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Geology of Vaseaux Lake area Christie, James Stanley 1973

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IS I OM GEOLOGY OF VASEAUX LAKE AREA by James Stanley C h r i s t i e B.Sc., University of B r i t i s h Columbia, 1965 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE iDEGREE OF DOCTOR OF PHILOSOPHY in the Department of Geology We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1973 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make It freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. The University of British Columbia Vancouver 8 , Canada Department (i) ABSTRACT A l o c a l s t ructural l i t h p l o g i c succession comprised of 5 map-units t o t a l l i n g more than 4,000 feet in present thickness has been established in the Vaseaux Formation (Bostock, 1940). Units 1-5 are comprised of high grade metamorphic rocks derived from possible greywacke suite sediments and volcanics that have undergone a complex 5-phase history of deformation, metamorphism and igneous intrusion. Phases 1, 2 and 3 each gave r i s e to large scale recumbent f o l d sets along respective northerly, north-westerly and westerly trends. Each i n turn brought about tightening and re-folding of e a r l i e r formed structures. Associated metamorphism reached upper greenschist facies during' phase 1 and culminated i n middle amphibolite facies at the time of emplacement of a synkinematic, g r a n i t i c pluton during phase 2. Meta-morphism again reached at least lower amphibolite facies during phase 3, possibly at a time of re-a c t i v a t i o n of e a r l i e r formed phase 3 structures during the Upper Jurassic. Phases 1, 2 and 3 are a l l of pre-late Mississippian age but t h e i r exact ages are not known. They are believed to be a l l related i n time to the lower Mississ-ippian Caribooan Orogeny. Phases 4 and 5 of deformation gave r i s e to respective northerly and northwesterly open, f l e x u r a l - s l i p folds. Phase 4 i s associated i n time with early T e r t i a r y volcanism and hydrothermal a l t e r a t i o n and has been K/Ar dated at 44 m.y.B.P. (Ross and Barnes 1972). Phase 5 folding, pre-Miocene i n age i s associated , with extensive fracturing and f a u l t i n g i n the d i s t r i c t . ( i i ) TABLE OF CONTENTS Page ABSTRACT . i TABLE OF CONTENTS. i i ACKNOWLEDGEMENTS i.:. v LIST OF FIGURES v i LIST OF TABLES v i i LIST OF PLATES v i i i LIST OF MAPS AND SECTIONS x i i CHAPTER ONE 1 GENERAL INTRODUCTION . . .1 PURPOSE AND SCOPE ,. ' 1 LOCATION AND ACCESS . ., 1 FIELD WORK 3 NATURE OF THE MAP AREA 3 PREVIOUS WORK 4 GENERAL GEOLOGY ! .10 CHAPTER TWO 13 STRUCTURAL SUCCESSION 13 LITHOLOGIC UNITS 18 Unit 1. 18 Unit 2 w 20 Unit 3. 21 Unit 4. . 23 Unit 5 26 ORIGIN AND DEPOSITIONAL ENVIRONMENT • 27 LITHOLOGIC CORRELATION-• • 28 CHAPTER THREE 2 9 STRUCTURE • 2 9 INTRODUCTION 2 9 ( i i i ) Page OUTLINE OF STRUCTURAL HISTORY 2 9 STRUCTURAL DOMAINS 32 FOLD SETS 38 PHASE 1 3 8 PHASE 2 . . 45 PHASE 3 52 Subset 3a 54 Subset 3b 59 Subset 3c 61 Relationships between Subsets 3a, 3b and 3c folds...65 PHASE 4 6 7 PHASE 5.... 70 Faulting related to Phase 5 73 Interference of Phase 3, 4 and 5 structures 76 SUMMARY .' .76 i i ' ' ' CHAPTER FOUR 79 IGNEOUS ROCKS ..79 INTRODUCTION 79 UNIT A 80 GRANITIC GNEISS-PEGMATITE COMPLEX 80 Size and Contact Relations 81 Lithology 81 Contact Relations ...82 Origin and Emplacement 85 Age.. 89 UNIT B . . . 9 0 LATE-KINEMATIC GRANODIORITE-QUARTZ MONZONITE 9 0 Lithology 90 Contact Relations 92 Emplacement and Relation to Structure 95 Age and Significance 98 METAMORPHOSED INTERMEDIATE TO BASIC DYKES..... 99 ULTRA-BASIC ROCKS AND AMPHIBOLITES 99 TERTIARY DYKES . 101 CHAPTER FIVE 103 METAMORPHISM. . 103 (iv) Page INTRODUCTION 103 EARLY METAMORPHISM 103 Conclusions 115 PHASE 3 METAMORPHISM 116 TERTIARY THERMAL EVENT....: 123 CHAPTER SIX 12 9 CONCLUSIONS 129 SUMMARY OF GEOLOGIC HISTORY (Contributions) 129 INTERPRETATION 13 3 REFERENCES CITED 136 (v) ACKNOWLEDGEMENTS The author wishes to express his thanks to Dr.J.V. Ross for his continued support and encouragement throughout thi s study. Funds for f i e l d work were g r a t e f u l l y obtained through National Research Council of Canada, Grant A-2134. A National Research Council Scholarship held during the f i r s t three years of the study provided much needed support and is g r a t e f u l l y acknowledged. . : 1 ! ! " ; I , Special thanks are due my wife, Dagmar, both for her help in the f i e l d and her continued support and assistance with such matters as drafting and typing. The author would also l i k e to express his appreciation to his associates at Quintana Minerals Corporation for t h e i r generous help in preparation and duplication of the f i n a l manuscript. (vi) LIST OF FIGURES Figure 1-1 Location of Map-Area 2 Figure 1-2 General Geology of the Southern Okanagan 11 Figure 2-1 Schematic structural l i t h o l o g i c succession 16 Figure 3-1 Structural Domains 31 Figure 3-2 Domain 1 ....33 Figure 3-3 Domain 2.. 34 Figure 3-4 Domain 3 35 Figure 3-5 Domain 4 36 Figure 3-6 Domain 5 37 Figure 3-7 Synopsis of phase 1 linear structures. 1 40 Figure 3-8 Synopsis of phase 2 structures 46 Figure 3-9 Geometry of subset 3a 53 Figure 3-10 Synopsis of subset 3a and 3b structures 55 Figure 3-11 Vergence and conjugate relationships between subset 3a and 3b structures 62 Figure 3-12 Schematic Cross-Section phase 3 63 Figure 3-13 Subset 3c structures compared to the geometry of subsets 3a and 3b 64 Figure 3-14 Synopsis of phase 4 structures 69 Figure 3-15 Synopsis of phase 5 structures.... 71 Figure 3-16 Phase 5 folds with fractures J2 i n a x i a l plane orientation 72 Figure 3-17 Break thrusts phase 5 72 Figure 3-18 Phase 5 and/or l a t e r fractures 74 Figure 4-1 Schematic Cross-Section phase 2 86 Figure 4-2 Schematic Cross-Section phase 3 and 5 88 Figure 4-3 Hypothetical Emplacement of the Pluton (Unit B)..96 Figure 4-4 Schematic Post-Kinematic Stage i n the Emplacement of Unit B 97 ( v i i ) LIST OF TABLES TABLE 2-1 SUMMARY OF THE CHARACTERISTICS OF MAP UNITS 1-5 15 TABLE 3-1 SUMMARY OF THE STRUCTURAL ELEMENTS 30 TABLE 5-1 MINERAL ASSEMBLAGES FORMED DURING EARLY METAMORPHISM (PHASE 2) ..105 ( v i i i ) LIST OF PLATES Plate 3-1 Northerly trending phase 1 f o l d i n Unit 3, 1/4 mile north of Mclntyre Canyon 39 Plate 3-2 I s o c l i n a l phase 1 f o l d i n Unit 3 at Shuttleworth Canyon 39 Plate 3-3 I s o c l i n a l phase 1 folds crossed by cleavage Unit 3 at Shuttleworth Canyon '-41 Plate 3-4 Northerly trending phase 1 folds deformed about F_ and crossed by cleavage F_ . Unit 2 south of Shuttleworth CreeKf -.41 Plate 3-5 Northerly trending phase 1 folds outlined by early granitoid material i n Unit 2 and re-folded about F2- South of Shuttleworth C k . - « « - 4 3 Plate 3-6 Detail of above phase 1 hinge zones 43 Plate 3-7 Phase 1 folds with c u r v i l i n e a r axes exposed on northerly trending j o i n t surface, and crossed by l a t e r cleavages F_. , F-,, and c . -r • 3a 3b A A fractures J2 q q Plate 3-8 Phase 1 f o l d with c u r v i l i n e a r axis exposed on an almost planar northerly trending surface. Later cleavages F, , and fractures J~ are shown. Western end of Shuttlewortn Canyon near Oliver Ranch 44 Plate 3-9 Northwesterly trending phase 2 f o l d crosscut by cleavage F^ and fractures J ~ . Unit 3 Shuttleworth Canyon. • • 48 Plate 3-10 Phase 2 folds.outlined by sheared pegmatite in Unit 2 and re-folded about F_ 48 j 3. Plate 3-11 Mobilized phase 2 hinge i n core of Vaseaux Lake Anti form ...50 Plate 3-12 Mobilized phase 2 hinge in core of Vaseaux Lake Antiform • 50 Plate 3-13 Phase 1 folds re-folded by a phase 2 antiform which has a c u r v i l i n e a r a x i s . L2 trends almost perpendicular to plane of photograph in upper l e f t but i s almost p a r a l l e l at lower center 51 Plate 3-14 Detail from above showing c u r v i l i n e a r L 2 , northerly trending phase 1 hinges and deformed L]_. Unit 4b Oliver Ranch south of Shuttleworth Creek. 51 (ix) Plate 3-15 Phase 3 f o l d (subset 3a) viewed from the east. Unit 4a, south of Shuttleworth Creek 56 Plate 3-16 Phase 3 folds (subset 3a) viewed from the west. Unit 3 south of Mclntyre Canyon near the core of Gallagher Lake Synform 56 Plate 3-17 Phase 3 folds (subset 3a) viewed from the west. Unit 3 i n roadcut near Vaseaux Lake. 58 Plate 3-18 Phase 3 folds (subset 3a) viewed from the west. Unit 2 east of Vaseaux Lake 58 Plate 3-19 Phase 3 folds (subset 3a) viewed from the west. Unit 4a south of Shuttleworth Creek 60 Plate 3-20 Open subset 3b flexural-flow folds i n mylonitic rocks of Unit 4a. Viewed from the west • 60 Plate 3-21 Phase 3 folds (subset 3b) within mylonite north of Shuttleworth Creek. Viewed from , the east i 66 i Plate 3-22 Phase 3 folds (subset 3c) developed about conjugate a x i a l surfaces 66 Plate 4-1 Penetrative f o l i a t i o n s F2 i n g r a n i t i c gneiss outlined by deformed quartz and b i o t i t e . Crossed p o l a r i z e r s . F i e l d 4.7 mm ...83 Plate 4-2 Phase 3 folds developed i n Unit A (granitic gneiss) outlined by the e a r l i e r f o l i a t i o n F2 on the hinge of Gallagher Lake Synform... 83 Plate 4-3 P o i k i l i t i c orthoclase megacrysts i n f o l i a t e d border phase of Unit B. Weaker F3 cleavage crosses obliquely. •• 91 Plate 4-4 P o i k i l i t i c habit of orthoclase i n grano-d i o r i t e s of Unit B. Crossed p o l a r i z e r s . F i e l d 4.7 mm 91 Plate 4-5 O s c i l l a t o r y zoned plagioclase i n granodiorite of Unit B. Crossed p o l a r i z e r s . F i e l d approx-imately 1.6 mm ........93 Plate 4-6 Xenolith of granite gneiss (Unit A) within granodiorite dyke-rock of Unit B as seen i n coarse f l o a t at the contact between the two units 93 Plate 5-1 Metasomatic orthoclase porphyroblasts i n semi-p e l i t i c granulite above a major sheet of g r a n i t i c gneiss •• ...109 (x) Plate 5-2 Laminated plagioclase diopside amphibolite displaying weakly developed cleavage F ?. Plane polarized l i g h t . F i e l d approximately 4.7 mm 109 Plate 5-3 Phase 2 minor f o l d hinge displaying micas p a r a l l e l and sub-parallel to F Q/F^ and F2-Plane polarized l i g h t . F i e l d approximately 4.7 mm 112 Plate 5-4 Same f i e l d as above but with polar i z e r s crossed to i l l u s t r a t e s t r a i n pattern i n quartz. See text ...112 Plate 5-5 Penetrative f o l i a t i o n s FTL? and F2 and bedding F Q i n garnet plagioclase (A ^ s ) b i o t i t e quartzite from Unit 4a. Plane polarized l i g h t . F i e l d approximately 4.7 mm....114 Plate 5-6 Same f i e l d as above but with polar i z e r s crossed to i l l u s t r a t e s t r a i n patterns in quartz. See text 114 Plate 5-7 Phase 3 biotite= aligned p a r a l l e l to the axi a l plane F3 of a minor f o l d . Plane i polarized l i g h t . F i e l d approximately 4.7 mm 118 1 Plate 5-8 Strain pattern in quartz o u t l i n i n g the f o l i a t i o n F3 across the hinge and limbs of a minor phase 2 f o l d . Plane polarized l i g h t . F i e l d approximately 4.7 iran..... 118 Plate 5-9 Flattened garnet bearing oblique inclusions of mica. Crossed p o l a r i z e r s . F i e l d approx-imately 4.7 mm . . . 120 Plate 5-10 Flattened garnet l y i n g p a r a l l e l to F2- Late s t r a i n - s l i p cleavage F.j a crosses obliquely. Plane polarized l i g h t . F i e l d approximately 4.7 mm. 120 Plate 5-11 I s o c l i n a l phase 2 structure i n pegmatite veined schist. Plane polarized l i g h t . F i e l d approximately 4.7 mm... 122 Plate 5-12 Oblique phase 3 structure developed across transposed pegmatitic layering i n schist. Plane polarized l i g h t . F i e l d approximately 4.7 mm. . . 122 Plate 5-13 Late cleavage F3 outlined by new b i o t i t e across transposed layering i n mylonite. Plane polarized l i g h t . F i e l d approximately 4.7 mm....124 Plate 5-14 Exsolution textures and r e l i c t zoning at the margin of a rhomb shaped pseudo-anothoclase 124 cont'd.. (xi) phenocryst. Crossed p o l a r i z e r s . F i e l d approximately 4.7 mm 124 Plate 5-15 Cataclastic texture i n bleached grano-d i o r i t e from the southern zone of a r g i l l i c a l t e r a t i o n . Plane polarized l i g h t . F i e l d approximately 4.7 mm.... 126 (xii) LIST OF MAPS AND SECTIONS (POCKET) Plate 1 Geology of the Vaseaux Lake Area Plate 2 . Phase 1 and Phase 2 Structures Plate 3 Phase 3 Structures Plate 4 Phase 4 and Phase 5 Structures Plate 5 Vertical Cross Sections AA and BB Plate 6 Vertical Cross Sections CC and DD - 1 -CHAPTER ONE GENERAL INTRODUCTION PURPOSE AND SCOPE This study was undertaken to determine the geometry, s t y l e , and r e l a t i v e time of development of successive phases of polyphase deformation within a small but well exposed segment of the Shuswap metamorphic complex. To thi s end, detailed mapping was necessary . to establish l o c a l stratigraphy and.structure, and to in t e r r e l a t e structural evolution, g r a n i t i c intrusion, and metamorphic events. In addition, i t was anticipated that this study might allow some statement about the age of the Shuswap complex by means of structural comparison with nearby l i t h o l o g i e s of known age. LOCATION AND ACCESS Vaseaux Lake map-area i s roughly centered on the Okanagari Valley of south-central B r i t i s h Columbia, some 20 miles north of the forty-ninth p a r a l l e l . I t includes about 60 square miles east of the Okanagan River between latitudes 49° 12' and 49° 21' north mapped by the author, and an adjacent area west of the Okanagan mapped by J.V. Ross i n 1968. Easy access i s provided by Highway 97 i n the Okanagan Valley, and secondary road systems which leave the highway east of Okanagan F a l l s and east of Vaseaux Lake. These secondary roads were developed i n i t i a l l y to service independent logging operations, but at present are not much used for logging. - 2 -Figure 1.1: Location of Map-Area Penticton in 01 ISKAHA i LAKE 3 T Okanagan Falls #.VASEAU> LAKj •49° 15' \Oliver Mt. Baldy Mt. Kobau OSOYOOS LAKE Anarchist Mtn. io Osoyoos BRITISH COLUMBIA WASHINGTON STATE 4 9 00 • — - 3 -The main roads are i n good repair and well t r a v e l l e d by the general p u b l i c , but many of the branch roads have f a l l e n into disuse, although most are s t i l l passable by vehicles with reasonable clearance. Access to southeastern parts of the area i s more d i f f i c u l t from the Wolfcub Creek road system which originates east of Oliver on Indian Reserve No. 1. A l l of the above mentioned roads are shown on accompanying maps. FIELD WORK Mapping was carried through the 1967 and 1968 seasons with a t o t a l of 9 months being devoted to f i e l d work. During t h i s period most bedrock exposures were v i s i t e d and mapped in d e t a i l on a e r i a l photographs with approximate scale of 4" = 1 mile. Geologic information thus recorded was l a t e r transferred to advance 1:50,000 topographic sheets which had been enlarged to the scale of 4" = 1 mile. This transfer was accomplished with a Saltzman projector using a " b e s t - f i t " technique and dependent on topographic features and barometric elevations recorded i n the f i e l d . NATURE OF THE MAP AREA Vaseaux Lake map-area i s part of the steep and rocky western flank of the Okanagan Highland (Holland 1964), formed through deep dissection of a highstanding Tertiary erosion surface by the Okanagan River (local base-level about 1,100 feet) and t r i b -u t a r i e s . At elevations above 4,500 feet gently sloping remnants -4-of t h i s erosion surface, variably mantled by g l a c i a l d r i f t , stand out in contrast to the steep v a l l e y slopes. Polished and s t r i a t e d bedrock exposures are found at a l l elevations, and further evidence of g l a c i a t i o n i s abundant. Kettled outwash and g l a c i a l lake deposits i n the Okanagan Valley are s t r i k i n g examples. Nasmith (1962) , has studied and described the late g l a c i a l history and s u r f i c i a l deposits of the region. Vegetation i s highly variable within the area. Except near watercourses, the f l o o r of the Okanagan Valley and the lower slopes are extremely a r i d , supporting l i t t l e but sagebrush, bunch-grass, cactus and scattered ponderosa pine. At higher elevations, and on north facing slopes f i r and hemlock become dominant and form dense forests. South facing slopes may have large open grass-covered t r a c t s , or open forests of ponderosa pine, f i r and hemlock. Forest f i r e s have l a i d to waste large areas in the uplands which are presently covered by an almost impenetrable second-growth of jack-pine and spruce. PREVIOUS WORK Highgrade metamorphic rocks loosely referred to the Shuswap terrane because of t h e i r highly c r y s t a l l i n e nature or indeterminable age have been mapped through south-central B r i t i s h Columbia1 and north-central Washington State over an area of some 3000 square miles. Whether the Shuswap as such contains rocks of a single age, or includes rocks of many d i f f e r e n t ages i s highly con-j e c t u r a l , but the l a t t e r seems probable. Early geologists' hypothesised that parts of the Shuswap -5-terrane represented a westerly extension of the Precambrian Shield, and that other parts included overlying Proterozoic and possibly Lower Paleozoic strata. Alternate suggestions have resulted from subsequent studies, but t h i s o r i g i n a l hypothesis remains to be proven or discredited. D i f f i c u l t i e s arise in most aspects of Shuswap geology. F o s s i l s have seldom been found, and could hardly be expected even i f present o r i g i n a l l y , because of the extreme deformation and ^metamorphism i n these rocks. Contacts with dated rocks are controversial or unknown for a variety of reasons, and thus far radiometric ages determined by the K/Ar method have given only i ages of metamorphism and igneous intrusion. Many Shuswap problems arise from the fact that most of the terrane has been mapped i n reconnaissance only, and d e t a i l s of lithology and structure are poorly known. Thus l i t h o l o g i c comparisons and correlations i s extremely tenuous even though some s i m i l a r i t i e s have been noted between parts of the Shuswap and Proterozoic and Lower Paleozoic sequences further east. Such correlation i s beyond the scope of t h i s thesis but i t i s necessary to review previous work from other parts of the Shuswap terrane to see the background and development of geologic problems pertinent to this study. j G.M. Dawson (1877), while conducting reconnaissance surveys in the southern i n t e r i o r of B r i t i s h Columbia, described schists and gneissic rocks i n the v i c i n i t y of Shuswap Lake which he l a t e r named the Shuswap Series. In 1898 the Shuswap Sheet, with geology and explanatory notes by Dawson was published, and the Shuswap Series was from then on referred to the Archaean on the basis of -6-l i t h o l o g i c s i m i l a r i t y with the Precambrian Grenville Series of eastern Canada. Dawson placed the sedimentary Nisconolith and volcanic Adams Lake Series of supposed Cambrian Age above the Shuswap. R.A. Daly (1912) conducted a geological survey of the North American C o r d i l l e r a along the 49th p a r a l l e l . South of Vaseaux Lake area, Daly mapped meta-sedimentary and volcanic rocks of probable Paleozoic age which he named the Anarchist Series. He also mapped s e v e r a lxg r a n i t i c batholiths and stocks i n the region, but he did not associate any of the above rocks with the Shuswap complex. In ,1911 Daly compiled, a comprehensive report on the Shuswap Sheet, previously mapped by Dawson. Based on an unconformity at Albert Canyon, near Revelstoke, which has since been d i s c r e d i t e d , i (Gunning, 1928 , Okulitch 1949 , Wheeler, 1962 , Daly concluded that both the Nisconolith and Adams Lake series were of Pre-Beltian age and were s t r a t i g r a p h i c a l l y equivalent to the more highly metamorphosed Shuswap Series. Accordingly i n 1915, Daly enlarged the Shuswap Series to include a l l of these pre-Beltian rocks and further subdivided the Shuswap into formations. At the same time he introduced the term Shuswap terrane i n reference to the entire assemblage of metamorphic, g r a n i t i c and pegmatic rocks comprising the complex. Throughout his work, Daly was impressed by the metamorphism in the Shuswap which he considered a c l a s s i c example of load metamorphism. In a 1917 paper e n t i t l e d Metamorphism and i t s Phases, Daly defined load metamorphism as one in which the stress dire c t i n g r e c r y s t a l l i z a t i o n was induced by deep b u r i a l and dead weight resulting i n s c h i s t o s i t y sensibly p a r a l l e l to the planes of s t r a t i f i c a t i o n . H.S. Bostock (1940-1941), mapping on a scale of 1 inch to 1 mile covered part of the present map-area, and introduced the name Vaseaux Formation for the schists and gneissic rocks around Vaseaux Lake. Bostock considered the Vaseaux Formation to be older than the less metamorphosed Kobau Group sediments of questionable Carboniferous age, which he also named and .mapped on Mt Kobau southwest of the Vaseaux Lake area. In 1934 Daly's postulated load metamorphism i n the Shuswap was questioned by J.A. G i l l u l y who showed that the metamorphism was of the dynamic type by means of petrofabric interpretation of planar and linear structures. In the same year B.B. Brock related s c h i s t o s i t y and li n e a r structure i n Shuswap gneisses east of Okanagan Mountain to the upward thrusting of g r a n i t i c magmas i n post-Triassic time. The geology of Kettle River West map-sheet, on which Vaseaux Lake i s c e n t r a l l y located, was compiled by C E . Cairnes i n 1940. He showed that the Shuswap metamorphic complex was continuous from the Shuswap Lake area along the east side of the Okanagan Valley, as far south as the 49th p a r a l l e l . Cairnes presented evidence to support his view that the metamorphism i n the Shuswap was a comparatively recent event in the geologic history of the terrane, and was related to Mesozoic b a t h o l i t h i c intrusions. He believed that the "sill-sediment complex" and structures con-formable with bedding were fundamental c h a r a c t e r i s t i c s of the Shuswap, while adjoining less metamorphosed formations where characterized by steeper structures. These differences Cairnes attributed to depth of b u r i a l during an episode of deformation, -8-metamorphism and g r a n i t i c intrusion which occurred during Mesozoic time. The large b a t h o l i t h i c masses he said, represented an extreme phase of g r a n i t i z a t i o n which occurred at great depth in the metamorphic complex, and were gradational through the "sill-sediment complex", a hybridized zone, to less altered l i t h o l o g i e s . In 1959 A.G. Jones mapped and described the Vernon map-area which includes a large part of the Shuswap Sheet o r i g i n a l l y mapped by Dawson. Jones re-organized the Shuswap stratigraphy and divided the terrane into the Monashee, Mt. Ida and Chapperon Groups whose stratigraphic relations with one another are s t i l l uncertain. Cache Creek rocks of questionable Carboniferous and i j Permian age were said by Jones to overlie the Shuswap uncon-formably, and a Precambrian age was postulated for the Shuswap. Jones also recognized older and younger episodes of metamorphism, deformation and g r a n i t i c intrusion and assigned a pre-Permian and probable Precambrian age to the older of these. H.W. L i t t l e (1961), revised Cairnes'Kettle River West map and extended the undivided Monashee Group southward to include the Vaseaux Formation. L i t t l e also correlated the g r a n i t i c rocks of the region with the Nelson and Valhalla plutonic rocks which occur further east. In 1964 V.A. Preto attempted to document the unconformity between the Shuswap and the overlying Cache Creek by mapping i n d e t a i l the l o c a l i t i e s c i t e d by Jones. He was unable to confirm the existence of the unconformity except at Salmon River, where the rocks involved may or may not belong to either the Shuswap or the Permian Cache Creek Formation. -9-J.R. Snook (1965) studied the Tonasket Gneiss of north-central Washington State, a d i r e c t southerly extension of the Shuswap terrane. He was unable to determine the stratigraphic position of the Tonasket Gneiss, but outlined a complex geologic history comprised of early high grade metamorphism and deformation followed by l a t e r mylonization, gentle folding and f a u l t i n g . N.B. Church (1967), described the Early T e r t i a r y continental volcanic and sedimentary rocks of White Lake map area which l i e unconformably on various pre-Tertiary l i t h o l o g i e s west of Vaseaux Lake. Faulting at intervals during and after deposition and an episode of gentle folding of probable pre-Miocene age were recognized. In 1969 A.V. Okulitch described the geology of Mt Kobau and was concerned p a r t i c u l a r l y with the geologic history of the Kobau Group of meta-sediments and meta-volcanics. Okulitch correlated the Kobau with the lower more deformed parts of the Anarchist Group which are of pre-Permian or possibly pire-Carboniferous age, and suggested that the Kobau may be equivalent with the Chapperbn Group (uppermost Shuswap in the Vernon area). He described a 3-phase deformational history i n the Kobau and t e n t a t i v e l y correlated e a r l i e s t Kobau structures with phase 2 structures found in the nearby Vaseaux Formation and suggested that t h i s deformation i s of pre-Permian and possibly pre-Carboniferous age. In recent years much geologic work has been done along the eastern margin of the Shuswap and the adjoining Selkirk Mountains and Kootenay Arc, and i s pertinent to stratigraphic and s t r u c t u r a l correlations and radiometric dating within the Shuswap. Information in papers by Fyles (1964), Hyndman (1968), Preto (1968), Read (1971), -10-Reesor (1965), Ross (1968), and Wheeler (1962, 1964, 1966), i s of interest, but i s much too complex and lengthy for review here. GENERAL GEOLOGY High grade metamorphic rocks of the Shuswap complex (Vaseaux Formation of this study) are the oldest known rocks in the southern Okanagan region of B r i t i s h Columbia. Their contact relationships with rocks of known age may i n some instances be inferred, but are generally not well understood for a variety of reasons, among which o b l i t e r a t i o n as a resu l t of subsequent deformation and metamorphism i s paramount. i • ' Relationships with some plder rocks i n the district-Kobau Group (Okulitch, 1970) and the Old Tom and Shoemaker Formations (Ross and Barnes, 1972)-have been established as a resu l t of recent work, and i t i s now apparent that the Vaseaux Formation was i n existence and underwent an early (phase 1) episode of deformation and metamorphism i n which the Kobau, Old Tom or Shoemaker Formations did not pa r t i c i p a t e . Later phase 2 and phase 3 deformation affected a i l of the above-mentioned l i t h o l q g i e s and phase 3 has been shown to be of probable pre-late Mississippian age. (Ross and Barnes 1972). The Vaseaux Formation i s thereby inferred to be of probable pre-mid-Paleozoic age. The Vaseaux Formation i s bounded i n large part by g r a n i t i c rocks of Mesozoic and probably older age (see figure 1-2) which comprise the "Okanagan Composite batholith" (Daly, 1912). On the west volcanic and sedimentary rocks of early Tertiary age l i e unconformably above and/or are in f a u l t contact with the Vaseaux Formation, but have participated i n only the l a t e s t phases 4 and 5 of deformation. - I I -49°Oo'N L E G E N D Sedimentary and Volcanic Early Tertiary ] g | Upper Triassic. [Tj Trlasste. Anarchist Gp. 3 ] Pennsyivanian and Permian. Cache Cr. Gp., Blind Cr Fm. (3 A ). [z] Kobau Gp. 1 1 ) Lower Paieazoic and/or Pre-Cambrian. Shuswap Complex, Monashee Gp. Intrusive Jurassic ami/or Cretaceous Okanogan Bathollth Comaplex Including Osoyoos (a),Slmttkmeen (b), CoW«le< c), Oil ve r (d), K rugerte), Folrvlew (f) intrusive bodies. Faults Seel* in Milts 0 10 eo FIGURE 1 - 2 GENERAL GEOLOGY O F T H E SOUTHERN OKANAGAN After A.V. Okuliteh 1969 -12-As a result of the present study, the Vaseaux Formation has been shown to consist of 5 d i s t i n c t i v e map-units comprised of granulite, schist and amphibolite with minor quartzite and carbonate. The s p e c i f i c mode of o r i g i n and environment of deposition of the succession i s not known, but o r i g i n a l bedded character i s implied by compositional layering present on a l l scales. A f f i n i t y with synorogenic sediments and basic volcanics of the greywacke suite i s suggested but not substantiated by f i e l d evidence. Map-units 1-5 form a structural succession i n which the r e l a t i v e age of units i s unknown. Five phases of deformation i ' . • are recognized, and large scale recumbent folding associated with each of phases 1-3 has brought about much re p e t i t i o n within the succession. Metamorphism in the amphibolite facies and intrusion of g r a n i t i c plutons accompanied phases 2 and 3. Phases 4 and 5 of deformation gave r i s e to open folds and fractures and these same structures are developed i n nearby early Tertiary rocks. Phase 4 i s related i n time to early Tertiary (44 m.y. B.P.) volcanism and l o c a l i z e d high heat flow (Ross and Barnes, 1972). Phase 5 folding and f a u l t i n g of probable ^re-Miocene age post-dates deposition of the early T e r t i a r y White Lake sediments (Church, 1967). -13-CHAPTER TWO STRUCTURAL SUCCESSION Previous mapping of high grade metamorphic rocks i n the Southern Okanagan was e s s e n t i a l l y reconnaissance i n nature (Bostock,1928-30, Cairns, 1940, L i t t l e , 1961) and did l i t t l e more than outline the p r i n c i p a l masses of paragneiss and orthogneiss. Bostock placed a l l of the paragneiss into a unit named the Vaseaux Formation, and i t i s with a part of the Vaseaux Formation that t h i s study i s concerned. Within the Vaseaux Formation of the present map-area, a lo c a l s t ructural succession exceeding 4000 feet i n present thickness has been established. The succession i s made up of 5 l i t h o l o g i c units (Units l r 5 ) , but neither top or bottom of the succession, nor the r e l a t i v e ages of the map-units are known. Among the 5 map-units, Unit 2, composed largely of sc h i s t , and Unit 4, of amphibolitic character, are l i t h o l o g i c a l l y d i s t i n c t markers. Units 1,3 and 5, although d i f f e r i n g s l i g h t l y from each other, consist almost e n t i r e l y of various types of g r a n u l i t e 1 1. The A.G;I. Glossary defines granulite as follows: "(1.) A metamorphic rock composed of even sized interlocking granular minerals. (2.) A metamorphic belonging to a high-temperature facies characterized by the presence of mica and hornblende. Coarse and fine bands alternate to produce a regular planar s c h i s t o s i t y . " Turner and Verhoogen (1960, p.454) i n defining granulite state; "Some degree of segregation banding and es p e c i a l l y alignment of f l a t lenses of quartz or feldspar t y p i c a l l y impart a regular f o l i a t i o n to the rock." As a textural term used i n the above sense, granulite describes many of the granular gneissic rocks of Vaseaux Lake map-area more f u l l y than the almost synonomous but more general term gneiss. Granulite i s s p e c i f i c a l l y not used as a qualifying term for a metamorphic fa c i e s , and regional metamorphism which gave r i s e to the granulites was i n the amphibolite fa c i e s . -14-and semi-pelitic granulite, and are distinguished by subtle variations in composition and character as summarized in . Table 2-1. Although lithology i s r e l a t i v e l y simple, and the succession s u p e r f i c i a l l y resembles a gently folded stratigraphic sequence, many structural and metamorphic complexities exist and require mention before the i i t h o l o g i c units are described. In d e t a i l , the units are deformed i n t e r n a l l y by numerous minor folds and associated transposition structures, and regionally by large recumbent folds and slides"*". Deformation i s polyphase, and three superposed large scale recumbent fo l d sets have given r i s e to much re p e t i t i o n of map-units. Further complexity stems from shearing and l o c a l imbrication at litholqgjic contacts and1 . di s l o c a t i o n along s l i d e s , but i n most instances i i t h o l o g y i s s u f f i c i e n t l y d i s t i n c t i v e to allow recognition of such structures and correlation across them. The oldest megascopic fold in the map-area i s a northerly trending, westerly closing i s o c l i n e named Mclntyre Bluff Fold. Whether i t i s an a n t i c l i n e or a syncline i s not known, but parts of i t s core and hinge have been mapped by Ross near Mclntyre B l u f f , 1' The A.G.I. Glossary defines s l i d e as follows; Slide A term proposed by Fleuty (1964) for a f a u l t formed i n close connection with f o l d i n g , and that i s conformable with the f o l d limb or a x i a l surface. It i s accompanied by thinning and/or disappearance of the folded beds. Usage of the term s l i d e in this study i s consistent with the above d e f i n i t i o n . TABLE 2-1 SUMMARY OF THE CHARACTERISTICS OF MAP UNITS 1-5 Lithology - b i o t i t e semi-pelitic granulite with very l i t t l e or no hornblende - schistose b i o t i t e r i c h layers c h a r a c t e r i s t i c - b i o t i t e rruscovite schists with interbedded semi-p e l i t i c granulite layers - minor marble, c a l c - s i l i c a t e , quartzite - semi-pelitic granulites t y p i c a l l y with more hornblende than b i o t i t e 1 - thin b i o t i t e r i c h schistose layers common - of amphibolitic character - basal f i s s i l e b i o t i t e r i c h granulites grading to laminated amphibolites -minor impure quartzite, c a l c - s i l i c a t e , marble - laminated and massive amphibolites - no granulites - basal f i s s i l e b i o t i t e semi-pelitic granulites - upper hornblende granulites - occasional amphibolite layers - thin b i o t i t e r i c h layers common See Chapter Five for Mineral Assemblages. - 1 6 -N. of Shuttleworth C r e e k S. of Shuttleworth Creek W.of W. of Vaseaux Gal I ag her Lake Lake Core of "} Mc In ty re Bluff fold Figure 2-1 Schematic structural l i thologic succession. Major structures affecting distribution of map units 1 - 5 are shown. Units 1 and / or 2 may, in addition, be locally missing against a slide (not shown). -17-and continuity of the core li t h o l o g y and r e p e t i t i o n of map-units are evidence of i t s regional development. Because deformation is polyphase and nothing i s known about r e l a t i v e ages of map-units, i t i s necessary to describe the units with respect to th e i r structural positions on the oldest f o l d recognized. This has been done by numbering the Units 1-5 as they occur respectively from core to envelope of Mclntyre B l u f f Fold as i l l u s t r a t e d schematically on figure 2-1. Repetition of the units due to later phase 2 and phase 3 folding i s also i l l u s t r a t e d , by means of schematic columnar sections representing d i f f e r e n t parts of the map-area. Thicknesses of the map-units are far from uniform. Variation from hinge to limbs of the larger folds accounts for s i g n i f i c a n t differences, but other factors contribute to even larger l o c a l variations. Among these gradual truncation against s l i d e s , d i l a t i o n through i n j e c t i o n of concordant g r a n i t i c and pegmatitic material, and r e p e t i t i o n due to small-scale internal folding are prominent. In view of these factors i t i s impractical to attempt estimates of o r i g i n a l thickness. Total present thickness of the units has been estimated where possible at several l o c a l i t i e s on the limbs of phase 2 folds which are s t r u c t u r a l l y representative of most of the area mapped. Maximum differences obtained are expressed as thickness ranges, and are meaningful only as an approximation of thickness most commonly observed. Complex fabrics characterized by intersecting planar and linear elements are found in a l l of the map-units. Rather than deal with such elements as cleavage and l i n e a t i o n i n isolated l i t h o l o g i c descriptions which would c a l l for much r e p e t i t i o n , a l l -18-f a b r i c elements are d e s c r i b e d i n context with s t r u c t u r e and metamorphism i n Chapters 3 and 5. Among the elements of f a b r i c however, c o m p o s i t i o n a l l a y e r i n g is of prime concern i n l i t h o l o g i c d e s c r i p t i o n . Compositional l a y e r i n g i s seen on a l l s c a l e s i n a l l map-units and some g e n e r a l -i z a t i o n s may be made concerning i t s nature and o r i g i n i n order to avoid r e p e t i t i o n . The terms s e g r e g a t i o n , l a y e r i n g , and g n e i s s i c s t r u c t u r e , have been used here t o d e s c r i b e d i f f e r e n t degrees of development of co m p o s i t i o n a l l a y e r i n g i n response to dynamic and metamorphic p r o c e s s e s . Q u a r t z o - f e l d s p a t h i c segregations impart a d i s t i n c t l a y e r e d s t r u c t u r e to a l l of the map-units. T y p i c a l l y they form d i s -^continuous but c l o s e l y , s p a c e d l a m e l l a e a few f r a c t i o n s of an i n c h t h i c k p a r a l l e l to l i t h o l o g i c l a y e r i n g or a prominent c l e a v a g e . S l i g h t l y t h i c k e r through-going l a m e l l a e have been l o c a l i z e d by shear planes and separate areas of d i s c o n t i n u o u s l a m e l l a e to which they are p a r a l l e l or s u b - p a r a l l e l . G n e i s s i c s t r u c t u r e i s r e s t r i c t e d to more h i g h l y sheared p a r t s of the map-units. Q u a r t z - f e l d s p a t h i c l a y e r s may be s e v e r a l times as t h i c k and more continuous than i n rocks which are l e s s sheared. G n e i s s i c zones i n some i n s t a n c e s l o c a l i z e d numerous concordant p e g m a t i t i c and g r a n i t i c sheets which f u r t h e r enhance t h e i r g n e i s s i c s t r u c t u r e . LITHOLOGIC UNITS Unit 1 Unit 1 c o n s i s t s e n t i r e l y of grey to brownish grey semi-p e l i t i c g r a n u l i t e wherein medium to f i n e g r a i n e d p l a g i o c l a s e -19-and quartz are the most abundant mineral components. B i o t i t e , ranging up to about 40%, i s a highly variable component, while hornblende, muscovite, and reddish-brown garnet occur i n minor proportions only. Compositional layering defined by iriequal d i s t r i b u t i o n of b i o t i t e within Unit 1 may be a r e l i c t feature of primary sedimentation and could represent bedding. B i o t i t e enriched layers ranging from thicknesses of 2-3 feet to thin schistose partings grade both sharply and imperceptibly to b i o t i t e d e f i c i e n t layers. Such layers are always bounded by narrow shear zones and cannot readily be ascribed to a unique primary sedimentation process. Mineral segregation layering i s well developed throughout Unit 1 and forms the conspicuous f o l i a t i o n . In exposures near Mclntyre B l u f f gneissic structure l o c a l l y predominates. 1 j . • ' . '. The minimum thickness of Unit 1 has been estimated at 150 feet, but i t s t o t a l thickness i s unknown as the Unit i s not completely exposed. Contacts with schists of Unit 2 are highly sheared and much of the movement has been within the schist. Although Units 1 and 2 appear conformable i t i s l i k e l y that parts of both units are missing due to thi s movement. Where Unit 1 i s truncated by a s l i d e , imbrication of Units 1 and 2 on anastomosing secondary shear planes i s evident. Unit 1 i s r e s t r i c t e d to the cores of the phase 1 Mclntyre Bluff Fold. East of the Okanagan River phase 2 and phase 3 folds have refolded and phase 1 structure, such that Unit 1 appears on the lower limb of phase 2 Shuttleworth Creek Synform, and further south on the inverted limb of phase 3 Gallagher Lake Synform. At both occurrences Unit 1 eventually disappears against a s l i d e . -20-Unit 2 Unit 2 i s composed primarily of reddish brown to grey weathering schist with interbedded semi-pelitic granulite and subordinate impure quartzite, marble and c a l c - s i l i c a t e . B i o t i t e i s the dominant mineral component of the sc h i s t s , but coarse flakes of muscovite l y i n g i n the plane of compositional layering are a c h a r a c t e r i s t i c feature which p e r s i s t s e s p e c i a l l y i n highly sheared portions of the unit. Quartz, feldspar and frequently reddish-brown garnet are variable but s i g n i f i c a n t components of the mineral assemblages. D i s t r i b u t i o n of the various l i t h o l o g i c types within Unit 2 i s not uniform. Homogenous sections of schist tens of feet thick, separated by much thinner schist:layers enveloped by semi-pelitic jgranulites are c h a r a c t e r i s t i c . Layers of semi-pelitic granulite, medium to fine grained mixtures of feldspar, quartz, and b i o t i t e with minor hornblende, epidote and garnet, make up no more than 20% of Unit 2,.and are f a i r l y evenly distributed. Thickness of the granulite beds i s never i n excess of 3 feet and i s most commonly i n the order of 3-8 inches. Blue-grey diopside marble and greenish grey to brown c a l c -s i l i c a t e granulite form less than 1% of the t o t a l volume of Unit 2, but are a widespread and d i s t i n c t i v e part of the lithology, These occur as discontinuous layers and pods which are as much as 20 feet thick on the hinges of phase 2 folds and continuous for 4 0-60 feet along s t r i k e . More commonly they are only a few feet thick and continue for 10-20 feet along s t r i k e . -21-Mineral segregation layering i s developed within the schists of Unit 2, but not to the extent that i t i s seen within the interbedded granulites, or the other g r a n u l i t i c units of the map-area. Gneissic structure i s only seen i n association with g r a n i t i c rocks where i t i s the r e s u l t of l i t - p a r - l i t i n j e c t i o n of g r a n i t i c materials and metasomatism. ; Unit 2 ranges from 350-550 feet i n thickness and contacts with Units 1 and 3 are highly sheared as a re s u l t of s l i p during the various phases of folding. Changes i n attitude are sometimes seen across these contacts but more commonly they appear concordant and may have been i n i t i a l l y conformable. Over much of the area Units 2 and 3 are i n contact across a s l i d e along which both are obliquely truncated. • , • : • . Unit 2 i s widely distributed throughout the map-area and is useful i n confirming a l l ofsthe major structure. Unit 2 closes on the hinge of the phase 1 Mclntyre B l u f f Fold, and east of the Okanagan i t i s present on the limbs of phase 2 folds. East of Gallagher Lake 1 imbricate s l i c e s of Unit 2 outline the hinge of the phase 3 Gallagher Lake Synform. Unit 3 A thick sequence of remarkably uniform grey to grey-brown weathering granulites comprises Unit 3. These rocks include both fine to medium grained, and semi-pelitic v a r i e t i e s of granulite i n which feldspar and quartz combined account for about 75% of the t o t a l mineral assemblage. Hornblende i s t y p i c a l l y somewhat more abundant than b i o t i t e , but b i o t i t e enriched layers are present and include a l i t t l e muscovite and garnet. Bedding, if-ever developed i n Unit 3, i s no longer e a s i l y -22-recognized, but l o c a l subtle changes i n proportions of hornblende and b i o t i t e probably r e f l e c t o r i g i n a l compositional differences. Thin schistose partings enriched i n b i o t i t e and inequally spaced throughout the Unit may represent o r i g i n a l bedding surfaces. Extremely well developed mineral segregation layering i s c h a r a c t e r i s t i c of the li t h o l o g y of Unit 3 and i s seen i n v i r t u a l l y a l l exposures. Gneissic structure i s also well developed, especially in the core of the Vaseaux Lake Antiform (phase 2) which i s exposed along the east shore of Vaseaux Lake. Unit 3 i s repeated at several s t r u c t u r a l levels as a r e s u l t of folding and appears on the limbs or i n the cores, of a l l major folds. Best exposures are i n roadcuts near Vaseaux Lake, i n the canyon section of Mclntyre Creek, and ! in' the canyon section of Shuttleworth Creek.' North and southeast of Shuttleworth Creek a thick section of Unit 3 l i e s above a s l i d e developed during phase 3 deformation, and probably occupies the core of a major phase 2 antiform (plate 1-pocket). Unit 3 at these l o c a l i t i e s i s greatly altered as a r e s u l t of probable Early Tertiary hydrothermal a c t i v i t y (Chapter 5). Thickness of Unit 3 i s d i f f i c u l t to estimate because of incomplete exposure. North of Mclntyre Creek up to 1300 feet of section i s present but the Unit thins northward to about 200 feet against a s l i d e . The contact with Unit 4 i s grad-ational, apparently conformable but weakly to strongly sheared. On the hinges of major phase 2 folds Unit 3 attains thicknesses greatly i n excess of 1300 feet measured p a r a l l e l to the.axial planes. On the limbs of the Vaseaux Lake Antiform and the s t r u c t u r a l l y higher phase 2 antiform north of Shuttleworth Creek -23-thicknesses of 1200-1500 feet have been estimated i n sections perpendicular to the s t r i k e of Unit 3. Unit 4 Unit 4 consists of a mixed assemblage of metasedimentary and metavolcanic rocks which are characterized by abundant amphibole. Additional l i t h o l o g i c d i s t i n c t i o n s allow subdivision into Units 4a and 4b within most of the map-area, as follows. Unit 4a consists of highly f i s s i l e s e mi-pelitic granulite interbedded with amphibolite and minor impure quartzite, c a l c -s i l i c a t e and marble. The f i s s i l e granulites form a zone about 100 feet thick at the base of Unit 4a, above which layers of fine grained laminated amphibolite ranging up to several feet in thickness appear and; become progressively more 'abundant.' ; A! few beds of rusty weathering quartzite as much as 12 feet thick and a few discontinuous marble and c a l c - s i l i c a t e layers occur in the s t r u c t u r a l l y higher parts of the Unit. Unit 4b i s composed of several types of amphibolite but contains l i t t l e or no granulite. Well laminated medium to dark gray amphibolite forms the bulk of the Unit within which layers of fine grained massive amphibolite up to 10 feet thick, and very thin layers of b i o t i t e r i c h amphibolite are inequally d i s t r i b u t e d . Laminated amphibolites consist of alternating dark and l i g h t layers i n which medium to fine grained mixtures of hornblende, plagioclase, epidote, clinopyroxene, b i o t i t e and quartz make up the mineral assemblages. Colour v a r i a t i o n i s dependent upon respective dominance of hornblende or plagioclase, and to.a lesser extent b i o t i t e , which forms schistose partings between some layers. -24-In contrast, massive amphibolites display l i t t l e i n t e r n a l v a r i a t i o n in composition, and medium to fine grained hornblende i s in excess of 70% of the t o t a l mineral content. Mineral segregation layering i s best developed within the granulites of Unit 4a but i s also seen within massive and laminated amphibolites where lamellae r i c h i n plagioclase and occasionally clinopyroxene are present. Gross compositional layering i n the laminated amphibolites, due possibly i n part to primary sedimentation, i s greatly enhanced by t h i s segregation layering. Units 4a and 4b are well exposed on the ridge south of Shuttleworth Creek where they outline the hinge and limbs of phase 2 Shuttleworth Creek Synform, and they have bee'n mapped in the same structural position west of the Okanagart River. Further south they appear again on the hinge of phase 3 Gallagher Lake Synform. Near Vaseaux Lake a few s l i c e s of Unit 4a are present i n .a gneissic zone within the cores of phase 2 Vaseaux Lake Antiform, but the complete'section i s not exposed. The contact between Units 4a and 4b i s highly sheared and shows some ch a r a c t e r i s t i c s of a s l i d e . Changes i n attitude across the contact are common and parts of one, or both Units may be missing. Contacts with Units 3 and 5 are also sheared but appear conformable. Thickness of Unit 4a range's from about 200-800 feet and Unit 4b ranges from 300-850 feet. Much of the v a r i a t i o n i n thickness i s sympathetic i n the sense that combined thickness of Units 4a and 4b remains f a i r l y constant throughout the area. Amphibolitic rocks thought to be part of Unit 4a and mapped -25-as Unit 4 undifferentiated on plate 1, are exposed in northwest and northeast parts of the map-area, above the phase 3 s l i d e . At the northwest occurrence they l i e on the lower limb of a major, phase 2 antiform while at the northeast they appear to l i e i n the core of the complimentary s t r u c t u r a l l y higher synform. The rocks at the northwest occurrence are laminated amphib-o l i t e s much l i k e Unit 4b but rocks resembling Unit 4a were not found. These laminated amphibolites may be i n tectonic contact with Units 3 and 5 such that part of Unit 4 i s missing. Contact relations are no longer e a s i l y discernable and l i t h o l o g y and internal structure have been obscured by pervasive hydrothermal a l t e r a t i o n which has d r a s t i c a l l y affected a l l of the rocks i n this area (plate,4-pocket and Chapter 5). ' ' ; At the northeastern occurrence a l t e r a t i o n i s much less intense, and the l i t h o l o g i c succession comprising the amphibolitic unit i s somewhat d i f f e r e n t than that found elsewhere within Unit 4. Above Unit 3 several hundred feet of f i s s i l e s emi-pelitic granulite with minor interbedded s c h i s t , quartzite and laminated amphibolite lead upwards to a contact with uniform amphibolite 1100 feet or more in thickness. While the rocks beneath th i s contact are not unlike the rocks of Unit 4a, the overlying uniform amphibolites bear l i t t l e resemblance to the laminated amphibolites of Unit 4b. They contain noticeably less hornblende and more plagioclase which here are present i n about equal proportions and together form at least 90% of the mineral assemblage. Minor quartz, b i o t i t e , epidote, garnet and sphene also occur, but diopside which i s rather abundant in laminated amphibolites was not found. Segreg-ation layering involving plagioclase and a l i t t l e quartz i s well -26-developed within the uniform amphibolites, and apart from infrequent schistose and pegmatitic layers, forms the only compositional layering found therein. Unit 5 Unit 5 i s composed of brownish grey and grey semi-pelitic granulites r i c h i n quartz, plagioclase and sometimes b i o t i t e with lesser hornblende, garnet, epidote and rare muscovite. LOwer parts of the Unit are brownish f i s s i l e mica r i c h granulites, but b i o t i t e decreases upwards and the upper parts are grey horn-blende granulites containing occasional layers of amphibolite. B i o t i t e enriched layers, and schistose partings occur throughout Unit 5 and may be an' expression of bedding, but segregation 1 ; •, layering forms the most conspicuous f o l i a t i o n . Unit 5 occupies the core of Shuttleworth Creek Synform east and west of the Okanagan River. I t i s also present in a limited area on the hinge of Gallagher Lake Synform and i s i n intrusive and f a u l t contact with highly altered g r a n i t i c rocks. In the northwestern map-area part of Unit 5 may be present i n tectonic contact with laminated amphibolites (Unit 4 u n d i f f e r -entiated) within a zone of intense hydrothermal a l t e r a t i o n above the phase 3 s l i d e . Unit 5 i s the uppermost member of the s t r u c t u r a l succession and i t s t o t a l thickness i s unknown. It i s apparently conformable with Unit 4 and up to 6 00 feet of section i s known within the map-area. i; i! -27-ORIGIN AND DEPOSITIONAL ENVIRONMENT Complex metamorphism and deformation within the Vaseaux Formation make speculation on the o r i g i n of these rocks tenuous. Primary structure, i f ever present, can no longer be recognized, and knowledge of the chemical composition of various rock types comprising the Vaseaux Formation i s presently i n s u f f i c i e n t to ! ! allow speculation about o r i g i n from a compositional basis. i Compositional layering on a l l scales within the Vaseaux Formation i s thought to be i n part an expression of an o r i g i n a l bedded character of the succession, and i s the only r e a l clue as to the o r i g i n . Several hypothetical origins and environments of deposition are therefore possible i n view of the nature of metamorphism and deformation. • The author would favour a view suggesting that the succession has a f f i n i t y with the greywacke suite. Best evidence for a near shore environment i s seen i n the granulites and semi-pelitic granulites where alternating but t e c t o n i c a l l y separated b i o t i t e enriched and b i o t i t e d e f i c i e n t layers suggest possible o r i g i n a l graded bedding on many scales, and therefore a t u r b i d i t e o r i g i n . Granulites are by far. the most abundant l i t h o l o g i c type within the map area and i t seems possible that they are in fact metamorphosed greywackes. Shales and basic volcanic rocks, also sometimes part of the greywacke suite, would under such a hypothesis be represented by Units 2 and 4 of the Vaseaux Formation. An alternate, perhaps less tenable hypothesis, i s that the succession was formed i n an open marine environment and i s the product of metamorphism of a mixed assemblage of argillaceous cherts, shales and basic volcanic rocks. Minor carbonate found -28-within the succession could well be present i n either open marine or near shore environments. LITHOLOGIC CORRELATION Rocks of the Monashee Group of the Vernon area (Jones, 1959) and the Tonasket Gneiss of Washington State (Snook, 1965) are similar in many ways to the metamorphic rocks of the Vaseaux Formation. Although detailed mapping has not been done in either of the above areas and comparison of stratigraphy i s not possible, i t i s suggested that these rocks may a l l be of approximately the' same age and may have accumulated i n the same basin of deposition. They a l l have undergone.complex geologic h i s t o r i e s , and now form part of a northerly trending high' grade metamorphic be l t l y i n g in , • i ' large part east of the Okanagan Valley. More easterly parts of the Shuswap terrane are also l i t h o l o g i c a l l y s imilar to the Vaseaux Formation but no basis for cor r e l a t i o n has been established or i s warranted at th i s time. CHAPTER THREE STRUCTURE INTRODUCTION Composite structure within, the metamorphic rocks near Vaseaux Lake i s the result of superposition of f i v e successive phases of deformation. Major folds have been formed during each successive phase, and the l a t e r phases have i n addition, produced fractures. Geometries of these f o l d sets and fractures are subject to comprehensive description on the following pages, as are their mutual time and interference relationships. Maps, cross-sections, schematic diagrams, lower hemisphere stereo-graphic plots, and wherever possible photographs are used to; i l l u s t r a t e and substantiate these descriptions. \ ' i '! Associated metamorphism, plutonism, metasomatism, and the evolution of fa b r i c as seen In thin-section are subjects covered in Chapters 4 and 5. OUTLINE OF STRUCTURAL HISTORY Table 3-1 summarizes the evolution of structure within the Vaseaux Lake area and presents the structural elements related to each phase of deformation. The e a r l i e s t structures (phase 1) are a northerly trending f o l d set upon which northwesterly trending phase 2 folds have been superposed. Phase 1 and 2 folds are both of similar s t y l e , and are associated with contemporaneous regional metamorphism which probably reached i t s highest grade during phase 2 folding. Phase 3 folds are of diverse trend and are grouped into subsets 3a, 3b, 3c. Subset 3a structures include westnorthwesterly TABLE 3-1 SUMMARY OF THE STRUCTURAL ELEMENTS FOLD SETS FOLD STYLE PLANAR STRUCTURES LINEAR STRUCTURES ASSOCIATED DISCONTINUITIES 1 Similar; i s o c l i n a l rootless; long planar limbs, sub-rounded hinge F l - a x i a l cleavage, quaquaversal dip L l - f o l d axes and pene-t r a t i v e lineations variably plunging N and S s l i d e s 2 Similar; t i g h t often rootless; planar limbs, sub-rounded to angular hinge F2 - a x i a l cleavage, quaquaversal dip L2 - f o l d axes and pene-t r a t i v e lineations gently plunging NW and SE reactivated FQ/F1 3a Similar; open, planar limbs, sub-rounded to angular hinge F3 - a x i a l s t r a i n -s l i p cleavage, i n c l -ined gently to SSW L3 - f o l d axes and pene-t r a t i v e lineations gently plunging WNW and ESE reactivated FD/F1, F2 3b Similar; t i g h t to open minor folds F3b - a x i a l s t r a i n -s l i p cleavage, i n c l -ined gently to NNE -l o c a l l y developed L3b - f o l d axes and pene-t r a t i v e lineations gently plunging WNW and ESE s l i d e i n c l i n e d to NE 3c Flexural-flow, open minor folds F3c - a x i a l cleavage variably i n c l i n e d to E and W - l o c a l l y -.. developed L3c -minor fold axes plunging NW and NE s l i d e i n c l i n e d to NE 4 F l e x u r a l - s l i p , open, rounded limbs and hinge JI -steeply dipping NE 1 l y fractures L4 -rare minor fo l d axes gently plunging N and S reactivated e a r l i e r f o l i a t i o n ; 5 F l e x u r a l - s l i p , open, rounded limbs and hinge J2 and J3 -steeply dipping W to NNW fractures ~ "_L5 -minor fold axes gently plunging NW and SE steeply dipping f a u l t s I I V i l l i I I I I I I I ' I S T R U C T U R A L D O M A I N S VASEAUX L A K E AREA D o m a i n Roundaries Axial trace Shuttleworth Creek Synform Axial trace Vaseaux Lake Antiform Axial trace Gallagher Lake Synform Phase 3 b mylonite Domain numbers Lithology Metamorphic rock Granite gneiss Late granitic rocks Scale Miles Figure 3 -1 - 3 2 -trending megascopic folds of similar style and were the f i r s t . structures produced during phase 3. Subsets 3b and 3c formed la t e r and are associated in space and time with the development of.a sli d e marked by mylonite. Phases 4 and 5 of the polyphase deformation produced broad, open f l e x u r a l - s l i p folds along successive north to northeasterly and northwesterly trends. Shear on the limbs of these folds gave mylonite and gouge. Steeply dipping j o i n t and f a u l t sets (J-^, J 2 , J 3 , J 4 ) are related to extensive fracturing which accompanied these l a t e s t phases of deformation,and perhaps even lat e r f a u l t i n g . STRUCTURAL DOMAINS . . , • ! ' ' • • Selection of perfectly homogeneous structural domains for analysis was impractical in view of a l l scale 5 phase f o l d i n g . A very large number of domains would be required to i s o l a t e properly zones cf homogeneity., and i n s u f f i c i e n t data was available to allow t h i s . I t was decided that most could be gained by selecting domains s u f f i c i e n t l y homogeneous to allow analysis of the effects of phase 2 and 3 deformations. This was done by taking the a x i a l traces of demonstrable major phase 2 and 3 f o l d s , and the phase 3 s l i d e as domain boundaries. The f i v e r e s u l t i n g domains are shown on figure 3-1. Attitudes of compositional layering and phase 1, 2 and 3 planar and lin e a r structures have been plotted for each domain (figure 3-2 and 3-10) and these diagrams are u t i l i z e d i n the text. Limitations are imposed by th i s selection of domains. I s o c l i n a l phase 1 folding has been ignored and cannot therefore be f u l l y described, although the re-orientation of phase 1 -33-N 1 Domain 1 F i g u r e 3-P 113 poles t O Fo / F, , contoured at 1-2-4-8-12°/o per unit area . • L3 -34-N T Domain 2 F i g u r e 3-3 37 poles to Fo/ Fj , contoured at 1-2-4-8.-12% per unit a rea . o L r + L2 . L3 -35-N O O O Q o o o o_ + Domain 3 Figure 3-4 125 poles to Fo/F^  , contoured at 12 4 8 1 2 % per unit area. o L, • L2 - 3 6-T Domain 4 Figure 3 - 5 4 8 poles to Fo/F^  contoured at 1 - 2 - 4 - 8 - 1 2 % per unit a rea . — 37-N 1 Domain 5 Figure 3 - 6 41 poles to Fo/Fj contoured at 1 - 2 - 4 - 8 - 1 2 % per unit area. -38-structures as a result of la t e r folding may be seen. For the same reason, no inference about the present orientation of bedding may be drawn from the attitudes of compositional layering which are plotted for each domain. Open phase 4 and 5 folding has also been ignored in the selection of domains and this leads to scattering of data on figures 3-2 to 3-10. Scattered data has been selected from these figures and plotted with synoptic phase 4 and 5 data (figure 14 and 15) to i l l u s t r a t e generally the geometries of phase 4 and 5 f o l d i n g . . ' ' I FOLD SETS : PHASE 1 Phase 1 folds are extremely appressed recumbent i s o c l i n e s found on a l l scales. O r i g i n a l l y they may have been abundant, but now are rare, perhaps because of almost ubiquitous destruction resulting from transposition of compositional layering which outlines phase 1 f o l d s . Where seen, they show a l l of the features of similar folds and are characterized by sub-rounded to sub-angular northerly trending hinges (plates 3-1, 3-2). Mclntyre Bluff Fold, named for the exposure of i t s core and hinge near Mclntyre B l u f f , i s a megascopic phase 1 structure which closes to the west and brings about rep e t i t i o n within the succession. The limbs of Mclntyre Bl u f f Fold are i s o c l i n a l , and a system of slides developed i n the core have caused imbrication and s l i c i n g of Units 1-3, in response to extreme attenuation of i this structure (plates 1, 2, 5-pocket). Minor folds are t y p i c a l l y rootless cores in an envelope of Plate 3-1 Northerly trending phase 1 f o l d in Unit 3 1/4 mile north of Mclntyre Canyon. Plate 3-2 I s o c l i n a l phase 1 fo l d i n Unit 3 at Shuttleworth Canyon. -40-Figure 3 - 7 Synopsis of phase 1 linear structures. Lineations U - A , • , + , o. Domains 1-5 consecutively. -41-Plate 3-3 I s o c l i n a l phase 1 folds crossed by cleavage Plate 3-4 Northerly trending phase 1 folds deformed about F0 and crossed by cleavage F., . Unit 2 south of Shuttleworth Creek. rock where compositional layering may be almost transposed to the plane of F]_ (plates 3-2, 3-3) . Thus F]_ cleavage which i s extremely well developed cannot always be readily separated from compositional layering (F Q) other than on the hinges of r e l i c t folds. Lineations L-^  include elongate mineral grains and aggregates, crenulations and intersection structures. These also are recognized mainly in proximity to r e l i c t phase 1 cores, having been obliterated elsewhere by ensuing deformation and r e c r y s t a l l i z a t i o n . Despite destruction and o b l i t e r a t i o n of phase 1 structures as a resu l t of la t e r deformation and metamorphism, enough data has been obtained to outline roughly the geometric re-orientation of phase 1 structures re s u l t i n g from re-folding. Obvious e f f e c t s are seen where the limbs and ax i a l planes of mesoscopic phase; 1 folds are deformed about phase 2 and phase 3 a x i a l surfaces (plates 3-4 to 3-6). Similar relationships e x i s t on a larger scale (plate 5-pocket) and have been recognized by mapping and observation of a systematic change in the orientation of across the hinges of some major folds (figure 3-7, plate 2-pocket). In general trends west of north on inverse limbs of phase 2 folds and north to northeast on upright limbs, but t h i s i s not en t i r e l y evident oh figure 3-7 which i s a plot of a l l measured data. Some ambiguity stems from the fact that domain 2 contains a phase 2 antiformal hinge, and large phase 2 folds probably also ex i s t within domain 1 (plate 2-pocket). The lin e a r structure has been measured on both limbs of these folds. Curvilinear phase 1 f o l d axes (plates 3-7 and 3-8) must also be responsible for some of the d i v e r s i t y in trend of seen on figure 3-7. Curved axes probably developed as phase 1 folds were P l a t e 3-5 N o r t h e r l y t r e n d i n g phase 1 f o l d s o u t l i n e d by e a r l y g r a n i t o i d m a t e r i a l i n U n i t 2 and r e -f o l d e d about F o . South o f S h u t t l e w o r t h Creek. P l a t e 3-6 D e t a i l o f above phase 1 h i n g e zones. Plate 3-7 Phase 1 folds with c u r v i l i n e a r axes exposed on northerly trending j o i n t surface, and crossed by l a t e r cleavages F, , F , and fractures J . Plate 3-8 Phase 1 f o l d with c u r v i l i n e a r axis exposed on an almost planar northerly trending surface. Later cleavages F^a, F^b' a n <^ fractures 3^ are shown. Western end of Shuttleworth Canyon near Oliver Ranch. - 4 5 -tightened in later phases of deformation. In becoming t i g h t l y appressed, any d i f f e r e n t i a l movement of remobilized core material within the plane of F± could e a s i l y give r i s e to the curvature. Variation in the trend of res u l t i n g from phase 3 folding . is not well known because of limited exposure and o b l i t e r a t i o n of on inverted phase 3 limbs. With respect to Gallagher Lake Synform (phase 3), L^ ranges from northnorthwest to northnortheast on the lower limb because of phase 2 r e - f o l d i n g , and appears to change from a northnorthwesterly trend in domain 4 to a southsouth-westerly trend in domain 5 across the hinge (compare domains 4 and 5 and see figure 3-9). The orientation of L^ has. been further modified by late f l e x u r a l - s l i p f c l d i n g . Phase 4 folding along northerly axes broadly p a r a l l e l to L1 has had less e f f e c t than phase 5 folding along oblique trends. Phase 5 has brought about gentle c u l -mination and depression of L^ across the hinges of antifc^rmal and synformal f o l d s , and therefore i s responsible for much of the variation i n plunge angle seen on figure 3-7. PHASE 2 Phase 2 folds are similar i n style and are abundant on a l l scales. In many structural positions these are tigh t recumbent folds but are usually more open than the i s o c l i n a l phase 1 structures. Megascopic phase 2 folds with amplitudes of 7-8 miles dominate the l o c a l structure and include Vaseaux Lake Antiform, Shuttleworth Creek Synform, and a t h i r d poorly exposed antiform in domain 2, and probably part of the same antiform and com-plimentary overlying synform in domain 1 which have been o f f s e t - 4 6 -N ± / Approximate o'0 pre-phase 4-! 0 J locus of 1 F 2 / / o oo , 0 /"Hocus related to *)jfk% Phase 5 folding o / • / • / * o7>7 f r Q £ l o ^ Figure 3 - 8 Synopsis of phase 2 structures Linear structures L 2 - • -a l l domains Poles to F 2 cleavage and minor fold axial p lanes- A , • , • / + , o, - in domains 1 - 5 consecutively. by movement on a phase 3 s l i d e (plates 1-2-5-6~pocket). . These major folds are formed about northwesterly trending axes, and their a x i a l planes dip variably but seldom steeply northeast and southwest as a consequence of l a t e r f o l d i n g . A x i a l plane cleavage F2 outlined by mica and flattened mineral aggregates i s extremely penetrative and forms a small angle with compositional layering on thei r limbs. Hinges are sub-rounded to angular, and the limbs of the major folds are curviplanar and almost i s o c l i n a l . Phase 2 minor folds are congruent with the major structures, and feature small but measurable angles between t h e i r limbs (plate 3-9). These minor folds may be either autochthonous or rootless i n t e r f o l i a l folds in most rock types, but within semi-p e l i t i c rocks and schist they are nearly always r o o t l e s s , and may be i s o c l i n a l . Linear structures L2 associated with phase 2 folding consist of elongate mineral grains, quartz rods, and the axes of small f o l d s , crenulations, and intersection structures a l l . o f which p a r a l l e l the megascopic axes. Re-folding of phase 2 structures along phase 3 axes has taken place on a l l scales. Among major structures, re-fo l d i n g of Vaseaux Lake Antiform about the a x i a l plane of phase 3 Gallagher Lake Synform i s best known (plates 1 and 5-pocket), and mesoscopic examples are numerous (plate 3-10). Megascopic phase 3 re-folding has also had the e f f e c t of tightening phase 2 folds about the i r o r i g i n a l axes, by f l a t t e n i n g and remobilizing rocks within t h e i r cores. Slides have developed and rocks of Units 3 and 4 for example, are highly sheared i n the core of the Vaseaux Lake Antiform as seen i n roadcuts east of Vaseaux Lake. Gneissic structure i s extremely well developed and - 4 8 -Plate 3-9 Northwesterly trending phase 2 fold crosscut by cleavage F_ and fractures J „ . Unit 3 Shuttleworth Canyon. Plate 3-10 Phase 2 folds outlined by sheared pegmatite i n Unit 2 and re-folded about F, . minor folds are t i g h t l y appressed. In some instances phase 2 minor folds form rootless cores which have moved en-masse away from the hinge of Gallagher Lake Synform (plates 3-11 and 3-12). There and elsewhere, phase 2 folds have developed curved axes in response to this tightening (plates 3-13 and 3-14), and in some instances phase 2 folds are re-folded about almost p a r a l l e l axes as a result of l o c a l reversals in shear d i r e c t i o n on t h e i r limbs. Re-orientation of phase 2 structures as a res u l t of phase 3 and l a t e r folding i s also evident of stereographic p l o t s . Poles to F.,, plotted for each domain, are shown on figure 3-8 where they are scattered along a broad northeast-southwest trending zone which represents the combined effects of a l l ' l a t e r f olding. The locus of poles to deformed F 2 i s no longer a simple great c i r c l e , although phase 3 folding may have given a cylindroidal! geometry (figure 3-9). The locus has been modified to i t s present form by open f l e x u r a l - s l i p folding during phases 4 and 5. The average locus related to northwesterly trending phase 5 folds i s shown on figure 3-8. This locus i s not well defined because poles to F 2 were previously spread along an almost perpendicular locus related to northerly trending phase 4 fo l d i n g . On figure 3-8 domains 1-4 represent the lower limb, and domain 5 the inverted limb of Gallagher Lake Synform (phase 3). In terms of the orientation of F 2, domains 1-4 were l i k e l y homogenous after phase 3, and an average F 2 pole from these domains compared with an average from domain 5 would give an approximate locus representing the deformation of F 2 during phase 3. This approximation has been made on figure 3-^-8 and i s s i g n i f i c a n t in that the pre-phase 3 orientation of F 2 must be represented by a pole lying on or close to t h i s locus, and i t s angle of dip must have been somewhat steeper -50-Plate 3-12 Mobilized phase 2 hinge i n core of Vaseaux Lake Antiform. -51-P l a t e 3-13 Phase 1 f o l d s r e - f o l d e d by a phase 2 antiform which has a c u r v i l i n e a r a x i s . trends almost perpendicular to plane of photograph i n upper l e f t but i s almost p a r a l l e l at lower center. P l a t e 3-14 D e t a i l from above showing c u r v i l i n e a r L 2 , n o r t h e r l y trending phase 1 hinges and deformed L]_. Unit 4b O l i v e r Ranch south of Shuttleworth Creek. than on the present phase 3 lower limb. From th i s i t may be concluded that prior to phase 3, F2 was inc l i n e d at some moderate angle to the northeast. Linear structures L 2 , also p l o t t e d o n figure 3-8, are shown deformed along a great c i r c l e locus. Relationships are somewhat confused because of the regional culmination and depression of L 2 produced during northerly phase 4 folding with respective north-westerly and southeasterly plunges of L2 coinciding with the dip directions of phase 4 limbs. Actually in many parts of the map-area, phase 2, 3 and 5 axes are almost p a r a l l e l , and re-folding during the l a t e r of these s p e c i f i c phases has not profoundly changed the orientation of e a r l i e r linear structures. Linear structures L 2 , L 3 and L 5 are now a l l horizontal or sub-horizontal structures and have prjofoably always been so. Since L2 was o r i g i n a l l y a nearly horizontal structure i t may be further argued that phase 1 folds may have been o r i g i n a l l y recumbent f o l d s . This follows from the facts that L 2 i s defined by the intersection between planar structures F 2 and F0/F]_ and that linear structures L2 and L^ make rather large angles with each other. The o r i g i n a l dip component of F^ along the i n t e r -section d i r e c t i o n L 2 rnay therefore have been small, and the dip angle of F l may not have been much greater than the o r i g i n a l plunge of L 2 . An unknown amount of intense f l a t t e n i n g about F 2 / L 2 during phase 2 or as a res u l t of phase 3 precludes any d e f i n i t e statement about the pre-phase 2 orientation of F]_. PHASE 3 Phase 3 folds are grouped into subsets 3a, 3b and 3c. This -53-N Figure 3 - 9 Geometry of subset 3a Gallagher Lake Synform in southern part of map-area * 1 F3 O L2 A Li - lower limb * LT - inverted limb order of grouping does not exactly correspond to the r e l a t i v e ages'.of these structures. It i s used as a convenient means of cl a s s i f y i n g and separating d i s t i n c t i v e fold geometries developed at various stages in phase 3 deformation. Subset 3a Subset 3a folds include Gallagher Lake Synform, a major southerly closing recumbent structure, and congruent minor folds which are well developed on both limbs. Part of the inverted limb and hinge of Gallagher Lake Synform are exposed in southern parts of the map-area, (plates 1-3-5-pocket) and i t s geometry there i s summarized on figure 3-9. Its ax i a l surface dips southsouthwest at 2 5 ° , and contains a near horizontal f o l d axis trending on the average 1 0 3 ° . Compositional layering dips 4° and 40° southsouthwest on respective average lower and invejrted limbs. With the exception of the schists of Unit 2 which form an attenuated wedge on the hinge of the . synform, the other map units have attained sub-rounded forms. Axial plane cleavage F7. i s a penetrative structure and a plane of fl a t t e n i n g normally outlined by tiny flakes of b i o t i t e . The intensity of increases towards the hinge of Gallagher Lake Synform, and within Its core and on the inverted limb i t ' becomes extremely penetrative and the rocks are highly f i s s i l e within the plane. Associated li n e a r structure L-, include 3a r 3a intersection structures, elongate mineral aggregates, the axes of minor folds and crenulations, a l l of which are p a r a l l e l with the axis of Gallagher Lake Synform (figure 3-9). The orientation of L-, , when considered across the entire J a map-area (plate 3-pocket, figure 3-10) varies moderately from - 5 5 -N V \ \ •••V o - % A-mm mm • a ^ 4 ? \ \ \ •\ • \ ... Figure 3-10 Synopsis of subset 3a and 3b s t r u c t u r e s . Lineat ions L 3a and L 3b Poles to F 3 a cleavage and ax ia l planes -A , • , * , o, - in domains l -5 consecutively • Poles to F b^ - all domains. P l a t e 3-15 Phase 3 f o l d (subset 3a) viewed from the e a s t . U n i t 4a, south of Shuttleworth Creek. P l a t e 3-16 Phase 3 f o l d s (subset 3a) viewed from the west. Unit 3 south of Mclntyre Canyon near the core of G a l l a g h e r Lake Synform. the trend of Gallagher Lake Synform. Some of t h i s v a r i a t i o n may be attributed to the effects of superposition of F^a on the limbs of pre-existent folds which would give r i s e to variable L^ intersection d i r e c t i o n s , and some of the v a r i a t i o n i s the e f f e c t of l a t e r f o l d i n g . Older linear structures L-^  and L2 appear to be systematically deformed about ,L^a as a r e s u l t of subset 3a f o l d i n g . Although data i s scanty on figure 3-9, and d i f f i c u l t to analyse, both L^ and appear to l i e along a great c i r c l e l o c i indicating that the folding i s probably similar in style (Ramsay 1960). These great c i r c l e s intersect the a x i a l surface along southsouth-3 a , westerly inclined lines (a-kinematic axes) which are approximately! normal to L^. A l t e r n a t e l y , since there i s also a suggestion of • ' . , I i ! 1 a small c i r c l e l o c i of L2 and L^ f l e x u r a l - s l i p folding'mayjI have been a factor in phase 3 deformation. It i s believed that phase 3 folds f i r s t may have developed by a mechanism of f l e x u r a l - s l i p but continued to develop by a mechanism of similar folding as they became t i g h t e r . Minor folds of subset 3a are abundant in a l l map units and . resemble the major structure in geometry and s t y l e . They are congruent with Gallagher Lake Synform and show the same northerly vergence in a l l positions. Because most of the map-area i s underlain by the lower gently dipping limb of the Synform subset 3a folds with the c h a r a c t e r i s t i c geometry of t h i s limb position are most abundant. These are r e l a t i v e l y open i n t r a f o l i a l and mesoscopic folds e s s e n t i a l l y of similar style characterized by a planar gently dipping limb, and a steeper southwesterly dipping . . . i inverted limb (plates 3-15 to 3-17) . Hinges of minor folds are sub-rounded in most rock types but may be angular to sub-angular P l a t e 3-17 Phase 3 f o l d s (subset 3a) viewed from the west. Unit 3 i n roadcut near Vaseaux Lake. P l a t e 3-18 Phase 3 f o l d s (subset 3a) viewed from the west. Unit 2 east of Vaseaux Lake. -59-in schist and some semi-pelitic rocks (plates 3-18, 3-19). On the inverted limb of Gallagher Lake Synform and in i t s core, subset 3a folds are tighter than on the lower limb, and the core structures are much less assymetric than those on either limb. Subset 3b . • Folds of subset 3b are r e s t r i c t e d to mesoscopic and micro-scopic scales, and are believed related i n time and space to outward (northerly) movement of a segment within the core of Gallagher Lake Synform along a northerly dipping s l i d e . This s l i d e i s marked by a mylonitic zone 40-60 feet or more i n thickness which cross-cuts compositional layering and megascopic folds formed during the e a r l i e r phase 1 and phase 2 deformations (phase 3 mylonite on plates 1-5-6-pocket). Subset 3b folds are found within and near proximity to the mylonites, and a penetrative cleavage F ^ s l i g h t l y oblique to the s l i d e often forms t h e i r a x i a l surface. The mylonite zone i t s e l f , when considered i n a regional sense, includes sheared derivatives of most rock types known i n the map-area. I t also exhibits extreme va r i a t i o n i n degree of shearing and groundmass r e c r y s t a l l i z a t i o n from place to place, and many l i t h o l o g i c and textural variations are therefore found within i t . C haracteristic rocks are well laminated fine grained mylonites ranging in colour through l i g h t to very dark grey and brown, often with numerous fine augen of quartz and feldspar. . Mylonitized rocks sometimes form anastomosing layers from a few inches to tens of feet thick, between s l i c e s of coarser grained augen gneiss and even less sheared and r e c r y s t a l l i z e d wallrock. Within the mylonites t i g h t i s o c l i n a l folds with a x i a l planes Plate 3-19 Phase 3 folds (subset 3a) viewed from the west. Unit 4a south of Shuttleworth Creek. Plate 3-20 Open subset 3b flexural-flow folds i n mylonitic rocks of Unit 4a. Viewed from the west. -61-p a r a l l e l to transposed layering occur. Their vergence i s consistent with northerly movement of the hanging-wall (same as Gallagher Lake Synform) and are therefore possibly phase 3 folds formed during mylonitization. A l t e r n a t i v e l y they may be r e l i c t phase 2 folds which survived mylonitization as t h e i r vergence i s also consistent with an inverted limb position with respect to Shuttleworth Creek Synform (phase 2) at the l o c a l i t i e s where they have been found. Subset 3b folds r e f o l d the i s o c l i n a l structure, and their vergence i s exactly opposite to that of the i s o c l i n a l structure. Subset 3b folds are often similar in s t y l e , but are sometimes better described as flexural-flow folds (Donath and Parker 1964), as they often appear to have been controlled by competent l i t h -ologies (plates 3-21) . They are co-axial with subset 3a! structures, but verge in an opposite (southwesterly) d i r e c t i o n about a x i a l planes in c l i n e d to the northeast (plate 3-pocket, figure 3-10). S t r a i n - s l i p cleavage may or may not be well developed in proximity to subset 3b folds within mylonites, and i s even less intense in other parts of the map-area. It i s not uniformly developed, but appears from place to place as a spaced s t r a i n - s l i p cleavage and gives r i s e to weak crenulation structures. Subset 3c . Members of a t h i r d set of minor folds related to phase 3 deformation also occur within the mylonitic zone and these i n many ways resemble subset 3b structures. They are flexural-flow folds (Donath and Parker 1964) outlined by l i t h o l o g i e s which appear to have been the more competent at the time of deformation. Subset 3c folds diminish rapidly in amplitude both up and down t h e i r a x i a l - 6 2 -Figure 3-tl Vergence and conjugate relationships between subset 3a and 3b s t ructures . North Outward Movement Figure 3-12 Schematic Cross - Section I l lustrating Relationships Be tween Subset 3a & 3b Folds,the Slide and a Pluton ( Unit B ). CD -64-N 1 Figure 3 -13 Subset 3c structures compared to the geometry of subsets 3a and 3b. + 1 axial planes of subset 3c folds. • subset 3c fold axes. - 6 5 -surfaces and die out on passing into more highly sheared l i t h o l o g i e s . In most instances subset 3c folds are rooted in these sheared materials which appear to have been simply injected into their cores. Subset 3c folds are formed along highly variable north-easterly and northwesterly trends (figure 3-13) and occur as single folds and i n conjugate arrangements (plate 3-22). As a whole, the orientations of these folds are broadly consistent with a conjugate pattern, but do not relate in any obvious way to the geometry of phase 3. Relationships between Subsets 3a, 3b and 3c folds Subset 3a and 3b f o l d s , as/ i l l u s t r a t e d on figures 3-10 and 3-11, appear to be a conjugate f o l d set developed about s t r a i n -s l i p cleavages F_ and F_, . Of the two, F^ i s by far the best and most uniformly developed and i s the dominant structural element of phase 3 deformation. The cleavage F_ probably originated as j a a s t r a i n - s l i p structure and continued to l o c a l i z e componential movements throughout phase 3 deformation. I t also.acted as a plane of fl a t t e n i n g i n the l a t e r stages of phase 3 deformation, and movement on F^a probably outlasted s i g n i f i c a n t movement on Fg^, although l o c a l l y F ^ has produced weak crenulation across subset 3a f o l d s . The cleavage F ^ i s thought to have developed at an i n t e r -mediate stage in phase 3 deformation, perhaps as the style of deformation changed from f l e x u r a l - s l i p to similar f o l d i n g . This would be the time when the s l i d e bounded wedge began to move out of the core of Gallagher Lake Synform and mylonite was formed. Resistance to thi s northerly motion may have given r i s e to the - 6 6 -P l a t e 3-21 Phase 3 f o l d s (subset 3b) w i t h i n mylonite north of Shuttleworth Creek. Viewed from the east. P l a t e 3-22 Phase 3 f o l d s (subset 3c) developed about conjugate a x i a l surfaces. -67-cleavage as well as the southwesterly verging f l e x u r a l - f low folds of subset 3b (figure 3-12). Subset 3c folds were probably formed at about the same time and may owe th e i r o r i g i n to l a t e r a l r e s t r i c t i o n within the developing mylonites. As shown on figure 3- 13, subset 3c geometry does not d i r e c t l y r e l a t e to the o v e r a l l phase 3 geometry, and cannot therefore r e f l e c t the mean s t r a i n which occurred within the mylonite zone. After the mylonites were developed, and movement on the s l i d e had ceased, phase 3 deformation continued by movement p a r a l l e l to F,' '•' The passive mylonite zone became deformed into open subset 3a folds, and the penetrative cleavage F_ was developed across i t . The reason for the change i n style of deformation during phase 3, and the continued development of F, ', after other movement's had ceased i s not known, but a tentative explanation i s given i n . • • • I • '• • i • Chapters 4 and 5. Simply stated, the f o r c e f u l emplacement of a synkinematic pluton (Unit B) along the inverted limb of Gallagher Lake Synform appears to have been i n part responsible for the continued development of F, , and may have also brought about a change i n style of deformation by changing the P/T environment (figure 3-12). PHASE 4 Total geometry of phase 4 folding i s not known. The hinge and parts of the limbs of a single megascopic antiform are seen within the map-area, and p a r a s i t i c minor folds are rare. The major antiform i s outlined by compositional layering and culminates east of Vaseaux Lake along a northerly trending axis which i s poorly defined because of interference with l a t e r phase 5 folds (plate 4- pocket). The hinge and limbs are rounded (plate 6-pocket) and the style of folding i s f l e x u r a l - s l i p . Shear p a r a l l e l to older f o l i a t i o n s F 0/F^ and F 2, i s c h a r a c t e r i s t i c of phase 4 deformation and narrow zones of dark mylonite have formed along re-activated surfaces. Phase 3 structures are o f f s e t , micas are sheeted, and trains of granulated mineral fragments are drawn out i n an east-west d i r e c t i o n approximately normal to the phase 4 fo l d axis. Minor folds are occasionally developed along phase 4 directions (plate 4-pocket, figure 3-14) and these include open flexures and crenulation structures. Crenulations i n p a r t i c u l a r are associated within closely spaced fractures (J^) i n an axiajl plane orientation. , . | . i • ' Variation In the,orientation of J,.throughout the area i s ; ' •' . . ' ' I" shown on plate 4 (pocket) and i s plotted on figure 3-14 where s u p e r f i c i a l l y appears to be a fanned fracture cleavage. However, f i e l d relationships are not always consistent with t h i s inter-! pretation under a hypothesis of f l e x u r a l - s l i p folding, because! at many l o c a l i t i e s two independent steeply dipping fracture se1 are developed and are perhaps better termed ab j o i n t s . Maximum development of fractures near the hinge of the major antiform indicates that fracturing may have served as release mechanism within the core zone as folding progressed, They may or may not be exactly p a r a l l e l to the phase 4 a x i a l plane. Since the exact trend of phase 4 folding i s not known these J^! fractures might conceivably be an oblique set of shear fractures related to f a i l u r e at the f i n a l stage of phase 4 fold i n g . In either case, fractures are the e a r l i e s t post phase 3 fracture set, and the only fractures which have consistently ts - 6 9 - i i N F i g u r e 3 - 1 4 Synopsis of phase 4 structures. i-1 fractures + axes of minor folds and crenulations. - 7 0 -l o c a l i z e d hydrothermal deposition of quartz, epidote, s e r i c i t e , and c h l o r i t e . Frequently slickensides are developed i n these hydrothermal materials providing evidence of re- a c t i v a t i o n , and this i s discussed more f u l l y in Chapter 5. PHASE 5 Phase 5 folds outlined by compositional layering, are found on a l l scales and are t y p i c a l l y of f l e x u r a l - s l i p s t y l e . These are northwesterly trending, gently plunging flexures and include a broad antiformal structure culminating In the v i c i n i t y of Vaseaux Lake, and a complimentary synform (Church 19 67, Okanagan F a l l s Syncline) which i s hinged just north of the map-area (plate 4 and 5-pocket). Minor folds on several scales are f a i r l y abundant on the gently rounded hinges and limbs of the major structures. Phase 5 folds are open structures developed about steeply dipping planes, and poles to compositional layering are weakly spread along a great c i r c l e locus (figure 3-15) as a re s u l t of the folding. Fracture set J 2 appears to be associated with phase 5 folding in much the same way as fractures are related to phase 4. These J 2 fractures vary considerably i n attitude from one exposure to the next (figure 3-15 and plate 4-pocket) and may actually consist of 2 or more individual sets. At some l o c a l i t i e s these are closely spaced and bear, an a x i a l plane rela t i o n s h i p to minor folds and crenulations (figure 3-16) , but elsewhere they are a j o i n t set approximately p a r a l l e l to the trend of phase 4. It therefore does not appear that a l l J 2 fractures are a x i a l plane cleavage, but they do seem to be planes of f a i l u r e related to phase 5 folding. These J 2 fractures are i l l u s t r a t e d on a number -7! -i i N 1 f igure 3-15 Synopsis of phase 5 structures. 1 J 2 fractures axes of minor fo lds . -72-Figure 3-16 Phase 5 folds with fractures J 2 in axial plane orientation. Unit 2 south of Shuttleworth Creek (sketched from photograph). Figure 3-17 Break thrusts associated with phase 5 minor folds viewed f rom the east (sketched from photograph). -73-of preceding photographs. Evidence of s l i p within the plane of compositional layering, normally expected in association with f l e x u r a l - s l i p f o l d i n g , i s abundant, especially where phase 5 minor folds are developed. Gouge f i l l e d break thrusts (figure 3-17) and limb shears are very common, and fractures of set are of f s e t against these younger shear surfaces. Faulting related to Phase 5 Faulting was an integral part of phase 5 deformation, and apparently f a c i l i t a t e d the development to folds by separating blocks then able to buckle independently. This f a u l t i n g may have proceeded by development 6f a new set of fractures (Jg)v and reactivation of e a r l i e r fractures which happened to be in a convenient orientation to allow buckling. Among the innumerable fractures developed only a few show appreciable o f f s e t s , and these are the fa u l t s shown on accompanying maps. None of the fa u l t s are well exposed as they underlie l i n e a r topographic depressions f i l l e d with talus and g l a c i a l debris. Adjacent closely spaced fractures show occasional slickensides but l i t t l e or no o f f s e t , and i t appears that most of the movement occurred along a central fracture. Slickensides p i t c h from O°-9,0° within these surfaces at d i f f e r e n t l o c a l i t i e s , and t h i s pattern i s probably consistent with the sort of movements which took place as folding progressed. To further i l l u s t r a t e the nature of phase 5 deformation elaboration on the environment, and pre-existing geometry of the rocks i s use f u l . At the time of deformation the rocks were b r i t t l e , near surface and had previously been deformed into a -74-Fiqure 3-18 Phase 5 and/or later fractures. • 1 J 3 x 1 J 4 fractures fractures broad northerly trending antiform. Complimentary synforms may have existed beyond the map-area. These pre-existent folds appear to have made phase 5 cross-folding d i f f i c u l t , in that a regionally continuous f o l d pattern could not develop, and f a i l u r e was by fracturing rather than f o l d i n g . The rocks must also have been strongly confined horizontally such that s t r i k e - s l i p move-ments could not be sustained on the f a u l t s . Rather, fracturing weakened the northerly grain and allowed folding to proceed within the smaller f a u l t bounded blocks. Thereafter the f a u l t s simply provided free surfaces along which the necessary horizontal and v e r t i c a l movements res u l t i n g from folding could be taken up. Phase 5 folds are e s s e n t i a l l y normal to these bounding f a u l t s and the i r axes tend to be discontinuous across them (plate 4-poeket). • • ' • :' , i ' ' i : ! i • i i i ; The downthrownside of each f a u l t i s indicated by a bar on plate 4. Of p a r t i c u l a r note are the two main faults'which :branch in the south, as both s u p e r f i c i a l l y appear to be hinge f a u l t s . These apparent hinge e f f e c t s are related to buckling of the block between, and the upthrown sides of each bound the main phase 5 antiformal zone southeast of Vaseaux Lake. To the north on passing into the realm of Okanagan F a l l s Syncline the sense of movement i s reversed on the more easterly f a u l t , and a similar reversal may occur on the more westerly as i t approaches the syncline northwest of the map-rarea. The youngest fracture sets, recognized (J^ and on plate 4-pocket and figure 3-18) may be related to phase 5 deformation. In p a r t i c u l a r fractures may be early or late-formed oblique planes of f a i l u r e developed independently within f a u l t bounded blocks. The fractures may be of similar o r i g i n , or altogether younger. -76-Iriterference of Phase 3, 4 and 5 structures Antiformal phase 4 and 5 folds intersect to form a regional domical structure culminating in an area of f l a t to gently dipping compositional layering southeast of Vaseaux Lake (plates 4, 5-pocket). This structure, i n terms of the .attitude of compositional layering, i s far from an ideal quaquaversally dipping dome. The flanks are actually greatly disrupted by pre-existent phase 3 folds which are r e l a t i v e l y open, and inhomogenous f a u l t bounded phase 5 folds, both of which are developed on several scales. Phase 3 planar and lin e a r structures have been re-orientated in a manner consistent with t h i s domal interference pattern. In general, the northerly trending phase 4 component has caused Lg to culminate on the crest and depress on,the flanks of the dome, while the northwesterly phase 5 component which i s broadly p a r a l l e l with Lg has caused l i t t l e re-orientation. Planar structures , F , and F. have been re-orientated, and t h e i r poles are J a j JD • jc scattered along a poorly defined l o c i representing a combined e f f e c t of the two la t e r phases of folding (figures 3-10 and 3-13). SUMMARY After deposition of an interbedded sedimentary and volcanic succession exceeding 4000 feet i n thickness, the following complex sequence of str u c t u r a l events was imposed on the rocks of Vaseaux Lake map-area. (1) Phase 1 folding, similar in style and along northerly trends, gave r i s e to Mclntyre Blu f f Fold and associated minor structures. These folds were probably o r i g i n a l l y recumbent, but thei r vergence i s unknown. Tectonic s l i d e s were developed and - 7 7 -probably continued to be active at various times during l a t e r deformation. (2) Phase 2 folding, also similar i n style but along north-westerly trends re-folded and tightened the e a r l i e r recumbent structures. Major folds formed during phase 2 are Vaseaux Lake Antiform, Shuttleworth Creek Synform, and other unnamed structures, and congruent minor folds are abundant i n association with these. Axial planes of phase 2 folds were o r i g i n a l l y i n c l i n e d at some moderate angle to the northeast and t h e i r axes were almost horizontal. (3) Phase 3 deformation, commenced with f l e x u r a l - s l i p folding along westnorthwesterly trends but progressed to a more duct i l e type of deformation (similar; folding) at a .later ;stage. Gallagher Lake Synform and congruent minor folds were formed early about southwesterly dipping a x i a l planes and near horizontal axes and continued to develop about the same directions throughout phase 3. As Gallagher Lake Synform continued to close a s l i d e developed and gave r i s e to mylonite and l o c a l minor folds of diverse trend. E a r l i e r formed phase 1 and 2 structures were re-folded, tightened and variously re-orientated. (4) Phase 4 folding, f l e x u r a l - s l i p i n s t y l e , gave r i s e to a major northerly trending antiform with a steeply dipping a x i a l plane and gently plunging axis. E a r l i e r structures were s l i g h t l y re-orientated on the limbs of this large antiform, and s l i p within the planes of pre-existing f o l i a t i o n s gave l o c a l d i s c o n t i n u i t i e s along which thin zones of mylonite were developed. Fracturing along steeply dipping northnortheasterly trending surfaces accompanied and/or followed phase 4 folding. (5) Phase 5 folding, also f l e x u r a l - s l i p in s t y l e , produced -78-open a l l scale northwesterly trending folds with steeply dipping axial planes and. shallowly plunging axes. These folds have resulted in further re-orientation of the earlier structures, and a large antiform intersects the earlier phase 4 antiform to give a broad domal structure near the center of the map-area. Phase 5 folding was accompanied by extensive fracturing and faulting and was accomplished primarily by buckling of independent fault bounded blocks. I CHAPTER FOUR IGNEOUS ROCKS INTRODUCTION Igneous rocks, p r i n c i p a l l y of g r a n i t i c composition, but also including intermediate, basic and ultra-ba s i c types, have been emp l a c e d into the metamorphic complex at various stages of i t s s t r u ctural development. The oldest are minor sheets of quartz monzonite which were emplaced into the succession before or during the f i r s t phase of deformation. These were succeeded by much l a r g e r volumes of g r a n i t i c rock and pegmatite emplaced during the second phase. These older g r a n i t i c rocks together form a g r a n i t i c gneiss-pegmatite .complex referred t o : c o l l e c t i v e l y as Unit A. ' 1 ' Younger less conspicuously f o l i a t e d g r a n i t i c rocks (Unit B) were emplaced late i n the t h i r d phase of deformation. They, include a westerly segment of an extensive b a t h o l i t h i c complex which underlies much of Okanagan Highland, s a t e l i t i c stocks, dykes, s i l l s and pegmatites. Narrow basic to intermediate dykes intruded the succession at some time between the second and t h i r d phases of deformation and became folded and metamorphosed during phase 3. Ultra-basic sheets, pyroxenites, dunites and amphibolites, are probably older than these dykes, and may have been t e c t o n i c a l l y emplaced at some early stage i n the second or even the f i r s t deformation. The younger igneous rocks to cut the succession are rhomb-porphyry and basic to intermediate dykes and s i l l s thought to be roughly equivalent i n age to the nearby Early Te r t i a r y Marron lavas. These rocks are involved i n the phase 4 and 5 deformations. . -80-The p r i n c i p a l masses of g r a n i t i c rock have not received intensive mapping and petrographic study, for the purpose of delineating in t e r n a l variations in composition, which undoubtedly exist. Emphasis has been placed on th e i r r e l a t i v e ages with respect to the polyphase deformation and the broadest aspects of their mode of o r i g i n and emplacement. To allow reasonably accurate description of the igneous rocks 51 rocks were examined i n thin-section, and of these 3 0 were of g r a n i t i c composition. Point counts were made on large sodium c o b a l t i n i t r a t e stained slabs for 8 of these, and the resu l t s were v i s u a l l y extrapolated to the remainder of the 30, and to a few additional specimens which were also stained. The modal compositions given on the following pages1 are thus only i ; i i ; I ! ' approximations of the actual modes|of thes^ g r a n i t i c rocks.;! Plagioclase compositions were determined p r i n c i p a l l y by f l a t -stage techniques, but i n several instances i t was necessary to make use of a universal stage. UNIT A GRANITIC GNEISS-PEGMATITE COMPLEX ,, Sheets of leucocratic granodiorite and rarer quartz monzonite and trondhjemite grading to pegmatite are c o l l e c t i v e l y referred to as g r a n i t i c gneiss, and are abundant within the succession. A few of these form an older phase and are involved i n the f i r s t deformation (plate 3-5, 3-6) but the vast majority were emplaced over an i n t e r v a l of time, during the second deformation. P r i n c i p a l features of the g r a n i t i c gneisses are strong secondary f o l i a t i o n s p a r a l l e l to FQ /P-^ and/or F 2 outlined by mica, • < I I • ' ' ' are thinner ( 6 0 j 0 ' feet - 8 1 -flattened quartz l e n t i c l e s and alternating coarse and f i n e r grained layers (shear domains). A usually weaker f o l i a t i o n F 3 , also outlined by quartz and mica, intersects the older planar structures to define a prominent li n e a r structure Lg s l i g h t l y oblique to the older l i n e a r structure L 2» Size and Contact Relations Sheets of g r a n i t i c gneiss are found ranging from fractions ' I of an inch to a few tens of feet thick and these are most abundant adjacent to the major sheets which are hundreds of feet thick. Major sheets, 3 i n number, are shown as Unit A on accompanying maps. Among these a lower sheet exposed on both sides of Okanagan Valley near Vaseaux Lake i s prominent, l o c a l l y reaching 1 5 0 0 feet i n ithickness. Overlying sheets maximum) and are l i k e l y crosscuttin'g apophyses of1 the lower (plate 5 - sections i n pocket). Lithology The major sheets of g r a n i t i c gneiss are p r i n c i p a l l y composed of leucocratic granodiorite and are of rather uniform i n t e r n a l composition. Their modes, as approximately estimated from stained slabs and thin-sections, range from plagioclase ( 4 3 - 5 5 % ) , quartz ( 1 9 - 3 0 % ) , orthoclase ( 1 5 - 3 0 % ) , b i o t i t e ( 4 - 1 0 % ) , hornblende ( 0 - 4 % ) , muscovite ( 0 - 2 % ) with accessory sphene, apatite, zircon, opaques and with minor garnet and epidote of possible metamorphic o r i g i n . Rocks of s l i g h t l y d i f f e r e n t composition, notably quartz monzonite and trondhjemite appear to be confined to smaller a n c i l l a r y sheets found elsewhere, and i n border migmatite complexes adjacent to the main sheets where they are associated with pegmatites and metasomatic looking g r a n i t i c rocks. In thin-section the g r a n i t i c gneisses exhibit c a t a c l a s t i c augen textures, and their o r i g i n a l textures, whether igneous or metamorphic, have been destroyed. Plagioclase (An 20-31) i n 15 thin-sections i s the p r i n c i p a l augen forming mineral. I t displays very weak normal zoning but the o v e r a l l composition of plagioclase within a given specimen appears remarkably uniform. Presumably plagioclase compositions were homogenized as a r e s u l t of metamorphism,, and variations now seen, such as the occurrence of more c a l c i c plagioclase i n hornblende bearing rocks i s a function of the o r i g i n a l bulk composition. Plagioclase augen have also contributed to the annealed groundmass (plate 4-1) i n which they are contained. Highly strained quartz forms a matrix which appears to jhave be'eh more mobile than the other s i l i c a t e s during deformation. Its extreme mobility lead to mechanical grinding and abrasion of the other s i l i c a t e s caught up i n the deforming quartz matrix but less able to deform i n t e r n a l l y . Contact Relations The contacts between the major sheets of g r a n i t i c gneiss and the invaded meta-sediments are of diverse character both from place to place and i n d i f f e r e n t rock types. Contacts with schist may be knife sharp along the lower surfaces of major sheets but grade to narrow zones of migmatite. Upper surfaces tend to be more complex broader zones of migmatite which may contain smaller sheets of uniform g r a n i t i c gneiss, pegmatite, and hosts of (narrow) metasomatic veins p a r a l l e l to compositional layering. Semi-p e l i t i c granulites i n the v i c i n i t y of the contacts are often d i f f e r e n t i a l l y feldspathized along inch to foot thick layers -83-P l a t e 4-1 P e n e t r a t i v e f o l i a t i o n s F 2 i n g r a n i t i c gneiss o u t l i n e d by deformed quartz and b i o t i t e . Crossed p o l a r i z e r s . F i e l d 4.7 mm. P l a t e 4-2 Phase 3 f o l d s developed i n Unit A ( g r a n i t i c gneiss) o u t l i n e d by the e a r l i e r f o l i a t i o n F 2 on the hinge of Gallagher Lake Synform. greatly accentuating th e i r o r i g i n a l layering. They also may contain a n c i l l a r y sheets of uniform g r a n i t i c gneiss and pegmatite and at a few l o c a l i t i e s the t r a n s i t i o n from semi-pelitic granulite to granite gneiss i s so gradational that a contact cannot be distinguished. Aside from the metasomatic effects which are prominent at contacts of major sheets, there i s no obvious thermal aureole associated with them. One sample of muscovite-biotite s c h i s t taken from a contact migmatite zone east of Dutton Creek contains microscopic s i l l i m a n i t e after muscovite, but this i s the only occurrence of the mineral or of any aluminum s i l i c a t e polymorph known within the map-area. Admittedly the immediate contact zone has not received detailed sampling and :i t i s probable that s i l l i m a n i t e may occur elsewhere at the contact, i ! The metamorphic state of the invaded rocks at the time of intrusion i s i n doubt. They may have been already metamorphosed to amphibolite facies assemblages and were therefore not responsive to the thermal conditions imposed by the g r a n i t i c gneiss. The major sheets of g r a n i t i c gneiss are not obviously folded as a resu l t of phase 2 deformation but l i e along the limbs and axia l planes of the megascopic phase 2 folds. They appear to have been emplaced along phase 2 structures which were already i n existence and are therefore thought to have participated i n only the f i n a l stages of the second deformation. Some of the minor g r a n i t i c sheets and pegmatites display i d e n t i c a l relationships with minor phase 2 structures, but many are anomalously involved in tight phase 2 minor folds. Some of these may belong to the e a r l i e r phase of g r a n i t i c gneiss known to have participated i n the f i r s t deformation, but no trace of a phase 1 structure can be found i n these rocks. The author favours a view that small sheets of g r a n i t i c gneiss and pegmatite were emplaced and extensive metasomatism affected the entire succession before the major sheets came i n . The emplacement of the major sheets may coincide with culmination of the thermal event associated with phase 2 and may have been a time of intense deformation. The time of development of the e a r l i e s t f o l i a t i o n i n the major sheets of granite gneiss i s not exactly known. I t may be p a r t i a l l y of protoc l a s t i e o r i g i n but has c l e a r l y continued to develop in the s o l i d state as the re s u l t of the d u c t i l e flow of quartz. (plate 4-1). It was. highly developed by the time i t became deformed about the penetrative f o l i a t i o n (plate 4-2). Although there i s evidence of re-activation of e a r l i e r f o l i a t i o n s during phase 3 (see Chapters 3 and 5 ), the author i s in c l i n e d to believe that phase 2 folds continued to close after the major sheets of g r a n i t i c gneiss were emplaced, and that some of the cat a c l a s t i c and du c t i l e deformation textures found therein were formed during the waning stages of the second deformation,and that some formed during the re-activation of F2 by phase 3 re-folding. Origin and Emplacement The g r a n i t i c gneiss-pegmatite complex of the Vaseaux Lake area are thought to represent the d i f f e r e n t i a t e d top, apophyses early and late-stage pegmatitic and metasomatic derivatives of a major g r a n i t i c pluton which rose and was frozen in i t s present position towards the end of the second deformation. Evidence for this hypothesis was obtained by reconnaissance mapping i n an area Immediately north of Vaseaux Lake map-area. Although the t o t a l N. Skaha Lake Okanagan Falls Map - Area North South I CD cn Figure 4-1 Schematic C r o s s - S e c t i o n I l lustrat ing Relationships Between Phase 2 Folds and D i f fe ren t ia ted Gran i t i c Gneiss Pluton ( Unit A ) at the End of Phase 2 Deformation . -87-structure i n thi s northern area i s not yet understood, i t i s • i apparent that major portions of the same pluton have been un-roofed over an area of some 30 square miles east of the north end of Skaha Lake. The.rocks in this northern area are hornblende granodiorite and quartz d i o r i t e gneisses which contrast sharply with the leucocratic rocks of Vaseaux Lake area. They represent a much deeper l e v e l in the pluton and the i r more mafic character suggests that c r y s t a l l i z a t i o n and d i f f e r e n t i a t i o n of the pluton may have been almost complete when i t reached the levels now seen i n Vaseaux Lake area. The major sheets of leucocratic grano-d i o r i t e gneiss are therefore thought to have been formed by a la s t upward surge of perhaps largely c r y s t a l l i n e magma at the top of this freezing d i f f e r e n t i a t e d pluton. Metasomatizing f l u i d s and pegmatites may have arrived well in advance of the c r y s t a l l i z i n g magmas and therefore may have become more involved in phase 2 deformation than the l a t e r magmatic phases. The forc e f u l emplacement of the major sheets, probably i s responsible for some of the deformation af f e c t i n g these e a r l i e r formed g r a n i t i c phases. Emplacement and l o c a l i z a t i o n of the major g r a n i t i c sheets was controlled by pre-existing planes of weakness within the succession. Lith o l o g i c layering, most notably within the schists of Unit 2, and the a x i a l f o l i a t i o n were important l o c a l i z e r s . Granitic magmas were injected along these zones of weakness and made room for themselves by d i l a t i o n of the succession. Since the major sheets l i e along megascopic phase 2 folds i t i s thought these folds may have absorbed the r e s u l t i n g d i l a t i o n by slowly becoming t i g h t e r . This tightening may have been accomplished by successive injections Figure 4-2 Schematic Cross-Sect ion Illustrating the Present Distribution of Grani t ic Gneiss Resulting f rom Interference of Phase 3 and 5 Fo lds . -89-of magma which " b u i l t up" the major sheets to their present thickness leaving narrow-screens of meta-sediment between successive sheets. Figure 4-1 i s a schematic cross-section along the Okanagan Valley which i l l u s t r a t e s the structural relationships between the pluton and megascopic phase 2 folds as they may have existed at the close of the second deformation. Figure 4-2 represents the present d i s t r i b u t i o n of g r a n i t i c gneiss r e s u l t i n g from the influence of l a t e r phase 3, 4 and 5 folding. The hornblende granodiorite gneiss east of Skaha Lake, a deeper l e v e l in the pluton, now has the form of a gneiss dome res u l t i n g from the interference of large phase 4 and 5 folds (northerly and westerly trends) although t h i s i s not obvious from the map-pattern (Liittle . . ' i 1961) because of l o c a l topography. Age L i t t l e (1961), based on his experience with g r a n i t i c rocks in southern parts of the Shuswap terrane and further east, considered the older g r a n i t i c gneisses found i n the Southern Okanagan region to be roughly equivalent i n age to the Jurassic Nelson Plutonic Rocks. The Nelson Batholith and similar nearby plutons have since been shown to be of late and post-kinematic types at the eastern margin of the Shuswap Complex (Ross 1968, Hyndman 1971, Read 1971). Late and post-kinematic plutons (Unit B), in Vaseaux Lake area, are associated with phase 3 deformation which i s of Jurassic or older age (this study), and these younger g r a n i t i c rocks cut the g r a n i t i c gneiss (Unit A). For the above reason, and because the g r a n i t i c gneisses are associated with an older phase of deformation (phase 2), they are - 9 0 -considered to be older, and perhaps are much older than Jurassic. UNIT B LATE-KINEMATIC GRANODIORITE-QUARTZ MONZONITE The metamorphic rocks of Vaseaux Lake area are bounded on the south and east by a westerly extension of a b a t h o l i t h i c complex which underlies much of Okanagan Highland further east. Within the map-area these rocks are granodiorites and quartz monzonites characterized by well developed marginal f o l i a t i o n s i n the v i c i n i t y of the i r contacts, and a less conspicuous but penetrative regional f o l i a t i o n F 3 (plate 4 - 3 ) . Commonly these rocks contain p o i k i l i t i c orthoclase megacrysts which are t y p i c a l l y much ^arger i i ' . than associated quartz and plagioclase (plate 4-4). Related dykes, s i l l s and pegmatite cut the succession and are f o l i a t e d p a r a l l e l to F 3 , but l i k e the pluton are only involved in the lat e s t part of phase 3 deformation, and. do not, themselves, outline phase 3 folds. A small stock exposed east of Vaseaux Lake i s of similar composition but i s not f o l i a t e d p a r a l l e l to F 3 . I t i s thought to be a post-kinematic phase of Unit B, and in some ways resembles the Oliver Quartz Monzonite which i s exposed southwest of the map-area. Lithology Unit B consists p r i n c i p a l l y of b i o t i t e granodiorite but grades eastward to b i o t i t e quartz monzonite as orthoclase megacrysts become larger and more abundant. No contact was observed between these two rock types and mapping i s not s u f f i c i e n t l y d e tailed to be assured that they are not separate phases. Estimated modal abundances of the primary minerals range as Plate 4 - 3 P o i k i l i t i c orthoclase megacrysts in f o l i a t e d border phase of Unit B. Weaker F^ cleavage crosses obliquely. Plate 4-4 P o i k i l i t i c habit of orthoclase i n granodiorites of Unit B. Crossed p o l a r i z e r s . F i e l d 4 .7 mm. follows; plagioclase (36-60%), quartz (16-30%), orthoclase (13-32%), b i o t i t e (4-15%), hornblende (0-2%). Accessories are apatite, sphene, zircon and opaques. In thin-section c a t a c l a s t i c textures are dominant but quartz forms a matrix which has undergone ductile flow. Mortar structure i s developed along feldspar boundaries, and b i o t i t e i s shredded and bent around the feldspar grains. In contact with quartz, b i o t i t e i s sub-parallel to F^, and p a r t i a l l y defines t h i s planar structure. Plagioclase (An 18-35) exhibits complex zoning (plate 4-5), a r e l i c t of an o r i g i n a l igneous texture. Its margins are embayed but t h i s may be the r e s u l t of deformation rather than a magmatic reaction. Orthoclase occurs i n a l l grain sizes from microscopic; specs in the matrix to inch long megacrysts, and larger grains t y p i c a l l y contain inclusions of plagioclase and quartz (plate 4-4). These inclusions are always much smaller than grains of the same minerals outside the orthoclase, and may have been reduced i n size by p a r t i c i p a t i o n i n the reaction which gave r i s e to these large c r y s t a l s . O p t i c a l l y continuous inclusions of plagioclase found i n one thin-section support t h i s hypothesis. C r y s t a l l i z a t i o n of orthoclase may have consumed most of the remaining l i q u i d phase in these rocks, and small intergrowths of myrmekite found- along i t s margins could represent c r y s t a l l i z a t i o n of the f i n a l l i q u i d s (plate 4-4). T y p i c a l l y larger c r y s t a l s of orthoclase, near extinction positions, exhibit s t r i k i n g i n t e r n a l s t r a i n patterns as shown on plate (4-4). Contact Relations Contacts between the metamorphic rocks, and the westerly P l a t e 4-5 O s c i l l a t o r y zoned p l a g i o c l a s e i n g r a n o d i o r i t e of U n i t B. Crossed p o l a r i z e r s . F i e l d approx-imately 1.6 mm. P l a t e 4-6 X e n o l i t h of g r a n i t e gneiss (Unit A) w i t h i n g r a n o d i o r i t e dyke-rock of Unit B as seen i n coarse f l o a t at the contact between the two u n i t s . - 9 4 -extension of the batholith complex (the pluton), are anomalous and int e r e s t i n g . The walls of the pluton dip moderately south and east away from the metamorphic complex such that the meta-morphic rocks form a somewhat ir r e g u l a r footwall against which the pluton rests. Further, the contact crosscuts a l l of the l i t h o l o g i c units suggesting that l i t h o l o g i c control has had l i t t l e influence on the l o c a l i z a t i o n and emplacement of the pluton, and i s not responsible for the observed shallow dips of the plutons' walls. Although some randomly orientated xenoliths occur within the pluton near i t s margins, the walls tend to be smooth, and stoping may not have been important i n the emplacement process. Border phases are strongly f o l i a t e d p a r a l l e l to the walls, and fo r c e f u l shouldering aside of the wall-rocks may have i ! played a much larger role i n the emplacement process than might be suspected in view of the discordant contact relationships. The thermal aureole which must have surrounded this pluton did not cause s t r i k i n g mineralogical changes i n the pre-existing amphibolite facies assemblages of the wall-rocks, and metasomatism has been limited to a narrow zone (several hundred feet) adjacent to the contact. Semi-pelitic granulites have been metasomatized to the greatest extent. They form gradational contacts with the pluton and are greatly enriched i n potassium feldspar. Schists and c a l c - s i l i c a t e s are also enriched i n orthoclase. Samples of muscovite-biotite s c h i s t , quartz-calcite marble and c a l c - s i l i c a t e taken further from the contact i n zones impregnated with s i l l s and pegmatite, do not appear to have developed new mineral assemblages, although they are intensely deformed. Again, the immediate contact zone has not been studied in s u f f i c i e n t d e t a i l to be absolutely certain that new mineral assemblages do not occur i n some rocks, - 9 5 -r i g h t at the contact. The narrowness of the obvious metasomatic zone adjacent to the pluton might be explained in terms of the footwall position that Vaseaux Lake area rocks occupied with respect to the pluton. V o l a t i l e phases would presumably tend to move towards an upward facing wall or a higher l e v e l , where they might escape more e a s i l y . Emplacement and Relation to Structure Although structure and contact relationships are largely unknown for the entire batholith complex to the east, that part of i t seen in Vaseaux Lake area i s c l e a r l y related to phase 3 deformation, and may be in part responsible for that deformation. At the Okanagan Valley the pluton appears to have come up along the inverted limb of the megascopic phase 3 structure, Gallagher Lake Synform. Yet in an easterly d i r e c t i o n i t truncates t h i s structure and reaches i t s hinge north of Mclntyre Creek. Assuming that stoping did not play an increasingly important role i n the emplacement process i n an easterly d i r e c t i o n , the limb of the Synform may not alone have l o c a l i z e d the i n t r u s i o n , although the inverted limb would have been thinning and highly strained during late phase 3. An alternate hypothesis, preferred by the wri t e r , i s that the pluton rose along a phase 3 structure that cross-cut the inverted limb something l i k e the shear zone hypothetically i l l u s t r a t e d on figure 4-3. Such a structure might have developed during phase 3 deformation as a re s u l t of the anisotropy imposed by the limbs of megascopic phase 2 f o l d s , which at t h i s stage, were being re-folded by a mechanism of flexure strongly influenced by the more competent l i t h o l o g i e s . OF MclNTYRE CREEK map - area ) Hypothetical Emplac the Pluton (Unit B) Controlled by a She which Crosscut into of Gallagher Lake Synform an Easter ly D i r e c t i North (0 cn l Figure 4 - 3 SECTION EAST OF OKANAGAN VALLEY (western part of map-area) the Emplacement of Unit B . The pluton may have worked i t s way up such a zone of weakness by slowly shouldering the walls aside. By adding heat to the wall-rock, i t may have brought about a change i n the style of deformation from a b r i t t l e to a more du c t i l e type. The wall-rocks might then have more e a s i l y responded by moving outward, absorbing some of the shouldering stresses, but the advancing pluton may also have begun to l i f t i t s ' roof. In Vaseaux Lake area, rocks which comprise the footwall of the pluton probably responded to the shouldering effects of intrusion by renewed closure (and flattening) of phase 3 and e a r l i e r . f o l d s , The s l i d e and mylonite found i n the northern part of the map-area, associated with outward (northerly) movement of a segment i n the core of Gallagher Lake Synform, may have (developed to a l l e v i a t e a room problem i n the core,of .the Synform brought on by further closure. Emplacement of the pluton might also be , responsible i n large part for the flatness of dip, and the atten-uation of Gallagher Lake Synform and parasitic, structures. Age and Significance The rocks of Unit B cannot be d i r e c t l y dated on geological grounds, and no radiometric ages are available within the map-area. They are however, l i t h o l o g i c a l l y very similar to the intermediate phase of the composite Oliver stock, a b i o t i t e quartz monzonite characterized by up to inch long p o i k i l i t i c microcline "phenocrysts" (Richards, 1968). The Oliver stock l i e s just beyond the south-west corner of the map-area, on st r i k e with Unit B, and has been dated at 136-144+6 m i l l i o n years by the K/Ar method (White, et a l , 1967 , and White, et a l , 1968). Stru c t u r a l l y , the Oliver stock i s marginally f o l i a t e d , but -99-has no penetrative regional f o l i a t i o n p a r a l l e l to F ^ , and i s more l i k e the small stock east of Vaseaux Lake than other parts of Unit B.- These stocks are thought to be the l a t e s t post-kinematic phases of Unit B, and the radiometric age 144+_6 m i l l i o n years i s therefore considered to represent a minimum age for phase 3 deformation. METAMORPHOSED INTERMEDIATE TO BASIC DYKES A few fine grained dykes composed p r i n c i p a l l y of b i o t i t e , hornblende and andesine with minor quartz, potassium feldspar, epidote, sphene and apatite are found i n Vaseaux Lake map-area. With respect to deformation and metamorphism these are dated as post-phase 2 and pre- or syn- phase 3 on the basis of t h e i r ! 1 contact relationships and internal structure. They may or may not a l l be of i d e n t i c a l age, but they have i n common well developed marginal, and secondary f o l i a t i o n s p a r a l l e l to F y At Shuttleworth Canyon one such dyke crosscuts a major sheet of phase 2 g r a n i t i c gneiss (Unit A), but i s deformed with the gneiss into open phase 3 folds, c l e a r l y dating the r e l a t i v e time of dyke emplacement. These dykes are s i g n i f i c a n t i n that they suggest phases 2 and 3 were separated by some in t e r v a l of time in which the rocks became cool and fractured. The two phases of deformation may not have evolved from a single continuous dyna-mothermal event as might be suggested by the almost co-axial phase 2 and phase 3 f o l d sets. ULTRA-BASIC ROCKS AND AMPHIBOLITES Elongate l e n t i c u l a r bodies and sheets of basic to u l t r a -basic rock with thicknesses to several hundred feet, l i e p a r a l l e l to compositional layering i n the northeastern part of the map-area. -100-These rocks are coarse grained b i o t i t e c a l c i c plagioclase amphibolites, c a l c i c plagioclase clino-pyroxenites and c l i n o -pyroxene dunites. Their age and o r i g i n i s uncertain, but their present form and mineralogy i s probably the r e s u l t of a long and complex history of deformation and metasomatism. The age of the ultra-basic rocks i s c l e a r l y greater than Unit B, as they are crosscut at many l o c a l i t i e s by weakly f o l i a t e d dykes and simple pegmatites related to Unit B. At one l o c a l i t y a small body of coarse, grained amphibolite i s cut and veined by g r a n i t i c gneiss (Unit A), and i t i s therefore possible that a l l of the ultra-ba s i c rocks date back to an early stage of the second or even the f i r s t deformation. They may be fragments of some early ultra-basic mass which became "sliced-up" • and t e c t o n i c a l l y emplaced during an early phase of deformation. They might equally well be parts of an oceanic lithospheric plate perhaps related to a continental c o l l i s i o n which gave r i s e to phase 1 folds? Extensive metasomatism which accompanied the emplacement of gr a n i t i c gneiss (Unit A) in a middle amphibolite facies environ-ment, may have d r a s t i c a l l y altered these rocks and established their present mineralogy. At one l o c a l i t y o l i v i n e clino-pyro-xenite i s p a r t i a l l y altered to b i o t i t e amphibolite suggesting that the amphibolite may have been a f i n a l stable assemblage. The pyroxenite however, may i t s e l f be a metasomatic rock as the coarse diopsidic pyroxene i s extremely p o i k i l i t i c with respect to fine grained anhedral magnetite, which may be r e l i c t s from some e a r l i e r (serpentinite ?) stage. Inclusions of magnetite pe r s i s t in the replacing amphibole, and are c h a r a c t e r i s t i c of the -101-coarse grained amphibolites found elsewhere. P a r t i a l serpentinization of dunite and pyroxenite may have occurred during phase 3 deformation or e a r l i e r . Evidence for this may be seen where dykes of Unit B cut the pyroxenites, and metasomatic ch r y s o t i l e , phlogophite t r e m o l i t e - a c t i n o l i t e assemblages have been produced i n the wall-rocks adjacent to the dykes and pass outwards to p a r t i a l l y serpentinized rock. These minerals also occur along fractures throughout p a r t i a l l y ser-pentinized pyroxenites, and with t a l c and carbonate i n small zones of hydrothermal a l t e r a t i o n not related to dykes. TERTIARY DYKES A few dykes and s i l l s of probable Early Tertiary age cut the metamorphic complex. These have compositions similar to volcanic rocks of the Marron Formation found northwest of the map-area (Church 1967), with which they are probably contempor-aneous. Unlike their volcanic equivalents, these dykes are strongly f o l i a t e d and weakly metamorphosed, as a r e s u l t of phase 4 deformation, and are therefore useful i n dating the l a t e r phases of deformation in Vaseaux Lake area. Anorthoclase bearing rhomb-porphyry s i l l s and i r r e g u l a r dykes found in the map-area, are similar to rocks of the basal Yellow Lake Porphyry Member of the Marron Formation. These have narrow c h i l l zones at th e i r contacts, and s i l l s i n p a r t i c u l a r have developed penetrative f o l i a t i o n s p a r a l l e l to t h e i r margins. Deformation of these rocks may have commenced before they were completely s o l i d , and probably continued as they cooled. Their metamorphic features such as the replacement of clinopyroxene by b i o t i t e and hornblende, and the unmixing of two feldspars from -102-anorthoclase may be related to simultaneous hydrothermal activity and shearing, as these s i l l s cooled. Other dykes, fine grained light to dark coloured rocks, may be equivalent to some of the younger Marron Lavas. Unlike the rhomb porphyry s i l l s , their emplacement was strongly con-trolled by the northerly trending fracture set, and they are themselves foliated parallel to the fractures in which they l i e . Their margins are distinctly c h i l l e d , and in thin-section contain zoned plagioclase microlites in an extremely fine.grained matrix. With respect to dating the later phases of deformation, development of fractures, a late-stage phase 4 event (Chapter 3 ) , would appear to coincide in time with volcanism which gave rise to the younger parts of the Marron Formation. Emplacement of rhomb porphyry s i l l s and shearing in the plane of compositional layering, which are perhaps expressions of the earlier flexural-slip folding aspect of phase 4 deformation, may have been in progress at the time Yellow Lake Porphyry lavas reached surface in the Early Eocene. -103-CHAPTER FIVE METAMORPHISM INTRODUCTION Study of the metamorphism i n Vaseaux Lake area i s i n many ways unrewarding. Mineral assemblages are r e l a t i v e l y simple, and are not themselves diagnostic of a precise type or physical condition of metamorphism, that may be simply i l l u s t r a t e d as a point on a P/T diagram. Further, no systematic v a r i a t i o n of mineral assemblages occurs within rocks of similar composition, and in general there would appear to be near equality of meta-morphic grade throughout the whole area. Metamorphism, which accompanied the second phase of def-ormation gave r i s e to the amphibolite facies mineral assemblages now found in Vaseaux Lake area. The nature of thi s metamorphism, and time relationships between metamorphic r e c r y s t a l l i z a t i o n and deformation are no longer e a s i l y recognized. They have been complicated by metasomatic and thermal conditions imposed by invading g r a n i t i c plutons of two ages, catac l a s i s associated with three l a t e r phases of deformation, and widespread hydrothermal a l t e r a t i o n which.accompanied the l a t e s t of these. EARLY METAMORPHISM While two early phases of deformation (phases 1 and 2) have been recognized, accompanying metamorphism was of a progressive nature. I t appears to have reached middle to upper greenschist facies during phase 1, and gone on to amphibolite facies during phase 2, and no evidence was found to suggest whether or not a long period of time intervened. Conceivably, phase 1 and phase 2 -104-folds may have been successively formed under the continued influence of a broad phase of progressive regional metamorphism, which culminated with plutonism and metasomatism during the second deformation, and gave r i s e to the present mineral assemblages. Later deformation, metamorphism and a l t e r a t i o n has had the e f f e c t of mechanically re-arranging and p a r t i a l l y r e - c r y s t a l l i z i n g these assemblages, but only l o c a l l y have they been d r a s t i c a l l y changed or completely obliterated. Mineral assemblages found within the succession, and thought to be representative of the early metamorphism are l i s t e d on table 5-1, where they are grouped on the basis of rock type. These assemblages, on the basis of plagioclase compositions, the presence of diopside i n amphibolites and c a l c - s j i l i c a t e s , and garnet i n most '• ' : • • ' 'i J.i . . 1 | j ' • • ! . . • , . , • • ,| I h • , 1 • j ' assemblages, are assigned to the 16werj or middle part of the amphibolite facies of Turner (1968) (almandine amphibolite facies of Winkler 1965 - Turner and Verhoogen 1960). Index minerals, such as s t a u r o l i t e , andalusite, kyanite etc., necessary to c l a s s i f y the metamorphism more s p e c i f i c a l l y , are not found. P e l i t i c rocks must have been o r i g i n a l l y somewhat impoverished i n alumina such that micas, feldspars and garnet, trapped alumina i n th e i r structures as i t became available, and the more aluminas index minerals could not form. Temperatures corresponding to the highest part of the. amphib-o l i t e facies (Sillimanite-almandine-orthoclase subfacies), char-acterized by the breakdown of muscovite i n favour of s i l l i m a n i t e and K-feldspar, were not attained. Muscovite i s a stable part of most p e l i t i c assemblages, and those assemblages which contain a single mica (biotite) lack s i l l i m a n i t e . Further, epidote p e r s i s t s TABLE 5-1 MINERAL ASSEMBLAGES FORMED DURING EARLY METAMORPHISM (PHASE 2) ROCK TYPE AND LITHOLOGIC UNIT NUMBER OF OCCURRENCES IN THIN-SECTION ASSEMBLAGE SCHISTS UNITS 2 , 4 Qtz, Plag ( A n 2 g _ 3 5 Qtz, Plag ( A n 3 Q _ 8 g Qtz, Plag ( A n 2 1 _ 2 g Qtz, Plag ( A n 1 8 _ 3 0 K-Felds. Qtz, Plag ( A n 2 8 _ 4 0 Garn. , Biot', K-Felds, , Biot, Garn. , Biot, Muse. , Biot, Muse, , Biot, Muse, Qtz, Plag (An, n), Biot, Muse, K-felds," S i l l , ( l o c a l Garn.). sphene + apatite zircon opaques IMPURE QUARTZITES UNITS 2 , 4 Qtz, Biot, Muse. Qtz, Biot, Muse, Plag ( A N 2 6 - 3 8 ^ ' Qtz, Biot, Muse, Plag ( A N4 0_ 4 2)' Garn. Qtz, Biot, Muse, K-felds. zxreon + apatites opaques 2 1 1 Cal. Cal, Qtz, Diop, Epid. Cal, Qtz, Diop, Epid, Scap. Cont'd, ROCK TYPE AND LITHOLOGIC UNIT NUMBER OF OCCURRENCES IN THIN-SECTION ASSEMBLAGE Cont'd. CARBONATES CALC-SILICATES UNITS 2, 4 Cal, Qtz,-Diop, Epid, Scap, Gros. Cal, Qtz, Diop, Epid, Scap, Gros, Plag ( c a l c i c ) . Cal, Qtz, Diop, Epid, Scap, Plag ( A n g 8 _ 7 4 ) , K-Felds. Cal, Qtz, Scap, K-Felds. Diop, Epid, Qtz, Scap, K-Felds. Biot, Epid, Qtz, Gros, Plag (An^g) K-Felds. muse sphene zircon + phlogophite zircon opaques B i o t , Hb, Qtz, Gros, Plag (An 3 g) GRANULITES AND SEMI-PELITIC GRANULITES UNITS 1-5 Qtz, Plag ( A n 3 2 ) , Biot, Hb. Qtz, Plag ( A n 2 g _ 3 Q ) , Biot, Hb, K-Felds. Qtz, Plag (An 3 n ^ 7 ) , Biot, Hb, K-Felds, Epid. Qtz, Plag ( A n 3 1 _ 3 9 ) , Biot, Hb, Epid, Garn. Qtz, Plag (An 7 3), Biot, Hb, Epid, Garn, Diop. sphene zircon + apatite a l l a n i t e opaques 1 2 Hb, Plag (An 3 2). Hb, Plag ( A n 4 8 _ 7 4 ) , Diop, Cont'd. ROCK TYPE AND NUMBER OF LITHOLOGIC UNIT OCCURRENCES IN THIN-SECTION ASSEMBLAGE Cont'd.. 2 Hb, Plag ( c a l c i c ) , Diop, Biot, Epid. sphene AMPHIBOLITES ( A n32-41> , Biot, Epid, 2 Hb, Plag apatite UNIT 4 Garn. — zircon opaques 3 Hb, Plag ( A n40-42 ) , Biot, Epid, Garn, Qtz Abbreviations Qtz. Plag. K-Felds. Biot. Muse. Garn. quartz plagioclase K-Feldspar b i o t i t e muscovite garnet Hb. S i l l . Cal. Diop. Epid. ' -- -Scap Gros. -hornblende s i l l i m a n i t e c a l c i t e diopside epidote scapolite grossularite i o —I I -108-i n many quartz bearing assemblages, but should have been elim-inated had conditions of the highest amphibolite subfacies pre-va i l e d (Winkler 1965). Regional metamorphism in Vaseaux Lake area cannot be e n t i r e l y separated from synkinematic plutonism (granitic gneisses of Unit A) and associated metasomatism. Potash metasomatism, i n p a r t i c u l a r , has given r i s e to orthoclase i n assemblages which otherwise might not include K-feldspar. Rocks such as the semi-p e l i t i c granulite, shown on plate 5-1, usually contain b i o t i t e , hornblende, quartz, plagioclase and possibly epidote and garnet. In t h i s Instance large porphyroblasts of orthoclase, as well as matrix orthoclase are also present, and are c l e a r l y metasomatic. At the l o c a l i t y shown on plate 5-1, the metasomatic zone i s several hundred feet thick and l i e s above a major sheet of g r a n i t i c gneiss. Here the metasomatism was a late phase 2 event, as porphyroblasts have grown across phase 2 structures on the hinges and i n the cores of phase 2 minor folds, and are themselves but weakly deformed. In rocks such as s c h i s t , which have undergone considerably more deformation since the emplacement of g r a n i t i c gneiss, meta-somatic K-feldspar i s d i f f i c u l t to recognize. Where the K-feldspar i s r e s t r i c t e d to pegmatitic and quartzo-feldspathic layers, a more normal si t u a t i o n , i t i s e a s i l y attributed to the metasomatism. Where i t forms part of a fine grained matrix, such as i n the K-feldspar bearing assemblages reported on table 5-1, i t s o r i g i n i s less certain. In these rocks the K-feldspar may be part of the o r i g i n a l assemblage, as i t i s not found i n contact with garnet and rarely occurs i n layers containing garnet. B i o t i t e or muscovite would be expected to form rather than K-feldspar, i f excess K^O were available i n an almandine bearing assemblage metamorphosed Plate 5-2 Laminated plagioclase diopside amphibolite displaying weakly developed cleavage F 2 . Plane polarized l i g h t . F i e l d approximately 4.7 mm. -110-in the lower part of the amphibolite facies (Winkler 1965). Time relationships between deformation, c r y s t a l l i z a t i o n of the various minerals, plutonism and metasomatism are not e n t i r e l y clear. The highest temperature assemblage recorded ( s i l l i -manite after muscovite) occurs at the contact of a major sheet of g r a n i t i c gneiss, but metamorphism probably reached amphibolite facies before g r a n i t i c magmas were emplaced. Whether metasomatic f l u i d s , in advance of the r i s i n g magmas, carried heat upwards and caused metamorphism to reach the amphibolite fac i e s , or whether the metamorphism i s part Of broader high grade regional metamorphic picture, cannot readily be said because of the smallness of the map-area. The p r i n c i p a l reason for associating the culmination of meta-morphism with phase 2 def ormatliori i s "the strong preferred 1 o r i e n t -ation of hornblende p a r a l l e l to , but hornblende appears to have formed at an early syn-kinematic stage. Hornblende, once formed, became affected i n various ways by l a t e r parts of the same def-ormation. In quartz r i c h s e m i - p e l i t i c granulites for example, hornblende, became subject to a high degree of cata c l a s i s as a r e s u l t of the internal deformation and flow of quartz. In quartz de f i c i e n t amphibolites, cata c l a s i s was less s i g n i f i c a n t . Hornblende, diopside, plagioclase assemblages had greater strength, and did not deform so much i n t e r n a l l y by a flow mechanism, (plate 5-2). Cata-c l a s i s was r e s t r i c t e d to discrete shears developed p a r a l l e l to F 2 and to the hinges of phase 2 folds. The orientation of hornblende prisms may have been governed by mimetic c r y s t a l l i z a t i o n along f o l i a t i o n intersections, because i t has also grown p a r a l l e l to L,, most notably on the hinges of r e l i c t - I l l -phase 1 folds. Otherwise two generations of hornblende, and area-wide r e c r y s t a l l i z a t i o n of hornblende during phase 2 deformation, are implied. There seems to be no reason to expect such wide-spread r e c r y s t a l l i z a t i o n • i f the metamorphism were of a progressive nature. Evidence for l a t e - or. post-kinematic growth of other minerals i s also hard to f i n d , although the true relationships are obscured by phase 3 and l a t e r deformation. In schists where F 2 i s a transposition structure, c r i s s - c r o s s i n g and intergrown micas suggest more than one period of growth before phase 3, but i t i s impossible to relate the growth of micas to any p a r t i c u l a r part of phase 2 deformation. In some less deformed rocks, quartz r i c h semi-pelitic granulites i n p a r t i c u l a r , micas exhibit relationships suggesting pre- or early phase 2 growth, followed by rotation into attitudes sub-parallel to F 2, l a t e r i n phase 2 deformation. For example plates 5-3 and 5-4 show the hinge of a minor phase 2 f o l d outlined by layers r i c h i n b i o t i t e , as they appear i n thin-section. Rather than sweeping smoothly around the hinges, many in d i v i d u a l micas appear to have been rotated away from the plane F Q / F ^ a n d now l i e sub-parallel to F 2- Their new attitudes, as seen with crossed po l a r i z e r s , are governed by grain boundaries of quartz, which as a r e s u l t of f l a t t e n i n g have become elongate p a r a l l e l to F 2- Micas trapped between f l a t t e n i n g grains of quartz appear to have become well orientated, while those bounding on feldspar are not so well orientated and are often bent or broken. Although some growth of b i o t i t e p a r a l l e l to F 2 may have occurred, the main period of mica growth preceded at least the f i n a l movements on F 2 , and may date back to an e a r l i e r stage in the second or even the f i r s t deformation. The conditions of metamorphism that may have prevailed during phase 1 deformation are part of the same perplexing problem. -112-P l a t e 5-3 Plane p o l a r i z e d l i g h t . F i e l d approximately 4.7 mm. P l a t e 5-4 Same f i e l d as above but with p o l a r i z e r s crossed to i l l u s t r a t e s t r a i n p a t t e r n i n quartz. See t e x t . Quartz-feldspar (largely plagioclase) segregation layers and lamellae are the obvious f a b r i c elements developed during the f i r s t phase of deformation and metamorphism. Where r e l i c t phase 1 folds are found, segregation layers are deformed on the hinges (plates 3-1 to 3-8), but are also developed to a lesser degree p a r a l l e l to F^. I t therefore appears, that the development of segregation layering preceded and overlapped the development of F-^ , and that segregation was controlled by an e a r l i e r f o l i a t i o n , perhaps p a r a l l e l to bedding. Segregation layering i s known to be well developed i n rocks deformed and metamorphosed i n the upper g r e e n s c h i s t f a c i e s , such as i n the Otago schists of New Zealand (Turner, 1968). By analogy, and lacking any evidence to suggest otherwise, conditions ! • ' ' : . ' !••• of at least middle to upper greenschist'facies are therefore suggested for the f i r s t deformation i n Vaseaux Lake area. During th i s metamorphism, the development of segregation layering might relate in time to gross chemical re-arrangement and dehydration associated with the breakdown of clays and c h l o r i t e s , and the formation of micas. Released water may have migrated along shear planes and given r i s e to segregation layering by a solution-nucleation process. The degree of development of the a x i a l f o l i a t i o n F-^ , during early deformation i s not known, and whether i t was o r i g i n a l l y a s t r a i n - s l i p structure or a flow-type cleavage cannot be said with certainty. Where possible vestiges of t h i s early cleavage are seen in thin-section, such as within the impure quartzite shown on plates 5-5 and 5-6, F^ i s outlined by flattened quartz and b i o t i t e . The mode of occurrence of these minerals suggest that d u c t i l e flow p a r a l l e l to F-, was at least a contributing factor i n the early -114-P l a t e 5-5 P e n e t r a t i v e f o l i a t i o n s F^? and F2 and bedding FQ i n garnet p l a g i o c l a s e (An^g) b i o t i t e q u a r t z i t e from U n i t 4a. Plane p o l a r i z e d l i g h t . F i e l d approximately 4.7 mm. P l a t e 5-6 Same f i e l d as above but with p o l a r i z e r s c rossed to i l l u s t r a t e s t r a i n p a t t e r n s i n q u a r t z . See t e x t . deformation, and that synkiriematic b i o t i t e may have formed and become coarse grained. Neither segregation layering nor F 3 are well developed i n plates 5 - 5 and 5 - 6 , and the observed compositional layering may be bedding (FQ) . B i o t i t e l i e s p a r a l l e l to FQ and F-^ , and both are planes of f l a t t e n i n g , i n which quartz grains have elongate shapes. The penetrative f o l i a t i o n F2> also outlined by quartz and b i o t i t e , cuts obliquely across both of these e a r l i e r s t r u c t u r e s . Conclusions: It would appear that metamorphism accompanying phase 1 deformation i n Vaseaux Lake area reached, at l e a s t , upper green-schist facies and gave r i s e to mica bearing assemblages and1 primitive . ' • 1 • -! 'I T '1 ! segregation layering. At some l a t e r time, during phase |2 def-ormation, metamorphism progressed to the amphibolite f a c i e s , and synkinematic c r y s t a l l i z a t i o n resulted i n hornblende aligned par-a l l e l to L2, and mimetically along vestiges of the e a r l i e r l i n e a r structure L]_. Micas probably continued to increase i n size i n the planes'F/F^ and new micas may have grown p a r a l l e l to F2. Some mica bounding on quartz as the re s u l t of fl a t t e n i n g and duc t i l e flow of quartz appears to have been rotated into attitudes sub-parallel to F^. Later, probably at the thermal culmination associated with phase 2 deformation, the succession was extensively metasomatized and veined with pegmatite, i n advance of a r i s i n g pluton (Unit A). Maximum grain size was probably attained as thick g r a n i t i c sheets were emplaced producing l o c a l higher temperature s i l l i m a n i t e bearing assemblages at th e i r immediate contacts. 1 With waning temperature, phase 2 deformation appears to have continued to af f e c t the succession, but was of a more b r i t t l e character. A l t e r n a t i v e l y b r i t t l e deformation p a r a l l e l to F 2 may be almost e n t i r e l y the r e s u l t of renewed closure of phase 2 folds during phase 3 or l a t e r deformations, as w i l l be seen i n the following sections. PHASE 3 METAMORPHISM In Chapters 3 and 4 i t has been suggested that phase 3 def-ormation progressed with increasing temperature from f l e x u r a l - s l i p folding, to a more du c t i l e type of deformation, as late-kinematic g r a n i t i c plutons (Unit B) were emplaced. Emplacement of the main g r a n i t i c mass may be responsible for the l a t e r more extreme part of the deformajtion. I t appears to have made room for i t s e l f by flat t e n i n g andi tightening Gallagher Lake Synform and some/earlier folds. Emplacement of Unit B probably also marked a l o c a l thermal high associated with phase 3 deformation, and may in a general way be considered the cause of metamorphism. Mineralogjically, phase 3 was by nature, a phy s i c a l l y des-i -tructive event characterized by r e c r y s t a l l i z a t i o n pre-existing amphibolite facies mineral assemblages. New mineral assemblages, i either prograde or retrograde, did not form, and new minerals grown from comminuted materials are those present in the o r i g i n a l assemblages, i Deformation and metamorphism are therefore thought to have culminated at temperatures and pressures that were neither much greater or less than those that produced the middle amphibolite facies assemblages during phase 2 deformation. Although temp-eratures probably decreased with distance from Unit B, conditions of at least lowest amphibolite facies are implied throughout the area at the culmination phase 3. Direct evidence o f metamorphism i n the lower amphibolite facies comes from a few basic and intermediate dykes which were metamorphosed for the f i r s t time during phase 3 (Chapter 4). Mineral assemblages i n these rocks consist p r i n c i p a l l y of andesine, b i o t i t e and hornblende with minor quartz/ K-feldspar, epidote, sphene, opaques. In previously metamorphosed rocks, growth of a new generation of b i o t i t e p a r a l l e l to F ^ , such as shown on plate 5-7, i s not i n -consistent with lower amphibolite facies metamorphism. B i o t i t e , i s the only mineral that can be d e f i n i t e l y shown to have grown during phase 3, although i n some schists tiny euhedral garnets in association with large flattened garnets also may have grown during phase 3. i ! i Pyroxenites and dunites, as indicated i n Chapter 14,,may have been p a r t i a l l y serpentinized during phase 3, suggesting an upper temperature l i m i t of about 500°C (Turner, 1968) within the limited area that such rocks are found. Metamorphism would then be r e s t r i c t e d to the lowermost amphibolite f a c i e s , but there i s unfortunately no way to exactly date the time of serpentinization, and i t , c o u l d , for example, be a very late phase 3 phenomenon, accomplished as temperatures waned. Although the rocks were not chemically responsive to temp-eratures and pressures p r e v a i l i n g during phase 3, they responded physically by deforming. Again various minerals present part-icipated in d i f f e r e n t ways and responded d i f f e r e n t l y depending on their s tructural position, and the mineralogical composition of the rock in which they occur. Quartz, for example, i n weakly deformed semi-pelitic granulites such as shown on plate 5-8, deformed by d u c t i l e flow p a r a l l e l to and developed pronounced s t r a i n -118-Phase 3 b i o t i t e a l i g n e d p a r a l l e l to the a x i a l plane F 3 of a minor f o l d . Plane p o l a r i z e d l i g h t . F i e l d approximately 4 . 7 mm. S t r a i n p a t t e r n i n quartz o u t l i n i n g the f o l i a t i o n F^ across the hinge and limbs of a minor phase 2 f o l d . Plane p o l a r i z e d l i g h t . F i e l d approximately 4 . 7 mm. -119-patterns (deformation bands of Carter et a l 1964). More b r i t t l e minerals such as feldspars, amphibolites and micas were mech-an i c a l l y abraded and sometimes marginally r e c r y s t a l l i z e d . Extreme deformation related to phase 3 was highly l o c a l i z e d by lithology (schist), pre-existing structure (phase 2 folds) and newly developed mylonitic zones of which the s l i d e i n the northern map-area i s a large-scale example. Some s i m i l a r i t i e s i n the sequence of events comprising phase 3 deformation, may be seen i n these intensely deformed rocks. Within schists, large garnets have been flattened i n the plane of F j , but are also s l i g h t l y to conspicuously elongate p a r a l l e l or sub-parallel to L^, which suggests that th e i r def-ormation must be a phase 3 feature. Just, how they attained such shapes during phase 3 i s a matter involving some speculation. Many of these garnets, as indicated by obliquely orientated inclusions of mica, have been rotated at some stage in th e i r history (plate 5-9). Whether rotation accompanied growth during phase 2, or occurred l a t e r , cannot be exactly said, but i t i s thought l i k e l y that at least some of the rotation occurred during phase 3, and might be the reason for elongation p a r a l l e l to . It i s argued that at some early stage i n phase 3 deformation, f l a t t e n i n g and rotational shear acted simultaneously in the plane of such that garnets were r o l l e d into "spindle-shapes", elongate approximately p a r a l l e l to L^. At a la t e r stage, an episode of non-rotational f l a t t e n i n g i n the plane of F 2 commenced, and garnets continued to f l a t t e n , but retained, to various degrees, elements of th e i r o r i g i n a l elongation p a r a l l e l to . The non-rotational episode of f l a t t e n i n g i s thought to coincide i n time with the late development of s t r a i n - s l i p cleavage F g a (plate 5-10) -120-Plate 5-9 Flattened garnet bearing oblique inclusions of mica. Crossed p o l a r i z e r s . F i e l d approximately 4.7 mm. Plate 5-10 Flattened garnet lying p a r a l l e l to F 2• Late s t r a i n - s l i p cleavage F^ a crosses obliquely. Plane polarized l i g h t . F i e l d approximately 4.7 mm. - 1 2 1 -which took up the shear component previously operating p a r a l l e l to F 2. Where garnets are not seen i n sc h i s t s , similar h i s t o r i e s may be sometimes inferred from minor folds. For example, i n plate 5-11, an i s o c l i n a l phase 2 structure has developed i n peg-matite veined schist under the influence of f l a t t e n i n g and ro t a t i o n a l shear (rotated porphyroblasts). Resulting transposed layering i s crossed by a l a t e r oblique cleavage F_ (plate 5-12) j c l which i s best developed i n zones of i n c i p i e n t phase 3 fol d i n g . In mylonites where phase 3 deformation i s even more intense, and transposition and r e c r y s t a l l i z a t i o n are almost complete, F, i s also a late formed cleavage. Rocks from the northern mylon-. i i t i c zone, in thin-section, display a well developed cleavage F_. i i I outlined by new b i o t i t e , grown from comminuted material's ' in ithe matrix (plate 5-13). Here F_ formed after movements p a r a l l e l to j 3. the transposed int e r n a l layering had ceased, at a time when shallow phase 3 folds were developed across the mylonites. The sequence of events inferred from rocks which became highly deformed during phase 3, i s consistent with an o v e r a l l picture of phase 3 deformation. At an early stage r o t a t i o n a l shear would be expected on the limbs of the megascopic phase 3 structure (Gallagher Lake Synform) which was developing by a mech-anism of f l e x u r a l - s l i p . Flattening, at the same time, must have been important, because of renewed closure of phase 2 folds as a r e s u l t of re-folding. As temperatures rose and phase 3 deformation was i n t e n s i f i e d i n response to the emplacement of Unit B, r o t a t i o n a l shear and fla t t e n i n g within the planes of pre-existing f o l i a t i o n s continued u n t i l interrupted by the development of phase 3 planar structures. -122-Plate 5-11 I s o c l i n a l phase 2 structure i n pegmatite veined schist. Plane polarized l i g h t . F i e l d approximately 4.7 mm. Plate 5-12 Oblique phase 3 structure developed across transposed pegmatitic layering i n schist. Plane polarized l i g h t . F i e l d approximately 4.7 mm. -123-This stage was reached when Gallagher Lake Synform became so t i g h t l y appressed that i t could close no further by a f l e x u r a l mechanism. A large segment within the core of the Synform, now bounded by the mylonitic zone i n the northern map-area, was forced outwards as further closure became d i f f i c u l t , at some t r a n s i t i o n a l stage. F i n a l l y , the penetrative cleavage F~ , a s t r a i n - s l i p structure as well as a plane of f l a t t e n i n g , developed and began to take up the shear component previously operating i n the planes of e a r l i e r f o l i a t i o n s . As the Synform continued to close, e a r l i e r f o l i a t i o n s as well as F^ planar structures continued to act as planes of f l a t t e n i n g . TERTIARY THERMAL EVENT Structural and petrographic evidence of an Early T e r t i a r y thermal-hydrothermal event i s found i n the rocks of Vaseaux Lake area, and probably coincides approximately i n time with volcanism in nearby areas. With respect to the development of structure, the thermal event overlapped phases 4 and 5 of deformation, both of which include episodes of open folding and f r a c t u r i n g . Rhomb porphyry s i l l s and dykes, equivalent i n age to the basal Marron lavas, were emplaced during the fourth phase of foldi n g , and developed strong f o l i a t i o n s p a r a l l e l to t h e i r margins (Chapter 4). Their margins are but weakly c h i l l e d , and i t i s thought that the w a l l-rocks may have been warm at the time they were emplaced, and 'that cooling may have been somewhat in h i b i t e d . Slow cooling i s further implied by the unmixing of. two feldspars i n anorthoclase (plate 5-14) although exsolution was probably f a c i l i t a t e d by simultaneous shearing, as i t i s best developed i n more highly Plate 5-13 Late cleavage F^a outlined by new b i o t i t e across transposed layering i n mylonite. Plane polarized l i g h t . F i e l d approximately 4.7 mm. Plate 5-14 Exsolution textures and r e l i c t zoning at the margin of a rhomb shaped pseudo-anothoclase phenocryst. Crossed p o l a r i z e r s . F i e l d approx-imately 4.7 mm. -125-sheared rocks. Another feature of highly sheared rhomb porphyries are pseudomorphs of hornblende rimed by b i o t i t e , after phenocrysts of clinopyroxene. I t i s thought that such hornblende and b i o t i t e may have formed by a late hydrothermal reaction aided by shearing as the rhomb porphyry bodies cooled, rather than by a reaction induced by a regional P/T environment approaching amphibolite fac i e s . Evidence of widespread hydrothermal a c t i v i t y , also of probable Early Tertiary age i s found throughout Vaseaux Lake map-area. Intense hydrothermal a l t e r a t i o n i s r e s t r i c t e d to two large areas, near the southern and northern boundaries of the map-area (plate 5-pocket), but i n c i p i e n t to weak replacement of b i o t i t e and horn-blende by c h l o r i t e , epidote-ichlorite veining, and jWeak s e r i c i t -i z a t i o n of feldspar i s often found elsewhere. Most highly altered rocks within the large zones of intense a l t e r a t i o n , are bleached white to grey derivatives of metamorphic and g r a n i t i c rock, veined and impregnated with clay minerals. Feldspars are replaced by clays and s e r i c i t e , ferromagnesian minerals are npt to be found, and textures are s t r i k i n g l y cata-c l a s t i c (plate 5-15). Outward through a broad zone, c h l o r i t e and epidote became progressively more abundant, and r e l i c t s of o r i g i n a l f a b r i c and texture may be recognized. S e r i c i t e p e r s i s t s in plagioclase, but saussurite becomes the dominant a l t e r a t i o n product, and small amounts of secondary carbonate and p y r i t e are found along fractures. At greater distance from the centers, beyond the zones shown on plate 5, the a l t e r a t i o n slowly diminishes to an i n c i p i e n t l e v e l , and i s not seen at a l l i n some distant areas. Zones of most intense a l t e r a t i o n appear to be s t r u c t u r a l l y -126-Plate 5-15 Cataclastic texture i n bleached granodiorite from the southern zone of a r g i l l i c a l t e r a t i o n . Plane polarized l i g h t . F i e l d approximately 4.7 mm. -127-controlled and are not, in any way, d i r e c t l y related to exposed igneous bodies. At the southern occurrence, most intense a l t e r a t i o n i s c l e a r l y related, to fau l t s which bound an i n t e r n a l l y fractured g r a n i t i c block (Unit B) on the north and east. In the north, the zone l i e s roughly along the a x i a l trace of Okanagan F a l l s Syncline (Church, 1967) , a major phase 5 f o l d containing volcanics and sediments of the Early Tertiary Marmara and White Lake Formations i n i t s core. Elsewhere, where a l t e r a t i o n i s less extreme, J i fractures have strongly bleached walls and contain c h l o r i t e , epidote., and s e r i c i t e . J 2 fractures may or may not be altered, and younger fracture sets and are e n t i r e l y younger than the hydrothermal event. The time of a l t e r a t i o n , from a structural point of view, would therefore be placed between late phase 4 deformation (J-^) and early phase 5 deformation (J 2); (isee Chapter 3) . Relationships between Ter t i a r y rocks i n the core of Okanagan F a l l s Syncline, and the underlying Vaseaux Formation also provide a clue to the age of the a l t e r a t i o n . The Tertiary rocks are, in general, unaltered with the exception of small zones that may be genetically related to volcanic rocks in the lower part of the • ! sequence. In contrast, the underlying Vaseaux Formation within 50 feet of the contact i s highly altered, and the broad zone of intense a l t e r a t i o n within the Vaseaux Formation projects d i r e c t l y into the very much less altered T e r t i a r y rocks. The d r a s t i c change in a l t e r a t i o n intensity i s d i f f i c u l t to explain without invoking a pre-Marmara and White Lake age for the a l t e r a t i o n despite the fact that the unconformity i s not exposed, and the contact may or may not be, i n part, a f a u l t ( L i t t l e , 1961). The observed relationships suggest that phase 5 folding -128-commenced (Okanagan F a l l s Syncline began to form) and fractures were opened along i t s hinge l o c a l i z i n g the most intense hydro-thermal a c t i v i t y . Locally altered Marmara volcanics and pyro-c l a s t i c s i n the lower part of the Tertiary p i l e may have accompani* or closely followed the period.of most intense a l t e r a t i o n , but overlying White Lake sediments were deposited l a t e r . Perhaps Okanagan F a l l s Syncline continued to grow and formed the basin of deposition i n which the White Lake sediments accumulated, and i n which they were ultimately deformed. Although intense a l t e r a t i o n i n the Vaseaux Formation does not d i r e c t l y coincide i n space with centers of Tertiary volcanism, both are related i n time, and are therefore considered to be related phenomena. In i t s broadest aspects (detailed play', mineralogy not. available) , the a l t e r a t i o n i s similar • toll tliat a f f ecting g r a n i t i c and volcanic rocks beneath presently active hot-springs such as Sulphur Bark and Steamboat Springs (Dickson and Tenell, 1967). Hot-springs therefore may have existed near the northern and southern boundaries of the map-area in the Early Tertiary. These became extinct before White Lake sediments were deposited i n Okanagan F a l l s Syncline, and thus might re l a t e i n time to either the Marron volcanics or the somewhat younger Marmara volcanics. -129-CHAPTER SIX CONCLUSIONS SUMMARY OF GEOLOGIC HISTORY (Contributions) Within the Vaseaux Formation of the present map area a l o c a l s t r u c t u r a l succession comprised of 5 l i t h o l o g i c units exceeding 4000 feet i n t o t a l present thickness has been est-ablished. These l i t h o l o g i c map-units consist of high grade metamorphic rocks that were probably derived from t u r b i d i t e sandstones, shales and basic volcanic rocks deposited and interbedded with minor carbonate and quartzite i n a near shore environment. Subsequently the Vaseaux Formation has undergone a complex history of:polyphase; deformation, metamorphism and 1 igneous intrusion as summarized below. 1. Phase 1 folding, similar i n style and along northerly trends, gave r i s e to Mclntyre Blu f f Fold and minor structures. i These ,folds may have been o r i g i n a l l y recumbent, and associated tectonic slides which developed probably continued to be active at various times during l a t e r deformation. Metamorphism which accompanied phase 1 deformation appears to have reached at least upper greenschist f a c i e s , and gave r i s e to primitive segregation layering. Minor sheets of quartz monzonite were emplaced into the succession before or during I phase 1 deformation. 2. Phase 2 folding, also similar i n style but along north-westerly trends re-folded and tightened the e a r l i e r recumbent structures. Major folds formed during phase 2 are Vaseaux Lake Antiform, Shuttleworth Creek Synform, and other unnamed structures, -130-and congruent minor folds are abundant in association with these. A x i a l planes of phase 2 folds were o r i g i n a l l y i n c l i n e d at some moderate angle to the northeast and t h e i r axes were almost horizontal. Metamorphism i n the amphibolite facies and ubictuous synkinematic r e c r y s t a l l i z a t i o n accompanied phase 2 deformation, and the metamorphism may or may not have been a continuation and culmination of that associated with phase 1. At the thermal culmination associated with phase 2, the succession was exten-si v e l y metasomatized and veined with pegmatite i n advance of a r i s i n g pluton (Unit A). A thick sheet of synkinematic g r a n i t i c gneiss with several crosscutting apophyses was then emplaced along the limbs and ax i a l planes of phase 2 folds. These g r a n i t i c rocks together form the d i f f e r e n t i a t e d top of a somewhat more mafic pluton (Unit A) which became frozen at the observed l e v e l at a late stage i n phase 2 deformation. Small lenses and sheets of u l t r a basic rock may have been t e c t o n i c a l l y emplaced at an early stage i n the second or during the f i r s t phase of deformation. Their o r i g i n i s unknown. 3. Phase 3 deformation commenced with f l e x u r a l - s l i p f o l d i n g along westnorthwesterly trends but progressed to a more d u c t i l e type of deformation (similar folding) as g r a n i t i c rocks of Unit B were emplaced. Callagher Lake Synform and congruent minor folds were formed early about southwesterly dipping a x i a l planes and near horizontal axes and continued development about the same directions throughout the l a t t e r part of phase 3 deformation. As Gallagher Lake Synform continued to close in response to fo r c e f u l emplacement of a sub-concordent pluton (Unit B) a s l i d e -131-developed, and gave r i s e to mylonite,and l o c a l minor folds of diverse trend. E a r l i e r formed phase 1 and 2 structures were re-folded, tightened and variously re-orientated throughout phase 3. Narrow basic to intermediate dykes intruded the succession at some time between phase 2 and phase 3 deformation. Their em-placement along steep fractures indicates that development of phase 2 and phase 3 folds along almost co-axial trends are not a result of a single long-continued dynamothermal event. Rather phases 2 and 3 were separated by a period of time of unknown duration when the rocks were cool and b r i t t l e . Later metamorphism, which accompanied phase 3, reached at i i least lower amphibolite facies;, possibly at about the time g r a n i t i c rocks of Unit B were emplaced. New mineral assemblages were formed i n the above mentioned dykes, while pre-existiing phase 2 assemblages remained unchanged. Minerals newly c r y s t a l -l i z e d from comminuted materials in the matrix were oriented along phase 3 directions. The minimum age of phase 3 deformation has been set at 14 0 m.y. (Upper Jurassic) by K/Ar dates on the post-phase 3 Olive r stock. 4. Phase 4 folding, f l e x u r a l - s l i p i n s t y l e , gave r i s e to a major northerly trending antiform with a steeply dipping a x i a l plane and gently plunging axis. E a r l i e r structures were s l i g h t l y re-orientated on the limbs of th i s large antiform, and s l i p with-in the planes of pre-existing f o l i a t i o n s gave l o c a l d i s c o n t i n u i t i e s along which thin zones of mylonite were developed. Fracturing along steeply dipping northnortheasterly trending surfaces accom-panied and/or followed phase 4 folding. -132-Phase 4 i s dated with respect to nearby early Tertiary rocks by anorthoclase bearing rhomb porphyry dykes involved in the deformation. These are equivalent i n age to anorthoclase bearing lavas of the basal Marron Formation and t h e i r age and the age of deformation has been set at 44 m.y. B.P. by K/Ar dating (Ross and Barnes 1972). Widespread hydrothermal a l t e r a t i o n , probably associated in space and time with r i s i n g early T e r t i a r y Marron lavas, and possibly related to hot-spring systems, affected the suc-cession during phase 4 and overlapped the i n c i p i e n t stages of phase 5 deformation. 5. Phase 5 folding, also f l e x u r a l - s l i p i n s t y l e ; produced open a l l scale northwesterly trending folds with steeply dipping ax i a l planes and shallowly plunging axes. These folds have resulted i n further re-orientation of the e a r l i e r structures, and a large antiform intersects the e a r l i e r phase 4 anitform to give a broad domal structure near the centre of the map-area. Phase 5 folding was accompanied by extensive fracturing and f a u l t i n g and was accomplished primarily by buckling of independent f a u l t bounded blocks. Phase 5 may have followed continuously from, or shortly after, phase 4 deformation but was by character a more b r i t t l e (cooler) deformation. The hydrothermal event associated with phase 4 c l e a r l y pre-dates deposition of White Lake sediments which now occupy the core of phase 5 Okanagan F a l l s Syncline. A minimum age of phase 5 deformation i s set at pre-Miocene by which time the late mature erosion surface preserved i n the d i s t r i c t had developed. -133-INTERPRETATION The age of the Vaseaux Formation and 5 l a t e r phases of deformation cannot a l l be determined by observation of r e l a -tionships withir the area mapped or within nearby areas. Ages of phases 4 and 5 of deformation are best known and may be set at 44 m.y.B.P. and post 44 m.y.B.P. - pre 25 m.y.B.P. respectively on the basis of K/Ar dating of Marron Rhomb por-phyry dykes which were deformed during phase 4 (Ross and Barnes 1972). Involvement of White Lake sediments i n only phase 5 folding and the development of a l a t e r mature erosion surface p r i o r to the Miocene (Church 1967) place l i m i t s on phase 5. A minimum 140 m.y.B.P. (Upper Jurassic) age for phase 3 deformation has been suggested previously on the basis of the K/Ar age (White et al.) of the post-phase 3 Oliver stock. Recent work west of the map-area (Ross and Barnes 1972), to the contrary has shown that phase 3 deformation i s pre-late M i s s i s -sippian i n age. The evidence for the foregoing statement i s found near O l a l l a and at Blind Creek where undeformed f o s s i l i -ferous limestones of late Mississippian or early Pennsylvanian age overlie highly deformed rocks of the Old Tom and Shoemaker Formations i n which structures equivalent to phases 2 and 3 i n the Vaseaux Formation are present. The Upper Jurassic minimum age for phase 3 deformation suggested by the Oliver stock would, therefore, seem to be erroneous, at least s u p e r f i c i a l l y . Further the synkinematic phase 3 pluton Unit B, despite i t s l i t h o l o g i c s i m i l a r i t y with parts of the Oliver stock, would seem to be much older and t o t a l l y unrelated. 1 -134-In explanation, an alternate hypothesis i s offered that seems more consistent with the history of phase 3 deformation and the implied synkinematic intrusion of Unit B. That i s , phase 3 structures which formed o r i g i n a l l y during a Paleozoic orogeny were reactivated during the Upper Jurassic at the time of intrusion of g r a n i t i c magmas and Unit B. As previously shown, Unit B was emplaced along pre-existing phase 3 structures (Figures 4-3 and 4-4) but no evidence was found to suggest that the intrusion had to be cl o s e l y associated i n time with the f i r s t development of that structure. Factual evidence only supports an argument that the penetrative f o l i a t i o n F3 remained active subsequent to emplacement of Unit B and, reactivation i s a possible explanation. ' • If the above hypothesis were true, phase 3 could no longer be regarded as a single, continuous dynamothermal event culmina-ting with the emplacement of g r a n i t i c magmas. An extended i n t e r v a l of time between late Mississippian and Upper Jurassic, when the rocks remained undeformed, would then separate the f i r s t and l a s t movements associated with phase 3. F i r s t movements might corres-pond to part of the Lower Mississippian Caribooan Orogeny (Douglas et a l . , 1968) with the l a t e r reactivation of phase 3 structures in response to the Upper Jurassic - Cretaceous Columbian Orogeny. The age of phase 1 and phase 2 deformation i n the Vaseaux Formation are not known other than by generalization that they must be older than the pre-late Upper Mississippian phase 3 event. I t seems conceivable that both might have originated during some early phase of the Lower Mississippian Caribooan Orogeny, but one or both might relate to some yet e a r l i e r event. -135-Structures equivalent to phase 2 i n the Vaseaux Formation have been recognized and correlated i n both the Kobau Group (Okulitch, 1969) and the Old Tom and Shoemaker Formations (Ross and Barnes 1972) and presumably a l l of the above rocks are of about the same age. Okulitch,196 9, suggested that the Kobau sediments were derived i n part from r i s i n g nappe structures developed during phase 1 folding of the Vaseaux Formation, and soon became involved i n the phase 2 re-folding of these nappes. If Okulitch i s correct, phases 1 to 3 of deformation may a l l relate i n time to the Caribooan Orogeny, and the l a t e r phase 2 and 3 folds might be l o c a l l y developed accommodations rather than regionally developed fold sets. For that reason correlations of f o l d sets across great distances within the Shuswap complex, without the benefit of detailed knowledge of intervening areas, could be very misleading and i s not warranted at t h i s time. 136 REFERENCES CITED BOSTOCK, H.S. 1940 1941 1941 Keremeos, B r i t i s h Columbia; Geol. Survey, Canada, Map 341A. Okanagan F a l l s , B r i t i s h Columbia; Geol. Survey, Canada, Map 627A. O l a l l a , B r i t i s h Columbia; Geol. Survey, Canada, Map 628A. BROCK, B.B. 1934 The Metamorphism of the Shuswap Terrane of B r i t i s h Columbia; J. Geol., v o l . 42, pp. 673-699. CAIRNS, CE, 1940 The Kettle River !Map-Area, West Half, B r i t i s h Columbia; Geol. Survey, Canada', Map 5 38A. CHURCH, B.N. 1967 Geology of the White Lake Area, B r i t i s h Columbia; unpublished Ph.D. Thesis, University of B.C. DALY, R.A. 1905 1911 1912 1915 1917 The Okanagan Composite Batholith of the Cascade Mountain System; B u l l . Geol. Soc. Am. v o l . 17, pp. 329-376. 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Surv. of Can. Economic Geol. Dept. No. 1. GILLULY, J.A. 1934 Mineral Orientation i n some Rocks of the Shuswap Terrane as a clue to t h e i r Metamorphism; Am. S. S c i . , v o l . 228, pp. 182-201. GUNNING, H.C. 1928 Geology and Mineral Deposits of the Big Bend Map-Area, B r i t i s h Columbia; Geol. Surv. Canada, Sum. Rept. 1928. HOLLAND, S.S. 1964 Land Forms of B r i t i s h Columbia. A Physiographic Outline; B u l l . No. ,48 -B.C. Dept. Mines & Pet r o l . Resources. HYNDMAN, D.W. 1968 Mid-Mesozoic Multi-Phase Folding along the Border of the Shuswap Metamorphic Complex; B u l l . Geol. Soc. Am., v o l . 79, pp. 575-588 JONES, A.G. 1959 Vernon Map-^Area, B r i t i s h Columbia; Geol. Surv. Canada, v o l . 296. Mem. LITTLE, H.W. 1961 Geology of Kettle River Map-Area, West Half, B r i t i s h Columbia; Geol. Surv. Canada, Map 15, 1961. 138 NASMITH, H. 1962 Late G l a c i a l History and S u r f i c i a l Deposits of the Okanagan Valley, B r i t i s h Columbia; B u l l . B.C. Dept. 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Thesis, Dept. Geol., University of B.C. ROSS, J.V. 1968 Structural Relations at the Eastern Margin of the Shuswap Complex near Revelstoke, Southeastern B r i t i s h Columbia; Can. J. Earch S c i . , v o l . 5, pp. 831-849. ROSS, J.V. & BARNES, W.C. 1972 Evidence for "Caribooan Orogeny" i n the Southern Okanagan Region of B r i t i s h Columbia, Can. S. Earth S c i . v o l . 9, No. 12. 139 SNOOK, J.R. 1965 Metamorphic and Structural History of the C o l v i l l e Batholith Gneiss, North Central Washington; B u l l . Geol. Soc. Am., v o l . 76, pp. 759-776. TURNER, F.J. 196 8 Metamorphic Petrology, Mineralogical and F i e l d Aspects, McGraw H i l l . TURNER, F.J. & VERHOOGEN, J. 1960 Igneous and Metamorphic Petrology; McGraw H i l l , N.Y. Second Ed., pp. 694. WHEELER, J.O. 1962 Rogers Pass Map-Area, B r i t i s h Columbia; Geol. Surv. Can. Paper 62-32. WHEELER, J.O., GABRIELSE, H. et a l 1972 The Cordilleran Structural Province. Geol. Assoc. of Can. Sp. Paper No. 11, WHITE, W.H. et a l 1967 1968 Absolute Age of Mineral Deposits in B r i t i s h Columbia; Abstr. Geol. Soc. Am., 1967 Annual Meeting, Rocky Mtn. Sect., Golden, Colorado, p. 72. Potassium-Argon Ages of some Ore Deposits i n B r i t i s h Columbia; B u l l . Can. Mining Met., November WINKLER, H.G.F. 1965 Petrogenesis of Metamorphic Rocks. Springer-Verlag. u 'o, o 6 |90_ 0 6 19 01 0 S Y M B O L S Lithologic contacts Slide (phase 1) Mylonite (phase 3 ) Faults- bar on downthrown side Topographic contours Streams and Lakes Bedrock exposures Roads AXIAL T R A C E S Phase 1 Phase 2 a) antiform b) synform Phase 3 - synform Dip and strike of Fry F I , (compositional layering -bedding?) Dip and strike of earliest foliation in granite gneiss - F 2 GEOLOGY of the VASEAUX LAKE A R E A BRITISH C O L U M B I A GEOLOGY BY J.S. Christie J.V. Ross 1967-68 1968 TRUE SCALE M I L E S 6 T H9 U ^ " D S J _ J ^ LITHOLOGIC LEGEND STRUCTURAL SUCCESSION Unit 1; semipelitic granulite m Unit 2; schist.semipeliticgranulite.minor quartzite.(c)-calc-silicate and/or marble Unit 3; semipelitic granulite. gneissic granulite Unit 4a; laminated amphibolite.granulite, schist.quartzite. calc-silicate Unit4b; massive amphibolite. laminated amphibolite Unit 4; undifferentiated Unit 5, semipelitic granulite GRANITIC ROCKS Unit A synkinematic granitic gneiss, granodiorite- trondhjemite-quartz monzonite UnitB; late-kinematic granodiorite, quartz monzonite ULTRA - BASIC ROCKS Plate 1 a) serpentinite b) amphibolite P H A S E 1 & P H A S E STRUCTURES Plate 2 : Dip 8. strike of gulf (bedding - compo-sitional layering) Dip & strike of Fj (earliest foliation in granitic gneiss ) Plunge of phase 1 linear structures Plunge of phase 2 linear structures Dip& strike of phase 2 planar structures Phase 1 axial trace - Mclntyre Bluff Fold Phase 2 synformal Creek Synform(S) Phase 2 antiformal J!J.>N trace - Vaseaux — w * Lake Antiform( (V) GEOLOGY BY J. S.Christ ie 1967- 68 J . V. Ross 1968 Drawn by JSC S C A L E MILES (along borcrer) LITHOLOGIC L E G E N D STRUCTURAL S U C C E S S I ON Unit 1; semipelitic granulite Unit 2; schist, semipelitic granul'rte.minor quartzite,(c)-calc-silicate and/or marble Unit 3; semipelitic granulite. gneissic granulite Unit 4a; laminated amphibolite.granulite, schist.quartzite.calc-silicate Unit 4b; massive amphibolite. laminated amphibolite Unit 4; undifferentiated Unit 5. semipelitic granulite GRANITIC ROCKS Unit A, synkinemat ic grani t ic gne iss , granodiori te- t rondhjemite-quar tz monzoni te P | Uni tB, l a t e - k i nema t i c q quar tz monzon 'm ranod io r i te e U L T R A - B A S I C R O C K S a) se rpen t i n i t e b) a m p h i b o l i t e F T Stratigraphic or intrusive contact Tectonic (sheared stratigraphic) contact Slide Mylonite (phase 3) Fault-bar on downthrown side Intense hydrothermal alteration Topographic contour Stream Lake Roads I T T . Wmwakmmm 119° 25' P H A S E 3 S T R U C T U R E S Plate 3 1 ; ' .1.";,".:'. • m T — 3a 13b w 3a 13b Dip& strike of Ff (bedding - compo-sitional layering) Dip & strike of fj (earliest foliation in granitic gneiss ) PHASE 3 DATA Plunge of minor fold axies Dip & strike of minor fold axial planes Plunge of linear structures Dip & strike of cleavage Axial trace Gallagher Lake Synform GEOLOGY BY J. S.Christie 1967- 68 J. V. Ross 1968 Drawn by JSC SCALE MILES (along border) LITHOLOGIC LEGEND STRUCTURAL SUCCESSI ON Unit 1; semipelitic granulite Unit 2; schist, semipeliticgranulite.minor quartzite,(c)-calc-silicate and/or marble Unit 3; semipelitic granulite. gneissic granulite Unit 4a; laminated amphibolite.granulite. schist.quartzite, calc-silicate Unit4b; massive amphibolite. laminated amphibolite Unit 4; undifferentiated Unit 5. semipelitic granulite GRANITIC ROCKS | | Unit A, synkinematic granitic gneiss, granodiorite- trondhjemite-quartz monzonite ] UnitB; late-kinematic granodiorite, quartz monzonite ULTRA-BASIC ROCKS a) serpentinite b) amphibolite Stratigraphic or intrusive contact Tectonic (sheared stratigraphic) contact Slide Mylonite (phase 3) Fault-bar on downthrown side Intense hydrothermal alteration Topographic contour Stream Lake Roads ~*.'._...3I 119° 25' P H A S E 4 & P H A S E 5 S T R U C T U R E S Plate 4 "I500 1500 1500 6 " c 67 Dip& strike of Ff (bedding - compo-sitional layering) Dip & strike of \j (earliest foliation in granitic gneiss ) Phase 4 fracture c leavage.S ab joints (JI) Phase 5 fracture cleavage 8 .a b joints (J 2 ) Phase 5 or young-| er joint set (J 3 ) Phase 5 or young-er joint set ( J 4 ) Phase 4 axial aces Phase 5 axial t r a c e s GEOLOGY BY J. S.Christie 1967- 68 J. V. Ross 1968 Drawn by JSC SCALE MILES (along border) LITHOLOGIC L E G E N D STRUCTURAL S U C C E S S I O N Unit 1; semipelitic granulite Unit 2; schist, semipelitic granulite.minor quartzite.(c)-calc-silicate and/or marble Unit 3; semipelitic granulite. gneissic granulite Unit 4a; laminated amph ibolite.granulite. schist.quartzite.calc-silicate Unit4b; massive amphibolite. laminated amphibolite Unit 4; undifferentiated Unit 5. semipelit ic granulite GRANITIC ROCKS Unit A. synkinemat ic grani t ic gne iss , granodior i te- t rondhjemite-quar tz monzoni te Uni tB, l a t e - k i nema t i c g ranod io r i te quar tz monzon i t e U L T R A - B A S I C R O C K S a) se rpen t i n i t e b) a m p h i b o l i t e u D Stratigraphic or intrusive contact Tectonic (sheared stratigraphic) contact Slide Mylonite (phase 3) Fault-bar on downthrown side Intense hydrothermal alteration Topographic contour Roads • LITHOLOGIC L E G E N D STRUCTURAL S U C C E S S I O N Unit 1; semipelitic granulite Unit 2; schist, semipelitic granulite.minor quartz ite,(c)-calc-silicate and/or marble Unit 3; semipelitic granulite. gneissic granulite Unit 4a; laminated amphibolite.granulite, schist.quartzite.calc-silicate Unit4b; massive amphibolite. laminated amphibolite Unit 4; undifferentiated Unit 5. semipelitic granulite A E L E V A T I O N FEET 5000 -I 3000 VERTI C A L C R O S S - S E C T I O N S V a s e a u x L a k e A r e a Lithologic contacts Slide i i ——— Mylonite Faults F1-F5 A x i a l traces MILES nr~ WLVHLM " ••M^ } Scale FEET THOUSANDS (- v , x \ x>.;^x I000 -A NORTH - 5000 L-3000 - I000 SOUTH ELEVATION F E E T 5 0 0 0 ^ GRANITIC ROCKS Unit A; synkinematic granitic g neiss, granodiorite- trondhjemite-quartz monzonite UnitB; late-kinematic g r a n o d i o r i t e . quartz monzonite \~? Vaseaux Lake <^ Ant i fo rm h 5 0 0 0 L-3000 1000 SOUTH P l a t e 5 c LITHOLOGIC L E G E N D STRUCTURAL S U C C E S S I O N ELEVATION FEET 5000-J 3000 H 1000 H W E S T Unit 1; semipelitic granulite Unit 2; schist, semipeliticgranulite.minor quartzite.(c)-calc-silicate and/or marble Unit 3; semipelitic granulite. gneissic granulite Unit 4a; laminated amphibolite.granulite, schist.quartzite.calc-silicate Unit4b; massive amphibolite. laminated amphibolite Unit 4; undifferentiated Unit 5. semipelitic granulite VERTI C A L C R O S S - S E C T I O N S V a s e a u x Lake A r e a Lithologic contacts Slide F r F% MILES 0 5 2 FEET Mylon i te Faul ts Axia l t r a c e s Scale 3 4 5 THOUSANDS F 3 } Vaseaux Lake -5000 3000 1000 E A S T GRANITIC ROCKS Unit A, synkinematic grani t ic gne iss , granodiorite- trondhjemite-quartz monzoni te Uni tB; l a te -k inemat i c g ranod io r i t e , quar tz monzon i te D D ELEVATION FEET 5000 -| 3000 H 1000 H N O R T H W E S T Mclnt'yre Bluff Fold Okanagan River h-5000 3000 1000 S O U T H E A S T P l a t e 6 

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