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UBC Theses and Dissertations

Structure and metamorphism north of Quesnel Lake and east of Niagara Creek, Cariboo Mountains, British… Engi, Jill Ellen 1984

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STRUCTURE AND METAMORPHISM NORTH OF QUESNEL LAKE AND EAST OF NIAGARA CREEK, CARIBOO MOUNTAINS, BRITISH COLUMBIA by J I L L ELLEN ENGI B.A., U n i v e r s i t y Of Washington, 1981 B . S c , U n i v e r s i t y Of Washington, 1981 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES Department Of G e o l o g i c a l Sciences We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA October 1984 © J i l l E l l e n Engi, 1984 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an advanced degree a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I agree t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by t h e head o f my department o r by h i s o r h e r r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f bdoXaiycuX tSo 'ejMcs The U n i v e r s i t y o f B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date ^5 OcA^hes ^ ^ M , A b s t r a c t An area of 15 km2, l o c a t e d on the northeastern boundary of the Shuswap Metamorphic Complex, was mapped at a s c a l e of 1:20,000 durin g the summer of 1983. A sequence of deformation and metamorphic events has been e s t a b l i s h e d based on petrography, s t r u c t u r a l a n a l y s i s , geothermometry, and geobarometry. Four phases of deformation and r e l a t e d metamorphism have been reco g n i z e d . Phase 1 deformation i s preserved p r i m a r i l y as a metamorphic f o l i a t i o n . R a r ely, i s o c l i n a l phase 1 f o l d s of bedding were observed. Metamorphic c o n d i t i o n s a s s o c i a t e d with t h i s e a r l y p e r i o d are not known. The major s t r u c t u r e s i n the map area are second phase f o l d s . These trend and plunge to the northwest and are southwestwardly v e r g i n g . M i n e r a l s which c r y s t a l l i z e d d u r i n g the main metamorphic event are syn- and post-kinematic to second phase s t r u c t u r e s . G a r n e t - b i o t i t e geothermometry y i e l d s temperatures of about 505°C in the k y a n i t e - s t a u r o l i t e zone and - 580°C i n the s i l l i m a n i t e zone, both at pressures of 5.0±.5 kbar. Geobarometry was based on the assemblage g a r n e t - r u t i l e -a l u m i n o s i l i c a t e - i l m e n i t e . A s s o c i a t e d with phase 2 f o l d i n g i s movement along low-angle reverse f a u l t s , which d i s r u p t both s t r a t i g r a p h y and e s t a b l i s h e d metamorphic zones. These f a u l t s are sheared h o r i z o n s , d i s t i n g u i s h e d by high s t r a i n f a b r i c s , with e x t e n s i v e r e c r y s t a l l i z a t i o n . In one shear zone, garnet and b i o t i t e temperatures are s y s t e m a t i c a l l y r e s e t and i n d i c a t e higher temperatures than i n surrounding rocks. F u r t h e r evidence of i i s h e a r - h e a t i n g i n c l u d e s an anomalous occur rence of s i l l i m a n i t e in t h i s shear zone. Phase 3 de fo rmat ion has produced u p r i g h t , n o r t h e r l y -t r e n d i n g f o l d s which p o s t - d a t e both metamorphic peak and r e v e r s e f a u l t i n g . T h i r d phase f o l d s are broad and open. They are expressed s t r o n g l y on ly at deeper s t r u c t u r a l l e v e l s . M i n e r a l assemblages of lower g r e e n s c h i s t f a c i e s were e s t a b l i s h e d p r i o r to phase 4 d e f o r m a t i o n , and may p r e - d a t e phase 3 f o l d s . R e l a t i v e l y h i g h - a n g l e f a u l t s d i s r u p t phase 3 s t r u c t u r e s . In p a r t i c u l a r , the boundary of the Shuswap Metamorphic Complex, as d e f i n e d by the e s t a b l i s h m e n t of the s i l l i m a n i t e zone (Reesor , 1970), i s separa ted from ad jacent k y a n i t e - s t a u r o l i t e rocks to the n o r t h by such a f a u l t . Geothermometry and geobarometry d e l i n e a t e a c o n s i s t e n t temperature d i s c o n t i n u i t y of a p p r o x i m a t e l y 75°C a c r o s s that f a u l t . In a d d i t i o n to the f a u l t s , phase 4 kink f o l d s are l o c a l l y deve loped throughout the a r e a . i i i T able of Contents A b s t r a c t i i L i s t of Tables v L i s t of F i g u r e s and P l a t e s v i Acknowledgement ix Chapter I INTRODUCTION 1 A. TECTONIC SETTING 1 REGIONAL GEOLOGY OF THE CARIBOO MOUNTAINS 7 B. THE MAP AREA 10 Chapter II STRATIGRAPHY 12 INTRODUCTION 12 STRATIGRAPHY: DESCRIPTION OF UNITS 13 A. INTERPRETATION 19 Chapter III STRUCTURE AND TIMING OF METAMORPHISM 22 A. INTRODUCTION 22 B. COVER DEFORMATION 22 C. COVER METAMORPHISM 3 5 3.1 I n t r o d u c t i o n 35 3.2 E a r l y Metamorphism 36 D. SHEAR ZONES AND ISAAC FORMATION .46 3.3 I n t r o d u c t i o n 46 3.4 Shear Zone Features 46 3.5 Shear Zone 2 47 3.6 Shear Zone 3 50 3.7 The Isaac Formation 55 3.8 Shear Zone 4 60 E. THE HIGH GRADE GNEISSES 68 3.9 I n t r o d u c t i o n 68 3.10 Deformation Of Domain 4 Gneisses 68 3.11 Metamorphism Of The High Grade Gneisses 75 a. I n t r o d u c t i o n 75 b. M i c r o s c o p i c Observations 75 c. Chemical Reactions Among M i n e r a l s 84 i v Chapter IV METAMORPHIC CONDITIONS 88 A. INTRODUCTION 88 B. GEOTHERMOMETRY 89 C. GEOBAROMETRY 93 D. RESULTS .94 Chapter V SYNOPSIS 104 A. SUMMARY OF TIMING RELATIONS 105 B. KINEMATICS OF FAULTING: POSSIBLE SCENARIO 109 BIBLIOGRAPHY , 112 APPENDIX A - ELECTRON MICROPROBE ANALYSES 122 ANALYTICAL TECHNIQUES 122 V L i s t of Tables I. Summary of deformation and metamorphism in the cover sequence 67 I I . Summary of deformation and metamorphism i n the high grade g n e i s s e s 87 I I I . Geothermometric e x p r e s s i o n s of F e r r y and Spear (1978), m o d i f i e d f o r no n i d e a l garnet mixing. 92 IV. E q u i l i b r i u m temperatures of 19 samples, c a l c u l a t e d u s ing the g a r n e t - b i o t i t e thermometer (three garnet models) 96 V. Summary of deformation and metamorphism, c o r r e l a t e d a cross the cover sequence i n t o high grade g n e i s s e s . 1 05 VI. Standards f o r microprobe a n a l y s i s of garnet and b i o t i t e ...128 V I I . I n t e r n a l standards f o r g a r n e t - b i o t i t e a n a l y ses ....129 V I I I . C o r r e c t i o n procedure f o r systematic e r r o r and d r i f t i l l u s t r a t e d f o r a g a r n e t - b i o t i t e p a i r 130 IX. Comparison of g a r n e t - b i o t i t e temperatures based on probe a n a l y s e s from U n i v e r s i t y of B r i t i s h Columbia and U n i v e r s i t y of Washington 131 X. S e l e c t e d e l e c t r o n microprobe analyses 132 v i L i s t of F i g u r e s and P l a t e s F i g u r e s 1. Major s t r u c t u r a l elements i n the southeastern Canadian C o r d i l l e r a 2 2. Physiographic D i v i s i o n s i n the southern B r i t i s h Columbia 4 3. Shuswap and Monashee complexes, d i v i d e d 6 4. Regional geology of the Cariboo Mountains .10 5. Schematic s u b d i v i s i o n of the f i e l d area i n t o s t r a t i g r a p h i c and s t r u c t u r a l domains 13 6. Reverse graded bedding i n g r i t c y c l e t y p i c a l of the Upper Kaza 15 7. Phase 3 minor f o l d s , s u b s i d i a r y to a phase 3 a n t i f o r m . Domain 2b 2 6 8. Poles to bedding (SO) from the cover sequence 27 9. Poles to m e t a - f o l i a t i o n (S1) from the cover sequence .28 10. D1 f o l d elements from the cover sequence 29 11. D2 pl a n a r elements (poles to S2) from the cover sequence 30 12. D2 f o l d axes (F2) from the cover sequence 31 13. D2 l i n e a r elements from the cover sequence 32 14. D3 f o l d elements from the cover sequence 33 15. D4 kink f o l d elements from the cover sequence 34 16. Map of metamorphic zones 40 17. B i o t i t e and garnet o v e r p r i n t phase 2 f o l d s . 43 18. Tightened phase 2 f o l d s adjacent to shear zone 2, Domain 1 48 19. D u c t i l e deformation of p e l i t e beds. T i g h t e n i n g of phase 2 hinges, Domain 1 49 20. Kink bands i n Isaac p h y l l i t e , domain 3 52 21. Garnet c o n t a i n i n g s t r a i g h t i n c l u s i o n t r a i l s , r o t a t e d to v i i a high angle with the e x t e r n a l s c h i s t o s i t y 55 22. Open phase 2 f o l d of marble, Domain 3 57 23. C h l o r i t o i d , r o t a t e d i n t o the main f o l i a t i o n (S1) and boudinaged by subsequent f l a t t e n i n g 58 24. I s o c l i n a l phase 1 f o l d s of micaceous h o r i z o n i n marble. 59 25. Poles to plan a r elements from the Isaac wedge and shear zones 2 and 3 62 26. D1 f o l d elements from the Isaac wedge 63 27. D2 elements from the Isaac wedge and shear zones 2 and 3 64 28. Comparison of f o l d elements (D3,D4) from the Isaac wedge and shear zones 2 and 3 65 29. S t r u c t u r a l data from shear zone 4 66 30. Poles to plan a r elements from the high grade gneiss complex 72 31. D2 elements from the hig h grade gneiss complex 73 32. F o l d elements from the high grade gneiss complex 74 33. S i l l i m a n i t e grew at the expense of s t a u r o l i t e and garnet 79 34. Second-stage garnet c o e x i s t i n g with aggregates of s i l l i m a n i t e , w h i t e mica, and b i o t i t e 80 35. S i l l i m a n i t e , white mica, and quartz pseudomorphic a f t e r s t a u r o l i t e 81 36. R e l i c k y a n i t e , p a r t i a l l y r e p l a c e d by s i l l i m a n i t e 83 37. L o c a t i o n of samples used i n geothermometry and geobarometry 97 38. E q u i l i b r i u m temperatures c a l c u l a t e d f o r g a r n e t - b i o t i t e p a i r s from sample K154 99 39. Comparison of r e s u l t s from thermometry and barometry with the l o c a t i o n of the A l 2 S i 0 5 phase diagram 101 40. D i s t r i b u t i o n of temperatures obtained f o r g a r n e t - b i o t i t e p a i r s from domains 2b and 4 103 41. Schematic c r o s s s e c t i o n i l l u s t r a t i n g the r e l a t i o n s h i p s V I 1 1 between s t r a t i g r a p h y , D2 f o l d s , i s o g r a d s , and shear zones 110 P l a t e s v ' . it i ' P l a t e I : G e o l o g i c map ^acHc-"pur"lrer£) P l a t e I I : Down-plunge (F2) p r o j e c t i o n of s t r u c t u r e s a c r o s s .^tue^X map a r e a (A-A') (aa^-potrkisrr) ^JjecfiiNv-1 I. INTRODUCTION T h i s study focuses on g e o l o g i c r e l a t i o n s w i t h i n an area that spans the t r a n s i t i o n between metamorphosed rocks of the Kaza and Cariboo Groups and those of the Shuswap Metamorphic Complex. An area of 15 km2, l o c a t e d on the n o r t h e a s t e r n rim of the complex, was mapped at a s c a l e of 1:20,000 du r i n g the summer of 1983. The map area i s s i t u a t e d north of Quesnel Lake and east of Niagara Creek, in the Southern Cariboo Mountains, B r i t i s h Columbia ( F i g u r e 4). A. TECTONIC SETTING The Southern Canadian C o r d i l l e r a i s s u b d i v i d e d i n t o an eastern Columbian orogen and a western P a c i f i c orogen (Wheeler and G a b r i e l s e , 1972). The Columbian orogen i n c l u d e s three p a r t s : (1) the Canadian Rocky Mountain f o l d and t h r u s t b e l t , (2) a metamorphic-plutonic complex, termed the Omineca C r y s t a l l i n e B e l t , and (3) a westernmost h i n t e r l a n d of P a l e o z o i c and Mesozoic v o l c a n i c and sedimentary rocks that i s part of the physiographic Intermontane B e l t ( F igure 1). The f i e l d area d i s c u s s e d i n t h i s study i s l o c a t e d w i t h i n the Omineca B e l t . The Omineca B e l t i s u n d e r l a i n by Upper P r o t e r o z o i c and Lower P a l e o z o i c metasedimentary-rocks. These were metamorphosed under Barrovian c o n d i t i o n s as high as upper amphibolite f a c i e s and were intruded by Mesozoic g r a n i t o i d p l u t o n i c r o c k s . The metamorphism and c o e v a l deformation are c o n s i d e r e d to r e s u l t from the c o l l i s i o n of the North American c o n t i n e n t with t e r r a n e s to the west (Davis et a l . , 1978; Monger et a l . , 1983). A younger age l i m i t f o r the peak of r e g i o n a l metamorphism in the Cariboo r e g i o n i s provided 2 F i g u r e 1 - Major s t r u c t u r a l elements in the southeastern Canadian C o r d i l l e r a . M o d i f i e d from Wheeler and G a b r i e l s e , 1972 3 by c r o s s - c u t t i n g p l u t o n s as o l d as 163 m.y. (Wheeler and G a b r i e l s e , 1972; Pigage, 1977). An o l d e r l i m i t i s provided by metamorphosed E a r l y J u r a s s i c sediments: during Middle J u r a s s i c to Mid-Cretaceous time, the Omineca B e l t was an u p l i f t e d t errane shedding c l a s t i c d e t r i t u s eastward i n t o a foredeep b a s i n on the c r a t o n and westward i n t o successor basins on o l d e r arc terranes ( E i s b a c h e r , 1974; E i s b a c h e r et a l . , 1974). Rocks mapped as Shuswap t e r r a n e i n F i g u r e s 1 and 2 have been metamorphosed through upper amphibolite f a c i e s c o n d i t i o n s in the B a r r o v i a n f a c i e s s e r i e s of r e g i o n a l metamorphism. The boundaries c o i n c i d e i n g e n e r a l with the s i l l i m a n i t e i s o g r a d ( C a i r n e s , 1939; Reesor, 1970). De f i n e d i n t h i s way, the Shuswap Complex i s the l a r g e s t of metamorphic complexes i n the Omineca B e l t , and c o n s i s t s broadly of the Monashee and Cariboo Mountains. The complex terminates to the northwest in the Cariboo Mountains (Figure 2). Basement gneiss domes are exposed w i t h i n the Shuswap t e r r a n e . From north to south, these i n c l u d e Frenchman Cap, Thor-Odin, and P i n n a c l e s ( r e f e r to F i g u r e 3). Orthogneisses and paragneisses exposed in the cores of the domes y i e l d ages ranging from 1.9 to 3 Ga (Wanless and Reesor, 1975; Duncan, 19*78; Armstrong, 1979). R e g i o n a l - s c a l e and d e t a i l e d mapping outward from these c u l m i n a t i o n s i n d i c a t e that the Shuswap Metamorphic Complex i s u n d e r l a i n and i n t e r f o l d e d with an e x t e n s i v e basement t e r r a n e (Brown, 1981). Recent i n t e r p r e t a t i o n s of the Omineca B e l t by Read and Brown (1981), Brown (1981), and Brown and Read (1983) d e l i n e a t e 4 F i g u r e 2 - P h y s i o g r a p h i c D i v i s i o n s i n the southern B r i t i s h Columbia. M o d i f i e d a f t e r Campbell, 1973 5 two s t r u c t u r a l l y high grade complexes w i t h i n the Shuswap t e r r a n e , the Shuswap and the Monashee Complexes (Figure 3). The Monashee Complex i s recognized by Read and Brown (1981) as a t e c t o n i c window w i t h i n the Shuswap Metamorphic Complex. The Monashee decollement, d e l i n e a t e d by a zone of m y l o n i t i z a t i o n and detachment f a u l t i n g , separates the Monashee Complex from o v e r l y i n g rocks of the Shuswap Complex. According to Read and Brown, the decollement represents a splay from the Columbia River F a u l t Zone, which i s a s h a l l o w l y eastward d i p p i n g mylonite zone that separates the eastern margin of the Monashee Complex from lower grade cover rocks, the S e l k i r k a l l o c h t h o n . Development of extensive mylonite zones on the borders of the Shuswap and Monashee Complexes o c c u r r e d d u r i n g the J u r a s s i c as these t e r r a n e s , together with a c c r e t e d t e r r a n e s to the west ( Q u e s n e l i i a ) , were t e l e s c o p e d and t r a n s p o r t e d eastward with respect to the c r a t o n . According to Monger et a l . (1982), eastward o v e r r i d i n g of the Shuswap ter r a n e by Q u e s n e l i i a i n the Middle J u r a s s i c i n i t i a t e d d u c t i l e s t r a i n , r e g i o n a l metamorphism, and low-angle detachment f a u l t i n g . The f a u l t s are c h a r a c t e r i z e d by mylonite zones which f l a n k the western margin of the Shuswap Metamorphic Complex (Rees, 1981; S t r u i k , 1981). A younger mylonite zone, the Columbia River F a u l t Zone, developed on the eastern s i d e of the Shuswap t e r r a n e as a r e s u l t of eastward movement of the S e l k i r k a l l o c h t h o n over the u n d e r l y i n g Monashee complex (Brown and Read, 1983). Major Middle J u r a s s i c f o l d s t r u c t u r e s and r e g i o n a l isograds are d i s r u p t e d a c r o s s the f a u l t , t h e r e f o r e e a r l y motion on the decollement and f a u l t o u t l a s t e d 6 South KamloopsT r/>°fnpsoti^ 1 MALTON GNEISS 2 FRENCH CREEK SLICE 3 GOLDSTREAM SLICE 4 CLACHNACUOAINN SLICE 5 ILLECILLEWAET SLICE 6 BATTLE RANGE BATHOLITH 7 GALENA BAY STOCK 8 KUSKANAX BATHOLITH 9 FRENCHMAN CAP DOME 10 THOR-ODIN NAPPE 117" 1 1 PINNACLE PEAKS NAPPE 12 WHATSAN BATHOLITH 13 BALDY BATHOLITH 14 RAFT BATHOLITH F i g u r e 3 - Shuswap and Monashee complexes, d i v i d e d (modified from Reed and Brown, 1981, and Brown, 1981). Note l o c a t i o n of map area. 7 the Middle J u r a s s i c peak of r e g i o n a l metamorphism. Motion on the f a u l t was terminated by the time of emplacement of the Galena Bay Stock, which c r o s s - c u t s the mylonites and has y i e l d e d a Rb-Sr whole-rock isochron of 157±2 m i l l i o n years (Armstrong, 1984, p e r s o n a l communication). Although major eastward t e l e s c o p i n g and t r a n s p o r t of cover rocks and h i g h grade g n e i s s e s r e l a t i v e to the c r a t o n was completed b e f o r e the end of the J u r a s s i c (Brown and Read, 1983), l a t e Eocene u p l i f t , normal f a u l t i n g , and high heat flow have been r e c o g n i z e d r e g i o n a l l y (Ewing, 1981; P a r r i s h and Raye, 1983)". A r c h i n g of the Shuswap t e r r a n e , development of l a t e normal f a u l t s , and r e a c t i v a t i o n of the Columbia R i v e r F a u l t and Monashee decollement probably o c c u r r e d d u r i n g the Eocene "thermal event". Lane (1984) i n t e r p r e t s the Columbia River F a u l t Zone to be a T e r t i a r y b r i t t l e f e a t u r e which i s broadly p a r a l l e l to the eastern exposure of the Middle J u r a s s i c d u c t i l e Monashee decollement. B r i t t l e f r a c t u r i n g along the f a u l t d i s r u p t s the e a r l y mylonite zone. REGIONAL GEOLOGY OF THE CARIBOO MOUNTAINS The P r o t e r o z o i c (Hadrynian or Windermere) Kaza Group and Isaac Formation u n d e r l i e the C e n t r a l and Southern Cariboo Mountains. These sediments were o r i g i n a l l y d e p o s i t e d near the base of the c o n t i n e n t a l margin sequence that rims c r a t o n i c North America and comprises the western b a s a l p a r t of the C o r d i l l e r a M i o g e o s y n c l i n e (Davis et a l . , 1978; Monger et a l . , 1983). The s t r u c t u r e of the C e n t r a l and Southern Cariboo Mountains i s dominated by a s e r i e s of p a r a l l e l a n t i c l i n o r i a and 8 s y n c l i n o r i a that plunge g e n t l y to the northwest away from a s t r u c t u r a l c u l m i n a t i o n i n the c e n t r a l part of the mountains (F i g u r e 4). Post-metamorphic u p l i f t of the Premier Range in the southeastern Cariboo Mountains t i l t e d the s t r u c t u r a l sequence i n t o i t s present northwestwardly plunging a t t i t u d e (Murphy, 1984, p e r s o n a l communication). Metamorphic i s o g r a d s u r f a c e s a l s o plunge to the northwest away from the Shuswap Complex. These s u r f a c e s cut a c r o s s s t r a t i g r a p h y (Campbell, 1968 and 1970). Based on 1:250,000 mapping of the Canoe R i v e r and McBride map areas, Campbell (1968 and 1970) and Campbell et a l . (1973) observe a t r a n s i t i o n i n s t r u c t u r a l s t y l e from northwest to southeast toward higher grade rocks. Unmetamorphosed Upper P r o t e r o z o i c to lower P a l e o z o i c rocks at the northwestern p o r t i o n of the Cariboo Mountains are l o c a l l y g e n t l y f o l d e d and are d i s p l a c e d along northwest- and n o r t h e a s t -t r e n d i n g high angle f a u l t s u r f a c e s . F u r t h e r downsection a t r a n s i t i o n zone of u p r i g h t f o l d s occurs, metamorphic grade i n c r e a s e s , and i n the southernmost p o r t i o n s of the range, at s i l l i m a n i t e grade, the P r o t e r o z o i c metasediments are t i g h t l y to i s o c l i n a l l y r e f o l d e d around g e n t l y d i p p i n g a x i a l s u r f a c e s . B. THE MAP AREA The study area covers a p o r t i o n of the Quesnel Lake Map Sheet (93A), which was mapped on a r e g i o n a l s c a l e by R.B. Campbell (1978, Open F i l e Map). The f i e l d area extends from g r e e n s c h i s t f a c i e s metasediments o u t s i d e the Shuswap Complex, a c r o s s the s i l l i m a n i t e - i n i s o g r a d , i n t o upper a m p h i b o l i t e grade rocks of the complex. From northeast to southwest along t h i s t r a v e r s e , L E G E N D P l e i s t o c e n e to Miocene: d o m i n a n t l y v o l c a n i c r o c k s O l i g o c e n e and Miocene: Endako Group ( a n d e s i t e , b a s a 1 t . dac i te ) Cre t a c e o u s or T e r t i a r y : M u s c o v i t e - b i o t i t e g r a n i t e Upper T r i a s s i c to Lower J u r a s s i c : T a k l a Group, p l u s p h y l l i t e . l i m e s t o n e , q u a r t z i t e LTD J u r a s s i c or E a r l y C r e t a c e o u s : g r a n o d i o r i t e to quar t z d i or i te Late T r i a s s i c : Takomkane B a t h o l i t h and b o d i e s of s i m i l i a r age and l i t h o l o g y yy > > M i s s i s s i p p i a n and (?) Younger: S l i d e Mountain Group Lower Devonian: B l a c k S t u a r t Formation M i d d l e t o Lower Cambrian: Gog Group, McNaughton F o r m a t i o n , p l u s younger l i m e s t o n e , d o l o m i t e , s h a l e Mapped F a u 1 t I n f e r r e d F a u 1 t • Lower Cambrian to Hadr y n i a n : C a r i b o o Group (Yanks Peak, Midas, M u r a l , Cunningham, Yankee B e l l e . Isaac Format i ons) H a d r y n i a n : Kaza Group P r e - H a d r y n i a n : Metamorphic r o c k s and g r a n i t i c o r thogne i ss AGE UNKNOWN Shuswap Metamorphic Complex Normal F a u l t ( h a t c h e s on hanging w a l l ) Thrust F a u l t ( t e e t h on hanging w a l l ) 1 - F l e t c h e r (Ph.D. 1978) F l e t c h e r and Greenwood (1979) 2 - P i g a g e (Ph.D. 1978) Ptgage and Greenwood (1982) 3 _ Murphy (Ph.D. i n p r o g r e s s ) Murphy and Journeay (1982) Murphy and Rees (1983) 4 " P e l 1 (Ph.D. 1984) P e l l and Simony (1981, 1982. 1984) vo 1111 !!!! Augen g r a n i t e , g n e i s s i c g r a n o d i o r i t e , g n e i s s Figure 4 - Regional geology of the Cariboo Mountains. Modified from map sheets 83 (1977) and 93 (1979), Geological Survey of Canada. 11 one moves g e n e r a l l y down s e c t i o n s t r u c t u r a l l y , and perhaps s t r a t i g r a p h i c a l l y , through Kaza Group metasediments i n t o the Shuswap complex. However, the t r a n s i t i o n i s not continuous. Northwest-trending shear zones i n t e r r u p t the t r a n s i t i o n , o b s c u r i n g the r e l a t i o n s h i p s between s t r a t i g r a p h i c and s t r u c t u r a l elements. The s t r u c t u r a l geometry, the v a r i a t i o n i n metamorphic grade, and the presence of shear zones suggest the r e g i o n a l c o r r e l a t i o n of s t r u c t u r e s i n the map area with s i m i l a r f e a t u r e s d e s c r i b e d by other workers who have mapped acr o s s the n o r t h e a s t e r n margin of the Shuswap in the Cariboo Mountains ( F l e t c h e r , 1972; Pigage, 1978). The present study a i d s i n d e l i n e a t i n g the s t r u c t u r a l , metamorphic, and s t r a t i g r a p h i c c h a r a c t e r i s t i c s that d e f i n e the boundary of the Shuswap Complex. 1 2 I I . STRATIGRAPHY INTRODUCTION The map a r e a has been d i v i d e d i n t o f i v e domains, based on s t r a t i g r a p h y , s t r u c t u r e , and p e t r o l o g y . Four d i s t i n c t shear zones a r e used t o d e f i n e the domain b o u n d a r i e s . F i g u r e 5 i l l u s t r a t e s the l o c a t i o n s of the shear zones w i t h r e s p e c t t o the domains. In t h i s c h a p t e r , the c h a r a c t e r i s t i c s of the r o c k s c o m p r i s i n g each domain a r e f i r s t summarized. Because of p e n e t r a t i v e f o l d i n g on v a r i a b l e s c a l e s , no e s t i m a t e s of o v e r a l l t h i c k n e s s have been made. In the next s e c t i o n , the sequences of metasedimentary r o c k s i n the f i e l d a r e a a r e t e n t a t i v e l y c o r r e l a t e d w i t h l i t h o s t r a t i g r a p h i c u n i t s mapped t o the e a s t and s o u t h e a s t of the f i e l d a r e a . STRATIGRAPHY: DESCRIPTION OF UNITS Domain j_ c o n s i s t s of i n t e r b e d d e d q u a r t z o f e l d s p a t h i c g n e i s s , p e l i t i c s c h i s t , f e l d s p a t h i c q u a r t z i t e , and minor c a r b o n a t e . These t r u n c a t e a b r u p t l y i n the northernmost p o r t i o n of the map a r e a a g a i n s t p h y l l i t e s , s l a t e s , and c a r b o n a t e s at shear zone 1. The r o c k s a r e m o s t l y c y c l e s of gray and g r e e n i s h q u a r t z o f e l d s p a t h i c g n e i s s e s . These weather b u f f t o brown and a r e i n t e r b e d d e d w i t h : green, t h i n l y l a m i n a t e d , brown-weathered p e l i t i c s c h i s t ; massive p i n k f e l d s p a t h i c q u a r t z i t e ; brown-weathered, dark g r a y , l a m i n a t e d c a l c a r e o u s mudstone; and v e r y r a r e , t h i n , g r a y , c a l c i t i c c a r b o n a t e . G r i t s and p e l i t i c s c h i s t s l o c a l l y c o n t a i n minor amounts of c a r b o n a t e . M a t r i x c h l o r i t e , which v a r i e s i n abundance p r i m a r i l y a c c o r d i n g t o b u l k c o m p o s i t i o n , i s r e s p o n s i b l e f o r the g r e e n i s h c o l o r of the g r i t s 13 F i g u r e 5 - S c h e m a t i c s u b d i v i s i o n o f s t r a t i g r a p h i c a n d s t r u c t u r a l d o m a i n s t h e f i e l d a r e a i n t o 1 4 and p e l i t e s . The g r i t u n i t s c o n t a i n c l a s t s of coarse f e l d s p a r and q u a r t z . Blue q u a r t z , t y p i c a l of Hadrynian c l a s t i c rocks i n the C o r d i l l e r a , i s present but not abundant. F e l d s p a r c l a s t s are u s u a l l y xenomorphic and rounded, are always r e c r y s t a l l i z e d , and account f o r approximately 10 percent of the rock. The coarse g r i t u n i t s e x h i b i t poor to good s o r t i n g . C l a s t i c c y c l e s , 20 to 50 cm t h i c k , c h a r a c t e r i s t i c a l l y s t a r t with graded beds c o n t a i n i n g abundant l a r g e f e l d s p a r s that have p o s i t i v e r e l i e f on weathered s u r f a c e s . Here, the f e l d s p a r s comprise up to 30 percent of the rock. F i g u r e 6 i l l u s t r a t e s a t y p i c a l c l a s t i c c y c l e with reverse g r a d i n g . The f e l d s p a r c l a s t s d e r i v e from an igneous source. Both d e t r i t a l z i r c o n and tourmaline are p r e s e n t . Cross beds are observed r a r e l y i n the f i n e r - g r a i n e d , w e l l -s o r t e d q u a r t z o f e l d s p a t h i c gneiss u n i t s . Where present, the c r o s s beds are t r u n c a t e d s h a r p l y at both base and top by interbedded, c y c l i c , o f t e n graded g r i t s . T a b ular, elongate, b u f f - c o l o r e d shale c l a s t s occur i n the Upper Kaza g r i t s . Rocks of Domain 2a , i n the f o o t w a l l of shear zone 3, d i s p l a y the same c h a r a c t e r i s t i c s as those i n Domain 1: G r i t dominates a sequence of stacked c y c l e s from graded g r i t to f e l d s p a t h i c q u a r t z i t e to p e l i t i c s c h i s t . F e l d s p a r metaclasts i n d i c a t e f a c i n g i n many of the c o a r s e r g r i t u n i t s . Pink-weathering f e l d s p a t h i c q u a r t z i t e u n i t s , t y p i c a l of Domain 1, a l s o occur i n Domain 2a. Carbonate u n i t s are r a r e and t h i n . Gray, f l a t t e n e d , t a b u l a r shale r i p - u p c l a s t s , studded with 1 5 F i g u r e 6 - Reverse graded bedding in g r i t c y c l e t y p i c a l of the Upper Kaza. Domain 2 a . 16 garnet, are observed in some p o r t i o n s of the g r i t beds. To the southwest, the c y c l e s of graded g r i t - p e l i t i c s c h i s t p e r s i s t i n t o Domain 2b. In the n o rthern, s t r a t i g r a p h i c a l l y higher p o r t i o n s of Domain 2b, graded g r i t u n i t s with s o r t e d white f e l d s p a r c l a s t s are observed. The r a t i o of g r i t to p e l i t e i s v a r i a b l e , and u n l i k e the d e p o s i t i o n a l c y c l e s i n Domains 1 and 2a, p e l i t i c s c h i s t s o f t e n predominate. P e l i t i c s c h i s t u n i t s are t y p i c a l l y 10 to 50 cm t h i c k and the g r i t s are 5 to 20 cm t h i c k . I n d i v i d u a l p e l i t i c u n i t s are as t h i c k as one metre and are i n t e r l a y e r e d with g r i t u n i t s of 5 to 50 cm t h i c k n e s s . The g r i t s weather brown or l i g h t gray and are g r e e n i s h - g r a y ; the p e l i t i c s c h i s t s are brown-weathered and are green laminated or gray with a white micaceous sheen. The t h i c k , massive pink f e l d s p a t h i c q u a r t z i t e s c h a r a c t e r i s t i c of Domains 1 and 2a are rare and t h i n i n Domain 2b. Further downsection, grading in the g r i t u n i t s becomes rare and concomitantly the v a r i e t y of sandstone compositions i n c r e a s e s . Brown-weathered, interbedded gray and green p e l i t i c s c h i s t s and g r i t s , 10 to 50 cm t h i c k , are i n t e r c a l a t e d with the f o l l o w i n g u n i t s : p i n k i s h gray, massive, q u a r t z o f e l d s p a t h i c g n e i s s e s ; pink or gray, c a l c a r e o u s , f e l d s p a t h i c q u a r t z i t e s ; white q u a r t z i t e ; and brown-weathering, sometimes r u s t y , dark gray, massive s i l i c e o u s c a l c i t i c marbles. The marbles are ra r e and are 0.5 to 1.0 metre t h i c k . The g n e i s s e s and p e l i t i c s c h i s t s throughout Domain 2b commonly c o n t a i n matrix c a l c i t e . Where carbonate beds occur, the adjacent gneisses and s c h i s t s are o f t e n i n t e r l a y e r e d with 0.5 to 2.0 cm bands of g r e e n i s h to 17 dark gray carbonate. Shear Zone 4 separates the rocks of Domain 2b from the s i l l i m a n i t e - z o n e g n e i sses and s c h i s t s of Domain 4. The sheared h o r i z o n s c o n s i s t of i n t e r c a l a t e d l i g h t gray, s i l i c e o u s , g r a p h i t i c , dominantly c a l c i t i c marbles, r u s t y p e l i t i c s c h i s t s , t h i n p i n k i s h and green f e l d s p a t h i c q u a r t z i t e , white q u a r t z i t e , and pink to r u s t y , white mica-bearing, massive, q u a r t z o f e l d s p a t h i c g n e i s s . In Domain 4 , l i g h t gray- and yellow-weathered, dominantly c a l c i t i c , white marbles are interbedded with l i g h t gray q u a r t z o f e l d s p a t h i c g n e i s s and brown-weathered f i n e - g r a i n e d p e l i t i c f e l d s p a t h i c q u a r t z i t e s . The marbles are medium-gr a i n e d , c o n t a i n t h i n g r a p h i t e - r i c h l a y e r s , and are f o l i a t e d . The f o l i a t i o n i s marked by f i n e l y d i s p e r s e d white mica. Downsection, p i n k i s h gray f o l i a t e d q u a r t z o f e l d s p a t h i c gneisses and p e l i t i c s c h i s t s , both c o n t a i n i n g white mica, are interbedded with a f a i r l y coarse, white mica-bearing, brownish yellow-weathered gray marble. An intermediate zone of c a l c - s i l i c a t e g n e i s s e s occurs between the marbles and p e l i t i c u n i t s . F u r t h e r downsection, t h i c k sequences of interbedded, brown-weathered p e l i t i c s c h i s t s and aluminous medium-grained g r i t s are i n t e r c a l a t e d with the f o l l o w i n g l i t h o l o g i e s : f i n e - g r a i n e d , l i g h t gray, q u a r t z o f e l d s p a t h i c g n e i s s e s that are n e a r l y devoid of p e l i t i c component; s i l i c e o u s marbles and a s s o c i a t e d a c t i n o l i t e - and g a r n e t - b e a r i n g c a l c - s i l i c a t e g n e i s s e s ; 2 to 10 cm t h i c k , white, massive quartz v e i n s , both conformable and c r o s s - c u t t i n g ; and minor conglomerates c o n t a i n i n g igneous 18 c l a s t s . The only c a l c a r e o u s l i t h o l o g i e s are d i r e c t l y adjacent to marble. Sedimentary s t r u c t u r e s other than bedding were not observed i n any of the u n i t s of Domain 4. The r a t i o of g r i t to p e l i t i c s c h i s t i s v a r i a b l e . However, s c h i s t s predominate and beds ranging from 30 cm to 1-2 metres i n t h i c k n e s s are commonly i n t e r c a l a t e d with g r i t u n i t s of 10 to 80 cm. In the highest grade s i l l i m a n i t e - b e a r i n g rocks, leuco-pegmatites and a s i n g l e u n i t of massive pink-weathering white mica q u a r t z i t e are found i n t e r l a y e r e d with the g n e i s s e s , marbles, and p e l i t i c s c h i s t s . To the n o r t h e a s t , i n Domain 3 , p h y l l i t e s and s l a t e s d e f i n e a wedge bounded by shear zones 2 and 3. The p h y l l i t e s and s l a t e s are s i l v e r y - g r a y or green, c a l c a r e o u s , and weather brown. They are i n t e r c a l a t e d with grey-weathered, dark grey, sandy marble u n i t s , which are i n turn i n t e r l a y e r e d with brown-weathered, dark grey, s i l i c a - r i c h marbles. These banded carbonate u n i t s are t h i n , never exceeding 5 metres i n t h i c k n e s s . No f o s s i l s have been found. D i s c o n t i n u o u s h o r i z o n s of s t r o n g l y sheared s i l i c e o u s marble, which occur i n t e r l a y e r e d with the brown-weathered marbles, c o n t a i n abundant ovoids, 2-3 mm i n s i z e (long a x i s ) . The ovoids are composed of f e l d s p a r that c o n t a i n s abundant carbonate plu s minor white mica and q u a r t z . The o r i g i n of these ovoids i s u n c l e a r ; they.do not appear to be t r a c e f o s s i l s (P.L. Smith, pe r s o n a l communication). In the southernmost p o r t i o n of the wedge, the p h y l l i t e s are interbedded with t h i n (5 to 20 cm t h i c k ) q u a r t z o f e l d s p a t h i c g n e i s s e s . I V 19 A. INTERPRETATION The sequence of c l a s t i c metasedimentary rocks i n the f i e l d area has been t e n t a t i v e l y c o r r e l a t e d with 1 i t h o s t r a t i g r a p h i c u n i t s based on the work of Campbell, Mount joy, and Young (1973), P e l l and Simony (1981, 1982, 1984), Murphy and Journeay (1982), and Murphy and Rees (1983). In p a r t i c u l a r , Kaza Group s t r a t i g r a p h y i s r e f e r e n c e d to the s u b d i v i s i o n s e s t a b l i s h e d by P e l l and Simony (1984) f o r a complete (3800 m) s e c t i o n of Kaza Group rocks measured between the North Thompson and Azure r i v e r s ( F igure 4). P e l l and Simony d i v i d e the s e c t i o n i n t o three main u n i t s ; Lower Kaza (700 m); Middle Kaza (1400 m); Upper Kaza (1700 m). Domain 1 c o n s i s t s e n t i r e l y of metasediments of the Upper Kaza Group ( P r o t e r o z o i c ? ) . The g r i t - d o m i n a t e d Upper Kaza i s d i s t i n g u i s h e d by "stacked" g r i t s , grit-psammite, and g r i t -psammite-pelite, with c y c l e s 5 to 20 metres t h i c k . P e l l and Simony (1984) note coarse channel d e p o s i t s at the base of the g r i t l a y e r s . Tabular and deformed p e l i t i c " r i p - u p " c l a s t s are common in the c e n t r a l , p o o r l y graded p o r t i o n s of the g r i t beds. Murphy and Journeay (1982) i n t e r p r e t the Kaza Group g r i t -dominated c y c l e s to have been d e p o s i t e d as t u r b i d i t e s and g r a i n flows. The sediments i n d i c a t e a proximal, c h a n n e l i z e d s e t t i n g and Murphy and Journeay suggest that d e p o s i t i o n may have occu r r e d on an e x t e n s i v e submarine fan complex. Metasediments of the Upper Kaza mapped north of Shuswap Metamorphic Complex, in the Cariboo Mountains, show well-developed channels, normal and reverse grading, sedimentary l u t i t e c l a s t s , and sharp, o f t e n scoured bases and tops t r a n s i t i o n a l to p e l i t i c i n t e r b e d s . 20 L a t e r a l t r a n s i t i o n s from conglomeratic channel f a c i e s d e p o s i t s to t h i n n e r , more p e r s i s t e n t , and f i n e r overbank d e p o s i t s can be t r a c e d . These f e a t u r e s are a l l c h a r a c t e r i s t i c of a proximal t u r b i d i t e f a c i e s . Rocks in Domain 2a are s i m i l a r i n l i t h o l o g y to those i n Domain 1, and are a l s o c o r r e l a t e d with the' Upper Kaza. Because the s t r a t i g r a p h i c sequence appears continuous w i t h i n both Domains 2a and 2b, and these two are not separated by a f a u l t , they may be s t r a t i g r a p h i c a l l y i n t a c t as w e l l . The interbedded p h y l l i t e s and marbles of Domain 3 are t e n t a t i v e l y c o r r e l a t e d with the Isaac Formation. Campbell et a l . d 974), Murphy and Rees (1983), and P e l l and Simony (1984) map as uppermost Kaza gray, q u a r t z o f e l d s p a t h i c sandstones and s h a l e s that t h i n and f i n e upward. A gradual t r a n s i t i o n occurs from the g r i t - d o m i n a t e d Kaza Group i n t o the f i n e r - g r a i n e d rocks of the Isaac Formation. T r a d i t i o n a l l y , the base of the Isaac i s p l a c e d above the h i g h e s t coarse-graded g r i t u n i t (Campbell et a l . , 1974). However, Murphy and Rees (1983) r e c e n t l y r e e v a l u a t e d the t r a n s i t i o n on the b a s i s of a s e d i m e n t o l o g i c a l model. In t h e i r mapping, they i n c l u d e d t h i n g r i t beds as part of the lowermost p o r t i o n of the Isaac Formation. Owing to the shear zones bounding the wedge of Isaac Formation, the s t r a t i g r a p h i c r e l a t i o n to adjacent rocks of the Kaza Group i s not e s t a b l i s h e d . The rocks i n s i d e the wedge have been a s s i g n e d to the Isaac Formation r a t h e r than the Kaza Group on the b a s i s of the f o l l o w i n g c r i t e r i a : p h y l l i t e s and marbles are abundant, whereas coarse q u a r t z o f e l d s p a t h i c u n i t s are 21 a b s e n t , e x c e p t f o r s o m e t h i n b e d s i n t h e s o u t h e r n m o s t p o r t i o n o f t h e w e d g e . T h e b r o w n - w e a t h e r e d s i l i c e o u s m a r b l e o b s e r v e d t h r o u g h o u t t h e w e d g e i s r a r e i n t h e U p p e r K a z a . 22 I I I . S T R U C T U R E AND T I M I N G OF M E T A M O R P H I S M A . I N T R O D U C T I O N I n t h i s s t u d y , f o u r p h a s e s o f d e f o r m a t i o n a r e r e c o g n i z e d i n r o c k s o f t h e S h u s w a p M e t a m o r p h i c C o m p l e x a n d i n t h e l o w e r g r a d e m e t a s e d i m e n t s t h a t r i m t h e c o m p l e x t o t h e n o r t h e a s t . I n t h e f o l l o w i n g s e c t i o n s , t h e s t r u c t u r a l a n d m e t a m o r p h i c e v o l u t i o n o f e a c h p r o v i n c e i s c o n s i d e r e d s e p a r a t e l y . F i r s t , f i e l d a n d p e t r o g r a p h i c e v i d e n c e f o r t h e g e o m e t r y o f e a c h p h a s e a r e p r e s e n t e d . M i c r o s c o p i c f a b r i c s a r e t h e n d i s c u s s e d i n r e l a t i o n t o t h e r e l a t i v e t i m i n g o f m i n e r a l c r y s t a l l i z a t i o n . F i n a l l y , a c o r r e l a t i o n i s o f f e r e d o f d e f o r m a t i o n a n d m e t a m o r p h i c e v e n t s b e t w e e n t h e S h u s w a p a n d l o w e r g r a d e r o c k s . B . C O V E R D E F O R M A T I O N M e t a s e d i m e n t s o f t h e K a z a G r o u p a n d I s a a c F o r m a t i o n , m a k i n g u p t h e c o v e r s e q u e n c e , h a v e u n d e r g o n e f o u r p h a s e s o f d e f o r m a t i o n . Two p h a s e s o f n o r t h w e s t e r l y t r e n d i n g a n d p l u n g i n g f o l d s (D1 a n d D 2 ) d e v e l o p e d p r i o r t o t h e m e t a m o r p h i c p e a k . S u p e r i m p o s e d o n t h e s e a r e t w o p h a s e s o f u p r i g h t f o l d i n g (D3 a n d D 4 ) . P r e - D 3 s h e a r z o n e s , w h i c h p r o b a b l y c u l m i n a t e D2 d e f o r m a t i o n , r e s u l t i n s t r a t i g r a p h i c a n d m e t a m o r p h i c o f f s e t s w i t h i n t h e c o v e r s e q u e n c e . T h e s h e a r z o n e s s t r i k e n o r t h w e s t - s o u t h e a s t a c r o s s t h e map a r e a , p a r a l l e l t o t h e s t r i k e o f D2 a x i a l p l a n e s . F i e l d a n d p e t r o g r a p h i c e v i d e n c e f o r t h e g e o m e t r y o f e a c h p h a s e a r e p r e s e n t e d i n t h e f o l l o w i n g s e c t i o n s . T a b l e I p r o v i d e s a s u m m a r y o f r e l a t i v e t i m i n g o f e v e n t s , o f s t r u c t u r a l e l e m e n t s , a n d o f t h e m e t a m o r p h i c g r a d e a t t a i n e d . F i r s t p h a s e d e f o r m a t i o n t h r o u g h o u t t h e c o v e r s e q u e n c e i s 23 e v i d e n c e d b y a w e l l - d e v e l o p e d f o l i a t i o n ( S 1 ) t h a t i s f o l d e d b y l a t e r f o l d s . SI i s c h a r a c t e r i z e d b y t h e p a r a l l e l o r i e n t a t i o n o f p h y l l o s i l i c a t e s a n d b y e l o n g a t e q u a r t z a n d f e l d s p a r g r a i n s . W h e r e m e t a m o r p h i c g r a d e i s l o w e s t , i n D o m a i n 1, t h e p h a s e 1 s c h i s t o s i t y i s a x i a l p l a n a r t o l o c a l l y - d e v e l o p e d , m i c r o s c o p i c f o l d s o f b e d d i n g ( S O ) . T h e s e f o l d s a r e t i g h t t o i s o c l i n a l . M e s o s c o p i c f i r s t p h a s e f o l d s a r e o b s e r v e d r a r e l y i n t h e c o v e r s e q u e n c e . N o n e w e r e o b s e r v e d i n d o m a i n s 1 o r 2 a , b u t i n D o m a i n 2 b , t y p e t h r e e i n t e r f e r e n c e p a t t e r n s ( R a m s a y , 1 9 6 7 ) , r e s u l t i n g f r o m D2 a c t i n g o n D 1 , w e r e r e c o g n i z e d . A l s o , i n s h e a r z o n e 3 , a m e t a c a r b o n a t e u n i t w h i c h d e f i n e s t h e l i m b o f a D2 f o l d c o n t a i n s D1 f o l d s o f b e d d i n g t o w h i c h S1 i s a x i a l p l a n a r . T h e b e d d i n g i s d e f i n e d b y s i l i c e o u s l a y e r s . V e r g e n c e o f p h a s e 1 s t r u c t u r e s i s n o t k n o w n . E q u a l a r e a s t e r e o n e t p l o t s o f p o l e s t o SO a n d t o S1 a r e p r e s e n t e d i n F i g u r e s 8 a n d 9 . S e c o n d p h a s e f o l d s a r e t h e m a j o r s t r u c t u r e s i n t h e m a p a r e a , s t r o n g l y o v e r p r i n t i n g f i r s t p h a s e s t r u c t u r e s . P h a s e 2 c o n s i s t s o f n o r t h w e s t - t r e n d i n g a n d p l u n g i n g , s o u t h w e s t w a r d l y v e r g i n g f o l d s o f r e g i o n a l s c a l e t h a t h a v e a c t e d o n b e d d i n g a n d p h a s e 1 f o l i a t i o n . T h r o u g h o u t t h e c o v e r s e q u e n c e , p h a s e 2 f o l d s a r e r e c u m b e n t . I n D o m a i n 1, t h e a x i a l s u r f a c e s o f t h e s e f o l d s d i p m o d e r a t e l y t o s t e e p l y t o t h e n o r t h e a s t ( F i g u r e 1 1 ) . H e r e , t h e f o l d s a r e c l o s e t o t i g h t a n d h a v e r o u n d e d t o a n g u l a r h i n g e s . T h o s e w i t h a n g u l a r h i n g e s , p l a n a r l i m b s , a n d m a r k e d a s y m m e t r y a r e w e l l - d e s c r i b e d a s f i r s t o r d e r k i n k s ( H o b b s e t a l . , p . 1 7 1 , 1 9 7 6 ) . D o w n s e c t i o n , v a r i a t i o n i n t h e d i p o f D2 a x i a l s u r f a c e s , d u e t o r e f o l d i n g b y p h a s e 3 s t r u c t u r e s , i s a c c o m p a n i e d b y a n 24 in c r e a s e i n metamorphic grade. i n domains 2a and 2b the f o l d s are c l o s e to t i g h t . A c r e n u l a t i o n cleavage (S2), d e f i n e d by the m i c r o s c a l e f o l d i n g of S1, i s a x i a l planar to mesoscopic D2 a x i a l s u r f a c e s . P a r t i a l t r a n s p o s i t i o n of the e a r l y s c h i s t o s i t y i n t o second phase a x i a l planes i s observed l o c a l l y i n some p h y l l i t i c and s c h i s t o s e p e l i t e u n i t s i n domains 2a and 2b. In interbedded g r i t and p e l i t e u n i t s , the S2 f o l i a t i o n i s c u r v i p l a n a r w i t h i n each bed due to i n t e r n a l grading, and i s s t r o n g l y r e f r a c t e d at l i t h o l o g i c boundaries. Poles to S2 show some spread i n t h e i r o r i e n t a t i o n s (Figure 11), and cleavage r e f r a c t i o n as w e l l as i n t e r f e r e n c e with phase 3 and 4 s t r u c t u r e s accounts f o r some of t h i s spread. The i n t e r s e c t i o n of S2 with SO r e s u l t s i n a no r t h w e s t e r l y and s o u t h e a s t e r l y plunging l i n e a t i o n (L0x2) that i s p a r a l l e l to the hinges of second phase f o l d s ( F i g u r e s 12 and 13). The l i n e a t i o n a l s o p a r a l l e l s L2, the d i r e c t i o n of e l o n g a t i o n of quartz and f e l d s p a r m e t a c l a s t s . Both L0x2 and L2 are prominent throughout the cover sequence. T h i r d phase minor s t r u c t u r e s were observed only in Domains 2b, 3, and shear zone 3, where they are only l o c a l l y developed. The e a r l y s t r u c t u r e s are f o l d e d about g e n e r a l l y u p r i g h t , n o r t h t r e n d i n g phase 3 a x i a l s u r f a c e s . D3 f o l d axes plunge g e n t l y to the north and the f o l d s are open ( F i g u r e s 7 and 14). The a x i a l s u r f a c e s are a s s o c i a t e d with a l o c a l l y -developed, higher order c r e n u l a t i o n cleavage that f o l d s S1 and S2, and i s a x i a l planar to D3 minor f o l d s . A t h i r d phase a n t i f o r m , which i s tr u n c a t e d to the south by shear zone 4, i s 25 m a p p e d i n t h e w e s t e r n m o s t p o r t i o n o f D o m a i n 2 b . S o u t h w e s t e r l y v e r g i n g D2 m i n o r f o l d s d o n o t c h a n g e t h e i r v e r g e n c e a c r o s s t h e D3 a x i a l s u r f a c e . F o u r t h p h a s e d e f o r m a t i o n c o n s i s t s o f n o r t h e a s t t r e n d i n g , h i g h a n g l e c r e n u l a t i o n s ( S 4 ) . T h e s e l o c a l l y r e v e r s e t h e p l u n g e s o f e a r l i e r f o l d a x e s a n d v a r y t h e m a g n i t u d e o f p l u n g e o f n o r t h w e s t e r l y - t r e n d i n g p h a s e 2 s t r u c t u r e s . T h e e f f e c t o f p h a s e 4 d e f o r m a t i o n o n t h i r d p h a s e s t r u c t u r e s i s n o t c l e a r . N o o u t c r o p s w e r e o b s e r v e d t h a t d e m o n s t r a t e d p h a s e 4 c r e n u l a t i o n s a c t i n g o n D3 s t r u c t u r e s . I n D o m a i n 1, w h e r e t w o s e t s o f l a t e c r e n u l a t i o n s a r e c o m m o n l y o b s e r v e d , t h e r e i s e v i d e n c e t h a t t h e y a r e c o e v a l , D4 s t r u c t u r e s . A n o r d e r o f s u p e r p o s i t i o n c a n n o t b e e s t a b l i s h e d , e i t h e r m e s o s c o p i c a l l y o r m i c r o s c o p i c a l l y . T h e t r e n d s o f t h e a x i a l p l a n e s a r e v a r i a b l e , a s s h o w n b y t h e s t e r e o n e t p l o t o f p o l e s t o S4 ( F i g u r e 1 5 ) . T h e o b s e r v e d s p r e a d i n p h a s e 4 a x i a l p l a n e s l e n d s s u p p o r t t o t h e c o n c l u s i o n t h a t D4 f o l d s a r e o f t e n d e v e l o p e d a s c o n j u g a t e k i n k s . 26 F i g u r e 7 - Phase 3 minor f o l d s , s u b s i d i a r y to a phase 3 a n t i f o r m . Domain 2b. F i g u r e 8 - P o l e s t o b e d d i n g ( S O ) f r o m t h e c o v e r s e q u e n c e . E q u a l a r e a s t e r e o g r a p h i c p r o j e c t i o n t o l o w e r h e m i s p h e r e . 28 Domain 1: 23 p o i n t s Domain 2a: 14 p o i n t s Domain 2b: 65 p o i n t s F i g u r e 9 - Poles t o m e t a - f o l i a t i o n (S1) from the cover sequence. Equal area s t e r e o g r a p h i c p r o j e c t i o n to lower hemi sphere. 29 Domain 2b: 3 p l u s signs 2 t r i a n g l e s N F i g u r e 10- D1 f o l d elements from the cover sequence. Plus signs represent f o l d axes (F1), t r i a n g l e s represent p o l e s to a x i a l planes (S1). Equal area s t e r e o g r a p h i c p r o j e c t i o n to lower hemisphere. 30 D o m a i n 1: 5 d i a m o n d s D o m a i n 2 a : 2 d i a m o n d s 7 t r i a n g l e s 6 t r i a n g l e s D o m a i n 2 b : 14 d i a m o n d s 19 t r i a n g l e s N F i g u r e 11 - D2 p l a n a r e l e m e n t s ( p o l e s t o S 2 ) f r o m t h e c o v e r s e q u e n c e . D i a m o n d s r e p r e s e n t a x i a l p l a n a r c l e a v a g e , t r i a n g l e s r e p r e s e n t a x i a l p l a n e s . E q u a l a r e a s t e r e o g r a p h i c p r o j e c t i o n t o l o w e r h e m i s p h e r e . F i g u r e 12 - D2 f o l d axes (F2) from the cover sequence. Equal area s t e r e o g r a p h i c p r o j e c t i o n to lower hemisphere. 32 Domain 1: 24 c r o s s e s Domain 2a: 12 c r o s s e s 1 octagon 6 octagons Domain 2b: 38 c r o s s e s 26 octagons N F i g u r e 13 - D2 l i n e a r elements from the cover sequence. Crosses represent i n t e r s e c t i o n l i n e a t i o n s (L0x2), octagons represent L2 l i n e a t i o n s (quartz r o d s ) . Equal area s t e r e o g r a p h i c p r o j e c t i o n to lower hemisphere. 33 Domain 2b: 8 plus s i g n s 8 t r i a n g l e s N F i g u r e 14 - D3 f o l d elements from the cover sequence. Plus s i g n s represent f o l d axes ( F 3 ) , t r i a n g l e s represent poles to a x i a l p l a n e s . Equal area s t e r e o g r a p h i c p r o j e c t i o n to lower hemi sphere. 34 Domain 1: 13 t r i a n g l e s Domain 2a: 2 t r i a n g l e s N N F i g u r e 15 - D4 kink f o l d elements from the cover sequence. T r i a n g l e s represent p o l e s to a x i a l planes ( S 4 ) , p l u s signs represent f o l d axes. Equal area s t e r e o g r a p h i c p r o j e c t i o n to lower hemisphere. 35 C. COVER METAMORPHISM 3.1 Introduct ion C r i t e r i a used i n d e l i n e a t i n g the timing of mineral growth r e l a t i v e to m i c r o s t r u c t u r e development i n metamorphic rocks have been f o r m a l i z e d by Zwart (1960 a, b, 1962, 1963), Spry (1963, 1969), and o t h e r s . More recent c o n t r i b u t i o n s by Powell and Treagus (1970, 1979), E l l i o t t (1972), Ferguson and Harte (1975), Vernon (1975, 1976, 1977, 1978), and Powell and Vernon (1979) modify the i n t e r p r e t a t i o n s presented i n the e a r l i e r works based on kinematic and p e t r o l o g i c c o n s i d e r a t i o n s . In t h i s study, p o r p h y r o b l a s t - f o l i a t i o n t e x t u r a l r e l a t i o n s a c r o s s the map area are d e s c r i b e d , and assignment of events in time i s based on a s y n t h e s i s of g u i d e l i n e s o u t l i n e d i n the more recent papers. P e t r o g r a p h i c evidence i n d i c a t e s a h i s t o r y of p r o g r e s s i v e metamorphism that began with metamorphic m i n e r a l growth dur i n g D1 and o u t l a s t e d s t r a i n s produced d u r i n g D2. While s t r u c t u r a l elements d e l i n e a t e two separate deformation phases, there remains no evidence to d i s t i n g u i s h two metamorphic peaks. In the f o l l o w i n g s e c t i o n s , t e x t u r a l r e l a t i o n s which document the minimum grade of metamorphism achieved p r i o r to phase 2 deformation are presented. The timing of metamorphism r e l a t i v e to the development of phase 2 and l a t e r s t r u c t u r e s i s then d i s c u s s e d . 36 3 . 2 E a r l y M e t a m o r p h i s m E v i d e n c e o f t h e g r a d e a t t a i n e d d u r i n g p h a s e 1 d e f o r m a t i o n i s e q u i v o c a l : a s y n - k i n e m a t i c e q u i l i b r i u m a s s e m b l a g e , e s t a b l i s h e d d u r i n g D 1 , w h i c h h a s c l e a r l y b e e n r e p l a c e d b y o r p r e s e r v e d a s i n c l u s i o n s i n l a t e r m e t a m o r p h i c m i n e r a l s , c a n n o t b e p r o v e n . H o w e v e r , a s e q u e n c e o f p r o g r e s s i v e l y h i g h e r g r a d e m i n e r a l a s s e m b l a g e s , w i t h a s s o c i a t e d m i c r o s t r u c t u r e s , i s o b s e r v e d a s o n e t r a v e r s e s d o w n i n t o t h e s t r u c t u r a l p i l e . I t i s p o s s i b l e t o r e c o g n i z e i n t h i s p r o g r e s s i o n a p r e s e r v e d e x p r e s s i o n o f a p r e s s u r e - t e m p e r a t u r e g r a d i e n t , e s t a b l i s h e d o v e r t i m e ( T u r n e r , 1 9 8 1 ) . T h e m e s o s c o p i c a n d m i c r o s c o p i c f a b r i c s a r e c o r r e l a t e d a c r o s s t h e g r a d e c h a n g e s , a n d i t i s t h i s p r o c e s s o f o b s e r v a t i o n a n d s y n t h e s i s t h a t e s t a b l i s h e s a t l e a s t a l o w e r P - T l i m i t f o r s y n - k i n e m a t i c D1 m e t a m o r p h i s m . T h e p h a s e 1 s c h i s t o s i t y p r e s e r v e s e v i d e n c e o f t h e e a r l y m e t a m o r p h i s m , i n t h e c h l o r i t e - b i o t i t e z o n e r o c k s o f D o m a i n 1 u p t h r o u g h t h e s t a u r o l i t e - k y a n i t e z o n e r o c k s o f D o m a i n 2 b . I n D o m a i n _]_,. w h e r e m e t a m o r p h i c g r a d e i n t h e c o v e r s e q u e n c e i s l o w e s t , t h e i n t e n s i t y o f s u b s e q u e n t d e f o r m a t i o n i s . l o w e n o u g h t o p r e s e r v e D1 f o l d s o f s e d i m e n t a r y b e d d i n g ( S O ) . R o c k s o f c h l o r i t e - b i o t i t e z o n e p r e d o m i n a t e , a n d p r e s e r v e c r y s t a l l i z a t i o n t e x t u r e s i n t e r p r e t e d t o b e s y n - k i n e m a t i c t o D1 d e f o r m a t i o n . C h l o r i t e a n d w h i t e m i c a , i n t e r g r o w n a l o n g t h e i r ( 0 0 1 ) f a c e s , l i e i n t h e p l a n e o f t h e e a r l y f o l i a t i o n ( S 1 ) a n d a r e k i n k e d a c r o s s t h e a x i a l s u r f a c e s o f m i n o r D2 c r e n u l a t i o n s ( S 2 ) . T h e s e m i n e r a l " s t a c k s " may h a v e o r i g i n a t e d b y m i m e t i c g r o w t h o n p r i m a r y c l a y m i n e r a l s ( C r a i g e t a l . , 1 9 8 1 ) , b y s t r a i n - c o n t r o l l e d g r o w t h o f 37 c h l o r i t e on d e t r i t a l mica n u c l e i ( V o l l , 1960; Roy, 1978), or by s t r a i n - c o n t r o l l e d intergrowth under lower g r e e n s c h i s t f a c i e s metamorphic c o n d i t i o n s , without the i n f l u e n c e of a primary bedding f a b r i c . In Domain 1, minor b i o t i t e a l s o grows with i t s basal cleavage in the plane of S1, i n d i c a t i n g syn-kinematic or l a t e D1, pre-D2 growth of b i o t i t e . The t r a c e s of D2 a x i a l s u r f a c e s c r o s s c o n c o r d a n t l y from the matrix i n t o the b i o t i t e s . The p o r p h y r o b l a s t s are r h y t h m i c a l l y kinked across these s u r f a c e s . A l a t e r , g e o m e t r i c a l l y d i s t i n c t p o p u l a t i o n of p o r p h y r o b l a s t i c c h l o r i t e - w h i t e mica stacks and b i o t i t e overgrow S1; t h e i r basal cleavages c r o s s c u t the e a r l y s c h i s t o s i t y at angles which vary from 10 to 80°. The high angle cleavages commonly p a r a l l e l S2. These l a t e r , second generation p o r p h y r o b l a s t s overgrow S1, but i t i s not c l e a r that phase 2 f o l d s are t r u n c a t e d . The g r a i n s appear to o v e r p r i n t D2 minor f o l d s , with subsequent f l a t t e n i n g of the f o l i a t i o n around the c r y s t a l s . The ambiguity of the t e x t u r e s i s e x e m p l i f i e d by the b i o t i t e s . The g r a i n s tend to grow in pockets of quartz plus f e l d s p a r , where matrix p h y l l o s i l i c a t e s are not abundant. The b i o t i t e s are p o i k i l o b l a s t i c with respect to these phases. If the b i o t i t e o v e r p r i n t s the D2 c r e n u l a t i o n cleavage, l i t t l e evidence of t h i s can be preserved as an i n t e r n a l s c h i s t o s i t y , given that the m i c r o f o l d e d S1 i s d e f i n e d p r i m a r i l y by the alignment of the sheet s i l i c a t e s , and these are rare i n the q u a r t z o f e l d s p a t h i c pockets. Throughout Domain 2a, t e x t u r e s formed d u r i n g phase 2 38 d e f o r m a t i o n i n d i c a t e g r e a t e r s t r a i n s a n d m o r e d u c t i l e . d e f o r m a t i o n t h a n t h o s e o b s e r v e d h i g h e r i n t h e s t r u c t u r a l p a c k a g e . S2 i s v e r y w e l l - d e f i n e d b y t h e s h a r p a s y m m e t r y o f t h e c r e n u l a t i o n f o l d s ; s h e e t s i l i c a t e s a r e r o t a t e d a n d r e c r y s t a l l i z e d ( M e a n s , 1 9 7 7 ; W i l l i a m s , 1 9 7 7 ) i n t o s t e e p , a t t e n u a t e d l i m b s a r o u n d D2 f o l d h i n g e s . A l s o , q u a r t z a n d f e l d s p a r g r a i n s a r e e l o n g a t e i n S1 a n d f o r m a t t e n u a t e d l i m b s t o D2 f o l d s t h a t p a r a l l e l S 2 a c r o s s p h a s e 2 h i n g e s . C u r v i p l a n a r c o n j u g a t e s e t s o f D2 c r e n u l a t i o n c l e a v a g e s a r e l o c a l l y d e v e l o p e d i n f i n e - g r a i n e d , s c h i s t o s e t o p h y l l i t i c p e l i t e s . R e t r o g r a d e f a b r i c s a s s o c i a t e d w i t h D4 k i n k f o l d s a r e w e l l - d e v e l o p e d i n p e l i t i c p h y l l i t e s a n d s c h i s t s . T h e r o c k s i n D o m a i n 2 a p r e s e r v e e v i d e n c e t h a t d a t e s t h e g r o w t h o f b i o t i t e a s l a t e - D 1 : l a r g e , t a t t e r e d b i o t i t e p o r p h y r o b l a s t s , p a r t i a l l y r e t r o g r a d e d t o c h l o r i t e , a r e o r i e n t e d w i t h ( 0 0 1 ) p a r a l l e l t o S1 , o v e r p r i n t r e c r y s t a i l l i z e d , c l a s t i c f e l d s p a r s , a r e c r e n u l a t e d b y D2 f o l d s , a n d a r e d e f o r m e d a n d f o l d e d b y p o s t - m e t a m o r p h i c D4 k i n k f o l d s . T h e s e s c h i s t o s i t y -p a r a l l e l g r a i n s s o m e t i m e s i n c l u d e t h e S1 f a b r i c , t h u s o v e r p r i n t i n g i t , a n d may h a v e c r y s t a l l i z e d l a t e i n D 1 , d u r i n g i n i t i a l D2 t i g h t e n i n g o f D1 s t r u c t u r e s . I t i s a l s o i n D o m a i n 2 a t h a t c r o s s - c u t t i n g b i o t i t e p o r p h y r o b l a s t s , p a r t i a l l y r e t r o g r a d e d t o c h l o r i t e o r a l m o s t c o m p l e t e l y r e p l a c e d b y c h l o r i t e p l u s s a g e n i t i c r u t i l e , o v e r p r i n t b o t h D1 a n d D2 s t r u c t u r e s . H e r e , u n l i k e D o m a i n 1, p h a s e 2 m i c r o f o l d s a r e t r u n c a t e d b y t h e l a t e p o r p h y r o b l a s t s . L a r g e c h l o r i t e p o r p h y r o b l a s t s o c c u r i n s o m e p h y l l i t i c 39 p e l i t e u n i t s i n t h e c h l o r i t e - b i o t i t e z o n e o f D o m a i n 2 a . B i o t i t e i s a b s e n t i n t h e s e r o c k s . B i o t i t e - a b s e n t u n i t s o c c u r i n t h e l o w e r g r a d e p o r t i o n o f D o m a i n 2 a a n d a r e c o m m o n t h r o u g h o u t D o m a i n 1. No r e a c t i o n b o u n d a r y h a s b e e n r e c o g n i z e d b e t w e e n b i o t i t e - a n d c h l o r i t e - b e a r i n g a s s e m b l a g e s a n d t h e i r r e s p e c t i v e o c c u r r e n c e m a y p r i m a r i l y r e f l e c t b u l k c o m p o s i t i o n a l d i f f e r e n c e s . T h e c h l o r i t e z o n e o f t h e B a r r o v i a n f a c i e s s e r i e s h a s t h u s p r o b a b l y b e e n e x c e e d e d b y a l l r o c k s i n t h e f i e l d a r e a . T h e c h l o r i t e p o r p h y r o b l a s t s , l i k e t h e b i o t i t e s , g r o w i n q u a r t z o f e l d s p a t h i c l a y e r s . T h e y a r e s m e a r e d i n a p p e a r a n c e . T h e g r a i n s a r e o r i e n t e d p a r a l l e l t o t h e p h a s e 1 s c h i s t o s i t y a n d b e a r a n i n t e r n a l s c h i s t o s i t y t h a t i s c o n t i n u o u s w i t h t h e e x t e r n a l s c h i s t o s i t y , w i t h t h e e x c e p t i o n o f m i n o r d i s c o n t i n u i t i e s c a u s e d b y l a t e r d e f o r m a t i o n . T h e b a s a l c l e a v a g e o f c h l o r i t e p a r a l l e l s t h e i n t e r n a l s c h i s t o s i t y , w h i c h i s d e f i n e d b y t h e a l i g n m e n t o f m a g n e t i t e , i l m e n i t e , q u a r t z , a n d f e l d s p a r . R u t i l e i n c l u s i o n s a r e a b s e n t . T h e c h l o r i t e p o r p h y r o b l a s t s b e a r t h e r e c o r d o f t w o d e f o r m a t i o n s : T h e y a r e f o l d e d w i t h b e d d i n g a c r o s s o p e n D2 h i n g e s , k i n k e d b y D4 f o l d s , a n d a r e c r o s s - c u t b y l a t e , p o s t - D 2 l a t h s o f w h i t e m i c a . T h e c h l o r i t e s m a y b e r e t r o g r a d e p s e u d o m o r p h s a f t e r b i o t i t e . B a s e d o n t e x t u r a l r e l a t i o n s , c h l o r i t e may b e s y n c h r o n o u s w i t h e a r l y b i o t i t e , h a v i n g g r o w n a s a p r o g r a d e p h a s e l a t e i n D 1 , d u r i n g D2 t i g h t e n i n g o f t h e e a r l y s t r u c t u r e s . T o t h e s o u t h , t h e f i r s t a p p e a r a n c e o f g a r n e t d e f i n e s a n i s o g r a d s u r f a c e i n D o m a i n 2 a ( F i g u r e 1 6 ) . F u r t h e r u p g r a d e , i n D o m a i n 2 b , k y a n i t e a n d s t a u r o l i t e a r e s t a b l e . A g e n e r a l 40 120*2 1' W I 2 0 , 2 S ' 120°22' 110*11' w F i g u r e 16 - Map of metamorphic zones • 41 c o a r s e n i n g of matrix p h y l l o s i l i c a t e s i s observed as grade i n c r e a s e s . Both white mica and b i o t i t e are common and abundant matrix phases, and d e f i n e a phase 1 s c h i s t o s i t y that i s r o t a t e d a c r o s s D2 a x i a l s u r f a c e s toward p a r a l l e l i s m with the phase 2 s c h i s t o s i t y . In c a l c a r e o u s g r i t and p e l i t e u n i t s , the sheet s i l i c a t e s c o e x i s t in the matrix with zoned, subidiomorphic c l i n o z o i s i t e g r a i n s . In very c a l c i t i c u n i t s , f o r example those which l i e immediately beneath shear zone 3 i n Domain 2a, epidote comprises up to 30 percent of the rock. The p r e s e r v a t i o n of b i o t i t e , c h l o r i t e , and white mica sheets p a r a l l e l to the phase 1 f o l i a t i o n p r o v i d e s an i n d i c a t i o n of grade achieved p r i o r to D2 deformation i n rocks of domains 1, 2a, and 2b. U n f o r t u n a t e l y , none of the observed t e x t u r e s e l i m i n a t e the p o s s i b i l i t y t h a t b i o t i t e grew m i m e t i c a l l y , perhaps a f t e r c h l o r i t e , d u r i n g phase 2 deformation. However, the t i m i n g of mineral c r y s t a l l i z a t i o n r e l a t i v e to phase 2 and l a t e r deformations i s w e l l - d e f i n e d . The f o l l o w i n g r e l a t i o n s h i p s are found i n rocks of the upper g r e e n s c h i s t f a c i e s i n domains 2a and 2b: D2 f o l d s are o v e r p r i n t e d by b i o t i t e , garnet, hornblende, k y a n i t e , and s t a u r o l i t e . Syn-kinematic growth of garnet d u r i n g phase 2 deformation i s i n d i c a t e d by mineral t e x t u r e s i n some t h i n s e c t i o n s . In the v i c i n i t y of the shear zones, m i c r o s c a l e f a b r i c s r e l a t e d to mesoscopic s t r u c t u r e s are developed: r i g i d p o r p h y r o b l a s t s d i s p l a y s t r o n g l y o r i e n t e d f a b r i c s ; m i c r o s c a l e shear s u r f a c e s are superimposed over e a r l i e r D1 s t r u c t u r e s but t h e i r r e l a t i o n to the l a t e r upper g r e e n s c h i s t f a c i e s phases i s 42 not c l e a r . M i n e r a l s that formed a f t e r the main peak of metamorphism and that have undergone l a t e f o l d i n g are documented i n a l l rocks. In the upper g r e e n s c h i s t f a c i e s p e l i t i c s c h i s t s of domains 2a and 2b, elongate q u a r t z , f e l d s p a r , and o r i e n t e d , zoned c l i n o z o i s i t e , ' together with a l i g n e d p h y l l o s i l i c a t e s , d e f i n e the. phase 1 s c h i s t o s i t y . S1 i s f o l d e d over D2 a x i a l s u r f a c e s . In Domain 2a, the c r y s t a l l i z a t i o n of l a r g e (0.5 to 1.0 cm diameter) p o i k i l o b l a s t i c garnet and b i o t i t e post-date D2 f o l d i n g i n c a l c a r e o u s p e l i t i c s c h i s t s l o c a t e d d i r e c t l y below shear zone 3. Proof of o v e r p r i n t i n g of the f o l d s i s pro v i d e d by the p r e s e r v a t i o n of sig m o i d a l i n c l u s i o n t r a i l s i n the c r o s s - c u t t i n g b i o t i t e as w e l l as i n c o e v a l garnet. The i n t e r n a l s c h i s t o s i t i e s , which c o n s i s t of q u a r t z , f e l d s p a r , and c l i n o z o i s i t e , mimic the composition of the e x t e r n a l f o l i a t i o n . In F i g u r e 17, garnet has nucleat e d adjacent to b i o t i t e , and the f o l d e d s c h i s t o s i t y passes c o n t i n u o u s l y from the matrix i n t o both g r a i n s . In t h i s rock, metamorphic hornblende i s i n the same r e l a t i o n to the D2 f o l d s as are the garnet and b i o t i t e . Q u a r t z o f e l d s p a t h i c u n i t s i n Domain 2a a l s o preserve D2 f a b r i c s o v e r p r i n t e d by garnet. Small (1 to 2 mm diameter) garnets overgrow an i n t e r l o c k i n g f a b r i c that c o n t a i n s minor p h y l l o s i l i c a t e s ; the sheet s i l i c a t e s d e f i n e the f o l d e d S1. The garnets grew by n u c l e a t i o n along the i n t e r l o c k i n g , elongate quartz and f e l d s p a r g r a i n s contained i n the e a r l y f o l i a t i o n . Thus, some h e l i c i t i c t e x t u r e s observed in garnet p o r p h y r o b l a s t s a c r o s s the cover sequence can be a t t r i b u t e d to 43 F i g u r e 17 - B i o t i t e and garnet o v e r p r i n t phase 2 f o l d s . S2 continuous through both p o r p h y r o b l a s t s . F i e l d of view 2 mm. 44 overgrowth of a p r e - e x i s t i n g f a b r i c . However, r o t a t e d garnets, syn-kinematic to D2 deformation, are i n d i c a t e d by t e x t u r e s i n many u n i t s . For example, in Domain 2a, s e v e r a l c o a r s e - g r a i n e d , p e l i t i c , q u a r t z o f e l d s p a t h i c g n e i s s e s c o n t a i n garnets with symmetric, s i g m o i d a l i n c l u s i o n t r a i l s that are continuous with the e x t e r n a l s c h i s t o s i t y . These are viewed i n s e c t i o n s normal to D2 f o l d axes and l i n e a t i o n s . The degree of f o l d i n g d i s p l a y e d by the i n t e r n a l s t r u c t u r e i s not mimicked by the D2 f o l d s i n the matrix. A l s o , garnets i n many of the p e l i t i c s c h i s t s c o n t a i n n e a r l y l i n e a r i n c l u s i o n t r a i l s that have a str o n g c u r v a t u r e only near the p o r p h y r o b l a s t rims and are continuous with the e x t e r n a l f o l i a t i o n . To the south, i n Domain 2b, a grade i n c r e a s e i s recorded by mine r a l assemblages i n the p e l i t e s and by m i c r o f a b r i c s . Kyanite and s t a u r o l i t e are s t a b l e , and overgrow the phase 2 f a b r i c . S t a u r o l i t e p o r p h y r o b l a s t s are bent and broken a c r o s s D3 f o l d hinges. S i l l i m a n i t e i s absent. Garnet p o r p h y r o b l a s t t e x t u r e s o u t l i n e two stages of growth: F i r s t - s t a g e garnets form l a r g e , subidiomorphic, p o i k i l o b l a s t i c g r a i n s . Second-stage garnets t y p i c a l l y form r e l a t i v e l y i n c l u s i o n - f r e e , idiomorphic rims around stage one garnet c o r e s . These rims f i r s t occur i n the k y a n i t e - s t a u r o l i t e zone and are absent i n the lower grade rocks to the north. The garnet c o r e s g e n e r a l l y c o n t a i n random i n c l u s i o n s of f e l d s p a r , q u a r t z , and c l i n o z o i s i t e . These phases are present i n the D1 s c h i s t o s i t y . These garnets are mantled by t h i c k second ge n e r a t i o n rims that bear fewer i n c l u s i o n s . Uncommonly, garnet 45 c o r e s w i t h a l i g n e d i n c l u s i o n s a r e ( o b s e r v e d , and the i n t e r n a l s c h i s t o s i t y e i t h e r p a r a l l e l s the e x t e r n a l s c h i s t o s i t y or l i e s a t a h i g h a n g l e t o the e x t e r n a l f o l i a t i o n . T h i n second-stage rims mantle these g r a i n s . S k e l e t a l , s t r o n g l y r e t r o g r a d e d g a r n e t s , which c r y s t a l l i z e d i n q u a r t z o f e l d s p a t h i c l e n s e s , c o n t a i n an i n t e r n a l s c h i s t o s i t y t h a t i s n e a r l y p e r p e n d i c u l a r t o the e x t e r n a l s c h i s t o s i t y . These g a r n e t s d i s p l a y no second-stage growth. Phase two f o l d s a re o v e r p r i n t e d by p o i k i l o b l a s t i c g a r n e t and b i o t i t e . As i n Domain 2a, a c o n t i n u a t i o n of the f o l d s from the m a t r i x i n t o a d j a c e n t b i o t i t e and g a r n e t p o r p h y r o b l a s t s i s observ e d i n some s e c t i o n s , and s u p p o r t s the i n t e r p r e t a t i o n of ove r g r o w t h . L a t e growth of c o a r s e w h i t e mica i s documented i n some p e l i t i c s c h i s t s of Domain 2b. M i c a s have grown both p a r a l l e l t o the c r e n u l a t e d S1 f o l i a t i o n , m i m i c k i n g i t , and randomly a c r o s s i t . The co n c o r d a n t g r a i n s a r e i n t e r g r o w n w i t h b i o t i t e , a r e f o l d e d a c r o s s D3 a x i a l s u r f a c e s , and are f l a t t e n e d a g a i n s t o l d e r garnet p o r p h y r o b l a s t s . The w h i t e mica i s not r e p r e s e n t e d as i n c l u s i o n s i n these g a r n e t s . B i o t i t e , which i s synchronous w i t h the g a r n e t , i s i n t e r g r o w n w i t h w h i t e mica a l o n g i t s b a s a l c l e a v a g e . The b i o t i t e s and w h i t e micas a r e f o l d e d a c r o s s a x i a l s u r f a c e s of phase* 3. 46 D. SHEAR ZONES AND ISAAC FORMATION 3.3 I n t r o d u c t i o n F i e l d and p e t r o g r a p h i c data f o r shear zones 2, 3, and 4 and the wedge of Isaac Formation p h y l l i t e s and metacarbonates from Domain 3 are summarized i n t h i s s e c t i o n . Rock f a b r i c and f a u l t -r e l a t e d l i n e a r and plan a r f e a t u r e s i n d i c a t e deformation ranging from b r i t t l e - d u c t i l e to d u c t i l e (Ramsay, 1967) i n the shear h o r i z o n s . The development of s i m i l a r f e a t u r e s i n the Isaac prism d i c t a t e s i t s i n c l u s i o n i n t h i s d i s c u s s i o n . 3.4 Shear Zone Features Shear zones 2 and 3 merge i n the map area to bound a wedge of p h y l l i t e s and metacarbonates of the Isaac Formation (Domain 3). Shear zone 4 separates the high grade gneisses i n Domain' 4 from k y a n i t e - s t a u r o l i t e zone rocks i n Domain 2b. Shear Zone 1 occurs i n the northernmost p o r t i o n of the map area, and separates rocks of the Upper Kaza from p h y l l i t e s and marbles of the Isaac Formation. Rocks i n the shear zones are d i s t i n g u i s h e d by f a b r i c s that i n d i c a t e high s t r a i n . D i s c o n t i n u i t i e s in s t r a t i g r a p h y and metamorphic grade occur a c r o s s the zones. The sheared h o r i z o n s , t h e r e f o r e , are zones of o f f s e t which are c h a r a c t e r i z e d by s t r a i n not evident i n the surrounding rocks. Mesoscopic and mi c r o s c o p i c f e a t u r e s i n the shear zones are summarized below. A l l of the shear zones are c h a r a c t e r i z e d by a dramatic change i n f a b r i c i n comparison with the country r o c k s : P e l i t i c rocks i n shear zones 2 and 3 are p h y l l i t i c and f i s s i l e . Late phase 4 kinks are p e r v a s i v e i n these f i n e - g r a i n e d r o c k s . Quartz boudins 47 are elongate i n the f o l d e d phase 1 f o l i a t i o n . C r o s s - c u t t i n g , random quartz v e i n s d i s r u p t phase 1 and 2 s t r u c t u r e s , and are present i n f a r g r e a t e r abundance i n shear zones 2 and 3 than anywhere o u t s i d e the cover sequence. Metamorphic minerals i n shear zones 2, 3, and 4 and i n the Isaac are h i g h l y retrograded to c h l o r i t e and s e r i c i t e . 3.5 Shear Zone 2 Shear zone 2 p l a c e s Upper Kaza Group metasediments s t r u c t u r a l l y above the wedge of Isaac Formation p h y l l i t e s and marbles, thus j u x t a p o s i n g o l d e r over younger roc k s . Near the shear zone, interbedded Kaza g r i t s and p e l i t e s are more h i g h l y s t r a i n e d by phase 2 f o l d s than any of the rocks found higher i n the s t r u c t u r a l package. F i g u r e 18 i l l u s t r a t e s dismembered minor f o l d s i n i n t e r l a y e r e d gneiss and s c h i s t . P e l i t i c m a t e r i a l f i l l e d in between the stacked f o l d hinges ( F i g u r e 19). S t r o n g l y boudinaged minor f o l d s occur i n zones of these f o l d s where an i n i t i a l c o n t r a c t i o n along bedding was f o l l o w e d by extension d u r i n g p r o g r e s s i v e metamorphism (Ramsay, 1967). B i o t i t e p o r p h y r o b l a s t s , a x i a l p l a n a r to the D2 c r e n u l a t i o n cleavage (S2), are a p p a r e n t l y o f f s e t p a r a l l e l to t h e i r b a s a l cleavage faces i n the hinges of the minor f o l d s . Retrograde c h l o r i t e rims these g r a i n s and grows along the (001) faces of b i o t i t e . L o c a l l y - d e v e l o p e d , p a r a l l e l a r r a y s of s l i g h t l y s i gmoidal q u a r t z - f i l l e d v e i n f i s s u r e s are common and prominent f e a t u r e s in shear zone 2 g n e i s s e s . A cleavage plane i s developed p e r p e n d i c u l a r to the gashes in some adjacent p h y l l i t e s , but i s not p e n e t r a t i v e at the mesoscopic s c a l e i n the 48 F i g u r e 18 - T i g h t e n e d phase 2 f o l d s a d j a c e n t t o shear zone 2, Domain 1 49 F i g u r e 19 - D u c t i l e d e f o r m a t i o n of p e l i t e beds. T i g h t e n i n g of phase 2 h i n g e s , Domain 1 50 q u a r t z o f e l d s p a t h i c g n e i s s e s . The t e n s i o n gashes and a s s o c i a t e d cleavages i n d i c a t e s e m i - b r i t t l e deformation by simple shear (Ramsay, 1967 and 1980). Under simple shear, v e i n a r r a y s develop normal to the maximum e l o n g a t i o n d i r e c t i o n of the incremental s t r a i n e l l i p s o i d , and at an angle of approximately 45° to the shearing s u r f a c e s . A s l a t y cleavage can form p e r p e n d i c u l a r to the maximum f i n i t e compressive s t r a i n , and t h e r e f o r e normal to the t e n s i o n f r a c t u r e s . The a r r a y s are good kinematic i n d i c a t o r s (Hanmer, 1983), but the data base e s t a b l i s h e d by f i e l d mapping near Niagara Creek i s n e i t h e r l a r g e enough nor s y s t e m a t i c a l l y r e p r e s e n t a t i v e enough to permit an e v a l u a t i o n of shear sense. 3.6 Shear Zone 3 Shear zone 3 juxtaposes the southern l i m i t of the Isaac Formation wedge above rocks that have been metamorphosed through k y a n i t e - s t a u r o l i t e grade. F a i l u r e o c c u r r e d along h i g h l y s t r a i n e d metacarbonate u n i t s i n the Isaac wedge. The amount of d i s l o c a t i o n a c r o s s the shear zone i s not known. The presence of t h i n (10 to 20 cm), interbedded q u a r t z o f e l d s p a t h i c gneisses in the p h y l l i t e s near the base of the Isaac lens may i n d i c a t e that f a u l t i n g i n these Cariboo Group metasediments occurred near the s t r a t i g r a p h i c base of the s e c t i o n (Murphy and Rees, 1983). In Shear Zone 3, b r e c c i a t e d , blocky boudins of q u a r t z o f e l d s p a t h i c g n e i s s are f l a t t e n e d i n the f o l i a t i o n , and p e l i t i c p h y l l i t e s have f i l l e d i n between them. Very f i n e g r a i n s i z e , a s t r o n g l y - d e v e l o p e d f o l i a t i o n , and o r i e n t e d p o r p h y r o b l a s t s c h a r a c t e r i z e the rocks i n the shear zone. F i n e -51 g r a i n e d sheet s i l i c a t e s , q u a r t z , a n d . f e l d s p a r of the matrix d i s p l a y a dimensional p r e f e r r e d o r i e n t a t i o n in the plane of f l a t t e n i n g . Late-D1 and post-D2 metamorphic minerals are s t r o n g l y and s y s t e m a t i c a l l y o r i e n t e d i n these rocks, as recorded by the rocks' i n t e r n a l f a b r i c s . A l l assemblages have s u f f e r e d extreme r e t r o g r a d e metamorphism i n the shear zone; s e r i c i t e and f i n e - g r a i n e d c h l o r i t e r e p l a c e metamorphic peak garnet, f e l d s p a r , and c h l o r i t o i d . P e l i t i c u n i t s i n shear zone 3 are p h y l l i t i c , f i s s i l e , and s t r o n g l y c r e n u l a t e d . However, in the most h i g h l y r e c r y s t a l l i z e d u n i t s , the rocks are st r e a k y and have a waxy appearance; the main s c h i s t o s i t y i s d i s c o n t i n u o u s and pinched out i n these h o r i z o n s . True mylonites do not occur i n the shear zone, as the c l a s t i c nature of the rocks i s not destroyed by r e c r y s t a l l i z a t i o n . The rocks are b e t t e r d e s c r i b e d as " p r o t o m y l o n i t i c " (Sibson, 1977). -Open phase 3 f o l d s and t i g h t phase 4 kink bands (Figure 20) are well-developed in shear zone 3 rocks and i n the o v e r l y i n g Isaac p h y l l i t e s . C r e n u l a t i o n s a s s o c i a t e d with these phases o v e r p r i n t p o r p h y r o b l a s t s of b i o t i t e , garnet, f e l d s p a r , and -c h l o r i t o i d . Mesoscopic phase 2 c l o s u r e s were not recognized i n the shear zone, but a n o r t h w e s t e r l y - t r e n d i n g i n t e r s e c t i o n l i n e a t i o n ( F i g u r e 27), L0x2, i s formed by the i n t e r s e c t i o n of the D2 c r e n u l a t i o n cleavage (S2) with bedding (SO). The c o n c e n t r a t i o n of s t r a i n that d e f i n e s shear zones 2 and 3 i s not a l l accomodated i n these narrow zones. In rocks below the boundaries of shear zone 3, the deformation i s d i s s i p a t e d 52 F i g u r e 20 - Kink bands i n Isaac p h y l l i t e , domain 3 53 across very h i g h l y s t r a i n e d g n e i sses and s c h i s t s i n t e r l a y e r e d with r e l a t i v e l y u n s t r a i n e d beds: East of the Isaac wedge high grade rocks which u n d e r l i e t h i s b a s a l shear zone c o n t a i n h i g h l y s t r a i n e d h o r i z o n s . In i n t e r l a y e r e d p h y l l i t i c p e l i t e s and g n e i s s e s , the more competent g n e i s s e s are f o l d e d by s o u t h w e s t e r l y - v e r g i n g , t i g h t , c h e v r o n - s t y l e minor f o l d s , and are b r i t t l y deformed. The rocks are broken up i n t o t h i n (2 to 3 cm t h i c k ) stacked planes that p a r a l l e l S1. The f o l d s and the b r i t t l e f e a t u r e s appear to o v e r p r i n t more open f o l d s . A s i g n i f i c a n t f e a t u r e i n shear zone 3 i s a strong p r e f e r r e d l i n e a r o r i e n t a t i o n of quartz and f e l d s p a r g r a i n s i n the phase 1 f o l i a t i o n . S t r o n g l y developed q u a r t z rods and elongate f e l d s p a r d e f i n e a n o r t h e r l y - t r e n d i n g l i n e a t i o n , with v a r i a b l e plunge. T h i s l i n e a t i o n i s p e r v a s i v e i n shear zone 3 and i n rocks beneath the f a u l t zone that are h i g h l y s t r a i n e d , and i s well-developed i n the prism of Isaac Formation ( F i g u r e s 13 and 27). P e t r o f a b r i c data summarized below i n d i c a t e post-metamorphic peak movement along the f a u l t s u r f a c e d e f i n e d by shear zone 3. Thin s e c t i o n s of some shear zone 3 rocks were cut p a r a l l e l to the n o r t h e r l y - t r e n d i n g l i n e a t i o n (L2) and p e r p e n d i c u l a r to the plane of f l a t t e n i n g (S1). In these s e c t i o n s , shear s u r f a c e s (or c - s u r f a c e s , a f t e r the terminology of Berthe and ot h e r s , 1979a) were i d e n t i f i e d as t h i n l a y e r s of a r e c r y s t a l l i z e d p o l y m i n e r a l i c aggregate with a reduced g r a i n s i z e ; s e r i c i t e and f i n e - g r a i n e d c h l o r i t e are r e c o g n i z a b l e . Matrix b i o t i t e s are tapered and kinked a c r o s s these zones. The shear s u r f a c e s appear to be d e f l e c t e d around garnets. Garnet and metamorphic f e l d s p a r in 54 I s a a c F o r m a t i o n r o c k s i n the shear zone p r e s e r v e i n t e r n a l s c h i s t o s i t i e s t h a t are c o n t i n u o u s w i t h the f o l i a t i o n i n the shear zone and o n l y s l i g h t l y s i g m o i d a l . Other p e l i t i c r o c k s i n the shear h o r i z o n c o n t a i n g a r n e t s w i t h s t r a i g h t t o s l i g h t l y s i g m o i d a l i n t e r n a l f a b r i c s , o r i e n t e d a t low t o h i g h a n g l e s t o the e x t e r n a l s c h i s t o s i t y when viewed normal t o L 2 ( F i g u r e 2 1 ) . P r e s s u r e shadows a r e w e a k l y - d e v e l o p e d around the p o r p h y r o b l a s t s . L a t e phase 3 and phase 4 c r e n u l a t i o n s a r e superimposed on t h e s e f a b r i c s . No s t r o n g l y - r o t a t e d , s y n - k i n e m a t i c f a b r i c i s e v i d e n t i n s e c t i o n s normal t o the e x t e n s i o n l i n e a t i o n . An anomalous o c c u r r e n c e of s i l l i m a n i t e was found i n a p e l i t i c h o r i z o n i n shear zone 3. S i l l i m a n i t e , b i o t i t e , and w h i t e mica mantle g a r n e t rims of stage two. B i o t i t e i n c l u s i o n s w i t h i n the stage one g a r n e t c o r e s a l s o c o n t a i n s i l l i m a n i t e . In the m a t r i x , s i l l i m a n i t e grows i n a g g r e g a t e s w i t h w h i t e mica and q u a r t z . No o t h e r o c c u r r e n c e of s i l l i m a n i t e , o u t s i d e of the h i g h grade g n e i s s e s of Domain 4, was o b s e r v e d i n the f i e l d a r e a . 3.7 The Isaac F o r m a t i o n P h y l l i t e s and marbles i n the I s a a c F o r m a t i o n wedge are h i g h l y s t r a i n e d and show r o t a t i o n of s t r u c t u r e s t h a t a r e near shear zone 3. M a r b l e u n i t s d i s p l a y the f o l l o w i n g f a b r i c s : 5 t o 10 cm l o n g q u a r t z boudins a r e e l o n g a t e i n the phase 1 f o l i a t i o n . E r r a t i c c a l c i t i c s t r i n g e r s c u t the s c h i s t o s i t y . The s c h i s t o s i t y i s commonly smeared i n appearance and p i n c h e d o u t . In brown-weathered, s i l i c e o u s c a l c i t e - m a r b l e u n i t s , c o a r s e w h i t e micas d e f i n e c o m p o s i t i o n a l bands. The micas are f l a t t e n e d and deformed i n S1 and d i s p l a y a n o r t h e r l y - t r e n d i n g c r e n u l a t i o n 55 F i g u r e 21 - Garnet c o n t a i n i n g s t r a i g h t i n c l u s i o n t r a i l s , r o t a t e d to a high angle with the e x t e r n a l s c h i s t o s i t y . Note l a t e k i n k s . F i e l d of view 2 mm 56 l i n e a t i o n t h a t i s s o s t r o n g l y d e v e l o p e d t h a t t h e m i c a s a p p e a r g r o o v e d . I n F i g u r e 22 t h e p h a s e 1 s c h i s t o s i t y , d e f i n e d b y a l i g n e d w h i t e m i c a , i s i s o c l i n a l l y f o l d e d a r o u n d p h a s e 2 a x i a l s u r f a c e s . S t r o n g o r i e n t a t i o n f a b r i c s , d e f i n e d b y a p r e f e r r e d o r i e n t a t i o n o f " o v o i d s " , a r e d e v e l o p e d i n s o m e c a l c a r e o u s p h y l l i t e s . T h e " o v o i d s " c o n s i s t o f f e l d s p a r , m i n o r q u a r t z , a n d a l i g n e d c a l c i t e . T h e y a r e o f t e n e l o n g a t e i n t h e m a i n f o l i a t i o n , a n d f o l d e d a c r o s s o p e n p h a s e t h r e e h i n g e s . G a r n e t a n d c h l o r i t o i d p o r p h y r o b l a s t s , b o t h s t r o n g l y r e t r o g r a d e d , o v e r p r i n t t h e D2 c r e n u l a t i o n c l e a v a g e . P r i s m a t i c c h l o r i t o i d c r y s t a l s l i e a t r e l a t i v e l y l o w a n g l e s t o t h e p h a s e 1 s c h i s t o s i t y a n d p r e s e r v e a h i g h a n g l e i n t e r n a l s c h i s t o s i t y d e f i n e d p r i m a r i l y b y f i n e o p a q u e s . T h e c h l o r i t o i d p o r p h y r o b l a s t s a p p e a r t o h a v e b e e n r o t a t e d t o w a r d p a r a l l e l i s m w i t h t h e s h e a r z o n e f o l i a t i o n . O c c a s i o n a l m i c r o - b o u d i n a g e d c h l o r i t o i d , s u b - p a r a l l e l t o t h e f o l i a t i o n a n d p a r t i a l l y r e p l a c e d b y c h l o r i t e , w a s a l s o o b s e r v e d ( F i g u r e 2 3 ) . S e v e r a l m a r b l e u n i t s i n t h e I s a a c w e d g e w e r e m a p p e d . T h e s e u n i t s a r e a p p a r e n t l y i s o l a t e d f o l d l i m b s . E a c h p r e s e r v e s a d i s r u p t e d i n t e r n a l f a b r i c t h a t i n c l u d e s i s o c l i n a l p h a s e 1 f o l d s ( F i g u r e 2 4 ) . T h e l i m b s t h e m s e l v e s may b e p h a s e 1 o r 2 s t r u c t u r e s . M e s o s c o p i c D2 m i n o r f o l d s i n t h e n o r t h e r n m o s t m a r b l e u n i t d e f i n e a c l o c k w i s e s e n s e o f s h e a r o n t h a t l i m b , b u t n o c l o s u r e w a s f o u n d . T h e s t r i k e o f t h e m a r b l e u n i t p a r a l l e l s t h e s h e a r z o n e . T h e m a r b l e i s t r u n c a t e d a t t h e e a s t e r n a n d w e s t e r n e d g e s o f t h e I s a a c p r i s m b y s h e a r z o n e 3 . M a r b l e u n i t s F i g u r e 22 - Open phase 2 f o l d of marble, Domain 3. White mica o u t l i n e s bedding (SO p a r a l l e l t o S1 ) 5 8 F i g u r e 23 - C h l o r i t o i d , r o t a t e d i n t o the main f o l i a t i o n (S1) and boudinaged by subsequent f l a t t e n i n g . F i e l d of view 3 mm. 59 F i g u r e 24 - I s o c l i n a l phase 1 f o l d s of micaceous h o r i z o n i n marble. Domain 3. 60 l o c a t e d adjacent to shear zone 3 s t r i k e to the northeast r e l a t i v e to the n o r t h w e s t e r l y - t r e n d i n g shear h o r i z o n . Phase 2 s t r u c t u r e s throughout the cover sequence s t r i k e to the northwest. I s o c l i n a l , s u b s i d i a r y phase 2 c l o s u r e s were mapped w i t h i n each of these marble u n i t s , but again no f i r s t order hinges were l o c a t e d . The geometries d e f i n e d by the marbles are not c o n s i s t e n t with those d e s c r i b e d f o r sheath f o l d s (Minnigh, 1979; Henderson, 1981). R o t a t i o n r e l a t e d to t r a n s p o r t of the Isaac prism may account f o r the d e v i a t i o n i n s t r i k e of the phase 2 marble u n i t s . 3.8 Shear Zone 4 Shear zone 4 separates k y a n i t e - s t a u r o l i t e zone rocks i n Domain 2b from s i 11imanite-bearing h i g h grade g n e i s s e s to the south (Domain 4). The shear zone i s mapped on the b a s i s of p e t r o f a b r i c s , s t r u c t u r a l r e l a t i o n s , geothermometry, and to some extent, topography. Highly s t r a i n e d marble u n i t s i n t e r l a y e r e d with p e l i t i c s c h i s t s , pink and green f e l d s p a t h i c q u a r t z i t e s , and q u a r t z o f e l d s p a t h i c gneisses occur throughout Shear Zone 4. The marbles are sheared, r e c r y s t a l l i z e d , and in some p l a c e s c a t a c l a s t i c a l l y d i s t u r b e d . Pinched-out l a y e r s of s t r o n g l y f o l i a t e d u n i t s , s m a l l - s c a l e c h a o t i c f o l d s , and randomly c r o s s -c u t t i n g v e i n s of c a l c i t e and quartz c h a r a c t e r i z e the marbles. These occur i n and j u s t north of a pronounced saddle i n the f i e l d a r e a. The topographic low appears to be an ex p r e s s i o n of the shear zone. Rocks w i t h i n t h i s shear zone are a f f e c t e d by p e r v a s i v e r e t r o g r a d e metamorphism, the extent of which i s much 61 g r e a t e r than i n adjacent u n i t s . E x t e n s i v e r e c r y s t a l l i z a t i o n of quartz and f e l d s p a r c h a r a c t e r i z e q u a r t z o f e l d s p a t h i c g n e i s s e s i n shear zone 4. In p e l i t i c s c h i s t s , the main s c h i s t o s i t y (S1) i s d e f i n e d by a l i g n e d b i o t i t e and coarse white mica. Quartz, f e l d s p a r , and c l i n o z o i s i t e are contained i n t h i s f o l i a t i o n . The f o l i a t i o n wraps around s k e l e t a l garnets, which preserve a l i g n e d , r e l a t i v e l y u n s t r a i n e d i n c l u s i o n s of quartz and f e l d s p a r . The angle between i n c l u s i o n t r a i l s and e x t e r n a l s c h i s t o s i t y v a r i e s from low to h i g h . Some of the garnets o v e r p r i n t phase 2 f o l d s . In some rocks, p o i k i l o b l a s t i c garnet (up to 1 cm i n diameter) are mantled by c l e a r second-stage garnet rims. No a l u m i n o s i 1 i c a t e was observed i n shear zone 4, but s t a u r o l i t e occurs i n f r e q u e n t l y . In one q u a r t z o f e l d s p a t h i c g n e i s s , s t a u r o l i t e occurs as f i n e , d i sseminated g r a i n s that p a r a l l e l a f o l d e d f o l i a t i o n d e f i n e d by i s o l a t e d l a y e r s of a l i g n e d white mica. Larger aggregates of s t a u r o l i t e , some p r e s e r v i n g an e i g h t - s i d e d o u t l i n e , o v e r p r i n t the phase 1 s c h i s t o s i t y . It has not been p o s s i b l e to determine the time of s t a u r o l i t e c r y s t a l l i z a t i o n r e l a t i v e to f o l d i n g . R e l a t i v e t i m i n g of movement along shear zone 4 i s i n d i c a t e d by r e s u l t s of g a r n e t - b i o t i t e geothermometry: a d i s c o n t i n u i t y i n temperature of approximately 75°C i s i n d i c a t e d a c r o s s the shear zone (see f o l l o w i n g c h a p t e r ) . Furthermore, a phase 3 a n t i f o r m in Domain 2b i s t r u n c a t e d by shear zone 4. Thus, displacement along t h i s shear zone post-dates, at l e a s t i n p a r t , both the peak of metamorphism and phase 3 f o l d i n g . 62 Domain 3: 23 squares Shear Zones 2,3: 19 squares Domain 3: 37 p o i n t s Shear Zones 2,3: 26 p o i n t s F i g u r e 25 ~ Poles to planar elements from the Isaac wedge and shear zones 2 and 3. Squares represent bedding (SO), p o i n t s represent f o l i a t i o n s (S1). Equal area s t e r e o g r a p h i c p r o j e c t i o n to lower hemisphere. 63 Domain 3: 2 p l u s s i g n s 2 t r i a n g l e s F i g u r e 26 - D1 f o l d elements from the Isaac wedge. Plus signs represent f o l d axes ( F 1 ) , t r i a n g l e s represent p o l e s to a x i a l planes ( S i ) . Equal area s t e r e o g r a p h i c p r o j e c t i o n to lower hemi sphere. 64 Domain 3: 4 diamonds Shear Zones 2,3: 2 t r i a n g l e s 7 t r i a n g l e s 3 p l u s s i g n s 14 p l u s signs F i g u r e 27 - D2 elements from the Isaac wedge and shear zones 2 and 3. Diamonds: a x i a l planar cleavage (S2) p o l e s ; t r i a n g l e s : a x i a l p l a n a r p o l e s ; p l u s s i g n s : f o l d axes (F2); c r o s s e s : i n t e r s e c t i o n l i n e a t i o n s (L0x2); octagons: L2 l i n e a t i o n s . 65 Domain 3: 2 t r i a n g l e s 3 plu s signs Phase: D3 Shear Zones 2,3: 1 t r i a n g l e 4 plus signs Phase: D3 Domain 3: 3 t r i a n g l e s 10 plus signs Phase: D4 Shear Zones 2,3: 7 t r i a n g l e 3 plu s signs Phase: D4 F i g u r e 28 - Comparison of f o l d elements (D3,D4) from the Isaac wedge and shear zones 2 and 3. T r i a n g l e s represent p o l e s to a x i a l planes, p l u s signs represent f o l d axes (F2). Equal area s t e r e o g r a p h i c p r o j e c t i o n to lower hemisphere. 66 13 poles to bedding (SO) N 14 poles to f o l i a t i o n (S1) 1 D1-axial plane: t r i a n g l e . 3 f o l d axes (F1) represented by p l u s s i g n s . 4 l i n e a t i o n s (L2) represented by octagons. 4 f o l d axes (F2): p l u s s i g n s N N F i g u r e 29 - S t r u c t u r a l data from shear zone 4. Equal area s t e r e o g r a p h i c p r o j e c t i o n to lower hemisphere. PHASE STRUCTURAL STYLE METAMORPHIC CONDITIONS D1 I s o c l i n a l f o l d s t r e n d i n g n o r t h w e s t e r l y . S t r u c t u r a l elements: S1 f o l i a t i o n Metamorphism a t l e a s t up t o lower g r e e n s c h i s t f a c i e s c o n d i t i o n s . D2 Major s t r u c t u r e s i n the map a r e a . F o l d s a r e open to t i g h t , recumbent, SW v e r g i n g . F o l d axes (F2) plunge NW. S t r u c t u r a l elements: S2 f o l i a t i o n ( c r e n u l a t i o n c l e a v a g e ) Minor f o l d s (F2: f o l d axes) L2 l i n e a t i o n : q u a r t z rods ( p a r a l l e i t o F2) L0x2 i n t e r s e c t i o n l i n e a t i o n (formed by S2 and SO, p a r a l l e i t o F2) S y n - k i n e m a t i c metamorphism through upper g r e e n s c h i s t f a c i e s cond i t i ons. Metamorphism o u t l a s t s D2 f o l d i n g : M i n e r a l s of a m p h i b o l i t e f a c i e s i n p a r t o v e r p r i n t D2 f o l d s . FAULTING High s t r a i n f a b r i c s i n shear zones 2 and 3. E l e v a t e d t emperature i n shear Zone 3. P o s t - k i n e m a t i c growth of s i 1 1 i man i t e . D3 Broad warping a c r o s s u p r i g h t , n o r t h -t r e n d i n g a x i a l s u r f a c e s . S t r u c t u r a l elements: S3 f o l i a t i o n ( l o c a l c r e n u l a t i o n c1eavage) Minor f o l d s (F3, f o l d axes) Lower g r e e n s c h i s t f a c i e s metamorphic c o n d i t i o n s . D4 Ki n k s e t s , l o c a l l y d eveloped, c o n j u g a t e i n uppermost s t r u c t u r a l domain. F a u l t s . T a ble I_ : Summary of d e f o r m a t i o n and metamorphism i n t h cov e r sequence. 68 E. THE HIGH GRADE GNEISSES 3.9 I n t r o d u c t i o n Interbedded g r i t s , p e l i t e s , conglomerates, and carbonates i n Domain 4_ have been metamorphosed through upper amphibolite f a c i e s c o n d i t i o n s i n the B a r r o v i a n f a c i e s s e r i e s . Immediately . s t r u c t u r a l l y below shear zone 4, s i l l i m a n i t e - b e a r i n g assemblages are p e r v a s i v e i n p e l i t i c g n e i s s e s and s c h i s t s , and p e r s i s t to the southern l i m i t of f i e l d mapping. These rocks r e c o r d four phases of deformation. Two phases of 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 s (P1 and P2) are c o a x i a l and plunge g e n t l y northwest and southeast. These s t r u c t u r e s developed p r i o r to the metamorphic peak. P o r p h y r o b l a s t s of garnet, k y a n i t e , s t a u r o l i t e , and s i l l i m a n i t e o v e r p r i n t P1 and P2 f o l d s t r u c t u r e s . Mesoscopic phase 3 (P3) f o l d s r e f o l d the e a r l i e r s t r u c t u r e s about.north- to n o r t h e a s t e r l y - t r e n d i n g a x i a l s u r f a c e s . L o c a l l y developed phase 4 (P4) kink f o l d s are superimposed on P1 and P2 s t r u c t u r e s . Phase 4 a x i a l s u r f a c e s are u p r i g h t and s t r i k e to the n o r t h e a s t . N o r t h w e s t - s t r i k i n g , steep f a u l t s d i s r u p t these e a r l i e r s t r u c t u r e s , as do l a t e b r i t t l e f e a t u r e s : N o r t h e r l y - and e a s t e r l y - t r e n d i n g v e r t i c a l j o i n t s ets cut PI, P2, and P3 f o l d s . Table II p r o v i d e s a summary of the s t r u c t u r a l events. 3.10 Deformation Of Domain 4 Gneisses Phase j_ deformation throughout domain 4 i s evidenced by a well-developed f o l i a t i o n (S1) that i s f o l d e d by l a t e r f o l d s ( F igure 30). S1 i s c h a r a c t e r i z e d by the p a r a l l e l alignment of coarse p h y l l o s i l i c a t e s and by the p r e f e r r e d o r i e n t a t i o n of elongate quartz and f e l d s p a r g r a i n s . The phase 1 s c h i s t o s i t y 69 t r a n s e c t s b e d d i n g a t l o w a n g l e s ( 1 0 t o 1 5 ° ) . P h a s e 1 f o l d s o f b e d d i n g ( S O ) , c o n t a i n e d w i t h i n p h a s e 2 l i m b s , w e r e r e c o g n i z e d i n a f e w m a r b l e u n i t s . S a n d y l a y e r s , c o n s i d e r e d t o b e b e d d i n g , a r e i s o c l i n a l l y f o l d e d a r o u n d t h e p h a s e 1 s c h i s t o s i t y . I n t h e s e m a r b l e s , S1 i s d e f i n e d b y t h e p r e f e r r e d o r i e n t a t i o n o f d i s s e m i n a t e d w h i t e m i c a a n d b y e l o n g a t e q u a r t z b o u d i n s . I n t e r l a y e r i n g o f g r a d e d q u a r t z o f e l d s p a t h i c g n e i s s e s w i t h p e l i t i c s c h i s t s a n d g n e i s s e s r e p r e s e n t s o r i g i n a l s e d i m e n t a r y b e d d i n g ( S O ) . R a r e l y , p h a s e 1 i s o c l i n a l f o l d s o f i n t e r b e d d e d s c h i s t s a n d g n e i s s e s w e r e o b s e r v e d o n t h e l i m b s o f P 2 s t r u c t u r e s . F i r s t p h a s e c l o s u r e s i n t h e s e c l a s t i c u n i t s w e r e a l s o r e c o g n i z e d w h e r e t h e s u p e r p o s i t i o n o f p h a s e 2 f o l d s r e s u l t s i n t y p e t h r e e i n t e r f e r e n c e p a t t e r n s ( R a m s a y , 1 9 6 7 ) . P h a s e 2 f o l d s a r e t h e m o s t p r o m i n e n t s t r u c t u r e s i n D o m a i n 4 . B e d d i n g ( S O ) a n d t h e p h a s e 1 s c h i s t o s i t y ( S 1 ) a r e i s o c l i n a l l y r e f o l d e d a c r o s s a x i a l s u r f a c e s t h a t s t r i k e g e n e r a l l y t o t h e n o r t h w e s t . T h e a x i a l s u r f a c e s d i p n o r t h e r l y i n t h e n o r t h e r n p o r t i o n o f t h e d o m a i n a n d s o u t h e r l y i n t h e s o u t h e r n p o r t i o n . I n t h e s t e r e o g r a p h i c p r o j e c t i o n o f p o l e s t o t h e s e s u r f a c e s ( F i g u r e 3 1 ) , t w o p o p u l a t i o n s a r e i l l u s t r a t e d . T h i s v a r i a t i o n i n o r i e n t a t i o n may b e d u e t o a l a t e r d e f o r m a t i o n . M i c r o - f o l d s o f S1 d e f i n e a c l e a v a g e t h a t i s a x i a l p l a n a r t o m e s o s c o p i c p h a s e 2 a x i a l s u r f a c e s . C o a r s e w h i t e m i c a s a n d b i o t i t e s a r e r e c r y s t a l l i z e d a r o u n d t h e h i n g e s o f t h e s e f o l d s . C o n v e r g e n t c l e a v a g e f a n s a r e o b s e r v e d i n s o m e P 2 m i n o r f o l d s . T h e p h a s e 2 s c h i s t o s i t y i n t e r s e c t s b e d d i n g t o f o r m a n o r t h w e s t e r l y - a n d s o u t h e a s t e r l y - p l u n g i n g l i n e a t i o n ( L 0 x 2 ) t h a t 70 i s p a r a l l e l to the hinges of second phase f o l d s . M u l l i o n rods are common i n these hinges. The l i n e a t i o n a l s o p a r a l l e l s L2, the d i r e c t i o n of e l o n g a t i o n of q u a r t z g r a i n s . The v a r i a t i o n in plunge, from northwest to southeast, of phase 2 f o l d axes and l i n e a r elements ( F i g u r e 31) i s due to r e o r i e n t a t i o n by l a t e r f o l d s . N o r t h e r l y - s t r i k i n g phase 3 a x i a l s u r f a c e s , and to a l e s s e r extent, phase 4 kink f o l d s , reverse the plunges of these o l d e r elements. Phase 3 a x i a l s u r f a c e s broadly r e f o l d the limbs of phase 2 f o l d s and e a r l i e r s t r u c t u r e s . V a r i a t i o n i n the o r i e n t a t i o n of P3 f o l d elements i s i n p a r t a t t r i b u t a b l e to measurement e r r o r i n the f i e l d ; the o r i e n t a t i o n s of the a x i a l s u r f a c e s were d i f f i c u l t to judge due to the broad, open, undulatory s t y l e of the f o l d s . Phase 3 deformation i s p e r v a s i v e throughout domain 4. S o u t h e r l y - p l u n g i n g i n t e r s e c t i o n l i n e a t i o n s (L0x3) are l o c a l l y -developed where phase 3 higher order c r e n u l a t i o n cleavages (S3) i n t e r s e c t bedding (Figure 32). No f i r s t order P3 s t r u c t u r e s were recognized, and the vergence of phase 3 minor f o l d s i s not known. The r e o r i e n t a t i o n of phase 2 a x i a l s u r f a c e s from north to south i n domain 4 may be a t t r i b u t e d to l a t e f a u l t i n g or to phase 3 f o l d i n g . A r e l a t i v e l y h i g h angle, east-west s t r i k i n g s t r u c t u r e i s i n d i c a t e d by the map p a t t e r n . A saddle which gives way to e a s t e r l y - and w e s t e r l y - t r e n d i n g creek v a l l e y s i s c o i n c i d e n t with the d i p change in phase 2 s t r u c t u r e s , and may be a topographic e x p r e s s i o n of a post-P2 high angle f a u l t . However, the ste r e o n e t d i s t r i b u t i o n of P2 a x i a l s u r f a c e s (Figure 71 31) i n d i c a t e s r e o r i e n t a t i o n of P2 f o l d elements by superimposed f o l d i n g . The d i s t r i b u t i o n of phase 3 f o l d elements, summarized in F i g u r e 32, supports the i n t e r p r e t a t i o n that a f i r s t order phase 3 s t r u c t u r e r e - o r i e n t s phase 2 f o l d s . Furthermore, the o r i e n t a t i o n of phase 3 l i n e a r elements suggests that P3 was c o a x i a l to P2 deformation. N e i t h e r the e x i s t e n c e of a f a u l t nor s u p e r p o s i t i o n of a phase 3 s t r u c t u r e can be a s c e r t a i n e d based on present f i e l d data. Phase 4 deformation i s represented by l o c a l l y developed u p r i g h t kink f o l d s . The phase 4 c r e n u l a t i o n a x i a l s u r f a c e s (S4) s t r i k e northeast (Figure 32), and are l o c a l l y r e s p o n s i b l e f o r plunge r e v e r s a l s of P2 s t r u c t u r e s . Very few kink bands were observed in domain 4 r o c k s . T h e i r e f f e c t , e s p e c i a l l y on P3 s t r u c t u r e s , i s not c l e a r . North- and e a s t - t r e n d i n g high angle j o i n t s e t s were observed i n the h i g h e s t grade p o r t i o n s of domain 4. No systematic measurements of the j o i n t s u r f a c e s were c o l l e c t e d ; t h e i r r e l a t i o n to e a r l i e r f o l d s t r u c t u r e s , or to post-phase 3 high angle f a u l t i n g along shear.zone 4, i s not known. 72 Domain 4: 59 squares N Domain 4: 85 p o i n t s N F i g u r e 30 - Poles to planar elements from the high grade gneiss complex. Squares represent bedding (SO), p o i n t s represent f o l i a t i o n s (S1). Equal area s t e r e o g r a p h i c p r o j e c t i o n to lower hemisphere. 73 Domain 4: 10 diamonds 28 t r i a n g l e s N F i g u r e 31 - D2 elements from the high grade gneiss complex. Diamonds : po l e s to a x i a l planar cleavage (S2); t r i a n g l e s : p o l e s to a x i a l planes (S2); p l u s s i g n s : f o l d axes (F2); c r o s s e s : i n t e r s e c t i o n l i n e a t i o n s (L0x2); octagons: L2 l i n e a t i o n s . 74 Domain 4 Phase: 6 plus s i g n s 8 t r i a n g l e s PI Domain 4 Phase: 6 1 2 P3 pl u s signs t r i a n g l e s Domain 4 Phase: 2 plus signs 3 t r i a n g l e s P4 F i g u r e 32 - F o l d elements from the high grade gneiss complex T r i a n g l e s represent p o l e s to a x i a l planes (S1,S3,S4), plu s s i g n s represent f o l d axes (F1,F3,F4). Equal area s t e r e o g r a p h i c p r o j e c t i o n to lower hemisphere. 75 3 . 1 1 M e t a m o r p h i s m O f T h e H i g h G r a d e G n e i s s e s a . I n t r o d u c t i o n T h e p e l i t i c s c h i s t s a n d g n e i s s e s i n d o m a i n 4 h a v e b e e n m e t a m o r p h o s e d t h r o u g h u p p e r a m p h i b o l i t e f a c i e s c o n d i t i o n s i n t h e B a r r o v i a n f a c i e s s e r i e s . P o r p h y r o b l a s . t - f o l i a t i o n r e l a t i o n s , a s i n t h e n o r t h e r n d o m a i n s , p r o v i d e i n s i g h t i n t o t h e r e l a t i v e t i m i n g o f m i n e r a l g r o w t h a n d d e f o r m a t i o n w i t h i n d o m a i n 4 , a n d p r o v i d e e v i d e n c e f o r c o r r e l a t i o n o f s t r u c t u r e s a n d m e t a m o r p h i c e v e n t s a c r o s s s h e a r z o n e 4 . b . M i c r o s c o p i c O b s e r v a t i o n s T h e p h a s e 1 s c h i s t o s i t y o f p e l i t i c s c h i s t s a n d g n e i s s e s i n d o m a i n 4 i s d e f i n e d p r i m a r i l y b y t h e p a r a l l e l a l i g n m e n t o f c o a r s e w h i t e m i c a a n d b i o t i t e l a t h s . T h e s e a r e o f t e n i n t e r g r o w n a l o n g ( 0 0 1 ) w i t h i l m e n i t e o r m a g n e t i t e . Q u a r t z - a n d f e l d s p a r -r i c h l e n s e s a n d b a n d s a r e s e g r e g a t e d f r o m d o m a i n s t h a t c o n t a i n a b u n d a n t p h y l l o s i l i c a t e s . P r o g r e s s i v e d e f o r m a t i o n a n d m e t a m o r p h i s m h a v e e n h a n c e d s e d i m e n t a r y c o m p o s i t i o n a l v a r i a t i o n s . S u p e r i m p o s e d f o l d i n g , l a t e p o r p h y r o b l a s t g r o w t h , a n d c o a r s e n i n g o f t h e f o l i a t i o n u p g r a d e c o m p l i c a t e t h e f a b r i c s , b u t a r e c o r d o f t h e s e q u e n c e o f e v e n t s s u r v i v e s . T w o m a i n s t a g e s o f g a r n e t g r o w t h a r e i n d i c a t e d . L a r g e ( 1 . 0 t o 1 . 5 cm d i a m e t e r ) , p o i k i l o b l a s t i c , x e n o m o r p h i c g a r n e t s o v e r p r i n t p h a s e 2 f o l d s . T h e f i r s t s t a g e g a r n e t s a r e m a n t l e d b y i d i o m o r p h i c , r e l a t i v e l y i n c l u s i o n - p o o r s e c o n d s t a g e r i m s . S e c o n d s t a g e g a r n e t s a l s o o c c u r a s s m a l l (1 t o 2 mm d i a m e t e r ) , i n c l u s i o n - f r e e , i d i o m o r p h i c p o r p h y r o b l a s t s t h a t o v e r p r i n t p h a s e 2 f o l d s . C o a r s e c h e m i c a l z o n i n g p r o f i l e s , o b t a i n e d b y 76 microprobe spot a n a l y s e s , i n d i c a t e "normal" zoning p a t t e r n s ( H o l l i s t e r , 1966) acr o s s both of these types of garnet. T r a v e r s e s a c r o s s the mantled garnets, from rim to core demonstrate the f o l l o w i n g : almandine and g r o s s u l a r content decrease as s p e s s a r t i n e and pyrope content i n c r e a s e . S i m i l a r p r o f i l e s were obtained f o r sm a l l , idiomorphic, second stage p o r p h y r o b l a s t s , but i n these chemical g r a d i e n t s are g e n t l e r . Mantled, p o i k i l o b l a s t i c garnets and i s o l a t e d idiomorphic garnets occur throughout Domain 4. Garnet, k y a n i t e , s t a u r o l i t e , s i l l i m a n i t e , p l u s l a t e b i o t i t e and white mica p o r p h y r o b l a s t s overgrow phase 2 c r e n u l a t i o n s of SI. F i r s t phase f o l d s were not recognized i n t h i n s e c t i o n . Only garnet, and r a r e l y s t a u r o l i t e , bear i n t e r n a l s c h i s t o s i t i e s that p reserve r e l i c phase 1 f o l i a t i o n s . F i r s t stage, mantled garnet, and o c c a s i o n a l l y s t a u r o l i t e , preserve sigmoidal i n t e r n a l s c h i s t o s i t i e s that are continuous with the f o l d e d phase 1 f o l i a t i o n . In some samples, garnet has grown along quartz and f e l d s p a r g r a i n boundaries, o v e r p r i n t i n g phase 2 f o l d s . In some garnet g r a i n s , r e l a t i v e l y s t r a i g h t i n t e r n a l s c h i s t o s i t i e s , o r i e n t e d at high angles to the e x t e r n a l f o l i a t i o n , preserve elongate b i o t i t e and white mica, as w e l l as f e l d s p a r and q u a r t z . The o r i e n t a t i o n and composition of the i n t e r n a l f o l i a t i o n i s the same as that of the e x t e r n a l f o l i a t i o n proximal to the garnets, suggesting o v e r p r i n t i n g . Mantled garnets with s t r a i g h t or s l i g h t l y s i g m o i d a l i n c l u s i o n t r a i l s are commonly observed. The i n c l u s i o n t r a i l s are o r i e n t e d at low to high angles to the e x t e r n a l s c h i s t o s i t y . 77. The r e l a t i v e t i m i n g of g a r n e t growth i s d i f f i c u l t t o a s s e s s : The g e n t l y s i g m o i d a l , symmetric t r a i l s may be i n t e r p r e t e d as s y n - k i n e m a t i c t o phase 2 f o l d i n g , w i t h most of the c r y s t a l l i z a t i o n o c c u r r i n g l a t e i n the P2 f o l d i n g . P o s t -c r y s t a l l i z a t i o n r o t a t i o n a l ( n o n c o a x i a l ) s t r a i n may have been s u f f i c i e n t t o r e o r i e n t the e x t e r n a l f o l i a t i o n r e l a t i v e t o garnet c o r e s , w i t h t h e i r i n t e r n a l f a b r i c s . G a r n e t s w i t h s t r a i g h t i n c l u s i o n t r a i l s may have o v e r p r i n t e d a f o l d e d f a b r i c where h i n g e s were not r e p r e s e n t e d . The t e x t u r e s suggest the f o l l o w i n g r e l a t i v e t i m i n g of i n i t i a l g a r n e t growth: g a r n e t c r y s t a l l i z a t i o n was s y n - k i n e m a t i c t o phase 2 f o l d i n g and c e r t a i n l y o u t l a s t e d t h a t d e f o r m a t i o n . K y a n i t e and s t a u r o l i t e occur as s u b i d i o m o r p h i c p o r p h y r o b l a s t s , w i t h v e r y l i t t l e i n c l u d e d m a t e r i a l . The s c a r c i t y of i n c l u s i o n s r e n der d i f f i c u l t the judgement of the t i m i n g of p o r p h y r o b l a s t growth r e l a t i v e t o the development of m i c r o s t r u c t u r e s . However, overgrowth of phase 2 f o l d s i s noted f o r r a r e p o i k i l o b l a s t i c s t a u r o l i t e . In p l a c e s , k y a n i t e , s t a u r o l i t e , and second s t a g e g a r n e t appear t o t r u n c a t e the f o l d e d phase 1 s c h i s t o s i t y . The f o l i a t i o n has been s u b s e q u e n t l y f l a t t e n e d around t h e s e g r a i n s . Large k y a n i t e c r y s t a l s , a s s o c i a t e d w i t h q u a r t z v e i n s , a r e m e s o s c o p i c a l l y k i n k e d by l a t e phase 3 a x i a l s u r f a c e s . S i l l i m a n i t e f i r s t appears i n Domain 4 as t h i n n e e d l e s d i s p l a y e d i n a ' h o r s e t a i l ' t e x t u r e , w i t h i n the main f o l i a t i o n . The s i l l i m a n i t e o c c u r s w i t h i n f i n e - g r a i n e d x e n o b l a s t i c w h i t e m i c a - and q u a r t z - r i c h zones t h a t s u r r o u n d s t a u r o l i t e , k y a n i t e , 78 and s m a l l , i s o l a t e d second stage garnet c r y s t a l s . The l a t t e r are p a r t i a l l y r e p l a c e d by r e t r o g r a d e s e r i c i t e and f i n e - g r a i n e d c h l o r i t e , but maintain idiomorphic g r a i n boundaries with respect to the mica, qu a r t z , and s i l l i m a n i t e . B i o t i t e i s o f t e n c o n t a i n e d w i t h i n the s i l l i m a n i t e - r i c h zones. In these same rocks, f i r s t stage garnet i s a l s o a s s o c i a t e d with s i l l i m a n i t e , b i o t i t e , white mica, and q u a r t z . The garnet i s commonly p a r t i a l l y r e p l a c e d by c r o s s - c u t t i n g zones of white mica, q u a r t z , and s i l l i m a n i t e . B i o t i t e mantles around blocky second stage garnet rims are l i t t e r e d with randomly o r i e n t e d s i l l i m a n i t e needles. B i o t i t e i n c l u s i o n s w i t h i n garnet cores c o n t a i n s i l l i m a n i t e . As grade i n c r e a s e s to the south, e x t e n s i v e microdomains dominated by f e l t y b i o t i t e p l u s f i n e - g r a i n e d quartz are f i l l e d with r a d i a t i n g and ' h o r s e t a i l ' knots of s i l l i m a n i t e . O c c a s i o n a l l y , s t a u r o l i t e g r a i n s are preserved as r e l i c i s l a n d s in these zones. In F i g u r e 33 , garnet and remnant s t a u r o l i t e are a s s o c i a t e d with s i l l i m a n i t e . Second stage garnet rims c o e x i s t with the s i l l i m a n i t e - white mica - b i o t i t e - quartz assemblages ( F i g u r e s 33 and 34). R a r e l y , idiomorphic garnets bear a ragged edge that i s i n c o n t a c t with b i o t i t e and s i l l i m a n i t e . In one c o a r s e - g r a i n e d , p e l i t i c , q u a r t z o f e l d s p a t h i c gneiss ( F i g u r e 35), white mica, s i l l i m a n i t e , q u a r t z , and minor retro g r a d e c h l o r i t e ( a f t e r b i o t i t e ) are pseudomorphic a f t e r s t a u r o l i t e ; only the o r i g i n a l o u t l i n e of the s t a u r o l i t e , a s i x -sid e d b a s a l s e c t i o n , i s p r e s e r v e d . In the highest grade p o r t i o n s of Domain 4, i n the v i c i n i t y 79 F i g u r e 33 - S i l l i m a n i t e grew at the expense of s t a u r o l i t e and garnet. F i e l d of view 2 mm 80 F i g u r e 34 - Second-stage garnet c o e x i s t i n g with aggregates s i l l i m a n i t e , w h i t e mica, and b i o t i t e . F i e l d of view 2 mm 8 1 F i g u r e 35 - S i l l i m a n i t e , white mica, and quartz pseudomorph a f t e r s t a u r o l i t e . F i e l d of view 2 mm 82 of pegmatite bodies, s t a u r o l i t e and kyanite are only i n t a c t i n q u a r t z o f e l d s p a t h i c l a y e r s . In the sheet s i l i c a t e - r i c h l e n s e s , l a r g e zones of s i l l i m a n i t e , q u a r t z , b i o t i t e , and white mica c o n t a i n ragged kyanite (Figure 36), s t a u r o l i t e , as w e l l as small idiomorphic garnet. Kyanite i s not always a s s o c i a t e d with s i l l i m a n i t e . However, f a i n t cleavages, i n zones of white mica and coarse s i l l i m a n i t e needles, may be r e l i c f a b r i c s of r e p l a c e d k y a n i t e . With the exception of r e t r o g r a d e phases, s i l l i m a n i t e was the l a t e s t to c r y s t a l l i z e i n the sequence of metamorphic minerals." Where metamorphic grade i s highest i n the f i e l d area, pegmatite bodies are concordant with the phase 2 s c h i s t o s i t y and bear phase 3 f a b r i c s . In the pegmatite, a n o r t h e r l y - s t r i k i n g , u p r i g h t t h i r d phase f o l i a t i o n , which may be a s o l u t i o n cleavage, c o n t a i n s a s o u t h e r l y - p l u n g i n g l i n e a t i o n d e f i n e d by quartz rods. The outcrop p a t t e r n of the main pegmatite body r e f l e c t s the e f f e c t of phase 3 f o l d i n g . Concordant, pink-weathered q u a r t z i t e s are a s s o c i a t e d with the pegmatite. The pegmatite mi n e r a l assemblage c o n s i s t s mainly of potassium f e l d s p a r , minor quartz and b i o t i t e , coarse white mica, and small idiomorphic garnet. The r e l a t i v e time of i n t r u s i o n of the pegmatite i s recorded by a s s o c i a t e d f a b r i c s . Late phase 2 deformation (metamorphic peak) i s an o l d e r age l i m i t f o r i n t r u s i o n ; the onset of p e n e t r a t i v e phase 3 f o l d i n g i s a younger l i m i t . Lower g r e e n s c h i s t f a c i e s c o n d i t i o n s may have been reached p r i o r to phase 3 deformation. In a d d i t i o n to the matrix white mica and b i o t i t e which form polygonal a r c s around phase 2 f o l d s , 3 3 F i g u r e 36 - R e l i c k y a n i t e , F i e l d of view 2 mm p a r t i a l l y r e p l a c e d by s i l l i m a n i t e . 84 l a r g e white micas are i n t e r l e a v e d with the f o l d e d s c h i s t o s i t y and are d i s c o r d a n t with phase 2 a x i a l s u r f a c e s . These micas are f l a t t e n e d around post-P2 p o r p h y r o b l a s t s and are f o l d e d by phase 3 and l a t e phase 4 kink s . The white mica l a t h s , and minor c r o s s - c u t t i n g b i o t i t e , do not c o n t a i n needles of s i l l i m a n i t e , and may have c r y s t a l l i z e d under lower g r e e n s c h i s t f a c i e s c o n d i t i o n s as metamorphic temperatures were d e c l i n i n g . In a d d i t i o n to these micas, r e t r o g r a d e c h l o r i t e p l u s s a g e n i t i c r u t i l e r e p l a c e b i o t i t e p o r p h y r o b l a s t s , s e r i c i t e and f i n e - g r a i n e d c h l o r i t e rim garnet, and hematite pseudomorphs some opaques. The r e l a t i o n s h i p of these r e t r o g r a d e minerals to l a t e deformation (P3 and P4) i s not known. c. Chemical Reactions Among M i n e r a l s T e x t u r a l r e l a t i o n s i n p e l i t i c s c h i s t s and gneisses i n domain 4 suggest that garnet and s t a u r o l i t e were breaking down to form b i o t i t e - white mica - s i l l i m a n i t e aggregates. The f o l l o w i n g s i l l i m a n i t e - f o r m i n g r e a c t i o n s may thus be i n f e r r e d : (1) 12 stau + 9 muse + 7 qtz = 58 s i l l + 3 bio + 12 H 20 (2) 8 gar + 9 muse = 14 s i l l + 3 b i o + 13 qtz (3) 1 ky = 1 s i l l S i m i l a r s i l l i m a n i t e - f o r m i n g r e a c t i o n s have been d e s c r i b e d from other regionally-metamorphosed t e r r a i n s ( F l e t c h e r , 1972; Yardley, 1977; Pigage, 1977 and 1978). The f i r s t two r e a c t i o n s can be balanced by r e g r e s s i o n techniques (Pigage, 1977 and 1978) for metamorphic mineral compositions i n a multi-component system. Reactions 1 and 2 are continuous i n such a system, with Mg and Fe p a r t i t i o n i n g among c o e x i s t i n g " r e a c t a n t " and "product" 85 phases. The s u p e r p o s i t i o n of the Mg-Fe exchange e q u i l i b r i a d i s p l a c e s , r e a c t i o n s 1 and 2 over temperature-composition f i e l d s . When c e r t a i n compositions of the s o l i d s o l u t i o n phases are reached, a d i s c o n t i n u o u s r e a c t i o n occurs (A.B. Thompson, 1976a). Paragonite content i n muscovite, g r o s s u l a r content i n garnet, and T i content i n b i o t i t e are not e x p l i c i t l y accounted f o r i n these r e a c t i o n s . To i n c o r p o r a t e these components, f u r t h e r phases are needed, f o r example p l a g i o c l a s e and i l m e n i t e (Pigage, 1977 and 1978) . F l e t c h e r (1972) and Pigage (1977, 1978), working in high grade gneisses along the n o r t h e a s t e r n boundary of the Shuswap Metamorphic Complex, conclude that garnet and s t a u r o l i t e were breaking down to form b i o t i t e , s i l l i m a n i t e , and muscovite. T e x t u r a l r e l a t i o n s were among the c o n s t r a i n t s used to s e l e c t probable r e a c t i o n s . Stepwise l i n e a r l e a s t squares r e g r e s s i o n a n a l y s i s was used to t e s t f o r l i n e a r dependencies among sets of mineral compositions i n one or more assemblages. A l l l i n e a r r e g r e s s i o n models y i e l d breakdown of s t a u r o l i t e and/or garnet to form s i l l i m a n i t e . F l e t c h e r (1972) c o n s i d e r e d the e f f e c t of Na on the r e a c t i o n s . Pigage i n a d d i t i o n c o n s i d e r e d the e f f e c t of Ca, Mn, and T i . In the present study, the t i m i n g of second stage garnet growth i s not c l e a r from t e x t u r a l r e l a t i o n s . Small, idiomorphic garnet g r a i n s and rims around e a r l i e r garnet cores c o e x i s t with the b i o t i t e - muscovite - s i l l i m a n i t e aggregates. Second stage garnet mantles p o i k i l o b l a s t i c garnet cores which appear to be unstable in these aggregates ( F i g u r e 34). Pigage (1978) 86 concludes that second stage growth r e s u l t e d from a continuous garnet-forming r e a c t i o n d u r i n g prograde metamorphism. Stage-two garnets are c o n s i d e r e d to overgrow i n i t i a l b i o t i t e - s i l l i m a n i t e aggregates. His microprobe analyses r e v e a l systematic Fe-Mg p a r t i t i o n i n g between second stage garnet rims and b i o t i t e ; t h i s i n d i c a t e s t hat the matrix phases have adjusted, t h e i r compositions to remain i n exchange e q u i l i b r i u m with garnet rims of stage-two. No c l e a r time r e l a t i o n between growth of stage-two garnet and s i l l i m a n i t e can be i n f e r r e d . What i s c l e a r , though, i s that f i r s t stage garnet i s a r e a c t a n t phase in s i l l i m a n i t e - f o r m i n g r e a c t i o n s . In c o n t r a s t to Pigage's c o n c l u s i o n s , t h i s scheme does not i n v o l v e overgrowth of s i l l i m a n i t e - b i o t i t e by second stage garnet. Instead, garnet of the second generation would grow at the expense of f i r s t g e n e r a t i o n garnet. PHASE STRUCTURAL STYLE METAMORPHIC CONDITIONS P1 I s o c l i n a l f o l d s t r e n d i n g n o r t h w e s t e r l y . S t r u c t u r a l elements: S1 f o l i a t i o n ( p a r a l l e l s SO) Metamorphism a t l e a s t up to lower g r e e n s c h i s t f a c i e s c o n d i t i o n s . P2 Dominant s t r u c t u r e s i n the domain. C o a x i a l to D1 s t r u c t u r e s . F o l d s a r e i s o c l i n a l , f o l d axes (F2) plunge NW and SE, a x i a l s u r f a c e s d i p to N and S. S t r u c t u r a l elements: S2 f o l i a t i o n ( a x i a l s u r f a c e s to m i c r o f o l d s ) Minor f o l d s (F2: f o l d axes, p a r a l l e l mull i o n rods) L2 l i n e a t i o n : q u a r t z rods ( p a r a l l e i t o F2) L0x2 i n t e r s e c t i o n l i n e a t i o n (formed by 52 and SO, para 11 e l to F2) I n t r u s i o n of p e g m a t i t e s S y n - k i n e m a t i c metamorphism through upper g r e e n s c h i s t f a c i e s cond i t i ons. Metamorphism o u t l a s t s P2 f o l d i n g : M i n e r a l s of a m p h i b o l i t e f a c i e s i n p a r t o v e r p r i n t D2 f o l d s . P3 R e f o l d i n g a c r o s s open f o l d s w i t h n o r t h -t r e n d i n g a x i a l s u r f a c e s of moderate d i p . S t r u c t u r a l elements: S3 f o l i a t i o n ( s o l u t i o n c l e a v a g e ? In pegmat i t e , a x i a l s u r f a c e s to m i c r o f o l d s ) L0x3 i n t e r s e c t i o n l i n e a t i o n (formed by SO and S3, s o u t h e r l y p i u n g i ng) Lower g r e e n s c h i s t f a c i e s ? FAULTING In shear zone 4: h i g h s t r a i n r a t e s and e l e v a t e d temperatures. P4 Kink s e t s , l o c a l l y developed o n l y . J o i n t s e t s . Table 11 : Summary of d e f o r m a t i o n and metamorphism i n the h i g h grade g n e i s s e s . 88 IV. METAMORPHIC CONDITIONS A. INTRODUCTION Pressure - temperature c o n d i t i o n s have been estimated using the f o l l o w i n g e x p e r i m e n t a l l y c a l i b r a t e d mineral e q u i l i b r i a : 1. a n d a l u s i t e = s i l l i m a n i t e s i l l i m a n i t e = kyanite kyanite = a n d a l u s i t e 2. F e 3 A l 2 S i 3 0 1 2 + K M g 3 A l S i 3 0 1 0 ( O H ) 2 almandine p h l o g o p i t e = M g 3 A l 2 S i 3 0 1 2 + K F e 3 A l S i 3 0 , o ( O H ) 2 pyrope annite 3. F e 3 A l 2 S i 3 0 1 2 + 3 T i 0 2 = 3 F e T i 0 3 + A l 2 S i 0 5 + 2 S i 0 2 almandine r u t i l e i l m e n i t e k y / s i l l quartz Estimates of temperature are based on F e r r y and Spear's (1978) c a l i b r a t i o n of exchange e q u i l i b r i u m 2. Pressure estimates are based on the c a l i b r a t i o n of exchange e q u i l i b r i u m 3 by Bohlen et a l . (1983) and on an i n t e r n a l l y c o n s i s t e n t a l u m i n o s i 1 i c a t e diagram, based on the experiments of Newton (1966a), Richardson et a l . (1968), and Holdaway (1971), and a recent c o m p i l a t i o n of heat c a p a c i t y data (Berman et a l . , 1984). Garnet and i l m e n i t e s o l u t i o n models were i n c o r p o r a t e d in the a p p r o p r i a t e e q u i l i b r i a to account f o r non i d e a l mixing. 89 B. GEOTHERMOMETRY Fe r r y and Spear (1978) c a l i b r a t e d the Mg-Fe exchange f o r bin a r y s o l i d s o l u t i o n s of s y n t h e t i c garnet and b i o t i t e ( e q u i l i b r i u m 2 ) . They d e r i v e an ex p r e s s i o n f o r the d i s t r i b u t i o n c o e f f i c i e n t (KD) from t h e i r experimental data at 2.07 kbar and 500 - 800°C (equation 1). A p p l i c a t i o n of t h e i r c a l i b r a t i o n to n a t u r a l g a r n e t - b i o t i t e p a i r s r e q u i r e s a knowledge of a c t i v i t y -composition r e l a t i o n s h i p s to account f o r non-binary components because, i n a d d i t i o n to temperature and pr e s s u r e , these non-binary components i n f l u e n c e KD and any temperature d e r i v e d from i t . A c t i v i t y models are r e q u i r e d , i n p a r t i c u l a r , f o r Ca and Mn in garnet, and f o r T i , A l ( V I ) , and Mn i n b i o t i t e . Garnet compositions in samples throughout the map area are t y p i c a l l y very high i n almandine and low in pyrope component. S p e s s a r t i n e and g r o s s u l a r components are s i m i l a r i n abundance to pyrope. The geothermometer-derived temperatures are t h e r e f o r e very s e n s i t i v e to how nonideal i n t e r a c t i o n s i n v o l v i n g Ca and Mn are t r e a t e d . B i o t i t e compositions i n the p e l i t i c rocks, however, are t y p i c a l l y much c l o s e r to the bin a r y Mg-Fe j o i n . To a good approximation, an i d e a l s o l u t i o n model may t h e r e f o r e account f o r nonbinary components i n b i o t i t e . Mixing p r o p e r t i e s of garnet have r e c e i v e d c o n s i d e r a b l e a t t e n t i o n . Ganguly (1979) reviewed a v a i l a b l e data on the mixing p r o p e r t i e s of garnet s o l i d s o l u t i o n and formulated a s o l u t i o n model that c o n s i d e r s the Fe-Mg, Mg-Ca, and Ca-Fe i n t e r a c t i o n s a l l to be n o n i d e a l . Margules parameters f o r each j o i n are taken from Ganguly and Kennedy (1974) and apply to compositions i n 90 which the mole f r a c t i o n 1 of Ca i s l e s s than or equal to 0.25 and the mole f r a c t i o n of Mn i s l e s s than or equal to 0.27. Newton and Haselton (1981) evaluated recent experimental and c a l o r i m e t r i c data and suggested a mixing model f o r low Mn g a r n e t s , where Mn i s l e s s than or equal to o n e - t h i r d of the Mg. In t h e i r model, a l l but the Ca-Mg i n t e r a c t i o n s are i d e a l . Ganguly and Saxena (1984) t r e a t the mixing p r o p e r t i e s of the quaternary garnet s o l i d s o l u t i o n using a s o l u t i o n model developed f o r t e r n a r y systems by Wohl (1946, 1953) and extended to quaternary systems by Jordan et a l . (1950). B e s t - f i t Margules parameters f o r the binary i n t e r a c t i o n s , a l l of which are c o n s i d e r e d to be n o n i d e a l , are d e r i v e d from analyses of f r a c t i o n a t i o n data from both n a t u r a l and s y n t h e t i c phases. The authors do not recommend use of the model for compositions i n which the mole f r a c t i o n of Ca or Mn i s g r e a t e r than 0.3 . Because a range in r e l a t i v e values of Ca, Mn, and Mg are represented i n garnets from the f i e l d area, temperatures were estimated using a l l three models. These were then t e s t e d f o r c o n s i s t e n c y with c r i t i c a l metamorphic assemblages and with barometric r e s u l t s . The s e n s i t i v i t y of each model to Mn content was a l s o e v a l u a t e d . F e r r y and Spear's (1978) e q u i l i b r i u m constant e x p r e s s i o n , s o l v e d f o r temperature i s : 1 Mole f r a c t i o n of Mn X(Mn):= a(Mn)/(a(Fe)+a(Mg)+a(Mn)+a(Ca)) where a ( i ) designates the atomic abundance (mol-%) of oxide i 91 2089 + .00956 P (bars) T(K) = (1) 0.7820 - InK where K Q = ( x ^ / ^ G A R , ( B I O Mg7 Fe (2) Nonbinary components can be c o n s i d e r e d by i n c o r p o r a t i n g excess f r e e energy terms i n t o the numerator of equation 1. The a c t i v i t y c o e f f i c i e n t r a t i o (Mg/Fe) f o r garnet can be expressed as f u n c t i o n s of excess f r e e energy parameters, temperature, and composition. The thermometric equations so d e r i v e d are s o l v e d by Lang and Rice (1984) f o r the garnet models developed by Newton and Haselton (1981) and Ganguly and Saxena (1984). Pigage and Greenwood (1982) so l v e the equations f o r Ganguly's (1979) s o l u t i o n model. The e q u i l i b r i u m constant equations, s o l v e d f o r temperature, are given i n Table I I I . 92 TABLE I I I : Geothermometric e x p r e s s i o n s of F e r r y and Spear (1978), m o d i f i e d f o r n o n i d e a l garnet mixing 1 . Ganguly (1979) model: 1 5 8 6 X ^ A R + 1380x£ A R + 2089 + .00956 P (bars) T ( K ) = ^ .7820 - InK 2 . Newton and Haselton (1981) model: (1661 -.755 T ) X ^ A R + 2089 + .00956 P (bars) T ( K ) = ^ .7820 - InK 3. Ganguly and Saxena (1984) model: T ( K , . " ' « " - * <*Fe - *Mq - •«>/» .7820 - InK 1510 X ^ A R + 1510 X ^ A R + 2089 + .00956 P (bars) .7820 - InK 93 C. GEOBAROMETRY Bohlen et a l . (1983) c a l i b r a t e d e q u i l i b r i u m 3 by experimental r e v e r s a l s . Garnet and i l m e n i t e are p o t e n t i a l s o l i d s o l u t i o n phases i n the e q u i l i b r i u m . For a p p l i c a t i o n to the n a t u r a l assemblages in t h i s study, Ganguly and Saxena's (1984) s o l u t i o n model f o r garnet was adapted to d e r i v e the a c t i v i t y c o e f f i c i e n t f o r the almandine component. The a c t i v i t y of F e T i 0 3 i n i l m e n i t e was d e s c r i b e d using the s o l u t i o n model of Spencer and L i n d s l e y (1981). For the b i n a r y j o i n i l m e n i t e - h e m a t i t e t h e i r model assumes r e g u l a r asymmetric behaviour. They d e r i v e d the i n t e r a c t i o n parameters by a l e a s t squares f i t of thermodynamic parameters to experimental data. The e f f e c t s of minor c o n s t i t u e n t s such as Mg, Mn, Cr, A l , and V are approximated to be i d e a l . Since a l l phases i n e q u i l i b r i u m 3 are anhydrous, i t may be assumed that the volume change f o r the r e a c t i o n i s independent of p ressure and temperature. D i r e c t c a l c u l a t i o n of the e q u i l i b r i u m pressure at any value of temperature and KD i s t h e r e f o r e p o s s i b l e : T T P = 1 + { " A r H ° 9 8 - / A rCpdT + T - ( A r S ° g 8 + / A.Cp/TdT) 298 298 - R . T . l n [ ( X F e T i 0 3 . 7 F e T . 0 3 ) 3 i L M / ( X a i m . 7 a i m ) G A R ] } / ( 3 ) where 7 F e ? i 0 3 " e x P { ( 1 - X i l i n * [ 5 H 8 7 - 35.548-T - 6 5 5 5 6 - X ^ + 63.3236-T-X i l m]/RT} (4) 94 and the a c t i v i t y c o e f f i c i e n t f o r the almandine component in garnet i s adapted from Ganguly and Saxena (1984). The enthalpy and entropy of r e a c t i o n f o r e q u i l i b r i u m 3, at standard s t a t e c o n d i t i o n s , were computed for the experimental b r a c k e t s r e p o r t e d by Bohlen et a l . (1983). L i n e a r programming techniques as d e s c r i b e d by Gordon (1977) were used to a s c e r t a i n the i n t e r n a l c o n s i s t e n c y of t h e i r data and, i n the process, to e x t r a c t enthalpy and entropy of r e a c t i o n . Heat c a p a c i t y and molar volume data were taken from Robie et a l . (1979) f o r T i -compounds, and from Helgeson et a l . (1978) f o r a l l other phases. D. RESULTS Previous pressure d e t e r m i n a t i o n s from f i e l d areas along the n o r t h e a s t e r n boundary of the Shuswap Metamorphic Complex range from 4500 bars ( P e l l and Simony, 1980) to 7500±1500 bars ( F l e t c h e r and Greenwood, 1979). Pigage and Greenwood (1982) o b t a i n a pressure of 5727±402 bars. In t h i s study, the k y a n i t e - s i 1 1 i m a n i t e t r a n s i t i o n i s observed i n rocks b e a r i n g white mica plu s q u a r t z . The P-T-i n t e r s e c t i o n of the breakdown of muscovite + quartz to K-f e l d s p a r + s i l l i m a n i t e + H 20 with the k y a n i t e - s i l l i m a n i t e boundary y i e l d s an upper T- and P-bracket f o r such rocks. Muscovite analyzed from these rocks t y p i c a l l y c o n t a i n s 10-15% pa r a g o n i t e component. Displacement of the u n i v a r i a n t breakdown curve f o r mica + quartz f u r t h e r extends the s t a b i l i t y f i e l d of the low-temperature assemblage, and the remaining P-T-bracket i s c o n s i s t e n t , but c l e a r l y not l i m i t i n g when compared to r e s u l t s 95 d i s c u s s e d below. The g a r n e t - b i o t i t e geothermometer i s only s l i g h t l y pressure-dependent (3-4° per kbar). Therefore, the f o l l o w i n g d i s c u s s i o n of r e s u l t s can be r e s t r i c t e d to temperatures computed fo r 5 kbar p r e s s u r e . The thermometry and barometry w i l l be coupled a f t e r t h i s d i s c u s s i o n to eva l u a t e P-T-conditions of metamorphism. G a r n e t - b i o t i t e temperatures obtained f o r 19 samples are summarized i n Table IV. F i g u r e 37 i l l u s t r a t e s the l o c a t i o n of these samples; the temperatures shown are those obtained using the garnet model of Newton and Haselton (1981). In Table IV, one sigma e r r o r brackets are i n d i c a t e d f o r each sample. For some of these, the true v a r i a n c e may not be w e l l estimated, f o r the c a l c u l a t i o n s are based on very few spot a n a l y s e s . As an a i d to i n t e r p r e t i n g the d i s t r i b u t i o n of temperatures computed f o r a s i n g l e sample, the r a t i o of Mg/Fe i n b i o t i t e was p l o t t e d a g a i n s t Mg/Fe i n garnet. These Nernst p l o t s proved u s e f u l i n i d e n t i f y i n g m i neral p a i r s that i n d i c a t e s i m i l a r temperatures. Where a n a l y t i c a l problems could be r u l e d out, r e s e t t i n g of the Mg/Fe r a t i o was i n f e r r e d f o r p a i r s p l o t t i n g f a r from isotherms d e f i n e d by the main p o p u l a t i o n . C o n s i s t e n t l y , small b i o t i t e i n c l u s i o n s i n garnet were found not to r e c o r d temperatures i n agreement with matrix p a i r s (e.g. K207 i n Table I V ) . Temperatures i n d i c a t e d by the three models are s y s t e m a t i c a l l y d i s p l a c e d with respect to one another. Temperatures d e l i v e r e d by Ganguly (1979) are always h i g h e s t . 96 Table IV: E q u i l i b r i u m temperatures of 19 samples, c a l c u l a t e d using the g a r n e t - b i o t i t e thermometer (three garnet models). # Garnet s o l u t i o n models #of p a i r s i n t e r p r e t a t i o n , N & H G G & S to t r e i reason f o r r e j e c t 26 480(33) 513(36) 449( 28) 3 0 27 564(11) 604(12) 520( 8) 2 0 30 719(13) 790(14) 657( •8) 4 0 r e g i o n a l ? 30 787(10) 871(20) 705( 7) 2 0 r e s e t up? 33 490(16) 504(16) 447( 12) 4 0 40 580(19) 634(20) 537( 17) 1 1 0 60 522(18) 563(20) 489( 17) 4 0 61 629(10) 660( 6) 585( 7) 4 0 63 569(31 ) 593(36) 528( 29) 6 0 73 575(50) 603(53) 526( 45) 3 0 92 658 747 627 1 0 1 00 520(12) 563(14) 483( 13) 7 0 101 566(23) 601(20) 51 5( 21 ) 5 2 bi o i n c l in gar 1 04 580( 6) 625( 7) 539( 6) 7 1 re s e t ? 1 10 555(21 ) 583(21 ) 523( 22) 7 0 1 54 588(31 ) 747(58) 561 ( 32) 1 6 2 re s e t ? 202 606(27) 669(28) 585( 27) 6 0 205 540( 7) 606( 7) 490( 5) 3 0 r e g i o n a l ? 205 618(11) 695(12) 564( 1 1 ) 9 0 r e s e t up? 207 898( 1) 1002( 0) 887( 0) 2 2 bi o i n c l in gar 208 523( 0) 586( 1) 51 0( 1 ) 4 0 1 7 20 16 avg. s t d . dev. N & G & H G S : Newton and Haselton ( : Ganguly (1979) : Ganguly and Saxena (1 1981 ) 984) Temperatures i n degrees C f o r P = 5 kbar. Values i n parentheses are one standard d e v i a t i o n . 97 F i g u r e 37 - L o c a t i o n of samples used in geothermometry and geobarometry. Temperatures shown were c a l c u l a t e d using the Newton and Haselton model f o r garnet. Metamorphic zones a l s o shown. 98 Newton and Haselton (1981) temperatures are c o n s i s t e n t l y i n t e r m e d i a t e . There i s a 51±32°C (one sigma) d i s c r e p a n c y between Ganguly (1979) and Newton and Haselton (1981), and a 37±14°C systematic d i f f e r e n c e s e p a r a t i n g Newton and Haselton (1981) from Ganguly and Saxena (1984). The average standard d e v i a t i o n f o r the samples i s high f o r Ganguly's model; t h i s can be t r a c e d to samples c o n t a i n i n g v a r i a b l e amounts of Mn. T h i s p o i n t i s w e l l i l l u s t r a t e d by sample K154, i n which the mole f r a c t i o n of Mn i n garnet v a r i e s from 0.07 to 0.29 . At the highest Mn-values, the l i m i t s of v a l i d i t y of a l l three garnet s o l u t i o n models are exceeded. N e v e r t h e l e s s , temperatures c a l c u l a t e d from these p a i r s document how w e l l the models account f o r the e f f e c t s of Mn. F i g u r e 38 i l l u s t r a t e s the e q u i l i b r i u m temperatures obtained. While i t i s p o s s i b i l e t h a t some of the samples ceased to e q u i l i b r a t e at d i f f e r e n t temperatures on c o o l i n g , the temperature-dependence suggested using Ganguly's model seems e x c e s s i v e . The model seems to overestimate metamorphic temperatures f o r garnets high i n Mn. The systematic o f f s e t between the three thermometers i s not, however, r e l a t e d to d i f f e r e n c e s i n t h e i r treatment of Mn content. Metamorphic c o n d i t i o n s suggested by mineral assemblages and independent barometry may h e l p in i d e n t i f y i n g a p r e f e r r e d model. A l l p e l i t i c samples analyzed f o r barometric c a l c u l a t i o n s c o n t a i n the assemblage a l m a n d i n e - r i c h garnet, a l u m i n o s i 1 i c a t e , i l m e n i t e , and q u a r t z . R u t i l e i s a l s o present, but i s always mantled by i l m e n i t e . C a l c u l a t i o n s based on e q u i l i b r i u m 3, owing to the reduced a c t i v i t y of T i 0 2 , would t h e r e f o r e i n d i c a t e 99 900 8 5 0 -1 1 1 1 1 1 A G - 7 9 : Ganguly •NH-81: Newton & Haselton xGS -84 : Ganguly & Saxena 5 0 0 - K154 I 2 I 4 6 T 8 1 10 T 12 I 14 Mn in garnet, wt—% F i g u r e 38 - E q u i l i b r i u m temperatures c a l c u l a t e d f o r g a r n e t - b i o t i t e p a i r s from sample K154. Comparison of the r e s u l t s obtained using three garnet s o l u t i o n models 100 maximum p r e s s u r e s . In f i g u r e 39, the P-T bounds f o r three samples are p l o t t e d f o r the Ganguly and Saxena model (A), and for the Newton and Haselton model (B). The s t a b l e A l 2 S i 0 5 polymorph i n K26 (from Domain 2b) i s k y a n i t e . S i l l i m a n i t e i s the s t a b l e polymorph i n samples K63 and K104 (from Domain 4), however r e l i c k y anite i s a l s o present i n K63. The p e r t i n e n t g a r n e t - b i o t i t e temperatures are superimposed on the diagram, and one sigma envelopes are i n d i c a t e d . Inasmuch as e q u i l i b r i a 1, 2, and 3 r e c o r d the same metamorphic c o n d i t i o n s , c o n s i s t e n t P-T values should be obtained f o r s i n g l e and nearby samples. Ganguly and Saxena's model y i e l d s pressure estimates in the 4.0±.6 kbar range ( F i g u r e 39). The s i l l i m a n i t e - b e a r i n g rock, K104, p l a c e s the most s t r i n g e n t c o n s t r a i n t s on the f e a s i b l e pressure range. Newton and Haselton's model prov i d e s a somewhat higher pressure estimate of 5.0 kbar. A l u m i n o s i 1 i c a t e r e l a t i o n s suggest an approximate u n c e r t a i n t y of ±0.5 kbar. Temperatures obtained using Newton and Haselton's garnet model place samples c o n t a i n i n g kyanite + s i l l i m a n i t e c o n s i s t e n t l y c l o s e to the k y a n i t e - s i l l i m a n i t e phase boundary, i n s i d e the s i l l i m a n i t e f i e l d ; t h i s i s i n agreement with observed m i n e r a l t e x t u r e s i n these samples. Ganguly's model y i e l d s p r e s s u r e estimates i n the 5 to 6.5 kbar range. The k y a n i t e - b e a r i n g rocks r e q u i r e a minimum pressure of 5 kbar. Based on these f i n d i n g s , the p r e f e r r e d a b s o l u t e temperatures are those obtained using Newton and Haselton's 101 TEMPERATURE (deg. C) TEMPERATURE (deg. C) F i g u r e 39 - Comparison of r e s u l t s from thermometry and barometry with the l o c a t i o n of the Al2Si05 phase diagram 1 02 model f o r garnet. Pressure c a l c u l a t i o n s based on e q u i l i b r i u m 3, i n the absence of r u t i l e , p l a y a minor r o l e i n a s s e s s i n g e q u i l i b r i u m pressure c o n d i t i o n s . T h e r e f o r e , the p a r t i c u l a r garnet model used in these c a l c u l a t i o n s i s not c r i t i c a l . In summary, F e r r y and Spear's (1978) thermometer with the garnet model of Newton and Haselton (1981), together with A l 2 S i 0 5 phase r e l a t i o n s , suggest e q u i l i b r i u m p r e s s u r e s of 5.0±.5 kbar. F i g u r e 40 d i s p l a y s temperatures c a l c u l a t e d f o r t h i s garnet model at 4 to 6 kbar. Only samples that are c l e a r l y not r e s e t are shown. Samples from domain 2b, where kyanite i s the only a l u m i n o s i l i c a t e p r esent, i n d i c a t e an average temperature of about 500°C at 5 kbar. Samples from domain 4, where kyanite i s wholly or completely r e p l a c e d by s i l l i m a n i t e , i n d i c a t e an average temperature of 565°C. Despite the a p p r e c i a b l e a b s o l u t e u n c e r t a i n t i e s i n each sample and, to a s m a l l e r extent, between samples from the same domain, the two c l u s t e r s obtained are c l e a r l y d i s c r e t e . I n s p e c t i o n of the s p a t i a l d i s t r i b u t i o n of temperature values ( F i g u r e 37) shows that there are no d i s c e r n a b l e g r a d i e n t s i n e i t h e r domain 2b or 4. However, samples c o l l e c t e d north and south of shear zone 4 axe c o n s i s t e n t l y o f f s e t by approximately 75° i n temperature. 103 Domain 2b Domain 4 6 0 0 0 -4 - 0 0 0 -1 — r — r 4 0 0 4 4 0 4 8 0 5 2 0 5 6 0 6 0 0 6 4 0 TEMPERATURE (deg. C) 6 0 0 0 -5 6 0 0 O • 5 2 0 0 Ld cn 3 OO if) Ld cr Q_ 4 8 0 0 -4 4 0 0 4 0 0 0 - 1 — i — i — i — ( 'i "I 1 i f i r i 4 0 0 4 4 0 4 8 0 5 2 0 5 6 0 6 0 0 6 4 0 TEMPERATURE (deg. C) F i g u r e 40 - D i s t r i b u t i o n of te m p e r a t u r e s o b t a i n e d f o r g a r n e t - b i o t i t e p a i r s from domains 2b and 4 1 04 V. SYNOPSIS A summary of the deformation and metamorphism, t e n t a t i v e l y c o r r e l a t e d a c r o s s the cover sequence and high grade g n e i s s e s , i s presented i n Table V. C o r r e l a t i o n between the two p r o v i n c e s i s d i f f i c u l t because shear zone 4 d i s r u p t s the s t r a t i g r a p h y and obscures any p o s s i b l e s t r a t i g r a p h i c r e l a t i o n to the high grade g n e i s s e s . Owing to f a u l t i n g , c o n t i n u i t y of s t r u c t u r e s i s d i f f i c u l t to e s t a b l i s h or r e f u t e . A. SUMMARY OF TIMING RELATIONS Two f a u l t i n g events, separated i n time, have a f f e c t e d the map area. Shear zone 3 preserves f a b r i c s that r e c o r d high d u c t i l e s t r a i n , produced during a f a u l t i n g event that culminated phase 2 deformation. Evidence of the r e l a t i v e t i m i n g of displacement along the shear zone i s summarized here. Phase 2 mesoscopic f o l d s are not observed i n the shear zone. Instead, the predominant f a b r i c i s a n o r t h e r l y - t r e n d i n g and -plunging l i n e a t i o n d e f i n e d by quartz rods. The l i n e a t i o n i s a l s o w e l l -developed i n h i g h l y s t r a i n e d u n i t s below the shear zone in Domain 2b, and in the wedge of Isaac Formation. The o r i e n t a t i o n s of the l i n e a t i o n s may be compared with phase 2 l i n e a r elements i n F i g u r e s 13 and 27. These l i n e a t i o n s are i n t e r p r e t e d as syn-kinematic to f a u l t i n g . A model of p r o g r e s s i v e homogeneous simple shear deformation (Escher and Watterson, 1974) accounts f o r the o r i e n t a t i o n of l i n e a r e x tension f a b r i c s t r a n s v e r s e to the boundaries of mobile b e l t s . According to Escher and Watterson, the planar element i n t e c t o n i t e f a b r i c s ( F l i n n , 1965), represented by f o l i a t i o n , COVER ROCKS METAMORPHISM HIGH GRADE GNEISSES D1 d e f o r m a t i o n R e g i o n a l metamorphism at l e a s t through lower g r e e n s c h i s t f a c i e s c o n d i t i o n s . P1 d e f o r m a t i o n D2 d e f o r m a t i o n R e g i o n a l metamorphism through upper a m p h i b o l i t e f a c i e s c o n d i t i o n s . S t r a i n - h e a t i n g i n shear zone 3 causes p a r t i a l and l o c a l r e s e t t i n g of m i n e r a l e q u i l i b r i a under h i g h e r temperatures P2 d e f o r m a t i o n Fau11 i ng P3 d e f o r m a t i o n D3 d e f o r m a t i o n R e g i o n a l metamorphism under lower g r e e n s c h i s t f a c i e s c o n d i t i o n s . D4 d e f o r m a t i o n . F a u l t i ng. P4 d e f o r m a t i o n . F a u l t i ng. B r i t t l e f r a c t u r i n g . T a ble V sequence Summary of d e f o r m a t i o n and metamorphism, c o r r e l a t e d a c r o s s the c o v e r i n t o h i g h grade g n e i s s e s . 106 s c h i s t o s i t y , or cleavage, i s p a r a l l e l to the XY-plane of the f i n i t e s t r a i n e l l i p s o i d . The l i n e a r element, represented by l i n e a r f a b r i c s , such as the e l o n g a t i o n l i n e a t i o n , i s p a r a l l e l to the x - a x i s . The y- s t r a i n a x i s l i e s p a r a l l e l to the s t r i k e of the detachment boundary and remains unchanged i n le n g t h d u r i n g p r o g r e s s i v e simple shear. With i n c r e a s e d deformation, the x-and z- s t r a i n axes are p r o g r e s s i v e l y r e o r i e n t e d by homogeneous simple shear. Consequently, as s t r a i n i n c r e a s e s , the tr e n d of l i n e a r or extension f a b r i c s are o r i e n t e d toward p a r a l l e l i s m with the d i r e c t i o n of shear. Furthermore, p r e - e x i s t i n g l i n e a r s t r u c t u r e s can become p r o g r e s s i v e l y r e o r i e n t e d toward p a r a l l e l i s m with the x - a x i s , depending on t h e i r o r i g i n a l o r i e n t a t i o n (Escher and Watterson, 1974; B e l l , 1978). Folds that are contemporaneous with shearing may i n i t i a l l y have axes s u b - p a r a l l e l to the s t r i k e of the mobile b e l t , but are r e o r i e n t e d toward the x-axis of the s t r a i n e l l i p s o i d as deformation p r o g r e s s e s . The n o r t h e r l y - t r e n d i n g l i n e a t i o n s d e f i n e d by qua r t z rods i n shear zone 3 (Figure 23) may have developed dur i n g p r o g r e s s i v e simple shear a s s o c i a t e d with f a u l t i n g . Late-D2 f a u l t i n g along shear zone 3 i s a l s o supported by mi c r o t e x t u r e s and geothermometry. M i c r o s c o p i c shear s u r f a c e s are d e f l e c t e d around p o r p h y r o b l a s t s that are syn- and post-kinematic to phase 2 deformation. The r e l a t i o n s h i p of the shear s u r f a c e s to phase 3 m i c r o s t r u c t u r e s i s not c l e a r . However, the absence of phase 2 f o l d c l o s u r e s and the p r e s e r v a t i o n of phase 3 and 4 minor f o l d s i n shear zone 3 suggests that the shear f a b r i c 107 may have developed p r i o r to phase 3 deformation. In the shear zone, phase 2 f o l d s were o b l i t e r a t e d . U n f o r t u n a t e l y , phase 3 s t r u c t u r e s were not mapped acr o s s Domain 2b and i n t o the shear zone. The l o c a l i z e d development of t h i r d phase s t r u c t u r e s made c o n t i n u i t y d i f f i c u l t to e s t a b l i s h . Temperatures i n shear zone 3 are approximately 100°C higher than r e g i o n a l temperatures recorded i n rocks immediately adjacent to the shear zone. T h i s 'spike' i n temperature i s not due to high Ca and Mn garnet compositions; rim compositions are w e l l w i t h i n the l i m i t s of v a l i d i t y of the Newton-Haselton garnet model. The mole percentage of g r o s s u l a r and s p e s s a r t i n e r e l a t i v e to pyrope and almandine component i s s i m i l a r to that in rocks that y i e l d r e g i o n a l temperatures, both w i t h i n and o u t s i d e of the shear zone. The only occurrence of s i l l i m a n i t e , o u t s i d e of the high grade gneisses i n Domain 4, i s i n a sample from shear zone 3 that y i e l d s an average temperature of 625°C. The temperature spike t h e r e f o r e appears to be r e l a t e d to s h e a r i n g ; a d d i t i o n a l heat was generated at a time when r e g i o n a l temperatures were a l r e a d y high (e.g. 505°C in k y a n i t e - s t a u r o l i t e - b e a r i n g r o c k s ) , presumably l a t e i n phase 2 deformation, but p r i o r to phase 3 deformation. F o l d s of phases 3 and 4 deform m i n e r a l s which c r y s t a l l i z e d under lower g r e e n s c h i s t f a c i e s c o n d i t i o n s . The mergence of shear zones 2 and 3 may i n d i c a t e that the two f a u l t s are contemporaneous. Isograds, e s t a b l i s h e d l a t e i n the phase 2 event, are d i s p l a c e d a c r o s s the shear zones. The t r a n s i t i o n from c h l o r i t e - b i o t i t e zone i n t o b i o t i t e - g a r n e t zone 1 08 occurs f u r t h e r to the southwest i n rocks of Domain 1, r e l a t i v e to those of Domain 2a (Figure 37).. Although the topographic r e l i e f in the area mapped i s i n s u f f i c i e n t to determine the three-dimensional o r i e n t a t i o n of i s o g r a d s u r f a c e s , t h e i r o f f s e t a c r o s s the shear zones i s l i k e l y due to post-metamorphic movement along f a u l t s . Shear zone 4 t r u n c a t e s phase 3 s t r u c t u r e s i n rocks to the nor t h . T h i s dates movement on the f a u l t as post- phase 3 deformation. A discordance i n metamorphic c o n d i t i o n s a c r o s s the f a u l t i s i n d i c a t e d by mineral assemblages, p e t r o f a b r i c s , and thermometry. Approximately 80°C separate k y a n i t e - s t a u r o l i t e zone rocks north of the f a u l t from s i l l i m a n i t e zone gneisses and s c h i s t s south of the f a u l t . No s i l l i m a n i t e was observed i n s c h i s t s of shear zone 4; only s t a u r o l i t e , garnet, b i o t i t e and white mica were found. However, exposure i s poor i n the f a u l t zone, and very few samples, p a r t i c u l a r l y of p e l i t i c s c h i s t s were c o l l e c t e d , as these rocks tended to be i n t e n s e l y weathered. A temperature spike a l s o i s i n d i c a t e d i n shear zone 4. The temperature i s c a l c u l a t e d based on analyses of one garnet-bearing q u a r t z o f e l d s p a t h i c g n e i s s . E x c e p t i o n a l l y high temperatures (719° and 787°C) are recorded. Although the temperatures w i t h i n shear zone 4 are not very well-known, the temperatures c a l c u l a t e d f o r rocks to the north and south are very c o n s i s t e n t and r e p r e s e n t a t i v e . A jump i n metamorphic grade c l e a r l y occurs a c r o s s the f a u l t . The r a p i d t r a n s i t i o n from k y a n i t e - s t a u r o l i t e zone i n t o s i l l i m a n i t e zone a c r o s s a boundary that i s the boundary of the Shuswap 109 Metamorphic Complex, i s due to f a u l t i n g . T h i s jump in grade i s not caused by steep, c l o s e l y spaced i s o g r a d s u r f a c e s . B. KINEMATICS OF FAULTING: POSSIBLE SCENARIO The geometry of the map area can be reproduced by two p e r i o d s of f a u l t i n g , i n support of the evidence presented above for two such events. Data c o l l e c t e d in the f i e l d do not r i g o r o u s l y d e f i n e the sense of movement on each of the shear zones. T h e r e f o r e , no attempt i s made here to c o n s t r u c t a d e t a i l e d kinematic model. S t r u c t u r a l , s t r a t i g r a p h i c , and thermometric r e l a t i o n s i n the map area do, however, permit the f o l l o w i n g t e n t a t i v e model. Shear zone 3, and p o s s i b l y shear zone 2 formed during phase 2 deformation, but p r i o r to phase 3 f o l d i n g . In p a r t , motion along these shear zones post-dates the e s t a b l i s h m e n t s of metamorphic i s o g r a d s . A reverse sense of movement, at l e a s t on shear zone 2, i s i n d i c a t e d by o f f s e t isograds and i n f o r m a t i o n on s t r u c t u r a l f a c i n g . The r e l a t i o n s h i p s of s t r a t i g r a p h i c , s t r u c t u r a l , and metamorphic elements to the shear zones i s i l l u s t r a t e d s c h e m a t i c a l l y i n F i g u r e 41. The simple geometry of phase 2 f o l d s w i t h i n domain 1 permits d e f i n i t i o n of s t r a t i g r a p h i c top. Overturned bedding in Upper Kaza metasediments i s t r u n c a t e d by shear zone 2. The boundary between Kaza and Isaac, i n the hangingwall of shear zone 2, i s t h e r e f o r e d i s p l a c e d i n a reverse sense over the Isaac Formation i n the f o o t w a l l . T h i s sense of displacement i s c o n s i s t e n t with that i n d i c a t e d by o f f s e t i s o g r a d s . Of course, the amount of o f f s e t i n d i c a t e d by the d i s r u p t e d i s o g r a d s r e p r e s e n t s only the 1 10 I S A A C \ U P P E R K A Z A X F i g u r e 41 - S c h e m a t i c c r o s s s e c t i o n i l l u s t r a t i n g t h e r e l a t i o n s h i p s b e t w e e n s t r a t i g r a p h y , D2 f o l d s , i s o g r a d s , a n d s h e a r z o n e s 111 post-metamorphic p o r t i o n of movement along shear zone 2. 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The c h r o n o l o g i c a l s u c c e s s i o n of f o l d i n g and metamorphism i n the C e n t r a l Pyrenees. Geologische Rundschau, 50, 203-218. 102. Zwart. H.J. 1963. Some examples of the r e l a t i o n s between deformation and metamorphism from the C e n t r a l Pyrenees. Geologie en Mijnbouw, 42, 143-154. 121 Acknowledgement F i e l d and l a b o r a t o r y work were supported by a grant from the G e o l o g i c a l Survey of Canada (EMR Research Agreement 905-2107 f o r the C a r i b o o Mountains P r o j e c t ) , h e l d by Dr. H.J. Greenwood. I am very g r a t e f u l to the G e o l o g i c a l Survey of Canada f o r t h e i r generous support, and i n p a r t i c u l a r , I thank Bert S t r u i k for s o l v i n g l o g i s t i c problems d u r i n g my f i e l d season. I have b e n e f i t e d g r e a t l y d u r i n g my course of study at the U n i v e r s i t y of B r i t i s h Columbia. I have developed and honed my s k i l l s under the p e r c e p t i v e guidance of Dr. H.J. Greenwood, whom I thank very much. Many have c o n t r i b u t e d g r e a t l y of t h e i r time and s k i l l s throughout t h i s p r o j e c t . Dr. J.V. Ross, Dr. R.L. Armstrong, and Don Murphy reviewed the t h e s i s and pr o v i d e d a c c u r a t e , l u c i d c r i t i c i s m . Bernard Evans and John Knight p r o v i d e d much h e l p i n o b t a i n i n g microprobe a n a l y s e s . Rob Berman, Jenny G e t s i n g e r , Jack R i c e , and C l a u d i a Owens aided g r e a t l y i n manuscript p r e p a r a t i o n . F i n a l f i g u r e s were d r a f t e d by Gordon Hodge, Melanie S u l l i v a n , and John Newlands. Ed Montgomery and Bryon Cranston provided c o n t i n u a l , always " l a s t minute" t e c h n i c a l support. Marie Cambon was a companion and a hard working f i e l d a s s i s t a n t during a very r a i n y summer. I thank a l l , and I thank M a r t i n E n g i . 1 22 APPENDIX A - ELECTRON MICROPROBE ANALYSES ANALYTICAL TECHNIQUES F i g u r e 37 i l l u s t r a t e s the l o c a t i o n of 19 p e l i t e samples chosen for microprobe a n a l y s i s . Samples were s e l e c t e d s p e c i f i c a l l y to d e l i n e a t e pressure-temperature g r a d i e n t s across the map area, u t i l i z i n g exchange e q u i l i b r i a 2 and 3. A l l phases p a r t i c i p a t i n g in these r e a c t i o n s were analyzed, with the exce p t i o n of q u a r t z , k y a n i t e , and s i l l i m a n i t e , which were assumed to be s t o i c h i o m e t r i c . Analyses were c o l l e c t e d on two d i f f e r e n t microprobes. A f i r s t set of g a r n e t - b i o t i t e analyses were c o l l e c t e d using a thre e - c h a n n e l , automated ARL SEMQ Experimental Mineralogy, at the U n i v e r s i t y of B r i t i s h Columbia. The instrument c o n d i t i o n s for these analyses were: an a c c e l e r a t i o n p o t e n t i a l of 15 kV, a specimen c u r r e n t (on aluminum) of 40 nanoamps, and an e l e c t r o n beam diameter of approximately 10 to 12 microns. I n t e g r a t i o n time was 20 seconds on peak and 10 seconds on background f o r a l l elements with the exception of f l u o r i n e . A c o u n t i n g time of 100 seconds and 40 seconds, f o r peak and background r e s p e c t i v e l y , were chosen to improve the counting s t a t i s t i c s f o r f l u o r i n e . For each i n t e g r a t i o n i n t e r v a l , t o t a l counts were normalized to a re f e r e n c e beam c u r r e n t determined on aluminum. N a t u r a l and s y n t h e t i c minerals from the U n i v e r s i t y of B r i t i s h Columbia c o l l e c t i o n were used as standards (Table V I ) . These were s e l e c t e d with regard to minimizing matrix c o r r e c t i o n s 123 while maximizing the c o n c e n t r a t i o n of oxide i n the standard. A l l a nalyses were c o r r e c t e d f o r background, dead time, and instrument d r i f t . In order to monitor machine d r i f t c l o s e l y , the unnormalized beam c u r r e n t was recorded f o r the f i n a l peak measured d u r i n g each a n a l y s i s . Count readings f o r a l l elements, with the exception of f l u o r i n e , were c o r r e c t e d f o r matrix e f f e c t s u s ing a Bence-Albee c o r r e c t i o n procedure (Bence and Albee, 1968) with alpha f a c t o r s taken from Albee and Ray (1970). The weight percent of f l u o r i n e present i n the unknowns was estimated using a f i r s t approximation. Counts per second, c o r r e c t e d f o r background, were p l o t t e d a g a i n s t weight percent; s y n t h e t i c f l u o r o p h l o g o p i t e p r o v i d e d the standard f o r the f l u o r i n e measurements. Due to s u b s t a n t i a l d r i f t problems t y p i c a l of the instrument used, a c o r r e c t i o n procedure based on monitoring systematic e r r o r as w e l l as machine d r i f t was a p p l i e d to each a n a l y s i s . For each phase measured d u r i n g a s e s s i o n on the microprobe, an i n t e r n a l standard from the same mi n e r a l group and of comparable composition (Table VII) was analyzed r o u t i n e l y at r e g u l a r i n t e r v a l s . Graphs p l o t t i n g the a b s o l u t e d e v i a t i o n of measured value from t r u e value a g a i n s t time were i n t e r p r e t e d , a f t e r each s e s s i o n , to i d e n t i f y systematic e r r o r due to matrix e f f e c t s and e r r o r due to machine d r i f t . Each measured oxide which d i s p l a y e d a s i g n i f i c a n t e r r o r i n the i n t e r n a l standard check was c o r r e c t e d by a f a c t o r equal to the r e l a t i v e d e v i a t i o n determined f o r the i n t e r n a l standard. Table VIII i l l u s t r a t e s the c o r r e c t i o n procedure f o r a g a r n e t - b i o t i t e p a i r . 1 24 Analyses were a l s o c o l l e c t e d on a f i v e - c h a n n e l , automated EMX2 e l e c t r o n microprobe at the U n i v e r s i t y of Washington, S e a t t l e . The instrument c o n d i t i o n s were: an a c c e l e r a t i o n p o t e n t i a l of 15 kV, a specimen c u r r e n t (on quartz) of 50 nanoamps, and an e l e c t r o n beam diameter of approximately 5 microns. I n t e g r a t i o n time was 20 seconds on peak and 10 seconds on background f o r a l l elements. T o t a l counts were normalized to a r e f e r e n c e beam c u r r e n t determined d u r i n g each i n t e g r a t i o n i n t e r v a l on the sample. N a t u r a l and s y n t h e t i c m i n e r a l s were chosen from the U n i v e r s i t y of Washington c o l l e c t i o n (Table V I ) . A l l a n a l y s e s were c o r r e c t e d f o r matrix e f f e c t s using a Bence-Albee c o r r e c t i o n procedure with alpha f a c t o r s taken from Albee and Ray (1970). Some aspects of data c o l l e c t i o n d i d not vary f o r the two machines employed. S e v e r a l g r a i n s i n each p o l i s h e d s e c t i o n were analyzed with 3 to 4 spot analyses on each g r a i n , m ineral p a i r s used i n geothermometry and b i o t i t e were analyzed i n d i f f e r e n t p o r t i o n s of a t h i n s e c t i o n in order to t e s t f o r l o c a l e q u i l i b r i u m and homogeneity. Garnet and p l a g i o c l a s e were the only zoned minerals d e t e c t e d , and spot analyses were performed a c r o s s these phases. Where zoning was present, the g r a i n edges were c o n s i d e r e d to represent the composition c l o s e s t to e q u i l i b r i u m with the matrix mineral assemblage. A s i n g l e set of standards (Table VI) was s e l e c t e d to analyze b i o t i t e and garnet g r a i n s used i n thermometric c a l c u l a t i o n s . T h i s method was chosen to minimize the danger of i n t r o d u c i n g systematic e r r o r s i n Mg/Fe f o r the two phases. 125 D i r e c t l y adjacent rims of g r a i n s were measured i n immediate s u c c e s s i o n . The f i n a l formulae that appear i n Table X were computed a c c o r d i n g to the f o l l o w i n g method: A l l weight percents were r e c a l c u l a t e d as c a t i o n p r o p o r t i o n s and normalized to the number of oxygen atoms present i n the s t r u c t u r a l formula. C a t i o n s i t e s were f i l l e d a c c o r d i n g to s t o i c h i o m e t r i c c o n s t r a i n t s ; t h i s i n c l u d e s the c a l c u l a t i o n of f e r r i c i r o n f o r garnet and water f o r b i o t i t e , white mica, and s t a u r o l i t e . The formula s t o i c h i o m e t r i e s accepted were: b i o t i t e ( K,Na)(Mg,Fe 2 +) 3 2 ( A l , T i ) 0 , ( A 1 2 3 ( S i , A l ) a 0 , 0 ( O H , F ) 2 garnet (Ca,Mg,Fe 2 + , M n ) 3 ( A l , F e 3 * ) 2 ( S i , A l ) 3 0 , 2 i l m e n i t e ( F e 2 + ,Mn,Mg,Ca,Fe3 + ) ( T i , F e 3 + ) 0 3 Garnet formulae were computed by f i r s t f i l l i n g the o c t a h e d r a l s i t e with A l and T i . The e i g h t - f o l d s i t e was f i l l e d next, and any excess was c o n s i d e r e d to be f e r r i c i r o n and was r e d i s t r i b u t e d from the e i g h t - f o l d to the o c t a h e d r a l s i t e . In that s i t e , any excess was f i n a l l y c a l c u l a t e d as t e t r a h e d r a l aluminum. Garnet was assumed to be anhydrous. In the c a l c u l a t i o n of b i o t i t e formulae, the t e t r a h e d r a l s i t e was f i l l e d f i r s t with S i and A l . A l l remaining A l was added to the o c t a h e d r a l s i t e . 1 26 A monitor of the extent of Tschermak s u b s t i t u t i o n 1 i n b i o t i t e i s p r o v i d e d by the r a t i o X(Tschk) i n Table X. T h i s r a t i o i s the mole f r a c t i o n of e a s t o n i t e present i n each b i o t i t e . For end-member p h l o g o p i t e (or a n n i t e ) , X(Tschk) i s equal to zero; f o r end-member e a s t o n i t e (or s i d e r o p h y l l i t e ) the mole f r a c t i o n i s equal to one. In c a l c u l a t i n g the f i n a l b i o t i t e formulae, a n a l y t i c a l e r r o r was d i s t r i b u t e d evenly between the fo u r - and s i x - c o o r d i n a t e d s i t e s by r e d i s t r i b u t i n g aluminum as r e q u i r e d . F e r r i c i r o n was not computed f o r b i o t i t e . Ca and Na were added to the a l k a l i s i t e with K. F i n a l l y , H 20 was computed s t o i c h i o m e t r i c a l l y , a f t e r having accounted f o r any f l u o r i n e p r e s e n t . Many of the an a l y s e s c o l l e c t e d on the U n i v e r s i t y of Washington microprobe f o r garnet and b i o t i t e are low in S i 0 2 . S i l i c o n measurement on that instrument i s very s e n s i t i v e to focus, causing v a r i a t i o n s of 1 or 2 weight percent (E. Mathez, 1984, p e r s o n a l communication). The dependence of the Mg/Fe r a t i o on S i 0 2 - v a l u e s was t e s t e d f o r garnet and b i o t i t e . Thermometric c a l c u l a t i o n s proved q u i t e i n s e n s i t i v e to the S i -d e f i c i e n c y i n b i o t i t e . However, very low S i 0 2 values f o r garnet t r a n s l a t e d to excess i r o n i n the e i g h t - f o l d s i t e , which i s computed as f e r r i c i r o n . The Mg/Fe r a t i o s are t h e r e f o r e s e n s i t i v e to the S i value f o r garnet. In an attempt to cope 1Tschermak s u b s t i t u t i o n : A1(VI) + A l ( I V ) = Mg(VI) + S i ( I V ) 1 27 with that d i f f i c u l t y , a nalyses of garnet s e l e c t e d f o r geothermometry were c o n s i d e r e d both u n c o r r e c t e d and with 2 weight percent S i 0 2 added. Poor analyses c o u l d thus be recognized and d i s c a r d e d ; those low in s i l i c o n , but otherwise a c c e p t a b l e , were r e c a l c u l a t e d with c o r r e c t e d s i l i c o n v a l u e s . R e p r e s e n t a t i v e analyses used i n thermometry and barometry are presented i n t a b l e X I I I . Analyses f o r which S i 0 2 values were r a i s e d , are i n d i c a t e d . Formulae in the t a b l e s are based on analyses conducted at both U n i v e r s i t y of Washington and U n i v e r s i t y of B r i t i s h Columbia. Agreement i s very good for c a l c u l a t i o n s based on samples analyzed at both i n s t i t u t i o n s . Table IX p r e s e n t s a comparison of thermometric r e s u l t s f o r one such rock, analyzed using the two microprobes. 128 Table VI: Standards f o r microprobe a n a l y s i s of garnet and b i o t i t e . U n i v e r s i t y of B r i t i s h Columbia C o l l e c t i o n ELEMENT STANDARD LOCALITY UBC ID Si ,A1 pyrope Kakanui, New Zealand 235 T i r u t i l e s y n t h e t i c 013 Fe f a y a l i t e synthet i c 250 Mn pyroxmangite Taguchi Mine, Japan 245 Mg, K,F f l u o r o p h l o g o p i t e s y n t h e t i c 024 Ca w o l l a s t o n i t e W i l l s b o r o , NY 021 Na a l b i t e L a n g l o i s , OR 020 U n i v e r s i t y of Washington C o l l e c t i o n ELEMENT STANDARD LOCALITY UW ID Si,A1,Mg,Fe pyrope-almandine Gore Mtn, NY T i ilmen i te Sawyer 1 3.20 Mn s p e s s a r t i n e Nuevo, NM 9.12 K b i o t i t e 7.60 Ca a n o r t h i t e Miyake, Japan 1 .09 Na r i e b e c k i t e 6.30 1 2 9 Table V I I : I n t e r n a l standards f o r g a r n e t - b i o t i t e analyses STANDARD OXIDE WT % ELEMENT ATOMS garnet n a t u r a l Si02 Ti02 A1203 Fe203 FeO FeO(tot) MnO MgO CaO Na20 Sum wt % 42. 1 0 0.38 23, 0, 9, 7, 0. 10 65 08 73 30 19.10 5.34 0.03 100.09 VI S i A l T i Fe 3 + Sum VI Fe 2 + Mn Mg Ca Sum VIII Na 3.0041 1.9427 0.0204 0349 9980 5421 0181 031 5 4083 0000 0, 1 , 0, 0, 2, 0, 3, 0.0042 b i o t i t e n a t u r a l Si02 Ti02 A1203 FeO MnO MgO CaO Na20 K20 H20 F Sum wt% 36.03 2.52 1 5.30 21 .66 0, 9, 41 80 0.01 0.08 9.70 3.73 0.30 99.54 S i A l IV Sum IV A l VI T i Fe 2 + Mn Mg Sum VI Ca Na K Sum ALK 2.7863 1 , 3, 0, 0, 1 , 1 560 9423 2385 1 466 4008 0.0269 1.1296 2.9423 0.0008 0.0120 0.9569 0.9698 130 Table V I I I : C o r r e c t i o n procedure f o r systematic e r r o r and d r i f t i l l u s t r a t e d f o r a g a r n e t - b i o t i t e p a i r Garnet 110.73 (spot 2.1, analyzed 28June84) OXIDE CPS MEASURED ABSOLUTE 1 CORRECTION2 CORRECTED WT % DEVIATION FACTOR WT % Si02 1864 36.90 -.50 1.0119 37.34 Ti02 2 .02 3 1.0000 .02 A1203 4927 21.21 .00 1.0000 21.21 FeO(tot) 521 9 36.05 + .20 .9794 35.31 MnO 184 1 .28 1.0000 1 .28 MgO 527 2.93 -.45 1.0236 3.00 CaO 848 2.29 1.0000 2.29 Na20 1 .02 1.0000 .02 K20 -1 .00 1.0000 .00 B i o t i t e 110.71 (spot 2.1, analyzed 28June84) OXIDE CPS MEASURED ABSOLUTE CORRECTION CORRECTED WT % DEVIATION FACTOR WT % Si02 1 725 33.88 -1.10 1.0305 34.91 Ti02 1 34 1 .67 1.0000 1 .67 A1203 4485 19.15 -.51 1.0333 19.79 . FeO(tot) 2690 18.96 .00 1.0000 18.96 MnO 3 .02 1.0000 .02 MgO 1 837 9.47 -.65 1.0663 10.10 CaO 2 .00 1.0000 .00 Na20 24 .36 1.0000 .36 K20 3522 9.37 .00 1.0000 9.37 'Absolute d e v i a t i o n = measured - tr u e value C o r r e c t i o n F a c t o r = a b s o l u t e d e v i a t i o n / wt% oxide in i n t e r n a l standard 3 F o r these e n t r i e s , the a b s o l u t e d e v i a t i o n was not c o n s i d e r e d s i g n i f i c a n t 131 Table IX: Comparison of g a r n e t - b i o t i t e temperatures based on probe analyses from the U n i v e r s i t y of B r i t i s h Columbia and U n i v e r s i t y of Washington. # Garnet s o l u t i o n model number EPMA model, N & H G G & S o f p a i r s s i t e 40 580(16) 633(17) 533(16) 5 EMX-2, U.Wash. 40 579(22) 635(24) 541(19) 6 SEMQ, U.B.C. 40 580(19) 634(20) 537(17) 11 combined r e s u l t s N & H : Newton and Haselton (1981) G : Ganguly (1979) G & S : Ganguly and Saxena (1984) Temperatures i n degrees C f o r P = 5 kbar. Values i n parentheses are one standard d e v i a t i o n . Table X: Selected electron microprobe analyses BIOTITE ANALYSES Sample Nr. 26 : 1 27 : 1 30: : 2 33 : 1 40 :1 60.: : 1 61 : 1 63 : 1 73 : 1 73 : 2 SiO* 33 . 65 33 . 27 37 .08 37 . 6 8 36 . 50 32 . 9 1 33 . 34 32 . 12 36 . 50 36 . 40 TiO* 0. .92 1 .62 1 88 1 . 74 1 . .80 1 . 49 1 .50 1 .81 2 . 18 2 . 18 Al *0 5 19 14 18 .63 18 .69 19 8 6 18 .85 18 . 38 18 .81 19 . 10 19 . 18 18 . 93 FeO 17 . 14 17 .57 19. . 27 15 . 12 18 .80 18 . 32 18 . 50 18 . 27 16. .47 16 .67 MnO 0 .21 0 . 18 0 .04 0 .03 0 .03 0 .04 MgO 10. .97 1 1 . 13 9 . 26 1 1 . . 74 10 34 10. . 55 9, .21 9 . 74 10 .95 1 1 . 13 CaO 0 . 01 0. 17 Na*.0 0. . 26 0 . 18 0 1 1 0 . 3 1 0. . 17 0 15 0. .09 0. 18 0. 37 0. .40 KiO 8 . 82 8 .67 9 . 80 9 . 2 1 9 . 79 9 . 10 9 . 10 8 . 92 9 . 36 9 . 42 HiO 3 . 79 3 . 79 3 . 86 4 . 07 4 . 00 3. 75 3 . 74 3 . 72 4 . 00 3 . 99 F 0. 27 Sum wt-% 94 . 69 94 .85 100. 43 9 9 . 74 100. 60 94 . 65 94 . 33 93 . 88 99 . 04 99 . 16 CJ FORMULA ^ OXYGEN 1 1 .0000 1 1 .0000 1 1 .0000 1 1 . 0 0 0 0 11 .0000 1 1 .0000 1 1 .0000 1 1 .0000 1 1 .oooo 1 1 .0000 S i 2 .6613 2 .6346 2 . 7845 2 . 7 7 4 0 2 . 7330 2 .6318 2 .6709 2 . 5904 2 .7381 2 . 7330 Al IV 1 . 3022 1 . 3394 1 .1179 1 . 1 3 2 4 1 . 1873 1 . 3362 1 . 2686 1 . 3696 1 .1701 1 . 1801 Sum IV 3 . 9635 3 . 9740 3 . 9024 3 . 9 0 6 3 3 . 9202 3 .968 1 3 . 9395 3 . 9600 3 .9082 3 .9131 Al VI O . 482 1 0 . 3999 0 . 5362 0 . 5 9 0 8 0 . 4762 0 . 3959 0 . 5070 0 . 4454 0 . 5257 O . 495 1 T i 0 .0549 0 . 0964 0 . 1062 0 . 0 9 6 3 0 . 1014 0 .0898 0 .0905 0 . 1095 0 . 1230 0. .1231 F e ! * 1 . 1338 1 . 1637 1 .2102 0 . 9 3 0 9 1 . . 1772 1 .2254 1 .2391 . 1 . 2322 1 .0333 1 . .0467 Mn 0 .0134 0 .0114 0 .0028 0 .0021 0 .0019 0 .0025 Mg 1 . 2927 1 .3141 1 .0365 1 . 2 8 8 3 1 . 1540 1 . 2570 1 . 1001 1 . 1707 1 . 2244 1 . 2456 Sum 2 .9635 2 .9740 2 . 9024 2 . 9 0 6 3 2 . 9202 2 . 968 1 2 . 9395 2 .9600 2 .9082 2 .9131 Ca 0 0 0 0 8 0. .0136 Na 0. .0394 0. .0273 0. .0160 0 .0442 0. 0247 0 .0237 0 .0140 0 .0281 0 .0538 0. .0582 K 0. . 8899 0 . 8755 0. . 9388 0 . 8 S 5 0 0. .9351 0. .9288 0. 9298 0 .9172 0 .8957 0 9023 Sum 0 .9293 0 .9029 0 . 9548 0. . 9 1 C 0 0. .9734 0. 9525 0. . 9438 0 . 9453 0. 9495 0 .9605 OH 2 . 0000 2 . 0000 1 . 9324 2 . eooo 2 . 0000 2 0000 2 . 0000 2 0000 2 . 0000 2 . 0000 F 0. .0676 RATIOS Mg/Fe 1 . . 1402 1 . . 1292 0. .8565 1 . 3 8 3 9 0. 9803 1 . 0257 0. 8878 0. 9501 1 . 1849 1 . 1900 X(Mg) 0. 5328 0. 5303 0. 4586 0. 5 8 0 5 0. 4926 0. 5063 0. 4697 0. 4868 0. 5419 0. 5428 X(Fe) 0. .4672 0. 4697 0. 5355 0. 4 1 9 5 0. 5025 0. 4937 0. 529 1 0. 5124 0. 4573 0. 4561 X ( T s c h k ) O. 1511 0. 1697 0. 0590 0 . 0 6 6 2 0. 0936 0. 168 1 0. 1343 0. 1848 0. 0850 0. 0900 X(OH) 1 , .0000 1 . 0000 0. 9662 1 . 0 0 0 0 1. 0000 1. 0000 1 . 0000 1 . 0000 1 . OOOO 1 . 0000 BIOTITE ANALYSES Sample Nr. 100:1 101:1 104:1 104:2 110:1 110:2 154:1 154:2 154:3 202:1 SiO* 34 . 65 33 . 76 33 . 30 3 1 .94 36 . 62 34 .91 35 .96 37 .55 36 .93 35 .63 TiO; 1 . .64 1 . 79 2 . 02 2 . 10 2 . 28 1 .67 1 . 38 1 . 54 1 . 72 1 . 79 Al *03 17 . 41 19 . 29 19 . 17 18 . 78 19 .81 19 .79 18 . 17 17 . 38 19 . 26 18 . 24 FeO 17 . 78 17 . 54 17 . 57 17 . 23 18 .41 18 .96 14 .94 15 .57 16 .25 21 .80 MnO 0 .06 0 .07 0 01 0 .02 0 .21 0 . 33 0 . 14 0 30 MgO 9. 92 10. . 34 9 94 10. .44 10. 08 10 . 10 13 13 12 .94 1 1 . .63 8 46 CaO 0 .01 0. . 19 0. . 34 Na*0 0. . 13 0. . 13 0. 12 0 . 15 0. 34 O . 36 0. . 15 0. .21 0. . 37 0. 1 1 K;0 8. .87 9 .05 9 . 13 8 . 70 . 9 . 46 9 .37 9 . 57 9 . 65 9 . 25 9 . 05 H,0 3 . 76 3 . 82 3 . 79 3 . 7 1 3 . 96 3 86 3 . 94 3 . 75 3 . 77 3 . 91 Sum wt-% 94 . 16 95 . 73 95 . 10 93 . 12 101 . 14 99 21 97 . 45 99 45 100. 03 99 . 63 FORMULA OXYGEN 1 1 .0000 1 1 .0000 1 1 .0000 1 1 . 0 0 0 0 1 1 .0000 1 1 .0000 1 1 .0000 1 1 .0000 1 1 .0000 1 1 .0000 S i 2 . 7626 2 . 647 1 2 .6346 2 . 5839 2 . 7 129 2 . 6562 2 . 7353 2 .8080 2 . 7448 2 . 7305 Al IV 1 . 1677 1 . 2997 1 . 3063 1 . 3820 1 . 1990 1 . 2836 1 .2126 1 . 1237 . 1 . 1729 1 .2016 Sum IV 3 .9303 3 .9468 3 . 9409 3 . 9G59 3 .9119 3 .9398 3 .9479 3 .9316 3 .9176 3 .9321 Al VI 0 . 4677 0 . 4829 0 . 48 14 0 . 4089 0 . 5306 0 . 491 1 0 .4166 0 . 4081 0 .5142 0 .4459 T i 0 .0983 0 . 1054 0 . 1203 0 . 1278 0 . 1270 0 0956 0 .0789 0 .0866 0 .0961 0 . 1032 F e 1 • 1 . 1853 1 .1501 1 . 1627 1 . 1656 1 . 1406 1 2065 0 .9503 0 .9737 1 .0100 1 . 3972 Mn 0. .004 2 0 .C050 0 .0006 0. .0013 0 .0135 0. .0209 0 .0088 0 .0195 Mg 1 . 1790 1 . 2084 1 . 1723 1 . 2587 1 .113 1 1 1454 1 . 4886 1. . 4423 1 . 2884 0 .9664 Sum 2 .9303 2 . 9468 2 .9409 2 . 9659 2 .9119 2 . 9398 2 .9479 2 . 9316 2 .9176 2 .9321 Ca 0 .0008 0 .0151 0 .0279 Na 0 .0195 0 .0204 0. .0178 0 .0238 0 .0488 0. .0531 0. 0218 0. .0304 0 .0533 0 .0163 K 0. .9022 0 .9047 0. .9212 0 . 8984 0 . 8940 0. 9095 0 9289 0 .9206 0. 8770 0 . 8848 Sum 0. .9216 0 .9250 0 9390 0 .9223 0. .9429 0. 9626 0. 9507 0. 9518 0. .9455 0. .9290 OH 2 . 0000 2 . O O O O 2 . OOOO 2 .0000 1. 9580 1 . 9569 2 . O O O O 1. 8703 1. 87 11 2 .0000 RATIOS Mg/Fe 0 9947 1 . .0507 1 . 0083 ' 1 . 0799 0. 9759 0. 9494 1 . 5666 1. 48 12 1. 2756 0. 69 1 7 X(Mg) 0 . 4987 0 .5124 0. 5012 0. 5181 0. 4938 0. 4868 0. 6070 0. 59 19 0. 5584 0. 4055 X(Fe) 0. .5013 0 . 4876 0. 497 1 0. 4798 0. 5060 0. 5127 0. 3875 0. 3996 0. 4378 0. 5863 X(Tschk) 0. .0839 0 . 1498 0. 153 1 0. . 1910 0. 0995 0. 1418 0. 1063 0. 0618 0. 0864 0. 1008 X(OH) 1 . .0000 1. .0000 1 . OOOO 1. OOOO 0. 9790 0. 9784 1 . O O O O 0. 9352 0. 9356 1. O O O O BIOTITE ANALYSES Sample Nr. 202:2 205:1 205:2 208:1 SiO* 36 . 46 36 .48 35 .65 35 .41 TiO* 1 . 77 1 .51 1 .70 1 . 48 A h O . 18 . 41 17 .93 18 .67 18 . 17 FeO 20. . 24 18 .03 16 .01 18 . 74 MnO 0 1 1 0 . 15 0 .08 0 . 18 MgO 9 . 16 1 1 . 22 1 1 . 75 9 . 36 CaO 0. .02 0 .02 Na*0 0. . 12 0 . 15 0 . 17 0 .08 K,0 9 . 49 9. . 55 9 . 53 9 . 32 rUO 3 . 95 3 .81 3 . 78 3 . 84 Sum wt-% 99 . 73 99. . 14 97 .63 96 . 59 FORMULA OXYGEN 1 1 . .0000 1 1 .0000 1 1 .0000 1 1 . 0 0 0 0 S i 2 . 7661 2 . 7652 2 .7218 2 . 7632 Al IV 1 . 1540 1 . 1715 1 . 2102 1 . 1589 Sum IV 3 , 9201 3. .9367 3 . 9320 3 . 922 1 Al VI 0. .4921 . 0 . 4304 0. .4698 0 .5120 T i 0. . 1010 0 .0861 0. .0976 0 .0869 1 . . 2842 1 .1430 1 . 0222 1 . 2225 Mn 0. .0071 0. .0096 0. 0052 0 .0116 Mg 1 . .0358 1. . 2677 1 . 3371 1. .0890 Sum 2 . 9201 2 .9367 2. .9320 2 .9221 Ca 0. .0016 0. .0016 Na 0. .0177 0. .0220 0. 0252 0. .0123 K 0. 9185 0. .9235 0. 9282 0. . 928 1 Sum 0. .9377 0. .9471 0. 9534 0. .9403 OH 2 . 0000 1 . ,9267 1 . 9262 2 . 0000 RATIOS Mg/Fe 0. . 8066 1 . .1091 1 . 3081 0. 8908 X(Mg) O, .4451 0. .5238 0. 5655 0. 4688 X(Fe) 0 . 5518 0 .4722 0. 4323 0. 5262 X(Tschk) 0. .0770 0. .0857 0. 1051 0. 0795 X(OH) 1 . 0000 0 . 9633 0. 9631 1 . 0000 208 : 2 34 . 14 1 . 38 18 .66 19.47 0. 12 9 .04 0.11 9 . 32 3.80 96 .04 11.0000 2.6966 1.2409 3.9375 0.4961 0.0819 1.2866 0.0083 1.0647 2.9375 0.0167 0.9394 0.9561 2.0000 0.8275 0.4512 O.5453 0.1204 1.0000 •P-Samp 1e Nr. 26 : 1 + 27 : 1 30: : 2 33 : 1 SiO* 36 . 56 35 . 63 37 . 72 37 . 55 TiOr 0 .03 Al 2O, 21 . 16 21 . 15 21 . 02 21 .07 F e i 0 3 0. . 26 FeO 32 . 18 32 . 12 29 . 57 34 . 77 MnO 0 .81 1 . 88 2 66 0 .09 MgO 2 . 25 3 . 01 3 . 10 3 .21 CaO 5. . 44 3. . 12 3 .96 2 . 85 Na*0 0 . 13 0 .01 KiO 0. 03 0. 03 0. 32 0. 01 Sum wt-% 98 . 43 97 . 20 98 . 48 99 . 59 OXYGEN 12 .0000 12 .0000 12 .0000 12 .0000 S i 2 .9778 2 .9457 3 .0424 3 .0160 A l IV 0 .0313 0 .0766 Sum IV 3 .0092 3 .0224 3 .0424 3 .0160 Al VI 2 .0000 1 . 984 1 1 . 9982 1 . 9946 T i ' 0 .00 18 F e 1 + 0 .0159 Sum 2 .0000 2 .0000 1 .9982 1 . 9964 F e 1 + 2 . 1918 2 . 2205 1 .9946 2 . 3356 Mn 0 .0558 0 . 1314 0 . 1817 0 .0061 Mg 0 . 2736 0 . 37 14 0 . 3727 0 . 3843 Ca 0 .4746 0. . 2767 0 . 3422 0 . 2453 Na 0 0203 0 .0016 K 0 .0031 0. 0032 0. 0329 0. .0010 Sum 2 . 9958 3 . OOOO 2 : 89 13 2 . 9712 Mg/Fe 0. . 1248 0. 1673 0. 1868 0. 1645 X(Mg) 0. . 1085 0. 1364 0. 1462 0. 14 10 X(Fe) 0. 8693 0. 8154 0. 7825 0. 8568 X(Tsc h k ) 0. .0104 0. 0254 GARNET ANALYSES 40: 1 36 . 96 0.07 20. 4 1 O. 22 30.93 2 . 28 2 . 83 4 . 48 0. 26 98 . 44 3.0119 3.0119 1.9602 0.0043 0.0138 1.9783 2.1077 0.1574 0.3437 0.3912 0.0270 3.OOOO 60: 1 + 36.85 20. 76 0.17 30.87 0.66 1 . 94 7 .08 0.04 98.37 2.9997 0.0026 3.0023 1.9894 0.0106 2.OOOO 2.1020 0.0454 0.2350 0.6176 O.0041 3.OOOO 61:1 34 . 16 20. 73 1.15 32 . 53 1 . 63 3 . 26 1.71 0.01 0.02 95 . 20 12.OOOO 2.9042 0. 15 10 3.0553 1.9262 0.0738 2.OOOO 2.3 130 0. 1 173 0.4135 0.1561 O.0016 0.0022 3.OOOO O.1788 0.1454 0.8133 0.0494 63 : 1 36 . 45 21.15 34 . 48 0. 49 2 .96 2 .43 0.02 0.03 98 .01 12.OOOO 2.9839 0.0400 3.0239 2.OOOO 2.OOOO 2.3604 0.0343 0.3610 0.2133 0.0032 0.0031 2.9690 0.1530 0. 1310 0.8566 0.0132 73 : 1 37 .40 0.01 20.48 34 . 51 1 . 42 3 . 38 1 .66 0.01 0.08 98 .95 12.OOOO 3.0332 3.0332 1.9576 0.0006 1.9582 2.3407 0.0975 0.4086 0.1442 0.0016 0.0083 2.991 1 0.1746 0. 1435 0.8222 73 : 2 37 . 19 0.01 21.11 33.85 1 . 42 3.52 1 . 79 0.02 0. 27 99 . 18 1 2.OOOO 3.0036 0.0100 3.0136 1.9994 0.0006 2.OOOO 2.2863 0.097 1 0.4237 0. 1549 0.0031 0.0278 2.962 1 0.1853 0.1509 0.8144 0.0033 RATIOS 0. 1631 0. 1118 0. 1318 0. .0987 0. 8079 0. 8823 0. . 0009 FORMULA 12.OOOO 12.OOOO Sample Nr. 100:1 101:1+ 104:1+ 104:'' S10* 36 . 02 37 . 15 35 .41 35 . 75 TiO* Al ;03 20. 18 20 .96 21 .18 2 1 . 30 F e i O i 0. 67 FeO 30. 27 33 . 18 32 . 24 32 . 28 MnO 0. 78 1 .03 2 .32 2 .70 MgO 2 . 05 3 . 29 3 .03 3 . 28 CaO 6. 58 2 .96 2 . 34 2 .03 NazO 0 .01 K*0 0. 02 0. .02 0 .04 0. .02 Sum wt-% 96 . 56 98 . 59 • 96 . 57 97. . 36 OXYGEN 12 .0000 12 .0000 12 .0000 12 .0000 S i 2 .9954 3 .0111 2 .9456 2 .9480 Al IV 0 .0192 0 .0024 0 .0765 0 .0700 Sum IV 3 .0147 3. .0135 3 .0222 3 0180 Al VI T 1 . .9584 2 .0000 2 .0000 2 . 0000 1 1 F e ] * 0 .0416 Sum 2 .0000 2 .0000 2 .0000 2 . 0000 Fe! * 2 .  1050 2. . 2487 2 . 2433 2 . 2262 Mn 0 .0549 0. .0707 0 1633 0. . 1886 Mg 0 . 2538 0 . 3969 0 . 3756 0 . 4038 Ca 0 5862 0. . 2568 0 . 2089 0. . 1795 Na 0 0016 K 0 .0021 0. 0021 0 .004 1 0. .002 1 Sum 3 .0000 2 . 9732 2 . 99 1 1 2 . 9980 Mg/Fe 0. 1206 0. 1765 0. 1674 0. 1814 X(Mg) 0. 1052 0. 1461 0. 1350 0. 1433 X(Fe) 0. 8721 0. 8278 0. 8063 0. 7898 X(Tschk) 0. 0064 0. 0008 0 0253 0. 0232 GARNET ANALYSES 1 10: 1 37 . 30 20. 56 34 . 98 1 . 28 2 . 82 2 . 10 0.01 0.01 99.06 3.0293 3.0293 1 .9680 1.9680 2.3759 0.0881 0.34 14 0.1827 0.0016 0.0010 2.9880 1 10: 2 37 . 34 0.02 2 1.21 0.12 35 . 19 1 .28 3.00 2 . 29 0.02 100.47 2.9921 0.0116 3.0037 1.9915 0.0012 0.0073 2.0000 2.3582 0.0869 0.3583 0. 1966 0.0031 3.0000 154 : 1 36.88 21 .63 O. 46 19.15 12.54 2.59 6.49 0.02 99.77 12.OOOO 2.9543 0.0696 3.0239 1.9720 0.0280 2.0000 1 .2828 0.8509 0.3096 0.5567 0.0020 3.0000 0.2413 0.1267 0.5250 0.0230 154 : 2 37 . 37 0.13 20.96 0.2 1 19 .05 12 .07 2 . 59 6.88 0.02 99.28 12.0000 2.9986 0.0028 3 0014 1.9794 0.0078 0.0127 2.0000 1.2784 0 82O3 0.3098 0.5915 0.0020 3.0000 0. 2423 0. 1286 0.5308 0.0009 154 : 3 37 . 38 0.08 21 . 32 28 . 80 4 .60 2 . 72 5.05 0.01 0.08 100.04 12.OOOO 2.9888 0.0140 3.0028 1 .9952 0.0048 2.0000 1.9258 0.3115 0.3242 0.4326 0.0016 0.0082 2 . 9942 0. 1683 0.1266 0.7518 0.0046 202 : 1 37 . 13 0. 46 2 1 . 40 32 . 15 2 . 35 2 . 10 5.15 0.03 0.04 100.81 12.OOOO 2 .9632 0.0405 3.0037 1 .9724 0.0276 2.OOOO 2.1458 0.1589 0.2498 0.4404 0.0046 0.0041 2.9948 O.1164 0.0978 0.8400 0.0135 RATIOS 0. . 1437 0. 1519 0. 12 17 0. 1278 0. 8469 0. 8412 0. 0039 FORMULA 12.OOOO 12.OOOO GARNET ANALYSES Sample Nr. 202:2 205:1 205:2 208:1 208:2 SiO* 37 .68 37 . 33 37 . 47 36 .44 36 . 57 TiO* 0. . 15 0 . 10 0 .06 A b O i 21 . 06 2 1 . 12 21 . 32 20 .62 20 . 74 F e i O i 0. . 37 0 . 60 0 . 17 FeO 31 . 15 28 . 7 1 29 . 30 30 5 5 29 . 74 MnO 2 . 59 3. 31 3 . 45 3 . 32 2 . 91 MgO 2 . 01 2 . 99 2 . 69 1 . 88 1 . .61 CaO 5 . 64 5 . 8 1 5 . 70 5 . 08 6 . 45 Na*0 0. 02 0. 02 0. .03 0. 03 K,0 0. 04 0. 06 0. .01 0. 02 0. 02 Sum wt-% 100. 34 99 . 82 100. 03 98 . 5 5 98 . 21 FORMULA OXYGEN 12 .0000 12 .0000 12 .0000 12 . 0 0 0 0 12 .0000 S i 3 .0115 2 .9869 2 .9916 2 . 986 1 2 . 9936 Al IV 0 .0199 0 .0098 0 .0287 0 .0113 Sum IV 3 .0115 3 .0067 3 .0014 3 .0148 3 .0050 Al VI 1 . 9838 1 .9718 1 .9964 1 . 9627 1 .9894 Ti 0 .0090 0 .0060 0. .0036 F e 1 + 0 . 0222 0 .0373 0 .0106 Sum 1 .  9928 2 .0000 2 .0000 2 . OCOO 2 .0000 F e ! * 2 .0820 1 .9210 1 . 9564 2 .0938 2 .0357 Mn 0, 1753 0. . 2243 0, . 2333 0. .2 305 •0. . 2020 Mg 0. 2394 0 . 3566 0. . 3201 0. 2295 0 . 1967 Ca 0. .4830 0. ,4981 0. . 4876 0. .4462 0, . 5656 Na 0. .0031 6. .0031 0. .0046 0, ,004 8 K 0. 0041 0. .006 1 0, .0010 0. 002 1 0. 0021 Sum 2. 9798 3 . OOOO 2 . 9974 3 . OOOO 3 OOOO RATIOS Mg/Fe 0. 1 150 0. 1856 0. 1636 0. 1096 0. 0966 X (Mg) 0. 0959 0. 1425 0. 1275 0. 0899 0. 0808 X(Fe) O. 8339 0. 7678 0. 7795 0. 8 199 0. 8362 X(Tschk ) 0. 0066 0. 0033 0. 0095 0. 0038 

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