to the north and south,form d i s t i n c t i v e fauna! and l i t ho s t ra t i g raph i c sequences which or ig inated in the much larger Paleozoic Pac i f i c Ocean In summary "Cache Creek" rocks of thesis area are Paleozoic, possibly Carboniferous in age and may correlated l i t ho s t r a t i g r aph i ca l l y with the basal member of Chi l l iwack Group to the west. Deposition occurred in a marine environment, probably as d i s ta l t u rb i d i t y f lows. Shuswap ~ "Cache Creek" Structural Correlat ion Structural and metamorphic cor re lat ion between Shuswap and "Cache Creek" complexes would be extremely useful in determining the overal l geological h istory of the map area. S im i l a r i t i e s in s t ructura l styles and or ientat ions indicate that the complexes may be structura l equivalents. Two fac to r s , however, necessitate caution in th i s course of analys i s . Shuswap rocks have undergone medium to high pressure amphibolite facies metamorphism whereas "Cache Creek" cumulative metamorphic grade atta ins only upper greenschist to a lb i te -ep idote -amphibolite fac ies . Furthermore, s pec i f i c structures are not d i r e c t l y tracable between complexes. The presumed Shuswap-"Cache Creek" contact in the thesis area i s not exposed. A review of the l i t e r a t u r e indicates widely d i f f e r i n g att itudes towards the f e a s i b i l i t y of s t ructura l cor re lat ion between assemblages of d i f f e r i n g tectonostratigraphic pos it ions. Fyson (1970, p.107) working along the western margin of the Shuswap 79 Complex near Shuswap Lake concludes: "Attenuated Fi i soc l ines with an ax ia l - surface sch i s tos i ty prominent i n the s t ruc tu ra l l y lower rocks are absent i n f r g i l l i t e , ind icat ing a dying out upward of the i n i t i a l deformation. F 2 recumbent folds in the sch i s tos i ty trend constantly i n some areas, but i n others veer abruptly without mutual interference to form a complex map pattern. Thus the change from folds that are upright in the suprastructure to recumbent in the in f rast ructure i s due to the dominance at each level of d i f fe rent generations." Reesor (1970, p.73) regarding the Thor-Odin gneiss dome northeast of the thesis area concludes: "In general the locus of gneiss domes i s not determined by superposed, large-scale cross f o l d s . " Okulitch (1973, p.l516)fjnotes that d i f f e ren t conclusions are reached a f te r more comprehensive study: "Reesor and Moore (1971) indicate that although fo ld ing phases may be intensely developed in one depth zone and i n s i gn i f i c an t in another, evidence of a l l phases of deformation i s present in a l l successions." This seems to a f f i rm the p o s s i b i l i t y of s t ructura l cor re la t ion through d i f f e r i n g st ructura l l eve l s . Working to the south of the thesis area Ryan (1973) d i r e c t l y traced early recumbent i s o c l i n a l fo lds in the high grade Vaseaux Formation to s im i l a r l y trending t i g h t , steeply dipping folds in the Anarchist Group, which may corre late with "Cache Creek" rocks of the thesis area (Monger, 1975). The present author fee ls that Reesor and Moores1 (1971) contention of the presence of a l l phases in a l l s t ructura l levels tends to refute Fysons' (1970) view of folds dying out with depth. In conclusion structural Corre lat ion between assemblages of d i f f e r i n g tectonostratigraphic posit ions based on structural s im i l a r -i t i e s appears feas ib le . The generalized sty les and orientations of the deformations recognized in Shuswap and "Cache Creek" rocks are l i s t e d in f igure 5-1. Structural sty les and or ientations of phase 4 and 5 deformations in 8 0 FIGURE 5-1 Structural and metamorphic relations between Shuswap and "Cache Creek" Complexes SHUSWAP phase 1 I s o c l i n a l R e c I i n e d F o I a 's A x i a I -IP I a n e s : i 32'/2($H A x e s : OOOXl 6° L o w G r a d e M e t a m o r p h i s m 1 "CACHE CREEK" Phase Phase 1 I s o c I i n a l F o I d s A x i a l P l a n e s * . 1 1 7//30°N Axes:. . 106/^)6* F a c i e s ! C u I m i n a t i o n l i b p l i t e M e t a m o r p h i c Phase 3 N e a r Iy I s o c I i n a l F o I d s A x i a l P l a n e s : 1 07X90° N A x e s : ; 253/^36" A l b i t e - E p i d o t e - A m p h i b o I - i t e F a c i e s M e t a m o r p h i s m Phase ; 2 T i g h t A n g u l a r F o l d s A x i a I P l a n e s " < A x e s *• 0-34//40*N 046'/l 4* T i g h t A n g u I a r F o I d s A x i a I P l a n e s ' . A x e s V 066>"B0°N 253>/36° Phase 4 and 5 O p e n B u c k l e F o I d s a n d F r a c t u r e s 4 5 A x . P i n s . * . 0 7 2 / 8 0°S 0 0 2/^84 'W A x e s : 0^/00" 0 0 0 / / 1 4 e H y d r o t h e r m a l A l t e r a t i o n Phase 3 and 4 F r a c t u r e s 3 4 A x . P i n s . : 056X90°W 000/76°W A x e s : 056/t»0° 356X05° H y d r o t h e r m a l A l t e r a t i o n ,81 : Shuswap rocks and phase 3 and 4 deformations in "Cache Creek" rocks are nearly i d e n t i c a l . Great c i r c l e l o c i i of poles to phase 3 ax ia l planes in Shuswap rocks, and phase 2 ax ia l planes in "Cache Greek" rocks, indicate that these l a te b r i t t l e events are cy l indro ida l in nature. Lack of concentrations of poles to compositional layering around macro-scopic phase 5 Shuswap fo ld s , and the gentle buckle geometry of meso-scopic folds implies a b r i t t l e , f l e x - s i i p s t y l e . The associated thermal events consist of quartz and c a l c i t e vein f i l l i n g , and hydrothermal a l te ra t i on of country rocks in the v i c i n i t y of f ractures . Thermal ef fects are of s im i l a r l im i ted extent in both complexes. S im i l a r i t i e s of these deformations and thermal events in Shuswap and "Cache Creek" rocks indicate that both complexes occupied s im i la r tectonostratigraphic pos i t ions, possibly close to the i r present pos i t ions, at that time. Assuming that the 42- 10 m.y. Sr/Rb date for Unit V represents thermal resett ing rather than Shuswap phase 2 defor-mation, an Ecocene age for phase 4 and 5 deformations andv \meta-morphism in Shuswap rocks i s deduced. This i s consistent with the resu lts of other workers (Ross, 1974; and Ross and Barnes, 1975) and regional tectonics in the Cord i l le ra at th i s time. Phase 3 Shuswap and phase 2 "Cache Creek" deformations produce t i gh t angular folds with easterly s t r i k i n g ax ia l planes. Fold geometry i s somewhat unusual, comprising one steeply and one shallowly dipping l imb, but i s consistent with in the two complexes. S im i l a r i t i e s between Shuswap and "Cache Creek" mesoscopic folds are i l l u s t r a t e d in f igures 2-2 and 3-22,. Average inter l imb angles and ax ia l trends are also s im i l a r . Axial plunges vary from gently westward plunging in "Cache Creek" rocks to gently eastward plunging in Shuswap rocks. 82 Fold axes of the e a r l i e s t recognized deformational phase in "Cache Creek" rocks are nearly coincident with Shuswap phase 2 axes, as are ax ia l traces of the two respective phases. Fold geometry approaches i s o c l i n a l form in both complexes. Axial surfaces dip norther ly, Shuswap gently and "Cache Creek" steeply. Based on these s i m i l a r i t i e s / , in s ty le and o r ientat ion , and the fact that no pr io r structures other than s t r a t i f i c a t i o n were observed in "Cache Creek" rocks, the author concludes that these are equivalent deformational phases in Shuswap and "Cache Creek" rocks. The differences in ax ia l plane or ientat ion between the two complexes may be related to differences in tectonostrat i graphic leve l s at the time of deformation. Metamorphic grades of Shuswap and i "Cache Creek" rocks; amphibolite and upper greenschist fac ies respect-i v e l y , support th i s hypothesis (see f igure 5-1). I t i s interest ing to note that Ryan (1973) found s imi la r var iat ions in ax ia l plane or ientat ions from low dips in the amphibolite fac ies Vaseaux Formation to high dips in the contiguous greenschist fac ies Anarchist Group along coincident structural trends. As discussed in section 4, amphibolite s i l l , un i t V.III-underwent a regional metamorphic episode at 178- 6 m.y. atta in ing a lb i te -ep idote -amphibolite fac ie s . This thermal event s t ruc tu ra l l y predated phase 3 and 4 deformations in "Cache Creek" rocks but no further structural l im i ta t ions are possible. If Unit VII I, which 1 i tho log i ca l l y defines the "Cache Creek" metamorphic culmination, i s re lated to the e a r l i e s t recognized deformation in "Cache Creek" rocks, then th i s phase and Shuswap phase 2 occurred at most 178j*tr6 m.y. B.P. and probably represent ef fects of the Colombian Orogeny. This point however, i s speculative due to the lack of substan-t i ve s t ructura l evidence. 83. Evidence of an early deformational phase in Shuswap rocks, phase 1, not recognized in "Cache Creek" rocks of Paleozoic, possibly Carboni-ferous age, indicates that some deformation and possible metamorphism occurred in the Paleozoic. Although of unknown magnitude, the early event was of regional extent, as phase 1 structures are found throughout Shuswap rocks of the thesis area. Phase 1 deformation could be related to the Caribooan or Antler Orogeny discussed by White (1959), and Ross and Barnes (1972). Strat igraphic re lat ions between Shuswap and "Cache Creek" rocks remain elus ive but the present study suggests that Okul i tch ' s contention of an unconformable re lat ionsh ip with "Cache Creek" sediments deposited on previously deformed Shuswap basement seems plausable. The actual contact remains to be found, possibly because of pa r t i a l o b l i t e r -ation by the l a te r s t ructura l culmination which involved both complexes. 84 REFERENCES Armstrong, R. L.A., 1974, Magmatism, erogenic t iming, and orogenic diachronism in the Cord i l le ra from Mexico to Canada. Nature. 247, pp. 348-351. Barnes, W.C. and Ross, J.V., 1975. The Bl ind Creek limestone, Keremeos, B r i t i s h Columbia: Structure and regional tectonic s i g -n i f icance. Can. J , Earth, S c i . , 12, pp. 1929-1933. B l a t t , H., Middleton, G., and Murray, R., 1972. Origin of Sedimentary Rocks. Prent ice-Ha l l . Bostock, H.S., 1940. Keremeos Map Sheet. Geol. Surv. Can., Map 341 A. Brock, B.C., 1934. The metamorphism of Shuswap Terrain of B r i t i s h Columbia. J . Geo!., 42, pp. 673-699. Cairnes, C.E., 1939. The Shuswap rocks of southern B r i t i s h Columbia. , ; ' Proc. Sixth Pac i f i c Sc i . Congress, 1, pp. 259-272. Campbell, R.B., 1973. Structural cross-section and tectonic model of the southeastern Canadian Co rd i l l e ra . Can. J . Earth. S c i . , 10, pp. 1607-1620. Campbell, R.B. and Okul i tch, A.V., 1973. Stratigraphy and structure of the Mount Ida Group, Vernon, Adams Lake and Bonaparte Lake map areas, B r i t i s h Columbia. Geol. Surv. Can., map. 73-1, Part A, pp. 21-23. Ch r i s t i e , J . C , 1973. Geology of Vaseaux Lake area. Unpublished Ph.D. thes i s , the University of B r i t i s h Columbia, Vancouver, B.C. Daly, R.A., 1912. Geology of the North American Cordi l leran at the for ty -n inth p a r a l l e l . Geol. Surv. Can. Mem., 38. Danner, W.R., 1976. The Late Paleozoic Exotic Belts of the Western Co rd i l l e ra , abstr . , Geol. Assoc. Can., p.68. Dawson, G.M. 1898. Report on exploration in the southern B r i t i s h Columbia: Shuswap sheet, Geol. Surv. Can., Map 143A. Fa i rba i rn , H.W., Hurley, P.M. and Pinson, W.H., 1964. I n i t i a l Sr87/86 and possible sources of granite rocks in southern B r i t i s h Columbia, Jour. Geophys, Res., 69, pp. 4889r4893. . Faure, G. and Powell, J . L . , 1972, Strontium Isotope Geology. Springer-Verlag-, New York. Fy/Ies, J.T., 1970, Structure of the Shuswap Complex in the Jordon x River area, northwest of Revelstoke, B r i t i s h Columbia. In Structure of the Southern Canadian Co rd i l l e r a . Geol. Assoc. Can. Special Paper, 6, pp. 87-98. 85 Fyles, J.T., H a r a j a l , J.E. and White, W.H., 1973. The Age of Sulf ide Mineral izat ion at Rossland B r i t i s h Columbia. Economic Geo!., 8, pp. 23-33. Fyson, W.K., 1970. Structural re lat ions in metamorphic rocks, Shuswap Lake area, B r i t i s h Columbia. Geol. Assoc. Can. Special Paper, 6, pp. 107-122. G i l l u l y , J.A., 1934. Mineral or ientat ion in some rocks of the Shuswap Terrain as a clue to the i r metamorphism. Amer. Jour. S c i . , 228, pp. 182-201. Gordon, T.M. and Greenwood, H.J., 1971. The s t a b i l i t y of grossu lar i te in H 20-C0 2 mixtures. Amer. Minera l . , 56, pp. 1674-1688. Greenwood, H.J., 1962. Metamorphic reactions involving two v o l a t i l e components._ Carnegie Inst. Wash. Year Book, 6, pp. 61-85. Holland, S.S., 1964. Land forms of B r i t i s h Columbia, a physiographic out l ine. B.C. Dept. of Mines and Pet ro l . Res., B u l l . , 48, p. 73. Hyndman, D.W., 1968. Petrology and structure of Nakusp map-area, B r i t i s h Columbia. Geol. Surv. Can., pp. 1-95. Hyndman, D.W., 1968. Mid-Mesozoic multiphase fo ld ing along the border of the Suuswap Metamorphic Complex. Geol. Soc. Amer. B u l l . , 79, pp. 575-588. Jones, A.G., 1959. Vernon map area, B r i t i s h Columbia, Geol. Surv. Can. Mem., 296. Nguyen, K.K., S i n c l a i r , A . J . and Libby, W.G., 1969. Age of the northern part of the Nelson batho l i th . Can. J . Earth. S c i . , 5, pp. 955-957. L iou, J .G. , 1971. Synthesis and S t a b i l i t y Relations of Prenite Ca 2 A l 2 Si2 0 l 0 C0H 2. Amer. Mineral, 56, pp. 507-531. Liou, J .G. , 1973. Synthesis and S t a b i l i t y Relations of Ep leftste, Ca2 A l 2 Fe Si3 0-|2 (OH). J . Petrology, 14, pp. 381-413. L iou, G.G., Kunigoshi, S., and Ito, K., 1974. Experimental studies of the phase re lat ions between greenschist and amphibolite in Basalt ic System. Amer. J . S c i . , 274, pp. 613-632. L i t t l e , H.W., 1960. Nelson map-anea (west half ) B r i t i s h Columbia. Geol. Surv. Can. Mem., 308. L i t t l e , H.W., 1971. Geology of the Kettle River area (west h a l f ) , B r i t i s h Columbia. Geol. Surv. Can, Map 15, 1961, Matthews, W.H., 1976, Anomalous K-Ar Dates from gneisses of the T r i n i t y H i l l s abst r . , Geol. Assoc. Can., pp. 47. 86 McMillan, W.J., 1970. West Flank, Frenchman's Cap gneiss dome, Shuswap T e r r a i n , B r i t i s h Columbia. In Structure of the Southern Canadian Co rd i l l e ra . Geol. Assoc, Can. Special Paper 6, pp. 99-106. Medford, G.A., 1976. Geology and Thermal History of an Area near Okanagan Lake, Southern B r i t i s h Columbia. Unpublished Ph.D. thes i s , University of B r i t i s h Columbia. Monger, J.W.H., 1970. Hope map-area, west ha l f , B r i t i s h Columbia. Geol. Surv. Can. Paper 69-41, pp. 47-69, Monger, J.W.H., 1975. Correlation of eugeosynclical tec tonos t ra t i -graphic belts in the North American Co rd i l l e r a , Geoscience Can., pp. 4-9. Okul i tch, A.V., 1970. Geology of Mount Kabau. Unpublished Ph.D. thes i s , Department of Geology, the University of B r i t i s h Columbia. Okulitcfe, A.V., 1973. Age and Correlation of the Kobau Group, Mount KobauV B r i t i s h Columbia. Can. Journ. Earth. S c i . , 10, pp. 1508-1518. Okul i tch, A.V., 1974. Stratigraphy and structure of the Mount Ida Group, Vernon, Seymour Arm, Bonaparte Lake and Kett le River map-area, B r i t i s h Columbia. In Report of A c t i v i t i e s , Apr i l to October, 1973, Geol. Surv. Can. Pap. 7 4 r l , Part A, pp. 25-30.. Okul i tch, A.V. and Cameron, B.E.B., 1976. Strat igraphic revis ions of the N ico la, Cache Creek and Mount Ida Groups, based on conodant co l lect ions from the western margin of the Shuswap Metamorphic Complex, south-central B r i t i s h Columbia. Can. J . Earth Sci/., 13, pp. 44-53. Okul i tch, A.V., Wanless, R.K. and Loveridge, W.D., 1975. Devonian plutonism in south-central B r i t i s h Columbia. Can. J . Earth S c i . , 12, pp. 1760-1769. Pett i john, F . J . , 1957. Sedimentary Rocks. Harper and Row, New York, p. 190. Preto, V.A., 1964. Structural re lat ionships between the Shuswap Terrain and the Cache Creek Group in southern B r i t i s h Columbia. Unpublished M.Sc. Thesis, Department of Geology, the University of B r i t i s h Columbia. Preto, V.A., 1967. Structure and petrology of the Grand Forks Group. Grand Forks, B r i t i s h Columbia. Unpublished Ph.D. Thesis, Department of Geology, McGill Univers i ty. Ramsay, J .G. , 1967, Folding and Fracture of Rocks, McGrawrHill Co., New York. pp. 359-372. Read, P.B., 1976. Tr iass ic orogeneses in B r i t i s h Columbia. Abstract, Geol. Assoc. Can., p. 69. "87 Reesor, J .E . , 1970. Some aspects of s t ructura l evolution and regional sett ing in part of the Shuswap Metamorphic Complex. In Structure of the Southern Canadian Co rd i l l e r a . Geol. Assoc. Can. Special Paper, 6, pp, 73-85. Reesor, J.E. and Moore, J.M., 1971. Petrology and structure of the Thor-Odin gneiss dome, Shuswap Metamorphic -Complex, B r i t i s h Columbia. Geol. Surv, Can. B u l l , 195. Roedder, E., 1970d. Appl icat ion of an improved crushing microscope stage to studies of gases in f l u i d inc lus ions. Schweiz. Mineral Petrog. M i t t . , 50 (1), pp. 41-58. Ross, J.V., 1968. Structural re lat ions of the eastern margin of the Shuswap Complex near Revel stoke, southeastern B r i t i s h Columbia. Can. J . Earth S c i ; , 5, pp. 831-849. Ross, J.V., 1970. Structural evolution of the Kootenay Arc, south eastern B r i t i s h Columbia. In Structure of the Southern Canadian Co rd i l l e r a . Geol. Assoc. Can. Special Paper, 6, pp. 53-65. Ross, J.V., 1973. Mylonit ic rocks and f lattened garnets in the southern Okanagan of B r i t i s h Columbia. Can. J . Earth S c i . , 10, pp. 1-17. Ross, J.V., 1974. A Tert iary thermal event in south-central B r i t i s h Columbia. Can. J . Earth S c i . , 11, pp. 1116-1122. Ross, J.V. and Barnes, W.C., 1972. Evidence for "Caribooan Orogeny" in the southern Okanagan region of B r i t i s h Columbia. Can. J . Earth S c i . , 9, pp. 1693-1702. Ross, J.V. and Barnes, W.C., 1975. Development of cleavages wi th in d iamict i tes of south eastern B r i t i s h Columbia. Can. J . Earth S c i . , 12, pp. 1291-1306. Ross, J.V. and Ch r i s t i e , J . C , 1969. Polyphase deformation with in the Shuswap Terrain of the southern Okanagan Val ley, B r i t i s h Columbia. Geol. Soc. Amer., abstr. Part 3, p. 57. Ryan, B.D., 1973, Geology and Rb-Sr geochronology of the Anarchist Mountain area, south central B r i t i s h Columbia. Unpublished Ph.D. Thesis, Department of Geology, the University of B r i t i s h Columbia. Skippen, G., 1974. An experimental model for low pressure metamorphism of s i l i ceous dolomitic marble. Amer. J . S c i . , 274, pp. 487-509. Stormer, J . C , 1975. A pract ica l two-feldspar. Amer. Mineralogist, 60, pp. 667-674. Storre, B. and Karot^ke, E., 1971. An experimental determination of the upper s t a b i l i t y l i m i t of muscovite + quartz in the range 7-20 Kb. water pressure. Fortschr. Mineral, 49, pp. 56-58. 88 Wanless, R.K,, 1976. Geochronologic studies of the Shuswap Meta-morphic Complex, southern B r i t i s h Columbia, abstract, Geol, Assoc. Can., p. 47. Wanless, R.K. and Okul i tch, A.V. 1976. Geochronologic studies of the Shuswap Metamorphic Complex, southern B r i t i s h Columbia, abstract, Geol. Assoc. Can., p. 47. Wanless, R.K. and Reesor, J . F . , 1974. Precambrian Zircon age of orthogneiss in the Shuswap Metamorphic Complex, B r i t i s h Columbia Can. J . Earth S c i . , 12, pp. 328-329. Waters, A.C. and Krauskopf, K., 1941. Protoc las t ic border of the Co1vi11e batho l i th . B u l l . Geol. Soc. Amer., 52, pp. 1355-1418. Wheeler, J.O., 1970. Summary and discussion. Geol. Soc. Can. Spec. Paper, 6, pp. 155-166. White, W.H., 1959. Cordi l leran tectonics in B r i t i s h Columbia. Amer. Assoc. Petro. Geol. B u l l . , 43, pp. 60-100. Wil l iams, H., Turner, F.J. and G i l be r t , CM . , 1954. Petrography. W.H. Freeman and Co. Winkler, H.G.F., 1974. Petrogenesis of metamorphic rocks. Springer-Verlag, New York. ' ~89 APPENDIX 1 Sr/Rb Geochronology sqmple-s o f C - ~ . . ' . J Six fresn^quartz monzonite; (Unit VI, j were dated by the Sr/Rb whole rock method using the University of B r i t i s h Columbia, Department of Geology, f a c i l i t i e s . The standard experimental procedures involved w i l l not be discussed. The samples define a 42- 10 m.y. B.f-'j isochron with an i n i t i a l S r 8 7 / S r 8 6 r a t i o of .7055 (figure A - l a ) , Although no S r 8 7 / S r 8 6 ra t i o determinations were conducted on surrounding layered un i t s , i n i t i a l rat ios of high grade Monashee metasediments average much higher, up to .710 (Ryan, 1973; Medford, 1976). The upper l i m i t of the uncontaminated basalt f i e l d of Eocene age rocks i s approximately .703 (Faure and Powell, 87 1972), therefore Unit V was probably contaminated with Sr from surround-ing Shuswap rocks. The s ign i f icance of th is Tert iary date i s discussed i n section 3f. K/Ar Geochronology A hornblende separate from amphibolite s i l l (Unit VIII) was dated at 178- 6 m.y. B.P. by J.E. Harakal, University of B r i t i s h Columbia, using the K/Ar method. Potassium analyses were performed on KY and KY-3 flame photometers and argon analyzes u t i l i z e d an MS-10 mass spectrometer. Potassium-argon data i s l i s t e d in f igure A- lb . The s ign i f icance of the Jurassic i sotopic date i s discussed in section 5. 90 .7090 /^>~ B .7080 s-c : .7070 — .7060 S-D 42±10 my (Sr e 7/S^) o = .7056 Rb 8 7/Sr 8 6 .7050 1 1 10 2.0 3.0 4.0 5.0 60 A-la 42 ±10 my Sr/Rb whole rock jsochron of quartz monzonite sill , unit V. A-lb K/Ar data from hornblende separates of amph i b o l i t e , u n i t VIII. Potass iurn (% K) *40Ar (lo*5 cc STP/g) * 4 0Ar / Total ^Ar *40Ar / 40K Apparent Age 0.864 6.4 x l C T 1 0.91 1 .092 x 10"2 178 ± 6 my 

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