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UBC Theses and Dissertations

Tectonic and stratigraphic relations between the Coast Plutonic Complex and Intermontane Belt, west-central… Heyden, Peter van der 1982

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TECTONIC AND STRATI GRAPH IC RELATIONS & ^ 4 * ^ P CJ^~*£%^^ BETWEEN THE COAST PLUTONIC COMPLEX and INTERMONTANE BELT, WEST-CENTRAL WHITESAIL LAKE MAP AREA, BRITISH COLUMBIA by PETER lVAN DER HEYDEN B.Sc. University of Leiden, Netherlands 1977 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES Department of Geological Sciences We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l 1982 (c) Peter van der Heyden, 1982 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date l<\ OCT |a&Z for scholarly purposes may be granted by the head of my DE-6 (3/81) FRONTISPIECE Unnamed peak, e l e v a t i o n 2088 m : gently dipping amphibolites and g r a n i t o i d gneisses belonging to the C e n t r a l Gneiss Complex s t r u c t u r a l l y o v e r l y i n g greenschist f a c i e s mylonites and s c h i s t s of the Gamsby Group i i ABSTRACT The upper Tsaytis River area, about 150 km2 in extent, straddles the Coast Plutonic Complex-Intermontane Belt boundary about 580 km northwest of Vancouver, B r i t i s h Columbia. The boundary, here, is the Sandifer Lake Fault Zone, a highly disrupted, northeastward directed, imbricated thrust complex of middle to Late Cretaceous age. Rocks of the Coast Plutonic Complex occur in imbricate sheets above a frontal thrust. In thi s gently dipping, homoclinal sequence of tectonic sheets, amphibolites, amphibolite-grade granitoid gneisses, migmatites and metacarbonates of the Central Gneiss Complex t e c t o n i c a l l y o verlie greenschist facies, metavolcanic and metaplutonic schists and mylonites of the Gamsby Group. The Central Gneiss Complex and the Gamsby Group appear to be s t r a t i g r a p h i c a l l y equivalent units, metamorphosed to di f f e r e n t grade and st r u c t u r a l l y juxtaposed in the thrust complex. Major and trace element chemistry of metavolcanic rocks in the Gamsby Group indicates that p r o t o l i t h s were t h o l e i i t i c and c a l c - a l k a l i n e basalt-andesite and c a l c - a l k a l i n e d a c i t e - r h y o l i t e which originated in a mature island arc setting. A minimum, Upper T r i a s s i c p r o t o l i t h age for the Gamsby Group is provided by a 210 Ma, near concordant U/Pb zircon date for metarhyolite, and a 230±39 Ma Rb/Sr whole rock isochron date. Mylonitic granite in the Gamsby Group gives a 160±24 Ma Rb/Sr whole rock isochron date, and amphibole from a related, deformed in j e c t i o n agmatite gives a 145±5 Ma K-Ar date. Hornblende from a dyke with c h i l l e d margins, which intrudes the Gamsby Group, gives a 66±2 Ma K-Ar i i i d a t e , i n d i c a t i n g t h a t t h e m etamorphic complex was c o l d and c l o s e t o t h e s u r f a c e b e f o r e t h e end of t h e C r e t a c e o u s . T h e s e r e s u l t s and g e o l o g y r e p o r t e d f o r t h e P r i n c e R u p e r t a r e a ( C r a w f o r d and H o l l i s t e r 1982, and u n p u b l i s h e d GSC and UBC z i r c o n d a t a ) i n d i c a t e t h a t a t t h i s l a t i t u d e i n t h e C o a s t P l u t o n i c Complex, r e g i o n a l metamorphism, p o l y p h a s e d u c t i l e d e f o r m a t i o n , and i n t r u s i o n of g r a n i t o i d m a t e r i a l o c c u r e d i n a t w o - s i d e d , J u r a s s i c and C r e t a c e o u s o r o g e n i c w e l t . The o r o g e n was s u p e r i m p o s e d on t h e p r e - U p p e r T r i a s s i c i s l a n d a r c i n t h e w e s t e r n edge o f S t i k i n i a , as a c o n s e q u e n c e of i n i t i a l s u t u r i n g of S t i k i n i a w i t h t h e a l l o c h t o n o u s W r a n g e l l i a - A l e x a n d e r t e r r a n e a t an unknown d i s t a n c e t o t h e s o u t h w e s t o f t h e t h e s i s a r e a . A Lower C r e t a c e o u s v o l c a n i c - p l u t o n i c complex forms t h e e a s t e r n and l o w e s t t h r u s t s h e e t o f t h e C o a s t P l u t o n i c Complex. The v o l c a n i c r o c k s may be c o r r e l a t i v e w i t h t h e Gambier G r o u p of t h e s o u t h e r n C o a s t P l u t o n i c Complex, and were p e r h a p s d e p o s i t e d u n c o n f o r m a b l y on t h e u p l i f t e d J u r a s s i c o r o g e n . They were i n v a d e d and h o r n f e l s e d by C r e t a c e o u s g r a n i t i c s t o c k s b e f o r e b e i n g t h r u s t n o r t h e a s t w a r d o v e r s t r a t a of t h e I n t e r m o n t a n e B e l t . M i d d l e - U p p e r C r e t a c e o u s s h o r t e n i n g and a s s o c i a t e d b r i t t l e s h e a r i n g a l o n g t h e S a n d i f e r Lake F a u l t Zone o c c u r e d i n a h i g h h e a t f l o w , b a c k - a r c s e t t i n g . The C e n t r a l G n e i s s Complex, Gamsby Group, and Gambier G r o u p ( ? ) were i m b r i c a t e d and t h r u s t o v e r I n t e r m o n t a n e B e l t r o c k s of t h e T e l k w a F o r m a t i o n . The i m b r i c a t e t e c t o n i c f r o n t was d i s r u p t e d , s u c c e s s i v e l y , , by s t r i k e - s l i p and d i p - s l i p f a u l t s i n L a t e C r e t a c e o u s t o e a r l y C e n o z o i c t i m e . The l a t e s t movement on h i g h a n g l e f a u l t s p o s t d a t e s E o c e n e i n t r u s i o n s , n e a r b y , and Eocene s t r a t a , i v r e g i o n a l l y , b u t p r e d a t e s M i o c e n e P l a t e a u b a s a l t s (Woodsworth 1979, 1980) . S e v e r a l d a t e d , c r o s s - c u t t i n g i n t r u s i v e s t o c k s i n t h e W h i t e s a i l Lake map a r e a (Woodsworth 1980), i n d i c a t e t h a t t h e S a n d i f e r Lake F a u l t Zone, j u x t a p o s i n g t h e C o a s t P l u t o n i c Complex and I n t e r m o n t a n e B e l t , had d e f i n i t e l y c e a s e d movement by Eocene t i m e and q u i t e p o s s i b l y by L a t e C r e t a c e o u s t i m e . V TABLE OF CONTENTS Page ABSTRACT i i LIST OF TABLES v i LIST OF FIGURES v i i ACKNOWLEDGEMENT v i i i CHAPTER 1 : INTRODUCTION 1 SCOPE AND PURPOSE OF.THESIS 1 LOCATION AND ACCESS 2 PHYSICAL FEATURES 4 PREVIOUS WORK 5 PRESENT WORK 6 CHAPTER 2 : DESCRIPTION OF MAP UNITS 8 STRATIFIED ROCKS 9 CENTRAL GNEISS COMPLEX 9 GAMSBY GROUP 25 LOWER CRETACEOUS (?) VOLCANIC AND SEDIMENTARY STRATA 42 PERMIAN, TRIASSIC AND JURASSIC STRATA 48 INTRUSIVE ROCKS 53 GRANITOID ROCKS 54 DYKES 57 CHAPTER 3 : GEOCHEMISTRY OF THE METAMORPHIC ROCKS 60 CHEMICAL ANALYSIS 60 CLASSIFICATION 60 TECTONIC SETTING OF THE METAVOLCANIC ROCKS 70 CHAPTER 4 : STRUCTURE 75 WESTERN DOMAIN 75 EASTERN DOMAIN 91 CHAPTER 5 : AGE RELATIONS AND GEOCHRONOLOGY OF THE METAMORPHIC ROCKS 95 CENTRAL GNEISS COMPLEX 96 GAMSBY GROUP 98 CHAPTER 6 : EVOLUTION OF THE UPPER TSAYTIS RIVER AREA 104 CHAPTER 7 : REGIONAL GEOLOGY 109 COAST PLUTONIC COMPLEX 109 INTERMONTANE BELT 122 CONCLUDING REMARKS 128 BIBLIOGRAPHY 131 APPENDIX 1 : XRF MAJOR ELEMENT ANALYSIS ON PRESSED POWDER PELLETS 139 APPENDIX 2 : MAJOR AND TRACE ELEMENT CHEMISTRY, CENTRAL GNEISS COMPLEX AND GAMSBY GROUP 155 APPENDIX 3 : GEOCHRONOLOGY : ANALYTICAL RESULTS AND TECHNIQUES 164 APPENDIX 4 : FOSSIL REPORTS 171 GEOLOGICAL MAPS in-pe&ke-t r vi LIST OF TABLES Page TABLE I : TABLE OF FORMATIONS AND MAP UNITS 10 TABLE II : MAJOR CONSTITUENTS OF 10 THIN SECTIONS, CENTRAL GNEISS COMPLEX 18 TABLE III : MAJOR CONSTITUENTS OF 27 THIN SECTIONS, GAMSBY GROUP 26 TABLE IV : PETROGRAPHIC CLASSIFICATION OF 26 THIN SECTIONS, TRIASSIC, JURASSIC AND LOWER CRETACEOUS STRATA AND ASSCOIATED INTRUSIVE ROCKS 59 TABLE V : SAMPLES AND CLASSIFICATION - CENTRAL GNEISS COMPLEX 65 TABLE VI : SAMPLES AND CLASSIFICATION - GAMSBY GROUP 66 TABLE VII : SUMMARY OF STRUCTURAL FEATURES, WESTERN DOMAIN 77 v i i LIST OF FIGURES Frontispiece Figure 1 2 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24" 25 26 27 28 29 30 31 32 Location of areas mentioned i n text Geological map and cross sections, upper Tsaytis River area Geological map of the West-Central Whitesail Lake area Sample locations, upper Tsaytis River area Folded migmatite, Central Gneiss Complex Banded mylonite, Gamsby Group F e l s i c mylonite, Gamsby Group Mafic mylonite, Gamsby Group Mylonitic granite, Gamsby Group Protomylonitic granodiorite, Gamsby Group Cobble gonglomerate, Lower Cretaceous (?) unit Volcanic breccia, Lower Cretaceous (?) unit Generalized s t r a t i g r a p h i c section, Lower Cretaceous (?) unit Stratigraphic section, Upper T r i a s s i c and Lower Jurassic units A l k a l i s - s i l i c a diagram, metavolcanic rocks T h o l e i i t i c vs. c a l c - a l k a l i n e discrimination p l o t s , Central Gneiss Complex artd Gamsby Group Normative color index vs. normative plagioclase composition, Central Gneiss Complex and Gamsby Group Nb/Y-Si0 2 and Z r / T i 0 2 - S i 0 2 diagrams, metavolcanic rocks Nb/Y-Zr/Ti0 2 diagram, metavolcanic rocks Normalized abundance patterns of incompatible trace elements i n meta-basalts Tectonic s e t t i n g discrimination diagrams, meta-basalts Homoclinal layering i n Gamsby Group Structural o r i e n t a t i o n s , Gamsby Group Structural o r i e n t a t i o n s , Central Gneiss Complex Orientation of c a t a c l a s t i c features and l a t e , high angle f a u l t s FI minor f o l d with i n c i p i e n t transposition f o l i a t i o n , Gamsby Group F2 disharmonic f o l d overprinting e a r l i e r deformed Gamsby Group Schematic representation of FI and F2 deformational features, western domain C a t a c l a s t i c shear zone / thrust f a u l t at base of Gamsby Group Sr evolution diagram, Central Gneiss Complex Sr evolution diagram, Gamsby Group Sr evolution diagram, mylonitic granite, Gamsby Group I 3 i n pocket^-oc. 3 i n pocketLcc-3 i n pocket 14 28 30 33 38 41 44 45 46 51 62 63 64 68 69 71 72 76 79 80 81 84 86 88 90 97 99 101 v i i i ACKNOWLEDGMENT I w o u l d l i k e t o a c k n o w l e d g e t h e e x c e l l e n t s u p e r v i s i o n g i v e n t o me d u r i n g a l l p h a s e s o f t h i s t h e s i s by R.L. A r m s t r o n g , of t h e U n i v e r s i t y of B r i t i s h C o l u m b i a . He was a l w a y s a v a i l a b l e f o r c h e e r f u l d i s c u s s i o n and much needed a d v i c e . From him I l e a r n e d t h e i n v a l u a b l e l e s s o n t h a t one c a n c l e a n o ut a p o t of camp ' g l o p ' w i t h a s much f i n e s s e a s one wo u l d a c o n t a i n e r of m i n e r a l s e p a r a t e . I am v e r y much i n d e b t e d t o G. Woodsworth, o f t h e G e o l o g i c a l S u r v e y o f Canada, who f i r s t i n t r o d u c e d me t o t h e wonders of t h e C o a s t M o u n t a i n s . W i t h o u t h i s f r i e n d s h i p , i n s p i r a t i o n and h e l p i n i n n u m e r a b l e ways, t h i s study, would n o t have been p o s s i b l e . R.L. A r m s t r o n g and G. Woodsworth c r i t i c a l l y r e v i e w e d p r e l i m i n a r y d r a f t s o f t h i s t h e s i s . F i e l d w o r k i n t h e C o a s t M o u n t a i n s would have been i m p o s s i b l e w i t h o u t t h e s u p p o r t I r e c e i v e d f r o m my f i e l d a s s i s t a n t s , Ken Brown o f P e t e r b o r o u g h , O n t a r i o , and R o b e r t K e l l y , o f V a n c o u v e r . T h e i r company p r o v e d i n d i s p e n s i b l e , e s p e c i a l l y d u r i n g l o n g , c l o u d - h i d d e n s p e l l s . G r a t e f u l acknowledgment i s made f o r o c c a s i o n a l l o d g i n g , f o o d , and t r a n s p o r t a t i o n t o Mr A. K u b i k , Mrs J . G i p p s and t o A l c a n , Kemano. At t h e Department of G e o l o g i c a l S c i e n c e s I b e n e f i t t e d t r e m e n d o u s l y from t h e h e l p and a d v i c e o f many p e o p l e . M a r t i n E n g i , S t a n y a H o r s k y , Ed Montgomery, Graham N i x o n , Randy P a r r i s h and K r i s t a S c o t t , h e l p e d and e n c o u r a g e d me a t v a r i o u s s t a g e s of t h i s t h e s i s . F i n a l l y , I would l i k e w i t h a l l my h e a r t t o a c k n o w l e d g e t h e s u p p o r t and p a t i e n c e of my w i f e , E l i a n H a l p e n n y . 1 CHAPTER 1 : INTRODUCTION SCOPE AND PURPOSE OF THESIS The C o a s t P l u t o n i c Complex i s a c o m p o s i t e b e l t o f g r a n i t o i d and m e t a m o r p h i c r o c k s w h i c h e x t e n d s from t h e F r a s e r V a l l e y i n t o t h e Yukon and A l a s k a ( i n s e t F i g . 1 ) . I t i s f l a n k e d on t h e e a s t by t h e I n t e r m o n t a n e B e l t , composed o f e s s e n t i a l l y unmetamorphosed v o l c a n i c and s e d i m e n t a r y r o c k s . T h i s t h e s i s i s a s t u d y o f t h e boundary between t h e s e two major g e o l o g i c a l b e l t s i n t h e w e s t - c e n t r a l W h i t e s a i l L a k e a r e a , B r i t i s h C o l u m b i a . The f i v e g e o l o g i c a l b e l t s o f t h e C a n a d i a n C o r d i l l e r a r e s u l t e d f r o m i n t e r a c t i o n s between d i s c r e t e t e c t o n o -s t r a t i g r a p h i c t e r r a n e s i n M e s o z o i c and T e r t i a r y t i m e (Monger and P r i c e 1979; Monger e t a l . 1982). The b o u n d a r i e s between some o f t h e t e r r a n e s a p p e a r t o be more or l e s s i n d e p e n d e n t o f t h o s e between t h e g e o l o g i c a l b e l t s . F o r i n s t a n c e , t h e p r e s e n t c h a r a c t e r of t h e C o a s t P l u t o n i c Complex may be t h e r e s u l t o f complex M e s o z o i c and C e n o z o i c p l u t o n i c and metamorphic o v e r p r i n t i n g of two i n i t i a l l y s e p a r a t e t e c t o n o - s t r a t i g r a p h i c t e r r a n e s (Woodsworth and T i p p e r 1980). In t h e s o u t h e r n C o a s t M o u n t a i n s t h e C o a s t P l u t o n i c Complex i s s u p e r i m p o s e d on W r a n g e l l i a , a P a l e o z o i c t e r r a n e w i t h h i g h l y anomalous M e s o z o i c p a l e o l a t i t u d e s ( Y o l e and I r v i n g 1980). The p r e - C e n o z o i c r o c k s of t h e C o a s t P l u t o n i c Complex i n t h e m o u n t a i n s n o r t h o f B e l l a C o o l a b e l o n g t o a t e r r a n e w h i c h a t t h e p r e s e n t t i m e r e m a i n s u n d e f i n e d r e l a t i v e t o n e i g h b o u r i n g t e r r a n e s . F u r t h e r n o r t h , t h e e a s t e r n C o a s t P l u t o n i c Complex a p p e a r s t o have o v e r p r i n t e d S t i k i n i a , an e x t e n s i v e P a l e o z o i c t e r r a n e w h i c h , l i k e W r a n g e l l i a , i s 2 allochtonous with respect to neighbouring cratonic North America (Monger and Irving 1980). S t i k i n i a probably underlies the Intermontane Belt in the Whitesail Lake area, but i t s relations with the Coast Plutonic Complex were not known before the most recent geological investigations in the area. In general, a clear understanding of the boundary relations between the two geological belts i s needed in order to place the Coast Plutonic Complex in a regional tectonic framework. Remapping of the Whitesail Lake area (Woodsworth 1979a) has indicated that the boundary between the Coast Plutonic Complex and the Intermontane Belt at this l a t i t u d e is a complex fault zone along which metamorphosed pre-Jurassic strata were juxtaposed against e s s e n t i a l l y unmetamorphosed Jurassic and younger volcanic and sedimentary rocks. In order to study this f a u l t zone and the stratigraphic relations between the bordering terranes, an area in the upper part of the Tsaytis River drainage system, south of Sandifer Lake, has been mapped in d e t a i l . Here the t r a n s i t i o n between the Coast Plutonic Complex and the Intermontane Belt i s well exposed. LOCATION AND ACCESS The study area i s located between latitudes 53°24'48" N and 53031'10" N and longitudes 127031'15" W and 127°45'35" W, approximately 580 km northwest of Vancouver, B.C. (Fig. 1 ) . A logging road connecting nearby Tahtsa Lake with the v i l l a g e of Kemano (Alcan power station) and Gardner Canal passes through a va l l e y in the northern part of the study area. Kemano i s reached 3 F i g . 1 Location of areas mentioned in text 4 by Alcan launch from Kitimat or floatplane from Terrace. Short spur roads on the logging road give limited access to the lower slopes of the v a l l e y . With some e f f o r t the entire study area is accessible on foot during the summer months, but backpacking for any extended mapping project i s not p r a c t i c a l due to the ruggedness of the terrane and dense coastal vegetation at lower a l t i t u d e s . For e f f i c i e n t study the area is best reached by helicopter from Terrace or Houston. PHYSICAL FEATURES The Tsaytis River area straddles the eastern edge of the Coast Mountains and the t r a n s i t i o n a l zone with the Interior Plateau to the east. Elevations range from about 550 meters in the Tsaytis River valley to 2309 meters on 'Khawachen Mtn.' (informal name pending approval by the Canadian Permanent Committee on Geographical Names). The rugged western and southern parts of the study area, with their deeply incised g l a c i a l v a l l e y s , are t y p i c a l of Coast Mountain physiography. Many of the mountain walls are accessible only with mountaineering techniques. Average r e l i e f in these areas i s 1250 meters. In the north-eastern part of the study area r e l i e f i s less pronounced, averaging about 600 meters, and a l l ridge slopes are accessible without d i f f i c u l t y . Along the ridges above tre e l i n e exposures are generally excellent, especially where recent g l a c i a l a c t i v i t y has scoured the surface. Since most outcrops are located above the alpine t r a n s i t i o n zone, geological mapping i s naturally biased toward these areas. About 40% of the area is covered by g l a c i e r s , 5 i c e f i e l d s and Quaternary cover. Timberline i s at approximately 1100 meters. Below the alpine t r a n s i t i o n zone, a dense cover of coniferous forest and underbrush impede geological mapping. In the Tsaytis River valley two stretches of canyon are v i r t u a l l y inaccessible. Two prominent gl a c i e r s are present within the study area. The g l a c i e r originating on the north side of 'Khawachen Mtn.' covers bedded outwash or kame gravels, which together with three d i s t i n c t terminal ridges in the outwash valley record a recent multistage history. G l a c i a l s t r i a e are generally abundant, but were not measured. Boulder-size e r r a t i c s of eastern provenance in the metamorphic terrane of the western part of the map area indicate some ice movement from the north or east during the Pleistocene. A p r e - g l a c i a l erosion surface i s evident in low r e l i e f remnants along the ridges west of the Tsaytis River at approximately 1200 meters elevation. The study area i s crossed by a major drainage divide in the northeastern corner. Creeks draining to the east are part of the Nechako drainage system, which feeds into the Fraser River. A l l other creeks are part of the Tsaytis and Kemano drainage systems, which feed d i r e c t l y into the sea in Gardner Canal. PREVIOUS WORK L i t t l e geological work was done in the general area prior to the present study. D u f f e l l f i r s t mapped the Whitesail Lake map area between 1947 and 1952 (D u f f e l l 1959), but did not cover large parts of the Coast Mountains due their i n a c c e s s i b i l i t y . The area immediately north of the present study area was mapped 6 in some d e t a i l by Stuart between 1952 and 1954, during construction of the Mean tunnel from Tahtsa Lake to Kemano (Stuart 1960). The f i r s t coverage of the present study area, by Read (unpubl rep.) in 1963, generated some interest due to the discovery of Permian f o s s i l s close to the Coast Plutonic Complex. Read recognized that the t r a n s i t i o n from unmetamorphosed volcanic rocks in the east to schists and gneisses in the west required detailed study. The area received no further study u n t i l 1977, when Woodsworth commenced remapping of the Whitesail Lake map area (Woodsworth 1978). This project was completed the following year (Woodsworth 1979a) and resulted in the publication of a second generation 1:250,000 scale preliminary map (Woodsworth 1980). PRESENT WORK Preliminary examination of parts of the thesis area occurred during the summer of 1978, when I was employed by the Geological Survey of Canada and assisted in remapping the Whitesail Lake map area. Five days were spent investigating metamorphic rocks of the Coast Plutonic Complex and volcanic rocks of the Intermontane Belt. During the 1979 and 1980 f i e l d seasons, a t o t a l of three months were spent mapping the area at a scale of 1:25,000, using a e r i a l photographs (BC Government Low Level series BC 7738, July 1975 and BC 7805, Sept. 1975). Emphasis was on determining structural and stratigraphic relations between the Coast Plutonic Complex and the Intermontane Belt and on defining the 7 nature and age relations of the Coast Plutonic Complex l i t h o l o g i e s . L i t t l e time was spent on study of metamorphism in the area. Forty six traverses were made, covering about 115 km2. Approximately 620 hand specimens were col l e c t e d , from which 64 thin sections were prepared by B. Cranston. Two rock samples were prepared for hornblende K/Ar dating, 22 for whole-rock Rb/Sr analyses, and approximately 80 kg of metavolcanic rock were processed to recover zircons for U/Pb dating. Thirty eight samples were analysed for major elements, 27 for trace elements. As part of t h i s thesis, procedures for major element analysis on pressed powder p e l l e t s were established in cooperation with S. Horsky and K. Fletcher. A computer program was developed to reduce the data generated by XRF-spectrometry. A n a l y t i c a l procedures and the computer program are included in Appendix 1. A geological map of the field-area (Fig. 2) was compiled using a Bausch and Lomb stereo transfer scope. Using additional f i e l d data kindly supplied by G. Woodsworth of the Geological Survey of Canada, and a variety of other sources, a 1:100,000 scale map (Fig. 3) comprising four 1:50,000 map-sheets (NTS 93E5, 93E6, 93E11, 93E12) was prepared, in order to show the thesis area in a regional framework. 8 CHAPTER 2 : DESCRIPTION OF MAP UNITS The western and southern parts of the map area (Fig. 2) are underlain by a metamorphic terrane composed predominantly of amphibolite facies gneisses and migmatites of the Central Gneiss Complex and greenschist facies metavolcanic and metaplutonic rocks belonging to the Gamsby Group (Woodsworth 1978). The Central Gneiss Complex extends beyond the map area to the northwest , west and south for many kilometers. In the eastern part of the map area altered and l o c a l l y hornfelsed, but otherwise unmetamorphosed volcanics and sediments form two d i s t i n c t assemblages possibly c o r r e l a t i v e with the Gambier Group (Woodsworth and Tipper 1980) and Hazelton Group (Tipper and Richards 1976a) respectively. A wide variety of intrusive rocks are present in both parts of the map area. A l l boundaries between the four groups mentioned above are fau l t s belonging to a major, complex fault zone. This zone is here c a l l e d the Sandifer Lake Fault Zone, following the name Woodsworth (1978) used for a high angle fault separating penetratively deformed Gamsby Group rocks from unmetamorphosed volcanic breccia just west of 'Khawachen Mtn.'. The Sandifer Lake Fault Zone, as w i l l be discussed l a t e r , i s primarily a zone of major, easterly to northeasterly directed thrusting, overprinted by later folding, high angle f a u l t i n g and intrusion of plutonic rocks and dyke swarms. Within t h i s zone, the Gamsby Group i s p a r t i c u l a r l y important as i t c o n t a i n s : s i g n i f i c a n t amounts of mylonitic and c a t a c l a s t i c rocks and has evidently been the locus of 9 c o n s i d e r a b l e t e c t o n i c f l a t t e n i n g and a s s o c i a t e d inhomogeneous s h e a r i n g . I t s p o s i t i o n between a h i g h g r a d e g n e i s s i c and m i g m a t i t i c t e r r a n e and e s s e n t i a l l y unmetamorphosed v o l c a n i c and s e d i m e n t a r y s t r a t a has i m p o r t a n t i m p l i c a t i o n s , d i s c u s s e d l a t e r i n t h i s t h e s i s , f o r t h e t e c t o n i c h i s t o r y o f t h i s r e g i o n . I n t h i s c h a p t e r t h e r o c k u n i t s a r e d e s c r i b e d i n d e t a i l . S t r a t i f i e d r o c k s a r e d i s c u s s e d f i r s t , i n o r d e r o f d e c r e a s i n g m e t a m o r p h i c g r a d e from west t o e a s t . I n t r u s i v e r o c k s are" d i s c u s s e d n e x t . Map u n i t s a r e t a b u l a t e d i n T a b l e I , and u n i t symbols a r e i n c l u d e d i n t h e t e x t f o r c r o s s r e f e r e n c e w i t h F i g u r e 2. Age r e l a t i o n s of metamorphic r o c k s a r e d i s c u s s e d i n C h a p t e r 5. P e t r o g r a p h i c c l a s s i f i c a t i o n s of most r o c k u n i t s a r e i n c l u d e d i n T a b l e s IV, V, and V I . STRATIFIED ROCKS CENTRAL GNEISS COMPLEX The main l i t h o l o g i e s of t h e C e n t r a l G n e i s s Complex a r e i r r e g u l a r l y l a y e r e d g n e i s s i c q u a r t z d i o r i t e t o g r a n o d i o r i t e , and banded a m p h i b o l i t e . L e s s e r amounts o f l e u c o g n e i s s , c a l c - s i l i c a t e s k a r n , m e t a - c a r b o n a t e and r a r e , s c h i s t o s e m e t a p e l i t e a r e l o c a l l y i n t e r l a y e r e d w i t h t h e a m p h i b o l i t e s . In many i n s t a n c e s t h e g n e i s s e s a r e m i g m a t i t i c ( F i g . 5 ) , c o n t a i n i n g a p p r e c i a b l e amounts of i n t e r l a y e r e d , l e n t i c u l a r and p o d l i k e m e t a p l u t o n i c m a t e r i a l w h i c h i s q u i t e o f t e n c o u r s e g r a i n e d and p e g m a t i t i c . A wide v a r i e t y of p o s t - k i n e m a t i c p l u g s and d y k e s have i n t r u d e d t h e meta m o r p h i c r o c k s . C o n t a c t s between t h e g r a n i t o i d g n e i s s e s and t h e 10 TABLE 1 : TABLE OF FORMATIONS AND MAP UNITS Period, epoch or stage Formation Map unit Lithology Thickness (m) Pleistocene and recent G l a c i a l , a l l u v i a l and f l u v i a l deposits v a r i a b l e , usually small Unconformable contact POST-THRUST INTRUSIVES Te r t i a r y -Upper Cretaceous Diabase and lamprophyre dykes -M i c r o d i o r i t e (plugs) -Intrusive contacts with older units Cretaceous KI Micrographic granite and associated dykes -K2 Pink granodiorite -K3 Muscovite leuco-granite -Intrusive contacts PRE -THRUST INTRUSIVES Albian(?) aK Altered granodiorite, minor pegmatite; l o c a l l y strongly c a t a c l a s t i c -Agmatite -Intrusive and f a u l t contacts with Hauterivian(?) s t r a t a ; thrust contact with Gamsby Group and Telkwa Formation Hauterivian(?) Augite porphyry s i l l s and dykes -Intrusive contact with Central Gneiss Complex STRATA FORMING HANGINGWALL OF THRUST COMPLEX Hauterivian(?) Gambier Group (?) 1K1 Maroon and red t u f f s , t u f f - b r e c c i a s and minor flows 175-200 1K2 Conglomerate, sandstone and shale 50-70 1K3 Green, pale green and red breccia, t u f f and flows; minor sandstone and shale up to 300 Thrust contact with Telkwa Formation and Gamsby Group Cretaceous or Jurassic JK Altered m i a r o l i t i c granite -Not i n contact Synmetamorphic in t r u s i v e s Mylonitic granite 75-100 (continued on next page) TABLE 1 (continued) 11 Period, epoch or stage Formation Map unit Lithology Thickness (m) Jurassic and older(?) Intrusive component of Gamsby Group Jg2 Amphibolite 20-30 Jg3 Protomylonitic grano-d i o r i t e (also l o c a l l y present i n Pcgl) 150-175 Jg4 Protomylonitic grano-d i o r i t e / q u a r t z d i o r i t e 50-75 Jg5 Mylonitic q u a r t z d i o r i t e ? Sheared (mylonitic} and interlayered ( l i t - p a r - l i t ) contacts with meta-volcanic rocks of Gamsby Group Central Gneiss Complex Jcg I r r e g u l a r l y banded granodiorite/quartz-d i o r i t e gneiss up to 300 Migmatitic contact with amphibolites and leuco-gneisses of Central Gneiss Complex STRATA FORMING FOOTWALL OF THRUST COMPLEX Sinemurian(?) Telkwa Formation 1J Red and maroon mudstone, s i l t s t o n e and polymictic conglomerate interlayered with green t u f f s and tuff-breccias'" minimum 75-100, possibly up to 1 km Probable erosional unconformity Upper T r i a s s i c uTl Green and purple volcanic breccia and minor flows 60-100 uT2 Green volcanic b r e c c i a , minor interbedded lime-stone; contains Lower Permian limestone c l a s t s 125-180 uT3 Shale and s i l t s t o n e , minor interbedded flows or s i l l s and massive limestone 115-150 Unconformable or 'olistostromal' contact Lower Permian Possible o l i s t o l i t h s i n Telkwa Formation and in Upper T r i a s s i c volcanics and sediments IP Grey limestone, t h i n bedded limestone, dolomitic limestone with chert nodules 100-150 Older rocks not exposed nearby STRATA FORMING UPPER PART OF HANGINGWALL OF THRUST COMPLEX; POSSIBLE BASEMENT FOR HAUTERIVIAN(?) VOLCANICS AND SEDIMENTS Permian and older (?) Gamsby Group Pgl Banded mylonites, sc h i s t s and p h y l l i t e s possibly up to i km Pg2 F e l s i c mylonite 25-50 Thrust contact (continued on next page) TABLE 1 (continued) 12 Period, epoch or stage Formation Map unit Lithology Thickness (m) Permian and older (?) Central Gneiss Complex Pcgl Banded amphibolite and leucogneiss 300-400 Pcg2 Meta-carbonate, c a l c -s i l i c a t e and minor meta-pelite up to 75 1 3 a m p h i b o l i t e s a r e g e n e r a l l y g r a d a t i o n a l t h r o u g h z o n e s o f s e m i -c o n c o r d a n t l i t - p a r - l i t i n t e r f i n g e r i n g , i n some c a s e s combined w i t h t h e p r e s e n c e of a g m a t i t e . L o c a l l y , f o l i a t e d a m p h i b o l i t i c b l o c k s i n t h e a g m a t i t e s a r e r o t a t e d w i t h r e s p e c t t o t h e f o l i a t i o n i n t h e i n t r u d i n g , g r a n i t o i d m a t e r i a l . On t h i s b a s i s , a t l e a s t some o f t h e g n e i s s i c p l u t o n i c r o c k s a r e e i t h e r p o s t -t e c t o n i c r e l a t i v e t o e a r l y f o l i a t i o n s , or s y n - t e c t o n i c , p r e s e r v i n g e a r l y d e f o r m a t i o n a l f e a t u r e s i n t h e i r x e n o l i t h s . T a b l e I I l i s t s t h e major c o n s t i t u e n t s o b s e r v e d i n 10 t h i n s e c t i o n s of t h e g r a n i t o i d g n e i s s e s and a m p h i b o l i t e s . G n e i s s i c q u a r t z d i o r i t e / g r a n o d i o r i t e ( J c g ) G n e i s s i c p l u t o n i c r o c k s o c c u r i n t h e f i e l d a s r e l a t i v e l y homogeneous, g r e y , l o c a l l y i r r e g u l a r l y banded l a y e r s r a n g i n g up t o 2 m i n t h i c k n e s s , and v e r y t h i c k , t a b u l a r o r l e n t i c u l a r b o d i e s e n c l o s e d w i t h i n t h e a m p h i b o l i t e / c a l c - s i l i c a t e / m e t a - p e l i t e s e q u e n c e . They a r e o f t e n a s s o c i a t e d , p o s s i b l y g e n e t i c a l l y , w i t h i r r e g u l a r l a y e r s and l e n s e s o f c o u r s e g r a i n e d , p i n k w e a t h e r i n g , p r e - as w e l l as p o s t k i n e m a t i c p e g m a t i t e and f i n e g r a i n e d , l o c a l l y d i s c o r d a n t b i o t i t e q u a r t z d i o r i t e g n e i s s . T h e s e o c c u r i n t h e n e i g h b o u r i n g a m p h i b o l i t e as w e l l , and i n b o t h u n i t s t h e p e g m a t i t e s a r e commonly f o l d e d and b o u d i n a g e d . I t i s n o t known i f t h e p e g m a t i t i c and g r a n i t o i d g n e i s s e s r e p r e s e n t p a r t i a l m e l t s d e r i v e d from t h e a m p h i b o l i t e s . Such an o r i g i n i s c o n s i d e r e d p r o b a b l e f o r a t l e a s t some o f t h e l e u c o c r a t i c m a t e r i a l . E x t e n s i v e p a r t i a l m e l t i n g and m o b i l i z a t i o n of t h e C e n t r a l G n e i s s Complex has been d e s c r i b e d by H u t c h i s o n (1982) i n t h e P r i n c e R u p e r t a r e a . F I G U R E 5 F o l d e d m i g m a t i t e , C e n t r a l G n e i s s C o m p l e x 1 5 Some of the g r a n i t o i d g n e i sses c o n t a i n o v a l shaped, ghost-l i k e i n c l u s i o n s up to 60 cm i n le n g t h , o r i e n t e d p a r a l l e l to the banding. Elsewhere, numerous f o l d e d and boudinaged l e n s e s and screens of amphibolite w i t h i n the g r a n i t o i d g n e i s s range up to 10 m i n l e n g t h . M i c r o s c o p i c a l l y these rocks are c h a r a c t e r i z e d by t h e i r f i n e g r a i n s i z e (<1 mm.), although some specimens c o n t a i n f e l d s p a r , amphibole and opaque m i n e r a l s up to 3.5 mm a c r o s s . Textures are dominantly g r a n o b l a s t i c and eq u i d i m e n s i o n a l . A f a i n t f o l i a t i o n i s d e f i n e d by p r e f e r r e d o r i e n t a t i o n of mafic m i n e r a l s , and to a l e s s e r extent by t h i n , l e n t i c u l a r q u a r t z - f e l d s p a r aggregates. In outcrop the mafic minerals tend to be somewhat segregated i n t o i r r e g u l a r l a y e r s up to 30 cm i n t h i c k n e s s . A l l samples show evidence of minor m i c r o s c o p i c deformation (mainly s t r a i n e d q u a r t z ) , and a few are m y l o n i t i c . The composition of these rocks v a r i e s from quartz d i o r i t e to g r a n o d i o r i t e . P l a g i o c l a s e and quartz occur i n approximately equal amounts, c o n s t i t u t i n g up to 60% of the mode. P l a g i o c l a s e composition ranges from A n 2 8 - A n 3 3 . The g r a i n s are anhedral, more r a r e l y s ubhedral. A l t e r a t i o n to s e r i c i t e , c a l c i t e and l e s s e r e p i dote i s common and l o c a l l y q u i t e pronounced. P o l y s y n t h e t i c twinning i s g e n e r a l l y w e l l developed, but i n many i n s t a n c e s i t i s very p o o r l y v i s i b l e and appears to have been l a r g e l y o b l i t e r a t e d . In these cases the r e f r a c t i v e i n d i c e s are compatible with a l b i t e compositions. These f e a t u r e s suggest r e t r o g r e s s i o n from c a l c i c to l e s s c a l c i c v a r i e t i e s . Quartz occurs i n s i n g l e , anhedral g r a i n s and i n l e s s abundant, f a i n t l y l e n t i c u l a r , p o l y g o n i z e d aggregates. A l l 16 individual grains are undulose. In mylonitic gneisses most of the quartz i s polygonized and forms well-developed l e n t i c u l a r aggegates, in which a few irregular strained domains represent r e l i c s of the o r i g i n a l grains. Myrmekite i s common only in the mylonitic gneisses. Potassium feldspar constitutes up to 20% of the mode. Generally i t occurs as anhedral grains in granular association with quartz, but l o c a l l y i t forms large pink augen. S e r i c i t i c a l t e r a t i o n i s widespread and gives the grains a rather cloudy appearance. Microcline cross-hatching and p e r t h i t i c exsolution lamellae are well developed only in the mylonitic gneisses. B i o t i t e i s the dominant mafic phase. Normally i t i s completely altered to c h l o r i t e and ilmenite, and i s associated with minor epidote. Locally however, red-brown pleochroic flakes are preserved, commonly containing sagenite inclusions. Some flakes have a pale brown to o l i v e brown pleochroism, and are intermediate in appearance between red-brown (fresh) and c h l o r i t i z e d (retrograde) b i o t i t e . Hornblende forms up to 15% of the mode in some specimens, but generally accounts for less than 5%. Pleochroism is usually from yellowish to olive-green, but in some specimens a more blue-green colour is present. Locally i t i s somewhat altered to c h l o r i t e and associated with small grains of secondary epidote. Garnet i s a minor component in some granitoid gneisses, forming small, subidioblastic grains. In the mylonitic gneisses i t forms f a i r l y large, xenoblastic grains with d i s t i n c t i v e p u l l -apart cracks at high angles to the mylonitic f o l i a t i o n . Chlorite and microcline have c r y s t a l l i z e d within these fractures. 17 Sphene i s conspicuous in most of the granitoid gneisses, forming up to 5% of the mode. It forms scattered, subhedral to rounded grains, generally about 0.3 mm across. Sphene appears to be absent in the mylonitic gneiss. Small grains of subhedral apatite and tiny, euhedral zircon needles occur in accessory amounts in a l l granitoid gneisses. Amphibolite and leucogneiss (Pcg1) Included under t h i s heading are a l l gneissic rocks not of plutonic o r i g i n , containing large proportions of hornblende, and fine grained leucogneiss, with which these rocks are frequently interlayered. The presence of a wide range in composition and texture somewhat complicates a general description of this unit. The coarse grained v a r i e t i e s of amphibolite tend to be d i o r i t i c in composition and commonly contain hornblende porphyroblasts up to several cm in length. In contrast, the finer grained rocks (<2 mm) contain appreciable amounts of quartz, b i o t i t e and garnet in addition to hornblende and plagioclase. In the f i e l d the rocks are frequently banded. The bands, which are defined by varying amounts of mafic minerals, may represent o r i g i n a l stratigraphic layers, metamorphic-tectonic d i f f e r e n t i a t i o n , or both. They are p a r a l l e l to stratigraphic contacts with interbedded marble and c a l c - s i l i c a t e layers, and are quite consistent along s t r i k e . In contrast, the banding in granitoid gneisses is i r r e g u l a r . Bands in amphibolite range from a few cm to several m in thickness. Locally, p a r t i c u l a r l y in the western part of the map area, the amphibolites are migmatitic. Here they interfinger with abundant pegmatitic and granitoid gneiss, which together form crj ro x> ro o> ro i LO LO • • LO 1 o i CN 1 00 LO i O OO 1 O OO o 00 I O 00 i o 00 l o 00 1 o 00 o 00 o 00 o 00 QUARTZ M M M M M M M M M M PLAGIOCLASE M M M P M M M M M M K-FELDSPAR P P M P ? HORNBLENDE m P P M M M M M P EPIDOTE/CLINOZOISITE r r r r ? r P P CHLORITE r r r r r r r r r MUSCOVITE A ) P BIOTITE P P P P m P P GARNET m m P P P P RUTILE m t t SPHENE m m t ni t APATITE t t t t t m t m m ZIRCON t t t OPAQUES UNDIF. m m m m m m m m m m TABLE II Major constituents of 10 t h i n sections, Central Gneiss Complex. Sample locations marked on Figure 4. Petrographic and chemical c l a s s i f i c a t i o n i n Table V. M major constituent; p mineral i s present; m minor constituent; r retrograde; t trace *) . . . . ' the majority of these specimens contain very f i n e s e r i c i t e flakes i n plagioclase and K-feldspar i—» 00 19 more than 60% of the outcrops. Mesoscopic structures are commonly chaotic, with amphibolite blocks and screens randomly oriented in f o l i a t e d muscovite pegmatites. Younger, crosscutting granitoid material and undeformed pegmatite are present as well and considerably complicate relationships between various units. Large, randomly oriented hornblende c r y s t a l s are developed in these zones. Toward their base, which i s a d i s t i n c t , south-southwesterly dipping thrust f a u l t , the gneissic rocks l o c a l l y grade from grey, banded amphibolites into fine grained, massive, dark green, epidote-bearing rocks. These somewhat resemble Gamsby Group l i t h o l o g i e s but are coarser grained. Elsewhere near the base the amphibolites interfinger with sheets of proto-mylonitic granitoid material (Jg3) similar to that occurring in the upper part of the Gamsby Group. In these areas the amphibolites themselves are l o c a l l y d i s t i n c t l y mylonitic. The mylonitic f o l i a t i o n i s defined by elongate quartz grains and ribbons, which are in part derived from quartz v e i n l e t s . Hornblende forms up to 40% of the mode, is generally i d i o b l a s t i c to subidioblastic and t y p i c a l l y shows a strong linear preferred orientation. Pleochroism i s yellowish to o l i v e -green, but some specimens contain s l i g h t l y bluish-green v a r i e t i e s . Some hornblende porphyroblasts are corroded by quartz and plagioclase, and the larger c r y s t a l s are commonly p o i k i l o b l a s t i c . Alteration to c h l o r i t e i s minimal and mostly the hornblende i s quite free of a l t e r a t i o n and inclusions. Plagioclase occurs as xenoblastic and subidioblastic grains. Compositions generally range from An a 6-An 5 8 at higher 20 st r u c t u r a l l e v e l s , but near the base of the sequence the amphibolitic gneisses are di f f e r e n t and contain only a l b i t e and olig o c l a s e . Locally some of the plagioclase i s s l i g h t l y zoned, and almost a l l grains show well developed a l b i t e and p e r i c l i n e twinning. Plagioclase i s occasionally s l i g h t l y saussuritized. It t y p i c a l l y forms about 30% of the amphibolite mode. B i o t i t e i s absent from most amphibolites, but l o c a l l y forms up to 5% of the mode. It is mostly altered to c h l o r i t e , s e r i c i t e and ilmenite. Small, red-brown pleochroic, r e l i c t flakes are present in several specimens. Quartz generally occurs in small, xenoblastic grains in association with plagioclase. Their combined texture i s t y p i c a l l y granoblastic. Quartz forms up to 40% of the mode. Coarser grains of quartz occur in lenses and patches which are probably derived from pre-or synkinematic v e i n l e t s . A l l quartz is undulose and in some specimens i t forms elongate grains and polygonized aggregates, r e f l e c t i n g the onset of mylonite formation. Garnet occurs as porphyroblasts up to several cm in diameter in many of the amphibolites, although i t i s absent in others. Most garnets are strongly p o i k i l o b l a s t i c , and they are frequently fractured at high angles to the f o l i a t i o n . Retrogression to a fine grained aggregate of c h l o r i t e , e p i d o t e / c l i n o z o i s i t e and opaques in some specimens from near the base of the sequence has almost completely obl i t e r a t e d the o r i g i n a l garnets. In some specimens r e c r y s t a l l i z e d quartz-rich pressure shadows occur marginal to many garnets, in others polygonized quartz ribbons c l e a r l y wrap around them. Some 21 specimens contain garnets surrounded by thin quartz coronas. A few garnets contain S-shaped inclusion t r a i l s of quartz. Less abundant minerals include orthoclase, muscovite, e p i d o t e / c l i n o z o i s i t e , sphene, r u t i l e ( l o c a l l y as cores in garnet), apatite, zircon and opaques. Most of the epidote i s secondary after mafic minerals (hornblende and b i o t i t e ) and l o c a l l y forms crosscutting v e i n l e t s , which are probably healed extension fractures. In a few places i t forms layers up to 10 cm thick. These are folded and boudinaged. In one specimen from near the base of the gneissic sequence, leucocratic layers contain about 20% epidote in granoblastic association with plagioclase and quartz. Here the epidote evidently forms part of the metamorphic assemblage. 'Metamorphic' epidote i s absent higher up in the sequence. The leucocratic layers within the amphibolite unit are fine grained (average <0.3 mm) and, due to their low mafic content, less well f o l i a t e d than the amphibolites. Crosscutting relations between the amphibolite and leocogneiss establish an intrusive o r i g i n for at least some of these rocks, but many of the concordant layers could well have been derived from primary, interlayered f e l s i c material. The main minerals are quartz and feldspar, in roughly equal proportions, forming a fine grained granoblastic mosaic. Together they constitute approximately 60% of the mode. The feldspar i s at least in part a l b i t i c , but since most grains are untwinned and considerably altered to white mica and nondescript cloudy material, exact compositions cannot be readily determined, and some of thi s material may in fact be potassium 22 feldspar. Some feldspar grains contain myrmekitic intergrowths of quartz. Chlorite and epidote form about 25% of the leucogneiss mode and define a faint f o l i a t i o n in the form of thin, irregular s t r i n g e r s . The c h l o r i t e i s most l i k e l y retrogressive after b i o t i t e . The remainder of the rock i s composed of secondary c a l c i t e , accessory sphene and apatite, and in some specimens conspicuous, macroscopically v i s i b l e grains of magnetite. Below the carbonate layer on the f i r s t bench west of the Tsaytis River, the leocogneisses contain approximately 15% corroded garnets, up to 3 mm in size, surrounded by r e c r y s t a l l i z e d quartz coronas. These rocks, although leococratic, contain mineral assemblages resembling those in neighbouring amphibolites. In a l l li k e l i h o o d they represent o r i g i n a l interlayered material. Metacarbonate and c a l c - s i 1 i c a t e layers (Pcg2) Metacarbonate, which provides excellent marker horizons within the gneissic terrane, occurs as layers up to 75 m thick. Three such layers are present within the map area. Frequently they appear to be only s l i g h t l y r e c r y s t a l l i z e d , and within some of these layers rare c r i n o i d stems have been found (Woodsworth personal communication). Locally the carbonates have been converted to coarse grained c a l c - s i 1 i c a t e skarns, p a r t i c u l a r l y in the more migmatitic areas, where they are often intruded by pegmatites. The skarns are macroscopically characterized by the metamorphic assemblage garnet-diopside-tremolite-calcite. Wollastonite i s l o c a l l y present adjacent to postkinematic granitoid plugs. 23 The most p r e v a l e n t v a r i e t y o f c a r b o n a t e i s t h i n l y banded and l a m i n a t e d and c o n t a i n s s t r i n g e r s and l e n s e s o f brown w e a t h e r i n g , g r i t t y s i l i c e o u s m a t e r i a l a r r a n g e d p a r a l l e l t o t h e f o l i a t i o n . In w e a t h e r e d o u t c r o p t h e s e s i l i c e o u s s t r i n g e r s s t a n d o u t a g a i n s t l e s s r e s i s t a n t c a r b o n a t e . The b a s a l p a r t o f t h e c a r b o n a t e l a y e r w hich c r o p s o u t a b o u t 4 km w e s t - n o r t h w e s t of 'Khawachen Mtn.' i s a c l e a n , m a s s i v e , g r e y - b l u e m a r b l e , composed a l m o s t e n t i r e l y o f c a l c i t e . M e t a - p e l i t i c r o c k s A s s o c i a t e d and i n t e r b e d d e d w i t h m a r b l e and s k a r n l a y e r s w i t h i n t h e a m p h i b o l i t e u n i t a r e m i n o r amounts of w e l l f o l i a t e d , a l m o s t p u r e b i o t i t e - m u s c o v i t e s c h i s t , b i o t i t e - m u s c o v i t e -h o r n b l e n d e - q u a r t z s c h i s t , and q u a r t z i t e . B e c a u s e t h e y r e p r e s e n t o n l y a v e r y m i n o r p r o p o r t i o n o f t h e g n e i s s i c p a c k a g e , t h e y were n o t mapped s e p a r a t e l y . B a s e d on t h e i r m i n e r a l o g i c a l c o m p o s i t i o n t h e s e r o c k s a r e i n t e r p r e t e d as metamorphosed p e l i t e and s e m i -p e l i t e . No a l u m i n o u s metamorphic m i n e r a l s were o b s e r v e d i n t h e s e r o c k s . F a b r i c and i n v e r t e d metamorphic s e q u e n c e of t h e g n e i s s i c u n i t E x c e p t f o r t h e m y l o n i t i c v a r i e t i e s , most of t h e r o c k s of t h e C e n t r a l G n e i s s Complex a r e c h a r a c t e r i z e d by t h e g r a n o b l a s t i c - p o l y g o n a l t e x t u r e o f t h e i r q u a r t z o - f e l d s p a t h i c component. However, i n some t h i n s e c t i o n s t h i s component c o n t a i n s vague remnants of a r e l i c t p e n e t r a t i v e f o l i a t i o n . T h e s e a r e d e f i n e d by e l o n g a t e s i n g l e c r y s t a l s and a g g r e g a t e s o f q u a r t z and f e l d s p a r , w h i c h i n some c a s e s wrap a r o u n d p o r p h y r o b l a s t i c g a r n e t . Some g a r n e t s , as p r e v i o u s l y m e n t i o n e d , have S-shaped i n c l u s i o n t r a i l s . R a r e l y , r e c r y s t a l l i z e d p r e s s u r e shadows a r e 24 p r e s e n t . C o l l e c t i v e l y t h e s e f e a t u r e s i n d i c a t e t h a t an e a r l i e r f a b r i c was a n n e a l e d t h r o u g h s t a t i c r e c r y s t a l l i z a t i o n . E v i d e n t l y t h i s o c c u r r e d under c o n d i t i o n s w h i c h d i d not d e g r a d e t h e p r i m a r y m e t a m o r p h i c a s s e m b l a g e . The p r e f e r r e d o r i e n t a t i o n o f t h e m a f i c m i n e r a l s i s assumed t o have f o r m e d i n r e s p o n s e t o t h e same f o r c e s t h a t p r o d u c e d t h e f o l i a t i o n d e s c r i b e d a b o v e . The f o l i a t i o n d e f i n e d by t h e m a f i c m i n e r a l s i s g e n e r a l l y w e l l p r e s e r v e d , p r e s u m a b l y b e c a u s e t h e s e m i n e r a l s r e c r y s t a l l i z e l e s s r e a d i l y t h a n do q u a r t z and f e l d s p a r . I t seems p r o b a b l e t h a t h i g h t e m p e r a t u r e s o u t l a s t e d i n i t i a l d e f o r m a t i o n i n much o f t h e C e n t r a l G n e i s s Complex, c a u s i n g t h e s t a t i c a l l y a n n e a l e d f a b r i c s j u s t m e n t i o n e d . A narrow zone a l o n g t h e base o f t h e C e n t r a l G n e i s s Complex, w h i c h i s l o c a l l y c h a r a c t e r i z e d by m y l o n i t e f a b r i c s , a p p e a r s t o have e s c a p e d s t a t i c r e c r y s t a l l i z a t i o n . T e m p e r a t u r e s were p r o b a b l y c o n s i d e r a b l y l o w e r i n t h i s zone compared w i t h t h o s e t o p o g r a p h i c a l l y and s t r u c t u r a l l y h i g h e r i n t h e s e q u e n c e . T h i s s u g g e s t i o n i s s u b s t a n t i a t e d by t h e p r e s e n c e of r e t r o g r a d e m i n e r a l a s s e m b l a g e s and a l b i t e - o l i g o c l a s e - e p i d o t e a m p h i b o l i t e s , w h i c h c o n t r a s t s h a r p l y w i t h t h e a n d e s i n e - l a b r a d o r i t e a m p h i b o l i t e s f o u n d above t h e b a s a l z o n e . These f e a t u r e s s u g g e s t t h e p r e s e n c e o f an i n v e r t e d metamorphic g r a d i e n t . A t t h e t i m e d e f o r m a t i o n c e a s e d hot g n e i s s i c m a t e r i a l must have been s i t u a t e d above c o o l e r m a t e r i a l . The f o r m a t i o n of r e t r o g r a d e a s s e m b l a g e s i n t h e b a s a l zone may have been e n c o u r a g e d by v o l a t i l e s r e l e a s e d f r o m u n d e r l y i n g s t r a t a . The s t r u c t u r a l c a u s e o f metamorphic i n v e r s i o n i s d i s c u s s e d i n C h a p t e r 4. 25 GAMSBY GROUP The Gamsby Group forms a northwesterly oriented band of rock adjacent to and partly underlying the Central Gneiss Complex, s t r u c t u r a l l y as well as topographically (Fig 2). In the map area the Gamsby Group consists mostly of intensely deformed, greenschist facies, f e l s i c to mafic, banded metavolcanic rocks. S t r u c t u r a l l y interlayered with these are a variety of metaplutonic rock-types. Many, i f not most, of the rocks in the Gamsby Group are mylonitic, indicating that they have undergone very high d u c t i l e s t r a i n . In addition, b r i t t l e c a t a c l a s t i c fabrics are in many places superimposed on the du c t i l e ones. As a result very few primary textures remain. The mylonitic and c a t a c l a s t i c fabrics prevent ready recognition of the o r i g i n a l nature of these rocks, but on the other hand they mark thi s entire unit as the locus of a tectonic zone of major importance. A wide variety of post-kinematic veins and dykes cuts the Gamsby Group. In part these have found easy access along c a t a c l a s t i c zones and l a t e , cross-cutting, steeply dipping f a u l t s . Excellent exposures of Gamsby Group strata occur on the ridge south of the Tahtsa Lake logging road. Here a continuous, r e l a t i v e l y simple section between the overlying Central Gneiss Complex and underlying, unmetamorphosed volcanics l i e s above t r e e l i n e . Table III l i s t s the major constituents observed in 27 thin sections of Gamsby Group l i t h o l o g i e s . o LTl CN ON 00 .—i NO CO cn ON vO .—i <r »—i i — i m CM NO r~ CM 00 r~-CM o ON i-H NO NO CN ON CM <f 00 CM m CO CO • 30 NO i—t I co i — • NO m CM <f NO i 00 CM i NO i-H | 00 m CM I 00 ON CN i o-CM | 00 <r CM 1 CM ON CM | <t ON CM | ON CM 1 1 ON r-~ I ON I ON r~ I ON 1 ON I ON f-~ t ON 1 ON 1 ON 1 ON 1 ON 1 ON r~ 1 ON i ON 1 ON r-~ i ON ON o 00 o 00 ON ON r~ ON ON ON r-~. ON ON ON QUARTZ M M M M M M M M M M M M P M M M M M M M M M M P M P M ALBITE M P P M M M M M M M M P M ? M M P M M M M M M M M M M K-FELDSPAR P P P M M ACTINOLITE m M P HORNBLENDE - M M M M EPIDOTE P m m m m P M M m P m m M P M P P P P t t P P P P m CHLORITE P P m m t P M . M P M M P P m m P m P P f m P P P P P BIOTITE m P P M MUSCOVITE M P P P P P M P t m t m P P m m m m P GARNET m m m CALCITE m M m m M P . P P APATITE m t t ra t t t t t t t m t t t SPHENE m t t t m m ZIRCON t t t t t t t t t t t PYRITE t m P P P P P m P P P GRAPHITE P MAGN./HEM. t t t m t P m ILMENITE m m t m m m OPAQUES UNDIF. t t --t m t m m m TABLE III Major constituents of 27 thin sections, Gamsby Group. Sample locations marked on Figure 4. Petrographic and chemical c l a s s i f i c a t i o n on Table VI. M major constituent; p mineral i s present; m minor constituent; t trace 27 Metavolcanic rocks (Pg1 and Pg2) Banded, very fine grained, white to pale green, grey, dark green and l o c a l l y purple mylonites, schists and p h y l l i t e s are the dominant rock types of the Gamsby Group in the map area (Fig. 6). Within the banded sequence individual layers range in thickness from a few mm to several m. Locally, r e l a t i v e l y non-schistose, massive greenstone layers reach several tens of m in thickness. A l l the thicker layers are more or less continuous along s t r i k e , although they commonly pinch and swell. In many places the f e l s i c layers are demonstrably l e n t i c u l a r . The thinner layers, however, p a r t i c u l a r l y laminated ones, are frequently i n t e r d i g i t a t e d with one another, suggesting truncation accompanied by varying amounts of s l i p of the compositional layers along low-angle d u c t i l e shear surfaces. Indeed, many of the banded rocks are characterized by advanced transposition fab r i c s , defined by isolated l e n t i c u l a r laminae and t y p i c a l 'flame structures' of f e l s i c material, some of which are rootless i n t r a f o l i a l folds f l o a t i n g in a very fine grained, green, strongly schistose matrix. Whereas the thick layers might represent o r i g i n a l bedding, the thinner banded sequences undoubtely represent tectonic layering. The textures and structures of these rocks show a complete gradation from schistose to mylonitic f a b r i c s . As i s discussed in Chapter 4, the fabrics r e f l e c t d i f f e r i n g amounts of f l a t t e n i n g and associated d u c t i l e shear in a inhomogeneously deforming sequence of rock. The dark green layers in the banded succession are composed mainly of very fine grained (average grain size about 0.25 mm) 28 FIGURE 6 Banded mylonite, Gamsby Group 29 assemblages of e p i d o t e / c l i n o z o i s i t e , c h l o r i t e , a l b i t e (frequently cloudy and altered to very fine grained s e r i c i t e ) and quartz. A c t i n o l i t e , b i o t i t e , muscovite and c a l c i t e may be present. The mineral proportions tend to vary somewhat throughout the sequence, with e p i d o t e / c l i n o z o i s i t e and c h l o r i t e usually predominating over feldspar and quartz. C a l c i t e i s l o c a l l y abundant and indicates the o r i g i n a l l y calcareous nature of some of these rocks. B i o t i t e occurs only in the upper parts of the Gamsby Group. Its l o c a l presence, coupled with that of l o c a l l y conspicuous amounts of muscovite probably indicates the presence of a primary p e l i t i c component in otherwise v o l c a n i c a l l y derived mafic st r a t a . A c t i n o l i t e was observed in only a single specimen from the upper part of the Gamsby Group. Its colour i s rather dark, making i t hard to d i s t i n g u i s h this amphibole from hornblende. The a c t i n o l i t i c composition i s suggested by small extinction angles. The f e l s i c layers are equally very fine grained and contain most of the minerals occurring in the mafic layers, but in d i f f e r i n g proportions. Quartz and a l b i t e are by far the most abundant and muscovite i s more prevalent in these rocks than in the mafic rocks. Epidote and c h l o r i t e are r e l a t i v e l y minor components; b i o t i t e and amphibole were not observed. Some of the f e l s i c rocks are very fine grained mylonites containing pulled-apart a l b i t e porphyroclasts (Fig. 7). In the upper part of the Gamsby Group, above the mylonitic granite, numerous thick, s i l l - l i k e , l e n t i c u l a r bodies of f e l s i c composition (Pg2) are present. These are absent in the lower part. Many are t e x t u r a l l y and compositionally similar to the 30 FIGURE 7 F e l s i c mylonite w i t h p u l l e d - a p a r t p l a g i o c l a s e p o r p h y r o c l a s t , Gamsby Group ; crossed n i c o l s 31 f e l s i c l a y e r s i n t h e banded s e q u e n c e , but a few a r e t e x t u r a l l y u n i q u e i n t h a t t h e y c o n t a i n p i n k f e l d s p a r p o r p y r o c l a s t s r e a c h i n g up t o 3 mm i n d i a m e t e r . T h e s e a r e s e t i n a v e r y f i n e - g r a i n e d , g r e y , f o l i a t e d m a t r i x composed o f g r a n u l a r q u a r t z , a l b i t e , K-f e l d s p a r , e p i d o t e and p r e f e r e n t i a l l y o r i e n t e d c h l o r i t e . The f o l i a t i o n bends a r o u n d t h e p o r p h y r o c l a s t s . T h e s e p o r p h y r o c l a s t i c g r a i n s a r e i n t e r p r e t e d as r e l i c t p h e n o c r y s t s i n o r i g i n a l l y p o r p h y r i t i c f l o w s o r s i l l s . A c c e s s o r y m i n e r a l s i n t h e banded r o c k s i n c l u d e a p a t i t e , s phene, . z i r c o n and opaques. L o c a l l y p y r i t e i s a b u n d a n t , as v e r y f i n e g r a i n s d i s s e m i n a t e d t h r o u g h o u t t h e r o c k , or as s c a t t e r e d , i d i o b l a s t i c c u b e s up t o 1.5 mm a c r o s s . M i c r o s c o p i c a l l y t h e f o l i a t i o n i s d e f i n e d p r i m a r i l y by p r e f e r r e d o r i e n t a t i o n o f m i c a s . Where t h e s e a r e ab u n d a n t t h e r o c k s a r e d i s t i n c t l y p h y l l i t i c . Where a m p h i b o l e s a r e p r e s e n t t h e y a r e a l s o p r e f e r e n t i a l l y o r i e n t e d and d e f i n e a c o n s p i c u o u s l i n e a t i o n . W i t h i n t h e m y l o n i t i c r o c k s t h e most e v i d e n t p l a n a r f e a t u r e i s t h e p r e s e n c e of l e n t i c u l a r b o d i e s o f e p i d o t e and q u a r t z , o r i e n t e d p a r a l l e l t o t h e f o l i a t i o n . L o c a l l y t h e s e have been b o u d i n a g e d , and o f t e n t h e y o c c u r as a l i g n e d a ugen. They p r o b a b l y r e p r e s e n t a t t e n u a t e d p r e - or s y n k i n e m a t i c v e i n s . On a m i c r o s c o p i c s c a l e s m a l l a l b i t e , e p i d o t e and q u a r t z p o r p y r o c l a s t s , o f t e n w i t h m a r g i n a l p r e s s u r e shadows o f q u a r t z and c h l o r i t e , a r e e n v e l o p e d by t h e f o l i a t i o n . R i b b o n s of f i n e g r a i n e d , s u t u r e d o r p o l y g o n i z e d q u a r t z , l o c a l l y c o n t a i n i n g r e l i c t , u n d u l o s e g r a i n s w i t h d i s t i n c t d e f o r m a t i o n l a m e l l a e , a r e f r e q u e n t l y p r e s e n t i n t h i n s e c t i o n . Some a r e u n d o u b t e d l y d e r i v e d f r o m p r e - k i n e m a t i c v e i n l e t s , but many may r e p r e s e n t f l a t t e n e d 32 and sheared phenocrysts or d e t r i t a l fragments. Small porphyroclastic grains of plagioclase are l o c a l l y present (Fig. 8). Some of these are andesine which i s apparently not in equilibrium with minerals of the enclosing mineral assemblage. Mostly the l i g h t coloured bands and lenses are very fine grained (^0.2 mm.), with dominantly granoblastic-equigranular textures, which together with the general lack of well defined f o l i a t i o n obscure the fact that these rocks are mylonitic. The observed textures are the result of dynamic recovery and r e c r y s t a l l i z a t i o n . Similar fabrics have been described as the f i n a l products of intense mylonitization by White et a l . (1980). The mylonitic fabric i s frequently accompanied by a conspicuous stretching l i n e a t i o n defined by elongate quartzo-feldspathic aggregates in the f o l i a t i o n plane. The f o l i a t i o n in many thin sections i s crenulated and cross-cut by a late fracture cleavage; fractures are f i l l e d with c h l o r i t e , c a l c i t e , epidote and limonite. Angles between this cleavage and the e a r l i e r f o l i a t i o n range up to 35°. Sub-parallel orientations appear to be most common. The fracture cleavage forms an anastomosing network of f o l i a e along which demonstrable s l i p has occurred. Microscopically i t offsets folded f o l i a t i o n s and l a t e , cross-cutting c a l c i t e v e i n l e t s . The wide variety of microfabrics present in these rocks precludes any simple generalizations concerning the exact nature and r e l a t i v e timing of metamorphic and deformational events. The entire Gamsby Group needs detailed examination in l i g h t of recent developments in research on mylonite f a b r i c s . Microscopic features similar to those observed in thin sections of Gamsby 33 FIGURE 8 Mafic mylonite w i t h abundant p l a g i o c l a s e porphyroclasts set i n a s t r o n g l y s c h i s t o s e matrix of c h l o r i t e and epidote, Gamsby Group; crossed n i c o l s 34 Group mylonites have been described by White et a l . (1980), White (1977), Etheridge and Wilkie (1979) and L i s t e r and Price (1978). It i s now clear that the Gamsby Group as a whole has undergone both du c t i l e and b r i t t l e deformation, resulting in well developed mylonitic and c a t a c l a s t i c textures, evident both in the f i e l d and under the microscope. Near the base of the Gamsby Group r e l i c t primary textures are l o c a l l y present. Most of these are represented by stretched l i t h i c fragments of presumed volcanic o r i g i n , around which the f o l i a t i o n i s deflected. Near i t s eastern contact on the ridge south of the logging road, the Gamsby Group contains irregular bodies of purple p h y l l i t e characterized by fabrics intermediate between mylonitic and c a t a c l a s t i c . Under the microscope these contain elongate domains with plagioclase mi c r o l i t e s arranged in trachytic to sub-ophitic textures, separated by very fine grained p h y l l i t i c laminae r i c h in c h l o r i t e and graphite. These rocks are enclosed in the more t y p i c a l banded rocks and may represent a d i s t i n c t , t e c t o n i c a l l y incorporated l i t h o l o g y . Most of the rocks in the Gamsby Group are very fine grained, highly deformed, and r e c r y s t a l l i z e d , so that their o r i g i n a l nature must be inferred. Their banded character, where not tectonic in o r i g i n , together with their mineralogical composition, suggests interbedded f e l s i c , intermediate and mafic volcanic and v o l c a n i c l a s t i c rocks. Major and trace element chemistry of these rocks (Chapter 3 and Appendix 2) i s in accord with t h i s suggestion. The v o l c a n i c l a s t i c rocks may contain primary carbonate and a minor p e l i t i c component. 35 Amphibolites within the Gamsby Group (Jg2) A 20-30 m thick zone of medium to coarse grained amphibolite overlies a tabular body of mylonitic granite, which i s a conspicuous marker horizon within the Gamsby Group. The granite w i l l be described in the following section. Mafic metavolcanic layers grade downward into the amphibolite. Its contact with the underlying granite is quite abrupt in some places, but more commonly i t i s marked by a conspicuous zone of agmatite. The mafic blocks in the agmatite are flattened and stretched p a r a l l e l to the f o l i a t i o n and li n e a t i o n in the neighbouring rocks. Textures range from coarse grained granoblastic (plutonic) in the cores of the blocks to f i n e l y laminated (mylonitic) at their borders. The g r a n i t i c material between the mafic blocks is everywhere mylonitic. Evidently there was considerable d u c t i l i t y contrast between the two l i t h o l o g i e s . The fabr i c s in the non-agmatitic amphibolites are variable, ranging from coarse grained non-foliated arrangements of plagioclase and hornblende to fine grained mylonitic amphibolite gneisses. The f o l i a t i o n i s defined by preferred orientation of hornblende, l e n t i c u l a r hornblende aggregates, c h l o r i t e and trains of epidote. Locally the f o l i a t i o n wraps around porphyroclasts of hornblende and plagioclase, c l e a r l y establishing the prekinematic o r i g i n of some of the components in these rocks. Hornblende forms up to 50% of the mode and occurs in subidioblastic c r y s t a l s up to 1.5 cm long. These are yellow to blue-green pleochroic. In some samples the c r y s t a l s are 36 p a r t i a l l y altered to secondary c h l o r i t e . The remainder of the mode i s composed of varying amounts of quartz, plagioclase, epidote, c h l o r i t e and p y r i t e . The plagioclase i s a l b i t i c , but l o c a l l y , within the cores of the mafic blocks, a c a l c i c plagioclase appears to have been retrograded to a l b i t e and ep i d o t e / c l i n o z o i s i t e . Most of these rocks are cut by b r i t t l e fractures which have been healed by epidote and c h l o r i t e . In addition there are numerous megascopic quartz/epidote lenses and stringers throughout the unit. This amphibolite i s interpreted as a deformed and metamorphosed ( p a r t i a l l y retrograded), l o c a l l y agmatitic contact aureole marginal to a prekinematic or early synkinematic g r a n i t i c intrusive body. A second, less d i s t i n c t zone with amphibolite i s developed close to the top of the Gamsby Group, within a protomylonitic granodiorite injection complex. This zone immediately underlies the Central Gneiss Complex in the western part of the map area. Meta-plutonic rocks (Jg1,Jg3,Jg4 and Jg5) At several locations within the Gamsby Group prekinematic or synkinematic granitoid intrusions are present. Most d i s t i n c t i v e among these are two d i f f e r e n t , tabular units, one occupying a more or less central position in the metavolcanic sequence along the ridge south of the Tahtsa Lake logging road, the other at the top of the Gamsby Group along the contact with the overlying Central Gneiss Complex. Small, l e n t i c u l a r bodies of similar lithology are present in a few places throughout the Gamsby Group, and several other meta-plutonic rock-types are 37 present in minor amounts. Mylonitic granite (Jg1) .: This unit i s a cream coloured, continuous layer, about 75-100 m thick. It i s characterized in most places by a strongly f o l i a t e d , mylonitic f a b r i c . In a few places the rocks are less well f o l i a t e d and are better described as proto-mylonitic. Locally the granite i s very strongly lineated rather than f o l i a t e d . It seems that these rocks are characterized by gradations from protomylonites to mylonites (S-tectonites) to strongly lineated mylonites (L-tectonites), commonly within a single outcrop. The granite is composed predominantly of quartz, a l b i t e , It-feldspar and muscovite, with lesser amounts of opaque material (ilmenite?), accessory zircon and apatite, and l o c a l l y minor c h l o r i t e and a few tiny garnets. The feldspars are a l l somewhat cloudy and altered. In d i s t i n c t l y mylonitic specimens the f o l i a t i o n i s defined by thin laminae and ribbons composed of very fine grained, polygonized quartz aggregates. Within these the individual quartz grains are somewhat undulose. These laminae are separated from one another by very thin laminae composed of granoblastic quartz and feldspar that contain p r e f e r e n t i a l l y oriented muscovite (Fig. 9). Somewhat coarser-grained porphyroclasts of plagioclase and p e r t h i t i c K-feldspar, l o c a l l y with pressure shadows composed of fine grained quartz and feldspar, are enveloped by the f o l i a t i o n . Many of these grains are bent and are evidently of prekinematic o r i g i n . The lamination is frequently crenulated. Where muscovite i s present i t i s polygonized about the crenulation folds. 38 FIGURE 9 M y l o n i t i c g r a n i t e w i t h l e n t i c u l a r laminae of r e c r y s t a l l i z e d quartz separated by t h i n laminae composed of quartz, f e l d s p a r and muscovite, Gamsby Group 39 In t h e l e s s w e l l f o l i a t e d , p r o t o - m y l o n i t i c samples t h e f a b r i c i s r a t h e r i r r e g u l a r and s u g g e s t i v e of r e l i c t i g n e o u s ( h y p i d i o m o r p h i c - g r a n u l a r ) t e x t u r e s . Here q u a r t z forms i n c i p i e n t m y l o n i t i c r i b b o n s , b u t many i r r e g u l a r , u n d u l o s e a g g r e g a t e s a r e p r e s e n t a s w e l l . T h e s e a r e c o a r s e r t h a n i n t h o s e r o c k s w i t h more extr e m e m y l o n i t i c f a b r i c s . The f e l d s p a r s t e n d t o o c c u r i n f a i r l y c o a r s e - g r a i n e d a g g r e g a t e s as w e l l , p a r t l y e n v e l o p e d i n i n c i p i e n t q u a r t z r i b b o n s . P r o t o - m y l o n i t i c g r a n o d i o r i t e ( J g 3 ) : T h i s u n i t forms an i n j e c t i o n complex i n t h e upper p a r t of t h e Gamsby Group. In t h e f i e l d i t o c c u r s a s l e n s e s and l a y e r s o f g r e y , s t r o n g l y p o r p h y r o c l a s t i c g n e i s s i n t e r l a y e r e d w i t h , but l o c a l l y c r o s s c u t t i n g t h e banded m e t a v o l c a n i c r o c k s o f t h e Gamsby Group. T h i s l i t - p a r - l i t i n j e c t i o n complex p a s s e s upward i n t o m a s s i v e , p r o t o - m y l o n i t i c g r a n i t o i d r o c k , w h i c h i s i n f a u l t c o n t a c t w i t h t h e o v e r l y i n g C e n t r a l G n e i s s Complex. In t h e c e n t r a l p a r t of t h e map a r e a , west of t h e T s a y t i s R i v e r , t h e g r a n o d i o r i t e a p p e a r s t o be a b s e n t f r o m t h e Gamsby Group, and i n s t e a d o c c u r s i n t h e b a s a l p a r t of t h e C e n t r a l G n e i s s Complex. In hand s p e c i m e n t h e s e r o c k s a r e f i n e g r a i n e d and c o n t a i n a b u n d a n t , e u h e d r a l t o s u b h e d r a l , commonly z o n e d p l a g i o c l a s e m e g a c r y s t s . The f i n e g r a i n e d m a t r i x i s composed o f q u a r t z , f e l d s p a r , e p i d o t e and c h l o r i t e . In hand s p e c i m e n no o b v i o u s f o l i a t i o n , o t h e r t h a n a f a i n t banded a p p e a r a n c e , i s p r e s e n t . However, i n t h i n s e c t i o n t h e s e r o c k s a r e se e n t o be d i s t i n c t l y m y l o n i t i c , w i t h a f o l i a t i o n d e f i n e d by p r e f e r r e d o r i e n t a t i o n o f c h l o r i t e a n d . p a r t i c u l a r l y by s t r a i n e d , f l a t t e n e d q u a r t z g r a i n s and s u t u r e d and p o l y g o n i z e d q u a r t z a g g r e g a t e s . T h i s f o l i a t i o n 40 wraps around the large feldspar porphyroclasts (Fig. 10), which frequently have marginal pressure shadows composed of r e c r y s t a l l i z e d quartz. The porphyroclasts are s l i g h t l y bent but otherwise retain their o r i g i n a l twinned and zoned character. Most grains are considerably altered to s e r i c i t e , epidote and a l b i t e , due to retrogression from a more c a l c i c plagioclase. Plagioclase forms about 40% of the mode. K-feldspar (15%) forms r e l a t i v e l y less abundant anhedral grains and together with quartz (30%) forms the major part of the matrix. A few larger orthoclase phenocrysts/porphyroclasts are present as well. The remainder of t h i s rock is composed of epidote (7%), c h l o r i t e (5%), garnet (1%), sphene (1%) and accessory amounts of zircon and apatite. Other meta-plutonic rocks : Other meta-granitoid bodies occur as l e n t i c u l a r bodies of r e l a t i v e l y small s i z e . Notable among these are : 1) Several f a i n t l y f o l i a t e d , proto-mylonitic granodiorite/quartz d i o r i t e lenses (Jg4) west of 'Khawachen Mtn.'; these contain quartz, a l b i t e , epidote, c h l o r i t e and muscovite in varying proportions. 2) Crumpled mylonitic quartz d i o r i t e (Jg5) at the western l i m i t of the map area along the logging road. This body i s of unknown si z e . It contains the metamorphic assemblage quartz (20%)-a l b i t e (40%)-epidote (15%)-biotite (20%)-actinolite (2%). 41 P r o t o m y l o n i t i c g r a n o d i o r i t e , Gamsby Group; crossed n i c o l s 42 LOWER CRETACEOUS (?) VOLCANIC AND SEDIMENTARY STRATA Along most of i t s eastern margin the Gamsby Group i s in fa u l t contact with pyroclastic rocks and volcanic flows of andesitic to r h y o l i t i c composition (1K1 and 1K3). These are readily distinguished from the penetratively deformed Gamsby Group by their massive, unfoliated character and by well preserved primary textures. The units have an estimated composite thickness of 500-600 m, and occur in three d i s t i n c t fault-bounded blocks. In the northeastern corner of the map area, as well as nortwest of h i l l 1490, the volcanic rocks are intruded by altered granite or granodiorite. Elsewhere the volcanic rocks are cl o s e l y associated with large masses of similar granodiorite, which contain abundant, large xenoliths of pyroc l a s t i c rock i d e n t i c a l to pyroclastic rocks in neighbouring stata. Here intrusive relations are obscured by the presence of la t e r f a u l t i n g along northerly and northeasterly trending shear zones. Locally the volcanic rocks are hydrothermally altered or metamorphosed to albite-epidote hornfels. Xenoliths in the intrusive rocks are commonly r e c r y s t a l l i z e d . Close to fault contacts with the Hazelton Group, the volcanic rocks grade into agmatite zones in which intruding g r a n i t i c material has converted the volcanic rocks to medium grained d i o r i t e and gabbro. These rocks may represent part of a disrupted and marginally sheared remnant of a roof pendant. The assemblage forms a d i s t i n c t , fault bounded sequence between regionally metamorphosed rocks to the west and the e s s e n t i a l l y unmetamorphosed Hazelton Group to the east.. 43 Occupying a central position within this largely volcanic unit i s a conspicuous member (1K2) of shale, arkose and conglomerate (Fig. 11), which separates a lower sequence (1K3) composed of grey and pale green, upward increasingly red pyroclastic rocks and flows from overlying, mainly brick red and mauve pyroc l a s t i c rocks (1K1; F i g . 12). Figure 13 shows a generalized section through the units, with b r i e f descriptions of the various rock types. A wide variety of dykes i s present within these units and in associated plutonic rocks. Some of these occur in conspicuous dyke swarms. These and other intrusive rocks w i l l be described in a later section. The sedimentary rocks are chemically immature and are characterized by the bimodal o r i g i n of their constituent material. The majority of grains, pebbles and boulders are derived from volcanic rocks similar to those underlying the sediments. L i t h i c material with trachytic and porphyritic textures and andesitic to d a c i t i c composition form up to 90% of the e l a s t i c s . Much less abundant, but no less conspicuous, are boulders and cobbles of granodiorite and quartz d i o r i t e . In the sandstones, d e t r i t a l grains of quartz, K-feldspar, plagioclase and b i o t i t e form the granitoid component. The sediments therefore contain firm evidence for the presence of exposed plutonic material within an active volcanic region, and suggest that the volcanic rocks may have been deposited in part on a g r a n i t i c basement. The depositional environment for much of these units was probably non-marine. The presence of plant fragments and 44 FIGURE 11 Cobble conglomerate, Lower Cretaceous (?) uni 45 FIGURE 12 V o l c a n i c b r e c c i a , upper part of Lower Cretaceous(?) u n i t 46 IK1 IK 2 Hote : T h i s s e c t i o n i s based i n p a r t on a t r a v e r s e i n t h e n o r t h e a s t c o r n e r of the s t u d y a r e a done by T. R i c h a r d s i n 1977. M a s s i v e , d o m i n a n t l y maroon and b r i c k - r e d aquagene t u f f s and b r e c c i a s . B r i c k - r e d , g r e e n and w h i t e c l a s t s a v e r a g e 30 c e n t i m e t e r s i n s i z e . Most a r e r h y o l i t i c t o a n d e s i t i c i n c o m p o s i t i o n . Many a r e f l o v b a n d e d o r s p e r u l i t i c , whereas o t h e r s e r e t h e m s e l v e s b r e c c i a s . L o c a l l y t h e o u t c r o p s show a f a i n t sense of graded b e d d i n g , but on t h e whole t h e s e r o c k s a r e p o o r l y s o r t e d and c o n t a i n no good t r a c e r u n i t s . They a r e i n t e r b e d d e d w i t h v e r y minor amounts of r e d and g r e e n , f i n e g r a i n e d t u f f and immature v o l c a n i c s a n d s t o n e , and w i t h l a y e r s of f l o v b a n d e d r h y o l i t e . L o c a l l y f r a g m e n t a l r o c k s have been cemented by j a s p e r and c h a l c e d o n y , and t h e y a r e f r e q u e n t l y c u t by a network of q u a r t z , e p i d o t e and a d u l a r i a . I n a d d i t i o n , t h e y a r e f r e q u e n t l y s e v e r e l y a l t e r e d and c o n t a i n l a r g e amounts of secondary c h l o r i t e and • p i d o t e . The l a t t e r o f t e n o c c u r s as i r r e g u l a r pods and l o c a l l y as a n g u l a r f r a g m e n t s w i t h i n t h e v o l c a n i c b r e c c i a s , and a s c o a t i n g s on f r a c t u r e s u r f a c e s . V 4 F i g . 13 Generalized s t r a t i g r a p h i c s e c t i o n , Lower Cretaceous(?) 200 "Lahar : c h i l l e d fragments of r e d and g r e e n v o l c a n i c m a t e r i a l i n a f l o w - t e x t u r e d b l a c k mudstone. S h a l e and s a n d s t o n e Conglomerate and s a n d s t o n e , g r a d e t i o n a l w i t h u n i t below. Grey c o b b l e and b o u l d e r c o n g l o m e r a t e ; 5-10% g r a n i t i c t o q u a r t z d i o r i t i c c o b b l e s , 90* h i g h l e v e l f e l d s p a r p o r p h y r y and v o l c a n i c b r e c c i a s s i m i l a r t o u n d e r l y i n g r o c k s . S i z e range from b o u l d e r s (1 meter) t o p e b b l e s (1 c e n t i m e t e r ) , cemented by Sandstone and s i l t . I n t e r b e d d e d b l a c k a r g i l l i t e s and g r e y , f i n e t o medium g r a i n e d a r k o s e . R i p p l e s , c r o s s b e d s , c u t and f i l l s t r u c t u r e s i n s a n d s t o n e s , l o c a l slump f e a t u r e s ( f l o w r o l l s , r i p - u p c l a s t s ) ; -.wood and l e a f - f r a g m e n t s i n s h a l e s . M a s s i v e , f i n e g r a i n e d , green a m y g d a l o i d a l ( a g a t e , j a s p e r , a d u l a r i a ) and l o c a l l y p o r p h y r i t i c v o l c a n i c f l o w s and g r e y - g r e e n t u f f s and t u f f - b r e c c i a s w i t h a n g u l a r r h y o l i t e c l a s t s (up t o 30 c e n t i m e t e r s i n s i z e ) . Amygdules a r e f r e q u e n t l y f l a t t e n e d . A few t h i n beds of r h y o l i t i c l a p i l l i - t u f f a r e p r e s e n t i n the l o w e r p a r t . T h i s member has a upward i n c r e a s i n g component of red v o l c a n i c s and s e d i m e n t a r y m a t e r i a l , s t a r t i n g w i t h t h i n , i r r e g u l a r s i l t l a m i n a e f o l l o w e d by p r o g r e s s i v e l y c o a r s e r g r a i n e d a r g i l l a c e o u s and a r k o s i c beds of up t o 2 meters t h i c k . The s e d i m e n t s a r e d o m i n a n t l y p l a n e l a m i n a t e d and l o c a l l y have a s c o u r e d b a s a l c o n t a c t w i t h u n d e r l y i n g v o l c a n i c s . The v o l c a n i c s o f t e n have a c h i l l e d appearance. L o c a l l y , l a y e r s (up t o 10 meters t h i c k ) o f r e d , a u g i t e b e a r i n g a n d e s i t e f l o w s and t u f f -b r e c c i a s a r e i n t e r b e d d e d w i t h t h i s sequence. A few fragments of c o a l were found i n the v o l c a n i c r o c k s of the upper p a r t of t h i s membe r . ' M a s s i v e , l a m i n a t e d p a l e green t u f f s , l o c a l l y c o n t a i n i n g a n g u l a r f r a g m e n t s of f e l d s p a r p o r p h y r y and r a r e p e b b l e s of c o a r s e g r a i n e d h o r n b l e n d e d i o r i t e . One c e n t r a l bed (5 meters t h i c k ) of g r e e n , p o o r l y s o r t e d v o l c a n i c b r e c c i a w i t h c l a s t s up t o 2.5 c e n t i m e t e r s i n s i z e . ''Massive, p a l e green aquagene t u f f c o n t a i n g w h i t e w e a t h e r i n g f e l s i t e c l a s t s up t o 5 c e n t i m e t e r s i n s i z e . F a i n t graded b e d d i n g . ''Massive p a l e g r e e n t u f f s g r a d i n g upward i n t o a 1 meter t h i c k r e d , a m y g d a l o i d a l ( e p i d o t e ) , f i n e g r a i n e d a n d e s i t e f l o w . ' H e l l bedded, p a l e g r e e n aquagene t u f f , immature v o l c a n i c s a n d s t o n e and p e b b l e c o n g l o m e r a t e c o n t a i n i n g flowbanded r h y o l i t e c l a s t s . Graded b e d d i n g . ' P o o r l y s o r t e d p a l e g r e e n v o l c a n i c b r e c c i a w i t h c l a s t s and b o u l d e r s (up t o 30 c e n t i m e t e r s i n s i z e ) , composed of green and mauve f e l d s p a r p o r p h y r y . S t r e a k s of r e d d i s h c o l o u r e d , f i n e g r a i n e d t u f f o r mudstone. S e v e r e l y f r a c t u r e d and l i m o n i t e s t a i n e d , medium g r a i n e d , c h l o r i t i z e d q u a r t z d i o r i t e or g r a n o d i o r i t e . 5 2 2 10 30 175 50 12 7 30 10 u n i t ; t h i c k n e s s i n meters 47 sporadic c l a s t s of coal in the shales and lahars, and the occurence of redbed sequences throughout the volcanic units indicate subaerial deposition. The regional environment was probably one of explosive volcanism building composite cones, with surrounding areas intermittently covered by lahar, lava flows, tuffaceous f a l l o u t and f l u v i a l - l a c u s t r i n e sediments. Part of the area may have been covered by forests. A few km northeast of the study area v o l c a n i c l a s t i c rocks similar to those described above contain abundant f o s s i l i z e d tree trunks (Woodsworth personal communication). No diagnostic f o s s i l s were found in these units, but their volcanic component i s similar, both in terms of lithology and regional setting, to volcanic rocks found approximately 70 km to the southeast near Tsaydaychuz Peak and Salient Mtn. These volcanics have yielded a hornblende K/Ar age of about 128 Ma (Woodsworth personal communication), and are l i t h o l o g i c a l l y similar to Hauterivian volcanics in the Mt. Waddington and Bella Coola map areas (Woodsworth 1979a). An Early Cretaceous (Hauterivian?) age i s inferred for the volcanics and sediments in the upper Tsaytis River area. Microscopically, the volcanic rocks show evidence of considerable hydrothermal a l t e r a t i o n . They frequently contain large amounts of secondary c a l c i t e , quartz, chalcedony, opal, prehnite, epidote and c h l o r i t e . Usually these minerals occur in .irregular patchworks within the rocks, less frequently as veins and fracture f i l l i n g s . The feldspars are mostly clouded with s e r i c i t e or nondescript low birefringent material. The mafic minerals have been largely replaced by fine grained c h l o r i t e and 48 epidote. In spite of the a l t e r a t i o n , most of the rocks s t i l l show their o r i g i n a l composition and texture. Trachytic, porp h y r i t i c , and c l a s t i c textures are t y p i c a l ; a few specimens contain r e l i c t shards of volcanic glass. Specimens from the v i c i n i t y of intrusive g r a n i t i c masses are recognizably r e c r y s t a l l i z e d , and l o c a l l y contain porphyroblastic a c t i n o l i t e , plus a l b i t e , c h l o r i t e and minor epidote, suggestive of metamorphism in the albite-epidote hornfels facies (Turner 1968). A conspicuous microscopic feature of some of the andesitic volcanic rocks i s the presence of augite phenocrysts. An augite porpyry dyke swarm exposed along the west side of the Tsaytis River within the Central Gneiss Complex may represent a feeder complex to some of these volcanics. If so, then a basement-cover relat i o n s h i p between the Cretaceous volcanics and the metamorphic complex i s indicated. PERMIAN, TRIASSIC AND JURASSIC STRATA The eastern part of the map area i s underlain mainly by interlayered v o l c a n i c l a s t i c and sedimentary rocks belonging to the Telkwa Formation of the Hazelton Group. About 4 km north of 'Khawachen Mtn.', in a complexely faulted area, these rocks occur together with small outcrops of Permian and T r i a s s i c s t r a t a , forming the depositional base of the Telkwa Formation. Permian rocks (IP) The existence of Permian rocks in t h i s area was f i r s t reported by Read (unpublished report), who discovered Lower •49 Permian f o s s i l s in one of the limestone bodies north of 'Khawachen Mtn.'. Examination by C. Ross of fus u l i n i d s collected from th i s l o c a l i t y in 1977 (Appendix 4), indicated a Sakmarian (Lower Permian) age. During remapping of the Whitesail Lake map area, the s i m i l a r i t y of the Permian limestones with those in the Terrace area was recognized ( D u f f e l l and Souther 1964, Woodsworth 1979a). Based on this s i m i l a r i t y the limestones are considered to be part of Monger's Stikine Assemblage (Monger 1977a). In the study-area the limestone bodies occur as large isolated blocks apparently enclosed in T r i a s s i c and Jurassic s t r a t a . These blocks are here interpreted as partly fault bounded o l i s t o l i t h s , but the p o s s i b i l i t y that some of the blocks represent f a u l t bounded or erosion sculpted fragments of an underlying stratigraphic unit cannot be dismissed. The limestones are highly folded, in contrast to the surrounding v o l c a n i c l a s t i c and sedimentary rocks. About 30 m of thin bedded, buff-grey weathering argillaceous limestone grades into 100 m of massive, s l i g h t l y dolomitic limestone containing thin, irregular bands and nodules of chert. Locally both members contain abundant c r i n o i d fragments, f u s u l i n i d s , bryozoans, brachiopods and varied types of s o l i t a r y corals. T r i a s s i c and Jurassic strata (uT1,uT2,uT3; 1J1) Sedimentary and volcanic strata of T r i a s s i c age are present in several scattered exposures in the northeast corner of the map area. One of these, just northeast of a s i l l - l i k e granitoid body (JK), i s very poorly understood. This area i s underlain by patches of interbedded black shales and s i l t s t o n e s , altered 50 g r a n i t o i d i n t r u s i v e m a t e r i a l , g r e y - g r e e n v o l c a n i c l a s t i c r o c k s , c h e r t y t u f f s and g r e y f e l d s p a r p o r p h y r y f l o w s . N o r t h w e s t o f t h i s complex a r e a , a w e l l - e x p o s e d s e c t i o n of T r i a s s i c s t r a t a u n d e r l i e s t h e Tel k w a F o r m a t i o n i n a n o r t h e a s t e r l y t r e n d i n g , f a u l t bounded b l o c k . T h i s f a u l t - b o u n d e d a r e a h as i t s e l f been d i s r u p t e d by n o r t h e r l y t r e n d i n g f a u l t s , a nd e a c h segment c o n t a i n s a s l i g h t l y d i f f e r e n t s u c c e s s i o n . A g e n e r a l i z e d s e c t i o n t h r o u g h t h e T r i a s s i c and J u r a s s i c s e q uence i s i l l u s t r a t e d i n F i g u r e 14. T r i a s s i c l i m e s t o n e l e n s e s i n t e r b e d d e d w i t h g r e e n v o l c a n i c b r e c c i a / c o n g l o m e r a t e (uT2) c o n t a i n upper K a r n i a n c o n o d o n t s (Woodsworth p e r s o n a l c o m m u n i c a t i o n ) . Below t h i s member a w e l l -bedded s e q u e n c e of s h a l e and s i l t s t o n e (uT3) c o n t a i n s H a l o b i a ( A p p e n d i x 4 ) . The T r i a s s i c u n i t s a p p e a r t o be o v e r l a i n c o n f o r m a b l y by v o l c a n i c l a s t i c and s e d i m e n t a r y r o c k s o f t h e Te l k w a F o r m a t i o n ( 1 J 1 ) . In o t h e r p a r t s o f t h e I n t e r m o n t a n e B e l t , t h e b a s a l member of t h e Telk w a F o r m a t i o n i s S i n e m u r i a n i n age and i s composed o f p o l y m i c t i c c o n g l o m e r a t e s ( T i p p e r and R i c h a r d s 1976a; Monger 1977b). In t h e s t u d y a r e a t h e d a t e d T r i a s s i c s e q u e n c e i s s e p a r a t e d from s i m i l a r p o l y m i c t i c c o n g l o m e r a t e s by abo u t 75 m o f m a s s i v e , g r e e n v o l c a n i c b r e c c i a ( u T 1 ) , of unknown age. B e c a u s e t h i s b r e c c i a b e a r s more r e s e m b l a n c e t o t h e u n d e r l y i n g K a r n i a n s t r a t a t h a n t o t h e T e l k w a F o r m a t i o n , i t i s h e r e i n c l u d e d i n t h e T r i a s s i c s u c c e s s i o n . I t s c o n t a c t w i t h t h e Te l k w a F o r m a t i o n i s i n t e r p r e t e d a s a d i s c o n f o r m i t y r e p r e s e n t i n g an Upper T r i a s s i c - L o w e r J u r a s s i c h i a t u s . T h i s h i a t u s c o i n c i d e s w i t h a change from m a r i n e t o f l u v i a l a nd s u b a e r i a l d e p o s i t i o n and i n d i c a t e s m a r i n e r e g r e s s i o n , p o s s i b l y due t o u p l i f t . 51 agmatite i n Lower CretaceousC?) yolcanics t hrus t _ f_au1t ~ F e l s i t e s i l l 'Red, brick-red and maroon mudstone, siltstone and polymictic conglomerate, containing minor Lower Permian limestone clasts. uT2 uT3 ® Grey-green, tan weathering volcanic breccia containing 20-25% cobbles and boulders (up to 50 centimeters in size) of lower Permian limestone. Minor siltstone at base, gradational contact with underlying member. Local thin lenses of coralline limestone containing upper Karnian conodonts. Hell bedded, dark grey to black, locally calcareous shale and siltstone containing Halobia. Minor interbedded basalt/andesite flows or s i l l s near the base. Member becomes gritty toward top and there contains sandsize angular chert fragments. fl^iSS_ si high .angle. JEaul.t Telkwa Formation 100 Pale green and purple volcanic breccia with massive green flows <gn at the top. 180 Siltstone with interbedded andesitic volcanics or s i l l s . Ribbed <Q Belemnite holes. Massive grey limestone. 5 100 F i g . 14 Stra t i g r a p h i c section, Upper Jurassic units; thickness i n T r i a s s i c meters and Lower 52 The T e l k w a F o r m a t i o n i s composed of i n t e r b e d d e d r e d and g r e e n , f i n e - t o m e d i u m - g r a i n e d t u f f s , mudstones, v o l c a n i c s a n d s t o n e s and p e b b l e c o n g l o m e r a t e s . Beds a r e g e n e r a l l y l e s s t h a n 3 m t h i c k . The g r e e n l a y e r s a r e l o c a l l y c o a r s e - g r a i n e d t u f f - b r e c c i a s c o n t a i n i n g c o b b l e s i z e d a n g u l a r c l a s t s o f t u f f a c e o u s m a t e r i a l . J u d g i n g by t h e i r a p p e a r a n c e , t h e g r e e n r o c k s may r a n g e from a n d e s i t e t o r h y o l i t e i n c o m p o s i t i o n . The r e d , s e d i m e n t a r y r o c k s range from v e r y f i n e c j r a i n e d mudstone t o c o a r s e - g r a i n e d p o l y m i c t i c c o n g l o m e r a t e s . The mudstones a r e f r e q u e n t l y m u d-cracked, n e a r b y e p i c l a s t i c s a n d s t o n e s a r e o f t e n c r o s s - b e d d e d . These f e a t u r e s i n d i c a t e a s h a l l o w w a t e r , p o s s i b l y f l u v i a l e n v i r o n m e n t w h i c h was from t i m e t o t i m e b l a n k e t e d by t u f f a c e o u s d e p o s i t s . The c o n g l o m e r a t e s c o n t a i n a wide v a r i e t y of v o l c a n i c l a s t i c f r a g m e n t s , v a r i c o l o u r e d c h e r t p e b b l e s , r a r e g r a n i t o i d p e b b l e s and c o n s p i c u o u s , but not a b u n d a n t , f o s s i l i f e r o u s Lower P e r m i a n l i m e s t o n e c l a s t s . L o c a l l y , n e a r t h e e a s t m a r g i n o f t h e map a r e a j u s t west o f a p r o m i n e n t s c h i s t o s e zone d e v e l o p e d w i t h i n t h e T e l k w a F o r m a t i o n , t h e r e a r e i r r e g u l a r pods and b o u l d e r s o f s i m i l a r l i m e s t o n e , f l o a t i n g i n s h e a r e d T e l k w a v o l c a n i c l a s t i c r o c k s . In most p l a c e s t h e T e l k w a s t r a t a a r e h i g h l y f r a c t u r e d and on t h e s o u t h s i d e of t h e map a r e a t h e y have a w e l l d e v e l o p e d f r a c t u r e c l e a v a g e p a r a l l e l t o b e d d i n g . The r o c k s i n t h e n o r t h e a s t t r e n d i n g f a u l t b l o c k a r e f r e q u e n t l y i n t e n s e l y s h e a r e d p a r a l l e l t o t h e b o u n d i n g , n o r t h e a s t t r e n d i n g f a u l t s . L o c a l l y , p e b b l e s i n t h e p o l y m i c t i c c o n g l o m e r a t e have been s t r e t c h e d t o s e v e r a l t i m e s t h e i r o r i g i n a l l e n g t h p a r a l l e l t o t h e s h e a r i n g 53 d i r e c t i o n . Near t h e e a s t e r n l i m i t o f t h e map a r e a t h e Telk w a F o r m a t i o n g r a d e s o v e r an i n t e r v a l o f a b o u t 3 m i n t o w e l l f o l i a t e d , n o r t h e r l y s t r i k i n g c h l o r i t e s c h i s t , w h i c h e x t e n d s beyond t h e map a r e a . The s c h i s t s somewhat r e s e m b l e m e t a v o l c a n i c s t r a t a o f t h e Gamsby Group and l i k e w i s e c o n t a i n e l o n g a t e pods o f e p i d o t e and q u a r t z . I t i s not known i f t h e s e s c h i s t s a r e m y l o n i t i c . B e c a u se t h e c o n t a c t w i t h t h e s t r a t a t o t h e west i s g r a d a t i o n a l , t h e s e s c h i s t s a r e c o n s i d e r e d t o be p a r t of t h e Te l k w a F o r m a t i o n . A l l r o c k s i n t h e e a s t e r n p a r t o f t h e map a r e a a r e c u t by c a l c i t e , q u a r t z and e p i d o t e v e i n s and a v a r i e t y of d y k e s , s i l l s and i g n e o u s p o d s , most commonly of f i n e - medium g r a i n e d d i a b a s e and f e l s i t e . L e s s common a r e t h i c k d y k e s o f medium g r a i n e d g r a n i t e and s e v e r a l s m a l l b o d i e s of g r a n o d i o r i t e . The p r e s e n c e i n b o t h T r i a s s i c and J u r a s s i c s t a t a of Lower P e r m i a n l i m e s t o n e p e b b l e s , c o b b l e s , b o u l d e r s and d e f o r m e d o l i s t o s t r o m a l b l o c k s , c o u p l e d w i t h t h e change from m a r i n e s e d i m e n t a r y c o n d i t i o n s i n t h e T r i a s s i c t o f l u v i a l s e d i m e n t a t i o n and s u b a e r i a l v o l c a n i s m i n t h e J u r a s s i c , has i m p l i c a t i o n s f o r t h e e a r l y M e s o z o i c t e c t o n i c h i s t o r y of t h i s r e g i o n . These i m p l i c a t i o n s a r e d i s c u s s e d i n C h a p t e r 7. INTRUSIVE ROCKS A g r e a t v a r i e t y of i n t r u s i v e r o c k s a r e p r e s e n t w i t h i n t h e s t u d y a r e a . S e v e r a l o f t h e s e have been m e n t i o n e d i n p r e v i o u s s e c t i o n s . The v a r i e t y of t e x t u r e s and c o m p o s i t i o n s e n c o u n t e r e d i n t h e f i e l d d e f i e s c o n c i s e d e s c r i p t i o n , and o n l y t h e l a r g e r b o d i e s and t h e more c o n s p i c u o u s d y k e s were mapped s e p a r a t e l y . 54 The ages of these rocks are not known, but geological relations indicate that most are younger than Early Cretaceous. GRANITOID ROCKS Apart from a few small plugs in the Central Gneiss Complex and the Telkwa Formation, a l l of the larger granitoid intrusives are associated with the Lower Cretaceous volcanics. The Central Gneiss Complex i s intruded by a coarse-grained muscovite-bearing leucogranite (K3) south of unnamed peak 2088. Near the summit of this peak there are a few small bodies of crosscutting, fine grained d i o r i t e . In the southwestern corner of the study area, the Central Gneiss Complex i s cut by thick dykes and pods of pink granodiorite (K2) with c h i l l e d margins. The Telkwa Formation contains a s i l l - l i k e body of altered, medium grained m i a r o l i t i c granite (JK). Micrographic granite (K1) The granitoid stock in the northeast corner of the area i s oval in shape and i s invaded by a northeasterly trending diabase dyke swarm, which l o c a l l y forms over 80% of the outcrop. The stock i s a massive, medium-grained, greenish-weathering, c h l o r i t i z e d and epidotized granite, which contains large andesine phenocrysts. The coarse grained matrix i s composed predominantly of micrographic intergrowths of quartz and microcline and contains small amounts of c h l o r i t i z e d b i o t i t e , opaques, secondary epidote and accessory zircon, apatite and sphene. Possibly genetically related to th i s stock are several nearby, thick dykes of fine to medium grained micrographic granite which are mineralogically and te x t u r a l l y similar to the stock. They are, however, finer grained and contain deeply 55 embayed, rounded phenocrysts of quartz. Another granitoid dyke which cuts across Telkwa pebble conglomerates and mudstones just east of the flood p l a i n , lacks micrographic texture but instead contains microsperulitic aggregates of intergrown c r i s t o b a l i t e and orthoclase and c r i s t o b a l i t e overgrowths on quartz phenocrysts. These dykes occur both in the Cretaceous and in the Jurassic units and therefore postdate the f a u l t along which these units were juxtaposed. Altered granodiorite (aK) An irregular, partly sheet-like body of altered, highly fractured and l o c a l l y d i s t i n c t l y c a t a c l a s t i c granodiorite i s sandwiched between the Cretaceous volcanic sequence and the Gamsby Group over a considerable area. Its intrusive r e l a t i o n with the Cretaceous volcanics, which was discussed previously, is somewhat obscured by the presence-of later f a u l t i n g along northerly and northeasterly oriented shear zones, which are an integral part of the Sandifer Lake Fault Zone. The granodiorite is t y p i c a l l y hypidiomorphic-granular and contains small, altered phenocrysts of andesine(25%) and microcline(25%). Minor amounts of altered hornblende and b i o t i t e , opaques, secondary c a l c i t e , c h l o r i t e , epidote and s e r i c i t e plus accessory zircon and apatite form the remainder of these rocks. The quartz is invariably strained, and within the main fault zone, west of h i l l 1490, microscopic deformational effects are well developed. The plagioclase c r y s t a l s are broken or bent, both quartz and K-feldspar are highly strained, and many of the grains have d i s t i n c t mortar textures along their boundaries. Vaguely l e n t i c u l a r and wedge-shaped aggregates of extremely fine 56 grained, comminuted microgranitic material occur i n t e r s t i t i a l to the main minerals and l o c a l l y separate disrupted plagioclase c r y s t a l s . Commonly the grain boundaries between quartz and feldspar are sutured. These deformational features are generally not macroscopically evident; limonite-coated fractures are the usual observation, but near the margins the granodiorite is frequently sheared and c l e a r l y c a t a c l a s t i c , with a well developed anastomosing fracture network. Within the main north-northwest trending fault zone xenoliths of Lower Cretaceous volcanics usually show a much more pronounced c a t a c l a s t i c texture than the enclosing granodiorite. The granodiorite i s intruded by swarms of diabase and lamprophyre dykes, p a r t i c u l a r l y along shear zones, which evidently provided easy intrusive pathways. Also present are rare r h y o l i t e porphyry dykes, one of which cuts across a sheared contact with the Cretaceous volcanic and sedimentary rocks, and isolated pockets of fine to medium grained d i o r i t e . Locally the granite contains small amounts of disseminated chalcopyrite. Cataclastic granodiorite and pegmatite form a very conspicuous, folded, sheet-like body which separates the small, westernmost block of Lower Cretaceous volcanic and sedimentary rocks from the Gamsby Group. The gr a n i t i c rocks are buff weathering, coarse grained, and strongly c a t a c l a s t i c . Outcrops are characterized by a well developed, anastomosing fracture network. These fractures p a r a l l e l the contacts with neighbouring rocks and the f o l i a t i o n in the adjacent Gamsby Group. The gra n i t i c sheet i s about 15-20 m thick. Abundant limonite-coated and c a l c i t e / c h l o r i t e - f i l l e d 57 f r a c t u r e s cut across a primary hypidiornorphic g r a n u l a r t e x t u r e i n which s t r a i n e d quartz(25%) and kinked, c h l o r i t i z e d b i o t i t e ( l % ) are the only primary minerals to show sign s of deformation. F a i n t l y zoned, a l t e r e d o l i g o c l a s e ( 4 0 % ) , k a o l i n i z e d o r t h o c l a s e ( 1 5 % ) , minor opaques and accessory z i r c o n and a p a t i t e make up the remainder of the rock. The u n i t i s l o c a l l y p e g m a t i t i c , composed predominantly of very coarse g r a i n e d q u a r t z , f e l d s p a r and muscovite. DYKES Dark, f i n e g rained diabase dykes are the most abundant. These are encountered i n a l l map u n i t s and commonly occur i n dyke swarms. I n d i v i d u a l dykes are g e n e r a l l y l e s s than 3 m t h i c k . They may be g e n e t i c a l l y r e l a t e d to small plugs and pockets of m i c r o d i o r i t e , which are present both i n the Coast P l u t o n i c Complex and i n the Intermontane B e l t . Less abundant, but no l e s s conspicuous, are hornblende lamprophyre dykes which l o c a l l y form dyke swarms but u s u a l l y occur as long, continuous bodies throughout the e n t i r e study area. Hornblende phenocrysts up to 1 cm long are set i n a f i n e g r a i n e d , s u b o p h i t i c groundmass i n which p l a g i o c l a s e encloses second g e n e r a t i o n amphibole and granules of opaque m a t e r i a l . C o m p o s i t i o n a l l y these dykes appear to be s p e s s a r t i t e or camptonite. Lamprophyre dykes are common i n p a r t s of the northern Coast Mountains, and have been dated as Miocene i n the P r i n c e Rupert area (R.L. Armstrong p e r s o n a l communication). G r a n i t o i d dykes a s s o c i a t e d with the micrographic g r a n i t e stock (K1), i n the no r t h e a s t e r n p a r t of the map area, were mentioned p r e v i o u s l y . A few r h y o l i t e porphyry dykes up to .10 m 58 thick were observed in the Cretaceous volcanic/plutonic complex. These dykes were not mapped separately, except for one, which cuts across a northeast trending thrust f a u l t , west of the flood p l a i n . This dyke contains small plagioclase phenocrysts and d i s t i n c t i v e , rounded and deeply embayed quartz phenocrysts, set in a very fine grained quartzo-feldspathic groundmass. Minor, completely c h l o r i t i z e d b i o t i t e flakes and accessory amounts of opaques, zircon and apatite are the remaining constituents. The rhy o l i t e porphyry dykes are believed to be genetically related to the micrographic granite stock, and are included in the same map unit. About 4 km west-northwest of 'Khawachen Mtn.', above the bench west of the Tsaytis River, a swarm of augite porphyry s i l l s occurs in the basal part of the Central Gneiss Complex. Microscopically these rocks are characterized by a severely altered intergranular to i n t e r s e r t a l matrix composed of r e l i c t andesine (50%, An f t 8-An 5 7) and hornblende (10%) m i c r o l i t e s , fine grained magnetite and ilmenite (5%), and secondary c a l c i t e and c h l o r i t e (25%). Enclosed in t h i s matrix are small augite phenocrysts (5%), which tend to be glomeroporphyritic, and aggregates of secondary s e r i c i t e and c a l c i t e (5%), which are pseudomorphs after plagioclase phenocrysts. Along margins and cracks the augite is altered to c h l o r i t e and minor fibrous u r a l i t e . As mentioned previously these dykes may have been feeders to o r i g i n a l l y overlying Lower Cretaceous volcanic rocks. TABLE IV Petrographic c l a s s i f i c a t i o n of 26 t h i n sections, T r i a s s i c , Jurassic and Lower Cretaceous s t r a t a and associated i n t r u s i v e rocks. SAMPLE MAP UNIT PETROGRAPHIC NAME CJ • H CO CO £t co a ca u T r i a s s i c rocks CO O rt CD 4 J CJ rt rt 4-1 01 CO u CD > • H CO CO ^ 79-388 1J Sheared pebble-conglomerate 79-400 1J Carbonatized basalt/andesite 79-430 JK Altered ( s e r i c i t e - c h l o r i t e - l i m o n i t e - c a l c i t e ) granite 79-431 JK Altered ( » " " " ) m i a r o l i t i c granite 79-483 uT2 Calcareous volcanic breccia/conglomerate (contains Lower Permian limestone c l a s t s ) 79-493 uTl C h l o r i t i z e d and epidotized c r y s t a l l i t h i c t u f f / t u f f - b r e c c i a 1K1 Andesitic lahar (hematitic mudstone cement) 1K1 Altered ( c a l c i t e - e p i d o t e - s e r i c i t e - c l a y minerals) a n d e s i t i c t u f f - b r e c c i a 1K2 Graphitic siltstone/shale 1K2 L i t h i c arenite (derived from a n d e s i t i c volcanics and g r a n i t o i d rocks) 1K3 Trachytic augite andesite (flow) 1K3 Hematitic augite andesite (flow) 1K3 Altered ( c a l c i t e - c h l o r i t e - s e r i c i t e ) quartz andesite/dacite 1K3 Meta-basalt ( a c t i n o l i t e - a l b i t e - e p i d o t e - c h l o r i t e hornfels) 1K3 Meta-tuff-breccia ( a c t i n o l i t e - a l b i t e ? - e p i d o t e - c h l o r i t e hornfels) ; contains abundant r h y o l i t i c and d a c i t i c fragments 1K3 Meta-tuff ( e p i d o t e - c h l o r i t e - a c t i n o l i t e hornfels) 1K3 Meta-tuff ( c h l o r i t e - a c t i n o l i t e hornfels) 79-27 aK Altered (chlorite-epidote) granodiorite 79-225 aK Ca t a c l a s t i c granodiorite 79-381 aK Cat a c l a s t i c granodiorite 79-217 aK Ca t a c l a s t i c granodiorite 79-501 KI Altered (chlorite-epidote) micrographic granite 79-462 KI Micrographic granite (dyke) 79-461 KI Mic r o s p h e r u l i t i c (crystobalite-orthoclase) granite (dyke) 79-144 KI Rhyolite porphyry (dyke) 79-84 - Hornblende lamprophyre (dyke; spe'ssartite or camptonite) 179-142 79-93 79-348 79-351 79-359 79-360 79-366 79-116 79-117-2 79-44 79-34 60 CHAPTER 3 : GEOCHEMISTRY OF THE METAMORPHIC ROCKS CHEMICAL ANALYSIS Thirty eight samples from the Central Gneiss Complex and the Gamsby Group were analysed for major element composition by X-ray fluoresence, using a whole-rock pressed-powder-pellet procedure developed as part of t h i s study (Appendix 1). This procedure i s based on a method o r i g i n a l l y described by Brown et a l . (1973), and allows major and trace element analysis using the same p e l l e t . Twenty seven samples were analysed for trace element composition. Operating conditions and data reduction routines for trace element analysis, as well as procedures for the analysis of H 20 and C0 2, have been described by Berman (1979). A l l analyses were performed using a P h i l l i p s PW 1410 spectrometer. Ana l y t i c a l results are presented in Appendix 2. CLASSIFICATION Twenty seven samples believed to be of volcanic o r i g i n were selected from the analysed rocks for c l a s s i f i c a t i o n purposes. Eighteen of these have been analysed for trace elements. The metavolcanic rocks were c l a s s i f i e d using the standard major element scheme of Irvine and Baragar (1971) and the immobile element scheme of Floyd and Winchester, which i s more r e l i a b l e for altered and metamorphosed rocks (Floyd and Winchester 1978). In c l a s s i f y i n g these rocks, i t was assumed that no foreign component was included with the volcanic rocks at their time of deposition, and that any metamorphism was isochemical. These 61 assumptions may not be v a l i d , but apart from petrographic c r i t e r i a no simple sample selection scheme i s available. These rocks may have undergone chemical modification through interaction with seawater, before regional metamorphism (Spooner and Fyfe 1973). A marine environment of deposition for the Gamsby Group i s suggested by the fact that to the south and north of the area studied, the metavolcanic rocks are underlain by a metasedimentary succession with several conspicuous carbonate members. Mass transfer during later deformation is to expected in these types of rocks as well (Kerrich et a l . 1977). Any c l a s s i f i c a t i o n based on mobile element abundances must be viewed with caution. C l a s s i f i c a t i o n according to Irvine and Baragar was done using FORTRAN programs written by G.T. Nixon. Input values for FeO, which was not measured, were derived from measured t o t a l Fe (reported as Fe 20 3) using average FeO/Fe 20 3 ratios for common volcanic rocks, extracted from tables published by Nockolds (1954). Samples high in CaO and C0 2 contained considerable amounts of secondary c a l c i t e , both as sheared and post-kinematic v e i n l e t s . The major element abundances for these specimens were adjusted by removing a l l C0 2 and a corresponding amount of CaO from the analyses and renormalizing prior to c l a s s i f i c a t i o n . Relevant output is tabulated in Tables V and VI and presented graphically in Figures 15 to 17. If the analyses r e f l e c t primary composition, the meta-volcanic rocks were derived from subalkaline precursors and represent a series ranging from t h o l e i i t i c basalt to c a l c - a l k a l i n e andesite, dacite and r h y o l i t e . 62 F i g . 15 : A l k a l i s - s i l i c a diagram; the d i v i d i n g l i n e for the a l k a l i n e and sub-alkaline f i e l d s i s from Irvine and Baragar (1971). Axes are i n weight %. 63 F F i g . 16 T h o l e i i t i c vs. c a l c a l k a l i n e d i s c r i m i n a t i o n plots, Central Gneiss Complex and Gamsby Group; A : Weight % A1203 vs. Normative Plagioclase Comp. B : AFM diagram; A= Na 20 + K 2 0 B= FeO + 0.8998 F e . 0 - ( i n weight %) MgO Divi d i n g l i n e s from Irvine and Baragar (1971). 64 • Gamsby Group Normative Plagioclase Composition Fig. 17 : Normative color index vs. normative plagioclase composition; Central Gneiss Complex and Gamsby Group; dividing lines are from Irvine and Baragar (1971). Axes i n % c a t i o n e q u i v a l e n t s . TABLE V : SAMPLES AND CLASSIFICATION - CENTRAL GNEISS COMPLEX Sample Map unit Petrographic name NCI I & B F & W U M C 4-1 4J <U CO CO 0 •r-l •i-l •rH 0 0 O cu CU a) Xi Xi CL. o u CO 4-1 4-> a c e oo o CU CU o •r-l a 0 i—i 4J cu <U o o r-l r-l fi cu CU CU o cn u M (U Xi fi O CJ o •i-i "-> ca o Xi u CU H H o * * A A * A A A * * A * * A * A A A * A A * A A A * A * A * A A A A * A 80-37b Jcg Granitoid gneiss 80-37a Jcg Granitoid gneiss 80-41 Jcg Mylonitic granodiorite gneiss 80-58 Pcgl Leocogneiss (injected?) 80-55 Pcgl Amphibolite 80-56 Pcgl Amphibolite 80-61 Pcgl Amphibolite 80-39 Pcgl Retrograded amphibolite 80-29 Pcgl Banded amphibolite 80-60 Pcgl Leucogneiss ( i n t e r s t r a t i f i e d ) 80-42 K3 Post-kinematic leuco-granite 80-59 - Post-kinematic augite porphyry 18.2 27.8 32.5 36.1 26.5 18.3 T h o l e i i t i c basalt T h o l e i i t i c basalt Calc-alkaline basalt T h o l e i i t i c basalt T h o l e i i t i c basalt Calc-alkaline andesite Andesite Basalt B a s a l t i c andesite ANCI : Normative Colour Index according to Irvine and Baragar I & B : C l a s s i f i c a t i o n according to Irvine and Baragar (1971) F & W : C l a s s i f i c a t i o n according to Floyd and Winchester (1978) TABLE VI : SAMPLES AND CLASSIFICATION - GAMSBY GROUP Sample Map unit Petrographic name NCI I & B F & W •r-l 4J O cu CO H a CU a >i cu U r - l 4J CU co a CU ' r H _ o a cu ni cu r f l r l £ O H O c o u r C o o CU o R-l J g l M y l o n i t i c granite A A A 79-258 J g l M y l o n i t i c granite A R-3 J g l M y l o n i t i c granite A R-5 J g l M y l o n i t i c granite A R-7 Jg l M y l o n i t i c granite A 79-298 J g l Protomylonitic granite A 79-297 Jgl/Jg2 Myl. granite + amphibolite A 79-256 Pg2 My l o n i t i c feldspar porphyry A A A A 80-64 Jg5 M y l o n i t i c quartz d i o r i t e A A 80-19 Jg3 Protomylonitic granodiorite A A 80-28 Jg3 Protomylonitic granodiorite A 79-176 Jg4 Protomylonitic granodiorite A A A 79-251 Pgl Mafic mylonite 31.2 T h o l e i i t i c basalt B a s a l t i c andesite A A A A 79-335 Pgl Mafic mylonite 28.3 T h o l e i i t i c basalt Basalt A A A A 79-190 Pgl Mafic mylonite 35.0 C a l c - a l k a l i n e andesite B a s a l t i c andesite A A A A 79-276 Pgl Mafic mylonite A 79-266 Pgl Mafic mylonite 41.2 C a l c - a l k a l i n e andesite Basalt A A A 79-168 Pgl Mafic mylonite 13.5 T h o l e i i t i c andesite A A A 79-173 Pgl Mafic mylonite 38.2 T h o l e i i t i c basalt B a s a l t i c andesite A A A A 79-278 Pgl Mafic mylonite 27.7 T h o l e i i t i c basalt B a s a l t i c andesite A A A 79-279 Pgl Mafic mylonite 23.3 T h o l e i i t i c basalt B a s a l t i c andesite A A A A 79-248 Jg2 Hornblende d i o r i t e gneiss 39.9 C a l c - a l k a l i n e basalt Basalt A A A 79-247 Jg2 Banded amphibolite A 80-66 Jg2 Hbl. quartz d i o r i t e mylonite A 79-292 Jg2 Amphibolite 26.0 C a l c - a l k a l i n e andesite Basalt A A A 79-294 Jg2 Amphibolite 39.2 T h o l e i i t i c basalt A A 79-284 Pgl Mafic p h y l l i t e / m y l o n i t e 26.7 C a l c - a l k a l i n e andesite Basalt A A A A 79-336 Pgl Mafic mylonite 28.1 C a l c - a l k a l i n e andesite B a s a l t i c andesite A A A 79-250 Pgl F e l s i c mylonite 12.4 C a l c - a l k a l i n e dacite Andesite A A A 80-31 Pg2 F e l s i c mylonite 5.5 'Peralkaline' Dacite A A A 80-26 Pgl F e l s i c mylonite 4.6 C a l c - a l k a l i n e r h y o l i t e Rhyodacite A A 79-189 Pgl F e l s i c mylonite 2.1 "Pe r a l k a l i n e ' Rhyodacite A A A A 80-50 Pg2 F e l s i c mylonite 4.6 . C a l c - a l k a l i n e r h y o l i t e A 79-169 Pgl F e l s i c mylonite 4.6 C a l c - a l k a l i n e r h y o l i t e A A A 79-174 Pgl F e l s i c mylonite 4.2 Ca l c - a l k a l i n e r h y o l i t e Rhyodacite A A A A 79-174a Pgl F e l s i c mylonite 3.5 C a l c - a l k a l i n e r h y o l i t e Rhyolite A A A A 80-27 - M i c r o d i o r i t e (dyke) A 67 Floyd and Winchester's discrimination scheme for metamorphosed volcanic rocks i s based on the abundance of Nb, Y, Zr, Ti and P, which are thought to be r e l a t i v e l y immobile during metamorphism (Pearce and Cann 1973; Winchester and Floyd 1976; Winchester and Floyd 1977; Floyd and Winchester 1978; Smith and Smith 1976). In plots of ratios of Nb/Y and Zr/Ti0 2 versus S i 0 2 (Fig 18), the data are r e s t r i c t e d to the sub-alkaline side of the diagrams and span the compositional range from basalt to r h y o l i t e . However, the position of each point is s t i l l subject to uncertainty due to the mobility of Si during metamorphism and deformation. A plot of Nb/Y vs Zr/Ti0 2 i s considered most r e l i a b l e for metamorphosed rocks because i t i s based e n t i r e l y on immobile elements. Figure 19 shows the same general d i s t r i b u t i o n of data points as the other two diagrams, but about three quarter of the samples plot in more basic delimiting f i e l d s , suggesting that the majority of the samples, p a r t i c u l a r l y the more basic ones, may have been enriched in S i . This is suggested as well by the presence of abundant, sheared quartz veinlets in many of the rocks. The trace element diagrams do not discriminate between ca l c - a l k a l i n e and t h o l e i i t i c rocks. Irvine and Baragar (1971) suggest using AFM and A1 20 3 vs normative plagioclase composition diagrams respectively in assigning acidic and basic rocks to the c a l c - a l k a l i n e or t h o l e i i t i c s e r i e s . Figures 16 and 19 used in conjunction in t h i s way indicate that the majority of samples are c a l c - a l k a l i n e , with several of the b a s a l t i c and b a s a l t i c -andesitic samples beiing t h o l e i i t i c . The association of 68 Rhyolitt Rhyodaclta and daclta ^ Trachyt* Comendlte and PantallarlU Andaalu Sub - a l k a l i n « Basal t • 9 8ub-alkalin* • -A » AtkaUna 0 Gamsby Group A Central Gneiss Complex .01 .10 Zr/TIO, 1.00 2 80 70 Rhyellla Rhyodaclta and Oaclta 8ub-alkalin« Basalt 8ub-alkallne Comandita and Pantallarlt* Trachyt* Baaanlta and Nephelinite 0 Gamsby Group A Central Gneiss Complex Alkaline .10 F i g . 18 1.00 Nb/Y Nb/Y - Si0 2 and Zr/Ti0 2 - Si0 2 diagrams, Central Gneiss Complex and Gamsby Group; d i v i d i n g l i n e s are from Floyd and Winchester (1978) 69 1.00 N b / Y F i g . 19 Nb/Y - Z-r/Ti0 2 diagram, Central Gneiss Complex and Gamsby Group; d i v i d i n g l i n e s are from Floyd and Winchester (1978). 70 t h o l e i i t i c basalts with c a l c a l k a l i n e andesites, dacites and r h y o l i t e s i s well known in the Archean greenstone belts of the Canadian Shield (Baragar 1966), and i s a normal feature in many volcanic belts of younger age (Irvine and Baragar 1971). TECTONIC SETTING OF THE METAVOLCANIC ROCKS A study of normalized incompatible trace element abundance patterns by Sun (1980) indicated that, r e l a t i v e to t y p i c a l mid-ocean ridge basalts and ocean island basalts, basalts from island arcs are enriched in Sr, K, Th, U, Ba, Rb, Cs and Pb and depleted in T i , Zr, Nb and Ta. A diagramatic comparison of trace element abundance patterns of basalts and b a s a l t i c andesites from the Gamsby Group and Central Gneiss Complex with those of t y p i c a l young oceanic and island arc volcanics i s shown in Figure 20. Although the rocks from the study area are not young, and t h e i r o r i g i n a l bulk chemistry may well have been highly disturbed during metamorphism and deformation, their trace element abundance patterns nevertheless suggest that these rocks originated in a island arc setting. They are characterized by depletion of Nb and enrichment of Ba, Sr and K. This is c l e a r l y the case for the greenschists of the Gamsby Group, somewhat less so for the amphibolites of the Central Gneiss Complex. The l a t t e r are here distinguished from the Gamsby Group mainly by their r e l a t i v e depletion of K. A volcanic arc o r i g i n for these rocks i s confirmed by using the graphical discrimination scheme of Pearce and Cann (1973) (Fig. 21). The Zr-Ti-Y diagram eliminates ocean island basalts and continental basalts from consideration, but the Ti-Zr 71 Fi g . 20 Normalized abundance patterns of incompatible elements i n meta-basalts, Central Gneiss Compl and Gamsby Group. Inset showing t y p i c a l patter for ocean islands, ocean ridges and island arc i s from Sun (1980) 72 T i / 1 00 B: D: ocean i s l a n d and continental basalts low-K t h o l e i i t e s , ocean f l o o r basalts and c a l c - a l k a l i n e basalts low-K t h o l e i i t e s c a l c - a l k a l i n e basalts Crntrtl f*»»l». Cf*t)r> Zr Y.3 E a a A.& D: ocean f l o o r basalts B & D: low-K t h o l e i i t e s C & D: c a l c - a l k a l i n e basalts A CrfttT.l Orteiw. 100 Zr ppm F i g . 21 Tectonic s e t t i n g d i s c r i m i n a t i o n diagrams, Central Gneiss Complex and Gamsby Group; d e l i m i t i n g f i e l d s are from Pearce and Cann (1973) 73 diagram, which distinguishes between ocean floor basalts, c a l c -a l k a l i n e basalts and low-K t h o l e i i t e s , does not offer such clear resolution. Three specimens plot in the ocean floor basalt f i e l d , contradicting the implications of the normalized trace element abundance pattern observed in F i g . 20. Perhaps the number of specimens analysed is not s u f f i c i e n t to generate meaningful information on the Pearce and Cann diagram. However, since most specimens plot in the c a l c - a l k a l i n e basalt and low-K t h o l e i i t e f i e l d s and a l l are nearby, the conclusion i s that the suite as a whole i s probably composed of these chemical types. Neither of the above schemes distinguishes between oceanic-and continental arcs. At the present time no r e l i a b l e discrimination, based either on trace element abundance or on isotope data, i s available. Miyashiro (1974,1975) has suggested that high proportions of c a l c - a l k a l i n e rocks in mature island arcs imply the presence of a depleted upper mantle wedge overlying the descending oceanic slab and advanced development of continental type crust beneath the the arc. Active continental margins have a r e l a t i v e l y higher percentage of c a l c -a l k a l i n e and s i l i c i c rocks than do mature island arcs. The meta-volcanic rocks of the Gamsby Group most l i k e l y represent a r e l a t i v e l y mature island arc assemblage of c a l c -a l k a l i n e and t h o l e i i t i c basalt and andesite, and ca l c - a l k a l i n e dacite and r h y o l i t e . The Central Gneiss Complex appears to contain no meta-rhyolites or meta-dacites. Leocogneiss believed to be of volcanic o r i g i n has an andesitic composition. A l l amphibolites are meta-basalts. These are depleted in K r e l a t i v e to meta-basalts of the Gamsby Group. Perhaps the Central Gneiss 74 Complex i s a high-grade, p a r t i a l l y migmatized equivalent of the Gamsby Group, with the leucosome representing 'sweats' or p a r t i a l melts derived in part from o r i g i n a l l y i n t e r s t r a t i f i e d f e l s i c volcanics. Mobilization of leococratic material may also have removed some of the K from the mafic volcanics. 75 CHAPTER 4 : STRUCTURE The upper Tsaytis riv e r area i s underlain by a major cr u s t a l d i s l o c a t i o n zone which forms the eastern boundary of the Coast Plutonic Complex at this l a t i t u d e . The fault zone displays a variety of structural and textural styles r e f l e c t i n g d i f f e r e n t conditions of deformation across the area. On a l l scales the dominant str u c t u r a l features were caused by inhomogeneous simple shear. The study area can be divided into two major, north-northwest trending domains, an eastern domain ( g r a n i t i c , Cretaceous, Jurassic and older rocks) characterized mainly by c a t a c l a s t i c shear, and a western domain (Central Gneiss Complex and Gamsby Group) characterized mainly by d u c t i l e shear. Structural data are plotted on the geologic map (Fig. 2) and on equal area projections (Figs. 23-25). WESTERN DOMAIN On a large scale, the metamorphic rocks of the Gamsby Group and the Central Gneiss Complex form a homoclinal, gently southwest dipping structural succession (Fig. 22). In d e t a i l , however, the structure is commonly complex, and is characterized by polyphase deformation. Four phases of deformation were recognized; these are summarized in Table VII. A well developed penetrative f o l i a t i o n in the Gamsby Group is p a r a l l e l or subparallel with compositional banding. Penetrative f o l i a t i o n i s only l o c a l l y observed in the Central Gneiss Complex, in which gentle dips are defined mostly by compositional banding. The s t a t i c r e c r y s t a l l i z a t i o n fabric in Central Gneiss Complex l i t h o l o g i e s , discussed previously, 7 6 FIGURE 22 Homoclinal layering i n Gamsby Group 77 TABLE VII : Summary of s t r u c t u r a l features, western domain Phase Description  FI Gradations from t i g h t - i s o c l i n a l mesoscopic folds without a x i a l planar cleavage, through zones with d i s t i n c t t r a n s p o s i t i o n f a b r i c , to well developped mylonitic f o l i a t i o n s and extension l i n e a t i o n s ( L l ) . Rootless i n t r a f o l i a l folds are common i n zones with trans-p o s i t i o n and mylonite f a b r i c s . FI fold-axes and L l l i e a t i o n s have the same o r i e n t a t i o n . Ea s t e r l y verging, open to t i g h t , disharmonic, assymmetric folds and crenulations (L2). Both F2 fold-axes and L2 l i n e a t i o n s are subparallel to FI and L l . A weakly developped a x i a l planar cleavage i s commonly present i n the hinges of F2 f o l d s . Westerly dipping c a t a c l a s t i c fractures and shear planes. Orientation with respect to FI f o l i a t i o n ranges from subparallel to discordant at angles of approximately 35°. Gentle, east-west trending, northerly verging(?) warps and flexur e s . These may be ge n e t i c a l l y associated with steep, westerly dipping f a u l t s (dextral s t r i k e - s l i p ? ? ) , which form much of the boundary between eastern and western domains. Slickensides along these f a u l t s have subhorizontal dips. 78 contrasts sharply with the schistose and mylonitic fabrics developed in the Gamsby Group. Nevertheless, the two units appear to have undergone the same deformational history. They have both been i s o c l i n a l l y folded (F1) about north-northwesterly trending, gently plunging f o l d axes and both contain i n c i p i e n t l y transposed banded sequences. The s l i p surfaces along which transposition movement occured have been r e c r y s t a l l i z e d in both units. The str u c t u r a l style and orientation of second (F2) and t h i r d (F3) generation folds are the same in both units. The only str u c t u r a l difference appears to be the absence of a pre-F2 mylonitic fabric in the Central Gneiss Complex, except near i t s base. The basal contact i s a d i s t i n c t s t r u c t u r a l break (Frontispiece) which is characterized by the sudden increase of both c a t a c l a s t i c and mylonitic fabrics in the underlying plutonic rocks of the Gamsby Group. The thrust appears to truncate the layering and f o l i a t i o n in the Gamsby Group at a small angle: the upper banded sequence of the Gamsby Group in the center of the map area, west of the Tsaytis River, is much thinner than the equivalent sequence further west, northeast of peak 2088. The latest movements along t h i s zone are therefore believed to have occurred at higher levels in the crust and lat e r than the movements associated with the formation of the mylonite f a b r i c s . The b r i t t l e , c a t a c l a s t i c fabrics in th i s zone are believed to have formed in response to the late movements. The Gamsby Group and Central Gneiss Complex in the thesis area are probably s t r a t i g r a p h i c a l l y equivalent. Woodsworth (1978;1979a) has correlated the Central Gneiss Complex with the Gamsby Group on the basis of str u c t u r a l s i m i l a r i t i e s and F i g . 23 S t r u c t u r a l orientations, Gamsby Group ; Equal area projections A Contoured poles to compositional layering and f o l i a t i o n , 325 points. Contour intervals : 6%, 4.5%, 3%, 1.5%, .3% per 1% area . FI + F2 A F4 Fold axes: F l + F2 and Lineations : F l + F2 F i g . 24 St r u c t u r a l orientations, Central Gneiss Complex ; Equal area projections A Contoured poles to compositional banding and f o l i a t i o n , 115 points. Contour intervals : 12.2%, 8.7%, 6.1%, 4.3% 2.6%, .9% per 1% area Fold axes : F l + F2 & Lineations : Fl + F2 Poles to c a t a c l a s t i c fractures and ' Poles to high angle f a u l t s , shear planes (F3), western domain . boundary between eastern and western , . j * Slickensides domains Slickensides F i g . 25 Orientation of c a t a c l a s t i c features and l a t e , high angle f a u l t s . Equal area projection 82 a p p a r e n t metamorphic g r a d a t i o n s between t h e two u n i t s . A l t h o u g h t h e c o n t a c t i n t h e T s a y t i s R i v e r a r e a i s a t h r u s t f a u l t , t h e r e a r e s e v e r a l i n d i c a t i o n s t h a t t h e r e may have been a l a t e r a l m e t a m o r p h i c g r a d a t i o n between them b e f o r e t h r u s t i n g t o o k p l a c e . I t i s n o t i m p o s s i b l e t h a t s u c h c o n t i n u i t y i s s t i l l p r e s e r v e d i n o t h e r p a r t s o f t h e W h i t e s a i l Lake map a r e a . F o r i n s t a n c e , a l o n g t h e T a h t s a Lake-Kemano r o a d , west o f t h e t h e s i s a r e a , t h e r e does not a p p e a r t o be a s t r u c t u r a l b r e a k between t o p o g r a p h i c a l l y low-l y i n g Gamsby Group and C e n t r a l G n e i s s Complex, and a c o n t i n u o u s , a l o n g - s t r i k e t r a n s i t i o n from g r e e n s c h i s t f a c i e s i n t o a m p h i b o l i t e f a c i e s may be p r e s e n t . As d i s c u s s e d i n C h a p t e r s 3 and 5, t h e t r a c e e l e m e n t c h e m i s t r y and Sr i s o t o p i c c o m p o s i t i o n s of t h e s e u n i t s o f f e r no e v i d e n c e t o c o n t r a d i c t t h e h y p o t h e s i s t h a t t h e y a r e c o r r e l a t i v e . A s t r a t i g r a p h i c h i n t i n f a v o r o f c o r r e l a t i o n i s p r o v i d e d by t h e o c c u r e n c e and d i s t r i b u t i o n of t h r e e c o n s p i c u o u s c a r b o n a t e l a y e r s and a s s o c i a t e d m e t a - p e l i t i c s t r a t a i n b o t h u n i t s , a few km s o u t h o f t h e t h e s i s a r e a ( F i g . 3 ) . The f a c t t h a t t h e s e d i s t i n c t i v e l a y e r s o c c u r i n d i f f e r e n t map u n i t s but a l o n g s t r i k e i n t h e T s a y t i s R i v e r v a l l e y i s p r o b a b l y n o t f o r t u i t o u s . The e s s e n t i a l d i f f e r e n c e between t h e C e n t r a l G n e i s s Complex and t h e Gamsby G r o u p i s t h e i r d i f f e r e n t m e t a m o r p h i c g r a d e and f a b r i c , and t h e p r e s e n c e i n t h e f o r m e r of l a r g e amounts o f g r a n i t o i d m a t e r i a l . I n i t i a l s t r u c t u r a l s u p e r p o s i t i o n of h i g h g r a d e m e t a m o r p h i c r o c k s o v e r l o w e r g r a d e e q u i v a l e n t s i n a l l l i k e l i h o o d o c c u r e d i n t h e n o r t e a s t w a r d o v e r t u r n e d l i m b of a l a r g e , recumbent f o l d . O n l y t h e d i s r u p t e d l o w e r l i m b o f t h i s f o l d i s p r e s e r v e d i n t h e map a r e a . Extreme f l a t t e n i n g r e s u l t e d i n l o c a l i z e d e x t e n s i o n a l f l o w and t h e f o r m a t i o n o f m y l o n i t e s . 83 T h i s zone was t h e l o c u s o f b r i t t l e f a i l u r e a t a l a t e r t i m e . S i m i l a r p r o c e s s e s have been d e s c r i b e d by Ross (1973) f o r m y l o n i t e z o n e s and a s s o c i a t e d b r i t t l e f a b r i c s i n t h e Shuswap Complex o f s o u t h e r n B r i t i s h C o l u m b i a . I t d o e s not a p p e a r t h a t any g r e a t amount of s h o r t e n i n g was a c c o m o d a t e d a l o n g t h e u p p e r t h r u s t i n t h e T s a y t i s R i v e r a r e a . F i v e km i s s u g g e s t e d a s a maximum. E a r l y d e f o r m a t i o n a l f e a t u r e s a r e l o c a l l y w e l l r e p r e s e n t e d i n t h e banded r o c k s of t h e Gamsby Group. F1 f o l d s were p r o g r e s s i v e l y f l a t t e n e d and r o t a t e d i n t o t h e p l a n e o f p r i n c i p a l s h e a r . In the- f i e l d t h e s e f o l d s o c c u r as r a r e , o u t c r o p - s c a l e , s i m i l a r s t y l e , t i g h t t o i s o c l i n a l f o l d s , commonly w i t h w e l l d e v e l o p e d p a r a s i t i c f o l d s a n d s m a l l s c a l e t r a n s p o s i t i o n f a b r i c s a l o n g t h e i r l i m b s ( F i g . 2 6 ) . The f o l d s i n v a r i a b l y have g e n t l y p l u n g i n g , n o r t h - n o r t h w e s t e r l y t r e n d i n g f o l d a x e s . W e l l d e v e l o p e d F1 f o l d s o c c u r o n l y i n s c h i s t o s e a r e a s w i t h few m y l o n i t i c r o c k s ; i n c i p i e n t t r a n s p o s i t i o n f a b r i c s a r e t h e o n l y e v i d e n c e of d u c t i l e s h e a r i n t h e s e a r e a s . In t h e m y l o n i t e s i s o c l i n a l f o l d s o c c u r l o c a l l y a s s m a l l s c a l e r o o t l e s s i n t r a f o l i a l f o l d s w h i c h f l o a t i n a d a r k , m y l o n i t i c m a t r i x . T h e s e may r e p r e s e n t t r a n s p o s e d F1 h i n g e s . A l t e r n a t i v e l y t h e y c o u l d have d e v e l o p e d s y n k i n e m a t i c a l l y d u r i n g m y l o n i t i z a t i o n as s m a l l s c a l e s h e a t h f o l d s ( C o b b o l d and Q u i n q u i s 1980). E l s e w h e r e t h e F1 f o l d s were p r o b a b l y c o m p l e t e l y d i s r u p t e d by t h e p r o g r e s s i v e f l a t t e n i n g a n d a s s o c i a t e d d u c t i l e s h e a r i n g , w h i c h e v e n t u a l l y p r o d u c e d t h e f i n e g r a i n e d m y l o n i t e f a b r i c s so t y p i c a l of much of t h e Gamsby Group. The e a r l y f o l d s , t r a n s p o s i t i o n f e a t u r e s and m y l o n i t e f a b r i c s a r e h e r e c o l l e c t i v e l y d e s i g n a t e d as F 1 . T o g e t h e r t h e s e f e a t u r e s i n d i c a t e 84 FIGURE 26 F l minor f o l d with i n c i p i e n t t r a n s p o s ition f o l i a t i o n , Gamsby Group 85 t h e inhomogeneous n a t u r e o f d e f o r m a t i o n . L o c a l l y p r e s e r v e d e n c l a v e s of m a s s i v e , u n f o l i a t e d g r e e n s t o n e i n t h e Gamsby Group s u p p o r t t h e i m p r e s s i o n t h a t d u c t i l e s h e a r i n g was m a i n l y c o n c e n t r a t e d a l o n g d i s c r e t e z o n e s . A measure of s t r a i n i n some of t h e n o n - m y l o n i t i c domains i s p r o v i d e d by t h e p r e s e n c e o f f o l d e d s y n k i n e m a t i c v e i n s and d y k e s w h i c h have i n t r u d e d t h e l a y e r e d r o c k s o b l i q u e l y . T h e i r f o l d a x e s a r e p a r a l l e l t o t h e r e g i o n a l l i n e a r t r e n d and t h e y a r e f o l d e d a b o u t t h e c o m p o s i t i o n a l bands. T h e s e f e a t u r e s c l e a r l y i n d i c a t e t h e e f f e c t o f f l a t t e n i n g p e r p e n d i c u l a r t o t h e f o l i a t i o n . T h a t t h i s was a c c o m p a n i e d by e x t e n s i o n a l f l o w i s shown by t h e p r e s e n c e of e l o n g a t e m i n e r a l a g g r e g a t e s , b o u d i n s and ' p i n c h and s w e l l ' s t r u c t u r e s i n n e a r b y , h e t e r o g e n e o u s l y l a y e r e d s e q u e n c e s . M i c r o s c o p i c t e x t u r e s i n d i c a t e t h a t p r o g r a d e metamorphism i n t h e Gamsby Group and C e n t r a l G n e i s s Complex a c c o m p a n i e d F1 d e f o r m a t i o n . F1 a p p e a r s t o have been f o l l o w e d by a s t a t i c e p i s o d e , d u r i n g which t h e C e n t r a l G n e i s s Complex r e m a i n e d a t h i g h t e m p e r a t u r e s , r e s u l t i n g i n a n n e a l e d F1 f a b r i c s ( C h a p t e r 2 ) . F o l l o w i n g t h i s e p i s o d e , t h e a r e a was s u b j e c t e d t o renewed f o l d i n g ( F 2 ) , p r o b a b l y a f t e r t h e c u l m i n a t i o n o f metamorphism, as F1 f e a t u r e s a r e w e l l p r e s e r v e d i n t h e Gamsby Group, and no new m i n e r a l a s s e m b l a g e s a s s o c i a t e d w i t h t h i s l a t e r p hase were o b s e r v e d . F2 i s r e p r e s e n t e d by a s y m m e t r i c , e a s t e r l y v e r g i n g , open t o t i g h t , d i s h a r m o n i c f o l d s and k i n k s r a n g i n g from m i c r o s c o p i c t o o u t c r o p s c a l e ( F i g . 2 7 ) . In a few c a s e s where F1 f o l d s were s e e n t o be r e f o l d e d by F2, t h e two p h a s e s were c o a x i a l . W i t h o n l y a few e x c e p t i o n s , t h e o r i e n t a t i o n s of a l l o t h e r F2 f o l d s s u g g e s t t h e y a r e c o a x i a l w i t h F1 as w e l l . Hence FIGURE 27 F2 disharmonic f o l d o v e r p r i n t i n g e a r l i e r deformed Gamsby Group 87 F1 and F2 are not distinguished on the equal area nets. In some cases a weakly developed a x i a l planar s t r a i n - s l i p cleavage i s present in the hinges of F2 folds. Some of the mylonites are crosscut by a crenulation cleavage. In the f i e l d F2 a x i a l planar cleavage has moderate, westerly to southwesterly dips. In thin section the angles between mylonitic f o l i a t i o n and crenulation cleavage do not appear to exceed 35°. A west over east sense of rotation implied by the F2 folds i s supported by the presence of rare, spherical or e l i p s o i d a l , rotated blocks of country rock with sigmoidal internal structure and l a t e r a l pegmatite t r a i l s . These rotation features appear to have behaved somewhat l i k e b a l l bearings. Figure 28 schematically i l l u s t r a t e s the main F1 and F2 deformational features. F2 deformation was followed by b r i t t l e shearing (F3), evidently under d i f f e r e n t conditions than those accompanying myIonitization. The associated structures are narrow fault zones, generally roughly p a r a l l e l to the F1 f o l i a t i o n and characterized by well developed c a t a c l a s t i c f a b r i c s . Where the c a t a c l a s t i c zones cut across e a r l i e r planar features, these are folded on a small scale about axes which are coaxial to F1 and F2 foldaxes. Internally these zones are marked by anastomosing fractures which are commonly polished and slickensided. Slickensides plunge gently in a westerly to southwesterly d i r e c t i o n . The fractures wrap around small, l e n t i c u l a r bodies of rock in which the older fabric elements, although l o c a l l y rotated and crushed, are mostly well preserved. These features are best developed and become more abundant toward the eastern 88 L2 CRENULATION TRANSPOSITION FABRIC F2 FOLD F1 FOLD F2 AXIAL PLANE CLEAVAGE F1 MYLONITE ZONES L1 EXTENSION LINEATION F i g . 28 Schematic representation of F l and F2 deformational features, western domain 89 contact of the Gamsby Group, where the f o l i a t i o n steepens and sheared lenses of foreign, presumably Lower Cretaceous, volcanic material are incorporated in Gamsby Group rocks. The oldest preserved contact with the rocks to the east i s abrupt (Fig. 29), and i s marked by a tabular body of phacoidal, c a t a c l a s t i c granite in which a prominent fracture network i s oriented p a r a l l e l to both c a t a c l a s t i c and mylonitic f o l i a t i o n s in the Gamsby Group. Close to the contact small lenses of Gamsby Group are incorporated in the granite. The other side of the granite body i s marked by well-developed poly-cataclastic fault breccias. The entire zone just described is a major, b r i t t l e shear zone, which in a l l likelyhood becomes more gently dipping at depth. It appears to connect along s t r i k e to the north with a gently westerly dipping shear zone, exposed along the Tahtsa Lake road. The overa l l concordance of t h i s shear zone with f o l i a t i o n s in the Gamsby Group suggest i t to be a l o c a l l y steepened thrust f a u l t . Later folding and f a u l t i n g have disrupted t h i s thrust, and only a small remnant is preserved on the east side of the ridge south of the logging road. The l a t e s t folding event (F4) in the metamorphic rocks i s represented by gentle, assymetric, north verging flexures about subhorizontal , east-west trending axes. 90 FIGURE 29 C a t a c l a s t i c shear zone / t h r u s t f a u l t at base of Gamsby Group . Dark rocks are sheared meta-volcanics, buff weathering rocks are sheared, p h a c o i d a l , c a t a c l a s t i c g r a n o d i o r i t e 91 EASTERN DOMAIN A number of closely related, north-northwest trending shear zones, which are younger than the thrust on which the Gamsby Group was emplaced, presently form most contacts between the eastern and western domains. They are marked by cohesive c a t a c l a s t i c fault-breccias as well as zones of extremely fine grained, varicoloured fault gouge, and are commonly associated with c a t a c l a s t i c quartz-muscovite pegmatite lenses. Slickensides on these fault surfaces indicate s t r i k e - s l i p displacement, at least for the latest movements. Minor dextral displacement, probably less than 5 km, i s suggested by offset of matching stratigraphic horizons of the Cretaceous volcanic and sedimentary rocks across the fault zone west of h i l l 1490. Perhaps the northerly verging flexures (F4) in the Gamsby Group are related to movements along t h i s f a u l t . A few north-northwest trending f a u l t s east of the contacts between the western and eastern domains appear to show minor s i n i s t r a l s l i p , but these fault s can also be interpreted as d i p - s l i p f a u l t s , with down-faulted western blocks. Near the eastern boundary of the map area, northeast of the gl a c i e r on the north flank of 'Khawachen Mtn.', a northerly trending, steeply dipping shear zone i s characterized by a well developed penetrative f o l i a t i o n in rocks of the Telkwa Formation. L i t h o l o g i c a l l y the sheared rocks resemble some rocks of the Gamsby Group, but they grade into the Telkwa Formation over distances of one to three m. Just west of the t r a n s i t i o n , the rocks of the Telkwa Formation are commonly sheared in a more b r i t t l e , c a t a c l a s t i c fashion. Yet further west the Telkwa 92 Formation i s traversed by discrete, north-northwest trending zones with a well-developed fracture cleavage p a r a l l e l to the steeply dipping bedding. S l i g h t l y northeast of the study area, the sheared rocks of the Telkwa Formation are bordered by a zone of agmatite and associated plutonic rock (Fig. 3). These may have provided heat for the formation of penetrative f o l i a t i o n and the development of greenschist facies assemblages (epidote, c h l o r i t e , a l b i t e ? ) . Further east the plutonic rocks are faulted against basal conglomerates of the Kasalka Group (Mclntyre 1976) and v o l c a n i c l a s t i c rocks of the Telkwa Formation. This i s the easternmost fault of the Sandifer Lake Fault Zone. With the possible exception of the shear zone near the eastern boundary of the map area, the north-northwest trending fa u l t s cut across an e a r l i e r northeast-southwest trending fault zone which, east of the prominent flood p l a i n , forms the boundary between the Cretaceous volcanic/plutonic complex and the Telkwa Formation. Along much of i t s length the fault zone has northerly dips shallow enough for i t to qua l i f y as a thrust. This thrust was disrupted during later events; the fault contact between the Cretaceous and the Telkwa Formation, west of the gl a c i e r at the head of the flood p l a i n , has steep westerly dips and a c u r v i l i n e a r trend. Although the geometric relations between th i s contact and other fault or shear zones in t h i s area are not well understood, i t seems l i k e l y that i t i s a highly disrupted thrust, along which rocks belonging to the Coast Plutonic Complex, including the Cretaceous volcanic/plutonic complex, were emplaced over rocks of the Intermontane Belt. The allochtonous nature of the Cretaceous complex with respect to 93 t h e I n t e r m o n t a n e B e l t i s d i s c u s s e d i n C h a p t e r 7. I t must be e m p h a s i z e d t h a t t h e t h r u s t j u s t d e s c r i b e d i s n o t r e a d i l y r e c o g n i z a b l e i n t h e f i e l d . The s i n g l e b e s t e x p o s u r e o c c u r s j u s t n o r t h of t h e a r e a w i t h P e r m i a n o l i s t o l i t h s . However, i n f o l l o w i n g t h i s zone a c r o s s t h e f l o o d p l a i n t o t h e west, i t a p p e a r s t o c o n n e c t w i t h a n o r t h e r l y d i p p i n g t h r u s t f a u l t w h i c h l i e s e n t i r e l y w i t h i n t h e C r e t a c e o u s complex. The l a c k of l i t h o l o g i c a l c o n t i n u i t y o f u n i t s a c r o s s t h e v a l l e y j u s t s o u t h o f t h i s f a u l t c o n t r a s t s w i t h t h e c o n t i n u i t y o f t h e C r e t a c e o u s s e d i m e n t a r y sequence a b o u t 1.5 km t o t h e n o r t h . The i n f e r e n c e i s t h a t t h e t h r u s t i s not a s i n g l e f a u l t , but i s c o m p l i c a t e d w i t h s u b s i d i a r y s p l a y s , and i s p a r t o f a l a r g e r s c a l e zone of a n a s t o m o s i n g t h r u s t f a u l t s . L a t e r movements a l o n g s t r i k e - s l i p f a u l t s , w h i c h may i n p a r t be r e j u v e n a t e d , s t e e p e n e d , t h r u s t f a u l t s , and a l o n g s t e e p l y d i p p i n g d i p - s l i p f a u l t s , c o m p l i c a t e m a t t e r s even more. The C r e t a c e o u s r o c k s west of t h e f l o o d p l a i n have been f o l d e d i n t o a n o r t h e a s t t r e n d i n g , g e n t l y p l u n g i n g s y n c l i n e . P r e s u m a b l y t h e f o l d i n g o c c u r e d i n r e s p o n s e t o c o m p r e s s i v e s t r e s s p r i o r t o o r s y n c h r o n o u s w i t h t h r u s t i n g . The o r i g i n o f t h e s t e e p , NNW t r e n d i n g f r a c t u r e c l e a v a g e , c a t a c l a s t i c f a b r i c , and p e n e t r a t i v e f o l i a t i o n i n t h e T e l k w a F o r m a t i o n i s p o o r l y u n d e r s t o o d . The f r a c t u r e c l e a v a g e may be y o u n g e r t h a n th e t h r u s t i n g w h i c h j u x t a p o s e d t h e C o a s t P l u t o n i c Complex a g a i n s t t h e I n t e r m o n t a n e B e l t . Below t h e n o r t h e a s t t r e n d i n g t h r u s t i t l o c a l l y a p p e a r s t o o v e r p r i n t a t h r u s t -r e l a t e d , e a s t - n o r t h e a s t e r l y s t r i k i n g c l e a v a g e , a s s o c i a t e d w i t h s t r e t c h e d l i m e s t o n e c o b b l e s i n T r i a s s i c v o l c a n i c b r e c c i a . To t h e 94 south, northeast of the glacier occupying the north flank of 'Khawachen Mtn.', the late cleavage i s well developed. There i t is oriented p a r a l l e l to bedding, and i s very evident because the rocks are fine grained mudstones, which lack any e a r l i e r , penetrative f a b r i c . The most recent structural features in the study area are steeply dipping d i p - s l i p f a u l t s and fractures. In part these late features follow e a r l i e r zones of weakness and have in turn provided conduits for the emplacement of a variety of veins and dykes. Two main orientations of steeply dipping faults and fractures are present, one with a northeast s t r i k e , the other with a north-northwest s t r i k e . Where evidence was found, the western sides of these faul t s are downdropped. One of the northeasterly s t r i k i n g f a u l t s , which is partly covered by the glacier feeding the Tsaytis River, may be of economic importance. Along i t s length are irregular masses of pyrite-bearing quartz. A grab sample of mineralized quartz assayed 0.52 oz/ton Au and 0.8 oz/ton Ag. 95 CHAPTER 5 : AGE RELATIONS AND GEOCHRONOLOGY OF THE METAMORPHIC ROCKS One of the objectives of the present study was to understand age relations of the Central Gneiss Complex and the Gamsby Group. No diagnostic f o s s i l material has been found to date in either group. Rare c r i n o i d stems, present in meta-carbonates of both groups (Woodsworth pers comm.), indicate a maximum age of Ordovician. Isotopic dating of the Central Gneiss Complex by Armstrong and Runkle (1979) has indicated a probable late Paleozoic to early Mesozoic age. However, to date no precise ages of deposition have been established for any of the metamorphic rocks in the northern Coast Plutonic Complex. Age assignments have depended on regional geologic c o r r e l a t i o n based on lithology and structural setting (e.g. Baer 1973; Roddick 1970; Hutchison 1982; Roddick and Hutchison 1974). Stuart (i960) and Read (unpubl rep.) correlated the greenschist facies l i t h o l o g i e s of the Tahtsa Lake-Tsaytis River area with the Jurassic Hazelton Group, which crops out only short distances to the east. Both workers interpreted the tr a n s i t i o n to be one of progressive westward increase in metamorphic grade. The metamorphic rocks were f i r s t recognized and named as a d i s t i n c t unit by Woodsworth (1978), who postulated a Paleozoic age on the basis of lack of l i t h o l o g i c c o r r e l a t i o n with known Mesozoic rocks to the east and the presence between them of a complexely faulted t r a n s i t i o n zone. Further f i e l d study of thi s zone has not resolved the question of age of the metamorphic rocks. 96 For the present study, samples of Central Gneiss Complex, Gamsby Group and related intrusives were co l l e c t e d for K/Ar, Rb/Sr . and U/Pb analysis. A n a l y t i c a l methods and results are given in Appendix 3. A l i s t i n g of analysed samples is included in Tables III and IV. For Rb/Sr isochrons the York-1 model (York 1967) has been used throughout. This gives errors based on the scatter of points about the regression. The scattered data obtained do not j u s t i f y more elaborate regression analyses. CENTRAL GNEISS COMPLEX-Rb/Sr analysis of seven samples of gneiss scatter widely on a Sr evolution diagram (Fig. 30). Except for specimen 80-55, the samples form an oval shaped cluster suggestive of f a i r l y low i n i t i a l 8 7 S r / 8 6 S r r a t i o s , 0.7035 to 0.7050. Specimen V80-55 comes from outcrops which immediately overly a prominent meta-carbonate package. Its higher r a t i o suggests that i t may have reacted with seawater and aquired an oceanic Sr component, which would have had a 8 7 S r / 8 6 S r r a t i o of 0.707 - 0.708 in Paleozoic time. The scatter in the remainder of the suite widely exceeds a n a l y t i c a l error and does not show any clear c o r r e l a t i o n between 8 7 S r / 8 6 S r and Rb/Sr r a t i o . This appears to be a common problem in Rb/Sr analysis of polymetamorphic terranes (Cameron et a l 1981). The samples represent two d i f f e r e n t suites (granitoid gneiss and amphibolite) which are probably not oogenetic; the individual data clusters for these two suites likewise do not hint at any isochron interpretation. The scatter of points may 0.708 0.7061 u vO CO u oo 0.7041 ~---°='*B ^ Amphibolite, Central Gneiss Complex | Granitoid gneiss, Central Gneiss Complex O Central Gneiss Complex, Hawksbury Island from Armstrong and Runkle (1979) ' • Gamsby Group 0.4 i 0.8 1.2 87„, ,86_ Rb/ Sr Fig. 30 Sr evolution diagram, Central Gneiss Complex VO 98 well be due to open system behaviour during magmatic injection and regional metamorphism. The new Central Gneiss Complex analyses scatter over the same area of the evolution diagram as the samples with lower Rb/Sr values reported by Armstrong and Runkle (1979), working on Central Gneiss Complex 100 km west of the study area. They concluded that the Sr isotopic composition of the Central Gneiss Complex i s compatible with* late Paleozoic to early Mesozoic precursor ages of mantle-derived volcanic rocks, and l o c a l presence of 8 7 S r / 8 6 S r enriched marine carbonate. The new analyses suggest a similar conclusion, but likewise f a i l to define a precise p r o t o l i t h age. GAMSBY GROUP Rb-Sr : Metavolcanic rocks Twelve samples, from two d i f f e r e n t areas, produce an isochron which yields a model age of 160 ± 24 Ma, with a i n i t i a l r a t i o of 0.7039 (Fig. 31). However, considering that these are samples from d i f f e r e n t l o c a l i t i e s and that several appear to be somewhat anomalous, (P174, P168 and P279), the samples can be grouped in a variety of ways. The resulting isochron dates range from 135 to 176 Ma, with a mean of about 157 Ma. This i s approximately equal to the age generated by a l l samples. Therefore, the 160 ± 24 Ma date is interpreted as s i g n i f i c a n t in terms of Sr evolution, but i t may not represent a p r o t o l i t h age. When sample P279, the only sample with a high Rb/Sr r a t i o , i s excluded from the groups, a l l calculated dates tend to be higher. For instance, the isochron date for seven samples from a F i g . 31 Sr evolution diagram, Gamsby Group 100 single l o c a l i t y on the ridge south of the logging road i s 230 ± 39 Ma, with an i n i t i a l r a t i o of 0.7039. This date may give an indication of the depositional age of the Gamsby Group. The 160 Ma date probably r e f l e c t s the time of regional resetting of Rb-Sr during a metamorphic event. Metamorphic resetting has been observed to result in loss of radiogenic Sr in samples high in Rb 8 7, providing an explanation for the anomalous position of specimen P279 with respect to the 230 Ma isochron. Samples from the 'Khawachen Mtn.' area, because of their proximity to several small synkinematic granitoid intrusive bodies, may also show the e f f e c t s of metamorphic resetting. However, the low 8 7 S r / 8 6 S r r a t i o of specimen P174 is enigmatic. The interpretation of these ages is in general agreement with data obtained from additional Rb/Sr, K/Ar and U/Pb determinations of Gamsby Group l i t h o l o g i e s , which are discussed below. The cluster formed by Gamsby Group points i s superimposed on F i g . 30 for comparison with the results for the Central Gneiss Complex. The extensive overlap of Central Gneiss Complex and Gamsby Group samples could mean that they are not s i g n i f i c a n t l y d i f f e r e n t in age or o r i g i n , but i s not proof of those propositions. Rb/Sr : Mylonitic granite Four samples of mylonitic granite (Jgl) form a tight cluster on a Sr evolution diagram (Fig. 32). The calculated isochron date i s 139 ± 99 Ma, with a i n i t i a l r a t i o of 0.7043. Forcing an isochron through the mean value and an assumed i n i t i a l r a t i o of 0.704, which i s closer to the calculated 0.708 u .7061 oo 0 0 u OO oo 0.704 O Mean value of 4 points Rb/ 8 6Sr F i g . 32 Sr evo l u t i o n diagram, mylonitic granite, Gamsby Group 102 i n i t i a l r a t i o for the Gamsby Group metavolcanics, gives an approximate age of 159 Ma. This age i s close to the suggested time of metamorphic resetting of the enclosing metavolcanic rocks, and may represent either a time of emplacement or time of metamorphism of an older granitoid intrusive body. K/Ar : Hornblende d i o r i t e and intrusive dykes Analysis of two hornblende separates, one from gneissic hornblende d i o r i t e (Jg2), the other from an undeformed, c h i l l e d -margin microdiorite dyke intrusive into the gneissic d i o r i t e , y i e l d ages of 145 i 5 Ma and 66 ± 2 Ma respectively. The f i r s t date i s interpreted as representing the time of cooling of the Gamsby Group through the hornblende Ar retention temperature (approximately 500°C). This could have been soon after granite emplacement or during subsequent dynamothermal metamorphism. The second date c l e a r l y represents the time of emplacement of the dyke into much cooler country rock. U-Pb : metarhyolite Approximately 80 kg of white, f i n e l y laminated meta-rhyolite from a interbedded sequence of f e l s i c and mafic meta-volcanics about 2 km west-southwest of 'Khawachen Mtn.', yielded 81.6 mg of zircon. Isotope analysis of this separate yielded a near concordant (concordant within a n a l y t i c a l error) U/Pb date of 210 Ma, which should be considered a minimum age for the sample. The 2 0 7 P b / 2 0 6 P b date i s 241 Ma. However, the r e l a t i v e l y large error in such young Pb/Pb dates precludes putting any great amount of confidence in this intercept. Likewise, an upper concordia intercept of 315 Ma, arrived at graphically by using the 160 Ma Rb/Sr resetting date as an assumed lower intercept, 103 cannot be taken too seriously. In conclusion, the available evidence suggests that the Gamsby Group i s upper Paleozoic to Upper T r i a s s i c in age. It appears to have been subjected to resetting of Rb/Sr isotopic systems in Middle Jurassic time, possibly in conjunction with intrusion of g r a n i t i c material. Cooling through the hornblende Ar retention temperature occurred in Upper Jurassic time and the rocks were cold and probably close to the surface by the end of the Cretaceous. The Central Gneiss Complex could be a high-grade equivalent of the Gamsby Group, but t h i s i s not proven. 1 04 CHAPTER 6 : EVOLUTION OF THE UPPER TSAYTIS RIVER AREA A comprehensive evolutionary picture of an area as small as the thesis area i s d i f f i c u l t to present without incorporating regional geological data. However, for the eastern Coast Plutonic Complex and western Intermontane Belt in central B r i t i s h Columbia the large scale evolution i s only poorly known. Chapter 7, in which an interpretation of the regional geology is presented, i s consequently rather speculative, and w i l l be subject to continual revision in l i g h t of new discoveries. This Chapter summarizes the history of the thesis area using as l i t t l e external information as possible. As w i l l be discussed in Chapter 7, the thesis area i s interpreted to occur in a single terrane, S t i k i n i a , which has southerly Mesozoic paleolatitudes with respect to neighbouring cratonic North America. Most of the events described in the following paragraphs probably occured far south of the present location of the upper Tsaytis River area. The oldest, widely exposed rocks of the thesis area are the upper Paleozoic or T r i a s s i c metavolcanics and metacarbonates of the Gamsby Group and Central Gneiss Complex. The volcanic rocks and associated carbonates, formed in a mature island arc environment, which was the s i t e of eruption of c a l c - a l k a l i n e and t h o l e i i t i c basalt and andesite, and c a l c - a l k a l i n e dacite and r h y o l i t e . At an unknown distance to the east there may have been a carbonate shelf (Monger 1977a), now represented by deformed and isolated Lower Permian carbonate o l i s t o l i t h s ( ? ) and other erosional debris enclosed in Upper T r i a s s i c and Lower Jurassic sedimentary and v o l c a n i c l a s t i c strata of the Intermontane Belt. 105 The Lower P e r m i a n c a r b o n a t e d e b r i s s u g g e s t s p o s t Lower Permian t o E a r l y J u r a s s i c t e c t o n i c i n s t a b i l i t y and e r o s i o n of P a l e o z o i c s t r a t a i n t h e I n t e r m o n t a n e B e l t . S y n c h r o n o u s t e c t o n i c a c t i v i t y i n t h e C o a s t P l u t o n i c Complex, i f i n d e e d i t o c c u r e d , has been e f f e c t i v e l y masked by l a t e r o r o g e n i c p r o c e s s e s . D u r i n g e a r l y M e s o z o i c t i m e t h e I n t e r m o n t a n e B e l t was t h e s i t e o f m a r i n e s e d i m e n t a t i o n , v o l c a n i s m and c a r b o n a t e d e p o s i t i o n , r e p r e s e n t e d by Upper T r i a s s i c s h a l e , s i l t s t o n e , v o l c a n i c b r e c c i a and c o r a l l i n e l i m e s t o n e . Between K a r n i a n and S i n e m u r i a n t i m e t h e a r e a may have been emergent. S i n e m u r i a n s e d i m e n t a r y and v o l c a n i c l a s t i c r o c k s , f o r m i n g t h e base of t h e Te l k w a F o r m a t i o n , were d e p o s i t e d i n a non-marine e n v i r o n m e n t . The S i n e m u r i a n v o l c a n i c l a s t i c r o c k s r e p r e s e n t i n i t i a l v o l c a n i c a c t i v i t y of t h e E a r l y J u r a s s i c H a z e l t o n a r c ( T i p p e r and R i c h a r d s 1976a). N o t h i n g i s known a b o u t t h e w e s t e r n p a r t o f t h e s t u d y a r e a i n Upper T r i a s s i c and Lower J u r a s s i c t i m e . The e a r l i e s t p o s t d e p o s i t i o n a l e v e n t known t o have a f f e c t e d t h e r o c k s of t h e C e n t r a l G n e i s s Complex and t h e Gamsby Group i s a complex o r o g e n i c c y c l e w h i c h l a s t e d i n t o M i d d l e and L a t e J u r a s s i c t i m e . D u r i n g t h i s t i m e t h e s t r a t i f i e d r o c k s o f t h e C o a s t P l u t o n i c Complex were i n t r u d e d by g r a n i t o i d m a t e r i a l , r e g i o n a l l y metamorphosed and p l a s t i c a l l y d e f o r m e d .. ( F 1 ) . The g e o l o g i c a l c o n f i g u r a t i o n a p p e a r s t o have been t h e e a s t m a r g i n of an o r o g e n i c w e l t i n w h i c h h o t , a m p h i b o l i t e f a c i e s g n e i s s e s o f t h e C e n t r a l G n e i s s Complex were f o l d e d and t h r u s t o v e r s t r a t i g r a p h i c a l l y e q u i v a l e n t b u t l o w e r g r a d e , g r e e n s c h i s t f a c i e s l i t h o l o g i e s o f t h e Gamsby Group. T h i s s u p e r p o s i t i o n may have 106 i n i t i a l l y o c c u r r e d i n a l a r g e s c a l e , e a s t e r l y v e r g i n g recumbent f o l d nappe. P r e s e n t l y o n l y i t s d i s r u p t e d l o w e r l i m b r e m a i n s . Nappe f o r m a t i o n was a c c o m p a n i e d by i n j e c t i o n of g r a n o d i o r i t i c m a t e r i a l i n t o r o c k s n e a r t h e a m p h i b o l i t e - g r e e n s c h i s t f a c i e s b o u n d a r y and a l s o by t h e d e v e l o p m e n t o f t r a n s p o s i t i o n , e x t e n s i o n and m y l o n i t e f a b r i c s , p a r t i c u l a r l y i n t h e Gamsby G r o u p . S t r u c t u r a l i n v e r s i o n i n t h e l o w e r l i m b o f t h e f o l d nappe o r t e c t o n i c i m b r i c a t i o n r e s u l t e d i n i n v e r s i o n o f metamorphic i s o g r a d s . The p r e s e n t d i s t r i b u t i o n o f metamorphic a s s e m b l a g e s i n t h e C e n t r a l G n e i s s Complex i n d i c a t e s t h a t t h e h i g h e s t t e m p e r a t u r e i s o t h e r m s d i d not have t i m e t o r e a d j u s t t o a s t e a d y -s t a t e c o n d u c t i v e h e a t - f l o w p a t t e r n . T h i s s u g g e s t s t h a t t h e p r o c e s s o f nappe f o r m a t i o n was f a i r l y r a p i d . The nappe c o r e was a t o r r e m a i n e d a t s u f f i c i e n t l y h i g h t e m p e r a t u r e s f o r many o f t h e d e f o r m a t i o n a l f e a t u r e s i n t h e C e n t r a l G n e i s s Complex t o be a n n e a l e d . R e t r o g r e s s i v e metamorphism o f t h e b a s a l p a r t of t h e g n e i s s i c s e q u e n c e p r o b a b l y o c c u r e d b o t h d u r i n g and a f t e r d e f o r m a t i o n a s a c o n s e q u e n c e o f p r o g r a d e d e h y d r a t i o n of t h e u n d e r l y i n g g r e e n s c h i s t s and m y l o n i t e s . C o n t i n u i n g movement and d u c t i l e d e f o r m a t i o n (F2) s u p e r i m p o s e d a s s y m e t r i c , d i s h a r m o n i c f o l d s on e a r l i e r s t r u c t u r e s . The metamorphic r o c k s c o o l e d t h r o u g h t h e h o r n b l e n d e K/Ar r e t e n t i o n i s o t h e r m i n L a t e J u r a s s i c t i m e . T h i s o r o g e n i c e p i s o d e i s not documented i n t h e e a s t e r n , I n t e r m o n t a n e B e l t p a r t o f t h e t h e s i s a r e a . The p o s t Lower J u r a s s i c s t r a t i g r a p h i c r e c o r d i s no l o n g e r p r e s e n t t h e r e . D u r i n g E a r l y C r e t a c e o u s t i m e ( H a u t e r i v i a n ? ) t h e e a s t e r n f l a n k of t h e C o a s t P l u t o n i c Complex was t h e s i t e o f nonmarine 107 e x p l o s i v e a n d e s i t i c t o r h y o l i t i c v o l c a n i s m a n d f l u v i a l s e d i m e n t a t i o n . The v o l c a n i c and s e d i m e n t a r y r o c k s may have been d e p o s i t e d on t h e e a s t e r n f l a n k of t h e u p l i f t e d J u r a s s i c o r o g e n ; t h e i r r e l a t i o n s h i p w i t h o l d e r r o c k s of t h e C o a s t P l u t o n i c Complex, a l t h o u g h not p r o v e n , i s h e r e i n t e r p r e t e d as a s t r u c t u r a l l y i n v e r t e d b a s e m e n t - c o v e r s e q u e n c e . P r i o r t o t e c t o n i c d i s r u p t i o n , t h e C r e t a c e o u s v o l c a n i c - s e d i m e n t a r y s e q u e n c e was i n v a d e d by g r a n i t i c p l u t o n s and p a r t i a l l y h o r n f e l s e d . Up t o t h i s p o i n t i n t i m e t h e t e c t o n i c h i s t o r y o f t h e C o a s t P l u t o n i c Complex and I n t e r m o n t a n e B e l t a p p e a r t o have been q u i t e i n d e p e n d a n t . Lower C r e t a c e o u s s t r a t a of t h e I n t e r m o n t a n e B e l t (Skeena G r o u p ) , w h i c h o c c u r o n l y a s h o r t d i s t a n c e t o t h e e a s t of t h e t h e s i s a r e a , a r e m a r i n e s e d i m e n t s w i t h an e a s t e r l y s o u r c e , a l t h o u g h m i n o r i n t e r b e d d e d t u f f s may have been d e r i v e d from v o l c a n o s i n t h e C o a s t P l u t o n i c Complex. The n o n-marine v o l c a n i c s t r a t a i n t h e upper T s a y t i s R i v e r a r e a do n o t show any t r a n s i t i o n i n t o t h e s e m a r i n e s e d i m e n t s . In M i d d l e or Upper C r e t a c e o u s t i m e ( C h a p t e r 7) t h e C o a s t P l u t o n i c Complex and t h e Lower C r e t a c e o u s v o l c a n i c - s e d i m e n t a r y -g r a n i t i c u n i t s were t h r u s t n o r t h e a s t o v e r t h e I n t e r m o n t a n e B e l t a l o n g a s e r i e s of i m b r i c a t e d and a n a s t o m o s i n g b r i t t l e s h e a r z o n e s . A s s o c i a t e d c a t a c l a s t i c d e f o r m a t i o n a l f e a t u r e s (F3) a r e p r e s e n t a t many l e v e l s of t h i s i m b r i c a t e c o m p l e x . C u m u l a t i v e s h o r t e n i n g a c r o s s t h e t h r u s t zone may have been s u b s t a n t i a l , c o n s i d e r i n g t h e d i f f e r e n t a p p e a r a n c e of t h e C o a s t P l u t o n i c Complex, i n t e r m e d i a t e t e c t o n i c s l i c e s , and t h e I n t e r m o n t a n e B e l t . N e v e r t h e l e s s , t h e t h r u s t zone i s c o n s i d e r e d t o be d e v e l o p e d e n t i r e l y w i t h i n S t i k i n i a . 108 The t i m e p e r i o d f o l l o w i n g t h r u s t i n g was marked by a change from c o m p r e s s i o n a l t e c t o n i c s , t h r o u g h a p e r i o d o f m i n o r s t r i k e -s l i p f a u l t i n g and a s s o c i a t e d d e f o r m a t i o n ( F 4 ) , t o e x t e n s i o n a l d i p - s l i p f a u l t i n g . E a r l i e r s t r u c t u r e s became s e v e r e l y d i s r u p t e d and c o n s e q u e n t l y a r e n o t e a s i l y r e c o g n i z e d i n t h e f i e l d . The j u x t a p o s e d u n i t s i n t h e e a s t e r n p a r t of t h e s t u d y a r e a were i n t r u d e d by a d i s t i n c t i v e s t o c k o f m i c r o g r a p h i c g r a n i t e and a s s o c i a t e d d y k e s . O t h e r p o s t - k i n e m a t i c i n t r u s i o n s a r e r e p r e s e n t e d by s m a l l p l u g s o f g r a n o d i o r i t e , g r a n i t e and m i c r o d i o r i t e , and by d i a b a s e and l a m p r o p h y r e d y k e s and dyke swarms. 109 CHAPTER 7 : REGIONAL GEOLOGY Remapping of the Whitesail Lake map area (Woodsworth 1980) has provided a.regional background for the present study. Figure 3 i s a regional compilation map of the west-central Whitesail Lake area, based primarily on information provided by G. Woodsworth of the Geological Survey of Canada and to some extent on personal experience in the area. The major map units present in Figure 3 have been described by Woodsworth (1979), and are b r i e f l y characterized on the legend. The general d i s t r i b u t i o n and i n t e r r e l a t i o n s of the various map-units are not s i g n i f i c a n t l y d i f f e r e n t from those on Woodsworth's map. However, several areas in Figure 3, such as those north and northeast of the Tsaytis River area, have been modified so that they f i t into a tectonic model based on detailed fieldwork in the upper Tsaytis River area. Detailed mapping of these other areas would undoubtedly improve the map, but the central hypothesis underlying the following discussion i s believed to be e s s e n t i a l l y correct. This discussion, f i r s t of the Coast Plutonic Complex and then of the Intermontane Belt, uses Figure 3 as a basis for a wide ranging review and analysis of the Coast Plutonic Complex-Intermontane Belt boundary. COAST PLUTONIC COMPLEX The Central Gneiss Complex and associated metamorphic and plutonic rocks have been described by a number of authors (e.g. Roddick 1970, Runkle 1979, Hutchison 1982). The Central Gneiss Complex forms a extensive, elongate belt along the core of the 110 Coast Mountains northwest of Dean Channel, Bella Coola map area. In southeastern Alaska high grade metamorphic rocks underly extensive areas of the Coast Plutonic Complex, and appear to be co r r e l a t i v e with the Central Gneiss Complex (Berg et a l . 1977, Smith 1977). These have been referred to as the Tracy Arm terrane (Berg et a l . 1978). Southeast of Dean Channel, gneiss and migmatite occur as isolated pendants enclosed in younger plutonic and metamorphic rocks; l i t t l e i s known about the stratigraphic continuity of these gneisses. It i s not certain i f the core gneisses of the northern and southern Coast Plutonic Complex represent a single tectono-stratigraphic unit. In several domains within the Central Gneiss Complex/Tracy Arm terrane the layering i s r e l a t i v e l y f l a t l y i n g ; gneiss forms extensive homoclinal slabs of con'siderable thickness (Berg et a l . 1977; Hutchison 1982; Roddick 1970; M.L. H i l l , personal communication). In part, these may represent limbs of large scale recumbent folds, such as those described by Hutchison in the Prince Rupert area. In the Douglas Channel map area, east of the Quottoon Pluton, Roddick recognized a gently to moderately northeast dipping gneissic sequence, which forms the eastern limb of the large scale, southwesterly overturned Foch antiform. Southeast, along Gardner Canal, a gently dipping succession of gneisses and migmatites i s interlayered with thick, granitoid s i l l s (Fig. 3), and further east, in the upper Tsaytis River area, the gneisses form the upper plate of the large scale thrust complex described in previous chapters. Steeply dipping sequences are not uncommon, but appear to occur only where the over a l l horizontal or gently dipping sequences have been 111 disrupted by folding, f a u l t i n g and intrusion of large, elongate plutons. Granitic bodies such as the Tsaytis Pluton and the Dubose Stock (Fig. 3) are an important part of the core zone of the Coast Plutonic Complex. Many bodies, such as the Quottoon and E c s t a l l Plutons in the Prince Rupert and Douglas Channel map areas, reach very large dimensions. These bodies are commonly somewhat enigmatic in that they exhibit both intrusive (discordant) and intimately interlayered and infolded relations with neighbouring gneisses. The g r a n i t i c rocks are commonly f o l i a t e d , p a r t i c u l a r l y along their margins. Folding of the Tsaytis pluton and marginal gneisses i s similar in style to F2 folds in the upper Tsaytis River area. The gneisses contain additional evidence for e a r l i e r , i s o c l i n a l folding, which is absent in the plutonic rocks. It may be that the plutons in the western Whitesail Lake map area were emplaced during the same orogenic event which produced the transposition and mylonite fabrics (F1) in the Gamsby Group. This event was dated at 145 to 160 Ma or e a r l i e r (Chapter 5). There is one problem in cor r e l a t i n g the gneisses surrounding the Tsaytis Pluton and the Dubose Stock with those in the upper Tsaytis River area. The gneisses and associated plutons in the western part of Figure 3 did not cool through the hornblende and b i o t i t e Ar blocking temperatures u n t i l Eocene time. The Tsaytis Pluton has concordant hornblende-biotite K-Ar dates of about 50 Ma (Wanless et a l . 1979). Parrish has calculated a 45 to 50 Ma K-Ar mica date for the Dubose Stock based on measured apatite and zircon f i s s i o n track dates and 1 1 2 regional heat-flow data (Parrish 1982). Contrasting with these Eocene dates are Cretaceous and Jurassic K-Ar dates for the metamorphic terrane which forms the eastern flank of the Coast Plutonic Complex. The gneisses in the Upper Tsaytis River area are s t r u c t u r a l l y and probably s t r a t i g r a p h i c a l l y c o r r e l a t i v e with the Gamsby Group, which has a hornblende K-Ar date of 145 Ma (Chapter 5). The Tahtsa Complex, a d i o r i t i z e d volcanic unit at the head of Tahtsa Lake, in which the volcanic component may be c o r r e l a t i v e with the Gamsby Group (Woodsworth 1978), has a hornblende K-Ar date of 175±10 Ma near i t s eastern margin (Woodsworth personal communication). Lastly, the Horetzky Dyke, a coarse grained, d i l a t i o n a l feature with c h i l l e d margins, which cuts across the Central Gneiss Complex-Gamsby Group-Tahtsa Complex boundaries, has a b i o t i t e K-Ar date of 73±2 Ma (Wanless et a l . 1979). This date is interpreted to be close to the time of emplacement, and i s similar to the 65±2 Ma date for a dyke with c h i l l e d margins which cuts the Gamsby Group in the thesis area (Chapter 5). The Dubose Stock i s separated from the Horetzky Dyke by a westerly dipping fault zone, which i s inferred to extend to the south beyond the boundary of Figure 3. Its connection with the eastern boundary of the Tsaytis Pluton just north of the Tsaytis River i s based on a traverse from just east of t h i s contact into the homoclinal part of the gneissic terrane. For a distance of about 2.5 km east of the contact the gneisses are highly folded and generally have steep dips, but no structural break is present. Further south, the eastern boundary of the plutonic rocks i s a d i s t i n c t shear zone. It i s suggested that this 1 13 thermal(?) and structural break, here informally c a l l e d the Kemano Fault, i s the eastern boundary of a large c r u s t a l block within the Central Gneiss Complex, which was rapidly u p l i f t e d in Eocene time. Rapid Eocene u p l i f t i s well documented for the core of the Central Gneiss Complex and associated plutons in the Prince Rupert area ( H o l l i s t e r and Sherwood 1980, H o l l i s t e r 1982) . Zonal d i s t r i b u t i o n of K-Ar ages in the western Coast Plutonic Complex has long been interpreted in terms of sequential u p l i f t . Crawford and H o l l i s t e r (1982) have suggested that the Work Channel lineament in the Prince Rupert area i s a major str u c t u r a l break between the Tsimpsean Peninsula with Cretaceous u p l i f t ages (about 85 Ma), and the core zone of the Central Gneiss Complex with rapid u p l i f t and cooling in Eocene time. P a r t i a l resetting of isotopic systems in the western terrane by heat from the r i s i n g , hot core zone during Eocene u p l i f t may have resulted in the gradual eastward increase in K-Ar dates; no sharply defined chronological break appears to be present. The east side of the Coast Plutonic Complex i s perhaps a mirror image of the west side, and the inferred Kemano Fault may be an analogue of the Work Channel lineament. It i s notable that the major structures in the two marginal domains have opposite vergence, suggesting that the Coast Plutonic Complex at this latitude i s part of a two-sided orogen. Included with the Coast Plutonic Complex in the thrust complex are three large, pre-kinematic plutonic masses which are not well understood. These are, from north to south : 1) A east-west oriented body of medium grained 1 1 4 granodiorite and quartz d i o r i t e west of the southern end of Nanika Lake. Stuart (1960) describes t h i s body as a composite intrusion, in which the granodiorite i s characterized by strongly developed c a t a c l a s t i c f a b r i c s . His description and i l l u s t r a t i o n (Stuart's Plate XVI) of this fabric however, are more suggestive of d u c t i l e deformation. These rocks are either p r o t o c l a s t i c (terminology of Higgins 1971) or they are true mylonites. Pre-Cretaceous dates obtained from p l a s t i c a l l y deformed granitoid rocks in the thesis area suggest a similar age range for the sheared body near Nanika Lake. 2) The Tahtsa Complex (Stuart 1960), which underlies a large area at the head of Tahtsa Lake. Woodsworth has interpreted t h i s complex as a d i o r i t i z e d volcanic unit similar to many basic complexes found in the Coast Plutonic Complex, and ten t a t i v e l y correlated i t with- the Gamsby Group. A 175±10 Ma hornblende K-Ar date for agmatite of the Tahtsa Complex indicates a pre-Middle Jurassic age for the volcanic component. In a few places near the western contact, screens of schistose rock strongly suggest that the Tahtsa Complex is a large scale agmatite body developed within the Gamsby Group. Stuart (1960) mentions that the Tahtsa Complex i s commonly sheared and fractured, and l o c a l l y intrusive quartz d i o r i t e i s characterized by a gneissic f o l i a t i o n which deflects around d i o r i t e blocks. These have been rotated and flattened p a r a l l e l to the f o l i a t i o n . Stuart's description of the gneissic f o l i a t i o n i s again suggestive of a mylonitic f a b r i c . The overa l l s i m i l a r i t y of f a b r i c , structure and K-Ar date of the complex with the d i o r i t i z e d and agmatized zone overlying the mylonitic granite in 1 15 the upper Tsaytis River area i s quite s t r i k i n g and supports Woodsworth's c o r r e l a t i o n . However, not a l l agmatite bodies in thi s general area are of the same age. D i o r i t i z a t i o n of the Lower Cretaceous volcanics in the hanging wall of the frontal thrust has produced agmatites which are indistinguishable from the undeformed v a r i e t i e s in the Tahtsa Complex. In addition, intrusive granitoid and d i o r i t i c bodies in both units are somewhat similar in appearance. Their close proximity near Sandifer Lake combined with the structural complexity of thi s area may mean that some of the d i o r i t i c and granitoid areas mapped as Tahtsa Complex may in r e a l i t y belong to the Cretaceous volcanic/plutonic assemblage and vice versa. The t r a n s i t i o n from Lower Cretaceous volcanic rocks into the topographically (and structurally?) low lying d i o r i t e complex needs to be examined further. 3)' The Black Dome Complex, a heterogeneous body composed of massive to well layered d i o r i t e , greenstone and mafic dykes which have been metamorphosed (retrograded?) under greenschist facies conditions (Woodsworth 1979a). Veins and dykes of quartz d i o r i t e have l o c a l l y produced agmatitic structures. Foliated and lineated screens resembling greenschists of the Gamsby Group, gradations into coarse grained hornblendite, and well developed north-northwest trending shear zones are l o c a l l y present. Along the western contact, the gently dipping Gamsby Group gradually steepens and at the contact both units have steep dips. Possibly t h i s unit represents a deformed and metamorphosed layered intrusion within the Gamsby Group. A hornblende K-Ar date of 344±88 Ma, obtained from layered d i o r i t e 116 (Woodsworth personal communication), is somewhat enigmatic in view of other age determinations for the Gamsby Group. However, i t s younger age l i m i t overlaps in middle Permian time with the older age l i m i t of the Gamsby Group as determined by Rb-Sr chronometry, and is within the range of ages suggested by the zircon U-Pb date. More isotopic dates are needed for the Black Dome Complex. The Gamsby Group appears to extend to the north beyond the Whitesail Lake area. This i s indicated by the presence of l i t h o l o g i c a l l y i d e n t i c a l greenschist facies f e l s i c and mafic metavolcanic strata and associated carbonate, east of the Central Gneiss Complex near Shames, along the Skeena River (Terrace map area). Five metavolcanic samples from t h i s area were analysed for Rb-Sr r a t i o and Sr isotopic composition as part of thi s thesis. A n a l y t i c a l results are l i s t e d in Appendix 3. The results y i e l d an isochron date of 150±47 Ma with a i n i t i a l r a t i o of 0.70504. When disregarding the sample highest in 8 7Rb, which may have lost radiogenic Sr during metamorphism, the res u l t i n g isochron i s considerably older, at 254±53 Ma, with a i n i t i a l r a t i o of 0.70475. Here, as in the upper Tsaytis River area, an upper Paleozoic or lower Mesozoic precursor age is implied. The somewhat higher i n i t i a l ratios of the Shames metavolcanics as compared with those of the Gamsby Group mirror a similar trend observed for higher grade gneisses of the Central Gneiss Complex, between Douglas Channel and Prince Rupert areas (R.L Armstrong personal communication). In the west-central Whitesail Lake area the Lower Cretaceous volcanic rocks, which are situated between the Coast 1 1 7 Plutonic Complex and the Intermontane Belt, were perhaps deposited on an orogenic land mass cored by the Central Gneiss Complex and Gamsby Group, west of a marine, Intermontane basin. Such a r e l a t i o n would be similar to the one developed in the Mt. Waddington and Taseko Lakes map areas in Early Cretaceous time (Tipper 1969). There, Lower Cretaceous volcanic and sedimentary rocks c o r r e l a t i v e with those in the Whitesail Lake area, rest unconformably on metamorphosed Upper T r i a s s i c rocks. They were deposited on the western flank of a Jurassic and Cretaceous marine sedimentary basin, the Tyaughton Trough. Interestingly, the structural and metamorphic relations in the Mt. Waddington area are also similar to those in the Whitesail Lake map area. The Upper T r i a s s i c volcanic rocks, c o r r e l a t i v e with the 'Wrangellian' Karmutsen Formation of Vancouver Island (Tipper, personal communication), increase dramatically in metamorphic grade into the Coast Mountains. Tipper postulated a Middle Jurassic orogeny to explain the metamorphism, both in the Coast Plutonic Complex and in the adjacent Intermontane Belt. After Early Cretaceous time the Upper T r i a s s i c rocks were thrust in a northeast d i r e c t i o n over their volcanic and sedimentary cover (Tipper 1969, 1978; Woodsworth 1979a). Lower Cretaceous (Hauterivian) volcanic and sedimentary rocks occur as isolated pendants across large parts of the southern Coast Mountains (for an example see Heah 1982), and along the eastern boundary of the Coast Plutonic Complex between the Mt. Waddington and Whitesail Lake areas. These rocks have been c o l l e c t i v e l y correlated with the Gambier Group (Woodsworth and Tipper 1980; Tipper et a l . 1981), and form the remnants of an extensive Lower Cretaceous 118 v o l c a n i c a r c . The C r e t a c e o u s t e c t o n i c f r o n t a l o n g t h e e a s t e r n b o u n d a r y of t h e C o a s t P l u t o n i c Complex i n t h e W h i t e s a i l Lake a r e a i s c h a r a c t e r i z e d by n o r t h e a s t e r l y d i r e c t e d , i m b r i c a t e o v e r t h r u s t i n g ( C h a p t e r 4 ) . The o r i e n t a t i o n o f t h e f r o n t a l t h r u s t i s n o r t h -n o r t h w e s t e r l y f r o m N a n i k a Lake t o 'Khawachen Mtn.', from where i t t a k e s on a more e a s t e r l y t r e n d . Between 'Khawachen Mtn.' and Mt. Musclow t h e Gamsby Group a p p e a r s t o r e s t d i r e c t l y on r o c k s of t h e I n t e r m o n t a n e B e l t . N o r t h o f 'Khawachen Mtn.' t h e f r o n t a l t h r u s t c o n t a c t i s between E a r l y C r e t a c e o u s (Gambier Group?) v o l c a n i c r o c k s and t h e T e l k w a F o r m a t i o n . I t i s t o be e x p e c t e d t h a t t h e s t r u c t u r a l s u c c e s s i o n w i l l n o t be c o n t i n u o u s a l o n g s t r i k e . The z o n e s of t h r u s t movement may have a l a r g e s c a l e a n a s t o m o s i n g c h a r a c t e r and i n d i v i d u a l l i t h o l o g i c a l u n i t s and t e c t o n i c s l i c e s w i l l p i n c h out a t f a u l t i n t e r s e c t i o n s . However, t h e b r i t t l e d e f o r m a t i o n a l c h a r a c t e r i s t i c s s h o u l d r e m a i n more or l e s s t h e same a l o n g t h e l e n g t h of t h e t e c t o n i c f r o n t . The t h r u s t complex i s d i s r u p t e d and masked by s t e e p l y d i p p i n g , n o r t h - n o r t h w e s t t r e n d i n g f a u l t s and s h e a r z o n e s . These o c c u r a s much as 25 km e a s t of t h e Kemano F a u l t and may a l s o be r e l a t e d t o e a r l y C e n o z o i c u p l i f t of t h e c o r e of t h e C o a s t M o u n t a i n s . L i m i t e d amounts o f s t r i k e - s l i p m o t i o n on t h e s e f a u l t s , a few km a t t h e most, c a n be i n f e r r e d , f r o m t h e map-p a t t e r n . The c u m u l a t i v e e f f e c t i s one o f e n - e c h e l o n d e x t r a l d i s p l a c e m e n t . L a t e r d i p - s l i p m o t i o n a l o n g o t h e r h i g h a n g l e f a u l t s has f u r t h e r c o n t r i b u t e d t o d i s r u p t i o n o f t h e t e c t o n i c f r o n t . The b o u n d a r y between t h e C o a s t P l u t o n i c Complex and 1 19 I n t e r m o n t a n e B e l t i n t h e Mt. W a d d i n g t o n and T a s e k o L a k e s a r e a s i s a c o m b i n a t i o n o f t h r u s t f a u l t s s u c h as t h o s e m e n t i o n e d above, and t h e d e x t r a l Y a l a k o m - T c h a i k a z a n t r a n s c u r r e n t f a u l t s y s t e m , w h i c h a p p e a r s t o have formed a l o n g t h e a x i s o f t h e m i d - M e s o z o i c T y a u g h t o n T r o u g h . F u r t h e r s o u t h , i n t h e A s h c r o f t a r e a , r e c e n t mapping h a s r e v e a l e d t h e p r e s e n c e o f w e s t e r l y d i p p i n g t h r u s t f a u l t s a l o n g t h e e a s t e r n f l a n k o f t h e C o a s t P l u t o n i c Complex (Monger 1982). Here t h e b o u n d a r y w i t h t h e I n t e r m o n t a n e B e l t i s th e F r a s e r F a u l t . C o n t i n u i n g s o u t h , a c r o s s t h e i n t e r n a t i o n a l b o r d e r , on t h e e a s t s i d e o f t h e S t r a i g h t C r e e k F a u l t , t h e J a c k M o u n t a i n t h r u s t has been i n t e r p r e t e d by M i s c h (1966) t o be an e a s t v e r g i n g s t r u c t u r e of m i d d l e C r e t a c e o u s t o e a r l y L a t e C r e t a c e o u s a g e . T h i s t h r u s t has j u x t a p o s e d v o l c a n i c r o c k s of t h e Hozameen G r o u p o v e r E a r l y C r e t a c e o u s s e d i m e n t a r y r o c k s o f t h e T y a u g h t o n T r o u g h . The t h r u s t s j u s t m e n t i o n e d a r e a p p r o x i m a t e l y t h e same age, and a l l a r e bounded on t h e i r west s i d e by v o l c a n i c , m e tamorphic and p l u t o n i c r o c k s w h i c h c a n n o t be matched l i t h o l o g i c a l l y w i t h c o r r e l a t i v e r o c k s f u r t h e r e a s t . The t h r u s t s a p p e a r t o be o l d e r t h a n m a j o r t r a n s c u r r e n t f a u l t s (Yalakom, F r a s e r , S t r a i g h t C r e e k ) ; t h e y o c c u r on e i t h e r s i d e of t h e s e f a u l t s and may have been p a r t l y t r u n c a t e d and d i s p l a c e d by them. N o r t h w e s t of t h e W h i t e s a i l Lake map a r e a , i n t h e v i c i n i t y o f S t e w a r t , G r o v e (1971) has d e s c r i b e d a complex, west d i p p i n g , m y l o n i t i c and c a t a c l a s t i c s h e a r zone a l o n g t h e e a s t e r n b o u n d a r y of t h e C o a s t P l u t o n i c Complex. I t must be m e n t i o n e d t h a t B e r g d e s c r i b e d w e s t - d i r e c t e d t h r u s t i n g o f I n t e r m o n t a n e B e l t l i t h o l o g i e s o v e r t h e C o a s t P l u t o n i c Complex i n t h e same a r e a 1 20 (Berg et a l . 1977). However, the map pattern for thi s structure in r e l a t i o n to topography suggests a east verging thrust, with rocks of the Coast Plutonic Complex overlying 1 the Intermontane Belt. Grove correlated sheared volcanic rocks with the Hazelton Group, but they are intruded by the mylonitic Texas Creek granodiorite (Smith 1977), which has yielded a K-Ar date of 210 Ma. The sheared volcanics are in some ways similar to the Gamsby Group. Perhaps they are part of the same tectonostratigraphic terrane; as previously mentioned, the Gamsby Group does appear to extend beyond the Whitesail Lake map area to the northwest, but how far i s not known. In the Stikine and A t l i n areas the boundary relations between the Coast Plutonic Complex and the Intermontane Belt are not c l e a r l y understood. Bultman (1979) mapped an east-dipping, high angle normal fault , the Llewellyn f a u l t , which separates amphibolite and greenschist facies metamorphic rocks of the Coast Plutonic Complex from Upper T r i a s s i c and Jurassic strata of the Intermontane Belt. Clasts of amphibolite and K-Ar dated Upper T r i a s s i c porphyritic granodiorite, i d e n t i c a l to rocks of the Coast Plutonic Complex, occur in basal conglomerates of the Upper T r i a s s i c Stuhini Group of the Intermontane Belt, suggesting the geographical coincidence of the Llewellyn fault with a major unconformity. Werner (1978) has also suggested an unconformable relationship between rocks of the Coast Plutonic Complex and Intermontane Belt, in the Mt. Mussen area at the south end of A t l i n Lake. The available information indicates that the northern boundary between the Coast Plutonic Complex and Intermontane Belt l i e s within a single, coherent terrane 121 ( S t i k i n i a ) . High grade metamorphic rocks occur as small, isolated domains within the Intermontane Belt in the Stikine area (Souther et a l . 1979), but whether or not they are c o r r e l a t i v e with the metamorphic terrane of the Coast Plutonic Complex to the west i s not known. The pre-Upper T r i a s s i c rocks of the northern Intermontane Belt have been affected by the Middle T r i a s s i c Tahltanian orogeny (Souther 1971,1972). Pre-Upper T r i a s s i c metamorphism of the northern Coast Plutonic Complex is indicated by discordant plutons with Upper T r i a s s i c K-Ar cooling ages (Bultman 1979). Deformational structures in the eastern Coast Plutonic Complex at this latitude are northeasterly verging folds and minor thrusts (Werner 1978, Bultman 1979), which contrast with the opposite vergence of sub-i s o c l i n a l folds further southwest, in the Juneau Ice F i e l d area (Forbes 1959). A fundamental question i s whether the metamorphic terrane of the central Coast Plutonic Complex is t r u l y allochtonous with respect to the Intermontane Belt, as appears to be the case along the southern, 'Wrangellian' part of the Coast Plutonic Complex, or i f i t i s perhaps u p l i f t e d basement of western S t i k i n i a , as appears to be the case along the northern Coast Plutonic Complex. The l a t t e r case seems to be the most l i k e l y one; the tectonic front along the eastern flank of the central Coast Plutonic Complex does not appear to be a suture such as would be expected to occur between tectono-stratigraphic terranes i n i t i a l l y separated by oceanic material. There i s also no evidence to suggest large scale transcurrent displacements along t h i s part of the Coast Plutonic Complex. 1 22 INTERMONTANE BELT The area east of the Cretaceous tectonic front of the Coast Plutonic Complex is underlain by volcanic, sedimentary and intrusive rocks representing a f a i r l y complete record of Mesozoic and Cenozoic time. In the west-central Whitesail Lake map area, the Intermontane Belt l i e s almost e n t i r e l y within the physiographic Coast Mountains. However, valley floors are d i s t i n c t l y wider than in the Coast Plutonic Complex and in the north-east corner, past Tahtsa Reach, they open up into the Interior Plateau. The position of the frontal thrust of the-Sandifer Lake Fault Zone roughly coincides with a l i n e connecting the head of a large lake system, which prior to the opening of the Alcan tunnel at the head of Tahtsa Lake in 1952 drained e n t i r e l y to the east. These lakes define the location of a Tertiary f l u v i a l system which drained off the eastern side of the ancestral Coast Mountains. Lower Permian and Upper T r i a s s i c strata are r e s t r i c t e d to the thesis area. The Lower Permian carbonates are co r r e l a t i v e with carbonates in the Terrace map area (Woodsworth 1979a), which also occur just east of the Coast Plutonic Complex. The Upper T r i a s s i c strata may be a unique, l o c a l volcanic-sedimentary feature because they cannot be readily matched with Upper T r i a s s i c strata elsewhere in the Intermontane Belt at these l a t i t u d e s . In the extreme northeast corner of the Whitesail Lake map area, the Upper T r i a s s i c strata are volcanic rocks belonging to the Takla Group. The presence of deformed Lower Permian c l a s t i c debris in 123 Upper T r i a s s i c v o l c a n i c l a s t i c rocks indicates erosion of an u p l i f t e d terrane and suggests the presence of an unconformity separating Upper T r i a s s i c and Permian rocks. Gaps in the tr a n s i t i o n from Paleozoic to Mesozoic time are present in many other areas of the Intermontane Belt. In northern B r i t i s h Columbia the Permian-Triassic unconformity i s associated with the Tahltanian orogeny (Souther 1971, 1972). The inferred gap in the stratigraphic record of the thesis area may be a result of i n s t a b i l i t y related to this orogeny. The suggested hiatus between marine Karnian and non-marine Sinemurian and the continued presence of Permian c l a s t i c material in the Sinemurian stra t a , indicate that tectonic i n s t a b i l i t y continued into Mesozoic time. Further east Sinemurian strata are marine (Tipper 1979); a similar facies pattern i s found in the Smithers area. (Tipper and Richards 1976b). In the Whitesail Lake map area the general pattern i s one of change from Early Jurassic, largely subaerial arc volcanism to Middle Jurassic marine successor basin sedimentation. The Middle Jurassic Nechako basin i s a southerly analogue of the Bowser basin, from which i t was separated by the Skeena Arch, which shed detritus into both basins from late Bajocian to early Callovian time. Near the Coast Mountains the Middle Jurassic sediments contain minor proportions of thin, tuffaceous beds, suggesting that volcanism may have continued in the Coast Mountains u n t i l this time. It would be of interest to find out i f any part of the western Nechako and Bowser basins received sediment from the west during Middle Jurassic time, when the Coast Plutonic Complex was the s i t e of a major orogeny. 1 24 Events of post-Callovian to e a r l i e s t Cretaceous time are not recorded in strata of the Nechako basin. The oldest post-Jurassic deposits are marine sandstones, shales, and conglomerates of the Albian Skeena Group. North of Coles Lake the contact between the Skeena Group and the Bowser Lake Group appears to be conformable, suggesting an Upper Jurassic and Lower Cretaceous hiatus without tectonism. Westerly and southwesterly transport directions indicate a easterly source terrane for the Skeena Group, probably the then emergent Omineca C r y s t a l l i n e Belt. West of Laventie Creek along Tahtsa Lake minor tuffaceous beds suggest volcanic a c t i v i t y further west, in the present location of the Coast Plutonic Complex. The absence of Lower Cretaceous volcanic rocks, such as those presently exposed nearby in the upper Tsaytis River and Sandifer Lake areas, is of considerable importance. The lack of l i t h o l o g i c continuity between non-marine and marine strata of approximately the same age, hints at s i g n i f i c a n t movement along the fro n t a l thrust of the Sandifer Lake Fault Zone. The western side of the Albian marine basin i s no longer exposed and may now be t e c t o n i c a l l y buried beneath part of the Coast Plutonic Complex. Unconformably overlying the Skeena Group are upper Albian to Cenomanian(?), non-marine sedimentary and volcanic rocks of the Kasalka Group (Maclntyre 1976). Their base i s a d i s t i n c t i v e red and green conglomerate composed predominantly of volcanic c l a s t s . Northwest of Seel Lake this conglomerate attains considerable thickness and contains abundant d i o r i t e boulders resembling rocks of the Tahtsa Complex (Woodsworth 1979a). This 125 conglomerate may represent a c l a s t i c wedge associated with the a r r i v a l of the Coast Plutonic Complex along the Sandifer Lake Fault Zone. It would be interesting to make an inventory of the dif f e r e n t c l a s t types in this conglomerate for comparison with known rocks in the upper plates of the thrust zone. The conglomerate i s extensive but not voluminous; soon after deposition i t became buried under thick deposits of andesitic to r h y o l i t i c pyroclastic rocks, lahars and minor flows. A detailed description of Kasalka volcanism and related, economically important subvolcanic intrusions, was provided by Maclntyre (1976), who interpreted the geology of this time period in terms of a large cauldron subsidence complex centered about the area north of Mt. Bolom, in a region undergoing extension. Thrusting along the Sandifer Lake Fault Zone probably began with the widespread marine regression in upper Albian time in the Intermontane Belt. This time period is c l e a r l y one of major tectonic importance, not just in the Whitesail Lake area, but along the entire eastern boundary of the southern Coast Plutonic Complex, where i t coincided with marine regression in the Tyaughton Trough (Tipper 1969). The sudden eruption of vast amounts of continental volcanics over an area previously characterized by marine successor basin deposition indicates a major, reorganization of tectonic elements in the western C o r d i l l e r a . The fr o n t a l thrust of the Sandifer Lake Fault Zone may have overridden the Kasalka Group, although there i s no evidence to support t h i s , and the time of cessation of thrust motion along on the Sandifer Lake Fault Zone is not precisely known. The 126 Horetzky Dyke i s similar in age and lithology to many of the subvolcanic intrusions described by Maclntyre, and i t cuts the upper plates of the thrust zone. The fr o n t a l thrust i s cut by the Eocene Gamsby Stock. A neighbouring Paleocene pluton, which intrudes both the Gamsby Group and strata of the Intermontane Belt, i s probably also post-kinematic. Available evidence therefore indicates pre-Eocene cessation, and suggests pre-Late Cretaceous cessation, at least for the upper thrusts. Within the Intermontane Belt three zones with northeasterly s t r i k i n g , imbricated thrust sheets occur in the Sibola, Whitesail and Chikamin Ranges respectively. These may be related to the emplacement of the Coast Plutonic Complex. North of Coles Lake small, northeast verging folds in one of the thrust plates suggest motion from the southwest. Other indications of northeasterly directed tectonic transport within the Intermontane Belt are present on Lindquist Peak, where a well developed, southwestward dipping fracture cleavage is present in rocks of the Skeena Group. Also, a gentle soutward dipping fracture cleavage i s present in some of the Lower Jurassic strata east of 'Khawachen Mtn.'. Evidence for northeast directed tectonic transport east of the Coast Plutonic Complex in middle to Late Cretaceous and early Cenozoic time i s present in widely separated parts of B r i t i s h Columbia. Brief examples of thi s are : 1) Northeast directed thrusting south of King Salmon Lake in northern B r i t i s h Columbia (Tipper personal communication). 2) Northeast directed assymetric folds and related thrusts in the Bowser and Sustut Basins (Eisbacher 1974, 1981). 127 3) Northeast directed thrusting in the Smithers map area (Tipper and Richards 1976a). 4) Northeast directed thrusting north of the Yalakom Fault in the Taseko Lakes area (Tipper 1978). 5) Northeast directed thrusting in the Manning Park area (Coates 1974). It may be that a l l these thrusts are related to the development of a continuous tectonic front along the entire eastern margin of the Coast Plutonic Complex. Motion along the front may have been time-transgressive and highly variable in intensity from place to place. The Cenozoic history of the Intermontane Belt was characterized by continental volcanism and high angle f a u l t i n g . In the Whitesail Lake map area Eocene time is marked by r h y o l i t i c and d a c i t i c p y r o c l a s t i c and subvolcanic rocks and flows of the Ootsa Lake Group; by basalt and andesite flows and minor gabbro plugs of the Endako Group; and by high l e v e l granitoid bodies such as the Gamsby Stock and the Nanika intrusions. Gentle easterly dips of Endako Group strata suggest that they were t i l t e d during Eocene u p l i f t of the Coast Mountains and block f a u l t i n g in the Intermontane region. In contrast, Miocene plateau basalts in Tweedsmuir Park east of Whitesail Range and beyond the area covered by Figure 3, occur in f l a t l y i ng sheets which have inundated a older topography represented by the Quanchus H i l l s . The plateau basalts have apparently not been affected by block f a u l t i n g . Woodsworth (1979) postulated a mid-Cretaceous age for the 128 o n s e t of b l o c k f a u l t i n g . I t would seem t h a t t h i s t y p e of f a u l t i n g m i g h t be r e l a t e d t o u p l i f t of t h e I n t e r m o n t a n e B e l t above sea l e v e l s i n c e l a t e A l b i a n t i m e . E a r l y h i g h a n g l e f a u l t s may have been c o n j u g a t e s e t s of s m a l l s c a l e s t r i k e - s l i p f a u l t s , w h i c h d e v e l o p e d i n r e s p o n s e t o c o m p r e s s i o n a l t e c t o n i c s a l o n g t h e t e c t o n i c f r o n t . D i p - s l i p m o t i o n , p a r t l y a l o n g t h e same f a u l t s , may n o t have o c c u r e d u n t i l a f t e r emplacement o f t h e C o a s t P l u t o n i c Complex was c o m p l e t e d . CONCLUDING REMARKS The r e g i o n a l g e o l o g y o f t h e w e s t e r n I n t e r m o n t a n e B e l t and e a s t e r n C o a s t P l u t o n i c Complex s u g g e s t s l a r g e s c a l e n o r t h e a s t -s o u t h w e s t t e c t o n i c s h o r t e n i n g a c r o s s p r e v i o u s l y amalgamated t e c t o n o - s t r a t i g r a p h i c t e r r a n e s ( W r a n g e l l i a / A l e x a n d e r and S t i k i n i a ) i n l a t e M e s o z o i c t i m e . M i d d l e - U p p e r J u r a s s i c o r o g e n y i n t h e c e n t r a l C o a s t P l u t o n i c Complex may be a r e f l e c t i o n of an e a r l y s t a g e of s u t u r i n g of t h e s e t e r r a n e s a l o n g a zone s i t u a t e d somewhere t o t h e s o u t h w e s t of t h e W h i t e s a i l Lake map a r e a . The metamorphosed and h i g h l y d e f o r m e d m e t a v o l c a n i c r o c k s of t h e C e n t r a l G n e i s s Complex and t h e Gamsby Group a r e t h e r e m a i n s of a upper P a l e o z o i c a n d / o r l o w e r M e s o z o i c i s l a n d a r c , w h i c h fo r m e d t h e w e s t e r n edge o f S t i k i n i a . The m e t a v o l c a n i c r o c k s and i n t e r b e d d e d m e t a c a r b o n a t e s and m e t a p e l i t e s may be c o r r e l a t i v e w i t h P e r m i a n and o l d e r s t r a t a of t h e S t i k i n e A s s e m b l a g e (Monger 1977a) o f c e n t r a l and n o r t h e r n B r i t i s h C o l u m b i a . Of t h e d i f f e r e n t g r o u p s w i t h i n t h i s a s s e m b l a g e t h e P e r m i a n A s i t k a G r o u p i s most l i k e t h e Gamsby Group i n t e r m s o f l i t h o l o g y , c h e m i s t r y and t e c t o n i c s e t t i n g . T h i s c o r r e l a t i o n was p r e v i o u s l y s u g g e s t e d 129 by Woodsworth (1978). However, the Asitka Group occurs in the eastern margin of S t i k i n i a and may have originated in a d i f f e r e n t arc than the Gamsby Group. The Lower Permian volcanic and carbonate rocks in the Terrace area and the Lower Permian o l i s t o l i t h s ( ? ) in the thesis area do not appear to be l a t e r a l l y contiguous with the volcanic arc suites. The arc volcanics of the Coast Plutonic Complex and the Lower Permian strata of the Intermontane Belt are here interpreted as d i f f e r e n t facies which were juxtaposed during middle or Late Cretaceous tectonic shortening. The formation of the tectonic front along the eastern boundary of the Coast Plutonic Complex may have been a continuation of the suturing process in a r e l a t i v e l y high heat flow environment, such as found in back-arc settings (Armstrong and Dick 1974). The Lower Cretaceous Gambier Group and intruding g r a n i t i c rocks may be remnants of the f i r s t arc to have formed following amalgamation of the Wrangellia/Alexander terrane and S t i k i n i a ; these remnants occur as a cover sequence on both terranes in and near the Coast Plutonic Complex. The contemporaneous subduction complex is the P a c i f i c Rim Complex of Vancouver Island and the Chugach terrane of southeastern Alaska. Tectonic shortening appears to have been accompanied or followed by a dramatic eastward jump of the volcanic arc into the Intermontane Belt, which from then on was to remain above sea l e v e l . The thrust complex along the Coast Plutonic Complex-Intermontane Belt boundary has apparently followed previous l i n e s of crustal weakness. In southern B r i t i s h Columbia 130 i t roughly p a r a l l e l s the suture between Wrangellia and S t i k i n i a ; in central B r i t i s h Columbia the thrust zone i s superimposed on S t i k i n i a , and coincides with the mylonitic eastern margin of the Middle and Upper Jurassic c o l l i s i o n a l orogen. In northern B r i t i s h Columbia the tectonic front, i f present, does not appear to be very well developed. Perhaps high angle faults have disrupted and obscured the presence of a Cretaceous thrust complex. In any case, the boundary between the tectonic belts in northern B r i t i s h Columbia i s probably situated well within S t i k i n i a . In summary, the Coast Plutonic Complex in central B r i t i s h Columbia i s considered to be the product of a Middle to Late Jurassic c o l l i s i o n a l orogeny in the western edge of S t i k i n i a . Jurassic-Cretaceous tectonic shortening occured in a high heat flow environment along the eastern flank of the orogen, with b r i t t l e structures overprinting a previously established zone of intense, mylonitic deformation. The suggested sequence of events is reminiscent of that in the Caledonian orogen in Scotland, where la t e , cratonward movement occured along the Moine Thrust (Dewey and Pankhurst 1970), long after formation of du c t i l e deformational features. Subsequent u p l i f t of the metamorphic core zone, perhaps concurrent with s t r i k e - s l i p movement along north-northwest trending f a u l t s , and extensional f a u l t i n g in Cenozoic time, have considerably disrupted the Cretaceous tectonic front. 131 BIBLIOGRAPHY Abbey, S. 1980 : Studies in "Standard samples" for use in the general analysis of s i l i c a t e rocks and minerals, Part 6 : 1979 edition of "Usable values" ; Geological Survey of Canada, Paper 80-14, 30 p. 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Werner, L.J. 1978 : Metamorphic terrane, northern Coast Mountains west of A t l i n Lake, B r i t i s h Columbia ; in Current research, Part A, Geological Survey of Canada, Paper 78-1A, pp. 69-70. White, S. 1977 : Geological significance of recovery and r e c r y s t a l l i z a t i o n processes in quartz ; Tectonophysics, v39, pp. 143-170. White, S.H., Burrows, S.E., Carreras, J ., Shaw, N.D. and Humphreys, F.J. 1980 : On mylonites in duct i l e shear zones ; Journal of Structural Geology, v2, no. 1/2, pp. 175-187. White, W.H., Erickson, G.P., Northcote, K.E., Dirom, G.E. and Harakal, J.E. 1967 : Isotopic dating of the Guichon batholith ; Canadian Journal of Earth Sciences, v4, pp. 677-690. Winchester, J.A. and Floyd, P.A. 1976 : Geochemical magma type discrimination : application to altered and metamorphosed basic igneous rocks ; Earth and Planetary Science Letters, v28, pp. 459-469. Winchester, J.A. and Floyd, P.A. 1977 : Geochemical discrimination of di f f e r e n t magma series and their d i f f e r e n t i a t i o n products using immobile elements ; Chemical Geology, v20, pp. 325-343. Woodsworth, G.J. 1978 : Eastern Margin of the Coast Plutonic Complex in the Whitesail Lake map-area, B r i t i s h Columbia ; in. Current Research, Part A, Geological Survey of Canada, Paper 78-1A, pp. 71-75. Woodsworth, G.J. 1979 : Geology of the Whitesail Lake map-area, B r i t i s h Columbia ; in Current Research, Part A, Geological Survey of Canada, Paper 79-1A, pp. 25-29. 138 Woodsworth, G.J. 1979-a : Metamorphism, deformation and plutonism in the Mount Raleigh Pendant, Coast Mountains, B r i t i s h Columbia ; Geological Survey of Canada, B u l l . 295, 58 P-Woodsworth, G.J. 1980 : Geology of Whitesail Lake (93E) map-area ; Geological Survey of Canada, Open F i l e map 708. Woodsworth, G.J. and Tipper, H.W. 1980 : Stratigraphic framework of the Coast Plutonic Complex, western B r i t i s h Columbia ; i_n Geol. Assn. Can. Programme and abstracts : Volcanogenic deposits and their regional setting in the Canadian C o r d i l l e r a , pp. 32-34 Yole, R.W. and Irving, E. 1980 : Displacement of Vancouver Island, paleomagnetic evidence from the Karmutsen formation ; Canadian Journal of Earth Sciences, V17, pp. 1210-1228. York, D. 1967 : The best isochron ; Earth and Planetary Science Letters, v2, pp. 479-482. APPENDIX 1 XRF MAJOR ELEMENT ANALYSIS ON PRESSED POWDER PELLETS P. van der Heyden S. Horsky K. Fletcher 140 I. Introduction A rapid XRF procedure to determine major element oxide compositions using pressed powder p e l l e t s has been developed. The method used i s based on that described by G.C. Brown et a l (1973). This procedure uses mass absorption c o e f f i c i e n t s from the Handbook of spectroscopy (1974) to correct for matrix e f f e c t s for both standards and unknowns. Sample background and instrumental d r i f t are also monitored and corrected for. The time consuming preparation of fused discs and the add i t i o n of a heavy element absorber to samples i s avoided. Results appear to be f a i r l y accurate : an i n t e r n a l c a l i b r a t i o n of a l l standards used gives values that deviate le s s than 1% from recommended values for most elements (recommended values are from Abbey (1980) ). However, at present no d e t a i l e d s t a t i s t i c a l analysis of the method has been done. This method i s therefore suggested where a rapid approximate analysis only i s r e -quired. I I . Sample preparation Samples should be ground as f i n e as possible (approx. 200 mesh) i n a r i n g -m i l l and then p e l l e t i s e d as described i n the XRF lab i n s t r u c t i o n sheets. I I I . Instrument settings Instrument settings are summarized on page 143.A d r i f t monitor ( USGS G-2 ) remains i n p o s i t i o n #1 of the sample chamber throughout a n a l y s i s . Each a n a l y t i c a l batch consists of the d r i f t monitor and three standards or unknowns. A coding form (page 144) has been prepared for recording count data. Note that the order i n which elements are analysed i s not the same as that required f o r data input into the computer program. 0 IV. Data handling A program l i s t i n g and example of input and output are provided on pg. 145-154. Data are entered onto cards and subsequently into a d i s c - f i l e i n the following manner : Card # Column / Format Contents '  1 20A4 T i t l e of run 2 10F3.0 Peak counting times i n order : Si,Al,Fe, Mg,Ca,Na,K,Ti,Mn,P 3 10F3.0 Background counting times i n above order. 141 Card # Column / Format Comtents 4 1-6 A6 Standard i d e n t i t y - 7-80 12F6.2 Standard recommended composition i n - weight % i n above order; as many cards as standards ( @ present 17 ) 21 Blank card 22 12X.4F7.0,12X.4F7.0 Count data; monitor and 3 standards for — peak and background; 10 element sets i n — above order; i f the l a s t card i n each set — i s f u l l ( i . e . contains data for 3 stds. ) — , follow i t by a blank card. 82 1-4 A6 Monitor i d e n t i t y ( i s not read by computer ) 5-24 3A6 Sample i d e n t i t y — 25-80 8F7.0 Count data; monitor and 3 samples for -- peak and background; 10 sets of up to 200 — samples. Note under standard count data also applies here. — See also data coding form app. 1 N 1-6 A6 Sample i d e n t i t y (i$ not V&tL t>y cavnfu*,t*\r \ 7-24 2F6.2 Weight % H20+ and C02 of samples; as many cards as samples, i n same order as count data input A normal card deck would look l i k e t h i s : (*) $SIGN0N cc i d pw $CREATE RUN 1 $C0PY *S0URCE* RUN 1 card deck as described above $ENDFILE $RUN PPXRF 5=RUN 1 6=-P $C0PY -P *PRINT* $LIST RIN 1 *PRINT* ( i f copy of input desired) $SIGN0FF V. Program ac t i o n The action of the program i s as follows : 1) Intensity r a t i o s for the standards are regressed against themr known chemical analyses and the r e s u l t i n g quadratic equation i s applied to the in t e n s i t y r a t i o s for a l l standards and unknowns to obtain f i r s t approximate r e s u l t s . 2) Total mass absorption c o e f f i c i e n t s for the standards are calculated from the known chemical analyses and mass absorption c o e f f i c i e n t s and are used *) A card-deck and d i s c - f i l e are a v a i l a b l e for general use; the cards contain a l l standard count and concentration data; the d i s c - f i l e contains an object-deck of the computer program (PPXRF). 142 to generate corrected standard i n t e n s i t y r a t i o s , which are then f i t t e d against the known chemical analyses to derive a new set of quadratic regression l i n e c o e f f i c i e n t s . 3) F i r s t approx. r e s u l t s from 1) are used i n conjunction with known mass absorption c o e f f i c i e n t s to generate t o t a l approximate mass absorption c o e f f i c i e n t s for standards and unknowns. A seires of r a t i o s , crudely corrected for mass absorption, i s then derived f o r standards and unknowns. The regression c o e f f i c i e n t s obtained i n 2) are applied to these crudely corrected r a t i o s to obtain a new a n a l y t i c a l r e s u l t , which i s then recycled i t e r a t i v e l y to generate new mass absorption corrected i n t e n s i t y r a t i o s and a further refined a n a l y s i s , u n t i l l successive r e s u l t s ( t o t a l s ) f o r each sample converge to a difference of le s s than 0.001 weight % oxide. During t h i s c a l c u l a t i o n the a n a l y t i c a l sums are normalized to 100% for both standards and unknowns. As a r e s u l t the f i n a l raw t o t a l s have no s i g n i f i c a n c e . Only the analyses normalized to 100% should be reported. 4) The f i n a l , mass absorption corrected analyses for the standards derived i n 3) are regressed against t h e i r known chemical analyses. This f i t should give straight l i n e s of unit gradient for each element, but minor deviation often occurs. Therefore : 5) F i n a l a n a l y t i c a l r e s u l t s are generated by applying the quadratic function of regression from .4) to the i t e r a t e d analyses from 3). In t h i s way wet chemical discrepancies are smoothed out and each standard i s e f f e c t i v e l y 'standardized' against the remainder of the standard block. F i n a l output includes : * F i n a l weight % analyses for standards and unknowns * Weight % analyses recalculated to 100% f o r standards and unknowns * Recommended values and difference between them and the recalculated values for standards only. For best r e s u l t s the program can be run a second time using smaller groups of l i k e standards and unknowns, y i e l d i n g a better inter-standard c o r r e l a t i o n . References : - G.C. Brown, D.J. Hughes and J . Essonj Chemical Geology,1973 v . l l , pp 223-229. - S. Abbey; Geological Survey of Canada, Paper 80-14, 1980. - W.J. Veigele;. Handbook of Spectroscopy, Kaman Science Corp.,1974. c TrtBL£ X OPEgrVrilOtT COKJDiTioK>£> (AnuMiuEO ow J u l y rj™, gBo ) ELEMENT LINE  2 8 TARGET CRYSTAL k V / m A COLLIMATOR COUNTER VACUUM GAIN COUNTER kV LOWER LEVEL WINDOW COUNT TIME K<* 57 SM Ufioo 6 0 / 3 5 12.8 e.01 « 2 150 10 sac S6 00 86. Ca 10.17 5o/j6 Co. % Ho. 40 136.7s-5o/w 152.15 Per 5O/H<> li9.3o X R F PRESSED PELLET A N A L Y S E S ELEMENT fit P N x % YD* rrv, \ LINE K<* — » - — » - — » - — — - • — » » 2 9 IHS-13 13900 8961 9260 4501 HH_oo 5 4 3 6 5 5 S O 6i 00 65.00 TARGET Cr W CRYSTAL P E T T L f l P UP ioo h V / m A & / 4 0 COLLIMATOR C F COUNTER F VACUUM Otf GAIN 128 6H \i£ COUNTER kV 8.0/ K a LOWER LEVEL 150 I60 ___.H]° — /So too Sec WINDOW COUNT TIME lo sec lo Sec lo Sec 2o sec V COMMENTS tlAujOtmi&utt, tLbtuAoMjCA. y PET oy&l ze Jot tad. uuv MLM. 144 1 C MAJOR ELEMENT XRF (PRESSEO POWDER METHOD) UBC SEPT. 1980 2 C ARRAYS ARE SET UP FOR UP TO 50 STANDARDS AND 200 SAMPLES 3 DIMENSION TITLE(20).TP(10).TB(10),C0NC(12),ID(250).C(50.12),CP(4). 4 1CB(4).RATIO(250. 10).P(4).NT(11),IU(4),AT(50, 10),AP(250. 12) , AM( 10) 5 2,BM(10),CM(10),0(10),AK(10,12),G(250.12),E(10).SUM(250),DIF ( 50.12) 6 3,SSUM(5O),V0L(25O) 7 REAL*8 IS.ID.IU 8 COMMON AT,NS,C,AM,BM,CM 9 C ELEMENT ORDER:SI,AL,FE,MG,CA,NA.K,TI,MN,P 10 C AK CONTAINS MAJOR ELEMENT OXIDE M.A.C.S (HANDBOOK OF SPECTROSCOPY 1974) 11 DATA AK/ 12 1727.8.1126.6,70.4,1840.1,337.2,2881.1,460.3.200.3.88.2,1755.3, 13 22314.3,983.0,63.6,1608.3,304.0,2530.1,414.0,180.6,79.6,1563.3, 14 32056.6.2881.2,59.8,4515.4,265.0,7000.9,358.1,160.2,73.9,1305.4, 15 42183.6,3294.3,56.9, 1365. 1 ,276.6,2160.2,379.1,163.5,71.5,1468.3, 16 51193.0.1708.6,243.4,2727.2,148.9,4320.1,200.9.644.9,300.9,752.5, 17 61992.3,3039.8,49.9,4881.2,245.7,1515.9,337.2,144.2,62.8. "i 328.4, 18 7983.6.1497.2,237.2,2412.7,1041.5,3788.2,177.1,639.4,294.7.659.5, 19 81338.0,1930.0,241.0,3072.0.166.6.4830.0,226.2,100.0,296.9.850.0. 20 91924.6,2690.4,55.2,4218.0,246.4,6569.4,332.9.149.7,69.3.1216.5. 21 8.787 . 1 . 1214 .9,77 .3, 1981 . 1 , 365 . 2 , 3 1 10 . 5 , 495 . 9 , 2 1 7 . 8 , 97 .0, 520 . 5 , 22 H932.6,1447.7,20.9,2371.4.107.5,3703.7.149.2,62.2.26.4,613.7, 23 C887.8,1382.1,19.6,2271.4,101.1,3572.1,140.6,58.4,24.7,582.3/ 24 C H e * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 25 C READ IN TITLE; COUNT TIMES ON PEAK AND BACKGROUND 26 C ***********************+************************+***************************+ 27 READ(5,100)TITLE o 28 READ(5.101)(TP(I).1=1,10) » S 29 READ(5,101)(TB(I), 1 = 1 , 10) ' O 30 N=0 S 31 NE=0 |> 32 C ***************************************************************************** S 33 C READ IN DATA FOR STANDARDS : IDENTITY.CONCENTRATION AND COUNTS;CALCULATE 34 C RATIOS 35 q •**+•**•++•***#++#*##*++**+**•**#*******+•**+**•***+****+**************•**+** 36 1 READ(5.200)15.(CONC(I).1=1.12) 37 IF(CONC(1 ) .E0.O.O)GO TO 3 38 N=N+1 39 ID(N)=IS 40 DO 2 1=1,12 41 C(N,I)=CONC( I ) 42 2 - CONTINUE 43 GO TO 1 44 C TOTAL STANDARD CONC. 45 3 DO 4 1=1,N 46 SSUM(I)=0.0 47 DO 4 J=1,12 48 4 SSUM(I)=SSUM(I)+C(I . J) 49 NS=N 50 5 NE=NE+1 51 IF(NE.EQ.11)G0 TO 9 52 IF(N.NE.NS)G0 TO 39 53 N=0 £ 54 C READ IN COUNTS(CP+CB) 55 6 READ(5,201)(CP(I).I=1,4),(CB(I),I=1,4) 56 IF(CP(1).EQ.0.0)G0 TO 5 57 C CALCULATE RATIOS 58 P1=CP( 1 )/TP(NE)-CB(1)/TB(NE) 59 DO 8 1=2,4 60 IF(CP(I))5.5.7 63 RATI0(N,NE)=P( I)/P1 64 8 CONTINUE 65 GO TO 6 66 C PUT % H20 5 C02 INTO ARRAY AP 67 9 DO 10 1=1.NS 68 DO 10 J=11,12 69 10 A P ( I , d ) = C ( I , J ) 70 C ***************************************************************************** 71 C READ IN DATA FOR SAMPLES:IDENTITY,C0UNTS;CALC. RATIOS;READ IN H20 & C02 72 C ***************************************************************************** 73 NE=0 74 1 1 NE=NE+1 75 NT(NE)=N 76 IF(NE.LE.2)G0 TO 12 77 IF(NE.EQ.11)G0 TO 16 78 IF(NT(NE).NE.NT(NE-1))G0 TO 40 79 12 N=NS 80 C READ IN IDENTITY AND COUNTS(CP+CB) 81 13 READ(5,202)(IU(vJ),J=1,4),(CP(I).I=1,4),(CB(I).I=1,4) 82 IF(CP(1 ) .EQ.O.O)G0 TO 11 83 C CALCULATE RATIOS 84 P1=CP( 1 )/TP(NE)-CB(1)/TB(NE) 85 DO 15 1=2,4 86 I F ( C P ( I ) )1 1 .11,14 87 14 N=N+1 88 ID( N ) - I U ( I ) 89 P(I)=CP(I)/TP(NE)-CB(I)/TB(NE) 90 RATIO(N,NE)=P(I)/P1 91 15 CONTINUE 92 GO TO 13 93 C READ % H20 & C02 INTO ARRAY AP 94 16 NU=NS+1 95 DO 17 I=NU,N 96 READ(5,203)(AP(I,J).d=11,12) 97 17 CONTINUE 98 C ***************************************************************************** 99 C CALIBRATE RATIOS FOR STANDARDS AGAINST CONCENTRATION USING QUADLS 100 C & USE COEFF. TO CALC. APPROXIMATE RESULTS FOR STANDARDS AND SAMPLES 101 C ***************************************************************************** 102 DO 19 1=1.NS 103 DO 18 J=1,10 104 AT(I.J)=RATI0(I,d) 105 18 CONTINUE 106 19 CONTINUE 107 CALL QUAD 108 DO 20 I=1,N 109 DO 20 J=1,10 1 10 AP(I,J)=AM(J)*RATI0(I,J ) **2+BM(J)*RATI0(I,J)+CM(d) 1 1 1 20 CONTINUE 1 12 C ***************************************************************************** 1 13 C CALCULATE MASS ABSORPTION (Q) FOR STANDARDS, APPLY TO RATIOS AND RERUN QUADLS 1 14 C ***************************************************************************** 1 15 DO 22 I=1,NS 1 16 DO 22 J=1.10 117 Q(J)=0.0 1 18 DO 21 K=1.12 1 19 21 Q(vJ)=Q( J)+C(I ,K)*AK(d.K) 120 AT(I,J)=RATIO(I.J)*Q(d) 121 22 CONTINUE 122 CALL QUAD 123 C ***************************************************************************** 124 C TAKE APPROXIMATE VALUES FROM AP.CORRECT FOR 0,DERIVE NEW RESULTS. 125 C REFINE 0 AND REFINE ANALYSIS BY ITERATION UP TO 50X 126 C ***************************************************************************** 127 DO 30 1=1,N 128 D=0.0 129 DO 23 U=1,12 130 D=D+AP(I,J) 131 23 G(1,J)=AP(I.J) 132 L=0 133 24 L=L+1 134 IF(L.EQ.1)G0 TO 42 135 G(L,11)=AP(1,11) 136 G( L,12)=AP(1,12) 137 D=D+G(L, 11)+G(L,12) 138 42 D=100.0/D 139 DO 26 J=1,10 140 0(J)=0.0 141 DO 25 K=1,12 142 25 0(J)=Q(U)+G(L.K)*AK(d.K)*D 143 26 E(J)=RATIO(I,J)*Q(J) 144 R=0.0 145 D=0.0 146 DO 27 K=1 ,10 147 G(L+1 ,K)=AM(K)*E(K)**2+BM(K)*E(K)+CM(K) 148 D=D+G(L+1.K) 149 27 R=R+G(L+1.K)-G(L.K) 150 IF(L.GE.50)G0 TO 28 151 IF(ABS(R) .GT.0.001)G0 TO 24 152 GO TO 29 153 28 WRITE(6,300)ID(I) 154 29 D=(100.0-G(L,11)-G(L.12))/D 155 DO 30 J=1,10 156 30 AP(I,J)=G(L+1.J)*D 157 C ***************************************************************************** 158 C RECALIBRATE USING REFINED VALUES OF STANDARDS AGAINST ACCEPTED VALUES 159 C ***************************************************************************** 160 DO 31 I=1.NS 161 DO 31 J=1,10 162 31 AT(I.d)=AP(I,J) 163 CALL QUAD 164 c ***************************************************************************** 165 C USE NEW CALIBRATION TO DETERMINE BEST VALUE FOR SAMPLES + STANDARDS 166 C ******************************************************•* + ****** + ************* 167 DO 32 1=1,N 168 DO 32 d= 1 .10 169 32 AP(I,d)=AM(J)*AP(I,d)**2+BM(J)*AP(I.vJ)+CM(J) 170 C TOTAL CONCENTRATION 171 DO 33 1=1.N 172 SUM(I)=0.0 173 DO 33 J= 1 ,12 £ 174 33 SUM(I)=SUM(I)+AP(I,d) •jyg C ***************************************************************************** 176 C OUTPUT STANDARDS ^•JJ Q * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 178 WRITE(6,306)TITLE 179 WRITE(6,305) 180 WRITE(6,301) 181 DO 36 1=1,NS 182 WRITE(-6.,-3024iD-U ), (AP(.I.,..l.)-,-.J=-1 , 12). SUM( I) 183 VOL(I )=AP(I, 1 1 )-AP(I,12) 184 DO 34 0=1,10 185 34 AP(I,0)=AP(I,J)*(1OO.O-VOL(I))/(SUM(I)-V0L(I)) 186 WRITE(6,303)(AP(I,0),0=1,12) 187 DO 35 0=1, 12 188 35 DIF(I,0)=AP(I,0)-C(I.0) 189 WRITE(6,307)(C(I,0),0=1.12),SSUM(I) 190 WRITE(6,309)(DIF(I,0).0=1,12) 191 36 CONTINUE 192 193 c OUTPUT SAMPLES 194 Q ***************************************************************************** 195 WRITE(6,304) 196 WRITE(6,301) 197 DO 38 I=NU,N 198 WRITE(6,302)ID(I ) ,(AP(I,0),0=1.12),SUM(I) 199 VOL(I)=AP(I,11)-AP(1,12) 200 DO 37 0=1,10 201 37 AP(I,0)=AP(I,0)*(100.0-V0L(I))/(SUM(I)-VOL( I )) 202 WRITE(6,303)(AP(I.0),0=1,12) 203 38 CONTINUE 204 STOP 205 Q ***************************************************************************** 206 39 WRITE(6,400)NE 207 GO TO 41 208 40 WRITE(6,401)NE 209 41 STOP 210 100 FORMAT(20A4) 211 101 FORMAT(10F3.0) 212 200 FORMAT(A6,12F6.2) 213 201 FORMAT(12X.4F7.0.12X.4F7.0) 214 202 F0RMAT(4A6,8F7.0) 215 203 F0RMAT(6X,2F6.2) 216 300 F0RMAT(1H1,'MORE THAN 50 ITERATIONS AT',1X,A6) 217 301 FORMAT(1H ,'IDENT',3X,'SI',4X.'AL',4X,'FE',4X.'MG'.4X.'CA',4X,'NA' 218 1,5X, 'K',4X,'TI',4X, 'MN',5X, 'P',4X, 'H20',3X, 'C02' ,7X, 'TOTAL' ) 219 302 FORMAT(1H0.A6,12F6.2,6X,F6.2,6X,'FINAL VALUE') 220 303 FORMAT(1H ,6X,12F6.2.18X,'NORM. VALUE') 221 307 F0RMAT(1H ,6X, 12F6.2,6X,F6.2.6X,'RECCOM. VALUE') 222 309 F0RMAT(1H ,6X,12F6.2,18X.'NORM.-RECC.') 223 304 FORMAT(1H1,50X,'SAMPLES') 224 305 FORMAT(1H0.50X.'STANDARDS') 225 306 F0RMAT(1H1,20A4) 226 400 F0RMAT(1H .'CARD MISSING IN STANDARD DATA FOR Z=',2X,I3) 227 401 FORMAT(1H .'CARD MISSING IN SAMPLES FOR Z=',2X,I3) 228 END 229 c * * * ************************************************************************** 230 SUBROUTINE QUAD 231 C FITS.BY LEAST SQUARES.TO QUADRATIC FUNCTION Y=AX*X+BX+C 232 DIMENSION SA(10),SB(10),SC(10),SD(10).SE(10),SF(10).SG(10),AM( 10) 233 DIMENSION BM(10).CM(10),AT(50,10),C(50,12) 234 COMMON AT,NS,C,AM,BM,CM 235 DO 47 0A=1,10 236 SA(OA)=0.0 237 SB(OA)=0.0 238 SC(OA)=0.0 239 SD(OA)=0.0 240 SE(OA)=0.0 241 SF(JA)=0.0 242 SG(JA)=0.0 243 47 CONTINUE 244 DO 48 dA=1,10 245 DO 49 1=1,NS 246 SA(JA)=SA(JA)+AT(I,OA) 247 SB(JA)=SB(JA)+AT(I,JA)**2 248 SC(dA)=SC(dA)+AT(I,dA)*AT(I,dA)**2 249 SD(JA)=SD(JA)+AT(I,JA)**2*AT(I,JA)**2 250 SE(JA)=SE(JA)+C(I,JA) 251 SF(dA)=SF(JA)+AT(I,JA)*C( I,JA) 252 SG(JA)=SG(JA)+AT(I,JA)**2*C( I,JA) 253 49 CONTINUE 254 U=SF(JA)*SA(JA)-SB(JA)*SE(JA) 255 V=FLOAT(N)*SF(JA)-SA(JA)*SE(JA) 256 W=FLOAT(N)*SB( JA)-SA(JA)**2 257 XA=SC(JA)*SA(JA)-SB(JA)**2 258 Y=FLOAT(N)*SC(JA)-SA(JA)*SB(JA) 259 Z = SC(JA)*SE(JA)-SB(JA)*SF( JA) 260 T=W*SD(JA)-Y*SC(JA)+XA*SB(JA) 261 T=1.0/T 262 AM(JA)=T*(W*SG(JA)-V*SC(JA)+U*SB( JA)) 263 BM(JA)=T*(V*SD(JA)-Y*SG(JA) + Z*SB( JA)) 264 CM(JA)=T*(-U*SD(JA)-Z*SC(JA)+XA*SG(JA)) 265 48 CONTINUE 266 RETURN 267 END End o f F i l e KD 1 7 3 4 5 6 7 8 9 40 11 12 13 1* 15 16 I 7 18 19 20 21 22 23 2* ? 5 26 27 23 29 3D 31 32 33 3* 35 36 3 7 38 39 40 41 42 43 44 45 46 47 48 4 T 53 51 52 53 54 55 56 57 58 59 63 1 0 10 10 10 BC«1 AC, VI DTSl Wl GH GA GSPl PCC1 NIM-N IM-P JBl SY2 NIM-S MRGl JG1 SY3 G2 TEST *U l . o tm 10 10 5 . 5 3 59.61 40.61 52 . 7? 75.35 69.9S 67.3? 42.1) 52.6'+ 51.13 52.63 50. 13 63.61 39.32 72.3b 59.68 69.22 10 i.oo 10 10 13. 72 17. 19 0. 25 15.02 12. 51 I*. 51 15.28 0. 73 16. 50 4. 18 14.62 12. 12 17.34 8.50 14.20 11.80 15.40 1.0 1.0 10 10 13.44 ,82 ,73 11.10 1.34 2.83 '•.28 8.29 8.89 12.79 9.05 6.27 1.40 17.85 2.17 6.42 2.67 20 10 20 10 3. 48 1.5 2 4 9.80 6. 63 0.03 0. 9 5 0.97 43. 50 7.50 2 5.33 7.76 2. 70 0.46 13.49 0.76 2.67 0.75 6.97 4.94 0.14 10.98 0.69 2.45 2.03 0.55 11.50 2.66 9.35 7.98 0.6R 14.77 2.17 0.26 1.96 3.30 1 . 70 2.26 0. 1H 0. 36 0.67 0.02 4.32 2. 92 1.06 0. 10 0.51 0. 78 0. 02 0. 01 0. 00 U.00 0. 12 0.00 0.42 C.07 2.15 0.64 1.07 0. 17 0. 14 0. 53 C.06 3.15 4. 76 0.08 0.05 0. 01 0.46 C. 14 3.55 4. 03 0.38 0. 09 0. 12 0. 87 0. 1 I 2.0 1 5. 51 0. 66 0. 04 0. 28 0. 58 C. 12 0.0L 0. 00 0. J l 0. 12 0. 01 4. ro 0.18 2 .46 0. 25 0.20 0. 18 0. 03 0.33 0. 10 0.3 7 0. 09 0.20 0. 22 0.02 0.26 o. oa 2.79 1. 42 1. 34 0. 15 0. 26 1.01 0. 18 4.34 4. 48 0.14 0 . 32 0.43 0.43 . C.46 0.43 15. 35 0.04 0. 01 0. 12 0. 22 0. 09 0. 71 0. 18 3.69 0. 17 0. 06 0.98 1.00 3.39 3. 96 0.27 0. 06 0.09 0.54 C.08 4 . 15 4. 20 0.15 0. 32 0.54 0.42 C.38 4.06 4 . 46 0.48 0 . 03 0. 13 0. 50 C.08 317282 234995 2 59409 132155 2 54 183 209 95 323166 215523 354066 305514 477 331 56 9 435 316394 319310 143919 202682 245 244 U l 156 .321758 196742 21 7519 2 64962 235 1 58 182 236 317391 292 131 158139 318751 247 269 156 226 310522 252U4 310522 231 206 231 31991 1 280 283 338316 5 748 1308 1207 1342 328 342493 3443 80 2824 34 299828 1296 1172 1179 1156 338647 343300 10717 3 76 53 7 1390 1392 35 7 1314 339821 87914 3 18524 264071 12 52 624 1 148 1123 340 866 402675 15 83 72 295383 1354 1484 922 1212 299269 221699 299269 1365 1147 1365 193295 892930 4904 00 8 3 7 422 1072 1592 1 33 8 1600 195624 747908 114589 194911 1905 2108 184 5 1919 194195 289609 817304 619894 1058 1140 I 58 5 1370 "1966 5 3 9 85753 622521 435279 1098 1637 138 8 1274 194984 957741066973 IR4616 1057 923 170 5 1073 1936 2 7 425493 193627 1093 1288 109 3 41 130 92029 506 502375 825 741 944 79 5 5643 41651 190984 8273 47983 733 1262 59 8 714 40014 413591684443 210903 745 758 4745 1324 "4166 8 "92i695 222908 92 200 742 2881 1 30 8 954 41354 24546 489558 47637 756 804 2 10 8 738 41099 89430 41099 7 39 935 73 9 159630 572736 4066 11 13951 2 39 613 44 3 128 161794 967363 57482 l ° 9 2 6 4 4 58 1745 28 7 518 159512 166532 52569 999578 229 258 16 1 910 "16148 3 "25 9284 7540 10 616187 237 344 712 593 160331 433041361954 175610 244 143 1262 243 161 73 I 631252 161781 251 639 25 t 64287 55187 625 79 6391 7 39 831 783 547 64428 42 340 60317 48973 720 8 40 657 668 64371 48761 6569 44 24 7 747 801 554 858 64312 "13886 47036 67682 751 649 86 3 982 63985 13549 19743 46199 697 972 102 7 663 64419 65441 64419 730 859 730 770049 314801 500133 6078 721 507 603 171 778362 131547 771861 704262 710 451 706 700 770298 956661 5'»7l 51003 744 864 20 2 362 C O 61 62 6 3 64 6"; 66 6 7 68 69 70 71 72 73 74 75 76 77 78 79 fl 0 81 82 83 84 85 86 87 88 99 90 91 92 93 9* 95 96 97 98 99 100 101 102 103 134 105 106 137 108 109 110 111 112 113 114 115 116 117 END OF F ILF 78063 ? 25620 27CO07 7PI 118 6<3d 264 510 885 76894325S2029 41151 699705 720 1931 47 6 654 76^200 745368 76 7200 736 9 79 736 115657 5464 56 26 1491 3033 463 647 512 400 118218 251131 22231 103775 848 10 73 66 5 798 I 13635 152488 3469 45*06 451 <t43 404 430 118208 61533 328445 " 29483 465 483 55 6 454 114750 9621 375 187 87815 430 3 74 844 392 113563 28709 113563 483 460 48 3 35^55 165256 9 86 50 167 709 4453 5117 4634 5601 35446 154321 54373 87 768 44 55 4655 3844 4066 35208 39231 1 5 77 68 164 798 4461 5453 5503 4265 3540 9 260360 135913 283315 4483 7091 4614 4823 3513 1 11414 141081 76 096 4437 3395 5044 3948 35053 282321 35053 4465 1 0854 446 5 3102 7794 9645 367 246 2 99 270 184 3156 4034 462 > 3063 263 302 239 251 3077 5951 368 1 145 264 258 186 273 " 3174 851 59 79 9368 260 2 75 28 3 302 3092 2696 2357 269 7 263 285 351 231 3106 11155 3106 264 303 26 4 G2 BCR1 A3V1 0TS1 317282 234995 2 59409 132155 2 54 183 209 95 G2 NIM-? JB1 SY2 321758 196742 217519 26496 2 235 158 18 2 236 G2 BCRl A3VI DT SI 319911 "2 8028 3 338316 5748 1308 1207 ~ 1342 328~ G2 NIN-P J B l SY2 339821 87914 31852 4 264071 1252 6 24 1148 1123 G2 BCRl A3 VI DTS1 1932S5 892930 490400 837422 10 72 1592 133 8 1600 G2 N I H - » J B l SY2 196653 985753 622521 435279 1098 1637 1388 1274 G2 BCRl ~ A G V i — OTSl" 41130 92029 5065020 75825' 741 944 ~ 79 5 5643 G2 N I M-i> J B l SY2 41668 921695 2 2 290 8 92200 742 2881 1308 954 G2 BCRl AGV1 DTS1 159630 572736 406611 13951 239 613 443 128 G2 NIM-P J B l SY2 161483 259284 754010 616187 237 344 712 593 G2 BCRl ~~A3vi"~ D t S l 64287 — 5518 7 62579 6391 739 831 " 783 547" G2 NIM-P J B l SY2 64312 13886 47036 67682 751 649 868 982 G2 BCRl A3VI DTSl 770049 314801 500133 6078 721 507 603 171 G2 NIM-i» J B l SY2 780632 2562 0 270007 791118 690 264 510 885 G2 BCRl ~" A3V1 ~ OTSl 1 15657 546456 26 1491 " 3033 463 647 512 400" G2 NIM-P J B l SY2 118208 61533 328445 29483 465 483 556 454 G2 HCRl A3V1 DTSl 354 55 165256 9 86 50 162 709 4453 5117 4634 5601 G2 NIM-> J B l SY2 35409 260360 135913 283315 44 83 7091 4614 4823 G2 HCRl A3 VI DTSl 3102 7794 9645 36 7 246 2 99 "~270 184 G2 NIM-P Ji l l SY2 3174 851 5979 9368 260 275 28 3 3C2 BCRl AGV1 DTSl NIM-P J B l SY2 0.67 0.73 0.42 6.26 1.01 0.43 0.02 0.02 0. 07 0.08 0. 18 0. 46 •j » 9 St • . TEST RUN I DENT SI AL FE IR CA NA K 3CRI 55.62 13 .99 13.1 1 2.72 6.55 3. 61 1.64 55.2 8 13 .90 13.33 2. 70 6.51 3 . 59 1.63 54.53 13 .72 13.*4 3.48 6.97 3. 30 1. 70 0.75 0.18 - 0 . ' * 1 - 0 . 78 - 0 . 4 6 0.29 -0 .07 AGVl 61.16 16.16 6.10 1.38 5.04 4. 12 2.80 61.19 16.17 6.31 1.38 5.04 4 . 13 2.80 59.61 17.19 6. 3 2 1.52 "' 4.94 4 . 32 2.92 1.58 - 1 . 0 2 -0 .3 I - 0 . 14 0. 10 - 0 . 19 - 0 . 12 3TS1 39.64 39.76 40.61 - 0 . 8 5 0.44 9.38 49.68 0.15 0.06 0.03 0.44 9.10 49.83 0.15 0.06 0.03 0 .25 fl.JL-49.B0_ 0.14 0.01 0 . 0 _ 0.19" 0.37 0.03 0.01 0.05 0.03 STANDARDS TI MN 2.17 2. 16 2.26 -0 . 10 1.09 1.09 I. 06 0.03 0.01 0.01 0 .0 o . o f 0.17 0.17 0. 18 -0.01 0. 10 0.10 0. 10 -0 .00 0.13 0. 13 0.12 0.0 1 0.35 0.34 0.36 -0.02 0.48 0.48 0.51 -0.03 0.01 0.01 0.0 0.1)1 H20 C02 0.67 0.02 0.6 7 0.02 0.67 0.02 0.0 0.0 0. 78 0.02 0. 78 0.02 0. 78 0.02 0.0 0.0 0.42 0.07 0.42 0.07 0.42 0.07 0. 0 0.0 TOTAL 100.61 100.63 99.94 59.79 99.71 100.15 FINAL VALUE NORM. VALUE HECCOM. VALUE NORM.-RECC. FINAL VALUE NORM. VALUE RECCOM. VALUE NORM.-RECC FINAL VALUE NORM. VALUE RECCOM. VALUE NORM.-RECC. <fl 51.90 15. 18 1 1.24 5.62 1 1. 13 51.27 15.98 11.10 5.55 10.99 52.72 15.02 11.10 6.63 10.98 - 1 . 4 5 0.96 0.30 - 1 . 0 8 0.01 74.91 12.17 76.00 12.35 75.85 12.51 0.15 - 0 . 1 6 l . t O 1.42 1.34 0.38 0.07 0.75 0.07 0.77 0.03 0.69 0.04 0.08 2.54 2.51 2 . 15 0.36 3.82 3.87 3.85 0.02 0.67 0.66 0.64 0.02 4.69 4. 76 4.76 -0.00 1.05 1.03 1.07 -0.04 0.09 0.09 0.08 0.01 0.16 0. 16 0.17 -0.01 0.05 0.05 0.05 0.00 0.15 0.15 0.14 0.01 0.01 3.01 0.01 -0.00 0.53 0. 53 0.53 0. 0 0.46 0.46 0.46 0.0 0.06 0.06 0.06 0 « ° ._. 0 . 14 0.14 0.14 0.0 101.22 101.21 98.56 99.77 FINAL VALUE NORM. VALUE RECCOM. VALUE NORM.-RECC. FINAL VALUE NORM. VALUE RECCOM. VALUE NORM.-RECC. GA" 59.41 13.88 70.12 14.02 69.96 14.51 0.16 - 0 . 4 9 ~2.&2 ?.S5 2.33 -0.13 1.30 2.69 1.31 2.72 0.95 2.45 0.36 0.27 3 . 14 3. 17 3.55 -0.38 4.31 4.35 4. 03 0.32 0.45 0.45 0.38 0.07 0.09 0.09 0.09 0.00 0.13 0.14 0.12 0.02 0.87 0.8 7 0.87 0.0 0.11 0.11 O . l l 0.0 98.99 FINAL VALUE NORM. VALUE 99.85 RECCUM. VALUE NORM.-RECC. GSP1 68.40 14.05 59.08 14.19 57.32 15.28 1.76 - 1 . 0 9 3. 56 3.70 4.2 8 -0.58 1.03 2.10 1.04 2.12 3.97 2.03 0.07 0.09 2.78 2. 80 2.81 -0 . 01 5.37 5.42 5.51 -0.09 0.63 0.63 0.66 -0.03 0.03 0.03 0.04 -6.01 0.27 0.28 0.28 -0.00 0. 53 0. 58 0. 58 0.0 0.12 0. 12 0.12 0.0 99.01 F INAL_V ALUE NORM. VALUE 99 . 88 RECCOM. VALUE NORM.-RECC. »CC1 41.27 0.75 8.71 43.48 0.54 0.07 0.03 0 . 01 41.33 0.75 8.72 43.54 0. 55 0.07 0.03 0 . 01 42. i n " 0 . 7 3 "8". 2 9 43.50 0.55" 6. 01 0.0 0 . 01 - 0 .77 0.02 0.V3 0.04 - 0 . 0 0 0. 06 0.03 0. 00 NIM->I 51.71 18.11 9.32 6.59 12.01 2.70 0.27 0 . 20 50.91 17.83 9.1 8 6.49 1 1.83 2 . 66 0.27 0.20 52.64 16.50 8.89 7.50 I 1.50 2.46 0.25 0 . 20 - 1 . 73 i . 3 3 0. 1 9 - i . o i 0.33 "0.20" " 0.02 - 6 . 00 MIM-P 52.09 5.56 12.33 25.59 2.85 0.52 0. 14 0 . 22 52.14 5.57 12.34 25.62 2.86 0. 52 0. 14 0 . 22 51.10 4.18 12.79 25.33 2.66 0 . 37 0.09 0. 20 1.04 1.39 - 0 . V 5 0.29 0.20 0. 15 0. 05 0. 02 J B l 53.14 15.64 9. 3 4 6.62 8.92 2.90 1.42 1. 37 52.80 15 .54 8.?8 6. 58 8. 86 2 . 88 1.41 1. 36 52.60 14.62 9.35 7.76 9.35 2.79 1.42 1. 34 0.20 0.92 -0 .37 -1 .18 - 0 . 4 9 0.09 -0 .01 0 . 02 0. 12 0.01 4. 70 0.18 99.88 FINAL VALUE 0.12 0.01 4.70 0.18 NORM. VALUE _ 0. 12 0.01 4. 70 0.18 100.20 " " " R E C C O M . VALUE 0.00 -0 .00 0.0 0.0 NORM.-RECC. 0.18 0.04 0.33 0.10 101.57 FINAL VALUE 0.18 0.04 0.33 0.10 NORM. VALUE 0.18 0.03 0.33 0.10 100.58 RECCOM. VALUE - 0 . 0 0 0.01 0.0 0.0 NURM.-RECC. 0.23 0.02 0.26 0.08 99.90 FINAL VALUE 0.23 0.02 0.26 0.08 NORM. VALUE 0.22 0.02 0.26 0.08 97.30 RECCUM. VALUE 0.01 0.00 0.0 0.0 NORM.-RECC. 0.14 0.25 1.01 0.18 100.63 FINAL VALUE 0.14 0.25 I.01 0.18 NORM. VALUE 0.15 0.26 1.01 0.18 100.53 RECCUM. VALUE -0.01 -0.01 0.0 0.0 NORM.-RECC. SV2 N11-5 IRLil J G l 5 9 . 8 0 1 2 . 4 2 6 0 . 1 7 1 2 . 5 0 5 0 . 1 0 1 2 . 1 ? 0 . 0 7 0 . 3 0 5 4 . 0 2 1 6 . 5 8 6 4 . 4 4 1 6 . 6 9 6 3 . 6 3 1 7 . 3 4 0 .81 - 0 . 6 5 6.2 2 2_.J>i 7 . 8 9 t.2t- 2 . 6 4 7 . 9 4 6 . ? 7 ? . 7 0 7 .98 •0 .31 - 0 . 0 6 - 0 . 0 4 I.V 6 ' 1 . 4 7 ' 1.4 0 0 . 3 7 0 . 4 9 0 . 5 0 3 . 4 6 0 . O 4 0 . 7 0 0 . 7 0 0 . 6 8 0 . 02 7 1 . 2 8 13 .21 7 2 . 1 5 1 3 . 3 7 7 2 . 3 6 1 4 . 2 0 - 0 . 2 1 - 0 . 8 3 2 . V 1 2 . 4 4 2.1 7 0.2 7 4 . 3 7 4 . 2 8 4 . 4 0 4 . 3 0 4 . 3 4 4 . 4 8 0 . 0 6 - 0 . 18 0 . 2 6 1 5 . 3 5 0 . 2 7 1 5 . 4 5 0 . 4 3 1 5 . 3 5 - 0 . 1 6 0 . 1 0 3 9 . 4 0 8 . 9 3 1 7 . 9 3 1 4 . 8 6 1 4 . 6 0 3 8 . 4 2 8 .71 1 7 . 4 9 1 4 . 4 9 1 4 . 2 3 3 9 . 3 2 8 . 5 0 1 7 . 3 5 1 3 . 4 9 1 4 . 7 7 - 0 . 9 0 0 . 2 1 - 0 . 3 6 1 .00 - 0 . 5 4 1 .25 2 . 3 4 1 .27 2 . 3 7 0 . 7 6 2 . 1 7 0 . 5 1 " 0 . 2 0 0 . 72 0 . 70 0 . 71 - 0 . 0 1 2 . 8 5 2 . 8" 3 . 3 9 - 0 . 5 0 0 . 19 0 . 18 0 . 18 0 . 0 0 4 . 26 4 .31 3 . 9 6 0 .35 0 . 13 0 . 13 0 . 14 - 0 . 0 1 0 . 0 5 0 . 0 5 0 . 0 4 0 .01 3 . 72 3 . 6 2 3 . 6 9 - 0 . 0 7 0 . 38 0 . 3 8 0 . 2 7 0 . 11 0 . 32 0 . 3 2 0 . 3 2 0 . 0 0 0 . 0 1 0 .01 0 .01 0 . 0 0 0 . 16 0 . 1 5 0 . 1 7 - 0 . 0 2 0 . 0 8 0 . 08 0 . 0 6 0 . 0 2 0 . 4 4 0 . 4 4 0 . 4 3 0 .01 0 .11 0 . 1 1 0 . 1 2 - 0 . 0 1 0 . 0 7 0 . 0 7 0 . 0 6 0 .01 0 . 1 2 0 . 12 0 . 0 9 0 . 0 3 0. * 3 0 . 4 6 99 .39 F INAL V Al LIE 0 . 43 0 . 4 6 NUkM. VALOE u. 43 0 . 4 6 9 9 . 7 7 KECCUM. VALUE 0 . 0 0 . 0 N O k M . - R E C C . 0 . 2 2 0 . 0 9 „ 9 9 . 3 5 . F I N A L . V A L U E 0 . 22 0 . 0 9 NUKM. VALUE 0 . 22 0 . 0 9 9 9 . 7 7 R E C t O M . VALUE 0 . 0 0 . 0 N O R M . - R E C C . 0 . 9 8 1 . 0 0 102 .55 F I N A L VALUE 0 . 9 8 1 . 0 0 NORM. VALUE 0. 98 1 . 0 0 100 .72 RECCOM. VALUE 0 . 0 0 . 0 NQKM.-R E C C . 0 . 54 0 . 0 8 9 8 . 8 0 F INAL VALUE 0 . 54 0 . 0 8 NUKM. VALUE 0 . 54 0 . 0 8 1 0 0 . 0 5 RECCOM. VALUE 0 . 0 0 . 0 N O R M . - R E C C . S / 3 32 5 9 . 7 3 1 2 . 1 5 6 . 3 2 2 . 6 4 8 .21 4 . 3 5 4 . 1 6 0 . 1 3 0 . 3 2 0 . 5 6 0 .42 0 . 3 8 9 9 . 3 7 F INAL VALUE 6 0 . 1 1 12 .22 6 . 36 2 . 6 5 8 . 2 6 4 . 38 4 . 19 0 . 13 0 . 3 2 0 . 5 7 0 .42 0 . 3 8 NORM. VALUE 5 9 . 6 8 1 1 . 8 0 6 .42 2 . 6 7 8 . 2 6 4 . 15 4 . 2 0 0 . 15 0 . 3 2 0 . 5 4 0 .42 0 . 3 8 9 8 . 9 9 RECCOM. VALUE 0 . 4 3 0 . 4 2 - 0 . 3 6 -.0.00 . o . 23 - 0 . 02 0 . 0 0 0 . 0 3 0 . 0 0 . 0 • - N O R M . - R E C C * 5 9 . 6 1 1 4 . 3 7 2 . . 2 1 .02 2 . 0 4 3 . 98 4 . 4 7 0 . 47 0 . 0 3 0 . 1 3 0 . 50 0 . 0 8 9 9 . 12 F INAL VALUE 7 0 . 2 3 1 4 . 5 0 2 . 4 4 1 . 0 3 2 . 0 5 4 . 02 4 .51 0 . 47 0 . 0 3 0 .1 3 0 . 5 0 0 . 0 8 NORM. VALUE 5 9 . 2 2 1 5 . 4 0 2 . 4 7 0 . 7 5 1.96 4 . 06 4 . 4 6 0 . 48 0 . 0 3 0 . 1 3 0 . 50 o . o a 9 9 . 7 4 RECCOM. VALUE 1 .01 - 0 . 9 0 - 0 . 2 3 3 . 2 8 0 . 0 9 - 0 . 04 0 . 0 5 - 0 . 01 0 . 0 0 0 . 0 0 0 . 0 0 . 0 NORM.-K E C C . I DENT SI AL FF •1G CA NA K T 1 n c u 55.62 55.28 13 .99 13 .90 13.11 13.33 2.72 2 .70 6.55 6.51 3. 3. 61 59 1.64 1.63 2. 2. 17 16 AJWl 61.16 61.19 16.16 16.17 6.3 0 6.3 1 1. 38 1.38 5.04 5.04 4 . 4 . 12 13 2.80 2.80 t . 1. 09 09 D T S l 39.64 39.76 0 .44 0 .44 9.38 9.1 0 49.68 49.83 0. 15 0.15 0. 0 . 06 06 0. 03 0.03 0. 0 . 01 01 NIM-P 52.09 52.14 5 .56 5 .57 12. 3 3 12.34 25.59 25.62 2.85 2.86 0 . 0. 52 52 0. 14 0. 14 0 . 0 . 22 22 J31 53.14 52.80 15 .64 15 .54 9.)4 8.98 6.62 6. 58 8.92 8.86 2.90 2.88 1.42 1.41 1. 1. 37 36 Sf 2 5 9.80 60. 17 12.42 12 .50 6.? 2 6. > 6 "' 2.63" 2.64 7.89 7.94 4 . 4 . 37" 40 4. 28 4.30 0 . 0 . 13 13 MN P H20 0 . 1 7 0 . 3 5 0 . 6 7 0 . 1 7 0 . 3 4 0 . 6 7 0 . 10 0 . 4 8 0 . Tt} 0 . 10 0 . 4 8 0. 78 0 . 1 3 0 . 0 1 0 . 4 2 0 . 1 3 0 .01 0 . 4 2 0 . 2 3 0 . 0 2 0 . 2 6 0 . 2 3 0 . 0 2 0 . 2 6 0 . 1 4 0 . 2 5 I.01 0 . 1 4 0 . 2 5 1.01 0 . 3 2 0 . 4 4 0 . 4 3 0 . 3 2 0 . 4 4 0 . 4 3 CU2 TOTAL 0 . 0 2 100 .61 0 . 0 2 0 . 0 2 9 9 . 9 4 0 . 0 2 0 . 0 7 9 9 . 7 1 0 . 0 7 0 . 0 8 "~ 9 9 . 9 0 0 . 0 8 0 . 1 8 100 .63 0 . 1 8 0 . 4 6 9 9 . 3 9 0 . 4 6 F INAL VALUE NORM. V A L U E F INAL VALUE NUkM. VALUE F INAL VALUE NORM. V A L U E F INAL VALUE NORM. V A L U E F INAL VALUE NORM. V A L U E f INAL VALUE NORM. VALUE o APPENDIX 2 MAJOR ANT) TRACE ELEMENT CHEMISTRY CENTRAL GNEISS COMPLEX AND GAMSBY GROUP MAJOR ELEMENT COMPOSITION - CENTRAL GNEISS COMPLEX SAMPLE i 1 CM ' O •H CO CO o CM CO o CM QJ fa o 60 s o 8 o CM rt Z o CM CM o •H H o w O CM + o CM o CM CM o o 80-37b 67.47 14.76 4.63 1.75 2.34 5.00 1.65 .61 .13 .17 * 1.40 .08 80-37a 57.80 14.30 9.52 3.80 5.50 4.03 1.50 .97 .22 .35 1.52 .51 80-58 65.94 13.99 5.20 2.47 4.26 3.36 1.76 .82 .15 .30 1.33 .08 .33 80-41 65.33 15.14 4.67 2.29 4.56 3.59 1.89 .47 .11 .21 1.02 .04 .67 80-55 63.60 15.54 7.46 2.23 7.57 2.39 .32 .38 .17 .22 TV .02 .09 80-56 58.56 15.73 7.60 5.21 7.86 2.53 .68 .56 .18 .17 .84 .04 .03 80-61 54.16 17.12 8.98 6.19 9.01 2.43 .11 .51 .19 .14 1.10 .05 80-39 55.26 14.65 12.07 6.77 4.82 .66 1.05 .61 .18 .18 3.54 .04 .18 80-29 62.54 13.29 7.82 4.29 6.48 2.86 .98 .68 .20 .19 ic .63 .05 .00 80-60 62.16 14.12 7.81 2.99 4.05 4.26 .34 1.06 .17 .48 2.03 .09 .45 80-42 76.05 13.67 .45 .10 .90 3.18 5.08 .04 .04 .01 .44 .04 80-59 45.99 12.57 8.13 13.90 8.83 .69 1.01 .82 .14 .14 3.69 .64 3.48 Loss on i g n i t i o n , other values determined with apparatus described by Berman (1979) COMMENTS : 1) A l l values reported are normalized to 100% , In wt.% 2) Total Fe reported as Fe 20 3 O N MAJOR ELEMENT COMPOSITION - GAMSBY GROUP C M o CO o C M SAMPLE R-l 79- 256 80- 64 80-19 79-176 79-251 79-335 79-190 79-266 79-168 79-173 79-278 79-279 79-248 79-292 79-294 CO o CM <D fa O O I? 8 'a CM 75.76 74.25 65.54 64.94 66.71 54.03 59.88 55.77 45.35 67.48 53.60 59.79 56.68 47.98 57.51 51.02 12.62 12.60 14.18 15.77 15.90 12.80 10.57 15.25 16.45 13.89 12.83 12.87 16.30 15.86 15.71 15.49 1.41 I. 92 4.73 3.93 2.90 12.38 8.77 10.20 8.¥l" 4.33 II. 84 11.13 9.72 10.57 6.86 8.37 .45 1.55 1.29 .87 3.89 4.08 3.26 3.34 2.44 2.77 4.75 7.22 3.54 9.95 7.55 1.45 4.14 3.19 5.19 2.59 2.95 2.77 4.25 1.91 4.03 2.90 2.12 .91 1.15 .16 3.22 .72 8.76 8.14 2.56 3.74 5.90 6.73 4.34 4.81 3.27 2.57 10.19 7.56 6.23 4.97 9.05 8.37 2.27 .65 2.52 3.78 1.39 4.12 2.21 .35 .52 3.68 2.54 1.02 3.42 .80 2.53 1.52 CM o •H H o m o CM cu + o CM i o CM CM o o * .18 .06 .04 .57 .03 * .28 .05 .08 .78 .10 .55 .11 .20 * .97 .03 .50 .07 .20 1.80 .05 .43 .08 .19 1.48 .08 .09 1.41 .15 1.35 2.46 .10 .31 .94 .26 .22 2.07 .21 2.26 1.13 .32 .22 2.05 .17 1.98 .64*" " 3 8 " .11 3.04 .18 5.34 * .73 .07 .13 .68 .09 1.29 .19 .34 1.63 .07 .08 .78 .21 .19 * 3.14 .17 .87 .18 .15 2.89 .01 3.19 .85 .18 .35 2.75 .07 .08 .67 .12 .25 2.38 .11 .97 .51 .18 .11 2.18 .11 .56 Loss on i g n i t i o n COMMENTS : 1) A l l values reported are normalized to 100% , 2) Total Fe reported as Fe 20 3 i n wt.% MAJOR ELEMENT COMPOSITION - GAMSBY GROUP (continued) SAMPLE 80-26 80-31 80-50 79-250 79-189 79-336 79-169 79-174 79-174a 79-284 < M o •H CO o CM rt O CM 0J O I? o 8 o CM o CM CM o •I-I H in O CM + o CM I o CM CM o u 72.79 72.85 73.75 66.17 79.97 55.92 70.51 71.83 75.89 51.87 13.62 2.40 .82 1.88 4.80 2.28 .35 .03 12.78 2.75 .51 1.06 8.22 1.05 .34 .06 13.20 2.37 ' .83 1.79 5.11 1.55 .35 .03 14.74 4.81 2.05 4.27 4.86 .86 .50 .07 9.83 1.32 .18 .54 6.40 .63 .20 .04 13.63 9.77 5.07 4.22 4.51 .77 1.06 .24 15.25 1.79 1.03 2.09 5.77 2.02 .17 .03 14.70 1.39 .59 .95 7.47 1.78 .13 .03 12.19 1.91 .43 1.16 5.15 2.22 .13 .03 14.77 10.44 4.19 5.95 4.75 1.16 1.34 .18 Loss on i g n i t i o n COMMENTS : 1) A l l values reported are normalized to 100% 2) Total Fe reported as Fe 20 3 .07 .07 .07 .70 .27 .83 .04 .03 .03 .03 .03 ,21 10 ,10 ,21 .04 2.33 .08 .19 .20 1.35 .03 .61 .30 2.15 .08 1.00 .05 1.02* .06 .02 .64 .11 .13 .44 1.60 .04 3.32 i n wt.% TRACE ELEMENT COMPOSITION - CENTRAL GNEISS COMPLEX SAMPLE Cr V Ni Ce Nd Nb Zr Y Sr Rb Ba 80-37b 105 55 3 48 20 7 134 34 282 38 881 80-37a 80 261 0.2 22 10 6 90 27 344 33 638 80-58 89 80 4 36 19 6 124 36 340 19 816 80-55 12 79 5 11 4 5 57 14 680 6 73 80-61 119 211 21 18 2 5 53 13 299 1 92 80-60 86 92 1 41 20 9 138 35 470 3 284 ( A l l value s i n ppm) TRACE ELEMENT COMPOSITION - GAMSBY GROUP SAMPLE Cr V Ni Ce Nd Nb Zr Y Sr Rb Ba R-l 85 8 1 44 16 7 111 17 176 63 1192 79-256 62 23 1 53 20 9 147 26 183 28 1080 80-19 77 81 18 34 14 4 104 5 772 30 896 79-176 52 43 3 39 18 6 114 6 514 60 1200 79-251 53 122 3 27 13 8 104 41 337 13 543 79-335 86 254 8 20 10 6 70 22 436 1 39 79-190 22 215 5 31 14 5 108 37 192 13 563 79-266 159 174 71 14 7 4 58 14 268 14 191 -79-173 66 324 2 25 15 7 102 29 490 30 821 79-278 81 174 3 18 8 5 82 27 395 3 240 79-279 64 162 1 18 8 6 90 24 80 47 1972 79-248 184 250 93 8 9 6 51 15 493 15 390 79-292 126 143 44 28 13 7 103 14 671 14 602 80-26 73 15 2 55 24 9 161 38 172 25 1250 80-31 65 6 2 57 25 9 155 45 133 10 594 79-250 70 88 3 26 10 5 92 15 367 18 345 79-189 36 36 1 65 25 7 161 18 62 8 404 79-336 29 170 4 23 8 5 81 27 180 14 174 79-174 95 16 0 50 21 4 122 7 280 27 1099 79-174a 116 19 0 99 43 10 221 41 154 30 1114 79-284 35 67 1 28 9 6 81 27 235 18 365 ( A l l values are reported i n ppm) 161 ANALYTICAL ERRORS Major elements : Standard deviations (la) on working curves for each major element oxide : S i .56 Al .44 Fe .19 Mg .39 Ca .19 Na .26 K .10 T i .03 Mn .005 P .01 Errors f o r I^O and CO2 were not determined. Computed r e s u l t s of a i n t e r n a l c a l i b r a t i o n of standards used i n generating working curves for the reported analyses are included on the following pages. Trace elements : Approximate la errors on working curves for the reported analyses, as generated i n routines described by Berman (1979) : Cr 2 V 6 Ni 3 Ce 10 Nd 1 Nb 1 Zr 7 Y 2 Sr 1.5 Rb 1 Ba 20 TSAYTIS RIVER MAJOR ELEMENT CHEMISTRY STANDARDS IDENT SI AL FE MG CA NA K TI MN P H20 BCR1 55. 48 14 . 18 13. 28 2. 68 6 . 61 3. 59 1 . 64 2 . 21 0. 17 0. 33 0. 67 55. 01 14 . 06 13 . 17 2. 66 6. 55 3. 56 1 . 62 2 . 19 0. 17 0. 33 0. 67 54 . 53 13 . 72 13. 44 3. 48 6 . 97 3 . 30 1 . 70 2 . 26 0. 18 0. 36 0. 67 0. 48. 0. 34 -0. 27 -0. 82 -0. 42 0. 26 -0. 08 -0. 07 -0. 01 -0. 03 0. 0 AGV1 60. 75 16. 28 6. 84 1 . 41 5 . 04 4 . 35 2 . 79 1 . 09 0. 10 0. 46 0. 78 60. 80 16 . 29 6 . 85 1 . 41 5. 04 4 . 36 2. 79 1 . 09 0. 10 0. 46 0. 78 59. 61 17 . 19 6. 82 1 . 52 4 . 94 4 . 32 2. 92 1 . 06 0. 10 0. 51 0. 78 1 . 19 -0. 90 0. 03 -0. 1 1 0. 10 0. 04 -0. 13 0. 03 -0. 00 -0. 05 0. 0 DTS1 39. 49 0. 62 9. 08 49. 60 0. 16 0. 20 0. 05 0. 01 0. 13 0. 02 0. 42 39. 55 O. 62 9. 09 49. 68 0. 16 0. 20 0. 05 0. 01 0. 13 0. 02 0. 42 40. 61 0. 25 8. 73 49. 80 0. 14 0. 01 0. 0 0. 0 0. 12 0. 0 0. 42 -1 . 06 0. 37 O. 36 -0. 12 0. 02 0. 19 O. 05 0. 01 0. 01 0. 02 0. 0 W1 52. 13 16. 16 1 1 . 21 5. 62 1 1 . 20 2 . 54 0 68 1 03 0. 16 0. 15 0 53 51 . 37 15. 92 1 1 . 04 5 54 11 . 04 2 . 50 0 67 1 01 0. 16 0. 15 0 53 52 72 15. 02 1 1 . 10 6 63 10 98 2 . 15 0 64 1 07 0. 17 0. 14 0 53 - 1 35 0. 90 -0. 06 -1 09 0 06 0 35 0 03 -0 06 -0. 01 0. 01 0 0 GH 74 71 12 10 1 40 0 35 0 76 3 66 4 69 0 09 0. 05 0 02 0 46 75 91 12 30 1 42 0 36 0 77 3 71 4 76 0 09 0. 05 0 02 0 46 75 85 12 51 1 34 0 03 0 69 3 85 4 76 0 08 0. 05 0 01 0 46 0 06 -0 21 0 08 0 33 0 08 -0 14 0 00 0 01 -0 00 0 01 0 0 GA 69 62 13 87 2 62 1 40 2 71 2 81 4 32 0 44 0 09 0 14 0 87 70 34 14 01 2 64 1 42 2 73 2 84 4 36 0 44 0 09 0 14 0 87 69 96 14 51 2 83 0 95 2 45 3 55 4 03 0 38 0 09 0 12 0 87 0 38 -0 50 -0 19 0 47 0 28 -O 71 0 33 0 06 -0 OO 0 02 0 0 GSP1 68 54 14 1 1 3 69 1 10 2 10 2 49 5 40 0 62 0 03 0 28 0 58 69 20 14 25 3 73 1 11 2 12 2 51 5 45 0 62 0 03 0 28 0 58 67 .32 15 28 4 28 0 97 2 03 2 81 5 51 0 66 0 04 0 28 0 58 1 .88 -1 03 -0 55 0 14 0 09 -0 30 -0 06 -0 04 -0 01 -0 00 0 O PCC1 41 .23 0 74 8 .77 43 53 O 52 0 20 0 03 0 01 0 12 0 02 4 .70 41 . 20 0 .74 8 .76 43 .51 0 52 0 20 0 .03 0 .01 0 12 0 02 4 . 70 42 . 10 0 .73 8 .29 43 .50 0 .55 0 .01 0 .0 0 .01 0 12 0 01 4 .70 -0 .90 0 .01 0 .47 0 .01 -0 .03 0 . 19 0 .03 -0 .00 0 00 0 .01 0 .0 NIM-N 51 .93 18 . 13 9 .43 6 .47 12 .07 2 .65 0 . 28 0 .20 0 19 0 .04 0 .33 51 .00 17 .81 9 .27 6 .35 11 .86 2 .60 0 .28 0 .20 0 18 0 .04 0 . 33 52 .64 16 .50 8 .89 7 .50 1 1 .50 2 .46 0 .25 0 .20 0 . 18 0 .03 0 . 33 - 1 .64 1 .31 0 .38 -1 . 15 0 .36 0 . 14 0 .03 -0 .00 0 .00 0 .01 0 .0 NIM-P 51 .72 5 .67 12 . 19 25 .89 2 .80 0 .91 0 . 15 0 .21 0 .24 0 .04 0 .26 51 .64 5 .66 12 . 17 25 .85 2 .80 0 .91 0 . 15 0 .21 0 . 24 0 .04 0 . 26 51 . 10 4 . 18 12 .79 25 .33 2 .66 0 .37 0 .09 0 .20 0 .22 0 .02 0 . 26 0 .54 1 .48 -0 .62 0 .52 0 . 14 0 .54 0 .06 0 .01 0 .02 0 .02 O .0 JB1 53 .46 15 .72 9 .09 6 .67 8 .93 2 .59 1 .43 1 . 36 0 . 15 0 .27 1 .01 53 .OO 15 .58 9 .02 6 .61 8 .85 2 .57 1 .42 1 .35 0 . 15 0 . 26 1 .01 52 .60 14 .62 9 .05 7 .76 9 .35 2 .79 1 .42 1 .34 0 . 15 0 . 26 1 .01 0 .40 0 .96 -0 .03 -1 . 15 -0 .50 -0 . 22 -0 .00 0 .01 -0 .00 0 .00 0 .0 C02 0.02 0.02 0.02 0.0 0.02 0.02 0.02 0.0 0.07 0.07 0.07 O.O 0.06 0.06 0.06 0.0 0. 14 0.14 0. 14 0.0 0.11 0.11 0. 1 1 0.0 0.12 0.12 O. 12 0.0 0. 18 0. 18 0. 18 0.0 O. 10 0. 10 0. 10 0.0 O. 08 0.08 0.08 0.0 0. 18 0. 18 O. 18 0.0 TOTAL 100.85 100.63 99.92 99.79 99.84 100.15 101 . 47 101.21 98.43 99.77 98.98 99.85 99.05 99.88 100.06 100.20 101.82 100.58 100.14 97.30 100.86 100.53 FINAL VALUE NORM. VALUE RECCOM. VALUE NORM.-RECC. FINAL VALUE NORM. VALUE RECCOM. VALUE NORM.-RECC. FINAL VALUE NORM. VALUE RECCOM. VALUE NORM.-RECC. FINAL VALUE NORM. VALUE RECCOM. VALUE NORM.-RECC. FINAL VALUE NORM. VALUE RECCOM. VALUE NORM.-RECC. FINAL VALUE NORM. VALUE RECCOM. VALUE NORM.-RECC. FINAL VALUE NORM. VALUE RECCOM. VALUE NORM.-RECC. FINAL VALUE NORM. VALUE RECCOM. VALUE NORM.-RECC. FINAL VALUE NORM. VALUE RECCOM. VALUE NORM.-RECC. FINAL VALUE NORM. VALUE RECCOM. VALUE NORM.-RECC. FINAL VALUE NORM. VALUE RECCOM. VALUE NORM.-RECC. C-4 O f m H > to C J N SY2 5 9 . 95 12 . 42 6 . 1 1 2 . 63 7 . 77 4 . 45 4 . 25 0. 12 6 0 . 34 12. 50 6 . 15 2. 65 7 . 82 4. 48 4 . 28 0. 12 6 0 . 10 12. 12 6 . 27 2. 70 7 . 98 4 . 34 4 . 48 0 . 14 0 . 24 0 . 38 - 0 . 12 - 0 . 05 - 0 . 16 0 . 14 - 0 . 20 - 0 . 02 NIM-S 6 3 . 55 16 . 44 1 . 45 1 . 01 0 . 69 0 . 67 15. 35 0. 05 6 3 . 78 16 . 50 1 . 45 1 . 01 0 . 69 0 . 67 15. 41 0. 05 6 3 . 63 17 . 34 1 . 40 0 . 46 0 . 68 0 . 43 15. 35 0. 04 0 . 15 - 0 . 84 0 . 05 0. 55 0. .01 0 . 24 0 . 06 0. 01 MRG1 39 . 38 9 . 00 17. 87 14. 44 14. ,53 1 . 67 0. 19 3. 71 38 . 23 8. .73 17 . 35 14. 02 14 . , 10 1 . 62 0. 18 3 .60 39 . 32 8 ,50 17. 85 13. ,49 14 . .77 0. 71 0. 18 3 .69 -1 . 09 0 ,23 - 0 . .50 0. ,53 - 0 . .67 0. .91 0. .00 - 0 . .09 JG1 71 . .46 13 .31 2. .41 1 .24 2 .35 2. .56 4 . 29 0. .37 72 , .34 13. .47 2 .44 1 .25 2 . 38 2 .60 4 . 34 0 .38 72 . .36 14. .20 2 . 17 .0 .76 2 . 17 3. ,39 3. ,96 0 . 27 - 0 . .02 - 0 . 73 0 .27 0 .49 0 .21 - 0 , , 79 0. .38 0 . 1 1 SY3 60 .03 12 . 17 6 . 15 2 .60 8 .20 4 .31 4 .09 0 . 13 60 .41 12 .25 6 . 19 2 .62 8 .25 4 .34 4 . 11 0 . 13 59 .68 1 1 .80 6 .42 2 .67 8 26 t 4 . 15 4 .20 0 . 15 0 . 73 0 .45 - 0 . 23 - 0 .05 - 0 .01 0 . 19 - 0 .09 -0 .02 G2 69 .62 13 .86 2 .44 1 . 13 2 .07 4 .07 4 .49 0 .46 70 .40 14 .02 2 .47 1 . 15 2 .09 4 . 1 1 4 .54 0 .47 69 . 22 15 .40 2 .67 0 .75 1 .96 4 .06 4 .46 0 .48 1 . 18 -1 .38 - 0 .20 0 .40 0 . 13 0 .05 0 .08 - 0 .01 0 . 33 0 . 43 0 . 43 0 . 46 9 9 . 35 FINAL VALUE 0 . 33 0 . 43 0. 43 0 . 46 NORM. VALUE 0 . 32 0 . 43 0 . 43 0 . 46 99 . 77 RECCOM. VALUE 0 . 01 0 . 00 0 . 0 0. 0 NORM.-RECC. 0 . 01 0 . 10 0. 22 0. 09 99 . 64 FINAL VALUE 0 . 01 0 . 1 1 0. 22 0. 09 NORM. VALUE 0 . 01 0 . 12 0. 22 0. 09 99 . 77 RECCOM. VALUE 0 . 00 - 0 . 01 0. 0 0. 0 NORM.-RECC. 0. 16 0. 08 0. 98 1 . 00 103. 01 FINAL VALUE 0. 16 0. .08 0. 98 1 . .00 NORM. VALUE 0. 17 0. .06 0. 98 1 . .00 100. .72 RECCOM. VALUE - 0 . .01 0. .02 0. .0 0. .0 NORM.-RECC. 0. .08 0. , 1 1 0. .54 0 .08 98 .80 FINAL VALUE 0. .08 0 . 12 0 .54 0 .08 NORM. VALUE 0. .06 0 .09 0 .54 0 .08 100 .05 RECCOM. VALUE 0. .02 0 .03 0 .0 0 .0 NORM.-RECC. 0 .31 0 .58 0 .42 0 .38 99 . 36 FINAL VALUE 0 .31 0 .58 0 .42 - 0 .38 NORM. VALUE 0 . 32 0 .54 0 .42 0 . 38 98 .99 RECCOM. VALUE - 0 .01 0 .04 0 .0 0 .0 NORM.-RECC . 0 .03 0 . 14 0 .50 0 .08 98 .90 FINAL VALUE 0 .03 0 . 15 0 .50 0 .08 NORM. VALUE 0 .03 0 . 13 0 .50 0 .08 99 .74 RECCOM. VALUE 0 .00 0 .02 0 .0 0 .0 NORM.-RECC. APPENDIX 3 GEOCHRONOLOGY : ANALYTICAL RESULTS AND TECHNIQUES Rb/Sr ANALYTICAL DATA Sample s u i t e : Central Gneiss Complex Sample // Description Lat. Long. ppm Sr ppm Rb 8 7Rb/ 8 6Sr 8 ? S r / 8 ^ r 80-41 Mylonitic' granodiorite II 10 698.9 58. 8 0.2441 0.7040 80-37a Granitoid gneiss o i II o i 53 27 20 127 44 II 10 352.9 35. 1 0.<2887 0.7049 80-37b Granitoid gneiss 53°27 ,20"l27 O44' 10" 278.2 37. 6 0.3915 0.7049 80-61 Amphibolite 53°26'45"l27 038' 50" 288.4 2. 1 0.0214 0.704 80-56 Amphibolite 0 I n 0 _ l 53 26 45 127 38 II 50 391.6 10. 5 0.0782 0.7042 80-55 Amphibolite 53 O27'00"l27 O39' 'so- 698.4 13. 7 0.0571 0.7069 80-60 Leucogneiss 53 026 ,45"l27 038' so" 479.1 14. ,8 0.0901 0.7050 A n a l y t i c a l technique : Rb and Sr concentrations were determined by r e p l i c a t e a n a l y s i s of pressed powder p e l l e t s using X-ray fluorescence. USGS rock standards were used f o r c a l i b r a t i o n . Mass absorption c o e f f i c i e n t s were obtained from Mo Compton sc a t t e r i n g measurements. Rb/Sr r a t i o s have a pr e c i s i o n of 2%(la) and concentrations a p r e c i s i o n of 5% ( l a ) . Sr i s o t o p i c composition was measured on unspiked samples prepared using standard ion exchange techniques. The mass spectrometer i s a ISOMASS 54R. Data a q u i s i t i o n i s d i g i t i z e d and automated usin° a HEWLETT PACKARD 85 computer. The precision of a s i n g l e 8 7Sr/ 8 6 S r r a t i o i s < 0.0001 ( l a ) . Rb/Sr dates are based on a Rb decay constant of 1.42 * 10 - 1 1 y e a r - 1 . The regressions are c a l c u l a t e d according to the technique of York (1967). Sample s u i t e : Gamsby Group metavolcanics Sample // Description Lat. Rb/Sr ANALYTICAL DATA Long. ppm Sr ppm Rb 87Rb/86Sr< 8 7Sr/ 8 69r 79-335 Mafic mylonite 79-190 Mafic mylonite 79-284 P h y l l i t e 79-189 F e l s i c mylonite 79-279 Mafic mylonite 79-251 Mafic mylonite 79- 256 Mylonitic feldspar porphyry 80- 31 F e l s i c mylonite 79-173 Mafic mylonite 79-174 F e l s i c mylonite 79-168 Mafic mylonite 79-169 F e l s i c mylonite 53 O29'30"l27 O39'lo" 441.8 S S ^ s V ^ ^ ' 7" 182.2 53°28'20"l27°39 ' 5" 230.4 53 028'54"l27 039' 7" 61.7 53°29 ,20"l27°39 ,50" 82.1 II J l" . it 2.5 0.0168 0.7038 11.3 0.1795 0 .7046 18.9 0.2380 0 .7045 9.8 0.4616 0 .7055 49.1 1.7320 0 .7078 14.0 0.1248 0 .7045 28.3 0.4338 0 .7053 10.6 0.2614 0 .7044 30.4 0.1841 0 .7042 28.7 0.2892 0.7038 46.2 0.5999 0 .7050 35.6 0.2542 0 .7043 Isochron date 160.2 - 24.3 Ma I n i t i a l 8 7 S r / 8 6 S r r a t i o : 0.7039 ± 0 . 00016 Comment : Excluding 79-279 and samples from W of 'Khawachen Mtn.' gives a date of 230.4 ± 39.5 Ma with i n i t i a l r a t i o of 0.70386 ± 0.00016 Rb/Sr ANALYTICAL DATA Sample s u i t e ; Gamsby Group mylonitic granite Sample # Description Lat. Long. ppm Sr ppm Rb 8 7Rb/ 8 6Sr 8 7Sr/ 8 6Sr R-l Mylonitic granite 53°29'00"127°40'30" 176.0 62.0 1.0200 0.7066 R-3 M „ II it 171.2 50.0 0.8470 0.7060 R-5 t i II .. „ 164.5 63.9 1.1261 0.7062 R-7 II II II II 169.3 50.0 0.8560 0.7059 Isochron date : 138.5 ± 99.0 Ma I n i t i a l r a t i o : 0.7043 ± 0.00136 Isochron through assumed i n i t i a l r a t i o of 0.7040 and mean composition of the four samples gives a date of 159.3 Ma Rb/Sr ANALYTICAL DATA Sample s u i t e : Meta-volcanlc rocks near Shames (Terrace area), B.C. Sample// Description Lat. Long. ppm Sr ppm Rb 8 7Rb/ 8 6Sr ^Sr/^Sr WW 50-1 Meta-rhyolite WW 80-26 Meta-rhyolite WW 80-25 Meta-andesite(?) TER 829 Meta-rhyolite(?) WVW 50-4 Meta-basalt Isochron date : 149.8 ± 46.8 Ma I n i t i a l r a t i o : 0.7050 ± 0.00029 Comment : Isochron excluding specimen TER 8 r a t i o of 0.7047 ± 0.00021 176.8 10. 1 0.1665 0.7053 67.9 12. 9 0.5529 0.7065 318.3 25. 2 0.2293 0.7058 247.9 70. 1 0.8186 0.7064 398.2 11. 8 0.0863 0.7049 gives a date of 253.5 ± 52.7 Ma with a i n i t i a l 169 K/Ar ANALYTICAL DATA Sample # ; 80-66 Description : Hornblende, q u a l i t y very f i n e , from gneissic to mylonitic quartz d i o r i t e , Gamsby Group Sample l o c a t i o n : Elev. 1150 m on southeast facing slope, approximately 300 i NNE of the foot of an unnamed g l a c i e r Lat.: 53°28'02" Long.: 127°41'44" K=x=0.567 ± 0.001% (n=2) Ar40=3.322*10~6cc/gm=1.482*10"10mol/gm 86.9% of I A r 4 0 Calculated age = 145 i 5 Ma Sample # : 80-27 Description : Hornblende (50-100 mesh), qu a l i t y very f i n e - f i n e , from a c h i l l e d margin microdiorite dyke i n t r u s i v e into amphibolites of the Gamsby Group Sample l o c a t i o n : as for spec. #80-66 K=x=0.344 ± 0.001% (n=2) Ar 4 0=0.8943*10~ 6cc/gm=0.3990*10 _ 1 0mol/gm 40-55.5% of I Ar Calculated age : 65.7 ± 2.3 Ma A n a l y t i c a l technique : K was determined i n duplicate by atomic absorption using a Techtron AA4 spectrophotometer and Ar by i s o t o p e ^ i l u t i o n using a MS-10 mass spectrometer and high pu r i t y Ar spike. A de t a i l e d o u t l i n e of the extraction system i s presented i n White et a l . (1967). Errors reported are for one standard deviation based on a n a l y t i c a l errors." , n , Constants used are : X K =0.581*10 *a £ A 4 0K ( 3=4.962*10" 1°*a" 1 40 K/K=0.01167 atom percent K analyses were done by K.L. Scott, Ar analyses were done by J.E. Harakal 170 U/Pb ANALYTICAL DATA Sample # : 79-174a-z Description : Zircons, 200 mesh, doubly terminated, slender, pink, non-magnetic, from schistose metarhyolite, Gamsby Group Sample weight :0.0816 gm Sample l o c a t i o n : @ small lake fed by prominent g l a c i e r on east slope of the Tsaytis River v a l l e y Lat. : 53°25'47" Long. : 127°35'34" PPM U : 361.83 PPM Pb : 15.12 Observed Pb i s o t o p i c composition* Blank % t o t a l Pb ** : 1.2 Common Pb age*** : 241 Ma % Common Pb : 22 Calculated ages 206/207 :0.11241 208/206 :0.25022 206/204 : 239.0 Decay constants 2 3 8U *0.155125*10"9a 1  2 3 SU =0.98485*10"V 1  2 3 8U/ 2 3 5 U = 137.88 206,,, . 238 Pb/ U : 209 Ma ( I .5%) 207 235 Pb/ U : 207 , 206 , Pb/ Pb 211 Ma (-241 Ma G 1%: No cor r e c t i o n was used f o r mass f r a c t i o n a t i o n on these rims ** Isotopic composition of blank Pb : 206/204 = 18.7 207/204 = 15.63 208/204 = 38.63 = modern Pb of Stacey & Kramers, 1975 *** Isotopic composition of common Pb based on Stacey-Kramers growth curve : 206/204 = 18.33 207/204 = 15.61 @ 241 Ma 208/204 = 38.19 A n a l y t i c a l technique : Zircon separate was prepared using standard grinding and heavy mineral separation procedures. Di s s o l u t i o n and i s o l a t i o n of U and Pb were done using the procedure of Krogh (1973). F i n a l p u r i f i c a t i o n of Pb was accomplished by aniodic electro-deposition. Samples were analysed using s i n g l e Re filament and s i l i c a gel techniques on a 90 degree, 12 inch mass spectrometer i n the Department of Geophysics, UBC, by B.D. Ryan. APPENDIX 4 FOSSIL REPORTS F o s s i l s were not submitted for t h i s t h e s i s ; these reports were received from G. Woodsworth of the Geological Survey of Canada. F o s s i l report No. Mlsc.-2-CAR-1978 F o s s i l s submitted by G.J. Woodsworth, 1977 Report by C A . Ross, Paleontology Subdivision, I n s t i t u t e of Sedimentary and Petroleum Geology, Calgary F i e l d //. L o c a l i t y , fauna and-age GSC Loc. // 77-WV-64 About 300 ms NW of 77-WV-58, Whitesail C-76645 Lake area, B.C. 53°20'2 nN, 127°33'o"w Massive grey carbonate Schwagerina (Pseudofuselina) ex gr. (P.) tschernyschewi (Schellwien) S. (P.) sp. c f . (P.) u r a l i c a (Krptow) ? Schubertella sp. nodosariids Age : Early Permian, Sakmarian, probably Tastubian 77-WV-58 About 3 km west of west end of Seel Lake, C-76646 Whitesail Lake area, B.C. 53°30'l"N, 127°33'3"W Orange, dolomitic carbonate Schwagerina (Pseudofuselina) sp. Pseudofuselinella sp. Age : Early Permian, l a t e A s s e l i a n to Sakmarian T r i t i c i t e s c f . T_. cheni Grozd. & Lebev. or C-76646/1 T_. densimedius Chen Schwagerina (Pseudofuselina) spp. Pseudofuselinella sp. ? Schubertella sp. Age : Early Permian, l a t e Asselian or early Sakmarian ( i . e . Tastubian). More l i k e l y Tastubian than l a t e Asselian. Schwagerina (Pseudofuselina) c f . (P.) £-76646/2 indigaensis (Grozd. & Lebev.) ? Pseudofuselinella sp. Age : Early Permian, early Sakmarian, Tastubian 

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